Topic: "Context, Internal Characteristics and Controls on Brookian "shelf-edge deltas", North Slope, AK: Insight From Integrated Seismic Facies Mapping and Core Description"
Speaker: Dr. Jennifer Aschoff, Department of Geological Sciences, University of Alaska, Anchorage
Throughout the geologic past, sea-level has fallen to the shelf-edge numerous times, exposing the shelf to erosion, and transporting large volumes of sediment across the shelf to the shelf-edge and basin-floor. The process can be driven by tectonics, sea-level and/or sediment supply, forming clinoforms with a wide range of heights, geometries and internal architectures. The repeated progradation of sediment to the shelf-edge is important for constructing continental margins over time, and forming shelf-edge and deepwater sandstone reservoirs. Various authors have reported “Basinward-thickening wedges with shingled internal reflections” within the Nanushuk and Torok formations, and these were interpreted as “shelf-margin deltas”, “shoreface prisms” or “shelf-edge wedges”. Previous studies suggest that shelf-edge delta deposits may be present, but little is known about their distribution, external controls on their formation, or their internal characteristics in the North Slope. This study presents a preliminary integrated stratigraphic analysis including high-resolution sequence stratigraphy, seismic sedimentary facies mapping, detailed core description, and log analysis to: 1) delineate “true” shelf-edge delta deposits from other near shelf-edge sands in the Brookian sequence, 2) map the distribution of these “true” shelf-edge delta deposits, and 3) quantify key characteristics of “true” shelf-edge delta deposits in comparison to other delta deposits. “True” shelf-edge delta deposits were situated within a mile from the previous paleo shelf-edge; these deposits form narrow, shoreline-parallel sandstones that are about 1-3 miles wide and 10’s of miles long. Many of these shelf-edge delta deposits are wave-dominated as indicated by their map-view geometry and internal characteristics from core, and their connectivity is variable. In contrast, inner-shelf and mid-shelf deltaic deposits are positioned further away from the paleo shelf-edge and tend to be more river- dominated to mixed-energy sandy successions. Furthermore, the sequence-stratigraphic context of “true” shelf-edge delta successions suggests that they may be more abundant in stratigraphic intervals characterized by numerous high-frequency sea-level drops. Spatially, the distribution of shelf-edge delta deposits shows a subordinate control by antecedent topography/sediment pathways but no clear control by structures. In conclusion, this study suggests an integrated approach to help discern “true” shelf-edge delta deposits from other types of deltaics, and provides some insight into the external/internal characteristics of Brookian shelf-edge deltas that can aid exploration/production in the North Slope.
Dr. Jennifer Aschoff is an Associate Professor of Stratigraphy in the Department of Geological Sciences at the University of Alaska, Anchorage. She currently manages a diverse research group focused on understanding the formation, fill and petroleum resources of foreland basins, including the Cordilleran Foreland Basin (Rocky Mtns) and North Slope, AK. Prior to joining the Department of Geological Sciences in 2014, she was a Stratigraphic Specialist at BP-America in Houston, TX where she worked on a range of access-, exploration- and production-scale problems in Global Unconventional Access, Renewal, North America Gas and Lower 48 Business Unit. Additionally, Dr. Aschoff was tenure-track faculty at Colorado School of Mines from 2008-2011, and research faculty concurrent with her role at BP from 2011-2014. Her technical expertise is focused in foreland basin dynamics, clastic sequence stratigraphy, and marginal marine deposits.
Time: Doors open at 11:30 am, talk is from 12-1 pm