cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

observations of ionospheric heating during the passage of solar coronal hole fast streams 1 using ionospheric temperature measurements made continuously by the poker flat incoherent scatter radar pfisr and eiscat svalbard radar esr during the international polar year ipy we provide evidence for directly driven ionospheric heating associated with the solar wind corotating interaction region cir both esr and pfisr operated almost continuously during the ipy which began on 1 march 2007 during this period 55 cir events occurred and when isr observations were available during these events ionospheric heating was observed this study is the first comprehensive observation of ionospheric heating by cirs demonstrated through case study comparisons and statistically over the 1 year ipy period these multiple day heating events are present in both the auroral and polar regions the quantitative one to one correlation between ace cir observations and isr ionosphere observations leads to a database that will enable the ionospheric heating efficiency of cir events to be determined

two million years of river and cave aggradation in ne brazil implications for speleogenesis and landscape evolution abstract this study characterizes and provides ages for an extensive sedimentary record occurring in lapa doce and torrinha caves ne brazil with 40 km of surveyed passages these caves integrate a distributary cave system fed by allogenic recharge from the surrounding sandstone plateaus sediment petrography together with descriptions of depositional facies and architectural elements shows four depositional units related to fluvial and standing water environments these include from bottom to top 1 a channel unit including lateral bars deposited during an ordinary flood regime 2 a sandy flood unit including minor channel and scour fills derived from bank full equivalent flood events 3 mud caps deposited in standing water that often reach the ceiling and 4 intraclast breccias associated with collapse of the mud caps under saturated conditions the deposits were dated using a combination of cosmogenic nuclide burial dating and u series dating of flowstone cosmogenic nuclide data point to fluvial aggradation being active since 1 91 0 12 my and extending until 0 36 0 08 my with intensive cave and valley aggradation events between 0 78 0 10 my and 0 44 0 12 my long term alluviation of the cave system seems to be important in forming passages determining their configuration and setting up a general distributary pattern evident in passage morphology and sedimentary sequences mud caps overlapping the fluvial deposits are interpreted as the products of successive rising and lowering of the water table static level radiometric ages of interstratified flowstones and speleothems show that these oscillations were active at least since 115 ky ago and finally ceased around 12 ky ago indicated by the recurrent age obtained from uneroded capping flowstones these long term water table oscillations may drive paragenetic expansion of the whole cave system valleys caves and other landforms in our study area are part of an ancient landscape with multiple episodes of burial and exhumation despite the possibility of much older sediment being preserved somewhere in the cave system our data indicate a younger quaternary age for the bulk of the sediment filling the study caves

geological setting and age of australopithecus sediba from southern africa we describe the geological geochronological geomorphological and faunal context of the malapa site and the fossils of australopithecus sediba the hominins occur with a macrofauna assemblage that existed in africa between 2 36 and 1 50 million years ago ma the fossils are encased in water laid clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system immediately above a flowstone layer with a u pb date of 2 026 0 021 ma the flowstone has a reversed paleomagnetic signature and the overlying hominin bearing sediments are of normal polarity indicating deposition during the 1 95 to 1 78 ma olduvai subchron the two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers

the role of organic matter in the metallogeny of the bohemian massif formations rich in organic matter occurred throughout most of the geologic history of the bohemian massif accumulation of organic matter was connected with basic submarine volcanic activity with transgressive sedimentary regimes and with limnic and paralic environments the largest carbon rich marine sediment accumulation occurred in late proterozoic and early paleozoic time in these periods substantial concentrations of trace elements and sulfur accumulated in black claystones where the metal associations were determined mostly by synchronous volcanicity in spite of the substantial amount of accumulated trace elements only subeconomic concentrations of pyrite pyrrhotite and u v sb au mineralizations were formed in association with proterozoic stromatolites subsequently cadomian and variscan metamorphic processes caused substantial remobilization of metals and sulfur in black claystones and produced disseminated gold and uranium deposits during the emplacement of postkinematic variscan granitoids organic matter and some metals were leached from the surrounding low metamorphic carbon rich sediments by hydrothermal solutions of deep crustal origin a typical feature of these deposits is the presence of isotopically light bitumens delta 13 c pdb 40 8 to 56 5ppm and the biological tracers phytane and pristane indicating a biogenic origin as a reducing agent organic carbon graphite controlled the localization of variscan hydrothermal uranium mineralization which occurs in graphitized shear zones in the highly metamorphosed basement of the bohemian massif the crystallinity of the graphitized organic matter decreases sharply in these zones probably due to hydrothermal decomposition of the graphite lattice the low crystallinity of graphite and anomalously light isotopic composition of the hydrothermal carbonates in this type of deposit delta 13 c pdb 6 to ppm indicate that graphitized organic matter was involved in the reduction of uranium bearing hydrothermal solutions during the formation of sandstone type uranium deposits in the carbon rich platform sediments of the bohemian massif the organic matter of host rocks became oxidized by the action of oxygen dissolved in ore bearing solutions this process gave rise to organic polymers similar to humic acids which reacted with uo super 2 2 to form insoluble uranium organic compounds

pleistocene deposits in pierre saint martin cave french pyrenees abstract pleistocene deposits in alpine pierre saint martin cave are preserved in an abandoned river gallery the deposits 300 m long and 25 m high are composed of a lower unit of fallen blocks overlain by debris flows a main unit of laminated clay and a series of river terraces inset into these units the lower and main units are each overlain by speleothems the lower unit represents a cold period probably isotope stage 10 corroded speleothems above it have given u th ages greater than 300 000 330 000 yr b p the main unit with carbonate rich varves devoid of pollen represents a glaciation that occurred before 225 000 yr b p and probably correlates with stage 8 even though such a glaciation has not been previously recognized in the pyrenees the river terraces covered by many noncorroded speleothems probably formed during stage 7 u th ages between 194 000 and 211 000 225 000 yr b p subsequent sinking of an underground river protected the deposits from erosion

climate change in southern illinois usa based on the age and δ13c of organic matter in cave sediments abstract matrix supported diamicton and uniform to laminated silty fine grained sediment deposited from about 42 500 to 27 600 cal yr b p under slackwater conditions nearly filled two caves in southwestern illinois at some point most of the sediment was flushed from the caves and from about 22 700 to 4000 cal yr b p floods deposited a drape of sandy and silty sediment on remnant slackwater successions cobbly alluvium and bedrock especially from 7700 to 4000 cal yr b p clay mineral analyses of the slackwater cave sediment reveal a provenance of chiefly petersburg silt a smectite and illite rich proglacial lacustrine unit present in the overlying illinois episode glacial succession today remnants of the ancient subterranean slackwater deposits nearly fill several secondary passages and in at least two locations cover a cobble mantled strath terrace 1 3 to 1 5 m above active stream channels slumping and sinkhole formation appear to have been important mechanisms for deposition of the ancient subterranean deposits slumping of these surficial deposits and associated vegetation can occur along the flanks of sinkholes in addition to sinkhole formation and enter caves however the finer organics some of them comminuted during transport into the caves become part of the cave alluvium this finer organic fraction is the modern analog of the humified organic matter disseminated in slackwater sediment dated in this investigation by radiocarbon methods twenty four 14c ages on humified organic matter provide chronologic control the 13c values of the organic matter reflect the proportion of c4 type to c3 type vegetation growing in and around swallets and sinkholes at the time of redeposition drought tolerant c4 type vegetation was more prevalent relative to c3 type vegetation from 42 500 to 31 200 cal yr b p compared to conditions from 28 800 cal yr b p to the present the 13c values are consistent with the results from other investigations of speleothems and organic matter from loessial paleosols

longitudinal variations of positive dayside ionospheric storms related to recurrent geomagnetic storms 1 we have performed an analysis of case events and statistics of positive ionospheric storms in the dayside region of the equatorial ionization anomaly during recurrent geomagnetic storms rgss which dominate in geomagnetic and ionospheric conditions on the declining phase of solar activity in 2004 to 2008 it is shown that total electron content tec has a tendency to minimize before the beginning of rgss and to peak 3 to 4 days after i e on the rgs recovery phase produced by high intensity long duration continuous auroral activity the maximum of tec coincides with the maximum of solar wind velocity within high speed solar wind streams an analysis of electron content vertical profiles derived from two independent methods using ionosondes and constellation observing system for meteorology ionosphere and climate formosa satellite mission 3 radio occultation showed that in the maximum of an ionospheric storm on 28 march 2008 the f2 layer thickens nmf2 increases by 50 and hmf2 elevates by a few tens of kilometers the response of positive ionospheric storms to solar heliospheric and geomagnetic drivers reveals a prominent longitudinal asymmetry in the longitudinal range from 90 to 90 the solar illumination plays a major role and in the range from 90 to 120 the influence of heliospheric and geomagnetic drivers becomes significant the highest correlations of the tec enhancements with the heliospheric and geomagnetic drivers were found during december february r increased from 0 3 to 0 5 we speculate that the dynamics controlling this might result from an effect of solar zenith angle storm time effects of thermospheric o n2 enhancement and penetrating electric fields of interplanetary and magnetospheric origin

lead isotope and pb pb model age determinations of ores from central europe and their metallogenetic interpretation the paper presents lead isotope data from 211 samples from phanerozoic lead bearing ore occurrences in central europe particularly from the southern part of the former german democratic republic the data are interpreted in terms of amov s dynamic model of continuous lead isotope evolution the relationships between thoro genic and urano genic model ages and the source of lead in different regional units are discussed we observed differences in lead isotope evolution in the hercynian internides and externides within the moldanubian and saxothuringian zones we distinguish five main lead bearing ore associations 1 cambrian stratiform base metal hermsdorf waldsassen 206pb 204pb 17 50 17 70 2 devonian vein type sb bearing metamorphogene neumuhle hartmannsdorf 17 80 18 00 3 upper carboniferous permian polymetallic including tin vein type kutna hora freiberg altenberg 18 00 18 20 4 triassic jurassic pb ba vein type st ibro halsbrucke 18 20 18 60 5 cenozoic polymetallic vein type riftogene roztoky banska stiavnica 18 80 19 10 pb isotope characteristics from ores of the montagne noire and the brioude massiac district correspond to this subdivision ore associations from the rheno hercynian zone display higher 207pb 204pb ratios which can be explained by more evolved and less metamorphosed source rocks mineralizations of the eastern harz strasberg neudorf belong to the permian association those from the western harz clausthal bad grund to the triassic jurassic because of pb isotope agreement the stratabound rammelsberg and the vein bound ramsbeck i mineralization are presumed to be isogenetic pb isotope identity of distinct mineralizations in the basement zone halsbrucke bad grund and in the triassic sediments gorny slask mechernich bleiglanzbanke suggests a strong genetic coherence pb isotope conformity between the upper carboniferous permian triassic ore associations and hercynian postkinematic granitoids and lamprophyric rocks also favours a close relationship pb isotope and other data indicate crustal sources as the age of the ore associations decreases crustal influences generally increase apart from the roztoky mineralization

cosmogenic burial ages reveal sediment reservoir dynamics along the yellow river china burial dating using cosmogenic al 26 and be 10 is an emerging technique for establishing chronologies of fluvial deposits ranging in age from ca 0 5 ma to 5 ma the determination of burial age however requires an assumption that sediment is buried with a known initial al 26 be 10 ratio using a sequence of well dated fluvial terraces along the yellow river in lanzhou china we demonstrate that this assumption may be violated when upstream sediment sources include neogene sedimentary basins samples of fluvial gravel from six terraces yield burial ages ranging from ca 0 83 ma to 2 81 ma comparison of these results to independent ages determined from magneto stratigraphic and loess paleosol studies demonstrates a high degree of correspondence between ages in the lower three terraces in the higher terraces however burial ages are systematically too old implying a previous burial history these results can be exploited to place quantitative constraints on the provenance of sediment in the terrace deposits our results reveal that rapid incision and excavation of late neogene sedimentary basins ca 1 7 ma led to injection of fluvial sediment with low initial al 26 be 10 ratios dilution of this source through time occurred as incision progressed into upstream bedrock ranges our results suggest that cosmogenic nuclides can illuminate the timing of long term storage and remobilization of sediment in continental scale river systems

response of the topside ionosphere to recurrent geomagnetic activity received 15 june 2010 revised 4 september 2010 accepted 24 september 2010 published 21 december 2010 1 in the present study we investigate the solar activity local time and latitudinal dependence of the topside ionosphere response to recurrent geomagnetic activity using 8 years 1998 2005 of data on total ion density ni retrieved from defense meteorological satellites program observations at about 840 km altitude it is the first attempt to explore the presence of oscillations in the topside ionosphere in response to recurrent geomagnetic activity results indicate that striking periodic oscillations around 9 days in ni are present during the latter part of the declining phase of solar cycle 23 the percentage of the magnitude of 9 day oscillations relative to background values in ni at 2130 lt tends to be 5 10 larger than at three other local times 0930 0510 and 1710 lt moreover latitudinal profiles of bandpass filtered 9 day perturbations in ni show multiple peaks as a function of local time and day of the year which is distinctly different from previous results at or around the f2 layer peak there are in phase correlations between kp and the ni responses in the winter hemisphere and at middle and low latitudes and approximately anti phase at high latitude in the summer hemisphere additionally the 9 day oscillations in ion temperature are is mainly restricted to high latitudes the combined effects of neutral winds e b drift auroral ionization precipitation and migration of subauroral trough region are possible candidates to explain the latitudinal profiles of the 9 day variations in ni

snežna jama slovenia interdisciplinary dating of cave sediments and implication for landscape evolution caves are important markers of surface evolution since they are as a general rule linked with ancient valley bottoms by their springs however caves can only be dated indirectly by means of the sediments they contain if the sediment is older than common dating methods one has to use multiple dating approaches in order to get meaningful results u th dating palaeomagnetic analysis of flowstone and sediment profiles cosmogenic dating of quartz pebbles and mammalian dating allowed a robust estimate of speleogenesis sediment deposition climatic change at the surface and uplift history on the periadriatic fault line during the plio pleistocene our dates indicate that sne na jama was formed in the upper miocene received its sedimentary deposits during the pliocene in a rather low lying hilly landscape and became inactive due to uplift along the periadriatic and sava faults and climatic changes at the beginning of the quaternary although it is only a single cave the information contained within it makes it an important site of the southern alps

river derived slackwater sediments in caves along cheat river west virginia abstract the november 1985 cheat river flood produced overbank slackwater deposits in caves of the cheat river canyon the deposits include loamy silt loamy sand to very fine sand and flotsam sediments deposited by the november 1985 flood lie within 1 m of the established high water mark and are good indicators of peak stage prehistoric overbank slackwater deposits are present in one cave these sediments are inferred to be 400 000 years old and are therefore unrelated to the modern cheat river overbank slackwater deposits are poorly preserved in the examined caves because cave streams actively remove sediments and the warm moist environment of the caves fosters decay of woody flotsam deposits of the 1985 flood are projected to survive at most a few centuries in contrast slackwater sediments inferred to be 400 000 years old are preserved within a cave shielded from significant runoff and biogenic activity

quaternary downcutting rate of the new river virginia measured from differential decay of cosmogenic 26al and 10be in cave deposited alluvium the concentrations of the cosmogenic radionuclides sup 26 al and sup 10 be in quartz can be used to date sediment burial here we use sup 26 al and sup 10 be in cave deposited river sediment to infer the time of sediment emplacement sediment burial dates from a vertical sequence of caves along the new river constrain its quaternary downcutting rate to 27 3 4 5 m m y and may provide evidence of regional tectonic tilt 32 refs 3 figs 1 tab

structure and stratigraphy of the tepla barrandian neoproterozoic bohemian massif a new plate tectonic reinterpretation abstract the tepla barrandian unit tbu of the bohemian massif exposes a section across the once extensive avalonian cadomian belt which bordered the northern active margin of gondwana during late neoproterozoic this paper synthesizes the state of the art knowledge on the cadomian basement of the tbu to redefine its principal component units to revise an outdated stratigraphic scheme and to interpret this scheme in terms of a recent plate tectonic model for the cadomian orogeny in the bohemian massif the main emphasis of this paper is on an area between two newly defined fronts of the variscan pervasive deformation to the nw and se of the barrandian lower paleozoic overlap successions this area has escaped the pervasive variscan late devonian to early carboniferous ductile reworking and a section through the cadomian orogen is here superbly preserved the nw segment of the tbu consists of three juxtaposed allochthonous belts of unknown stratigraphic relation the kralovice rakovnik radnice kralupy and zbiroh sarka belts differing in lithology complex internal strain patterns and containing sedimentary and tectonic melanges with blocks of diverse ocean floor meta basalts we summarize these three belts under a new term the blovice complex which we believe represents a part of an accretionary wedge of the cadomian orogen the se segment of the tbu exposes the narrow picin belt which is probably a continuation of the blovice complex from beneath the barrandian lower paleozoic and a volcanic arc sequence the davle group their stratigraphic relation is unknown flysch units the st chovice group and svrchnice formation overlay the arc volcanics and both units contain material derived from volcanic arc the former was also sourced from the nw segment whereas the latter contains an increased amount of passive margin continental material in contrast to the blovice complex the flysch experienced only weak cadomian deformation the new lithotectonic zonation fits the following tectonic scenario for the cadomian evolution of the tbu well the s to se directed cadomian subduction beneath the tbu led to the involvement of turbidites chaotic deposits and 605 39 ma ocean floor in the accretionary wedge represented by the blovice complex the accretionary wedge formation mostly overlapped temporally with the growth of the volcanic arc the davle group at 620 560 ma upon cessation of the arc igneous activity the rear of the wedge and some elevated portions of the arc were eroded to supply the deep water flysch sequences of the st chovice group whereas the comparable svrchnice formation 560 to

late quaternary paleoclimate in semiarid northeastern brazil from u series dating of travertine and water table speleothems abstract fossil travertine and subaqueous speleothems in presently dry caves suggest periods of enhanced ground water recharge during the quaternary period in semiarid northeastern brazil travertine deposits and water table speleothems were dated by the 230 th 234 u technique yielding new evidence for the timing of past periods of increased rainfall the travertine was deposited in two distinct phases extensive in situ deposits during marine isotope stage 2 and fragmentary indurated deposits dating to ca 400 000 yr b p possibly marine isotope stage 10 or 12 dating of water table speleothems showed that the regional water table was 13 1 m above the present level at the last glacial maximum a second site yielded ages suggesting a still higher water table during marine isotope stage 6 these new data demonstrate that northeastern brazil did not follow the general pattern of a dry last glacial maximum as suggested by other continental records in amazonia and southeastern brazil and as depicted in recent general circulation model gcm simulations our results thus indicate that significant variability in regional rainfall patterns occurred in the area during glaciations and caution against overgeneralization of paleoclimate patterns

mobile sediment in an urbanizing karst aquifer implications for contaminant transport here we investigate geochemical characteristics of sediment in different compartments of a karst aquifer and demonstrate that mobile sediments in a karst aquifer can exhibit a wide range of properties affecting their contaminant transport potential sediment samples were collected from surface streams sinkholes caves wells and springs of a karst aquifer the barton springs portion of the edwards balcones fault zone aquifer central texas and their mineralogy grain size distribution organic carbon content and specific surface area analyzed statistical analysis of the sediments separated the sampling sites into three distinct groups 1 streambeds sinkholes and small springs 2 wells and 3 caves sediments from the primary discharge spring were a mix of these three groups high organic carbon content and high specific surface area gives some sediments an increased potential to transport contaminants the volume of these sediments is likely to increase with continued urbanization of the watershed

copper zinc chromium and osmium isotopic compositions of the tepla barrandian unit black shales and implications for the composition and oxygenation of the neoproterozoic cambrian ocean abstract two neoproterozoic cambrian shale suites that consist of normal nbs and metal rich hmbs black shales from the tepla barrandian unit bohemian massif czech republic are studied in terms of their cu zn cr and re os isotopic compositions to improve our knowledge of elemental and isotopic mass balance of these elements in earth s oceans in the past and the extent of surface oxygenation at the neoproterozoic cambrian boundary the rock compositions indicate that the inputs of cu and zn have been controlled by variable proportions of metal rich authigenic and low metal terrigenous sources the latter having exceptionally low 65cu and partially 66zn in this respect our data confirm previous studies conclusions that organic rich sediments with high a terrigenous flux play an important role in the sinking of light zn in the oceans and provide new evidence that these types of rocks also represent the currently unidentified burial of very light cu in the ocean the chromium isotopic composition reveals a complex history of cr uptake and fractionation through the dominant cr input from different terrigenous sources with variable 53cr followed by cr fractionation that was controlled by redox states nbs on the other hand mixing and or continuous equilibrium isotopic exchange between seawater and hydrothermal cr was the dominant process for the hmbs the re os contents of the nbs were controlled by hydrogenous components which yield a poorly defined re os age for the least disturbed samples of 555 60 ma indicating an open system behavior while the hmbs re os composition was largely influenced by hydrothermal fluids during deposition the calculated authigenic 65cu which is similar to that in the present day ocean and highly positive 53cr values of the hmbs suggest high levels of surface oxygenation during the neoproterozoic cambrian transition furthermore the authigenic 66zn which is indistinguishable from that in the present day ocean may imply a constant zn isotopic composition of the oceans from the neoproterozoic because of the well balanced cycle of phosphates which were strongly adsorbed by fe hydroxides the radiogenic nature of the initial 187os 188os 0 6 although with a high associated error seems to not confirm previous indications of an abrupt increase of seawater 187os 188os during the late neoproterozoic due to the large scale radiogenic os flux into the ocean

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

evolution of uranogenic and thorogenic lead 1 a dynamic model of continuous isotopic evolution a dynamic model of the continuous isotopic evolution of uranogenic and thorogenic lead based on the minimum possible number of assumptions is proposed here the model is based on the simple assumption that the rate of change of the ratios 238 u 204 pb and w 232 th 204 pb present day values increased initially and after attaining a maximum started decreasing because of surface cooling of the earth the time t m when the and w rates of change attained their maximums is a model parameter depending on the age of formation of the different layers of the crust or in mixing processes on the participation of materials from the older or younger crust and mantle mathematically this is suitably described by a two parameter function which is the product of a linear and an exponential function the deduced equations of the model are calibrated according to the isotopic data on ore lead from the isotopic ratios of a lead sample it is possible to determine the two model ages uranogenic and thorogenic and the model parameter t m or another parameter t related to t m the values of the model parameters t m or t indicate the time of the enrichment ancient or younger in u pb which is an extremely important index for identifying the pb source type the use of these model parameters provide the possibility of a better theoretical description of the pb isotopic characteristics in the different types of sources

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

high speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008 1 to demonstrate high speed stream effects during the recent deep solar minimum year 2008 we have analyzed manually scaledfof2 and hmf2 at jicamarca and total electron content tec in the equatorial ionization anomaly eia region over the america longitudinal sector our results reveal that a prominent 9 day oscillation appears in the hmf2 and fof2 at the dip equator the 9 day oscillation amplitudes of fof2are not always positively correlated with tec in the equatorial ionosphere and they show nonlinear dependence on the intensity of geomagnetic disturbances with the outputs of fejer and scherliess s 1997 empirical model we found that this periodicity is also present in equatorial vertical drifts caused by disturbance dynamoelectric field ddef but absent in the drifts due to prompt penetration electric field ppef ddef effects on the equatorial periodic variations alone are not sufficient to explain the observed phenomena other mechanisms such as thermal expansion contraction and neutral composition changes are also the plausible causes of the periodic oscillation in the equatorial ionosphere further the complicated patterns appear in the 9 day band pass filtered tec perturbations in the eia region and they are quite different from the patterns of global coherent thermospheric oscillations triggered by high speed streams we also found that the latitudinal variations of band passed filtered tec present different behaviors involving tilt latitudinal configuration antiphased correlation between the crests and trough and south north asymmetry which vary as a function of season local time or even from event to event

neoproterozoic to early cambrian franciscan type melanges in the tepla barrandian unit bohemian massif evidence of modern style accretionary processes along the cadomian active margin of gondwana abstract melanges have been reported from a variety of modern tectonic settings and are a hallmark of the franciscan type subduction accretion complexes in the precambrian however well documented examples of melanges become extremely scarce this paper describes in detail neoproterozoic to early cambrian melanges recently recognized in the cadomian basement of the tepla barrandian unit bohemian massif the melanges are of sedimentary and tectonic origin and include voluminous successions of graywackes interpreted to represent mass transport deposits presumably along the upper slope of an accretionary wedge the clast compositions indicate multiple episodes of mixing of terrigenous arc derived and deep water pelagic material moreover abundant bodies of meta basalts interpreted as dismembered seamounts or pillow volcanoes were emplaced tectonically into various structural levels of this sedimentary melange by two different mechanisms at an upper level the irregular to elongated bodies of basalts were offscraped only weakly strained and incorporated in the sedimentary matrix that exhibits steep cleavage indicating horizontal pure shear shortening and oblate strain in contrast at a lower level disc shaped and closely spaced basalt bodies are ductilely sheared and reworked into a flat lying prolate to plane strain fabric suggesting horizontal ductile flow presumably along the base of the accretionary wedge during flat slab oceanic subduction our new u pb ages also reveal that the melange formation continued until the early cambrian

evolution of uranogenic and thorogenic lead 2 some differences in the variations of the206pb 204pb and208pb 204pb ratios abstract on the basis of a dynamic model of a continuous pb isotope evolution the variations in the isotopic ratios of uranogenic and thorogenic pb in a number of young ore deposits ocean sediments and volcanic rocks from mid ocean ridges oceanic islands island arcs and continents are evaluated the deviations in the th u ratio from its model values are calculated a model parameter t which indicates a more ancient enrichment in u pb crustal type pb sources or younger enrichment in u pb mantle type pb sources is also calculated the relative change in the th u ratio is close to 1 for mantle type pb sources lower t values and decreases for crustal type pb sources higher t values an interpretation of these changes could be connected with the differences in the u and th geochemical behaviours in metamorphic processes under the conditions of a deeper mantle or crustal source owing to the differences in their valence states in some cases they have similar u 4 and th 4 migration abilities in others u 6 and th 4 considerably different

sediment production and delivery in the amazon river basin quantified by in situ produced cosmogenic nuclides and recent river loads we use cosmogenic nuclide derived denudation rates from in situ produced 10 be in river sediment to determine sediment production rates for the central amazon river and its major tributaries recent developments have shown that this method allows calculating denudation rates in large depositional basins despite intermediate sediment storage with the result that fluxes of the sediment producing hinterland can now be linked to those discharged at the basins outlet in rivers of the central amazonian plain sediment of finer grain sizes 125 500 m yields a weighted cosmogenic nuclide derived denudation rate of 0 24 0 02 mm yr that is comparable to the integrated rate of all main andean draining rivers 0 37 0 06 mm yr which are the beni napo mamore ucayali and maranon rivers coarser grained sediment 500 m of central amazonian rivers is indicative of a source from the tectonically stable cratonic headwaters of the guyana and brazilian shields for which the denudation rate is 0 01 0 02 mm yr respective sediment loads can be calculated by converting these cosmogenic nuclide derived rates using their sediment producing areas for the amazon river at obidos a sediment production rate of 610 mt yr results non andean source areas contribute only 45 mt yr a comparison with published modern sediment fluxes shows similarities within a factor of 2 with an average gauging derived sediment load of 1000 mt yr at obidos for example we attribute this similar trend in cosmogenic versus modern sediment loads first to the absence of long term deposition within the basin and second to the buffering capability of the large amazon floodplain the buffering capability dampens short term high amplitude fluctuations climatic variability in source areas and anthropogenic soil erosion by the time the denudation rate signal of the hinterland is transmitted to the outlet of the basin

electrodynamic response of the ionosphere to high speed solar wind streams 1 a combination of dawn and dusk observations from the dmsp f13 satellite and output from the thermosphere ionosphere electrodynamics general circulation model tie gcm are used to study the electrodynamic response of the ionosphere to quasi 9 day recurrent geomagnetic activity driven by solar wind high speed streams during 2005 superposed epoch analysis of the zonal and vertical plasma drifts reveal that significant electrodynamic perturbations occur in response to the high speed streams during 2005 the peak response occurs around 0 5 days after the high speed stream interface and the drift perturbations slowly relax back to quiet levels over 4 6 days the observed and modeled zonal drift perturbations are in good agreement near dusk however the amplitude of the zonal drift perturbations at dawn slightly differ at low and midlatitudes the modeled drift perturbations are westward at all local times with the largest westward drifts occurring near midnight at dawn the dmsp observations at low and midlatitudes reveal 20 m s 1 eastward drift perturbations while the tie gcm simulates weaker eastward drifts at midlatitudes and westward drifts in the equatorial region at dusk the low and midlatitude perturbation drifts are 10 20 m s 1 westward in both the dmsp observations and tie gcm simulations owing to equatorial expansion and strengthening of the high latitude two cell convection pattern the high latitude zonal drift perturbations are eastward in the morning and westward in the afternoon and evening less agreement is present between the simulated and observed vertical drift perturbations near dawn at all latitudes upward drift perturbations are revealed by both the tie gcm simulation 5 m s 1 and dmsp observations 10 15 m s 1 however at dusk the dmsp observes an upward drift perturbation on the order of 25 35 m s 1 while the tie gcm simulates vertical drift perturbations less than 10 m s 1 the disagreement may be related to errors in the dmsp observations or deficiencies in the model based on the results presented we conclude that the disturbance dynamo mechanism is an important mechanism for driving the electrodynamic response at dawn and dusk to recurrent geomagnetic activity driven by solar wind high speed streams

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

isotopic composition of lead in proterozoic anoxic metasedimentary and volcanogenic rocks from the bohemian massif czech republic with metallogenetic implications abstract the isotopic composition of lead in normal and metal rich black shales and associated volcanogenic rocks has been studied in the barrandian upper proterozoic of the bohemian massif which is a part of the central european variscan belt these rocks played an important role in the metallogeny of the bohemian massif the late proterozoic age of metamorphism is evidenced by the slope of the secondary isochron of the uranogenic lead corresponding to the age of 635 45 ma and by the model age of 540 590 ma of thorogenic lead in the samples with low th u ratios in most of the samples the leached pb is less radiogenic than the residual pb no correlation was established between the presence of more radiogenic samples and the distance towards variscan granitoids the samples are mostly associated with the upper proterozoic volcano sedimentary sequences far from variscan intrusions and only some occur in the exocontacts of variscan plutons this suggest that most of the uranium was introduced into rocks during cadomian metamorphism rather than variscan tectonomagmatic phases however a possible contribution of radiogenic lead in connection with the latter events as well as some heterogeneity in u pb and th pb ratios from the time between sedimentation and metamorphism cannot be excluded the comparatively low 208 pb 204 pb ratios indicate that thorium was not mobilized by the metamorphic fluids and testifies that th is less mobile under metamorphic conditions the 207 pb 204 pb values 15 57 15 63 of less radiogenic lead in the rocks are close to those of galenas from different variscan polymetallic mineralizations in the bohemian massif which suggests a common source from a well mixed reservoir as observed in ore leads in mature island arcs or at active boundaries between continental and oceanic plates

heinrich h1 and 8200 yr b p climate events recorded in hall s cave texas measurements of magnetic susceptibility ms have been performed on a continuous set of samples from a well dated 3 m sequence of sediments collected from hall s cave edwards plateau central texas three major climatic events are represented by distinctive ms increases in the sequence 1 the heinrich event h1 from 17 500 to 17 000 yr b p 2 the end of full glacial conditions on the edwards plateau at 14 200 yr b p and 3 the 8200 yr b p climatic event from 8250 to 8050 yr b p in addition a minor event at 4400 yr b p is also well defined here and in canada indicating that it is a broadly regional event these data indicate that all four events represent a shift toward milder climatic conditions accompanied by increased rainfall at this location the general climatic trends interpreted from the ms data are consistent with independent vertebrate assemblages floral indicators and isotopic data recovered from the cave

a new chronology for the age of appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments the relative chronology of landscape evolution across the unglaciated appalachian plateaus of kentucky and tennessee is well documented for more than a century geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide valley straths and smaller terraces constraining the timing of river incision into the appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials today burial dating using the differential decay of cosmogenic 26al and 10be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground multilevel caves linked hydrologically to the incision history of the cumberland river contain in situ sediments equivalent to fluvial deposits found scattered across the eastern highland rim erosional surface cave sediments correlate with 1 thick lafayette type gravels on the eastern highland rim deposited between c 5 7 and c 3 5 ma 2 initial incision of the cumberland river into the eastern highland rim after c 3 5 ma 3 formation of the parker strath between c 3 5 ma and c 2 0 ma 4 incision into the parker strath at c 2 ma 5 formation of a major terrace between c 2 0 ma and c 1 5 ma 6 shorter cycles of accelerated incision and base level stability beginning at c 1 5 ma and 7 regional aggradation at c 0 85 ma initial incision into the appalachian uplands is interpreted as a response to eustasy at 3 2 3 1 ma incision of the parker strath is interpreted as a response to eustasy at 2 5 2 4 ma a third incision event at c 1 5 ma corresponds with glacial reorganization of the ohio river basin widespread aggradation of cave passages at c 0 85 ma is interpreted as the beginning of intense glacial interglacial cycling associated with global climate change copyright 2006 john wiley sons ltd