Submarine depositional terraces in the Tyrrhenian Sea as a proxy for paleo-sea level reconstruction: Problems and perspective

In the last decade great effort was put in the study of relative sea-level changes on Mediterranean coastlines through the integration of geophysical modelling and proxy data of paleo-shorelines. In this paper, we show potential and limitations of using additional marine geomorphic/sedimentary markers for earlier and lower sea levels. These markers are submarine depositional terraces (SDTs), i.e., deposits formed by a set of small prograding sedimentary wedges, having a terraced shape and found at variable shallow-water depths (mainly the first -150 m) on continental and insular shelves in the Tyrrhenian Sea. The shallowest terraces (near-shore) have their edges at depths between -10 m and -30 m, approximating the modern, local storm-wave base level. Their formation is thought to be associated with the modern sea-level highstand and thus, can be used as the modern analogue for deeper terraces formed in the past when the sea level was on the middle and outer shelf. Mid-shelf terraces have their edges at variable depths between -40 m and -90 m and probably formed during the last sea-level rise. They show a patchy spatial distribution and a large variability in their internal structure, so that they are not suitable for correlation on a regional scale. Shelf-edge terraces have their edges at depths between -120 m and -170 m, which is close or deeper than the Last Glacial Maximum (LGM) sea-level stand. They show a remarkable lateral continuity and a prograding internal structure similar to those at shallower depth and, thus, represent a proxy for the sea-level position at around 20 ka. However, the position of SDTs' edges is not a direct measure of paleo sea level positions because their depth depends on a complex interplay of several factors, such as the base of the storm wave and its variation in response to coastal physiography, as well as the occurrence of subsequent erosional or depositional processes. Depending on the geophysical and mapping methods used to determine their depth, the associated error range can also differ. Based on the analysis of these complexities and a wide range of physiographic settings of the Tyrrhenian Sea, we discuss these error ranges in order to assess potential and limitation of the SDT for analyses of vertical mobility of an area