Abstract:
The Late Neoproterozoic to Early Cambrian represents a critical period in geological history. In the Keping area of the Tarim Basin, Xinjiang, the Ediacaran to Cambrian strata are well-exposed, but research on chemostratigraphy is relatively limited. This study selected the Lower Cambrian Yurtus Formation in the Xiaoerbulake Xigou and Kungaikuotan sections in the Keping area as the research subject. Carbon and Strontium isotope geochemistry were used to establish regional and global stratigraphic correlations and constrain the depositional age of the Yurtus Formation. The geochemical characteristics of the samples, including
δ13C
carb-
δ18O
carb crossplots,
δ18O
carb, and Mn/Sr ratios, confirmed that the
δ13C
carb and
87Sr/
86Sr of most samples were not altered by later diagenesis and preserved the seawater characteristics at the time of deposition. Crossplots of
87Sr/
86Sr versus Sr content and Rb content of the samples indicated that there was no significant addition of silicate components during the dissolution process. The inorganic carbon isotope results showed that two negative carbon isotope excursions were recorded in the carbonates from the Yurtus Formation in both sections, located at the base of limestone and shale interbeds and in the upper argillaceous limestone member, respectively, which could be correlated with other sections in the Keping area. The
87Sr/
86Sr ratios of Yurtus Formation carbonates exhibited a "decline-rise" pattern, which could be correlated with the
87Sr/
86Sr variations in the Tommotian Stage of Morocco and southeastern Siberia. The global positive carbon isotope excursion ZHUCE event was not identified within the Yurtus Formation. Combined with
87Sr/
86Sr variation characteristics and paleontological data, it is inferred that there was a sedimentary hiatus within the formation, resulting in the absence of the middle and lower Stage 2 strata. Based on carbon and strontium isotope stratigraphic correlations combined with previous studies, it is concluded that the middle dolomite member of the Yurtus Formation lies near the Fortunian and Stage 2 boundary, and the upper limestone and shale interbeds to the top of the Yurtus Formation belong to the late Stage 2 and early Stage 3 of the Cambrian.