At Site 1224, basaltic basement was recovered from four holes (Holes 1224A, 1224D, 1224E, and 1224F) out of the six that were drilled. At this site the top of igneous basement was inferred to be at 28 meters below seafloor (mbsf). Igneous basement down to 170 mbsf is divided into three lithostratigraphic units: Unit 1 = massive flow, Unit 2 = pillow breccia, and Unit 3 = intermixed pillows and thin flows (Shipboard Scientific Party, 2003a) (Fig. F2).
Cores from Unit 1, the shallowest unit, had recovery of 30%–50%. This unit shows massive structure with some altered layers and vein deposits. The primary mineral phases are plagioclase, clinopyroxene, opaque minerals, and rare pigeonite. The majority of the basalt is holocrystalline to hypocrystalline lava flows. This unit is divided into two thick lava flows based on grain size, stratigraphy, and alteration layers.
Intermediate-depth Unit 2 differs from Unit 1; however, core recovery was so low (<10%) that the characteristics of the in situ rock are difficult to describe. Many of the small pieces retain almost circumferential alteration halos and thus were not significantly rounded by churning of rubble broken from the hole by the bit. Several pieces still retain fresh or altered glass, most probably representing pieces of chilled margins of pillow lava. Some calcite-cemented hyaloclastite layers were also found. The difference in induration between Units 1 and 2 is so great that the drill bit broke at the boundary.
Unit 3, the deepest unit, shows features similar to Unit 1. Fracture and alteration patterns are similar to those of Unit 1, with reddish brown stains forming halos on small pieces and parallel fractures lined with iron oxyhydroxides and calcite in larger pieces. Portions of at least two cooling units were recovered, possibly more. Recovery in Unit 3 was lower than that in Unit 1 but higher than that in Unit 2 (~20%–30%).