Aptian/Albian Sediment Volume and Accumulation Rates, Alaska North Slope and Beaufort Shelf, from Sequence Stratigraphic Interpretation and Modeling (thesis)

Abstract

We present a regional sequence-stratigraphic interpretation of the Torok-Nanushuk clinothem in the National Petroleum Reserve of Alaska (NPRA), Alaskan state lands and Beaufort shelf using 2-D seismic reflection data, augmented by surface and well data. We take into account the adjacent geology in a consistent regional context. This interpretation refines previous interpretation of the Aptian-Cenomanian clinothem. From this interpretation, we created a 3D model which includes nineteen individual sequences, each representing approximately 1 Ma of sedimentation. We calculated sediment accumulation volumes and rates for the Torok-Nanushuk system represented in the study area. Our bulk estimates of volume in the study area is more than than 638,660 km3 deposited over 20 million years, or an average of 0.08 km per million year. This is a minimum rate for the total Torok-Nanushuk sequence in Arctic Alaska, as we do not take into account erosion or decompaction. Along the southwestern edge of the Coleville basin, the Torok Formation onlaps the Lower Cretaceous Mount Kelly Graywacke and interfingers Fortress Mountain Formations. Onshore, the Torok-Nanushuk clinothem downlap onto a relict shelf margin which was later draped by a marine transgressive unit, the Hauterivian-Aptian pebble shale unit and gamma ray zone. Offshore, the Torok-Nanushuk clinothem downlap onto a lower Cretaceous unconformity. The ultimate shelf margin occurs just east of the Coleville River, where it is terminated by a lowstand sequence boundary.