Application of confocal laser-scanning microscopy (CLSM) to autofluorescent organic and mineral matter in peat, coals and siliciclastic sedimentary rocks — A qualitative approach

• The confocal laser-scanning microscopy (CLSM) method was applied to organic and mineral matters.
• Qualitative approach involved in situ characterization at micron to sub-micron scale.
• CLSM revealed fine scale microstructure in autofluorescent macerals.
• CLSM enabled projections and reconstruction of 3D morphology at high resolution.
• CLSM can be applied to autofluorescent organic matter in peat, coals, shales and bitumens.

Organic matter occurring in the form of macerals and natural solid bitumens in peats, coals, and siliciclastic sediments of various stratigraphic ages and locations was studied by means of conventional incident light microscopy and CLSM. Classical optical microscopic investigations are restricted by conventional 2-D imaging and are often hindered by the associated out-of-focus-blur effects. The qualitative application of CLSM overcomes these limitations, permitting to reveal precisely 3-D morphology and detailed microstructure of autofluorescent organic matter. The in depth examinations along Z-axis in XY, XZ, or YZ scanning modes at increments of 250 nm are capable to reconstruct 3-D internal configuration and arrangement occurring in autofluorescent macerals. The non-invasive and non-destructive laser-raster technique is applied to characterize in situ autofluorescent organic particles at micron to sub-micron scale resolution in polished whole rock pellets. In this study, we demonstrate that CLSM is suitable to (i) detect fine-scale microstructure of autofluorescent organic matter, (iii) reconstruct 3-D morphology at cellular and tissue level, (iii) analyze maceral composition in terms of its relicts and fragments beyond the classical optical assignment limits, (iv) detect and examine inorganic components enclosed in the embedding mineral-bituminous groundmass, and (v) differentiate mineral constituents from the remaining organic matter.CLSM as an optical microscopic technique was applied to generate high-resolution 2-D and 3-D images, projections as well as 3-D reconstructions of autofluorescent objects excited with aid of laser-induced light operating at variable visible wavelengths. CLSM is applicable to support microscopic studies of thermally immature and mature organic matter within the oil and early gas windows enclosed either within siliciclastic and carbonate sediments or in peat and low to medium rank coals.The application of this technique will be of great interest to a wide range of geology related disciplines such as petroleum geology, biostratigraphy, marine geology, peat petrography, and archeology.