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首页> 外文期刊>Journal of African earth sciences >Exploration of the hypothetical impact ejecta layer around the Maadna structure (Talemzane, Algeria) using georadar technique
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Exploration of the hypothetical impact ejecta layer around the Maadna structure (Talemzane, Algeria) using georadar technique

机译：使用雄径技术探索Maadna结构周围的Maadna结构周围的突出喷射物层（Talemzane，阿尔及利亚）

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摘要

The Maadna structure (Talemzane, Algeria) is located approximately 400 km south of Algiers and is formed within Upper-Cretaceous to Eocene limestones from the Saharan Platform. It is a bowl-shaped crater roughly 1.7 km in diameter. The present-day crater rim is 60 m higher than the bottom of the depression, and is raised slightly compared to the surrounding terrain. So far, several aspects of Maadna structure cratering process remain poorly known. Recent study, geological and geophysical investigation, do not support an impact origin for this structure but suggest an alternative dissolved diapir with inverted relief. At present, geophysical studies revealed many interesting features of known terrestrial impact craters. In particular, observed signatures yielded useful information on the impact-induced physical changes in targeted rocks. These observations motivated our investigation of Maadna crater, which uses several different geophysical surveys with particular emphasis on the GPR technique. This later is used as a valuable tool for near surface explorations. Although GPR technique has a limited use in case of impact structures, it is used in this study to discriminate between electromagnetic signatures of supposed ejectas, which were widely used to describe Maadna structure origin. Typical GPR antennas were used to test a survey protocol in several situations during the GPR field deployment stage. In order to characterize the target thin and shallower layer, most of the common profiles were acquired using a 500 MHz shielded antenna. Otherwise, to ensure maximum waves penetration depths, "NS & EW" profiles were also acquired using a lowest frequency 30 MHz unshielded rough terrain antenna (RTA) system with a flexible "snakelike" design. Moreover, the ensued GPR characterization is then used to constrain occurred cratering process. Our GPR survey results helped us to improve our knowledge of the structure subsurface features expression. A suitable post-acquisition processing and analyses of the collected data lead us to reject the existence of any electromagnetic signature that may be attributed to the presence of any atypical materials, such as melted iron-rich material or those with distinctive physico-chemical properties, which induces electromagnetic signal modification or dissipation. Besides, our different scans could help truthful geological interpretation linked to Maadna structure. For example, scans operated on the prevailing structural unit surrounding the Maadna crater show clearly the most documented structural features at this crater, such as bedrocks fracturation, locally collapses, overturned and/or vertical movement of strata, etc. Specifically, the topographically corrected scans are presently interpretative against the alternative scenario of the cratering process at Maadna, since our various analyses do not support any meteoritic evidence. As a result, valuable insights into the hypothetic diapiric piercement have been then gained from this analysis. This leads us to conclude that GPR data can be used to build another strong argument in favor of the diapiric origin at Maadna crater.
机译：Maadna结构（Talemzane，Algeria）位于阿尔及尔以南约400公里处，形成于撒哈拉平台的eocene石灰岩内。它是一个大约1.7 km直径的碗状火山口。本日火山口轮辋高于凹陷底部60米，与周围地形略微升高。到目前为止，Maadna结构的若干方面仍然众所周知。最近的研究，地质和地球物理调查，不支持这种结构的影响，但是建议替代溶解的催化，倒置浮雕。目前，地球物理研究揭示了已知的陆地冲击陨石坑的许多有趣特征。特别地，观察到的签名产生了有关靶向岩石的影响引起的物理变化的有用信息。这些观察结果激励了我们对Maadna火山口的调查，它使用几种不同的地球物理调查，特别强调GPR技术。此后，将其用作近地表探索的有价值的工具。尽管GPR技术在撞击结构的情况下使用有限，但是在该研究中使用它以区分所谓的喷射物的电磁签名，这被广泛用于描述Maadna结构来源。典型的GPR天线用于在GPR现场部署阶段的几种情况下测试调查协议。为了表征目标薄和较浅的层，使用500 MHz屏蔽天线获取大多数公共轮廓。否则，为了确保最大波穿透深度，还使用具有柔性“Snakelike”设计的最低频率30 MHz非屏蔽粗糙地形天线（RTA）系统来获取“NS和EW”配置文件。此外，随后将随后用于约束发生的起跑过程的GPR表征。我们的GPR调查结果帮助我们提高了我们对结构地下特征表达的了解。收集数据的适当的采集后处理和分析引导我们拒绝任何可能归因于存在任何非典型材料的电磁特征，例如熔化的铁富含物质或具有独特物理化学性质的那些，这会引起电磁信号修改或耗散。此外，我们的不同扫描可以帮助与Maadna结构相关的真实地质解释。例如，在Maadna Crater周围的普遍结构单元上操作的扫描显然显示了这种火山口的最具记录的结构特征，例如基岩骨折，局部折叠，划分和/或垂直运动，具体地，地形校正扫描目前对Maadna的起跑过程的替代方案进行了解释，因为我们的各种分析不支持任何陨石证据。结果，从该分析中获得了对假设涂抹式穿孔的有价值的见解。这导致我们得出结论，GPR数据可用于建立另一个强大的论据，支持Maadna火山口的浸润起源。

著录项

  • 来源
    《Journal of African earth sciences》 |2020年第12期|103975.1-103975.13|共13页
  • 作者

    Lamali Atmane; Hamai Lamine; Nadjemi Abdelmadjid; Yelles-Chaouche Abdelkrim; Abtout Abdeslam; Merabet Nacer-Eddine; Bentridi Salah Eddine; Djadia Leila; Mokhtar Sid Ahmed;

  • 作者单位

    Ctr Rech Astron Astrophys & Geophys Route Observ BP 63 Algiers Algeria|Univ Djillali Bounaama Khemis Miliana Lab Energie & Syst Intelligents LESI Fac Sci & Technol Route Theniat El Had Khemis Miliana 44225 Ain Defla Algeria;

    Ctr Rech Astron Astrophys & Geophys Route Observ BP 63 Algiers Algeria|Univ Djillali Bounaama Khemis Miliana Lab Energie & Syst Intelligents LESI Fac Sci & Technol Route Theniat El Had Khemis Miliana 44225 Ain Defla Algeria;

    Univ Djillali Bounaama Khemis Miliana Lab Energie & Syst Intelligents LESI Fac Sci & Technol Route Theniat El Had Khemis Miliana 44225 Ain Defla Algeria;

    Ctr Rech Astron Astrophys & Geophys Route Observ BP 63 Algiers Algeria;

    Ctr Rech Astron Astrophys & Geophys Route Observ BP 63 Algiers Algeria;

    Ctr Rech Astron Astrophys & Geophys Route Observ BP 63 Algiers Algeria;

    Univ Djillali Bounaama Khemis Miliana Lab Energie & Syst Intelligents LESI Fac Sci & Technol Route Theniat El Had Khemis Miliana 44225 Ain Defla Algeria;

    Ctr Rech Astron Astrophys & Geophys Route Observ BP 63 Algiers Algeria;

    Ctr Rech Nucl DRARIA BP 43 Algiers Algeria;

  • 收录信息
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Impact crater; Maadna crater; GPR; Ejectas; Diapir;

    机译：冲击陨石坑;Maadna陨石坑;GPR;喷射液;催情;

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