摘要
对柴达木盆地下侏罗系河流夹沼泽相沉积和第三系以来湖相沉积的粘土矿物进行了X射线衍射、电镜等分析和观察 ,在此基础上讨论粘土矿物的成因 ,母岩分布和性质、水介质条件和古气候对粘土矿物形成和演化的影响 ,并通过粘土矿物含量和组合对比 。
The Qaidam basin is a non marine, petroliferous basin on the northeastern margin of the Qinghai Tibetan Plateau, with an area of about 120,000 km 2. Almost all strata are cropped out except Archaean group. The oil and gas discovered are distributed mainly in the reservoir of Jurassic(J 1),Tertiary(R) and Quaternary(Q). Jurassic section is mainly composed of fluvial facies and offshore shallow lake deposition, interbedded with paludal sediment, the lithology is characteristic of sandstone and mudstone, interbedded with coals. However, Cenozoic is composed of lucustrine and fluvial facies, and the lithology is characteristic of sandstone, mudstone, carbonate rock, interbedded with salt rock, gypsum, with the palaeosalinity ranging 15‰～60‰. Illite, illite smectite, montmorillonite, chlorite, kaolinite and a small amount of chlorite montmorillonite, palygorskite,holloysite are major clay mineralsin Qaidam basin. The clay mineral in sandstone is considered to be automorphic crystal which is produced in diagenetic period. The monoblastic texture of illite, kaolinite and chlorite in mudstone is anhedral crystal, and its smooth, irregular outline reflected the terrigenous genesis of clay mineral. The clay mineral contents vary with different depth and horizon. The kaolinite content is 44.4% in J 1 and 5.6% in E 1 3-E 2 3. The chlorite content vary between 18.9%～12% in Cenozoic.However, it decreases to 9.9% in Jurassic. Montmorillonite is concentrated in Quaternary and modern sediment. The content of illite smectite in N 1-N 3 2 is 42.3% in highest, and it lacks in modern irregular sediment. The content of illite in J 1 section decreases to 29.1% .The content of smectite in illite smectite decreases as the strata get older or burial depth increase. There are 5 kinds of clay mineral combination i.e. I-CH,I-S(+I/S), S(+I/S)-I, K-I or K-S(+I/S), of which I-CH or I-S(+I/S) is mainly contributed in Cenozoic, K-I or K-S(+I/S) is in J 1 lower Jurassic. S(+I/S)-I is in N 1-N 3 2 section. It is warm and humid climate at Jurassic in Qaidam basin. The parent rocks consisted by volcanics and metamorphite are subjected to strong chemical weathering to produce a great amount of kaolinite. Meanwhile, acidic water medium in coal bearing strata creates a kaolinite perserving environment. The characteristic of arid semiarid arid climate in Cenozoic represents that parent rocks mainly are subjected to physical wethering, next to chemical wethering, and it supports material basis for a great amount of illite formation. The rich K + in water medium creates an environment for kaolinite and smectite transforming to illite in Tertiary. The transported trace shows clay mineral feature and margin outline in mudstone, reflecting clay mineral terrigenous genesis. The difference of clay mineral content is correspondent with palaeoclimte, parent rock property, and water medium condition. The special combination of clay mineral reflectes the inheritance of clay mineral genesis.
出处
《沉积学报》
CAS
CSCD
北大核心
2001年第1期66-70,共5页
Acta Sedimentologica Sinica
