Abstract of paper presented at American Geophysical Union 1984 Fall Meeting, San Francisco, California.
Trans. American Geophysical Union (Eos), v. 65, p. 869.

Paleomagnetism of drillcore from the Navarin Basin COST Well No. 1: Implications for the accreted terrane history of the Bering Sea

D. R. Van Alstine, Z-Axis Exploration
J. W. Whitney, ARCO Alaska, Inc.

To elucidate the paleogeographic and tectonic history of the terranes underlying the Bering Sea shelf, we paleomagnetically studied 228 plug samples taken from 12 cored intervals of the Navarin Basin COST Well No. 1. The sampled intervals range in depth between 7,602 and 16,342 feet and range in age between Oligocene and late Cretaceous (Campanian). The predominant lithology is siltstone deposited in both marine and non-marine environments. An angular unconformity at 12,780 feet separates flat-lying Eocene sediments from underlying late Cretaceous rocks tilted 30° to the north.

As is common in paleomagnetic studies of drillcore, most of the Navarin Basin samples contain a predominant normal-polarity magnetization pointing northward and steeply downward. This component almost certainly represents a secondary magnetization imposed during drilling and aligned either with the present magnetic field or with the present axial dipole field at the wellsite. Although thermal demagnetization was more effective than AF demagnetization in removing this drilling-induced overprint, the overprint commonly exhibits broader coercivity and blocking-temperature spectra than does the characteristic magnetization. Thus, in this study characteristic magnetization directions were generally determined by using a modified “convergence of remagnetization circle” technique.

Reversed- and normal-polarity magnetizations were found in the Oligocene sediments, and exclusively reversed-polarity characteristic magnetizations were found in the Eocene and late Cretaceous rocks. The paleomagnetic inclination derived from the Eocene sediments is 73±4°, corresponding to a paleolatitude of 59±6°. The paleomagnetic inclination derived from the Cretaceous sediments before correcting for northward dip is 80±7°, corresponding to a paleolatitude of 71±13°; after correcting for the northward dip, the late Cretaceous paleomagnetic inclination is 50±2°, corresponding to a paleolatitude of 31±2°. The simplest interpretation of these paleomagnetic results is that the late Cretaceous rocks underlying the Navarin Basin appear to be part of an allochthonous terrane that experienced a high rate of northward motion (> 100 mm/yr) between the Campanian and Eocene.