- Email: [email protected]
Tertiary palaeoclimatic history of the southeastern Colorado Plateau
Palaeogeography, Palaeoclimatology, Palaeoecology, 86 (1991): 283-296
283
Elsevier Science Publishers B.V., Amsterdam
Tertiary palaeoclimatic history of the southeastern Colorado Plateau Karl-Heinz Schmidt
Institut fiir Physische Geographie, Freie Universitiit Berlin, Altensteinstr. 19, 1000 Berlin 33, German>' (Received April 18, 1990; revised version accepted January 18, 1991)
ABSTRACT Schmidt, K.-H., 1991. Tertiary palaeoclimatic history of the southeastern Colorado Plateau. Palaeogeogr., Palaeoclimatol., Palaeoecol., 86: 283-296. On the southeastern Colorado Plateau Tertiary erosion surfaces have been preserved below the cover of the Eocene Chuska Sandstone and the late Tertiary Bidahochi Formation. Investigations of the geomorphological attributes of the erosion surfaces and laboratory analyses of the soils and weathering materials as well as the sediments on the surfaces gave substantial information on the climate and the relief-forming processes which were responsible for their formation. In some places the surfaces cut across the underlying Mesozoic sedimentary rocks with a marked angular unconformity, but these truncating reaches are restricted to areas where soft material crops out. Resistant rocks form lithologicallycontrolled cuestas, hogbacks and residual hills below the Tertiary cover. X-ray analysis of the clay minerals shows that the surfaces have not been subject to intensive chemical weathering and soil-forming processes. There is no change in the mineral content from the bedrock to the weathered material. These results apply to the (early) Eocene to Palaeocene Tsaile surface (underlying the Chuska Sandstone) and the Miocene Hopi Buttes surface (underlying the Bidahochi Formation), The results demonstrate that the climatic conditions have not changed decisively during the Cenozoic and were much the same as today. It is concluded that the Colorado Plateau has been dominated by a dry climate since the Laramide orogeny with the possible exception of the early Palaeocene. Thus the Colorado Plateau is out of phase with the general palaeoclimatic situation in western North America in the early Tertiary where at that time warm and moist conditions prevailed. The Colorado Plateau, before its separation from the Basin and Range province, was situated in a topographically lower position in the rain shadow of the southern Rocky Mountains and the Central Arizona Highlands, which at that time formed a barrier stretching from western Arizona to New Mexico.
Introduction Present-day w e a t h e r i n g a n d erosional processes on the C o l o r a d o P l a t e a u are c o n t r o l l e d by the arid to semiarid climate. There is a p r e d o m i n a n c e of m e c h a n i c a l w e a t h e r i n g a n d selective erosion. As a c o n s e q u e n c e o f the very limited i m p o r t a n c e o f chemical weathering no kaolinite develops a n d m o n t m o r i l l o n i t e a n d illite are the most frequent clay minerals. I n the s e d i m e n t a r y rocks, which are only gently to m o d e r a t e l y inclined, structural landforms such as cuestas, h o g b a c k s a n d h o r i z o n t a l plateaus characterize the present relief assemblage (Schmidt, 1988). C a n y o n c u t t i n g a n d scarp retreat are the d o m i n a n t g e o m o r p h o l o g i c a l processes. Only in some places, especially in the s u r r o u n d 0031-0182/91/$03.50
.L) 1991
ings of the laccolithic centres a n d in less resistant rocks in the footzone of large cuesta scarps pediments are being formed. Structurei n d e p e n d e n t t r u n c a t i n g surfaces are only o f very limited significance (cf. Lucchitta, 1984; Schmidt, 1988). Most palaeoclimatic i n f o r m a t i o n o n the Colorado Plateau relates to the H o l o c e n e a n d late Pleistocene, The early Q u a t e r n a r y a n d the Tertiary are n o t well d o c u m e n t e d . Pleistocene a n d H o l o c e n e climatic fluctuations resulted in the f o r m a t i o n of terraces a n d the a l t e r n a t i o n of depositional a n d erosional periods a l o n g the m a i n water courses (Hack, 1942; Euler et al., 1979; Wells, 1982; Hereford, 1984). Away from these lines of process c o n c e n t r a t i o n the l a n d f o r m s reacted less sensi-
ElsevierScience Publishers B.V.
284
tively, the cuesta scarps and plateaus were not affected to a comparable degree. Structurally and lithologically controlled relief-forming processes prevailed throughout the Quaternary.
Possibilities of Tertiary palaeoclimatic reconstruction After the Laramide period the great basins on the Colorado Plateau (Uinta, Piceance and San Juan Basin) were areas of almost continuous sedimentation during the Palaeocene and Eocene including large deposits of salts in the Green River Formation on the northern Colorado Plateau (Eugster and Surdam, 1973; Robson and Saulnier, 1981). There are rich faunal and floristic remains in the lake basins (cf. Cashion, 1967). In the San Juan Basin on the southeastern Colorado Plateau the Palaeocene Nacimiento Formation was deposited in a paludal and lacustrine environment with fish, aquatic lizards and turtles (Baltz, 1967). Deduced from faunas, an older member of the early Eocene San Jose Formation in the San Juan Basin was deposited in a swampy environment and the younger parts in dry savannah conditions (Baltz, 1967). But there is conflicting evidence, and what is still more important, the information from the lake basins gives no direct indication of the palaeoclimatic conditions outside the lacustrine environments. The lakes might only represent "oasis conditions" within a dry environment. There is always an inherent tendency to deduce a more humid climate than actually existed from lake sediment information. Direct information on the palaeoclimate in the non-aquatic Tertiary environments carl be collected from geomorphological attributes of old erosion surfaces, from palaeosols and fossil weathering products, but erosion has erased most of the Tertiary palaeoclimatic record. This kind of evidence is only preserved when very favourable conditions are given, i.e. burying and conservation of a surface or a profile by sedimentation or a lava flow after its formation. A Campanian to late Palaeocene palaeoweathering profile in Upper Cretaceous sandstones, which is overlain by the early Tertiary Wasatch Formation, has been described from the Piceance Basin on the northern Colorado
K.-H. SCHMIDT
Plateau (Johnson and May, 1980). The profile, about 100 m in thickness, is characterized by feldspar breakdown and subsequent accumulation of kaolinite. This kind of weathering is typical of warm and humid climates. Kaolinization has also been found in Palaeocene to early Eocene palaeosols in southwestern California (Peterson and Abbott, 1979). These tropical weathering products are overlain by middle to late Eocene sediments, which were deposited under semi-arid conditions. Deeply weathered granitic profiles have also been described from southern Arizona (Moss, 1977). On the southeastern Colorado Plateau old erosion and aggradation surfaces have been preserved below the cover of Tertiary sediments (Table 1). Especially the erosion surfaces offer the possibility of investigating whether there have been major deviations from the present dry climate.
Tertiary surfaces on the southeastern Colorado Plateau and their implications for palaeoclimatic history In the Navajo section of the Colorado Plateau Tertiary erosion surfaces have been fossilized below the cover of the Chuska Sandstone and the Bidahochi Formation (Fig. 1). The surfaces have been interpreted in the framework of the Davisian cyclic concept (cf. Cooley et al., 1969). Attempts at a palaeoclimatic interpretation have not been made. It is demonstrated, that investigations of the geomorphological attributes of the erosion surfaces and laboratory analyses of the soils and weathering materials as well as the sediments on the surfaces give substantial information on the climate and the relief-forming processes which were responsible for their formation.
Palaeoclimate of the Chuska Mountains Introduction The Chuska Mountains are a topographic barrier between the San Juan Basin in New Mexico and the Defiance Plateau in Arizona (Figs. 1 and 2). The bedrock underlying the Chuska Mountains is the Chuska Sandstone, which in greater detail was described by Wright (1956). The Chuska Sandstone was previously thought to be of Miocene
TERTIARY PALAEOCLIMATIC H1STORY OF THE SOUTHEASTERN COLORADO PLATEAU
285
TABLE 1 System of (erosion) surfaces in the Chuska Mountains and in the outcrop area of the Bidahochi Formation Surface
Age
Remarks
Zuni surface
Pliocene
Hopi Buttes surface
Miocene
pre-lava surface (Valencia surface of Cooley) older Oligocene erosion surface (pre-volcanic surface) Tsaile surface
Oligocene
aggradation surface, below the middle and upper Bidahochi Formation erosion surface in the Hopi Lake basin, underlies the lower Bidahochi Formation aggradation surface, older than the second volcanic phase in the Chuska Mountains surface with great differences in relief, older than the early volcanic phase in the Chuska Mountains underlies the Chuska Sandstone
pre-middle Oligocene (early) Eocene to Palaeocene
age (Cooley et al., 1969). In many places the Chuska Sandstone is intruded and covered by magmatic material (Figs. 2 and 3). The volcanism in the Chuska Mountains belongs to the minette province (Akers et al., 1971), which has more recently been dated to be of middle Oligocene age. Naeser (1971) provided fission track data for the Buell Park kimberlite diatreme (31.9 _+ 3.2 my; location see Fig. 2) and for two minette dikes at Mitten Rock (32.5 _ 3 my) and at Shiprock (27.0 _ 3 and 32.0 ___ 3 my). Both localities lie just northeast of the map area of Fig. 2. Additional K-Ar age determinations of volcanic rocks in the Chuska Mountains (31 my) were communicated by Pohlmann (1967) and Pye (1967). The datings from the Chuska Mountains and vicinity centre around 30-31 my, so do all the minette province data from the southeastern Colorado Plateau (Naeser, 1971). The dating of the volcanics and geomorphic history (see below) indicate that the sandstone is at least of early Oligocene age (cf. Hackman and Olson, 1977), more probably of Eocene age (Schmidt, 1988). The following succession of events with the respective palaeoclimatic backgrounds can be inferred from field investigations and laboratory analyses: (1) Field results After the Laramide deformation an erosion surface (Tsaile surface) was formed, which cuts across the Laramide structures. But this surface is not
entirely a real truncating or planation surface. Planation was restricted to areas, where soft material crops out (cf. Figs. 2 and 3). Within the Jurassic (J) series no major cliff-forming rocks are found on the Tsaile surface, it lies beyond the southern limit of the deposition of the Salt Wash Sandstone of the Morrisson Formation. Yet the Tsaile surface has a variable topograpy in the outcrop area of the Jurassic rocks reflecting differences in resistance of the various rock types. The Triassic Wingate Formation (Trw) is only composed of the less resistant Rock Point Member, which consists of soft siltstones with only minor lenses of silty sandstones. The Lukachukai Member, which forms conspicuous cliffs in other parts of the Colorado Plateau, is not present in this area. The upper Chinle Formation (Trc) consists of the siltstones with interbedded limestones of the Owl Rock Member and the claystones of the Petrified Forest Member. The more resistant Shinarump conglomerate of the Chinle Formation (Trcs) is only exposed west of the Chuska Mountains. In more resistant rocks, in the Dakota Sandstone (Kd), the Gallup Sandstone (mapped together with the Mancos Shale) and the sandstones of the Mesaverde Formation (Kmv), lithologically controlled hogbacks were formed by selective weathering and erosion. The hogbacks are best exposed, where the East Defiance Monocline disappears below the cover of the Chuska Sandstone, on the eastern side of the Chuska Mountains near Toadlena and on the western side near Todilto Park
286
K.-H. SCHMIDT 1
I
110 °
10g° ~e
Carrizo Mountains ~~. ~ j /
0
25
.
~.,
2453,
0
Lukachukai
ARI BLACK
1,8 :
• 11615
~,,'~•19 5 7
NEW
ME P~ 2531 2047A 2134 ~ _- _-_-_-_-_-~ -- -..- _- _- _% -;
1801 •
Fluted Rock
Tohatchi
J
2255 .~, (..)
*J~t~_+_~._~..t_J Carrizo Mountains laccolith Chuska Sandstone L
~
Lower Bidahochi Formation
Upper Bidahochi Formation ,,,,,,
,Lv •
scarp altitude
25 k m
0 I
I
I
.;--_ Fig. 1. Location map of the Chuska Mountains and the depositional area of the Bidahochi Formation.
(Figs. 2 and 3). The hogbacks near Todilto Park have also been described by Wright (1956, plate
processes in a warm and humid climate with intensive chemical weathering.
1).
Laboratory analyses: samples for X-ray diffraction Interpretation." the lithological and structural control of the relief makes evident that the Tsaile surface was not formed by sheet-wash planation
analyses were taken on the western side of the Chuska Mountains, where the Tertiary/Mesozoic contact is not covered by landslides (cf. Fig. 2),
TERTIARY PALAEOCLIMATIC HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
from the basal Chuska Sandstone, from weathering layers and from the bedrock near the Tsaile surface. Table 2 summarizes the results and lists the sample sites together with the elevation of the Tsaile surface at these points. The locations can thus be identified in Fig. 2. The table also describes the positions in the exposures. Kaolinite is not present or only in small quantities. The dominant clay minerals are illite and montmorillonite. These clay minerals are also the dominant components of the bedrock material (Schultz, 1963; Cadigan, 1972). Calcite and feldspars are found in close proximity to the surface.
Interpretation." the close resemblance of the clay mineral composition of the weathered material with the original bedrock and the virtual absence of newly formed kaolinite show that no intensive chemical weathering processes can have occurred during the formation of the Tsaile surface. Both the geomorphotogical attributes of the Tsaile surface and the laboratory results show that there was no warm and moist tropical climate with nonselective weathering and erosion. There is ample evidence for a dry climate with arid geomorphological processes at least for the later stages of the formation of the Tsaile surface.
287
Interpretation; zeolites are indicators of the presence of saline water, which points to dry conditions during the time of cementation. (4) Field results The deposition and cementation of the Chuska Sandstone was followed by a period of vigorous erosion, which cut deep valleys into the sandstone and in some places also into the underlying Mesozoic rocks. In this period the pre-middle Oligocene, pre-volcanic high relief erosion surface was formed (Table 1, Fig. 3). The maximum incision is about 350 m (Appledorn and Wright, 1957). The valleys flowed in an eastern and western direction from the highest elevations of the present Chuska Mountains.
Interpretation." as the Chuska Sandstone was deposited in a basin, afterwards a complete relief inversion must have taken place. The deep erosion cannot have been effected without an intense uplift of the region and an increase in humidity. But the sandstone on the slopes of the valleys is unweathered, so the inferred increase in humidity was not strong or long enough to cause the development of weathering profiles.
(2) Field results The Chuska Sandstone with a maximum thickness of more than 500 m was deposited on the Tsaile surface. Only the basal ~ 70 m are of fluvial origin. The main body is of eolian origin and was deposited in a desert basin by prevailing southwesterly winds (Wright, 1956).
Interpretation." apparently the climate during the sedimentation of the sandstone became progressively drier.
(5) Field results Middle Oligocene volcanic activity followed this period of erosion. The first phase of volcanism was characterized by phreatic explosions (Appledorn and Wright, 1957). The valleys were filled with pyroclastic and fluvial material. There were non-depositional periods when soils were formed in the valley fills. Figure 4 shows an exposure of a more than 100 m thick valley fill near Washington Pass, from which samples were taken (e.g. sample 64, Table 2).
(3) Field results and laboratory analyses After its deposition the sandstone was cemented in alternating beds of firmly and loosely consolidated material. The cementing agents are calcium carbonate and in some places opal and chalcedony. Heulandite, a zeolite, was also found (Table 2, samples 60 and 63).
Interpretation." the mineralogical composition of the soils is very similar to the parent rock. There are no newly formed clay minerals in the soils. No indications of a more intensive chemical weathering and more humid palaeoclimatic conditions are found.
288
K.-H. SCHMIDT
TAqLE 2 X-ray analyses of samples from the Chuska Mountains No.
Location
Position in the exposure
56
east of White Cone (2320 m) east of White Cone (2320 m) east of White Cone (2320 m) White Cone (2332 m) White Cone (2332 m) east of White Cone (2320 m) Little White Cone (2320 m) Little White Cone (2320 m) Washington Pass Todilto Park (2470 m)
weathered Trco, 20 cm below contact 50 cm below contact
57
58
59 60 61
62
63
64 65
Montmorillonite
Kaolinite
Calcite Feldspar
Quartz Special characteristics
75
-
+
-
+ +
-
100
-
-
-
+ +
-
50
-
-
-
+ +
-
-
+ +
-
+ +
-
100
-
+ +
-
+
Heulandite
90
I0
-
-
+
+
-
90
5
5
-
-
+
-
+
Heulandite dominant
25
-
basal Chuska Sandstone
50
ledge, Trco
75
ledge, basal Chuska Sandstone basal Chuska Sandstone, unconsolidated weathered material, Trwr, 5 cm below contact basal Chuska Sandstone soil in valley fill weathered Menefee Formation
lllite
-
100
.
.
.
.
80
20
-
-
-
(+)
Heulandite
90
5
5
-
+
+
-
The elevation in brackets below the location names refer to the altitudes of the sampling sites ( = elevation of the Tsaile surface). These figures may serve to identify the sampling sites on Fig. 2. Little White Cone is an outlier just south of the Palisades. The sample at Washington Pass was taken from the basal part of the valley fill shown in Fig. 4. The clay mineral content is given in percentages. (+): traces. + : frequent. + + : abundant. Trwr: Wingate Sandstone, Rock Point Member. Trco: Chinle Formation, Owl Rock Member.
(6) Field results
been a considerable timespan between the deposi-
The second Oligocene volcanic phase was char-
tion of the Chuska
acterized by more
v i s c o u s flows, w h i c h e r u p t e d
Sandstone
and
the Middle
O l i g o c e n e v o l c a n i c p h a s e . S o it is r e a s o n a b l e assume that the Chuska
( t h e V a l e n c i a s u r f a c e o f C o o l e y e t al., 1969). F o r t h i s p e r i o d t h e r e is n o i n f o r m a t i o n f o r p a l a e o c l i -
age and that the Tsaile surface was formed in P a l a e o c e n e t o ( E a r l y ) E o c e n e t i m e s . A t n o t i m e in
matic reconstruction.
the Tertiary Mountains
Sandstone
to
onto a aggradation surface of only moderate relief
relief development
is o f E o c e n e '
of the Chuska
is t h e r e a n y e v i d e n c e f o r a w a r m a n d
Conclusion." as t h e s u c c e s s i o n o f t h e d i f f e r e n t s t a g e s
moist
of the relief history demonstrates, there must have
mates with only moderate fluctuations in humidity
subtropical
climate. Arid
t o s e m i a r i d cli-
Fig. 2. Geologic map of the Chuska Mountains and vicinity. Redrawn with modifications from the original maps by O'Sullivan and Beikman (1963) and Hackman and Olson (1977). Elevations of the Tsaile surface are indicated.
ERTIARY PALAEOCLIMATIC HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
~
\
\'
289
....... ~ ~_--_ -_ ~ _- j~ -
~ Oakota Sandstone ~[Landslide debris (QI) ~(Lower(?)and Up~-:-~per Cret,) (Kd)
-- - [-~,-~
Volcanic material
EX~
~-~-~.-._ t~' ~,t(Oligocene)(Tv) ~_~_-- ~ _.._ ~ ~-~ChuskaSandstone _
" ,
.
~/ , /
/
' ,c;b-'~"
Menefee Formation
t
-
/ •
• ~
•
* • "
" :2,"
[~r;~7; Upper Chinle ~//X/Formation L,:-Z_L,a (Triassic) (~Rc) ~ Shinarump I" _°." !Con~lomerate , " ~ (Triassic) (~ cs)
I~ - 7 -I(MesaverdeGroup,
L ~ Upper Cret.)(Kmf) - " - ~Lower Mesaverde /,~. BeAuTiYOC - .I;/~//~Group (Upper Cret.) g4~ _~qo~T~ ] ~%/~L ~///>'/~ (Kmv) .~ -~- _ - _- _ ~MaoGos SHale (Upper I. - - IGret.)(n~heast of the~<,><,><~ Palaeozoic (P) ~- --~-~7I- - -jChuskaMountainswith~ uallupSandstone)(Km)
" ,'
~
-
' ~ , ~
/k"
~WingateFormation I i(Triassic) (~w)
- h_m._~(Eocene) (To)
..........
Jurassic (J )
"~
altitude of the Tsaile surface
';'v
,.';
i
2743
\
S
~,,
2777
.,A 37 /
k
--
-
-
% Shee~
.
u
2362
~%% WASHINGTON
136,
l- :o?;
L
~
A,
(-
.
.
.
.
.
K.-H.SCHMIDT
290 CHUSKA MOUNTAINS
2d00
~
,
Lava flows (30 my) - pro-lava surface (pro-upper Oligocene) valley fill with periods of soil formation (middle Otigooene) older Oligocene erosion surface (pro-middle Oligocene)
.......
Chuska Sandstone(Eocene)
- 2 ~oo
~
Kmv Mesaverde Group Km ManeosShale
_///
~
~saile surface [Palaeoconoand (early) Eocene]
"',,
p
~
~
P
.... Kd Dakota Sandstone J Jurassic
~w J Kd Km
'~ w Wingata Formation ~ c ChinleFormation
Defiance monocline(Laramide)
"~ P
csShinarump Conglomerate Palaeazoicand older
Fig. 3. Profile of the Chuska Mountains with a summary of the succession of events (horizontal distance not to scale, vertical scale in meters)
seem to have prevailed from the Late Palaeocene (formation of the Tsaile surface) to the Middle Oligocene (valley fills). Palaeoclimate in the Hopi Lake area Introduction The Bidahochi Formation was deposited in the Black Mesa basin in northeastern Arizona (Fig. 1).
The Bidahochi Formation is subdivided into three different units, a lower lacustrine member, a middle volcanic and an upper mainly fluvial member. The volcanic member has been dated, it is of very late Miocene to early Pliocene age (4.1-6.7 my: Evernden et al., 1964; Naeser, 1971; Sutton, 1974). The lower Bidahochi Formation was deposited in the basin of the Hopi Lake on the Hopi Buttes surface during Miocene times. The White Cone fossil
Fig. 4. Valley fill near Washington Pass. Note person in the centre for scale.
291
I'ERTIARY PALAEOCLIMATIC HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
Stripped surfaces are found on the dip slopes of resistant beds, for instance in the Dinosaur Canyon Sandstone of the Moenave Formation southwest of Ganado on the western side of Pueblo Colorado Wash (Fig. 1).
assemblage in the upper part of the Lower Bidahochi beds (Nations and Landye, 1984) indicates a lake-shore community in an arid to semiarid environment (Smiley, 1984). The Hopi Buttes surface at the base of the Bidahochi Formation is an erosion surface, the Zuni surface is an aggradation surface and underlies the middle and upper members of the Bidahochi Formation (Table 1, Fig. 5). The investigations were concentrated on the Hopi Buttes surface, which furnishes information on the morphoclimatic conditions of the Miocene.
Laboratory analyses The contact between the Mesozoic bedrock and the lacustrine member of the Bidahochi Formation is exposed in many places (cf. Fig. 6). Samples for X-ray analyses were taken from the basal Bidahochi layers and from the bedrock below the contact. Table 3 summarizes the results, lists the locations and elevations of the sample sites and the positions in the exposures. In some places there is a bleached horizon below the contact, which is a few centimeters to half a meter thick. The clay mineralogy of this bleached horizon is not different from the unbleached bedrock (compare sample 48 with samples 46 and 47, and samples 52 and 70 with sample 71). There is no kaolinite enrichment in the bleached material. Montmorillonite is dominant in all samples. Chlorite, which easily weathers under humid and warm conditions, is present close to the surface. Gypsum and salts are also found, but these minerals are possibly younger than the formation of the Hopi Buttes surface and may have originated in the lake environment. Conglomerates in the basal Bidahochi beds contain silt-
Field results The lower Bidahochi Formation overlies strata from the Triassic Chinle Formation to the Upper Cretaceous Mancos Shale. The Hopi Buttes surface is a truncating surface only in areas where soft rocks of relatively homogeneous resistance crop out. More resistant rocks form structurally and lithologically controlled landforms protruding above the surface. Despite the marked topographic irregularities there is a general trend of increasing elevation of the Hopi Buttes surface from east to west (Fig. 5), the lowest altitude (1800 m) is found where Pueblo Colorado Wash enters the outcrop area of the lower Bidahochi Formation (Fig. 1), the surface reaches the greatest altitude (1900 m) on the side of Round Top Mountain (Fig. 5).
W
Black
Mesa
E ISW
Basin
NE
Ganado
9ueb\o Co\o~ac~o
RoundTop Mountain
Bidahochi Zuni
I
-
~
(Tbo) UpperBidahochi Formation (Tbv)Middle Bidahochi Formation
-
=
I
- -
surfoc e
-
---
~J~s~
j/ ,
RobertsMesa / surlace /
~
Tbo
-
I Hop';u't.... rlace I (Tbl) Lower Bidahochi Formation (Tc) Chuska Sandstone
(Km) Mancos Shale
(J) Jurassic
(Kd) Dakota Sandstone
('li) Triassic
Fig. 5. Profile showing the Hopi Buttes and Zuni surfaces in the Hopi Buttes area (not to scale).
Castle Butte (1825 m) Castle Butte (1825 m) Castle Butte (1825 m) Echo Spring Mtn. (1870 m) Echo Spring Mtn. (1870 m) Echo Spring Mtn. (1870 m) Bidahochi Butte (1830 m) Bidahochi Butte (1830 m) Bidahochi Butte (1830 m) Greasewood (road) (1810 m) Greasewood (road) (1810 m) Greasewood (road) (1810 m)
43
71
70
52
51
50
49
48
47
46
45
44
Location
No.
bleached Trwl, 10 cm below contact bleached Trwl, 20 cm below contact Trwl, 1 m below contact
10 cm below (weathered) contact, Trwr 20 cm below contact, Trwr
basal Tbl
white weathering layer, directly below contact, Trwr
red weathering layer, grading into bedrock, Trwr
red weathering layer, grading into bedrock, Trwr
Trwr, unweathered
Tbl, white upper portion
red Tbl upper slope
Position in the exposure
95
95
95
95
100
95
90
90
90
95
85
85
Montmorillonite
X-ray analyses of samples in the outcrop area of the Bidahochi Formation
TABLE 3
5
-
-
2,5
-
5
10
5
5
5
10
10
Illite
-
-
+
(+ )
-
(+)
-
-
2,5
-
-
-
Kaolinite
5
5
2,5
(+)
-
(+ )
(+ )
5
2,5
-
5
5
Chlorite
-
-
-
+ +
+
+
+ +
+
+ +
(+ )
+
+
Calcite
+
+
+
+
+
+
+
+ +
+
+
+
+
Feldspar
+
+
+
+
+
+
+
+
+
+
+
+
Quartz
Salts
Anatase in larger quantities Salts
-
Gypsum
Gypsum
-
Analcime
Analcime
-
-
-
Special characteristics
_~
-~
b,)
Trmod, 30 cm below contact basal Tbl
Trmod, I0 cm below contact
95
50
50
5
5
5
-
-
(+) + +
-
+
+
+ +
+
+
coarse material, few clay minerals
Corensite, Anatase in small quantities same as 53
Tbl: Lower Bidahochi Formation. Trmod: Moenave Formation, Dinosaur C a n y o n Sandstone. Trwr: Wingate Sandstone, Rock Point Member. Trwl: Wingate Sandstone, Lukachukai Member. ( + ): traces. + : frequent. + + : abundant. The clay mineral content is given in percentages. The elevations in brackets refer to the altitudes of the Hopi Buttes surface in the given locations. Castle Butte and Echo Spring M o u n t a i n lie on the southwestern margin of the outcrop area. Castle Butte is an isolated outlier in the central part of a syncline. Bidahochi Butte lies directly south of the small settlement Bidahochi (Fig. 1). The sample site Greasewood (road) is situated directly north o f Bidahochi and the exposure Greasewood is located near the lowest point of the Hopi Buttes surface southwest o f G a n a d o on the western side o f Pueblo Colorado Wash (Fig. 1).
(1800 m)
Greasewood (1800 m) Greasewood
54
55
Greasewood (1800 m)
53
294
K.-H. SCHMIDT
Fig. 6. Contact between the lower Bidahochi Formation and the Wingate Sandstone (head of the person is close to the contact). The lower Bidahochi Formation is overlain by middle Bidahochi volcanics. The upper parts of the Wingate Sandstone are bleached. Samples 52, 70 and 71 were taken from this exposure.
stones, which must have come from nearby sources not affected by intensive chemical weathering.
Interpretation: as in the case of the Tsaile surface there is abundant evidence for the Miocene Hopi Buttes surface having been formed under the weathering and erosion conditions of a dry climate: (1) Lithologically controlled landforms as indicators of selective weathering and erosion characterize the surface. (2) There are no indications of intensive chemical weathering, because no newly formed kaolinite is present in the samples, because there is no change in mineral content from parent rock to weathering mantle and because chlorite, calcite, gypsum, salts and analcime are present close to the surface. Conclusion The results of the geomorphological and mineralogical investigations in the Chuska Mountains and in the Hopi Buttes area demonstrate that the climatic conditions on the southeastern Colorado
Plateau have not changed decisively during the Cenozoic and were much the same as today. The presence of structurally and lithologically controlled landforms on the Tertiary erosion surfaces and the absence of indicators of intensive chemical weathering in the palaeosols and the sediments on the surfaces reveal the predominance of arid-zone selective erosion and mechanical weathering. It is concluded that the Colorado Plateau has been dominated by dry climates since the Laramide orogeny with the possible exception of the early Palaeocene It is not surprising that there is no evidence of more humid climatic condition in late Tertiary times, because at that time dry climates also prevailed in the surrounding areas. But during the late Palaeocene and Eocene the Colorado Plateau is out of phase with the general palaeoclimatic situation in western North Amcrica, where at that time moist and warm conditions were predominant (Dorf, 1964; Wolfe and Hopkins, 1967; Peterson and Abbott, 1978) (see Fig. 7). The only deep weathering profile on the Colorado Plateau has
295
TERTIARY PALAEOCLIMAT[C HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
humid A warm
~
~
\
WOLFE+ HOPKINS (1967) PETERSON + ABBOTT
..........
( 1978 ) f
/
DORF (1964)
%../
/f
dry climate ascertained on the southeastern Colorado Plateau
.-,.. cooldry
, =L[
MIOCENE,JOUGO, CENEJ,EOCENE.I 10
20
30
40
50
PAL.,~CRE] 6o 70 my
Fig. 7. Generalized palaeoclimatic graphs for the Tertiary of western North America. Periods of dry climate on the southeastern Colorado Plateau are indicated by the bars.
developed at the t u r n o f the Cretaceous a n d Tertiary periods ( J o h n s o n a n d May, 1980). The exceptional dryness o f the C o l o r a d o P l a t e a u d u r i n g the early Tertiary is explained by its position in the rain s h a d o w o f the r a i n - b e a r i n g s o u t h e a s t e r n to southwestern winds. The C o l o r a d o Plateau, before its s e p a r a t i o n from the Basin a n d R a n g e Province in Oligocene times, lay in a t o p o g r a p h i c a l l y lower position on the leeside o f the s o u t h e r n R o c k y M o u n t a i n s a n d the C e n t r a l A r i z o n a Highlands, which at that time formed a barrier stretching from western A r i z o n a to N e w Mexico.
Acknowledgements The investigations were s u p p o r t e d by a g r a n t of the D F G ( G e r m a n Research Association). I t h a n k Prof. T h o r N.V. K a r l s t r o m , U S G S , Flagstaff, Arizona, for s t i m u l a t i n g discussions a n d a j o i n t field trip to the Black Mesa b a s i n a n d the C h u s k a M o u n t a i n s . Dr. Riedel, Geologisches Institut, Ruhr-Universit/it, B o c h u m , m a d e the X - r a y analyses a n d helped with the i n t e r p r e t a t i o n , K a r i n Heine assisted in the p r e p a r a t i o n of the text a n d the tables.
References Akers, J.P., Shorty, J.C. and Stevens, P.R., 1971. Hydrogeology of the Cenozoic igneous rocks, Navajo and Hopi Indian
Reservations, Arizona, New Mexico, and Utah. U.S. Geol. Surv. Prof. Pap., 521 D. Appledorn, C.R. and Wright, H.E., 1957. Volcanic structures in the Chuska Mountains, Navajo Reservation, ArizonaNew Mexico. Geol. Soc. Am. Bull., 68:445 468. Baltz, E.H., 1967. Stratigraphy and regional tectonic implications of part of Upper Cretaceous and Tertiary rocks, EastCentral San Juan Basin, New Mexico. U.S. Geol. Surv. Prof. Pap., 552:1 101. Cadigan, R.A., 1972. Sedimentary petrology. In: J.H. Stewart, E.G. Poole and R.F. Wilson (Editors), Stratigraphy and Origin of the Chinle Formation and Related Upper Triassic Strata in the Colorado Plateau Region. U.S. Geol. Surv. Prof. Pap., 690: 56-62. Cashion, W.B., 1967. Geology and fuel resources of the Green River Formation, Southeastern Uinta Basin, Utah and Colorado. U.S. Geol. Surv. Prof. Pap., 548:1 48. Cooley, M.E., Harshbarger, J.W., Akers, J.P. and Hardt, W.F., 1969. Regional hydrogeology of the Navajo and Hopi Indian Reservations, Arizona, New Mexico and Utah. U.S. Geol. Surv. Prof. Pap., 521 A: 1-61. Doff, E., 1964. The use of fosil plants in paleoclimatic interpretation. In: A.E.M. Nairn (Editor), Problems of Paleoclimatology. Wiley, New York, NY, pp. 13-30. Eugster, H.P. and Surdam, R.C., 1973. Depositional environment of the Green River Formation of Wyoming, a preliminary report. Geol. Soc. Am. Bull., 84:1115 1120. Euler, R.C., Gumerman, G.C., Karlstrom, T.N.V., Dean, J.S. and Hevly, R.H., 1979. The Colorado Plateaus: cultural dynamics and palaeoenvironment. Science, 205:1089-1101. Evernden, J.F., Savage, D.E., Curtis, G.H. and James, G.T., 1964. Potassium-argon dates and the Cenozoic mammalian chronology of North America. Am. J. Sci.: [45-198. Hack, J.T., 1942. The changing physical environment of the Hopi Indians of Arizona. Peabody Mus. Pap., 35:1 86. Hackman, R.J. and Olson, A.B., 1977. Geology, structure and
296 uranium deposits of the Gallup 1° x 2° quadrangle, New Mexico and Arizona. U.S. Geol. Surv. Misc. Inv. Ser. Map 1-981. Hereford, R., 1984. Climate and ephemeral stream processes: Twentieth-century geomorphology and alluvial stratigraphy of the Little Colorado River, Arizona. Geol. Soc. Am. Bull., 95: 654- 668. Johnson, R.C. and May, F., 1980. A study of the CretaceousTertiary unconformity in the Piceance Creek basin, Colorado. The underlying Ohio Creek Formation (Upper Cretaceous) redefined as a member of the Hunter Caynon or Mesaverde Formation. U.S. Geol. Surv. Bull., 1482 D: 1-22.
Lucchitta, I., 1984. Development of landscape in northwestern Arizona: the country of plateaus and canyons. In: T.L. Smiley, J.D. Nations, T.L. Pewe and J.P. Schafer (Editors), Landscapes of Arizona. Univ. Press of America, Lanham, MD, pp. 269-301. Moss, J.H., 1977. The formations of pediments: scarp backwearing or surface downwasting? In: D.O. Doehring (Editor), Geomorphology in Arid Regions. Allen and Unwin, London, pp. 51-78. Naeser, C.W., 1971. Geochronology of the Navajo-Hopi diatremes, Four Corners area. J. Geophys. Res., 76: 4978-4985. Nations, J.D. and Landye, J.J., 1984. Cenozoic plant and animal fossils of Arizona In: T.L. Smiley, J.D. Nations, T.L. Pewe and J.P. Schafer (Editors), Landscapes of Arizona. Univ. Press of America, Lanham, MD, pp. 7-35. O'Sullivan, R.B. and Beikman, H.M., 1963. Geology, structure and uranium deposits of the Shiprock quadrangle, New Mexico and Arizona. U.S. Geol. Surv. Misc. Inv. Ser. Map 1-345. Peterson, G.L. and Abbott, P.L., 1979. Mid-Eocene climatic change, Southwestern California and Northwestern Baja
K.-H. SCHMIDT California. Palaeogeogr., Palaeoclimatol., Palaeoecol., 16: 73-87. Pohlman, H.F., 1967. The Navajo Indian Nation and Dineh bi Kayah. In: New Mexico Geol. Soc. Guidebook, DefianceZuni-Mt. Talor region, pp. 63-69. Pye, W.D., 1967. How unique Arizona syenite oil reservoir formed. World Oil, 165: 81-83. Robson, S.G. and Saulnier, G.J., 1981. Hydrogeochemistry and simulated solute transport, Piceance Basin, Northwestern Colorado. U.S. Geol. Surv. Prof. Pap., 1196: 1-65. Schmidt, K.-H., 1988. Die Reliefentwicklung des Colorado Plateaus. Berl. Geogr. Abh., 49: 1-183. Schultz, L.G., 1963. Clay minerals in Triassic rocks of the Colorado Plateau. U.S. Geol. Surv. Bull., 1147 C: 1-71. Smiley, T.L., 1984. Climatic change during landform development. In: T.L. Smiley, J.D. Nations, T.L. Pewe and J.P. Schafer (Editors), Landscapes of Arizona. Univ. Press of America, Lanham, MD, pp. 55-77. Sutton, R.L., 1974. The geology of Hopi Buttes, Arizona. In: T.N.V. Karlstrom et al.(Editors), Geology of Northern Arizona. In: Geol. Soc. Am. Rocky Mount. Sect. Meet., pp. 647-67 I. Wells, S.G., Bullard, T.F. and Smith, L.N., 1982. Origin and evolution of deserts in the Basin and Range and the Colorado Plateau provinces of western North America. Striae, 17: 101-111. Wolfe, J.A. and Hopkins, D.M., 1967. Climatic changes recorded by Tertiary land floras in Northwestern North America: Tertiary correlations and climatic changes in the Pacific. In: 1lth Pacific Sci. Congr., Sendai, pp. 67-76. Wright, H.E., 1956. Origin of the Chuska Sandstone, ArizonaNew Mexiko: A structural and petrographic study of a Tertiary eolian sediment. Geol. Soc. Am. Bull., 67: 413-434.
283
Elsevier Science Publishers B.V., Amsterdam
Tertiary palaeoclimatic history of the southeastern Colorado Plateau Karl-Heinz Schmidt
Institut fiir Physische Geographie, Freie Universitiit Berlin, Altensteinstr. 19, 1000 Berlin 33, German>' (Received April 18, 1990; revised version accepted January 18, 1991)
ABSTRACT Schmidt, K.-H., 1991. Tertiary palaeoclimatic history of the southeastern Colorado Plateau. Palaeogeogr., Palaeoclimatol., Palaeoecol., 86: 283-296. On the southeastern Colorado Plateau Tertiary erosion surfaces have been preserved below the cover of the Eocene Chuska Sandstone and the late Tertiary Bidahochi Formation. Investigations of the geomorphological attributes of the erosion surfaces and laboratory analyses of the soils and weathering materials as well as the sediments on the surfaces gave substantial information on the climate and the relief-forming processes which were responsible for their formation. In some places the surfaces cut across the underlying Mesozoic sedimentary rocks with a marked angular unconformity, but these truncating reaches are restricted to areas where soft material crops out. Resistant rocks form lithologicallycontrolled cuestas, hogbacks and residual hills below the Tertiary cover. X-ray analysis of the clay minerals shows that the surfaces have not been subject to intensive chemical weathering and soil-forming processes. There is no change in the mineral content from the bedrock to the weathered material. These results apply to the (early) Eocene to Palaeocene Tsaile surface (underlying the Chuska Sandstone) and the Miocene Hopi Buttes surface (underlying the Bidahochi Formation), The results demonstrate that the climatic conditions have not changed decisively during the Cenozoic and were much the same as today. It is concluded that the Colorado Plateau has been dominated by a dry climate since the Laramide orogeny with the possible exception of the early Palaeocene. Thus the Colorado Plateau is out of phase with the general palaeoclimatic situation in western North America in the early Tertiary where at that time warm and moist conditions prevailed. The Colorado Plateau, before its separation from the Basin and Range province, was situated in a topographically lower position in the rain shadow of the southern Rocky Mountains and the Central Arizona Highlands, which at that time formed a barrier stretching from western Arizona to New Mexico.
Introduction Present-day w e a t h e r i n g a n d erosional processes on the C o l o r a d o P l a t e a u are c o n t r o l l e d by the arid to semiarid climate. There is a p r e d o m i n a n c e of m e c h a n i c a l w e a t h e r i n g a n d selective erosion. As a c o n s e q u e n c e o f the very limited i m p o r t a n c e o f chemical weathering no kaolinite develops a n d m o n t m o r i l l o n i t e a n d illite are the most frequent clay minerals. I n the s e d i m e n t a r y rocks, which are only gently to m o d e r a t e l y inclined, structural landforms such as cuestas, h o g b a c k s a n d h o r i z o n t a l plateaus characterize the present relief assemblage (Schmidt, 1988). C a n y o n c u t t i n g a n d scarp retreat are the d o m i n a n t g e o m o r p h o l o g i c a l processes. Only in some places, especially in the s u r r o u n d 0031-0182/91/$03.50
.L) 1991
ings of the laccolithic centres a n d in less resistant rocks in the footzone of large cuesta scarps pediments are being formed. Structurei n d e p e n d e n t t r u n c a t i n g surfaces are only o f very limited significance (cf. Lucchitta, 1984; Schmidt, 1988). Most palaeoclimatic i n f o r m a t i o n o n the Colorado Plateau relates to the H o l o c e n e a n d late Pleistocene, The early Q u a t e r n a r y a n d the Tertiary are n o t well d o c u m e n t e d . Pleistocene a n d H o l o c e n e climatic fluctuations resulted in the f o r m a t i o n of terraces a n d the a l t e r n a t i o n of depositional a n d erosional periods a l o n g the m a i n water courses (Hack, 1942; Euler et al., 1979; Wells, 1982; Hereford, 1984). Away from these lines of process c o n c e n t r a t i o n the l a n d f o r m s reacted less sensi-
ElsevierScience Publishers B.V.
284
tively, the cuesta scarps and plateaus were not affected to a comparable degree. Structurally and lithologically controlled relief-forming processes prevailed throughout the Quaternary.
Possibilities of Tertiary palaeoclimatic reconstruction After the Laramide period the great basins on the Colorado Plateau (Uinta, Piceance and San Juan Basin) were areas of almost continuous sedimentation during the Palaeocene and Eocene including large deposits of salts in the Green River Formation on the northern Colorado Plateau (Eugster and Surdam, 1973; Robson and Saulnier, 1981). There are rich faunal and floristic remains in the lake basins (cf. Cashion, 1967). In the San Juan Basin on the southeastern Colorado Plateau the Palaeocene Nacimiento Formation was deposited in a paludal and lacustrine environment with fish, aquatic lizards and turtles (Baltz, 1967). Deduced from faunas, an older member of the early Eocene San Jose Formation in the San Juan Basin was deposited in a swampy environment and the younger parts in dry savannah conditions (Baltz, 1967). But there is conflicting evidence, and what is still more important, the information from the lake basins gives no direct indication of the palaeoclimatic conditions outside the lacustrine environments. The lakes might only represent "oasis conditions" within a dry environment. There is always an inherent tendency to deduce a more humid climate than actually existed from lake sediment information. Direct information on the palaeoclimate in the non-aquatic Tertiary environments carl be collected from geomorphological attributes of old erosion surfaces, from palaeosols and fossil weathering products, but erosion has erased most of the Tertiary palaeoclimatic record. This kind of evidence is only preserved when very favourable conditions are given, i.e. burying and conservation of a surface or a profile by sedimentation or a lava flow after its formation. A Campanian to late Palaeocene palaeoweathering profile in Upper Cretaceous sandstones, which is overlain by the early Tertiary Wasatch Formation, has been described from the Piceance Basin on the northern Colorado
K.-H. SCHMIDT
Plateau (Johnson and May, 1980). The profile, about 100 m in thickness, is characterized by feldspar breakdown and subsequent accumulation of kaolinite. This kind of weathering is typical of warm and humid climates. Kaolinization has also been found in Palaeocene to early Eocene palaeosols in southwestern California (Peterson and Abbott, 1979). These tropical weathering products are overlain by middle to late Eocene sediments, which were deposited under semi-arid conditions. Deeply weathered granitic profiles have also been described from southern Arizona (Moss, 1977). On the southeastern Colorado Plateau old erosion and aggradation surfaces have been preserved below the cover of Tertiary sediments (Table 1). Especially the erosion surfaces offer the possibility of investigating whether there have been major deviations from the present dry climate.
Tertiary surfaces on the southeastern Colorado Plateau and their implications for palaeoclimatic history In the Navajo section of the Colorado Plateau Tertiary erosion surfaces have been fossilized below the cover of the Chuska Sandstone and the Bidahochi Formation (Fig. 1). The surfaces have been interpreted in the framework of the Davisian cyclic concept (cf. Cooley et al., 1969). Attempts at a palaeoclimatic interpretation have not been made. It is demonstrated, that investigations of the geomorphological attributes of the erosion surfaces and laboratory analyses of the soils and weathering materials as well as the sediments on the surfaces give substantial information on the climate and the relief-forming processes which were responsible for their formation.
Palaeoclimate of the Chuska Mountains Introduction The Chuska Mountains are a topographic barrier between the San Juan Basin in New Mexico and the Defiance Plateau in Arizona (Figs. 1 and 2). The bedrock underlying the Chuska Mountains is the Chuska Sandstone, which in greater detail was described by Wright (1956). The Chuska Sandstone was previously thought to be of Miocene
TERTIARY PALAEOCLIMATIC H1STORY OF THE SOUTHEASTERN COLORADO PLATEAU
285
TABLE 1 System of (erosion) surfaces in the Chuska Mountains and in the outcrop area of the Bidahochi Formation Surface
Age
Remarks
Zuni surface
Pliocene
Hopi Buttes surface
Miocene
pre-lava surface (Valencia surface of Cooley) older Oligocene erosion surface (pre-volcanic surface) Tsaile surface
Oligocene
aggradation surface, below the middle and upper Bidahochi Formation erosion surface in the Hopi Lake basin, underlies the lower Bidahochi Formation aggradation surface, older than the second volcanic phase in the Chuska Mountains surface with great differences in relief, older than the early volcanic phase in the Chuska Mountains underlies the Chuska Sandstone
pre-middle Oligocene (early) Eocene to Palaeocene
age (Cooley et al., 1969). In many places the Chuska Sandstone is intruded and covered by magmatic material (Figs. 2 and 3). The volcanism in the Chuska Mountains belongs to the minette province (Akers et al., 1971), which has more recently been dated to be of middle Oligocene age. Naeser (1971) provided fission track data for the Buell Park kimberlite diatreme (31.9 _+ 3.2 my; location see Fig. 2) and for two minette dikes at Mitten Rock (32.5 _ 3 my) and at Shiprock (27.0 _ 3 and 32.0 ___ 3 my). Both localities lie just northeast of the map area of Fig. 2. Additional K-Ar age determinations of volcanic rocks in the Chuska Mountains (31 my) were communicated by Pohlmann (1967) and Pye (1967). The datings from the Chuska Mountains and vicinity centre around 30-31 my, so do all the minette province data from the southeastern Colorado Plateau (Naeser, 1971). The dating of the volcanics and geomorphic history (see below) indicate that the sandstone is at least of early Oligocene age (cf. Hackman and Olson, 1977), more probably of Eocene age (Schmidt, 1988). The following succession of events with the respective palaeoclimatic backgrounds can be inferred from field investigations and laboratory analyses: (1) Field results After the Laramide deformation an erosion surface (Tsaile surface) was formed, which cuts across the Laramide structures. But this surface is not
entirely a real truncating or planation surface. Planation was restricted to areas, where soft material crops out (cf. Figs. 2 and 3). Within the Jurassic (J) series no major cliff-forming rocks are found on the Tsaile surface, it lies beyond the southern limit of the deposition of the Salt Wash Sandstone of the Morrisson Formation. Yet the Tsaile surface has a variable topograpy in the outcrop area of the Jurassic rocks reflecting differences in resistance of the various rock types. The Triassic Wingate Formation (Trw) is only composed of the less resistant Rock Point Member, which consists of soft siltstones with only minor lenses of silty sandstones. The Lukachukai Member, which forms conspicuous cliffs in other parts of the Colorado Plateau, is not present in this area. The upper Chinle Formation (Trc) consists of the siltstones with interbedded limestones of the Owl Rock Member and the claystones of the Petrified Forest Member. The more resistant Shinarump conglomerate of the Chinle Formation (Trcs) is only exposed west of the Chuska Mountains. In more resistant rocks, in the Dakota Sandstone (Kd), the Gallup Sandstone (mapped together with the Mancos Shale) and the sandstones of the Mesaverde Formation (Kmv), lithologically controlled hogbacks were formed by selective weathering and erosion. The hogbacks are best exposed, where the East Defiance Monocline disappears below the cover of the Chuska Sandstone, on the eastern side of the Chuska Mountains near Toadlena and on the western side near Todilto Park
286
K.-H. SCHMIDT 1
I
110 °
10g° ~e
Carrizo Mountains ~~. ~ j /
0
25
.
~.,
2453,
0
Lukachukai
ARI BLACK
1,8 :
• 11615
~,,'~•19 5 7
NEW
ME P~ 2531 2047A 2134 ~ _- _-_-_-_-_-~ -- -..- _- _- _% -;
1801 •
Fluted Rock
Tohatchi
J
2255 .~, (..)
*J~t~_+_~._~..t_J Carrizo Mountains laccolith Chuska Sandstone L
~
Lower Bidahochi Formation
Upper Bidahochi Formation ,,,,,,
,Lv •
scarp altitude
25 k m
0 I
I
I
.;--_ Fig. 1. Location map of the Chuska Mountains and the depositional area of the Bidahochi Formation.
(Figs. 2 and 3). The hogbacks near Todilto Park have also been described by Wright (1956, plate
processes in a warm and humid climate with intensive chemical weathering.
1).
Laboratory analyses: samples for X-ray diffraction Interpretation." the lithological and structural control of the relief makes evident that the Tsaile surface was not formed by sheet-wash planation
analyses were taken on the western side of the Chuska Mountains, where the Tertiary/Mesozoic contact is not covered by landslides (cf. Fig. 2),
TERTIARY PALAEOCLIMATIC HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
from the basal Chuska Sandstone, from weathering layers and from the bedrock near the Tsaile surface. Table 2 summarizes the results and lists the sample sites together with the elevation of the Tsaile surface at these points. The locations can thus be identified in Fig. 2. The table also describes the positions in the exposures. Kaolinite is not present or only in small quantities. The dominant clay minerals are illite and montmorillonite. These clay minerals are also the dominant components of the bedrock material (Schultz, 1963; Cadigan, 1972). Calcite and feldspars are found in close proximity to the surface.
Interpretation." the close resemblance of the clay mineral composition of the weathered material with the original bedrock and the virtual absence of newly formed kaolinite show that no intensive chemical weathering processes can have occurred during the formation of the Tsaile surface. Both the geomorphotogical attributes of the Tsaile surface and the laboratory results show that there was no warm and moist tropical climate with nonselective weathering and erosion. There is ample evidence for a dry climate with arid geomorphological processes at least for the later stages of the formation of the Tsaile surface.
287
Interpretation; zeolites are indicators of the presence of saline water, which points to dry conditions during the time of cementation. (4) Field results The deposition and cementation of the Chuska Sandstone was followed by a period of vigorous erosion, which cut deep valleys into the sandstone and in some places also into the underlying Mesozoic rocks. In this period the pre-middle Oligocene, pre-volcanic high relief erosion surface was formed (Table 1, Fig. 3). The maximum incision is about 350 m (Appledorn and Wright, 1957). The valleys flowed in an eastern and western direction from the highest elevations of the present Chuska Mountains.
Interpretation." as the Chuska Sandstone was deposited in a basin, afterwards a complete relief inversion must have taken place. The deep erosion cannot have been effected without an intense uplift of the region and an increase in humidity. But the sandstone on the slopes of the valleys is unweathered, so the inferred increase in humidity was not strong or long enough to cause the development of weathering profiles.
(2) Field results The Chuska Sandstone with a maximum thickness of more than 500 m was deposited on the Tsaile surface. Only the basal ~ 70 m are of fluvial origin. The main body is of eolian origin and was deposited in a desert basin by prevailing southwesterly winds (Wright, 1956).
Interpretation." apparently the climate during the sedimentation of the sandstone became progressively drier.
(5) Field results Middle Oligocene volcanic activity followed this period of erosion. The first phase of volcanism was characterized by phreatic explosions (Appledorn and Wright, 1957). The valleys were filled with pyroclastic and fluvial material. There were non-depositional periods when soils were formed in the valley fills. Figure 4 shows an exposure of a more than 100 m thick valley fill near Washington Pass, from which samples were taken (e.g. sample 64, Table 2).
(3) Field results and laboratory analyses After its deposition the sandstone was cemented in alternating beds of firmly and loosely consolidated material. The cementing agents are calcium carbonate and in some places opal and chalcedony. Heulandite, a zeolite, was also found (Table 2, samples 60 and 63).
Interpretation." the mineralogical composition of the soils is very similar to the parent rock. There are no newly formed clay minerals in the soils. No indications of a more intensive chemical weathering and more humid palaeoclimatic conditions are found.
288
K.-H. SCHMIDT
TAqLE 2 X-ray analyses of samples from the Chuska Mountains No.
Location
Position in the exposure
56
east of White Cone (2320 m) east of White Cone (2320 m) east of White Cone (2320 m) White Cone (2332 m) White Cone (2332 m) east of White Cone (2320 m) Little White Cone (2320 m) Little White Cone (2320 m) Washington Pass Todilto Park (2470 m)
weathered Trco, 20 cm below contact 50 cm below contact
57
58
59 60 61
62
63
64 65
Montmorillonite
Kaolinite
Calcite Feldspar
Quartz Special characteristics
75
-
+
-
+ +
-
100
-
-
-
+ +
-
50
-
-
-
+ +
-
-
+ +
-
+ +
-
100
-
+ +
-
+
Heulandite
90
I0
-
-
+
+
-
90
5
5
-
-
+
-
+
Heulandite dominant
25
-
basal Chuska Sandstone
50
ledge, Trco
75
ledge, basal Chuska Sandstone basal Chuska Sandstone, unconsolidated weathered material, Trwr, 5 cm below contact basal Chuska Sandstone soil in valley fill weathered Menefee Formation
lllite
-
100
.
.
.
.
80
20
-
-
-
(+)
Heulandite
90
5
5
-
+
+
-
The elevation in brackets below the location names refer to the altitudes of the sampling sites ( = elevation of the Tsaile surface). These figures may serve to identify the sampling sites on Fig. 2. Little White Cone is an outlier just south of the Palisades. The sample at Washington Pass was taken from the basal part of the valley fill shown in Fig. 4. The clay mineral content is given in percentages. (+): traces. + : frequent. + + : abundant. Trwr: Wingate Sandstone, Rock Point Member. Trco: Chinle Formation, Owl Rock Member.
(6) Field results
been a considerable timespan between the deposi-
The second Oligocene volcanic phase was char-
tion of the Chuska
acterized by more
v i s c o u s flows, w h i c h e r u p t e d
Sandstone
and
the Middle
O l i g o c e n e v o l c a n i c p h a s e . S o it is r e a s o n a b l e assume that the Chuska
( t h e V a l e n c i a s u r f a c e o f C o o l e y e t al., 1969). F o r t h i s p e r i o d t h e r e is n o i n f o r m a t i o n f o r p a l a e o c l i -
age and that the Tsaile surface was formed in P a l a e o c e n e t o ( E a r l y ) E o c e n e t i m e s . A t n o t i m e in
matic reconstruction.
the Tertiary Mountains
Sandstone
to
onto a aggradation surface of only moderate relief
relief development
is o f E o c e n e '
of the Chuska
is t h e r e a n y e v i d e n c e f o r a w a r m a n d
Conclusion." as t h e s u c c e s s i o n o f t h e d i f f e r e n t s t a g e s
moist
of the relief history demonstrates, there must have
mates with only moderate fluctuations in humidity
subtropical
climate. Arid
t o s e m i a r i d cli-
Fig. 2. Geologic map of the Chuska Mountains and vicinity. Redrawn with modifications from the original maps by O'Sullivan and Beikman (1963) and Hackman and Olson (1977). Elevations of the Tsaile surface are indicated.
ERTIARY PALAEOCLIMATIC HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
~
\
\'
289
....... ~ ~_--_ -_ ~ _- j~ -
~ Oakota Sandstone ~[Landslide debris (QI) ~(Lower(?)and Up~-:-~per Cret,) (Kd)
-- - [-~,-~
Volcanic material
EX~
~-~-~.-._ t~' ~,t(Oligocene)(Tv) ~_~_-- ~ _.._ ~ ~-~ChuskaSandstone _
" ,
.
~/ , /
/
' ,c;b-'~"
Menefee Formation
t
-
/ •
• ~
•
* • "
" :2,"
[~r;~7; Upper Chinle ~//X/Formation L,:-Z_L,a (Triassic) (~Rc) ~ Shinarump I" _°." !Con~lomerate , " ~ (Triassic) (~ cs)
I~ - 7 -I(MesaverdeGroup,
L ~ Upper Cret.)(Kmf) - " - ~Lower Mesaverde /,~. BeAuTiYOC - .I;/~//~Group (Upper Cret.) g4~ _~qo~T~ ] ~%/~L ~///>'/~ (Kmv) .~ -~- _ - _- _ ~MaoGos SHale (Upper I. - - IGret.)(n~heast of the~<,><,><~ Palaeozoic (P) ~- --~-~7I- - -jChuskaMountainswith~ uallupSandstone)(Km)
" ,'
~
-
' ~ , ~
/k"
~WingateFormation I i(Triassic) (~w)
- h_m._~(Eocene) (To)
..........
Jurassic (J )
"~
altitude of the Tsaile surface
';'v
,.';
i
2743
\
S
~,,
2777
.,A 37 /
k
--
-
-
% Shee~
.
u
2362
~%% WASHINGTON
136,
l- :o?;
L
~
A,
(-
.
.
.
.
.
K.-H.SCHMIDT
290 CHUSKA MOUNTAINS
2d00
~
,
Lava flows (30 my) - pro-lava surface (pro-upper Oligocene) valley fill with periods of soil formation (middle Otigooene) older Oligocene erosion surface (pro-middle Oligocene)
.......
Chuska Sandstone(Eocene)
- 2 ~oo
~
Kmv Mesaverde Group Km ManeosShale
_///
~
~saile surface [Palaeoconoand (early) Eocene]
"',,
p
~
~
P
.... Kd Dakota Sandstone J Jurassic
~w J Kd Km
'~ w Wingata Formation ~ c ChinleFormation
Defiance monocline(Laramide)
"~ P
csShinarump Conglomerate Palaeazoicand older
Fig. 3. Profile of the Chuska Mountains with a summary of the succession of events (horizontal distance not to scale, vertical scale in meters)
seem to have prevailed from the Late Palaeocene (formation of the Tsaile surface) to the Middle Oligocene (valley fills). Palaeoclimate in the Hopi Lake area Introduction The Bidahochi Formation was deposited in the Black Mesa basin in northeastern Arizona (Fig. 1).
The Bidahochi Formation is subdivided into three different units, a lower lacustrine member, a middle volcanic and an upper mainly fluvial member. The volcanic member has been dated, it is of very late Miocene to early Pliocene age (4.1-6.7 my: Evernden et al., 1964; Naeser, 1971; Sutton, 1974). The lower Bidahochi Formation was deposited in the basin of the Hopi Lake on the Hopi Buttes surface during Miocene times. The White Cone fossil
Fig. 4. Valley fill near Washington Pass. Note person in the centre for scale.
291
I'ERTIARY PALAEOCLIMATIC HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
Stripped surfaces are found on the dip slopes of resistant beds, for instance in the Dinosaur Canyon Sandstone of the Moenave Formation southwest of Ganado on the western side of Pueblo Colorado Wash (Fig. 1).
assemblage in the upper part of the Lower Bidahochi beds (Nations and Landye, 1984) indicates a lake-shore community in an arid to semiarid environment (Smiley, 1984). The Hopi Buttes surface at the base of the Bidahochi Formation is an erosion surface, the Zuni surface is an aggradation surface and underlies the middle and upper members of the Bidahochi Formation (Table 1, Fig. 5). The investigations were concentrated on the Hopi Buttes surface, which furnishes information on the morphoclimatic conditions of the Miocene.
Laboratory analyses The contact between the Mesozoic bedrock and the lacustrine member of the Bidahochi Formation is exposed in many places (cf. Fig. 6). Samples for X-ray analyses were taken from the basal Bidahochi layers and from the bedrock below the contact. Table 3 summarizes the results, lists the locations and elevations of the sample sites and the positions in the exposures. In some places there is a bleached horizon below the contact, which is a few centimeters to half a meter thick. The clay mineralogy of this bleached horizon is not different from the unbleached bedrock (compare sample 48 with samples 46 and 47, and samples 52 and 70 with sample 71). There is no kaolinite enrichment in the bleached material. Montmorillonite is dominant in all samples. Chlorite, which easily weathers under humid and warm conditions, is present close to the surface. Gypsum and salts are also found, but these minerals are possibly younger than the formation of the Hopi Buttes surface and may have originated in the lake environment. Conglomerates in the basal Bidahochi beds contain silt-
Field results The lower Bidahochi Formation overlies strata from the Triassic Chinle Formation to the Upper Cretaceous Mancos Shale. The Hopi Buttes surface is a truncating surface only in areas where soft rocks of relatively homogeneous resistance crop out. More resistant rocks form structurally and lithologically controlled landforms protruding above the surface. Despite the marked topographic irregularities there is a general trend of increasing elevation of the Hopi Buttes surface from east to west (Fig. 5), the lowest altitude (1800 m) is found where Pueblo Colorado Wash enters the outcrop area of the lower Bidahochi Formation (Fig. 1), the surface reaches the greatest altitude (1900 m) on the side of Round Top Mountain (Fig. 5).
W
Black
Mesa
E ISW
Basin
NE
Ganado
9ueb\o Co\o~ac~o
RoundTop Mountain
Bidahochi Zuni
I
-
~
(Tbo) UpperBidahochi Formation (Tbv)Middle Bidahochi Formation
-
=
I
- -
surfoc e
-
---
~J~s~
j/ ,
RobertsMesa / surlace /
~
Tbo
-
I Hop';u't.... rlace I (Tbl) Lower Bidahochi Formation (Tc) Chuska Sandstone
(Km) Mancos Shale
(J) Jurassic
(Kd) Dakota Sandstone
('li) Triassic
Fig. 5. Profile showing the Hopi Buttes and Zuni surfaces in the Hopi Buttes area (not to scale).
Castle Butte (1825 m) Castle Butte (1825 m) Castle Butte (1825 m) Echo Spring Mtn. (1870 m) Echo Spring Mtn. (1870 m) Echo Spring Mtn. (1870 m) Bidahochi Butte (1830 m) Bidahochi Butte (1830 m) Bidahochi Butte (1830 m) Greasewood (road) (1810 m) Greasewood (road) (1810 m) Greasewood (road) (1810 m)
43
71
70
52
51
50
49
48
47
46
45
44
Location
No.
bleached Trwl, 10 cm below contact bleached Trwl, 20 cm below contact Trwl, 1 m below contact
10 cm below (weathered) contact, Trwr 20 cm below contact, Trwr
basal Tbl
white weathering layer, directly below contact, Trwr
red weathering layer, grading into bedrock, Trwr
red weathering layer, grading into bedrock, Trwr
Trwr, unweathered
Tbl, white upper portion
red Tbl upper slope
Position in the exposure
95
95
95
95
100
95
90
90
90
95
85
85
Montmorillonite
X-ray analyses of samples in the outcrop area of the Bidahochi Formation
TABLE 3
5
-
-
2,5
-
5
10
5
5
5
10
10
Illite
-
-
+
(+ )
-
(+)
-
-
2,5
-
-
-
Kaolinite
5
5
2,5
(+)
-
(+ )
(+ )
5
2,5
-
5
5
Chlorite
-
-
-
+ +
+
+
+ +
+
+ +
(+ )
+
+
Calcite
+
+
+
+
+
+
+
+ +
+
+
+
+
Feldspar
+
+
+
+
+
+
+
+
+
+
+
+
Quartz
Salts
Anatase in larger quantities Salts
-
Gypsum
Gypsum
-
Analcime
Analcime
-
-
-
Special characteristics
_~
-~
b,)
Trmod, 30 cm below contact basal Tbl
Trmod, I0 cm below contact
95
50
50
5
5
5
-
-
(+) + +
-
+
+
+ +
+
+
coarse material, few clay minerals
Corensite, Anatase in small quantities same as 53
Tbl: Lower Bidahochi Formation. Trmod: Moenave Formation, Dinosaur C a n y o n Sandstone. Trwr: Wingate Sandstone, Rock Point Member. Trwl: Wingate Sandstone, Lukachukai Member. ( + ): traces. + : frequent. + + : abundant. The clay mineral content is given in percentages. The elevations in brackets refer to the altitudes of the Hopi Buttes surface in the given locations. Castle Butte and Echo Spring M o u n t a i n lie on the southwestern margin of the outcrop area. Castle Butte is an isolated outlier in the central part of a syncline. Bidahochi Butte lies directly south of the small settlement Bidahochi (Fig. 1). The sample site Greasewood (road) is situated directly north o f Bidahochi and the exposure Greasewood is located near the lowest point of the Hopi Buttes surface southwest o f G a n a d o on the western side o f Pueblo Colorado Wash (Fig. 1).
(1800 m)
Greasewood (1800 m) Greasewood
54
55
Greasewood (1800 m)
53
294
K.-H. SCHMIDT
Fig. 6. Contact between the lower Bidahochi Formation and the Wingate Sandstone (head of the person is close to the contact). The lower Bidahochi Formation is overlain by middle Bidahochi volcanics. The upper parts of the Wingate Sandstone are bleached. Samples 52, 70 and 71 were taken from this exposure.
stones, which must have come from nearby sources not affected by intensive chemical weathering.
Interpretation: as in the case of the Tsaile surface there is abundant evidence for the Miocene Hopi Buttes surface having been formed under the weathering and erosion conditions of a dry climate: (1) Lithologically controlled landforms as indicators of selective weathering and erosion characterize the surface. (2) There are no indications of intensive chemical weathering, because no newly formed kaolinite is present in the samples, because there is no change in mineral content from parent rock to weathering mantle and because chlorite, calcite, gypsum, salts and analcime are present close to the surface. Conclusion The results of the geomorphological and mineralogical investigations in the Chuska Mountains and in the Hopi Buttes area demonstrate that the climatic conditions on the southeastern Colorado
Plateau have not changed decisively during the Cenozoic and were much the same as today. The presence of structurally and lithologically controlled landforms on the Tertiary erosion surfaces and the absence of indicators of intensive chemical weathering in the palaeosols and the sediments on the surfaces reveal the predominance of arid-zone selective erosion and mechanical weathering. It is concluded that the Colorado Plateau has been dominated by dry climates since the Laramide orogeny with the possible exception of the early Palaeocene It is not surprising that there is no evidence of more humid climatic condition in late Tertiary times, because at that time dry climates also prevailed in the surrounding areas. But during the late Palaeocene and Eocene the Colorado Plateau is out of phase with the general palaeoclimatic situation in western North Amcrica, where at that time moist and warm conditions were predominant (Dorf, 1964; Wolfe and Hopkins, 1967; Peterson and Abbott, 1978) (see Fig. 7). The only deep weathering profile on the Colorado Plateau has
295
TERTIARY PALAEOCLIMAT[C HISTORY OF THE SOUTHEASTERN COLORADO PLATEAU
humid A warm
~
~
\
WOLFE+ HOPKINS (1967) PETERSON + ABBOTT
..........
( 1978 ) f
/
DORF (1964)
%../
/f
dry climate ascertained on the southeastern Colorado Plateau
.-,.. cooldry
, =L[
MIOCENE,JOUGO, CENEJ,EOCENE.I 10
20
30
40
50
PAL.,~CRE] 6o 70 my
Fig. 7. Generalized palaeoclimatic graphs for the Tertiary of western North America. Periods of dry climate on the southeastern Colorado Plateau are indicated by the bars.
developed at the t u r n o f the Cretaceous a n d Tertiary periods ( J o h n s o n a n d May, 1980). The exceptional dryness o f the C o l o r a d o P l a t e a u d u r i n g the early Tertiary is explained by its position in the rain s h a d o w o f the r a i n - b e a r i n g s o u t h e a s t e r n to southwestern winds. The C o l o r a d o Plateau, before its s e p a r a t i o n from the Basin a n d R a n g e Province in Oligocene times, lay in a t o p o g r a p h i c a l l y lower position on the leeside o f the s o u t h e r n R o c k y M o u n t a i n s a n d the C e n t r a l A r i z o n a Highlands, which at that time formed a barrier stretching from western A r i z o n a to N e w Mexico.
Acknowledgements The investigations were s u p p o r t e d by a g r a n t of the D F G ( G e r m a n Research Association). I t h a n k Prof. T h o r N.V. K a r l s t r o m , U S G S , Flagstaff, Arizona, for s t i m u l a t i n g discussions a n d a j o i n t field trip to the Black Mesa b a s i n a n d the C h u s k a M o u n t a i n s . Dr. Riedel, Geologisches Institut, Ruhr-Universit/it, B o c h u m , m a d e the X - r a y analyses a n d helped with the i n t e r p r e t a t i o n , K a r i n Heine assisted in the p r e p a r a t i o n of the text a n d the tables.
References Akers, J.P., Shorty, J.C. and Stevens, P.R., 1971. Hydrogeology of the Cenozoic igneous rocks, Navajo and Hopi Indian
Reservations, Arizona, New Mexico, and Utah. U.S. Geol. Surv. Prof. Pap., 521 D. Appledorn, C.R. and Wright, H.E., 1957. Volcanic structures in the Chuska Mountains, Navajo Reservation, ArizonaNew Mexico. Geol. Soc. Am. Bull., 68:445 468. Baltz, E.H., 1967. Stratigraphy and regional tectonic implications of part of Upper Cretaceous and Tertiary rocks, EastCentral San Juan Basin, New Mexico. U.S. Geol. Surv. Prof. Pap., 552:1 101. Cadigan, R.A., 1972. Sedimentary petrology. In: J.H. Stewart, E.G. Poole and R.F. Wilson (Editors), Stratigraphy and Origin of the Chinle Formation and Related Upper Triassic Strata in the Colorado Plateau Region. U.S. Geol. Surv. Prof. Pap., 690: 56-62. Cashion, W.B., 1967. Geology and fuel resources of the Green River Formation, Southeastern Uinta Basin, Utah and Colorado. U.S. Geol. Surv. Prof. Pap., 548:1 48. Cooley, M.E., Harshbarger, J.W., Akers, J.P. and Hardt, W.F., 1969. Regional hydrogeology of the Navajo and Hopi Indian Reservations, Arizona, New Mexico and Utah. U.S. Geol. Surv. Prof. Pap., 521 A: 1-61. Doff, E., 1964. The use of fosil plants in paleoclimatic interpretation. In: A.E.M. Nairn (Editor), Problems of Paleoclimatology. Wiley, New York, NY, pp. 13-30. Eugster, H.P. and Surdam, R.C., 1973. Depositional environment of the Green River Formation of Wyoming, a preliminary report. Geol. Soc. Am. Bull., 84:1115 1120. Euler, R.C., Gumerman, G.C., Karlstrom, T.N.V., Dean, J.S. and Hevly, R.H., 1979. The Colorado Plateaus: cultural dynamics and palaeoenvironment. Science, 205:1089-1101. Evernden, J.F., Savage, D.E., Curtis, G.H. and James, G.T., 1964. Potassium-argon dates and the Cenozoic mammalian chronology of North America. Am. J. Sci.: [45-198. Hack, J.T., 1942. The changing physical environment of the Hopi Indians of Arizona. Peabody Mus. Pap., 35:1 86. Hackman, R.J. and Olson, A.B., 1977. Geology, structure and
296 uranium deposits of the Gallup 1° x 2° quadrangle, New Mexico and Arizona. U.S. Geol. Surv. Misc. Inv. Ser. Map 1-981. Hereford, R., 1984. Climate and ephemeral stream processes: Twentieth-century geomorphology and alluvial stratigraphy of the Little Colorado River, Arizona. Geol. Soc. Am. Bull., 95: 654- 668. Johnson, R.C. and May, F., 1980. A study of the CretaceousTertiary unconformity in the Piceance Creek basin, Colorado. The underlying Ohio Creek Formation (Upper Cretaceous) redefined as a member of the Hunter Caynon or Mesaverde Formation. U.S. Geol. Surv. Bull., 1482 D: 1-22.
Lucchitta, I., 1984. Development of landscape in northwestern Arizona: the country of plateaus and canyons. In: T.L. Smiley, J.D. Nations, T.L. Pewe and J.P. Schafer (Editors), Landscapes of Arizona. Univ. Press of America, Lanham, MD, pp. 269-301. Moss, J.H., 1977. The formations of pediments: scarp backwearing or surface downwasting? In: D.O. Doehring (Editor), Geomorphology in Arid Regions. Allen and Unwin, London, pp. 51-78. Naeser, C.W., 1971. Geochronology of the Navajo-Hopi diatremes, Four Corners area. J. Geophys. Res., 76: 4978-4985. Nations, J.D. and Landye, J.J., 1984. Cenozoic plant and animal fossils of Arizona In: T.L. Smiley, J.D. Nations, T.L. Pewe and J.P. Schafer (Editors), Landscapes of Arizona. Univ. Press of America, Lanham, MD, pp. 7-35. O'Sullivan, R.B. and Beikman, H.M., 1963. Geology, structure and uranium deposits of the Shiprock quadrangle, New Mexico and Arizona. U.S. Geol. Surv. Misc. Inv. Ser. Map 1-345. Peterson, G.L. and Abbott, P.L., 1979. Mid-Eocene climatic change, Southwestern California and Northwestern Baja
K.-H. SCHMIDT California. Palaeogeogr., Palaeoclimatol., Palaeoecol., 16: 73-87. Pohlman, H.F., 1967. The Navajo Indian Nation and Dineh bi Kayah. In: New Mexico Geol. Soc. Guidebook, DefianceZuni-Mt. Talor region, pp. 63-69. Pye, W.D., 1967. How unique Arizona syenite oil reservoir formed. World Oil, 165: 81-83. Robson, S.G. and Saulnier, G.J., 1981. Hydrogeochemistry and simulated solute transport, Piceance Basin, Northwestern Colorado. U.S. Geol. Surv. Prof. Pap., 1196: 1-65. Schmidt, K.-H., 1988. Die Reliefentwicklung des Colorado Plateaus. Berl. Geogr. Abh., 49: 1-183. Schultz, L.G., 1963. Clay minerals in Triassic rocks of the Colorado Plateau. U.S. Geol. Surv. Bull., 1147 C: 1-71. Smiley, T.L., 1984. Climatic change during landform development. In: T.L. Smiley, J.D. Nations, T.L. Pewe and J.P. Schafer (Editors), Landscapes of Arizona. Univ. Press of America, Lanham, MD, pp. 55-77. Sutton, R.L., 1974. The geology of Hopi Buttes, Arizona. In: T.N.V. Karlstrom et al.(Editors), Geology of Northern Arizona. In: Geol. Soc. Am. Rocky Mount. Sect. Meet., pp. 647-67 I. Wells, S.G., Bullard, T.F. and Smith, L.N., 1982. Origin and evolution of deserts in the Basin and Range and the Colorado Plateau provinces of western North America. Striae, 17: 101-111. Wolfe, J.A. and Hopkins, D.M., 1967. Climatic changes recorded by Tertiary land floras in Northwestern North America: Tertiary correlations and climatic changes in the Pacific. In: 1lth Pacific Sci. Congr., Sendai, pp. 67-76. Wright, H.E., 1956. Origin of the Chuska Sandstone, ArizonaNew Mexiko: A structural and petrographic study of a Tertiary eolian sediment. Geol. Soc. Am. Bull., 67: 413-434.