International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 05, May 2019, pp. 910-929, Article ID: IJCIET_10_05_092 Available online at http://iaeme.com/Home/issue/IJCIET?Volume=10&Issue=5 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication RECONSIDERATION OF THE LOWER CAMBRIAN EXTENSION IN THE ANTI-ATLAS BELT, MOROCCO * Mohamed Yazidi, Khadija Kaid Rassou and Bouchra Razoki Natural Resources Geosciences Laboratory (LGRN), Department of Geology Faculty of Science, IbnTofail University.BP 133, 14000. Kenitra. Morocco. Geoscience and Geodidactics Team (EGG), Department of Life and Earth Sciences Regional Centre for Education and Training Professions (CRMEF, Marrakech).Avenue Al Mozdalifa- B.P.797- 40000 Marrakech, Morocco Fouad Benziane and Abdelaziz Yazidi Laboratory of Geology, The National School of Mines of Rabat (ENIM), Rabat, Morocco Saïd Chakiri, Zohra Bejjaji and Mohamed Allouza Natural Resources Geosciences Laboratory (LGRN), Department of Geology, Faculty of Sciences, IbnTofail University. Kenitra, Morocco Hassan El Hadi Laboratory of Geodynamics of Old Belts (LGCA), Faculty of Science Ben M'sik, Hassan II University, AV Driss El Harti B.P.7955, Sidi Othmane, Casablanca, Morocco. Said Ettazarini Laboratory of Remote sensing and geomatics. Multidisciplinary faculty Taza. University Sidi Mohamed Ben Abdellah. Morocco Scientific and Educational Research Group within the Life and Earth Sciences Section. CRMEF Casablanca, Morocco *Corresponding Author ABSTRACT The Anti-Atlas belt, which is located in the western part of the West African Craton, is the result of Eburnean, Pan African and Variscan successive orogenies, during the Paleoproterozoic, the Neoproterozoic and the Paleozoic. The subsequent crustal accretions enlarged the craton, forming a series of belts in form of crowns. In the Anti-Atlas, the Cambrian can be defined by paleontological or radiometric dating. In the first case, the definition of its chronological lower limit can fluctuate according to new results. In the second case, the intercalated volcanic levels are younger and younger. In this study, we have grouped Adoudounian and Taliwinian in a large lower Cambrian and not in any terminal Neoproterozoic. http://iaeme.com/Home/journal/IJCIET 910 [email protected] Reconsideration of the Lower Cambrian Extension in the Anti-Atlas Belt, Morocco The volcano-sedimentary and sedimentary formations of the Adoudounian and the Taliwinian cover the Precambrian formations of the different domes. Key words: Anti-Atlas, West African Craton, orogenies, lower Cambrian, Adoudounian and Taliwinian. Cite this Article: Mohamed Yazidi, Khadija Kaid Rassou, Bouchra Razoki, Fouad Benziane, Abdelaziz Yazidi, Saïd Chakiri, Zohra Bejjaji, Mohamed Allouza, Hassan El Hadi, Said Ettazarini, Reconsideration of the Lower Cambrian Extension in the Anti-Atlas Belt, Morocco, International Journal of Civil Engineering and Technology 10(5), 2019, pp. 910-929. http://iaeme.com/Home/issue/IJCIET?Volume=10&Issue=5 1. INTRODUCTION The interest of stratigraphic series of the Moroccan Anti-Atlas is very important for several reasons. The most important is that outcrops are continuous and well exposed. Indeed, the transition from the Upper Neoproterozoic to the Cambrian is still the subject of much debate (Choubert and Faure-Muret 1962; Landing et al., 1998; Benziane, 2007; Alvaro et al., 2008, Alvaro et al., 2014; Geyer and Landing, 2016; Yazidi et al 2016; Pouclet et al., 2018). Indeed, the importance of stratigraphic series is essential for the understanding of the Neoproterozoic - Lower Cambrian boundary. Many previous works have focused on the description and characterization of the stratigraphic boundary separating Upper Ediacaran and Lower Cambrian in the Anti-Atlas (Geyer and Landing, 1995, 2004 and 2006, Maloof et al., 2005 and 2010; Alvaro et al., 2014; Landing et al., 2018). The present work aims at a revised description of the Lower Cambrian based on geological mapping research data carried out in recent years in the Anti-Atlas (Yazidi et al., 2002, 2008 and 2016; Benziane et al., 2002, 2007, 2008 and 2016; Harrison and al., 2008, Walsh et al., 2002 and 2008), supplemented by data available in the literature such as those of : Ducrot and Lancelot, 1977; Boudda et al., 1979; Bertrand-Sarfati, 1981; Benziane et al., 1983, Destombes et al., 1985; Buggisch et al., 1988; Geyer; 1989, 1990a, b and 1995; Soulaimani et al., 2003 and 2013; Gasquet et al., 2005; Soulaimani et al., 2014; Alvaro et al., 2008 and Alvaro et al., 2014. The available dating data in Benziane et al., (2016) is also used to discuss the redefinition of the "Lower Cambrian" subperiod and its extension. 2. GEOGRAPHIC CONTEXT Numerous studies on the Anti-Atlas and more particularly those of Choubert (1963) and Choubert and Faure-Muret (1970 and 1983) allow subdividing this region into three structural domains (Choubert and al., 1980) (Figures 1 and 2): The western part, which contains the Siroua, Tagragra of Tata and Ifni inliers; The central part which includes the Bou Azzer, Zenaga and Siroua inliers; The eastern part, which contains the Saghro and Ougnat inliers. Meanwhile, according to Leblanc (1975), the Anti-Atlas is subdivided into two major structural domains separated by the Major Fault of the Anti-Atlas (Figures 1 and 2): An old (Eburnean) south-western domain; A recent (pan-African) north-eastern domain. The studies carried out in each field by numerous authors allow establishing chrono- lithostratigraphic successions that may be different from one author to another. Therefore, the http://iaeme.com/Home/journal/IJCIET 911 [email protected] Mohamed Yazidi, Khadija Kaid Rassou, Bouchra Razoki, Fouad Benziane, Abdelaziz Yazidi, Saïd Chakiri, Zohra Bejjaji, Mohamed Allouza, Hassan El Hadi and Said Ettazarini correlation of formations by considering two or three domains in the Anti-Atlas becomes very difficult. This study will present the Lower Cambrian series on the basis of subdivisions derived from previous geological mapping work covering many areas of the Anti-Atlas (Benziane et al., 2002, 2007, 2008 and 2016; Walsh et al., 2008 and Yazidi et al., 2002, 2008 and 2016). Figure 1 General map of West African Craton. According to Dallmeyer and Lécorché (1991) cited in Piqué (2001). 3. GEOLOGY OVERVIEW OF THE ANTI-ATLAS The chain of the Anti-Atlas is located on the northern edge of West African Craton (figure 1). Its general shape is a large anticline where the inliers constitute the heart. The Anti-Atlas range covers an area of approximately 750 km long and 250 km wide, oriented SW-NE, from the Atlantic Ocean in the west to Algeria in the east. The Anti-Atlas is limited to the north by the major South Atlas fault (figure 2). Figure 2 Schematic geological map of the Moroccan Anti-Atlas. http://iaeme.com/Home/journal/IJCIET 912 [email protected] Reconsideration of the Lower Cambrian Extension in the Anti-Atlas Belt, Morocco The Precambrian consists of Proterozoic rocks that crop out in inliers after erosion under a Paleozoic cover. Paleozoic formations surround the Precambrian formations and correspond to platform deposits in a shallow sea environment, in regular subsidence (Robert-Charrue, 2006). Their deformation during the Variscan Orogeny influenced the current shape of the Anti-Atlas. The Paleozoic series are more than 10,000 m thick in the western Anti-Atlas, and do not exceed 6,000 m in the eastern Anti-Atlas. They begin with platform carbonate deposits of the Lower Cambrian (Boudda et al., 1979, Geyer and Landing, 1995). The Paleozoic of the Anti-Atlas domain begins with lower Cambrian series lying with concordance on the upper Ediacaran alkaline basalts and only separates them from an erosion unconformity. Early Paleozoic cover rocks deposited in a shallow marine platform environment. The Cambrian formations crop out largely in the field. In this study, we will adopt on the one hand the international stratigraphic scale for the terms and the chronological limits and on the other hand the subdivision of the Anti-Atlas into three practical domains for the understanding of the pan-African orogenesis. In the Anti-Atlas, one distinguishes the outcroppings attributed to the Cambrian, according to their palaeontological content, and those dated by the radiometric methods. The "paleontological" Lower Cambrian begins with a new transgression with deposits of a limestone and clay series where trilobites and Archaeocyata will proliferate; The "radiometric" Cambrian where the interbedded volcanic levels in the sediments of the Adoudou Formation gave radiometric ages between 532 ± 12 Ma (Pouclet et al., 2008) and 517 ± 1.5 Ma (Landing et al., 1998). The Cambrian cycle began at an age of less than 541.0 ± 1.0 Ma (Cohen et al., 2018). 4. LITHOSTRATIGRAPHIC EVOLUTION OF THE CAMBRIAN BELOW THE ANTI-ATLAS The geological history of the Anti-Atlas inliers began in the Paleoproterozoic and continued during the Middle Neoproterozoic (Cryogenian or NP2) and Upper Neoproterozoic (Ediacarian or NP3) and Paleozoic to the present day (Yazidi and al., 2016). Also, no tectonic unconformity separates the lower Cambrian from the upper Ediacaran (Benziane et al., 2016). Indeed, the main feature of the Anti-Atlas is the considerable development of lower Cambrian limestones that can reach 5000 meters thick in the northwest of the Western Anti- Atlas. These limestones crop out in the western Anti-Atlas and in the southern part of the central Atlas (Choubert and Marçais, 1952). Lower Cambrian limestones of the Eastern Anti- Atlas are less thick (figure 3). These observations suggest that after the volcanic and plutonic phase of the Upper Ediacaran (NP3s), the northern edge of the West African Craton performed as a passive margin. A marine transgression from the NW in the Western Anti-Atlas deposited platform formations, carbonates and silts. http://iaeme.com/Home/journal/IJCIET 913 [email protected] Mohamed Yazidi, Khadija Kaid Rassou, Bouchra Razoki, Fouad Benziane, Abdelaziz Yazidi, Saïd Chakiri, Zohra Bejjaji, Mohamed Allouza, Hassan El Hadi and Said Ettazarini Figure 3 Lower Cambrian deposits in the Anti-Atlas.