西藏拉萨地块设兴组孢粉化石新发现及其地层学意义

New Palynological Materials from the Shexing Formation in the Lhasa Block, Tibet, and Their Stratigraphic Significance

拉萨地体的典中 那玛剖面设兴组上部新发现孢粉组合 ,其特征为 :孢粉化石多为第三纪常见分子 ,未发现早白垩世和晚白垩世特征分子。因此样品产出的层位不可能属于白垩纪的沉积。孢粉组合以落叶、阔叶植物为主体 ,主要为桦科的桤木粉 (Alnipollenites)、桦粉 (Betulaepollenites)、枥粉 (Carpiniptes) ,山毛榉科的栎粉 (Quercoidites)胡桃科的胡桃粉 (Juglans pollenites) ,榆科的榆粉 (Ulmipollenites) ,椴科的椴粉 (Tiliapollenites)等 ,热带、亚热带植物孢粉少量出现 ;草本植物花粉出现很少 ,如晚第三纪常见的藜科 (Chenopodiaceae) ,菊科 (Compositae) ,禾本科 (Gramineae)及蓼科 (Polygonaceae)等 ,指示了样品所在层位沉积时的气候并不干旱 ;早第三纪早期大量出现的三孔沟 ,网面三孔沟等花粉少量出现 ;孢粉总的面貌反映了温凉、湿润的温带气候 ,指示了落叶、阔叶森林广泛分布。孢粉组合更接近于早第三纪中晚期的面貌 ,其时代可能属于始新世 渐新世。本次孢粉的面貌与伦坡拉盆地的牛堡组中段孢粉化石面貌有些相似 ,与牛堡组上段和牛堡组之上的丁青组 (渐新统 )孢粉面貌相差甚远。因此推测 ,典中 那玛剖面设兴组产出孢粉的层位与牛堡组中段可能处于大致相同的时代或稍晚的时代。典中 那玛剖面的设?

New materials of sporopollen were discovered in the upper part of the Shexing Formation along the Dianzhong Nama section of the Lhasa block. The sporopollen assemblage has the following characteristics:Most of the sporopollens found are common elements of Tertiary, so the related strata cannot be Cretaceous sediments; Deciduous and latifoliate vegetation, including Alnipollenites, Betulaepollenites, Carpiniptes, Quercoidites, Juglanspollenites, Ulmipollenites, and Tiliaepollenites, constitute dominant species in this assemblage; Tropic sporopollen and semi tropical vegetation occur in a relatively small amount. Herbage sporopollens, such as Chenopodiaceae, Compositae, Gramineae, and Polygonaceae, are rarely seen. All this indicates that the climate was not drought when they deposited. Triporopollenites and Tricolporopllenites which are very widely spread in Palaeogene also occur in small amounts; The whole conditions of sporopollen imply warm cool and moist climate of temperate zone at that time, suggesting wide distribution of deciduous and latifoliate forests. The Sporollen assemblage is close to that of the middle and late Palaeogene, probably belonging to Eocene Oligocene. The condition of the sporollen assemblage in the upper part of the Shexing Formation is similar to that of the middle Member of Niubao Formation in Lunpola Basin, indicating that the age of the sporopollen assemblage was nearly contemporaneous with the middle Member of Niubao Formation or a little later. The Shexing Formation includes not only the upper part of the Upper Cretaceous but also the lower part of the Lower Tertiary.