Paleolatitudes and magnetostratigraphy for Cenozoic sediments, ODP Leg 182: The Great Australian Bight

Abstract

Cenozoic northward drift of the Australian plate was determined from paleomagnetism of Middle Eocene through Pleistocene sediment cores from ODP Leg 182 (Sites 1126, 1128, and 1134) in the Great Australian Bight. Paleolatitude estimates are based on stepwise AF and thermal demagnetization of ∼400 discrete samples, of which ∼250 provided reliable data. The characteristic magnetization of the sediments resides in magnetite and magnetic sulfides. Middle Eocene through Lower Oligocene (∼36 Ma) paleolatitudes of ∼52° (±2°) change gradually to Late Miocene (∼9 Ma) paleolatitudes of ∼48° (±2°). These data, combined with Australian paleomagnetic pole data, indicate a slow rate of northward motion through much of the Cenozoic (∼28 mm/yr). These data also indicate an abrupt acceleration in the Late Miocene (drift rate ∼115 mm/yr), coinciding with tectonic events in Southeast Asia. Paleolatitude estimates support Miocene versions of the Australian apparent polar wander path that place the Oligocene-Miocene pole (∼25 Ma) at ∼70°S–125°E and the Late Miocene pole at ∼70°S–105°E (e.g., Idnurm, 1985, 1994). Inclination data for discrete samples also provide a refined magnetostratigraphy for portions of the Miocene, Oligocene, and Eocene carbonate and siliciclastic section of the Great Australian Bight.