Sedimentary successions formed by fifth-order glacio-eustatic cycles in the middle to upper Quaternary formations of the Oga Peninsula, northeast Japan

The northern coast of the Oga Peninsula is a type locality for Quaternary s edimentary exposures on the Sea of Japan side of northeast Japan. Middle to late Pleistocene shallow marine to nonmarine sediments are continuously ex posed on sea cliffs along the Anden Coast. These sediments have been mapped and classified into nine sedimentary facies, based on grain size, sediment ary structures, intensity of bioturbation, and associated fossils. The depo sitional environments and paleo-water depths of each facies have been estim ated, based on comparison with the present sub-bottom sedimentary features observed in coastal systems around the Oga Peninsula. On the basis of sedim entary facies analysis, variations in the depositional depth through time h ave been reconstructed and correlated with the SPECIMAP delta(18)O curve, u sing four marker tephras as time controls. The two curves generally agree b etween approximately 80 and 450 ka, suggesting that the sedimentary cycles at the Anden Coast faithfully record 5th- and 6th-order glacio-eustatic spa level changes. Peak-to-peak comparison between the reconstructed depositio nal depth curve and the delta(18)O curve reveals that (1) unconformities ar e formed during the late eustatic sea-level falls and/or the following lows tands, (2) transgressive lag deposits are mainly formed below wave base, (3 ) deepening-upward successions, which sometimes occur below the ravinement surfaces, are formed in the inner part of estuary or barrier-island environ ments where wave action was minor, (4) shoaling-upward successions formed d uring eustatic sea level falls are deposited under the influence of intense wave action in a strand plain-coastal plain system, and (5) the characteri stic combination of thinner deepening-upward successions and thicker shoali ng-upward successions reflects the asymmetric pattern of glacio-eustatic se a level changes and/or lower sediment supply during transgression.