Journal of Conference Abstracts

Looking for Palaeooceanographic Tracers Locked in Carbonate Sequences

Michal Gruszczynski (beerbear@twarda.pan.pl)

ING PAN, ul.Twarda 51/55, 00-818 Warsaw, Poland

The most useful element which has been incorporated in calcium carbonate sediments and skeletons is barium. Barium concentrations and Ba/Ca ratios are potential traces of biogenic productivity and palaeoenvironment. While the positive shift of the carbon isotope values for the carbonate sediment coincides with increase of Ba/Ca ratios, one might calculate even an amount of carbon gained by "new palaeoproduction". Whereas the positive trend in carbon isotope values coincides with a drop in the Ba concentration in the belemnite rostra, one might suggest that a fraction of the barium was involved in enhanced settling of POC due to increased productivity and organic matter burial. As for the detailed studies, a decrease of carbon isotope values together with the opposite trend in Ba/Ca ratios for juvenille ammonite might suggest the young ammonite lived in shallow waters in the proximity of the anoxic sea floor and/or chemo-redoxcline. Quite recently, a negative correlation of the carbon isotope values and Fe concentrations in the belemnite rostra has been interpreted in terms of iron being the moderator of primary producers' ecosystem. The major sedimentary structure in the carbonate sequences reflecting the crises of calcium carbonate precipitation, are hardgrounds. In most of the cases, the cessation of calcium carbonate precipitation was because of increase of the carbonate alkalinity and/or increase of partial pressure of the carbon dioxide. The excess of the carbonate alkalinity caused a decrease in free calcium ions. This was because, a geochemically different seawater invaded the shallow sea floor, usually originated in the anoxic seawater boxes. The renewal of sedimentation after calcium carbonate precipitation crises sometimes took place under conditions where the surface waters were still controlled by stratified seawater zones.

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