The top interval of Basement Unit 6 is rusty brown dolomite resembling that of Basement Unit 4. The interbedded sediments indicate bathyal water depths during late Eocene to early Oligocene extrusion of the lava flows. Pelagic deposition in a bathyal environment continued uninterrupted until at least middle Miocene time. Comparison between cores and logging data indicate that these flow units are 4.4 to 23.4 m thick. The thick massive lobes are probably sheet flows.
Thick sheet flows and absence of rubbly talus suggest low to moderate slopes.
While small pillows cannot advance far before freezing, the larger sheets could efficiently transport magma from a distant vent. The flows are cryptocrystalline to fine-grained, and generally only sparsely vesicular. Vesicles are largely restricted to chilled margins. Vesicularity varies within the units, but is consistently low, suggesting the deep water corroborated by bathyal sediments. Calcareous sediment or carbonate veins commonly fill sutures between pillows.