重庆万州下侏罗统自流井组湖相遗迹化石新类型及其古环境意义

A NEW TYPE OF LACUSTRINE ICHNOFOSSILS FROM THE LOWER JURASSIC ZILIUJING FORMATION IN WANZHOU OF CHONGQING AND ITS PALEOENVIRONMENTAL SIGNIFICANCES

描述在重庆万州区铁峰山下侏罗统自流井组大安寨段首次发现的遗迹化石,鉴定为新种Palaeophycus tiefengshanensis。该种以潜穴表面瘤状凸起特征与较大的潜穴尺寸区别于古藻迹其他遗迹种。遗迹组构分析表明该遗迹化石产出层位的层面生物扰动指数为最高级5,说明原始沉积环境的食物供给充足,氧含量高,造迹生物大量繁盛并活动频繁。根据沉积相变化特征,四川盆地东部地区自流井组沉积期经历了与四川盆地北部地区类似的古环境变迁即湖退过程。两者区别在于四川盆地东部自流井组局部层段可能更适宜底栖动物生存。

The Early Jurassic trace fossil is reported for the first time from the Da＇nanzhai Member of the Lower Jurassic Ziliujing Formation in Tiefeng Mountain of Wanzhou, Chongqing. The newlyfound trace fossil is attributed to a new ichnospecies-Palaeophycus tiefengshanensis, which differs from other ichnospecies of Palaeophycus by its large size and nodular surface. Ichnofabric analysis shows that the bedding-plane bioturbation indice of the Palaeophycus ichnofabric is 5 representing the highest level of bioturtation, which suggests abundant food supply, high level of oxygen content and frequent animal activities. Based on the sedimentary facies changes of the Tiefengxiang section, the eastern region of Sichuan Basin experienced a similar environmental transformation of lake regression as the northern region of Sichuan Basin; the differences are the locally more habitable environment for ichnofauna in the studied area.