Silurian shales of the East European Platform in Poland : some exploration problems

its reasonably well-constrained geological framework, entails a number of contentious issues that need to be resolved before this emerging shale gas play will enter a stage of successful development. The succession is thought to have originated in a Caledonian foredeep encroaching distally onto a pericratonic shelf ramp. However, the geochemical signature of the mudrocks is consistent with a cratonic rather than orogenic sourcing, the proximal part of the foredeep basin-fill is apparently missing, and the shale succession juxtaposes in part across the Teisseyre-Tornquist Zone against suspected terranes with no evidence of Silurian tectonism. Organic-rich Llandovery– Wenlock shales form a NW-SE striking central belt that is increasingly calcareous toward the craton (NE) and more silty toward the inferred orogen (SW), with the TOC content decreasing in both directions perpendicular to the strike. The TOC trend seems consistent with the deep-downlap model of black shale deposition suggested for many Paleozoic foredeep basins, but does not quite agree with the outer neritic to upper bathyal depths assumed for the shale