Molecular characterization of organic matter in sediments from the Keg River formation (Elk Point group), western Canada sedimentary basin

Distributions of free and sulfur-bound biomarkers in organic-rich sediments from the lower and upper Keg River formation (Elk Point group, western Can ada) reveal deposition of these sediments under reducing conditions, in agr eement with the geological data. The predominance of aryl isoprenoids of Ch lorobiaceae origin indicates that photic zone anoxia occurred during time o f deposition. A series of novel aryl isoprenoids with a carboxylic acid fun ction was identified by GC-MS and the structure of the predominant 3-methyl -5-(2',3',6'-trimethylphenyl)pentanoate was proven by synthesis of an authe ntic standard. The occurrence of these acids gives evidence that oxidative breakdown at least partially accounts for the diagenetic fate of aromatic c arotenoids. Li/EtNH2 desulfurization of two kerogen concentrates yielded on ly low amounts of sulfur-bound hydrocarbons, and suggests that either sulfu r sequestration was not a predominant process or, more probably, that a maj or part of the hydrocarbons, initially sulfurized, were released upon matur ation, giving further evidence that (poly)sulfide bonds are cleaved at rela tively low levels of thermal stress. (C) 1998 Elsevier Science Ltd. All rig hts reserved.