Temporal and spatial patterns of modern shelf sedimentation in the Adriatic Sea

Modern shelf sedimentation is examined in the epicontinental Adriatic Sea to provide insight into the sedimentary processes that have formed much of the ancient stratigraphic record. Short- and long-term sediment deposition and accumulation are assessed to elucidate how sedimentary strata are created and preserved.; ∼4.6 x 107 t of sediment are delivered annually to the western Adriatic shelf. In the north, near the Po River delta, flood sedimentation largely controls longer-term (100-y) sediment accumulation, especially near the main distributaries. This is indicated by observations following a ∼100-y flood of the Po River, which occurred in October 2000. The seabed deposit can be identified by its radiochemical and textural properties (i.e., uniform 7Be and low 210Pb activities, fine grain size). The low 210Pb activity of flood sediment, due to the hindered scavenging ability of high-concentration sediment suspensions, is related to the fluctuating activities observed in profiles used in sediment accumulation measurements.; About half of the Po River sediment load can be accounted for on the adjacent shelf, and the remainder likely is transported southward under the prevailing circulation of the Adriatic to join with sediment supplied by the Apennine Rivers. These rivers are a series of small, distributed fluvial sources (i.e., a line source), and a clinoform has developed on the adjacent shelf throughout the Holocene. Usually, sediment accumulation rates on the foreset of clinoforms are significantly higher than the topset and bottomset, which is the case south of the Tronto River. Northward, this is not true, which indicates that the clinoform may not be actively prograding everywhere at present, likely due to anthropogenic activities (e.g., dam construction) that have decreased the sediment loads of the Apennine Rivers over the last ∼50 y.; The presence of a delta and a clinoform adjacent to the Po and Apennine Rivers, respectively, is unusual in that both features have developed from similar sediment supply and oceanographic conditions. This suggests that other factors, such as differences in the timing of floods and storms, are important for shaping the geometry of seabed deposits.