OPEN FILE REPORT 125
PETROLOGY,
EOCENE
AND
DIAGENESIS,
BACA
AND
FORMATION,
VICINITY,
GENETIC
ALAMO
SOCORRO
STRATIGRAPHY
NAVAJO
COUNTY,
APPROVED :
NEW
OF
RESERVATION
MEXICO
THE
PETROLOGY,
DIAGENESIS,
EOCENE
BACA
AND
AND
FORMATION,
VICINITY,
GENETIC
ALAMO
SOCORRO
STRATIGRAPHY
OF THE
NAVAJO
COUNTY,
RESERVATION
NEW
MEXICO
Graduate
School
by
STEVEN
MARTIN
B.S.
CATHER,
THESIS
Presented
to
The
the
Faculty
of the
Universityof Texas at Austin
in
Partial
of
the
for
the
MASTER
THE
Fulfillment
Requirements
of
Degree
OF
ARTS
UNIVERSITYOF TEXAS AT AUSTIN
August 1980
of
ACKNOWLEDGMENTS
I w i s h t o sincerely
thank
C.
E.
Chapin
f o rt h e i r
enthusiasm
toward
a
t h e ipr a t i e n c ietnu t o r i n g
r e s p e c t i v fei e l d s
and
of facies
concerning
A.
their
Socorro
for
Blodgettserved
acknowledge
S c o t t provided
l a c u s t r i n see d i m e n t a t i o n
w i t h Bruce
Johnson
thank
my
helpful
Baca-Eagar b a s i n .
c o l l e a g u e isn
Austin
comments
J e r r yG a r c i a ,
and
and criticisms.
a s s t u d e n te d i t o r .F i n a l l y ,
Bob
I would l i k e t o
who providedunending
inspiration
t h e course of t h i s s t u d y .
F i n a n c i a ls u p p o r tf o r
of this manuscript
their
my understanding of t h e d i s t r i b u t i o n
and motivation throughout
f i e l d work and
wa-s generously provided
Bureau of Mines and
Mineral
Resources.
Texas
Geology
t h i s study and
J.
and paleoenvironments within the
I would a l s o l i k e t o
e
Dr.
t h e s iisl l u s t r a t i o n sD
. iscussions
c o n t r i b u t e dg r e a t l yt o
Folk
and
L.
n o v i cg
e e o l o g i sitn
of e x p e r t i s e .
many h e l p f u l comments
R.
Drs.
the
writing
by t h e N e w Mexico
The
University
of
F o u n d a t i oanl sp
or o v i d efdu n dfsotrr a v e l
expenses and f i e l d work.
This thesis was
submitted
June, 1980.
iii
t ot h e
committee
in
PETROLOGY, DIAGENESIS, AND GENETIC STRATIGRAPHY OF THE
EOCENE BACA FORMATION,
AND V I C I N I T Y ,
A I A M O NAVAJO RESERVATION
SOCORRO COUNTY, NEW MEXICO
by
Steven M .
Cather
ABSTRACT
The
correlative
Eocene
Baca
Formation
Eagar
Formation
and
Arizona
comprise
a
of
New
Mogollon
Mexico
R i m gravels of
redbed
sequence
conglomerate,
of
sandstone, mudstone,and
c l a y s t o n e which crops out
from near
Socorro, New Mexico, t o t h e Mogollon R i m of Arizona.
sediments
were
deposited
in
present i n western New Mexico
Laramide time.
the
exposureof
of
u p l i f t s ,t ot h e
by
the
Morenci
an
approximately
The
uplift.
1 2 mi’(31
kmL)
the
north
end
Mountains about 20 m i (32 km) northwestof
Magdalena, New Mexico.
(289
southwest
by t h eS i e r r a - S a n d i a
t h e Baca Formationlocatedalong
t h eG a l l i n a s
f t
easternArizonaduring
Mogollon Highland, t o t h ee a s t
s t u d ayr ecao n s i s t s
940
large
intermontane
basin
and
Zuni, andLucero
u p l i f t , and t ot h es o u t h e a s t
of
a
These
The Baca-Eagar b a s i n i s bounded t o t h e n o r t h
by theDefiance,
by
and.
m)
thick
I n t h e studyarea,
and
iv
can
t h e Baca i s about
be
subdivided
into
three
V
informal members (lowerred,middlesandstone,
units)
which
system
Mountains v i c i n i t y d u r i n g Baca
Three component f a c i e s
in
large-scale
i n a l a r g e ,c l o s e dl a c u s t r i n e
p r e s e n ti nt h eB e a r - G a l l i n a s
Baca
to
agreen e t i c a rl leyl a t e d
l a k e - l e v e lf l u c t u a t i o n s
time.
and upper r e d
t hset u dayr e a .
were
r e c o g n i z ew
d i t h itnh e
These
a rtehdei s t ablr a i d e d
a l l u v i a l - pflianien-,g r al ai nc eudsdt reilnt ae,
and
l a c u s t rb
i naes i fnaacl i e s .
The
d i r e c t i o ni nt h eG a l l i n a s
from t h e Morenci u p l i f t and
t h a tp o r t i o n
be
were
Baca sediments i n t h e s t u d y a r e a
derivedpredominantly
of
to
Mountains v i c i n i t ya p p e a r s
toward t h e n o r t h e a s t .
westernflank
r e g i opnaalle o c u r r e n t
from
the
of t h eS i e r r a - S a n d i au p l i f t
I
which l i e s t o t h e s o u t h
of t h e a r e a .
Three episodes of s t r u c t u r a l developmenttookplace
in
a
t shteu a
d rye(faao:)r m a t i o fn
Laramide
of t h e a r e a ,
m o n o c l i n a lf l e x u r ei nt h es o u t h e a s t e r np o r t i o n
(b) Neogene
e x t e n s i o n afla u l t i n gd,r afgo l d i n g ,
and dike
i n t r u s i o n , and ( c ) u p l i f t of t h e Colorado P l a t e a u i n
time,
which
resulted
in
(?)
the
shallow
southward
dip
Neogene
of t h e
s t r a t a i n t h e area.
L i t h o l o g i e sp r e s e n tw i t h i n
Baca c o n g l o m e r a t ec l a s t s
includemetaquartzite,limestone,chert,granite,sandstone,
s i l t s t o n e ,s c h i s t ,
t hs ea n d s t o n e s
mudstone, and volcanics.
in
The majority of
t hset u dayr eaarl ei t h iacr k o s e s ,
f e l d s p a t h i cl i t h a r e n i t e s ,
and s u b l i t h a r e n i t e s .
Two
genetic
vi
quartztypes,
common and metamorphic q u a r t z ,a r ep r e s e n ti n
subequalproportions.
followed
by
. Orthoclase
microcline
v a r i e t i ei n
s clude
and
i s t h e dominant
plagioclase.
metamorphic,
chert,
suggest
fragment
mudstone,
granite/
in
sandstone
mineralogy
progressive
"unroofing"
of
Precambrian
source
the
terrand
e su r i nbga s a l
Baca
sedimentation.
suites
Baca
sandstones
from
non-red
alteration
Miocene
e
Rock
and sandstone rock
g n e i s sv, o l c a n i cc, a r b o n a t es,i l t s t o n e
fragments.
Upsection
changes
feldspar,
by
Heavy-mineral
show
evidence
with
negative-Eh
groundwaters
associated
d i k ei n t r u s i o n
of
and dolomitecementation.
I l l i t e is
t h e dominant d e t r i t a l c l a y m i n e r a l i n t h e s t u d y a r e a .
Four t y p e so c
f e m e n t s( c a l c i t ek, a o l i n i t eq, u a r t z ,
and
dolomita
ep
r) er e s e tinh
nt e
Baca
sediments.
The
environment of d e p o s i t i o n s t r o n g l y c o n t r o l l e d t h e d i a g e n e t i c
h i s t o r yo ft h es e d i m e n t si nt h es t u d ya r e a .
redcoloration
of the.Baca w a s produced
i n t r a s t r a t adli s s o l u t i o n
of
m i n e rpa rl e
s ,c i p i t a t i o n
of
dehydration
Yellow-gray
The widespread
unstable
iron-bearing
heavy
limonite,
of t h i s l i m o n i t e t o
and
subsequent
form t h e h e m a t i t e c o l o r a n t .
c o l o r a t i o n i s r e s t r i c t e d t o permeable sandstones
locatednearmafic
recent
outcrop
weathering
dikes, and occurred by oxidationduring
of
reduced
iron
primarilyincorporatedwithindolomitecements
0
d i a g e n e t i c a l l y ,b y
synchronously with dike intrusion in
which
was
t h a t formed
Miocene time.
.
TABLE
OF
CONTENTS
TEXT
Page
.....................
Study Area . . . . . . . . . . . . . . . . . . . .
Purpose and Methods
ofStudy
...........
GENERAL STRATIGRAPHY . . . . . . . . . . . . . . . . .
Late Cretaceous Crevasse Canyon Formation. . . . .
Eocene Baca Formation . . . . . . . . . . . . . . .
Correlation and previous work
.........
Lower Tertiary equivalents . . . . . . . . . . .
Age and fossils
................
Contacts . . . . . . . . . . . . . . . . . . . .
units . . . . .
General description and informal
Lower red unit . . . . . . . . . . . . . . .
Middle sandstone unit
............
Upper red unit. . . . . . . . . . . . . . .
Oligocene Spears Formation. . . . . . . . . . . .
Miocene Dikes . . . . . . . . . . . . . . . . . . .
Piocene ( ? ) to Holocene PiedmontGravels . . . . .
Quaternary Alluvium. . . . . . . . . . . . . . . .
LARAMIDE TECTONICS . . . . . . . . . . . . . . . . . .
Styles of Deformation. . . . . . . . . . . . . . .
INTRODUCTION
~
.
..............
...............
Cordilleran foldbelt
f basement uplifts ofthe Laramide
Rocky Mountains
Colorado Plateau monoclinal flexures
Baca-Eagar Basin Tectonic Framework .
Mogollon Highland
Lucero uplift
Zuni uplift
Defiance uplift
Sierra-Sandia uplift
Morenci uplift
Plate Tectonics and
the Development of
the Laramide Foreland
......
. ......
......... ......
. . . . . . . . . . .. . . . . .
............ ......
................
..............
........... ......
.............
STRUCTURAL GEOLOGY . . . . . . . . . . . . . . . . . .
Laramide Folding . . . . . . . . . . . . . . . . .
Early Rift Faults. Drag Folds. and Dikes . . . . .
Colorado Plateau Uplift. . . . . . . . . . . . . .
vii
1
1
3
5
6
7
7
9
12
15
17
20
21
21
22
23
24
25
26
26
26
29
33
35
37
38
38
39
40
43
47
53
53
55
57
viii
Page
.................
Braided Alluvial-Plain System
............
Distal braided alluvial-plain facies
......
Facies characteristics . . . . . . . . . . .
Depositional processes . . . . . . . . . . .
Braided alluvial plain model . . . . . . . .
Lacustrine System . . . . . . . . . . . . . . . . .
Lacustrine fine-grained delta facies
......
Facies characteristics . . . . . . . . . . .
Depositional processes . : . . . . . . . . .
Basinal facies . . . . . . . . . . . . . . . . .
.
Faciescharacteristics . . . . . . . . . . .
DEPOSITIONAL SYSTEMS
~
...........
Depositional processes
General characteristicsof the
1acustrine.system
Lacustrine model
58
58
59
59
62
65
68
69
69
78
80
80
80
. . . . . . . . . . . . . . 82
. . . . . . . . . . . . . . . . 87
DEPOSITIONAL RECONSTRUCTION . . . . . . . . . . . . . 91
Sediment Dispersal Patterns
. . . . . . . . . . . . 91
Depositional History . . . . . . . . . . . . . . . 95
PETROLOGY . . . . . . . . . . . . . . . . . . . . . .
102
Conglomerate Petrology . . . . . . . . . . . . . . 102
Clast composition . . . . . . . . . . . . . . . 102
Clast morphology. . . . . . . . . . . . . . . . 106
Sandstone Petrology . . . . . . . . . . . . . . . . 110
Quartz . . . . . . . . . . . . . . . . . . . . . 111
Common quartz . . . . . . . . . . . . . . . . . 113
Metamorphic quartz . . . . . . . . . . . . . 114
Feldspar . . . . . . . . . . . . . . . . . . . . 120
Orthoclase . . . . . . . . . . . . . . . . . 128
Microcline . . . . . . . . . . . . . . . . . 128
Plagioclase . . . . . . . . . . . . . . . . . 128
Rock fragments. . . . . . . . . . . . . . . . . 129
Metamorphic rock fragments . . . . . . . . . . 129
Chert . . . . . . . . . . . . . . . . . . . . 134
Granite and gneiss rock fragments
. . . . . . 137
Volcanic rock fragments. . . . . . . . . . . . 137
Mudstone rock fragments
. . . . . . . . . . . . 140
. . . 141
Sandstone and siltstone rock fragments
.
. . 142
Carbonate rock fragments. . . . . . .
Heavy minerals . . . . . . . . . . . . . . . . 144
Mudstone Petrology . . . . . . . . . . . . . . . . 150
PROVENANCE . . . . . . . . . . . . . . . . . . . . . .
156
e
DIAGENESIS
.....................
.....................
Cements
Calcite
Quartz
Kaolinite
Dolomite
Source of Coloration
Red coloration
Soil-derived red coloration
Diagenetic red coloration
Source of red coloration in
Baca Formation
Yellow-gray coloration
Porosity
Primary porosity
Secondary porosity
Diagenesis Summary
*
.
ix
....................
....................
...................
...................
...............
................
........
.........
the
..............
............
.....................
...............
..............
................
PALEOCLIMATE . . . . . . . . . . . . . . . . . . . .
ECONOMIC GEOLOGY . . . . . . . . . . . . . . . . . .
Uranium Occurrences . . :. . . . . . . . . . . .
Ore Genesis . . . . . . . . . . . . . . . . . . .
SUMMARY OF BACA-EAGAR BASIN DEPOSITIONAL SYSTEMS . .
SUMMARY AND CONCLUSIONS
APPENDIX A: Baca
160
160
160
171
178
182
187
187
187
189
190
198
199
199
200
201
205
207
207
208
210
...............
212
.....
218.
Formation
Measured
Section
APPENDIX B: Summary of Point-Count Data for
.
Study-Area Sandstone Thin Sections
229
REFERENCES CITED
231
VITA
...
..................
...................
' .
....
244
X
LIST
OF
TABLES
Page
-
Table
.... .."
1
Summary of Previous
2
Summary of Fossil
3
Distal Braided Alluvial-Plain
Characteristics
4
Studies
....
13
.............
60
Age
Determ'inations
Lacustrine Fine-Grained
Characteristics
Lacustrine Basinal
10
Delta
Facies
.............
Facies Characteristics. .
~
.....
Summary of Pebble Composition Data
Distribution of Coloration, Cements,
Porosity, and Heavy Minerals in
Relation to the Various Baca Facies
...
71
81
103
203
LIST OF FIGURES
Page
Figure
1
2
Location of study area andBaca,
and Mogollon Rim gravels
Eagar,
.........
Map showing outcrop areas of lower
Tertiary units in New Mexico and
areas.
2
adjacent
li
..................
Cloven hoof prints found in a Baca deltaplain sandstone. Lens cap is approximately
14
seven cm in diameter.
...........
Hematitic mudstone-filled ostracod
m,
sample 49. Field width=0.8 m
crossed nicols.
test
in
..............
16
Comparison of generalized Baca stratigraphic
sections measured inthe Gallinas and Bear
Mountains, showing similarity of lithofacies
and probable correlationof informal units.
10 mi (16 k m ) .
Sections are separated by about
Bear Mountains section modified from
19
Massingill (1979).
.............
xi
e
Figure
6
Map showing distribution and structural
styles of Laramide uplifts in western
North America, and the location of the
Baca-Eagar basin. Modified from Eardley
(1962) and Drewes (1978).
. . . . . . . . . . 27
7
Section across Spring Mountains, southern
Nevada, showing typical Cordilleranfoldbelt style of deformation. Note
imbricate, east-verging thrust plates.
...
8
28
Two hypothetical
styles of deformation in
Laramide Rocky mountain uplifts. (a)
Uplift caused by vertical forces acting
along range-bounding faults which steepen
with depth. Section through Owl Creek
.uplift,-.Wyoming. -From Couples and Stearns
(1978). (b) Uplift created by horizontal
stresses acting along thrust faults. Cross
section through theWind River Mountains,
31
Wyoming. Modified from Sales (1968).
Experimental deformational model showing
probable styleof Colorado Plateau
monoclinal flexures, using "strata" of
kaolinite and modeling clay resting on
rigid "basement" of pine board. Davis
34
(1978).
....
e
9
...................
10
Laramide tectonic framework in eastern Arizona
and western New Mexico. Heavy barbed line
is 'northeastward.
limit.of Cordilleran
foldbelt (according to Drewes,1978). BacaEagar-Mogollon Rim gravel outcrop areas are
also shown. Reference points: S=Socorro,
M=Magdalena, D=Datil, Sp=Springerville,
SL=
Show Low, SC=Silver
City, T=Tucson.
36
Modified from Eardley (1962).
........
11
Location of Morenci lineament and distribution
of Laramide plutons adjacent to the BacaEagar basin.. Presumably the majority of
these plutons (circled) were associated with
coeval volcanic centers. Reference points
10, except MoSMorenci.
same as Figure
Lineament and plutondata from Chapin and
others (1978).
44
...............
xii
Page
Figure
12
Distribution of lineaments (stippled) in the
Four Corners area which controlled the
development of monoclines (heavy lines).
The coalescingCow Springs (CS), Organ Rock
(OR), and Comb Ridge (CR) monoclines are
about the same length and trend the same
direction asthe proposed Morenci uplift.
Modified from Davis (1978).
46
.........
13
Map showing plate positions and relative motion
vectors prior to Laramide orogeny. F=Farallon
plate, K=Kula plate, P=Pacific plate, NA=NorthAmerican plate. Vectors show motion
of
Farallon (Far) and North American (NA) plates
relative to hot-spot frame of reference.
Resultant shows direction and magnitude of
plate convergence. Spreading centers shown
by stippled areas between parallel lines,
subduction zonesby heavy barbed lines,
thrust belts by
light barbed lines, metamorphic
core complexes by fine wavey lines, and arc
terranes by short, dashed lines. Modified
from Coney (1978).
49
..............
14 Map showing plate positions and relative motion
vectors during Laramide orogeny.
Uplifts
areas.
shown by small, elongate, closed
Other symbols same
as Figure 13. Modified
from Coney (1978).
. . . . . . . . . . . . . . 50
15
Map showing plate positions and relative motion
vectors during post-Laramide, middle-Tertiary
ignimbrite flare-up. CP=Colorado Plateau.
Dotted areas are large caldera complexes.
Other symbols sameas Figure11. From Coney
(1978).
52
.....................
16 Structure index map
of study area.
. . . . . . . . 54
17 Typical vertical section of distal braided
alluvial-plain facies. Modified from Johnson
(1978).
61
.....................
xiii
Page
__
Figure
18
Map showing distribution of bar types and
sedimentary structures in proximal and midfan facies of Scott glacial outwash fan,
67 (1978).
Johnson
From
Alaska.
........
19
Typical vertical section of lacustrine finegrained delta facies, showing upwardcoarsening cycles. Modified from Johnson
(1978).
...................
70
20
Branching horizontal burrows (feeding traces?)
in a red, lacustrine sandstone. . . . . . . . . 7 3
21
Baca fine-grained delta deposit exhibiting
unusually steeply inclined prodelta foreset
beds. . . . . . . . . . . . . . . . . . . . . . . 1 5
22
Gently inclined prodelta foreset beds overlain
by quasi-spheroidally weathering delta front
deposits. Hammer handle points in direction
of delta progradation.
76
...........
0
23
Exceptionally large deltaic distributary-channel
deposit. Note the low width-to-depth ratio
(less than 1O:l) and the highly symmetrical
nature, which are characteristic of distributary
channel deposits in marine deltas.
71
.....
24
Map showing crude, concentric zonation of facies
in EoceneLake.Gosiute,Wyoming, during a high
.. - Marginal facies is
stand-(Tipton..Shale Lime)
composed of calcareous sandstones and siltstones,
somewhat similiar to the lacustrine system rocks
in the study area. Surdam and Wolfbauer
(1975).
....................
89
25
Well-developed parting-step lineation in
a finegrained Baca sandstone. Paleoflow was parallel
to trend of mechanical pencil. . . . . . . . . 9 2
26
Comparison of paleocurrent data in western (a,b)
and eastern (c,d) portions of study area. The
significant portions of the bidirectional rose
diagrams (shaded) were determined by comparison
with associated unidirectional data. The area
was arbitrarily divided along the line between
Indian Spring Canyon and Indian Mesa quadrangles.
94
.....................
xiv
Figure
__
Page
27 Generalized Baca stratigraphic section in the
study area showing relationships between
shoreline migrations, depositional systems,
and informal units.
97
.............
28 Generalized stratigraphy of the Green River
Formation in Bridger and Washakie basins of
Wyoming,. showing alternation of high stands
(Tipton and Laney Shales) and low stands
(Luman Shale, Wilkins Peak)
in Eocene Lake
Gosiute. From Surdam and Wolfbauer (1975).
101
-
29 Ternary plot of Baca pebble compositions. Data
from 15 pebble counts within the study area.. 105
30
Sphericity-form diagram showing shapes of 71
Baca pebbles. Average effective settling
sphericity is 0.754. L=long diameter,
I=intermediate diameter, S=short diameter.
Sphericity-form diagram from Folk (1974).
107
..
e
3 1.
Classification of Baca sandstones based on data
from 26 thinsections. Cross shows average
112
composition. After Folk (1974).
......
32Stretchedmetamorphicquartzgrain.Sample
crossed nicols, field width=0.75mm.
68,
....
115
33 Schistose metamorphic quartz grain. Note minor
amounts of parallel oriented muscovite and
C,
:.elongated. quartz cry~stallites. .-Sample
crossed nicols, field width=0.75 mm.
116
....
34Recrystallizedmetamorphicquartzgrain.Note
equant shapeof and simple boundaries between
crystallites. Sample 32, crossed nicols,
€ield width=0.75 mm.
117
............
35
Plot of grain size vs. metaquartz/common quartz
for 27 Baca
sandscnes, showing tendency
towards-increasing abundances of metaquartz
with increasing grain size.
119
..........
xv
Figure
36
Page
Plot of metaquartz/total quartz ratios as a
function of stratigraphic position. Mean
grain size ranges between 1.6 and 2.96.
121
...
37
Cavernous dissolutioninanorthoclase grain
from a fluvial sandstone (sample 48). Secondary porosity within the grain appears blue,
due to impregnation of sample with colored
epoxy. Plane light, field width=0.75 mm.
122
..
38
Orthoclase grain being replaced by Falcite.
Sample 34, crossed nicols, field width=
0.75 mm.
123
..................
39
Plot of feldspar abundanceas a function of
stratigraphic position. Mean-grain size of
. samples ranges between 1.6 and 2.96.
....
40
a
127
Quartzose metamorphic rock fragment. Note
abundant inclusions of muscovite. Sample 48,
130
crossed nicols, field width=0.75 mm.
....
41
Argillaceous metamorphic rock fragment which
has been ductilely deformed by adjacent
grains during compaction. Sample C, crossed
132
nicols, field width=0.75 mm.
........
42
of metamorphic rock fragments
Plot of abundance
as a function of stratigraphic position. Mean
grain size ranges between 1.6 and 2.96
133
.....
43
44
Chert grain. Sample A, crossed nicols, field
width=0.75 mm.
...............
135
Plot of chert abundance as a function
of stratigraphic position. Mean grain size ranges
between 1.6 and 2.96.
136
............
45
Volcanic rock fragment showing lath-like plagioclase crystals in dark, aphanitic groundmass.
Sample 45, crossed nicols, field width=
m
.
139
0.75 m
..................
46
Well-developed oolite in an upper-delta sandstone. Note both concentric and radial
structures. Sample 73, plane.light,field
width=0.75 mm,
143
...............
xvi
Page
Figure
41
Typical heavy-mineral grain mount from a
Baca sandstone (sample 48). Note dominance
of magnetite/ilmenite/specular hematite.
White grains are leucoxene. Field width=
0.8 m
m
.
red
...................
48
146
Typical heavy-mineral suite from a yellow Baca
sandstone (sample 5 6 ) , showing dominance of
limonite-stained leucoxene grains. Note sub147
hedral zircon grain. Field width=0.8 mm
..
49
Hexagonal biotite observed in
a heavy-mineral
Width of field
grain mount from sample 48.
=0.75
50
m
m
. ...................
149
Churned, disrupted texture typical of Baca
lacustrine mudstones, which
was probably
produced by intense bioturbation. sample
152
F, crossed nicols, field width=3.0 mm. .
- .
51
Large, spar-filled void spaces in a sandy
lacustrine mudstone (sample 8), which are
indicative a very early, pre-compactional
cementation. Crossed nicols, field width=
3.0 m
m
.
-1.54
..................
52
Plot of metaquartz/total quartzratios and
abundances of feldspar, chert', and metamorphic rock fragments within Baca sandstones
as a function. of stratigraphic position.
.
Samples were taken from
a section measured by
the writer in the study area.
Mean grain
size of the sandstones ranges
between 1.6
and2.9#.
.158
.................
53
Plot of metaquartz/total ratios and abundances
of feldspar, chert, and metamorphic rock
fragments within Baca sandstones
as a function
of stratigraphic position. Samples were
taken from Massingill's (1979) measured
section in the Bear Mountains vicinity. Mean
grain size varies widely, therefore caution
is :advised in the interpretationof this
data.
159
....................
xvi
0
-
Page
-
Figures
54
55
Well-developed calichified paleosol showing
numerous tube-shaped rhizoconcretions.
...
161
Baca caliche as seen in thin section. Note
wide range in calcite crystal sizes and the
presence of numerous grains which exhibit
hematitic clay cutans. Sample 34, crossed
nicols, field width=0.8 mm.
163
.........
56
Coarsely crystalline spar cement in an upperdelta sandstone (sample C). Crossed nicols,
field width=0.8 mm
165
.............
57
Coarsely crystalline sparry calcite cement in
cigar-shaped sandstone concretion (sample 49).
Loosely packed fabricis indicative of very
early cementation (prior to compaction).
mm.
166
Crossed
nicols,
field
width=0.8
.....
58
Hematite-stained fine-grained sparry calcite
in a frontal-splay sandstone (sample
13).
Note poorly compacted nature of this earlycemented lacustrine sandstone. Crossed
169
nicols, field width=0.75 mm.
........
59
Syntaxial overgrowth on detrital quartz grain
Sample 45, crossed nicols, field width=
0.75 m
m.
172
..................
60
61
Flamboyant megaquartz cement. Sample M50,
crossed nicols, field width=0.8mm. . . .
..
173
Inhibition of syntaxial quartz overgrowth
by
coarsely crystalline sparry calcite cement.
Sample B , crossed nicols, width of field=
m
.
174
0.75 m
..................
62
Plot of authigenic quartz content in studyarea sandstones as a function of stratigraphic position.
. . . . . . . . . . . . . . 176
63
Plot of authigenic quartz content in Baca sandstones as a function
of stratigraphic position.
Data from point counts made by the writer on
thin sections from Massingill's (1979) measured
section in the Bear Mountains area.
177
.....
i
xviii
Page
-
Figure
64
Authigenic kaolinite. Bluish tint is due
to impregnation of kaolinite microporosity
with blue epoxy. Sample 48, crossed nicols,
179
field width=0.15 mm.
............
65
Scanning electron photomicrograph of vemicular
stacks of kaolinite crystallites on a quartz
sand grain. Sample
56, 5,OOOX.
180
......
66
Dolomite cement showing alternating iron-rich
and iron-poor zones. Sample B, crossed nicols,
field width=0.75 n
un.
183
............
67
Dolomite rhombohedron replacing adjacent quartz
grain. Sample B, crossed nicols, field width=
0.75 mm.
:
184
...
68
e
..............
Generalized map ofthe study area showing coincidence of occurrence of dikes and areas in
which Baca sandstones are yellow-gray in
186
color (stippled areas).
...........
69
Distribution of coloration for 52 Baca sandstone
samples fromthe study area. Values were
Soil
determined bycomparison with Munsell
Color Chart. Color terminology after Folk
188
(1969).
...................
70
Hematite flecks uniformly distributed on Baca
sand grains, except at contact points between
grains. Sample P, plane Light, field width=
0.15 mm.
192
..................
71
Scanning electron photomicrographof euhedrally
terminated hematite crystals on
quartz sand
193
grain. Sample P, 7,OOOX.
..........
72
Change of color with geologic are shown on
plot of hue vs. saturation. Third color
dimension oflightness shown by the numbers
4/ etc. anddegree of darkening of the
squares. C, initial unweatheredsand; A ,
Sf, Simpson
Saharan sands, data from Alimen;
age; Sm,
Desert, surface fluff of Holocene
a
xix
Figures
Page
-
Simpson Desert, modal color en masse
of fine
Sp,
Simpson
Desert,
c
z
o
r
of
hematitesands;
clay cutans in pits, formed during Pleistocene
lateritization; P , other Pleistocene sediments
Hm, color of powdered pure hematite; +PyM,
color of Mesozoic and younger Paleozoic red
rocks; Po, Older Paleozoic and Precambrian
rocks. Processes that create these changes
shown by the "evolutionary" arrows. (Modified
from Folk, 1976).
197
..............
73 Diagenesis flowchart for the Baca sediments
within the study area.
...........
74 Plot
a
202
of grain size vs. percent cement plus
primary porosityzowing tendency towards
looser packing in the fine-grained lowerdelta and lacustrine basinal sediments. Note
the presence of yellow-gray coloration only
in the coarser grained, non-lacustrine sandstones.
204
...................
75
Hypothetical
model
for
the
distribution
of
facies and paleocurrents in the Baca-Eager
basin during early Baca time (high lake
stand). Letters in parentheses indicate
paleocurrent data sources. J=Johnson (1978),
P=Pierce (19791, S=Snyder (19711, C=Cather
(this study). Reference points same as
211
Figure 10.
.................
INTRODUCTION
Study Area
The
Eocene
Baca
Formation
of
,correlative
Eagar
Formation
Arizona .comprise
a
and
and
Mexico
s t u d ya r e ac o n s i s t s
exposure
.of
the
to
thestudy
Alamo
Band
which
o ui n
t
a west-trending b e l t from near
of
an
approximately
Baca
crops
the Mogollon R i m of
Arizona.
New Mexico (Fig.
a t h en o r t h
(32
1).
area i s located on the
km)
km
end
of
2
)
the
northwest
of
The e a s t e r nt w o - t h i r d s
of
mi
20
The
m i 2 (31.1
12
Formation
Gallinas
Mountains
about
Magdalena,
and
R i m g r a v e l s Of
Mogollon
claystone
discontinuous exposures -along
New
Mexico
redbed
sequence
conglomerate,
of
sandstone,
mudstone,
Socorro,
New
s o u t h e r np o r t i o n
Navajo Reservation.Quality
of
the
of exposureranges
from e x c e l l e n t l y exposed stream c h a n n e il n c i s i o n st ov e r y
The best exposuresare
poorlyexposedbadlandstopography.
intheeasternportion
t h ea r e a
of t h e studyarea.
i s about 400 f t (123 m ) ,
and t h ea v e r a g ee l e v a t i o n
i s approximately 6700 f t (2061 m ) .
semiarid
climatic
zone
and
receives
precipitation during July
Maximum r e l i e f i n
The area l i e s
most
andAugust.
1
within
a
of i t s annual
2
0 Baca Formation
n Eagar Formation
Mogollon R i m gravels
Figure 1. . L o c a t i o n of study a r e a and Baca, Eagar, and Mogollon
R i m gravels.
3
Purpose and Methods of S t u d y
The p r i m a r y
objectives
describethepetrology
i n thestudy
of
the
a)
and provenance of t h e Baca Formation
c ) to
d e f i n teh e n v i r o n m e n t s
sediments;
of
deposition and dispersal p a t t e r n s of t h e Baca.sediments
the
study
area,
to
b ) t o d e t e r m i n et h ed i a g e n e t i ch i s t o r y
area;
Baca
were:
of t h i s study
and;
d)
in
and summarize t h e
td
oelineate
:tectolric.-framework
-and
paleoenvironments
entire
f otrh e
Baca-Eagar b a s i n .
Pebble
counts,
petrographic
examination
sandstones,andpetrographic
mudstones and
petrology
and
sediments.
history
claystones
Data
of
and x-raymineralogicstudy
were
u t i l i z e tdo
describe
determine
the
provenance
for
of
reconstruction
Baca
tdhiea g e n e t i c
optical
and
Detailed mapping a t a s c a l e of 1:24,000
(Plate
l),
,the
sediments
provided
the
by
of
was
of
the
of
scanning electron microscopy.
paleocurrent
measurement,
and
the
measurement
one
of
complete and s e v e r a l p a r t i a l s t r a t i g r a p h i c s e c t i o n s p r o v i d e d
t hbea sfiroser c o n s t r u c t i o n
of
paleoenvironments
sediment dispersalpatterns.Depositionalenvironments
and
were
i n t e r p r e t euds'i tnfhg
oel l o w i cnrgi t e r il ai t:h o ' f a c i e s '
geometry, l a t e r a l and v e r t i c a lv a r i a t i o ni ng r a i n
sedimentary
. s t r u c t u r en sa,t u r e
of
contacts
size
and
between
.
e
4
l i t h o f a c i e s ,p e t r o g r a p h i cd a t a ,
Interpretation
environmental h i s t o r y o f
of
and f o s s i l s .
the
tectonic
reconnaissance
level
alongthe
paleoand
t h e Baca-Eagar b a s i n was based both
on my own d a t a and t h a t . o fo t h e rw o r k e r s .
on
a
I
the
Baca-Eagar outcrop b e l t .
I
majority
of
I ' have
have
examined
t h e exposures
r e l i e dh e a v i l y
upon Johnson ( 1 9 7 8 ) f o r h i s h i g h l y a c c u r a t e f a c i e s a n a l y s e s ,
e s p e c i a l l yi n
the ,western
portion
o.ft h e
outcrop
belt.
Addi.tiona1. p a l . e o r u r r e n t ~.data
~
was drawn from Snyder(19711,
Pierce and others(19791,
and Johnson(1978).
e
GENERAL STRATIGRAPHY
Upper
exposed
C r e t a c e otuhsr o u g
Qhu a t e r n asrtyr a t a
along t h e n o r t h e r nf l a n k
of t h e G a l l i n a s
The o l d e s tr o c k s . p r e s e n ta r et h es a n d s t o n e s
the
Late
Cretaceous
Crevasse
are
and
..
a
redbed
tuffs,
a
by
and
Numerous
These a r e
in
the
T h e Baca i s
t h ev o l c a n i c l a s t i cs e d i m e n t a r yr o c k s ,
lavas
the
Oligocene
of
eastern
portion
Extensivepiedmontgravels
ash-flow
Formation.
Spears
north-trending
mafic
dikes
Miocene time i n t h e
were emplaced
during
of
the
s t u da
yr e a .
of l a t e P l i o c e n e ( ? ) t o Holocene
agerepresentcoalescedalluvial-fandepositsresulting
the
study
sequence
sandstones,
of
-mudstones; "claystones,andminorconglomerates.
overlain
of
shales
Canyon Formation.
o v e r l a i n by t h e Eocene Baca Formationwhich,
a r ce o
a ,n s ios ft s
Mountains.
from
southward e r o s i o n a l retreat of t h e steep n o r t h e r nf l a n k
of theGallinasMountains.Quaternarysands
p r e s e n t i n and along
valleyfill.
and g r a v e l s are
modern ephemeral stream channels and as
Only t h e Baca Formation was s t u d i e d i n d e t a i l .
5
e
6
Late Cretaceous
Crevasse Canyon Formation
The Crevasse Canyon Formation wasnamed
Balk
(1954)
Basin.
the
"
..
f o r exposures on th'e w e s t s i d e o ft h e
It i s e q u i v a l e n tt o
Mesa
by Allen
San Juan
the Dilco and Gibson Members
Formation
Verde
and
and
. . interaal.
between.the..Gallup..and
Of
occupies the s t r a t i g r a p h i c
. Point
lookout
Formations.
Tonking (1957) w a s the f i r s t t o u s e t h e term Crevasse Canyon
i nt h eB e a r - G a l l i n a s
0
section
1,052
ft
Mountains v i c i n i t y .
(324
Formation d i r e c t lnyo r t h
(1920)
c o l l e c t e df l o r a l
m)
t h i c ikn
of
the
Tonkingmeasured
the Crevasse Canyon
study
area.
Winchester
remains
from t h C
e revasse
Canyon
which were i d e n t i f i e d by Knowlton as being of Montanan
Gardener
or lower Montanan.
The Crevasse Canyon Formation consists of
of
yellowish-gray,
fine-
to
The
paludalenvironments
sea
formation
was
and
sandstones,
a
few
d e s o s i t e idlni t t o r a l
thin
and
as t h eL a t eC r e t a c e o u se p i c o n t i n e n t a l
w i t h d r e w northeastward from west-central
thelast
a sequence
medium-grained
carbonaceous
shales,
medium-gray t o black
coal
beds.
age.
either
( 1 9 1 0 t)e n t a t i v e l yd a t e dt h ef o r m a t i o na s
upperColoradan
a
time (Tonking,1957).
New Mexico f o r
7
Eocene
Baca Formation
Baca Formation
I nt h es t u d ya r e a ,t h e
Crevasse
Canyon
Formationand,
o v e r l i e st h e
i nt u r n ,
i s o v e r l a i n by t h e
TheBaca
records the f i r s t
v o l c a n i c l a s t i c Spears Formation.
area.
Tertiary sedimentat.ion in the
C o r r e l a t i o n and Previous Work
Winchester
(1920)
published
one
of
New Mexico.
geologic maps of west-central
the
first
In this b u l l e t i n ,
he proposed the name "DatilFormation"foranapproximately
of
2000-ft
(615
m)-thick
sequence
non-volcanic
,rocks
Wilpolt
in
exposed
T e r t i a rvyo l c a n i c
western
Socorro
and others (1946) d e f i n e d t h e
and
County.
Baca Formation a s t h e
basal non-volcanicportionofWinchester'sDatilFormation.
However,
t h e Baca s e c t i o n which t h e y measuredand
w a s i n t h e J o y i t a H i l l s , and n o t where they defined
section.'
The
Baca
and i s l o c a t e di nt h e
e a s t e r ,nf l a n k
County.
Baca
of
described
t h e type
t y p e s e c t i o n i s 684 f t (210.5 m) t h i c k
upper
the
part
Bear
Baca
Canyon
Mountains
Wilpolt and others
(1946)
teoq u i v a l e n
r ot c kesx p o s ei d
n
of
also
on
the
iw
n e s t e rS
nocorro
extended
the
the
Joyita
term
Hills
8
vicinity about 30 mi (48km)
east of the type locality.
Wilpolt and Wanek(1951) further extended the Baca southeast
of
the
type
locality
into
the
Carthage
area.
Within New Mexico, the Baca Formation
has
been
tracedwestwardalongadiscontinuousoutcropbeltby
Tonking (1957), Givens (1957), Willard and Givens (19581,
(1964).
'Willard and Weber (1958), Willard (1959), and Foster
Baca-equivalent rocks have also been described
in
east-central
Arizona.
The
Mogollon
Rim
gravels
were
interpreted by Hunt (1956) to be Late Cretaceous
to
Eocene
in age. Pierce and others (1979) state that these gravels
were derived from Precambrian sources to the southwest
duringEocene-Oligocenetime.TheBaca-equivalentsandstones and conglomerates of the Eagar Formationwere named
and described by Sirrine (1956).
(1978) was
In his regional Baca-Eagar study, Johnson
the first to correlate the Baca, Eagar, and Mogollon Rim
gravels. Based
on the continuity
'
of gravel compositions,
paleocurrent indicators, lateral facies variations, and the
configuration of the early Tertiary tectonic framework in
the southwestern United States,
I
strongly support this
correlation.
Very few previous investigations within
area have been carried out. Tonking (1957) studied
geologyofthePuertecitoquadrangle,anareawhich
the
study
the
9
encompasses
t heea s t e rt n
wo-thirds
Givens (1957) s t u d i e d t h e w e s t e r n
a r e ai nh i s
work
these studies
..
t hs et u dayr e a .
of
one-third
of
t h es t u d y
on t h e Dog Springs
quadrangle.
Both of
were reconnaissance i n n a t u r e .
in
Recently, much d e t a i l e d work hasbeenperformed
a r e aasd j a c e nttohset u d y
Jackson ( i np r o g r e s s )
to
areas
the
east
respectiv~ely.Laroche
a
portion
Mountains.
the
Rio
'
have
and
area.
studied
and.
i n c l u d i n gt h e
of
the
detail
area,
and
mapped
exposed i nt h eG a l l i n a s
Baca
Arizona-New
Baca exposednorth
in
t hs teu d y
( . i n p r o g r e s s )h a ss t u d i e d
Snyder
(1971)
studied
the
Grande
and
mapped
northeast
t h ev o l c a n i cr o c k s
of
Mayerson (1979) and
exposed
between
Mexico
state line,
of t h e G a l l i n a s
Mountains.
A summary of p r e v i o u s work i s presented i n Table 1.
Lower T e r t i a r y E q u i v a l e n t s
Several lower Tertiary formations are present
Mexico
(Fig.
2).
These
include
the
Raton,
Nacimiento, G a l i s t e o , Cub Mountain, McRae,
Formations.
These
San Jose,
and
Love'
Ranch
u n i t s were deposited i n isolated b a s i n s
which were c r e a t e d by the Late Cretaceous
orogeny.
i n New
t o Eocene Laramide
10
Table 1
Summary of Previous
Studies
Location of
Workers
Study
Carthage
!
j_
Joyita
Bear
Hills
Mountains
Gallinas
Datil
Mountains
Mountains
Gardener (1910)
Wilpolt and Wanek (1951)
Wilpolt and others (1946)
Winchester (19201
Wilpolt and .others
Tonking (1957)
Potter (1970)
Massingill (1979)
(1946)
Tonking (1957)
Givens (1957)
Mayerson (1979)
Willard and Givens (1958)
Schiebout, J.A.
(ongoing research)
Quemado
Willard and Weber (1958)
Schiebout, J.A.
(ongoing research)
Schrodt, K. (in progress)
Red
Hill
O’Brien (1956)
Springerville
Sirrine (1956)
Mogollon
Rim
Hunt (1956)
Pierce and others (1979)
Regional
Studies
Willard (1959)
Snyder (1971)
Johnson (1978)
11
Figure 2.
Map showing outcrop areasof lower Tertiary
units in New Mexico and adjacent areas. .
12
Age and F o s s i l s
The Baca andEagarFormations
and t h e
gravels have been assigned ages ranging
t oe a r l yO l i g o c e n e .
an
Eocene
from Late Cretaceous
a gf o
et hr e suen i t s .
sediments
Rim
Most agedeterminations,however,give
The
80 and 40 m.y.
occurred
between
about
The
Mogollon
of
orogeny
Laramide
ago
(Coney,
1971).
t h e Baca and e q u i v a l e n tu n i t sa p p a r e n t l y
were derived from Laramide u p l i f t s , t h u s l e n d i n g s u p p o r t f o r
a Late Cretaceous t o Eocene a g ef o rt h e s es e d i m e n t s .I nt h e
Joyita
Hills,
a
m.y.
37.1
radiometric
has
date
been
obtained f r o m a v o l c a n i c c l a s t i n t h e S p e a r s F o r m a t i o n
which
(Weber,
overlies t h e Baca
area,
the
Baca
must
1971).
Therefore, i n
o l d tehr aena r l i eO
s tl i g o c e n e .
be
d e t e r m i n a t i o n fs o trh e
the
study
area.
cloven-hoof
p r i n t si n
The
writer
Photographs of
Baca have been
t h e lower red member of
t h e sper i n t s
of
the
American
were
Dr.
Texas a t Austin and D r .
Museum
the
31, T.2N.,
v e r t e b r a t e .p a l e o n t o l o g i s t s ,i n c l u d i n g
theUniversityof
the
made i n
d i s c o v e r es d
e v e rfaol s s i l
SE 1/4, SE 1/4, sec.
3).
1/4,
and
summarized i n Table 2.
No age determinations for the
Nw
Age
Baca and
Eagar
Formations
Mogollon R i m g r a v e l s a r e
the
that
shown
Baca
R.6W.
to
(Fig.
several
Wann Langstonof
Beryl E.
Taylor
of N a t u r a l History, New York.
y e t , no one has been able t oi d e n t i f yo r
at
date
these
As
trace
Table 2
Summary o f Fossil
Location Unit
Age
Age How Dated
Author
Pierce and
others (.1979)
Determinations
Mogollon
Mogollon
Rim
radiomekric
Rim Eocenegravels
Sirrine (1956)
Springerville
Eagar pollen,
spores
Belcher, R.
(pers. comm,,
Johnson, 1978)
Springerville
Eagarrhinoceros
Eocene
tooth
Oligocene
L. Cretaceous
Gardener (.1910)
Baca
Carthaye
Palaeosyops,
middle
Eocene
rhinoceroslike mammal
Schiebout, J'.A.
(pers. comm.1
Baca
Quemado,Datil,
Mountains
tuetle,
croc-
titwothere,
Eocene-early
Oligocene
odile, lizard
Snyder (1971
Baca
Datil
Mountains
Protoreondon
~pumu'lus, sheeplike mammal
Chaiffetz (1979)
Baca
Bear
Mountains
pollen,
spores
Eocene
late
Eocene
Figure
3.
Cloven hoof prints found in a Baca delta-plain
sandstone. Lens cap is approximately seven cm
in diameter.
15
Many o s t r a c o d s were observedwhileexamining
fossils.
area ( F i g .
Sections from t h es t u d y
later,
As I
4).
will
thin
discuss
t h e soes t r a c o dpsr o v i daed d i t i o n aelv i d e n c e
l a r g e l yl a c u s t r i n ee n v i r o n m e n t
however,
I
havenotbeen
of a
of d e p o s i t i o nf o rt h e
Baca,
able t o use them f o rd a t i n gt h e
unit.
The onlyotherfossilremainsobservedconsistof
carbonaceous
and
s i l i c e o u sp l a n t
G a l i s t e o Formation,which
and wood fragments.
The
i s exposed s o u t h of Santa Fe,
has
o r Eocene on t h eb a s i s
beendatedasPaleocene
plantremains
(Lee and Knowlton,1917).
of f o s s i l
Such d a t i n gh a sn o t
y e t been attempted i n t h e Baca.
Contacts
The c o n t a c t of t h e Baca w i t h t h e s u b j a c e n t C r e v a s s e
Canyon
Formation
area.
Where
unconformity
is
a t the
mudstone.
Canyon
Formation.
These
e
formed
in
a
low-relief
erosfonal
of little o r no a n g u l a r i t y .
observed t o be
developed
Crevasse
is
it
visible,
of t h e Baca was
mapped
sandstone
or
exposed i n t h es t u d y
g e n e r a l l yp o o r l y
base
Rare
i nt h e
directly
t h ef i r s tr e d d i s h
p a l e o c a l i c hheo r i z o n s
uppermost
below
paleocaliches
of
The lowercontact
portion
were
of
t h ec o n t a c w
t i t ht h e
were
produced
the
Baca
by
a r i d o rs e m i - a r i dc l i m a t i cc o n d i t i o n sd u r i n gt h e
soils
16
1
Figure 4.
Hematitic mudstone-filled ostracod test in
m, crossed nicols.
sample 49. Field width=0.8 m
17
hiatus between
and
final
deposition
of
Crevasse
the inception of Baca sedimentation.
Canyon
sediments
In some areas, a
poorly exposed pebble lag appearsto be present along the
Baca-Crevasse
Canyon
contact,
perhaps
representing
a
paleo-deflationsurfacewhichdeveloped
on
theuncon-
solidated
Crevasse
Canyon
sediments
prior
to
Baca
deposition. In areas outside the study area,
contact
is
reported
the
lower
to beunconformabletoapparently
conformable '(Willard, 1959; Tonking, 1957; Potter,
1970).
The upper contact of the Baca with the Spears
Formationgenerallyisgradational,
e
the
contactbeing
defined at the first occurrence of megascopically visible
volcanic
material.
The
gradation
between
Bacaand
Spears-type
General
lithologies
Description
and
takes
place
Informal
within
a
few
meters.
Units
In the study area, the Baca Formation consists of a
redbed sequence of sandstone, mudstone, claystone, and minor
conglomerate.
One
complete
stratigraphic
section
was
measured in the eastern portion of the study area. It has a
total thickness of 941.5ft (289.7 m), and is
Appendix A.
e
presented in
18
In the Bear Mountains area, Potter
(1970) divided
the Baca into three informal members which
he termed, in
ascending order, the lower red unit, the middle sandstone
unit, and the upper red unit.
I found this terminology
applicable in the study area, but
I must emphasize that
these informal units are genetically related to lake-level
fluctuations in a large Eocene lacustrine system present
in
the
ga the
Bear-Gallinas Mountains area and are not applicable
to
preaominantly
fluvial
Baca-Eagar-rocks
to the
west
or
to
the Baca exposed east of the Kio Grande. This subject will
be discussed in detail in later sections. On the basis
a
of
thickness,
stratigraphic
position,
and
similarity
of
lithofacies,theunitsdefinedinthestudyareaare
probably directly correlative with the units of Potter
(1970) in
theBearMountains(Fig.
5),
although
the
paleo-continuity of these units has yet to be demonstrated
due to.late
Tertiary
structural
complications
and
cover.
In his work in the Bear Mountains area, Massingill
(1979) recognized the same three informal units
in the Baca
as
did
Potter.
However,
Massingill
chose
to
abandon
Potter's terminology
in
favor of, in ascending order, the
conglomeratic, the gray sandstone, and
members.
I
the
red mudstone
favor retention of Potter's terminology on
the
basis of the following criteria: a) the lower red unit
e
the
study
area
(equivalent
in
to Massingill's
conglomeratic
19
ChLLIrnS
mUNPAINS
SECTION
Figure 5.
Comparison of generalized Baca stratigraphic
sections measured in the Gallinas and Bear
Mountains, showing similarity of lithofacies
and probable correlation of informal units.
Sections are separated by about 10 mi (16 k m ) .
Bear Mountains sectionmodified from Massingill
(1979).
20
member)containsverylittleconglomerate,
as
willbe
discussed in a later section. The conglomeratesin the Bear
Mountain area are present due
to the relative proximity of
the
source area, thus the term lower red unit
is more
descriptively viableon a regional level; b)the coloration
of! Massingill's gray sandstone member reflects only the
diagenetichistory of
the sediment. Indeed,
sandstone
study
unitin the
area
is
often
the
middle
red.
The lower red, middle,sandstone, and upper red unit
of reference and
terminology will be utilized only for ease
to facilitate generalized lithologic descriptions,
as below.
e
For the more detailed descriptions and interpretations in
later sections, the principlesof genetic stratigraphy will
be
employed
to
subdividetheformationintocomponent
(1972).
depositional systeq as defined by Fisher and Brown
Lower Red Unit. The lower red unitis 323 ft
(99.4
"
m) thick at
the measured section and is composed of red,
gray, and yellow sandstones intercalated with red mudstones
to mudstone is about
and claystones. The ratio of sandstone
1:l.
Minor amounts of conglomerate are present
as thin
lenses within sandstone units. Sandstone beds in the lower
red
unit
average
a few inches
0
to
18 ft (5.5 m) thick andrange
about
25 ft ( 7 . 7
m) in thickness.
thicker beds canbe traced for as much as a mile
between
Some of the
(1.6
km)
21
along
strike.
f t (3.1 m )
Mudstone and claystone beds averageabout
10
m)
in
The middle s a n d s t o n eu n i t
is
thick
thickness.
and
range
up
to
50 . f t
(15.4
Mudstone u n i t sa r ec a l c a r e o u sa n de f f e r v e s c ei n
cold,dilutehydrochloricacid.
Middle SandstoneUnit.
(75.7 m) t h i c k a t t h e
246, f t
of f i n e - t o coarse-grainedyellow,gray,
a l m o s te n t i r e l y
red
measured s e c t i o n and c o n s i s t s
The s-andstones are most o f t e nh o r i z o n t a l l y
sandstone.
laminated, but frequently display well-developed,
large-scale
trough
crossbedding
e
or
bedding.
Mudstones
and
and
medium- t o
rare
t a b u l acrr o s s rare
c l a y s t o n easrvee r y
in
the
s a n d s t ounnoeict ,c u r r ipnrgi m atrh
ai lisy
n,
middle
discontinuous clay drapes within the sandstones.
T h e upper red u n i t i s very
Upper ".Red Unit.
in
to
appearance
the
lower
red
s e c t i o n , it c o n s i s t s of a 372.5 f t
red,
yellow,
and
mudstonesand
unit.
similar
A t the measured
(114.6
m)
sequence
of
red
g r asya n d s t o n ei n
s t e r c a l a t ew
di t h
claystones.
Conglomerates a r e r a r e and
a st h i nl e n s e sw i t h i ns a n d s t o n eu n i t s .
occur
T h e upper red u n i t
contains less conglomeratethanthelower.This'has
been
noted
in
Johnson,
1978;
e
mudstone
the
Bear
Mountains
Massingill,
ratio
is
about
1979).
1:l.
also
a r e( a
Potter,
The
Mudstones
1970;
sandstone
aurseu a l l y
to
22
calcareous.
Both sandstone and mudstone beds tend
to
be
thicker in the upper red unit than in the lower. Sandstones
range in thickness to as much as about
mudstones can be as thick
100
(30.8 m):
ft
as80 ft (36.9.m).
Oligocene
'
Spears Formation
Tonking(1957)dividedallbutthebasalBaca
portion of Winchester's (1920) Datil Formation into' three
a
members. These members are, in ascending order, the Spears,
HellsMesa,andLaJaraPeak.TheSpearsMemberwas
(1978).
upgraded to. formational status by Chapin and others
A
section of Spears measured by Tonking (1957)
in the Bear
Mountains, about 12 mi (19.4 km) east of the study area,
indicates a thickness of 1,340
ft (412.3 m).
The Spears
Formation has been dated radiometrically with dates ranging
between 37 and 33 m.y.B.P.
(Chapin and others,1978).
The Spears is composed of
a sequence
of
grayish-
purple volcaniclastic sandstones, conglomerates, and mudflow
deposits, with interbedded lavas and ash-flow tuffs in the
upperpart.
The
formation is
latitic to
andesiticin
composition
and
represents
the
early
intermediate-
a
composition phaseoftheDatil-Mogollonvolcanicfield
23
(Chapin
and
Seager,
1975).
volcanicflows
The
Spears
contains
more
s o u t h , i n d i c a t i n ge r u p t i v ec e n t e r si n
tothe
t h adt i r e c t i o nT. r e n d s
of
m u d f l o w - f i l l ep
d a l e o v a l l e yisn
of t h e s t u d y area i n d i c a t e a
the basal Spears directly south
, .
generally northward transport'direction.
\
Miocene
Dikes
I
Numerous n o r t h - t r e n d i n d
g i k easreex p o s e idtnh e
0
eastern
portion
t h se t u d y
a r e aT. h e s e . d i k e rsa n g ien
of
width u p t o about f i v e f e e t ( 1 . 5
and
in
km).
The d i k e s , w e r e emplaced
with
the
Potassium/argondating
much as 1 . 5 m i (2.4
a l o nfga u l tasnfdr a c t u r e s
opening
of
the
Rio
of two d i k e si nt h e
vicinity yielded dates
E.
d i pn e a r l yv e r t i c a l l y ,
some cases may be traced f o r a s
associated
(C.
m),
of
Chapin,
unpublished
Grande
rift.
Mountains
Bear
and 24.W-0.6
m.y.B.P.
24.3-kO.8
dates).
Dike rocks
are
generally
greenish-black
and
range
from
texturally
c r y s t a l l i n e .I nt h e
have
been
1979).
margins.
a p h a nvitetori y
c - f i n e - g r a i nheodl o Bear Mountains a r e a , these
dikerocks
c l a s s i f i eadbsa s a l t iacn d e s i t e(sM a s s i n g i l l ,
The
dikes
Baked
commonly
zones
are
exhibit
common
fine-grained
in
the
chilled
country
rock
24
a d j a c e n tt ot h e
azone
d i k e s , b u t a l t e r a t i o n i s u s u a l l yl i m i t e dt o
less than a f o o t ( 0 . 3 m ) t h i c k .
Pliocene ( ? ) t o Holocene
Piedmont
Gravels
L
Extensive piedmont g r a v e l as r p
e r e s e ntth r o u g h o u t
t h ec e n t r a l
and
western
portions
u n i t s of d i f f e r i n agg e s
were
of t h e
study
area.
mapped.
The
topographicallyhigherthanthe
older
youngerandforms
d e p o s i t sc a p p i n gt h eh i g h e ra r e a sn o r t h
Mountains
escarpment.
of
occupies
a large,continuousarea
t h es t u d ya r e a .
The
of
t h eG a l l i n a s
younger
100 f t (30.7 m ) .
the
younger
unit
o l d e r , and ranges up t oa b o u t
locally overlie the
is
westward.
m).
of
consistingpredominantlyof
and
The
Both
units
Baca with angular unconformity.
cobbles.
Clast
composition
Mesa,
of
of t h e
Grain s i z e i n both u n i t s ranges from coarsesand
aells
of
However,
l e s st h a nt h a t
50 f t (15.4
up
gravel
i n t h ec e n t r a lp o r t i o n
t h i se l e v a t i o nd i f f e r e n c ea p p e a r st od e c r e a s e
is
isolated
The d i f f e r e n c e i n e l e v a t i o n of t h e b a s e s
t h e two u n i t s i s as much asabout
thickness
unit
The o l d e r piedmont gravelranges
200 f t (61.5 m) i n thickness.
t oa b o u t
'
Two
A-L
both
units is identical,
s u b e q u a l p r o p o r t i o n s of
Peak
Tuff
to
Spears,
l i t h o l o g iPees b
. ble
25
imbrication
indicates
flow
piedmont
t hG
eallinas
r e t r e a t of t h e s t e e p n o r t h e r n f l a n k
Mountains.
westernSocorrocountyrange
Holocene
Tnese
g r a v e l sr e p r e s e n t . c o a 1 e s c e da l l u v i a l - f a nd e p o s i t s
related to the erosional
of
was generally
northward.
Similar
piedmont g r a v e lisn
i n age from l a t e P l i o c e n e ( ? ) t o
(J.
Hawley,,1979, o r a l commun.).
The
i ne l e v a t i o no f
t h e two g r a v e l u n i t s i n d i c a t e s
difference
a
periodof
e r o s i o n p r i o r t o d e p o s i t i o n of the younger u n i t .
Quaternary
Alluvium
Locallyderivedsandsandgravelsarepresentin
n e aprr e s e n t layc t i v e
ephemeral
valley f i l l in the northern portions
stream
channels
of t h e s t u d y a r e a .
and
and as
LARAMIDE TECTONICS
S t y l e s of Deformation
m u l t i t u d e of basins
The Baca-Eagar b a s i n i s oneofa
and'
u p l i g t s whichformed
d u r i n g theLateCretaceous
i n w e s t e r n North America ( F i g .
EoceneLaramideorogeny
Threegeneralstructuralprovinces
deformation
can
be
skinned",
low-angle
!
i
foldbelt,theasymmetric
0
of
t h ec l a s s i c
to late
6).
and a s s o c i a t e ds t y l e s
6,
thin-
delineated.
These
thrusts
f o l d s of t h C
e ordilleran
and
basement-cored
are
of
the
a n t i c l i n a lu p l i f t s
Laramide Rocky Mountains, and themonoclinal
f l e x u r e s of the Colorado Plateau.
Cordilleran Foldbelt
The C o r d i l l e r a nf o l d b e l t
from
Guatemala
to
of
Alaska
(Drewes,
19781,
and
p r e d o m i n a n t l yd u r i n gL a t eJ u r a s s i ct ol a t e
dominant
style
verging,low-angle
of
deformation
extends
North
America
is
was a c t i v e
Eocene time.
The
one of i m b r i c a t e a s t -
t h r u s t i n gw i t ha s s o c i a t e df o l d i n gw i t h i n
a l l o c h t h o n o up
s l a t e (sF i g .
7).
of those i n southern
Arizona
and
sheets generally did not involve
With the
notable
,exception
New
Mexico,
the
thrust
Precambrianbasementrocks.
Amounts of s u p r a c r u s t a l t r a n s p o r t t h r o u g h o u t t h e C o r d i l l e r a n
26
27
Asymmetrical
basementcored anticlinal
uplifts
7
Eaatward limit of
Cordilleran foldbelt
Figure
6.
a D
Colorado P l a t e a u
monoclinal flexures
Cordilleran foldbelt
uplifts
..........
Colorado Plateau
boundary
Map showing d i s t r i b u t i o n and s t r u c t u r a ls t y l e s
of Laramide u p l i f t s i n w e s t e r n North America,
and t h e l o c a t i o n of t h e Baca-Eagar b a s i n .
Modified from Eardley(1962)
and D r e w e s (1978).
28
W
Figure
E
7. . Section across Spring Mountains, southern
Nevada, showing-typical,Cordilleran-foldbelt
style of deformation. Note. imbricate, eastverging thrust plates.
29
30 and 60 m i ( 5 0 t o 100
foldbeltprobablyaveragedbetween
km), and may be a s much a s 1 2 0 m i ( 2 0 0 km) i n
(Drewes,
some
regions
are
1 9 7S8t)r.u c t uw
r ei tsfth
ohilen
dbelt
indicative
of
compressional
deformation,
although
mechanisms
by
which
t h es t r e s s e s
the
were t r a n s m i t t e d and t h e
dynamics 'of t h r u s t p l a t e movements a r e h i g h l y c o n t r o v e r s i a l .
T h r u s t i n gi n
Nevada andUtah,west
of t h ec l a s s i c
Laramide
Rocky Mountains, ceased i n LateCretaceoustime(Armstrong,
1 9 6 8 1 , . b u t major
thrust
movements
i nt h eC o r d i l l e r a
Mexico and Canada p e r s i s t e d u n t i l l a t e Eocene
of
time(Coney,
1976).
Basement U p l i f t s of t h e Laramide Rocky Mountains
The g e o g r a p h i c d i s t r i b u t i o n ,
deformation,
of
distinctlydifferent
the
classic
the
as w e l l as t h e s t y l e o f
Laramide
basement
uplifts is
from Chat of t h e C o r d i l l e r a n f o l d b e l t ;
former was favoredon
the t h i n c r a t o n i c s h e l f w h i l e
l a t t e r was favored inthePaleozoicmiogeosyncline
1978).
The
asymmetrical
basement-cored
of t h e Laramide Rocky Mountains form a
from
southern
n o r t h e r np o r t i o n
e
Montana
to
southern
the
(Coney,
a n t i c l i n au
l plifts
belt
New
which
Mexico.
extends
Itnh e
of t h eb e l t ,t h eu p l i f t st r e n dg e n e r a l l y
northwestward,
while
i nt h ec e n t r a l
they t r e n d northward.
The
and s o u t h e r np o r t i o n s
u p l i futssu a lcloyn t alianr g e
30
exposures of Precambrian basement and are often bounded on
oneormoresidesbythrustfaults.Structuralrelief
between
uplifts
and
adjacent
basins
may
be
as
much
as
49,000
ft (15,000 m) (Coney, 1976).
Theoriesconcerningtheoriginofthebasement
uplifts can be broadly divided into two schools of thought:
vertical and horizontal tectonism (Fig. 8a, b).
of
vertical
tectonism
suggest
that
the
Proponents
uplifts
were
produced
bydifferentialverticalmovementsofhigh-angle-faultbounded basement blocks driven by phase changes or plastic
flowage in the lower crustor upper mantle, with resultant
drape folds and subsidiary thrusts in the overlying strata
(Stearns,
1978;
Palmquist,
1978;
Woodward,
Arguments
1976).
in favor of vertical tectonism are largely based
onevidenceagainst
the
alternativehorizontal-stress-
generatedbasement-upthrustmodel,suchas:(a)space
problemsresultingfromrelativethrust-blockmovement
(Stearns,
1978;
Palmquist,
1978);
(b)
necessary
major
wrench faults bounding lateral edges of thrust blocks have
not
been
observed
(Stearns,
1978);
(c)
non-uniform
direction of thrust-block motions throughout the Laramide
Rocky
Mountains
suggests
that
the
uplifts
were
not
by
formed
unidirectionalhorizontalcompressivestresses(Stearns,
.I
1978). Proponents of vertical tectonism believe the thrust
faults in the Laramide Rocky Mountains,steepen with depth.
31
S
N'
. .
E
/--\
a
0
I
10 km
, .
.Figcrre.:.
8 L . . ..Two hy.po.thetica1 styles of deformation in
Laramide Rocky Mountain basement uplifts.
(a) Uplift caused by vertical forces acting
along range-bounding faults whichsteepen
through Owl Creek
Section
with depth.
uplift, Wyoming. From Couples and Stearns
(1978). (b) Uplift created by horizontal
stresses acting along thrust faults. Cross
section through Wind River.Mountain.5,
Wyo-'
ming. Modified from Sales
(1968).
32
The
contrasting
point
of
view
is the
that
uplifts
of
the classic Laramide foreland were created by.horizonta1
stresses,eitherhorizontallydirectedcompression(e.g.
of horizontally
Coney, 1976; Thom, 1955) or a combination
directed compression and left-lateral shear (Sales,
1968).
These horizontal stresses resulted in uplifted basementcored
blocks
faults or
which
were
upthrust
along
moderate-angle
were uplifted due to underthrusting
thrust
by another
thrust block. Evidence for creation of basement uplifts by
horizontal stresses includes:
Of
(a) rapid oblique subduction
the Farallon plate under the North American plate
resulted in strong southwest-northeast-directed compressive
stresses throughout the foreland during Late Cretaceous to
late
Eocene
time
(Coney,
1976);
(b)
COCORP
seismic
profiiing indicates that the southwestern boundary
of the
..
Wind River uplift, Wyoming,-is a thrust fault which extends
of least
at abouta .30.-to 35:.degree-angle to a depth at
24
km, which suggests horizontal motions were more important
than
verticalin
thedevelopment
of
the
uplift
(Smithson
others, 1978); (c) thrust faults are widespread throughout
theLaramideRockyMountainsstructuralprovince;(dl
superincumbent. folding commonly associated
upliftsiseasilyexplainedbylarge-scalehorizontal
movements
of
the
basement.
with basement
and
33
Deformation i n t h e Laramide Rocky Mountains f o r e l a n d
was
Cretaceous
i n i t i a t e di nL a t e
time and
ended
much as 60
Eocene time (Tweto, 1975), and may a c c o u n t f o r a s
mi
(100
km)
corfu s tsahl o r t e n i n g
by l a t e
(Coney,
1976),
but
generally more modest amounts a r e v i s u a l i z e d .
i
i
Fl e x u r e s
ColoradoPlateauMonoclinal
The g e n e r a l lfyl a t - l y i nsgt r a t a
Plateau are locally interrupted
Laramide
of
age
e
of
the
Colorado
by large monoclinal flexures
(Kelley,
1955)
(Fig.
9).
The
a rceu r v i l i n e aor ,f t ebnr a n c h i nisg
nh a p e
monoclines
and
N55'E.
classic
two dominant trend directions
Rocky
Mountains
of
monoclines.
Monoclines
origintodraping
high-anglereverse
to
is u s u a l lnyo t
.Precambrian
basement.
of N20°W and
i s g e n e r a l l y less t h a n t h a t i n t h e
S t r u c t u r a lr e l i e f
Laramide
t h e north and e a s t .
exposed
along
t h e Colorado
Plateau
of s t r a t a over basement r e l i e f c r e a t e d
by
f a u l t s formed i nt h en o r t h e a s t - s o u t h w e s t
s t a t e st h a tt h e s em o n o c l i n e s. c a nb e
interdependent network
of
also
f i t t o a systematic,
regional
lineaments
inferred
to
r e p r e s e nbt a s e m e n t - f r a c t u r z
eo n e s
r e - a c t i v a t ead
rse v e r s e
the
owe t h e i r
Laramide compressive stress f i e l d (Davis,1978).Davis
e
be
b u t Davis
hundredsofkilometerslong.Trendsarevariable,
(1978)recognizes
may
f a u l t s during
Laramide
which
are
which w e r e
time.
34
a
a
Figure
9.
Experimental deformational model showing
probable style ofColorado Plateau monoclinal flexures, using "strata"of kaolinite
and modeling clay resting on rigid "basement" of pine board. Davis (1978).
..:
35
s t y, l e and
The reasons f o r t h e d i f f e r e n c e s i n
of deformation between
Che Colorado Plateau
Rocky Mountains is n o t w e l l understood.
of
deformation
in
the
Laramide
and the Laramide
The g r e a t e rd e g r e e
Rocky Mountains may have
occurred due t o t h e p r e s e n c e o f p r e v i o u s l y
deformed basement
producedduring
u p l i f t i n g -o ft h eL a t eP a l e o z o i ca n c e s t r a l
Rocky
in
uplifts
Nountains
that
area
may i n i t i a l l y d e v e l o p
c u t by f a u l t s a s
degree
(Coney,
1978).
.
Basement
as monoclines which a r e later
the u p l i f tc o n t i n u e st or i s e
(Woodward
and
others, 1972).
Baca-Eagar
The Baca-Eagar
depression
which
'
Basin Tectonic
b a s i n w a s a w e s t - t r e n d i n gs t r u c t u r a l
formed i n t h e s o u t h w e s t e r n p o r t i o n o f
Colorado
Plateau
during
Paleogene
deposite
i nd
the
Baca-Eagar
Laramide
b a s i n . were
uplifts
10).
to the basin.
the
sediments
derived
from
Examples
of
all
( C o r d i l l e r afno l d b e l t
uplifts,asymmetricalbasement-coredanticlinal
ColoradoPlateaumonoclinal
The
time.
surrounding Laramide u p l i f t(sF i g .
t h r eset y l eosf
Framework
uplifts,
and
f l e x u r e s ) a r e ' p r e s e n ta d j a c e n t
36
Figure 10.
Laramide tectonic framework in eastern Ari'zona
and western New Mexico. .Heavy barbed line is
northeastward limit of,Cordiller'anfolabelt
(according to Drewes, 1978). Baca-Eagar. .
Mogollon Rim gravel outcrop
areas are also.
shown. Reference points: S=Socorro, M=Magdalena, D=Datil, Sp=Springerville, SL=Show Low,
SC=Silver City, T=Tucson. Modified from
Eardley (1962).
37
Mogollon Highland
The
Mogollon
Highland
southern
of
Arizona
southwestern
New
and
Mexico forms thesouthwesternboundary
t h e basin and w a s the dominant c o n t r i b u t o r
the
basin.
of
Of
d e t r i t u st o
t h e segment of the
The h i g h l a n dc o i n c i d e s ' w i t h
New
C o r d i l l e r a nf o l d b e l p
t r e s e n it ns o u t h e r nK r i z o n aa n d
Mexico
(Drewes,
1 9 7 8 )E. a r lT
y e r t i a rtyh r u s t i npgr o b a b l y
c r e a t e dt h er e l i e fi nt h eh i g h l a n d sd u r i n g
the
Little
Hatchet
Loring and L o r i n g( i n
i nt h a tp o r t i o n
Mountains
of
southwestern
in
the
In
New Mexico,
prep.) have shown t h a tt h et h r u s t i n g
t h e Mogollon Highland i s Paleocenein
t o Drewes
age.
According
deformation
of
time.
Baca
( 1 9 7 8 )t h
,e
highland
was
dominant
Of
imbricate t h i n -
one
of
similar
skinned t h r u s t i n g and
folding
style
t ot h a it nt h o s e
p o r t i o n s of t h e C o r d i l l e r a n f o l d b e l t p r e s e n t i n s o u t h w e s t e r n
Canada, n e a r S a l t Lake City and
Las
Vegas
States,
and n o r t h e r n Mexico.
in
the
United
states
Davis
(1979),
however,
t h a tt h ee a r l yT e r t i a r yd e f o r m a t i o ni ns o u t h e a s t e r nA r i z o n a
is
related
to
the
formation of l a r g e basement u p l i f t si n
t h a ta r e a ,
similar t ot h o s e
Mountains
to
t h e north.
p o s i t i va
er ed
auring
s o u r ctee r r a n e
of t h ec l a s s i c
The MogollonHighland
Mesozoic t i m e .
for
Laramide
b o tthh e
Jurassic
Morrison
Formations
(Cooley
It
Triassic
was
Rocky
w a s often a
an
important
Chinle
and
and
Davidson,
1963;
Upper
e
38
Dodge,
i n t h eh i g h l a n di n c l u d e
1 9 7 3 )L
. i t h o l o g i e sp r e s e n t
Precambrian q u a r t z i t e s , g r a n i t e s ,
and s c h i s t s , and Paleozoic
rocks
and . carbonate
q u a r t z i t e ss, a n d s t o n e s
(Dodge, 1973;
Hayes, 1978).
S i l v e r , 1978;
Lucero U p l i f t
The n o r t h e r n boundary
of
defined
by theLucero,Zuni,andDefianceuplifts
Laramide monoclinal flexures
of
the
Colorado
Plateau
is
which a r e
t y p i c a l of the Colorado Plateau
The Lucero u p l i f t l i e s on t h e e a s t e r n
(Kelly,1955).
e
basin
Baca-Eagar
the
and
consists
of
margin
broadly
arched,
westward-dipping s t r a t a except along i t s e a s t e r n f l a n k which
i s marked by a
complexly
faulted
and
folded
section
of
s t e e p l ye a s t - d i p p i n gs t r a t a( C a l l e n d e r
Sedimentary
rocks
ranging
Triassic
uplift.
comprise
in
the
and Z i l i n s k i , 1 9 7 6 ) .
age
from
m a j o r i to
yf
the
The s t r u c t u r a l l y low area between
Pennsylvanian
exposures
on
the
Lucero
the
to
and
Zuni u p l i f t s i s termed t h e Acoma sag(Kelly,1951).
Zuni Uplift
. .
The Zuni u p l i f t t r e n d s n o r t h w e s t e r l y
asymmetric;
Juan
basin,
t h e n o r t h e a s t e r nf l a n k
while
and i s markedly
dips g e n t l y i n t o t h e
th
s oe u t h w e s t efrlna n k
(the
San
Nutria
39
monocline)
d ispt se e pt loyw atrhde
Baca-Eagar
exposed i n
Precambrian g n e i s s e s and s c h i s t s a r e
of
t huep l i f t .
The
majority
exposures on t h eu p l i f ct o n s i s t
Permian
-
than
f t
8,000
The
of
the
remainder
of
sedimentary
rocks
is
of t h e
termed
of
the
Gallup
sag.
m) of s t r u c t u r a rl e l i e f
(2462
between t h e h i g h e s t p a r t
sag.
. t h ec e n t e r
The s t r u c t u r a l l y low a r e a between
t oT r i a s s i ca g e .
t h e Z u n i and D e f i a n c eu p l i f t s
More
basin.
of t h e Z u n i u p l i f t and
s t r u c t u r arle l i e f
between
deepest part of the
San Juan basin
13,000 f t (4,000 m )
(Kelly,1955)-
exists
theGallup
t hue p l i f t
and t h e
t o the north
i s more than
is
asymmetrical
Defiance U p l i f t
The n o r t h - t r e n d i n gD e f i a n c eu p l i f t
with
s t e e p eastern flank,facingtheGallupsag
its
and t h e
SanJuan
bas~in. The s t e e p e a s t e r n boundary o€ the u p l i f t i s
defined
by
the
sinuous
Defiance
monocline.
Structural
r e l i e f between the h i g h e s t p a r t o f t h e u p l i f t
sag
is
1960).
a tl e a s t
With t heex c e p t i o n
Precambrian
Out
in
8,000
ft
of
( 2 4 6 2 m) (Kelley and C l i n t o n ,
a
q u a r t z i t e ,t h em a j o r i t y
th
Dee f i a n u
ce
p l iafrte
sedimentary rocks.
and t h e G a l l u p
few
small
exposures
Of
of t h e . r o c k s whichcrop
Permian
to
Triassic
40
Sierra-Sandia Uplift
Eardley
(1962)
proposed
the
existence
of
Laramide
two
u p l i f t sa d j a c e n t ot h ee a s t e r n
boundary of t h e
Colorado P l a t e a u i n New Mexico and termed
and
S i e r rua p l i f t s .
term
t o denoteboththe
hereinbeused
Of
The
Eardley
(1962)
and
that the area
will
S i e r r a - S a n d iuap l i f t
will
Sierra and S a n d i a u p l i f t s
(1971),
was a
be
discussed
Sandia
between them.
and
study
this
between t h e S i e r r a and S a n d i a u p l i f t s
i n t h eS o c o r r ov i c i n i t y
e
the
t h ei n t e r v e n i n ga r e a
Data from Johnson
(1978),
Snyder
suggest
them
in
Laramide
later
Evidence f o rt h i sc o n c l u s i o n
p o s i t i v ea r e a ,a s
s e c t i o ni n
s
includes:
more
detail.
( a )p a l e o c u r r e n t
and
from t h e Baca outcrops e a s t of t h e
paleoenvironmentaldata
Rio Grande (between t h e J o y i t a
the
presence
of
southeastward
E i l l s and C a r t h a g e )i n d i c a t e
to
northward
flow
i n an
alluvial-fanenvironment(Johnson,1978),thussuggesting
source
area
nearby
t toh e
generally southwest-directed
Mountains
v i c i n(iJt o
yh n s o n ,
west;
( b ) p a l e o c u r r e n tasr e
i n t h e Baca exposed i n t h e Bear
1978;
Snyder,
presumably r e p r e s e nftl o w
o ftfhw
e e s t e rfnl a n k
uplift;
(c)
lacustrine
system
t hper e s e n c e
in
a
1971)
and
of
the
of a l a r g ep, e r s i s t e n tc,l o s e d
the
Bear-Gallinas
Mountains
area
i n d i c a t e s the p r e s e n c e of a damming element t o t h e e a s t .
41
The generallywest-dippingPaleozoicstrataexposed
in
and Magdalena Mountains and Socorro
t h e Ladron,Lemitar,
Peak probablyrepresentthewesternflankoftheSierraSandia u p l i f t , a l t h o u g h
anabpreciable
issu r e lrye l a t etrdoo t a t i o n
rifting.
of
component of t h i s d i p
f a ubl lt o c k
dsu r i n g
The geometry of t h e n o r t h e r n p o r t i o n
of t h e u p l i f t
i s p r o b l e m a t i c a l .E a r d l e y( 1 9 6 2 )d e p i c t st h eS a n d i au p l i f t
as
encompassingboth
t h e Nacimiento u p l i f t and t h e p r e s e n t -
day S a n d i u
a p l i f tP. a l e o c u r r e nat n a l y s io
stfh G
e alisteo
Formation,
however,
i n d i c a t etsh at h
t vei c i n i t y
present-day
Sandia
uplift
may
of t h e
a
not
have
been
Laramide
p o s i t i v e area (Gorham and I n g e r s o l l ,1 9 7 9 ) .D r i l l - h o l ed a t a
i n t h e w e s t e r n p o r t i o n of t h e Albuquerque-Belen b a s i n
t hp
eresence
of
earlT
y e r t i a r sye d i m e n t(sF o s t e r ,
t h u sr e q u i r i n gt h ew e s t e r n
lie
u p l i f tt o
of
the
t o <he e a s t of t h a t area.
19781,
SierraSandia
I n t h i ss t u d y ,
I
t o r e s o l v et h ec o n t r o v e r s yc o n c e r n i n gt h e
w i l l notattempt
geometry
boundary of
shows
the
Laramide
u p l i f t s i n n o r t h e r n New Mexico.
The u p l i f t c o n f i g u r a t i o n s d e p i c t e d i n F i g u r e
10 i n t h a t a r e a
should be regarded as h i g h l y t e n t a t i v e .
Baca sedimentsderived
are
arkosic
and
s c h i s t clasts.
rocks
are
contain
from t h e S i e r r a - S a n d i a u p l i f t
abundant
Precambrian
granite
Only a f e w isolatedexposures
presentalong
the Rio
Grande
Thus, t h e Precambrian d e t r i t u s
in
the
and
of Precambrian
r i f t nearSocorro.
Baca
was
probably
42
largely
derived
from
subsequently
downfaulted
analogous
s o u r ct eer r a n e s
which
i n the R i o Grande
This
rift.
is
Laramide Tularosa u p l i f t i n southern New
t ot h e
in
Mexico (Eardley,
1962;
Kottlowski,
1967),
central portion
have
been
of t h e u p l i f t h a s c o l l a p s e d t o
which
the
form a graben
during late Tertiary regional extension.
The
S i e r r a - S a nudpiilam
i fpt l i e s
Grande
rift.
e a r lsyt a g e
This
of
compressive
and C l i n t o n (1960,
p.
tectonism
has
been
noted
by
Kelly
55).
Laramide
p r i o r t o l a t e Tertiaryextensionalong
compression$lphase
t h e Rio
a
They s t a t e :
.
..there i s much evidencealong
the Rio Grande
troughof
an early tectonic compressional history.
Caballos
Mountains
(Kelly
The s t r u c t u r e s of t h e
and S i l v e r ,
1952,
p.
136-146)
a r ec l e a r l ye a r l y
)
T e r t i a r y and compressional.
Low-angle
(15'
f a u l t s i n which g n e i s s rests on Cambrian limestone
are c l e a r l yd i s p l a y e dw i t h i n
a few hundredyards
in
the
Fra
Cristobal
of t h e Rio Grande t r o u g h
County, New Mexico (Jacobs, 1957,
Range &:Sierra
p.
257).
Thrusts
and
overturns
have
been
mapped
i n many p l a c
tS
ihenaesn d i a
and
Manzano
uplifts
...
T h r u s t s ofLaramideagehave
eastern
margin
of
the
a l s ob e e nr e p o r t e da l o n gt h e
rift
in
the
- v i c i n i t y of Socorro
(Wilpolt and Wanek, 1951).
On t h e basis
of
t r e n dg,e o g r a p h ilco c a t i o nt h
,e
presence of t h r u s t f a u l t s a l o n g
e
f o rl a r g ee x p o s u r e s
i t s east f l a n k , and evidence
of Precambrian rocksalong
its
crest,
43
I
the
Sierra-Sandia
u p l i fpt r o b a b l y
represents
s t r u c t u r a l s t y l et ot h e
c o r e da n t i c l i n a lu p l i f ts i m i l a r, i n
classic
Laramide
Front
a basement-
Range
uplifts
Colorado
of
and
Wyoming.
Morenci U p l i f t
a Laramide drainage divide
The probable existence of
alongthesoutheastern
was
margin of t h e Baca-Eagar b a s i n which
s u b s e q u e not b
l ys c u r e dt' h
baiyc k
cumulations
of
mid-TertiaryDatil-Mogollonvolcanicrocks
I'
t o t h e w r i t e r by C.
presenceoflarge
was pointed o u t
Chapin
(1980,
E.
amountsof
oral
commun.).
Laramide v o l c a n i c and p l u t o n i c
rocks i n southwestern N e w Mexico and adjacentArizona
11)
and
of
(see volcanic rock fragment section)
the
Baca
The Morencilineament(Chapin
along
of
of v o l c a n i c
and others,1978)provides
which
a
d r a i n ad
g iev i d e
developed.
may
a
have
I
M p n o c l i n a lf l e x u r e sr e p r e s e n tt h e
dominant s t y l e
deformation
the
Colorado
on
Plateau
during
the
Laramide,
Davis(1978)
belt
of the Baca-Eagar b a s i n .
m a t e r i a l si n t ot h ee a s t e r np a r t
site
outcrop
implies t h e p r e s e n c e
an i n t e r v e n i n g u p l i f t which p r o h i b i t e d t h e i n p u t
I
(Fig.
the
nearly
complete
lack
volcanic-derived
of
d e t r i t u si nt h ee a s t e r np o r t i o n
likely
The
s t a t e st h a t
these monoclineswereproducedby
of
and
44
F'igure 11.
Location of Morenci lineament and distrir:
bution of Laramide plutons adjacent to the
Baca-Eagar basin. Presumably the majority
of these plutons (circles) were associated
with coeval volcanic centers. Reference
points same as Figure 10, except Mo=Morenci.
Lineament and pluton data from Chapin and
others (1978).
45
reactivation
along
basement
fracture
zones
(lineaments)
Thus;
during
early
Tertiary
compression.
divide
was p r e s e n t i n t h e v i c i n i t y o f
during
Baca
time,
possiblymonoclinal
s e t s ofdominant
lineaments
i nn a t u r e .
which
the
Morenci
Lineament
is
is
uplift.
Davis (1978)recognized
two
12).
c l o s e l yp a r a l l e lt o
existence
b e l t .. (Johnson,1978,
the v i c i n i t y
of
isolated
the
by
a
of
Morenci
abundanceof
northeast-
p.
km i n l e n g t h ,
for t h e Morenci
uplift
would
also
v o l c a n i cc l a s t si n
the
t h e w e s t e r np o r t i o n
of
t h eo u t c r o p
87-88);-.-the~-Laramidevolcanics i n
Norenci,
Arizona,
d r a i n a gdei v i d e
s u p p l i e dv o l c a n i cd e t r i t u s
Baca-Eagar
t h a t of t h e
of
m a y be as much a s about175
g r a v e l si n
of
Cow Springs, Organ Rock, and Comb
e x p l a i nt h ei n c r e a s e d
Baca-Eagar
Of
The o r i e n t a t i o n
approximately t h e l e n g t hi n f e r r e d
The
N .55O E )
C o a l e s c i ns g
eries
trendingmonoclines(e.g.
which
was
development
of.Colorado-
(Fig.
set.
northeast-trending
Ridgemonoclines)
uplift"
c o n t r o l l e tdh e
P l a t e a u monoclinal
flexures
"Morenci
(N 2 O o W 'and
t r e n dd i r e c t i o n s
drainage
the Morenci lineament
so-called
this
a
if
would
and
not
have
been
h a veea s i l y
could
t o t h ew e s t e r np o r t i o no ft h e
basin.
On t h eo t h e rh a n d ,a d d i t i o n a ld a t ai n d i c a t i n gt h e
existence
of
an
uplift
in
the
vicinity
lineament i s lacking.Residual
of t h e Morenci
Bouguer g r a v i t y maps of
Datil-Mogollon volcanic province do not suggest
the
the presence
47
Of
a Laramide
but
u p l i fittnh ae r e a ,
manifestation
of
such
an
t hger a v i m e t r i c
u p l i fct o u l d
easily
have
been
masked bysubsequentmid-Tertiaryvolcanismandplutonism.
Colorado
containlargeexposures
of Precambrianrocks.
s t u d y area (see provenance section)
Baca-Eagar
uplift
not
However,
the
amounts of metamorphic d e t r i t u s i n t h e
occurrenceoflarge
the
do
Plateau
monoclinal
flexures
generally
and elsewhere throughout
o u t c r obpe li tn d i c a t etsh at th e
Morenci
must
have
contained
significant
exposures
of
Precambrian t e r r a n e s .
P l a t e Tectonics and t h e Development
of t h e Laramide Foreland
Numerous
of
mechanics
and
t h e o rcioensc e r n
otirhn
ieggi n
Laramide
foreland
deformation
have
been
I n order t o u n d e r s t a n d t h er e l a t i o n s h i p
proposed.
Baca-Eagar b a s i n and a s s o c i a t e d u p l i f t s t o
Tertiary tectonic
the
the overall Early
I will
framework i n westernNorthAmerica,
t o , b r i e f l yd e s c r i b et h ee v o l u t i o no ft h e
attempt
of
Laramide
foreland.
I n Late J u r a s s i c t o Late Cretaceous time,
t hi ne c e p t i o n
deformation
foldbelt
of
i tnh e
which
the
Laramide
orogeny,
for'eland
was
p r i o rt o
t hl o
ecus
of
a l o nt g
hCeo r d i l l e r a n
extended
without
major
interruption
from
48
Alaska t o Guatemala ( D r e w e s ,
time,
motion
of
the
American p l a t e
(Coney,
was
1978)
(Fig.
13).
During
this
F a r a l l o np l a t er e l a t i v et ot h eN o r t h
east-northeastward
a t ' about
8
cm/yr
1978).
Deformation
along
the
Cordilleran
foldbelt
continued
throughout
Laramide
time
in
Mexico
time i n Nevada
1976), b u t ceased i nL a t eC r e t a c e o u s
(Coney,
and
Canada
andUtah(Armstrong,1968).
About 80 m.y.
ago t h e r e l a t i v e p l a t e
motionbetween
t h e North American and F a r a l l o n p l a t e s c h a n g e d , r e s u l t i n g i n
theNorth
0
American p l a t e .
The magnitude
of
convergence r a t e s also changed,increasing
(Coney,
1978)
(Pig.
America
and
Laramide
orogeny
(Coney,
1976;
(1978)
suggest
formed i n
that
shallowlydipping
along the bottom
westernUnited
the
stress
0
f i e lidn
the
beginning
of
the
u p l i € t so ft h e
and Snyder
Laramide f o r e l a n d
aby
very
t o s u b h o r i z o n t a l s u b d u c t e d p l a t es c r a p i n g
of
the
States.
zone
and
Laramideorogen.
a strong
compression
generated
c o n t i n e n t alli t h o s p h e rien
the
This model seems t o e x p l a i nb o t h
Laramide
deformation
took
subduction
t o about 1 4 cm/yr
1978).
Dickenson
to
response
marked
to
r e l a t i v e plate
These
changes
created
14).
northeast-southwest-directed
compressive
western
North
respect
t h e F a r a l l o np l a t ew i t h
northeastwardmotionof
place
the
so
f airn b o a r d
of
largely
m a g m a t in
c a t u ro
ef
I n Late Cretaceous t o Paleocene time,
asymmetric
basement-cored
a n t i c l i n au
l plifts
how
the
the
the
of
Colorado-
49
Figure 13.
Map showing plate positions and relative
motion vectors prior to Laramide orogeny.
F'Farallon
plate, X=Xula plate, P=Pacific
plate, NA=North American plate. Vectors
show motion of Farallon (Far) and North
American (NA) plates relative to hot-spot
frame of reference. Resultant shows dirof plate convergence.
ection and magnitude
Spreading centers shown by stippled areas
between parallel lines, subduction zones
by heavy barbed lines, thrust belts by
cornlight barbed lines, metamorphic core
plexes by fine wavey lines, and arc terranes by short, dashed.1ine.s. Modified
from Coney (1978).
50
.
.
.Figure 14. Map showing plate positions and relative
motion vectors during Laramide orogeny.
Uplifts shown by small, elongate, closed
areas. Other symbols same as Figure 13.
Modified from Coney (1978).
51
Wyoming and themonoclinalflexures
began
to
form,
creating
l a r g eo, f t e n
c l o s e di,n t e r m o n t a n e
basins between
them.
began
to
forin
The
Baca-Eagar
b a s ip
nr o b a b layl s o
b u t d i f f e r e d from t h e
t h i sp e r i o d ,
during
deeper,better-knownLaramidebasins
its
of t h e ColoradoPlateau
southwesternboundary.
in
t ot h en o r t h
and dominant'source.of
was comprised by a segmentof
that
detritus
t h eC o r d i l l e r a n 'f o l d b e l t ,t h e
Mogollon Highland.
About
m.y.
40
ago
t e c t o anci ct i vni e
t ya r l y
synchronouslyceasedalongtheentireCordillera,including
i n t h e Laramide Rocky MountainsandColorado
the deformation
Plateau
s t r u c t u r apl r o v i n c e s
(Fig.
15).
T h i cs e s s a t i o n
deformation
coincides
chronologically
with
a
decrease
r e l a t i v ep l a t ec o n v e r g e n c er a t e sa l o n gt h ew e sct o a s t
North America (Coney,
1976).
The
t e c t o n i c a l lqyu i e s c e n t
the end of t h e Laramideorogeny
t h e development
of
surface
of
low
foreland
(Epis
Cenozoic
widespread
l a, t e
and Chapin, 1 9 7 5 ) .
by
resulted i n
Eocene
erosional
r e l i e f i n some a r e a s of t h e Rocky Mountain
t e c t o n i ch i s t o r y
represented
in
of
periodfollowing
a
of
The
next
of
the
of t h e western United S t a t e s i s
the
widespread
Oligocene
calc-alkaline
i g n i m b r i t e flare-up.
phase
52
I
I
100'w
Figure 15.
Map showing plate ,positions and relative
motion vectors during post-Laramide,' middleTertiary~ignimbriteflare-up. CP= Colorado
Plateau. Dotted areas are large caldera
complexes. Other symbols same as Figure 11.
From Coney ( 1 9 7 8 ) .
STRUCTURAL GEOLOGY
The s t u d y a r e a i s l o c a t e di n
between the Colorado Plateau
t r a n s i t i o nz o n e
the
t o the n o r t h and the RioGrande
r i f t system t ot h es o u t h e a s t .T h r e ee p i s o d e s
~
development
havemodified
of
the s t u d ya r e a .
A poorlydefined
probable Laramide age
monoclinalflexureof
t h es o u t h e a s t e r np o r t i o n
of t'he area.
f a u l t s and a s s o c i a t e d d r a g
structural
is
p r e s e n ti n
North-trendingnormal
folds and m a f i c d i k e s a r e
i n t h e e a s t e r n p a r t of t h e area andwereproduced
common
by Neogene
e x t e n s i oE
np
. e i r o g e nui c
p ltioh
C
ffteo l o r a d
Pol a t e a u
e
during
Neogene
resulted
time
i n the southward t i l t i n g of
strata in the region.
Laramide Folding
M o n o c l i n afll e x u r etsy p i f tyh e
deformation
of
Laramide
style
The presence of a
the
Colorado
Plateau.
poorly
defined
southeast-facing
monocline
s o u t h e a s t e r np a r t
of
of t h e s t u d ya r e a
steepened
bedding
and
the
(oral
e
commun.,
in
the
i s i n d i c a t e d bya
zone
abrupt
termination
i s about 250 f t ( 7 7 m ) .
1978)
of
a
Maximum s t r u c t u r a l r e l i e f
p l u n g i nagn t i c l i n( eF i g
1 .6 ) .
alongthemonocline
of
C.
E.
Chapin
suggests t h a t t h e s t r u c t u r e may have
r e s u l t e d from d r a p i n g o f s e d i m e n t a r y s t r a t a o v e r
53
a
vertical
54
Figure 1 6 .
S t r u c t u r ei n d e x
map of s t u d y area.
55
displacement
basement along a northeast-
in the crystalline
trendinglineament.
A similar o r i g i n , f o r monoclineson
Colorado
Plateau
has
been
proposed
Baca
Davis
(1978).
t h a t t h e monocline may
Paleocurrentdatasuggest
activeduring
by
the
havebeen
w i l l be discussed i n a
d e p o s i t i o n a, s
later section.
The monocline l i e s approximately on t r e n d
which i s w e l l exposed i nT i j e r a s
Tijeraslineament,
Mexico.
Chapin
and
near Albuquerque, New
related
the
Canyon
others
(1979)
features w e s t o f , t h e R i o Grande
d e s c r i b es e v e r a lT e r t i a r y
which may be
with
to
r e a c t i v a t i o anl o n tgh e
Tijeras
lineament.
EarlyRiftFaults,
Drag Folds,
andDikes
The
rift
Rio
Grande
consists
of
e s s e n t i a l lpya r a l l enl ,o r t h - t r e n d i nhgo r s t s
formed by Neogene r e g i o n a le x t e n s i o n
mi
(966
km)
from
near
El
a
series
and
grabens
and extendsabout
Paso,
Texas,
of
600
L
t oe a d v i l l e ,
Colorado.
Numerous north-trending normal f a u l t s a r e exposed i n
t he a s t e r p
nart
o f . the
study
area ( F i g .
15).
Magdalena Mountains, similar f a u l t s may be a s o l d a s
(C.
E.
Chapin,
1979,
o r a l commun.).
In the
32 m.y.
Mafic dikes dated a t
56
24-25 m.y.
Chapin,
unpubl.
E.
(C.
dates)
have
been
i n t r u d e d along many of t h e s e f a u l t s .
westward
Most of t h ef a u l t sd i ps t e e p l y
'
and
range
from
o r no h o r i z o n t a l
exhibit
large
component.
€3, and
displacements
C
( F i g1. 4 ) ,
however,
of a s much a s 750 f t ( 2 3 1 m ) .
350 f t (108 m ) , and 830 f t ( 2 5 5 m ) ,
respectively.
t hl e
arge-displacemen
f at u l d
t sispt e e p l y
e x h i b i t down-to-the-west
Vertical
i s g e n e r a l l y l e s s than a few
F a u l t s A, .
t e n s of f e e t .
about
55
was generally
s e p a r a t i o na l o n gt h ef a u l t s
a
v e r t i c atlo
d e g r e eRsa.srlei c k e n s i diensd i c astlei p
v e r t i c a lw i t hl i t t l e
All
in
movement.
t h ee a s t e r np a r t
of t h ea r e a .
facesIeastward and thefo,ldaxisplungessouthward
five
d e g r e e st,e r m i n a t i n a
gb r u p t l y - a g a i n s t
facingmonoclinedescribedpreviously.
the anticline corresponds to that
due t o
down-to-the-west
of
westward
and
A large
south-plunging
asymmetrical
anticline
present
are
dip angles average
downthrown tw
thoeeF
s ta.u l t - p l a n e
about 75 degrees,
and
movement
The s t e e p limb
at
about
the southeast-
The c o n f i g u r a t i o n of
of a f o l d produced - by drag
a l o nfga u l t
small-scale
drag
folds
associated
with
normal
faults
are
common throughout the study area.
is
B.
Local
57
Colorado P l a t e a u U p l i f t
The Colorado P l a t e a u i s a b r o a d ,s t a b l e ,r e l a t i v e l y
segment of t h e c r u s t comprisingabout150,000
undeformed
(388,500 k m 2 )
of
northwestern
Arizona,
southeastern
Utah,
New
and
by
northeastern
southwestern
Colorado.
s t r a t a of the p l a t e a u a r e
L o c a l l y ,t h eg e n e r a l l yf l a t - l y i n g
interrupted
Mexico,
mi2
large
m o n o c l i n afll e x u r e s
of Laramide age
Davis, 1 9 7 8 ) .
(Kelly, 1955;
T h e study area
i s located i n a west-trending b e l t of
gently
south-dipping
sedimentary
rocks
along
the
southern
e
marginof
the
t h e Colorado P l a t e a u ;
Mogollon
t h i sb e l th a s
slope
(Fitzsimmons,
1959).
beentermed
'
Except
where
modified by normal f a u l t i n g a n dd r a gf o l d i n g ,s t r a t aw i t h i n
area
t h es t u d y
from
dip
Southward t i l t i n gr e s u l t e d
theColorado.Plateau
~
t h r e e t o s i x degrees
southward.
f r o m the
which
(Chapin
and
Seager,
1975).
produced
the
previously.
i nt h e
(1979).
Bear
began
This
epeirogenic
i ne a r l y
uplift
of
Miocene time
t i l t i npgr o b a b a
l yl s o
of t h ea n t i c l i n ed e s c r i b e d
southward
plunge
S i m i l a r southward t i l t i n g ofpre-Miocene
strata
Mountains v i c i n i t y w a s reported by Massingill
'.
DEPOSITIONAL
k
SYSTEMS
depositional system is a genetically defined,
three-dimensional, physical stratigraphic unit composed of a
contiguous
set
of
process-related
sedimentary
facies
Depositionalsystemsarethestrati-
(Gal'loway, 1977).
graphic manifestation of major ancient geomorphic features,
such as barrier islands, lakes, eolian dune fields, etc.
Criteria utilized
in
discrimination of paleoenvironments
include lithofacies geometry, lateral and vertical variation
in grain size and sedimentary structures, nature of contacts
between lithofacies, petrographic data, and fossils.
Two ancient depositional systems are present
in the
Baca Formation
are
the
in the Gallinas Mountains vicinity. These
lacustrine
Braided
The
and
braided
alluvial-plain
Alluvial-Plain
systems.
System
importance
braided-stream-dominated
of
depositional systems within the Baca-Eagar basin
demonstrated
by
Johnson
(1978),
has been
who
described
the
depositional framework of the entire basin. In
this study I
Willusetheterm"braidedalluvialplain"instead
Johnson's "humid alluvial
Of
fan", although the sediments and
depositionalprocessesrepresentedbybothsystemsare
58
*
59
identical.
I chose t o abandonJohnson'sterminologyforthe
followin
r ega s o n(tsah
a:)d
ejective
intended
"humid",
t od i s t i n g u i s ht h i s
although
system from i t s a r i da l l u v i a l
f a nc o u n t e r p a r t ,c o n n o t e sc l i m a t i cc o n d i t i o n st h a t
present
during
Baca
time i nw e s t - c e n t r a l
t h e r e i s no e v i d e n cfeo r
a
braided-stream-dominated
this
were
not
New Mexico;
(b)
€an-shaped
geometry
Baca-Eagar
f o trh e
I n contrast,
system.
system
probably
consisted
of
a
series
of
highly
coalescedfansforminganextensive,low-gradient,piedmont
slope o r b r a i d e d a l l u v i a l p l a i n .
Johnson
0
recognized
proximal-,
(1978)
mid-,
the Baca-Eagar o u t c r o pb e l t .
d i s t a l - f a nf a c i e sw i t h i n
the distal facies i s present in the study
and
Only
area.
D i s t a l Braided A l l u v i a l - P l a i n F a c i e s
The distal braided a l l u v i a l
F a c i e s. C h a r a c t e r i s t i c s .
plainfacies
t hb
easal
comprises t h e e n t i r e middlesandstoneunit
40 f t ( 1 3
characteristic
a sr e
otfh e
m)
summarized
t a l l yl a m i n a t e d ,f i n e
e
Table
and
as
s a n d s t o nLeas r. g e - s cvael e
rtical
3.
dominance
t o coarsesandstone
conglomerate.
of
Mudstones
occurring
primarily
in
1 7 ) shows a
v e r t i c asl e c t i o n
(Fig.
unit.
lower
red
A
of
and
'Facies
typical
horizon-
with minor l e n s e s
c l a y s t o narea
r ser e ,
t h i nd,i s c o n t i n u o ulsa y e rw
s ithin
textural
trends
are
Table 3
Distal
Sedimentary
Braided
Alluvial-Plain
Facies
Characteristics
Lithology
Moderate- to well-sorted, very coarse- to Dominantly horizontal laminations
fine-grained sandstone with minor
with subordinate trough crossbedding
conglomerates and mudstones. Conglomerates
and minor tabular crossbedding.
occur as thin, discontinuous lenses within Vertical textural trends are generally
sandstones. Mudstones Qccur as isolated,
lacking, but upward-fining sequences
thin layers within sand units. Sandstone/
are sometimes observed. Channels are
mudstone
ratios
are
very
high.
poorly
developed
and
exhibit
high
width-to-depth ratios. Root mottling
is locally abundant.
m
0
61
SAND %
pVE
nI.
LlTH
Gr
c
= roots
Figure 17.
Typical vertical section of distal braided
alluvial-plain facies. Modified from Johnson
(1978).
e
62
generallylacking;
however,upward-finingsequences
a s 6 f t ( 2 m ) t h i c k were
a r ep o o r l yd e f i n e d
occasionally
observed.
Channels
a n d range i n w i d t h u p t o 150 f t ( 4 6 m ) .
Channel d e p o s i t s e x h i b i t high
widthldepth
between
abou
5 t0t:ol
is
Foreset
crossbedding
much
medium
as
scale
Root mottling
and
plant
fragments
are
(ranging
medium-
one
meter
to
thick.
,and o c c u rrsa r e l y .
common.
Contorted
bedd-ing Land. dewakering. strnctures _are..sporadically abundant.
Coloration of sandstonesranges
and
e
ratios
and
abundant
1OO:l)
large-scale
trough-crossbeds
as
.. .
a s much
is
from red t oy e l l o w i s hg r a y
c o n t r o l l e d by d i a g e n e s i s , . a s w i l l be d i s c u s s e di n
a
later section.
Depositional
Processes.
laminationswithin
The
d i s t a l braided a l l u v i a l - p l a i ns a n d s t o n e s
representplane-bedtransport
and aggradationpredominantly
occurringduringoverbankflow
areas
during
prevaleh
no
t rizontal
flood events.
i n broad, f l a ti n t e r c h a n n e l
h o r i z o n t alla m i n a t i o n s
Similar
M c K e e and o t h e r s ( 1 9 6 7 ) i n the r e c e n t
havebeenreportedby
overbank flooddepositsofephemeralBijouCreek,Colorado.
were
Large-scale,
upward-fining
sequences
predominantly i n o v e r b a n ka r e a si n
f l o wv e l o c i t yd u r i n g
1967).
a
a
deposited
regimeofdecreasing
waning f l o o d s t a g e s
( M c K e e and others,
63
Channel deposits a r ec h a r a c t e r i z e d
of
by
anabundance
trough
crossbeds,
minor
tabular
crossbeds,
and
often
containthinconglomeraticlenses.Horizontallaminations,
s i m i l a rt o
described
above,
are
those
crossbedding i s
result
the
sinuous-crested dunes
of
deposition
The trough
by
subaqueous
which migrated down the channel during
high-discharge
periods.
intrachannel
trough
Similar
crossbedding has been described
of
Bijou
common.
i n the r e c e n t f l o o d d e p o s i t s
Creek, Colorado (McKee and
others,
1967).
Dunes
were t h e dominant bedform w i t h i n c h a n n e l s i n r e c e n t f l o o d i n g
of sandyephemeral
e
1971).
Rare
streams i nc e n t r a lA u s t r a l i a( W i l l i a m s ,
tabular
crossbeds
were
produced
by l a t e r a l
a c c r e t i o n on f o r e s e t s u r f a c e s of t r a n s v e r s e o r l i n g u o i d b a r s
during
waning andlow-flow
stages.
Such bars a r e common i n
channel
areas
of
braided
streams
during
(Williams and
Rust,
sometimes
Harms
stages
and
Fahnestock,
1965;
Thin,
"discontinuous
conglomerate
lenses
Williams, 1 9 7 1 ) .
are
1969;
low-flow
p r e s e nitn
thbea s aplo r t i o notsfr o u g h
cross-sets.
These
conglomerates
represent
channel-lag
gravels
I
were
migrating
dunes.
preceeding
dune
(1971).
t
which
deposited i ns c o u r s
Similar
lobes
on t h el e e
s i d e of
recent
pebble-floored
hollows
have
been
described
by
Williams
64
Mudstones
arraew
r ei t htid
hnies tbarla i d e d
to thin
a l l u v i a l - p l afi a
nc i eO
s .c c u r r e n c a
elrsiem i t e d
a few c e n t i m e t e r s t h i c k ) , d i s c o n t i n u o u s
(generallylessthan
layerswithinsandstone
These l a y e r s wereformed
units.
s e t t l i n g of s i l t and c l a yw i t h i n
rarely
preserved;
they
These claydrapes
were
subsequent
high-discharge
events
in
c l alsagtgr a v e l s
deposits
in
formed
havebeendescribed
Williams ( 1 9 7 1 )
and
ponds i n bothchannel
floodplainareasfollowingfloodevents.
were
by
usually
and
reworked
by
occur
as
claystone-
superjacent
sediments.
Thin
clay
post-flood
pools
and cut-off
channels
i n central Australian braided streams
by
.
Braided streams of t h e d i s t a l b r a i d e d a l l u v i a l - p l a i n
f a c i e se x h i b i t e df l a s h yd i s c h a r g ec h a r a c t e r i s t i c s
have
been
ephemeral.
deposits
and
t h es c a r c i t y
f a c i e sd i f f e r s
1970;
The
central
Australia
flood
of tabularcrossbedding
models
(Williams,
of
f a c i e sM
. iall
istics.
p l a ndte b r i s
Lack
(Smith,
1976;
The ephemeral
braided
streams
1971)
and
Colorado (McKee and o t h e r s , 1 9 6 7 ) provideuseful
the
braided
streams
i n this
1972a;
Cant
and
Walker,
Rust,
C o s t e l l o and Walker, 1 9 7 2 ) .
Of
abundance
overbank
of
from perennialbraidedstream
Kessler, 1971;
and may
Bijou
Creek,
models
for
t h ed i s t a b
l r a i d e da l l u v i a l - p l a i n
( 1 9 7 7 ) summarizes braided
stream
character-
of
and
e o l i a fne a t u r e s
r o omt o t t l i n g
and presence of common
may
i n d i c a tvee g e t a t i v e
65
stabilization
of
of t h e
sediments,
although
the
nature
vegetation i s n o t known.
Braided
described
an
Johnson
(1978)
extensive
braided-stream-dominated
study)
this
Model.
humid
system (renamed b r a i d e da l l u v i a l - p l a i ns y s t e m
alluvial-fan
in
A l l u vPi laal i n
the
western
portion
in
of t h e Baca-Eagar
is
basin, of which o n l yt h ed i s t a lf a c i e s
study
area.
The
discussion
following
present
of
in
tbhrea i d e d
a l l u v i a l - p l a i n system i s drawn l a r g e l y fromJohnson
(1978).
Two a l l u v i a l - p l a i n models a r e commonly c i t e d i n
e
literature.
(Bull,
The
first
Hooke,
1972;
is
is
which
1967),
braided-stream,
r e c e nft a n s
grain
mudflow,
of t h ea r i d
size,
sieve,
and
the
t h fea m i l i aar r i d
a l l u v i afla n
characterized
by
of s y s t e m a t i c
r e l a t i v e l ys m a l ls i z e ,s t e e pg r a d i e n t s ,l a c k
downstream decrease i n
the
and
the
presence
of
and e o l i adne p o s i t s .
semiarid
southwestern
The
United
Statesarestereotypicalaridalluvialfans.
I n c o n t r a s t , humid o r t r o p i c a l a l l u v i a l f a n s e x h i b i t
gentle,
smooth
decreases i n g r a i ns i z e
downstream,
and
the
dominance
of
braided-streamprocesses
t ot h ev i r t u a l .e x c l u s i o n
others.
c i t e dr e c e n t
The
most
commonly
f a n sa r et h eS c o t p
t r o g l a c i ab
l raided
e
e x t e n t s , systematic
g r a d i e n t sl,a r g ae r e a l
a l l u v i a lf a n )
i n Alaska(Boothroyd
examples
of a l l
of
these
outwash f a n (humid
and Ashley,1975)(Fig.
66
and
la),
i n India(Gole
t h eK o s it r o p i c a lf a n
are perennial
streams on t h e s ef a n s
1966).Braided
and C h i t a l e ,
n oet x h i b itth ef l a s h yd i s c h a r g ec h a r a c t e r i s t i c s
of a r i d
alluvial
fan
ephemeral
braided
streams.
fluvia
plr o c e s s e s
and
The
relatively
the
do
and
dominance
of
uniform
discharge
characteristicsofbraided-outwashanatropical-fanbraided
from a r i d a l l u v i a lf a n s .
s t r e a m sd i s t i n g u i s ht h e s ef a n s
I
The
sporadic supply of coarse, unsorted sediments by
mudflows t o
a l ls u r f a c e so fa r i d , a l l u v i a lf a n sp r e v e n t st h e
development
of
tshyes t e m a t i c
downstream
c h a r a c t e r i s t iocbfr a i d e d
which
mudflow
decrease
and
outwash
or
p r o c e s sareraser e
o r a l commun.)
Boothroyd,1979,
'
g r asi inz e
t r o p i c afla n s ,
absent
(3.
on
C.
The r e l a t i v e l y u n i f o r m f l o w
and
conditions
braided-outwash
of
streams r e s u l t i n s t e a d y ,
.
in
tropical-fan
braided
long-term d e p o s i t i o n , which f a v o r s
t h e development of the large, low-gradient surfaces of these
the Kosi t r o p i c a lf a nr a n g e
fans.Gradientson
and f i v ef e e tp e rm i l e ,
betweenone
and a v e r a g ea b o u t h r e ef e e tp e r
mile.
The S c o t t braided outwash f a n (Boothroyd and Ashley,
1975)
and
the
Kosi
both
provide
useful
models
a l l u v i a l - p sl ayisnt e m ,
between
the
(Gole and Chitale,
1966)
f ot rh &
however,
satisfactory
(Johnson,
1978).
exist
t r o p i c a fl a n
Two
Baca-Eagar
neither
important
is
braided
entirely
differences
braided outwash model and the analogous
67
CHANNEL ANDBAR
MORPHOLOGY
- %ORIZONTAL STPATIPIED SAND
"
CROSS STPATIFED SAND
0%-
CfiAyEL
htlloa
0
0
Kllanatsrs
8
.
.
~.
Figure 18.
.
e
.
Map showing distribution of bar types and
sedimentary structures in proximal
and midfan faczes of Scott glacial outwash fan,
Alaska. From Johnson (1978), after Boothroyd
and Ashley (1975).
68
system i n t h e Baca andEagarFormations.
Of
proglacialbraided
km)
f o rt h e
t o a length
thattheScottbraided
(during
Baca-Eagar
earlyTertiary.Secondly,
thefact
been a c t i v e f o r
and
Recent
b r a i d eadl l u v i apll a i n
of years
was
during
the
Baca-Eagar braidedstreams
more f1ashy;perhaps
show
evenephemeral,flow.
i s comparable i n s i z e w i t h t h e
braided
alluvial-plain
system,
grainedsediments
mi
100
the braided streams of t h eS c o t t
f a na r ep e r e n n i a l ,w h i l et h e
Kosi t r o p i c a l f a n
by
Pleistocene
presumably a c t i v ef o rs e v e r a lm i l l i o n s
evidenceof
about
beexplained
outwash fanhasonly
a relatively
short'period
w h i lteh e
of
Baca-Eagar b r a i d e da l l u v i a l - p l a i ns y s t e m .
This s i z ed i f f e r e n c ec a np r o b a b l y
time),
t o ten
outwash f a n s i s only about five
miles ( 8 t o 1 6 km),
compared
(160
F i r s t , t h el e n g t h
but
The
Baca-Eagar
c o n t a i n s . more
fine-
i n its distal portions.
Lacustrine System
The l a c u s t r i n e system i s widespreadthroughout
Baca-Eagar
two
b a s i nL. a c u s t r i nsee d i m e n t a t i o tno o p
k l a cien
g e n esr ea tl t i n( g
Jo
s hnson,
semipermanent
*
the
l a k e ss i t u a t e d
1978):
in
small,
on fluvial-systemfloodplains;
( b ) i n a l a r g es,h a l l o wp, e r s i s t e nlta k leo c a t e d
Bear-Gallinas Mountains a r e a .
(a)
in
the
.
69
Johnson
r e c o g n i zleadc u s t r ifnaen - d e l t a ,
(1978)
the Baca-Eagar
fine-grained delta,
and b a s i n a l f a c i e s w i t h i n
l a c u s t r i n e system.
Only t h el a c u s t r i n ef i n e - g r a i n e dd e l t a
and
i n t h eG a l l i n a s
b a s i n a fl a c i e sa r ep r e s e n t
area.
The l a c u s t r i n e systemcomprises
member
and
all
of
the
a l l u v i a l - p l asiyns t e m ,
I n c o n t r a s t ot h eb r a i d e d
mudstones
and
c l a y s t o naerse
volumetrically
important
constituent
sandstone/mudstone
system;
red
t h ee n t i r eu p p e r
red u n i t i n t h es t u d ya r e a
lower
40 f t (13m).
exceptthebasal
Mountains
of
the
a
lacustrine
ar b
aatorie
uots
1:l.
Coloration i s c o n t r o l l e d by t h ed i a g e n e t i ch i s t o r yo ft h e
e
I
sediment and ranges from red to yellowish gray.
Lacustrine Fine-grained Delta Facies
Facies
Characteristics.
Cyclical
upward-coarsening
sequences
(Fig.
4.
19).
summarized i n
F a c i e sc h a r a c t e r i s t i c sa r e
I n d i v i d u a lc y c l e s
1 2 0 f t ( 6 t o 35 m ) ,
'
thickv
) e r y - f i n et o
30 f t ( 9 m) t h i c k .
of a n i d e a l i z e d
l a t e r a l lp
y e r s i s t e ncta l c a r e o u s
i n t e r c a l a t e dw i t ht h i n l y
Table
range i n t h i c k n e s s from about 20 t o
andaverageabout
The b a s a l p o r t i o n
a
i n this f a c i e s
c h a r a c t e r i zv
e e r t i c asle q u e n c e s
cycle c o n s i s t s
mudstone
ocrl a y s t o n e
bedded ( g e n e r a l l yl e s st h a n
medium sandstones.
content,
determined
by
weighing
samples
before
and
of
25
cm
Mudstone c a r b o n a t e
after
70
..
G R A I N SIZE
1 Sd lSiC
SAND %
Gr
0
1
" t.
L
u
U
E
F i g u r c 19.
T y p i c a lv e r t i c a ls e c t i o n
of l a c u s t r i n e f i n e g r a i n e d d e l t a f a c i e s , showing upwardfrom Johnson
coarseningcycles.Modified
(1978)
-
tructures
Table 4
Lacustrine
Sedimentary
Fine-Grained
Delta
Facies
Characteristics
Lithology
Upward-coarsening sequences of mudstones
.
Mudstones: burrows and rare
and sandstones with minor conglomerates.
laminations.Sandstones:horizontal
Mudstones are generally highly calcareous. laminations, parting step lineations,
Sandstones are very fine to coarse grained ripple cross-lamination, occasional
and moderately to well sorted. Sandstone/ trough crossbeds, rare tabular
mudstone
ratios
are
about
1:l.
crossbeds.
Conglomerates
form
rare
thin, discontinuous lenses in the
upper parts of delta cycles. Largescale, gently inclined foresets are
of
sometimes present near the bases
cycles. Burrows and root mottling
are locally abundant.
72
a c i d i z a t i o nw i t h
ranges
between
cold, d i l u t eh y d r o c h l o r i c
10
and
more
in
Mudstones
in
detail
and
homogeneous,
burrows.
Burrowing
it n
he
is
of
pervasive.
portions
of
texture
which
gives
In
deltaic
but
exhibitwell-definedburrows,
r a t h e r show a churned,curdled
microscopically,
usually
w itethh
xec e p t i o n
lower
mudstonesdonot
are
and
mudstones
c o n t r a stto
s a n d s t o n e isn
the
and
td
h iea g e n e ssiesc t i o n .
r a r eelxyh i b
l ai tm i n a t i o n s
structureless
cycles,
by
weight.
Carbonate
upward w i t h i n d e l t a i c c y c l e s , as w i l l be
contentdecreases
.discussed
1p5e r c e n t
acid, g e n e r a l l y
bothmegascopically
r i s e t ot h e
homogeneous
n a t u r e of t h e mudstones.
S t r u c t upr er es s w
e ni t thhi ie
nn l y
s a n d s t o n e si n t e r c a l a t e d
bedded
w i t h t h e above-describedmudstones
i n c l u d eh o r i z o n t a l a m i n a t i o n s ,c u r r e n t - r i p p l el a m i n a t i o n s ,
p a r t si n
lt iegnpe a t i o n
(McBride
Yeakel,
and1963).
o c c a s i o n a l normal-graded
beds,
and
burrows.
20) arevertical,horizontal,
Burrows
and oblique,range
from 1/4 t o 2 i n (1 t o 5 c m ) , andsometimes
surface
ornamentation
(Johnson,1978,
are
similar
p.
and
77).
i n diameter
exhibit
knobby
b a c k f illal m i n a e
According t o Johnson t h e s e burrows
t o Scoyena s p . , which a r e common i n non-marine
redbeds(Hantzschel,1975),
formed
by
polychaete
0
scoop-shaped
(Fig.
carbonate
nodules
and a r e b e l i e v e dt oh a v e
worms.
and
mudcracks
been
of calcium-
Rare
horizons
were
observed
within
the
73
Figure 20.
Branching horizontal burrows (feeding traces?)
in a red, lacustrine sandstone.
74
mudstones.
The
thinly
bedded
sandstones
.in
p o r t i o n s of cycles a r e o f t e n
inclined
(Fig.
with
l a r g e - s c a lfeo r e s e t s
degrees i n
rare
instances.
only
a
few
degrees
(Fig.
a n g l eas r e
i n c l i n e dt h a tt h ea n g u l a r i t y ~
up
t o 15
more
commonly
so g e n t l y
and a roe f t e n
22),
lower
forming
21),
angles
ranging
dip
Dip
the
i s n o tr e a d i l ya p p a r e n ti n
a
s o l i t a r y exposure.
The
overlain
are
above-described
units
by
horizontal
a
and
transitionally
current-ripple-laminated,
which
l a t e r a lcloyn t i n u o ufcistn
o,oe
a rssaen d s t o n e
averages
about
a
5
f t ( 1 . 5 m ) i nt h i c k n e s sO
. rientation
of
c u r r e n t - r i pcprlloaesm
s i n a t iu
osnusai n
l ldyi c a t e
direction
at
of
flow
a
p a l e o c u r r e n ti n d i c a t o r sw i t h i nt h e
w e l l - s o r t e d ,n e a r l y
gives rise t o
22).
a
same d e l t a i cc y c l e .
The
homogeneous n a t u r e of thesesandstones
’
quasi-spheroidalweatheringhabit(Fig.
Colorationof
given cycle
t o t h a t shown by o t h e r
h i g ha n g l e s
t h i s and superjacentsandstoneswithin
a
may be red or yellowish gray, whereas coloration
of p r e v i o u s l y d e s c r i b e d s u b j a c e n t i n t e r c a l a t e d
mudstonesand
sandstones i s almost always red.
Moving upsection, t h e next and uppermost p a r t of
cycle
ideal
will
sometimes
exhibit
an
large,
symmetrical,
channel-shaped u n i t s which
have
erosional
bases.
Channels
may
a
be
( F2i g
3 .) ,
as
much
as 50 f t ( 1 5 m) wide and 1 5 f t ( 5 m) deep
b u t agreen e r a l l y
much
smaller.
Intrachannel
75
Figure 21.
Baca fine-grained delta deposit exhibiting
unusually steeply inclined prodelta foreset
beds.
Figure 22.
Gently inclined prodelta foreset beds overlain
by quasi-spheroidally weathering delta front
deposits. .Hammer handle points in direction
of delta progradation.
77
Figure '23.
Exceptionally large deltaic distributarychannel deposit. Note the low width-to-depth
ratio (less'than10:l) and the highly symmet-rical nature, which are characteristicof
distributary channel deposits in marine deltas.
78
sedimentary
structures
include
beds.
crossbedding and plane
shaped
is
represented
e r o s i o n a sl u r f a c e .
The
trough
symmetrical
channel-
base of t h e upper p a r t of
by
ainr r e g u l alro, w - r e l i e f ,
remainder
of
the
upper
portion
of
i s composed of f i n e - t o coarse-grainedsandstones
t h ec y c l e
with
Where
u n i t s are n o t p r e s e n t , t h e
each
cycle
medium-scale
,
minorconglomeratesandmudstonesexactlysimilar
to
the rocks of the distal braided alluvial-plain facies.
Depositional
Processes.
The c y c l i c asle d i m e n t s
record
t hf e
i n e - g r a i n edde l ft a c i e s
e
alternate
p r o g r a d a t i o n and abandonment i n a shallowlake.
lithofacies
of
deltaic
Geometry of
v e r t i c a l and l a t e r a l sequences of t e x t u r e s
and
and sedimentary
structures
are
similar
t ot h o s e
found
lobatehicjh-constructivemarinedeltas(Fisher
and o t h e r s ,
are i n f e r r e dt ob et h e
1969).Depositionalprocesses
in
same
as . i n t h e s e m a r i n e d e l t a s ( J o h n s o n , 1 9 7 8 ) .
The lower intercalatedmudstones
in
sandstones
were
deposited
delta-front
environment.
settling
from
a
and
prodelta
were
S i l t and c l a y
suspension.
The
thinly
bedded
and
distal
deposited
t h si na n d s t o n e
by
beds a r e
frontal-splay
deposits,
probably
representing
prodelta
turbidites.
turbidites,
e
Normal
are
graded
beds,
occasionally
seen
a
t y p i cfael a t u r e
of
ti h
n e s ea n d s t o n e s .
T u r b i d i t e s i n l a c u s t r i n e environmentshave
been described by
79
many
workers,
including
Theakstone (1976),and
The
Norniark
and
Grover and Howard (1938).
quasi-spheroidally
latec
r aolnl tyi n u o u s ,
and rippled sandstones
weathering,
horizontally
laminated
are d e l t a - f r o n t deposits.
in
These
sandstones
were
deposited
channel-mouth bars Lor i n longshor'e-current-redistributed
bars.
The
plane-bed
primary
processes
aggradation
and
on
t hdee l tfar o n t
ripple
migration.
divergence
between
paleocurrent
directions
delta-front
ripples
and
were
The
large
shown
by
t h a t of o t h e ri n d i c a t o r sw i t h i n
a
given deltaic c y c l e s u g g e s t t h a t
e
(19761,
Dickson
w a s predominantly controlled
ripple migrationdirection
by longshore currents.
The large,
symmetrical,
channel-shaped
sandstones
sometimes
p r e s e n ti nt h e
upper p a r to fd e l t a i cc y c l e sa r e
distributary-channel
deposits.
Sedimentary
structures
i n d i c a t teh apt l a n e
beds
and
subaqueous
dunes
were t h e
dominant bedforms w i t h i n. d i s t r i b u t a r yc h a n n e l s .V e g e t a t i v e
stabilization of delta-platform
thelakeallowed
f o r t h e developmentof
relatively
w i d t h - t o - d e p t h - r a t i od i s t r i b u t a r yc h a n n e l s .
low
D e l t a i cd e p o s i t s
non-stabilization
(Gilbert,
1885;
large,symmetrical,
w h i c hl a c kd i s t r i b u t a r yc h a n n e l si n d i c a t e
of
delta-platformstreamchannels,
common i n c l a s s i c " G i l b e r t - t y p e ' '
a
braided stream channels near
as i s
delta orfan-deltadeposits
Theakstone,
1976).
The remainder of t h e
upper d e l t a i c c y c l e i s composed of delta-platform sandstones
80
minor
and
conglomerates
deposited
processes
by
of
i d e n t i c a l tthoo s e
a l l u v i a l - p l faai n
cies.
These
the
analogous
d i s tbarla i d e d
sediments
represent
the
braided-stream-dominatedsubaeria1,portion
are
braided-stream
t ot h et o p s e tb e d s
of t h e d e l t a ,
and
of c l a s s i cG i l b e r t - t y p e
deltas.
Basinal Facies
FCah
ca
i er sa c t e r i s t i c s .
When
p r et h
sent,
lacustrin
b ea s i nfaalc i o
e sc c udr si r e c tbl ye n e atthhe
e
above-described
delta
facies
structureless
and
mudstones
and
claystones
i n t e r b e d s of veryfinesandstone
burrowing
is
generally
w i t h sparse, t h i n
and s i l t s t o n e .
The b a s i n a lf a c i e s
lower p r o d e l t a p o r t i o n
w i t ht h ee x c e p t i o nt h a tt h e
Evidenceof
than
those
and less abundant
is
i d e n t i c a lt o
of t h e f i n e - g r a i n e d d e l t a f a c i e s
sand and s i l t i n t e r b e d s
b a s i n a lf a c i e sa r en e v e ri n c l i n e d
boundarybetween
of
a b u n dFaan
cch
ti.ae rsa c t e r i satriec s
summarized i n Table 5.
the
consist;s
of
the
and a r eg e n e r a l l yt h i n n e r
of
t hd
e e l t faa c i e s .
The
the two f a c i e s i s arbitrary.
Depositional
Processes.
Basinal
depositional
p r o c e s s easreex a c t ltyh e
e
p r o d e l t a i cp o r t i o n
same
a st .h o s e
of t h e
fine-grained elta
facies,
of
t h e lower
and
s
Table 5
Lacustrine
Sedimentary
Basinal
Facies
Characteristics
Lithology
Dominantly mudstones with sparse, thin
Mudstones: burrows and rare horizontal
interbeds of sandstones and siltstones.
laminations. Sandstones and siltstones:
.
Mudstones are usually highly calcareous. horizontal laminations, ripple lamito
Sandstones and siltstones are poorly
nations, burrows, and parting step
well sorted and are usually calcareous. lineation.
82
of
i n c l usdeet t l i n g
silt
and
d e p o s i t i o n of s i l t
and
sand
by
homogenization
of
mudstones
and
The t h i ns,p a r sne a t u r . e
of
i n d i c a t e sd e p o s i t i o nf a r
the
clay
from
suspension,
t u r b i d i t cyu r r e n t s ,
and
c l a y s t o n e s by
burrowing.
and
sand
interbeds
silt
of c o a r s e
from nearshoresources
sediments.
General Characteristics
of t h e L a c u s t r i n e System
The l a t e r a l l yp e r s i s t e n tn a t u r e
and
0
d e l tpal a t f o r m
sandstones
and
of t h ed e l t af r o n t
t hgee n e r al al c k
destructional-phase features indicate that
deltas
were
of
Baca f i n e - g r a i n e d
and
m a i n lh
y i g cho n s t r u c t i vleo b a t(eF i s h e r
others, 1969), which s u g g e s t sp r o g r a d a t i o ni n t or e l a t i v e l y
shallowwater.
The o t h e r v a r i e t y
i s t h ee l o n g a t e
o r b i r d s f o o td e l t a ,
by
from
of h i g h - c o n s t r u c t i v e d e l t a
which
is
characterized
which r e s u l t
lateralld
y i s c o n t i n u o ubs a r - f i n g esra n d s
progradatio
i nndt o
e e pw
e ra t e r .
indicated
by
the
p r o d e l t af o r e s e tb e d s ,
During
d e p o s i t i oo
ntfh e
Water
thickness
of
prodelta
w a s g e n e r a l l yl e s st h a n
as
mudstones
and
20 f t ( 6
m).
upper
red
unit,
however,
water
depth may havebeenconsiderablydeeper,
large thicknesses of
depth,
as a t t e s t e d by
mudstones i n t h a t u n i t .
the
83
Baca d e l t a i c and basinalsediments
Mountains
area
show
l a c ubs at rsiinne.
evidence
of
Evidence
concentrations
of
in
t h eG a l l i n a s
deposition
includes:
i n a closed
high
(a)
e( p
a r ley- c o m p a c t p
i ohnr )e,a t i c ,
a u t h i g e n i c c a l c i t e i n b a s i n a l and lower-delta mudstonesand
sandstone
( s edei a g e n e ssi e
s ction):
l a c u s t r i n e megafauna.
observed.
The
Only a few s c a t t e r e do s t r a c o d s
in
climate
west-central
Baca time was probablysemiarid
Langbein
were
New Mexico d u r i n g
(see p a l e o c l i m a t es e c t i o n ) .
s t a t ehcsal o
t sleadkaerse
(1961)
exclusively i n a r i d
e
( b ) r a r i t y of
and
and
found
semiarid
regions.
Closed
lakes
u s u a l l ye x h i b i tw i d e l yf l u c t u a t i n gw a t e rl e v e l s( L a n g b e i n ,
1961).
Rare
basinal
and p r o d e l t a sediments a r e i n d i c a t i v e
low s t a n d s .
sandstone
caliches
horizons
The presence of t h ef l u v i a l l y
unit
and lower r e d
which
and
mudcracked
was
between
units
a
Baca
of lake-level
dominated
t h ep r e d o m i n a n t l yl a c u s t r i n e
indicates
probablycaused
in
middle
upper
l a r g e - s c a lree g r e s s i o n ,
by a d r a s t i cd r o p
i n lake l e v e l
due t o a c l i m a t i c change ( s e e d e p o s i t i o n a l h i s t o r y s e c t i o n ) .
S t e e p l yi n c l i n e dG i l b e r t - t y p ef o r e s e t sa r er a r e
in
t h ef i n e - g r a i n e dd e 1 t a . f a c i e . s .F a c t o r sc o n t r i b u t i n gt ot h e
development
of
f o r e s ei nt sc l u d( a
e ):
homopycnal
flow
(inflow,densityapproximatelyequaltolake-waterdensity)
*
whichcausesthree-dimensionalmixingandanabruptdecrease
in
current
v e l o c i t rye, s u l t i nri n
g
apd
i de p o s i t i o n
of
84
sediment (Bates, 1953);
water
(McGowen,
( b ) d e l t a i cp r o g r a d a t i o ni n t o
1970;
Axelsson,
1967;
Hjulstrom,
1952);
and ( c ) t r a n s p o r t of
coarse
bedload
sediments,
of
are 'composed,
G i l b e r t - t y pfeo r e s e t s
The c o n d i t i o n sl i s t e d
rarely
p r e s e ndt u r i n g
deposition
d e l t a s i nt h eG a l l i n a M
s ountains.area.
shallow
and
sediments
Baca
coarser
than
coarse
sand.
implies
a
jet
depths
were
Water
i n the s t u d y area were r a r e l y
The c l o s e d
nature
of
formation
(Bates,
1953).
a
v e l o coi tvye r
r e s u l t i n gi nd e p o s i t i o n
from
development of a
Lack
jet
the
t om a i n t a i n
of
sediments
over
the
distributary
mouth.
a
Canyon
which
foresets
The
Gilbert-type
area
(Johnson,
1978)
probably
of
coarse,
conglomeratic
sediments
derived
t h e nearbySierra-Sandiauplift.
e
t o the
T h ilse a d s
g e n t lsyl o p i np
gr o d e l tsau r f a c e ,
Baca
its
considerable
formed i n response t op o s s i b l ed e e p e r - w a t e rc o n d i t i o n s
t h ei n p u t
three-
r e l a t i v el oldynigs t a nbcaes i n w a r d ,
s e e n i tnhfei n e - g r a i n e d e l tfaa c i e s .
in
and
of
p r o d u c e st h et y p i c asl h a l l o w l yi n c l i n e dp r o d e l t a
deltas
t h el a k e
water, producing
hypopycnal
flow
dimensional
mixing.
causes
the
plane
distance
of t h e Baca
l a k e waters were more dense ( d u e t o s a l i n i t y )
that
t h a ni n f l o w i n gr i v e r
plane
which
to
thd
eistributary
mouth (Smith,
1975;
Axelsson,
1967).
above
were
deep
'
and
from
85
Thin,
destructional-phase
shoreface
sequences
producedbyreworkingofupper-deltasediments
by waves and
l o n g s h cour er r efnotlsl o w d
i negl t a i c
subsidence(Fisher
abandonment
and
are r a r e l ys e e n .
and others,1969)
The
paucityofdestructional-phaseshorefacesequencessuggests
relatively
low-energy
Attenuation of wave
may
depths
c o n d i t i o nw
s i t h itnhlea kbea s i n .
e n e r g rye s u l t i n g
from
shallow
water
e x p l atriha
nerdiotefys t r u c t i o n a l - p h a s e
features.
The large,shallow
time
0
in
lake systempresentduring
Bear-Gallinas Mountains area would tend t o be
the
p o l y m i c t i c( f r e q u e n to v e r t u r n )s i n c es u r f a c e
eddy
Baca
diffusion
would
be
expected
s e v e r a lt e n so f e e t( J o h n s o n ,
burrowingofbasinal
at least
t op e n e t r a t e
1978).
to
mixing
due
Evidence of
abundant
and p r o d e l t as e d i m e n t si n d i c a t e s
that
lake-bottom
sediments
were
oxygenated,
supporting
a
of
polymictic
regime.
Preservation
laminations i n lake-
to
i s u s u a l l y restricted
bottom
sediments
m e r o m i c t i c( p e r m a n e n t l ys t r a t i f i e d )l a k e s ,i n
oxygen
inhibits
the
p.
Johnson
(1978,
activities
8 5 )s t a t e s
oligomictic
and
which l a c k of
burrowing
of
organisms.
t h a t t h e shallow,
polymictic
n a t u r e of the B a c a l a c u s t r i n e system r e s u l t e d . i n o x y g e n a t e d
lake-bottomwaters
complete
lack
e
sediments.
which may be r e s p o n s i b l ef o r
of reduced
(gray
Lake
and
bottom
sediments
green)
in
Baca
t h e almost
lacustrine
shallow,
frequent-
86
overturn,
Lake
(Mothersill,
Chad,
are
Africa,
dark
yellowish
1975), which p r o b a b l yi n d i c a t e s
limoniteand,thus,positive-Ehconditions.
l e s st h a n
brown
t h e p r e s e n t of
Upon b u r i a l
6 0 c m , however, the bottomsedimentsof
Of
Lake Chad
assume a darkgreenish-graycoloration,probablyindicative
of
reduced
iron
and
negative-Eh
from anoxygenating
conditions.
This
t o a reducingregime
removal,
during
burial,
change
is probably due
bottom
of sediments
from
of
presence of oxygenated
lake
waters.
Isolation
for the
waters
f r e e oxygen i nt h ei n t e r s t i t i a l
decomposition of o r g a n i c m a t e r i a l
coloration
the
of
Baca
through
by a e r o b i c b a c t e r i a ,
would lead t o negative-Ehconditions.
the
bottom
sedimentsfromoxygenatedlakewaterswouldallow
uptake
of
to
which
of
The m a j o r i t y
sediments ( i nb o t hl a c u s t r i n e
to
f l u v i afl a c i e s i)nt h es t u d ya r e a p p e a r s
be
due
the
and
to
i n t r a s t r a t as lo l u t i o noi,rf o n - b e a r i nm
g i n e r a l sp,r e c i p itation
of
dehydration
h y d r a tierd
ooxni d e s ,
of
and
the
o sxei d e s ,
which
development of hematite pigment.
did
n o tn e c e s s a r i l yc o n t a i n
d e p o s i t i o n ;i nf a c t ,
t h el a c u s t r i n es e d i m e n t s
the
subsequent
r e s u l t s tihne
Thus, t h e . Baca
sediments
any iron-oxidecolorants
upon
there i s some evidence t o s u g g e s t t h a t
were reducingandcontainediron
s u l f i d e s which l a t e rp r o v i d e di r o n
for
red
w i l l be d i s c u s s e d i n t h e d i a g e n e s i s s e c t i o n .
coloration,
as
a7
e x i s t which
Several o t h e r l i n e s ofevidence
a
of the B a c a
l a c u s t r i n ei n t e r p r e t a t i o nf o lra r g ep a r t s
Formation
in
area.
Bear-Gallinas
Mountains
the
i n c l u d e :( a )t h ep r e s e n c e
support
of r a r e o o l i t e s
These
and o s t r a c o d s and
common i n t r a c l a s t s which were observed i n t h i n s e c t i o n s from
many
parts
of
Baca
the
i tnh set u d a
yr e a ,
as w i l l be
discussed i n t h e s a n d s t o n ep e t r o l o g ys e c t i o n .
work
on
t h ep a l y n o l o g y
Mountains
upper
red
units,
stated
which
i n t e r p r et ot
I
a
few
alga,
g r a i n s and t h e fresh-water
sample
shale
from
flora,
I,
states
...p erhaps requires
t htahte
be
Pediastrum.
a
thin
dominantly
However,
a
mudstone i n t h e
(I
was
present
from a wide
during
sampling)
produced
spores
and
pollen
(1979)
further
his
p o o r lpyr e s e r v epdo l l e n
' f l u v i a l l y dominated m i d d l e s a n d s t o n e
unit
v a r i e t y upland
of
In
t h e lower and
Baca sediments ( i . e .
l a c u s t r i n ey)i e l d eodn l y
greenish-gray
(b)
of t h e Baca Formation i n the Bear
v i c i n iC
t yh, a i f f e( 1
t z9 7 9 )
predominantlypink-gray
.
i n c l u d i ncgo n i f e rC
s .h a i f f e t z
t h at htper e s e n c e
Pediastrum
of
some standing fresh-water bodies
r e g i o n a t t h a t time".
.
I..
i n the
88
Lacustrine Model
The limitedexposures
make
comparison
t o modern and ancientanalogues
Exposures i n t h e s t u d y a r e a
only
of
directions
of t h e Baca l a c u s t r i n es y s t e m
difficult.
and t h e Baca Canyon a r e a c o n s i s t
m a r g li ancaul s t rdienpeo sPi at sl e
. ocurrent
in
the
(see
study
area
sediment
dispersal
p a t t esrencst igaoernn
e)e r anlol y
r t h edaisr te c t e d ,
indicating that the location
direction.
was i n t h a t
of t h e b a s i n c e n t e r
The n a t u r e of t h eb a s i n - c e n t e rd e p o s i t sa r en o t
known due t oe r o s i o n asl t r i p p i n gf o l l o w i n gl a t eT e r t i a r y
uplift
of
the
Colorado
Plateau.
Any
lacustrine
system
must
characteristics:
( a ) shallow
water
depth:
lake
l e v e l s(:cr)a r i t y
model of the Baca
take
into
account
the
following
(b) fluctuating
of l a c u s t r i n e megafauna;
and
cements i n
h i g hc o n c e n t r a t i o n so fe a r l ya u t h i g e n i cc a l c i t e
marginal lacustrine
sediments.
Surdam andWolfbauer(1975)haveproposed
basin,playa-lake
l a c u s t r i n es y s t e m .
closedlake
closed-
t h ec h a r a c t e r i s t i c s
of
the
Lake Gosiute was a l a r g e ,s h a l l o w ,
which e x h i b i t e dw i d e l yf l u c t u a t i n gl a k el e v e l s
and crude, concentric zonation
facies (Fig.
a
model f o r Eocene Lake Gosiute. i n Wyoming
which adequately f i t s most
of
Baca
(d)
24).
of bothchemical
The marginal
facies
characterized
calcareous
by
sandstones
and d e t r i t a l
of Lake
and
Gosiute
is
siltstones
89
Figure 2 4 . ~ Map;-showing crude,concentric zonation
of
facies in Eocene Lake Gosiute, Wyoming,
during a high stand (Tipton Shaletime).
Marginal facies is composed of calcareous
sandstones and siltstones, somewhat similar
to the lacustrine system rocks in the study.
area. Surdam and Wolfbauer (1975).
90
p.
(Surdam and
Wolfbauer,
1975,
Baca
339)
m a r g i n al al c u s t r i nreo c k s .
somewhat
r e e f s ,a n df i s h .
lacustrine
to
Megafaunal d i v e r s i t iyn
Lake Gosiute was g r e a t e rt h a nt h a to f
l a c u s t r i n es y s t e m ,
similar
Baca
the
Formation
and includedostracods,molluscs,algal
The more restricted assemblageof
system
may
t h e Baca
( a ) lack
of
exposure
be due t o :
of
p o t e n t i a l l y more f o s s i l i f e r o ubs a s i n - c e n t edr e p o s i t s ;
(b)
from h i g h e re v a p o r a t i o nr a t e si n
h i g h e rs a l i n i t yr e s u l t i n g
t h e more s o u t h e r l y B a c a l a c u s t r i n e s y s t e m .
Deep Springs Lake i n InyoCounty,
19651,
a'
e x h i b i t s quasi-concentriczonation
t o t h a t of
19751,
California(Jones,
and
ancient
may
Lake
Gosiute
represent
a
of f a c i e s similar
(Surdam
and
modern
1
analogue of the Baca
l a c u s t r i nsey s t e mitn
.hBe e a r - G a l l i n a s
Marginal
sediments
of
Deep
Wolfbauer,
Mountains
Springs
Lake
area.
c o n t ahi n
igh
carbonate
minerals.
Certain
c o n c e n t r a t i o n s of authigenic
a s p e c t s of Lake Chad, A f r i c a ,( M o t h e r s i l l ,1 9 7 5 )a r es i m i l a r
to
those
inferred
for
the
include:
(a)
polymictic
regime;
Baca
lacustrine
system.
These
( b ) closed
nature
5 m).
l a k e ;a n d( c )s h a l l o ww a t e rd e p t h( l e s st h a n
,
of t h e
DEPOSITIONAL
RECONSTRUCTION
Sediment Dispersal P a t t e r n s
were
P a l e o c u r r einntd i c a t o r s
types
of
were
-include
imbricated
has
and
direction
e
streams.
Two g e n e r a l
p a l e o c u r rienndt i c a t ourns i, d i r e c t i o n a l
bidirectional,
(197213)
delineate
the s t u d y area.
d i s p e r s a l p a t t e r n si n
sediment
to
used
and
u t i l i z eU
d .n i d i r e c t i o n,ai ln d i c a t o r s
axes.
pebbles and
trough-crossbed
documented
the
relationship
imbricated
pebble
Rust
between
flow
o r i e n t a t i oi nn
modern
T h e coincidence of t h e azimuths of trough-crossbed
axes w i t h flow d i r e c t i o n
(1973),
High
and
has
been
demonstrated
(1974),
and
Picard,
by
occur
braided-stream-dominated
portion
f i n e - g r a i n e dl a c u s t r i n e
delta-platform
d e l t a f a c i e sa n d
(1967).
Meckel
U n i d i r e c t i opnaalle o c u r rienndti c a t o r s
Dott,
in
of
the
the
t h e d i s t a lb r a i d e d
alluvial-plain facies.
P a r t i n g step l i n e a t i o n s ( M c B r i d e and
Yeakel,
1963)
t h e b i d i r e c t i o n a li n d i c a t o r sa n d ,
( F i g2
. 5 )c o n s t i t u t e
to
their
dominant
abundance
and
ease
of
p a l e o c u r r e nitn d i c a t our t i l i z e idn
Stokes
(1947)
has
documented
that
t r e n d i s p a r a l l e l t o c u r r e n t flow.
e
measurement,
n a t upr e
a ,r,t i n g - sl ti enpe a t i o n
the
t h i s study.
p a r t i n g - s t e lpi n e a t i o n
Due t o i t s b i d i r e c t i o n a l
data
91
were
due
must
be
used
in
92
I
..:_i
~
Figure 25.
Well-developed parting-step lineation in a
fine-grained Baca sandstone. Paleoflow was
parallel to trend of mechanical pencil.
93
with
conjunction
t o determine
u n i d i r e c t i o n a ld a t ai no r d e r
are
t ht e
r ut e
r a n s p ov
r te c t oP
r .a r t i n g - s t el p
ineations
sometimes
s e e inb
nraided-stream
d e p o s i tistnhd
eeltadelta facies
platform portion of the fine-grained lacustrine
They are very
and t h e d i s t a l b r a i d e d a l l u v i a l - p l a i n f a c i e s .
commonly
observed
sandstones.
th
in
'ipnr,o d efl rt o
a ntal-splay
,.
d i s c u s sperde v i o u stlhyes, saen d s t o n e s
As
probably
represent
deltaic
t u r b i d i t y - c u r r ednetp o s i t s .
Parting-steplineationwithinturbiditeshasbeendescribed
byCrowell
(1955).
P a l e o c u r rdei n
r et c t ivioa
nnrsy
systematic
t h se t u d y
mannerfrom
area.
paleocurrents
26 a ,
b),
paleocurrent
(Fig.
a
t h ew e s t e r nt oe a s t e r np o r t i o n s
I nt h ew e s t e r np a r t
were
of
of
t h es t u d ya r e a ,
generally
northeastwardirected
(Fig.
whereas,
eastern
i tnh e
directions
26 c; d ) .
somewhat
part
of
t haer e a ,
trendgenerallyeast-southeastward
Thisdivergenceofpaleoflow
may havebeen
caused by a c t i v i t y a l o n g t h e p r e v i o u s l y d e s c r i b e d n o r t h e a s t t r e n d i nm
g o n o c l i n af l e x u rper e s e nitn
thseo u t h e a s t e r n
portion
of t h e
of
the area.
Downwarping of t h es o u t h e a s t e r n
monocline
during
topographically
low
Baca
area
time
may
side
have
created
a
which may be . r e s p o n s i b l ef o rt h e
d e f l e c t i o n of p a l e o c u r r e n t st ot h ee a s t - s o u t h e a s it nt h e
e a s t e r np o r t i o no ft h es t u d y
area.
If t h i sh y p o t h e s i s
t r u e t, h e nt h e" r e g i o n a l " p
. a l e o c u r r e nd
t i r e c t i o ni nt h e
is
94
V,
bldireccional
Figure 26.
bidirectional
Comparison of paleocurrent data in western
(a,b) and eastern (c,d) portions of study
area. The significant portions of the
bidirectional rose diagrams (shaded) were
determined by comparison with associated
unidirectional data. The study area was
arbitrarily divided along the line between
Indian Spring Canyonand Indian Mesa.
quadrangles.
95
Gallinas
Mountains
area
was
probably
northeastward,
as
in
r e p r e s e n t e d by the p a l e o c u r r e n ti n d i c a t o r s
portion
of
t haer e a
which
were
farther
presumablyunaffectedby,themonocline.
the study area
t h ew e s t e r n
away from,
and
in
Baca sediments
were probably derived mainly
from t h e Morenci
u p l itftoh
ts' o
e u t h w e satl,t h o u gdhe t r i tianl p u t
'by
t r i b u t a r i e sd r a i n i n gt h ew e s t e r nf l a n k
of t h a tp o r t i o n
of
which l i e s t o the south of t h e a r e a
the Sierra-Sandia uplift
may have a l s o been important.
Depositional History
The rocks of t h e Baca Formation i n
study
the
area
r e c o r dt h ea l t e r n a t ep r e v a l e n c eo fd i s t a lb r a i d e da l l u v i a l
plain
and
lacustrine
a l t e r n a t i o n ' of
environments
deposition.
of
these
The
two environments r e f l e c tl a r g e - s c a l e
f l u c t u a t i o n s of w a t e r l e v e l
i n a large,shallowlakepresent
d u r i n g Baca time i n the Bear-Gallinas
Mountains v i c i n i t y .
Baca sedimentation i n t h es t u d ya r e a
by
braided-stream
deposition
predominantly
derived
of
sands
from the
southwest
erosionalsurfacedeveloped
was
initiated
and
minor
gravels
on
a
on theLateCretaceousCrevasse
Canyon Formation.Braided-streamsedimentation
Baca
e
is
low-relief
i n thelower
r e p r e s e n t e db yt h ed i s t abl r a i d e da l l u v i a l - p l a i n
facies which comprises t h eb a s a l
40 f t ( 1 3 m) of
the
lower
96
red unit (Fig.
The
27).
initial
interval
of braided-stream
sedimentation
was followed by
a prolonged period of marginal lacustrine
sedimentation, as
isrepresented by the cyclical deposits of
the fine-grained delta and lacustrine basinal facies, which
comprise the remaining283 ft (86 m) of the lower red unit.
These lacustrine deposits indicate a large-scale southwestward transgression of the shoreline of a lake whose center
was to the northeast (as suggested by paleocurrent data),
which resulted in onlap of lacustrine sediments over older
braidedstreamdeposits,Local,small-scaleregressive-
e
transgressive sequences within this initial transgressive
phase
of
Baca
sedimentation
are
recorded
by
cyclical
deltaic
progradation, abandonment, and subsidence.
The initial period of lacustrine sedimentation was
followed by
a return to a braided-stream-dominated regime,
as represented by
the
sediments of
the distal braided
alluvial-plainfacieswhichcomprisetheentiremiddle
sandstone unit. The return to fluvially dominated processes
to
indicates a large-scale regression of the lake shoreline
the
northeast.
The final phaseof Baca sedimentation in the study
area is represented by the dominantly lacustrine sediments
of the upper red unit. These sediments indicate a second
.major,
widespreadshoreline,transgressioncoupled with
minor
99
t hleo c u s
of
l a c u s t r i nsee d i m e n t a t i o n
w i t h i nt h eb a s i n :
activity
due
( b ) i n c r e a s e de r o s i o n
ttoe c t o n i s m
caused by
t hseo u r caer e aw, i trhe s u l t a nlta r g e - s c a l e
in
r e g r e s s i o n due t o progradation of a l l u v i a l a p r o n s
(c)
importance
and
of
regressive
phases.
each
of
However,
s u g g e s t st h a c
t l i m a t i cc h a n g e s
l a k e - l e v efll u c t u a t i o n s .
one
line
is
and
mudstones
conditions.
implies
unit,
of probable
saline,
closed-lake
of
temporary
a
change
t h et r a n s g r e s s i o n
in
other
t o more fresh-waterconditions
wasdue
t o achange
a
amounts
of t h e b a s a l
canexplainthe
mudstone of t h e upperred
Large-scale
lake-level
fluctuations
aneousEocene
by
of f r e s hw a t e trot h e
of t h et e c t o n i ca l t e r n a t i v e s
non-calcareous.nature
unit.
large
If
t o a wetterclimate,
t h el o w - s a l i n ec h a r a c t e r i s t i c sc o u l db ee a s i l ye x p l a i n e d
of
by
mudstones)
of t h e second t r a n s g r e s s i v ep h a s e .
d u r i n g thebeginning
lake.Neither
the
of t h e upper red u n i t ( 2 p e r c e n t c a l c i t e
compared with 10-15 p e r c e n t
t h ei n t r o d u c t i o n
the
a r eh i g h l y
The essentially
non-calcareous
nature
mudstone
weightas
in
mudstone of
i n theupperred
indicative
evidence.
cause of t h e
area.,withtheexceptionoftheprodelta
calcareous
relative
of
were
major
a
The l a c u s t r i n e
t h eb a s a ld e l t a i cc y c l e
basal
The
the
above-listed
hypotheses
d i f f i c utdlote t e r m i n e .
e
basinward:
c l i m aftliucc t u a t i ownriest shu l t laanrtg e - s c a l e
transgressive
study
tectonic
Lake Gosiute, Wyoming, havebeen
in
contempor-
attributed to
97
Type o f
Shoreline
Migration
Depositional
System
Unit
‘
Lacustrine
Upper
Red I
Unit
Braided
Alluvial
Plain
Middle
Sandstone
Unit
Lacustrine
Lower
Red
Unit
- transgression
100
ft
0
i
30
m
0
-regression
-
Figure 2 7 .
transgression”---Braided Alluvial Plain
Generalized Baca stratigraphicsectioninthestudy
area showing relationships between shoreline migrations,
depositional systems, and informalunits.
98
similar t o t h o s e of t h e
d e l t a i cr e g r e s s i v es e q u e n c e s ,
Water
transgressive
phase.
t r a n s g r e s s i v ep h a s e
as
first,
the
during
depths
second
may havebeendeeperthanthose
shown
by
prodelta
mudstones
first
of
the
and
the
large
t h i c k n e s s eo
s bf a s i n a l
itnh e
upper
red
unit.
Lacustrine
some p a r t s of t h es t u d y
conditionscontinued
t op r e v a i li n
area during deposition
of t h e lowermost Spears Formation, as
attested
by t h e o c c u r r e n c e
t h a t u n i ti n
portionof
of d e l t a i c d e p o s i t s i n t h e b a s a l
some. a r e a s( b a s a l
deltaic
Spears
deposits a r e w e l l exposed i n SW 1/4 and NW 1/4, SW 1/4,sec.
R.6W.).
24, T.lN.,
e
Examination by the writer
sectio
i nn
Baca
Canyon
revealed
coarser-grained,vertical.sequence
area,
t hset u d y
a
stratigraphic
similar,
although
of f a c i e s t o t h a t s e e n i n
and
i n d i c a t i ntgh at thter a n s g r e s s i o n s
r e g r e s s i o n sr e c o r d e di nt h es t u d ya r e a
featuresb
, ut
of t h e Baca
were n o t
w e r e .manifestedthroughout
t h e lake b a s i n .
The Baca l a c u s t r i n e system i n' t h eB e a r - G a l l i n a s
vicinity
may havebeen
initiated in response
t h e LaramideSierra-Sandia
element
across
the
local
just
Mountains
t o c r e a t i o n of
u p l i f t which a c t e d as
a
damming
generally
eastward-dipping
regional
paleoslope.
Three p o s s i b le x p l a n a t i o n s
s c a l et r a n s g r e s s i o n s
and
sediments i n t h e study area.
exist
for
regressionsrecorded
These are:
the
large-
i nt h e
Baca
(a) s h i f t i n g
of
100
c l i m a t i c changes by Surdam
and
of occurrence, and number of
EoceneLake
in
present
during
in
v i c i(nFi it g
y.
regressive
system
the
Bear-Gallinas
Although
28).
Mountains
c l i mfaltui c t u a t i o n s
enough d a t a i s a v a i l a b l e
generallyaffectlargeregions,not
between
d e t e r m ipnoes s i br el el a t i o n s h i p s
transgressive
and
is
sequence
t h el a r g el a c u s t r i n e
in
time
Baca
transgressive
It
Gosiute (Suxdam and Wolfbauer, 1975)
i s very
s i m i l atro
those
to
(1975).
t o n o t et h a tt h er e l a t i v et h i c k n e s s e s ,
interesting
phases
Wolfbauer
and r e g r e s s i v e p h a s e s
tthhee
of Lake Gosiute and t h e
Baca l a c u s t r i n e system.
The existence
SpearsFormation
that
tbe
of
d e l t a idce p o s i t s
t hbea s a l
i n some p a r t s of t h es t u d ya r e ai n d i c a t e s
l a kpee r s i s t efdo r
a
not
is
include climatic chanae
short
known.
during
the
L i k e lpyo s s i b i l i t i e s
and r a p i d i n f i l l i n g
v o l c a n i c l a s t i c sediments.
time
The cause of t h ef i n a l
beginning
of
Oligocene
volcanism.
demise of t hlea k e
in
of the lake with
101
I
Figure 28.
Generalized stratigraphy of the Green River
Formation in Bridger and Washakie basins of
Wyoming, showing alternation of high stands
(Tipton and Laney Shales) andlow stands
(Luman Shale, Wilkins Peak) in Eocene Lake
Gosiute. From Surdam and Wolfbauer (1975).
PETROLOGY
Conglomerate Petrology
but
Conglomeratesarescarce
t h e s t u d y area.
widespread
They occurprimarily
l e n s e sw i t h i ns a n d s t o n e s
of
throughout
a s t h i n ,d i s c o n t i n u o u s
t h ed i s t a l
alluvial-
.braided
p l a i n facies and i n t h e u p p e r p o r t i o n s o f l a c u s t r i n e d e l t a i c
cycles.
Clast size averagesabout
1.6. i n ( 4 cm)
,
and ranges
up t o a s much as 5 i n ( 1 2 . 5 c m ) .
Clast Composition
Pebble counts from 1 5 l o c a l i t i e sw i t h i n
a r e a were u t i l i z e d t o d e t e r m i n e
the clast composition
Baca c o n g l o m e r a t e sL. i t h o l o g i epsr e s e nitn
erates
are
lithologies,
however,
i m p o r t acnot n s t i t u e nitns
are
and
chert.
a ar el spor e s e n t
some
areas.
l o c a l l y abundant i n t h e
upper red units.Pebblecompositiondata
Table 6.
the
of t h e
conglom-
Many
other
and
often
are
Silicified
102
wood
middle sandstone and
is
A t e r n a r y p l o t of pebblecompositions
i n Figure 29.
,
of
highly
v a r i a b l ae n d
c o n s i spt r e d o m i n a n t l y
metaquartzite,
limestone,
fragments
study
the
summarized
in
i s presented
I
Table 6
Summary
Lithology
Range
metaquartzite
(%)
of
Pebble
Composition
Average ( %)
Data
Color
Remarks
0-90 black,
red,44.2
pinkgray
white, multicolored
limestone
0-85
29.4dark tomedium
gray
chert
0-65
10.4
dark
gray
to
Usually well
subequant.
rounded
and
I
Dominantly micrite.
Sometimes contains a
few crinoid stem
fragments or septarian
cracks.
black
granite
0-75
sandstone
and siltstone
0-40
5.6
gray I pink I
red
Some may be
sediments.
schist
0-20
1.6
medium
to
dark gray
Contains abundant biotite.
grayish-pink
6.2
Contains abundant pink
orthoclase.Usually
present in small amounts.
High concentrations (75%)
only seen at one locality.
reworked
Baca
P
0
W
Ln
d
W
d
I
0
0
m
.
N
0
I
0
i
104
105
Quartzite,
schist
/
Limestone,
Granite,
volcanics
sandstone,
cher.t,
siltstone,
mudstone
Figure 29.
Ternary plot of Baca pebble compositions.
Data from 15 pebble counts within the study
area.
106
Baca conglomerate c l a s t s a r e l i t h o l o g i c a l l y
t o rocksexposed
i n t h a t p o r t i o n of t h e S i e r r a - S a n d i a u p l i f t
Mountains.
now represented by t h e Magdalena
nature
of
in
t hcel a scto m p o s i t i o n s
suggests
derivation
The
from
nearby
sources.
s h od
r ti s t a n c e s
of
transport,
e i t h edr e r i v e d
from
a
Some
and,
Morenci
e
reported
thus,
were
,probably
i n the
the
or
an
from
of l a c u s t r i noer i g i n
lower
red
i n t h e BearMountains
Formation
p.
in
the
whichimply
uplifts
intraformational
source.
Limestones
have
been
of
Paleozoic
limestone
source
or
nearby
Sierra-Sandia
variable
Baca conglomerates
c a r b o n a t ec l a s t se x h i b i tf r a g i l e ,p l a t ys h a p e s ,
'
similar
unit
of
the
Baca
v i c i n i t y( M a w i n g i l l ,
1979,
100).
C l a s t Morphology
Baca conglomerateclastsfrom'withinthestudyarea
are
usually
highly
spherical.
Thirty-eight
approximately
equal-sized (2-3 c m i n l e n g t h )i n t e r n a l l yi s o t r o p i cc l a s t s
from
~
two
localities within the study area
t h e writer and 33 clasts fromone
members
of R.
L.
a
Most
by
l o c a t i o n were measured
by
Folk's Geo 391 Sediments and Sedimentary
Rocks c l a s s and p l o t t e d ona
30).
weremeasured
p o i n tpsl o t t e d
sphericity-form
in
diagram
t hceo m p a c t ' p l a t y ,
bladed, and compact e l o n g a t e fdi e l d sw
, ith
a
few
(Fig.
compact
points
.
107
COMPACT
.9
Figure 30.
Sphericity-form diagram showing shapes of
71 Baca~pebbles. Average-maximumprojection
sphericity is 0.754. L=long diameter,
I=intermediate diameter, S=short diameter.
Sphericity-form diagram from Folk (1974).
10%
in
falling
t h e compact, bladed, and p l a t yf i e l d s .
'A
maximum p r o j e c t i o ns p h e r i c i t y
1958)
for
( (S2/LI) )
less
usually
(Sneed
and
t h e samples was 0.754.
According
o r a l commun.), the mean
maximum
0.75
sediments
between 0 . 6 6 and
and
braided-stream
for
pebbles.
in
mode
t h es t u d ya r e a
Baca
of
transport
greater
As
described
of
the
Baca
(and', presumably,
upstream
t h e s t u d y a r e a ) was by braided
o b t a i n efdot rh e
is
p r o j e c t i o ns p h e r i c i t y
t h a n 0.66 f o r beachpebbles,
previously,
the
primary
Folk,
t o Folk (1978,
0.75,-for
non-braided-stream
fluvial
pebbles,
than
Average
streams.
The
0.754
of
value
pebbles
thus
marginally
supports
Folk's hypothesis.
Dobkins
and
sphericity, platy
Folk
i s caused
form of Tahiti-Nuibeachpebbles
by s l i d i n g backand
backwash.
low-
(1970). s t a t h
e taht e
of
f o r t h d u e t ot h ee f f e c t s
swash
of braided stream pebbles may
The h i g h s p h e r i c i t y
reflect the flashy discharge characteristics typical
braided
streams.
manner.
This
to
d i s t r i b u t i o n of a b r a s i vaec t i o n
p e b b l e st h
, ufsa v o r i ntgh e
clasts.
more
which would f a v o trr a n s p o r t
in
a
in
nearly
equal
turbulent,
a 1s1u r f a c e s
development
Non-braided f l u v i asly s t e m s ,
t y p i c a l l ye x h i b i t
e
result
would
of most
common i n braided
High-discharge
events,
streams, would t e n d t ot r a n s p o r p
t ebbles
chaotic
and
on
of
the
of nearly
equant
t hoe t h e r
hand,
uniform d i s c h a r g ec h a r a c t e r i s t i c s ,
of
pebbles
by
rolling
along
109
t h e isrh o r t
and
intermediate
axes.
preferentially abrade the short
in
p e b b l erse, s u l t i n g
a
Such
r o l l i n g would
and intermediate axes
of t h e
moderate-sphericity,
bladed
or
e l o n g a t e form t y p i c a l ofnon-braided
fluvial clasts.
According t ot h ev i s u a l - c o m p a r i s o nr o u n d n e s ss c a l e
of Powers (1953), Baca p e b b l e s a r e g e n e r a l l y
rounded t o w e l l
rounded.
Fine-grained,
well-indurated
pebble
types
(e.g.
m e t a q u a r t z i t e ,c h e r t ,m i c r i t e )
the
t e n d t o be more rounded than
less
coarser-grained
or
w e l l - i n d u r a t el idt h o l o g i e s .
i n t h e Baca
A l t h o u g hm e t a q u a r t z i t ec l a s t ss i m i l a rt ot h o s e
are p r e s e n t i n s e v e r a l Mesozoic u n i t s
Mexico,
such
in
at h
sTer i a s s iCch i n l e
west-central
New
Formation
(Givens,
1957), and i n s e v e r a l Precambrian u n i t s i n southernArizona
(J.
MacMillan, 1980, o r a l commun.), t h e well-rounded
of t h e Baca c l a s t sd o e sn o n
t ecessarily
In fact,the
p e b b l e sa r em u l t i c y c l e .
t hoeb v i o u s lfyi r s t - c y c lceo b b l e s
imply
that hese
well-roundednature
and
boulders
p r o x i m abl r a i d e a
dl l u v i a l - p l a i fna c i e s
Mogollon R i m i m p l i e st h a t
many
of
nature
the
of
of
the
exposed
along
the
well-rounded
Baca
pebbles are probably first cycle.
Baca pebbles i n t h e s t u d y a r e a o f t e n e x h i b i t s m a l l ,
c r e s e n t i cp e r c u s s i o n
f e a t u r easrien d i c a t i v e
1974,
p.
marks on t h e i r s u r f a c e s .
of
These s u r f a c e
high-velocity
impacts
(Folk,
12), whichprobablyoccurredduringtransport
b r a i d e d streams.
.
in
110
Sandstone Petrology
Twenty-six t h i n s e c t i o n s o f
area
study
were
examined
Baca sandstones from the
and 2 0 0 random p o i n t s from each
t h i n s e c t i o n were counted.Thinsection
in
Appendix
I
S i e v e - e q u i v a l e ng
t r a i ns i z e
B.
from t h i n - s e c t i o nd a t au s i n gH a r r e l l
was c a l c u l a t e d
Eriksson's(1979)
f o r m u l a , a sf o l l o w s :( s i e v eg r a i ns i z ei n
l i n e a rr e g r e s s i o n
+
phi u n i t s ) = 0.227
size
0.973(thin-sectiongrain
u n i t s ) .S i e v e - e q u i v a l e n tg r a i n
s e c t i o n s examined
ranges
e
and
presented
is
data
phi
s i z e f o r the s a n d s t o n et h i n
from 0.6#
( c o a r s es a n d t)o
3.1+
most samples f a l l i n gi nt h e
( v e r yf i n es a n d ) ,w i t h
in
medium
and f i n es a n dc a t e g o r i e s S
. a n d s t o n es o r t i n gv a l u e sr a n g e d
from
t o w e l l s o r t e d , andaveragedmoderately
verypoorly
moderately w e l l sorted.
mature
Most
o r submature,however,
sandstones
as
immature
(Folk,
(1953)
visual-comparison
roundness
(illite)
1951).
scale,
most
were
grains
categories.
of rounded t o well-roundedquartzgrains
were
observed,
however,
and
probably
represent
multicycle
gr
.
ains
and
According t o Powers'
examined f e l l i n t o t h e subangular andsubrounded
A smallpopulation
texturally
two samples c o n t a i n e dg r e a t e r
t h a nf i v ep e r c e n d
t e t r i t ac
l l a ym a t r i x
classified
were
to
111
According t o
Folk's
classification,
most
petrographically
are
a r e n i t e so,r
of
sandstone
(1974)
mineralogic
the
Baca
sandstones
examined
s u b l i t h a r e n i t ef se ,l d s p a t h i c
a r k o s e( sF i g
3.1 ) .
lithic
lith-
Only one sample
p l o t t e d i n e i t h e r t h e s u b a r k o s eo rl i t h a r e n i t ep o r t i o n s
the
triangle
diagram.
Contrary
t o t h e ' i n t e r p r e t a t i o n s of
previousworkers(Givens,1957;Tonking,19571,none
Baca
sandstones
from t h e s t u d ya r e a
t h i n section
could
defined
by
classifiea
ds
be
Folk,1974).
Baca
Canyon
area,
of t h e
which were examined i n
"true"
arkoses
Average f e l d s p a rc o n t e n t
sandstones i s 1 4 . 3p e r c e n t
of
(as
of these
of t h e framework g r a i n s .I nt h e
however,
Baca Formation
sandstones
are
very feldspathic, probably
due t o d e r i v a t i o n from t h e n e a r b y
S i e r r a - S a n d iuap l i fi tn
which
Precambrian
granites .are
common.
Q u a r t z (47-84%, average 66% of framework g r a i n s )
Quartz i s t h e v o l u m e t r i c a l l y most important
mineral
of
thistudy,
categories:
t h e - B a c a sandstones w i t h i n t h es t u d y
I hava
essigned
q u a r t tzy p e tso
common
quartz
two
detrital
area.
In
genetic
and metamorphic quartz.
These
two g e n e t i cc a t e g o r i e sr e f l e c to n l yt h ep r o b a b l eu l t i m a t e
sourcerocktypeand
h a s been reworked
are n o t meant t o imply t h a t no quartz
from
older,
sedimentary
rocks.
Within
112
Quartz
Feldspar plus
Granite/Gneiss
Rock Fragments
Figure 31.
Rock
Other
Fragments
Classification of Baca sandstones based on
data from 26 thin sections. Cross shows
average composition. After Folk (1974).
113
t h e s e two g e n e r a l c a t e g o r i e s , s e v e r a l
empirical quartz types
types (Krynine,1946)can
(Folk, 1974) and g e n e t i c q u a r t z
be
delineated.
Common Quartz
(12-59%,
average
grains;
average,
of
55%
quartg
z rains
which showed
e x t i n c t i o(ne x t i n c t i o n
37%
of
framework
t o tqaul a r t zM
) .o n o c r y s t a l l i n e
s t r a i g h tt os l i g h t l yu n d u l o s e
shadow
sweeps
were
s t a g er o t a t i o no ff i v ed e g r e e so rl e s s )
c l a s s i f i e di n
t hci sa t e g o r G
y .r a i n
a su
r es u a l sl y
ubequant
morphic.
A small
percentage
sind xeno-
of
(generally less than five percent)
which
randomly
formed
vacuoles
occur
q u a r tg
z rains
e x h i b i t probable reworked
Common q u a r t zg r a i n so f t e ne x h i b i t ’ a
are
probably
common
of d e r i v a t i o n from oldersedimentary
l i k e l yi n d i c a t i v e
sources.
the
o r a r e anomalously w e i l rounded, which i s
quartz overgrowths
most
with
a c r o sgsr a i n s
few
vacuoles
d i s t r i b u t e tdh r o u g h o utthg
er a ia
nn d
d u r icnr g
ystallization.
ilni n e a r
More
zones
within
grains
rarely,
and
may
represh
en
ea
t iln
ioncfg
i p i fernatc t u rM
e si.c r o l i t e s
(mineral
inclusions)
were
occasionally
observed.
Minute,
h a i r - l i k e r u t i l e i n c l u s i o n s were p r e s e n t i n a few grains.
Common q u a r t z i s most o f t e n d e r i v e d
gneissic
source
rocks
and,
lized igneous
from p l u t o n i c o r
less commonly, from recrystal-
v e i n s andmetamorphicrocks(Folk,1974).
114
Metamorphic Q u a r t z (13-51%, average30%of
framework
grains;average45%oftotalquartz)Monoc,rystallinequartz
g r a i n s i n which t h e e x t i n c t i o n
greater
f i v ed e g r e e sr o t a t i o n
than
unduloseextinction)
with
shadow sweeps t h e g r a i n
of the s t a g e( s t r o n g l y
and p o l y c r y s t a l l i n e( c o m p o s i t e )q u a r t z
g r a i n s were placed i n t h i s c a t e g o r y . I n d i v i d u a l c r y s t a l s i n
p o l y c r y s t a l l i nger a i nuss u a l leyx h i b istt r o n g luyn d u l o s e
extinction,
composed of c r y s t a l s
extinction.
with
s t r a i g h tt os l i g h t l y
According
to
quartz
types,
i f i c a t i oonf
a
32), w i t h minoramounts
undulose
Krynine's
(1946)
genetic
classBaca
predominantly composed o f s t r e t c h e d
Of
these g r a i n s are
however, a smallpercentageof
metamorphic
quartz
metamorphic q u a r t z ( F i g .
( g e n e r a l l y less t h a n a f e w
s c h i s t o(sFei3g3. )
and
is
recrystallized
percent)
metamorphic
q u a r t(zF i g3.4 ) .
The r e l a t i v e abundance of
q u a rttyz p e s
is,
in
part,
a
thevariousmetamorphic.
function
p o l y c r y s t a l l i n eh,i g h luyn d u l o sqeu a r t z
common
is
grain
usually
size;
more
i n t h e coarsergrainsizes,whereasmonocrystalline.
s c r o n g l yu n d u l o s eg r a i n st e n dt o
finer-grainedsandstones.
petrographically,
percentages
Indeed,
even
of
no
be more
p r e v a l e n ti n
the
Thus, due t o t h e e f f e c t s of t h e
wide range i ng r a i ns i z e
.:
of
of
the
attempt
tv
h ae r i o u s
t h ree l a t i v e
Baca
sandstones
was
made
metamorphic
examined
to
tabulatexact
quartz
types.
abundances
of
metamorphic
and
115
Figure 32..
Stretched metamorphic quartz grain. Sample 68,
crossed nicols, field width=O,.Y5 rmn.
116
F-,-re
33.
-2histose metamorphic. ,lartz
Note
minor amounts of parallel oriented muscovite
and elongated quartz crystallites. Sample C,
crossed nicols, field width=0.75
mm.
117
Figure 34.
Recrystallized metamorphic quartz grain. Note
equant shape of and simple boundaries between
crystallites. ‘Sample 32, crossed nicols,
field width=O,.75
m
m
.
common q u a r t z
35
i n d i c a t e s a vague t r e n d towardshighermetamorphic/total
size.
q u a r t z ratios w i t h i n c r e a s i n g r a i n
The
diminished
is
i n the finergrainsizes
abundanceofmetamorphicquartz
due t o t h e f a c t t h a t i n c r e a s i n g l y s t r a i n e d c r y s t a l l a t t i c e s
are
necessary
with
t o producestronglyunduloseextinction
decreasing grain size
and t h a t p o l y c r y s t a l l i n e q u a r t z g r a i n s
\
are less common i n t h e f i n e r s a n d s t o n e s .
Metamorphic q u a r t g
z rains
and
xenomorphic
.
They
generally
subequant
a
o f t ec n
ontain
exhibit
dispersedvacuolesandsometimes
e
are
few
randomly
minuteinclusions
muscovite.
of
Quartz
grains
containing
large,
aligned
were
m u s c o v i ct er y s t a l s
classified
as
metamorphic
rock
fragments.
According t o Folk
(19749,
monocrystalline,
highly
is
undulose
quartz
metamorphicand
most
commonly
gneissicsources,
d e r i v e d from stretched
b u t a l s o may occur i n some
s t r a i n e dg r a n i t e s P
. o l y c r y s t a l l i n eg r a i n s
u n d u l o s ee x t i n c t i o n
type indicator
showing s t r o n g l y
are probably t h e most
of a metamorphicsource
primarily from g n e i s s e s
and
\
r e l i a b l eq u a r t z -
area. and are derived
stretched
metamorphic
rocks.
Polycrystallin
g er a i n
ex
s h i b i t i ns g
t r a i gstho
lti g h t l y
u n d u l o s ee x t i n c t i o n
*
and
recrystallized
are most commonly d e r i v e d
metamorphic
from
schists
r o c k s , , b u t may, t o a small
e x t e n t , be derived from g r a n i t e s( F o l k ,1 9 7 4 ) .
Basedon
his
119
.
.
.-...
.
. ..* . .
.. .
. . .. .
I
0.
36
4'
0.0
1
0.2
I
0.4
I
0.6
Metaquartz/Total
Figure 35.
I
1
0.8
1.0
Quartz
Plot of grain sizev s . metaquartz/common quartz
for 27 Baca sandstones, showing tendency',.
towards increasing abundancesof metaquartz
with increasing grain size.
120
study
of
quartz
from
sediments
with
known s o u r c a
er e a s ,
s t a t e s t h a tm o n o c r y s t a l l i n e ,s t r o n g l yu n d u l o s e
Blatt(1967)
and
quartzgrains
p o l y c r y s t a l l i n eg r a i n s
composed of l e s s
t h a nf i v ec r y s t a u
l n i t sa r en o u
t s e f u il nd i s t i n g u i s h i n g
between p l u t o n i c andmetamorphic
study,
however,
degree .of
and
Basu
others
(1975)
found
that
both
polycrystallinity
and
type
of
extinction w a s
u s e f u il nd i s c r i m i n a t i n gs o u r c er o c kt y p e s .
of
metaquartzite
pebbles
The
i n t h es t u d ya r e a
large
portion
otfh e
quartz
in
the
probably
e
derived
a similar
s o u r c ea r e a s .I n
implies t h a t a
sandstones
Baca
from
a
abundance
was
sim
l iitlhaor l o g y .
The
m e t a m o r p h i c / t o t a lq u a r t zr a t i oa p p e a r st oi n c r e a s ei nt h e
b a s a lp o r t i o n
of t h es e c t i o n( F i g .3 6 ) .
Feldspar(6-308,average
14% of framework g r a i n s )
are
Three
types
of
feldspars
sandstones
itnhset u dayr e a .
present
These
are,
in
the
Baca
ionr d e r
of
decreasing
abundance,
orthoclase,
microcline,
and
p l a g i o c lA
a slet e. r a t y
iiop
nne
c slvuadceu o l i z a t i o n ,
s e r i c i t i z a t i o nc. a v e r n o u sd i s s o l u t i o n( F i g3
. 7),
calcitization
( F i g3. 8 )V
. acuolization
t y s e of a l t e r a t i o n
producedby
seen
in
Baca
and
i s t h e most common
feldspars,
and
may
s u r f a c ew e a t h e r i n g ,h y d r o t h e r m a la l t e r a t i o n ,o r
as i n c l u s i o n tsr a p p e d
within
thc
erystallizing
feldspar.
!
minor
be
121
Metaquartz/Total
0
.2
.4
.6
.8
quartz
1.0
__.
30
P
' 1
_
.
J
50
e
Middle
Sandstone
Unit
loo
feet
G
Lower
Red
Unit
1
,
o J-
0. meters
E
C
B
34
Sample
Number
Figure 36.
Plot of metaquartz/total. quartz ratios as
function of stratigraphic position. Mean
grain size rangesbetween 1.6 and'2.9$1.
.
.
a
122
Figure 37.
Cavernous dissolution in an orthoclase grain
from a fluvial sandstone (sample 48). Secondary porosity within the grain appears blue,
due to impregnation of sample with colored
m
.
epoxy. Plane light, field widtht.0.75 m
L
124
is
Sericitization
most
of hydrothermal
o f t e nt h ep r o d u c t
it may a l s o formunder
alteration,although
weathering
conditions
(Folk,
1974, p.
arid or semiarid
Calcitization
84).
of f e l d s p a r by c a l c i t e i n an
takes place through replacement
a l k a l i n ee n v i r o n m e n t .D i s s o l u t i o np o r o s i t yw i t h i nf e l d s p a r s
can form i n an a c i d i c environment i n s o i l s (Begle,1978)or
in
t hseu b s u r f a c eo,r
feldspars
(Jonas
ranges
impossible.
decalcitization
making
recognition
Degreeof
altered, followed
of
alteration
tfheel d s ptayrp e
a l t e r a t i o n i s , i n p a r t , a f u n c t i o n of
is
i s c o n s i s t e n tw i t h
r e l a t i v es t a b i l i t i e s
of
g e n e r a l ltyh e
most
most r e p o r t s on
the
t h e s e three f e l d s p a rt y p e s( F o l k ,
84).
in
A l t e r a t i o n ~0.ff e l d s p a r s cantakeplace
d i f f e r es n
etting
( as):
by
processes i n t hseo u r caer e a ;
zones;
of
by o r t h o c l a s e and microcline, which i s t h e
l e a s ta l t e r e d .T h i s
~~
of c a l c i t i z e d
u n a l t e r( e
f rde x
tsoh
t r)e m a
e l tye r e d ,
feldspar
composition.
Plagioclase
1974, p.
Extent
1977).
and
McBride,
from
occasionally
by
or
deuteric
(b)
in
several
hydrothermal
s o u r c e - a r esao i l
( c ) i n s o i l zones i n t h ed e p o s i t i o n a lb a s i n ;
and ( e ) i n
modern
l i n e of evidence s u g g e s t st h a tw
, ith
the
r e a c t i o nw i t hg r o u n d w a t e r sa f t e rb u r i a l ;
Soil
zones.
One
exception o f minor v a c u o l i z a t i o n
within
probablyoccurred
tahlet e r a t i o n
of
( d ) by
Baca
sericitization
which
the s o u r c ea r e a ,t h em a j o r i t y
of
and
f e l d s p taorpo
slk
apcoes t -
125
depositionally,
due
i nt toe r a c t w
i oginrt h
oundwaters
migratingthroughpermeablesandstones.
which
The t h i nS a n d s t o n e s
r e p r e s e n tf r o n t a l - s p l a yd e p o s i t si nt h el o w e rp o r t i o n
exhibit
of d e l t a iccy c l e s
tightly
textures
noncompacted
cemented w i t hf i n e - g r a i n e ds p a r r yc a l c i t e ,
and
are
and t h u s
indicatecementationwithinthe.,lacustrineenvironmentor
f o l l o w i nvge rsyh a l l o b
wu r i a( sl edei a g e n e s isse c t i o n ) ;
us to
and completecementationenables
Thisveryearly
view
as
other components of thesesandstones
t h ef e l d s p a r sa n d
they
appeared
when
they
p e r m e a b i l i t yi n h e r e n t
were
from
deposited
t h;vee r y
t h et i g h t l y
low
cemented n a t u r e of
thesesandstonesprotectedthefeldspars
from t h e e f f e c t s of
later-diagenetic
groundwaters.
Feldspars
within
these
s a n d s t o n e sa r eg e n e r a l l yf r e s h ,
minor
b u t sometimes e x h i b i t
v a c u o l i z a t i o na n d / o rs e r i c i t i z a t i o n .
feldspars i n
explained
the
by
would
sandstones
can
be
and d e p o s i t i o ni na n
climate and/or
rapiderosion
p r o t e c ft e l d s p a r s
weathering
processes
mittent
Baca
e r o s i o n ,t r a n s p o r t a t i o n ,
a r i d or
semiarid
which
early-cemented
The abundance of f r e s h
and
burial
from
prolonged
exposure
(Folk, 1 9 7 4 ) .
n a t u roterf a n s p o irm
t plied,
However,
by
~
to
t hi n
eterthe
possibly
ephemeral Baca braided streams suggests lohg residence
for
times
sedimentswithinthenear-surfacefluvialenvironment,
and t h ufsa v o rtsh p
ereservation
climate.
of
f e l d s p a rbs y
a
dry
126
On t h o
e t h ehr a n dt,h sea n d s t o n e s
n o n - l a c u s t r i n ep o r t i o n s
of d e l t a i c c y c l e s
b r a i d e da l l u v i a l - p l a i nf a c i e s
which
r e s u l tiend
of
upper,
the
and of t h e d i s t a l
were
incompletely
cemented,
moderate
htiopgohr o s i t i e s
and
p e r m e a b i l i t i e sa n d t, h u s f, a v o r e dt h eu t i l i z a t i o no ft h e s e
sandstones
as
a q u i f e r sF. e l d s p a rw
s i t h i tnh e spe e r m e a b l e
sandstonesarealmostinvariably
more a l t e r e d t h a n t h o s e i n
tphree v i o u sdl eys c r i bteidg h t l y
Degree
of
cemented
alteratio
r ann g e s
from
sligh
t ot
sandstones.
extreme.
A l t e r a t i toynpiensc l uvdaec u o l i z a t i osne,r i c i t i z a t i o n ,
calcitization,
e
dissolution,
cavernous
and
and
dissolution.
t o feldspars
f l u v i asla n d s t o n e s
in
the
Cavernous
i s almost
which
produces
secondary
porosity,
e n t i r e l yr e s t r i c t e d
deltaic
-
permeable
upper-
(see d i a g e n e s isse c t i o n ) .
Feldspars
exhibiting
secondary
porosity
occur
it n
he
majority of t h e s e s a n d s t o n e s .
Feldsparsobserved
range
i n t h i ns e c t i o na r ee l o n g a t et o
roundness
subequant,
and
subrounded.
F e l d s p a rc o n t e n ti n c r e a s e s
portion
the
of
Baca
in
(Fig.
39).
a n g u tl o
ar
upwards i n t h e b a s a l
s t r a t i g r a p h isce c t i o n ,
r e l a t i v e l yc o n s t a n tt h r o u g h o u tt h er e m a i n d e r
from
and
remains
of t h e s e c t i o n
127
.Percent of Framework Grains
-
0
10 20
30
40 50
30
P
J
Middle
'Sandstone
Unit
G
-
Lower
Red
Unit
E
C
B
34
Sample
Number
Figure' 39.
.
.
Plot of feldspar abundance as a function of
stratigraphic position. Mean grain size of
samples ranges between 1.6 and 2.9+..
128
Orthoclase (4-238,
74% of
average
average 11%of framework
Orthoclase i s t h e most
t o t a l .feldspar).
abundant feldspar
i n the Baca sandstones whichwereexamined
inthinsection.
A l l untwinnedfeldspars
microcline
may 'havebeenincluded
i t s a v a i l a b i l i t y ,o r t h o c l a s e
terrigenoussandstones,
.general.ly more
Granites
and
w e r e c l a s s i f i e d as
small amounts of untwinned p l a g i o c l a s e
o r t h o c l a s e ,t h u s
I
grains;
and
Due t o
i nt h i sc a t e g o r y .
i s t h e most common f e l d s p a r
despite t h e f a c t t h a t m i c r o c l i n e
in
is
r e s i s t aatnlot e r a t i o
(F
n o l1k9, 7 4 ) .
gneisses
are
the
for
primary
source
rocks
orthoclase.
.
Microcline(0-lo%,average
average
3 % of
framework
21% of t o t a lf e l d s p a r ) .M i c r o c l i n e
a l l except one
of
Despite
.
the
w a s p r e s e n ti n
s a n d s t o n teh i n
sections
examined.
i t s r e l a t i v e l yh i g hs t a b i l i t y ,m i c r o c l i n e
l e s s abundantthanorthoclase,even
sandstones.Microcline
grains;
i nh i g h l y
i s dominantlyderived
i s always
altered
Baca
from p l u t o n i c ,
pegmatite, and g n e i s s i cs o u r c er o c k s( F o l k ,1 9 7 4 ) .
Plagioclase.(O-3%,average
average
5% of
t o t a l feldspar).
about half o f ~ t h e' s a n d s t o n e s
e
graphically.
It
1%of
framework^ g r a i n s ;
P l a g i o c l a s e i s p r e s e n ti n
which
were
examined
i s e v e n l yd i s t r i b u t e dt h r o u g h o u t
s t r a t i g r a p h i cs e c t i o n ,
which suggests t h a t
petrothe B a c a
t h ep l a g i o c l a s e
*
129
was
not
derived
of
from
contemporaneous,
sporadic
supply
by Eocene volcanic centers
a i r b o r n ev o l c a n i ce j e c t a
it was probablyderived
south.Instead,
in
and/or
plutonic
rocks
exposed
from oldervolcanic
t hseo u r caer e a .
fragments throughout the
The
of volcanic
rock
widespread
occurrence
of
minor
amounts
~.
t ot h e ,
Baca s t r a t i g r a p h i c s e c t i o n s u g g e s t s
a largely volcanic source for the plagioclase.
Rock Fragments (8-29%, average 20% offramework
Rock
e
(in
include
chert,
fragments
present
the
Baca
sandstones
orcier
decreasing
of
abundance)
metamorphic,
mudstone,
siltstone
in
grains)
granite/gneiss,
volcanic,
carbonate,
and sandstonerockfragments.
Most rock-fragment
i n abundance
with
v a r i e t i e sd e c r e a s e
decreasing
sandstone
grain size.
-
Metamorphic Rock Fragments (2-20%,
framework
grains).
Two
fragments
were
observed.
average
major
types
of
The
10% of
metamorphic
rock
first,
and
most
common,
c o n s i s t s of strongly undulose, often composite, quartz
which
,
contains numerous a l i g n em
d u s c o v i tcer y s t a l s
Fragments
I
of
th
t yi sp e
Precambrian
micaceous
e
The
major
othe
t yr p e
were
metaquartiites
(Fig.
probably
derived
in
40).
from
t h seo u r c ae r e a .
metamorphic
of
rock
fragment
is
130
Figure 40.
Quartzose metamorphic rock fragment. Note
abundant inclusions of muscovite. Sample 48,
crossed nicols, field width=0.75
nun.
131
composed aligned
of
c r y s t a il n
s terspersed
illite
and
with
small
fine-grained
muscovite
quartz(Fig.41).Theserockfragmentsoften
of
d u c t i l ed e f o r m a t i o nb ya d j a c e n t
compaction.
Fragments
of
this
show evidence
framework g r a i n s dur'ing
type
were
derived
from'
low-rank,
metamorphic
rocks,
p h y l l i t eA
s .r g i l l a c e o u s
metamorphic
rock
fragments
distinguished
from
silt-sized
of
amounts
such
as
argillites
and
were
mudstone
rock
fragments
by
the
more
of
coarsely crystalline and generally better-oriented nature
t h e i r a r g i l l a c e o u s and micaceous components,and
Of
r ecdo l o r a t i o n
that
is
by t h e l a c k
c h a r a c t e r i s t iocf
most
Baca
mudstone fragments.
Metamorphic rockfragments
inthestudyarea
t o a lesser e x t e n t , from
However,.due t o t h ee f f e c t s
t r a n s p o r to nt h es o f t ,
thecontribution
Baca
were derivedpredominantly
metaquartzitesand,
argillites.
from the
frommicaceous
phyllites
and
of abrasionduring
low-rankmetamorphicrockfragments,
of d e t r i t u s by a r g i l l i t e s and p h y l l i t e s t o
the Baca-Eagar b a s i n w a s probably much l a r g e r t h a n
assumed
Formation
byexamination
would
be
of t h e sandstones i n t h e study area.
The abundanceofmetamoxphic
rock fragments increases
upward
through t h e b a s a l p o r t i o n of t h e Baca s t r a t i g r a p h i c s e c t i o n ,
and remains r e l a t i v e l y c o n s t a n t t h r o u g h o u t
t h es e c t i o n( F i g .
42).
the remainder
of
132
Figure 41.
Argillaceous metamorphic rock' fragment which
has been ductilely deformed by adjacent grains
during compaction. Sample C, cros'sed nicols,
field width=0.75
m
m
.
133
.Percent of Framework Grains
-
0
10
20
30
40
50
30
P’
Middle
Sandstone
Unit
loo
G
Lower
Red
Unit
feet
o
1
-I-o meters
E
C
B
34
Sample
Number
,Figure 42.
Plot of.abundance of metamorphic rock fragments a s ’ a Tunetion of stratigraphic position.
Mean grain size ranges between 1.6 and 2.9+..:
134
(1-17%,
Chert
of
average
4%
framework
grains).
i s a r e l a t i v e l ym i n o rc o n s t i t u e n t
Chert.(Fig.43)
but
Baca s a n d s t o n e si nt h es t u d ya r e a ,
e v e r yt h i ns e c t i o nt h a t
it
was examined.
m i c r o c r y s t a l l i n eq u a r t za v e r a g i n g
was
of t h e
p r e s e n ti n
of
Grainsconsisting
less t h a n
20
microns
in
d i a m e tw
e recr e
lassifie
ca d
h
s e rfti:n ecl y
rystalline'
quartz
grains
than
20
appears
whose a v e r a g c
e r y s t adl i a m e t e r
be
crystalline
a
gradation
metamorphic
which may i n d i c a t e t h a t
e
derived
as metamorphicquartz.There
micronswerecounted
to
from
o r i g i n( F o l k ,
between
q u a r t zi n
chert
and
t h e sandstones s t u d i e d ,
meta-cherts.
Chert
L974), b u t may beprimary(e.g.derived
reworkedfrom
t r a c e amounts.Approximately
whi-ch
is
from
an older sandstone.
Chertabundancedecreases
Baca
h a l fo f
t h i s chalcedony i s
(Folk andPittman,
upwards i n the
s t r a t i g r a p h isce c t i oinn
remains r e l a t i v e l yc o n s t a n tt h r o u g h o u t
s e c t i o(nF i g4.4 ) .
sandstones
i n d i c a t ifovofer m a t iaionnn
alkaline,sulfate-richenvironment
the
was
i s always of sedimentary
Detrital chalcedony w a s also p r e s e n t i n t h e Baca
length-slow,
finely
some of t h e metamorphicquartz
a s i l i c i f i e d limestone)or
in
greater
was
basal
the
1971).
portion
study
of
area, and
the remainderof
the
t
135
Figure 4 3 .
Chert grain. Sample A, crossed nicols, field
width=0.75 m
m.
136
.Percent of Framework Grains
0
-
10 20
8
I
30
40
I
I
50
I
30
P
J
Middle'
Sandstone
Unit
*O0
1
50
1
loo'
G
Lower
Red
Unit
E
C
B
34
Sample
Number
Figure 4 4 .
Plot of chert abundance as a function
of
stratigraphic position. Mean.grain size ranges
between 1.6 and 2.9$.
137
-
Granite and Gneiss Rock Fragments (0-7%, average
of
framework
rock
g r a i n sT) .h e s e
fragments
consist
of
of f e l d s p a r and quartz.Feldspartypes
varyingproportions
includ
oe
rthoclase
and
m i c r o c l i nQ
e .u a r t z
s t r a i g h t os t r o n g l yu n d u l o s ee x t i n c t i o n .
the
1%
may
The
exhibit
majority
of
granite/gneissrockfragmentsconsistpredominantly
one mineral,suchas
orthoclase.
a g r a i nc o n t a i n i n g
and
a
of
smaller
one
of
a l a r g ec r y s t a l
quartz.
of
Types
and
occurrence of a l t e r a t i o n w i t h i n c o m p n e n t f e l d s p a r c r y s t a l s
a re x a c t l y
the
same
atsh o sdee s c r i b ep
dr e v i o u s lfyo r
feldspar grains.
The
relative
importance
of
contributions
is difficultto
g r a n i t i cv e r s u sg n e i s s i cs o u r c e s
determine.
The occurrence of minor amounts of g r a n i t ep e b b l e s
Baca
imply
t h a ta tl e a s t
a
the
rock
g r a n i t isco u r c eG. r a n i t e /
gneiss
rock
fragments
and
the
remainder
in
in
some of t h eg r a n i t e / g n e i s s
fragments were d e r i v e d from
fragmentswhich
from
of
the
rock
w i l l besubsequentlydiscussedarepresent
s u c hs m a l q
l u a n t i t i e st h a t
I do n o t f e e l it would be
meaningful t o make any s t a t e m e n t s c o n c e r n i n g v e r t i c a l
trends
i n t h e i r abundance.
Volcanic
framework
Rock
Fragments
(0-6%,
average
1% of
grains).
Volcanic
rock
fragments
are
widespread, b u t minor,component
a
of t h e Baca
sandstones
in
138
thestudyarea.
They occurred i n aboutone-halfofthethin
examined.
sections
fragments
range
Grains
counted
volcanic
as rock
appearance from d a r ka, p h a n i t i cg r a i n s
in
c o n t a i n i nlga t h - s h a p epdl a g i o c l a scer y s t a l s
grains
which
a rs ei m i l a
t or ,
chert-like
and
(see
d i s t i n g u i s h from, c h e r t
rock
fragments
Folk,
were
s i l i c i fvi eodl c arnoi c k s
(X.
comhun.),
however,
45)
(Fig.
to
to
o f t edni f f i c u l t
p.
1974,'
81).
probably
derived
L.
t hcel a s s i f i c a t i o n
of
from
oral
1979,
Folk,
The
many
of t h e s e
g r a i n s i s equivocal.
The presence
of
only
minor
amounts
of
volcanic-
derived d e t r i t u s i n t h e Baca sediments i n t h e s t u d y a r e a h a s
some importantimplicationsconcerningthe
t h e Baca-Eagar basin ( C .
southeastern marginof
this
portionof
b a s i n was t h es i t e
the
volcanism and plutonism.
of
sediments i n t h ee a s t e r np a r t
of
Morenci u p l i f t ;
the
Chapin,
a
of widespread
The f a c tt h a to n l ys m a l l
were
v o l c a nm
i ca t e r i a l
t heex i s t e n c e
E.
of
D u r i n g t h e Laramide, t h ea r e aa d j a c e n t
1980, o r a l commun.).
to
geometry
amounts
i n c o r p o r a t ei n
dtth
oe
Baca
of t h eo u t c r o pb e l ti m p l i e s
d r a i n a gdei v i d(eh e r e i n
see t e c t o n i c framework
termed t h e
section)
basinward
of t h e Laramide volcanic centers i n southwestern New Mexico.
The non-peaked s t r a t i g r a p h i c d i s t r i b u t i o n of
fragments
in
the
Baca
volcanicrock
were
s u g g e s t st h a t h e s ef r a g m e n t s
derived from older
volcanic
rocks
(Precambrian?)
in
the
139
f
Figure 45.
Volcanic rock fragment showing lath-like
plagioclase crystals in dark, aphanitic groundmass. Sample 45, crossed nicols, field width
=0.75
mm.
140
source
a r e aa, n d
n obt y
sporadic
airborne
supply
to
the
b a s i n by Eocene v o l c a n i cc e n t e r st o
Blatt
(1971)
show
.-
abundance,
which
d e t r i t u si n
miles of braided-stream
t h aatb r a s i odnu r i ntgr a n s p o r t
the
nearly
complete
lack
of
volcanic
the e a s t e r np o r t i o n
of
small
percentage
of
basin.
the
Thus,
volcanic
rock
fragments
in
sandstones i n t h e study area suggests
were
their
implies
cannot
account
for
and
rock
s i g n i f i c ar endt u c t iionn
a
I
Cameron
t hf a
e tl s i c - s i l i cviocl c a n i c
fragments can endure several hundred
t r a n s pw
o ri t h o u t
the s o u t h .
the Baca
that
a r e l a t i v e l y minor l i t h o l o g y i n t h e
the
volcanicrocks
source a r e a d u r i n g
Laramide time.
Mudstone
framework
Rock
grains).
Fragments
(due
to
hematite
s i g n i f i c a n t amounts
of
average
2%
Mudstone
rock
fragments
occur
one-half of t h et h i ns e c t i o n s
red
(0-5%,
i na b o u t
are
usually
may
contain
examined. . They
pigmentation)
and
q u a r t z and f e l d s p a r silt.
When
.masked by red c o l o r a t i o n , .the component c l a y s g e n e r a l l y
yellowishbirefringenceandanindexhigherthan
which
is
characteristic
Some mudstone
rock
fragments
of
of
not
show
balsam,
illite
(Folk, 1974, p.
exhibit
evidence
of
ductile
squashing by adjacent grains during compaction.
91).
141
The r e dc o l o r a t i o n
of the
from
i n d i c a t eds e r i v a t i o n
mudstone
rock
fragments
such as the
a . redbed
source,
Permian A b 0 Formation o r t h e Triassic ChinleFormation,
penecontemporaneous
reworking
of
Baca mudstones.
e a s i l y abraded n a t u r e
fragments
suggests
short
of
these
d i s t a n c eo
stfr a n s p o r t
land,
or
The s o f t ,
t h u s , f a v o rds e r i v a t i o n
from
i n t r a f o r m a t i o n a ls o u r c e s .
Sandstone and S i l t s t o n e
framework
grains).
presen
it n
rt a c e
.
one-fourth
Fragments
These
rock
fragments
tthhseienc t i o n s
observed
examined.
detrital
in
grains
of
betweenbothtypes
of theserockfragments.Sandstone
amounts
of
about
exists
and
but
rock
fragments
are
highly
quartzose
contain
minor
o r i g i n adl e t r i t agl r a i nas r e
Sandstone
sometimes
vacuolized,
distinguishing
and
siltstone
may
orthoclase.
Grains
within
these
l uartz;
fragments are t i g h t l y cemented w i t h s y n t a x i a q
facilitates
of
complete
A
g r a d a t i oisnni z e
siltstone
component
(0-2%
agr e n e r a l l y
were
amounts
and
of
Rock
between
grains
the
which
and
cement.
rock
fragments
were
derived
o l d esre d i m e n t a rryo c kistnhseo u r caer e a .
quartzose,
silica-cemented
nature
from
The
highly
of these
rock
fragments
precludes t h e p o s s i b i l i t y of a n i n t r a f o r m a t i o n a l
source.
142
Carbonate
Rock
Fragments
framework g r a i n s ) .C a r b o n a t e
about
one-third
They
(0-8%,
average
1% of
in
rockfragmentswere'present
of t h se a n d s t o n teh i n
sections
o f t e na r es t a i n e dr e d
examined.
by hematite and aredominantly
composed of w e l l - s o r t e d s, u b e q u a n ts p a r r yc a l c i t ec r y s t a l s
10-15 microns i n diameter.;
Carbonate
rock
averaging
about
f r a g m e n t s ' a r e more abundant i n lower-deltasandstonesthan
i n a d d i t i o nt ot h ef a c tt h a tt h ec a l c i t e
elsewhere.This,
i n these
fragments
closely
resembles
the
early-diagenetic
l a c u s t r icnaer b o n a t e
s u g g e s t tsh a t
many of
the
carbonate
rock
fragments
were
penecontemporaneously
derived
basin, and t h e r e f o r e a r e
(Folk,
p.
1974,
limestonepebbles
carbonate
rock
( sdeiea g e n e ssiesc t i o n ) ,
cements
from
w i t h itnhlea c u s t r i n e
more properly termed
"intraclasts"
The presence of probable
Paleozoic
160).
i n t h e Baca, however', i m p l i e st h a tt h e s e
fragments were, i n p a r t ,d e r i v e d
from o l d e r
limestones exposed i n t h e s o u r c e a r e a .
The presence of t r a c e amounts
of
was
noted
averageabout
and
in
several
of
o o l i t e s( F i g .
t h teh i sne c t i o n s .
0.3 -mm i n diameter.
46)
The o o l i t e s
They areusuallycomplete
show little o r no e f f e c t s of abrasion d u r i n g t r a n s p o r t ,
which i n d i c a t e st h a t
t h e o o l i t e s were l o c a l l yd e r i v e e .
s p o r a d i co c c u r r e n c eo fo o l i t e s
sandstones implies that the oolites
i n b o t hd e l t a i c
The
and f l u v i a l
were not formed i n s i t u ,
but were probably derived intraformationally
and t r a n s p o r t e d
143
Figure 46.
Well-developed oolite in an upper-delta sandstone. Note both concentric and radial
structures. Sample 73, plane light, field
width=0.75 m
m
.
144
a shod
r ti s t a n cper i otdo
r e p o s i t i o nO. o l i t e s
current-
i n modern l a k e ss, u c ha st h eG r e aS
t alt
Utah
(Sandberg,
(Swirydczuk
and
can
and
orwave-agitated,carbonate-richenvironments,
have
been
noted
Lake,
in
form
be
1 9 7 5 ) , ana i n a n c i e n lt a k ed e p o s i t s
The composition
of
others, 1979).
i n i t i a l l eyi t h ecra l c i t e
oolites
a r a g o n i t e , however,
or
a r a g o n i t ei n v e r t sr e l a t i v e l yr a p i d l yt oc a l c i t eA
. ssereto
and
Folk
(1976)
s t a t et h a t
N o square-ended
i n d i c a t e an i n i t i a la r a g o n i t i cc o m p o s i t i o n .
rays
seen i n t h e few o o l i t e s whichwere
were
quantities
of
oolites
a v a i l a b l ef o r
d u e t o the lack of s u f f i c i e n t
petrographicexamination,but,
f e e lt h a t
i n pisolites
square-ended
rays
which
could be inspected, I donot
an i n i t i a al r a g o n i t i cc o m p o s i t i o nc a n
be
ruled
in
trace
out.
Heavy Minerals ( t r a c e )
Heavy
amounts
minerals
(tl$)
were
w i t h itnh e
although abundances
of
g e n e r a l lpyr e s e n t
Baca
as
much
s a n d s t o nteh isne c t i o n s ,
asse v e r aple r c e n t
were
piln
a c ePr se .t r o g r a p h i c
occasionally , . ~o b s e r vwe idt h
examination of s i x heavy-mineralgrain
presence
of
abundance):
the
mounts
f o l l o w i n gs p e c i e s( i no r d e r
magnetite/ilmenite/specular
e nzei r, c ogna,r n a
ep
t ,a t i b
t ei ,o t i t e ,
r e v e a l e dt h e
of decreasing
hematite,
leucoxand
muscovite.
145
Magnetite,
ilmenite,
and
specular
hematite
differentiated.
were
in
The m a j o r i t y of t h e heavy mineralsrange
s i z e from 0.1 to 0 . 2
mm.
The r e l a t i v e
abundance
leucoxene)appears
of
several
of
the
heavy
i l m e n i t e , specularhematite,
mineralspecies(magnetite,
t o be a f u n c t i o n of thedegree
and
and
type
of a l t e r a t i o n of t h e i rh o s ts a n d s t o n e .M a g n e t i t e ,
ilmenite,
and s p e c u l a rh e m a t i t ea r et h e
of
mostabundanttypes
i n t h er e l a t i v e l yl i t t l e - a l t e r e d ,
mineralspresent
47).
m i n e r aflr a c t i o(nF i g .
Baca sandstones, which show
heavy
red Baca
90 p e r c e n t of the heavy
sandstones, usually comprising about
e
not
However, t h e yellow t o gray
evidence
for
the
passage
of
(see d i a g e n e s i s e c t i o n )c, o n t a i n
negative-Eh
groundwaters
little or none of these m i n e r a l s I. n s t e a d t, h ey e l l o w
graysandstonescontainabundantleucoxene(which
is present
i n t h ree d
s a n d s t o n e s()F i g .
481,
o n l y i n minor
amounts
which
was
ilmenite.
sample
presumablyproduced
A heavy-mineral
(54)
showed
removal
s u i t e from
one
yellow-sandstone
of
magnetite/
and leucoxene.
This
incomplete
of magnetite/ilmenite/specular h e m a t i t ei n d i c a t e s
l e s sdeer g r e e
sandstone,
of
or
which
by
of
negative-E
a lht e r a t i o n
probablytookplace
of a s m a l l e r volume
rock,
of
a sa na l t e r a t i o np r o d u c t
subequal
proportions
ilmenite/specular
hematite
e
to
of
the
interaction
with
host
by e i t h e rt h ep a s s a g e
reducing
groundwater
through
the
more
mildly
reducing
a
146
Figure 47.
Typical heavy-mineral grain mount from a red
Baca sandstone (sample 48). Note dominance
of magnetite/ilmenite/specular hematite.
White grains are leucoxene. Field width=0.8
mm.
147
Figure 48.
Typical hea'vy-mineral suite from' a yellow Baca
sandstone (sample ,561, showing dominance of
limonite-stained leucoxene 'grains. Note subhedral zircon grain. Field width=O,.%
mm.
148
The common o c c u r r e n c e o f
groundwaters.
and
i l m e n i t ei n
absence
of
red
these
with,
intercalated
non-red
was
redbeds
noted
by
a
d i s s o l u t i oi n
the heavy-mineral
summary,
dominated
by
w i t h i no,r
Miller and Folk
i s due t o t h e i r
non-red portionsofredbedsequences
removal
by
is
areas
l a c k of magnetite and ilmenite
(1955), who conclude t h a t t h e
in the
the near or complete
sediments
and
m i n e r a lisn
abundant
magnetite
reducing
environment.
In
s u i t e of t h e red Baca sandstones
magnetite/ilmenite/specular
hematite,
t h a t i n the yellow t o graysandstonesaregenerally
whereas
dominatedbyleucoxene.
Compared
with
the
volumetric
importance
of
minor.Zircon
mounts.
It
was present in all
exhibits
in
r e l i eufs, u a l l y
and
ranges
from
well
typ
i necs l u d e
edges,
but
a
clear
to
rounded
to
biotite
of b o t h
varietieu
s sually
muscovite.
Flakes
abraded
of the heavy-mineralgrain
extreme
Mica
shape.
is
remaining
heavy
minerals
the
slightly
pinkish
color,
euhedral
above-described
minerals,
the
show
and
ragged,
f e w of t h e b i o t i t e g r a i n se x h i b i t e d
hexagonal o u t l i n e( sF i g
4 .9E
) .u h e d r a
b li o t i t e
is
most
commonly
p.
88).
derived
A p a t i t eg r a i n s
range
from
from volcanic
rocks
(Folk,
1974,
are usually clear, e x h i b i t
subhedral
clear t o
pink
in
color,
conchoidal
.fractures,
and
t eou h e d r ailn
shape.
commonly
are
low
exhibit
most
relief,
and
Garnets are
well-developed
o f t eann h e d rtaol
14 9
Figure 49.
Hexagonal biotite observed in a heavy-mineral
grain mount from sample 48. Width of field
=0.75
m
m
.
150
subhedral i n shape.
Garnets
from
one
of
exhibit crystallographically
cemented sandstonesamples(51)
controlled,
etched
surfaces.
Both
a u t h i g e n ik
ca o l i n i t e
and
t hkea o l i n i t e -
precipitation
the
dissolution
p l a c e i n an acidic environment, as
of
of g a r n etta k e
w i l l be f u r t h e r d i s c u s s e d
Ln the diagenesis section.
Mudstone Petrology
Baca mudstones i n the s t u d ya r e aa r eg e n e r a l l y
i n color,devoid
of sedimentarystructuresexceptoccasional
poorlydevelopedburrows,and
amounts
red
of s i l t .
lacustrine
facies
commonly
containappreciable
i n t h eb a s i n a l
Mudstonesdominantlyoccur
and
in
t h 'el o w epr r o d e l t p
a ortion
of
i n the
f i n e - g r a i n elda c u s t r i ndee l t a st h
; e iorc c u r r e n c e
d i s t a lb r a i d e da l l u v i a lp l a i nf a c i e s
and t h e
of
and
lacustrine
discontinuous
mudstones,
deltas
mud-drape
is
rare
upperportion
limited
d e p o s i tPsr.o d e l t a
tthoi n ,
and
basinal
i n t h e lowermost p o r t i o n of t h e
e x c e p tf o rt h o s e
highly
c a l c a r e o u sC
. alcite
upper red u n i t , are g e n e r a l l y
content,asdeterminedbyweighingcrushedsamplesbefore
and a f t e ra c i d i z a t i o nw i t hc o l d ,
ranges
between
10
and
15
dilute
percent
hydrochloricacid,
by
weight,
with
the
exception of t h e b a s a l mudstone i n t h e upper red u n i t , which
contains
about
two
p e r c e ncta l c i t e .
The t h i n mudstones
151
which
represent
The
careous.
mud-drape
are
deposits
usually
noncal-
c
r eodl o r a t i toynp, i c a l
most
of
Baca
will
mudstones, was probablyproduceddiagenetically,as
be
discussed i n a l a t e r s e c t i o n .
Six thin sections
w e r e examined.
area
30
p e r c e nqtu) a r t z
mudstone
( a s much a s
Most dontainedappreciable
and
feldspar
silt.
lacustrine
All
degrees, a
t h isne c t i o ne sx h i b i t e td
vo,a r y i n g
churnedand
d i s r u p t e d t e x t u r e (Fig.
producedby
bioturbation.
' ,
5 0 ) which was
mudstones
lake-bottom muds wereoxygenated,
thatthe
polymictic
regime
for
.
.
the
C a r b o n a t ew
s i t h ilna c u s t r i n e
homogeneously d i s t r i b u t e ds, m a l l
of
crystals
probably
This e x p l a i n st h eg e n e r a ll a c k
sedimentary s t r u c t u r e s i n t h e Baca
e
t hs e
tudy
of Baca mudstonesfrom
Baca
suggests
and
which supports a
system.
lacustrine
mudstones
of
usually
occur
as
micron),
subequant
(10-15
is
c a l c i st ep aT
r .h ci sa l c i t e
similar i n
appearance t o t h a t observed i nt h el o o s e l y
packed,
cemented
a rien t e r c a l a t e d
.
frontal-splay
sandstones
with t h e - l a c u s t r i n e mudstones.
early
in
t hde i a g e n e t ihc i s t o r y
which
These
cements
of
formed
the
containedlargevoidspaces(as
diameter)which
diagenesis
mode of occurrence of c a l c i t e was observed
i n one lacustrine-mudstone
thin
section
(sample
sample
very
the Baca l a c u s t r i n e
s e d i m e n t s , and w i l l be f u r t h e r discussed i n
section.Another
tightly
8).
This
much a s 1 . 5 mm i n
were s u b s e q u e n t l y f i l l e d w i t h l a r g e
crystals
152
Fiwre 50.
Churned, d i s r u p t e dt e x t u r et y p i c a l
of Baca
lacustrine mudstones,. which was probably
produced by i n t e n s eb i o t u r b a t i o n .
Sample
F,crossednicols,field
width=3.0
nun.
153
of sparry c a l c i t e ( F i g .5 1 ) .
f i l l e dw i t h
Many of thesevoidspacesare
a s i n g l e ,l a r g ec r y s t a l
a rree m i n i s c e n t
The
t o compaction) of t h e
cementation m u s t haveoccurred
environment
have
been
or
i n t h el a c u s t r i n e
upon v e r ys h a l l o wb u r i a l .
reported
lacustrine
i n limestones
p r e s e n co
le
af r gsep, a r - f i l l evdo i d s
impliesveryearlycementation(prior
mudstone:
These f e a t u r e s
" b i r d ' s - e yset r u c t u r e s "
of
(Folk,
1959).
of s p a r .
by
Van
mudstones
of
Houten
(1962)
the
New
Formation
of
west-central
Similar features .
Upper
Jersey
itnhree d
Triassic
Lockatong.
and
adjacent
Penn-
sylvania.
When not maskedby
Baca
mudstones
from
th
s teu d y
y e l l o w i sbhi r e f r i n g e n c e
balsam,
91).
six
which
is
hematitestain,theclaysinthe
g e n e r a lel y
xhibit
have
an
index
greater
than
and
c h a r a c t e r i s t i c of i l l i t e (Folk,
1974,
X-ray d i f f r a c t i o nd a t af o r
Baca
area
mudstonesamples
w i t h ' minor
amounts
of
t h e c l a y - s i z ef r a c t i o n
Similar
compositions
for
Baca
and
of
of i l l i t e
i n d i c a t e st h ep r e s e n c e
montmorillonite
p.
kaolinite.
c l atiy
G
hnsea l l i n a s
Mountains area havebeenreportedbyJohnson(1978,p.99).
that portion of
ArgillaceousPrecambrianrocksexposedin
t h e S i e r r a - S a n d iu
ap l i f t
Mountains
(Sumner,
now
1980)
and
c o n t r i b u t o r of i l l i t e t o t h e
comprised
were
by
the
probably
Baca l a c u s t r i n e system
Bear-Gallinas
Mountains
vicinity.
See
Johnson
(1978)
Magdalena
a
major
i nt h e
for
154
Figure 51.
Large., spar-filled void spaces in a sandy
lacustrine mudstone (sample 8 1 , which are
indicative of very early, pre-compactional
cementation. Crossed
nicols, field width=
3.0 n
un.
155
more i n f o r m a t i o nc o n c e r n i n gt h ed i s t r i b u t i o n
throughout the
\
Baca-Eagar outcrop b e l t .
of
c l a yt y p e s
PROVENANCE
The occurrence of large amounts of metamorphic- and
igneous-derived
detritus
in
both
Baca
conglomerates
(metaquartzite, granite, schist') and sandstones (metamorphic
quartz, orthoclase, microcline, metamorphic rock fragments,
granite and gneiss rock fragments) indicates that a large
portion, possiblythe
majority,of the Baca sediments
in the
study area were suppliedby a Precambrian source terrane,
although
some
was
undoubtedly
derived
from
older
sedimentary
rocks containing Precambrian detritus. The red coloration
e
of the majority of the Baca sediments and the abundance of
detrital ilmenite and magnetite in these sediments indicate
that much
of the Baca detritus was not recycled from older
sediments but must have
been derived from a metamorphic
or
igneous source (Miller and Folk, 1955). Minor occurrences
of plagioclase, volcanic
'
rock fragments, and euhedral
biotite imply that volcanic rocks made small contributions
to the Baca sediments. The presence or significant amounts
of detritus derived from sedimentary rocks
in both the Baca
conglomerates
(chert,
limestone,
sandstone,
siltstone,
mudstone) and sandstones (chert, carbonate rock fragments,
sandstone, siltstone, and mudstone rock fragments) indicate
both
extraformational
and
intraformational
sedimentary
a
. sources.
156
157
There i s much evidence t os u g g e s t h ep r o g r e s s i v e
"unroofing" of a Precambrianp1utoni.c
a r e a d u r i n g Baca time.
The
upward
and metamorphic source
in
increase
feldspar,
metamorphic
rock
fragments,
and
metamorphic/total
quartz
of
r a t i o sw i t h i nt h eb a s a 1 , p o r t i o n
section,
and
the
Baca
i n t h e abundance of
the
c o i n c i d e ndt e c r e a s e
c h e r t upward throughthe
stratigraphic
52),
strongly
can
envision
no
same i n t e r v a l( F i g .
suggests
the
diminishing
importance
of
older
sedimentary
sources
during
mechanism,
early
whether
Baca
pre-
or
time. . 1
post-depositional,
i n mineralogy of
explaintheobservedupsectionchanges
a
Baca
which can
the
s a n d s t o n e sx c e fpo
itnr c r e a s i ncgo n t r i b u t i o n s
Precambrian
.plutonic
and
metamorphic
in
counts
t e r r a n e ast h,t e
during
expense
sedimentary
of
sources,
sedimentation
basal
Baca
t shteu d
a ryeIan.t e r e s t i n g lpyo, i n t
b y , t h e w r i t e r on f i v e t h i n
made
by
sections from G.L.
M a s s i n g i l l ' s (1979) Baca Formation measured s e c t i o n n e a r t h e
Bear
Mountains
show
s i m i l aur p s e c t i o n
changes ( F i g .
in
However, due t o
thg
e r e a t evr a r i a b i l i t y
grain
size
and
t h eu t i l i z a t i o n
from t h e BearMountains
the
data
cautiously.
in
Figure
ofonly,
thin-section
f i v et h i ns e c t i o n s
s t r a t i g r a p h i cs e c t i o n ,
53
53).
shoub
lidn
eterpreted
I
f e e lt h a t
somewhat
158
Percent of Framework Grains
J
2oo
Middle
Sandstone
Unit
e
loo
feet o
G
-
1
50
1
Lo
meters
E
Lower
Red
Unit
C
B
34
-
I
I
.4
.
I
.8 1.0
Metaquartzltotal quartz
0
.2
.6
- -Feldspar
Metamorphic
Rock
Fragments
-.,------Chert
- - "MetaquartzITotal Quartz
.'
e
Figure 52. Plot of metaquartz/total quartz ratios and abundances
of feldspar, chert, and metamorphic rock fragments
within Baca sandstones aasfunction of stratigraphic
position. Samples were taken from
a section measured
by the writerin the study area. Mean grain size of
the sandstones ranges between
1.6 and 2 . 9
+.
159
Percent
0
of
10
Framework
20
30
40
Grains
50
Middle
Sandstone
Unit
50
0
meters
Lower
Red
Unit
0
.2
.4
.6
.8
1.0
Metaquartzftotal quartz
"-
""_
Feldspar
Metamorphic
Rock
Fragments
Chert
"_
MetaquartzfTotal
Quartz
Figure 53.' Plot of metaquartzftotal quartz ratios and abundances
of feldspar, chert, and metamorphic rock fragments
. ..
within Baca sandstones as
a function of stratigraphic.
position. Samples were taken from Massingill's (1979)
measured section in the Bear Mountains vicinity.
Hean grain size varies widely, therefore caution is
advised in the interpretation of this data.
DIAGENESIS
Cements
~
Four
of
types
cements
o c cw
u ri t htihne
These a r e ( i n order of
i n t h es t u d ya r e a .
sedimentary.rocks
Baca
d e c r e a s ianbgu n d a n c e
a )l c ikt a
eo
, l i n iqt u
e ,a r t z ,
and
dolomite.
C a l c i t e (0-48%, mean 18%, median.l2%of
e
Authigenic calcite
cementing
agent
in
There a r e t h r e e
b u l k rockvolume)
i s t h e most abundant and e a r l i e s t
Baca sediments i n t h es t u d ya r e a .
the
modes of occurrence of c a l c i t e i n
which i s associatedwith
s e c t i o n s :f i n e l yc r y s t a l l i n es p a r
sediments,
l a c u s t r i np
e r o d e l taan d ' b a s i n a l
t h et h i n
large,
blocky,
in
p o r e - f i l l icnagl c ci trey s t adlosm i n a n o
t lcyc u r r i n g
upper-delta
and
b r a i d eadl l u v i a l - p l a si n
a n d s t o n e.sa,n d
b u t widespread,
within
the
c a l i c h eC
. a l i c h easrsec a r c e ,
Baca.
They
occu
a
t hsr i lna,t e r a l p
l ye r s i s t e not f, t e n
n o d u l a rh o r i z o n sw i t h i nb o t hl a c u s t r i n e
sediments.
represent
stands.
0
and non-lacustrine
C a l i c hw
e si t hlianc u s t r irnoec k s
soils
which
developed
during
lake-level
A l a t e r a l lcyo n t i n u o u s
( c a l i c h i f i e rdo o t
presumably
zone
of
low
rhizoconcretions
tubes) ( F i g . .54) i s p r e s e n t i n t hbe a s a l
160
161
Fi'gure 54.
Well-developed calichified paleosol showing
numerous tube-shaped rhizoconcretions.
162
p o r t i o n of t h e lower red u n i t i n t h e e a s t e r n p o r t i o n
study
In
area.
size
ranges
e q u a n tc r y s t a l s
(Fig.
55).
c r y s t a sl i z e s
from
of s p a ra s
and
morphologies.
micrite ((4 microns) t o blocky,
much a s 60
in
microns
of
c o a t e dg r a i n s t, y p i c a l
common.
a r ep r o d u c e d . i nt h e
'
climates
calcite crystal size
of s o i lz o n e s ,a r e
The
(Goudie,
1973).
ClayCaliches
widely
varying
I n c i p i e nct a l i c h e s
site
w i t htih
lnae1s,t3 0
y0
ears
at
(R.
stands,
however,
c o n s i d e r a b l syh o r t epr e r i o d
highly calcareous nature
of
may
time,
have
Israel,
Yinam,
Tel
Folk, 1 9 7 9 , o r a l
L.
Caliches produced i n l a c u s t r i n e mudstones
low
and
i n the caliches reflect the fluctuating
formed i n t haer c h a e o l o g i c a l
lake-level
spar.
alkaline soils i n arid
B-horizonof
vadose-zone
chemical
environment.
commun.).
diameter
w i t h i n L c a l i c h aeorsef t e n
D e t r i tga rl a i n s
surrounded by h o r r e n t loyr i e n t ebdl a d e s
semiarid
the
t h isne c t i o nc ,a l i c hceh a r a c t e r i s t i c a l l y
e x h i b i t s a wide range of
Crystal
of
have
due
during
formed over a
t ot h ei n i t i a l
of these sediments.
Large c r y s t a l s of b l o c k yp, o r e - f i l l i n gs p a a
r re
common
cement
t y p e i n thesandstones
alluvial-plain facies
of
deltas.
Occurrence
of t h ed i s t a lb r a i d e d
and the upper, non-lacustrine portions
of
t h ti y
spe
of
cement
lower-delta and l a c u s t r i n e b a s i n a l sediments i s
minor,
a
s p a r - f i l l e d voidspaces
within
limited
to
w i t h i n l a c u s t r i n e mudstones,
as has been p r e v i o u s l y d e s c r i b e d i n t h e
mudstone
petrology
163
Figure 55.
Baca caliche as seen in thin section. Note
wide range in calcite crystal sizes and the
presence oSnumerous grains whichexhibit
hematitic clay cutans. Sample 34, crossed
nicols ,,field width=O. 8
mm.
164
section.
The s p a rc r y s t a l sa r em o d e r a t e l y
r e s p e ct o
t
size (Fig.
,between
about
cements
were
calcite
and
80
the
56);
250
mean
w e l l s o r t e dw i t h
g r a isni zrea n g e s
micronP
s .o i k i l o t o p icca l c i t e
o c c a s i o n a l loyb s e r v e dC. o a r s e lcyr y s t a l l i n e
sometimes
p a r t i a l rl y
eplace
f es l d s p a r
lacustrin
s ae n d s t o n (essfeeel d s p,asre c t i o n ) .
Sand
non-
In
thin
cements g e n e r a l l y e x h i b i t
section,coarselycrystallinespar
p a t cdhiys t r i b u t i o n .
in
grains
within
spar-cemented
p a t c h e sa r et y p i c a l l yl o o s e l yp a c k e d ,i n d i c a t i n gt h a tt h e s e
d i a g e n e t i ch i s t o r y
in
e a r l(yp r i otcroo m p a c t i o n )
a r e a s were cemented
of thesediment.
the
The patchy,incomplete
nature of t h ee a r l yc a l c i t ec e m e n t a t i o nw i t h i nu p p e r - d e l t a
0
and
distal
braided
r e l a t i v e l yh i g hp o r o s i t i e s
sandstones
and
resulted i n
a l l u v i a l - p l a i sna n d s t o n e s
and p e r m e a b i l i t i e sw i t h i nt h e s e
favored
t h e iur t i l i z a t i o n
a as q u i f e r s
by
later-diageneticgroundwaters.
S e vpearraall l e l - o r i e n t e d ,
c o n c r e t i o n sa s
much
observedwithinsandstones
NW
l/4,
SW
as
brown,
cigar-shaped
6 inches (15 c m ) i n diameter were
unit
of t h e middlesandstone
1/4, NW 1/4, Sec.
6, T . l N . ,
R.6W.
Sand g r a i n s
withintheseconcretionsexhibitveryloosepacking,
'
tightly
and
0
andaxe
completely,cemented
with
coarse
sparry
calcite
which i s m o r p h o l o g i c a l l yi d e n t i c a lt ot h a t
(Fig.
at
57).
cigar-likeshape,
described
above
The r e a s o n fs o trh ep a r a l l eol r i e n t a t i o nt,h e
and t h et i g h t l y
cemented n a t u r e
of
these
165
Figure 56.
Coarsely crystalline spar
delta sandstone (sample C).
field width=0.8
mm.
cement
in an upperCrossed nicols,
166
Figure 57.
Coarsely crystalline sparry calcite cement in
cigar-shaped sandstone concretion (sample 49).
Loosely packed fabric is indicative of very
early cementation (pr.iorto compaction).
Crossed nicols, field width=0.8 n
un.
167
concretions are not
known.
The moderatelywell-sortednature
of
coarsely
the
under
crystallin
sp
eiam
r p l icees m e n t a t i o
t ono
pk
lace
r e l a t i v e l y uniform, s t a b l e
and t h e l a c k
geochemical
of c h a r a c t e r i s t i c vadose-cement
a sg r a v i t a t i o n a l l yo r i e n t e d
shows
table.
The g e n e r a l l y
loosely
cemented
that
cementation
occurred
nature
of
The
t h sep a r -
of
and
magnesium/calcium
ratio
p.
about 2 : l
(Folk, 1974,
p.
the
176).
is
t h,es t u d ayr e a
w e l l - s o r t e ds,p a r r c
ya l c i t e ,
i s present
fine-grained
(10-15
micron),
very
which
sediments.
and
basinal.
well-sortednature
of
time of c r y s t a l l i z a t i o n was less than
a tt h e
The t h i r d v a r i e t y of c a l c i t e cementwhich
.
1977,
McBride,
subequant,
subhedral
morphology
of
the
calcite
porewaters
delta
the
water
g r a i n isn d i c a t e c
sementation
p r i otro
burial
c r y s t a l ss u g g e s t st h a t h e
in
(Dunham,
below
packed
more t h a n a few t e n s of f e e t( J o n a s
73).
i n d i c a t o r s such
cements
and meniscate
1971),
This,
conditions.
of t h i sc a l c i t e
is
The
is
abundant
in
lower-
f i nger a isni z e
similar
t ot h a t
and
of
microspar, which i s produced by a g g r a d a t i o n a l neomorphism of
micrite (Folk,1965).
.However, d u e t o the completeiack
of
micrite i n t h e Baca ( w i t h t h e e x c e p t i o n
of t h a t i n c a l i c h e s )
and
l a c u s t r i nbea s i n a l
t hf e
a tcht laot w e r - d e l t a
sediments
never
contain
and
more
than
( g r e a t e r abundancesofcarbonatecouldnot
48
percen
ca
t lcite
be .accommodated
168
i n veryloosely
asporefilling
n e c e s s i t a t et h e
packed sandstones and would
of carbonate mud
formerpresence
thesediments),
I b e l i e v et h a tt h ef i n e - g r a i n e dl a c u s t r i n e
c a l c i t e formed assi m p lpeo rfei l l i n g s
and
i s commonly
thesecarbonates.Fine-grainedcalcite
by
h e m a t i t (eF i g .
mudstones
and
grains
not
through
Thus, t h e term microspar i s n o ta p p l i c a b l et o
neomorphism.
red
in
matrix
stained
58) and occurs i n b o t h
lacustrine
t h i n - f r o nst p
a lsaayn d s t o n D
e se. t r i t a l
w i t h i n t h ef r o n t a l - s p l a ys a n d s t o n e sa r ev e r yl o o s e l y
packed, which i n d i c a t e s t h a t c e m e n t a t i o n t o o k p l a c e p r i o r t o
The l a c u s t r i n e sediments a r et y p i c a l l yt i g h t l y
compaction.
e
and
completely
resulting
in
cemented
ve.ry
weiat rhl y - d i a g e n es tpiacr ,
low p o r o s i t i e s and p e r m e a b i l i t i e s which
precluded a l t e r a t i o n by l a t e r groundwaters.
The
-
f i n e - g r a i npeodr,e - f i l lsipnagcrarlyc i t e
c r y s t a l s are g e n e r a l l y well s o r t e d , i n d i c a t i n g p r e c i p i t a t i o n
i n a u n i f o r m ,s t a b l e ,a l k a l i n e
geochemicalenvironment.
vadose-zone
lack
of
cementation
gravitationalo
l yr i e n t e d
1971)
and
indicators
and
meniscate
cements
The
such
as
(Dunham,
of t h ec a l c i t es t r o n g l y
t h ew e l l ' - s o r t e dn a t u r e
suggest t h a t the fine-grainedspar
formed
below
t a b loew
r i t h itnhlea c u s t r i neen v i r o n m e n t .
t h ew a t e r
The l o o s e l y
packed n a t u r e of t h e spar-cemented,frontal-splaysandstones
i m p l i e st h a tc e m e n t a t i o nt o o kp l a c eb e f o r eb u r i a l
0
than a f e w t e n s of f e e( tJ o n a s
and McBride, 1977,
p.
of more
73).
169
Fit_
!
58.
Hematite-stai
ne-_ ined sparry calcite
in a f.ronta1-splay sandstone '(sample 13).
Note poorly compacted nature of this earlycemented lacustrine sandstone. Crossed
nicols, field width=0.75
mm.
170
calcite
Subequant
c r y s t aml o r p h o l o g i e si n
- d i c a tper e c i p -
i t a t i o n from pore waters withmagnesium/calcium
about 2:l
l e s st h a n
ratios
(Folk, 1974,p.176).
The boundarybetweenupper
delta sediments
which are
incompletely
cemented
with
coarsely
crystalline
spar
i s sharp and generally corresponds
withfine-grainedcalcite
ttohaep p r o x i m a tpeo s i t i o n
of
t ho
e r i g i n alla k lee v e l
The
progradation.
deltaic
and
which a r e t i g h t l y cemented
lower-delta and basinal sediments
during
of
e a r l cya l c i tcee m e n t a t i o n
i n e x t e n t of
contrast
between
upper
and
lower
sediments suggests that the lower-delta
delta
and basinal d e p o s i t s
were cemented w i t h i nt h el a c u s t r i n e n v i r o n m e n ti:b
f oth
upper
and
lower
d e l t sae d i m e n t s
water t a b lfeo l l o w i n b
gu r i a l ,
exhibit
similar
were
cemented
one
providedby
oral
The .finer-grained
may
of c r y s t a l growthby
clays in the lacustrine
commun.),
e x p e cbto ttho
degrees
of
cementation.
nature of t h el a c u s t r i n ec a r b o n a t e s
(a) inhibition
would
below t h e
explained
be
by:
as magnesium,
ions,such
environment(Folk,1979,.
or ( b ) r a p i dc r y s t a l l i z a t i o n
r a t e s caused by
high
concentrations
of
carbonate
within
the
closed-lake
system.
The
presence
lacustrinesandstones
of- similar g r a i n s i z e
n o ts t r o n g l yc o n t r o l l e d
spaces.
The
of
f i n e - g r a i nsep
oda
n
in
rl y
and n o ti nn o n - l a c u s t r i n e' s a n d s t o n e s
shows t h a t c a r b o n a t e c r y s t a l
by thediameter
of the
incomplete
cementation
upper-delta
of
size was
interstitial
and
e
171
d i sbt raal i dael ldu v i a l - p l saai n d s t o n e s
coarsely
by
crystallinecalciteprobablyoccurred
Slow c r y s t a l l i z a t i o n from
followingshallowburial.
c o uilndh i b
c ir ty s t a l
growth
relatively large calcite crystal
may
explain
volume)
Cements
Following
early-diagenetic
calcite,
quartz
the
i
next
t o form i n t h e Baca sandstones i n t h es t u d y
in
The m a j o r i t y of t h e
authigenic
quartz
area.
sandstonestakesthe
the
Baca
form of simplesyntaxialovergrowths
5 9 ) , b u t a small amount
(Fig.
the
s i z e i n thesesandstones.
Quartz (0-9%, mean l%, median 0.5% of bulk rock
were
dilute
of s u b s t a n t i a l amounts of clay
p h r e a t ' i cw a t e r so rt h el a c k
which
below t h e w a t e r t a b l e
radiallyorientedflamboyant
o r a l commun. ) ( F i g .
60).
(less
than
megaquartz ( K .
5 % ) occurs
as
M i l l i k a n , 1979,
,Quartz cements were onlyobserved
i n upper-delta and d i s t a l b r a i d e d a l l u v i a l - p l a i n S a n d s t o n e s ;
early,completecalcitecementationprecluded
of
quartz
sediments.
quartz
in
subsequent
and
cements
Indeed, even i n
the
lacustrine
the
non-lacustrine
sandstones
and c a l c i t e o c c u ra n t i p a t h e t i c a l l y , .D e t r i t a lq u a r t z
grains were oftenobserved
which e x h i b i t e ds y q t a x i a lq u a r t z
of
overgrowths
except
along
those
portions
boundary
which
Recognition
I
the
formation
a r e cemented w i t hc a l c i t es p a r
of
g r a i n sw i t ho l d e r ,
th
g er a i n
(Fig.
reworkedovergrowths
61).
was
172
i
Figure 59.
Syntaxialovergrowth on d e t r i t a l q u a r t z g r a i n .
Sample 45, c r o s s e d n i c o l s ? f i e l d w i d t h = 0 . 7 5
m
m
.
174
Figure 61.
Inhibition of syntaxial quartz overgrowth by
coarsely crystalline sparry calcite cement.
Sample B, crossed nicols, width of field=
0.75 m
m
.
175
difficult.
However, t h eo c c u r r e n c e
of r a r e ,i s o l a t e dq u a r t z
in
grains
with
syntaxial
overgrowths
l a c u s t r i n es e d i m e n t si n d i c a t e st h a t
smallpercentage
of
i n t h en o n - l a c u s t r i n er o c k s
thequartzovergrowthsobserved
The
were
probably
reworked.
a
the
early-cemented
presence
minute
of
hematite
of red c o l o r a t i o n i n t h e Baca;
flecks(theprimarysource
see colorationsection)beneathquartzovergrowthssuggests
i t s hydrated
iron-oxide
precursor,
t h a t h eh e m a t i t e o
,r
formed
prior
to
quartz
cementation.
The
concentrationsofauthigenicquartz
wereobservednear
t o p of t h e Baca s t r a t i g r a p h i cs e c t i o n
6 2 ) , which s u g g e s t s t h a t
(Fig.
highest
in
t h es t u d ya r e a
much of t h e s i l i c a f o r t h e s e
thus,
cements was derived from theoverlyingvolcanicsand,
i m p l i etsh aqtu a r tcze m e n t a t i o n
following
the
inception
time.
similar
.P
in
of
volcanism
the
in
Baca t o op
kl a c e
early
Oligocene
upward increas,e i n a u t h i g e n i cq u a r t z
observed by t h e w r i t e r i nt h i ns e c t i o n s
from
Baca measured s e c t i o n i n t h e BearMountains
(Fig.
63).
increasing
pH
and
The only
conclusions
geochemical
solubility
of
vicinity
q u airnt zc r e a sweist h
temperature
(Jonas
which
can
be
was
Massingill's
(1979)
The
the
and McBride, 1 9 7 7 ) .
drawn
concerning
the
n a t u r eo ft h ei n t e r s t i t i a lw a t e r sd u r i n gq u a r t z
p r e c i p i t a t i o n i s t h a tt e m p e r a t u r e s . w e r ep r o b a b l yr e l a t i v e l y
low
(<
10.5).
200'
C?)
and
the
pH was n ost t r o n g l ya l k a l i n e
(<
176
Percent of Bulk Rock Volume
i
*O0
l-
50
Middle
Sandstone
Unit
Lower
Red
Unit
Samp1e
Number
Figure 62.
Plot of authigenic quartz content in studyarea sandstones as a function o f stratigraphic position.
177
Percent of Bulk Rock Volume
0
-
5
10
15
20
25
50
200
Middle
Sandstone
Unit
70,
27 .
100
0
feet
Lower
Red
Unit
50
.o
meters
16.
3.
Sample
Number
Figure 63.
Plot of authigenic quartz content in
function 0.f
Baca sandstones' as
stratigraphic position. Data from
point'counts madeby the writer'on . .
thin sections from Massingillis ( 1 9 7 9 )
measured section in the bear Mountains
area. .
178
Followingquartz,kaolinite
t h ed i a g e n e t i ch i s t o r y
area.
as
was t h en e x t
cement
of t h e Baca sediments i nt h es t u d y
is the
The d i s t r i b u t i o n of a u f h i g e n i ck a o l i n i t e
that
of
in
it
quartz;
same
occurs
only
in
upper-delta
and
,.
fluvia
sa
l n d s t o n eK
s .a o l i n i toec c u r s
between
as
of
quartz in interstitial areas
by e a r l y p
, atckily
occurrence
b o tkha o l i n i t e
which were n o t t i g h t l y
d i s - t r i b u k e d s p a rr e s u l t si nt h e
of b o t h k a o l i n i t e
s p a c eI.o
nt h e r
p o rfei l l i n g
cemented w i t h
g r a i n s which havenotSeenpreviously
c a l c i toeqru a r t zP. r e c i p i t a t i o n
e
a
and quartz within
words, q u a r t z
and
nature
of
relative to
period
of
of these cements.
a givenpore
areas
a
indicates
compaction s r i o r t o k a o l i n i t ep r e c i p i t a t i o n .I n
64,
d i f f r a c t i o nd a t a
comnan
observed i n t h i n s e c t i o n
and
low
and
p o s i t i v ar e l i e f .
on t h ec l a y - s i z e df r a c t i o nf r o =o n e
clay-cementedsandstone(sample
Tkie
as t i n y f l e c k s o r v e r m i c u l a r
6 5 ) as much a s 30 microns i nl e n g t h
e x h i b i t s very low b i r e f r i n g e n c a
*
a given pore
The more closelypacked
adjacent
calcite-cemented
s t a c k s( F i g .
kaol.inite.
common
the
kaolinite-cemented
areas
within
sandstones
thin section, kaolinite appears
X-ray
cemented
k a o l i n i to
eften
occur
t o g e t h e r ,w h e r e a sc a l c i t er a r e l yo c c u r sw i y n i n
s p a c ew i t he i t h e r
and
5 6 ) confirmsthe
vermicular
'habit
presence of
of t h e
kaolinite
and i t s r e l a t i v e l y l a t e o c c u r r e n c e
179
Figure 64.
Authigenic kaolinite. Bluish tint is due
to impregnation of kaolinite microporosity
with blue epoxy. Sample 48, crossed nicols,
m
.
field width=0.15 m
18 0
Figure 65.
Scanning electron photomicrograph of vermicular stacks of kaolinite crystallites ona
quartz sand grain. Sample 56, 5,OOOX.
181
in
t h ed i a g e n e t i ch i s t o r y
i s a u t h i g e n i c .I nc o n t r a s tt ot h eo t h e r
t h a t t h ek a o l i n i t e
Baca
of t h e Baca sedimentsindicate
sandstone
k a o l i n ictoen t a ianpsp r e c i a b l e
cements,
m i c r o p o r o s iet y
sp
, ecially
when
thus
may
vermicular
i n p e r m e a b i l i t i eass
s t a c kT
s .h im
s i c r o p o r o s i trye s u l t s
much a8s . 8
in
arranged
mD (Jonas and
McBride,
p.
81-82),
1977,
and
s i g n i f i c a n t l y enhance t h ea q u i f e rc h a r a c t e r i s t i c s
of kaolinite-cemented
sandstones.
Microporosity
produces
the
t i n t of k a o l i n i t e when observed i n
t y p i c a ll i g h t - b l u e
thin sections
which have been impregnated with bl,ue epoxy.
K a o l i n i t e forms
under
e
where
is
there
s l i g h t layc i d icco n d i t i o n s
anexcess
of s i l i c a b u t few potassium and
magnesium i o n si ns o l u t i o n( J o n a s
common
association
of
and
McBride,
corroded
feldspars
cement i n t h i ns e c t i o n ,t h ei n s t a b i l i t y
and
of
The
1977).
kaolinite
under
feldspar
acidic conditions requisite for kaolinite precipitation,
t hper e s e n c e
replaced
of
by
a
few
f e l d s p agrr a i n s
kaolinite
imply
producing cavernous dissolution
which
and
have
been
that
secondary-porosity-
of Baca f e l d s p a r s took p l a c e
synchronously
with
kaolinite
cementation.
The e t c h i n g . o f
garnetswithinkaolinite-cementedsandstonesprobablyalso
time.
took
placa
etth i s
provided
some
precipitation,
of
F e l d s p adr i s s o l u t i o n
may have
t shiel i n
ce
a c e s s afrkoyar o l i n i t e
however, d u e t ot h er e l a t i v e l ys m a l l
of f e l d s p a r which havebeendissolved,
I do
volumes
n o tf e e lt h a t
e
182
feldspar dissolution could have supplied
a l l of t h e s i l i c a .
Dolomite ( 0 - l o % , mean 1%,median 0% ofbulkrock
Dolomite w a s t h e f i n a l
volume)
cementing a g e n ti nt h e
Baca
sandstones'inthestudyarea.
\ I t s occurrence i s r e s t r i c t e d
tonon-lacustrinesandstones,
as i s the. case w i t h q u a r t z
and
kaolinite
cements.
Unlike
the
earlier
cements,
however,
dolomite
only
occurs
sandstones.
awing
0
much
(as
as
is
to
the
be
extenq
t ,u a r t(zF i g .
s m a l l ,i s o l a t e d
Folk,
L.
I tnh i sne c t i o nd, o l o m i tg
eenerally
rhombohedra
which
o f t eenx h i b i t
and iron-poor
zones
(Fig.
a
not
small
Dolomite commonly c o n t a i n s
well-formed
replacementproduct
it
dolomite tloi m o n i t e
a s a few p e r c e n t ) of i r o n ( R .
a l t e r n a t i nigr o n - r i c h
usually
of
Baca
s o u r c e of y e l l o wc o l o r a t i o ni nt h e s es a n d s t o n e s
1980, o r a l commun.).
occurs
yellow-gray
(non-red)
outcrop
weathering
appears
( s e ec o l o r a t i o ns e c t i o n ) .
amounts
the
f a cot ,x i d a t i o n
In
modern
predominant
in
66).
b u t appears as a
s i m p lpe o rfei l l e r ,
of k a o l i n i t e , c a l c i t e , a n d , t o
67).
It
Dolomite
most
a
lesser
o f t eonc c u r s
as
rhombohedra withinsandstones.exceptwhere
or k a o l i n i t e - f i l l e d
r e p l a c e sr e l a t i v e l yl a r g ec a l c i t e -
void spaces, i n which case it appears
developed,intergrownrhombohedral
as
numerous,
crystals.
poorly
183
Figure 66.
Dolomitecementshowing
and iron-poorzones.
f i e l d width=0.75
mm.
a l t e r n a t i n gi r o n - r i c h
Sample €3,c r o s s e dn i c o l s ,
184
F i g u r e 67
Dolomite
grain.
0.75
rhombohedron
replacing
adjacent quartz
width=
Sample B, crossed n i c o l s ,f i e l d
m
m
.
185
The formation of golomite w i t h i n t h e
is
apparently
r e l a t e db o t hs p a t i a l l y
i n t r u s i o n of Miocene mafic d i k e s i n
shows
the
coincidence
Baca sandstones
and t e m p o r a l l yt o
area.
the
study
area.
shown
68
of
in
dikes
i n alkaline
environments.
amounts of Fe8. i n thedolomite
Dolomite
forms
The i n i t i a l p r e s e n c e
(as
Figure
occurrence yellow-gray,
of
in
dolomite-bearing sandstones w i t ht h el o c a t i o n
the
the
ofsmafl
by recent l i m o n i t i ca l t e r a t i o n )i m p l i e s
.reducing
conditions a t t h e t i m e of p r e c i p i t a t i o n .
The following i s a
possible
model
the
cements.
During d i k e emplacement, oxidizing,carbonate-rich
were
groundwaters
delta
and
€or
the
formation
migrating
through
permeable
Baca upper-
the
As
t hien t r u s i o n st h
, epyr o g r e s s i v e l y
due t o t h e i n t r o d u c t i o n
reduced,presumably
by
Baca dolomite
braide
ad
l l u v i a l - p l asi a
nn d s t o n e s .
watyrs
neared
S?)
of
these
became
of r e d u c t a n t s (Hz
These reducing groundwaters
dissolved
dikes.
in
hematite and magnetite and a l t e r e d ilmenite t o leucoxene
t h eh o s ts a n d s t o n e( s e e
heavy m i n e r a ls e c t i o n ) .
time, thegroundwaters
causing
dolomite
became heated by
within
thedolomite
the above-described
dissolution
this
model
A t t h e same
thenearby
dikes,
tpor e c i p i t a t(ec a r b o n a tseo l u b i l i t i e s
decrease
with
increasing
temperatures).
incorporated
,
presents
explanation
both
for
the
occurrence
a
of
Much
o€
t h ei r o n
was probablyderived
heavy
minerals.
from
Thus,
geochemically
viable,
simple
of
yellow-gray,
186
. .
Figure
68. Generalized map of the study area showing coincidence
of occurrence of dikes and areas in which Baca sandstones
are yellow-gray in color (stippled areas).
e
187
dolomite-bearing sandstones in proximity to dikes, and the
anomalousheavy-mineralsuitewithintheseyellow-gray
sandstones.
Source of Coloration
..
mere are two modes in the coloration of the Baca
sediments in the study area (Fig.69).
sediments average about 10R
6/2
The majority of the
(weak light red-orange).
Upper-delta and distal braided alluvial-plain sandstones
which are near mafic dikes are often non-red, averaging
e
about lOYR 7/3 (very light yellow-orange).
Red
Coloration
In
thegrossestsense,theoriesconcerning
the
genesis of redbeds can be lumped intotwo basic schools of
thought: soil-derived and diagenetic red coloration.
latterprocessis
sedimentary
The
the most important in the red Baca
rocksin the
study
area.
Soil-derived
Red
Coloration.
red
- Soil-derived
coloration
is
oneoftheoldestandmostwell-rooted
theories of redbed genesis, and was popularized by Krynine
0
(1949,1950)andVanHouten(1948).Accordingtothis
188
V.
uenk
/I
i2 . 5 ~
5~
Red
7.5~
loa
2 . 5 ~ ~ SYR
orange
7 . 5 ~ ~~ O Y R
2 . 5 ~
5~
Yello"
HUE
Figure 69. Distribution of coloration for52 Baca
sandstone samples from the study area.
Values were determined by comparison with
Munsell Soil Color Chart. Color terminology
after Folk (1969).
189
from
were
r e s u l t from
sediments
which
theory,
redbeds
lateritic soils
derived
which formed i n igneousormetamorphic
t e r r a n e s i n t r o p i c a la r e a sw i t hs e a s o n a l l yh i g hr a i n f a l l .
heavy minerals i n t h e A h o r i z o n '
I n these areas, iron-bearing
of l a t e r i t i c s o i l s become s e v e r e l ya l t e r e d
such
processes
as
hydrolysis
and
humic a c i d sD
. estruction
of
and
leached
a t t a c k by carbonic and
these
heavy
minerals
yields
clay
minerals
(also
derived
from
the
weathering
f e l d s p a r s ) and h y d r a t e idr o o
n x i d e(sl i m o n i t e )
transported
oxides and c l a y m i n e r a l s
basin
form
of
yellowish
of
are
I n the B
and t h e s e h y d r a t e d i r o n
form c u t a n s ( c l a y c o a t s )
Upon erosion, these s o i l sp r o v i d el a r g e
the
of
which
downward by percolatinggroundwaters.
soil horizon illuviation takes place
e
by
on g r a i n s .
amounts of i r o n ,
in
g r a i n cs o a t e d
with
f e r r u g e n o u cs l a yt,o
the
deposition.
brown
i r o n o x i d e (Van
ration results in
When
incolor
Houten,
deposited,
the
sediment
due t ot h eh y d r a t e dn a t u r e
1964).
Post-depositional
is
of t h e
. dehyd-
hematite forming within the cutaris, giving
the redbeds t h e i r c o l o r a t i o n .
Diagenetic
Red
Coloration.
Walker
(1963,
1967)
~
proposed
that
redbeds
i n t r a s t r a t a ld i s s o l u t i o n
this
method,any
o ft h ec l i m a t ei n
can
form
diagenetically
of iron-bearing heavy minerals.
by
By
heavy-mineral-bearingsediment,regardless
the s o u r c ea r e a ,c a nl a t e r
become
red
if
190
set
t hrei g h t
,
of
or
deposition.
Igneous
n e c e s s a r yt op r o v i d e
metamorphic
are
source
rocks
t h e heavy m i n e r a l s ( M i l l e r and Folk,
burial,
1955).
After
of
c o n d i t i o npsr e v a i litsnhbea s i n
the
iron-bearing
heavy
minerals
silicates)
( p a r t i c u l a r l yi r o n
a r el e a c h e d
by i n t r a s t r a t a l
and
s o l u t i oy
n ise, l d ihnygd r a tfeedror ixci d e s
minerals.
Dehydration r e s u l t s i nt h ef o r m a t i o n
red
place
water
the
of h e m a t i t e
coloration.
Dehydration
can
take
which provides
the
below
clay
table
is alkaline
itfhw
e ater
(Walker,1974).
is
D i a g e n e t i c a l l y produced r e dc o l o r a t i o n
e
dependent- upon
According
to
of d e p o s i t i o n .
c o n d i t i o n sw i t h i nt h eb a s i n
Walker
primarily
(1967,
366),
p. these
conditions
of i r o n - b e a r i ndge t r i t aglr a i n s ,
i n c l u d e( :ao)c c u r r e n c e
(b) post-depositionalconditionsthatfavortheintrastratal
dissolution
%-pH
of
(c)
iron-bearing
grains,
an i n t e r s t i t i a l
environment t h afta v o rtshfeo r m a t i o n
( d ) absenceofsubsequentreduction
f e r r i co x i d e s ,
oxides, ( e ) enough
occur,
and
of
time
( f )r e l a t i v e l y
f od
r e h y d r a t i o nt o
hydrated
of f e r r i c
~
hematite
to
warm temperatures
(above
about
'65-70 F ) .
Source of Red
Coloration
"
Through
e
Of
i n t h e Baca
"-
Formation.
thepetrographicmicroscope,thepredominantsource
r ecdo l o r a t i o n
i n t h e Baca s a n d s t o n eistnhset u d ayr e a
e
191
a p p e a rtso
be
small
micron) flecks of hematite
(0.5-3.0
which a r u
e niformly
distributed
grains.
These
on
the
surfaces
f l e c k sa r ep r e s e n t
the source
(Fig.
70).
and
a tc o n t a c tp o i n t s
Similar f l e c k sa r e
assumed t o be
of c o l o r a t i o n of t h e red Bacamudstones,however,
t h eb i r e f r i n g e n c e
and carbonate i n theserocks
of t h e c l a y s
the hematite impossible.
made determination of the nature of
Morphologically
e
sand
on b o t ht h ec o r n e r s
embayments of g r a i n s , b u t do notoccur
betweengrains
of
indistinct
p o w e r w i t ht h e
evenunderhigh
o p t i c a l microscope,theseflecks
are u s u a l l ys e e nw i t ht h e
scanningelectronmicroscopeto
be p l a t e - l i k e i n shapewith
r a g g e di r, r e g u l aerd g e sa,l t h o u ghhe m a t i tcer y s t a lw
s ith
e u h e d r atle r m i n a t i o n sa r en o t
uncommon ( F i g .
71).
N o clay
cutans are associated with these flecks.
Three
occurrence
a d d i t i o nraell,a t i v e l y
minor
A few
magnetite/ilmenite/specular
I n two t h i ns e c t i o n s ,
h e m a t i t eh a l o s .
of p o r e - f i l l i n gh e m a t i t e
*
minor amounts ( <
cement were observed.
black i n handspecimen,however,and
hematite
and w e r e surrounded by
grains exhibited dissolution features
two
of
h e m a t i t e were observed i n t h e Baca sandstone
of
t h i ns e c t i o n s .
tothe
modes
1%)
This appears
thus does not contribute
red c o l o r a t i o n of t h e Baca Formation.Approximately
percent
of
the
sand
grains
examined
' w ti h
t he
petrographic
.microscope
displayed~
hematitic
clay
cutans.
These
cutans
typicakly
show
t hy
eellow
birefringence
of
192
Figure 70.
Hematite flecks uniformly distributed on
Baca sand grains, except at contact points
between grains. Sample P I plane light, field
m
.
width=0.15 m
193
Figure 71.
Scanning electron photomicrograph of euhedrally terminated hematite crystals on quartz
sand grain. Sample P , 7 , 0 0 0 ~ .
194
c l a yh
: e m a t i t eo c c u r sa s
a d i f f u s es t a i nw i t h i nt h ec l a y
coats.Possiblesources
of theclay-coatedgrainsinclude
s o i l zones i n t h e s o u r c e a r e a o r o l d e r P a l e o z o i c o r
Mesozoic
redbedsequences.
I believe that the majority
the
Baca
Formation
of t h e red c o l o r a t i o n i n
was d i a g e n e t i c a l l y produced.
Evidence
of
f o trh i si n c l u d e s(: a t)h ep r e s e n c e
i n o t h e rd i a g e n e t i c a l l y
c r y s t a l ss i m i l a rt ot h o s ed e s c r i b e d
produced redbeds
distribution
(Walker,
of
euhedral
hematite
, 1 9 6 7 , 365):
p.
h e m a t iftlee c k s
uniform
(b)
on
both
corners
and
embayments of g r a i n s and l a c k of f l e c k sa tc o n t a c tp o i n t s
e
between
grain
i nsd i c a t tehstahtey d r a t ei rdo n - o x i d e
p r ehcteu
hm
rteo
saotri t e
was
p r e c i p i t aptoe sdt -
( c ) t h ep o r e - f i l l i n gn a t u r e
depositionally;
of t h eh e m a t i t e
cement shows t h a tp o s t - d e p o s i t i o n a lp r e c i p i t a t i o n
oxides
did
occur:
from,
sandstones
derived
predominantly
metamorphic
tchaes e
with
dissolution
,365)
of
the
iron
( d ) p a u c i t y of a u g i t e and hornblende i n
suites
heavy-mineral
of
and
Baca)
from
igneoussourceareas(as
is
i n d i c a t tehsiantt r a s t r a t a l
(Walker, 1967, p.
thesemineralstookplace
( t hgee n e r a l lfyr e snha t u roetf h
.fee l d s p a ri sn
early-cemented
Baca
sandstones
shows
t htahte h
s ee a v y
minerals w e r e probably not destroyed within source-area soil
zones):
(e)
general
lack
e
t h atth ree d
coloration
did
not
of c l a y - c o a t eg
dr a i nisn d i c a t e s
form
pedogenically;
(f)
e
195
hematite
halos
around
iron-bearing
heavy-mineral
grains
indicate that intrastratal dissolution has occurred.
I n t r a s t r a tdails s o l u t i o n
of
iron-bearing
heavy
m i n e r a lps r o v i d e d
t h ier o n
f otrh h
e e m a t i t ce o l o r a n t .
l a r g ep o r t i o n
by
of t h i s i r o n ,
A
however, may have been
. which
formed'
a u t h i g e n iicr osnu l f i d e s
w i t h itnh e
These i r o ns u l f i d e sa r e
lake-bottomsediments.
a n a e r o b i c ,s u l f a t e - r e d u c i n gb a c t e r i at h a t
th
l aec u s t r i n
sediments
which
probably
supplied
produced
by
may havelived
in
became
anoxic
follow
s hi n
ablgluoSrw
iuallf.a t e - r e d ubcai n
cg
teria
typically
e
(Love,
produce
small
1971).
such
No
observed,
however,
sulfides
(0.03-1.0
pyrite
framboids
mm)
framboid-shaped
hematite
was
which i n d i c a t e st h a ti fa u t h i g e n i ci r o n
e x i s t e d i n t h el a c u s t r i n es e d i m e n t s ,t h e y
were not
1
i t s precursor.
pseudomorphously replacedbyhematiteor
lacustrine
sediments
a r e ,g e n e r a l l y
The
redder t h a na s s o c i a t e d
non-lacustrinerocks,whichimplieshigherconcentrations
of
hematite i n t h e l a c u s t r i n e r o c k s a n d , t h u s ,
may i n d i c a t e t h e
formerpresence
i n these rocks.
of a u t h i g e n i c i r o n s u l f i d e s
The presence of h e m a t i t ef l e c k s
sand
of
of
red,
grains
within
calcite-cemented
portions
non-lacustrine sandstones
both
on t h es u r f a c e s
onsand
and t h e o c c u r r e n c e of t h e s e f l e c k s
g r a i n s and i n t e r s p e r s e dw i t h i ns p a r
cement i n
l a c u s t r i n e sediments i n d i c a t e st h a ti r o nm o b i l i z a t i o nt o o k
p l a cvee reya r l(yp r i ot o
r
and d u r i n g c a l c i tcee m e n t a t i o n )
e
196
h i s t o r y of
i n thd
e iagenetic
ration
of
the
sediments.
Baca
Dehyd-
the
hydrated-iron-oxide
hematite
precursor
have
occurred
during
lake-level
low
may
s t a n dos r
below
the
i n an alkalineenvironment(Walker,1974).
w a t e rt a b l e
The
presence of c a l i c h e s and otherearly-authigeniccarbonates
in
the
Baca i m p l i e st h a tg r o u n d w a t e r s
th
ee
a rpl yo r t i o n
of
were a l k a l i n e d u r i n g
th
d ei a g e n e thi ci s t o r y
of
the
sediments.
Folk
(1976)
s t at h
e sa t
evolutionary
change
in
time
color
through
(Fig.
evolutionarysequence,thepale-redsandstones
Baca s a n d s t o n e s e x h i b i t
than
would
be
do n o t .
lower s a t u r a t i o n v a l u e s ( a v e r a g e
expected
for
an
according t o Folk
(1976)
Eocene
t h issa t u r a t i o v
nalue
l i g h tf o r
Moreover, t h e
an e a r l yT e r t i a r y
relativelycoarselycrystallinenature
-
is
probably
the
cause
for
t h i sc r y s t a l l i n i t y
saturation
values.
is
thefactthatthehematite
soil-derived
(R.
of t h e Baca
L'.
The
is
The
redbed
sequence.
t h e large
discrepancy
p r e d i c t e d and
observed
/2)
is .more
of the red Baca sediments ( 6 / )
averagevalue(lightness)
Red
redbed
sequence:
t y p i c a' olafE
n a r lPya l e o z o isca n d s t o n e .
somewhat
72).
Baca sandstones f i t w e l l i n t o t h i s
Although t h e yellow-gray
e
redbeds
undergo
an
hematite
between
reason
for
n o t known, b u t it may be r e l a t e dt o
formed. d i a g e n e t i c a l l y and i s
Folk,
1980,
oral
commun.).
not
197
RED
SR
Fig.
ZSR
RED-ORWGE'
IOR
, 25YR
. .
.
ORANGE
5YR
YELLOW-OR-
ZSYR
IOYR
7 2 Change of mlor with gmlogic axe shown on a pldt of hue m. raturatioe Third color dimasion
of lightness shova by the numbers 4/ e t c and degree of dackening of the squires. C, initialunweathered
quartzose sand; A, Saharan sandr. data fmm Alimm; SI.Slmpson Deserc surface fluff of Holocene age;
S.. S i p s o n Desert, modal wlor nl mnrrc of fine sands; S,. Simpron Desert, mbr of hematite-clay cutan$
in pits. formed duringPleistocene latcritiration; P, otherPleistocene sediments; Hm.color of powdered
pure hematite; F'y 4- hl, wlor of Mcramic m d younger Palmzoic red r
ocks: Po, Older Palmzoic and
Pr-bnan
rocks. Procases that create thue Fhvlges shown by the "~olutionuy"a r m x ~
(Modified from F o l k , 1976)
198
Yellow-gray Coloration
Permeable u p p e r - d e l t aa n dd i s t a lb r a i d e da l l u v i a l dikes are
plain
s a n d s t o n ew
s hich
a r leo c a t e d
n e am
r afic
t o orange i n color (average lOYR
o f t e ny e l l o w i s h - g r a y
.
The
m a j o r i to
yf
coloration
this
as
o u t c r ow
pe a t h e r i n g ,
was
non-red
a
on
were:
(a)
s i g n i f i c a npt o r t i o n
of
as a
c a l c i t e and k a o l i n i t e c e m e n t s
d e t r i t a l g r a i n s .I n
t h e development
of
yellowish
Baca
the
the B a c a s a n d s t o n e so c c u r s
diffuse limonitic stain within
and
l i m o n i tdeu r i nrge c e n t
a
c o l o r a t i o ni n
of
p r e v i o u s ldyi s c u s s eidn
d o l o m i tsee c t i o nA. d d i t i o n a l l y ,
the
i s cue t oa l t e r a t i o n
to
iron-bearing
carbonate
cements
7/3).
summary, the e v e n t sl e a d i n gt o
t oo r a n g ec o l o r a t i o ni nt h e
o x i d i z i nagl k
, a l ignreo u n d w a t e r s
which
migratedthroughpermeablenon-lacustrinesandstones
became
reduced d u e t o i n t e r a c t i o n w i t h r e d u c t a n t s (HZS?) associated
w i t h dike emplacement i n
Miocene
time
(These
negative-Eh
g r o u n d w a t e rd
s i s s o l v e dh e m a t i t ea n dm a g n e t i t ea n d
i l m e n i t et ol e u c o x e n ei n
.
iron
from
these
the . h o s t
dolomite
cements
and
sandstones);
formed
(b)
Heating
r e s u l t e di np r e c i p i t a t i o n
Tertiary uplift
0
of
sandstones.
Dissolved
was
heav
myi n e r a l s
i n c o r p o r a t ei n
dt o
d i f f u sset a i nws i t h i n
groundwater
of d o l o m i t e ;
anderosionalstripping,
‘ b e a r i n gs a n d s t o n e s
altered
were exposed t o
(c)
by
the
the
dikes
F o l l o w i n g. l a t e
these reduced-iron-
n e a r - s u r f a c ew e a t h e r i n g
199
c o n d i t i o n s ,r e s u l t i n gi no x i d a t i o n
of t h er e d u c e di r o nt o
limonite, which g i v e s r i s e t o t h e
present-daycoloration
of
these sandstones.
,
Porosity
I
a veryimportantrole
P o r o s i t yd i s t r i b u t i o n sp l a y e d
i nt h ed e t e r m i n a t i o n
which
of t h e sequence of d i a g e n e t i ce v e n t s
a f f e c t tehde
Baca
sediments.
porositydistributionwithinthe
teox p l o r a t i o n i s t s
0
in
Knowledge
tohfe
sediments may proveuseful
delineating
probable
pathways
of
migration
uranium-bearing
of
groundwaters.
Porosity
were
determinations
made
blue-epoxy-impregnated
porosity,
primary
sediments
in
using
point-count
tshe icnt i o n s .
and
secondary,
the
Two
types
e x i sw
t ithin
,the
s t u d ya r e a .
of
Baca
Average o v e r a l p
l o r o s i t yi n
the. Baca (primaryplussecondaryporosity)
andrangesfrom
from
data
is
about
3.6%,
essentially zero to ten percent.
Primary P o r o s i t y
as
Primary p o r o s i t yo c c u r s
Baca
virtually
and
no
lacustrine
primaryporosity,
areas
in
w i t h ' cement.
s a n d s t o n etsh aht a vn
e obt e e fni l l e d
Lower-delta
e
intergranular
basinal
sediments
exhibited
due t oe a r l y
and
complete
200
cementationwithfine-grainedcalcite.Priniaryporosity
within non-lacustrine sandstones averages about
3.2%, and
rangesfrompracticallyzerototenpercent.Ofthe
non-lacustrinesandstones,theyellowish-graysandstones
contain
the
greater
!average
primary
values
porosity
for
these
do the
than
sandstones
red
sandstones,
being
about
1.5%, respectively. Microporosity in kaolinite cements may
contribute slightly to the overall porosity of
the Baca
Formation.
Secondary
Porosity
Secondary porosity is diagenetically produced and
predominantlyoccursascavernousdissolutionfeatures
within feldspars. Skeletalized
magnetite/ilmenite/specular
hematite grains within yellow-gray sandstones are
a minor
sourceofsecondaryporosity.Early-cementedlacustrine
sediments exhibit virtually no secondary porosity. Within
upper-delta and distal braided alluvial-plain sandstones,
,
the average secondary porosity value is about
ranges from essentially zero to
0.4%, and
two percent. Secondary
porositywithinred,non-lacustrinesandstonesaverages
about
0.2%'
averages about
0
whereasthat
.-withinyellow-graysandstones
0.7%.
Cavernous dissolution of feldspars
took place intrastratally, due to interaction with acidic
5.1
and
201
groundwaters
(see
feldspar
and
kaolinite
sections).
Skeletalization
of
magnetite/ilmenite/specular
hematite
grainswithinyellow-graysandstonesprobablyoccurred
duringdolomiteprecipitation
in an
alkaline,reducing
environment.
1
Diagenesis
Summary
A flow chart depicting the diagenetic sequence of
events
for
in Figure
the
73.
Baca
sediments
in
the
study
area
Thepresent-daycharacteristicsof
is
presented
the
sediments are highly dependent on their environment of
deposition. Table 7 summarizes the distribution of cements,
heavy minerals, porosity, and coloration among the various
Baca
,facies.
The
lower-delta
and
lacustrine
basinal
sediments tend to be finer grained and less compacted than
the non-lacustrine sediments. A plot of percent cement plus
primaryporosityvs.grain
- size(Fig.74)indicates
a
trend towards increasingly looser packing in the finegrainedlacustrinesediments,andreflectstheearly,
pre-compactional cementation of these sediments. Figure 74
also shows the presence of yellow coloration only in
coarse-grained, non-lacustrine sediments.
the
202
DBFJSITION
I
Figure 73.
Diagenesis flowchart for the Baca sediments
within the study area.
UPPER-DELTA
AYD DISIN.
m m w ALLWW
PLAIN
swmms
LOUER-DELIA
LACUSTRINE
BASINAL
AND
swmws
Table 7.
red
t
WILINM
HFAW HIHEPALS
wnosnr
D i s t r i b u t i o n o f c o l o r a t i o n , cements,porosity,
in relation to the various
Baca f a c i e s .
"
"
"
"
andheavy
minerals
N
0
W
204
0
r
COLORATION
1
GRAIN
SIZE
3
I.
I
10
I
I
30
20
I
1
40
50
PERCENT CEMENT PLUS
PRIMARY POROSITY
.
s.
Figure 74. Plot of grain size
percent cement plus primary
porosity showing tendency towards looser
packing
in the fine-grained lower-delta and lacustrine
basinal sediments. Note the presence of yellow-gray
coloration only in the coarser grained, non-lacustrine
sandstones.
PALEOCLLMATE
New
during
Mexico
(Snyder, 1971;
Johnson,
Baca
time
during
P o t t e r , 1 9 7 0 ) t o subhumid (Massingill, 1979;
Evidence
from
1978).
the
t h i ss t u d yp o i n t st o
in
Eocene.
a
the
i n an a r i dt os e m i a r i d
where
less than
about
rainfall
turtle,
exposures
near
and
Quemado and
progress)
suggest
a
were
Goudie (1973)
in
The
c r o c o d i lfeo s s i l s
(J,, A.
presence
in
t h e Baca
The
common
of sediments and,thus,
since
i m p l itehsaartci o
d n d i t i od
nnispd
orte v a i l ,
vegetation.
water
must
Modern
in
and t h e lack of e o l i a nf e a t u r e s
i n d i c a t e sv e g e t a t i v es t a b i l i z a t i o n
sufficient
of
Schiebout,
savanna-type
climate.
occurrence of rootmottling
semiarid
i’n a savanna) and
annually.
Datil
1961).
pedogenically
favored
i s s e a s o n a l( a s
20 i n (50 c m )
titanothere,
!
of t h e Baca
environment.
is
area
Mountains v i c i n i t y i s
Baca
s t a t tehscaat l i c h
fo
er m a t i o n
climates
study
of semiaridoraridconditions(Langbein,
paleocaliches
within
produced
a hot,
the
The probableclosednature
l a c u s t r i n e system i n the Bear-Gallinas
indicative
west-central
range from a r i dt os e m i a r i d
semiarid,possiblysavanna-.likeclimate
Rare
in
I n t e r p r e t a t i o n s of t h ep a l e o c l i m a t e
.
have been a v a i l a b l et os u p p o r tt h i s
ephemeral
braided
streams
which
are
similar t o the flashy-discharge Baca braided streams usually
e
occur
in
arid
and
semiarid
climates.
205
However,
the
206
pre-Miocene
lackofabundantuplandgrasses
h i g h sediment y i e l d s , l a r g e amounts of
r i vdeirs c h a rcghea r a c t e r i s t i c s
(Schumm, 1968).
The i n i t i a l steps
are
runoff,
even
in
i nt h e
diagenetic red pigmentation are favored
andan
may havecaused
.and
wet
climates
development
F e l d s p a r sw i t h i n
of
by h i g h t e m p e r a t u r e s
which
alkalinegroundwaterchemistry(Walker,1967),
commonly
flashy
associated w i t h s e m i a r i dc l i m a t i cc o n d i t i o n s .
Baca sandstonesweregenerally
d e p o s i t i o ann sdu g g e spt r e s e r v a t i o n
fresh
upon
a r i d o r semiarid
by
climatic c o n d i t i o n s .
,
ECONOMIC GEOLOGY
Uranium Occurrences
Uranium i s t h o
enly
resource
p.
which o c c u r s ; i nt h e
34-35)
economically
important
Baca Formation.
described
three
associatedwith
and
known
minor
uranium
occurrences
carbonaceous m a t e r i a l sw i t h i nt h e
units
middle
sandstone
e
(1959).
been described by Griggs(1954)
The
Red
currently
Basin
deposits
may
being
investigated
(1957)
occurrences
along
Jaralosa
consists
of
delta-front
d e l t a i cc y c l e
lower
I
Minerals,
west
Inc.
uranium
of
the
Bear
prospect,
lies
. .
excavated
delta-plainsandstones
of t h e upper
red
unit.
and
are
examined by t h e writer.
and
was
grained,
conglomeratic,
e
Gulf
Hook. Ranch
. sandstonesareyellowishgraytogray,
materials.
economic
and
s e v eer a
xlp l o r a t ipoint s
and
and Anonymous
r e p o rste v e r a l
Creek,
One of t h e s et h
, e
w i t h i nt h es t u d ya r e a
be
by
Bachman, Baltz, and Griggs
Mountains.
between t h e Baca
i n t h e Red Basinareanorth
Formation and Cretaceousrocks
D a t i lh a s
lower red
Baca
Canyon.
Uranium
in
m i n e r a l i z a t i o no c c u r r i n gn e a rt h ec o n t a c t
of
P o t t e r (1970,
contain
The
into
of t h eb a s a l
uranium-bearing
medium t o very coarse
much
Carbonaceous debris ranges t o a s
carbonaceous
much a ss e v e r a l
centimeters i n length and i s more abundant i n
207.
It
t h ep r o s p e c t
208
s a n d s t o n et h
s ainno n - m i n e r a l i z e d
.from
s a n d s t o nteh i sne c t i o (n# 7 3 )
examined.
It
Baca sandstones.
One
prospect
was
the
Hook
e x h i b i t er edl a t i v ehl yi gp ho r o s i(t b
yo t h
primary and secondary) and c o n t a i n e d c a l c i t e , k a o l i n i t e , and
was
dolomite
cements.
Leucoxene
the
predominant
opaque
h e a vmyi n e r aA
l .l t e r a t i oo
inlfm e n i tl o
eucoxene
by
oxygen-deficient groundwaters has been reported by
o t h e r s( 1 9 7 4 )i n
Adams and
t h e u r a n i f e r o u ss a n d s t o n e so ft h eJ u r a s s i c
Morrison Formation.
O r e Genesis
as
Baca uranium d e p o s i t s ,u c h
Ranch,
the
of
carbonaceous
debris
w i t h negative-Eh
waters
1
which
emplacement
of
mafic
Kaiser (1979).
a q u es o u
l ust i o n s ,
c o n d i t i o nuss,u a l l y
(Douros,
1967).
e
is
Uranium
but
to
The
upward
been
reported
by
has
with
the
of uranium-bearing
. d i k e sR. e d u c t i o n
Texas
by r e a c t i o n
associated
s o l u t i o n sb ys u l f i d e - r i c hg r o u n d w a t e r sl e a k e d
f a u l t si ns o u t h
Hook
by the reducing
a n dp, o s s i b l y ,
were
at
of uraniumfrom
p r o b a b l yo r i g i n a t e db yc o n c e n t r a t i o n
verydilute,oxidizinggroundwatersolutions
action
one
along
Galloway
and
h i g h lsyo l u b lioe
nx i d i z i n g
p r e c i p i tu
an
tree
dsd
eu
r cing
form
complex
organic
compounds
t h iscekq u e nvocofel c a nriocc k s
o v e r l y i n g the Baca Formation probably
were t h e s o u r c e of t h e
209
uranium,
although
intrastratal
dissolution
of heavy
minerals
may also have beena source (Walker, 1975). Future uranium
exploration efforts
in
the Baca in the Gallinas Mountains
vicinity
should
be
restricted
to
permeable,
non-red
upper-delta
and
braided
alluvial-plain
sandstones
which
been altered by reducing groundwater solutions, and areas
which contain anomalously
aceous
materials.
high
concentrations of carbon-
have
SUMMARY OF BACA-EAGAR
BASIN
DEPOSITIONAL SYSTEMS
Johnson
(1978)
recognized
humid
alluvial-fan
(renamed
.
braided
alluvial
plain
in
this
study),
meanderbelt,
and lacustrine depositional systems within the Baca-Eagar
outcrop
belt
in
west-central
New
Mexico
and
eastern
Arizona.
Within
each
of
these
depositional
systems,
Johnson
delineatedtwoormorecomponentfacies.Based.onthe
facies distribution of Johnson (1978), the paleocurrent data
fromSnyder,(1971),Johnson(1978),Pierceandothers
(1979),
and
this
study,
and
the
Baca-Eagar
tectonic
framework proposed
in this study,a hypothetical model for
the basin-wide distribution of facies and paleocurrents is
presented
in
Figure
75.
210
211
Figure 75.
Hypothetical model for the distribution of
facies and paleocurrents in the Baca-Eagar
basin during early Baca time (high lake
stand). Letters in parentheses’indicate
paleocurrent data sources. J=Johnson (1978),
P=Pierce (19791, S=Snyder (19711, C=Cather
(this study). Reference points same as
Figure 10.
SUMMARY AND CONCLUSIONS
The sediments
correlative
Arizona
Eagar
of
the
Formation
Arizona d u r i n g
bounded
R i m gravels of
and
Mogollon
of
t tohn
eo r t h
southeast
by
the
time.
by
the
The
Baca-Eagar
eastern
basin
is
Defiance, Zuni, and Lucero
uplift,
to
and t ot h ee a s t
the
by t h e
These Laramide u p l i f t s ,p a r t i c u l a r i l y
were
Highland,
t h e dominant c o n t r i b u t o r s of
A l l threestyles
detritustothebasin.
( C o r d i l l e r a nf o l d b e lu
t plifts,
anticlinau
l plifts,
large
by the Mogollon Highland,
Morenci
S i e r r a - S a n d i au p l i f t .
Mogollon
a
i n western N e w Mexicoand
Laramide
u p l i f t s ,t ot h es o u t h w e s t
0
Formation
and
r e p r e s e tnh
bt ea s i n - f idl el p o s i t s
intermontane basin present
the
Eocene
Baca
of Laramide u p l i f t s
asymmetrical
basement-cored
and Colorado
Plateau
monoclinal
flex-
u r e s ) are present adjacent to the basin.
Within t h e s t u d y a r e a , t h e
m)
thick
and .upper
the
Bear-Gallinas
units)
in
which
a large,
which w a s present d u r i n g Baca
Mountains v i c i n i t y .
f l u c t u a t i o n s were probably
caused
semiarid,
red
large-scale
ake-leve
fluctuations
closedlacustrinesystem
in
members
and can be subdividedintothreeinformal
(lowerred,middlesandstone,
reflect
Baca i s about 940 f t ( 2 8 9
by
time
These lake-level
climatic
changes.
A
savanna-type c l i m a t e is proposed f o rw e s t - c e n t r a l
New Mexico d u r i n g Baca time.
Facies which
212
were
recognized
213
e
in
the
study
area
include
d i s t a l braided a l l u v i a l - p l a i n ,
f i n e - g r a i nlead
c u s t r idneel t a ,
facies.
The
l a c u s t r ibnaes i n a l
is
d i sb
t ar la i daeldl u v i a l - p l af ianc i e s
dominantlycomprised
conglomerates
and
of f i n e tocoarsesandstones
were
which
deposited
by
supplied
d'eltas,
whose
sediment
to
t h fei n e - g r a i n e d
lacustrine
upward-coarsening
sequences
by
which
and
Similar
i
d e p o saictrh
sea r a c t e r i z e d
d e l t a ip
cr o g r a d a t i o n
minor
low-gradient,
streams.
flashy-discharge
(ephemeral?)
braided
streams
and
abandonment
cyclical
r e p r e saelnt e
t rnate
in
a
shallow
lake.
L a c u s t r i n eb a s i n a sl e d i m e n t sa r es i m i l a rt ot h o s e
e
of deltaicsequences
lower p r o d e l t ap o r t i o n
red,
calcareous
mudstones
intercalated
sandstone and s i l t s t o n e beds.
of
t h el a c u s t r i n e
of t h e
and
consist
with
t h ifn
ine-
Of
The h i s h l yc a l c a r e o u sn a t u r e
sediments i n d i c a t e s a closedlake
system.
The c h a r a c t e r i s t i c s of t h e l a c u s t r i n e b a s i n - c e n t e r d e p o s i t s ,
if
any
were
present', i s not known, ' a se r o s i o n a ls t r i p p i n g
f o l l o w i n gl a t eT e r t i a r yu p l i f t
removed
all
but
the
of the ColoradoPlateauhas
marginal
" r e g i o n a l "p a l e o c u r r e n td i r e c t i o n
to
be
towards
i n thestudyareaappears
northeast;
the eastward-directed
the
no r t i o n
p a l e o c u r r e n t s i n t heea s t e r p
probably
resulted
The
l a c u s t r i ndee p o s i t s .
from
monocline i n t h a t a r e a .
flow
of
deflection
t hset u dayr e a
by
a
Laramide
214
transition
i s l o c a t e di nt h e
The s t u d ya r e a
zone
between t h e C o l o r a d o P l a t e a u t o t h e n o r t h and t h e R i o Grande
rift system t o t h e southeast.Threeepisodes
development
have
modified
t ha er e a .
of
p o o rdl y
efined
A
monoclinal f l e x u r e of.probable
Laramide
age
the
normal f a u l t s a n da s s o c i a t e dd r a gf o l d s
common
Neogene
time
Neogene
North-trending
are
andwereproducedby
uplift
extension.
Epeirogenic
in
present
and mafic dikes
i n the eastern p a r t of t h e a r e a
P l a t e aduu r i n g
is
of the s t u d y area.
s o u t h e a s t e r np o r t i o n
structural
resulted
of
Colorado
the
i tnh e
southward
t i l t i n g of s t r a t a i n t h e r e g i o n .
Baca conglomerates i n t h e s t u d y a r e a
range
of
exhibit a
wide
of
c l al istth o l o g i ei ns c
, l u d i(onirg
nd e r
decreasing
abundance)
metaquartzite,
limestone,
chert,
siltstone,
g r a n i t es a
, n d s t o naen d ,
s c h i sm
t ,u d s t o n e ,
and
v o l c a n irco c k sC. o n g l o m e r a tcel a s tasrhei g h lsyp h e r i c a l
andusually
w e l l rounded.
t h e s t u d ya r e a
and
The m a j o r i t y o f t h e s a n d s t o n e s i n
are l i t h i c a r k o s e s , f e l d s p a t h i c l i t h a r e n i t e s ,
sublitharenites.
Two g e n e t i cq u a r t zt y p e s ,
.
common and
metamorphic q u a r t za,rpe r e s e nitsnu b e q u apl r o p o r t i o n s .
Orthoclase
is
the
most
common f e l d s p atry p ef,o l l o w e d
m i c r o c l i n e and p l a g i o c l a s e .
in
Rock f r a g m e n tv a r i e t i e s ,
by
listed
order
decreasing
of
abundance,
include
metamorphic,
chert,
mudstone,
sandstone
and
siltstone
g r a n i t e / g n evios sl c, acnai rcb, o n a t e ,
rock fragments.
Upsection
changes
215
in sandstone
mineralogy
indicate
increasing
contributions
Precamhrianplutonicandmetamorphicterranes,at
expense
of
'
by
the
sedimentary
sources,
during
basal
Baca
sedimentation.ThedominantsourceareasfortheBaca
Formation in
the
western flank
whichliesto
exhibit
study
area
were
the
Morenci
uplift
and
the
of that portion of the Sierra-Sandia uplift
the
southof
the
area.Bacasandstones
two distinct heavy-mineral suites. The first is
associated
with
red
sandstones
and
consists
predominantly
of
magnetite/ilmenite/specular hematite. Non-red (yellow-gray)
Baca sandstones, on the otherhand, contain a heavy-mineral
suite which is dominated by leucoxene. Subordinate amounts
e
of zircon, garnet, apatite,
'biotite, andmuscoviteare
present in both of these suites. The anomalous heavymineral
suite
in
the
non-red
sandstones
was
produced
through
interaction with negative-Eh groundwaters associated with
dike emplacement and dolomite cementation during Miocene
time. Illite
study
is the dominant detrital clay mineral in the
area.
FourtypesofcementarepresentintheBaca
sedimentsin
the
studyarea.Theseare,inorderof
decreasing
abundance,
calcite,
kaolinite,
quartz,
and
.
dolomite. Calcite cements,
and coarse-grained spar, were
0
in the form of caliche, finethe
first to precipitate.
These formed during very shallow burial or within the
216
l a c u s t r i n e environment.
Quartz
form
and,
is
as
cements
were
next
to
cements, a r e
the
case.
with
subsequent
restrictedtopermeableupper-delta
the
and
b r a i d e da l l u v i a l -
plain
sandstones.
Authigenic
quartz
content
increases
at
t h e top of t h e Baca s t r a t i g r a p h i cs e c t i o n ,i n d i c a t i n gt h a t
much
of
t h es i l i c a
units.
volcanic
Kaolinite
and
precipitation,
probably i derived from overlying
was
cements
a rien d i c a t i v e
of
followed
quartz
a c i d i c groundwater
~
conditions.
Dolomite
occurring as
e '
precipitated
d u r i n gd i k ei n t r u s i o ni n
limonite
to
coloration i n t h e Baca.
the
Baca
is
limonite,
from
which a r e n e a r
alkaline
mafic
groundwaters '
Miocene time.Recentoxidation
is
of
t h e predominant source of
yellow
The widespread
red
produced
dissolution of u n s t a b l e
usually
of k a o l i n i t e and c a l c i t e .
i n permeablesandstones
and
was
dolomite
cement,
tfh
i ne a l
a replacement product
I t onlyoccurs
dikes,
was
by
coloration
in
e a r l y - d i a g e n e ti n
ctrastratal
heavy
m i n e r a l sp, r e c i p i t a t i o n
and subsequentdehydration
of l i m o n i t et o
of
produce
t h e hematite colorant.
Uranium i s t h o
e nly
resource
in
the
Baca.
known
economically
important
.The Hook Ranch uranium p r o s p e c t ' i s
present i n a d e l t a i c sandstone u n i t i n t h ee a s t e r np o r t i o n
of
study
the
area.
dominantlygray
a
debris.
The
i nc o l o r
mineralized
sandstones
are
and contain
abundantcarbonaceous
Uranium e x p l o r a t i o ne f f o r t sw i t h i nt h e
Baca i n t h e
217
Gallinas Mountains vicinity should be restricted to
sandstones which
are
non-red
indicative of the former presence of
reducing groundwaters, and areas which contain anomalously
high concentrations of carbonaceous materials.
APPENDIX A
Baca Formation
Measured Section
EGplanation
of Symbols
Structures
SedimentaryBioturbation
h 4
TI-
roots
JJ11/1
l a cmr iop
nsp
astl ieo n
///////
burrows
u
trough crossbedding
Lithology
OoOe conglomerate
0
....... . . sandstone
*
.
.
a
*
-- mudstone
c
"
tabular
crossbedding
,
219
SEDIMENTARY
STRUCTURES
AND TEXTURES
BASIC
ROCK
TYPE
GRAIN S I Z E
zran
css
fss silt clav
" -
I i \I
i
i
i
I I
I t
220
SEDIMENTARY
STRUCTURES
BASIC
ROCK
TYPE
cl
0
U
GRAIN SIZE
eran
css
fss silt clav
"_ -- 5 R %
""
"
"
"
"
"
"
. . ....-I
L
I
!
I
!
! \ I
~
................
,.-.. ... ,.._ IDYR%
~ : .'..*
* .
:"
*
I
REMARKS
221
SEDIMENTARY
STRUCTURES
GRAIN S I Z E
BASIC
ROCK
TYPE
REMARKS
222
SEDIMENTARY
STRUCTURES
AND TEXTURES
BASIC
ROCK
TYPE
REMARKS
GRAIN S I Z E
gran
css
fss s i l t clay
I
- .. .
. . .. ......
. .. , _ .
. .-.:
.
. * .... .
. ...*.. ... .
.I.
~
. .-
.- . .
.....
.. . ..- .
e
e
.
.- . .-. . .
. .. . .- .(
.~
I I Ii
iI-”
I
.....
-. - .. .. .
:
I
!
I
I
\ I
.”
”
-. ... .. ... ..
... .. . .. ..
. . .
”
”
-
”
” -
e
-
223
SEDIMENTARY
STRUCTURES
AND TEXTURES
BASIC
ROCK
TYPE
REMARKS
GRAIN SIZE
gran
css
fss silt clay
I
1
i
SEDIMENTARY
STRUCTURES
"I
I
I -L
I
i
SEDIMENTARY
STRUCTURES
GRAIN SIZE
BASIC
ROCK
TYPE
c
225
REMARKS
226
SEDIMENTARY
STRUCTURES
BASIC
ROCK
TYPE
cf
0
V
GRAIN SIZE
gran
css
fss silt clav
1
e
75
I
i
227
SEDIMENTARY
STRUCTURES
AND TEXTURES
GRAIN S I Z E
a
850
a00
BASIC
ROCK
TYPE
REMARKS
228
I
SEDIMENTARY
STRUCTURES .
AND TEXTURES
I
APPENDIX E
Summary of Point-count Data for Study-area Sandstone Thin Sections
N
N
W
I
APPENDIX B (continued)
N
W
0
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\
Rocky Mountain
N. Mex. Geol.
VITA
Steven
Martin
b oirnn
A f t egr r a d u a t i n g
Cather.
High
School
in
Woodland
Hills,
from
s t u d i e isn
migrated
to
e n r o l l e da s
e
MiningandTechnology
employed
Kerr-McGee.
in
of
Mexico
a t New
i nS o c o r r o .
University
two
short-term
uranium
geology
jobs
with
Texas
For the
May, 1976.
his
t h e g r a d u a t es c h o o l
a t Austin.
Master of A r t s d e g r e ieg
neology,
he w a s
graduation,
Oil And Minerals,Inc.
CorporationandHouston
of
of
Institute
There he graduated w i t h a
y e af o
r llowing
h ee n t e r e d
he
New Mexico, where he w a s
the
I n September,
1977,
his
Angeles,
Los
B a c h e l o ro fS c i e n c ed e g r e ei ng e o l o g yi n
m a j o r i toyf
entered
he
the i n t e n t of
hinterlands
a t r a n s f e rs t u d e n t
Real
and
began
overpopulated
madness
of
the
Camino
El
geology.
In
June,'
1974,
with
the
Nuys,
Eugeneand
California,
California
State
University
aN
t orthridge
escaping
Van
on J u l y 25, 1953, t h e son ofFranklin
California
Betty
Joel
was
Cather
the
at
While working
towards
he
was
employed
the
as
a
t e a c h i n g a s s i s t a n t by t h e DepartmentofGeologicalSciences.
H e i s p r e s e n t l y employed by t h e New MexicoBureau
andMineral
I
*
Mines
Resources.
Permanent address:
T h i st h e s i s
of
111 Clancy, T r u t h o r Conseqences, 'N.
w a s typedbySteveCatheron
computer a t NMIMT.
the
M.
DECsystem-20