西藏南部和地中海西部白垩纪中期放射虫化石的对比

CORRELATION OF MID-CRETACEOUS RADIOLARIANS BETWEEN THE SOUTHERN TIBET AND WESTERN MEDITERRANEAN REGIONS

白垩纪放射虫化石种类繁多,目前全球的分带对比还较困难。藏南的白垩纪放射虫硅质岩广泛分布,各时期的放射虫化石均有报道,但有待进一步的古生物学和生物地层学研究。O’Dogherty(1994)建立了一个有价值的西地中海地区白垩纪中期的放射虫分带,但将藏南赛诺曼期冲堆组的一些放射虫化石属种的时代,归入阿普特期,导致一些错误的对比结果。本文将冲堆组一块灰岩标本(80-153)的23种化石示于图版Ⅰ,它们都是西地中海地区放射虫化石的共同种或相近种,据O’Dogherty(1994)提供的这些种的时代分布,表明冲堆组的放射虫化石组合宜与西地中海地区赛诺曼阶中下部的Spica亚带对比。

The Cretaceous radiolarian fossils are of great variety.So far it is difficult to correlate their zonations bet-ween different regions in the world.In the southern Tibet Cretaceous radiolarian cherts are widespread and radiolarian assemblages with varying ages have been reported.Further paleontological and biostratigraphical work remains to be done.O＇Dogherty（1994）proposed a valuable mid-Cretaceous radiolarian zonation for the western Mediterranean region.However,some radiolarian genera and species from Cenomanian Congdu Formation in the southern Tibet were regarded as Aptian taxa in his work,that led to some errors in the stratigraphic correlation.In this paper 23 radiolarian taxa from a limestone sample（80-153）of the Congdu Formation are shown in Plate 1.They are conspecific or closely related to those forms described by O＇Dogherty（1994）.Their stratigraphic ranges provided by O＇Dogherty（1994）indicate that the radiolarian assemblage of the Congdu Formation is most appropriate to be correlated with early Cenomanian Spica Subzone in the western Mediterranean region.