四川盆地北缘亢家洞灯影组四段焦沥青Re-Os定年与烃源岩示踪

四川盆地及邻区的震旦系灯影组四段白云岩中普遍存在充填孔洞沥青。然而，烃源岩和沥青的高成熟度以及复杂的地质构造活动增加了恢复油气成藏史的难度。近年来，Re-Os放射性同位素体系被越来越多的应用于油气生成期定年和油源对比。陕西宁强亢家洞震旦系灯影组四段古油藏中的高成熟度沥青(R_b约为1.4%~2.5%)构建了约260Ma、60~70Ma和8~13Ma的Re-Os等时线年龄。其中，60~70Ma和8~13Ma的Re-Os年龄可能指示原油在受热裂解形成焦沥青过程末段地层抬升、地温降低、Re-Os体系封闭的时刻。而较老的约260Ma的Re-Os年龄与普遍的二叠纪是前寒武系、寒武系烃源岩主生烃期的观点一致，说明在原油热裂解之外，高成熟度沥青的Re-Os年龄也有可能指示生油期。同时，在263Ma时亢家洞大部分沥青与筇竹寺组烃源岩样品的¹⁸⁷Os/¹⁸⁸Os范围较为一致，而灯影组三段和麦地坪组烃源岩同时期的¹⁸⁷Os/¹⁸⁸Os较低，筇竹寺组可能是亢家洞古油藏沥青的主要烃源岩。上述认识对四川盆地北缘灯影组天然气勘探领域评价具重要的指导意义。

Re-Os dating and oil-source correlation of the pyrobitumen in the Member 4, Dengying Formation of the Kangjiadong paleo-reservoir,northern margin of the Sichuan Basin

There are pervasive pore-filling bitumen found in the dolomite reservoir of the Member 4, Sinian Dengying Formation. However, the high maturity of the source rocks and bitumen and the complex geological tectonic activities make it difficult to restore the history of hydrocarbon accumulation. In recent years, the Re-Os radioisotope system has been increasingly used for the dating of the oil and gas generation and oil-source correlation. The high-maturity bitumens (Rb of ca. 1.4%~2.5%) from the Member 4, Sinian Dengying Formation in the Kangjiadong paleo-reservoir, Ningqiang, Shaanxi have defined Re-Os isochron ages of ca. 260Ma, 60~70Ma and 8~13Ma. The Re-Os ages of 60~70Ma and 8~13Ma may indicate the time of when the Re-Os system was closed at the end of the crude oil being thermally cracked and the pyrobitumen forming process due to the uplift and temperature decrease. The older Re-Os age of about 260Ma is consistent with the general view that the Permian is the main hydrocarbon generation period of the Precambrian and Cambrian source rocks. It shows that besides the thermal cracking of crude oil, the Re-Os age defined by high-maturity bitumen may also indicate the crude oil generation. Meanwhile, at 263Ma, most of the Kangjiadong bitumens are consistent with the 187Os/188Os range of the Qiongzhusi Formation source rock samples rather than the lower 187Os/188Os ranges of the Member 3 of the Dengying Formation and the Maidiping Formation. The Qiongzhusi Formation may be the main source rock of the bitumen in the Kangjiadong paleo-reservoir. These understandings are important for the evaluation of natural gas exploration in the Dengying Formation in the northern margin of the Sichuan Basin.