23-10 Problematic Taxa of the Upper Cambrian Deadwood Formation in the Black Hills of South Dakota

Session: Paleontology of North America (Posters)

Presenting Author:

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Abstract:

The Deadwood Formation in the Black Hills of South Dakota preserves late Cambrian through early Ordovician microfossils deposited in a shallow marine paleoenvironment. While some of the Deadwood taxa, particularly trilobites, have received scholarly attention, a detailed taxonomic analysis remains lacking. Furthermore, new samples have revealed specimens that represent unidentified or taxonomically problematic forms.

In the summer of 2025, ten new field samples were collected from the Little Elk Creek section of the Deadwood Formation described in Stitt and Perfetta 2000. The samples represent a 19.6 m stratigraphic section from the lower to middle Deadwood Fm. and are primarily composed of sandstone lithologies that become increasingly glauconitic and calcareous up-section. These samples, along with 10 samples from the MU collections (collected by Stitt), were macerated in 7% dilute acetic acid and sorted into fine and coarse grain residues.

Microfossils were picked from the residues and subsequently examined using light microscopy, X-ray tomographic microscopy (μCT), and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). Identifiable taxa include moldic trilobite sclerites, lingulid brachiopods, the paraconodont Prooneotodus rotundatus, and orthothecids (Hyolitha). However, the analysis revealed several taxa that do not fit neatly within existing descriptions. These specimens may represent bradorids, bryozoans, Linnarsonella, and ostracods, as well as fragments potentially attributed to spicules and glauconitic concave forms with perpendicular layers. This presentation will provide a report of the known Deadwood taxa and describe the unknown taxa recovered from the Little Elk Creek section samples.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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