The Paleocene—Eocene Niubao Formation in the Nyima Basin of Xizang(Tibet)was recently proved to be a set of petroliferous succession.However,a systematic stratigraphic division scheme still lacks.Thus,we try to use elemental proxies to do a chemo- stratigraphic analysis on the Niubao Formation from the perspectives of geochemistry and autogenic/allogenic processes.With the expectations of not only establishing a stratigraphic scheme for the Niubao Formation,but also exploring a reliable and practical stratigraphic division method.Methods: Based on the early field work,and the later whole-rock X-ray fluorescence (XRF) measurements, sedimentary geochemistry,principal component analysis (PCA),complementary ensemble empirical mode decomposition(CEEMD),and autocorrelation function (ACF),the base level curves of deposition with specific geochemical meanings were reconstructed.Results:XRF analysis detected 10 kinds of major elements(expressed in metallic oxides%)and 12 kinds of trace elements(inμg/g)with good quality,based on which principal component analysis unveiled that the Niubao Formation was mainly controlled by factors of fine terrigenous inputs,carbonate contents,redox—productivity level,and coarse terrigenous inputs.Complementary ensemble empirical mode decomposition (CEEMD) analysis on PCA results,and the further autocorrelation function (ACF)analysis on intrinsic mode functions(IMFs)revealed that the strata were characterized by prominent and multi-scale allogenic forcing,which enables the reconstruction of geochemical base level of deposition,thus the chemo-stratigraphic scheme of the Niubao Formation can be established.Conclusions:The chemo-stratigraphic scheme of the Niubao Formation based on aforementioned methods and processes can be correlated with traditional lithostratigraphic schemes and sedimentary facies,but with more explicit geological meanings,which at the same time can be utilized to regional stratigraphic correlation,testifying the reliability of our chemo-stratigraphic scheme.