New Implications for Paleoenvironmental Reconstruction of the Eau Claire Formation in its Type Area

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

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Abstract:

The Hi-Crush Proppants Augusta OB-1 rotosonic core was drilled in the Augusta Hi-Crush Quarry in southeastern Eau Claire County, Wisconsin. This study aims to enhance understanding of the stratigraphy and depositional environments through the OB-1 Core, which includes from oldest to youngest the Mount Simon Formation, which sits directly on regolith of Precambrian granite, followed by the Eau Claire Formation, and ending with the Wonewoc Formation, which is unconformably truncated by the modern soil horizon. The core was drilled near the Eau Claire and Mount Simon type sections and has the potential to be a key reference section for these units. However, the use of rotosonic drilling in coring disturbed friable sandstones throughout the succession. Herein, we focus on the Mount Simon and Eau Claire formations due to their completeness in the core and better recovery. At the type section, the Mount Simon Formation consists of crossbedded, coarse to granule, quartz sandstone interbedded with lenses of blue-grey shales. In the OB-1 core, the Mount Simon was lithologically similar to previous descriptions of the formation, but sedimentary structures such as cross-stratification were not well preserved due to the drilling method disturbing the friable sandstone. The Eau Claire Formation near its type section is a mix of interbedded fine grained, often glauconitic sandstones and blue-grey shales. Beds of disarticulated trilobites and lingulid brachiopods are common. The OB-1 core differs in that the Eau Claire Formation lacks body fossils and glauconite, displays only rare bioturbation, and has coarse to granule-sized grains.

Herein, the Mount Simon Formation is interpreted as being deposited in a fluvial to marginal marine depositional setting similar to previous interpretations. On the other hand, interpretation of the Eau Claire Formation depositional setting is less clear. A lack of marine fossils and glauconite indicate a shallower depositional setting than the type sections, which are located more distal from the Wisconsin Dome and Arch, the prominent paleotopographic highs during the Cambrian. However, previous interpretations of the Eau Claire Formation intertidal equivalents consist of planar sandstone-dominated successions. Given the proximity of the OB-1 Core Eau Claire succession to the type sections, this study therefore has important implications for paleogeographic reconstructions and Eau Claire Formation facies determinations.