Quaternary stratigraphy of distal tephra layers in the Mediterranean—an overview

This paper reviews the results of fifty years of tephra studies in the Mediterranean basin. The tephrostratigraphy of the Eastern Mediterranean is defined well and has been developed in conjunction with detailed biostratigraphy. Currently about thirty marker tephra have been identified and characterised, some being widespread over large sectors of the basin. Sedimentation in both Tyrrhenian and Aegean Seas is influenced by the proximity of the source volcanoes and hence primary tephras frequently exhibit evidence for reworking and post-depositional phenomena. In contrast to the long marine tephrostratigraphy there are still only a few studies reporting continental tephra deposits; these mainly concern lacustrine sequences and archaeological excavations. Recent investigations have employed electron probe microanalysis of discrete glass shards. These have illustrated the considerable geochemical variability of the principal tephra markers including those related to large-volume explosive events. In some instances this variability can be shown to mirror the heterogeneous composition of related pyroclastic formations in the proximal areas. Integration of a wide range of these findings, has enabled the construction and update of distribution maps for the main markers. This will permit revised estimations of the volume of the erupted material enabling consideration of the ecological and climatic impacts of the related explosive events. However, in spite of the increased chronostratigraphical information available for many of the source areas, some significant tephra layers remain uncorrelated. This uncertainty should stimulate further investigation to enable evaluation of the volcanic hazard in these densely populated regions.