The equatorial Pacific high-productivity belt: elements for a synthesis of Deep Sea Drilling Project Leg 85 results.

Abstract

Leg 85 of the Deep Sea Drilling Project operated in the eastern central Pacific in the region of the equatorial high-productivity belt. We recovered uppermost Eocene to Quaternary reference sections amenable to fine-scale stratigraphic and paleoceanographic research, using primarily the hydraulic piston corer. Four sites (572 to 575) were drilled along an east-west (about 114 to 133oW) and north- south (about 0.5 to 6oN) transect across the equatorial belt. Results of Leg 85 contributed to advances in the four elements needed for an eventual paleoceanographic synthesis: 1) a high-resolution, multidisciplinary, and integrated datum-plane scheme and time scale, with an overall resolution of 0.13 to 0.38 m.y., was established; 2) a system of correlatable acoustic reflectors was delineated over vast distances, and these reflectors were calibrated against age and physical and chemical properties at Sites 574; 3) a fine-scale geochemical (stable isotope and CaCO3) and micropaleontological climatic reconstruction was developed (discontinuously) from Oligocene to Pleistocene; and 4) broadly correlatable hiatuses (NH, PH), defined by previous work, were recognized at Sites 573 to 575. The interval from 8 to 9 Ma serves to outline how integration of the foregoing elements could lead to a future synthesis. In the central basin of the equatorial Pacific, the interval from 8 to 9 Ma is marked by a hiatus (NH5) in siliceous clays. A correlative hiatus occurs in carbonate oozes of the equatorial region and in the northeastern Pacific rim, and may be correlated with the 'Purple' equatorial Pacific reflector. The interval is characterized globally by a regression, by strong carbonate dissolution, and by isotopic and micropaleontological evidence of marked cooling. Further study of these paleoceanographic phenomena in a variety of depositional environments will lead to an understanding of their relationships and functioning.-from Authors