4
-.
T e r t i a r y and Quaternary
-
..
Baca Formation
, .
The Datil Formation (Winchester, 1920), a name
now
abandoned (Elston, 1 9 7 6 , p. 1 3 4 ) , has been . s e p a r a t e d i n t o
t h e Baca Formation,SpearsFormation,
A-L
..
.
PeakTuffand
Hells Mesa Tuff,
.
.
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 . k i l p o l t . ,
.
.
.
..
.
.
.
.
.
.
.
.
m)-:of'
-:.
.
..
and
o t h e r s ( 1 9 4 6 ) . d e s i g n a t e d . t h e b a s a l '684 f t ( 2 0 8 . 5
.
.
... . . . .. ..:
Winchester's (1920)-measured s e c t i o n of t h e D a t i l F o r m a t i o n
,
.
.
.
as '&e type sec%ion f o r . t h e Eaca Formation.This.
. .
~~~
~
1 N.
, R.
-.
.measured section bf'the
4 I?.
, and
sec.tion
. .
i
,
.
EacaFormation
exposed".
Palae'osyops,, a smaLl rhinocekas-type
.
.
,
..
. .
anima1'of.Bridger'
. .
from t h e Baca Formati'on.
..
North of
.
. .
D a t i l , t e e t h and borie fragments of Protoreodon bjumilus~a.. . . .
l a t e Eocene x e l a t i v e of t h e modern-day sheep, were 'found i n ,
.
I
Baca s t r a t a (Snyder, '1970). Fossil wood from t h e Baca has
b e e n ' i d e n t i f i e d as' Palmoxyl'on sp..
- and Leguminoxylon sp.
which supports t h e Eocene ageassignment(Snyder,,
..
.
. , ..
.
and o t h e r s ais0
i n d i c a t e t h e Baca t o be a t l e a s t a s young a s Eocene
(Chaiffetz , i n p r e p a r a t i o n )
.
1971) ..
I
.. .
.
'.I
" .%.
. .
. .
. .
Tilia-type pollen, Jugladaceous forms,
,
. .
. .
.
.
a t t h e type .locality.
..
At.Carthage , Gardner (1910) recovered a t o o t h of
. .
!
.
..
(Middle Eocene)age
'
i s t h e only published
~
. .
..
.
. _.r.
365 f t (111.3 m) was "covered"
or "not
. ..
O f t h a ts e c t i o n ,
'
Baca Canyon, secs. 4 ,
was measured in t h e upper portion of
5,. 8 , and 9 , T.
...
.
.
.
.
.
..
.
,
9
89
. .
Potter (19701, in an unpublished thesis, reported,
making
several
partial
measurements
which
he.compiled,
in
. .
words, by "somewhai questionable correlations" into
his o&
a complete section. Potter (1970) found the Baca to be
697 ft (212.5 m) thick at Baca' Canyon, secs.
4,. 5 and 8,
,
R.
T. 1 nf.,
4 W..
The thickness of
the'Baca
.
'(762.0
.. .
m) as
not exceed
indicatedby driliing,
..
.
but
1150ft (350.5 m)
..
;'
in
..
,
is2500, ft
.
typical'iy.'
.
outcrop
. . . .. ..
.
the
.
it
.
Carihage
and
Joyita:
0ther.formations
to
time
I
.
.
Hills'areas
.
that
.
equivalent
,
.
are
.
to
.
.
of
.
',
.
similar
. ..
.
those
in'
Baca
lithologies
and
.
,
include
the
Eagar,
.
Canyon.
close
. .
-
Baca
.
.is.'
.
.
the
.
.
with
,..
'th%ckness
about 6 0 0 ft.'(182.9 rn) ' (Snyder,. 1971).
. .
.
. ...
.
Wilpolt and others( 1 9 4 6 ) correlated rocks'
of the
..
does
..
McRae,
,
Cub Moun't;lin, ..and Galisteo. The age of the Eagar Formation,
. .
. . .
a westward continuation 'the
of Baca in Arizona (Snyder,
..
19711,
and
is'
coal
uncertain..
in
Formation,
the
basal
Elephant
and is therefore
but
.it
contains
portion
Butte
dam
.
(Sirrine,
area,
.
.a
,
.
post-Laramide
Galisteo
age
fauna
.1956)
The McRae
'
contains
Triceratops
Cretaceous in part (Lee and Knowltori, 1917).
The Cub Mountain'Formation,Capitan-Ruidosoarea, .
.
.I
Cretaceous
.
..
is
.
.
.
,
I..
topre-Oligocene in age .(Keiley, 197i).The
Formation,
withina range
south'
of Santa
.
.
from
Pe,
Paleocene
is
to'
of
uncertain
Eocene onbased
limited plant remains (Lee and Knowlion, 1917)'.
'
Sedimentation
in
the
Sari Juan
and
Raton
basins
continued
throughout the lqte Cretaceous and ea'rly !Pert$&, Fqunql
.
.
. .
.
. .
evidence
.
indicatesa Eocene
age
for
the
San
Jose
Formation
(Lucas; 1977).
Because early Tertiary rocks are similar lithologically,
.
separated geographically,, and differing ages,
it is "
. . .
reasonable..
to
conclude.
that
sedimentation
.
and
western
Arizona
occurred
in
New
Mexico
.
from
the
Cretaceous
through
. .
the Eocene in isolated but somewhat geneticaily'. related
..
..
'
.
. ,
. . . . .. .. . . :. ,.
. . .. .
. . .basins,.,(Tonking,L1957)...
. . . -.-.:
. .
.- . . . . . .. .. .. . . . .
. . . . . *... ." - .
" _ . T.he..times~.-and,.ratesi,of.~:.s,ubsldence
.-. . . . . . . . .
.
...
. . .
. .
...
1
..
I
.
and
.
~
.-
,
. . .
.
"
sediment
..
accumulation
..,
.
undoubtedly
.
. . . .
to.basin.
The
stratigraphic
.
fluctuated
.
position
and
sediment
of sparse
record
are
basin
duration
of 'gaps
. .
..
in <he
from
, .
difficult
.to
establish.
because
paieontological Contrbl.
The
.base
of
the
Baca
rests'
...
.
Mesaverde,
a relationship
,.
.
that
.
unconformably
on the
.
can
be
'demonstrated
. . difficult
to ascertain
at a single
but'
is
',
.
.
location. The boundary 'between the formations changes
regionally
. .
character'
laterally
. .
In general,
the
occurrence
.
colored
.
lower
of
.
.
..
.
.
and
shale
red
.
o r .
.
. . .
stones of the'
and,
this
..
color
sandstone
that"
.shales
change
is useful
in
contact
of
,Formationsis marked
..
lithologies
.
pink-
sand-
distinguishing
hue .
.
the
. . ..
.
.
and
Mesaverde
t a k e on a greenish
.
formations.
The
contains
..
.
.
uppermost
.
.
bounhary'.is. at
placed
the f'irst
the
feldspar. . ,.Often
potassium
. .
.
places
is difficult''to delineate.
in
Baca
.
the
by
Baca
.
and
alternating
overlying
beds
of
Spears
Baca
and
Spears
andwas mapped at the lowest bed containing.,;.
*
91
volcanic detritus. Beds of the Baca are arkosic and
of the Spears, on
rich in granitic rock fragments. Beds
the other hand, contain abundant volcanic material.a At
distance
the
Baca
and
Spears
can
generally
be
differentiated
on the basis of color and weathering. The Baca
strata'are
various hues of red, generally forming
low plains with
'
isolated light-gray conglomerate or sandstone ledges,
. .
.
.
.
. . . ..
...
.
.
,:th.e-Spears
a.s.
. . . . rounded,
...
l;ight-p.u,~~~e,,.,...,.i
. .. . ... . ... . :.. . . .
. .. ouf:
.. ...
- crops
. .
,
. .
. .. .
whereas
. . . . . .. ..
.
. .
. . . .. . . . . .
. .. . . :
. .
. . . . .
.
I_
rough-textured sandstone hiils.
. . . . . . .
.
.
.
Potter (1970) divided the Baca 'into three informal
.
.
members. These'members are, in ascending order: a lower
red
mudstone-sandstone
member,
an
arkosic
sandstone
member,
. . ..
and an upper red mudstone-sandstone member.
In the study
I
aiea
three
.
informal
members.
of
the
Baca
are
easily
.
distinguished. 'Potter'.& (1970) terminology of' these'.members'#
. .
..
. . .
-
however, lacks descriptive viability and therefore
a
..
.
.
.
'
'
.
.
:
slightly 'modified version of terminology
is proposed;. The
...
. .
lower .red mudstone could more accurately be called .the
.
,
conglomeratic
.~ .
memberas conglomerates in the
restricted
to
.
. .
khis.
out the Baca:
be
the
A
the
rest
more
gray
of
portion;
The
arkosic
.sandstone'
.
.
member is 'misleadingas .arkosic
.
from
are
. . .
largely
would'
Baca
'
'
sandstones
descriptive
sandstone
the
Baca
ncme
for
member'
by
its
are
found
this
as
.
through-
subdivision
this
Dortion
characteristic
of Potter's
color. The upper red,mudstone-sandstone member
is sufficiently descriptive. Therefore] the terminology
differs
.gray-yelIow
and
quartzite
fragments
are
Precambrian rocks. 'Rounded
considered
limestone'
to
be-derived
fragments
are
from
.
.
commonly fossiliferous, containing crinoid stems, brachiopods,
bryzoans
and
other
fossils
of
Mississippian
to
Permian
age.
..
Two
types
of
fossilized
wood,occur
.unrounded
and
genetically
related
in
to
the
the
Baca; isone
Baca,
a
and
...
second type is darker in
colo~,rounded, and
presumed to;
. .
..
. .
. . .
Conglomeratic
..
. .
strata
are
. . . . . . . ..
...
. . . .. .
. .
.
.. . . .
............
-:...
..:~
.
. ..:
. ..:......
~
fiave.been reworked-.
from the.Triassic,
:(Potter.,'
1970):z:
.
.
.
. .
.
.
. . . .
. .
.
X..'
generally,
a grayish
type
color
. .
. .
..
. .
in. contrast to 'the
reddish hue of the mudstone.
The sand.
..
. .
.
.
..
stones
. . .
and
. .. . .
. .
. .
conglomerates
are
mudstone
and
more
.
. . .
. ..
:
. . . . . .
'stepped'ledges
nature.
and
.I
form
.. . .
'
than
. . . _. .
in thickness
that
'vary
. . .
the
I.
,
resistant
to .erosion
~
.....
due to
'
their
lenticular
Trough
very-low-angle
...
:.
cross-stratification
is
common
.
. . . .
thickest'
sandstone.or
in
.
the
conglomerate
The
sandstones.
'
unit
measured,
27, unit
..
is 35 ft (10.7
thick.' Siltstones and claystones are
m)
.
burxowed in many places. The burrows are non-branching,
.
vertical and horizontal, about inch( 6 mm) in diameter, :'
. .
. .
,
'
.
.
,
.
.
.
'and several inches
long.
. .
:~
.
The gray sandskone
..
.
member, . units
. 29 through 3 2 , is
. .
. .
composed almost entirely of interbedded, light-greenish.
" ,
,. .
. .
. . .
gray (S GY 8/1) and
.
thin-bedded
.
yellowish-gray
( 5 Y 8/1) ,
clayey, sandstones and siltstones (fig.2 5
shales
occur
in
this
..
interval..
The
&
26).
gray
No red
sandstone
''
member
is 176'ft (53.6 m) thick, loosely consolidated, and forms
.
.
slopes or level plains. The rock is composed predominately
,
:
-700'
.
.
-600'
..
Figure 26.
..
Upper'253 ft (77.3 m) of the Baca Formation
e
0
of-silt-to
coarse-sand-sized
quartz
and
97
gray-colored
potassium feldspar. The grains are moderately sorted and
-
subrounded to subhedral. Yellow limonite halos commonly
encircle
organic
debr.is
and
fossilized
tree
,
trunks
in this
.
member (fig. 27). Conglomeratic cross-bedded sand lenses,
as well ,as limestone beds are present localiy,9 and
secs
11, T. 1 N.,
. . ...
.~
:.
.
.
The
.
R. 4 W..
.
..
r8d
mudstone
.
.
.
. .
.member,
'Tuniks'33:'through
...
. .. . .
.
.
.. .
. .
.-5X.
.'i.
s 244
. . ; '. . -.
.
,
ft. (74.5 m) thick and composed mostly of grayish-red
..
. . .
'(10 R 4/2) to
. .
..
.
reddish-brown'
(1.0 R 4/4) silty mudstone.
.
. .
.
3 inches (8 cm) thick, are interThin sandstones:, about
. .
.
bedded in
the lower portion
of this segment.
The sandstones
..
.
.
are
very
light'gray
'(N
8)
..
rounded,'
well
sorted, very-fine-sand-to silt-tsized grains.In the
. .
..
.
portion of the member pale-red (10
as25 Et (8..6 m)
thick
..
.
.
6/2) sandstones
.
.asmuch
.
upper
'
.
. .. .
. -
, composed'of
are
.
.
..
.
interbedded'
with
,
mud-
stones.. The sandstones consist of moderately sorted,'
!
''
.
.
,
. . .
loosely consolidated coarse arkosic sand. Numerous veins
.
. .
. .
of satin spar gypsum and one thin vein of light blue
Telestite.
w a s observed
. .
.
.
. ..
.
the type locality.
in
the
.
'upper
of
portion
the'
'
.
, I
,.
.
.
.
1
.
Baca
.at
. .
'
~
.
'The sand-and silt-sized constituents
of the Baca
.
are
about30 percent
quartz,20 percent
percent
quartzite,10 percent
percent
dividedamo:lg plagioclase,
..
.
'
.
chert,
microcline,20
. .
and
the
potassium
remaining
20
feldspar
,
. .
carbonate, muscovite, and mudstone grains. The cement 'of
.
..
the sandstones is partly an early generation of silicia
'
but is largely a later genGration carbonate. The grains
are
conkonly
layerof hematite.
coated abythin
.:,.
'.
Fine-'
.
grained 'hematite "and carbonate occurs
in shales'of
Baca Formation.
.
'
.
the'
.
The Baca accumulated in one
of many basins produced by
the Laramide orogeny. The .dimensions and shape
&e of
..
. .
Baca
basin
belt.
are
the
unknown
.basin
.
'
but
.judging
from the
.
probably
present
oukcrop
..
was
elongate
east.
to
west
and
.
slightly sinuous between highland masses. Highlands
. .
. . .
.
bordering the basin during Baca depositon include: Zuni,
.
DefiJ.nce
on
the
and
Lucero
east,
. .
'uplifts
on the
.
.
Magdalena
north,
.
Joyita
Hills
uplift
.
uplift
to
the
south,
and'Mogollon
highlands to the southwest.' Undoubtedly, smaller, local
.. . . .
..
uplifts also influenced
Baca
.,
sedimentation.
.. . .
Snyder (1971) interpreted the ciimate during Baca
deposition to'be arid to semiarid, and g'ave the following
..
as evidence:
entrenched
ij
.,
..
coarse-grained sediments in deeply
channels;2).reddish
.
.
.
coloro f the
finer
grained
.
rocks; 3) lack of abundant organic trash (believed by Snyder
.
to be
.
dueto the.'paucityof vegetation); and 4) 'presence
.
.
of continental limestones thoughf
to be ca'liche. Johnson
(1978) .advocatesa wetter
climate,
in
.the
range,
of 'semiarid
to subhumid. As evidence he cites the following: 1) lack
of obvious'
..
indicators.or
aridity,
. .
such
as
primary
evaporites,
2) the fact that caliche,
wind reworked sand, and carbonates;
........................ .......
........
,,~
....
(L.
..
.i.-X':.I.I.'.:..........?.~'...~.
.??.&
~,
...?..
100
described
by
Potter
(1970), develops
best
in.
semiarid
rather
climates;
3 ) abundance of.root
even
than
arid
if
actual
organic
tropical
floras
and
Although
the
.
that
..
the
debris
faunas
writer
mottling
4) humid
scarce;
and
is
of
i
3
neighboring
.concurs
with
Eocene
basins.
' ,
Johnson%
..
conclusion,
'
.
climate
was
wet
and
hot
during
Baca
deposition,
. .
certain points should be made. First, limestones found
in
.......
gray shales. . .and have . yielded
Lacustrine. algae
(Chaiffetz,
in
. . . .
. .
. .
preparation). A lacustrine
..
origin, not soil-profile caliche,
,'
.
.
.
.
....
..
'
is postulated for. these beds. Mudcracks in the Baca
(Tonking,
1957),
suggests
alternate
"wetting
and'
drying.
I
Second, the MacRae'.,, . basin that Johnson (1978) advances
?
as proof of a wet climate for the'middle Eocene
is in part
,
'
. . .
late
. .
Cretaceous
Formation
middle
of
In
the
Eocene
'
age,
San.
as
in the
older
Juan
Baca
than
Basin
in
the The
Baca.San
is
New
Jose
'
unquestipnably
Mexico
from
the
(Bridger)
limited
faunal evidence available. The fauna of' San
the Jose
Formation are.typical
(LucaS, 1977).
Thirdly,
of
savanna-like
upland
.
'assemblages
,
~
'only
'the
.clay . constituents
. of
the
Baca
sediments are characteristically red.
'Siltand sand clasts
..
are
shadesof gray.withonly a few
grains
with
coatings
of
iron oxides. Magnetite and other iron-bearing minerals 'in
. .
....
the
Baca
are
mainly
unaltered,
pigment is not a product of in
situ
indicating
tha.t
the
rea
alteration:
of iron-bgaring
detrital
grains,a process described by Walker
(1967).
Because the red pigment is almost exclusively in the clay
'
fraction
.
of
.
due to
the
rocks'the-origin
the.weathering aofsoil
of
the red
rich
in
color
brown
is
probably'
ferric
material.
. .
The
.
.
sediment
is
transported
in
the
brown'hydrated
form,
and
..
converted ,toa bright red by dehydration and oxidation after
"
,
deposition (Van' Houten,
1968). The oxidation probably
was
. .
. .. . .
. . _ .. * .
_ . . -. ..
.~I
ciose.-to the deposifionai interface lsecause"after-deepel:'
. .
.
i:
,'
'.
'
buria.1 clayey-sediments
could not.oxidize easily.
A
..
..
. .
. .
seasonallyrainy,hot,savanna-1,ikeclimateisanideal
.
.
,.
.
.
setting for. drying ferric hydroxide to hematite (Schmalz,
..
-1968).
. .
,
.
.
.
.
,
'
I
.
Baca clasts are
varied and Snyder
(1971) concluded tha.t
. .
the
Baca
The
clasts
granitic,
sediments
in
the
. were
.
derived
from
,area
studied
were
metamorphic
and
fron
the
source
.rock
must
source
derived
primarily
The
sources.
limestone
. .
.
multiple
..
'
.
areas.
.
from
distance
.
have.
.
been
short
for
the
following
reasons.: 1) large size of 'granitic boulders in the Bacat
2) angularity
,.
euhedral
of some
of the constituent.:;
and
unaltered. . feldspars,
and 4) presence.of
clasts. Potter
of the
Baca
3 ) occurrence of
'
,
.
'~
limestone
(1970) concluded that."some of the constituents
were
transported
no
morea few
'thanmiles.
'I
Blatt
and others (1972) state:thatfeldspar grains are fairly durable
and
can
be
transported
great
distances
without,significant
Feductiori in total. volume percentage, but are greatly .~
"
..
reduced
insize,whentransported
distances
of
only.20 to 25
.
e
102
"_
Alluvium
BacaFormati:on,
m i d d i eu n i t
i n d i c a t e d by s t i p p l i n g
.
. -.
.
Current d i r e c , t i o n , p e b b l e
imbrication .
Bimodal c u r r e n t i n d i c a t o r , l o g
a1 ign'ment
0
.
1 mile
I
F i g u r e . .28,
,
.
'mi (32.2 to 40.2 km). Judging from the granite boulders
in the lower Baca,
a nearby source for at least this
of boulder size,
material is.-indicated. Other constituents
principally
limestone
could
come
and
quartzite,
are
more
rounded
and
.
have
from
more
distant
. ..'
,
sources.
.Pebble imbrications, cross-bedding,. ripples, and long
. .
,
axis'of tree
trunks
members of the
in
Baca
the
conglomera.tic
. ..
and gray sandstone
..
. .. . . . ..
. . . .
. .
flowing current
.. ...
indicate southeastward
'a
(fig. 28).
Therefore, the' source area probably was 'to .the
.,
..
.
. . . . .:.
northwest. Potter (1970) and Johnson (1978) proposed the
. .
Lucero uplift and Snyder
(1971) .,theZuni
'
uplift
as
the
source of the Baca sediments in the area studied. Although
. .
.. .
the.
Lucero.
..
uplift
is closer
and
.
.
Paleozoic
.
could'
limestone
to
'have
provided
..
, .
or'quartzites
.granites
the
Baca,
no
area
during
the oEocene
r at present.
. .
were
exposed
The'Ladron
in
that
Mountains,
with
.a
Precambrian
.granitic
and
. .
guartzite core,is a Miocene uplift (Bruning,
1973) and
'
could
. not
.. .
have
The,
Zuni
is
could
have
contributed
the
been
closest
. ..
the
source
. . .
but as the
area
Zuni
studied,
to.
Eocene
Baca
sedimentation.
" .
known. to.uplift,
the northwest
of
granitic.and
quartzitic
seems
unlikely
that
boulders
of
the
of
granite
.
and
large
angular
material;
.
is 60 mi (96.6,km). northwest
Tplift
it
that
feldspars
could,
have
came
.
.
from
a . such
distant source., Yet, no alternate source area to the'nortihwest
can
..
be
. .
suggested.
104
e
Until 1978, most workers have considered the Baca as
.
a fluvial 'channel and floodplain sequence (Potter, 1970;
-
and Snyder, 1971) However, Johnson (1978) interpreted the
Baca,
from
'west
to
east,
to
a progression of
generally
be
facies from humid alluvial fan, fluvial-meander belt, to
lacustrine d.elta. In the area studied Johnson.(l978) ,calls
.
'the
.
..
. .
lower
conglomeratic.
.
.the
. ..
'.
.
.
.
.
..
member,
a lacustrine
. ..
. .
. .
.
,
fan'
.. ...
.
delta;
. .
..
middle . gray
sandstone member,
a distai h&id
.
.
..
.alluvial
, .
;
. . ..
.
fa.n; and the upper red .mudstone-sandstone member,
a
.
. .
. ..
..
lacuskine fine-grained
fan
delta.
. .
,
The
writer
believes
the
Baca
to
..
.
. .
,
be a.fluvia1
largely
. .
sequence. The .disagreement
with Johnson is based on the
.
...
gollowing reasons.. First, evidence for
a large lake in
..
<
I
3
.this. area is lacking. There are ..no
sLoreline deposits
or
. .
. .
. .
.. . .
... .
supportive faunal evidence. Second, the red colorof the
. .
..
..
sediments
is
more:suggestive
of
subaerial.than
.
subaqueous
'
.
I
exposure. Johnson' (1978) defends this point by suggesting
..
. .
.. ,
lake
o r lakes:
a shallow; polymictic (frequent overturn)
. .
.
'
the
frequent
overturn
would
allow
.
.
. .
dxidation.
.
-and
cause
red.coloration. However, because
the thicknesses
of deltaic
.
.
.
,
,
.... .
. sand. bodies describeh by Johnson" a s .are
much as, 30 .ft
.
the,
.
.
. .
.
.
1
.
(9.1 m) thick they therefore require similar water depths.
Thirdly;
the
fan
delta
complex
is,
composed
of many.small
. .
deltaic sand bodies that would require an extensive fluvial
. .
'
system to supply the material. However,.the fluvial facies
tract .is
. only a small
segment
of
Johnson's
(1978)
.
....<.:.
.
.
example, on t h e west side ofthe
interpretation.For
MountainsJohnson(1978)
Bear
shows t h e e n t i r e Baca s e c t i o n ,
. .
about 500 f t (152.3 m) of l a c u s t r i n e d e l t a i c f a c i e s , , w i t h o u t
a s s o c i a t e df a c i e s .F o u r t h l y ,a c c o r d i n g
to Johnson(1978)
a deltaic origin for parts
evidence for
of the Baca are t h e
upward coarsening of g r a i n s i z e per sedimentary package;
..
,
I
.
mud t o sand r a t i o ;
extensiveburrowing;convolutebedding;high
. .
afld 'vertical',sequence
.: of
. sedimentary
. ..
. . . ..
..
"
structures..
.
:
.
t
.
.,
..
..
.
,
,
.I.n. .o p p o s i t i o n ,
:,
.
. .
.
_. _~ -
:
t h e writer points out that convolute bedding, burrowing and
.
root mottling
.
Singh, 1975)
are common i n ' f l u v i a l s e q u e n c e s ( R e h e c k
..
. .
'
I n t h e B,ada' t h e sand:mud
estimated .to be about
1:l.
realm o ff l u v i a ls y s t e m s .
.:.
.
.
.
.
upward.
.
. .
may n o t
.
.
Bluck
.
(1971) has shown ' t h a t t h e head p o r t i o n o f p o i n t b a r s i n
coarse-grained meanderbelt can coarsen
. '.
upward
.
.
r e p r e s e n t a t r u ed e p o s i t i o n a lc y c l e .A d d i t i o n a l l y
.
. .
..
This r a t. i. o i s n o t o u t s i d e , t h e
d e p o s i t i o n a l package t h a t Johnson(1978)promotes
..
I.
...
.
.
Also; t h ec o a r s e n i n g
. r
and
.
ratio is
.
._
. ..
.
.
a
Also, t h e
.
. .
writer has found the sandstone bodies
variable i n b o t h g r a i n s i z e
. .
throughout and
document.
'
i n t h e Bacll t o be
and sedimentary structures
.
.
a t y p i c a l v e r t i c a l sequence d i f f i c u l t t o
,. .
.
.
.,
..
.
Baseh on' t h e d a t a above t h e 'writer concludes t h a t t h e .
.
.
.
Baca i n t h e a r e a ' s t u d i e d w a s deposited by streams c a r r y i n g
coarse-grained.seaiment
and t h e climate .subhumid.
.
..
'
The f l o o d p l a i n w a s savanna-like
I n t h e s t u d i e d az&
the south-
. .
. .
.
.