NE Africa Research Articles

Tracing Oligocene−Miocene source-to-sink systems in the deep Levant Basin: A sandstone provenance study

The Levant Basin in the Eastern Mediterranean contains an ∼3-km-thick, predominantly siliciclastic section of Oligocene−Miocene age, which hosts large hydrocarbon reservoirs (“Tamar Sands Play”). Here, we present a provenance study of Oligocene−Miocene sandstones based on detrital zircon U-Pb-Hf and heavy mineral assemblages. Samples were retrieved from four boreholes across the Levant Basin: Myra-1, Dolphin-1, Leviathan-1, and Karish North-1. Our investigations revealed that the sediments are dominated by Neoproterozoic and older Precambrian zircons with variable Hf isotopic composition, indicating that they were mainly reworked from Paleozoic−Mesozoic sandstones of African-Arabian provenance, with minor derivation from the Neoproterozoic basement of the Arabian-Nubian Shield. Variations in the proportions of pre−900 Ma zircons were encountered in various levels of the siliciclastic section. These zircons were markedly enriched (44%−57%) in the Rupelian and Aquitanian−Burdigalian intervals, accompanied by abundant detrital apatite peloids in the heavy mineral fraction, and relatively sparse (21%−38%) in the Chattian−Aquitanian and Langhian−Tortonian intervals, alongside scarce Mesozoic−Cenozoic zircons. These findings allow us to associate the deep-basin detrital record with two sedimentary transport systems that reached the Levant Basin from both NE Africa and Arabia simultaneously until the late Miocene, when sediment transport from Arabia ceased. While Rupelian and Aquitanian−Burdigalian sediments, including the main section of the “Tamar Sands,” were derived mainly from Arabian sources via the Levant continental margin, Chattian−Aquitanian and Langhian−Tortonian sediments were primarily sourced from NE Africa via the Nile Delta. Detrital contribution from the Eurasian side of the Eastern Mediterranean was not identified, suggesting that sand originating in the Arabia-Eurasia collision belt did not reach the Levant Basin.

Early Cretaceous palynoflora from palaeotropics of NE Africa (correlation and significance): an example from the Shushan Basin, Egypt

We re-assessed and re-evaluated the diverse spores and pollen associations, presently recovered from clastics of the Shushan Basin. Eight (informal) Early Cretaceous (Valanginian to middle Cenomanian) spores/pollen zones are suggested, dated and correlated with regional/interregional records. Palynological dating offered bases for borehole stratigraphic resolution and basin correlation. It permitted revision of the homogeneous Early Cretaceous sediments of the borehole. Intrabasinal correlation, based on closely-spaced palynologically- productive samples, revealed the existence of an undetected sediment hiatus east of the basin, manifested by the wedging/missing of the Aptian Dahab clastics from west to east. The Shushan palynoflora exhibits great similarity with their counterparts in other provinces of the Northern Gondwana continent. But, however, A fern-dominated hygrophilous spores, along with Classopollis pollen, validated previous assumptions that humid conditions were responsible for the delayed appearance and scarcity of Dicheiropollis pollen in NE Africa (Egypt, Libya and Sudan), by the late Hauterivian. This humidity is thought to have triggered the production of Afropollis in the regional North African records, which reached an acme. Three main peaks of this pollen are inferred from the late Aptian, early Albian and early-middle Cenomanian intervals of the Shushan-1X well. Chronologically, these peaks can be of great stratigraphic value in NE Africa or other areas in Northern Gondwana that witnessed wet palaeoclimates during the Early Cretaceous.

Seismicity pattern of African regions from 1964–2022: b-value and energy mapping approach

The African continent is one of the few tectonic plates where very few earthquakes have been reported. Sporadic poor data have jeopardized efforts to assess seismic hazards. In light of the tectonic setting, a review of the continent’s seismicity is crucial for predicting seismic hazards. For this study, seismicity data from USGS and ISC catalogs were collected from 1964–2022, in the latitude range of 40oS-40oN and longitude 20oW-52oE, from the surface to 700 km deep. Gutenberg’s parameters as well as the spatial variation of seismic energy were then analyzed as an assessment of Africa’s seismicity. The results show that NE Africa is at a higher stress level in terms of energy release than NW Africa. The Richter and Guttenberg’s constants of a = 5.61, b = 0.59; a = 6.55, b = 0.77; a = 6.44, b = 0.78; a = 7.41, b = 0.92; a = 5.94, b = 0.86; a = 5.97, b = 0.77 with the corresponding magnitude of completeness, mc, observed to be 3.7, 4.1, 4.4, 4.7, 4.8 and 4.6 were found for regions NW, NE, southern, eastern, western and central Africa, respectively. The distribution of focal depths vs. magnitude revealed that most of the seismicity is inherently shallow in its nature with an average focal depth of 21.22 km. In comparison, NW experiences relatively more profound events with an average depth of 32.19 km. A substantial rise in focal depth in North Africa is associated with the collision boundary. This information as a constraint on the tectonic plate near convergent boundary could be useful in plate modeling. Key Policy Highlights The higher stress observed in the North Africa and East Africa continent is vital for policy makers for sustainable built environment The estimated minimum magnitude cut-off Mw 3.7 reveals that the recording facilities in African continent is now improving. An increased focal depth distribution of events in North Africa infers there is plate convergence and can be used to constrain African tectonic plate for plate modeling.

Simplorabanitina gen. nov. (type species S. simplex sp. nov.) provides further evidences for the high diversity of Nezzazatidae (Foraminifera) in Cenomanian shallow-water carbonate platforms

ABSTRACT A new genus of the Nezzazatidae is here introduced as Simplorabanitina simplex gen. et sp. nov. from the Cenomanian Sarvak Formation of south-western Iran. The main architectural constraints used to discriminate the new taxon from its close ally Rabanitina Smout lies in the complete lack of skeletal elements collectively called the ‘median plate’ or ‘complex longitudinal plate’, and by the occurrence of pseudo-keriotheca characterising the chamber wall. The new occurrence increases the number of species of Nezzazatidae throughout the shallow-water carbonate platforms of the Arabian Plate prior to the extinction related to the Oceanic Anoxic Event 2 of the Cenomanian-Turonian boundary, indicating high diversity. Unlike some other Cenomanian Nezzazatidae that have been commonly found from Mexico to the Middle East, the biogeographic affinity of Simplorabanitina n. gen. seems to be restricted to the Arabian Plate and perhaps might also be found in the coeval successions of NE Africa. 37F231ED-05B8-4BCA-9F9D-2B38AFA55296

The anorogenic late Ediacaran granite-rhyolite porphyries of Gabal Abu Durba, Sinai: termination of magmatism in the Neoproterozoic Arabian-Nubian Shield crust

ABSTRACT Anorogenic magmatism in the northern Arabian-Nubian Shield occurred during a long-lasting crustal extension event (<580 Ma), which succeeded the formation of the Pan-African orogenic belt in NE Africa and Arabia. Late Neoproterozoic anorogenic felsic volcanic-subvolcanic rocks, along with post-collisional granitoid suites, are exposed in the Gabal Abu Durba mountain range along the eastern flank of the Gulf of Suez in Sinai. These rocks include granite and rhyolite porphyries, metaluminous to weakly peralkaline with distinct potassic alkaline and ferroan affinities. Major and trace element characteristics such as K2O/MgO >16, total alkalis >8.5 wt.%, (K2O + Na2O)/CaO >10, agpaitic index (NK/A) >0.85 and Zr (>250 ppm), Nb (>20 ppm), Y (>80 ppm), Zn (>100 ppm) and Ce (>100 ppm), and 10,000 × Ga/Al >2.6 and [Zr + Nb + Y + Ce] >350 ppm are suggestive of an A-type granite genesis. Zircon U-Pb dating of two representative samples returned crystallization ages of 569 ± 2.6 Ma and 561.7 ± 3.2 Ma for granite and rhyolite porphyries, respectively. The melting temperatures estimated at 997–1020°C are consistent with high-temperature liquidus conditions. Fractional crystallization, coupled with less significant crustal assimilation, was likely the main mechanism of formation of these rocks from a common primitive asthenospheric mantle-derived trachytic magma in an anorogenic intra-plate setting. The A-type alkali granite and rhyolite porphyries of Gabal Abu Durba are manifestations of mantle upwelling and lower crust underplating in the late Ediacaran anorogenic stage. These felsic subvolcanic intrusions (≈ 569–562 Ma) along with their volcanic counterparts constitute a new unmatched rock unit that most probably represent the last chapter of the anorogenic magmatism in the Neoproterozoic Arabian-Nubian Shield crust before the beginning of Phanerozoic era.

A striking new species of Blepharis (Acanthaceae) from north-eastern Somalia

Blepharis eilensis (Acanthaceae) is described as new to science. Blepharis eilensis belongs to subg. Acanthodium sect. Acanthodium. It is endemic to north-eastern Somalia, in the Nogal (Nugaal) region and is presently known only from the type collection. The species is compared with similar species from NE Africa (B. forgiarinii, B. diplodonta) and preliminary information on the ecology, distribution and conservation status of this new species is provided.

Lagoonal carbonate deposition preceding rifting-related uplift: evidence from the Bartonian–Priabonian (Eocene) of the northwestern Gulf of Suez (Egypt)

Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene. This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian–Priabonian succession cropping out in this area. Bartonian–Priabonian carbonate deposits in five stratigraphic sections constitute, from base to top, the Gebel Hof, Observatory, Sannur, Qurn, and Wadi Hof Formations. These formations contain four local assemblage zones of larger benthic foraminifers. Analyses of litho-, bio-, and microfacies in the succession resulted in the recognition of 12 lithofacies types. These litho-facies are represented by packages of lime-mudstones, wackestones, packstones, pack- to grainstones, grainstones, rudstones, boundstones and dolomites. These lithofacies have been grouped into four genetically-related facies associations that represent, respectively, tidal flats/shallow subtidal, restricted-shelf/lagoonal, shoal bar, and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting. The vertical transitions of these facies associations, representing facies changes through time, imply fluctuations of the regional sea level. The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises; the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity. The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian–Priabonian.

Syn-collisional detrital zircon source evolution in the northern Moroccan Variscides

U–Pb dating and Hf isotopic analyses of detrital zircon grains from Cambrian-Devonian strata in the Moroccan Mesetas were undertaken in order to constrain its Paleozoic paleogeographic evolution. In this work, we analyzed 12 Late Devonian-Late Carboniferous samples of syn-collisional detrital rocks from the Western and Eastern Moroccan Mesetas. All our samples present significant Ediacaran (ca. 620 Ma) and Rhyacian (ca. 2.1 Ga) detrital zircon populations, suggesting that the West African Craton remained the main source of sediments for northern Morocco at least until the Late Carboniferous. Locally, a Stenian-Tonian (ca. 1.0 Ga) detrital zircon population is also present, probably fed from intermittent and distant source areas located in NE Africa (e.g. Sahara Metacraton). The collisional evolution started with the approach of an Avalonian promontory to the northern Gondwana continental margin (latest Devonian - earliest Carboniferous), after the closure of the Rheic Ocean. This process entailed the former subduction of the Rheic oceanic lithosphere underneath the Avalonian continental terrane and the formation of a magmatic arc in the upper plate. In this scenario, the first syn-collisional sediments (Tournaisian; Tiflet and Debdou-Mekkam areas) are characterized by a Devonian detrital zircon population (ca. 370 Ma), presumably derived from the magmatic arc, and an increasing number of Mesoproterozoic dates, putatively also sourced from the continental crust of the Avalonian terrane. After the initial collision, only the Visean samples located in areas close to the exotic terrane (e.g. Ben Slimane area) displayed a minor Avalonian component. Finally, the Late Carboniferous samples from the Jerada area recorded an important Middle Carboniferous (ca. 330 Ma) detrital zircon population, probably sourced from Variscan granitoids emplaced in the Eastern Moroccan Meseta and attesting to crustal thickening and subsequent thermal maturation of the Gondwana continental crust in this area.

Detrital zircon provenance of north Gondwana Palaeozoic sandstones from Saudi Arabia

AbstractWe present the first comprehensive detrital zircon U–Pb age dataset from Palaeozoic sandstones of Saudi Arabia, which provides new insights into the erosion history of the East African Orogen and sediment recycling in northern Gondwana. Five main age populations are present in varying amounts in the zircon age spectra, with age peaks at 625 Ma, 775 Ma, 980 Ma, 1840 Ma and 2480 Ma. Mainly igneous rocks of the Arabian–Nubian Shield are suggested to be the most prominent sources for the Ediacaran to middle Tonian zircon grains. Palaeoproterozoic and Archaean grains may be xenocrystic zircons or they have been recycled from older terrigenous sediment. A primary derivation from Palaeoproterozoic and Archaean basement is also possible, as rocks of such age occur in the vicinity. Approximately 4 % of the detrital zircons show Palaeozoic (340–541 Ma) ages. These grains are likely derived from Palaeozoic post-orogenic and anorogenic igneous rocks of NE Africa and Arabia. A few single grains gave up to Eoarchaean (3.6–4.0 Ga) ages, which are the oldest zircons yet described from Arabia and its vicinity. Their origin, however, is yet unknown. Detrital zircons with U–Pb ages of 1.0 Ga are present in varying amounts in all of the samples and are a feature of terrigenous sediment belonging to the Gondwana super-fan system with an East African – Arabian zircon province.

Cadomian (ca. 550 Ma) magmatic and thermal imprint on the North Arabian-Nubian Shield (south and central Israel): New age and isotopic constraints

The Arabian-Nubian Shield (ANS) is a province of mostly juvenile Neoproterozoic continental crust in NE Africa and Arabia, forming the northern extension of the East-African orogen. Subsequent to widespread, mostly late- to post-orogenic early-Ediacaran calc-alkaline granitoid emplacement, the latest magmatic phase in the ANS saw the intrusion of alkaline shallow plutons alongside volcanic massifs and dikes of variable compositions. While some of these intrusions were dated to 550–530 Ma by Rb-Sr and Ar-Ar, U-Pb zircon data has mostly limited ANS magmatism to no younger than ca. 580 Ma. Here we report new age and isotopic data from latest Neoproterozoic intrusions along a N-S transect within the northern ANS and its periphery, substantiating the record of a ca. 550 Ma igneous-thermal event in the area. In the northern Negev of Israel, mafic igneous rocks intruded into the subsurface late Neoproterozoic clastic wedge of the Zenifim Formation produced apatite U-Pb isochron ages between 557 and 545 Ma. In the Amram alkaline massif, 150 km to the south, an alkali-granite was dated to 605 ± 2.5 Ma by zircon U-Pb, but apatite U-Pb ages from all rocks of the massif concentrate at ca. 550 Ma indicating thermal resetting. Apatites from the zircon dated 611 ± 5 Ma Roded quartz diorite in the Elat area, south of Amram, produced a 600 ± 4 Ma U-Pb age, demonstrating that southern segments were not thermally reset at ca. 550 Ma. Nd isotopes in apatite and whole rock show the ca. 550 Ma igneous rocks to be variable in their isotopic composition, ranging between εNd(t)=(-4) – (+2), far less juvenile than typical ANS magmas. The ca. 550 Ma intrusions resemble in their age and isotopic properties Cadomian granites and volcanic rocks that are known from southern Turkey, Iran and Europe. We interpret the ca. 550 Ma igneous overprint and thermal resetting documented in the northernmost ANS as related to the superposition of Cadomian orogeny on the ANS periphery. This can be related to the late Ediacaran subduction of proto-Tethys accompanying the accretion of the Cadomian basement of the Tauride block to NE Africa and Arabia, before the area was overstepped by Cambrian platform sedimentation.

Rock art from Andriamamelo Cave in the Beanka Protected Area of western Madagascar

Stylistically unique black rock drawings have been discovered in Andriamamelo Cave in western Madagascar. Several image groupings comprise naturalistic scenes with anthropomorphic, zoomorphic, and therianthropic figures. These complex images are not similar to the polychrome painted symbols previously described from the Isalo region of SW Madagascar. Eight instances were noted where images and themes suggest Ptolemaic Egyptian mythological characters and symbols, some possibly of stellar constellations. One type of M-shaped figure occurred 16 times throughout the entire design field. We have not found this figure in other rock art around the Indian Ocean, except a rare occurrence in Borneo, believed to have been created about 2000 years ago. It also matches one distinctive character found in the Amharic alphabet of Ethiopia. One set of eight curvilinears resemble Arabic characters or indigenous Sorabe. Extant animals were tentatively identified, and also three of the extinct megafauna may be pictured (elephant bird, tortoise, and sloth lemur). The latter appears in an inferred hunting scene, with a hunter pointing a weapon, the giant lemur upside down, and two dogs. Images suggest connections between traditional Malagasy symbology and the disparate worlds of the island’s ancient influences, both from NE Africa and Borneo. Milligram-sized samples of the black pigment were collected from an image for AMS 14C dating, but they contained insufficient carbon in aggregate.

Paleozoic glaciation in NE Africa: field and remote sensing-based evidence from the South Eastern Desert of Egypt

ABSTRACT Exhumed Paleozoic glacial deposits and landforms of the North Gondwana are reported here for the first time from the South Eastern Desert (SED) of Egypt. Using field observations and remote sensing datasets (Advanced Land Observing Satellite [ALOS], Phased Array L-band Synthetic Aperture Radar [PALSAR] radar, multispectral Landsat TM datasets, and digital elevation models [DEMs]), we mapped the distribution of Paleozoic glacial features (i.e. deposits and landforms) in the SED. Two main glaciogenic facies were identified in three locations in the SED: (1) massive, poorly sorted, matrix supported, boulder-rich diamictites in Wadi El-Naam and Korbiai, and (2) moderately-sorted, occasionally bedded outwash deposits in Betan area. Inspection of radar, DEMs, and Landsat Operational Land Imager (OLI) images revealed previously unrecognized ENE-WSW trending glacial megalineations (MLs) over the peneplained Neoproterozoic basement rocks in the central sections of the SED, whose trends align along their projected extension with those of glacial features (tunnel valleys and striation trends) reported from Saudi Arabia. The glaciogenic features in the SED are believed to be largely eroded during the uplift associated with the Red Sea opening, except for those preserved as basal units beneath the Nubia Sandstone Formation or as remnant isolated deposits within paleo-depressions within the basement complex. The apparent spatial correlation of the SED glacial features with well-defined Late Ordovician deposits in North Africa and in Saudi Arabia, and the reported thermochronometric analyses and fossil records are consistent with a Late Ordovician age for the SED glaciogenic features and support models that call on the continuation of the Late Ordovician (Hirnantian) ice sheet from the Sahara into Arabia through the SED of Egypt.

Step-drawdown test as a tool for the assessment of the Nubia sandstone aquifer in East El-Oweinat Area, Egypt

The Cretaceous Nubia sandstone aquifer is the main aquifer in East El-Oweinat area along the Egyptian–Sudanese borders and in NE Africa. East El-Oweinat project has been recently considered one of the main agricultural projects in the southwest of the Egyptian Western Desert. So, the hydrogeological assessment for the Nubia aquifer in East El-Oweinat area has been done through studying and characterising the hydraulic parameters and step-drawdown test. The well and aquifer losses coefficients (C and B, respectively), the specific capacity, and the well efficiency as well as the aquifer and aquitard thickness have been estimated and traced through a total of 46 wells that have been distributed through the study area in two sectors, southern and northern. For the purpose of further exploration, the effective porosity (∅), hydraulic conductivity (K), and transmissivity (T) have been estimated for the wells in the northern sector. In addition, an aquifer assessment quality index has been introduced to assess and to rank the studied aquifer. Therefore, it is concluded that the hydraulic and the step-draw down parameters as well as the aquifer and aquitard thicknesses are prospective for further exploration to the north and the east of the northern sector in the study area. The well efficiency is mostly affected by the studied parameters, particularly the well loss coefficient, the hydraulic parameters and the well design as well. GIS approach and ArcGIS software have been applied to delineate the spatial distribution of the well performance characteristics, in order to compare between the studied groundwater wells and to integrate the different-acquired data. A set of isocontour maps have been introduced to match the lateral variation of the studied parameters and the aquifer potential to refer to the best direction for further underground water exploration.

Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C–H–O–S Isotopes

The Koka gold deposit is located in the Elababu shear zone between the Nakfa terrane and the Adobha Abiy terrane, NW Eritrea. Based on a paragenetic study, two main stages of gold mineralization were identified in the Koka gold deposit: (1) an early stage of pyrite–chalcopyrite–sphalerite–galena–gold–quartz vein; and (2) a second stage of pyrite–quartz veins. NaCl-aqueous inclusions, CO2-rich inclusions, and three-phase CO2–H2O inclusions occur in the quartz veins at Koka. The ore-bearing quartz veins formed at 268 °C from NaCl–CO2–H2O(–CH4) fluids averaging 5 wt% NaCl eq. The ore-forming mechanisms include fluid immiscibility during stage I, and mixing with meteoric water during stage II. Oxygen, hydrogen, and carbon isotopes suggest that the ore-forming fluids originated as mixtures of metamorphic water and magmatic water, whereas the sulfur isotope suggests an igneous origin. The features of geology and ore-forming fluid at the Koka deposit are similar to those of orogenic gold deposits, suggesting that the Koka deposit might be an orogenic gold deposit related to granite.

Reconnaissance of Prehistoric Sites in the Red Sea Coastal Region of the Sudan, NE Africa

ABSTRACTThis paper reports results of a recent Stone Age-focused archaeological survey in the Red Sea coastal region of the Republic of Sudan, northeast Africa. Bifaces (handaxes) are the most conspicuous artifact class encountered during the survey and are characteristic of the Acheulean technocomplex. Other recorded artifact types include points, scrapers, and prepared core products referable to the Nubian and recurrent Levallois methods. Most of the artifact-bearing localities lie landward—outside of the coastal margin—thus, the evidence does not signify direct coastal adaptation per se. Our preliminary findings suggest that multiple Pleistocene-age hominin settlements tied to a terrestrial niche existed in the region. The western margin of the Red Sea occupies a pivotal location, linking the Horn of Africa and the Levant, two vital regions in human evolutionary research. Thus, the Stone Age data from the Sudan region has direct relevance for assessing hominin dispersal routes out of Africa.

Elusive “Libyans”: Identities, Lifestyles and Mobile Populations in NE Africa (late 4th–early 2nd millennium BCE)

Abstract The term “Libyan” encompasses, in fact, a variety of peoples and lifestyles living not only in the regions west of the Nile Valley, but also inside Egypt itself, particularly in Middle Egypt and the Western Delta. This situation is reminiscent of the use of other “ethnic” labels, such as “Nubian,” heavily connoted with notions such as ethnic homogeneity, separation of populations across borders, and opposed lifestyles. In fact, economic complementarity and collaboration explain why Nubians and Libyans crossed the borders of Egypt and settled in the land of the pharaohs, to the point that their presence was especially relevant in some periods and regions during the late 3rd and early 2nd millennium BCE. Pastoralism was just but one of their economic pillars, as trading activities, gathering, supply of desert goods (including resins, minerals, and vegetal oils) and hunting also played an important role, at least for some groups or specialized segments of a particular social group. While Egyptian sources emphasize conflict and marked identities, particularly when considering “rights of use” over a given area, collaboration was also crucial and beneficial for both parts. Finally, the increasing evidence about trade routes used by Libyans points to alternative networks of circulation of goods that help explain episodes of warfare between Egypt and Libyan populations for their control.

Preliminary detrital zircon signatures from the southern Asir terrane, Saudi Arabia: A link to Yemen or the Nubian Shield?

The Arabian Shield comprises early Neoproterozoic to Cambrian (∼850–530 Ma) tectonostratigraphic terranes formed by the closure and accretion of juvenile volcanic arcs and back-arc basins associated with Gondwana assembly. Unlike the Nubian Shield which preserves crustal isotopic signatures, the Arabian Shield is distinctly juvenile with the exception of the Paleoproterozoic (∼1800–1670 Ma) Khida subterrane in Saudi Arabia and the terranes of Yemen. This study presents the first combined zircon U-Pb, O and Hf isotope data of metavolcanic and metasedimentary rocks from southwestern most Saudi Arabia, near the Yemen border – a region thought to contain some of the oldest (>815 Ma) lithologies in Saudi Arabia, including the Atura Formation and the Tayyah Belt. One volcaniclastic metasediment sample from the Atura Formation yields zircon U-Pb age peaks of 741, 672, 646 Ma (n = 131), δ18O(V-SMOW) ranging from 4.6 to 8.3‰ and ɛHf (t) from +7.7 to +12.5. Two samples from the Tayyah Belt include an older metasandstone and a late intruding granitic dyke which provides a minimum age for the Tayyah Belt. The former yields two significant U-Pb peaks of 812 (n = 8) and 999 (n = 6) Ma, δ18O and ɛHf (t) values ranging from 4.4 to 9.6‰ and −10.1 to +12.4, respectively; the later yields a concordia age of 645.8 [±1.7] Ma (n = 29), δ18O ranging from 5.7 to 6.6‰, and ɛHf (t) of +5.9 to +9.6. The zircon age and juvenile Hf signatures from the Atura Formation are consistent with the synorogenic phase in the Shield. Sedimentation was likely associated with arc volcanism during the previously documented eastward phase of accretion at ∼740–640 Ma and the closure of the Mozambique Ocean. In contrast, the data from the texturally more mature Tayyah Belt metasediment indicate a more distal, and more evolved crustal input at the time of sediment deposition which is unusual for the Saudi Arabian Shield. Consequently, the Tayyah metasediments are likely sourced from areas with greater continental affinity, such as the cratonic basement and/or reworked crust of the Sahara metacraton in NE Africa.

Neogene palaeochannel deposits in Sudan – Remnants of a trans-Saharan river system?

The start of Nile-type trans-Saharan drainage systems in NE Africa during the Cenozoic is disputed. Stratigraphical and sedimentological data in Egypt are partly in conflict with the uplift history of potential source areas of water and sediment in East Africa. Here, we investigate outcrops of the Wadi Awatib Conglomerate in Sudan that provide the first evidence of northerly flowing Neogene rivers in the region. Dimension and relief of basal erosion surfaces, overall geometry of deposits and palaeocurrent indicators demonstrate that the deposits represent the fill of northward-oriented incised valleys. The conglomerates were deposited in deep gravel-bed rivers, by hyperconcentrated flows, tractions carpets and gravel bars, primarily during heavily sediment-laden floods of probably monsoonal origin. Stratigraphical and geomorphological relationships show that the deposits are between Eocene and Pliocene in age. Considering the structural history of the region and periods in the Cenozoic with palaeoclimatic conditions suitable for the production and transport of gravels, we hypothesize that the dramatic base-level fall during the Late Miocene Messinian salinity crisis in combination with a favorable palaeoclimate caused the incision of valleys and their subsequent filling with conglomerates. Sea-level change in the Mediterranean Sea and headward erosion of streams that were connected to the Egyptian Nile might have been the primary cause of valley incision and deposition of conglomerates, despite a location far inland from the coastline. We suggest that the deposits document a relatively young Neogene (Messinian to early Pliocene) trans-Saharan river system unrelated to uplift of the Ethiopian Plateau.

Directional change during a Miocene R‐N geomagnetic polarity reversal recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA

AbstractRecurring transitional field directions during three Miocene geomagnetic reversals provide evidence that lateral inhomogeneity of the lower mantle affects flow in the outer core. We compare new paleomagnetic results from a composite sequence of 15.2 Ma lava flows in north central Nevada (Sheep Creek Range; 40.7°N, 243.2°E), erupted during a polarity reversal, to published data from Steens Mountain (250 km to the northwest in Oregon) and the Newberry Mountains (650 km to the south in California) that document reversals occurring millions of years and many polarity switches earlier. Alternating field demagnetization, followed by thermal demagnetization in half the samples, clearly isolated the primary thermoremanent magnetization of Sheep Creek Range flows. We correlated results from our three sampled sections to produce a composite record that begins with a single virtual geomagnetic pole (VGP) at low latitude in the Atlantic, followed by two VGPs situated near latitude 30°N in NE Africa. After jumping to 83°N (one VGP), the pole moves to equatorial South America (one VGP), back to NE Africa (three VGPs), to high southern latitudes (two VGPs), back to equatorial South America (three VGPs), and finally to high northern latitudes (nine VGPs). The repeated visits of the transitional VGP to positions in South America and near NE Africa, as well as the similar behavior recorded at Steens Mountain and the Newberry Mountains, suggest that lower mantle or core‐mantle boundary features localize core flow structures, thereby imparting a discernible regional structure on the transitional geomagnetic field that persists for millions of years.

Early Carboniferous anorogenic magmatism in the Levant: implications for rifting in northern Gondwana

ABSTRACTThe Variscan orogenesis in Europe peaked during the Late Devonian–Early Carboniferous times when Gondwanan terranes collided with Laurasia. Hitherto it has been thought that Carboniferous tectonics in northern Arabia and the adjacent parts of NE Africa were broad swells (‘arches’) and depressions (‘basins’) that formed as a far-field contractional effect of the Variscan compression. The discovery of a 351 ± 3 Ma (U–Pb in zircon) within-plate felsic volcanism in the Helez borehole, southern coastal Israel, suggests that the Levant Arch is, instead, extensional in origin. Felsic volcanism was associated with gabbro underplating of the crust, an extreme (~50°C/km) crustal thermal gradient, major uplift, and truncation of the ≥2.5 km section. Taken together with the recent discovery of the ~340 Ma oceanic crust in the Eastern Mediterranean, the Levant Arch is interpreted as an uplifted shoulder of a rift, preceding ocean spreading.