Implications for peat formation in Maritsa-West Basin, SE Bulgaria: Insights from organic petrology, palynology and biomarker assemblage

Alexander Zdravkov, Maya Stefanova, Elzbieta Worobiec, Achim Bechtel, Stefan Marinov, Jordan Kortenski

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung

3 Zitate (Scopus)

Abstract

The paper reports the results of the organic petrological, palynological and geochemical characterization of lignite samples from the Kipra lignite seam (Late Miocene, Maritsa-West Basin, Bulgaria). The bulk of the organic matter (OM) is represented by highly gelified detrohuminite with locally abundant leaf-derived ulminite. Liptinite group is characterized by predominance of microsporinite and liptodetrinite, locally with cutinite and fluorinite. Terpene resinite and suberinite are rare. Low TPI and high GI indices indicate peat formation from vegetation with low preservation potential, deposited under water-logged environment of marsh- or fen-type. The palynological results reveal a vegetational community representing different habitats (i.e. mesophytic, marginal and aquatic). The relatively poor preservation of the palynomorphs, however, suggests vegetation that was more diverse during peat formation. Although gymnosperm palynomorphs predominate, the gymnosperm organic matter contribution was probably minor as indicated by the low contents of sesqui- and diterpenoid biomarkers. Because of the absence of triterpenoid biomarkers of neither oleanane, nor lupane or ursane-type, it is considered that angiosperms that do not synthesize their precursors predominated, or the depositional environment had unfavorable characteristics, which prevented the transformation of the triterpenoid precursors. The extractable organic matter yield from the Kipra lignite is low, and dominated by saturated compounds, while polar compounds and asphaltenes occur in low amounts. Aromatic compounds are completely absent. The saturated hydrocarbons are mainly composed of n-alkanes, accompanied by minor amounts of branched- (including isoprenoids) and cycloalkanes, sesqui- and diterpenoids, steroids and hopanoids. Straight chain alkanes are prevailed by long-chain homologues, but show rather mature distribution with CPI ~ 1. Biological (e.g. bacterial) activities and/or environmental control are considered as the main factor/s controlling the observed uncommon n-alkane distributions. A rather uncommon pentacyclic terpenoid, i.e. onocerane I, was tentatively identified in one sample, based on its characteristic fragmentation pattern. Based on its presence, a very specific plant community is considered, and/or specific palaeoenvironmental conditions occurred at least temporarily during the peat formation. However, the responsible plants could not be identified. The low amounts of hopanoid biomarkers, together with the low amounts of n-alkanones, are consistent with limited aerobic biodegradation of the plant remains. The mature 22S/(22S + 22R) C 30 hopane ratio (~ 0.55), as well as the random huminite reflectance values (~0.3–0.4%), which are more than twice higher than previously reported, argue for a local increase of coalification degree, presumably due to increased thermal influx around major faults.

OriginalspracheEnglisch
Aufsatznummer103447
Seitenumfang18
FachzeitschriftInternational journal of coal geology
Jahrgang222.2020
Ausgabenummer1 April
Frühes Online-Datum13 März 2020
DOIs
PublikationsstatusVeröffentlicht - 1 Apr. 2020

Bibliographische Notiz

Funding Information:
Financial support from the Bulgarian Science-Research Fund through projects VU 05/06 and DN-04/5 is greatly acknowledged. In addition, we would like to express our sincere gratitude to Prof. Dr. I. Kostova and Dr. D. Apostolova (Sofia University “St. Kl. Ohridski”) for their support with huminite reflectance measurements. The palynological study was supported by the W. Szafer Institute of Botany , Polish Academy of Sciences , through its statutory funds. We would like to thank Grzegorz Worobiec (W. Szafer Institute of Botany PAS) for his help in photographing palynomorphs. The paper benefitted also from the critical reviews of two anonymous reviewers.

Publisher Copyright:
© 2020 Elsevier B.V.

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