Sedimentology and Stratigraphy of the Douglas Creek Member in the Green River Formation, Main Canyon, Uinta Basin, Utah

Abstract

The early to late Eocene Green River Formation represents lacustrine deposition across economically significant basins in Utah, Colorado, and Wyoming. In the Uinta Basin of Utah, the Douglas Creek Member is the stratigraphically lowest section of the Green River Formation which has received little published attention. Main Canyon offers excellent outcrop exposures of the Douglas Creek Member, where this study incorporates 6 measured sections from a 20 km transect to document the vertical and lateral variation in the mixed carbonate and siliciclastic system. Three distinct stratigraphic intervals are observed. The lowermost ∼50 m interval of study consists largely of weakly- to moderately-channelized sandstone bodies interbedded with siltstone and pedogenically-modified fine-grained deposits, representing a fluvial-deltaic succession. A ∼50 m intermediate interval of the Douglas Creek Member is represented by fine-grained deposition of siltstone and carbonate interbedded with sandstone and mixed carbonate-sandstone deposited in littoral and sublittoral lacustrine-deltaic environments. Microbialites and carbonate beds demark sediment starved periods, which are capped by cyclic 5-10 m coarsening upwards packages of siltstone and tabular to weakly-channelized sand bodies, representing periods of deltaic growth. An upper ∼50 m interval of Douglas Creek strata consists of fine-grained siliciclastic and carbonate deposits interbedded with erosionally-based, discontinuous sandstone bodies as thick as 10 m and laterally extensive for approximately 100-150 m. These sand bodies contain tar accumulation. The upper interval represents the deltaic transition to the lacustrine Parachute Creek Member. Climate and/or tectonics are likely the major control on changing Douglas Creek Member deposition captured in this study. Eocene hyperthermal events in particular may have driven changes in sediment availability, resulting in the alternation between carbonate and siliciclastic deposition in the intermediate interval. The observed vertical and lateral variability of the Douglas Creek Member provides insight into changing depositional environments and related sediment distribution in the understudied southeastern Uinta Basin during early Lake Uinta evolution.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016