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Date Permissions Signed

8-28-2019

Date of Award

Summer 2019

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Housen, Bernard Arthur

Second Advisor

Burmester, Russell F.

Third Advisor

Foreman, Brady

Abstract

Two contradictory apparent polar wander paths (APWPs) of North America (NA) for most of Jurassic time have been the subject of many studies since the 1990s, and are important to rectify if in order to constrain the tectonic evolution of the continent. Among various efforts to resolve this persistent issue, additional results from well-dated kimberlite volcanics have been used to support a higher-latitude APWP (Kent et al., 2015), and the controversy was blamed on inclination error (IE) in paleomagnetic results of sedimentary units, most of which are from the U.S. South Western interior. Those paleomagnetic poles define the other, lower-latitude path (Kent and Irving, 2010).

Here we present paleomagnetic results from Upper Triassic (Garita Creek, Trujillo, and Redonda Formations) and Middle Jurassic (Entrada, Summerville, and Lower Morrison Formations) sedimentary units of east-central New Mexico, which have magnetostratigraphy that can be correlated with geomagnetic polarity time scales (GPTSs). Positive reversal and fold tests confirm the primary magnetization in these units, which is mostly carried by detrital hematite. Interpretation of noisy and non-linear demagnetization paths, especially ones from Middle Jurassic units, was facilitated by a smoothing scheme, which did not bias the line and great circle fits. The less-than-ideal quality of the Middle Jurassic data could be due to the high rate of polarity reversals for this time period. As a side effect, the frequent usage of the great-circle fits to demagnetization paths was inevitable. We used the sample-level directions from the line fits to estimate the IE using the elongation/inclination (E/I) method of Tauxe and Kent (2004). IE for the Upper Triassic units is negligible because mean directions are horizontal. IE estimated for the Middle Jurassic units is ~20°, however with large 95% confidence limits.

Paleomagnetic poles for Trujillo, Redonda, Summerville, and Lower Morrison Formations of east-central New Mexico, even with IE-correction streak approximately along the 60° parallel (in present coordinates) for most of the Jurassic time, which validates the lower-latitude APWP.

Regardless of the robustness of E/I results, the effects of different amounts of IE can be simply simulated. From existing ca. 163 Ma Summerville Formation paleomagnetic poles, new ones were simulated assuming a possible range of IE. These results show that no amount of the IE correction to the sedimentary results would produce poles consistent with the high-latitude APWP so some other explanation for the discrepancy is required.

Type

Text

Publisher

Western Washington University

OCLC Number

1117448571

Subject – LCSH

Paleomagnetism--New Mexico; Paleogeography--New Mexico; Polar wandering--North America; Geology, Stratigraphic--Triassic; Geology, Stratigraphic--Jurassic

Geographic Coverage

New Mexico; North America

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Available for download on Friday, August 28, 2020

Included in

Geology Commons

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