LATE PALEOZOIC-MESOZOIC TECTONIC CONTROLS ON NORTH SLOPE BASIN DEVELOPMENT, NW ALASKA

Geophysical well logs and 2-D reflection seismic data were analyzed to investigate the tectonic history of the North Slope Basin in the National Petroleum Reserve, Alaska (NPRA). The stratigraphy and structures of the study area were evaluated by mapping subsurface horizons imaged along various seismic lines in the eastern part of NPRA. Subsurface reflections were correlated with stratigraphic data from nearby well geophysical logs in order to conduct a time/depth conversion of the regional seismic lines. From this, isopach maps for selected stratigraphic intervals were constructed in order to delineate the overall stratigraphic architecture of the region and identify basin depocenters. Interval thicknesses, lithologic compositions, estimated porosities, stratigraphic ages, and paleo-water depths were then compiled in order to conduct a subsidence analysis of the study area.

The results of the geohistory analysis show that during the Carboniferous, the region experienced rapid subsidence related to rifting and passive margin development. This was them followed by a depositional hiatus during the Permian and relatively low rates of basin accommodation development during Triassic-Jurassic time. Beginning in the earliest Cretaceous the basin was flexurally partitioned during early development of the Brookian foreland-basin system. The return of rapid rates of subsidence in the basin during the Aptian corresponds to the timing of initial migration of the Brookian foredeep into the region as thrust loading in the developing Brooks Range propagated to the north.