中文摘要：

在塔里木盆地塔河油田4区沙79井、6区沙85井奥陶系鹰山组岩芯的详细观察基础上，对裂隙、溶洞及巨型洞穴中的方解石晶体的晶胞参数、化学成分、碳、氧同位素、流体包裹体中的氢同位索等分析与研究表明，至少存在两种成岩环境：一是以大气淡水表生环境，方解石中晶胞参数（c）=17.057－17.062А，Fe2O3=0.06％－0.07％，Sr=53.3×10^-6－96.2×10^-6、Ba=19×10^-6－28×10^-6，Mg/Ca（×10^-3）=1.94－5.14，Sr／Ba=2.12－5.24，δ18 OPDB较低（-15‰－-17‰）、较低δ18 CPDB（-4‰－-2.0‰），不含或较少含烃类，流体包裹体中氢δDPDB=-94.99‰－-109.54‰为特征；另一是地层混合水埋藏环境为主，方解石中晶胞参数（c）=17.064－17.065А（个别达17.212А）、Fe2O3=0.06％－0.18％，Sr=111×10^-6－208×10^-6、Ba=215×10^-6－479×10^-6，Mg／Ca（×10^3）=1.53－1.76，Sr／Ba=0.49－0.58，方解石δ18 OPDB低（-9.6‰－-13.7‰）、流体包裹体中氢δDPDB=-77.5‰－-88.2‰为特征；另外，在巨型洞穴中方解石中组分的剧烈变化反映了洞穴充填发生于不同的水文地质-地球化学体系。

英文摘要：

Abstract Based on observation of core of the Middle and Lower Ordovician carbonate in Wells S85 and S79, a wide range geochemical methods has been used to characterize the diagenetic settings of paleo-caves and fractures -filling ＆ vugs calcites and to decipher their origin, which includes X-ray diffraction of crystal cell, carbon and oxygen iso- tope composition, fluid inclusion, hydrogen isotope of fluid inclusion and chemical elements analysis. Two diagenetic environments are defined and believed to be prevailing in the formation of paleo-caves and fractures -filling ＆ rugs calcites, the first is diagenetic environment with prevailing hypergen fresh water, mostly related to phreatic zones in subaerial process and of characteristic of crystal cells c = 17.057-17.062А and Fe2O3=0.06%-0.07% ,Sr= 53.3×10^-6-96.2×10^-6,Ba = 19×10^-6-28×10^-6,Mg/Ca（×10^3） = 1.94-5.14,Sr/Ba =2.12-5.24 , the lowest values of δ^18 OPDB（-15‰--17‰） , the considerable lower values of δ^13 CPDB（-4‰--2‰） for calcites, without or with few hydrocarbon inclusions and δD PDB = -94.99 — -109.54‰ of its fluid inclusion ; the second is believed to occur in freshwater-seawater mixing and formed during some degree of burial environment, and of features of crystal cell parameters （c） = 17. 064-17.065А（exceptional for 17.212А）, the considerable high values Fe2O3 = 0.06%-0.18% ,Sr=111×10^-6-208×10^-6,Ba =215×10^-6-479×10^-6,the considerable lower ratios Mg/Ca（×10^3） = 1.53-1.76, Sr/Ba = 0.49-0.58 for calcites, the lower values of δ^18 OPDB（ -9.6‰--13.7‰） for calcites, the considerable higher δD PDB = -77.5‰--88.2‰ of fluid inclusion. In addition, the study also demonstrated that differential hydro-geochemical systems had been developed in the formation of the gigantic speleothem calcite crystal at the 5960 -5966 m depth of burial with more than 6 m in height palaeocave in Well S85 in Tahe oil field.