55-2 Oceanic Anoxic Event 2 at the northern Western Interior Seaway – Arctic nexus: Heightened organic carbon burial along an Alaska deepwater-to-shelf transect

Session: Sequence Stratigraphic, Geochemical, and Geochronologic Correlation of the Cenomanian-Turonian Ocean Anoxic Event 2 (OAE2) in the Cretaceous Western Interior Seaway (KWIS) and the Gulf Coast

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Abstract:

The epicontinental Cretaceous Western Interior Seaway (KWIS) spanned >35° of latitude (>4500 km) from the Gulf Coast region to the Arctic Ocean. The high-latitudes have been invoked as key regions for Cretaceous carbon cycling and greenhouse climatic feedbacks including during Oceanic Anoxic Event 2 (OAE2); however, high-resolution empirical data are sparse across much of the northern KWIS – Arctic region. Here, we establish an OAE2 stratigraphic framework across the Arctic Alaska margin north of ~75°N paleolatitude from a 350-km-long shelf-to-deepwater transect.

First, the deepwater Hue Shale records a 7-m-thick OAE2 interval with a +2.5‰ carbon isotope excursion (CIE) and doubling of total organic carbon (TOC) contents at two sites. A highly resolved 10 cm (~10 kyr) d¹³C_org data series at the Hue Creek outcrop captures a relatively conformable record of OAE2 that preserves the characteristic CIE segments. Preliminary time-domain spectral analyses of TOC data, assuming a linear sedimentation rate based on CIE correlation to well-dated records from the US Western Interior Seaway, exhibit significant spectral peaks (28–50 kyr/cycle) around the short obliquity cycle band, consistent with high-latitude climatic forcing of Arctic marine organic carbon (OC) burial.

Second, the shelfal Seabee Formation at the Umiat #1 well records a 27-m-thick OAE2 interval with a +3.0‰ CIE and four-fold increase in TOC that coincides with late Cenomanian and early Turonian regional zonal markers of Inoceramus pictus and Mytiloides labiatus, respectively. Enhanced marine productivity is suggested by an abrupt increase to 200-500 Hydrogen Index values and abundant fishbone fragments. Also, degree of pyritization and carbonate content data suggest that deoxygenation and potentially ocean acidification occurred earlier on the shelf at Umiat #1 (preceding OAE2) than in the coeval deepwater interval at Hue Creek.

Overall, we estimate that OC mass accumulation rates increased by factors of 2 and 4 during OAE2 for Arctic Alaska deepwater and shelf environments, respectively, in contrast to the well-oxygenated, OC-lean facies of the lower-latitude KWIS during OAE2. When extrapolated regionally, the circum-Arctic may account for one-third of the global excess (above background) OC burial estimated for OAE2. Our results support the theory that high-latitude regions played an outsized role for the Cretaceous carbon cycle with obliquity-paced processes that enhanced primary productivity and preservation of OC in the Arctic Ocean, particularly during OAE2.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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