148-5 Investigation of Seasonal Environmental Conditions in PETM Diatomites From the Mid-Norwegian Continental Margin (IODP Exp. 396) and the Fur Formation in Denmark.

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches (Posters)

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Abstract:

PETM aged diatomites and ash-bearing diatom muds were recovered in the Norwegian Sea during IODP Expedition 396. They accumulated in a hydrothermal vent crater associated with the PETM carbon isotope excursion (Berndt et al., 2023, NatGeosci). Some diatomite are microlaminated, containing exceptionally preserved diatom assemblages. These laminae are interpreted to represent seasonal depositional pulses, offering rare insight into surface ocean conditions during the early PETM, a time of extreme global warmth and environmental stress. SEM analysis reveals micro laminae composed of alternating monospecific and mixed diatom assemblages, interpreted as the preserved signature of individual seasonal deposition. Layers (~30–100 µm thick) are dominated by either Hemiaulus, a chain-forming coastal plankton genus, or by araphid pennate diatoms such as Sceptroneis, Grunoviella and Synedropsis. The consistent alternation of these assemblages suggests strong seasonal variation in surface water properties, likely driven by precipitation patterns, nutrient availability, and stratification. Hemiaulus-dominated layers (~100 µm) reflect blooms of small, curved taxa that likely formed long, coiled chains in nutrient-rich, well-mixed surface waters, potentially associated with high runoff and strong freshwater input. In contrast, thinner laminae (~30 µm) dominated by araphids are hypothesized to reflect periods of reduced precipitation and surface water stagnation, potentially associated with the seasonal expansion of benthic or macroalgal habitats. These ecological shifts indicate extremely rapid accumulation without bioturbation, preserving a remarkably detailed seasonal archive. To complement this early PETM record, ongoing work on the Fur Formation (Denmark) focuses on the close of the PETM and post-hyperthermal transitions. The Fur Fm contains similarly well-preserved diatom-rich sediments with numerous volcanic ash layers. Diatom assemblages are being used to assess surface water conditions, ecological change, and volcanic influence. A major oceanographic shift is evident between the Fur and Norwegian records, pointing to changes in regional circulation and/or nutrient delivery. Together, these high-resolution diatom records from both the onset and close of the PETM provide a rare view into seasonal-scale ecosystem dynamics during one of Earth’s most extreme climate events. 

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

doi: 10.1130/abs/2025AM-10199

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