International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

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Early-diagenetic dolomitization of Middle Triassic platform/ramp carbonates driven by geothermal convection in the Bükk Mts. (North Hungary)

Published: Apr 2024

Pages: 99 - 115

DOI: https://doi.org/10.31577/GeolCarp.2024.05

Authors: JÁNOS HAAS, TAMÁS BUDAI, NORBERT NÉMETH, GYÖRGY CZUPPON, KINGA HIPS, OLGA PIROS, ANDREA CZÉBELY, LÁSZLÓ RINYU, ORSOLYA GYŐRI

Abstract: Shallow marine carbonates of the Anisian Hámor Dolomite Formation in the Bükk Mountains, NE Hungary were studied to determine the mechanism and controlling factors of the dolomitization. Petrographic features, along with C and O stable isotope properties of the investigated rocks, indicate near-surface/shallow burial dolomitization of the shallow, subtidal–peritidal carbonate succession. This occurred via long-term circulation of relatively low-temperature fluid of sea-water origin. Geothermal convection may have been the driving force of this circulation. For application of this model, we need to assume that segmentation of a previously-established shallow ramp had already initiated in the Western Neotethys earlier in the middle Anisian. Unfortunately, we have only indirect evidence of this in the studied area. Still, the structural evolution and the related paleogeographic setting may have been the basic controlling factors of the pervasive early diagenetic near-surface/shallow burial dolomitization of the Hámor Formation. The coarse crystalline dolomite cement in the fractures and pores was precipitated from relatively high temperature (cc. 170 °C) water. Comparing the stable isotope values of the bulk rock and the fracture-occluding dolomite cement phase suggests a host-rock buffered fluid flow probably in the Late Cretaceous deformation phase.

Keywords: carbonate platform, dolomitization, stable isotopes, Middle Triassic, Bükk Mountains

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