185-10 Great Ordovician Biodiversification Event in the Ibex Region, Western Utah: Examination of Skeletal Abundance and Diversity in Carbonates

Session: New Advances and Voices in Geobiology (Posters)

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Abstract:

The Great Ordovician Biodiversification Event (GOBE) is the largest increase in biodiversity and abundance of the Phanerozoic, spanning from approximately 497 Ma to 467 Ma. While it is well known that diversity increased substantially during the GOBE, what has received less attention is how skeletal abundance varied spatially and between different carbonate environments. Here we present data on skeletal fossil abundance and diversity from Lower to Middle Ordovician units in the Ibex region of western Utah, by using the grain-solid point counting method on thin sections. We investigated 197 samples from the lower and upper Fillmore (lower–middle Floian), Wah Wah (upper Floian), Juab (lower Dapingian), Kanosh (upper Dapingian, lower Darwillian) and Lehman (middle Darwillian) formations exposed across the Ibex region. Mann-Whitney U tests show that the skeletal abundance in rocks of the same facies (mudstone/wackestone vs packstone/grainstone) varies significantly between some of these units, but does not increase or decrease unidirectionally across the section. In contrast, diversity, calculated using the Shannon Diversity Index, is lowest in the lower Fillmore Formation (0.78), and generally increases throughout this succession (1.52 in the Lehman Formation). Although trilobites, echinoderms and brachiopods are among the most common fossils in thin section, Nuia, an enigmatic putative calcareous alga, is also an abundant rock-forming fossil, making up 12% of fossil points in the Wah Wah, as an example. Nuia first appears in the upper Fillmore Formation and remains common until the lower Kanosh Formation and does not appear again in the overlying Lehman Formation. Future work will seek to resolve the influence of environmental variation on increases in skeletal abundance, the apparent decoupling between increases in diversity and abundance in this region, and how these data inform our understanding of the GOBE globally.

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

doi: 10.1130/abs/2025AM-9269

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