Site 120

Abstract

Site 1208 is located at lower bathyal (3346 m) water depth, close to center of the Central High of Shatsky Rise. The site lies on seismic line TN037-8 (Fig. F1). Sediments of the Central High have not been cored before; thus, the stratigraphy was unknown prior to drilling at Site 1208. Moreover, correlation of reflectors and the major seismic units with the Southern and Northern Highs, where units and reflectors are calibrated with drill holes, is speculative. Site 1208 coring was designed to provide knowledge of the stratigraphy of the Central High, as well as correlation of units and reflectors with the Southern and Northern Highs. The site was located at the point where the stratigraphic se- quence appears to be most complete. The objective at Site 1208 was to recover a Paleogene through Upper Cretaceous section for paleoceanographic investigation. Highly tenta- tive predrilling correlation with the Southern High seismic units of Sliter and Brown (1993) suggested relatively thick seismic Units 1 (Neo- gene) and 2 (Paleogene) characterized by predominantly weak, largely horizontal reflectors and a relatively thin Unit 3 (Upper Cretaceous). The Upper Cretaceous to Holocene sequence was expected to contain a number of minor disconformities as indicated by prominent, but hori- zontal reflectors. At depth, a major angular unconformity suggests ero- sion of a significant part of the mid-Cretaceous sequence (Fig. F1). The total thickness of the sedimentary section at Site 1208 was estimated at ~785 m. Basement underlying the site was formed during Magneto- chron CM15 in the Berriasian (Nakanishi et al., 1989). The drilling strategy was to double core down to the uppermost chert horizon in the Upper Cretaceous using the advanced piston corer/extended core barrel (APC/XCB).