1. Exploration and Development Research Institute of Daqing Oilfield Co. Ltd., Daqing 163712, Heilongjiang, China;
2. Langfang Branch, Research Institute of Petroleum Exploration and Development of PetroChina, Langfang 065007, Hebei, China

The Permian Zhesi and Linxi formations are widely distributed in Linxi area, Inner Mongolia, consisting of a set of dark mudstone, sandstone and carbonate rock sedimentary assemblages, which are important source rocks in the region. Rare earth elements and trace elements in carbonate rocks near the boundary between Zhesi and Linxi formations in Guandi, Linxi County were analyzed by ICP-MS inductively coupled plasma mass spectrometry. The results show that there are obvious differences in the composition of trace elements and rare earth elements between Linxi and Zhesi formations. The total average value of rare earth elements (REE+Y) in Zhesi Formation is 40.51×10^-6, which is significantly lower than that in Linxi Formation (82.12×10^-6). After PAAS standardization, both of them are deficient in light rare earth elements relative to medium rare earth elements and heavy rare earth elements. Moreover,the Zhesi Formation carbonate rocks show larger positive ��Eu and ��Ce anomalies than Linxi Formation, with different REE distribution patterns from normal marine and lacustrine carbonate rocks. The content of trace elements in the carbonate rocks at the boundary between Zhesi and Linxi formations shows a sudden change. Among them, the contents of trace elements such as Cu, Zn, Rb and Zr, which characterize terrestrial contamination, increase significantly above the boundary. The characteristic parameters of Sr/Ba > 1, V/Cr > 4.25 and V/(V+Ni) > 0.54, indicating that the main sedimentary bodies were deposited marine and strong reductive environment during the Middle and Late Permian. The subduction and magmatism of the Paleo-Asian Ocean plate and their extreme strong reduction environment and hydrothermal effection are the main reasons for the significant positive anomalies of ��Eu and the general positive anomalies of ��Ce in carbonate rocks along the boundary between the Zhesi and Linxi formations in studied area.