Abstract: Heterogeneity study of lacustrine source rocks relys heavily on a deeper understanding of the major controlling factors on their formation.Geochemical,petrological and sequence stratigraphy analyses of two sets of source rocks(K₁sh and K₁yc)in southern Changling Depression,Soliao Basin,reveal that multiple factors played roles in shaping the distribution of organic matters there.Al/Ti ratio was used to evaluate their paleoproductivity.Parameters like V/Cr,V/(V+Ni),Sr concentration,Sr/Ba,and Sr/Cu as well as paleoclimatic indexes,were also employed to study their sedimentary settings.Results show that high-quality source rocks(mainly in upper Shahezi Formation)were developed in a highstand system tract and lacustrine transgressive system tract that featured in medium paleoproductivity,humid paleoclimate,low paleosalinity and low deposition rate.They are rich in Al,Ba,Cu,Cr,V and Ni,but lack of Mn and S.Meanwhile,low-quality source rocks(maninly found in the Yingcheng Formation),were developed in lowstand system tract(LST)that was characterized by low paleoproductivity,semi-arid paleoclimate,high paleosalinity and high deposition rate.They are abundant in Co,Sr and V but lack of Al,Ba,Cr,Cu,Mn and Ni.We therefore suggest that,in the study area,(1)system tracts controlled the distribution of source rocks,(2)moderate-to-good primary productivity was a critical precondition for the development of high-quality source rocks,and(3)humid climate,low salinity as well as favorable sedimentation rate,were the reasons behind organic matter accumlations.

Key words: trace element, paleoproductivity, sedimentary setting, high-quality hydrocarbon source rock, Changling Depression, Songliao Basin