Reconstruction of sediment supply from mass accumulation rates in the Northern Adriatic Basin (Italy) over the past 19,000 years

Reconstruction of sediment supply is hampered by the incompleteness of the stratigraphic record. This problem may be partly circumvented by studying mass accumulation rates in closed systems, i.e., basins in which no sediment has bypassed the site of deposition over the time interval of interest. We present time-averaged basin-wide mass accumulation rates and their associated uncertainties from a well-documented closed basin, the Northern Adriatic Basin (Italy), spanning the time interval from 19 ka B. P. to the present. The sediment masses of five basin-wide lithosomes and their associated uncertainties are derived by means of stochastic simulation, using high-resolution seismic data, porosity profiles, and radiocarbon datings. This study demonstrates that inferring rates of sediment supply from conformity-bounded stratigraphic units is feasible, as indicated by the excellent agreement of our results of mass accumulation over the past 400 years with two independently derived estimates. Formation of the stratigraphic record is not an instantaneous process. By comparing spatial patterns of mass accumulation rates on three different timescales (decadal, centennial, and millennial) we demonstrate a low preservation potential of sediments presently accumulating near the coast, and a continuous cross-shore and alongshore sediment transport regime. The change from transient to persistent accumulation patterns in the highstand systems tract of the Northern Adriatic Basin occurs at the centennial to millennial timescale. Intrabasinal erosion and recycling of sediments obscure the relation between rates of sediment supply and net basin-wide mass accumulation, which limits the amount of information that can be extracted from the stratigraphic record. Hence, a mismatch between rates of sediment supply and accumulation rates is expected for unconformity-bounded sequence-stratigraphic units. Given the uncertainties associated with our estimates, we are unable to reject the hypothesis that net basin-wide mass accumulation rates have been constant over the time interval of 19,000 years (at a 10% significance level).