渤海湾盆地黄骅坳陷湖相碳酸盐岩微量元素特征及沉积环境

Trace element characteristics and sedimentary environment of lacustrine carbonate rocks in the Huanghua Depression,Bohai Bay Basin

渤海湾盆地黄骅坳陷沙一下段主要以碳酸盐岩储层为主,是区内主要油气储层。黄骅坳陷孔店—羊三木地区、齐家务地区和歧南地区沙一下段微量元素特征表明,其含量及分布在不同区带差异明显,但Sr、Ba、Mn等元素的含量在各区较为接近,而Ni、Pb、Zn等元素的含量由齐家务向孔店—羊三木一带趋于减少,反映了黄骅坳陷湖盆碳酸盐岩在沉积成岩过程中沉积环境条件的变化。齐家务地区B元素含量为(7.55~92.8)×10^(-6),平均42.8×10^(-6),孔店—羊三木地区B元素含量为(7.2~97.4)×10^(-6),平均45.21×10^(-6),反映出湖盆水体在沙一下段沉积期均具有咸化与淡化的交替过程。孔店—羊三木地区沙一下段各类样品中的Ti含量为(946~3 495)×10^(-6),平均2 319×10^(-6),显示近物源的特点。V/(V+Ni)比值变化显示出全区强还原环境的特点,同时Th/U比值较低的特征,说明湖盆水体盐度较高或受到了入侵海水的影响。

Carbonate rocks dominate in the lower part of the first member of Shahejie Formation in the Huanghua Depression,Bohai Bay Basin.The geochemical characteristics of trace elements in Kongdian-Yangsanmu,Qijiawu and Qinan show that the content and distribution of trace elements varied in different pays,but those of Sr,Ba,V,Mn,Th,U were similar,and the contents of Ni,Pb,Zn and others tended to decrease from Qijiawu to Yangsanmu,indicating environmental changes during the diagenesis process.The B content varied(7.5-92.8) ×10^(-6) with an average of 42.8 × 10^(-6) in Qijiawu,and varied(7.2-97.4) × 10^(-6) with an average of 45.21 × 10^(-6) in Kongdian-Yangsanmu,indicating an alternating process of saline to fresh water environments.The Ti content varied(946-3 496) ×10^(-6) and averaged 2 319×10^(-6) in the lower part of the first member of Shahejie Formation from Kongdian to Yangsanmu,showing nearby provenance characteristics.The V/(V+Ni) ratio indicated strong reducingenvironment in the study area,and the low Th/U ratio showed a higher salinity of lake water or the influence of seawater intrusion.