西藏措勤盆地晚侏罗世牛津期—基默里奇期沉积环境及油气勘探意义

Sedimentary Environment and Hydrocarbon Exploration of the Late Jurassic Oxfordian–Kimmeridgian Strata in the Coqen Basin, Tibet

前人长期认为措勤盆地的晚侏罗世古地理格局为“南陆北海”,即盆地南部为古陆环境,北部为大面积的碎屑岩相滨浅-斜坡环境。然而,近几年来,在措勤盆地内部的仲巴县仁多地区、申扎县雄梅地区、班戈县保吉地区,及其北侧毗邻的改则县物玛地区、双湖县多玛地区相继发现了厚度数百米到上千米厚的上侏罗统碳酸盐岩地层。这些地层的发现说明盆地南部并不是地层缺失的古陆,盆地北部也不是大面积的碎屑岩沉积。晚侏罗世牛津期—基默里奇期盆地并非表现为从南向北水体明显加深的趋势,而是中部和北部为碳酸盐岩台地环境,南部为斜坡环境。措勤盆地晚侏罗世牛津期—基默里奇期较为稳定的碳酸盐岩台地环境和广阔的空间为生物礁的发育提供了有利条件,措勤盆地晚侏罗世牛津期—基默里奇期的生物礁应该有广阔的分布,显示出其良好的油气勘探潜力。

The Late Jurassic palaeogeographic pattern of the Coqen Basin,for a long time,has been considered as“land in the south,sea in the north”,namely,it is a continental environment in the southern basin but a large area of clastic rock facies offshore-slope environment in the northern basin.In recent years,however,Late Jurassic carbonate formation has been found,which is several hundred to more than one thousand meter thick,in Rendo area of Zhongba County,Xiongmei area of Xainza County,Baoji area of Bange County within the basin and Wuma area of Gaize County,and Duoma area of Shuanghu County in the adjacent area to the north of the basin.The discovery of these strata indicates that the southern part of the basin is not the ancient land,and the northern part of the basin is not a large area of clastic rocks.In Late Jurassic Oxfordian–Kimmeridgian period,it did not tend to become deeper from the south to the north in the basin;on the opposite,it was a vast carbonate platform in the north,and became deeper to slope in the south.In Late Jurassic Oxfordian–Kimmeridgian period the extensive carbonate sedimentary environment provided favorable conditions for the growth and reproduction of reefs in the Coqen Basin.Therefore,Late Jurassic Oxfordian–Kimmeridgian reef should have had a wide distribution,which indicates good oil and gas potential in the Coqen Basin.