Two time-migrated, multichannel seismic reflection profiles pass close to Site 898 (Fig. 2). They are the north-south Sonne Line 75-17 (Fig. 3) and the east-west Lusigal Line 12 (see Fig. 2, "Background and Scientific Objectives" section, this chapter) on which Site 898 is located. Site 898 is situated over a basement high that is 5 to 6 km wide in the east-west direction and 10 to 12 km wide in a north-south direction. The top of the high dips gently to the west and south and is about 900 ms two-way traveltime or 890 mbsf at its shallowest known point. The basement appears to be cut by three or four large normal faults that have a westerly component of dip; these are most clearly seen in Figure 1. Sediments fill the several small half-graben(?) basins, apparently formed by the faulting, on the high. Site 898 is located over the highest point of the basement. Sediments predicted to be Late Cretaceous in age cover the basement high, and older sediments onlap the high. The basin section to the west is thicker than that to the east. The sedimentary section at Site 898 consists of four main seismic units (Fig. 1). The topmost unit (0-210 ms two-way traveltime; Acoustic formation 1A of Groupe Galice, 1979) exhibits horizontal continuous parallel reflectors that we interpreted to be terrigenous turbidites. Thisunit is substantially thicker to the west than to the east of the site. The second unit (210-360 ms two-way traveltime; top part of formation 1B of Groupe Galice, 1979) consists of discontinuous wavelike reflectors. The third unit (360-480 ms two-way traveltime; bottom part of formation 1B of Groupe Galice, 1979) consists of parallel inclined reflectors that dip to the west or southwest. The region in which these inclined reflectors are observed was mapped during Leg 149 (Fig. 4). The fourth unit (480-900 ms two-way traveltime; formation 2 of Groupe Galice, 1979) consists of parallel, continuous, high-amplitude reflectors. Formation 2 does not change thickness across the basement high. An apparently reverse fault, having an easterly component of dip, was observed in the sediment just to the east of Site 898. It extends from the east side of formation 2 (Fig. 1).
Magnetic data (Fig. 7, Site 897 chapter, "Site Geophysics" section, this volume; P.R. Miles, J. Verhoef, and R. MacNab, pers. comm., 1993) show that Site 898 is located on the southeastern side of a magnetic anomaly high. The magnetic high is only slightly elongated in the north northwest-south southeast direction and is not parallel to the margin, as are most of the magnetic anomalies farther to the west. Beslier et al. (1993) and Whitmarsh, Miles, and Mauffret (1990) have interpreted seismic and magnetic profiles, respectively, to indicate that Site 898 is located over extended continental crust.