济阳坳陷奥陶系碳酸盐岩及缝洞充填方解石C、O同位素特征及其意义

对济阳坳陷奥陶系碳酸盐原岩及孔洞缝中充填方解石进行了C、O同位素测定,结果表明孔洞缝充填方解石的δ¹³C和δ¹⁸O值比原岩偏负。奥陶系三山子组和马家沟组孔缝中充填的方解石C、O同位素演化有很大区别,前者的δ¹³C和δ¹⁸O值均为负值,δ¹³C向较高负值偏移,δ¹⁸O值向较低负值偏移;马家沟组八陡段孔缝充填方解石的δ¹³C和δ¹⁸O值也多为负值,δ¹³C向较正值方向偏移,δ¹⁸O值向较高负值偏移。奥陶系碳酸盐岩孔缝充填方解石形成于大气淡水环境和埋藏成岩环境,次生孔洞可能主要形成于早期表生阶段,裂缝形成于中-新生代的构造运动,方解石主要充填于埋藏环境中。次生孔缝的主要形成时期早于油气大量运移期,对古潜山油藏的形成有利。

CHARACTERS AND IMPLICATIONS OF C, O ISOTOPES IN THE ORDOVICIAN CARBONATE ROCKS AND CALCITE FILLED IN POROSITIES/FISSURES IN THE JIYANG DEPRESSION

The C,O stable isotope compositions of the Ordovician carbonate rocks and calcite filled in porosities/fissures from the Jiyang Depression were analyzed.The results showed an obviously evolutional difference between the C,O isotopes of calcite in porosities/fissures in the Sanshanzi and Majiagou Formations.The δ¹³C and δ¹⁸O values of the former were all negative,with the δ¹³C values shifting towards relatively higher negative values and the δ¹⁸O values shifting towards relatively lower negative ones.The δ¹³C and δ¹⁸O values of the calcite filled porosities/fissures in the Badou Member,Majiagou Formation were almost negative,but their evolution regularities were different from that in the Sanshanzi Formation,with the δ¹³C values shifting towards positive values and the δ¹⁸O values shifting towards relatively higher negative ones.These characters might imply two diagenetic environments once exisiting:the meteoric and buried diagenetic environments.The porosities/caverns of secondary generation were mainly formed during early exposing period,and the fissures created in Mesozoic tectonic movements with buried diagenetic environment.The formation time of the secondary porosities/fissure was earlier than that of oil-gas migration,which should be favorable for the buried hill oil pools’formation.