浙江长兴煤山下三叠统和龙山组、南陵湖组沉积地球化学特征与古环境意义

Sedimentary Geochemistry Characteristics and Paleoenvironmental Meaning of Helongshan Formation and Nanlinghu Formationin Meishan,Changxing County,Zhejiang Province

对全球二叠系-三叠系界线层型剖面——中国浙江长兴煤山D剖面和龙山组、南陵湖组47件样品的地球化学特征(常量元素、微量元素和稀土元素)的系统分析表明,和龙山组的w(MgO)/w(CaO)及w(SiO2)、w(Al2O3)、w(K2O)等变化不大,稀土元素和微量元素丰度自下而上的变化趋势基本一致,反映其形成时的气候条件变化不大,气候主要从潮湿向略干旱转变,但其中也具有多个微小的变化旋回,反映每个小旋回的环境变化较小;从南陵湖组底部开始,w(MgO)/w(CaO)变化明显,形成的岩石中w(SiO2)、w(Al2O3)、w(K2O)急剧下降,岩石的稀土元素和微量元素总量也下降,反映南陵湖期海平面持续下降,沉积水体变浅,物源区较近,气候的变化比较大,总体向干旱转变。

The study of samples from the Helongshan Formation and the Nanlinghu Formation at Meishan section D,the GSSP of the Permian-Triassic boundary in Changxing County,Zhejiang Province,China,makes it possible to know the characteristics of sedimentary geochemistry and paleoenvironment.It shows that the ratio of w(MgO)/w(CaO),the content of SiO_2,Al_2O_3,K_2O of Helongshan Formation changes little,and the trend of REE and trace elements is generally consistent from bottom to top.It indicates that there is little change in climate.There were many tiny gyres and the environment of every gyre was hardly alterant. The climate changed from wetness to slight drought on the whole,and w(MgO)/w(CaO)changed clearly with the content of SiO_2,Al_2O_3,K_2O declining rapidly from the bottom of Nanlinghu Formation. The gross of trace elements and REE fell down simultaneously.It is inferred that:①the sea level during Nanlinghu Period declined continuously;②the water depth became shallow;③the source of sedimentary matter was rather near,and the transformation of the climate was prominent and turned into drought as a whole.