Transgression-Regression and Eustasy

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  • 海進・海退と海面変化
  • カイシン カイ タイ ト カイメン ヘンカ

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The relationship of transgression-regression with eustasy is examined in this paper on examples of the stable areas in the Cretaceous period. The factual data can be summarized in a diagram (Fig. 1). The scale of major transgression seems to have been enlarged from the Neocomian, through the Aptian-Albian, to the Late Cretaceous ones and the post-Cretaceous (i.e. Palaeocene) regression was of a global scale.<BR>Minor cycles of transgression-regression were not necessarily synchronous between separated areas. Some of them were, however, synchronous or nearly so especially between the areas facing the same oceanic basin.<BR>Eustasy alone was not the cause of the phenomena of transgressions and regressions. Certain kinds of tectonic movements which affected even the stable areas were also responsible for the phenomena. The combined effects of both causes may have been remarkable in the Cretaceous examples.<BR>It is tentatively suggested that the sea-level gradually uprised during the Cretaceous period by the combined effects of active upheaval of oceanic rises, volcanic effusion, appearance and development of orogenic mountains from geosynclinal belts, increasing sedimentary deposition due to intense erosion of uprising mountains, etc. In short, global activity may have been responsible for the Cretaceous major transgressions. The pause of this activity, followed by isostatic adjustment in certain parts of continents and that of oceanic areas may have been the cause for the Palaeocene global regression.

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