Authigenic Albite in a Jurassic Alkaline, 

Saline Lake Deposit, Colorado PlateauEvidence for Early Diagenetic Origin

U.S. GEOLOGICAL SURVEY BULLETIN 1808-P
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Chapter P

Authigenic Albite in a Jurassic Alkaline, 

Saline Lake Deposit, Colorado PlateauEvidence for Early Diagenetic Origin

By NEIL S. FISHMAN, CHRISTINE E. TURNER, and 

ISABELLE K. BROWNFIELD

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
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, 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: 1995

For sale by

U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Fishman, Neil S.

Authigenic albite in a Jurassic alkaline, saline lake deposit, Colorado plateau 

Evidence for early diagenetic origin/ by Neil S. Fishman, Christine E. Turner, and 

Isabelle K. Brownfield.

p. cm. (U.S. Geological Survey bulletin ; 1808-P) 

(Evolution of sedimentary basins San Juan Basin; ch. P)

Includes bibliographical references.

1. Albite Colorado. 2. Albite New Mexico. 3. Geology, Stratigraphic 

Jurassic. 4. Minerals Colorado. 5. Minerals New Mexico. 

I. Turner, Christine E. II. Brownfield, Isabelle K. III. Title. IV. Series. 

V. Series:

Evolution of sedimentary basins San Juan Basin ; ch. P. 

QE75.B9no. 1808-P 

[QE391.P55]

557.3s dc20 94-11339 

[549'.68] CIP
CONTENTS

Abstract PI 

Introduction PI 

Methods P3 

Geology P5

Stratigraphy P5

Ancient Lake Too'dichi' P5

Thermal history P5 

Modes of occurrence of authigenic albite P7

Albitic tuff beds P8

Albite cement in sandstone beds P8 

Discussion P12 

Conclusions P13 

References cited P13

FIGURES

1. Map showing outcrops of the Upper Jurassic Morrison Formation and 

locations of measured sections P2

2. North-south stratigraphic section of the Morrison Formation,

Colorado Plateau P4 

3, 4. Maps showing distribution of:

3. Diagenetic mineral zones in altered tuff deposited in Jurassic 

Lake Too'dichi' P6

4. Tertiary and Quaternary igneous intrusive and extrusive rocks 

in study area and vitrinite reflectance values for coal samples from 

the Dakota Sandstone and from the Brushy Basin Member of the 

Morrison Formation P7

5. Photograph showing albite diagenetic mineral zone of the Brushy

Basin Member of the Morrison Formation at Piedra River locality P8

6. Photomicrograph of albitic tuff beds from Norwood Hill locality P8

7. Photomicrographs and scanning electron microscope photograph 

showing various types of authigenic albite in sandstone interbedded 

with tuff in albite diagenetic mineral zone of the Brushy Basin 

Member of the Morrison Formation Pll

TABLES

1. Electron microprobe data for authigenic albite from the Brushy Basin Member of 

the Morrison Formation, eastern Colorado Plateau P3

2. Modal analyses of selected samples of sandstone interbedded with and underlying 

albitic tuffs in the Brushy Basin Member of the Morrison Formation, eastern 

Colorado Plateau P9

3. Unit-cell parameters for authigenic albite from the Brushy Basin Member of the 

Morrison Formation and from other sedimentary rocks P9

Contents

EVOLUTION OF SEDIMENTARY BASINS SAN JUAN BASIN

Authigenic Albite in a Jurassic Alkaline, 

Saline Lake Deposit, Colorado PlateauEvidence for Early Diagenetic Origin

By Neil S. Fishman, Christine E. Turner, and Isabelle K. Brownfield

Abstract

Authigenic albite in the Brushy Basin Member of the 

Upper Jurassic Morrison Formation, Colorado Plateau, 

probably formed at low (25°C-60°C), synsedimentary temperatures. This albite is present in tuff beds as the alteration product of silicic volcanic ash deposited in Jurassic Lake 

T'oo'dichi'. The albitic tuff beds form the central diagenetic 

mineral zone in a concentric progression that is, from lake margin basinward, smectite^clinoptilolite »analcime±potassium 

feldspar »albite. The conformity of the outer boundary of the 

albite diagenetic mineral zone with boundaries of the other 

diagenetic mineral zones suggests that albite formed in 

response to the same lateral hydrogeochemical gradient 

responsible for the formation of other authigenic minerals and, 

therefore, at low, synsedimentary temperatures. Although 

albite is reported in minor amounts in other alkaline, salinelake settings, this is the first reported occurrence of albite as a 

distinct diagenetic mineral zone.

Fluvial sandstone beds interbedded with and underlying 

the albitic tuff beds contain abundant authigenic albite as overgrowths, pore-filling laths, and replacement of detrital feldspar 

grains. The close spatial association of albitic tuff beds and 

albitized sandstone beds suggests that pore water in sediments 

of Lake T'oo'dichi', in which cations were enriched from the 

alteration of silicic ash, moved into nearby sands during early 

diagenesis. The coarseness of the albite in the sandstone beds 

makes it more amenable to study than the aphanitic albite in 

the tuff beds. Microprobe analysis of the albite cement indicates a plagioclase composition of <An 1r almost pure 

NaAISi 3O8, and unit-cell determinations indicate that the 

albite is highly ordered. High minus-cement porosity in albitecemented sandstone (as high as 33 percent) and the nature of 

grain contacts confirm an early diagenetic origin for the albite 

cement.

Alkaline, saline lakes may act as solar ponds because 

brine that develops by evaporative concentration has a high 

heat capacity. The high heat capacity of saline lakes may result 

in water temperatures higher than 25°C, perhaps as high as

50°C-60°C Because warm lake water may have infiltrated into 

underlying sediments, we postulate temperatures between 

25°C and 60°C for the formation of authigenic albite in Lake 

T'oo'dichi' tuff beds and associated sandstone beds. Porewater chemistry can thus drive crystallization of albite at 

temperatures less than 85°C. Our results significantly expand 

the temperature range in which authigenic albite can form in 

sedimentary rocks and thus limit the use of albite as a geothermometer.

INTRODUCTION

Authigenic albite is common in sedimentary rocks of 

various ages (Moore, 1950; Baskin, 1956; Milton, 1957; 

Kastner and Waldbaum, 1968; Kastner, 1971; Desborough, 

1975; Boles and Franks, 1979; Kastner and Siever, 1979; 

Cole, 1985; Saigal and others, 1988; Milliken, 1989), especially with increased depth of burial and temperature. Some 

rocks that have experienced burial temperatures of 100°C or 

greater show a dramatic increase in authigenic albite, as 

replacement of, or overgrowth on, detrital feldspar grains 

(lijima and Utada, 1972; Merino, 1975; Boles, 1982; Helmold and van de Kemp, 1984; Milliken, 1985; Gold, 1987), 

although recent studies suggest that albite may form at 

about 85°C (Pittman, 1988) or slightly lower (Saigal and 

others, 1988).

The presence of authigenic albite in some lacustrine 

rocks suggests temperatures of formation lower than 85°C. 

Authigenic albite is in the Green River Formation (Moore, 

1950; Milton, 1957; Desborough, 1975; Cole, 1985) in an 

area where vitrinite-reflectance data (Nuccio and Johnson, 

1988) confirm a cool (<70°C) thermal history. Authigenic 

albite is in Miocene rocks near Boron, California, where it 

formed at temperatures of less than 58°C, as indicated by its 

coexistence with primary borax (Williamson 1987), a

Jurassic Alkaline, Saline Lake Deposit, Colorado Plateau PI
110° 109° 108° 107°

39°

38°

37°

36°

35°

MONUMENT

BECLABITO DOME 

OAK SPRINGS

O 

Albuquerque

Figure 1 . Map of the study area showing outcrops of the Upper Jurassic Morrison Formation (shaded 

areas) in the Colorado Plateau and locations of measured sections used for this report (solid circles). 

Line of section A-A' (fig. 2) is also shown.

P2 Evolution of Sedimentary Basins San Juan Basin
mineral that alters to kernite at temperatures greater than 

58°C (Christ and Garrels, 1959).

Studies of alkaline, saline lake deposits in the Brushy 

Basin Member of the Upper Jurassic Morrison Formation, 

eastern Colorado Plateau (fig. 1), indicate that authigenic 

albite is present in interbedded silicic tuff beds and sandstone beds (Fishman and others, 1986; Turner-Peterson and 

others, 1986; Turner-Peterson, 1987; Turner and Fishman, 

1991). Both the confinement of albite primarily to the central lake facies and petrographic constraints suggest an 

early, low-temperature origin, probably related to the alkaline, saline pore-water chemistry. Because the albite seemed 

to have formed at low, synsedimentary temperatures, an 

integrated case study of the distribution, mode of occurrence, timing of formation, and thermal history of the albitic 

rocks was undertaken.

Acknowledgments. Discussions, both in the laboratory and in the field, with Richard L. Hay (University of 

Illinois), Richard L. Sheppard (U.S. Geological Survey), 

and Blair F. Jones (U.S. Geological Survey) were extremely 

important and helpful and contributed much to our knowledge of alkaline, saline-lake systems. Vito Nuccio (U.S. 

Geological Survey^ kindly performed vitrinite-reflectance

studies on coal samples, and Joan Fitzpatrick (U.S. Geological Survey) kindly made unit-cell determinations. This 

manuscript was improved by the critical reviews by George 

Breit, Joan Fitzpatrick (U.S. Geological Survey), Arthur S. 

Trevena (Unocal), Earle M. McBride (University of Texas), 

and Enrique Merino (Indiana University).

METHODS

Samples of interbedded albitic tuff beds and sandstone beds were collected from four localities: Durango, 

Norwood Hill, Piedra River, and Vancorum, Colorado (fig. 

1). The sections were measured and described in detail by 

Turner-Peterson (1987).

Petrologic studies were performed using X-ray diffraction, electron microprobe, scanning electron microscope, and petrographic microscopic techniques. Selected 

areas of thin sections were powdered in situ using a diamond-tipped objective, and the powdered material was then 

mounted on a gelatin fiber for X-ray analysis using a 

powder camera and CuKoc radiation. Exposure times varied 

from 2 to 12 hours. This powder-camera technique allowed

Table 1. Electron microprobe data for authigenic albite from the Brushy Basin Member of the Morrison Formation, eastern 

Colorado Plateau.

[Sample localities are shown in figure 1. n is number of data points per grain. Oxide abundances are in weight percent (NazO, ±0.15 percent; KzO, 

±0.01 percent; CaO, ±0.03 percent; SiO2, ±0.34 percent; A12O3, ±0.13 percent; Fe2O3, ±0.02 percent; BaO, ±0.03 percent). Anorthite (An) content is 

<1 mole percent for all samples]

Sample 

locality

Piedra River

Piedra River

Piedra River

Piedra River

Piedra River

Piedra River

Piedra River

Durango

Durango

Durango

Durango

Durango

Durango

Durango

Durango

Norwood Hill

Norwood Hill

Norwood Hill

Norwood Hill

Norwood Hill

Sample 

type

Framework grain

Framework grain

Framework grain

Framework grain

Framework grain

Framework grain

Overgrowth

Framework grain

Framework grain

Framework grain

Overgrowth

Overgrowth

Overgrowth

Overgrowth

Overgrowth

Framework grain

Framework grain

Interstitial cement

Interstitial cement

Interstitial cement

n

14

5

3

5

5

2

5

7

6

5

2

1

1

1

1

5

5

1

1

1

Na2O

12.40

11.66

11.64

11.83

11.77

11.81

11.91

12.48

12.67

12.90

12.64

12.79

12.63

12.49

13.01

12.17

12,12

12.21

12.40

12.32

K2O

0.03

0.04

0.03

0.01

0.04

0.01

0.03

0.07

0.04

0.04

0.02

0.05

0.05

0.06

0.08

0.01

0.00

0.03

0.03

0.02

CaO

0.05

0.04

0.12

0.06

0.03

0.05

0.05

0.16

0.02

0.02

0.03

0.05

0.00

0.05

0.02

0.03

0.06

0.03

0.05

0.06

SiO2

68.19

67.36

67.27

67.01

67.28

67.67

67.19

68.53

67.98

68.24

67.99

68.01

67.38

65.76

66.43

67.21

66.79

67.19

67.55

67.52

AI 2 03

19.61

19.48

19.64

19.58

19.79

19.60

19.84

19.79

19.66

19.62

19.68

19.67

19.76

19.74

19.79

19.40

20.02

19.96

20.05

20.30

Fe2 03

0.02

0.04

0.01

0.03

0.05

0.00

0.01

0.05

0.08

0.01

0.02

0.00

0.01

0.08

0.00

0.01

0.02

0.00

0.00

0.00

BaO

0.03

0.02

0.03

0.01

0.00

0.04

0.02

0.00

0.01

0.01

0.00

0.00

0.00

0.00

0.04

0.01

0.00

0.00

0.03

0.00

Total

100.33

98.63

98.74

98.53

98.96

99.18

99.05

101.08

100.46

100.84

100.38

101.48

99.83

98.18

99.37

98.84

99.01

99.39

100.11

100.22

Norwood Hill Interstitial cement 12.48 0.02 0.00 66.83 19.78 0.05 0.07 99.23

Jurassic Alkaline, Saline Lake Deposit, Colorado Plateau P3
for analysis of individual crystals or of areas that were also 

examined in thin section. All tuff samples were also powdered and X-rayed. Albitized detrital grains, identified by 

their white, opaque appearance, were picked by hand from 

a disaggregated sandstone sample, and the material was 

then used for determination of unit-cell parameters.

Major element (Na, K, Ca, Si, Al) and minor element 

(Ba, Fe, Sr) compositions of authigenic albite in sandstone 

beds were determined through quantitative analysis of 

grains in polished thin sections using an electron microprobe (accelerating voltage 15 keV, beam current 10 nA, 

beam size 5 (im) (table 1). The microprobe data were 

reduced using the methods described by Ziebold and 

Ogilvie (1964), Albee and Ray (1970), and Bence and

Albee (1968). Strontium content was below the detection 

limit (0.02 percent) in all samples analyzed.

Forty-one thin sections were studied; most of these 

were stained with sodium cobaltinitrite for determination of 

potassium feldspar and with alizarine red S and potassium 

ferricyanide for determination of carbonate type and composition, respectively. Point counts (at least 300 points per 

section) were performed on the thin sections from sandstone samples. Selected samples were viewed using a scanning electron microscope that was equipped with an 

energy-dispersive X-ray analyzer.

The thermal history of the Morrison Formation was 

determined by study of the vitrinite reflectance of organic 

material chiefly from coal beds in the lower part of the

NORTH

A

COLORADO 

NATIONAL 

MONUMENT

ESCALANTE 

CANYON

48km

BIG

GYPSUM 

VALLEY

72 km 35 km

NORWOOD 

HILL

COLORADO | NEW MEXICO

PIEDRA BECLABITO

RIVER

OAK 

SPRINGS

TOADLENA

SOUTH

A'

GOAT 

MOUNTAIN

122km 154km 10km 63km 136km

: . Westwater Canyon 

 '. -".: --'-. Member''-". '..-

Lower Brushy Basin Member^^4J

EXPLANATION

Diagenetic mineral zones in 

tuff of Brushy Basin Member

Fluvial sandstone 

Eolian sandstone

Interbedded sandstone 

and mudstone

Smectite 

Clinoptilolite 

' "' £ Analcime±potassium feldspar 

Albite

-L- 0

Figure 2. North-south stratigraphic section of the Morrison Formation in the Colorado Plateau. Diagenetic mineral zones in the 

alkaline, saline lake deposits in the Brushy Basin Member were determined from authigenic minerals in tuff beds (Turner-Peterson 

1987). The relationship between the Junction Creek Sandstone and the Morrison Formation is uncertain. Line of section is shown 

in figure 1 ; datum is base of Cretaceous rocks. J 5 unconformity as described in Pipiringos and O'Sullivan (1978).

P4 Evolution of Sedimentary Basins San Juan Basin
Upper Cretaceous Dakota Sandstone, a unit that either 

unconformably overlies the Morrison or is separated from 

the Morrison locally by the Lower Cretaceous Burro Canyon 

Formation (0-60 m thick). Even though an unconformity 

separates the Dakota from the Morrison, the Dakota coal 

samples would have experienced the same post-Late Cretaceous thermal history as the Morrison. Maximum burial 

depths occurred in the Tertiary, and the nearby San Juan 

volcanic field was active in the Tertiary. Thus, the Morrison's thermal history would be close to that of overlying 

Dakota coals. A single sample from an organic-rich horizon 

in the Brushy Basin Member of the Morrison Formation was 

also collected and used for vitrinite reflectance studies.

GEOLOGY 

Stratigraphy

The Brushy Basin Member, except locally where 

overlain by the Jackpile Sandstone Member, is the uppermost member of the Morrison Formation on the Colorado 

Plateau and is recognized from the southern margin of the 

San Juan Basin northward to Grand Junction, Colorado 

(fig. 2). In the study area, it conformably overlies the 

fluvial Westwater Canyon, Recapture, or Salt Wash 

Members of the Morrison Formation. In an area 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 (Turner-Peterson, 1987). The name 

Recapture is not extended much beyond the pinchout of the 

Westwater Canyon, and the entire interval of Morrison 

above the Salt Wash Member is mapped as Brushy Basin 

in this area (fig. 2).

Ancient Lake T'oo'dichi'

Deposits of a large, ancient alkaline, saline lake, 

Lake T'oo'dichi' (Turner-Peterson, 1987), have been 

recognized in the upper part of the Brushy Basin Member 

north of the Colorado-New Mexico State line and extend 

south to include the entire Brushy Basin Member in New 

Mexico (fig. 2). The lake sediments accumulated in a 

large, shallow basin that included the present-day San Juan 

and the ancestral Paradox Basins (Turner-Peterson, 1987) 

(fig. 3). The lake deposits are as thick as 100 m and 

contain intervals of altered volcanic ash (Turner-Peterson, 

1987). The ash was derived from a magmatic arc several 

hundred kilometers to the west of the Colorado Plateau 

region (Burchfiel and Davis, 1975; Hamilton, 1978). 

Differential alteration of the ash, which reflects lateral

hydrogeochemical gradients established during deposition 

in an alkaline, saline lake, resulted in development of four 

concentric diagenetic mineral zones. The zones are defined 

on the basis of the dominant diagnostic authigenic 

mineral(s) in tuff beds that were deposited in the lake. The 

three outer zones, which basinward are the smectite, 

clinoptilolite, and analcime±potassium feldspar zones, are 

similar to those recognized in Pliocene and Pleistocene 

alkaline, saline lake deposits studied by others (Sheppard 

and Gude, 1968; Surdam and Sheppard, 1978) and are part 

of the data that led to the interpretation of this interval of 

the Brushy Basin Member as lacustrine. However, a 

central albitic diagenetic mineral zone, such as occurs in 

deposits of Lake T'oo'dichi' (fig. 3), has not been 

described from other ancient alkaline, saline lake deposits.

Thermal History

Because high temperature (>85°C) is commonly 

considered necessary for albite formation, it is important to 

evaluate the thermal history of the Brushy Basin Member, 

which contains albitic tuff beds to determine if 

temperatures ever exceeded 85°C. Two factors, burial 

history and igneous activity, have contributed to the 

thermal history of the region.

Following deposition of the Morrison Formation, 

about 1,000 m of Cretaceous and Tertiary sediments accumulated. Burial depths of Morrison sediments were 

probably somewhat uniform until the Late Cretaceous and 

early Tertiary Laramide orogeny, during which time downwarping of the San Juan Basin occurred. Samples used to 

define the diagenetic mineral zones in Lake T'oo'dichi' 

were collected from outcrops of the Brushy Basin Member 

of the Morrison Formation that flank the San Juan Basin or 

are distant from the basin; therefore, the structural effects 

of the Laramide orogeny are negligible. On the basis of 

stratigraphic reconstruction, the maximum depth of burial 

for the outcrops sampled is uniformly about 2,000 m. Vitrinite reflectance data (fig. 4) indicate that outcrops containing albitic tuff beds never were subjected to 

temperatures in excess of 70°C (Barker and Pawlewicz, 

1986), which is consistent with the relatively shallow 

burial. This inferred temperature is below the 85°C commonly considered to be the minimum temperature required 

for formation of authigenic albite.

The vitrinite reflectance data, in addition to recording burial history, would show thermal effects of igneous 

activity in the region. The San Juan volcanic field (fig. 4), 

which developed 35-20 Ma (Steven, 1975; Lipman and 

others, 1978), is thought by some workers to have left a 

regional thermal imprint; however, the uniformity of 

vitrinite reflectance data across the region indicates no 

thermal effects from the San Juan volcanic field.

Jurassic Alkaline, Saline Lake Deposit, Colorado Plateau P5
110° 109° 108° 107° 106°

33°

38°

37°

36°

35°

Santa Fe

O Albuquerque

EXPLANATION

Boundary of outcrop area of Morrison 

Formation See figure 1 for detail

Western and southern boundary of 

sandstone lithofacies

Core hole 

Sample locality

Axis of uplift Showing direction of 

plunge. Dashed where inferred

Boundary of diagenetic mineral zone Dashed 

where inferred. Zones include:

Smectite 

Clinoptilolite

Analcime±potassium feldspar 

Albite

Figure 3. Map showing the distribution of diagenetic mineral zones in altered tuff deposited in Jurassic Lake 

T'oo'dichi'. Modified from Turner and Fishman (1991).

P6 Evolution of Sedimentary Basins San Juan Basin
110° 109° 108° 107° 106°

39°

38°

37°

36°

35°

34°

100 KILOMETERS

Figure 4. Map showing the distribution of Tertiary and Quaternary igneous intrusive and extrusive rocks (shaded areas) in 

the study area and vitrinite reflectance values (in percent) for 

coal samples from the Dakota Sandstone (solid circles), which 

overlies the Morrison Formation, and from a sample in the 

Brushy Basin Member of the Morrison Formation (indicated by 

asterisk). Note uniformity of vitrinite reflectance values across

the region and the lack of thermal effects from the San Juan volcanic field; in fact, a vitrinite reflectance value of 0.53 percent 

is in coal from very near the volcanic field. Diagenetic mineral 

zone boundaries (heavy solid and dashed lines) in the Brushy 

Basin Member of the Morrison Formation (from fig. 3) are also 

shown; note how lithofacies boundaries are unaffected by 

proximity to volcanic field.

MODES OF OCCURRENCE OF 

AUTHIGENICALBITE

The coincidence of the outer boundary of the albitic 

diagenetic mineral zone with the boundaries of the other 

diagenetic mineral zones led us to infer an alkaline, saline

lake origin for the albite in the Brushy Basin Member of 

the Morrison Formation. This conformity remains one of 

the more compelling arguments for a low-temperature, 

syndepositional origin for the albite. Additional lines of 

evidence are provided by petrographic observations of tuff 

beds and sandstone beds interbedded with and underlying 

tuff beds of the central albitic zone.

Jurassic Alkaline, Saline Lake Deposit, Colorado Plateau P7
Albitic Tuff Beds

Albitic tuff beds are characteristically siliceous, well 

indurated, and aphanitic and form prominent ledges in steep 

cliff exposures (fig. 5). The tuff beds are grayish green (5G 

5/2) on both fresh and weathered surfaces, a color produced 

by authigenic clays. Local weathering of the pyrite in the 

tuff beds gives them a light-brown color (10YR 7/2). 

Locally, shard morphologies are preserved in albitic tuff 

beds (fig. 6). A distinctive spherulitic texture, diagnostic of 

authigenic analcime, preserved in some albitic tuff beds 

suggests an analcime precursor. The abundance of shard 

morphologies observed in thin sections of albitic tuff beds 

(fig. 6) contrasts with the relative paucity of shard morphologies in the analcime diagenetic mineral zone (TurnerPeterson, 1987). If the growth of spherulitic analcime crystals destroys shard morphologies, then the abundance of 

shard morphologies in the albitic tuff argues for direct 

replacement of volcanic glass or clinoptilolite by authigenic 

albite. Scarcity of the spherulitic analcime texture further 

suggests a lack of an analcime precursor, although the conversion of analcime to albite might have destroyed the 

spherulitic texture. Some albitic tuff beds exhibit the spherulitic analcime texture; here the albite must have formed 

from an analcime precursor.

Albite Cement In Sandstone Beds

Thin sandstone beds (from several centimeters to several meters thick), which represent fluvial episodes in the 

development of the alkaline, saline lake, are interbedded

with albitic tuff beds. Authigenic albite in the sandstone is 

present as overgrowths on detrital plagioclase grains, as 

intergranular cement, and as a replacement (albitization) of 

detrital feldspar grains. No evidence for precursor cements 

was observed in any of the albite-cemented sandstone samples. Albite overgrowths on detrital plagioclase grains generally are clear, have few or no vacuoles, and are well 

defined by sharp, euhedral faces (fig. 7A). The albite overgrowths typically are twinned, and twin planes commonly 

are aligned with those of the parent detrital core. Microprobe analysis indicates that the overgrowths are less than 

Ant, almost pure NaAlSi3O8 (see table 1). The overgrowths 

may be as long as 50 |im; they compose less than 2 percent 

of the volume of the sandstone.

Albite intergranular cement has been identified 

optically, by microprobe, and by X-ray diffraction. It fills 

primary intergranular pores and is present as euhedral, 

tabular crystals (>5 (im long) that generally are clear, 

contain no vacuoles, and compose between 1 and 15 percent 

of the volume of the sandstone beds on the basis of point 

counts (see table 2). The interstitial albite generally is 

twinned and forms a network of intergrown crystals (figs. 

IB, C). Similar to albite overgrowths, the pore-filling albite 

has an anorthite composition of less than Ant (table 1).

Albitization of detrital plagioclase grains is widespread, and albitization of detrital potassium feldspar grains 

was observed in varying abundance. Microprobe (table 1) 

and X-ray diffraction (table 3) analyses confirm that detrital 

feldspar is albitized. Determination of the original composition of detrital feldspar was made by examining unaltered 

grains in sandstone distant from the albite diagenetic mineral zone (N.S. Fishman and P.L. Hansley, unpub. data, 

1984; Fishman and Reynolds, 1986). These unaltered

Figure 5. Albite diagenetic mineral zone of the Brushy Basin 

Member of the Morrison Formation at Piedra River locality 

(fig. 1). Prominent ledges are predominantly stacked tuff beds 

that contains authigenic albite and silica. Some of the ledges 

are thin (<1 m) sandstone beds, which also are cemented with 

albite and silica.

>-^*4t*»

jf^V^ F- f "* ^.,<^'- ^5».'£i3Fi. l ""£M^ %^l "' "*v.^«« * j ^ p- - . a> - ; ' f} i?1 -^ i

': *nMm$M* *

Figure 6. Photomicrograph of albitic tuff beds from Norwood 

Hill locality (fig. 1). Albite is in groundmass, whereas shards 

(dark, curved shapes) are filled mostly with iron oxide minerals, chalcedony, and minor albite. Note preservation of delicate shard morphologies. Bar is 0.40 mm long.

P8 Evolution of Sedimentary Basins San Juan Basin
Table 2. Modal analyses of selected samples of sandstone interbedded with and underlying albitic tuffs in the Brushy Basin 

Member of the Morrison Formation, eastern Colorado Plateau.

[In volume percent. Sample localities are shown in figure 1. Abbreviations: Qtz, quartz; K-spar, potassium feldspar; Flag, plagioclase; Diss, dissolved 

grain; Rk. frag, rock fragments; QO+chal, quartz overgrowths+chalcedonic quartz; Alb, albite as overgrowths and pore-filling cement; Cal, calcite. 

Leaders ( ) indicate not present]

Detrital grains

Sample locality

Norwood Hill

Norwood Hill

Norwood Hill

Norwood Hill

Norwood Hill

Durango

Durango

Durango

Piedra River

Piedra River

Piedra River

Piedra River

Piedra River

Qtz

52

35

49

57

55

51

57

43

52

48

40

47

51

K-spar

2

--

_

1

__

5

4

7

5

1

Flag

7

10

6

_

11

4

8

2

2

4

3

7

5

Diss

6

1

5

4

1

1

1

3

5

-

Rk. frag

9

26

15

9

12

11

5

21

15

14

18

11

13

Authigenic cement

QO+chal

16

4

18

28

13

10

24

18

6

7

29

24

24

Alb

4

3

3

_

11

15

1

-

3

3

3

2

Cal

8

13

-

1

3

-

4

10

14

6

4

4

Clays

2

3

3

_

1

7

~

4

4

1

1

-

Percent 

minus-cement 

Void porosity

5

_

1

-

-

3

2

~

1

30

23

28

29

29

32

27

29

25

23

33

32

31

grains include microcline, orthoclase, sanidine, and calcic 

plagioclase (as much as 4.5 weight percent CaO, equivalent 

to An22)- Even the detrital plagioclase grains that are albitized commonly retain their original textural features (such 

as twinning characteristics). Some albitized grains were 

observed to have chessboard (checkerboard in appearance) 

twinning (fig. ID), but these grains contain no obvious 

relicts of the original grains and no K2O; thus, it is impossible to discern the composition of the chessboard grain 

prior to albitization. Grains of similar appearance in other 

rocks have been described as albitized potassium feldspar 

(Walker, 1984; Gold, 1987; Pittman, 1988; Saigal and others, 1988), and in the Morrison some detrital potassium 

feldspar grains may have been completely albitized, leaving

only the chessboard texture. X-ray diffraction analyses 

reveal that the unit-cell parameters of the albitized grains 

are similar to those of authigenic albite reported from other 

sedimentary geological environments (table 3). In addition, 

on the basis of the separation of the 131-131 peaks, the 

tetrahedral aluminium-silicon distribution of the albite in 

the Morrison is highly ordered, similar to that of authigenic 

albite in other sedimentary rocks (Kastner and Waldbaum, 

1968; Kastner, 1971), with the exception of authigenic 

albite in the Green River Formation (Desborough, 1975).

Point counts of albite-cemented sandstone beds reveal 

high minus-cement porosity in samples where albite and 

quartz are the dominant cements (table 2). The minuscement porosity ranges from 29 to 33 percent, almost as high

Table 3. Unit-cell parameters for authigenic albite from the Brushy Basin Member of the Morrison Formation and from other 

sedimentary rocks.

[Standard deviation (xKT4) is given in parentheses. Cell dimensions a, b, and c are in angstroms, and lattice angles a, P, and y are in degrees. Unit-cell 

volume (v) is in cubic angstroms. The d^i-dili separation is in angstroms]

Sample locality

Norwood Hill1 

Greece2 

Crete2 

Greece3 

Wyoming4

a

8.140(2) 

8.138(14) 

8.135(19) 

8.137(21) 

8.164(9)

b

12.796(3) 

12.788(13) 

12.781(15) 

12.785(18) 

12.804(6)

c

7.159(2) 

7.157(8) 

7.156(8) 

7.158(13) 

7.143(4)

a

94.220(3) 

94.230(13) 

94.206(14) 

94.170(25) 

93.923(4)

P

116.62(2) 

116.61(9) 

116.58(12) 

116.61(14) 

116.58(3)

Y

87.93(3) 

87.81(13) 

87.82(16) 

87.81(25) 

88.86(4)

V

664.9(2) 

664.1(20) 

663.6(26) 

664.0(32) 

666.2(6)

d, 31 -d,3,

1.15 

1.14 

1.14 

1.13 

1.46

Albitized detrital plagioclase (this study). 

2Kastner and Waldbaum (1968). 

3Kastner (1971). 

4Desborough (1975).

Jurassic Alkaline, Saline Lake Deposit, Colorado Plateau P9
Figure 7 (above and facing page). Various types of authigenic albite in sandstone 

interbedded with tuff in the albite diagenetic mineral zone of the Brushy Basin Member of 

the Morrison Formation. See figure 1 for sample localities. A, Photomicrograph of albitized 

detrital plagioclase (outlined area) with large twinned albite overgrowth (arrows). Durango 

locality. Bar is 0.13 mm long. B, Photomicrograph of large, twinned albite laths filling large 

primary pores between detrital quartz grains (Q). Norwood Hill locality. Bar is 0.26 mm 

long. C, Scanning electron microscope photograph of large, pore-filling albite laths in sandstone enclosed within a sequence of albitic tuff. Norwood Hill locality. Bar is 5 \am long. 

D, Photomicrograph of albitized detrital potassium feldspaK?) grain displaying chessboardtwinning texture. Textural features of this grain are similar to those described by Walker 

(1984) for albitized potassium feldspar; however, no relicts of potassium feldspar are in the 

grain. Piedra River localitv. Bar is 0.13 mm lone.

PI 0 Evolution of Sedimentary Basins San Juan Basin
!U

as primary porosity for medium to poorly sorted, fine- to 

medium-grained sandstone beds (Beard and Weyl, 1973). 

The high minus-cement porosity indicates that the albite and 

quartz cements filled available pore space before significant 

reduction in primary porosity, which suggests early cementation. The character of grain contacts corroborates early 

cementation; floating grains are common and grain contacts 

are chiefly point to point.

Sandstone beds that contain carbonate cements (ferroan and nonferroan) and minor albite and quartz have

somewhat lower minus-cement porosity (table 2). The calcite 

cement is paragenetically later than albite and quartz; thus 

some compaction occurred after introduction of the early 

albite and quartz cements and before precipitation of calcite.

DISCUSSION

Because high temperature is commonly thought to 

be required for formation of albite in sedimentary rocks,

Jurassic Alkaline, Saline Lake Deposit, Colorado Plateau P11
the albitic tuff beds and albite-cemented sandstone beds in 

the Brushy Basin Member were considered in light of the 

thermal history of the region. Several lines of evidence 

preclude a high-temperature (>85°C) origin for the albite 

in this study. First, the vitrinite reflectance data indicate 

that the Morrison Formation never was subjected to temperatures much greater than 70°C, either as a result of 

burial or from local igneous sources, including the San 

Juan volcanic field. Moreover, if the authigenic albite had 

formed in response to heat caused by deeper burial, the 

boundary of the albite diagenetic mineral zone would not 

coincide with the other boundaries of diagenetic mineral 

zones in the alkaline, saline-lake deposits (fig. 3). Similarly, if hot fluids from the San Juan volcanic field or 

other igneous sources had been responsible for albite formation, the albite zone would have formed a halo around 

the sources of hot fluids, which it does not (fig. 4).

The petrographic evidence also constrains the origin 

of the albite. Minus-cement porosity in the albitecemented sandstone beds is almost as high as that 

expected for initial primary porosity of the sandstone beds, 

which suggests an early diagenetic origin for the albite. 

To infer a high-temperature origin for this albite would 

imply that high primary porosity was preserved through a 

70-100-m.y. burial history, from deposition of the 

Morrison Formation until either the Laramide orogeny (for 

an origin by burial diagenesis) or batholithic activity 

associated with the San Juan volcanic field (for generation 

of hot fluids). The hypothesis that a precursor cement 

filled primary pore spaces and was subsequently 

completely replaced by albite and quartz, leaving no 

relicts, is possible but not probable. If this had occurred, 

the restriction of albite overgrowths to detrital plagioclase 

grains would be difficult to explain. This selectivity is 

readily explained if it is assumed, as it is here, that albite 

precipitated directly as a primary cement because albite 

overgrowths on plagioclase grains are common in the rock 

record. Thus, the contrived scenarios required to support 

a late, hot origin for the authigenic albite, such as 

vanished precursors or maintenance of high primary 

porcsity over millions of years, highlight the difficulties in 

proposing such an origin.

An early, low-temperature, syndepositional origin 

for the albite in both the albitic tuff beds and albitecemented sandstone beds in the Brushy Basin Member 

readily accommodates all of the observations. In the tuff 

beds the conformity of the outer boundary of the albite 

diagenetic mineral zone with boundaries between other 

diagenetic mineral zones (fig. 3) implies that all the zones 

formed during early diagenesis in alkaline, saline lake 

sediments. We infer that the albite in ancient Lake 

T'oo'dichi' formed in the central part of the lake basin, in 

response to lateral hydrogeochemical gradients in the pore 

waters. These same hydrogeochemical gradients caused 

the volcanic ash to alter to authigenic clays, zeolites, and

feldspar in the other diagenetic mineral zones (fig. 3); 

such alterations are thought to occur between 1,000 and 

500,000 years after deposition in alkaline, saline lakes 

(Hay, 1966, 1986; Sheppard and Gude, 1968; Taylor and 

Surdam, 1981), and it is reasonable to infer a similar time 

span for precipitation of the albite.

Albite cement in sandstone beds that underlie the 

albitic tuff beds in Lake T'oo'dichi' probably formed by 

the downward flux of alkaline, saline pore water. Density, 

as well as elevation, is a factor in determining hydrologic 

head. In modern alkaline, saline lakes, the increased density of lake water due to evaporative concentration can 

create a net downward flux of waters into underlying sediments (Hardt and others, 1972; Friedman and others, 

1982). A density-driven, downward movement of pore 

waters from the sediments of Lake T'oo'dichi' is suggested by the presence of albite-cemented sandstone beds 

underlying albitic tuff beds; this mechanism of albite 

authigenesis is consistent with the nonmarine volcaniclastic model for albite formation in sandstone beds advanced 

by Kastner and Siever (1979).

Although we propose a low-temperature, syngenetic 

origin for the albite, the temperature of formation may not 

have been as low as 25°C because the behavior of alkaline, saline lakes as solar ponds can result in water temperatures as high as 56°C (Milton and Eugster 1959). The 

warm lake water may have infiltrated below the sedimentwater interface during albite precipitation and may have 

helped to overcome any kinetic inhibition of the reaction 

to form albite. Because we have no way of knowing 

whether Lake T'oo'dichi' behaved as a solar pond, we can 

only postulate the extant temperatures during albite 

formation. To include the possibility of warmer lake 

water temperatures, in line with an inferred arid to semiarid paleoclimate (Turner-Peterson, 1987), we postulate 

temperatures of albite formation in sediments of Lake 

T'oo'dichi' between 25°C and 60°C.

Although the interpretation of albitic tuff beds in the 

context of an alkaline, saline lake environment best fits all 

of our data and observations, albite is not commonly 

reported from other alkaline, saline lakes. Authigenic 

albite has been reported from tuff beds in the Eocene 

Green River Formation (Moore, 1950; Milton, 1957; 

Desborough, 1975; Cole, 1985) and from middle Miocene 

tuffaceous lacustrine deposits from Boron, California 

(Williamson, 1987), but not from Pleistocene Lake 

Tecopa, California (Sheppard and Gude, 1968), or from 

the Pliocene Big Sandy Formation, Arizona (Sheppard and 

Gude, 1973). Albite, an anhydrous mineral, is thermodynamically favored over analcime, a hydrous mineral, under 

conditions of increased salinity or decreased activity of 

water (Hay, 1966; Surdam and Sheppard, 1978). Also, 

assuming a favorable NaVK* ratio, the increase in activity 

of silica with an increase in pH favors albite with respect 

to analcime (Garrels and Christ, 1965). These factors may

P12 Evolution of Sedimentary Basins San Juan Basin
account for the formation of albite in tuff beds of the 

central diagenetic mineral zone of Lake T'oo'dichi'. 

Similar conditions may account for the presence of authigenic albite in lacustrine rocks of both the Green River 

Formation and the middle Miocene deposits near Boron, 

California.

CONCLUSIONS

1. Albitic tuff beds and albite-cemented sandstone 

beds, which are interbedded with and underlie the tuff 

beds, are restricted to a zone in the central part of Lake 

T'oo'dichi', an ancient alkaline, saline lake in the Brushy 

Basin Member of the Jurassic Morrison Formation, Colorado Plateau.

2. The spatial relationship between the albite zone 

and other diagenetic mineral zones in the lake deposits 

resulted from differential alteration of silicic volcanic ash 

in response to lateral hydrogeochemical gradients that 

developed in Lake T'oo'dichi'.

3. Petrographic observations indicate an early 

diagenetic and, therefore, low-temperature origin for the 

authigenic albite cement in sandstone beds. Vitrinitereflectance data corroborate a low-temperature origin for 

albite because the tuff beds and sandstone beds were never 

subjected to temperatures in excess of about 70°C.

4. Albite-cemented sandstone beds that underlie the 

albitic tuff beds in Lake T'oo'dichi' provide evidence for 

downward movement of pore water similar to that which 

occurs in modern lakes characterized by dense brines.

5. Because Lake T'oo'dichi' may have behaved as 

a solar pond, we must allow for somewhat elevated 

temperatures (>25°C) for lake water and possibly pore 

water in the underlying sediments. We therefore postulate 

a temperature between 25°C and 60°C for albite formation.

6. Our results indicate that pore-water chemistry 

can facilitate formation of authigenic albite at temperatures well below 85°C. This, in turn, significantly 

expands the temperature range in which authigenic albite 

can form in sedimentary rocks and thus limits the use of 

albite as a precise geothermometer.

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P14 Evolution of Sedimentary Basins San Juan Basin

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Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports 

of wide and lasting interest and importance to professional scientists and 

engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic.

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in scope or geographic coverage than Professional Papers. They include the results of 

resource studies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrology, availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific information of wide popular interest in a format designed for distribution at no cost to the public. Information is usually of short-term 

interest.

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS 

publications series. Copies are reproduced on request unlike formal 

USGS publications, and they are also available for public inspection at 

depositories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at depositories. They are a nonpermanent form of publication that may be cited in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on topographic bases in 7 1/2- or 15-minute quadrangle formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering 

geology. Maps generally include brief texts; some maps include structure 

and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric bases at various scales, they show results of surveys using geophysical techniques, such as gravity, magnetic, seismic, or radioactivity, 

which reflect subsurface structures that are of economic or geologic significance. Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photogeologic maps on planimetric 

bases which show geology as interpreted from aerial photographs. The 

series also includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, 

stratigraphy, and structural relations in certain coal-resource areas.

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum potential.

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology in relation to specific mining or mineral-deposit problems; post-1971 maps 

are primarily black-and-white maps on various subjects such as environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; the principal 

scale is 1:24,000, and regional studies are at 1:250,000 scale or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive 

listings of U.S. Geological Survey publications are available under the 

conditions indicated below from USGS Map Distribution, Box 25286, 

Building 810, Denver Federal Center, Denver, CO 80225. (See latest 

Price and Availability List.)

"Publications of the Geological Survey, 1879-1961" may be purchased by mail and over the counter in paperback book form and as a set 

microfiche.

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a set 

of microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" mav i~ 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased by mail 

and over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and Water-Supply Reports and Maps For (State)," may be purchased by mail 

and over the counter in paperback booklet form only.

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet 

form only.

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" is available free of charge by mail or may be 

obtained over the counter in paperback booklet form only. Those wishing a free subscription to the monthly catalog "New Publications of the 

U.S. Geological Survey" should write to the U.S. Geological Survey, 

582 National Center, Reston, VA 22092.

Note.-Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the prices 

charged may differ from the prices in catalogs, announcements, and publications.
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