human resilience to holocene climate changes inferred from rodent middens in drylands of northwestern patagonia argentina abstract we reconstruct the holocene vegetation climate and archaeological history for drylands of northwestern patagonia argentina based on multiproxy analysis plant macrofossil pollen and parasites of rodent middens integrated with a database of 14c dates associated with human occupations the local scale corresponds to the huenul paleoecological and archaeological locality emplaced in north western patagonia neuquen province argentina the rodent midden record from the huenul series reflects subtle vegetation changes driven by climatic variability at millennial timescale drier than present environmental conditions prevailed during the early holocene 10 500 9400 cal yr bp peaking during the mid holocene 9200 5500 cal yr bp when wetter than present conditions established during the late holocene 4400 2500 cal yr bp these environmental and climatic dynamics agree with other paleoclimatic records from northern patagonia suggesting the winter precipitation dynamics related to the southern westerlies as a common driver the diachronic distribution of anthropogenic radiocarbon dates from the western area of the south american arid diagonal between 32 40 s conforms to a fitted exponential model of steady background population growth not suggesting significant demographic changes that may have been the result of the impact of climate change this record indicates that these human populations coped successfully with aridity particularly during the mid holocene these findings reinforce the need to integrate multi scalar interdisciplinary analyses to assess the impact of climate change in human societies

a vegetation history from the arid prepuna of northern chile 22 23 s over the last 13 500 years the quaternary paleoclimate of the central andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region the exact timing duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another and there have been few opportunities to compare climatic records from the same proxy along environmental gradients vegetation histories from fossil rodent middens provide one such opportunity on the pacific slope of the andes we previously reported a vegetation history from the upper margin 2400 3000 m of the absolute desert in the central atacama desert of northern chile that record identified a distinct wet phase that peaked between 11 8 and 10 5 ka when steppe grasses and other upland elements expanded as much as 1000 m downslope and a secondary wet period during the middle to late holocene 7 1 3 5 ka the latter wet phase remains controversial and is not as readily apparent in our lowelevation midden record we thus sought to replicate both phases in a midden record from the mid elevations 3100 3300 m of the arid prepuna where slight precipitation increases would be amplified midden records from these elevations identify conditions wetter than today at 13 5 9 6 7 6 6 3 4 4 3 2 and possibly 1 8 1 2 ka dry phases occurred at 9 4 8 4 ka and possibly at ca 5 1 ka present floras and modern hyperarid conditions were established after 3 2 ka the records from the two elevational bands generally match with some important differences these differences could reflect both the discontinuous aspect of the midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert 2003 elsevier science b v all rights reserved

impact of water saturation on seismoelectric transfer functions a laboratory study of coseismic phenomenon s u m m a r y seismic waves propagating in a porous medium under favourable conditions generate measurable electromagnetic fields due to electrokinetic effects it has been proposed following experimental and numerical studies that these so called seismoelectromagnetic couplings depend on pore fluid properties the theoretical frame describing these phenomena are based on the original biot s theory assuming that pores are fluid filled we study here the impact of a partially saturated medium on amplitudes of those seismoelectric couplings by comparing experimental data to an effective fluid model we have built a 1 m length scale experiment designed for imbibition and drainage of an homogeneous silica sand the experimental setup includes a seismic source accelerometers electric dipoles and capacitance probes in order to monitor seismic and seismoelectric fields during water saturation apparent velocities and frequency spectra in the kilohertz range are derived from seismic and electrical measurements during experiments in varying saturation conditions amplitudes of seismic and seismoelectric waves and their ratios i e transfer functions are discussed using a spectral analysis performed by continuous wavelet transform the experiments reveal that amplitude ratios of seismic to coseismic electric signals remain rather constant as a function of the water saturation in the s w 0 2 0 9 range consistently with theoretically predicted transfer functions

experimental and theoretical basis of self potential phenomena in volcanic areas with reference to results obtained on mount etna sicily abstract self potential anomalies observed on volcanoes may be closely associated with thermoelectric electrochemical or electrokinetic couplings calculations based on irreversible thermodynamics and on laboratory measurements of streaming potentials allow us to estimate the amplitude of the anomalies generated by each mechanism in order to obtain realistic results values of the parameters used in the calculations or used to draw conclusions from the streaming potential measurements were chosen according to in situ tests or laboratory measurements with samples of volcanic origin results show clearly the pronounced predominance of the streaming potentials effects 300 mv upon thermoelectric 30 mv and electrochemical 10 mv couplings

river terraces and alluvial fans the case for an integrated quaternary fluvial archive abstract the fluvial archive literature is dominated by research on river terraces with appropriate mention of adjacent environments such as lakes despite modern sedimentary basins comprising a significant 88 volume of distributive fluvial systems of which alluvial fans 1 km

pollen taphonomy of cave sediments what does the pollen record in caves tell us about external environments and how do we assess its reliability cave sediments may contain important long term records of past environments and human activity pollen provides key evidence since it disperses widely and is relatively durable we still know relatively little about the dispersal of pollen into caves and its preservation within cave sediments compared with our relatively detailed knowledge of pollen taphonomy in other sedimentary environments pollen taphonomy in caves is dependent on a variety of transport pathways and seems to be very contingent on local circumstance the airfall component of cave pollen assemblages often seems comparable with airfall spectra in the landscape outside the cave but bees birds and bats may transport considerable quantities of pollen into caves and the entrance flora may also be significant cave sediments are rarely waterlogged and pollen within them can be subject tomicrobial and chemical degradation sedimentation in caves is often episodic with episodes of storage and deposition sometimes redeposition of sediment which means that biostratinomic preservational factors become very significant comparison with sequences outside caves is difficult because few caves are found in landscapes where there are comparable pollen records from lakes and bogs here we review the factors affecting cave pollen taphonomy and hence the reliability of palynological analysis of sediments from caves with suggestions for future investigation

theory of electrokinetic effects occurring at the final stage in the preparation of a tectonic earthquake crustal deformation processes occur with relative rapidity when short term precursors appear at the final preparatory stage of a tectonic earthquake this paper contains calculations of crustal bulk strain before an earthquake based on the model of a rigid inclusion the data give initial conditions for the problem of fluid percolation in a two phase medium accompanied by electrokinetic effects the solution provides a description of systems of currents arising in the vicinity of the source region an analysis of this theoretical evidence yields information on the behaviour of short term precursors in telluric currents and the geomagnetic field

modern pollen climate calibration for southern south america abstract using the response surface technique a modern pollen climate calibration is presented for the mid latitudes in southern south america between latitudes 39 s and 44 s extending from the west coast in chile across the andes into the patagonian steppe region the climate parameters identified that relate to the present day pollen distribution of the nine most important pollen types nothofagus dombeyi type nothofagus obliqua type podocarpus weinmannia caldcluvia eucryphia type cupressaceae myrtaceae misodendrum and steppe types are summer precipitation summer and winter temperatures using the modern pollen climate data set three fossil pollen records mallin aguado and lago moreno east of the andes and caunahue west of the andes are interpreted in terms of these three seasonal climate parameters despite intervals of no analog fossil pollen assemblages the reconstruction shows similar climate trends on both sides of the andes during the last 21 000 cal yr bp 17 000 yr bp with summer precipitation as low or markedly lower than today prior to 17 000 cal yr bp 14 500 yr bp as high or higher than today between 15 000 and 12 500 cal yr bp 12 500 and 10 500 yr bp and again lower than today between 12 500 and 8000 cal yr bp 10 500 and 7200 yr bp summer and winter temperatures were low or high when summer precipitation was high or low

the climate of the altiplano observed current conditions and mechanisms of past changes abstract the large scale controls on the climate of the south american altiplano are investigated using local observations reanalysis data and general circulation model experiments the objective is to gain understanding of causes of climate variability and climate change by relating mechanisms that operate on timescales ranging from the intraseasonal to the glacial interglacial our results suggest that on all timescales the climatic conditions on the altiplano are closely related to the upper air circulation with an easterly zonal flow aloft favoring wet conditions and westerly flow causing dry conditions different factors influence the upper air circulation on the different timescales intraseasonal variability is a reflection of the position and intensity of the bolivian high which is modulated by rossby waves emanating from the midlatitude south pacific the annual cycle of dry winter and wet summer conditions is caused by the seasonal expansion of the equatorial easterlies in the upper troposphere rather than direct insolation forcing over the altiplano or moisture changes in the source area interannual variability is primarily related to changes in the mean zonal flow over the altiplano reflecting changes in meridional baroclinicity between tropical and subtropical latitudes which in turn is a response to sea surface temperature changes in the tropical pacific orbitally forced changes in the land sea contrast drive continental scale circulation changes which significantly alter the zonal flow over the altiplano on glacial interglacial timescales the contrast in heating between northern and southern hemispheres during the glacial leads to upper air easterly anomalies throughout the tropics on modern timescales the marked submonthly seasonal and interannual changes of moisture over the altiplano cannot be accounted for by moisture changes in the humid tropical lowlands however the model experiments suggest that cooler conditions during a glacial reduce moisture availability from the tropical lowlands which counteracts the effect of the upper level circulation resulting in little overall change in precipitation this observational and modeling analysis provides a physical framework for relating the mechanisms of both internal and forced climate change on the altiplano on a wide range of timescales

streaming potential measurements 2 relationship between electrical and hydraulic flow patterns from rock samples during deformation streaming potential and resistivity measurements have been performed on fontainebleau sandstone and villejust quartzite samples in a triaxial device during compaction uniaxial compression and rupture measurements on individual samples do not show any clear intrinsic dependence of the streaming potential coefficient with permeability an apparent dependence of the streaming potential coefficient with permeability is however observed during deformation the effect of surface conductivity is taken into account and is small compared with the observed changes in the streaming potential coefficient the observed dependence is therefore interpreted in terms of a difference in the evolution of the electrical and hydraulic connectivity patterns during deformation this effect causes the streaming potential coefficient and consequently the inferred potential to be reduced by a geometrical factor r g representing the electrical efficiency of the hydraulic network estimates of the r g factor varying between 0 2 and 0 8 for electrolyte resistivity larger than 100 m are obtained by comparing the values of the potential inferred from intact rock samples with the values obtained from crushed rock samples where the geometrical effects are assumed to be negligible the reduction of the streaming potential coefficient observed during compaction or uniaxial compression suggests that the tortuosity of the hydraulic network increases faster than the tortuosity of the electrical network before rupture an increase in the streaming potential coefficient associated with the onset of dilatancy was observed for three samples of fontainebleau sandstone and one sample of villejust quartzite the changes in streaming potential coefficient prior to failure range from 30 to 50 during one experiment an increase in the concentration of sulfate ions was also observed before failure these experiments suggest that observable streaming potential and geochemical variations could occur before earthquakes

late holocene environmental change in the northwestern namib desert margin new fossil pollen evidence from hyrax middens abstract the lack of anoxic environments in arid lands makes well preserved fossil pollen difficult to find the scarcity of continental palaeobotanical data in tropical arid zones restricts the understanding of aridification processes in these endangered ecosystems it is essential to improve the knowledge about their environmental histories during the holocene and therefore we attempt to investigate the causes and describe the patterns of vegetation change in northern namibia with that aim we analyzed pollen from fossil hyrax dung that accumulated over long periods of time by sampling stratigraphically coherent sequences in five radiocarbon dated middens the fossil hyrax middens were found in rock shelters on the eastern desert edge in the northwestern kaokoveld within the so called nama karoo biome this is an ecotonal area between the namib desert and the savanna biomes which reflects features from both systems and its life form composition largely depends on an erratic rainfall pattern thirty three samples were analyzed for pollen and the pollen record reflects a non continuous vegetation history over the last 5200 yr with a hiatus between ca 4200 and 1690 yr bp the pollen spectra reflect arid savanna vegetation with a marked increase in the tree grass ratio from ca 1300 cal yr bp the most likely cause for this change is a decline in moisture that we relate to intrinsic savanna dynamics with early pastoralism megahervibore migration and changes in the hyrax diet playing a minor role

fossil hyrax dung and evidence of late pleistocene and holocene vegetation types in the namib desert abstract pollen was derived from fossil dung of herbivorous hyraxes deposited in a rock shelteron the highest mountain in namibia da ures or brandberg situated on the namib desert margin radiocarbon dating ranging in age between modern times and 30000yrbp showed it representsthe rst empirical pollen evidence of continental palaeovegetation during the late pleistocene alongthe western escarpment of southern africa the initial results indicate last glacial maximum vegeta tion differed totally from the current pattern as vegetation types were dominated by small asteraceaeshrubs in contrast to those of the holocene and modern times which show more succulents grassandwoody elements arboreal pollen the resultssuggest that cape oral communities didnot reachinto thetropics along thewestern escarpment ofafrica despite such pollentypes occurring inmarinecores copyright 2004 john wiley sons ltd keywords palynology namibia restionaceae late pleistocene last glacial maximum

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

numerical simulation of electrokinetic potentials associated with subsurface fluid flow a postprocessor has been developed to calculate space time distributions of electrokinetic potentials resulting from histories of underground conditions pressure temperature vapor saturation concentrations of dissolved species flow rate etc computed by unsteady multidimensional geothermal reservoir simulations electrokinetic coupling coefficients are computed by the postprocessor using formulations based on experimental work reported by ishido and mizutani 1981 the postprocessor was applied to both numerical modeling of natural self potential sp anomalies in geothermal fields and production induced sp changes the essential features of the sp anomalies and sp changes which have actually been observed in real geothermal fields are reproduced reasonably well in these calculations for both single phase liquid and two phase vapor liquid geothermal reservoirs the postprocessor was also applied to predicting the magnitude of electrical earthquake precursory signals caused by dilatant strains taking place within a narrow vertical fault zone if the rate of porosity increase is high enough to induce substantial pore pressure decrease two phase flow develops in the fault zone and produces observable signals at the ground surface if a high conductivity channel connects the near surface region and the deep fault zone

zeta potential estimation of volcanic rocks on 11 island arc type volcanoes in japan implication for the generation of local self potential anomalies 1 from streaming potential measurements we deduced the zeta potential of 73 volcanic rock samples collected in 11 volcanoes where self potential sp surveys had also been conducted experiments with crushed rock samples and 0 001 mol l nacl solution showed a large variation in streaming potential coefficient which ranged from 2860 to 2280 mv mpa deduced zeta potential ranged from 45 1 to 37 2 mv among the 73 samples 9 samples showed positive values and 11 samples showed small absolute values less than 10 mv even in a volcano the zeta potential values of rocks were sometimes highly variable to investigate the reason for the variation in zeta potential we performed x ray fluorescence xrf measurements on the rock samples however no significant correlations between zeta potential or isoelectric point and weight percentage of major elements were found implying that the zeta potential of the volcanic rocks is not controlled by chemical composition but by mineralogical composition or crystalline structure in volcanic areas rocks with positive or small absolute values of zeta potential which are considered to be unusual frequently exist in areas along with local positive sp anomalies although positive sp anomalies are usually interpreted as an indication of hydrothermal upflow this correlation suggests that in addition to the groundwater flow pattern the polarity of zeta potential should also be considered for interpretation of sp data therefore in cases where detailed zeta potential measurements have not been conducted local positive sp anomalies should be interpreted with caution

laboratory measurements anomalous 0 1 0 5 hz streaming potential under geochemical changes implications for electrotelluric precursors to earthquakes streaming potentials resulting from flow of various salt solutions in rock were measured on saturated sediments fontainebleau sandstones the streaming potential v was found to be proportional to the driving pore pressure p pulses of amplitude 15 40 mv in the frequency range of 0 1 to 0 5 hz were observed when the conductivity of the injected water was decreased and the fluid flow rate was relatively low corresponding to a darcian velocity of 17 to 30 cm h the amplitudes of these pulses are 47 to 133 of the corresponding steady components of the v values such geochemically induced effects may possibly be responsible for the frequency signals from 0 1 to 0 5 hz that were sometimes observed before an earthquake

measurement of streaming potential coupling coefficient in sandstones saturated with high salinity nacl brine 1 we present measurements of the streaming potential coupling coefficient in intact sandstone samples saturated with nacl brines at concentrations up to 5 5 moll 1 the values we record at low salinity are consistent with those reported previously as brine salinity increases the coupling coefficient decreases in magnitude but is still measureable up to the saturated concentration limit the magnitude of the zeta potential also decreases with increasing salinity but approaches a constant value at high salinity this behaviour is not captured by current models of the electrical double layer our results suggest that streaming potential measurements may be used to monitor flow in saline subsurface environments such as deep saline aquifers and hydrocarbon reservoirs however they were obtained at laboratory temperature future work will focus on the effect of elevated temperatures at high salinity

self potential observations during hydraulic fracturing 1 the self potential sp response during hydraulic fracturing of intact sierra granite was investigated in the laboratory excellent correlation of pressure drop and sp suggests that the sp response is created primarily by electrokinetic coupling for low pressures the variation of sp with pressure drop is linear indicating a constant coupling coefficient cc of 200 mv mpa however for pressure drops 2 mpa the magnitude of the cc increases by 80 in an exponential trend this increasing cc is related to increasing permeability at high pore pressures caused by dilatancy of microcracks and is explained by a decrease in the hydraulic tortuosity resistivity measurements reveal a decrease of 2 prior to hydraulic fracturing and a decrease of similar to 35 after fracturing an asymmetric spatial sp response created by injectate diffusion into dilatant zones is observed prior to hydraulic fracturing and in most cases this sp variation revealed the impending crack geometry seconds before failure at rupture injectate rushes into the new fracture area where the zeta potential is different than in the rock porosity and an anomalous sp spike is observed after fracturing the spatial sp distribution reveals the direction of fracture propagation finally during tensile cracking in a point load device with no water flow a sp spike is observed that is caused by contact electrification however the time constant of this event is much less than that for transients observed during hydraulic fracturing suggesting that sp created solely from material fracture does not contribute to the sp response during hydraulic fracturing

noise reduction in long term self potential monitoring with travelling electrode referencing the long term monitoring of the electric self potential sp in geophysical systems is affected by electrode degradation and drift this error contribution can be reduced if the electrodes of measuring dipoles are referenced to the same accessory electrode moved in turn at each pole the benefit of this travelling electrode referencing scheme ter has been evaluated in a dedicated experiment performed from march 2000 to march 2001 at tribhuvan university nepal two prototype monitoring points separated by 55 m have been instrumented with pairs of lead lead chloride petiau electrodes installed in buckets filled with salted bentonite at a depth of 1 and 2 meters the electrical potential at 1 and 2 meters depth was also accessible from the surface by pipes filled with salted bentonite over one year the measurement error defined as the standard deviation of the difference between the measured potential and the true sp at a given time is estimated to be 5 mv this error value is reduced to less than 1 mv with ter after correction a smooth annual variation with amplitude of 10 to 15 mv is observed and is interpreted as streaming potentials associated with the monsoon and subsequent drying these results provide significant guidelines for precision long term sp monitoring in particular in tropical volcanic or tectonically active regions

electromagnetic emissions from dry and wet granite associated with acoustic emissions 1 triaxial deformation experiments were performed to compare electromagnetic emissions emes from dry and wet granite specimens associated with acoustic emissions aes cylindrical specimens of initially intact granite were tested at room temperature we measured both high frequency 10 khz to 1 mhz and low frequency dc to 500 hz components of the electric potential variations in general it is difficult to detect emes in wet conditions because wet rock has very short electric relaxation time which is proportional to its electric resistivity however in the wet experiment using a granite specimen saturated with distilled water under a constant pore pressure emes in the high frequency range were detected and accompanied with aes although emes in the low frequency range were not observed in contrast in the dry granite experiment emes were detected in both the high frequency and low frequency ranges in the high frequency range the dry specimen generated eme more frequently than the wet specimen the generation mechanism can be explained based on piezoelectricity and compensation charges the difference in the eme generation from wet and dry granite is attributed to the difference of electric relaxation time also electromagnetic fields due to an electric polarization in a dielectric and conductive medium are discussed including the frequency dependence of the skin depth

evidence of the theoretically predicted seismo magnetic conversion summary seismo electromagnetic phenomena in porous media arise from seismic wave induced fluid motion in the pore space which perturbs the equilibrium of the electric double layer this paper describes with details the original experimental apparatus built within the ultra shielded chamber of the low noise underground laboratory of rustrel france we measured seismo magnetic conversions in moist sand using two induction magnetometers and a pneumatic seismic source to generate the seismic wave propagation we ensured to avoid the magnetometer vibrations which could induce strong disturbances from induction origin interpretation of the data is improved by an analytical description of phase velocities for fast pf and slow ps longitudinal modes transverse mode s as well as the extensional mode due to the cylindrical geometry of the sample the purpose of this paper is to provide elements to measure correctly coseismic seismomagnetic fields and to specify their amplitude the seismic arrivals recorded in the sample showing a 1200 1300 m s 1 velocity have been associated to p and extensional waves the measured seismo magnetic arrivals show a velocity of about 800 m s 1 close to the calculated phase velocity of s waves therefore we show that the seismo magnetic field is associated to the transverse part of the propagation as theoretically predicted by pride 1994 but never measured up to now moreover the combined experimental and analytical approaches lead us to the conclusion that the measured seismo magnetic field is probably about 0 035 nt for a 1 m s 2 seismic source acceleration 0 1 g

streaming potential properties of westerly granite with applications this paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of westerly granite data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5 70 c for 1 1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately 4 mv atm m and for 2 1 electrolytes 2 mv atm m the effect of temperature was small 0 05 mv c temperature increase and indicates that the zeta potential was independent of temperature preliminary experimental results using mixed electrolytic solutions nacl cacl2 and two phase fluid flow are also described two phase flow can enhance streaming potentials by as much as a factor of 3 or 4 the laboratory data are used to interpret streaming potentials in geological problems such as earthquake prediction geothermal prospecting using the self potential method and surface conductivity contribution to the electrical resistivity of rocks

a review on modeling inversion and interpretation of self potential in mineral exploration and tracing paleo shear zones abstract this study discusses the improvements of different modeling and inversion approaches to self potential sp anomaly associated with shallow and deep subsurface imaging the study also focuses on the fundamental foundations of self potential which have been advanced with time and event cause system and application in different investigation fields in addition a point by point forward modeling of different subsurface idealized geological bodies is discussed various sp techniques utilized for interpretation have likewise been examined for each use of sp anomaly besides the uncertainty associated with the understanding of self potential interpretation has also been discussed additionally the above studies were used to examine the diverse subsurface idealized geologic bodies deciphered from different inversion and elucidation strategies combinations of 17 real field illustrations were examined and a similar investigation was conducted for different interpretation strategies moreover a similar study was carried out to gain insights to mineralized bodies associated with different subsurface structures and the depth of the ore body and the rest of the model parameters are also discussed a correlation between the field information and the interpreted model information is shown considering different elucidation techniques wherever information was available the significance of this type of study is its multi purpose application in investigating various subsurface problems related to mineral exploration and tracing paleo shear zones this study would be very useful to scientists investigating the use of self potential in mineral ore investigation and in tracing paleo shear zones in continental crust

holocene environmental changes and cultural patterns in coastal western india a geoarchaeological perspective abstract geomorphological studies carried out around coastal sites at hazira kanmer padri and sanjan in gujarat and chaul and kelshi in maharashtra indicate human activity throughout the holocene the offshore site at hazira of early holocene age is the only submerged prehistoric site at a depth of 20 40 m below the present sea level in the entire 7000 km long coastline of india protohistoric harappan sites at kanmer and padri are of mid holocene age the sites of sanjan chaul and kelshi represent an early historic cultural phase belonging to the late holocene age the site of hazira was located on the banks of a buried channel adjusted to the low sea level phase of the early holocene cultural development of the harappan site at kanmer in the present semi arid rocky landscape of kachchh was closely related to the existence of 2 5 m deep water in the presently dried up part of rann of kachchh throughout the mid holocene on the other hand the economy of the harappan site of padri depended on salt manufacturing in a stable estuarine environment close to the present sea level of the gulf of cambay sanjan chaul and kelshi appear to have depended on a trading economy these sites are situated in estuarine environments involving lateral transgressive regressive phases more or less within the present intertidal zone of arabian sea in a humid environment

from proxy data to paleoclimate interpretation the mid holocene paradox of the atacama desert northern chile abstract the question whether the mid holocene climate between ca 9 and 4 cal kyr b p in the atacama desert and the central andes in general was humid or dry has wide implications with regard to the understanding of long term climate variability in south america paleosols regional groundwater tables abiotic proxy data and pollen of aquatic plants in lake sediments show a marked and rapid shift from very humid late glacial early holocene climatic conditions between ca 14 and 9 5 kyr b p to extremely dry mid holocene conditions more arid than today between ca 9 and 4 kyr b p an exception during this hyperarid period is a century scale more humid interval around ca 5 5 6 kyr b p that appears systematically in lake sediment archives in contrast pollen for most terrestrial plants preserved in lake sediments do not show major changes during the holocene whereas more humid mid holocene conditions compared with late holocene conditions were inferred from plant macrofossils in rodent middens is the reason for this disagreement to be attributed to misinterpretation of the paleoenvironments or of the proxy records themselves or to incomplete paleoclimatic interpretation of the paleoenvironments we argue that these different paleoclimate archives record different aspects and facets of climate while paleosols and groundwater in the atacama desert record low frequency climate variability at century to millennium scales lake sediments on the altiplano record decade to century scale variability terrestrial vegetation responds to shorter high frequency climate variability at seasonal to inter annual scales and preferably to humid years vegetation remains in hibernation or does not germinate during arid years thus information from these three types of archives is not a priori comparable and requires careful site specific archive specific and time scale specific evaluation what is natural in modern climatology is also true for paleoclimatology a comprehensive assessment must account for the complex daily and seasonal cycles for the range of climate variability and trends at different scales in space and time for impacts of short term extreme events and for specific often non linear responses of individual bio geo physical archives to any of the numerous aspects of climate

calibrating the pollen signal in modern rodent middens from northern chile to improve the interpretation of the late quaternary midden record abstract the use of rodent middens from northern chile as paleoecological archives has at times been questioned due to concerns about their biogenic origin and the degree to which their record represents vegetation composition rather than rodent habits to address such concerns we carried out a modern calibration study to assess the representation of vegetation by pollen records from rodent middens we compared vegetation censuses with soil surface and midden matrix and feces pollen samples from sites between 21 and 28 s the results show that 1 the pollen signal from the midden matrix provides a more realistic reflection of local vegetation than soil surface samples due to the pollen deposition processes that occur in middens and 2 in contrast to feces pollen assemblages which feature some biases rodent dietary habits do not seem to influence midden matrix pollen assemblages probably because midden agents are dietary generalists our finding that modern pollen data from rodent middens reflect vegetation patterns confirms the reliability of midden pollen records as paleoecological archives in northern chile

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

plausibility of long distance electrotelluric precursors to earthquakes a systematic analysis of the plausibility of different classes of models which could account for low frequency precursory electrotelluric signals observable at large distances from a large earthquake is carried out first we consider linear models for which either a stationary electrical field is generated by a current dipole in the source volume or a static deformation field results from a precursory strain in the source volume linearly inducing a streaming potential effect near the electrode in the former case only the conjunction of very favorable circumstances may lead to an electrical field larger than 10 mv km at more than 100 km with the constraint that no anomaly exceeds a few volts per kilometer in the source area it indeed requires a powerful electrical dipole current 104 a length 1 km which might be produced by a streaming potential effect associated with the connection of nonhydrostatic fluid reservoirs pore pressure difference up to 100 mpa a two dimensional channeling of the electrical currents from the source to the electrode area which would result from high conductivity horizontal layers and finally a local amplification factor of typically 100 near the electrodes which might be produced by a narrowing of the conductive channel for an elastic long distance interaction an electric field of 10 mv km at a distance 10 times the source length 100 km away from a m 6 earthquake requires a precursory deformation larger than the coseismic deformation if no strong local amplification is considered alternatively nonlinear models are proposed and discussed assuming that the crust is stuffed with small scale local instabilities fractures and nonhydrostatic fluid reservoirs among which a number are close to their instability threshold these instabilities may follow their own evolutionary process inducing sporadic fluid flow and hence streaming potential effect in the vicinity of the electrodes without any relation to a remote tectonic activity however these instabilities may be sensitive to very small changes in the stress field and hence be triggered by the elastic precursory deformation of a remote seismic source this requires that the precursory deformation near the instability is at least larger than the tidal strain 10 7 this necessary condition is met at a distance of up to 10 times the source dimension when the precursory strain source is only 10 of the coseismic deformation provided that the strain source is double the size of the seismic fault itself this model could account for the absence of self potential anomalies related to the earthquake itself as a large proportion of the available instabilities could have been swept away by the precursory strain furthermore with such a model a precursory strain in the source area could induce a detectable change in the background seismic activity over a vast area which may give a new interpretation of the times of increased probability observations for short distances the triggering of fluid instabilities by strain perturbation and the associated streaming potential effect may well be a promising model for explaining low frequency electric and magnetic precursors

late quaternary environmental dynamics in the atacama desert reconstructed from rodent midden pollen records in the past two decades much has been learned about the late quaternary climate history of the atacama desert with some details still unclear about the seasonality timing and extent of wet and dry phases modern climate studies reveal that far from exhibiting a unique pattern seasonal precipitation originates from many sources and mechanisms for the last 16 ka we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22 25 s in northern chile widespread wet conditions prevailed during the late pleistocene and early holocene particularly between 13 and 9 ka evidenced by 400 m lowering of pollen zones plant communities compared to today regional differences in the timing and magnitude of this displacement may be related to the prevailing source tropical extra tropical or mode nnw se of tropical precipitation through time wet conditions persisted well into the early holocene lasting 1 1 5 ka longer than previously suggested the pollen record suggests extreme drying 8 ka possibly associated with a northward shift of the inter tropical convergence zone tracking minimum insolation values at subtropical latitudes during the austral summer the establishment of conditions similar to today happened 4 ka copyright 2017 john wiley sons ltd

streaming potential and permeability of saturated sandstones under triaxial stress consequences for electrotelluric anomalies prior to earthquakes the streaming potential due to fluid circulation in rock was measured on saturated sediments fontainebleau sandstones the electrokinetic coupling coefficient which is the ratio of the streaming potential and the excess pore pressure is proportional to the fluid resistivity additionally for a fluid conductivity of 10 3 s m the electrokinetic coupling coefficient varies from 10 to 6642 mv 0 1 mpa for sample permeability in the range of permeabilities from 0 15 10 15 to 1220 10 15 m2 the different values of the electrokinetic coupling coefficient have been explained by the effect of increasing surface conductivity which becomes nonnegligible compared to fluid conductivity for low permeability when the sample is deformed under triaxial stress up to failure the vertical permeability along the principal stress drops by about 0 20 0 1 mpa when failure occurs the typical variation of the electrokinetic coupling coefficient is a large increase beginning with the onset of the localization of the shear band at about 75 of the yield stress and stopping at the failure this increase of the electrokinetic coupling coefficient is due to an increase of potential in the shear zone when new surfaces are created and connected possible consequences of our results are given concerning the electrical fields which could appear during the preparation of an earthquake it is shown that in some cases self potential anomalies reported in the deformed zone preceding an earthquake occurrence could be due to an increase of the electrokinetic coupling coefficient from 75 of the yield stress to rupture in the vicinity of one of the electrodes any variation of fluid resistivity or permeability in the vicinity of one electrode could change the electrokinetic coupling coefficient inducing a surface electrokinetic potential anomaly in regard to the interpretation of the electrokinetic effect which occurs at large distance from the epicenter a larger electrokinetic potential anomaly could be measured between electrodes situated along a vertical fluid flow for instance in a shallow borehole an electrokinetic potential anomaly up to 30 mv for a fluid conductivity of 0 01 s m and a rock permeability of 10 12 m2 could be observed with a change of the underground water table level as slight as 50 cm 50 mbar moreover if the permeability between the electrodes is increased by a factor of 8 103 the electrokinetic coupling coefficient could be enhanced by a factor up to 650

streaming potential in volcanic rocks from mount pelee streaming potential and electric conductivity have been measured in a laboratory on 11 consolidated samples coming from five deposits of the different evolutionary stages of mount pelde volcano the streaming potential coupling coefficient ranges from 35 to 4905 mv mpa 1 and increases with increasing permeability this increase is mainly due to the dependency of rock effective conductivity with permeability the permeability of the samples varies from 0 146x10 12 to 34x10 12 m 2 the zeta potential at ph 7 and water conductivity of 2 1x10 4 s m l is relatively small for the majority of the samples it ranges from 4 to 19 rev according to water conductivity analysis on mount pel e streaming potential coupling coetficients of 25 to 406 mv mpa 1 can be expected for this volcano

three dimensional inversion of self potential data used to constrain the pattern of groundwater flow in geothermal fields 1 we propose an algorithm to invert self potential signals measured at the ground surface of the earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems the self potential signals result from the divergence of the streaming current density groundwater flow can be either driven by topography of the water table free convection or deformation of the medium the algorithm includes the electrical resistivity distribution of the medium obtained independently by dc resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements inversion of the distribution of the source current density from ground surface and borehole self potential measurements is achieved by solving the inverse problem using tikhonov regularization solutions that are compatible with the physics of the primary flow problem by introducing assumptions regarding the smoothness or the compactness of the source and the three dimensional distribution of the electrical resistivity of the system the inverse problem can be solved in obtaining the three dimensional distribution of the current source density in the ground however an annihilator can be added to the inverted source geometry without affecting the measured self potential field annihilators can be obtained from boundary conditions synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm an application is presented to the geothermal field of cerro prieto baja california mexico using literature data inversion of the self potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part the temperature anomaly associated with the existence of this plume is independently observed by interpolating borehole temperature measurements we found a good agreement between the distribution of the temperature and the inverted source current density the proposed method appears therefore as a noninvasive method for remote detection and three dimensional mapping of subsurface groundwater flow

vegetation invasions into absolute desert a 45 th000 yr rodent midden record from the calama salar de atacama basins northern chile lat 22 24 s plant macrofossils percentage abundance of grass taxa fecal pellet d13 c and plant cuticle contents from 49 fossil rodent middens dated by 14 c record changes in local vegetation and precipitation since 45 ka calibrated or measured to thousands of calendar years before present in the central atacama desert lat 228 248s of northern chile the midden sites are along the hyperarid upper margin 2400 3100 m of the absolute desert in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs conditions between 40 and 22 ka may have been at least intermittently dry and possibly cooler as implied by four middens with low species richness we infer a large increase in summer rainfall between 16 2 and 10 5 ka on the basis of the lowering of steppe grasses by as much as 1000 m prominence of c4 grasses and summer annuals high species richness and displacement of northern species at least 50 km south of their modern ranges the precipitation increase was greatest for a cluster of middens between 11 8 and 10 5 ka abrupt drying evident in a dramatic decrease in grass abundance occurred after 10 5 ka at all four midden localities increased percentages of

permeability dependence of streaming potential in rocks for various fluid conductivities streaming potentials have been measured on sandstone and limestone samples in a large range of permeabilities the electrokinetic coupling coefficient increases with permeability and we explain this effect by the related variation of surface conductivity a model is proposed to study this effect for various fluid conductivities and it is shown that the dependence of the electrokinetic coupling coefficient on permeability is stronger for high fluid resistivity and is weaker for lower fluid resistivity when fluid resistivity is below 1 m permeability and streaming potential are no more related