Dolomitization of Late Norian carbonate deposits of restricted basin facies in the Keszthely Mts., Transdanubian Range, Hungary

János Haas,Tamás Budai,Gábor Héja,Anikó Horváth,György Czuppon,Orsolya Győri,Kinga Hips

doi:10.1007/s00531-021-02113-w

Abstract

In the Transdanubian Range (Hungary), a wide spectrum of Triassic dolomites is known. Mechanism of dolomitization of the platform carbonate successions was subject of a number of studies but the study of dolomitization of basinal carbonates is very limited. Petrographical and isotope–geochemical characteristics of the Upper Triassic dolomitized carbonate deposits, formed in a fault-controlled intraplatform basin, and interpretation of the dolomite-forming processes are presented in the current paper. From the latest Carnian to Middle Norian under semi-arid climatic conditions density-driven flux of seawater derived mesohaline fluids was the dominant mechanism of the near-surface pervasive dolomitization of the thick platform carbonate succession. In the late Middle Norian incipient rifting of the Alpine Tethys led to establishment of an extensional structural regime and onset of the formation of the Kössen Basin. In the study area, above the dolomitized platform carbonate succession, platform-derived carbonate sediments were accumulated in a fault-bounded, semi-restricted sub-basin of the Kössen Basin, whereas talus breccias and debrites were deposited near a basin-bounding master fault. The basin deposits (lower and upper members of the Rezi Dolomite Formation) were subject of early diagenetic dolomitization in shallow burial setting. Enhanced salinity seawater was the dolomitizing fluid; the synsedimentary fracturing may have promoted the fluid flow and thereby the dolomitization. Thick-bedded carbonates (middle member of the Rezi Dolomite Formation) representing a progradational tongue of the ambient platform are intercalated between the basin deposits. The dolomitization of this unit can be explained by the reflux model.

Highlights

In spite of more than 200 year research activity of generations of earth scientists, many aspects of the dolomite genesis are still rather enigmatic
In the area of the Keszthely Mts., the pervasive dolomitization of the Norian carbonate sediments was the result of near-surface early diagenetic processes that were controlled mainly by the paleogeographic setting, the climatic conditions, and the structural evolution of the region
In the latest Carnian a widely extended carbonate platform system came into being in the area of the TRU that was a sector of the passive margin of the western Neotethys Ocean

Summary

Introduction

In spite of more than 200 year research activity of generations of earth scientists, many aspects of the dolomite genesis are still rather enigmatic. Understanding of the syndepositional/penecontemporaneous dolomite forming processes is strongly hampered by the facts that there are only a few examples for dolomite formation in recent/ sub-recent deposits and the laboratory experiments for the reconstruction of dolomite formation under surface conditions have not yielded unambiguous results (McKenzie 1991; Purser et al 1994; Land 1998; Machel 2004; Gregg et al 2015). Due to these aspects, the case studies are still. That is why the presentation of petrographical and geochemical characteristics of the dolomitized slope and basin dolomites and interpretation of the dolomite-forming processes are placed into the focus of the current paper

Methods

Results

Discussion

Conclusion