FLUOREN-9-ONES AND CARBAZOLES IN THE POSIDONIA SHALE, HILS SYNCLINE, NORTHWEST GERMANY

The distributions of alkylated fluoren-9-ones and carbazoles, includin g their benzo-and dibenzo- and/or naphtho-annellated derivatives, have been investigated in rock extracts from a maturity sequence of Posido nia Shales from the Hils Syncline of northwest Germany. The fluoren-9- one and carbazole derivatives are quantitatively the most important co mpound types in the low polar heterocompound fraction obtained from th e Posidonia Shale bitumens by liquid chromatography. This fraction com prises 9.3-27.5% of the total bitumen depending on maturity. The conce ntration of the fluoren-9-ones in the bitumens systematically increase s with increasing maturity. Generally, a trend of decreasing degree of alkylation is observed with increasing maturity. However, at the mole cular level, less systematic maturity-dependent variations are observe d for the fluoren-9-one distributions than for the carbazole distribut ions. A remarkable exception is the 1-ethylfluoren-9-one/(1-ethylfluor en-9-one + 1,8-dimethylfluoren-9-one) ratio which linearly decreases o ver the entire maturity range (0.48-1.45% R-r). Among the carbazoles, dibenzo-and/or naphtho-annellated derivatives become more abundant at higher maturity. An oxidation of fluorenes may be ruled out as the maj or process for the formation of fluoren-9-ones since Posidonia Shale w as deposited under anoxic conditions and fluorenes are not present in high amounts even in samples of low maturity. The fluoren-9-ones may r ather be produced by cyclisation reactions of suitable precursors in t he organic matter. Particularly, 2-carboxybiphenyls could be transform ed to fluoren-9-ones either catalysed by Lewis acids, e.g, clay minera ls, or solely under the influence of higher temperatures. The constant ratio of fluoren-9-ones and benzofluoren-9-ones suggests that selecti ve formation/degradation and interconversion during maturation plays a minor role. This seems to be different for the carbazoles where a sig nificant influence of maturity on the distribution of derivatives with different numbers of aromatic rings was observed. (C) 1998 Elsevier S cience Ltd. All rights reserved.