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Re-arranged hopanes and novel re-arranged tricyclic terpanes in Paleozoic rock extracts and oils in the Anadarko Basin, Oklahoma

2022; Elsevier BV; Volume: 173; Linguagem: Inglês

10.1016/j.orggeochem.2022.104493

1873-5290

Paul Philp, Matthew Wood, Yagmur Sumer Gorenekli, Thanh X. Nguyen, Gregory T. Connock, Catherine Pezzaro, Carl Symcox, Damián Villalba,

NMR spectroscopy and applications

An ongoing study of oils and Paleozoic source rock extracts from the Anadarko Basin, Oklahoma, revealed the presence of multiple series of novel tricyclic terpanes in addition to the commonly observed series of 13β(H),14α(H) tricyclic terpanes. The precise structures of these novel tricyclic compounds are not known but several proposed spectral and chromatographic similarities with known compounds suggests the tentatively identified analytes are rearranged and structural isomers of the 13β(H),14α(H) tricyclic terpanes. The occurrences and relative abundances of these compounds are predominantly lower in more carbonate-rich formations, which implies a potential role of clay minerals in their formation. The presence and distributions of these unique tricyclic terpane configurations are seemingly unaffected by thermal maturation, although relative concentrations may increase as a result of preferential thermal degradation of the less thermally-stable hopanes. Many of the samples bearing the novel rearranged tricyclic terpanes also contain varying proportions of four previously reported series of rearranged hopanes, which are formed via rearrangement reactions catalyzed by clay minerals. The rearranged hopanes include the commonly observed Ts and C30 diahopanes in addition to 9,15-dimethyl rearranged hopanes and 21-methyl-28,30-dinorhopanes (28-norspergulanes) that have been previously reported in a number of basins worldwide but not the Anadarko Basin. No apparent relationship was identified between the presence of the rearranged tricyclic terpanes and the rearranged hopanes. Both groups require the presence of clay minerals, as determined from empirical relationships with source rock lithology, and are observed to co-occur in many of the samples studied. Still, the lack of a clear correlation between rearranged tricyclic terpanes and rearranged hopanes suggests additional controls, beyond lithology, on their genesis and preservation in the geologic record.