Paleoproductivity conditions of lower member of Cambrian Xiaoerbulak Formation in Kalpin thrust belt, Tarim Basin

Based on geological investigation of several outcrops, the analyses of 75 samples and the previous achievements, the authors studied the paleoproductivity conditions of lower member of Cambrian Xiaoerbulak Formation in Kalpin thrust belt. In order to get the reliable content of biogenic elements, the authors used the Ti element to deduce the terrigenous elemental content of Ba, Cu and Zn and obtain the corrected values of the biogenic elements Ba_xs, Cu_xs and Zn_xs. According to the results, it can be concluded that the lower member of Cambrian Xiaoerbulake Formation has a high level of paleoproductivity. The values of the biogenic elements Ba_xs, Cu_xs and Zn_xs of individual layers are higher, and this indicates that individual layers have higher paleoproductivity. The acritarchs microfossils such as Leiomarginata sp., Granomarginata squamacea Volkova, Dictyotidium priscum Kirjanov and Volkova and Lophosphaeridium sp. were found in the Cambrian Xiaoerbulak Formation, and all these factors provided a good material basis for the deposition of organic matter. The identifying indices such as Pr/Ph, V/(V+Ni), U/Th and δCe indicate that the lower member of Cambrian Xiaoerbulak Formation source rocks were developed under a favorable condition with an anaerobic sedimentary environment. The type of organic matter is Type Ⅰ-Ⅱ, and the organic matter has the characteristics of high maturity stage and potential of hydrocarbon generation. In summary, the lower member of Cambrian Xiaoerbulak Formation can be regarded as the potential source rock.