EARLY CRETACEOUS TO TERTIARY EVOLUTION OF THE COLVILLE FORELAND BASIN – LINKED TECTONICS AND SEDIMENTATION

HOUSEKNECHT, David W., U.S. Geol Survey, 956 National Center, Reston, VA 20175, [email protected]

Although the initial development of the Colville foreland basin likely was related to collision of North America with oceanic terranes during middle Jurassic to early Cretaceous (Neocomian) time, subsequent tectonic dismemberment and cannabilism of nascent foreland-basin strata limit reconstruction of that phase of basin history. In contrast, relatively well preserved Barremian to Tertiary strata record evolution of the Colville foreland basin as the Arctic Alaska microplate simultaneously rifted from North America on one side and collided with oceanic terranes on the opposite side. Coeval rift-shoulder development along the northern (present coordinates) plate margin and additional collision along the southern plate margin largely controlled regional patterns of uplift and subsidence. Although the rift shoulder progressively subsided owing to thermal contraction and sediment loading, it acted as an accommodation sill during foreland basin filling. Episodic contraction, punctuated by extension and magmatism, along the Brooks Range – Herald arch – Chukotka orogen controlled accommodation and sediment flux across the foreland. These regional patterns were influenced by an earlier structural grain inherited mostly from pre-Permian rifting.

Brookian strata of Barremian to Tertiary age represent at least four distinct phases of linked tectonic-sedimentary evolution. (1) Barremian-Cenomanian strata were deposited in foredeep and foreland platform settings characterized by tectonically driven accommodation and a huge sediment flux from the orogen. (2) Turonian-Maastrichtian strata accumulated in passive accommodation space during tectonic quiescence and modest sediment flux. (3) Paleocene-Eocene strata were deposited during tectonic segmentation of the foreland involving transtension in the Chukchi Sea, low-relief uplift across the western North Slope, and tectonic subsidence linked to renewed northward migration of the Brooks Range across the eastern North Slope. This phase was characterized by high sediment flux and the complete filling of the foreland basin in the east. (4) Post-Eocene strata were deposited as generally northward offlapping sequences on the rifted-margin and into the Canada basin, with high sediment flux related to the north-verging orogenic belt.