saharan wind regimes traced by the sr nd isotopic composition of subtropical atlantic sediments last glacial maximum vs today new nd sr isotopic data on the 30 m lithic particles of surface and last glacial maximum sediments recovered along the african margin between the equator and the gibraltar strait are presented in combination with grain size measurements this 30 m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions in the eolian fraction both sr and nd isotopic tracers reveal the same major northwestern origin mauritania mali southern algeria and morocco the archaean formations of the western saharan shield could be the source of the very unradiogenic ratios observed here the more southern regions senegal guinea act only as secondary sources a similar pattern is observed for the lgm lithic particles are mostly transported by both trade and saharan air layer sal winds along an approximate ne sw axis this main feature matches the southern plume characterizing the dust transport observed during winter no significant latitudinal shift of the belt winds is observed between the lgm and today at the lgm however dust fluxes were 2 4 times higher than today leading to a more archaean type imprint in the deposits we do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the lgm and the location of the major wind systems both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical africa during the last glacial period

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

new insights on 3 d plates interaction near taiwan from tomography and tectonic implications abstract recent tomographic results are used to trace the south china sea and philippine sea subducting slabs south and northeast of taiwan along the manila and ryukyu trenches respectively in particular the 3 d plates interaction beneath taiwan is discussed based on a close up view of the tomographic sections together with earthquake hypocenters distribution our study indicates that 1 the east dipping south china sea slab can be followed to the north up to the latitude of hualien 2 the eurasian plate subducts beneath most part of the taiwan island down to the 670 km depth discontinuity 3 the north dipping philippine sea slab can be followed slightly west of the longitude of hualien both plates thus interact beneath northern taiwan where the arc continent collision is paroxysmal 4 slab detachment is envisaged at the northern edge of the subducted eurasian plate beneath the coastal range of taiwan which may facilitate the northwestward motion of the philippine sea plate with respect to eurasia slabs geometries obtained from tomographic sections allow us to reconstruct the late neogene plate kinematics and dynamics in this region our main conclusions are 1 the size of the original south china sea was about twice its present size 2 the subducted part of the west philippine basin i e the largest oceanic basin of the philippine sea plate extends only 400 km north of the ryukyu trench 3 slab detachment might have occurred 3 5 my ago beneath the central and northern ryukyu arc along a weak zone that is aligned with the gagua ridge an ancient plate boundary 4 the ryukyu trench has propagated westward from 126 e of longitude southeast of miyako island to the locus of the present arc continent collision along a major lithospheric tear that cut through the continent ocean boundary first and then through the continental lithosphere as a consequence the southern ryukyu margin developed progressively from east to west as a subduction zone during the last 8 my it has been elaborated onto a passive margin which corresponded to the edge of the eurasian continental shelf bordering the south china sea prior to pliocene 5 the southern okinawa trough rifted during the last 2 1 ma following the propagation of the subduction zone 6 subduction of the eurasian margin probably stopped recently beneath northern taiwan and a flip of subduction from west to east is being initiated near hualien

petrology of basaltic sills from ocean drilling program sites 794 and 797 in the yamato basin of the japan sea the basement rocks drilled at ocean drilling program sites 794 and 797 in the yamato basin of the japan sea are composed dominantly of aphyric plagioclase phyric and olivine and plagioclase phyric tholeiitic sills intruded into wet sediments the rocks can be divided into an incompatible element depleted type and an enriched type based on their mineral and bulk rock compositions site 794 drilled an upper suite of dominating aphyric enriched basaltic sills the upper part of which contains relatively calcic plagioclase phenocrysts an85 90 and the lower part of which contains occasionally olivine phenocrysts a lower suite at site 794 is composed of dominating aphyric depleted sills with plagioclase and olivine microphenocrysts occasionally in chilled margins site 797 recovered an upper suite of sparsely plagioclase and olivine phyric to aphyric depleted sills and a lower suite of sparsely plagioclase phyric and aphyric enriched sills the groundmass phases of all suites suggest a systematic enrichment in feo tio2 na2o and k2o during solidification in addition there is evidence that olivine ceases to crystallize approximately when augite appears during groundmass crystallization irrespective of the enriched versus the depleted magma type the rock compositions reveal two contrasting evolution trends which can be related to fractionation processes in crustal magma chambers a tholeiitic evolution trend with increasing feo and tio2 and decreasing al2o3 can be modelled by fractional crystallization of 40 to 50 plagioclase olivine and augite a mildly calc alkalic evolution trend with decreasing feo increasing al2o3 and nearly constant tio2 can be modelled by 8 to 12 olivine fractionation one atmosphere anhydrous melting experiments on a basalt from hole 797c produced liquid compositions very similar to the basalts that exhibit the feo enrichment trend there is mineralogical evidence that the contrasting trends may be related to the effect of small amounts of water during crystallization relatively high water activity will suppress plagioclase crystallization and thus produce the iron depletion trend while nearly anhydrous crystallization involves the early appearance of plagioclase which is responsible for the iron enrichment trend the tholeiitic suites occur in lower parts of the drill cores while the calcalkalic suites occur in the upper parts this suggests a magmatic and tectonic evolution of the japan sea perhaps reflecting a transition between calc alkalic magmatism related to subduction zone activity and tholeiitic magmatism related to back arc spreading furthermore any model must be able to account for the range in parental magmas from depleted to enriched types throughout the magmatic history of the yamato basin

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

palaeoclimate in the saharan and arabian deserts during the middle palaeolithic and the potential for hominin dispersals to disperse out of sub saharan africa it was necessary for hominins to cross the deserts of either the sahara and or arabia thus understanding the palaeoclimate of the saharo arabian region is central to determining the role these deserts played in the peopling of the planet when did they act as barriers and when were they more humid opening dispersal routes across them to address these questions we have conducted a temporal and spatial evaluation of dated sites from 20 to 350 ka using combined probability density function pdf and geographical information system gis analyses of all sites dated using uranium thorium u th or optically stimulated luminescence osl methods radiocarbon dates were not considered because of contamination problems in this time range the results show that during mis 2 there is little evidence for humidity in arabia as would be expected during the height of the last glacial maximum however the sahara shows a sharp rise in probability at the beginning of mis 2 peaking near the boundary with mis 3 at 29 ka there appear to be brief periods of humidity in mis 3 and 6 though at different times in the sahara ca 37 44 138 154 and 180 ka and arabia ca 40 54 and 163 ka during mis 5 both regions show much evidence for humidity with pdf peaks corresponding to insolation maxima though not all maxima are represented in either the saharan or arabian record this situation can be explained by eccentricity modulated precession when eccentricity is strong insolation is enhanced but also more variable and the desert climate is generally more humid particularly at times of high insolation the opposite happens when eccentricity is low and deserts tend to be more arid but local factors exert more of an influence on climate affecting the timing and strength of the brief humid periods experienced so that they no longer coincide with insolation maxima the spatial distribution of humid sites is compatible with a number of different modern human dispersal theories southern arabia experienced humid periods centred on 54 ka and 125 ka and this could have facilitated dispersal from east africa to southern arabia and beyond via the bab el mandab the sahara shows considerable evidence for humidity during mis 5 and may have had dispersal across its expanse at this time

african monsoon variability during the previous interglacial maximum abstract little is known about centennial to millennial scale climate variability during interglacial times other than the holocene we here present high resolution evidence from anoxic unbioturbated sediments in the eastern mediterranean sea that demonstrates a sustained 800 yr climate disturbance in the monsoonal latitudes during the eemian interglacial maximum 125 ka bp results imply that before and after this event the intertropical convergence zone itcz penetrated sufficiently beyond the central saharan watershed 21 n during the summer monsoon to fuel flooding into the mediterranean along the wider north african margin through fossil river wadi systems that to date have been considered only within a holocene context relaxation in the itcz penetration during the intra eemian event curtailed this flux but flow from the nile with its vast catchment area was not affected previous work suggests a concomitant eurasian cooling event with intensified impact of the higher latitude climate on the mediterranean basin the combined signals are very similar to those described for the holocene cooling event around 8 ka bp the apparent type of concurrent changes in the monsoon and higher latitude climate may reflect a fundamental mechanism for variability in the transfer of energy latent heat between the tropics and higher latitudes

re entering the central sahara at the onset of the holocene a territorial approach to early acacus hunter gatherers sw libya abstract the central sahara was intensely occupied at the very onset of the holocene when moister conditions re established after the younger dryas in the study area sw libya a solid 14c chronology dates the occupation of early acacus h g between 9800 and 8900 bp it is likely that the colonization by these small groups of specialized hunter gatherers was rapid entering unfamiliar areas characterized by the presence of lakes and ponds whether or not the very first re entry was a uniquely holocene phenomenon is still debated we favour an arrival from the north considering current palaeoenvironmental archaeological and possibly genetic evidences the archaeological record consists of around ninety sites surface occurrences and a few excavated sequences standing as regional and supra regional references sites are located on different geomorphological contexts and are task specifically organized subsistence relied on specialized hunting of barbary sheep and on some vegetal species the provenance and circulation of lithic raw materials reveals a high mobility at a regional but also at a wider scale tool kits are light bladelet based curated and dominated by backed armatures early acacus occupation reveals strong differences compared to the subsequent late acacus phase 8900 7400 bp when a profound reorganization in the subsistence settlement system featuring an increase in the delayed use of resources i e corralling of barbary sheep and storage of wild cereals occurred in this work we present an overview of the early acacus archaeological data with an emphasis on the territorial analysis of lithic assemblages

the 1909 taipei earthquake implication for seismic hazard in taipei the 1909 april 14 taiwan earthquake caused significant damage in taipei most of the information on this earthquake available until now is from the written reports on its macro seismic effects and from seismic station bulletins in view of the importance of this event for assessing the shaking hazard in the present day taipei we collected historical seismograms and station bulletins of this event and investigated them in conjunction with other seismological data we compared the observed seismograms with those from recent earthquakes in similar tectonic environments to characterize the 1909 earthquake despite the inevitably large uncertainties associated with old data we conclude that the 1909 taipei earthquake is a relatively deep 50 100 km intraplate earthquake that occurred within the subducting philippine sea plate beneath taipei with an estimated m w of 7 0 3 some intraplate events elsewhere in the world are enriched in high frequency energy and the resulting ground motions can be very strong thus despite its relatively large depth and a moderately large magnitude it would be prudent to review the safety of the existing structures in taipei against large intraplate earthquakes like the 1909 taipei earthquake

a 25 000 year record of climate induced changes in lowland vegetation of eastern equatorial africa revealed by the stable carbon isotopic composition of fossil plant leaf waxes the debate of climate versus co2 in controlling the long term dynamics of tropical african vegetation has focused on events at the upper tree line since the relevant paleodata tend to be from mid elevation sites 2000 3000 m less well known is the relative importance of co2 in regulating the dynamics of tropical lowland 1500 m vegetation particularly that of the dry open woodlands bush and grasslands covering much of eastern equatorial africa here we examine the stable carbon isotopic composition of n alkanes in the sediment record of lake challa a lowland crater lake near mt kilimanjaro covering the last 25 000 years the distributions of the n alkanes with dominance of the long chain odd carbon numbered components and their isotopic composition reveal a mixed origin the c23 and c25 n alkanes are depleted in 13c with 13c values between 30 and 50 in shallow lakes these n alkanes are thought to derive from non emergent aquatic plants but this is unlikely in this steep sided crater lake as it lacks a significant littoral habitat the c27 n alkanes are predominantly derived from leaf wax lipids of terrestrial plants brought into the lake predominantly by local soil run off their 13c values in particular that of the n c31 alkane reveal a marked transition in local lowland vegetation from being dominated 70 100 by c4 plants during the glacial period until 16 5 cal kyr bp to a more mixed c3 c4 composition 30 60 c4 during the holocene the start of the late glacial trend towards a greater proportion of c3 plants coincided with the start of increasing monsoon rainfall 1500 years after the onset of the rise in atmospheric co2 and 3500 years after the onset of post glacial warming the transition was interrupted during the dry younger dryas period 13 0 11 7 cal kyr bp when c4 plants again became much more prevalent almost reaching their glacial period abundance notably the principal trend in leaf wax 13c values infers c4 dominance during both wet and dry phases of the glacial period and a mixed c3 c4 vegetation during both wet and dry phases of the holocene our results indicate that long term variation in pco2 exerted important control on the composition of drought adapted savanna vegetation in this currently semi arid lowland region of equatorial east africa

mapping of c4 plant input from north west africa into north east atlantic sediments abstract mapping the abundance of 13c in leaf wax components in surface sediments recovered from the seafloor off northwest africa 0 35 n reveals a clear pattern of 13c distribution indicating systematic changes in the proportions of terrestrial c3 and c4 plant input at 20 n latitude we find that isotopically enriched products characteristic of c4 plants account for more than 50 of the terrigenous inputs this signal extends westward beneath the path of the dust laden sahara air layer sal high c4 contributions apparently carried by january trade winds also extend far into the gulf of guinea similar distributions are obtained if summed pollen counts for the chenopodiaceae amaranthaceae and the poaceae are used as an independent c4 proxy we conclude that the specificity of the latitudinal distribution of vegetation in north west africa and the pathways of the wind systems trade winds and sal are responsible for the observed isotopic patterns observed in the surface sediments molecular isotopic maps on the marine sedimentary time horizons e g during the last glacial maximum are thus a robust tool for assessing the phytogeographic changes on the tropical and sub tropical continents which have important implications for the changes in climatic and atmospheric conditions

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

middle stone age human occupation and dispersals in the messak plateau sw libya central sahara abstract research conducted since the 1990s in sw libya has provided wide ranging data on the pleistocene archaeology of this vast region which principally relies on surface scatters of lithic artefacts a series of soundings and two msa aterian dated sites the middle stone age of the region is thought to date from roughly mis 6 5 to approximately 60 ka the latest dated aterian occurrence its distribution varies from sand seas to mountain ranges with different states of preservation and archaeological visibility this paper presents data from the last surveys 2010 2011 carried out on 46 transects across the messak massif one component of the research strategy was specifically designed to handle the impressive pleistocene record through sampling a series of spots placed at fixed distances along predetermined survey strips field documentation of the techno typological traits allowed the creation of a territorial data set used to infer patterns of raw material exploitation technological variability and the significance of the principal chrono cultural markers quartzarenite the most available and used raw material is a diffusely distributed resource this should have played a role in patterns of land use and mobility and ultimately in the composition of archaeological assemblages mostly characterised by complete reduction sequences variability in the application of the levallois method highlights widespread adoption of recurrent and lineal schemes among the latter point production is extremely rare the retouched blanks inventory is dominated by scrapers and notches whereas more specialised tool classes i e tanged pieces points foliates are less common the dimensions of a small sample of aterian artefacts provisionally signal a higher degree of homogeneity among pointed tanged specimens than other types despite the overwhelming presence of roughly labelled msa contexts these show little evidence of a msa stricto sensu chrono cultural signature among which scanty but precise elements are comparable with the sub saharan and nile valley early middle stone age reinforcing the picture of multiple dispersals across the sahara and north africa around mis 6 5 the evolution of msa occupation and its cultural trajectories is difficult to assess while the last phases represented here by the aterian can be framed in hyperarid mis 4 after the dates from acacus and likely represent the adaptation of residual groups almost confined to mountain environments

a middle late pleistocene palustrine lacustrine travertine system borj edouane unit nw tunisia sedimentology stable isotopes and palaeohydrological implications the carbonate borj edouane unit represents the northernmost documented middle late pleistocene continental carbonate deposits in tunisia the unit consists of two main facies associations asymmetrically distributed 1 calcrete palustrine laminar crust 2 microbialites the first accumulated carbonate formed in the distal zone of alluvial fans calcretes and in shallow lakes subjected to periodic exposure palustrine facies that occupied the westernmost strip of the basin the second association formed in permanent lakes stromatolites oncoids and planar stromatolites located in the central areas of the basin fed by springs associated with a concentration of vertical faults in the eastern area of the basin travertine facies at time of deposition these facies communicated with the lake via a transitional lacustrine travertine environment transitional travertine stromatolite facies all facies show a restricted range of 18o values around 5 8 0 5 suggesting formation from paleoprecipitation largely of atlantic derivation brought about by westerly winds as for the 13c values these show a wide range 6 4 to 11 7 overall relatively high values for all facies with the lower values corresponding to the calcrete palustrine association and the higher ones linked to the microbialite facies the trend in travertines probably mimics an increasing influence of carbon derived from dissolution of carbonate bedrock of the cretaceous substrate while that of palustrine samples records increasing respired c contribution the sedimentological and isotopic characteristics of the borj edouane unit reflect wetter conditions at the time of deposition and point to a humid period at the middle late pleistocene transition

estimating the hydrogen isotopic composition of past precipitation using leaf waxes from western africa abstract the hydrogen isotopic composition of plant leaf wax n alkanes d wax is a novel proxy for estimating d of past precipitation d p however vegetation life form and relative humidity exert secondary effects on d wax preventing quantitative estimates of past d p here we present an approach for removing the effect of vegetation type and relative humidity from d wax and thus for directly estimating past d p we test this approach on modern day late holocene 0 3 ka sediments from a transect of 9 marine cores spanning 21 n 23 s off the western coast of africa we estimate vegetation type c 3 tree versus c 4 grass using 13 c of leaf wax n alkanes and correct d wax for vegetation type with previously derived apparent fractionation factors for each vegetation type late holocene vegetation corrected d wax d vc displays a good fit with modern day d p suggesting that the effects of vegetation type and relative humidity have both been removed and thus that d vc is a good estimate of d p we find that the magnitude of the effect of c 3 tree c 4 grass changes on d wax is small compared to d p changes we go on to estimate d vc for the mid holocene 6 8 ka the last glacial maximum lgm 19 23 ka and heinrich stadial 1 hs1 16 18 5 ka in terms of past hydrological changes our leaf wax based estimates of d p mostly reflect changes in wet season intensity which is complementary to estimates of wet season length based on leaf wax 13 c

delayed fractionation of basaltic lavas the phenocryst cores of the basaltic lavas from jan mayen and hawaii display a range in compositions the textural features of the phenocrysts also vary both euhedral and skeletal phenocrysts are present in the same thin section apparently the basaltic magmas underwent crystallization within a temperature interval of 50 200 c before they became fractionated the fractionates of basaltic lavas are therefore average compositions of the phenocryst assemblages rather than liquidus compositions this type of fractionation is called delayed fractionation it is considered that most tholeiitic and alkalic basaltic lavas undergo delayed fractionation

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

holocene rock varnish on the messak plateau libyan sahara chronology of weathering processes abstract rock varnish coats subaerially exposed rock surfaces on the messak settafet plateau se libya central sahara holocene surfaces host three microlayers formed by different accretion processes that record a climatic transition from a wet environment to progressively more arid conditions sem eds and optical investigations shed light on the processes leading to the formation of microlaminae while direct ams 14c dating on microlayers and relative radiocarbon dating on dark varnished pastoral neolithic stone monuments suggest a reliable chronology for varnish development the innermost microlayer includes illuvial clay and calcite incorporated during the early to middle holocene 9200 to 5500 uncal ybp under wet environmental conditions the second microlayer is more typical mn rich rock varnish biomineralized during a phase of growing aridity in the middle holocene 6000 to 4000 uncal ybp the upper microlayer is composed of mostly aeolian dust and it dates back to the last hyperarid millennia a positive correlation between varnish chronological development and climate changes in the sahara reflects also broad regional control on microlamination deposition

osl dating of the aterian levels at dar es soltan i rabat morocco and implications for the dispersal of modern homo sapiens the aterian is a distinctive middle palaeolithic industry which is very widely spread across north africa its dating and significance have been debated for nearly a century renewed interest in the aterian has arisen because of a recent proposal that its development and spread may be linked to the dispersal of anatomically modern humans the industry contains technological innovations such as thin bifacially flaked lithic points and pedunculates as well as evidence for personal ornaments and use of red ochre such markers as shell beads are believed to be indicative of symbolic behaviour dar es soltan i on the atlantic coast of morocco contains a thick sequence of aterian deposits that were thought to represent the later stages of development of this industry new optically stimulated luminescence dates and geomorphological study indicate a much older sequence and so far the earliest yet recorded ages for the aterian they suggest an appearance in the maghreb region during mis marine isotope stage 5

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

3d numerical modeling of mantle flow crustal dynamics and magma genesis associated with slab roll back and tearing the eastern mediterranean case interactions between subduction dynamics and magma genesis have been intensely investigated resulting in several conceptual models derived from geological geochemical and geophysical data to provide physico chemical constraints on these conceptual models self consistent numerical simulations containing testable thermo mechanical parameters are required especially considering the three dimensional 3d natural complexity of subduction systems here we use a 3d high resolution petrological and thermo mechanical numerical model to quantify the relative contribution of oceanic and continental subduction collision slab roll back and tearing to magma genesis and transport processes our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3d slab dynamics and related asthenospheric flow moreover the decrease of the bulk lithospheric strength induced by mantle and crust derived magmas promotes the propagation of strike slip and extensional fault zones through the overriding crust as response to slab roll back and continental collision reduction of the lithosphere asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust similarities between our modeling results and the late cenozoic tectonic and magmatic evolution across the eastern mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region which in turn promotes lithospheric deformation by mantle drag via melt induced weakening effects

palaeohydrology of the fazzan basin and surrounding regions the last 7 million years abstract we have integrated information on topography geology and geomorphology with the results of targeted fieldwork in order to develop a chronology for the development of lake megafazzan a giant lake that has periodically existed in the fazzan basin since the late miocene the development of the basin can be best understood by considering the main geological and geomorphological events that occurred thought libya during this period and thus an overview of the palaeohydrology of all libya is also presented the origin of the fazzan basin appears to lie in the late miocene at this time libya was dominated by two large rivers systems that flowed into the mediterranean sea the sahabi river draining central and eastern libya and the wadi nashu river draining much of western libya as the miocene progressed the region become increasingly affected by volcanic activity on its northern and eastern margin that appears to have blocked the river nashu in late miocene or early messinian times forming a sizeable closed basin in the fazzan within which proto lake megafazzan would have developed during humid periods the fall in base level associated with the messinian desiccation of the mediterranean sea promoted down cutting and extension of river systems throughout much of libya to the south of the proto fazzan basin the sahabi river tributary know as wadi barjuj appears to have expanded its headwaters westwards the channel now terminates at al haruj al aswad we interpret this as a suggestion that wadi barjuj was blocked by the progressive development of al haruj al aswad k ar dating of lava flows suggests that this occurred between 4 and 2 ma this event would have increased the size of the closed basin in the fazzan by about half producing a catchment close to its current size 350 000 km2 the fazzan basin contains a wealth of pleistocene to recent palaeolake sediment outcrops and shorelines dating of these features demonstrates evidence of lacustrine conditions during numerous interglacials spanning a period greater than 420 ka the middle to late pleistocene interglacials were humid enough to produce a giant lake of about 135 000 km2 that we have called lake megafazzan later lake phases were smaller the interglacials less humid developing lakes of a few thousand square kilometres in parallel with these palaeohydrological developments in the fazzan basin change was occurring in other parts of libya the lower pliocene sea level rise caused sediments to infill much of the messinian channel system as this was occurring subsidence in the al kufrah basin caused expansion of the al kufrah river system at the expense of the river sahabi by the pleistocene the al kufrah river dominated the palaeohydrology of eastern libya and had developed a very large inland delta in its northern reaches that exhibited a complex distributary channel network which at times fed substantial lakes in the sirt basin at this time libya was a veritable lake district during humid periods with about 10 of the country underwater

petrology of lavas from the puu oo eruption of kilauea volcano iii the kupaianaha episode 1986 1992 the puu oo eruption has been remarkable in the historical record of kilauea volcano for its duration over 13 years volume 1 km3 and compositional variation 5 7 10 wt mgo during the summer of 1986 the main vent for lava production moved 3 km down the east rift zone and the eruption style changed from episodic geyser like fountaining at puu oo to virtually continuous relatively quiescent effusion at the kupaianaha vent this paper examines this next chapter in the puu oo eruption episodes 48 and 49 and presents new icp ms trace element and pb sr and nd isotope data for the entire eruption 1983 1994 nearly aphyric to weakly olivine phyric lavas were erupted during episodes 48 and 49 the variation in mgo content of kupaianaha lavas erupted before 1990 correlates with changes in tilt at the summit of kilauea both of which probably were controlled by variations in kilauea s magma supply rate these lavas contain euhedral olivines which generally are in equilibrium with whole rock compositions although some of the more mafic lavas which erupted during 1990 a period of frequent pauses in the eruption accumulated 2 4 vol olivine the highest forsterite content of olivines 85 in kupaianaha lavas indicates that the parental magmas for these lavas had mgo contents of 10 wt which equals the highest observed value for lavas during this eruption the composition of the puu oo lavas has progressively changed during the eruption since early 1985 episode 30 when mixing between an evolved rift zone magma and a more mafic summit reservoir derived magma ended the normalized to 10 wt mgo abundances of highly incompatible elements and cao have systematically decreased with time whereas ratios of these trace elements and pb sr and nd isotopes and the abundances of y and yb have remained relatively unchanged these results indicate that the hawaiian plume source for puu oo magmas must be relatively homogeneous on a scale of 10 20 km3 assuming 5 10 partial melting and that localized melting within the plume has apparently progressively depleted its incompatible elements and clinopyroxene component as the eruption continued the rate of variation of highly incompatible elements in puu oo lavas is much greater than that observed for kilauea historical summit lavas e g ba y 0 09 a 1 vs 0 03 a 1 this rapid change indicates that puu oo magmas did not mix thoroughly with magma in the summit reservoir thus except for variable amounts of olivine fractionation the geochemical variation in these lavas is predominantly controlled by mantle processes

wet phases in the sahara sahel region and human migration patterns in north africa the carbon isotopic composition of individual plant leaf waxes a proxy for c3 vs c4 vegetation in a marine sediment core collected from beneath the plume of sahara derived dust in northwest africa reveals three periods during the past 192 000 years when the central sahara sahel contained c3 plants likely trees indicating substantially wetter conditions than at present our data suggest that variability in the strength of atlantic meridional overturning circulation amoc is a main control on vegetation distribution in central north africa and we note expansions of c3 vegetation during the african humid period early holocene and within marine isotope stage mis 3 50 45 ka and mis 5 120 110 ka the wet periods within mis 3 and 5 coincide with major human migration events out of sub saharan africa our results thus suggest that changes in amoc influenced north african climate and at times contributed to amenable conditions in the central sahara sahel allowing humans to cross this otherwise inhospitable region

hydroclimate variability in the nile river basin during the past 28 000 years it has long been known that extreme changes in north african hydroclimate occurred during the late pleistocene yet many discrepancies exist between sites regarding the timing duration and abruptness of events such as heinrich stadial hs 1 and the african humid period ahp the hydroclimate history of the nile river is of particular interest due to its lengthy human occupation history yet there are presently few continuous archives from the nile river corridor and pre holocene studies are rare here we present new organic and inorganic geochemical records of nile basin hydroclimate from an eastern mediterranean em sea sediment core spanning the past 28 ka bp our multi proxy records reflect the fluctuating inputs of blue nile versus white nile material to the em sea in response to gradual changes in local insolation and also capture abrupt hydroclimate events driven by remote climate forcings such as hs1 we find strong evidence for extreme aridity within the nile basin evolving in two distinct phases during hs1 from 17 5 to 16 ka bp and from 16 to 14 5 ka bp whereas peak wet conditions during the ahp are observed from 9 to 7 ka bp we find that zonal movements of the congo air boundary cab and associated shifts in the dominant moisture source atlantic versus indian ocean moisture to the nile basin likely contributed to abrupt hydroclimate variability in northern east africa during hs1 and the ahp as well as to non linear behavior of hydroclimate proxies we note that different proxies show variable gradual and abrupt responses to individual hydroclimate events and thus might have different inherent sensitivities which may be a factor contributing to the controversy surrounding the abruptness of past events such as the ahp during the late pleistocene the nile basin experienced extreme hydroclimate fluctuations which presumably impacted paleolithic cultures residing along the nile corridor

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

contrasting compositions of saharan dust in the eastern atlantic ocean during the last deglaciation and african humid period abstract during the african humid period ahp much of the modern hyperarid saharan desert was vegetated and covered with numerous lakes in marine sediments off northwestern africa the ahp is represented by markedly reduced siliciclastic sediment flux between 12 3 and 5 5 ka changes in the origin of this terrigenous sediment fraction can be constrained by sediment chemistry and radiogenic isotope tracers at ocean drilling program odp site 658 hole c 20 44 95 n 18 34 85 w 2263 mbsl the neodymium nd isotope composition of terrigenous detritus shows little variability throughout the last 25 kyr indicating that the contributing geological terranes have not changed appreciably since the last glacial period in contrast there were large and abrupt changes in strontium sr isotope ratios and chemical compositions associated with the ahp during which 87 sr 86 sr ratios were markedly less radiogenic and sediments show higher chemical indices of alteration we show that sediment geochemical changes during the ahp cannot be attributed to changes in the source terranes physical sorting or intensity of chemical weathering the low 87 sr 86 sr and high sr concentrations of ahp age samples also conflict with the interpretation of increased fine grained fluvially derived sediments we propose that the most significant compositional changes at odp 658c are due to the addition of an aluminosilicate component that has a highly altered major element signature but is enriched in soluble elements like sr and magnesium mg compared to aluminum al and has low 87 sr 86 sr relative to local terrigenous source areas we interpret these characteristics to reflect authigenic sediment supply from extensive north african paleolake basins that were prevalent during the ahp

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

micromorphological approach to polycyclic pedogenesis on the messak settafet plateau central sahara formative processes and palaeoenvironmental significance the messak settafet is a wide plateau located in the libyan central sahara sw fezzan it is cut into the nubian sandstone and interpreted as relic of a tertiary peneplain heavily affected by aeolian deflation notwithstanding degradation phenomena discontinuous thin soil bodies are locally preserved below the hamada several profiles located in correspondence of different geomorphological units the hamada the endorheic depressions and the southern escarpment were described and sampled for micropedological analyses micromorphology outlined that the main characteristics of the residual b horizons from each geomorphological units are i high concentration of ferruginous nodules ii multiple generations of clay illuviation iii fragmentation and deformation of textural pedofeatures and iv calcite mobilization and redeposition according to horizon macro and micromorphological characteristics these pedologic bodies do not seem to be in equilibrium with the present day climatic conditions and should be regarded as paleosols generated by processes regulated by large water availability and warm temperature such as rubification clay translocation and calcite redistribution the development of horizons acted mainly since the early middle pleistocene during subsequent pluvial periods and was interrupted by several erosional and aeolian input phases arid periods pedological processes ended at the onset of the severe dry environmental conditions at the mid late holocene transition the development of this kind of paleosols in the central sahara is also discussed in comparison with pedogenetic processes occurring in temperate regions during interglacial and interstadial intervals

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

response of global deep water circulation to earth s climatic change 135 000 107 000 years ago the response of deep ocean circulation to major climatic events of the past 135 000 years is inferred using carbon 13 analyses of benthic foraminifera from the major ocean basins the results demonstrate that the circulation of the world ocean deep water is very sensitive to climate and that it changes drastically during climatic transitions

stratigraphic placement and age of modern humans from kibish ethiopia in 1967 the kibish formation in southern ethiopia yielded hominid cranial remains identified as early anatomically modern humans assigned to homo sapiens however the provenance and age of the fossils have been much debated here we confirm that the omo i and omo ii hominid fossils are from similar stratigraphic levels in member i of the kibish formation despite the view that omo i is more modern in appearance than omo ii 40ar 39ar ages on feldspar crystals from pumice clasts within a tuff in member i below the hominid levels place an older limit of 198 14 kyr weighted mean age 196 2 kyr on the hominids a younger age limit of 104 7 kyr is provided by feldspars from pumice clasts in a member iii tuff geological evidence indicates rapid deposition of each member of the kibish formation isotopic ages on the kibish formation correspond to ages of mediterranean sapropels which reflect increased flow of the nile river and necessarily increased flow of the omo river thus the 40ar 39ar age measurements together with the sapropel correlations indicate that the hominid fossils have an age close to the older limit our preferred estimate of the age of the kibish hominids is 195 5 kyr making them the earliest well dated anatomically modern humans yet described

the generation and shape of feeder dykes from mantle sources the criterion for fracture propagation suggests that the primary magma generated in the mantle ascends in a stepwise fashion initially a pulse of magma forms a dyke above the mantle source and ascends for some distance whereafter it stops a subsequent pulse of magma joins the first one and the ascent of the accumulating body of magma continues for some distance each time a new pulse of magma reaches the body of magma situated in the top of the dyke in this manner a dyke is formed that may extend either partly or the whole way from the mantle source to the surface this model may explain the large pressures up to 2000 bars that prevail during basaltic eruptions the calculated shape of the ascending pulses of magma suggests that their heights and widths are similar

155 000 years of west african monsoon and ocean thermal evolution a detailed reconstruction of west african monsoon hydrology over the past 155 000 years suggests a close linkage to northern high latitude climate oscillations ba ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the gulf of guinea in the eastern equatorial atlantic eea reveal centennial scale variations of riverine freshwater input that are synchronous with northern high latitude stadials and interstadials of the penultimate interglacial and the last deglaciation eea mg ca based sea surface temperatures ssts were decoupled from northern high latitude millennial scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low latitude solar insolation the onset of enhanced monsoon precipitation lags behind the changes in eea ssts by up to 7000 years during glacial interglacial transitions this study demonstrates that the stadial interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the west african monsoon dynamics through an atmospheric linkage

tectonic analysis and the evolution of a curved collision belt the hsuehshan range northern taiwan abstract detailed studies of fracture patterns and paleostress reconstructions based on analyses of fault slip data sets allow identification of four main patterns of compressional paleostress orientations in the cenozoic rocks of northern taiwan these patterns correspond to five successive tectonic events dominated by 1 n s 2 wsw ene 3 wnw ese 4 nw se and 5 wnw ese directions of compression the first two events are characterized by relatively minor structures in the foreland fold and thrust belt the first event probably reflects major left lateral shear along nne ssw trends which occurred in the adjacent eastern metamorphic belt during the middle late miocene these first two events do not affect the plio pleistocene in the localities studied in contrast the last three events created the major compressional structures of the foreland belt during the plio pleistocene collision in taiwan preliminary studies suggest that the magnetic fabric of the rocks has been significantly influenced by compressional deformation along wnw ese and nw se trends especially in the slate belt thus confirming the importance of these last three events on the basis of paleomagnetic work in progress the northernmost segment of the taiwan belt has been affected by a clockwise rotation of about 20 taking into account the distribution of successive compressional paleostress patterns we conclude that of the 55 angle of the sharply curved belt of northern taiwan about 20 probably correspond to actual clockwise rotation during the plio pleistocene whereas the remaining 35 reflect the initial shape of the curved plio quaternary belt the paleostress history of northern taiwan is examined in terms of geodynamic evolution and kinematic reconstructions the plio quaternary development of the collision between the luzon arc and eurasia followed a late miocene predominantly transform motion from south to north of the philippine sea plate relative to eurasia the succession of plio pleistocene paleostress patterns in northern taiwan is found to be consistent with the longitudinal shift from northeast to southwest and the transverse migration from the inner to the outer zones of compressional phenomena related to the evolution of oblique collision some major changes in compressional trends are also accounted for by variations in the kinematics of plate convergence the most recent charge comprises a counterclockwise change in the direction of philippine sea plate eurasia convergence

fast teleconnections to the tropical atlantic sector from atlantic thermohaline adjustment 1 we examine the first decade of adjustment of the north atlantic climate following an abrupt freshening of the high north atlantic and resulting slowdown of the atlantic meridional overturning circulation amoc in a coupled model with reference to previously proposed teleconnection mechanisms after an initial ocean driven cooling at the subtropical subpolar gyre boundary subsequent equatorward progression is dominated by an atmosphere surface ocean mechanism driving evaporative cooling in the tropical north atlantic and resulting in an anomalous southward itcz displacement by year 2 the tropical cooling is countered by fast ocean baroclinic adjustment to the reduced overturning that increases the volume of tropical surface waters as well as ocean circulation changes to the increased northeasterly trades however it is the atmosphere surface ocean teleconnection that explains the hemispheric asymmetric nature of the tropical atlantic surface climate impact to amoc slowdown underlining its crucial importance in high to low latitude teleconnections

slab breakoff as a mechanism for flipping of subduction polarity in taiwan we propose a model that involves breakoff of the east dipping eurasian slab beneath the taiwan orogen to account for the flipping of subduction polarity in northern taiwan the breakoff was initiated in southern ryukyu in the early pliocene and then propagated southwestward into taiwan like an opening zipper detachment of the eurasian slab has created a mantle window for the north dipping philippine sea plate to move in laterally causing a switch in the subduction polarity slab breakoff not only provides a testable model for the lithospheric structure of taiwan but also accounts for the high heat flow rapid uplift synorogenic extension deep focus earthquakes and north diminishing crustal contraction in the taiwan mountain belt

effect of solid flow above a subducting slab on water distribution and melting at convergent plate boundaries 1 hydrous fluids derived by dehydration of the downgoing slab at convergent plate boundaries are thought to provoke wet melting in the wedge above the downgoing plate we have investigated the distribution of hydrous fluid and subsequent melt in the wedge using two dimensional models that include solid mantle flow and associated temperature distributions along with buoyant fluid migration and melting solid mantle flow deflects hydrous fluid from their buoyant vertical migration through the wedge melting therefore does not occur directly above the region where hydrous fluids are released from the slab a melting front develops where hydrous fluids first encounter mantle material hot enough to melt wet melting is influenced by solid flow through the advection of fertile mantle material into the wet melting region and the removal of depleted material the region of maximum melting occurs where the maximum flux of water from slab mineral dehydration reaches the wet melting region the extent of melting f and melt production rates increase with increasing convergence rate and grain size due to increased temperatures along the melting front and to increased fractions of water reaching the melting front respectively the position of isotherms above the wet solidus varies with increasing slab dip and thereby also influences f and melt production rates applying the understanding of wet melting from this study to geochemical studies of the aleutians may help elucidate the processes influencing fluid migration and melt production in that region estimates of the timescale of fluid migration seismic velocity variation and attenuation are also investigated

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

tomography of the westernmost ryukyu subduction zone and the serpentinization of the fore arc mantle 1 three dimensional tomographic images of the subducting philippine sea slab and the fore arc mantle beneath ne taiwan and the westernmost ryukyu were generated in this study more than 5600 events recorded simultaneously by seismic networks in taiwan and japan were relocated for the inversion for variations in vp vs and vp vs analysis of the trade off between the data variance reduction and model variance helps to determine the appropriate strictness for regularization to avoid either overinterpretatioin or underinterpretation of data the regularization parameters were also chosen to ensure suppression of artificial vp vs anomalies the subducting slab is characterized by high vp high vs and intermediate to low vp vs notable in the mantle wedge is the high vp vs anomalies that abut the surface of the subducting slab at depths of 30 80 km the previously identified positive vp vs channel connecting the slab and the arc volcano interpreted to be a melt pathway is not reproduced in this study we convert vs and vp vs to perturbations of temperature and serpentinization of the mantle the slab is cooled by 200 c 400 c relative to the mantle in accord with the estimates from theoretical modeling of subduction the serpentinization reaches 15 or 2 water content at 50 km depth in the fore arc mantle we interpret the peak serpentinization as hydrated by the water released from the basalt eclogite metamorphic reaction in the oceanic crust of the subducting philippine sea plate the spatial limitation of the present seismic networks in this region with respect to subduction zone events hinders a full description of the pattern of melting in much of the mantle wedge resolution tests of the tomographic inversion provide a basis to guide our interpretation to better resolved regions

pleistocene and holocene palaeoclimates in the gebel akhdar libya estimated using herbivore tooth enamel oxygen isotope compositions abstract the palaeoclimate of the gebel akhdar massif in cyrenaica northeast libya is investigated using the stable oxygen isotope ratio 18 o of herbivore tooth enamel from the archaeological faunal assemblages of the haua fteah and hagfet ed dabba caves samples accumulated through human activity at the sites thus climatic interpretations are in direct chronological association with periods of human presence in the local landscape wild ammotragus lervia barbary sheep and bos sp auroch and domestic ovis sp and capra sp from the levalloiso mousterian 73 3 43 5 ka to the neolithic 9 3 5 4 ka cultural phases are analysed results indicate that the most arid environment represented by the samples occurred at 32 ka when populations associated with dabban lithic assemblages were present within the region climatic instability increased during oxygen isotope stage 2 consistent with other palaeoenvironmental investigations in the gebel akhdar there is no evidence for hyper arid events during the last glacial and surface water most probably in the form of local springs was available throughout the time periods considered overall results indicate that different cultural groups occupied the gebel akhdar landscape under different climatic conditions but that climate variations appear to have been of lower magnitude than those that occurred at inland north african locations these reconstructions provide further support to the theory that the gebel akhdar may have served as a refugium for human populations in north africa during times of global climatic extremes

middle to late pleistocene vegetation and climate change in subtropical southern east africa in this study we investigate pleistocene vegetation and climate change in southern east africa by examining plant leaf waxes in a marine sediment core that receives terrestrial runoff from the limpopo river the plant leaf wax records are compared to a multi proxy sea surface temperature sst record and pollen assemblage data from the same site we find that indian ocean sst variability driven by high latitude obliquity exerted a strong control on the vegetation of southern east africa during the past 800 000 yr interglacial periods were characterized by relatively wetter and warmer conditions increased contributions of c3 vegetation and higher sst whereas glacial periods were marked by cooler and arid conditions increased contributions of c4 vegetation and lower sst we find that marine isotope stages mis 5e 11c 15e and 7a 7c are strongly expressed in the plant leaf wax records but mis 7e is absent while mis 9 is rather weak our plant leaf wax records also record the climate transition associated with the mid brunhes event mbe suggesting that the pre mbe interval 430 800 ka was characterized by higher inputs from grasses in comparison to relatively higher inputs from trees in the post mbe interval 430 to 0 ka differences in vegetation and sst of southern east africa between the pre and post mbe intervals appear to be related to shifts in the location of the subtropical front comparison with vegetation records from tropical east africa indicates that the vegetation of southern east africa while exhibiting glacial interglacial variability and notable differences between the pre and post mbe portions of the record likely did not experience such dramatic extremes as occurred to the north at lake malawi

constraints on backstop geometry of the southwest ryukyu subduction based on reflection seismic data abstract based on the analysis of 45 seismic reflection profiles the top of the ryukyu arc basement is mapped in the forearc region east of taiwan the ryukyu arc slope dips 10 trenchward while beneath the forearc basins the arc basement shows a series of morphologic along arc highs and lows one of the basement highs the nanao basement rise has been described as an area uplifted by the subduction of the gagua ridge the other one the hoping basement rise is suggested in this study to be an uplifted feature caused by the subduction or the underplating of some local asperity the nature of this asperity could either be a detached block of the luzon arc an isolated seamount or some material removed from the frontal part southernmost extremity of the ryukyu margin from seismic reflection profiles we infer that the right lateral transcurrent fault system located at the rear of the accretionary wedge defines the surface projection of the southern termination of the ryukyu arc basement two crustal sections across the ryukyu subduction system demonstrate that the backstop terminates in the form of a near vertical wall with its height over 5 km such an unusual geometry could be produced by crustal truncation at the toe of the backstop

the crustal deformation of the ilan plain acted as a westernmost extension of the okinawa trough abstract we analyze the current deformation in ilan plain of northeastern taiwan considered as the western extension of okinawa trough based on 34 geodetic sites observed between 2002 and 2006 the station velocities are between 1 9 mm yr and 43 0 mm yr in a direction between 38 and 143 relative to stable continent margin of eurasian plate this largest velocity is moving southeastward 143 at a rate of 43 mm yr was enhanced by a seismic doublet that occurred on march 6 2005 the station velocities at the northern margin of ilan plain are insignificant with a magnitude of 1 9 mm yr to 7 5 mm yr on the contrary the station velocities increase approximately southward along the southern margin of ilan plain the stations are moving roughly e w with a magnitude of 5 8 mm yr to 21 8 mm yr further southward the station velocities increase to a value of 43 0 mm yr in a direction of 143 the most prominent feature of the strain distribution patterns in ilan plain are the remarkable extensional strain rates observed in central and southern flank of the ilan plain the largest extensional rate is found 2 66 strain yr in 147 with a shortening rate in the perpendicular direction 1 28 strain yr in 57 indicating transtensional deformation mode in the northeastern flank of ilan plain insignificant or minor deformations are observed overall the extensional rates in this area clearly increase from north to south the extension directions in study area mostly trend e w to nw se directions using the velocity field of 34 gps stations and its strain rate filed we suggest the lateral extrusion process towards mechanically weak domain adjacent ryukyu subduction zone the lateral extrusion is facilitated by the opening of the okinawa trough we conclude that the northeast taiwan is subjected to both the compressional force exerted by the indentation of philippine sea plate and the tensile force induced by trench retreat related to the suction force at the ryukyu trench due to the interaction of two forces the stress regime rapidly changes from pure compression in the taiwan collision belt to transtension near ilan plain and its offshore area

mesozoic east north american alkaline magmatism part 1 evolution of monteregian lamprophyres quebec canada abstract the cretaceous monteregian alkaline igneous province is composed of shallowly emplaced plutonic complexes and cogenetic dykes and sills the mafic dykes are principally camptonites monchiquites and alnoites and sample the magmas that fed the plutons the three principal dyke suites have different incompatible trace element ratios y ce zr nb and are not interrelated by closed system fractional crystallization zonation of pyroxene grains imply a polybaric crystallization history indicating that magmas ascended as mafic crystal charged mushes intrasuite chemical variations among monchiquites are broadly consistent with segregation of the suspended phenocrysts from interstitial syenitic melts partial resorption of suspended amphibole megacrysts assimilation of syenitic material 5 8 and exsolution of carbonatitic melt are required to explain the variations of ba rb k 2 o th la and tio 2 chemical variations among mafic camptonites are acceptably modelled by fractionation of pyroxene and olivine only implying that their amphibole rich character is the result of postfractionation crystallization under volatile rich conditions high zr nb camptonites and rb rich ac monchiquites could not unequivocably be linked to the main lineages and may represent distinct sources or have been affected by crustal contaminants

refining the image of the san andreas fault near parkfield california using a finite difference travel time computation technique abstract the parkfield area seismic observatory paso was a dense telemetered seismic array that operated for nearly 2 years in a 15 km aperture centered on the san andreas fault observatory at depth safod drill site the main objective of this deployment was to refine the locations of earthquakes that will serve as potential targets for safod drilling and in the process develop a high for passive seismological techniques resolution image of the fault zone structure a challenging aspect of the analysis of this data set was the known existence of large 20 25 contrasts in seismic wavespeed across the san andreas fault the resultant distortion of raypaths could challenge the applicability of approximate ray tracing techniques in order to test the sensitivity of our hypocenter locations and tomographic image to the particular ray tracing and inversion technique employed we compare an initial determination of locations and structure developed using a coarse grid and an approximate ray tracer thurber c roecker s roberts k gold m powell m l and rittger k 2003 earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod geophys res lett 30 3 10 1029 2002gl016004 with one derived from a relatively fine grid and an application of a finite difference algorithm hole j a and zelt b c 1995 3 d finite difference reflection traveltimes geophys j int 121 2 427 434 in both cases we inverted arrival time data from about 686 local earthquakes and 23 shots simultaneously for earthquake locations and three dimensional vp and vp vs structure included are data from an active source seismic experiment around the safod site as well as from a vertical array of geophones installed in the 2 km deep safod pilot hole drilled in summer 2002 our results show that the main features of the original analysis are robust hypocenters are located beneath the trace of the fault in the vicinity of the drill site and the positions of major contrasts in wavespeed are largely the same at the same time we determine that shear wave speeds in the upper 2 km of the fault zone are significantly lower than previously estimated and our estimate of the depth of the main part of the seismogenic zone decreases in places by 100 m tests using virtual earthquakes borehole receiver gathers of picks for surface shots indicate that our event locations near the borehole currently are accurate to about a few tens of meters horizontally and vertically

the earliest occupation of north africa the moroccan perspective abstract the long sequence at casablanca covers the past 5 5 ma the oldest lithic assemblages are found in late lower pleistocene deposits ca 1 ma in unit l of thomas quarry 1 and consist of acheulean artefacts made from quartzite and flint the first human remains discovered in this area were found in younger middle pleistocene deposits and cover an important period of human evolution between homo erectus and modern homo they are associated with acheulean artefacts and rich faunal assemblages in caves littorina cave at sidi abderrahman caves at thomas quarries 1 and 3 the variability of acheulean assemblages is well documented following recent excavations in various sites around the well known locality of sidi abderrahman bears cave cap chatelier unit l and hominid cave at thomas quarry 1 rhino cave at oulad hamida quarry 1 sidi abderrahman extension and sidi al khadir open air sites the casablanca sequence offers useful data for comparison with those from other african areas where hominids appeared and developed and should thus be considered in the debate on the earliest occupation of europe

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

population density and zoning of olivine phenocrysts in tholeiites from kauai hawaii the population density of olivine phenocrysts of the tholeiites display an exponential variation which is typical of igneous as well as contact metamorphic rocks the exponential variation is explained by a new growth probability model which is consistent with experimental work the forsterite content of the olivine phenocrysts decreases with decreasing size various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place

olivine phenocrysts of hawaiian olivine tholeiite and oceanite olivine phenocrysts of hawaiian tholeiites display a variety of textures and a variation in composition which is due to supercooled crystallization the highest forsterite content measured is 91 and the highest magnesia content estimated for a tholeiitic liquid is 17 using the olivine geothermometer the liquid of this composition may be either a primary magma or a primitive magma it is not yet possible to specify any particular composition range for the primary hawaiian tholeiites

a tear fault boundary between the taiwan orogen and the ryukyu subduction zone more than twenty seismic lines were analysed across the intersection of the taiwan orogen and the ryukyu arc forearc system the main results of this study concern the recognition of two superposed sedimentary basins that were previously unknown we have named the recent one the hoping basin and the older tectonized one the suao basin the suao basin containing sediments more than 3 km thick records subsidence of about 3 km on its southwestern portion after being shortened in the direction of plate convergence on the basis of seismicity gravity present day plate kinematics as well as seismic reflection data we relate the dramatic subsidence of the suao basin to the initiation of a wnw trending tear fault within the philippine sea plate this tear fault decouples the subducting philippine sea plate to the northeast and the apparent overthrusting philippine sea plate in the coastal range to the southwest back arc rifting may thus occur in the westernmost section of the okinawa trough above the sinking philippine sea slab while lithospheric shortening prevails south of hualien as a consequence the triangular area located southwest of the tear fault between the taiwan coastline and the toe of the yaeyama ridge no longer belongs to the ryukyu forearc it is now passively transported with the non subducting portion of the philippine sea plate we propose an evolutionary model for the relative chronology of tectono sedimentary events in this region over the last 5 m y

melting features along the western ryukyu slab edge northeast taiwan tomographic evidence 1 behind the sedimentary ryukyu arc lies the okinawa trough whose termination is located at the tip of the ilan plain northern taiwan just above the ryukyu slab edge the present day active volcanic front is located 80 100 km above the ryukyu slab and extends from japan to kueishantao island an islet situated 10 km offshore the ilan plain between december 1990 and may 1999 3370 earthquakes recorded in northern taiwan by 65 seismic land stations were used to determine the three dimensional vp and vs velocity structures and vp vs ratios a low vs but high vp vs sausage like body 30 km in diameter lies within the eurasian mantle wedge on top of the western ryukyu slab extremity at depths ranging between 20 and 100 km we suggest that the h2o rich component formed by dehydration processes from subducting sediments oceanic crust and serpentinized mantle above the ryukyu slab and along the vertical portion of the slab edge might explain the presence of the sausage like body a low vs but high vp vs channel rises obliquely from the sausage like body at a depth of 40 km in direction of the andesitic kueishantao island we propose that the h2o rich component and or melt rise up from the sausage like body and interfere with the okinawa trough back arc basin magmas formed in the upper mantle lower crust then magmas propagate upward within the upper brittle crust through veins and or narrow conduits

middle stone age reduction strategies at the desert s edge a multi site comparison across the gebel akhdar of northeast libya abstract haua fteah cave situated between the mediterranean coast and the gebel akhdar of northeast libya preserves rich middle stone age msa and late stone age lsa cultural horizons excavated in the 1950s and more recently the richness and time depth of the cave s archaeological record are unsurpassed by any other site in northern cyrenaica as a result the haua fteah sequence has long been used to represent the culture history of the region as a whole recent geoarchaeological surveys of the gebel akhdar as well as pre desert and desert biomes further to the south have resulted in the discovery of numerous msa and lsa sites the vast majority of these sites consist of surface lithics that cannot be dated currently in contrast parts of the haua fteah sequence have been dated using various chronometric methods using data collected through lithic attribute analysis coupled with various statistical approaches including discriminant function analysis or dfa this paper explores variation in core reduction strategies within haua fteah from the early msa to early lsa collections of cores from various sites located throughout the landscape are contrasted against those from haua fteah by comparing undated cores from the landscape with those from different occupation phases at haua fteah dfa classification is tested as a method for imparting an approximate chronology to the former the results indicate notable variation in reduction strategies within the msa at haua fteah and notable similarities between early msa pre aurignacian and early lsa early dabban core morphologies and technologies because of the latter in particular together with several other factors that may be underpinning spatio temporal variability in core reduction strategies caution is recommended in loosely assigning approximate chronologies to surface lithic sites

aeolian transport and deposition of plant wax n alkanes across the tropical north atlantic ocean long chain n alkanes are terrestrial higher plant biomarkers analysed in marine sedimentary archives to reconstruct continental palaeoclimatic and palaeohydrological conditions latitudinal variation in their concentration and distribution in marine sediments relatively close to the continent has been widely studied but little is known on the extent to which this continental signal extends to the ocean furthermore no studies have examined the seasonal variation in the deposition of these biomarkers in marine sediments here we studied longitudinal variation in the composition of long chain n alkanes and two other terrestrial higher plant biomarkers long chain n alkanols and long chain fatty acids in atmospheric particles as well as longitudinal and seasonal variation in long chain n alkanes in sinking particles in the ocean at different water depths and in surface sediments all collected along a 12 n transect across the tropical north atlantic ocean the highest abundance of all three biomarker classes was closest to the african coast as expected because they are transported with saharan dust and the largest part of the dust is deposited close to the source at this proximal location the seasonal variability in long chain n alkane flux and the chain length distribution of the n alkanes in sinking particles was most pronounced due to seasonal change in the dust source or to change in vegetation composition in the source area related to the position of the intertropical convergence zone itcz in contrast in the open ocean the seasonal variability in both the long chain n alkane flux and chain length distribution of the n alkanes was low the abundance of the alkanes was also lower as expected because of the larger source to sink distance at the western part of the transect close to south america we found an additional source of the alkanes in the sinking particles during spring and autumn in the year 2013 the 13c values of the alkanes in the surface sediment closest to the south american continent indicated that the isotope signal was likely derived from c3 vegetation from the amazon implying an input from the amazon river as there is no significant aeolian input from south america there since the prevailing wind direction is from the east finally the concentration of the alkanes was similar in the material collected from the atmosphere the particles collected while settling through the marine water column and in the surface sediments providing evidence that degradation of long chain n alkanes from the atmosphere to settling at the sediment water interface at deep open ocean sites is minimal

magma solidification processes beneath kilauea volcano hawaii a quantitative textural and geochemical study of the 1969 1974 mauna ulu lavas sents a late magma component formed in the summit magma storage region our results are consistent with the hypothesis that the components of the mu magmas followed two different routes the deformed olivine bearing magma moved along the deep basal

oceanic link between abrupt changes in the north atlantic ocean and the african monsoon abrupt changes in the african monsoon which have been recorded throughout the late pleistocene and early holocene epochs tend to coincide with changes in north atlantic thermohaline circulation a numerical simulation shows that the interaction between thermohaline circulation in the north atlantic ocean and wind driven currents in the topical atlantic ocean contributes to the rapidity of african monsoon transitions during abrupt climate change events

the seasonal evolution of the atmospheric circulation over west africa and equatorial africa abstract this paper examines the mean annual cycle of rainfall and general circulation features over west africa and central africa for 1958 97 rainfall is examined using a 1400 station archive compiled by the first author other circulation features are examined using the ncep ncar reanalysis dataset important features of the reanalysis zonal wind field are shown to compare well with the seasonal evolution described by the radiosonde observations in addition to the well known african easterly jet aej of the northern hemisphere the seasonal evolution of its southern hemisphere counterpart is also described thermal wind calculations show that although the southern jet is weaker its existence is also due to a local reversal of the surface temperature gradient in the upper troposphere a strong semiannual cycle is shown in the 200 mb easterlies and a feature like the tropical easterly jet tej is evident south of the equator in january and february the paper describes the movement of the rainbelt

simulation of an abrupt change in saharan vegetation in the mid holocene climate variability during the present inter glacial the holocene has been rather smooth in compar ison with the last glacial nevertheless there were some rather abrupt climate changes one of these changes the desertication of the saharan and arabian region some 4 6 thousand years ago was presumably quite important for human society it could have been the stimulus leading to the foundation of civilizations along the nile euphrat and tigris rivers here we argue that saharan and arabian de sertication was triggered by subtle variations in the earth s orbit which were strongly amplied by atmosphere vegeta tion feedbacks in the subtropics the timing of this tran sition however was mainly governed by a global interplay between atmosphere ocean sea ice and vegetation

pleistocene sea level fluctuations and human evolution on the southern coastal plain of south africa abstract humans evolved in africa but where and how remain unclear here it is proposed that the southern coastal plain scp of south africa may have served as a geographical point of origin through periodic expansion and contraction isolation in response to glacial interglacial changes in sea level and climate during pleistocene interglacial highstands when sea level was above 75 m human populations were isolated for periods of 360 3400 25 yr generations on the scp by the rugged mountains of the cape fold belt climate and vegetation barriers the scp expands five fold as sea level falls from 75 to 120 m during glacial maxima to form a continuous unobstructed coastal plain accessible to the interior an expanded and wet glacial scp may have served as a refuge to humans and large migratory herds and resulted in the mixing of previously isolated groups the expansive glacial scp habitat abruptly contracts by as much as one third in 300 yr during the rapid rise in sea level associated with glacial terminations rapid flooding may have increased population density and competition on the scp to select for humans who expanded their diet to include marine resources or hunted large animals successful adaptations developed on an isolated scp are predicted to widely disperse during glacial terminations when the scp rapidly contracts or during the initial opening of the scp in the transition to glacial maxima the hypothesis that periodic expansion and contraction of the scp as well as the coastal plain of north africa contributed to the stepwise origin of our species over the last 800 thousand years kyr is evaluated by comparing the archeological dna and sea level records these records generally support the hypothesis but more complete and well dated records are required to resolve the extent to which sea level fluctuations influenced the complex history of human evolution

the middle pleistocene al mahruqah formation in the murzuq basin northern sahara libya evidence for orbitally forced humid episodes during the last 500 000 years abstract geological and geomorphological work in the endorheic murzuq basin fezzan in the northern sahara desert sw libya has revealed that the middle pleistocene al mahruqah formation consists of at least four limestone beds at four distinct elevations the corresponding limestone beds are named from oldest to youngest the antalkhata member the brak member the bi r az zallaf member and the aqar member the four members are interpreted as lacustrine deposits and they are well distinguished by their spatial extent and lithology twenty five radiometric and thermal ionisation mass spectrometric tims 230th u ages ranging from about 490 130 ka have been determined on these lacustrine limestones according to these radiometric 230th u ages the accumulation of the four limestone members of the al mahruqah formation followed the orbitally forced milankovitch eccentricity cycle of 100 ka during at least the last 400 ka the four members formed in humid episodes of several tens of thousands of years duration when large lakes might have existed the 13c and 18o values from samples of the four members of the al mahruqah formation provide independent genetic evidence on the lacustrine origin of the deposits in the murzuq basin the spatial extent of the limestone deposits and thus the intensity of the humid episodes decreases at least from the brak member to the aqar member from about 52 000 km2 to 1400 km2 respectively in spite of the limited precision and reliability of the new 230th u ages it seems possible that short humid episodes interrupted the intervening arid episodes other long term palaeohydrological records from northern and southern africa as well as the mediterranean region support the palaeoclimatic results from the murzuq basin

a pleistocene lacustrine episode in southeastern libya fossiliferous lacustrine deposits of middle pleistocene age have been found in central fezzan libya 1 on each side of the east west depressions of the wadi shati south of the precambrian qarqaf anticline1 8 they represent the shoreline of a former brackish water lake fig 1 which some 130 000 yr bp covered an area about 100km long and 10 20 km wide at present the area may be classified as hyperarid since 1978 a collaborative study of the fossil assemblages has been undertaken it included macro and micropalaeontological determination th u dating stable isotope and chemical analyses in parallel with sedimentological and archaeological studies of the sites here we consider the th u dating and the isotopic palaeohydrology of the lacustrine episode

pleistocene and holocene herbivore diets and palaeoenvironments in the gebel akhdar libya implications for past human populations the gebel akhdar massif in cyrenaica northeast libya has yielded a long record of human occupation going back at least 100 000 years to date there is only a limited understanding of how the landscape of the region varied in response to the climatic fluctuations of the last glacial interglacial cycle and the implications of these changes for local human populations remain largely unexplored this study provides an isotope based interpretation of past environments directly linked to the archaeological record tooth enamel stable carbon isotope ratios 13c from herbivore species hunted by past human populations are used to infer the isotopic characteristics of past diet and vegetation and in turn the likely environmental conditions that prevailed during periods when humans were active within the landscape to provide a baseline from which to interpret the archaeological 13c data modern samples are considered in relation to their diet and environmental origin archaeological samples come from 2 cave sites haua fteah and hagfet ed dabba and span a period from oxygen isotope stage 4 to the mid holocene whilst results indicate a more arid environment in the pleistocene and an increase in humidity at the onset of the holocene the overall picture is one of relative environmental stability the biggest landscape change observed in the data occurs during the mid holocene neolithic when c4 plant species become evident in the herbivore diet for the first time there is little evidence to suggest that this occurred at a time of any large scale climate variation and thus the contribution of anthropogenic influences to vegetation change is considered likely

the southwestern edge of the ryukyu subduction zone a high q mantle wedge abstract the lateral edge of a subduction zone is usually depicted as an opening to the asthenosphere where invigorated dynamics and amplified magmatism take place in this study we present evidence from seismic data suggesting the presence of a cold and dynamically sluggish edge environment at the southwest end of the ryukyu subduction system we measured attenuation or 1 q for p waves from subduction zone events at 100 km depths received by obss in the okinawa trough and land stations in ne taiwan in the okinawa trough 100 200 km from the edge q values are lower than 100 in the vicinity of the edge q values increase from 100 to over 1000 towards taiwan to reconcile arguments from geophysical and geochemical observations we propose that the mantle wedge near the edge has high q values due to low temperatures and probably low water content these may result from coupling of the slab laterally with the thick eurasian lithosphere which inhibits back arc rifting retards subduction and reduces the water supply to the mantle wedge the sw ryukyu subduction system represents a subduction zone edge type distinct from more commonly documented free or warm edges

a model for the termination of the ryukyu subduction zone against taiwan a junction of collision subduction separation and subduction boundaries 1 the nw moving philippine sea plate psp collides with the eurasian plate eup in the vicinity of taiwan and at the same time it subducts toward the north along sw ryukyu the ryukyu subduction zone terminates against eastern taiwan while the ryukyu trench is a linear bathymetric low about 100 km east of taiwan closer to taiwan it cannot be clearly identified bathymetrically owing to the deformation related to the collision making the location of the intersection of the ryukyu with taiwan difficult to decipher we propose a model for this complex of boundaries on the basis of seismicity and 3 d velocity structures in this model the intersection is placed at the latitude of about 23 7 n placing the northern part of the coastal range on eup as psp gets deeper along the subduction zone it collides with eup on the taiwan side only where they are in direct contact thus the eurasian plate on the taiwan side is being pushed and compressed by the nw moving philippine sea plate at increasing depth toward the north offshore of northeastern taiwan the wedge shaped eup on top of the ryukyu subducting plate is connected to the eup on the ryukyu side and coupled to the nw moving psp by friction at the plate interface the two sides of the eup above the western end of the subduction zone are not subjected to the same forces and a difference in motions can be expected the deformation of taiwan as revealed by continuous gps measurements geodetic movement along the east coast of taiwan and the formation of the hoping basin can be understood in terms of the proposed model

des a lupane in an east african lake sedimentary record as a new proxy for the stable carbon isotopic composition of c3 plants we studied the high resolution and well dated 25 000 year sedimentary record of lake challa a deep tropical crater lake in equatorial east africa to explore new proxies for paleoenvironmental and paleohydrological change sedimentary biomarker analysis revealed the presence of des a triterpenoids with oleanane ursane and lupane carbon skeletons microbial degradation products of angiosperm plant triterpenoids their increased influx from 16 000 years ago corresponds with previously documented changes in the terrestrial vegetation of the lake challa basin during postglacial warming in particular the relative increase in c3 c4 plant ratio inferred from the stable carbon isotopic signature 13c of sedimentary n alkanes derived from plant leaf waxes in contrast to this n alkane 13c signature the 13c of des a lupane maintains a constant value of 27 4 1 1 across the glacial interglacial transition since des a lupane is derived from c3 plants its 13c signature is here proposed to represent a novel and independent proxy for the time variable carbon isotopic composition of local terrestrial c3 plants which can improve estimates of the c3 c4 plant ratio based on two end member mixing models of n alkane 13c values

on some fundamentals of igneous petrology the age old process of crystal fractionation leading to the diversity of the igneous rocks and earth itself is an exceedingly well understood chemical process in magmatism and physical chemistry but the broader physical aspects of this and related processes have proven elusive on many fronts especially in its relation to the spatial variations in rock composition texture and macroscopic features like layering magmatic systems be they volcanic dikes sills or plutons are generally analyzed with a problem at hand and an end result in mind the processes invoked to solve these problems which are most often purely chemical are often unique to each problem with few if any general principles emerging that are central to understanding the wider perspective of magmatic processes and problems an attempt is made at the outset to provide a list of inviolate magmatic first principles that are relevant to analyzing most magmatic problems these involve initial conditions critical crystallinity solidification fronts transport and emplacement fluxes phenocrysts xenocrysts primocrysts crystal size layering and crystal sorting thermal convection magmatic processes are physical along with these principles two reference magmatic systems are suggested where the initial conditions and outcome are unequivocal the sudbury impact melt sheet and the hawaiian lava lakes sudbury formed in 5 min by superheated magma crystallized to a near uniform sequence while the tiny lava lakes formed of crystal laden slurries form a highly differentiated layered sequence the major difference is in the initial conditions of formation especially the nature of the input materials the challenge is to construct and analyze magmatic systems i e magma chambers sills dikes and lavas using these reference end members and the suggested principles the hawaiian 500 000 year volcanic record exhibits what can be expected as input materials namely a highly varied output of magma of an overall composition reflecting the abundance of entrained olivine primocrysts the provenance of these crystals is varied and within any single sample the population may be highly heterogeneous in composition from crystal to crystal yet the overall pattern of chemical fractionation is exceedingly regular and well defined if similar inputs go to form large intrusions these systems will undoubtedly be dominated by crystal rich slurries which provide a vast set of physical processes promoting exotic layering and at the same time given the effects of annealing and continued crystal growth a final chemical record adhering to all the time honored effects of crystal fractionation the long assumed initial condition of instantaneously emplaced crystal free magmas cannot reasonably produce the observed rock records

a petrologic perspective of kīlauea volcano s summit magma reservoir two hundred years of magmatic history are documented by the lavas and tephra sampled from k olauea s historical summit eruptions this paper presents detailed petrographic and geochemical data for a comprehensive suite of samples erupted within or near k olauea s summit caldera since the 17th century our results elucidate the range of magmatic processes that operate within the volcano s summit magma reservoir and document two compositional trends that span nearly the entire known range for the volcano prior to the 1924 summit crater collapse a trend of increasing incompatible element and cao and decreasing sio2 abundances at a constant mgo prevailed thereafter the trend reversed direction and has persisted for the rest of the 20th century including during the current puau a oa o eruption the rapid and systematic nature of these temporal geochemical variations indicates that the summit reservoir is a single relatively small body rather than a plexus of dikes and sills olivine fractionation is the dominant petrologic process within this reservoir petrographic observations and olivine and whole rock geochemical data suggest that the summit reservoir has a crown of aphyric more evolved low density magma differentiation within this crown involving clinopyroxene and plagioclase is more extensive than previously recognized in k olauea summit lavas the effects of crystal fractionation are superimposed upon an evolving hybrid magma composition produced by mixing new mantle derived magmas with more fractionated reservoir magma frequent eruptions of these hybrid reservoir magmas document the rapid variation in parental magma composition these compositional variations correlate with magma supply rate both are thought to be influenced by the degree of melting of small scale source heterogeneities within the hawaiian plume however k olauea s source compositions and partial melting processes have varied only within a narrow range over the past 350 kyr

three dimensional p velocity structures of the lithosphere beneath taiwan from the analysis of taiger and related seismic data sets 1 the convergence of the philippine sea and the eurasian plates in the taiwan region led to the formation of a young collisional mountain between two subduction zones of nearly orthogonal polarities the geological processes underlying the collision and its relation to subduction are the primary targets of taiger taiwan integrated geodynamic research project newly acquired passive and active sources data on land supplemented by ocean bottom as well as permanent seismic network data are used to derive a new 3 d tomographic velocity model using the 7 5 km sec contour as a marker for crustal deformation two trend parallel roots one under the central range with a maximum depth of 55 km and the other under the coastal range at 40 km are found to extend from southern to central 24 n taiwan between the two roots and lying approximately beneath the longitudinal valley the 7 5 km sec contour rises to 25 km depth in the upper mantle a high velocity zone east dipping and its upper surface coinciding with a wadati benioff zone in the south 22 8 n becomes near vertical and ill defined in the north 23 9 n the crustal deformation as defined by the roots and the along trend variations of the upper mantle structures under taiwan provide key information for the orogeny with the thickening of crust to 55 km or more processes such as eclogitization and delamination may come into play

late middle palaeolithic surface sites occurring on dated sediment formations in the thar desert abstract the dominance of erosional sedimentary processes in desert regions results in palaeolithic records rich in surface scatters engaging with this abundant archaeological resource including incorporating them within absolute chronologies or schemes of environmental variability is critical to understanding hominin habitation in arid landscapes extensive archaeological surveys in the thar desert of india and pakistan over the past 60 years have identified a large number of palaeolithic surface sites in a diverse range of geographic contexts in the past twenty years a rich upper pleistocene palaeoenvironmental record has been developed within the region due to the application of chronometric dating techniques however as yet there have been few attempts by archaeologists to survey previously dated sediment formations in the thar desert and capitalise upon the potential to attribute preliminary terminus post quem dates to surface sites surface survey has been undertaken targeting sediment deposits that may preserve evidence for hominin behaviour between marine isotope stage 5 and 3 a period in which technological and demographic overhauls in hominin populations appear to occur in south asia following brief review of the palaeolithic archaeology and palaeoenvironmental history of the thar desert the results of recent archaeological survey of dated sediments at chamu karna and shergarh tri junction are presented the results offer tentative evidence for the presence of late middle palaeolithic populations in the region which are evaluated and discussed within the context of contemporary occupations across southern asia

evolution of alkalic lavas at haleakala volcano east maui hawaii the postshield and posterosional stages of haleakala volcano contain intercalated alkalic basalt and evolved alkalic lavas isotopic and incompatible element abundance ratios in the haleakala postshield basalts changed systematically with time providing evidence for significant temporal changes in the mantle components contributing to the magmatic sources specifically a depleted i e low87sr 86sr and high143nd 144nd mantle component is more abundant in younger lavas however as magma production rates decreased during the postshield and posterosional stages basaltic melts in magma reservoirs cooled and fractionated leading to evolved residual melts such as hawaiite because primary basalt compositions changed with time the evolved haleakala lavas formed from a range of parental compositions however basalts and evolved lavas of similar age and isotopic ratios sr and nd have major and trace element contents that are consistent with a crystal fractionation model although alkalic basalt and hawaiite are the dominant lavas of the postshield stages of both haleakala and mauna kea volcanoes there are important differences between their lavas for example compositional differences between the hawaiite suites at haleakala and mauna kea indicate that on average the evolved lavas at haleakala formed at lower pressures also at haleakala basalts are intercalated with hawaiites whereas at mauna kea basalts and hawaiites are separated by a sharp boundary these differences probably reflect a higher magma supply rate to the haleakala volcano

transition from oblique subduction to collision earthquakes in the southernmost ryukyu arc taiwan region tectonic characteristics of the region between taiwan and the southernmost ryukyu arc are inferred from a detailed analysis of local seismicity and source parameters of 62 recent earthquakes of 5 5 mb 6 6 five major seismogenic structures can be delineated the collision seismic zone csz the interface seismic zone isz the wadati benioff seismic zone wbsz the lateral compression seismic zone lcsz and the okinawa seismic zone osz in the csz located along the east coast of taiwan and offshore earthquake focal mechanisms show horizontal p axes distributed in two directions 287 10 and 333 16 possibly reflecting a strain partition associated with the relative plate convergence between the eurasia plate and the philippine sea plate the corresponding seismic strain tensor indicates a maximum compressive strain rate of 1 2 10 7 yr 1 along 293 and a comparable extension in vertical direction presumably resulted from plate collision in the region the geometry of the isz which is distorted significantly at its westernmost end can be approximated by a north dipping plane that is gradually pushed northward with increasing dip the seismogenic portion of the interface spans a short depth range from 10 km to 35 km a clear pattern of earthquake slip partition is observed the average slip vector residual is as large as 35 seismic strain patterns within the subducted philippine sea slab show predominantly downdip extension between 80 and 120 km and downdip compression at 270 km different from the pattern of strain segmentation observed for the rest of the ryukyu arc where the northern and southern portions are dominated by downdip extension and compression respectively owing to the large convergence obliquity the slab is descending at a rate significantly slower near taiwan than in the southern ryukyu thus we interpret the appearance of downdip extension within the subducted lithosphere as a combined result of oblique subduction and the slab s negative buoyancy a number of thrust or oblique strike slip earthquakes between isz and wbsz show a consistent pattern of lateral compression with p axes oriented roughly parallel to the local strike of the trench arc system they are probably due to the compressive strain originated from the collision and transmitted laterally within the lithosphere shallow normal faulting earthquakes show successive rotation of t axes from approximately n s in the okinawa trough to approximately e w in northeast taiwan possibly as a result of interaction between the extension from the opening of the okinawa trough and the compression from collision one normal event january 18 1991 mb 5 9 occurred in the central range with t axis roughly parallel to the structural trend of taiwan implying that the nature of the orogeny in taiwan has changed from thin skinned deformation to lithospheric collision involving the whole crust and uppermost mantle

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

astronomically forced variations in western african rainfall 21 n 20 s during the last interglacial period this study documents the long term evolution of western african precipitation during the last interglacial lig we compare geochemical records obtained on nine sediment cores from the western african margin to a transient simulation 130 115 ka performed with an ocean atmosphere general circulation model and insolation as sole forcing good agreement between proxy records and model outputs indicates that long term changes in western african precipitation largely responded to insolation variations during most of the lig after an early lig dry phase related to high latitude iceberg melting or dating uncertainties boreal summer insolation controlled the intensification of the north african monsoon between 127 and 122 ka perhaps facilitating human migrations out of africa equatorial african rainfall slightly increased throughout the lig in response to increasing annual insolation east west contrasting rainfall evolutions at 10 20 s illustrate the complex southern african response in contrast to more direct responses of north and equatorial western africa to insolation forcing

human occupation of northwest africa a review of middle palaeolithic to epipalaeolithic sites in morocco abstract this paper provides a summary of all available numerical ages from contexts of the moroccan middle palaeolithic to epipalaeolithic and reviews some of the most important sites particular attention is paid to the so called aterian albeit those so labeled assemblages fail to show any geographical and chronological pattern for this reason this phenomenon should not be considered a distinct culture or techno complex and is referred to hereinafter as middle palaeolithic of aterian type whereas anatomical modern humans amh are present in northwest africa from about 160 ka onwards according to current research some middle palaeolithic inventories are more than 200 ka this confirms that for this period it is impossible to link human forms with artifact material perforated shell beads with traces of ochre documented from 80 ka onwards certainly suggest changes in human behavior the transition from middle to upper palaeolithic here termed early upper palaeolithic at between 30 and 20 ka remains the most enigmatic era however the still scarce data from this period requires careful and fundamental revision in the frame of any future research by integrating environmental data in reconstruction of population dynamics clear correlations become obvious high resolution data are lacking before 20 ka and at some sites this period is characterized by the occurrence of sterile layers between middle palaeolithic deposits possibly indicative of shifts in human population after heinrich event 1 there is an enormous increase of data due to the prominent late iberomaurusian deposits that contrast strongly from the foregoing accumulations in terms of sedimentological features fauna and artifact composition the younger dryas shows a remarkable decline of data marking the end of the palaeolithic environmental improvements in the holocene are associated with an extensive epipalaeolithic occupation

coherent high and low latitude control of the northwest african hydrological balance variability in northwest african humidity has been documented for the holocene period but less is known about the development of the hydrological balance during the pleistocene period sedimentary records and numerical simulations for the past 120 000 years show abrupt millennial scale changes in humidity which may be related to changes in the strength of the north atlantic meridional overturning circulation