中国西北地区侏罗纪煤系油气形成(之一)

Petroleum formation in Jurassic coal bearing basins, Northwest China (Part 1).

侏罗纪是中国西北地区最主要的聚煤期。侏罗纪西北地区气候温暖潮湿，植被繁盛，发育六大原盆地沉降带，形成沼泽、浅湖、半深湖沉积环境，广泛沉积了河流相—沼泽相—湖相煤系地层，普遍发育煤、炭质泥岩（页岩）、油页岩和湖相暗色泥岩这４类烃源岩。侏罗系烃源岩在阿尔金断裂带南、北两侧差异较大：北侧新疆地区中、下侏罗统煤系泥岩和煤均很发育；南侧蒙甘青地区早侏罗世沉积范围很小，中侏罗世虽发育泥岩，但一般不发育煤层。侏罗系烃源岩中主要的成烃显微组分是壳质体、藻类体、基质镜质体等，木栓质体和树脂体等早期成烃组分含量很低。煤系泥岩一般为中等到差油源岩，少数为好油源岩，煤一般为差油源岩。新疆地区下侏罗统烃源岩生烃潜力高于中侏罗统烃源岩。

Jurassic is the main coal forming period in Northwest China. Palaeoplants bloomed and their species were variform due to the warm and wet palaeoclimate during the Jurassic. Six subsidence zone and depositional proto basins developed in Northwest China, forming the depositional environments of coal swamps, shallow and deep water lakes. Coal bearing strata widely deposited in these proto basins. There are 4 kinds of source rocks in these Jurassic coal bearing basins, which are coal, carbonaceous shale, mudstone and oil shale. The distribution of these source rocks in the north of Altun fault, Xinjiang Autonomous Region, differs from that in the south of Altun fault, Inner Mongolia, Gansu and Qinghai provinces. In the north of Altun, the source rocks distribute in Lower to Middle Jurassic. Whereas in the south of Altun, they generally distributed in Middle Jurassic. Furthermore, coalbeds less developed in the south than in the north, and the Lower Jurassic formation deposited in some small regions in the south. In the Jurassic coal bearing source rocks, main macerals of hydrocarbon generation are sporinite, cutinite, alginite, bituminite, liptodetrinite and desmocollinite. Suberinite and resinite are extremely low in concentration, which are generally regarded as macerals generating hydrocarbon in immature and low mature. Majority of black mudstone in Jurassic coal bearing strata is low to middle potential source rock, and minority of it is high potential. Oil shale is high potential source rock, but coal is generally poor potential source rock in Jurassic coal measures. Besides, in the north of Altun, whether the coal or the mudstone in Lower Jurassic, their oil generation potential is higher than those in Middle Jurassic.