Geochemical evidence for enhanced productivity during S1 sapropel deposition in the eastern Mediterranean

Abstract

The geochemistry of the youngest Mediterranean sapropel layer suggests changes in productivity and water column oxygen conditions during sapropel deposition. The Ba‐enriched interval is broader than the organic‐carbon‐rich interval of this sapropel. We suggest that the Ba‐enriched horizon records the original thickness of the sapropel prior to subsequent partial oxidation. The main carrier of Ba is barite, as microcrystals (0.5–5 µm ) having a morphology characteristic of marine barite, particularly abundant beneath high productivity regions. Ba concentrations do not change at the sapropel layer oxidation front and diagenetic barite crystals are absent, thus the Ba‐enriched layer reflects original oceanic conditions of increased biological productivity during sapropel deposition and not diagenetic Ba remobilization. Paleoredox indicators point to restricted oxygenated bottom water but not to fully anoxic conditions. Detrital elements within this layer indicate a lower eolian terrigenous input, enhanced humidity, and increased precipitation/runoff, thus likely higher nutrient supply.Supporting table is available on diskette or via Anonymous FTP from kosmos.agu.org, directory APEND (Username = anonymous, Password = Guest). Diskette may be ordered by mail from AGU, 2000 Florida Ave., N. W., Washington, DC 20009 or by phone at 800‐966‐2481; $15.00. Payment must accompany order.