The early Neoproterozoic sedimentary Succession B of northwestern Laurentia: Correlations and paleogeographic significance

Abstract

The Mesoproterozoic–Neoproterozoic stratigraphic record of ancestral North America (Laurentia) comprises three, unconformity-bounded sedimentary successions that are termed, from oldest to youngest, A, B, and C. Recent and ongoing detailed stratigraphic studies of Succession B, along with improved geochronology, allow extension and refinement of existing correlation schemes for northwestern Canada and Alaska. Succession B strata include the Shaler Supergroup of the Amundsen Basin, Mackenzie Mountains supergroup of the Mackenzie Mountains fold belt, Pinguicula group of the Wernecke Mountains inlier, Fifteenmile group of the Ogilvie Mountains inliers, and the lower Tindir Group of Tatonduk inlier. The Katakturuk Dolomite, in the northeast Brooks Range of Alaska, is included with Succession B on the basis of platformal character, geochronology, and inferred paleogeographic affinity. The framework for regional lithostratigraphic correlation of Succession B is built on recognition of four distinctive lithostratigraphic assemblages: two thick stromatolitic platformal carbonate assemblages separated by two largely subaerial siliciclastic assemblages. The correlation is supported by geochronology of detrital zircons from the upper quartzarenite assemblage, which indicates a maximum age of ca. 1000 Ma for the lower part of Succession B. These rocks are interpreted to be remnants of a northwesterly trending (present coordinates) early Neoproterozoic basin-margin promontory (Amundsen-Ogilvie-Mackenzie platform) that developed within an intracratonic basin on the northwest margin of Laurentia. The Neoproterozoic stratigraphic record of northwestern North America bears striking similarity to contemporaneous stratigraphy on other continents, particularly in the Amadeus Basin and Adelaide fold belt of central and southern Australia. Reconstructions of the Neoproterozoic supercontinent juxtapose the eastern margin of ancestral Australia against the western margin of Laurentia during the time these strata were being deposited. The Amundsen-Ogilvie-Mackenzie platform consequently may represent a segment (of the margin) of a large intracratonic basin that rifted apart with the breakup of the supercontinent during the latest Proterozoic. This hypothesis provides a template for future sequence stratigraphic, chemostratigraphic, biostratigraphic, paleomagnetic, and geochronologic comparisons and has implications for predictive economic geology in both areas. Capitalization of group and supergroup indicates formalization according to the International Stratigraphic Code. Noncapitalization indicates that the names have not been formalized.