Carbonaceous kerogen

The isotopic composition of carbon in carbonaceous organic material (kerogen) from ancient sedimentary rocks gives information on whether photosynthetic organisms were present during rock formation or not. It can also provide information on biological activities if cellular structures had already been destroyed. Sulphur can be used in a similar way (Schopf, 1999). 

The Murchison meteorite shown in Figure 6.7, like all meteorites, is named after the place from which it was recovered and in this case it is the town of Murchison, Victoria in Australia about 100 km north of Melbourne. The fall occurred in 1969 and was followed by an analysis of the chemical composition in some considerable detail. The Murchison meteorite is a carbonaceous chondrite containing about 2 per cent carbon, some as inorganic carbonates, and some as soluble compounds such as amino acids but the bulk as a macromolecular heterogeneous material referred to as kerogen. 

The kerogen-like material from the Murchison meteorite is shown in Figure 6.8 and consists of a rich macromolecular carbonaceous material made from aromatic and aliphatic compounds observed in fluorescence following excitation at 280 nm. 

Kerogen The carbonaceous material found around minerals and chondrules in meteorites such as the Murchison meteorite. 

Kerridge JF (1983) Isotopic composition of carbonaceous-chondrite kerogen evidence for an interstellar origin of organic matter in meteorites. Earth Planet Sci Lett 64 186-200 Kerridge JF, Haymon RM, Kastner M (1983) Sulfur isotope systematics at the 21°N site. East Pacific Rise. Earth Planet Sci Lett 66 91-100... 

Kerridge JF, Chang S, Shipp R (1987) Isotopic characterization of kerogen-hke material in the Murchison carbonaceous chondrite. Geochim Cosmochim Acta 51 2527-2540 Kharaka YK, Berry FAF, Friedman I (1974) Isotopic composition of oil-field brines from Kettle-man North Dome, California and their geologic implications, Geochim Cosmochim Acta 37 1899-1908... 

We start out by considering the effect of such adsorption sites on the isotherms of apolar and weakly monopolar compounds. For these types of sorbates, hydrophobic organic surfaces and/or nanopores of carbonaceous materials are the most likely sites of adsorption. Such hydrophobic surfaces may be present due to the inclusion of particles like coal dust, soots, or highly metamorphosed organic matter (e.g., kerogen). Because of the highly planar aromatic surfaces of these particular materials, it is reasonable to assume that planar hydrophobic sorbates that can maximize the molecular contact with these surfaces should exhibit higher affinities, as compared to other nonplanar compounds of similar hydrophobicity. 

Kerogen a complex carbonaceous (organic) material that occurs in sedimentary rocks and shales generally insoluble in common organic solvents. 

Stricktly speaking, kerogens are always inhomogeneous and always contain impurities" such as graphite particles, carbon-black carbonaceous particles at various degrees of metamorphic alteration and mineral impurities. An electron microscope is a particularily suitable tool for studying these phases present in kerogens, since particles less than 1 pm can be examined (Oberlin et al., 1980) 19). 

The find has the size and shape of a cell and consists of fossilized carbonaceous matter (kerogen). The body can be separated from the rock by demineralization and then remains as a coherent spherical or filamental skin. 

About 70-95% of the organic matter in carbonaceous chondrites consists of an ill-defined, insoluble macromolecular material, often referred to as polymer or kerogen . A typical elemental composition for Murchison polymer (Hayatsu et al., 1980a), on a dry, ash-free basis, is C 76.5%, H 4.5%, N 2.4%, S 4.3%, and O 12.4% (by difference). 

Two examples in which the solid itself is reactive are the shale oil retorts of Figure 17.29. Crushed oil shale is charged at the top, air and gaseous fuel at the bottom. When the shale moving downward reaches a temperature of 900°F, the kerogen decomposes into oil vapor, gas, and carbonaceous residue. There are many designs of pilot plant retorts, but the only commercial units at present are in the USSR and China. 

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. 

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