The Maokou Formation Conodont And Its Biostratigraphy Of The Middle Permian In West Of Sichuan Basin

This study aims to discuss conodonts in the Chang Jianggou, Liu Jinggou, andLong Mendong of the Sichuan Basin, these of which are typical sections of MiddlePermian.Through collecting conodonts samples, we obtained231samples in theMaoKou Formation, a total of4species in12genera were indentified. Most samplesare the genera of Jinogondolella and Hindeodus, including9important species:Jinogondolella nankingensis，J. aserrata，J. postserrata，J. shannoni，J. altudaensis,J. prexuanhanensis，J. xuanhanensis，Hindeodus excavatus，H. minutus.According to the research of the taxonomy, dividing the three sections’ conodontzones. The Chang Jianggou Section was divided into three conodont zones, includingJ. nankingensis zone，J. aserrata zone and J. postserrata zone; the Liu JinggouSection into three conodont zones, namely J. altudaensis zone, J. prexuanhanensiszone and J. xuanhanensis zone; the Long Mendong Section, in ascending orders, theyare J. shannoni zone and J. xuanhanensis zone. The conodont sequence has beenaccurately compared with several classical sections, such as Penglaitan section, Laibin,Guangxi; Dukou section, Xuanhan, Sichuan; the Bird Mine section in Texas, USA.Then the division and correlation of the Middle Permian in the study area have beenproposed.After comparing, we find that five conodont zones were missing in the ChangJianggou Section, but only two conodont zones were missing in the the Liu Jinggouand the Long Mendong Sections. Through considering the Emeishan basalt eruptioncenter, thickness distribution, and the law of CAI, we proposed the numbers and thelaw of missing on the top strata of MaoKou Formation are related to basaltdistribution, which protect the underlying strata. The strata are relatively successiveand complete in the Long Mendong and Liu Jinggou sections, because of the largethickness of basalt protecting, but the Chang Jianggou Section lack of large conodontzones without basalt covered.