准噶尔盆地东北缘石炭纪古盐度与古环境

Paleo-salinity and paleo-environmental analysis of Carboniferous in northeast Junggar basin

综合古盐度定性分析和定量计算结果,结合区域构造和沉积背景,对准噶尔盆地东北缘石炭纪古环境进行深入分析.研究区石炭系样品硼含量为18.72～74.50 μg/g,下石炭统硼含量平均为51.32 μg/g,上石炭统硼含量平均为38.40 μg/g；石炭系样品Sr/Ba值为0.15～1.85,下石炭统Sr/Ba值平均为0.69,上石炭统Sr/Ba值平均为0.40;2种方法计算的古盐度平均值分别为4.28‰和6.54‰；说明研究区早石炭世古沉积水体为半咸水—咸水环境,晚石炭世古沉积水体为淡水环境,且石炭纪沉积古水体盐度远低于正常海水盐度.由于研究区石炭纪整体处于大陆边缘,早石炭世处于岛弧—弧后盆地沉积体系,平面上受多个岛弧分割,古沉积水体盐度变化大；晚石炭世,受区域构造背景影响,整体抬升为陆,古沉积水体盐度整体降低.

Based on the content of Ba and ratio method of Sr/Ba in sediment, this paper makes qualitative analysis of sedimentary water body salinity of Carboniferous period in the northeast margin of Junggar basin. On this basis, and combing with the content of clay mineral in fine clastic rocks, we make quantitative calculation of the salinity of ancient water body, and the results show that, in early Carboniferous the ancient sedimentary water body was brackish water to salt water, while in late Carboniferous it was fresh water. Furthermore, the salinity of ancient water body in Carboniferous is far lower than normal salinity of sea water. Comprehensive analysis shows that the northeast margin of Junggar basin was generally located in the margin of continental in Carboniferous. In the early Carboniferous, the sedimentary background of northeast margin was arc-back arc basin and divided by many arcs in plane, as a result, the salinity changed considerably; while in the late Carboniferous, influenced by regional tectonic setting, this area was lifted and became land, and the salinity was decreased in general. Depth analysis of ancient water salinity will have a profound understanding and significance to the Carboniferous tectonic paleogeography and hydrocarbon exploration.