TRANSGRESSIVE, TIDAL- AND WAVE-DOMINATED COASTAL-SYSTEM DEVELOPMENT IN THE NORTHEASTERN SARDINIAN RELICT SHELF: INSIGHTS INTO THE ORIGIN OF SPATIAL AND TEMPORAL VARIATIONS IN COASTAL PROCESS REGIME

Most of the modern coastal areas are mixed-energy environments with spatial changes of dominant processes. In addition, temporal variations in the relative intensity of tidal, river and wave processes, at a range of time scales, have been documented in individual coastal systems. Outcrop and subsurface studies of such temporal and spatial variations in coastal environments are often complicated and mostly incomplete. On the contrary, the study of relict shelf portions can lead to the complete reconstruction of coastal system evolution during the last sea-level rise. Here, we present such a study, through the interpretation of multibeam bathymetry and Chirp profiles, on the northern Sardinian relict shelf.

Tidal- and wave-dominated sectors were developed at the same time in different portions of the investigated area. Wave-dominated coastal systems prevail in the north, where three coastal barrier systems developed at progressively shallower depths during the last rise of sea level. They bounded tidal basins opened to the north, where tidal channels and bars developed. Tidal inlets and tidal deltas are present in between the single barrier islands. In the southern area, a barrier island system was initially in continuity with the northern one. It enclosed a large basin with tidal bars and channels. Successively, the barrier was reworked by tidal currents and elongated bars and channels formed within a tide-dominated estuary. With continuing sea-level rise, a further barrier formed landward, and enclosed a wave-dominated estuary with tidal channels and bars.

Our study shows that, as a result of the spatial variations of controlling processes, coeval coastal systems with variable degrees of wave- and tide- domination can develop. Our study also shows that the relative importance of tide and wave processes can vary in time due to oceanographic and morphologic changes inherent to sea-level rise. In particular, our results show that tide-influenced deposits can be an important constituent of coastal successions developed in small bodies of water, such as the Mediterranean Sea. In general, our results show that sequence stratigraphic models for coastal deposits, which generally assume a regionally prevailing process constant in time, largely overlook temporal and spatial changes in dominant regime.