Anoxic vs oxic sedimentation in the Bannock Basin Area, 35,000 B.P. to present

Two cores, one raised from a plateau and containing normal pelagic sediments, and one raised from a low, and characterized by dark sediments deposited in an anoxic recenr environment in the Bannock Basin area (eastern Mediterranean) were investigated in detail for the interval encompassing Tephra Y-5 (estimated age 35,000 yrs B.P) and the sediment-water interface (time zero). Compositional differences in the anoxic and oxic sediments seem to be related to changes in the diagenetic conditions and show: - high inorganic carbon, low organic carbon and selective dissolution of biogenic opal in the normal pelagic sediments. - low inorganic carbon, high organic carbon and preservation of biogenic opal related to the occurrence of anoxic and hypersaline bottom conditions and to the high content in organic matter in the anoxic sediments. The organic C content of the anoxic sediments is lower than that of sapropels deposited during shon duration episodes o{ basinwide anoxia, but a marked increase is recorded at the level of Sapropel S-1, thus showing that the regional signal is superimposed to the local one. Anoxic sediments are less compacted and more watery than coeval oxic and consequently the sediment accumulation rate is higher.