CHANGES IN MOLECULAR BIOMARKER AND BULK CARBON SKELETAL PARAMETERS OFVITRINITE CONCENTRATES AS A FUNCTION OF RANK

A sequential extraction scheme to differentiate between molecular alka nes and those covalently-bound to the macromolecular structure has bee n applied to a suite of vitrinite concentrates handpicked from six UK bituminous coals covering the rank range % R(o) = 0.47-1.32 (at 546 nm ). The aim was to ascertain whether the biomarker maturity indices (i) were consistent with the measured vitrinite reflectance values and (i i) differ markedly for the easily extractable, clathrated, and covalen tly-bound phases. The quantitatively reliable single-pulse excitation (SPE) solid state C-13 NMR technique has also been used to elucidate t he changes in the bulk vitrinite structure across the relatively narro w rank range investigated. Although both hopane and methylphenanthrene parameters for easily extractable species are sensitive to small vari ations in vitrinite reflectance, significant variations have been foun d between the biomarker parameters for easily extractable, clathrated, and covalently-bound material. In general, the steric protection affo rded to covalently-bound biomarker species by the macromolecular struc ture make the latter less mature, as reflected by the hopane, sterane, and methylphenanthrene parameters, than the easily extractable and cl athrated molecular species. Solid state C-13 NMR revealed that the var iations in carbon aromaticity and the degree of condensation of the ar omatic structure occurring in the % R(o) range of ca. 0.45-0.80 are re latively small.