Aptian/Albian Sediment Volume and Accumulation Rates, Alaska North Slope and Beaufort Shelf, From Sequence Stratigraphic Interpretation and 3-D Backstripping

Abstract

The Aptian to Cenomanian Torok and Nanushuk Formations of Arctic Alaska form a clinothem that extends across much of the Chukchi shelf, North Slope, and Beaufort shelf. The Torok-Nanushuk depositional system, whose main sediment source was the Chukotka orogen, prograded eastward to fill the Colville basin and overstepped the Barrow arch to build part of the passive margin of the Canada Basin. Along the southwestern, orogenic side of the Colville basin, Torok and lower Nanushuk moderate to deep water facies onlap a tectonic wedge comprising mainly sandstone and conglomerate of the Aptian Mt. Kelly Formation. Onshore, the Torok and lower Nanushuk basin-floor to shelf facies downlap/onlap onto a Hauterivian-Aptian condensed section. The ultimate shelf margin of the Torok-Nanushuk sequence occurs just east of the Colville River. To the east, the Torok-Nanushuk depositional system is terminated by a lowstand sequence boundary, which was subsequently covered by a Cenomanian to Turonian transgressive systems tract[HDW1]. Along the northern coast of the National Petroleum Reserve in Alaska (NPRA), the Torok-Nanushuk Formations are deeply incised, likely the result of the terminal lowstand. These canyons are filled with Upper Cretaceous strata. North of the Barrow arch and beneath the Beaufort shelf, the Torok-Nanushuk clinothem expand northward across large growth faults. A regional sequence stratigraphic interpretation of the Torok-Nanushuk sequence in NPRA, Alaska state lands and inner Beaufort shelf was performed using 2-D seismic reflection data, augmented by surface and well data. In our interpretation, we mapped foreset, bottomset, and topset seismic relationships in order to characterize the time-transgressive depositional facies. We created a 3D model from this interpretation, which includes nineteen individual sequences, each representing approximately 1 Ma of sedimentation. We performed backstripping to calculate sediment accumulation volumes and rates for the Torok-Nanushuk system represented in the study area. Our initial bulk estimates of volume in the study area is more than than 270,000 km³ deposited over 20 My, or an average of 13,500 km³/My. This represents a minimum rate for the total Torok-Nanushuk sequence in Arctic Alaska because of erosion, and because the study does not consider the Torok-Nanushuk Formations in the Chukchi Sea.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016