REDISTRIBUTION AND GEOCHEMICAL BEHAVIOR OF REDOX-SENSITIVE ELEMENTS AROUND S1, THE MOST RECENT EASTERN MEDITERRANEAN SAPROPEL

The youngest eastern Mediterranean sapropel (S1) is generally believed to have formed 7-9 C-14 ky B.P. The distribution of redox-sensitive e lements above, in and below the sharply defined, organic-rich unit rev eal that S1 has already suffered heavy diagenetic alteration. Its pres ent thickness, based on its dark colour, is only a fraction of its ori ginal thickness. In one core, visual evidence of S1 with an inferred i nitial thickness of 6 cm has been destroyed, and a similar thickness a ppears to have been lost from the tops of another two examples. This i s caused by oxidation of the upper reaches of Sl by a progressive oxid ation front which commenced 5.2-5.4 C-14 ky ago, and still appears to be active in the three cores studied. Diagenetic relocation of many re dox-sensitive elements has occurred. Most elements expected to be enri ched in sapropels or sulphide-rich sediments already have maximum conc entrations above or below, rather than in, the present S1 layers. Simi larities are observed in the geochemical behaviour of As, Fe, and P; o f Co, Cu, Mn, Ni, and Zn; and of Cd, Mo, Sb, Tl, U, and V. The behavio ur of Ba is distinctive, and its immobility as barite makes it an indi cator for palaeoproductivity and the original high S1 C-org content. T he elements Se and I exhibit particularly large, sharp concentration p eaks, and together are proposed as useful indicators of the present bo undary between oxic and post-oxic conditions.