新疆北部石炭纪—二叠纪孢粉组合的植物区系性质初步探讨

A PRELIMINARY DISCUSSION ON PHYTOPROVINCIAL CHARACTERS OF CARBONIFEROUS--PERMIAN PALYNOFLORAS IN N. XINJIANG, NW CHINA

新疆北部石炭纪—二叠纪孢粉植物群总体上属亚安加拉区,但其形成、发展经历了若干阶段,即由 C_1(Tournaisian-Visean)的泛世界性+欧美型+安加拉土著分子→C_2早期(Bashkirian早期)安加拉型为主+欧美型成分→亚安加拉区形成(Bashkirian晚期—Moscovian)、扩张(Stephani-an—P_1)→P_2—T_1欧美色彩成分和泛世界性成分增加的过程。从巴什基尔晚期起混生有冈瓦纳色彩成分,但目前难以找到合理的解释;与华夏植物群关系微弱。

It is of vital importance to understand phytoprovincial characters of Carboniferous andPermian palynofloras in N. Xinjiang in both palaeontological and regional stratigraphic stud-ies. However,this subject has not been well studied so far. Some palaeobotanists believedthat the Permian flora in this area belongs to the Angara Province (Pan, 1959; Wu, 1983;Hu,1987),because many taxa in the flora are in common with those of the latter,such as An-garopteridium, Zamiopteris, Noeggerathiopsis, Iniopteris sibirica Zal., ‘Callipteris’zeilleriZal.,Comia dentata,etc. But a few other authors drew a different conclusion based on theirpalynological studies. For example, Zhang(1983)considered that the Late Palaeozoic flora ofN. Xinjiang was not comparable in botanical character with the Angara Flora (Kuznetsk Flo-ra)of former USSR. Although there is some intrinsic difficulty to investigate the phyto-provincial characters using sporopollen data (for instance, the apparent form-similarity ofspores does not necessarily indicate the real kinship of plants),we still try to choose somecomparatively diagnostic taxa of greater provincial importance for discussion,from the abun-dant and diverse Carboniferous and Permian spores and pollen found in N. Xinjiang. Some ofthe taxa show the aspects of Angara (Pl. Ⅰ,Ⅱ), Euramerian+Subangara (Pl.Ⅲ)and Gond-wana (Pl. Ⅳ)Provinces. We hope that this study will help improving our knowledge of thephytoprovincial characters solely derivcd from fossil megaplant records. Based on correlation analysis of palynofloras, we arrived at the following conclusions: 1. As a whole,the Carboniferous--Permian flora belongs to the Subangara Province,but it has experienced several stages in its formation and development,i. e.,from cosmopolitan+Euramerian+Angarian+endemic taxa to Angarian+Euramerian taxa,then to the formationand expansion of Subangara Province and finally to the increase of Euramerian and cos-mopolitan taxa. 2. The early Early Carboniferous(Tournaisian)palynoflora, as represented by the Verru-cosisporites nitidus--Vallatisporites vallatus Assemblage of the Gennaren Formation, is domi-nated by the cosmopolitan-Euramerian taxa, including Retusotriletes, Convolutispora, Reticu-latisporites, Densosporites, Cristatisporites, Crassispora, Cingulizonates, Tumulispora, Valla-tisporites, Kraeuselisporites, Auroraspora, Cyrtospora, Laevigatosporites, Tuberculatosporites,etc. It also contains endemic taxa and those forms with an Angara aspect, such asLophotriletes erinaceus (Waltz ex Naum.), L. minisculus Naum., L. mirus (Isch.), Acan-thotriletes acerosus Naum., Reticulatisporites similis (Kedo), Densosporites dentatus (Waltz),and Camarozonotriletes mosolovicus Naum. ex Kedo. During middle and late Early Carbonifer-ous (late Tournaisian--Visean,Visean--Namurian A; the Dishuiquan Group and Alemali For-mation), taxa of Angara aspect increased with the presence of Dibolisporites spinotuberosus(Luber), Convolutispora grandicornis (Luber), Concentricisporites concentricus Byvsh., Hy-menozonotriletes densus Medv., Neoraistrickia lascinus (Luber), Converrucosisporites nodosusLuber,Acanthotriletes ferus Isch. and Remysporites spp.,although the assemblages are gener-ally still dominated by cosmopolitan--Euramerian elements (e. g., Lycospora, Densosporites,etc.). 3. In early Late Carboniferous (early Bashkirian, the Batamaineishan Formation), al-though some cosmopolitan--Euramerian forms still existed in the flora,the Angara aspectwas very pronounced as displayed by the common presence of Remysporites psilopterus(Luber), R. varicus (Naum.), R. marginella (Luber), R. marginatus (Luber) and Potonieis-porites macropterus (Luber) and the comparable sudden change as also occurred in the fossilmegaplant records (Meyen, 1982, 1987). As compared with those of the Early Carboniferous,the assemblages of this period changed qualitatively and became relatively poorer in diversi-ty, possibly indicating a vegetation dominated by pteridosperms(represented by Remysporitesand Striatolebachiites) and a climatic cooling event('Esterogian epi