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O'Connell, Kristin, 2009

Sedimentology, structural geology, and paleomagnetism of the Ghost Rocks Formation; Kodiak Islands, Alaska

Bibliographic Reference

O'Connell, Kristin, 2009, Sedimentology, structural geology, and paleomagnetism of the Ghost Rocks Formation; Kodiak Islands, Alaska: University of California, Davis, M.S. thesis, 119 p.


Twenty-two hundred kilometers of Alaskan coastline, from Sanak to Baranof Islands, contains evidence of a Cretaceous to Eocene trench-ridge-trench (TRT) triple junction. Due to the long-term presence of inboard right-lateral strike-slip faults, the original location of the TRT triple junction with respect to North America is unknown. Previous paleomagnetic studies of the Ghost Rocks Formation of the Kodiak Islands, AK indicate a Latest Cretaceous to Early Paleocene TRT triple junction location of ?42 degrees north latitude (Plumley et al., 1983). However, this data set has proved controversial in the literature due to discordant site mean directions between the two major bays studied (Alitak and Kiliuda) as well as a 2-stage structural correction in Alitak Bay and possible remagnitization (e.g. Haeussler et al., 2003a). This study presents new sedimentologic, structural geologic, and preliminary paleomagnetic data in an attempt to resolve the location of TRT the triple junction. The Ghost Rocks Formation is part of an accretionary complex which contains turbidites interlayered with pillow lavas and intruded by gabbro and mafic sills. New structural geologic mapping of the Ghost Rocks Formation shows a mean bedding strike of ?250 degrees, and small-scale block rotations in Alitak Bay. Oriented samples across the formation were taken to include a baked contact test, conglomerate test, and fold test to ensure reliable data. 14 sites from Alitak Bay have been fully analyzed, and 12 sites have been partially analyzed. Second-removed magnetic components represent primary magnetization, and 13 sites showed reliable demagnetization behavior and bedding measurements. In-situ site mean direction for these 13 sites (D=349, I=-45, n=13, k=4.3, ?95=22.8) is improved when corrected for local stratigraphy and structural block rotations (D=178, I=-63, n=13, k=29.2, ?95=7.8). These results are in partial agreement with the original data, and show an improved agreement between the original Kiliuda Bay and the new Alitak Bay declination directions. Continued study of remaining sites will further constrain the data.

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