幕式构造沉降过程中可容纳空间的变化规律——以掀斜式半地堑盆地为例

EVOLUTION LAWS OF THE ACCOMMODATION SPACE IN THE COURSE OF EPISODIC TECTONIC SUBSIDENCE ——A CASE FROM TILTED HALF-GRABEN BASIN

掀斜式半地堑盆地构造活动的幕式变化强调每一幕构造活动是控边断裂由强变弱的过程。这一过程变化不是盆地的简单整体沉降和可容纳空间的整体增加。在盆地不同部位，可容纳空间的变化是不一致的，那么在全盆地寻找统一的地层层序界面来建立等时地层格架就成为研究的难点。对半地堑盆地几何形态和运动过程的简化模型定量分析，表明经历一期掀斜式旋转运动后，沉降中心向缓坡带方向迁移，盆地绝对水平面是下降的，缓坡带和陡坡带均有先前水下地层的暴露，由盆缘向盆内可容纳空间不变的临界点，可容纳空间总体是变小的，但都有向盆内增加的趋势；可容纳空间在临界点之间总体是变大的，且向沉降中心都有增加的趋势。在半地堑型的博兴洼陷中，沙四段和沙三段段沉积时期4个受掀斜式构造活动所控制的层序特征证明了上述观点。这对指导建立掀斜式半地堑盆地的等时沉积层序格架具有重要的现实意义。

Each episodic tectonic movement in tilted half graben basin is the changing process of boundary-control- ling faults from strong to weak, which doesnt simply mean the subsidence of the whole basin and the increase of ac- commodation space. The space is varied with the different parts of the basin. It is difficult to find out the common stratigraphic sequence interfaces in all over the basin to construct isochronous stratigraphic framework. That is the bottle neck in the study. The quantitative analysis of the simplified model of geometric configuration and movement process of half-graben basin shows that after one episode of tilted turning movement, the subsidence center moves towards the gentle ramp belt, and the absolute water level of the basin is descendent. The strata previously below the water are exposed in both gentle ramp belt and steep ramp belt. There are two threshold points where accommo- dation space is constant from basin margin to basin bottom. In general, the basin accommodation space becomes smaller, but there is the tendency of increase toward the inner of the basin; the space between the two threshold points becomes larger in a whole, and moreover enlarges towards the subsidence center. In the half-graben Buoxing I^w, the above statements have been proven by the sequence characteristics controlled by 4 tilted structural activi- ties in Sha No. 4 and No. 3 Members＇ sedimentary period. It possesses realistic significance to guide the establish- ment of isochronous framework of sedimentary stratigraphic sequences in tilted half-graben basin.