2019 Volume 125 Issue 1 Pages 55-72
New formation mechanisms of post-LGM incised-valley fill have been inferred on the basis of the sequence stratigraphy and paleogeography of strata beneath the Tokyo and Nakagawa lowlands. The new findings are as follows: (1) Channel sands consisting of meandering river sediments show anastomosed geometry and vertical accretion during rapid sea-level rise, whereas during slow sea-level rise they show sheet-like geometry and lateral accretion; (2) some transgressive estuary systems should be classified as river-dominated estuaries, and these systems comprise fining-upward sand lobes in the subtidal zone of the bayhead portion; and (3) a tide-dominated bay such as a drowned valley can be naturally filled by lateral accreting mud discharged from outside of the bay, and such bays show a fining-upward lithological succession. The first finding, in particular, implies that the change in the rate of sea-level rise is an important control on the formation of fluvial strata in coastal lowlands, as it is also on the formation of shallow-marine strata.
