Paleocoastline modelling – What a difference a few meters of sediment make?

Paleoreconstructions of coastal and near-coastal areas have always served as a tool towards better understanding of past, present and future geological and geomorphological processes. The reliability of paleocoastline and sea-land extent modelling is controlled by input data. Here the difference between paleoreconstructions based on present-day bathymetry and a paleotopographic elevation model are examined on the example of the Gulf of Trieste (northern Adriatic sea) - a low-gradient submerged Last Glacial Maximum alluvial plain with fairly well-resolved bathymetry and pre-transgressional paleotopography. Results presented in this study show striking differences between the spatial extent of the two modelled sets of paleocoastlines which in places exceeds tens of kilometers. These results demonstrate the importance of using an appropriate geologically-supported elevation model for paleoreconstruction as unsuitable models can result in significant errors and unreliable reconstructions. This is especially noteworthy for low-gradient settings where even a slight variation in sea level can affect vast areas. Finally, the results of this study provide insight into the Early Holocene evolution of the present-day area of the Gulf of Trieste as an abrupt and predominant northeasterly oriented transgression direction is indicated from the paleocoastline reconstructions.