Graduation Year

2014

Graduation Month

December

Document Type

Thesis

Degree Name

Bachelor of Science

School or Department

Geosciences

Major

Geosciences

Faculty Mentor Department

Geosciences

Faculty Mentor

James R Staub

Keywords

volcanic, vertebrate, fossils, Haystack Butte, dinosaur

Subject Categories

Geology | Paleontology | Sedimentology | Stratigraphy

Abstract

In May 2013, the Two Medicine Dinosaur Center (TMDC) began excavation on a dinosaur bonebed in the St. Mary River Formation on Carey Butte, Montana. Since excavation started, four additional bonebeds have been discovered in the surrounding area. They display different depositional environments; two are in sandstone and the other three are in siltstone. The purpose of this study is to provide a depositional setting for the area that links all five sites together comprehensively by examining the sedimentology of the area. A stratigraphic analysis of the St. Mary River Formation of Carey Butte revealed four distinct facies associations. Facies Association 1 is made up of large sandstone lenses, which are interpreted as a large river channel. Facies Association 2 is made up of small sandstone lenses, which are interpreted as splay channels. Facies Association 3 is a series of thin sandstone and siltstone sheets, which are interpreted as crevasse splays. Facies Association 4 is a series of shale and siltstones, which are interpreted as overbank fines or floodplains. They are rich in organic material, both plant and vertebrate, and are heavily bioturbated. Together, these facies associations suggest that the depositional environment in this area was an anastomosing river system. This interpretation will provide a lithologic context for further paleontological work done on Carey Butte.

Honors College Research Project

1

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© Copyright 2014 Stacia M. Martineau