Stratigraphy, sedimentology and palynology of Cretaceous and Tertiary strata, southwest Bylot Island, Northwest Territories, Canada

Abstract

Four new formations (the Bylot Island, Pond Inlet, Navy Board and Aktineq formations) are defined from the upper portion of Eclipse Group strata on the southwest coast of Bylot Island. The Bylot Island Formation represents basin plain deposition during a Late Maastrichtian transgression. The overlying Early Paleocene sandstones of the Pond Inlet Formation were deposited in basin margin fan-deltas and a shelf through submarine fan complex. This unit reflects a rejuvenation of local and distal source areas, and marks the beginning of a marine regression. The shale of the Navy Board Formation is the deeper, basin plain component of this depositional sequence. The deltaic sequence at the top of the Navy Board Formation and the fluviatile deposits of the Aktineq Formation mark the final regressive phase when a fluvial system of late Early Paleocene age prograded across the older marine units. A eustatic sea level fall is suggested as the control of sedimentation during this period. -- Two informal palynomorph zones identified in these rocks support intrabasinal lithostratigraphic correlations and establish formation ages. The Late Maastrichtian Hamulatisporis amplus - Ulmipollenites sp. 1 (HU) assemblage zone (dominated by long ranging species) contains specimens of Hamulatisporis amplus Stanley, Ulmipollenites sp. 1, Pesavis parva Kalgutkar and Sweet and Ceratiopsis diebelii (Alberti) Vozzhennikova. This zone is restricted to the Bylot Island Formation. The Early Paleocene Trivestibulopollenites betuloides - Triatriopollenites sp. 1 (TT) assemblage zone is dominated by reworked and long ranging species. It contains specimens of Trivestibulopollenites betuloides Thomson and Pflug, Triatriopollenites sp. 1, Sequoiapollenites paleocenicus and Ceratiopsis speciosa (Alberti) Lentin and Williams. This zone is further divided into two subzones (TTa and TTb) on the basis of abundance of selected species. These abundance changes reflect a change in depositional environment. -- KEY WORDS: Bylot Island; Eclipse Group; Cretaceous; Tertiary; Stratigraphy; Sedimentology; Palynology.