148-4 Investigating the Response of Calcareous Nannoplankton to the Late Cretaceous Oceanic Anoxic Event 2 (OAE2, 94 Ma) Using Novel Statistical Techniques and Integrated Nannofossil and Elemental Geochemical Datasets

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

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Abstract:

Over the Cenomanian/Turonian boundary (CTB; ca. 94 Ma), there was widespread deoxygenation of the global ocean known as the Oceanic Anoxic Event 2 (OAE2). Geochemical and micropaleontological evidence points to elevated primary productivity as being a potential cause, or amplifier, of anoxia. However, over the event, calcareous nannoplankton, the dominant phytoplankton of the Cretaceous oceans, seem to be characterized by oligotrophy. Additionally, there was minor turnover in nannoplankton species over the CTB, the cause of which is enigmatic. We hypothesized that this apparent disconnect between an apparent highly fertile ocean and oligotrophic nannoplankton assemblages is in part due to a misinterpretation of nannofossil paleoecology. To better refine nannoplankton paleoecology over the CTB, we combined geochemical sediment data collected through handheld X-ray fluorescence (XRF) with high-resolution nannofossil abundance data from cores and outcrops across the North American Western Interior Seaway (WIS), spanning from modern-day New Mexico to Nebraska and central Canada. Furthermore, published nannofossil data from Europe and the Atlantic was utilized contextualize WIS data globally. In a novel approach, we employed a Canonical Correspondence Analysis (CCA) on this combined dataset to establish paleoecological links between nannoplankton assemblages and elemental geochemical proxies.

The resulting placement of elements and species along CCA axes allowed us to interpret nannofloral paleoecological gradients along productivity, salinity, and water column oxygenation. During OAE2, our results a decline in salinity and a variable response to productivity. Axopodorhabdus albianus and Corrolithion kennedyi, two species that went extinct during OAE2 shared a similar preference for an open marine, high productivity environment. Therefore, a change in these conditions over OAE2 may have been a primary extinction mechanism. Another important bio-event of the interval was the evolution of Eprolithus moratus from Eprolithus floralis. Our CCA analysis indicates these taxa had different niches, and the evolution of E. moratus during the event may have also been triggered by paleoceanographic changes during OAE2. We then used a non-metric multidimensional scaling (NMDS) analysis of a more global nannofossil dataset and determined that our initial paleoecological interpretations appear valid across the Atlanic and Tethys Oceans. Our results show that the use of multivariate statistical analysis on integrated fossil and geochemical datasets will help establish a greater understanding of the nannoplankton ecology of the Late Cretaceous.

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

doi: 10.1130/abs/2025AM-5406

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