PLEISTOCENE AND HOLOCENE SEA LEVEL CHANGES

The classic glacio-eustatic theory, as it was conceived by Depéret and his supporters, is briefly presented, and the objections against it are discussed. Bourcart's continental flexure is mentioned. More recent considerations concerning uplifts interfering with variations in sea level, and resulting possibly from erosional discharge, were developed by Gigout and by Battistini. But these new theories do not imply that the glacio-eustatism is out of date: its principle remains valid. Recent methods allow more accuracy in dating former sea levels: the 14C method, and the 230Th/234U method. Two interglacial high sea levels are especially note-worthy: they resulted in the Holsteinian and Eemian shorelines which now stand above present-time sea level in areas where no subsidence occurred. The Eemian (Normannian, Ouljian, etc.) shoreline has left widespread remnants throughout the world, particularly in western Europe and around the Mediterranean, but also in many oceanic islands. The writer criticizes the British conception, which relates the raised beaches belonging to this series to the last Interglacial but one, not to the last one as commonly accepted. The low Quaternary marine sea levels are then discussed. During one of the glaciations at least, the sea level was certainly depressed down to 100 m, probably to 150 m, and perhaps to 200 m or even more. Evidences for this large regression are produced. Drowned valleys and submerged strandlines are still recognizable. Recent techniques allow better investigations of these features. It may be that the sea level rose temporarily to its present position during an interstade of the Würm Glaciation: but objections against this view are serious. The rise of the sea level after the end of the Würm Glaciation can be followed in detail in some areas, such as The Netherlands and the Gulf and Atlantic coasts of the United States. Much discussion, however, persists about the problem of the maximum level reached by this transgression: some authors think that the sea surpassed by 1-3 m the present datum during the past few thousands of years, whereas others do not accept the evidence presented in this respect. © 1969.