The Paleocene-Eocene thermal maximum in the Arctic Beaufort-Mackenzie Basin -- Palynomorphs, carbon isotopes and benthic foraminiferal turnover

Abstract

Abstract Examination of samples from exploration wells in the Arctic Beaufort-Mackenzie Basin has resulted in the documentation of the global Paleocene-Eocene thermal maximum (PETM) interval in 6 out of 12 wells examined. The PETM, a brief period of extreme global warming at about 55 Ma, occurs within the upper part of the deltaic-influenced Aklak Sequence. The PETM was recognized primarily by the occurrence of the dinoflagellate cyst Apectodinium augustum — globally associated with the PETM. Thermophilic pollen, e.g. Intratriporopollenites (Tilia) and Platycaryapollenites, are also associated with the PETM in the Beaufort-Mackenzie Basin wells. Carbon isotope analyses from one well, Natiak O-44, indicate a carbon isotope (δ13C) excursion of about −0.72‰ associated with the A. augustum acme. This excursion is low relative to continental settings for the PETM, but closer to some oceanic values. In Natiak O-44, the PETM interval is unusually thick, at about 100 m. This is consistent, however, with rapid deltaic sedimentation of the Aklak Sequence (nearly 5 km thick). A comparison of palynological and foraminiferal data indicates that the index foraminifera Reticulophragmium boreale becomes extinct at approximately the PETM interval. Furthermore, there is a pronounced foraminiferal turnover at or near the PETM. The turnover is apparently of circum-Arctic extent and caused by the extreme global warming and oceanic change of the Paleocene-Eocene transition. Recognition of the PETM in the Beaufort-Mackenzie Basin provides an important chronostratigraphic datum in complex deltaic sediments that are typically difficult to date precisely.