青藏高原北羌塘盆地中部发现晚巴通期-早卡洛夫期菊石

The discovery of Late Bathonian-Early Callovian ammonites in the middle of northern Qiangtang basin,Tibetan Plateau

最近在北羌塘盆地中部半岛湖地区索瓦组下段中发现了丰富的中侏罗世晚巴通期—早卡洛夫期菊石。这些菊石保存好,特征明显,可以与西特提斯地中海区菊石带进行精细对比。根据区域菊石化石群的对比,含菊石的地层可能不是索瓦组下段,而是夏里组。早卡洛夫期大头菊石的出现与同期全球海平面的上升同步,而地方性的含大头菊石的层序通常也指示了区域性的海侵。羌塘盆地早卡洛夫期大头菊石生物群的发现,证明羌塘盆地在早卡洛夫期还存在区域性的海侵,北羌塘盆地中部的半岛湖地区处于相对较深的广海碳酸盐台地环境,而不是前人所认为的羌塘盆地在卡洛夫期即发生大规模的海退,发生海退的时间应该在早卡洛夫期之后。晚巴通期—早卡洛夫期菊石生物群的发现对于重新认识羌塘盆地沉积构造演化历史具有重要意义。

Recently,a number of ammonites were discovered in the Bandao Lake area of northern Qiangtang basin,ranging in age from the Late Bathonian to Early Callovian（Middle Jurassic）.The ammonite assemblages sampled in the Changhong River area are of good preservation and have obvious features,thus providing a solid basis for comparison with the Western Tethys ammonoid zones.According to the comparison with regional ammonoid assemblages,the fossiliferous strata are probably Xiali Formation instead of the lower part of the Suowa Formation.The generation of Macrocephalites in the Early Callovian time was closely connected with the global rising sea level,and the endemic Macrocephalites sequences often indicate a regional transgression event.The existence of Early Callovian Macrocephalites in the middle Qiangtang basin implies that a regional transgression took place in the Qiangtang basin during the Early Callivian period,and the Bandao Lake area in the middle of the northern Qiangtang basin was in a relatively deep carbonate platform environment.The regression event in Middle Jurassic occurred later than Early Callovian instead of in Callovian.The discov ery of the Late Bathonian-Early Callovian ammonoid assemblages is of great importance for the understanding of sedimentary-tectonic evolution of the Qiangtang basin.