Seismites in the fluviatile Bima sandstones: identification of paleoseisms and discussion of their magnitudes in a Cretaceous synsedimentary strike-slip basin (Upper Benue, Nigeria)
Seismites in the fluviatile Bima sandstones: identification of paleoseisms and discussion of their magnitudes in a Cretaceous synsedimentary strike-slip basin (Upper Benue, Nigeria)
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DOI：
10.1016/0040-1951(93)90312-8
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发表时间：
1993-10
期刊：
影响因子：
2.9
通讯作者：
M. Guiraud;J. Plaziat
中科院分区：
文献类型：
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作者：
M. Guiraud;J. Plaziat
上贝努埃盆地(尼日利亚东北部)是一个复杂的走滑盆地，由早白垩世活跃的同沉积N60°C-E向走滑断裂控制的一系列次盆地组成。由比马砂岩组上段中-细粒砂岩组成的斜面交错层受各种软沉积即早期成岩但软沉积变形构造的影响。它们不仅在同沉积断裂附近存在，而且在更大的区域尺度上也存在。描述了三种主要类型的构造(波状和横卧褶皱交错层理、错位卷曲和整合微角砾岩、不协调流体侵入体)。这些变形构造的局部组织性、相对于同沉积断层的空间展布以及相对于边缘古斜坡的独立性，表明它们不能用滑塌或洋流阻力来解释。所有的变形都与孔隙水排出有关，并提出所需的砂体重组是由地震波触发的。不同类型形变构造的空间和时间分布及强度表明，它们是在不同震中周围产生的，与同沉积走滑构造有关的不同震级的地震反复发生。
The Upper Benue Basin (northeastern Nigeria) is interpreted as a complex strike-slip basin which consists of a set of sub-basins controlled by synsedimentary N60°C E-trending, strike-slip faults which were active during Early Cretaceous times.The oblique planar cross-beds made of the medium- to fine-grained sandstones of the upper member of the Bima Sandstone Formation are affected by various soft-sediment i.e., early diagenetic but soft-sediment deformational structures. These are present not only close to the synsedimentary faults but also on a larger regional scale. Three main types of structures (undulated and recumbent-folded cross-bedded lamination, dislocated convolutions and concordant microbreccias, discordant fluidised intrusions) are described. These are related to processes of sediment deformation favored by sand hydroplasticity, liquefaction and fluidization.The local organization of these soft-sediment intrastratal deformational structures, their spatial distribution with respect to synsedimentary faults, and their independance with respect to marginal paleoslopes, suggest that they cannot be explained by slumping or current drag. All the deformations are related to pore water expulsion and it is proposed that the required sand reorganization was triggered by seismic waves. The spatial and chronologic distribution and intensity of the various types of deformation structures suggest that they were produced around different epicenters repeated by earthquakes of varying magnitudes associated with the synsedimentary strike-slip tectonics.