Abstract
Abstract In the Middle Anisian, extensional tectonic movements led to the development of isolated carbonate platforms in the area of the southwestern part of the Transdanubian Range. The platforms are made up of meter-scale peritidal–lagoonal cycles bounded by subaerial exposure surfaces. One of the platform successions (Tagyon Platform) consists predominantly of limestone that contains partially and completely dolomitized intervals, whereas the other one (Kádárta Platform) is completely dolomitized. Drowning of the platforms took place in the latest Pelsonian to the early Illyrian interval when submarine highs came into existence and then condensed pelagic carbonate successions with volcanic tuff interbeds were deposited on the top of the drowned platforms from the late Illyrian up to the late Ladinian. The comparative study of dolomitization of the coeval platforms, affected by different diagenetic histories, is discussed in the current paper. Traces of probably microbially-mediated early dolomitization were preserved in the slightly dolomitized successions of the Tagyon Platform. This might also have been present in the successions of the Kádárta Platform, but was overprinted by geothermal dolomitization along the basinward platform margin and by pervasive reflux dolomitization in the internal parts of the platform. The Carnian evolution of the two submarine highs was different, and this may have significantly influenced the grade of the shallow to deeper burial dolomitization.
Highlights
In spite of the efforts of generations of researchers, the main controlling factors and the mechanism of dolomite-forming processes are still rather enigmatic
In the Middle Anisian, extensional tectonic movements led to the development of isolated carbonate platforms in the area of the southwestern part of the Transdanubian Range
Drowning of the platforms took place in the latest Pelsonian to the early Illyrian interval when submarine highs came into existence and condensed pelagic carbonate successions with volcanic tuff interbeds were deposited on the top of the drowned platforms from the late Illyrian up to the late Ladinian
Summary
In spite of the efforts of generations of researchers, the main controlling factors and the mechanism of dolomite-forming processes are still rather enigmatic. The study of this section revealed that, the sedimentological characteristics of the exposed upper part of the completely dolomitized Tagyon Formations are similar to that of the Szentkiralyszabadja Quarry, the stable O and C isotope values are remarkably different. This means that a reconsideration and modification of the previous dolomitization are necessary; the story is probably more complex than was previously supposed. These results inspired the compilation of the current paper containing the results of our petrographic and isotope-geochemical studies of the recently exposed section of the Kadarta Quarry. The new data were compared to and combined with the results of the previous studies, providing the basis for the reconstruction of the history of platform evolution and for the evaluation of controlling factors and processes of dolomitization of the platform carbonates
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