29 Evolution of Life in the Cambrian Seas: Biotic, Biogeochemical, and Sedimentological Contexts (Posters)

This session is dedicated to studies that illuminate the biotic, geobiological, sedimentological, and geochemical contexts of the evolution of early animal life in the oceans, with a particular focus on the Cambrian Period.

Sunday, 19 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Currents of Change: Storm-Induced Sedimentation and Biotic Richness of the Upper Cambrian Davis Formation, Missouri

Paper number: 29-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Upper Cambrian of Missouri represents a critical interval of shallow marine sedimentation on the interior Laurentian craton. This interval is marked by a transgressive-regressive sequence of carbonate and siliciclastic deposits, laid down on a broad passive margin shelf surrounding the pre-Cambrian St. Francois Mountains, and it preserves one of the most complete and accessible shallow marine successions of this age in North America. A significant basin-wide shift from the carbonate-dominated Bonneterre Formation to the mixed carbonate-siliciclastic Davis Formation is associated with the SPICE event (Steptoean Positive Carbon Isotope Excursion) and a coeval trilobite extinction. This study focuses on the fossiliferous Davis Formation (~497–485 Ma) in southeastern Missouri, with the goal of reassessing its sedimentology and biotic diversity. Field observations, particularly along Highway 8, reveal that most (if not all) carbonate intervals are composed of conglomeratic beds, interpreted as storm deposits (tempestites). These beds host the majority of identifiable fossils—excluding trace fossils, which are more frequently preserved in silty shale horizons. In addition to the well-documented trilobites (Elvinia Zone), organophosphatic brachiopods (Linnarssonella Zone), and stromatolites, the Davis Formation also yields tubular fossils (possibly Salterella?), as well as remains of echinoderms and monoplacophorans. Notably, these fossils are typically concentrated in the upper parts of storm beds, which often begin with basal pebble lags, suggesting that storm activity played a key role in concentrating and preserving biotic remains. Altogether, the Davis Formation represents a unique mixed siliciclastic–carbonate system, where storm-dominated sedimentation contributed to the preservation of an unusually diverse biotic assemblage for the Late Cambrian, prior to the onset of the Great Ordovician Biodiversification Event (GOBE).

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

doi: 10.1130/abs/2025AM-413729

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