A cratonic Middle Jurassic paleopole: Callovian-Oxfordian stillstand (J-2 cusp), rotation of the Colorado Plateau, and Jurassic North American apparent polar wander

摘要

Paleomagnetic results have been obtained from two sequences of the upper Middle Jurassic (upper Callovian) Summerville Formation which are located on the North American craton (north central New Mexico). The thicker of the two sections (Trujillo) exhibits a well-defined dual-polarity remanence, forming a magnetostratigraphy of at least 12 relatively short polarity intervals. The high reversal frequency is consistent with that recorded by the oceanic crust at this time. The second section (Romeroville) is thin, gypsiferous, and poorly indurated; consequently, only a short interval (5 m) was successfully sampled. The characteristic magnetization was wholly normal polarity. In the rapid reversals of the thicker section, that thickness of normal polarity is unique and thus forms the basis of magnetostratigraphic correlation between the two sections. A cratonic late Middle Jurassic paleomagnetic pole at 148.2°E, 57.3°N (k = 30.3, α_(95) = 6.0°) was obtained from the larger Trujillo sequence. Despite large confidence limits, the small sample population of the Romeroville sequence displayed the same pole.