The top of acoustic basement is flat-lying, and overlying basement is a sediment sequence approximately 500 m thick. Sedimentary objectives at Site 1139 were to determine sequence facies, to define the ages of seismic sequence boundaries, to estimate the duration of possible subaerial and shallow marine environments, to obtain minimum estimates for basement age, and to determine the paleoceanographic history of this high latitude site. As discussed below, we largely achieved our goals at Site 1139. We drilled 233 m into igneous basement that is overlain by early Oligocene shallow marine sediments. Sediments were recovered from the upper 461 mbsf of Hole 1139A, whereas extensively altered felsic volcaniclastic rocks and mafic to intermediate composition lava flows were recovered from the lower 233 m of the hole.
Trace fossils are very common.
Unit II records a substantial influx of terrigenous clay from an adjacent volcanic landmass. Sediments become semilithified by 100-110 mbsf. We observed very rare tephra layers and disseminated volcanic ash, locally concentrated in burrows. Within this depth interval, three volcanic ash layers have high compressional wave velocities. Units I to III represent deep-marine pelagic sedimentation.