Variations in organic geochemistry and lithology of a carbonate sequence deposited in a backplatform basin (Triassic, Hungary)

M. Hetényi, Alice Brukner-Wein, Csanád Sajgó, J. Haas, Mária Hámor-Vidó, Z. Szántó, Mária Tóth

Research output: Contribution to journalArticle

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Abstract

The variations in the organic matter quantity and quality were studied with respect to the mineral composition of the carbonate sequences accumulated on a gentle slope (Zl-1 well) and at the toe of the slope (Rzt-1 well) located between a Late Triassic carbonate platform and a backplatform basin. Parallel variations observed in mineral composition and organic geochemical features of the successions appeared to be controlled by the change in climate and by sea-level fluctuations. The repetitive sea-level changes resulted in a variation in the carbonate-rich basin facies and in the mineralogically heterogenous slope and toe-of-slope ones. According to Rock Eval pyrolysis, organic petrography and carbon isotope ratios, the immature organic matter is of predominantly marine origin and composed of mainly liptinites in both of the studied boreholes. The results of the GC and GC/MS analyses of the saturated hydrocarbon fractions of bitumens together with the composition of kerogen pyrolysates reveal a predominant algal input with a minor variable bacterial and subordinate terrestrial contribution for the Rzt-1 borehole. In the Zl-1 borehole a significantly higher proportion of the bacterial biomass contributed to the organic precursors. The δ13C values and the composition of the kerogen pyrolysates together with the results of the maceral analysis and GC data suggest a relatively higher, but moderate, higher plant derived contribution in the slope facies and at the top of the toe-of-slope facies. The elementary composition of kerogens and Rock Eval data display type II-S kerogen in the basin and the slope facies, and type I-II-S one in the toe-of-slope facies. Variations in the hydrogen content of the organic matter mainly reflect variations in the preservation conditions and in primary productivity. The presence of the 2,6,10,15,19-pentamethyleicosane and the extremely low pristane/phytane ratios indicate a relatively high methanogenic bacterial activity and strongly anoxic depositional conditions in the Rzt-1 well, especially in two most organic-rich toe-of-slope facies.

Original languageEnglish
Pages (from-to)1571-1591
Number of pages21
JournalOrganic Geochemistry
Volume33
Issue number12
DOIs
Publication statusPublished - 2002

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organic geochemistry
Geochemistry
Lithology
Carbonates
Kerogen
lithology
Triassic
carbonate
Boreholes
Biological materials
Chemical analysis
basin
kerogen
Sea level
Minerals
Rocks
Carbon Isotopes
Petrography
borehole
organic matter

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Variations in organic geochemistry and lithology of a carbonate sequence deposited in a backplatform basin (Triassic, Hungary). / Hetényi, M.; Brukner-Wein, Alice; Sajgó, Csanád; Haas, J.; Hámor-Vidó, Mária; Szántó, Z.; Tóth, Mária.

In: Organic Geochemistry, Vol. 33, No. 12, 2002, p. 1571-1591.

Research output: Contribution to journalArticle

Hetényi, M. ; Brukner-Wein, Alice ; Sajgó, Csanád ; Haas, J. ; Hámor-Vidó, Mária ; Szántó, Z. ; Tóth, Mária. / Variations in organic geochemistry and lithology of a carbonate sequence deposited in a backplatform basin (Triassic, Hungary). In: Organic Geochemistry. 2002 ; Vol. 33, No. 12. pp. 1571-1591.
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