Abstract：
Siliceous deposits(or chert),generally being dark grey to black and thin-bedded,widely occurred in the strata from the Emsian to Frasnian of the Devonian in Nanning area,Guangxi,which were intercalated commonly with brownish tuffites(or tuffaceous chert).This paper presented the rare earth element(REE) geochemistry of siliceous deposits there from which the depositional setting and basin evolution were elucidated.The total REE contents(∑REE) were generally lower in the cherts,with an average being 18.59?10-6,12.28?10-6,27.44?10-6 and 43.07?10-6 in the Emsian,Eifel,Givetian and Frasnian,respectively.The shale-normalized REE abundances in the cherts were featured with weak to moderate negative Ce contents in late Early Devonian to early Late Devonian,with Ce anomalies(avg.Ce/Ce* values,being 0.85,0.72,0.85 and 0.67 respectively),generally lower positive Eu anomalies(avg.Eu/Eu* values,being 1.08,1.21,1.46 and 1.04 respectively),intermediate(La/Ce)N values(avg.1.42,1.50,1.35 and 1.73 respectively),and intermediate to lower(La/Yb)N values(avg.1.19,1.19,1.24 and 0.45 respectively).These data suggested that these siliceous deposits were initially precipitated in an intracontinental rift basin with significant terrigenous influences in the Early Devonian,which was rapidly transformed into an open marine basin with a little terrigenous influences in the early Late Devonian(Frasnian) due to a rapid extension of the basin.Although the precipitation of the cherts was influenced by the hydrothermal venting,it was generally weak,probably away from hydrothermal vents in a distance.
Wang Zhuozhuo,Chen Daizhao,Wang Jianguo. REE GEOCHEMISTRY AND DEPOSITIONAL SETTINGS OF THE DEVONIAN CHERTS IN NANNING AREA,GUANGXI[J]. Chinese Journal of Geology, 2007, (3): 558-569.
2007, Vol. 
