抄録
“Inverse grading” structure characterized by upward-coasening sequence is known to be well developed in flood deposits of meandering sand-bed rivers in Japan. This structure consists of two layers, the lower mud and upper sand, formed during a single flood. The depositional process was already elucidated.
The flood deposits on floodplain are composed of the alternation of sand and mud with many “inverse grading” structures. They are commonly recognized in following three subenvironments, slipoff slope, natural levee and backswamp. The deposits of each subenvironment contains many intercalated sand layers with characteristic sedimentary structures.
Many “inverse grading” structures are found out from the Late Pleistocene fluvial deposits in the Tsukuba Upland, Ibaraki Prefecture. We can easily dicide the subenvironments of flood deposits from the strata by means of the “inverse grading” structure.
The “inverse grading” structure is a distinctive indicator of flood deposits in meandering system.
