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.
MA YunQiXIAO YingKaiHE MaoYongXIAO JunSHEN QuanJIANG ShengXiang
