Dedolomityzacja w górnojurajskich skałach węglanowych z okolic Krakowa
Abstract
Dedolomitization of Upper Jurassic carbonates in the Cracow area (southern Poland).
S u m m a r y. The Upper Jurassic limestones in the vicinity of Cracow underwent extensive dedolomitization process. Petrographic and cathodoluminescent analyses of carbonates in four test areas confirm the dedolomitization as have been developed with various intensity. The alteration of dolomite into calcite occurs as centripetal and centrifugal dedolomitization. Both processes lead finally to a complete disintegration of the dolomite crystals; calcite pseudomorphs after dolorhombs are the end products. These calcite pseudomorphs are abundant in limestones of St. Anna Mt. and in the Kostrze quarry, but are scarce in the Twardowski Cliffs area and in the outcrop of Księża Mt., which indicates a less advanced and slower dedolomitization process in the latter two areas. Most probably the initiation of dedolomitization started from the moment when a carbonate bank emerged from the sea water (Vierek, 2003); temperature of mixing fluids decreased considerably, whereas Ca2+/Mg2+— ratio in the same fluids increased.
S u m m a r y. The Upper Jurassic limestones in the vicinity of Cracow underwent extensive dedolomitization process. Petrographic and cathodoluminescent analyses of carbonates in four test areas confirm the dedolomitization as have been developed with various intensity. The alteration of dolomite into calcite occurs as centripetal and centrifugal dedolomitization. Both processes lead finally to a complete disintegration of the dolomite crystals; calcite pseudomorphs after dolorhombs are the end products. These calcite pseudomorphs are abundant in limestones of St. Anna Mt. and in the Kostrze quarry, but are scarce in the Twardowski Cliffs area and in the outcrop of Księża Mt., which indicates a less advanced and slower dedolomitization process in the latter two areas. Most probably the initiation of dedolomitization started from the moment when a carbonate bank emerged from the sea water (Vierek, 2003); temperature of mixing fluids decreased considerably, whereas Ca2+/Mg2+— ratio in the same fluids increased.