Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 4
Presentation Time: 4:00 PM


STEINER, Maureen B., Geology & Geophysics, University of Wyoming, 1000 E University, dept 3006, Laramie, WY 82071,

Continuous exposure of Upper Carboniferous through Upper Permian sedimentary strata in north central Texas provided an opportunity to examine the motion of the North American portion of Pangea during amalgamation of the supercontinent. During Pangean formation, two important events happened. Climate changed substantially: an “icehouse” to “greenhouse” transition. Furthermore, the configuration of the supercontinent changed, from a Pangea B assemblage of continental pieces to a subsequent Pangea A assemblage. Paleomagnetic sampling of latest Pennsylvanian through the entire Permian sedimentary sequence determined the paleolatitudes of southern Laurentia during this time and the movements that created Pangea A. The palleomagnetic data shed light on the timing and rate of the Pangea B to A change. These data indicate that southernmost margin of North America/ Laurentia had near-equatorial locations through the Early And Middle Permian. The site paleopoles show an essentially continuous westward motion of North America/Laurentia from latest Pennsylvanian (Virgilian) through the Middle Permian (middle Guadalupian), indicating that Pangea B changed to Pangea A through the Early and Middle Permian. In addition, the data record another event in Pangean history: the beginning of the breakup of Pangea in the Late Jurassic. About 60% of the approximately 300 samples display a secondary magnetization in the unblocking temperature range of 350 to 475 degrees C. That remanence direction is the same as that of the latest Jurassic, upper Morrison Formation. Tectonic events during that time were a rotation of the Colorado Plateau and opening of the Gulf of Mexico. Origin of the Late Jurassic secondary magnetization could be either thermally induced or a fluid migration.