A spectroscopic investigation of the banding or lithotypes occurring in Victorian brown coal seams

Solid-state ¹³C n.m.r. and infrared spectroscopy were used to investigate the gross differences in chemical structural between the five primary lithotypes or coal bands present in Victorian brown coal seams. Examination of a series of coal lithotypes, along with their insoluble kerogen fractions, indicated significant structural variation between the light and dark samples, particularly in their aromaticities and levels of lignin-derived structures. Comparison of K₂₉₂₀ (cm mg⁻¹) and K₁₇₁₀ (cm mg⁻¹) infrared data revealed that the aliphatic C-H content did not exhibit the level of lithotype dependence shown by carbonyl/carboxyl concentration. Correlation with ¹³C n.m.r. data revealed a direct inverse relation between aromaticity and carbonyl/carboxyl content. Aromaticity and carbonyl/carboxyl content are suggested to be the main gross chemical structural properties affecting lithotype classification. Investigation of a depth profile of the light lithotype revealed that gross structural variation between the samples did not result from rank effects. Rather, the depth profile reflects minor depositional variations which did not affect their lithotype classification. The gross chemical characterization of the lithotypes supports paleobotanical interpretation regarding the different depositional environments and inputs responsible for the observed coal banding.