THE MARKER-BED OF THE MEDITERRANEAN RIDGE DIAPIRIC BELT - GEOCHEMICALCHARACTERISTICS

A prominent marker-bed, jet black in colour, with a sharp basal contac t and a few centimetres in thickness, is ubiquitous in the Mediterrane an Ridge crestal area, where collision between the European plate and the African plate occurs, and where mud diapirism is a common phenomen on. The marker-bed is consistently recorded in the upper part of the s ediment cores, within the Holocene pteropod-foraminiferal oozes, above sapropel S-l which documents the last, youngest, postglacial sapropel ic episode recorded in the eastern Mediterranean. The marker-bed consi sts of numerous Mn-micronodules of bacterial origin and presents an ab normal concentration of metals, especially of manganese. Of the 25 cor es recovered during the R/V Gelendzhik 1993 Cruise TTR 3-Leg2, 12 cont ained the marker-bed, but 13 did not. The large majority of the latter (10) consisted of extruded mud breccia up to the core top and one con sisted of pre-Holocene sediment. Eight cores of the 12 containing the marker-bed had a pelagic make up, the remaining ones contained the dia piric mud-breccia of deep provenance. Seven cores were investigated ge ochemically for their elemental composition. The new results confirm a nd support the previous ones, and record percentages of Mn within the marker-bed ranging from 2.98 to 16.12%, values that exceed by at least one order of magnitude those of the adjacent layers, suggesting an or igin independent from the local environment and dependent on an episod e probably linked to the Santorini Bronze-age eruption.