Sites 897, 899, and 900 were drilled on basement highs within the ocean/continent transition (Fig. 1). Among the several holes drilled at each site, Holes 897C, 897D, 899B, and 900A yielded basement samples.
At Holes 897C and 897D, 100 m apart, the basement was reached under 650 and 680 m, respectively, of Pleistocene to mid-Eocene sedimentary rocks. The basement section recovered is almost completely ultramafic. In Hole 897C, additional rare and small pieces of volcanic breccias were recovered between the ultramafic cobbles of the top of the basement section. In Hole 897D, a few pieces of strongly altered basaltic lavas, doleritic rocks, and undeformed microgabbros were recovered from the sediments immediately overlying the basement (Shipboard Scientific Party, 1994a).
About 20 km east-southeast of Site 897, Hole 899B was drilled on a basement high detected during the cruise, at a water depth of 5291 m. At that site, the acoustic basement was reached under 369.9 m of Pleistocene to upper Eocene sedimentary rocks, and over 180 m of basement was cored. The sedimentary column has been divided into three units. Unit IV is basement and was subdivided into Sub-units IVA and IVB. Subunit IVA is 95 m thick and is composed of unsorted ultramafic breccias with accessory mafic metamorphosed clasts (Fig. 2). Subunit IVB is a 19-m-thick transition zone consisting of composite serpentinite breccias, basaltic lavas, and sediments underlain by about 78 m of unbrecciated boulders of peridotite with intercalations of siltstone, basaltic lavas, undeformed microgabbros, and mafic metamorphic rocks. The succession of sedimentary layers inserted in Unit IV, down to 540 mbsf, is normal and consists entirely of lower Aptian rocks (Comas et al., this volume). A cataclastic breccia and varied boulders in a mass-flow deposit would be consistent with this puzzling sequence (Shipboard Scientific Party, 1994b).
Hole 900A was drilled at about 60 km east of Hole 899B, at a water depth of 5037 m. At Site 900, the basement was reached under 748.9 m of Pleistocene to Paleocene sedimentary rocks. Over 56.1 m of basement was drilled and 27.71 m of basement core was recovered, composed entirely of sheared gabbros (Shipboard Scientific Party, 1994c).