aspects of organic geochemistry of nigerian coal university of ibadan

The predominance of C27 steranes in non-marine strata indicates a deep lake facies
and source input of plankton (algae) while C29 sterane predominance shows a swamp
shallow water environment and a terrestrial higher plant input (Volkman, 1986; Peters
and Moldowan, 1993; Volkman et al., 1999; Otto et al., 2005; Jauro et al., 2007).
C28 sterane is a unique biomarker signature of organic matter deposited in saline
lacustrine facies. Sterane/hopane ratio is often used as a measure of the relative inputs
of eukaryotic versus prokaryotic debris (Peters and Moldowan, 1993). Low
sterane/triterpane ratio (Norgate et al., 1999) has been postulated to favour terrestrial
paralic facies rather than peat swamp facies as organic matter source. Sterane
isomerisation at C-20 have been found useful in assessing the level of thermal
maturity of oil and sediments (Fig. 2.2). The 20S/20S+20R ratio (usually measured
using the C29ααα steranes) is one of the most widely applied molecular maturity
parameters in petroleum geochemistry (Farrimond et al., 1998). It is based on the
relative enrichment of the 20S isomer compared with the biologically inherited 20R
stereochemistry with increasing maturity.
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