The age of the Dingjiazhai Formation has been problematic. Until recently, it has been assigned to the Upper Carboniferous (Yang, 1983; Fang Runsen, 1994; Zhang, 1996) owing to the presence of the Triticites -dominated fusulinid assemblage in the upper part of the Dingjiazhai Formation. However, Nie et al. (1993) argued for a late Sakmarian to Artinskian age instead mainly based on the Stereochia litostyla (=Callytharrella sp. of Shi et al., 1996)fauna, and suggested that the Carboniferous elements such as Triticites and Syringothyris (=Cyrtella sp. of Shi et al., 1996, probably Punctocyrtella ) may have been reworked from the underlying Pumenqian Formation and mixed with the Early Permian Eoparafusulina fauna and Stereochia litostyla (=Call-ytharrella sp., text fig.1, J-L) fauna respectively. This view, however, contradicts the fact that the Pumenqian Formation belongs to the Early Carboniferous and no Triticites can be found in the pre-Dingjiazhai formations. According to our examination of the fusulinid fauna from the upper part of the Dingjiazhai Formation, most of the so-called Triticites should be included in the genus Eoparafusulina instead and the fauna includes the following species: Eoparafusulina pseudosimplex, E. pusilla, E. contracta, Schwagerina schencki,S. quasivulgaris, S. cf. paranana, Triticites stuckenbergi. This is a typical Early Permian Eoparafusulina fauna. Just as Jin et al. (1994) pointed out, the boundary between the Tastubian and the Sterlitamakian coincides with the base of Eoparafusulina genozone. Therefore, a Sterlitamakian age is preferred for the upper part of the Dingjiazhai Formation. This conclusion is consistent with the assessment of the age of the Dingjiazhai brachiopod fauna presented by Shi et al. (1996). The redeposition hypothesis of Nie and co-workers (1993) does not hold water since the so-called Carboniferous elements Triticites and Syringothyris(= Cyrtella sp., text fig.1, M) have been proved to be of Early Permian age. In addition, palynomorphs have been recorded from the middle part of the Dingjiazhai Formation (Yang, 1997; Gao, 1998). The assemblage is characterized by a content of monosaccate pollen ranging from 50 to 60 per cent, disaccate pollen 25 to 30 per cent, pteridophytic spores 10 to 15 per cent. On the one hand, the assemblage is dominated by radially symmetrical monosaccates and trilete spores of Australian affinities, suggesting its equivalence with Stage 2 or Unit II palynofloras of the Australian sequence. On the other hand, disaccate pollen grains of the Dingjiazhai palynoflora are evidently higher than the Stage 2 and Unit II palynofloras and dominated by Striatiti forms, such as Striatopodocarpites and Protohaploxypinus. The Dingjiazhai assemblage is dated as Early Permian (Asselian-Tastubian) and is regarded as an Australian-affinity palynoflora mixed with some elements shared by Euramerican, Cathaysian and Angaran palynofloras, such as Wilsonites delicatus, Guthoerlisporites magnificus, Vittatina vittifera, V. costabilis, V. fasciolata, Angulisporites triverrucosus, Cordaitina and others. In sum, the age of the Dingjiazhai Formation is assigned to the Asselian to Sterlitamakian. It is interesting to note that the common occurrence of the Tethyan Eoparafusulina fauna with the Australian-affinity brachiopod fauna and palynoflora in the Dingjiazhai Formation, indicating that the Baoshan block might lie in an intermediate position in Paleotethys during the Early Permian instead of being attached to the Gondwanaland (Fang, 1991, 1994, Shi and Archbold, 1998).
国家自然科学基金项目 !(No .4 9672 1 4 7)