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

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.

Effects of sodium and potassium concentrations on dolomite formation rate, stoichiometry and crystallographic characteristics

“…It has long been noted that dolomites inferred to have formed in peritidal depositional environments under evaporative conditions are generally more abundant and exhibit higher stoichiometry than their non‐evaporative counterparts (Alderman, 1965; Lumsden & Chimahusky, 1980; Sass & Katz, 1982; Rosen et al ., 1989; Sun, 1994; Warren, 2000; Qing et al ., 2001; Machel, 2004; Eren et al ., 2007; Dravis & Wanless, 2018; Manche & Kaczmarek, 2021; Rivers et al ., 2021; Haas et al ., 2022; Noorian et al ., 2022). These observations are often interpreted within the framework of a popular dolomitization model referred to as hypersaline reflux (Adams & Rhodes, 1960; Hsü & Siegenthaler, 1969; Jiang et al ., 2013; Saller et al ., 2014; Dravis & Wanless, 2018; Haas et al ., 2022). According to this model, evaporation in restricted environments increases the density of seawater, causing it to seep downward and dolomitize underlying limestone strata (Adams & Rhodes, 1960).…”

Comparison of rapid preparation methods for Pb isotope analysis of high‐Pb ceramic glazes: A case study of late medieval Besztercebánya/Banská Bystrica‐type stove tiles

“…Pb sample solutions for isotope ratios were measured by a Neptune Plus multiple‐collector inductively coupled plasma mass spectrometry (MC‐ICP‐MS (Thermo Scientific) equipped with an Aridus‐3 (CETAC)) desolvating nebulizer system (dry plasma) at (ICER) in Debrecen, Hungary (Cavazzuti et al, 2021; Haas et al, 2022; Újváry et al, 2021). The raw measurement data were normalized to a standard solution of 35 ppb prepared from the NIST SRM 981 international Pb standard (National Institute of Standards and Technology).…”

Complex deformation history of the Keszthely Hills, Transdanubian Range, Hungary

“…From the end of the Middle Norian (Budai and Kovács, 1986) intraplatform basins opened, and some of them persisted into the Rhaetian. These intraplatform basins were filled up by the late Middle to Upper Norian Rezi Dolomite and the latest Norian-Rhaetian Kössen Marl (Budai and Kovács, 1986;Budai and Koloszár, 1987;Budai et al, 1999a;Haas, 1993;Csillag et al, 1995;Haas et al, 2021). The Rezi Formation is composed of dark-grey cherty, bituminous laminated dolomite with porous dolomite intercalations.…”

“…A detailed description of the eastern wall of the quarry can be found in the paper of Héja et al (2018). A recent study indicates that dolomitization of the matrix and the blocks themselves can be related to fault-driven fluid flow (Haas et al, 2021).…”

“…Blocks of this sedimentary breccia are frequently made up of redeposited carbonates of shallow water origin. These shallow water carbonates lithified shortly after sedimentation (Haas et al, 2021), which made its re-deposition as sedimentary breccia possible.…”