Micropalaeontological and palaeomagnetic approaches to stratigraphic anomalies in rift basins: ODP Site 1109, Woodlark Basin

Abstract

AbstractThe stratigraphic succession of the western Woodlark Basin is examined in detail relative to ODP Site 1109, where c. 55 m of Pliocene sediment lies anomalously shallow owing to slumping between c. 1.10 and 0.65 Ma in the tectonically active rift basin. Palaeomagnetic reversals and varying percentages of the characteristic microfossils, Globigerinoides fistulosus and discoasters, within the deformed sediment defining the slump indicate that the Pliocene sediment was periodically introduced by a number of slumps rather than being emplaced by a single slump event. Palaeomagnetic and biostratigraphic events in the remainder of the hemipelagic section of Site 1109 to c. 4 Ma appear undisturbed and consistent with those at adjoining sites. Globorotalia truncatulinoides first appeared between 2.65 and 2.71 Ma at these low-latitude sites, which extends the previously reported area of evolution of the species in the southwestern Pacific toward the Equator. Seven of the nine coiling changes in Pulleniatina through time are recognized and dated using sedimentation rates. Along with palaeomagnetic events and microfossil species datum levels, these coiling changes can be used to correlate between sites in the area.