the thermal structure of mantle plumes axisymmetric or triple junction summary a mantle plume is probably a complex 3 d thermal structure that possesses approximate axisymmetry as it approaches the base of the lithosphere from below but followed down towards the base of the layer probably consists of a triple junction or quadruple junction of connected hot sheets a relatively weak hot sheet rising only part way through the layer probably connects two neighbouring mantle plumes these conclusions are suggested by numerical experiments on a 3 d constant viscosity plane layer with stress free boundaries which detail the gradational change in the planform of a convecting layer from the top of the layer to its base the planform of a convecting layer is a map in the horizontal plane of the principal thermal anomalies in the layer these anomalies are the main sources of positive for hot fluid or negative for cold fluid buoyancy and therefore they drive the convective flow they may appear in cross section as structures with either axial symmetry columns planar symmetry sheets or some complex asymmetric form when convection is driven at least partially by basal heating the planform near the top of the layer may be described as a network of cold sinking sheets and isolated hot columns while near the base of the layer it appears as a network of hot rising sheets and isolated cold columns the hot columns near the upper surface arise from the vertices or nodes of the network of hot sheets on the lower surface and similarly the cold columns at the base of the layer form below the vertices of the network of cold sheets near the upper surface near the upper surface the apparent planform of this experiment is analogous to that of mantle convection the cold sheets compared to subduction zones and the hot columns compared to mantle plumes the hot plumes impinging on the upper surface produce approximately axisymmetric temperature anomalies surface uplift and extensional stress fields however the relatively minor deviations from axisymmetry of surface observables reflect the deep structure of the mantle plume formed by the junction of three or four hot sheets on the base of the layer it seems likely that the commonly occurring triple junction form of continental rifts may reflect an underlying structure that is implicit in the convective circulation of the mantle beneath

magmatic history of red sea rifting perspective from the central saudi arabian coastal plain a newly recognized tertiary dike complex and comagmatic volcanic rocks exposed on the central saudi arabian coastal plain record early stages of magmatism related to red sea rifting intrusive and stratigraphic relationships and new potassium argon dating indicate episodic magmatism from about 30 ma to the present additional stratigraphic and radiometric evidence suggests that limited rift related magmatism began as early as about 50 ma an early phase of crustal extension in the region was accompanied by faulting and graben formation and by dike swarm intrusion the style of extension and intrusion changed at 20 ma localized volcanism and sheeted dike injection ceased and were replaced by the intrusion of thick gabbro dikes this change may mark the onset of sea floor spreading in the central red sea the dikes and volcanic rocks consist of a bimodal mafic felsic suite with transitional subalkaline to alkaline chemistry although no unique petrogenetic model can be developed for the suite the following observations and conclusions have been drawn from the available reconnaissance geochemistry 1 strontium isotopic initial ratios overlap in the range 0 7031 to 0 7047 and are not clearly related to alkalinity or silica content the bimodality and alkalinity of the suite are therefore not products of contamination by the radiogenic precambrian upper crustal granitic rocks exposed in the region 2 several of the evolved rocks rhyolites and comendite show large to extreme negative europium anomalies and heavy rare earth element hree enrichment features that cannot be explained by low pressure crystal fractionation of potential parent magmas an intriguing possibility is that hree enrichments and large negative eu anomalies of some peraluminous rhyolites and granites may result from the complete melting of garnet from middle or lower crustal rocks 3 most of the basalts are light rare earth element lree enriched consistent with derivation from fertile mantle in a continental rift setting however interaction of the mafic melts with lower continental crust cannot be ruled out a model of poly baric mantle melt derivation producing several alkaline subalkaline cycles best explains magmatism in the red sea region differences in the depths and dynamics of mantle melt extraction and transport brought about through changes in crust and mantle structure as the rift and paar developed may account for the transition from mixed alkaline subalkaline bimodal magmatism of the pre 20 ma rift basin to exclusively subalkaline tholeiitic magmatism at the red sea spreading axis and to predominantly alkali basalt volcanism inland within the arabian shield

submarine groundwater discharge driven nitrogen fluxes to long island sound ny terrestrial vs marine sources abstract bottom waters in smithtown bay long island sound ny are subject to hypoxic conditions every summer despite limited nutrient inputs from waste water and riverine sources while modeling estimates of groundwater inputs are thought to be insignificant terrestrial and marine fluxes of submarine groundwater discharge sgd were quantified to smithtown bay using mass balances of 222 rn 224 ra 226 ra and 228 ra during the spring and summer of 2014 2015 in order to track this seasonal transition period intertidal pore waters from a coastal bluff terrestrial sgd and from a barrier beach marine sgd displayed substantial differences in n concentrations and sources traced using a multi isotope approach 222 rn ra 15 n no 3 18 o no 3 no 3 in terrestrial sgd did not display any seasonality and was derived from residential septic systems and fertilizer marine sgd n concentrations varied month to month because of mixing between oxic seawater and hypoxic saline pore waters n concentrations were greatest during the summer when no 3 was derived from the remineralization of organic matter short lived 222 rn and 224 ra sgd fluxes were used to determine remineralized n loads along tidal recirculation flow paths while long lived 228 ra was used to trace inputs of anthropogenic n in terrestrial sgd 228 ra derived terrestrial n load estimates were between 20 and 55 lower than 224 ra derived estimates excluding spring 2014 228 ra may be a more appropriate tracer of terrestrial sgd n loads terrestrial sgd no 3 derived from 228 ra to smithtown bay varied from 1 40 12 8 10 6 mol n y 1 with comparable marine sgd no 3 fluxes of 1 70 6 79 10 6 mol n y 1 derived from 222 rn and 224 ra remineralized n loads were greater during the summer compared with spring and these may be an important driver toward the onset of seasonal hypoxic conditions in smithtown bay and western long island sound seawater recirculation through the coastal aquifer can rival the n load from terrestrial sgd from a heavily polluted aquifer

the arabian continental alkali basalt province part i evolution of harrat rahat kingdom of saudi arabia the harrat rahat lava field forms a major component of an extensive but poorly known continental alkali basalt province extending from yemen in the south through saudi arabia and jordan to syria in the north the continental intraplate volcanism which produced the arabian lava fields harrats was contemporaneous with opening of the red sea collision of the arabian and eurasian plates and uplift of the afro arabian dome harrat rabat has evolved over the past 10 m y it contains two prominent lateritic disconformities which separate three stratigraphic units the shawahit 10 2 5 ma hammah 2 5 1 7 ma and madinah 1 7 recent basalts comprising 68 19 and 13 of the total harrat volume respectively the shawahit basalt is composed of coarse grained dictytaxitic olivine transitional basalt otb and minor 10 alkali olivine basalt aob which erupted through scoria cones and shield volcanoes in contrast the hammah basalt is dominated by equal volumes of fine grained intergranular to intersertal aob and hawaiite which erupted mainly through scoria cones and relatively few shield volcanoes sparse domes and flows of mugearite and benmoreite first appear in the hammah basalt the madinah basalt spans the full compositional range of harrat rahat 103 analyzed samples comprise otb 8 aob 47 hawaiite 32 mugearite 4 benmoreite 8 and trachyte 2 here scoria cones dominate whereas shield volcanoes are sparse and occur only in the lower madinah basalt domes and associated pyroclastic deposits are common the final events of harrat volcanism include 11 post neolithic eruptions 4 500 yr old and two historical eruptions in 641 and 1256 a d arabian harrat magmatism may have been initiated by partial melting of garnet perido tite in the asthenosphere at a depth 100 km accumulation of this partial melt at the crust mantle boundary 37 44 km may have resulted in miocene uplift of the afro arabian dome harrat rahat volcanism began shortly after significant initial uplift with the voluminous extrusion of shawahit otb lava chemical and petrographic data suggest that these otb magmas ascended rapidly with little crustal residence time the data support a model of open system fractionation for aob and hawaiite lavas of the younger hammah and madinah basalts in this model some of the potential shawahit otb was trapped in crustal chambers during magma ascent crystal fractionation in these chambers was accompanied by their periodic replenishment by rising otb magma this resulted in the mixing of magma types and the development of aob and hawaiite magmas which are anomalously enriched in highly incompatible elements the mugearite benmoreite and trachyte lavas are the products of advanced fractionation in these crustal chambers with little or no magma replenishment

central gulf of aden conjugate margins yemen somalia tectono sedimentary and magmatism evolution in hybrid type margins abstract magma rich and magma poor passive margins are generally studied separately yet the spatial evolution from one type to another is not well understood central gulf of aden margins are at the transition between these two types of margins based on new seismic data published wells and gravity data we determine seismic stratigraphy and structural patterns we map the distinct crustal domains continental ocean continent transition oct oceanic domains and propose a tectonic evolution of the yemeni and somalian conjugate margins in an oblique rifting context the most striking results are the significant segmentation narrowness and asymmetry of conjugate margins as well as the gradual eastward decrease in the intensity of magmatic activity of these hybrid type margins west of bosaso hami fracture zone bhfz the hami ahl medo segment presents magmatic type margin features in the distal yemeni margin related to the strong influence from the afar plume seaward dipping reflectors develop since the late syn rift stage 21 18 ma near the xiis al mukalla fracture zone conversely east of bhfz the bosaso sayhut margins segment is characterized by magma poor margins for which the exhumation stage is characterized by the unroofing of mantle along multiple detachment faults in the oct and shortly followed by diachronous volcanism 18 ma the central gulf of aden is affected by a major uplift during the final syn rift stage and up to oct formation this event is associated with the formation of erosional surfaces in the east and with gravitational deformation taking place on decoupling surfaces at the base of the syn rift sequence lower ghaydah fm that lead to the sliding of syn rift units on top of the exhumed mantle rocks in the oct

lithospheric extension and the opening of the red sea sediment basalt relationships in yemen this paper analyses new field and radiometric age data on the timing of extension sedimentation and magmatism related to the opening of the red sea the first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine tawilah formation of cretaceous to early tertiary age the first indication of magmatism is the eruption of alkaline basalts 43 5 21 2 ma on to marine and non marine sandstones of lower to middle tertiary age the lack of an angular unconformity at the sediment basalt contact over a period of 25 myr corroborates a diachronous relationship between the tawilah sandstones and the yemen volcanics these data also indicate that the onset of volcanism in yemen was in the eocene as is the case in ethiopia and saudi arabia a passive rifting model is supported by early extension and sedimentation followed by syn and post tectonic magmatism

nitrogen biogeochemistry of submarine groundwater discharge to investigate the role of the seepage zone in transport chemical speciation and attenuation of nitrogen loads carried by submarine groundwater discharge we collected nearshore groundwater samples n 5 328 and examined the distribution and isotopic signature d15n of nitrate and ammonium in addition we estimated nutrient fluxes from terrestrial and marine groundwater sources we discuss our results in the context of three aquifer zones a fresh groundwater zone a shallow salinity transition zone stz and a deep stz groundwater plumes containing nitrate and ammonium occurred in the freshwater zone whereas the deep stz carried almost exclusively ammonium the distributions of redox cycled elements were consistent with theoretical thermodynamic stability of chemical species with sharp interfaces between water masses of distinct oxidation reduction potential suggesting that microbial transformations of nitrogen were rapid relative to dispersive mixing in limited locations in which overlap occurs between distribution of nitrate with that of ammonium and dissolved fe2 changes in concentration and in d15n suggest loss of all species concurrent removal of no and nh z both in freshwater and the deep stz might occur through a range of mechanisms including heterotrophic or autotrophic denitrification coupled nitrfication denitrification anammox or mn oxidation of nh z loss of nitrogen was not apparent in the shallow stz perhaps because of short water residence time despite organic cpoor conditions the nearshore aquifer and subterranean estuary are biogeochemically active zones where attenuation of n loads can occur extent of attenuation is controlled by the degree of mixing of biogeochemically dissimilar water masses highlighting the critical role of hydrogeology in n biogeochemistry mixing is related in part to thinning of the freshwater lens before discharge and to dispersion at the fresh saline groundwater interface features common to all submarine groundwater discharge zones

hot spot activity and the break up of pangea abstract the mesozoic and cenozoic positions of the continents that formed pangea in the triassic jurassic were derived from paleomagnetic and intraplate volcanic data paleoclimatic observations such as reef and fossil flora distribution and geological observations major hot spots helped to determine the longitudinal position of pangea and to construct a model of plate motion during the pangean break up the position of the northern part of pangea was constrained using iceland and jan mayen hot spots the iceland hot spot was traced from its present day position to greenland in the paleocene to baffin bay in the late cretaceous to the alpha ridge in the early cretaceous to the chukchi borderland in the middle late jurassic to franz joseph land in the early jurassic the yenisei khatanga trough in the middle triassic and finally to west siberia in the late permian early triassic the hot spot activity is expressed by eastern and western greenland volcanics the siberian trap basalts and perhaps by alpha ridge and chukchi borderland volcanics the chukchi borderland volcanics are related to the early stage of the opening of the canadian basin the position of the southern part of pangea was constrained using the bouvet hot spot this hot spot was tracked from its present day position to western antarctica in the early cretaceous late jurassic and to south africa in the early jurassic late triassic this hot spot activity produced the ferrar and karoo volcanics the model of plate motion obtained agrees with other data on intraplate volcanics which are also related to hot spots at the time of the opening of the central atlantic the cape verde and canary island hot spots were located along the ocean s spreading axis the long lasting location of hot spot and associated mantle upwelling plumes could help to explain forces driving the tethys transit plates opening of the ligurian ocean and eastern mediterranean the european hot spots are related to the several mesozoic phases of rifting for example the rhine graben hot spot may have been located at the rifting axis in the north sea several authors have already discussed the contribution of hot spots to the opening of the south atlantic and indian oceans mantle plumes associated with hot spots play an active role in rifting and initial phases of spreading the lithospheric displacement caused by upwelling combined with sometimes remote collisional forces on the other side of continental plate may result in compression and basin inversion

fission track analysis of basement apatites at the western margin of the gulf of suez rift egypt evidence for synchroneity of uplift and subsidence fifty six apatite fission track ages and 52 horizontal confined track length measurements are reported from precambrian crystalline rocks along the western margin of the gulf of suez egypt ages fall in the range of ca 11 385 m y and older ages often occur within very close geographic proximity to younger ones indicating non uniform uplift the wide range in ages is accompanied by a systematic variation in the distribution of horizontal confined fission track lengths on the basis of apatite fission track ages and their length distributions data fall into three distinct groups group i ages ranging from 43 to 385 m y length distributions are all positively skewed and with decreasing age become progressively broader with shorter mean track length group ii ages ranging from 23 to 31 m y length distributions are negatively skewed with either a distinct tail or a small peak of short tracks group iii ages ranging from 11 to 20 5 m y length distributions are al unimodal narrow negatively skewed and have the longest mean lengths among samples studied apatite ages from groups i and ii are interpreted as mixed ages as a result of cooling during uplift from different levels within the apatite partial track annealing zone ages from group iii are interpreted as cooling ages due to uplift from the apatite total track annealing zone with minor partial annealing correcting the ages of the two oldest samples in this group for track length reduction yields ages of21 2 2and23 1 5m y it is proposed that the onset of rift flank uplift in the gulf of suez northern red sea area occurred between 21 and 23 m y ago fission track analysis in combination with subsidence data from the gulf of suez basin indicate that commencement of basement uplift postdate the start of rifting and is interpreted as evidence for passive rifting at the gulf of suez furthermore this uplift is contemporaneous with and is directly related to the process of extension and subsidence at the gulf of suez

geochemical and physical characterization of lithic raw materials in the olduvai basin tanzania abstract the invention and proliferation of stone tool technology in the early stone age esa marks a watershed in human evolution patterns of lithic procurement manufacture use and discard have much to tell us about esa hominin cognition and land use however these issues cannot be fully explored outside the context of the physical attributes and spatio temporal availability of the lithic raw materials themselves the olduvai basin of northern tanzania which is home to both a wide variety of potential toolstones and a rich collection of esa archaeological sites provides an excellent opportunity to investigate the relationship between lithic technology and raw material characteristics here we examine two attributes of the basin s igneous and metamorphic rocks spatial location and fracture predictability a total of 244 geological specimens were analyzed with non destructive portable xrf pxrf to determine the geochemical distinctiveness of five primary and secondary sources while 110 geological specimens were subjected to schmidt rebound hardness tests to measure fracture predictability element concentrations derived via pxrf show significant differences between sources and multivariate predictive models classify geological specimens with 75 80 accuracy the predictive models identify naibor soit as the most likely source for a small sample of three lithic artifacts from bed ii which supports the idea that this inselberg served as a source of toolstone during the early pleistocene clear patterns in fracture predictability exist within and between both sources and rock types fine grained volcanics show high rebound values associated with high fracture predictability while finer grained metamorphics and coarse grained gneisses show intermediate and low rebound values respectively artifact data from bed i and ii suggest that fracture predictability played a role in raw material selection at some sites but other attributes like durability expediency and nodule size and shape were more significant

the timing of uplift volcanism and rifting peripheral to the red sea a case for passive rifting prior to the formation of the red sea the northeastern afro arabian continent had low relief and was largely below sea level from the late cretaceous to the early oligocene the events leading to the formation of the red sea followed the sequence 1 alkaline volcanism and rifting beginning about 30 32 ma affecting a narrow linear zone in the continent 2 rotational block faulting and detachment faulting well underway by 25 ma 3 gabbro and diorite magmatism andesite to rhyolite volcanism and fine grained nonmarine sedimentation in the rift between 20 and 25 ma 4 fine grained marine sedimentation in the rift as the early shelves started to subside in the middle miocene and 5 uplift of the adjacent continents about 3 km and subsidence of the shelves about 4 km between 13 8 and 5 ma the youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the proterozoic arabian shield that range in age from 13 8 to 568 ma the youngest of these ages coupled with the present high relief along the arabian escarpment and published heat flow measurements indicate that 2 5 4 km uplift has occurred in the last 13 8 m y the sequence volcanism rifting followed by uplift leads to our adoption of a passive mantle model for rift origin models that require uplift to create the rift are rejected because of the late uplift we advocate a model of lithospheric extension caused by two dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere it is acknowledged that traction models could explain the observed data but they imply a rigid static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions neither requirement is necessary in the extension model the rift starts with mechanical extension in a narrow zone of lithosphere between 25 32 ma in our model the thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis once partially melted rocks formerly part of the continental lithosphere join the upwelling asthenosphere resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge the resulting density decrease explains the uplift we think that the red sea began as a consequence of changing plate geometries resulting from the collision of india and eurasia after the collision the segment of the owens fracture zone north of the carlsberg ridge became locked forcing the northeast corner of afro arabia to rotate with the indian plate away from the rest of africa

role of the tectonic facies concept in orogenic analysis and its application to tethys in the eastern mediterranean region abstract the purpose of this paper is to advocate the use of a tectonic facies concept which aids systematic and objective analysis of orogenic belts the tectonic facies concept as discussed here focuses on the recognition of discrete tectonic settings mainly those exposed at high crustal levels in orogenic belts application of the tectonic facies concept can help field geologists to relate plate scale processes to outcrop geology tectonic facies are recognised based on knowledge of the modern oceans and margins and well constrained land settings tectonic facies analogous to sedimentary facies can be identified from integrated sets of field data and related laboratory studies a number of tectonic facies models can be recognised in this way their identification aids interpretation and comparisons of orogenic belts palinspastic reconstructions require additional information particularly age kinematic and palaeomagnetic data in this paper the tectonic facies concept is tested by application to a well documented mainly high level orogenic segment tethys in the eastern mediterranean area and is found to be an effective way both of the describing and interpreting this region other methods of tectonic analysis e g recognition of tectono stratigraphic terranes may also be found useful in certain settings and can be used in conjunction with the tectonic facies concept

the larger mammal palimpsest from tk thiongo korongo bed ii olduvai gorge tanzania ever since mary leakey s initial excavations in the 1960s tk thiongo korongo has been recognized as one of olduvai gorge s most important acheulean sites the significant concentrations of lithics and fauna reported by mary leakey have been augmented in recent years by santonja et al who argue that human activities appear to be largely related to the manufacture of lithic implements in contrast the faunal remains have been interpreted to be of uncertain origin and their anthropogenic nature remains in question this paper presents new data on the formation of the tk bone accumulation our results reveal a diverse list of taxa many of which reflect open habitats only limited evidence of anthropogenic activity is documented

ages of continental shelf waters determined from 223ra and 224ra coastal surface waters in the south atlantic bight contain elevated activities of 223ra t1 2 11 4 days and 224ra t1 2 3 66 days these elevated dissolved activities are due to continual input of the short lived tracers near the coast the presence of these tracers in an offshore water sample implies that the water is less than six half lives removed from the source of the tracer the absence of the tracer implies the water is more than six half lives old or has been diluted substantially with old water containing little tracer in this paper i use models based on 223ra and 224ra to derive ages of continental shelf waters these models compensate for tracer dilution by normalizing the short lived tracers to each other or to long lived 228ra if the water on the inner shelf 0 20 km from shore is assigned a zero age ages for waters 80 100 km from the inner shelf are 20 30 days

geologic influence on groundwater salinity drives large seawater circulation through the continental shelf observations of offshore freshened groundwater and saline groundwater discharge along continental shelves have important implications for water resources ecosystem function and the composition of the ocean but they cannot be explained by basic theory we show that these independent observations are linked and result from processes that drive variable density groundwater flow through the spatial heterogeneity that is ubiquitous in geologic formations we use lithologic data to develop geostatistical models that mimic the architecture of coastal aquifers simulation of groundwater flow and salt transport through these random realizations shows that heterogeneity produces spatially complex subsurface salinity distributions that extend tens of kilometers offshore even at steady state the associated density gradients drive high saline groundwater circulation rates that cannot be predicted by equivalent homogeneous models results suggest that these phenomena may be common along continental shelves potentially altering estimates of ocean chemical budgets and impacting coastal water management for future generations

importance of geochemical transformations in determining submarine groundwater discharge derived trace metal and nutrient fluxes abstract seasonal spring and summer 2002 concentrations of dissolved 3 po 4 si and doc were determined in groundwater samples from 5 wells aligned along a 30 m shore normal transect in west neck bay long island ny results show that significant systematic changes in groundwater trace metal and nutrient composition occur along the flowpath from land to sea while conservative mixing between west neck bay water and the groundwaters explains the behavior of si and doc non conservative inputs for co and ni were observed concentration increases of 10 and 2 fold respectively and removal of po 4 and no 3 decreases to about half along the transport pathway groundwater associated chemical fluxes from the aquifer to the embayment calculated for constituents not exhibiting conservative behavior can vary by orders of magnitude depending on sampling location and season e g co 3 4 10 2 8 2 10 3 mol d 1 using measured values from different wells as being representative of the true groundwater endmember chemical composition also results in calculation of very different fluxes e g cu 6 3 10 3 mol d 1 inland freshwater well vs 2 1 10 5 mol d 1 seaward well s 17 ppt this study suggests that seasonal variability and chemical changes occurring within the subterranean estuary must be taken into account when determining the groundwater flux of dissolved trace metals and nutrients to the coastal ocean

timing of mantle upwelling evidence for a passive origin for the red sea rift mantle xenoliths from western saudi arabia some 220 km east of the red sea margin indicate temperatures as high as 900 c in the mantle at about 40 km depth beneath an area of the arabian shield where surface heat flow is lower than the world average this suggests that there has been a large increase in the mantle temperature that has not had time to equilibrate at the surface the amount of uplift and the difference between the observed xenolith temperature and that obtained by projecting the surface heat flow to depth suggests that the lithosphere has been thinned by 30 to 100 km to its present calculated thickness of about 80 km calculations of the time necessary for thermal reequilibration indicate that the lithospheric thinning probably occurred less than 20 m y ago so it postdates rifting which started about 30 ma if there was a prolonged upwelling of deep mantle material resulting in a thinner lithosphere prior to rifting there should have been enough time for some reequilibration at the surface and the observed heat flow should be higher over the broad area of uplift adjacent to the red sea our calculations are consistent with a postrift age of uplift adjacent to the red sea as determined from regional geologic evidence and fission track ages on apatites from shield rocks the red sea appears to have begun with alkaline volcanism on the arabian shield followed by rifting uplift and lithospheric thinning adjacent to the red sea rift began 5 10 m y after rifting this suggests that the red sea is a passive rift that formed because of two dimensional plate motions rather than as a consequence of mantle upwelling a possible cause for the stress in the plates might have been the change of plate motions in the indian ocean that resulted from the collision of india with eurasia

tectono stratigraphic development of the qamar basin eastern yemen abstract the qamar basin is a polyphase rift basin located in eastern yemen adjacent to the indian ocean it probably originated as part of an extensive rift system which developed during the late jurassic to early cretaceous and led to the break up of gondwanaland rift reactivation during the mid cretaceous affected limited areas including the qamar basin a third episode of rifting occurred during the oligo miocene prior to sea floor spreading in the gulf of aden since spreading in the gulf began in the middle miocene the offshore qamar basin has been thermally subsiding in contrast the onshore part of the basin has been elevated by over 1 km the nature of the pre mid cretaceous basin fill is unknown during santonian to early campanian times thick fluvio deltaic clastics accumulated in a rapidly subsiding depocentre marked deepening during the early campanian led to deposition of deep water limestones during the late campanian prograding deep marine clastics infilled the basin minor transgression during the maastrichtian caused a resumption of marine carbonate deposition sedimentation was interrupted during the early palaeocene following which shallow marine carbonates were deposited over a large area of the arabian peninsula after a hiatus spanning the late eocene to late oligocene carbonate sedimentation resumed offshore in an active rift basin deep water carbonates and carbonate turbidites accumulated in lows whilst reefs developed on footwall highs from the late miocene onwards the reefs have been gradually drowned by rapidly accumulating clastics onshore the tertiary rift episode was associated with major uplift and only a thin veneer of recent wadi deposits overlies the rift topography the superposition of jurassic cretaceous and tertiary rifts which has not been described elsewhere in the region is tentatively related to the evolution of the indian ocean

particle size distribution of lithic assemblages and taphonomy of palaeolithic sites abstract lithic debris derived from knapping and used tools can be assimilated to simple sedimentary particles that may undergo size sorting when exposed to geomorphic processes such as streamflow or overland flow sorting can be identified by comparing the size distribution of archaeological assemblages to that of experimental core reduction sequences a new database including different types of raw material mainly flint and quartzite and palaeolithic debitage blade levallois discoid on anvil and shaping has been built for this purpose palaeoeskimo data have also been added to illustrate microlithic industries for all the debitages and raw materials the particle size of knapping products 2 mm in width fits with a power law distribution and shows only minor fluctuations the range of which is always

study of the shk main site faunal assemblage olduvai gorge tanzania implications for bed ii taphonomy paleoecology and hominin utilization of megafauna recent excavations at the shk main site olduvai gorge tanzania have unearthed a dense concentration of stone tools and faunal remains here we describe how the site contributes to the understanding of hominin subsistence strategies and paleoecology during bed ii times 1 78 1 34 ma this palimpsestic site is located within and on the over bank of a river channel taphonomic analyses suggest that a heterogeneous set of taphonomic agents played a role in the accumulation and modification of the faunal assemblage although hominins played a rather marginal part in this assemblage s faunal accumulation and modification the recovered faunal assemblage includes evidence that is consistent with hominin exploitation of hippopotamus and equid this evidence underscores the possibility that by 1 5 ma hominins were diversifying their diet and enlarging their ecological niche by exploiting probably opportunistically megafaunal remains more commonly than previously documented taphonomic spatial analysis shows differences in bone preservation and modification according to whether faunal specimens were located inside the river channel or on its over bank we also show that spatial taphonomic analysis can contribute to the understanding of palimpsest site formation as well as to the reconstruction of diverse taphonomic agents responsible for that formation a comparative analysis of taxonomic diversity between shk versus other upper bed ii sites supports the notion that the environment was fairly open prior to the beginning of the bed iii deposits the large number of lithic artifacts concentrated at the shk main site when considered in conjunction with the small amount of evidence for carcass processing suggests that hominins engaged in a diversity of activities beyond butchery

evaluation of 224 ra as a tracer for submarine groundwater discharge in long island sound ny abstract the approach to quantify submarine groundwater discharge using ra isotopes generally involves developing a ra mass balance in an estuary bay or lagoon in this work we present a 224ra mass balance used to evaluate the importance of the submarine groundwater discharge sgd in long island sound ny us the third most important estuary in us located between long island and connecticut that is usually affected by summertime hypoxia in the western basin three surveys were conducted between april 2009 and august 2010 where 25 water stations were sampled for ra isotopes oxygen and mn stations were oriented along 4 transects one axial extending from the western to the eastern sound and three longitudinal transects in the western central and eastern sound the inventory of 224ra in the water column in summer was circa 2 times greater than in winter suggesting an increased 224ra flux to the sound in summer a mass balance for 224ra was constructed considering tidal exchange inputs from rivers desorption from resuspended particles diffusive fluxes including bioirrigation from bottom sediments and radioactive decay in the water column fluxes of 224ra from bottom sediments were measured by incubating cores under oxic conditions in a continuous flow mode such that the overlying water was circulated through a mn oxide fiber to maintain a constant activity of 224ra fluxes from muddy sediments comprising 67 of the sound bottom ranged from 127 to 312 dpm m 2 d 1 and were 60 dpm m 2 d 1 in sandy sediments 33 of the sound incubations under hypoxic conditions showed variable fluxes depending on reduction and mobilization of mn the 224ra mass balance shows a net input of ra to the sound of 106 50 1012 dpm y 1 in spring and 244 112 1012 dpm y 1 in the summer that is attributed to sgd elevated 224ra values were observed near shore and in the pore fluids of the coarse beach sands along the long island and connecticut coasts suggesting that sgd driven by tidal recirculation through the beach face is a major source of 224ra to the sound seasonal variation in this source seems unlikely and the calculated 224ra sgd fluxes for spring and summer overlap within the uncertainties nevertheless we conclude that variations in the 224ra water column inventories could be produced by seasonal changes in bioirrigation and or redox cycling of mn as well as sediment resuspension and desorption of 224ra from resuspended particles and that our mass balance underestimates these terms particularly in the summer 224ra fluxes from sediments in estuaries especially those with significant areas of muddy sediments and seasonal hypoxia are important and should be well constrained in future uses of this isotope as a tracer for sgd

timing of tertiary extension in the railroad valley pioche transect nevada constraints from 40ar 39ar ages of volcanic rocks time space relations of extension and volcanism place critical constraints on models of basin and range extensional processes this paper addresses such relations in a 130 km wide transect in the eastern great basin bounded on the east by the ely springs range and on the west by the grant and quinn canyon ranges stratigraphic and structural data combined with 40ar 39ar isotopic ages of volcanic rocks document a protracted but distinctly episodic extensional history field relations indicate four periods of faulting only one of these periods was synchronous with nearby volcanic activity which implies that volcanism and faulting need not be associated closely in space and time based on published dates and the analyses reported here the periods of extension were 1 prevolcanic pre 32 ma 2 early synvolcanic 30 to 27 ma 3 immediately postvolcanic about 16 to 14 ma and 4 pliocene to quaternary the break between the second and third periods is distinct the minimum gap between the first two periods is 2 ma but the separation may be much larger temporal separation of the last two periods is only suggested by the stratigraphic record and cannot be rigorously demonstrated with present data the three younger periods of faulting apparently occurred across the entire transect the oldest period is recognized only at the eastern end of the transect but appears to correlate about 150 km northward along strike with extension in the northern snake range kern mountains area therefore the oldest period also is regional in extent but affected a different area than that affected by younger periods this relation suggests that distinct extensional structures and master detachment faults were active at different times the correlation of deformation periods of a few million years duration across the railroad valley pioche transect suggests that the scale of active extensional domains in the great basin may be greater than 100 km across strike

geo archaeological and geometrically corrected reconstruction of the 1 84 ma flk zinj paleolandscape at olduvai gorge tanzania a geomorphological sedimentological stratigraphic and geometric study of 30 trenches excavated around flk zinj bed i olduvai gorge has enabled the partial reconstruction of the paleolandscape surrounding this site for a radius of 1000 m this is the largest sample of geological and archaeological information yet available to reconstruct the topography ecology and geomorphology of the zinj paleosurface and the hominin activities preserved within it contrary to previous interpretations which place flk zinj on an isolated and narrow peninsula it appears that the site was located on the edge of an elevated platform traceable for hundreds of meters hominins created flk zinj and other sites such as the recently discovered ptk and amk within the wooded habitats of this platform rather than the more open and grassy environments situated on lower portions of the lacustrine floodplain input areas probably in the form of alluvial fans existed to the south following a north south direction these input areas are partially responsible for changes in the type sequence restricted erosion documented on the wooded platform was mostly caused by runoff processes an archaeological study of the excavated trenches reveals a sharp contrast in fossil and stone tool density between flk zinj and the surrounding landscape further supporting the contention that the site may have acted as a central place where repeated carcass transport butchery and consumption took place taphonomic studies indicate that at this stage of human evolution hominins had primary access to carcasses and were not dependent on other carnivores for obtaining meat

solute transport into the jiulong river estuary via pore water exchange and submarine groundwater discharge new insights from 224ra 228th disequilibrium abstract pore water exchange pex and submarine groundwater discharge sgd represent two mechanisms for solute transport from the seabed into the coastal ocean however their relative importance remains to be assessed in this study we pursued the recently developed 224ra 228th disequilibrium approach to quantify pex fluxes of 224ra into the jiulong river estuary china by constructing a full mass balance of water column 224ra we were allowed to put various source terms i e sgd diffusive and advective pore water flow pex and river input in a single context this led to the first quantitative assessment of the relative importance of pex vs sgd in the delivery of solutes into an estuary we carried out two surveys in the jiulong river estuary one in january 2014 winter survey the other in august 2014 summer survey by virtue of a 1 d mass balance model of 224ra in the sediment column we demonstrated that pex fluxes of 224ra were highly variable both temporally and spatially and can change by 1 2 orders of magnitude in our study area moreover we identified a strong correlation between 224ra based irrigation rate and 234th based sediment mixing rate our results highlighted irrigation as the predominant pex process for solute transfer across the sediment water interface total pex flux of 224ra in 1010 dpm d 1 into the jiulong river estuary was estimated to be 22 3 3 0 and 33 7 5 5 during the winter and summer surveys respectively in comparison total sgd flux of 224ra in 1010 dpm d 1 was 11 3 8 6 and 49 5 16 3 in the respective seasons by multiplying the pex fluxes of 224ra by the ratio of the concentration gradients of component 224ra at the sediment water interface we quantified the total pex fluxes of dissolved inorganic carbon dic and nutrients nh4 no3 and h4sio4 into the jiulong river estuary in the meantime net export of dic and nutrients via sgd were estimated by multiplying the sgd fluxes of 224ra by the dic nutrients 224ra ratios in the sgd end members around this area our results revealed that pex driven fluxes of solutes rival net sgd input and river input in an estuary an additional new finding is that water column no3 in the surface estuary was effectively sequestered due to sgd probably as a result of intense denitrification occurring in the anoxic subterranean estuary

autochthony and orientation patterns in olduvai bed i a re examination of the status of post depositional biasing of archaeological assemblages from flk north flkn recent excavations at flk north olduvai gorge tanzania have produced new information on the orientation of archaeological materials at various levels of the site this information includes the uniform distribution of material azimuths which contrasts with previous inferences of highly patterned orientations of materials in the bed i archaeological sites those previous inferences of patterned material orientations are based on mary leakey s 50 year old drawings of artifact and fossil bone distribution but are not verified by our precise measurements of archaeological objects made in situ nor do those previous results agree with the general lack of geological geomorphological and or taphonomic data that would indicate significant post depositional movement of archaeological materials in the sites we argue here that leakey s drawings are incomplete only portions of each assemblage were drawn and inaccurate in their representation of the original locations shapes and orientations of most archaeological specimens this argument is supported by several important mismatches in object representations between a photograph taken of a small portion of the flk 22 zinjanthropus site floor before the removal of the archaeological items and the sketch of the same area drawn by leakey thus we conclude that primary orientation data of excavations i e direct measurements taken from items generated prior to object removal are the only valid indicators of the relative isotropy or anisotropy of these important paleoanthropological assemblages

using the radium quartet to quantify submarine groundwater discharge and porewater exchange abstract the specific ingrowth rates of different radium isotopes make them valuable tracers to distinguish processes occurring at different temporal scales here we demonstrate the use of the radium quartet 223ra 224ra 226ra and 228ra to differentiate flows of submarine groundwater discharge and porewater exchange to a coastal embayment alfacs bay nw mediterranean sea based on the assumption that these processes occur on different time scales in order to evaluate the seasonal dynamics of groundwater and porewater inputs to the bay we conducted three seasonal samplings at alfacs bay during which samples for ra isotopes were collected from bay waters groundwater springs porewaters and irrigation channels activities of short lived ra isotopes in the bay showed a strong seasonality e g average 224ra activities in summer 32 dpm 100 l 1 up to 4 times higher than in winter 8 dpm 100 l 1 in contrast the activities of the long lived ra isotopes were fairly constant throughout the year e g activities of 226ra were 16 and 14 dpm 100 l 1 in summer and winter respectively the relatively short exposure to sediments of recirculation fluxes resulted in porewaters significantly enriched in short lived ra isotopes relative to the long lived ones e g 224ra 1100 1300 dpm 100 l 1 226ra 17 99 dpm 100 l 1 whereas coastal groundwaters were enriched in all the ra isotopes e g 224ra 120 150 dpm 100 l 1 226ra 200 400 dpm 100 l 1 the distinct signatures of different sources allowed us to construct seasonal ra mass balances to estimate both groundwater discharge which ranges from 40 60 103 m3 d 1 in summer to 310 200 103 m3 d 1 in winter and porewater exchange fluxes ranging from 1200 120 103 m3 d 1 in summer to 270 40 103 m3 d 1 in winter whereas the seasonal variability of groundwater inputs is likely governed by the terrestrial hydraulic gradient a qualitative evaluation of the drivers of porewater exchange suggested that the strong seasonality of the seawater recirculation inputs is likely mediated by seasonal cycles on the activity of benthic infauna ra isotopes are thus valuable tracers to differentiate fluxes of both submarine groundwater discharge and porewater exchange allowing a more accurate evaluation of the fluxes of freshwater and solutes to coastal ecosystems as well as their implications for coastal biogeochemical cycles

the yemen trap series genesis and evolution of a continental flood basalt province abstract the yemen basaltic plateau trap series was built up by fissure eruptions related to tensional tectonics in the afro arabian plate two main phases of activity have been identified and dated between 30 and 26 and 23 and 19 ma respectively the first phase was dominated by eruptions of alkaline to transitional basalts with a few rhyolitic ignimbrites during the second phase rhyolites with minor transitional basalts were erupted in the southern and southwestern part of the area geochemical and isotopic data indicate that the basalts are the result of combined processes of crystal fractionation and crustal contamination on mantle derived parental liquids the degree of crustal contamination generally decreases from south to north

tectonic configuration of the western arabian continental margin southern red sea the young continental margin of the western arabian peninsula is uplifted 3 5 to 4 km and is well exposed rift related extensional deformation is confined to a zone 150 km wide inland of the present coastline at 17 to 18 n and its intensity increases gradually from east to west extension is negligible near the crest of the arabian escarpment but it reaches a value of 8 to 10 in the western asir a highly dissected mountainous region west of the escarpment there is an abrupt increase in extensional deformation in the foothills and pediment west of the asir about 40 km inland of the shoreline where rocks in the upper plate of a system of low angle normal faults with west dips are extended by 60 to 110 the faults were active 23 to 29 ma ago and the uplift occurred after 25 ma ago tertiary mafic dike swarms and plutons of gabbro and granophyre 20 to 23 ma old are concentrated in the foothills and pediment as well the chemistry of the dikes suggests 1 fractionation at 10 to 20 kbar 2 a rapid rise through the upper mantle and lower crust and 3 differentiation and cooling at 1 atm to 5 kbar structural relations between dikes faults and dipping beds indicate that the mechanical extension and intrusional expansion were partly coeval but that most of the extension preceded the expansion a tectonic reconstruction of pre red sea afro arabia suggests that the early rift was narrow with intense extension confined to an axial belt 20 to 40 km wide steep moho slopes probably developed during rift formation as indicated by published gravity data two published seismic interpretations and the surface geology

geological evolution of the afro arabian dome abstract the afro arabian dome includes the elevated continental regions enclosing the red sea gulf of aden and the ethiopian rift system and extends northwards as far as jordan it is more than an order of magnitude larger than other african uplifts both the structures and the igneous rocks of the dome appear to be products of the superimposition of two perhaps three semi independent generating systems initiated at different times but all still active a strain pattern dominated by nw trending basins and rifts first became established early in the cretaceous by the end of the oligocene much of the extensional strain had been taken up along the red sea and gulf of aden axes which subsequently developed into an ocean palaeogene trap volcanism of mildly alkaline to transitional character was related to this horizontal extension rather than to doming further west the east sahara swell has a history of intermittent alkaline volcanicity which began in the mesozoic and was independent of magmatism in the afro arabian dome volcanicity specifically related to doming began in the miocene along a n s zone of uplift extending from ethiopia to syria this elongated swell forms the northern termination of the east african system of domes and rifts characterized by episodic vertical uplift but very little extension superimposition of epeirogenic uplift upon structures formed by horizontal extension took place in the neogene volcanicity related to vertical tectonics is mildly alkaline in character whereas transitional and tholeiitic magmas are found along the spreading axes

the arabian continental alkali basalt province part ii evolution of harrats khaybar ithnayn and kura kingdom of saudi arabia three coalesced basaltic lava fields harrats khaybar ithnayn and kura constitute the largest contiguous area of cenozoic basalt in saudi arabia similar in extent 20 564 km2 and volume 1 850 km3 to harrat rahat which is situated only 25 km to the south harrat kura with an age range from about 11 to 5 ma is the oldest of these harrats it contains a single stratigraphic unit the kura basalt primarily composed of alkali olivine basalt aob with subordinant basanite and hawaiite and a single cluster of four phonolite domes in contrast harrats khaybar 5 ma to present and ithnayn 3 ma to present are composed of more mildly alkaline basalt types the two oldest units on harrat khaybar the jarad and mukrash basalts are dominated by dictytaxitic to ophitic olivine transitional basalt otb flows which were extruded primarily from major arterial lava tubes to form unusual morphological features here designated whaleback lava flows the lava tubes emanate from a 50 km long north trending fault scarp along the western edge of the central vent zone which marks the site of voluminous outwelling of otb lava the fault scarp ceased to be a major site of extrusion at the end of mukrash time immediately to the east of the fault scarp a thin 0 7 to 1 0 km uptilted slab of crust formed the roof of a high level magma chamber 60 x 25 km that dominated the eruptive history of the abyad basalt the youngest stratigraphic unit on harrat khaybar the abyad basalt occurs as seven stratigraphic subunits the two youngest of which qb6 and qb7 are post neolithic and historical in age in contrast to the jarad and mukrash basalts the abyad basalt is dominated by aob and hawaiite with only minor otb no abyad differentiated rocks occur on harrat ithnayn however fractional crystallization in the high level magma chamber beneath harrat khaybar has resulted in an extreme compositional range of rock types from mugearite to benmoreite trachyte and comendite the vent distribution at harrat khaybar shows a distinct zonation indicative of a high level compositionally stratified magma chamber whole rock chemistry suggests that even the most primitive basalts are not primary magmas but rather fractionated melts derived from primary magmas of variable melt fractions generated at differing mantle depths the more undersaturated harrat kura basalts were derived from primary magmas representing the smallest degrees of partial melting at the greatest depth crystal fractionation of most primary magmas appears to have taken place in reservoirs at the crust mantle boundary chemical and petrographic data suggest that open system magma recharge was an important process in the high level magma chamber beneath harrat khaybar the chemical and mineralogical heterogeneity of the harrat khaybar comendites their sr isotope values and their zr nb ratios all indicate that they were derived by varying degrees of crystal fractionation 95 crustal melting and halogen complexing the north trending volcanic axes of harrats rahat khaybar and ithnayn form a single 600 km long linear vent system designated the makkah madinah nafud mmn volcanic line the three transitional to mildly alkaline harrats extruded from this volcanic line differ from most arabian harrats which like harrat kura to the west are significantly more undersaturated the relatively large degrees of partial melting evident in harrats rahat khaybar and ithnayn suggest that the mmn volcanic line may overlie a north south thermal lineation in the mantle the petrochemical stratigraphic sequence in these three harrats is nearly identical early voluminous extrusions of otb were followed by later less extensive extrusions of minor otb and abundant aob hawaiite and differentiated lavas as this petrochemical stratigraphy evolved it progressed northward along the mmn trend with time beginning on harrat rahat about 10 ma on harrat khaybar about 5 ma and on harrat ithnayn about 3 ma the interplay of open system magmatic processes beneath this migrating volcanic line has resulted in a classic example of a strongly fractionated mildly alkaline basalt series

two phases of cretaceous tertiary magmatism in the eastern desert of egypt paleomagnetic chemical and k ar evidence abstract paleomagnetic and radiometric data confirm the existence of two phases of igneous activity in the late mesozoic and cenozoic history of eastern egypt in the mid to late cretaceous the earlier and more extensive episode produced the wadi natash alkaline basalts and numerous small trachytic intrusions the ring complexes of abu khrug and gebel el kahfa were also emplaced at this time the mean paleopole position for the intrusive rocks is at 65 3 n 111 2 w a 95 11 4 31 sites chemical analyses of the trachytes show that they are enriched in nb zr and y and depleted in sr ba cr and ni suggesting either prolonged fractionation or limited partial fusion the second phase of activity during oligo miocene time is represented by small tholeiitic basalt flows on the red sea coast and along the nile valley the mean paleopole position for the flows is at 68 2 n 101 5 e a 95 27 8 3 sites the wide scatter is interpreted as reflecting secular variation the chronological and chemical data are used with studies of sedimentary formations coeval with the igneous rocks to apply a general model of continental rifting to the northern red sea the earlier alkaline phase of igneous activity is related to regional uplift while the second tholeiitic phase is associated with widening of the rift valley

miocene magmatism of sinai related to the opening of the red sea extension associated with the initial early miocene stages of opening of the red sea resulted in intrusion of a widespread system of dikes and smaller bodies primarily along the northeastern margin of the red sea gulf of suez axis dikes some up to more than 800 km in length were emplaced dominantly parallel to the red sea gulf of suez from the sinai peninsula to yemen intrusive rocks are mainly basaltic in composition but minor granophyres are also present in the sinai this magmatic event is about 20 m y old dikes of the southern and southeastern sinai crop out in precambrian terrane in the central and northern sinai they occur in phanerozoic terrane where they may be associated with linear grabens and cryptovolcanic features basaltic dikes of the sinai underwent variable degrees of alteration alteration phases include seriate quartz smectite chlorite and serpentine x ray diffraction and petrographic analysis indicate that in spite of extensive alteration primary minerals still control the major element compositions of the rocks basalts are tholeiitic in composition with sio2 48 5 to 50 and na2o k2o 3 to 3 5 rb and sr concentrations are probably dominated by alteration and by introduction of secondary material primarily carbonate zr tio2 which is relatively unchanged during alteration substantiates that the basaltic rocks are subalkaline initial 87sr 86sr determined after leaching of samples is approximately 0 7043 0 7063 much higher than red sea axial trough basalts 0 703 we infer that these sinai basalts equilibrated at depths of 35 50 km possibly within an enriched mantle whether the main trough of the red sea is underlain by extended and modified continental crust or by oceanic crust is controversial since miocene dikes were intruded along both coasts but primarily the saudi arabian coast of the red sea gulf of suez axis in a zone up to 150 km wide they may also underlie the main trough of the red sea and result at least partially in the discontinuous magnetic and gravity anomalies observed there possibly the abundance of dikes beneath the main trough is much greater than adjacent to the red sea giving rise to properties intermediate between those of continental and oceanic crust downwarping and widespread intrusion of dikes along the red sea 18 26 m y ago probably signified crustal dilation and the initiation of a continental rift because tholeiitic basalts of the sinai are higher in 87sr 86sr than red sea axial trough basalts we infer that the conditions of their origin must also be very different we suggest that the sinai basalts may have been generated within but near the base of subcrustal continental lithosphere perhaps indicating thermal thinning of lithospheric mantle above upwelled asthenosphere associated with continental rifting this inference if correct would indicate that the lithosphere was at least 35 50 km thick during the early miocene phase of rifting but possibly not much thicker since dikes farthest from the red sea are apparently identical in composition to those closest asthenospheric upwarping must have been broad enough that all magmas were derived from approximately the same depth in the yemen ethiopia areas volcanism began earlier about 30 m y ago and was much more voluminous than elsewhere along the red sea gulf of suez axis suggesting the presence of underlying mantle upwelling accompanying rifting of the red sea in spite of differences in age and volume the presence of large volumes of tholeiites among the miocene basalts of the yemen ethiopia areas suggests that the lithosphere was similarly thinned along the entire length of the red sea

the cooling history of silurian to cretaceous alkaline ring complexes south eastern desert egypt as revealed by fission track analysis abstract forty fission track ages of apatite zircon and sphene and nine horizontal confined track length distribution patterns in apatite have been used to establish the cooling history of nine silurian to late cretaceous alkaline ring complexes which intrude precambrian basement in the southern eastern desert of egypt zircon or sphene fission track ages were determined from three complexes for whichk ar andrb sr ages on the same samples were also available these ages are concordant and are interpreted as emplacement ages resulting from rapid cooling following high level crustal intrusion into relatively thick volcanic piles average apatite ages for each of the eight ring complexes range from 33 to 167 m y track length distribution patterns for apatites taken together with their ages invite subdivision into two groupings those complexes yielding early oligocene apparent apatite ages suggest cooling from the total track annealing zone followed by a relatively lengthy residence near the base of the partial annealing zone whereas those with late cretaceous ages indicate cooling from a shallower level in the partial annealing zone variations in cooling history resulted from differential uplift between fault bound blocks one block that containing the late cretaceous abu khruq complex was relatively stable and the different degrees of partial resetting recorded in apatites of this complex are attributed to the thermal effect of localised tertiary dyke intrusion fission track analysis in combination with geologic data indicates that in the south eastern desert of egypt a phase of uplift commenced in late oligocene time and was accompanied by paleogeothermal gradients of ca 40 50 c km uplift was more pronounced at least 2 2 5 km in areas within about 100 km from the present red sea coast this uplift which is viewed as part of a broader regional tectonism related to the opening of the red sea occurred along a northwest fracture pattern and was controlled by pre existing lines of weakness in the basement complex

geoarchaeology in a meandering river a study of the bk site 1 35 ma upper bed ii olduvai gorge tanzania abstract bk site hosts 8 archaeological levels preserved inside the channel of a meandering river this river is not found in a floodplain but encased in a wide karstified carbonate surface with no edaphic development the river at bk has been recurrently used by hominins for carcass processing in the river channel coinciding with a high concentration of vegetation and water resources along the channel banks the spatial distribution of the different archaeological levels is the result of a complex sedimentary record such complexity in meandering river deposits is due to processes such as erosion transport and sedimentation occurring simultaneously and coarse and very fine sediments being deposited at the same time throughout the same isochronal surface bk site offers a unique opportunity thanks to its abundance in archaeological remains and the quality of the outcrop to geoarchaeologically depict and describe an archaeological site in a meandering channel the geology of this fluvial environment is considered regarding a fluvial architecture b facies distribution and c fluvial dynamics furthermore the abundance of archaeological remains and megafauna found inside the channel at bk contrasts with the absence of any remains outside the channel we hypothesize that this area was preferred by hominins since it offers a high concentration of water resources and vegetation as well as a greater protection against predators than an open plain a detailed reconstruction of the paleolandscape will try to uncover the reason behind the huge contrast existing between the abundance of remains found inside and outside the channel leading to the interpretation that an ecological or landscape related factor is conditioning the location and formation of the archaeological assemblage

unmodified lithic material at olduvai bed i manuports or ecofacts the existence of high percentages of so called manuports in the olduvai sequence has given way to abundant papers on the behavioural explanation of such accumulations of raw material for this paper we performed a first hand re examination of the lithic collections of two of the most relevant sites in olduvai bed i flk zinj and flk north the analysis has unearthed extremely significant differences between the unmodified lithic material the so called manuports and the other stone collections which has demanded the search for alternative hypotheses to explain the presence of the supposed manuports at these sites thus we have revised the site formation processes and have compared them with other similar sedimentary contexts in olduvai and in nearby lacustrine basins on the basis of our findings we demonstrate the existence of different sized clasts in low energy contexts and propose a natural deposition as the answer to the existence of the supposed manuports at olduvai bed i in all our analysis suggests that a great part of the unmodified lithic material from the olduvai sites is not indicative of human action but the product of natural causes thus being ecofacts and not genuine manuports

gombore ii melka kunture ethiopia a new approach to formation processes and spatial patterns of an early pleistocene acheulean site abstract to assess the integrity of pleistocene archaeological sites is crucial in the analysis of human behaviour most of the early palaeolithic sites are in active fluvial environments where it is necessary to understand the degree of sedimentary disturbance the analysis of the formation processes through geoarchaeological and geostatistical techniques offers new tools to evaluate if the archaeological assemblage is in autochthonous or allochthonous position gombore ii 850 ka within the archaeological and paleontological complex of melka kunture ethiopia extends over estimated 1000 m2 and yielded a large number of acheulean artefacts fossil mammal bones and two fossil hominin remains the geomorphological setting and deposition patterns of high energy sedimentation in a fluvial channelized environment are similar to those of many other early palaeolithic african sites this is traditionally described as producing a disturbed record with the fortuitous association of faunal remains and lithic industry driven by fluvial processes to assess this hypothesis we analyse here the formation processes and the spatial patterning of the remains we apply geoarchaeological orientation and fabric and spatial tests density grouping k means to the mapped archaeological surfaces and to a present day fluvial surface we observe substantial differences in geoarchaeological features and spatial patterning between the archaeological record lithic materials and faunal remains and the natural clasts of both the archaeological deposit and the bed of the present day river this suggests different depositional processes or temporal events we conclude that the remains produced by the hominins did not haphazardly accumulate after extensive erosion and re sedimentation they rather preserve a reasonable degree of taphonomic and spatial integrity and are possibly representative of different activities

new archaeological and geological research at shk main site bed ii olduvai gorge tanzania abstract this work presents the new round of archaeological research undertaken in shk main site since 2009 through new geological correlations and dating within the bed ii sequence and a new stratigraphic description of the site new chronological and contextual information is provided for this site archaeo stratigraphic analysis of the vertical distribution of the archaeological aggregate a gis based restitution of the horizontal associations and a taphonomic interpretation of the formation processes allow a first intra site analysis of this high density anthropogenic patch within the paleo landscape of the olduvai basin

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

carbon nutrient and trace metal cycling in sandy sediments a comparison of high energy beaches and backbarrier tidal flats abstract in order to evaluate the importance of coastal sandy sediments and their contribution to carbon nutrient and metal cycling we investigated two beach sites on spiekeroog island southern north sea germany and a tidal flat margin located in spiekeroog s backbarrier area we also analyzed seawater and fresh groundwater on spiekeroog island to better define endmember concentrations which influence our study sites intertidal sandy flats and beaches are characterized by pore water advection seawater enters the sediment during flood and pore water drains out during ebb and at low tide this pore water circulation leads to continuous supply of fresh organic substrate to the sediments remineralization products of microbial degradation processes i e nutrients and dissolved trace metals from the reduction of particulate metal oxides are enriched in the pore water compared to open seawater concentrations the spatial distribution of dissolved organic carbon doc nutrients po43 no3 no2 nh4 si oh 4 and total alkalinity trace metals dissolved fe and mn as well as sulfate suggests that the exposed beach sites are subject to relatively fast pore water advection which leads to organic matter and oxygen replenishment frequent pore water exchange further leads to comparatively low nutrient concentrations sulfate reduction does not appear to play a major role during organic matter degradation high nitrate concentrations indicate that redox conditions are oxic within the duneward freshwater influenced section while ammonification denitrification manganese and iron reduction seem to prevail in the ammonium dominated seawater circulation zone in contrast the sheltered tidal flat margin site exhibits a different sedimentology coarser beach sands versus finer tidal flat sands and nutrients dissolved manganese and doc accumulate in the pore water ammonium is the dominant pore water nitrogen species and intense sulfate reduction leads to the formation of sulfide which precipitates dissolved iron as iron sulfide these findings are due to slower advective pore water exchange in the tidal flat sediments this study illustrates how different energy regimes affect biogeochemical cycling in intertidal permeable sediments

relation between continental rifting and uplifting evidence from the suez rift and northern red sea abstract the suez rift and the northern red sea are flanked by high standing shoulders with elevations often exceeding 2 km and with a structural relief reaching 4 5 km in this area pre rifting erosion was small not more than a few hundred meters there is no evidence that a precursory uplift formed along the site of future rifting uplifting and erosion began essentially at the same time as rift faulting and magmatism in late oligocene and early miocene limes in the gebel serbal area sinai where the uplifting history is resolved best the tectonic relief reached about 800 m by the end of the early miocene and a similar amount of tectonic uplifting developed in later times other parts of the rift shoulders probably had a similar uplifting history but the total uplifting was often less considerable erosion in places more than 3 km occurred mainly since middle miocene times and caused considerable isostatic rebound this magnified the uplifting and caused the structural and topographic relief to be considerably greater than the tectonic uplifting initial uplifting and contemporaneous magmatic activity were probably caused by rising of deep hot material which thinned the lithosphere and heated it such deep seated processes probably continued to operate also during the later stages of tectonic uplifting though igneous activity no longer occurred on the surface stretching of the lower lithosphere under the rift shoulders could have also contributed to their uplifting the features of uplifting history of the studied region may well be typical of other active rifts

224ra 228th disequilibrium in coastal sediments implications for solute transfer across the sediment water interface national basic research program 973 program of china 2009cb421203 natural science foundation of china nsfc 41076041 41276062 funds for creative research groups of the national natural science foundation of china 41121091

nutrient inputs to the coastal ocean from submarine groundwater discharge in a groundwater dominated system relation to land use kona coast hawaii u s a we evaluated the magnitude and composition in terms of salinity 223ra and 224ra activity and nutrient concentrations of submarine groundwater discharge sgd fluxes at 11 sites on the kona coast of hawaii discharging groundwater was typically brackish to saline and had high ra activity relative to ocean water and fresher inland groundwater brackish sgd fluxes estimated using a mass balance approach based on excess coastal ocean 224ra activity ranged from 3 to 1300 l m21 of coastline min21 fluxes of the freshwater component of sgd calculated based on salinity ranged from 2 to 310 l m21 min21 nutrient fluxes into coastal waters from sgd varied by up to three orders of magnitude among sites nitrate nitrite n n phosphate and silica concentrations showed strong inverse linear correlations with salinity in coastal seawater and groundwater these correlations were consistent with previous work that documented conservative mixing between fresh highnutrient groundwater and saline low nutrient seawater at a few coastal ocean sites we extend this conservative relationship to more coastal ocean sites and to groundwater in the coastal aquifer n n concentrations in the fresh component of discharging groundwater were higher at sites near golf courses and those with a greater percentage of bare land within a 5 km radius and silica concentrations in the fresh component of discharging groundwater were higher at sites with more bare land and lower population densities however neither urbanization nor agriculture was significantly correlated with groundwater nutrient concentrations on this relatively undeveloped coast

quantifying groundwater discharge from different sources into a mediterranean wetland by using 222rn and ra isotopes summary groundwater discharge constitutes the main water inflow of many coastal wetlands despite the potential of ra isotopes and 222rn as tracers of groundwater discharge the use of these radionuclides to quantify the groundwater inflow in coastal wetlands has been only scarcely addressed in the literature the main goal of this study is to evaluate the use of 222rn and ra isotopes to estimate the contribution of distinct groundwater sources into a mediterranean coastal wetland the peniscola marsh castello spain the peniscola marsh is a small shallow wetland nourished by groundwater coming from four different flowpaths i a deep flow from the regional carbonate aquifer of el maestrat ii a shallow flow and iii an intermediate flow both from the irta range and the detritic vinaros peniscola aquifer and iv seawater intrusion data on 226ra 222rn and salinity obtained in summer 2007 revealed that the deep groundwater contribution was 15 of the total water inflow whereas the shallow and intermediate flow paths represented 32 and 48 respectively seawater accounted only for the remaining 5 inputs to the wetland ra isotopes also allowed estimating the marsh water age in 1 2 days both the groundwater contributions derived from 222rn measurements and the ra derived marsh water age agreed well with the direct measurements obtained using propeller flow meters evidencing the effectiveness of the used methods an interannual comparison between the estimated groundwater inflow and the precipitation revealed that shallow groundwater flows respond to local precipitation whereas the deep groundwater flow from the carbonate aquifer is dominated by a constant baseflow

the gravity field of the red sea and east africa abstract reevaluation of all gravity data from the red sea the gulf of aden and east africa permitted the compilation of a new bouguer anomaly map the intensity of the gravity field and its regional pattern correlate closely with the topographic features of the region the maximum bouguer values 100 mgal are located over the median troughs of the red sea and gulf of aden dense juvenile oceanic crust in these rifts and intruding magmas in stretched continental areas produce excess mass responsible for the anomaly highs in the red sea the orientation of the gravity highs is nw se in the south turning to ne sw in the north almost parallel to the aqaba dead sea strike this pattern reveals that the present basin axis is not identical with that which formed the tertiary coastal margins and the pre red sea zones of crustal weakness in the gulf of aden new oceanic crust along the tadjura trench and its eastward extension is also expressed in the bouguer anomaly map by gravity highs and a sharp bending of the isolines a maximum of approx 150 mgal is located over the central section of the sheba ridge bouguer gravity values over the east african and yemen plateaus are of the order of 180 to 240 mgal indicating significant crustal thickening on the somali plateau the marda fault also has a strong gravity signature that can be traced towards somalia by constraining crustal thickness and structure with seismic data and density values from the velocity distribution by means of the nafe drake and birch relationships we computed density models for the crust and upper mantle the crustal thickness is of the order of 40 km beneath the plateaus and only 5 to 6 km at the oceanized parts in the central and southern portions of the red sea median trough the flanks of the southern red sea and the corresponding arabian side are underlain by 12 to 16 km thick stretched continental type crust oceanization offshore sudan and egypt is asymmetrical the continental crust terminates abruptly at about 20 km off the coastline followed by an oceanic crust of early miocene age that was produced in pull apart basins by contrast the eastern side of the red sea trough offshore saudi arabia is floored by stretched continental crust that extends far into the sea seafloor spreading and the generation of oceanic crust in organized spreading centres are limited to the median troughs off sudan and the northern part of ethiopia and commenced approx 5 m y bp they are absent in the northern red sea where crustal fracturing occurs only in pull apart basins of dead sea aqaba orientation distributed in en echelon pattern

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter

driving mechanisms for groundwater flow and salt transport in a subterranean estuary this paper presents field measurements and numerical simulations of groundwater dynamics in the intertidal zone of a sandy meso tidal beach the study focusing on vertical hydraulic gradients and pore water salinities reveals that tides and waves provide important forcing mechanisms for flow and salt transport in the nearshore aquifer such forcing interacting with the beach morphology enhances the exchange between the aquifer and ocean the spatial and temporal variations of vertical hydraulic gradients demonstrate the complexity and dynamic nature of the processes and the extent of mixing between fresh groundwater and seawater in a subterranean estuary these results provide evidence of a potentially important reaction zone in the nearshore aquifer driven by oceanic oscillations land derived contaminants may undergo important biogeochemical transformations in this zone prior to discharge