From Greenhouse to Icehouse: An Arctic-wide Cenozoic Climatic-Biostratigraphic Scheme

Jonathan Bujak

Temperature changes accompanying the Cenozoic greenhouse to icehouse shift had a massive impact in the Arctic, resulting in impoverished assemblages that are difficult to correlate with those from lower latitudes using traditional biostratigraphic techniques. It is therefore essential to use a scheme that integrates shifts in sea-surface and air temperatures with changes in marine and non-marine biotas. The resulting climatic-biostratigraphic scheme has Arctic-wide application because the Arctic Basin was centered on the North Pole throughout the Cenozoic and underwent the same regional temperature changes during the greenhouse to icehouse shift. One exception is the Barents Sea which had warmer conditions due to local inflow of the proto-Gulf Stream during the Oligocene and Neogene. The Cenozoic Arctic succession begins in a Paleocene to Early Eocene greenhouse state inherited from the Mesozoic, with the Early Eocene Thermal Maximum (EETM), aka the Paleocene Eocene Thermal Maximum (PETM), being characterized by an influx of the warm-water dinoflagellate Apectodinium. The greenhouse to icehouse shift began near the end of the Early Eocene when the floating freshwater fern Azolla repeatedly colonized surface freshwater plumes, sequestering large quantities of atmospheric CO2 which were incorporated into Arctic sediments. Initiation of the Arctic Azolla Event probably resulted from late Ypresian closure of the Turgay Strait, leading to a largely landlocked Arctic Ocean similar to today’s Black Sea with its basin stratification and bottom-water anoxia. The Azolla Event ended in the early part of the Lutetian and was followed by a series of Middle and Late Eocene cooling steps relating to global oceanic and tectonically driven CO2 sequestration events. These caused the successive extinction of temperature-sensitive marine and non-marine fauna and flora in the Arctic, with the terminal Eocene cooling event eliminating more than 90% of Arctic dinoflagellate and angiosperm taxa. The resulting Oligocene cold phase, which had highly impoverished biotas, ended as Arctic temperatures increased, permitting dinoflagellates and angiosperms to migrate back into the Arctic during the Miocene. Major cooling during the Plio-Pleistocene finally led to their decline across the region and also resulted in the succession of orbitally-induced glacial-interglacial cycles that characterize today’s climate. This integration has implications for the occurrence of Cenozoic petroleum source rocks such as the EETM and Azolla intervals, and provides a circum-Arctic biozonation that can be correlated with lower latitude chronostratigraphy. It also helps us understand the importance of the Arctic region in past climate change and its possible role in anthropogenic reversal of the greenhouse to icehouse shift.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013