Tertiary Marine Events of the Beaufort-Mackenzie Basin and Correlation of Oligocene to Pliocene Marine Outcrops in Arctic North America

Abstract

The benthic foraminiferal succession from the Beaufort-Mackenzie Basin of arctic Canada reflects many of the major oceanographic and climatic events of the Tertiary. The Paleocene-Eocene epochs are characterized by restricted marine circulation and pronounced foraminiferal endemism. Paleogeographic reconstruction illustrates that the Paleocene-Eocene Arctic Ocean was markedly different from its modern counterpart and it is thus referred to as the "Arctic Gulf." Marine connections between the Arctic and Atlantic oceans were broadened and deepened during the Oligocene. The Arctic Gulf thus evolved into a modern Arctic Ocean configuration by sea floor spreading in the Greenland-Norwegian Sea. The Oligocene index, Turrilina alsatica Andreae, appeared in the arctic regions concurrent with increased circulation between the North Atlantic and Arctic oceans. In the Beaufort-Mackenzie subsurface, Turrilina alsatica has proven to be a widespread and reliable zone index. In outcrop, it is known from only one locality, the Nuwok Member of the Sagavanirktok Formation on Carter Creek, Alaska. During the Miocene, increased circulation between the Arctic and Atlantic oceans was further established, and a moderate warming trend developed after a cool early Oligocene episode. The foraminifer Asterigerina staeschei (Franke) is an abundant and widespread marker of this phase of arctic marine history. Asterigerina staeschei became extinct in the middle Miocene in both the arctic and North Atlantic regions. In the Beaufort-Mackenzie Basin, many associated species ranged through into the late Miocene but disappear abruptly at the terminal Miocene unconformity. Major faunal and depositional sequence changes mark this as one of the most significant events in arctic Tertiary history, and the unconformity itself was caused by a widespread relative drop in sea level. A major faunal turnover in the Pliocene is characterized by Cibicides grossus ten Dam and Reinhold, which first appeared in the early Pliocene but became extinct through the North Atlantic and arctic regions at approximately 2.4 Ma, closely approximating the climate deterioration and initiation of continental glaciation in the late Pliocene. Cibicides grossus has a widespread distribution in arctic North America, occurring in the subsurface of the Beaufort-Mackenzie Basin and in outcrops of the marine tongue of the Beaufort Formation on Meighen Island, in unnamed strata on White Point of northwest Ellesmere Island, on eastern Baffin Island, and on eastern and northern Greenland.