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Paleomagnetism of the Black Hills of South Dakota and Wyoming, implications for North American Apparent Polar Wander Paths

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism, Part I

Presenting Author:

Bernard Housen

Author:

Housen, Bernard A¹

(1) Geology Department, Western Washington University, Bellingham, WA, USA,

Abstract:

Paleomagnetic results of units of Permo-Triassic to Eocene ages from the Black Hills of South Dakota and Wyoming will be presented. New data from the Permo-Triassic Spearfish Fm combined with data from Weil and Yonkee (2012) have a tilt-corrected mean of D= 332, I = 25, n=77, k = 30, α₉₅ = 4, with an E/I corrected inclination of Ic= 37. The Callovian Sundance Fm (Kilanowski, 2002) has a tilt-corrected mean of D = 346, I = 57, N = 14, k= 55, α₉₅ = 5.4, with an E/I corrected inclination of Ic = 66. The Oxfordian-Tithonian Morrison Fm (Gregiore, 2001) has a tilt-corrected mean of D = 000.4, I = 61.5, N = 15, k= 58, α₉₅ = 5.5, with an E/I corrected inclination of Ic = 68. Post-deformation Eocene (58 to 45 Ma) intrusive rocks (Housen et al., 2003) have mean of D = 345, I = 60.3, N = 8, k= 30, α₉₅ = 10.5.

The paleomagnetic results from the Jurassic units (Sundance and Morrison Fms) have previously been interpreted to represent Eocene-aged remagnetizations- due to the nearly exact coincidence between the in-situ directions of these Jurassic units with the Eocene directions from the intrusive rocks, and of Eocene expected directions from the NA APWP. This conclusion can be reconsidered (see Meert et al, 2020) in light of the occurrence of reversals and positive reverals tests for the Spearfish, Sundance, and Morrison Fms. Fold tests for these units were not conclusive, due to the predominantly gentle dips of the Black Hills strata, and also due to the effects of inclination error on the precision of these fold tests. Comparisons of these updated will highlight recent models of North America APWP by Kent and Irving, 2010, Kent et al, 2015, Muttoni and Kent (2019), Muttoni et al., 2024, Mirzaei et al., 2021, Kulakov et al., 2021, and Vaes et al., 2023. For Jurassic through Early Cretaceous (~130 Ma) time, APWP that use combined global models place NA at very high paleolatitudes during, whilst inclination-corrected data from sedimentary strata from place NA at more moderate paleolatitudes.