Sedimentary Environment And Provenance Analysis Of The Neoproterozoic Sibao And Danzhou Groups In Northern Guangxi

Depositional age,sedimentary environment and source characteristics of the Neoproterozoic Sibao and Danzhou groups in northern Guangxi are of great significance for understanding the evolution of Neoproterozoic sedimentary basins in Southern China.Systematic sedimentological,stratigraphic and geochronological analyses were conducted in order to reveal the depositional environment and facies,and detrital zircon provenance of the Neoproterozoic Sibao Group and Danzhou Group combined with the published data.The results thus provided new constraints on the evolution of the Neoproterozoic sedimentary basins in Southern China.Stratigraphic sequence and sedimentary structures indicate that the Jiuxiao Formation of the Sibao Group is a semi deep-sea and deep-sea turbidite facies.The Baizhu Formation of the Danzhou Group had evolved from shallow water density-current deposits to fluvial to delta,and to shelf facies.LA-ICP-MS zircon U-Pb isotopic dating results show that ages of tuffs and tuffaceous sandstone in the second part of the Hetong Formation and in the Gongdong Formation are 792.1±3.2 Ma and 773.8±9.8 Ma,respectively.According to the published data,the results show that the depositional age of the Baizhu Formation of the Danzhou Group is 820~805 Ma.The depositional age of the first part of the Hetong Formation is 805~800 Ma,whereas the second part is 800~780 Ma.The depositional age of the Gongdong Formation of the Danzhou Group is 780~725 Ma.LA-ICP-MS detrital zircon U-Pb dating results show that the main peak of the detrital zircon age of the Jiuxiao Formation is 861 Ma,with subordinate age peaks at 994 Ma,1720 Ma and 2480 Ma.The main peak age of detrital zircon of the bottom conglomerate of the Baizhu Formation of Danzhou Group,unconformably underlain by the Sibao Group,is 822.6 Ma,with subordinate age peaks at 927 Ma,1594 Ma and 2468 Ma.The main age of the detrital zircon in the upper part of the Baizhu Formation is 834 Ma,with secondary peaks at 1576 Ma,1900 Ma and 2415 Ma.The main age of the detrital zircon in the first part of the Hetong Formation is 798.4Ma,and the secondary peaks are 1720 Ma,2200 Ma and 2600 Ma.Based on the analysis of the detrital zircon U-Pb age spectrum and the paleoflow direction,this paper suggests that the sediments of the Jiuxiao Formation of the Sibao Group and the Baizhu Formation of the Danzhou Group may mainly source from the Archaean-Paleoproterozoic basement in the Northeastern Cathaysian Block,whereas clastics of the Baizhu Formation and the Hetong Formation mainly derived from the Archean basement rocks in the Northwestern Yangtze block,accompanied by sediments from of the Cathaysian Block.