a basin redox transect at the dawn of animal life multiple eukaryotic clades make their first appearance in the fossil record between 810 and 715 ma molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic radiation animals require oxygen to fuel their metabolism and low oxygen levels have been hypothesized to account for the temporal lag between metazoan origins and the cambrian radiation of large ecologically diverse animals here paleoredox conditions were investigated in the fifteenmile group ogilvie mountains yukon canada which hosts an 811 ma ash horizon and spans the temporal window that captures the inferred origin and early evolution of animals iron based redox proxies redox sensitive trace elements organic carbon percentages and pyrite sulfur isotopes were analyzed in seven stratigraphic sections along two parallel basin transects these data suggest that for this basin oxygenated shelf waters overlay generally anoxic deeper waters the anoxic water column was dominantly ferruginous but brief periods of euxinia likely occurred these oscillations coincide with changes in total organic carbon suggesting euxinia was primarily driven by increased organic carbon loading overall these data are consistent with proposed quantitative constraints on proterozoic atmospheric oxygen being greater than 1 of modern levels but less than present levels comparing these oxygen levels against the likely oxygen requirements of the earliest animals both theoretical considerations and the ecology of modern oxygen deficient settings suggest that the inferred oxygen levels in the mixed layer would not have been prohibitive to the presence of sponges eumetazoans or bilaterians thus the evolution of the earliest animals was probably not limited by the low absolute oxygen levels that may have characterized neoproterozoic oceans although these inferred levels would constrain animals to very small sizes and low metabolic rates

sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

biostratigraphic and chemostratigraphic correlation of neoproterozoic sedimentary successions upper tindir group northwestern canada as a test case recent advances in proterozoic micropaleontology and sedimentary isotope geochemistry suggest that improved interbasinal correlation of neoproterozoic 1000 540 ma successions is possible because widely varying interpretations of its age have been suggested and no reliable radiometric dates or paleomagnetic data are available the upper tindir group of northwestern canada provides an opportunity to test this hypothesis the age of these strata is of paleontological importance because silicified carbonates near the top of the group contain disc shaped scale microfossils that may provide insights into the early evolution of biomineralization a reinterpretation of upper tindir microfossil assemblages suggests a late riphean age although diagenesis and contact metamorphism have altered the isotopic compositions of some carbonates least altered samples indicate that delta 13c of contemporaneous seawater was at least 4 7 typical of neoproterozoic but not cambrian carbonates strontium isotopic compositions of the least altered samples yield values of approximately 0 7065 which can be uniquely correlated with late riphean seawater together micropaleontology and the isotopic tracers of c and sr constrain the upper tindir carbonates and their unique fossils to be late riphean likely between 620 and 780 ma

desert pavement coated surfaces in extreme deserts present the longest lived landforms on earth all exposed rocks on earth s surface experience erosion the fastest rates are documented in rapidly uplifted monsoonal mountain ranges and the slowest occur in extreme cold or warm deserts millennial submeterscale erosion may be approached only in the latter the oldest previously reported exposure ages are from boulders and clasts of resistant lithologies lying at the surface and the slowest reported erosion rates are derived from bedrock outcrops or boulders that erode more slowly than their surroundings thus these oldest reported ages and slowest erosion rates relate to outstanding features in the landscape while the surrounding landscape may erode faster and be younger we present erosion rate and exposure age data from the paran plains a typical environment in the near east where vast abandoned alluvial surfaces 10 2 10 4 km 2 are covered by well developed desert pavements these surfaces may experience erosion rates that are slower than those documented elsewhere on our planet and can retain their original geometry for more than 2 m y major factors that reduce erosion converge in these regions extreme hyperaridity tectonic stability fl at and horizontal surfaces i e no relief and effective surface armoring by a clast mosaic of highly resistant lithology the 10 be concentrations in amalgamated desert pavement chert clasts collected from abandoned alluvial surfaces in the southern negev israel representing the sahara arabia deserts indicate simple exposure ages of 1 5 1 8 ma or correspond to maximum erosion rates of 0 25 0 3 m m y 1 the 36

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

pedogenic carbonates forms and formation processes abstract soils comprise the largest terrestrial carbon c pool containing both organic and inorganic c soil inorganic carbon sic was frequently disregarded because 1 it is partly heritage from soil parent material 2 it undergoes slow formation processes and 3 has very slow exchange with atmospheric co2 the global importance of sic however is reflected by the fact that sic links the long term geological c cycle with the fast biotic c cycle and this linkage is ongoing in soils furthermore the importance of sic is at least as high as that of soil organic carbon soc especially in semiarid and arid climates where sic comprises the largest c pool considering the origin formation processes and morphology carbonates in soils are categorized into three groups geogenic carbonates gc biogenic carbonates bc and pedogenic carbonates pc in this review we summarize the available data and theories on forms and formation processes of pc and relate them to environmental factors after describing the general formation principles of pc we present the specific forms and formation processes for pc features and the possibilities to use them to reconstruct soil forming factors and processes the following pc are described in detail earthworm biospheroliths rhizoliths and calcified roots hypocoatings nodules clast coatings calcretes and laminar caps the second part of the review focuses on the isotopic composition of pc 13c 14c and 18o as well as clumped 13c and 18o isotopes known as 47 the isotopic signature of pc enables reconstructing the formation environment the dominating vegetation 13c temperature 18o and 47 and the age of pc formation 14c the uncertainties in reconstructional and dating studies due to pc recrystallization after formation are discussed and simple approaches to consider recrystallization are summarized finally we suggest the most important future research directions on pc including the anthropogenic effects of fertilization and soil management in conclusion pc are an important part of sic that reflect the time periods and formation processes in soils a mechanistic understanding of pc formation is a prerequisite to predict terrestrial c stocks and changes in the global c cycle and to link the long term geological with short term biological c cycles

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

organism substrate interactions and astrobiology potential models and methods abstract organism substrate interactions and their products biogenic structures are important biosignatures on earth this study discusses the application of ichnology the study of organism substrate interactions to the search for present and past life beyond earth three main questions are addressed 1 why to look for biogenic structures i e traces and ichnofabrics beyond earth 2 what biogenic structures to expect on other planets moons and asteroids 3 how to study extraterrestrial biogenic structures review of terrestrial evidence highlights a set of properties that make traces and ichnofabrics important for the search of potential extraterrestrial life trace fossils preserve the activity of soft bodied organisms biogenic structures are resilient to processes that obliterate other biosignatures i e mechanical and chemical degradation diagenesis tectonism and metamorphism traces are very visible biosignatures traces indicate environment and behaviour traces can be universal biosignatures i e biosignatures ideally suited for detecting any type of life a model of organism substrate interactions beyond earth is here proposed expected extraterrestrial traces are those that manifest behaviours that allow to maintain homeostasis excavations meandering traces and biodeposition structures most of the existing rovers and orbiters provide basic instruments for searching these traces it is here suggested that the search for extraterrestrial biogenic structures by rovers would also benefit from artificial adjustable lighting gpr lidar and drilling equipment with optical televiewer in this study open access databases of rover and orbiter imagery have been searched for traces and ichnofabrics but no unquestionable evidence of biogenic structures beyond earth has been found besides those produced by humans this sounds along the lines of the famous fermi paradox if the universe is teeming with aliens where are their traces results of this search show that habitable environments are not the only place to look for biogenic structures non habitable environments such as moons without atmosphere can favour the preservation of shallow tier traces the better preservation potential of traces compared to other biosignatures greatly widens the issue of planetary protection including the interaction between astronauts or vehicles and the substrate may produce disturbances although this study highlights a new direction of study with the tools and concepts of ichnology dialogue between the astrobiological and ichnological communities is needed to use its full potential and possibly answer one of the major questions of science does life exist beyond earth

new insight into pedogenic processes in extremely arid environments and their paleoclimatic implications the negev desert israel abstract stratigraphic studies conducted on the alluvial fill of several ephemeral stream channels in the southern arava valley dead sea rift indicate the existence of a calcic soil developed 50 100 cm beneath the channel surfaces this anomalous calcic soil does not fall within the categories of any standard soil or paleosol definition and thus has been termed fluvial pedogenic unit fpu the fpu occurs at the lower limit of the contemporary scour and fill processes in the aerated zone and it defines the maximum scour and fill during floods the fpu is also found in late pleistocene and holocene terraces termed paleo fpu indicating that the hydrological regime of past floods was similar to the present one the formation of a calcic fpu in this unique environmental setting is associated with the cumulative influence of persistent differences in water availability to various parts of the channel before and during flood events the carbonate accumulation results from low recurrence of flood events relatively limited moisture amounts and almost no involvement of vegetation in its formation the isotopic analyses of calcic crusts in the fpu and in the paleo fpu indicate that arid climatic conditions prevailed during their formation this indicates that the flood regime under arid climatic conditions characterized most of the negev desert during the late pleistocene and the holocene however a clear difference in the 18 o and the 13 c values was detected between the active channels and the terraces this difference suggests a change in the rainwater composition rather than changes of temperature or amounts of rainfall

stable isotope ratios of carbon in phytoliths as a quantitative method of monitoring vegetation and climate change the 13c 12c ratios of occluded carbon within opal phytoliths from the northern great plains show potential as a basis for paleoclimatic reconstruction a significant correlation exists between the carbon isotopic composition of a host plant and that of the organic matter in its phytoliths the 13c 12c ratios for phytoliths from surface layers of soils along climatic gradients reflect the current proportions of c3 and c4 plants variations in the 13c values of phytoliths with soil depth are caused by a variety of processes burial of soil surface by dust bioturbation and possible illuviation by percolating water also contributions of phytoliths by dust and roots have unknown isotopic effects the 13c values of phytoliths from soils increase with decreasing 14c age suggesting that the proportion of c4 plants in this region has increased during the holocene phytoliths of apparent mid holocene age suggest exclusive dominance by c4 plants which agrees with paleoclimatic interpretations of an arid middle holocene climate

a tonian age for the visingso group in sweden constrained by detrital zircon dating and biochronology implications for evolutionary events detrital zircon u pb ages from samples of the neoproterozoic visingso group sweden yield a maximum depositional age of 886 9 ma 2 a minimum depositional age is established biochronologically using organic walled and vase shaped microfossils present in the upper formation of the visingso group the upper formation correlates with the kwagunt formation of the 780 740 ma chuar group in arizona usa and the lower mount harper group yukon canada that is older than 740 ma mineralized scale microfossils of the type recorded from the upper fifteenmile group yukon canada where they occur in a narrow stratigraphic range and are younger than 788 ma are recognized for the first time outside laurentia the mineralized scale microfossils in the upper formation of the visingso group seem to have a wider stratigraphic range and are older than c 740 ma the inferred age range of mineralized scale microfossils is 788 740 ma this time interval coincides with the vase shaped microfossil range because both microfossil groups co occur the combined isotopic and biochronologic ages constrain the visingso group to between 886 and 740 ma thus tonian in age this is the first robust age determination for the visingso group which preserves a rich microfossil assemblage of worldwide distribution the organic and mineralized microorganisms preserved in the visingso group and coeval successions elsewhere document global evolutionary events of auto and heterotrophic protist radiations that are crucial to the reconstruction of eukaryotic phylogeny based on the fossil record and are useful for the neoproterozoic chronostratigraphic subdivision

pleistocene paleosol development and paleoenvironmental dynamics in east africa a multiproxy record from the homo bearing aalat pedostratigraphic succession dandiero basin eritrea abstract the climatic changes during the early middle pleistocene transition are a key to understand the ecosystem dynamics that involved the homo erectus ergaster distribution the aalat pedostratigraphic succession represents a continental archive in the african rift valley eritrea where remains of homo around 1 ma were identified high resolution magnetostratigraphy dated this succession between the base of the jaramillo subchron and the lower brunhes chron despite the present arid desert climate the aalat section records a persistence of water driven fluvio lacustrine environments which suggests a major tectonic control on sedimentation although climate changes are clearly overprinted macro and micromorphological physico chemical mineralogical and geochemical features up to now poorly available for pleistocene paleosols in east africa depict a poor to moderate degree of development although calcic and petrocalcic petrogypsic horizons at different stratigraphic heights indicate phases of geomorphic stability the concurrent alternation of these horizons with iron stained layers suggests cyclical changes from dry to wet conditions which fit well with aeolian dust fluxes and marine isotope stages of glacials and interglacials at higher latitudes stable isotope data are consistent with these climatic cycles and suggest a succession of monsoonal and non monsoonal conditions the homo erectus settlement lasted apparently for a short time span because a long high discharge fluvial sedimentation and or an aridity phase at the base of the fluvial facies could have made the area less suitable for human settling and could have hindered preservation of fossils and artifacts

strontium and carbon isotope tracers and the origins of soil carbonate in south australia and victoria abstract calcium carbonate occurs in soils in association with a variety of rock types in coastal and inland south australia and victoria the 87 sr 86 sr ratios of the coastal soil carbonates fall between 0 7094 and 0 7098 showing that the ocean is the principal source of calcium to nearly all soils near the coast and that contributions from bedrock are generally small an exception is the soil formed on the young volcano at mt gambier in which the average ratio for carbonate is about 0 7070 compared to 0 7041 for the volcanic ash the basaltic ash of the volcano is readily weathered and rich in calcium roughly 40 of strontium and 10 to 20 of the calcium in the soil carbonate derives from the ash and the balance from marine sources the 87 sr 86 sr ratios from soil carbonate gradually increase inland reaching values of 0 7152 these higher ratios reflect at least in part the increasing 87 sr 86 sr ratio of inland dust in contrast the ocean does not contribute significantly to the carbon pool of the soils we studied the 13 c pdb values of soil carbonates on kangaroo island and the higher rainfall areas of eastern victoria fall between 11 0 and 8 7 indicating that the carbonate formed in equilibrium with the c3 dominated vegetation typical of the region in the warmer inland areas to the north such as the eyre peninsula the 13 c value of soil carbonate averages 5 3 reflecting the higher proportion of c4 plants in the local biomass mixing with marine sources of carbonate cannot account for the observed carbon isotopic patterns the flux of carbon into soils from the ocean therefore must be small compared to that derived from plant respiration and decay

organic walled microfossils from earliest cambrian or latest proterozoic tindir group rocks northwest canada abstract uppermost tindir group limestones exposed in the headwaters of tindir creek yukon territory canada contain a diverse and abundant microbiota of mineralized and organic walled microfossils preserved primarily in chert modules and chert beds the organic walled forms include mat building cyanobacterial filaments and coccoids accompanied by less common bacteria fungi and forms of uncertain affinity as well as planktonic coccoidal cyanobacteria and acritarchs several lines of evidence support interpretation of an early cambrian age whereas others suggest a late proterozoic age of the 54 organic walled taxa recognized 12 are newly described yukonosphaeridion interior awramik n gen n sp microagglomeratus borealis awramik n gen n sp phacelogeminus lineatus awramik n gen n sp palaeoanacystis magna awramik n sp cephalophytarion majesticum allison n sp heliconema bulbosa allison n sp trachyhystrichosphaera magna allison n sp fusilabellum brevistriatum awramik n gen n sp sphaeranasillos irregularis allison n gen n sp hyalocyrillium clardyi allison n gen n sp eophycomyces herkoides allison n gen n sp and archeomyces dimakeloides allison n gen n sp

tracing the provenance of fine grained dust deposited on the central chinese loess plateau eolian dust deposits in north china provide an excellent means of determining past variations in continental paleoclimate and atmospheric circulation however debate still exists on which deserts in east asia are the dominant sources of chinese loess and whether the dust provenance has shifted significantly at different time scales here we present new constraints on the provenance of fine grained dust deposited on the central chinese loess plateau clp by combining electron spin resonance signal intensity and crystallinity index of fine grained quartz contained in samples from two loess paleosol sequences our results show that the fine grained dust deposits on the clp originate mainly from the gobi desert in southern mongolia and the sandy deserts in northern china primarily the badain juran and tengger deserts rather than from the taklimakan desert in western china at least during the last climatic cycle the dominant source of fine grained dust varied significantly from southern mongolia during cold periods to northern china during warm periods the glacial interglacial provenance fluctuations are strongly coupled with changes in the intensity of the near surface northwesterly winter monsoon

a threshold in soil formation at earth s arid hyperarid transition the soils of the atacama desert in northern chile have long been known to contain large quantities of unusual salts yet the processes that form these soils are not yet fully understood we examined the morphology and geochemistry of soils on post miocene fans and stream terraces along a south to north 27 to 24 s rainfall transect that spans the arid to hyperarid transition 21 to 2 mm rain y 1 landform ages are 2 my based on cosmogenic radionuclide concentrations in surface boulders and ar isotopes in interbedded volcanic ash deposits near the driest site indicate a maximum age of 2 1 my a chemical mass balance analysis that explicitly accounts for atmospheric additions was used to quantify net changes in mass and volume as a function of rainfall in the arid 21 mm rain y 1 soil total mass loss to weathering of silicate alluvium and dust 1030 kg m 2 is offset by net addition of salts 170 kg m 2 the most hyperarid soil has accumulated 830 kg m 2 of atmospheric salts including 260 kg sulfate m 2 and 90 kg chloride m 2 resulting in unusually high volumetric expansion 120 for a soil of this age the composition of both airborne particles and atmospheric deposition in passive traps indicates that the geochemistry of the driest soil reflects accumulated atmospheric influxes coupled with limited in soil chemical transformation and loss long term rates of atmospheric solute addition were derived from the ion inventories in the driest soil divided by the landform age and compared to measured contemporary rates with decreasing rainfall the soil salt inventories increase and the retained salts are both more soluble and present at shallower depths all soils generally exhibit vertical variation in their chemistry suggesting slow and stochastic downward water movement and greater climate variability over the past 2 my than is reflected in recent 100 y rainfall averages the geochemistry of these soils shows that the transition from arid to hyperarid rainfall levels marks a fundamental geochemical threshold in wetter soils the rate and character of chemical weathering results in net mass loss and associated volumetric collapse after 105 to 106 years while continuous accumulation of atmospheric solutes in hyperarid soils over similar timescales results in dramatic volumetric expansion the specific geochemistry of hyperarid soils is a function of atmospheric sources and is expected to vary accordingly at other hyperarid sites this work identifies key processes in hyperarid soil formation that are likely to be independent of location and suggests that analogous processes may occur on mars

biogenic β fabric features in the hard laminated crusts of the mersin and adana regions southern turkey and the role of soil organisms in the formation of the calcrete profiles abstract this paper describes fabric features and their distribution in the calcretes and emphasizes the role of soil organisms in the formation of the calcrete profiles quaternary calcretes are common in the mersin and adana provinces occurring as powdery nodular tubular fracture infill and various forms of crusts the stable isotope values indicate calcrete development under semi arid climatic conditions and a pedogenic origin biogenic or fabric constituents are abundant in the hard laminated crust these are the rhizoliths alveolar septal structures needle fiber calcites calcified filaments spherical calcite bodies microcodium and vadose calcrete pisoliths rhizoliths have mainly formed by the petrification of roots and often contain cellular cortex structures the alveolar septal structure comprises root voids separated by a micritic wall or a bundle of tangentially oriented calcite needles needle fiber calcite is common in the hard laminated crust as monocrystalline rods and polycrystalline needles monocrystalline rods are smooth and small

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

red sedimentary units as indicators of early pleistocene tectonic activity in the southern negev desert israel abstract alluvial units termed red units accumulated along the western margin of the dead sea rift dsr valley southern negev desert israel in the early pleistocene these sedimentary units consist of coarse to fine grained alluvium of local origin which contain calcic paleosols the sediments of the red units accumulated in stream valleys and newly forming semi closed local tectonic basins during a tectonic phase that deformed the western margin of the dsr as a result of this deformation the pliocene northward flowing regional drainage system of the southern negev disintegrated to the present northeast flowing ephemeral drainage systems of nahal zihor nahal hiyyon and nahal paran all of them draining to the arava valley in the dsr this change was induced by two deformation episodes 1 reactivation of the zihor and the milhan faults two major northeast trending tectonic lines and 2 east and northeast tilting of the entire region during upwarp arching of the central negev the paleosols of the red units are characterized by pedogenic features such as rhizoconcretions and bk horizons the paleosols developed in the alluvial sediments that were deposited and preserved in local small structural basins along the main fault lines and in reversed or abandoned westward flowing pliocene stream valleys formation of paleosols was initiated in the stream valleys when they attained a near horizontal gradient due to gradual eastward directed regional tilting followed by low rates of deposition the sections of the red units in the pliocene valleys were incised due to continuing tilting which completely reversed the primary westward gradient of the valleys and they were incised by new east and northeast flowing streams the red units have paleoclimatic implications since the middle pleistocene the southern negev has been characterized by gypsic and salic soils typical of an extremely arid climate while the calcic soils detected in the red units point to a semi arid climate this indicates a gradual transition from more humid conditions in the early pleistocene to the present extreme aridity therefore the red units reflect a distinct tectonic and climatic regime and can serve as regional morphostratigraphic marker of early pleistocene age in this paper we used this marker to reconstruct the tectonic deformation that established the present configuration of the southern negev terrain

calcium carbonate nodules in soils 13o 16o and 13c 12c ratios and 14c contents abstract 18 o values 13 c values and 14 c ages were determined in ten caco 3 nodule populations collected from soil and paleosols in the israeli coastal plain the selected soils were carbonate free when formed and the nodules in them represent either reprecipitation of carbonate illuviated from overlying horizons descending mode or precipitated from a raised brackish water table ascending mode the 14 c ages represent the times of migration illuviation or eustatic movement both climate related and the stable isotopic conditions reflect the environmental conditions at such times the 13 c values of most populations were found to have a wide range and cannot be used to reconstruct former climates this wide range is attributed to microvariations of pco 2 in the soil because the 18 o ranges in the same samples are usually comparable to analytical uncertainties and because the 18 o mean values follow an age correlated pattern they permit us to place the soils in one of three categories in two cases where nodules were soft both turned out to be young 1000 years and to have wide ranges in 18 o values the latter are apparently due to continual re equilibration with new soil solutions in three cases of the descending mode of nodule formation 12 000 14 000 year old hard nodules had very narrow 18 o whose means reflect the rainfall value at that time the period between 12 000 14 000 years b p is independently known to be one of higher precipitation evaporation ratio and of more intensive soil formation these ascending mode populations of hard nodules had narrow ranges in 18 o reflecting a mixture of sea water and rainfall and all turned out to be 3 000 4 000 years old at this period the sea reached its highest elevation resulting in raising the nearcoast water table

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

stages and rate of the gravel shattering process by salts in desert reg soils abstract gravel shattering by salts is a common process in gravelly young to mature desert reg soils the shattered gravel is found on the surface and in the b and c horizons down to a maximum depth of 50 cm field studies on the process of salt weathering in deserts are scarce therefore the objectives of this study are to present the stages of development of the gravel shattering process by salts in desert reg soils and to discuss factors influencing the rate of development under natural conditions prevailing in the negev desert the studied reg soils were developed on two alluvial fan chronosequences in the negev desert the fan of nahal ze elim and the fan of nahal shehoret the development of the shattering process can be divided into five stages a e based on chemical physical and micromorphological features of the reg soils stages a d very young yo young reg soils represent the early holocene to the present some 14 000 years salinity values are between 0 27 16 mmho cm and the percentage of the shattered gravel is between 20 and 70 the shattered gravel however still maintains its original shape stage e mature reg soil represents the middle pleistocene to early holocene or 500 000 years salinity values at this stage reach 62 mmho cm although part of the gravel does not keep its original shape and starts to disperse in the profile the percentage of shattered gravel is only 75 80 it was found that the process of salt shattering in reg soils does not depend on concentrations or mineralogy of the salts but on the micro environmental conditions of the soil profile the process requires extreme and rapid variations of temperatures and moisture conditions such as found close to the soil surface to cause salt crystallization in a confined system with time the sealing of the soil surface through the development of desert pavement and a gravel free b horizon results in a change in the soil micro environment this change impedes the process irrespective of the amounts concentrations and types of salt minerals which exist in the profile the fact that in extreme arid regions the gravel shattering process develops primarily close to the reg soil surface suggests that it can be used to identify buried reg soils and to reconstruct climatic and micro environmental conditions of paleosols

the role of rare rainstorms in the formation of calcic soil horizons on alluvial surfaces in extreme deserts abstract soils in similar geomorphic settings in hyperarid deserts 1 should have similar characteristics because a negative moisture balance controls their development however reg soils in the hyperarid southern negev and namib deserts are distinctly different soils developed on stable alluvial surfaces with only direct input of rainfall and dust depend heavily on rainfall characteristics annual rainfall amount can be similar 15 30 mm but storm duration can drastically alter reg soil properties in deserts the cooler fall winter and dry hot summers of the southern negev desert with a predominance brief 1 day rainstorms result in gypsic saline soils without any calcic soil horizon although the namib desert receives only 50 60 of the southern negev annual rainfall its rainstorm duration is commonly 2 4 days this improves leaching of the top soil under even lower annual rainfall amount and results in weeks long grass cover the long term cumulative effect of these rare rain grass relationships produces a calcic gypsic saline soil the development of these different kinds of desert soils highlights the importance of daily to seasonal rainfall characteristics in influencing soil moisture regime in deserts and has important implications for the use of key desert soil properties as proxies in paleoclimatology

quaternary evolution of a hyperarid drainage under climatic fluctuations and rift margin base level fall ne negev israel abstract the long term bedrock incision of streams in the northeastern negev has been dictated since the early pliocene by the subsidence of the dead sea basin however this incision is accompanied by very long intervals of sediment aggradation here we document the quaternary scale fluvial response to changing base level lithology structure and climate along the hyperarid nahal zafit ne negev the oldest 1 2 ma alluvial remnants point to a widespread beveled bedrock pediment at the base of the hazera anticline this pediment like other stream pediment anticline relationships in the region provides the baseline framework into which nahal zafit incises during the early to middle pleistocene this pediment was the base level for all streams emerging out of the anticlines the tectonic subsidence of the regional base level at the rift margin farther downstream has caused incision and upstream migration of bedrock knickpoints triggering the development of a wide incised valley in the mazar syncline adjacent to the hazera anticline since 330 ka fluvial terraces landslides and taluses record intervals of basin wide fluvial deposition under prevailing hyperarid to arid climate despite the general arid climate prolonged fluvial deposition intervals occurred at ca 330 265 230 125 and 110 20 ka rapid and quite short duration bedrock incision occurred in between these much longer intervals of aggradation in addition to the proposed climatic imprint on fluvial aggradation incision cycles and the first order base level control of the rift margin fault the formation of strath terraces and distribution of stored sediments within the drainage basin point to the fundamental role that lithology and structure play in the quaternary evolution of the ne negev watersheds

relationship between climate and vegetation and the stable carbon isotope chemistry of soils in the eastern mojave desert nevada abstract the relationship between the stable c isotope composition of the soil environment and modern climate and vegetation was determined empirically along a present day climatic transect in the eastern mojave desert the 13c of the soil co2 and carbonates decreased with increasing elevation and plant density even though plant assemblages at all elevations were isotopically similar several factors including differences in the ratios of pedogenic of limestone calcite and differences in past vegetation were considered as explanations of this trend however it appears that in the sparsely vegetated mojave desert the 13c of pedogenic carbonate is controlled by differences in plant density and biological activity this relationship may provide a tool for assessing past vegetational densities as long as the vegetation is isotopically homogeneous

the role of the nile in initiating a massive dust influx to the negev late in the middle pleistocene the late middle pleistocene initiation of loess accretion in the negev desert israel resulted from a chain of events starting with the exposure of shallow offshore nile delta sands beginning 180 ka during a period of glacially lowered eustatic sea level this exposure allowed the formation of the dunes of the sinai negev erg and the eastward movement of the dunes under the gusty glacial time winds in northern sinai this eastward dune advance occurred by eolian saltation that generated the coarse silts that accumulated downwind as loess we postulate that the absence of earlier negev loess is not a result of interglacial erosion as previously proposed but is due to the relatively recent convergence of the above conditions necessary for loess formation we based our interpretation on analyses of two long term natural dust traps and the association of coarse quartz silt production with the advancing quartz rich dunes over this carbonate terrain although the nile delta is considered an early to middle pleistocene feature and therefore could have been the source of sand throughout the quaternary it attained the shallow depth range of glacial interglacial sea level changes only during late marine oxygen isotope stage 7 to early stage 6 allowing its wide exposure in quaternary times prior to erg formation negev dust was finer composed of silt and clays derived from distal sources in the sahara and arabian deserts

tropical plumes over eastern north africa as a source of rain in the middle east tropical plumes tps reflect tropical extratropical interaction associated with the transport of moisture from the tropics to extratropical latitudes they are observed in satellite images as continuous narrow cloud bands ahead of upper level subtropical troughs at times when the subtropical jet is highly perturbed rainstorms usually develop in the exit regions of tps so their presence over northern africa has an impact on the precipitation regime in the southeastern mediterranean based on satellite images and rainfall measurements from israel 10 tps over eastern north africa between 1988 and 2005 in which considerable rain was recorded were selected using the ncep ncar reanalysis data the structure and evolution of these tps were characterized and their regional canonical features were identified a typical tp that occurred in march 1991 is described in detail the main canonical characteristics are as follows the tp development is preceded by an incubation period expressed either as a stationary upper level trough persisting 2 6 days or as two consecutive tp pulses the preferred location for tp origin is 5 15 n 5 w 15 e the tp is separated from the underlying dry saharan pbl the subtropical trough undergoes a phase locking with the lower tropical trough the cloudiness in the tp induced rainstorm is mostly stratified with continuous moderate rain originating from midlevel moisture and the tp tends to be followed by a midlatitude cyclogenesis over the eastern mediterranean this analysis proposes several explanations for the efficiency of the tps in transporting moisture over a 2000 km distance

reconstructing the history of sediment deposition in caves a case study from wonderwerk cave south africa we applied cosmogenic isotope burial dating magnetostratigraphy and grain size distribution analysis to elucidate the history of the sedimentary sequence composed of fine quartz sands and silts of wonderwerk cave located on the southern edge of the kalahari desert south africa the source for the quartz sand is the kalahari sand dunes presently located 100 km to the north of the cave field observations and grain size analysis suggest a sediment transport scenario that includes eolian transport of kalahari sand abraded to a size of 70 100 m to the kuruman hills temporary storage on the hill slopes and valleys surrounding wonderwerk cave and later transport and deposition inside the cave our results suggest simple burial ages for sediments from both the front and back of the cave that range between 2 63 0 17 ma and 1 56 0 10 ma following initial exposure of 310 620 k y however 26 al 10 be ratios of 3 98 0 24 and 4 08 0 22 measured in a sand sample collected from the surface outside the cave may imply an initial burial signal equivalent to 0 78 0 15 ma thus reducing the possible age range of the buried samples to between 1 85 0 23 and 0 78 0 18 ma the paleomagnetic results for the front of the cave gave a polarity sequence of n r n n where n indicates normal polarity and r indicates reverse polarity this sequence can be correlated with both the older and younger cosmogenic burial age ranges the correlation suggests that in the cave front cosmogenic burial ages and the acquisition of stable remanent magnetization were not significantly affected by chemical and physical processes and that postburial production of cosmogenic isotopes was insignificant in contrast at the back of the cave the paleomagnetic polarity sequence of r n cannot be correlated with the cosmogenic burial ages since the temporal gap between the initial penetration of the sediment into the cave and the final acquisition of a stable remanent magnetization may have been long 10 5 yr and the single polarity transition can be correlated to any reverse normal transition that occurred during the quaternary this highlights the need for caution when cosmogenic burial ages and paleomagnetic sequences are compared the buried sediments in wonderwerk cave show similar grain size distributions to the fine sand sediment presently exposed at the surface in the vicinity of the cave furthermore calculated preburial 10 be concentrations for the buried sediment are similar to those measured in sediment outside the cave these similarities suggest that the environmental conditions and rates of geomorphic processes that persisted during sand deposition in wonderwerk cave during the late pliocene and early pleistocene may have been similar to those currently experienced in the southern kalahari the kuruman hills and the western ghaap plain these conditions favor the transport of fine grained quartz sand to the vicinity of the cave

fluvio pedogenic processes in an ephemeral stream channel nahal yael southern negev israel abstract a detailed stratigraphic survey conducted in the alluvial fill of the channel of nahal yael a small catchment in the southern negev desert indicates the existence of a continuous compacted red colored unit at an average depth of 50 cm beneath the surficial grey non cohesive alluvium granulometric distinction between the grey and the red alluvium is evident only within the fine

10be exposure ages of ancient desert pavements reveal quaternary evolution of the dead sea drainage basin and rift margin tilting abstract early to late pleistocene 10 be exposure ages of abandoned surfaces in the negev desert reveal the regional drainage evolution history and its relationship with the subsidence of the western margin of the dead sea rift the dated desert paved surfaces have developed over originally westward flowing rivers which were abandoned by early pleistocene and whose relicts are now progressively tilted towards the rift axis the slow and non destructive subsidence coupled with extreme hyperaridity enabled the preservation of these ancient surfaces along some of the main water divides in the negev nearly irrespective of their distance from the rift axis constraints on the tilting history are obtained from analyzing the spatial pattern of the exposure ages suggesting subsidence rates as low as 120 300 m ma 1 in the southern arava valley since the late pliocene it is shown that the transition from the pliocene to current drainage pattern occurred over a short period during the early pleistocene and that the governing fluvial response that followed the delineation of current basins is represented by a continuous spectrum of ages of inset terraces

early pleistocene lake deposits and lower paleolithic finds in nahal wadi zihor southern negev desert israel abstract an early pleistocene fluvio lacustrine sequence from the extremely arid southern negev desert israel indicates that climatic conditions during that period were humid enough to support the formation of a lake lake zihor there the lacustrine sediments were deposited in a tectonic valley that developed along the zihor tectonic line after the deposition of the pliocene arava formation they intercalate with fluvial sediments that contain several horizons of reddish calcic paleosols the lacustrine sequence comprises three sedimentary cycles each starts with a dark clay layer overlain by a white limestone unit both of which contain abundant freshwater fauna and terminates with a green detrital limestone that contains only one type of brackish water ostracod the top of each green limestone unit is characterized by pedogenic features and microrelief indicating desiccation of the lake and soil development isotope data support the hypothesis that the white limestone was deposited in an open freshwater lake the incision of the present channel of nahal wadi zihor in the lacustrine sediments is manifested by a series of rock cut and fluvial terraces q1 q4 capped by gypsic salic soils which reflect the onset of the present extremely arid climate over 100 find spots and larger occurrences of prehistoric artifacts assigned to the lower paleolithic were discovered near lake zihor on the basis of techno typological and stratigraphic considerations these assemblages are divided into two groups the first of which may be contemporaneous with the lake while the second is found mainly on the younger q1 and q2 terraces it is estimated that the lake existed for more than 100 000 years the climate during this period was probably semiarid but water budget calculations suggest that in addition to surface runoff seepage of groundwater along the zihor line contributed a considerable amount of water to the lake

application of the apatite oxygen paleobarometer aop across the neoproterozoic cambrian transition abstract fluorescence signatures of samarium3 substituted into apatite for calcium2 have been shown experimentally to correlate with oxygen availability such substituted apatite being a principal diagenetic mineral emplaced in shallow water environments during the neoproterozoic cambrian global phosphogenic event coeval with the cambrian explosion of life the occurrence of sm3 substituted apatite encrusting infilling and permineralizing components of shallow water microbial communities suggested that quantification of these fluorescence signatures might provide a widely applicable mineral based paleobarometer by which to measure oxygen concentrations in the environment in which such apatite precipitated to test this hypothesis fluorescence spectroscopic analyses have been carried out on the sm3 substituted apatite of photic zone microscopic fossils and fossil associated ooids of near shore facies of the ediacaran doushantuo south china and early cambrian chulaktau south kazakhstan formations and of the open ocean apatite biomineralized phytoplanktonic scale fossils characodictyon of the mid neoproterozoic tonian fifteenmile group yukon canada results obtained quantified by the newly devised apatite oxygen paleobarometer metric indicate a low

significance of primary hilltop loess in reconstructing dust chronology accretion rates and sources an example from the negev desert israel 1 although high latitude loess sequences have been studied extensively for reconstructing past climates loess in desert margins has been mostly overlooked moreover many low latitude loess studies have focused on secondary reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control in this respect the spatial distribution of the loess and its different types are crucial in this study we differentiate primary and secondary loess using remote sensing and field criteria we present remote sensing and geographic information system procedures for mapping loess distribution in general and for identifying pristine hilltop loess sequences in particular then we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary hilltop loess sequence in the negev desert that show that the late pleistocene negev loess started accumulating at 95 ka much earlier than previously proposed 70 ka it was preceded by a previously unknown middle pleistocene period of loess formation at 180 130 ka the ages also suggest that the threshold of dust accretion rate needed for loess formation is 0 02 mm a 1 30 g m 2 a 1 a factor of 2 or more lower than previously thought 0 04 to 1 0 mm a 1 our results also provide insights into causes of late pleistocene loess accretion and its close association with regional dune field activity the methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other more remote desert areas

holocene palaeolimnology of kajemamm oasis northern nigeria an isotopic study of ostracodes bulk carbonate and organic carbon a high resolution 5500 year palaeolimnological record from kajemarum oasis a closed basin in the manga grasslands of northern nigeria provides evidence of environmental change in subsaharan africa during the holocene palaeohydrological variations mainly changes in the balance between precipitation and evaporation are recorded by stable oxygen isotope ratios in bulk carbonate and ostracod calcite and by the sr ca ratio in ostracode shells variations in the carbon isotope ratios in carbonates indicate changes in primary productivity in the lake whereas the carbon isotope composition of organic carbon reflects ecophysiological processes within the lake and its surrounding catchment results indicate that there have been marked environmental changes in the manga grasslands over the last 5500 years a more variable climate set in around 1500 cal a bp a prolonged drought between 1200 and 1000 cal a bp with reduced aquatic productivity was followed by a switch to a wetter but still unstable climate moist conditions prevailed during the little ice age the results indicate that drought has affected the sahel episodically over the last 1500 years and is not solely a twentieth century phenomenon

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

iron and phosphorus biochemical systems and the cryogenian ediacaran transition jacadigo basin brazil implications for the neoproterozoic oxygenation event abstract termination of the marinoan snowball earth ice age 635 ma marked the transition to a greenhouse world this climate change forever modified the biogeochemical cycling of iron and phosphorus ended large scale iron formation deposition began accumulation of phosphorus on marine shelves and led to the ediacaran radiation of eukaryotes the jacadigo basin brazil contains a nearly complete record of this critical transition glaciomarine diamictites and iron formation accumulated during two marinoan ice advances with hydrothermal input of iron delivered via ice margin upwelling biochemically precipitated rhythmites of siderite sedimentary apatite and hematite represent microbially mediated sub sea ice precipitation siderite laminae preserve microbial textures and have a mean 13c 8 80 pdb 0 86 reflecting degradation of organic matter at the seafloor these millimeter scale rhythmites are a sensitive record of sub ice dynamics because they formed in response to short term fluctuations of o2 due to seasonal sub ice photosynthesis they demonstrate the connection between ice cover o2 and cycling of iron and nutrient elements such as phosphorus these biochemical rhythmites suggest that cryogenian sea ice limited oxygen production prior to the onset of the neoproterozoic oxygenation event o2 increased enough to concentrate bioavailable phosphorus at the seafloor which was essential for later diversification of metazoans in the ediacaran such sub ice cryogenian biochemical systems may provide earth based analogs for life on ice covered worlds such as europa and enceladus

middle late quaternary paleoclimate of northern margins of the saharan arabian desert reconstruction from speleothems of negev desert israel abstract speleothems in arid and hyper arid areas of negev desert israel are used in paleoclimate reconstruction of northern margins of saharan arabian desert focused on the following objectives 1 precise u th dating of the timing of speleothem growth as an indicator of periods of humid climate i e positive effective precipitation 2 the origin of rainfall using the speleothem 18 o and changes in spatial pattern of speleothem deposition and speleothem thickness along a north south transect 3 changes of vegetation cover based on speleothem 13 c variations during the last 350 ka major humid periods referred to herein as negev humid periods nhp occurred in the central and southern negev desert at 350 310 ka nhp 4 310 290 ka nhp 3 220 190 ka nhp 2 and 142 109 ka nhp 1 nhp 4 nhp 2 and nhp 1 are interglacial events whereas nhp 3 is associated with a glacial period during nhp 1 2 and 3 the thickness and volume of the speleothems decrease from the north to the south and in the most southern part of the region only a very thin flowstone layer formed during nhp 1 with no speleothem deposition occurring during nhp 2 and 3 these data imply that the eastern mediterranean sea was the major source of the rainfall in northern and central negev more negative speleothem 18 o values relative to central parts of israel soreq cave are attributed to rayleigh distillation because of the increasing distance from the mediterranean sea speleothem deposition during the nhp 4 in the southern negev was more intensive than in most of the central negev suggesting the prominence of the tropical rain source decrease in speleothem 13 c during nhp events indicates growth of the vegetation cover nevertheless the ranges of 13 c values show that the vegetation remained semi desert c4 type throughout the nhps with an additional significant carbon fraction coming from the host rock and the atmosphere these observations together with small thickness of the speleothem layers favor that nhp events consisted of clusters of very short humid episodes interspersed with long droughts nhp events were contemporaneous with climate periods with monsoon index of 51 cal cm 2 day and with the formation of sapropel layers in the mediterranean sea such simultaneous intensification of the monsoon and atlantic mediterranean cyclones is probably related to the weakening of the high pressure cell above sub tropical atlantic ocean which enabled more rainfall to penetrate into the saharan arabian desert from the north and south the contemporaneous occurrence of the nhp events and the increased monsoon rainfall could have opened migration corridors creating climatic windows of opportunity for dispersals of hominids and animals out of the african continent

patterns and implications of plant soil δ13c and δ15n values in african savanna ecosystems abstract southern african savannas are mixed plant communities where c3 trees co exist with c4 grasses here foliar 15n and 13c were used as indicators of nitrogen uptake and of water use efficiency to investigate the effect of the rainfall regime on the use of nitrogen and water by herbaceous and woody plants in both dry and wet seasons foliar 15n increased as aridity rose for both c3 and c4 plants for both seasons although the magnitude of the increase was different for c3 and c4 plants and for two seasons soil 15n also significantly increased with aridity foliar 13c increased with aridity for c3 plants in the wet season but not in the dry season whereas in c4 plants the relationship was more complex and non linear the consistently higher foliar 15n for c3 plants suggests that c4 plants may be a superior competitor for nitrogen the different foliar 13c relationships with rainfall may indicate that the c3 plants have an advantage when competing for water resources the differences in water and nitrogen use likely collectively contribute to the tree grass coexistence in savannas such differences facilitate interpretations of palaeo vegetation composition variations and help predictions of vegetation composition changes under future climatic scenarios

environmental changes recorded in the upper pleistocene along the desert boundary southern israel abstract most paleoclimatic studies in the middle east and africa suggest large changes in climate during the last 100 000 years a specific area of interest is the record of environmental changes along the desert boundary this study was conducted in such a boundary in the northern negev israel sedimentological evidence and the 18 o 16 o 13 c 12 c and 14 c content of carbonate nodules formed within the sediments were examined data obtained in two study areas 35 km apart suggest that while soil formation was occurring in the northwest only fluviatile and lake deposition occurred to the southeast the results of this study suggest that during the late pleistocene the boundary was much steeper than in the holocene the period before 35 000 yr b p periodically was wetter than at present with freshwater lakes and soil covered by c 3 plants a change to a more arid condition occurred during the last glacial maximum in europe 18 000 yr b p a second wet period not as wet as the earlier one occurred with the retreat of the glaciers in europe at this time decrease of loess supply and formation of the top soil occurred at both study locations in the southern area this wet period ended with highly evaporated sabkha deposits about 11 000 yr b p the holocene record suggests progressive aridity which was accompanied in the southeast location by covering the area with dunes

airborne dust transport to the eastern pacific ocean off southern california evidence from san clemente island 1 islands are natural dust traps and san clemente island california is a good example soils on marine terraces cut into miocene andesite on this island are clay rich vertisols or alfisols with vertic properties these soils are overlain by silt rich mantles 5 20 cm thick that contrast sharply with the underlying clay rich subsoils the silt mantles have a mineralogy that is distinct from the island bedrock silt mantles are rich in quartz which is rare in the island andesite the clay fraction of the silt mantles is dominated by mica also absent from local andesite and contrasts with the subsoils dominated by smectite ternary plots of immobile trace elements sc th la and ta nd cr show that the island andesite has a composition intermediate between average upper continental crust and average oceanic crust in contrast the silt and to a lesser extent clay fractions of the silt mantles have compositions closer to average upper continental crust the silt mantles have particle size distributions similar to loess and mojave desert dust but are coarser than long range transported asian dust we infer from these observations that the silt mantles are derived from airborne dust from the north american mainland probably river valleys in the coastal mountains of southern california and or the mojave desert although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin examination of satellite imagery shows that easterly santa ana winds carry abundant dust to the eastern pacific ocean and the california channel islands airborne dust from mainland north america may be an important component of the offshore sediment budget in the easternmost pacific ocean a finding of potential biogeochemical and climatic significance

the evolution of holocene reg gravelly soils in deserts abstract reg soil is an aridisol developed upon a stable alluvial surface composed of sand to coarse gravel the objectives of the present study were 1 to examine the initial evolution of reg soil properties with time 2 to assess and explain the rates of development of different properties 3 to establish the suitability of different soil properties for relative age dating the time dependent soil properties examined were 1 mechanical weathering of surficial rocks and desert pavement evolution 2 chemical and biological weathering of surficial rocks 3 the thickness of soil profiles and soil horizons 4 soil texture in the different horizons 5 salts and gypsum distribution and concentration in different soil horizons 6 degree of mechanical weathering of gravel in c horizons fifteen successive surfaces of the nahal wadi ze elim sequence of alluvial fans were selected for study dead sea region israel under an extremely arid climate the sequence is of holocene age 14 000 years b p to recent the main conclusions are 1 reg soils develop rather fast in several 10 3 years since their initiation however the various soil properties developed at different rates 2 the rates of change of three soil properties decrease with time these are the texture in different horizons change in added airborne and rain washed dust salinity within the soil profile change in added salts and gypsum and the amount of mechanically shattered rocks 3 soil thickness is established rather rapidly young and older holocene soil have practically the same depth surficial weathering rates appear to remain fairly constant with time 4 in coarse gravel the evolution of reg soils is dependent on added fines and salts of airborne origin and the resultant changing hydrologic regime in the soil profile the run off infiltration ratio changes as more fines and salts are added to the soil profile and as desert pavement develops 5 surficial features and fine clay in the soil profile may be used for approximate dating of otherwise undatable holocene alluvial surfaces salts and gypsum content should be cautiously used in a rather general way

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

permanent quaternary hyperaridity in the negev israel resulting from regional tectonics blocking mediterranean frontal systems although various episodes of wet quaternary climates have been suggested in studies of the negev desert here we demonstrate that reg soils developed on flat alluvial surfaces and sensitive to minor changes in precipitation indicate that the southern negev has been permanently hyperarid at least since the middle pleistocene the wetter episodes were restricted to the northern negev currently mildly arid gypsic saline reg soils that de veloped on stable surfaces during 200 k y in the southern negev are cumulative and polygenetic but none exhibits even the weakest development of calcic horizons under current climate conditions in the negev calcic soils are widespread in areas with rainfall 80 mm yr 21 the fact that the hyperarid 50 mm yr 21 southern negev lacks any calcic horizons indicates that it never experienced an average rainfall of 80 mm yr 21 during the middle late pleistocene whereas the northern negev was wetter this negev dichotomy is explained by the main physical features controlling rainfall over the negev i e the southward decreasing depth of the atmospheric boundary layer with distance from the mediterranean and the altitude of the central negev highland 1000 m the interaction between these two features often prevents the passage of rain clouds into the southern negev the holocene and pleistocene gypsic salic soil distribution across the negev closely matches the current circumstances we suggest that hyperaridity has prevailed over the southern negev since the last stages of the uplift of the central negev highland in the late pliocene early pleistocene

depositional and preservational environments of the ediacara member rawnsley quartzite south australia assessment of paleoenvironmental proxies and the timing of ferruginization abstract the paleoenvironmental setting in which the ediacara biota lived died and was preserved in the eponymous ediacara member of the rawnsley quartzite of south australia is an issue of longstanding interest and recent debate over the past few decades interpretations have ranged from deep marine to shelfal to intertidal to terrestrial here we examine the evidence in support of and against various paleoenvironmental interpretations of the fossiliferous ediacara member as well as exploring in depth a range of paleoenvironmental proxies that have historically been employed in such studies we emphasize the importance of reconciling paleoenvironmental analysis with an understanding of sedimentological processes and outline which proxies are consistent with this approach a careful assessment of paleoenvironmental parameters is essential to the reconstruction of the depositional and early diagenetic history of the ediacara biota and thus the physical chemical and biological factors that shaped the development and the fossilization of these earliest examples of complex life we find no compelling evidence for a terrestrial setting for the ediacara member and strong support for a shallow marine depositional environment

organic walled microfossils from the late mesoproterozoic to early neoproterozoic lower shaler supergroup arctic canada diversity and biostratigraphic significance abstract the diversification of acritarchs organic walled vesicular microfossils of unknown affinity filamentous and multicellular microorganisms happened during a time of profound environmental biological and ecological change the mesoproterozoic to neoproterozoic transition is a key interval notably for eukaryotic organisms new assemblages of organic walled microfossils from the ca 1230 ma to 900 ma lower shaler supergroup of arctic canada record an impressive diversity including macroscopic compressions of chuaria circularis and numerous unambiguous eukaryotic taxa the index taxon trachyhystrichosphaera aimika co occurs with eukaryotic taxa hitherto reported only from earlier dictyosphaera gigantosphaeridium satka favosa sensu javaux and knoll 2016 or later microlepidopalla time intervals five new taxa comprising the spheroidal acritarchs with inner wall sculpture nunatsiaquus cryptotorus n gen n sp and daedalosphaera digitisigna n gen n sp the acanthomorphs spiny acritarchs with regularly distributed processes herisphaera arbovela n gen n sp and herisphaera triangula n sp and the process bearing multicellular ourasphaira giraldae n gen n sp are reported along with three unnamed forms collectively these remarkable microfossils 63 taxa including 25 eukaryotic forms demonstrate the greatest diversity of eukaryotes ever recorded for this time interval

sources of strontium and calcium in desert soil and calcrete the carbon cycle significance of soil carbonate fluxes is subject to large uncertainties because it is not clear precisely how much calcium is derived from atmospheric sources compared with that from the chemical weathering of silicate minerals in the petrocalcic horizon calcrete of a pleistocene soil from the usda scs desert project area near las cruces nm approximately 1 5 g ca cm 3 has been added with an associated expansion of the profile of200 strontium isotope values for the labile cations and carbonate from the a b and k soil horizons have 87 sr 86 sr values that range from 0 7087 to 0 7093 similar to the values for easily soluble local dust and rain the parent material non calcareous camp rice alluvial sediment has a 87 sr 86 sr ratio of0 7165 mixing calculations indicate a minimum atmospheric contribution to soil carbonate calcium of 94 the more likely scenarios indicate at least 98 of the ca originated from atmospheric input the variations in 87 sr 86 sr ratios of soil silicate 0 7131 to 0 7173 are consistent with weathering of volcanogenic sediments and neoformation of clay minerals in the petrocalcic horizon moreover the sr isotope data suggest that 50 70 of silicate in the uppermost 25 cm of the profile could be atmosphere derived the isotopic composition of labile strontium in the a horizon and the mass distribution of silicon and calcium indicate that the uppermost portion of the profile is the present zone for the release of cations due to silicate weathering steady state models of the whole profile yield a sr weathering flux ranging from200 to 400 m gc m 2 ma 1 the results indicate that both the present day and long term contribution of calcium from silicate weathering is less than 2 of that supplied from the atmosphere and confirm that desert soil formation is not a significant sink for atmospheric carbon 1999 elsevier science b v all rights reserved

evolution of reg soils in southern israel and sinai abstract reg soils mostly camborthids and gypsiorthids cover some 15 of the negev and sinai deserts analytical data of seven profiles on depositional surfaces of increasing age in the negev show clear relationships between ages of surfaces and soil profile features exemplified in the development of the cambic salic and gypsic horizons the youngest soil a coarse desert alluvium soil typic torriorthent of dry wadi beds up to a few thousand years old has little profile differentiation and is generally non saline or slightly saline on the higher terraces connected with the lisan formation about 70 000 12 000 years b p clear profile differentiation and the beginning of development of cambic horizons can be discerned evident in their colour textural p differences the soils are already saline and somewhat gypsiferous both soils are not yet defined as regs because of their negligible or restricted profile differentiation reg soils on the older and higher geomorphic surfaces in the arava rift valley several hundred thousand years old have well differentiated profiles with cambic salic and gypsic horizons below their stony desert pavements typical reg soils have light coloured vesicular horizons over mellow very pale brown loam frequently with laminar structure almost completely stone free layers the reddish brown loamy to clay loam b horizons are very saline and show intensive salt weathering of gravels gypsic and petrogypsic horizons occur at depth such reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering

late holocene climates of the near east deduced from dead sea level variations and modern regional winter rainfall the dead sea is a terminal lake of one of the largest hydrological systems in the levant and may thus be viewed as a large rain gauge for the region variations of its level are indicative of the climate variations in the region here we present the decadal to centennialresolution holocene lake level curve of the dead sea then we determine the regional hydroclimatology that affected level variations to achieve this goal we compare modern natural lake level variations and instrumental rainfall records and quantify the hydrology relative to lake level rise fall or stability to quantify that relationship under natural conditions rainfall data pre dating the artificial dead sea level drop since the 1960s are used in this respect jerusalem station offers the longest uninterrupted pre 1960s rainfall record and jerusalem rains serve as an adequate proxy for the dead sea headwaters rainfall principal component analysis indicates that temporal variations of annual precipitation in all stations in israel north of the current 200 mm yr 1 average isohyet during 1940 1990 are largely synchronous and in phase 70 of the total variance explained by pc1 this station also represents well northern jordan and the area all the way to beirut lebanon especially during extreme drought and wet spells we a determine the modern and propose the past regional hydrology and eastern mediterranean em climatology that affected the severity and length of droughts wet spells associated with multiyear episodes of dead sea level falls rises and b determine that em cyclone tracks were different in average number and latitude in wet and dry years in jerusalem the mean composite sea level pressure and 500 mb height anomalies indicate that the potential causes for wet and dry episodes span the entire em and are rooted in the larger scale northern hemisphere atmospheric circulation we also identified remarkably close association within radiocarbon resolution between climatic changes in the levant reflected by level changes and culture shifts in this region

synchronous timing of abrupt climate changes during the last glacial period abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records but our understanding of their absolute timing and regional synchrony is incomplete our compilation of 63 published independently dated speleothem records shows that abrupt warmings in greenland were associated with synchronous climate changes across the asian monsoon south american monsoon and european mediterranean regions that occurred within decades together with the demonstration of bipolar synchrony in atmospheric response this provides independent evidence of synchronous high latitude to tropical coupling of climate changes during these abrupt warmings our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice core chronologies

the mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern negev israel

soils at the hyperarid margin the isotopic composition of soil carbonate from the atacama desert northern chile we evaluate the impact of exceptionally sparse plant cover 0 20 and rainfall 2 114 mm yr on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet the atacama desert in northern chile d 13 c and d 18 o values of carbonates from the atacama are the highest of any desert in the world d 13 c vpdb values from soil carbonate range from 8 2 at the wettest sites to 7 9 at the driest we measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of cerling 1984 earth planet sci lett 71 229 240 in which we assumed an exponential form of the soil co2 production function and relatively shallow 20 30 cm average production depths overall we find that respiration rates are the main predictor of the d 13 c value of soil carbonate in the atacama whereas the fraction c3 to c4 biomass at individual sites has a subordinate influence the high average d 13 c value 4 1 of carbonate from the driest study sites indicates it formed perhaps abiotically in the presence of pure atmospheric co2 d 18 o vpdb values from soil carbonate range from 5 9 at the wettest sites to 7 3 at the driest and show much less regular variation with elevation change than d 13 c values d 18 o values for soil carbonate predicted from local temperature and d 18 o values of rainfall values suggest that extreme 80 in some cases soil dewatering by evaporation occurs at most sites prior to carbonate formation the effects of evaporation compromise the use of d 18 o values from ancient soil carbonate to

active sand seas and the formation of desert loess abstract loess is a widespread eolian deposit dominated by coarse silt and very fine sand quartz grains 20 80 m that serve as an important archive of information on quaternary climate change despite the intensive research during the past century on desert loess formation its origin remains poorly understood and is still a fundamental problem in sedimentology the ongoing debate is focused on the first stage of loess formation the production of coarse silt quartz grains although laboratory experiments indicate the potential of dunes with their abundant quartz sand grains as a primary source for generating coarse silt grains this concept has been generally rejected because field based evidence of abrasion from sand grains eolian abrasion is scarce here we have adopted a global view of the sand sea loess association and examine in detail several well known late pleistocene loess regions in different subtropical deserts africa the middle east and arabia this analysis demonstrates that all these loess regions are located downwind of adjacent sand seas together with evidence of mineralogical similarity between the loess and the sand dunes and the contemporaneous deposition of the loess and movement of the dunes these observations suggest that sand seas are an important source for desert loess because there is only limited silt storage in sand dunes we postulate that the silt grains comprising most of the loess are not reworked from the dunes but are generated probably through active eolian abrasion of the sand grains under past climates characterized by intensified winds as a result the role of sand dunes and eolian abrasion in the formation of desert loess may be more important than previously thought

early neoproterozoic scale microfossils in the lower tindir group of alaska and the yukon territory the tindir group is a 4 km thick neoproterozoic succession exposed in the tatonduk inlier of east central alaska and the western yukon territory the tindir group is informally divided into the lower tindir group which consists of 2 km of mixed carbonate and clastic rocks and the overlying upper tindir group which contains two cryogenian glacial deposits and an additional ediacaran succession of mixed carbonate and clastic strata unique mineralized scale microfossils have been recovered from sections previously correlated with the upper tindir group and interpreted variously as cryogenian to early cambrian in age our remapping of the area indicates that these sections are stratigraphically below an early cryogenian glacial diamictite unit 2 of the upper tindir group and are actually part of the lower tindir group carbon and strontium isotope correlations further suggest that the fossiliferous lower tindir group is correlative with early neoproterozoic strata of the northwestern canadian cordillera this new age model is consistent with the accompanying microfossil assemblage and indicates that the diverse microfossils in the lower tindir group can be added to the early neoproterozoic record of eukaryotic evolution

co evolution of eukaryotes and ocean oxygenation in the neoproterozoic era the oxygenation of the earth s deep oceans is often thought to have triggered the evolution of simple animals a review article proposes that instead the evolution of animal life set off a series of biogeochemical feedbacks that promoted the oxygenation of the deep sea

phosphate biomineralization in mid neoproterozoic protists the origin and expansion of biomineralization in eukaryotes played a critical role in earth history linking biological and geochemical processes however the onset of this phenomenon is poorly constrained due to a limited early fossil record of biomineralization although macroscopic evidence for biomineralization is not known until the late ediacaran we here report biologically controlled phosphatic biomineralization of scale microfossils from mid neoproterozoic pre sturtian strata of northwest canada primary biological control on mineralization is supported by the identification of apatite in both chert hosted and limestone hosted specimens the conspicuously rigid original morphology of the scale microfossils relative to co occurring organic walled cyanobacteria and acritarchs and the microstructure of the constituent phosphate cell enveloping mineralized scales occur in a wide range of extant protists but the apparent restriction of phosphate scales to one modern taxon of green algae suggests a possible affiliation for these fossils documentation of primary phosphate biomineralization in fifteenmile group yukon territory canada microfossils greatly extends the known record of biologically controlled mineralization and provides a unique window into the diversity of early eukaryotes

in situ analyses of phosphorus contents of carbonate minerals reconstruction of phosphorus contents of seawater from the ediacaran to early cambrian abstract the ediacaran and cambrian periods were one of the most important periods for the evolution of life the biodiversity drastically expanded in the period however the origins are still ambiguous because surface environmental changes through the time have not been well understood yet we conducted in situ analyses of the phosphorus contents of carbonate minerals with a laser ablation inductively coupled plasma mass spectrometer la icp ms to estimate the phosphorus contents of seawater from the ediacaran to the early cambrian carbonate rocks contain not only the carbonate minerals but also detrital and authigenic materials such as silicate and phosphate minerals therefore the whole rock compositions of carbonate rocks are not directly related with seawater composition to avoid the influence of the involvement of the phosphate minerals we performed the microscopic observation elemental mapping of si ca mg fe and p contents with an electron probe microanalyzer epma and investigation of time profiles of signal intensities of ca sr mn p la and ba with the la icp ms especially samples with low mn sr ratios and primary textures such as oolites are suitable to estimate the primary phosphorus contents of the carbonates the chemostratigraphy of the phosphorus contents of carbonates from the drill core and outcrop samples displays that the phosphorus contents decrease from ca 400 ppm in the ediacaran through ca 200 ppm around the terminal ediacaran and the beginning of the cambrian to ca 50 ppm in the early cambrian previous works on 87sr 86sr chemostratigraphy from the ediacaran to the cambrian sections suggested relatively high continental influx in the middle ediacaran and around the precambrian cambrian pc c boundary the high phosphorus content in the ediacaran was possibly due to the high continental flux on the other hand previous works on chemostratigraphy of carbon isotope values of carbonate carbon from the ediacaran to the cambrian sections showed some large negative anomalies in the ediacaran and around the precambrian cambrian pc c boundary and suggested that the negative anomalies were caused by remineralization and respiration of dissolved organic matter the degradation of the organic matter also accounts for the high phosphorus contents in the ediacaran the high phosphorus content of seawater favors enhancement of primary productivity and formation of phosphorites the high phosphorus contents in the seawater possibly led to the emergence of the large and motile organism through the enhancement of primary productivity and the consequent increase of oxygen content of the seawater

late quaternary weathering erosion and deposition in nahal yael israel an impact of climatic change on an arid watershed in their seminal paper in 1979 bull and schick proposed a conceptual model for the geomorphic response to pleistocene to holocene climate change based on the hyperarid nahal yael watershed in the southern negev desert in this model the change from semiarid late pleistocene to hyperarid early holocene climates reduced vegetation cover increased the yield of sediment from slopes and accelerated aggradation of terraces and alluvial fans the model is now over 30 yr old and during this time chronologic paleoenvironmental and hydrogeomorphic research has advanced here we reevaluate the model using data acquired in nahal yael over the 30yr since the original model was proposed recent studies indicate that the late pleistocene climate was hyperarid and a transition from semiarid to hyperarid climates did not occur the revised chronology reveals a major 35 20 ka episode of accelerated late pleistocene sediment production on slopes with lower rates probably already at ca 50ka due to increased frequency of wetting drying cycles caused by frequent extreme storms and floods between 35 and 27 ka without lag time these sediments were transported and aggraded in depositional landscape components fluvial terraces and alluvial fans this intensified sediment production and delivery phase is unrelated to the pleistocene holocene transition the depositional landforms were rapidly incised between 20 and 18 ka since and or soon after this last glacial maximum lgm incision most material leaving the basin originated from sediments stored in depositional landforms and was not produced from bedrock using these new data we propose a revision to the bull and schick model in this hyperarid environment our revision suggests that the model should include the frequent storms and floods responsible for a late pleistocene pulse of intense weathering due to numerous cycles of wetting and drying on slopes and coeval sediment transport to fluvial terraces and alluvial fans we also discuss the common use and pitfalls of using the bull and schick conceptual model to explain observations in diverse arid environments usually without sufficient data on basin specific stratigraphic chronologic paleoenvironmental and paleoclimatic information

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities