Chemometric study of functional groups in Pennsylvanian gymnosperm plant organs (Sydney Coalfield, Canada): Implications for chemotaxonomy and assessment of kerogen formation

摘要

The samples comprise the foliage of four pteridosperm-medullosalean plant fossil species of differing preservation states and one of a cordaitean species from two Canadian Maritime sub-basins of Carboniferous age (300. Ma; Sydney and Stellarton coalfields, Nova Scotia, respectively). Included in the sample set were some coal samples from Sydney Coalfield, along with published data for coal macerals for comparison. By applying Schulze's maceration process to the fossil foliage to obtain the cuticles, five sample forms evolved, viz. compressions, cuticles and fossilized cuticles, and acidic and alkaline solutions from Schulze's process, to which was added the Sydney coal samples as the sixth form. Area integration of the absorbance spectra from solid and liquid state Fourier transform infrared (FTIR) spectroscopy, produced functional chemical parameters which were organized into a data matrix of eight variables and 62 samples (8 × 62 matrix). Since we were interested in grouping the sample forms as a function of phytochemistry (functional groups) to assess primarily the palaeophytotaxonomic potential as a general approach to Carboniferous taxonomy, principal components were extracted from the matrix, and a subset of 4 × 33 samples in order to refine the grouping results from the initial component analysis. In each case, a two component model resulted, accounting for least 80% of the cumulative variance.Overall, the results are encouraging in offering increasing support for fossil-leaf chemotaxonomy, but bearing in mind the limited sampling number (56) and restricted sampling of genera (5). Apart from this general conclusion, which supports our previous FTIR work vis-à-vis chemotaxonomy, we noted functional-group similarities in our FTIR data with types of kerogen and coal macerals. On this basis, we hypothesize that, in combination with the different preservation states of our fossil specimens, these factors have a bearing on kerogen genesis from plant material, i.e. the oil and gas prone Types I and II.