Electronic Theses and Dissertations

Identifier

6067

Date

2017

Date of Award

11-29-2017

Document Type

Thesis

Degree Name

Master of Science

Major

Earth Sciences

Concentration

Geology

Committee Chair

Mervin J Bartholomew

Committee Member

Daniel Larsen

Committee Member

Youngsang Kwon

Abstract

Layer-parallel-shortening (LPS) strain records the first strain experienced by rocks during tectonic events. LPS indicators preserved in vertical to overturned fold limbs along the leading edge of the fold-thrust belt in southwestern Montana are used to determine which deformation came first there: Sevier or Laramide. LPS-strain was analyzed for 22 samples collected in the Dixon Mountain area from different beds containing ooids, Pentacrinus, or brachiopods within a 580-meter stratigraphic interval. Field orientations of strain ellipses were then adjusted for: 1) trend and plunge of fold axes; 2) rotation of thrust sheets relative to the trend of the Sevier-emplaced, overturned Deadwood Gulch syncline; and 3) bedding dip. Retrodeformed orientations of 15 samples show an average shortening direction of ~227o, consistent with Sevier shortening (~213o); 4 samples show a shortening direction of ~268o; and 3 samples show a shortening direction of ~171o, perhaps indicating Sevier shortening across a lateral ramp.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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