在滇东北永善莲峰新发现的万和剖面,奥陶系-志留系交界地层发育良好、地层连续,化石丰富,含有笔石、腕足类、三叶虫、牙形类、几丁类和疑源类化石,包括了大渡河组、产Hirnantia动物群的观音桥层和龙马溪组。此处大渡河组可分为上、下两段,下段为灰岩与钙质泥页岩互层,上段为钙质泥岩夹灰岩。笔石自下而上可识别为Dicellograptus complexus带、Paraorthograptus pacificus带(下亚带、Tangyagraptus typicus亚带和Diceratograptus mirus亚带)以及Metabolograptus extraordinarius带,为凯迪晚期至赫南特早期。几丁类尚未在上段发现,下段属于Eisenackitina ripae带。上段底部(即Tangyagraptus typicus亚带底)产腕足类Kassinellasp.,Leptellinasp.,Paromalomenasp.等,属于深水BA5(底栖组合),在华南同期地层中未见及。观音桥层产典型的Hirnantia动物群,属于BA3,为标准的浅凉水组合。依据万和及相邻地区的资料,厘定了大渡河组。大渡河组分布于扬子台地西部(滇东北—川西南),与扬子台地内部广布的五峰组和扬子台地西南缘的铁足菲克组(大部分)、西缘的大箐组(上部)属同期异相。从产BA5腕足类的大渡河组上段底部,到产BA3赫南特贝动物群的观音桥层,再到龙马溪组下部黑色页岩,是奥陶纪末大灭绝第一幕和第二幕全球气候快速变冷和转暖、海平面迅速地先降后升在扬子海盆的充分反映。 In the Wanhe section newly discovered at Yongfeng, Yongshan, Yunnan, the Ordovician-Silurian boundary strata developed well with continuous stratigraphy and rich fossils, including penoliths, brachiopods, trilobites, dentals, chitin And suspected fossils, including the Daduhe Formation, the Guanyinqiao Formation and the Longmaxi Formation of the Hirnantia fauna. Here Daduhe Formation can be divided into upper and lower two sections, the lower section of interbedded limestone and calcareous shale, the upper section of calcareous mudstone limestone. Penoliths can be identified as Dicellograptus complexus band, Paraorthograptus pacificus band (Tangyagraptus typicus and Diceratograptus mirus sub-belts) and Metabolograptus extraordinarius band from the bottom to the early period of Kaidi to Early Nannant. Chidin class not yet found in the upper section, the lower section belongs to Eisenackitina ripae zone. The bottom of the upper segment (ie, the bottom of the Tangyagraptus typicus subfacies) produces the brachiopods Kassinellasp., Leptellinasp., Paromalomenasp., Etc., belonging to the deepwater BA5 (benthic assemblage) and not found in the contemporaneous formations in South China. The typical Hirnantia fauna of the Guanyin Bridge, belonging to BA3, is a standard combination of shallow and cool water. Based on the data from Wanhe and its adjacent areas, the Daduhe Formation was determined. The Daduhe Formation is located in the western part of the Yangzi platform (northeast Yunnan-southwest Sichuan) and is closely related to the widely distributed Wufeng Formation in the Yangtze platform and the Tiezufeike Formation (mostly) on the southwestern margin of the Yangtze platform, Belong to the same phase out of phase. From the bottom of the upper part of the Daduhe Formation that produces BA5 brachiopods to the Guanyin Bridge that produces the BA3 Hernantube fauna and to the lower black shale of the Longmaxi Formation are the first and second episodes of the Ordovician mass extinction Rapid cooling and warming of the global climate, the sea level quickly and then drop in the Yangzi basin fully reflected.