Paleomagnetism, Paleolatitudes, and Magnetic Overprinting on the North Slope, Alaska: ABSTRACT

Several paleomagnetic studies have been made in Arctic Alaska, by industry, by the U.S. Geological Survey, and by the University of Alaska. In general, the results available to the public have been disappointing--most samples of pre-Cretaceous rocks give very steep magnetic inclinations with respect to present horizontal. This has been generally interpreted in terms of a Cretaceous overprinting event. A study of the paleomagnetism of Cretaceous rocks from the North Slope shows that although the Cretaceous field was steeply inclined, it was not as steep as conventional paleogeographic reconstructions would indicate, and not as steep as the bulk of the apparently remagnetized older rocks. This finding leaves open the possibility that the steeper directions recorded by the older rocks are the result of regional tilt, or the result of a paleogeography that allowed an earlier, steeper remagnetizing field. The shallower inclinations seen in the Cretaceous sediments of the Nanushuk Group (Albian-Cenomanian based on the fossil record with one K-Ar age of 100 Ma from an ash parting) give paleolatitudes of about 75°N. The predicted paleolatitude based on North American paleogeographic reconstructions is 80-85°N. Circumstantial evidence that the paleolatitude was shallower than 80-85°N comes from the enormous biogenic productivity needed to form the extensive coal deposits of the Nanushuk Group. Lower paleolatitudes also may be needed to explain the apparent existence of broad-leaved evergreens and the recently reported dinosaur tracks and skin imprints in the Nanushuk Group. End_of_Article - Last_Page 680------------