拉萨北部堆龙德庆县设兴组古近纪孢粉化石的发现及其地质意义

Discovery of Paleogene sporopollen in the Shexing Formation in Doilungdêgên County, northern Lhasa, and its geological significance

在拉萨北部堆龙德庆县马乡设兴村设兴组命名剖面顶部灰黑色泥岩夹层中的SX31样品中发现了Osmundaciditessp.,Deltoidosporasp.,Leiotriletessp.,Punctatisporitessp.,Ilexpollenitessp.,Quercoiditessp.,Caryapollenitessp.,Betulaceoipol鄄lenitessp.,Sporopollis?sp.,Ulmipollenitessp.,Compositoipollenitessp.,Tricolporollenitessp.等孢粉化石,主要为被子植物和蕨类植物花粉,未发现裸子植物花粉。这些孢粉指示的地层时代接近于始新世—渐新世。在剖面下部的4件样品中零星发现了Tricolpitessp.,Shizaeoisporitessp.,Compositoipollenites?sp.,Leiotriletessp.,Cyathiditessp.,Neoraistrackiasp.,Con鄄verrucosisporritessp.,Cycadopitessp.,Pinuspollenitessp.,Retitricolpitessp.等孢粉化石,指示的地层时代可能略早。从而说明设兴组与上覆林子宗群之间的角度不整合所代表的构造运动发生在始新世—渐新世或其后。

This paper reports the discovery of sporopollen fossils in sample SX31 in the grayish black mudstone interbed at the top of the naming section of the Shexing Formation at Shexing Village, Maxiang Township, Doilungdêgên County, northern Lhasa, Tibet. The sporopollen includes Osmundacidites sp., Deltoidospora sp., Leiotriletes sp., Punctatisporites sp., Ilexpollenites sp., Quercoidites sp., Caryapollenites sp., Betulaceoipollenites sp., Sporopollis? sp., Ulmipollenites sp., Compositoipollenites sp. and Tricolporollenites sp., which are mainly pollen of angiosperms and pteridophytes, no gymnosperm pollen being found. The age of the strata indicated by the sporopollen is close to Eocene-Oligocene. In four samples in the lower part of a section the authors also found sparse sporopollen such as Tricolpites sp., Shizaeoisporites sp., Compositoipollenites? sp., Leiotriletes sp., Cyathidites sp., Neoraistrackia sp., Converrucosisporrites sp., Cycadopites sp., Pinuspollenites sp. and Retitricolpites sp., indicating a possible slightly early stratigraphic age. This suggests that the tectonic movement represented by the unconformity between the Shexing Formation and the overlying Linzizong Group occurred in the Eocene-Oligocene or later.