Dolomitization and karst-related dedolomitization of Muschelkalk carbonates, in South Hungary

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Abstract

Middle Triassic carbonates of the Villány Mountains were deposited on a homoclinal carbonate ramp system. Within the 700 m-thick carbonate ramp sequence many of the carbonates show partial or complete dolomitization. The study describes the major petrological and geochemical constraints of the dolomitization process of the Zuhánya Limestone Fm. The dolomites occur in the limestone as small, irregular mottles with a maximum diameter of 20 cm. The characteristic textural types are planar-e dolomites, planar-s dolomites and nonplanar xenotopic dolomites. The initial phase of dolomitization is characterised by the formation of scattered dull maroon to non-luminescent dolomite rhombs, in the later-phase xenotopic dolomites and stylolite/ fracture-related saddle dolomites were formed. These dolomites differ significantly from earlier ones both in CL luminescence and in geochemistry. The calcite cementation appears in several distinct phases. The first phase, the replacement of aragonite and high-Mg calcite by low-Mg calcite precedes the dolomitization. Later-phase karst-related calcite cementation is characterised by multiple generations of calcite fissures with generally no to dull luminescence having a highly negative stabile isotope composition. The first phase of dolomitization is proposed to occur in a shallow subsurface setting, and was enhanced by further overburden resulting in the formation of xenotopic and saddle dolomites. Later-phase karst-related processes caused the partial dedolomitization of former dolomites. The complexity of dolomite cementation, calcite cementation and dedolomitization is related to the complex geohistory of the region, to changes of fluid geochemistry and migration. Fissures caused by tectonic activity could have served as pathways for migrating fluids.

Original languageEnglish
Pages (from-to)441-462
Number of pages22
JournalActa Geologica Hungarica
Volume40
Issue number4
Publication statusPublished - Dec 1 1997

Keywords

  • Carbonate diagenesis
  • Cathodoluminescence
  • Dolomitization
  • Middle Triassic
  • Ramp
  • South Hungary
  • Stable isotope

ASJC Scopus subject areas

  • Geology

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