30-2 Unusual Taphonomy of Early Triassic Ophiuroids from the Olenkian Virgin Limestone Member, Southern Nevada, U.S.A

Session: Laws of the Grave: Advances in Taphonomy Across the Paleontologic Record (Posters)

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Abstract:

During the end-Permian mass extinction, the largest extinction of the Phanerozoic, up to 68% of marine genera and 92% of marine species were eliminated. The subsequent Early Triassic interval was characterized by some opportunistic taxa, abundant microbialites, and a delay in ecosystem recovery. Recent studies on the Virgin Limestone Member report Lower Triassic fossils preserved in unusual ways: molded by apatite, glauconite, and iron-bearing minerals. This work examines the diversity and taphonomy of ophuroid fossils preserved in insoluble residues across three localities of the Virgin Limestone Member: Lost Cabin Springs, Blue Diamond, and Muddy Mountains Overton. We dissolved limestone samples in dilute acetic acid and picked ophiuroid lateral arm plates and arm vertebrae from each locality that belonged to the newly described species Ophiosuperstes praeparvus. The preservation style of the O. praeparvus specimens varies across location, with the most offshore section of the Virgin Limestone at Lost Cabin Springs preserving apatitic stereomic molds, specimens from the middle shelf setting at Blue Diamond being mostly silica stereomic molds with a few apatite examples, and specimens from the nearshore section at Muddy Mountains Overton preserving entirely silica molds. These taphonomic differences may indicate environmental and/or biological controls on taphonomy, including specimen size, pore-water oxygen level, and/or sedimentation rate. Furthermore, O. praeparvus was the only ophiuroid found at these localities, and we therefore suggest that this species was tolerant of post-extinction conditions across the Panthalassa shelf. The warm, dysoxic Early Triassic oceanic conditions likely contributed to the expansion of stress-tolerant generalists while fostering unusual taphonomic modes during early diagenesis.

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

doi: 10.1130/abs/2025AM-8307

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