A PERSPECTIVE OF THE STUDY OF THE MIDDLE AND LATE CAMBRIAN CONODONTS FROM WESTERN HUNAN

The Middle and Upper Cambrian sections in western Hunan are of clear superiority in the contest of Global Stratotype Section and Point (GSSP), in which great progress has been made in the field of the study on trilobite biostratigraphy during recent years. However, the conodonts from some important intervals of Cambrian of this region have not been carefully studied up to now. Conodonts are playing more and more important roles in the study of GSSP. In this paper the status and problems of the studies on Middle and Late Cambrian conodonts from western Hunan are introduced in detail. Considering the demands on biostratigraphy of GSSP made by ICS in 《International Stratigraphy Guide》 (second version) and the latest work progress made by the International Subcommission on Cambrian Stratigraphy (ISCS) and its Cambrian Subdivision Working Group, the main task of Middle and Late Cambrian conodont study of this region in the future is proposed, which is to erect the standard conodont biozones of the candidate GSSP of Middle and Upper Cambrian in western Hunan in order to provide important basis for challenging Golden Spikes of Cambrian subdivisions and listing the Chinese stages of Cambrian into 《International Stratigraphic Chart》. Excellent outcrops of Middle and Upper Cambrian strata in western Hunan, which mainly consist of limestones containing abundant trilobites and conodonts, are favorable for this study. These trilobites have been well studied since 1963. However, the conodonts are relatively less concerned, furthermore, most of the former conodont collections focus on the traditional Middle Upper Cambrian boundary interval, which corresponds to the FAD of Liguagnostus reconditus . Unfortunately, the ISCS formally proposed the FAD of Glyptagnostus reticulatus as the base of the Upper Cambrian Series last year because the latter is much more important and significant in global correlation than the former. Thus, more attention must be paid on the conodonts in the Glyptagnostus reticulatus bearing interval. Last fall, the present author and the others carried out a detailed sampling to Paibi Section of Huayuan County, northwestern Hunan Province, which is the most potential candidate for the GSSP of the base of a global unnamed series. Now the in door work is undergone. The most important task of conodont study in the following years is to erect the standard conodont zones for the interval bearing the base of the Waergangian Stage and the Wangcunian Stage from two sections of northwestern Hunan. Both of these sections are potential candidates of GSSP (the FAD of Glyptagnostus reticulatus and the FAD of Ptychagnostus punctuosus ). These points are two of the six points newly suggested by the ISCS to define the bases of series and stages of Cambrian. In addition, the standard conodont zones of Wangcunian, Youshuian, Waergangian and Taoyuanian should also be erected in the coming years.