黄骅坳陷孔南地区孔二段时期元素地球化学特征及其意义

ELEMENT GEOCHEMISTRY OF THE SECOND MEMBER OF KONGDIAN FORMATION IN SOUTHERN HUANGHUA DEPRESSION AND ITS IMPLICATIONS

黄骅坳陷孔南地区孔二段采集碳质泥岩样品5块,用X-荧光和ICP-MS测定全岩常量、微量和稀土元素。用锶钡法（Sr/Ba）、硼镓法（B/Ga）、硼元素法（B）及碳氧同位素法对古盐度进行恢复,进而分析孔二段沉积时期的古气候环境和湖盆的封闭性,结果显示孔南地区孔二段时期为气候潮湿,降水丰富,半咸水-淡水的内陆封闭湖盆沉积。根据La-Th-Sc、Th-Sc-Zr/10判别图解和稀土元素特征显示,研究区构造背景为活动大陆边缘的坳陷盆地。本区泥岩低稀土元素（∑REE=135.14～190.6）、富轻稀土（LREE/HREE=9.44～10.96）、Eu负异常（δEu=0.54～0.71）,暗示源区以花岗岩为主,也有沉积岩。

Lithology,trace elements and rare earth elements were studied for the 5fresh samples of carbonaceous mudstone taken from the 2nd Member of the Kongdian Formation in the southern Huanghua Depression.X fluorescence and ICP-MS are used for determination of element geochemistry and barium strontium method（Sr/Ba）,boron gallium method（B/Ga）,boron element method（B）and C,O isotope method used for restoration of paleo-salinity.Upon the basis,the paleo-climatic environment and the openness of the basin are discussed.The results show that during the period while the 2nd Member of the Kongdian Formation was deposited,the climate was humid,and rich in rainfall.It was a closed inland lake basin filled with fresh or subsaline water.The La-Th-Sc,Th-Sc-Zr/10 diagrams and the characteristics of rare earth elements show that the study area was tectonically a marginal depression along an active continental margin.The mudstone is low in rare earth elements（∑REE=135.14～190.6）,and high in light rare earth elements（LREE/HREE=9.44～10.96）,with negative abnormal Eu（δEu=0.54～0.71）,suggesting agranite dominated source area with some sedimentary rocks.