Print this pageIllitization in Permian Arkosic Sandstones Due to Fault-Related and Cross-Formational Fluid Flow, Northern Germany
GAUPP, REINHARD, THOMAS DEUTRICH, NORBERT CLAUER, and HORST ZWINGMANN
Structural position of Late Permian Rotliegend sandstones in the North Germany Basin is a major control on reservoir qualities. Permian red bed sequences juxtaposed against Carboniferous Coal Measures typically show increased growth of clay minerals, bleaching, and bitumen impregnation. Mesodiagenetic growth of clay minerals is particularly intensive in close proximity (stratigraphic or tectonic contact) to the Carboniferous Coal Measures.
'Clay mineral aureoles' along these contacts show a distinct zonation with a narrow (<250 m) dickite/kaolinite zone, followed by a wide (>1 km) zone of illitization. Illites from the zoned aureoles show trends in morphology, crystallography, crystal chemistry, trace elements, abundance, and K/Ar-ages.
Illite isotopic ages coincide with the onset of gas generation from Carboniferous coals and a period of major extensional fault reactivation and halokinetic movements in central northern Germany (Late Triassic to Liassic).
Fault reactivation during the opening of the central Atlantic triggered cross-formational and fault-controlled flow of fluids with organic maturation products from the Carboniferous sources into the Permian reservoir rocks, which caused dickite and illite growth, and extensive feldspar dissolution.
Mesodiagenetic clay mineral assemblages from the Permian gas reservoir rocks can be used to predict fault proximity while drilling.