Variations in Fluvial Sand-Body Architecture within the Depositional Systems of the Cretaceous Mesaverde and Eocene Wasatch Formations, Greater Uinta Basin, Utah
Howard White, Rachel Friedman, Sean Kelly, and Rex Cole
Fluvial sand-body geometries within the Cretaceous Mesaverde and Eocene systems in eastern Utah and western Colorado range from crevasse splay, single to multi-storied channels to very thick, amalgamated complexes. The Mesaverde alluvial system began as proximal fan deposits shed from the emerging Sevier Orogenic Belt and continued to build and prograde eastward toward Colorado during the Campanian. Early Tertiary Laramide deformation defined the Uinta Basin and the subsequent basin fill, including the Eocene Wasatch Formation. Mesaverde outcrops within Tusher and Sego canyons, east central Utah, show dominant amalgamated sands with limited preservation of overbank fines or periods of low sand input. Depositionally, these more proximal successions supplied sand detritus to the more varied Mesaverde sand bodies of Greater Natural Buttes Field in the eastern Uinta Basin, approximately 50 mi down depositional dip. The 2000 ft of Mesaverde in GNB Field contains the full range of sand-body types and can be stratigraphically divided into intervals of comparatively low net-to-gross (i.e., individual to scattered multi-storied channels) to more amalgamated zones of high net-to-gross input. Observed differences in channel stacking and amalgamation likely resulted from a combination of local changes in accommodation space (local structural control) and tectonically(?) initiated pulses in sediment supply. Thirty miles to the east (further down the Mesaverde depositional system), exposures in the Douglas Creek Arch of northwest Colorado exhibit an even more segregated architecture and fewer amalgamated sands. Progradational fluvial systems present in the Arch continued down trend supplying detritus to the succession of Mesaverde shoreline systems in eastern Piceance Basin. Wasatch sand bodies, by comparison, are confined and controlled by intermountain basin accommodation conditions and peripheral sediment supply. In Tusher and Sego canyons the Wasatch is lower net-to-gross than the amalgamated Mesaverde and exhibits dominant single channels and limited multi-story to amalgamated development. Cored intervals of Wasatch in GNB Field display an even lower net-to-gross deposition. Single to infrequent multi-story channels comprise the hydrocarbon reservoirs within the basin-center Wasatch.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012