RESTUDY AND DEFINITION OF THE LUDLOW CHEJIABA FORMATION OF THE GUANGYUAN AREA,SICHUAN PROVINCE

The Late Silurian stratigraphy of the Guangyuan area,northern Sichuan Province,was subdivided into three formations including,in ascending order,the Jintaiguan Fm,Chejiaba Fm and Zhongjianliang Fm. On the basis new lithostratigraphic and biostratigraphic data,these three formations are combined into the Chejiaba Fm. The Chejiaba Fm,consisting of sandstone and mudstone with near shore marine red beds,intercalated occasionally with calcareous sandstone and limestone lenses in the middle and upper parts; thin-bedded argillaceous sandstone and silt mudstone in the upper,represents a sea-level rise sequence. The conodont Ozarkodina crispa previously reported from the Chejiaba Fm is be re-identified as Ozarkodina snajdri,which represent this first report of this species in Silurian of China. The age of the Chejiaba Fm is re-determined as late mid-Ludlow to early late-Ludlow,which is earlier than the Kuanti Fm of Eastern Yunnan Province. The chitinozoan assemblage of Sphaerochitina sp. is found in the Chejiaba Fm and is correlated with the O. snajdri conodont zone and the bohemicus tenus-kozlowskii graptolite zone.