柴达木盆地宗马海湖地区始新统下干柴沟组轮藻植物群

EOCENE CHAROPHYTE FLORA FROM THE XIA GANCHAIGOU FORMATION IN ZONGMAHAI LAKE AREA,QAIDAM BASIN,NORTHWEST CHINA

柴达木盆地北缘宗马海湖地区始新统下干柴沟组在一道沟剖面出露良好,本文详细描述了该剖面下干柴沟组的岩性特征,该组以棕红色泥岩为主,局部夹浅灰绿色含石膏中细砂岩、含钙质粉砂质细砂岩及少量含砾中粗砂岩、褐红色灰岩。在该剖面发现轮藻化石2属2种:Lamprothamnium ganchaigouensis(Tang and Di)Li et al.comb.nov.和Lychnothamnus vectensis(Groves)Soulié-M?rsche,前者为新联合属种。L.vectensis主要发现于欧洲始新统渐新统,在我国始新统系首次报道。本文以居群为单位,讨论了L.vectensis的种内形态变化,包括藏卵器尺寸和顶部装饰的连续变化。欧洲L.vectensis居群的藏卵器尺寸随着纬度的升高有变大的趋势,而柴达木盆地的纬度低于欧洲埃布罗盆地和巴黎盆地的纬度,它所产的L.vectensis居群藏卵器尺寸却更大,推测与柴达木盆地古湖泊水体清澈度和/或温度更高相关。

The Qaidam Basin is the largest terrestrial basin with the most continuous Cenozoic sediments in the northeastern Tibetan Plateau.It is located in the northwestern Qinghai Province,northwestern China,triangular in shape,bounded by the Altyn-Tagh to the northwest,the Qilian Mountain-Nan Mountain to the northeast,and the Eastern Kunlun Mountain to the south.The basin has an area of^200000 km^2,with altitude between 2600 and 3000 meters.The Cenozoic consists of 7 formations,in ascending order:Lulehe,Xia Ganchaigou,Shang Ganchaigou,Xia Youshashan,Shang Youshashan,Shizigou,and Qigequan formations.The charophyte fossils are very abundant and display different floral assemblages with different ages in the Qaidam Basin,according to previous charophyte biostratigraphy studies for oil exploration over the last 60 years.The Eocene Xia Ganchaigou Formation is well exposed in the Yidaogou Section in the Zongmahaihu area,the northern Qaidam Basin.The lithology was described in detail,dominated by brownish-red mudstone,interbedded with light grayish-green gypsum-containing fine sandstone,calcareous silty fine sandstone,and a small amount of gravel-containing coarse sandstone and brownish red limestone.Two species belonged to two genera of charophytes were found from this formation including Lamprothamnium ganchaigouensis(Tang and Di)Li et al.comb.nov.and Lychnothamnus vectensis(Groves)Soulié-M?rsche.L.ganchaigouensis was newly combined.L.vectensis,previously known from the Eocene to Oligocene in Europe,is reported in China Eocene deposits for the first time,and its intraspecific variation is discussed based on population,including size range and continuous variations of apical ornaments.The population of L.vectensis has a tendency to increase in gyrogonite size with the increase of latitude.On the contrary,the latitude of the Qaidam Basin is lower than that of the Ebro and Paris basins in Europe,but the population from the Qaidam Basin is larger in gyrogonite size than those from the latter two basins.It was speculated that higher water clarity and/or higher temperature of palaeolakes produced larger gyrogonites in the Qaidam Basin.