Present-day infralittoral prograding wedges (IPWs) in Central-Eastern Tyrrhenian Sea: Critical issues and challenges to their use as geomorphological indicators of sea level

A census of 83 Infralittoral Prograding Wedges (IPWs) was carried out in the Central-Eastern Tyrrhenian Sea, to learn more about their morpho-bathymetric variability and test their reliability as environmental indicators of current sea level. With this aim, a database recording for each wedge the main morphometric indices, the effective fetch and the significant height of the storm waves- here used as proxies for sea state forcing - and the ground elevation in the backshore - here used as a numerical descriptor of the coastal morphology- was realized (Campania Region IPWs Database). The statistical analysis of the whole IPWs dataset explored the relationship between the environmental and morphometric variables, leading to the identification of the main forcing factors controlling their depth. The Principal Component Analysis grouped the variables into two clusters, governed by sea state forcing and energy of relief in the backshore, respectively. Multi-regression analysis highlighted significant correlation of IPW depth with effective fetch and extreme significant wave height and moderate correlation with the ground elevation in the backshore. Outcomes of observational laws on present-day IPWs were then applied to relict IPWs, currently lying on the continental shelf and at the shelf margin, with the aim of establishing their original depth of formation. This procedure aims to solve the non-trivial issue on the reliability of paleo-IPWs as proxies for past sea levels. Thus, a simplified equation based only on the use of geographical variables is proposed here to roughly establish the original depth (with errors of few metres) of paleo-IPWs whose geographical exposure is known and the effective fetch computable. Although the applicability of this method suffers from spatial and temporal restrictions, due to the girth of the original dataset, it provides a first analytical procedure for gauging the original depth of formation of paleo-IPWs which, over the last decade, have been increasingly used as environmental indicators of past sea levels. This study highlights the relationship between the depth of these sedimentary coastal bodies and sea storm wave climate at a regional scale and provides clues for the use of their past counterparts as morphological proxies of past sea level stands. Further developments of this study could using a wider dataset to extend the observational law on present-day IPWs to a Mediterranean scale and strengthen the applicability of the method to a spatially broader set of paleo-IPWs.