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我们描述用伸展断弯褶皱理论解释裂谷盆地中不对称半地堑的几何学和构造史的一种分析方法。利用中苏门答腊盆地的地震反射剖面和平衡正演模型,我们展示了相对于沉积速率的构造沉降的局部变化是如何形成已褶皱裂谷同期地层的典型样式和记录盆地历史的不整合面的。如果沉积速率超过局部沉降速率,褶皱的生长地层形成向上变窄的膝折带,这在先前描述为生长三角带。相反,如果沉积速率小于或等于局部沉降速率,生长地层被褶皱并在半地堑边缘的表面遭受剥蚀。随后,相对于沉降速率的沉积速率的增加,在半地堑边缘附近形成角度不整合。这些不整合在不需要侵蚀的情况下形成,并由持续的断层滑动所褶皱。在半地堑较深部位,不整合面上、下的地层是整一的。因此,半地堑边缘上的角度不整合有助于确定可能反映沉积和构造沉降速率变化的层序边界。另外,对断弯褶皱的解释得出了断层的几何形态及水平伸展量的大小,这二者控制了三维半地堑的几何形态和容纳空间。我们展示了断层几何形态中沿走向的变化如何形成盆地内的构造,这些构造可以成为有远景的油气富集带及局部沉积中心。
We describe an analytical method to explain the geometry and tectonic history of the asymmetric half-graben in the rift basins using extensional bend-fold theory. Using seismic reflection profiles and balanced forward modeling from the Central Sumatra basin, we show how local variations in tectonic subsidence relative to sedimentation rates formed the typical pattern of convolutions in the folded rift and recorded the unconformity of the basin history. If the deposition rate exceeds the local sedimentation rate, the folded growth strata form an upwardly narrowing knee strap, which was previously described as a growth girdle. Conversely, if the deposition rate is less than or equal to the local sedimentation rate, the growth formation is wrinkled and subject to erosion at the surface of the half-graben edge. Subsequently, an increase in sedimentation rate relative to the rate of sedimentation led to the formation of angular unconformity near the edge of the half-graben. These unconformities are formed without erosion and are wrinkled by continued fault slip. In the deeper part of the semi-graben, unconformity, the upper and lower strata are one. Therefore, the angular disintegration on the edge of the half-graben helps to determine the sequence boundaries that may reflect changes in sedimentation and tectonic subsidence rates. In addition, the interpretation of broken folds gives the geometry of the fault and the extent of horizontal extension, both of which control the geometry and storage space of the three-dimensional half-graben. We show how the changes along the strike in the fault geometry form structures within the basin that can become prospective hydrocarbon-rich zones and local sedimentary centers.