Tertiary Synorogenic Sedimentation Along the Brookian Tectonic Front, Eastern U.S. Beaufort Sea and Arctic National Wildlife Refuge (ANWR) Coastal Plain

David W. Houseknecht
U.S. Geological Survey, Reston, VA

The eastward transition from a passive continental margin “growth fault province” to a contractional “ridges and sub-basins province” is recorded by seismic data in the Beaufort Sea and ANWR coastal plain. West of 145.5°W, Tertiary strata thicken northward across listric growth faults that sole into Paleogene basinal mudstones. Limited data suggest the Tertiary section is overpressured below the transition from sand-prone topsets to mud-prone clinoforms. East of 145.5°W, Tertiary strata are segmented into sub-basins separated by east-west-oriented, elongate uplifts containing deformed, growth-faulted Tertiary strata and cored by overpressured and intensely deformed Paleogene basinal mudstones. Seismic geometries suggest that uplifts were initiated by thrust faults rooted in pre-Upper Cretaceous rocks and were modified by ductile deformation, perhaps including diapirism, of overpressured Paleogene mudstones. This “ridges and sub-basins province” continues eastward into the Canadian Beaufort – Mackenzie Basin.

The uplifts were not significant sediment sources but acted as accommodation sills to trap sediment derived from the Brooks Range in trailing sub-basins. Each sub-basin is characterized by mostly parallel seismic reflections representing sand-prone, shallow marine and nonmarine strata, which pinch out or thin northward onto the paired uplift. At the northern flank of the uplift, these seismic reflections terminate into top-lapping clinoforms representing mud-prone, marine slope strata, indicating that the bathymetric shelf break was localized by the growing uplifts. These stratal geometries combined with regional correlation of depositional sequences indicate northward migration of the orogenic front across the earlier formed growth faulted margin, with uplift ranging from Paleocene onshore to Holocene offshore.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005