23-16 A Microanalytical Study of the Lower Deadwood Formation at Little Elk Creek in the Black Hills, South Dakota

Session: Paleontology of North America (Posters)

Presenting Author:

Authors:

Abstract:

The Deadwood Formation is host to diverse Upper Cambrian to Ordovician-aged (Guzhangian-Tremadocian) marine microfossil assemblages. The stratigraphy of the Deadwood Formation in the Black Hills of South Dakota has not been assessed since the late 1990s, and complete lithologic descriptions of the formation were last made in the 1960s. In July of 2025, we visited the Black Hills to make detailed lithologic and biostratigraphic descriptions, as previous studies have primarily focused on the stratigraphy of generalized lithologic or faunal zones. The previous work on trilobite biostratigraphy has been particularly extensive, with hundreds of Black Hills trilobites reposited at the University of Missouri in Columbia (MU). Our work indicates discrepancies in these works regarding the heights of measured sections and specific nuances of exact specimen locations.   

Herein, we systematically redescribe the bio- and lithostratigraphy of the Little Elk Creek section of the Deadwood Formation. Ten new field samples and ten samples from the MU collections were macerated in 7% dilute acetic acid, and microfossils were picked from the resulting residues. Microfossils were analyzed using X-ray tomographic microscopy (μCT) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) for more detailed taxonomic and chemical analyses. We report previously described moldic trilobite sclerites, lingulid brachiopods, the paraconodont Prooneotodus rotundatus, and orthothecids (Hyolitha), along with numerous unidentified specimens. Problematic specimens include glauconitic “tongues” and possible sponge spicules, bryozoans, and arthropods like bradorids and ostracods.  Additionally, lithology was reexamined from thin sections and SEM EDS mapping of thick sections. 

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

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