Forming Mechanism of Structural Slope-Break and Its Control on Sequence Style in Faulted Basin
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摘要: 断陷盆地是典型的构造活动型盆地, 盆地中各种类型的坡折带均有其发育的构造背景和控制机制.以中国东部中新生代断陷盆地的研究为基础, 提出了断陷盆地构造坡折带的分类方案, 描述了各类构造坡折带的基本特征和形成的构造机制, 建立了陆相断陷盆地层序发育的综合模式.断陷盆地中的构造坡折带可分为断坡带、弯折带、挠曲带和枢纽带4种类型.断坡带受控于断陷盆地内各种类型的同生断裂作用, 弯折带则与主控边界断层的几何学形态密切相关, 形成于铲式正断层控制的断层上盘内, 而挠曲带与基底正断层的隐伏式活动有密切的关系.上述3种类型的构造坡折带都是由盆地上盘的变形作用所产生的, 而枢纽带的发育则是盆地上盘的旋转掀斜作用引起的变位所致, 同时这类坡折带发育于主边界断层为陡倾平面状正断层控制的断陷盆地内.构造坡折带的发育特征、空间分布、演化过程和组合样式决定了盆地的可容空间和物源系统, 因而制约了沉积物的分散过程和砂体的分布样式.揭示构造坡折带与沉积相的展布关系, 将有助于阐明盆地内部沉积体系分布规律, 有效地进行砂体预测.Abstract: Faulted basin is a kind of typical tectonic active basin, in which there are various kinds of tectonic slope-breaks controlled by different tectonic backgrounds and mechanisms. Based on the researches on Mesozoic and Cenozoic faulted basinsin eastern China, classification system on structural slope-break of faulted basin is put forward, basic characteristics and forming mechanism of various kinds of structural slope-break have been described in detail and synthetic models of sequence stratigraphic development in continental faulted basin are set up in this paper. Structural slope-break in faulted basin can be divided into fault slope-break, bend slope-break, flexure slope-break and pivotal slope-break. The fault slope-break is controlled by syndepositional faulting within the basin, the formation of the bend slope-break is related to listric geometry of major boundary fault in faulted basin, while the flexure slope-break often results from activity of blind normal fault in the basin basement. Different from above three slope-breaks, the formation of the pivotal slope-break is a result of rotational tilting of hanging wall of normal fault, the development is mainly controlled by main boundary normal fault with steep dip and plane geometry. Development, distribution in space, evolution process and assemblage pattern of structural slope-break determind accommodation and sediment influx system in faulted basin, further it restricts sediment disperse process and distributional pattern of sand bodies in faulted basin. The researches on relationship between structural slope-break and depositional facies will be a great help to illustrate distribution of depositional systems and promote prediction availability of sand bodies in sedimentary basin.
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Key words:
- faulted basin /
- tectonic slope-break /
- tectonic active basin /
- sequence stratigraphy
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图 1 拉伸断层上盘变形实验(据Withjack et al., 1995)
Fig. 1. Experiment about hangingwall deformation of extensional fault
图 3 断层扩展式褶皱作用和挠曲带的发育
a.垂向剖面演化; b.平面侧向演化
Fig. 3. Fault-propagation folding and formation of flexure slope-break
图 4 断块掀斜作用与层序和体系域构成样式
Fig. 4. Tilting of fault block and style of sequences and systems tracts
图 5 陆相断陷盆地层序构成样式
SB-T1.Ⅰ型层序; SB-T2.Ⅱ型层序; LST.低位域; EST.湖扩域; HST.高位域
Fig. 5. Sequence styles of continental faulted basin
表 1 坡折带的分类
Table 1. Classification of slope-break
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