塔里木盆地哈6井石炭系、志留系砂岩自生伊利石K-Ar、Ar-Ar测年与成藏年代

K-Ar and Ar-Ar dating of authigenic illite and hydrocarbon accumulation history of Carboniferous and Silurian sandstone reservoirs in Well Ha 6,Tarim Basin

利用自生伊利石K-Ar、Ar-Ar测年技术对塔里木盆地哈6井石炭系、志留系砂岩油气藏的成藏年代进行测定与研究。哈6井石炭系角砾岩段自生伊利石K-Ar年龄为86Ma,相当于晚白垩世,表明为燕山晚期成藏;志留系沥青砂岩自生伊利石K-Ar年龄为125Ma,相当于早白垩世晚期,表明为燕山中晚期成藏。石炭系、志留系砂岩是塔里木盆地的重要储层,广泛分布于塔中隆起、北部坳陷和塔北隆起,已知的自生伊利石年龄范围分别是:石炭系东河砂岩为231～285Ma,志留系沥青砂岩为204～383Ma。与塔里木盆地其他地区相比,本次研究的哈6井石炭系、志留系砂岩的自生伊利石年龄明显偏小,表明哈6井石炭系、志留系油气藏的成藏期明显偏晚,对其勘探意义应该开展深入研究。哈6井石炭系、志留系砂岩自生伊利石的Ar-Ar年龄分别为148～159Ma和189～195Ma,与其K-Ar年龄相比明显偏老,可能不具有明确的地质意义,更不能反映油气注入事件和代表成藏期,快中子照射过程中的39 Ar反冲丢失是其主要原因。

The hydrocarbon charge history of Carboniferous-Silurian sandstone reservoirs in Well Ha 6, Tarim Basin, was comprehen- sively studied by applying SEM observation, clay mineral XRD characterization, illite genetic type identification and the K-Ar and Ar-Ar dating of authigenic illite. The result shows that the authigenic illite K-Ar age of Carboniferous sandstone reservoirs in Well Ha 6 is 86 Ma, corresponding to Late Cretaceous and indicating the primary formation of the Carboniferous oil pool mainly in the late Yanshanian period, while the authigenic illite K-Ar age of Silurian bituminous sandstone reservoirs in Well Ha 6 is 125 Ma, corre- sponding to a late stage of Early Cretaceous and indicating the primary formation of the Silurian oil pool mainly in the middle to late Yanshanian period. Carboniferous-Silurian sandstones are one of the important reservoirs in Tarim Basin and they are well developed in Tazhong uplift, the northern depression and Tabei uplift. Their dated authigenic illite ages range from 231 Ma to 285 Ma for the Carboniferous Donghe sandstone and from 204 Ma to 383 Ma for the Silurian Bituminous sandstone, respectively. Compared with au- thigenic illites in other major regions of Tarim Basin, the age of authigenic illites in the Carboniferous-Silurian sandstones from Well Ha 6 is obviously young, indicating that the accumulation of Carboniferous-Silurian pools in Well Ha 6 occurred more lately, there fore, detailed investigations on the implication of this occurrence in oil exploration should he conducted as well. Authigenic illite Ar- Ar ages of the Carboniferous and Silurian sandstone reservoirs in Well Ha 6 are 148- 159 Ma and 189- 195 Ma, respectively, appea- ring much older than the corresponding K-Ar ages, which indicates that the Ar-Ar ages probably have no definite geological mean- ings, and can not be representative of the hydrocarbon charging time. The 39 Ar recoil loss during neutron irradiation seems the main reason for these older Ar-Ar ages.