Structural Architecture Below the North Slope’s Sub-Mississippian Unconformity: Constraints From Geological Mapping in the Brooks Range, Alaska

Abstract

The Brooks Range of northern Alaska is a fold-and-thrust belt with a long and complex geological history. It preserves a record of orogenic events from the early Paleozoic, Mesozoic, and into the Cenozoic. The adjacent foreland basin, the North Slope, is famous for its prolific petroleum discoveries. Most of these discoveries occur along basement highs, principally the Barrow arch, which are truncated by a prominent sub-Mississippian unconformity observed throughout the North Slope subsurface. The unconformity, and the pre-Mississippian rocks below it, are also well exposed in parts of the northeastern and central Brooks Range. Structural trends within the sub-Mississippian rocks have long been considered to reflect early Paleozoic orogenic events. Preliminary mapping and stratigraphic correlation of rocks exposed in northeastern and central Brooks Range was performed by integrating field-based observations with remote sensing data such as the new 5 m ArcticDEM and satellite imagery from Google Earth. Two dimensional structural restorations across the northeastern and central field areas reveal a complex pre-Mississippian structural history. We postulate that the basement of the North Slope was assembled via the amalgamation of at least three disparate terrains, which include (1) a Cambrian to Silurian volcanic arc complex, named the Doonerak arc and exclusively exposed in the central Brooks Range; (2) a Cambrian to Ordovician(?) fragment of oceanic crust, informally named the Whale Mountain allochthon; and (3) a parautochthonous succession of Neoproterzoic to Early Devonian(?) passive margin and foreland basin deposits. The boundaries separating these terrains exhibit strong control on the structural styles of the subsequent Mesozoic and Cenozoic structures of the Brooks Range and possibly the basement highs in the subsurface of the North Slope.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018