Temporal and Spatial Variations of Accommodation and Sediment Accumulation during Transgressive to Highstand Stages as Reconstructed from a Latest Pleistocene to Holocene Sequence in the Intra-Arc Osaka Basin, Japan ()
ABSTRACT
Temporal and spatial
variations in accommodation (i.e., paleo-water depth) and sediment
accumulation (amount of deposition) in the intra-arc Osaka Basin, Japan, were
reconstructed from the post-glacial transgression through the sea-level
highstand, a total of 9000 years. At the beginning of the marine transgressive
stage (about 11,000 cal y BP), paleo-water depths were shallow and the sediment
accumulation was large. The area occupied by Osaka Bay gradually extended and
sediment deposition decreased from 11,000 to 6000 cal y BP. During the period
of maximum transgression (6000 - 5000 cal y BP), an inner bay, Kawachi Bay with
a water depth of 5 - 10 m, was expanded in the inland eastern Osaka area, and
paleo-water depths reached a maximum and depositional rates reached a minimum.
During the subsequent highstand and small regression (about 5000 cal y BP to
the present), however, deposition increased rapidly as a result of river delta
and shoreline progradations. Regional differences were observed in
accommodation and accumulation between the outer bay area and the inner bay
area. During both the transgressive and regressive stages, deposition decreased
in the inner bay area. In contrast, in the outer bay area and in the basin
overall, deposition was high during the first part of the transgressive stage
but it decreased during the maximum transgression, before reaching a maximum
during the subsequent highstand and regression. During the regressive stage,
fluvial delta progradation led to the formation of a thick sequence of delta
body sediments. Sediment accumulation was 30% - 40% higher during the
regressive stage than that during the transgressive stage.