past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

paleo sea ice conditions of the amundsen gulf canadian arctic archipelago implications from the foraminiferal record of the last 200 years 1 four boxcores were collected as part of the canadian arctic exchange shelf study cases in the amundsen gulf at water depths of 59 m to 600 m data from these cores help to develop a record of changes in the oceanographic history of the area over the last 200 years with particular reference to the indication of paleo sea ice formation a key element of the arctic ecosystem the four sites cover a range of water depths and environments to provide a basis for comparison the benthic foraminifera of sites ca 06 253 m water depth and ca 18 600 m water depth show an increase in arctic surface water associated agglutinated foraminifera over the last 100 years uppermost 8 to 16 cm these are indicating a decrease in sea ice cover and in cold saline arctic bottom water influence these are similar to canadian arctic archipelago postglacial faunas this contrasts with abundant planktic foraminifera at the same stations suggesting strong oceanic arctic surface influence little freshwater in the central gulf the foraminifera of sites 403b 59 m water depth and 415b 56 m water depth at the outermost edges of amundsen gulf indicate that the present day location of the winter flaw lead has been in place for at least the last 100 years with foraminiferal faunas similar to those of the beaufort shelf additionally station 415 is on an earlier holocene shoreline that is covered with cobbles

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

1 500 year cycle in the arctic oscillation identified in holocene arctic sea ice drift decadal to centennial scale variability has been identified in the arctic oscillation but less is known about variations on the millennial scale a record of sea ice drift from off the alaskan coast shows a 1 500 year cycle in the phase of the arctic oscillation

spatial variations in geochemical characteristics of the modern mackenzie delta sedimentary system the mackenzie river in canada is by far the largest riverine source of sediment and organic carbon oc to the arctic ocean therefore the transport degradation and burial of oc along the land to ocean continuum for this riverine system is important to study both regionally and as a dominant representative of arctic rivers here we apply sedimentological grain size mineral surface area and organic and inorganic geochemical techniques oc 13c oc and 14c oc 143nd 144nd 2h and 18o major and trace elements on particulate bank channel and lake surface sediments from the mackenzie delta as well as on surface sediments from the mackenzie shelf in the beaufort sea our data show a hydrodynamic sorting effect resulting in the accumulation of finer grained sediments in lake and shelf deposits a general decrease in organic carbon oc to mineral surface area ratios from river to sea furthermore suggests a loss of mineral bound terrestrial oc during transport through the delta and deposition on the shelf the net isotopic value of the terrestrial oc that is lost en route derived from relationships between 13c oc and surface area is 28 5 for 13c and 417 for 14c we calculated that oc burial efficiencies are around 55 which are higher 20 than other large river systems such as the amazon old sedimentary oc ages up to 12 14c ky suggest the delivery of both a petrogenic oc source with an estimated contribution of 19 9 as well as a pre aged terrestrial oc source we calculated the 14c age of this pre aged biogenic component to be about 6100 yrs or 501 which illustrates that terrestrial oc in the watershed can reside for millennia in soils before being released into the river surface sediments in lakes across the delta n 20 showed large variability in oc 0 92 5 7 and 13c 30 7 to 23 5 high closure lakes flooding only at exceptionally high water levels hold high sedimentary oc contents 2 5 and young biogenic oc with a terrestrial or an autochthonous source whereas no closure lakes permanently connected to a river channel hold sediments with pre aged terrestrial oc the intermediate low closure lakes flooding every year during peak discharge display the largest variability in oc content age and source likely reflecting variability in for example the length of river lake connections the distance to sediment source and the number of intermediate settling basins bank channel and suspended sediment show variable 143nd 144nd values yet there is a gradual but distinct spatial transition in 143nd 144nd nearly three e units from 11 4 to 13 9 in the detrital fraction of lake surface sediments from the western to the eastern delta this reflects the input of younger peel river catchment material in the west and input of older geological source material in the east and suggests that lake sediments can be used to assess variability in source watershed patterns across the delta

sediment provenance changes in the western arctic ocean in response to ice rafting sea level and oceanic circulation variations since the last deglaciation two sediment piston cores were recovered from the chukchi alaskan 05jpc and canadian beaufort 02pc margins to investigate grain size geochemical and mineralogical compositions this allowed the reconstruction of changes in detrital sediment provenance and transport related to climate variability since the last deglaciation the end member modeling analyses of grain size indicate that sea ice and nepheloid transport and the mackenzie river sediment plume are major factors influencing sedimentation in the chukchi alaskan and canadian beaufort margins respectively unmixing of the sediment composition indicates that detrital sediments in core 02pc are derived mainly from the mackenzie river whereas sediments from core 05jpc are derived mainly from the mackenzie river during the deglaciation and include a mixture of holocene sediments from the bering strait mackenzie river and eurasian margin the dolomite rich ice rafted debris recorded in both cores could be related to the different phases of iceberg discharges from the amundsen gulf ice stream quartz and feldspar rich ice rafted debris dated at 13 and 10 6 ka cal bp before present are related to the lake agassiz outburst in core 02pc and meltwater discharge from the brooks range glaciers in core 05jpc detrital proxies in core 02pc support the hypothesis that large meltwater and iceberg discharges from the lake agassiz outburst to the arctic ocean and amundsen gulf ice stream may have triggered the younger dryas finally similar trends observed between sea level curves and our detrital proxy suggest that the sea level changes in the western arctic ocean have an important influence on the sediment dynamic during the early to middle holocene keywords bulk and clay mineralogy elemental geochemistry grain size distribution sediment provenance canadian beaufort sea chukchi sea

spatial and temporal variability of sea ice in the southern beaufort sea and amundsen gulf 1980 2004 1 changing extent location and motion of the arctic perennial pack affect the annual evolution of seasonal ice zones canadian ice service digital ice charts covering the southern beaufort sea and amundsen gulf are used to illustrate summer and winter conditions and trends between 1980 and 2004 for several sea ice stages of development results illustrate average sea ice conditions within the region in summer and winter for predominant sea ice types and changes in the relative concentration of sea ice types in summer and winter in summer a trend toward increased old sea ice concentration occurred near the mouth of amundsen gulf with a trend toward decreasing summer first year sea ice farther west in winter increasing thick first year sea ice extent appears to be replacing young sea ice within the flaw lead system in the region the dynamically driven breakup of sea ice in spring in the amundsen gulf is a highly variable event taking anywhere between 2 and 22 weeks to completely remove ice from the gulf the timing and duration of the open water season depends upon the extent and timing of old ice influx freezeup occurs very quickly proceeding from west to east with little temporal variability the results of this paper are used to set the context for the canadian arctic shelf exchange study cases in terms of sea ice dynamic and thermodynamic processes

active mud volcanoes on the continental slope of the canadian beaufort sea the major geochemical characteristics of red sea brine are summarized for 11 brine filled deeps located along the central graben axis between 19 n and 27 n the major element composition of the different brine pools is mainly controlled by variable mixing situations of halite saturated solution evaporite dissolution with red sea deep water the brine chemistry is also influenced by hydrothermal water rock interaction whereas magmatic and sedimentary rock reactions can be distinguished by boron lithium and magnesium calcium chemistry moreover hydrocarbon chemistry concentrations and 13 c data of brine indicates variable injection of light hydrocarbons from organic source rocks and strong secondary bacterial or thermogenic degradation processes a simple statistical cluster analysis approach was selected to look for similarities in brine chemistry and to classify the various brine pools as the measured chemical brine compositions show remarkably strong concentration variations for some elements the cluster analysis indicates two main classes of brine type i brine chemistry oceanographer and kebrit deeps is controlled by evaporite dissolution and contributions from sediment alteration the type ii brine suakin port sudan erba albatross discovery atlantis ii nereus shaban and conrad deeps is influenced by variable contributions from volcanic magmatic rock alteration the chemical brine classification can be correlated with the sedimentary and tectonic setting of the related depressions type i brine filled deeps are located slightly off axis from the central red sea graben a typical collapse structure formation which has been defined for the kebrit deep by evaluating seismic and geomorphological data probably corresponds to our type i brine type ii brine located in depressions in the northern red sea i e conrad and shaban deeps could be correlated to volcanic intrusion extrusion related deep formation the chemical indications for hydrothermal influence on conrad and shaban deep brine can be related to brines from the multi deeps region in the central red sea where volcanic magmatic fluid rock interaction is most obvious the strongest hydrothermal influence is observed in atlantis ii brine central multi deeps region which is also the hottest red sea brine body in 2011 68 2 c

quaternary ice transport in the canadian arctic and extent of late wisconsinan glaciation in the queen elizabeth islands most of the ice rafted debris in channels off the queen elizabeth islands nunavut is of local origin particularly in the inner part of the archipelago but samples from the arctic shelf contain as much as 40 grains from sources as far away as 2000 km including the siberian shelves particle transport by drifting sea ice from distant shelves is an important process on the arctic continental shelf of the queen elizabeth islands in the interior of the queen elizabeth islands and in the viscount melville and lancaster sounds particle transport is limited to distances of approximately 200 km mixing is more common among grains of coarse silt to fine sand than in the 250 m fraction but even the latter contains debris from sources far apart during the late wisconsinan the northern southern and eastern queen elizabeth islands were covered by glaciers flowing radially from ice centers on the islands into the inter island channels queens channel was completely filled by ice and a glacier lobe moved

composition and discrimination of sandstones a statistical evaluation of different analytical methods the discriminative power of four analytical approaches to sandstone composition is evaluated with respect to the separation of different formations and source areas the case study is cretaceous synorogenic sandstones litharenites from the eastern alps of europe which belong to four different formations and are derived from two source areas methods evaluated are light mineral analysis petrographic framework composition heavy mineral analysis major element xrf analysis and trace element xrf analysis the statistical parameters calculated percentages of well classified samples mahalanobis distance applying the logratio approach suggest that light mineral analysis has a significantly lower discriminative power than the other three methods taking into account the analytical expenditure for data acquisition trace element analysis appears to be the most efficient method for discrimination of at least the sandstone units examined although based on a single case study these results are interpreted to have a more general meaning with respect to sandstone discrimination based on composition concerning sandstone provenance trace element analysis provides a quick tool to estimate the discriminative potential of a sample suite i e the potential to discriminate between contrasting source areas if a provenance model already exists and discriminate functions between contrasting source areas are calculated trace element analysis is considered to be most efficient in correctly assigning an unknown sample to its source area these results cannot be extended to all kinds of sands and sandstones but they cast serious doubt on the belief that petrographic point count methods are the best approach to discriminate between sandstones

modern river discharge and pathways of supplied material in the eurasian arctic ocean evidence from mineral assemblages and major and minor element distribution clay mineral heavy mineral and elemental distributions in sediments from the arctic ocean and the adjacent laptev and kara seas can be attributed to the geology of the hinterland and the transport of terrigenous material by rivers onto the shelves kara sea sediments are characterized by increased contents of smectite and elevated ni al ti al and cr al ratios in the western laptev sea sediments are enriched in smectite and clinopyroxene and increased in ti al cr al and ca al ratios the composition of the sediments reflects suspended matter input from the large trap basalt of the putoran mountains the eastern laptev sea sediments display increased illite and amphibole contents as well as a chemical composition similar to average shale this composition is due to the discharge from the lena and yana rivers which drain a large catchment area consisting of sedimentary mesozoic and paleozoic rocks material from the eastern laptev sea is transported by ocean currents and sediment laden sea ice along the transpolar drift into the central arctic ocean this is indicated by similar values of ti al cr al rb al and k al ratios as well as increased concentrations of amphibole and illite determined in sediments from the lomonosov ridge a minor input from the beaufort sea into the central arctic ocean is suggested from increased ca al ratios and increased contents of opaque minerals

the freshwater budget and under ice spreading of mackenzie river water in the canadian beaufort sea based on salinity and 18o 16o measurements in water and ice observations of salinity and oxygen isotope composition 18o were made for the beaufort shelf mackenzie estuary waters in september 1990 just prior to ice formation and for both the water column and ice in april may 1991 at the end of winter these measurements are used to determine the apportioning of fresh water in the estuary between its two main sources runoff and sea ice melt changes in disposition of water between seasons and amounts frozen into the growing ice sheet are also derived two domains are considered in order to construct a freshwater budget for the mackenzie shelf the nearshore within which landfast ice grows in winter and the outer shelf most of the winter inflow from the mackenzie river appears to remain impounded as liquid under the ice within the landfast zone at the end of winter and about 15 of it is incorporated into the landfast ice oxygen isotopes 18o in ice cores collected from across the shelf record the progress beneath the ice of new mackenzie inflow as it invades the nearshore throughout winter rates of spreading are about 0 2 cm s 1 away from the coast and 1 3 cm s 1 along the coast as this inflow spreads across the shelf it progressively shuts off convection driven by brine production at locations within the landfast ice salinity and 18o in the offshore water column suggest that about 3 m of sea ice was formed in the outer shelf domain since both brine and newly formed sea ice can be advected off the shelf a complete budget for brine or sea ice production cannot be established without first measuring the advection of one of these two components

microbially mediated carbonate precipitation in a hypersaline lake big pond eleuthera bahamas microbial metabolism impacts the degree of carbonate saturation by changing the total alkalinity and calcium availability this can result in the precipitation of carbonate minerals and thus the formation of microbialites here the microbial metabolic activity the characteristics and turnover of the extracellular polymeric substances and the physicochemical conditions in the water column and sediments of a hypersaline lake big pond bahamas were determined to identify the driving forces in microbialite formation a conceptual model for organomineralization within the active part of the microbial mats that cover the lake sediments is presented geochemical modelling indicated an oversaturation with respect to carbonates including calcite aragonite and dolomite but these minerals were never observed to precipitate at the mat water interface this failure is attributed to the capacity of the water column and upper layers of the microbial mat to bind calcium a layer of high mg calcite was present 4 to 6 mm below the surface of the mat just beneath the horizons of maximum photosynthesis and aerobic respiration this carbonate layer was associated with the zone of maximum sulphate reduction it is postulated that extracellular polymeric substances and low molecular weight organic carbon produced at the surface i e the cyanobacterial layer of the mat bind calcium both aerobic and anaerobic heterotrophic microbes consume extracellular polymeric substances each process accounting for approximately half of the total consumption and low molecular weight organic carbon liberating calcium and producing inorganic carbon the combination of these geochemical changes can increase the carbonate saturation index which may result in carbonate precipitation in conclusion the formation and degradation of extracellular polymeric substances as well as sulphate reduction may play a pivotal role in the formation of microbialites both in marine and hypersaline environments

sources of sediment found in sea ice from the western arctic ocean new insights into processes of entrainment and drift patterns 1 the geochemical fingerprint of entrained fe oxide mineral grains in arctic ocean sea ice is used to determine precise sources of this sediment this approach substantiates the importance of the laptev sea as a source of sea ice and even the presence of russian ice in the beaufort sea off alaska fe oxide grains from the laptev sea were found in floes in the beaufort sea chukchi borderland and central arctic ocean demonstrating the importance of sea ice in distributing itself throughout the arctic ocean and the potential of transporting sediment from russian rivers to north american shelves banks island shelf is the most important source of sediment sampled from ice floes in the beaufort sea northern chukchi sea and chukchi borderland area although most of the entrained sediment fits the criteria for suspension freezing in shallow water the presence of winter polynyas with offshore winds and not the size of shallow areas appears to be the critical factor for sea ice entrainment seven of the 18 ice floes sampled contained fe oxide grains from more than one source area the two most common sources that are found in the same ice floes are banks island and the laptev sea multiple sources in ice floes suggest that either mingling of fragmented ice floes occurs or that a source area containing grains from both these sources has yet to be located the addition of fine sand sized windblown sediment is not thought to be significant

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

a sediment and organic carbon budget for the canadian beaufort shelf abstract the arctic ocean accounts for 20 of the world s continental shelves because the arctic is sensitive to global change budgets of organic carbon for its shelves are of immediate interest the mackenzie shelf of the canadian beaufort sea is the best north american proxy for the enormous eurasian shelves large area large river input and the only site for which a complete organic carbon budget can be attempted due to an extensive data base a mass balance for the mackenzie shelf has been constructed for sediments terrestrial organic carbon and primary produced carbon we have considered allochthonous inputs from the mackenzie river from coastal erosion from smaller rivers from groundwater from the atmosphere and import by ice the mackenzie river dominates the supply to the beaufort shelf of inorganic sediment 127 mt a 1 and paniculate and dissolved terrestrial carbon 2 1 mt a 1 poc 1 3 mt a 1 doc the combined input from all other sources contributes only about 5 of the mackenzie load using sediment accumulation data we estimate that about half of the sediment supply is trapped in the delta about 40 on the shelf and the remainder escapes the shelf edge by various processes autochthonous primary production in the delta and on the shelf adds a further 3 3 mt a 1 of particulate organic carbon a box model has been constructed to account for sediment terrestrial organic carbon and primary produced carbon whereas about 60 of the terrestrial poc is preserved in delta and shelf sediments it appears that most 97 of the primary produced carbon is recycled and not preserved in sediments confidence in the budget should be improved by focusing future research on the determination of modern sedimentation rates on the delta and shelf measurement of organic carbon content of deltaic sediments determination of primary production on the shelf and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments

the mackenzie delta sedimentary processes and facies of a high latitude fine grained delta the mackenzie delta is a large fine grained delta deposited in a cold arctic setting the delta has been constructed upon a flooding surface developed on a previous shelf phase delta there are three principal depositional zones the subaerial delta plain the distributary channel mouth region and the subaqeous delta the subaerial delta plain is characterized by an anastomosing system of high sinuosity channels and extensive thermokarst lake development this region is greatly influenced by the annual cycle of seasonal processes including winter freezing of sediments and channels ice jamming and flooding in the early spring and declining river stage during the summer and autumn deposition occurs on channel levees and in thermokarst lakes during flood events and is commonly rhythmic in nature with discrete annual beds being distinguishable in the channel mouth environment deposition is dominated by landward accretion and aggradation of mouth bars during river and storm surge induced flood events the subaqeous delta is characterized by a shallow water platform and a gentle offshore slope sediment bypassing of the shallow water platform is efficient as a result of the presence of incised submarine channels and the predominance of suspension transport of fine grained sediments facies of the shallow platform include silty sand with climbing ripple lamination offshore facies are dominated by seaward fining fine sand to silt tempestites sea ice scouring and sediment deformation are common beyond 10 m water depth where bioturbated muds are the predominant facies the low angle profile of the shallow water platform is interpreted to be the combined response of a fine grained delta to 1 storm sediment dispersal 2 autoretreat as a result of the increasing subaerial and subaqeous area of deposition as the delta progrades out of its glacial valley 3 limited water depth above the underlying flooding surface and 4 efficient nearshore bypassing of sediment through subice channels at the peak of spring discharge several indicators of the cold climate can be used as criteria for the interpretation of ancient successions including thermokarst lake development submarine channel scours freeze thaw deformation and ice scour deformation structures permafrost inhibits compaction subsidence and together with the shallow water setting also limits autocyclic lobe switching the cold climate can thus influence stratal architecture by favouring the development of regional scale clinoform sets rather than multiple smaller scale lobes separated by autocyclic flooding surfaces

the slave province a distinct archean craton the slave province is a relatively small late archean craton that exhibits distinctive rock associations and structures by comparison with the much larger superior province differences are evident in i the abundance of sedimentary versus volcanic rocks and of felsic versus mafic volcanic rocks ii the greater evidence for sialic basement iii the higher proportion of more evolved potassium rich granite iv the type setting and timing of gold and base metal mineralization and v a regional zonation of gold deposits that seems to be a unique feature of the slave province contrasts in structure are also significant the large scale linear belts and boundaries sutures that characterize the superior province have no obvious counterpart in the slave province despite some similarities with other archean cratons the distinct features of the slave province are important for they imply that no single archean craton should be used to develop a universal paradigm for the genesis and tectonic evol

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

continental weathering and redox conditions during the early toarcian oceanic anoxic event in the northwestern tethys insight from the posidonia shale section in the swiss jura mountains abstract the geochemistry and mineralogy of organic rich sediments of the rietheim succession in northern switzerland were studied to evaluate the main impacts of the early toarcian oceanic anoxic event t oae 183 ma ago on the depositional environment in the nw tethys ocean the geochemical data obtained notably 13corg 13ccaco3 rock eval pyrolysis toccff support the hypothesis that the negative c isotope excursion at the onset of the t oae mainly reflects a major perturbation in the global carbon cycle rather than local environmental changes e g basinal restriction productivity rock eval pyrolysis and 13corg 15ntotal crossplots indicate that the organic matter was primarily of marine origin during the t oae and deposited in an epicontinental sea setting detrital proxies notably detritus index siliciclastic balance and ln al2o3 na2o suggest that the elevated pco2 levels and greenhouse climate prevailing during the t oae induced significant acceleration of the hydrologic cycle and an increase in continental chemical weathering rates redox sensitive proxies relative pyrite contents organic and sulfide balances v v ni ratios trace elements enrichment factors trace element toc co variation patterns and toc ptotal molar ratios indicate that the rietheim posidonia shale sediments accumulated under oxic to dysoxic bottom water conditions with more reducing conditions during the t oae anoxic and possibly euxinic these changes in redox conditions were probably induced by substantial thermohaline stratification driven by enhanced freshwater input and the recurrent influx of brackish arctic seawater into the nw tethys through the viking corridor in agreement with previous sedimentological and geochemical evidences from the nw tethys ocean in the studied succession such conditions were perhaps also responsible for sequestration of most of the regenerated p in the deeper water column by adsorption and or co precipitation into authigenic phases overall the major palaeoenvironmental changes documented in this study provide a robust example of earth s possible responses to the rapid onset of extreme greenhouse conditions

regional variations in sediment geochemistry on a transect across the mendeleev ridge arctic ocean abstract inorganic geochemical investigations were performed on three arctic surface sediment cores ps72 408 4 ps72 410 2 and ps72 422 4 recovered during rv polarstern expedition ark xxiii 3 on a transect across the mendeleev ridge dark brown layers are geochemically characterized by elevated mn al and fe al ratios and trace metal enrichments trace metals such as as co cu mo and ni seem to be adsorbed onto mn fe oxyhydroxide surfaces due to scavenging from the water column similar enrichment patterns of mn co mo and ni suggest that these trace metals are predominantly bound to mn whereas different patterns for fe as and cu reveal that these trace metals are most probably mainly bound to other sediment phases like fe oxyhydroxides or clay minerals calculating mn and fe excess amounts reveals that the dark brown color of the layers which so far has predominantly been attributed to enhanced mn oxyhydroxide contents alone may as well result from a higher fe oxyhydroxide contribution in the investigated surface sediments mn rich layers seem to originate primarily from particulates formed within the water column this implies that the composition of brown layers may be spatially variable even at short distances a diagenetic overprint is not necessarily required putting constraints on the large scale correlation of brown layers across arctic basins the mn enrichments are presumably related to both siberian river discharge and coastal erosion material input related to ice rafted debris is documented in ca al mg al and tic patterns indicating the occurrence of dolomite from the canadian archipelago this material is transported via the beaufort gyre and shows decreasing abundance towards the west along the transect a more basaltic component presumably originating from the east siberian hinterland is characterized by low si al and k al records cabio and srxs patterns may serve as additional indicators for biogenic carbonate input and glacial interglacial changes

modern dirty sea ice characteristics and sources the role of anchor ice extensive dirty ice patches with up to 7 kg m 2 sediment concentrations in layers of up to 10 cm thickness were encountered in 2005 and 2007 in numerous areas across the central arctic the fe grai

evolution of paleo sea surface conditions over the last 600 years in the mackenzie trough beaufort sea canada abstract in order to document long term climate trends and predict future climate change for the arctic we need to look at the geological record to establish the link between historical and pre industrial sea surface parameters dinoflagellate cysts dinocysts are used as proxy indicators of sea surface parameters temperature salinity sea ice cover primary productivity jointly with transfer functions and a modern dinocyst reference database to reconstruct the evolution of sea surface conditions at decadal and multi decadal timescales here we present the fossil dinocyst assemblages established from three sediment cores collected along an inshore offshore transect in the mackenzie trough during the 2004 cases canadian arctic shelf exchange study cruise the chronology of each core was determined using 210 pb activity and ams 14 c measurements in core 912a sediment cores 912a 909b and 906b cover the last 600 200 and 100 years respectively palynomorph influxes increase from the bottom to the top of each core illustrating an increasing productivity over the last 600 years until 1850 ad when we observe a decrease of productivity until today we determined a succession of two assemblages over the last 600 years assemblage i at the base of each core is mostly composed of dinocysts from heterotrophic taxa the modern assemblage assemblage ii at the top of each core is mostly composed of dinocysts from autotrophic taxa quantitative reconstructions of sea surface parameters reveal a sharp increase in summer august temperature 2 to 5 c throughout the study area from 1400 ad until 1800 1850 ad after which the increase between 0 5 and 1 0 c is much slower until modern times

co2 fluxes across the air sea interface in the southeastern beaufort sea ice free period 1 surface mixed layer co2 fugacities fco2 sw calculated from carbonate system parameters in the southeastern beaufort sea during the ice free period ranged from 240 to 350 atm in fall 2003 and from 175 to 515 atm in summer 2004 the surface mixed layer remains mostly undersaturated with respect to atmospheric co2 378 atm and therefore acts as a potential co2 sink throughout this period air sea co2 fluxes fco2 were first computed assuming ice free conditions and ranged from 32 4 to 8 6 mmol m 2 d 1 in fall 2003 and summer 2004 respectively then we included a reduction factor to account for ice cover ic and we computed the resulting fluxes fco2 ic in fall 2003 fco2 ic ranged from 4 7 mmol m 2 d 1 in the relatively open water of the cape bathurst polynya to 0 1 mmol m 2 d 1 in the southeastern beaufort sea limited by the presence of the multiyear sea ice in summer 2004 fco2 ic ranged from 13 1 mmol m 2 d 1 on the western mackenzie shelf to 8 6 mmol m 2 d 1 at cape bathurst the variability being ascribed to competing effects of vertical mixing temperature variations and possibly biological production on average a net sink of 2 3 3 5 mmol m 2 d 1 was estimated for the ice free period over the study area nevertheless the fco2 displays strong variability due to ice coverage freshwater input and upwelling events the potential responses direction and intensity of potential feedbacks of the carbon cycle in the study area to a changing arctic climate are discussed

sources and dispersal patterns of clay minerals in surface sediments from the continental shelf areas off alaska the three mineral suites were recognized in the gulf of alaska the glaciomarine sediments of fjords and the eastern shelf consist typically of the primary phyllosilicates micas and chlorites derived locally from argillite graywacke and metavolcanics under conditions of mild chemical weathering more glycol expandable clay minerals gecm in the north gulf substantiate clay supply to that region primarily from the yakataga and poul creek formations and to a lesser extent from the copper river the northern gulf clay mineral suite is transported to central prince william sound and northeast kodiak shelf by the alaska coastal current in the western gulf clay minerals adjacent to the alaska peninsula are derived principally from the susitna river via cook inlet whereas those of the outer shelf presumably have their provenance in kodiak island and the katmai ash submarine deposit in the southeast bering sea a progressive northwestward decrease in gecm from 65 to 11 is caused by a gradually decreased sediment export from the alaska peninsula and the aleutians with a possible minor increase in illite from the kuskokwin river the yukon river is the predominant clay source for the north bering sea as signified by an abrupt increase in that area of gecm 20 to 35 and of kaolinite chlorite ratios clay mineralogy indicates that the central chukchi sea is the major repository of the yukon clays suggesting that clay mineral stratigraphic studies have implications for interpretation of the quaternary paleogeography of beringia in the beaufort sea nearshore influence of different fluvial inputs and their dispersals by currents are sharply defined the lack of a definite pattern to the distribution of clay minerals in the outer continental shelf may be due to haphazard transport of clays by ice rafting and or reworking and redistribution of sediments resulting from ice gouging of the sea substrate movement of sediment to the west in the alaskan portion of the inner shelf of beaufort sea is evident an apparent seaward increase in illite gecm ratio in the colville delta is tentatively ascribed to regeneration of degraded illite micas by k fixation in saline waters an isolated area of sediment rich in expandable clay minerals in the central beaufort shelf presumably is relict

pine point orebodies and their relationship to the stratigraphy structure dolomitization and karstification of the middle devonian barrier complex mississippi valley type ore field on the south side of great slave lake pine point has produced 58 2 million tons of 3 0 percent pb and 6 7 percent zn with present reserves of 25 7 million tons of 2 7 percent pb and 6 3 percent zn most pine point orebodies were deposited in interconnected paleokarst networks that developed at the lower limits of coarse dolomite alteration of upper barrier limestones karstic structures which exhibit the largest cavity development and consequently the greatest amounts of infilling internal sediments host the best grades of mineralization the following conclusions are suggested the barrier developed due to subtle epeirogenic crustal movements and or eustatic sea level changes affecting normal sedimentary processes deformation of the barrier is possibly due to differential sediment compaction or warping of underlying evaporites coarse dolomitization and paleokarstification metals introduced by chloride rich brines brines expelled by overburden pressures migrated eastward along the barrier and precipitated metals in paleokarst structures upon encountering reduced sulfur species modified journal abstract

copper mineralization around the ahar batholith north of ahar nw iran evidence for fluid evolution and the origin of the skarn ore deposit abstract this investigation presents and interprets fluid inclusion data from different lithological units of the cu skarn deposits at mazraeh north of ahar azarbaijan nw iran the results provide an assessment of the p t conditions and mineral fluid evolution and suggest new exploration parameters five types of inclusions are recognized from quartz and garnet the temperature of homogenization of type i inclusions with daughter minerals halite and sylvite ranges from 312 to 470 c with total salinity of 52 to 63 wt nacl equiv type ii and iii inclusions with halite have homogenization temperatures of 230 to 520 c and salinity of 31 to 50 wt nacl equiv the salinity of types iv and v biphase liquid vapor inclusions based on their final ice melting temperature varies between 10 2 to 20 8 wt nacl equiv t h vs salinity plots of inclusions show that the salinity of the fluids correlates positively with temperature the inclusions formed at low pressure changes in the temperature and salinity of the fluids can be reconstructed from the inclusions highly saline high temperature fluids were most abundant during the main chalcopyrite ore forming phase in the skarn and mineralized quartz veins low salinity aqueous fluids were abundant in barren veins in which there is no evidence for early hot high salinity brine and might have resulted from late stage dilution and mixing of hydrothermal fluids with meteoric water based on petrographic features and fluid inclusion data early stage magnetite deposition is related to boiling of fluid at temperatures of about 500 c at a later stage boiling at temperatures of around 320 to 400 c favored the deposition of sulfides and fe mobility was decreased at these lower temperatures the following inclusion characteristics may be used as exploration parameters in the mazraeh area i presence of high temperature salt bearing inclusions with t h between 300 and 500 c ii high salinity fluid inclusions and iii inclusions showing evidence of boiling of the fluid in addition the presence of magnetite is an important exploration parameter

sedimentary evidence of deglacial megafloods in the northern gulf of mexico pigmy basin abstract cored sediments from the pigmy basin northern gulf of mexico were analyzed in order to better constrain late deglacial and early holocene paleoenvironmental and sedimentary changes in response to north american climate evolution mineralogical and geochemical proxies indicate the succession of two sedimentary regimes dominantly detrital during the deglaciation 15 12 9 cal ka bp whereas biogenic contribution relatively increased later on during the younger dryas and early holocene 12 9 and 10 cal ka bp geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the mississippi river rather than modifications of redox conditions in the basin specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode meltwater spike described or modeled in previous marine or continental studies during this episode most parameters display stair step like pattern variations highlighting three successive steps within the main meltwater flow variations in grain size and clay mineral assemblage recorded in the pigmy basin indicate that the erosional regime was very strong on land during the first part of the meltwater spike and then milder inducing more subtle modifications in the sedimentary regime in this part of the gulf specific geochemical and mineralogical signatures notably clay minerals and trace metal geochemistry pinpoint a dominant origin from nw north america for detrital particles reflecting meltwater outflow from the south western laurentide ice sheet lis margin during the most intense freshwater discharge the observed decrease of the sedimentation rate from about 200 to 25 cm ka at ca 12 9 ka evidenced a drastic decrease of erosional processes during late phase of discharge consistently with the hypotheses of major reduction of meltwater flow the major modification at 12 9 cal ka bp is interpreted to result from both modifications of the main mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the younger dryas and the increase of sea surface temperature linked to insolation finally slight grain size modifications suggest that some freshwater discharges may have episodically reached the gulf of mexico after the younger dryas reflecting possible small adjustments of the postglacial hydrological regime

late quaternary chronostratigraphic framework of deep baffin bay glaciomarine sediments from high resolution paleomagnetic data 1 the late quaternary baffin bay sediments provide exclusive records of greenland innuitian and laurentide ice sheet margin activities as well as information about the arctic and northern atlantic ocean linkages through the canadian arctic archipelago because of specific oceanographic conditions foraminiferal 18o stratigraphies and radiocarbon ages fail to provide reliable chronologies here we propose an original chronostratigraphy spanning the last glacial cycle based on high resolution paleomagnetic investigations on a 741 cm long core hu2008 029 016pc raised from the deep central baffin bay near odp site 645 two major difficulties were encountered 1 the high frequency occurrence of rapidly deposited layers related to short ice sheet margin events e g ice surges and 2 the magnetic grain size variability physical and magnetic mineralogical properties were used to screen out unreliable magnetic sediment layers the obtained relative paleointensity rpi proxy matches reference paleomagnetic stacks and regional records moreover the resulting record depicts two major excursions which were assigned to the laschamp and the norwegian greenland sea events it has thus been possible to derive a robust 115 ka chronology for the cored sequence we concluded that even under such a dynamic sedimentary regime magnetic properties of the sediments can provide a reliable chronostratigraphy together with information on sedimentary processes

sedimentary chemofacies characterization by means of multivariate analysis abstract multivariate statistical analysis is applied to geochemical data from three sections forming part of the stratigraphic record of the cerro pelado formation oligocene miocene in the central region of the falcon basin northwestern venezuela our main goal is introducing and testing a statistical protocol for the identification of chemofacies in the studied sections the first step involves data preparation and cleaning selection of relevant components convenient replacement of values below the detection limit and determination of outliers second a biplot analysis allows us to infer geochemical processes that can be interpreted from a paleoenvironmental point of view detrital association redox organic matter association and carbonatic association considering such geochemical associations a constrained cluster analysis is then carried out to determine the chemofacies for each section according to the compositional nature of geochemical data all statistical analysis is conducted within a log ratio analysis framework in addition robust statistical methods are considered for outlier detection and biplot representation in order to smooth the influence of potential outliers on the estimates

origin and fate of particulate organic matter in the southern beaufort sea amundsen gulf region canadian arctic canadian arctic shelf exchange study cases natural sciences and engineering research council of canada nserc fonds quebecois de la recherche sur la nature et les technologies fqrnt department of earth and planetary sciences at mcgill university

multiple failure styles related to shallow gas and fluid venting upper slope canadian beaufort sea northern canada abstract the continental slope of the canadian beaufort sea presents an exceptional opportunity to study the relationship between the fluid venting and the formation of mass transport deposits the continental shelf was emergent and partially ice free during the last glaciation and is underlain by widespread permafrost water column backscatter has shown the locations of more than 40 active gas vents along seaward margin of the subsea permafrost at the shelf break and upper slope new multibeam bathymetry and subbottom profiler data show shallow potentially late holocene failures and mass transport deposits on the upper slope upslope from a prominent headscarp undulating seabed with apparent growth faults overlies an acoustically incoherent to stratified horizon at 50 m sub bottom interpreted as a decollement surface over which progressive creep has occurred similar creep is present in places on the upper slope and in places seems to have evolved into small translational slides involving more compacted sediment buried 25 m or into muddy debris flows where sediments buried

high resolution paleomagnetic secular variation and relative paleointensity records from the western canadian arctic implication for holocene stratigraphy and geomagnetic field behaviourthis article is one of a series of papers published in this special issue on the theme polar climate stability network geotop contribution 2008 0024 two piston cores recovered from the chukchi and the beaufort seas document arctic holocene geomagnetic field behaviour and highlight the potential of secular variation and relative paleointensity as a regional chronostratigraphic tool several centennial to millennial scale holocene declination and inclination features can be correlated in both cores with other high resolution western north american lacustrine and volcanic paleomagnetic records and with records of changes in earth s dipole moment supporting the geomagnetic origin of these features and implying that they are associ ated with changes in earth s dipole moment resume deux carottes sedimentaires prelevees dans les mers de beaufort et de chukchi ont permis de reconstruire les variations d intensiteet d orientation de haute resolution du champ magnetique terrestre au cours de l holocene afin de caracteriser le comportement du champ geomagnetique dans l arctique ainsi que d explorer la possibilited utiliser les variations du champ geomagnetique comme outil chronostratigraphique au cours de l holocene la declinaison et l incli naison magnetique des deux sequences etudiees peuvent etre correlees entre elles avec des enregistrements paleomagne tiques lacustres ou volcaniques de l ouest de l amerique du nord a des echelles de temps au moins seculaires les variations de paleointensiterelative des deux carottes analysees sont egalement coherentes avec des enregistrements des variations du dipole geomagnetique confirmant ainsi l origine geomagnetique de ces variations et suggerant leur nature di polaire

mineralisation at the carrock fell tungsten mine n england paragenetic fluid inclusion and geochemical study tungsten ore at carrock fell mine comprises wolframite and scheelite in polyminerallic quartz veins which traverse the grainsgill granite cupola and surrounding country rocks in the veins a wolframite scheelite apatite assemblage pre dates a scheelite arsenopyrite pyrite plus other sulphides assemblages temperatures of mineralisation declined from a peak near 350 c to 170 c and the hydrothermal fluid contained about 6 weight nacl and 3 wt nahco3 contemporaneous greisenisation involved loss of na cr ca and ba from granite but si and k were retained while b be and al increased slightly sn also increased but is always a trace constituent and f appears to have decreased zones of intense alteration contain high concentrations of quartzhosted fluid inclusions resulting from penetration of the granite by fluid chemically similar to that in the vein quartz the w rich sn poor nature of the mineralisation may relate to the weakly saline f deficient but co2 rich fluid chemistry the alteration and mineralisation processes took place during late cooling of the lower devonian skiddaw granite cross cutting quartz ankerite veins and argillitic zones which may be considerably younger than those producing the tungsten ore have a distinct mineral suite lacking w and as and including major pb and zn temperatures at this late stage were below 150 c and the fluid is estimated to have contained approximately 12 wt nacl and 15 wt cacl2

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

anaerobic methane oxidation and the formation of dolomite abstract we examine the link between organic matter degradation anaerobic methane oxidation amo and sulfate depletion and explore how these processes potentially influence dolomitization we determined rates and depths of amo and dolomite formation for a variety of organic rich sites along the west african margin using data from ocean drilling program odp leg 175 rates of amo are calculated from the diffusive fluxes of ch4 and so4 and rates of dolomite formation are calculated from the diffusive flux of mg we find that the rates of dolomite formation are relatively constant regardless of the depth at which it is forming indicating that the diffusive fluxes of mg and ca are not limiting based upon the calculated log iap values log ksp values for dolomite were found to narrowly range between 16 1 and 16 4 dolomite formation is controlled in part by competition between amo and methanogenesis which controls the speciation of dissolved co2 amo increases the concentration of co32 through sulfate reduction favoring dolomite formation while methanogenesis increases the pco2 of the pore waters inhibiting dolomite formation by regulating the pco2 and alkalinity methanogenesis and amo can regulate the formation of dolomite in organic rich marine sediments in addition to providing a mechanistic link between amo and dolomite formation our findings provide a method by which the stability constant of dolomite can be calculated in modern sediments and allow prediction of regions and depth domains in which dolomite may be forming

fluid inclusion chemistry in the exploration for mississippi valley type deposits an example from east tennessee u s a scanning electron microscopy and energy dispersive analysis of fluid inclusion decrepitates in sparry dolomite cements associated with sphalerite mineralization in the mascot jefferson city missis sippi valley type district of east tennessee show a markedly lower najca ratio than those in dolomites unassociated with ore the exploration potential of this variation in fluid inclusion chemistry has been evaluated by analyzing inclusion decrepitates from white sparry dolomite along a 150 m traverse in the new market west mine area the traverse extends from the central portion of a large domal collapse breccia orebody with greater than 3 zn into the dolomite veined but unmineralized knox group limestones ratios of na ca as low as 0 8 1 2 were common in dolomite hosted decrepitates from the high grade collapse ores this anomalous decrepitate chemistry was not observed in sparry dolomites less than 12 m from the margins of the breccia bodies where na ca ratios ranged from 1 8 to 3 6 dolomite cements in idly grade 1 0 zn parts of the collapse bodies showed the greatest variation in na ca ratio with values ranging from 0 9 to 3 5 no systematic trends were observed in k na and s c1 ratios from the same samples

high silver content of fluid inclusions in quartz from guadalcazar granite san luis potosi mexico a contribution to ore genesis theory besides sodium and potassium manganese and iron were found in significant amounts the results confirm that the base metal and silver transporting capability of some early magmatic fluids is considerable chloride complexes were the most favorable species for transporting silver and base metals an electron probe in the energy dispersive mode was used to analyze the precipitates formed upon the decrepitation of fluid inclusions modified journal abstract

the origin of a mississippi valley type deposit in the viburnum trend southeast missouri petrologic and isotopic studies of the base metal sulfide mineralization in the buick mine have established the following paragenesis an early stage of fine grained pyrite and marcasite replaced the dolostone host rock the iron disulfides and dolostone were replaced by sphalerite during the main stage of sphalerite precipitation delta 34 s sp 16 5 to 19 0ppm following the sphalerite two main stages of galena were precipitated a cuboctahedral stage delta 34 s gn 21 3 to 10 0ppm during which galena replaced dolostone and sphalerite and grew in vugs in the dolostone and in the sphalerite and a cubic stage delta 34 s gn 10 5 to 0 9ppm the two stages of galena precipitation were separated by a period during which the main stage of sphalerite and the cuboctahedral galena were partially dissolved and bladed marcasite delta 34 s mc 2 3 to 4 1ppm was precipitated and followed by a period of mild etching of the cubic galena minor amounts of pale sphalerite delta 34 s sp 14 0 to 16 5ppm were then precipitated white and colorless rhombs of dolomite were precipitated at the same time as some of the main stage of sphalerite the cubic galena and the pale sphalerite after the pale sphalerite was precipitated chalcopyrite quartz and siegenite were precipitated followed by calcite and finally kaolinite the paragenetic and textural data for both galena and sphalerite in the buick mine strongly suggest that these minerals were precipitated and dissolved repetitively during ore formation similar textural evidence for galena reported by other workers for different mines in the viburnum trend implies that repetitive precipitation and dissolution of galena was probably an important process during the formation of the entire viburnum trend fluid inclusions in late quartz crystals coprecipitated with chalcopyrite have filling and freezing temperatures within the ranges reported for sphalerite from other parts of the viburnum trend demonstrating that the ore forming solutions in the viburnum trend were probably at temperatures in the range 105 degrees to 141 degrees c assuming a maximum pressure correction of about 11 degrees c and were extremely saline containing about 4 0 to 5 0 molal chloride consideration of typical chemical analyses of fluid inclusions from other mississippi valley type deposits suggests that the maximum likely concentration of dissolved co 2 in the ore forming solutions was about 0 05 molal at these concentrations the ore forming solutions that travelled to the site of deposition could have had ph9s about two units less than neutral and still have been in equilibrium with dolomite or calcite the ranges of sulfur and lead isotopic compositions of galena from the buick mine are very similar to those established by earlier studies of the old lead belt and adjacent subdistricts however the correlation of isotopically lighter sulfur with more radiogenic lead is much stronger for the viburnum trend suggesting that galena was precipitated from many solutions each of which carried lead and sulfur together and had different lead and overall sulfur isotopic compositions the textural paragenetic and isotopic data for the buick mine cannot be easily explained either by a sulfate reduction model in which sulfate was reduced by organic matter or methane or mixing models in which base metals and reduced sulfur were transported separately to the site of deposition instead the data strongly support a reduced sulfur model for ore formation according to which the base metals were transported together with reduced sulfur as h 2 s in the same solutions to the sites of deposition the reduced sulfur model is also supported by a theoretical calculation of the solubilities of galena and sphalerite which demonstrate that low but economically significant concentrations of lead or zinc could have been transported as chloride complexes together with equivalent concentrations of reduced sulfur at temperatures of 100 degrees to 150 degrees c and ph9s of one to two units less than neutral and could have been precipitated by ph increases cooling or dilution at the sites of deposition

meteorological forcing of sea ice concentrations in the southern beaufort sea over the period 1979 to 2000 1 northern hemisphere sea ice areal extent and perhaps thickness have shown a detectable reduction over the past several decades this situation is particularly apparent in the southern beaufort sea the region encompassing the mackenzie shelf the cape bathurst polynya and the canada basin mobile pack ice all occur in a region referred to here as the canadian arctic shelf exchange study area cases in this paper we present results from an analysis of atmosphere sea ice and ocean coupling over the period 1979 to 2000 as a means of setting a physical science context for the cases research network operating over the period 2001 2005 results show that the cape bathurst polynya complex can be considered as a recurrent polynya particularly the flaw leads associated with the early opening of the polynya the polynya appears to be a consequence of the beaufort sea gyre acting like an ice bridge and a series of flaw leads creating conditions conducive to oceanic upwelling the sea ice average areal extent has been decreasing in this region over the period 1979 to 2000 large regional reductions are found i north of the yukon and alaska coasts in the region between the canada basin pack ice and the landfast sea ice and 2 at the eastern limit of the cape bathurst polynya in amundsen gulf the meteorological forcing of sea ice anomalies occurs through a full range of timescales and space scales at hemispheric scales a statistical cross correlation analysis between weekly sea ice concentration anomalies and the arctic oscillation accounts for a maximum of about 25 percent of the explained variance and show a surprising spatial coherence in correlation magnitudes both within the study area and northward along the canadian archipelago coast at local scales positive and negative concentration anomaly periods can be explained through local scale advective processes associated with regional scale sea level pressure 500 hpa geopotential heights and surface temperature anomalies

late holocene paleoceanography and climate variability over the mackenzie slope beaufort sea canadian arctic abstract late holocene paleoceanography and climate variability of the southeastern beaufort sea canadian arctic have been investigated on the basis of sedimentary cores collected over the mackenzie slope piston trigger and box cores were sampled at station 803 in 2004 aboard the ccgs amundsen at 218 m water depth the chronology of the piston core is constrained by 4 ams 14 c dates as the sedimentation rate in the box core is assessed from 210 pb data we obtain a continuous composite sequence covering the last 4600 years with a sedimentation rate of 140 cm kyr 1 transfer functions modern analogue technique based on dinoflagellate cyst dinocyst assemblages were used to reconstruct the evolution of sea surface conditions over the time period covered by the cores palynological data reveal that dinocyst assemblages are dominated by operculodinium centrocarpum sensu lato mean of 43 3 throughout the core with the accompanying taxa brigantedinium spp 19 6 islandinium minutum 15 6 and cysts of pentapharsodinium dalei 13 7 four zones have been established on the basis of dinocyst relative abundances dinocyst assemblage zone 1 d1 from 4600 to 2700 cal years bp is dominated by o centrocarpum mean of 49 0 in zone d2 2700 1500 cal years bp the relative abundances of o centrocarpum decrease 34 4 in favour of the opportunistic heterotrophic taxa brigantedinium spp 28 8 and cysts of polykrikos sp var arctic quadratus 2 8 dinocyst zone d3 1500 30 cal years bp or 450 1920 ad is characterised by the high relative abundance of the peridinioid taxa i minutum 19 9 the last zone d4 spanning from 1920 to 2004 ad is again dominated by o centrocarpum 44 5 and shows low relative abundances of brigantedinium spp and cf echinidinium karaense quantitative reconstructions of past sea surface parameters august sea surface temperature sst august sea surface salinity sss and duration of sea ice cover indicate relatively stable conditions over the last 4 6 kyr with episodic cooling events sst of 1 5 c below the modern value of 6 c that took place between 700 and 1820 ad we associate the last and the longest of these cooling events 1560 1820 ad with the little ice age reconstructed sss shows decadal oscillations since 1920 ad that we tentatively associate with the accumulation of freshwater by the beaufort gyre and the subsequent great salinity anomalies our data suggest that similar salinity anomalies could have occurred ca 1860 and 1790 ad stable isotopic data show a slight increase in 13 c values from 27 1 at the base to 25 8 at the top over the last 4 6 kyr that we associate with the gradual increase in atmospheric co 2 concentration as recorded by antarctic ice cores variations in the 15 n profile suggest variations in pacific water influence from 4600 to 1300 cal years bp associated with centennial scale shifts of the arctic oscillation phases

magnetic fingerprints of surface sediment in the bohai sea china abstract the understanding of the surrounding river impacts on the sediment supply to the bohai sea northern china is insufficient in this study magnetic measurements on surface sediment from the bohai sea and surrounding rivers were performed to interpret the distribution and origin of sediment in the bohai sea different magnetic properties in the analyzed material correspond to seven provenance areas the magnetic mineral content decreases gradually toward the central bohai sea from its marginal areas sediment in the central and northern parts contains higher concentrations of finer magnetic minerals than the southern bohai sea the western bohai sea western bohai and liaodong bays has high contents of magnetic minerals because its provenance areas contain abundant old metamorphic rocks with magnetite the yellow river with the most elevated sediment flux contributes with fine high corercivity magnetic minerals e g hematite to the southern bohai sea mainly in the northwestern laizhou bay some local rivers e g fuzhou river are also important contributors to the coastal waters due to the magnetic similarities sediment from the north yellow sea is magnetically similar to the yellow river detritus the results highlight the use of the rapid magnetic method in provenance tracing

subglacial bedform evidence for a major palaeo ice stream and its retreat phases in amundsen gulf canadian arctic archipelago ascertaining the location of palaeo ice streams is crucial in order to produce accurate reconstructions of palaeo ice sheets and examine interactions with the ocean climate system this paper reports evidence for a major ice stream in amundsen gulf canadian arctic archipelago mapping from satellite imagery landsat etm and digital elevation models including bathymetric data is used to reconstruct flow patterns on southwestern victoria island and the adjacent mainland nunavut and northwest territories several flow sets indicative of ice streaming are found feeding into the marine trough and cross cutting relationships between these flow sets and utilising previously published radiocarbon dates reveal several phases of ice stream activity centred in amundsen gulf and dolphin and union strait a large erosional footprint on the continental shelf indicates that the ice stream ca 1000 km long and ca 150 km wide filled amundsen gulf probably at the last glacial maximum subsequent to this the ice stream reorganised as the margin retreated back along the marine trough eventually splitting into two separate low gradient lobes in prince albert sound and dolphin and union strait the location of this major ice stream holds important implications for ice sheet ocean interactions and specifically the development of arctic ocean ice shelves and the delivery of icebergs into the western arctic ocean during the late pleistocene copyright c 2006 john wiley sons ltd

fluorine concentrations of ore fluids in the illinois kentucky district evidence from sem eds analysis of fluid inclusion decrepitates abstract the illinois kentucky district is an atypical occurrence of mississippi valley type mvt mineralization that consists predominantly of fluorite rather than metal sulfide minerals a long standing assumption for the predominance of fluorite in the illinois kentucky district is that the ore fluids there were anomalously rich in dissolved fluorine compared to typical sedimentary brines and other mvt ore fluids this hypothesis is based on the unusual close temporal and spatial association of fluorine rich ultramafic igneous rocks to mvt mineralization in the district high k and sr concentrations in the igneous rocks and in mvt ore hosted fluid inclusions a significant mantle 3he 4he component in ore hosted fluid inclusions and reaction path models that show titration of a hf rich fluid into sedimentary brine is capable of producing a fluorite dominated mvt ore mineral assemblage the purpose of the present study was to test this hypothesis more directly by determining the fluorine concentration of the illinois kentucky ore fluid through sem eds analysis of evaporative solute mounds resulting from thermal decrepitation of fluid inclusions hosted in sphalerite all 26 evaporative solute mounds from illinois kentucky sphalerite samples analyzed contained detectable concentrations of fluorine of 1 4 weight percent based on calibration to standard solutions and previously published fluid inclusion major element concentrations these solute mound fluorine concentrations correspond to fluid inclusion fluorine concentrations of about 680 4300 ppm indicating that the illinois kentucky ore fluids were quite rich in fluorine compared to typical sedimentary brines which have fluorine concentrations mainly on the order of 1 s to 10 s of ppm in contrast solute mounds from sphalerite hosted fluid inclusions from the tri state district did not contain fluorine in excess of the detection limit the detection limit equates to an aqueous fluorine concentration between 87 and 169 ppm the high apparent fluorine concentrations of the illinois kentucky fluid inclusions suggest that the ore fluids were very acidic with a ph ranging between 0 and 1 4 much lower than the typical ph range of mvt ore fluids of 4 5 5 such a low ph would have greatly increased the solubility of metal sulfide minerals suppressing their precipitation and contributing further to the predominance of fluorite in the illinois kentucky district

fluid inclusion evidence for fluid mixing mascot jefferson city zinc district tennessee inverse correlation between homogenization temperature and salinity temperature of formation changes at near constant salinity and low salinity low to moderate temperature inclusion fluids are found in sphalerite formed in limestone an evolved basinal brine component was recognized by its characteristic temperature 100 degrees to 120 degrees c freezing point depression 1 fundamental chemical requirements for formation of pb zn ba f deposits from metal bearing basinal brines modified journal abstract

chemical evolution of brines during mississippi valley type mineralization evidence from east tennessee and pine point the major element chemical composition of inclusion fluids from mississippi valley type deposits has been evaluated semiquantitatively using scanning electron microscopy and energy dispersive analysis of individual inclusion decrepitates in ore and gangue minerals the volcano shaped decrepitates are produced by heating polished plates above the decrepitation temperature of the inclusions forcing the enclosed fluids to the surface where the nonvolatile components precipitate energy dispersive analyses of these precipitates here called decrepitates are expressed in cation and anion weight ratios and carry errors of or 10 percent application of this technique to fluid inclusions in sphalerite and dolomite from the mascot jefferson city zinc district of east tennessee and the pine point lead zinc district of the northwest territories reveals that fluids attending sulfide deposition in both districts are dominantly na ca chloride brines subordinate but significant amounts of k mg and locally sr and fe are also present cacl 2 cacl 2 nacl weight ratios vary greatly among the samples from both deposits but are consistently lower 0 1 0 3 in gangue dolomites not associated with sulfides than in sphalerite and ore stage dolomite 0 2 0 6 at east tennessee 0 4 0 8 at pine point although cl is the only significant anion detected in the east tennessee analyses a significant proportion of decrepitates from sphalerite and ore associated dolomite at pine point contain appreciable s occasionally in amounts equal to or exceeding cl mass balance calculations show that the increase in the cacl 2 cacl 2 nacl ratio in decrepitates associated with ore from both districts cannot result simply from limestone dissolution at the site of brecciation and mineralization instead they appear to require either fluid mixing or a chemical evolution of the fluids entering the carbonate host rocks the presence of significant ca and s together in the pine point fluid inclusions and the absence of daughter anhydrite requires that most s was reduced which lends support to mixing models involving metal rich brines and sulfur rich waters in ore formation in that district further the presence of excess s in ore stage decrepitates from pine point suggests that sulfide de position there was limited by the amount of metal rich brine entering the h 2 s rich barrier reef complex in contrast the lack of detectable sulfur in the decrepitates from mascot jefferson city ores suggests that mineralization there may have been limited by the availability of s but does not permit selection between mixing and fluid evoluton as a cause of ore deposition

bivalve shell horizons in seafloor pockmarks of the last glacial interglacial transition a thousand years of methane emissions in the arctic ocean we studied discrete bivalve shell horizons in two gravity cores from seafloor pockmarks on the vestnesa ridge 1200 m water depth and western svalbard 79 00 n 06 55 w to provide insight into the temporal and spatial dynamics of seabed methane seeps the shell beds dominated by two genera of the family vesicomyidae phreagena s l and isorropodon sp were 20 30 cm thick and centered at 250 400 cm deep in the cores the carbon isotope composition of inorganic 13c from 13 02 to 2 36 and organic 13c from 29 28 to 21 33 shell material and a two end member mixing model indicate that these taxa derived between 8 and 43 of their nutrition from chemosynthetic bacteria in addition negative 13c values for planktonic foraminifera 6 7 to 3 1 concretions identified as methane derived authigenic carbonates and pyrite encrusted fossil worm tubes at the shell horizons indicate a sustained paleo methane seep environment combining sedimentation rates with 14c ages for bivalve material from the shell horizons we estimate the horizons persisted for about 1000 years between approximately 17 707 and 16 680 years b p corrected the seepage event over a 1000 year time interval was most likely associated with regional stress related faulting and the subsequent release of overpressurized fluids

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

foraminiferal assemblage changes over the last 15 000 years on the mackenzie beaufort sea slope and amundsen gulf canada implications for past sea ice conditions 1 two cores one from the beaufort sea slope at 1000 m water depth core 750 and one from the amundsen gulf at 426 m core 124 were collected to help determine paleo ice cover in the holocene and late glacial of this area site 750 is particularly sensitive to changes in paleo ice cover because it rests beneath the present ice margin of the permanent arctic ice pack core 124 was sampled just in front of the former glacier that moved out into the amundsen gulf and started to recede about 13 ka b p both cores have a strong occurrence of calcareous foraminifera in the upper few centimeters but these disappear throughout most of the holocene suggesting more open water in that time period than present in the sediments representing the end of the last glacial period dated at 11 500 14 000 calibrated years b p cal b p a calcareous fauna with an abundant planktic foraminiferal fauna suggests a return to almost permanent ice cover much like the central arctic today together with the foraminifera there was also abundant ice rafted debris ird in both cores between 12 000 cal b p and 14 000 cal b p but those units are of different ages between cores suggesting different events the ird in both cores appears to have the same magnetic and chemical signals but their origins cannot be determined exactly until clay mineralogy is completed there is abundant organic debris in both cores below the ird units the organics in core 750 are very diffuse and not visually identifiable but the organic material in core 124 is clearly identifiable with terrestrial root fragments these are 14c dated at over 37 000 years b p this is a marine unit as it also has glacial front foraminifera in the sediment with the organic debris that must have been originating from subglacial streams the seismic and multibeam data both indicate glaciers did not cross the core 124 site

origin of pingo like features on the beaufort sea shelf and their possible relationship to decomposing methane gas hydrates 1 the arctic shelf is currently undergoing dramatic thermal changes caused by the continued warming associated with holocene sea level rise during this transgression comparatively warm waters have flooded over cold permafrost areas of the arctic shelf a thermal pulse of more than 10 c is still propagating down into the submerged sediment and may be decomposing gas hydrate as well as permafrost a search for gas venting on the arctic seafloor focused on pingo like features plfs on the beaufort sea shelf because they may be a direct consequence of gas hydrate decomposition at depth vibracores collected from eight plfs had systematically elevated methane concentrations rov observations revealed streams of methane rich gas bubbles coming from the crests of plfs we offer a scenario of how plfs may be growing offshore as a result of gas pressure associated with gas hydrate decomposition

dating of holocene western canadian arctic sediments by matching paleomagnetic secular variation to a geomagnetic field model a recently recovered w6 m long holocene sedimentary sequence piston core 2004 804 650 collected from the beaufort sea western canadian arctic was dated by combining the paleomagnetic secular variation psv and a time varying spherical harmonic model of the geomagnetic field cals7k 2 a u channel based paleomagnetic study reveals the presence of a stable single component of magnetization mad 5 carried by low coercivity ferrimagnetic minerals most likely magnetite in the pseudo single domain grain size range an age depth model spanning the last w6000 calbp was established from nine paleomagnetic tie points obtained by comparing the magnetic declination profiles of core 650 and the cals7k 2 model output in order to verify the robustness of the method both the magnetic inclination and the relative paleointensity rpi records of core 650 were then compared with western north american lacustrine and volcanic holocene psv records as well as with previously published rpi records from the beaufort and chukchi seas several common magnetic inclination features and similar millennial scale fluctuations are detected among the records supporting a common geomagnetic origin of the records and implying consistency of the derived age model these results show the potential of using both the cals7k 2 model output and psv of the geomagnetic field as a practical dating tool

mineralogical geochemical and magnetic signatures of surface sediments from the canadian beaufort shelf and amundsen gulf canadian arctic mineralogical geochemical magnetic and siliciclastic grain size signatures of 34 surface sediment samples from the mackenzie beaufort sea slope and amundsen gulf were studied in order to better constrain the redox status detrital particle provenance and sediment dynamics in the western canadian arctic redox sensitive elements mn fe v cr zn indicate that modern sedimentary deposition within the mackenzie beaufort sea slope and amundsen gulf took place under oxic bottom water conditions with more turbulent mixing conditions and thus a well oxygenated water column prevailing within the amundsen gulf the analytical data obtained combined with multivariate statistical notably principal component and fuzzy c means clustering analyses and spatial analyses allowed the division of the study area into four provinces with distinct sedimentary compositions 1 the mackenzie trough canadian beaufort shelf with high phyllosilicate fe oxide magnetite and al k ti fe cr v zn p contents 2 southwestern banks island characterized by high dolomite k feldspar and ca mg loi contents 3 the central amundsen gulf a transitional zone typified by intermediate phyllosilicate magnetite k feldspar dolomite and al k ti fe mn v zn sr ca mg loi contents and 4 mud volcanoes on the canadian beaufort shelf distinguished by poorly sorted coarse silt with high quartz plagioclase authigenic carbonate and si zr contents as well as high magnetic susceptibility our results also confirm that the present day sedimentary dynamics on the canadian beaufort shelf is mainly controlled by sediment supply from the mackenzie river overall these insights provide a basis for future studies using mineralogical geochemical and magnetic signatures of canadian arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late quaternary climate and oceanographic changes keywords mineralogy elemental geochemistry magnetic properties surface sediment sediment provenance redox condition canadian beaufort shelf amundsen gulf

sr ca and mg ca ratios in niger delta sediments implications for authigenic carbonate genesis in cold seep environments we report on a reconnaissance analysis of the geochemical composition of authigenic carbonates and sediment samples collected from various seepage sites on the niger deep sea fan our aim has been to investigate whether evidence for the presence of authigenic carbonates and gas hydrates within sediments is discernible from solid phase sediment geochemistry we show that sedimentary sr ca and mg ca ratios can be used to infer the presence of authigenic aragonite sr rich and mg rich carbonate phases high mg calcite dolomite in cold seep settings using sr ca and mg ca ratios the proportion wt of authigenic carbonates in niger fan sediments can be calculated from a mixing model between sediment fractions of terrigenous material biogenic calcite aragonite and high mg calcite this approach was applied to high resolution geochemical profiles along sediment cores recovered from various cold seep settings mud volcano diapirs pockmarks gas hydrate bearing sediments our data reveal that authigenic carbonates occur as discrete phases in sediments from gas hydrate bearing areas suggesting that such carbonate rich sediment layers may represent paleo indicators for ancient methane seepage in marine sediments possibly associated to gas hydrate reservoirs

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

multiple meltwater discharge and ice rafting events recorded in the deglacial sediments along the beaufort margin arctic ocean abstract the first regional model for the deglacial history of the beaufort margin slope in the western arctic is presented the conceptual model was developed using new high resolution chirp seismic reflection multibeam bathymetry and sediment core data acquired along the margin this synthesis provides important constraints on sediment source and dispersal patterns for the last deglaciation the continental slope from barrow canyon to the mackenzie trough is characterized by thick holocene sediments mostly sourced from barrow canyon and continental discharge this acoustically transparent fine grained unit overlies acoustically laminated sediments sourced from the mackenzie river and ice rafting the deglacial history of the margin from mackenzie trough to the amundsen gulf is characterized by many ice rafting and meltwater discharge events ice rafted debris layers were deposited around 14 6 ka and 14 1 ka and likely document enhanced ice shedding events from the amundsen and m clure ice streams as they retreated there are three inferred meltwater discharge events all sourced from the mackenzie region the oldest discharge event had two phases one sometime between 14 5 ka and 14 2 ka and another between 14 0 ka and 13 0 ka this discharge deposited finely laminated sediments more than 7 m thick sourced from proglacial lakes in the area following this was a flood event starting at 12 94 ka which generated high amplitude reflectors deposited coarse debris and caused a lowering in the 18o record this is possibly a major outburst flood from glacial lake agassiz with an additional component of agassiz meltwater that was diverted from its southern drainage pathway down the mississippi to the gulf of mexico finally a third discharge event was initiated by 11 3 ka which deposited coarse laminated sediments focused in the mackenzie trough timing of these second and third events correlates with the onset of the younger dryas cold period and the preboreal oscillation event respectively suggesting that fresh water discharge may have reached a tipping point leading to those climate events

clay mineral dispersal patterns in the north bering and chukchi seas abstract characterization of the clay mineralogic constituents of the m e s d equivalent spherical diameter size fraction of contemporary marine and fluvial sediments from the north bering sea chukchi sea region and adjacent land areas has resulted in delineation of suites dominated by broadly defined illitic and expandable group components with lesser amounts of chlorite and kaolinite distribution patterns elucidated indicate net northward transport of sediments relatively enriched in the expandable group with predominant terrigen ous source from the yukon river system this material is distributed across the study area in a medial zone along a general north south trend with peripherally decreasing relative amounts of this expandable group component and concomitant relative increases in the illitic components these patterns are consistent with known physical oceanographic and regional geologic relationships in terms of sediment sources transport processes and depositional mechanisms the foregoing suggest further that consideration of the stratigraphic relationships of these clay mineral component types as a function of time in relevant marine sediments north and south of the present bering strait should be informative with respect to regional quaternary paleogeography as related to global sea level fluctuations during glacial and interglacial episodes

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

microthermometry and geochemistry of fluid inclusions from the tennant creek gold copper deposits implications for ore deposition and exploration gold copper bismuth mineralization in the tennant creek goldfield of the northern territory occurs in pipe like ellipsoidal or lensoidal lodes of magnetite hematite ironstones which are hosted in turbiditic sedimentary rocks of proterozoic age fluid inclusion studies have revealed four major inclusion types in quartz associated with mineralized and barren ironstones at ten nant creek 1 liquid vapour inclusions with low liquid vapour ratios type i 2 liquid vapour inclusions with high liquid vapour ratios or high vapour liquid ratios and characteristic dark bubbles type ii 3 liquid vapour halite inclusions type iii and 4 liquid vapour inclusions with variable liquid vapour ratios type v type i inclusions are present in the barren ironstones and the unmineralized portions of fertile ironstones whereas types ii and iii inclusions are recognized in fertile ironstones trails of types ii and iii inclusions cut trails of type i inclusions type i fluid inclusions have homogenization temperatures of 100 to 350 c with a mode at 200 to 250 c type ii inclusions in mineralized ironstones e g juno white devil eldorado tc8 and gecko k 44 deposits have homogenization temperatures of 250 c to 600 c with a mode of 350 c type i fluid inclusions have a salinity range of 10 to 30 nacl equiv wt salinity measurements on fluid inclusions in the mineralized zones gave a range of 10 to 50 nacl equiv wt with a mode of 35 nacl equiv wt fluid inclusion studies indicate that the tennant creek ironstones were formed from a relatively low temperature and moderately saline fluid where as gold and copper mineralization was deposited from later hydrothermal fluids of higher temperature and salin ity gas analysis indicates the presence of n2 and co2 with very minor ch4 in types ii inclusions but no n2 or ch4 gases in type i inclusions microprobe analysis of the fluid inclusion decrepitates indicates that the inclusions from tennant creek contain sodium and calcium as dominant cations and potassium in a subordinate amount the high temperatures 350 c high salinities 35 nacl equiv wt and cation composition of the tennant creek ore fluids suggest that the ore fluids were derived from upward migrating heated basinal brines although contribution from a magmatic source cannot be ruled out close association of vapour rich type iib and salt rich type iii inclusions in the mineralized ironstones e g juno white devil eldorado tc8 and gecko k 44 indicates heterogeneous trapping of ore fluids this heterogeneous trapping is interpreted to be due to unmixing exsolution of a gas rich e g n2 fluid during the upward migration of the metal bearing brines and or due to degassing caused by reaction of oxidized ore fluids and host ironstones fluid inclusion data have important implications regarding the deposition of gold in the ironstones and may have application in discriminating fertile from barren ironstones

provenance of terrigenous detritus of the surface sediments in the bering and chukchi seas as derived from sr and nd isotopes implications for recent climate change in the arctic regions abstract strontium and nd isotope analysis of the detrital fractions extracted from the marginal sea sediments in the arctic was applied to examine regional and temporal changes in the inflow and transportation of terrigenous material in the chukchi and bering seas over the past 100 years regional distributions of the sr and nd isotopes of the surface sediments show higher sr isotope ratios and lower nd isotope ratios in the chukchi sea 87 sr 86 sr 0 7106 0 7150 e nd 10 1 to 8 3 and lower sr isotope ratios and higher nd isotope ratios in the eastern bering sea 0 7045 0 7109 8 6 to 3 0 in addition the rb and sr contents and ree patterns e g eu eu changed noticeably across the bering strait these variations mean that the sediments in the bering and chukchi seas have clearly distinct sources the terrigenous detritus in the chukchi sea is mainly derived from northeastern siberia 87 sr 86 sr 0 711 e nd 9 and bering strait inflow essentially from the yukon river and additionally from the mackenzie river basin including the canadian shield 0 732 0 734 14 the detritus in the eastern bering sea mainly consists of two components the continental material from the yukon river basin mainly underlain by mesozoic and paleozoic rocks in the alaskan mainland 0 708 0 709 9 to 8 and the aleutian arc volcanics 0 703 6 to 10 transported northward by the alaska coastal and bering shelf waters the eastern bering sediments over the past 100 years show slight variations of the sr isotope ratio and relatively wide variations of the nd isotope ratio and the variations and trends of the time series of the northeastern bering sea in the sr nd isotope diagram are probably controlled by changes in the grain size of the detritus from the yukon river basin some of the e nd time series show periodic fluctuations correlating with the annual mean surface air temperature sat for the arctic the e nd value is low in the high sat period and high in the low sat period in the warm period the yukon river was likely to supply a higher amount of the fine grain material with a relatively low e nd value such as surficial overburden probably because partial melting of continental glaciers and permafrosts in the alaskan mainland increased more detailed analysis with high time resolution is needed to clearly understand the effects the sat have on the arctic continental and marine environments

seismic stratigraphy sedimentary architecture and palaeo glaciology of the mackenzie trough evidence for two quaternary ice advances and limited fan development on the western canadian beaufort sea margin abstract a comprehensive grid of high resolution 2 d seismic reflection data from the western canadian beaufort sea margin is used to reconstruct past ice stream dynamics within the mackenzie trough eight seismic facies and five sequences divided into two megasequences are identified from the mackenzie trough stratigraphy evidence for two quaternary ice advances to the shelf break is provided by two sequences of acoustically chaotic to semi transparent facies interpreted as subglacial till buried landforms interpreted as lateral moraines and a grounding zone wedge record the positions of still stands or re advances in the ice margin the continental slope beyond the trough is characterised by canyons separated by inter canyon ridges and thin glacigenic debris flows correlation with the onshore record suggests that the older of the two ice advances which excavated the mackenzie trough probably occurred during the illinoian or early wisconsinan glaciations the younger ice stream advance is interpreted to have occurred during the last late wisconsinan glaciation the onset of cross shelf glaciation on the western canadian beaufort sea margin is inferred to have been initiated significantly later than on the eastern beaufort sea and eastern canadian arctic margins which have a longer history of ice advance and were less peripheral to the ice sheet centre the architecture of the slope beyond the mackenzie trough reflects this comparatively short history of ice advance and lacks the progradational architecture and major glacial sedimentary depocentre or trough mouth fan that is characteristic of slopes seaward of cross shelf troughs on formerly glaciated margins

sediment generation in humid mediterranean setting grain size and source rock control on sediment geochemistry and mineralogy sila massif calabria abstract grain size control on sediment composition is investigated in modern proximal sediment from the sila massif where basic to felsic intrusive rocks are exposed in a mediterranean humid temperate upland climate samples were taken from small creeks and weathering profiles from three areas reflecting different bed rock compositions samples were separated into eleven grain size fractions from very coarse sand to clay and analyzed by i x ray fluorescence for chemical composition and ii x ray diffraction and mineral liberation analysis for mineralogical composition the chemical composition vs grain size relations were modeled by compositional linear regression mineralogical composition of selected samples is used to substantiate the interpretations based on geochemistry results reveal a high degree of chemical weathering with chemical index of alteration cia up to 92 high cia values are restricted to the fine grained fractions while sand sized sediment average at low to moderate cia values 60 although strongly weathered the three sample suites reflecting basic to felsic plutonic bed rock can be effectively discriminated across all grain size classes using trace elements such as v rb and sr linear trend modeling and mineralogical data reflect similar patterns for all sample suites implying similar processes independent of source rock composition this includes overall decrease of quartz and k feldspar over the full grain size range from very coarse sand to clay which is contrasted by overall increase of sheet silicates from coarse to fine among the latter increase of clay minerals strongly outpaces the increase of micas in silt to clay fractions a more complex behavior is shown by plagioclase which is most abundant in intermediate grain size fractions for all sample suites this is likely caused by initial hydrolysis along cleavage and twinning planes and subsequent breakage of plagioclase crystals into smaller fragments towards finer grain size intense hydrolysis has destroyed most feldspars

holocene sea level history of the canadian beaufort shelf new radiocarbon ages pertaining to the holocene sea level history of the canadian beaufort shelf are presented the ages were obtained on samples of freshwater and tidal marsh peat beds from offsho