扬子陆块北缘汉中地区成冰纪冰期沉积岩与锆石U-Pb年龄OA

[Objective]Neoproterozoin"Snowball Earth"(Cryogenian)glaciations is a long-standing hot topic in sedimentology.In South China,well-preserved sedimentary records during Cryogenian Period have been found in many places in the Yangtze Block.However,there are relatively few reports on deposits of this time in Kangdian Rift Basin on western margin of the Yangtze Block,and in the rift basin between northern margin of the Yangtze Block and southern margin of the Qingling Orogen.[Methods]This study focuses on the Cryogenian glacial deposits in the Gangchang-Yuanba section,Hanzhong area,northern margin of the Yangtze Block.Based on the field observations and measurements,zircons were selected from the bottom tuff layer and upper sandstones for U-Pb dating analysis us-ing laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).Detailed features of the sedimentary rocks and their regional correlation are also discussed.[Results]Two sets of tillites were identified for the first time within the Neoproterozoic glacial sedimentary rocks in this region,both from a continental glacier.Several layers of sandstone and siltstone are presented between and above the tillite sets.Zircons from the bottom tuff yielded the earli-est mean concordant age of(719±11)Ma,indicating the beginning of glaciation in this region.Considering their lithological succession and sedimentary structures,these Cryogenian deposits are thought to have been formed during Sturtian glaciation,corresponding respectively to the Chang'an and Gucheng glaciation periods.The timing of this glaciation event,and the sedimentary associations,are consistent with contemporaneous sediments in the adjacent Zhenba and Chengkou areas,and also show similarities to Sturtian sediments widely distributed in other parts of South China.