SHRIMP U–Pb zircon age of tephra identified in the Yahe section of Liushan Basin and its significance as a regional stratigraphic marker

Abstract

Three tephra layers in the middle part of the Yahe section have been discovered in Liushan Basin in Nanzhao County, Henan Province. This paper presents zircon U–Pb ages measured on the sensitive high-resolution ion microprobe (SHRIMP)-II from zircons separated from one of these tephra layers. Thirteen analyses yielded a 206Pb/238U weighted mean age of 237 ± 2.5 Ma (95 % confidence, Mean Square of Weighted Deviates = 0.72). This age suggests that the Yahe section strata were deposited as early as the Middle Triassic. The new SHRIMP U–Pb data on the tephra from the Yahe section provides strong age constraints on the Triassic stratigraphic subdivision in Liushan Basin. By comparing the reported ages for similar tephra exposed around Liushan Basin, we infer that the tephra layers may be the sedimentary response to the first episode of the Indosinian tectonism and can be used as a marker bed for regional stratigraphic correlation.