Precursor biostructures in kerogen matrix revealed by oxidative degradation: oxidation of kerogen from Estonian kukersite

The products of stepwise alkaline permanganate degradation of kerogen from Estonian kukersite are considered as possible derivatives of preserved bios tructures of the microfossil G. prisca. The aliphatic component, constituti ng ca, 25% of the matrix, was oxidized giving n-alpha,omega -alkyldicarboxy lic (C-4-C-15), alpha -methyldicarboxylic (C-7-C-12, C-14, C-15), branched dicarboxylic (C-5-C-10), and n-alkylmonocarboxylic (C-14-C-18, C-22) acids. When compared with previously studied kerogens, the oxidation products of kukersite differ (short carbon chains < C-20, dicarboxylic acids' maximum s hifted towards smaller number of carbon atoms, and a much higher degradatio n "loss") indicating that the aliphatic moieties in the kukersite kerogen c orrespond to unusually short carbon chains with significant alkylsubstituti on. The occurrence of such moieties is in agreement with the supposed featu re of the aliphatic components of the resistant biopolymer comprising G. pr isca cell walls. Hetero- and alicyclic structures constituting ca, 10% of t he matrix yielded C-6-C-18 alkyltri- and C-8-C-14 alkyltetracarboxylic acid s. The similarities in the distributions of alkyltri- and tetracarboxylic a cids (C-n(tri) vs. C-n-3(tetra)) suggested that the precursor moieties of t hose acids had the same source. Furthermore, similarities in the distributi on of n-alpha,omega -alkyldicarboxylic and alkyltetracarboxylic acids (C-n( di) vs. C-n+1(tetra)) may mean that some, at least, of these structures wer e produced diagenetically from terminally bifunctional alkyl-chains in pres erved biopolymers. Alkylsuccinic acids (C-10, C-11 and C-15) and alkylsucci nic acids containing an O-functional group in the alkyl chain (C-11-C-20), were obtained in appreciable yield (ca. 4% w/w of the matrix). Their precur sor moieties, although still unknown. were most probably structural buildin g blocks of the microfossil, Benzenediol derivatives, characteristic of kuk ersites, were not observed as they are not amenable to analysis using the m ethods employed in this study. (C) 2001 Elsevier Science Ltd. All rights re served.