Kerogen Elemental Analysis

Elemental Analysis of Kerogens (Normalized Ash-Free) Sample Information... 

Table I. Elemental analysis of "kerogens" of living plant, surface sediments and buried sediments from Abu Dhabi recent sedimentary system...

Organic petrography and organic element analysis reveal that the source of the kerogen is algal (lamosites dominating) while other maceral forms dominate locally to form carbonaceous shale and humic coals. 

Analytical methods are described in (2). Standard methods were employed for total organic carbon (TOC) and Fischer Assay (FA) analyses. Kerogen was isolated by solvent extraction to remove bitumen and acid dissolution to remove mineral matter. Elemental analysis was performed only on kerogen with low ash content (<25% by weight). 

Nevertheless, it is surprising how often one refers to elemental analysis to confirm the presence of a humic or fulvic acid. It is useful in determining whether a brown, macromolecular acidic material is from a coal, soil, marine sediment, or kerogen. It is most useful in characterizing structural trends in a specific environment, such as in sediments or soil profiles. Atomic ratios, especially 0/C ratios, are the simplest way to display elemental composition of humates. They also help one devise hypothetical structures for humates. As a guide in the synthesis of artificial humic substances, they are invaluable. In addition, atomic ratios help the investigator identify nonhumate contaminants. 

Figure 5a and Table la contain data for a set of samples taken from a 1500 m thick section of the Monterey shales. The kerogens were isolated (HCl, HCl/HF removal of carbonates and silicates and dilute nitric acid to remove the pyrite) for some of the core samples, but the total rock was used for the Rock Eval T ax determination to estimate maturation levels. The was measured for the extracted bitumen of each sample. The increase in T ax with depth is correlated with maturation indicating that burial of the samples increased their maturation. Two trends are indicated by the values one starts at +15.6 and increases to +17.7%o, and the second from +19.0 to +21.3%o. The data indicate that the bitumen produced at higher level of maturation is enriched with the heavier isotope. The elemental analysis of the bitumen shows that the shallowest (1400 m) sample has —11% S, whereas the deepest at 2490 m... 

The second column in Table 1.8 marks a limit corresponding to LMO occurrence inside which i is almost constant at 0.25 to 0.26 A (3.7 to 3.9 A). It occurs at 84 to 88 wt% C for all samples. These values correspond to an inflection point around 460°C in the curves of H/C t versus HTT. From series III kerogens to oil derivatives (except pitches), the slopes strongly decrease [3,76,89,91]. When the temperature of LMO occurrence was determined by eye in TEM (Table 1.6), the values obtained were almost constant at 460 to 475°C. The upper limit was arbitrarily chosen for LMO occurrence to obtain an elemental analysis that would be accurate enough. 

FIGURE 1.51 Pi versus Flmo for kerogens, coals, and asphaltenes (see samples in Table 1.9) with addition of oxidized samples. (From D. Joseph. L oxydation des matieres carbonSes. Thfese d Etat Orleans 1982. D. Joseph and A. Oberlin. Oxidation of carbonaceous matter, (a) Parti Elemental analysis andIR spectrometry. Carbon 21,559-564 (1983) (b) Part II X-ray diffraction and TEM. Carbon 21, 565-571 (1983). With permission.)... 

Wolbach, W. S., and Anders, E. (1989). Elemental carbon in sediments determination and isotopic analysis in the presence of kerogen. Geochim. Cosmochim. Acta 53, 1637-1647. 

Pyrolysates. The quantities of products from the pyrolysis experiments on the two kerogen samples, along with elements and isotope analysis... 

---