Dolomity epigenetyczne w utworach górnojurajskich monokliny śląsko-krakowskiej

Ewa Górecka, Tomasz Zapaśnik

Abstrakt


EPIGENETIC DOLOMITES IN UPPER JURASSIC ROCKS IN THE SILESIAN-CRACOW MONOCLINE

Summary
Epigenetic (ankerite) dolomites were found in borehole columns and outcrops of limestone and marly Callovian and Oxfordian rocks in the Silesian-Cracow Monocline (Figs. 1-2). Distribution of dolomites is determined by lithological features of rocks forming a given lithostratigraphic unit on the one hand and tectonics on the other. All the studied dolomites occur in those proximity of faults. Dolomite bodies, generally small in size, are distributed along fractures, slickensides and small pores in rock. Selective replacement of' limestone rock by dolomite and partial dolomitization of calcite organic remains are also characteristic here.
Ankerite dolomite is accompanied by pyrite, fine crystals of which are scattered among dolomite rhombohedrons. The origin of authigenic quartz grains was related to epigenetic (hydrothermal) changes, responsible for dolomitization and pyritization of Upper Jurassic limestones. Small accumulations of such quartz are sometimes found within dolomitized zones or their close neighbourhood. Various siliceous deposits occurring in the Jurassic or even Upper Cretaceous acted as a source for silica. The dolomite and ore-bearing deposits presumably originated in the time interval from the latest Jurassic to the latest Cretaceous.

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