Fluvial Depositional Variability in the Douglas Creek and Parachute Creek Members, Green River Formation, Uinta Basin, Utah

Abstract

The Eocene Green River Formation consists of continental strata deposited in western USA Laramide ponded basins. This study documents alluvial and lacustrine strata from the Douglas Creek and Parachute Creek Members of the middle Green River Formation in Main Canyon, southeastern Uinta Basin, Utah, and utilizes fluvial sedimentary expressions to interpret depositional controls with implications for reservoir geometry and connectivity. The 180-m thick section of interest was divided into three distinct, stratigraphically separated depositional settings: (1) the lowermost Interval 1 is dominated by laterally extensive, weakly erosive, amalgamated sandstone channels that contain abundant upper-flow-regime sedimentary structures. The channels are interpreted to represent seasonal fluvial flood deposition in a semi-arid to sub-humid climate. (2) Interval 2 is dominated by cyclic littoral lacustrine deposits, interpreted as pulsed siliciclastic input from a fluvial source into shallow Lake Uinta with periods of local fluvial inactivity represented by carbonate deposition. (3) The uppermost Interval 3 is dominated by laterally confined, erosionally based, trough cross bedded sandstone channels that contain significant tar accumulation, and are interbedded with deltaic and lacustrine deposits. The Interval 3 channels are interpreted as perennial fluvial deposits with relatively little variation in annual discharge and sediment deposition rates. The transition from seasonally controlled fluvial flood deposition in Interval 1 to perennial fluvial deposition in Interval 3 indicates changing fluvial controls, which is interpreted as the result of a climatic shift from the hyperthermal regime of the Early Eocene Climatic Optimum (EECO) to a more stable post-EECO climate.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018