early mis 3 occupation of mochena borago rockshelter southwest ethiopian highlands implications for late pleistocene archaeology paleoenvironments and modern human dispersals abstract between 70 and 50 ka bp anatomically modern humans dispersed across and out of africa to eventually populate all inhabitable continents knowledge of paleoenvironments and human behavioral patterns in africa prior to and during these dispersals is crucial for understanding how and why hunter gatherers were able to adapt rapidly to the new environments they encountered however few well dated sites from this time period are known from the horn of africa one of the purported staging areas for population movements into southern arabia and asia excavations at mochena borago rockshelter situated on the western slopes of a dormant volcano where the sw ethiopian highlands meet the ethiopian rift have yielded the first securely dated archaeological sequence for later periods of the dispersal three major lithostratigraphic groups incorporating occupational episodes have yielded charcoal radiocarbon ages 53 38 ka calbp deeper deposits have been tested but remain undated archaeological assemblages consist mainly of obsidian flaked stone artifacts manufactured from small minimally prepared single to multi platform flake cores radially prepared cores are rare and blade cores are absent small unifacial to bifacial points from non radial cores dominate the earliest shaped tool assemblages and backed pieces first appear by 45 ka calbp by 43 ka calbp scrapers and backed pieces are predominant rather than points however there is little evidence for technological change other than the appearance of bipolar technology mochena borago s archaeological sequence thus cannot be neatly classified as middle stone age later stone age or transitional and calls into question some of the principles by which archaeologists have attempted to classify african toolmaking traditions

new chronological constraints for middle palaeolithic mis 6 5 3 cave sequences in eastern transylvania romania abstract the middle to upper palaeolithic transition is one of the crucial periods of change in the prehistory of europe due to the full emergence continent wide of modern human lithic technologies and detrimental of neanderthal survival knowledge about the transition is growing however the evidence for cultural and technological developments for the middle palaeolithic in the carpathian lower danube basin is still rather sparse here we discuss latest findings arising from a chronological investigation of middle palaeolithic assemblages within the varghis karst eastern transylvania romania combining our first chronological results with information from previous excavations we can distinguish two main stages of habitation albeit middle palaeolithic lithics and faunal remains appear scattered throughout the investigated profile within the abri 122 rock shelter in order to augment the typological cultural considerations we applied direct radiocarbon dating on bones and charcoal from within the occupation layers radiocarbon dating of bones suggests that the middle palaeolithic sequence is older than the upper dating limit of the method whereas direct luminescence ages on the lowermost productive horizon and immediately above it indicate surprisingly old ages of ca 106 141 ka osl optically stimulated or 99 174 ka irsl infrared stimulated multiple protocol dating of charcoal found within the two habitation layers produced ages 38 14 c ka bp also suggesting that the lowermost lithic rich horizon pertains to the middle palaeolithic industries overall the recovered lithics currently forming one of the most significant collections for romania are fully consistent with two main habitation phases connected to middle palaeolithic cultural affinities the occurrence of a volcanic ash layer within ursului cave and originating from the ciomadul volcanic complex carpathians is first reported here recently dated to 43 50 ka it might represent an important marker horizon providing that it is identified within other palaeolithic cave assemblages

marine derived 14c calibration and activity record for the past 50 000 years updated from the cariaco basin abstract an expanded cariaco basin 14c chronology is tied to 230th dated hulu cave speleothem records in order to provide detailed marine based 14c calibration for the past 50 000 years the revised high resolution cariaco 14c calibration record agrees well with data from 230th dated fossil corals back to 33 ka with continued agreement despite increased scatter back to 50 ka suggesting that the record provides accurate calibration back to the limits of radiocarbon dating the calibration data document highly elevated 14c during the glacial period carbon cycle box model simulations show that the majority of observed 14c change can be explained by increased 14c production however from 45 to 15 ka 14c remains anomalously high indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today additional observations of the magnitude spatial extent and timing of deep ocean 14c shifts are critical for a complete understanding of observed glacial 14c variability

geology geochronology and rift basin development in the central sector of the main ethiopia rift based on stratigraphic relationships and k ar dating of volcanic rocks from both of the escarpments flanking plateaus and from the rift floor of the central sector of the main ethiopian rift six major volcanic episodes are recognized in the rift9s development over a time span from the late oligocene to the quaternary using the k ar data correlation of volcanic units from the six periods of activity throughout the study area forms the basis for establishing six time stratigraphic chronozones for the central sector that are related to volcanism in the ethiopian cenozoic volcanic province the oldest basalt and rhyolite flows exposed along the rift margins of the central sector are time correlative to or older than those in river canyons for example blue nile on the adjacent northwest plateau a thinned mesozoic stratigraphic sequence along the guraghe western rift margin suggests that doming may have preceded volcanism and rifting of the cenozoic by late miocene time at least by 8 3 ma and 9 7 ma the eastern and western faulted margins respectively of the rift had formed at guraghe and at agere selam as indicated by containment of flows of that age within the rift wall during eruption a paroxysm of calc alkaline ignimbrite activity produced voluminous flows nearly fully contained within the rift during the pliocene epoch the munesa crystal tuff 3 5 ma a prominent marker tuff exposed on both rift margins is present at depth in a geothermal well beneath the rift floor and indicates a minimum of 2 km of downthrow in the central sector since its eruption structural and stratigraphic relationships in the central sector indicate a two stage rift development this is characterized by an early phase late oligocene or early miocene of a series of alternating opposed half grabens along the rift with alternating polarity such as that in the present gregory and western rifts of east africa and symmetrical rifts that evolved from these grabens in late miocene or early pliocene time thus evolution from alternating half graben to a full symmetrical graben with a medially located neovolcanic zone that is bifurcated to marginal grabens in the northern part of the study area may be a fundamental part of the rifting process the study indicates that there are major petrologic and tectonic differences between the main ethiopian rift and the gregory kenyan rift

oxygen diffusion in quartz diffusional oxygen exchange between quartz and water was studied by determining 18o profiles in the quartz using an ion microprobe inverse error function plots of the data are linear as required for a diffusion mechanism one natural and two synthetic samples were used and although they had different impurity concentrations oh na and al per 106 si atoms are 7 4000 35 835 and 67 127 respectively the d values were the same within experimental uncertainty diffusion parallel to c is about 2 orders of magnitude faster than that normal to c at 700 c and diffusion normal to the rhombohedron is intermediate the data indicate a change in slope on an arrhenius plot at the boundary at 100 mpa 1 kbar water pressure the preexponential factors do in square centimeters per second and activation energies q in kilojoules per mole for quartz 500 550 c are as follows do 190 and q 284 parallel to c and do 8 10 2 and q 238 normal to the rhombohedron for quartz 600 800 c do 4 10 7 and q 142 parallel to c do 9 10 7 and q 155 normal to the rhombohedron and do 1 10 4 and q 234 normal to c d increases with ph 2 o and between 25 and 350 mpa log d versus log h 2 o has a slope of approximately 1 1 these d values are all several orders of magnitude larger than previously reported values for oxygen diffusion in water free systems

paleoenvironmental change in the late middle pleistocene holocene kibish formation southern ethiopia evidence from ungulate isotopic ecology abstract east africa has produced the earliest record of homo sapiens 200 ka and a punctuated record of middle stone age and later stone age behaviors we lack however a detailed late quaternary paleoenvironmental record for the region particularly during humid periods without a regional record hypotheses about the evolution and ecology of early homo sapiens in east africa remain vague and untestable the kibish formation of southern ethiopia presents a long albeit punctuated record of late middle pleistocene to holocene faunal change in east africa which was deposited during humid periods here we present oxygen and carbon stable isotope data of the kibish ungulates and test whether there are environmental changes within the kibish formation significant differences in 18o enamel isotopes are consistent with more humid conditions during the holocene age member iv 13 4 ka than either pleistocene age member i 196 ka or member iii 104 ka mesowear data document a shift toward more attritional wear among grazers in member iv and are correlated with more depleted 18o enamel values suggesting that the wear pattern shift is linked to the onset of more humid conditions during the holocene 13c enamel values show subtle variations through time but do not suggest any major changes in diets we propose that the paleoenvironmental differences evident in member iv based on 18o enamel values mesowear and bovid abundances may be explained by cooler and wetter conditions at the beginning of the holocene in the lower omo valley the evidence suggesting that the holocene humid phase is more pronounced than earlier humid phases may explain why arid adapted grassland ungulates became extinct in east africa by the pleistocene holocene transition but persisted through previous humid phases of the late quaternary

planet four probing springtime winds on mars by mapping the southern polar co2 jet deposits abstract the springtime sublimation process of mars southern seasonal polar co2 ice cap features dark fan shaped deposits appearing on the top of the thawing ice sheet the fan material likely originates from the surface below the ice sheet brought up via co2 jets breaking through the seasonal ice cap once the dust and dirt is released into the atmosphere the material may be blown by the surface winds into the dark streaks visible from orbit the location size and direction of these fans record a number of parameters important to quantifying seasonal winds and sublimation activity the most important agent of geological change extant on mars we present results of a systematic mapping of these south polar seasonal fans with the planet four online citizen science project planet four enlists the general public to map the shapes directions and sizes of the seasonal fans visible in orbital images over 80 000 volunteers have contributed to the planet four project reviewing 221 images from mars reconnaissance orbiter s hirise high resolution imaging science experiment camera taken in southern spring during mars years 29 and 30 we provide an overview of planet four and detail the processes of combining multiple volunteer assessments together to generate a high fidelity catalog of 400000 south polar seasonal fans we present the results from analyzing the wind directions at several locations monitored by hirise over two mars years providing new insights into polar surface winds

environmental change and human occupation of southern ethiopia and northern kenya during the last 20 000 years abstract our understanding of the impact of climate driven environmental change on prehistoric human populations is hampered by the scarcity of continuous paleoenvironmental records in the vicinity of archaeological sites here we compare a continuous paleoclimatic record of the last 20 ka before present from the chew bahir basin southwest ethiopia with the available archaeological record of human presence in the region the correlation of this record with orbitally driven insolation variations suggests a complex nonlinear response of the environment to climate forcing reflected in several long term and short term transitions between wet and dry conditions resulting in abrupt changes between favorable and unfavorable living conditions for humans correlating the archaeological record in the surrounding region of the chew bahir basin presumably including montane and lake marginal refugia for human populations with our climate record suggests a complex interplay between humans and their environment during the last 20 ka the result may contribute to our understanding of how a dynamic environment may have impacted the adaptation and dispersal of early humans in eastern africa

experimental studies of the role of water in the plasticity of quartzites experiments on several quartzites at 300 mpa confirming pressure show them to behave as if near the brittle ductile transition at 900 sup 0 c when oven dry and in a more ductile fashion at 1000 sup 0 c when extra water is added in both cases the stress strain curves are substantially higher than would be expected on the basis of the strength of hydrolytically weakened synthetic crystals containing less water than the rocks as measured by the broad infrared absorption at low temperature thus would appear that relative to the single crystals the effective concentration of the water related species that is active in mechanical weakening within the grains is only a small fraction of the water present the presence of glass in the grain boundaries of wet deformed specimens suggest that grain boundary weakening may also be significant in these experiments questions of equilibrium and of geological extrapolation are discussed

isotope calibrated greenland temperature record over marine isotope stage 3 and its relation to ch4 large temperature variations on millennial time scales in greenland characterised the last ice age abrupt warmings known as dansgaard oeschger do events can be traced in the 18oice record of greenland ice cores however it has been shown that 18oice is not a direct temperature proxy measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer here we present a continuous temperature record based on high resolution 15n measurements and firn model studies it covers a sequence of 9 do events 9 17 during the time period from 38 to 64 kyr bp for which temperature changes of 8 to 15 c were estimated the difference between the modern and the glacial 18oice t relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation a detailed comparison of the temperature evolution with reconstructions of the atmospheric methane ch4 concentration shows that ch4 rises lag temperature increases at the onset of do events by 25 to 70 yr within data resolution the strong correlation between greenland temperature and ch4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

effect of water on the rheology of experimentally deformed quartzite empirical flow laws have been determined for simpson quartzite samples deformed to mechanical steady state in the quartz stability field using griggs blacic solid medium deformation apparatus experiments were conducted on samples both as received dry and with water added via the dehydration of a talc confining medium wet best fits of the power law type yield a stress exponent of 2 72 0 19 an activation enthalpy of 134 32 kj mol 1 and a preexponential constant of 1 16 1 15 0 58 10 7 mpa 2 72 s 1 for the dry quartzite law and are 2 61 0 15 145 17 kj mol 1 and 5 05 5 00 10 6 mpa 2 61 s 1 for the wet quartzite the enhanced hydrolytic weakening of the wet experiments appears to affect the flow laws mostly in the preexponential constants possibly as a defect concentration term that is higher in the wet than in the dry law over the range of experimental conditions 750 900 c 10 7 to 10 4 s 1 and 1 0 1 25 gpa confining pressure dry specimens are 1 5 2 5 times stronger than wet samples deformed at the same conditions the microstructures produced are analogous to those observed in many natural quartz tectonites recrystallization is well developed in the wet but not the dry specimens at flow stresses below 500 mpa microstructures indicative of recovery are well developed a comparison of our creep activation enthalpies with those determined from diffusion experiments are consistent with deformation of wet simpson quartzite that is limited by oxygen self diffusion inconsistencies between the present study and previous studies are probably the result of differences in sample material sample treatment and sample assemblies chemical environment

araneiform terrain formation in angustus labyrinthus mars abstract the south polar area of mars exhibits an abundance of distinctive and exotic landforms most of which occur within the region covered by the seasonal co2 cap araneiform terrain also referred to as terrain covered by spiders is one of these unusual geomorphic features resulting from co2 sublimation driven seasonal erosion the high resolution imaging science experiment hirise on board nasa s mars reconnaissance orbiter mro spacecraft has repeatedly imaged angustus labyrinthus informally known as the inca city region 81 s 296 e over a period of four martian years showing a variety of classic polar features associated with sublimation and deposition including spiders we mapped the spiders spatial distribution in the inca city region and classified them in view of their morphological and topographic characteristics into four types fat thin half and elongated spiders the latter two are reported for the first time in this work we find that the formation mechanisms of half and elongated spiders were substantially influenced by ridge boundaries topography and pre existing linear depressions respectively based on our observations we extend the conceptual model of spider erosion explaining new elements of the spider formation process we interpret the causes of deviating araneiform species from thin spiders i e half elongated and fat spiders in the context of the extended model we consider the migration of pressurized co2 through the porous substrate towards breaches in the ice cover and the influence of the substrate s cohesive strength on the development of spider legs analysis of the spatial distribution of a fat spider population revealed that the initiation locations of spiders are not random but more evenly spaced indicating the existence of an inhibited zone around a newly formed spider consistent with our interpretations of the formation mechanism our case study in the inca city region provides new understanding in the formation process of basal sublimation driven features and thus offers new insight into polar surface processes

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

the hargeisan revisited lithic industries from shelter 7 of laas geel somaliland and the transition between the middle and late stone age in the horn of africa abstract this paper presents the lithic analysis from the stratified deposits of one of the laas geel rock shelters in somaliland shelter 7 this set of sites identified in 2002 is composed of around 20 rock shelters most featuring polychromic paintings attributed to the holocene moreover shelter 7 yielded numerous remains that are divided into two major chono cultural phases microlithic industries from the upper part of the deposit are ascribed to the late stone age lsa in contrast the industries from the lower part of the deposit feature an association of lsa characteristics but quite different from the ones from the upper part of the deposit with technical traits that belong to the msa and especially the presence of a levallois technology this association reintroduces the question of the existence of an industry or facies once labeled hargeisan and characterized by mixed features from the msa and the lsa in this part of africa at the end of the pleistocene our analysis of these industries culminates in a reconsideration of the definitions proposed by clark in his seminal book the prehistory of the horn of africa 1954 this study provides new typo technological data from the upper part of the laas geel shelter 7 deposit that contribute to refining clark s definition of the somaliland wilton industry in addition the association of blade bladelet production with typical levallois production in the lower part of this site s deposits supports a comparison with the hargeisan industry the industries recovered from laas geel shelter 7 reintroduce debates on the existence of the hargeisan industry and provide new data on the technological transition between the msa and the lsa in the horn of africa

abrupt or gradual change point analysis of the late pleistocene holocene climate record from chew bahir southern ethiopia we used a change point analysis on a late pleistocene holocene lake sediment record from the chew bahir basin in the southern ethiopian rift to determine the amplitude and duration of past climate transitions the most dramatic changes occurred over 240 yr from similar to 15 700 to 15 460 yr during the onset of the african humid period ahp and over 990 yr from similar to 4875 to 3885 yr during its protracted termination the ahp was interrupted by a distinct dry period coinciding with the high latitude younger dryas stadial which had an abrupt onset less than similar to 100 yr at similar to 13 260 yr and lasted until similar to 11 730 yr wet dry wet transitions prior to the ahp may reflect the high latitude dansgaard oeschger cycles as indicated by cross correlation of the potassium record with the northgrip ice core record between similar to 45 20 ka these findings may contribute to the debates regarding the amplitude and duration and mechanisms of past climate transitions and their possible influence on the development of early modern human cultures

fabric transitions in quartz via viscoplastic self consistent modeling part i axial compression and simple shear under constant strain quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures leading to the development of different types of crystallographic preferred orientation cpo patterns in this contribution we present the results of an extensive modeling of quartz fabric transitions via a viscoplastic self consistent vpsc approach for that we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems we have performed these simulations in axial compression and simple shear regimes under constant von mises equivalent strain of 100 1 73 assuming that the aggregates deformed exclusively by dislocation glide some of the predicted cpos patterns are similar to those observed in naturally and experimentally deformed quartz nevertheless some classical cpo patterns usually interpreted as result from dislocation glide e g y maxima due to prism slip are clearly not developed in the simulated conditions in addition we reported new potential preferred orientation patterns that might happen in high temperature conditions both in axial compression and simple shear we have demonstrated that cpos generated under axial compression are usually stronger that those predicted under simple shear due to the continuous rotation observed in the later simulations the fabric strength depends essentially on the dominant active slip system and normally the stronger cpos result from dominant basal slip in followed by rhomb and prism c slip whereas prism slip does not produce strong fabrics the opening angle of quartz 0001 fabric used as a proxy of temperature seems to be reliable for deformation temperatures of 400 c when the main slip systems have similar behaviors

100 000 years of african monsoon variability recorded in sediments of the nile margin abstract multiproxy analyses were performed on core ms27pt recovered in hemipelagic sediments deposited on the nile margin in order to reconstruct nile river palaeohydrological fluctuations during the last 100 000 years the strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source oscillating between a dominant aeolian saharan contribution during arid periods and a dominant nile river contribution during pluvial periods iron content shows a strong correlation with strontium and neodymium isotopes this allows the use of a high resolution continuous fe record as a proxy of blue nile sediment input over the last 100 000 years the detailed fe record with approximately 10 years resolution during pluvial periods is consistent with subtropical african records of well dated lake level fluctuations and thus constitutes a first continuous high resolution record of the east african monsoon regime intensity over ethiopia the detailed fe record shows the two main known pluvial periods attributed to strengthening of the african monsoon over ethiopia the nabtian period from 14 to 8 ka cal bp and the saharan period from 98 to 72 ka bp for the first time the last glacial period marine isotope stage mis 2 3 and 4 is documented with a continuous record showing large oscillations between high and low east african palaeo monsoon regimes the end of the nabtian period occurred at 8 ka in core ms27pt i e much earlier than on the east equatorial african region where it ended around 5 5 ka we interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the eastern ethiopian highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka during the last glacial period two wet periods are present around 60 50 ka bp and 38 30 ka bp these two humid periods are in phase with the rise of atmospheric ch4 concentrations suggesting that wetland tropical african area was one of the sources of the atmospheric ch4 during the mis 3 during the last glacial maximum and mis 4 high saharan aeolian influxes in phase with records of aeolian dust deposited in east antarctica are documented this study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low and high latitude climate variability at millennial timescales

microstructural development of fine grained quartz aggregates by syntectonic recrystallization abstract experimental study of syntectonic recrystallization of fine grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition agate was axially compressed with a constant strain rate apparatus experiments were conducted at 4 kbar solid confining pressure 700 1000 c and 10 4 10 6 sec 1 to 10 45 strain in all runs deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium two different types of microstructure were distinguished in the deformed specimens one is p type which is characterized by equant equidimensional and polygonal grains the other is s type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis the p type microstructure is developed at higher temperatures and slower strain rates while the s type developed at lower temperatures and faster strain rates the transition between the s and p types is found to be very sharp

radiocarbon dating from 40 to 60 ka bp at border cave south africa abstract we present 21 radiocarbon dates on 19 charcoal samples from the sedimentary sequence preserved in border cave south africa the background radiocarbon activity for charcoal from the cave was determined to be 0 050 0 018 percent modern carbon from the analysis of a radiocarbon dead sample from unit 5wa radiocarbon ages for individual samples ranged from 25 2 to 58 2 ka bp the error weighted mean ages for successively older strata are 38 5 0 85 0 95 ka bp for unit 1wa 50 2 1 1 1 0 ka bp for units 2bs lr a and 2bs lr b 56 5 2 7 2 0 ka bp for unit 2bs lr c and 59 2 3 4 2 4 ka bp for unit 2wa this radiocarbon chronology is consistent with independent chronologies derived from electron spin resonance and amino acid racemization dating the results therefore provide further evidence that radiocarbon dating of charcoal by the abox sc technique can yield reliable radiocarbon ages beyond 40 ka bp they also imply that border cave 5 a modern human mandible predates 58 2 ka bp and that the middle stone age mode 3 later stone age mode 5 transition of border cave was largely effected between 56 5 and 41 6 ka ago

soil carbon isotope evidence for holocene habitat change in the kenya rift valley in eastern africa the altitude of the boundary between montane forest and lowland savanna grassland changed substantially in response to climate change during the later holocene but this is not clearly reflected in regional pollen records the carbon 13 to carbon 12 ratios of tropical grasses are higher than those of most other plants and this difference is preserved in soil organic carbon stable isotope ratios soil organic matter 13 c 12 c ratios in profiles along an altitude transect in the central rift valley of kenya suggest that the forest savanna boundary advanced more than 300 meters in altitude this could have implications for understanding the effects of climate change on the configuration of floral zones prehistoric hunter gatherer land use patterns and the timing of the advent of neolithic food production

timing and hydrological conditions of sapropel events in the eastern mediterranean as evident from speleothems soreq cave israel this paper explores the connection between the timing of sapropel events in the eastern mediterranean sea and the time of low 18o events in speleothems of the soreq cave israel a new well dated 18o and 13c profile of the soreq cave speleothems for the last 140 kyr reveals five prominent low 18o events dated at 124 to 119 kyr with the main peak at 122 kyr event v 108 to 100 kyr with peaks at 107 and 102 kyr event iv 85 to 79 kyr with peak at 80 kyr event iii 55 to 52 kyr with a peak at 54 kyr event ii and 8 5 to 7 kyr with peaks at 8 5 and 7 kyr event i these events are characteristic of period of enhanced rainfall in the eastern mediterranean area particularly so for events v and i where the marked decrease in 18o and the correspondingly marked increase in 13c indicate very wet conditions the chronology of the low 18o events v iv iii and i match the ages estimated for the formation of sapropels s5 s4 s3 and s1 which are also associated with high hydrological activity thus it is suggested that the low 18o events in the soreq cave speleothems constrain the maximum duration of the sapropel formation pollen data from the sapropel layers and the isotopic pattern of the speleothems indicate that sapropels s5 and s1 were deposited during very wet periods when there were major decrease in the sea surface salinity coupled with frost free winters and drought free summers sapropels s4 and s3 were formed during periods of increased precipitation but ones in which the general climate was mediterranean semi arid

formation of martian araneiforms by gas driven erosion of granular material 1 sublimation at the lower surface of a seasonal sheet of translucent co2 ice at high southern latitudes during the martian spring and rapid outflow of the co2 gas generated in this manner through holes in the ice has been proposed as the origin of dendritic 100 m 1 km scale branched channels known as spiders or araneiforms and dark dust fans deposited on top of the ice we show that patterns very similar to araneiforms are formed in a hele shaw cell filled with an unconsolidated granular material by slowly deforming the upper wall upward and allowing it to return rapidly to its original position to drive air and entrained particles through a small hole in the upper wall straight braided and quasiperiodic oscillating channels unlike meandering channels on earth were also formed

the rate of water penetration in experimentally deformed quartzite implications for hydrolytic weakening abstract in order to determine the rate at which water penetrates the grains of a quartzite we performed several types of experiments including water added deformation and hydrostatic experiments on vacuum dried samples and hydrostatic annealing experiments on previously deformed quartzites samples of heavitree quartzite with an average grain size of 200 m and intragranular water concentration of 1750 420 h 10 6 si as measured by ftir were vacuum dried at 800 c 6 pa for 12 h after vacuum drying the grains showed thermal cracks with an average spacing of 50 m and an intragranular water concentration of 240 60 h 10 6 si one constraint on the rate of water penetration into quartz was obtained by deforming vacuum dried samples with 0 3 wt 20 000 h 10 6 si water added at 800 c 1500 mpa and a strain rate of 10 6 s conditions at which as is quartzite undergoes climb accommodated dislocation creep the time between reaching experimental conditions and yielding of the sample was between 2 and 9 h the samples had yield stresses of 100 250 mpa values well below the yield stress of 1500 mpa for a vacuum dried sample deformation of the grains was homogeneous on both optical and tem scales indicating that the grains had fully equilibrated with the water related defect that is responsible for water weakening ftir measurements are consistent with this interpretation one of the deformed samples has an intragranular water concentration of 820 160 h 10 6 si and vacuum dried samples hydrostatically annealed for 3 or 10 h at the same conditions as the deformed samples have an average intragranular water concentration of 730 180 h 10 6 si to obtain a second constraint on the rate of water penetration hydrothermal annealing experiments were performed on portions of a sample of heavitree quartzite which were previously deformed without water added at 700 c 1200 mpa and 10 5 s and have a high 10 16 m 2 and homogeneous dislocation density two samples were annealed at 700 c 1500 mpa for 24 h one with 0 2 wt water and one with no water added the grains in the water added sample have a rim approximately 15 m wide with dislocation recovery microstructures indicating equilibration with the water related defect the sample with no water added has a homogeneous dislocation density throughout the grains which is similar to that of the original deformed sample the 15 m wide recovered rim suggests a penetration rate approximately an order of magnitude faster than the rate of oxygen diffusion under hydrothermal conditions the observed rate of penetration of the water related species is consistent with theoretical considerations and calculations which predict a diffusion rate for h 2 o that is an order of magnitude faster than the rate of hydrothermal oxygen diffusion we infer from our experiments that the rate of water penetration into quartz is consistent with diffusion of h 2 o

the middle to upper paleolithic transition in the southern levant new insights from the late middle paleolithic site of far ah ii israel abstract far ah ii is an open air site in the north western negev desert israel previous excavations in the 1970 s revealed a rich in situ middle paleolithic mp assemblage composed of flint and limestone artifacts animal bones and charcoal renewed excavation at the site were undertaken in 2017 to re date it and provide a more accurate constrain to the sites age as well as collect samples for paleoclimatic proxies our new optically stimulated luminescence and 14c ages together with the stable oxygen isotope signature of the loess sediments constrain the age of the upper archaeological horizon to

hirise observations of gas sublimation driven activity in mars southern polar regions iii models of processes involving translucent ice abstract enigmatic surface features known as spiders found at high southern martian latitudes are probably caused by sublimation driven erosion under the seasonal carbon dioxide ice cap the mars reconnaissance orbiter mro high resolution imaging science experiment hirise has imaged this terrain in unprecedented details throughout southern spring it has been postulated kieffer h h titus t n mullins k f christensen p r 2000 j geophys res 105 9653 9700 that translucent co 2 slab ice traps gas sublimating at the ice surface boundary wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and or downwind and deposited in a fan shape here we model two stages of this scenario first the cleaning of co 2 slab ice from dust and then the breaking of the slab ice plate under the pressure built below it by subliming ice our modeling results and analysis of hirise images support the gas jet hypothesis and show that outbursts happen very early in spring

strain localization during high temperature creep of marble the effect of inclusions abstract the deformation of rocks in the earth s middle and lower crust is often localized in ductile shear zones to better understand the initiation and propagation of high temperature shear zones induced by the presence of structural and material heterogeneities we performed deformation experiments in the dislocation creep regime on carrara marble samples containing weak limestone or strong novaculite second phase inclusions the samples were mostly deformed in torsion at a bulk shear strain rate of 1 9 10 4 s 1 to bulk shear strains between 0 02 and 2 9 using a paterson type gas deformation apparatus at 900 c temperature and 400 mpa confining pressure at low strain twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at 0 1 0 2 peak shear stress at the imposed conditions is about 20 mpa which is 8 lower than the strength of intact samples strain progressively localized within the matrix with increasing bulk strain but decayed rapidly with increasing distance from the inclusion tip microstructural analysis shows twinning and recrystallization within this process zone with a strong crystallographic preferred orientation dominated by r and c slip in recrystallization induced weakening starts at local shear strain of about 1 in the process zone corresponding to a bulk shear strain of about 0 1 in contrast torsion of a sample containing strong inclusions deformed at similar stress as inclusion free samples but do not show localization the experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips recrystallization induced grain size reduction may only locally promote grain boundary diffusion creep accordingly the bulk strength of the twisted aggregate is close to or slightly below the lower isostress strength bound determined from the flow strength and volume fraction of matrix and inclusions

how martian araneiforms get their shapes morphological analysis and diffusion limited aggregation model for polar surface erosion abstract araneiforms are radially converging systems of branching troughs exhibiting fractal properties they are found exclusively in the southern polar regions of mars and believed to be result of multiple repetitions of cold co2 gas jets eruptions araneiform troughs get carved by the overpressurized gas rushing underneath a seasonal ice layer towards a newly created opening current work is an attempt to quantitatively analyze araneiforms patterns and model their formation mechanism araneiform shapes range from small and simple structures of one or two connected branches to intricate dendritic patterns several kilometers across the dendritic quality of most araneiforms are suggestive that they can be described in terms commonly applied to terrestrial rivers the main difference between rivers and araneiforms from the morphological point of view is that araneiform patterns are not directed or in any way influenced by the local gravitational gradient we have adapted and for the first time applied to martian araneiforms qualitative morphological analysis typically used for terrestrial rivers for several locations in the martian southern polar regions we have calculated the largest order of tributaries tributary densities and bifurcation ratios we have shown that the large and well developed araneiforms with tributary orders larger than 4 closely follow horton s law of tributary orders and have bifurcation ratio that falls well inside the range of terrestrial rivers we have implemented a two dimensional diffusion limited aggregation dla model that describes formation of dendrite shapes by mathematical probabilistic means we compared modeled dendrite shapes to the araneiform shapes observed in the martian polar regions and evaluated their similarity using the morphological analysis of araneiforms we showed that dla model can successfully recreate 2d shapes of different observed araneiforms to simulate the patterns that deviate from central symmetry it is required to modify the main governing parameter of dla model its two dimensional probability field an analog to the governing probability field in the case of araneiforms is the gas pressure in the cavity underneath the ice layer right before the gas starts moving towards the newly created escape vent thus modeling the creation of araneiform patterns with dla leads to better understanding of seasonal processes that create them

fabric asymmetry and shear sense in movement zones asymmetry between lattice preferred orientation and shape fabrics is commonly observed in microstructural studies of many deformed mineral aggregates e g ice carbonate rocks peridotites and quartzites theoretical predictions are limited by the nature of the models available and more can be gained by discussion of the mechanisms which give rise to such asymmetry in specific natural and experimental situations

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

the role of cryptotephra in refining the chronology of late pleistocene human evolution and cultural change in north africa abstract sites in north africa hold key information for dating the presence of homo sapiens and the distribution of middle stone age msa middle palaeolithic mp and later stone age lsa cultural activity in the late pleistocene here we present new and review recently published tephrochronological evidence for five cave sites in north africa with long msa mp and lsa cultural sequences four tephra horizons have been identified at the haua fteah cyrenaica libya they include cryptotephra evidence for the campanian ignimbrite ci eruption dating to 39 ka that allows correlation with other palaeolithic sequences in the eastern mediterranean and as far north as russia cryptotephra have also been recorded from the moroccan sites of taforalt rhafas and dar es soltane 1 at taforalt the geochemical composition suggests a provenance in the azores while examples from sodmein egypt appear to derive from central anatolia and another unknown source in these latter examples chemical compositional data from relevant proximal volcanic centres is currently lacking so the identification of tephra in layers of known age and cultural association provides the first reliable age determinations for distal volcanic events and their geographical extent the future potential for tephrochronological research in north africa is also discussed

fabric development in experimentally sheared quartzites abstract a fine grained quartzite was deformed under a combination of simple shear and axial compression to varying amounts of shear strain 1 3 to 2 9 the experiments were conducted at 800 c 1500 mpa and an axial strain rate of 10 6 s in the dislocation creep regime shear zone boundaries were oriented at 45 or 30 to the compressior axis the progressive development of deformation microstructures including planar fabrics and c axis preferred orientations was studied as a function of increasing shear strain elongate original grains define a foliation s which rotates from 45 to 0 to the shear zone boundary with increasing strain producing a sigmoidal foliation in a single shear zone a second foliation invariant in orientation is defined by elongate recrystallized grains which lie at about 30 40 to the shear zone boundaries no c surfaces parallel to the shear zone boundaries were observed however extensional crenulation cleavages c defined by parallel zones of recrystallized grains as well as impurity and melt segregations were observed even at low strain lying at approximately 30 to the shear zone boundaries and these could easily be mistaken for c surfaces c axis preferred orientations of original grains define symmetric type i crossed circle girdles at low strain 2 with the greater concentration of c axes in the direction of shear these features are very similar to those observed in natural ductile shear zones

dating volcanic and related sediments by luminescence methods a review abstract applications of luminescence dating of geological materials have undergone extensive development and refinement since 1974 when wintle first attempted to date volcanic lava using thermoluminescence tl today luminescence techniques are potentially highly useful methods for dating volcanic and related materials and events over timescales ranging from 10 2 to 10 6 years while luminescence approaches generally do not possess the precision afforded by techniques such as 40 ar 39 ar and 14 c methods they offer a useful alternative approach with advantages in terms of age range and scope of material although the application of luminescence methods has in some cases been successfully described a comprehensive study outlining and defining protocols for routine luminescence dating of volcanic materials has not been forthcoming this review surveys previous attempts to develop luminescence techniques to date volcanic products and discusses the state of knowledge of the luminescence behaviour of the four principal materials currently used for luminescence dating of volcanic events particular attention is paid to the red luminescence emissions primarily because of previous successes in using red thermoluminescence rtl of quartz and feldspar for dating volcanic products for which the upper age limit may extend beyond a million years proposals are made for future research directions these include technological developments in the measurement of optically stimulated red luminescence the systematic characterization of rtl and optically stimulated red luminescence as key luminescence parameters in volcanic quartz feldspar glass and polymineral sample fractions and optimization of luminescence dating methods to define a comprehensive protocol for routine dating of volcanic materials

late pleistocene to holocene human palaeoecology in the tropical environments of coastal eastern africa abstract the ecological adaptations that stimulated the dispersal and technological strategies of our species during the late pleistocene remain hotly disputed with some influential theories focusing on grassland biomes or marine resources as key drivers behind the rapid expansion and material culture innovations of homo sapiens within and beyond africa here we present novel chronologically resolved zooarchaeological taxonomic and taphonomic analysis and stable isotope analysis of human and faunal tooth enamel from the site of panga ya saidi c 78 0 4 ka kenya zooarchaeological data provide rare insights into the fauna associated with and utilized by late pleistocene holocene human populations in tropical coastal eastern africa combined zooarchaeological and faunal stable isotope data provide some of the only dated on site archives of palaeoenvironments beyond the arid interior of eastern africa for this time period while stable isotope analysis of humans provides direct snapshots of the dietary reliance of foragers at the site results demonstrate that humans consistently utilized tropical forest and grassland biomes throughout the period of site occupation through a transition from middle stone age to later stone age technological industries and the arrival of agriculture in the region by contrast while coastal resources were obtained for use in symbolic material culture there is limited evidence for consumption of marine resources until the holocene we argue that the ecotonal or heterogeneous environments of coastal eastern africa may have represented an important refugium for populations during the increasing climatic variability of the late pleistocene and holocene and that tropical environments were one of a diverse series of ecosystems exploited by h sapiens in africa at the dawn of global migrations

sublimation of mars s southern seasonal co2 ice cap and the formation of spiders 1 in this paper we define and describe morphological features that have colloquially been termed spiders and map their distribution in the south polar region of mars we show that these features go through a distinct seasonal evolution exhibiting dark plumes and associated fan shaped deposits during the local defrosting of the seasonal cap we have documented the seasonal evolution of the cryptic region and have found that spiders only occur within this terrain these observations are consistent with a geyser like model for spider formation association with the transparent cryptic portion of the seasonal cap is consistent with basal sublimation and the resulting venting of co2 gas also consistent with such venting is the observation of dark fan shaped deposits apparently emanating from spider centers spiders are additionally confined to the polar layered deposits presumably due to the poorly consolidated and easily eroded nature of their upper surface

cold jets in the martian polar caps 1 mars seasonal polar caps display dark ice local darker spots aligned elongate patches and radially dendritic forms that reverse albedo contrast the unexpected variety and sequence of these features are explained on the basis of processes involving co2 dust sand and h2o these processes are largely related to the atmosphere being near its saturation temperature and they have few terrestrial analogies in the simplest case the 1 m thick seasonal cap initially dusty cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents the slab ice sublimates at the base and is levitated on high pressure gas causing humidity exchange with deeper layers subslab gas converging toward the vents erodes channels in the soil and ejects this material in high velocity jets recent spectral observations indicate great variety in the details

reconstructing prehistoric settlement models and land use patterns on mt damota sw ethiopia abstract although high altitude mountain habitats are often regarded as unfavorable for human occupation e g aldenderfer 2014 on the other hand tropical highlands in africa are suggested as potential refugia during times of environmental stress e g basell 2008 brandt et al 2012 archaeological investigations on mount damota 2908 m a s l located on the boundary between the southwest ethiopian highlands to the west and the southern main ethiopian rift valley to the east yielded a large number of archaeological sites from the middle stone age period until historical times in this paper we try to reconstruct settlement models for the late pleistocene and holocene occupation in this area and speculate about potential land use patterns such complex topics demand a landscape archaeological approach that includes open air sites and rock shelters the results from our excavations at mochena borago rock shelter and evidence from open air sites that were recorded during intensive surveys on the slopes and plateau of the mountain allow a first reconstruction of the settlement history of the area

pyrolysis combustion 14c dating of soil organic matter abstract radiocarbon 14c dating of total soil organic matter som often yields results inconsistent with the stratigraphic sequence the onerous chemical extractions for som fractions do not always produce satisfactory 14c dates in an effort to develop an alternative method the pyrolysis combustion technique was investigated to partition som into pyrolysis volatile py v and pyrolysis residue py r fractions the py v fractions obtained from a thick glacigenic loess succession in illinois yielded 14c dates much younger but more reasonable than the counterpart py r fractions for the soil residence time carbon isotopic composition 13c was heavier in the py v fractions suggesting a greater abundance of carbohydrate and protein related constituents and 13c was lighter in the py r fractions suggesting more lignin and lipid related constituents the combination of 14c dates and 13c values indicates that the py v fractions are less biodegradation resistant and the py r fractions are more biodegradation resistant the pyrolysis combustion method provides a less cumbersome approach for 14c dating of som fractions with further study this method may become a useful tool for analyzing unlithified terrestrial sediments when macrofossils are absent

early human occupation at devil s lair southwestern australia 50 000 years ago abstract new dating confirms that people occupied the australian continent before the earliest time inferred from conventional radiocarbon analysis many of the new ages were obtained by accelerator mass spectrometry 14c dating after an acid base acid pretreatment with bulk combustion aba bc or after a newly developed acid base wet oxidation pretreatment with stepped combustion abox sc the samples charcoal came from the earliest occupation levels of the devil s lair site in southwestern western australia initial occupation of this site was previously dated 35 000 14c yr b p whereas the aba bc ages are indistinguishable from background beyond 42 000 14c yr b p the abox sc ages are in stratigraphic order to 55 000 14c yr b p the abox sc chronology suggests that people were in the area by 48 000 cal yr b p optically stimulated luminescence osl electron spin resonance esr ages u series dating of flowstones and 14c dating of emu eggshell carbonate are in agreement with the abox sc 14c chronology these results based on four independent techniques reinforce arguments for early colonization of the australian continent

hirise observations of gas sublimation driven activity in mars southern polar regions i erosion of the surface the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro has imaged the sublimation of mars seasonal co2 polar cap with unprecedented detail for one complete martian southern spring in some areas of the surface beneath the conformal coating of seasonal ice radiallyorganized channels are connected in spidery patterns the process of formation of this terrain erosion by gas from subliming seasonal ice has no earthly analog the new capabilities high resolution color and stereo images of hirise enable detailed study of this enigmatic terrain two sites are analyzed in detail one within an area expected to have translucent seasonal co2 ice and the other site outside that region stereo anaglyphs show that some channels grow larger as they go uphill implicating gas rather than liquid as the erosive agent dark fans of material from the substrate are observed draped over the seasonal ice and this material collects in thin to thick layers in the channels possibly choking off gas flow in subsequent years resulting in inactive crisscrossing shallow channels in some areas there are very dense networks of channels with similar width and depth and fewer fans emerging later in the season are observed subtle variations in topography affect the channel morphology a new terminology is proposed for the wide variety of erosional features observed

new radiocarbon dating of the transition from the middle to the upper paleolithic in kebara cave israel the middle to upper paleolithic transition mp up transition is considered a major technological and cultural threshold at the time when modern humans spread out of africa expanded from the levant into europe and possibly into central and northern asia the dating of this techno cultural transition has proved to be extremely difficult because it occurred sometime before 40 000 radiocarbon years before present 14c years bp which is close to the end of the effective dating range of radiocarbon other dating methods such as thermoluminescence tl or electron spin resonance esr are not sufficiently precise to date the recorded archaeological mp up transition in the levant here we report a consistent set of stratified radiocarbon ages on freshly excavated charcoal from kebara cave mt carmel israel that span the late middle paleolithic mp and early upper paleolithic eup this study applied novel strategies to improve sample preparation techniques and data analysis to obtain high resolution radiocarbon models from this study it is proposed that the mp up transition for this site can be placed immediately after 45 200 700 14c years bp and before 43 600 600 14c years bp or from 49 48 to 47 46 radiocarbon calibrated years before present years cal bp

chronology of the later stone age and food production in east africa abstract evidence from several archaeological sites in sub saharan africa suggests that the transition to modern human technology marked by the change from the middle to the later stone age lsa occurred first in east africa enkapune ya muto rockshelter in the central rift valley of kenya contains the oldest known archaeological horizons spanning this transition radiocarbon and obsidian hydration dates from this 5 6 m deep cultural sequence show that the later stone age began substantially earlier than 46 000 years ago ostrich eggshell beads were made 40 000 years ago early dates for the lsa and beads may have implications for the origin and dispersal of modern human behaviour and modern humans out of africa this site also contains the only known occurrences dating to the middle holocene dry phase in highland kenya and tanzania as well as occurrences that span the transition from hunting and gathering to food production and from the neolithic to the iron age the adoption of domestic animals by indigenous eburran hunter gatherers in highland east africa occurred gradually between 4900 and 3300 uncorrected radiocarbon years bp and the neolithic later iron age transition occurred around 1300 bp

quartz fabric transition in a cooling syntectonic granite hermitage massif france abstract the hermitage granite situated in the northwest massif central france is a syntectonic hercynian leucogranite emplaced along an active transcurrent shear zone during emplacement and cooling the progressive deformation is marked by the development of a primary homogeneous foliation gradually affected by ductile shear bands c s mylonites increase in strain heterogeneity during cooling corresponds to a change of dominant deformation mechanism of the quartz phase from grain growth and migration recrystallization to intracrystalline a slip and rotation recrystallization migration recrystallization is characterized by preferred orientations of c axes close to the principal extension direction we discuss relevant deformation mechanisms and rheological implications for syntectonic plutons in particular we argue that the transitions between homogeneous and heterogeneous accumulation of strain cannot generally be correlated with transition between magmatic and solid state flow

classifying past climate change in the chew bahir basin southern ethiopia using recurrence quantification analysis the chew bahir drilling project cbdp aims to test possible linkages between climate and evolution in africa through the analysis of sediment cores that have recorded environmental changes in the chew bahir basin in this statistical project we consider the chew bahir palaeolake to be a dynamical system consisting of interactions between its different components such as the waterbody the sediment beneath lake and the organisms living within and around the lake recurrence is a common feature of such dynamical systems with recurring patterns in the state of the system reflecting typical influences identifying and defining these influences contributes significantly to our understanding of the dynamics of the system different recurring changes in precipitation evaporation and wind speed in the chew bahir basin could result in similar but not identical conditions in the lake e g depth and area of the lake alkalinity and salinity of the lake water species assemblages in the water body and diagenesis in the sediments recurrence plots rps are graphic displays of such recurring states within a system measures of complexity were subsequently introduced to complement the visual inspection of recurrence plots and provide quantitative descriptions for use in recurrence quantification analysis rqa we present and discuss herein results from an rqa on the environmental record from six short 17 m sediment cores collected during the cbdp spanning the last 45 kyrs the different types of variability and transitions in these records were classified to improve our understanding of the response of the biosphere to climate change and especially the response of humans in the area

cultural and human dynamics in southern arabia at the end of the middle paleolithic abstract the arabian peninsula has long been considered as a region devoid of long term human settlement until the holocene period as a result of drastic climatic changes throughout the pleistocene it might be expected that the area was deserted during hyper arid and arid periods and populated by new migrant groups during humid events according to a push and pull phenomenon although this scenario may be perfectly valid for a large part of the peninsula a set of recent data points to the persistence of populations in several regions which may have served as refugia for human groups who developed their own technological traditions such a scenario is suggested by 1 the succession of dense human occupations under arid conditions between ca 60 and 50 ka in the wadi surdud basin a small sedimentary basin in the foothills of the yemeni western highlands this archaeological site complex encompasses several successive human settlements characterized by a middle paleolithic tradition which significantly differs from the middle paleolithic and middle stone age contemporaneous traditions from neighboring regions 2 the regional diversity of the middle paleolithic throughout the saharo arabian arid belt during mis 3 expressed by an array of local techno typological facies that likely relate to distant and disconnected source regions where populations contracted when climate worsened together with a set of high resolution archaeological contexts recently discovered in the arabian peninsula and dated to mis 5 these data suggest that the major human expansion waves which occurred in the region during the upper pleistocene are correlated with the wet phases of mis 5 while populations probably contracted into a few refugia areas at the beginning of mis 3

a contribution to late middle paleolithic chronology of the levant new luminescence ages for the atlit railway bridge site coastal plain israel abstract the atlit railway bridge arb prehistoric site is located on the northern coastal plain of israel within natural caves which formed in calcareous aeolianites kurkar perhaps during a high sea stand flint artifacts belonging to the levantine later mousterian tradition and faunal remains were found embedded in the kurkar infill of two caves the aeolianites in which the caves had developed were previously constrained by irsl 50 dating of feldspars to be older than the last interglacial highest sea stand frechen m et al 2004 chronology of pleistocene sedimentary cycles in the carmel coastal plain of israel quaternary international 121 1 52 providing a maximum age for the artifacts samples for luminescence dating were collected from the infill of the two caves ii and iii from the same deposits as the archaeological finds both quartz and alkali feldspars kf were extracted and measured using four different luminescence signals optically stimulated luminescence blue osl and violet stimulated luminescence vsl on quartz and the infrared stimulated luminescence irsl post ir ir 290 signal and the ir 50 signal corrected for anomalous fading on kf the ages obtained from analyses of the different minerals and signals mostly agree within errors the new luminescence ages date the sediment infill in caves iii and ii to 90 ka and 70 ka respectively indicating that hominin occupation of this locality is coeval with the nearby skhul cave and layer b in tabun cave

indian ocean climate and an absolute chronology over dansgaard oeschger events 9 to 13 oxygen isotope ratios of a stalagmite from socotra island in the indian ocean provide a record of changes in monsoon precipitation and climate for the time period from 42 to 55 thousand years before the present the pattern of precipitation bears a striking resemblance to the oxygen isotope record from greenland ice cores with increased tropical precipitation associated with warm periods in the high northern latitudes the largest change at the onset of interstadial 12 occurred very rapidly in about 25 years the chronology of the events found in our record requires a reevaluation of previously published time scales for climate events during this period

north and south subice gas flow and venting of the seasonal caps of mars a major geomorphological agent 1 dark polygons associated with fans and spots appear during the spring on the southern seasonal cap the basal sublimation of the translucent cap and the venting of the co2 gas are responsible for their formation as previously proposed for the spots and fans dark polygons appear when dark material emerges from elongated vents whereas spots and fans form from point sources a class of erosive features etched polygons is associated with depressions a few meters to tens of meters in diameters connected to a network of radiating troughs spiders spiders are shaped by the scouring action of the confined gas converging toward point sources whereas the etched polygons result from the forced migration of the co2 gas over longer distances the minimum age of the spiders is 104 years they result from one of the most efficient erosive processes on mars displacing 2 orders of magnitude more dust per year than a typical dust storm or than all the dust devils during the same time period in the north parts of the seasonal cap are translucent between ls 355 and ls 60 and are associated with spots fans dark polygons and possibly spiders suggesting that the basal sublimation and venting of the cap triggers a subice gas and dust flow that is modifying the morphology of the surface layer however perennial features are extremely uncommon on the north regolith indicating that the conditions for their formation or conservation are not met the reduced basal energy budget of the north cap compared to the south and the shorter seasonal life time of the north translucent ice may explain the relative scarcity of features in the north the polar layered deposits contain the stratigraphic record of climatic changes and catastrophic events both polar deposits may have been locally disrupted by the seasonal subice gas flow and the stratigraphic record may have been partially lost

planet four terrains discovery of araneiforms outside of the south polar layered deposits abstract we present the results of a systematic mapping of seasonally sculpted terrains on the south polar region of mars with the planet four terrains p4t online citizen science project p4t enlists members of the general public to visually identify features in the publicly released mars reconnaissance orbiter context camera ctx images in particular p4t volunteers are asked to identify 1 araneiforms including features with a central pit and radiating channels known as spiders 2 erosional depressions troughs mesas ridges and quasi circular pits characteristic of the south polar residual cap sprc which we collectively refer to as swiss cheese terrain and 3 craters in this work we present the distributions of our high confidence classic spider araneiforms and swiss cheese terrain identifications in 90 ctx images covering 11 of the south polar regions at latitudes 75 n we find no locations within our high confidence spider sample that also have confident swiss cheese terrain identifications previously spiders were reported as being confined to the south polar layered deposits spld our work has provided the first identification of spiders at locations outside of the spld confirmed with high resolution hirise high resolution imaging science experiment imaging we find araneiforms on the amazonian and hesperian polar units and the early noachian highland units with 75 of the identified araneiform locations in our high confidence sample residing on the spld with our current coverage we cannot confirm whether these are the only geologic units conducive to araneiform formation on the martian south polar region our results are consistent with the current co 2 jet formation scenario with the process exploiting weaknesses in the surface below the seasonal co 2 ice sheet to carve araneiform channels into the regolith over many seasons these new regions serve as additional probes of the conditions required for channel creation in the co 2 jet process

an early mis 3 pluvial phase in southeast arabia climatic and archaeological implications climatic changes in arabia are of critical importance to our understanding of both monsoon variability and the dispersal of anatomically modern humans amh out of africa the timing of dispersal is associated with the occurrence of pluvial periods during marine isotope stage mis 5 ca 130 74 ka after which arid conditions between ca 74 and 10 5 ka are thought to have restricted further migration and range expansion within the arabian interior whilst a number of records indicate that this phase of aridity was punctuated by an increase in monsoon strength during mis 3 uncertainties regarding the precision of terrestrial records and suitability of marine archives as records of precipitation mean that the occurrence of this pluvial remains debated here we present evidence from a series of relict lake deposits within southeastern arabia which formed at the onset of mis 3 ca 61 58 ka at this time the incursion of monsoon rainfall into the arabian interior activated a network of channels associated with an alluvial fan system along the western flanks of the hajar mountains leading to lake formation multiproxy evidence indicates that precipitation increases intermittently recharged fluvial systems within the region leading to lake expansion in distal fan zones conversely decreased precipitation led to reduced channel flow lake contraction and a shift to saline conditions these findings are in contrast to the many other palaeoclimatic records from arabia which suggest that during mis 3 the latitudinal position of the monsoon was substantially further south and did not penetrate the peninsula additionally the occurrence of increased rainfall at this time challenges the notion that the climate of arabia following mis 5 was too harsh to permit the further range expansion of indigenous communities

preparation and deformation of synthetic aggregates of quartz synthetic quartz aggregates of low porosity have been fabricated from natural quartz powder impure silica gel and high purity silicic acid by hydrothermal isostatic pressing at 300 mpa the resulting specimens have water contents comparable to those of natural quartzites and have been used for deformation tests the flow stress at 1200 1300 k was found to vary in an inverse relationship to the water pressure estimated under the assumption that the measured water content homogeneously filled the measured porosity it is questionable that the natural quartz origin specimens were fully equilibrated in respect to the activity of the water but equilibration has probably been achieved in the amorphous silica origin specimens which crystallized under the experimental conditions in the deformation of the latter materials the experimental activation energy at water pressures approaching the confining pressure was found to be about 150 kj mol 1 for both however the impure gel origin material gave a stress exponent of about 2 3 whereas the high purity silicic acid origin material gave a stress exponent of about 4 in spite of the grain sizes being about 90 m and 20 m respectively it is concluded that while the impure specimens have higher intragranular strengths there is also a significant contribution of grain boundary processes to the strain in them which is absent in the high purity specimens

the role of dynamic recrystallization in the development of lattice preferred orientations in experimentally deformed quartz aggregates abstract experiments on coaxially deformed quartz aggregates show that when dynamic recrystallization involves grain size reduction the lattice preferred orientation lpo of the recrystallized grains depends on the recrystallization mechanism at low temperatures and fast strain rates strain induced grain boundary migration recrystallization favors growth of grains oriented poorly for slip on the basal and prism planes resulting in an lpo of c axes parallel to the 1 direction at higher temperatures or slower strain rates progressive subgrain rotation produces recrystallized grains which inherit the small circle girdle lpo of their deformed host grains and which continue to re orient by slip at even higher temperatures and slower strain rates progressive subgrain rotation is accompanied by rapid grain boundary migration which does not favor grains of any particular orientation thus the lpo is again similar to that of non recrystallized grains in contrast when dynamic recrystallization involves grain growth driven by surface energy reduction a strong lpo of c axes parallel to 1 develops during grain growth but then evolves with increasing strain toward a small circle girdle the correlation of lpos with recrystallization mechanisms has important implications for the assumption of homogeneous strain in theoretical models of lpos and for interpreting natural lpos in recrystallized rocks

patterns of alluvial rivers the pattern planform of a river can be considered at vastly different scales depending upon both the size of the river and the part of the fluvial system that is under consideration figure 1 for example in the broadest sense river patterns comprise a drainage network dendritic parallel trellis etc figure la the type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs at another scale a river reach which in figure lb is meandering is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior and to the engineer who is charged with maintaining navigation and preventing major instability when a single meander is examined figure 1 c the hydraulics offtow the sediment transport and the potential for bank erosion are of concern in addition the sedimentologist is interested in the distribution of sediment within the bend bed forms within the channel figure ld and sedimentary structures figure ie which also establish a component of roughness for the hydraulic engineer finally the individual grains figure if provide geologic information on the sediment sources the nature of sediment loads and the feasibility of dredging for gravel there is an interaction of hydrology hydraulics geology and geomorphology at all scales which emphasizes the point that the fluvial system as a whole cannot be ignored even though only a component of the system is to be studied in this review only the patterns or planforms of alluvial rivers are discussed although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin figure la as well as its geologic history cannot be ignored in the explanation of the pattern of any river

hirise observations of gas sublimation driven activity in mars southern polar regions ii surficial deposits and their origins abstract the high resolution imaging science experiment hirise onboard mars reconnaissance orbiter mro has been used to monitor the seasonal evolution of several regions at high southern latitudes and in particular the jet like activity which may result from the process described by kieffer jgr 112 e08005 doi 10 1029 2006je002816 2007 involving translucent co 2 ice in this work we mostly concentrate on observations of the inca city 81 s 296 e and manhattan 86 s 99 e regions in the southern spring of 2007 two companion papers hansen et al this issue and portyankina et al this issue discuss the surface features in these regions and specific models of the behaviour of co 2 slab ice respectively the observations indicate rapid on set of activity in late winter initiating before hirise can obtain adequately illuminated images ls 2 titus et al 2007 agu abstract p41a 0188 these deposits originate from araneiform structures spiders boulders on ridges cracks on slopes and along linear cracks in the slab ice on flatter surfaces the type of activity observed can often be explained qualitatively by considering the local topography some dark fans are observed to shorten enormously in length on a timescale of 18 days we consider this to be strong evidence that outgassing was in progress at the time of hirise image acquisition and estimate a total particulate emission rate of 30 g s 1 from a single typical jet feature brighter deposits at inca city become increasingly hard to detect after ls 210 in the inca city region the orientations of surficial deposits are topographically controlled the deposition of dark material also appears to be influenced by local topography suggesting that the ejection from the vents is at low velocity 1 and that a ground hugging flow process a sort of cryo fumarole may be occurring the failure up to this point to obtain a clear detection of outgassing though stereo imaging is consistent with low level transport the downslope orientation of the deposits may result from the geometry of the vent or from catabatic winds at many sites more than one ejection event appears to have occurred suggesting re charging of the sources around ls 230 the brightness of the surface begins to drop rapidly on north facing slopes and the contrast between the dark deposits and the surrounding surface reduces this indicates that the co 2 ice slab is being lost completely in some areas at around this time by ls 280 at inca city the ice slab has effectively gone crism band ratios and themis brightness temperature measurements are consistent with this interpretation

late stone age variability in the main ethiopian rift new data from the bulbula river ziway shala basin abstract research conducted along the bulbula river ziway shala basin main ethiopian rift has yielded archaeological assemblages that document various phases of the upper pleistocene and the early holocene the oldest period documented is dated to 34 33 000 cal bp dw1 and the second is dated to the pleistocene holocene transition between 14 000 and 11 000 cal bp b1s1 dw2s2 and dw2s1 the analysis of these assemblages and their comparison offer new perspectives on early lsa industries and on the development and diversity of partially microlithic industries at the end the pleistocene and the beginning of the holocene through the characterization of techno economic changes in the context of shifting environments and their exploitation by humans our results intend to provide new insights into human behavioral evolution on a local scale and for a time period that is currently insufficiently known this study highlights the existence of major breaks in the archaeological record of the area during mis 3 1

the influence of pretreatment chemistry on the radiocarbon dating of campanian ignimbrite aged charcoal from kostenki 14 russia the presence of an independently dated marker in an archaeological site offers rare opportunities for assessing the reliability of radiocarbon dates especially when these are close to the age limit of the technique two different pretreatment protocols routine aba and more rigorous abox sc were employed in the chemical preparation of the same charcoal sample from a layer closely associated to the campanian ignimbrite tephra at the russian palaeolithic site of kostenki 14 markina gora the aba treated fraction gave an age of 33 14c ka bp comparable to a previous determination from the same layer whereas the abox sc produced an older age of 35 14c ka bp this is the first radiocarbon determination of an archaeological sample to provide an age consistent with the calendar age for the ci tephra marker

alkali extraction of archaeological and geological charcoal evidence for diagenetic degradation and formation of humic acids charcoal forms a crucial source of archaeological and palaeoenvironmental data providing a record of cultural activities past climatic conditions and a means of chronological control via radiocarbon 14c dating key to this is the perceived resistance of charcoal to post depositional alteration however recent research has highlighted the possibility for alteration and degradation of charcoal in the environment an important aspect of such diagenesis is the potential for addition of exogenous humic acids has to affect the accuracy of archaeological and palaeoenvironmental reconstructions based upon chemical analyses of ha containing charcoal however the release of significant quantities of ha from apparently pristine charcoals raises the question whether some ha could be derived via diagenetic alteration of charcoal itself here we address this question through comparison of freshly produced charcoal with samples from archaeological and geological sites exposed to environmental conditions for millennia using elemental c h o and isotopic 13c measurements fourier transform infrared spectroscopy ftir and proton liquid state nuclear magnetic resonance 1h nmr the results of analyses show that the presence of highly carboxylated and aromatic alkali extractable ha in charcoal from depositional environments can often be attributable to the effects of post depositional processes and that these substances can represent the products of post depositional diagenetic alteration in charcoal

stratigraphic and spatial distribution of ochre and ochre processing tools at porc epic cave dire dawa ethiopia abstract reassessment of the archaeological assemblages recovered by kenneth d williamson in 1975 and 1976 at porc epic cave dire dawa ethiopia demonstrates that the middle stone age msa levels of this site yielded one of the richest known collections of ochre and ochre processing tools from this period in terms of quantity we analyze the vertical and horizontal distribution of all ochre fragments n 4213 and ochre processing tools n 23 of known provenance and compare them with the distribution of other categories of archaeological remains our results suggest that no major post depositional reworking occurred at the site virtually no ochre fragments and processing tools are recorded in the superficial levels of the site 0 60 cm below datum concomitant and statistically significant changes in the location of ochre and ochre processing tool concentrations are observed at various depth intervals in deeper levels interpreted as changes in the location of the area devoted to ochre processing comparison of the vertical distributions of ochre fragments and lithics highlights that in most cases ochre and lithics covary the vertical distribution of gastropod opercula interpreted by other authors as ornaments and of ochre fragments throughout the sequence also follows the same trends however concentrations of ochre and ochre processing tools do not coincide with that of the opercula spatially 14c determinations obtained at porc epic indicate a relatively short chronology for the accumulation of the main archaeological deposits and date to ca 40 ka cal bp the levels containing most of the ochre this is consistent with the fact that no significant typo technological variations in the lithics are observed throughout the sequence and argues in favour of the site reflecting a phase of the transition from the middle stone age to the later stone age lsa in this region of africa

the great arc of dispersal of modern humans africa to australia abstract during the late pleistocene anatomically modern humans amh dispersed out of africa across the continents their routes obeyed the limitations placed on any large terrestrial mammal dependent on daily drinking water following certain climate permissive corridors amh first spread north with game across the sahara to the levant during the eemian interglacial c 125 ka but failed to continue to europe then occupied by neanderthals the savannah ecosystem in north africa and the middle east then dried up and amh vanished from the levantine fossil record being replaced there by neanderthals later amh successfully left africa as a single group by the southern route to india the added ability to make short but deliberate open water crossings allowed them first to cross the mouth of the red sea from eritrea and subsequently wallace s line to reach the isolated sahul continent at least by 48 000 years ago and possibly by 60 50 000 years ago they only finally arrived in europe from south asia around 45 50 000 years ago probably linked to climatic amelioration during ois 3

how the martian residual south polar cap develops quasi circular and heart shaped pits troughs and moats the martian residual south polar cap rspc is a 1 10 m thick deposit of permanent co 2 ice perched on the much larger h 2o ice cap the co 2 ice is dissected into mesas by erosional landforms that can be broadly classified as i quasi circular pits ii heart shaped pits iii linear troughs and iv moats we use hirise 25 50 cm px images taken at a cadence of days to months to track meter scale changes in the rspc in order to investigate the mechanisms that lead to the development of these four distinct morphologies for the first time we report the development of dark fans on the sides of the co 2 mesas and the fracturing and deterioration of the initially smooth upper surface of co 2 mesas we interpret these features as indicating the sublimation and subsequent escape of co 2 from the interiors of mesas which undermines structural support of mesa tops causing them to collapse the collapse of mesa tops along with uneven deposition of co 2 ice creates steep scarps that erode during the summer due to preferential sunlight absorption during the winter co 2 deposition acts to smooth topography creating gently sloping ramps we propose that the interplay between the steep scarps and gentle slopes leads to either quasi circular pits heart shaped pits linear troughs or moats depending on local conditions

silica diagenesis origin of inorganic and replacement cherts abstract silicification of originally non siliceous sediments affects a wide variety of rock types and materials and ranges from minor to pervasive partial and minor chertification occur mostly in phanerozoic carbonates carbonate bearing sandstones evaporites and fossil wood the source of the silica is predominantly biogenic in petrified wood the silicification mechanism is a permeation or void filling process not a replacement in this example the sequence of silica phase transformation is the same as that in deep sea siliceous sediments in many silicified rocks particularly in certain carbonates the transformation sequence is different from that in radiolarites or diatomites the chemical environment and conditions of early diagenetic chert formation in shallow water carbonates are delineated by the general mixing model of knauth 1979 but remain unknown for most other types an exception are the flint nodules and bands of the english chalk a detailed geochemical study of the paramoudra flint structures by clayton 1986 provided remarkable insight into the replacement process seven different recurring silica fabrics have been recognized in chert replaced carbonates including equigranular microcrystalline quartz or microquartz and megaquartz and fibrous types chalcedony quartzine or length slow chalcedony lutecite zebraic chalcedony and microflamboyant quartz among the latter quartzine and microflamboyant quartz are common in but by no means restricted to chert replaced evaporites for which milliken 1979 recognized a sequence of seven quartz fabrics as a single criterion only anhydrite inclusions in megaquartz quartzine or microflamboyant quartz provide unequivocal evidence for an evaporite precursor the relative timing between silicification and well established diagenetic carbonate reactions shows that virtually all theoretically possible sequences occur chertification of carbonate host sediment thus may take place during early intermediate or late diagenesis and even during anchimetamorphism pervasive to complete silicification has been described in lacustrine pedogenic and hydrothermal volcanogenic rocks and occurs on the scale of individual beds members or entire formations it may affect some of the aforementioned rock types too for example carbonates the source of the silica is predominantly inorganic chert formation in these environments includes direct chemical silica precipitation from solution through a gel stage magadi type cherts result from the conversion of the hydrous sodium silicate magadiite into microcrystalline quartz which has occurred in east african rift valley lakes such as lake magadi in late pleistocene time they are closely related to directly precipitated inorganic cherts which have been observed in alkaline environments of playa lakes silcretes originate from weathering and soil forming processes under climatic and environmental conditions conducive to the formation of duricrusts and laterites in more humid climates however non weathering profile silcretes occur which have been distinguished from weathering profile silcretes four to five different silcrete fabric types have been established including the 1 grain supported or quartzitic 2 floating terrazzo 3 matrix albertinia and opaline and 4 conglomeratic types in volcanic edifices silicification related to hydrothermal activity occurs 1 along the ascent routes of the fluids vents within the volcanic complexes 2 in isolated ponds and depressions on the sea floor where the fluids discharge mostly in the median rift valley of mid ocean ridges and 3 in geothermal areas on land associated with spreading lineaments volcanic islands arcs transform faults or continental hot spots attention has focussed on the associated base metal concentrations and less on the silicification and accompanying iron enrichment processes the precambrian banded iron formations may be indirectly or directly related to hydrothermal volcanic processes the origin of these cherty iron formations certainly requires more than one genetic model and at present remains a major unresolved problem despite massive efforts to tackle it

climatic change recorded in the sediments of the chew bahir basin southern ethiopia during the last 45 000 years abstract east african paleoenvironments are highly variable marked by extreme fluctuations in moisture availability which has far reaching implications for the origin evolution and dispersal of homo sapiens in and beyond the region this paper presents results from a pilot core from the chew bahir basin in southern ethiopia that records the climatic history of the past 45 ka with emphasis on the african humid period ahp 15 5 ka calbp geochemical physical and biological indicators show that chew bahir responded to climatic fluctuations on millennial to centennial timescales and to the precessional cycle since the last glacial maximum potassium content of the sediment appears to be a reliable proxy for aridity showing that chew bahir reacted to the insolation controlled humidity increase of the ahp with a remarkably abrupt onset and a gradual termination framing a sharply defined arid phase 12 8 11 6 ka calbp corresponding to the younger dryas chronozone the chew bahir record correlates well with low and high latitude paleoclimate records demonstrating that the site responded to regional and global climate changes

millennial scale variability during the last glacial the ice core record the oxygen isotope records from greenland ice cores show a very strong reproducible pattern of alternation between warm greenland interstadials gi and cold greenland stadials gs at millennial scale during the last glacial period here we summarise what is known about this variability from ice core records the typical cycle has a sawtooth pattern with a very rapid warming event occurring in a few decades a slow cooling trend and then a final fast cooling 25 such events have been numbered in the last glacial the recent gicc05 age scale provides the best available age scale that can be directly applied to this stratigraphy and we summarise the timing of the warming events and the length and strength of each event the greenland stratigraphy can be transferred to other records if we make assumptions about the contemporaneous nature of rapid events in different archives other parameters such as the snow accumulation rate and the concentration of terrestrial dust and sea salt recorded in the greenland cores also show a strong contrasting pattern between gi and gs methane concentrations are generally high during gi and lower during gs with the increase from gs to gi occurring within a century antarctic ice cores show a different pattern each gi has an antarctic counterpart but antarctica appears to warm while greenland is in a gs and cool during gi these changes are consistent with a mechanism involving ocean heat transport but the rapid nature of warmings poses a challenge for modellers while the rapid methane changes pose questions about the pattern of land biosphere emissions during the glacial that are also relevant for understanding glacial interglacial methane variability

40ar 39ar dating into the historical realm calibration against pliny the younger laser incremental heating of sanidine from the pumice deposited by the plinian eruption of vesuvius in 79 a d yielded a40ar 39ar isochron age of 1925 94 years ago close agreement with the gregorian calendar based age of 1918 years ago demonstrates that the 40ar 39ar method can be reliably extended into the temporal range of recorded history excess 40ar is present in the sanidine in concentrations that would cause significant errors if ignored in dating holocene samples

experimental investigation of insolation driven dust ejection from mars co2 ice caps mars polar caps are depending on hemisphere and season partially or totally covered with co2 ice icy surfaces such as the polar caps of mars behave differently from surfaces covered with rock and soil when they are irradiated by solar light the latter absorb and reflect incoming solar radiation within a thin layer beneath the surface in contrast ices are partially transparent in the visible spectral range and opaque in the infrared due to this fact the solar radiation can penetrate to a certain depth and raise the temperature of the ice or dust below the surface this may play an important role in the energy balance of icy surfaces in the solar system as already noted in previous investigations we investigated the temperature profiles inside co2 ice samples including a dust layer under martian conditions we have been able to trigger dust eruptions but also demonstrated that these require a very narrow range of temperature and ambient pressure we discuss possible implications for the understanding of phenomena such as arachneiform patterns or fan shaped deposits as observed in mars southern polar region

development of fluid veins during deformation of fluid rich rocks close to the brittle ductile transition comparison between experimental and physical models to understand the factors affecting the orientation and spacing of fluid veins in deforming silicate matrices experimental results on the deformation of sub micron flint have been examined new results and data from the literature show that deformation of flint at high temperature fluid rich conditions 6 vol fluid and strains less than 0 1 0 2 leads to the development of fluid banding orthogonal to consistent with theoretical expectations on the other hand above these strains and with fluid poor conditions 1 vol conjugate r1 and r2 riedel bands are observed related to brittle fracture these latter bands cross the first generation of 45 bands formed at lower it is of note that for strains up to 0 5 the strain rate remains uniform throughout the entire sample but that above this value deformation is concentrated in a single prominent riedel band to understand and rationalize these observations one dimensional numerical modelling of fluid rock separation during shear has been performed the model assumes a constant strain rate and uses the interstitial fluid dependence of the pressure solution viscosity of quartz at the beginning of the numerical simulation fluid and solid pressures are equal pf ps but shearing leads to the development of zones of compaction from which fluid is expelled pf drops and the solid viscosity rises sharply because strain rate is uniform across the bulk sample the model implies that local stress rises sharply in the compaction bands but remains low in zones where fluid accumulates indeed the model shows that in the zones of fluid extraction both the deviatoric stress and the excess pressure pf ps have the same amplitude their value exceeds the bulk shear stress by a factor of about five in light of these numerical results we tentatively suggest that in certain experimental studies low angle fluid rich veins may be initiated by transient embrittlement of the rock in zones of fluid loss subsequently a drop in permeability orthogonal to cracking may lead to compaction in that direction filling the cracks with fluid consideration of the strain rate conditions of the mantle calls into question whether low angle melt veins will occur or not in natural olivine basalt systems although such veins may be relevant for fluid percolation in quartz fault gouges

the khormusan evidence for an msa east african industry in nubia abstract there is clear evidence of lithic technological variability in middle paleolithic mp assemblages along the nile valley and in adjacent desert areas one of the identified variants is the khormusan the type site of which site 1017 is located north of the nile s second cataract the industry has two distinctive characteristics that set it apart from other mp industries within its vicinity one is the use of a wide variety of raw materials the second is an apparent correlation between raw material and technology used suggesting a cultural aspect to raw material management stratigraphically site 1017 is situated within the dibeira jer formation which represents an aggradation stage of the nile and contains sediments originating from the ethiopian highlands while it has previously been suggested that the site dates to sometime before 42 5 ka the dibeira jer formation can plausibly be correlated with nile alluvial sediments in northern sudan recently dated to 83 24 ka mis 5a this stage coincides with the 81 ka age of sapropel s3 indicating higher nile flow and stronger monsoon rainfall at these times other sites which reflect similar raw material variability and technological traditions are the bns and khs sites in the omo kibish formation ethiopia dated to 100 ka and 190 ka respectively based on a lithic comparative study conducted it is suggested that site 1017 can be seen as representing behavioral patterns which are indicative of east african middle stone age msa technology adding support to the hypothesis that the nile valley was an important dispersal route used by modern humans prior to the long cooling and dry trend beginning with the onset of mis 4 techo typological comparison of the assemblages from the khormusan sites with other middle paleolithic sites from nubia and east africa is used to assess the possibility of tracing the dispersal of technological traits across the landscape and through time

the dating of the upper paleolithic layers in kebara cave mt carmel abstract renewed excavations in kebara cave mt carmel made it possible to obtain a series of radiocarbon dates from the upper paleolithic layers of the site the various readings indicate the presence of early ahmarian industries around 43 36 ka bp while the levantine aurignacian is dated to 36 32 ka bp combined with the previously published tl dates for the uppermost mousterian layers it is suggested that during the transition from the middle to the upper paleolithic the cave was abandoned and that this cultural phase should be dated to c 46 45 43 42 ka bp

middle stone age archaeology at olduvai gorge tanzania abstract this paper describes the motivation procedures and results of archaeological and geological field survey of the ndutu unit olduvai gorge conducted in june and july of 2013 survey focused upon the area of olduvai gorge between the second fault and the obalbal depression although selective survey occurred in other areas in and around the gorge over 72 archaeological find spots were recorded and hundreds of middle stone age msa artifacts were recovered as was a small sample of fauna geological observations provisionally suggest that the ndutu was formed in part from a series of pyroclastic density flow and ash fallout events from neighbouring volcanoes this contrasts slightly with previous interpretations of the deposits in that at least some of the beds are thought to be in primary stratigraphic context our initial field findings are conducive to discussions of a number of issues directly relevant to the msa in east africa and overall we conclude that there is strong potential for olduvai s ndutu unit to shed light on the behavior adaptations and evolution of homo sapiens prior to during and just after its physical emergence