underwater observations of active lava flows from kilauea volcano hawaii underwater observation of active submarine lava flows from kilauea volcano hawaii in march june 1989 revealed both pillow lava and highly channelized lava streams flowing down a steep and unconsolidated lava delta the channelized streams were 0 7 1 5 m across and moved at rates of 1 3 m s the estimated flux of a stream was 0 7 m 3 s jets of hydrothermal water and gas bubbles were associated with the volcanic activity the rapidly moving channelized lava streams represent a previously undescribed aspect of submarine volcanism

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

origin of calcium in pedogenic carbonate nodules from silicate watersheds in the far north region of cameroon respective contribution of in situ weathering source and dust input significant amounts of pedogenic ca carbonate nodules have been observed in the far north region of cameroon in the carbonate free watershed of the mayo tsanaga thus a priori not favourable for carbonate nodules accumulations these nodules are associated with a clay rich parent material crpm covering either a granitic upstream or a greenstone bedrock downstream in this peculiar context the amount of pedogenic carbonate nodules represents large quantities of ca and c therefore determining the ca sources for pedogenic carbonate nodules is a key point regarding the mechanisms leading to carbonate nodule precipitation and their role in the biogeochemical cycle of ca three sites two on granite and one on greenstone were studied by combining sr et nd isotope systematics in order to assess the ca sources of carbonate nodules and the origin of the crpm associated with nodules carbonate nodules have a distinct sr isotopic composition in each profile pointing to the contribution of a local source for ca sr isotopic compositions of plagioclases and carbonate nodules display a concomitant variation in each profile indicating that plagioclases acted as a sr and thus ca source for the carbonate nodules nevertheless carbonate nodules have a higher sr isotopic signature than plagioclases implying the contribution of another more radiogenic sr source sr and nd isotope data from the crpm show that it is a mixture of weathered bedrock compounds and saharan dust this result highlights two other potential sr and ca sources biotite and saharan dust calculations of their respective contributions demonstrate that in situ weathering significantly adds to the ca source of nodules this result contrasts with many other studies from similar settings that highlight the importance of allochthonous marine aeolian inputs this conclusion points out that a substantial part of ca is transferred from the local bedrock to the carbonate nodules this mechanism seems to have been possible as peculiar edaphic conditions preserved the primary ca sources making in situ weathering a significant process for providing ca

saharan wind regimes traced by the sr nd isotopic composition of subtropical atlantic sediments last glacial maximum vs today new nd sr isotopic data on the 30 m lithic particles of surface and last glacial maximum sediments recovered along the african margin between the equator and the gibraltar strait are presented in combination with grain size measurements this 30 m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions in the eolian fraction both sr and nd isotopic tracers reveal the same major northwestern origin mauritania mali southern algeria and morocco the archaean formations of the western saharan shield could be the source of the very unradiogenic ratios observed here the more southern regions senegal guinea act only as secondary sources a similar pattern is observed for the lgm lithic particles are mostly transported by both trade and saharan air layer sal winds along an approximate ne sw axis this main feature matches the southern plume characterizing the dust transport observed during winter no significant latitudinal shift of the belt winds is observed between the lgm and today at the lgm however dust fluxes were 2 4 times higher than today leading to a more archaean type imprint in the deposits we do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the lgm and the location of the major wind systems both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical africa during the last glacial period

permo carboniferous magmatism of the northeast german basin abstract variscan continent continent collision in central europe was followed by a period of syn to late tectonic magmatism involving the extrusion of large volumes of permosilesian age volcanic rocks particularly in the northeast german basin the volcanic suite up to ca 2000 m thick comprises rhyolites acid and basic andesites and tholeiitic and alkali basalts tectono geochemical analysis in conjunction with volume calculations and petrography reveals changes in volcanic activity over time a total of five eruptive stages are recognised beginning in the stephanian and extending up into the upper rotliegend permian these include the stephanian late carboniferous andesite pre ignimbrite stage i lower rotliegend permian age explosive ignimbrite stage ii post ignimbrite stage iii late rhyolite stage iv and upper rotliegend permian age late basalt stage v in addition several volcanic centres including at least two large caldera like structures are recognised the total calculated volume for the northeast german basin volcanics is ca 48 000 km3 comprising rhyolitic rocks and ignimbrites ca 70 andesitic rocks ca 26 and basalts with cogenetic dolerites ca 4 regional variations in composition and geochemistry are related to diverse crust mantle regimes which correlate with differing positions relative to the heterogeneous basement of the variscan foredeep or within the rhenohercynian orogenic zone the crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre existing subduction influenced basaltic magma source

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

development distribution and palaeoenvironmental significance of terrestrial carbonates in the petra region southern jordan abstract terrestrial carbonate deposits are common in both natural and human modified landscapes in petra and its surroundings three broad genetic categories are recognized cementations of pre existing clastics veins crusts cemented cobbles free water deposits massive laminated deposits mld rhizoliths carbonate blisters coatings on archaeological water delivery systems and pedogenic deposits nodules calcrete the oxygen isotopic composition of carbonates suggests mainly precipitation from stored water that reflects the weighted isotopic average of rainfall in the area oxygen and carbon isotope data indicate that a combination of evaporation and co2 degassing are the mechanisms for precipitation depending on the setting and climate at the time of deposition strontium isotopes of carbonates point to an aeolian source from adjacent sources for the calcium the cementations of pre existing clasts are both markers of previous base levels in the case of cemented cobbles and the presence of soil above impermeable bedrock in the case of crusts and veins these types of deposits help to discover previously terraced sites the open water deposits reflect humid pleistocene conditions and their presence inform on the extent and distribution of water resources that may have been available in the late pleistocene and early holocene

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

characterising the stable δ88 86sr and radiogenic 87sr 86sr isotopic composition of strontium in rainwater rainwater plays a major role in determining the transfer of elements and pollutants to soils and hydrological catchments with compositional variations reflecting the extent of mixing between marine sea salt terrestrial dust and vegetation and anthropogenic aerosols while the radiogenic strontium isotope system 87sr 86sr is often used to help constrain the different sources of atmospheric sr the degree of variability in the stable strontium isotope system 88 86sr remains unresolved in order to determine how atmospheric sr affects the 88 86sr composition of water entering the hydrological cycle this study analysed a suite of rainwater samples collected over the course of a year in central paris rainwater 88 86sr compositions were found to range from 0 13 to 0 32 with 87sr 86sr ratios varying between 0 70796 and 0 71093 no seasonality was observed in 88 86sr whereas 87sr 86sr ratios were observed to be generally more radiogenic in the summer and less radiogenic in the winter strontium enrichment factors significantly above seawater implied a predominantly terrestrial non sea salt origin of sr in rainwater with the 88 86sr and 87sr 86sr composition of this terrestrial fraction consistent with a mixture of sr derived from carbonate dust and agricultural fertiliser evidence for a 0 1 decrease in the 88 86sr composition of the river seine as it passes through paris suggests that anthropogenic pollutants may contribute to significant regional variations in the composition of sr in the hydrological cycle together these results demonstrate that there is significant potential for both temporal and spatial variations in the 88 86sr and 87sr 86sr composition of rainwater that need to be taken into consideration when studying 88 86sr variations in localised catchments

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

formation and preservation of pedogenic carbonates in south india links with paleo monsoon and pedological conditions clues from sr isotopes u th series and rees the influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the western ghats karnataka plateau south west india has been studied along the climosequence the current mean annual rainfall mar varies within a 80 km transect from 6000 mm at the edge of the plateau to 500 mm inland pedogenic carbonates occur in the mar range of 500 1200 mm in the semi arid zone mar 500 900 mm carbonates occur i as rhick hardpan calcretes on pediment slopes and ii as nodular horizons in polygenic black soils i e vertisols in the sub humid zone mar 900 1500 mm pedogenic carbonates are disseminated in the black soil matrices either as loose irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size they also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate cemented lumps of centimetric to decimetric size chemical and isotopic sr 87 sr 86 compositions of the carbonate fraction were determined after leaching with 0 25 n hcl the corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed the trend defined by the sr 87 sr 86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition considering the residual fraction of each sample as the most likely lithogenic source of ca in carbonates it is estimated that from 24 to 82 55 on average of ca is derived from local bedrock weathering leading to a consumption of an equivalent proportion of atmospheric co2 these values indicate that climatic conditions were humid enough to allow silicate weathering mar at the time of carbonate formation likely ranged from 400 to 700 mm which is 2 to 3 fold less than the current mar at these locations the sr u and mg contents and the u 234 u 238 activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation the relatively high concentrations of sr u and mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite possibly due to a better confinement of the pore waters which is supported by their high u 234 u 238 signatures and or to higher content of dissolved carbonates in the pore waters the occurrence of ce mn and fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation the carbonate ages determined by the u th method range from 1 33 0 84 kyr to 7 5 2 7 kyr and to a cluster of five ages around 20 kyr i e the last glacial maximum period the young occurrences are only located in the black soils which therefore constitute sensitive environments for trapping and retaining atmospheric co2 even on short time scales the maximum age of carbonates depends on their location in the climatic gradient from about 20 kyr for centimetric nodules at mule hole mar 1100 mm yr to 200 kyr for the calcrete at gundlupet mar 700 mm yr durand et al 2007 the intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils c 2010 elsevier ltd all rights reserved

isotopic evidence for the source of ca and s in soil gypsum anhydrite and calcite in the atacama desert chile abstract the origin of pedogenic salts in the atacama desert has long been debated possible salt sources include in situ weathering at the soil site local sources such as aerosols from the adjacent pacific ocean or salt encrusted playas salars and extra local atmospheric dust to identify the origin of ca and s in atacama soil salts we determined 34 s and 87 sr 86 sr values of soil gypsum anhydrite and 87 sr 86 sr values of soil calcite along three east west trending transects our results demonstrate the strong influence of marine aerosols on soil gypsum anhydrite development in areas where marine fog penetrates inland results from an east west transect located along a breach in the coastal cordillera show that most soils within 90 km of the coast and below 1300 m in elevation are influenced by marine aerosols and that soils within 50 km and below 800 m in elevation receive 50 of ca and s from marine aerosols 34 s values 14 and 87 sr 86 sr values 0 7083 in areas where the coastal cordillera is 1200 m in elevation however coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced most pedogenic salts from inland soils have 34 s values between 5 0 to 8 0 and 87 sr 86 sr ratios between 0 7070 and 0 7076 these values are similar to average 34 s and 87 sr 86 sr values of salts from local streams lakes and salars 5 4 2 34 s and 0 70749 0 00045 87 sr 86 sr in the andes and atacama suggesting extensive eolian reworking of salar salts onto the surrounding landscape ultimately salar salts are precipitated from evaporated ground water which has acquired its dissolved solutes from water rock interactions both high and low temperature along flowpaths from recharge areas in the andes therefore the main source for ca and s in gypsum anhydrite in non coastal soils is indirect and involves bedrock alteration not surficially on the hyperarid landscape but in the subsurface by ground water followed by eolian redistribution of ground water derived salar salts to soils the spatial distribution of high grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local marine and salar salt supporting arguments for tropospheric nitrogen as the main source for soil nitrate

pedo sedimentary constituents as paleoenvironmental proxies in the sudano sahelian belt during the late quaternary southwestern chad basin abstract climate and environmental changes since the last glacial maximum in the tropical zone of west africa are usually inferred from marine and continental records in this study the potential of carbonate pedo sedimentary geosystems i e vertisol relics to record paleoenvironmental changes in the southwestern part of chad basin are investigated a multi dating approach was applied on different pedogenic organo mineral constituents optically stimulated luminescence osl dating was performed on the soil k rich feldspars and was combined with radiocarbon dating on both the inorganic 14cinorg and organic carbon 14corg soil fractions three main pedo sedimentary processes were assessed over the last 20 ka bp 1 the soil parent material deposition from 18 ka to 12 ka bp osl 2 the soil organic matter integration from 11 cal ka to 8 cal ka bp 14corg and 3 the pedogenic carbonate nodule precipitation from 7 cal ka to 5 cal ka bp 14cinorg these processes correlate well with the chad basin stratigraphy and west african records and are shown to be related to significant changes in the soil water balance responding to the evolution of continental hydrology during the late quaternary the last phase affecting the vertisol relics is the increase of erosion which is hypothesized to be due to a decrease of the vegetation cover triggered by i the onset of drier conditions possibly strengthened by ii anthropogenic pressure archaeological data from far north cameroon and northern nigeria as well as sedimentation times in lake tilla northeastern nigeria were used to test these relationships the increase of erosion is suggested to possibly occur between c 3 cal ka and 1 cal ka bp finally satellite images revealed similar geosystems all along the sudano sahelian belt and initial 14cinorg ages of the samples collected in four sites gave similar ages to those reported in this study consequently the carbonate pedo sedimentary geosystems are valuable continental paleoenvironmental archives and soil water balance proxies of the semiarid tropics of west africa

sheet hyaloclastite density current deposits of quench and bubble burst fragments from thin glassy sheet lava flows seamount six eastern pacific ocean abstract new observations with the submersible alvin and deep tow camera show that bedded sheet hyaloclastites are common deposits between 2024 and 1723 m depth on the upper flank of seamount six located on the cocos plate at 12 45 n 102 35 w the individual sheets are highly localized and of small areal extent 2 though no vent sites were found several facies associations of hyaloclastite with pillow talus knobbly fist sized lava fragments and thin sheet lava deposition of hyaloclastites occurred from lateral density currents formed by transformation from convective suspension settling grain size distribution settling behaviour of different co deposited shard types and sedimentary structures together with pelagic ooze in the matrix and geochemically mixed shard populations indicate some erosion traction reworking and turbulence during transport critical observations are that contorted sheet lava protrudes through hyaloclastite and that sheet lava flow vugs commonly contain pelagic ooze facies associations plus consideration of limu formation allow the establishment of a new multi component model of hyaloclastite formation it is inferred that the formation of limu bearing sheet hyaloclastite involves entrapment of pelagic sediment beneath or within lava this leads to limu bubble formation and suppressed tephra jetting together with convectively rising water heated by the lava flow these processes loft shards slightly into the water column from which they settle singly or in vertical sediment gravity flows that are redirected to flow along the seafloor

palaeoclimate and structure the most important factors controlling subsurface temperatures in crystalline rocks a case history from outokumpu eastern finland summary the present work contributes to the study of heat transfer mechanisms in crystalline bedrock we present evidence from a thoroughly investigated case history in outokumpu eastern finland in the fennoscandian or baltic shield which shows that the subsurface temperature field is controlled by the thermal conductivity structure and downward diffusion of palaeoclimatic ground temperature variations the subsurface temperature profiles from three continuously cored boreholes 790 1 100 m deep were used for a detailed 2 d modelling of structural hydrogeological and palaeoclimatic effects on the subsurface temperature field the boreholes are situated in a subdued topography and they intersect early precambrian folded lithologies such as mica gneisses black schists skarn rocks quartzites and serpentinite talc rocks finitedifference techniques were used in the numerical solution of the heat and masstransport equations the 2 d models of thermal conductivity and hydraulic permeability that were compiled were based on an extensive set of data relating to geological structure in situ hydraulic permeability groundwater composition and thermal conductivity of drill core samples down to about 1 km depth it was found that the thermal effect of topographically driven groundwater convection is very small with peclet numbers typically of the order of 10 4 10 5 the effect of anisotropy of thermal conductivity was found to be one order of magnitude smaller than the effects of heatflow refraction in the inclined rock layers which produce horizontal components of heat flow density ranging from 15 to 5 mw m basal heat flow 35 mw m since the advective heat transfer could be neglected we tried to find a palaeoclimatic groundtemperature history that would explain the measured data first an inversion algorithm based on heat conduction in laterally homogeneous media was used for the reconstruction of palaeoclimatic ground temperature history but it yielded spurious results because of the strong 2 d conductivity effects the only means to reconstruct the past ground temperature changes was forward modelling using a conductive transient 2 d model with time dependent surface temperature variations the surface temperatures at different times between 100000 yr bp and the present and the basal heat flow density were varied in order to reach a reasonable fit between the modelled and measured borehole temperatures to reach this goal the ground temperature history must include the main climatic events during the last 100000 yr such as the last glacial epoch and the little ice age from about 1300 ad to 1700 ad followed by warmer temperatures in more recent times our results suggests that subsurface temperatures in conditions similar to those of the outokumpu case can yield a wealth of palaeoclimatic information when an appropriate approach for modelling heat transfer in the bedrock is chosen

crustal memory and basin evolution in the central european basin system new insights from a 3d structural model abstract the central european basin system cebs is composed of a series of subbasins the largest of which are 1 the norwegian danish basin 2 the north german basin extending westward into the southern north sea and 3 the polish basin a 3d structural model of the cebs is presented which integrates the thickness of the crust below the permian and five layers representing the permian cenozoic sediments structural interpretations derived from the 3d model and from backstripping are discussed with respect to published seismic data the analysis of structural relationships across the cebs suggests that basin evolution was controlled to a large degree by the presence of major zones of crustal weakness the nw se striking tornquist zone the ringkobing fyn high rfh and the elbe fault system efs provided the borders for the large permo mesozoic basins which developed along axes parallel to these fault systems the tornquist zone as the most prominent of these zones limited the area affected by permian cenozoic subsidence to the north movements along the tornquist zone the margins of the ringkobing fyn high and the elbe fault system could have influenced basin initiation thermal destabilization of the crust between the major nw se striking fault systems however was a second factor controlling the initiation and subsidence in the permo mesozoic basins in the triassic a change of the regional stress field caused the formation of large grabens central graben horn graben gluckstadt graben perpendicular to the tornquist zone the ringkobing fyn high and the elbe fault system the resulting subsidence pattern can be explained by a superposition of declining thermal subsidence and regional extension this led to a dissection of the ringkobing fyn high resulting in offsets of the older nw se elements by the younger n s elements in the late cretaceous the nw se elements were reactivated during compression the direction of which was such that it did not favour inversion of n s elements a distinct change in subsidence controlling factors led to a shift of the main depocentre to the central north sea in the cenozoic in this last phase n s striking structures in the north sea and nw se striking structures in the netherlands are reactivated as subsidence areas which are in line with the direction of present maximum compression the moho topography below the cebs varies over a wide range below the n s trending cenozoic depocentre in the north sea the crust is only 20 km thick compared to about 30 km below the largest part of the cebs the crust is up to 40 km thick below the ringkobing fyn high and up to 45 km along the teisseyre tornquist zone crustal thickness gradients are present across the tornquist zone and across the borders of the ringkobing fyn high but not across the elbe fault system the n s striking structural elements are generally underlain by a thinner crust than the other parts of the cebs the main fault systems in the permian to cenozoic sediment fill of the cebs are located above zones in the deeper crust across which a change in geophysical properties as p wave velocities or gravimetric response is observed this indicates that these structures served as templates in the crustal memory and that the prerift configuration of the continental crust is a major controlling factor for the subsequent basin evolution

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

thermal conductivity and radiogenic heat production of sedimentary and magmatic rocks in the northeast german basin thermal rock properties were determined for the northeast german basin a subbasin of the southern permian basin in europe the new thermal data provide new aspects for the determination of heat flow and for hydrocarbon and geothermal resource evaluation in the basin thermal conductivity was measured on drill core samples using the optical scanning method values for permian and pre permian clastic rocks are variable 2 3 4 8 w m k because of different depositional environments compaction and cementation reflected in lithology permian carboniferous igneous rocks show lowest thermal conductivity in basalts 2 2 w m k and highest 3 1 w m k in granitoids anisotropy of thermal conductivity in all rocks is low formation thermal conductivity was determined by upscaling the values determined for single lithotypes radiogenic heat production was determined on drill cores for the upper paleozoic sediments and igneous rocks for the younger formations without sample control a well log approach was used the heat production of sedimentary rocks is lowest 0 4 w m3 in the permian zechstein salt and anhydrite and highest 2 1 w m3 in the permian rotliegende clastic rocks heat production of the permian carboniferous rhyolites and granitoids is on the order of 2 6 3 8 w m3 and heat production of andesites and basaltoids is on the order of 0 9 1 9 and 0 1 0 7 w m3 respectively the contribution to surface heat flow by these up to 2 km 1 2 mi thick igneous complexes amounts to 7 mw m2 at a maximum on the same order is the total heat budget provided by the supra permian sedimentary succession in the basin

the formation of deep sea limu o pele deep sea sheet hyaloclastite consists mostly of sand sized blocky and splinter shaped shards but also contains subordinate mm to cm sized thin curved and wrinkled plates and sheets of sideromelane this latter type of shard termed limu o pele has been observed forming subaerially on kilauea by entrapment of water in flowing lava followed by expansion of steam to form large bubbles which burst into thin fragments deep marine limu has been inferred from comparative morphological studies and assessment of physical bubble forming conditions to form in a similar way but with the increased ambient pressure and the higher viscosity of water reducing bubble expansion differing mechanisms of heat transfer and rates of magma chilling also modify the limu forming process in the deep sea this paper evaluates a variety of deep sea limu forming processes and develops a new and quantitatively supported model based on observed limu forming processes and criteria derived from dive samples and observations at seamount six cocos plate it is inferred that water and or water saturated sediment was trapped in extremely thin fluid and rapidly advancing lava flows by various processes bubble formation might also occur during small scale magma fountaining driven by magmatic volatile exsolution and extreme vent constriction or during collapse of pillows and rapid drainage of the magma but we found no deposits clearly resulting from these processes

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

evolution of the northeast german basin inferences from a 3d structural model and subsidence analysis abstract a 3d structural model of the northeast german basin was evaluated with special emphasis on its evolution as an intracontinental depression the study includes investigations on subsidence history and structural setting of the basin thickness evolution and calculated tectonic subsidence volumes of permian to quaternary sediments in the northeast german basin indicate that the subsidence history was related to five stages of basin evolution which differ in their subsidence mechanisms for the initial rift phase in the late carboniferous to early permian a dominant thermal event and subordinate horizontal stresses were indicated by thickness variation evolution and by structural evidence the main part of basin subsidence occurred in a nw se oriented basin in the subsequent phase of thermal relaxation with maximum subsidence from early permian rotliegend to middle triassic muschelkalk from middle triassic the thermal subsidence pattern was superposed by further tectonic events in the middle triassic regional extension led to a reconfiguration of the southern part of the basin where new nne ssw trending troughs rheinsberg and gifhorn troughs developed in the jurassic the northwestern part of the basin was uplifted while in the south the keuper subsiding areas continued to sink and nw se trending depressions related to salt margins became important differentiation continued into cretaceous times when regional compression caused uplift of the southeastern part of the basin and basin margins a final subsidence phase occurred in the cenozoic this was accompanied by intensive salt movement recent basin configuration reflects the superposition of structural elements resulting from different evolution stages the main structural characteristics of the basin are 1 a vertical tectonic zonation in a pre zechstein succession which lacks significant internal structures and a strongly deformed post zechstein succession which was decoupled due to the thick zechstein salt and 2 a marked asymmetry of the basin with a shallow northern slope and a steep bounding fault at the southern margin elbe fault system the northwestern part of the basin shows the structural properties of an intracratonic sag basin with persisting subsidence and with minor salt mobilisation in contrast initial structures in the southeastern part are strongly overprinted by younger tectonic events including middle triassic to jurassic extension late cretaceous inversion and late to post cretaceous salt movements tectonic elements that deform the whole sedimentary succession are restricted to the basin s southern eastern and northeastern margins where salt thickness decreases combined volumetric and backstripping investigations show that 2 3 of the total subsidence was induced by the sediment load and 1 3 was caused by tectonics the tectonic subsidence history varies laterally across the basin while tectonic subsidence curves in the northwestern part of the basin show fast subsidence during the permian and early triassic decreasing exponentially with time subsidence curves in the southeastern part indicate repeated tectonic activity however the tectonic subsidence volume created during permian to late triassic is significantly higher than the tectonic subsidence during younger phases of basin history

geothermal evidence of very low glacial temperatures on a rim of the fennoscandian ice sheet 1 the mean ground temperature as low as 10 c and the existence of more than 500 m thick permafrost during the last glacial are apparent from the analysis of deep borehole temperature profiles in north eastern poland the largest thickness of the permafrost and its survival deep into the holocene was restricted to a region known for its low terrestrial heat flow where the negative temperature gradient is observed in the uppermost 400 m we have shown that the profiles are consistent with warming from the glacial mean of 10 c to the holocene mean of 7 c 14 ka ago and to 8 c in the last 150 years

an integrative geothermal resource assessment study for the siliciclastic granite wash unit northwestern alberta canada this study explores the siliciclastic granite wash unit in northwestern alberta as a potential geothermal reservoir the approach covers regional 3d structural geological modelling of a 90 km 70 km area based on well log and legacy 2d seismic data the fault strike was interpreted from lineaments which were identified with the refined trend surface analysis method the stress state of the granite wash reservoirs was determined by an integrated approach of 3d fault modelling stress ratio definition based on frictional constraints and slip tendency analysis the results show that the best site for a geothermal application is located in the southwestern study area where the highest temperatures above 70 c coincide with the largest thickness above 20 m and zones of elevated porosity and permeability the integrated stress analysis indicates an in situ stress regime from normal to strike slip faulting maintaining a non critically stressed reservoir or faults therein assuming a friction coefficient of 0 7 the granite wash reservoirs could be used for heating of greenhouses domestic warm water provision and district heating

sensitivity of 3d thermal models to the choice of boundary conditions and thermal properties a case study for the area of brandenburg ne german basin based on newly available data of both the structural setting and thermal properties we compare 3d thermal models for the area of brandenburg located in the northeast german basin to assess the sensitivity of our model results the structural complexity of the basin fill is given by the configuration of the zechstein salt with salt diapirs and salt pillows this special configuration is very relevant for the thermal calculations because salt has a distinctly higher thermal conductivity than other sediments we calculate the temperature using a femethod to solve the steady state heat conduction equation in 3d based on this approach we evaluate the sensitivity of the steady state conductive thermal field with respect to different lithospheric configurations and to the assigned thermal properties we compare three different thermal models a a crustal scale model including a homogeneous crust b a new lithosphere scale model including a differentiated crust and c a crustal scale model with a stepwise variation of measured thermal properties the comparison with measured temperatures from different structural locations of the basin shows a good fit to the temperature predictions for the first two models whereas the third model is distinctly colder this indicates that effective thermal conductivities may be different from values determined by measurements on rock samples the results suggest that conduction is the main heat transport mechanism in the brandenburg area

contrasting compositions of saharan dust in the eastern atlantic ocean during the last deglaciation and african humid period abstract during the african humid period ahp much of the modern hyperarid saharan desert was vegetated and covered with numerous lakes in marine sediments off northwestern africa the ahp is represented by markedly reduced siliciclastic sediment flux between 12 3 and 5 5 ka changes in the origin of this terrigenous sediment fraction can be constrained by sediment chemistry and radiogenic isotope tracers at ocean drilling program odp site 658 hole c 20 44 95 n 18 34 85 w 2263 mbsl the neodymium nd isotope composition of terrigenous detritus shows little variability throughout the last 25 kyr indicating that the contributing geological terranes have not changed appreciably since the last glacial period in contrast there were large and abrupt changes in strontium sr isotope ratios and chemical compositions associated with the ahp during which 87 sr 86 sr ratios were markedly less radiogenic and sediments show higher chemical indices of alteration we show that sediment geochemical changes during the ahp cannot be attributed to changes in the source terranes physical sorting or intensity of chemical weathering the low 87 sr 86 sr and high sr concentrations of ahp age samples also conflict with the interpretation of increased fine grained fluvially derived sediments we propose that the most significant compositional changes at odp 658c are due to the addition of an aluminosilicate component that has a highly altered major element signature but is enriched in soluble elements like sr and magnesium mg compared to aluminum al and has low 87 sr 86 sr relative to local terrigenous source areas we interpret these characteristics to reflect authigenic sediment supply from extensive north african paleolake basins that were prevalent during the ahp

carbon dioxide in scree slope deposits a pathway from atmosphere to pedogenic carbonate abstract a continuum of carbon from atmospheric co2 to secondary calcium carbonate has been studied in a soil associated with scree slope deposits in the jura mountains of switzerland this approach is based on former studies conducted in other environments this c continuum includes atmospheric co2 soil organic matter som soil co2 dissolved inorganic carbon dic in soil solutions and secondary pedogenic carbonate soil parameters pco2 temperature ph cmin and corg contents soil solution chemistry and isotopic compositions of soil co2 dic carbonate and soil organic matter 13cco2 13cdic 13ccar and 13csom values have been monitored at different depths from 20 to 140 cm over one year results demonstrated that the carbon source in secondary carbonate mainly needle fiber calcite is related to the dissolved inorganic carbon which is strongly dependent on soil respiration the heterotrophic respiration rather than the limestone parent material seems to control the pedogenic carbon cycle the correlation of 13corg values with rock eval hi and oi indices demonstrates that in a soil associated to scree slope deposits the main process responsible for 13c enrichment in som is related to bacterial oxidative decarboxylation finally precipitation of secondary calcium carbonate is enhanced by changes in soil pco2 associated to the convective movement of air masses induced by temperature gradients heat pump effect in the highly porous scree slope deposits the exportation of soil c leachates from systems such as the one studied in this paper could partially explain the gap in the european carbon budget reported by recent studies

elemental and isotopic composition of surface soils from key saharan dust sources saharan dust contains significant amount of p an important macronutrient to all living organisms which has been shown to exert large effects on nearby and remote ecosystems located across the dust transport pathways the biological effect of saharan dust depends on the amount and nature of the p speciation of the dust however thus far relatively small numbers of samples from potential source areas psa has been analyzed here we report the p speciation resin p hcl p fe bound p and organic p the 18op values the elemental composition and the 87sr 86sr and 143nd 144nd of the fine fraction and bulk soil from 5 important psas across northern africa we found the hcl p concentrations between different source areas were relatively constrained but that these concentrations were higher in the fine fraction which here is used a surrogate for dust the 18op values for soils from sand dunes varied from 15 0 to 21 4 which is in the range of phosphate minerals from sedimentary origin the 18op values of soils from dry lakes were significantly higher 24 0 28 5 probably since their p is derived from fossilized plankton that lived in the lake as it dried up the 87sr 86sr and end values ranged from 0 7219 to 0 7276 and 12 7 to 14 0 in eastern samples and from 0 7146 to 0 7185 and 11 9 to 13 4 in western samples suggesting a different source for the siliciclastic material of eastern and western samples our analysis indicates that the 18op values are decoupled from the sr and nd isotopic systems together the new chemical and isotope data are specific for different psas and thus are used for source apportionment purposes such data can be used to provide more accurate estimates of the flux of potentially bioavailable p to marine and terrestrial ecosystems these estimates can be used in global climate models to determine the magnitude and distribution of p control on carbon uptake

3d lithosphere scale density model of the central european basin system and adjacent areas abstract to analyze the first order structural features characterizing the crust and the lithospheric mantle below the central european basin system and adjacent areas a new lithosphere scale 3d structural density model has been derived that integrates published knowledge with 3d gravity modeling with this study we aim to integrate previous results on sub domains of the study area and regional results of limited resolution in conjunction with 3d gravity analysis to derive the configuration of the lower crust and lithospheric mantle that is consistent with the known density distribution of the sediment fill and with observed deep seismic data as well as with observed gravity the derived 3d density model resolves the internal configuration of the crystalline crust below the central european basin system and adjacent areas at the regional scale and shows that the crystalline crust is characterized by a layered structure the upper to middle crystalline crust is characterized by relatively low seismic p wave velocities and densities it shows strong variations in thickness across the study area that partly correlate spatially with the inherited segmentation in response to crustal amalgamation this upper to middle crystalline crust is underlain by a continuous high density high velocity lower crustal layer locally more than 30 km thick beneath the east european craton and generally decreasing in thickness from the older to the younger tectonic domains though the thickness of this high density lower crust is generally small below the permo cenozoic central european basin system it can reach locally more than 18 km below the northeast german and the norwegian danish basins the derived depth to the lithosphere asthenosphere boundary confirms previously proposed geometries and is up to 230 km deep beneath the precambrian domain but less than 100 km deep beneath the phanerozoic domains implying that the average thermal gradient is higher in the phanerozoic lithosphere than in the precambrian part

are mima like mounds the consequence of long term stability of vegetation spatial patterning abstract the origins of large 5 m diameter 1 m height and regularly spaced i e over dispersed non anthropogenic earth mounds e g mima mounds heuweltjies nabhkas that occur across all biomes remain unresolved an extensive literature documenting diverse explanations for mound genesis has accumulated that primarily ascribes mound formation to faunal agents recent modeling efforts suggest that both abiotic and biotic processes commonly interact to produce striking vegetation patterning e g spots labyrinths the hypothesis that many earth mounds apart from those with a clear faunal genesis e g termitaria may result from vegetation trapping of sediment or aeolian dust and or protection of soil from erosion is reviewed here the literature on the occurrence and properties of some of these mima like mounds is reviewed and the evidence for their origins evaluated some mounds such as coppice dunes otherwise known as nabkhas clearly form as a consequence of aeolian deposition of sediment around vegetation patches however the clay stone and rock content of some mima like mounds is not consistent with purely aeolian origins instead it is suggested that non aeolian mound over dispersion elongation volumes soil properties and stratigraphy are consistent with vegetation patches protecting soil from erosion resulting in preferential erosional deflation of the inter mound area leaving regularly spaced mounds although mima like mounds around the world are formed in diverse vegetation types climates and edaphic conditions many may be long term products of vegetation spatial patterning in which plant canopies and root systems increase sediment capture and reduce erosional losses

meteorological causes of harmattan dust in west africa we investigated the temporal dynamics of dust entrainment in the bodele depression central sahara to better understand the intra annual variability of aerosol emission in the world s largest dust source the linkages between dust entrainment and large scale meteorological factors were examined by correlating several meteorological variables in the mediterranean and africa north of the equator with the aerosol concentrations in the bodele depression separately for winter and summer the methodological tools applied are ncep ncar reanalysis data and the aerosol index of the total ozone mapping spectrometer toms ai available for 15 years from 1978 to 1993 we found that dust mobilisation during the harmattan season is highly dependent on air pressure variability in the mediterranean area high pressure to the north of the bodele intensifies the ne trade winds leading to an increased entrainment of dust in the bodele depression in summer dust mobilization cannot be explained by the large scale meteorological conditions this highlights the importance of local to regional wind systems linked to the northernmost position of the intertropical convection zone itcz during this time

neodymium and strontium isotopic constraints on soil sources in barbados west indies abstract neodymium and strontium isotopic compositions and sm nd ratios are used to constrain the sources of silicate rich soils developed on uplifted pleistocene coral reef limestones on barbados west indies the geographic and geologic setting of barbados facilitates the application of these tracers to the evaluation of the following soil sources 1 pleistocene reef limestone regolith 2 tertiary carbonate rocks sandstones and mudstones that are exposed in northeastern barbados 3 volcanic ash erupted from the lesser antilles arc 4 saharan dust transported by trade winds and 5 fertilizer the soils have nd values that range from 6 6 to 1 9 87 sr 86 sr values of 0 70890 to 0 71067 and sm nd ratios of 0 223 0 260 the pleistocene limestone component is the most significant source of sr in the soils and a negligible source of nd comparison of sm and nd concentrations and neodymium isotopic compositions of soil samples that are weathered to varying extents indicates that sm and nd are relatively unfractionated and retained in the soils during weathering nd and sm nd variations in the soils therefore primarily reflect the compositions and proportions of the silicate sources mass balance calculations based on sm nd systematics require that the silicate soil components contain between 30 85 volcanic ash with the remaining silicate fraction comprised of old continentally derived sediment in contrast to sm and nd sr is mobilized and removed from the soils during weathering strontium from volcanic and carbonate sources is preferentially removed relative to continental silicate sources the strontium isotopic compositions of the soils therefore reflect the combined effects of the degree of weathering and the compositions and proportions of the soil sources mass balance calculations indicate that at least 35 60 of the initial sr in the soils has been removed by weathering these results illustrate 1 the utility of radiogenic isotopes in identifying and quantifying soil sources and weathering processes 2 the compositional influence of numerous sources on soils even those developed in a relatively isolated area such as barbados and 3 the domination of barbados soil sm nd systematics by nonregolith eolian components

deep 3d thermal modelling for the city of berlin germany this study predicts the subsurface temperature distribution of germany s capital berlin for this purpose a data based lithosphere scale 3d structural model is developed incorporating 21 individual geological units this model shows a horizontal grid resolution of 500 500 m and provides the geometric base for two different approaches of 3d thermal simulations 1 calculations of the steady state purely conductive thermal field and 2 simulations of coupled fluid flow and heat transport the results point out fundamentally different structural and thermal configurations for potential geothermal target units the top of the triassic middle buntsandstein strongly varies in depth 159 2 470 m below sea level and predicted temperatures 15 95 c mostly because of the complex geometry of the underlying permian zechstein salt the top of the sub salt sedimentary rotliegend is rather flat 2 890 3 785 m below sea level and reveals temperatures of 85 139 c the predicted 70 c isotherm is located at depths of about 1 500 2 200 m cutting the middle buntsandstein over large parts of berlin the 110 c isotherm at 2 900 3 700 m depth widely crosscuts the sedimentary rotliegend groundwater flow results in subsurface cooling the extent of which is strongly controlled by the geometry and the distribution of the tertiary rupelian clay the cooling effect is strongest where this clay rich aquitard is thinnest or missing thus facilitating deep reaching forced convective flow the differences between the purely conductive and coupled models highlight the need for investigations of the complex interrelation of flow and thermal fields to properly predict temperatures in sedimentary systems

salt as a 3d element in structural modeling example from the central european basin system abstract based on a well constrained 3d structural model of the central european basin system 3d modeling has been carried out to understand the regional scale regularities between movements of the upper permian zechstein salt and the major post permian tectonic events the 3d reconstruction of the paleo thickness of upper permian salt at the end of the permian period demonstrates that areas of thickened upper permian salt correlate with the present day distribution of the largest salt structures within the central european basin system this spatial correlation implies that the distribution of salt thickness at the end of deposition partially controlled the structural style of the basin during post permian phases of salt tectonics moreover the results of 3d salt redistribution for post permian times indicate that the initiation of salt movements took place in the triassic the triassic extensional events triggered several phases of salt movements within the coeval depocenters of the central european basin system such as the glueckstadt graben the horn graben the norwegian danish basin the fjerritslev trough and the himmerland graben and the polish basin during the late jurassic early cretaceous extensional transtensional tectonic event the strongest salt movement occurred within the central graben the lower saxony basin and the pompeckj block the intensity of the late jurassic early cretaceous phase of salt tectonics is essentially declining from the marginal areas of the central european basin system towards the horn graben the glueckstadt graben and adjacent areas the late early cretaceous early late cretaceous is characterized by tectonic quiescence without strong salt movements over the entire study area the next regional phase of salt movements was triggered by late cretaceous early cenozoic inversion involving almost the entire central european basin system in terms of renewed salt movements inversion related thick skinned salt tectonics is observed along the nw se trending elbe fault system and the teisseyre tornquist zone where strongest compressional deformations were localized on the contrary a thin skinned character of salt movements was prevailing within the largest part of the north german basin post inversion cenozoic subsidence was also accompanied by salt activity related either to diapiric rise due to regional shortening and or to local roughly e w directed extension the cenozoic phase of salt movements was especially prominent within the marginal troughs of the glueckstadt graben

soil formation on calcium carbonate rich parent material in the outer carpathian mountains a case study abstract in this study ten stratified calcium carbonate rich soil profiles from the polish outer carpathians were investigated in order to identity the influence of parent material variability and slope processes on soil diversity and their evolution moreover we evaluated the morphological and physico chemical soil properties to recognize the diagnostic horizons and classification of such soils while it is usually thought that carbonate rich soils are considered as formed in situ these study soils clearly presented layering and contribution of materials as they were developed from mixed substrates of different origin e g as the result of mass movements and possible aeolian silt contribution irrespective of the type of parent material every investigated soil showed traces of slope processes resulting in heterogeneous soil profiles further a few different patterns of primary calcium carbonate arrangement were found in general the studied soils were characterized by enrichment with calcium carbonate not only due to inheritance from calcium carbonate rich parent material but also translocation of calcium carbonate within soil profiles the latter depending on soil stratification based on the obtained results four pathways of soil evolution were formulated leptosols which represent initial calcium carbonate rich soils may evolve in different directions first formation of the thick layer suitable for cambic horizon development under deciduous forests which enables the classification of such soils as cambisols depends on slope processes and allochthonous material deposition in turn the decrease of mineralization rates for organic matter delivery of soil material from the upper parts of the slope as well as mixing of organic matter by mesofauna result in the formation of mollic horizons and transformation of leptosols into phaeozems further erosion and redeposition of fine soil material provide two types of slope sediments i those with silt loam texture dominance and ii clay loams interstratified with silty substrates the first type of sediments are more suitable for water percolation and after carbonate leaching clay dispersion and translocation occur in such materials luvisols may develop sediments with a prevalence of clay loam aided stagnosol formation in which pools of carbonates were stabilized due to the reduction of water percolation leading to stagnation

geological 3 d model of the larger altensalzwedel area germany for temperature prognosis and reservoir simulation in the framework of the german r d programme clean co2 large scale enhanced gas recovery in the altmark natural gas field the geological structure of an area encompassing the altensalzwedel sub field and its surrounding was analysed in detail a 3 d model was developed that contains the major geological formations and their general lithology including the natural gas reservoir in the permian rotliegend the immediate cap rock permian zechstein of the reservoir and its overburden based on this geological model a 3 d steady state thermal model was generated as part of a shared earth model the parameterisation of the geological model layers with thermal rock properties is based on laboratory and well log data the model shows temperature changes in dependence of geological structure and of different rock thermal conductivity the calculated surface heat flow is high 80 mw m 2 for most of the area which is in accordance to measured surface heat flow temperature on top of the rotliegend reservoir is variable ranging from 110 to 150 c the quantification of temperature changes versus depth as well as laterally in the reservoir are valuable input data for modelling the dynamic processes of co2 injection within clean

the structure of basaltic scoria and reticulite and inferences for vesiculation foam formation and fragmentation in lava fountains in this investigation pyroclast structures are used to constrain degassing in basaltic lava fountains vesicle size shape number density interconnectedness and packing character are quantified and related to 1 the kinetics of bubble nucleation and growth 2 the structural evolution of magmatic foams and 3 the influence of vesiculation rate on magma fragmentation measurements made on a diverse suite of pyroclasts from kilauea volcano indicate that basaltic foams evolve through an initially disordered closed celled spherical state to a well ordered open celled polyhedral state as the vesicularity rises from 75 to 98 the structural changes occur rapidly 10 s in the conduit and fountain in response to an intense vesiculation burst vesicle size distribution systematics indicate bubble nucleation rates 2 104 events cm 3s 1 that are approximately three orders of magnitude greater than those found for effusive eruptive activity bubble growth rates 9 10 4 cm s exceed effusive estimates by a factor of 3 the observed runaway rate of bubble production indicates strong supersaturations at the onset of nucleation we speculate that the rise speed of the magma as it reaches the level where significant volatile exsolution begins determines the intensity of the vesiculation burst and hence the vigor of the eruption rapid expansion and acceleration of the magma under these conditions may provide the impetus for fragmentation

salinization problems in the negb results from thermohaline simulations the occurrence of salty waters close to the surface is a well known problem in the north east german basin previous numerical simulations showed that near surface brine occurrences are due to the interaction of hydrostatic and thermally induced forces mixed convection the influence of hydraulic permeabilities and thermal conductivities on the observed patterns remained an open question based on a hydro geochemical dataset thermohaline simulations are carried out in order to quantify the impact of these physical parameters on brine migration the results indicate that the salinity and temperature profiles are strongly controlled by hydraulic permeabilities and can locally be influenced by thermal conductivities

origins of peri saharan dust deposits traced by their nd and sr isotopic composition abstract isotopic ratios of sr and nd can be used as very precise tracers in conjunction with mineralogical geochemical tracers and climatic models to identify the origins of dust deposit and to quantify their fluxes both today and throughout the last climati cycles this technique is useful for constraining aeolian transport and atmospheric circulation trajectories from desert sources and over the oceans the present work concerns dust deposits surrounding the saharan desert on the canary islands the african fraction of the dust deposits displays isotopic values which are typical of moroccan origin on the other hand tunisian loesses have been derived from the northern part of the sahara in this case tracers are sensitive enough to distinguish between center saharan shield origin and peri saharan secondary sources allowing us to distinguish between transport due to the trade winds vs the harmattan or mediterranean wind regimes

volcaniclastic deposits from the north arch volcanic field hawaii explosive fragmentation of alkalic lava at abyssal depths submarine explosive eruptions are generally considered to become less likely with increasing depth due to the increasing hydrostatic pressure of the overlying water column volcaniclastic deposits from the north arch volcanic field north of oahu have textural characteristics of explosive fragmentation yet were erupted in water depths greater than 4 200 m

heat flow and lithospheric thermal regime in the northeast german basin abstract new values of surface heat flow are reported for 13 deep borehole locations in the northeast german basin negb ranging from 68 to 91 mw m 2 with a mean of 77 3 mw m 2 the values are derived from continuous temperature logs measured thermal conductivity and log derived radiogenic heat production the heat flow values are supposed free of effects from surface palaeoclimatic temperature variations from regional as well as local fluid flow and from thermal refraction in the vicinity of salt structures and thus represent unperturbed crustal heat flow two d numerical lithospheric thermal models are developed for a 500 km section along the dekorp basin 9601 deep seismic line across the basin with a north eastward extension across the tornquist zone a detailed conceptual model of crustal structure and composition thermal conductivity and heat production distribution is developed different boundary conditions for the thickness of thermal lithosphere were used to fit surface heat flow the best fit is achieved with a thickness of thermal lithosphere of about 75 km beneath the negb this estimate is corroborated by seismological studies and somewhat less than typical for stabilized phanerozoic lithosphere modelled moho temperatures in the basin are about 800 c heat flow from the mantle is about 35 to 40 mw m 2 in the southernmost part of the section beneath the harz mountains higher moho temperatures up to 900 to 1000 c are shown while the relatively high level of surface heat flow in the negb obviously is of longer wave length and related to lithosphere thickness changes in crustal structure and composition are responsible for short wave length anomalies

calcretes in semi arid alluvial systems formative pathways and sinks late quaternary deposits in gujarat western india show an abundant development of calcretes three major sinks of carbonate in the alluvial deposits are recognized 1 groundwater calcretes 2 pedogenic calcretes and 3 calcrete conglomerates groundwater calcretes originate from carbonate saturated waters travelling preferentially along stratification planes pedogenic calcretes form through soil forming processes typically in extra channel areas calcrete conglomerates occur as ribbons sheets and lenses due to the reworking of both pedogenic as well as groundwater calcretes as a result a pathway of calcretization develops that has the route groundwater calcrete to pedogenic calcrete to calcrete conglomerate the formation of pedogenic calcretes over sediments containing groundwater calcretes demonstrates that 1 apart from aeolian dust river waters are also a major source of carbonate and 2 pedogenic carbonates may attain large sizes at accelerated rates due to the presence of pre existing groundwater calcretes consequently the maturity of a soil may be overestimated if determined by following established morphogenetic sequences

tracing spatial and temporal variations in the sources of calcium in pedogenic carbonates in a semiarid environment abstract in arid environments significant amounts of calcium ca are stored in pedogenic carbonates that develop in soils there are two sources for ca in pedogenic carbonates in soils local parent material and dust deposited on the surface in this study the strontium sr isotopes 87 sr 86 sr ratios were used as a tracer for ca from these sources we studied spatial and temporal variations in the sources of ca in pedogenic carbonates in soils developed in six quaternary basalt flows and a cinder deposit in the zuni bandera volcanic field near grants nm young basalt is an excellent rock type on which to study soil development because it provides a chemically and isotopically uniform substrate age dating of the flows provides control for the beginning of soil development other rock types with varying 87 sr 86 sr ratios cropping out around the basalt provide an opportunity to evaluate spatial variations in sources of ca and sr the 87 sr 86 sr ratio of pedogenic carbonates average 0 7078 is similar to the average ratio of marine limestone cropping out in the region and is distinctly different from that of basalt bedrock average 0 7053 indicating that chemical alteration of dust is the principle source of ca there is a strong correlation between the 87 sr 86 sr ratio of pedogenic carbonate and the labile fraction of dust and a soil horizon samples there is little correlation between the 87 sr 86 sr ratio of pedogenic carbonate and that of the residual silicate fraction of dust or a horizon samples this indicates that the major source of ca cycling through these soils is chemical weathering of carbonate minerals in dust and that only a minor component is from chemical weathering of silicate minerals either in dust or the underlying basalt mixing calculations using sr isotopes as a tracer for ca support the qualitative observations some variability in the 87 sr 86 sr ratio of pedogenic carbonates was found on a local scale several hundred meters to several kilometers and can be attributed to changes in dust composition due to contributions from local bedrock there was no correlation found between the age of a basalt flow and the 87 sr 86 sr ratio of the pedogenic carbonate developed on them indicating that the composition of dust has not changed significantly over the last 0 7 ma

modeling of the 3d thermal field in the northeast german basin the regional thermal field of the ne german basin is modeled by a three dimensional finite element approach and is compared to classical one dimensional extrapolations two alternative boundary conditions are assumed at the approximate depth of the moho a constant temperature distribution and a constant heat flow surprisingly both results are almost identical down to approximately 10 km depth based on the models presented the results are due to a complex interaction of different strata and the related regional variability of conductivities in addition the available temperature maps for different depths hurtig et al 1992 indicate a relative high heat flow at the basin margins especially at the southern and eastern boundary the models are able to reproduce the generalized pattern by regarding only a conductive heat flow however because both models are successful at shallow depth we conclude that the current techniques of thermal modeling require improvement even on the theoretical aspects of depth continuation and inversion

calcium in regolith carbonates of central and southern australia its source and implications for the global carbon cycle abstract the widespread regolith carbonates of the australian continent are a potential sink for co 2 we have used sr isotopes to investigate the source of the ca in regolith carbonates that cover approximately 1 6 10 6 km 2 of inland australia 87 sr 86 sr ratios for nearly all the carbonates were in the range 0 7094 to 0 7211 the results show that only about 10 of the ca in regolith carbonates is derived from weathered bedrock with the remaining component being derived from an external marine source the exceptions are the most northerly samples with a range of 0 7270 to 0 7374 in which bedrock content may be as high as 30 the likely ca source areas are sedimentary carbonates located on the continental shelf and calcareous aeolianites that surround much of the southern and western australian coastline winds passing over these carbonates continually rework and transport the material over the australian continent where it has settled and formed the regolith carbonates we see today the impact of this process is that despite the immense area covered australian regolith carbonates do not capture any additional co 2 instead the carbonate is simply being remobilised from one pool marine to another terrestrial

diverse basalt types from loihi seamount hawaii loihi seamount is the southeasternmost active volcano in the hawaiian emperor volcanic chain the seamount is considered representative of the early phase of hawaiian volcanism because of its youth small size and location near the melting anomaly seventeen dredge stations recovered transitional basalt alkalic basalt and basanite in addition to the expected tholeiitic basalt four flows of alkalic basalt contain common small dunite xenoliths the recovered samples have thin palagonite rinds and almost no manganese on the glassy surfaces we estimate that the lavas are less than about 4 000 yr old and many are less than 1 000 yr old loihi seamount is apparently in a transitional growth phase between the early eruption of alkalic lavas and the commonly observed subaerial tholeiitic eruptive phase previously thought to dominate hawaiian volcanism from inception until the postcaldera collapse alkalic stage

stable isotope compositions of pedogenic carbonates and soil organic matter in a temperate climate vertisol with gilgai southern russia abstract a vertisol gilgai complex from the north caucasus russia was studied to evaluate the climatic and environmental conditions governing pedogenesis the stable isotope compositions of soil organic matter som and carbonate pedofeatures in the vertisol record a complex but interpretable pedogenic history variability in the isotopic composition of pedogenic carbonate as a function of morphology position in gilgai microrelief and soil depth emphasizes the importance of these parameters to interpreting pedogenic conditions the isotopic compositions and age of som record evidence of pedogenesis in an earlier 5000 yr bp environment that was warmer and drier than modern conditions with a significant component of c4 flora up to 30 this portion of the soil history is preserved only in the deepest portions of the microlow 140 cm or in the central portion of the microhigh chimney a change to cooler and wetter conditions was accompanied by a shift to an ecosystem dominated by c3 vegetation 95 and resulted in a wetter soil environment particularly in gilgai microlow positions most pedogenic carbonate preserves isotopic compositions reflecting only the more recent climate history the wetter environment contributed to recrystallization of pedogenic carbonate nodules and formation of soft carbonate masses there are systematic differences in the isotopic composition of hard nodules and soft masses that indicate the influence of greater soil water evaporation a greater proportion of xerophytic plants and or lower rates of soil respiration in the gilgai microhighs self consistent interpretation of the pedogenic and paleoclimate history of these vertisols requires consideration of a full suite of information including carbonate pedofeature micromorphology the stable isotope composition and age absolute and relative of these features and other soil characteristics

eolian contribution to soils on mount cameroon isotopic and trace element records abstract we determined sr nd and pb isotopic compositions and major and trace element compositions of soil samples recovered from three soil profiles developed on relatively young pyroclastic deposits less than 10 000 years old of the mount cameroon volcano the time elapsed since then is short compared with the half lives of rb sm u and th suggesting that radioactive decay can be neglected we therefore assumed that i these polyphase soils developed on isotopically homogenous substrates and ii any isotopic variation within such profiles cannot be due to selective dissolution of primary minerals with isotopic compositions different from that of bulk bedrock any sr nd or pb isotopic variation would therefore record an allochtonous input occurring either in a solid or dissolved state sr and nd isotope compositions change systematically with depth in the soil profile in particular 87 sr 86 sr ratios are far greater in the humic horizons than in the underlying horizons except in the ca9h soil profile although smaller than for sr isotope compositions 143 nd 144 nd ratios displayed an inverse relationship with a decrease towards the uppermost organic rich horizons these isotope shifts correlate with changes in sr and nd contents suggesting an allochtonous input characterized by significantly different isotope compositions and slightly lower sr contents but higher nd contents pb isotopic compositions and pb concentrations in the uppermost horizons were distinct from those of underlying horizons in the soil sequences since an anthropogenic contamination such as from leaded petrol cannot explain the pb shifts a natural source has to be invoked for pb as well as for sr and nd considering both the wind paths in west africa and the isotopic shifts registered in the uppermost horizons saharan dust appears to be the best candidate to explain such variations these inputs probably happened in winter when dry warm harmattan wind blows from the northeast a maximum of 8 of saharan dust accretion was calculated for the mount cameroon soils this corresponds to average dust deposition rates between 1 3 and 0 8 g cm 2 ka 1 values that are much higher than those found in hawaiian soils by kurtz et al kurtz a c derry l a chadwick o a 2001 accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances geochim cosmochim acta 65 1971 1983 and are probably related to shorter distance between dust source and deposit any elemental mass balance calculated in the upper organic rich horizons should be then corrected from allochtonous wind borne saharan dust before evaluating weathering linked chemical mobilities

modelling of fractured carbonate reservoirs outline of a novel technique via a case study from the molasse basin southern bavaria germany fluid flow in low permeable carbonate rocks depends on the density of fractures their interconnectivity and on the formation of fault damage zones the present day stress field influences the aperture hence the transmissivity of fractures whereas paleostress fields are responsible for the formation of faults and fractures in low permeable reservoir rocks fault zones belong to the major targets before drilling an estimate for reservoir productivity of wells drilled into the damage zone of faults is therefore required due to limitations in available data a characterization of such reservoirs usually relies on the use of numerical techniques the requirements of these mathematical models encompass a full integration of the actual fault geometry comprising the dimension of the fault damage zone and of the fault core and the individual population with properties of fault zones in the hanging and foot wall and the host rock the paper presents both the technical approach to develop such a model and the property definition of heterogeneous fault zones and host rock with respect to the current stress field the case study describes a deep geothermal reservoir in the western central molasse basin in southern bavaria germany results from numerical simulations indicate that the well productivity can be enhanced along compressional fault zones if the interconnectivity of fractures is lateral caused by crossing synthetic and antithetic fractures the model allows a deeper understanding of production tests and reservoir properties of faulted rocks

the 7 13 march 2006 major saharan outbreak multiproxy characterization of mineral dust deposited on the west african margin mineral dust deposits were collected at mbour senegal throughout the spring of 2006 and especially during the well documented march 7 13 large saharan dust outbreak during this 7 day period significant changes in mass flux grain size clay mineralogy and sr and nd isotopic compositions were recorded indicating distinct provenances for the dust transported and deposited during and outside the event all these terrigenous proxies as well as freshwater diatom taxa also showed significant temporal variations during the outbreak implying contributions from at least two different provenance regions tri dimensional back trajectories and satellite imaging enabled us to link those distinct signatures to regions increasingly to the southeast within a large area covering mauritania mali and southern algeria identified by the total ozone mapping spectrometer toms as the main source of the prominent winter spring plume over the tropical atlantic the multiproxy characterization of the march 7 13 dust fall therefore enables us to typify the terrigenous signature of two different regions supplying dust off west africa and provide valuable clues for the interpretation of northeastern tropical atlantic ocean dust sedimentary records in terms of changes in provenance regions and transport systems additionally because dust deposition data are scarce flux and grain size data obtained in this study among other parameters such as clay assemblages provide important constraints for atmospheric transport models and dust deposition budget estimates in this area

can mima like mounds be vertisol relics far north region of cameroon chad basin abstract non anthropogenic earth mounds defined as mima like mounds in this study have recently been observed in non carbonate watersheds along the sudano sahelian belt in the chad basin in the diamare piedmont northern cameroon they are particularly well developed within stream networks in less eroded areas they occur as whaleback flattened morphologies or even as buried features all these shapes are composed of clay rich sediment associated with high proportions of secondary carbonate nodules and fe mn micro nodules their soil structure is prismatic to massive and vertical cracks are observed locally grain size distributions emphasize the clay rich nature of the sediment with average clay contents of 32 12 8 n 186 which is significantly higher than the clay content in the adjacent sediments in the landscape mean 10 4 n 21 moreover high proportions of smectite characterize the soil with average contents of 34 7 n 25 at the micro scale the groundmass has a cross striated b fabric with embedded smooth subangular quartz and feldspar grains of the silt size fraction all the characteristics point to altered vertic properties in the clay rich sediment composing the mima like mounds mima like mounds are thus interpreted as degraded vertisols compared to present day vertisols occurring in the piedmont mima like mounds are located upstream it is thus proposed that the vertisol areas were more extensive during a former and wetter period than the present day subsequent changing climatic conditions increased erosion revealing the gilgai micro relief by preferential erosion in micro lows rather than in micro highs mima like mounds of the chad basin might thus result from pedogenesis combined with later erosion these local processes can be inherited from regional climatic variations during the late pleistocene holocene and likely be related to the african humid period

cooling rates of hyaloclastites applications of relaxation geospeedometry to undersea volcanic deposits glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits we found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0 15 k min 1 the most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples the very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition because of the onset of crystallization instead they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures the thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models

micromorphological fabrics and developmental stages of carbonate nodular forms related to soil characteristics abstract carbonate nodules often constitute the first stage of calcrete formation micromorphological analysis of carbonate nodules and nodular fabrics in different soil materials shows that their development is a function of several factors nature of the host matrix texture porosity carbonate and non carbonate clay distribution bulk density and the interactions among them different micromorphological stages therefore exist in different soil materials in calcareous medium textured soil materials the stages of nodule formation are related to the increase of the density of the nodule caused by the accumulation of microcalcites in such a soil material the following stages occur 1 microcalcites within the low to moderate density matrix 2 microcalcites of moderate to high density and moderately dense diffuse nodules parallel calcans may occur 3 microcalcites of high density with dense microcalcitic nodules during these stages the amount of non carbonate clay decreases but is homogeneously dispersed and disseminated with the microcalcites in general the size of microcalcites 1 8 m is inversely related to the clay content in non calcareous medium to fine textured soil materials secondary carbonate precipitates in intrapedal and or interpedal voids as large sparry crystals due to pedoturbation processes the nodules thus formed are subjected to recrystallization resulting in a microsparry pattern the development stages are 1 few calcans and crystal chambers 2 crystic nodules mainly of sparry crystals and an increase of calcans and crystic chambers 3 recrystallized nodules composed mainly of microspars in coarse grained materials secondary carbonates precipitate directly in voids as sparry crystals and the resulting nodules are of the crystic type the large crystals are often subjected to recrystallization in partly calcareous coarse grained materials with additions of calcareous dust particular micromorphological carbonate forms occur in the c horizon cutanic calciasepic fabric forms besides zones of crystic fabric which gradually become calciasepic in the b horizon and include the typical nodular forms of the calcareous medium textured soil material together with appreciable amounts of glaebular halos the processes leading to the formation of these stages occur essentially without a significant biogenic influence where carbonate segregation occurs as rhizomorphs surrounding active roots the fabric is always micritic even in coarse textural soil material

the role of climate and aeolian dust input in calcrete formation in volcanic islands lanzarote and fuerteventura spain calcretes are widely described in non marine settings with carbonates in their catchment or vicinity areas but in volcanic islands without carbonates in their substrate calcretes are not very common in lanzarote and fuerteventura canary islands characterized by impressive volcanic landscapes the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits in these settings very well developed calcretes cover large areas of the present landscape the source of calcium required for the formation of these calcretes has not been discussed in much detail till now although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes the petrological and geochemical studies 87sr 86sr ratios 13c 18o major trace and ree carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits our study indicates that these interbeddings were the result of several stages in which during dry periods aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants insects and bacteria played an important role in carbonate precipitation the 18o 2 70 to 2 22 vpdb and 13c 8 21 to 0 24 vpdb values indicate that calcretes were formed by pedogenic processes comparison of calculated 18o values for the canary calcretes with continental mid latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island oceanic settings calcrete87sr 86sr ratios 0 706357 to 0 709208 show strong affinity with those obtained in aeolian carbonate dust and marine deposits and are relatively different from those obtained in basalts ree major and trace element concentrations show that ca bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the sahara and sahel or sand dunes

the source of pedogenic carbonate associated with gold calcrete anomalies in the western gawler craton south australia abstract elevated au concentrations above bedrock mineralization are commonly closely associated with calcrete in arid residual and semi residual soils in australia the origin of australian calcrete has been argued for many years but there have been very few published studies calcrete from au deposits and prospects and elsewhere in the gawler craton south australia were studied for their geochemical composition and sr and c isotope ratios by comparing carbonate 87 sr 86 sr ratios with underlying weathered rock and bedrock it is demonstrated that many samples have overwhelmingly atmospheric sr 94 and by inference ca 98 rather than a local bedrock or soil mineral origin the isotopic composition of calcretes at the challenger gold deposit lie on a mixing trend of decreasingly marine sr from the nullarbor plain to tarcoola 300 km to the east the 13 c pdb values 7 5 to 0 1 suggest that the carbonate c in calcrete has a mixed origin derived from c3 and c4 plants a model is presented to explain how the au ca association may form in calcrete at challenger based on these new sr and c isotope data and in which the role of plants and atmospherically deposited sr and ca combine with pre existing au in the soil the implication for mineral exploration is that since most of the ca is derived from marine sources it is not a pre requisite that autochthonous soil minerals derived from underlying weathered bedrock supply ca for calcrete to form and for the au ca association to occur thus the independence of the ca with respect to underlying lithology reaffirms the usefulness of calcrete as a sampling medium for au exploration

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

investigation of a new hdr system with horizontal wells and multiple fractures using the coupled wellbore reservoir simulator tough2mp well eos3 geothermal energy is renewable sustainable and available in large amounts the hot dry rock hdr systems in particular have the largest potential for long term sustainability and therefore draw a lot of attention the combination of horizontal wells and the technology of multiple transverse fractures technology is an attractive approach of such hdrs which is called in this paper as the specific egs enhanced geothermal system the main objective of this paper is to study the heat extraction over a period of 20 years by water circulating in a deep geothermal reservoir using this specific egs the wellbore flow module t2well eco2n is implemented in the parallelized simulator tough2mp as a new code tough2mp well eos3 which enables coupled wellbore reservoir simulations using this newly developed code the sensitivity of heat extraction against various parameters of the formation and fractures is assessed the influences of the fracture geometry and the space of two neighborhood fractures on the geothermal energy performance are analyzed according to the results in this paper the injection rate the wellbore radius and the fracture permeability are three main influence factors for the distribution of total flow through individual fractures a large injection rate a small wellbore radius and a large fracture width will cause the short circuit effect which reduces the performance of this specific egs compared with the classic hdr system doublet or triplet vertical wells single fracture this specific egs has a much higher performance and a longer duration of the economic production furthermore the horizontal wells can also be drilled in both directions of the minimum horizontal stress instead of in just one direction so that the energy performance is doubled and the investment cost per kw energy production is decreased and the advantage of this specific egs is significantly enlarged

ca sr and 87sr 86sr ratios as tracers of ca and sr cycling in the rio icacos watershed luquillo mountains puerto rico abstract we investigated ca and sr cycling in a humid tropical forest by analyzing ca sr ratios and 87sr 86sr ratios in soil minerals soil exchangeable cations soil porewater and plant roots wood and leaves and calculating the relative contributions of sr from atmospheric inputs and weathering of local bedrock an unexpectedly large contribution of bedrock derived sr and presumably ca is cycled through the vegetation reflecting the important role of geological processes in controlling the cycling of base cation nutrients even in a system with intensely weathered soil this is surprising because over 99 of the ca and sr that was originally in the bedrock is leached out of the soil and saprolite during early stages of weathering at this site and because there are large atmospheric inputs to the site of both sea salt and saharan dust substantial differences in ca and sr cycling are seen on small spatial scales between a ridgetop and an adjacent steep hillslope site measured ca sr ratios reflect fractionation between these elements during biogeochemical cycling fractionation was particularly evident between wood and foliar tissue but fractionation during soil exchange processes is also likely in comparing the ca sr ratios of plants exchangeable cations and bulk soils we found that foliar ca sr ratios were greater than exchangeable cation ca sr ratios which in turn were greater than soil ca sr ratios similar to patterns observed at other highly weathered tropical sites

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

geochemical and isotopic characterization of the bodele depression dust source and implications for transatlantic dust transport to the amazon basin the bodele depression chad in the central sahara sahel region of northern africa is the most important source of mineral dust to the atmosphere globally the bodele depression is purportedly the largest source of saharan dust reaching the amazon basin by transatlantic transport here we have undertaken a comprehensive study of surface sediments from the bodele depression and dust deposits chad niger in order to characterize geochemically and isotopically sr nd and pb isotopes this dust source and evaluate its importance in present and past african dust records we similarly analyzed sedimentary deposits from the amazonian lowlands in order to assess postulated accumulation of african mineral dust in the amazon basin as well as its possible impact in fertilizing the amazon rainforest our results identify distinct sources of different ages and provenance in the bodele depression versus the amazon basin effectively ruling out an origin for the amazonian deposits such as the belterra clay layer by long term deposition of bodele depression material similarly no evidence for contributions from other potential source areas is provided by existing isotope data sr nd on saharan dusts instead the composition of these amazonian deposits is entirely consistent with derivation from in situ weathering and erosion of the precambrian amazonian craton with little if any andean contribution in the amazon basin the mass accumulation rate of eolian dust is only around one third of the vertical erosion rate in shield areas suggesting that saharan dust is consumed by tropical weathering contributing nutrients and stimulating plant growth but never accumulates as such in the amazon basin the chemical and isotope compositions found in the bodele depression are varied at the local scale and have contrasting signatures in the silica rich dry lake bed sediments and in the calcium rich mixed diatomites and surrounding sand material this unexpected finding implies that the bodele depression material is not pre mixed at the source to provide a homogeneous source of dust rather different isotope signatures can be emitted depending on subtle vagaries of dust producing events our characterization of the bodele depression components indicate that the bodele calcium rich component identified here is most likely released via eolian processes of sand grain saltation and abrasion and may be significant in the overall global budget of dusts carried out by the harmattan low level jet during the winter

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

the deep geothermal potential of the berlin area in this study we model the geothermal potential of deep geological formations located in the berlin region in germany berlin is situated in a sedimentary geological setting northeastern german basin comprising low enthalpic aquifers at horizons down to 4 5 km depth in the berlin region the temperature increases almost linearly with depth by about 30 k per kilometer thus allowing for direct heating from deep aquifer reservoirs in principle our model incorporates eight major sedimentary units jurassic keuper muschelkalk upper middle lower buntsandstein zechstein salt and sedimentary rotliegend owing to lack of available petro physical rock data for the berlin region we have evaluated literature data for the larger northeastern german basin to develop a thermodynamic field model which regards depth corrected equations of state within statistical intervals of confidence integration over the thicknesses of the respective structural units yields their heat in place energy densities associated with the pore fluid and the rock matrix under local conditions in joule per unit area at the surface the model predicts that aquifers in the middle buntsandstein and in the sedimentary rotliegend may well exhibit energy densities about 10 gj m 2 for the pore fluids and 20 gj m 2 to 40 gj m 2 for the rock matrices on average referring these figures to the city area of berlin about 892 km2 a significant hydrothermal potential results which however remained undeveloped until today for the reason of present development risks the model accounts for these risks through statistical intervals of confidence which are in the order of 60 to 80 of the trend figures to minimize these uncertainties scientific field explorations were required in order to assess the petro physical aquifer properties locally

the geothermal potential of the underground of the salento peninsula southern italy the low enthalpy geothermal energy systems exploit the underground as a heat reservoir by coupling it with highly efficient heat pumps in winter the energy stored in the subsoil can be transferred to the surface to heat buildings whereas in summer the surplus heat in buildings can be transferred back to the ground providing a cooling action despite the high costs for installation low enthalpy geothermal systems have high energy efficiency and therefore contribute to energy saving to the use of renewable energy sources to environmental sustainability the effects on the hydrogeological cycle are often negligible and to the reduction in fuel consumption and in gas emissions in this paper a simple methodology is proposed to assess the geothermal potential of the underground of the salento peninsula southern italy at the regional scale by calculating the equivalent thermal performance of the subsoil which expresses the thermal power that is potentially extractable and useful to heat or cool a building since the possibility of exploiting the underground as a heat reservoir depends on the physical properties and water saturation of rocks previous detailed studies on the hydrostratigraphic setup of the region are the basis for this analysis of geothermal potential the equivalent thermal performance depends on the thermal efficiencies of different lithological units whose ranges of values for heating only are provided in literature for this case study a stochastic approach has been applied several combinations of thermal efficiencies were randomly selected from the intervals of reference values for every hydrostratigraphic formation and the corresponding minimum depths below the ground surface that must be reached to get the desired equivalent thermal performance are computed the results show that the underground of the salento peninsula has great potentialities for heating of buildings except for some coastal areas because the saltwater intrusion phenomenon could cause problems for the realization of low enthalpy geothermal energy systems

the deep thermal field of the glueckstadt graben with this paper we assess the present day conductive thermal field of the glueckstadt graben in nw germany that is characterized by large salt walls and diapirs structuring the graben fill we use a finite element method to calculate the 3d steady state conductive thermal field based on a lithosphere scale 3d structural model that resolves the first order structural characteristics of the graben and its underlying lithosphere model predictions are validated against measured temperatures in six deep wells our investigations show that the interaction of thickness distributions and thermal rock properties of the different geological layers is of major importance for the distribution of temperatures in the deep subsurface of the glueckstadt graben however the local temperatures may result from the superposed effects of different controlling factors especially the upper sedimentary part of the model exhibits huge lateral temperature variations which correlate spatially with the shape of the thermally highly conductive permian salt layer variations in thickness and geometry of the salt cause two major effects which provoke considerable lateral temperature variations for a given depth 1 the chimney effect causes more efficient heat transport within salt diapirs as a consequence positive thermal anomalies develop in the upper part and above salt structures where the latter are covered by much less conductive sediments in contrast negative thermal anomalies are noticeable underneath salt structures 2 the thermal blanketing effect is caused by thermally low conductive sediments that provoke the local storage of heat where these insulating sediments are present the latter effect leads to both local and regional thermal anomalies locally this translates to higher temperatures where salt margin synclines are filled with thick insulating clastic sediments for the regional anomalies the cumulative insulating effects of the entire sediment fill results in a long wavelength variation of temperatures in response to heat refraction effects caused by the contrast between insulating sediments and highly conductive crystalline crust finally the longest wavelength of temperature variations is caused by the depth position of the isothermal lithosphere asthenosphere boundary defining the regional variations of the overall geothermal gradient we find that a conductive thermal model predicts observed temperatures reasonably well for five of the six available wells whereas the steady state conductive approach appears not to be valid for the sixth well

atmospheric input vs in situ weathering in the genesis of calcretes an sr isotope study at galvez central spain strontium isotopes have been analyzed in a typical calcrete profile developed on granite in the toledo mountains central spain the pedogenic carbonates show clear petrographic evidence of pseudomorphic replacement of the weathered parent granite calcretes display 87sr 86sr ratios between 0 70961 and 0 71059 in sharp contrast to the granite whole rock 0 72856 and minerals 0 71359 to 0 91351 this difference shows that the contribution of sr from the granite to the calcretes is at most 33 and may be as low as 3 direct measurements in rains and aerosols show that the allochtonous source of ca and sr is clearly related to the atmospheric input mainly as dry deposit a slight decrease of sr concentration is observed from the upper horizon composed of continuous calcrete to the deeper calcrete veins in the saprolite this may be due to a kinetic control of the sr ca fractionation and different crystallization rates of the carbonates in the different units of the profile finally local groundwaters have sr isotopic compositions similar to the calcretes and the atmospheric input very different from waters running on the granite

pedogenic carbonates archive modern and past precipitation change a transect study from soils and loess paleosol sequences from northern iran abstract stable carbon and oxygen isotope compositions in soil carbonates and in soil organic matter provide insights into paleo climatic conditions especially in arid and semiarid regions where carbonate is abundant in soils we here investigate 13c and 18o isotope composition of bulk carbonate pedogenic carbonate nodules and organic carbon from modern soils developed along a precipitation gradient entisol inceptisol mollisol and alfisol and paleosols formed within loess units in northern iran 13c values of organic carbon in the modern soils ranged from 19 5 in the arid and semiarid regions to 24 in the more humid regions with forest vegetation 13c values of bulk carbonate in the modern soils ranged from 12 1 at the wettest sites to 0 8 at the drier sites and thus a 550 mm increase in precipitation leads to a 11 decrease in 13c values of bulk carbonate in the modern soils 13c values of pedogenic carbonate nodules in the semiarid areas show higher values by 3 4 more than the regions with forest vegetation unlike 13c values of pedogenic carbonate nodules the 18o values of pedogenic carbonate nodules of modern soils in this study did not display pronounced changes across the sections the change in 13c of carbonates and organic carbon is consistent with the present above ground vegetation consisting of a mosaic of habitats with differences in the proportion of c3 and c4 vegetation tending to larger c4 contribution with increasing aridity the 13c values of carbonates coupled with climate data of the region confirm seasonal bias in the formation of carbonate nodules in the modern soils seen in studies elsewhere the 13c values of pedogenic carbonate nodules in the paleosols range from 10 in humid areas to 7 2 in semiarid areas the trends in 13c composition in modern soils are also visible in the 13c composition in the paleosols suggesting that in the foothills of the alborz and iranian loess plateau a precipitation gradient existed also in the last interglacial

isotopic tracers of the origin of ca in a carbonate crust from the middle atlas morocco abstract carbonate crusts developed on basalt were studied at tazouta in the moroccan middle atlas the chosen representative weathering profile is 2 8 m thick and is composed from base to top of a fresh basalt overlain by a coherent saprolite a friable saprolite and a surface soil carbonate crust genesis occurs by replacement of primary and secondary clay minerals by low mg calcite the 14 c dates of the calcite range from 15 to 14 ka in the coherent saprolite and from 12 to 8 5 ka in the friable saprolite smectitic weathering and replacement of si bearing minerals by carbonate are coupled processes leading to a strong calcium net gain 300 kg m 3 within the friable saprolite the low weathering rate of basalt compared to the calcrete genesis rate and the high mobility of calcium in supergene weathering mantles limit the basaltic ca contribution to calcrete genesis the contribution of the triassic sediment is also limited by the mineralogical unavailability of ca the 87 sr 86 sr ratios confirm the low contribution of basalt and indicate an external origin of ca the sr isotope ratios of calcrete are different from those of the adjacent liassic carbonates and are close to rainfall values the carbon isotope compositions of carbonates 8 to 9 vs pdb imply a significant contribution of c3 dominated organic carbon during carbonate precipitation oxygen isotopic compositions of carbonates average 5 24 vs pdb show that carbonates are 18 o enriched compared to meteoric waters 4 to 3 5 vs smow

no depth limit to hydrovolcanic limu o pele analysis of limu from lō ihi seamount hawai i deep sea limu o pele are shards of basaltic glass commonly described as bubble walls when first identified they were inferred to form in submarine fire fountains but were then reinterpreted as the products of hydrovolcanic volcanism formed when submarine lava flows entrapped and vaporised seawater limu discovered below the c 3 km critical depth of seawater where superheated water exists as a supercritical fluid instead of a vapour led to the hydrovolcanic model of limu o pele formation being discarded in favour of a magmatic co2 driven strombolian like model this revised magmatic mechanism has been widely accepted by the scientific community we describe a newly discovered limu o pele rich deposit at 1 052 mbsl on the northeast summit plateau region of l ihi seamount hawai i the limu at this site is concentrated in a chemically monomict ash lens interbedded with thin lava sheets that are separated from overlying volcaniclastic material by a discontinuity the geometry and geochemistry of the deposit provide compelling evidence for a hydrovolcanic sheet flow related origin the exceptional abundance and preservation of limu at this site allows 4 morphologic subtypes of limu thin film plateau border convex film and pele s hair to be identified and linked to portions of the isolated rupturing bubbles from which they are derived we extend our discussion to beyond this new l ihi deposit by including a review of limu o pele occurrences and thermodynamic considerations that demonstrate the hydrovolcanic model of limu formation to be more tenable than the magmatic model at all depths including below the critical depth of seawater

characterization of main heat transport processes in the northeast german basin constraints from 3 d numerical models to investigate and quantify main physical heat driving processes affecting the present day subsurface thermal field we study a complex geological setting the northeast german basin negb the internal geological structure of the negb is characterized by the presence of a relatively thick layer of permian zechstein salt up to 5000 m which forms many salt diapirs and pillows locally reaching nearly the surface by means of three dimensional numerical simulations we explore the role of heat conduction pressure and density driven groundwater flow as well as fluid viscosity related effects our results suggest that the regional temperature distribution within the basin results from interactions between regional pressure forces as driven by topographic gradients and thermal diffusion locally enhanced by thermal conductivity contrasts between the different sedimentary rocks with the highly conductive salt playing a prominent role in contrast buoyancy forces triggered by temperature dependent fluid density variations are demonstrated to affect only locally the internal thermal configuration locations geometry and wavelengths of convective thermal anomalies are mainly controlled by the permeability field and thickness values of the respective geological layers

lava bubble wall fragments formed by submarine hydrovolcanic explosions on lō ihi seamount and kīlauea volcano glassy bubble wall fragments morphologically similar to littoral limu o pele have been found in volcanic sands erupted on l ihi seamount and along the submarine east rift zone of k lauea volcano the limu o pele fragments are undegassed with respect to h2o and s and formed by mild steam explosions angular glass sand fragments apparently form at similar and greater depths by cooling contraction granulation the limu o pele fragments from l ihi seamount are dominantly tholeiitic basalt containing 6 25 7 25 mgo none of the limu o pele samples from l ihi seamount contains less than 5 57 mgo suggesting that higher viscosity magmas do not form lava bubbles the dissolved co2 and h2o contents of 7 of the limu o pele fragments indicate eruption at 1200 300 m depth 120 30 bar these pressures exceed that generally thought to limit steam explosions we conclude that hydrovolcanic eruptions are possible with appropriate pre mixing conditions at pressures as great as 120 bar