X-Ray Diffraction Studies of the 

<0.5-,um Fraction from the Brushy Basin 

Member of the Upper Jurassic 

Morrison Formation, Colorado Plateau 

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Chapter G 

X-Ray Diffraction Studies of the 

<0.5-J.tm Fraction from the Brushy Basin 

Member of the Upper jurassic 

Morrison Formation, Colorado Plateau 

By DOUGLASS E. OWEN, CHRISTINE E. TURNER-PETERSON, 

and NElL S. FISHMAN 

A multidisciplinary approach to research studies of sedimentary 

rocks and their constituents and the evolution of sedimentary 

basins, both ancient and modern . 

U.S. GEOLOGICAL SURVEY BULLETIN 1808 

EVOLUTION OF SEDIMENTARY BASINS-SAN JUAN BASIN 
DEPARTMENT OF THE INTERIO"R 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1989 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Owen, Douglass E. 

X-ray diffraction studies of the <0.5-~-Lm fraction from the Brushy Basin 

· Member of the Upper Jurassic Morrison Formation, Colorado Plateau : a 

multidisciplinary approach to research studies of sedimentary rocks and their 

constituents and the evolution of sedimentary basins, both ancient and modern 

I by Douglass E. Owen, Christine E. Turner-Peterson, and Neil S. Fishman. 

p. em. - (Evolution of sedimentary basins-San Juan basin ; ch. G) 

(U.S. Geological Survey bulletin ; 1808-G) 

Includes bibliographies. 

Supt. of Docs. no.: I 19.3: 1808-G 

1. Clay minerals-New Mexico-Composition. 2. Geology, 

Stratigraphic-Jurassic. 3. Geology-New Mexico. 4. Morrison Formation. 

I. Turner-Peterson, Christine E. II. Fishman, Neil S. Ill. Title. IV. Series. 

V. Series: U.S. Geological Survey bulletin ; 1808-G. 

QE75.B9 no. 1808 G 

[QE 389.625] 

557.3 s-dc20 89-600180 

[549' .6] CIP 
CONTENTS 

Abstract Gl 

Introduction Gl 

Geologic setting G3 

Methods G5 

Results G6 

Distribution of clays G6 

Discussion G6 

Conclusions G9 

References cited Gll 

Appendix. X-ray data for <0.5-p.m fraction G13 

FIGURES 

1. Map showing extent of ancient Lake T'oo'dichi' and outcrop areas of 

Morrison Formation, eastern Colorado Plateau G2 

2. Schematic cross section showing stratigraphy of the Morrison Formation 

from the southern margin of the San Juan basin northward to the Colorado 

National Monument G4 

3-5. X-ray diffractograms of: 

3. Highly smectitic mixed-layer clay from Toadlena G6 

4. Highly illitic mixed-layer clay from Blue Mesa G6 

5. Chlorite-rich sample from McElmo Canyon G7 

6-22. Graphs showing amount of smectite in some mixed-layer clays from: 

6. Blue Peak G7 

7. Capulin Peak G7 

8. Colorado National Monument GS 

9. Courthouse Draw GS 

10. Lisbon Valley GS 

11. Montezuma Creek GS 

12. Sanostee Wash G9 

13. Toadlena G9 

14. Beclabito Dome G9 

15. Big Gypsum Valley G9 

16. Deadman's Peak GlO 

17. McElmo Canyon GlO 

18. Oak Springs GlO 

19. Blue Mesa GlO 

20. Durango Hospital Gll 

21. Norwood Hill Gll 

22. Piedra River Gll 

Contents Ill . 
CONVERSION FACTORS FOR SOME Sl METRIC AND U.S. UNITS OF MEASURE 

To convert from 

Feet (ft) 

Miles (mi) 

Pounds (lb) 

Degrees Fahrenheit (°F) 

IV Contents 

To 

Meters (m) 

Kilometers (km) 

Kilograms (kg) 

Degrees Celsius ec) 

0.3048 

1.609 

0.4536 

Multiply by 

Temp °C=(temp °F-32)/1.8 
EVOLUTION OF SEDIMENTARY BASINS-SAN JUAN BASIN 

X-ray Diffraction Studies of the 

< 0.5-,um Fraction from the Brushy Basin 

Member of the Upper Jurassic 

Morrison Formation, Colorado Plateau 

By Douglass E. Owen, Christine E. Turner-Peterson, and Neil S. Fishman 

Abstract 

Studies of the < 0.5-~Lm fraction of ~am pies from tuffaceous beds of ancient Lake T'oo'dichi', a large saline, 

alkaline lake complex in the Brushy Basin Member of the 

Upper Jurassic Morrison Formation, Colorado Plateau, 

reveal an interesting trend in the distribution of clay minerals. 

In the outer part of the lake the clay mineral population is 

dominated by smectitic mixed-layer illite/smectite, whereas 

in the inner part of the lake the clay mineral population is 

predominantly illitic mixed-layer illite/smectite. Mixed-layer 

clay minerals in the area between the outer and inner parts 

exhibit a high degree of variability. Vertically adjacent beds 

may contain very different mixed-layer clay populations. 

Chlorite generally is present where illitic mixed-layer clay 

minerals are common. 

The distribution of mixed-layer illite/smectite in the 

lacustrine units did not result from depositional processes 

because most of the samples were from tuff beds that 

contain little admixed detrital material. Furthermore, the 

absence of illitic clays in the outer margin of the lake system 

precludes a detrital origin for illitic clays farther basinward 

because the illitic clays would necessarily have crossed the 

smectitic zone in transit. The distribution of mixed-layer clays 

also cannot be explained by the Gulf Coast model of illitization-progressive illitization due. to burial and attendant 

heating. The Gulf Coast model cannot be used to explain 

vertically adjacent beds in the Brushy Basin Member that 

contain very different mixed-layer clay populations because 

these beds would undoubtedly have experienced a similar 

burial and thermal history. Instead, the trend of increasingly 

illitic mixed-layer clays toward the center of Lake T'oo'dichi' 

can more readily be attributed to changes in pore-water 

chemistry. In fact, the trend in clay-mineral composition 

Manuscript approved for publication, May 26, 1989. 

coincides with the hydrogeochemical gradient of increasing 

salinity and alkalinity associated with the saline, alkaline lake; 

hence, pore-water chemistry alone appears to have 

controlled clay composition in the lacustrine sediments of 

Lake T'oo'dichi'. 

INTRODUCTION 

Certain mineral transformations are used as geethermometers to provide evidence for minimum 

temperatures in the host rock at their time of formation. 

The conversion of smectite to illite-rich mixed-layer 

illite/smectite is widely used in this manner; this 

conversion is commonly thought to begin at 

approximately 90 °C (Burst, 1969; Hower and others, 

1976; Freed, 1980; Milliken and others, 1981; Pollastro 

and Scholle, 1986). Because this conversion can be 

related to temperature, it commonly is used to determine 

if a sedimentary sequence has been heated· to sufficient 

temperatures to generate hydrocarbons (Gautier and 

others, 1985). The conversion also is used to obtain 

information on the thermal and burial history of 

sedimentary basins, and, as such, it is critical to know if 

exceptions to the paradigm exist. 

Pore-water chemistry is assumed to be an 

important constraint in the illitization of smectite 

because a source of potassium is required (Hower and 

others, 1976; Johnston and Miller, 1984). It is not 

generally thought, however, that pore-water chemistry 

alone can drive the reaction in the absence of elevated 

temperatures. There are clues, however, to indicate that 

illitic mixed-layer clay may form under synsedimentary 

conditions. Illitic clays believed to be authigenic have 

been reported in modern lake sediments in Africa 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G1 
109° 

----- Colorado National 

Monument 

~~~~.~ 

Montrose ' ' ' ' \ 

\ 

\ 

\ 

\ 

\ -----------~~LOR~O----------~----- NEWMEXICO \ 

\ 

Deadman's Peak \ 

Capulin Peak~~ ~) 

~ 

\ 

I 

I 

0 Albuquerque 

__ ., / 

/ 

0 Santa Fe 

0 100 KILOMETERS '-------...J 

Figure 1. Extent of ancient Lake T'oo'dichi' (solid and dashed line) in Brushy Basin Member of the 

Morrison Formation, eastern Colorado Plateau. Dashed line indicates where boundary of lake is 

uncertain. Sample localities (circles) and outcrop areas of Morrison Formation (pattern) are also 

shown. Modified from Turner-Peterson (1987). 

(Singer and Stoffers, 1980) and are thought to be a 

predictable consequence of the extreme pore-water 

chemistry in the lake sediments. Thus, saline, alkaline 

lakes appear to be convenient natural laboratories in 

which to test the hypothesis that pore-water chemistry 

alone can facilitate the formation of authigenic illitic 

clays. 

In order to evaluate the role of pore-water 

G2 Evolution of Sedimentary Basins-San Juan Basin 

chemistry in the formation of mixed-layer illite/smectite, 

we studied the mineralogy and distribution of authigenic 

clays in tuffaceous beds of ancient Lake T'oo'dichi', a 

large saline, alkaline lake in the Brushy Basin Member of 

the Upper Jurassic Morrison Formation, eastern 

Colorado Plateau (Turner-Peterson, 1987) (fig. 1). The 

ancient lake sequence consists of saline, alkaline lake 

deposits, as thick as 100 m, that are characterized by 
thick intervals of altered silicic volcanic ash. Differential 

alteration of the ash reflects the lateral hydrogeochemical gradient in a saline, alkaline lake complex 

and resulted in the development of concentrically zoned 

authigenic mineral facies (Bell, 1986; Fishman and 

others, 1986; Turner-Peterson and others, 1986; TurnerPeterson, 1987). Our hypothesis is that the distribution of 

authigenic iiiite/smectite reflects the same hydrogeochemical gradient that is reflected in the distribution 

of authigenic aluminosilicate minerals across the lake. 

The lacustrine deposits of Lake T'oo'dichi' in the 

Brushy Basin Member of the Morrison Formation are 

particularly suitable to our purposes for several reasons. 

First, in a study of the Brushy Basin Member, Keller 

(1962) noted a west-east change in clay-mineral 

composition, from smectitic mixed-layer clays in eastern 

Utah to iiiitic mixed-layer clays in western Colorado. The 

lateral trends noted by Keller coincide with lateral trends 

in authigenic aluminosilicate minerals in tuff beds in the 

same area (Turner-Peterson, 1987). Thus, the Brushy 

Basin Member seems a good natural laboratory in which 

to test our hypothesis relating lateral trends in clay 

authigenesis to lateral changes in pore-water chemistry. 

In addition, the abundance of tuff beds in Lake 

T'oo'dichi' increases the likelihood of obtaining an authigenic, rather than a detrital, suite of clay minerals; most 

of the tuff beds contain abundant relict shards that attest 

to the air-fall origin of much of the material. 

In this report, we present the results of the first 

phase of our study, the goal of which was to document 

the occurrence and distribution of clay minerals in 

ancient Lake T'oo'dichi'. Our studies of the diagenetic 

history of Lake T'oo'dichi' continue, and, ultimately, we 

plan to evaluate the distribution of authigenic clay 

minerals with respect to the authigenic aluminosilicate 

minerals in the lacustrine complex and to model the 

pore-water chemistry during formation of all these authigenic minerals. 

Acknowledgments.-We owe special thanks to 

Gene Whitney, who trained us to use laboratory 

equipment to process our samples, to make slides and to 

use the X-ray diffractometer, on which we ultimately ran 

more than 1,000 slides of clay separates. He also 

provided many ho_urs of consultation and help with 

interpretation. We also owe special thanks to Rick 

Mahrt, who was always helpful and wiiiing to 

demonstrate how to use the lab equipment and many 

times made quick repairs or adjustments to the 

instruments that saved us much ·tim·e and maintained the 

quality of the data; and to Ken Esposito who generated 

the publication-quality diffractograms included in this 

report. Charles Pierson and Gene Whitney reviewed the 

paper and provided many helpful suggestions and 

criticisms. This study was entirely funded by the Gilbert 

Fellowship Program of the U.S. Geological Survey. 

GEOLOGIC SETTING 

The Brushy Basin Member is the uppermost 

member of the Upper Jurassic Morrison Formation and 

covers an area of approximately 150,000 km2 in the 

eastern Colorado Plateau (fig. 1 ). In the study area, the 

Brushy Basin conformably overlies the fluvial Westwater 

Canyon, Recapture, or Salt Wash Members of the Morrison, and is unconformably overlain by either the Lower 

Cretaceous Burro Canyon Formation or the Upper 

Cretaceous Dakota Sandstone. The Brushy Basin 

Member is recognized from the southern margin of the 

San Juan basin in New Mexico northward to near Grand 

Junction, Colo. (fig. 1). North and east of Grand 

Junction, the Morrison Formation is not subdivided into 

members, and thus, the Brushy Basin Member is not 

formally recognized. At the type section near Blanding, 

Utah, the Brushy Basin is 137 m thick (Gregory, 1938); 

elsewhere on the Colorado Plateau it is locally thicker. 

North of the Colorado-New Mexico State line, beyond 

the depositional pinchout of the Westwater Canyon 

Member, beds equivalent to the Brushy Basin Member 

in New Mexico rest directly on beds that are equivalent to 

the Recapture Member of the Morrison Formation 

(Turner-Peterson, 1987). The name Recapture is not 

extended much beyond the pinchout of the Westwater 

Canyon, and the entire interval above the Salt Wash 

Member is mapped as the Brushy Basin Member in this 

region (fig. 2). 

For this study, it was important to distinguish beds 

within the Brushy Basin Member that are equivalent to 

the Recapture Member farther south from those 

equivalent to the vertically more restricted Brushy Basin 

Member in New Mexico. The lower part of the Brushy 

Basin Member and the upper part of the Brushy Basin 

Member are used, respectively, to make this distinction 

(Turner-Peterson, 1987) (fig. 2) and are hereafter 

referred to as lower Brushy Basin Member and upper 

Brushy Basin Member. 

The lower Brushy Basin Member was deposited 

dominantly by alluvial processes that involved delivery of 

detrital material, including detrital clay, from a 

heterogeneous source area several hundred kilometers 

to the southwest. The dominantly clastic lower Brushy 

Basin Member is only locally punctuated by tuff beds of 

air-fall origin. In contrast, the upper Brushy Basin 

Member originated chiefly as airborne volcanic ash that 

erupted in an arc region to the southwest and was carried 

northeastward by prevciling winds to the depositional 

basin. This interval is interpreted as a saline, alkaline 

lake, Lake T'oo'dichi'. Interbedded with the tuffs in the 

upper Brushy Basin Member are fluvial sandstone beds 

that represent episodic flooding of clastic material across 

a playa surface (Turner-Peterson, 1987). The distinction 

between the two intervals within the member is readily 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G3 
NORTH 

Escalante 

Canyol') 

EXPLANATION 

Big 

Gypsum 

Valley 

1.: <<·l Fluvial sandstone 

~Eolian sandstone 

t¢j lntl!lrpedded sandstone 

and mudstone 

Norwood 

Hill 

Piedra 

River 

Beclabito 

Dome 

Oak 

Springs 

San Rafael Group 

Toad lena 

SOUTH 

Goat 

Mountain 

Figure 2. Schematic cross section showing stratigraphy of the "'!orrison Formation from the southern margin of the San 

Juan basin northward to the Colorado National Monument (fig. 1). The upper part of the Brushy Basin Member of the 

Morrison Formation is defined by the saline, alkaline lake deposits; lithofacies include smectite (S), clinoptilolite (C), 

analcime ±potassium feldspar (A/K), and albite (AL). The lower part of the member consists chiefly of fluvial sandstone 

and floodplain mudstone and claystone. J5 marks the unconformity that separates the Morrison Formation from underlying 

rocks; queried where questionable. Horizontal scale variable. Modified from Turner-Peterson (1987). 

apparent at most localities. The lower Brushy Basin 

Member consists chiefly of fluvial sandstone and floodplain mudstone and claystone, whereas the saline, 

alkaline lake deposits of Lake T'oo'dichi', chiefly altered 

volcanic tuff, are restricted to and help define the upper 

Brushy Basin Member (fig. 2). The lateral change in 

authigenic mineralogy in the lacustrine beds of the 

Brushy Basin Member shown in figure 2 reflects a 

hydrogeochemical gradient in a saline, alkaline lake. 

Water levels fluctuate considerably in these lakes, and 

the composition of pore waters in the underlying lake 

sediments reflects these fluctuations. During periods of 

high lake levels, all sediments are exposed to relatively 

fresh water and minerals reflecting this fresher water 

form at this time; during low stands, pore waters of 

increased salinity and alkalinity in the central part of the 

lake alter minerals formed during high stands to minerals 

that reflect the increased salinity and alkalinity. The net 

effect of these fluctuations is a distribution of authigenic 

minerals that reflects an overall hydrogeochemical 

gradient (fig. 2). 

The upper contact of the Brushy Basin Member 

can be difficult to determine where the member is 

overlain by the Lower Cretaceous Burro Canyon 

G4 Evolution of Sedimentary Basins-San Juan Basin 

Formation. Both units contain mudstone, and suspected 

mudstone-on-mudstone contact at many localities make 

the contact difficult to establish with certainty. Tuffaceous mudstone, which exhibits a characteristic 

"popcorn" weathering, is confined to the Brushy Basin 

Member. Mudstone in the Burro Canyon Formation 

commonly does not exhibit "popcorn" weathering; thus 

the nature of the weathering commonly is a useful 

criterion in distingu~shing the two units. This study 

demonstrates, however, that tuffaceous mudstone in the 

Brushy Basin Member locally contains illitic rather than 

smectitic mixed-layer illite/smectite and does not exhibit 

"popcorn" weathering and is thus not readily 

distinguished from the mudstone of the overlying Burro 

Canyon Formation. Color is locally a useful criterion 

because mudstone in the Burro Canyon typically is red 

and green, whereas mudstone in the Brushy Basin is 

commonly green and brown. 

Pebbles in conglomeratic sandstone beds within 

the mudstone slopes in question also provide clues that 

help to distinguish the Burro Canyon Formation from the 

Brushy Basin Member of the Morrison Formation. The 

Burro Canyon Formation typically contains only white, 

gray, or black chert pebbles. In contrast, the Brushy 
Basin Member contains a heterogeneous suite of 

pebbles, most notably a distinctive suite of green and red 

chert pebbles. The contact between the two · units 

typically is determined on the basis of a combination of 

criteria listed herein, but placement of the contact is not 

always certain. Despite these difficulties, error in placing 

the contact probably does not exceed 12m at any locality. 

METHODS 

Our goal was to test the role of pore-water 

chemistry in the formation of authigenic clays in a saline, 

alkaline lake setting, and most of our samples were 

collected from lacustrine deposits of ancient Lake 

T'oo'dichi'. Samples were collected from throughout the 

Brushy Basin Member in the southern part of the study 

area, but chiefly from the upper Brushy Basin Member in 

the northern part of the study area (fig. 2). In addition, 

locally, samples were collected from units of the lower 

Brushy Basin Member and from the lowermost mudstones of the Burro Canyon Formation so that these clay 

minerals could be contrasted with clay minerals in units 

of the upper Brushy Basin Member. In all, 441 samples 

were collected from 17 outcrop localities (fig. 1 ): most 

samples (323) were collected from tuff beds and the 

others from mudstone (67) and claystone (51). Most, if 

not all, of the claystone samples are tuffaceous. 

The sall)ples were crushed to granule size in a jaw 

crusher and placed in 250-mL beakers. The beakers were 

then filled with distilled water and the samples sonified 

for 3 minutes. Flocculation of the clay suspensate was 

rare. When flocculation occured, the suspension was 

diluted; if flocculation remained a problem, a dispersant 

(sodium hexametaphosphate) was added. The suspended 

clays were placed in 10-cm-high centrifuge bottles and 

spun at 1,000 rpm for 33 minutes to settle the > 0.5-~.tm 

fraction, the time being determined by Stokes' Law. The 

< 0.5-~.tm fraction, which remained in suspension, was 

selected for two reasons: (1) Ex·amination of several size 

fractions on representative samples indicated that the 

< 0.5-~.tm size fraction gave the most easily interpreted 

data and the least interference from quartz. (2) This size 

fraction was less likely to contain detrital clays. 

The < 0.5-~.tm fraction for each sample was suctioned onto 0.45-~.tm-pore filters and then transferred to 

two glass slides; this method for producing slides of 

oriented clay minerals is as described by Drever (1973) 

and modified by Pollastro (1982). One slide was heated 

at 550 °C (1,022 °F) for 1 hour, and the second slide was 

placed over a reservoir of ethylene glycol in an oven at 60 

oc (140 °F) overnight. The slides were then X-rayed by 

using Cu Ka radiation and scanning from 2° to 35° 28 or 

from 2° to 52° 28 at 3° 28/min. The resulting X-ray 

diffractograms were interpreted by using the techniques 

described in Brown and Brindley (1980) and Reynolds 

(1980). 

Identified clay minerals include smectite, mixedlayer illite/smectite, chlorite, and kaolinite'. The term 

smectite Is used to refer to clays that swell upon glycolation to --17 A, exhibit integrally spaced peaks, and 

collapse to -10 A upon heating. To determine the 

expandability (percent smectite layers) of mixed-layer 

illite/smectite, the position of the illite/smectite peaks 

found between 8.52 and 10.16 A and between 5.62 and 

5.01 A was noted; both peak positions were compared 

with table 4.5A in Reynolds (1980) to determine amount 

of smectite (in percent). Smectitic mixed-layer illite/smectite is used to refer to clays having a high percentage of 

smectite, and illitic mixed-layer illite/smectite refers to 

clays having a low percentage of smectite. If only one 

peak was used to determine the percentage of smectite, it 

is noted in the data tables (appendix). The percent 

smectite listed in the tables should be considered as 

approximate rather than absolute (see Srodon, 1980). 

Although the percentages are approximate, the data set 

is internally consistent and certainly suitable for 

comparison of one outcrop locality with another. Diffractograms for a highly expandable or smectitic mixed-layer 

clay having integrally spaced peaks are shown in figure 3, 

and. diffractograms for a low expan~able or highly illitic 

mixed-layer clay are shown in figure 4. 

The presence of chlorite or kaolinite was 

determined by the presence of a peak between 7.1 and 

7.2 A (12.5-12.3° 28) and a more diagnostic peak 

between 3.5 and 3.6 A (25.5-24.7° 28) on the .diffractogram from the glycolated sample. Figure 5 shows diffractograms for a sample containing abundant chlorite. Chlorite was distinguished from kaolinite by the presence of a 

peak at -6° 28 (13.9 A.) on the diffractogram of the 

heated sample; at 550 °C, chlorite collapses to one peak 

at this position and kaolinite disappears. Other minerals 

were also determined by using peak positions. A 

subjective ranking by abundance was made based on 

relative peak intensity for minerals other than mixedlayer illite/smectite, and the abundanc~ of these minerals 

was categorized as trace, present, or abundant. 

Interpretations for all of the X-ray patterns are 

shown in the appendix (tables 1-17). The percentage of 

smectite layers in either smectite or mixed-layer illite/-

smectite for each sample and the relative abundance of 

the other minerals in each sample are given. Sample 

elevations are in feet and meters above the base of the 

Brushy Basin Member of the Morrison Formation. A 

brief megascopic description of each sample is also given 

and includes the color and rock type. 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G5 
0 

0 

x 

(/) 

!z 966 

::J 

0 

u 

(/) 

1-

z 

::J 

0 

322 

u 966 

322 

1/S 

16.66 

Glycolated 

Heated 

0~----~~~~~==~~~====~==~~ 

0 10 20 30 40 50 

DEGREES 29 

Figure 3. X-ray diffractograms of highly smectitic mixedlayer clay from Toadlena locality (fig. 1). Note integral 

spacing of reflections. 1/S, illite/smectite; all peaks labeled in 

angstroms. 

RESULTS 

Distribution of Clays 

Our chief interest was the distribution of mixedlayer illite/smectite in ancient Lake T'oo'dichi', which 

includes all of the Brushy Basin Member in New Mexico 

and the upper Brushy Basin Member elsewhere. Smectitic or highly expandable clays predominate in ancient 

Lake T'oo'dichi' at Blue Peak, Capulin Peak, Colorado 

National Monument, Courthouse Draw, Lisbon Valley, 

Montezuma Creek, Sanostee Wash, and Toadlena (figs. 

1, 6-13). At Colorado National Monument and Lisbon 

Valley (figs. 1, 8, 10), the persistence of highly smectitic 

mixed-layer illite/smectite in the uppe; Brushy Basin 

Member contrasts markedly with the more illitic 

(Colorado National Monument) or more variable mixedlayer illite/smectite clays (Lisbon Valley) of the lower 

Brushy Basin Member. Chlorite or kaolinite is in some 

samples and quartz is commonly present in trace 

amounts (appendix). Some localities, such as Blue Peak 

(fig. 6), are dominantly, though not completely, smectitic. 

Clays from Beclabito Dome, Big Gypsum Valley, 

Deadman's Peak, McElmo Canyon, and Oak Springs 

(figs. 1, 14-18) are highly variable from one sample 

G6 Evolution of Sedimentary Basins-San Juan Basin 

(/) 

1-

z 

::J 

0 

u 

(/) 

1-

z 

::J 

0 

u 

Giycolated 

Heated 

0~----~==~~==~~~==~~==~~ 

0 10 20 30. 40 50 

DEGREES 29 

Figure 4. X-ray diffractograms of highly illitic mixed-layer 

clay from Blue Mesa locality (fig. 1). 1/S, illite/smectite; all 

peaks labeled in angstroms. 

horizon to another. At these localities, smectitic mixedlayet: clays are· present, but many tuff beds also contain 

mixed-layer clays having only 10-20 percent smectite 

layers. Chlorite or kaolinite and trace amounts of quartz 

are in most samples from these localities (appendix). 

Figure 5 shows a representative X-ray pattern for a 

sample from the McElmo Canyon locality that contains 

abundant chlorite. 

Clays from Blue Mesa, Durango Hospital, Norwood Hill, and Piedra River are dominantly illitic mixedlayer illite/smectite (figs. 1, 19-22). At all of these 

localities, smectitic mixed-layer illite/smectite is rare to 

absent. At Piedra River, for instance, only 3 of 77 

samples ·contain a highly smectitic mixed-layer clay (fig. 

22). Chlorite is present in almost all of the samples from 

the four localities; a few samples contain kaolinite (see 

appendix). The samples also contain trace amounts. of 

quartz. 

Discussion 

The distribution of mixed-layer illite/smectite clays 

with respect to the outline of ancient Lake T'oo'dichi' as 

shown in figure 1 reveals a significant basinward trend. 

That part of the Brushy Basin Member deposited in the 

outer part of the saline, alkaline lake contains 
Glycolated 

20 30 

DEGREES 29 

Figure 5. X-ray diffractograms of chlorite-rich sample 

from McEimo Canyon locality. Chi, chlorite; 1/S, illite/smectite; Qtz, quartz; all peaks labeled in angstroms. 

predominantly smectitic clays (figs. 6-13), wJllheas the 

part deposited in the inner part of the lake contains 

predominantly illitic clays (figs. 19-22). Between these 

two zones, mixed-layer illite/smectite varies greatly (figs. 

14-18). 

A detrital origin for the illitic mixed-layer clays in 

Lake T'oo'dichi' can be ruled out. (1) Thednajotity of 

beds sampled are tuff beds, which frequently contain 

volcanic ash of airfall origin and little admixed detrital 

material. (2) If a detrital illite component had been 

added to the airfall material, it would necessarily have 

crossed the smectitic zone in transit; the absence of illitic 

clays in the smectite zone around the outer margins of 

the lake system precludes a detrital origin for the illitic 

clays farther basinward. 

The Gulf Coast model for illitizatibn-illitization 

by progressive burial and attendant heating-also cannot 

be applied to the Brushy Basin Member because it does 

not explain the interbedding of tuff beds that contain 

variable compositions of mixed-layer clays, from almost 

pure smectite to almost pure illite, over vertical distances 

on the order of a few meters or less. Examples of this 

vertical variability are at the Beclabito Dome, Big Gypsum 

Valley and Deadman's Peak localities. These patterns 

cannot be explained by the Gulf Coast model because 

adjacent beds would undoubtedly have experienced a 

similar burial and thermal historf. Localized pbtential 

75r-------------------------------------~ 

a: 

w 

Ql 

~ 

~ 60 

2 

Ui 

<( 

Ql 

>- il5 45 

:::> 

a: 

Ql 

u. 

0 

w 

~ 30 Ql 

w 

> 

0 

Ql 

<( 

ti:i 15 w 

u. 

0~----~------~------~------~------~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 6. Amount of smectite in some mixed-layer clays in 

samples from Blue Peak locality (fig. 1). Complete set of data 

in appendix (table 4). 

240.----------------------. 

ffi B~r~c:!~o~~~~l~!_ ___ ------ _ 

~ 200 Brushy Basin Member w 

~ 

z 

Ci) 

~ 160 

~ II) 

:::> 

a: 

Ql 120 LL. 

0 

w 

II) 

<( 

Ql 

~ Ql 

<( 

.... 

80 

lli 40 LL. 

o~---~---~---~---~--~ 0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 7. Amount of smectite in some mixed-layer clays in 

samples from Capulin Peak locality (fig. 1). Complete set of 

data in appendix (table 5). 

heat sources also cannot explain the observed vertical 

variation in clay distribution. 

The distribution of mixed-layer clays in Lake 

T'oo'dichi' is similar to that reported in similar 

depositional environments and probably reflects the 

pore-water chemistry at the time of diagenesis in the 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G7 
340r---------------------------------~----~ 

320 

. ffi 300 

CD 

-~ 280 UJ 

~ 260 

z 

Vi 240 <t' 

CD 220 >- Vi 200 

=> 

~ 180 

l:) 160 

~ 140 <t' 

CD 120 UJ 6 100 CD 

<t' 80 1-

. ttl 60 ~ 

40 

20 

Upper part of the Brushy Basin Member 

------------------------------------- Lower part ·of the Brushy Basin Member 

o~------~------~------~------~------~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 8. Amount of smectite in some mixed-layer clays in 

samples from Colorado National Monument locality (fig. 1 ). 

Complete set of data in appendix (table 6). Note· dramatic 

difference between the amount of smectite in mixed-layer 

clays in the lower and upper parts of the Brushy Basin 

Member. 

300 r--------------------"--------------------

a: 

UJ 

CD 

::2: 

UJ 240 ~ 

z 

Vi 

<t' 

CD 

>-

:I: 180 '(/) 

=> 

a: ~ CD 

u. 

0 ~ 

UJ 

(/) 120 '<t' 

CD 

UJ 

> 

0 

CD 

<( 

I- 60 UJ 

UJ 

u. 

0 

0 2Q 40 60 80 100 

PERCENT.SMECTITE IN ILLITE/SMECTITE 

Figure 9. Amount of smectite in some mixed-layer clays in 

samples from Courthouse Draw locality (fig. 1). Complete set 

of data in appendix (table 7). 

lacustrine sediments. In studies of Jake deposits in the 

Green River Formation, Surdani and Parker (1972) 

observed that montmorillonite (smectite) is associated 

with units interpreted to have been deposited in relatively 

Ga Evolution of Sedimentary Baslns·-san Juan Basin 

400r---------------------------------------~ 

ffi -"' _ ----- ___ .: __ . ..:§~!~~ £'!.f!'(q~X~r_r!_l~!i~_!l_? _______ -------------- co 

~ 320 

::2:. 

z· 

~ ~ 

?c 240 3· Upper part of the Brushy Basin Member 

a:. 

CD 

u. 

o: 

~ 160 " <t' 

CO· 

UJ 

> 

0 

co 

<t' 

I- 80 UJ 

UJ 

u. 

0~------~------~------~------~------~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 10. Amount of smectite in some mixed-layer clays in 

samples from Lisbon Valley locality (fig. 1). Complete set of 

data in appendix (table 10). Note dramatic difference between 

the amount of smectite in mixed..-layer clays in both lower part 

of Brushy Basin Member and Lower Cretaceous Burro Canyon 

Formation, and the upper part of Brushy Basin Member. 

a: 

UJ 

co 

::2: 

UJ 280. Brushy Basin Member 

::2: 

z 

Vi 

<t' 

co 

>- :I: 210 (/) .... r ·,. 

=> 

a: 

co 

u. 

0 

UJ 

(/) 140 <t' 

CD 

UJ 

> 

0 

CD 

<( 

._:.. 70 UJ 

UJ 

u. 

0 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILUTE/SM_ECTITE 

Figure 11. Amount of smectite in some mixed-layer clays in 

samples from Montezuma Creek locality (fig. 1). Complete set 

of data in appendix (table 12). 

fresh water, an observation consistent with what we 

observe in the Brushy Basin Member. Smectite occurs in 

tuff beds around the outer edge of ancient Lake 

T'oo'dichi', an area where there would have been an 
125 

a: .j w 

CXl 

~ 100 ~ 

z 

u; 

~ ~ CXl 

> 

::t 75 en 

::> 

a: 

CXl 

u. 

0 

w 

en 50 ~ 

CXl ~ 

w ~ 

> 0 

CXl 

~ 

1- 25 w 

w 

u. 

o~---~---~---~---~---~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 12. Amount of smectite in some mixed-layer clays in 

samples from Sanostee Wash locality (fig. 1). Complete set of 

data in' appendix (table 16). 

160.-------------------------, 

a: 

w 

CXl 

~ 

w 

~ 120 z 

~ CXl 

> 

::t 

en 

::> 

a: 

CXl 80 u. 

0 

w 

~ CXl 

~ o· 

~ 40 

1-

w 

w 

u. 

o~---~---~---~---~~---~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 13. Amount of smectite in some mixed-layer clays in 

samples from Toadlena locality (fig. 1). Complete set of data in 

appendix (table 17). 

influx of fresh water. The illite in the center of Lake 

T'oo'dichi' probably· reflects the more saline, alkaline 

porewater in the center of the lake. Singer and Stoffers 

(1980) examined mixed-layer illite/smectite clays in~ two 

cores from two saline lakes in Africa and observed a 

similar pattern. 

200.---------------------------, 

a: 

w 

CXl 

~ 

w 

~ 

I 

160 · __ -~~~r_o_~!_n_Y_C:~ _F_?_r~~~~~ ~ ______________________ -,- __________ _ 

z Brushy Basin Member 

U5 

~ 

CXl 

> 

::t 

en 120 

::> 

a: 

CXl 

u. 

0 

w 

en 

~ 80 

CXl 

w 

> 0 

CXl 

~ 

1-

w 40 w 

u. 

0~---~---~---~----~---~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 14. Amount of smectite in some. mixed-layer clays in 

samples from Beclabito Dome locality (fig. 1). Complete set of 

data in appendix (table 1). 

40Qr-----------------...-----=-=-e 

a: 

w 

CXl 

~ ro _.-------~--------.,------__;;:::::::..e_ 

CXl 

> 

~ 240 ::> 

a: 

CXl 

u. 

0 

w 

~ 160 CXl 

w 

> 0 

CXl 

~ 

t;J 80 w 

u. 

-

Up'per part of the 

Brushy Basin Member 

Lower part of the 

Brushy Basin Member 

o~---~----~----~----~---~ 

0 20 40 • 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 15. Amount of smectite in ·some mixed-layer clays ih 

samples from Big Gypsum Valley.locality (fig. 1). Complete set 

of data in appendix (table 2). 

CONCLUSIONS 

The distribution of mixed-layer illite/smectite ·in 

tuffaceou·s beds of ancient Lake T'oo'dichi', a large 

saline, alkaline lake 'complex in the Brushy Basin 

Member of the Upper Jurassic Morrison Formation, can 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G9 
240 

a: 

UJ 

CD 

~ 200 UJ 

~ 

z 

U5 

<( 

CD 160 

>- I 

en 

::::> 

a: 

CD 120 u. 

0 

UJ 

en 

<( 

CD 

UJ 80 > 0 

CD 

<( 

IUJ 

UJ 40 u. 

0 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 16. Amount of smectite in some mixed-layer clays in 

' samples from Deadman's Peak locality (fig. 1). Complete set of 

data in appendix (table 8). 

30 

a: 

UJ 

CD 

~ 

UJ 

~ 

z 

U5 

<( 20 CD 

>- I 

en 

::::> 

a: 

CD 

u. 

0 

UJ 

en 

<( 

CD 

UJ 10 > 

0 

CD 

<( 

IUJ 

UJ 

u. 

o~~----~------~------~------~------~ 

0 20 40 60 80 100 . PERCENT SMECTITE 'IN ILLITE/SMECTITE 

Figure 17. Amount of smectite in some mixed-layer clays in 

samples from McEimo Canyon locality (fig. 1). Complete set of 

data in appendix (table 11). 

more readily be attributed to changes in pore-water 

chemistry than to any other factor. We can rule out other 

possible explanations, such as the introduction of detrital 

illite or the conversion of smectite to illite with increasing 

temperature associated . with buriaL The trend of 

G10 Evolution of Sedimentary Basins-San Juan Basin 

200.---------------------------------------~ 

a: 

UJ 

CD 

~ 160 , ~ 

z 

U5 

<( 

CD 

>- I 120 en 

::::> 

a: 

CD 

u. 

0 

UJ 

~ 80 

CD 

UJ 

> 

0 

CD 

<( 

tu 40 UJ 

u. 

0~------~------~~----~------~------~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 18. Amount of smectite in some mixed-layer clays in 

samples from O~k Springs locality (fig. 1). Complete set of 

da~a in appendix (table 14). 

360 .. --------------------------------------~ 

a: 

UJ 

~ 300 UJ 

~ 

z 

U5 

<( 

CD 

>- I 

en 

::::> 

a: 

CD 

u. 

0 

UJ 

en 

<( 

CD 

UJ 120 > 

0 

CD 

<( 

1--

t!j' 60 u. 

Upper P<!rt of the Brushy Basiri Member 

Lower part of the Brushy Basin Member 

0~------~------~------~------~------~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 19. Amount of smectite in some mixed-layer clays in 

samples from Blue Mesa locality (fig. 1 ). Complete set of data 

in aRpendix (table 3). 

increasingly illitic . clays toward the center of Lake 

T'?o'dichi' coincjdes with the hydrogeochemical gradient 

of incre~sin~ salinity and alkalinity associated with the 

lake. Thus, pore-water chemistry, rather than increased 

temperature associated with increased depth of burial, 
120 

a: 

w 

~ 100 

w 

~ 

z 

u; 

<x: 80 cc 

>- ::J: 

(/) 

:::> 

a: 

cc 60 LL 

0 

w 

(/) 

<x: 

cc 

w 40 

> 0 

cc 

<x: 

1-

w 

w 20 LL 

0 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 20. Amount of smectite in some mixed-layer clays in 

samples from Durango Hospital locality (fig. 1). Complete set 

of data in appendix (table 9). 

3so.-----------------------, 

a: 

~ 300 

~ 

w 

~ 

z 250 

~ cc 

>-

::J: 

~ 200 

a: 

cc 

LL 

0 

w 150 

~ Upper part of the Brushy Basin Member cc --------- --,..----------------------------------------------- w Lower part of the Brushy Basin Member 

~ 100 cc 

<x: 

1-

w 

w 

LL 50 

oL----~---~----~---~---~ 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 21. Amount of smectite in some mixed-layer clays in 

samples from Norwood Hill locality (fig. 1). Complete set of 

data in appendix (table 13). 

was probably the more critical factor in controlling clay 

composition. The results of this study demonstrate 

formation of low-temperature illite in a saline, alkaline 

lake environment. Additional studies, including radiometric dating of the clays, are currently underway to test 

this conclusion. 

350 

a: 

~ 300 

~ 

w 

~ 

~ 250 

<x: 

cc 

>- ::J: 

~ 200 

a: 

cc 

LL 

0 

w 150 (/) 

<x: 

cc 

w 

~ 100 cc 

<x: 

1-

w 

w 

LL 50 

0 

0 20 40 60 80 100 

PERCENT SMECTITE IN ILLITE/SMECTITE 

Figure 22. Amount of smectite in some mixed-layer clays in 

samples from Piedra River locality (fig. 1). Note that only 3 of 

77 samples contain highly smectitic mixed-layer clays. 

Complete set of data in appendix (table 15). 

REFERENCES CITED 

Bell, T.E., 1986, Deposition and diagenesis in the Brushy Basin 

and upper part of the Westwater Canyon Members of the 

Morrison Formation, San Juan basin, New Mexico, in 

Turner-Peterson, C.E., Santos, E.S., and Fishman, N.S., 

eds., A basin analysis case study; the Morrison 

Formation, Grants uranium region, New Mexico: 

American Association of Petroleum Geologists Studies 

in Geology 22, p. 77-92. 

Brown, G., and Brindley, G.W., 1980, X-ray diffraction 

procedures for clay mineral identification, in Brindley, 

G.W., and Brown, G., eds., Crystal structures of clay 

minerals and their X-ray identification: Mineralogical 

Society of London, p. 305-359. 

Burst, J.F., 1969, Diagenesis of Gulf Coast clayey sediments 

and its possible relation to petroleum migration: 

American Association of Petroleum Geologists Bulletin, 

v. 53, p. 73-93. 

Drever, J.l., 1973, The preparation of oriented clay mineral 

specimens for X-ray diffraction analysis by a filtermembrane peel technique: American Mineralogist, v. 58, 

p. 553-554. 

Fishman, N.S., Turner-Peterson, C.E., and Hay, R.L., 1986, 

Authigenic albite in the Morrison Formation; evidence 

for early diagenetic formation: Society of Economic 

Paleontologists and Mineralogists Midyear Meeting, 

Abstracts with Program, p. 3 7. 

Freed, R.L., 1980, Shale mineralogy of the No. 1 Pleasant 

Bayou geothermal test well; a progress report: 

Geopressured-Geothermal Energy Conference, 

University of Texas, 4th, Austin, Tex., Proceedings, 

p. 153-165. 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G11 
Gautier, D.L., Kharaka, Y.K., and Surdam, R.c.; 1985, 

Relationship of organic matter and mineral diagenesis: 

Society of Economic Paleontologists and Mineralogists 

Short Course 17, 247 p. 

Gregory, H.E., 1938, The San Juan country: U.S. Geological 

Survey Professional Paper 188, 123 p. 

Hower, John, Eslinger, E., Hower, M., and Periy, E.A., 1976, 

Mechanism of burial metamorphism of argillaceous 

sediments; I, mineralogical and chemical evidence: 

Geological Society of America Bulletin, v. 87, 

p. 725-737. 

Johnston, R.M., and Miller, H.G., 1984, The effect of pH on the 

stability of smectite: Atomic Energy of Canada Limited, 

AECL-8366, 45 p. 

Keller, W.D., 1962, Clay minerals in the Morrison Formation of 

the Colorado Plateau: U.S. Geological Survey Bulletin 

1150, 90 p. 

Milliken, K.L., Land, L.S., and Loucks, R.G., 1981, History of 

burial diagenesis determined from isotopic geochemistry, 

Frio Formation, Brazoria County, Texas: American 

Association of Petroleum Geologists Bulletin, v. 47, 

p. 1199-1218. 

Pollastro, R.M., 1982, A recommended procedure for the 

preparation of oriented clay-mineral specimens for X-ray 

diffraction analysis; modifications to Drever's filter 

membrane peel technique: U.S. Geological Survey 

Open-File Report 82-71, 10 p. 

Pollastro, R.M., and Scholle, P.A., 1986, Diagenetic· 

relationships in a hydrocarbon-productive chalk; the 

G12 Evolution of Sedimentary Basins-San Juan Basin 

Cr~taceous Niobrara Formation, in Mumpton, F.A., ed., 

Studies in diagenesis: U.S. Geological Survey Bulletin 

1578, p. 219-236. 

Reynolds, R.C., 1980, Interstratified clay minerals, in Brindley, 

G.W., and J;3rown, G. eds., Crystal structures of clay 

minerals and their X-ray identification: Mineralogical 

Society of London, p. 249-303. 

Singer, A., and Stoffers, P., 1980, Clay mineral diagenesis in two 

East African lake sediments: Clay Minerals, v. 15, 

p. 291-307. 

Srodon, Jan, 1980, Precise identification of illite/smectite interstratifications by X-ray powder diffraction: Clays and 

Clay Minerals, v. 28, p. 401-411. 

Surdam, R.C., and Parker, R.D., 1972, Authigenic aluminosilicate minerals in the tuffaceous rocks of the Green 

River Formation, Wyoming: Geological Society of 

America 1,3ulletin, v. 83, p. 689-700. 

Turner-Peterson, C.E., 1987, Sedimentology of the Westwater 

Canyon and Brushy Basin Members of the Morrison 

Formation, Colorado Plateau, and relationship to 

uranium mineralization: Boulder, University of 

Colorado, Ph.D. thesis, 169 p. 

Turner-Peterson, C.E., Fishman, N. S., and Hay, R.L., 1986, 

Recognition of an extensive Jurassic playa-lake complex; 

the Brushy Basin Member of the Morrison Formation, 

Colorado Plateau: Society of Economic Paleontologists 

and Mineralogists Midyear Meeting, Abstracts with 

Program, p. 111. 
APPENDIX 
Table 1. X-ray identification of <0.5-Jlm fraction, Beclabito Dome 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) M~asco~ic descri~tion smectite Other minerals 

Brushx Basin Member 

2 10 3.0 Green tuff 80 Chlorite-trace to present 

3 27 8.2 Green tuff 90-100 Chlorite-present 

4 33 10.0 Green tuff 100 Chlorite-present to abundant; quartz-trace 

5 34 10.4 Green tuff 10-20 Chlorite-abundant to present; quartz-trace 

6 50 15.2 Green tuff 10-20 Chlorite-abundant to present; quartz-trace 

7 54 16.5 Green tuff 20-30 Chlorite-present; quartz-trace 

8 59 18.0 Green tuff 20-30 Chlorite-present to abundant; quartz-trace 

10 65 19.8 Green tuff 20-25 Chlorite-present to abundant; quartz-trace 

11 66 20.1 Green tuff 10-20 Chlorite-present; quartz-trace? 

12 70 21.3 Green tuff 10-20 Chlorite/kaolinite?-present; quartz-trace 

13 94 28.6 Green tuff 80-90 Chlorite-present; quartz-trace; mica/feldspar? 

14 110 33.5 Green tuff 80 (1 peak) Chlorite-present to abundant; quartz-trace 

15 113 34.4 Green tuff =75 Chlorite-present; quartz-trace 

16 114 34.8 Green tuff 40-50 Chlorite-present 

17 117 35.7 Green tuff =70 {1 Eeakl Chlorite-trace 

Burro Canxon Formation? 

18 162 49.4 Brown mudstone 30-40 None observed 

20 176 53.6 White claxstone 30-40 None observed 

G14 Evolution of Sedimentary Basins-San Juan Basin 
Table 2. X-ray identification of <0.5-JJ.m fraction, Big Gypsum Valley 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) M~ascoEic descriEtion smectite Other minerals 

Lower Eart of Brush):: Basin Member 

4 107 32.6 Green claystone 0-10 Chlorite-present 

5 117 35.7 Green mudstone -=50 (1 peak) Chlorite-present 

7 144 43.9 Green mudstone 0-10 Chlorite ?-present 

8 153 46.6 Green mudstone 70-80 (1 peak) Chlorite-Eresent; guartz-trace 

UEEer Eart of the Brush):: Basin Member 

9 161 49.1 Blue tuff 0-10 Chlorite-present; quartz-trace 

10 172 52.4 Pink tuff 60-70 (1 peak) None observed 

11 175 52.4 Green tuff 100 Chlorite-present to abundant 

13 180 54.9 Green mudstone 50 (1 peak) None observed 

14 182 55.5 Green mudstone 60-70 Chlorite-trace 

15 188 57.3 Mottled red/green mudstone -=50 Chlorite-present 

16 196 57.3 Green claystone 70-80 (1 peak) Chlorite-present to abundant 

17 198 60.4 Green tuff 70 (1 peak) Chlorite-present; quartz-trace 

18 200 61.0 Green claystone -=50 None observed 

19 206 62.8 Green tuff 60-70 (1 peak) Chlorite to abundant 

21 217 66.1 Green tuff 70-80 (1 peak) Chlorite-present to abundant; quartz-trace 

22 224 68.3 Green tuff 0-10 Chlorite-trace; quartz-trace 

25 251 76.5 White tuff 60-70 None observed 

26 253 77.1 Red tuff 50-60 1 peak) None observed 

27 260 79.3 Gray tuff 50-60 Chlorite-trace 

28 262 79.9 Gray tuff 60-70 None observed 

29 265 80.8 Brown claystone 30-40 Quartz-trace 

33 295 89.9 Green tuff 70-80 (1 peak) Chlorite-present; quartz-trace 

34 299 91.1 Blue tuff 70-80 (1 peak) Chlorite-present; quartz-trace 

35 310 94.5 Orange tuff 70-80 (1 peak) Chlorite-present; quartz-trace 

36 311 94.8 Green tuff 0-10 Chlorite-present 

37 312 95.1 Green tuff 90-100 (1 peak) Chlorite-present to abundant; quartz-trace 

39 321 97.8 Orange tuff 80-90 None observed 

40 326 99.4 Green tuff 60-70 (1 peak) Chlorite?-trace; quartz-trace 

41 330 100.6 Green tuff 80 (1 peak) Chlorite-present; quartz-trace 

42 332 101.2 Green tuff 80-90 (1 peak) Chlorite-present 

43 334 101.8 Orange tuff 70-80 (1 peak) Chlorite-present; quartz-trace 

44 340 103.6 Blue tuff 0-10 Chlorite-present to abundant; quartz-trace 

47 346 105.5 Blue tuff 0 Chlorite-present to abundant 

48 349 106.4 Green tuff 90-100 Chlorite-present 

49 352 107.3 Green tuff 80-90 (1 peak) Chlorite-trace; quartz-trace 

50 354 107.9 Green tuff 100 (1 peak) Chlorite-present to abundant 

51 356 108.5 Orange tuff 60 (1 peak) Chlorite-present; quartz-trace 

52 359 109.4 Brown mudstone 60-70 (1 peak) Chlorite-present; quartz-trace 

53 363 110.6 Brown tuff 70-80 Chlorite-present; quartz-trace 

54 367 111.9 Brown tuff 10-20 Kaolinite?-trace to present 

55 380 115.8 Orange tuff 70-80 (1 peak) Chlorite-trace; quartz-trace 

56 387 118.0 Blue tuff 70-80 Quartz-trace 

57 399 121.6 Blue tuff 100 Quartz-trace 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G15 
Table 3. X-ray identification of <0.5-J.Lm fraction, Blue Mesa 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation 

no. (ft) (m) 

2+14 14 

3+19 44 

5+32 100 

10+3 169 

10+13 179 

10+25 191 

10+28 194 

10+30 196 

12+12 224 

12+14 226 

12+76 288 

14+17 328 

4.3 

13.4 

30.5 

51.5 

54.6' 

58.2 

59.2 

59.7 

68.3 

68.9 

87.8 

100.0 

Percent 

Megascopic description smectite · · Other minerals 

Lower part of the Brushy Basin Member 

Red mudstone 

Gray-green mudstone 

Red mudstone 

20-30 None observed 

= 70 Chlorite-abundant; quartz-trace 

=10 Chlorite-trace; quartz-trace; feldspar?-trace 

Upper part of the Brushy Basin Member 

Green mudstone 

Green tuff 

Blue tuff . 

Blue-green tuff· 

Blue-green tuff 

Green tuff 

Green tuff 

Green tuff 

Green tuff 

10-20 Chlorite-trace; quartz-trace 

0 None observed · 

0-10 None observed : 

0-10 Chlorite-trace; quartz-trace 

10-20 Chlorite-present; quartz-trace 

0-10 Chlorite-trace; quartz-trace? 

0 Chlorite-present 

0-10 (1 peak) None observed 

10-20 Quartz-trace? 

Table 4. X-ray identification of <0.5-J.Lm fraction, Blue Peak 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?) indicates 

identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) ·Megascopic description smectite Other minerals 

1 5 1.5 Green mudstone 90-100 None observed 

2 7 2.1 Green mudstone 100 None observed 

3 10 3.0 Green mudstone 100 None observed 

4 13 4.0 Green mudstone 100 Chlorite-present 

5 15 4.6 Green mudstone 40-50 None observed 

6 16 4.9 Green mudstone 80 None observed 

7 18 5.5 Red mudstone =95 None observed 

8 -21 6.4 Green mudstone =30 None observed' 

9 25 7:6 Green mudstone 60-70 None observed 

10 28 8.5 Green mudstone 90-100 Chlorite/kaolinite? -trace 

11 34 10.4 Green claystone 100 None observed 

12 35 10.7 Green claystone 100 None observed 

13 37 11.3 Green claystone 90-100 None observed 

14 42 12.8 Green claystone 100 None observed 

15 44 13.4 Green claystone 100 None observed 

16 46 14.0 Green mudstone 100 None observed 

17 48 14.6 Yellow claystone =90 None observed 

18 51 15.5 Green mudstone 100 None observed 

19 53 16.2 Green mudstone 100 None observed 

20 58 17.7 Green claystone 90-100 None observed 

21 60 18.3 Green mudstone 100 None observed 

22 66 20.1 Green claystone 100 None observed 

23 71 21.6 Green claystone 80-90 None observed 

G16 Evolution of Sedimentary. Basins-San Juan Basin 
Table 5. X-ray identification of <0.5-J.Lm fr~ction, Capulin Peak 

[Locality shown in fig. 1. Elev~tion is height above base of Brushy Basin Member. Query (?)indicate~ identificati~ uncertain] 

Sample Elevation Percent 

no. (ft} (m) M~ascoeic descrietion smectite Other minerals 

Brushy Basin Member 

1 30 9.1 Orange tuff 90-100 Chlorite? -trace; quartz-trace 

2 31 9.4 Green claystone 60-70 Mica? 

3 33 10.1 Orange tuff =60 Kaolinite-present 

4 58 17.7 Green tuff 90-100 Kaolinite?-trace; mica? 

5 64 19.5 Orange tuff 90-100 Kaolinite-t.Tace; quartz-trace; clinoptilolite?-trace 

6 67 20.4 Orange tuff =60 Kaolinite-trace; quartz-trace; clinoptilolite?-trace 

7 69 21.0 Gray tuff 70-80 (1 peak) Clinoptilolite? -present 

8 71 21.6 Brown claystone =60 Quartz-trace 

9 82 25.0 Orange tUff . 80-90 (1 peak) Kaolinite-present; clinoptilolite? -present 

10 85 25.9 Orange tuff 50-60 Kaolinite-trace; quartz-trace 

11 92 28.0 Orange tuff 50-60 (1 peak) Clinoptilolite? -trace 

12 96 29.3 Orange tuff . 80-90 (1 peak) Kaolinite-present; clinoptilolite? 

13 108 32.9 Orange tuff 80-90 Kaolinite-present 

15 137 41.8 Yellow claystone =100 None observed 

16 142 43.3 Green tuff' =100 Kaolinite-present; mica?-trace; quartz-trace 

17 167 50.9 Orange tuff =70 (1 peak) Kaolinite-abundant; quartz-trace 

18 191 58.2 Yellow claystone 100 kaolinite-abundant-present 

19 196 59.7 Green mudstone 100 Kaolinite-abundant 

20 200 61.0 Gray mudstone 100 Kaolinite-eresent to abundanti guartz-trace 

Burro Canyon Fonnation? 

21 212 64.6 Green mudstone =40 Kaolinite-abundant; quartz-trace to present 

23 218 66.4 Green tuff 100 Kaolinite-abundant; guartz-trace to eresent 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G17 
Table 6. X-ray identification of <0.5-J.l.m fraction, Colorado National Monument 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) Megasco~ic descri~tion smectite Other minerals 

Lower ~rt of the Brushx Basin Member 

1 10 3.0 Red mudstone 0-10 None observed 

2 35 .10.7 Red mudstone 10-20 None observed 

3 58 17.7 Red claystone 20-30 None observed 

4 63 19.2 Red mudstone 10-20 None observed 

6 94 28.6 Brown mudstone 10-20 (1 peak) Chlorite-trace 

7 112 34.1 Brown mudstone 10-20 Quartz-trace 

U~q~art of the Brushx Basin Member 

8 128 39.0 Green mudstone 90-100 Mica/feldspar?-trace 

9 131 39.9 Green mudstone -=100 None observed 

10 141 43.0 Green mudstone 80-90 None observed 

12 149 45.4 Green mudstone 100 None observed 

13 162 49.4 Green mudstone -=90 None observed 

14 167 50.9 Green mudstone -=90 Quartz-trace 

16 179 54.6 Green mudstone 90-100 None observed 

18 193 58.8 Green mudstone 90 None observed 

19 204 62.2 Yellow claystone 90-100 None observed 

20 218 66.5 Gray mudstone 90-100 None observed 

21 227 69.2 Brown mudstone 100 Mica? -trace 

22 238 72.5 Green mudston~ 100 None observed 

23 243 74.1 Green mudstone 100 None observed 

24 253 77.1 Yellow claystone 90-100 None observed 

25 255 77.7 Green tuff? 90-100 Chlorite-present; quartz-trace 

26 260 79.2 Green claystone 90 None observed 

28 267 81.4 Brown mudstone 100 None observed 

29 278 84.7 Green tuff 100 None observed 

30 280 85.3 Green claystone 100 None observed 

31 281 85.6 Blue tuff 100 (1 peak) Kaolinite-present 

32 286 87.2 Brown tuft 100 Chlorite-present to abundant; quartz-trace 

33 287 87.5 Green claystone 90-100 None observed 

34 289 88.1 Purple tuff 90-100 None observed 

35 296 90.2 Green claystone 90-100 None observed 

36 308 93.9 Blue tuff 90-100 Kaolinite/chlorite?-present to trace 

37 314 95.7 Green claystone 100 Kaolinite-trace; quartz-present; mica? 

38 320 97.5 Brown mudstone 60 (1 peak) Chlorite-present to abundant 

39 332 101.2 Green mudstone 100 None observed 

Table 7. X-ray identification of <0.5-J.l.m fraction, Courthouse· Draw 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample 

no. 

5+19A 

5+41 

5+179 

Elevation 

(ft) (m) 

138 42.1 

160 48.8 

298 90.8 

Megascopic 

descri~tion 

Orange tuff 

Orange tuff 

Green tuff 

Percent 

smectite 

90-100 

90-100 

100 

G18 Evolution of Sedimentary Basins-San Juan Basin 

Other minerals 

Clinoptilolite/mica? -present; quartz-trace; chlorite/kaolinite? -trace 

Clinoptilolite?-trace to present; quartz-trace 

Mica?-present 
Table 8. X-ray identification of <0.5-~m fraction, Deadman's Peak 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) Megasco~ic descri~tion smectite Other minerals 

2 7 2.1 Green tuff 60-70 (1 peak) Chlorite-present 

3 10 3.0 Brown tuff =80 (1 peak) Chlorite-trace; quartz-trace 

6 16 4.9 Green tuff 10-20 Chlorite-trace 

8 23 7.0 Green tuff 70-80 (1 peak) Kaolinite-present to trace 

13 41 12.5 Green tuff 80-90 (1 peak) Kaolinite 1 -trace; quartz-trace 

14 45 13.7 Green tuff =70 (1 peak) Kaolinite-trace; quartz-trace 

17 89 27.1 Green tuff 20-30 Chlorite-trace; quartz-trace 

19 106 32.3 Green tuff =80 (1 peak) Kaolinite-trace; quartz-trace 

21 108 32.9 Green tuff 30-40 (1peak) Chlorite/kaolinite?-present 

23 113 34.4 Green tuff =60 (1 peak) Quartz-trace 

24 116 35.4 Green tuff 80-90 None observed 

25 118 36.0 Orange tuff 10-20 (1 peak) Chlorite-trace; quartz-trace 

30 127 38.7 Green tuff 20-30 (1 peak) Kaolinite-trace; quartz-trace 

33 138 42.1 Green tuff 70-80 (1 peak) Kaolinite-abundant; quartz-trace; mica-trace 

35 144 43.9 Green tuff 10-20 (1 peak) Kaolinite-trace; quartz-trace 

38 157 47.8 Green tuff 10-20 Kaolinite-abundant; quartz-trace 

39 162 49.4 Green tuff 100 Chlorite-abundant; quartz-trace 

43 174 53.0 Green tuff =30 Kaolinite-abundant; quartz-trace 

46 199 60.7 Blue tuff 0-10 Kaolinite-abundant; quartz-trace 

49 209 63.7 Blue tuff 0-10 Kaolinite-present to abundant; quartz-trace 

52 218 66.4 Green tuff 10-20 ~1 Eeak} Kaolinite-Eresent to abundant; guartz-trace 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau. G19 
Table 9. X-ray identification of <0.5-J.Lm fraction, Durango Hospital 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (7) indicates identification uncertain] 

Sam pi~ Elevation Percent 

no. (ft) (m) Megascoeic descrietion smectite Other minerals 

3 24 7.3 Blue tuff 0-10 None observed 

4 25 7.6 Green tuff =10 Quartz-trace 

5 26 7.9 Green tuff 0-10 None observed 

6 27 8.2 Green tuff 0-10 Quartz-trace 

7 28 8.5 Green tuff 0-10 None observed 

8 31 9.4 Blue tuff 10-20 None observed 

9 32 9.8 Green tuff 10-20 None observed 

10 34 10.4 Green tuff =10 (1 peak) Quartz-trace 

11 37 11.3 Green tuff 10-20 Quartz-trace 

12 38 11.6 Green tuff 10-20 None observed 

13 39 11.9 Gray tuff 0-10 Quartz-trace 

14 42 12.8 Blue tuff 10-20 None observed 

15 44 13.4 Brown tuff 10-15 None observed 

16 46 14.0 Brown tuff =10 Chlorite/kaolinite7-trace 

17 47 14.3 Green tuff 10-20 Quartz-trace 

18 49 14.9 Blue tuff 0-10 None observed 

20 52 15.8 Gray tuff 10-20 Kaolinite 7-trace 

21 53 16.2 Green tuff · =10 Chlorite-trace 

22 54 16.5 Green tuff 10-20 None observed 

23 55 16.8 Green tuff 10-20 (1 peak) Quartz-trace 

24 57 17.4 Blue tuff 0-10 None observed 

25 59 18.0 Green tuff 0-10 None observed 

28 74 22.6 Green mudstone 10-20 None observed 

29 77 23.5 Blue tuff =10 Chlorite-trace to present; quartz-trace 

30 79 24.1 Green tuff 10-20 Chlorite 7-trace 

31 80 24.4 Green tuff 10-20 Chlorite-trace; quartz-trace 

32 82 25.0 Green tuff 10-20 Chlorite-present; quartz-trace 

33 85 25.9 Gray tuff 10-20 Quartz-trace 

34 86 26.2 Green tuff 10-20 Chlorite-present to abundant; quartz-trace 

35 88 26.8 Green tuff 10-20 Chlorite-present; quartz-trace 

36 91 27.7 Green tuff 10-20 Chlorite-present; quartz-trace 

37 94 28.6 Blue tuff 10-20 (1 peak) None observed 

38 97 29.6 Blue tuff 10-20 Chlorite-present; quartz-trace 

39 101 30.8 Blue tuff 10-20 Chlorite-present; quartz-trace 

40 102 31.1 Blue tuff .10-20 Chlorite-abundant; quartz-trace 

41 107 32.6 Green tuff 10-20 Chlorite-abundant; quartz-trace 

42 110 33.5 Green tuff 10-20 Chlorite-present; quartz-trace 

43 112 34.1 Blue tuff 10-20 Chlorite 7-trace 

44 113 34.4 Green tuff 10-20 Chlorite-present to abundant 

'45 116 35.4 Blue tuff 10-20 Chlorite-trace to present 

46 117 35.7 Purple tuff 0 Chlorite/kaolinite 7-trace 

47 119 36.3 'Brown tuff 10-20 None observed 

• 

G20 Evolution of Sedimentary Basins-San Juan Basin 
Table 10. X-ray identification of <0.5-~m fraction, Lisbon Valley 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?) indicates identification uncertain] 

Sample Elevation Percent 

no. (ft} (m) Megasco~ic descri~tion smectite Other minerals 

Lower eart of the Brush~ Basin Member 

3 82 25.0 Brown mudstone 60-70 None observed 

6 140 42.7 Brown claystone =10 None observed 

7 148 45.1 Purp claystone 20-30 None observed 

8 156 47.6 Green tuff 100 Quartz-trace 

9 162 49.4 Brown claystone 20-30 None observed 

10 202 61.6 Brown cla~stone 90 None observed 

Ueeer eart of the Brush~ Basin Member 

13 220 67.1 Green tuff 100 None observed 

14 223 68.0 Gray tuff 95-100 None observed 

15 224 68.3 Orange tuff 95-100 None observed 

16 226. 68.9 Green tuff 100 Chlorite-present to abundant; quartz-trace 

18 239 72.8 Orange tuff 90-100 None observed 

19 246 75.0 Brown tuff 90-100 None observed 

20 255 77.7 Green tuff 90-100 None observed 

21 257 78.3 Green tuff 100 Quartz-trace 

22 260 79.2 Green tuff 100 Quartz-trace 

23 262 79.9 Green tuff 100 Quartz-trace 

24 264 80.5 Green tuff 100 None observed 

25 272 82.9 Green tuff 90-100 None observed 

26 275 83.8 Orange tuff 95-100 None observed 

28 294 89.6 Green tuff 100 Quartz-trace 

29 296 90.2 Purple tuff 95-100 None observed 

30 297 90.5 White tuff 90-100 Quartz-trace 

31 304 92.7 Purple tuff 100 Quartz-trace 

32 306 93.3 Purple tuff 100 None observed 

33 310 94.5 Brown mudstone 75-85 None observed 

34 313 95.4 Blue tuff 90-100 Kaolinite?-trace 

Burro Can;ton Fonnation? 

36 352 107.3 Green tuff 100 Kaolinite?-trace; quartz-trace 

37 354 107.9 Brown mudstone 80 Kaolinite/chlorite?-trace 

38 372 113.4 Green mudstone 90-100 None observed 

39 383 116.7 Red cla;tstone 10-20 Kaolinite? -trace 

Table 11. X-ray identification of <0.5-~m fraction, McEimo Canyon 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates amount unknown] 

Sample Elevation Percent 

no. (ft) (m) Megasco~ic descri~tion smectite Other minerals 

1 3 0.9 Green tuff ? None observed 

2 6 1.8 Green tuff ? Chlorite-present 

3 9 2.7 Green tuff 60-70 (1 peak) Chlorite-present; quartz-trace 

4 12 3.7 Green tuff 70-80 (1 peak) Chlorite-abundant; quartz-trace 

5 15 4.6 Green tuff 10-20 (1 peak) Chlorite-present to abundant; quartz-trace 

6 18 5.5 Green tuff 80-90 (1 peak) Chlorite-present; quartz-trace 

7 21 6.4 Green tuff 10-20 (1 peak) Chlorite-present; quartz-trace 

8 24 7.3 Green tuff 80-90 (1 peak) Chlorite-present; quartz-trace 

9 27 8.2 Green tuff 20-30 ~1 ~akl Chlorite-eresent 

X-ray Diffraction Studies of the Morrison Fo.rmation, Colorado Plateau G21 
Table 12. X-ray identification of <0.5-J..Lm fraction, Montezuma Creek 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) MegascoEic descriEtion smectite Other minerals 

Brush~ Basin Member 

2 12 3.7 Green tuff 100 Kaolinite? -trace; quartz-trace 

4 18 5.5 Green tuff 100 Chlorite-trace to present 

6 23 7.0 Green tuff 80-90 None observed 

7 26 7.9 Green tuff 90-100 None observed 

8 28 8.5 Green tuff 100 Chlorite-present 

9 30 9.1 Green tuff 100 Chlorite-present 

10 58 17.7 Orange tuff 90-100 Chlorite-present; quartz-trace; clinoptilolite'l 

11 60 18.3 Green tuff =100 Kaolinite-present 

13 64 19.5 Green tuff 100 Chlorite-trace 

14 66 20.1 Orange tuff 90-100 Chlorite-present 

15 69 21.0 Blue tuff 100 Chlorite-present 

17 75 22.9 Orange tuff 100 Chlorite-present-trace 

18 114 34.8 Green tuff 100 (1 peak) Chlorite-present 

20 121 36.9 Green tuff 100 None observed 

22 126 38.4 Pink tuff 100 Mica?-trace 

23 127 38.7 Green tuff 80 Chlorite-present to abundant 

25 129 39.3 Pink tuff 90-100 None observed 

24 130 39.6 Green tuff 100 Chlorite-trace to present 

26 132 40.2 Pink tuff 100 None observed 

27 134 40.8 Green tuff 100 Chlorite-present 

28 137 41.8 Green tuff 100 Chlorite-present 

29 139 42.4 Green tuff 100 Chlorite-present 

30 142 43.3 Green tuff 100 Chlorite-present to abundant; quartz-trace 

31 144 43.9 Green tuff 100 None observed 

32 146 44.5 Orange tuff 100 None observed 

33 149 45.4 Orange tuff 100 None observed 

34 151 46.0 Green tuff 100 Chlorite-present to trace; quartz-trace 

35 152 46.3 Green tuff 100 None observed 

36 157 47.8 Pink tuff 100 None observed 

37 164 50.0 Green and orange tuff 100 Quartz-trace 

38 166 50.6 Green tuff 100 None observed 

39 168 51.2 Brown tuff 90-100 None observed 

42 176 53.6 Pink tuff 90-100 None observed 

43 179 54.6 White tuff 100 None observed 

44 182 55.5 Purple tuff 100 None observed 

45 190 57.9 Purple tuff 100 None observed 

46 196 59.7 White tuff 90-100 Feldspar? -trace 

47 210 64.0 Purple tuff 100 None observed 

48 216 65.8 Pink tuff 90-100 None observed 

50 222 67.7 Pink tuff 100 None observed 

51 224 68.3 Purple tuff =100 None observed 

52 227 69.2 Pink tuff 80-90 None observed 

54 249 75.9 Green claystone 90-100 None observed 

55 250 76.2 Green tuff 70-80 (1 peak) Chlorite-present 

56 263 80.2 Green tuff 80-90 {1 ~ak} Chlorite-trace to eresent 

Burro Can~on Formation? 

59 344 104.8 Green tuff 30-40 p eeak~ Kaolinite-abundant 

G22 Evolution of Sedimentary Basins-San Juan Basin 
Table 13. X-ray identification of <0.5-J.lm fraction, Norwood Hill 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation Percent 

no. 

2 

4 

7 

12 

18 

19 

20 

21 

22 

23 

24 

25 

26 

28 

29 

31 

34 

36 

37 

38 

40 

41 

42 

43 

44 

45 

47 

48 

49 

50 

51 

52 

54 

55 

57 

(ft) (m) Megasco~ic descri~tion smectite Other minerals 

Lower Eart of the Brushx Basin Member 

25 7.6 Green claystone 10-20 Chlorite-trace 

47 14.3 Green mudstone 10-20 Chlorite-trace 

61 18.6 Red claystone 10-20 Chlorite-present-trace; quartz-trace 

82 25.0 Green claxstone 20-30 Chlorite-Eresent-trace 

UEEer ~rt of the Brushx Basin Member 

158 48.2 Green tuff =10 Chlorite-present; quartz-trace 

159 48.5 Green claystone =10 Chlorite-present 

160 48.8 Green tuff 10-20 Chlorite-present 

161 49.1 Green tuff 0-10 Chlorite-present; quartz-trace 

163 49.7 Green tuff 0 Chlorite-present to abundant 

164 50.0 Green claystone =20 None observed 

165 50.3 Green tuff 10-20 (1 peak) Chlorite-present to abundant 

167 50.9 Green tuff 10-20 Kaolinite?-present to abundant 

168 51.2 Green tuff 20-30 Chlorite-abundant; quartz-trace 

171 52.1 Orange tuff =30 Quartz-trace 

173 52.7 Green tuff 20-30 Chlorite-present; quartz-trace 

185 56.4 Brown claystone =20 Chlorite-present 

205 62.5 Green tuff 20-30 Chlorite-trace to present; quartz-trace 

207 63.1 Green tuff 10-20 Chlorite-trace to present; quartz-trace 

209 63.7 Green tuff 10-20 Chlorite-trace; quartz-trace 

211 64.3 Brown tuff =20? Chlorite-trace; quartz-trace 

215 65.5 Blue tuff 10-20 .Chlorite-present; quartz-trace 

216 65.8 Blue tuff 20-30 Chlorite-trace to present; quartz-trace 

218 66.4 Green tuff =30 Chlorite-trace to present; quartz-trace 

226 68.9 Green tuff 20-30 Quartz-trace 

234 71.3 Brown tuff 10-20 Chlorite-present; quartz-trace 

239 72.8 Green tuff 10-20 Chlorite-abundant; quartz-trace 

245 74.7 Green tuff 10-20 Chlorite-present; quartz-trace 

248 75.6 Green mudstone =10 Chlorite-trace to present; quartz-trace 

261 79.6 Green tuff 10-20 Chlorite-abundant; quartz-trace 

265 80.8 Green tuff 40-50 Chlorite-present to abundant, quartz-trace 

279 85.0 Green tuff 10-20 'Chlorite-present; quartz-trace 

281 85.6 Green tuff 10-20 Chlorite-trace; quartz-trace 

283 86.3 Green tuff 20-30 Chlorite-abundant; quartz-trace 

298 90.8 Green tuff =20 Chlorite-abundant; quartz-trace 

325 99.1 Green tuff 10-20 Kaolinite?-Eresent; guartz-trace 

Table 14. X-ray identification of <0.5-J.lm fraction, Oak Springs 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query(?) indicates identification 

uncertain] 

Sample Elevation Percent 

no. (ft) (m) Megasco~ic descrietion smectite Other minerals 

3 55 16.8 Green tuff =20 (1 peak) Chlorite-abundant 

4 94 28.6 Orange tuff =90 None observed 

5 103 31.4 Orange tuff 90-100 None observed 

6 109 33.2 Orange tuff 100 None observed 

7 111 33.8 Green/orange tuff 90-100 Kaolinite? -trace 

8 112 34.1 Green tuff 70-80 Chlorite-present; quartz-trace 

9 126 38.4 Green tuff 30-40 (1 peak) Quartz-trace 

10 134 40.8 Orange tuff 90-100 None observed 

12 148 45.1 Green tuff 80-90 Chlorite-abundant 

13 151 46.0 Pink tuff 90-100 None observed 

15 152 46.3 Pink tuff 100 None observed 

17 153 46.6 Pink tuff 90-100 None observed 

19 155 47.2 Gray tuff =60 Chlorite-present; quartz-trace 

20 156 47.6 Gray tuff 100 None observed 

21 187 57.0 Green tuff =60 Chlorite/kaolinite?-trace 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G23 
Table 15. X-ray identification of <0.5-J..Lm fraction, Piedra River 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (?)indicates identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) Megascoeic descrietion smectite Other minerals 

6 48 14.6 Brown tuff 10-20 (1 peak) Kaolinite? -trace 

7 50 15.2 Green tuff ::::10 Chlorite-abundant-present; quartz-trace 

8 51 15.5 Green tuff ::::20 Chlorite-present; quartz-trace 

9 54 16.5 Green tuff 0-10 Chlorite-present; quartz-trace · 

10 56 17.1 Green tuff 10-20 Chlorite-present 

11 57 17.4 Green tuff =20 Chlorite-trace to present 

12 58 17.7 Green tuff 10-20 Chlorite-present to trace; quartz-trace 

13 60 18.3 Orange tuff 10-20 Chlorite-trace;quartz-trace 

14 61 18.6 Green tuff 20-30 Chlorite-present; quartz-trace 

15 62 18.9 Green tuff 10-20 (1 peak) Chlorite-present 

17 65 19.8 Green tuff =20 Chlorite-present to abundant 

18 66 20.1 Green tuff 10-20 Chlorite-abundant; quartz-trace 

19 69 21.0 Gray tuff 10-20 Chlorite-present 

20 71 21.6 Green tuff =10 Chlorite-trace to present; quartz-trace 

21 76 23.2 Gray tuff 10-20 Chlorite-present to abundant; quartz-trace 

22 80 24.4 Green tuff =10 Chlorite-present; quartz-trace 

23 83 25.3 Green tuff 40 Chlorite/kaolinite? -trace 

24 85 25.9 Brown tuff 10-20 Chlorite-trace; quartz-trace 

25 87 26.5 Blue tuff 10-20 Chlorite-present; quartz-trace 

26 89 27.1 Brown tuff =20 Chlorite-present; quartz-trace 

27 92 28.0 Green tuff .,.() Chlorite? -trace; quartz-trace 

28 93 28.4 Green tuff 20-30 (1 peak) Chlorite-present; quartz-trace 

29 97 29.6 Green tuff 10-20 Chlorite-present; quartz-trace 

30 101 30.8 Brown tuff 10-20 None observed 

31 103 31.4 Brown tuff 10-20 Kaolinite/chlorite?-trace to present; quartz-trace 

32 106 32.3 Green tuff 40-50 Kaolinite? -trace; quartz-trace 

33 110 33.5 Green tuff 10-20 None observed 

34 113 34.4 Brown tuff 10-20 Chlorite?-trace; quartz-trace 

35 116 35.4 Orange tuff =20 Kaolinite? -trace 

36 119 36.3 Green tuff 10-20 Chlorite-present; quartz-trace 

37 124 37.8 Brown tuff 10-20 Kaolinite? -trace 

38 129 39.3 Brown tuff =10 Chlorite-trace 

39 131 39.9 Green tuff 10-20 None observed 

40 135 41.2 Green tuff 10-20 (1 peak) None observed 

42 139 42.4 Green tuff 10-20 Quartz-trace 

43 142 43.3 Green tuff 10-20 None observed 

44 144 43.9 Green tuff ... tQ-20 Quartz-trace 

45 146 44.5 Green tuff =10 Quartz-trace 

46 148 45.1 Green tuff 10-20 (1 peak) None observed 

47 151 46.0 Green tuff 10-20 Quartz-trace 

48 156 47.6 Green tuff 10-20 (1 peak) None observed 

49 164 50.0 Green tuff 10-20 (1 peak) Kaolinite/chlorite?-trace 

51 172 52.4 Green tuff =10 Chlorite-trace to present; quartz-trace 

53 185 56.4 Green tuff 10 (1 peak) Quartz-trace 

54 188 57.3 Brown tuff =10 (1 peak) Chlorite-trace; quartz-trace 

55 1 196 59.7 Brown tuff =40 (1 peak) None observed 

56 200 61.0 Green tuff 70-80 (1 peak) Quartz-trace 

58 210 64.0 Green tuff =10 Chlorite-abundant; quartz-trace 

59 215 65.5 Green tuff 90-100 Chlorite-abundant-present;quartz-trace 

61 220 67.1 Green tuff =20 Chlorite-present; quartz-trace 

.62 227 69.2 Green tuff 30-40 Chlorite-present 

63 235 71.6 Green tuff 20-30 Chlorite-abundant; quartz-trace 

64 240 73.2 Green tuff =100 (1 peak) Chlorite-present 

66 248 75.6 Green tuff 10-20 (1 peak) Chlorite-present 

67 266 81.1 Brown tuff 10-20 Chlorite-abundant; quartz-trace 

68 269 82.0 Green tuff 10-20 Chlorite-abundant; quartz-trace 

69 272 82.9 Green tuff =20 Chlorite-present; quartz-trace 

70 285 86.9 Green tuff =10 Chlorite-present to abundant; quartz-trace 

71 291 88.7 Green tuff =20 Chlorite-present to abundant; quartz-trace 

73 295 89.9 Green tuff 10-20 None observed 

74 299 91.1 Green tuff 10-20 Chlorite-abundant; quartz-trace 

75 304 92.7 Green tuff 10-20 Kaolinite? -present 

76 318 96.9 Green tuff 10-20 Kaolinite?-trace; quartz-trace 

77 320 97.5 Gra~ tuff =10 Kaolinite-Eresent; 9uartz-trace 

G24 Evolution of Sedimentary Basins-San Juan Basin. 
Table 16. X-ray identification of <0.5-J.Lm fraction, Sanostee Wash · 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (7) indicates identification 

uncertain] 

Sample Elevation Percent 

no. (ft) (m) Megasco~ic descri~tion smectite Other minerals 

B-7 40 12.2 Orange mudstone 90-100 None observed 

B-10 44 13.4 Orange tuff 90-100 Chlorite-present; quartz-present 

B-15 84 25.6 Gray claystone 90-100 None observed 

B-19 114 34.8 Green tuff 100 Kaolinite/chlorite7-trace 

Table 17. X-ray identification of <0.5-J.Lm fraction, Toadlena 

[Locality shown in fig. 1. Elevation is height above base of Brushy Basin Member. Query (7) indicates 

identification uncertain] 

Sample Elevation Percent 

no. (ft) (m) M~asco~ic descrietion smectite Other minerals 

1 3 0.9 Gray mudstone 80-90 None observed 

2 14 4.3 Green mudstone 100 None observed 

3 27 8.2 Green claystone 60-70 None observed 

4 36 11.0 Green/red mudstone 20-30 None observed 

5 38 11.6 Green mudstone 80-90 None observed 

6 41 12.5 Green claystone 70-80 None observed 

7 42 12.8 Green mudstone 90-100 None observed 

8 47 14.3 Red mudstone 70-80 None observed 

9 51 15.5 Green claystone 100 None observed 

10 56 17.1 Yellow claystone 100 None observed 

11 65 19.8 Green claystone 100 None observed 

12 67 20.4 Green claystone 100 None observed 

13 71 21.6 Green mudstone 100 None observed 

14 108 32.9 Purple mudstone 90 None observed 

15 117 35.7 Green mudstone 90-100 None observed 

16 119 36.3 Brown mudstone 90-100 None observed 

17 121 36.9 Green claystone 80 None observed 

18 133 40.5 Green claystone 90-100 Kaolinite-present; quartz-trace 

19 136 41.5 Gray claystone 100 None observed · 

20 140 42.3 Gray claystone 100 None observed 

21 148 45.1 Green claystone 100 None observed 

22 154 46.9 Green cla~stone 100 None observed 

X-ray Diffraction Studies of the Morrison Formation, Colorado Plateau G25 

• U.S. GOVERNMENT PRINTING OFFICE: 1989·0·173·047/06017 
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