Leg 146 recovered advanced piston cores from a basin in the California borderland that is characterized by a very high deposition rate of hemipelagic sediment.
Since the early days of the ocean drilling programs, an important objective has been to provide the means to decipher the record of terrigenous material in pelagic and hemipelagic sediment accumulations.
Apparently two controlling factors operate on distribution of planktic and benthic foraminifers in the Cenomanian-Turonian hemipelagic sediments of W-Europe: (1) relative sea-level changes, (2) changes in the surface-water productivity of the oceans.
Detailed inspection of the "productivity-dominated" style of hemipelagic sediments shows, that relative sealevel changes are not necessary to explain variations in foraminiferal abundances and cyclic variations in lithology.
In the southern areas, like the Basque-Cantabrian Basin and the W-Tethys, foraminiferal numbers from Cenomanian hemipelagic sediments suggest rather low primary export productivity (Grafe and Wendler, 2003, fig.
The hemipelagic sediments
are characterized by higher U concentrations due to higher contents of organic matter (Patino et al.
Detailed stratigraphic work in the Shimanto belt of Japan, for example, showed an orderly sequence before disruption: oceanic basement (basalts), pelagic sediments, hemipelagic sediments
with silicic tephras and muddy turbidites, and coarser grained turbidites, basically similar to that found in the Nankai Trough.
abundant hemipelagic sediments and rare shallow- marine sediment than the calcareous sediment on the Indian subcontinent to the south.
Their associations with hemipelagic sediments show that alkaline rocks were erupted in a hemipelagic environment.