SEQUENCE STRATIGRAPHY OF THE UPPER PART OF THE PLIOPLEISTOCENE KAKEGAWA GROUP, WESTERN SHIZUOKA, JAPAN

The Kakegawa Group is exposed in Shizuoka, central Japan, It is the fi ll of a Plio-Pleistocene fore-are basin and constitutes a third-order sequence (2.6-1.0 m.y.), The upper Kakegawa Group consists of a transg ressive systems tract (TST) and a highstand systems tract (HST), The T ST comprises parasequence sets that are retrogradational on the shelf and progradational on the slope, The shelf parasequences consist of up ward-coarsening facies of tempestites, bounded by ravinement surfaces, The shelf parasequences can be traced downslope, where they comprise upward-thinning turbidite successions (fourth- or fifth-order transgre ssion) containing backstepping sand-dominated intervals, and silt-domi nated, upward-thickening successions (regression), The HST consists of progradational parasequence sets, The shelf parasequences are similar to those of the TST except for greater basinward distribution of shel f sand, Outer-shelf to upper-slope parasequences incorporate silt-domi nated, upward-thinning successions (transgression) and overlying upwar d-thickening turbidite successions (regression) including sand-dominat ed intervals at their tops, The upward-thinning successions are much t hinner than those in the TST, A condensed interval dividing these syst ems tracts consists of bioturbated silt and might include the maximum flooding surface. In the TST parasequences, slope sand packets are thi cker, are present on the lower slope, and were formed during fourth- o r fifth-order transgression, In contrast, the HST slope turbidite sand s are thinner, are present on the outer shelf to upper slope, and were deposited during fourth- or fifth-order regression, During transgress ion, the large volumes of sediment derived from intense shoreface eros ion bypassed the narrow shelf (ca, 10 km wide), and contributed to cha nneling on the upper slope and accumulation of larger packets on the l ower slope, In the HST, deposition of slope turbidites was induced by progradation of shelf sand during regression, Smaller rate supply of s andy sediment to the slope resulted in deposition of smaller packets, The sand might have been deposited at the outer edge of a wider shelf (15-20 km) of the HST.