Kuroshio Current-influenced sandy contourites from the Plio–Pleistocene Kazusa forearc basin, Boso Peninsula, Japan
Published:January 01, 2002
Makoto Ito, 2002. "Kuroshio Current-influenced sandy contourites from the Plio–Pleistocene Kazusa forearc basin, Boso Peninsula, Japan", Deep-Water Contourite Systems: Modern Drifts and Ancient Series, Seismic and Sedimentary Characteristics, D. A. V. Stow, C. J. Pudsey, J. A. Howe, J.-C. Faugères, A. R. Viana
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Lithofacies features of bottom current influenced deep-sea sandy deposits (sandy contourites) have been studied by detailed outcrop analyses of the Plio–Pleistocene infill of the Kazusa forearc basin on Boso Peninsula, Japan. Sandy contourites are characterized by traction structures, such as parallel lamination and ripple cross-lamination, together with minor inverse grading and wave ripple-lamination. Ripple cross-lamination is commonly associated with mud drapes and flaser and lenticular bedding. These sedimentary structures do not display any regular vertical sequences. Sandy contourites are commonly associated with turbidites and comprise turbidite-to-contourite continuums. In general, sandy contourites are better sorted than associated turbidites and have sharp or gradational basal contacts with underlying turbidites or hemipelagites, and sharp upper contacts with overlying hemipelagites. The framework composition of sandy contourites, in contrast, is largely equivalent to that of the associated turbidites. Palaeocurrent directions of sandy contourites are variable in time and space and alongslope-and upslope-directed palaeocurrents are dominant. Turbidite-to-contourite continuums show spatial and temporal variation in bed thickness and lithofacies features. These variations suggest varying intensity of deep-sea bottom currents in the Kazusa forearc basin. Analogous flow conditions have been documented from the modern, deep-water mass of the Kuroshio Current. Thus, the observed variations in lithofacies features and palaeocurrents of turbidite-to-contourite continuums can best be interpreted in terms of fluctuating strength of the deep-water palaeo-Kuroshio bottom current during the Pliocene through Pleistocene
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Deep-Water Contourite Systems: Modern Drifts and Ancient Series, Seismic and Sedimentary Characteristics
Countourites are a widespread but poorly known group of sediments linked to the action of powerful bottom currents in deep water. Although we know they are especially common along continental margins and through oceanic gateways, they have been surrounded by contoversy since they were first recognized in the early 1960s. Where correctly recognized and decoded they can provide one of the keys to our better understanding of bottom water circulation and of the ocean–climate link. They are part of the spectrum of deposits that confronts the oil industry as exploration moves into progressively greater water depths.
This memoir is an important outcome of the International Geological Correlation Project 432 on Bottom Currents, Contourites and Palaeocirculation. It includes 30 papers involving over 75 key scientists from around the world. Following an introductory state–of–the–art paper by the editors, there are 25 separate case studies on modern drifts and four on ancient contourite series. Each contribution highlights the specific geological and oceanographic setting, bathymetry, physiographic and stratigraphic context, seismic attributes and sedimentary characteristics of that drift. Case studies range from some of the well-documented North Atlantic drifts to those much less known from the Mediterrenean, from important syntheses of the Gulf of Cadiz and Vema Channel Gateway, to completely new data on South Atlantic, Pacific and Antartic margin systems. The four papers on ancient series from Japan, China and Cyprus serve to emphasise the complex nature and subtle characteristics of contourites, which make their identification a scientific challenge.
This volume is dedicated to the memory of Charlie Hollister (1936–1999), one of the founding fathers and pioneers of countourite research.