organic carbon fractions and estimation of organic carbon storage in the lake sediments in inner mongolia plateau china organic carbon oc in lake sediments plays an important role in terrestrial ecosystem carbon cycle the inner mongolia plateau contains a number of shallow and freshwater lakes with a total lake area of more than 8 000 km2 accounting for an approximate 10 of the total lake area in china the inner mongolia plateau lakes act as important oc sink in mid high latitude regions in this study heavy and light fractions of oc and oc species were analyzed in sediments from four typical lakes in the inner mongolia plateau meanwhile to identify oc origins allochthonous and autochthonous oc were calculated based on a binary model furthermore total organic carbon toc storage active carbon pool acp and stable carbon pool scp over the past 150 years were estimated in the inner mongolia plateau the dominating direct findings of the current research are that heavy fraction oc plays a key role as carbon sink in mid high latitude regions due to its percentage of more than 90 in toc the percentages of allochthonous oc in toc are high 86 4 66 7 and 72 5 in daihai lake dh dalinuoer lake dlne and hulunhu lake hlh respectively which indicates that allochthonous oc is dominant in dh dlne and hlh the range of humin is 62 15 84 03 in these four lakes the average oc accumulation rate calculated in this work is 1 37 g c m 2 year 1 in these four lakes comparatively oc storages in sediments from lakes in the inner mongolia plateau are relatively more stable than from those lakes located in tropical and sub tropical regions an estimate of the toc burial scp and acp in lake sediments would be 1 64 1012 1 52 1012 and 1 20 1011 g c respectively over the past 150 years in the inner mongolia plateau

transversal and oblique structures at the serres de llevant thrust belt mallorca island the serres de llevant thrust and fold segment outcrops along the se coast of mallorca balearic isles spain and represents the eastern continuation of the external zones of the alpine betic range the structure of the serres de llevant consists mainly of northwest directed thrusts which involve a sedimentary series ranging in age from upper triassic to middle miocene the thrusts form a thrust system developed both by piggy back and out of sequence thrusting thrust sheets are imbricated to the se and to the sw and in the northern part also to the ne giving rise to a complex 3 d pattern the thrusts and related folds developed during the oligocene and the lower and middle miocene the thrust transport direction has been inferred from the stratigraphic facing directions of all mapped ramps and has been determined with the aid of other transversal structures the resulting transport direction is from se to nw n310e one of the most significant structural features of the serres de llevant thrust segment is the existence of several lateral and oblique structures these structures are ramps which display stratigraphic facing directions both to the ne and sw other lateral structures represented in the northern part of the thrust segment are tear and drop faults in the southern part kilometric scale oblique folds are exposed

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

holocene climate changes in the monsoon arid transition reflected by carbon concentration in daihai lake of inner mongolia two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for total inorganic and organic carbon tic and toc concentrations the tic concentration is inferred to reflect temperatures over the lake region and an increase in the tic concentration implies an increase in the temperature toc concentration is considered to reflect the precipitation in the lake basin and higher toc concentrations denote more precipitations thus ams 14c time series of the tic and toc records of daihai lake sediments uncovers a detailed history of changes in temperature and precipitation in north central china during the last c 12 000 yr the holocene an epoch of postglacial warmth started c 11 500 cal yr bp and can be subdivided into three stages the early c 11 500 8100 cal yr bp middle c 8100 3300 cal yr bp and the late holocene c 3300 0 cal yr bp the climate was warm and dry during the early holocene warm and wet during the middle holoce

application of allochthonous organic carbon and phosphorus forms in the interpretation of past environmental conditions organic matter in sediments for instance carbon nitrogen and phosphorus can be used to reconstruct the paleoecological and pollution history of lakes and their catchment basins in this paper the contents of allochthonous organic carbon allochthonous oc and autochthonous organic carbon autochthonous oc in sediment cores taken from wuliangsuhai lake and daihai lake in northern china are quantified by using a binary model and phosphorus forms in the sediment cores from the two lakes are extracted by sequential extraction techniques the results indicate that the palaeoenvironment and paleoclimate of daihai lake and its catchment basin in the recent 250 years can be well reconstructed based on the content of allochthonous oc the climate was relatively humid and warm in the period of 1865 2005 while relatively dry and cold in the period of 1765 1865 the sedimentary information of allochthonous oc in the 22 42 cm portion of the sediment cores in daihai lake corresponds to the final cold fluctuation of the little ice age that occurred since the middle holocene the difference of phosphorus forms in the sediment cores between the two lakes indicates that phosphorus input to the lakes and the correlation between phosphorus forms and distribution and the changes of environment are influenced by the eutrophication mechanisms and environmental conditions of the two lakes

late pleistocene carbonate aeolianites on mallorca western mediterranean a luminescence chronology abstract coastal outcrops of upper pleistocene deposits in north eastern mallorca balearic islands spain have been examined and a chronological framework established using optically stimulated luminescence osl dating the outcrops record a complex interaction between aeolian colluvial and alluvial fan deposition that result in a variable stratigraphical architecture dating and facies analysis make it possible to identify four aeolian activity episodes during mis 5c b 4 and 3 and also add to the understanding of the environmental history of north eastern mallorca over the last 100 ka the new data suggest enhanced aeolian transport and dune formation during cold climatic intervals when sea level was low sediment supply exposed marine carbonate sediment was high winter windiness was high and vegetation on coastal plains at a minimum

conditions of rhodochrosite nodule formation in neogene pleistocene deep sea sediments evidence from o c and sr isotopes calcic rhodochrosite occurs as nodules around burrows in late neogene early pleistocene pelagic sediments of the galapagos ridge in the guatemala basin eastern equatorial pacific dsdp leg 68 site 503 growth was accomplished in the suboxic zone delta

geochemistry of daihai lake sediments inner mongolia north china implications for provenance sedimentary sorting and catchment weathering abstract to advance the understanding of sediment distribution catchment weathering hydraulic sorting and sediment provenance in a tectonically stable basin the geochemistry of surface sediment samples from daihai lake in north china is presented mud bulk sediments were analyzed for 10 major and 30 trace elements organic carbon and nitrogen and for 87sr 86sr ratios in silicate fraction acid insoluble ai and carbonates acid soluble as enrichment in fe2o3 cao mno mgo k2o and p2o5 and their positive correlation with al2o3 rb sr ratios and bivariate discrimination diagrams of k vs rb and th u vs th suggest low chemical weathering intensity under semiarid conditions in the daihai catchment accumulation of clays in deeper water sites by sedimentary sorting results in an evident distribution of sediment composition with the lake water depth although similar chondrite normalized ree rare earth element patterns of lake sediment samples with lree light rare earth element enrichment negative eu anomalies and an almost flat hree heavy rare earth element pattern may suggest similar sedimentary source rocks original sediment provenance can be recognized on the basis of their distinctive 87sr 86sr ai ratios and immobile th zr ti and nb trace element signature separating from weathering and sedimentary processes as well as from grain size effect

terminal pleistocene holocene palaeoenvironmental changes revealed by mineral magnetism measurements of lake sediments for dali nor area southeastern inner mongolia plateau china abstract mineral magnetic properties sirm arm hirm and s ratios are presented for two ams 14c dated pit sequences of lake sediments recovered from haoluku and liuzhouwan 43 n 117 e the two sites fall in the semi humid to semi arid climate transition zone dali nor area of the southeast inner mongolia plateau china complemented by data for loss on ignition loi total organic carbon toc carbon nitrogen c n grain size and pollen these mineral magnetic measurements provide additional insights into environmental changes occurring at this area over the last 13 500 years conditions were extremely dry and windy as shown by the low sirm arm and hirm and high s ratios before 13 500 yr bp the environment began to ameliorate gradually since then and a further humidification occurred at 10 300 yr bp in haoluku the northern site and at 9400 yr bp in liuzhouwan the southern one as implied by the increased but only moderately high sirm arm and hirm and decreased s ratios as indicated by the remarkably increased sirm arm hirm and s ratios a deterioration commenced at 5600 yr bp in haoluku and at 4700 yr bp in liuzhouwan in haoluku conditions have been generally dry and windy since 5600 yr bp despite a minor amelioration at 4500 3000 yr bp a short but marked amelioration occurred at 1200 700 yr bp in liuzhouwan s ratios seem to be a reliable indicator of environmental aridity for this area

initiation and evolution of the valencia trough western mediterranean constraints from deep seismic profiling and subsidence analysis abstract the structure and evolution of the valencia trough western mediterranean a neogene basin bordered in the north by prominent oligocene early miocene grabens in the catalan coastal ranges and to the south by the early miocene thrust sheets of the betic belt is investigated through a deep seismic reflection profile shot across the basin this profile shows that extensional features related to the rifting are concentrated in the catalan valencian domain in the north whereas in the south the betic balearic domain shows little extensional structures and no clear thrusting the smooth quite symmetrical moho uplift seems to cross cut strong se dipping reflectors which are clearly visible below the moho in the central basin deep seismic data tied on wells and industrial lines are used to establish a regional depth section which is backstripped and along which the history of tectonic subsidence is investigated assuming local isostasy we find out that observed tectonic subsidence shows a classical exponential decay for the period 0 15 2 ma consistently with observed moho attenuation even to the south where a foreland type mechanism of subsidence is not recognized little subsidence is found for the period 25 2 20 ma we also indicate that some brittle basement readjustement must have occurred around 15 2 ma and that the heat flow although variable is not inconsistent with theoretical model of uniform lithosphere attenuation we therefore propose that the development of the valencia trough occurred in two rifting stages the first the oligo miocene west european rifting event had minor effects in the deep basin and affected mostly the catalan margin the second serravallian in age 15 2 10 2 ma is responsible for present day moho uplift and explains the post mid miocene basin development this second rifting is coeval with the opening of the tyrrhenian basin its significance at the west of the western mediterranean remains to be investigated

minor elements in quaternary sediment from the sea of japan a record of surface water productivity and intermediate water redox conditions sediment of quaternary age from oki ridge 903 m depth in the sea of japan 3500 m deep records six episodes of high accumulation rates of cd cr cu mo ni u v and zn the high rates correspond to periods of sulfate reduction in the water column at the intermediate depth of oki ridge the intervening low values correspond to periods of denitrification and oxygen respiration the maxima have a period of 41 k y the youngest having an age of 1 10 ma the 41 k y cycle is similar to the cycle of 18 o values of open ocean plankton of the same age the similarity between the cycles of minor element accumulation in sea of japan sediment and 18 o values of atlantic ocean foraminifera indicates that redox changes in the water column of the sea of japan during the quaternary forced by major shifts in water column advection and minor shifts in photic zone productivity reflect global events

uranium disequilibrium dating of phosphate deposits from the lau group fiji uranium series methods of absolute age determinations were first applied to fossil coral reefs1 and more recently to fossil bone2 marine apatite3 6 and insular apatite7 8 past sea level stands climatic conditions primary productivity and other factors are thought to be influential in the deposition of avian guano and subsequent insular phosphorite formation9 some deposits appear to have formed during high stands of the sea while others may be related to glacial epochs8 we report here an attempt to determine the absolute age of two phosphate deposits in the lau group fiji by uranium series disequilibrium techniques in order to assist in the evaluation of their origin in terms of known palaeoclimatic information

composition and origin of early cambrian tiantaishan phosphorite mn carbonate ores shaanxi province china abstract the tiantaishan phosphorite mn carbonate ores occur in the early cambrian tananpo formation in complexly folded and faulted rocks located in southern shaanxi province about 65 10 6 tonnes of 17 p 2 o 5 ore reserves exist and mn ore reserves are about 8 3 10 6 tonnes of 18 mn the stratigraphic sequence in ascending order consists of black phyllite black to gray phosphorite ore black phyllite rhodochrostone ore mn mixed carbonates and dolostone data are presented from microprobe mineral chemistry whole rock chemistry stable isotopes of carbonates x ray mineralogy petrographic and sem observations and statistical analysis of chemical data the dominant ore forming minerals are hydroxy and carbonate fluorapatite and ca rhodochrosite with mg kutnahorite and dolomite comprising the mn mixed carbonate section pyrite occurs in all rock types and alabandite mns occurs throughout the rhodochrostone section the mean p 2 o 5 content of phosphorite is 31 and argillaceous phosphorite is 16 while the mean mno content of rhodochrostone ore is 37 phosphorite ores are massive spheroidal laminated and banded while rhodochrostone ores have oolitic spheroidal and granular fabrics the most distinguishing characteristics of the ores are high total organic carbon toc contents mean 8 4 in the phosphorite and high p 2 o 5 contents mean 2 7 in the rhodochrostone ore the atypically high toc contents in the tiantaishan phosphorite probably result from very strong productivity leading to high sedimentation rates accompanied by weak reworking of sediments poor utilization of the organic matter by bacteria and or partial replacement of bacterial or algal mats by the apatite the depositional setting of the ores was the margin of an epicontinental seaway created as a direct consequence of global processes that included break up of a supercontinent formation of narrow seaways creation of extensive continental shelves overturn of stagnant metal rich deep ocean waters and marine transgression water depth increased from deposition of the black phyllite sequence through deposition of the mn mixed carbonate sequence then shallowed again during deposition of the overlying dolostone sequence bottom waters were mostly dysoxic to suboxic but fluctuated from oxic to anoxic productivity was high during deposition of the black phyllite sequence increased during precipitation of phosphorite and then decreased to moderate levels during precipitation of rhodochrostone ores biosilica contributions occur in each lithology but are greatest in rhodochrostone changes in sedimentation were determined by changes in water depth productivity upwelling sea level change and ventilation of the depositional basin the source of the phosphorus was organic matter produced in great quantities during deposition of the black phyllite and phosphorite sequences in a zone of coastal upwelling organic matter accumulation was rapid globally mn was supplied by overturn of stagnant metal rich deep ocean waters which were redistributed to areas of coastal upwelling and seaways that process may have been initiated by latest proterozoic glaciations which would have promoted density stratification and accumulation and storage of metals regionally mn was supplied by terrigenous input into the shallow seaway and hydrothermal input into the deeper water parts of that seaway locally mn sources included leaching and transport of metals from the sediment column manganese was stored locally in low oxygen not anoxic seawater prior to mn ore formation the source of the carbon in the mn carbonates and dolostones was predominantly seawater bicarbonate and secondarily co 2 derived from the oxidation of organic matter in the bacterially mediated diagenetic zone of sulfate reduction

the impact of quaternary sea level and climatic change on coastal alluvial fans in the cabo de gata ranges southeast spain conventionally a fall in base level is seen as stimulating incision into the distal zones of alluvial fans in the cabo de gata ranges of southeast spain evidence exists to the contrary two sets of quaternary coastal alluvial fans demonstrate the interaction between climatically driven variations in the supply of sediment and eustatically driven changes in base level the fans are supplied from miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development the evolution of the east coast fans has been affected by variations in sediment supply and changes in sea level the west coast fans were buffered from the effects of changes in sea level by coastal barriers three phases of past sedimentation can be identified on the fans these can be differentiated on the basis of field observations of soil profiles particularly colour of the b horizons and accumulation of caco3 and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties the two earlier major sedimentation phases were coincident with global glacials ca 135 ka and ca 85 10 ka based on the stratigraphy and uranium thorium dating of the coastal sediments high sea levels during the intervening interglacial and during the holocene caused erosion of the distal zones of the east coast fans which led to channel incision into the fan surfaces on the west coast fans no such incision occurred simply proximal incision by small fanhead trenches the youngest relatively minor phase of fan sedimentation has occurred during the holocene these contrasting contexts have produced differing styles of fans with telescopic fan morphology on the east coast and stacked morphology on the west coast fans the differences are reflected in the fan profiles with steeper gradients dominating the east coast fans and extensive lower gradient distal surfaces on the west coast fans fan morphometry based on analysis of the residuals from drainage area to fan area and gradient regressions also differentiates between the fan contexts the fan building phases appear to be controlled proximally by climatically driven pulses of sediment supplied to the fans these occurred during global glacials coincident with low sea levels and caused fan progradation onto the exposed foreshore the intervening global interglacials were times of little fan sedimentation and on the east coast where high sea levels were able to erode the fan toes deep through fan dissection ensued

uranium mineralization and its radioactive decay induced carbonization in a black shale hosted polymetallic sulfide ore layer southwest china the black shale in the lower cambrian niutitang formation southwest china which has been dated to 532 3 0 7 ma by u pb radiometric measurements hosts a sedimentary layer with abnormally high ni mo pge au contents this layer is enriched in ni up to 3 8 wt mo up to 7 7 wt and u up to 595 ppm but its genesis is still controversial here we report the first direct observation of uranium bearing minerals and their radioactive effects on the surrounding matter in the polymetallic sulfide ore x ray absorption fine structure analyses confirmed the reduced valence state of uranium in combination with high resolution electron microscopy and electron probe microanalysis the mineral was identified as coffinite usio4 a strong positive correlation between the sizes of the coffinite crystals and their surrounding carbonized rings reveals that the coffinite is authigenic and its crystallization produced radiation resulted in the radiolysis of surrounding organic matter the association of various biogenic metal sulfides phosphates and abundant organic substances within the ni mo sulfide enriched ore suggests that biological adsorption may have participated in the enrichment of soluble u vi and that microbial sulfate reduction might have facilitated the uranium mineralization

analysis of the geological evolution and vertical movements in the valencia trough area western mediterranean abstract the valencia trough located between the iberian peninsula and the balearic islands corresponds to the south west prolongation of the provencal basin the analysis of recently released seismic lines shows that the present day tectonics of the valencia trough are the result of the coeval development of 1 a system of horsts and grabens in the north west part of the basin during the late oligocene early miocene catalan valencian domain and 2 a thrust and fold system which lasted up to the middle miocene and which was followed by extensional tectonics during the late miocene betic balearic domain in an attempt to characterize the evolution of the valencia trough subsidence curves have been calculated for 18 wells and three regional cross sections distributed across the basin backstripping of these data shows two major stages of tectonic subsidence history 1 a first stage coeval with basin formation 30 15 my characterized by a rapid and strong tectonic subsidence which attains its maximum values in the central basin areas and close to the balearic islands and 2 a second stage 15 0 my in which the tectonic subsidence decreases gradually the amount of crustal thinning estimated from a comparison of the observed and modelled tectonic subsidence ranges between 1 5 iberian margin areas and 4 5 central and south western basin areas these values agree with the crustal thicknesses inferred from seismic refraction data and gravimetric modelling nevertheless such a degree of thinning cannot be explained by the neogene extensional structure the presence of thick mesozoic deposits suggests that the present crustal thinning is partly due to previous mesozoic extension

a structural outline of the serra de tramuntana of mallorca balearic islands abstract the structural and stratigraphic aspects of the balearic islands are described by outlining the geology of the serra de tramuntana this range is part of the southeastern margin of the valencia trough and has the typical features of thrust tectonic areas a stratigraphic column a structural map and three cross sections show the main features of this range thrusts dip to the southeast and are arranged in an imbricate system with a transport direction to the nw the thrusts recorded involve upper paleozoic to middle miocene rocks imbricates bearing thin slices and duplexes developed where thin sequences with pronounced competency contrasts exist folds are also present they usually trend ne sw except in local areas where they are interpreted as being associated with oblique ramps fold axes plunge sub horizontally and folds face the northwest thrust displacements of up to 10 km are deduced from the existence of klippes and windows and shortening of around 50 is deduced from a comparison of deformed and restored cross sections the onset of the main contractional event is pre miocene probably late oligocene in age but major thrust emplacement occurred during the middle miocene the widespread occurrence of compression structures in the balearic islands developed from late oligocene to middle miocene put strong constraints on the models explaining the origin of both the valencia trough and the algerian basin the first must be considered at least in part as the balearic foreland basin and the second could be superimposed on the internal zone of the western mediterranean orogenic belt

chemical depositional environments of calcic marine black shales the economically important black shale facies contains several discrete chemical groupings in visually similar rocks we examined the elemental compositions of more than 300 black shales and anoxic sediments in order to understand the relation of their chemical variability to the depositional environment the low calcic shales were found to contain at least four discrete groupings 1 4 whose depositional and early diagenetic redox conditions are suggested by their fe mn and v concentrations the calcic shales 72 paleozoic 50 mesozoic and 42 cenozoic 50 000 ppm al 4 000 ppm ca were examined in terms of the four thermodynamic groups previously defined for the low calcic shales the ca mn ratios of the calcic black shales fall into four i iv discrete clusters as opposed to a continuum this differentiation reflects the stability of mn minerals in overlying and interstitial waters under varying redox conditions one cluster ca mn i from a period of glaciation ordovician silurian boundary has high mn concentrations and falls on the line mn 0 065 ca 1 280 ppm r 0 95 n 7 a second group ca mn ii from many different localities and ages falls on a line with a lower slope mn 0 038 ca 187 ppm r 0 92 n 21 the third group ca mn iii falls on the line mn 0 011 ca 152 ppm r 0 95 n 19 the greatest number of samples ca mn iv fall on the line mn 0 0027 ca 144 ppm r 0 85 n 69 in order to establish the depositional environment associated with each of the groups more modern sediments whose depositional settings are better defined were explored as a result the samples from both ca mn i and ii can be associated with deposition under oxic water those from ca mn i remained oxic during early diagenesis after deposition ca mn ii samples became anoxic releasing mn to interstitial waters the ca mn iii and iv group samples were deposited under anoxic waters in order to establish the thermodynamic environment of the shale component of the calcic shales it is necessary to extrapolate to the no calcium intercept to determine the mn content then apply the rules determined for the low calcic shales this study demonstrates the wide variety of black shale depositional environments from oxic to methanogenic accordingly black shales can not all be assigned to anoxic sulfidic environments without additional chemical analysis and interpretation the proper environmental assignment should be useful in assessing the economic potential of particular black shale deposits

reconciling the roles of tectonism and climate in quaternary alluvial fan evolution tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin fill architecture yet their roles and relative importance are far from resolved the madison range and madison river valley southwestern montana were affected during late quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations we are thus able to evaluate the impact of tectonism and climate on fan evolution two primary fan deposits were correlated along the range front they were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge during the present interglacial period these deposits were entrenched and secondary fans formed on lower fan areas temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment in contrast stratigraphic relations between fan deposits and surface faults do not support a direct relation either spatial or temporal between local faulting and fan deposition because tectonism produces and maintains the relief necessary for fans to form its primary role is long term controlling the duration over which fan deposition may occur along a mountain front if quaternary alluvial fan evolution is representative of ancient alluvial fan evolution this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences

holocene weak monsoon intervals indicated by low lake levels at hulun lake in the monsoonal margin region of northeastern inner mongolia china a 170 cm long sediment core spanning the last 10 000 years was recovered from hulun lake in the northeastern margin of the east asian summer monsoon the sediment core was analyzed at 1 cm intervals for grain size distribution and sedimentary component partition these data provide a proxy record of the monsoon variability on millennial to centennial scales during the holocene we used a lognormal distribution function fitting method to partition three to six components from fine to coarse modes within the individual polymodal distributions into overlapping lognormal distributions three coarse components representing nearshore suspension saltation and traction together with the sand fraction percentage and the median grain size of bulk samples indicate the lake levels that fluctuated in response to the intensity of the monsoonal precipitation higher percentages of the nearshore components accompanied by more sand fraction proportions and coarser median grain sizes reflect lower lake stands resulting

geochemical studies on permian manganese deposits in guichi eastern china implications for their origin and formative environments abstract permian manganese ore deposits are widely distributed in southwestern and eastern china guichi permian manganese district in southern anhui province central eastern china is currently the most important manganese metal producers in eastern china manganese ores mno 18 2 45 4 wt in guichi region occur in calcareous argillaceous and siliceous mn bearing sequence of the permian gufeng formation in contrast to mn bearing rocks the ores have higher mn fe p sr more than 1500 ppm and ni contents 480 ppm higher mn fe 5 and lan cen 2 values and lower co ni

paleo redox depositional conditions inferred from trace metal accumulation in two cretaceous paleocene organic rich sequences from central egypt abstract cretaceous paleocene organic rich sediments in egypt occur as an east west trending belt extending from the quseir safaga district red sea to the kharga dakhla western desert region they are associated with the duwi formation phosphate bearing and the overlying dakhla formation deeper epicontinental shale marl this study aims to reconstruct the paleo redox conditions during deposition of these thermally immature organic rich sediments using carbon sulfur iron systematics and trace metal proxies in two cores one each from the quseir and abu tartur areas paleoproductivity based on p content seems to have been higher in the quseir section than in the abu tartur section the quseir section also records a relatively greater occurrence of anoxic conditions during the accumulation of these sediments than the abu tartur section this difference is indicated by its markedly higher total organic carbon toc content as well as higher contributions of redox sensitive and sulfide forming metals mo u ni v and co a weak correlation exists between s and toc and a positive s intercept 1 was observed in most of the rock units of the study sections a high consistency between the toc s fe relations and trace metals findings was found the uppermost duwi and the lowermost dakhla strata which have the highest toc and represent a maximum sea transgression during the late cretaceous have the highest contents of redox sensitive trace metals the carbonate dominated transgressive baris and beida members of the dakhla formation record relatively stronger oxygen depleted conditions during their accumulation than others which led to relatively higher toc contents and redox sensitive metal accumulations a scenario for the environmental conditions that existed during the deposition of these organic rich successions based on compiled trace metals and toc s fe implications is reconstructed here

manganese mineralogy and diagenesis in the sedimentary rock record oxidation of manganese ii to manganese iii iv demands oxidants with very high redox potentials consequently manganese oxides are both excellent proxies for molecular oxygen and highly favorable electron acceptors when oxygen is absent the first of these features results in manganese enriched sedimentary rocks manganese deposits commonly mn ore deposits which generally correspond to the availability of molecular oxygen in earth surface environments and yet because manganese reduction is promoted by a variety of chemical species these ancient manganese deposits are often significantly more reduced than modern environmental manganese rich sediments we document the impacts of manganese reduction and the mineral phases that form stable manganese deposits from seven sedimentary examples spanning from modern surface environments to rocks over 2 billion years old integrating redox and coordination information from synchrotron x ray absorption spectroscopy and x ray microprobe imaging with scanning electron microscopy and energy and wavelength dispersive spectroscopy we find that unlike the mn iv dominated modern manganese deposits three manganese minerals dominate these representative ancient deposits kutnohorite camn co 3 2 rhodochrosite mnco 3 and braunite mn iii 6mn ii o 8sio 4 pairing these mineral and textural observations with previous studies of manganese geochemistry we develop a paragenetic model of post depositional manganese mineralization with kutnohorite and calcian rhodochrosite as the earliest diagenetic mineral phases rhodochrosite and braunite forming secondarily and later alteration forming mn silicates

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

rare earth elements in the phosphatic enriched sediment of the peru shelf abstract apatite enriched materials from the peru shelf have been analyzed for their major oxide and rare earth element ree concentrations the samples consist of 1 the fine fraction of sediment mostly clay material 2 phosphatic pellets and fish debris which are dispersed throughout the fine grained sediment 3 tabular shaped phosphatic crusts which occur within the uppermost few centimeters of sediment and 4 phosphatic nodules which occur on the seafloor the bulk ree concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction analysis of the fine grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale ree values the analysis of the fish debris suggested that the apatite fraction might have seawater values the seawater contribution of ree s is negligible in the nodules and crust in which the apatite occurs as a fine grained interstitial cement that is the concentration of ree s and the ree patterns are predominantly a function of the amount of enclosed fine grained sediment by contrast the ree pattern of the pelletal apatite suggests a seawater source and the absolute ree concentrations are relatively high the ree p 2 o 5 ratios of the apatite fraction of these samples thus vary from approximately zero in the case of the crust and nodules to as much as approximately 1 2 10 3 in the case of the pellets the range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the ree content of this authigenic fraction of the sediment pelletal glauconite was also recovered from one sediment core its ree concentrations closely resemble those of the fish debris

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

holocene climate changes in the mid high latitude monsoon margin reflected by the pollen record from hulun lake northeastern inner mongolia pollen assemblage data from a sediment core from hulun lake in northeastern inner mongolia describe the changes in the vegetation and climate of the east asian monsoon margin during the holocene dry steppe dominated the lake basin from ca 11 000 to 8000 cal yr bp suggesting a warm and dry climate grasses and birch forests expanded 8000 to 6400 cal yr bp implying a remarkable increase in the monsoon precipitation from 6400 to 4400 cal yr bp the climate became cooler and drier chenopodiaceae dominated the interval from 4400 to 3350 cal yr bp marking extremely dry condition artemisia recovered 3350 2050 cal yr bp denoting an amelioration of climatic conditions both temperature and precipitation decreased 2050 to 1000 cal yr bp as indicated by decreased artemisia and the development of pine forests during the last 1000 yr human activities might have had a significant influence on the environment of the lake region we suggest that the east asian summer monsoon did not become intensified until 8000 cal yr bp due to the existence of remnant ice sheets in the northern hemisphere changes in the monsoon precipitation on millennial to centennial scales would be related to ocean atmosphere interactions in the tropical pacific

the cr th ratio in precambrian pelites from the kaapvaal craton as an index of craton evolution the cr th ratio in precambrian pelites from the kaapvaal craton in southern africa correlates with pelite th sc and co th ratios and appears to monitor changes in source composition it is a more sensitive indicator of provenance than other commonly used ratios including eu eu la yb and th u pelite cr th ratios are controlled most strongly by the effects of local provenance and local tectonics secular decreases in this ratio the most prominent of which occurred at 2 4 2 3 ga in pelites of the kaapvaal craton record rapid uplift exposing granite decreases in the ratio reflect increases in the abundance of komatiite basalt in sediment sources in response to arc collisions rift hotspot volcanism or intracratonic uplift of older greenstones relatively constant cr th ratios appear to require widespread uplift or and efficient sediment mixing during tectonic stability changes in cr th ratio of kaapvaal pelites reflect a complex tectonic history of the craton from about 3 3 ga to 1 8 ga and do not favor single stage cratonization in the late archean

investigation on the role of microorganisms in manganese mineralization from abadeh tashk area fars province southwestern iran by using petrographic and geochemical data abstract hydrothermal manganese and ferromanganese deposits associated with neyriz ophiolite colored melange occurred as small ore deposits in the abadeh tashk area se of fars province sw iran the deposits are found in three types a banded syngenetic ores b massive boudin and lens shaped diagenetic ores and c vein and veinlet epigenetic ores microtextural geochemical and mineralogical data associated with petrographic raman ftir and sem studies indicated that the primary fe compounds formed series of microbially mediated biomats and mn compounds were precipitated as an amorphous oxide on an active oxide surface accompanying silica gels field relationships between ore and host rock high mn fe ratio 17 43 to 40 79 lree positive eu and negative ce anomalies in syngenetic ore types reveal that the ores were formed by hydrothermal fluid in an oceanic floor environment manganese was fractionated from iron due to physicochemical changes as well as microbial activities in the sedimentary environment microbial remains as filamentous beads with regular circular shapes vermiform structures series of fe rich biomats traces of embedded organic material besides trace metals and ree concentrations in mn ores emphasize the role of microorganisms in fe and mn precipitation syngenetic mineralization took place under suboxic neutrophilic conditions while diagenetic processes resulted in variably reduced fe and mn oxides via organic matter decomposition forming rhodochrosite as the end product braunite formation occurred most probably as a biogeochemically mediated early diagenetic product diagenetic and epigenetic mn ores were formed when primary mn deposits underwent subsequent diagenetic and remobilization redeposition events respectively

relative contributions of silicate and carbonate rocks to riverine sr fluxes in the headwaters of the ganges abstract exhumation of the himalayan tibetan orogen is implicated in the marked rise in seawater 87sr 86sr ratios since 40 ma however both silicate and carbonate rocks in the himalaya have elevated 87sr 86sr ratios and there is disagreement as to how much of the 87sr flux is derived from silicate weathering most previous studies have used element ratios from bedrock to constrain the proportions of silicate and carbonate derived sr in river waters here we use arrays of water compositions sampled from the head waters of the ganges in the indian and nepalese himalaya to constrain the end member element ratios the compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two component mixing of silicate and carbonate derived components and lie on a plane in multicomponent composition space key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes na 0 for carbonate and constant ca na for silicate the fractions of sr derived from silicate and carbonate sources are then calculated by mass balance in sr ca mg na composition space comparison of end member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low mg trace calcite in silicate rocks may explain discrepancies in sr ca na mg covariation alternatively composition dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation ratio diagrams however the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained silicates are calculated to provide 50 of the dissolved sr flux from the head waters of the ganges assuming that discrepancies between ca mg na covariation and the silicate rock compositions arise from addition of trace calcite if the ca mg na mixing plane is rotated by composition dependent secondary calcite deposition this estimate would be increased moreover when 87sr 86sr ratios of the sr inputs are considered silicate sr is responsible for 70 16 1 of the 87sr flux forcing changes in seawater sr isotopic composition since earlier studies predict that silicate weathering generates as little as 20 of the total sr flux in himalayan river systems this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated

seawater as the source of minor elements in black shales phosphorites and other sedimentary rocks many of the minor elements in seawater today have a concentration depth profile similar to that of the biologically essential nutrients no 3 and po3 4 they show a relative depletion in the photic zone and enrichment in the deep ocean the difference between their surface and deep ocean values normalized to the change in po3 4 approaches the average of measured minor element p ratios in marine plankton although individual analyses of the latter show extreme scatter for a variety of reasons despite this scatter in the minor element analyses of plankton agreement between the two sets of data shows unequivocally that an important marine flux of many minor elements through the ocean is in the form of biogenic matter with a composition approaching that of plankton this interpretation is further supported by sediment studies particularly of sediments which accumulate in shelf slope environments where biological productivity in the photic zone is exceptionally high and organic carbon contents of the underlying sediment elevated the interelement relations observed for some of these sediments approach the average values of plankton these same interelement relations are observed in many marine sedimentary rocks such as metalliferous black shales and phosphorites rocks which have a high content of marine fractions e g organic matter apatite biogenic silica and carbonates many previous studies of the geochemistry of these rocks have concluded that local hydrothermal activity and or seawater with an elemental content different from that of the modern ocean was required to account for their minor element contents however the similarity in several of the minor element ratios in many of these formations to minor element ratios in modern plankton demonstrates that these sedimentary rocks accumulated in environments whose marine chemistry was virtually identical to that seen on continental shelf slopes or in marginal seas of the ocean today the accumulation of the marine fraction of minor elements on these ancient sea floors was determined largely by the accumulation of organic matter settling from the photic zone and with a composition of average plankton a second marine fraction of minor elements in these rocks accumulated through precipitation and adsorption from seawater the suite of elements in this fraction reflects redox conditions in the bottom water as determined by bacterial respiration for example high mn high cr v and high mo concentrations above those which can be attributed to the accumulation of planktonic matter characterize accumulation under bottom water oxidizing denitrifying and sulfate reducing conditions respectively

characteristics of the devonian xialei manganese deposit guangxi zhuang autonomous region china abstract the xialei mn deposit occurs in the late devonian famenian wuzhishan formation and consists of three ore horizons composed of three ore types 1 mn carbonate 2 mn silicate mn carbonate and 3 mn oxide mn silicate mn carbonate ore beds consist of mn carbonates and associated rhodonite stilpnomelane actinolite chlorite mn epidote biotite and mn fe antigorite these minerals are mixed with each other and form thin beds bands pelletal and pisolitic grains and horizontal or wavy laminae abundant oolitic and pisolitic grains in mn ore beds show distinct boundaries and nuclei of mn carbonate and mn silicate minerals rarely clastic grains the ore deposit is divided into three zones 1 an inner zone composed of mn carbonate silicate and oxide minerals 2 a transitional zone consisting of mn carbonate and stilpnomelane and 3 an outer zone characterized by mn carbonate argillaceous limestone at the base of the ore beds has a mean 13 c pdb of about 0 0 indicating that the carbon was derived from seawater bicarbonate the 13 c pdb of mn carbonate ranges from 2 8 to 14 3 mean 7 1 indicating that the carbon was derived from both degradation of organic matter and seawater bicarbonate ores formed in a trough on a carbonate platform primary sedimentary mn carbonates precipitated from alkaline and negative eh waters in the diagenetic zone of sulfate reduction which occurred either during shallow burial or at the seafloor oolites and pisolites formed by sedimentary processes on the seafloor in places deposits were reworded and transported by gravity flow processes the region where these sedimentary diagenetic mn deposits formed was intruded by magma and hydrothermal fluids with dissolved metals leached from volcanic and sedimentary rocks ascended along fractures the mn silicate mn carbonate ore may have been produced by contact metamorphism of primary carbonate ore and metal sulfides deposited by hydrothermal fluids which overprinted the primary sedimentary ore

magnitude and significance of carbon burial in lakes reservoirs and peatlands globally lakes are currently accumulating organic carbon oc at an estimated annual rate of about 42 tg yr 1 most of the oc in all but the most oligotrophic of these lakes is autochthonous produced by primary production in the lakes the sediments of reservoirs accumulate an additional 160 tg annually and peatlands contribute 96 tg annually these three carbon pools collectively cover less than 2 of the earth9s surface and constitute a carbon sink of about 300 tg yr 1 although the oceans cover 71 of the earth9s surface they accumulate oc at a rate of only about 100 tg yr 1

minimal climatic control on erosion rates in the sierra nevada california climate is widely thought to regulate erosion rates but the relationships among precipitation temperature and erosion rate have remained speculative because long term erosion rates have been difficult to measure we used cosmogenic nuclides to measure long term erosion rates at climatically diverse sites in the sierra nevada california spanning 20 180 cm yr in annual precipitation and 4 15 8c in mean annual temperature average erosion rates vary by only 2 5 fold across these sites and are not correlated with climate indicating that climate only weakly regulates nonglacial erosion rates in mountainous granitic terrain

two major cenozoic episodes of phosphogenesis recorded in equatorial pacific seamount deposits seamount phosphorites have been recognized since the 1950s but this is the first study to provide an in depth exploration of the origin and history of these widespread deposits representative samples from equatorial pacific cretaceous seamounts were analyzed for chemical mineralogical and stable isotope compositions the phosphorites occur in a wide variety of forms but most commonly carbonate fluorapatite cfa replaced middle eocene and older carbonate sediment in a deep water environment 1000 m element ratios distinguish seamount phosphorites from continental margin plateau and insular phosphorites uranium and thorium contents are low and total rare earth element ree contents are generally high ree ratios and shale normalized patterns demonstrate that the rees and host cfa were derived from seawater strontium isotopic compositions compared with inferred cenozoic seawater curves define two major episodes of cenozoic phosphatization late eocene early oligocene 39 34 ma and late oligocene early miocene 27 21 ma three minor events are also indicated the major episodes occurred at times of climate transition the first from a nonglacial to glacial earth and the second from a predominantly glacial to warm earth the paleoceanographic conditions that existed at those times initiated and sustained development of phosphorite by accumulation of dissolved phosphorus in the deep sea during relatively stable climatic conditions when oceanic circulation was sluggish fluctuations in climate sealevel and upwelling that accompanied the climate transitions may have driven cycles of enrichment and depletion of the deep sea phosphorus reservoir as temperature gradients in the oceans increased antarctic glaciation expanded and oceanic circulation and upwelling intensified expansion and intensification of the oxygen minimum zone may have increased the capacity for midwater storage of phosphorus supplied by dynamic upwelling around seamounts however the bottom waters never became anoxic during the phosphogenic episodes fluctuations in the ccd and lysocline co2 fluxes and changes in bottom water circulation and temperatures may have bathed the seamount carbonates in more corrosive waters which coupled with increased supplies of dissolved phosphorus promoted replacement processes the late eocene early oligocene phosphogenic episode recorded in seamount deposits is not matched by large phosphorite deposits in the geologic record whereas the late oligocene early miocene episode and middle miocene event are matched by large deposits distributed globally the seamount phosphorites are exposed at the surface of the seamounts and have been for most of the neogene and oligocene the phosphorites do not show signs of etching that would indicate substantial undersaturation of seawater phosphate with respect to cfa mass balance calculations indicate that about 5 4 19 1012 g of p2o5 are locked up in equatorial pacific seamount phosphorites that amount is equivalent to about 2 7 years of the present annual input from rivers

carbon sedimentation at lago grande de curuai a floodplain lake in the low amazon region insights into sedimentation rates we studied recent organic carbon sedimentation in an amazonian floodplain using sediment trap samples and one core sediment traps were placed in several lakes of the lago grande de curuai floodplain during different water level phases the end of the period of water level reduction falling water and the start of the period of water level increase rising water vertical seasonal fluxes of settling particles sp are very difficult to estimate and interpret especially during falling water periods when the concentration of suspended matter in the water column is greater than during rising water periods probably due to resuspension processes vertical fluxes of settling particles sp varied between ca 4 and 2000 g m 2 day 1 fluxes of organic carbon ranged between 5 50 g c m 2 day 1 during the falling water and between 0 041 4 g c m 2 day 1 during the rising water the core is characterised by two laminated sedimentological units sediments in the upper unit which generally coarsens upwards are interpreted as a progradation sequence of the sand and silt flat at the entrance of an inflow channel where the core was collected this unit is composed of three sub units a superficial layer reworked by bioturbation a lower sub unit characterised by horizontal and sub horizontal laminations of fine sands and silts and a basal sub unit composed of horizontal laminations of fine silts and clays the lower unit is characterised by horizontal and sub horizontal laminations of fine sands and silts and corresponds to the top of an older accumulating sequence these changes show that the sedimentary environment is very dynamic at the centennial scale sedimentation rates generally ranged between 0 42 and 1 34 cm year 1 and were estimated to range from 0 56 to 1 35 cm year 1 after normalisation for clay sized particles 4 m floodplain sediment accumulation generally varies between 0 42 1 16 and 1 10 g m 2 year 1 within the first second and third sub units respectively in the second unit the non supported 210pb date is close to the detection limit carbon content is relatively low around 1 sediment weight through the core although mean carbon accumulation rates are very high generally 100 g m 2 year 1 and peaking at 250 g m 2 year 1 these results suggest that amazon floodplain lakes may constitute an important sink for organic carbon

fe mn hydr oxide carbonate crusts from the kebrit deep red sea precipitation at the seawater brine redoxcline lithified crusts located within the sediment and recovered from the kebrit deep red sea are composed of fe and mn hydr oxides carbonates and sulfides mineralogical and geochemical features of these crusts suggest that they are metalliferous layers lithified by carbonates and formed in the narrow band where the transition zone between the anoxic brine and deep seawater crossed the seafloor carbonates cementing the fe mn hydr oxides precipitated from normal saline seawater at t 20 30 degrees c precipitation of fe mn hydr oxides was superimposed the carbonate precipitation in the transition zone a pumping mechanism involving cyclic fe and mn hydr oxide precipitation redissolution operated through the transition zone and produced an enrichment of a number of elements in the crusts the microbiota played an important role in the geochemical cycle of the elements through the redoxcline and in the mineralogy of the sediments underlying the redoxcline waters diagenetic processes led to formation of bi and ternary carbonates and disulfides c 2006 elsevier b v all rights reserved

the role of african dust in the formation of quaternary soils on mallorca spain and implications for the genesis of red mediterranean soils abstract african dust additions explain the origin of terra rossa soils that are common on the carbonate platform island of mallorca spain mineralogical and geochemical analyses indicate that quaternary carbonate eolianites on mallorca have a very high purity usually composed of more than 90 carbonate minerals calcite dolomite and aragonite in contrast terra rossa soils developed on these eolianites have lower carbonate contents and contain higher concentrations of quartz and other silicates analyses of immobile trace elements indicate that the non carbonate fractions of the eolianites have distinctive zr hf la yb cr sc and th ta values that differ from the superjacent terra rossa soils these observations indicate that even if sufficient dissolution of the eolianite had taken place to create the soils by residual accumulation immobile element ratios in the soils require an external source however zr hf la yb cr sc and th ta values in the soils fall within the range of values for these element ratios in african dust collected on barbados and mainland spain we conclude that the silicate fractions of terra rossa soils on mallorca are derived mainly though not wholly from far traveled african dust and this process may explain the origin of other terra rossa soils found in southern europe

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

first occurrence and stable isotope composition of authigenic γ mns in the central gotland deep baltic sea the occurrence of authigenic mns in organic matter rich sediments of the central gotland deep is reported for the first time the hexagonal manganese sulfide was found in a thin sediment layer with an approximate age of 1130 years and has an isotopic composition of 34s 13 vs v cdt this indicates that the bonded sulfur is derived from the anaerobic microbial reduction of pore water sulfate sem analysis reveals that mns occurs as idiomorphic crystals of about 200 m length and 150 m width much larger than the diameters of co existing calcian rhodochrosite globules 6 m it is suggested that formation of mns took place in a diagenetic environment which was locally free from reactive iron

evolution of neodymium isotopic signature of seawater during the late cretaceous implications for intermediate and deep circulation neodymium isotopic compositions end have been largely used for the last fifty years as a tracer of past ocean circulation and more intensively during the last decade to investigate ocean circulation during the cretaceous period despite a growing set of data circulation patterns still remain unclear during this period in particular the identification of the deep water masses and their spatial extension within the different oceanic basins are poorly constrained in this study we present new deep water end data inferred from the nd isotope composition of fish remains and fe mn oxyhydroxide coatings on foraminifera tests along with new end data of residual partly detrital fraction recovered from dsdp sites 152 nicaraguan rise 258 naturaliste plateau 323 bellinghausen abyssal plain and odp sites 690 maud rise and 700 east georgia basin south atlantic the presence of abundant authigenic minerals in the sediments at sites 152 and 690 detected by xrd analyses may explain both middle rare earth element enrichments in the spectra of the residual fraction and the evolution of residual fraction end that mirror that of the bottom waters at the two sites the results point towards a close correspondence between the bottom water end values of sites 258 and 700 from the late turonian to the santonian since the deep water nd isotope values at these two sites are also similar to those at other proto indian sites we propose the existence of a common intermediate to deep water mass as early as the mid cretaceous the water mass would have extended from the central part of the south atlantic to the eastern part of proto indian ocean sites beyond the kerguelen plateau furthermore data from south and north of the rio grande rise walvis ridge complex sites 700 and 530 are indistinguishable from the turonian to campanian suggesting a common water mass since the turonian at least this view is supported by a reconstruction of the rio grande rise walvis ridge complex during the turonian highlighting the likely existence of a deep breach between the rio grande rise and the proto walvis ridge at that time thus deep water circulation may have been possible between the different austral basins as early as the turonian despite the presence of potential oceanic barriers comparison of new seawater and residue end data on nicaraguan rise suggests a westward circulation of intermediate waters through the caribbean seaway during the maastrichtian and palaeocene from the north atlantic to the pacific this westward circulation reduced the pacific water influence in the atlantic and was likely responsible for more uniform less radiogenic end values in the north atlantic after 80 ma additionally our data document an increasing trend observed in several oceanic basins during the maastrichtian and the palaeocene which is more pronounced in the north pacific although the origin of this increase still remains unclear it might be explained by an increase in the contribution of radiogenic material to upper ocean waters in the northern pacific by sinking to depth these waters may have redistributed to some extent more radiogenic signatures to other ocean basins through deep water exchanges

paleo sea level changes and relative sea level indicators precise measurements indicative meaning and glacial isostatic adjustment perspectives from mallorca western mediterranean abstract paleo relative sea level rsl indicators formed during the marine isotope stage mis 5e have been reported by a large number of studies worldwide despite this three main aspects are seldom reported 1 use of high precision survey techniques applied to mis 5e rsl indicators 2 application of modern analogs to understand the indicative meaning of mis 5e rsl indicators 3 estimates of the effects of glacial isostatic adjustment gia on the mis 5e records in this study we show how the three points above have been addressed in a focused study on last interglacial outcrops on the island of mallorca we measured the elevation of several rsl indicators with high accuracy differential gps vertical accuracies down to 0 1 m and we established the relationship between each rsl indicator and the paleo sea level through calculation of the indicative meaning for each rsl indicator in particular we present a novel technique to calculate the indicative meaning of fossil beach deposits with a phase averaged morphodynamic model cshore we show how this approach helps overcoming difficulties with the survey of the modern analogs for these indicators our results show that two paleo rsls are imprinted in mallorca at 2 9 0 8 m and 11 3 1 0 m we then compare our field based results with modelled paleo rsl calculated from the predictions of the ice earth coupled anice selen model using few different ice sheet melting scenarios during mis 5e we conclude that indicative ranges can be derived from relatively simple morphodynamic models and that the comparison of field derived and modelled rsl values is a good method to validate possible scenarios of mis 5e sea level variability especially in absence of precise dating

the vendian cambrian δ13c record north iran evidence for overturning of the ocean before the cambrian explosion continuous fossilliferous successions across the precambrian cambrian pc c boundary in the elburz mountains of northern iran show a remarkable negative 13c excursion just below the pc c boundary high concentrations of manganese phosphorus barium and high abundances of fossil phytoplankton and black shale coincide with the excursion worldwide stratigraphic correlation shows that the isotopic anomaly is a global event the initial metazoan diversification coupled with13c enrichment occurs stratigraphically just above the excursion we propose the following scenario for oceanic environmental changes before the cambrian faunal explosion based on new data from iran a global warm climate following the last precambrian glaciation resulted in a generally stagnant oceanic condition so that surface water was oxic deep water was dysoxic depleted in13c and enriched in nutrients massive upwelling of deep water vertical advection of nutrients and13c depleted co2 caused enhanced phytoplankton productivity and a sharp drop in 13c in shallow water carbonate and organic carbon we conclude that latest cryptozoic overturning of ocean stratification preceded the cambrian explosion

phosphorus phosphorites and skeletal evolution at the precambrian cambrian boundary clustering of sedimentary phosphate deposits around the precambrian cambrian boundary is related to a global phosphogenic event this event probably resulted from a complex interplay of factors and had a profound effect on the biota with high concentrations of phosphorus in the photic zone producing an increase in the total shallow marine biomass faunal diversification the precipitation of skeletal structures and explosive evolution

uranium series ages of fossil corals from mallorca spain the neotyrrhenian high stand of the mediterranean sea revisited abstract the emergent marine deposits of the mediterranean basin have been recognized as an important record of quaternary sea level history for more than a century previous workers identified what have been interpreted to be two separate high stands of sea in the late quaternary namely the eutyrrhenian thought to be 120 ka and the neotyrrhenian thought to be either 100 ka or 80 ka on mallorca spain both of these named deposits lie close to present sea level implying paleo sea levels slightly above present during both marine isotope stages mis 5 5 5e and either 5 3 5c or 5 1 5a if these interpretations are correct they conflict at least in part with sea level records from far field localities we analyzed corals from the neotyrrhenian beds on mallorca which gave u series ages from 126 ka to 118 ka these ages are consistent with previously published amino acid data that show that the neotyrrhenian and eutyrrhenian deposits are not significantly different in age a fossil molluscan fauna from the neotyrrhenian deposits on mallorca has a warm water paleozoogeographic aspect with nine southward ranging species and four extralimital southern species when compared with sea surface temperatures obtained from planktonic foraminifera and alkenones from odp core 977 in the nearby alboran sea the only time period that shows comparable warmth is mis 5 5 5e consistent with the u series ages of corals from the neotyrrhenian deposits we propose that the neotyrrhenian deposits are a beachrock facies of the same age as the eutyrrhenian deposits this interpretation is consistent with the differences in physical sedimentology of the two deposits explains the u series and amino acid data indicating the same age is consistent with the very slight elevation difference of the neotyrrhenian and eutyrrhenian beds and explains the similar though not identical paleozoogeographic aspects of their fossil faunas

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

origin and environment of manganese rich sediments within black shale basins abstract sediments with unusually high manganese contents occur in anoxic basins of the central baltic sea we present a new model for the enrichment of manganese which is based on sedimentological and geochemical analyses of holocene sediments from the gotland deep and on published hydrographic data due to salinity stratification and high primary production bottom waters of the central baltic sea are anoxic and rich in dissolved mn 2 episodically bottom waters become oxygenated by inflows of denser water from the north sea mixing results in oxidation of mn 2 to fine grained particulate oxides which accumulate in the deepest parts of the basins where currents are mostly absent here anoxic conditions are re established within a few months or years and manganese oxides are again dissolved causing high concentrations of mn 2 in the near bottom layer alkalinity is high as a consequence of bacterial reduction of manganese oxides and sulphate under these conditions manganese is reprecipitated and forms a layer of ca rich rhodochrosite on the top of laminated sapropels occasionally periods of such extremely and rapidly changing redox conditions are followed by long term oxygenation of bottom waters in that case a layer rich in manganese oxides forms on the top of a bioturbated layer due to dissolution of rhodochrosite and oxidation of manganese in the near surface sediment return of anoxic conditions results again in the transformation of manganese oxides into rhodochrosite varying rhodochrosite contents in the basinal sediments therefore record a detailed history of redox conditions in bottom waters the manganese rich sediments of the baltic sea share many features with some occurrences of lower jurassic and lower carboniferous manganese ores in western and central europe we therefore suggest that these manganese enrichments were formed by similar processes

sedimentary manganese metallogenesis in response to the evolution of the earth system abstract the concentration of manganese in solution and its precipitation in inorganic systems are primarily redox controlled guided by several earth processes most of which were tectonically induced the early archean atmosphere hydrosphere system was extremely o2 deficient thus the very high mantle heat flux producing superplumes severe outgassing and high temperature hydrothermal activity introduced substantial mn2 in anoxic oceans but prevented its precipitation during the late archean centered at ca 2 75 ga the introduction of photosystem ii and decrease of the oxygen sinks led to a limited buildup of surface o2 content locally initiating modest deposition of manganese in shallow basin margin oxygenated niches e g deposits in india and brazil rapid burial of organic matter decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the archean proterozoic transition concurrently a massive drawdown of atmospheric co2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused paleoproterozoic glaciations 2 45 2 22 ga the spectacular sedimentary manganese deposits at ca 2 4 ga of transvaal supergroup south africa were formed by oxidation of hydrothermally derived mn2 transferred from a stratified ocean to the continental shelf by transgression episodes of increased burial rate of organic matter during ca 2 4 and 2 06 ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere black shale hosted mn carbonate deposits in the birimian sequence ca 2 3 2 0 ga west africa its equivalents in south america and those in the francevillian sequence ca 2 2 2 1 ga gabon are correlatable to this period tectonically forced doming up attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric co2 drawdown causing glaciation on the neoproterozoic rodinia supercontinent tectonic rifting and mantle outgassing led to deglaciation dissolved mn2 and fe2 concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation during the sturtian glacial interglacial event ca 750 700 ma interstratified mn oxide and bif deposits of damara sequence namibia was formed the varangian marinoan ca 600 ma cryogenic event produced mn oxide and bif deposits at urucum jacadigo group brazil the datangpo interglacial sequence south china liantuo nantuo varangian event contains black shale hosted mn carbonate deposits the early paleozoic witnessed several glacioeustatic sea level changes producing small mn carbonate deposits of tiantaishan early cambrian and taojiang mid ordovician in black shale sequences china and the major mn oxide carbonate deposits of karadzhal type central kazakhstan late devonian the mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans during the early jurassic oae organic rich sediments host many mn carbonate deposits in europe e g urkut hungary in black shale sequences the late jurassic giant mn carbonate deposit at molango mexico was also genetically related to sea level change mn carbonates were always derived from mn oxyhydroxides during early diagenesis large mn oxide deposits of cretaceous age at groote eylandt australia and imini tasdremt morocco were also formed during transgression regression in greenhouse climate the early oligocene giant mn oxide carbonate deposit of chiatura georgia and nikopol ukraine were developed in a similar situation thereafter manganese sedimentation was entirely shifted to the deep seafloor and since ca 15 ma b p was climatically controlled glaciation deglaciation assisted by oxygenated polar bottom currents aabw nadw the changes in climate and the sea level were mainly tectonically forced

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

a review of apatites iron and manganese minerals and their roles as indicators of biological activity in black shales abstract biological contribution to the formation of minerals has become more than a descriptive area in geological thought and research mechanisms of specific mineral accumulation and deposition in oceancs lakes and even desert environment are studied using interdisciplinary approaches and applied in the interpretation of earth processes phosphorus iron and manganese are and probably were essential elements in life forms the common minerals of these elements apatite and magnetite for example can be found in a variety of sedimentary environments both ancient and modern where they could be useful indicator minerals to interpret geologic environments the crystal morphological structural and chemical including isotopic attributes of these usually fine grained minerals can be compared with bulk chemical and stratigraphic information to augment our understanding of the mechanisms of formation and diagenesis in sediments such as black shales

the process of formation of manganese carbonate deposits hosted in black shale series the two most important types of manganese deposits in china are sedimentary and supergene which account for 71 and 15 percent of the total manganese reserves respectively according to the host rock associations sedimentary manganese deposits can be classified into 1 a mud rock type 2 a black shale series type 3 a carbonate rock type and 4 a chert limestone mudstone type the black shale series type manganese deposits account for 48 percent of the total manganese reserves and are large or medium sized deposits the black shale series or dark colored sedimentary association consists of dark colored mudrock chert carbonate rocks rich in sulfides and organic matter c organic or 1 the term black shale series type manganese deposits is a general name for all manganese deposits hosted in black shale black chert black siliceous shale dark gray limestone etc black shale series type manganese deposits are distributed in 13 stratigraphic horizons from middle proteozoic to early triassic they can be divided into three subtypes 1 a black shale subtype 2 a black chert siliceous shale subtype and 3 a dark gray limestone subtype subtype 1 consists mainly of primary mn carbonate ores subtypes 2 and 3 consist mainly of mn containing limestones weathering and leaching processes can change the mn limestones into mn oxide ores which form large and high quality supergene deposits for example the mugui and dongxiangqiao deposits manganese carbonate ores hosted in the black shale series consist mainly of rhodochrosite calcio rhodochrosite kutnohorite manganocalcite mn containing calcite mn containing dolomite etc the ores are black dark gray light gray yellowish and pink in color and have banded laminated massive oolitic spotted and brecciated structures commonly changes in the ore bearing sequences show from bottom to top 1 black shale series 2 mn carbonate ore bed 3 light colored rocks this indicates that ore beds formed in the transition from reduced to slightly oxidized and from weakly alkaline to alkaline conditions the evolution of the ore bearing sequence indicates that manganese mineralization occurred during the early stage of regression the important mn carbonate deposits hosted in the black shale series resulted from three main processes during formation concentration in seawater precipitation from seawater and enrichment in the sediments anoxic conditions are a basic factor for manganese concentration in seawater a weak oxic and alkaline environment is favorable for mn carbonate precipitation and microbiological activities play an important role for early diagenetic enrichment of manganese in the deposits

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

chemostratigraphy of paleoproterozoic carbonate successions of the wyoming craton tectonic forcing of biogeochemical change the archean wyoming craton is flanked on the south and east by belts of paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop however carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy the 10 km thick paleoproterozoic snowy pass supergroup in the medicine bow mountains was deposited on the present day southern flank of the wyoming craton it contains three discrete levels of glacial diamictite correlative with those in the huronian supergroup on the southern margin of the superior craton the nash fork formation of the upper snowy pass supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the paleoproterozoic glacial epoch carbonates at the base of the nash fork formation record remarkable 13 cenrichment up to 28 v pdb whereas those from overlying members of the lower nash fork formation have d 13 c values between 6 and 8 carbonates from the upper nash fork formation above the carbonaceous shale have carbon isotope values ranging between 0 and 2 5 the transition from high carbon isotope values to those near 0 in the nash fork formation is similar to that at the end of the ca 2 2 2 1 ga carbon isotope excursion in fennoscandia this chemostratigraphic trend and deposition of bifs mn rich lithologies carbonaceous shales and phosphorites at the end of the global ca 2 2 2 1 ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the kenorland supercontinent correlative carbonates from the slaughterhouse formation in the sierra madre wy and from the whalen group in the rawhide creek area in the hartville uplift wy have highly positive carbon isotope values in contrast carbonates from other exposures of the whalen group in the hartville uplift and all carbonate units in the black hills sd have carbon isotope values close to 0 combined with existing geochronologic and stratigraphic constraints these data suggest that the slaughterhouse formation and the succession exposed in the rawhide creek area of the hartville uplift are correlative with the lower and middle nash fork formation and were deposited during the ca 2 2 2 1 ga carbon isotope excursion the estes and roberts draw formations in the black hills and carbonates from other exposures in the hartville uplift postdate the ca 2 2 2 1 ga

characteristics and origin of the middle proterozoic dongshuichang chambersite deposit jixian tianjin china abstract the jixian type boron manganese b mn deposits include both chambersite and rhodochrosite deposits from which dongshuichang is economically the best chambersite deposit although the ore bodies of the region are relatively small they contain a rare b mn ore that is scientifically significant chambersite mn 3 b 7 o 13 cl is a rare mineral discovered as a mineral in 1957 and as an ore in 1971 at the dongshuichang deposit near jixian tianjin city the deposit forms a monocline with a southwest dip and covers an area of 2 km 2 in the mine area the gaoyuzhuang formation the upper member of the middle proterozoic changcheng system consists mainly of stromatolitic and muddy dolostone with b mn bearing siliceous shale and dark gray dolostone individual ore lenses range in length from 1 to 4 m with a mean thickness of 0 25 m the ores can be divided into high grade and low grade the former is composed of spindle and granular chambersite aggregates and the latter of spheroidal chambersite in dark gray micritic dolostone the center of spheroids is commonly composed of micritic and columnar chambersite dolomite clay minerals and organic matter around which columnar chambersite grew forming a sunflower shape the organic carbon content in high grade ores is 0 63 in low grade ores 0 83 and in overlying black siliceous shale 3 75 total rare earth element ree contents of two chambersite ore samples are 29 and 35 ppm whereas that of rhodochrosite ore is 22 ppm the chondrite normalized ree patterns of chambersite and rhodochrosite ores are similar with small negative ce and eu anomalies and a small positive gd anomaly the 13 c pdb values of two rhodochrosite ore samples are 4 3 and 7 3 indicating that the carbon source of mn carbonate minerals was mainly seawater bicarbonate with a small contribution from the degradation of organic carbon the source of the dongshuichang ore components was mainly submarine volcanic eruptions and a small amount from the weathering of pre proterozoic boron deposits the chambersite precipitated under conditions of high salinity high b mn and mg concentrations and weak alkalinity low oxygen conditions might be favorable for precipitation of chambersite

palaeoclimate and palaeoenvironmental responses in the western mediterranean over the last 140 ka evidence from mallorca spain climatic change in the western mediterranean basin over the last 140 ka has been investigated from sediment and soil sequences along the coast of the northeastern part of mallorca spain palaeoclimate and palaeoenvironments are reconstructed from sediment and soil structures marine and terrestrial molluscan fauna grain size distributions mineral magnetics sediment and soil chemistry sem and oxygen isotope values dating is by osl and amino acid geochronometry along with marine molluscan faunal assemblages all oxygen isotope stages and substages from ois 6 to 1 are recorded mean annual temperatures m a t of c 19 2 c for the climatic optimum of the last interglacial compare with c 17 3 c for the present and are associated with high sea level extensive woodland and stable soils although wide temperature ranges are detected during this stage with values as low as c 10 3 c through ois 5d to 5a m a t fluctuated from 8 2 c to 17 9 c low sea level open vegetation effective river activity and aeolian sand and dust deposition characterize 5d and 5b while relatively high sea level and soil development on stable landscapes dominate ois 5c and 5a ois 4 is represented by m a t of c 4 9 c with aeolian sand and loess deposition limited river activity and weak soil development loess deposition persisted into ois 3 but at this time the m a t was c 13 c and with higher humidity and vegetation growth during the lgm ois 2 m a t was c 8 1 c and effective river slope and aeolian processes along with associated with limited vegetation cover were responsible for the most extensive changes in the landscape major rates of change occur during periods of climatic deterioration when the high levels of geomorphic energy were imposed on a landscape undergoing a breakdown of vegetation cover

source and distribution of pollen in the surface sediment of daihai lake inner mongolia daihai lake lies in the transitional area from semi humid to semi arid region and also in the north margin of the east asia monsoon the analysis of 65 pollen samples from the surface sediment of daihai lake and alluvium of its inflow rivers revealed the characteristics of pollen distribution and different transport vectors most pollen grains in daihai lake come from its inflow rivers although rain out and wind are also important activities of insects birds and humans may also carry pollen into the lake the pollen assemblages are consistent with the regional vegetation in general the variance of pollen assemblages in different parts of the lake reflects changes of local vegetation near the lakeshore pollen concentrations in the lake sediment surface are lower than that in fresh alluvium in its inflow rivers and the highest percentages and concentrations of major pollen types mainly appear in the margin part of the lake dca demonstrated that there are more similarities between lake sediments and the inflow rivers than there are differences

stable isotope chemical and mineral compositions of the middle proterozoic lijiaying mn deposit shaanxi province china abstract the lijiaying mn deposit located about 250 km southwest of xian is a high quality ore characterized by low p and fe contents and a mean mn content of about 23 the ore deposit occurs in shallow water marine sedimentary rocks of probable middle proterozoic age carbonate minerals in the ore deposit include kutnahorite calcite mn calcite and mg calcite carbon 0 4 to 4 0 and oxygen 3 7 to 12 9 isotopes show that with a few exceptions those carbonate minerals are not pristine low temperature marine precipitates all samples are depleted in rare earth elements rees relative to shale and have negative eu and positive ce anomalies on chondrite normalized plots the fe mn ratios of representative ore samples range from about 0 034 to

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

geomorphological characteristics and slope processes associated with different basins mallorca western mediterranean abstract we compare the different geomorphological processes which occurred in pliocene quaternary times on two very similar slopes in mallorca one located at the tramuntana range and the other in the llevant ranges both slopes have the same geological structure the same stratigraphic and lithological levels and the same altitude and orientation the different slope processes are due to the relationship between the accommodation space and the sedimentation rate in the adjacent basins in the valencia trough located n of the tramuntana range the sedimentation rate has not been sufficient to fill the accommodation space whereas in the alcudia basin adjacent to the llevant ranges the sedimentation rate has been sufficient to fill the accommodation space this difference has resulted in major landslides on the tramuntana slope whereas the llevant slope is characterized mainly by alluvial fans and debris screes

bacterially mediated diagenetic origin for chert hosted manganese deposits in the franciscan complex california coast ranges numerous manganese deposits in the franciscan complex california occur as conformable lenses within bedded radiolarian chert argillite sequences that are in turn intercalated within thicker sections of sandstone and shale the field relations composition and petro graphic and isotopic characteristics indicate that the manganese was concentrated by diagenetic reconstitution of siliceous and hemipelagic sediment during burial the ore lenses are mn rich and fe poor assemblages consisting largely of rhodochrosite manganese silicates opal ct disordered cristobalite tridymite and quartz highly negative 13 c values for the carbonate carbon in rhodochrosite indicate that co 2 likely originated from oxidation of methane less negative values result from mixing of methanogenic carbon and co 2 derived from bacterial degradation of organic matter the 18 o values for the carbonate of rhodochrosite indicate temperatures of formation between 12 and 100 c the oxidation of methane prior to carbonate precipitation may have used the minor 0 4 0 5 mn and fe oxyhydroxides and oxides deposited with the sediment the mobilization of manganese from biogenic and terrigenous sources in the sediment column into discrete horizons and the fractioriation of manganese from iron reflect the presence of oxidation reduction boundaries and gradients in the sediment column fluids derived from compaction and silica dehydration reactions in the transformation of opal a x ray amorphous biogenic silica to quartz were involved in transportation of principal components sedimentary and geochemical attributes suggest that the deposits formed in a deep water environment in a zone of oceanic upwelling near a continental margin

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member