Southern Sinai Research Articles

Tectonic evolution and setting of the Sa’al Complex, southern Sinai, Egypt: A Proterozoic continental back-arc rift model

The Sa’al Complex is a mainly low grade metamorphosed polydeformed volcanosedimentary sequence exposed in the northern central Sinai basement, Egypt. Details of the stratigraphy, sedimentology and petrography of the three formations: Agramiya, Ra’ayan and Zaghara Formations are described. The earliest deformation (D1) is related to extensional tectonism and HT-LP regional metamorphism. The main D1 structure is a bedding-parallel S1 foliation with at least 50% vertical shortening in the well-foliated Ra’ayan phyllites. Earlier models that explained S1 by bedding-parallel shearing are rejected. The Sa’al volcanism, D1 extension and HT metamorphism were probably associated with back-arc rifting in a continental arc setting, similar to the modern Taupo Zone of New Zealand. Later deformations, D2 and D3, involved folding about NE-trending and NW-trending axial planes, respectively. D2 was probably a result of compressional stresses typical of continental back-arc regions, and resulted in development of steep NW-vergent imbricate thrusts and NE-trending F2 meso- and macrofolds. The Firinga gabbro and the Wadi Murad foliated diorite intruded along D2 backthrusts, while the main diorite intrusion dominating the centre of the complex intruded along D2 steepened imbricate thrusts. F3 deformation may be related to the latest convergence of the east and west Gondwana, and has correlatives in the Kid and Feiran Complexes. A final deformation D4 that generated the main strike-slip faults in the area correlates with NE–SW trending σ1, inconsistent with a Najd origin. Recent geochronological results from U/Pb zircon studies are difficult to reconcile with stratigraphic and intrusion field evidence, and apparently require very tight time constraints on the main metamorphism, D1 and D2 deformations of the complex.

Mosses of the Egyptian conservation areas: III. Two new Pottiaceae records to Saint Catherine Protected Area and Egypt

T wo species of Pottiaceae; Anoectangium handelii Schiffn. and Hymenostylium crassinervium Broth. & Dix. are recorded here for the first time from Egypt (Saint Catherine Protected area, Southern Sinai). Anoectangium Schwagr is a new genus to Egypt. Descriptions, illustrations, and distribution comments on both species are given.

Allozymic and Morphologic Differentiation between three Ballota Species (Labiatae) growing in Southern Sinai, Egypt

Ballota undulate (rare), B. Saxatilis (endangered), and B. Kaiseri (extremely endangered and endemic) are three of Mediterranean origin species grow in southern Sinai Mountains. They are very close morphologically and have been confused and mixed in their natural habitats. The present study aimed to provide genetical and morphological differentiation among the three Ballotas peceis using allozyme, PCA, and discriminant analyses for plants growing in a common environment. Electroporetic analysis of enzymes coded by 21 gene loci demonstrated that there is a high degree of genetic similarity among the three Ballota species suggesting that speciation apparently has occurred in this genus with little divergence at genes coding for allozymes. Twelve quantitative and nine qualitative characters were selected for the study of phenotypic similarity and morphological variation in a sample of 147 plants, served as OUT’s. The analyses could differentiate between B. undulata as one group and B. kaiseri and B. saxatilis as another group, but could not separate B. saxatilis from B. kaiseri. The incomplete isolation of B. undulata, B. kaiseri, and B. saxatilis, in combination with their high genetic identities and their very similar morphology, raise the question as to whether they should be retained as separate species.

Characterization of fault structures in southern Sinai Peninsula and Gulf of Suez region using geophysical data

In this work, an integrated study was carried out to delineate the prevailing subsurface fault structures and their tectonic position in the southern part of the Sinai Peninsula. The study area is selected due to its active tectonic situation. This study is implemented using the available geophysical data; these include magnetic, Bouguer gravity, seismic data to trace the delineated fault structures in shallow subsurface and magnetotelluric data to trace down these structures at deeper depths. To achieve this goal, several techniques have been applied in the interpretation of the data including least squares, trend analysis, Euler deconvolution, 3-D modeling and analytical signal techniques. The results indicate that the main fault structural trends are N 35°–45° W, N 15°–25° E and E–W directions, in accordance with the regional tectonics of the Gulf of Suez rift and Gulf of Aqaba, transform as well as the Tethyan tectonics. The depths to the basement rocks are widely varying from 0 km to about 4 kms. Two seismic lines (EG 31 and MP-70), compiled by Egyptian General Petroleum Cooperation, have been interpreted as well as a geologic cross section derived from well-logging data. The results illustrate that the study area has been affected by the fault structures prevailing there and affecting the rock units and dividing them into several major blocks. The results obtained from 2-D inversions of magnetotelluric soundings show that the fault structures that have E–W trends extend to deeper depths than faults which have N35°–45°W, N15°–25°E.

Morphotectonics of Kid drainage basin, Southeastern Sinai: A landscape evolution coeval to Gulf of Aqaba – Dead Sea rifting

The Pleistocene fluvio-tectonic conditions have shaped the landscapes of Sinai Peninsula through development of small sedimentary traps following preexisting lineaments. In the Gulf of Aqaba region, orientation of these lineaments with respect to the Pleistocene stress field develops strike-slip simple and dip-slip pure extensional shear models that induced rifting of the Gulf of Aqaba – Dead Sea fault system. The Beida and Nabq grabens are two major rift-related depressions at the southwestern coast of the Gulf of Aqaba region. Both grabens are landscapes that received alluvial sediments of the Kid drainage basin (KDB), which is one of the largest drainage systems in the western region of the Gulf of Aqaba fault-scarp. The Beida graben is formed at a horse tail structure next to Abiad and Kid faults, while the Nabq graben is a pull-apart structure formed as onshore continuation of the Dakar deep. The geometry and origin of these landscapes are the intrinsic themes of this study to investigate the morphotectonic evolution of the KDB terrain within the tectonic framework of the Gulf of Aqaba – Dead Sea rift.The hanging terraces and canyons being at higher elevations on the Gulf of Aqaba fault-scarp; and the accumulation of younger alluvial fans, talus cones and bajada on its footslope indicate that the KDB landscape is basically shaped; and evolutionary modified by hinterland uplifting of the Gulf of Aqaba region. Hence, two morphotectonic evolution periods of the KDB terrain coincide with the early NE- and late NNE-trending extensional Pleistocene axes. The early period started with deposition of the older alluvial fan sediments that emerged at the outlet of KDB, and partially buried the Gulf of Aqaba fault-scarp. Subsequent hinterland uplifting revived the Gulf of Aqaba fault-scarp with development of hanging alluvial and bed-rock terraces; and the older alluvial fan sediments are uplifted on the footwall of southward-dipping normal faults whose hanging-wall received sediments of younger alluvial fans. Nature of the sediments constituting the Quaternary paleolakes and rift-related depressions, and their structural settings in Sinai, indicate that the Sinai terrain is basically shaped by crustal uplifting of the southern Sinai massif with severe rifting at the Gulf of Aqaba region.

Unraveling sources of A-type magmas in juvenile continental crust: Constraints from compositionally diverse Ediacaran post-collisional granitoids in the Katerina Ring Complex, southern Sinai, Egypt

The Ediacaran post-collisional magmatic cycle of the Katerina Ring Complex, northern region of the Arabian–Nubian Shield (ANS; southern Sinai, Egypt), is characterized by a large diversity of A-type felsic igneous rocks: quartz syenite porphyries, microsyenites, quartz monzonites, aluminous syenogranites, alkali feldspar granites and aplites, and peralkaline granites. Estimated magmatic temperatures show a large range of variation: 1) >900°C in quartz syenite porphyries and quartz monzonites, characterized by early saturation in respectively augite+enstatite and fluorian–titanian magnesiohastingsite+andesine; 2) ca. 712–784°C in microsyenites with diopside in metaluminous compositions and aegirine–augite overgrown by aegirine in nearly peralkaline compositions; 3) ca. 880°C in aluminous syenogranites with annite that changed to siderophyllite+phengite in more evolved aluminous alkali feldspar granites and aplites at <800°C; and 4) <825°C in peralkaline granites with groundmass montdoritic mica+potassian arfvedsonite crystallized from residual melts. Calculated melt F contents are high in the most evolved fluorite-bearing aluminous granites and peralkaline granites. However, calculated melt Cl contents are, in general, low, suggesting that a Cl-rich aqueous fluid could have been exsolved from the magmas.All rock types from the Katerina Ring Complex present positive εNdi values and relatively young Nd model ages that are consistent with the juvenile nature of the ANS. This causes important limitations for determining the sources of the A-type magmatism as there is not enough isotopic contrast to discriminate between crustal and mantle source regions. Element ratios such as Y/Nb versus Th/Nb, Th/Ta and Ce/Pb may provide new constraints for unraveling the origin of A-type granitoids, despite the fact that crystal fractionation of REE–Nb–Ta-rich accessories may modify them. Alkalic metaluminous quartz syenite porphyries and peralkaline granites having Silicate Earth-normalized trace-element patterns with negative Nb and Pb anomalies were generated by high-pressure fractionation and low-pressure fractionation, respectively, of magmas derived from mantle sources with, most probably, minor involvement of the continental crust. By contrast, alkali-calcic, metaluminous to peraluminous quartz monzonites and alkali-calcic, essentially peraluminous, syenogranites with negative Nb and positive Pb anomalies were apparently formed from a source with a major crustal component. The fractionation of LREE accessories from aluminous syenogranites led to the production of alkali feldspar granites without a negative Nb anomaly.Although an A2-type affinity can be established for the A-type magmatism in the Katerina Ring Complex, its mantle source contrasts with those from typical convergent margins characterized by a positive Pb anomaly. Magmas with a negative Nb anomaly combined with a flat or negative Pb anomaly may be a signature for a carbonatite, in contrast to an aqueous silicate, agent in the mantle wedge, as inferred from xenoliths from the Arabian lithospheric mantle.

Copper–Gold–Sulphide Mineralization Associated with Late Precambrian Volcanic Ring Structures, Southern Sinai, Egypt

The paper considers the Precambrian ring structures in an island arc and their associated mineralization in the southern Sinai. Several ring structures in an island arcsetting have been recognized within the volcanic field in southern Sinai including the Kid Ring structure, St. Katarina Ring Structure, and the Iqna Ring Structure. All ring structures are associated with mineralization, the largest one is the Kid Ring Structure located in southeastern Sinai, and represented by a succession of Dokhan volcanic and Hammamat sediments intruded by younger granites and albitite. The mineralization includes stockwork, rhyolite bearing-sulphide, alteration zones in the El Samra area, alteration zones, gossans, quartz veins, silicified carbonate metatuffs, and skarn mineralization in the Um Zerriq area. Geochemical investigation reveals that Wadi El Samra is dominated by Au–Cu–Zn. Wadi Ghorabi–El Hatemeia is dominated by Cu–Au mineralization, while the Wadi Khashm El Fahk is dominated by Cu–Au–Zn in the El Samra area. Um Zerriq I is dominated by Au–Cu-dominated mineralization, and the Um Zerriq II and III are dominated by Zn–Pb–Cu–Au. Major mineralization of the south Sinai is closely associated with last phase of volcanism within the ring structure, and is closely related in time and space to porphyritic, intermediate composition magma emplaced within the ring complex structures.

Late Ediacaran (605–580 Ma) post-collisional alkaline magmatism in the Arabian–Nubian Shield: A case study of Serbal ring-shaped intrusion, southern Sinai, Egypt

The Serbal pluton is a late Neoproterozoic (605–580Ma) post-collisional A-type granites in southern Sinai, Egypt (northernmost Arabian–Nubian Shield, ANS). It is characterized by discontinuous ring-shaped outcrops dislocated by later faulting. The pluton intrudes late Neoproterozoic metamorphic and high-K calc-alkaline rocks. The Serbal pluton mostly comprises an outer zone of alkali feldspar granite surrounding a core of peralkaline granite. Gradational and sharp contacts in the Serbal granites suggest that they were emplaced with a very short time interval, still before complete crystallization of the earlier batch. Serbal granites are highly evolved (75.98–78.52wt.% SiO2) and display the typical geochemical characteristics of post-collisional A-type granites, namely high SiO2, Na2O+K2O, FeO*/MgO, Ga/Al, Zr, Nb, Ga and Y and low CaO, MgO, Ba, and Sr. They are rich in REE and have extreme Eu-negative anomalies (Eu/Eu*=0.01–0.23). The chemical characteristics indicate that the peralkaline granite shares many features of granites with the tetrad REE effect. The Serbal pluton evolved through fractional crystallization of a parental magma derived through partial melting of a juvenile crustal protolith that had been extracted from a source having mantle geochemical and isotopic characteristics. The crystallization temperatures using Fe–Ti oxides of the Serbal granites point to their formation at high temperatures, up to 650–850°C at a shallow depth of emplacement (<10km).

Soil seed bank contributes significantly to genetic variation of Hypericum sinaicum in a changing environment

The contribution of soil seed bank of a desert endemic plant species in maintaining genetic diversity has been addressed in this paper through investigating the differences in genetic diversity and structure (using AFLP markers) between plants grown from soil seed bank and standing crop plants within and among five populations of H. sinaicum growing at St. Katherine Protectorate, southern Sinai, Egypt. Standard genetic diversity measures showed that the molecular variation within and among populations was highly significantly different between standing crop and soil seed bank. While soil seed bank had lower genetic diversity than standing crop populations, pooling soil seed bank with standing crop samples resulted in higher diversity. The results revealed also that soil seed bank had lower differentiation (7 %) than among populations of the standing crop (18 %). Results of neighbor-joining, Bayesian clustering and principal coordinate analysis showed that soil seed banks had a separate gene pool different from standing crop. The study came to the conclusion that the genetic variation of the soil seed bank contributes significantly to the genetic variation of the species. This also stresses the importance of elucidating the genetic diversity and structure of the soil seed bank for any sound and long-term conservation efforts for desert species. These have been growing in small-size populations for a long time that any estimates gained only from aboveground sampling of populations may be ambiguous.

Geospatial technology and structural analysis for geological mapping and tectonic evolution of Feiran–Solaf metamorphic complex, South Sinai, Egypt

The Sinai Peninsula constitutes an important district of the Egyptian lands where it forms a triangular portion in northeastern Egypt. The southern Sinai metamorphic complexes are the northern uppermost part of the Arabian–Nubian Shield revealing the upper and middle crust from the East African Orogeny, in which they tectonically evolved. The Feiran–Solaf metamorphic complex (FSMC) of Sinai, Egypt is one of the highest grades metamorphic complexes of a series of basement domes that trends NW and crops out throughout the Arabian–Nubian Shield. The main aim of the present study is to apply the geospatial technology and to represent the capability of the geospatial technology to estimate the combined influence of lithology and structure studies, and to construct the lithological and structural maps of FSMC. Furthermore, detailed structural analysis is carried out to reveal the different ductile and brittle deformational events and proposed the tectonic evolutionary model for the study area. Mainly geospatial technology and structural analysis software have been used to go well with the aim of the present study. Developing specific image processing of satellite images and structural analysis were succeeded to discriminate the various lithological rock units, and the geological structural features of the FSMC, using geographic information system tools to construct the different thematic maps, were extracted. The present detailed investigations of the enhanced satellite images, structural analysis, and field verification reveal that the FSMC reached its present tectonic setting through more than four deformational phases concluding that the Pan-African Najd Fault System continued in Sinai and was reactivated during Red Sea tectonics as indicated by the dextral shear zone (Rihba) bordering the northern side of the FSMC.

The Maghara (Sinai) Family Revisited

This article examines an unusual Old Kingdom graffito from the turquoise mining site of Wadi Maghara in Southern Sinai, depicting a man, woman and child, probably a family. New readings of the wife’s name are suggested, and unusual features of the relief, such as the wife being the tallest member of the group, are discussed. Family members are rarely represented in reliefs at mining sites, and it is uncertain whether the wife and child actually came to Wadi Maghara with the husband.

THE PALEOGEOGRAPHY OF GAZELLA GAZELLA AND GAZELLA DORCAS DURING THE HOLOCENE OF THE SOUTHERN LEVANT

ABSTRACT An excavation of the Pre-Pottery Neolithic B (PPNB) site from southern Sinai revealed a rich faunal assemblage containing, amongst other species, gazelle remains which were identified, by comparison with recent material, as Gazella gazella. It is suggested that Gazella gazella was the only species of gazelle existing in Israel until after the Pre-Pottery Neolithic B period. In the last glacial period the Gazella gazella range expanded southwards and reached southern Sinai Gazella dorcas is a relatively new post-Glacial invasion from North-East Africa into the arid zone of the Levant whence it replaced Gazella gazella by way of exclusion. The desert subspecies of G. gazella in the southern 'Arava Valley can be considered as a glacial isolate within the new domain of Gazella dorcas.

FRESHWATER MOLLUSCS OF THE SINAI PENINSULA

ABSTRACT In a revision of the freshwater species of molluscs in the Sinai Peninsula it was found that five species inhabit the entire area. Two of these: Melanoides tuberculatus O.F. Muller and Hydrobia musaensis (Frauenfeld) are, as a rule, restricted to the coastal brackish springs. Physa subopaca Lamarck is mostly limited to the foothills and low mountains of southern Sinai. Valvata saulcyi Bourguignat occupies the highest mountains of the peninsula and Melanopsis praemorsum Linne is confined to a single spring located at the northeastern corner of the peninsula ('Ein el Qudeirat = Qadesh Barnea). The scattered distribution of Melanoides in extremely isolated water bodies in the desert of Sinai suggests an ancient arrival of this species to the area. Melanopsis arrived much later (late Miocene or Pliocene) when passages further to the south were already blocked by the developing southern palaearctic desert belt. Physa and Valvata may have been dispersed through the air by insects and birds. Hydrobia mu...

The Origin of African Sheep: Archaeological and Genetic Perspectives

Indigenous African sheep genetic resources have been classified into two main groups, fat-tailed and thin-tailed sheep. The fat-tailed sheep are the most widely distributed, being found in a large part of North Africa (from Egypt to Algeria) and in Eastern and Southern Africa (from Eritrea to South Africa). The thin-tailed sheep are present mainly in Morocco, Sudan and in West Africa. African sheep were domesticated outside Africa. They share a common ancestry with European and Asian sheep. Archaeological information supports separate introductions and dispersion histories for the African thin-tailed and fat-tailed sheep. The first sheep entered Africa via the Isthmus of Suez and/or the southern Sinai Peninsula, between 7500 and 7000 BP. They were likely of the thin-tailed type. Fat-tailed sheep entered Africa through its northeastern part and the Horn of Africa. Mitochondrial DNA analysis supports a common maternal ancestral origin for all African sheep, while autosomal and Y chromosome DNA analysis indicates a distinct genetic history for African thin-tailed and sub-Saharan fat-tailed sheep. The main ancestral population of southern African fat-tailed sheep likely originated in East Africa. Further work is needed to assess the possible dispersion of sheep from western Africa to the southern African regions.

A panorama of the fossil algae: from cyanobacteria and calcimicrobes to the green calcareous algae

Initiated in the first half of the 19th century, investigationsof calcareous algae flourished after the Second World War,in connection with the intensification of oil exploration incarbonate reservoirs. This field of research immediatelyprovided a new micropaleontological tool for stratigraphicand paleoecological characterization of sedimentary strata.When a representative community working on fossil cal-careous algae had become established by the 1970s and1980s, such investigations reached a peak. This communitygathered at specialized international meetings, where thetop results were shared. The late Professor Erik Flu¨gel wasthe one who organized the first international symposium onfossil algae in Erlangen in 1975. Eric Flu¨gel was wellknown in the international scientific community for hisstudies on carbonate rocks, especially on fossil calcareousalgae. More than that, he was widely appreciated for hisexceptional mentoring qualities, from which numerousgenerations of students in this field benefited. At Erlangen,he founded the carbonate microfacies and calcareous algaeschool; in 1979 he initiated the journal Facies, currently oneof the most prominent publications in the field. As a sign ofour deep appreciation, we dedicate this volume to hismemory.The symposium organized in Erlangen represented thestart of a quadrennial series of international reunions thatsuccessively took place in Paris (1979), Golden, Colorado(1983), Cardiff (1987), Capri (1991), Ankara (1995),Nanjing (1999), Granada (2003), Zagreb (2007), andCluj-Napoca (2011). These scientific meetings encouragedthe development of the study of calcareous algae, as well asinternational collaborations in the field. Accordingly, theInternational Fossil Algae Association (IFAA) decided toinitiate an additional conference series, timed in-betweenthe international meetings. The latter were defined as‘‘regional meetings’’, being organized as fieldwork-basedworkshops. Nevertheless, they always had an internationalcharacter, from the participants and topic point of view.The first regional IFAA symposium took place in Granada(1989), followed by the ones in Munich-Vienna (1993),Krakow (1997), Cluj-Napoca (2001), Ferrara (2005), andMilan (2009). In the last decades, the proceedings of theseinternational and regional symposia summed up the state ofthe art in calcareous algae research. We hope that thecurrent issue of Facies will continue this trend.The current volume gathers some of the presentationsgiven at the 10th International Symposium on Fossil Algae(Cluj-Napoca, September 2011), as well as some otherrecent results in the study of calcareous algae. The con-tributions cover a wide range of topics, from the study ofsome end-products of cyanobacteria and calcimicrobes tostudies of red and dasycladalean green algae.Basso et al. (2013) describe in their contribution thepresent-day formation of microbialites containing cyano-bacteria, bacteria, and microalgae colonies in southern Sinai(Egypt). Based on macroscopic morphology, texture, anddegree of lithification, four categories of microbialites wererecognized. Their presence in the area is considered to resultfrom the combination of local sedimentary dynamics andaccommodation space in a peritidal tropical environmentwith high variations of temperature and salinity.Various fossil microbialites associated with micro-encr-ustersaredescribedbyPles¸ etal.(2013)fromUpperJurassiclimestones in the Southern Carpathians (Romania). Thedepositsmainlyconsistofmassifreeflimestonesincludingavariety of microbialites associated with micro-encrusters.The high abundance of dense micrite, the presence of

Eolian and fluvial sedimentation in the southwestern Sinai Mountains, Egypt: a record of flash floods during the late Pleistocene

Wadis emerging from the southwestern Sinai Mountains (Egypt) westwards to the Gulf of Suez are filled by &amp;gt;40 m thick late Pleistocene sediments, which have been subsequently incised to bedrock after the Last Glacial Maximum (LGM). Sedimentation and erosion resulted from changes in the basin's hydrological conditions caused by climate variations. Sediment characteristics indicate distinct processes ranging from high to low energy flow regimes. Airborne material is important as a sediment source. The fills are associated with alluvial fans at wadi mouths at the mountain fronts. Each alluvial fan is associated and physically correlated with the respective sediment fill in its contributing wadi. The alluvial fans have steep gradients and are only a few kilometers long or wide. The alluvial fans converge as they emerge from the adjacent valleys. According to optically stimulated luminescence dating, the initial sediment has an age of ∼45 ka and the sedimentation ends ∼19 ka, i.e., happened mainly during marine isotope stage (MIS) 3 and early MIS 2 formation and initial incision sometime during LGM. As the delivery of sediments in such a hyper-arid environment is by extreme floods, this study indicates an interval of intense fluvial activity, probably related to increased frequency of extreme floods in Southern Sinai. This potentially indicates a paleoclimatic change in this hyper-arid environment.

Constraints on the crustal structure beneath the Sinai subplate, SE Mediterranean, from analysis of local and regional travel times

The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift, the Dead Sea Transform fault, and the Red Sea rift. The upper and lower crustal structures of this tectonically active, rapidly developing region are yet poorly understood because of many limitations. For this reason, a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network (ENSN) from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai. Because the velocity model used for routine earthquake location by ENSN is one-dimensional, the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures. Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west. The crustal Vp/Vs ratio is 1.74 from shallow (depth ≤ 10 km) earthquakes and 1.76 from deeper (depth > 10 km) crustal events. The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model (PREM), implying that the seismic stations are located above widely distributed, tectonically-induced low-velocity zones. These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures. The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities, which should be excluded from major future development projects and large constructions in central and southern Sinai.

Microbialite formation in southern Sinai (Egypt)

Ongoing microbialite formation is described at two previously unreported sites in southern Sinai, Egypt. Samples were collected in the peritidal tropical environment of Nabq Bay and Hidden Bay (southern Sinai, Egypt). Field observations and sample analyses show evidence of both sediment trapping and biostabilization in bacterial mucilaginous sheaths and microbially induced mineralization, producing a suite of increasingly lithified material: from agglomerated, consolidated sand to lithified crusts and oncoids. Thin-sections show evidence of bacteria (cyanobacteria and sulphate-reducing bacteria) among the constituent grains in the form of gelatinous filaments (green and red sheaths), and microalgal colonies along the outer edge, accompanied by a very high grade of clast alteration. The alternation of planar to irregular dark, superposed layers, and clastic layers is visible at the surface and/or inside some crusts. Widespread filaments of Schizothrix among grains have been identified, as well as extracellular polymeric substances (EPS), sheaths stabilizing particles, and calcareous tubular encrustations around cyanobacteria filaments. Carbonate precipitates include diffuse micrite, microcrystals of high-Mg calcite precipitating in the EPS matrix, and acicular aragonite as isopachous rims around grains. Cementation is accompanied by partial dissolution and progressive alteration of original grain boundaries. We describe four microbialite categories on the basis of their macroscopic morphology combined with different texture and lithification grade. The occurrence of the southern Sinai microbialites is explained by the interplay of local sedimentary dynamics and accommodation space in a peritidal tropical environment undergoing large temperature and salinity variations.

Stress analysis and tectonic trends of southern Sinai Peninsula, using potential field data analysis and anisotropy technique

Abstract The aim of the present work is to evaluate the stress direction and the tectonic trends of the study area using magnetic anisotropy and potential field data interpretations (Bouguer and aeromagnetic). The specific objective of the gravity and aeromagnetic interpretation is to establish the trend and depth of the structural configuration of the basement rocks. Horizontal gradient techniques could to delineate directions of deep sources and enabled tracing several faults, lineaments and tectonic boundaries of basement rocks. The trend analysis shows N40°–50°W, N10°–20°W and N10°–20°E which may be related to the Gulf of Suez, Red Sea and Gulf of Aqaba stresses. However, Euler Deconvolution technique was applied using the aeromagnetic data to provide reliable information about penetrated source depth (100 m and ∼10.0 km) and trends of the subsurface sources (principally in NW and NE directions). Moreover, representative 72 oriented rock samples have been collected from seven sites in the study area. The rock magnetic properties and magnetic anisotropy analysis have been determined for all the studied samples. The interpretation clearly defined magnetic lineation at all sites and anisotropy of magnetic susceptibility (AMS) parameters. The stress direction of the studied area has been evaluated using magnetic anisotropy and geophysical analysis. Generally the estimated geophysical data analysis (Bouguer and aeromagnetic) are well consistent with the AMS interpretations of this study. The results indicated that the directions of predominant faults and foliations are NW-SE (related to the Gulf of Suez and Red Sea rifting) which indicate that the main stress and tectonic trend is NE-SW, which is more predominant in southern Sinai region. Moreover, it is clear that, the studied area was affected also by less predominant sources trended in NE-SW direction, which related to the tectonic activity of Gulf of Aqaba. The least predominant is north 40°–50° east that is probably due to the Syrian Arc system. Finally, our results are extremely coincided with the previous stress directions derived from geological, seismological and tectonic analysis in northern Red Sea rift, Gulf of Suez and Sinai regions.

Geochemistry, geochronology, and Sr–Nd isotopes of the Late Neoproterozoic Wadi Kid volcano-sedimentary rocks, Southern Sinai, Egypt: Implications for tectonic setting and crustal evolution

The Kid Group is one of the few exposures of Neoproterozoic metavolcano-sedimentary rocks in the basement of southern Sinai in the northernmost Arabian–Nubian Shield. It is divided into the mostly metamorphosed volcaniclastic Melhaq and siliciclastic Um Zariq formations in the north and the mostly volcanic Heib and Tarr formations in the south. The Heib, Tarr, and Melhaq formations reflect an intense episode of igneous activity and immature clastic deposition associated with core-complex formation during Ediacaran time, but Um Zariq metasediments are relicts of an older (Cryogenian) sedimentary sequence. The latter yielded detrital zircons with concordant ages as young as 647±12Ma, which may indicate that the protolith of Um Zariq schist was deposited after ~647Ma but 19 concordant zircons gave a 206Pb/238U weighted mean age of 813±6Ma, which may represent the maximum depositional age of this unit. In contrast, a cluster of 11 concordant detrital zircons from the Melhaq Formation yield a weighted mean 206Pb/238U age of 615±6Ma. Zircons from Heib Formation rhyolite clast define a 206Pb/238U weighted mean age of 609±5Ma, which is taken to approximate the age of Heib and Tarr formation volcanism. Intrusive syenogranite sample from Wadi Kid yields a 206Pb/238U weighted mean age of 604±5Ma. These constraints indicate that shallow-dipping mylonites formed between 615±6Ma and 604±5Ma. Geochemical data for volcanic samples from the Melhaq and Heib formations and the granites show continuous major and trace element variations corresponding to those expected from fractional crystallization. The rocks are enriched in large ion lithophile and light rare earth elements, with negative Nb anomalies. These reflect magmas generated by melting of subduction-modified lithospheric mantle, an inference that is further supported by εNd(t)=+2.1 to +5.5. This mantle source obtained its trace element characteristics by interaction with fluids and melts from subducting oceanic crust during the Late Cryogenian time, prior to terminal collision between fragments of East and West Gondwana at ~630Ma. Positive εNd(t) values and the absence of pre-Ediacaran zircons in all but Um Zariq metasediments indicate minor interaction with Cryogenian and older crust. A model of extensional collapse following continental collision, controlled mainly by lithospheric delamination and slab break-off is suggested for the origin of the post-collision volcanics and granites at Wadi Kid. No evidence of pre-Neoproterozoic sources was found. Kid Group Ediacaran volcanic rocks are compositionally and chronologically similar to the Dokhan Volcanics of NE Egypt, which may be stratigraphic equivalents.