Abstract of paper presented at American Geophysical Union 1985 Fall Meeting, San Francisco, California.
Trans. American Geophysical Union (Eos), v. 66, p. 865.

Paleomagnetism of cores from the Yakutat Well, Gulf of Alaska

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

Cores from Oligocene and Early/Middle Eocene sedimentary rocks from the Yakutat exploratory well apparently have retained primary, reversed-polarity magnetizations. A total of 61 plugs, from three different cores from depths between 7,585 and 17,807 feet, were collected and analyzed. The cores represent marine claystones and siltstones tilted 13° to the north.

In most of the samples, six superimposed magnetizations are present (youngest to oldest): (1) CRM acquired during thermal demagnetization ("new magnetite"); (2) drill-press-induced remanent magnetization (the plugging overprint); (3) pre-plugging, post-coring magnetization (the storage overprint); (4) drilling-induced remanent magnetization (the coring overprint); (5) present-axial-dipole-field VRM (the present-north indicator); (6) characteristic magnetization (the paleogeographic indicator).

Although the characteristic magnetization could not be completely isolated from normal-polarity overprints, reasonably precise estimates could be made using principal component analysis. These calculations indicate that the Yakutat block probably occupied a paleolatitude of 52° ±3° in the early Middle Eocene (48 ± 2 m.y.B.P.); early Narizian to Ulatisian) and between 42° and 61° in the Oligocene. Comparison of these paleolatitudes with the APWP for North America puts the Yakutat wellsite at 48 m.y.B.P. opposite Seattle, between the two southernmost fragments of Wrangellia (Vancouver Island and Hells Canyon). This location implies about 13° of post-Early Eocene northward transport with respect to North America, offering a compromise between the 5° proposed by Plafker to account for possible source terranes, versus the 30° proposed by Keller et al. to explain the microfaunal assemblages. The paleomagnetic data suggest that the Yakutat block may have been attached to North American (opposite Washington or Vancouver Island) until some time after 48 m.y.B.P. and that it rotated no more than 20° during its northward migration.