Brookian Synorogenic Sedimentation, Easternmost Beaufort Sea and Arctic National Wildlife Refuge (ANWR)

By

D.W. Houseknecht (U. S. Geological Survey)

Seismic data in the easternmost Beaufort Sea and ANWR coastal plain, together with sparse well control offshore and scattered outcrops onshore, yield a provocative glimpse of a dynamic relationship among tectonism, diapirism(?), and sedimentation in Tertiary through Holocene strata representing the youngest portion of the Brooks Range orogenic front. Strata are segmented into syntectonic sub-basins separated by linear uplifts involving deformed and geopressured, Tertiary mudstones of marine slope and deep basin origin.

Seismic geometries suggest that uplifts were initiated by thrusts rooted in pre-Upper Cretaceous rocks and modified by ductile deformation of geopressured mudstones. The uplifts were not significant sediment sources. Rather, they controlled accommodation and acted as dams to trap most coarse-grained detritus derived from the Brooks Range. Sedimentation was contemporaneous with uplift as indicated by onlap and thinning of strata, as well as convergence of local angular unconformities, onto the uplifts. South of the uplifts, sub-basins are mostly filled with parallel seismic reflections representing sand-prone, shallow marine and non-marine strata. On the northern flanks of uplifts, seismic re- flections roll over into clinoforms representing mud-prone, marine slope and deep basin strata. These relationships indicate that shelf margins were localized by the growing uplifts. Seismic correlation of depositional sequences suggests stepwise northward migration of the orogenic front, with timing of uplift ranging from Paleocene in the southeastern ANWR coastal plain to Holocene in the Beaufort Sea. Although this geologic setting differs from older parts of the orogenic front to the west (continental margin vs. foredeep), it nevertheless provides insights for interpreting the origin of structurally dismembered Cretaceous strata exposed in the Brooks Range foothills of the central and western North Slope.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.