volcano and climate driven changes in atmospheric dust sources and fluxes since the late glacial in central europe atmospheric dusts are an important part of the global climate system and play an important role in the marine and terrestrial bio geochemical cycles of major and trace nutrient elements a peat bog record of atmospheric deposition shows considerable variation in dust deposition during the past 15 k y with abrupt changes in fluxes at 12 9 2 8 4 7 2 and 6 cal kyr b p using nd isotopes and rare earth elements it is possible to clearly distinguish between volcanic inputs and those driven by climate change such as the long term aridification of the sahara and regional erosion due to forest clearing and soil cultivation activities our results indicate that a major dust event in north africa and europe preceded the 8 2 kyr b p cold event by 200 yr this dust event may have played an active role in the following climate cooling of the 8 2 kyr b p event nd isotope evidence also indicates a relatively slow change in dust regime over europe from 7 to 5 kyr b p due to sahara expansion these fi ndings show that the inorganic fraction in high resolution peat records can provide remarkably sensitive indicators of dust load and sources our study supports the priority to better identify the impact of dust loading during the holocene in terms of direct and indirect impacts on environmental and climate changes

geochemical and mineralogical control of different genetic types of deep sea nodules from the pacific ocean deep sea nodules from the northeast pacific nodule belt and the southeast pacific sonne basin being formed in areas bordering the equatorial zone of high biological productivity accumulate by two basically different growth processes a early diagenetic growth by supply from pore water and b hydrogenetic growth by supply from near bottom sea water these growth processes lead to different genetic types of nodules early diagenetic type a hydrogenetic type b and mixed type ab a further type ac very rich in mn is being formed by increasing influence of early diagenesis these types can clearly be distinguished by their shapes surface textures mineral constituents of oxide fraction internal microstructures and geochemistry a genetical classification is being proposed on the basis of statistically computed interelement relationships todorokite very poor in fe is the main mn phase in the early diagenetic substance mno2 intimately intergrown with feooh xh2o is the main phase in the hydrogenetic substance consequently an important difference can be pointed out the metal supply for the growth of the early diagenetic nodules is based on an ionic solution of me2 e g mn2 ni2 cu2 zn2 whereas the supply for the hydrogenetic nodules is caused by transport of colloidal particles mobilization of mn2 and fractionation from fe is controlled by the amount of decomposing organic matter in the peneliquid layer of the sediments the main factor controlling the intensity of early diagenesis is the biological productivity in surface waters the crucial point of reversal at a mn fe ratio of about 5 obtained by hyperbolical regression of the analyses of nodules from the southeast pacific represents best concentrations in ni and cu mn fe quotients greater than 5 cause a decrease of ni and cu content nodules from the northeast pacific nodule belt generally contain higher concentrations in cu than nodules from the southeast pacific this can be explained by an additional supply of cu transported below ccd by siliceous plankton

central european vegetation response to abrupt climate change at 8 2 ka oxygen isotope records show a major climatic reversal at 8 2 ka in greenland and europe annually laminated sediments from two lakes in switzerland and germany were sampled contiguously to assess the response of european vegetation to climate change ca 8 2 ka with time resolution and precision comparable to those of the greenland ice cores the pollen assemblages show pronounced and immediate responses 0 20 yr of terrestrial vegetation to the climatic change at 8 2 ka a sudden collapse of corylus avellana hazel was accompanied by the rapid expansion of pinus pine betula birch and tilia linden and by the invasion of fagus silvatica beech and abies alba fir vegetational changes suggest that climatic cooling reduced drought stress allowing more drought sensitive and taller growing species to out compete corylus avellana by forming denser forest canopies climate cooling at 8 2 ka and the immediate reorganization of terrestrial ecosystems has gone unrecognized by previous pollen studies on the basis of our data we conclude that the early holocene high abundance of c avellana in europe was climatically caused and we question the conventional opinion that postglacial expansions of f silvatica and a alba were controlled by low migration rates rather than by climate the close connection between climatic change and vegetational response at a subcontinental scale implies that forecasted global warming may trigger rapid collapses expansions and invasions of tree species

characterization of late glacial continental dust in the greenland ice core project ice core twelve glacial dust samples extracted from the greenland ice core project ice core have been characterized in terms of mineralogy sr and nd isotopic composition and rare earth element concentrations the ice samples are taken from the younger dryas the bolling the last glacial maximum and both cold and mild glacial periods back to 44 kyr b p a comparison with samples from possible dust source areas determines eastern asia as being the main source area at all times hereby confirming and extending earlier results biscaye et al 1997 this finding is partly in agreement with recent atmospheric general circulation model simulations of glacial atmospheric dust transport andersen et al 1998 mahowald et al 1999 a low intersample variability in tracer characteristics is discussed in the context of a volcanogenic influence grain size dependence and variability in the conti nental dust source areas the clay mineralogy of the ice core dust shows a weak climatic de pendence while the isotopic composition of sr and nd does not correlate with climate this is interpreted as a geographical variation of source areas on a regional scale within asia two ice dust samples were size fractionated at 2 gm and the grain size dependence on tracer characteristics is in accordance with the literature

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

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

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

cryptomelane a tool to determine the age and the physical chemical regime of a plio pleistocene weathering zone in a granitic terrain hagendorf se germany abstract cryptomelane a k mn bearing oxide is widespread in the lowermost part of the weathering supergene alteration zone of the hagendorf pegmatite se germany this supergene mn mineral has been used in the present study for k ar dating of weathering and paleohydraulic processes as young as plio pleistocene different cryptomelane age data found in the same weathering and paleohydraulic system resulted from continuous hydraulic processes in the weathering system rather than from a stepwise uplift that shaped the landscape in the granitic area of the ne bavarian basement an almost pure cryptomelane mineralization is indicative of the basal zone of supergene alteration because a complete separation of mn from fe can favorably be achieved only in the infiltration zone under slightly reducing conditions or in the percolation zone under slightly oxidizing conditions cryptomelane is precipitated under slightly oxidizing conditions from alkaline solutions in the percolation zone and cast as a marker for fluctuating paleo water levels manganese oxides uranyl phosphates and silicates were found at different depths in the weathering zone of this granitic terrain they were dated by different dating methods k ar and u pb and yielded the same age of formation consequently the 4 ma signal of both groups of supergene minerals has geomorphological and paleohydraulic connotation and is related to a unique geomorphological process the pliocene peneplanation gradual hydraulic adjustments gave rise to the younger pleistocene age found at shallow depth in the weathering zone

pb zn deposits and salt bearing diapirs in southern europe and north africa many diapirs with triassic evaporite successions in southern europe and north africa are accompanied by strata bound pb zn mineral deposits these are of two types 1 epigenetic mineralization filling cavities exhibiting analogies with mississippi valley type deposits and 2 syndiagenetic mineralization in sediments rich in organic materials this second type is very similar to the so called volcanic exhalative type in most of these ore deposits diapirism seems to be a determining factor in the development of base metal concentrations diapir growth can be divided into four distinct stages initiation ascent piercement and subsequent deformation study of north african and southern european deposits has led to a genetic model of diapir emplacement and associated pb zn mineralization the source of these metals is unknown the transport of the metals is provided or facilitated by the brine from adjacent triassic evaporites deposition of sulfides occurs where the deep fluids meet the upper beds these deposits can be remobilized with each new phase of diapir growth

detailed mineralogy and petrology of manganese oxyhydroxide deposits of the imini district morocco manganese ore in the cenomanian turonian dolostone of the imini district south of the high atlas morocco displays a high mn content due to the occurrence of pyrolusite cryptomelane hollandite sensu stricto coronadite romanechite and lithiophorite the orebodies occur mainly as three stratabound layers along the 25 km long ore belt following a wsw ene direction using scanning electron microscopy sem eds coupled with x ray diffraction xrd we here refine the mineralogy and petrology of mn oxides and oxyhydroxides in order to constrain the paragenetic sequence and define the main processes of ore formation deposition and concentration of mn oxyhydroxides follow a two step sequence after dolomitization 1 replacement of dolomite fabric dolomite micrite and dolomite rhombs by hollandite group minerals leading to a textural conservation and then 2 neoformation of collomorphous aggregates in an opened and brecciated system these observations are consistent with a multistage evolution including multiple reworking and brecciation pyrolusite is the main mn oxide observed in the imini district during both early and late stages the superficial environment provides supergene conditions suitable for the deposition of only mn oxyhydroxides this supergene environment and the occurrence of multiple bands of hollandite group minerals indicate an external migration allochthonous supply of mn and associated elements contemporaneous to an in situ chemical and mechanical dissolution of the host dolostone the lithological heterogeneities of dolostone and its chemical environment compared to less permeable surrounding rocks may have provided the conditions to concentrate mn oxides and oxyhydroxides

mixed carbonate siliciclastic record on the north african margin malta coupling of weathering processes and mid miocene climate we investigated rock outcrops spanning the middle miocene global climate cooling step on the maltese islands in order to reconstruct continental weathering rates and terrigenous fluxes as well as to explore the coupling between these later regional climate and carbonate accumulations sedimentation at this location was dominated during the oligocene and early miocene by a transitional platform to slope carbonates but progressively switched to a clay rich carbonate slope system in the middle miocene around 13 ma an abrupt change toward clay dominated marls occurred and marl deposition persisted until the tortonian ca 12 ma when a shallow water carbonate ramp was reestablished clay mineralogy and bulk rock oxygen isotope analyses suggest that the deposition of the blue clay formation was mainly caused by global climate change and related change in the rate of continental weathering a significant negative correlation r 2 0 65 exists between the carbonate content and the 1 8 o record this combined with the variation of mass accumulation rate of terrigenous material suggests that shorter term periods of globally cooler climate mi events were associated with higher rates of accumulation in continental derived material since during the miocene malta was attached to the north african margin we propose that the observed trends were due to a regional increase in rainfall during cooler periods which consequently increased continental weathering and runoff we further suggest that this pattern was linked to the perturbation of atmospheric fronts due to an increased thermal gradient during the miocene thus regional increase in rainfall might have been linked to the northward migration of the intertropical convergence zone itcz

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

the first continuous late glacial holocene peat bog multi proxy record from the dolomites ne italian alps abstract paleoclimate and paleoenvironmental studies in the north eastern italian alps have been hampered by the rarity of well preserved high altitude deposits and the lack of high resolution multi proxy records with adequate chronological control this paper presents the first complete late glacial to holocene peat succession from the dolomites danta di cadore belluno italian alps a 7 m core was used to evaluate the potential of the ombrotrophic val di ciampo peat deposit 1400 m a s l as an archive of environmental and climate change the depth age scale is based upon independent 14 c and 210 pb dates and combined with peat stratigraphy demonstrates that the peat core covers more than 13 200 cal bp extending to the end of the last part of the late glacial bulk density inorganic matter content pore water ph conductivity ca mg ratios and ca sr and ti trends were used to identify changes in trophic conditions through the bog the boundary between ombrotrophic and minerotrophic conditions occurs at approximately 400 cm below the surface and demonstrates that this core is the longest eastern alpine ombrotrophic record yet obtained corresponding to 7000 cal bp the high resolution chemical data of this peat archive improves our understanding of european alpine holocene climate variability and the relationship between natural climate fluctuations and anthropogenic climate change during the present interglacial in the dolomites

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

recent spatial and temporal changes in the stress regime along the southern tunisian atlas front and the gulf of gabes new insights from fault kinematics analysis and seismic profiles tectonic deformations in the southern atlassic front of tunisia saft and the gulf of gabes result from the nubia eurasia convergence this study based on the inversion of geologically determined fault slip vectors presents evidences for spatial and temporal changes in the stress state fault kinematics analyses reveal a temporal change in states of stress during the late cenozoic a paleostress miocene pliocene state is characterized by a regional compressional tectonic regime with a mean n134 09 e trending horizontal maximum stress axis 1 a modern quaternary to present day state of stress also corresponds to compressional tectonic regime with a regionally mean n05 10 e trending horizontal 1 the saft corresponds to two distinct domains a far foreland atlassic front related to contractional deformation associated with southward propagate thrusting and eastward the gulf of gabes characterized by normal component nw to wnw trending faults at the crustal margin scale probably related with a transtensional tectonic regime we propose that the spatial and temporal changes in the stress during the miocene pliocene and quaternary may result from the geodynamic evolution of the tunisian atlas in relation to the rotation of corsica sardinia blocks and the separation of the sicilian continental lithosphere from the ionian oceanic lithosphere these temporal and spatial stress changes along the saft and the gulf of gabes are probably the engine behind the moderate seismicity leading at the same time to a reactivation of the inherited major structures created during the evolution of the southern tethyan margin

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

a 14 500 year record of the accumulation of atmospheric mercury in peat volcanic signals anthropogenic influences and a correlation to bromine accumulation a 14 500 calendar year record of mercury accumulation rates has been obtained from an ombrotrophic peat bog in the swiss jura mountains the range of natural pre industrial mercury accumulation rates varied from 0 3 to 8 0 w gm 32 yr 31 during the late glacial and holocene climatic and volcanic signals were evident in the mercury record mercury accumulation rates increased by a factor of ca 5 during the younger dryas cold period short term spikes in mercury accumulation rates which correspond in time to known volcanic eruptions occur during the late boreal and older atlantic periods when volcanic influences on mercury deposition appear to have been intensified due to increased atmospheric humidity a correlation of mercury to bromine accumulation is observed throughout the preanthropogenic period during the holocene mercury accumulation only exceeded the range of this correlation for a few short periods of elevated mercury deposition which correspond to known volcanic eruptions during the older atlantic during historical times mercury accumulation rates have exceeded the range of the correlation of mercury to bromine continuously since ca 1330 ad this excess in mercury accumulation is interpreted as an indication of pollution during the industrial period mercury accumulation rates reached 107 6 w gm 32 yr 31 of which 84 was mercury that exceeded the correlation range mercury accumulation rates peaked again during the 1970s with 78 8 wg m 32 yr 31 early 20th century pollution appears to have been dominated by non swiss emissions from coal burning whereas swiss mercury emissions appear to have been the dominant pollution source during the mid and late 20th century current mercury accumulation rates at the site are similar to those ca 10 years ago with modern deposition rates being ca 15 times their prehistorical average anthropogenic emissions of reactive brominated compounds could be contributing to increased atmospheric deposition rates of mercury a 2002 elsevier science b v all rights reserved

elevated dust deposition in tierra del fuego chile resulting from neoglacial darwin cordillera glacier fluctuations atmospheric mineral dust is intrinsically linked with climate although dust flux variability on glacial interglacial timescales is well documented holocene dust records remain scarce to fill this gap we conducted elemental isotopic and sedimentological analyses on a peat core from the karukinka natural park in tierra del fuego an 8000 year old mineral dust record was extracted indicating three periods of elevated dust deposition i 8 1 7 4 cal ka bp ii 4 2 cal ka bp and iii 2 4 1 4 cal ka bp the two oldest peaks are related to volcanic eruptions of the hudson and monte burney volcanoes respectively the most recent dust peak however has a rare earth element and neodymium isotopic composition that resembles the geochemical signature of outwash plain sediments from the darwin cordillera since the timing of this dust peak corresponds to a period of glacier retreat between neoglacial advances iii and iv we infer that holocene aeolian dust fluxes in southern patagonia are mostly driven by glacial sediment availability our results underline the important role of glaciers in producing aeolian dust in high latitude regions and they imply that the current retreat of glaciers worldwide may result in elevated atmospheric dust loads

comparative evaluation of the mineralogical composition of sphagnum peat and their corresponding humic acids and implications for understanding past dust depositions abstract with 6 5 m of peat accumulated during the past ca 15 000 years etang de la gruere egr represents the longest continuous record of atmospheric dust deposition in northern hemisphere this paper presents a comparative study of the mineralogical composition of sphagnum peat samples and their corresponding humic acids ha from a peat core collected at egr bog the purpose of this study was to better understand the dominant process responsible for the amount and distribution of mineral matter in ombrotrophic i e rain fed peat specifically the goal was to separate the relative importance of the changing rates of atmospheric mineral dust deposition during the past two millennia from the mineralization of organic matter om for the distribution of the ash fraction of the peat profile the results suggest that variations in ash content at egr are mainly the result of an increase in the rate of supply of dust particles and cannot be attributed simply or exclusively to differences in the degree of om decay evidence is provided by both acid insoluble ash aia profiles and the correlations among lithogenic elements al si ti y and zr total ash content and aia moreover our findings suggest that part of the aia occurring in peat extremely is stable and is unaffected by the extreme chemical conditions used to extract the ha fraction this may be partly due to the inherent stability of quartz and heavy minerals such as zircon and rutile but organic coatings developed on mineral surfaces during peat diagenesis or the formation of some other kind of organo mineral complex might also play a role consequently testimonies of past dust depositions can be observed also into the recalcitrant ha fraction of the peat

gravity and aeromagnetic constraints on the extent of cenozoic volcanic rocks within the nefza tabarka region northwestern tunisia bouguer gravity and aeromagnetic data are analyzed to determine the extent of miocene magmatism in the nefza and tabarka regions of northwestern tunisia construction of magnetic intensity and enhanced analytic signal eas maps indicated the existence of at least two regions containing probable subsurface igneous bodies that correlate to the small scattered igneous outcrops in the nefza and tabarka regions because of the lack of lateral resolution of the eas techniques 3 d magnetic and 2 5 d gravity models were constructed over the anomalies at nefza and tabarka the final models indicate that the maximum depths of the igneous bodies are between 2 5 and 2 7 km with maximum widths between 15 and 22 km the final models also indicate that the bodies are tabular with a combination of laccolithic and lopolithic shapes and were probably emplaced in the shallow levels of the crust at least 3 km these widths greatly expand the region of known miocene magmatism in northwestern tunisia combined with geochemical and petrological data of the surface volcanic rocks the gravity and magnetic models imply a wider range of miocene volcanic activity in northern tunisia probably related to a subduction zone

geochemistry and origin of mn deposits in the waziristan ophiolite complex north waziristan pakistan the waziristan ophiolite complex is located along the western margin of the indian plate in northwestern pakistan the mn deposits in the saidgi and shuidar areas are part of this ophiolite complex these deposits both banded and massive in nature are hosted by metachert and are generally overlying metavolcanics braunite and cryptocrystalline quartz are the main constituents of the manganese ores in both areas hematite occurs in the shuidar deposits as a minor phase metacherts are microcrystalline aggregates of microcrystalline quartz chalcedony and lesser hematite chemically the studied mn deposits and associated metacherts are very similar to those formed by submarine hydrothermal effusive processes the deposits originated along sea floor spreading centers mid ocean ridges within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

diffuse flow hydrothermal manganese mineralization along the active mariana and southern izu bonin arc system western pacific 1 abundant ferromanganese oxides were collected along 1200 km of the active izu bonin mariana arc system chemical compositions and mineralogy show that samples were collected from two deposit types fe mn crusts of mixed hydrogenetic hydrothermal origin and hydrothermal mn oxide deposits this paper addresses only the second type mn oxides cement volcaniclastic and biogenic sandstone and breccia layers mn sandstone and form discrete dense stratabound layers along bedding planes and within beds stratabound mn the mn oxide was deposited within coarse grained sediments from diffuse flow systems where precipitation occurred below the seafloor deposits were exposed at the seabed by faulting mass wasting and erosion scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 a and 7 a manganate minerals the fundamental chemical difference being high water contents in the amorphous mn oxides alternation of amorphous and crystalline laminae occurs in many samples which likely resulted from initial rapid precipitation of amorphous mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages the chemical composition is characteristic of a hydrothermal origin including strong fractionation between fe mean 0 9 wt and mn mean 48 wt for the stratabound mn generally low trace metal contents and very low rare earth element and platinum group element contents however mo cd zn cu ni and co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits for the mn sandstones fe mean 8 4 and mn 12 4 are not significantly fractionated because of high fe contents in the volcaniclastic material however the proportion of hydrothermal fe nondetrital fe to total fe is remarkably constant 49 58 for all the sample groups regardless of the degree of mn mineralization factor analyses indicate various mixtures of two dominant components hydrothermal mn oxide for the stratabound mn and detrital aluminosilicate for the mn cemented sandstone and two minor components hydrothermal fe oxyhydroxide and biocarbonate biosilica our conceptual model shows that mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along the flanks and within calderas the main source of hydrothermal fluid was seawater that penetrated through fractures faults and permeable volcanic edifices the fluids were heated by magma enriched in metals by leaching of basement rocks and sediments and mixed with magmatic fluids and gases dikes and sills may have been another source of heat that drove small scale circulation within sedimentary prisms

diagenetic constraints on the use of cerium anomalies as palaeoseawater redox proxies an isotopic and ree study of cambrian phosphorites seawater rare earth element ree distributions show heavy ree enrichment and cerium depletion but these characteristics are only rarely found in ancient marine authigenic minerals such as carbonate fluorapatite and calcite this enigma may be due to changing ree distributions in seawater through time or to post depositional redistribution of ree differentiating between these two factors is however far from straightforward as their relative importance is likely to vary and evidence is often ambiguous in this article we present ree as well as strontium and sulphur isotope data for basal cambrian phosphorites of south china which confirm the emerging rule of thumb that granular phosphorites seldom reveal extreme departures from the seawater norm and tend to undergo therefore less diagenetic alteration of ree spectra than skeletal apatites and other phosphate types this study reveals stratigraphic trends in ce anomalies ce ce that could be taken to imply the preservation of a palaeoenvironmental signal however further investigation of our data shows that such trends in phosphorites can also be caused by post depositional alteration which tends to 1 increase ree contents 2 reverse ce depletion 3 alter eu anomalies and 4 concentrate preferentially the middle ree mree further alteration which may be due to weathering has led to hree depletion and positive la and y anomalies tetrad effect this is the first study where ceanom and phosphate bound sulphate s isotope values could be compared for one particular stratigraphic section which provides us with an additional tool for the interpretation of diagenetic redox conditions least altered phosphorites from meishucun that yield a strongly negative ceanom constrain early cambrian seawater 34s to about 33 we conclude that phosphorite ceanom primarily records variations in the local conditions of diagenesis while outlining some special cases in which diagenetic redox conditions may broadly reflect local bottom water redox conditions

deciphering human climate interactions in an ombrotrophic peat record ree nd and pb isotope signatures of dust supplies over the last 2500 years misten bog belgium abstract a high resolution peat record from eastern belgium reveals the chronology of dust deposition for the last 2500 years ree and lithogenic elements in addition to nd and pb isotopes were measured in a 173 cm age dated peat profile and provide a continuous chronology of dust source and intensity calculated dust flux show pronounced increases c 300 bc 600 ad 1000 ad 1200 ad and from 1700 ad corresponding to local and regional human activities combined with climate change the industrial revolution samples 1700 1950 ad are characterised by a significant enrichment in sc normalised ree abundance sum ree sc 25 due to intensive coal combustion for the pre industrial revolution samples the sc normalised ree abundance 10

manganese ores in tunisia genetic constraints from trace element geochemistry and mineralogy abstract northern and central tunisia hosts few small scale stratiform and stratabound mn deposits low to medium in grade mn

rapid atmospheric co2 changes associated with the 8 200 years b p cooling event by applying the inverse relation between numbers of leaf stomata and atmospheric co2 concentration stomatal frequency analysis of fossil birch leaves from lake deposits in denmark reveals a century scale co2 change during the prominent holocene cooling event that occurred in the north atlantic region between 8 400 and 8 100 years b p in contrast to conventional co2 reconstructions based on ice cores from antarctica quantification of the stomatal frequency signal corroborates a distinctive temperature co2 correlation results indicate a global co2 decline of 25 ppm by volume over 300 years this reduction is in harmony with observed and modeled lowering of north atlantic sea surface temperatures associated with a short term weakening of thermohaline circulation

introduction to and classification of manganese deposits of china abstract manganese mn ore deposits are widely distributed in china and can be divided into six types based on origin and subsequent modifications 1 sedimentary 2 volcanic sedimentary 3 metamorphosed 4 hydrothermally modified 5 hydrothermal and 6 supergene sedimentary and supergene mn ore deposits are economically the most important mn ore deposits and ore bearing sequences are distributed temporally from the proterozoic through the quaternary but they principally are middle proterozoic sinian cambrian ordovician devonian carboniferous permian triassic and quaternary ages the largest mn metallogenic periods in china are sinian and devonian in contrast to the widespread proterozoic cretaceous and oligocene mn deposits found elsewhere in the world mn bearing stratigraphic successions in china can be divided into six types of lithologic associations 1 black shale series 2 chert mudstone limestone 3 carbonate 4 mudrock carbonate 5 volcanic sedimentary and 6 epeirogenic clastic rock types the most important mn metallogenic regions in china are 1 yanliao 2 border of hunan sichuan guizhou hubei provinces 3 southern shaanxi and northeastern sichuan 4 middle guizhou and eastern yunnan 5 southwestern guangxi 6 southeast yunnan 7 hunan guangxi guangdong fujian and 8 xinjiang the most striking characteristics of mn ore deposits in china are the wide distribution in geological ages and variety of compositional types of ores such as fe mn b mn p mn co mn ca mn ca mg mn among others the primary mn ores of china are mainly mn carbonates

disentangling dust and sand deposition using a peat record in ce europe northern romania a multiproxy approach abstract aeolian sediments play an important role in the global climatic system and occur in the atmosphere due to soil and bedrock erosion here we applied three different methods geochemical xrf manual and laser based particle size analysis to an ombrotrophic peat profile in the carpathian mountains to determine changes in aeolian deposition and wind storm activity over the last 7800 years the results show the following changes in aeolian fluxes dust and sand over time 7800 4150 cal yr bp generally low dust fluxes with a periodic intensification of sand fluxes 4150 2300 cal yr bp intense deposition of both dust and sand 2300 150 cal yr bp fluctuating dust and sand fluxes the last 200 years the highest amplitude of both sand and dust fluxes this study found that patterns in aeolian fluxes were influenced by a combination of climate and human impact but with anthropogenic drivers such as disturbance by fire becoming more important in recent times we also found a good agreement with other studies of dust fluxes for the earlier part of this record but an increasing divergence over the last 3500 years in terms of a methodological approach we suggest that the three approaches each have both advantages and disadvantages though overall laser based particle size dust and sand reconstruction appears to best capture the most complex changes in both aeolian deposition rates and sources

sequential leaching of marine ferromanganese precipitates genetic implications abstract sequential leaching experiments were carried out on twenty one hydrogenetic crust samples from different locations in the central pacific and the results are compared with four crust and nodule samples of different genetic origin fe vernadite mno2 is the most important minor and trace metal bearing mineral phase and shows high concentrations of co ni cd ti ba zn and cu which are present in seawater mainly as hydrated and labile complexed cations elements forming carbonate and hydroxide complexes and oxyanions in seawater like pb mo v and minor proportions of cu and zn are bound in the fe00h fraction the ca carbonate phase and the residual fraction which consists of aluminosilicates and crystalline oxides show only minor heavy metal associations e g cu and zn only a small part of the high ti concentrations in hydrogenetic crusts is of detrital origin ti mainly forms a hydrogenetic phase probably consisting of ti02 2h20 intergrown with the amorphous fe00h phase analyses of different sample types and crust layers show that aging and diagenetic effects can change the phase associations of some elements the most notable change was observed for pb which during phosphatization of crusts is transferred from the mn fe oxide fraction to the apatite fraction a colloid chemical model for the hydrogenetic precipitation of ferromanganese crusts on seamounts is proposed in the first stage mn2 rich water from the oxygen minimum zone is mixed with oxygen rich deep water and oxidized mn iv and other metals like fe ti al and si form oxide and hydroxide colloids these form mixed colloidal phases and scavenge trace metals by sorptive processes which are dominated by coulombic and chemical interactions between colloid surfaces and dissolved metal species in stage two the colloidal phases precipitate on the substrate rocks of the seamounts as ferromanganese oxide encrustations incorporating the sorbed heavy metals into the mineral phases

a peat bog record of natural pre anthropogenic enrichments of trace elements in atmospheric aerosols since 12 370 14 c yr bp and their variation with holocene climate change abstract a peat bog in the jura mountains switzerland provides a continuous record of peat accumulation since 12 370 14 c yr bp periods of enhanced soil dust deposition 10 590 14 c yr bp 8230 14 c yr bp and after 5320 14 c yr bp are characterized by strongly elevated ti sc and zr sc ratios which imply an increase in the abundance both relative and absolute of heavy minerals such as ilmenite and zircon with respect to trace elements such as cu zn as cd sb and au the m sc ratios are at their lowest and often approach crustal values during periods of enhanced soil dust deposition the lowest rates of atmospheric deposition of soil dust date from 8030 to 5320 14 c yr bp corresponding to the holocene climate optimum but here many trace elements exhibit their greatest natural enrichments the average enrichment factor calculated using sc as the reference element and normalizing to crustal abundance was zn 4 1 1 4 sb 4 8 1 4 cu 8 8 3 3 as 14 9 3 2 au 53 9 25 1 and cd 357 4 53 8 these enrichments cannot be explained by chemical diagenesis within the deeper sections of the peat profile during or subsequent to peat formation but rather reflect the chemical composition of airborne material supplied to the surface layers of the bog at the time of deposition the enrichments of trace metals in ancient peats relative to crustal abundance most likely reflects the natural enrichment of these elements in the fine fraction of soils during rock weathering periods of enhanced soil dust deposition such as the younger dryas cold climate phase 10 590 14 c yr bp are characterized by reduced vegetation cover greater exposed soil surface and higher wind strengths these conditions promote the transport of locally derived soil materials of greater particle size lower concentration of trace metals and m sc ratios approaching crustal values during the holocene climate optimum vegetation cover was extensive and with lower wind strengths and a reduction in erodible soil materials long range transport of soil dust became relatively more important to the soil dust inventory of the bog soil dust particles in this size class are characterized by strong enrichments of a wide range of trace elements at the end of the holocene optimum dust fluxes increased once again due mainly to soil erosion resulting from the combined effects of human activities tillage and the climatic deterioration at the beginning of the neoglaciation period this promoted the supply of local more coarse soil particles with m sc ratios approaching those of crustal rocks while biological cycling and volcanic emissions probably also contributed to the atmospheric supply of many of these elements in the pre anthropogenic past these contributions appear to be less important than the chemical weathering physical fractionation and atmospheric transport of soil dust particles

geochemical characterization ree nd and pb isotopes of atmospheric mineral dust deposited in two maritime peat bogs from the st lawrence north shore eastern canada dust deposited on two ombrotrophic peat bogs baie and idh bogs of the st lawrence gulf and estuary north shore quebec was geochemically characterized using rare earth element ree concentrations nd and pb isotopes along with particle grain size both cores display similar nd values which suggests either a common source or sources with similar signatures in both regions combining nd isotope data with ree patterns and particle size allowed for better insights into the source of deposited dust and the inference of past environmental and climatic conditions in both regions rees nd and grain size distribution suggest that over the last 2000 years the baie bog received more local dust due to increased local storminess in response to greater regional hydroclimatic variability the same phenomenon occurred in the idh bog since 620 cal a bp i e during the little ice age where hydroclimatic and paleoecological changes have been previously documented while the dust reconstructions and regional climatic records agree relatively well the discrepancies between paleodust records highlight the complex and variable structure of late holocene changes in paleoclimate and more particularly past dust deposition in eastern canada

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite abstract rare earth element concentrations in biogenic apatite of conodonts fish debris and inarticulate brachiopods were determined in over 200 samples from cambrian to modern sediments tests for experimental bias caused by the chemicals used to separate fossils from the rock matrix and for interlaboratory interexperiment or interspecies related variations clearly show that no resolvable fractionation of ree occurs incorporation of ree in biogenic apatite of recent fish debris occurs near the sediment water interface soon after deposition and reflects characteristics of seawater the original ree signature apparently survives subsequent burial and diagenesis cerium variations in fish debris from modern environments are controlled by redox potential ce is fractionated by co precipitation with metallic oxides under oxidizing conditions this fractionation produces a negative ce anomaly ce anom in seawater that is reflected in the sedimented fish debris conversely no fractionation of ce occurs under reducing conditions resulting in ce concentrations that are normal to enriched in anoxic seawater and fish debris deposited under local or basinwide anoxic conditions extrapolation of observations of the redox control of ce anom in modern oceans to fossil apatite indicates that anoxic conditions were prevalent in lower paleozoic and lower triassic oceans whereas in the upper paleozoic the world ocean was generally oxidizing

the influence of suboxic diagenesis on the formation of manganese nodules in the clarion clipperton nodule belt of the pacific ocean abstract polymetallic nodules and a single fe mn crust from the clarion and clipperton zone ccz of the equatorial eastern pacific have been analyzed to determine their chemical and mineralogical compositions icp oes analyses of bulk nodules from the ccz indicate that the nodules formed under oxic diagenetic conditions with typical mn fe ratios of 4 6 ni cu values of 2 3 wt co contents of 0 12 0 17 wt however detail analyses of individual growth layers by electron microprobe analyses empa reveal much larger chemical heterogeneity of individual layers with mn fe ratios ranging from 800 two different genetic types of layers can be distinguished layer type 1 dense layer with average mn fe ratios of 1 80 average ni cu of 0 81 wt co contents of 0 30 wt hydrogenetic metal precipitation from oxic waters these layers consist of fe vernadite mno2 epitaxially intergrown with feroxyhyte feooh nanoparticles layer type 2 growth structures dendritic growth structures and dense layers with average mn fe ratios of 96 ni cu of 3 9 wt co contents of 0 08 wt and a distinct ni cu maximum of 6 51 wt at a mn fe ratio of 56 suboxic diagenetic metal precipitation from suboxic pore waters type 2 layers mainly consist of turbostratic phyllomanganates such as 10 a vernadite 7 a vernadite and todorokite are minor compounds mixed layer type 3 these layers can occur as zones of low reflectivity in the transition from layer type 1 to 2 or build up inhomogeneous growth structures of nm thin layers of low or high reflectivity the mn fe ratios of this material range between 3 and 11 ni cu of 1 4 6 wt and co contents are between 0 02 and 0 77 wt in most cases these growth structures represent a mixture of type 1 and 2 layers x ray photoelectron spectroscopy xps of the recent outermost nm layers of nodules top rim and bottom side indicates hydrogenetic accretion processes under recent oxic conditions both from seawater and pore water the mixed type ccz nodules are interpreted to consist of an oxic hydrogenetic and a suboxic diagenetic end member calculations of the proportions of the individual layer end members show that suboxic layers make up about 50 60 of the chemical inventory of the ccz nodules whereas oxic hydrogenetic layers comprise about 35 40 the remaining part 5 10 consists of incorporated sediment particles occurring along cracks and pores these results demonstrate that suboxic conditions alternate with oxic conditions during the growth of nodules in the eastern ccz this is probably due to fluctuating bioproductivity in the equatorial pacific surface waters during glacial interglacial periods which led to changing organic carbon flux to the sediment and changing oxygen consumption in near surface sediments furthermore reduced ventilation of the deep ocean during glacial periods may have led to suboxic conditions in near surface sediments our investigations prove that bulk chemistry data of whole nodules only provides an average of individual layers that build up the nodules and is inappropriate for genetic interpretation

variation of thermal conductivity and heat flux at the earth s core mantle boundary the two convective systems that dominate earth s internal dynamics meet at the boundary between the rocky mantle and metallic liquid core energy transfer between processes driving plate tectonics and the geodynamo is controlled by thermal conduction in the lowermost mantle d we use atomic scale simulations to determine the thermal conductivity of mgsio3 perovskite and post perovskite under d conditions and probe how these two convective systems interact we show that the thermal conductivity of post perovskite 12 w mk is 50 larger than that of perovskite under the same conditions 8 5 w mk and is anisotropic with conductivity along the a axis being 40 higher than conductivity along the c axis this enhances the high heat flux into cold regions of d where post perovskite is stable strengthening the feedback between convection in the core and mantle reminiscent of the situation in the lithosphere there is potential for deformation induced texturing associated with mantle convection to modify how the mantle is heated from below we test this by coupling our atomic scale results to models of texture in d and suggest that anisotropic thermal conductivity may help to stabilise the roots of mantle plumes over their protracted lifetime

petrography mineralogy and geochemistry of the late eocene oolitic ironstones of the jebel ank southern tunisian atlas abstract the oolitic ironstones ore deposit of jebel ank central tunisia is a simply folded stratiform ore body of about 2 5 8 m thickness located in the upper part of the epicontinental souar formation late eocene and is covered by the continental segui formation mio pliocene the deposit contains about 20 mt of ore with an average grade of 50 fe generally oolitic iron deposition occurs in shallow water lagoonal environments the jebel ank deposit lies between two regional disconformities late eocene and miocene and is evidence of a transitional stage at the end of regional regression before renewed transgression the footwall of the oolitic iron ore bearing bed consists of a fine grained sandstone bed 10 20 cm thick pinching out laterally westward into green clays the hanging wall is composed of thin bedded limestone and clay alternations 2 3 5 m thick iron occurs in the form of cryptocrystalline goethite with limited al fe substitution the goethite contains around 48 fe 5 al and up to 1 5 p jarosite alunite and manganese minerals cryptomelane psilomelane and manjiorite are supergene secondary minerals probably related to descending surface fluids these manganese minerals occur as accessory minerals with the goethite and are most abundant at the lowermost part of the succession showing varied morphologies local cement space filling and free centimeter sized nodules fe oolites in the deposit are similar to those documented in many other oolitic ironstone deposits the dominant fe oolite type 90 has a concentrically laminated cortex with no nucleus the nuclei of the oolites that do have a nucleus are most commonly detrital quartz grains major elements in high grade samples fe 2 o 3 65 vary within a limited range and show higher concentrations of sio 2 average 7 85 and al 2 o 3 average 5 1 with minor tio 2 mno mgo na 2 o k 2 o and so 3 less than 1 paas normalized trace elements of bulk samples and fe oolite generally show similar behavior both are enriched in v co ni mo as zn and y and are depleted in cu rb zr nb ba and hf anomalous v cr ni zn and ree y are correlated with goethite paas normalized ree y patterns of both bulk samples and fe oolite show slight hree enrichment positive ce with negative y anomalies the mineralogy goethite and cryptomelane along with the geochemistry si vs al as cu mo pb v zn vs ni co binary plots zn ni co triangular diagram ree y content and patterns and ce ce vs nd and ce ce vs y n ho n binary plots of the studied oolitic ironstone are congruent with a hydrogenetic type while two possible sources of iron for jebel ank ironstone can be proposed i submarine weathering of glauconite rich sandstone and ii detrital iron from adjacent continental hinterland the later is the more plausible source of iron based on paleogeographic setting the occurrence of fine sandstone underlying the iron level occurrence of mn ores in the lower part of the fe ores succession high phosphorous zinc ree y concentrations and y ho ratios and low la ce ratios

manganese nodules in the miocene bahia inglesa formation north central chile petrography geochemistry genesis and palaeoceanographic significance abstract manganese nodules recovered from two stratigraphic horizons of tortonian messinian late miocene age in the bahia inglesa formation of north central chile were studied using xrd sem and geochemical analysis the dominant mineral in the nodules is todorokite which suggests a diagenetic marine environment this is supported by field observations of nodules replacing ophiomorpha burrows preliminary traditional statistical analysis of the nodule geochemistry including single element binary and ternary ratios suggests that the nodules are of the supergene deep marine type as also indicated by the presence of foraminifers typical of the upper continental slope as well as debris flow and turbidity current deposits in an associated submarine palaeocanyon however abnormally low cu concentrations seem to contradict this interpretation so that additional analyses were carried out this included multiple discriminant analysis mda as well as a new technique applied for the first time to manganese nodules namely artificial neural network analysis ann in both methods central log ratio clr normalization was applied to the raw data the results in particular those of the ann analysis suggest that the bahia inglesa nodules present a chemical signature distinct from that of nodules described to date a new class is therefore proposed namely supergene intermediate marine partially restricted basin

genesis of ferromanganese crusts from the tag hydrothermal field the rare earth element ree geochemistry and nd isotopic composition of marine ferromanganese crusts allow insight into their environment of deposition we present ree along with major and trace element data from a suite of samples collected near an active hydrothermal site from the mid atlantic ridge and demonstrate extreme ree variability over short spatial scales both positive and negative ce anomalies are observed along with varied fractionation of the rees some of the fe mn crusts are formed directly from low temperature hydrothermal fluids channelled over 3 km from any high temperature vent site a significant hydrothermal component is observed in one fe mn crust sampled other samples collected from the same area are predominantly hydrogenous and form at a wide range of accumulation rates depending on the hydrothermal plume input the identification of extreme heterogeneity in source and depositional environment within one hydrothermal field suggests that 1 this variability can be resolved both spatially and temporally within a fossil hydrothermal deposit and 2 the integrated record provided by bulk analysis should be interpreted with caution

lake belau and its catchment northern germany a key archive of environmental history in northern central europe since the onset of agriculture the environmental history since the onset of agriculture was reconstructed from sediments and soils in the catchment area of lake belau schleswig holstein northern germany the established chron

genetic diversity of manganese deposition in the terrestrial geological record terrestrial manganese deposits formed by hydrothermal sedimentary and supergene processes ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction related settings and those deposited from terrestrial hot springs are discussed sedimentary mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea level changes mn carbonate deposits probably formed by diagenesis through mn oxyhydroxide reduction coupled with organic matter oxidation climatic variation and basin water stratification responsible for mn concentration were manifestations of atmospheric coz content prompted by tectonism supergene manganese enrichment in continental weathering profiles was mainly dictated by climate topography and drainage systems manganese deposits of diverse genetic types occur in the terrestrial geological record roy 1981 these were produced by direct hydro thermal activity sedimentary processes and continental weathering although the processes may be interrelated each involves distinct mechanisms that place the deposits into specific genetic types some of these processes are best understood in preset day depositional sites the ancient environments were determined by the intensity and style of tectonism volcanism and hydrothermal activity the composition of the atmosphere and the hydrosphere and the development of the biosphere which all varied with time it is my intention to unfold the total panorama of the environmental evolution during different time envelopes that produced a variety of manganese deposits in the past only major deposits and those providing distinctive evidence of their environment of deposition will be considered here

contrasting mineralogical geochemical signatures of manganese oxides guides to metallogenesis manganese oxides have a strong sorption capacity for cationic species in the depositional fluid this sorption capacity is reflected in the chemistry of the oxides which is different from that for the oxides precipitated from fresh water seawater and hydrothermal fluids characteristic mineralogical geochemical enrichment and geochemical association defined statistically signatures in conjunction with several diagnostic plots can be employed to distinguish between the following different genetic types of manganese deposits supergene hydrothermal supergene marine terrestrial supergene dubhite and supergene marine hydrothermal sedimentary exhalative sedex dubhites are manganese oxides derived from the weathering of a mineralized sequence i e base and precious ore minerals and gangue hydrothermal deposits characteristically show geochemical enrichments in the assemblage as ba cu li mo pb sb sr v zn and an mn as geochemical association supergene marine deposits show na k ca mg sr and co cu ni geochemical enrichments whereas supergene terrestrial deposits tend to have very high ba contents and an mn ba association dubhites contain high levels of pb and zn show an mn pb base metal association and are composed of significant quantities of base metal bearing manganese oxides bixbyite braunite hausmannite huebnerite jacobsite and pyrochroite occur predominantly only in hydrothermal deposits whereas chalcophanite coronadite crednerite delta mno 2 groutite hollandite lithiophorite manganite nsutite quenselite ramsdellite romanechite todorokite and woodruffite are generally of supergene origin in addition to established plots presently used to identify marine sedimentary exhalative deposits the following diagnostic graphs were devised na vs mg distinguishes deposits of marine and fresh water origin co ni vs as cu mo pb v zn discriminates between hydrothermal and supergene oxides and pb vs zn can be used to recognize dubhites and therefore prospective sequences

deep ocean mineral deposits as a source of critical metals for high and green technology applications comparison with land based resources abstract ferromanganese fe mn crusts are strongly enriched relative to the earth s lithosphere in many rare and critical metals including co te mo bi pt w zr nb y and rare earth elements rees fe mn nodules are strongly enriched in ni cu co mo zr li y and rees compared to fe mn crusts nodules are more enriched in ni cu and li with subequal amounts of mo and crusts are more enriched in the other metals the metal ions and complexes in seawater are sorbed onto the two major host phases feo oh with a positively charged surface and mno 2 with a negatively charged surface metals are also derived from diagenetically modified sediment pore fluids and incorporated into most nodules seafloor massive sulfides sms especially those in arc and back arc settings can also be enriched in rare metals and metalloids such as cd ga ge in as sb and se metal grades for the elements of economic interest in sms cu zn au ag are much greater than those in land based volcanogenic massive sulfides however their tonnage throughout the global ocean is poorly known and grade tonnage comparisons with land based deposits would be premature the clarion clipperton fe mn nodule zone ccz in the ne pacific and the prime fe mn crust zone pcz in the central pacific are the areas of greatest economic interest for nodules and crusts and grades and tonnages for those areas are moderately well known we compare the grades and tonnages of nodules and crusts in those two areas with the global terrestrial reserves and resources nodules in the ccz have more tl 6000 times mn te ni co and y than the entire global terrestrial reserve base for those metals the ccz nodules also contain significant amounts of cu mo w li nb and rare earth oxides reo compared to the global land based reserves fe mn crusts in the pcz have significantly more tl 1700 times te 10 times more co and y than the entire terrestrial reserve base other metals of significance in the pcz crusts relative to the total global land based reserves are bi reo nb and w ccz nodules and pcz crusts are also compared with the two largest existing land based ree mines bayan obo in china and mountain pass in the usa the land based deposits are higher grade but lower tonnage deposits notably both land based deposits have

diapirism in northern tunisia abstract the diapirs of northern tunisia composed mainly of evaporitic triassic material are the result of a complex evolution initiated by local basement movements of nne ssw faults which at the end of the early cretaceous this first uplift occurring during a period without any folding of the sedimentary series is purely halokinetic such diapiric activity remained in active progress throughout the cretaceous and early tertiary causing local disturbance in the related series and then during the alpine atlas orogeny the diapiric structures underwent deformation according to their position in the orogenic area

coal derived rates of atmospheric dust deposition during the permian despite widespread evidence for atmospheric dust deposition prior to the quaternary quantitative rate data remains sparse as dust influences both climate and biological productivity the absence of quantitative dust data limits the comprehensiveness of models of pre quaternary climate and biogeochemical cycles here we propose that inorganic matter contained in coal primarily records atmospheric dust deposition to test this we use the average concentration of inorganic matter in permian coal to map global patterns and deposition rates of atmospheric dust over pangea the dust accumulation rate is calculated assuming permian peat carbon accumulation rates in temperate climates were similar to holocene rates and accounting for the loss of carbon during coalification coal derived rates vary from 0 02 to 25 g m 2 year 1 values that fall within the present day global range a well constrained east west pattern of dust deposition corresponding to expected palaeoclimate gradients extends across gondwana with maximum dust deposition rates occurring close to arid regions a similar pattern is partially defined over the northern hemisphere patterns are consistent with the presence of two large global dust plumes centred on the tropics the spatial patterns of dust deposition were also compared to dust cycle simulations for the permian made with the community climate system model version 3 ccsm3 key differences between the simulations and the coal data are the lack of evidence for an antarctic dust source higher than expected dust deposition over n and s china and greater dust deposition rates over western gondwana this new coal based dust accumulation rate data expands the pre neogene quantitative record of atmospheric dust and can help to inform and validate models of global circulation and biogeochemical cycles over the past 350 myr

multistage genesis of the late cretaceous manganese karst hosted tasdremt deposit high atlas morocco the eastern part of the souss basin morocco contains several mn deposits in the tasdremt district three mn orebodies occur within the cenomanian turonian dolostones and the senonian coniacian to maastrichtian detrital series the main orebody being located at the boundary between them the mn ores consist of coronadite group minerals mostly coronadite and hollandite in a karstified dolostone new field observations petrographic analyses and geochemical data define the tasdremt deposits as a karst hosted accumulation 11 60 wt mn particularly enriched in ba 1 5 8 2 wt and pb 1 0 5 0 wt with poor contaminations in al fe and p this study shows that the ore forming process is similar to that occurring in the imini c3 level located 100 km to the north east such similarities with the high grade pyrolusite bearing ore suggest that the tasdremt deposit is a lateral equivalent of the imini deposits however the scarcity of pyrolusite in tasdremt results in lower mn grades the tasdremt ores being considered an aborted incomplete system in comparison with the imini deposits 40ar 39ar geochronology of k bearing mn oxides yields late cretaceous ages defining three phases at 91 5 ma 77 5 82 ma and 65 67 ma although the source of metals remains hypothetical mineralizing fluids were carried by o2 free groundwater that mixed with o2 rich shallow meteoric waters at the tasdremt depositional site the dissolution of the host dolostones and the karst environment have provided suitable conditions for the precipitation of mn oxides causing the coeval increase of ph and eh respectively the early atlasic deformation during the late cretaceous is associated with mineralization events and was responsible for creation of low stand reliefs from tasdremt to imini this period enabled karstification and mineralization connecting the tasdremt deposits to other african mn deposits is difficult since the latter consist of laterite resting above paleoproterozoic mn protores and consequently formed under different conditions from karst hosted deposits it is likely that other mn occurrences formed along the atlas belt in similar settings

late holocene atmospheric dust deposition in eastern canada st lawrence north shore dust deposition in two ombrotrophic peatlands baie and ile du havre peatland idh bogs of the estuary and gulf of the st lawrence in eastern canada was reconstructed using elemental geochemistry the rare earth elements rees and other lithogenic element concentrations were measured by icp oes and q icp ms along two peat cores spanning the last 4000 years principal component analyses on the geochemical profiles show that rees display the same behavior as al ti sc and zr all conservative elements which suggests that rees are immobile in the studied peat bogs and can be used as tracers of dust deposition plant macrofossils were also used to infer past environmental and humidity changes the dust fluxes were reconstructed using the sum of rees ree the range of dust deposition varies from 0 2 to 3 8 g m 2 yr 1 in the baie bog while the idh bog shows lower fluxes ranging between 0 1 and 1 2 g m 2 yr 1 the highest dust fluxes in the baie bog were recorded from 1750 1000 cal bp to 600 100 cal

stepwise holocene aridification in ne africa deduced from dust borne radiogenic isotope records abstract transfer of tropical heat to higher latitudes is the major driving force of the earth s climate consequently sediments in regions to the north and south of the tropics potentially retain an archive of past major climate reconfigurations the climate of one such region around the arabian sea sensitively depends on the coupled asian and african monsoons that also control the dust transport here we use the sr nd isotope ratios of the dust fraction from core 905 arabian sea off somalia as a novel tool to deduce the holocene weathering history of the horn of africa with emphasis on the climate transition that took place from a wet early to a dry late holocene the highly variable sr isotope ratios are interpreted to reflect mainly changes in the evaporation precipitation balance over ne africa whilst the nd isotope measurements record no significant variations and point to a prevailing ne african dust source the sr isotope record shows that the first aridification step occurred at 8 5 kyr bp followed by an unstable transitional period up to 6 kyr bp characterized by decadal scale high amplitude variations in the evaporation precipitation balance a second aridification step began at 6 kyr bp and ceased at 3 8 kyr bp when modern day dry climate was established the combined sr and nd isotope records probably reflect north south shifts of the intertropical convergence zone controlling the evaporation precipitation balance over ne africa

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

potentials and problems of building detailed dust records using peat archives an example from store mosse the great bog sweden mineral dust deposition is a process often overlooked in northern mid latitudes despite its potential effects on ecosystems these areas are often peat rich providing ample material for the reconstruction of past changes in atmospheric deposition the highly organic up to 99 in some cases matrix of atmospherically fed mires however makes studying the actual dust particles grain size mineralogy challenging here we explore some of the potentials and problems of using geochemical data from conservative lithogenic elements al ga rb sc y zr th ti and ree to build detailed dust records by using an example from the 8900 yr peat sequence from store mosse the great bog which is the largest mire complex in the boreo nemoral region of southern sweden the four dust events recorded at this site were elementally distinct suggesting different dominant mineral hosts the oldest and longest event 6385 5300 cal yr bp sees a clear signal of clay input but with increasing contributions of mica feldspar and middle ree rich phosphate minerals over time these clays are likely transported from a long distance source 100 km while dust deposition was reduced during the second event 5300 4370 cal yr bp this is the most distinct in terms of its source character with eu eu ucc revealing the input of plagioclase feldspar from a local source possibly active during this stormier period the third 2380 2200 cal yr bp and fourth 1275 1080 cal yr bp events are much shorter in duration and the presence of clays and heavy minerals is inferred elemental mass accumulation rates reflect these changes in mineralogy where the relative importance of the four dust events varies by element the broad changes in major mineral hosts grain size source location and approximated net dust deposition rates observed in the earlier dust events of longer duration agree well with paleoclimatic changes observed in northern europe the two most recent dust events are much shorter in duration which in combination with evidence of their local and regional character may explain why they have not been seen elsewhere

genesis and paragenesis of the tetravalent manganese oxides of the australian continent the tetravalent manganese oxide minerals of the weathering crust of the australian continent are grouped into lateritic association ultramafic association carbonate association shale association lacustrine association ancient marine crust association and desert varnish association on the basis of field observations of mineral occurrences although the formation of manganese oxides is controlled by the well known eh ph relationship the specific manganese mineralogy is hypothesized to be influenced by the presence of accessory ions or structural templates characteristic of specific geologic environments

baseline determination of the atmospheric pb sr and nd isotopic compositions in the rhine valley vosges mountains france and the central swiss alps abstract the pb sr and nd isotopic compositions of biomonitors lichen moss bark and soil litter from different regions in the rhine valley as well as of

regional variations in the chemical and helium carbon isotope composition of geothermal fluids across tunisia abstract tunisia has numerous thermo mineral springs previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology however little work has been done so far to study the isotopic composition of volatiles associated with these geothermal manifestations here we report on the results of an extensive survey of both natural hot springs and production wells across tunisia aimed at investigating the spatial distribution of thermal fluids geochemical characteristics and he c isotopic composition the chemistry of the analyzed samples highlights the heterogeneity of the water mineralization processes in tunisia as a consequence of the complex geological and tectonic setting of the country in terms of chemical composition we are able to conclude however that dissolution of halite and gypsum plays a key control on groundwater chemistry helium and carbon isotope systematics confirm the prevalently crustal origin of the volatiles interacting with the aquifer systems consistent with the absence of any recent magmatism most samples are characterized by crustal type helium 3 he 4 he in the range 0 02 ra 0 4 ra associated with a co 2 predominantly metamorphic in origin with the exception of the saharan platform where the carbon content is low and mostly organically derived in eastern tunisia however a few samples have he c isotope compositions which suggest at least partial mantle derivation of the dissolved gas phase the 3 he 4 he ratio reaches 2 4 ra corresponding to 30 of mantle derived helium at the ain garci site a co 2 rich mineral spring located some 30 km south of the city of zaghouan this mantle signature is consistent with the fact that the pelagian block to which eastern tunisia belongs has been deeply affected by extensional and transtensional tectonics since the opening of the tethys a process which is still ongoing in the sicily channel pantelleria rift as a whole however our results show that the italian mantle gas anomaly only marginally extends to northwestern africa

radiogenic isotopes for deciphering terrigenous input provenance in the western mediterranean abstract radiogenic isotopic signatures in marine sediments can be used to trace terrigenous source areas and transport mechanisms which are in turn related to climate variability to date most of the published studies using this approach have been focused on eastern mediterranean sediments in contrast we study here the terrigenous input provenance in the westernmost mediterranean alboran sea basin by using radiogenic isotope proxies and nd model ages in a marine record spanning the last 20 ka nd sr and pb isotopes obtained from carbonate free samples from the

paleodust deposition and peat accumulation rates bog size matters abstract we present a high resolution peat paleodust and accumulation rate record spanning the last 8300 years from draftinge mosse 400 ha southern sweden 57 06 27 6 n 13 42 54 1 e the record was analysed for peat accumulation rates par elemental concentrations mineralogy and plant macrofossil content five periods of increased mineral deposition were recorded the first event occurred between 6280 and 5570 cal bp during the fen to bog transition this is followed by four atmospheric mineral dust events de which were recorded in the ombrotrophic section of the sequence at cal bp 2200 1385 1150 830 590 and from 420 to the present statistical analysis and elemental ratios indicated that both the mineralogy and grain size shifted when the system transitioned from fen into bog showing that the governing transport process shifted with the peatland succession stages this highlights the importance of identifying peatland succession stages within peat paleodust studies following all four de increases in par were observed implying a coupling to dust deposition comparison of de and par with a paleodust record from store mosse a 20 times larger bog located ca 18 km away kylander et al 2016 showed that both par and dust deposition are largely represented by single core reconstructions indicating that they are driven by a common climate forcing mechanism however higher par and dust deposition rates were observed in the more moderately sized draftinge mosse suggesting that the size of the bog is important to consider in peat paleodust studies furthermore the smaller bog responded more rapidly to hydrological changes indicating that the size of the bog affects its buffering capacity authigenic carbonates observed here during episodes of rapid peat growth coincide with changes in ree ratios indicating that authigenic peat processes potentially cause ree fractionation

simulation of an abrupt change in saharan vegetation in the mid holocene climate variability during the present inter glacial the holocene has been rather smooth in compar ison with the last glacial nevertheless there were some rather abrupt climate changes one of these changes the desertication of the saharan and arabian region some 4 6 thousand years ago was presumably quite important for human society it could have been the stimulus leading to the foundation of civilizations along the nile euphrat and tigris rivers here we argue that saharan and arabian de sertication was triggered by subtle variations in the earth s orbit which were strongly amplied by atmosphere vegeta tion feedbacks in the subtropics the timing of this tran sition however was mainly governed by a global interplay between atmosphere ocean sea ice and vegetation

linking forest cover soil erosion and mire hydrology to late holocene human activity and climate in nw spain this article is distributed under the terms of the creative commons attribution noncommercial 3 0 license http www creativecommons org licenses by nc 3 0 which permits non commercial use reproduction and distribution of the work without further permission provided the original work is attributed as specified on the sage and open access page http www uk sagepub com aboutus openaccess htm

a salt diapir related mississippi valley type deposit the bou jaber pb zn ba f deposit tunisia fluid inclusion and isotope study the bou jaber ba f pb zn deposit is located at the edge of the bou jaber triassic salt diapir in the tunisia salt diapir province the ores are unconformity and fault controlled and occur as subvertical column shaped bodies developed in dissolution collapse breccias and in cavities within the late aptian platform carbonate rocks which are covered unconformably by impermeable shales and marls of the fahdene formation late albian cenomanian age the host rock is hydrothermally altered to ankerite proximal to and within the ore bodies quartz as fine grained bipyramidal crystals formed during hydrothermal alteration of the host rocks the ore mineral assemblage is composed of barite fluorite sphalerite and galena in decreasing abundance the ore zones outline distinct depositional events sphalerite galena barite ankerite and fluorite fluid inclusions commonly oil rich have distinct fluid salinities and homogenization temperatures for each of these events sphalerite galena 17 to 24 wt nacl eq and th from 112 to 136 c ankerite barite 11 to 17 wt nacl eq and th from 100 to 130 c fluorite 19 to 21 wt nacl eq th from 140 to 165 c the mean temperature of the ore fluids decreased from sphalerite 125 c to barite 115 c and increased during fluorite deposition 152 c then decreased to 110 c during late calcite precipitation laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of fluid inclusions in fluorite are metal rich hundreds to thousands ppm pb zn cu fe but the inclusions in barite are deficient in pb zn cu fe inclusions in fluorite have cl br and na br ratios of several thousand consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a br enriched brine derived from evaporation plus a component of halite dissolution the salinity of the barite hosted fluid inclusions is less than obtained simply by the evaporation of seawater to halite saturation and requires a dilution of more than two times by meteoric water the higher k na values in fluid inclusions from barite suggest that the brines interacted with k rich rocks in the basement or siliciclastic sediments in the basin carbonate gangue minerals ankerite and calcite have 13c and 18o values that are close to the carbonate host rock and indicate fluid equilibrium between carbonate host rocks and hydrothermal brines the 34s values for sphalerite and galena fall within a narrow range 1 to 10 with a bulk value of 7 5 indicating a homogeneous source of sulfur the 34s values of barite are also relatively homogeneous 22 with 6 higher than the 34s of local and regional triassic evaporites 15 the latter are believed to be the source of sulfate temperature of deposition together with sulfur isotope data indicate that the reduced sulfur in sulfides was derived through thermochemical sulfate reduction of triassic sulfate via hydrocarbons produced probably from late cretaceous source rocks the 87sr 86sr ratio in the bou jaber barite 0 709821 to 0 711408 together with the lead isotope values of bou jaber galena 206pb 204pb 18 699 to 18 737 207pb 204pb 15 635 to 15 708 and 208pb 204pb 38 321 to 38 947 show that metals were extracted from homogeneous crustal source s the tectonic setting of the bou jaber ore deposit the carbonate nature of the host rocks the epigenetic style of the mineralization and the mineral associations together with sulfur and oxygen isotope data and fluid inclusion data show that the bou jaber lead zinc mineralization has the major characteristics of a salt diapir related mississippi valley type mvt deposit with superimposed events of fluorite and of barite deposition field relations are consistent with mineral deposition during the eocene miocene alpine orogeny from multiple hydrothermal events 1 zn pb sulfides formed by mixing of two fluids one fluid metal rich but reduced sulfur poor and a second fluid reduced sulfur rich 2 barite precipitation involved the influx of a meteoric water component that mixed with a barium rich fluid and 3 fluorite precipitated from a highly saline fluid with higher temperatures

tree rings and ice cores reveal c 14 calibration uncertainties during the younger dryas the younger dryas interval during the last glacial termination was an abrupt return to glacial like conditions punctuating the transition to a warmer interglacial climate despite recent advances in the layer counting of ice core records of the termination the timing and length of the younger dryas remain controversial also a steep rise in the concentration of atmospheric radiocarbon at the onset of the interval recorded primarily in the cariaco basin has been difficult to reconcile with simulations of the younger dryas carbon cycle here we discuss a radiocarbon chronology from a tree ring record covering the late glacial period that has not been absolutely dated we correlate the chronology to ice core timescales using the common cosmic production signal in tree ring 14c and ice core 10be concentrations the results of this correlation suggest that the cariaco record may be biased by changes in the concentration of radiocarbon in the upper ocean during the early phase of the younger dryas climate reversal in the cariaco basin this bias in the marine record may also affect the accuracy of a widely used radiocarbon calibration curve over this interval our tree ring based radiocarbon record is easily reconciled with simulated production rates and carbon cycle changes associated with reduced ocean ventilation during the younger dryas attaching a floating tree ring chronology to ice core records that cover the abrupt younger dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly the chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean which may affect the accuracy of a popular radiocarbon calibration program during this interval

iron mobilization in mineral dust can anthropogenic so2 emissions affect ocean productivity 1 for fe contained in long range transported aeolian dust to act as a micronutrient for oceanic phytoplankton it must be first dissolved or mobilized we propose that fe mobilization can occur in mineral dust from east asia by the incorporation of so2 into the advecting dust plumes and subsequent acidification of the dust through heterogeneous so2 oxidation to test this hypothesis we consider a dust plume that originated from the gobi deserts and advected over the pacific ocean data collected over the yellow sea confirm that this plume contained high concentrations of dust and so2 significant gaseous hno3 concentrations indicate that the dust particles were acidified i e ph 2 at these ph s 1 2 of the fe contained in a deliquescent mineral dust particle would be mobilized within 3 5 days these results suggest a possible link between the rate of c fixation in so called high nitrate low chlorophyll regions of the pacific ocean and so2 emissions from east asia

structures and tectonics of tunisia abstract in the tunisian atlas nothing is known about the nature of the acoustic basement and in the saharan cratonic part only a few deep exploration wells have reached the precambrian below a thick unfolded palaeozoic sequence north of the craton a major set of faults w e or wnw ese represents the southern limit of palaeo tethys thick sequences of marine late carboniferous and permian were developed below the jeffara and chott jerid triassic evaporites are thick below the tunisian atlas which has enabled detachment of the cover from the basement and folding into plis de couverture structures large diapiric intrusions are known especially in the northwestern sillon tunisien tunisian trough from east to west there is a progressive variation from the stable platform on the eastern side to the unstable shelf of western tunisia between these a zone of tectonic instability named the north south axis corresponds to a deep fault system that acted as a positive suture characterized by tilted blocks gaps in sedimentation and reduced or condensed sequences in the north the unstable shelf of western tunisia grades to the deep furrows where the sediments now forming the tellian and numidian nappes were deposited these nappes overthrust the autochthonous foreland during the miocene orogeny the main folding took place in the pliocene and early pleistocene recent tectonic activity occurs along the main fault zones

environments and processes of manganese deposition concentration of manganese in solution and its deposition takes place by redox controlled processes in a variety of modern and ancient geologic and geochemical environments modern mn deposition occurs predominantly in deep sea areas rather than shallow water domains although deep sea sedimentary deposits dominate hydrothermal contribution of mn to the ocean system may be substantial mn deposition from hydrothermal solutions at or near sea floor spreading centers and less commonly in island arc areas is known in addition near and far field dispersion of mn from vent sites is also substantial such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of mn in seawater thus even in sedimentary deposit domains at least partial derivation of mn from a hydrothermal source is possible sedimentary fe mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid water column oxygen minimum zones thus the presence or absence of volcanic rocks is not a clear indication of whether sedimentary mn deposits particularly in the ancient geologic record are the result of a totally terrigenous or a totally volcanogenic source abyssal fe mn nodules are considered to form from a basin water hydrogenous and or pore water early diagenetic supply of metals but in most cases the extent of supply from either of the sources is unknown the metal incorporation mechanisms of free moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition therefore no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition the determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules biological participation directly or indirectly controls mn deposition the stratified black sea demonstrates the concentration of mn in solution in an anoxic zone its advection toward the redox interface and its precipitation in an oxygenated condition similar stratified basins are contemplated for ancient mn deposition in shallow water basin margin areas geologic and geochemical signatures indicate that during sea level highstands stratified basins formed in which mn was concentrated in solution in the anoxic part corresponding transgression led to the impingement of the redox interface on the continental shelf and precipitation of mn oxides could take place across the interface during transgression regression cycles offshore in anoxic or dysaerobic conditions mn carbonate could form by early diagenetic reaction of mn super 2 with co 2 or hco 3 super produced by organic carbon oxidation critical mn deposits occurring in transgressive glaciogenic and black shale bearing ancient sequences support this paleoenvironmental model for mn deposition

a novel geochemical approach to paleorecords of dust deposition and effective humidity 8500 years of peat accumulation at store mosse the great bog sweden both bog surface wetness and atmospheric dust deposition are intricately linked to changes in the hydrological cycle and pairing these types of records at the same site provides complementary infor

increased atmospheric dust deposition during the neoglacial in a boreal peat bog from north eastern canada abstract dust deposition in north eastern canada was estimated from the geochemical signature of a boreal peat bog from the james bay lowlands the rare earth elements and other lithogenic elements as well as nd isotopes were measured by q icp ms icp oes and mc icp ms respectively along a 4 20 m peat core covering the last 7000 years a principal component analysis performed on the geochemical dataset shows that rees display the same chemical behavior as other lithogenic elements such as al and ti which suggests that they are immobile in the peat column and can be used as tracers of dust deposition after 4000 cal yr bp peaks in dust deposition associated with greater variability in testate amoebae assemblages and plant macrofossil composition as well as a change in nd values are observed between 7000 and 4100 cal yr bp the nd values varied from 36 to 29 while they gradually increased from 4100 cal yr bp until 1500 cal yr bp suggesting proportionally less dust from local source s is deposited in favor of more regional source s from 1500 cal yr bp nd values remained relatively stable around 15 and 12 most of the dust peaks correspond to documented cold and dry periods likely linked to intrusion of arctic air masses a migration of the polar front might explain the more frequent intrusion of arctic air masses in the region and the greater variability in the lg2 record over the last 4000 years

crystal residence times from trace element zoning in plagioclase reveal changes in magma transfer dynamics at mt etna during the last 400 years abstract trace element zoning in plagioclase of selected alkaline lavas from the historic 1607 1892 ad and recent 1983 2013 ad activity of mt etna volcano has been used to explore the possible role that volcano tectonics exert on magma transfer dynamics the observed textural characteristics of crystals include near equilibrium textures i e oscillatory zoning and textures with variable extent of disequilibrium patchy zoning coarse sieve textures and dissolved cores historic crystals exhibit lower k concentrations at lower anorthite contents a feature in agreement with the general more potassic character of the recent lavas if compared to the historic products historic plagioclases have statistically higher ba and lower sr concentrations than the recent crystals which result in different sr ba ratios for the two suites of plagioclase variations in the anorthite content along core to rim profiles obtained on crystals with different types of textures for both the historic and recent eruptive periods were evaluated particularly versus sr ba at comparable average an contents crystals characterized by oscillatory zoning which are representative of near equilibrium crystallization from the magma display distinct sr ba ratios we suggest that these features are primarily related to recharge of a new geochemically distinct magma into the storage and transport system of the volcano in addition to distinct trace element and textural characteristics of plagioclase sr diffusion modeling for plagioclase suggests that residence times are generally shorter for crystals found in recently erupted lavas 25 77 years average 43 years compared to those of the historic products 43 163 years average 99 years shorter residences times correlate with gradual increases in eruption volume and eruption frequency rates through time we attribute these features to an increasing influence since the 17th century of extensional tectonic structures within the upper 10 km of the etnean crust which have promoted shorter residence times and higher eruption frequency

distribution of rees and yttrium among major geochemical phases of marine fe mn oxides comparative study between hydrogenous and hydrothermal deposits abstract mineralogy and geochemistry of the ferromanganese oxides collected from two seamounts in the andaman sea have been investigated with special reference to the solid phase partitioning behavior of rare earth elements rees bulk elemental compositions indicate that the oxides from a volcanic cratered seamount csm are hydrothermal while those from another seamount sm2 are hydrogenous in origin the distributions of rees and yttrium in four geochemical phases viz easily exchangeable mn oxide fe oxyhydroxide and residual of csm oxides were distinctly different from that of sm2 oxides in csm oxides the rees and yttrium are mainly associated with fe oxyhydroxide phase while in sm2 oxides both mn oxide and fe oxyhydroxide phases contain the major fraction of these elements the exchangeable and residual phases of both hydrothermal and hydrogenous oxides have extremely low ree content the shale normalized negative ce anomalies and relative enrichment of heavy ree characteristic of hydrothermal oxides are retained in fe oxyhydroxide phase in hydrogenous oxides the positive ce anomalies occurred in both fe and mn oxide phases while negative y anomalies were found only in fe oxyhydroxide phase the phase distribution of rees and yttrium in hydrothermal oxides is described in terms of co precipitation and adsorption of their halide complexes and available free ions in hydrothermal solutions instead adsorption of major carbonate species from seawater primarily regulates the partitioning of rees among the co existing phases of hydrogenous oxides

coupled manganese and carbon isotopic events in marine carbonates at the cenomanian turonian boundary abstract the boundary interval between the cenomanian and turonian stages of the upper cretaceous shows a positive excursion in the carbon isotopic composition of organic matter and carbonate in many epicontinental and oceanic sections of the atlantic tethyan realm some of the studied epicontinental sections contain an excursion in the manganese content of carbonates coincident with the shift in carbon isotopic values in a key reference section at pueblo colorado the stratigraphic position and magnitude of the manganese excursion are described with respect to the carbon isotopic excursion coincident excursions in manganese contents and carbon isotopic values are verified for a section in normandy france the depositional setting for these two sections is persistently to intermittently we l oxygenated with the accumulation of interbedded chalky and marly sediments no shift in manganese values was detected through the isotopic excursion in a section from northern nebraska where fossils are preserved only as bedding plane impressions due to extensive early diagenetic dissolution of carbonate the carbon isotopic and manganese excursions begin at the same stratigraphic position but manganese contents return to background values within the lower half of the carbon isotopic excursion the relative timing and duration of these signals suggest the existence of a large manganese reservoir that was rapidly mobilized transfer of manganese from deep sea oxides mn4 to epicontinental carbonates mn2 is inferred to have occurred during expansion of oceanic oxygen minimum zones with associated changes in redox gradients and boundaries simultaneous excursions in carbon isotopic values and manganese contents can occur at sites of carbonate accumulation when the carbon and manganese cycles are linked through the reducing potential of widespread oxygen deplete water masses

iron mineralisation in mio pliocene sediments of the tamra iron mine nefza mining district tunisia mixed influence of pedogenesis and hydrothermal alteration abstract the tamra iron mine nefza mining district n tunisia has been exploited for about one century there are however very few publications modelling the mineralisation within this 50 m thick messinian zanclean sedimentary series we present the result of a detailed sedimentological mineralogical and geochemical study on the siliciclastic sediments heavily mineralised in iron in their present state of preservation these are rather unusual sediments wherein most of sedimentological information is obliterated by iron impregnation the whole series consists of a succession of fining upward sequences a few meters in thickness that are capped by clay bearing variegated and mottled horizons each sequence being interpreted as a shallowing upward sequence topped by an emersive horizon corresponding to a paleosoil we propose that alteration and or pedogenesis by the downward percolation of meteoric fluids accounts for most of the initial iron concentration while a hydrothermal overprint linked to the neighbouring miocene magmatic rocks and associated mineral deposits sidi driss fe pb zn mine accounts for the existing extreme iron enrichment the proposed model is likely to apply to several other iron mines linked to the miocene magmatic activity in the whole maghreb area and especially along the apenninic thrust front locally known as tell rif front

the role of the earth s mantle in controlling the frequency of geomagnetic reversals a series of computer simulations of the earth s dynamo illustrates how the thermal structure of the lowermost mantle might affect convection and magnetic field generation in the fluid core eight different patterns of heat flux from the core to the mantle are imposed over the core mantle boundary spontaneous magnetic dipole reversals and excursions occur in seven of these cases although sometimes the field only reverses in the outer part of the core and then quickly reverses back the results suggest correlations among the frequency of reversals the duration over which the reversals occur the magnetic field intensity and the secular variation the case with uniform heat flux at the core mantle boundary appears most earth like this result suggests that variations in heat flux at the core mantle boundary of the earth are smaller than previously thought possibly because seismic velocity anomalies in the lowermost mantle might have more of a compositional rather than thermal origin or because of enhanced heat flux in the mantle s zones of ultra low seismic velocity

manganese deposits in a carboniferous paleokarst profile um bogma region west central sinai egypt the carboniferous carbonates of the um bogma formation of the west central sinai include two rock successions the lower succesion consists of karstic carbonates intrakarstic products weathering varieties manganese deposits and soil cover the lower karstic rocks and the associated soil cover are preserved under a rhythmic alternation of dolostone and shale forming the upper rock succession of the um bogma formation the all over congruent relations between the manganese deposits and the fossilized karst profile karst products and the associated pedogenesis demonstrate the role of weathering in the accumulation of these deposits during carboniferous karstification it is clear that the manganese oxides were deposited during the mature stage of carboniferous karstification i e during the soil formation preceeding initial diagenetic change of the karstic rocks and final deposition of the related late diagenetic caliche cement the geochemical behavior of mn during the karstification and the microbiological processes involved in pedogenesis played an essential role in the concentration of the manganese ore in the subsoil horizon of the paleokarst profile the um bogma formation has been subjected to another episode of karstification during the quaternary and resulted in lowering of the landforms of the carboniferous carbonates and destruction of the carboniferous karst and the associated manganese deposits in some localities