The Yubunegawa Black Shale Member of the Muraoka Formation in the Miocene Hokutan basin was deposited during a highstand of the sea level and records storm sedimentation in a middle to outer shelf environment. In the lowermost part of the Yubunegawa shelf sequence which rests on the transgressive deposits, intercalations of a couplet of a thick sandstone bed and an overlying thick mudstone bed produce cyclic appearance of the succession which is principally made up by the monotonous interbedding of thin sandstones and mudstones. Such a couplet intervening the monotonous succession suggests that an extraordinary intense storm carried considerable volume of sand away from the coast and resulted in a sand-starved condition in the coastal zone for some long period, during which sand availability on the stormy shelf was extremely low. The control of sand availability on storm sedimentation was a cosequence of rise in base level due to a rapid transgression, which probably caused reduction of the rate of sediment supply through alluvial system into the coastal zone.

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The lower part of the Tatsukushi Formation in the Miocene Misaki Group, southwestern Shikoku, represents storm-modified shallow marine sand-bar deposits. Within the lower part of the Tatsukushi Formation, two principal components are distinguished; interbedded sandstones and mudstones, and thick-bedded sandstones. Sandstone beds of interbedded sandstones and mudstones are mainly hummocky cross-stratified. These sandstones are interpreted as the deposits on the margin of sand bars, and represent intermittent as the sand supply on the mud floor chirefly during storms. Thick-bedded sandstones are mainly composed of thick, amalgamated hummocky cross-stratified sand-stones. These sandstones are interpreted as the deposits of main body of sand bars which were intensely affected by storms. The transition from interbedded sandstones and mud-stones to thick-bedded sandstones are either gradually or abrupt. The gradual transition implies outgrowth of a sand bar. The abrupt transition is marked by a remarkable erosion surface at the base of the thick-bedded sandstone unit, and is suggestive of deep erosion caused by intense outflow from river mouths. In the formation of the Tatsukushi sand bars, sand transport and deposition were basically controled by fluvial discharge from the river mouth. Storm waves reworked bar sands to mold hummocky cross-stratified sandstones. Consequently, records of fluvial-influenced sedimentation were mostly unpreserved in rock records.

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Program for grain-size analysis is developed by FutureBASIC II-J using personal computer (Macintosh series). The program calculates average, median-size, sorting, skewness and kurtosis by moment and graphic methods, and draws histogram, cumulative frequency curve, probably cumulative curve and overlapped graphs. The grain-size data can be inputted into program from keyboard, spread sheet software and table data file of Kanto Kagaku Service Corporation.
The program is approved by published data. Calculated results by the program are sufficiently confided.

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