四川宣汉晚三叠世孢粉组合及其古植被与古气候意义

对四川盆地东北缘宣汉七里峡剖面须家河组进行了详细的孢粉学研究,发现丰富的孢粉化石,共计59属113种,其中包括蕨类植物孢子35属62种,裸子植物花粉22属47种,苔藓类植物孢子1属3种,以及藻类化石1属1种。据此建立一个孢粉组合,命名为Dictyophyllidites-Lunzisporites-Chasmatosporites组合(简称DLC组合),并进一步分为上、下两个亚组合。根据孢粉组合内一些重要分子的地质时代延限及与国内外有关孢粉组合的对比,提出其地质时代属于晚三叠世诺利期—瑞替期(Norian—Rhaetian)。该孢粉植物群反映了一个以蕨类植物的真蕨类、石松类和裸子植物的松柏类和苏铁类群等占主导且较为繁盛的植被面貌,揭示出温暖潮湿的亚热带—热带气候环境。

LATE TRIASSIC SPORE-POLLEN ASSEMBLAGE FROM XUANHAN OF SICHUAN,CHINA

A detailed investigation of well-preserved spore-pollen assemblage is performed for the Upper Triassic Xujiahe Formation in Xuanhan,northeastern Sichuan Province,southwestern China.This assemblage contains 113 species of spore-pollen in 59 genera.Based on the quantitative analysis,a spore-pollen assemblage is recognized as Dictyophyllidites-Lunzisporites-Chasmatosporites(DLC)Assemblage.The features of the assemblage are summarized as follows:1)Pteridophyte spores are the dominant group in this assemblage(average 61.7%).Among them,Dictyophyllidites and Concavisporites are the highest in abundance(25.2%),including Dictyophyllidites harrisii,D.intercrassus,and Concavisporites toralis.Lunzisporites ranks the second in percentage(13.1%),including Lunzisporites lunzensis,L.sparsus and L.pallidus.Cyathidite and Deltoidosporaare the third abundant group(8.3%),mainly represented by Cyathidites minor,C.australis and Deltoidospora minor.The zonate spores attains a percentage of4.9%,and are marked by several species of Asseretospora(3.5%).In addition,some rare zonate spores are present,including species assigned to Annulispora,Kraeuselisporites,Kyrtomisporis,Canalizonosporaand Densoisporites.2)Gymnosperm pollen grains are less abundant in the assemblage(37.0%),represented by bisaccate taxa(17.7%),such as Pinuspollenites divulgatus,P.globosaccus,P.alatiopollenites,P.elongatus,P.minutus,Quadraeculina anellaeformis,Q.limbata,Q.minor,Pseudopinus pectinella,P.cavernosa,Alisporites australis,A.rutundus,A.Parvus and Pseudopicea variabiliformis.The remaining conifer bisaccate grains are less common,maily including Protoconiferus,Caytonipollenites,Piceites,Podocarpidites and Platysaccus.The striate and laesurate bisaccate pollen are rare(1.2%),including Taeniaesporites albertae and Parataeniaesporites pseudostriatus.It is noted that among the pollen grains,Chasmatosporites(11.1%)is the second abundant taxon group,yielding a diverse species.Cycadopites ranks the third in content(4.1%),comprising Cycadopites subgranulosus,C.reticulata,C.magnus,C.deterius,and C.parvus.In addition,Psophosphaera are common(2.5%)among pollen grains,yielding Psophosphaera minor,P.tenuis,etc.The present spore-pollen assemblage is assigned to the late Late Triassic based on stratigraphic distribution of important taxa,such as Kyrtomisporis,Canalizonospora,Aratrisporites,Taeniaesporites,Lunzisporites,Parataeniaesporites,Ovalipollis,Ricciisporites,Dictyophyllidites,and Chasmatosporites.The DLC assemblage shows similarities to the coeval spore-pollen assemblages previously reported from the neighboring regions of the Sichuan Basin,e.g.the Shezi Formation of Yunnan,the Anyuan and Sanqiutian formations in Pingxiang,Jianxi,and the Tumengela Formation in Tibet.This assemblage is also comparable with other assemblages from the Rhaetian assemblage of Austria,Sweden and Poland,showing ageological age of Norian to Rhaetian.This palynoflora indicates a prosperous vegetation aspect occurred in the Late Triassic in Xuanhan region of the Sichuan Basin,and is dominated by the ferns,horsetails,conifers and cycads,inferring a subtropical and tropical climate condition.