The four depositional stages of this Late Carboniferous-Pennian carbonate platforrn show different patterns of diagenesis and porosity control because of differences in sediment composition and depositional setting. Initial mixed siliciclastic-carbonate strata (Moscovian-Gzhelian) have mostly low porosity. The following shallow-water, photozoan limestonefdolomite strata (Gzhelian-early Sakmarian) contain multiple zones of high porosity, reflecting low abundance of both early-marine and late-burial calcite cement, together with early leaching of aragonite and moderate degrees of dolomitization. This combination of porosity-favourable factors resulted from deposition in a platforrn-interior location during a time of major sea-level fluctuation and low accommodation creation. The overlying interval of open-shelf, heterozoan limestone (Late Sakmarian-Artinskian) has uniformly low porosity due to extensive late-burial calcite cementation. The final stage of deepfcold-water deposition (mid-Late Pennian) culminated in high-porosity, carbonate-poor spiculite at the top of the platform succession.
S. N. Ehrenberg, Statoil, N-4035 Stavanger, Norway;
T. A. Svånå, Statoil, postboks 40, N-9401 Harstad, Norway;
E. B. Nielsen and L. Stemmerik, Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400, Copenhagen NV, Denmark.