141-13 High-Resolution Event Stratigraphy as a Tool for Studying Evolution: An Example from the Upper Cretaceous of the Mississippi Embayment

Session: New Advances in Geobiology

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High-resolution event stratigraphy combines data such as event beds and the first and last occurrences of taxa from multiple measured sections or wells to construct a single composite section. This ordinal composite provides a framework for examining the relationship between basin stratigraphy and the evolutionary patterns of their faunal constituents. In this study, data from 108 measured sections, three pseudo­sections, eight discrete events, 268 taxa of ostracods and planktonic foraminifera, and 353 sam­ples from Santonian-Maastrichtian deposits on the eastern flank of the Mississippi Em­bayment (USA) into a single event compos­ite using the heuristic software CONOP (Constrained Optimization). Two preparatory strategies were used prior to running the analyses: the construc­tion of composite reference sections and inte­gration of sequence boundaries. These methods yielded 544 events over a ∼20-million-year interval, averaging of one event approximately every 36,764 years. Diachrone­ity of the lithostratigraphic units also provides insight into the sluggishness of relative sea level change during the Late Cretaceous.

Patterns in ostracod diversity, evolutionary appearances, and extinction rates reveal three community stasis intervals, each separated by periods of elevated evo­lutionary turnover: the Lower Campanian, the Upper Campanian, and the uppermost Campanian-Maastrichtian. In the older two turnover intervals, spikes in evolutionary appearances preceded spikes in extinctions, resulting in temporary peaks in diversity followed by subsequent declines. Ostracod diversity reaches a maximum of more than 90 species during the mid-Campanian, coinciding with the maximum flooding surface of the deepest Creta­ceous sequence in the region. No Cretaceous ostracod species survived the Cretaceous-Paleogene (K-Pg) boundary event.

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

doi: 10.1130/abs/2025AM-10624

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