Isotopic Characteristics of Formation Waters in the North of Songliao Basin and Its Geological Significances 

Key words: 
•   /
• formation water /
• waterrock interaction /
• SrDO isotope /
• Songliao Basin /
•  /

Abstract: The basin fluid is the very active factor in the sedimentary basins.  The hydrogeochemistry is mainly controlled by fluid rock interaction. The source and genesis of the formation water are very complex. It is difficult to determine the genesis and source just according to the general component ions concentration and the interrelationship of ions. In this case, it is necessary to combine the trace elements and isotopic components to explain the genesis and source of the formation water. Applying isotopic chemistry method to research the formation water, in order to find the source, carry out the intensity of waterrock interaction, trace fluid flow direction, and compute the paleotemperature, age and residence time of the basin fluid. Based on hydrogeochemical characters of formation water and analysis of SrDO isotope data, this article researches on the northern area of Songliao Basin, discusses the relationship of waterrock interaction and SrDO isotope. It is of great theoretical significance for the isotope tracers in the enrichment of waterrock interaction. The result of the hydrogenoxygen isotope testing suggests that formation water in the western area is evidently influenced by the ancient precipitation, and the positive excursion of the δ18O in the central depression is probably caused by the strengthing of waterrock interaction. The formation water is a mixture of meteoric water and primary sedimentary water, the slight value of the δD reflects the original sediment belongs to the continent depositional water. In the groundwater, the concentration of Sr2+ increases with TDS, Sr comes from the dissolution of rock dissolved by groundwater. The groundwater from Quantou Group (K2q) and Yingcheng Group (K1yc) has  same character as the continent depositional water. Meanwhile, the groundwater from Qingkoushan Group shows the character of the sea depositional water obviously. The groundwater from Quantou Group and Yingcheng Group shows the character of the continent depositional water obviously. The distribution range of 87Sr/86Sr values from different formation water is concentrated, and has homologue. In all salt rocks, except those from Quantou Group, the distribution range of 87Sr/86Sr values from different formation rock is also concentrated, and has the same type of source. The salt rocks from Quantou Group are from distinct source and the higher value of 87Sr/86Sr should be inflected by the siliconaluminium rock from the crust source. The 87Sr/86Sr value of formation water is slightly lower but the concentration of Sr2+ is higher, the formation water is a mixture of high 87Sr/86Sr value fluid end member and low 87Sr/86Sr value fluid end membera mixture of surface source water and deep formation water, which is also obtained from mantle deep water like high Sr2+ value and low 87Sr/86Sr value volcanic geothermal water. 