Was volcanic activity during the Ordovician-Silurian transition in South China part of a global phenomenon? Constraints from zircon U–Pb dating of volcanic ash beds in black shales. (April 2020) - Du, Xuebin
Abstract: Whether volcanic activity during the Ordovician-Silurian transition (OST) in South China (SC) contributed to global volcanic activity has always been a controversial subject. Volcanic ash is the most direct evidence for volcanic activity and represents a good marker to compare SC with the global stratigraphic correlation. Here, we analyze the distribution of volcanic ash beds in three outcrops in SC and precisely determine the ages of volcanic ash zircons using the LA-ICP-MS and SHRIMPII methods. A comparison of the volcanic ash beds in three different outcrops of SC during the OST; indicates that relatively large-scale volcanic activity occurred during this period. The newly obtained zircon U–Pb ages show that the starting time of the Ordovician Wufeng Fm. was approximately 449.2 Ma (or 449.3 Ma), the starting time of the Ordovician Guanyingqiao bed (the ending time of the Wufeng Fm.) was approximately 445.6 Ma, and the starting time of the Longmaxi Fm. was approximately 444.2 Ma. In addition, the durations of the Wufeng Fm. and Guanyingqiao bed were 3.6 Ma and 1.4 Ma, respectively, and the duration of the Hirnantian stage in SC was 1.4 Ma. Most of the ages obtained in this study were basically consistent with that of the International Commission on Stratigraphy (GST 2018). These results provide insights into the volcanic activity during the OST in SC as well as age data for a global stratigraphic framework. Graphical abstract: Image 1 Highlights: Volcanic ash beds in three outcrops of South China were investigated in detail. 6 examples are precisely determine the zircon ages using the two methods. Volcanic activity in South China is part of a global phenomenon. The duration of the Hirnantian stage is 1.4 Myr and consistent with the MGST 2018 The starting time of the Wufeng Fm. and Guanyingqiao bed are 449.2 Ma and 445.6 Ma.