Audio-magnetotelluric surveys to constrain the origin of a network of narrow synclines in Eocene limestone, Western Desert, Egypt

Tarabees, Elhamy A.; Tewksbury, Barbara J.; Mehrtens, Charlotte J.; Younis, Abdellatif

doi:10.1016/j.jafrearsci.2017.03.001

Cited by 9 publications

(3 citation statements)

References 15 publications

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“…Meanwhile, the study [9] mapped voids and caves between carbonate units, cavityfilling sediments, and groundwater. Researchers have also used Magnetotelluric (MT) surveys to identify subsurface dry fracture networks and caves beneath synclines resulting from subsurface karst decay [10]. Moreover, studies have examined shallow and deep structures, as well as the understanding of collapse and cracking due to karst dissolution processes [11].…”

Section: Introductionmentioning

confidence: 99%

Investigating Land Use and Karst Disaster Mitigation through Geoelectric and Magnetotelluric Methods: A Case Study in Sendang Biru, Malang, Indonesia

Wahid,

Susilo,

Sianturi

et al. 2023

IJDNE

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offers significant tourism and fisheries potential, supported by the nearby Sempu Island Nature Reserve and a Fish Auction Site (FAS). However, the coastal region is prone to karstification, which may be exacerbated by recent land use developments in the surrounding area. This study aims to analyze the rock layer structures and assess the vulnerability of karst land use to the ongoing karstification process. Electrical Resistivity Tomography (ERT) and Magnetotelluric (MT) methods were employed to investigate karst land within the study area. The findings revealed the presence of karst aquifers in Zone A, extending to a depth of 250 m, characterized by low resistivity values. In Zone B, karst limestone deformation was observed at several locations due to karstification, with moderate resistivity values detected at a depth of 300 m on the surface, indicating vulnerability to karst disasters. High resistivity values dominated areas with massive karst limestone, ranging from the surface to a depth of 400 m. Furthermore, it was found that a significant portion of karst land is utilized for settlements, plantations, and rice paddies, potentially disrupting the karst ecosystem due to household, plantation, and agricultural waste. This study highlights the importance of understanding the impact of land use on karst vulnerability and informs mitigation strategies for sustainable development in the Sendang Biru region.

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Section: Introductionmentioning

confidence: 99%

Investigating Land Use and Karst Disaster Mitigation through Geoelectric and Magnetotelluric Methods: A Case Study in Sendang Biru, Malang, Indonesia

Wahid,

Susilo,

Sianturi

et al. 2023

IJDNE

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“…We have previously reported the discovery of an unusual network of synclines in lower Eocene limestones in Egypt and characterized the network across an area of about 4,000 km 2 in the Western Desert (Tewksbury et al, 2017a. ;Tarabees et al, 2017) (Figures 1, 2). We evaluated a number of hypotheses for the origin of the synclines and proposed hypogene karst at depth as one of the viable hypotheses.…”

Section: Introductionmentioning

confidence: 99%

Inferring Hypogene Karst at Depth from the Patterns of Non-Tectonic Syncline Networks in Eocene Limestones, Western Desert, Egypt

et al. 2021

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Indirect indicators are critically important for recognizing hypogene karst that is too deep-seated to have explorable hypogene caves. We have suggested in previous publications that an extensive network of non-tectonic synclines in otherwise flat-lying Eocene limestone in Egypt might be such an indirect indicator. We proposed that synclines formed by sag of limestone layers overlying a zone of hypogene karst that today remains deep below the surface and suggested that hypogene speleogenesis resulted from ascending aggressive fluids associated with crustal extension and magmatism in Egypt during Red Sea Rift initiation. Without hypogene caves to explore, however, we were unable to provide compelling evidence for hypogene karst processes. By doubling our mapping area from 4,000 to 8,000 km2, a clear picture has emerged of patterns in the syncline network that provide compelling evidence for hypogene speleogenesis. Over this larger area, the network displays two distinct patterns: 1) synclines and ridges that outline polygons 700–2,000 m across, and 2) narrow N–S zones of synclines spaced 5–10 km apart, with WNW–ESE to NW–SE trending shallow synclines and ridges traversing the panels between N–S zones. The geometries suggest that the syncline network is controlled by two structural patterns in rocks underlying the limestones: 1) polygonal faults in underlying shales and 2) reactivated N–S, left-lateral basement faults that are largely blind at the current level of erosion. These structures served as conduits that conveyed fluids upward into the overlying Eocene limestones, triggering dissolution at depth and a pattern of sag above that was inherited from the nature and pattern of faults and fractures in rocks underlying the limestones. The unique patterns and characteristics of this network of synclines are applicable elsewhere as an indirect indicator of deep-seated hypogene karst. Our new data also strongly suggest that syncline formation spanned the time of crustal extension in Egypt associated with onset of Red Sea rifting ∼23–22 Ma. Endogenic CO2 associated with mantle-derived basaltic magmas was likely a significant component of fluids, perhaps involving highly aggressive supercritical CO2. Mantle-derived C and He in modern Egyptian oasis water suggest that hypogene speleogenesis may still be locally active.

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“…It is similar to standard magnetotelluric measurement in that it utilizes a passive natural source, but in AMT the frequency band is limited to the audio range, generally from 0.1 Hz to 8000 Hz. AMT has wide applications in mineral and ground water exploration as well as in environmental tasks such as fault‐zone mapping, geothermal investigation, and engineering detection (Barcelona et al, ; Huang et al, ; Share et al, ; Tarabees et al, ; Tuncer et al, ; Yamaguchi et al, ). The main application of the AMT method, the modeling of subsurface resistivity structures, requires inversion of the AMT responses.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional regularized inversion of AMT data based on rotation invariant of Central impedance tensor

Xiao-zhong¹,

Liu²,

Li³

2018

Earth and Planetary Physics

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Considering the uncertainty of the electrical axis for two‐dimensional audo‐magnetotelluric (AMT) data processing, an AMT inversion method with the Central impedance tensor was presented. First, we present a calculation expression of the Central impedance tensor in AMT, which can be considered as the arithmetic mean of TE‐polarization mode and TM‐polarization mode in the two‐dimensional geo‐electrical model. Second, a least‐squares iterative inversion algorithm is established, based on a smoothness‐constrained model, and an improved L‐curve method is adopted to determine the best regularization parameters. We then test the above inversion method with synthetic data and field data. The test results show that this two‐dimensional AMT inversion scheme for the responses of Central impedance is effective and can reconstruct reasonable two‐dimensional subsurface resistivity structures. We conclude that the Central impedance tensor is a useful tool for two‐dimensional inversion of AMT data.

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Audio-magnetotelluric surveys to constrain the origin of a network of narrow synclines in Eocene limestone, Western Desert, Egypt

Cited by 9 publications

References 15 publications

Investigating Land Use and Karst Disaster Mitigation through Geoelectric and Magnetotelluric Methods: A Case Study in Sendang Biru, Malang, Indonesia

Investigating Land Use and Karst Disaster Mitigation through Geoelectric and Magnetotelluric Methods: A Case Study in Sendang Biru, Malang, Indonesia

Inferring Hypogene Karst at Depth from the Patterns of Non-Tectonic Syncline Networks in Eocene Limestones, Western Desert, Egypt

Two-dimensional regularized inversion of AMT data based on rotation invariant of Central impedance tensor

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