Genesis of Upper Triassic peritidal dolomites in the Transdanubian Range, Hungary

J. Haas, Georgina Lukoczki, Tamás Budai, A. Demény

Research output: Article

9 Citations (Scopus)

Abstract

In the Late Triassic, a 2–3-km-thick platform carbonate succession formed along the passive margin of the Tethys Ocean. Certain parts of the succession were affected by pervasive dolomitization whereas other parts are only partially dolomitized or non-dolomitized. In the Transdanubian Range, Hungary, the Upper Triassic platform carbonates are extensively distributed and numerous data are available for the space and time relations of the dolomitized and non-dolomitized units. This geological setting provides a unique opportunity for the study of paleogeographical and diagenetic controls of dolomitization of the whole platform complex. This paper presents the characteristic features of the dolomite types of the dolomite-bearing formations and lithofacies types, with a view to interpret the dolomite-forming processes and to determine the main controlling factors of the dolomite genesis. Petrographic features and stable isotope characteristics of the studied successions suggest the predominance of penecontemporaneous and early diagenetic dolomite genesis. Study of the transitional interval between the pervasively dolomitized and the non-dolomitized sequences revealed the general presence of microcrystalline dolomite in the peritidal microbial deposits and the characteristics of partial dolomitization both in the peritidal and subtidal facies. In the peritidal facies, microbially induced Ca–Mg carbonate precipitation is inferred, which was probably complemented by penecontemporaneous mimetic dolomitization of precursor carbonates due to evaporative pumping or seepage influx. Dolomitization of the subtidal facies took place via reflux of slightly evaporated seawater. Dolomitization of the previously deposited carbonate mud commenced during subsequent subaerial exposure but the process of early diagenetic dolomitization may have continued during later exposure events. Recurring subaerial exposure is one of the factors that determine the areal extent of the early dolomitization of the platform carbonates. However, climatic conditions were also crucial. Although the sea-level-controlled, unconformity-bound cyclic facies pattern did not change significantly in the internal platform belt during the nearly 20-My-long time range, a drier climate favored dolomite formation while increasing humidity led to a gradual decreasing intensity of early dolomitization.

Original languageEnglish
Pages (from-to)1-28
Number of pages28
JournalFacies
Volume61
Issue number3
DOIs
Publication statusPublished - júl. 1 2015

Fingerprint

dolomitization
dolomite
Triassic
carbonate platform
subaerial exposure
carbonate
passive margin
Tethys
lithofacies
unconformity
seepage
pumping
humidity
stable isotope
mud
sea level
seawater
climate
ocean

ASJC Scopus subject areas

  • Geology
  • Palaeontology
  • Stratigraphy

Cite this

Genesis of Upper Triassic peritidal dolomites in the Transdanubian Range, Hungary. / Haas, J.; Lukoczki, Georgina; Budai, Tamás; Demény, A.

In: Facies, Vol. 61, No. 3, 01.07.2015, p. 1-28.

Research output: Article

Haas, J. ; Lukoczki, Georgina ; Budai, Tamás ; Demény, A. / Genesis of Upper Triassic peritidal dolomites in the Transdanubian Range, Hungary. In: Facies. 2015 ; Vol. 61, No. 3. pp. 1-28.
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N2 - In the Late Triassic, a 2–3-km-thick platform carbonate succession formed along the passive margin of the Tethys Ocean. Certain parts of the succession were affected by pervasive dolomitization whereas other parts are only partially dolomitized or non-dolomitized. In the Transdanubian Range, Hungary, the Upper Triassic platform carbonates are extensively distributed and numerous data are available for the space and time relations of the dolomitized and non-dolomitized units. This geological setting provides a unique opportunity for the study of paleogeographical and diagenetic controls of dolomitization of the whole platform complex. This paper presents the characteristic features of the dolomite types of the dolomite-bearing formations and lithofacies types, with a view to interpret the dolomite-forming processes and to determine the main controlling factors of the dolomite genesis. Petrographic features and stable isotope characteristics of the studied successions suggest the predominance of penecontemporaneous and early diagenetic dolomite genesis. Study of the transitional interval between the pervasively dolomitized and the non-dolomitized sequences revealed the general presence of microcrystalline dolomite in the peritidal microbial deposits and the characteristics of partial dolomitization both in the peritidal and subtidal facies. In the peritidal facies, microbially induced Ca–Mg carbonate precipitation is inferred, which was probably complemented by penecontemporaneous mimetic dolomitization of precursor carbonates due to evaporative pumping or seepage influx. Dolomitization of the subtidal facies took place via reflux of slightly evaporated seawater. Dolomitization of the previously deposited carbonate mud commenced during subsequent subaerial exposure but the process of early diagenetic dolomitization may have continued during later exposure events. Recurring subaerial exposure is one of the factors that determine the areal extent of the early dolomitization of the platform carbonates. However, climatic conditions were also crucial. Although the sea-level-controlled, unconformity-bound cyclic facies pattern did not change significantly in the internal platform belt during the nearly 20-My-long time range, a drier climate favored dolomite formation while increasing humidity led to a gradual decreasing intensity of early dolomitization.

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KW - Upper Triassic

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