Arctic Alaska Basin Response to Jurassic-Tertiary Plate-Margin Tectonics

David W. Houseknecht¹ and Alison B. Till^2
1U.S. Geological Survey, Reston, VA.
²U.S. Geological Survey, Anchorage, AK.

The Jurassic-Tertiary history of the Arctic Alaska-Chukotka microplate (AAC) involved plate-margin tectonic events that significantly influenced Arctic Alaska basin evolution. Jurassic-Early Cretaceous rift-shoulder uplift along the northern margin of AAC during opening of the Canada Basin was accompanied by closing of the South Anyui ocean basin, which culminated in collision with northeast Asia along the western margin of AAC (Chukotkan orogeny), and closing of the Angayucham ocean basin, which culminated in arc-continent collision along the southern margin of AAC (initial Brookian orogeny). These largely coeval events generated the hybrid Colville trough partly by flexural subsidence typical of foreland basins and partly by load-induced foundering of the moribund rift shoulder.

Progressive rift-shoulder uplift is reflected in a succession of southward-offlapping sequences in the Kingak Shale, deposited on the flank of the rift shoulder. Coeval strata deposited far to the south include earliest foreland-basin strata of the Okpikruak Formation, deposited in the ancestral Colville trough, which likely formed in response to tectonic loading by obducted oceanic rocks.

Early Cretaceous convergence along the western and southern margins of AAC culminated during the Aptian-Albian. Accommodation space in the Colville trough was narrowed by a northward propagating tectonic wedge of the ancestral Brooks Range and by syntectonic, wedgetop deposition of the Fortress Mountain Formation. A relatively large influx of sediment from significant uplift along the Chukotkan orogen fed the longitudinal west-to-east filling of the Colville trough, reflected in a thick and regionally extensive depositional sequence comprising the Torok and Nanushuk formations, which include evidence of syntectonic sedimentation, especially in the western part of the basin.

Following the Early Cretaceous docking of AAC with northeast Asia along the South Anyui suture, the Okhotsk-Chukotka volcanic belt (OCVB) developed as the result of subduction of a Pacific plate beneath northeast Asia. This is reflected throughout Arctic Alaska by abrupt reduction in sediment influx, increase in volcanic components in sandstones, and deposition of voluminous volcanic ash. Upper Cretaceous strata are of relatively modest volume and contain smaller scale depositional sequences compared to the Lower Cretaceous.

Tertiary convergence along the southern Alaska margin and stress transfer northward shaped the modern Brooks Range. This phase of tectonism affected the entire width of the Brooks Range during the Paleogene, and northward migration of deformation continued along the eastern Brooks Range where the modern tectonic front is active beneath the Beaufort shelf. Tertiary uplift of the range yielded a huge sediment influx that completed the filling of the remnant Colville trough and built most of the continental embankment along the southern Canada basin, north of the former rift shoulder.

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.

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