东营凹陷青南地区沙四上亚段时期浅水洼陷沉积

DEPOSITION OF THE SHALLOW WATER LOW IN QINGNAN AREA OF DONGYING SAG AT THE STAGE OF UPPER SUB-MEMBER SHA-4

针对东营凹陷青南地区沙四上亚段沉积时期古地理格局认识不清的问题,从构造演化、沉积相类型及展布、泥页岩有机地球化学特征等三个方面入手进行了深入分析探讨。研究结果表明:青南地区沙四上亚段沉积时期整体呈现为一个断陷湖盆中的浅水洼陷,以滨浅湖相沉积为主,除沙四上亚段沉积早期南部物源体系的三角洲和沙四上亚段沉积晚期北部物源体系的扇三角洲砂体外,滨浅湖滩坝砂体长时期广泛发育,呈现满盆含砂的特点;沙四上亚段沉积时期青南地区古地貌整体平缓稳定,高差不大,现今地震剖面显示"山高水深"的构造格局是沙三下亚段沉积地层沉积后,在洼陷中心继承性沉降作用下逐步形成的。泥页岩地质地球化学特征分析表明:不同于典型半深湖一深湖环境下形成的油页岩,青南地区中心小范围分布的沙四上亚段暗色泥岩形成于同时具备高古生产力和缺氧条件的咸化浅湖一半深湖环境。

In the light of the unclear paleogeographic pattern of Qingnan area in Dongying Sag during the sedimentation of Upper Sub-member Sha-4, the deep analyses of the structural evolution, sedimentary phase type and spread, organic geochemical features of the mudstone and so forth are explored. The researches show that a shal- low-water low appeared during the whole sedimentation period and was characterized mainly by coastal shallow-lake facies sedimentation. In addition to the deltas of the early-stage southern source system and the fan deltas of the late-stage southern source system sedimentated in Upper Sub-member Sha-4, shallow lake-beach bars were widely developed for quite a long time. And moreover the sandstone was distributed everywhere in the sag; during the sed- imentation of Upper Sub-member Sha-4, the paleogeomorphy in Qingnan area was gentle and stable in a whole and had small altitude difference, but the present structural framework of ＂ high mountain and deep water＂ shown in the seismic profiles is formed gradually after the sedimentation and inherited settlement of Upper Sub-member Sha- 4 formation. The analyses of the geological and geochemical characteristics of the mud shale show that distinguished from the typical oil shale formed in semi-deep and deep lake environments, the dark mudstone distributed in Center Qingnan in a small size was generated in the salty shallow and semi-deep lake environments with high paleo-produc- tivity and oxygen starvation.