兰州盆地早第三纪植物及古气候意义

化石采自甘肃省兰州盆地咸水河组底部，经研究认为有29种，归属20属12科。它们是：樟科 Lauraceae (Daphnogene)，木通科Lardizabalaceae(Akebia)，小檗科Berberidaceae(Berberis)，榆科Ulmaceae (Planera，Ulmus，Zelkova)，桦木科Betulaceae(Alnus，Carpinus)，杨梅科Myricaceae(Myrica)，杨柳科Sali- caceae(Populus，Salix)，紫金牛科Myrsinacese(Ardisia)，蔷薇科Rosaceae (Prunus，Sorbus，Sorbaria，Spir- aea)，豆科Leguminosae(Gleditsia，Sophora)，漆树科 Anacardiaceae(Rhus)，忍冬科Caprifoliaceae(Viburnum) 等。经植物区系组成与叶相分析显示，该植物区系的大多数成员是落叶阔叶乔、灌木，少数为常绿灌木。其中特殊的分子是 Rhus turcomanica Korov．ex Vassilvesk，该成分是早第三纪中、晚期的标志化石植物。另一化石植物 Sorbaria callicomifolia Kornilova曾出现在中亚的早渐新世，最晚至早中新世。同一层位采集的孢粉样分析结果显示：该组合仅约20种，种类相对贫乏，并以被子植物的花粉占优势。其中出现裸子植物的麻黄粉，被子植物的白刺粉及蒿粉等，这几个类型均指示沉积时期经历干旱气候。综合植物大化石及孢粉分析研究，均出现一些指示气候为亚热带干旱或周期性干旱气候的特点，并据Rhus turcomanica出现的最晚记录，推测咸水河组底部的地质时代大约是早渐新世晚期。

Early Tertiary fossil plants and paleoclimate of Lanzhou Basin

Fossil plants from the lower part of Xianshuihe Formation in the Lanzhou Basin, Gansu Province were studied. The flora contains 29 species, representing 20 genera and 12 families, which include Lauraceae (Daphnogene), Lardizabalaceae (Akebia), Berberidaceae (Berberis), Ulmaceae (Planera, Ulmus, Zelkova), Betulaceae (Alnus,Carpinus), Myricaceae(Myrica), Salicaceae (Populus,Salix), Myrsinaceae(Ardisia), Rosaceae (Prunus, Sorbus, Sorbaria, Spiraea), Leguminosae (Gleditsia, Sophora), Anacardiaceae (Rhus), Caprifoliaceae(Viburnum). An analysis of the floristic elements and their foliar physiognomy shows that most members of the flora are deciduous broad-leaved trees or shrubs with a few evergreen shrubs. The most noteworthy species is Rhus turcomanica which was present in the Middle Eocene to Late Eocene of Central Asia (Kazakhstan, Turkmenistan). Generally, Rhus turcomanica occurred at the same beds as Palibinia, an extinct fossil plant whose presence indicates a subtropical dry climate. Another species, Sorbaria callicomifolia Kornilova was present from the Early Oligocene to Early Miocene of Central Asia (Kazakhstan and Turkmenistan). According to an analysis of spores and pollen, this flora contains over 20 species. It is predominated by the angiosperm pollen. There appeared Ephedripites and Nitrariadites which were important elements in the dry area. Ephedripites was found from the Upper Cretaceous to Early Tertiary. Nitrariadites occurred in the Late Miocene, whereas Rhus turcomanica and Sorbaria callicomifolia were both reported in the subtropical dry area from the Middle Eocene to Early Oligocene. The latest record of Rhus turcomanica is from the Middle Eocene to Early Oligocene of Central Asia. The presence of this element in the lower part of Xianshuihe Formation may indicate that its age is the latest stage of the Early Oligocene.