Supercritical flood-flow sedimentation and its preservation potential in geologic records

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Supercritical flood-flow sedimentation and its preservation potential in geologic records were studied in the Permo-Carboniferous Talchir Formation of Orissa and Jharkhand, Cretaceous Athgarh Formation of Orissa and Miocene Itowo and Kunimi formations in southwestern Japan. Among them, the important results were obtained from the Talchir Formation in Orissa, the Athgarh Formation and Kunimi Formation.The Talchir Formation reveals sedimentation and basin evolution controlled by recession and final disappearance of the Gondwana glacier. In the initial stage of deglaciation, a collapse of a glacier and a failure of montane glacial lakes frequently occurred and gave rise to generation of a highly sediment- laden debris flow and a catastrophic flood, which brought abundant coarse clastics into the lake and built a steep-faced fan delta on the basin margin. The flood-flow deposits show middle-to large-scale, gently undulating, low-angle cross stratification of an antidune origin and demonstr … More ate sedimentation in the supercritical regime of high velocity sheet floods.The Athgarh Formation was deposited in an alluvial fan environment. Within the upper fan deposits, diffusely subhorizontally stratified pebbly sandstones are interpreted as sheet flood deposits. Diffuse stratification was possibly resulted from alternate dominance of a super- and undercritical flow conditions within a flood flow. The fan was dominated by stream flow processes and the sheet flood deposits were not preserved in the middle and lower fan areas.The alluvial fan deposits in the Kunimi Formation preserve the supercritical flood flow deposits especially in the lower fan succession. The flood flow deposits show gently undulating, low-angle cross stratification. Such stratification is most possibly the product of an antidune bedform under a supercritical flow condition. In the Kunimi fan, sheet floods were dominated compared with stream flow and debris flow processes and the supercritical flood-flow deposits had high preservation potential especially in the lower fan segment. Less