accelerator mass spectrometry radiocarbon dating of rock varnish accelerator mass spectrometry ams 14c dating off rock varnish provides minimum limiting ages for landforms and archaeological artifacts in arid and semiarid lands that are undatable by conventional radiocarbon methods experiments on sample collection the effect of different individuals preparing samples the influence of different chemical extraction procedures the incorporation of carbonate detritus possible contamination from rock underlying varnish the role of bio geochemical erosion of varnish and other influences reveal procedures that yield reproducible results conventional radiocarbon dates from charcoal beneath lava flows of hualalai volcano hawaii and from arid sites in western north america provide controls to test varnish radiocarbon dating ams radio carbon ages on the very bottom layer of varnishes are typically 10 younger than the 14c ages of these controls applications are illustrated here for fluvial aeolian peri glacial hillslope lacustrine and glacial geo morphology as well as rock art research in archaeology

marine shell dates and surface lithic assemblages on the west coast of south africa archaeological surface finds are difficult to date there are several useful methods but each requires special circumstances and has one drawback or another on the west coast of south africa marine shell are abundant on surface sites but they are rarely dated because they are perceived to be in disturbed context and in questionable association with artefacts this paper attempts to rectify this misconception and shows that although far from perfect a large suite of surface dates can shed as much light as excavated data on the vredenburg peninsula they help refute the hypothesis that two economically and culturally distinct populations shared this pre colonial landscape since 2000 bp

models of rock varnish formation constrained by high resolution transmission electron microscopy nanometre scale transmission electron microscope imagery of manganiferous rock varnishes from death valley california peru antarctica and hawaii confirms prior infrared mineralogy studies the building blocks of rock varnish are clay minerals that are cemented to the rock by oxyhydroxides of manganese and iron rock varnish is layered on the scale of nanometres with the basic structure defined by the subparallel alignment of detrital clay minerals although only a few examples of bacteria were found possible cell wall encrustations are ubiquitous and aligned with the clay minerals mn fe oxides appear to be mobilized from bacterial casts and then reprecipitate on clay minerals that weather into monolayers these observations have implications for varnish dating and palaeoenvironmental techniques k ar and uranium series dating of rock varnish oxides can only yield minimum ages however this small spatial scale of mobilization would not alter the signal from micron scale microchemical laminations

integrated hyperspectral remote sensing geochemical and isotopic studies for understanding hydrocarbon induced rock alterations abstract the main objective of this work was to determine if there are characteristic mineral assemblages and chemical changes in areas affected by hydrocarbon microseepages for this purpose remote sensing was utilized for mapping surficial rock alterations and geochemical tools were used to understand the alteration processes the key area chosen for this type of work were altered and unaltered wingate sandstone outcrops in lisbon valley utah the spectral angle mapper method was applied on hymap hyperspectral data to classify the extent of altered and unaltered outcrops as well as to map the changes in mineral content within the outcrops the spectral feature fitting method was used to identify lithological changes in the area reflectance spectroscopy thin section studies major minor and trace element analyses and stable carbon and oxygen studies on both bleached altered and unbleached unaltered samples were successfully used to delineate areas of similar rock composition and relate changes due to hydrocarbons leaking from underlying petroleum reservoirs unbleached wingate sandstone samples had higher hematite and feldspar content than bleached wingate samples which were characterized by larger amounts of clay calcite and pyrite some bleached samples also had higher concentrations of elements u mo characteristic of hydrocarbon related reducing environments and were depleted in 13c when compared to the unbleached samples based on these results the following model of chemical reactions is suggested for diagnostic changes within wingate sandstone hydrocarbon induced reducing environment caused the transformation of sulfate ion obtained from groundwater or from oxidation of h2s to sulfide ion resulting in the reduction of hematite to pyrite the released hydrogen ion from this reaction reacted with available feldspars in the rock leading to precipitation of kaolinite these conditions favor the reaction between bicarbonate ion and ca2 ions that can be obtained from the groundwater leading to precipitation of calcite in pore spaces left open after the reduction and removal of hematite

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

quaternary alkalinity fluctuations recorded in rock varnish microlaminations on western u s a volcanics abstract rock varnish contains an alternating micron scale layering of manganese rich and manganese poor microchemical laminations holocene varnishes have lower mn fe ratios when exposed to alkaline environments and higher mn fe ratios when exposed to less alkaline environments this is consistent with abiotic and biotic mechanisms of varnish formation as alkalinity inhibits the concentration of manganese in both models mn fe variations with depth in varnishes in the western u s are interpreted as fluctuations in alkalinity or local microenvironmental influences if enough varnishes are sampled from different rocks in a region local effects can be ruled out k ar dating of volcanics in the coso cima lunar crater and crater flat volcanic fields in the western basin and range provide numerical age control throughout the quaternary and allow the number of alkalinity fluctuations to be assessed for given periods of time alkalinity fluctuations in varnishes are likely tied to fluctuations in the abundance of alkaline aerosols which are in turn related to fluctuations in the cover of water over playas and the cover of vegetation over soils microchemical laminations in varnish therefore have the potential to serve as an indicator of environmental fluctuations for the entire quaternary

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

cool la nina during the warmth of the pliocene the role of el nino southern oscillation enso in greenhouse warming and climate change remains controversial during the warmth of the early mid pliocene we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial pacific consistent with the prevalence of a la nina like state rather than the proposed persistent warm el nino like conditions our pliocene paleothermometer supports the idea of a dynamic ocean thermostat in which heating of the tropical pacific leads to a cooling of the east equatorial pacific and a la nina like state analogous to observations of a transient increasing east west sea surface temperature gradient in the 20th century tropical pacific

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

pedogenic manganese oxide coatings calcium buserite on fracture surfaces in tortonian upper miocene red mudstones southern turkey abstract fracture surfaces of red mudstones overbank deposits within the kuzgun formation of late miocene tortonian age are coated by thin black colored manganese oxide beneath a thin soil cover in the mersin area of southern turkey these manganese oxide coatings have been investigated by a range of analytical techniques including x ray diffraction xrd infrared spectral ir differential thermal analysis thermal gravimetric dta tg scanning electron microscopy and energy dispersive x ray sem edx analyses the basal reflections at 10 00 7 22 5 00 3 35 2 50 2 29 and 2 10 a sharp infrared spectral lines at 469 and 519 cm 1 and typical dehydration of interlayer water

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

dating climatic change in hot deserts using desert varnish on meteorite finds abstract a thin coating of desert varnish occurs on forrest 009 and nurina 004 both equilibrated ordinary chondrite l6 finds from the nullarbor plain australia this finely laminated deposit is chemically and petrographically comparable to the varnish found on terrestrial rocks forrest 009 which has a terrestrial age of 5 9 kyr has a 100 130 m thick coating of desert varnish that has a laterally consistent chemical microstratigraphy comprising a narrow ba and mn poor lower region a thick ba and mn rich central area and a narrow outer zone almost devoid of both cations the interior of the meteorite contains fe oxide and oxyhydroxide veins that have formed by chemical weathering of metals and sulphides as these veins do not cross cut the varnish it must have accreted rapidly relative to the weathering rate of the meteorite the 70 m thick varnish on nurina 004 which has a terrestrial age of 33 4 kyr lacks a consistent chemical microstratigraphy but it is cross cut by fe oxide and oxyhydroxide veins some of which have supplied fe to the varnish this implies that the chemical weathering rate of nurina 004 s interior was slow in comparison to the accretion rate of the varnish the petrography and chemical composition of varnish on forrest 009 indicates that this meteorite may have resided in a relatively humid environment for most of its 5 9 kyr terrestrial history and that the nullarbor recently became more arid this conclusion supports results from an analysis of fe bearing weathering products in the interior of the meteorite by mossbauer spectroscopy which also indicate that forrest 009 experienced an early period of rapid weathering under relatively humid conditions the petrography of varnish on nurina 004 shows that the interior of the meteorite weathered relatively slowly probably because it fell during an arid time which is again in agreement with previous mossbauer spectroscopy results results from both meteorites are in agreement with palaeoclimate data derived from a number of other proxies the implications of this work are that the large number of meteorites that have been collected from several hot deserts of the world may be a powerful source of information on climate change over the last 30 35 kyr

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

planktonic foraminiferal faunal and stable isotopic indices of upwelling a sediment trap study in the san pedro basin southern california bight

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

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

chronology of rock falls and slides in a desert mountain range case study from the sonoran desert in south central arizona abstract in order to respond to the general paucity of information on the chronology of ubiquitous small rock falls and slides that litter the slopes of desert mountain ranges a case study in the sonoran desert reveals new insight into the desert geomorphology of mountain slopes rock falls and rock slides in the mcdowell mountains that abut metropolitan phoenix usa fall in three chronometric groupings dated by conventional radiocarbon and rock varnish microlamination methods first the oldest events are 74 ka and take the form of stable colluvial boulder fields positive relief features that are tens of meters long and a few meters wide second randomly sampled slides and falls of various sizes and positions wasted during wetter periods of the terminal pleistocene and holocene third an anomalous clustering of slides and falls occurred during the late medieval warm period medieval climatic anomaly when an extreme storm was a possible but unlikely trigger one speculative hypothesis for the cluster of medieval warm period events is that a small to moderate sized earthquake shook heavily shattered bedrock close to failure just enough to cause a spate of rock falls and slides a second speculative hypothesis is that this dry period enhanced physical weathering processes such as dirt cracking however the reasons for the recent clustering of rock falls remain enigmatic while the temporal distribution of slides and falls suggests a minimal hazard potential for homes and roads on the margins of the mcdowell mountains this finding may not necessary match other desert ranges in metropolitan phoenix or mountains with different rock types and structures that abut other arid urban centers

constraining the timing of alluvial fan response to late quaternary climatic changes southern tunisia the evolution of the oued es seffaia alluvial fan during the last 50 000 years is analyzed in the light of chronometric data derived from ams radiocarbon and optical dating techniques these ages have enabled the temporal constraint of the distalward progression of the intersection point the upper limit of the locus of deposition which has resulted in the telescopic segmentation of the fan comparison of these data with the late quaternary climatic history of the maghreb highlights several problems of interpretation due both to our limited knowledge of regional palaeoclimates and of the response of dryland fluvial systems to climate changes however our data provide some evidence to suggest that fan incision and formation of telescopic segments occurs in response to changes from arid to less arid conditions supporting the conclusions of some of the work from other areas

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

spatial temporal and geographic considerations of the problem of rock varnish diagenesis article i nfo the rock varnish literature hosts an abundance of prima facie contradictory empirical data past and perhaps future empirical contradictions however can be resolved by theoretical considerations of different spatial and temporal scales of varnish diagenesis as well as the geomorphic position of different types of varnishes for example twentieth century contamination by lead and other heavy metals has led to claims of accumulation rates in the last century far more rapid than prior published empirical studies a consideration of spatial scales resolves this contradiction nanoscale processes allow migration of lead into varnish deposited well before the twentieth century time of heavy metal pollution evidence of nanometer scale disequilibrium in three samples led to claims that varnish cannot be used in paleoclimatic research these data rest in contrast to replicable patterns in varnish deposition observed by dr tanzhuo liu and others in over ten thousand micro sedimentary basins this contraction can be resolved by understanding that the types of varnishes studied differ and that processes differ substantially between the nanoscale and the micron scale a lack of evidence of mn oxidizers in genetic analyses contrasts with culturing studies and in situ evidence of mn enhancement by bacteria this contradiction has a likely resolution in vastly different temporal scales dna material analyzed may be no older than 200 years but in situ fossilized remains of bacteria may be preserved for thousands of years recording palaeoecological conditions favoring growth of mn enhancing bacteria

identification of debris flow hazards in warm deserts through analyzing past occurrences case study in south mountain sonoran desert usa abstract after recognition that debris flows co occur with human activities the next step in a hazards analysis involves estimating debris flow probability prior research published in this journal in 2010 used varnish microlamination vml dating to determine a minimum occurrence of 5 flows per century over the last 8100 years in a small mountain range of south mountain adjacent to neighborhoods of phoenix arizona this analysis led to the conclusion that debris flows originating in small mountain ranges in arid regions like the sonoran desert could pose a hazard two major precipitation events in the summer of 2014 generated 35 debris flows in the same study area of south mountain providing support for the importance of probability analysis as a key step in a hazards analysis in warm desert settings two distinct mechanisms generated the 2014 debris flows intense precipitation on steep slopes in the first storm and a firehose effect whereby runoff from the second storm was funneled rapidly by cleaned out debris flow chutes to remobilize pleistocene debris flow deposits when compared to a global database on debris flows the 2014 storms were among the most intense to generate desert debris flows indicating that storms of lesser intensity are capable of generating debris flows in warm desert settings the 87 sr 86 sr analyses of fines and clasts in south mountain debris flows of different ages reveal that desert dust supplies the fines thus wetter climatic periods of intense rock decay are not needed to resupply desert slopes with fines instead a combination of dust deposition supplying fines and dirt cracking generating coarse clasts can re arm chutes in a warm desert setting with abundant dust

the oxygen isotope composition of planktonic foraminifera from the guaymas basin gulf of california seasonal annual and interspecies variability abstract sediment trap samples collected over a seven year period february 1991 october 1997 from guaymas basin in the gulf of california were used to study the oxygen isotope composition of five species of planktonic foraminifera globigerinoides ruber white globigerina bulloides neogloboquadrina dutertrei pulleniatina obliquiloculata and globorotalia menardii the 18o data were analyzed for temporal and interspecies variability and were compared to local hydrography to evaluate the use of each species in reconstructing past oceanographic applications the two surface dwelling species g ruber and g bulloides displayed the lowest 18o values 0 0 to 5 0 while 18o values for the thermocline dwelling n dutertrei p obliquiloculata and g menardii were higher 0 0 to 2 0 the 18o of g ruber most accurately records measured sea surface temperatures ssts throughout the year g bulloides 18o tracks ssts during the winter spring upwelling period but for the remainder of the year records slightly colder subsurface temperatures the difference between the 18o of the surface dwelling species g ruber and g bulloides and that of the thermocline dwelling species n dutertrei p obliquiloculata and g menardii was used to estimate the surface to thermocline temperature gradient during the winter these 18o differences are small 0 50 reflecting a well mixed water column these interspecies 18o differences increase during the summer 1 90 in response to the strong thermal stratification that exists at this time of year

takarkori rock shelter sw libya an archive of holocene climate and environmental changes in the central sahara abstract rock shelters in the central saharan massifs preserve anthropogenic stratigraphic sequences that represent both a precious archive for the prehistory of the region and a powerful proxy data for holocene palaeoenvironments the geoarchaeological micromorphology and archaeobotanical pollen analysis approaches were integrated to investigate the anthropogenic sedimentary sequence preserved within the takarkori rock shelter a holocene archaeological site located in the libyan central sahara southern tadrart acacus massif the site was occupied throughout the early and middle holocene african humid period by groups of hunter gatherers before and by pastoral communities later the investigation on the inner part of the sequence allows to recognize the anthropogenic contribution to sedimentation process and to reconstruct the major changes in the holocene climate at the bottom of the stratigraphic sequence evidence for the earliest frequentation of the site by hunters and gatherers has been recognized it is dated to c 10 170 cal yr bp and is characterized by high availability of water freshwater habitats and sparsely wooded savannah vegetation a second early holocene occupation ended at c 8180 cal yr bp this phase is marked by increased aridity sediments progressively richer in organics testifying to a more intense occupation of the site and pollen spectra indicating a decrease of grassland and the spreading of cattails which followed a general lowering of lake level or widening of shallow water marginal habitats near the site after this period a new occupational phase is dated between c 8180 and 5610 cal yr bp this period saw the beginning of the frequentation of pastoral groups and is marked by an important change in the forming processes of the sequence sediments and pollen spectra confirm a new increase in water availability which led to a change in the landscape surrounding the takarkori rock shelter with the spreading of water bodies the upper part of the sequence dating between c 5700 and 4650 cal yr bp records a significant environmental instability towards dryer climatic conditions consistent with the end of the african humid period though some freshwater habitats were still present increasing aridity pushed the expansion of the dry savannah the final transition to arid conditions is indicated by the preservation of ovicaprines dung layers at the top of the sequence together with sandstone blocks collapsed from the shelter s vault on the contrary the outer part of the sequence preserves a significantly different palaeoenvironmental signal in fact the surface was exposed to rainfall and a complex pedogenetic evolution of the sequence occurred encompassing the formation of an argillic laminar horizon at the topsoil the evolution of a desert pavement and the deposition of mn rich rock varnish on stones these processes are an effect of the general environmental instability that occurred in the central sahara since the middle holocene transition finally the local palaeoclimatic significance of the sequence fits well with holocene regional and continental environmental changes recorded by many palaeohydrological records from north africa this highlights the potential of geoarchaeological and archaeobotanical investigations in interpreting the palaeoenvironmental significance of anthropogenic cave sediments in arid lands

modes of eastern equatorial pacific thermocline variability implications for enso dynamics over the last glacial period 1 changes in el nino southern oscillation enso variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first order climate signal here we address this problem by reconstructing thermocline structure from a marine sediment core retrieved from the eastern equatorial pacific at the core location changes in hydrologic parameters within the thermocline are linked to enso activity with a reduced influence of seasonal variability compared to surface waters we performed repeated isotopic analyses 18o on single specimens of the thermocline dwelling planktonic foraminifera neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance a parameter supposed to reveal changes in enso no fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background however our data suggest that long term variations in the thermocline variability occurred over the last 50 ka with the highest and lowest enso activities occurring during the last glacial period and the last glacial maximum respectively

spectral and geochemical characterization of onshore hydrocarbon seep induced alteration in the dezful embayment southwest iran the presence of hydrocarbon seeps at the surface is indirect evidence of the presence of mature source rocks within a geological system at depth chemical changes in the environment of surface rocks caused by hydrocarbon seeps cause mineralogical alterations to determine the nature of the alterations and the influences of lithology and type of seep rock samples were collected from altered and unaltered evaporite and marly limestone formations in the dezful embayment southwest iran reflectance spectroscopy bulk rock wet chemical analyses and sulfur carbon and oxygen isotopic analyses were used to delineate surficial alterations and relate alterations to hydrocarbons seeping from underlying reservoirs in addition the boosted regression trees brt method was used to predict the presence of alterations from spectral indices comparisons of geochemical data and spectral data of altered evaporites and altered marly limestones showed that the minerals within alteration facies have distinctive spectral chemical and isotopic signatures gas induced alterations were characterized by the formation of gypsum and native sulfur and depletion in the released in natural gas reacted with gypsum in the evaporite sediments and calcite in the marly limestone formations which led to precipitation of secondary gypsum and native sulfur oil induced alterations were characterized by formation of secondary calcite and depletion in the oxidation of seeping oil and reactions between this oil and host rocks caused precipitation of secondary calcite within both formations the combination of fieldwork data and spectral geochemical data showed a connection exists between surficial alterations and underlying petroleum reservoirs which can be used in exploration campaigns

role of tropics in changing the response to milankovich forcing some three million years ago appeared in regions that today have intense oceanic upwelling the eastern equatorial pacific and the coastal zones of southwestern africa and california there was furthermore a significant change in the earth s response to milankovich forcing obliquity signals became large but those associated with precession and eccentricity remained the same the latter change in the earth s response can be explained by hypothesizing that the global cooling during the cenozoic affected the thermal structure of the ocean it caused a gradual shoaling of the thermocline around 3 ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions this brought into play feedbacks involving

millennial scale varnish microlamination dating of late pleistocene geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a climate based correlative age determination technique used to correlate and date various geomorphic features in deserts in this study we establish a generalized late pleistocene 18 74 ka millennial scale microlamination sequence in fine grained fast accumulating rock varnish for the drylands of western usa radiometrically calibrate the sequence and correlate it with the 18 o record in the gisp2 greenland ice core we then use this climate correlated varnish microstratigraphy to estimate surface exposure ages for radiometrically dated late pleistocene geomorphic features in the study region the vml dating of debris flow deposits on the sehoo recessional shorelines of lake lahontan at the jessup embayment of central nevada yields a minimum limiting age of 14 95 15 95 ka in good agreement with a calibrated 14 c age of 15 22 0 12 ka for the timing of the lake recession the vml dating of a giant ejecta block on the rim of meteor crater in northern arizona yields a minimum limiting age of 49 15 ka closely matching a thermoluminescence tl age of 49 3 ka and slightly younger than a recently updated cosmogenic 36 cl age of 56 0 2 4 ka for the meteor impact event the vml dating of distal q2c fan surfaces on hanaupah canyon alluvial fan in death valley california yields a minimum limiting age of 73 55 ka in accord with cosmogenic 36 cl depth profile ages of 66 22 14 ka and 72 24 20 ka for the same fan deposits the close agreement between the vml age estimates and the independently derived radiometric ages for these geomorphic features attests to the validity and reliability of millennial scale vml dating to further assess its potential in desert geomorphological research we use the vml method to study alluvial fan responses to millennial scale climatic changes the vml dating of a small tributary fan in death valley reveals two episodes of fan aggradation one ceasing at 73 55 86 75 ka during the dry period of the last interglacial mis 5a and the other finishing at 66 15 ka during the wet period of the last glacial mis 4 the vml and 36 cl dating of the distal q2c fan surfaces on hanaupah canyon fan reveal two episodes of large scale fan aggradation ended at 72 24 20 ka and 73 55 ka during the wet period of mis 4 fanhead incision and associated within channel or fantoe aggradation are found to take place during the relatively dry period of the glacial to interglacial climatic transition 12 24 ka and the holocene interglacial dry period 0 12 ka these data indicate that on the millennial to sub milankovitch timescale 10 3 10 4 years fan aggradation is a discrete sedimentational process under various climatic conditions because fan aggradation is ultimately controlled by the intensity and frequency of precipitation events which in turn are modulated by major climatic oscillations such as heinrich events dansgaard oeschger do events and glacial interglacial shifts these major climatic changes could be the pacemaker of regionally contemporaneous large area fan segmentation

characterization of microseepage induced diagenetic changes in the upper red formation qom region iran part ii a new insight using reflectance spectroscopic analysis abstract the classic microseepage model supports the notion that hydrocarbon pools leak to the surface over time and trigger an array of diagenetic physicochemical and mineralogical changes in the overlying sediments mapping the induced alteration mineralogy for microseepage targeting has been an appealing yet ambiguous practice mostly because of our incomplete understanding of the diversity of changes occurring in the environment to close this gap an integrated spectroscopic approach is adopted here to investigate the variability quantity and physicochemistry of diagenetic minerals induced by active microseepage systems over the alborz oil reservoir in the qom region iran the area includes an effectively sealed carbonate reservoir overlain by thick oligocene sediments of the upper red formation a large suite of samples collected from microseepage affected zones was spectrally characterized in the 350 2500 nm wavelength region and then statistically contrasted against unaffected samples gathered from a nearby control area the analysis reveals a novel array of mineralogic indicators for microseepage systems it indicates that smectites montmorillonite nontronite al rich mixed layer illite smectite fe rich chlorite and traces of palygorskite constitute the clay alterations this array is associated with the enrichment of k2o and loss of na2o and mgo from the system as indicated by x ray fluorescence measurements in the arid climate of the region the iron rich red beds fe2o3 6 are only moderately bleached and thus the subsequent chemical weathering of the relict irons has triggered goethite al poor and likely ferrihydrite and maghemite precipitation consequently besides the typical ferric iron bleaching the modification in the mineralogy of iron oxides oxyhydroxides marked by a shift in the absorption minimum at 900 nm is suggested as an additional indicator of microseepage systems fe chlorites constitute the dominant ferrous mineral present in the environment the affected strata are also associated with prevalent calcite and gypsum cements and occasionally jarosite occurrences based on the silica contents of the host rock the microseepage induced alterations are classified into two categories namely felsic and mafic wherein the latter is typified by the assemblages described here this study provides new insights into microseepage induced alterations and highlights the significance of reflectance spectroscopic techniques in facies determination and the alteration footprints mapping of onshore microseepage systems

cupressus dupreziana a dendroclimatic record for the middle late holocene in the central sahara dendroclimatology of cupressus dupreziana the tassili cypress has been attempted on samples obtained from the door beams of the old cities of ghat and barkat located at the foot of the tassili where the cypress still lives the tree rings of 20 samples were measured and dated by 24 ams 14c dates a mean ring width chronology has thus been obtained spanning though discontinuously 5220 to 100 14c bp 5990 65 cal bp as the tree ring width in dry lands depends mainly on water availability the mean ring width chronology represents a detailed record of changes in rainfall on a decade scale for the middle and late holocene of the central sahara it indicates main drought spells at 5200 5000 14c bp 5900 5760 cal bp and at 4350 bp 5120 cal bp followed by phases of enhanced precipitation and by the onset of extreme arid conditions at 1550 14c bp 1500 cal bp

systematic mn fluctuations in laminated rock varnish developed on coeval early holocene flint artifacts along a climatic transect negev desert israel abstract this study presents an assessment of the potential application of mn content in rock varnish laminae as a paleoclimate indicator to investigate the environmental controls on varnish formation we determined mn composition in rock varnish formed on flint artifacts produced during the earliest holocene from eight coeval prehistoric sites in the negev desert israel these sites lie along a north south annual rainfall transect ranging between 120 and 30 mm yr 1 the varnish is 100 times enriched in mn relative to the content in the desert dust source material chemical profiles across the varnish display 4 6 distinct mn peaks in all sampled sites pointing to systematic fluctuations within the varnish along a wide range of environmental settings the mean mn contents in the various sites range between 10 7 and 15 6 at yet within this range the mn content in the negev varnish does not show a correlation with mean annual rainfall as moisture is needed for mn mobility wetting cycles by dew or light rain which are not adequately represented by the mean annual rainfall amounts but control the number of wetting drying cycles may explain the variance within the results from the arid and hyperarid negev varnish

warm upwelling regions in the pliocene warm period 1 given the importance of upwelling processes to coastal productivity and regional climate it is critical to study the role of upwelling regions within the context of global climate change we generated sea surface temperature sst records for the last 5 million years in three important upwelling regions the eastern equatorial pacific the california margin and the peru margin prior to 3 0 ma ssts at all sites were significantly warmer than today by 3 9 c indicating that cold upwelling regions that characterize the modern pacific ocean did not exist in the early pliocene warm period 4 6 to 3 1 ma earth s most recent period of sustained global warmth alkenone phosphorus and organic carbon mass accumulation rate records indicate that changes in productivity and sst were decoupled and that upwelling of nutrient enriched water occurred even when ssts were warm during the early pliocene thus the long term trends in sst are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling favorable winds alone the fact that gradual cooling of upwelling regions began before the onset of significant northern hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions our results suggest that the long term average ssts of upwelling regions are influenced by global changes in the depth and or temperature of the ventilated thermocline

a review of the history of dating rock varnishes the history of rock varnish dating spans almost 20 years from the initial suggestion to use uranium series isotopes through the use of a geochemical ratio cation ratio dating to the current application of accelerator mass spectrometry radiocarbon dating ams 14c uranium isotopes were ignored while other dating methods were tested exhaustively on several continents evidence of the unreliable dating of the formation of varnishes using cation ratios was demonstrated by examples of environmental and textural observations reflecting localised leaching and by chemical analyses that contradicted the fundamental assumptions of the method the radiocarbon dating of substances embedded in varnishes is also problematic where carbon compounds and sources are not identified the incompatible coexistence of different carbonaceous components a recent controversial issue is explained with reference to different environments of formation the future of ams 14c dating of rock varnishes centres around overcoming the practical limitations of sampling and analysing extremely small quantities of carbon bearing substances future directions for dating varnished rock surfaces may include innovative refinements to the u series cosmogenic isotope and luminescence methods

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

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

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

remote sensing and geochemistry for detecting hydrocarbon microseepages this work tests the hypothesis that chemical and mineralogical alterations in rocks and soils are related to hydrocarbon microseepages above some of the major oil fields in this study we used hyperion hyperspectral imaging sensors to map alterations that appear to be associated with hydrocarbon microseepages in the patrick draw area of wyoming our mineralogical geochemical and carbon isotope data support the presence of hydrocarbon microseepages satellite imagery training classifications defined by areas of hydrocarbon microseepage have resulted in the successful identification of the areal extent of an anomalous area geochemical characteristics of samples that define this anomalous area were then compared to the remaining non anomalous samples using x ray diffraction xrd reflectance spectroscopy and carbon isotope techniques xrd analyses demonstrated the increased presence of feldspars in non anomalous samples compared to anomalous samples spectroscopy results demonstrated higher proportions of clays within the anomalous samples compared to non anomalous samples the 13 c values range from 2 88 to as low as 45 32 indicating hydrocarbon sources these methods may provide a foundation upon which further hydrocarbon exploration techniques can develop

high eustatic sea level during the middle pliocene evidence from the southeastern u s atlantic coastal plain the middle pliocene approximately 3 5 2 5 ma was a period of global warmth preceding the growth of major northern hemisphere ice sheets the authors report on eustatic sea level for the middle pliocene based on microspaleontologic study of marine deposits of the duplin formation of south carolina and north carolina the duplin was deposited during a middle pliocene marine transgression that formed the orangeburg scarp a prominent wave cut geomorphic paleoshoreline of the southeastern u s atlantic coastal plain they concluded that 1 the scarp in south carolina was formed mostly during the middle pliocene 3 5 3 0 ma 2 eustatic sea level was about 35 plus minus 18 m higher than modern sea level the scarp has been uplifted about 50 65 m since the middle pliocene and 3 ocean water temperatures along eastern north america were warmer when the scarp was formed that they are at present

characterization and differentiation of rock varnish types from different environments by microanalytical techniques abstract we investigated rock varnishes collected from several locations and environments worldwide by a broad range of microanalytical techniques these techniques were selected to address the challenges posed by the chemical and structural complexity within the micrometer to nanometer sized structures in these geological materials femtosecond laser ablation inductively coupled plasma mass spectrometry fs la icp ms scanning transmission x ray microscopy near edge x ray adsorption fine structure spectroscopy stxm nexafs in combination with scanning electron microscopy sem of focused ion beam fib ultra thin 100 200 nm sections conventional and polarization microscopy as well as electron paramagnetic resonance epr measurements were used to obtain information about these rock varnishes rock varnishes from different environments which cannot readily be distinguished based on their macroscopic appearance differ significantly in their constituent elemental mass fractions e g of mn fe ni co ba and pb and their rare earth element ree patterns structural characteristics such as the particle sizes of embedded dust grains internal structures such as layers of mn fe and ca rich material and structures such as cavities varied between varnishes from different environments and regions in the world the epr spectra were consistent with aged biogenic mn oxides in all samples but showed subtle differences between samples of different origin our observations allow us to separate rock varnishes into different types with differences that might be indicators of distinct geneses five different types of rock varnish could be distinguished type i v of which only type i might be used as potential paleoclimate archive each varnish type has specific characteristics in terms of their elemental composition element distribution and structures the combination of element ratios mn ba al ni mn rey mn ce mn pb lan ybn and ce ce total ree contents and structures can be used to separate the different types of rock varnish from each other

clay illuviation in red mediterranean soils abstract theories regarding pedogenesis in red mediterranean soils have undergone several stages of development the concept of clay illuviation in these soils was not a part of early theories and it is not yet unanimously accepted as a leading soil forming process a methodology is presented for studying the illuviation of clay in these soils emphasizing typology of textural features and fabrics the problem of age determination is also addressed through the use of radiometric dates and correlation with archaeological artifacts clay illuviation in red mediterranean soils under present day environmental conditions suggests that it occurs presently only on humid and sub humid margins of the mediterranean basin elsewhere illuvila clay accumulations are inherited from interglacial periods red mediterranean soils during glacial periods were eroded coluviated aggraded with aeolian dust calcitic fraction of which was redistributed in form of calcitic features and eventually were affected by water logging an example of water logging of red mediterranean soils mamora morocco which took place during the last glacial cycle consists of yellow illuvial clays accompanied by a yellowing of the ground mass during earlier cycles water logging resulted in whitish grey stains in which hydromorphic textural features were deposited

characteristics and origin of rock varnish from the hyperarid coastal deserts of northern peru abstract the characteristics of a new type of rock varnish from the hyperarid coastal deserts of northern peru combined with laboratory experiments on associated soil materials provide new insights into the formation of rock varnish the peruvian varnish consists of an fe rich mn poor component covering up to 95 of a varnished surface and a fe rich mn rich component found only in pits and along cracks and ridges the alkaline soils plus the catalytic fe oxyhydroxides that coat much of the varnish surfaces make the peruvian situation ideal for physicochemical precipitation of mn however the low mn content of the dominant fe rich mn poor component suggests that such precipitation is minor this plus the presence of abundant bacteria in the mn rich varnish and the recorded presence of mn precipitating bacteria in varnish elsewhere suggests that bacteria are almost solely responsible for mn precipitation in rock varnish a set of experiments involving peruvian soil samples in contact with water co2 solutions indicates that natural fogs or dews release mn but not fe when they come in contact with eolian materials on rock surfaces this mechanism may efficiently provide mn to bacteria on varnishing surfaces the lack of fe in solution suggests that a large but unknown proportion of fe in varnish may be in the form of insoluble fe oxyhydroxides sorbed onto the clay minerals that form the bulk of rock varnish the results of this study do not substantively change r i dorn s paleoenvironmental interpretations of varnish mn fe ratios but they do suggest areas for further inquiry

rock varnish in new york an accelerated snapshot of accretionary processes abstract samples of manganiferous rock varnish collected from fluvial bedrock outcrop and erie barge canal settings in new york state host a variety of diatom fungal and bacterial microbial forms that are enhanced in manganese and iron use of a dual beam focused ion beam scanning electron microscope to manipulate the varnish in situ reveals microbial forms that would not have otherwise been identified the relative abundance of mn fe enriched biotic forms in new york samples is far greater than varnishes collected from warm deserts moisture availability has long been noted as a possible control on varnish growth rates a hypothesis consistent with the greater abundance of mn enhancing bioforms sub micron images of incipient varnish formation reveal that varnishing in new york probably starts with the mortality of microorganisms that enhanced mn on bare mineral surfaces microbial death results in the adsorption of the mn rich sheath onto the rock in the form of filamentous networks clay minerals are then cemented by remobilization of the mn rich material thus the previously unanswered question of what comes first clay mineral deposition or enhancement of mn can be answered in new york because of the faster rate of varnish growth in contrast very slow rates of varnishing seen in warm deserts of microns per thousand years make it less likely that collected samples will reveal varnish accretionary processes than samples collected from fast accreting moist settings

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

the calcareous tufa in the tadrart acacus mt sw fezzan libya an early holocene palaeoclimate archive in the central sahara article i nfo the palaeoclimatic signi cance of calcareous tufa deposits found in the presently hyperarid tadrart acacus massif central sahara sw libya is discussed on the basis of u th datings stable isotope analyses and the regional hydrogeological context these deposits formed mostly between c 9600 and 8100 yr bp the isotopic signature 18 o and 13 c of this tufa indicates that the water forming these carbonates originated as isotopically depleted rainwater as a result of the northward expansion of the sw african monsoon system during the early holocene carbonate sedimentation in the tadrart acacus decreased shortly before c 8000 yr bp attributed to a drop in precipitation in the course of the well known 8 2 kyr event a correlation between tufa development and climate change in n and e africa and in the mediterranean basin during the early holocene is discussed the effect of early holocene climate change on both the landscape and the dwellers living in the tadrart acacus region is also evaluated

holocene rock varnish microstratigraphy and its chronometric application in the drylands of western usa abstract analyses of hundreds of rock varnish samples from latest pleistocene and holocene geomorphic features in the drylands of western usa reveal a regionally replicable holocene microlamination sequence this sequence consists of 12 approximately evenly spaced weak dark layers intercalated with 13 orange yellow layers preliminary radiometric age calibration indicates that six dark layers in the upper portion of the sequence were deposited during the last 6000 yr diagnostic of the little ice age and late holocene wet events five dark layers in the lower portion of the sequence were deposited after the termination of the pleistocene but slightly before 7000 ybp indicative of the early holocene wet events and one dark layer in the middle portion of the sequence was deposited around 6500 ybp suggestive of the middle holocene wet phase our age calibration further indicates that the holocene wet events represented by the dark layers largely correlate in time with the millennial scale holocene cooling events in the north atlantic region this radiometrically calibrated and climatically correlated holocene microlamination sequence was then used as a unique correlative dating tool to determine surface exposure ages of geomorphic and geoarchaeological features in western usa deserts the varnish microlamination vml dating of debris flow fan deposits in death valley california yields minimum ages of 12 500 12 500 11 100 11 100 10 300 9400 and 2800 ybp for six debris flow fan building events suggesting that such events were more likely to have occurred during relatively wet periods of the holocene the vml dating of a prehistoric grinding stone from chili of northern new mexico yields a minimum age of 900 1100 ybp for the abandonment of this occupation site by the anasazi indians the vml dating of a prehistoric flaked stone a primary core from ocotillo southern california yields a minimum age of 12 500 ybp for the flaking of this stone artifact suggesting at least a paleo indian human occupation at ocotillo during the terminal pleistocene these results indicate that when properly applied the vml dating technique has the great potential to yield numerical age assignments for surface stone tools petroglyphs and geoglyphs of prehistoric age in the drylands of western usa

blind testing of rock varnish microstratigraphy as a chronometric indicator results on late quaternary lava flows in the mojave desert california rock varnish is a manganiferous dark coating ubiquitous in desert landscapes to test the validity of varnish microstratigraphy as a chronometric indicator varnish samples were collected from radiometrically dated and undated late quaternary lava flows in amboy cima and pisgah volcanic fields avf cvf pvf in the mojave desert of california western united states varnish microstratigraphies show a replicable layering sequence that appears to record regional climate changes that likely correspond in time to the younger dryas and heinrich events in the north atlantic region microstratigraphic patterns on these volcanic fields match patterns found in varnishes from other western us sites with available radiometric age constraints based on this regional chronology varnishes from the a flow h flow and a stone pavement surface in the cima volcanic field were estimated to be 16 5 24 74 85 and 74 85 ka respectively these ages are consistent with previously published cosmogenic 3 he ages of 18 20 72 74 and 80 85 ka for these geomorphic surfaces varnishes from the i flow at cima yielded a puzzling age estimate of 39 ka which is consistent with an older 3 he age of 37f6 ka reported for the i flow but inconsistent with a younger 3 he age of 31f7 ka and a cosmogenic 36 cl age of 27f1 3 ka for the same flow reinterpretation of the original varnish age data with knowledge of then available field mapping results of the i flow suggests that the i cone is polycyclic and different flow units were probably unintentionally sampled in the field the revised varnish ages of 30 and 39 ka for the i flow thus may be in good agreement with their corresponding 3 he and 36 cl ages in a blind test of the method varnishes from the phase 1 flow at pisgah an unnamed flow called here the ivflow at cima and the amboy flow were estimated to be 24 30 46 60 and 74 85 ka respectively these ages agree well with 36 cl ages of 22 5f1 3 46f2 and 79f5 ka reported for the same flows by phillips geomorphology 2002 these test results provide convincing evidence that varnish microstratigraphy once radiometrically calibrated can be used as a valid dating tool to estimate surface exposure ages of desert landforms in the western us drylands d 2002 elsevier science b v all rights reserved

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

a 5 million year comparison of mg ca and alkenone paleothermometers geochemical sea surface temperature sst proxies such as the magnesium to calcium ratio mg ca in foraminifera and the alkenone unsaturation index uk 37 are becoming widely used in pre pleistocene climate records this study quantitatively compares previously published mg ca and uk 37 data from ocean drilling program odp site 847 in the eastern equatorial pacific to assess the utility of these proxies to reconstruct tropical sst over the last 5 ma foraminiferal mg ca sst calibrations that include a dissolution correction are most appropriate at this location because they provide sst estimates for the youngest sample that are close to modern mean annual sst the long term trends in the two records are remarkably similar and confirm a 3 5 c cooling trend from the early pliocene warm period to the late pleistocene noted in previous work absolute temperature estimates are similar for both proxies when errors in the dissolution correction used to estimate sst from mg ca are taken into account comparing the two sst records at odp site 847 to other records in the region shows that the eastern equatorial pacific was 2 4 c warmer during the early pliocene compared to today

construction of a polynomial model of glacio eustatic fluctuation estimating paleo sea levels continuously through time sea level curves for the late quaternary are typically reconstructed with data from reef tracts and terraces preserved along actively uplifting coastlines recording highstands and in some cases lowstands of the world9s oceans through time as a result sea level curves reconstructed from these data are fixed at the maxima highstands and minima lowstands but either make no predictions about the intervening time or use arbitrary or free hand methods of interpolation these curves fail to meet the need of many applications of sea level data for continuous quantitative information a new method for calculating sea levels during intervening times produces a polynomial expression of sea level through time lagrange polynomial interpolation is used to fit a series of fourth order equations to existing data of late quaternary sea level fluctuations producing a systematic and realistic model of continuous sea level elevations with time the method is germane to any and all models of sea level based on discrete data points here the model advanced by bloom et a1 is reexamined and a new polynomial model which estimates eustatic sea levels continuously in the range 0 140 ka is developed from the huon data the method includes an error analysis procedure that accounts for the effects of error in radiometric dates and theodolite measurements in the original data set and extrapolates this error through the continuous model polynomial form and error estimation are indispensible to rigorous quantitative applications of sea level data and supplant less rigorous methods used to approximate sea level and rates of sea level rise

enhanced zoogeomorphological processes in north africa in thehuman impacted landscapes of the anthropocene abstract new zoogeomorphological features discovered in dryland landscapes of northern africa reflect human animal agency since prehistory and attest to complex networked activities over great distances we discuss the role of zoogeomorphology in shaping earth s surface since the beginning of the anthropocene the timeframe when natural processes shifted and landscape evolution became more human dominated we focus on contexts in arid and semiarid lands of northern africa which are metastable sensitive ecosystems that are prone to modifications triggered by climatic and anthropogenically forced factors studying the geoarchaeological record in context of landscape impact and animal procurement by people throughout antiquity is important for reconstructing domestication and husbandry of cattle sheep and goats in this region among the features we recognize in association with transhumance pastoralism and herding are trails trackways footholds animal daybeds stables animal dwellings rockshelters game blinds and monuments to name a few related activities with landscape scale impacts include herding transport corralling and browsing of cattle bos sp goats and sheep ovicaprines as well as pasturage activities like cropping fire setting and manuring these activities were disturbances that affected surface processes like erosion and dust mobilization as well as reduced vegetation and ecosystems productivity in dryland africa and especially in the sahara intensive herding led to the alteration of the pristine aspects of bare rock surfaces and of the stone desert pavement i e the hamada many regions preserved evidence of middle late holocene animal daybeds trampled areas and barren tracks and trails we suggest that human and herd animal activities affected geomorphic surfaces that affected slope stability intensified erosion and dust mobilization and enhanced dust export from the african continent offshore we reinterpret the increased dust emission from north africa during the mid holocene at the end of the african humid period as has been interpreted from ocean cores aridification of the green sahara followed the insolation forced monsoonal maximum and was exacerbated by human animal activities across the sahara and the sahel we argue that the spread of human activities and intensive husbandry of cattle and caprines goat and sheep in this region significantly influenced the geomorphic stability ecosystem and landscape sustainability in a comparable manner of overuse observed in present day arid and marginal environments where pastoral overgrazing pressure increases erosion processes and enhances dust mobilization we suggest that human animal activities have amplified dust generation from the north african continental interior since 7 ka bp this evidence of prehistoric human impacts on surface processes in north africa supports arguments for an early beginning of the anthropocene

significance of hydrocarbon seepage relative to petroleum generation and entrapment near surface indications of migrating hydrocarbons provide the petroleum systems analyst critical information about source organic matter type maturation organic maturity migration migration pathway delineation and in selected geologic settings specific prospect hydrocarbon charge all petroliferous basins exhibit some type of near surface signal but the hydrocarbon leakage to surface is not always detectable with conventional seep detection methods understanding the petroleum seepage system hence petroleum dynamics of a basin is key to understanding and using near surface geochemical methods for basin assessment and prospect evaluation the relationships between near surface hydrocarbon seepage and subsurface petroleum generation and entrapment are often complex the petroleum seepage system contain four key elements seepage activity qualitative expressions of relative leakage rates active vs passive and episodic vs continuous seepage type concentration of migrated thermogenic hydrocarbon relative to in situ material macro vs micro migration focus major direction of bulk flow leakage relative to the subsurface hydrocarbon generation and or entrapment and near surface seep disturbances near surface processes which can greatly alter or block seepage signals the rate and volume of hydrocarbon seepage to the surface greatly control near surface geological and biological responses and thus are the best method of sampling and analysis to detect hydrocarbon leakage effectively to properly predict subsurface petroleum properties interpretation of near surface geochemical data must recognize many potential problems including recent organic matter input transported hydrocarbons bacterial alteration mixing contamination and fractionation effects surface geochemical data should always be integrated with other geological data calibration datasets to determine the utility of near surface geochemical techniques within particular basinal settings are essential when evaluating prospects for hydrocarbon charge