Abstract

Tidal conditions in ancient shallow-marine basins, as revealed by preserved sedimentary deposits, reflect the strong influence of the paleobathymetry. Use of a tidal-circulation model can test existing paleobathymetric reconstructions. Meso- and macrotidal conditions are believed to have existed throughout most of the Miocene Molasse (France and Switzerland) seaway. Tidal simulations using external tidal ranges of 2 and 4 m entering from the south (Mediterranean) fail to generate mesotidal conditions in the majority of the seaway, because of a narrow constriction in the present Alpes du Dauphiné and Drôme areas. Meso-tidal conditions are simulated in the Rhône-Alp part of the seaway only after the postulated paleobathymetry is widened in the Alpes du Dauphiné area; this change allows tidal penetration from the Mediterranean. Despite this widening, the new simulations fail to generate mesotidal conditions in the Swiss part of the seaway. Mesotidal conditions are simulated in Switzerland with the addition of a second tidal input from eastern Switzerland, favoring an interpretation that the Swiss part of the seaway was connected with either the eastern Mediterranean or the Indo-Pacific Ocean. The revised paleobathymetry brackets uplift events that affected the basin margin.

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