In the Early Ordovician Zhaogezhuang Section of Tangshan , North China, the Yeli Formation is composed of an entire third-order sequence, with facies ranging from the inner ramp restricted platform and open marine t...In the Early Ordovician Zhaogezhuang Section of Tangshan , North China, the Yeli Formation is composed of an entire third-order sequence, with facies ranging from the inner ramp restricted platform and open marine to the middle and even outer ramps. The Liangjiashan Formation is dominated by highstand system tracts （HST） with predominantly inner ramp grain-shoal and lagoon facies. Analyzing the carbon and oxygen isotope during the whole-rock carbonate reveals the 613C values in the Yeli Formation range from -7.11%o-0.76%o （PDB）, with the mean value at -2.98%0, while the 6180 values range of-9.09%o- -4.65%o with the mean value at -6.12%o. The 613C values in the Liangjiashan Formation range of -1.15%o-0.3%o, and the mean value of -0.57%0; the 61SO values are -8.76%0- -7.48%0, and the mean value is -8.06%o. The 613C values in the Yeli Formation decrease, but at the bottom of the Liangjiashan Formation the values increase steadily. In the middle-upper formation, there is an extended fluctuation between 0- -1.00%o. The 613C trend in the studied section is similar to that of the contemporary sections, except that it has much lower 613C values and a more negative excursion. The correlation between the 613C changes and the eustatic events, as well as the sedimentary facies, indicates that in the Tangshan area, the carbon isotope evolution can be attributabled to the processes of the eutrophic sea/oligotrophic sea, the seafloor organism- mediated oxidation in shallow water and the organic reduction after maximum flooding. The changes in the carbon isotope contents were primarily affected by the regional relative sea level changes. Compared to the other coeval data, the Early Ordovician of the Tang shan area is also severely depleted in 180, with all of the 6180sample values being Delow 5%o, except for one sample with a value ot -4.02%0. Witlt the ancient sea- water having a 6180 value of-5.5%0 （SMOW）, it is reasonable to delineate a temperature of less than 37 C.展开更多
基金supported by the National Natural Science Foundation of China(No.41372039)
文摘In the Early Ordovician Zhaogezhuang Section of Tangshan , North China, the Yeli Formation is composed of an entire third-order sequence, with facies ranging from the inner ramp restricted platform and open marine to the middle and even outer ramps. The Liangjiashan Formation is dominated by highstand system tracts （HST） with predominantly inner ramp grain-shoal and lagoon facies. Analyzing the carbon and oxygen isotope during the whole-rock carbonate reveals the 613C values in the Yeli Formation range from -7.11%o-0.76%o （PDB）, with the mean value at -2.98%0, while the 6180 values range of-9.09%o- -4.65%o with the mean value at -6.12%o. The 613C values in the Liangjiashan Formation range of -1.15%o-0.3%o, and the mean value of -0.57%0; the 61SO values are -8.76%0- -7.48%0, and the mean value is -8.06%o. The 613C values in the Yeli Formation decrease, but at the bottom of the Liangjiashan Formation the values increase steadily. In the middle-upper formation, there is an extended fluctuation between 0- -1.00%o. The 613C trend in the studied section is similar to that of the contemporary sections, except that it has much lower 613C values and a more negative excursion. The correlation between the 613C changes and the eustatic events, as well as the sedimentary facies, indicates that in the Tangshan area, the carbon isotope evolution can be attributabled to the processes of the eutrophic sea/oligotrophic sea, the seafloor organism- mediated oxidation in shallow water and the organic reduction after maximum flooding. The changes in the carbon isotope contents were primarily affected by the regional relative sea level changes. Compared to the other coeval data, the Early Ordovician of the Tang shan area is also severely depleted in 180, with all of the 6180sample values being Delow 5%o, except for one sample with a value ot -4.02%0. Witlt the ancient sea- water having a 6180 value of-5.5%0 （SMOW）, it is reasonable to delineate a temperature of less than 37 C.
