55-1 Stratigraphy of the Cenomanian–Turonian of the eastern margin of the Western Interior Seaway: Insights from new cores and outcrops in Kansas, Nebraska, and Iowa, USA

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

Presenting Author:

Authors:

Abstract:

The Cenomanian–Turonian (Late Cretaceous, ca. 94 Ma) North American Western Interior Seaway (NAWIS) has a critical geologic and paleontologic record of Oceanic Anoxic Event 2 (OAE2), but there is an important lack of data from its eastern margin. Here, we describe newly discovered cores from Nebraska and known outcrops in Kansas and Iowa that contain strata from the Cenomanian–Turonian Graneros Shale and Greenhorn Limestone. Our analysis of these sections included lithofacies analysis, detailed calcareous nannofossil biostratigraphy, and X-ray fluorescence chemostratigraphy. We developed a regional correlation of Cenomanian–Turonian strata from central Kansas to northwestern Iowa and refined the stratigraphic framework of Nebraska and Iowa allowing integration with other sections across the NAWIS.

The OAE2 interval was recovered in all studied sections to varying levels of completeness. We noted a distinct shift to carbonate facies and an increase in bioturbation in all sections from the uppermost Cenomanian into the Turonian. Inoceramid-rich horizons increased during the event suggesting more vigorous bottom water flow. Geochemically, a rise in Ca/Al was observed that coincided with the change in more carbonate deposition in the Greenhorn Limestone. We also noted that the rise in Ca/Al corresponded to a subsequent increase in Al/Ti, which indicates more eolian sediment input either from drier climates or elevated volcanic activity. Prior to OAE2, lithofacies and stratigraphic thickness indicate there was substantial detrital sediment input derived from the eastern North American craton; however, during and after the event, the eastern-derived sediment seems to lessen significantly compared to sediment from the west. Such a change could have resulted from transgression trapping sediment in embayments along the eastern margin or changes in climate which lessened fluvial input along the east coast.

We then compared our results to published Cenomanian–Turonian sections from Colorado and west Texas. In all sections, there is the observed shift to more carbonate deposition and increase in apparent oxygenation over the Cenomanian/Turonian boundary. However, there are subtle differences in lithofacies that could be important to understanding regional variability in the response of the NAWIS to OAE2. Importantly, our results from the understudied eastern margin of the NAWIS help better identify and understand these complexities and open a new region for further research of OAE2 in the NAWIS.

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

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