西藏申扎地区早二叠世冰海相地层中孢粉化石的发现

The discovery of sporopollen fossiles bearing Lower Permian Glacio-marine sequences of Xainza area, Tibet

拉萨地块下二叠统拉嘎组是一套与冈瓦纳地区晚古生代大规模冰川作用有直接联系的沉积地层,作者在西藏申扎地区的拉嘎组中分析出孢粉化石,说明早二叠世蕨类植物孢子和裸子植物花粉的出现与冈瓦纳大陆冰川消退事件有密切联系.该套孢粉组合中蕨类植物孢子含量远低于裸子植物花粉含量,双囊具肋花粉和单囊花粉含量最高,Hamiapollenites与Striatoabieites两属地位尤为突出;组合中蕨类植物孢子含量虽低但分异度较高,单气囊花粉Cordaitina所占比例较大,双囊具肋花粉Hamiapollenites,Striatoabieites,Protohaploxypinus的种数很多,可建立Hamiapollenites-Striatoabieites组合.值得注意的是,除了少数"冈瓦纳型"分子Parasaccites obscurus,P.cf.radiplicatus,Plicatipollenites indicus的存在外,其余含量极高的分子则可与新疆北部早二叠世孢粉组合相对比,说明早二叠世冈瓦纳和亚安加拉共有某些植物类群的可能性是极大的.这类孢粉组合在早二叠世冰海相沉积物中的出现表明,拉萨、南羌塘等地块由冈瓦纳北缘向华夏区转换的过程中,微植群发生的混生可能比古动物群响应的更早,至少在早二叠世的冰期末或冰期结束后就已经发生了.

The Lower Permian Lagar Formation on the Lhasa Terrane is a set of glacio-marine sequences directly related to the Late Palaeozoic Gondwanaland glaciation. The sporeopollen fossils reported for the first time in the Largar Formation in this paper suggested that the appearence of Early Permian pteridophyta spores and gymnosperm pollens have close connection with the Gondwanaland deglaciation In the palynofloras assemblage of the Lagar Formation, content of the gymnosperms pollens is much higher than that of the pteridophyta spores even if the latter has high diversity. In the gymnosperms pollens, it is dominated by rib-bisaccate pollen and monosaccate pollen. They are dominated by the genera Hamiapollenites, Striatoabieites and Cordaitina respectively. Besides, the species of Hamiapollenites, Striatoabieites, Protohaploxypinus also have large quantity, so the assemblage Hamiapollenites Striatoabieites can be established. It is worth noting that the highly content elements of palynofloras could be compared with Lower Permian palynofloras of North Xinjiang excepted for a few typical ＂Gondwana-＂elements such as Parasaccites obscurus, P. cf. radiplicatus and Plicatipollenites indicus. It suggests that there was a common Early Permian palynofloras between Gondwanaland and Sub-Angara. Such an interesting palynofloras links between the blocks from the north hemisphere and that of south hemisphere may have suggested that the mixing of palynofloras began sooner after the deglaciation. And, the mixing of palynofloras was ealier than the paleobiogeograhic change of marine faunas occurred in the South Qiangtang and Lhasa blocks.