Sedimentary provenance of siliciclastic rocks from the Lalla Mouchaa Calcschists Formation (Coastal Block, Western Rehamna): Evidence of denudation of ca. 2 Ga basement in the Moroccan Meseta.

Paleoproterozoic basement rocks (ca. 2Ga) are scarce along the European and North African Paleozoic mountain chains (Fig.1a). In Morocco, ca. 2.2-2Ga granitic rocks (Gasquet et al., 2008; Kouyaté et al., 2013) have been exclusively reported in the Western Anti-Atlas at southwest of the Anti-Atlas Major Fault, (Choubert, 1963). In Eastern and Central Anti-Atlas and in the Moroccan Meseta, the existence of a Paleoproterozoic basement has only been recognized through indirect evidence (Gasquet et al., 2008; Michard et al., 2010). In the Anti- Atlas belt, ca. 2Ga detrital zircon grains are found in the Ediacaran siliciclastic rocks of the Bou Salda, Saghro and Taghdout groups (Abati et al., 2010). In the Moroccan Meseta, Paleoproterozoic (ca. 2Ga) zircon grains were extracted from gneiss and granitic xenoliths found in Triassic lamprophyre dykes, and from Carboniferous granophyric microgranite intrusions of central Jebilet (Dostal et al., 2005, Essaifi et al., 2003). Recently, a porphyritic rhyolite from the Rehamna Massif was dated at ca. 2.05Ga (Pereira et al., 2015), demonstrating for the first time, the exposure of the Eburnian basement in the Western Meseta. These Eburnian arc-related magmatic rocks, which are exposed to the south of the Permian Sebt Brikiyine granite in the core of anticlines from the Lalla Mouchaa Anticlinorium, are allegedly unconformably overlained by transgressive siliciclastic and carbonate beds (Corsini, 1988; Pereira et al., 2015). At north of the Sebt Brikiyine granite the probable Lower Cambrian sequence (Lalla Mouchaa Calcschists Formation; Guezou & Michard, 1976; Corsini, 1988) comprises a basal unit of microbreccias, arkosic sandstones and siltstones (lower member) that pass towards the top to centimeter-thick beds of calcschists interbedded with limestones and dolomites (upper member) that are conformably overlain by the “Paradoxides Shale Formation” composed of siltstone, greywacke and sandstone with Middle Cambrian fauna. In order to study the potential sources of the Lalla Mouchaa Calcschists Formation (probable Lower Cambrian), we have sampled a microbreccia at the Koudiat El Hamra region, for U-Pb geochronology on detrital zircon. This foliated microbreccia is composed of elongated Kfeldspar and quartz phenocrysts surrounded by a fine-grained matrix. Detrital zircon grains gave 206Pb/238Ub ages that in the Probability density plot curve are distributed by two main age peaks at ca. 2.05Ga and ca. 2.03Ga (Fig.1b), yielding a 206Pb/238U age-weighted mean of ca. 2.04Ga (El Houicha et al., 2018). The obtained U-Pb results point to a provenance from a Paleoproterozoic source, suggesting a possible contribution from rocks of the same age of the 2Ga porphyritic rhyolite exposed at south of the Sebt Brikiyine granite. Thus, there is a possibility that the Paleoproterozoic basement extends bellow the Paleozoic and Neoproterozoic sequences of the Rehamna massif

U-Pb geochronology of the El Jadida rhyolite and relation to possible Lower Cambrian recycling (Coastal block, Moroccan Meseta).

The El Jadida (Mazagan) dome, whose existence was reported as early as 1934 by Yovanovitch and Freys, constitutes one of the first outcrops of the Moroccan Meseta where the Precambrian (PIII?)-Paleozoic (Lower Cambrian?) boundary was established (Gigout, 1951; Cornée et al., 1984). Since then, it is listed as one of the few locations where the basement of the Moroccan Variscan belt can be observed (Hoepffner et al.. 2005; Michard et al., 2010).Despite, the absence of geochronological and biostratigraphic precise data to constrain the time interval recorded here, there are stratigraphic similarities that allow a correlation with the Ediacaran-Cambrian geological record of Anti-Atlas belt (Cornée et al., 1984). In this study, we developed a petrographic, geochemical and U-Pb geochronological study using zircon extracted from: (i) the El Jadida rhyolite with the aim of characterizing the magma source and estimate the age of crystallization; (ii) a microbreccia sampled at the base of the El Jadida Dolomitic Formation for determining provenance

New discoveries of archosaur and other tetrapod footprints from the Timezgadiouine Formation (Irohalene Member, Upper Triassic) of the Argana Basin, western High Atlas, Morocco - Ichnotaxonomic implications

© 2016 Elsevier B.V.New discoveries of tetrapod footprints from the Irohalene Member (T5, Upper Triassic, Carnian) of the Timezgadiouine Formation near Irohalene (Argana Basin, Morocco) are assigned to Parachirotherium isp., Atreipus-Grallator isp. (Dinosauromorpha), Brachychirotherium isp. (crocodylian-stem archosaurs), Apatopus lineatus (phytosaurs) and Rhynchosauroides (lepidosauromorphs/archosauromorphs). Parachirotherium is present on the surfaces with different tetradactyl-pentadactyl extramorphological variations, similar to the preservation mode observed at the type locality of the ichnogenus in the Middle Triassic of the European Germanic Basin. Described specimens permit a re-evaluation of footprints described earlier from the Irohalene locality that are synonymized here with Parachirotherium and Atreipus-Grallator. The presence of Brachychirotherium is the second record in North Africa and Morocco. The assemblage is similar in composition to other T5 localities and to some ichnofaunas in North America and central Europe. Biostratigraphically, the occurrence of Brachychirotherium indicates the respective biochron that can be cross-correlated with the Carnian-Rhaetian interval

Zircon U-Pb geochronology and geochemistry of Cambrian magmatism in the Coastal Block (Oued Rhebar volcanic complex, Moroccan Meseta): Implications for the geodynamic evolutionary model of North-Gondwana

U-Pb dating (SHRIMP) of magmatic zircons from an intermediate-mafic agglomerate of the Oued Rhebar Volcanic Complex (Coastal Block, Western Meseta) yielded a weighted mean age of 507 ± 5 Ma. The obtained middle Cambrian age (Series 3, Stage 5) seems to be the best estimate for the crystallization of the ORVC volcanic rock, providing a maximum depositional age for the overlying Bouznika volcanosedimentary Formation. The ORVC rock is representative of middle Cambrian crust generation in North-Gondwana, but contains Ediacaran (ca. 546-542 Ma) and early Cambrian (ca. 536-526 Ma) inherited zircon which might be derived from recycling of older continental crust. This geochemistry study corroborates the existence of calcalkaline rhyolites, basaltic andesites and andesites in the ORVC rocks, but also of the existence, albeit to a lesser volume, of tholeiitic basalt. The relative higher volume of calc-alkaline compared to tholeiitic signature might reflect, in some extent, contamination of depleted mantle-derived magmas by the upper continental crust, as has been proposed for the origin of the same age rift-related igneous rocks from North-Gondwana, as the Iberian correlatives

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

The Pre-Pan-African rifting of Saghro (Anti-Atlas, Morocco) : example of the middle Neoproterozoic Basin of Boumalne

In the Anti-Atlas, the Boumalne basin includes 3,000 m of Middle Neoproterozoic sediments. It consists of turbiditic deposits folded during the major Pan-African event ca 685 Ma. A syn-sedimentary basaltic pile of lava flows is interbedded in the upper part of the lower formation. These lavas show an initial rift tholeiite (IRT) chemical signature. Petrographical analysis of sediments and typology of detrital zircons indicate a continental margin sedimentation, without any volcano-sedimentary supply from a close volcanic arc. It is concluded that the Boumalne Basin formed in a continental passive margin evolving from an intracontinental rift. This interpretation differs clearly from that of a back-arc basin which is commonly accepted. Hence, the opening of this basin is related to the pre-Pan-African Saghro rift synchronous to the Central Anti-Atlas oceanization, and not to the demise of this oceanic domain along an active margin

New discoveries of archosaur and other tetrapod footprints from the Timezgadiouine Formation (Irohalene Member, Upper Triassic) of the Argana Basin, western High Atlas, Morocco - Ichnotaxonomic implications

© 2016 Elsevier B.V.New discoveries of tetrapod footprints from the Irohalene Member (T5, Upper Triassic, Carnian) of the Timezgadiouine Formation near Irohalene (Argana Basin, Morocco) are assigned to Parachirotherium isp., Atreipus-Grallator isp. (Dinosauromorpha), Brachychirotherium isp. (crocodylian-stem archosaurs), Apatopus lineatus (phytosaurs) and Rhynchosauroides (lepidosauromorphs/archosauromorphs). Parachirotherium is present on the surfaces with different tetradactyl-pentadactyl extramorphological variations, similar to the preservation mode observed at the type locality of the ichnogenus in the Middle Triassic of the European Germanic Basin. Described specimens permit a re-evaluation of footprints described earlier from the Irohalene locality that are synonymized here with Parachirotherium and Atreipus-Grallator. The presence of Brachychirotherium is the second record in North Africa and Morocco. The assemblage is similar in composition to other T5 localities and to some ichnofaunas in North America and central Europe. Biostratigraphically, the occurrence of Brachychirotherium indicates the respective biochron that can be cross-correlated with the Carnian-Rhaetian interval

New discoveries of archosaur and other tetrapod footprints from the Timezgadiouine Formation (Irohalene Member, Upper Triassic) of the Argana Basin, western High Atlas, Morocco - Ichnotaxonomic implications

© 2016 Elsevier B.V.New discoveries of tetrapod footprints from the Irohalene Member (T5, Upper Triassic, Carnian) of the Timezgadiouine Formation near Irohalene (Argana Basin, Morocco) are assigned to Parachirotherium isp., Atreipus-Grallator isp. (Dinosauromorpha), Brachychirotherium isp. (crocodylian-stem archosaurs), Apatopus lineatus (phytosaurs) and Rhynchosauroides (lepidosauromorphs/archosauromorphs). Parachirotherium is present on the surfaces with different tetradactyl-pentadactyl extramorphological variations, similar to the preservation mode observed at the type locality of the ichnogenus in the Middle Triassic of the European Germanic Basin. Described specimens permit a re-evaluation of footprints described earlier from the Irohalene locality that are synonymized here with Parachirotherium and Atreipus-Grallator. The presence of Brachychirotherium is the second record in North Africa and Morocco. The assemblage is similar in composition to other T5 localities and to some ichnofaunas in North America and central Europe. Biostratigraphically, the occurrence of Brachychirotherium indicates the respective biochron that can be cross-correlated with the Carnian-Rhaetian interval

New discoveries of archosaur and other tetrapod footprints from the Timezgadiouine Formation (Irohalene Member, Upper Triassic) of the Argana Basin, western High Atlas, Morocco - Ichnotaxonomic implications

© 2016 Elsevier B.V.New discoveries of tetrapod footprints from the Irohalene Member (T5, Upper Triassic, Carnian) of the Timezgadiouine Formation near Irohalene (Argana Basin, Morocco) are assigned to Parachirotherium isp., Atreipus-Grallator isp. (Dinosauromorpha), Brachychirotherium isp. (crocodylian-stem archosaurs), Apatopus lineatus (phytosaurs) and Rhynchosauroides (lepidosauromorphs/archosauromorphs). Parachirotherium is present on the surfaces with different tetradactyl-pentadactyl extramorphological variations, similar to the preservation mode observed at the type locality of the ichnogenus in the Middle Triassic of the European Germanic Basin. Described specimens permit a re-evaluation of footprints described earlier from the Irohalene locality that are synonymized here with Parachirotherium and Atreipus-Grallator. The presence of Brachychirotherium is the second record in North Africa and Morocco. The assemblage is similar in composition to other T5 localities and to some ichnofaunas in North America and central Europe. Biostratigraphically, the occurrence of Brachychirotherium indicates the respective biochron that can be cross-correlated with the Carnian-Rhaetian interval

Geodynamic evolution of the northwestern Paleo-Gondwanan margin in the Moroccan Atlas at the Precambrian-Cambrian boundary

International audienceIn the southern Moroccan Atlas, abundant volcanic and sedimentary formations, dated from the Ediacaran to Cambrian time, were set at the northwestern Paleo-Gondwanan margin, after the main Pan-African orogenic event. The Precambrian-Cambrian geodynamic transition is characterized by an Early Cambrian marine transgression. We examine the tectonic conditions of this transgression and the magmatic signatures of the volcanic rocks that were produced just before and around the Precambrian-Cambrian boundary. Significant angular unconformities are evidenced, between the Late Neoproterozoic formations and the Cambrian deposits, in the central and eastern Anti-Atlas, which are due to a late Ediacaran NNE-SSW compressional event. The Late Neoproterozoic formations are related to an intracontinental volcanic chain of andesitic to rhyolitic lavas dated to the Ediacaran period. These calc-alkaline rocks were generated by melting of the mantle, previously metasomatized during the Pan-African orogenic stage, and of continental crust. The Late Ediacaran to Early Cambrian formations are analyzed in the Agoundis-Ounein and Toubkal areas, southwest of the old block of High-Atlas. An important basaltic pile unconformably overlies the Ediacaran rhyolitic formation and is overlain by Tommotian sediments. These basalts are continental tholeiites generated by melting of a normal subcontinental mantle. They outpoured from an important N 30°-trending fissural system over a basin floor. Some lherzolite fragments have been sliced along southwest-northeast faults, in the Lower Cambrian sediments. They originated from a transitional mantle between continental and oceanic domains. Farther east of the central Anti-Atlas, the Tommotian Djbel Boho volcano exhibits olivine basalts having an intraplate enriched asthenospheric signature type of ocean island basalt. The magmatic characteristics of the Late Ediacaran to Early Cambrian volcanic rocks, the structural features, and the presence of lherzolite fragments are consistent with a volcanic passive margin rift setting in a WNW-ESE extension regime. The meaning of this extensional event is discussed in relationships to the opening of a Cambrian basin and the drifting of the Avalonian terranes