The origin of Upper Permian basinal dolomites in SW Poland: Impact of ascending brines

The conventional mechanism for dolomitization in evaporitic basins is by drawdown-related reflux of brines, but it seems that ascending brines were responsible in the case of basal Zechstein (Wuchiapingian) strata. Dolomite of basinal sections of the Zechstein Limestone in SW Poland show mostly fabric-destructive dolomitization and wide delta O-18(V)PDB and delta C-13(VPDB) ranges (-3.78 to 6.47 parts per thousand and -1.64 to +5.3 parts per thousand respectively). The maximum delta O-18 value reflects the temperature of dolomitizing fluid equal to approximately 38 degrees C, if the delta O-18 of water = +4 parts per thousand is assumed. The Sr-87/Sr-86 ratios of the dolomite samples vary from 0.707924 to 0.711164 and are clearly enriched with respect to the contemporaneous seawater values. The basinal dolomites have originated owing to interaction of low-temperature brines from the underlying red beds and hypersaline brines originated during the Zechstein evaporite deposition. The conventional concept connecting the highly radiogenic strontium values recorded in dolomites with the overlying formations, and thus implying the reflux mechanism of dolomitization, should be re-evaluated.

Automated summary

The text discusses the formation of dolomite in certain geological regions, where the mechanism involving ascending brines is responsible for dolomitization, contrary to the traditional drawdown-related reflux mechanism. In the Zechstein Limestone of southwestern Poland, dolomite exhibits fabric-destructive features and a wide range of oxygen and carbon isotopes. Additionally, the Sr-87/Sr-86 ratios of dolomite samples suggest interaction between low-temperature brines and hypersaline brines during the Zechstein evaporite deposition.