目前,早白垩世欧特里夫期尚无可世界广泛对比的放射虫带.但一些地区,特别是西特提斯地区,该时间段放射虫化石组合记录,已为其他地区欧特里夫期放射虫硅岩时代的厘定提供了可能.西藏南部日喀则地区的下鲁硅岩,己发现早侏罗世-白垩纪中期的多个放射虫带,标志着新特提斯东段一个长期存在的大洋盆地.建立下鲁硅岩的完整放射虫分带系统,对东特提斯广泛分布的硅质岩时代确定及地质演化历史的研究,都有重要意义,但包括欧特里夫期在内的一些时期的放射虫组合尚未发现.为寻找欧特里夫期化石记录,本文对日喀则地区下鲁硅岩的样品80-133重新研究,描述放射虫化石26属的41种,包括5个新种.其中,与下鲁硅岩瓦兰今期(标本80-141)化石组合的共同种仅有3个.而Alievium regulare(Wu et Li),Archaeodictyomitra coniforma Dumitrica,A.minoensis(Mizutani),A.tumandae Dumitrica,Cryptamphorella crepida O'Dogherty,C.clivosa(Aliev),Hemicryptocapsa capita Tan,Praeconosphaera sphaeroconus(Rüst),Pseudodictyomitra lanceloti Schaaf,Thanarla pacifica Nakaseko et Nishimura的存在,显示该组合可与西特提斯、阿曼、日本和西太平洋等地的欧特里夫期放射虫动物群对比,为下鲁硅岩该时期放射虫化石的首次报道.
HAUTERIVIAN(EARLY CRETACEOUS)RADIOLARIANS FROM THE XIALU CHERT,SOUTHERN XIZANG
Radiolarian zones for worldwide correlation of the Hauterivian Stage have not been widely recognized so far.However,in some areas,especially in the western Tethyan,radiolarian assemblages for that time interval have been recorded and provide the possibility for dating coeval radiolarian-bearing strata in other areas.A number of radiolarian assemblages between the early Jurassic to the mid-Cretaceous have been found from the Xialu chert in the Xigaze area of the southern Xizang,indicating an oceanic basin lasting for more than 80 m.y.in the eastern Tethys.However,the fossil records in some stage including Hauterivian have not been reported.Establishing radiolarian zonal scheme in the Xialu chert is valuable to dating radiolarian chert sequences/blocks widely exposed in the Yarlung Zangbo suture zone,vital for reconstructing the geological history of the east Tethys.Here we report a Hauterivian radiolarian assemblage,from sample(80-133)collected in the Xialu chert,composed of 41 species assigned to 27 genera,including a systematic description of 5 new species.The Hauterivian assemblage is revealed by the presence of Alievium regulare(Wu et Li),Archaeodictyomitra coniforma Dumitrica,A.minoensis(Mizutani),A.tumandae Dumitrica,Cryptamphorella crepida O'Dogherty,C.clivosa(Aliev),Hemicryptocapsa capita Tan,Praeconosphaera sphaeroconus(Rust),Pseudodictuomitra lanceloti Schaaf and Thanarla pacifica Nakaseko et Nishimura,which is well correlated with those Hauterivian radiolarian assemblages of the west Tethys and of other areas.Only 3 species from this assemblage are present in the Valanginian fauna of the Xialu chert(Wu et al.,2021).
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