|
United Kingdom |
Department of Geological Sciences, University of Aston, Aston Triangle, Gosta Green, Birmingham B4 7ET
Isotope Department, Weizmann Institute of Science, Rehovet, Israel
Detailed mineralogical, chemical and stable isotope analyses have been made of single core through the Marl Slate in order to investigate the Zechstein transgression and its associated mineralization. The core (VT8), drilled by the National Coal Board off the coast of NE England, contains three subfacies: (1) dark grey, organic-rich, sapropelic siltstones; (2) organic-dolomite laminites; (3) massive finely crystalline dolostones. Two cycles of deposition which include the sequence sapropel
There are some close correlations between the lithological and geochemical variables, including the stable isotope values. The sapropelic units are characterized by high Fe content (as iron sulphide) and strongly negative
The distribution of base metals in the Marl Slate in this core strongly suggests that they were introduced by freshwater influx. Although Pb shows no clear relationship to the depositional cycles, Cu and Zn contents are relatively low in the lower sapropelic parts of the cycles and become higher in the upper parts. We take this to indicate that Cu and Zn sulphides were precipitated interstitially when more ‘normal’ marine conditions were re-established in the later part of each cycle.
laminitedolostone are present although the lower one (112 cm) is much thicker than the upper (32 cm). 
18O values in associated carbonate minerals. Quartz silt and organic carbon are also higher in these units but diminish upwards in each depositional cycle. Each cycle of deposition appears to have been initiated by an influx of freshwater into the Zechstein basin which promoted surface productivity, water stratification and regional anoxic conditions. The relative change in 13C to more positive values higher in the Marl Slate is independent of lithological variation and indicates progressive enrichment of 13C in the Zechstein Sea in response to the precipitation of large amounts of organic matter.
