CONTROLLING FACTORS ON DEPOSITION OF SALINE LACUSTRINE SEDIMENTS IN THE EOCENE GREEN RIVER FORMATION OF FOSSIL BASIN, WYOMING
Palynological analysis of oil shales in the upper unit provides insight into climatic conditions during deposition of the upper unit. The overall palynoflora of the upper unit suggests a slightly drier climate than earlier in the lake history. Vegetation from the surrounding uplands becomes predominant, while the lake margin vegetation is poorly represented. A well-developed lake margin flora would suggest a prolonged period of wetter climate. However, the occurrence of Platycarya in the oil shales indicates a climate of high humidity and abundant summer rainfall during the transgressive facies of the upper unit.
The upper unit fits into the underfilled lake basin category in the three end-member classification of lake basins (i.e., overfilled, balanced-fill, and underfilled). High-frequency wet-dry cycles with minimal fluvial input characterize underfilled basins. The palynological data corroborate the sedimentological evidence for wet cycles during deposition of the upper unit and its classification as an underfilled basin.