羌塘盆地侏罗系展布重力反演预测及蒸发岩沉积洼陷优选评价

Gravity Inversion of Jurassic Depressions and Evaluation of Favorable Depressions for Evaporate Sedimentation in the Qiangtang Basin

利用露头和岩心物性的统计资料和对羌塘盆地统一改算后的1∶50万重力资料的波谱结构分析,应用匹配滤波法分离出羌塘盆地6个构造层。通过带地形的重力反演法计算了侏罗系构造层顶底界面深度及构造层厚度,预测了羌北坳陷中5个沉积洼陷和羌南坳陷中4个沉积洼陷。这9个侏罗纪洼陷分布在中央隆起带的南北两侧,羌北坳陷侏罗纪沉积岩以海陆过渡相蒸发盐岩为主,沉积体量比羌南坳陷略小。结合地面岩矿地层分析、湖水和泉水化学测试分析和卫星遥感图像解译资料综合评价认为,羌北坳陷比羌南坳陷具有更有利的蒸发岩沉积条件,初步预测羌北坳陷QB2和QB3洼陷为一级有利的含钾沉积洼陷,羌南坳陷QN1和QN2洼陷为二级有利的含钾沉积洼陷。

By statistical analysis of petrophysical properties of outcrop and core samples and spectral structure of1∶500,000 integrated reduced gravity data,6tectonic layers of Qiangtang Basin were identified and separated by matched filter.Gravity inversion algorithm coupled with topography was employed to caclculat the top/bottom structures and the thickness of the Jurassic tectonic layer.5depressions in the Northen Qiangtang sag and 4 depressions in the Southen Qiangtang sag were predicated.These 9depressions are distributed along with the periphery of central uplift belt,the sediments in the 5depressions in Northern Qiangtang are attributed to evaporates of transitional facies with total sedimentary volume slightly less than that in Southern Qiangtang.In combination with Jurassic outcrop lithology and stratigraphy,lake and spring water geochemical data and remote sensing image interpretation the depressions in Northern Qiangtang were estimated to have more favourable conditions for halite-sylvite sedimentation than those in Southern Qiangtang.Two depressions（QB2and QB3）in Northern Qiangtang were preliminarily evaluated as the first-rank prospective ones for evaporate sedimentation and two depressions（QN1and QN2）in Southern Qiangtang as the second-rank ones.