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Master of Science (MS)
Housen, Bernard Arthur
Burmester, Russell F.
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.
Western Washington University
Subject – LCSH
Paleomagnetism--New Mexico; Paleogeography--New Mexico; Polar wandering--North America; Geology, Stratigraphic--Triassic; Geology, Stratigraphic--Jurassic
New Mexico; North America
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Mirzaei Souzani, Masoud, "Paleomagnetic results from Upper Triassic and Middle Jurassic strata of east-central New Mexico, and implication for North American APWP" (2019). WWU Graduate School Collection. 909.
Available for download on Friday, August 28, 2020