RAMAN MICROSPECTROMETRY OF ACCUMULATED NON-GRAPHITIZED SOLID BITUMENS

Solid bitumens (SB) occur accumulated in sedimentary, metasedimentary and volcanic rocks from the central and western part of the Bohemian M assif (Czech Republic). Structural features of asphaltic-like (ALSB) a nd hard (HSB) solid bitumens from sedimentary and metasedimentary rock s of Paleozoic and Precambrian age have been obtained using Raman micr ospectrometry. Structural and microtextural imaging were carried out u sing 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 car bonized HSB from basaltic rocks (H/C atomic ratio about 0.1) which cro ss-cut a black shale formation of Upper Proterozoic age. Both these gr oups of accumulated forms of SB differ from dispersed kerogens, isolat ed from regionally metamorphosed black shales of the same primary sedi mentary basin. First-order Raman spectra of both ALSB and HSB differ c onsiderably from those obtained on dispersed carbonaceous matter forms from black shales and schists (from nonmetamorphic to medium range bi otite 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) (E-2g) Raman band (65-73 cm(-1)) in comparison with dispe rsed 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. (C) 1997 John Wiley & Sons, Ltd.