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Clay Mineralogy of Pleistocene Lake Tecopa Inyo County, California

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Clay Mineralogy of Pleistocene Lake Tecopa Inyo County, California Clay Mineralogy of *• V-? •*' Pleistocene Lake Tecopa Inyov County,y * California $ WE VET Ft Of E S S I 0 K A L ]PAfER Clay Mineralogy of Pleistocene Lake Tecopa, Inyo County, California By HARRY C. STARKEY and PAUL D. BLACKMON GEOLOGICAL SURVEY PROFESSIONAL PAPER 1061 In a saline lake with pH above 8.5 authigenic sepiolite and detrital lithium-bearing saponite were deposited in mudstones which were interlayered with volcanic tuffs UNITED STATES GOVERNMENT PRINTING OFFICE, W ASHINGTON : 1 9 7 9 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Starkey, Harry C. Clay mineralogy of Pleistocene Lake Tecopa, Inyo County, California. (Geological Survey Professional Paper 1061) Bibliography: p. 33 Supt.ofDocs.no.: 119.16:1061 I. Clay minerals—California—Inyo Co. 2. Meerschaum—California—Inyo Co. 3. Saponite—California—Inyo Co. 4. Saline waters—California—Inyo Co. L. Blackmon, Paul D., joint author. II. Title. III. Series: United States Geological Survey Professional Paper 1061. QE389.625.S73 549'.6 77-608318 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-03185-0 CONTENTS Page Page Abstract .......................... ...................... I Nonclay minerals—Continued Introduction ...................... ...................... 1 Other minerals.......................................... 18 Location and geographic setting., ...................... 1 Clay minerals............................................... 20 Acknowledgments ............. ...................... 1 Chlorite and chlorite-mica ................................ 20 Scope of investigation .................................... 3 Mica and illite .......................................... 20 Previous work ........................................... 3 Lithian saponite ........................................ 23 Montmorillonite ........................................ 25 Geology of the basin .......................................... 3 Sepiolite ............................................... 25 Description of the mudstones and siltstones .................... 4 Tecopa basin occurrence ............................. 25 Laboratory methods ......................................... 5 Previous work on sepiolite ........................... 26 Nonclay minerals ............................................ 9 Modes of sepiolite formation ......................... 26 Quartz and plagioclase feldspar ........................... 9 Sources of magnesium and silica ...................... 27 Potassium feldspar...................................... 16 Sepiolite formation in Lake Tecopa ................... 30 Carbonates............................................. 16 Discussion ................................................. 31 Magadiite .............................................. 17 Sequence of events ...................................... 31 Zeolites and amorphous material......................... 18 Conclusions ................................................ 31 Saline minerals ......................................... 18 References cited ............................................ 33 ILLUSTRATIONS Page FIGURE 1. Index and sample locality maps, Pleistocene Lake Tecopa drainage basin, Calif......................... 2 2. Photograph from sample locality 54 looking northeast toward Shoshone, Calif.......................... 4 3. Generalized stratigraphic section of the Pleistocene Lake Tecopa deposits ............................. 4 4. Photograph of sample locality 44 showing gravel mixed with clay ..................................... 5 5. Flow sheet for laboratory procedures used for mineral identification of Pleistocene Lake Tecopa deposits 9 6-11. Transmission electron micrographs: 6. Suspended sepiolite .......................................................................... 14 7. Sepiolite fibers more than 2|*m long .......................................................... 14 8. Surface replica of sepiolite .................................................................... 15 9. Suspended saponite.......................................................................... 15 10. Suspended crystals of magadiite from Lake Tecopa basin ....................................... 19 11. Suspended crystals of magadiite from Trinity County, Calif...................................... 19 12. Vertical distribution of clay-mineral content in stratigraphic section ................................. 21 13. X-ray diffraction curves of typical gradation from mica to mixed-layer mica-saponite .................. 22 14. Photograph of mud cracks in saponite at sample locality 57.......................................... 24 15. Map of samples taken within 1 m of tuff A and their clay mineral content............................. 28 16. Map of samples taken within 1 m of tuff B and their clay mineral content............................. 29 IV CONTENTS TABLES Page TABLE 1. Localities and particle size distribution of samples .................................................................... 6 2. Mineral content of samples ........................................................................................ 10 3. X-ray diffraction data for magadiite ................................................................................ 18 4. Comparison of X-ray diffraction spacings of sepiolite and saponite from Pleistocene Lake Tecopa with those of previously reported occurrences ................................................................................ 20 5. Chemical comparison of Pleistocene Lake Tecopa saponite with other smectites ........................................ 23 6. Weight percent of Mg, Li, and F in samples from Pleistocene Lake Tecopa mudstones and siltstones ..................... 24 7. Li and F in samples outside of lake beds in local drainage ............................................................. 26 CLAY MINERALOGY OF PLEISTOCENE LAKE TECOPA, INYO COUNTY, CALIFORNIA By HARRY C. STARKEY and PAUL D. BLACKMON ABSTRACT INTRODUCTION Pleistocene Lake Tecopa in southeastern Inyo County, Calif., was LOCATION AND GEOGRAPHIC SETTING formed when the Amargosa River was blocked at the southern end of its valley. The lake acted as a settling basin for detrital material The basin of former Pleistocene Lake Tecopa, in being transported by the river. This detritus consisted of clays, southeastern Inyo County, Calif., is located in the Mo- quartz, feldspars, and micas which became mudstones and jave Desert about 32 km east of Death Valley National siltstones. These mudstones and siltstones, much eroded and Monument within Tps. 20, 21, and 22 N., and Rs. 6 and dissected after the draining of the lake, extend over the entire basin and are interbedded with tuffs formed by the intermittent deposi­ 7 E. The area is shown in figure 1. The nearest large ci­ tion of volcanic ashfalls in the former lake waters. These light- ty is Las Vegas, Nev., which is located about 97 km to colored mudstones and siltstones are tough and well indurated and the east. break with a conchoidal fracture. The town of Shoshone is located in the northern part The predominant clay mineral in these detrital beds is a lithium- of the basin, and the town of Tecopa is located in the bearing saponite, which is found not only in the lake beds but also in the area beyond the boundaries of the lake, especially in fluvial southern part; Shoshone is on State Route 127, which deposits in the drainage basin of the Amargosa River to the north. runs generally north-south through the basin. This saponite does not contain enough lithium to be classified as a The lake basin is bounded on the west by Dublin hectorite, and we have observed no indications that this clay con­ Hills, Ibex Hills, and the southern part of the Green- sists of a mixture of two phases, such as hectorite and a diluent. water Range and on the east by the southern parts of Some authigenic dioctahedral montmorillonite, found only in small quantities close to the tuffs, was formed by alteration of the the Nopah Range and Resting Spring Range. To the volcanic glass of the tuffs and was then admixed with the overlying south are the Sperry Hills through which the or underlying detrital clays. Amargosa River flows, draining the study area. The only authigenic clay-type mineral found in any significant The lake beds cover an area about 18 by 23 quantity is sepiolite, found near the edges of the lake basin and kilometers. The elevation of lowest exposures of the stratigraphically located mainly within a meter of the two upper­ most tuffs. This sepiolite probably was precipitated when silica beds is at about 396 m near the south end of the lake, became available to the magnesium-bearing lake water through and the highest beds are at about 549 m at the margins dissolution of the volcanic ash. Precipitation of sepiolite probably of the lake. The hills and mountain ranges to the east did not occur within the tuffs owing to the presence of alumina in and west of the basin have elevations of about solution. Zeolites were produced there and sepiolite formed outside 914-1,219 m. Sperry Hills to the south are about the margins of the tuffs. Also formed by the high-pH lake waters were water-soluble 610-762 m above sea level. minerals, which were found widely dispersed in crusts or streaks on the clays. Much of the calcite was likely precipitated from the lake ACKNOWLEDGMENTS waters, especially near the north
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