0
OF-
GEOLOGY OFTHE
CORKSCREW CANYON
SOCORRO
COUNTY,
--
ABBE'SPRT-YG
AREA,
ABBE'SPRT-.G
AREA,
NEW MEXICO
by
D a v i d L. Mayerson
.
Submitted i n P a r t i a l F u l f i l l m e n t
of t h e R e q u i r e m e n t s f o r t h e D e g r e e
Master of Science i n G e o l o g y
Of
N e w Mexico I n s t i t u t e of Mining and Technology
Socorro, N e w Mexico .
J u l y , 1979
CONTENTS
-
-,
Page
Abstract
vi
Introduction
P u r p o s eo ft h eI n v e s t i g a t i o n
Location
Access
M e t h o d so fI n v e s t i g a t i o n
. P r e v i o u sI n v e s t i g a t i o n s
Acknowledgments
Stratigraphy
Triassic
C h i n l eF o r m a t i o n
Upper C r e t a c e o u s
Dakota Sandstone
Mancos S h a l e
AlamitoWelltongue
Tres Hermanos S a n d s t o n e Member
D-CrossTongue
G a l l e g oS a n d s t o n e
MesaverdeFormation
Tertiary
BacaFormation
Spears Formation
H e l l s Mesa T u f f
A-L P e a k T u f f
Gray-massive member
P i n n a c l e s member
La J a r a P e a k B a s a l t i c A n d e s i t e
P o p o t o s a Formation
T e r t i a r y M a f i cI n t r u s i v e s
Plio-PleistoceneandHolocene.deposits
19
20
23
27
30
36
45
45
54
60
62
63
64
66
69
74
77
Structure
Regional
Local
Folding
Faulting
T r a n s v e r s es t r u c t u r a lz o n e s
79
82
82
89
92
7
7
12
12
EconomicGeology
Uranium
Coal
O i l andGas
Other
99
103
106
107
Conclusions
108
ii
-
Page
References cited
112
Appendices
120
.*
iii
5
. o
PLATES
.-.
Page
--
Geology of t h e CorkscrewCanyon
N e w Mexico
a r e a ,S o c o r r oC o u n t y ,
Abbe S p r i n g
pocket
FIGURES
1.
R e l a t i o no fs t u d ya r e a( r u l e d )t oa d 2 a c e n ta n d
n e a r b yt h e s i sa r e a s .
2.
C h a n n e ls a n d s t o n e si n ' t h e
3.
S l i c k e ' n s i d e sa l o n g
D a k o t aS a n d s t o n e
6
C h i n l e Formation
18
a faultcuttingthe
14
4.
Wood c a s t s i n t h e D a k o t a S a n d s t o n e
16
5.
C o n c r e t i o n si nt h e
29
6.
Lopha s a n n i o n i sf r o mG a l l e g oS a n d s t o n e" b r o w n
bed"
34
ContactbetweentheBacaandMesaverde
formations
39
Cross-stratified
Formation
42
7.
8.
9.
10.
D-Cross S h a l e
"brownbed"
i n Mesaverde
G r a d a t i o n a lc o n t a c tb e t w e e nS p e a r sa n d
formations
Baca
L a r g e - s c a l e ,t a n g e n t i a lc r o s s - s t r a t i f i c a t i o n
t h sea nodfs t o n e
Baca Formation
49
in
Baca F o r m a t ~ i o n
51
11.
C o n g l o m e rw
a tiet lhoi w
n er
12.
Mudflows i n ltohw
S
e pe reFaor sr m a t i o n
13.
Thin,fining-upwardbeds
14.
R e g i o n satlr u c t u r sael t t i n g
15.
View a l o n g f a u l t p l a n e w i t h i n t h e D a k o t a
Sandstone
9C3
Map s h o w i n gg e n e r a l i z e dd o m a i n s
s t r i k e and d i p
94
16.
11.
57
i n P o p o t o s aF o r m a t i o n
o f s t u da yr e a
Puertecito f a u l t
52
73
83
of c o n t r a s t i n g
96
iv
posits
Page
18.
Stratigraphic intervals favorable for coal and
uranium
100
TABLES
Table 1:
Uranium analyses
101
Table
analysis
2:
Coal
104
APPENDICES
Appendix I:
Definitions of descriptive sedimentary
terms
in
used
.text
120
Appendix 11: Petrography of the sedimentary formations
A: Definitions
codes’
and
121
B: data
Petrographic
123
V
.
D
Abstract
L i t h o l o g i c a n dp a l e o n t o l o g i ce v i d e n c es u g g e s t st h a t
t w om a j o rt r a n s g r e s s i v e - r e g r e s s i v em a r i n ec y c l e sa r e
p r e s e r v e di n
t h e C r e t a c e o u sr o c k s
u n i t si n c l u d e di n
of t h es t u d ya r e a .
t h e s e c y c l e s are t h eD a k o t aS a n d s t o n et ol o w e r
T r e s Hermanos Sandstoneand
t h e u p p e rT r e s ’ Hermanos
S a n d s t o n et ol o w e r m o s tM e s a v e r d eF o r m a t i o n .
Formation is g r a d a t i o n a l l y o v e r l a i n
Formation w h i c h i n d i c a t e s t h a t
The EoceneBaca
by t h e O l i g o c e n e S p e a r s
t h e s t u d ya r e a
is s i t u a t e d w i t h i n a n
time.
a r e ao fc o n t i n u a ld e p o s i t i o nf r o mB a c ai n t oS p e a r s
t u f f s i n t h e s t u d ya r e a
a r e thin;twoofthem
r e l a t i o n s h i p s w i t h u n d e r l y i n gu n i t s
t h e s o u t h .T h e s eo b s e r v a t i o n s
s o u r c ec a u l d r o n s ,
The
Ash-flow
e x h i b i t unconformable
t h a t a r e n o to b s e r v e dt o
r e f l e c t t h e d i s t a n c e from
and p o s s i b l y t h e i n f l u e n c eo ft h eT i j e r a s
lineament.
The broad Abbe S p r i n g a n t i c l i n e i n c o r p o r a t e s r o c k s
a s . y o u n g a s . t h e MesaverdeFormationandwasprobablyformed
b yL a r a m i d ec o m p r e s s i o n a lt e c t o n i c s .E x t e n s i o n a lf a u l t i n g ,
b e g i n n i n gl o c a l l yb e t w e e n
2 8 and 3 2 m.y.
w i t h numerousdown-to-the-westnormalfaults.
f a u l t s w e r ei n t r u d e d
by m a f i cd i k e s .F a u l t s
B.P.,
b r o k et h ea r e a
Many of t h e
with greater
t h a n 5 0 0 f t (152.4 m ) of v e r t i c a l d i s p l a c e m e n t a r e p a r a l l e l e d
on t h e i r downthrown s i d e s by axes of n a r r o w a n t i c l i n e s .
These f o l d s a r e m o s t l i k e l y
effects.
attributable toreversedrag
Late O l i g o c e n e - e a r l yM i o c e n eb l o c kf a u l t i n gc a u s e d
vi
5
t h eP u e r t e c i t of a u l ts y s t e m
t h eM u l l i g a n
w h i c h i s t h e we'ste'rjborderof
G u l c h g r a b e n .A c t i v a t i o no f
.
a transverse
s t r u c t u r a lz o n e ,t h eT i - j e r a sl i n e a m e n t ,d u r i n ge x t e n s i o n a l
on many of t h e e x t e n s i o n a l
f a u l t i n ga b s o r b e dd i s p l a c e m e n t
f a u l t s , and l o c a l l yc a u s e dr e v e r s a l so f
structural dips.
Mulligan Gulch graben is a l s o o f f s e t t o t h e
The
west i n two
l o c a t i o n s by t h i s t r a n s v e r s e s t r u c t u r a l z o n e .
D i s c o n t i n u o u sc o a l
and t h et o p
s a n d s t o n e so f
beds o c c u ra tb o t ht h eb o t t o m
of theMesaverdeFormation.Coarse-grained
t h e BacaFormation
m a t e r i a la n du r a n i u mm i n e r a l i z a t i o n .
h a v eb e e nl o c a l l yd e v e l o p e d
l o c a l l yc o n t a i nc a r b o n a c e o u s
B o t h o f these r e s o u r c e s
on a s m a l l s c a l e .
.
vii
Introductlcn
P u r p o s eo ft h eI n v e s t i g a t i o n
The o b j e c t i v e s o f
this' investigation are to
d e t e r m i n e t h e s t r u c t u r a l and s t r a t i g r a p h i c r e l a t i a n s h i p s i n
theCorkscrew
Mexico.
Canyon
--
Abbe S p r i n g a r e a , S o c o r r o C o u n t y ,
T h e s e r e l a t i o n s h i p sa r ei m p o r t a n t
New
for t h e following
reasons:
1. The a r e a i s l o c a t e da l o n gt h e - p o o + l y - d e f i n e db u t
common m a r g i n s of t h e C o l o r a d o P l a t e a u , R i o G r a n d e
t h e r i f t , a n dt h eD a t i l - M o g o l l o nv o l c a n i c
field.
Structuralandstratigraphicdatadevelopedin
t h i s study w i l l helptodeciphertheorigin
e v o l u t i o no ft h e s em a j o rt e c t o n i c
and
andmagmatic
features.
2. The area i s l o c a t e da l o n ga no u t c r o p
C r e t a c e o u sa n dE o c e n ef o r m a t i o n s
p o t e n t i a lf o rc o a l
drilled inthe
area.
oil and g a s p o t e n t i a l r e q u i r e s
d e t a i l. e. .d s t ..r a t i g r a p h i c
"
t h a t have
a n du r a n i u mr e s o u r c e s .
3 . O i l t e s t s h a v e r e c e n t l yb e e n
E v a l u a t i o no ft h e
b e l t of
and s t r u c t u r a l s t u d i e s .
4 . Mapping of t h i s area will p r o v i d e a l i n k b e t w e e n
s t u d i e s i n t h e a d j a c e n t Bear a n d G a l l i n a s
mountains.
Location
The s t u d y a r e a
northwestofMagdalena,
i s l o c a t e da b o u t1 5
m i ( 2 4 . 1 km)
New M e x i c o ,w i t h i nt h eb r o a ds a d d l e
b e t w e e nt h en o r t h - n o r t h w e s t - t r e n d i n gB e a rM o u n t a i n st ot h e
e a s t a n dt h en o r t h w e s t - t r e n d i n gG a l l i n a sM o u n t a i n st ot h e
west.
T h e s t u d ya r e a
of t h eR i oG r a n d er i f t
i s on t h em a r g i n
a n dw i t h i nt h eb o u n d a r ya r e ab e t w e e nt h eD a t i l - M o g o l l o n
A l l b u tt h e
v o l c a n i cf i e l da n dt h eC o l o r a d oP l a t e a u .
i s i n c l u d e dw i t h i nt h e
n o r t h e a s t e r nc o r n e ro ft h es t u d ya r e a
I n d i a nS p r i n g
Canyon7.5-minutequadrangle.
c o r n e re x t e n d si n t ot h e
Major a r r o y o s
--
The northeastern
Mesa C e n c e r r o7 . 5 - m i n u t eq u a d r a n g l e .
J a r a l o s a C r e e k , ChavezCreek,and
Abbe
S p r i n g Canyon -- d r a i n n o r t h w a r d i n t o t h e R i o S a l a d o w h i c h
d r a i n se a s t w a r di n t ot h eR i oG r a n d e .F a u l t - c o n t r o l l e d
springs
--
among t h e mB i r dS p r i n g
(sec. 9 , T l N , R5W), Abbe
S p r i n g (sec. 8 , T l N , RSW), Montoya S p r i n g( s e c .
(sec. 2 3 , T l N , R6W)
andReidSpring
--
2 , T l N , R6W),
f l o wy e a r - r o u n d .
Access
Main a c c e s s r o u t e s
i n t o t h es t u d ya r e aa r eb y
.
w h i c hl e a v e s
which l e a v e s US 60 a t t h e w e s t e r n e d g e
F o r e s t Road 1 2 3 ,
of Magdalena.The
tracksprovide
1.5 m i (2.4
NM 5 2 ,
of Magdalena,andby
N M 5 2 t e n miles (16.1 km) n o r t h
d r y bed of J a r a l o s a Creek and many d i r t
access by f o u r - w h e e l - d r i v e v e h i c l e t o w i t h i n
k m ) o fn e a r l ye v e r yp o i n t
A l m o s tt h r e e - q u a r t e r s
of t h e s t u d y a r e a
i n t h es t u d ya r e a .
i s p r i v a t e l y owned.
?3
’
.
.
S e c t i o n s 11, 1 2 , 1 4 , a n dt h en o r t h e r nh a l f
arecontrolled
Methodsof
by t h e Alamo T r i b a l C o u n c i l .
Investigation
t h e s t u d y area was mapped on
The s u r f a c e g e o l o g y o f
U.S.
o f 1 3 ( T l N , R6W)
G e o l o g i c a lS u r v e yt o p o g r a p h i cm a p so fI n d i a nS p r i n g s
Canyonand
Mesa C e n c e r r o {1:24,000) d u r i n g t h e s u m m e r and
f a l l monthsof1977.
v o l c a n i cr o c k s
Two s m a l l ,c o m p l e xa r e a su n d e r l a i n
by
were mapped on e n l a r g m e n t s (1:12,000) o ft h e s e
m a p s ,a n dw e r es u b s e q u e n t l ys i m p l i f i e di nr e d u c t i o n .
from
B l a c k - a n d - w h i t ea n dc o l o ra e r i a lp h o t o g r a p h s( 1 : 3 1 , 6 8 0 )
t h e U.S.
F o r e s tS e r v i c e
were u t i l i z e d a s g u i d e s t o t h e
l o c a t i o n and c o n f i g u r a t i o n o f o u t c r o p s a n d
T w e n t y - e i g h tt h i ns e c t i o n sw e r e
samplesof
area.
structures.
made fromrock
t h e s a n d s t o n ea n dv o l c a n i cu n i t si nt h es t u d y
T h e s e wereexaminedusing
a Zeiss b i n o c u l a r
p e t r o g r a p h i cm i c r o s c o p e .P o i n tc o u n t so fa p p r o x i m a t e l y
500
g r a i n s per s l i d e were made o f t h e s e d i m e n t a r y u n i t s
using a
S w i f t pointcounter
w i t h a g r i ds p a c i n go f
P a r e n t h e t i c a lr e f e r e n c e si n
d e s c r i p t i o n si nA p p e n d i x
1 mm by 1 mm.
t h e t e x t refer t op e t r o g r a p h i c
11.
Modal c o m p o s i t i o n so ft h e
v o l c a n i c ’ r o c k s were estimated v i s u a l l y .
PreviousInvestigations
T h i s s t u d yr e p r e s e n t st h e
mappingof
t h e Corkscrew Canyon
f i r s t c o m p r e h e n s i v eg e o l o g i c
--
Abbe S p r i n g area u t i l i z i n g
D
4
"l
.
. a
.
r e c e n ta d v a n c e si nt h es t r a t i g r a p h yo fC r e t a c e o u ss e d i m e n t a r y
r o c k sa n dT e r t i a r yv o l c a n i cr o c k s .H e r r i c k
firstgeologicinvestigationof
S a l a d o ,t h e nc a l l e d
( 1 9 0 0 ) made t h e
t h e a r e aa l o n gt h eR i o
AlamosaCreek,
i n w h i c hh ed e s c r i b e dt h e
the first
C r e t a c e o u sr o c k sW
. i n c h e s t e (r 1 9 2 8 p
) roduced
g e o g r a p h i ca n dg e o l o g i c
a s c a l e o f 1:125,000.
"Red Beds"and
map w h i c h i n c l u d e d t h e s t u d y a r e a a t
D a r t o n ' s (1928) s t u d y of New Mexico's
a s s o c i a t e df o r m a t i o n si n c l u d e s
a geologic
d e s c r i p t i o n a n d a sketch.mapwhichencompassedpart
s t u d ya r e aT
. o n k i n g( 1 9 5 7 p
) ublished
of t h e
a reconnaissance
g e o l o g i c map a n d r e p o r t o f t h e P u e r t e c i t o 1 5 - m i n u t e
quadrangle;
H i s s t u d y ,w h i c h
was e x c e l l e n tf o r
its time,
r e f e r r e dt ot h eC r e t a c e o u ss t r a t ab e t w e e nt h eD a k o t a .
as t h e
S a n d s t o n ea n dt h eM e s a v e r d eF o r m a t i o no ft h i sr e p o r t
L a CruzPeakFormationoftheMesaverdeGroup.Current
w o r k e r sh a v ea b a n d o n e dt h i st e r m i n o l o g ya n dr e c o g n i z et h r e e
t o n g u e s or members o f t h e
G a l l e g oS a n d s t o n e
Mancos S h a l e o v e r l a i n
(Hook, 1 9 7 7 , o r a l commun..)..
l o gt h r o u g ht h es t u d ya r e ab a s e d
by t h e
A
was
u p o nT o n k i n g ' sr e p o r t
p u b l i s h e d by Weber a n d W i l l a r d( 1 9 6 3 ) S
. nyder
(1971),
t h e Baca
J o h n s o n( 1 9 7 8 ) ,a n dC a t h e r( i np r e p . )h a v es t u d i e d
F o r m a t i o n ,i n c l u d i n ge x p o s u r e s
field^ t r i p
i n t h es t u d ya r e a .
( 1 9 7 2 ) , Simon ( 1 9 7 3 ) ,a n dC h a m b e r l i n
Brown
( 1 9 7 4 ) h a v es t u d i e dt h e
v o l c a n i c rocks n o r t h . a n d- n o r t h w e s to fM a g d a l e n a .
A composite
s t r a t i g r a p h i c c o l u m no fv o l c a n i cr o c k si nt h e
S o c o r r o - M a g d a l e n aa r e ah a sb e e np u b l i s h e d
o t h e r s( 1 9 7 8 ) .
A p r e l i m i n a r yr e p o r t
by Chapinand
on t h ec o a l ,
uranium,
and o i l a n d g a s p o t e n t i a l
of t h e R i l e y - P u e r t e c i t o a r e a h a s
on open f i l e by Chapin and o t h e r s ( 1 9 7 9 ) .
beenplaced
1 shows t h e l o c a t i o n
Figure
to
and r e l a t i o n s h i p o f t h e s t u d y a r e a
i n the vicinity.
o t h e rs t u d i e s
Acknowledgments
of
I would l i k e t o a c k n o w l e d g e t h e c o n t r i b u t i o n s
some o f t h e
many i n d i v i d u a l s who h a v eh e l p e d
i n thisstudy.
Dr. Gary' M a s s i n g i l l p r o v i d e d e a r l y h e l p o n t h e s t r a t i g r a p h y
of my t h e s i s a r e a .
Dr. S t e p h e n Hook p r o v i d e dp a l e o n t o l o g i c a l
i d e n t i f i c a t i o n sf o rt h i sp r o j e c t .
The Alamo T r i b a lC o u n c i l
Drs. J o h n MacMillan and
a l l o w e da c c e s st or e s e r v a t i o nl a n d s .
ClaySmithservedon
my t h e s i s c o m m i t t e e a n d c r i t i c a l l y r e a d
the manuscript.
A s p e c i a lt h a n k s
who s e r v e d a s
i s e x t e n d e dt o
my t h e s i s a d v i s o r
Dr.
C h a r l e sC h a p i n
a n ds u p p l i e dh e l p
t h r o u g h o u tt h es t u d y .O t h e ri n d i v i d u a l s
and i d e a s
who made major
. c o n t r i b u t i o n s t o t h e success of t h i s p r o j e c t i n c l u d e d R o b e r t
A.
Jackson,Glenn
R.
O s b u r n ,a n dJ u d i t h
Raymond.
Funding f o r t h i s p r o j e c t was p r o v i d e d by a g r a n t
f r o mt h e
N e w MexicoEnergy
ofMiningandTechnology.
I n s t i t u t e a t N e w Mexico I n s t i t u t e
Some f i e l dt r a n s p o r t a t i o n
p r o v i d e d by t h e N e w MexicoBureauofMines'andMineral
Resources.
was
ooo'o~z I
f
9
31V3S
'
52
7
..+
Stratigraphy
Triassic
C h i n l eF o r m a t i o n
Winchester ( 1 9 2 0 ) made r e f e r e n c e t o
w h i c h w h i c h were
which h eb e l i e v e dt ob eo fT r i a s s i ca g ea n d
u n c o n f o r m a b l yo v e r l a i n
referredto
"Red Beds"
by t h eD a k o t aS a n d s t o n e .W e l l s
(1919)
these r o c k s a t e x p o s u r e s n e a r P u e r t e c i t o
P u e r t e c i t oF o r m a t i o n ,b u tD a r t o n( 1 9 2 8 )b e l i e v e d
o b s e r v a t i o n would r e v e a l c o r r e l a t i o n b e t w e e n
T r i a s s i c r o c k sr e c o g n i z e di n
firstcalledthese
as t h e
t h a t careful
t h e s e r o c k s and
t h e Zuni u p l i f t .T o n k i n g( 1 9 5 7 )
b e d s t h e C h i n l eF o r m a t i o n ,t h e
name g i v e n
Triassic rocks i n Chinle
by Gregory(1917)
t oe x p o s u r e so f
V a l l e y ,A r i z o n a .
The C h i n l eF o r m a t i o ne x p o s e di nt h es t u d y
a r e a i s p r o b a b l yT o n k i n g ' su p p e rs i l t s t o n e - s h a l e
w h i c hh ea s c r i b e d
a maximum t h i c k n e s s o f
C o l b e r ta n dG r e g o r y( i n
unit, to
2 0 0 f t (61 m ) .
Reeside a n do t h e r s ,1 9 5 7 )r e p 0 r t . a
middle Upper T r i a s s i c a g e f o r
t h e C h i n l eF o r m a t i o nf r o ml a n d
vertebratefossilsfoundinnorthern
and c e n t r a l New Mexico.
is a
T h e C h i n l eF o r m a t i o ni nt h es t u d ya r e a
s l o p e - f o r m i n gu n i t
composed dominantlyofmaroonand
P e t r i f i e d wood
v a r i e g a t e dm u d s t o n e s ,s i l t s t o n e s ,a n ds h a l e s .
f r a g m e n t sw e r ef o u n di nf l o a t
a t o n el o c a l i t y .
poorlyexposedbeneathhogbacksformed
r e s i s t a n tD a k o t aS a n d s t o n ei n
s t u d ya r e a
(sec. 5 , T l N , R5W).
The C h i n l e is
by t h e o v e r l y i n g
t h e n o r t h e a s t e r n p a r t of t h e
The maximum t h i c k n e s so ft h e
8
1
7
C h i n l ee x p o s e d
i n t h es t u d ya r e a
is a b o u t1 2 0
o c c u r s on t h e w e s t - f a c i n g s l o p e o f h i l l
1/4,
-
. *
f t (36.6 m ) and
"6687." (E 1/2, NW
sec. 5 ) .
is poorly
The u p p e rc o n t a c to ft h eC h i n l eF o r m a t i o n
exposeddue
t o slumpingofblocksofDakotaSandstone
f o l l o w i n ge r o s i o no ft h eu n d e r l y i n gC h i n l es i l t s t o n e s .
Where
i s scouredanderoded.
exposed, t h e t o po ft h eC h i n l e
uppermostChinleFormationvariesfrom
The
a very-dark-red
(5R2/6) s i l t s t o n e i n t h en o r t h e r n m o s te x p o s u r e st o
dark-gray
a
o r a l i g h t - g r a y (N7), w e a t h e r i n g
(N3) s i l t y s h a l e
t od a r k - y e l l o w i s h - o r a n g e( l f l Y R 6 / 6 ) ,s i l t s t o n ei n
the
s o u t h e r n m o s et x p o s u r e s A
. n g u l a ru n c o n f o r m i t yw i t ht h e
o v e r l y i n gD a k o t aS a n d s t o n e
(Givens, 1957).
e v i d e n t on a r e g i o n a l s c a l e
The C h i n l e F o r m a t i o n
(5R3/4) t ov e r y - d a r k - r e d
it is
is n o to b v i o u s ,a l t h o u g h
i s d o m i n a n t l yd u s k y - r e d
(5R2/6) c a l c a r e o u ss i l t s t o n e s
t h i n l yl a m i n a t e ds i l t ys h a l e s .
and
T h e s e r o c k sa r eo f t e n
v a r i e g a t e d i n s h a d e s . .o.f r.e.d. a n d . l i g h t ~ . g r a y . . T h i s . v a r i e g a t i o n
i s e s p e c i a l l yp r o m i n e n ti nn o d u l a rb e d s
t o 18.2-cm)
thick.
(3.8-
The n o d u l e s a r e v e r yc a l c a r e o u sa n d
e l l i p s o i d a l ,w i t ha na v e r a g el o n gd i a m e t e ro f
cm).
1.5- t o 4 - i n .
They r a n g ei nc o l o r
f r o mv e r yd a r k
1.5
i n . (3.8
red (5R2/6)through
l i g h t g r a y( N 7 ) .
A f e wt h i n - b e d d e dl i m e s t o n e so c c u rn e a rt h et o po f
t h eC h i n l eF o r m a t i o n .T h e s el i m e s t o n e sa r e
commonly g r a y i s h
r e d ( 1 0 R 4 / 2 )a n dm o t t l e db yc a l c a r e o u sa r e a so fp a l eg r e e n
(5G7/2).
A t y p i c a ll i m e s t o n e
(Trc-1) c o n s i s t so f2 5 %
silt
9
.->
0
_.
g r a i n s , 4 5 %m i c r o s p a r ,a n d3 0 %h e m a t i t i c - l i m o n i t i cs t a i n e d
c l a y s .P o r o s i t y
i s e s s e n t i a l l ya b s e n td u et oi n f i l l i n g
i s bimodal.
b l o c k yc a l c i t ec e m e n t .G r a i n - s i z ed i s t r i b u t i o n
Onemode
by
h a sa na v e r a g ea p p a r e n tg r a i nd i a m e t e r
mm
of0.05
I
and i s c o m p r i s e do fw e l l - s o r t e d ,s u b a n g u l a r ,e l o n g a t et o
i n t e r m e d i a t e ,r u f i l a t e dq u a r t zw i t hu n d u l o s ee x t i n c t i o n
s l i g h t l ys e r i c i t i z e dp o t a s s i u mf e l d s p a r .
and
The o t h e r mode,
w h i c hc o m p r i s e s8 5 %o ft h ed e t r i t a lc o m p o n e n t s ,h a sa n
0 . 6 mm.
a v e r a g ea p p a r e n tg r a i nd i a m e t e ro f
I t i s comprised
p r i m a r i l yo fm u d s t o n ea n dh e m a t i t i cm u d s t o n ef r a g m e n t s .T h e
mudstonefragmentsrange
i n s i z e from 0 . 2 mm t o 1 . 5
mm, and
are g e n e r a l l ys u b a n g u l a ra n de l o n g a t ei ns h a p e .T h e ya r e
composed o f 6 5 % c l a y m i n e r a l s ( w i t h
as much a s 5 % r e p l a c e m e n t
by c h l o r i t e ) ; 2 0 % c l e a r , a n g u l a r q u a r t z g r a i n s w i t h u n d u l o s e
e x t i n c t i o n ; 7 % h e m a t i t e ; 3 % f e l t e dm u s c o v i t er e p l a c i n gc l a y
m i n e r a l s ; 1%a n g u l a r ,s e r i c i t i z e dp o t a s s i u mf e l d s p a r ;a n d
3%
( 1 9 7 9 , o r a l commun.) a s s e r t s
p a t c h yc a l c i t ec e m e n t C
. hapin
thatthemudstonefragments-represent-areas
of a n o r i g i n a l
l i t h o l o g y w h i c h s u b s e q u e n t l y was l a r g e l y c a l c i f i e d .
are
T h r e es t a c k e d ,c h a n n e l - s h a p e ds a n d s t o n eb o d i e s
e x p o s e di nt h et o p
20 f t ( 6 . 1 m ) of t h eC h i n l eF o r m a t i o ni n
L a J a r a Canyon (SW 1 / 4 ,
NW 1/4,
s a n d s t o n e i s m o d e r a t ey e l l o w i s h
t og r a y i s h . o r a n g e
(10YR7/4),
s e c .5 ;f i g .
2).
brown(10YR5/4),
The
weathering
medium g r a i n e d , m o d e r a t e l y
i n d u r a t e d ,a n dc a l c a r e o u s .P e t r o g r a p h i c a l l y
(Trc-2)
,
the
s a n d s t o n e i s p o o r l ys o r t e da n dc o m p r i s e do f3 5 %f r a m e w o r k
g r a i n s , 1 5 %p a t c h yc a l c i t ec e m e n t ,
3 %p o r o s i t y , . a n d 4 7 %
11
5
*
.
-
O
c
m a t r i x .U h t w i n n e d ,p a r t i a l l ys e r i c i t i z e dp o t a s s i u mf e l d s p a r
c o m p r i s e s 4 0 % o ft h ef r a m e w o r kg r a i n s ;q u a r t zc o m p r i s e s
18%
I
of t h e f r a m e w o r kc o m p o n e n t s .P o l y c r y s t a l l i n eq u a r t zg r a i n s
I
are slightly
of m o n o c r y s t a l l i n e ,
m o r ea b u n d a n tt h a ng r a i n s
c l e a rq u a r t zw i t hu n d u l o s ee x t i n c t i o n .
w h i c hc o n s t i t u t e
L i t h i c fragments,
a t l e a s t 2 4 % of t h e frameworkcomponents,
s e r i c i t e and 7 %
a r es o f tm a s s e sc o m p r i s e do f9 3 %c l a y sa n d
s u b a n g u l a rc o r r o d e dp o t a s s i u mf e l d s p a ra n h e d r a .
m a t e r i a lo fc l a y
The m a t r i x
and s e r i c i t e , and a t l e a s t some of t h e
potassiumfeldspar,
may b e d e r i v e d
by d e f o r m a t i o no fm u d s t o n e
l i t h i cf r a g m e n t s O
. t h e rf r a m e w o r kc o m p o n e n t si n c l u d e
s u b r o u n d e d ,s l i g h t l ye l o n g a t ec h e r t1 5 % ) ;r a g g e dm u s c o v i t e
l a t h s ( 4 % ) ; a n df r e s hc a l c i cp l a g i o c l a s e .
T h e p o r t i o n so ft h eC h i n l eF o r m a t i o ne x p o s e di nt h e
s t u d ya r e aa r en o n m a r i n ef l o o a p l a i nd e p o s i t s( T o n k i n g ,1 9 5 7 ) .
T h e n o n m a r i n eo r i g i n
is s u b s t a n t i a t e d by o b s e r v a t i o n s o f
v e r t e b r a t er e m a i n s{ T o n k i n g ,l 9 5 7 ) ,p e t r i f i e d
wood, t h er e d
c o l o ro ft h es e d i m e n t s ,a n dt h ea b s e n c e . o f . m a r i n ef o s s i l s .
Nodularbeds
may r e p r e s e n t a r e a s o f s u b a e r i a l e x p o s u r e t o
d e s i c c a t i n gc o n d i t i o n s( R e i n e c ka n dS i n g h ,1 9 7 5 ) .
Upper C r e t a c e o u s
Dakota Sandstone
T h e D a k o t aS a n d s t o n e ,t h e
name g i v e n by Meek and
Hayden (1862) t o t h eb a s a lC r e t a c e o u ss a n d s t o n eu n i tn e a r
Dakota,Nebraska,
i s now t h e a c c e p t e d i d e n t i t y
C r e t a c e o u ss a n d s t o n ei nc e n t r a l
geologistsin
N e w Mexico.
New Mexicoused
s u f f i x e d q u e r yt oi m p l y
o f t h eb a s a l
Earlier
t h e name "Dakota" w i t h a
t h i s p r o b a b l ec o r r e l a t i o n ,
which r e c e n t l y h a s b e e nd i s c o n t i n u e d T
. onking
a practice
(1957)
o b s e r v e dt h a tt h eD a k o t aS a n d s t o n eu n c o n f o r m a b l yo v e r l i e s
p r o g r e s s i v e l yo l d e r
s t u d ya r e a ,
To t h en o r t ho ft h e
t h e D a k o t aS a n d s t o n eu n c o n f o r m a b l yo v e r l i e s
MorrisonFormation
s t u d ya r e a ,
b e d s southward.
the
of J u r a s s i ca g e .S o u t h w a r d ,i n c l u d i n gt h e
it o v e r l i e s p r o g r e s s i v e l y o l d e r b e d s o f t h e t h e
.Triassic C h i n l eF o r m a t i o n .
Lee ( 1 9 1 5 ) p o s t u l a t e dt h a tt h eb a s a lD a k o t a
S a n d s t o n e was d e p o s i t e d i n
b a s e - l e v e l e ds u r f a c e .
a n e a r s h o r ee n v i r o n m e n to v e r
a
Long p e r i o d s of wave s o r t i n ga n d
reworking of s e d i m e n t sp r o d u c e d
the characteristic
w e l l - s o r t e dq u a r t z o s es a n d s t o n ea n dq u a r t z i t ec o n g l o m e r a t e
which m a k e up t h e D a k o t a t h r o u g h o u t
The D a k o t a S a n d s t o n e i n n o r t h w e s t e r n
f o r m a t i o n of l a t e E a r l y C r e t a c e o u s
ages (Dane
and
Bachman,
1957).
t h e RockyMountainarea.
N e w Mexico is a
and e a r l y L a t e C r e t a c e o u s
I t i s comprisedof
shale,
s a n d s t o n e ,c o n g l o m e r a t i cs a n d s t o n e ,c o n g l o m e r a t e ,a n dc o a l ,
r e p r e s e n t i n gd e p o s i t so fm a r i n e ,m a r g i n a lm a r i n e ,a n d
5
13
-
.
4
c o n t i n e n t a lo r i g i n s .
Young ( 1 9 6 0 ) p r o p o s e dt h ee l e v a t i o n
t h e Dakota t o g r o u p s t a t u s w i t h
two s u b d i v i s i o n s f o r
of
its
o c c u r r e n c e s on t h eC o l o r a d oP l a t e a u :
The D a k o t aS a n d s t o n e
is a r e s i s t a n t ,
well-indurated,.quartzosesandstonewiththinconglomeratic
b e d sa n dl e n s e sw h i c hc o n t a i np e b b l e so fq u a r t z i t ea n d - c h e r t .
I t i s a c l i f f - f o r m i n g u n i t a n dc r o p so u ta s
a s e r i e so f
g e n t l yd i p p i n gh o g b a c k si nt h en o r t h e a s t e r nc o r n e ro f
s t u d ya r e a( s e c s .
5 and 6 , T l N , R 5 W ) .
the
The h o g b a c k sa r e
formed by e i g h td o w n - t o - t h e - w e s ta n dt h r e ed o w n - t o - t h e - e a s t
n o r m a lf a u l t sw h i c hr e p e a tt h eD a k o t aS a n d s t o n ea n dt h et o p
of t h eu n d e r l y i n gC h i n l eF o r m a t i o n .
The l o c a t i o n so ft h e
f a u l t p l a n e s are g e n e r a l l y w e l l - d e f i n e d
by b r e c c i a and
s l i c k e n s i d e s i n t h eb r i t t l eD a k o t aS a n d s t o n e( f i g .3 ) .
D a k o t aS a n d s t o n ei nt h es t u d ya r e a
The
i s e s t i m a t e dt ob ea b o u t
30 f t (9.1 m ) t h i c k .
C h i n l e Formation is
The c o n t a c t w i t h t h e u n d e r l y i n g
poorlyexposedd~ueto
erosion^ o f t h e s o f t C h i n l e s h a l e s a n d
s i l t s t o n e s , and t h e r e s u l t a n t s l u m p i n g
s l u m p b l o c k s a r e m o r ee x t e n s i v et h a n
c l i f ff a c e s .( T h e s e
shownon
ofDakotaSandstone
t h eg e o l o g i c
map; many h a v eb e e no m i t t e dd u et o
l i m i t a t i o n s of s c a l e . ) .
Where e x p o s e d ,t h et o po ft h eC h i n l e
c l e a r l yh a sb e e ne r o d e da n ds c o u r e d :
The b a s eo ft h eD a k o t a
Sandstone i s commonly m a r k e db ya ni r r e g u l a r
cm), y e l l o w i s h - g r a y
0 t o 7 i n . (17.8
( 5 Y 7 / 2 ) , d e e p l yw e a t h e r e dc o n g l o m e r a t i c
s a n d s t o n e ,c o n t a i n i n gw e l l - r o u n d e dg r a ya n dw h i t eq u a r t z i t e
and c h e r tp e b b l e s
are
a n d2 - i n .( 5 . l . c m ) - l o n gw h i t es i l t s t o n e
I
Figure 3:
S l i c k e n s i d e sa l o n g a f a u l t c u t t i n gt h eD a k o t a
S a n d s t o n e ; Abbe S p r i n ga n t i c l i n e
(NW 1/4, SE 1/4,
sec. 5 , TlN, R5W). J a c o b ' ss t a f fg r a d u a t i o n
is 6
i n . (15.2 cm).
15
.
*
#
c h i p sw e a t h e r e da n de r o d e df r o mt h et o po ft h e
1
._
Chinle.
it i s
c o n t a c ta p p e a r st ob ec o n f o r m a b l e ,a l t h o u g h
a r e g i o n a l scale ( G i v e n s , 1 9 5 7 ) .
unconformableon
The
The
c o n t a c t of t h e D a k o t a S a n d s t o n e w i t h t h e o v e r l y i n g A l a m i t o
Mancos S h a l e i s e x p o s e do n l yo nt h e
Well t o n g u eo ft h e
easternslopeofthemostsouthward-extending
(SE 1 / 4 ,
sec. 5 ) .
.Dakotahogback
The c o n t a c t i s p o o r l ye x p o s e d
b u t appears
c o n f o r m a b l ea n dg r a d a t i o n a l .
The main body o ft h eD a k o t aS a n d s t o n e
g r a y (5GY6/1),andweathersgrayishyellow
m o d e r a t ey e l l o w
cove.redwith
(Nl),
is g r e e n i s h
or
(10R7/4)
brown(10YR5/4).Theexposed
f a c e is o f t e n
a l a y e ro fd a r k - r e d d i s h - b r o w n( 1 0 R 3 / 4 )t ob l a c k
s h i n yd e s e r tv a r n i s h .
On some e x p o s u r e s ,d u s k y - r e d
30 mm a c r o s s c o a t t h e
( 5 R 3 / 4 ) ,a n g u l a rh e m a t i t ep l a t e sa b o u t
e x p o s e ds u r f a c e .
Red, round t oo b l o n g f, e r r u g i n o u ss a n d s t o n e
n o d u l e sw e a t h e rt op o s i t i v er e l i e f
Liesegangbanding
andoccur
commonly.
i s a l s o a common s u r f i c i a l f e a t u r e .
d a r kp a r t i c l e s( p r e s u m a b l yh e m a t i t e )o n
h i g h l i g h tt h i np l a n a r
laminae and 6 - i n .
Small
many e x p o s u r e s
(15.2 c m ) - t h i c k
t a b u l a r s e t s of s t r a i g h t ,h i g h - a n g l ec r o s s - l a m i n a e .T h e s e
. f r e q u e n t l yc h a n g eu p w a r d si nt h e
t r o u g h - s h a p e dc r o s s - l a m i n a e .
( 2 . 5 cm) t h i c k by 1 2i n .( 3 0 . 5
G r a i ns i z e
frosted.
Wood c a s t s a s
much a s 1 i n .
c m ) l o n ga l s oo c c u r( f i g .
i s medium t o f i n e s a n d ; t h e s a n d g r a i n s
sortedtovery
the unit.
u n i t tolarge-scale,
a r e well
well s o r t e d t h r o u g h o u t
S a n dg r a i n s
4).
i n handspecimenappearroundedand
Figure 4 :
Wood c a s t si nD a k o t aS a n d s t o n e ;
Abbe S p r i n g
a n t i c l i n e (NE 1/4, SW 1/4, sec. 5, TlN, R5W)
P e n c i l is 5.5 i n . (14 cm) l o n g .
.
5
17
I
P e t r o g r a p h i c a l l y , tGe DakotaSaAdstone
(Kd-1)
is
c o m p r i s e do fr o u n d e d ,w e l l - s o r t e d ,p r e d o m i n a n t l y
monocrystallinequartzgrainswithanaverageapparentgrain
d i a m e t e r of 0 . 3 mm.
The g r a i n s are c e m e n t e db yq u a r t z
s y n t a x i a l rim cement.Thecementovergrowthsforman
a rock w i t h
i n t e r l o c k i n gm o s a i co fq u a r t zc r y s t a l s ,p r o d u c i n g
a ne s t i m a t e d3 %p o r o s i t y .
The d e t r i t a l q u a r t z g r a i n o u t l i n e s
c a nu s u a l l yb ed i s c e r n e du n d e r
u n c r o s s e db yv i r t u eo f
oftheframeworkcomponents
comprise 9 0 %
of t h e rock.
a r e s l i g h t l yu n d u l o s e .
q u a r t zg r a i n s
limonite,
a t h i nd u s t i n go fh e m a t i t e ,
or c l a ya r o u n dt h e i rp e r i p h e r i e s .T h e s eg r a i n s
.
nicols
low l i g h t w i t h t h e
T h em a j o r i t y
of t h e
Common i d e n t i f i , a b l e
inclusionswhichoccurinthemajorityofthedetritalquartz
g r a i n s a r e z i r c o ns u b h e d r a ,m u s c o v i t es h r e d s ,a n dr a n d o m l y
is a l s o
d i s t r i b u t e db u b b l e s .W e l l - r o u n d e dd e t r i t a lz i r c o n
t r a c e amounts.The
o b s e r v e di n
w h i c hc o n s t i t u t e
3 % of t h e frameworkcomponents,
c o m p r i s e dp r i m a r i l y
well-rounded
d e t r i t a ll i t h i cf r a g m e n t s ,
of s u b a n g u l a rq u a r t z i t e .
are
One
l i t h i c fragment o fc l a y s t o n ea n do n er o u n d e d
l i t h i c f r a g m e n t of f e l t e d m u s c o v i t e w i t h
a limoniticcenter
a l s oo c c u r .
T h ec o n g l o m e r a t i cl e n s e sa n db e d sh a v e
t h i c k n e s s e so f
cm) t h i c k .
4 i n (. 1 0 . 2 - c m )a n da v e r a g ea b o u t
2 in.
(5.1
The p e b b l e s a r e s u b r o u n d e da n dp o l i s h e dg r a ya n d
. w h i t ec h e r ta n dq u a r t z i t e ,a v e r a g i n ga b o u t0 . 2 5
i nd i a m e t e r .
maximum
A c a s t of a small c r i n o i dc o l u m n a 1
i n . ( 0 . 6 4 cm)
was o b s e r v e d
on one white .chert pebble.
-
18
L
'
0
4
e
P e t r o g r a p h i c a l l y ,t h ec o n g l o m e r a t i cl e n s e sa n db e d s
(Kd-2) a r ec o m p r i s e do fa b o u t
s y n t a x i a l rim cement,and
82% d e t r i t a l g r a i n s ,
15%q u a r t z
3 % p o r e s .M o n o c r y s t a l l i n e ,
r o u n d e d ,m o d e r a t e l ys o r t e dq u a r t zg r a i n sw i t hu n d u l o s e
e x t i n c t i o nc o m p r i s e5 0 %o ft h ed e t r i t a lg r a i n s .A b o u t
5% o f
t h e s eq u a r t zg r a i n se x h i b i t
small n u c l e i k h i c h
are n o ti n
o p t i c a lc o n t i n u i t yw i t ht h e
r e s t o ft h eg r a i n ;
15%o f t h e
q u a r t zg r a i n se x h i b i tt i n yi n t e r n a l
Inclusion
cracks.
m i n e r a l o g i e s a r e s i m i l a r t o t h o s eo b s e r v e di nt h eq u a r t z
g r a i n so ft h es a n d s t o n eb e d s .C l o u d y ,p a r t i a l l ys e r i c i t i z e d
p o t a s s i u mf e l d s p a r
components.
comprises a n o t h e r 5 % o f t h e framework
L i t h i cf r a g m e n t sa n dc h e r t ,c o m p r i s i n g
4 0 % of
t h e d e t r i t a l components, a r e v e r y p o o r l y s o r t e d a n d
i s c h e r t ,w h i c h
subrounded.Thedominantlithology
is
commonly c u t by v e i n so fd r u s ya n db l o c k y ,u n d u l o s e ,s u t u r e d
order of d e c r e a s i n g
q u a r t zc r y s t a l s .O t h e rl i t h o l o g i e s ,i n
abundance, a r e s l i g h t l y s e r i c i t i z e d a r k o s i c
a n do t h e r s ,
wacke ( P e t t i j o h n
1 9 7 5 ) , m e t a q u a r t z i t e ,a n dq u a r t z - m u s c o v i t e
schist.
T h et o p
3 t o 5 f t (0.9 t o 1 . 5 m ) of t h e D a k o t a
Sandstone crops o u t a s a n u n e v e n s o i l - c o v e r e d s l o p e .
Medium-dark-gray
(N4)
.s h a l e f l o a t f o u n d h e r e s u g g e s t s t h a t
t h e r e may be some t h i n s h a l e b e d s i n t e r c a l a t e d w i t h t h e
s a n d s t o n e s .T h e s es a n d s t o n e s
a r e f i n e - g r a i n e da n do c c u ri n
4 - i n .( 1 0 . 2c m ) - t h i c kp l a n a rb e d s .
e-
The Dakota S a n d s t o n e i s commonlyassumed
b e e nd e p o s i t e db ya ' t r a n s g r e s s i n g
sea.
A nearshore
t o have
environment i s i n d i c a t e d bywood
m a r i n ef o s s i l s
c a s t s ,a n dt h ea b s e n c eo f
a n db i o t u r b a t i o n .
The c o n g l o m e r a t i cb e d s
l e n s e s may r e p r e s e n t s m a l l f l u v i a l
s e d i m e n t si n t r o d u c e d
or t i d a l c h a n n e l s ,
and
or
by s t o r m s .
The D a k o t a S a n d s t o n e h a s b e e n r e c o g n i z e d a s
h y d r o c a r b o nr e s e r v o i rr o c ki n
f i r s td i s c o v e r yo fg a si n
t h e S a nJ u a nB a s i n
a good
since t h e
1 9 2 1 (Reese, 1 9 5 2 ;B u r t o n ,1 9 5 5 ) .
i s r e p o r t e da sm i n o r
U r a n i u m p r o d u c t i o nf r o mt h i sf o r m a t i o n
( S m i t h ,1 9 5 5 ) .
Mancos S h a l e
T h e Mancos S h a l e was f i r s t named by Cross (1899) f o r a
t h i c ks h a l e
Its original
bodynearMancos,Colorado.
d e f i n i t i o nl i m i t e d
it t ot h es t r a t i g r a p h i ci n t e r v a lb e t w e e n
t h e DakotaSandstoneandtheMesaverdeFormation.
TheMancos
S h a l e i s t h u s a l i t h o l o g i c u n i t t h a tt r a n s c e n d st i m el i n e s
t h r o u g h o u t i t s a r e a le x t e n t .
southwardfrom
The
Mancos
i t s t y p el o c a l i t ya n d
S h a l et h i n s
i s known t o i n t e r t o n g u e
w i t ht h eb a s a lM e s a v e r d eF o r m a t i o n( H u n t ,1 9 3 6 ;
Dane and
o t h e r s ,1 9 5 7 ) .
. In
t h es t u d y
shale.tongues
--
a r e a , t h e Mancos S h a l e c o n s i s t s o f
two
t h e A l a m i t o Well and D-Cross t o n g u e s
s e p a r a t e d by t h eT r e s
Hermanos S a n d s t o n e Member.
t h i c k n e s so ft h i sf o r m a t i o n
t h e Mancos S h a l e i n t h e s t u d y
--
Total
i s a b o u t 850 f t ( 2 5 9 m ) .
Above
area i s t h e G a l l e g oS a n d s t o n e ,
p r e s e n t l y a u n i t of unknown e x t e n t b u t t h o u g h t t o b e l o n g
in
20
5%
i s e l s e w h e r ep a r to ft h e
t h eG a l l u pS a n d s t o n e ,w h i c h
0
MesaverdeGroup
-
' =
( 1 9 7 8 , Hook, o r a l commun.).
Alamito Well tongue
TheAlamito
Well tongueof
t h e Mancos S h a l e ,
d e f i n e d Ss t h e s h a l e i n t e r v a l b e t w e e n t h e u n d e r l y i n g D a k o t a
S a n d s t o n ea n dt h eo v e r l y i n g
Tres Hermanos S a n d s t o n e Member,
was named a t e x p o s u r e s i n
Canon d e l A l a m i t o{ s e c .
R4W) by M a s s i n g i l l ( 1 9 7 9 ) .
M a s s i n g i l lr e p o r t s
a b o u t 5 5 6 f t (169.5 m ) a t t h e t y p e s e c t i o n ,
2 0 , T2N,
a t h i c k n e s so f
w h i c hi n c l u d e s
f t ( 2 . 1 m ) of s i l l s and 8 1 f t (24.7 m ) o fc o v e r .
n o r t h{ J a c k s o n ,
To t h e
1 9 7 9 ) a n dn o r t h e a s t( M a s s i n g i l l ,
1 9 7 9 ) o ft h e
Well Tongue i s s p l i t by theTwowells
s t u d ya r e a ,t h eA l a m i t o
Tongueof
7
t h eD a k o t aS a n d s t o n e .
The s t r a t i g r a p h i ci n t e r v a l s
b e l o wa n da b o v et h eT w o w e l l sS a n d s t o n ea r ec a l l e dt h e
W h i t e w a t e rA r r o y oa n dt h eR i oS a l a d ot o n g u e so f
S h a l er e s p e c t i v e l y .
An 8 - f o ~ o t( 2 . 4m ) - t h i c ks a n d s t o n e
H 2 and H3
recognizedonelectric.logsofdrillhole
(Transocean O i l Co.,Houston,
f t (59.4and64.0
m ) b e l o wt h e
TX) o c c u r sb e t w e e n
Sandstone.
195 and210
Tres Hermanos Sandstoneand
may b e t h e e q u i v a l e n t o f t h e T w o w e l l s
.
t h e Mancos
However a s t h i ss a n d s t o n e
Tongueof
t h eD a k o t a
i s n o to b s e r v e d
at the
s u r f a c ew i t h i nt h es t u d ya r e a ,t h eW h i t e w a t e r
Arroyo-Twowells-RioSaladonomenclaturehasnotbeenused.
TheAlamito
Well t o n g u e i s a l s o p r e s e n t
s o u t h e a s t of t h e s t u d y
i n t h eC a r t h a g ea r e a
area ( M a s s i n g i l l ,1 9 7 8 ,o r a l
commun.).
. .-
23
O u t c r o p s of t h e Alamito Well t o n g u e a r e l i m i t e d t o
t h en o r t h e a s t
T 1 N ; R5W).
corner of t h es t u d ya r e a( s e c s .5 ,
6 , and 8 ;
i s t h ea r e ao fi n t e r s e c t i o n
U n f o r t u n a t e l y ,t h i s
o f t h e P u e r t e c i t of a u l ts y s t e m ,f o r m i n gt h ew e s t e r nb o r d e r
of
a n o r t h e a s t - t r e n d i n gz o n e
t h eM u l l i g a nG u l c hg r a b e n ,a n d
of
f a u l t s and d i p r e v e r s a l s r e l a t e d t o t h e T i j e r a s l i n e a m e n t .
Complex f a u l t i n g ,i g n e o u si n t r u s i o n ,a n de r o s i o n a ld i s s e c t i o n
i n t h i s a r e a make t h e t a s k o f
a t h o r o u g hs t r a t i g r a p h i c
d e s c r i p t i o nd i € f i c u l t .O b s e r v a t i o n sa r em a i n l yl i m i t e dt o
t h eb a s a l
20 f t (6.1 m;
( 1 8 . 3m ) - t h i c ks e c t i o ne x p o s e da l o n g
n o r t h and e a s t
a n i n t r u d e d6 0 - f o o t
T r e s Hermanos hogbacks),and
L a Ja'ra Creekpresumably
(sec. 5 , T l N , R5W).
n e a r e rt ot h eb a s et h a nt ot h et o p
Well t o n g u e is g r a d a t i o n a l
The b a s eo ft h eA l a m i t o
T h i s c o n t a c t was
w i t ht h eu n d e r l y i n gD a k o t aS a n d s t o n e .
d e l i n e a t e da tt h ef i r s tm e d i u m - l i g h t - g r a y
a p p r o x i m a t e2 - f o o t
of
SE 1/4, s e c .5 ,n o r t h
t h e t o p 1 0 0 f t (30.5 m;
T i j e r a sl i n e a m e n t ) ,
s l o p e so f
SW 1 / 4 ,
( N 6 ) s h a l eu n i t
( 0 . 6 1 m ) t h i c k n e s s .E x p o s u r e s
Of
in this
a r e a are e x t r e m e l y p o o r , b u t f l o a t s u g g e s t s s e v e r a l t h i n ,
very-fine-grained,moderate-brown(5YR3/4),
may o c c u ra b o v et h i sb a s a ls h a l e .
however, i s d a r k - g r a y
s i l t ys a n d s t o n e s
The d o m i n a n tl i t h o l o g y ,
(N3) t o g r a y i s h - b l a c k
(NZ),
fissile,
c a l c a r e o u s ,s i l t ys h a l e .
The a b r u p tu p p e r
w i t ht h eo v e r l y i n g
contact o ft h eA l a m i t o
Well t o n g u e
T r e s Hermanos Member i s well-exposedon
t h e e a s t s l o p eo fh i l l
l i t h o l o g yo ft h eA l a m i t o
'6597'
(sec. 6).
Well t o n g u ea g a i n
The dominant
is s h a l e , now
.i
22
-7
medium l i g h t g r a y
(N6).
Mammites d e p r e s s u sw a sf o u n dw i t h i n
l i m e s t o n ec o n c r e t i o n si nt h e s eu p p e rs h a l e se x p o s e da l o n gt h e
e a s ts i d eo f
Abbe S p r i n g Canyon.The
f t (0.46 m)
i nd i a m e t e r ,
c o n c r e t i o n sa v e r a g e1 . 5
and a r es m o o t h ,
d a r k - y e l l o w i s h - o r a n g e( 1 0 Y R 6 / 6 ) - w e a t h e r i n ge l l i p s o i d s .
S c i p o n o c e r a sg r a c i l e
was c o l l e c t e d f r o m
l i m e s t o n eb e da p p r o x i m a t e l y
9 0 f t (27.4
m ) b e l o wt h e
4 in.
a medium-gray(N5)
( 1 0 . 2 cm) t h i c k andabout
Tres Hermanos Member a t t h e same
l o c a t i o n .O c c u r r e n c e so fP y c n o d o n t en e w b e r r ia r ea l s o
r e p o r t e df r o mt h i sl i m e s t o n e( M a s s i n g i l l ,
commun.')
1917, o r a l
.
The s e c t i o n of t h e A l a m i t o
Well tongueexposed
a l o n g La J a r a Creek i s c o m p r i s e do fi n t e r b e d d e dd a r k - g r a y
(N3), c a l c a r e o u s s h a l e s
and g r a y i s h - o l i v e
{ l B Y 4 / 2 ) - w e a t h e r i n g ,v e r y - f i n e - g r a i n e d ,m a s s i v es a n d s t o n e .
The s h a l e u n i t s a r e between 6 i n .
t h i c k ; t h e s a n d s t o n e sr a n g ef r o m
(15.2 cm) and 3 f t ( 0 . 9 m)
2 in.
(5.1 cm) t o 1 2 i n .
are
(0.3 m ) t h i c k .C o n t a c t sb e t w e e nt h e s el i t h o l o g i e s
relativelysharp.
The A l a m i t o Well t o n g u ec o n s i s t so fl o w - e n e r g y ,
is a
o f f s h o r es h e l fd e p o s i t s .I n c l u d e dw i t h i nt h i sr e c o r d
c h a n g ef r o mm a r i n et r a n s g r e s s i o n
a t thebasetomarine
.
r e g r e s s i o n a t t h e t o p ;s h o r e l i n es a n d sa r ep r e s e r v e db e l o w
andab0v.e
t h i s u n i t as theDakotaSandstoneand
Member, r e s p e c t i v e l y .I n t e r b e d d e ds a n d s t o n eb e d s
Tres Hermanos
may
r e p r e s e n ts t o r m - g e n e r a t e dd e p o s i t s( R e i n e c ka n dS i n g h ,1 9 7 5 ) .
t9
23
-
I
The S c i p o n o c e r a s g r a c i l e z o n e
i s a widespread
marks t h e boundarybetweenCenomanianand
ammonitezoneand
Turonian time (89m.y.;ObradovichandCobban,L975).
Pycnodontenewberri,found
atthe
a s S. g r a c i l e , i s f o u n do n l yi n
same s t r a t i g r a p h i c l o c a t i o n
t h e F o u rC o r n e r ss t a t e s
(Hook
1977).
andCobban,
Tres Hermanos S a n d s t o n e Member
The T r e s Hermanos S a n d s t o n e Member o f t h e
Mancos
S h a l e was named by H e r r i c k ( 1 9 0 0 ) f o r e x p o s u r e sn e a rT r e s
Hermanos B u t t e s (sec. 2 6 , T3N, R7W).
Tonking
(1957)
( 1 9 2 0 ) s t r a t i g r a p h i cs e c t i o n
m i s i n t e r p r e t e dW i n c h e s t e r ' s
s o u t h of P u e r t e c i t o , a n dm i s t a k e n l yi d e n t i f i e dt h eT w o w e l l s
Tongue of t h e D a k o t a S a n d s t o n e a s
t h e Mancos S h a l e .
t h e Tres Hermanos Member of
T h e T r e s Hermanos Member o f t h i s r e p o r t
was i n c l u d e dw i t h i nT o n k i n g ' s
La Cruz P e a k Formation.
mistake was c o r r e c t e d by Dane,Landis,andCobban
(1971).
They a l s o r e p o r t e d a n e a r l y C a r l i l e a g e f o r t h e T r e s
Member baseduponrecovery
This
Hermanos
of C o l l i g n o n c e r a s w o o l l g a r i .
M a s s i n g i l l ( 1 9 7 9 ) r e p o r t s a t h i c k n e s s o fa p p r o x i m a t e l y2 3 1
( 7 0 . 4 m ) t o t h e n o r t h e a s to f
t h e s t u d ya r e a .
The Tres Hermanos. Member c r o p s o u t i n
the
n o r t h e a s t e r ns e c t i o no ft h es t u d ya r e a ,a n da g a i n
J a r a l o s a C r e e k a n ds o u t ho f
f t
west of
Dove SpringCanyon.Exposures
a r eg e n e r a l l yp o o rd u et os l u m p i n ga n de x t e n s i v ee r o s i o n .I n
a d d i t i o n , a l l o u t c r o p so f
a r ef a u l t e d ,
t h e Tres Hermanos i n t h e s t u d y area
and i n t h e n o r t h e a s t e r n s e c t i o n , e x t e n s i v e l y
1
24
-9
.
D
.
The Tres Hermanos i s e s t i m a t e dt o
intruded.
be 250 f t ( 7 6 . 2
m ) t h i c k i n t h e s t u d ya r e a .
Tres Hermanos Member w i t h
The b a s a l c o n t a c t o f t h e
t h eA l a m i t o
Well t o n g u e i s w e l l - e x p o s e d o n t h e e a s t s i d e o f
h i 3 1' 6 5 9 7 '( s e c .6 ,
T l N , R5W).
o v e r l y i n g D-CrossTonghe
west o fd r i l l h o l e
c o n t a c t sa r e
'
The u p p e rc o n t a c tw i t h -t h e
i s well-exposed i n J a r a l o s a C r e e k
H 1 (sec. 35, T l N , R6W).
B o t ho ft h e s e
marked by s h a r pl i t h o l o g i cc h a n g e s .
The T r e s
Hermanos Member i s i n f o r m a l l y d i v i d e d i n t o t h r e e g r a d a t i o n a l
u n i t s by t h eo c c u r r e n c eo f
a n o n m a r i n ei n t e r v a l
of
o r g a n i c - r i c hs a n d s t o n e s ,s i l t s t o n e s ,s h a l e s ,a n dl i g n i t e
b e t w e e nu p p e ra n dl o w e ri n t e r v a l so fm a r i n es a n d s t o n e
c o n t a i n i n gm i n o ri n t e r c a l a t e ds h a l e .
The lower marine s e c t i o n f o r m s g e n t l y d i p p i n g
hogbacks i n t h en o r t h e a s t e r nc o r n e ro ft h es t u d ya r e a .
s e c t i o n is e s t i m a t e dt ob ea b o u t8 0
t o medium-bedded
a f r e s h l yb r o k e ns u r f a c ea r ey e l l o w i s h
g r a y( 5 Y 8 / 1 ) ,l i g h tg r e e n i s hg r a y
C o l o r so nw e a t h e r e ds u r f a c e s
(10YR8/2)
f t (24.4 m ) t h i c k .T h i n -
s a n d s t o n e is d o m i n a n ti nt h i ss e c t i o n .
S a n d s t o n ec o l o r so n
(N7).
This
o r p a l ey e l l o w i s h
(5GY8/1)
or v e r yl i g h tg r a y
are v e r yp a l eo r a n g e
brown(10YR6/2),
a t times m o t t l e d
by d a r ky e l l o w i s no r a n g e( 1 8 Y R 6 / 6 )M
. assingill
r e p o r t sC o l l i g n o n c e r a s( S e l w y n o c e r a s )
t h e ' " 6 a s eo ft h i ss e c t i o n .F o s s i ld e b r i s
(1979)
mexicanum(Bose)from
i s common i n t h e
s a n d s t o n e sn e a rt h et o po ft h el o w e rm a r i n es a n d s t o n eu n i t .
High-angle,
small-scale, f o r e s e tc r o s s b e d sa n da s y m m e t r i c
r i p p l e sa r e
common.
Framework g r a i n s a r e medium t o f i n e s a n d
25
-3
.
.
Z
w i t h some t e n d e n c yt oc o a r s e nu p w a r d s ;t h es a n d s t o n e sa r e
m o d e r a t e l yt ow e l l - s o r t e d .I n t e r c a l a t e ds h a l ep a r t i n g sa r e
medium g r a y (N5) t od a r kg r a y( N 3 ) ,g e n e r a l l ys i l t y ,
( 5 . 1 cm) t h i c k .
average 2 in.
and
P e t r o g r a p h i ca n a l y s i s( K t h - 1 )
i n d i c a t e sc l e a r ,a n g u l a rq u a r t zg r a i n s ,w i t hu p
t-o 6 0 %
e x h i b i t i n g r e l i c t f i n e - g r a i n e ds i l c i c e o u sc e m e n t ,c o m p r i s e
of
thedominantframeworkmineralogy.Lesseramounts
s u b a n g u l a r ,s e r i c i t i z e dp o t a s s i u mf e l d s p a r
c o r r o d e dp l a g i o c l a s e
(An66,av,erageof
and h i g h l y
4 g r a i n s , Michel-Levy
L i t h i c fragments are
method)areminorframeworkcomponents.
g e n e r a l l ys u b r o u n d e db a l l so fp h y l l o s i l i c a t e" h a s h " .T h e s e
1 7 %o ft h e
t o g e t h e rw i t hr o u n d e dc h e r tg r a i n sc o n s t i t u t e
d e t r i t a lc o m p o n e n t s .
was a l s oo b s e r v e d .
One g n e i s s i c - t e x t u r e dl i t h i cf r a g m e n t
Rounded g l a u c o n i t e p e l l e t s a r e p r e s e n t i n
t r a c ea m o u n t s .M a t r i xa n de m p t yp o r e sc o n s t i t u t ea b o u t
2% of
t h et o t a lr o c k ;f r a m e w o r kg r a i n sc o m p r i s e7 3 %a n d
f i n e - g r a i n e dc a l c i t ec e m e n tc o n s t i t u t e s2 5 % .I n t e r c a l a t e d
The c e n t r a l nonmarine. se.ction Ls w.ell-exposed along
t h ea r r o y os o u t h w e s t
of M i d d l eW e l l( s e c .3 5 ,
is e s t i m a t e dt ob ea p p r o x i m a t e l y
n o n m a r i n ei n t e r v a lc r o p so u ta s
1 0 0 f t (30.5 m ) t h i c k .
medium-bedded,
much a s 2 0 %
is i n t e r c a l a t e dw i t hg r e e n i s h - g r a y
(5GY6/1) t o
g r e e n i s h - b l a c k4 5 G 2 / 1 ) ,o r g a n i c - r i c hs i l t s t o n ea n ds h a l e .
T h e s eu n i t s
are g e n e r a l l yb e t w e e n
The
by s h a l e and
f i n e - g r a i n e dq u a r t z o s es a n d s t o n ec o n t a i n i n ga s
o r g a n i cd e b r i s
It
low s a n d s t o n eb e n c h e s ,
s e p a r a t e d by s h a l l o w v a l l e y s ' u n d e r l a i n
s i l t s t o n e .M o d e r a t e l ys o r t e d ,t h i n -t o
T l N , R6W).
1- and10-feet(0.3and3.0
m)-thick.
T h e s a n d s t o n e sa r ec h i e f l yy e l l o w i s h - g r a y
w e a t h e r i n gt ol i g h t - y e l l o w i s h - g r a y
c o n t a i nt a b u l a r
crossbeds.
(5Y8/1),
(5Y7/2), and commonly
s e t s o fs m a l l - s c a l e ,l o w - a n g l et a n g e n t i a l
Wood c a s t si nt h es a n d s t o n e sa r e
common.
The
i s l o c a l l yh i g he n o u g ht o
o r g a n i cc o n t e n to ft h es h a l e s
c o m p r i s et h i nl i g n i t eb e d s .
T h e t o p7 0 - f o o t
t h e Tres HermanosTongue
( 2 1 . 3 m ) - t h i c km a r i n es e c t i o n
of
i s similar t ot h el o w e rs e c t i o n .
A
1 0 - f o o t( 3 . 0m ) - t h i c k , .m a s s i v e ,e x t e n s i v e l yb i o t u r b a t e d
1 0 f t ( 3 . 0 m ) below t h e t o po f
s a n d s t o n eo c c u r sa p p r o x i m a t e l y
t h e TresHermanos.
From t h i s s a n d s t o n e , whi.ch i n t h e f i e l d
i s v e r ys i m i l a ri na p p e a r a n c et ot h eG a l l e g oS a n d s t o n e ,
r e c o v e r e dL o p h ab e l l a p l i c a t a
C o i l o p o c e r a sc o l l e t i
was
(NE 1/4, sec. 6 , T l N , R6W)
.
was r e c o v e r e d f r o m t h e s i l t y s h a l e
b e n e a t h t h e b i o t u r b a t e ds a n d s t o n e .
The l o w e ra n du p p e rm a r i n es e c t i o n so ft h e
HermanosTongue
are deposits left
Tres
by r e g r e s s i n g a n d
t r a n s g r e s s i n gs e a s ,r e s p e c t i v e l y .
The r e v e r s eg r a d i n g
i n the
s a n d s t o n e s of t h e l o w e r m a r i n e s e c t i o n c a n b e a t t r i b u t e d t o
wave-swash
s o r t i n g( C l i f t o n ,
1969).
Crossbedding
and
a s y m m e t r i c a lr i p p l e sw h i c ho c c u ri nb o t h
marine i n t e r v a l s a r e
characteristicoftheuppershorefacedepositional
environment(ReineckandSingh,1975).
The b i o t u r b a t e d
s a n d s t o n ei nt h eu p p e rm a r i n ei n t e r v a l
d e e p e rs h o r e f a c es e d i m e n t a t i o n .
may r e p r e s e n t somewhat
The c e n t r a n
l onmarine
sectionpreservesdepositsofnearshoreorinland
e n v i r o n m e n t s .T h i si n t e r v a l ,c h a r a c t e r i z e d
by wood c a s t s ,
27
_.
f i n e - g r a i n e ds a n d s t o n e s ,o r g a n i cs h a l e s ,a n dt h i n
lignite
b e d s ,r e p r e s e n t sn e a r s h o r ed e p o s i t so fb a c k s h o r em a r s h e sa n d
t h e Menefee and
t i d a lf l a t ss i m i l a rt ot h o s ed e s c r i b e df o r
L a n c e f o r m a t i o n s( S e l l e y ,
W i t h i nt h i si n t e r v a l ,t h e
1912).
s e a ~ l e v e lp r o b a b l yr e m a i n e dn e a r l ys t a t i c
and t h e s h o r e l i n e
to transgression.
p o s i t i o nc h a n g e df r o mr e g r e s s i o n
D-CrossTongue
Dane, Wanek, andReeside(1957)proposedtorename
P i k e ' s ( 1 9 4 7 ) P e s c a d oT o n g u e . o ft h e
M o u n t a i n( s e c s .
Mancos S h a l e a t
11 and 1 8 , T3N, R8W) t h e D-CrossTongue.
They r e c o g n i z e d t h i s s t r a t i g r a p h i c i n t e r v a l
e v i d e n c et o
D-Cross
by f a u n a l
be a d i s t i n c t a n dh i g h e rt o n g u et h a n
Pike's
PescadoTongue.TheydefinedtheD-CrossTongueasthe
persistentmarineshaleoflatestCarlileageunderlyingthe
G a l l e g oS a n d s t o n e( t h e nt h eu p p e rG a l l u pS a n d s t o n e ) .T o n k i n g
( 1 9 5 7 )h a di n c l u d e dt h eD - C r o s sT o n g u ew i t h i nh i s
La Cruz
P e a k Formation.
of t h e Mancos S h a l e i s b e s t
T h e D-CrossTongue
exposed i n a f a u l t e da n di n t r u d e d4 0 - f o o t
s e c t i o n on t h e west s i d e o f J a r a l o s a
sec. 35, T l N , R6W).
(12.2 m ) - t h i c k
Creek (NW 1 / 4 ,
SE 1/4,
Maximum t h i c k n e s s i n t h es t u d ya r e a
a p p r o x i m a t e l y 95 f t ( 2 9 m).
Tongue w i t h t h e u n d e r l y i n g
The b a s a lc o n t a c to ft h e
is
D-Cross
Tres Hermanos Member i s s h a r p ; a
marked l i t h o l o g i c c h a n g e o c c u r s b e t w e e n t h e m o d e r a t e l y
c o n s o l i d a t e ds a n d s t o n e so ft h eT r e s
s i l t y ,g r a ys h a l e so ft h e
Hermanos Member and t h e
D-CrossTongue.Theupper
contact
28
of the D-Cross Tongue with the overlying Gallego Sandstone is
gradational and is best exposed in a canyon cut into the
northern edge of the extensive pediment surface (SE 1/4, SW
1/4, sec. 6 , TlN, R5W)
.
Within the top 10 f t (3.0 m) of the
D-Cross Tongue, the shale grades upwards into medium-gray
(N5)-weatheringr fine-grained, massive sandstone.
The grain
size increases and color lightens upwards into the Gallego
Sandstone.
The contact isdrawn beneath the first resistant
sandstone.
Shales are silty near both the base and the top
of the D-Cross Tongue.
The D-Cross Tongue is generally comprised of
medium-dark-gray (N4), weathering to grayish-black (NZ),
fissile shale.
At.the previously mentioned exposure on
Jaralosa Creek, 1- to 5-in. (2.5- to 12.7-cm)-thick
olive-black (5Y2/1)-weatheringr very-fine-grained,
silty
sandstones are gradationally interbedded with the shales.
The shales are generally concretionary, with concretions
locally forming irregular discontinuous beds.
Two distinct
types of sandy limestone concretions occur within the D-Cross
Tongue.
The first ofthese are smooth and oblate, weather to
moderate brown (5YR4/4), and often contain ammonites (fig.
5A).
The second type are septarian and oblate, weather to
light brown (5YR5/6) or grayish black (N2), and are rarely
fossiliferous.(fig. 5B).
The centers of both types of
concretions (usually the latter type) may be comprised of
brownish-black (5YR2/1) massive calcite.
Concretions range
29
A
F i g u r e 5:
C o n c r e t i o n si nt h e
B
D-Cross S h a l e
A . s m o o t hv a r i e t y
B. S e p t a r i a n v a r i e t y
Aammer h a n d l e i s 1 2 . 5 i n . (31.8 cm) l o n g .
6 i n . ( 1 5 . 2 cm) t o 30 i n .
i nd i a m e t e rf r o m
(0.76 m ) .
Fossils
r e c o v e r e df r o mt h eD - C r o s sT o n g u ei nt h es t u d ya r e ai n c l u d e
S c a p h i t e sw h i t f i e l d i ,P r i o n o c y c i u sn o v i m e x i c a n u s ,a n d
Inoceramus s p . .
A 6 - i n .( 1 5 . 2c m ) - t h i c k ,m o d e r a t e - r e d d i s h - o r a n g e
( 1 0 R 6 / 6 ) - w e a t h e r i n g ,s i l t yl i m e s t o n ew i t ha ni r r e g u l a r
s u r f a c e i s w e l l - e x p o s e dt o
t h ea r r o y ow e s t
T l N , R6W).
t h e e a s t o f t h es t o c k . p o n d
of Middle Well (NW 1 / 4 ,
SE 1 / 4 ,
T n i s bed i s l o c a t e da p p r o x i m a t e l y
abovethebaseoftheD-CrossTongue,and
sec.
dam i n
35,
8 f t (2.4 m)
may r e p r e s e n t t h e
J u a n a Lopez e q u i v a l e n t i n t h e s t u d y
a r e a (Hook, 19'17, o r a l
..
commun )
T h e D-Cross Tongue of t h e Mancos S h a l e r e c o r d s t h e
c h a n g ef r o mm a r i n et r a n s g r e s s i o na tt h eb a s et om a r i n e
r e g r e s s i o n a t t h et o p .
TheD-CrossTongueaccumulated
m a r i n es h e l fe n v i r o n m e n t .S a n d s t o n eb e d s
d e p o s i t s( R e i n e c ka n dS i n g h ,
in a
may r e c o r ds t o r m
1975).
G a l l e g oS a n d s t o n e
Winchester ( 1 9 2 0 )g a v et h e
name G a l l e g oS a n d s t o n e
totheresistantsandstoneoccurringabout
9 0 0 f t (274 m )
a b o v et h eD a k o t aS a n d s t o n e
Mesa n e a r G a l l e g o
at Pueblo Viejo
C r e e k (sec. 1 7 , T4N, R7W).
He i n c l u d e dt h i ss a n d s t o n eu n i t
w i t h i n h i s MiguelFormation.
P i k e ( 1 9 4 7 )c l a i m e dt oh a v e
t r ' a c e dt h eG a l l u pS a n d s t o n ei n
t h e S a nJ u a nb a s i ni n t o
W i n c h e s t e r ' sG a l l e g oS a n d s t o n e
Member of h i s Miguel
31
-
. e
Formation.Dane,
Wanek, a n dR e e s i d e( 1 9 5 7 )r e g a r dt h e
G a l l e g oS a n d s t o n ea sb e i n g
a r e g r e s s i v es a n d s t o n e
member of
( 1 9 7 4 ) s u g g e s t s from
t h e upperGallupSandstone.Molenaar
o f m e a s u r e ds e c t i o n st h a tt h eG a l l e g oS a n d s t o n e
hisstudies
a t p u e r t e c i t o is
Member o ft h eu p p e rG a l l u pS a n d s t o n e
comprisedof
two b a r r i e r - b a rs a n d s t o n e ss e p a r a t e d
t r a n s g r e s s i v em a r i n es h a l e .
by a
H i s l o w e rb a r r i e rb a r
is the
G a l l e g oS a n d s t o n eo ft h i sr e p o r t ;t h eu p p e rb a r r i e rb a r
and
t h ei n t e r y e n i n gs h a l eh a v eb e e ni n c l u d e di nt h eM e s a v e r d e
F o r m a t i o ni n
t h i s r e p o r t .R e c e n t l y ,t h eU n i t e dS t a t e s
G e o l o g i c a lS u r v e yS t r a t i g r a p h i c
s u g g e s t e dt h a t
Names Committeeinformally
t h e c o r r e l a t i o no ft h eG a l l e g oS a n d s t o n ew i t h
t h eG a l l u pS a n d s t o n e
o r a l commun.).The
is, a t p r e s e n t , i n v a l i d
iHook,1978,
G a l l e g oS a n d s t o n ep i n c h e so u tt ot h ee a s t
o ft h es t u d ya r e a( M a s s i n g i l l ,
1979).
The G a l l e g o S a n d s t o n e i n t . h e t h e s i s a r e a c r o p s o u t
a s rounded c l i f f s o r lowhogbacks.Thicknessof
t h e Gallego
S a n d s t o n e a t a c a n y o nc u ti n t ot h en o r t h e r ne d g e
ofthe
e x t e n s i v ep e d i m e n ts u r f a c e
a p p r o x i m a t e l y 50 f t (15.2 m ) .
C r e e k( s e c .3 5 ,
west o fJ a r a l o s a
I na na r r o y o
T l N , R6W), t h eG a l l e g oS a n d s t o n e
approximately 40 f t (12.2 m ) t h i c k .
underlyingD-CrossTongue
a t t h ef o r m e rl o c a t i o n .
is
The c o n t a c tw i t ht h e
of t h e Mancos S h a l e is well-exposed
The c o n t , a c th e r e
is g r a d a t i o n a la n d '
is drawn a t t h e f i r s t r e s i s t a n t s a n d s t o n e .
w i t ht h eo v e r l y i n gM e s a v e r d eF o r m a t i o n
The b a s eo ft h e
is
(sec. 6 , T l N , R 5 W )
The u p p e rc o n t a c t
is r e l a t i v e l y s h a r p .
l a t t e r i s a s i l t y ,d a r k - g r a y
(N3) s h a l e a t
*
3
32
.
.-
2
e x p o s u r e s a t MiddleWell
(sec. 35, T l N , R6W) andsouthof
1, T I S , R6W).
CorkscrewCanyon(sec.
The b a s eo ft h eG a l l e g
0
Sandstone i s a no l i v e - b l a c k( 5 Y 2 / 1 )t h i c k - l a m i n a t e ds a n d s t o n e
t h a tw e a t h e r s
t o1 5 - f t
(2.4-
t o m o d e r a t ey e l l o w i s h
brown ( Y R 5 / 4 ) .
t o 3.0-m)-thick.Coloron
It is 8-
a f r e s hs u r f a c e
becomes y e l l o w i s hg r a y( 5 y 8 / 1 )u p w a r d si n t ot h em a i nb o d yo f
t h eG a l l e g oS a n d s t o n e .
The b a s a ls e c t i o n ,w h i c h
is
a p p r o x i m a t e l y 2 0 f t ( 6 . 1 m) t h i c k , i s medium- t o v e r y
s e t s of p l a n a r
t h i c k - b e d d e dL
. a r g e - s c a l e l, o w - a n g l e t, a b u l a r
c r o s s b e d so c c u rl o c a l l y .L o c a le r o s i o n a ls u r f a c e sa r em a r k e d
by c h a n n e ls c o u r sa n dv e r yt h i ns i l t s t o n el e n s e s .B e d d i n g ,
however, i s g e n e r a l l yo b s c u r e d
5.25 i n .
( 0 ; 6 4 cm) wideand
by numerous v e r t i c a l b u r r o w s
cm) l o n g .
a s much as 6 i n .( 1 5 . 2
T h e s e burrows s t a n d o u t p r o m i n e n t l y
on a w e a t h e r e d s u r f a c e
and a r e a c h a r a c t e r i s t i c f e a t u r e o f t h e G a l l e g o S a n d s t o n e .
A s a r e s u l t of t h e e x t e n s i v e b u r r o w i n g , t h e G a l l e g o S a n d s t o n e
commonly assumes a m a s s i v ea p p e a r a n c e .O r g a n i cm a t e r i a l
u s u a l l yo c c u r so n
a f r e s hr o c ks u r f a c e .
P e t r o g r a p h i c a l l y{ K g - 1 ) ,t h e s es a n d s t o n e sa r e
c o m p r i s e dd o m i n a n t l yo fw e l l - s o r t e d ,m o n o c r y s t a l l i n e ,
s u b a n g u l a r ,q u a r t zg r a i n sw i t hs l i g h l yu n d u l a t o r ye x t i n c t i o n
o ff i n es a n ds i z e .A l t h o u g hm o s t
of t h e s e g r a i n s a r e
"
a s m a l lp e r c e n t a g ec o n t a i nl i n e a rt r a i n s
g r a i n s . w i t h r e l i c t f i n e - g r a i n e ds i l i c e o u s
o f b u b b l e s .T h r e e
cement a l s o o c c u r .
C l o u d y ,p a r t i a l l ys e r i c i t i z e dp o t a s s i u mf e l d s p a r
amounts of m i c r o c l i n ec o m p r i s e
components.only
clear,
and t r a c e
1 4 % o ft h er o c k ' sf r a m e w o r k
4 % p l a g i o c l a s eg r a i n sw e r eo b s e r v e d ;
33
53
. ’
h o w e v e r ,t h e s ew e r ee x t e n s i v e i ’ yr e p l a c e dd ys e r i c i t e
and
c a l c i t e , and were u s u a l l yr e c o g n i z a b l eo n l yb yt w i n n i n g
. t h e rf r a m e w o r k
“ g h o s t s “ i n t h er e p l a c i n gm i n e r a l s O
a n d a.
c o n s t i t u e n t si n c l u d er a g g e dm u s c o v i t ec l e a v a g el a t h s
fewrounded
The m a t r i x of c l a y s and o r g a n i c
c h e r tg r a i n s .
d e b r i sc o m p r i s e s
2 8 % o ft h er o c k .I n t e r s t i t i a lc l a y s
by s e r i c i t e o r c h l o r i t e .
commonly show p a r t i a l r e p l a c e m e n t
of p h y l l o s i l i c a t e
P a t c h yc a l c i t ec e m e n ta n dt r a c ea m o u n t s
cementcomprise
about 2%.
Open p o r es p a c e
1 0 % o fr o c k .
i s e s t i m a t e da t
of
I t s h o u l d be n o t e d ,h o w e v e r ,t h a ti n d u r a t i o n
is o n l y m o d e r a t e , a n d e f f e c t s o f
theGallei0sandstone
weatheringprocessesarethoughttopermeatequitedeeply
of t r u e
i n t ot h er o c k .T h u s ,a na c c u r a t ec h a r a c t e r i z a t i o n
is d i f f i c u l t .
petrographicproperties
G e n e r a l l yo n eo r
two 1 4 - i n .
( 3 5 . 6c m ) - t h i c k
t h e upper 8 t o
f o s s i l i f e r o u ss a n d s t o n eb e d sa r ep r o m i n e n ti n
18 f e e t ( 2 . 4 t o 3.0 m ) o ft h eG a l l e g oS a n d s t o n e .T h e s eb e d s
commonly w e a t h e rb r o w n i s hg r a y
(5YR4/1)
t od a r ky e l l o w i s h
brown (19YR4/2) and are more r e s i s t a n t t h a n t h e
Gallego S a n d s t o n e .
On a f r e s hs u r f a c e ,c o l o r
moderate brown 45YR3/4) t o medium l i g h t g r a y
d e c r e a s i n gs a n dc o n t e n t .
common.
v a r i e s from
(N6) w i t h
f o s s i l is Lopha
w i t h t h i c k ,c u r v i n gr i b st h a ta v e r a g e s
s a n n i o n i s ,a no y s t e r
1 . 5i n .
Thedominant
r e s t of t h e
( 3 . 8 c m ) l o n g( f i g .
6).
N e a r l yu n b r o k e nf o s s i l s
are
T h e s ef o s s i l i f e r o u sb e d sa r ec h a r a c t e r i s t i co ft h e
G a l l e g oS a n d s t o n e
i n thestudyarea,as
t ot h en o r t h( J a c k s o n ,
well a s i n e x p o s u r e s
1 9 7 9 ) and e a s t( M a s s i n g i l l ,1 9 7 9 ) .
Figure 6:
Lopha s a n n i o n i s from GallegoSandstone"brown
b e d " ;J a r a l o s aC r e e k
at Middle Well (SW 1 / 4 , NE
1 / 4 , s e c . 3 5 , TlN, R6W).
P e n c i l i s 5.5 i n . ( 1 4
cm) long.
>.
35
'
. >
The o v e r l y i n gM e s a v e r d eF o r m a t i o nc o n t a i n sn o n f o s s i l i f e r o u s
i n a p p e a r a n c et o
s a n d s t o n eb e d ss i m i l a r
e x p o s u r e s i n t h en o r t h e a s tc o r n e ro f
T l N , R5W).
t h e G a l l e g o (.as a t
t h e s t u d ya r e a ;s e c .
8,
T h u s ,t h ef o s s i l i f e r o u sb e d si nt h eG a l l e g oa r e
i m p o r t a n tt of o r m a t i o ni d e n t i f i c a t i o n .
. Petrographically(Kg-2),theframeworkcomponents
b e d s a r ec o m p r i s e do f1 5 % ,p r e d o m i n a n t l y
o ft h ef o s s i l i f e r o u s
m o n o c r y s t a l l i n eq u a r t zw i t hs l i g h t l yu n d u l a t o r ye x t i n c t i o n ;
8 % a n g u l a r ,e x t e n s i v e l ys e r i c i t i z e dp o t a s s i u mf e l d s p a r ;a n d
7 % p l a g i o c l a s e (An49, a v e r a g eo f
m e t h o d )r e p l a c e dl o c a l l y
E g r a i n s , Michel-Levy
by c a l c i t e .
Burrowedfragmentsof
Lopha s a n n i o n i s ,w h i c hc o m p r i s ea n o t h e r
4 0 % oftheframework
components, commonly e x h i b i t p r e s e r v a t i o n o f i n t e r n a l
structure.
shell
A few smaller f r a g m e n t s a r e r e p l a c e di n t e r n a l l y
by p s e u d o s p a r ,w h i c ho f t e ns h o w s" g h o s t s "o ft h eo r i g i n a l
i n t e r n a ls t r u c t u r e .O t h e r
s u b r o u n d e dc h e r t ,
framework c o n s t i t u e n t si n c l u d e
3% m u s c o v i t e s h r e d s a n d l a t h s ,
3%
4% organic
t r a s h , and t r a c e s o f s u b r o u n d e d l i t h i c f r a g m e n t s o f
q u a r t z - m i c as c h i s t .
t o t a lr o c k ,
Matrix m a t e r i a l ,c o m p r i s i n g1 5 %o ft h e
i s c a l c a r e o u s mud.
About 3 0 % o ft h e
mud o c c u r s
as r e l a t i v e l y s a n d - f r e e r o u n d e d m a s s e s , w h i c h a r e i n f e r r e d t o
r e p r e s e n te r o s i o no fl o c a l l y - d e r i v e dc a l c a r e o u s
mud.
Cement
material is p r i n c i p a l l y small c r y s t a l s o f c l e a r c a l c i t e .
CastsofCardiumsp.andInoceramus
u b i q u i t o u sa n dl o c a l l ya b u n d a n t
G a l l e g oS a n d s t o n e .P r i o n o c y c l u s
sp. a r e .
i n themiddleandupper
SQ.
was c o l l e c t e d from t h e
t o p of t h e G a l l e g o S a n d s t o n e f r o m e x p o s u r e s s o u t h w e s t o f
J a r a Canyon (SE 1/4, SE 1/4
sec. 6 , TlN, R6W)
.
La
36
. J
0
*
i s o b v i o u s l y marine a s
The G a l l e g oS a n d s t o n e
i n f e r r e d from t h e u b i q u i t y o f m a r i n e ' f o s s i l s t h r o u g h o u t t h e
formation.
The d i s t r i b u t i o n of t h i s f o r m a t i o n and i t s
p i n c h o u tt ot h en o r t h e a s t
of t h e s t u d y a r e a s u g g e s t s t h a t t h e
G a l l e g oS a n d s t o n er e p r e s e n t sa ne l o n g a t es a n db o d y .T h i s
f a c t ,t o g e t h e rw i t ho b s e r v e ds e d i m e n t a r ys t r u c t u r e s
b i o t u r b a t i o n , i s s t r o n g l ys u g g e s t i v e
and
of a b a r r i e r - b a r
(1974) interpretation.
d e p o s i t ,i na g r e e m e n tw i t hM o l e n a a r ' s
S u c hf e a t u r e s . a r ed e s c r i b e df o rb a r r i e rs a n d - b a r si nS e l l e y
( 1 9 7 2 ) , R e i n e c ka n dS i n g h( 1 9 7 5 ) ,a n dP e t t i j o h na n do t h e r s
( 1 9 7 3 ) .S e l l e y
( 1 9 7 2 ) s t a t e st h a tc l a ym a t r i x
porosityarecharacteristics
C h a n n e ls c o u r s
andlow
of r e g r e s s i v e b a r r i e r s a n d s .
may b e a s c r i b e d t o s t o r m w a s h o v e r s .
F o s s i l i f e r o u s " b r o w nb e d s "p r o b a b l yr e p r e s e n ts h o r te p i s o d e s
o fs l i g h tt r a n s g r e s s i o n
and s l i g h t l y h i g h e r e n e r g y c o n d i t i o n s
as i n d i c a t e d by t h ep r e s e n c eo fi n t r a c l a s t s .
Swamp d e p o s i t s ,
commonly comprised i n p a r t of c o a l s , may o c c u r t o t h e
l a n d w a r ds i d e
of s u c h b a r r i e r b a r s ( S e l l e y ,
and o t h e r s ,1 9 7 3 ) .
1972; Pettijohn
The l o w e s tc o a l - b e a r i n gu n i t so ft h e
basalMesaverdeFormation
may b e t h e c o a l s o f y o u n g e r
swamps
l e f t by t h e r e g r e s s i n g s e a .
MesaverdeFormation
*
TheMesaverdeGroup
wasnamed
by Holmes ( 1 8 7 7 ) f o r
e x p o s u r e so nM e s a v e r d ei ns o u t h w e s t e r nC o l o r a d o W
. inchester
( 1 9 2 0 ) i n c l u d e dt h er o c k sh e r e i n
mapped a s t h e
Mesaverde
37
D
F o r m a t i o nw i t h i nh i s
ChamisoFormation.
t h a t t h e term"Mesaverde"
name s o u t ho ft h e
was u s e d l o o s e l y a s
type l o c a l i t y .
MesaverdeFormation
a formational
H i s d e f i n i t i o n of t h e
a t D-CrossMountainincluded
t h e Gallego
41957) c a l l e dt h e
S a n d s t o n eo ft h i sr e p o r t T
. onking
MesaverdeFormation
P i k e ( i 9 4 7 ) observed
of t h i s r e p o r t t h e C r e v a s s e
Canyon
( 1 9 5 7 ) , i n t h e a r e a west ofTonking,had
Formation.Givens
o b s e r v e dt h el i t h o l o g i cs i m i l a r i t i e so f
t h i s stratigraphic
i n t e r v a l w i t h t h et y p e - s e c t i o nC r e v a s s e
Canyon.
However,
C r e v a s s e Canyon F o r m a t i o n , a s d e f i n e d
by A l l e n . a n d B a l k
the
( 1 9 5 4 ) , i n c l u d e st h es t r a t ab e t w e e nt h et o po ft h eG a l l u p
S a n d s t o n ea n dt h eb a s eo ft n eP o i n tL o o k o u tS a n d s t o n e .
As
thePointLookouthasnotyetbeenidentified
within the
s t u d ya r e aa n d
is u n c e r t a i n ,
t h e G a l l u p - G a l l e g oc o r r e l a t i o n
t h i ss t r a t i g r a p h i ci n t e r v a l
is h e r e i nr e f e r r e dt o
as t h e
MesaverdeFormation.
TheMesaverdeFormation
p o r t i o n s o f t h es t u d y
area.
is e x p o s e d i n t h r e e
major
The m o s te x t e n s i v eo u t c r o p s
o c c u ri nt h en o r t h - c e n t r a lp o r t i o n ,n o r t h
of t h e
n o r t h e a s t - t r e n d i n gT i j e r a sl i n e a m e n t .H e r e ,t h ee x t e n s i v e l y
f a u l t e dM e s a v e r d eF o r m a t i o n
1 0 0 0 f t (304.8
e x p o s e de a s t
Canyon.
i s e s t i m a t e d t o be a p p r o x i m a t e l y
m) t h i c k .A n o t h e rf a u l t - a b r i d g e dp o r t i o n
.
is
of J a r a l o s a Creek i n t h e v i c i n i t y o f C o r k s c r e w
A . s h o r ts e c t i o n
i s e x p o s e da l o n gt h e
a n t i c l i n a lf o l di nt h es o u t h w e s t e r nc o r n e r
The u n d e r l y i n gG a l i e g oS a n d s t o n e
a x i s o fa n
of t h e s t u d ya r e a .
is sharply
o v e r l a i n by a b o u t 60 f t (18.3 m ) of d a r k - g r a y
(N3) m a r i n e
5
38
0
Well (sec. 3 5 , T l N ,
s h a l e west o f J a r a l o s a C r e e k a t M i d d l e
R6W).
East o fJ a r a l o s aC r e e k( s e c .
6 , T I N , R5W)
i s a b o u t 25 f t (7.6 m) t h i c k .O v e r l y i n g
,
t h i ss h a l e
t h e basalMesaverde
s h a l e i s a l i g h t - o l i v e - g r a y( 5 Y 5 / 2 ) ,m o d e r a t e l y - s o r t e d ,
i s a p p r o x i m a t e l y 4 0 f t (12.2
m a s s i v em a r i n es a n d s t o n ew h i c h
m ) t h i c ka tM i d d l eW e l l .
exhibitsslight
upperofMolenaar’s
.This
medium-grainedsandstone
upward c o a r s e n i n ga n dc o r r e s p o n d st ot h e
(1974) two b a r r i e ;b a r s .
The T e r t i a r y Baca F o r m a t i o nu n c o n f o r m a b l yo v e r l i e s
t h e MesaverdeFormation.
t h e Hot S p o tm i n ev i c i n i t y ,
in
T h i s c o n t a c t is r e l a t i v e l ys h a r p
where t h e a r k o s i c , l i t h i c - r i c h
s a n d s t o n e s of t h e B a c a F o r m a t i o n a r e e a s i l y i d e n t i f i a b l e .
west o f Chavez
T h i sc o n t a c t
is a l s o r e a d i l y i d e n t i f i a b l e
Creek,where
t h e b a s a l Baca u n i t is a p o o r l ys o r t e d ,s a n d y ,
h e t e r o l i t h i cc o n g l o m e r a t e .I nt h ev i c i n i t yo fC o r k s c r e w
C a n y o n ,h o w e v e r ,B a c a - t y p ea r k o s i cs a n d s t o n e sa r ei n t e r b e d d e d
w i t ho r g a n i c - r i c hM e s a v e r d e - t y p es h a l e s ,s i l t s t o n e s ,a n d
s a n d s t o n e so v e r
f t (9.1 m ) .
a s t r a t i g r a p h i ci n t e r v a l
ofapproximately
The c o n t a c t was d e l i n e a t e d a t t h e b a s e
l i m e s t o n e - c o b b l ec o n g l o m e r a t e( f i g .
30
of a
7).
The Mesaverde i s mainlycomprised
f l u v i a l and swamp d e p o s i t s .A p p r o x i m a t e l y
of nonmarine
200 f t (61 m ) of
d a r k - g r a y (N2) o r g a n i cs h a l e sc o n t a i n i n gi n t e r b e d so fc o a l
a n ds a n d s t o n eo v e r l i et h eb a s a lm a r i n es e c t i o n .
r a n g e i n t h i c k n e s sf r o m
The c o a l s
1 t o 2 f t (0.30 t o 0 . 6 1 m ) and a r e
i n t e r c a l a t e dw i t ho r g a n i cs h a l e sa n dt h i no l i v e - g r a y
v e r y - f i n e - g r a i n e d s, i l t ys a n d s t o n e s P
. a l y n o l o g i c a dl a t a
..
(5Y4/1),
39
Figure 7 :
Contact between. the Baca and Mesaverde formations;
Corkscrew Canyon vicinity (NW 1/4, SW 1/4, sec.
36, TlN, R6W). Basal Baca bed is a
limestone-cobble conglomerate. Hammer handle is
12.5 in. (31.8 cm) long.
40
i n d i c a t e a c o a s t a l or deltaicplainenvironmentof
a c c u m u l a t i o n w i t h b r a c k i s hw a t e ri n f l u e n c e
C h a p i na n do t h e r s ,1 9 7 9 ) .P e t r o g r a p h i c a l l y
(M.
Chaiffetz i n
(Kmv-1)
,
the
s a n d s t o n e sa r ec o m p r i s e do f8 7 %a n g u l a r ,s l i g h t l yu n d u l a t o r y ,
m o n o c r y s t a l l i n eq u a r t zg r a i n s .S u b r o u n d e dc h e r tg r a i n s
c o m p r i s ea n o t h e rl l % ' o ft h e
c e m e n t i n ga g e n t
hue.
framework c o n s t i t u e n t s .
is l i m o n i t i c c h e r t y s i l i c a w i t h
Each u n i t of s h a l e andcoal
The
a greenish
i s o v e r l a i n by dusky-yellow
( 5 Y 6 / 4 ) - w e a t h e r i n gf,i n e - g r a i n e d
s a n d s t o n eT. h e s se a n d s t o n e s
a r eu s u a l l yt h i n - b e d d e da n do f t e ne x h i b i ts m a l l - s c a l e ,
l o w - a n g l e ,p l a n a rc r o s s b e d s .
They r a n g e i n t h i c k n e s sf r o m
f t (0.6 m) t o 1 0 f t (3.1 m ) .
A p p r o x i m a t e l ye i g h tc o a la n d
s a n d s t o n es e q u e n c e s' o c c u ri nt h eM e s a v e r d eF o r m a t i o n
e x p o s u r e se a s to fJ a r a l o s aC r e e k
and n o r t ho fC o r k s c r e w
Canyon.
Above t h e s e u n i t s , t h em o d e r a t e l yi n d u r a t e d
50 f t (15.2 m ) o r more.Such
s a n d s t o n e sr a p i d l yt h i c k e nt o
s a n d s t o n e sf o r mh i g hb l u f f sa l o n gJ a r a l o s aC r e e ki nt h e
n o r t h - c e n t r a ls e c t i o no ft h eo u t c r o p
w e a t h e rt o
a grayish-yellow
(1!3YR7/4) c o l o r ;o n
belt.
T h e s es a n d s t o n e s
(5Y8/4) or a g r a y i s h - o r a n g e
a f r e s hs u r f a c et h e ya r eu s u a l l ym o d e r a t e
y e l l o w i s h brown ( 1 E ) Y R 5 / 4 ) .
Framework c o n s t i t u e n t so ft h e s e
s a n d s t o n e s (Kmv-2) are g e n e r a l l yf i n e -t om e d i u m - s a n d - s i z e ,
m o d e r a t e l ys o r t e ds, u b a n g u l a r
g.r.@.in,s,, E x t e n s i v e l y
s e r i c i t i z e dp o t a s s i u mf e l d s p a rc o m p r i s e s4 5 %o ft h ef r a m e w o r k
g r a i n s .C l e a r ,m o n o c r y s t a l l i n e ,q u a r t zw i t hs t r a i g h t
e x t i n c t i o nc o m p r i s e sa n o t h e r3 2 % .
About 1 0 % o ft h e s eq u a r t z
2
g r a i n s a f er u t i l a t e d .L i t h i cf r a g m e n t s ,c o m p r i s i n g
1 4 % of
t h e framework c o n s t i t u e n t s , a r e p r i m a r i l y c l a y a n d s e r i c i t e
balls.
The c e m e n t i n ga g e n t
c a r b o n a t ec r y s t a l s P. o r o s i t y
( 0 . 6 4 cm) t o 6 i n .( 1 5 . 2c m ) .
i s a b u n d a n t ,a sa r et w i gi m p r i n t s .S m a l l -a n d
l a r g e - s c a l e ,l o w - a n g l e ,p l a n a r
commonly.
is t i n yi n t e r l o c k i n g
i s v e r y low.
Bedding
0.25 i n .
t h i c k n e s s e sr a n g ef r o m
O r g a n i cd e b r i s
of t h er o c k
o r t r o u g hc r o s s b e d d i n go c c u r s
S a n d yd, a r k - r e d d i s h - b r o w (nI 0 R 3 / 4 )h, e m i s p h e r i c a l
n o d u l e so f t e nw e a t h e ro u t
commonly 2 i n .
i n b o l dr e l i e f .T h e s en o d u l e sa r e
( 5 cm) or l e s si nd i a m e t e r .
A very-resistant,
g r a y i s h - b r o w n( 5 Y R 3 / 2 ) - w e a t h e r i n g f, i n e - g r a i n e ds a n d s t o n e
o f t e nc a p st h en o d u l e . - b e a r i n gu n i t s( f i g .
g r a i n s i n t h i sr e s i s t a n ts a n d s t o n e
Theframework
8).
(Kmv-3) a r eg e n e r a l l y
s u b a n g u l a ra n dm o d e r a t e l ys o r t e d .Q u a r t zw i t hs t r a i g h t
e x t i n c t i o nc o m p r i s e s
6 1 % o ft h e s ef r a m e w o r kg r a i n s .
I n c l u s i o n s o fs t u b b ym u s c o v i t el a t h s ,r u t i l e ,a n db u b b l e s
o c c u r commonly.
R e l i c ts y n t a x i a ls i l i c a
cementoccurson
a b o u t 1 0 % o ft h e s eg r a i n s .O t h e rf r a m e w o r kc o n s t i t u e n t s
include 12%sericitized po'tassium feldspar, 13% organic-r ich
c l a ya n d
s e r i c i t e b a l l s , and 9 % s u b r o u n d e dc h e r t .B l o c k y
c a l c i t e c e m e n th a sf i l l e dm o s tp o r e si nt h e s e
rocks.
Small-
t o l a r g e - s c a l e ,h i g h - a n g l e ,t r o u g hc r o s s b e d ss t a n do u t
.
m a r k e dtilhnye bs e d s .
Between t h e s e s a n d s t o n e
u n i t s a r eo r g a n i cs h a l e , -
l i g n i t e , and i n t e r c a l a t e d s i l t y s a n d s t o n e u n i t s ,
e
f t ( 1 . 5 m) o r less t h i c k .
w e a t h e rd a r kg r e e n i s hb l a c k
commonly 5
The s h a l e s and l i g n i t eg e n e r a l l y
(5GY4/1).
S i l t ys a n d s t o n e s ,
42
Figure 8:
Cross-stratified "brown bed" in Mesaverde
Formation; H o t Spot mine vicinity (NW 1/4, N W
1/4, sec. 18, TlN, R5W). Jacob's staff is
graduated in feet.
"
43
-
.
. 1
weathering grayish brown (5YR3/2) to grayish olive (10Y4/2),
are gradational with these shale and lignite units, and
rarely exceed 3 in. (7.6 cm) in thickness.
The uppermost approximately 100 ft (3b.5 m) of the
Mesaverde Formation is similar in appearance to the basal
coal-bearing section.
The coals in this part of the
Mesaverde Formation were mined from several adits.at the Hot
Spot mine-(NW 1/4, sec. 18, TlN, R5W).
here is 5 ft (1.5 m) thick.
The thickest coal bed
These coals exhibit rapid
lateral thickness variation as well as rapid lithologic
gradation into dark-gray (N3), silty shaie and
pale-yellowish-brown (10YR6/2), very-fine-grained silty
sandstone. Vertically: the
coals also grade into
medium-dark-gray (N4) shale and grayish-olive-green
(5GY3/2)-weathering mudstone with 16.25 in. (0.64 cm) thick
wavy laminations. Each
coal sequence is capped by
grayish-olive (10Y4/2), thin-bedded to massive,
very-fine-grained sandstone.
These sandstones commonly
weather to 'dark yellowish brown (lBYR4/2), and contain
fossilized twigs and twig imprints. In contrast to the coals
of. the basal Mesaverde Formation, pollen recovered from coal
of the upper Mesaverde Formation indicate isolated upper
I
coastal plain swamp environments (M. Chaiffetz in Chapin and
others, 1979).
Associated with the coal-bearingunits of both the
e
basal and upper Mesaverde Formation are ironstone
concretions.
These concretionsareblackish-red
i
(5R2/2),and
I
~
~~
~~
44
3
.
r a n g ei ns i z ea n ds h a p ef r o m
3 in.
( 7 . 6 cm) o b l a t e masses.
1 in.
o
( 2 . 5 cm) e l o n g a t ec h i p s
The c o n c r e t i o n sa r ea l w a y s
found a s f l o a t , a n d o f t e n c o m p l e t e l y m a n t l e t h e g r o u n d
s u r f a c e .S i l i c i f i e d
coal-bearingunits
wood was f o u n do n l yi nt h eu p p e r
a t CorkscrewCanyon.
to
45
Tertiary Eocene
Baca Formation
I
Winchester (1920) inciuded the present-day Baca
Formation within his Datil Formation.
The Baca Formation was
separated' from the Datil Formation and named for exposures
along Baca.Canyon (secs. 4, 5, 8 , 'and 9; TlN, R4W) by Wilpolt
.and others (1946).
Their description of this formation,
however, was taken from exposures in the Joyita
Hills-Carthage area.
They described the Baca Formation as
consisting of conglomerates, red and white sandstones, and
red clays.
Clastic material comprising the conglomeratic
units was derived from Precambrian quartzite and granite, the
Madera Limestone, and the Ab0 Formation.
Tonking (1957)
stated that the Baca Formation ranges in thickness from 0 to
700 ft (0 to 213.4 m).
Potter (1970) measured a composite
section of 695 ft (211.8 m) at Baca Canyon and also
designated tnree informal sections.
Snyder (1971) reported a
maximum thickness of 25@0 ft (762 m) from a Tenneco o i l test
drilled south of Pie Town, New Mexico.
Massingill (1979)
measured a 754-ft (230 m)-thick section about two miles (3.2
km) north of the type section.
Gidley (in Gardner, 1910) identified a fossil tooth
found in variegated beds unconformablyoverlying the
Mesaverde Formation in the Carthage area as Paleosyops of
c
.'
__
5
I
.,
-
*
m i d d l e 8oc;Zne age.
Sgyder
( 1 9 7 0 , 1 9 7 1 ) r e p o r t e it h e
d i s c o v e r y ~ i .a p a r t i a l s e c t i o n o f
a j a w b o n ec o n t a i n i n gf o u r
in the’
t e e t hw h i c ih a dw e a t h e r e df r o mt h eB a c aF o r m a t i o n
D a t i lM o u n z a i n s
(SE 1/4,
SW 1 / 4 ,
was i d e n t e i e d by Dr. C . L .
G a z i n of t h e U.S.
a s b e i n g k a t o fP r o t o r e o d o np u m i l u s
N a t i o n a l Museum
of l a t e E o c e n e a g e .
S t r a t i g r a F r i c a n ds e d i m e n t o l o g i cs t u d i e so f
I
The jaw
s e c . 31, T2N, R9W).
t h e Baca
i n t h es t u d ya r e a ,h a v eb e e n
or mat ion, i n c l u d i n ge x p o s u r e s
c o n d u c t e d by Snyder ( 1 9 7 1 ) , J o h n s o n( 1 9 7 8 ) ,a n dC a t h e r( i n
prep.).
T f e s e s t u d i e s h a v ea t t e m p t e dt or e c o n s t r u c tt h e
e n v i r o n m e n z so fd e p o s i t i o na n dt r a n s p o r td i r e c t i o n so fB a c a
sediments.
?heBacaFormation
i s exposed i n a n e a s t - t r e n d i n g
e l o n g a t e b e l t t h a t i s a p p r o x i m a t e l y 1 2 0 m i (193 km) l o n g by
2 0 m i (32 km) wide.
O t h e rf o r m a t i o n sw h i c h
may b ep a r t l y
c o n t e m p o r a n e o u sw i t ht h eB a c aF o r m a t i o ni n c l u d et h e
McRae,
G a l i s t e o ,a n dR a t o nf o r m a t i o n s( L e e ,1 9 1 5 ;W i l p o l ta n d
o t h e r s , 1 9 4 6 ; T o n k i n g1, 9 5 7 )K
. e l l e ya n dS i l v e (r 1 9 5 2 a) n d
T o n k i n g( 1 9 5 7 )b e l i e v et h a tt h e s ef o r m a t i o n sr e p r e s e n t
d e p o s i t so fi s o l a t e db a s i n s .S n y d e r
( 1 9 7 1 ) andJohnson
( 1 9 7 8 )h a v es u g g e s t e dt h a tt h eE a g a rF o r m a t i o n
of e a s t e r n
A r i z o n a i s a l a t e r a l e q u i v a l e n t of theBaca.
I n t h es t u d ya r e a ,t h eB a c ac r o p so u ti n
a broad
s w a t ht h r o u g ht h ew e s t e r n ,c e n t r a la n ds o u t h e a s t e r nr e g i o n s .
E x t e n s i v ef a u l t i n ga n dl o c a lf o l d i n go c c u rt h r o u g h o u tt h i s
b e l t .S m a l l e ro u t c r o p so c c u ri nt h es o u t h w e s t e r nc o r n e r
t h ef l a n k s
o f a s m a l la n t i c l i n e .
.
on
A maximum t h i c k n e s s of 950
3 ,
J
*
ft (289.6 m) was approximated from structural cross-sections.
The Baca Formation crops out as a series of gently dipping
discontinuous sandstone ridges and hogbacks which are
generally elongated in a northerly direction.
Between these
ridges are shallow valleys underlain by less-resistant shales
and siltstones.
The nature of the depositional contact between the
Baca and the underlyingMesaverde Formation shows rapid
variation within the study area. Generally, west of Jaralosa
Creek, this contact is marked by an irregular pinkor white
sandy conglomerate.
45.7-cm)-thick.
This bed is 4- to 18-in. (18.2- to
Clasts are a poorly sorted, well-rounded mix
of iron concretions, petrified wood, and siltstone chips,
presumably derived from the Mesaverde Formation.
Other
lithologies include well-polished, multicolored quartzite and
silicified siltstone which are more common in the upper
conglomeratic units of the Baca Formation.
Above the basal
conglomerate, the red, white, and yellow units of the Baca
are unmistakeable.
Slight angular unconformity between the
Baca and Mesaverde is also evident at these locations. East
.
of Jaralosa Creek, the basal conglomerate of the Baca is
comprised at least in part of rounded concretions and clasts
of massive, gray limestone (fig. 7).
The abundance of
limestone clasts in this conglomerate generally increases
southwards to Corkscrew Canyon.
*
South of Corkscrew Canyon,
limestone concretions and clasts occur within the Baca over a
stratigraphic interval of approximately 30 ft (9.1 m).
In
"
5
this area, Mesaverde-type sandstones, grgy siltstones and
.
i
shales are interbedded with Baca-type sandstones,
conglomerates, and red shales.
The two formations appear to
be conformable.
The contact of theBaca Formation with the
overlying Spears Formation is well-exposed on the western
faces of eastward-dipping hogbacks along the east bank of
Jaralosa Creek (SE 1/4, sec. 1 3 and E 1/2, sec. 24, TlN, R6W;
fig. 9 ) and north of theHook Ranch headquarters (SW 1/4,
sec. 24, TlN, R6W).
This contact is interbedded and
.
gradational over a stratigraphic interval of about 50
(15.2
m).
ft
Within this interval the Baca Formation is
comprised of thinly bedded, medium-grained, moderately
sorted, moderate-red (5R6/4), arkosic sandstones.
The Spears
Formation is comprised of thinly bedded, medium-grained,
moderately sorted, grayish-red-purple (5RP4/2),
volcaniclastic sandstones and siltstones.
The Baca Formation is usually comprised of
sequences of sandstone, siltstone, and shale that average
about 15 to 40 ft (4.6 to 12.2 m) in thickness.
These units
become finer grained from bottom to top; however, the basal
sandstones of these sequences have a slight tendency to
coarsen upwards.
The units become slightly coarser grained
"
toward the middle and upper portions of the Baca Formation
where shales and mudstones are less common.
The sandstones
in the lower half
of the Baca Formationweather grayish
orange (10YR7/4) to pinkish gray (5YR8/1).
Towards the top
Figure 9:
Gradational contact between Spears and Baca
formations; east bank of Jaralosa Creek across
from Hook uranium prospect (SW 1/4, SE 1/4, sec.
3, T l N , R6W). Volcanic fragments occur within the
siltstones and medium-grained sandstones between
the two prominent sandstone beds,as well as
within the lower sandstone bed, Contact is
designated above highest Baca-type sandstone.
50
'i
>.
a
of the-formation, the sandstones we:ther
moderate red (5R5/4)
i
to pale reddish brown (18R5/4).
Bedding thicknesses range from 1 in. to 2 ft (2.5
cm to 0.6 m).
High-angle, small- and Large-scale trough
cross-bedding is commonly (fig. 18).
The sandstones commonly
contain near their base chips of siltstone as long as 4 in.
(10.2 cm) derived from the'top of the underlying sequence.
Brown wood casts
are
commonthroughout the sandstones.
Dark-gray (N3) silicified wood occurs throughout the Baca
Formation, but it is larger and more abundant in.the
top-third of this formation.
The sandstones are comprised of
medium to coarse sand grains;
sorting is poor to moderate.
A
few polished quartzite pebbles are occur within the
sandstones.
Petrographically (Tb-2), the sandstones are
comprised of approximately 50% monocrystalline quartz with
undulatory extinction, 18% sericitized potassium feldspar,
13% well-rounded hematitic chert grains, and 18% lithic
fragments.
The lithic fragments are comprised chiefly of
sericitic mudstone.
Near the middle of the Baca Formation, the basal
few inches of sandstone beds are often conglomeratic
sandstone (fig. 11).
The clasts are a poorly sorted,
frequently imbricated mixture of well-rounded and polished
"
multicolored'quartzite and chert
withlesser amounts
granite and red, silicified siltstone.
of
Well-rounded,
medium-light-gray (N6) limestone clasts locally occur in
these basal conglomerates.
Clasts from the conglomerates
will often completely mantle the
groundsurface.
Figure 18:
Large-scale, tangential cross-stratification in
sandstone of ttie Baca Formation; south of
Corkscrew Canyon (sec. 2, TlS, RbW).
Hammer
handle is 12.5 in. (31.8 cm) long.
Figure 11:' Conglomerate within lower Baca Formation; south
of Corkscrew Canyon (sec. 2, TlS, R6W). Hammer
handle is 12.5 in. (31.8 cm) long. Clasts are
well sorted, well rounded, and imbricated. They
are comprised chiefly of multicolored quartzite
with some-banding o r quartz veining. Overlying
unit is a bleached, subangular, medium-grained,
moderately sorted quartz-feldspar sandstone.
1
Gradationally overlying bandstonessin the lower
Baca Formation are dark-reddish-brown (10R3/4) siltstone and
shale units that range from 5 to 8 ft (1.5 to 2.4 m) thick.
Thin discontinuous pods and lenses of dark-greenish-gray
(5G4/1) mudstone occur infrequently below the basal sandstone
of the succeedingsandstone and siltstone sequence in the
lower-third of theBaca FormatiDn. Towards the top of the
Baca Formation, siltstones and sandy siltstones replace
shales.
The thickest siltstone interval occurs approximately
315! ft (9.1 m) below the top of the Baca Formation and'is
about 18@ ft (30.5 m) thick. It
forms the broad valley north
of the Hook Ranch headquarters (SE 1/4, sec. 23, TIN, R6W)
and presumably underlies Jaralosa Creek in the vicinityof
Little Well (secs. 13 and 24, 'TlN, R6W).
A 3-in.
(7.6 cm)-thick, light-gray (N7)
nonfossiliferous limestone bed occurs westof Jaralosa Creek
(SE 1/4, sec. 26, TlN, R6W).
Limestone float of similar
appearance occurs near the base ofthe Baca Formation in the
southwestern corner of the study area (sec. 2, TlS, R6W).
The origin of the Baca Formation is presently in
dispute. Snyder
(1971) and Massingill (1978, oral commun.),
on the basis of observations which are similar to those of
the author, suggest that the Baca Formation is comprised of
cyclic, fining-upward deposits of fluvial and lacustrine
origin.
In contrast, Johnson (1978) and Cather (1978,
written commun.) have described cyclic coarsening-upward
sequences which they believe represent deposits of lacustrine
.
deltas.
The m a j o rd i f f e r e n c eb e t w e e nt h e s ei n t e r p r e t a t i o n s '
o fd e p o s i t i o n a le n v i r o n m e n t s
l i e s i n t h e i n t e r p r e t a t i o n of
what c o n s t i t u t e s a g e n e t i c s t r a t i g r a p h i c i n t e r v a l .
Oligocene
S p e a r sF o r m a t i o n
T o n k i n g( 1 9 5 7 )s u b d i v i d e dW i n c h e s t e r ' s
F o r m a t i o ni n t ot h r e e
membersand
named t h e b a s a l member a f t e r
t h e Guy S p e a r s Ranch (sec. 8 , TlN, R4W).
c o n s i s t s of n e a r l y1 3 5 0
Oligoceneage(37.1m.y.,
( 1 9 7 1 a )e l e v a t e d
H i s t y p es e c t i o n
f t ( 4 1 1 . 5 m) o f v o l c a n i c l a s t i c
B u r k e a n do t h e r s( 1 9 6 3 )r e p o r t e da ne a r l y
s e d i m e n t a r yr o c k s .
n e a r t h e t o po f
(1920) D a t i l
K/Arl
b i o t i t e ) for a l a t i t e b o u l d e r
t h e S p e a r si nt h eJ o y i t a
Hills.
Chapin
t h e S p e a r st of o r m a t i o n a ls t a t u s .
The S p e a r sF o r m a t i o n
d e r i v e df r o me r o s i o n
i s a v o l c a n i c l a s t i ca p r o n
s u i t e of
of t h e e a r l i e s t c a l c - a l k a l i c
t h eM o g o l l o n - D a t i 1 , v o l c a n i cf i e l d( E l s t o na n do t h e r s ,
1976).
N o r t h e a s t - t r e n d i n gp a l e o v a l l e y so c c u r r i n gw i t h i nt h eS p e a r s
F o r m a t i o n . w e r es t r u c t u r a l l yc o n t r o l l e d
by t h eM o r e n c i
l i n e a m e n ta n di n d i c a t es o u r c ea r e a st ot h es o u t h w e s t( C h a p i n
a n dS e a g e r 1, 9 7 5 ) .
i n t o twomembers
comprisedof
Brown ( 1 9 7 2 ) d i v i d e dt h eS p e a r sF o r m a t i o n
i n t h eM a g d a l e n aa r e a .
T h e lower
.. member i s
l a t i t i ct oa n d e s i t i cc o n g l o m e r a t e s ,
mudflow
d e p o s i t s ] and t h i n ,i n t e r b e d d e dv o l c a n i c l a s t i cs a n d s t o n e s .
The upper member is comprised of b a s a la m y g d a l o i d a l" t u r k e y
*
track" andesite flows, the tuff of Nipple Mountain, and
overlying andesitic lava flows and latitic ash flow tuffs
with interbedded mudflow deposits and conglomerates
Massingill (1979) reports a thickness of 1259.5 ft (383.9 m)
for the Spears Formation northeast of the study area (sec.
17, TlN, R4W)
.
Malor outcrops of the Spears Formation occur in the
south-central portion of the study area, along the eastern
and western margins.
Maximum thickness of the Spears is
estima.ted at approximately 1U00 ft (304.8 m).
The lower 100
ft (30.5 m) of this formation crops out in a series of
hogbacks; the remainder crops out as low, rounded hummocks.
The basal contact with the underlying Baca
Formation is well-exposed on the western face of the gently
dipping hogbacks along the east bank of Jaralosa Creek (SE
1/4, sec. 13 and NE 1/4, sec. 24, TIN, R6W) and on the
western face of a wedge-shaped fault block north of the Hook
Ranch headquarters (sec. 24, TlN, R6W).
At these locations
the gradational and interbedded nature of this contact over a
stratigraphic interval of about 50
seen (fig. 11).
ft (15.2 m ) can be clearly
Within this zone, the Baca Formation is
comprised of thin-bedded, medium-grained, moderately sorted,
moderate-red (5R6/4) arkosic sandstones.
The Spears
i
Formation is comprised of thinly bedded, medium-grained,
moderately sorted, grayish-red-purple (5RP4/2) volcaniclastic
sandstones
.
.?
i
An upper contact with the Hells Mesa Tuff is poo;ly
-
exposed on thenorth face of the hogback west of Abbe Spring
(SW 1/4, sec.25, TlN, R 5 W ) , and somewhat better exposed in a
stream cut east of Jaralosa Creek (SW 1/4, sec.25, TIN, R6W).
The contact in each of these places appears unconformable.
The Hells Mesa Tuff appears at the latter location to have
filled channels eroded into the Spears Formation.' Over much
of its outcrop extent within the study area, the upper Spears
Formation is fault bounded.
However, a depositional contact
of the Popotosa Formation on the Spears was mapped in a
canyon east of Jaralosa Creek (NE 1/4, sec. 25, TIN, R6W).
This may record the burial of an earlier fault scarp by
Popotosa sediments.
The main body of the Spears
Formationconsists
predominantly of moderately to well-indurated channel
conglomerates, mudflow deposits, and lithic sandstones (fig.
12).
Bedding ranges from approximately 2 in. (5.1 cm) to 2
ft (0.61 m) in thickness, and at times exhibits low-angle,
large-scale, tangential cross-stratification.
range from grayish red purple (RP4/2)
Outcrop colors
to pale pink (5RP8/2).
Propyllitic alteration, forming a chlorite-epidote-calcite
assemblage, gives some areas of the formation a greenish-gray
(l0G4/2) color.
Fining-upward sequences are common within
the channel deposits. Clasts are commonly subrounded and
range in diameter from 0.125 to -4 in. (0.32 to 10.2 cm).
The
clasts are comprised dominantly of latitic to andesitic rocks
consisting of felted plagioclase laths in a gray, aphanitic
Figure 12:
Mudflows in the lower Spears Formation; east of
the Book Ranch headquarters (NW 1/4, NW 1/4, sec.
25, TlN, R6W). Hammer handle is 12.5 in.
(31.8
cm) long. Clasts are subangular to roundgd,
poorly sorted, and heterolithic. They are
comprised chiefly of volcanic lithologies with
lesser amounts of gray Pennsylvanian limestone,
red siltstone (Abo Formation?), and quartzite.
58
*
J
1
groundmass.
Red siltstone clasts, derived from the Abo
Formation of Permian age, and clasts of Pennsylvanian
limestones and Oligocene basaltic-andesites also occur.
Petrographically (Ts-1, Ts-2), the sandstones and
conglomerates are very poorly sorted and have low porosity
due t o high matrix content.
The lithic fragments are
comprised of argillized plagioclase crystals (average
composition An48, average of 20 grains, Michel-Levy method)
and green hornblende, extensively replaced by calcite and
magnetite, within a groundmass of tiny subparallel
plagioclase crystals and hematite-stained microlites.
Cementing agents of these lithic fragments are usually
present only in small amounts and are chiefly limonite with
lesser amounts of patchy calcite.
Potassium feldspar is
essentially absent from the thin sections examined, with the
exception of the groundmass of the lithic fragments.
Dark-greenish-black (5GY4/1) andesite flows form
discontinuous outcrops in the upper Spears Formation,
especially in the area south of the Hot Spot mine (E 1/2,
sec. 24, TlN, R6W).
These flows, which Tonking (1957) termed
"turkey-track'' andesites, are generally porphyritic.
The
phenocrysts consist of as much as 75% lath-shaped
plagioclase, 18% magnetite, and 15% corroded hornblende.
The
flows generally do not exceed 20 ft (6.1 m) in thickness.
Discontinuous exposures of two tuffs within the-
c
Spears Formation were mapped in the study area.
The lower
tuff (Tstl) is light gray (N7), crystal poor and poorly
.
5,
.
welded.
Petrographically, it consists
-
Of
10% rod-shaped
pumice fragments, 2 % potassium feldspar subhedra, 2% rounded
to subangular latitic litnic fragments, 1% magnetite anhedra,
and trace amounts of brownish-red biotite.
The groundmass is
comprised of fine hematite and magnetite, arcuate glass
shards, and microlites.
throughout the rock.
Large patches of calcite occur
The upper tuff (Tst2) is
grayish-orange-pink (IEIR8/2)
and is found near, or at, the
,
upper contact of the Spears Formation.
Petrographically, it
consists of 15% corroded plagioclase subhedra (An45, av.erage
of 15 grains, Michel-Levy method) with some partial calcite
replacement, 5% ragged brown biotite flakes and 3 % magnetite
anhedra in a matrix of hematite-stained, parallel-aligned
arcuate glass shards and microlites.
de€ined by the glass
A crude foliation is
shards and the biotite phenocrysts.
Subrounded andesitic lithic fragments can comprise as much as
5% of the total rock.
Each of these tuff units is no more
than 15 ft ( 4 . 6 m) thick; they occur only as small, isolated
remnants witnin the study area.
The occurrence of mudflow deposits with randomly
oriented clasts in an unsorted matrix and conglomerates with
low-angle cross-stratification support the interpretation
that the Spears Formation represents alluvial-fan deposits.
"
Such features are described by Reineck and Singh (1975) for
alluvial-fan deposits in tectonically active areas.
The axis
of one channel observed in the study area seemingly supports
Chapin and Seager's (1975) assertion that transport was
directed'away from source areas in the Magdalena and San'
Mateo mountains or beyond.
Hells Mesa Tuff
Tonking ( 1 9 5 7 ) included within his Hells Mesa
Member of theDatil Formation, the Hells Mesa Tuff and the
A-L Peak Tuff of this report.
Subsequent redefinition by
Deal ( 1 9 7 3 ) and Chapin ( 1 9 7 4 ) revised the Hells Mesa Tuff to
formational status and restricted it to the basal
crystal-rich ash-flow tuff.
Elston and others ( 1 9 7 6 )
consider the Hells Mesa Tuff to be one of the youngest
ash-flow tuffs of a calc-alkalic suite exposed on the
Mogollon Plateau. The Hells Mesa Tuff was erupted from the
North Baldy cauldron in the central Magdalena Mountains
(Chapin and others, 1 9 7 8 ) .
Outcrops of the Hells Mesa Tuff
are very widespread andoccur northwards to the northern .
terminus of the Bear Mountains.
Weber and Bassett ( 1 9 6 3 ) obtained a K-Ar date of
30.6 + 2.8
m.y.
(biotite) from the base of the Hells Mesa
Tuff at Tonking's ( 1 9 5 7 ) type section on Hells Mesa.. Burke
and others ( 1 9 6 3 ) reported a K-Ar date of 3 2 . 1
0.2
m.y.
(biotite) from a sample collected from south of Dog Springs
Canyon in the Gallinas Mountains (SE 1/4,
and another K-AT date of 32.4 m.y.
sec. 7, TlN, R8WkI
(biotite) from a sample
collected from the basal Hells Mesa Tuff in fhe Joyita
Hills.
,
. .
D
”
The Hells Mesa Tuff crops out in the study area
principally as steep, rubble-covered hogbacks west of Abbe
Spring (SW 1/4, sec. 8, TlN, R5W) and east of Jaralosa Creek
(SW 1/4, sec. 25, TlN, R6W).
Its unconformable basal contact
with the underlying Spears Formation is well-exposed at the
latter location in the stream cut between the two hogbacks.
Osburn (1978, oral commun.) suggested that a
moderate-orange-pink ( l $ R 7 / 4 ) ,
poorly welded, quartz-bearing
tuff observed east of the Hot Spot mine (NW 1/4, NE 1/4, sec.
18, TlN, R5W) represents the base of the Hells Mesa Tuff.
This particular rock, however, was not observed at any of the
other outcrops of the Hells Mesa Tuff.
blaximum thickness of
the Hells Mesa Tuff in the study area is about 200 ft (61 m )
east of Jaralosa Creek (sec. 25).
Both north and south of
this location, the Hells Mesa Tuff thins rapidly to zero feet
thickness.
At the southern terminus of its outcrop, a
conglomerate with clasts derived exclusively from the Hells
Mesa Tuff was observed.
Emplacement of the Hells Mesa Tuff
appears to have been controlled by channels cut into the
underlying Spears Formation.
The
Hells
Mesa
Tuff
is generally a pale-red
(10R6/2), densely welded crystal-rich rhyolitic tuff that
weathers to grayish-red (10R4/2) angular blocks.
Abundant
phenocrysts, at times constituting 50% of the total rock, are
observable by the naked eye in hand specimen. They include
clear to smoky quartz, copper-colored biotite flecks,
plagioclase, and sanidine.
Pumice fragments comprise
D L
.
*
D
*
.
approximately 25% of the rock near the base. The fragments
are round o r rod-shaped and impart a moderately good
foliation t o an outcrop. Pumice content decreases to less
than 10% near the top of the formation. Angular lithic
fragments of average diameter 1 cm (0.4 in.) and comprised of
purplish andesite occur sparsely.
Brown (1972) attributes
these clasts to the underlying Spears Formation.
Petrographically, clear, angular quartz anhedra to
3 mm (0.12 in.) in diameter increase in abundance from
approximately 8 % of the phenocrysts at the base to 2 8 % near
the top.
Plagioclase euhedra of average composition An54
(average of 5 grains, Michel-Levy method) comprise 60% of the
phenocrysts near the base.
Plagioclase decreases in
abundance upwards in the unit to 3 3 % and becomes more calcic
(An65, average of 6 grains, Michel-Levy method).
Fresh
sanidine subhedra increase in abundance from about 1 7 % near
the base, to 30% near the top.
Pumice fragments are
generally devitrified in a spherulitic manner.
The
groundmass is comprised of glass and spherulites with reddish
hematitic pigmentation.
A-L Peak Tuff
Tonking ( 1 9 5 7 ) included the A-L Peak Tuff within
his Hells Mesa Member of the Datil Formation.
Brown (1972)
did the first definitive work on this formation in the Bear
Mountains, where he mapped and described two units of what he
.
*
:I
.-
informally called the tuff of Bear Springs.
.Deal (19731, and
-
Deal and Rhodes (1976) formally named these rhyolitic
ash-flow tuffs for a 2000-ft (609.6 m) section exposed on A-L
Peak in the northern San Mateo Mountains and inferred a
source in the Mt. Withington cauldron.
Smith and others
(1974) determined a fission~trackage of 31.8
2 1.7 m.y. for
the A-L Peak Tuff at the type locality. Chamberlin (1974)
mapped three cooling units in the Council Rock'district.
According to Elston and others (1976), the A-L Peak Tuff is
representative of the basal flows of a high-silica alkali
rhyolite suite found in the Mogollon Plateau area.
The A-L Peak Tuff occurs as two cooling units
separated by approximately 330 ft (100.6 m) of La Jara Peak
BasalticAndesite in the study area.
Outcrops occur in the
vicinity of Abbe Spring, east of the Hot Spotmine, and east
of Jaralosa Creek to the southeast of the Hook Ranch
headquarters.
Gray-massive member:
The gray-massive member of the A-L Peak Tuff crops
out almost exclusively as a rubble-covered slope in the study
area.
Platy fragments, commonly 0.75 by 3 in. (1.9 by 7.6
cm), mantle the ground surface.
.
Its basal contact with the
Hells Mesa Tuff east of Jaralosa Creek (SW 1/4, sec. 25, TlN,
R6W), and with the Spears Formation south of the ChavezRanch
(NW 1/4, sec. 9, TlN, R5W), is unconformable.
An upper
contact was not observed in the study area due to ground
.
64
i
r?
cover.
Tne gray-massive membef apFLars to have. filled
topographic lows resulting from post-Hells Mesa erosion.
It
ranges in thickness from about 20 to 300ft (6.1 to 91.4 m)
with rapid local variation.
The gray-massive member is moderate orange pink
(5YR8/4) in color andpoorly welded at the base; it becomes
grayish orange pink (5YR7/2) and densely welded towards the
top.
Pumice fragments, comprising 18% of the total rock, are
oblate- to rod-shaped with long dimensions generally parallel
to bedding.
Fresh sanidine subhedra are the dominant
phenocrysts, comprising as much as 5% of the rock.
these sanidine phenocrysts are perthitic.
A few of
Other phenocrysts,
present in trace amounts, include clear quartz anhedra and
magnetite subhedra.
measure by hematite.
The latter is commonly replaced in large
Groundmass material is comprised of
roughly equal amounts of arcuate glass shards with
subparallel alignment and irregular areas of quartz and
alkali feldspar developed by vapor-phase crystallization.
Andesitic lithic fragments can comprise as much as
rock.
3%of the
A typical fragment is .3 mm in diameter and composed of
plagioclase microlites and magnetite euhedra.
Pinnacles member:
The pinnacles member, interbedded within the La
Jara Peak Basaxtic Andesite, is well-exposed on
Forest
Road
123 near Abbe Spring (sec. 8, TlN, R5W) and east of Jaralosa
r
Creek (sec. 18, TlN, R6W).
It crops out as a steep cliff o r
5
65
~
-
slope. Both upper and lower contacts are disconformable with
the La Jara Peak Basaltic Andesite.
Blocks of La Jara Peak
Basaltic Andesite are caught up in the base of thepinnacles
member. Lithic
fragments of La Jara Peak average 3 cm in
diameter and occur throughout the entire unit.
The pinnacles
member is 78 ft (23.7 m) thick in the Abbe Spring area, but
thins rapidly westward to less than'1D ft (3.0 m) thick.
A
180L3-foot (384.8 m)-thick accumulation in an area east of
Jaralosa Creek may be attributable to ponding in a
paleovalley along theTijeras lineament.
The color of the tuffat the base of the pinnacles
member is light brown (5YR5/6), weathering to grayish red
purple (5RP4/2).
'
Upwards in the unit, the color of a
weathered surface grades into pale reddish brown (19R5/4).
Pumice fragments are sandy-textured and elongate, and range
from 0.32- to 17.8-cm long.
A
prominent foliation is defined
by these well-flattened fragments. In exposures in Abbe
Spring Canyon, sanidine crystals as long as 3.2 cm are
gradationally more abundant in a 20-foot (6.1 m) zone
beginning 13
ft (4 m) from the top of the unit.
Pumice fragments comprise 1@% of the rock.
These
pumice fragments are seen in thin section to be replaced
*
internally by a 0.1 mm thick layer of axiolites, and by
interlayered hematite-stained quartz and alkali feldspar
anhedra.
Small anhedra of magnetite occur in trace amounts.
Sanidine euhedra, exhibiting very little alteration, are
approximately 2 mm long and comprise 5 % of the rock.
Other
66
fl
minor constituents include magnetite anhedra, replaced in
part by hematite, and basaltic-andesite lithic fragments.
Plagioclase was not observed in the thin section examined.
The groundmass is comprised principally of 0.7 mm long,
subparai ail el, devitrified glass shards outlined by hematite
dust, and anhedral crystals of quartz and alkali feldspar.
La Jara Peak Basaltic Andesite
Tonking (1957) named the basaltic and andesitic
flows overlying his Hells Mesa Member, the La Jara Peak
Member of the Datil Formation.
The unit derives its name
from La Jara Peak, a prominent volcanic neck in sec. 11 (T2N,
R5W).
Willard (1959) correlated the La Jara Peak Basaltic
Andesite with the post-Datil Mangas Basalt in Catron County.
This correlation was accepted by Weber who proposed exclusion
of the LaJara Peak rocks from the Datil Formation (1963,
1971).
Chapin (1971a) reports a whole-rock K-Ar date of 23.8
+ 1.2 m.y. from the east'side of
the
BearMountains at Cedar
Spring ( N E 1/4, N E 1/4, sec. 31, TlN, R4W).
Brown (1972) and Massingill (1979) have mapped the
La
JaraPeak Basaltic Andesite in the Bear Mountains to the
southeast and northeast of the study area, respectively.
Chamberlin (1974) attributed the absence of the La Jara Peak
rocks in the Council Rock district southwest of the study
area to possible damming along a monoclinal fold (pp.
116-117).
67
C k - a p i na n dS e a q e r( 1 9 7 5 )p o s t u l a t et h a tt h e
p e a kB a s a l t i . =
La J a r a
A n C e s i t e was emplacedbeginning
after theic-eption
Of b l o c k f a u l t i n g i n
of t h e xisins C o l o r a d oP l a t e a u .
a c l o s e db a s i ns o u t h
They a l s oo b s e r v et h a t
p r e s e n td e s l z n a t i o n“ b a s a l t i c - a n d e s i t e ‘ ‘
comesfrom
k a n t r u e b a s a l t s ,a n dh a v ef i e l d
the
a n dp e t r o g r a p h i c
c h a r a c t e r i s t r c si n t e r m e d i a t eb e t w e e nb a s a l t s
a n da n d e s i t e s .
within
Th= La JaraPeakBasalticAndesiteoccurs
t h r e ea r e a sz l o n gt h ee a s t e r nm a r g i n
usuallyas
t h e A-L
t--0
t o n g u e ss e p a r a t e d
P e a kT u f f .
of t h es t u d ya r e a ,
by t h e p i n n a c l e s
The lowertonguehas
3 5 0 f t (106.7 m )
member of
a t h i c k n e s so fa b o u t
n e a r Abbe S p r i n ga n de a s t
of J a r a l o s aC r e e k .
T h i s tongue r e s t s unconformablyonthegray-massive
or on t h eH e l l s
t h e A-L PeakTuff
c o n t a c to ft n i st o n g u e
t h e A-L
T h e u p p e rt o n g u eo ft h e
The upper
member of
Abbe S p r i n g (secs. 8 and
La J a r a P e a k B a s a l t i c
a maximum t h i c k n e s s of655
Abbe Springand
a minimum t h i c k n e s so f
of t h e HotSpotMine.Thelowercontactof
d i s c o n f o r m a b l ew i t ht h ep i n n a c l e s
Near Abbe S p r i n g ,t h eb a s e
b l o c k sa s
member of
is disconformable.
9 , TIN, R5W),
Tuff.
Mesa T u f f .
w i t h t h eo v e r l y i n gp i n n a c l e s
Peak T u f f ,a so b s e r v e dn e a r
A n d e s i t eh a s
the
t h e s e f l o w sa r eg e n e r a l l yh i g h e ri ns i l i c a
r e c o g n i t i o n= h a t
andpotash
4 t o 5 m.y.
f t (199.6 m) n e a r
300 f t ( 9 1 . 4 m ) e a s t
t h i st o n g u e
member of t h e A-L
is
PeHk
of t h i st o n g u ec o n t a i n s
much a s 3 f t (0.91 m) l o n g of t h e u n d e r l y i n g
p i n n a c l e s member.
I n t e r b e d d i n g of t h e La J a r a Peakrocks
w i t ht h eo v e r l y i n gP o p o t o s aF o r m a t i o n
was o b s e r v e d a t one
68
.
location.
D
This interbedding occurs through a stratigraphic
interval of approximately 5 0 ft (15.2 m) at a canyon mouth
east of Jaralosa Creek (NW 1/4, NW 1/4, sec. 36, TlN, R6W).
The
La
Jara
Peak Basaltic Andesite crops out
primarily as steep, rounded, rubble-covered hillslopes often
dissected by steep, V-shaped canyons.
Individual flow
thicknesses are between 3 and 25 ft (0.91 and 7.6 m).
Weathered outcrop color ranges from brownish black (5YR2/1)
in the massive central zone of anindividual flow to dusky
red (5R3/4) in scoriaceous autobrecciated zones.
Hematitic
pseudomorphs of pyroxene averaging 1.5 mm in diameter are a
distinctive feature in hand specimens. Almond-shaped
vesicles are common and are.often filled completely with
calcite and/or quartz.
Toward the middle of most flows,
partings parallel to foliation and spaced 1 in. (2.5 cm) to 1
ft (43.3 m) apart are evident.
These parting surfaces exhibit
a greenish-black (5G2/1) sheen in hand specimen.
Lenses of moderately sorted, coarse-grained
volcaniclastic sandstone, commonly thin-bedded, occur
sparsely between flows of the La
in the study area.
JaraPeak Basaltic Andesite
They usually weather a
dark-yellowish-orange color (18YR6/6).
69
Miocene
Popotosa Formation
The Popotosa Formation, the basal formation of the
Santa Fe Group in the Socorro area, was named by Denny (1940)
for exposures in Arroyo Popotosa along the southeast side of
the Ladron Mountains (T2N, R2W).
Tonking (1957), unable to
differentiate the Popotosa Formation from the overlying units
of the Santa Fe Group
on the basis of Denny's description,
mapped all the Tertiary basin-fill as the Santa Fe Group.
The Popotosa Formation and the Spears Formation were
miscorrelated in the BearMountains and in the western
Lemitar and Socorro mountains by Spiegel (1962) and Debrine
and others (1963); see also Weber (1963).
Bruning's (1973)
comprehensive study of the Popotosa Formation in Socorro
County corrected these miscorrelations.
He interpreted the
basin-fill sedimentary rocks along the northwest flank of the
Bear Mountains as fanglomerate deposits of the Popotosa
Formation.
Bruning inferred an early Miocene age for these
rocks based on Chapin's (1971a) 24 m.y. date for the.
interbedded La Jara Peak Basaltic Andesite.
From pebble
imbrications in.exposures of the Popotosa Formation adjacent
to the studyarea, Bruning derived a general flow direction
toward the eastsoutheast, indicating source areas in the
Gallinas Mountains and the Colorado Plateau.
However, from
pebble imbrications in basal beds of the Popotosa Formation
interbedded with the La Jara Peak Basaltic Andesite, he
78
. J
.
D
inferred a southern source of detritus, possibly in the
Magdalena Mountains (Bruning, 1973, p. 8 9 ) .
Chapin and Seager (1975) state that the Popotosa
depositional basin was originally about 40 mi (64 km) wide
during middle Miocene time, and was subsequently segmented
,
into three parallel 11- to 14-mile (18- to 22-km)-wide basins
by uplift and block faulting during latest Miocene o r early
Pliocene time.
The sedimentary fill along the eastern edge
of the original Popotosa basin has been largely removed by
erosion.
Brown (1972) mapped a facies of the Popotosa
Formation in the southern Bear Mountains and Mulligan Gulch
graben which he called the fanglomerate of Dry.Lake Canyon.
These sediments were shed westward off the north end of the
ancestral Magdalena Range and consist almost entirely of
andesitic detritus derived from the
LaJara Peak Basaltic
Andesite.
The eastern boundary of this study is the western
boundary of the Popotosa outcrop belt.
Therefore, only
general observations of the basal IO@ ft (30.5 m) are herein
presented.
It should be noted that the outcrops mapped as
Popotosa Formationon the geologic map are only indurated
rocks.
The areas along the eastern boundary mapped as
colluvium (Qco), piedmont gravels (Qpm), and pediment gravels
(Qpg) may represent, in part, outcroppings of weathered
Popotosa Formation.
71
The Popotosa Formation adjacent t o the study area
is a moderately to poorly indurated, very-light-gray (NS),
weathering to yellowish-gray (5Y8/1), sandy conglomerate.
Depositional contacts with underlying formations are rarely
exposed in the study area. Exposures of such a contact with
the LaJara Peak .Basaltic Andesite east of Forest Road 123
(secs. 4 and 9, TlN, R5W), and with the Spears Formation east
of Jaralosa Creek (sec. 2 5 , TlN, R6W) show considerable
angular unconformity.
Two particularly interesting outcrops should be
noted.
One of these, along a canyon floor east of Jaralosa
Creek (SE 1/4, sec. 25, TlN, R6W) is a poorly indurated
conglomerate composed principally of bleached clasts of A-L
peak Tuff (pinnacles member?).
Osburn (1978, oral commun.)
suggested that this might record the position of a buried
fault scarp.
The other outcrop, at the canyon mouth
southwest of the latter location (NW 1/4, sec. 3 6 , TlN, R6W)
exhibits lense-shaped bodies of conglomeratic sandstone as
long as 8 ft ( 2 . 4 m) preserved at the base of La Jara Peak
Basaltic Andesite flows.
These conglomerates include cobbles
derived from both the LaJara Peak Basaltic Andesite and the
Hells Mesa Tuff and were mapped as Popotosa Formation.
Elsewhere, the Popotosa Formation is a poorly
sorted conglomeratic sandstone;-.withclasts derived
principally from the La Jara Peak Basaltic Andesite, A-L Peak
Tuff, and Hells Mesa Tuff.
Lesser amounts of clasts of
"turkey-track'' andesite from the Spears Formation, chert,
72
:J
.
D
r e d d i s h - b r o w ns i l i c i f i e ds i l t s t o n e ,c r y s t a l l i n el i m e s t o n e ,
a n dr h y o l i t i ct u f fa l s oo c c u r .
rangeup
t o 7 in.
T h e l o n gd i a m e t e r so fc l a s t s
( 1 7 . 8 cm).
O u t c r o p sa r e
thin- t o
s e t s of
t h i c k - b e d d e da n df r e q u e n t l ye x h i b i tw e d g e - s h a p e d
l o w - a n g l ec r o s s b e d sa s
b e d sa r e
much a s 10;feet
(3 m) thick.
Graded
common, s o t h a t t h e t o p s a r e o f t e n c o m p r i s e d
c o a r s e - g r a i n e dp
, o o r l ys o r t e ds a n d s t o n e( f i g .
m a t r i xo ft h ec o n g l o m e r a t e s
p o o r l ys o r t e d .C a l c i t e
sometimesresembles
13).
is g e n e r a l l y a n g u l a r
i s t h ec e m e n t i n gm a t e r i a l
a caliche.
of v e r y
T h e sandy
andvery
and
73
Figure 13:
Thin, fining upward beds in the Popotosa
Formation; roadcut in Corkscrew Canyon (SE 1/4,
N W 1/4, sec. 1, TlS, R6W). Hammer handle is 12.5
in. (31.8 cm) long.
'
. 74
'
Tertiary Mafic Intrusives
u?
Numerous d i k e s w i t h o r i e n t a t i o n s r a o g i n g
fr'om N7'5W
.
.
.
t o N 2 5 E t r a n s e c tt h es t u d ya r e a .
,
C h a p i na n do t h e r s( 1 9 7 4 6 , b )
i n t h eM a g d a l e n aa r e at o' i n t r u s i o n
a s c r i b et h e s ed i k e s
of
Rio
m a f i c magmas a l o n g e x t e n s i o n a l ' f a u l - t z o n e s r e l a t e d t o t h e
Grande r i f t .
T h em a ) o r i t y . o fd i k e st r e n db e t w e e n
N l @ Z and many o c c u p yf a u l t s .
t h a nt h eS p e a r sF o r m a t i o n .
I
.
N30W and
Xost d i k e si n t r u d e ' s t r a t ao l d e r
Howev.er, f o u rd i k e si n t r u d et h e
S p e a r s F o r m a t i o n .e a s to fJ a r a l o s a
Creek ( E 1/2,
sec. 2 4 , ' a n d
S E 1/4, sec. 1 3 , T l N , R6W) a n do n es h o r td i k ei n t r u d e st h e '
S p e a r sF o r m a t i o n
R6W).
i n Dove S p r i n g Canyon (SW 1/4, sec. 2 6 , TlN,
Also, t h e f a u l t
is
b0undin.g t h e MulLiganGulch'graben
i n t r u d e d i n t h en o r t h e a s t e r nc o r n e ro ft h es t u d ya r e a
4 , T l N , R5W) a n da g a i ne a s to fJ a r a l o s aC r e e k
(sec.
sec.
(NW 1/4;
14, TlN, R5W).
The d i k e sr a n g e
m ) and i n l e n g t hf r o m
The l o n g e s td i k e
i n widthfrom
a few f e e t t o s e v e r a l ~ t h o u s a n d f e e t .
i s o v e r 3 m i (4.8 km) long.
75 d e g r e e s t o v e r t i ' c a l .I no u t c r o p ,t h e
I"
t o traceinthe
a e r i a lp h o t o g r a p h s .I no n ei n s t a n c e ,w h e r e
d i k ei n t r u d e st h e
'
Dips r a n g ef r o m
d i k e s g e n e r a l l y' f o r m
n o n v e g e t a t e d ,r e s i s t a n tr i d g e sw h i c ha r ee a s y
f i e l d andon
1 t o 6 f t (Ol3 t o 1 . 8
a
Tres
more r e s i s t a n t s a n d s t o n e s o f t h e u p p e r
Hermanos Member of t h e Mancos S h a l e west of La J a r a Canyon
(SW 1 / 4 ,
s e c . 6 , TlN, 'R5W) , t h e d i k e
shallow depression.
i s w e a t h e r e dt o
a
.
'
..
i n r o c k sy o u n g e rt h a nt h e
S i l l s were n o to b s e r v e d
Well Tongueand
shalesoftheAlamito
.
sills intrude
lower
Mesaverde
Formation.
The
majority
of
t h el o w e rm a r i n e
s e c t i o n of t h e Tres Hermanos S a n d s t o n e i n t h e n o r t h e a s t e r n
s i l l o c c u r sw i t h i n
t h e M e s a v e r d eo u t c r o pa r e ai nt h e
n o r t h e a s t e r nc o r n e ro f
t h e s t u d ya r e a
A l s o , a dikewhichbecomes
bank of J a r a l o s aC r e e k
TlN, R6W)
(sec. 7 , TlN, R5W).
a s i l l was o b s e r v e d a l o n g t h e w e s t
( S E 1/4, sec. 1 and N E 1/4, sec. 1 2 ,
.
Most of t h e d i k e s a n d
t o a greenish-black
o f t e ns t a i n e d
sills a r ep e r v a s i v e l ya l t e r e d
(5G2/1) t od a r k - g r e e n i s h - g r a y
c o l o r on f r e s h s u r f a c e s ;
A few of
a
One i n s t a n c e of a d i k ec u t t i n g
s e c t i o no ft h es t u d ya r e a .
(5G4/1)
on a w e a t h e r e ds u r f a c et h e ya r e
by l i m o n i t e t o d u s k y y e l l o w i s h
t h ed i k e si nt h en o r t h e a s t e r nc o r n e r
brown ( 1 0 Y R 2 / 2 ) .
of t h e s t u d y
a r e aa r es l i g h t l yv e s i c u l a r .P e t r o g r a p h i c a l l y ,t h e ya r e
comprised of f e l t e d p l a g i o c l a s e l a t h s
a s much a s 5 mrn ( 0 . 2
i n . ) l o n g (An60, a v e r a g e of 18 c r y s t a l s , Michel-Levymethod),
ragged brown h o r n b l e n d e a n d b r o w n b i o t i t e l a t h s a l t e r i n g t o
m a g n e t i t ea n dc a l c i t e ,h i g h l yc o r r o d e dp y r o x e n er e p l a c e d
by
c a l c i t e a n dh o r n b l e n d e ,a p a t i t ep r i s m s ,a n ds c a l ya g g r e g a t e s
of l i g h t - g r e e nc h l o r i t e .
c o m p r i s e do fl i m o n i t i c ,s p h e r u l i t i c
W a l l - r o c ka l t e r a t i o nz o n e s
r a r e l ye x c e e d
is
The a p h a n i t i cg r o u n d m a s s
material.
f o r t h e s ei n t r u s i v e s
1 f t (0.3 m ) i nw i d t h .I n t r u d e ds a n d s t o n e sa r e
g e n e r a l l yb l e a c h e da n d
become s l i g h t l y m i c a c e o u s
if the
s a n d s t o n ec o n t a i n e da p p r e c i a b l ec l a ym a t r i x .I n t r u d e ds h a l e s
.
'.">
76
.,
e x h i b i t somewhat w i d e r z o n e s o f a l t e r a t i o n t h a n d o t h e
i n t r u d e ds a n d s t o n e s .O r g a n i cs h a l e s ,s u c ha sa r ef o u n di n
t h e M e s a v e r d eF o r m a t i o n ,a r eo f t e nb l a c k e n e da n d
well-indurated.
Brown ( 1 9 7 2 ) s t a t e st h a t h ep e r v a s i v e
a l t e r a t i o n of i n t r u s i v e s a n d t h e p r e s e n c e
a l t e r a t i o nz o n e sa r es u g g e s t i v e
s u b s e q u e n tt ot h ee m p l a c e m e n t
of w a l l - r o c k
of h y d r o t h e r m a l a l t e r a t i o n
of t h e i n t r u s i v e s .
.
71
.
P l i o - P l e i s t o c e n ea n dH o l o c e n ed e p o s i t s
The o l d e s t P l i o - P l e i s t o c e n e d e p o s i t s o c c u r a l o n g
t h ee a s t e r nm a r g i no ft h es t u d ya r e a .T h e s eu n c o n s o l i d a t e d
p i e d m o n tg r a v e l so v e r l i e
70bfl f t (2134 m )
a g e n t l ys l o p i n gp l a i n ,a b o v ea b o u t
was formed by c o a l e s c i n g
i ne l e v a t i o n ,t h a t
a l l u v i a lf a n sd e r i v e df r o mt h eG a l l i n a sM o u n t a i n s .
s u r f a c eh a sb e e nd i s s e c t e d
This
and i t s
by J a r a l o s aC r e e k
t r i b u t a r i e s s o t h a t it i s now s e p a r a t e df r o m
T h e g r a v e l sa r e
Mountains.
a p o o r l ys o r t e d
t o r o u n d e dc o b b l e s p
, e b b l e s a, n ds a n d .
l i t h o l o g i e s of t h e c l a s t s a r e
a l s op r e s e n t .
mix of s u b a n g u l a r
The p r ~ i n c i p a l
Hells Mesa T u f f , A-L
and t h e La J a r a Peak B a s a l t i cA n d e s i t e .
P r e c a m b r i a ng r a n i t e
t h e Gallinas
PeakTuff,
Minoramountsof
and q u a r t z i t e andMaderaLimestone
A s p r e v i o u s l yn o t e d ,
are
t h e l i t h o l o g yo ft h e s e
g r a v e l s i s s i m i l a rt ot h a to ft h eP o p o t o s aF o r m a t i o n .
c o l l u v i a la p r o na l o n gt h ee r o d e de d g e
A
of t h ep i e d m o n ts u r f a c e
makes d i s t i n c t i o n of t h e s e g r a v e l s f r o m t h e P o p o t o s a
Formationdifficultat
some l o c a l i t i e s .
A r e m n a n to fa ne x t e n s i v ep e d i m e n ts u r f a c e
e x p o s e di nt h en o r t h e a s t e r nc o r n e ra n dn o r t h - c e n t r a l
o ft h es t u d y
area.
( 2 0 5 4 and 2 1 0 9
T h i ss u r f a c e
section.
is between 6 7 4 0 and 6 9 2 0 f t
m) i n e l e v a t i o n andwas.developedonrocksof
thelowerMesaverdeFormation.
northwardand
is
The s u r f a c es l o p e sg e n t l y
was p r o b a b l y g r a d e d t o
The c o m p o s i t i o n of t h e s e g r a v e l s
a n ancestralRioSalado.
i s much t h e same as t h a t o f
t h ep i e d m o n tg r a v e l s ,e x c e p tt h a tc l a s t s
u n i t sa r ea b s e n t .T h e s eg r a v e l sa r eb e t w e e n
to 3.16 m ) t h i c k and a r e u s u a l l yc e m e n t e d
of t h en o n v o l c a n i c
5 a n d 1 0 f t (1.5
by w h i t e c a l i c h e .
>:
-
78
. s
Renewed d o w n c u t t i n g by t h eR i oS a l a d oc a u s e d
d i s s e c t i o n of t h e two p r e v i o u s l y d i s c u s s e d s u r f a c e s
and
f o r m e dt h ep r e s e n td r a i n a g es y s t e m .E a r l i e rs t a g e s
of t h i s
d r a i n a g e may b er e p r e s e n t e d
by t h e o l d e r a l l u v i a l d e p o s i t s
( Q a g )w h i c hm a n t l eb r o a ds h a l l o wt o p o g r a p h i cd e p r e s s i o n s .
T e r r a c ed e v e l o p m e n ta c c o m p a n i e dt h ee s t a b l i s h m e n t
p r e s e n td r a i n a g es y s t e m .
,poorlysorted
of t h e
The t e r r a c e sa r et h i nv e n e e r s
g r a v e l s o nn a r r o wb e n c h e sa l o n gJ a r a l o s aC r e e k
and Abbe S p r i n g Canyon.The
p r e s e n t s.treambedsare
comprised of h e t e r o l i t h i c ,s u b r o u n d e d ,p o o r l ys o r t e ds a n da n d
gravel.
.
of
79
Structure
Regional Structure
Structural patterns in and around the study area were
developed during late Cretaceous
-- early Tertiary (Laramide)
compressional foIding and late Tertiary extensional faulting.
Basaltic-andesite magmatic activity accompanied the early
stages of extensional faulting.
The Laramide episode of
compressional tectonics formed broad uplifts and basins in
New Mexico and adjacent areas during the time period of 50
75 m.y. B.P.
(Chapin and others, 1974b).
to
Elongate stocks,
dikes, veins and joint sets of plutons in Arizona indicate an
ENE-trending axis of regional compression (Rehrig and
Heidrick, 1972, 1976).
On the Colorado Plateau, Laramide
structures have been described as broad folds, monoclines,
and thrust belts (Kelley and Wood, 1946; Tonking, 1957;
Kelley and Clinton, 1960; Woodward, 1976).
The area of the
present-day Magdalena Range was included in a broad Laramide
uplift that encompassed most of the area west of the Rio
Grande and south of San Acacia (Chapin and others, 1978).
The northern and eastern boundaries of this uplift can be
roughly established from the unconformable relationship of
the Spears Formation w’ith underlying rocks of Eocene to
Paleozoic age.
By medial Eocene time, a neutral stress field
replaced the Laramide compressional stress field (Chapin,
%J
80
_.
1974).
E r o s i v eb e v e l i n g
o fL a r a m i d eu p l i f t sc o n t i n u e dd u r i n g
7 t o 1 2 m.y.
t h es u c c e e d i n g
a c t i v i t y( C h a p i n ,
1974).
during a h i a t u s i n volcanic
E r o s i o np r o c e e d e d
u n t i l a surface
of low r e l i e f e x t e n d e d t h r o u g h o u t s o u t h e r n C o l o r a d o
Mexico ( E p i s and C h a p i n ,1 9 7 3 ) .
and N e w
T h e EoceneBacaFormation,
w h i c hu n c o n f o r m a b l y - o v e r l i e st h eM e s a v e r d eF o r m a t i o ni nt h e
v i c i n i t yo ft h es t u d ya r e a ,
i s t h o u g h tt ob ec o m p r i s e d
d e t r i t u sf r o mt h i se p i s o d eo fe r o s i o n( S n y d e r ,
W i d e s p r e a da n d e s i t i ct o
a b o u t 37 m.y.
B.P.
1971).
l a t i t i c volcanismbegan
and was f o l l o w e d by t h ef o r m a t i o n
i g n i m b r i t ep l a t e a u s
of
of
andnumerouscauldroncomplexes(Chapin,
1 9 7 4 ; ChapinandSeager,
1 9 7 5 ; E l s t o na n do t h e r s ,
1976).
D e t r i t u sf r o mt h ee r o s i o no ft h ee a r l ya n d e s i t i ca n dl a t i t i c
v o l c a n i cr o c k s
was d e p o s i t e da st h eS p e a r sF o r m a t i o n .
The
Hells Mesa T u f f w a s e r u p t e d f r o m t h e N o r t h B a l d y c a u l d r o n
about33
m.y.
B.P.
andformed
t h e S p e a r sF o r m a t i o n .
a b r o a di g n i m b r i t es h i e l do v e r
The He.lls Mesa i s r e p r e s e n t a t i v e of a
i n time
c a l c - , a l k a l i c s u i t e t h a t was o v e r l a p p e da n ds u c c e e d e d
on t h e Mogollon P l a t e a u by a h i g h - s i l i c a a l k a l i c s u i t e
( E l s t o na n do t h e r s ,
1976).
r e p r e s e n t a t i v eo ft h el a t t e r
T h e A-L
PeakTuff
is
s u i t e i n t h e s t u d ya r e a .
The
.c h a n g ef r o mc a l c - a l k a l i c ,t w o - f e l d s p a rt u f f st oh i g h - s i l i c a ,
o n e - f e l d s p a rt u f f sa n di n t e r b e d d e db a s a l t i c - a n d e s i t el a v a s
marks t h eb e g i n n i n go fr e g i o n a le x t e n s i o ni nt h eM a g d a l e n a
a r e a( C h a p i n ,1 9 7 8 ) .
T h eb e g i n n i n go fb i m o d a lv o l c a n i s ma n de a s t - w e s t
e x t e n s i o no c c u r r e d
i n t h eM a g d a l e n aa r e aa b o u t3 2
m.y.
B.P.
.
-
a
(Chapin, 1 9 7 8 ) .
81
Numerous normal faults with an average N 1 B f
trend breached Oligocene batholiths, causing widespread
pluton and dike emplacement (Chapin and others, 1 9 7 4 b ) .
Uplift and erosion of the Magdalena Range throughout the
episode of regional extension is reflected in the lithology
and transport directions of the basalPopotosa Formation
(Bruning, 1 9 7 3 ) .
Voluminous basaltic-andesite magmas were
penecontemporaneously extruded wherever areas of high heat
flow were intersectedby extensional faults (Chapin and
Seager, 1 9 7 5 ) .
This magmatic episode, represented by the La
Jara Peak Basaltic Andesite in the study area, overlapped the
end of thehigh-silica alkalic volcanic suite.
As north-trending normal faults continued to
develop, northeast-trending basement faults were reactivated.
Many of theseare observable today as lineaments on Landsat
imagery (Knepper, 1 9 7 8 ) .
These transverse fault zones often
absorbed the energy andmovement of intersected
north-trending faults.
En echelon basins of the Rio Grande
rift created by such transverse faults developed opposing
structural asymmetry (Chapin, 1978; Chapin and others, 1 9 7 8 ) .
The SanAugustin graben formed as a bifurcation of the Rio
Grande rift along the Morenci lineament, one of these
1
northeast-trending structural zones.
Tectonic influence by
this lineament *in the Socorro-Magdalena area
throughout the past 3 2 m.y.
hasoccurred
(Chapin and others, 1 9 7 8 ) .
The
Colorado Plateau and the San Mateo and Gallinas ranges began
to rise about 2 4 m.y. B.P.
(Bruning, 1 9 7 3 ; Bruning a.nd
Chapin, 1 9 7 4 ; Chapin and S e a g e r 1
, 975)V
. o l c z n i s md e c l i n e d
t o 1 3 m.y.
duringmiddleMiocenetime(20
B.P.;
1 9 7 8 ) .B l o c kf a u l t i n ga c c e l e r a t e di nl a t e s t
P l i o c e n e time.
Chapin,
Miocene t o
T h i s renewed o r o g e n i ca c t i v i t ys e g m e n t e d
o r i g i n a l 40-mi
(64.4-kmI-wide
the
P o p o t o s ad e p o s i t i o n a lb a s i n
of
t h eS o c o r r o - " a g d a l e n aa r e ai n t ot h r e eg r a b e n ss e p a r a t e d
i n t r a r i f th o r s t s( C h a p i na n d ' s e a g e r ,1 9 7 5 ) .
L e m i t a rm o u n t a i n so c c u p yt h ea x i so f
b a s i n( C h a p i n 1
, 971b).
G u l c hg r a b e n ,
area.
by
T h e S o c o r r oa n d
t h e o r i g i n a lP o p o t o s a
One o ft h e s eg r a b e n s ,t h eM u l l i g a n
l i e s a l o n gt h ee a s t e r nm a r g i n
of t h es t u d y
its
t h i s g r a b e nv a r i e sc o n s i d e r a b l yo v e r
The d e p t ho f
e x t e n t( W i l k i n s o n ,
1 9 7 6 ) a n ds h a l l o w ss o u t h w a r da c r o s s
the
M o r e n clii n e a m e n(t C h a p i na n do t h e r s1, 9 7 8 )E
. peirogenic
u p l i f t and r i f t i n g , accompanied i n p a r t by magmatic
i n t r u s i o n ,h a sc o n t i n u e di n t ot h ep r e s e n t( R e i l i n g e ra n 0
o t h e r s ,1 9 7 8 ) .F i g u r e
1 4 p r e s e n t s a viewof
t h e regional
s t r u c t u r a l s e t t i n g o ft h es t u d ya r e a .
LocalStructure
Folding:
The f a u l t e dn o s eo f
( h e r et e r m e dt h e
Abbe S p r i n ga n t i c l i n e ,
i nt h en o r t h e a s tc o r n e r
C-C').
a s o u t h w a r d - p l u n g i n ga n t i c l i n e
of t h e s t u d y a r e a
E r o s i o nh a se x p o s e d
see f i g . )
i s exposed
(see c r o s s - s e c t i o n
t h e C h i n l eF o r m a t i o ni nt h e
c e n t e r of t h e N10W-trending f o l d .
The maximum d i pp r o d u c e d
I
I
I
Normalfaultwith
/
downthrown side
\
\
Anticlinal axis showing ,direction
of plunge
Synclinal, axis showing direction
o f plunge
,.e*.*
.
.
.
.
.
e
,.'.',>Y
.
..
':
SCALE
Approximate
area
of
structural zone
in
transverse
study area
Colorado
Plateau
margin
I : 250,000
REGIONAL.STRUCTURAL
()SFlgure
14:
1979;
4
a
SETTING
OF
STUDY
AREA
Massingill, 1979; Osburn, unpobl.)
(compiled
from
Jockson,
84
b yf o l d i n gs e l d o me x c e e d s2 5d e g r e e s .T h ec e n t e ro ft h e
a n t i c l i n e i s a ni n t r u d e d
g r a b e n .A n t i t h e t i cf a u l t i n g ,m o s tn o t a b l ei nt h ec l o s e l y
s p a c e df a u l t sw h i c hc u tt h ee a s t e r nl i m b
of t h e a n t i c l i n e ,
h a s l i t t l e a s s o c i a t e df a u l t - b l o c kr o t a t i o n .A c c o r d i n g
p.
Dennis(1972,
3 1 3 ) ,a n t i t h e t i cb l o c kf a u l t i n g
to
is o f t e n
produced by k e y s t o n ec o l l a p s eo fd o m a ls t r u c t u r e s .I nt h i s
p a r t o ft h es t u d y
a r e a , s u c ha n t i t h e t i cf a u l t i n gh a sp r o d u c e d
a s e r i e. s o fe a s t w a r d - d i p p i n gh o g b a c k sc a p p e d
Dakota Sandstone.
A small, t i g h t s, o u t h w e s t - p l u n g i n g
anticlinalfoldintheTres
a b o u t0 . 7 5
Abbe S p r i n ga n t i c l i n e .
small f o l d t r e n d s
m i (1.2 k m ) .
n o r t ho ft h es t u d y
The f o l dc a n n o tb ef o l l o w e dt ot h e
a r e a d u e t o p o o re x p o s u r e sa n de x t e n s i v e
(152.4 m ) o fd i s p l a c e m e n tb o u n d st h i s
east.
The e a s t e r nl i m bo ft h ef o l d
(338 m)' wideand
(see below).
The
N15E a n dc a nb ef o l l o w e df o r
A down-to-the-west
a l l u v i a lc o v e r .
mi
HermanosSandstoneoccurs0.75
( 1 . 2 km) west o ft h ea x i so ft h e
axisofthis
by t h e r e s i s t a n t
f a u l t w i t ha b o u t5 0 0
f t
small a n t i c l i n e o n t h e
is approximately l l 0 l j f t
may r e p r e s e n t r e v e r s e d r a g a l o n g t h i s f a u l t
To t h es o u t ht h ez o n e
strata parallels thefaultand
of e a s t w a r d - d i p p i n g
becomeswider
as displacement
increases.
Two small a n t i c l i n a l f o l d s i n v o l v e
b a s a l 100 f t (30.4 m ) o ft h e
shown i n c r o s s - s e c t i o n B-B'.
N5W a n dp l u n g e s
Baca Formation.
One o ft h e s e
is
The a x i s o f t h i s f o l d t r e n d s
t o t h es o u t h .T h e
a ni n t r u d e dh o r s tb l o c ka n d
a t least the
c r e s t of t h i s a n t i c l i n e
is
i s c u t by f a u l t s t r e n d i n g o b l i q u e
85
lack o fe x p o s u r e so nb o t ht h e
t o t h e f o l da x i s .F a u l t i n ga n d
e a s t and west l i m b s p r e v e n t t h e d e t e r m i n a t i o n
a g e of t h i sf o l d .
of t h e minimum
The o t h e rs o u t h w a r d - p l u n g i n ga n t i c l i n e ,
shown o nc r o s s - s e c t i o n
A-A',
o c c u r si n
t h e s o u t h w e s tc o r n e r
a r e a . The a x i s o f t h i s a n t i c l i n e t r e n d s
o ft h es t u d y
The e a s t e r nl i m b
i s t r u n c a t e da g a i n s t
down-to-the-west
f a u l tw i t h1 2 0 0
Reconnaissancemapping
t h a tt h ew e s t e r nl i m b
N25W.
a major .
f t ( 3 6 5 . 8 m ) ofthrow.
t o t h e west o f t h e s t u d y
area s u g g e s t s
is a l s o t r u n c a t e d by a down-to-the-west
fault.
The Abbe S p r i n g a n t i c l i n e may n o t i n v o l v e t h e
Formationand
from i t s
i s a l m o s tc e r t a i n l yo fL a r a m i d eo r i g i n
area
b r o a da n dg e n t l ef o r m .T h eo t h e rf o l d si nt h es t u d y
i n v o l v e s t r a t a o ft h eb a s a l
Baca
Baca F o r m a t i o n .F a u l t i n ga n d
l a c k of e x p o s u r e s make it i m p o s s i b l e t o d e t e r m i n e w h e t h e r
f o l d i n gh a si n v o l v e d
s t r a t a y o u n g e rt h a nt h i s .S i n c et h e
b a s a lS p e a r sF o r m a t i o ni n t e r t o n g u e sw i t ht h e
F o r m a t i o ni n
t o p o f t h e Baca
t h e s t u d y a r e a , i t i s p r o b a b l et h a tf o l d i n g
w h i c hi n v o l v e st h e
Baca F o r m a t i o n a l s o i n v o l v e t h e S p e a r s
Formation.However,
t h i s wouldbe
a t v a r i a n c ew i t hr e g i o n a l
e v i d e n c et h a tL a r a m i d ec o m p r e s s i o n a lf o l d i n ge n d e d '
50 m.y.
B.P.
thatthe
( C h a p i na n do t h e r s 1
, 974bE
; lston,
by a b o u t
1 9 7 6 ) and
Baca i s a p o s t - L a r a m i d ef o r m a t i o nc o m p r i s e do f
d
e.r o d e d
. e...t r i .t u. s/.
;,
from L a r a m i d eu p l i f t s( S n y d e r ,
possibleresolution
of t h i s p r o b l e m
unconformity may e x i s t w i t h i n t h e
Formationbelow
1971).
One
i s t h a t a major
Baca Formation.The
t h i su n c o n f o r m i t yc o u l dh a v eb e e ni n v o l v e d
Baca
in
86
.
-
e
l a t e - s t a g eL a r a m i d ef o l d i n g ,w h i l et h es e d i m e n t sd e p o s i t e d
a
a b o vt hesi u
s rface
would
be
dateablefossils
a r e aS
. nyder
from t h e Bacahavebeenfound
i nt h es t u d y
( 1 9 7 0 , 1 9 7 1 ) r e p o r t sa nE o c e n ea g ef o rt h e
on t h e b a s i s of v e r t e b r a t e f o s s i l s c o l l e c t e d
'
No
r e l a t i v eul yn d e f o r m e d .
Baca
2 0 m.i (32.1 k m )
n o r t h w e s to ft h es t u d ya r e a .T h i sa g e
i s c o n s i s t e n tw i t ht h e
o t h e rv e r t e b r a t ea g ed e t e r m i n a t i o nf o r
t h e Baca(Gardner,
1910).
in
However, t h ea u t h o rh a se x p e r i e n c e dd i f f i c u l t y
distinguishingthebasal
MesaverdeFormation
Bacafrom
t h eu n d e r l y i n gC r e t a c e o u s
a t some l o c a t i o n s .O t h e rw o r k e r sh a v e
r e p o r t e ds i m i l a rp r o b l e m si n ' p i c k i n gt h eB a c a - M e s a v e r d e
c o n t a c(tT o n k i n g1, 9 5 7 ;
Anonymous-11,
1963;
Snyder,
The b a s a l BacaFormation
a t some l o c a t i o n s may beof
C r e t a c e o u s o r P a l e o c e n ea g ea n dt h e s eb e d s
f o l d e dd u r i n gt h eL a r a m i d ed e f o r m a t i o n .
1971).
may havebeen
A t t h i s time,
however, t h e a u t h o ra n do t h e rr e s e a r c h e r s( S n y d e r ,
J o h n s o n 1, 9 7 8 M
; assingill;
late
1 9 7 9 ; C a t h e r ,i n
1971;
prep.) h a v en o t
observedsuchanunconformity.
An a l t e r n a t i v e , a n d p e r h a p s b e t t e r , e x p l a n a t i o n
is
s u g g e s t e d by H a m b l i n ' s( 1 9 6 5 )o b s e r v a t i o n so fr e v e r s ed r a g
a l o n gn o r m a lf a u l t s
on t h ew e s t e r nC o l o r a d oP l a t e a u .S u c h
d r a g was found t o be commonly a s s o c i a t e d w i t h t h e
b l o c k s of f a u l t s w i t h g r e a t e r t h a n
downthrown
.
1 0 0 f t (30.5 m )
4
d i s p l a c e m e n t .B o t ho ft h ef o l da x e su n d e rd i s c u s s i o nr o u g h l y
*,
p a r a l l e lm a j o rd o w n - t o - t h e - w e s tf a u l t sw i t hl o c a l
d i s p l a c e m e n t i n excess of 8 0 0 f t (243.8 m).
s o u t h w e s t e rcno r n eotrfhset u dayr e a
T h e f o l di nt h e
is more d i f f i c u l t o
.
. 1
interpret.
87
.
~
I t s a x i sr o u g h l yp a r a l l e l s
a m a j o rf a u l tf o r - 1 . 5
m i ( 2 . 4 k m ) , . b u tt h e na p p e a r st od i v e r g ew e s t w a r do u to ft h e
i n t h eS p e a r so u t c r o pb e l tn o r t ho f
s t u d ya r e a .E x p o s u r e s
t h i s l o c a t i o n and west of t h i s f a u l t a r e p o o r
and y i e l d
d i v e r s es t r i k et r e n d s ;h o w e v e r ,t h ea t t i t u d e sr e c o r d e d
suggest that this strata
may a l s o be f o l d e d a n t i c l i n a l l y .
North of t h e same t r a n s v e r s ez o n e( f i g .
this fault
16), d i s p l a c e m e n to n
is g r e a t l y d i m i n i s h e d a n d f o l d i n g
A d i s c o n t i n u o u sz o n e
i s n o te v i d e n t .
of s t e e p e a s t - d i p p i n g s t r a t a
o c c u r sa d j a c e n tt ot h ew e s t e r nb o u n d a r yf a u l ts y s t e m
MulliganGulchgraben.Thiszone
t h ev o l c a n i cr o c k s .T h ez o n e
of t h e
i s e s p e c i a l l yp r o m i n e n ti n
of s t e e p l yd i p p i n gs t r a t ah a s
b e e nr e c o g n i z e ds o u t h w a r da l o n gt h ee a s tf l a n ko ft h e
Gallinasuplifttosouthof
a l o n gt h ee a s tf l a n ko ft h eS a n
1974).
The w i d t ho ft h i sz o n e
Highway 6 0 , and may c o n t i n u e
MateoMountains(Chamberlin,
of s t e e pd i p s
i n t h es t u d y
a r e a is u s u a l l y d i f f i c u l t t o a s c e r t a i n d u e t o c o v e r
pediment g r a v e l s o r c o l l u v i u m .I nt h ev i c i n i t yo f
v o l c a n i cs e c t i o n
thedevelopment
i nt h eC o u n c i l
Abbe
T l N , R5W), a p p r o x i m a t e l y 1 5 0 0 f t ( 4 5 7 m ) o f
S p r i n g( s e c .8 ,
d i p sC
. hamberlin
by
i s i n v o l v e di nt h e
s t e e p zone of e a s t w a r d
( 1 9 7 4 ) i n f e r r e d a l a t e - O l i g o c e n ea g ef o r
of a 1 - m i
(1.6-kmI-widemonoclinalhingezone
Rock area a l o n gt h i sg r a b e nm a r g i n .
*The
development.oftheeastward-dippingflexureprecededandwas
modified by b a s i na n dr a n g ef a u l t i n g .A r e a so fd e c r e a s e dd i p
w e r ea s c r i b e d
by Chamberlin ( 1 9 7 4 ) t o s u b s e q u e n t f a u l t
r o t a t i o n .D r a ga l o n gt h ed o w n - t o - t h e - e a s tb o u n d a r y
faults
was e l i m i n a t e d a s a mechanismbecausesuchdrag
o b s e r v e dt oe x t e n d
wss n o t
more t h a n 500 f t ( 1 5 2 m ) f r o m f a u l t s
e l s e w h e r eI. n s t e a dC
, h a m b e r l i n( 1 9 7 4 p) r o p o s e db a t h o l i t h i c
i n t r u s i o na n dc o n c o m i t a n tu p t h r u s t i n ga l o n gn o r t h - t r e n d i n g
basementfaultsas.the
mechanism f o r c r e a t i n g t h i s m o n o c l i n a l
f l e x u r e (pp. 99-102).
T h ea u t h o rc a n n o ta g r e ew i t hC h a m b e r 1 i n I . s( 1 9 7 4 )
m e c h a n i s mo ff o r m a t i o nf o rt h i sz o n eo fs t e e p l yd i p p i n g
strata.
T h i sz o n ec l o s e l y
p a r a l l e l s t h ef a u l t so ft h e
g r a b e n - b o u n d a r ys y s t e mi nt h es t u d y
g e n e t i c a l l yr e l a t e dt o
a r e a and i s m o s t l i k e l y
them.Theamount
postulatedforthefaults
of d i s p l a c e m e n t
of t h i s s y s t e m s u g g e s t s d r a g
f o l d i n g a s t h e most l i k e l y mechanism of f o r m a t i o n .
synclinewithinthePopotosaFormation
A
e a s t of t h e s t u d y
area
i s s u b p a r a l l e lt ot h eg r a b e nb o u n d a r y( O s b u r ni nC h a p i na n d
o t h e r s , 1979)and
may a l s oh a v eb e e nc a u s e d
west s i d e of t h e
T h ea g eo ft h em o n o c l i n a lf l e x u r ea l o n gt h e
M u l l i g a nG u l c hg r a b e np o s t d a t e st h e
m.y.
B.P.;
B.P.)
A-L
a n dp r e d a t e st h eb a s a l to fC o u n c i l
Chapin,1979,
o r a l commun.).
by f a u l t d r a g .
P e a kT u f f( a b o u t
32
Rock ( 1 7 m.y.
89
C>
-
-
Faulting:
i n t h es t u d ya r e ar a n g e
E x t e n s i o n a lf a u l tt r e n d s
from N40W t o d u e n o r t h , w i t h t h e m a j o r i t y o f f a u l t s c l u s t e r e d
n e a r N10W.
F a u l t i n g is p a r t i c u l a r l ys e v e r ei nt h en o r t h e a s t
c o r n e ro ft h es t u d ya r e a ,w h e r en u m e r o u ss t e p - f a u l t sa r e
a s s o c i a t e dw i t hk e y s t o n e - c o l l a p s eo ft h e
Abbe S p r i n g
a n t i c l i n e . The c r o s s - s e c t i o n ss u g g e s tt h a ts t e p - f a u l t i n g
t h ed o m i n a n ts t r u c t u r a ls t y l ei n
t h i s a r e a .D i s p l a c e m e n to n
1 0 0 f t (30.5 m ) .
a n ys i n g l ef a u l ts e l d o me x c e e d s
thetotalstructuralrelief
same senseofmotioncan
f t (152.4 m ) .
Many o ft h el o n g i t u d i n a l
f a u l t s l o s e much o r a l l o f t h e i r r e l a t i v e
movementupon
next
c r o s s i n gn o r t h e a s t - t r e n d i n gs t r u c t u r a lz o n e s( s e e
section).
However,
on s e v e r a l p a r a l l e l ,
c l o s e l y - s p a c e d f a u l t s w i t ht h e
f r e q u e n t l ye x c e e d5 0 0
is
Many f a u l t s a r e i n t r u d e d by m a f i cd i k e s N
. ormal
d r a go nf a u l t e ds t r a t a
down-to-the-west
is l o c a l l ya s s o c i a t e d
f a u l t s .R e v e r s ed r a g
w i t h t h em a j o r
is b e l i e v e dt ob e
a s s o c i a t e dw i t ht h em a j p rd o w n - t o - t h e - w e s tf a u l t sa s
d i s c u s s e di nt h ep r e c e d i n gs e c t i o n .F a u l tp l a n e se x p o s e d
t h es u r f a c ed i pf r o m
6 5 d e g r e e st o
Hamblin ( 1 9 6 5 ) andAnderson
flattenatdepth;if
s p a c ec r e a t e d
North-<rending
vertical (fig. 15).
( 1 9 7 1 ) s u g g e s tt h a t , n o r m a lf a u l t s
s o r e v e r s ed r a g
by t h e l a t e r a l
at
is required t o f i l l t h e
componentof
f a u l t movement.
f a u l t s ( e x c e p tt h ew e s t e r ng r a b e n - b o u n d a r y
f a u l ts y s t e m )u s u a l l yh a v ed o w n - t o - t h e - w e s tm o t i o n T
. hese
f a u l t sf r e q u e n t l yc u r v et o w a r dt h e
e a s t a s t h e ya p p r o a c ht h e
g r a b e nm a r g i n .T h i sc h a n g eo ff a u l tt r e n ds u g g e s t sr o t a t i o n
98
~ A ~ ,
F i g u r e 15:
.
View a l o n g f a u l t p l a n e w i t h i n t h e D a k o t a
S a n d s t o n e ; La J a r a Canyon (NW 1 / 4 , SW 1 / 4 ,
5 , T l N , R5W). DakotaSandstone
on t h e l e f t
f a u l t e da g a i n s tA l a m i t oW e l lT o n g u e .
sec.
is
91
’ .
V
-.
by s u b s e q u e n t movement o nt h eg r a b e nb o u n d a r yf a u l ts y s t e m .
T h e n o r t h - t r e n d i n gn o r m a lf a u l t sc u tf o r m a t i o n sa s
t h eS p e a r s
and a r e t h e r e f o r e o f O l i g o c e n e
F a u l t sw h i c hc u t
young a s
or youngerage.
t h e v o l c a n i cu n i t sa l o n gt h ee d g e
of t h e M u l l i g a n G u l c h g r a b e n e x h i b i t d i v e r s e t r e n d s
and
g e n e r a l l yd on o te x t e n df a ri n t ob o r d e r i n go u t c r o p s
of t h e
S p e a r sF o r m a t i o n .T h e s ef a u l t sh a v ed i s p l a c e m e n t so f
1 @ 0f t
(30.5 m ) or l e s s andproducejumbledblocksofvolcanic
rocks.
I t i s l i k e l yt h a tt h e s es m a l lf a u l t sa r eg e n e t i c a l l y
r e l a t e dt ot h ei n t e r s e c t i o no ft r a n s v e r s es t r u c t u r a lz o n e s
withthePuertecitofaultsystemboundingtheMulliganGulch
graben.
A faultsystemwithpredominantlydown-to-the-east
r e l a t i v em o t i o nd e f i n e s
t h e western e d g eo ft h eM u l l i g a n
G u l c hg r a b e n .T h i sg r a b e n ,w h i c h
i s s i t u a t e da l o n gt h e
e a s t e r nm a r g i no ft h es t u d ya r e a ,
is f i l l e dp r i m a r i l yw i t h
s e d i m e n t a r yr o c k so ft h eP o p o t o s aF o r m a t i o n .W i n c h e s t e r
( 1 9 2 0 ) mapped a s h o r ts e g m e n to fo n eo ft h e s eb o u n d a r yf a u l t s
t h e s t u d y area and named i t t h e P u e r t e c i t o
tothenorthof
fault.
T o n k i n g( 1 9 5 7 )a l s o
o ft h es t u d ya r e aa n de s t i m a t e d
f t (15.2and
mapped t h eP u e r t e c i t of a u l tn o r t h
a d i s p l a c e m e n to f5 0
t o 300
91.4 m ) .
T h i s f a u l t i s now r e c o i n i z e d t o b e
c o n s i s t i n g ofone
a widezone
t o t e n f a u l t s (see a l s o J a c k s o n ,
The P u e r t e c i t o f a u l t z o n e
northeast-trending f a u l t s .
1979).
is d e f l e c t e d l a t e r a l l y b y z o n e s o f
I n t h en o r t h e r np a r t
a r e a , t h e P u e r t e c i t o f a u l t z o n ej u x t a p o s e s
of t h es t u d y
Mesaverde o r Baca
92
V
rocks against upper La Jara Peak- Basaltic Andesite.
In the
southern part of the study area, the Popotosa Formation is
faulted down against the Baca or Spears formations.
The age
of the latest major displacement on this fault system is
inferred.to be late Miocene, concurrent with the division of
the original Popotosa depositional basin into three segments
(Chapin and Seager, 1 9 7 5 ) .
Total displacement on the
Puertecito fault system is estimated to range from 300 to
3000 ft (91.4
to 914.4 m) in the study area.
Displacement
decreases in thevicinity of the transverse fault zones where
some of the movement of this boundary fault system is
absorbed.
East of the Hook Ranch (sec. 25, TlN, R6W), the
Popotosa Formation unconformably overlies the Spears
Formation and the pinnacles member of the A-L Peak Tuff.
The
Popotosa Formation along this contact is comprised dominantly
of clasts of thesubjacent lithologies, suggesting that an
original fault contact has been buried.
A discontinuous 'zone
of steep east-dipping strata on the west side of the
Puertecito fault system and a syncline in the Popotosa
Formation east of this fault zone (Osburn, 1 9 7 9 ) are inferred
to represent normal drag.
Transverse s'tructural zones:
r
The western edge of the Mulligan Gulch graben is
deflected to the west twice in the study area by zones of
northeast-trending faults.
southeast motion.
These faults have down-to-the-
Volcanic rocks crop out in jumbled blocks
93
'0
-
along the northeast-trending fault zones adjacent to the
western boundary fault system of the Mulligan Gulch graben.
East of Jaralosa Creek (SE 1/4, sec. 25, TlN, R6W) , an
unusually thick section of the Pinnacles member of the A-L
Peak Tuff crops out against an ENE-trending fault.This
suggests that a fault scarp at the time of A-L Peak
deposition formed a structural barrier.
The limited and
close association of the volcanic rocks with these transverse
structural zones in the study area, the rapid northward
thinning of these units (Chamberlin, 1979, oral commun.;
Laroche, in prep.), and the existence of local unconformities
between the Spears Formation, Hells Mesa Tuff and A-L Peak
Tuff suggest even earlier structural influence of these
zones. At Bird
Spring (NW 1/4, sec. 9, TlN, R5W), Osburn
(1979, oral commun.) has observed anomalously steep eastward
dips in the Popotosa Formation where the northernmost
transverse structural zone intersects the graben boundary
fault system.
'
This suggests that movement on the transverse
fault system continued into Popotosa time.
Away from the edge of the Mulligan Gulch graben,
the northernmost transverse structural zone becomes a
discontinuous zone of southeastward-dipping strata that
separates domains of predominantly east- and west-dipping
strata (fig. 16).
On color aerial photographs, the area of
southeast-dipping strata in the Baca Formation is easily
traced.
The general trend of this transverse zone is
suggested from the southwest elongation of the pediment
'
94
.IZED
DOMAINS OF CONTRASTfNG
STRIKE AND DIP
. e
surface ( S E i/4, sec. 7,' TlN, R6W) and from the upturning and
termination of theSpears outcrop belt on the western margin
of the study area (sec. 2 3 , TlN, R6W).
The transverse structural zones apparently absorb
some of the movement of intersecting longitudinal faults
(fig. 16).
North of Bird Spring (NW 1/4, sec. 9, TlN, R5W),
the graben boundary fault system juxtaposes the lower
Mesaverde Formation against the upper La'Jara Peak Basaltic
Andesite, requiring a total displacement of nearly 3 0 0 0 ft
(914.4 m).
This displacement rapidly decreases southward.
At a good exposure of the graben boundary fault near the
Chavez Ranch headquarters (fig. 17) .the Gray-massive member
of the A-L Peak Tuff is faulted against the Popotosa
Formation.
Total displacement here is only 7 3 3 f t ( 2 2 3 . 3 m).
Displacement decreases southward toward Abbe Spring ( S E 1/4,
sec. 8, TlN, R5W), and then gradually increases.
South of
the Hot Spot mine (sec. 18, TlN, R 5 W ) , displacement on the
boundary fault system again begins to decrease towards the
next transverse structural zone; first the Baca and then the
Spears formations are juxtaposed with the Popotosa Formation.
Other faults intersecting these transverse structural zones
show similar changes of total displacement.
Another transverse structural zone
south of the study area.
may
lie
to the
This is suggested by a westward
bend in the boundary fault system, by exposures of the Hells
Mesa Tuff (Laroche, 1979, oral commun.), and by the southward
plunging of an anticlinal reverse drag fold in the southwest
F i g u r e 17:
P u e r t e c i t of a u l t ;e x p o s u r eb e h i n dC h a v e z
Ranch
h e a d q u a r t e r s (NW 1/4, sec. 9 , TlN, R5W).
PopotosaFormationon
l e f t f a u l t a g a i n s t A-L Peak
Tuff (Gray-massive member) o nr i g h tE. x c a v a t i o n
f o r ranchhouse.
p r o v i d e dw a t e r
c o r n e r of t h es t u d y
are;.
O t h e rs o u t h w a r d - p l u n g i n gr e v e r s e
d r a gf o l d s ,d i s c u s s e dp r e v i o u s l y ,t e r m i n a t ea g a i n s tt h e s e
t r a n s v e r s ez o n e s ,s u g g e s t i n gt h a tt h el a t e s t
movement on
t h e s ez o n e sp o s t d a t e st h ef o r m a t i o no ft h e s ef o l d s .
The t r e n d o f t h e s e t r a n s v e r s e s t r u c t u r a l z o n e s
parallelsthat
of a number o f o t h e r n o r t h e a s t - t r e n d i n g s h e a r
z o n e s now r e c o g n i z e d t o d o m i n a t e t h e s t r u c t u r a l g r a i n
b a s e m e n tr o c k si nt h es o u t h e r n
1 9 7 8 ) .C h a p i na n do t h e r s
" T i j e r a sl i n e a m e n t "
Rocky Mountains(Warner,
( 1 9 7 9 ) h a v ep r o p o s e dt h e
name
f o r t h et r a n s v e r s es t r u c t u r a lz o n et h a t
is r e c o g n i z e d i n t h e
c r o s s e st h es t u d ya r e a .T h i sl i n e a m e n t
a r e an o r t h e a s to f
of
t h e s t u d ya r e a( M a s s i n g i l l ,
c r o s s e st h eS a n d i au p l i f ta tT i j e r a s
1 9 7 9 ) , and
Canyon.Elsewhere,such
of t h eR i o
t r a n s v e r s el i n e a m e n t sc o n n e c te ne c h e l o ns e g m e n t s
Grande r i f t ( C h a p i n 1, 9 7 8 ) .
One o ft h e s e ,t h eN o r e n c i
l i n e a m e n t ,c r o s s e st h eR i oG r a n d er i f ta tS o c o r r oa n dh a s
i n f l u e n c e dl o c a lt e c t o n i c sf o rt h ep a s t
o t h e r s ,1 9 7 8 ) .
TheMorencilineament
3 2 m.y.
(Chapinand
i s e x p r e s s e di nt h e
Magdalena a r e a by a z o n e o f n o r t h e a s t - t r e n d i n g f a u l t s
1 9 7 2 ; C h a p i na n do t h e r s ,1 9 7 4 b ) ,
ofleft-lateral
two ofwhich
(Brown,
show e v i d e n c e
movement c o n s i s t e n t w i t h n o r t h w e s t w a r d d r i f t
of t h e C o l o r a d oP l a t e a u( C h a p i n ,
1971b).
C h a p i na n do t h e r s
( 1 9 7 8 )c i t et h ef o l l o w i n gc h a r a c t e r i s t i c so ft r a n s v e r s e
lineaments:
" . . . t h e s el i n e a m e n t sa r ed e e p l yp e n e t r a t i n gf l a w si n
t h el i t h o s p h e r et h a tt e n dt o" l e a k "
magmas and t o i n f l u e n c e
d e f o r m a t i o ni nt h eb r i t t l en e a r -s u r f a c er o c k s .u n d e r g o i n g
rotation and step faulting in opposite directions
This
shear,zone i s a c t i n g as a n i n c i p i e n t t r a n s f o r m f a u l t
c o n n e c t i n gs e g m e n t so ft h eR i oG r a n d er i f t . "( p . 1 1 5 )
...
-
T h e s et r a n s v e r s ez o n e sa r ea l s oc h a r a c t e r i z e d
by h i g hh e a t
t h u s , may b e e x p l o r a t i o n t a r g e t s
f o r geothermal
flowand,
energy.
99
Economic Geology
Uranium (see fig. 1 8 and Table 1)
Regionally, the Baca Formation is considered to
offer the.best possibilities for uranium mineralization. A
small uranium prospect exists north of the Hook Ranch
headquarters on the west bank of Jaralosa Creek (sec. 13,
TIN, R6W).
The mineralization occurs in a lenticular, very
poorly sorted, conglomeratic sandstone stratigraphically
about 1 5 0 ft (45.7 m) below the top of the Baca.
Uranium
mineralization occurs as haloes around abundant stlicified
wood.
A
small amount of this sandstone body was mined during
the middle 2 9 5 0 ' s .
Preparations for an in situ leaching
operation were begun by M.P.
Grace in 1 9 7 4 - 1 9 7 5 .
These
preparations included the drilling of several shallow
exploration holes in an attempt to delineate the extent of
the mineralized sandstone.
The project was abandoned before
completion due to a contract dispute.
To date further
exploitation of this small prospect has not been attempted
(C.T. Smith, 1 9 7 8 , oral commun.).
Uranium mineralization occurs at several other
localities in the study area in conjunction with limonitic
x,
wood casts.
Anonymous ( 1 9 5 9 ) reports uranium mineralization
in purple rocks of the Baca Formation in the JaralosaCreek
area; the uranium is either disseminated in lenticular
~.
Figure 18: STRATIGRAPHIC INTERVALS
AND
URANIUM
DEPOSITS
FAVORAt3LE FOR. COAL
~.
,
"
.
.
~
,
.
.101
T a b l e 1:
Uranium a n a l y s e s
Datatakenfrom
Bachman, B a l t z , a n d G r i g g s (1957).
Sample
Location
Formation
A
B
C
D
E
18,lN.SW
18;lN;SW
13,1NI6W
24,1N,6W
35,1N,6W
Baca
Mesaverde
Baca
Baca
Baca
Eq. U308
Ch.
0.14%
0.001%
2.0%
0.24% 2.98%
0.13%
0.26%
0.1%
3.27%
0.19%
0.036%
9.21%
U308
-
Ch. V205
-
0.1%
102
. s
~
channel sandstones or associated with carbonaceous debris.
He suggests that the purple .color may be caused by vanadium
In general, most of the Baca Formation within the
compounds.
study area does not appear to be as favorable for uranium
concentration as it appears to be to the east in the Riley
area (Chapin and others, 1979).
Sandstone bodies are
generally thin and lenticular with little organic trash.
Reduced shale occurs only as’small lense-shaped bodies at the
base of sandstones, primarily in the lower part of the Baca
Formation.
Average grain size increases and sorting becomes
poorer towards the top of the Baca, possibly favoring the
movement of groundwater.
The top of the Cretaceous Mesaverde Formation may
also offer some potential f o r uranium concentration.
Nonuraniferous radioactivity was detected from carbonaceous
rocks of this formation locally (Anonymous, 1959, p . 135).
The Mesaverde is an aggregate of fluvial sandstones, organic
shales, siltstones, and coal exposed over,. o r underlying,
approximately 50% of the study area.
In the Red Basin area,
west of the studyarea, uranium occurrences are reported from
organic-rich sandstones in the upper portion of this
formation (Anonymous, 1959).
The most likely origin for the uranium is leaching
from overlying rhyolitic tuffs (Anonymous, 1959).
Anonymous
suggests, alternatively, that the uranium may have been
derived from ascending hydrothermal fluids associated with
the eruptive centers of the volcanic units to the south.
103
V
.
I
Anonymous ( 1 9 5 9 )s t a t e st h a tt h e r e
is l i t t l e 'evidence to
i n f o r t h e uranium
s u p p o r t a s y n g e n e t i cs e d i m e n t a r yo r i g
m i n e r a l i z a t i o n i n t h i sa r e a .
The o b s e r v a t i o n ofbleached
t h e lower
mudflow d e p o s i t sa n dc o n g l o m e r a t e si nc h a n n e l so f
Creek (sec. 25, TIN, R6W)
S p e a r sF o r m a t i o ne a s to fJ a r a l o s a
may i n d i c a t ep a s s a g eo fm i n e r a l i z ~ e dw a t e r s .U r a v i u md e p o s i t s
i nt h eu p p e rR i oS a l a d oa r e aa p p e a rt o
be r e l a t e d t o
groundwater movement a si n f l u e n c e d
by s t r u c t u r e ,
p e r m e a b i l i t y ,a n dt h ep r e s e n c eo fo r g a n i cm a t e r i a l
(Anonymous, 1 9 5 9 ) .
C o a l( s e ef i g .
1 8 a n dT a b l e
2)
The b a s a l 200 f t (61 m ) oftheMesaverdeFormation
i s c o m p r i s e do fo r g a n i cs h a l e s ,v e r y - f i n e - g r a i n e ds a n d s t o n e s
a n ds e v e r a lc o a lb e d s .T h e s ec o a l sa r ei n t e r p r e t e dt oh a v e
a c c u m u l a t e di n
a l o w e rc o a s t a l
w i t h b r a c k i s hw a t e ri n f l u e n c e
others, 1979).
o r d e l t a i cp l a i ne n v i r o n m e n t
(M.
C h a i f f e t z i n Chapinand
A t e x p o s u r e sn e a rC o r k s c r e wC a n y o n ,c o a lb e d s
r a n g e from 1- t o 2 - f t ( 0 . 3 0 . t o
0 . 6 1 m ) - t h i c k .T h e s eb e d s
exhibitrapidlateralandverticalgradationintoorganic
shales.
A t l e a s te i g h to ft h e s ec o a l - b e a r i n gl i t h o l o g i c
sequencesoccurhere:more
may b ec o v e r e d .A l t h o u g ht h i s
is r e c o g n i z e d t o
c o a l - b e a r i n gs e c t i o no ft h eb a s a lM e s a v e r d e
t h en o r t h( J a c k s o n ,
1 9 7 9 ) a n dn o r t h e a s t( M a s s i n g i l l ,
faultingandsurficialcoverconceal
t h es t u d ya r e a C
. h a p i na n do t h e r s
1979),
it t h r o u g h o u t m o s t o f
(1979),
Idble 2:
Coal analysis
Analysis of sample from Hot Spot Mine (NW1/4, NW 1/4, sec.
18, TlN, R5W).
Analysis provided by United States Bureau of
Mines (1976). Values reported for coal sample as received.
Proximate analysis:
Moisture
Volatile matter
Fixed carbon
Volatile matter
Ash
6 .'6 %
32.&%
54.2%
32.8%
6.4%
Ultimate analysis:
Hydrogen
Carbon
Nitrogen
Sulfur
Oxygen
Ash
5.0%
67.2%
1.3%
0.5%
19.6%
6.4%
BTU
11,555
Heating
value
105
CY
_
o
from their regional observations of coal occurrences, suggest
that the northeast-trending Tileras lineament may.have
influenced coal development in the lower Mesaverde. They
observe that coal is more abundant in the lower Mesaverde
southeast of the lineament and attribute this to possible
differences in subsidence and sedimentation rate across the
Tijeras lineament.
Coal from the uppermost strata of the Nesaverde
Formation was mined from three adits at the Hot Spot mine (NW
1/4, sec.
ft (1.5 m).
18, TlN, R5W).
The thickest coal seam here is 5
These coals grade laterally into sil’ty shale and
silty sandstone within 0.75 mi (1.2 km); outcrops do not
occur elsewhere in the study area.
Federal records show that
a mining permit was issued to F.L. Dugger on July 15,1927.
Dugger drove a 90-ft (27.4 m) drift into a 46 in. (116 cm)
coal bed before encountering a shale roll which thinned the
bed to 12 in. (30.5 cm) (Nichelson and Frost, in press).
Efforts to continue mining through the roll and to meet the
coal bed on the other side were unsuccessful and hampered by
financial problems.
The prospect produced a recorded 8 5 tons
of coal through June 30, 1931, before the expiration of the
permit (Nichelson and Frost, in press).
Little remains at
the site today. One adit remains open, but it is in very
poor condition.
The rock outline of a small shelter is also
visible near the largest mine dump.
186
.
O
O i l andGas
i n the
H y d r o c a r b o ns h o w sf r o ma nu n s p e c i f i e du n i t
H 1 ( s e c .3 5 ,
s u b s u r f a c ew e r er e p o r t e df r o md r i l l h o l e
R6W;
D. B e l k n a p 1, 9 7 8 o, r a l
commun.).
TlN,
E l s e w h e r ei nS o c o r r o
C o u n t y ,h y d r o c a r b o n sa r er e p o r t e df r o mP e n n s y l v a n i a ns t r a t a
(Anonymous-111,
1 9 6 3 )A
. l t h o u g hn u m e r o u si n t r u s i o n so c c u ri n
t h es t u d ya r e a ,t h e r m a le f f e c t s
s t r a t a a r e minorand
r e s t r i c t e dt on a r r o wz o n e sa l o n gt h e
margins of i n t r u s i v e s ( M .
1979).
upon i n t r u d e dC r e t a c e o u s
C h a i f f e t zi nC h a p i n
I n a d d i t i o n ,b u r i a ld e p t h
of C r e t a c e o u ss t r a t ai nt h e
is v e r ys h a l l o w .T h u s ,
t h e s i sa r e a
potentialforoil
and o t h e r s ,
i t w o u l da p p e a rt h a tt h e
and g a s g e n e r a t i o n f r o m
t h e Cretaceous
u n i t s is poor.
Structural foldtrapsforpossiblehydrocarbon
a c c u m u l a t i o na r el i m i t e dt ot h r e es o u t h w a r d - p l u n g i n g
anticlines.
Of t h e s e , t h e two i n t h e n o r t h e a s t and n o r t h w e s t
s e c t i o n sa r ee x t e n s i v e l yf a u l t e d .
i nt h es o u t h w e s t e r nc o r n e ro f
b o t hf l a n k s
The s m a l la n t i c l i n e
t h e s t u d ya r e a
by major NNW-trending
mapped
i s t r u n c a t e d on
f a u l t s and c u t by two
n o r t h e a s t - t r e n d i n gf a u l t so fm i n o rd i s p l a c e m e n t .A d d i t i o n a l
h y d r o c a r b o nt r a p s
may h a v eb e e nc r e a t e d
f a u l t s mapped i nt h es t u d ya r e a
by t h em a j o rn o r m a l
(see f i g . 1 6 ) .
Chapinand
o t h e r s ( 1 9 7 9 ) n o t ea p p a r e n tc h a n g e so fs e d i m e n t a t i o nr a t e s
across the Tijeras lineament 'reflected within Cretaceous
strata(the
T w o w e l l sS a n d s t o n e ,G a l l e g oS a n d s t o n e ,a n dt h e
M e s a v e r d ec o a lb e d s ) .
sedimentationrates
They s u g g e s tt h a tt h e s ec h a n g e so f
were c a u s e d by d i f f e r e n t i a l movement on
107
the Tileras lineament.
-
Similar movement on the Tijeras
lineament during Paleozoic sedimentation may have caused
facies changes and thickness variations. These, in turn, may
have influenced hydrocarbon entrapment.
Other
One fault cutting the Chinle Formation and the
Dakota Sandstone in the northeast corner of the study area
has an associated narrow zone of copper mineralization (sec.
5, TlN, R5W).
This was prospected in two locations by a
shallow shaft and an adit. Minerals observed on the dumps
include malachite, chalcocite, and bornite.
No production
records are known. The quantity of dump material does not
suggest a very long or extensive production history.
remains o€ two stone buildings are located nearby.
The
A small
exploration pit dug into a similar fault on the eastern side
of the Dakota outcrop does not show mineralization.
A short
chalcocite vein was observed along a fault south of the Hot
Spot mine within the Baca Formation (SW.1/4, NW 1/4, sec. 18,
TlN, R5W).
The San Andres Limestone and other Paleozoic
carbonate units which underlie the study area (Tonking, 1957)
may have locally generated C02
flow and igneous intrusion.
evaluate this possibility.
gasduring times of high heat
However no data is available t o
1.9 8
Conclusions
1. Stratigraphy
a) Rock units of the following formations, from
oldest to youngest, are exposed a t the surface within the
study area:
Chinle Formation, Dakota Sandstone, Alamito Well
tongue of the Mancos Shale, Tres Hermanos'Sandstone Member of
the Mancos Shale, D-Cross Tongue of the Mancos Shale, Gallego
Sandstone, Mesaverde Formation, Baca Formation, Spears
Formation, Hells Mesa Tuff, A-L Peak Tuff, La Jara Peak
Basaltic Andesite, and the Popotosa Formation.
The
differentiation and nomenclature of these units reflect
advances in stratigraphy since Tonking's (1957)
reconnaissance map
of the Puertecito
quadranglewhich
included the area of this report.
b) Lithologic and paleontologic evidence suggest
that the Dakota Sandstone-lower Tres Hermanos Sandstone and
the upper Tres Hermanos Sandstone-lowermost Mesaverde
Formation record two major transgressive-regressive cycles.
The final eastward marine regress'ion from the study area
began during deposition of the D-Cross Tongue, and was
followed by deposition of the alluvial and paludal deposits
of the nonmarine portion of the Mesaverde Formation.
c) The volcaniclastic Spears Formation intertongues
with the top of theBaca Formation in the study area.
towards the Magdalena Mountains, the Spears Formation
South
109
0
u n c o n f o r m a b l yo v e r l a p ss u c c e s s i v e l yo l d e rP a l e o z o i cs t r a t a .
m u s t b el o c a t e d
T h e r e f o r et h es t u d ya r e a
i n a na r e ao f
time.
c o n t i n u o u ss e d i m e n t a t i o nf r o mB a c ai n t oS p e a r s
d ) The H e l l s Mesa and A-L
t h e A-L PeakTuff
In
t h e s o u t ha r em i s s i n g .
t h i n , and o t h e rt u f f sf o u n dt o
addition,theHells
Peak t u f f s a r e r e l a t i v e l y
Mesa Tuffandthegray-massive
member of
fillchannelserodedintounderlyingunits.
T h e s es t r a t i g r a p h i cr e l a t i o n s h i p sh a v en o tb e e no b s e r v e dt o
t h es o u t h
and i n d i c a t e t h a t t h e s t u d y a r e a
was l o c a t e d n e a r
t h ed i s t a le d g eo ft h e s ea s h - f l o ws h e e t s .D i f f e r e n t i a l
v e r t i c a l movements a l o n g t h e T i j e r a s l i n e a m e n t
may a l s o h a v e
i n f l u e n c e dt h et h i c k n e s so ft h ea s h - f l o ws h e e t s .
e ) The p i n n a c l e s member of t h e R-L Peak Tu'ff is
interbeddedwithinthe
2.
La J a r a P e a k B a s a l t i c A n d e s i t e .
Structure
a ) One b r o a d ,s o u t h w a r d - p l u n g i n ga n t i c l i n a lf o l d ,
t h e Abbe S p r i n ga n t i c l i n e ,
i s e x p o s e di nt h es t u d ya r e a .
X e s a v e r d eF o r m a t i o na p p a r e n t l y
is t h e y o u n g e s t
was f o l d e d .T h i sa n t i c l i n em o s tl i k e l y
strata t h a t
was formed by t h e
l a t e C r e t a c e o u s - e a r l yT e r t i a r yL a r a m i d eo r o g e n y .
No o t h e r
Laramidestructureswithinthestudyareacanbedefinitely
identified.
b )R e g i o n a le x t e n s i o nr e l a t e dt od e v e l o p m e n to ft h e
RioGrande
riftfracturedthestudyareawithnumerous,
c l o s e l ys p a c e d ,p r e d o m i n a n t l yd o w n - t o - t h e - w e s tn o r m a lf a u l t s .
M a f i cd i k e sw e r ee m p l a c e di n
The
many o f t h e s e n o r t h - t r e n d i n g
110
faults.
n
T h e l a r g e r of t h e s ef a u l t s- - “ t h o s ew i t hg r e a t e r
t h a n 5 6 0 f t ( 1 5 2 . 4 m ) o fv e r t i c a ld i s p l a c e m e n t
a p p r o x i m a t e l yp a r a l l e l e d
--
are
on t h e i r downthrown s i d e s by a x e s o f
n a r r o wa n t i c l i n e s .T h e s ef o l d s ,a f f e c t i n gr o c k sa sy o u n ga s
t h eS p e a r sF o r m a t i o n ,p r o b a b l ya r ec a u s e d
e f f e c t ss i m i l a rt ot h o s ed e s c r i b e d
by r e v e r s e d r a g
by Hamblin ( 1 9 6 5 ) .
.
c ) The M u l l i g a nG u l c hg r a b e n ,s i t u a t e da l o n gt h e
e a s t e r nb o r d e r
of t h es t u d ya r e a ,
was f o r m e dd u r i n gl a t e
O l i g o c e n e - e a r l y ~M i o c e n eb l o c kf a u l t i n g .
i t s westernedge
by a complexsystemofpredominantly
d o w n - t o - t h e - e a s tf a u l t s .
b o t hs i d e s
The s t e e pe a s t w a r dd i po fs t r a t ao n
of t h i s f a u l ts y s t e m
n o r m a lf a u l t sa n d
structurein
I t i s boundedalong
i s u n u s u a lf o rl a t eC e n o z o i c
may r e f l e c t r e a c t i v a t i o n
of a major
t h e subsurface.
d ) The MulliganGulchgrabenmargin
is d e f l e c t e d
westward i n two a r e a sa l o n gd o w n - t o - t h e - s o u t ht r a n s v e r s e
f a u l tz o n e s .
Away f r o mt h eg r a b e nm a r g i n ,
o ft h e s ez o n e s
t h e more n o r t h e r l y
i s e v i d e n c e d by d i s c o n t i n u o u s r e g i o n s o f
p r e d o m i n a n t l ys o u t h e a s t - d i p p i n gs t r a t a A
. c r o s st h e s ez o n e s ,
theregionaldip
i s r e v e r s e da n df a u l td i s p l a c e m e n t
d e c r e a s e s .T h e s et r a n s v e r s es t r u c t u r a lz o n e sa r eb e l i e v e dt o
r e p r e s e n tf l e x u r e sa b o v eb a s e m e n tf a u l t s
n o r t h e a s t - t r e n d i n g T i j e r a s lineamen‘t.
.....
.
of t h e
.
u
111
3 . Economic
a) The b a s a l 2 0 0 f t ( 6 1 m ) oftheMesaverde
F o r m a t i o nc o n t a i n sc o a l ,o r g a n i cs h a l e s ,a n di n t e r c a l a t e d
t h i ns a n d s t o n e s .O u t c r o p so fa tl e a s te i g h t
(0.30-
1- t o 2 - f t
t o 0 . 6 1 - m ) - t h i c kc o a lb e d so c c u ri n
t h e v i c i n i t y of
C o r k s c r e wC a n y o n .T h e . c o a lb e d sg r a d el a t e r a l l ya n d
v e r t i c a l l yi n t oo r g a n i cs h a l e s .L o c a l l yt h i c k ,b u t
d i s c o n t i n u o u s ,c o a lb e d sa tt h et o po ft h i sf o r m a t i o ni n
s i m i l a rl i t h o l o g i cp a c k a g e sh a v eb e e ne x p l o i t e di nt h ep a s t
atthe
Hot S p o tm i n e( s e c .
1 8 , T l N , R5W).
b )E x p l o r a t i o ne f f o r t sf o ru r a n i u mh a v eb e e n
c o n c e n t r a t e di nt h eB a c aF o r m a t i o nb a s e du p o nc h a r a c t e r i s t i c s
f a v o r a b l et os a n d s t o n e - t y p eu r a n i u mm i n e r a l i z a t i o n .T h e s e
c h a r a c t e r i s t i c sa r eb l e a c h e d ,p e r m e a b l es a n d s t o n e sc o n t a i n i n g
t r a c e s of m i n e r a l i z a t i o n .
o r g a n i cm a t t e ra n d
thestudy
a
(sec. 13, T l N , R6W) hasbeendevelopedon
u r a n i u mp r o s p e c t
s m a l ls c a l e .
The Hook
On thewhole,however,the
Baca Formation of
area a p p e a r s t o b e u n f a v o r a b l e f o r d i s c o v e r y o f
l a r g eu r a n i u mo r e b o d i e sb e c a u s eo ft h el e n t i c u l a r i t yo ft h e
c h a n n e ls a n d s t o n e s .
The t o po f
some l o c a t i o n s a p p e a r s t o h a v e t h e
characteristicswhich
concentration.
wouldbe
t h e MesaverdeFormation
same l i t h o l o g i c
favorableforuranium
Many o ft h es a n d s t o n e si nt h i sf o r m a t i o n
more a r e a l l y e x t e n s i v e t h a n a r e s a n d s t o n e s o f t h e B a c a
Formation.
in
are
112
D
References C i t e d
A l l e n , J . E . , and B a l k , R . , 1 9 5 4 ,M i n e r a lr e s o u r c e so f
D e f i a n c ea n dT o h a t c h iq u a d r a n g l e s ,A r i z o n aa n d
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R e s o u r c e s B u l l e t i n 36, p. 192.
Fort
New
Anderson, R . E . , 1971,Thin
s k i n d i s t e n s i o ni nT e r t i a r yr o c k s
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i n the Datil
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N e w Mexico: N e w
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Guidebook, p. 135-143.
i n t h e area around
Anonymous-11, 1963,BacaFormation
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p. 1U0-101.
1 4 t hF i e l dC o n f e r e n c e ,G u i d e b o o k ,
Anonymous-111, 1963, O i l a n dg a si nS o c o r r oC o u n t y ,
New
Mexico: N e w M e x i c oG e o l o g i c a lS o c i e t y ,1 4 t hF i e l d
Conference,Guidebook,
p. 217-219.
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Brown, D.M.,
SocorroCounty,
N e w Mexico [M.S. t h e s i s ] :S o c o r r o ,
110
New Mexico I n s t i t u t eo fM i n i n ga n dT e c h n o l o g y ,
PP.
Bruning, J . E . ( 1 9 7 3 ) ;O r i g i n of t h e P o p o t o s aF o r m a t i o n ,
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Ph.D. d i s s e r t a t i o n , N e w Mexico I n s t i t u t e o f M i n i n g
p.
andTechnology,132
Bruning, J . E . andChapin,
C.E.,
1974,ThePopotosaFormation
-- a M i o c e n er e c o r do fB a s i na n dR a n g ed e f o r m a t i o n ,
SocorroCounty,
N e w M e x i c oL a b s . ] :G e o l o g i c a lS o c i e t y
v . 6 , no. 5, p .
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430.
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Kenny, G . S . c O t t o , J . B . ,
a n do t h e r s ,1 9 6 3 ,
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Crossbedding:
h i g h - a n g l e :g r e a t e rt h a n1 5d e g r e e sf r o mb e d d i n g
plane
1 5 d e g r e e sf r o mb e d d i n g
l o w - a n g l e :l e s st h a n
plane
large-scale:
small-scale:
g r e a t e rt h a n
18 f e e t ( 3 . 1 m )
l e s s t h a n 1 0 f e e t (3.1 m )
B e d d i n gt h i c k n e s s e s( I n g r a m 1
, 954):
v e r y t h i c kb e d d e d :
g r e a t e rt h a n
1 m (3 f t )
30 t o 1B0 cm
t h i c kb e d d e d :
medium bedded:
10 t o 3 0 cm
3 t o 1 0 cm
t h i nb e d d e d :
1 t o 3 cm
v e r yt h i nb e d d e d :
121
Petrography of
formations
A . Definitions and code
D :
Sort:
RO :
%G :
average apparent grain size in mm. (visual est.)
using chart of Folk (1968)
sorting (visual est.)
vw - very well
w - well
m - moderate
p - poor
vp - very poor
roundness (visual est.) using chart of
Krumbein and S l o s s (1963)
8.1 - angular
8.9 - well rounded
percent framework grains of total rock (visual
est.) using chart of Terry and Chilingar ( 1 9 5 5 )
number of grains counted upon which the following
percentages are based.
Qm : monocrystalline quartz
QP : polycrystalline quartz
K : potassium feldspar
P1 : plagiocla'se
Ch : chert
Li : lithic fragments
T : dominant lithology of lithic fragments
qz - quartzite
ms - mudstone
cs - claystone
ps - phyllosilicate balls
sc - quartz-mica schist
fp - felted plagioclase laths
ig - igneous
Mi : micas
0 : other, including opaques and nonopaques, fossils,
and organic debris
N :
Appendix IIA continued
%M
:
percent matrix material of total rock (visual est.)
using chart of Terry and Chilingar ( 1 9 5 5 )
%C
:
Min
:
percent cement material o f total rock (visual est.)
using chart of T e r r y and Chilingar ( 1 9 5 5 )
dominant cement mineralogy
bc - blocky calcite
PC - patchy calcite
s - syntaxial silica
ph - phyllosilicate
li - limonite
ch - chert
%P
:
tr:
percent porosity of total rock (visual est.)
using chart of Terry and Chilingar ( 1 9 5 5 )
trace amount (less than 2%)
Thin-section abbreviations correspond to
mapsymbols.
123
~
B. Petrographic d3ta
Tr c-1
TIC-2
__
Kd-1
Kd- 2
Kth-1
Kth-2
(6.05,0.6
0.13
0.3
0.18
0.15
VP
W
0.5,3.2
m, v p
0.7,w.5
82
W,VP
0.3,d.3
0.1
25
35
496
cs
50
0.7
80
500
10
tr
2
tr
tr
85 .
ms
tr
tr
W
W
0.3
73
8.5
78
500
50
tr
5
tr
40
tr
505
64
tr
450
17
12
7
24
500
85
5
tr
tr
3
3
tr
tr
16
tr
tr
q=
2
2
q=
PS
4
5
tr
4
tr
tr
2
tr
tr
15
25
Ph
li
2
tr
10
8
40
tr
30
45
bc
15
15
15
PC
s
S
tr
3
3
3
'
Notes: Trc-1 is
a bimodal, clastic limestone.
Kd-2 is a sandy conglomerate.
..
*;>
,
...."..
,.: ..:.
77
tr
7
ms
tr
4
7
124
Appendix IIB continued
Kmv- 1
Kmv- 2
Kmv- 3
Tb- 1
-
Tb- 2
0.18
m
0.3
35
0.24
0.20
m
0.3
58
L3.25
m
0.3
50
0.3
0.35
P
0.5
50
0.1
75
500
80
tr
14
4
502
25
tr
440
32
613
61
tr
tr
45
5
tr
tr
tr
4
tr
sc
3
48
tr
12
2
9
13
PS
tr
tr
476
68
2
14
2
496
87
tr
tr
tr
11
tr
ms
tr
tr
28
15
10
5
7
10
2
Kg-l
D
-
Sort
RO
%G
-
%C
-
0.16
W
0.3
60
"
8
7
W
0.3
65
2
14
PS
2
3
10
3
cs
tr
tr
W
500
50
tr
5
3
35
5
fP
tr
tr
10
50
Min
PC
bc
20
ch
35
PC
40
bc
40
PC
20
PC
%P
-
2
tr
5
2
tr
tr
3
_
.
Notes:
Kg-2 is a fossiliferous, sandy limestone.
Tb-1 is a nodular sandstone.
I.
125
u
Appendix IIB continued
Tb-3
Ts-1
-
Ts-2
D
Sort
1.0
0.45,1.25
0.6
RO
-
0.3
53
0.30.1,O.l
70
532
502
tr
tr
tr
30
%G
75 -
m
VPrVP
VP
40
ig
tr
30
402
tr
tr
tr
20
tr
70
ig
tr
10
7
tr
10
%C
tr
Min
li
40
PC
27
li
%P
-
25
tr
Note:
Ts-1 is a bimodal rock.
50
2
18
5
13
10
ms
tr
tr
%M
-
tr
15
This thesis is accepted on behalf of the faculty of the