Butane and pentane were detected from below 570 mbsf with maximum readings of 28 ppm and 32 ppm, respectively, at the bottom of the hole. We received courageous approval to deepen the site to 850 mbsf under the condition that rigorous safety monitoring did not preclude further drilling. To ensure sufficient time for deepening Hole 1148B we drilled ahead from 145 to 440 mbsf and from 646 to 700 mbsf. The sediments at Site 1148 reflect a complex sequence of hemipelagic deposition, the beginning of which is coeval with the initiation of sea floor spreading in the South China Sea at about 32 Ma. The dominant lithologies are grayish green clay with quartz and nannofossils, olive gray and reddish brown clay with nannofossils, light grayish green clayey nannofossil ooze, brown nannofossil clay, and greenish gray nannofossil clay mixed sediment.
Lower sections have the same composition but contain slumped and faulted intervals.
This spliced interval from this site can be combined with the spliced record from nearby Site 1147 to construct an unambiguous, continuous splice from 0 to 155.34 mcd. At Site 1148, seven lithologic units are identified on the basis of compositional, facies and especially color variations. The sediment at Site 1148 is more variable than at the other sites drilled on Leg 184. Dominant lithologies are clay with variable concentrations of nannofossils. None of these units show any evidence of sediment redeposition and are representative of continuous hemipelagic sedimentation.