3-1 Testing for Extreme pH in Lake Deposits of the Triassic Spearfish Formation of North Dakota

Session: Lakes of the World Through Space and Time: Archives of Climate, Paleoenvironments, Ecosystems, Geohazards, and Economic Resources

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Abstract:

Extreme acid saline lakes were prevalent during Permo-Triassic time in tropical Pangea. However, the temporal extent of this extreme lake chemistry is largely unknown. The newly recovered EERC Halite #1 core of the Triassic Spearfish Formation from the Williston Basin of western North Dakota may provide clues about the temporal longevity of these acid saline lake systems. The Triassic Spearfish Formation is composed of red siliciclastics, bedded halite (aka the Pine Salt), and displacive halite; a lithologic assemblage similar to the underlying Permian Opeche Shale, which hosts primary fluid inclusions in bedded halite with pH less than 1. Primary fluid inclusions in halite chevron crystals from the Spearfish Formation serve as repositories of the parent waters of Triassic saline lakes and provide details on the lake chemistry. Petrography reveals that primary inclusions contain liquid and vapor, as well as “accidental” daughter crystals, and microbes. Laser Raman spectroscopy has identified dissolved sulfate in the inclusion liquid and detected sulfate minerals as accidental daughter crystals. The presence of sulfate minerals and dissolved sulfate ions point to the Triassic lake chemistry. Here, we present preliminary results that reveal that the bedded halites of the Spearfish Formation were precipitated from sulfate-rich shallow lake waters.

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

doi: 10.1130/abs/2025AM-6987

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