古龙凹陷青一段米兰科维奇旋回识别及其沉积响应

Identification of Sedimentary Responses to the Milankovitch Cycles in the K2qn1 Formation,Gulong Depression

松辽盆地青山口组湖相深水细粒沉积岩厚度大,具有巨大的非常规油气勘探潜力。利用小波变化和频谱分析方法,对研究区取芯井青一段地层的大段深水细粒沉积岩进行米兰科维奇旋回划分,并通过地球化学、全岩矿物等参数分析古沉积环境,将古环境的沉积响应与所划分的旋回进行对应分析,建立受控于米兰科维奇旋回的地层响应特征。研究表明,青一段地层中共识别出四级米氏旋回,分别为68个米级旋回、25个Ⅴ级旋回、6个Ⅳ级旋回以及1个Ⅲ级旋回界面,地层沉积主要受控于128 ka短偏心率和48 ka斜率旋回。青一段沉积环境整体上具有气候由干到湿,水体加深、还原性增强、盐度降低的旋回变化特征,6种环境组合表明了厚层泥页岩岩相与沉积环境之间的对应关系,其中暖湿气候控制的层状灰质泥岩有利于油页岩层发育。因此利用米氏旋回细分深水细粒沉积层,有望对页岩油气勘探获得突破。

The great thickness of deep-water fine-grained sedimentary rock in the K2 qn Lake,Songliao Basin,offers the potential for very large-scale unconventional oil and gas exploration. Spectral analysis and wavelet analysis were used in a study of the Milankovitch cycle recorded in the K2 qn1 Formation. The sedimentary paleoenvironment and its response to the Milankovitch cycle for the deep-lake facies in the Gulong Depression,Songliao Basin,were analyzed by whole-rock X-ray diffraction to determine geochemical elemental data. The formation responses to the Milankovitch cycle were established,revealing four-stage Milankovitch cycles in the K2 qn1 Formation:68 meter-scale cyclic sequences,25 level-V Milankovitch cycle sequences,6 level-IV Milankovitch cycle sequences,with one stage-Ⅲ cycle sequence interface. The lacustrine sedimentation in the K2 qn1 Formation was mainly controlled by a short-term eccentricity of 128 ka and a slope of 48 ka. The sedimentation environment indicates that the climate changed from dry to wet,with increasing water depth,reductive enhancement,and decreasing salinity. The combination of the six environments indicates the relationship between the thick shale lithology and the sedimentary environment. The layered gray mudstone deposited in a warm,humid climate is conducive to the development of oil shale formation.