湖北当阳陆相白垩系-古近系界线层型问题值得深入研究

陆生恐龙的绝灭是白垩系-古近系界线事件中最引人注目的。陆相地层是恐龙绝灭等事件信息的重要载体。全球白垩纪、古近纪陆相地层发育、分布广泛,单一的白垩系-古近系全球界线层型(GSSP)不能满足建立一个明确而可操作的界线标准的需要,建立陆相白垩系-古近系界线层型很有必要,其意义和重要性实际上不亚于建立GSSP。中国的白垩系、古近系绝大多数为陆相沉积,且陆相白垩系-古近系界线方面存在许多问题,而中国目前正在做陆相地层建阶和完善"中国区域年代地层表"工作,不解决好陆相白垩系-古近系界线问题,中国古近系最下面的一个阶便建不好,"中国区域年代地层表"将不完善,所以建立陆相白垩系-古近系界线层型对于中国更加迫切并具实际价值。全球白垩纪-古近纪过渡时期(特别是古新世早期)的连续陆相生物地层记录十分匮乏,寻找合适的剖面建立陆相白垩系-古近系界线层型非常困难。从轮藻角度出发,湖北当阳跑马岗组露头剖面拥有全球迄今所知最连续丰富多样的白垩纪-古近纪过渡时期特别是古新世早期的陆相生物地层记录。界线层段的介形类生物地层记录也非常连续且丰富多样,并具建立界线层型的其他许多条件。它是中国至今所知惟一具有潜力成为全球(或大区性、或中国)的陆相白垩系-古近系界线层型、也即中生界-新生界界线层型的候选剖面(露头剖面),从而也可能是中国古近系、也即新生界最下面一个阶的最合适的建阶剖面或层型剖面。为此,湖北当阳陆相白垩系-古近系界线层型问题无疑值得重视和深入研究。

A PROPOSAL TO FURTHER INVESTIGATE THE CRETACEOUS-PALEOGENE BOUNDARY SECTION AT DANGYANG HUBEI PROVINCE

The mass extinction of terrestrial dinosaurs is the most important evolutionary event across the Cretaceous-Paleogene boundary.Continental Cretaceous-Paleogene strata are important information carriers of this extinction event.The continental strata of the Cretaceous and Paleogene are well developed and widely distributed in the world.It is unlikely that a single Cretaceous-Paleogene GSSP will satisfy all criteria necessary for an unambiguous and practicable standard of this boundary,and establishing a continental Cretaceous-Paleogene boundary stratotype is essential and its significance and importance are no less than the GSSP.Since the Cretaceous and Paleogene of China are mostly continental deposits and there are many stratigraphic problems concerning the Cretaceous-Paleogene boundary,and since ongoing work to establish stages of continental strata and the Regional Chronostratigraphic Chart of China is being conducted in China,it is imperative to resolve the problems of the Cretaceous-Paleogene boundary in China and to establish the lower boundary of the Paleogene and the Cenozoic of China.Otherwise,the Regional Chronostratigraphic Chart of China would be incomplete.Thus,the establishment of a continental stratotype will have practical values.The continuous biostratigraphic record of the Cretaceous-Paleogene transition and particularly the early Paleocene is scarce in the continental domain,and searching a section suitable for establishing the continental Cretaceous-Paleogene boundary stratotype is very difficult.From the viewpoint of charophytes,the outcrop section of the Paomagang Formation in Dangyang,Hubei Province(Central China),contains the most continuous,abundant and diverse terrestrial biostratigraphic records of the Cretaceous-Paleogene transition,in particular the early Paleocene,known so far in the world.The biostratigraphic record of ostracods in the transition is also very continuous,rich and diverse.Thus,this section meets critical requirements as a candidate for a boundary stratotype.The Dangyang section is the only outcrop section known so far in China that has potential to become a candidate for a global or regional continental stratotype of the Cretaceous-Paleogene(and Mesozoic-Cenozoic)boundary.It is also the best section for establishing the lowermost stage of the Paleogene or the Cenozoic of China.Therefore,the Dangyang section is undoubtedly worth further investigation in greater detail.