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The AAPG/Datapages Combined Publications Database
Rocky Mountain Section (SEPM)
Mesozoic Apparent Polar Wander and Plate Motions of North America
Paleomagnetic studies of Triassic and Jurassic sedimentary rocks of the Colorado Plateau define a detailed path of apparent polar motion for the North American plate. The stratigraphic superposition of the formations allows a continuous path of apparent change in pole position to be observed, and provides relative timing of the changes. Early Triassic Moenkopi, State Bridge and Chugwater formations show a consistent position for the Early Triassic pole. Poles from the Chinle and Kayenta formations indicate that an apparent eastward displacement of the pole occurred by Late Triassic time and remained in that position through earliest Jurassic time. A pole from the Summerville Formation indicates a small apparent westward displacement of the pole between late Early and late Middle Jurassic time. These data indicate only a little apparent polar motion from Late Triassic through Middle Jurassic. Published pole positions from eastern North America tell the same story. Subsequent to Middle Jurassic (Summerville) time, poles from the Morrison Formation indicate rapid apparent polar motion in the Late Jurassic. The apparent polar wander path derived from Colorado Plateau rocks has important implications for the opening of the Atlantic Ocean, and the time preceding that opening. African paleomagnetic poles indicate that Africa was essentially stationary during the Jurassic, and thus the entire opening of the central Atlantic was accomplished by the movement of the North American plate westward. North America data also indicate that North America was moving independently of Africa during Triassic time. The Late Triassic-Early Jurassic data indicate a clockwise rotation of North America against a stationary African plate. After possibly only a short time in the Atlantic pre-rift configuration, North America began to move westward, perhaps in the late Early Jurassic. During the Middle Jurassic, no APW is observed but other evidence indicates North America was moving westward. In early Late Jurassic, a change in direction of plate motion occurred so that APW is observed for this time. In about Kimmeridgian time, North America changed direction again, moving northwest until Cretaceous time. In the region of the Colorado Plateau, this movement produced a rapid increase in paleolatitude in Late Jurassic time, in contrast to the low, near equatorial paleolatitudes of the Triassic and Early through Middle Jurassic.
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