新疆若羌石灰华中的植物化石及古环境*

根据首次从富阳西湖组发现的孢子及其垂直分布特征,划分出下段 LH 组合和上段 DP 组合,分别归入晚泥盆世法门晚期(斯图年期)和早石炭世早期(杜内早期),即泥盆-石炭系界线通过西湖组内部,与江苏五通组类似.

SPORE ASSEMBLAGES FROM DEVONIAN-CARBONIFEROUS TRANSITIONAL BEDS OF HSIHU FORMATION, FUYANG, W. ZHEJIANG

The "Chienligang Sandstone" mainly composed of quartzose sandstones and widespread in W. Zhejiang was named by Liu and Chao (1927); it was subdivided into two parts, with the lower part 0-500 m and the upper part about 200 m in thi ness. Subsequently, the Chienligang "Group" has been redefined by the Chinese geologists as comprising three formations (Table I) in ascending order, namely the Tangjiawu Formation, the Hsihu Formation and the Zhuzangwu Formation, with an overlying coal-bearing formation, the Yehchiatang Group, yielding the Late Visean-Namurian Archaeocalamites scrobiculatus-Neuropteris gigantea Flora (Zhao et al., 1986). The Tangjiawu Formation was dated Silurian, and the Zhuzangwu Formation Early Carboniferous or the latest Devonian to Tournaisian due to the presence of Lepidodendropsis cf. hirmeri Lutz, "Sublepidodendron" wusihense (Sze), Sublepidodendron mirabile (Nath.) and Bothrodendron fuyangense Chen, whereas the Hsihu Formation has generally been dated Late D vonian mainly based on the lithological similarity to the Wutung Formation in N. Zhejiang and Jiangsu and the possible presence of Leptophloeum rhobicum in this formation at the locality of Chun'an. The Wutung Formation in Jiangsu consists of two parts, i.e. the Guanshan Member below and the Leigutai Member above. The Leigutai Member has been distinguished into at least two spore assemblage zones, i.e. the Retispora lepidophyta-Apiculiretusispora hunanensis (LH) Assemblage Zone (Strunian) below and the Dibolisporites distinctus-Auroraspora macra (DM) Assemblage Zone (late Tn 1_b-Tn 2) above. Based on the occurrence of a few spores including Cymbosporites conatus, Discernisporites micromanifestus and Spelaeotriletes exiguus in the Guanshan Formation, Cai et al. (1988) suggest that the whole Wutung Formation should be Strunian-early Tounaisian in age. In other words,the Wutung Formation contains the Devonian-Carboniferous boundary although the exact boundary still has to be determined (Ouyang and Chen, 1987a, b; 1989; Chen and Ouyang, 1987). Consequently, it has become an interesting problem on the stratigraphical correlation between the Wutung Formation in Jiangsu and the Hsihu Formation in Zhejiang. The materials on which the present investigation is based were collected from the Hsihu Formation outcropped at the locality of Xindian, Fuyang, W. Zhejiang, attaining about 224 m in thickness (Text-fig. 1). Among the 17 macerated samples, 7 of them derived from three horizons (22-HB_1-2 23-HB_1-2 24-HB_1-3 in the upper part of the section have been proved to contain spores. Except Aneurospora sp., altogether 34 species referred to 23 genera are recorded and illustrated. Based on an analysis of the vertical distribution, especialy the appearance/dispperance of some diagnostic species, two spore assemblages have been recognized, namely, the Retispora lepidophyta-Apiculiretusispora hunanesis (LH) Assemblage below and the Dibolisporites distinctus-Cordylosporites papillatus (DP) Assemblage above. The former is dated Strunian in age, and the latter is most likely of early Tournaisian (late Tn 1_b-Tn 2); thus he Devonian-Carboniferous boundary is possibly placed between Horizons 22 and 23. Both assemblages may roughly be correlated with the LH Assemblage and the DM Assemblage from the Wutung Formation in Jiangsu respectively, although they are much less diverse in composition and contain no acritarchs as compared with the latter assemblage. This result provides another Devonian-Carboniferous transition sequence in China and a rather reasonable basis for dating the Hsihu Formation. In addition to the appearance/disappearance of those diagnostic species, the LH assemblage is characterized by the relative abundance of retusoid spore (Retusotriletes, Apiculiretusispora) and Auroraspora cf. poljessica, while the DP assemblage by macroreticulate, foveolate and granulate spores and Grandispora sp. B.