Low sea-level stand emplacement of megaturbidites in the western and eastern Mediterranean Sea

Piston cores from the Balearic and Herodotus Abyssal Plains in the Mediterr anean Sea show that the Late Pleistocene to Holocene sedimentary sequence i s dominated by turbidite muds. On each plain, one turbidite bed is conspicu ous by its thickness, and this bed can be correlated basinwide on the basis of geochemical compositional analysis and its apparent correspondence with a distinct acoustically transparent layer on high-resolution seismic recor ds. These megabeds on the two plains represent megaturbidites of very large volume (300-600 km(3) each) and are shown by AMS radiocarbon dating to hav e been emplaced during the last low stand of sea-level at the height of the last glacial maximum. The megabed on the Balearic Abyssal Plain is derived from the southern European margin and is the main sedimentation event over the last 120 ka. It emplaced as much material as was deposited by smaller flows during the previous 25 ka. Sedimentation rate curves for the Balearic Abyssal Plain show that falling sea-level correlates with increased terrig enous deposition, and that gross sedimentation rates in the basin increased as sea level fell from 120-18 ka due to more frequent emplacement of dista l turbidites. The Herodotus Abyssal Plain megabed is derived from the Libya n-Egyptian continental shelf west of the Nile Delta and was the dominant se dimentation event in this basin during the past 60 kyr. High-resolution sei smic profiles from the Ionian and Sirte Abyssal Plains in the central Medit erranean also suggest possible low sealevel emplacement of megabeds in thes e regions. Available evidence suggests widespread emplacement of megaturbid ites throughout the Mediterranean at the last glacial maximum. Although the triggering mechanisms for these events remain speculative, catastrophic de stabilisation of the margin after a long period of accumulation with an inc reased rate of sediment supply is suggested. (C) 2000 Elsevier Science B.V. All rights reserved.