Two migrated multichannel seismic-reflection profiles pass through Site 900 (Fig. 2). They are the north-south Sonne Line 75-21 (Fig. 3), and the east-west Lusigal Line 12 (see Fig. 1). Site 900 is located over a basement high that is 14 km wide on Lusigal Line 12 (west to east) and 10 km wide on Sonne Line 75-21 (south to north). The high is triangular in west-east cross section (Fig. 1). The apparent dip of the basement on the west side of the high is 7° and on the east side of the high is 16°. At its shallowest known point, the top of the high is at 750 ms two-way traveltime below the seafloor or 720 mbsf. Site 900 is located slightly to the west of the top of the basement high, where the basement is predicted to be at 770 mbsf. Sediments thought to be Paleocene in age cover the basement high; older sediments onlap this high, and the basin section to the east is thicker than that to the west. The sedimentary section at Site 900 consists of three main seismic units (Fig. 1). The, topmost unit (0-380 ms two-way traveltime below seafloor, 0-360 mbsf) consists of discontinuous undulating reflectors. The second unit (380-580 ms two-way traveltime below seafloor, 360-540 mbsf) consists of parallel inclined reflectors that dip to the west or southwest. We mapped the regional distribution of these inclined reflectors during Leg 149 (Fig. 4, "Site 898" chapter, this volume). The third unit (580-800 ms two-way traveltime below seafloor, 540-770 mbsf) consists of parallel, continuous, high-amplitude reflectors.
A magnetic anomaly map (Fig. 7, "Site 897" chapter, this volume; P.R. Miles, J. Verhoef, and R. MacNab, pers. comm., 1993) shows that Site 900 is located on the western side of a roughly circular, about 20-km diameter, magnetic anomaly low. Beslier et al. (1993) and Whitmarsh, Miles, and Mauffret (1990) interpreted seismic and magnetic data, respectively, to indicate that Site 900 is located over extended continental crust.