Stratigraphy, structure, and palinspastic synthesis of the western Brooks Range, northwestern Alaska

Abstract

This chapter describes the stratigraphy and structure of the western Brooks Range. During the orogeny that created the Brooks Range in Jurassic and Cretaceous time, a stable continental shelf containing Devonian to Lower and Middle( ) Jurassic sediments was broken up and telescoped by numerous thrust faults, the combined displaced measuring hundreds of kilometers. In the first section of this report a tectonostratigraphic scheme is outlined in an attempt to simplify and catalog the thrust-faulted stratigraphy. This section is followed by a palinspastic synthesis in which the rock units are restored to their original basins of deposition. The report concludes with a plate-tectonic model that seems to explain the principal orogenic processes which created the Brooks Range. The palinspastic synthesis of the western Brooks Range concentrates on a 300-m.y. period from Devonian to Cretaceous time. This period includes the time of deposition of most of the regional sedimentary rocks units that crop out in the northern and western parts of the western Brooks Range. In the southeastern part, Precambrian and lower Paleozoic rocks are exposed, but mush of their geologic history was obscured by regional metamorphism during the Brooks Range orogeny in Jurassic and Cretaceous time. The tectonostratigraphic scheme presentedmore » in this report is based on 12,000 km{sup 2} of geologic field mapping at a scale of 1:63,360 (1 in. = 1 mi). Field work was done during the summer moths of 1978, 1979, and 1981. This mapping project, undertaken in order to achieve a better understanding of the complex structure and stratigraphy of the western Brooks Range, was carried out in connection with the exploration program of the National Petroleum Reserve in Alaska. Seven open-file maps or Miscellaneous Field Investigations Maps of this area are currently available, and others are being prepared for publication.« less