error) (Mahoney et al., 2005; Sager, in press b).
During Ocean Drilling Program (ODP) Leg 198, 46 m of basalt was cored at Site 1213 (31°34.6402´N, 157°17.8605´E) on the flank of the Southern High of Shatsky Rise (Fig. F1). The basement section consists of three basaltic sills of approximately equal thickness (Table T1), intruded into Berriasian age (lowest Cretaceous) pelagic sediments (Shipboard Scientific Party, 2002). These three igneous units were interpreted as sills because they are thick (>7 m), massive igneous units, they have a coarse-grained texture that becomes finer toward chilled margins at top and bottom, vesicles and contraction cracks occur preferentially at the margins, and metamorphosed sediments are found above and intercalated with the igneous units (Shipboard Scientific Party, 2002). Two samples from the sills have been dated using 40Ar/39Ar radiometric techniques, producing indistinguishable dates that average 144.6 ± 0.8 Ma (2 error) (Mahoney et al., 2005; Sager, in press b).
Paleomagnetic data from basaltic cores are important because they give a reading of paleolatitude of the plate at the age of rock formation. Results from a small number of units, as were cored at Site 1213, have limited use by themselves because they do not properly average paleosecular variation. Nevertheless, they are important because they can be combined with other paleomagnetic data of similar age (Peirce, 1976; Cox and Gordon, 1984). In addition, few data of Jurassic or Early Cretaceous age are available for the Pacific plate (Larson et al., 1992). Our motivation in this study was to determine paleoinclinations of Site 1213 basalt units to give geologic insights about the basement of Shatsky Rise (e.g., how fast the basement erupted, polarity, and a hint at paleolatitude). Paleomagnetic data from the Berriasian host sediments are given in a companion article (Sager et al., this volume).
