NE Africa Research Articles

Spatio-temporal aerosol trace metal concentrations and sources in the Levantine Basin of the Eastern Mediterranean

Abstract The current study considers the spatial and temporal variability in aerosol trace metal concentrations (Al, Fe, Mn, Cr, Cu, Pb, Cd, Zn) in the Levantine Basin of the Eastern Mediterranean, utilising an extensive sample library (n=621) collected between 1999 and 2001, at two coastal sites located at the northern, Erdemli (Turkey) and southeastern, Tel Shikmona (TS, Israel), region of the Basin. A critical evaluation of the datasets from the two locations was presented. Enhanced concentrations of Al (1.7×), Fe (1.8×), Mn (2.1×) were detected at the more southerly sampling station, during common dust events, owing to the greater proximity of desert dust sources (NE Africa and Saudi Peninsula); leading to a gradual decline in crustal inputs northwards across the basin. An insignificant Pb gradient was noticed across the Levantine Basin, which has exhibited a decadal decrease (40%). Cr was enriched in the north by a factor of three accounted by local sources. Cu was also enriched, to a lower extent, by about a factor of two. Seasonal variations of the crustal elements (Al, Fe, Mn) at Erdemli were detected (transitional>summer>winter) owing to both, a greater frequency and intensity of dust events during the transitional period and a greater washout effect during winter. It is likely that similar variations occur at TS as both sites experienced similar dust and rainfall events. It was observed at Erdemli that all elements (except Pb and Cd) exhibit their lowest concentrations in the winter period due to a greater washout effect. The lack of seasonal difference between winter and summer for Pb and Cd may have been due to the relatively high emission intensities of regional sources rapidly regenerating aerosol concentrations and their association with fine particles which are less efficiently scavenged during rain events. During the summer, Zn derived from local transportation and agricultural activities, was more pronounced, leading to an enhancement of around 10% in its concentration.

Gravitational collapse origin of shear zones, foliations and linear structures in the Neoproterozoic cover nappes, Eastern Desert, Egypt

The Um Esh–Um Seleimat area lies to the west of the Meatiq Core Complex (MCC), in the Central Eastern Desert (CED), Egypt, which forms part of the Neoproterozoic Arabian–Nubian Shield in NE Africa and Western Arabia. The study area is a NW-trending zone of intensely foliated ophiolitic melange and molasse sedimentary rocks. There is a single regional foliation, S 1, defined mainly by low- to very low-grade metamorphic phases, though grade increases to amphibolite facies in the areas bordering the MCC. S 1 is associated with shearing and passes directly into the mylonites of the MCC sheared carapace. The foliations and mylonites together define an originally subhorizontal thick ductile shear zone of regional extent. The sense of shearing is top-to-the-NW, parallel to NW–SE trending stretching lineations, L 1. S 1 is folded by open rounded symmetrical mesoscopic F 2 folds with NW–SE trending subhorizontal hinges and variably dipping axial planes. F 2 folds are folded by coaxial (i.e. NW–SE trending) but non-coplanar close to tight macroscopic folds ( F 3). Subhorizontal S 1 foliation formed continuously during F 2 folding and perhaps also into the early stages of F 3 folding. This reflects top-to-the-NW shearing under laterally confined conditions produced by the onset and gradual dominance of NE–SW shortening. SW-ward thrusts and NW–SE trending sinistral brittle faults are late stage structures. The NW-ward shear translation of the ophiolite and molasse cover nappes results from gravitational collapse following arc-collision and crustal thickening. A gliding–spreading nappe emplacement mechanism is most consistent with the field evidence. The steep metamorphic gradient from low-grade cover rocks downwards into gneissic rocks is interpreted as a result of vertical thinning of the ductile shear zone during collapse. Amphibolite facies conditions are found at the base of other top-to-the-NW low-angle major shear zones associated with gneissic complexes in the CED (e.g. El-Sibai, El-Shalul complexes) suggesting that the crustal level of the shear zone may be determined by thermally controlled rock rheological factors.

Plutonic and metamorphic rocks from the Keraf Suture (NE Sudan): a glimpse of Neoproterozoic tectonic evolution on the NE margin of W. Gondwana

The Keraf Shear Zone (KSZ) of NE Sudan formed in Neoproterozoic time when juvenile crust of the Arabian–Nubian Shield collided with reworked older crust of the Saharan Metacraton. Orthogneisses and deformed granitoids which intrude carbonate sediments are calc-alkaline, medium-K, metaluminous and I-type diorites and granodiorites, with subduction-related trace element signatures. 207 Pb / 206 Pb zircon single grain ages are ∼730 Ma for the high-grade gneiss and ∼710 Ma for granitoids. K/Ar ages are 660 Ma for hornblende from the granitoids and 560 Ma for biotite from the high-grade gneiss and the plutons. The geochronologic data indicate that the crust formed ∼730–710 Ma and that orogenic activity ended by ∼565 Ma. Cooling occurred over much of NE Africa at about the same time, possibly caused by orogenic collapse or unroofing caused by extensive glaciation. Pb isotopic ratios indicate an oceanic source for both the magmatic and metamorphic rocks in the KSZ. Sm/Nd model ages are 620–770 Ma for the post-tectonic plutons and 830–900 Ma for the gneiss, indicating negligible involvement of a pre-Neoproterozoic material in the evolution of Keraf igneous rocks. The ( 87 Sr / 86 Sr ) i values range from 0.7026 to 0.7046, which are indistinguishable from initial ratios for juvenile crust of the Arabian Nubian Shield and are lower than initial Sr isotopic compositions for the Saharan Metacraton. The isotopic data indicate that Keraf igneous rocks are juvenile additions to the crust and that the boundary between the Saharan Metacraton and the Arabian–Nubian Shield lies to the west.

New species, a new combination and synonyms in Compositae from NE Africa

Two species of Compositae from Ethiopia are described as new, viz. Senecio leptopterus and Vernonia friisii. Comparisons were also made with morphologically similar species found in other parts of Africa. The new combination Sphaeranthus ramosus is made and a detailed description of the species is provided. Arctotis pygmaea and Anthemis semiensis are placed as synonyms of Haplocarpha rueppellii and Anthemis tigrensis, respectively.

A molecular phylogeny and generic rearrangement of the stapelioid Ceropegieae (Apocynaceae-Asclepiadoideae)

Representatives of nearly all genera of the taxon-rich stem-succulent stapeliads and most of the few related, leafy genera were analyzed. Sequence data from two non-coding molecular markers (ITS region of nrDNA and trnT-L and trnL-F spacers as well as the trnL intron of cpDNA) support the traditional tribal affiliation of the genera, which form a monophyletic group. This monophylum breaks into a basal Neoschumannia/Anisotoma/Riocreuxia/Sisyranthus nk;clade, from which the core Ceropegieae are derived. The four Ceropegia species included are not monophyletic, and their relationship to Brachystelma changes depending on the marker studied. The stem succulent taxa fall in a number of well supported, but unresolved clades, the most prominent being the predominantly southern African clade comprising Orbea, Stapelia and some other genera. The most derived taxa of NE Africa, Duvaliandra and White-sloanea, are basal to this southern African clade. The other clades comprise the more basal genera of stem-succulent stapeliads, including the members of the Caralluma complex. Of the 17 genera accepted by Plowes for the Caralluma complex, seven are recognized: Caralluma, Apteranthes, Australluma, Boucerosia, Caudanthera, Desmidorchis and Monolluma. New combinations are proposed in 15 cases; Caralluma adscendens var. geniculata is raised to specific rank. Anomalluma is reinstated, and Pseudolithos mccoyi is transfered to it. A broadened concept for Orbea (incl. Angolluma and Orbeopsis) is recognized, but Orbeanthus is kept separate. The monotypic Ballyanthus, recently separated from Orbea, is nested within Duvalia. Piaranthus (incl. Huerniopsis) is monophyletic. The bitypic Notechidnopsis is reduced to the type species, N. tessellata, while N. columnaris is transferred to a new genus, Richtersveldia.

Early Paleozoic sediments of NE Africa and Arabia: Products of continental-scale erosion, sediment transport, and deposition

Early Paleozoic sediments of NE Africa and Arabia: Products of continental-scale erosion, sediment transport, and deposition

The status of the genusPhrynobatrachusGünther 1862 in Ethiopia and Eritrea, including description of a new species (Amphibia Anura Ranidae)

Three species of the genus Phrynobatrachus Günther 1862 are recognised in Ethiopia. The largest, which has relatively extensive webbing between the toes and ranges northwards into Eritrea, is primarily a denizen of lowland savanna and not recorded in NE Africa at altitudes greater than 2200 m. It is current practice to call this taxon P. natalensis (Smith 1849) and the names bottegi Boulenger 1895, zavattarii Scortecci 1943 and sciangallarum Scortecci 1943 are considered to represent conspecifics. The two remaining species are much smaller, with conspicuously reduced webbing and are most commonly associated with montane habitats. Morphological variation in Phrynobatrachus minutus (Boulenger 1895) is here described for the first time on the basis of adequate Ethiopian material. Recorded in this country from elevations of 800–2800 m, the species appears to be present also in the mountains of Kenya and may perhaps extend as far south as the northern highlands of Tanzania. Phrynobatrachus inexpectatus n. sp. is at present known from just two sites spanning 2600–2650 m and could prove to be a true Ethiopian endemic. At its type locality, the new species has been found occupying the same pools as P. minutus and its distinguishing features include still smaller size, even more restricted webbing and the possession of an obviously darker throat in the adult male.

Distribution and Habitat Associations of Baboons (Papio hamadryas) in Central Eritrea

At least three diurnal primate taxa are still present in Eritrea, NE Africa: hamadryas baboons (Papio hamadryas hamadryas), olive baboons (Papio h. anubis) and grivet monkeys (Chlorocebus aethiops aethiops). However, information on status and distribution of primates and their habitats in Eritrea is outdated and incomplete. We conducted a primate survey, focussing on hamadryas baboons, to obtain data which will be integrated in a national wildlife management and conservation plan in Eritrea. We obtained information about the geographical distribution and abundance of baboons, their altitudinal range, habitat quality of their home-ranges, aggregation sizes at sleeping cliffs and predator presence. We described habitat quality via the Normalized Difference Vegetation Index (NDVI), a vegetation classification of Landsat MSS satellite data. Hamadryas and olive baboons are still present in Eritrea in ample numbers. Their geographical distributions in 1997 and 1998 did not deviate significantly from their historical distributions. An estimated 15,000 Papio hamadryas hamadryas lived in the 25,000-km2 area of survey (0.58 baboons/km2). Population densities of hamadryas baboons in many parts of the survey area are higher than at Kummer's (1968) study site in Ethiopia. Hamadryas baboons live at all altitudes in four of five ecogeographical zones of Eritrea. Olive baboons replaced them in the western lowlands. Both baboon taxa tend to select better quality habitats, characterized by a higher normalized difference vegetation index (NDVI) than the average for the respective ecogeographical zones. Hamadryas baboons show a greater ecological plasticity than olive baboons, which are confined to riverbeds with extended gallery forest. By the end of 1999, a hybrid zone could not be confirmed.

Magmatism and Metallogeny in the Crustal Evolution of Rio Grande do Sul Shield, Brazil

The State of Rio Grande do Sul has a complex Precambrian/Cambrian shield, which has been investigated for four decades. This complexity involves ages ranging from 2.55 Ga (possibly 3.3 Ga) to 550 Ma (and even 470 Ma). The three major juvenile accretionary episodes occurred at 2.55 Ga, 2.26-2.02 Ga and 900-700 Ma, while a continental-scale crustal reworking (collisional) orogeny occurred from 780 to 550 Ma. The three accretionary orogenies are known as the Jequié, Transamazonian and Brasiliano Cycles, respectively. The Brasiliano Cycle includes the collisional orogeny. Magmatism was tholeiitic low-K bimodal basic-acid in the Archean (Santa Maria Chico granulites), and evolved to tonalitic-trondhjemitic-granodioritic in the Paleoproterozoic (Encantadas Complex). During the Paleoproterozoic/Archean transition, komatiites and basalts were formed in greenstone belts (Passo Feio Sul Formation). The end of the Transamazonian Cycle was the beginning of a long period of tectonic quiescence, and the region remained in the interior of the Atlantica Supercontinent until the beginning of the Brasiliano Cycle at ca. 900 Ma (Passinho Diorite). This Neoproterozoic cycle displays two classical orogenic types, namely the São Gabriel accretionary orogeny in the western part of the State and Dom Feliciano collisional orogeny in its eastern part. Accretion generated juvenile tonalite-trondhjemite-granodiorite associations with related ophiolites (Cerro Mantiqueiras Ophiolite), while the collision formed the voluminous and mostly peraluminous and high-K calcalkaline granites of the Dom Feliciano orogeny. The waning stages of the orogeny were responsible for the outpouring of a very expressive silica-saturated volcanism and eventually finished with the Rodeio Velho basalts at 470 Ma. Comparable Paleoproterozoic/Neoproterozoic Precambrian terranes surround the shield in Uruguay, in Santa Catarina and in western Africa. Comparable Neoproterozoic juvenile and reworked terranes occur in NE Africa. Widespread indications of metals are a good sign of possible deposits, but the two major types of deposits are the orogenic epizonal Bossoroca gold deposit and the distal magmatichydrothermal Lavras/Camaquã copper-gold deposits.

Phanerozoic geodynamic evolution of northeastern Africa and the northwestern Arabian platform

The Northeast African–Arabian plate formed a segment of the passive margins of, successively, the Paleotethys and the Neotethys. During the Paleozoic, rifting events were relatively minor, but epicontinental sagging focused deposition within the N–S-trending Ghazalat–Tehenu basin of the Western Desert, the Jafr basin of southern Jordan, and along a proto-Gulf of Suez trend. Gentle arching occurred at the end Silurian, end Devonian, end Serpukhovian and Late Carboniferous. The opening of the Neotethys in the Permian marked the onset of a new geodynamic episode. Extensional faulting was pronounced along the present Mediterranean margin region from the Permian to the Jurassic. Early Cretaceous intra-continental rifting occurred in the E–W-trending arm of the Sirt basin, and in the Abu Gharadiq and the Shushan–Matruh basins of the Western Desert. In the Santonian, a major shift in tectonics swept the Tethyan realm, producing dextral transpression across NE Africa and marking the onset of the main Syrian arc folding and reverse faulting. By the Campanian–Maastrichtian, extension resumed, with subsidence focused in the Sirt, Abu Gharadiq and Azraq–Sirhan basins. A compressive pulse marked the Cretaceous–Paleocene transition, followed by renewed rifting during the Paleocene–Eocene in the Sirt basins and El Gindi basin of northern Egypt. At approximately the Bartonian–Priabonian boundary, strong dextral transpression again affected northern Egypt and the E–W Aswan fault swarm. In the Late Oligocene, the Gulf of Suez–Red Sea rift initiated, often reactivating older tectonic trends. During the Middle Miocene, the Red Sea divergent plate boundary abandoned the Gulf of Suez and broke through the Arabian plate via the Gulf of Aqaba–Dead Sea transform fault, establishing the present-day plate kinematic framework. A rapid rotation of stress fields occurred in the Late Pleistocene, with active faulting continuing to the Recent along the central Sinai–Cairo fault zone and the Gulf of Aqaba–Red Sea plate boundary.

A Neoproterozoic supra-subduction terrane in northern Eritrea, NE Africa

The western part of a tectonic block in the complex Pan-African architecture of northern Eritrea contains partly re-equilibrated low- T , high- P assemblages (550°C, 14.5 kbar), basalts with oceanic geochemistry and a major olistostrome containing lenses of serpentinite. These features demonstrate subduction zone products. East of this accretionary wedge the block is dominated by island-arc volcanic and volcaniclastic rocks, and various calc-alkaline plutons. A bimodal volcanic suite of primitive andesitic basalts and evolved dacites and ignimbrites represents early submarine arc development and emergent volcanism, respectively. Intense, polyphase deformation culminated in sinistral transpression with crustal-scale imbrication between several east-verging thrusts. A tectonically bounded unit in the internal part of this arc association also contains relict high- P assemblages (650°C, 10–13 kbar) in oceanic basalts, which are possibly products of tectonic underplating as the arc developed. Oceanwards collapse of the tectonically inflating arc may explain formation of evolved, subaerial volcanic rocks within small extensional basins. Down-to-west extensional structures may have been inverted during terrane accretion to act as east-verging shear zones during late thickening. The area remains to be correlated with those areas in Arabia that were juxtaposed with it before Red Sea opening.

Gaillonia (Rubiaceae‐Paederieae) in Africa and Arabia

The circumscription of Gaillonia is extended to include Crocyllis as a new generic synonym. Gaillonia then becomes a genus with a marked disjunction between NE Africa and Arabia, and SW Africa. Nine species of Gaillonia are recognized in Africa and Arabia: G. yemenensis sp. nov. and G. jolana sp. nov. in Yemen, G. crocyllis comb. nov. in Namibia and South Africa, G. calcicola comb. nov. and G. somaliensis comb. nov. in Somalia, and G. puberula, G. putorioides comb, nov., G thymoides and G. tinctoria on Socotra (Yemen). Several names are lectotypified. A previous record of Jaubertia aucheri from Yemen is based on a misidentified specimen of G. jolana. The close relationship between Gaillonia and the small Mediterranean genus Putoria is pointed out.

Tectonic controls on the petroleum geology of NE Africa

Abstract During the Palaeozoic and early Mesozoic, the NE sector of the African craton remained an entire, integral part of Gondwanaland. It experienced two episodes of intracratonic sagging and marginal cratonic rifting, linked to episodes of strike-slip affecting both the craton interior and its northern margins. Source kerogens accumulated during Palaeotethyan highstands within these sags, across which reservoir clastics prograded during the corresponding lowstands. Such source-reservoir associations are known from the Silurian, Devonian and Carboniferous. The fragmentation of the NE African margin with Mesotethys took place over the period Mid Triassic-Bathonian. From Palestine to Cyrenaica, a rift propagated westwards, detaching crustal terranes along shears that later formed Asia Minor. Deep marine shales within this rift have some proven oil-generating potential. However, the principal Jurassic oil kerogen is found associated with coal swamp-delta clastics, deposited during the Bathonian lowstand, in basins formed between the shears along the new cratonic edge. There is also now evidence for a Mid-Triassic rift penetrating the Sirt Basin from the northwest. Sinistral strike-slip associated with these Mesotethyan shears penetrated deeper into NE Africa during the Late Cretaceous, with subsidence reaching a maximum in the Jebel el Akhdar, Abu Gharadiq and proto-Clysmic Basins, in which rich oil-prone marine source rocks accumulated during the Turonian-Coniacian lowstand. Inversion followed, as the sense of strike-slip reversed with the onset of ‘Syrian Arc’ movements, starting in the latest Cretaceous, and proceeding as a series of pulses into the Late Oligocene. The final phase of ‘Syrian Arc’ tectonics was linked to the opening of the Red Sea and Gulf of Suez Basins, and transtension along the Gulf of Aqaba in the Early Miocene. Falling Miocene sea levels then permitted the accumulation of the restricted ‘Globigerina Marls’ facies within the active graben system of the Gulf of Suez.

Vegetational patterns within coastal salines in southern Yemen

AbstractFor the first time, the species diversity and zonation of coastal dunes and littoral salt marshes of the extensive coastal belt of southern Arabia is analyzed by means of two transects (Aden/Madinat as‐Shab; al‐Mukalla/Feleq). The vegetation analysis results five (Aeluropus lagopoides‐, Halopeplis perfoliata‐, Halopyrum mucronatum‐, Sevada schimperi‐association, and one rest group – Aden transect) respectively seven (Anabasis ehrenbergii‐, Arthrocnemum macrostachyum‐, Cyperus conglomeratus‐, Stipagrostis paradisea‐, Urochondra setulosa‐Arthrocnemum macrostachyum‐, Urochondra setulosa‐association, and one rest group – Feleq transect) homogenous ecological groups, which form clearly defined belts following a strong edaphical gradient. While the associations in the vicinity of Aden are in good accordance with those, reported from the coasts of the Red Sea and the Arabian Gulf, three new associations, partly rich in endemics are reported from the southern coast of Hadramout (Feleq transect). Due to the plantgeographical relationships of the taxa (Eritreo‐Arabian chorotype), they are strongly related to the coasts of NE Africa. In addition, Coelachyrum piercei is reported as new to the flora of Yemen, closing herewith a gap in the distribution pattern of this Omano‐Makranian taxon.All taxa were examined with respect to their photosynthetic pathway type (Kranz syndrome, δ13C‐values) to clarify, if there is a correlation between the distribution of C3‐/C4‐plants and the ecological requirements of the halophytes. It turned out, that hygrohalophytes and oligohaline, xerix associations are dominated by C3‐plants, whereas C4‐plants are typical of xerohalophytic associations and those, showing an intermediate position with respect to soil salinity and available water.

Thrust tectonics in crystalline domains: The origin of a gneiss dome

Structural geological field work, microscopic and magnetic fabric studies have been applied in order to assess the structural origin of a gneiss dome, based on a regional example from the Neoproterozoic Pan-African Belt of NE Africa, the Wadi Hafafit Culmination (WHC). The culmination is dominated by a number of major shear zones, which form both the boundaries between the gneissic core and surrounding low grade successions as well as those of minor structural units within the gneisses. These shear zones form a linked fault system, which, based on shear criteria, fault-bend fold and overall geometric interrelationships, can be classified as an antiformal stack. The relative age sequence of the shear zones/thrusts with the highest thrust oldest and the lowermost youngest points to a forward-propagating thrust system. This, together with the shear criteria, exclude an origin of the WHC as a metamorphic core complex, where the highest shear zone should be youngest. The geometry of the WHC antiformal stack is documented by maps and sections as well as section balancing and restoration. Microscopic work showed brittle deformation in feldspar and dynamic recrystallization in quartz ribbons. The asymmetry of the fabric confirmed the macroscopically determined shear sense. However, there is one example of an earlier, perhaps extensional shear movement. Mylonitic foliation and transport-parallel lineation have also been determined by magnetic fabric studies. The observations suggest that thrusts may cut across both previously folded crystalline rocks as well as homogeneous granitoid plutonic bodies. According to the regional tectonic picture the large-scale structure of the gneiss dome originated after a phase of (late-orogenic) extensional collapse. It is speculated that during late-orogenic cooling the upper part of the lithosphere was sufficiently strong to allow brittle thrusting whilst the lithosphere as a whole was still weak enough to allow large-scale compressional deformation, perhaps in a transitional stage from lateorogenic to intra-cratonic deformation.

Remote sensing strategies for lithological mapping of pan African assemblages in arid environments: a case study in Eritrea, NE Africa

Over a 30 year period, when major advances were made in understanding the evolution of the Arabian-Nubian Shield, military conflicts prevented the geological mapping and tectonic interpretation of Eritrea, NE Africa. The indication of small occurrences of ultramafic rocks through ancient work in the NW extremity of the country prompted many workers on regional tectonics to propose the line of the Barka river as a Neoproterozoic (Pan African) suture. Several attempts based on remote sensing data have been considered to resolve about the existence of such structure in this region. These previous approaches, based on Landsat TM band ratios, fail comprehensively in Eritrea both to unequivocally map ultramafic occurrences and to serve as a good basis for lithological mapping, producing inconclusive and divergent overall results. In this paper we attempt to verify and amplify the hypothesis of a suture zone in N W Eritrea, employing a novel remote sensing strategy and detailed field work. Using statistically-selected Landsat TM enhanced false colour composites together with renditions from residual information of favored Principal Components (pseudo-ratios), we demonstrate that many important components of the Pan African Terranes of Eritrea - i.e. ophiolitic assemblages - can be mapped with a high degree of confidence. This remote sensing strategy transcends the problems encountered in previous approaches in Eritrea and can potentially serve as a powerful tool for geological mapping of similar arid terrains elsewhere.

A new species from Ethiopia and an interesting disjunction in Tylophora (Asclepiadaceae)

A new species of Tylophora, T. corollae Bullock ex Meve & Liede (Asclepiadaceae), is described from Ethiopia. This delicate twiner is characterized by yellow, shield-shaped corona lobes with apical appendages.The non-twining shrub up to lm high, T. fleckii (Schltr.) N.E. Br., so far known to be endemic to Namibia, is for the first time recorded from NE Africa. The interesting biogeographical implications resulting from the extraordinary gap of 4500km in its distribution are discussed.

Two newEragrostistaxa(Gramineae)

Abstract Scholz, H.: Two new Eragrostis taxa (Gramineae). — Willdenowia 26: 229–232. 1996. — ISSN 0511-9618. Eragrostis rivalis, a riverside and coastal plant from the southwestern part of the former USSR, up to now wrongly identified with the Saharian E. aegyptiaca, is described as a species new to science. In desert regions of NE Africa E. aegyptiaca comprises two taxa, E. aegyptiaca subsp. aegyptiaca and subsp. humifusa; the latter subspecies is described as new to science.

Mapping Precambrian structures in the Sahara Desert with SIR‐C/X‐SAR radar: The Neoproterozoic Keraf Suture, NE Sudan

A major N‐trending Neoproterozoic suture between composite arc terranes of the Arabian‐Nubian Shield in the east and older crust of the Nile Craton to the west is inferred to trend N‐S close to the Nile in northern Sudan. We used shuttle imaging radar (SIR) C/X synthetic aperture radar (SAR) imagery to find and map these structures in the poorly known Keraf Suture which are not apparent on visible or near IR imagery due to extensive sand cover. L band (23 cm wavelength) radar images best resolve geologic structure; the other frequencies of the SIR‐C/X‐SAR system (X and C bands) permit qualitative evaluation of the effects of surface versus subsurface backscattering. Interpretation of L band images supported by field work indicates that the Keraf Suture is ∼50 km wide and >550 km long, making it the longest basement structure recognized to date in NE Africa. The northern part of the Suture comprises ophiolitic rocks which were thrust westward over tightly folded sediments of the Nile Craton. The southern Keraf Suture is dominated by N‐ and NNW‐trending, left‐lateral strike‐slip faults that affect previously deformed passive margin sediments. Associated with these faults are NE‐trending transpressional folds and a possible transtensional basin. These structures are interpreted to be due to NW‐SE oblique collision between the Arabian‐Nubian Shield and the Nile Craton, as east and west Gondwana collided in the last 150 m.y. of Neoproterozoic time.

Hepatitis A, B, C and D in a community in Italy of immigrants from NE Africa

A total of 213 subjects from a community in Italy of immigrants from Somalia and other NE African countries were enrolled in this study to evaluate the prevalence of HAV, HBV, HCV and HDV infections and to assess their possible risk factors. Of the subjects, 45 per cent (96) were female and 24 per cent (52) were under 12 years old. The age range was from 1 to 67 years and the mean age was 24 years. Eighty-three per cent (177 subjects) were born in Somalia, 10 per cent (21 subjects) in Ethiopia, and the rest in Djibouti, Egypt or Saudi Arabia. The 213 subjects were administered a questionnaire which covered socio-demographic characteristics and risk factors resulting from Western medical practice, traditional medicine, personal behaviour and living conditions. Blood was drawn from 209 subjects to ascertain the presence of HbsAg, HBeAg, anti-HAV, anti-HBc, anti-HBs, anti-HCV and anti-HDV. The results of this study show an HAV prevalence of 96 per cent (an 87.5 per cent prevalence in children under 12), and an HBV prevalence of 32 per cent (a 3.3 per cent prevalence of HBsAg carriers). No subject under 11 was HBV positive and no woman tested positive for HBeAg, confirming the extreme unlikelihood of vertical transmission of HBV. The prevalence of HBV is closely correlated with age (ranging from 2 per cent in those under 12 to 59 per cent in subjects over 39).(ABSTRACT TRUNCATED AT 250 WORDS)