摘要
鄂尔多斯盆地中部三叠系延长组长6段是石油勘探开发的重要层位,该段普遍发育高自然伽马砂岩,但对其相关研究却很薄弱。一般认为,该区长6段砂岩自然伽马异常高是与长石、黑云母、粘土含量及火山凝灰岩有关。文中通过对高伽马砂岩及邻近常规砂岩的显微镜薄片观察、X光衍射及粘土矿物分析、电子探针及质谱仪化学元素分析以及沉积与分布特征分析,认为与常规砂岩相比,高伽马砂岩具有以下特点:钾长石、绿泥石、铁泥质粘土杂基含量明显上升,石英含量明显减少,长石高岭石化强烈,岩屑含量较高,且岩屑假杂基化较为普遍。Th、U、K放射性元素含量较高,其中Th元素含量上升最为显著,主要存在于独居石、金红石、铁泥质粘土、钾长石及部分锆石、磷灰石、黑云母、岩屑中;U元素主要存在于大多数的锆石、部分磷灰石、黑云母及含镁方解石中;K元素主要存在于钾长石、黑云母、金红石、铁泥质粘土、部分钠长石及岩屑中。高伽马砂岩不受沉积相的控制,火山凝灰岩与高伽马砂岩的形成无必然联系,高伽马砂岩与来自于盆地东北方向的物源有一定的亲缘性。综合分析认为,深部热液活动可能导致了高伽马砂岩的形成。
The Member Chang 6 of Triassic Yanchang Formation in central Ordos Basin is an important layer for petroleum exploration and exploitation. In this member high natural gamma sandstones are wide-spread, but they are poorly studied. Previous studies suggest that the high natural gamma anomaly is related with feldspar, biotite, clay mineral contents and volcanic tuff. However, through the microscopic thin section study, X diffraction analysis of clay minerals, electron microprobe and mass spectrometer analysis of chemical elements in minerals, and the study of distribution characteristics of sediments we found that in contrast with conventional sandstones the high natural gamma sandstones are higher in K-feldspar, chlorite and ferruginous clay matrix contents while the content of quartz is significantly lower. The contents of biotite and calcite is slightly increased. Feldspar in some high gamma sandstone is seriously kaolinized. Some high gamma sandstones are higher in lithic fragments which are commonly intensively altered forming pseudo matrix. As compared with conventional sandstones, the contents of Th, U, K in high natural gamma sandstone are higher. Among them the content of Th is significantly increased, which is mainly existed in monazite, rutile, ferruginous clay, feldspar, some of the zircon, apatite, biotite and lithic fragments. The radioactive element of U mainly exists in most of zircon, some of apatite, biotite and magnesium calcite. The radioactive element of K is mainly contained in K feldspar, biotite, rutile, ferruginous clay, and some of albite and lithic fragments. The sedimentary facies is not the controlling factor for the high gamma anomaly in the sandstone formation. There is not any inevitable connection between volcanic tuff and the formation of high gamma sandstone. To a certain degree, the high gamma sandstone is indigenous to the material source from northeast of the basin. On the whole, the deep hydrothermal activity may probably have resulted in the formation of high gamma sandstones.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2013年第5期149-165,共17页
Earth Science Frontiers
基金
中国石油测井有限公司项目
关键词
鄂尔多斯盆地
延长组长6段
高伽马砂岩
放射性元素
热液活动
Ordos Basin
Member Chang 6 of Yanchang Formation
high natural garmna sandstone
radioac- tive element
hydrothermal activity
