Identifying globally synchronous Permian–Triassic boundary levels in successions in China and Vietnam using Graphic Correlation

Abstract

Understanding the timing and correlation of significant global events in Earth history is facilitated by the Global Boundary Stratotype Section and Point (GSSP) concept, along with multi-proxy correlation techniques. As an example, the Permian–Triassic boundary (PTB) GSSP is used herein to correlate three PTB successions in east and southeast Asia. The PTB is defined using the First Appearance Datum (FAD) of the conodont Hindeodus parvus at the Meishan D section in China. By definition then, Meishan D is the only section on Earth where the FAD of H. parvus represents the beginning of the Triassic, at ~251.88Ma, and thus the end of the Permian. Therefore, when correlating strata in any other section back to the PTB using biostratigraphic data, the local Lowest Observed Occurrence Point (LOOP) of H. parvus will probably not equate precisely to the defined FAD GSSP level (the PTB) for the beginning of the Triassic at Meishan D. The Graphic Correlation method, applied to PTB sites in China and Vietnam, is used herein to demonstrate that LOOPs of H. parvus in other successions are not equivalent in time to the PTB FAD. The LOOP and Highest Observed Occurrence Point (HOOP) for conodont data at two other successions studied, Huangzhishan in China, and Lung Cam in Vietnam, are used to determine the approximate level where the Triassic begins in these successions, resulting in high-resolution correlation among the sections and correlation back to the PTB GSSP level. It is demonstrated that when critical biostratigraphic data are missing, multiple proxy correlation techniques, geochemical, geophysical and, in some regional instances, unique lithostratigraphic information such as coeval ash beds, can be used to aid in locating the boundary in successions that are not the defining GSSP. LOOP and HOOP data are used to establish a Line of Correlation to differentiate between a defining PTB H. parvus FAD versus the H. parvus LOOP in secondary successions, and to project the PTB FAD into secondary sections to define the PTB at these localities. In addition, the timing of H. parvus arrivals at these sections is used to establish rough dispersal rates and patterns in the region.