Calcareous plankton biostratigraphy (foraminifers and nannoplankton) and magnetostratigraphy of the upper Oligocene to Pleistocene have been studied in hydraulic piston Cores 516-1 to 516-44, 516A-5 to 516A-11, and 516F-1 to 516F-11, Rio Grande Rise (water depth 1313 m). Some 80 biostratigraphic datum events have been correlated to the magnetic polarity stratigraphy over an interval representing the Matuyama to

Measurements of the detrital remanent magnetization (DRM) of redeposited deep-sea sediment of the silty clay grade are described. Variations in the magnitude of an observed remanence inclination error are related to conditions of sediment accumulation, contrasted here as grain-by-grain settling from a dilute dispersion or by settling from a concentrated slurry. For these artificial redepositions post-depositional compaction is shown to be a major factor in shallowing the observed inclination from the ambient field inclination. The term compactive DRM is tentatively assigned to describe such behaviour. Present address: The British Petroleum Company Limited, Britannic House, Moor Lane, London ECZY 9BU.

The late Neogene succession continuously cored at Hole 397 has been investigated in detail from Cores 69 to 19 to calibrate datum planes based on calcareous nannofossils and planktonic foraminifers with the sequence of magnetic reversals detected in the cores. Nine datum planes based on calcareous nannofossils, 7 based on planktonic foraminifers, and 15 magnetic reversals were detected from Section 57-3 to Core 19. The interval spans 5 m.y., and encompasses paleomagnetic Epoch 7 (partim) to the Matuyama Epoch (partim). Correlations are presented for the Bou Regreg section of northwestern Morocco; the Melilla section of northern Morocco; Rio Mazzapiedi section of northern Italy (Tortonian stratotype); Cape Rossello, Sicily (Zanclean stratotype); and DSDP Site 132 (Tyrrhenian Basin). The Tortonian/Messinian, Messinian/Zanclean, and Zanclean/ Piacenzian boundaries are biostratigraphically recognized and located with accuracy. Taxa ^^\T otal Abundance Amaurolithus amplificus Amaurolithus delicatus Amaurolithus primus Amaurolithus tricorniculatus Ceratolithus acutus Ceratolithus rugosus Ceratolithus telesmus Cyclococcolithus leptoporus Cyclococcolithus macintyrei Discoaster asymmetricus Discoaster bellus Discoaster berggrenii Discoaster bollii Discoaster brouweri Discoaster calcaris Discoaster challengeri Discoaster decorus Discoaster hamatus Discoaster icarus Discoaster intercalaris Discoaster loeblichii Discoaster neohamatus Discoaster neorectus Discoaster pentaradiatus Discoaster pseudovariabilis Discoaster quinqueramus Discoaster surculus Discoaster tamalis Discoaster variabilis s.i.

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