SEDIMENT DEPOSITION AND ACCUMULATION ON THE APENNINE SHELF CLINOFORM, ADRIATIC SEA

The central western coast of the Adriatic Sea is characterized by a series of small, distributed fluvial sources (i.e., a line source) draining the Apennine mountains and delivering approximately 2.4x10⁷ tons of sediment annually to the adjacent shelf. In this region, a shelf clinoform has formed through the late Holocene oriented parallel to the coastline. Recent investigations into the pattern of sediment accumulation (i.e., using ²¹⁰Pb geochronology; half-life 22.3 years) on the Apennine clinoform have revealed that across-shelf rates of accumulation reach a maximum value (~1 cm/y) on the foreset, which is a relationship observed on other clinoforms. The along-shelf maximum of accumulation rates is reached near the Gargano Peninsula at the southern boundary of the dispersal system. This pattern of sedimentation differs from other line-source systems. In the Gulf of Alaska distinct shelf deposits are observed from each individual river, and in the Gulf of Papua, river input coalesces into a central locus of accumulation. The differences lend further insight into sediment dispersal systems with line sources.

Anthropogenic activities have significantly impacted sediment deposition and accumulation on the Apennine shelf clinoform. These activities, primarily dam construction and river stabilization, increased after the second World War and have resulted in a reduction of sediment accumulation in the area, evidenced by changes in ²¹⁰Pb profiles. However, sedimentation near the Pescara and Biferno Rivers, which was examined during the winter of 2002-2003 using the short-lived radioisotopes ⁷Be (half-life 53.3 days) and ²³⁴Th (half-life 24.1 days), indicates that some new sediment was delivered to these areas during times of elevated river discharge. The present rate of sediment supply is likely less than during periods when the clinoform morphology was created.