广东乳源地区棋梓桥组—天子岭组碳酸盐岩地球化学特征及其古环境意义

Geochemical characteristics and paleoenvironmental significance of Qiziqiao-Tianziling Formation carbonate rocks in Ruyuan area,Guangdong,China

通过运用对沉积环境反应敏感的Sr、Ba、Cu、Fe、Mn、Ca、Ni、V等元素,结合δ^(13)CV-PDB、δ^(18)OV-PDB数据及沉积学特征,对粤北韶关盆地乳源地区泥盆系棋梓桥组—天子岭组的古盐度、古气候、古水深、氧化-还原性等古环境参数进行综合研究。结果表明:棋梓桥组Z值普遍较低(121.56~123.34),Sr/Ba值(质量分数之比)变化明显(4.77~24.66),沉积时期古温度为17.49~25.49℃,Fe/Mn值为13.12~38.45,Sr/Cu值为6.41~32.64,V/(V+Ni)值均大于0.54,古水深曲线与沉积相特征显示为一次海平面升降旋回;天子岭组Z值较高(125.53~128.12),沉积时期古温度平均为20.54℃,具有异常高的Sr含量,Fe/Mn平均值为44.22,V/(V+Ni)值均大于0.54,古水深曲线与沉积相特征显示4次海平面升降旋回。研究区的弗拉斯阶(天子岭组)整体继承了吉维特阶(棋梓桥组)的海侵格局,由西向东海域面积进一步扩大,海平面升降旋回性增强,气候向适宜古生物生长繁殖的方向转变;吉维特阶海水的厌氧特征以及弗拉斯阶海平面的高频升降旋回和核形石的大规模发育现象,为乳源地区F-F生物大灭绝事件提供了时间和环境因素方面的证据。

By using Sr,Ba,Cu,Fe,Mn,Ca,Ni,V and other sedimentary environment sensitive elements,combined withδ^(13)C V-PDB andδ^(18)O V-PDB data and sedimentary characteristics,the paleoenvironmental parameters,such as paleo-salinity,paleoclimate,paleo-water depth and oxidation reducibility of the Devonian Qiziqiao-Tianziling Formations in Ruyuan area of Shaoguan Basin,northern Guangdong Province,are comprehensively studied.The results show that the Z value of Qiziqiao Formation is generally low(121.56~123.34),the Sr/Ba value(mass fraction ratio)changes obviously(4.77~24.66),the paleo-temperature of the sedimentary period is 17.49~25.49℃,the Fe/Mn value is 13.12~38.45,the Sr/Cu value is 6.41~32.64,the V/(V+Ni)values are all greater than 0.54,and the paleo-water depth curve and sedimentary facies are characterized by a sea level rise and fall cycle.Meanwhile,the Z value of Tianziling Formation is high(125.53~128.12),with average paleo-temperature of 20.54℃during the sedimentary period,the content of Sr is unusually high,the average value of Fe/Mn is 44.22,the value of V/(V+Ni)is greater than 0.54 and the paleo-water depth curve and sedimentary facies characteristics show four sea-level rise and fall cycles.In the study area,the Frasnian(Tianziling Formation)inherited the transgression pattern of the Givetian(Qizqiao Formation)as a whole,and the sea area was further expanded from west to east,with enhanced sea level cycle,and the climate changed to the direction suitable for the growth and reproduction of palaeobios.The anaerobic characteristics of Givetian stage seawater,the high frequency fluctuation cycle of Frasnian stage sea level and the large-scale development of oncolite provide evidence for the F-F mass extinction event in the Ruyuan area.