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fabio Trincardi, ISMAR (CNR) (Italy)
Antonio Cattaneo , IFREMER (France)
Domenico Ridente, IGAG (CNR) (Italy)
Giuseppe Verdicchio, EDISON (Italy)
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The Adriatic basin records the impact of relative sea level change and abrupt fluctuations of sediment flux. Relative sea level changes are a complex function of eustasy, loading, compaction and regional tectonics. Detailed interpretations of sea-floor morphology and internal geometry of marine deposits allows definition of the impact of very short-term supply fluctuations (on time scales of decades to centuries), and offer increasing evidence of the pervasive role played by advection in dispersing sediment along the Adriatic margin.
Modern deltas - Short-term (natural or anthropogenic) changes in sediment flux are well recorded in the recent deposits of the modern Po delta, an asymmetric delta which reflects the dynamical balance between oceanographic regime and sediment-load partitioning among several delta mouths. Shore-parallel advection causes a complex stacking of multiple prodelta lobes. When a delta lobe becomes abandoned up current of a new lobe, a significant sediment volume is cannibalized from the former and advected to the latter. On the contrary, when the lobe that becomes abandoned is down current, the new lobe exerts a sheltering effect allowing a greater preservation of, and producing a marine onlap against, the abandoned lobe. This role of sediment advection is even more evident where human intervention fixed the branches of multi-lobe deltas and natural avulsion is no longer possible. In this case, any change in partitioning of sediment load among each delta mouth results in the rapid growth or retreat of individual lobes, impacting the prodelta on variable distances.
Confined shelf clinoforms - Shore-parallel clinoforms form both during high-stand and falling sea level, are tens of meters thick and rest on regional downlap surfaces. The thinning of clinoforms through the bottomset reflects the energetic impact of the West Adriatic bottom water flowing along the contour, impinging the sea floor thereby limiting the basin ward growth of the clinoforms. In this view, bottom currents induce lateral advection rather than basin-ward sediment transport and form elongated clinoform bodies characterized by a peculiar shore-parallel strike of the foreset. Borehole PRAD1.2 proves that the bulk of Pleistocene clinoforms within 100-kyr sequences record almost exclusively interglacial stages (Stage 5, 7 and 9) confirming that shore-parallel advection is at peak during high stands.
Cascading Water - Cold and very dense water form on the broad North Adriatic shelf, reach the shelf break and cascade across the South Adriatic slope impacting the sea floor and generating a composite suite of large-scale bedforms, including sediment waves, comet marks, scours and furrows. Production of dense water masses was strongly reduced during the Last Glacial low stand when most of the shelf was exposed. Cascading water is enhanced during intervals of sea level rise and high stand when the shelf in the north is drowned and dense water production onset.
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