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Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Syncline folded rock looks like an open bowl or trough basin. The rock simulates a concave shape, whereas an anticline assumes a convex structure. Syncline is a large downward arch, created by the downward bending of the middle portion of the rock layer and in which the sides (limbs) of rock layer go upward. A syncline rock is a trough (valley) of folded strata. The presence of anticline and syncline rock structures indicates that the area has been subjected to geological compressional stress. The rock plays no role in underground petroleum systems.
Groundwater Flow Properties
Published in Zekâi Şen, for Scientists and Engineers, 2017
The answer is that it is a function of neither of these topographies. Figure 7a shows the cross section of an alluvial fill in a subsurface depression filled with Quaternary deposits. There, the groundwater is at rest and therefore the piezometric line is horizontal which indicates that there is no relationship whatsoever to the aquifer bed or earth surface topography. Anticline and syncline are continuous parts of any geological formation such as the one depicted in Figure 7b.
Study on stress evolution law and rock burst mechanism in upright fold structure area of deep mine
Published in Geomatics, Natural Hazards and Risk, 2023
Chengchun Xue, Anye Cao, Guowei Lv, Yingyuan Wen, Yaoqi Liu, Songwei Wang, Qi Hao
The fold structure is formed by the bending deformation of the rock stratum due to the extrusion of crustal movement. It is the most basic geological structure type. The fold structure can be divided into the basic form of syncline and anticline (Foster and Gray 2000; DeCelles and Coogan 2006). As shown in Figure 1, The rock stratum in the syncline area is concave downward, and the rock stratum in the anticline area is convex upward. The fold structure has many geometric features. The slopes on both sides of the fold are called limbs. The line connecting the maximum bending point in the syncline or anticline area is called the axial line. The surface is perpendicular to the maximum bending point in the syncline or anticline area is called the axial plane. The distance between the arc tops of two adjacent synclines or anticlines is the wavelength of the fold. The distance between the two arc tops of the adjacent syncline and anticline on the axial plane is twice the amplitude of the fold.
Mapping geological configuration using geophysics data: an investigative approach in targeting iron ore, gold mineralization and other commodities, a case study of Toko-Nlokeng area (Nyong Greenstone Belt, SW Cameroon)
Published in Applied Earth Science, 2023
Yannick Saturnin Evina Aboula, Joseph Mvondo Ondoa, Paul-Désiré Ndjigui
High magnetic response anomalies are associated with hinges of drag folds, particularly where early folds are modified by obliquely cross-cutting, younger shear zones in the Toko-Nlokeng area (Figure 15). Then, refined interpretations of fold axial traces were constrained by high magnetic response anomalies, especially in the TNF11 deposit map area. Given the isoclinal geometry of complex folds, foliation along fold limbs is sub-parallel, and magnetic response increases with proximity to hinges. Therefore, high anomaly values in fold hinges would be expected and are commonly observed (Figure 15). In some cases, the high magnetic response also correlates to fold interference patterns (e.g. Santos et al. 2021; Perrouty et al. 2017). For example, the anomalously high zone in the TNF11 area highlights where early isoclinal folds are refolded by later z-folds and drag folding related to the TNF11 prospect (Binam et al. 2018; Nabavi and Fossen 2021). The aeromagnetic–radiometric analysis also provides further geological insight into structures poorly defined by field mapping. For example, the location of the Kienké river antiform axial trace in the TNF11 prospect is well defined by the structural/lithology mapping results. This structure was originally interpreted by Binam et al. (2018); however, uncertainty in the location and geometry of the structure persisted, in part, due to dense vegetation and coincident with the feature. Using magnetic and radiometric trend lines results, the axial trace of the fold was extended to the west until it is offset by late northwest-trending faults. In addition to the mesoscale folds with their corresponding parasitic folds, outcrop-scale recumbent folds are found in ductile shear zones developed commonly in the hinterland of orogens (e.g. Yassaghi et al. 2000; Williams and Jiang 2005; Bastida et al. 2014; Santos et al. 2021). In these cases, near-isoclinal anticline – syncline fold pairs are common. Many folds have curved hinges and are sometimes sheath folds characteristic of cumbent folds. TNF11 Sheath folds (Figure 10d) are strongly non-cylindrical folds with hinge lines curve of more than 90◦, formed in zones of simple shear by gradual rotation of fold hinges toward the shear direction and by drag effect associated with rigid inclusions during non-coaxial deformation. In cross-section, sheath folds typically exhibit elliptical shapes (Alsop and Carreras 2007; Alsop and Holdsworth 2012; Nabavi et al. 2020; Alsop et al. 2021).
GIS-based soil planar slide susceptibility mapping using logistic regression and neural networks: a typical red mudstone area in southwest China
Published in Geomatics, Natural Hazards and Risk, 2021
Shuai Zhang, Can Li, Jingyu Peng, Dalei Peng, Qiang Xu, Qun Zhang, Bate Bate
The study area is located in Nanjiang, Sichuan Province of China, which lies between the longitudes of 106°27′ to 107°28′E and latitudes of 31°53′ to 32°45′N (Figs. 1a and b). In general, according to the topographical map (Fig. 1c), the altitude of the south and middle sections of the study area ranges from 500 to 1000 m and increases to above 1000 m in the north of the area. This area is characterized by widely distributed cuesta (Fig. 3a) with gently inclined rock layers and quasi cuesta, and most of the hillslope area has been explored as cultivated land and paddy field in a ladder shape (Zhang et al. 2017). The slope angle of the rock layers ranged from 10° to 30°. As shown in Fig. 3a, tectonic structure is developed in the northern mountainous area of Nanjiang County, which is not active in the southern area. The main fault structure in the county is the Lanchaiba Fault. The main fold structures are the Zhongzi Mountain Synclinore, the Liang Anticlinorium, Guomatan syncline, the Shatan Anticline, the Xinhua Syncline and the Longfengchang Anticline. On the whole, the tectonic movement in Nanjiang County is mainly manifested as fold tectonic movement. And the fault structure in Nanjiang County is underdeveloped, only some small faults are developed. Lithology is rather complicated in the study area, where the main lithology formations are loose soil, shale, mudstone, dolomite, and diorite (Fig. 3b). Mesozoic Jurassic and Cretaceous strata are the two basic underlying rock layers that consist of the most distributed red mudstone layers in this area. Most of the exposed red mudstone is deeply fractured and highly weathered. During the rainy seasons, these materials are easily weathered and softened. Due to the low strength of the red layer materials, it is easy to collapse under the changing climate conditions (Zhang et al., 2016). Hence, rainfall-induced landslides occur frequently in the study area. During the extreme rain event on 16 September 2011, over 1700 landslides were triggered in Nanjiang County. Over 90% of soil landslides in Nanjiang were concentrated in the red mudstone area (Fig. 3b). The uneven distribution of soil landslides can contribute to the poor mechanical properties of red mudstone, which is characterized by low strength, strong water sensitivity, and well-developed structural plane. Such soft rock can weather rapidly under the effect of dry-wet cycles. Weak layers between the upper soil and lower bedrock can develop due to water infiltration. Thus, the completely or highly weathered red mudstone can easily become the source of a potential landslide. To perform more accurate modeling, the red mudstone area in the south of Nanjiang has been chosen as the target study area of this research.