T76 The Geological Evolution of Northern Alaska: A Session in Honor of Charles ?Gil? Mull

Monday, 10 October 2022
8:00 AM - 12:00 PM
Mile High Ballroom 3C

PULSED DEEPWATER CARBON BURIAL IN ARCTIC ALASKA DURING MIDDLE CRETACEOUS GREENHOUSE OCEANIC ANOXIC EVENTS (OAE1D, OAE2, AND HITCH WOOD)

Paper number: T76-2
Program: Technical Sessions
Time: 8:05 AM – 8:20 AM

Authors

Abstract

The peak warmth of the middle Cretaceous greenhouse was marked by a series of Oceanic Anoxic Events (OAEs) that recorded profound environmental change. Coeval positive carbon isotopic excursions (CIEs) suggest enhanced global burial of organic carbon. However, the role and response of high-latitude regions like the semi-restricted Arctic Ocean during middle Cretaceous OAEs remains enigmatic. We present the first Arctic deepwater OAE record that characterizes conditions offshore of the Alaska margin north of 75°N paleolatitude. Organic carbon isotopes (d13Corg) and tephra zircon U-Pb dates from the distal condensed Hue Shale record Albian-Cenomanian-Turonian-Coniacian stage boundary CIEs associated with the OAE1d, OAE2, and Hitch Wood events during 102-89 Ma. Elevated total organic carbon (TOC) maxima of 14-17% occur during each OAE and programmed pyrolysis data indicate a marine source. We integrate mudstone geochemical and mineralogical data with timing of sea level / shelf margin dynamics to examine controls on polar greenhouse carbon burial. Mo and other redox-sensitive trace elements (RSTE) suggest an oxygen minimum zone setting adjacent to continental margin upwelling. RSTE enrichment indicates 102-98 Ma euxinia that peaked during OAE1d, but muted enrichment afterwards suggests anoxic, non-sulfidic (98-91 Ma) to intermittently euxinic (91-89 Ma) conditions. Heightened carbon burial during OAE2 and Hitch Wood is associated with increased continental nutrient input (illite, K, Rb) and marine productivity (Ba, P) following major Arctic transgressions which expanded high-latitude marine environments. Our new high-resolution OAE2 record exhibits tight coupling between Arctic Alaska d13Corg, carbon burial, productivity, and anoxia during the global first buildup, second buildup, and plateau subevents of the OAE2 CIE. An efficient Arctic biological pump of carbon to the deep ocean is suggested by the -3‰ d13Corg gradient between Alaska deepwater and Canadian shelfal records. During peak middle Cretaceous warmth, multiple episodes of widespread transgression and an enhanced hydrological cycle increased nutrients and productivity in the Arctic Ocean, suggesting that this region represents a significant yet underappreciated carbon sink during global greenhouse events like OAE2.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-378757

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