Raman microspectrometry of accumulated non-graphitized solid bitumens

Abstract

Solid bitumens (SB) occur accumulated in sedimentary, metasedimentary and volcanic rocks from the central and western part of the Bohemian Massif (Czech Republic). Structural features of asphaltic-like (ALSB) and hard (HSB) solid bitumens from sedimentary and metasedimentary rocks of Paleozoic and Precambrian age have been obtained using Raman microspectrometry. Structural and microtextural imaging were carried out using the lattice fringes mode of transmission electron microscopy (TEM). Weakly carbonized ALSB of sedimentary origin are characterized by a relatively high H/C atomic ratio (about 1) and differ from highly carbonized HSB from basaltic rocks (H/C atomic ratio about 0.1) which cross-cut a black shale formation of Upper Proterozoic age. Both these groups of accumulated forms of SB differ from dispersed kerogens, isolated from regionally metamorphosed black shales of the same primary sedimentary basin. First-order Raman spectra of both ALSB and HSB differ considerably from those obtained on dispersed carbonaceous matter forms from black shales and schists (from non-metamorphic to medium range biotite metamorphic zone). SB display a higher surface ratio of the 1350 to the 1582 cm-1 Raman bands (0.8–2.2) and higher half-width of the 1582 cm-1 (E2g) Raman band (65–73 cm-1) in comparison with dispersed forms (0.1–1.2 and 21–55 cm-1, respectively). Only HSB display second-order Raman spectra: the first band at 2680 cm-1 is broad and the second band at 2930 cm-1 is sharp. These features of the Raman spectra confirm the low structural order of SB, which is in agreement with X-ray and TEM results. © 1997 John Wiley & Sons, Ltd.