Review about sea level oscillations during the last hemi cycle and tectonic stability of coastal sectors

Abstract

This paper summarizes the major contributions to understanding the sea-level oscillations during the last climatic hemicycle. More than seventy fundamental publications are reviewed bearing on the dynamics of eustatic processes and on the tectonic and isostatic behaviour of coastal sectors. The critical analysis of methodologies and results yielded by different reserchers has allowed to propose a new correlation scheme for sea-level data in different parts of the world. The improvement in datation techniques and the theoretical modelling of both glacio-eustatic variations and isostatic rebounds of coastal sectors to deglaciation, have been pivotal in sea-level researches during the 70 and '80. During the last decade, the refinement of radiodating techniques has prompted the correlation of sea-level data from different parts of the world. The available data set has grown from coral reefs and morpho-depositional units such as marine terraces and transitional coastal deposits, to include oxygen-isotopic analysis of deep-sea muds, their relationships with changes of ice volumes, datation of submerged speleothems and marin biogenic overgrowths. Comparative analysis of data on relative sea-level changes in different coastal sectors has pointed out the need for evaluating the tectonic and isostatic behaviour of the investigated coastal sectors. Based on the results of our research and the review of existing literature, a new reference marker is proposed in order to allow data correlation from different coastal sectors on the ground of their tectonic and isostatic stability. Such marker is represented by the eustatic sea level related to the substage 5e. The "relative eustatic variation" during the late Pleistocene-Holocene is here defined as the sea-level change caused by water volume variation induced by climatic variation relative to the present-day sea level. Such change is deduced from geological-geomorphological indicators such as terraces and notches found in coastal areas which are proved to be stable since the "Eutyrrhenian". The rate of vertical uplift for these areas must be below 0.016 m/ka, equal to about 2 m in the last 125 ka. The difficulty in constructing previsionai eustatic models is finally discussed in the light of the complexity of the process itself and of the concurrence of anthropic activity. This problem can be only alleviated by the availability of a greater number of data from tectonicvally stable area.