Publication Date

2021

Document Type

Dissertation/Thesis

First Advisor

Fischer, Mark P.

Second Advisor

Frank, Mark R.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Earth, Atmosphere and Environment

Abstract

The Hell Creek Formation is known for its abundant vertebrate fossils from the end of the Cretaceous. Its internal stratigraphy is poorly defined and it is therefore difficult to determine the precise stratigraphic location of a paleontological feature. This challenge could be overcome if a consistently appearing easily recognizable time horizon, such as the Chicxulub impact debris, or a well defined formational contact could be identified over a wide area of the Hell Creek Formation exposure, but these have been difficult to establish in some localities. The Carthage Institute of Paleontology (CIP) has collected Hell Creek specimens near Ekalaka, Montana for over a decade. A tonstein deposit was discovered in CIPs field area, stratigraphically where the impact debris would be expected, near the top of the Hell Creek Formation, an ideal location to establish a persistent time-stratigraphic horizon for the region. With the aim of establishing the precise location, physical and geochemical characteristics of the candidate horizon, strata bounding the formational contact and tonstein were measured using differential GPS and sampled for lab analysis across several kilometers of publicly accessible land.Simple models were constructed using Golden Software’s SurferTM program. These models are the first step in creating a detailed time stratigraphic model that can incorporate multiple types of geologic and paleobiological data. The current model can be used to calculate the expected formational contact elevation, even in areas where the contact has been eroded. Use in the field will allow for additional contact locations to be located quickly. A simplified right hand rule strike and dip of 196.5 / 0.47 was determined for the contact, which does not align with any known local or regional structural features. To test the validity of the tonstein horizon as the impact debris layer, XRD, SEM/EDS, ICP-OES, carbon isotope chemostratigraphy, and palynology were utilized. The tonstein horizon is dominated by kaolinite minerals, like that of other verified impact horizons present in the Hell Creek Formation, however, it does not contain any of the other markers associated with the impact debris. Isotope chemostratigraphy identified several negative excursions near the proposed formational contact, but they do not correlate to other isotope curves from similar studies from verified Cretaceous-Paleogene (K-Pg) sites. All palynological analyses including those from two meters below the proposed formational boundary were dominated by taxa associated with the Paleogene and were largely free of K-taxa thought to have gone extinct at the K-Pg boundary.

Extent

112 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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Text

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