Paleomagnetic records from carbonate legs in the Southern Oceans and attendant drilling and coring related effects

Ocean Drilling Program (ODP) Leg 182, to the Great Australian Bight (GAB), Leg 189 around Tasmania, and Leg 194 off the Great Barrier Reef on the Marion Plateau, all sampled thick carbonate sections that tested the coring techniques and the magnetics instrumentation on the JOIDES Resolution. Coring overprints were demonstrated due to: (1) sediment deformation during initial penetration of the advanced piston corer, (2) disturbance by core “suck in” during recovery, (3) the magnetic fields of the bottom hole assembly, (4) magnetic contamination of core liners, and (5) core splitting and storage. All of these effects can cause problems in determining the magnetostratigraphy of carbonates.The principal highlights of the magnetostratigraphy of these three ODP legs were as follows. (1) The discovery during Leg 182 of an extended Brunhes section of carbonates in the GAB that was hundreds of meters thick. (2) Documentation in Hole 1172 of Leg 189 of the timing of the Eocene–Oligocene transition from the “Greenhouse” to “Icehouse” state and the rapid deepening of the Tasmanian Gateway. (3) Recovery of a complete magnetostratigraphy from Plio-Pleistocene carbonates with a sedimentation rate of some 20 m/Ma and the discovery of a small hiatus including the top of the Matuyama (C1r) and the Jaramillo (C1r.1n). (4) The documentation of a chronology from Sites 1193, 1194, and 1195 of Leg 194 gave ages for the critical sequence boundary at each site consistent with biostratigraphy that was used to evaluate the late middle Miocene eustatic sea level fall.