New, early tertiary, ages for basal pelagites, Northeast Santa Isabel, Solomon Islands (Central southwest flank, Ontong Java Plateau)

Abstract

Basal pelagites deposited within the sequence of basal basic pillowed lavas are found in river sections on northeastern Santa lsabel. These deep-water carbonates are tough and lightly metamorphosed, and have to be studied in thin-section. Thin section determination of the planktic foraminifera indicate the presence of pelagites ranging in age from Late Paleocene through to Early Oligocene; younger tuffaceous sediments lie above. The lavas, pelagites and other sediments can be correlated with Malaitan sequences to the east and south-east and support the notion that northeastern lsabel is also a part of the central south-west flank of the Ontong Java Plateau. The ages of the pelagites are especially significant to the basal ages obtained in DSDP Sites 288 and 289: it appears that the plateau was created by spreading and that it is more youthful from north to south, that is, it youngs to the south.