Year of Award

2021

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Geosciences

Department or School/College

Department of Geosciences

Committee Chair

Nancy W. Hinman

Commitee Members

Megan Dethier, Roy Plotnick, Robert Riding, J. B. Alexander Ross

Keywords

Carbonates, Carboniferous, Invertebrate Paleontology, Lagerstatten

Abstract

The Bear Gulch Limestone of the late Mississippian central Montana is a significant Konservat Lagerstätte known and a part of one of the most complete mid-Carboniferous stratigraphic sections in the world. Despite containing a well-described fish fauna, the most diverse and abundant Carboniferous fish fauna known, nothing was known of the invertebrate assemblages, and many aspects of the geology remained enigmatic. With few rocks of this age available for study worldwide, the Bear Gulch Limestone contains an important record of life and Earth history near the Pennsylvanian boundary, a time of climatic change.

Using new outcrop data combined with subsurface information a multidisciplinary integrative study was necessary to gain a fuller understanding of the Bear Gulch. In this study, the first of its kind undertaken in the Bear Gulch, I combined sedimentology, limited preliminary geochemistry, and invertebrate paleontology to understand the physiochemical parameters that led to the formation of the flinz and fäule laminasets and the important record of life they contain. The flinz and fäule are, broadly, the only two facies to have been recognized in the Bear Gulch Limestone. Detailed microfacies analysis, presented here, has identified 5 facies that elucidate the development of the basin. This higher resolution insight reveals that the BGL shallowed through time—the fully marine giving way to the increasingly estuarine conditions of the upper Tyler formation and glacial Pennsylvanian.

Furthermore, I confirmed the stratigraphic position of the Bear Gulch Limestone within the late Mississippian portion of the Tyler Formation. The Bear Gulch Limestone is a marine limestone tongue that transitions to the increasingly fluvial upper Tyler Formation within the Big Snowy Trough of central Montana.

Finally, this work represents the first comprehensive collection and taxonomic analysis that included all fossils found; vertebrate, invertebrate, botanical, and trace. New fossil collections with modern collecting techniques that include detailed locality and stratigraphic information allow testing of various hypotheses related to the fauna of the flinz and fäule. Invertebrate diversity and abundance, previously underestimated from historic collections, have been reported here for the first time.

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© Copyright 2021 Amy Elizabeth Singer