QUATERNARY TIME-SCALE FOR THE ONTONG-JAVA PLATEAU - MILANKOVITCH TEMPLATE FOR OCEAN DRILLING PROGRAM SITE-806

A 2 m.y. oxygen isotope record of Globigerinoides sacculifer from the Ontong Java Plateau, based on cores from Ocean Drilling Program Leg 13 0, is dated by matching variations to an orbital template. The procedu re allows us to present the most complete Quaternary record available for the western equatorial Pacific. The template-generating algorithm describes a balance between growth and melting of ice. Following basic Milankovitch theory, ice growth is taken as constant, while melting i s taken to depend on summer insolation, current ice mass, and average past ice mass. Template settings must be changed once, between 1 and 1 .2 Ma, to reflect a major shift in climate. Template fits are striking ly good over much of the record and can be used to detect and fill gap s from core breaks and other disturbances. One result of template dati ng is an exact age for the Brunhes-Matuyama magnetic reversal boundary , at 790 +/- 5 ka, as well as several other precise dates (900 ka for the middle Pleistocene climate shift; 1070, 1240, and 1450 ka for isot ope stages 31, 37, and 47, respectively). Sedimentation rates fluctuat e between 18 and 28 m/m.y., a ca. 400 ka cycle being the most prominen t. Major anomalies arise within the transitional regime (1.2 to 1 Ma). The origin of the cycles is unknown; we propose productivity variatio ns in the western equatorial Pacific.