Upper Permian (Zechstein) microbialites: Supratidal through deep subtidal deposition, source rock, and reservoir potential

Zechstein 2 (Z2) carbonate microbialites flourished under arid paleoclimatic conditions in the Late Permian. Microbial carbonates from the Roker Formation outcrop in northeast England, with its subsurface equivalent being the Main Dolomite from northwest central Poland. The Z2 carbonate deposits developed in supra-tidal through deep subtidal zones and consist of various stromatolites and thrombolites. Planar stromatolites and thrombolites characterize intertidal and supratidal facies, and biohermal stromatolites with oolitic grain-stone and crinkled stromatolites typify shallow sub-tidal facies. The Z2 subtidal and/or intertidal microbialites with oolites form complexes more than 10 m (33 ft) thick and are important reservoir facies for hydrocarbons. Subtidal (slope) and intertidal (lagoonal) microbial mudstone and wackestone have poor reservoir properties but contain total organic carbon as much as 2 wt. % and are considered as potential source rocks. The thermal maturity assessed from C-27 17 alpha-trisnorhopane (Tm) and C-27 18 alpha-trisnorhopane (Ts) as the Ts/(Ts + Tm) ratio, C-30 moretane/hopane ratio, sterane ratio expressed as 20S/(20S + 20R), and beta/beta(beta + alpha alpha) ratio shows to indicates a mature character of organic matter with respect to oil generation.