55-7 Beyond Milankovitch: Testing Hypotheses for Environmental Drivers Associated with Ocean Anoxic Event 2 in the GC-3 Core, South Central Texas.

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:

Rose Carlson

Authors:

Carlson, Rose L.¹, Flaum, Jason A.², French, Katherine L. ³, Birdwell, Justin E.⁴, Wan, Chuyan⁵, Jacobson, Andrew D.⁶, Sageman, Bradley B.⁷

(1) Dept. of Earth, Environmental, and Planetary Sciences, Northwestern University, Evanston, IL, USA, (2) USGS, Denver, CO, USA, (3) USGS, Denver, CO, USA, (4) USGS, Denver, CO, USA, (5) Dept. of Earth, Environmental, and Planetary Sciences, Northwestern University, Evanston, IL, USA, (6) Dept. of Earth, Environmental, and Planetary Sciences, Northwestern University, Evanston, IL, USA, (7) Dept. of Earth, Environmental, and Planetary Sciences, Northwestern University, Evanston, IL, USA,

Abstract:

Mesozoic ocean anoxic events have long been a focus of research because they preserve evidence of the confluence of major Earth system processes, which produced global scale impacts. In this study, we analyze geochemical archives of the Cenomanian–Turonian Ocean Anoxic Event 2 (OAE2) in the southern Cretaceous Western Interior Seaway (KWIS) to investigate factors influencing environmental change. The USGS Gulf Coast 3 (GC-3) core was collected by the United States Geological Survey Energy Resources Program in 2018 at a site approximately 30 miles southeast of Del Rio, Texas, corresponding to the southern aperture of the KWIS. Previous analysis of GC-3 confirmed the well-established positive shift in δ¹³C_org that defines OAE2. However, the event onset lacks δ¹³C_org data due to a thick limestone bed with low total organic carbon (TOC) content at that horizon. We present data showing a distinct negative shift in δ¹³C_carb values within this bed that suggest prolonged diagenetic CaCO₃ cementation caused by siliciclastic starvation. Chemostratigraphic correlation of the interval to regional chronostratigraphy, based on δ¹³C and Os_i profiles, indicates that this bed corresponds with a major eustatic transgression that occurred during the onset of OAE2. Evidence for this transgression is found throughout the KWIS, as well as in many other global locations. We also generated δ^44/40Ca values using a high-precision thermal ionization mass spectrometry (TIMS) method. Using the TIMS method, we found evidence for a distinctive positive δ^44/40Ca excursion previously documented at other OAE2 sites. In GC-3, the positive δ^44/40Ca excursion postdates the transgressive event and diagenetic episode. The temporal offset supports assertions that the positive δ^44/40Ca excursion reflects a primary signal reasonably attributed to ocean acidification following massive release of volcanic CO₂. Given the consensus that OAE2 was initiated by a major LIP eruption, our study seeks to test hypotheses for possible common causes of eustatic rise and widespread ocean acidification as consequences of the eruption and submarine emplacement of massive volumes of basalt.

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

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