Primary and diagenetic signals in Mediterranean sapropels and North Atlantic turbidites: origin and fate of trace metals and palæo-proxies

Abstract

Marine sedimentary records may contain important information on environmental changes in the past. Modellers of global changes need such information to make a more accurate description of past climates, and to predict more precisely possible future climate changes. Signals in sediments can be divided in two groups: I. primary signals caused by variations in terrigenous and biological inputs, occurring before and during sediment deposition and 2. secondary signals, which are formed after deposition. These secondary signals form as a result of variation in primary signals and external changes, such as diagenetic changes or tectonic influences. This thesis deals with the cause of primary and secondary signals and their interaction, in marine sediments from the Mediterranean and North-Atlantic. In the Mediterranean, especially the eastern part, organic rich layers are found that are intercalated in hemipelagic "normal" marine sediment. These layers, "sapropels", have aroused tremendous interest in the scientific community because of their alleged similarities to Cretaceous Black Shales. In chapter 2, one of the primary signals in sapropels, 8180, is reassessed. Depletions in 81SO, coinciding with sapropels, are important evidence for the development of a low salinity surface layer. Such a layer is a prerequisite for a reversal of circulation in the Mediterranean, which has been suggested to be the cause for sapropel formation. We show that this is not necessarily true, because these depletions can as well be explained within the present-day circulation pattern of the Mediterranean.