Abstract: Stromatolites in Eocene Green River Formation

Ronald C. Surdam, J. L. Wray, L. L. Lundell

Since the outstanding work of Bradley, stromatolites have been known to occur in the shore facies of the lacustrine Eocene Green River Formation. Recent work on these stromatolites has resulted in a detailed understanding of the dynamics of ancient lakes Gosiute and Uinta. The position of the stromatolites in stratification sequences, the sedimentary structures associated with stromatolites and spatially related rocks, the orientation of stromes, the thickness of stromatolitic layers, and the internal fabric and external morphology of stromes document shoreline geometry, fluctuations in water depth, nature of shorelines (transgressive versus regressive), and topographic gradients in the ancient lakes.

The stromatolites in the Green River Formation are of two types--algal or tufa. The algal stromatolites are similar both in internal fabric and external morphology to the stromatolites at Shark Bay, Australia. The tufa stromatolites are similar in internal fabric and external morphology to the tufa deposits at Mono Lake, California. The algal stromatolites in the Green River Formation commonly form thin sheets. The thickness of these sheets can be related to the topographic gradient at the site of deposition. In contrast, the tufa deposits are mound shaped (bioherms). The position of these mounds commonly is related to faults associated with tectonically active areas in the ancient lake basins.

Both types of stromatolites may show evidence of diagenesis, particularly if they were subjected to early subaerial exposure, such as along a regressive shoreline. Commonly the diagenesis includes dolomitization and/or the development of vadose pisolites.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma