THE REVIEW OF SOME NOVEL BIOMARKERS IN SEDIMENTARY ORGANIC MATTER
Annotatsiya
A series of novel C33-C35 hexacyclic benzohopanes have been identified in coals and crude oils \nof different ages from all over the world [1]. They differ from regular benzohopanes by the presence \nof methyl group in position C-31. These compounds are more abundant in coals and terrestrial oils. \nThe investigation also showed that mature samples have distributions of benzohopanes distinct from \nimmature ones, which are characterised by a greater number of benzohopane isomers. Although exact \nstructures of the additional isomers were not determined, it seems they were formed by an \nisomerisation of alkyl groups attached to the aromatic ring. \nTwo novel monoaromatic hydrocarbons (MW = 270; basic fragment ions m/z 255 and 146) \nwere identified in coals, mudstones and crude oils. Their structures were determined as cis- and transicetexa- \n8,11,13-trienes (or dehydroicetexanes) using NMR spectroscopy. Dehydroicetexanes are \npotential biomarkers of Cupressaceae (cypress conifers). \nBenzo[b]naphtho[d]furans (BNFs) have been identified in oils, condensates, source-rocks, \ncoals and coaly shales, being more abundant in the latter. We detected BNFs (m/z 218) in relatively \nhigh amounts in the aromatic fractions of pyrolysates of brown coals which attained the maturity \ncorresponding to vitrinite reflectance of 1.80 %Rr [2]. This result suggests that BNFs can be attractive \nfor investigations of mature fluids that originate from gas/condensate prone sources, rich in type III \nkerogen, which are usually depleted in biomarkers. Recently, it was observed that [2,1]/[1,2]BNF \nratio can be used to describe lithofacies [3]. This ratio is much lower in sediments from fluvial-deltaic \nsystems than in clay-depleted sediments from marine environments. \n1-Chloro-n-alkanes (m/z 91) have been identified in saltmarsh vegetation, recent sediments \nfrom estuarine setting and freshwater lake sediments [4]. Despite their absence in the investigated \ncrude oils, we identified a series of 1-chloro-n-alkanes in pyrolysates of the corresponding \nasphaltenes, obtained at 250 oC. This result indicates very good preservation of biomarkers occluded \ninside asphaltenes and announces a possible application of 1-chloro-n-alkanes in correlation studies.