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Mg and Sr distribution in carbonate rocks from the Maastrichtian/Danian boundary of the Danish subbasin and the North Sea Central Graben |
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| Authors: | Niels Oluf Jrgensen |
| Institution: | Institute of Historical Geology and Palaeontology, University of Copenhagen, Copenhagen, Denmark |
| Abstract: | Examination of the Mg and Sr concentrations in carbonate rocks in a number of sections provides the basis for the establishment of two geochemical facies within the region studied: (1) a basinal facies, including the axial part of the Danish Subbasin and the North Sea Central Graben, indicating relatively stable geochemical conditions; and (2) an eastern marginal facies in the Danish Subbasin reflecting unstable geochemical conditions and distinguished by partial cementation and increasing Mg and Sr concentrations towards the northeastern limits of the basin. A slight microtextural variation in the chalk between the basinal and marginal facies indicates that the origin and composition of the biogenic carbonate components strongly influence the bulk-rock geochemistry. The elemental distribution reveals a negative correlation between the Mg and Sr concentrations in the topmost Maastrichtian chalk, expressed by increasing Mg and decreasing Sr upwards towards the Maastrichtian/Danian boundary. This relation occurs in both geochemical facies and in all sections studied and is believed to have been governed by changing physicochemical conditions in the late Maastrichtian sea. |
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