A few metres-sized dolomite body is present in the Lower Jurassic limestone strata of the Kálvária Hill of the Gerecse Mts. The dolomite making up this body is unique, both in the outcrop itself and in the Jurassic beds of the Gerecse Mts. It is laminated, yellow-red and follows a fracture, thus further invading the host Jurassic limestone along a bedding plane. The dolomite that effectively replaces the host rock is fine to medium crystalline; locally, saddle dolomite crystals have also been observed. A breccia zone cuts across the dolomite body, although brecciation is not evident within the dolomite and only calcite veins are present. The breccia zone is cemented by white-grey-yellow calcite that incorporates dolomite crystal fragments. Calcitized dolomite crystals can be found in the host Jurassic limestone next to the breccia zone. The three different dolomite types are most probably associated with the same dolomitization event. Dolomitizing fluids could have migrated through fractures and occasionally along bedding planes. Dolomite crystal fragments — found within zones of the breccia-cementing calcites — could have their origins in the dolomitized host rock. The stable isotope data of the dolomite suggest that dolomitization probably took place in the burial realm, either from the existing pore water or hydrothermal fluids; the latter would have migrated through fractures in the lithified Lower Jurassic limestone. The post-sedimentary character of the fractures suggests a post-Late Jurassic age for the dolomitization. The meteoric origin of the calcite found in fractures — and as cement in the breccia zone — points to subaerial exposure. This would imply the occurrence of a pre-Late Cretaceous–Palaeogene dolomitization event.
ASJC Scopus subject areas
- Geochemistry and Petrology