PALEOMAGNETISM OF LOWER CRETACEOUS KSM TURBIDITES NEAR HAMILTON POINT, KUPREANOF ISLAND, ALASKA

Southeast Alaska, part of the Northern Cordillera, is composed of oceanic crust, continental fragments, and island-arc complexes of varying age and origin. This study examines the paleomagnetism of Cretaceous aged sedimentary rocks from Wrangellia, a terrane that is thought to have formed near the equator approximately 200 million years ago. Wrangellia has been closely studied because it may have moved to its present day latitude along a complex series of transform faults.

Sixty-six cores were collected from Hamilton Point on Kupreanof Island, Alaska for paleomagnetic analysis. The sites cored represent the entire Ksm turbidite unit of Brew, et al. 1984, a lower Cretaceous age unit composed of fine-grained sandstone interbedded with mudstone, calcareous concretions, and carbon-rich shale. The age of Ksm was determined by fossils (Muffler, 1967) collected near Hamilton Point. Plant fossils and fossil fragments occur throughout the section studied and will be examined further to obtain age constraints.

The Ksm unit preserves a normal polarity magnetization (NRM) that is detectable above the noise level. Zijderveld projections indicate a general northern declination and a moderate downward inclination for the sites sampled. Preliminary NRM measurements and selective removal of secondary NRM through alternating-field demagnetization has reveal complex multi-component magnetizations. The initial paleomagnetic signatures obtained indicate magnetic latitudes of approximately thirty-five degrees to forty degrees. Stereographic plots illustrate that the magnetizations are clustered, suggesting reliable declinations and inclinations. The present-day latitude of Hamilton Point (59 deg) is significantly farther north than the Ksm magnetic latitude suggesting significant post-Cretaceous northward translation.