Paleomagnetism of Upper Triassic continental sedimentary rocks from the Dan River—Danville rift basin (eastern North America)
A magnetic polarity stratigraphy and a corresponding paleomagnetic pole position are reported from 113 sampling sites representing 3000 m of Late Triassic continental sedimentary rocks that crop out in the Dan River—Danville basin of North Carolina and Virginia. Characteristic magnetizations isolated by thermal demagnetization for either the hematite-bearing red siltstones or the interbedded magnetite-bearing gray to black mudstones of the Leakesville Formation are indistinguishable in mean direction and pass reversal tests. The magnetic polarity sequence consists of 11 magnetozones that vary from ≈100 m to 800 m in thickness and can be uniquely correlated within biostratigraphic constraints to magnetochrons E9n to E14n of the Newark geomagnetic polarity time scale. According to this correlation, the sampled section is the age equivalent of the uppermost Stockton, the entire Lockatong, and the lowermost Passaic formations of the Newark basin, and represents ≈7.5 m.y. of deposition. The late Carnian Dan River—Danville paleopole is located at 55.4°N 100.1°E (A_95 = 1.9°), which is not significantly different from paleopoles reported from essentially coeval rocks in the Newark basin. Considering that the Dan River—Danville and Newark basins are ≈600 km apart, the close agreement of the coeval paleopoles argues strongly for the overall tectonic coherence of these rift basins with respect to each other and, most probably, with respect to cratonic North America. Discordant latest Triassic paleopoles from the southwestern United States, which have tended to be attributed to fast apparent polar wander for North America in the Late Triassic and predict anomalously high paleolatitudes for eastern North America, are best accounted for by a large net clockwise rotation of the Colorado Plateau.
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- Geological Society of America Bulletin