Geochemistry of Lower Eocene Sandstones in the Rocky Mountain Region GEOLOGICAL SURVEY PROFESSIONAL PAPER 789 Geochemistry of Lower Eocene Sandstones in the Rocky Mountain Region By JAMES D. VINE and ELIZABETH B. TOURTELOT With a section on DIRECT-READER SPECTROMETRIC ANALYSES By RAYMOND G. HAVENS and ALFRED T. :MYERS GEOLOGICAL SURVEY PROFESSIONAL PAPER 789 A regional study of element distribution) petrology) and diagenesis among samples of fluvial sandstone from basins of Tertiary age in the Rocky Mountain region UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 72-600317 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 Price (paper cover) 75 cents domestic postpaid or 55 cents GPO Bookstore Stock Number 2401-Q0275 CONTENTS Page Page Abstract ____________________________________________________________________________________ _ 1 Petrology and mineralogy-Continued Introduction and acknowledgments-------------------------------------- 1 Diagenesis and metamorphism______________________________________ 18 Geologic setting _______________________________________________________________________ _ 2 Chemical composition of sandstones_____________________________________ 20 Distribution and paleogeography _________________________________ _ 2 Statistical methods___________________________________________________________ 20 Stratigraphic relations __________________________________________________ _ 3 Means_________________________________________________________________________________ 20 Sampling plan __________________________________________________________________________ _ 6 Methods of analysis ________________________________________________________________ _ Geochemical relations______________________________________________________ 25 12 Analysis of variance________________________________________________ 25 Direct-reader spectrometric analyses, by Raymond G. Havens and Alfred T. Myers _______________________________ _ 13 Component analysis------------------------------------------------- 27 Geochemistry of sample areas _________ _._____________________ 29 X-ray diffraction analyses _____________________________________________ _ 13 Petrology and mineralogy _____________________________________________________ _ 14 Discussion__________________________________________________________________________________ 32 Mineral composition and classification of samples ___ _ 14 SummarY-----------------------------------------------------------------------------------· 33 Cement and matrix _________________________________________________________ _ 17 References cited________________________________________________________________________ 33 ILLUSTRATIONS Page FIGURE 1. Map showing basins and major uplifts in early Eocene time, present outcrop pattern of lower Eocene sedimentary rocks, and sample localities·-------------------------------------------------------------------------------------------------------------· 4 2. Generalized cross section of an Eocene basin...... ----------------------------------------------------------------------------------------------·--·-···· 5 3. Triangular diagram showing average composition of lower Eocene sandstone in 36 areas in the Rocky Mountain region ____ ·---------------------------------------------------------------------------------------------------------------------------------------------------- 14 4. Photomicrograph of quartz-chert sandstone from the Willwood Formation, Bighorn Basin____________________________ 14 5. Map showing distribution of lower Eocene sandstone types, and colors of the sandstone in powdered sam- ples in 36 areas in the Rocky Mountain region _________________________________________________________________________________ :_____________________ 15 6-14. Photomicrographs: 6. Arkosic sandstone from the Wind River Formation, Wind River Basin__________________________________________________ 16 7. Intermediate sandstone, Great Divide Basin·------------------------------------------------------------------------------------------------- 16 8. Lithic sandstone from the Wind River Formation, Wind River Basin_____________________________________________________ 17 9. Etched quartz grain from the Wasatch Formation, Wasatch Range________________________________________________________ 17 10. Altered feldspar grain from the Hanna Formation, northern Hanna basin_____________________________________________ 17 11. Sandstone, showing a uniformly textured clay cement from the Willwood Formation, west flank of the Bighorn Basin·--------------------------------------------------------------------------------------·············································-····- 18 12. Sandstone, showing a montmorillonite matrix from the Wasatch Formation, Sand Wash basin........ 19 13. Laumontite-cemented sandstone from the Cuchara Formation, Raton basin__________________________________________ 19 14. Feldspar grain partly replaced by epidote in arkosic sandstone from the Wasatch Formation, Great Divide Basin.·-----------------··---------·-······-··--·-------·····------------··----------------------------------------------------·····--------------------·· 19 15. Diagram showing concentration range of major constituents in 216 samples of lower Eocene sandstone in the Rocky Mountain Region ______________________________ ------------------------------------------------------------------------------------------------------- 24 16. Diagram showing concentration range of minor elements in 216 samples of lower Eocene sandstone in the Rocky Mountain region·--------------------------------------------------------------------------------------------------------------------------------············ 25 17. Vector diagram for 216 samples of lower Eocene sandstone.--------------------------------------------------------------------------------· 26 18. Vector diagram for color subsets of the sandstone samples·----------------------------------------------------------------------------------- 30 TABLES Page TABLE 1. Sample localities, stratigraphic assignments, and petrographic descriptions of 216 samples of lower Eocene sandstone ______________________________________________________________ --------------------------------------------------------------------------------------------····------- 7 2. Arithmetic mean, standard deviation, geometric mean, and geometric deviation of the analysis of 10 splits from one sample·-------------------------------------------------------------------------------------------------------------------------------------------------------- 12 III IV CONTENTS Page TABLE 3. Analytical conditions for the direct-reader spectrometric analysis of sandstone ______________________________________________ _ 13 4. Spectral lines used for the elements reported and the concentration ranges covered ______________________________________ _ 13 5. Comparison of direct-reader spectrometric analyses with recommended values _________________________________________________ _ 13 6. Limits of detection and values used to replace indeterminate analyses-----------------------------------------------------------------· 20 7. Distribution of constituents in 216 samples of lower Eocene sandstone and in 36 areas and four color subsets of the samples·---------------------------------------------------------------------------------------------------------------------------------------------- 21 8. Variance components·-------------------------------------------------------------------------------------------------------------------------------------------------------- 27 9. Areas where any constituent mean value for six samples is greater than one geometric mean times the geometric deviation of all samples or is less than one geometric mean divided by the geometric devia- tion of all samples·---------------------------------------------------------------------------------------------------------------------------------------------------- 29 GEOCHEMISTRY OF LOWER EOCENE SANDSTONES IN THE ROCKY MOUNTAIN REGION By JAMES D. VINE and ELIZABETH B. TouRTELOT ABSTRACT Early diagenetic alteration is evidenced by widespread The composition of lower Eocene fluvial sandstones in the authigenic clay, carbonate, and zeolite minerals, the etching Rocky Mountain region was studied to aid in interpretation of quartz, the presumed dissolution of mafic silicate minerals, of the regional geochemical environment of uranium and and the enrichment of minor elements in areas of intermedi­ other mineral deposits in rocks of early Eocene age. The ate rock rather than in areas rich only in feldspar, quartz, or study was based on 216 samples, from 18 basins, collected carbonate. In many areas, red sandstone probably represent according to a hierarchial plan that involved the random rocks that were origi~ally greenish gray and that were altered selection of three pairs of beds in each of 36 sample areas. at a later stage. Although rock color can be the result of The geometric means of the constituents (in percent) and many processes, the red alteration may have been caused by of the minor elements (in parts per million) for these 216 the introduction of oxygenated meteoric ground. waters and samples are as follows (geometric deviation in parentheses) : the accompanied leaching of iron and many of the more mo­ Si02, 72.9 (1.2);