Ratios of low molecular weight alkylbenzenes (C0–C4) in Chinese crude oils as indicators of maturity and depositional environment

摘要: Abstract A total of 37 oils from three basins in China were analyzed using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC–TOFMS) investigate the distributions low molecular weight (LMW) alkylbenzenes (C 0 –C 4 ). Thermal maturity and depositional environment exert dominant controls on carbon number isomer LMW alkylbenzenes, while secondary alteration, such as biodegradation or evaporative fractionation, cannot be ruled out. With increasing maturity, relative abundance C 3 decreases 2 increase. Some variations are also attributed maturation, illustrated by ratios ( m - +  p -)/ o -propyltoluene (3,5- + 3,4-)/(2,5- + 2,4-ethylxylene). The 1,2,3,5-/1,2,3,4-tetramethylbenzene ratio (TeMBr) is proposed distinguish derived source rocks formed under anoxic rather than oxic/dysoxic conditions. data suggest that TeMBr  1.5 suggests an environment. Quantitative show differences values mainly due variable 1,2,3,5-TeMB concentrations, whereas range 1,2,3,4-TeMB concentration relatively constant. enriched deposited conditions, but depleted reducing