the role of climate in the accumulation of lithium rich brine in the central andes abstract lithium rich brine within the sub surface of the salar del hombre muerto shm salt pan in the andes of northwestern argentina has a chemical and isotopic composition which is consistent with li derived from several sources the modern halite saturated lagoon li rich salts and brines formed recently and dissolution of halite which precipitated from ancient saline lakes shm lies in the closed basin that includes part of the massive cerro galan caldera which is drained by the rio los patos which is responsible for 90 of surface runoff into the salar the low li isotope composition 3 4 of this river is consistent with significant contributions of geothermal spring water as water drains through the volcaniclastic deposits which cover a large proportion of the basin li removal as indicated by decreasing li na occurs but without significant isotope fractionation this indicates a mechanism of surface sorption onto smectite or ferrihydrite rather than li incorporation into octahedral structural sites of clays these observations suggest that conditions in this high altitude desert have limited the dilution of hydrothermal spring water as well as the formation of clay minerals which jointly have allowed the li resource to accumulate rapidly changes in climate on a multi millennial time scale specifically in the hydrologic budget have resulted in solute accumulation rates that have been variable through time and decoupled li and na fluxes inflow to the salar under modern conditions has high li na 7 9 10 3 by wt with 7 li indistinguishable from basement rocks 0 3 to 6 4 while under pluvial climate conditions the li na of the saline lake was 40 times lower than the modern lagoon 0 1 0 3 10 3 compared to 10 6 13 4 10 3 with slightly higher 7 li 6 9 to 12 3 reflecting the uptake of 6 li into secondary minerals which formed under a wetter climate

the origin of a severe thunderstorm in kansas on 10 may 1985 abstract this study of the oklahoma kansas area on 10 may 1985 undertakes to explain why severe convection developed in only a small portion of northwestern kansas despite large potential instability for surface air over the entire region and despite the approach of a mobile upper level trough from the southwest special soundings from the o k prf storm program showed that a persistent thermodynamic lid above the warm moist surface boundary layer separated this layer from the middle and upper troposphere in which the instability could be realized and was almost completely effective in suppressing deep convection only one of the soundings with these characteristics showed temporary removal of this lid and the only convective storm developed near the place and time of this removal this coincidence points to removal as the likely although not certain cause isentropic trajectories showed that adiabatic lifting was the cause and that this lift was part of a series of mesoscale waves with wavelengths of

anoxic vs dysoxic events reflected in sediment geochemistry during the cenomanian turonian boundary event cretaceous in the umbria marche basin of central italy abstract one of the most spectacular expressions of global oceanic anoxic events oaes of the cretaceous is the livello bonarelli of central italy deposited during the cenomanian turonian boundary event ctbe or oae2 at around 93 5 ma at furlo in the umbria marche basin in italy the bonarelli consists of approximately 1 m of c org rich shales interbedded with radiolarian rich layers and contrasts sharply with the extensive over and underlying siliceous limestones several minor c org rich intervals herein termed black levels average thickness 4 5 cm are interbedded within the scaglia bianca beneath the bonarelli x ray fluorescence and icp ms analyses show that these sediments consist of different mixing systems with three end members 1 sio 2 caco 3 scaglia bianca 2 average shale caco 3 black levels and 3 average shale sio 2 bonarelli given the sharp lithologic contacts and the little geochemical mixing between the groups these are thought to represent rapid switching events between sedimentary modes major element concentrations are generally low except for si and p owing to dilution by silica up to 96 and carbonates as al normalised ratios for elements such as ti or zr taken as proxies for higher energy environments are close to average shale values excess sio 2 is most likely linked to biogenic processes rather than quartz element al ratios of ti mg k rb and zr are fairly constant pointing to a mostly homogeneous source area the black levels and bonarelli are characterised by lower mg al ratios compared to the scaglia bianca sediments suggesting variability in chlorite input which could be linked with short term sea level drops indicated by ti al ratios the bonarelli sediments are severely depleted in mn which is indicative of oxygen depleted bottom water conditions and an open marine environment while the black levels appear to have been deposited in a much more restricted setting a model involving partial physical isolation of the furlo site by a sill coupled to omz variations by extra basinal forcing mechanisms is proposed to account for these conflicting data based on re mo ratios the bonarelli sediments were deposited under varying oxygen depletion levels from suboxic to anoxic while re mo ratios in the black levels show deposition under less oxygen deficient conditions most minor elements many of them redox sensitive or sulphide residing are strongly enriched in the c org rich sediments further documenting the absence of oxygen and potential availability of hydrogen sulphide in the water column at times while high zn concentrations suggest elevated submarine hydrothermal activity during this time interval ba is also present in very high concentrations up to 1 4 with an average weighed concentration of 0 6 for the entire bonarelli and is probably indicative of high paleoproductivity in this area this is further supported by high p concentrations hinting at nutrient availability at this site

periodicities of caco3cycles in the pliocene of sicily discrepancies with the quasi periods of the earth s orbital cycles a high resolution caco3 record in combination with a detailed magnetostratigraphy is presented for the rhythmically bedded marly sequence of the pliocene trubi formation on sicily italy magnetostratigraphic age calibration and subsequent spectral analysis of the variatrions in caco3 content yield a remarkably consistent discrepancy between the resulting periodicities and the corresponding quasi periods of the earth s orbital cycles this discrepancy can only be explained by assuming that ages assigned to polarity reversal boundaries in the geomagnetic polarity time scale lack sufficient precision a new polarity time scale is presented for the major part of the gilbert and gauss chron using the radiometrically dated gilbert gauss chron boundary at 3 40 ma as an age reference point and extrapolating an average quasi period of 21 7 kyr of the precession cycle as the periodicity of small scale colour annex caco3 cycles

paleoenvironmental changes at the lower pleistocene montalbano jonico section southern italy global versus regional signals abstract integrated high resolution data from calcareous plankton assemblages foraminifera and nannofossils together with geochemical and mineralogical investigations have been collected at the on land montalbano jonico section southern italy in order to reconstruct the paleoenvironmental changes through marine isotope stages mis 23 37 time series analysis on globigerina bulloides and cassidulina carinata 18o records and on selected calcareous plankton proxies mainly revealed the occurrence of precession and obliquity forcing the deposition of sapropel layers which are interbedded in the montalbano jonico section was driven by water column stratification insolation cycle i 104 and enhanced sea surface water productivity insolation cycle i 112 i 102 and i 86 different paleoenvironmental conditions mark the sedimentary evolution of the section from 1240 to 1082 ka mis 37 mis 32 high percentage abundances of warm and oligotrophic planktonic foraminifera and calcareous nannofossil taxa indicate the establishment of oligotrophic and stratified surface water conditions a key paleoenvironmental change occurred during mis 31 from about 1080 to 1065 ka which was a very warm interglacial characterized by an increase of tropical subtropical globigerinoides ruber group and globigerinoides trilobus and low salinity braarudosphaera bigelowii sea surface water taxa during this interval more humid climate conditions coupled with changes in local paleomorphology may have triggered a higher and unusual freshwater input and the creation of a new entry point for sediment supply into the basin from a different drainage area from about 1065 to 1010 ka mis 30 mis 29 a cool and dry climate prevailed in the circum mediterranean area during a time of precession maxima this favored lowered sea surface temperatures and an increase of polar water neogloboquadrina pachyderma left coiling there are also indications of a reduction of the terrigenous input from the new source area from 1010 ka upward mis 28 mis 23 the higher abundances of globigerina bulloides turborotalita quinqueloba and calciosolenia spp indicate enhanced productivity conditions probably related to high turbidity of sea surface waters triggered by a more conspicuous sediment input from land analysis of the long term trends in the multiproxy patterns suggests that the major paleoenvironmental changes occurred as a consequence of the combined effect of orbitally controlled global climate and regional processes

geochemical and paleomagnetic evidence for the occurrence of missing sapropels in eastern mediterranean sediments the cyclic occurrence of sapropels appears to be associated with maxima in the 65 n summer insolation target curve studies of the most recent sapropel have revealed extensive oxidation of organic matter or even the complete removal of this unit geochemical and magnetic signals allow for the detection of such a missing sapropel in older sediments these signals are altered by ongoing diagenetic processes an important parameter to reveal missing sapropels is ba elevated concentrations of ba are always found in visible sapropels and even after oxidation of part of the sapropel the initial ba profile remains visible we use this tool to trace down missing sapropels in kc01b a 37 m kullenberg core from the calabrian ridge eastern mediterranean at least 8 of 11 sampled intervals around insolation maxima contain evidence of a completely oxidized sapropel ba trace metal distributions and magnetic parameters are similar to those observed around visible sapropels

why some mediterranean sapropels survived burn down and others did not abstract we have evaluated using a numerical model the burn down depth depth of post depositional oxygenation of organic matter rich sapropels under aerobic conditions at the seafloor the model suggests that sapropels may be erased by burn down to depths of at least 5 cm after 10 kyr of bottom water reoxygenation a test of the sensitivity shows that the parameters exerting a major control over the burn down process are the flux of freshly sedimenting organic carbon the oxygen concentration of the bottom water the amount of organic matter in the sapropel and the sedimentation rate in comparison bioturbation is of minor importance the result implies that burial of elevated concentrations of non refractory organic carbon is generally improbable when the sedimentation rate is lower than 1 2 cm kyr 1 the record of sapropel deposition in the mediterranean sea and elsewhere may thus be biased towards depositional environments where the sedimentation rate is large enough to shield the organic rich layer from oxygenation

the behaviour of manganese in atlantic carbonate sediments abstract manganese porewater and solid phase data are considered from two different atlantic carbonate sediments both with good geochemical characterisation the first case is a continuously accumulated alternating pelagic marl carbonate ooze where there is a correlation in post oxic conditions between mn ii porewater levels and an acetate leachable mn fraction of the sediment this leachable mn appears to have an association with calcite and in this example the leached residue mn content approximates to that of shale in the second case a very recent compositionally homogeneous calcareous turbidite is underlain by mn oxyhydroxide at the former sediment surface which is now acting as a source of mn ii by reduction sorption of mn by the turbidite sediment and shale like leached residue mn levels in anoxic conditions are again observed as mn ii diffuses towards present oxic conditions although no unique equilibrium is achieved similar older buried turbidites have concentration decreases in solid phase mn content preserved from bottom to top as relict evidence that this process has occurred in these turbidites 54 64 of the total mn is leachable by the acetate method and therefore presumed to be sorbed by calcite the oldest example has persisted for 125 kyr it is suggested that the slow breakdown of metastable mn oxyhydroxide and sorption of mn ii to calcite surfaces are important controls on the behaviour of mn in pelagic carbonates in mildly reducing conditions where accumulation fluctuations occur these processes act together with accumulation to limit overall mn migration and to prevent the large mn enrichments seen near the sediment surface in more reducing environments

geochemical and sedimentological patterns in the thermaikos gulf north west aegean sea formed from a multisource of elements surface sediment samples from thermaikos gulf were analysed for organic carbon cd pb cr cu zn mn ni co and fe and were subjected to grain size analysis the results showed that pb cu and zn had the same source of pollution in the following order of importance the sewage outfall the industrial zone and the axios river the concentration of these metals increased with decreasing mean grain size suggesting their association with the fine fraction of the sediments the clays and the organic matter cadmium was more loosely correlated with the metals of the previous group being derived from the community activities and also from the weathering of land based ophiolitic rocks iron cr ni co and mn are of natural origin the weathering of mafic and ultramafic rocks being responsible for their enrichment this was more apparent in the case of ni which was more enriched in the coarser and better sorted sediments near the delta of the river aliakmon

chemical cycles in pliocene sapropel bearing and sapropel barren eastern mediterranean sediments abstract high resolution 3 4 cm investigations of major and minor elements were carried out on sediment cores from odp leg 160 sites 964 ionian basin 969 mediterranean ridge 967 and 966 northern slope and top of eratosthenes seamount south of cyprus at site 967 element al ratios display pronounced cyclic records that are related to astronomically forced climatic variations sediments from the top of eratosthenes seamount site 966 show a similar pattern to those from site 967 but they are more disturbed by bioturbation and also strongly influenced by long term variations in sediment dispersal sediments from site 969 display similar trends to those from site 964 i e they are characterized by higher mg al slightly higher k al and lower ti al ratios during sapropel formation higher ti al ratios at site 969 compared with sediments from site 964 may be explained by a westward transport of material from a source in the east where ti al ratios are highest sites 966 and 967 elevated mg al ratios at site 969 during sapropel intervals are due to river derived material transported through the kithira strait between peloponnesus and crete from the northwestern aegean sea which originates from ultramafic rocks a change in intermediate water currents current reversal during sapropel formation may explain the enhanced supply of mg rich and the relatively diminished supply of ti rich material we propose that during deposition of the reddish intervals at site 969 a change in circulation did not occur because a drastic decrease in ti al ratios is not evident in these sediments ba peaks indicative of former sapropels are not present ba enrichments in the same sapropel barren intervals at site 967 northern slope of eratosthenes seamount suggest that during such intervals the burn down process was more effective than during the sapropel bearing intervals mn contents in all investigated pliocene sediments correlate with the carbonate contents higher mn contents of the sapropel barren sediments suggest that during time intervals of sapropel formation either mn accumulation at the margins of the permanently oxic upper water column or mn export into the western mediterranean might have occured the latter could only be explained by sub or anoxic conditions in large parts of the water column

geochemistry and tectonic environment of basaltic rocks from the misis ophiolitic melange south turkey abstract the miocene misis tectonosedimentary melange was formed during the closing stages of the neotethys in what is now the adana basin of southern turkey a major part is characterized by large disorientated limestone blocks set in a predominantly volcanogenic matrix of bedded and chaotic units comprising basaltic pillow lavas associated hyaloclastites serpentinites and various acidic tuffs all the basaltic rocks are mildly metamorphosed zeolite facies variably vesicular and differentially altered to smectite chlorite fe oxides zeolites and carbonate petrographic and chemical data on the least altered pillow lavas indicate they were originally sparsely olivine plagioclase clinopyroxene phyric tholeiites and minor amphibole phyric basaltic andesites the basaltic clasts in the melange matrix are genetically related to the pillow lava sequences with the observed variation throughout the suite being governed by low pressure fractional crystallization as a group the basalts are characterized by low zr y 2 4 relatively high th yb 0 5 0 7 and la nb 1 5 2 5 ratios and moderate chondrite normalized light ree enrichment la yb n 3 patterns the basalts have a mildly enriched subduction related chemistry and were possibly formed initially in a back arc basin setting the supra subduction zone characteristics of the misis basaltic units are similar to other tethyan basalts in eastern mediterranean ophiolites

origin of late glacial holocene hemipelagic sediments in the aegean sea clay mineralogy and carbonate cementation abstract four hemipelagic lithological units are identified in the late glacial to holocene sediments in the aegean sea these lithologies are silty clay and clay in texture and include a varying mixture of loose terrigenous sediments supplied from the adjacent landmass gravel to sand sized cemented carbonate clasts and nodules sand to silt sized air born volcanic debris and biogenic remains sediment dispersal during the past 14 000 years was controlled mainly by the fluvial discharge rate by sea level variations which determined the proximity of basins to river mouths and by oceanographic conditions in the aegean sea cemented carbonate clasts and nodules occur in all sediments except unit c sapropel s1 they are well to friably cemented mottled to peloidal micrite or microcrystalline inter granular cement between terrigenous and bioclastic debris and the carbonate is 10 11 mole magnesium calcite during the deposition of sapropel s1 unit c the aegean sea was strongly stratified with colder more saline water masses occupying the deep basins which prevented the development of cemented carbonate nodules and clasts aragonite as pteropods and microcrystalline aragonite is present throughout the cores and together with the cemented carbonate clasts and nodules show that shallow pore waters in the aegean sea have been saturated to supersaturated with respect to both aragonite and magnesium calcite for at least the past 14 000 years results of xrd studies show that unit c sapropel s1 is characterized by lower smectite and kaolinite and higher illite and chlorite than the other units lower smectite illite and kaolinite chlorite ratios in unit c may reflect increased supply of illite and chlorite from european lowland rivers flowing into the black sea from rivers discharging directly into the northern and eastern aegean sea and decreased supply of kaolinite which is mainly of north african origin

geomorphology and spatial distribution of monogenetic volcanoes in the southern puna plateau nw argentina abstract monogenetic volcanoes are the most common volcanic landforms on earth several works have shown that the study of geomorphology and spatial distribution of such small volcanoes reveals important aspects related to the volcanic field from eruption dynamics to tectonic processes the altiplano puna plateau 15 to 27 s central andes comprises the largest non collisional plateau on earth characterized by intensive deformation uplift and volcanism this region is marked by the presence of hundreds of mafic monogenetic volcanoes despite its discrete occurrence the monogenetic volcanoes show a close relationship with large scale lithospheric foundering events in the region in this contribution we applied a geographic information system gis approach in order to build the first complete catalog of monogenetic landforms present in the southern puna plateau 24 30 to 27 00 s nw argentina exploring their evolution and relationship with geotectonic events combining spatial analysis with a geomorphological study of each volcano it was possible to identify the presence of 285 monogenetic volcanoes in the region which could be grouped in seven clusters southern puna shows a predominance of cinder cones and lava domes suggesting a small influence of water in the eruption dynamics despite its high clustering degree southern puna monogenetic vents present a low density 8 3 10 3 vents km2 when compared to other monogenetic fields around the world in addition puna plateau cones show a close relationship with monogenetic cones associated with an extensional environment considering their back arc context based on relative and available absolute ages it was possible to map the volcanism evolution through time the results indicate that the first monogenetic volcanoes appeared in the central region of the plateau sierra de calalaste mainly associated with large scale nne ssw reactivated faults the activity then expanded antofalla and antofagasta regions and finally reached the borders of the plateau pasto ventura and arizaro regions which show volcanoes associated with nw se normal faults

quaternary geochemical evolution of the salars of uyuni and coipasa central altiplano bolivia risacher f and fritz b i99 i quaternary geochemical evolution ofthe salars of uyuni and coipasa central altiplano bolivia chem geol 90 21 1 231 the central trough of the bolivian altiplano is occupied by two wide salt crusts the salar of uyuni which is probably the largest salt pan in the world 10 000 km and the salar of coipasa 2 500 km both crusts are essentially made of porous halite filled with an interstitial brine very rich in li k mg b up to 4 7 g l li 4 3 g l b 30 g l k and 75 g l mg lithium reserves are the highest known in the world around 9x io6 tons potassium magnesium and boron reserves in brines are also important around 194x io6 tons k 8x 10 tons b and 21 1 x io6 tons mg the cnists are the remnant of saline lake tauca 13 000 10 000 yr bp its salinity was estimated approximately at 80 g l its paleochemistry was derived in two ways 1 by dissolving the present amounts of all chemical components in the former lake volume and 2 by simulating the evaporation of the major inflows to the basin the resulting chemical compositions are quite different the dissolution derived one is 5 to 50 times less concentrated in li k mg b than the evaporation simulated ones however all compositions present the same na and ci contents this suggests either a removal of bittern salts or an enrichment of the former lake water in na and ci the most probable interpretation is that lake tauca redissolved a salt crust akin to that existing today several older lakes have been detected on the altiplano nevertheless such an explanation only pushes the problem back it is likely that the anomaly was transferred from one lake to an other three hypotheses may be put forward 1 bittern seepage through bottom sediments 2 uptake of the missing components by minerals and 3 leaching of ancient evaporites from the catchment area at the beginning of the lacustrine history of the basin the excess halite could have been recycled from lake to lake this latter process seems to be the most effective to explain the large excess of na and ci over the bittern solutes li k mg and b the occurrence of almost pure na ci saline springs flowing out from a gypsum diapir in the northern altiplano gives substantial support to this hypothesis

modification and complete removal of eastern mediterranean sapropels by postdepositional oxidation sapropels unusually dark organic rich sediment layers whose origin is controversial are widespread in the eastern mediterranean the upper surfaces of these layers appear sharp and show little evidence of bioturbation it has been suggested that postdepositional oxidation may have removed the dark coloration from the upper part of the original layer so that the top of the visible layer now lies somewhat below the original position of the sapropel top such a diagenetic alteration has considerable implications for the interpretation of the sedimentary record where the tops of dark layers are usually correlated with the cessation of sapropel formation geochemical data demonstrate that all visual evidence of a thin example of the most recent eastern mediterranean sapropel has been removed from the sedimentary record by oxidation processes such a process may have thinned all sapropel units by several centimetres the most recent period of sapropel formation probably ended as recently as 5 ka cf cited values between 6 0 and 7 6 ka

on the timing and forcing mechanisms of late pleistocene glacial terminations insights from a new high resolution benthic stable oxygen isotope record of the eastern mediterranean abstract benthic oxygen isotope records of deep marine sedimentary archives have yielded a wealth of information regarding ice sheet dynamics and climate change during the pleistocene however since they often lack independent age control these records are generally bound by a fixed phase relationship between orbital forcing and the climate response e g ice volume changes we present the first long 1 2 ma benthic oxygen isotope record from the eastern mediterranean based on odp sites 967 and 968 which clearly reflects the behavior of global climate on a glacial interglacial scale throughout the late pleistocene time period the age model for our record is based on tuning the elemental ratio of titanium versus aluminum ti al against insolation the ti al record is dominated by the precession related changes in northern african climate i e monsoonal forcing and hence largely independent of glacial interglacial variability we found the largest offset between our chronology and that of the widely applied open ocean stacked record lr04 lisiecki and raymo 2005 for t vii 624 ka which occurred 9 kyr earlier according to our estimates though in agreement with the aicc2012 d ice chronology of epica dome c bazin et al 2013 spectral cross correlation analysis between our benthic 18 o record and 65 n summer insolation reveals significant amounts of power in the obliquity and precession range with an average lag of 5 5 0 8 kyr for obliquity and 6 0 1 0 kyr for precession in addition our results show that the obliquity related time lag was smaller 3 0 3 3 kyr prior to 900 ka than after 5 7 1 1 kyr suggesting that on average the glacial response time to obliquity forcing increased during the mid pleistocene transition much later than assumed by lisiecki and raymo 2005 finally we found that almost all glacial terminations have a consistent phase relationship of 45 45 with respect to the precession and obliquity driven increases in 65 n summer insolation consistent with the general consensus that both obliquity and precession are important for deglaciation during the late pleistocene exceptions are glacial terminations t iiib t 36 and potentially t 32 and t vii t 24 and t 34 which show this consistent phase relationship only with precession only with obliquity our findings point towards an early 1200 ka onset of the mid pleistocene transition vice versa the timing of t vii which can only be explained as a response to obliquity forcing indicates that the transition lasted until at least after mis 15

active post depositional oxidation of the most recent sapropel s1 in sediments of the eastern mediterranean sea abstract over a wide area of the eastern mediterranean basin two mn rich layers have been observed above the most recent sapropel s1 one immediately above the sapropel top and one a few centimetres closer to the sediment surface different mechanisms have been proposed to explain the occurrence of these two mn peaks either both peaks have a diagenetic origin in which case the upper mn peak is actively forming or the lower peak is actively forming and the upper peak has a different formation mechanism high resolution porewater including a gel sampler used for the first time in marine sediments and solid phase data are now used to demonstrate that the oxidation front is located at the level of the lower mn peak which therefore is presently being formed a barium organic carbon relationship is used to calculate the initial organic carbon profile of the s1 sapropel the palaeoproductivity profiles generated by this method demonstrate that the original sapropel unit was bounded by the upper mn peak this implies that the interval between the two mn peaks where a low organic carbon content is now observed was originally part of the sapropel the initially deposited organic carbon has been oxidised by a progressive downwards moving oxidation front the penetration depth of this oxidation front i e the distance between the two mn peaks is mainly determined by the organic carbon content the sediment accumulation rate and the bioturbation depth the upper mn peak appears to have formed as a result of either mn precipitation upon oxygenation of previously anoxic eastern mediterranean deep water or preservation of a surficial mn peak at the end of the high productivity episode in either case the upper mn peak marks the end of sapropel formation as indicated by the ba profiles this means that formation of the s1 sapropel ceased more recently than is indicated by radiocarbon dating of the visible top of s1

unraveling north african riverine and eolian contributions to central mediterranean sediments during holocene sapropel s1 formation hydroclimate variability has exerted a fundamental control on the alternating deposition of organic lean marl and organic rich sapropel sediments in the eastern mediterranean sea ems however the exact mechanisms regarding the freshwater sources and related changes are still debated here sr and nd isotopes and high resolution elemental data are used to constrain different riverine and eolian supplies to the central mediterranean over the past 9 8 ka the detrital sediments in core cp10bc taken at the margin of the libyan shelf in the southwestern ionian sea can be described by a three endmember mixing system based on sr and nd isotopic compositions the same systematics can also be deduced from ti and k compositional variability the endmembers comprise saharan dust aegean nile and libyan soil representing the eolian supply from north africa the riverine inputs from the aegean nile areas as well as the riverine and shelf derived fluxes from the libyan tunisian margin respectively for the sapropel s1 period in particular we find important detrital supplies from fossil river wadi systems along the libyan tunisian margin activated by intensified african monsoon precipitation combining the temporal profiles with the consistent variability observed in the 87sr 86sr 1000 sr diagram such libyan contribution has been most prominent during the uppermost period of sapropel s1 in core cp10bc this observation is in agreement with hydroclimate reconstructions of northwestern libya comparison of the sr nd isotope data between core cp10bc and four cores taken along a west east transect throughout the ems shows that this detrital supply originated mainly from western libya tunisia and was transported as far eastward as 25 e while being diluted by an increasing nile contribution

petrogenesis of early neogene magmatism in the northern puna implications for magma genesis and crustal processes in the central andean plateau of uolm 2 and mm group rocks assuming the same endnew compositional data and petrogenetic models are presented for member compositions the modelling suggests genesis of the mm pre upper miocene volcanism in the northern puna of argentina magmas at higher pressure than the uolm 2 centres 10 kbar 22 s 24 s two phases of volcanism produced small dome vs 7 kbar which may reflect the influence of crustal thickening in complexes of mainly silicic andesite to low sio2 rhyolite the the plateau region by the mid miocene the felsic dome complexes upper oligocene lower miocene phase uolm 20 17 ma of this study are compositionally similar to the large volume calderaproduced two distinct groups of rocks the uolm 1 group is sourced felsic ignimbrites that dominated volcanism in the region metaluminous and mainly andesitic with isotopic compositions like from 10 to 2 ma and our results suggest that there is no fundamental those of the recent arc sr srt 0 706 ndt 3 the difference in magma genesis between them the differences in the uolm 2 group is more silicic and peraluminous and has isotopic volumes and the mode of eruption reflect changes in the stress and compositions indicating a substantial crustal contribution sr thermal regime with time srt 0 713 ndt 8 the mid miocene phase mm 15 12 ma produced rocks similar in composition to those of the uolm 2 group sr srt 0 710 ndt 7 but with higher incompatible element contents ratios of ba nb and zr

hydrogeochemical fluxes and processes contributing to the formation of lithium enriched brines in a hyper arid continental basin abstract the accumulation of solutes delivered via shallow groundwater and surface water in arid to hyper arid closed basins and the complex hydrogeochemical processes associated with their transport are key to deciphering mechanisms responsible for the formation of brines and salts in these environments a rigorous investigation of the hydrogeochemical fluxes and the formation of the li enriched brine in the hyper arid basin of the salar de atacama chile is presented water fluxes within the salar de atacama basin range from 0 003 m3 s to 1 50 m3 s with a poor correlation between discharge and drainage basin area the inflowing waters have major elemental and li concentrations that are within the same order of magnitude over a period of several decades the element fluxes indicate for example that 58 of the li in the halite nucleus and brines is derived from the south and southeast parts of the basin the average 18ovsmow and dvsmow of inflow waters indicate that there are varied sources of recharge corresponding to the defined sub watershed regions the average water flux weighted 87sr 86sr of inflow waters allows further definition of where in the regional watershed the solutes are derived the predicted water flux weighted 87sr 86sr of the brines 0 70813 compared to the measured average 87sr 86sr 0 70801 indicates that there may be unaccounted sources of water and solutes to the basin brines elemental accumulation time scales for the volume of halite and brine in the nucleus balance on time frames of 0 5 ma mg 1 0 ma ca 1 9 ma li and 2 2 ma k as compared to 47 ma na and 53 ma cl further evidence that na and cl require additional sources not accounted for in the modern inflows to the topographic watershed dissolved noble gas concentrations of marginal and nucleus brines specify that the brines formed in an atmospheric equilibrated state and have since been isolated below the salt crust a process based model is presented to explain the extremely high concentrations of li in brines which incorporates the 7li isotope signatures of waters in the basin to further decipher on a first order the contributions of processes such as low temperature weathering and secondary phase formation

fluid geochemistry of a deep seated geothermal resource in the puna plateau jujuy province argentina abstract this study focused on the geochemical and isotopic features of thermal fluids discharged from five zones located in the high altitude puna plateau jujuy province between s 22 20 23 20 and w 66 67 i e granada vilama pairique coranzuli and olaroz partially mature waters with a na cl composition were recognized in all the investigated zones suggesting that a deep hydrothermal reservoir hosted within the paleozoic crystalline basement represents the main hydrothermal fluid source the hydrothermal reservoirs are mainly recharged by meteoric water although based on the 18 o h 2 o and d h 2 o values some contribution of andesitic water cannot be completely ruled out regional s oriented faulting systems which generated a horst and graben tectonics and ne nw and we oriented transverse structures likely act as preferentially uprising pathways for the deep originated fluids as also supported by the rc ra values up to 1 39 indicating the occurrence of significant amounts of mantle he up to 16 carbon dioxide the most abundant compound in the gas phase associated with the thermal waters mostly originated from a crustal source although the occurrence of co 2 from a mantle source contaminated by organic rich material due to the subduction process is also possible relatively small and cold na hco 3 type aquifers were produced by the interaction between meteoric water and cretaceous palaeogene to miocene sediments dissolution of evaporitic surficial deposits strongly affected the chemistry of the thermal springs in the peripheral zones of the study area geothermometry in the na k ca mg system suggested equilibrium temperatures up to 200 c for the deep aquifer whereas lower temperatures from 105 to 155 c were inferred by applying the h 2 geothermometer likely due to re equilibrium processes during the thermal fluid uprising within relatively shallow na hco 3 aquifers the great depth of the geothermal resource possibly 5000 m b g l is likely preventing further studies aimed to evaluate possible exploitation although the occurrence of li and ba rich deposits associated may attract financial investments giving a pulse for the development of this remote region

geochemical studies of the recent sapropel and associated sediment from the hellenic outer ridge eastern mediterranean sea i mineralogy and chemical composition abstract the mineralogy major and minor element geochemistry and the accumulation rate of a single kastenlot core from the eastern mediterranean is reported the sapropel is similar mineralogically and in its major element composition to the associated marl ooze and calcareous clay it differs from these sediments in having higher concentrations of ba cr cu mo ni sr and zn and lower concentrations of mn the enrichments are explained by increased fertility ba organic matter or sulphide association cr cu mo ni and zn and the presence of aragonitic pteropods sr the organic material has a marine origin based on the carbon isotopic value 13 c 20 and c n ratio 10 the sapropel accumulated 3 to 5 times faster than the associated sediments in this particular core the evidence is consistent with the formation of this sapropel by an increased flux of carbon to the sea floor this would have been caused by increased marine primary production in the eastern mediterranean during periods of reversed circulation brought about by high post glacial runoff primarily from northern africa the additional carbon flux would have lowered the oxygen levels of the bottom waters but it is not known whether anoxic conditions ensued or whether they would have been necessary to preserve the deposited carbon

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

anoxic events in the mediterranean sea in relation to the evolution of late neogene climates stable isotopic and micropaleontological studies were made of selected sapropels organic rich sediments deposited in the mediterranean sea during the last 5 0 m y to determine the processes responsible for their formation distinct isotopic and faunal changes occur across sapropels of late pleistocene early pleistocene and latest pliocene age while smaller isotopic changes and more stable faunal assemblages are associated with the early and mid late pliocene sapropels the large 18o depletions and euryhaline fauna associated with latest pliocene pleistocene sapropels supports a density stratification model with a low salinity surface layer in contrast early pliocene and mid late pliocene sapropels appear to have been formed as the result of sluggish circulation and low oxygen contents in bottom waters of the eastern mediterranean due to the stable warm climatic conditions of that time period

organic carbon accumulation in bannock basin evaluating the role of productivity in the formation of eastern mediterranean sapropels abstract three sediment cores from bannock basin a hypersaline anoxic basin in the eastern mediterranean have been studied to evaluate the importance of productivity on organic carbon accumulation and sapropel formation in this region organic carbon accumulation rates were determined for two cores from within the anoxic hypersaline zone and for one core from the oxygenated portion of this basin organic carbon accumulation rates are higher by an order of magnitude in the surficial sediments of the anoxic zone due to better preservation an empirically derived preservation factor which allows calculation of paleoproductivity during the deposition of the most recent sapropel si indicates that productivity increased by an order of magnitude during the formation of si we conclude that increased productivity was coupled with a density stratification and a circulation reversal in the eastern mediterranean which together led to sapropel formation

geochemical study of sediments from northern euboekos bay greece with regard to the presence of submarine mineral deposits abstract chemical analyses of surface sediment cores from northern euboekos bay greece show that this area is markedly enriched in metals e g ni cr mn relative to aegean shelf sediments these enrichments are partly related to the presence of an fe ni ore body on the seafloor formed by the dumping of a metal rich slag and partly to natural geological processes in a zone on the northwestern coast of euboea island considerable enrichments of ni cr and mn are attributed to weathering of mafic and ultramafic rocks present on the island and probably extended onto the continental shelf it is suggested that the geological and oceanographic conditions in this area are favourable for the formation of placer mineral deposits similar and even greater enrichments of fe ni cr mn zn and cu identified in two older geological horizons are associated with coarse sediments and may be the result of the following processes 1 the weathering of ophiolitic rocks or fe ni deposits or both extending from onshore below the seafloor 2 the production of greater amounts of metal rich weathering products in the past due to climatic changes and 3 lowering of the sea level at times when metal rich horizons were being formed closer to the continent

the origin of rhythmic bedding in the pliocene trubi formation of sicily southern italy abstract foraminiferal palynological stable isotope geochemical clay mineralogical and granulometric data have been gathered for the successive layers of four rhythmic alterations of relatively carbonate poor and carbonate rich beds in the early pliocene trubi formation of sicily southern italy the marly rhythmites consist of a grey layer and a white more indurated layer in which an additional beige less indurated layer is intercalated they are therefore more complex than the well known marl limestone couples elsewhere these rhythmites probably originate from the alternate predominance of increased dilution of river supplied terrigenous material grey and decreased carbonate production in the surface waters beige the grey layers are considered to correspond to periods of increased local run off and higher surface water temperatures and productivity the beige layers signal more arid and cooler climatic conditions lower surface water productivity and stronger or more frequent dust loaded southern winds the white layers apparently reflect intermediate climatic and environmental conditions these periodical changes probably brought about by astronomical precession appear to have occurred not only during the pliocene but also during the late miocene

paleoenvironmental changes during sapropel 19 i cycle 90 deposition evidences from geochemical mineralogical and micropaleontological proxies in the mid pleistocene montalbano jonico land section southern italy an integrated micropaleontological geochemical and mineralogical study has been performed across the mid pleistocene sapropel 19 i cycle 90 from the montalbano jonico land section southern italy to reconstruct the paleoenvironmental conditions at time of its formation the sapropel interval is characterized by two oxygen depletion phases phase a and c interrupted by a temporary re oxygenation interval phase b the beginning and the end of sapropel deposition are dated at 957 0 81 kyr and 950 0 86 kyr respectively the duration of the interruption is estimated to 0 350 0 32 kyr the multiproxy approach highlights that deposition of sapropel 19 reflects a period of enhanced freshwater runoff induced by a wetter climate as a consequence of a more efficient fluvial erosion a higher terrigenous input mostly ascribable to a southern apennines source and an increased turbidity of surface waters accompanied most of sapropel deposition biotic and abiotic proxies document that different paleoenvironmental conditions occur through phases a c the beginning of phase a is characterized by warm on land paleoclimate as well as warm and oligotrophic surface water conditions during the upper part of phase a temperature starts decreasing and surface waters appear more productive this change probably represents the prelude to cooler and drier conditions characterizing phase b which displays a river supply reduction and an eolian input increase sahara dust during phase c the restored depleted oxygen environment at the bottom sediments is clearly coupled with the re establishment of humid conditions and increased river supply at the same time enhanced mixing of water column a cooler paleoclimate and increased productivity of surface waters are recorded the latter likely favored by the enhanced mixing of water column and also increased delivery of land derived nutrients the end of phase c is marked by a restored normal run off enhanced productivity in surface waters and low oxygen conditions at the bottom sediments persist slightly above phase c the overall results suggest that the onset of sapropel deposition is related to water stratification that caused low oxygen exchanges with the sea bottom although enhanced productivity characterizes most of the sapropel deposition it was not the primary factor triggering sapropel deposition

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

the early palaeozoic high grade metamorphism at the active continental margin of west gondwana in the andes nw argentina n chile the evolution of the early palaeozoic orogen of west gondwana in the cambrian to ordovician basement of the andes between 18 and 32 s is investigated for pressure and temperature conditions and age of metamorphism it is characterized by mid crust temperatures commonly above the wet granite solidus 650 c widespread felsic migmatite and rare granulite formed at pressures of ca 0 5 0 7 gpa locally 1 0 gpa these rocks represent the deepest exhumed sections of the early palaeozoic crust high pressure low temperature rocks are absent the crystallization ages compiled from the literature in combination with new data for near peak metamorphic conditions of these high grade metamorphic rocks in nw argentina and n chile are 530 500 ma and 470 420 ma both age groups are spatially overlapping radiogenic isotope signatures sr nd pb are used to characterize the early palaeozoic basement the pb and sr isotope compositions of the early palaeozoic basement indicate mixing arrays between pre palaeozoic unradiogenic and radiogenic crust crustal residence ages sm nd tdm indicate a prominent event of crust formation around 2 ga which is known continent wide this material was recycled during midproterozoic and early palaeozoic orogenies without prominent additions of new crust present in the isotope record i e accretion of compositional exotic material is absent

the evaluation of brine prospects and the requirement for modifications to filing standards the recent increase in demand for lithium has led to the development of new brine prospects particularly in the central andes the brines are hosted in closed basin aquifers of two types mature halite dominant and immature clastic dominant the estimate of elemental resources in these salars depends on a detailed knowledge of aquifer geometry porosity and brine grade the geometry of the aquifers can be evaluated by classical geophysical and drilling techniques but because the resource is a fluid with the attendant problems of in aquifer mixing and reorganization existing codes for filing resource and reserve estimates need modification total porosity is relatively straightforward to measure but effective porosity and specific yield which are required to estimate the resource are more difficult recovery factors are low compared with most metalliferous and industrial mineral deposits due to reliance on pumping of the brine from wells for extraction these and related issues lead us to believe that modifications to the existing standards for reporting mineral resources and reserves are required for these prospects

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

lithium and boron bearing brines in the central andes exploring hydrofacies on the eastern puna plateau between 23 and 23 30 s internally drained basins of the andean plateau are lithium and boron bearing systems the exploration of ionic facies and parental links in a playa lake located in the eastern puna 23 23 30 s was assessed by hydrochemical determinations of residual brines feed waters and solutions from weathered rocks residual brines have been characterized by the cl so4 na k ratio residual brines from the playa lake contain up to 450 mg l of boron and up to 125 mg l of lithium and the las burras river supplies the most concentrated boron 20 mg l and lithium 3 75 mg l inflows of the basin the hydro geochemical assessment allowed for the identification of three simultaneous sources of boron 1 inflow originating from granitic areas of the aguilar and tusaquillas ranges 2 weathering of the ordovician basement and 3 boron rich water from the las burras river most of the lithium input of the basin is likely generated by present geothermal sources rather than by weathering and leaching of ignimbrites and plutonic rocks however xrd analyses of playa lake sediments revealed the presence of lithian micas of clastic origin including taeniolite and eucriptite this study is the first to document these rare li micas from the puna basin thus both residual brines and lithian micas contribute to the total li content in the studied hydrologic system

mid holocene extreme hydrological events in the eastern great rann of kachchh western india abstract the present study is an attempt to reconstruct the paleohydrological conditions during the mid holocene in the hyper arid terrain of the northern great rann of kachchh remote sensing detailed field geomorphology sedimentology geochemistry and optical chronology suggests that the fluvial sediments fringing the khadir island were transported locally and deposited during the extreme hydrological events corresponding to the mid to late holocene indian summer monsoon ism variability overall five extreme hydrological events are deciphered during the last 5 ka which broadly correlates with periods of strengthened ism our data indicate that the emergence and decline of the harappan civilization was unrelated to any major fluvial system in the region

redistribution and geochemical behaviour of redox sensitive elements around s1 the most recent eastern mediterranean sapropel the youngest eastern mediterranean sapropel s1 is generally believed to have formed 7 9 14c ky b p the distribution of redox sensitive elements above in and below the sharply defined organic rich unit reveal that s 1 has already suffered heavy diagenetic alteration its present thickness based on its dark colour is only a fraction of its original thickness in one core visual evidence of s1 with an inferred initial thickness of 6 cm has been destroyed and a similar thickness appears to have been lost from the tops of another two examples this is caused by oxidation of the upper reaches of s 1 by a progressive oxidation front which commenced 5 2 5 4 14c ky ago and still appears to be active in the three cores studied diagenetic relocation of many redox sensitive elements has occurred most elements expected to be enriched in sapropels or sulphide rich sediments already have maximum concentrations above or below rather than in the present s 1 layers similarities are observed in the geochemical behaviour of as fe and p of co cu mn ni and zn and of cd mo sb ti u and v the behaviour of ba is distinctive and its immobility as barite makes it an indicator for palaeoproductivity and the original high s1 corg content the elements se and i exhibit particularly large sharp concentration peaks and together are proposed as useful indicators of the present boundary between oxic and post oxic conditions

the diagenetic formation of metal rich layers in sapropel containing sediments in the eastern mediterranean two cores recovered from different locations in the eastern mediterranean contain intercalations of organic rich sapropels in organic poor hemipelagic sediments in both cores enrichments of mn and fe were found in the oxidised section of the sediment above the sapropel s1 the sediments followed a diagenetic cycle which began after the sapropel formation finished about 7000 years ago first during a non steady state diagenetic phase metal rich layers were formed at a downward moving oxidation front the front decelerated at the top of the sapropel as a consequence of increasing amounts of corg and sulphides that had to be oxidised during the second part of this non steady state phase the oxidation front starts moving upwards with respect to the sapropel manganese is remobilised in preference to iron due to thermodynamics reinforced by kinetics when the upward movement of the oxidation front becomes equal to the sedimentation rate steady state is established with respect to the new organic poor sedimentary circumstances at location 31g1 the system is at or close to steady state at location 9g1 however this steady state phase has never been reached between 1900 and 1350 years bp the organic carbon accumulation rate probably increased suddenly inducing a retreat of the oxidation front and the non steady state formation of double peaks

combined organic and inorganic geochemical reconstruction of paleodepositional conditions of a pliocene sapropel from the eastern mediterranean sea layers of organic carbon rich sapropels in the sediment record of the mediterranean sea give evidence of repetitive changes in regional plio pleistocene climate results from biomarker molecule and major and trace element analyses of closely spaced samples are used to reconstruct the conditions leading to deposition of a pliocene sapropel at ocean drilling program odp site 969 on the mediterranean ridge organic carbon concentrations increase from 0 2 outside the sapropel and peak to more than 30 within it major and trace elemental composition and biomarker derived parameters indicate elevated productivity depletion of water column dissolved oxygen content and changes in sediment provenance in response to climatic changes budgets of rhenium thallium and other trace metals indicate that deep water exchange between the mediterranean subbasins and the atlantic ocean was not completely interrupted during sapropel formation enrichment factors of redox sensitive and sulfide forming trace metals as well as the presence of isorenieratene derivatives and high stanol sterol ratios point to an extended zone of anoxic water masses depth profiles of biomarker compositions sterols long chain alkenones alkandiols and ketols fatty acids indicate great floral diversity during deposition of a single sapropel and highlight the sensitive response of the marine community to variable environmental conditions changes in water mass circulation and eolian transport can be reconstructed by use of both lithogenic elements and average chain lengths of n alkanes acl index

chemical and isotopic composition of lower to upper ordovician sedimentary rocks central andes south bolivia implications for their source abstract fifty million years of erosional history of the early paleozoic orogen in the central andes are documented in the 12 km thick ordovician siliciclastic sedimentary section from south bolivia transport directions in the north south trending basins allow a distinction between sediment sources from the proterozoic brazilian shield to the east and the early paleozoic mobile belt to the west major and trace element and isotopic nd sr pb compositions of stratigraphically well defined samples of tremadocian to arenigian ages have been studied the element patterns and isotopic composition of the ordovician sedimentary rocks end450 ma 7 5 to 11 87sr 86sr450 ma 0 71 0 72 206pb 204pb450 ma 17 2 18 8 207pb 204pb450 ma 15 60 15 73 208pb 204pb450 ma 36 9 39 1 nd depleted mantle model ages tdm 1 7 2 2 ga are typical of upper crustal felsic rocks which underwent one or more cycles of erosion and deposition the compositional range of the ordovician sedimentary rocks is similar to that of

giant evaporite belts of the neogene central andes large volumes of continental evaporites accumulated within the central andes during neogene uplift of the altiplano puna plateau and development of the andean volcanic arc halite and gypsum are dominant minerals along with local and economically important borates playa conditions have existed since ca 15 ma halite and borate deposition has occurred for the past 7 to 8 m y evaporites formed in salar environments e g playa lakes and are characterized by complex mineral assemblages occurrence zonation and geochemistry evaporite deposition was controlled by volcanism geothermal activity closed drainage and climate these andean deposits and their controls differ from evaporites in other continental and marine environments

the ages and tectonic setting of the faja eruptiva de la puna oriental ordovician nw argentina abstract the ordovician faja eruptiva de la puna oriental is a magmatic predominantly intrusive belt in the puna of northwestern argentina with a n s extension of ca 400 km scarce isotope geochemical ages and biostratigraphic data on some of the folded faja eruptiva country rocks assign the magmatism either to the lower and lower middle ordovician or to the latest ordovician interpretations of origin and tectonic framework of the faja eruptiva are controversial and vary between arc back arc and collisional orogenic settings we present high resolution la icp ms u pb age and hf isotope data on zircons from 10 plutonic samples covering the magmatic belt along a length of 200 km in the northern argentinian puna the xenocrystic and magmatic zircon age data have a wide spread between 2700 ma and 440 ma concordia and weighted mean age data document protracted magmatism in two phases between 480 and 460 ma and between 453 and 444 ma and constrain the time of the last intrusions at 444 3 ma and at 445 2 ma thus defining this last and main phase of intrusion at 444 ma ehf t values define a main vertical trend centered at 500 ma with ehf t values between 3 and 16 indicating significant mixing of juvenile early paleozoic melts with paleoproterozoic crustal components a second trend is formed by zircons with ages between 1 1 ga and c 500 ma and predominantly positive ehf values between 8 and 3 and originates in juvenile mantle compositions between 1 6 and 1 1 ga the spread of the zircon and hf data document that the faja eruptiva intrusives have experienced large scale contamination by the hosting crustal basement it follows that the basement of the puna is formed either by the upper proterozoic lower cambrian puncoviscana formation as an erosional product of the proterozoic orogenic belts of sw amazonia or that the puna including its puncoviscana basement is underlain by a crust shaped by these orogenies the main intrusive event at 444 ma has been linked to the ocloyic orogeny in the late ordovician the plutons intruded very likely in a sinistral strike slip regime after the main folding phase of the ocloyic orogeny had deformed the ordovician sedimentary country rocks

collisional processes in the eastern mediterranean in the eastern mediterranean the collision of the erastosthenes and the anaximander seamounts with the cyprus arc results in a unique tectonic setting due to the small size of the eastern mediterranean basin as a result of the collision some of the motion between the african plate and the eurasian plate is taking place by thrust faulting along the north african passive margin it seems that the stress at the plate boundary along the cyprus arc may be transmitted southward to cause the reactivation of a pre existing fault zone along the passive margin of eastern north africa

pliocene holocene evolution of depositional conditions in the eastern mediterranean role of anoxia vs productivity at time of sapropel deposition a multiproxy geochemical study of nine sapropel layers from odp hole 964a odp leg 160 in the eastern mediterranean spanning the pliocene holocene time interval provides new insights into the evolution of sapropel deposition paleoenvironmental proxies were used for reconstruction of productivity ba derived from marine barite oxygen conditions trace metal ratios and sedimentary regime clay minerals detrital elements these proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition although preservation also played an important role furthermore major differences exist in depositional conditions including both oxygenation and productivity since the pliocene productivity fluctuated substantially and was higher during the pliocene and pleistocene than during the holocene at the same time decreasing oxygen availability parallels the enhanced productivity dysoxic to anoxic conditions appear to coincide with marine productivity maxima thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation this correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability