Boron isotopic composition of Paleozoic brachiopod and coeval coral calcites in Yunnan-Guizhou Plateau, China  

作　　者：MA YunQi XIAO YingKai HE MaoYong XIAO Jun SHEN Quan JIANG ShengXiang 

机构地区：[1]Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China [2]Key Laboratory of Salt Lake Resources and Chemistry, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China [3]State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi ＇an 710075, China [4]Geological Team 1, Yunnan Geoexploration and Development Bureau of Mineral Resources, Qujing 655000, China [5]Graduate University of Chinese Academy of Sciences. Beijing, 100049. China

出　　处：《Science China Earth Sciences》2011年第12期1912-1925,共14页中国科学（地球科学英文版）

基　　金：supported by National Natural Science Foundation of China (Grant Nos. 407760071 and 40976074)

摘　　要：Boron isotope values in Paleozoic brachiopods and corals, collected from the Yunnan-Guizhou Plateau, China, can be used to constrain the boron isotope compositions of past oceans. All brachiopod shells and coral samples were screened for diagenetic recrystallization by cathodoluminescence microscopy, trace element geochemistry of B, Fe, Mn, Sr, and scanning electron microscopy. The boron isotope ratios for brachiopods in Silurian, Devonian, Carboniferous, and Triassic calcites are in the ranges 8.9‰-14.0‰, 8.8‰-13.8‰, 10.3‰-16.3‰, and 6.7‰-12.4‰, respectively. The boron isotope ratios of coral calcites in the Silurian, Devonian, and Permian are 9.1‰-12.2‰, 6.1‰-13.8‰, and 9.2‰-16.1‰, respectively. The δ11B values for both brachiopods and corals are significantly lower than those for modern biogenic carbonates, indicating that the Paleozoic oceans were depleted of δ11B by up to 10‰. Our results are consistent with previous published studies. The boron isotope compositions of corals and brachiopods show the consistent trends. The low δ11B values may be explained by an enhanced riverine flux of boron from the continents.Boron isotope values in Paleozoic brachiopods and corals, collected from the Yunnan-Guizhou Plateau, China, can be used to constrain the boron isotope compositions of past oceans. All brachiopod shells and coral samples were screened for diagenetic recrystallization by cathodoluminescence microscopy, trace element geochemistry of B, Fe, Mn, Sr, and scanning electron microscopy. The boron isotope ratios for brachiopods in Silurian, Devonian, Carboniferous, and Triassic calcites are in the ranges 8.9‰-14.0‰, 8.8‰-13.8‰, 10.3‰-16.3‰, and 6.7‰-12.4‰, respectively. The boron isotope ratios of coral calcites in the Silurian, Devonian, and Permian are 9.1‰-12.2‰, 6.1‰-13.8‰, and 9.2‰-16.1‰, respectively. The δ^11B values for both brachiopods and corals are significantly lower than those for modern biogenic carbonates, indicating that the Paleozoic oceans were depleted of δ^11B by up to 10‰. Our results are consistent with previous published studies. The boron isotope compositions of corals and brachiopods show the consistent trends. The low δ^11B values may be explained by an enhanced riverine flux of boron from the continents.

关 键 词：boron isotope CORAL BRACHIOPOD PALEOZOIC 

分 类 号：P343.3[天文地球—水文科学] P931.5[天文地球—地球物理学]