Mineralogy and geochemistry of Mississippian and Lower Pennsylvanian Black Shales at the Northern Margin of the Variscan Mountain Belt (Germany and Belgium)

Exploration of unconventional gas resources from Paleozoic formations in northwestern Germany is just getting started. Large, potential gas reservoirs are presumed to be present north of the Rhenish Massif, where Mississippian and Pennsylvanian marine black shales occur. This paper comprises geochemical and mineralogical data and other important aspects of potentially economic black shale formations of the Carboniferous. Additionally, the burial and thermal history was reconstructed using 1D modeling software (Schlumberger). These 1D models were calibrated with vitrinite reflectance data from outcrops and shallow wells. In general, all Paleozoic black shales are at present highly mature, between about 1.5 and > 3% vitrinite reflectance. The shales of the uppermost Mississippian (Upper Alum Shale/Chokier Formation) have high contents of organic carbon, are tens of meters thick and can be regarded as potential gas shale targets. Most other Mississippian and Pennsylvanian black shales are relatively thin. Adjacent carbonates are often stained black and rich in solid bitumen, indicating former oil impregnation of these reservoirs.

► Mississippian black shales in Western Europe are characterized for the first time.
► Maturity is in the gas window with vitrinite reflectance ranging from 1.1–3.9 %.
► The Upper Alum Shale could become an interest target for gas shale exploration.