Abstract
In Yanshan, located in the northern part of North China, Mesoproterozoic carbonate sequences (1.6–1.4 Ga) form a 10, 000 m thick succession in an aulacogen basin. Carbon and oxygen isotope (δ13O and δ18O, resp.) data were obtained from 110 carbonate samples across three sections of these Mesoproterozoic deposits. From the early to late Mesoproterozoic, low negative values of δ13O appear, followed by low positive variation and then a stable increase. An abrupt decrease in δ13O values, with subsequent rapid increase, is found at the end of the Mesoproterozoic. During the whole Mesoproterozoic, δ18O shows a mainly negative trend and occasional highly negative isotopic shifts (from lower to upper deposits). Whole-rock carbon and oxygen isotopic compositions and profiles must be studied to provide a paleogeochemical record that can be associated with paleocean sedimentary environments, temperature, biological productivity, and sea-level fluctuations. Results of the present study correlate well with other international carbon and oxygen isotope profiles, suggesting that a global marine geochemical system existed during the interval of 1.6–1.4 Ga under a globally united tectonic, sedimentary, and geochemical background.
Highlights
Yanshan, located in the northern part of North China, has a well-developed Mesoproterozoic marine strata-type section, that is nearly 10,000 m thick (Figure 1)
To better understand paleoceanic geochemistry of the Yanshan Mountains during the Mesoproterozoic (1.6– 1.4 Ga) and regional, or global, Mesoproterozoic stratigraphic correlation, this study examined oxygen and carbon isotopes in the Mesoproterozoic stratigraphy of Yanshan, North China
Because of the possible complex postdepositional history of carbonates in the study area, we expected that all samples would show geochemical evidence and nonalteration; many carbon isotopic studies of Paleozoic and Proterozoic carbonates have shown that carbon isotopic composition is less sensitive to diagenetic alteration than are δ18O or trace element (Fe, Mn, Sr) compositions, as long as diagenetic fluids are relatively carbon-poor
Summary
Yanshan, located in the northern part of North China, has a well-developed Mesoproterozoic marine strata-type section, that is nearly 10,000 m thick (Figure 1). Since establishment of the strata type in Yanshan in the 1930s [2], numerous studies have examined the stratigraphy, sedimentology, paleontology, geochronology, and geochemistry [3] and reported on carbon and oxygen isotopes [4,5,6,7,8,9,10,11,12]. Zhong and Chen [4] examined the isotopic composition of the Gaoyuzhuang Formation and the Yangzhuang Formation based on oxygen and carbon isotopic data (152 values) collected from the Gaoyuzhuang to Yangzhuang Formations at the Ming Tombs, Beijing and in Jixian, Tianjin. Li et al [11] and Chu et al [12] studied the oxygen and carbon isotopic compositions, respectively, of Mesoneoproterozoic samples from Jixian, Tianjin
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