The advantages of using n -alkanes, triterpane, and steranes to determine the characterization of sedimentary organic ma
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ORIGINAL PAPER
The advantages of using n-alkanes, triterpane, and steranes to determine the characterization of sedimentary organic matter Adel Arfaoui
Received: 6 October 2012 / Accepted: 11 December 2012 # Saudi Society for Geosciences 2012
Abstract The current geochemical study of n-alkanes, steranes, and triterpanes in bitumen from the Late Maastrichtian–Paleocene El Haria organic-rich facies in West of Gafsa, southern Tunisia, was performed in order to characterize with accuracy their geochemical pattern. The type of organic matter as deduced from nalkanes, steranes, and triterpanes distributions is type II/ III mixed oil/gas prone organic matter. Isoprenoids and biomarkers maturity parameters (i.e., Ts/Tm, 22S/(22S+ 22R) of the C31 αβ-hopanes ratios, 20S/(20R + 20S) and ββ/(ββ + αα) of C 29 steranes), revel that the organic-rich facies were deposited during enhanced anoxic conditions in southern Tunisa. The organic matter is placed prior to the peak stage of the conventional oil window (end of diagenesis–beginning of catagenesis). All these result are suggested by total organic carbon analysis, bitumen extraction and liquid chromatography data. Thus, the n-alkanes, triterpane, and steranes study remains valuable and practical for geochemical characterization of sedimentary organic matter. Keywords Southern Tunisia . Organic matter . n-alkanes/ steranes/triterpanes
Research highlights • Organic matter characterization on the basis of combination by confrontation of total organic carbon analysis, bitumen extraction, liquid chromatography, and gas chromatography–mass spectrometry analysis. • Utility of biomarker in the characterization of the source and the depositional environment of Upper Cretaceous– Palaeocene organic matter • Oriented the hydrocarbon exploration to the southern Tunisia. A. Arfaoui (*) Research Unit of Macromolecular Biochemistry and Genetics, B.MG. 05/UR/09-14, Sciences Faculty, Department of Earth Sciences, University of Gafsa, Sidi Ahmed Zarroug, P.O. Box 2112, Gafsa, Tunisia e-mail: [email protected]
Introduction The organic geochemical characterization of sedimentary source rocks is typically based on various analytical techniques, such as total organic carbon (TOC) analysis, bitumen extraction, and liquid chromatography. In addition, gas chromatography–mass spectrometry (GC/ MS) analysis has been popular in the past few decades, mainly because of its advantages in detecting complex polycyclic biomarkers biological precursors produced by plants, bacteria, and algae. Biomarkers analysis of aliphatic fractions such as n-alkanes, steranes, and pentacyclic triterpanes and their derivatives have received much attention in past few decades, mainly because of their usefulness as organic matter types and quality, depositional condition (e.g., salinity, oxicity, anoxicity, etc.), assessment of maturity level, biodegradation extent, and lithology. Such features have made biomarkers potentially applicable to oil-to-oil correlations (Waples and Machihara 1991; Isaksen 1993; Peters and Moldowan 19
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