correlation of fluvial sequences in the mediterranean basin over the last 200 ka and their relationship to climate change macklin mark fuller i c lewin j maas g a 2002 correlation of fluvial sequences in the mediterranean basin over the last 200 ka and their relationship to climate change quaternary science reviews 21 14 15 pp 1633 1641 rae2008

the grain size gap and abrupt gravel sand transitions in rivers due to suspension fallout median grain sizes on riverbeds range from boulders in uplands to silt in lowlands however rivers with 1 5 mm diameter bed sediment are rare this grain size gap also marks an abrupt transition between gravel and sand bedded reaches that is unlike any other part of the fluvial network abrupt gravel sand transitions have been attributed to rapid breakdown or rapid transport of fine gravel or a bimodal sediment supply but supporting evidence is lacking here we demonstrate that rivers dramatically lose the ability to transport sand as wash load where bed shear velocity drops below 0 1 m s forcing an abrupt transition in bed material grain size using thresholds for wash load and initial motion we show that the gap emerges only for median bed material grain sizes of 1 5 mm due to reynolds number dependencies in suspension transport the grain size gap therefore is sensitive to material properties and gravity with coarser gaps predicted on mars and titan

sedimentary characteristics of the gravel sand transition in the river rhine abstract a gravel bed river often changes abruptly into a sand bed river the causes of such so called gravel sand transitions have been elucidated in recent years but detailed observations of gravel sand transitions in large rivers are scarce the present study fills this knowledge gap by investigating the sedimentary characteristics of the gravel sand transition in the river rhine data on bed composition and flow characteristics are used in combination with a novel method for the evaluation of the bed structure the analysis shows that in contrast to common belief the bed structure in the gravel sand transition zone does not change from fully clast supported to fully matrix supported instead there is a strong cross stream variation in bed structure especially upstream of the transition zone the analysis also shows that the downstream decrease in gravel mobility in the gravel sand transition zone which is usually attributed to the change in bed structure and the so called patchiness effect is at least partly caused by the larger scale bend sorting process which concentrates gravel in outer bends where it is only infrequently mobile dune sorting which has been suggested to have an effect on the gravel mobility similar to that of bend sorting was found to be relatively unimportant in the rhine partly because it is strongly counteracted by armoring processes that affect an uncommonly thick sediment layer the gravel sand transition in the rhine with its length of 50 km is much less abrupt than the gravel sand transitions of smaller rivers reported on in the literature although the dependence of the transition length on river size intuitively is correct the exact causes remain unclear

the stratigraphy and paleogeography of the middle paleolithic open air site of ein qashish northern israel abstract the middle paleolithic site of ein qashish is located on the floodplain of the qishon stream northern israel which drains into the mediterranean sea it is located at the inlet to a narrow water gap between mt carmel and tiv on hills the excavation and 3 trenches up to 5 m deep provide the stratigraphy and allow a reconstruction of the paleogeography and depositional environments the archaeological layer osl dated to about 64 4 ka is composed of carbonate gravel and overlies 66 4 ka mis4 black heavy alluvial clays deposited by the qishon stream which represents marsh environment the site is covered by another clay unit representing a second marsh period between 50 3 and 41 3 ka mis3 this sedimentary complex is unconformably covered by coarse gravel and reddish clay matrix dated to between 15 1 0 7 and 10 5 0 5 ka which is derived from wadi qashish a steep mountainous stream of mt carmel the mineralogical analyses of the clays indicate high quartz concentrations and smectitic is which support the interpretation of qishon basin origin versus illitic is from mt carmel slopes the duration of the prehistoric human activity is estimated at sea level during the occupation period was between 100 and 60 m b s l and the coastline was located 10 7 km westward the proposed mechanism for the marsh development is a repeated episodes of blockage of the qishon stream outlet at the narrow water gap by aeolian sand transported by westerly winds inland over the exposed continental shelf the accumulation of sand and sandstone over the coastal plain during this period supports this idea b based on hydrological correlation with the lake lisan levels the flows in the qishon stream were low with large component of baseflows characterizing warmer and wetter periods that could not cut through the sand blockage and forced the water upstream into marshes the marshes drained during the colder and drier heinrich events h6 h5a and h4 which were characterized by higher frequency of large floods

pb isotopes in surficial pelagic sediments from the north atlantic we measured pb isotopic composition and concentration in sediment samples close to the sea water interface in 6 box cores from the ne atlantic 2 box cores from the sargasso sea and one from the us continental shelf the anthropogenic pb input to marine sediments due to the increase of pb contamination over the ocean during the last century can be identified in all these cores in the eastern part of the atlantic i e in regions under aeolian influence from europe pb pollution can be recognized using its distinctive unradiogenic composition clearly different from the upper crustal values commonly found in pre holocene sediments in contrast pb pollution in regions influenced by north american sources can be identified only in detailed concentration profiles because the american pb pollution has an isotopic composition much closer to that of the natural detrital pb input coming from weathering of the continental crust pb excess inventories are in good agreement with fluxes estimated from sedimenttrap data and with the time record of pb contamination increase given by analyses in coral growth bands inventories of pb contamination to the sediments of the mud patch american shelf are tenfold higher 84 g cm2 than those to hatteras and bermuda abyssal plains 4 3 and 2 8 g cm2

lichenometric application to historical and subrecent dynamics and sediment transport of a corsican stream figarella river france abstract lichenometry has been applied to blocks canyon walls and terrace deposits a growth curve specific to corsica was made based on information obtained from tombstones old monuments from the genoese occupation of corsica and roman megaliths this allowed us to create a curve going as far back as 2000 years the curve is similar to those developed in mediterranean environments cevennes and eastern pyrenees but is very different from those developed in alpine and arctic regions lichens present on boulders of the bedload allow the time at which the boulders were laid down to be determined the lichenometric study of the figarella shows firstly that there is high stream competence blocks approximately 100 cm wide are moved during the 5 year flood recent important flood events were identified in 1973 and 1869 these correspond well with historical sources other older and much more important floods were also identified this analysis has allowed us to extend the specific streampower curves proposed by costa geol soc am bull 94 1983 986 and williams geogr ann 65a 1983 227 to blocks of more than 2 m wide lichens present on the canyon walls and on terrace sides in the plain allowed the last main incision phase to be dated to the little ice age aerial photograph analysis has shown that the present braided system in the lower course of the river is no longer active

geochronologies and environmental records of quaternary fluvial sequences in the guadalope basin northeast spain based on luminescence dating

numerical study of alternate bars in alluvial channels with nonuniform sediment rivers typically present heterogeneous bed material but the effects of sediment nonuniformity on river bar characteristics are still unclear this work investigates the impact of sediment size heterogeneity on alternate bars with a morphodynamic numerical model the model is first used to reproduce a laboratory experiment showing alternate bar formation with nonuniform bed material subsequently the influence of sediment size heterogeneity on alternate bars is investigated distinguishing hybrid from free bars definition based on the presence absence of morphodynamic forcing considering the results of nine scenarios in four of them a transverse obstacle is used to generate forcing the computations are carried out with the telemac mascaret system solving the two dimensional shallow water equations with a finite element approach accounting for horizontal and vertical sediment sorting processes the results show that sediment heterogeneity affects free migrating and hybrid bars in a different way the difference lies in the presence absence of a migration front so that distinct relations between bed topography bed shear stress and sediment sorting are obtained sediment sorting and associated planform redistribution of bed roughness only slightly modify free migrating bar morphodynamics whereas hybrid bars are greatly impacted with decreased amplitude and increased wavelength increased sediment size heterogeneity increases the degree of sediment sorting while the sorting pattern remains the same for both free and hybrid bars moreover it produces averagely higher longer and faster free bars while in the case of hybrid bars their wavelength is increased but no general trend can be determined for their amplitude

experiments on downstream fining of gravel ii wide and sandy runs this is the second of two papers about experiments on downstream fining of gravel here we briefly summarize the complete series of runs described in the first paper where the influence of sediment feed rate was evaluated in a narrow channel we then present results for variation in two more conditions sand content and channel width the experiments were carried out in a long flume with an effective 40 m long test section with two different widths of 0 3 and 2 7 m in addition two sediment mixtures were used with different sand contents i e 33 and 55 with the remainder being gravel the following results were obtained the increase in channel width allowed the formation of transverse topography enhanced the development of sediment patches and increased the fining rate of gravel for id d5 d0 and finer percentiles increasing sand content rendered the long profile of the bed much more concave caused marked patch development and most notably increased the fining rate for all percentiles of gravel sized bed material

direct radiometric age determination of carbonate diagenesis using u pb in secondary calcite abstract carbonate rocks and corals from the middle devonian lucas formation ontario have 238 u 204 pb values ranging from 132 to 559 and give concordant apparent 206 pb 238 u and 207 pb 235 u ages in approximate agreement with the primary age of sedimentation a carbonate rock from one part of the section gives an anomalously young age and contains patches of secondary calcite spar this spar is predominantly pale purple under cathodoluminescence cl and contains 250 600 ppb u and 15 22 ppb pb the values range from 2 10 3 10 4 making the pb very radiogenic apparent 206 pb 238 u ages range from 208 to 249 ma and 232 th 238 u values are from 0 005 to 0 040 the younger ages are correlated with an increase in orange cl and higher apparent values the age scatter is attributed to mixing of a subordinate calcite spar which infiltrated the older spar the young calcite is bright orange under cl has 7200 ppb u of 6 2 10 4 a of 0 23 and is dated at 45 ma the age of the older spar has been determined by a sequential dissolution technique the resulting u pb data can be plotted as u pb age spectra and yield lplateau dates ranging from 231 5 1 4 to 244 9 1 6 ma and an integrated 206 pb 238 u age of 238 2 1 1 ma also the sequential dissolution increases the values progressively to a5 10 4 making these ages independent of the initial pb correction the occurrence of two young ages of diagenetic calcite in these strata is consistent with the idea of recurrent fluid activity along fracture zones in subsurface sediments in the michigan basin this study shows that it is now possible to date secondary carbonate diagenesis by u pb and by inference to determine precisely the timing of activity on ancient fracture zones in carbonate rocks

a model for archaeologically relevant holocene climate impacts in the aegean levantine region easternmost mediterranean abstract a repeating pattern of multi centennial scale holocene climate events has been widely globally documented and they were termed rapid climate change rcc events non seasalt potassium ion k series in greenland ice cores provide well constrained timings for the events and a direct timing relationship has been inferred between these events and the frequency of northerly cold polar continental air outbreaks over the eastern mediterranean sea through gaps in the mountain ranges along the northern margin of the basin there also appears to be a remarkable timing agreement with major archaeological turnover events in the aegean levantine region yet no physically consistent assessment exists for understanding the regional climatic impacts of the events around this critical region we present a simple 2 dimensional lagrangian model which yields a broad suite of physically coherent simulations of the impacts of frequency changes in winter time northerly air outbreaks over the aegean levantine region we validate this with existing reconstructions from palaeoclimate proxy data with emphasis on well validated sea surface temperature reconstructions and a highly resolved cave speleothem stable oxygen isotope record from lebanon given that the rccs were clearly marked by negative sea surface temperature anomalies in the region we find that the predominant climatic impacts of this winter time mechanism were cold and wet in contrast with intercalated warmer and more arid conditions of non rcc periods more specifically the rccs are found to be periods of highly variable conditions with an overall tendency toward cold and wet conditions with potential for flash flooding and for episodic snow cover at low altitudes at least in the lower altitude lower 1 1 5 km regions of crete and the levant the modelled winter anomaly process cannot address underlying longer term astronomically forced trends or the relatively warm and arid anomalies in between rccs the latter require further study for example with respect to potential summer time extension of evaporative subtropical conditions over the region finally our results imply that the amount effect observed in levantine cave 18o and precipitation or drip water 18o may not reflect the conventional concept related to temperature dependent fractionation and rayleigh distillation instead it appears to arise from a complex and somewhat counter intuitive mixing in shifting proportionalities between advected external and evaporated mediterranean moisture

cathodoluminescence and composition of calcite cement in the taum sauk limestone upper cambrian southeast missouri abstract study of calcite cements in the taum sauk limestone upper cambrian southeast missouri using cathodoluminescence petrography and microprobe analysis has shown that 1 distinct luminescent zones correspond to distinct compositional zones 2 the degree of luminescent intensity of a particular calcite zone appears to be controlled by the fe mn ratio of the zone not by the absolute concentrations of either cation 3 manganese may induce luminescence in calcite at concentrations as low as 300 ppm and 4 there may be no critical concentration of ferrous iron in calcite above which there can be no luminescene

first direct radiometric dating of archaean stromatolitic limestone here we report the first direct dating of the depositional age of a sedimentary carbonate rock using long lived radioactive decay schemes the mushandike stromatolitic limestone from the masvingo formerly fort victoria greenstone belt of southern zimbabwe1 2 yields a pb pb isochron age of 2 839 33 myr published claims3 for an age of 3 5 gyr for the mushandike limestone were based on its supposed intrusion by the mushandike granite for which a rb sr whole rock age of 3 445 260 myr had been reported4 new rb sr and pb pb isotope data for the mushandike granite indicate a probable emplacement age of 2 900 myr and new field evidence j l o p t j f w in preparation suggests that the granite forms part of the basement on which the limestone was deposited thus the new dates do not support an age of 3 5 gyr for the algal stromatolites at mushandike the pb pb isochron method may have wide applicability to dating the time of deposition of precambrian fossiliferous and unfossiliferous limestones and thus to the problem of the antiquity of life

modeling the evolution of incised streams i model formulation and validation of flow and streambed evolution components a robust computational model for simulating the long term evolution of incised and restored or rehabilitated stream corridors is presented the physically based model simulates the three main processes that shape incised streams hydraulics sediment transport and streambed and bank adjustments a generalized implicit preissmann scheme is used for the spatial and temporal discretization of the flow governing equations to accommodate large time steps and cross sections spaced at irregular intervals the solution method introduces several enhancements that increase its robustness specifically to simulate flashy flows transport of cohesive or cohesionless graded bed material is based on a total load concept and suspended and bed load transport modes are accounted for through nonequilibrium effects the model simulates channel width adjustment by hydraulic erosion and gravitational mass failure of heterogeneous bank material the present paper focuses mainly on the treatment of streamflow hydraulics and evolution of graded streambeds and reports simulations of published experiments on degrading and aggrading channels with graded bed material description and validation of the model s stream bank erosion component and the application of the model to incised stream systems are presented elsewhere

palaeoflood record of the tagus river central spain during the late pleistocene and holocene abstract palaeoflood hydrology of the tagus river central spain was reconstructed from slackwater deposits and palaeostage indicators in two canyon reaches located at el puente del arzobispo in the central part of the catchment 35 000 km 2 in drainage area and in alcantara at the lower part of the catchment 52 000 km 2 in drainage area near the portuguese border the palaeoflood record with more than 80 flood events shows clusters of floods at specific periods from 9440 to 9210 14 c yr bp 8540 8110 bc 8500 to 8000 14 c yr bp 7500 7000 bc 6750 14 c yr bp 5000 bc 1200 to 950 14 c yr bp ad 785 1205 410 14 c yr bp ad 1450 1500 170 to 80 14 c yr bp ad 1670 1950 the largest flood s occurred during the periods 9440 to 9210 14 c yr bp 6750 14 c yr bp and 1200 to 950 14 c yr bp reaching minimum discharge estimates of between 4000 and 4100 m 3 s 1 in the el puente del arzobispo reach and 13 700 15 000 m 3 s 1 in the alcantara reach these periods with increased flood magnitude and or frequency in the tagus river are strongly related to increased moisture influx and winter precipitation in the iberian peninsula especially in the western zone proxy records sensitive to winter precipitation such as lake levels and vegetation changes indicated by pollen records are in good agreement with the clusters of floods found in the tagus river this flood variability seems to correspond to changes in the prevailing atmospheric circulation pattern affecting the iberian peninsula

the impact of recent climate change on flooding and sediment supply within a mediterranean mountain catchment southwestern crete greece maas g s macklin m g 2002 the impact of recent climate change on flooding and sediment supply within a mediterranean mountain catchment southwestern crete greece earth surface processes and landforms 27 10 1087 1105

sedimentation control on growth of stromatoporoid reefs in the silurian of gotland sweden silurian stromatoporoid dominated reefs of gotland sweden are bioherms and biostromes formed during phases of reduced clastic supply well exposed examples are in the early wenlock hogklint formation and middle ludlow hemse group reef development culminated in shallow water biostromes laterally expanded over a stabilized substrate and associated with frequent erosion surfaces hogklint reefs began as bioherms to be replaced by biostromal phases as water shallowed with vertically zoned communities biostromal phases are considered equivalent to the whole of individual stromato poroid biostromes without biohermal phases of the hemse group which developed in shallow low to moderate energy water on stabilized substrate low clastic supply associated with these reefs reduced not only the clay input which is otherwise common in most non reef environments on gotland but also is interpreted to have lowered available nutrient levels modern reefs develop best in conditions of low nutrients and also show a suppressed bioerosion and b increased symbiosis between corals and algae which conserves nutrients in the reef biota hogklint reefs show reduced bioerosion while hemse reefs show almost complete lack of bioerosion symbiosis between stromatoporoids and corals interpreted as a response to the need for nutrient conservation occurs in the reefs but is much more common in hemse reefs both hogklint and hemse reefs are regarded as having grown in nutrient deficient conditions in line with modern reefs although the effect on hemse reefs is believed to have been greater because they appear to have grown in quieter conditions on a broad shelf and may have had reduced access to nutrients in a regressive regime throughout the ludlow reduced clastic supply while the gotland reefs grew could have been due to regional tectonism controlling local sea level change however the hogklint formation and hemse group reef phases coincide with times of proposed eustatic sea level falls reef growth on gotland could therefore relate to eustatic tectonism by subduction related or plate flexure processes or climatic control an oceanographic model for the silurian proposed alternating wet and dry episodes interpreted as co 2 driven and could have controlled clastic input permitting the development of fossiliferous reefs and the carbonate platforms on which they formed these interpretations provide a revised framework for examining the reef growth

skeletal mineralogy of devonian stromatoporoids abstract previous investigators interpreted stromatoporoids to have been composed originally of aragonite however petrographic observations of stromatoporoid microstructure indicate that those within the devonian helderberg strata of new york state were originally composed of high magnesian calcite the delicate reticulate structure of pillars and growth laminations of the original stromatoporoid coenosteum is represented by a neomorphic fabric of microdolomite rich zones of inclusions in low magnesian calcite in comparison co existing constituents that were originally composed of low magnesian calcite e g brachiopods display 1 better preservation of their ultrastructure than do the stromatoporoids and 2 an absence of microdolomite gastropods originally composed of aragonite are ll represented by micrite envelopes encompassing pore filling spar accumulations i e complete loss of ultrastructure the style of preservation of the stromatoporoids is essentially identical to that of associated echinodermal debris an original high magnesian constituent both the stromatoporoids and echinoderms are preserved as microdolomite bearing diagenetic low magnesian calcite consequently these stromatoporoids were originally composed of high magnesian calcites

experiments on downstream fining of gravel i narrow channel runs we present the results of three laboratory experiments in which longitudinally sorted deposits were formed by feeding poorly sorted sediment at the upstream end of a narrow 45 m long channel the input sediment had a median size of 6 mm and included significant amounts of material up to 64 mm and down to 0 2 mm water discharge was constant at 49 l s and sediment discharge varied from 0 048 to 0 19 kg s downstream fining was produced in all three runs the variation in sediment feed rate had relatively little effect on the fining profiles in all three runs the formation of a longitudinally sorted deposit was mediated by the formation of a coarse surface layer the surface layer remained at the top of the deposit during aggradation by continually reforming itself at the deposit surface the coarse surface layer fined by approximately a factor of 2 in d90 and d50 consistently in all three experiments the deposit subsurface fined less with d90 fining more strongly than d50 the short channel length a

erosion in mediterranean landscapes changes and future challenges abstract intense erosion processes are widespread in the mediterranean region and include sheet wash erosion rilling gullying shallow landsliding and the development of large and active badlands in both subhumid and semi arid areas this review analyses the main environmental and human features related to soil erosion processes and the main factors that explain the extreme variability of factors influencing soil erosion particularly recent land use changes the importance of erosion in the mediterranean is related to the long history of human activity in a region characterized by low levels of annual precipitation the occurrence of intense rainstorms and long lasting droughts high evapotranspiration the presence of steep slopes and the occurrence of recent tectonic activity together with the recurrent use of fire overgrazing and farming these factors have resulted in a complex landscape in which intensification and abandonment wealth and poverty can co exist the changing conditions of national and international markets and the evolution of population pressure are now the main drivers explaining land use changes including farmland abandonment in mountain areas the expansion of some subsidized crops to marginal lands and the development of new terraces affected by landslides and intense soil erosion during extreme rainstorm events the occurrence of human related forest fires affecting thousands of hectares each year is a significant problem in both the northern and southern areas of the mediterranean basin here we highlight the rise of new scientific challenges in controlling the negative consequences of soil erosion in the mediterranean region 1 to reduce the effects and extent of forest fires and restructure the spatial organization of abandoned landscapes 2 to provide guidance for making the eu agricultural policy more adapted to the complexity and fragility of mediterranean environments 3 to develop field methods and models to improve the identification of runoff and sediment contributing areas 4 to contribute to the conservation of landscapes i e bench terraced fields having high cultural and productivity values 5 to improve knowledge of the hydrological and geomorphological functioning of badlands with the aim of reducing sediment yield and accessibility 6 to better understand the effect of climate change on soil erosion in the mediterranean region and 7 to improve quantitative information on long term soil erosion

rb sr and k ar dating of precambrian clays and glauconies abstract isotopic dating of sedimentary material requires a different approach from the isotopic dating of plutonic volcanic and high grade metamorphic rocks the present contribution presents mineralogical criteria such as clay composition illite or glauconite crystallinity indices illite or glauconite polymorphic types sedimentological criteria such as mechanisms of genesis as well as chemical criteria such as the sr composition and content of the carbonates associated with the studied clays and glauconies these criteria help in the interpretation of the numerical results and should always be considered in attempts to obtain radiometric ages of sedimentary clays and or glauconies it is emphasized that a difference between measured and expected age seldom means that the chronometer used is inaccurate but it commonly means that a parameter was not recognized or even disregarded a critical review of the uncertainties typically related to sedimentary dating is also proposed they may be grouped into four types 1 genetic uncertainties dependent on the genetic mechanisms of the studied minerals 2 historic uncertainties dependent on the alteration events imprinted in the sediments since deposition weathering diagenesis and or tectono metamorphism 3 stratigraphic uncertainties dependent on the precision of the sample location in the sedimentary sequence and 4 analytic uncertainties dependent on the representativeness and the preparation of the samples as well as the accuracy of the measurements a reliability test of the rb sr and k ar methods as applied to dispersed precambrian clays and glauconies is discussed from an extensively studied sequence from west africa it shows that the k ar system of these minerals is much more sensitive to later modifications than the rb sr system therefore the two techniques may be complementary in geochronological studies of precambrian sediments

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

mass balance effects in depositional systems abstract net deposition is necessarily accompanied by overall loss of sediment mass from the transport system on long time scales the deposition compensates for subsidence and creates the stratigraphic record although its spatial pattern changes and it can be locally stopped or reversed depositional mass loss is a fundamental driving influence on the morphology and behavior of depositional systems mass extraction to deposition leads directly to facies changes as sediment flux declines indirectly it usually leads to down channel sediment fining as deposition preferentially removes coarser particles laboratory experiments illustrate the effects of systematic mass extraction on fluvial channel stacking and deposit grain size and show how a mass balance framework allows consistent comparison of facies despite major shifts in depocenter location mass balance analysis of experimental fluvial and turbidite systems and a turbidite mini basin from the gulf of mexico show a change from channel dominated to lobe dominated deposits at about 80 total mass extraction experimental and field studies also show a close connection between rate of mass loss and rate of downstream grain size fining as predicted by a mechanistic theory based on mass balance these are first steps towards a framework for quantitative basin analysis based on mass extraction a mass balance framework allows for consistent quantitative comparison across basins of varying scale and shape mass balance frameworks can account for overall and or generic mass balance effects and help separate them from local effects one way to use such generalized models effectively is to view the results as reference cases of down transport change resulting from the basic interplay of spatial mass extraction pattern and sediment supply where such reference cases do not provide detailed predictions of specific field cases they can still provide a baseline to separate local case specific features from generic system behavior the approach is analogous to the way the geoid serves as a reference case against which to measure gravity anomalies

lead concentrations in the northeast pacific evidence for global anthropogenic perturbations lead concentrations were determined by isotope dilution mass spectrometry in 34 surface and deep water samples collected in the northeast pacific between hawaii and california and off the california coast using a deep water sampler protected against fouling by contamination from the ship and hydrowire measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90 or more of the total lead is in a dissolved form lead concentrations are about 10 fold higher in surface and thermocline waters than in deep waters values drop as low as 1 ng kg 5 pmol kg below 3500 m depth lead profiles thus appear different compared to those of most trace metals which show enrichment in deep waters compared to surface concentrations lead concentrations in surface waters increase from 5 to 15 ng kg 25 to 75 pmol kg along a transect starting from a location 200 km off the california coast and continuing towards the center of the north pacific gyre this increase is congruent with that observed for 210 pb concentrations in the same waters sampled at the same time lead is supplied to the open north pacific largely from the atmosphere at a rate of about 60 ng cm 2 yr which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold this excess originates from emissions from smelters and combustion of leaded gasoline overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers vertical lead concentration profiles below the surface mixed layer are probably not in steady state there concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters based on an estimated 10 fold input and concentration increase since the mid eighteenth century in the surface mixed layer in the central northeast pacific it is calculated that the 10 ng kg average concentration between 100 and 900 m is 2 to 5 times larger and the 1 8 ng kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid eighteenth century profiles of lead concentrations in the north atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the north pacific because of the effects of greater industrial lead contamination while lead concentration profiles in the south pacific are expected to be shifted generally to lower values compared to the north pacific by about this same factor because of the effects of lesser industrial lead contamination

infiltration processes and flow rates in developed karst vadose zone using tracers in cave drips the purpose of this research was to identify groundwater recharge mechanisms and measure flow velocities through the epikarst and the vadose zone in a typical site of mediterranean carbonate karst in natural rain conditions by avoiding artificial flushing more realistic travel times could be measured and the effective resultant vadose flow velocity could be inferred additionally detailed monitoring enabled better description and quantification of infiltration and percolation processes nine different cave drips were monitored and sampled for three hydrological years in fractured karst lithology on mount carmel israel at three drips discharge was measured continuously by tipping buckets rainfall and soil water content were recorded above the cave an artificial tracer experiment was conducted using uranine placed in a joint and at the soil rock interface at soil pockets both 27 m above the cave four hydrological types of drips post storm seasonal perennial and overflow were identified each demonstrating different characteristics in terms of discharge and chemistry the maximum effective flow velocities uranine dye arrival times were 41 76 cm h tracer mass flux was computed from the uranine breakthrough curves and drip hydrographs the dominant flow velocities derived from the peak of tracer mass flux were 0 35 0 41 cm h from post storm drips and 22 24 cm h from the other drips pulse through intra event piston flow was indicated by the time lags between the increase in drip rate and the time of drop in salinity and appearance of the tracer in most of the measured drips chloride concentrations were used to distinguish between old matrix water and preferential flow water in the perennial drips demonstrating a two component mixing model in 2005 2006 preferential flow water reached up to 20 25 from annual discharge of these drips this study promoted a method to compute dominant effective flow rates in the vadose zone in natural rain conditions copyright 2010 john wiley sons ltd

the laidlaw volcanics a late silurian point on the geological time scale mapping mineralogical and chemical studies of an area west and northwest of canberra southeastern australia have shownthat the laidlaw volcanics are unique in the region and that their age is tightly controlled stratigraphically as they lie both above and below early ludlow late silurian fossiliferous sediments k ar mineral analyses previously published rb sr mineral analyses and new rb sr wholerock and mineral analyses together give the laidlaw volcanics an age of 420 7 2 2 m y this result for the early ludlow is identical numerically with a recently published age of 421 3 m y for the ashgillian late ordovician stockdale rhyolite and suggests either that the time interval between the ashgill and ludlow does not exceed a few million yearsor that the age estimate for the stockdale rhyolite is too young

geochronology of late caledonian magmatism in northern britain rb sr k ar ar ar and sm nd isotopic data are presented for mineral separates and whole rock samples from old red sandstone ors lavas associated minor intrusions and 9newer granite9 intrusive complexes from the cheviot hills north to shetland these data yield 16 internally consistent rb sr mineral ages and one each of ar ar sm nd and k ar ages when considered with precise and reliable published data it is clear that there are systematic differences in the age of late caledonian magmatism through the geological regions of scotland in the grampian highlands and the scottish midland valley magmatism was concentrated during the period 423 to 410 ma ors volcanism in the highlands occurred around 420 ma with plutonism continuing to about 408 ma volcanism and plutonism in the midland valley took place between 415 and 410 ma in the southern uplands magmatism occurred earlier in the north with all magmatism close to the southern uplands fault dated around 408 ma and that close to the iapetus suture dated at around 394 ma as no evidence exists for ocean closure prior to c 400 ma the age of igneous activity north of the southern uplands fault is consistent with chemical evidence for a relationship to active nw directed subduction the younger magmatism of the s part of the southern uplands cannot be subduction related and the c 408 ma plutons nearer the southern uplands fault can only be subduction related if tectonic construction of the southern uplands was a two stage process

slope retreat rates estimated from chronology of tufa deposits sheltered by inland notches on mt carmel israel abstract inland notches are elongated half tube indentations that develop on the carbonate rocky cliffs of mountainous zones occasionally tufa accumulates within notches as stalactites drapes and crusts covering the cavity backwall or floors in attempt to determine the age of the latest stage of notch formation and calculate the relative rate of slope retreat u th dating was used on 16 tufa samples from 2 notches providing 28 ages tufa grow during the time interval between the backwall erosion and visor collapse and therefore tufa age is an approximation of the timing of the formation of the surface it developed on i e the age of the notch the oldest known tufa sample is 39 0 10 4 ky 2 and the ages of other tufa samples range from 2 1 to 23 3 ky at the nahal oren notch the present day backwall formed by the end of the last glacial period 14 to18 ky whereas the visor in its present form is from the early holocene 7 to10 ky the oldest sample was found 1 m from the backwall suggesting that backwall retreat rate ranges from 20 to 35 mm ky other samples were deposited 50 to 200 cm from the visor edge suggesting that slope retreat order of magnitude ranges from 101 to 102 mm ky the backwall of the nesher notch formed between 10 and 14 ky our results correspond with the rates of tens of meters per million years similar to the magnitude of denudation found by previous studies in the mediterranean zone of israel dating tufa deposits is a good proxy to estimate the rate of erosion in carbonate slope retreat however a precautionary approach should be taken as rock particles from the eroded bedrock might embed within the tufa affecting the age results questionable samples can be identified using cathodoluminescence cl microscopy

short term changes in the magnitude frequency and temporal distribution of floods in the eastern mediterranean region during the last 45 years nahal oren mt carmel israel short term changes in eastern mediterranean precipitation affecting flow regime were documented in nahal oren a 35 km 2 ephemeral stream in mt carmel a 500 m high mountain ridge located at the nw coast of israel the rainy winter of the mediterranean type climate csa in mt carmel is characterized by average annual rainfall of 550 mm at the coastal plain to 750 mm at the highest elevation while the summer is hot and dry stream flow generates after accumulated rainfall of 120 150 mm while large floods defined as flows with peak discharge of n 5m 3 s 1 and or n150 000 m 3 in volume are generated in response to rainfall of over 100 mm hence large floods in nahal oren stream occur not earlier than december precipitation and flow data were divided into two sub periods 1957 1969 and 1991 2003 and compared to each other the results indicate a clear increase in the frequency of large floods their magnitudes and volumes during the second period with no parallel change in the annual precipitation similarly an increase in storm rainfall runoff ratio from b5 to n15 and a decrease in the threshold rainfall for channel flow by 16 25 were documented these short term variations in flooding behavior are explained by the clear decrease in the length of the rainy season and by the resulting significant shortening in the duration of the dry spells the increase in the number of large rainfall events and the large floods in each hydrological year together with the increasing number of years with no floods indicate strengthening of their uncertainty of behavior

u pb dating of a remagnetized paleozoic limestone the upper ordovician trenton group of new york state is one of a number of appalachian limestones which yields paleomagnetic poles suggesting disturbance in the late paleozoic calcite fractions dissolved from samples of the trenton limestone define a 238u 206pb age of 454 8 ma mswd 12 8 in excellent agreement with 40ar 39 ar and u pb ages for the deposition of the underlying diecke bentonite this requires that the u pb system in the calcite has been preserved since deposition and early diagenesis if late paleozoic remagnetization of this limestone was induced by fluids these fluids did not interact with significant amounts of carbonate the apparent robustness of the u pb system and the large spread in values 18 17 118 8 offers potential precision of 1 ma in determining the paleozoic time scale

a new technique for measuring the bed surface texture during flow and application to a degradational sand gravel laboratory experiment we present a new image analysis technique for measuring the grain size distribution texture of the bed surface during flow in a laboratory experiment a camera and a floating device are connected to a carriage used to take images of the bed surface over the entire flume length the image analysis technique which is based on color segmentation provides detailed data on spatial and temporal changes of the areal fraction content of each grain size at the bed surface the technique was applied in a laboratory experiment conducted to examine a degradational reach composed of a well sorted two fraction mixture of sand and gravel the initial bed consisted of an upstream reach that was characterized by an imposed stepwise fining pattern the bimodal reach and a downstream sand reach a lack of sediment supply and partial transport conditions led to the formation of a static armor in the bimodal reach which resulted in a more abrupt spatial transition in the bed surface mean grain size the associated spatial transition in slope led to a backwater effect over the bimodal reach a streamwise reduction in sand mobility and so a static armor that was governed by a downstream fining pattern although a morphodynamic equilibrium state under steady flow is generally characterized by normal flow here the partial transport regime prevented the bed from adjusting toward normal flow conditions and the morphodynamic steady state was governed by a backwater we applied a numerical morphodynamic sand gravel model to reproduce the laboratory experiment the numerical model captured the hydrodynamic and morphodynamic adjustment and the static armor well yet the armoring occurred too slowly although the final configuration of the experiment shows features of a gravel sand transition i e a sudden transition in slope and mean grain size we are hesitant to claim similarities between our results and the physical mechanisms governing a gravel sand transition in the field

direct dating of stromatolitic carbonates from the schmidtsdrif formation transvaal dolomite south africa with implications on the age of the ventersdorp supergroup pb isotopic analyses of stromatolitic limestones from the schmidtsdrif formation transvaal dolomite of south africa give a late archean isochron age of 2 557 plus minus 49 2 sigma ma the new date significantly changes the position of the archean proterozoic boundary in the kaapvaal province and suggests that a possible division of the transvaal supergroup is necessary it also resolves the long standing controversy about the age of the ventersdorp supergroup whose zircon u pb data of ca 2 7 ga must be more acceptable than the rb sr dates of about 2 3 ga the study provides a new example that demonstrates the great potential of employing the u pb systems of carbonate rocks for direct dating of sedimentary sequences

water percolation process studies in a mediterranean karst area to investigate processes of water percolation the drip response of stalactites in a karstic cave below a 143 m2 sprinkling plot was measured the experiment was conducted in mount carmel israel at the end of the dry season and intended to simulate a series of two high intensity storms on dry and wet soils in addition to hydrometric measurements soil moisture surface runoff stalactite dripping rates two types of tracers electrical conductivity and bromide were used to study recharge processes water origin and mixing inside a 28 m vadose zone results suggested that slow continuous percolation through the rock matrix is of minor importance and that percolating water follows a complicated pattern including vertical and horizontal flow directions while bromide tracing allowed identification of quick direct flow paths at all drips with maximum flow velocities of 4 3 m h mixing analysis suggested that major water fractions were mobilized by piston flow pushing out water stored in the unsaturated zone above the cave under dry preconditions 80 mm of artificial rainfall applied in less than 7 h was not enough to initiate significant downward water percolation most water was required to fill uppermost soil and rock storages under wet preconditions during the second day sprinkling higher water contents in soils and karst cavities facilitated piston flow effects and a more intense response of the cave drips results indicate that in mediterranean karst regions filling of the unsaturated zone including soil and rock storages is an important precondition for the onset of significant water percolation and recharge this results in a higher seasonal threshold for water percolation than for the generation of surface runoff copyright 2010 john wiley sons ltd

direct dating of phanerozoic sediments by the 238 u 206 pb method direct radiometric age determination of phanerozoic carbonates has been a long standing problem in geochronology rb sr and k ar dating schemes commonly used to constrain the chronology of phanerozoic sediments have so far proved to be unsuccessful in dating these rocks because of their poor enrichment in radiogenic 87sr and 40ar and also because of analytical difficulties recent studies1 2 have demonstrated that large amounts of radiogenic pb exist in some carbonates and that they could be dated by the pb pb method however the precision of this method is severely limited to samples having very high uranium to lead ratios because by the beginning of the phanerozoic 590 myr ago 98 of 235u originally present in the earth had decayed to 207pb here we report the first isochron age of carbonates using the 238u 206pb method on corals this method which gives good accuracy even for low u concentrations has great potential for the direct dating of sedimentary sequences and should be valuable for refining the phanerozoic timescale

pb sr and nd isotope systematics of uranium mineralised stromatolitic dolomites from the proterozoic cuddapah supergroup south india constraints on age and provenance abstract the pb sr and nd isotopic compositions were determined on uranium mineralised and barren stromatolitic dolomite samples from the vempalle and tadpatri formations of the cuddapah supergroup in southern india subsamples from individual handspecimens were analyzed to minimize the potential of heterogeneous initial pb compositions all of the u mineralised samples gave pb pb ages close to 1800 ma but with high mswd values presumably due to local redistribution of u and pb in the samples the best pb pb age of 1756 29 ma is interpreted as the time of u mineralisation and as a minimum age for carbonate sedimentation and dolomitisation within the cuddapah supergroup the sr isotopic compositions of the samples vary with the mineralised samples being more radiogenic even the lowest 87 sr 86 sr of the barren sample exceeds the seawater 87 sr 86 sr about 1800 ma ago on the other hand the nd systematics of the samples does not appear to have been disturbed by processes subsequent to carbonate sedimentation the calculated initial nd isotopic compositions suggest a dominant continental crustal source that was at least 600 ma old at the time of deposition of the carbonate sediment

dynamics of suspended sediment delivery to the eastern mediterranean continental shelf this study provides data on the fluvial sediment transport at the eastern mediterranean an area in which the regional importance for comparative study has often been raised by investigators but the data are rather scarce we analysed long and short term hydrologic and sedimentological data from one of the largest coastal streams of israel qishon river 1100 km2 and its estuarine environment the results indicate that during 65 years 1944 2009 a total 140 floods have contributed to the sea an amount of approximately 2 58 106 tons of sediment during this period i the number of floods with a return period of more than 10 years has almost doubled during the last 30 years and ii the mean annual discharge during last 10 years increased by approximately 175 the analysis of the short 2 years hydrological and sediment data revealed that approximately 30 of the upstream channel loads do not reach the river mouth and are deposited along the channel bed even during major flood events this observation was attributed largely to the facts that the lower river bed is incised below sea level to the very low slopes and to the correspondingly low stream power and transport capacity the results of this study highlight the effect of interchannel dynamics as well as the constraints of interaction between fluvial system and estuarine processes on sediment transport copyright 2012 john wiley sons ltd

pb pb dating of hydrocarbon migration into a bitumen bearing ore deposit north wales previous attempts at u pb dating of uraniferous bitumens have had limited significance because of radioelement migration pb pb dating which can be undertaken regardless of recent lead migration has been successfully applied to uraniferous solidified bitumen from the ty gwyn copper deposit north wales analyses of five bitumen samples with variable mixtures of radiogenic and common lead yield a sup 207 pb sup 206 pb age of 248 plus minus 21 ma early triassic this age is interpreted as the date of hydrocarbon migration into the deposit and is reasonably consistent with the timing of hydrocarbon generation calculated from the regional burial history the pb pb dating method could be applied to date uraniferous bitumens representing hydrocarbon migration in diverse geologic environments

experimental evidence of uraninite formation from diagenesis of uranium rich organic matter abstract this study focuses on the experimental diagenetic evolution of an uranium rich lignite from the coutras uranium deposit gironde france located in eocene sediments three samples containing 6 to 15 5 wt uranium were analysed and compared to two barren samples located outside the ore deposit in a stratigraphically equivalent unit uranium in the mineralized samples is present as uranyl carboxylic complexes dry thermal maturation was simulated in a cold seal autoclave at 150 200 250 300 and 350 c at 100 mpa for 24 h with increasing temperature uranyl carboxylic complexes decompose while uraninite forms the chemical composition of the experimentally matured barren samples when plotted in a van krevelen diagram h c vs o c parallels the natural trend of land derived type ill organic matter evolution while mineralized samples are characterized by a higher loss of hydrogen above 250 c reduction to form uraninite is directly related to the dehydrogenation of lignite the resulting uraninite has a similar unit cell edge to that of natural uraninites observed in sedimentary environments uraninite not only forms in the pore space but also replaces the lignite constituents the results demonstrate that uraninite may form during thermal evolution of uranium rich organic matter during diagenesis

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

water worked gravel beds in laboratory flumes a natural analogue an investigation has been conducted to identify the key parameters that are likely to scale laboratory sediment deposits to the field scale two types of bed formation were examined one where sediment is manually placed and screeded and the second where sediment is fed into a running flume this later technique created deposits through sequential cycles of sediment transport and deposition detailed bed surface topography measurements have been made over a screeded bed and three fed beds in addition bulk subsurface porosity and hydraulic conductivity have been measured by comparing the four beds results revealed that certain physical properties of the screeded bed were clearly different from those of the fed beds the screeded bed had a random organization of grains on both the surface and within the subsurface the fed beds exhibited greater surface and subsurface organization and complexity and had a number of properties that closely resembled those found for water worked gravel beds the surfaces were water worked and armoured and there was preferential particle orientation and direction of imbrication in the subsurface this suggested that fed beds are able to simulate in a simplified manner both the surface and subsurface properties of established gravel bed river deposits the near bed flow properties were also compared it revealed that the use of a screeded bed will typically cause an underestimation in the degree of temporal variability in the flow furthermore time averaged streamwise velocities were found to be randomly organized over the screeded bed but were organized into long streamwise flow structures over the fed beds it clearly showed that caution should be taken when comparing velocity measurements over screeded beds with water worked beds and that the formation of fed beds offers an improved way of investigating intragravel flow and sediment water interface exchange processes in gravel bed rivers at a laboratory scale copyright 2008 john wiley sons ltd

modelling geomorphic response to environmental change in an upland catchment in the uk s upland catchments river terraces and alluvial features indicate a history of periodic aggradation and degradation linked to holocene changes in land use primarily deforestation and climate change altering flood frequency and magnitude although both factors are important calculating their individual effects is complicated by the likelihood of their concurrent alteration to investigate the relative impacts of land use and climate change a cellular model is applied to the upland catchments of cam gill beck above starbotton north yorkshire this is divided into 1 million 2 m by 2 m grid cells to which a range of process laws are applied these include approximate expressions for mass movement rates soil creep the influence of vegetation and hillslope hydrology as well as fluvial erosion and deposition in ten grain size fractions this provides a good representation of valley floor geometry while retaining a fully dynamic interaction with the surrounding valley sides previous applications of this model have shown the detailed formation of bars and berms as well as examples of braiding avulsion and channel range running on a silicon graphics origin 2000 computer an ensemble of simulations were completed bracketing a wide range of environmental scenarios involving changes in flood frequency magnitude and vegetation cover over time scales ranging from 10 to 100 years these showed that decreasing tree cover and increasing rainfall magnitude individually produced similar 25 to 100 increases in sediment discharge whereas in combination they generated a 1300 rise furthermore channels formed by the model in response to increased rainfall magnitudes are located where relic channels are found in cam gill beck implying that these are the products of previous periods of high rainfall magnitudes copyright 2000 john wiley sons ltd

pb pb dating of young marbles from taiwan direct determination of the depositional age of a sedimentary sequence usually relies on isotopic analyses of authigenic minerals such as glauconite1 and fine grained clay minerals2 4 moorbath et al 5 recently reported the first direct dating of sedimentary carbonates using the whole rock pb pb method the success of this method depends on the chemical fractionation of u from pb and the consequent variation in 206pb 204pb and 207pb 204pb ratios the high values and large variation of u pb ratios in sedimentary carbonates long known to marine geochemists have however not been exploited by geochronologists until recently5 6 here i report a pb pb isochron age for a relatively young carbonate sequence in taiwan and demonstrate that the long lived u pb decay scheme can be used to determine events as young as mesozoic age the new results also lead to the identification of an early jurassic 170 myr bp thermal event which has never before been recognized in the polymetamorphic schist belt the tananao schist of taiwan but is widespread in southeastern continental china and other parts of eastern asia7 10

a conceptual model for groundwater circulation using isotopes and geochemical tracers coupled with hydrodynamics a case study of the lez karst system france abstract geochemical and isotopic tracers 18o 2h 87sr 86sr and 13ctdic were used to constrain origins and chemical evolution of groundwater in a mediterranean karst system the lez spring is the main perennial outlet of this karst system and supplies the metropolitan area of montpellier southern france with drinking water groundwater samples were collected at the lez spring and surrounding springs and wells under different hydrodynamic conditions during two hydrological years from june 2008 until may 2010 the results show that multiple hydrological compartments interact through an important network of fractures and faults they notably reveal connections between the main jurassic limestone aquifer and the overlying cretaceous valanginian compartment and between the surface and deep levels of the karst system isotopic tracers provided information about atmospheric recharge origins lithological signatures and chemical evolution of waters long residence time groundwaters issued from deep layers have a triassic hydrochemical fingerprinting being enriched in 13ctdic and characterized by high concentrations in cl as well as high sr ca mg ca and 87sr 86sr ratios evidences suggest that these waters mix with waters from the lower layers of the main jurassic aquifer constitute an intermediate storage compartment prone to rise through piston flow mechanism a two end member hydrograph separation based on ec tds was used to determine the proportion of the deep compartment s contribution to the lez spring outflow on average over the study period the main aquifer compartment and the deep aquifer compartment are estimated to contribute 92 6 and 7 4 of groundwater flow at the lez spring respectively

vegetation and soil erosion under a semi arid mediterranean climate a case study from murcia spain the objectives of the present work are to analyse some relationships between soil and vegetation parameters for mediterranean matorral in the el ardal experimental field site in murcia spain the response of this system in terms of erosion and runoff and the pedological and vegetation effects of some disturbing factors such as agricultural use and grazing the el ardal experimental field which is provided with automatic weather stations erosion plots and other devices have been used over a period of two years to study the evolution of factors such as erosion runoff vegetation cover biomass litter production soil moisture water retention capacity and aggregate stability the results obtained show that in general the pedological and vegetation properties are far from those expected in semi arid mediterranean environments runoff and sediment losses in the erosion plots are low as a result of the efficient control of the same by the matorral at the scale of the hillslope the abandoned field shows a good capacity to recover its pedological and vegetation characteristics after disturbances such as agricultural use finally grazing does not seem to seriously affect the dynamics of the matorral which shows values of primary production close to those found in other mediterranean scrublands although there are other indirect effects on pedological and vegetation characteristics due to livestock trampling

whole rock pbpb isotopic ages of late archaean limestones karnataka india application of the pbpb isotopic dating technique to metamorphosed limestones from late archaean low and high temperature greenschist amphibolite facies terrains in karnataka southern india has revealed distinct differences in the evolution of each terrain and in their model 1 values the western low temperature terrain is characterised by tracts of late archaean volcanic and sedimentary rocks dharwar supergroup their basement of orthogneisses and granodiorites 3400 2900 ma and enclaves of older supracrustal rocks intrusions of late archaean granite 2600 ma occur sporadically in the low temperature terrain in contrast the eastern high temperature terrain is dominated by late archaean polyphase syn and post tectonic granites 2500 ma which intruded tracts of supracrustal rocks that are similar to the dharwar supergroup in the low temperature terrain the low and high temperature terrains are separated by a n to nnw trending steep belt of mylonites which is over 400 km in length the pbpb data show that metamorphic recrystallisation of the limestones in the low temperature terrain took place 2639 32 ma ago whereas limestones in the high temperature terrain recrystallised 2475 65 ma ago this finding is consistent with previously published ages of late archaean granites in the low and high temperature terrains limestones from the low temperature terrain have a 1 value of 7 79 whereas those from the high temperature terrain have a 1 value of 8 50 these values suggest that the u and pb that was incorporated in the limestones of the low temperature terrain came from a less evolved source than the u and pb in the limestones in the high temperature terrain and indicate a further contrast between these two divisions of the archaean craton in karnataka the nature of the sources is enigmatic but they may reflect differences in composition of the lithospheric plates that were involved in the dharwar collision system data from the high temperature terrain indicate disequilibrium between the measured pb isotopic ratios of carbonate and residue components of the limestones pb isotopic compositions of hci insoluble residues are consistently more radiogenic than those of associated carbonate minerals and they define a younger rotated palaeoisochron that has no age significance this is the first documentation of carbonate residue disequilibrium on the scale of a single hand specimen it highlights the need for a thorough evaluation of pb isotope systematics and the potential effects of acid leaching for multi component limestones

can terra rossa become water repellent by burning a laboratory approach abstract fire usually induces water repellency wr in soils reduction in infiltration rates increase of runoff and erosion are some of the consequences of wr in fire affected soils most forest soils can develop wr by burning however some previous observations in burned terra rossa soils have shown little changes in wr laboratory controlled experiments have been done with samples of terra rossa from 14 different sites the objectives are to confirm whether the observed is a common behaviour of terra rossa and to explore the factors controlling the wettability of this soil type after burning samples from the upper 2 5 cm of terra rossa were collected from 12 forest sites of the alicante province spain and from 2 sites in the mt carmel haifa israel with similar environmental conditions laboratory burning of samples at 250 c 300 c and 350 c was performed with and without the addition of litter of pinus halepensis the results confirm that all soils have a very low susceptibility to become water repellent by burning without the addition of litter wr was not detected in any soil sample at any temperature of burning with the addition of litter wr was present only in six of the soils after some of the heating treatments although all soils had enough soil organic matter som to develop wr by heating the ratio between som and clay content was considerably lower compared to other types of forest soils of the region in which wr has been found after forest fires this could explain in part the lower susceptibility of terra rossa to become water repellent by burning since as some authors have indicated fine textured soils are less prone to develop soil wr due to their high specific surface area from mineralogical analysis of the clay fraction we found that the dominant clay types in the studied terra rossa were kaolinite and illite with the exception of one soil where ca montmorillonite content is higher than kaolinite and illite ca montmorillonite was present in only three of the soils comparing the soil properties between the group of terra rossa that in no case become water repellent wettables with the group that in some cases developed wr potentially water repellents some differences were found the kaolinite content is higher in the wettables group p vs kaolinite contents the kaolinite content being the main factor contributing to this separation these results are in agreement with those obtained in experiments with clay additions to water repellent soils in order to reduce the wr and also with some studies which found that kaolinite is one of the most effective clay minerals for this purpose

downstream fining in large sand bed rivers abstract downstream fining of bed sediments is a well known phenomenon in gravel bed rivers but also occurs in large sand bed rivers the underlying processes however are not necessarily the same due to the difference in sediment mobility grain size distribution width and geographical setting downstream fining studies focusing on large sand bed rivers are scarce nevertheless in this paper the processes that affect downstream fining in gravel bed rivers are reviewed and it is evaluated to what extent they are relevant for large sand bed rivers furthermore several new downstream fining processes are discussed ending in a conceptual model of downstream fining in large sand bed rivers in deriving the conceptual model downstream fining processes are divided into three categories abrasion selective transport and sediment addition extraction abrasion rates in large sand bed rivers are small due to the durable lithologies the small grain size the high degree of rounding the dominance of grinding as abrasion process and the dominant suspended transport mode of the bed sediment only in the upstream part of large sand bed rivers abrasion rates may be somewhat higher selective transport rates in large sand bed rivers everywhere overrun abrasion rates but are small compared to selective transport rates in gravel bed rivers because the unimodal sediments in sand bed rivers exhibit stronger hiding exposure effects during threshold of motion conditions but especially because many sand bed rivers though not all are in state of fully mobilised transport making differences in threshold of motion between coarse and fine grains relatively unimportant selective transport in these rivers is probably mainly the result of the presence of suspended load transport in combination with the effects of dune and perhaps bend sorting which are all processes that act on a relatively large scale within sand bed rivers the degree of selective transport probably decreases downstream due to the change in mixture bimodality and sorting efficiency there are indications that coarse grains may sometimes even be more mobile than fine grains in the downstream part of sand bed rivers note that in contrast to abrasion selective transport only produces a stable downstream fining pattern if the river profile is concave generally a stronger profile concavity leads to a higher aggradation rate and a stronger downstream fining trend sediment addition and extraction processes can obscure the effects of abrasion and selective transport in sand bed rivers overbank sedimentation for instance may significantly decrease the downstream fining rate in large sand bed rivers because especially fine grains are removed from the bed dredging can also strongly affect the downstream fining trend depending on the volume and the grain size of the sediment involved meander migration may cause a nett loss of coarse grains from the channel in aggrading circumstances increasing the downstream fining rate river bifurcations can cause a discontinuity in the downstream fining pattern because bend sorting upstream of the bifurcation causes the river branch that originates in the outer bend of the main channel to be much coarser than the other branch all these addition and extraction processes not only have a direct effect on the grain size composition of the river bed but also indirectly influence downstream fining by their effect on the longitudinal bed profile other sediment addition and extraction processes such as tributary confluences non alluvial sediment sources and dumping are less common in large sand bed rivers but can locally have a great effect a full determination of the relative importance of all downstream fining processes in large sand bed rivers requires extensive field measurements the construction of detailed fractionwise sediment balances and the development of numerical downstream fining models that incorporate all processes described above

stromatolites at 3 500 myr and a greenstone granite unconformity in the zimbabwean archaean two controversial areas of geological endeavour are the establishment of the antiquity of life and the tectonic setting of greenstone sequences we record here the recent discoveries in the fort victoria greenstone belt of stromatolites in limestones assigned to 3 500 myr minimum age sebakwian group rocks of the rhodesian archaean craton within zimbabwe and a nearby outcrop of a thin sedimentary formation basal to a thick 2 700 myr volcanic pile resting with definite unconformity on 3 500 myr mushandike granite

formation and evacuation of a large gravel bar deposited during a major flood in a mediterranean ephemeral stream nahal me arot nw israel abstract an unusual 240 mm rainstorm and a consequent major flood peak discharge 110 m 3 s 1 with an estimated recurrence interval of about 50 years occurred on dec 31 1998 in nahal me arot an ungauged 25 km 2 coastal ephemeral stream in mt carmel nw israel the flood caused morphological modifications along the channel including intensive stripping of the channel bed and floodplain along several segments and deposition of large gravel bars downstream of these segments one of such segments served as a study reach composed of a massive 1270 m 3 coarse 200 m long gravel bar formed downstream of a segment 150 m long that was deeply scoured the study reach was carefully mapped cross sections and driftwood lines allowed the calculation of the hydraulic parameters and peak flow using the slope area method the bar s sedimentological characteristics such as surface and substrate texture and stratigraphy were studied in detail using a survey of 15 pits the initial recovery of the channel started when dense low shrub vegetation re stabilized along the affected reaches a year later two smaller floods 3 and 4 years later evacuated and reworked the sediment until it lost most of its volume the study suggests that the flood s large impact and disturbance was local short lived and the channel almost returned to its pre flood state within about 4 years