Exploration of the hypothetical impact ejecta layer around the Maâdna structure (Talemzane, Algeria) using georadar technique

Lamali, A.; Hamai, Lamine; Nadjemi, Abdelmadjid; Yelles‐Chaouche, Abdelkrim; Abtout, Abdeslam; Merabet, N.; Bentridi, Salah-Eddine; Djadia, Leila; Mokhtar, Sid Ahmed

doi:10.1016/j.jafrearsci.2020.103975

Cited by 3 publications

(5 citation statements)

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“…In addition to the findings and arguments of Lamali et al (2016, 2020), these deductions corroborate particularly with their exclusion of any enrichment to be necessarily attributed to whether or not an impact event occurred, and/or from postimpact superficial processes such as produced by intense erosion of ejecta blanket to the depression. The carbonate composition of the target rock also plays a significant part in defining the observed radiometric signature.…”

Section: Discussionsupporting

confidence: 77%

“…Likewise, Lamali et al (2016) have demonstrated a magnetic susceptibility enhancement that fits within this arable soil in this zone. The same research team discussed typical ground penetrating radar signal attenuations within this surficial part of pedogenesis (Lamali et al, 2020). Owing to this pedogenesis, this central zone or wadi beds are often colonized by vegetation.…”

Section: Discussionmentioning

confidence: 99%

“…They have defined evidence for carbonate melting as effects resulting from shock metamorphism. In contrast, Lamali et al (2016, 2020) pointed out the previous authors’ misinterpretation of an unusual breccia or what appears as black varnish on weathered limestone and/or some type of outcrops (e.g., Pliocene breccias or neoformed concretions), as melting materials. An analogy was already made by Lamali et al (2016, 2020) between these litho‐type zones, within and outside of the crater, and referred to their fieldwork and petrographic analysis of their large number of samples.…”

Section: Geological Settingmentioning

confidence: 98%

“…However, its actual formation mechanism is still controversial. Lamali et al (2016Lamali et al ( , 2020 reported data from detailed fieldwork, structural geological analysis, and geophysical studies that were not conclusive to provide unambiguous supporting evidence for an impact interpretation. They concluded that the Maâdna structure could alternatively be the result of a local diapiric emplacement, although they did not exclude the impact hypothesis.…”

Section: Introductionmentioning

confidence: 99%

“…Others proposed that the remnant-melted material can have a significant presence within the fracture network or buried beneath the recent sediment of the crater depression, either as a primary phase or as an erosion product (Belhai et al, 2017). Although the work by Lamali et al (2020) did not indicate any anomalous near-surface electromagnetic signatures of such typical material, the debate about its hidden character is still ongoing. For all these reasons, we propose a new field exploration using radiometric methods, from which we can at least be confident that it will contribute to possibly supplementing the knowledge about the hypothetical melt rock from the Maâdna structure.…”

Section: Introductionmentioning

confidence: 99%

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Field gamma ray spectrometry as a diagnostic tool for the assessment of hypothetical melt rocks from the Maâdna structure (Talemzane, Algeria): Implications for the crater formation process

Lamali

Hamai

Mokhtar

et al. 2022

Meteorit & Planetary Scien

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Among all geophysical methods, gamma ray spectrometry is not widely used in impact cratering studies, despite its efficiency in the investigation of physical/chemical changes in rocks. The application of gamma ray spectrometry method to data from the Maâdna crater is aimed at detection and verification of the presumed impact‐derived melt rocks or breccias, as well as discussing its implications on process of formation. The resulting information also demonstrates the potential of these specific data regarding our general understanding of impact cratering, while a few case studies have been reported in the literature to date within the impact community. Maâdna crater is dated at 2.6–3.1 Ma of ~1.7 km and is emplaced in Upper‐Cretaceous to Eocene limestones of the northern part of the Algerian Saharan platform. Although originally accepted as an impact crater, its origin is still controversial. Several thousands of field measurements were taken using a field portable gamma ray spectrometer. The measurements can be equivalently expressed by up to about 42 km footpath recordings in real‐time ground acquisitions, covering the entire structure and surrounding areas beyond the crater edge. The collected data included the total count (Tc) and the concentrations of the radionuclides calculated in wt% for K and in ppm for U and Th. The spectra rates recorded inside and outside the crater did not exceed the maximum average concentrations corresponding to 75.3 Cps, 4.94 ppm, 10.5 ppm, and 1.79 wt% for Tc, U, Th, and K, respectively. The database was processed using various gridding data methods, from which the minimum curvature was adopted as it provides a powerful visualization and interpretation of the anomalous distribution of radioactive elements and their corresponding ratios maps. In addition, an improved statistical analysis was carried out in order to extract a maximum of information about the radiometric response of each rock unit. This analysis consisted of a series of multiple linear regression, mean differencing, Q–Q (quantile–quantile) plots, and ternary mapping. Maps and plots of various models allowed us to examine the background variability in the distribution of K, Th, and U concentrations at the surface of the three distinctive litho‐type zones in the surveyed area, which are the central part, the crater edge, and the outside of the crater including the wadi deposits. Observed results of different radiometric responses clearly reflect the effect of various lithological units, especially in the areas with high K concentration. Note that this positive K‐anomaly has been observed in recent deposits that fill the Maâdna depression or external wadi beds. In contrast, the surrounding limestone rocks showed lower levels of radioelement concentrations. Relevant similarities found between the radiometric signatures of the Neogene formations inside and outside the crater can be considered as a strong argument to exclude preferential radionuclides enrichment caused by an impact event. Consequently, the natural...

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Section: Discussionsupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%