南华系建系问题探讨

南华系的研究与关于成冰系的研究配合不多,把南华系简单地理解为原震旦系下统,侧重于原震旦系下统底界年龄的测定,把国外给定的关于"成冰系"的起始年龄值(即850Ma)看得过重,忽略了它的不确定性。对于作为南华系主体的新元古代冰期地层的研究比较薄弱,与国际冰川沉积学研究水平差距大。为此,有必要根据界线层型剖面的要求开展建系工作,重点深入研究新元古代冰川沉积地层的基本特征,包括层序地层学、同位素地层学、磁性地层学、岩石地层学、化学地层学、生物地层学和年代地层学等,明确其内涵,寻找全球对比的界线标志。建议以贵州黎平肇兴剖面为代表开展候选层型剖面和层型点所需内容研究。

PROBLEMS IN DEFINING THE NANHUAN PERIOD

The work on defining the Nanhuan Period began quite early,however,the focus was then on the newly defined Sinian and not on the Nanhuan Period,therefore,its definition was not emphasized.The international informal stratigraphic unit Cryogenian(850—650Ma) was then considered to be equivalent to Nanhuan,and in addition,equivalent to the lower series of the former Sinian.In last few years,domestic reseach on the Nanhuan did not pay much attention to the progress in the definition of Cryogenian,and emphasised the dating of the base of the former lower series of Sinian.Probably,the informal onset age constrain 850Ma of the informal unit Cryogenian was incorrectly taken to be formal.Study on the Neoproterozoic glacial strata,the main body of the Nanhuan(Cryogenian),has not been fully organised,and therefore,it was not fully known by the outside world.It is urgent to practise strictly the rule of the stratigraphic guide.This paper emphasises that the characteristics,including sequence stratigraphy,isotopic stratigraphy,magnetostratigraphy,lithostratigraphy,chemostratigraphy,biostratigraphy and chronostratigraphy of the Neoproterozoic glacial records in China,should become the main criteria in defining the content and boundary of Nanhuan,including the GSSP or GSSA.At the moment,the Zhaoxing section can be considered as a representative of the Global Stratotype Section and Point(GSSP).Multidicipline study is important for providing contribution to the definition of Cryogenian.