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Abstract: Carbonate Cycles in Green River Formation, Wyoming

H. Previous HitPaulTop Buchheim, Ronald C. Surdam

Well-developed repetitive stratification sequences characterize the lacustrine carbonate rocks in the Laney Member of the Green River Formation of Wyoming. These sequences commonly consist of two parts: a lower calcite-dominated part (oil shale) and an upper dolomite-dominated part (dolomicrite). The calcitic rocks are characterized by well-developed laminations, fossil fish, and high kerogen content. The dolomitic rocks are massive or poorly laminated, contain saline mineral casts and molds, and are associated with stromatolites, mud cracks, ripple cross-laminations, and scour-fill structures.

Individual sequences (average 2 m thick) can be traced laterally for 50 to 60 km. Toward the margins of the depositional basin the stratification sequences are diluted by siliciclastics, and contain immature fish, insects, plant remains, abundant ostracods, and siliciclastic debris associated with a variety of strandline deposits. The sequences at the center of the basin contain higher carbonate and kerogen contents and adult fish.

These stratification sequences and the distribution of carbonate rocks are interpreted as the result of lacustrine transgressions and regressions across a low topographic gradient in a hydrographically closed basin. Dolomitic sediments were generated on fringing mud flats during regressive stages of the lake. Subsequent traction transport redistributed the dolomitic sediments on the fringing mud flat and into the adjacent lacustrine environment. Calcite and/or aragonite precipitated from the water column as a result of the interaction of relatively fresh surface waters and more alkaline lake waters.

AAPG Search and Discovery Article #90964©1978 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah