塔东地区古城4井上寒武统-中、上奥陶统流体地球化学示踪

Geochemical Tracing of Fluid from Upper Cambrian-Ordovician in Well Gucheng 4,Eastern Tarim Basin

通过对塔东地区古城4井上寒武统和中、上奥陶统碳酸盐岩围岩及充填物的碳、氧、锶同位素地球化学和流体包裹体成分的对比研究表明,充填于中、上奥陶统和上寒武统的流体分属于2个不同来源的流体体系。充填于中、上奥陶统灰岩裂缝中方解石脉的w（87Sr）/w（86Sr）介于0.7084~0.7088,它与早奥陶世海水的w（87Sr）/w（86Sr）相近;流体体系为CH4-H2O体系;充填物与围岩间具有明显的碳、氧同位素差异,表明上部流体体系中的流体来自于奥陶系地层本身。上寒武统白云岩裂缝中方解石脉的w（87Sr）/w（86Sr）为0.7138,明显地高于同时代海水的锶同位素值;流体体系为CO2-H2O体系;下部流体体系中的流体为外来富锶流体。上、下流体体系间互不连通暗示着上寒武统地层具有相对较好的保存条件。

Comparison studies for Upper Cambrian and Ordovician in well Gucheng 4 in eastern Tarim basin based on carbon, oxygen, strontium isotope geochemistry and fluid inclusions between country rocks of carbon- ate and fills in fissure, suggest that source of fluid in the Middle-Upper Ordovician is much different from that in Upper Cambrian. 87 St/S6 Sr of calcites filled in limestone fissure in Middle-Upper Ordovician is 0. 708,4- 0. 708,8 and it is similar to that from Ordovician seawater; the fluid belongs to CH4-H20 system. Obvious iso- topic differences of carbon and oxygen between fills in fissure and country rock indicate that the fluid is not directly from the country rock and from Ordovician carbonate at other locations. The ^87Sr/^86Sr of calcites filled in dolomite fissure in Upper Cambrian is 0. 713,8 and it is higher than that of contemporary seawater, and the fluid belongs to CO2-H20 system. Fluid in the lower system is an introduced fluid with abundant Sr. Different fluid sources in Upper Cambrian and Ordovician imply that Upper Cambrian has a better preservation condition.