57-10 Chemostratigraphic and geochronologic constraints of the Beta Member, James Ross Island, Antarctica

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records, Part II

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Abstract:

James Ross Island (Antarctic peninsula) is home to one of the most important and continuous sequences of Cretaceous marine strata in the Southern Hemisphere. The Cretaceous in Antarctica saw drastic climatic and environmental changes. Climatic changes include the Cretaceous Thermal Maximum (ca. 93 to 82 Ma) when little to no polar continental ice existed, and sea surface temperatures in polar regions were 20°C higher than today. During this time, flowering plants (angiosperms) evolved and quickly diversified, eventually replacing gymnosperms (e.g., conifers) as the dominant plant group. In order to better understand the timing of these events, we use stable organic carbon isotope (d13Corg) chemostratigraphy and U-Pb geochronology to constrain the timing of the deposition of a 78.3m thick section of the Beta Member of the Santa Marta Formation at a fossil locality known as Sitio Feliz, near Santa Marta Cove in northern James Ross Island. This locality is important because it preserves a diversity of exceptionally preserved angiosperms and gymnosperms, including 3D flowers, fruits, seeds, and cones. Previous biostratigraphic and magnetostratigraphic work had the Beta Member spanning from 82.2 Ma to 79.3 Ma. The section at Sitio Feliz only represents a portion of this time span, and we look to constrain it further. 

A total of 66 samples were analyzed for d13Corg (‰ VPDB) yielding a minimum of -28.85‰, a maximum of -24.93‰, and an average of -26.21‰. An isotope excursion has been identified, and we hypothesize that the excursion may be the Mid-Campanian Event (approx. 81 Ma) if the locality is in the lower part of the Beta Member, or the Late Campanian Event (approx. 76 Ma) if it is in the upper part. U-Pb geochronology analyses of early diagenetic calcite infills from fossils will further aid in constraining the section age. Preliminary petrographic analysis (traditional and cathodoluminescence) shows multiple generations of calcite (between 2 and 8 per sample) that will be analyzed using LA-ICP-MS. By combining any U-Pb dates with the chemostratigraphic data, we will refine the timing of this section for future paleoclimatic, paleoenvironmental, and palaeobotanical work. 

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

doi: 10.1130/abs/2025AM-10597

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