Comparison has been made of the occurence of aromatic series in chloroform fraction between immature and mature sedimentary rocks from the Hang.2 well in Chaidamu Basin. According to the general formula CaH2n-p (p=6, 8, 10, ..., 20), the molecular ion distribution of 11 series have been studied by capillary gas chromatography and GC-MS. It has been found that the immature.mature evolution of aromatic homologous obeys the rules in thermodynamics and can be summaried as: (1) The alkyl side chains decrease and become shorter in compounds of each series. (2) Alkyl and cycloalkanes aromatics (1--3 ring) increase, but cycloalkanes aromatics with more (4-5) rings decrease. (3) Aromatization is observed in alkyl benzene, alkyl naphthalene and alkyl phe.nanthrene series. (4) The bimodal distribution of carbon number curve changes into unimodal distribution. It seems that the variation in aromatic homologous distribution can be used as a potential indicator of maturatlon or as fingerprints for source-rock correlation.
