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Controls on the Evolution of Late Cretaceous to Paleocene Coastal to Deltaic Systems of the Prince Creek and Schrader Bluff Formations, North Slope of Alaska


Facies, sandbody-shale geometries, architectures, stacking pattern, and key surfaces in shallow-marine to continental successions in evolving foreland basins are strongly influenced by sediment supply, fluctuating base level, active tectonics and the relative influence of fluvial-floods, tides, and waves. A decade-long field study of the Cretaceous-Paleocene Schrader Bluff (SB) and Prince Creek (PC) formations on the North Slope of Alaska examines the effects of forcings on the character of these deposits, which are outcrop analogs for shallow, viscous- to heavy-oil reservoirs. The lowermost 400 m at Shivugak Bluffs along the Colville River contains river-dominated deltas comprising distributary mouth bars (DMBs), subaqueous terminal distributary channels (TDCs), interdistributary bays, medial delta front deposits, distal delta front deposits, prodelta deposits, proximal shelf deposits, and wave-reworked DMB-TDC complexes. The uppermost SB contains a mud-rich, river-dominated delta with muddy prodelta and delta-front deposits comprising hyperpycnites, subaqueous terminal distributary channels, interdistributary bays, and mouth bars that transition to lower delta plain lakes, floodbasins and distributary channels. Overlying Cretaceous PC strata are dominated by interconnected meandering and fixed distributary channels, splays, shallow lakes, thin coals, and weakly-developed paleosols. In contrast Paleocene PCF deposits comprise isolated meandering distributary channels encased in organic-rich floodplain deposits that include significantly thicker lacustrine deposits and thicker coals. Cretaceous PC facies and architectures suggest a relatively low subsidence rate and low accommodation. Alternatively, Paleocene deposits including isolated sandbodies encased in thick organic floodplain facies, thick lacustrine deposits and thick coals suggest a higher subsidence rate and higher accommodation. Lower accommodation during the Cretaceous may reflect a more distal position relative to the orogenic belt and foredeep, and proximity of to a paleo-high (Barrow Arch). Higher accommodation during the Paleocene likely reflects deposition proximal to the foredeep and higher subsidence likely driven by lithospheric-orogenic loading. An understanding of the relationship between facies trends, sandbody geometries, stacking pattern and their relationship to relative forcings will ultimately improve reservoir models and net/gross estimates for North Slope PCF reservoirs.