Geochemical characteristics of organic matter from overcoal sediments and dump materials (Maritza-East Coal Basin, Bulgaria)

The aims of the study were to characterize the geochemistry of organic matter from dump materials and overcoal sediments (Maritza-East Coal Basin, Bulgaria) as well as to try to find some differences among them from a chemical point of view. Three samples were studied: Sm. 1 – dump materials from “Iztok” Dump composed of a mixture of black clays and coals; Sm. 2 – gray schist-like clayey dump materials from ”Staroseletz” Dump; Sm. 3 – overcoal massive black clayey sediments from “Trojanovo-3 mine”.
   The samples were subsequently extracted by chloroform and ethanol-benzene (1:1, v/v). After asphaltene precipitation by n-hexane (1:50, v/v), the extracts were concentrated and subjected to Silicagel column chromatography separation. Solvents with increasing polarity were used for fractions preparation: n-hexane, for elution of alkanes/cycloalkanes (F. I); benzene for aromatic components (F. II); acetone for polar resins (F. III). Sulphur was removed from the first fraction by Cu grit treatment and thus cleaned F. I was studied by GC/MS. By specific m/z fragment monitoring different homologue series were detected, i.e. n-alkanes, steranes, hopanes, tricyclic terpanes, seco-hopanes, diterpanes, etc. The relative content of n-alkanes as well as their patterns of distribution was determined. CPI values and ratios of the regular isoprenoids Pristine (Pr) and Phytane (Ph) were calculated.
   The highest total, soluble and non-soluble organic matter (OM) content was obtained with dump materials from “Iztok” Dump (Sm. 1), lower values - were obtained with Sm. 2, and negligible ones - with Sm. 3. The same order kept the values for the yields of chloroform and ethanol-benzene bitumen A. Typical for all extracts is a domination of asphaltene over resins content. In Sm. 1 the aromatics content is higher compared to the alkane/cyclane fraction content. As for the other two samples - a reverse relation was established. For Sm. 1 and 2, short chain alkanes (nC₁₅-nC₂₀) content was lower than mid-chain alkanes (nC₂₁-nC₂₅) content, and the highest values were calculated for the sum of long chain homologues (nC₂₆- nC₃₃). For Sm. 3 - a reverse distribution pattern was observed, namely the lowest contents of long-chain alkanes was calculated. In all samples studied, the highest rel. % for n-alkanes was determined in the range nC₂₃-nC₂₉ which is an indication for terrestrial input in OM formation. This observation was also supported by the high values for the CPI ratio. The low content of the regular isoprenoid, i.e. Pr and Ph, and the low Pr/Ph ratio (< 1) were a hint to assume reductive conditions by the primary sediments deposition.
   Hopanes traced back by m/z 191 characteristic fragment show low (<2 rel. %) content. It should be emphasized that hopane distribution strongly differs for Sm. 1 and 3. In the first one (dump materials) “bio”– hopanes with ββ configuration and unsaturated hopanes dominate, and both feature to immature OM. For Sm. 3 (black clayey sediments) preponderant H27β hopane and H29ββ-H31ββ hopanes series were accompanied by hopanes with αβ configuration. In addition, in Sm. 3 only, tricyclic terpanes (6.6 rel. %) maximizing at C₂₃ homologue were registered. In the same sample only, a tetracyclic terpane, 17,21-secohopane, C₂₄, M⁺330 and steranes in the range of C₂₇-C₂₉ were recognized.
   In all samples studied the content of tetracyclic diterpenoid 16α(H)-Phyllocladane, M⁺274 (ca. 30 rel. %) is the highest among the diterpenoids. Simonellite (C₁₉H₂₄) was the other abundant (12.7 rel. %) tricyclic diterpenoid. The diterpenoids assemblage established could be interpreted as an indicator for gymnospermous Cupressaceae/ Taxodaceae presence in the former mire as a predominant palaeocommunity.
   Acknowledgements: The study is a part of project VU-11/06 financed by NSF, MES, Sofia, Bulgaria.