Carbonate cements marine, dissolution

Dissolution of biogenic marine carbonate as the source of the early cements does not exclude moderate migration distances of the precipitating fl uids. The occurrence of sandstones rich in calcite cement above fossil-rich calcareous shales points towards import of the carbonate cements from adjacent shales by upward-moving pore fluids expelled by shale compaction. The presence of carbonate cements in sandstone zones free of fossil or carbonate fragments (Fig. 13A), and, vice versa, their absence in some of the fossil-rich zones (Fig. 17D) also supports carbonate redistribution or an external (although possibly nearby) source. 

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