西秦岭南缘白水江群晚古生代微体化石的发现及其地质意义

西秦岭南秦岭白水江群不是单一的地层,而是由一套浅变质的碎屑岩、灰岩块体、基性和超基性岩块组成,由于缺乏古生物化石证据,多年来一直划分为早古生代志留系地层。因此,通过地层剖面的测制和微体化石采样和分析,在碎屑岩所夹的砂屑灰岩、硅质岩中,获得晚二叠纪放射虫化石和遗迹化石。结合在白水江群所夹的灰岩块体中发现的奥陶纪和泥盆纪化石,以及在火山岩块体中获得元古代的锆石U-Pb年龄,进而推断出白水江群为晚古生代最终形成的混杂岩。

Discovery of Late Paleozoic Microfossils and Significance of Baishuijiang Group in South Belt of West Qinling Mountain

The Baishuijiang Group is composed of low-grade metamorphic clastic rocks, limestone blocks andmafic-ultramafic rock blocks in the south belt of western Qinling. Because it is lack of fossils evidence, theBaishuijiang Group was regarded as Silurian stratum. According to the measuring crossing section and samplingin fieldwork, and ofter analyzing the samples, the fossils including later Permian radiolarians and trace fossilswere discovered in intercalary arenaceous limestones and silica. With the discovered Ordovician and Devonianfossils in limestome blocks, and with the acquired Proterozoic U-Pb date in the volcanic rock pieces, theBaishuijiang Group is considered to be the late paleozoic mélange.