Origin of an extensive network of non-tectonic synclines in Eocene limestones of the Western Desert, Egypt

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

doi:10.1016/j.jafrearsci.2017.02.017

Cited by 11 publications

(24 citation statements)

References 33 publications

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“…The only information about what directly underlies our study area comes from a borehole that was drilled in the 1960s along the Assiut-Kharga road (Barakat and Asaad, 1965), although the hole did not penetrate to basement, and correlation with more recently measured sections is complicated by changes in stratigraphic nomenclature. For this paper, we will use the same stratigraphic column (Figure 3B) that we presented in Tewksbury et al (2017a), which uses the Thebes Group nomenclature. Figure 3B also shows our best estimate for stratigraphic thicknesses under our study area based on recent work by King et al (2017), combined with data from the Assiut-Kharga well.…”

Section: Background and Prior Work Geologic Settingmentioning

confidence: 99%

“…Note: Supplementary Figure S1 shows all image locations in map view. nomenclature and thicknesses are provided in Tewksbury et al (2017a).…”

Section: Background and Prior Work Geologic Settingmentioning

confidence: 99%

“…Data from El-Azabi and Farouk (2011), King et al (2017), Said (1960, 1962, 1990), El Hinnawi et al (1978, Issawi (1972), Issawi et al (2009), , Khalil and El-Younsy (2003), El Hinnawi et al (2005). Reprinted from Tewksbury et al (2017a) with permission from Elsevier. (C) Colorized shaded relief map for same area shown in 3A, with illumination direction from the NW.…”

Section: Background and Prior Work Geologic Settingmentioning

confidence: 99%

“…Non-siliceous limestone layers are white in both outcrop and imagery and range from moderately resistant, dense, low porosity limestone to non-resistant, porous, chalky limestone. These differences in color and resistance to erosion (Figures 2B-E), combined with nearly complete exposure on the undissected hyperarid desert surface of the plateau, made it possible for us to map the synclines in high resolution satellite imagery (Tewksbury et al, 2017a).…”

Section: Syncline Network Characteristicsmentioning

confidence: 99%

“…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).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Background and Prior Work Geologic Settingmentioning

confidence: 99%

“…Note: Supplementary Figure S1 shows all image locations in map view. nomenclature and thicknesses are provided in Tewksbury et al (2017a).…”

Section: Background and Prior Work Geologic Settingmentioning

confidence: 99%