During the Japan Trench Transect (DSDP Legs 56 and 57, September-December 1977), 377 cores from 15 holes at 7 DSDP sites were taken (Figure 1, Table 1). The DSDP sites represent water depths of 1552 meters (Hole 438) to 5986 meters (Site 434), from the continental slope (Sites 434, 435, 438-441) to the ocean basin (Site 436). (No sediment was recovered at Site 437.) Predominantly Miocene to Quaternary sediment was recovered, although some Cretaceous sediment was cored at Sites 436 and 439 and possible uppermost Oligocene sediment at Site 438. Sediments recovered during the Japan Trench Transect provide excellent Neogene siliceous reference sections for the northwest Pacific from an open ocean environment (Site 436) to an upper slope environment (Site 438). The location of the transect near the confluence of the cold-water Oyashio Current and the warmwater Kuroshio Current results in a mixture of highand low-latitude microfossil assemblages throughout the Neogene and allows correlation of the various highand low-latitude zonations that are used in the North Pacific. Diatoms and radiolarians are the most abundant, continuously present microfossils, and provide the best biostratigraphic control. Planktonic foraminifers and calcareous nannofossils also contribute important biostratigraphic and paleoclimatic information. Benthic foraminifers are useful for Paleobathymetric interpretation and date the upper Oligocene and Upper Cretaceous sequences that contain no planktonic faunas or floras. Planktonic microfossil zonations used for Legs 56 and 57 are modified from zonations previously applied to the North Pacific. The diatom zonation is essentially that of Koizumi (1975), although new subzones and an additional zone have been added (Barron, this volume) to allow additional refinement at this latitude in the northwest Pacific. Generally, the subzones are defined by diatom events that have been tied to the paleomag-