Multi-stage Dolomitization of the Upper Permian Zechstein
Limestone (Ca1) Carbonates (SW Poland)
Peryt, Tadeusz
Marek1, Marek Jasionowski1 (1) Panstwowy Instytut Geologiczny, Warszawa, Poland
The earlier study on evaporite-related,
Upper Permian Zechstein dolomites showed that they
are products of both the early- and late diagenesis,
and the pattern of occurrence of dolomite is complex. In the basinal facies of the Zechstein Limestone in SW Poland, carbonate buildups
(termed reefs) were encountered which are surrounded laterally and covered by evaporites. The carbon and oxygen isotopic investigation on
213 samples showed quite varied Δ18O and Δ13C values: the range of
Δ13C values is 0‰ to +6‰ PDB in calcite (average +2.7‰) and 0‰ to +8‰ PDB
in dolomite (average +4.8‰), and the Δ18O values are from +3‰ to -13‰ PDB
in calcite (average -5.1‰) and +3‰ to -9‰ PDB in dolomite (average -4‰). Two
groups of dolomites can be distinguished. The first group is represented by
laminated or structureless and cavernous dolomicrites with anhydrite and pisolitic
deposits that were syndepositionally dolomitized in the sabkha
environment, and their &delta18O values range from 0‰ to +3‰ PDB. Assuming
the crystallization temperature of 40°C, sabkha
deposits originated from water characterized by &delta18O values close to
0‰ PDB, which corresponds to slightly evaporated
Permian seawater. A part of the isotopic heavier deposits is also represented
by dolomitized grainstones
showing perfectly preserved primary fabric (fabric-preserving dolomitization). These dolomites might have originated
through dolomitization in the sabkha
environment due to reflux. The isotopic composition of other dolomites is
characterized by low &delta18O values (from -2‰ do -10‰ PDB) due to burial
conditions at relatively high temperatures, which is compatible with the
recorded presence of saddle dolomite. However, the most common petrographic texture of dolomite is planar, which is
characteristic for low-temperature diagenetic
environments, and thus, it is concluded that these textures are inherited after
earlier, low-temperature phases of dolomite formation.