Magnetostratigraphy of DSDP Leg 94 sediments

The primary objective of DSDP Leg 94 was to obtain continuous paleoclimatic records along a roughly north-south transect in the North Atlantic. The magnetostratigraphy of 21 holes at 6 sites cored with the hydraulic piston corer and extended-core-barrel corer is presented here and establishes an independent chronology for these sediments. Nearly complete records were obtained for the last 2.5 m.y.; in addition, deeper drilling at three sites to satisfy tectonic and paleoceanographic objectives produced older sections suitable for magnetostratigraphic study, allowing first-order correlations of the polarity sequences with calcareous and siliceous micro fossil events. The sections with high sediment accumulation rates yielded very detailed records of polarity history and allowed three short normal-polarity zones within the Matuyama Chronozone to be detected, in addition to the Jaramillo and Olduvai subchronozones. A short reversed-polarity zone also occurs, within the upper intervals of the Gauss Chronozone. These short zones are present in multiple holes, ruling out the possibility that they might be of local origin. Correlation of these short zones with radiometrically dated polarity zones in igneous rocks strongly supports the interpretation of these polarity zones as records of true geomagnetic polarity chrons.

Upper Eocene to Oligocene strontium, carbon and oxygen isotope record of DSDP holes

We improved upper Eocene to Oligocene deep-sea chronostratigraphic control by integrating isotope (87Sr/86Sr, delta18O, delta13C) stratigraphy and magnetostratigraphy. Most previous attempts to establish the timing of isotope fluctuations have relied upon biostratigraphic age estimates which have uncertainties of 0.5 to over 4.0 m.y. Deep Sea Drilling Project (DSDP) Site 522 contains the best available upper Eocene to Oligocene magnetostratigraphic record which allows first-order correlations of isotope records (87Sr/86Sr, delta18O, delta13C) to the Geomagnetic Polarity Time Scale (GPTS). Empirical calibrations between the 87Sr/86Sr of foraminifera and magnetochronology at Site 522 allow more precise correlation of ,unknown' samples with the GPTS. For example, shallow water and high-latitude sections may be tied into the deep-sea record. Sr-isotope stratigraphic resolution for the latest Eocene to Oligocene is approximately 2 m.y.

Paleogene calcareous nannofossil stratigraphy of ODP Leg 120 sites

Calcareous nannofossils are abundant in the Paleogene sediments recovered during Ocean Drilling Program Leg 120. Although no continuous Paleogene section was obtained, Sites 747 through 751 complemented each other so as to provide a virtually complete composite stratigraphic section. The calcareous nannofossil biostratigraphy at Sites 747, 748, and 749 is discussed. Correlation of calcareous nannofossil biozones and magnetozones at these sites suggests some diachrony with low-latitude areas, as well as on a regional basis. Changes in calcareous nannofossil diversity throughout the Paleogene are analyzed and interpreted as reflecting major paleoclimatic events.