Primary and diagenetic signals in Mediterranean sapropels and North Atlantic turbidites : origin and fate of trace metals and palæo-proxies
1993
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.
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