List of Contributors. Preface. Technical note and abbreviations. 1. Introduction p P.R. Bown, J.R. Young. 2. Techniques P.R. Bown, J.R. Young. 3. Triassic P.R. Bown. 4. Jurassic P.R. Bown, M.K.E. Cooper. 5. Lower Cretaceous P.R. Bown, D.C. Rutledge, J.A. Crux, L.T. Gallagher. 6. Upper Cretaceous J.A. Burnett. 7. Palaeogene O. Varol. 8. Neogene J.R. Young. 9. Quaternary N. Hine, P.P.E. Weaver. References. Taxonomic Index. Subject Index.

Calcareous Nannofossil Biostratigraphy

Summary We present a revised Neogene geochronology based upon a best fit to selected high temperature radiometric dates on a number of identified magnetic polarity chrons (within the late Cretaceous, Paleogene, and Neogene) which minimizes apparent accelerations in sea-floor spreading. An assessment of first order correlations of calcareous plankton biostratigraphic datum events to magnetic polarity stratigraphy yields the following estimated magnetobiochronology of major chronostratigraphic boundaries: Oligocene/Miocene (Chron C6CN): 23.7 Ma; Miocene/Pliocene (slightly younger than Gilbert/Chron 5 boundary): 5.3 Ma; Pliocene/Pleistocene (slightly younger than Olduvai Subchron): 1.6 Ma. Changes to the marine time-scale are relatively minor in terms of recent and current usage except in the interval of the middle Miocene where new DSDP data reveal that previous correlations of magnetic anomalies 5 and 5A to magnetic polarity Chrons 9 and 11, respectively, are incorrect. Our revized magnetobiostratigraphic correlations result in a 1.5-2 m.y. shift towards younger magnetobiochronologic age estimate in the middle Miocene. Radiometric dates correlated to bio- and magnetostratigraphy in continental section generally support the revized marine magnetobiochronology presented here. Major changes, however, are made in marine-non-marine correlations in the Miocene in Eurasia which indicate African-Eurasian migrations through the Persian Gulf as early as 20 Ma. The 12.5 Ma estimate of the Hipparion datum is supported by recent taxonomic revisions of the hipparions and magnetobiostratigraphic correlations which show that primitive hipparions first arrived in Eurasia and North Africa at c. 12.5 Ma and a second wave in the tropics (i.e. Indian and central Africa) at c. 10 Ma.

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The Neogene: Part 2: Neogene geochronology and chronostratigraphy

The sediments of the eastern Atlantic contain excellent historical records of the patterns of oceanic and atmospheric circulation in the subtropics. This is particularly the case at the low relief northwest African continental margin which favors unrestrained interaction of the land- sea climatic system and which forms a schematic, vertical cross section through the ocean from the equator to Mediterranean latitudes. Our synthesis of the Neogene and Quaternary evolution of paleoenvironments along this margin tries to show that oceans and land respond in a complementary way to global climatic events and mechanisms.

Atmospheric and Oceanic Circulation Patterns off Northwest Africa During the Past 25 Million Years

Quantitative biochronology of Pliocene and early Pleistocene calcareous nannofossils from the Atlantic, Indian and Pacific oceans

The magnetostratigraphic age of the oldest loess sediments in the central Chinese loess plateau investigated so far has recently been placed at ca. 2.4 million years B.P. Thus, glaciations in Central Asia, which are believed to provide the detritus for the formation of Chinese loess, commenced at the same time as the first ice-rafted debris sank into the ocean basins of the northern hemisphere [Shackleton et al., 1984], Lithologic, palaeontologic, geochemical and especially rock-magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition. The variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen-isotope record [Shackleton and Opdyke, 1976] and establish for the first time a continuous record of the Pleistocene glacial and interglacial stages in a continental section. Spectral analysis of the rock-magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils. Variable aeolic sediment influx as well as erosion and/or polygenetic soil formation may also strongly influence the sedimentary history.

Y. Takayanagi

Papers

Towards a quaternary time scale