Mixed Carbonate and Clastic Mass Failures in a Sub-Lacustrine Settings: Implications for Unconventional Hydrocarbon Systems, a Study of the Green River and Uinta Formations (Eocene), Uinta and Piceance Basins, Utah and Colorado

Abstract

Mixed carbonate and siliciclastic failures occur prolifically in both submarine and sublacustrine settings, acting as reservoir, seal and source in these settings, and often acting as all of the above. The Green River Formation, one of the largest lake-deposited oil shale deposits in the world, contains frequent and extensive, oil shale breccia beds which are characterized by clasts of oil shale within an oil shale matrix. In contrast, the Uinta Formation, which represents the late phase filling and clastic progradation over the lake deposits of the Green River Fm. contains extensive, large sandy delta-front mass failures. These massive homogeneous sands toe down into the late stage lake deposits intertonguing with the oil rich (22% TOCs) shales of the Parachute Creek Mbr of the upper Green River. These large-scale delta front failures appear analogous to many of the major reservoirs found in rift basins of central China. However the oil shale breccias are more enigmatic and do not appear to be as broadly occurring worldwide. These mass failure types outcrop extensively allowing examination in detail of their facies, petrography, deformation structures, basal and upper contact nature, as well as healing phase sediments overlying these deposits. Pollen data provide details on climate and vegetation changes linked to failures. Failures which can comprise nearly 60% of some stratigraphic sections/core sections were mapped and characterized throughout the study area. Lake mass failures are significantly smaller in size and extent than those found in marine settings. However, these lake margin-attached failures act to flux water and sediments from the lake margins into very distal portions of the lake, changing water chemistry, sediment mixes and even inducing significant lake tsunamigenic waves.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019