碳酸盐结合态Fe与As、Ce的相关性对沉积条件的指示

Correlations between carbonate-associated Fe and As/Ce as new proxies for the tracing of sedimentary conditions

文章对神农架地区中元古界神农架群野马河组和温水河组碳酸盐岩开展研究,采用5%的HCl对新鲜碳酸盐岩样进行溶解,对溶液开展Fe、As、Ce测定,对酸溶残渣开展拉曼光谱和X射线衍射分析,同时采用分级提取法开展样品的黄铁矿矿化度(degree of pyritization,DOP)测定。结果表明:石墨拉曼光谱法和绿泥石结晶度法测定的2套地层变质温度相同,均为300℃左右;野马河组样品DOP值均小于0.42,该地层沉积环境相对氧化;1/2温水河组样品的DOP值大于0.42,该地层沉积环境相对还原;野马河组中碳酸盐结合态(carbonated-associated)Fe(Feca)与Asca、Ceca均呈正相关性,而温水河组中Feca与Asca、Ceca均无相关性。研究发现:Feca与Asca、Ceca的相关性可以示踪沉积氧化还原条件,即正相关指示氧化性沉积条件,不相关指示还原性沉积条件;300℃左右的变质温度对该指标没有影响。

This study analyzed carbonates from the Yemahe and Wenshuihe Formations of the Mesoproterozic Shennongjia Group,which is located at the Shennongjia area,China.After dissolution by 5%HCl,the solutions were detected for Fe,As,and Ce concentrations,and the solid residues were analyzed by Raman spectroscopy and X-ray diffraction.Besides,sequential extraction was carried out to study the degree of pyritization(DOP).The results show that the metamorphic temperature for both formations is about 300℃.All samples from Yemahe Formation have DOP values less than 0.42,suggesting relatively oxidized sedimentary conditions.Half samples from Wenshuihe Formation have DOP values above 0.42,suggesting relatively reductive sedimentary conditions.For samples from Yemahe Formation,carbonate-associated Fe(Feca)is positively correlated to carbonate-associated As(Asca)and Ce(Ceca).For samples from Wenshuihe Formation,no correlation is observed between Feca and Asca and Ceca.It is considered that the correlations between Feca and Asca and Ceca are potential proxies which can be used for tracing sedimentary redox conditions,where the positive correlations indicate oxidative sedimentary condition,while no correlation indicates reductive sedimentary condition.Such proxies are not affected by 300℃metamorphic temperature.