Assessing the quantitative reliability of solid-state 13C NMR spectra of kerogens across a gradient of thermal maturity.
Five type II kerogens, shown by elemental analysis and Rock-Eval pyrolysis to represent a gradient of thermal maturity, were further characterized using a range of solid-state 13C NMR spectroscopic techniques. 13C cross polarization (CP) NMR spectra of the kerogens confirmed the well-established pattern of increasing aromaticity with increasing thermal maturity. Spin counting showed that CP observability was around 50% for the immature kerogens, and only 14-25% for the mature kerogens. Spin counting also showed that the direct polarization (DP) observabilities were >80% for all but one of the kerogens. Despite the large differences in observability between the two techniques, aromaticities derived from corresponding CP and DP spectra differed by only 1-15%. The RESTORE technique showed that the low CP observability of the immature kerogens was due mostly to rapid T(1rho)H relaxation, whereas both rapid T(1rho)H relaxation and slow polarization transfer contributed to the low CP observability of the mature kerogens.
Smernik
Ronald J
RJ
Soil and Land Systems, School of Earth and Environmental Sciences, The University of Adelaide, Waite Campus, Urrbrae, SA 5064, Australia. ronald.smernik@adelaide.edu.au
Schwark
Lorenz
L
Schmidt
Michael W I
MW
D002247:Carbon Isotopes; D019015:Geologic Sediments / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009930:Organic Chemicals / Q000032:analysis*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012995:Solubility; D013057:Spectrum Analysis / Q000379:methods*; D013696:Temperature
D002247:Carbon Isotopes; D009930:Organic Chemicals