川滇陆相侏罗系-白垩系界线划分

Nonmarine Jurassic-Cretaceous boundary in Sichuan and Yunnan, China

云南禄丰川街剖面侏罗系—白垩系混合磁极性超带的M19极性带位于安宁组下段顶部,四川泸州纳溪剖面M18r极性亚带位于蓬莱镇组二段上部。上述古地磁界线与马门溪龙、叶肢介、双壳类等所形成的生物界线相吻合。因此陆相侏罗系—白垩系界线在滇中被置于安宁组下段与上段之间或妥甸组上段的2个亚段之间;在四川此界线则被置于蓬莱镇组第二段的中上部。

The polarity zone M19 of the J/K mixing polarity superzone in the Chuanjie section of Lufeng, Yunnan, is located in the upper part of the lower member of the Anning Formation and the polarity subzone M18r in the Naxi section of Luzhou, Sichuan is located in the upper part of the second member of the Penglaizhen Formation. The paleogeomagnetic boundary coincides with the biological boundary marked by the distribution of Mamenchisaurus, appearance of new genera and species and conspicuous changes in abundance and diversity of bivalves and conchostracans in the Anning Formation, the upper member of the Tuodian Formation and the second member of the Penglaizhen Formation. Therefore the nonmarine Jurassic-Cretaceous boundary is located between the upper and lower members of the Anning Formation and between two submemebers of the upper member of the Tuodian Formation in central Yunnan; whereas in Sichuan the boundary is placed between the middle and upper parts of the second member of the Penglaizhen Formation.