There exist Penman Dalong Fomaation and Lower Triassic Luolou Formation along Dongpan section crossing PTB. Da- long Formation contains Ophiceras sp., and Luolou Formation contains Ophieeras tingi Tien, suggesting that they are continuous. The evidence from paleontology indicates the PTB lies between 12-3 and 13-1A. There exists several claystone layers near the Penman Triassic boundary, and the layers have obvious volcanic debris and tuffite structure. Geochemical data also show that clay- stones have volcanogenic features. U-Th-Pb zircon isotope data show a weighted mean ^206Pb/^238U age of 254.7Ma±3.7Ma, which represents the crystallization age of the protolith of the clays, roughly identical with the zircon U-Pb age 253.4Ma±0.2Ma of the bottom boundary of the Changhsingian period. It is also shown that strong volcanic eruptions occurred in this area.