| Research Abstract |
Lithofacies characteristics of bottom-current-influenced sandy deposits (sandy contourites) were studies based on detailed outcrop analyzes of late Cenozoic deep-sea successions in the Boso Peninsula and those from some other late Cenozoic sedimentary basins, such as the Kakegawa, Miyazaki, and Kumano Basins. Sandy contourites are characterized by traction structures, such as parallel lamination and ripple cross-lamination, together with minor inverse grading and wave ripple-lamination. In particular, ripple cross-lamination is commonly associated with mud drapes and flaser and lenticular bedding. These sedimentary structures, in general, do not show any regular vertical sequences, such as the Bouma sequence in turbidites.
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. Framework composition of sandy contourites, in contracts, is largely equivalent to that of associated turbidites. Paleocurrents of sandy contourites are variable in time and space and spatial and temporal variations intypes of turbidite-to-contourites continuums suggests varying intensity of deep-sea bottom currents in the late Cenozoic sedimentary basins.
Variations in speed and direction of deep-water currents under the modern Kuroshio Current and its associated deep-sea environments have been documented off the Japanese Islands. Thus, analogous processes appear to have been responsible for the deposition of sandy contourites in the late Cenozoic sedimentary basins in Southwest Japan.
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