DENSITY GRADIENT CENTRIFUGATION - APPLICATION TO THE SEPARATION OF MACERALS OF TYPE-I, TYPE-II, AND TYPE-III SEDIMENTARY ORGANIC-MATTER

Samples of organic matter from nine well-known geological units (Green River Fm., Tasmanian Tasmanite, Lower Toarcian Sh. of the Paris Basin , Duwi Fm., New Albany Sh., Monterey Fm., Herrin No. 6 coal, Eocene co al, and Miocene lignite from Kalimantan) were processed by density gra dient centrifugation (DGC) to isolate the constituent macerals. Optima l separation, as well as the liberation of microcrystalline pyrite fro m the organic matter, was obtained by particle size minimization prior to DGC by treatment with liquid Nz and micronization in a fluid energ y mill. The resulting small particle size limits the use of optical mi croscopy, thus microfluorimetry and analytical pyrolysis were also emp loyed to assess the quality and purity of the fractions. Each of the s amples exhibits one dominant DGC peak (corresponding to alginite in th e Green River Fm., amorphinite in the Lower Toarcian Sh., vitrinite in the Herrin No. 6, etc.) which shifts from 1.05 g mL(-1) for the Type I kerogens to between 1.18 and 1.23 g mL(-1) for Type II and II-S. The characteristic densities for Type III organic matter are greater stil l, being 1.27 g mL(-1) for the hydrogen-rich Eocene coal, 1.29 g mL(-1 ) for the Carboniferous coal and 1.43 g mL(-1) for the oxygen-rich Mio cene lignite. Among Type II kerogens, the DGC profile represents a com positional continuum from undegraded alginite through (bacterial) degr aded amorphinite; therefore chemical and optical properties change gra dually with increasing density. The separation of useful quantities of macerals that occur in only minor amounts is difficult. Such separati ons require large amounts of starting material and require multiple pr ocessing steps. Complete maceral separation for some samples using pre sent methods seems remote. Samples containing macerals with significan t density differences due to heteroatom diversity (e.g., preferential sulfur or oxygen concentration in the one maceral), on the other hand, may be successfully separated (e.g., coals and Monterey kerogen).