潮汐環境の堆積物 : 日本の干潟の理解に向けて(<特集>干潟の自然,その過去と現在)

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This paper reviews depositional processes in tide-influenced coasts, toward comprehension of tidal-flats in Japan. The tidal-flats of Japan occur restrictedly in embayments sheltered from strong ocean waves. These embayments resemble to the estuary, with respect to common properties that tidal processes dominate rather than decreased ocean waves and that their waters have river-inflow producing brackish-water. Tidal processes have considerable influence upon tidal-flats and estuaries (tide-dominated estuary). Tidal current and fluctuation of a water level promote a mixing sea and river waters and a bidirectional sediment-supply from fluvial and sea in estuarine environments. The mixing of sea and river waters also involves mud deposition with flocculation and settling-scar lag effects. These peculiar processes of mud-deposition are important factor of the depositional architecture in tidal-flats and estuaries. Rhythmic occurrence of tidal currents controls strongly the depositional process in tidal environments. As the result, the tidal rhythms are recorded in ancient strata as the alternation of sand and mud layers. These sand and mud layers deposit during current and slack water stages respectively. Furthermore, flood-ebb and neap-spring cycles are reconstructed from ancient strata, based on spectrum analysis of thickness variations of sand layers in the alternation.
日本古生物学会の論文
2004-09-22