Middle Jurassic and Cretaceous Charophytes from Chaoshui Basin, NW China

Li Zuwang, Wang Qifei and Yang Jinglin

pp. 202-217, 3 plates, in Chinese, with English abstract

Abstract:

The fossil Charophytes studied in this paper were obtained from the Middle Jurassic and Cretaceous rocks of the Chaoshui Basin and reported for the first time. The present authors identified 6 genera and 17 species and established 3 Charophyte assemblages.

I. Aclistochara abshirica-A. nuguishanensis Assemblage. It only contains Aclistochara abshirica, A. major, A. nuguishanensis, A. yongpingensis and A. sp., yielding from the upper member of Ningyuanpu Formation. This low-diversity assemblage is similar to that in Middle Jurassic upper Lufeng Formation, Hepingxiang Formation and Upper Jurassic Tuodian Formation in Yunnan area, so the age of this assemblage is referred to the late Middle Jurassic, corresponding to Callovian of Europe.

II. Peckisphaera paragranulifera-Clypeator jiuquanensis Assemblage, yielying from Huihuipu Group. This assemblage includes Peckisphaera paragranulifera, Clypeator jiuquanensis, Flabellochara jurongica, Aclistochara huihuibaoensis, A. mundula, Mesochara stipitata and Obtusochara sp., among them all the known species are common fossils of Early Cretaceous, especially Clypeator jiuquanensis is thought as a predominant species of Barremian. The age of Assemblage II is attributed to Early Cretaceous, probably Barremian.

III. Aclistonchara songliaoensis-Mesochara stankevistchii Assemblage, yielding from Jinganquan Formation. The assemblage contains Aclistonchara jilinensis, A. mundula, A. mundula var. elliptica, A. songliaoensis, A. (Caucasuella) subglobosa, A. (C.) heilongjiangensis var. nonganensis and Mesochara stankevitschii, all of them belong to Late Cretaceous. And Gobichara is absent in this assemblage, which is common in late Late Cretaceous. Thus the age of Assemblage III is regarded as Cenomanian to Turonian of Late Cretaceous.

Keywords: charophytes, Middle Jurassic, Cretaceous, Chaoshui Basin