断陷湖盆沟谷及构造坡折对砂体的控制作用

Control of valley and tectonic slope-break zone on sand bodies in rift-subsidence basin

对渤海湾盆地下第三系古地貌和砂体发育关系的研究表明:断陷湖盆的盆缘发育断槽、断裂调节带和下切河谷3种基本沟谷类型,这3种沟谷控制了砂、砾岩扇体发育的位置;沟谷处的同沉积构造坡折带进一步控制了砂、砾岩体在湖盆内的展布,即砂体厚度在坡折带之下增厚,砂体展布方向与构造坡折带走向一致。各裂陷幕同沉积构造坡折带特征及其对砂体发育的控制作用也存在着较大的差异:初始裂陷幕发育陡坡控盆断裂和缓坡反向断裂,主裂陷幕发育陡坡控盆断裂和缓坡同向断裂,这些断裂形成的各种同沉积断裂坡折带控制了砂体的发育;裂陷收敛幕断裂活动减弱,部分同沉积断裂坡折转化为挠曲坡折,两者共同控制了砂体的发育。

The relationship between palaeogeomorphology and development of sand bodies shows that there developed fault through, fauhs-transfer zone and incised valley in the depression wedges of the Paleogene of Bohai Bay Basin. Three basic valleys all controlled the positions of sandstone and conglomerate fan. The syndepositional tectonic slope-break zone controlled the distributions of sandstone and conglomerate. The thickness of sandstone and conglomerate is bigger at lower part of tectonic slope-break zone,and the distribution directions of sandstone and conglomerate are same as that of the syndepositional tectonic slope-break zone. The characteristics of syndepositional tectonic slope-break zone and its control to the distribution of sand bodies are different in different rifting episode. The main steep-slope faults and gentle-slope faults with dip-reverse strata were developed in the rift initiation episode. The main steep-slope ~aults and gentle-slope faults with dip-same strata were developed in the rift climax episode. Many syndepositional faulted slope-break zone resulted from above faults controlled the distribution of sand bodies. In post-rift episode, part syndepositional faulted slope-break zone changed into bent slope-break zone. The two kinds of slope-break zones together controlled the distribution of sand bodies.