12 The Chemistry That F o r m e d G r e e n R i v e r F o r m a t i o n Oil S h a l e
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JOHN WARD SMITH Consultant, 1472 North Fifth Street, Laramie, WY 82070
The Green River Formation with its energy-rich o i l shales and its remarkable collection of huge amounts of novel minerals is the product of a gigantic chemical process system which established itself in ancient lakes surrounding Utah's Uinta Mountains. Once established the chemical process system stabilized and maintained itself, repeating the same chemical processes continuously for millions of years on the raw materials entering the lake. This chemistry produced uniform hydrogen-rich organic matter, a simple authigenic mineral suite, and massive deposits of sodium carbonate minerals like nahcolite (NaHCO ),dawsonite [NaAl(OH) CO ], shortite (Na CO •2CaCO ), and trona (Na CO •NaHCO •2Η O). The probable character of these chemical processes and their origin are reviewed. 3
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The Green River Formation o i l shales have produced only a limited amount of effort aimed at describing how they came to be. Much that has appeared looks at only one facet of a complex, integrated system. In 1925 Bradley (1) postulated a stratified lake to account for development of Green River Formation o i l shale. The stratified lake concept has much strength although Bradley ultimately was moved away from this postulate. Smith and Robb (2_), Smith (3), and Smith and Lee (4) have extended Bradley's postulate to develop a comprehensive picture of the chemistry and mechanics of genesis of the Green River Formation deposits. These concepts are summarized here. Green River Formation Characteristics The o i l shales of the Green River Formation in Colorado, Utah, and Wyoming formed from sediments deposited in Eocene lakes 0097-6156/ 83/0230-0225S07.00/0 © 1983 American Chemical Society Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
around the U i n t a Mountains. What remains of these d e p o s i t s i s o u t l i n e d i n F i g u r e 1. These o i l shales have been estimated t o o f f e r an o i l resource of 1.8 χ 10 b a r r e l s (260 χ 10 t ) of shale o i l i n p l a c e ( 5 ) . They dwarf most other o i l shale d e p o s i t s of the world i n both r i c h n e s s and resource. During t h e i r l i f e spans the Green R i v e r l a k e s , named Gosuite i n Wyoming and U i n t a i n Colorado and Utah, f l u c t u a t e d e x t e n s i v e l y i n s i z e . Conse quently the o i l s h a l e d e p o s i t s are v a r i a b l e pods of s p e c i a l i z e d l a c u s t r i n e sediments r e s t i n g on and enclosed i n the Wasatch Formation. The long l i v e d Green R i v e r l a k e s created sedimentary columns which d i f f e r between the Utah-Colorado d e p o s i t s and the Wyoming Deposits. Colorado's Green R i v e r Formation i n Piceance Creek B a s i n i s the t h i c k e s t and most continuous deposit and probably the l o n g e s t - l i v e d . F i g u r e 2 i s a north-south cross s e c t i o n of the Piceance Creek Basin (6) showing both s t r a t i g r a p h y and s t r u c t u r e of the Green R i v e r Formation. Most but not a l l of the Colorado o i l s h a l e occurs i n the Parachute Creek Member of the Green R i v e r Formation. A d d i t i o n a l o i l shale up t o about 400 f e e t t h i c k u n d e r l i e s the Parachute Creek Member i n the n o r t h c e n t r a l p a r t of the b a s i n . As i n d i c a t e d i n F i g u r e 2 t h i s o i l shale i s c l a s s e d as o c c u r r i n g i n the Garden Gulch and Douglas Creek Members. Although U.S.G.S. has attempted to preserve the two member names, t h e i r type s e c t i o n s overlap ( 7 ) . I n the b a s i n ' s d e p o s i t i o n a l center these members can't be r e a l i s t i c a l l y d i v i d e d . They represent a p r o g r e s s i o n from normal l a c u s t r i n e t o s a l i n e l a k e d e p o s i t i o n . A change i n m i n e r a l composition from c l a y - r i c h to d o l o m i t e - r i c h o i l shale marks the bottom of Colorado's Para chute Creek Member. A long sequence of s a l i n e m i n e r a l d e p o s i t i o n which formed n a h c o l i t e , dawsonite, and some h a l i t e begins a t the bottom of the Parachute Creek Member. Ground water has removed n a h c o l i t e and perhaps h a l i t e from the upper p a r t of the s e c t i o n where the s a l i n e minerals i n i t i a l l y formed. This s e c t i o n i s r e f e r r e d t o as the leached zone. The Mahogany zone (Figure 2) near the top of the Parachute Creek Member i s a s t r a t i g r a p h i e a c t i o n of very r i c h o i l shale marking the maximum expansion of ancient Lake U i n t a . Utah's Green R i v e r Formation o i l shales c o n s i s t almost e n t i r e l y of d e p o s i t s at o r above the Mahogany zone (8). The Wyoming d e p o s i t s of Green R i v e r Formation o i l shale r e c e i v e d d i f f e r e n t s t r a t i g r a p h i e names, but they show some s t r i k i n g s i m i l a r i t i e s to the d i s t r i b u t i o n i n Colorado (9)· The bottom s e c t i o n c a l l e d the T i p t o n Shale Member i s predominately c l a y - r i c h o i l s h a l e s i m i l a r to that i n Colorado. The next s e c t i o n , c a l l e d the W i l k i n s Peak Member, contains d o l o m i t e - r i c h o i l s h a l e l a y e r s i n t e r s p e r s e d w i t h l a y e r s of s a l i n e m i n e r a l s , p a r t i c u l a r l y t r o n a , or w i t h c l a s t i c d e p o s i t s away from the d e p o s i t i o n a l c e n t e r s . The uppermost s e c t i o n , c a l l e d the Laney Member, c o n s i s t s o f d o l o m i t e - r i c h d e p o s i t s formed d u r i n g a r e expansion of ancient Gosuite Lake.
Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Green River Formation Oil Shale
Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 29, 2018 | https://pubs.acs.org Publication Date: August 1, 1983 | doi: 10.1021/bk-1983-0230.ch012
SMITH
5. Ref. Figure 1. The Green River Formation. (Reproduced with permission from Copyright 1980, Colorado School of Mines.)
Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983. WHITE RIVER
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