塔里木盆地西部晚白垩世钙质超微化石

本文分析研究了塔里木盆地西部晚白垩世钙质超微化石,划分出Quadrumgartneri,Eprolithus floralis两个组合,从一个新的角度为探讨库克拜组和乌依塔克组的地层时代及其沉积环境提供有关的论据.

LATE CRETACEOUS CALCAREOUS MANNOFLORA FROM THE WEST TARIM BASIN OF XINJIANG

The Late Cretaceous calcareous nannoflora dealing with in this paper is found from the west Tarim Basin (Fig. 1) in the Kukebai and the Wuytak Formations of the Yingjisha Group (Tab. 1). As compared with those of typical pelagic origin this fossil flora is less abundant, of low generic and specific diversity and highly effected by calcareous overgrowth. 24 genera and 30 species (Tab. 2 and Tab. 3 ) are identified which are mostly near shore shallow water forms and representa-tive forms of epicontinental sea. Two assemblages in this fossil flora indicating two different depsitional environments are recognized in the Kukebai and the Wuytak Formation of the Akchey Section, which are (1) the Quadrum gartneri Assemblage has a stratigraphical distribution in the Kukebai Formation and the basal part of the Wuytak Formation, represented mainly by Quadrum gartneri, Rhagodiscus spp. , Calculites spp. , Tetralithus spp. , and Rucinolithus spp., and a few subordinate elements such as Zeugrhabdiscus spp. , Scapholithus sp., Nan-noconus sp. , Quadrum gothicum and Micula sp. , The age of this assemblage is probably from the Late Cenomanian to the Turonian. As indicated by change of general aspect of the assemblage, the depositional environment during this period changes from an open to a bloking bay milieu; (2) The Eprolithus floralis Assemblage stratigraphically ranges from the middle member to the upper member of the Wuytak Formation, which is more abundant and diveritied than the Quadrum gartneri Assemblage and repres-ented mainly by Eprolithus floralis, E. sp. , Braarudosphaera bigelowii, B. turbinea, B. cf. discula, Chiastozygus litterarius, C. striatus, Tranolithus phac-elocus,Watznaueria barnesae, Cyclageloshaera margerelii, C. sp.,Arkhangelskiella sp. and Micula spp. with a few less abundant forms, such as Eiffelithus eximius and Pervilithus. The age of this assemblage is probably from the Coniacian to the Campanian. The assemblage is more abundant and divers- itied in the middle member of the Wuytak Formation, but becomes less so in the upper member, and the foraminiferal fauna occurring in association with it in the middle member comprises a number of planktonic forms. The facts indicate that during the depositional period of these two members the bay milieu changed from open to more or less blocked. Occurring in association with the calcareous nannoflora there are a number of unknown fossil forms similar in size and composition to calcareous nannofossils and composed of several radiating rays, which are illustrated in plates Ⅲ and Ⅳ.