major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

tectonics and sedimentary environment of the north scotia ridge region revealed by side scan sonar the north scotia ridge is a series of islands and submarine ridges extending 2000 km from tierra del fuego to south georgia in the western south atlantic the ridge forms the elevated northern tectonic margin of the scotia sea and accommodates e w sinistral strike slip motion at the south american scotia plate boundary existing studies have shown that the northern flank of the north scotia ridge is a large and continuous accretionary prism formed during presumed mid late cenozoic n s convergence in this study we present long range side scan sonar gloria images and seismic reflection profiles which show the structural style of the accretionary prism for the first time the youngest accreted sediments show a uniform fabric of initial deformation symmetric gently asymmetric folds of 1 4 km wavelength which has been subsequently disrupted at shallower depths by additional shortening and uplift between 52 o 459w and 50 o 30 9 w the deformation front is exposed at the sea floor and the falkland trough retains the appearance of an active convergent margin elsewhere however the deformation front is buried beneath younger undeformed drift sediments indicating that convergence has ceased gloria sonographs also show geological features consistent with current control of sedimentation non deposition and erosion beneath the antarctic circumpolar current in particular this study describes current influenced sedimentation in the falkland trough and steep sided eroded depressions and diffuse slope parallel fabric on the elevated falkland plateau

facies distribution and textural variation in faro drift contourites velocity fluctuation and drift growth abstract detailed study of seismic profiles piston cores and bottom photographs from the faro drift on the southern margin of portugal has led to a better understanding of drift development and its relationship to bottom current circulation data on the contourite facies characteristics and the surface microphysiography have been published elsewhere here we concentrate on sediment distribution and geometry longitudinal trends in facies types mean grain size sedimentary structures and composition can be interpreted in terms of relative intensity of currents over different parts of the drift these are generally more intense in the marginal channels and at the upstream or eastern end of the drift three different scales of vertical variation of facies can be identified at the large scale 300 500 m of sediment has accumulated over 4 6 ma in a regular vertical succession due to the northward progradation of the drift at the medium scale the upper 20 30 m of sediment shows alternating phases of active lateral progradation and uniform vertical accumulation that may correlate with episodes of more and less current activity related to high and low sea level stands respectively over the past 0 3 ma at the small scale the topmost 2 3 m of sediment deposited in approximately 0 03 ma shows three zones of coarser grained sediments separated by finer grained contourites this sequence can also be interpreted in terms of long term fluctuation in bottom current activity although the signal is clearly complex this kind of analysis of sedimentary drifts can lead to more accurate reconstruction of paleocirculation patterns

quaternary history of the antarctic circumpolar current evidence from the scotia sea within the scotia sea the axis of the antarctic circumpolar current acc is geographically confined and sediments therefore contain a record of palaeo flow speed uncomplicated by acc axis migration we outline holocene and last glacial maximum lgm current controlled sedimentation using data from 3 5 khz profiles cores and current meter moorings geophysical surveys show areas of erosion and deposition controlled by neogene basement topography deposition occurs in mounded sediment drifts or flatter areas where 500 1000 m of sediment overlies acoustic basement 3 5 khz profiles show parallel continuous sub bottom reflectors with highest sedimentation rates in the centre of the drifts and reflectors converging towards marginal zones of non deposition locally on the flanks of continental blocks e g south georgia downslope processes are dominant the absence of mudwaves on the sediment drifts may result from the unsteadiness of acc flow a core transect from the acc axis south to the boundary with the weddell gyre shows a southward decrease in biogenic content controlled by the polar front and the spring sea ice edge both these features lay farther north at lgm the cores have been dated by relative abundance of the radiolarian cycladophora davisiana and by changes in the biogenic ba content a palaeoproductivity indicator sedimentation rates range from 3 to 17 cm ka the grain size of holocene sediments shows a coarsening trend from south to north consistent with strongest bottom current flow near the acc axis though interpretation is complicated by the presence of biogenic grains year long current meter records indicate mean speeds from 7 cm s in the south to 12 cm s in the north with benthic storm frequency increasing northwards lgm sediments are predominantly terrigenous and show a clearer northward coarsening trend with well sorted silts in the northern scotia sea assuming a constant terrigenous source this implies stronger acc flow at the lgm contrasting with weaker weddell gyre flow deduced from earlier work

stable isotope stratigraphy from the antarctic continental margin during the last one million years abstract a stable isotope record from the eastern weddell sea from 69 s is presented for the first time a 250 000 yr record from the southern ocean can be correlated in detail to the global isotope stratigraphy together with magnetostratigraphic sedimentological and micropalaeontological data the stratigraphic control of this record can be extended back to 910 000 yrs b p a time scale is constructed by linear interpolation between confirmed stratigraphic data points the benthic 18o record epistominella exigua reflects global continental ice volume changes during the brunhes and late matuyama chrons whereas the planktonic isotopic record neogloboquadrina pachyderma may be influenced by a meltwater lid caused by the nearby antarctic ice shelf and icebergs the worldwide climatic improvement during deglaciations is documented in the eastern weddell sea by an increase in production of siliceous plankton followed with a time lag of approximately 10 000 yrs by planktonic foraminifera production peak values in the difference between planktonic and benthic 13c records which are 0 5 higher during warm climatic periods than during times with expanded continental ice sheets also suggest increased surface productivity during interglacials in the southern ocean

petrology of glacial sand implications for the origin and mechanical durability of lithic fragments the petrology of first cycle unmodified and second cycle reworked sand at the termini of eleven valley glaciers eroding coarse to fine grained bedrock types is determined in order to evaluate the origin and mechanical durability of lithic sands first cycle sands are coarse to medium grained poorly sorted fine skewed non modal lithic sands with an average composition of q21f6l73 grain size distributions do not vary with composition or source rock types although sands derived from finer grained source rocks contain more lithic fragments than sands from coarser grained sources by contrast second cycle sands are medium grained poorly sorted fine to coarse skewed arkosic to lithic sands with an average composition of q19f40l41 and contain fewer lithic fragments than do first cycle sands we propose that the origin mechanical durability and survival potential of lithic fragments are related to the types and abundances of their internal planes of weakness and the particular stress field of the transporting medium as a result of abrasion glacial clasts and lithic fragments are subjected to shear stress so that fractures propagate along intracrystal and intercrystal planes of weakness resulting in a continuous grain size spectrum of lithic fragments and monomineralic grains irrespective of the type of source rock upon subsequent aqueous transport in the proglacial environment lithic fragments are subjected to point loading during saltation in addition to shear stress point loading produces extensional fractures which preferentially propagate along intercrystal planes of weakness so the lithic fragments break into smaller monomineralic grains and or lithic fragments lithic fragments of very coarse sand size are abundant in first cycle sands thus refuting at least for glacial sands the widely held view that grains of this size are deficient in nature the presence of fewer grains of this size in second cycle sands indicates that very coarse sand size lithic fragments can survive recycling but in greatly reduced proportions due to breakage

silurian s type granite related w mo mineralization in the nanling range south china a case study of the pingtan w mo deposit abstract the pingtan deposit in southwestern hunan province is a newly discovered large sized w mo deposit this deposit is situated in the northwestern part of the miao ershan granite batholith western nanling range the tungsten mineralization is mainly hosted in biotite monzogranite and the alteration related to mineralization is controlled by a ne trending fault zone in this paper we present new molybdenite re os and zircon u pb ages zircon lu hf isotope and ree geochemical data aiming to constrain the w mo mineralization age and ore hosting granite petrogenesis in the pingtan w mo deposit molybdenite re os dating of eight ore samples yielded a weighted average model age of 427 0 5 4 ma mswd 0 24 the la icp ms zircon u pb analysis of two biotite monzogranite yielded 206pb 238u ages of 430 8 2 4 ma and 431 0 1 8 ma respectively suggesting that the w mo mineralization is spatial temporally associated with the biotite monzogranite the ore related granites have high contents of sio2 and k2o belong to weakly to strongly peraluminous a cnk 1 00 1 30 and geochemically classified as s type affinity molybdenite re contents 2 262 7 297 g g zircon ehf t 10 34 5 87 and 176hf 177hf 0 282241 0 282376 values of the biotite monzogranite suggest that the ore forming materials are predominantly derived from the crust this is the first identification of tungsten mineralization related to silurian s type granites caledonian granites in the miao ershan granite intrusion indicating caledonian is an important mineralization period of w in the western part of nanling range south china

spatiotemporal heterogeneity of the palaeoecological record in a large temperate palaeolake sur southwest slovakia comparison of pollen macrofossil and geochemical data abstract aquatic macrophytes living within shallow lakes are particularly sensitive to climate change and fluctuations in water depth in the dabubian lowland of southwestern slovakia sediments from the large shallow palaeolake named sur provide a unique opportunity to reconstruct changes in water depth to analyse succession within local aquatic and terrestrial vegetation here we used a multi core multi proxy approach macrofossils pollen and geochemistry in order to reconstruct water depth changes and its influence on aquatic and terrestrial vegetation succession during the holocene additionally we also consider how heterogeneity in proxy data varied across time and space using particular macrophyte taxa found in the macrofossil assemblage which have specific water depth requirements our results demonstrate changes in water depth created a long term mosaic of vegetation succession in the early holocene aquatic macrophytes suggest the water column was high 100 cm during the middle holocene water depths decreased creating mosaics of aquatic succession by ca 4200 cal yr b p terrestrialization had occurred in the former lake area regional vegetation succession was likely more influenced by the presence of fluvial sands and or by low precipitation and high evaporation rates which delayed the expansion of temperate trees and favoured pinus until 8850 cal yr b p macrofossils exhibit the lowest temporal variation among all proxies which suggests a rather stable macrophyte community when water depth was high pollen data show very low spatial variation given by the size of the accumulation basin which reflects regional pollen rain higher spatial variation was observed in the geochemistry and macrofossil data compared to the pollen data which could be the result of different mosaics of aquatic plants local dispersion of propagules or changes in sediment types we conclude that changes in water depth were not homogenous but rather heterogeneous in space and time

dinoflagellate cysts from sediment traps deployed in the bellingshausen weddell and scotia seas antarctica dinoflagellate cysts have been recovered from six long term 1 2 yr sediment trap moorings deployed in the bellingshausen weddell and scotia seas antarctica these traps mostly moored near the sea bed to sample the nepheloid layer were located both within and to the north of the maximum sea ice limit the numbers of cysts together with the composition of the assemblages reinforce the importance of the maximum sea ice limit as a modern biogeographic boundary for the distribution of dinoflagellate cysts cysts derived from heterotrophic dinoflagellates make up the highest proportions within the assemblages recovered from the traps one trap sampled the export production revealing little difference in cyst flux over those sampling the nepheloid layer cyst flux appears to be highest in areas closest to the antarctic convergence north of the maximum sea ice limit and to high nutrient availability there are however differences between the sediment trap assemblages and those recovered from core top samples at the same or nearby sites these differences in the greater number of cysts and in the higher numbers of round brown protoperidinium cysts in the traps may reflect annual differences in the primary productivity and or cyst production in the area in some areas the sediment record may preserve little information about local surface water productivity because of the activity of bottom water currents for example those arising from the antarctic circumpolar current

late quaternary changes in antarctic bottom water velocity inferred from sediment grain size in the northern weddell sea abstract newly formed bottom water 0 7 c in the northern weddell sea flows e or ne at speeds up to 10 15 cm s with velocity decreasing towards the centre of the weddell gyre preliminary results from long term current meter moorings upper quaternary sediments from this area contain a fine grained terrigenous component from the nepheloid layer plus biogenic silica mostly diatoms with a small amount of ice rafted debris in cores from between 61 and 66 s and from 3300 m to 4700 m water depth the proportion of biogenic silica increases northwards corresponding to increasing seasonal extent of open water vs sea ice cover and the proportion of silt and well sorted fine sand in surface sediments increases with average current velocity downcore diatom rich and diatom poor sediments alternate on a scale of 1 3 m and intervals with more diatoms contain a higher proportion of silt to clay preliminary stratigraphy suggests the cyclicity in composition and texture is related to glacial interglacial cyclicity during warm periods indirectly correlated with isotope stages 1 3 5 etc biogenic silica production takes place during several months of each year and silt and fine sand are transported by bottom currents during glacial periods with greater sea ice cover than at present biogenic productivity was suppressed and no silica was preserved in the sediments in addition a lower proportion of terrigenous silt implies that bottom currents were weaker at sites with a present day average velocity of 10 cm s a last glacial maximum average velocity of 1 cm s or less is inferred from grain size measurements

geology geochemistry and tectonic settings of the molybdenum deposits in south china a review abstract south china block scb is the area including the yangtze craton and the huanan orogen where scattered precambrian terranes are usually regarded as segments of cathaysia land it is the third most important molybdenum metallogenic province in china next to the qinling dabie area and northeast china containing 29 mo only or mo dominated 9 w mo sn bi and 8 cu mo deposits these 46 deposits are located mainly in 1 the lower yangtze river belt of the northeastern yangtze craton 2 the northern jiangnan orogenic belt that is generally considered a meso neoproterozoic magmatic arc complex accreted onto the southeastern margin of the yangtze craton 3 the wuyi yunkai orogenic belt characterized by local exposures of proterozoic metamorphic terranes and the more widespread sinian uppermost proterozoic to triassic sedimentary sequences and 4 the southeast coastal volcanic belt characterized by yanshanian andesitic to felsic volcanic rocks their genetic types are dominated by porphyry and skarn mineral systems with only a few quartz vein systems the orebodies form veins lens cylindrical shapes pipes or irregular in shape usually controlled by faults at various scales and volcanic subvolcanic complexes the host rocks are variable in lithologies including granites porphyries volcanic breccias and tuffs clastic sediments and carbonate rocks but the high grade orebodies are usually hosted in carbonate shale sequences hydrothermal mineralization processes can be generally divided into four stages from early to late they are 1 k feldspar quartz veins or veinlets 2 quartz molybdenite stockworks 3 quartz polymetallic sulfide stockworks and 4 quartz carbonate fluorite veinlets fluid rock interaction as exemplified by wallrock alteration evolved from k silicate alteration k feldspar quartz mica through phyllic quartz sericite chlorite epidote to propylitic or argillic alteration with skarn alteration typically occurring in skarn type mineral systems hydrothermal mineral assemblages vary between two end members namely the dry system formed by co2 rich fluids and marked by quartz k feldspar fluorite carbonate and epidote and the wet system mainly originated from co2 poor fluids and composed of biotite sericite and chlorite the ore forming fluids are magmatic in origin and show high temperature and high salinity the melt fluid systems forming cu mo deposits are more oxidizing than those forming the w mo or mo deposits as suggested by accessory minerals in granitoids and daughter minerals in fluid inclusions the cu mo deposits are related to the i type granitic rocks adakite like whereas the w mo and mo only systems are related to granitic rocks of s or a types although all of them show high k contents available isotope ages show that the mo and mo bearing deposits were predominantly formed in the early yanshanian orogeny 170 134 ma followed by the late yanshanian orogeny 110 92 ma and the caledonian orogeny 450 410 ma the caledonian mo mineralization has been observed only in the wuyi yunkai orogenic belt and related to the collision between the yangtze craton and the pre devonian huanan orogen or terranes separated from the cathaysia land linked to the assembly of the gondwana supercontinent the early yanshanian mineralization affected the entire huanan orogen and the eastern yangtze craton and resulted from the syn to post collisional tectonism following the closure of eastern paleo tethys the late yanshanian mo deposits mainly occur in the southeast coastal volcanic belt and the southeastern margin of the wuyi yunkai orogenic belt and are related to the westward subduction of the paleo pacific plate the skarn type mineral systems generally show lower re contents than the porphyry type deposits in a same tectonic unit suggesting that carbonate host rocks have lower re contents than the causative porphyries the re contents in molybdenites from porphyry or porphyry skarn cu mo systems are 50 ppm mainly 100 ppm suggesting a source significantly contributed by the mantle whereas the re contents in molybdenites from the mo only or w mo dominated deposits are

surface lithofacies biofacies and diatom diversity patterns as models for delineation of climatic change in the southeast atlantic ocean abstract distribution of diatom species in surface sediments of the southeast atlantic ocean is regulated by present day oceanographic and hydrodynamic processes five assemblages vectors defined by factor vector analysis reflect different environments and conditions assemblage a is a high diversity flora associated with the nutrient rich relatively cold waters south of the polar front in the diatom ooze belt occurrence of this flora on maud rise and vicinity may reflect periodic occurrence of a polynya in that area assemblage b is a reworked assemblage that dominates the southern portion of the study area productivity there is low reflecting sea ice cover during most of the year the area north of the polar front is dominated by assemblage c whose characteristic species reflect the relatively warm subantarctic surface water winnowing and frustule breakage have altered assemblage d found in three isolated samples by removing relatively delicate forms leaving lag deposits of more robust species assemblage e is a low diversity stress flora reflecting unstable unpredictable environments along the polar front antarctic slope and the northern boundary of winter sea ice these sites are characterized by the sinking of cold water downcore analysis of cores lying adjacent to the polar front and the diatom ooze pelagic clay boundary show evidence for past climatic variation the low trophic level occupied by diatoms and the subsequent sensitivity of these organisms to abiotic environmental parameters such as light quality make relative diatom abundance a useful tool for monitoring fluctuations of winter sea ice and the temperature changes responsible for these fluctuations the position of the polar front has migrated at least three times within the last 0 015 m y b p within the last 0 3 m y b p warm maxima have occurred at approximately 0 0 0 015 0 125 and 0 3 m y b p

late quaternary sediment dating and quantification of lateral sediment redistribution applying230thex a study from the eastern atlantic sector of the southern ocean high resolution records of the natural radionuclide230th were measured in sediments from the eastern atlantic sector of the antarctic circumpolar current to obtain a detailed reconstruction of the sedimentation history of this key area for global climate change during the late quaternary high resolution dating rests on the assumption that the230thex flux to the sediments is constant short periods of drastically increased sediment accumulation rates up to a factor of 8 were determined in the sediments of the antarctic zone during the climate optima at the beginning of the holocene and the isotope stage 5e by comparing expected and measured accumulation rate of230thex lateral sediment redistribution was quantified and vertical particle rain rates originating from the surface water above were calculated we show that lateral contributions locally were up to 6 5 times higher than the vertical particle rain rates at other locations only 15 of the expected vertical particle rain rate were deposited

an analysis of the optical features of the near bottom and bottom nepheloid layers in the area of the scotian rise profiles of light transmission versus depth have been studied in the region of the scotian rise of the north atlantic at bottom depths between 4900 and 5000 m a component model has been developed and consists of three components of transmission which can be combined to duplicate accurately any given transmission profile two of the components are shown to be representative of several basic phenomena the particle concentration within a uniform flow and the separation of a benthic nepheloid layer in the case of a uniform flow it is the relative magnitudes of settling and eddy diffusion which determine the shape of the transmission profile separation of the benthic nepheloid layer was inferred to be caused by an occasional cross slope velocity component the physical interpretation of the third component was ambiguous eulerian and lagrangian transformations of the data show that benthic storms that were detected at one location and time appeared nearly identical at a later time downstream and that benthic storms can be detected over a large distance distance and time scales obtained from these transformations show the area of the scotian rise to be one characterized by bottom storms which keep their general form over periods of at least 2 weeks and for distances traveled of at least 400 km

weddell sea abyssal sediments a record of antarctic bottom water flow abstract deep circulation in the weddell sea is a clockwise gyre with bottom water formed by mixing along the southern and western margins most antarctic bottom water originates here leaving the weddell sea to the east depths 4500 m or to the north depths 16 m ma sediments from the deep weddell basin are hemipelagic muds with ash laminae and mainly in the centre of the gyre distal turbidites derived from the southwest thin debris flows occur near seamounts the hemipelagic muds become coarser from the centre to the edge of the gyre winnowing by strong bottom currents is localised along the northern margin of the basin the absence of diatoms from the weddell basin sediments may result from dissolution as well as low productivity sediments from jane basin consist of alternating diatomaceous and barren hemipelagic muds considered to represent interglacial and glacial conditions respectively the diatomaceous sediments contain more silt suggesting that bottom water flow increases during interglacial periods

glacial contourites on the antarctic peninsula margin insight for palaeoenvironmental and palaeoclimatic conditions deep sea finely laminated and barren glacial sediments occur in the sediment drift field offshore the pacific margin of the antarctic peninsula where a weak contour current flows at present to the sw atypical sedimentary facies were related to the coexistence and interaction of different sedimentary processes three end members of radiograph facies were defined to represent the sedimentary sequences controlled by a dominant process as follows 1 direct influence of turbidity currents on sedimentation is observed in the area surrounding the alexander channel system with silty layers interbedded with laminated mud free of ice rafted debris ird 2 distal meltwater turbid flows dominate the more proximal area of the top plateau with structureless and coarser grained sediments containing ird 3 along the crest of the drift persistent weak bottom currents control the deposition of fine grained sediments conveyed into the system through other processes these laminated sediments contain ird and are atypically not bioturbated because of unusual climatically related environmental conditions of suppressed primary productivity and oxygen reduced deep waters these glacial contourites were observed on most of the antarctic margin with the exception of the areas in which polynyas were maintained during the glacial stages glacial contourites can be used as a proxy to define temporal and spatial extension of the antarctic sea ice deep sea sediments of the sediment drifts offshore the pacific margin of the antarctic peninsula were investigated within the sedano sediment drifts of the antarctic offshore and mogam morphology and geology of antarctic margins antarctic peninsula and wilkes land projects of the italian programma nazionale di ricerche in antartide fig 1 the continental shelf of the pacific margin of the antarctic peninsula is dissected by a number of modern u shaped troughs that reflect the neogene path of large ice streams rebesco et al 1998 2002 sediments across the continental shelf were transported mainly by ice streams and delivered to the continental slope and rise during the periods of maximum glacial expansion the continental rise hosts a number of large sediment drifts separated by dendritic deep sea channel systems that originated on the lower continental slope in alignment with the reaches of each glacial trough amblas et al 2006 rebesco et al 2007 two main alternating lithologies related to climatic changes were initially distinguished pudsey camerlenghi 1998 pudsey 2000 interglacial brown bioturbated mud containing sparse icerafted debris ird and glacial grey laminated mud further detailed studies consisting of over 1000 sedimentological compositional and biostratigraphic analyses diatoms foraminifers and nannofossils allowed lucchi et al 2002a to distinguish four distinctive sets of sedimentary facies connected to a sequence of four climatic stages each characterized by the onset of typical sedimentary processes fig 2 as follows 1 strongly bioturbated mud with abundant ird and aeolian sediment input was produced during the interglacial phase fig 2a the increased bioactivity is matched by insignificant downand along slope processes negligible suspended load and sediment transport by the southwesterly flowing bottom currents is occurring at present on the continental rise giorgetti et al 2003 2 terrigenous structureless mud including a series of close spaced ird layers was produced during the deglaciation transition from glacial to interglacial conditions by the disintegration of the retreating grounded ice sheet fig 2b the absence of calcareous microfossils is related to strong carbonate dissolution and rise of the carbonate compensation depth ccd as a result of major meltwater discharge which in turn caused water stratification with less oxygenated and nutrient enriched conditions at the sea bottom 3 a large variety of from viana a r rebesco m eds economic and palaeoceanographic significance of contourite deposits geological society london special publications 276 111 127 0305 8719 07 15 00 the geological society of london 2007

circulation in the glacial north atlantic inferred from grain size measurements records of nutrient proxies in marine sediments indicate that the nutrient distribution and hence circulation of the glacial north atlantic ocean was markedly different from that of today1 2 but these tracers are influenced by several biogeochemical factors unrelated to ocean circulation3 6 and thus do not provide a direct measure of the vigour of circulation distributions of grain size in marine sediments can provide such information owing to the sorting effects of currents7 8 if the characteristics of the input sediment flux are known here we present a record inferred from grain size measurements of variations in the relative strength of deep and intermediate currents in the eastern north atlantic over the past 25 000 years we find that glacial intermediate water flowed rapidly at depths of between 1 100 and 2 000 m in contrast deep water circulation was sluggish during the last glaciation but increased in strength shortly after the glacial maximum this would have resulted in increased heat flux to high latitudes and may have triggered sudden deglaciation deep current strengths declined again at the start of termination stage ia and during the younger dryas perhaps as a result of iceberg discharges the so called heinrich events9 10 a remarkably similar record of grain size variations has been found in the western north atlantic11 indicating that these changes in circulation are ocean wide

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

quaternary history of calcium carbonate fluctuations in the western equatorial indian ocean somali basin abstract a study of the quaternary history of calcium carbonate fluctuations in the equatorial indian ocean based on the swedish deep sea expedition core 154 demonstrates that the calcite compensation depth ccd was shallower during interglacial periods than during glacials higher percentages of calcium carbonate lower percentages of dissolution resistant planktonic foraminifera and lower values of the berger dissolution index suggesting better calcium carbonate preservation are recorded during glacial periods and or at glacial interglacial transitions in contrast interglacial periods are marked by stronger calcium carbonate dissolution the data indicate that dissolution is the main controlling factor of calcium carbonate in the western equatorial indian ocean higher dissolution during interglacial periods and enriched 13 c are due to higher noncarbonate productivity and enhanced antarctic bottom water aabw ventilation in the equatorial indian ocean

chronology and correlation of quaternary magnetostratigraphy and nannofossil biostratigraphy in norwegian greenland sea sediments paleomagnetic analyses of a series of sediment cores from the norwegian greenland sea document the existence of seven short lived geomagnetic events during the last about 500 000 years calcareous nannofossil biostratigraphy correlated to oxygen isotope chronostratigraphy provides a time framework to infer age and duration of these periods of extreme divergence of the earth s magnetic paleofield from the regular normal polarity configuration of the brunhes chron the geomagnetic events typically extend over 5 to 10 kyr two events are observed within the oxygen isotope stage 2 4 interval a short event is recorded at the stage 4 5 boundary and another just below the stage 5 6 boundary additional three geomagnetic events are identified in oxygen isotope stage 6 at the stage 9 10 boundary and near the top of oxygen isotope stage 13 respectively

late tertiary quaternary magnetostratigraphy and biostratigraphy of vema channel sediments abstract twenty one piston cores in a transect of the vema channel near 31 s were analyzed magnetostratigraphically and biostratigraphically in order to ascertain the depositional continuity in the late tertiary and quaternary the cores span a depth interval of 2941 4235 m and represent three distinct physiographic provinces each of which shows a relatively consistent accumulation pattern the deepest cores are from the broad terraces which flank the vema channel axis on both the west 3650 mm and east 4150 4250 m these cores show the highest accumulation rates in the region 20 m m y 2 and no evidence of unconformities twelve cores from the flanks of the rio grande rise 2941 3950 m show depositional continuity in the late quaternary and normal pelagic accumulation rates 5 10 m m y 2 with evidence in two of the cores for minor erosional hiatuses on a local scale perhaps due to slumping a relatively narrow transition zone between the rio grande rise flanks and the eastern terrace 3950 4150 m shows buried manganese pavements and near outcrops of miocene pliocene strata indicating intermittent erosion during the late tertiary and quaternary perhaps due to episodes of intensified aabw flow modern flow within this transition zone and over the eastern terrace is relatively weak gu 2 cm s 2 and southward the presence of well developed sediment waves on the terrace and buried erosional unconformities upslope to the east suggests substantially higher current velocities during the late tertiary than those present today

sedimentology and stratigraphy of box cores from the hebble site on the nova scotian continental rise abstract fifty box cores were obtained from the 2 4 km site of the high energy benthic boundary layer experiment hebble on the lower nova scotian continental rise at 4820 m the oldest unit occurring in two gravity cores is a pre holocene dark grey gravelly mud probably of debris flow origin above this is a soft grey mud overlain by brown sandy mud whose sand is largely foraminiferal with some terrigenous material from interbedded turbidites in some places this unit has a stiff brown gravelly mud at its base which is always overlain by sandy mud containing dispersed gravel it is suggested that the dispersed gravel originated from the underlying gravelly mud and has been dispersed upwards by the action of burrowing organisms foraminifera indicate a holocene age down to about 65 cm and thus a net accumulation rate of about 6 cm ka 1 the surface unit of brown mud named the hebble mud is spatially variable in both thickness and sand content which average about 4 cm and 6 respectively sand percentage is not related to silt size or percentage but varies inversely with deposition rate and thickness suggesting a relation to local winnowing the size and peak height of the main silt mode 10 17 m are closely correlated and the peak height is inversely related to the percentage of clay this is attributed to fractionation during deposition of the mud wherein fine silt and clay deposition is suppressed at flow speeds from 10 to 18 cm s 1 leaving coarser silt there is more clay on the upstream and downstream sides of a low spur suggesting spatial variation of shear stress that may be due to a standing internal wave added to the mean flow silt mode size is variable downcore although clay percentages are similar to those at the surface the overall silt size is probably controlled by turbidite input thus silt size is likely to be an unreliable indicator of current speeds down core though peak height of the silt mode may be satisfactory

origin of detrital fluxes in the southeast indian ocean during the last climatic cycles because of a close relationship between detrital flux variations and magnetic susceptibility ms flux ms cm 3 of bulk sediment multiplied by the linear sedimentation rate variations in the southeast indian basin of the southern ocean ms flux profiles have been used to examine the spatial and temporal detrital flux changes in this basin during the last climatic cycle results indicate a general increase in detrital material input during the coldest periods suggesting a widespread phenomenon at least on the basin scale mineralogical data geochemical data and 87sr 86sr isotopic ratios have been used to determine the origin and transport mechanisms responsible for increased detrital flux during glacial periods mineralogical and geochemical data show that these glacial highs are due to increases in both kerguelen crozet volcanic and antarctic detrital inputs the 87sr 86sr isotopic composition of the 45 m fraction indicates that the kerguelen crozet province contributes to at least 50 of the coarse particule input to the west this contribution decreases eastward to reach less than 10 these tracers clearly indicate that the crozet kerguelen province was a major source region of detrital in the western part of the basin during glacial times in contrast material of antarctic origin is well represented in the whole basin fine and coarse fractions because of the minor amount of coarse particles in the sediments volcanic particles from kerguelen and crustal particles from antarctica have most probably been transported by the antarctic bottom water current and or the circumpolar deepwater current during glacial periods as is the case today nevertheless the presence of coarse particles even in low amount suggests also a transport by ice rafting sea ice and icebergs originated from both kerguelen and antarctic sources however the relative importance of both hydrographic and ice rafting modes of transport cannot be identified accurately with our data during low sea level stands glacial maximum periods increasing instability and erosion of the continental platform and shallow plateaus could have resulted in a more efficient transfer of crustal and volcano detrital material to the southeast indian basin at the same time extension of the grounded ice shelves over the continental margins and increase in the erosion rate of the antarctic ice sheet could have induced a greater input of ice rafted detritus ird to southern ocean basins enhancement of the circumpolar deepwater current strength might have also carried a more important flux of detrital material from kerguelen however an increase in the bottom water flow is not necessarily required

origin signature and palaeoclimatic influence of the antarctic circumpolar current the antarctic circumpolar current acc is today the strongest current in the world s ocean with a significant influence on global climate its assumed history and influence on palaeoclimate while almost certainly equally profound are here called into question in this paper we review 30 years of accumulated data interpretation and speculation about the acc deriving mainly from dsdp and odp drilling in the southern ocean for most of this time a conventional view of acc development signature and influence has held sway among palaeoceanographers and marine geologists in this view the acc began at about 34 ma close to the eocene oligocene boundary the time of onset of significant antarctic glaciation and the time of creation of a deep water gap tasmanian seaway between australia and antarctica as the south tasman rise separated from north victoria land this is the smoking gun of synchroneity the southern ocean sediment record shows a latest eocene development and subsequent geographic expansion of a siliceous biofacies its northern limit taken to indicate the palaeoposition of the acc axis in addition the acc was considered to have caused antarctic glaciation by isolating the continent within a cold water annulus reducing north south heat transport a different and later date for antarctic south american opening drake passage was proposed but the timing of acc onset there was disputed and the simple story survived recent developments however call it into question modern physical oceanography shows that all or most of present day acc transport is confined to narrow jets within deep reaching circumpolar fronts and numerical modelling has suggested that a steady reduction in greenhouse gas concentration through the cenozoic could cause antarctic glaciation with or without a contribution from ocean circulation change the rapidity of antarctic glacial onset at the eocene oligocene boundary and coeval creation of a deep water gap south of tasmania both survive but in light of the new information the presence of a siliceous biofacies cannot be claimed as evidence of the existence of a continuous deep reaching oceanic front and therefore of an acc and the possibility arises that cool and cold sea surface temperatures were effects of antarctic glaciation rather than evidence of a major contributor to its cause in considering future work we emphasise the importance of additional information from ancillary fields better definition of the necessary and sufficient properties of oceanic fronts additional determinations of cenozoic atmospheric pco2 and further developments in models of antarctic glaciation but also suggest the way forward in marine geology our knowledge of the development and palaeoclimatic significance of the acc will be best served by grainsize studies of bottom current strength at selected locations and geochemical or mineralogical studies of clays and ird as a way of examining provenance and therefore surface and bottom current directions and the existence of interocean connections

carbonate grain size distribution in hemipelagic sediments from a laser particle sizer laser grain sizer instruments provide the opportunity to study the grain size distribution of sediments across a wide size range in a short time automatic measurements can therefore be made on a routine basis for a great number of samples oceanic studies have proved the utility of these methods in characterizing both climatic changes and changes in sediment provenances in addition carbonate content is estimated either directly by caco 3 measurement by visual observations or by proxies such as sediment color reflectance nevertheless the grain size distribution of the carbonate fraction is still a matter of speculation and only optical observations can distinguish the nature of each carbonate fraction here we present the improvements on a method to study rapidly with a high resolution the grain size distribution of the carbonate fraction by use of a laser grain sizer we describe the basic methodology and apply it to an example from the pleistocene of the northern atlantic ocean

a sediment record of cyclic bottom current variability from the northwest weddell sea cores and 3 5 khz sub bottom profiles collected from the continental slope and rise near 64 s 52 w off the tip of the antarctic peninsula reveal transport and depositional processes in a high energy environment a large channel runs downslope from the shelf break the remaining slope area is smooth and shows no acoustic penetration except locally in the lee of topography sediments on the slope and rise were mainly deposited by suspension from a 150 to 300 m thick nepheloid layer periodic resuspension and winnowing by bottom currents has produced coarse lags of ice rafted debris throughout these deposits and has also produced an elongated field of mudwaves running parallel to the base of the slope these low amplitude asymmetric features were formed by currents flowing from west to east parallel to the local slope short gravity cores show a compositional and textural cyclicity developed between two distinct lithologies intervals of poorly sorted sediment barren of fauna and with mud dominated size distributions are interpreted to result from a cold climate and low bottom current strength production of weddell sea bottom water probably lessened during these times and there was a greater duration of sea ice cover these sediments are interbedded with winnowed and better sorted deposits comprising fine sands and silts that contain abundant planktonic foraminifera interpreted as implying warmer climatic conditions and stronger current activity a varied calcareous benthic foraminiferal assemblage also indicates that these intervals lay above the ccd during deposition renewed and invigorated production of bottom water is implied contemporaneous with a shorter duration of sea ice cover petrographic evidence indicates an antarctic peninsula source throughout the cycles are considered to be the result of climatic fluctuations occurring over the timespan of glacial interstadials although confirmation of this timescale awaits acquisition of an absolute chronology

bottom current speed in the vema channel recorded by particle size of sediment fine fraction abstract the particle size distribution of the carbonate free silt fraction was determined in forty two core top samples from the east flank of the vema channel in order to allow comparison of the mean particle size with near bottom current speed based on nearby ctd and current meter observations the silt mean particle size fluctuates insignificantly between 1450 3950 m but coarsens markedly below 4000 m under antarctic source bottom currents the top of the zone of coarse sizes approximates the top of lower circumpolar water lcpw at 4000 m the steep gradient to coarsest sizes in the axis of the channel marks the transition to antarctic bottom water aabw the vertical profile of mean particle size on the east flank correlates in general respects with the vertical velocity gradient in the channel axis although the core sites on the east flank are as far as 200 miles from the current meter arrays nevertheless this relationship is used to infer that the non carbonate particle sizes deposited on the east flank of the channel may be an indication of bottom current speed and therefore the mean size is used to reconstruct profiles of mean current speed for three time slices 18 120 and 140 ka b p during glacial isotopic stages 2 and 6 the particle sizes deposited on the east flank of the channel are characterized by finer sizes at nearly all depths and the zone of coarse sizes corresponding to lcpw and aabw deepens during interglacial isotopic stage 5e the particlesize profile is very similar to the modern profile however lcpw and aabw appear to be deeper than at present the finer particle sizes deposited at nearly all depths during glacial periods indicates that the velocity of deep circulation in the atlantic was reduced in response to the ice ages deep circulation during isotopic stage 5e closely resembled modern circulation however aabw production rates may have been less that at present

late quaternary deep stratification climate coupling in the southern ocean implications for changes in abyssal carbon storage the southern ocean plays an important role in modulating pleistocene atmospheric co2 concentrations but the underlying mechanisms are not yet fully understood here we report the laser grain size distribution and mn geochemical data of a 523 kyr long sediment record core ant30 p1 02 off prydz bay east antarctica to trace past physical changes in the deep southern ocean the core sediments are predominantly composed of clay and silt sized material three grain size end members em as well as three sensitive grain size classes sc were discerned interpreted as ice rafted debris em1 and sc1 and coarse em2 and sc2 and fine em3 sc3 materials deposited from bottom nepheloid layers respectively ratios of em2 em2 em3 and sc2 sc3 reveal changes in the local bottom current strength which is related to the deep ocean diapycnal mixing rate showing higher values during interglacial periods and lower values during glacial periods mno was enriched at each glacial termination probably caused by abrupt elevations in antarctic bottom water aabw formation rate lower aabw formation rate and reduced deep diapycnal mixing during glacial periods enhanced deep southern ocean stratification contributing to glacial atmospheric co2 drawdown the elevated aabw formation and enhanced deep diapycnal mixing during glacial terminations alleviated such deep stratification promoting deeply sequestered co2 to outgas

calibration of a point counting technique for estimation of biogenic silica in marine sediments the simple technique of point counting is very quick and is suitable for shipboard use or in any study where high accuracy is not necessary point counting smear slides yields results different from measurements of weight percent silica if there are systematic differences in shape and density of biogenic and terrigenous grains in this note i present calibration curves for synthetic biogenic terrigenous mixtures to show how the accuracy of point counting may be improved

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

zircon la icp ms u pb ages of granitoid rocks and molybdenite re os age of shedong w mo deposit in cangwu county of guangxi and its geological significance located in southern margin of dayaoshan uplift the shedong tungsten and molybdenum deposit in cangwu county of guangxi is a porphyry skarn quartz vein type ore deposit related to granitoids zircon la icp ms u pb dating of granitoids yielded the isochron age of granite porphyry 91 05 0 31 ma and that of granodiorite 435 8 1 3 ma in sheshan multiple stock as well as the isochron age of granodiorite porphyry 432 0 1 7 ma in pingtoubei ore blocks re os isochron age of molybdenite hosted in quartz veins related to granodiorite porphyry veins is 437 8 3 4 ma these high precision dating data suggest that tungsten and molybdenum mineralization was formed in early silurian related closely to granodiorite porphyry this new evidence provides constrains on the time of the caledonian orogeny and magmatic activity in southern china and indicates the probable existence of an intense w mo cu au mineralization during caledonian period in dayaoshan uplift

sea ice winter convection and the temperature minimum layer in the southern ocean the structure of the near surface waters in the southern ocean poleward of the antarctic polar front but away from continental margins is investigated with a three dimensional time dependent numerical model which resolves the annual sea ice cycle the growth and decay of the ice field is predicted using one of semtner s 1976 thermodynamic ice models in terms of specified atmospheric data and computed thermohaline characteristics of the ocean layers the ice field is found to be sensitive to the lateral advection of heat by the oceanic circulation as well as vertical heat transports due to deep winter convection the model treats the temperature minimum layer in the southern ocean as the remnant of a deep winter mixed layer which becomes capped by surface heating and precipitation in summer the predicted thermohaline characteristics of the temperature minimum layer and the surface mixed layer are in good agreement with observations finally the annual air sea heat exchange predicted by the model is discussed the model s predicted area averaged heat loss experienced by the ocean south of the atlantic polar front is much smaller than was previously estimated this is attributed to errors in the southern region of the model domain it is suggestedmore that models which include the interactions between sea ice and surface deep and bottom waters along the continental margins are needed to investigate this region less

high resolution diatom stratigraphy of quaternary sediments from the scotia sea upper quaternary pelagic and hemipelagic sediments from the scotia sea and south scotia ridge range from diatom ooze to diatom bearing mud diatom content increases northwards and at most sites diatom rich and diatom poor sediments alternate downcore on a scale of metres a local stratigraphy is based on relative abundance of six prominent diatom taxa eucampia antarctica rhizosolenia spp thalassiosira spp chaetoceros spores nitzschia kerguelensis and othernitzschia species and one silicoflagellate species distephanus speculum these stratigraphic units defined using diatoms are correlated with radiolarian abundance stratigraphy cycladophora davisiana and with palaeomagnetic stratigraphy information from modern environments phytoplankton and sediment trap studies indicates that changes in diatom species composition are related to n s movement of the winter ice edge and of the antarctic convergence

clay mineral distribution in surface sediments of the south atlantic sources transport and relation to oceanography abstract surface samples mostly from abyssal sediments of the south atlantic from parts of the equatorial atlantic and of the antarctic ocean were investigated for clay content and clay mineral composition maps of relative clay mineral content were compiled which improve previous maps by showing more details especially at high latitudes large scale relations regarding the origin and transport paths of detrital clay are revealed high smectite concentrations are observed in abyssal regions primarily derived from southernmost south america and from minor sources in southwest africa near submarine volcanoes of the antarctic ocean south sandwich bouvet island smectite contents exhibit distinct maxima which is ascribed to the weathering of altered basalts and volcanic glasses the illite distribution can be subdivided into five major zones including two maxima revealing both south african and antarctic sources a particularly high amount of mg and fe rich illites are observed close to east antarctica they are derived from biotite bearing crystalline rocks and transported to the west by the east antarctic coastal current chiorite and well crystallized dioctaedral illite are typical minerals enriched within the subantarctic and polarfrontal zone but of minor importance off east antarctica kaolinite dominates the clay mineral assemblage at low latitudes where the continental source rocks west africa brazil are mainly affected by intensive chemical weathering surprisingly a slight increase of kaolinite is observed in the enderby basin and near the filchner ronne ice shelf the investigated area can be subdivided into ten large scale clay facies zones with characteristic possible source regions and transport paths clay mineral assemblages of the largest part of the south atlantic especially of the western basins are dominated by chlorite and illite derived from the antarctic peninsula and southernmost south america and supported by advection within the circumantarctic deep water flow in contrast the east antarctic provinces are relatively small assemblages of the eastern basins north of 30 s are strongly influenced by african sources controlled by weathering regimes on land and by a complex interaction of wind river and deep ocean transport the strong gradient in clay mineral composition at the brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins

petrogenesis of the yupo w bearing and dali mo bearing granitoids in the dayaoshan area south china constraints of geochronology and geochemistry abstract the geological significance of early paleozoic caledonian magmatism and associated mineralization in south china is as yet poorly understood compared to the well documented mid late mesozoic yanshanian magmatism and associated mineralization the early paleozoic granitoids were previously thought to be rarely mineralized both caledonian granitoids and yanshanian granitoids occur in the dayaoshan area from the qin hang metallogenic belt south china zircon u pb ages of granodiorite at the yupo skarn w deposit and the monzonite and granodiorite at the dali porphyry mo deposit all i type granites analyzed by sensitive high resolution ion micro probe shrimp and or laser ablation inductively coupled mass spectrometry la icp ms are 441 9 1 9 ma 2 104 6 1 6 ma 2 and 105 3 1 4 ma 2 respectively both elevated zircon 18 o v smow values 5 8 7 7 and negative e hf t values 3 2 to 0 2 indicate that these plutons formed via partial melting of a mesoproterozoic continental crust with minor mantle materials the caledonian w bearing yupo granodiorite is relatively reduced fmq 0 57 whereas the yanshanian mo bearing granodiorite at dali fmq 1 11 is more oxidized than the associated ore barren monzonite fmq 0 52 thus it is likely that the contrasting mineralization between the two plutons was controlled by redox states of granitic magmas

bottom current pathways in the argentine basin revealed by mean silt particle size regional circulation patterns in the deep sea are very difficult to determine because of time constraints on the acquisition of large physical oceanographic data sets from abyssal depths in addition the large number of long term 1 yr current meter arrays needed to delineate bottom current pathways are extremely costly an alternative method for inferring benthic flow patterns described here is to map the mean size of the silt fraction of sediment on the sea floor because of the availability of a large number of core samples in the argentine basin the particle size approach provides a useful method for determining bottom current pathways in that deep basin

distribution of organic walled dinoflagellate cysts in surface sediments of the southern ocean eastern atlantic sector between the subtropical front and the weddell gyre abstract thirty two surface sediment samples from the southern ocean eastern atlantic sector between the subtropical front and the weddell gyre were investigated to provide information on the distribution of modern organic walled dinoflagellate cysts in relation to the oceanic fronts of the antarctic circumpolar current acc a clearly distinguishable distribution pattern was observed in relation to the water masses and fronts of the acc the dinoflagellate cysts of species characteristic of open oceanic environments such as impagidinium species are highly abundant around the subtropical front whereas south of this front cosmopolitan species such as nematosphaeropsis labyrinthus and the cysts of protoceratium reticulatum characterise the transition from subtropical to subantarctic surface waters the subantarctic surface waters are dominated by the cysts of heterotrophic dinoflagellates such as protoperidinium spp and selenopemphix antarctica the cysts of protoperidinium spp form the dominant part of the assemblages around the antarctic polar front whereas s antarctica concentrations increase further to the south the presence of s antarctica in sediments of the maud rise a region of seasonal sea ice cover reflects its tolerance for low temperatures and sea ice cover a previously undescribed species cryodinium meridianum gen nov sp nov has a restricted distribution pattern between the antarctic polar front and the acc weddell gyre boundary

a model for sedimentation by tidewater glaciers sampling of sediment from the fjord floor in front of tidewater glaciers in glacier bay alaska has provided information about processes in this restricted glacimarine dreimanis 1979 setting sediment sampling in conjunction with oceanographic and glacial dynamics data has also enabled the discrimination of sediment types and their facies associations deposits are strongly controlled by sea water characteristics position and sediment discharge of melt water streams iceberg calving and rate of glacierfront retreat five distinct facies associations have been found to reflect glacier fjord regimes the facies associations and ice fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers the model can be used to predict i rapid retreat of an actively calving ice front ii slow retreat or stabilization of a calving ice front at a channel constriction iii stabilization of a melting very rarely calving ice front when the glacier base is near tidewater elevation and iv large outwash delta progradation into a fjord when the ice front retreats onto land this model can be used to interpret facies associations found in a stratigraphic record

a 1 3 myr palaeoceanographic record from the continental margin off dronning maud land antarctica a 12 5 m long core was retrieved from the continental margin off dronning maud land antarctica magnetostratigraphy stable isotopes 14 c accelerator mass spectrometer and amino acid analyses indicate a continuous sediment record going back 1 3 myr comparison of caco 3 results with those from odp site 1089 and an index of north atlantic deep water nadw influence in surface waters indicate that nadw upwelled along the antarctic continental margin during the whole of this period the midpleistocene transition 1 0 0 6 ma was accompanied by an apparent decline in the nadw influence and was followed by extended carbonate dissolution during the interglacials of marine isotope stages mis 13 and 11 less extensive periods of dissolution occur at the end of the interglacials younger than mis 11 while interglacial dissolution is characteristic of the pacific and indian oceans the carbon isotopes return to pre transition values indicative of renewed nadw upwelling the concentration of ice rafted debris may reflect changes in the relative rate of interglacial sedimentation it is speculated that the high ice rafted debris ird concentrations during interglacials younger than 400 kyr may be due to a reduced relative sedimentation rate of other interglacial components whereas the low concentrations during interglacials before the mid pleistocene transition may be due to a higher relative sedimentation rate of these

the margins of the south orkney microcontinent marine geophysical studies of the south orkney microcontinent show two intersecting tectonic fabrics of different age the older fabric is oriented e w and represents the magmatic arc and fore arc created by subduction related processes at the pacific margin during the mesozoic the younger oriented nnw to sse comprises half graben related to e w rifting at both the eastern and western margins of the microcontinent both fabrics provide constraints on a 40 ma reconstruction which shows a highly systematic distribution of arc and fore arc provinces and points to the importance of e w strike slip in regional tectonic evolution the rifting apparently of oligocene age is associated with back arc extension which created the oceanic basins to either side of the microcontinent this strongly supports the existence of subduction with the same orientation as the present south sandwich arc as far back as 35 or 40 ma

geometry and development of glacial continental margin depositional systems in the bellingshausen sea we present multi channel seismic mcs reflection profiles and bathymetry data acquired across a remote and poorly surveyed part of the antarctic continental margin in the bellingshausen and amundsen seas this new information has been combined with published data and used to interpret the style of sedimentation on the continental shelf slope and rise and to describe sedimentation processes which have been active in this region most seismic reflection profiles crossing the continental margin show prograded sequences beneath the outer shelf and upper slope and we infer that the stratal characteristics of these sequences indicate that grounded ice sheets reached the shelf edge during previous glacial times although there are general similarities in stratal geometry on these profiles in detail they reveal significant longitudinal variations in sediment input from the shelf to the upper slope on several profiles we found evidence of mass wasting of the continental slope in the form of slump and debris flow deposits at greater depth turbidity flows bottom currents and coriolis force have controlled the further transportation and deposition of sediment which has resulted in the development of mounds channels and sediment wave fields the distribution and variations in the size and geometry of the mounds reflect sediment input and the relative contribution of these other factors which control sedimentation on the continental rise

the formation of the late cretaceous xishan sn w deposit south china geochronological and geochemical perspectives abstract the xishan sn w deposit is spatially related to k feldspar granites in the yangchun basin western guangdong province south china la icp ms zircon u pb dating for the xishan pluton defines an emplacement age of 79 ma 78 1 0 9 ma 79 0 1 2 ma 79 3 0 8 ma consistent with the mineralization age of the xishan sn w deposit constrained by molybdenite re os isochron age 79 4 4 5 ma and la icp ms cassiterite u pb ages 78 1 0 9 ma and 79 0 1 2 ma for the cassiterite quartz vein these indicate a close genetic relationship between the granite and sn w mineralization the xishan k feldspar granites have geochemical characteristics of a type granites e g high total alkali na 2 o k 2 o 7 88 10 07 wt high ga al ratios 10000 ga al 2 6 and high zr nb ce y concentrations 350 ppm they are further classified as a 2 type granites the whole rock isotopic compositions of k feldspar granites initial 87 sr 86 sr 0 705256 0 706181 e nd t 5 4 to 4 8 and zircon e hf t values 7 8 to 2 0 suggest a mixed magma source the low zircon ce 4 ce 3 ratios 12 88 of k feldspar granites suggest low oxygen fugacities which is key for enrichment of tin in primary magmas the k feldspar granites have experienced strong differentiation as indicated by their high rb sr and k rb ratios and low nb ta and zr hf ratios which play an important role in ore forming element transportation and concentration a type granite characteristics of the xishan pluton show that it formed in an extensional environment the high f and low cl characteristics of the k feldspar granite are most probably attributed to slab rollback in the late cretaceous the xishan sn w deposit was located near the interaction of the circum pacific and the tethys tectonic realms late cretaceous sn w deposits including the xishan deposit form an ew trending belt from guangdong to yunnan province in south china this belt is in accordance with the direction of the neo tethys slab rollback in the late cretaceous in addition the ns trending extension has been recognized in the late cretaceous in south china we propose that the xishan sn w deposit should be attributed to the neo tethys slab rollback in the late cretaceous

late quaternary deep ocean circulation a review of paleoceanographic studies dealing with late quaternary deep water circulation in the oceans is presented these studies which are based on the analysis of deep sea benthic foraminiferal faunal and geochemical data and sedimentological data are discussed in light of physical oceanographic conditions in the modern ocean we include in this review a re evaluation of benthic foraminiferal data from north atlantic and southern ocean piston cores and suggest that the dominance of uvigerina during glacial intervals reflects increased amounts of organic carbon at the sea floor compared to modern values a number of geochemical studies have suggested that the production or characteristics of north atlantic deep water nadw changed during glacial times although these changes have been thought to result from a cessation of overflow water from the norwegian greenland seas it is suggested here that seasonal sea ice cover was possible over southern portions of the norwegian sea during glacial intervals the presence of seasonally open water would have allowed norwegian sea overflow water to have been produced although perhaps at lower volumes and with different hydrographic properties than at present the record of antarctic bottom water aabw circulation does not show a simple relationship with paleoclimatic oscillations indicating that changes in oceanographic conditions in the southern ocean had little effect on aabw formation the aabw record contrasts with the glacial interglacial cycles of nadw suggesting no direct link between aabw and nadw circulation a variety of data suggests that changes in pacific deep water circulation occurred as a result of glacial production of north pacific deep water or from an increased flux of southern ocean water

the potential of organic walled dinoflagellate cysts for the reconstruction of past sea surface conditions in the southern ocean abstract in this study we investigate the potential of organic walled dinoflagellate cysts dinocysts as tools for quantifying past sea surface temperatures sst in the southern ocean for this purpose a dinocyst reference dataset has been formed based on 138 surface sediment samples from different circum antarctic environments the dinocyst assemblages of these samples are composed of phototrophic gonyaulacoid and heterotrophic protoperidinioid species that provide a broad spectrum of palaeoenvironmental information the relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of canonical correspondence analysis cca among the variables tested summer sst appeared to correspond to the maximum variance represented in the dataset to establish quantitative summer sst reconstructions a modern analogue technique mat has been performed on data from three late quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the atlantic sector of the southern ocean these dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial interglacial cycles during glacial conditions the relative abundance of protoperidinioid cysts was highest whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts the mat palaeotemperature estimates show trends in summer sst changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140 000 years based on other proxies however by comparing the dinocyst results to quantitative estimates of summer ssts based on diatoms radiolarians and foraminifer derived stable isotope records it can be shown that in several core intervals the dinocyst based summer ssts appeared to be extremely high in these intervals the dinocyst record seems to be highly influenced by selective degradation leading to unusual temperature ranges and to unrealistic palaeotemperatures we used the selective degradation index kt index to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates we show that after correction the dinocyst based ssts correspond reasonably well with other palaeotemperature estimates for this region supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies

deep sea bottom currents differentiated from texture of underlying sediment abstract forty five core top samples taken in the vema channel southwest atlantic within the deduced boundaries of two important bottom currents have been analyzed for the particle size distribution of the noncarbonate silt size fraction this was done in order to characterize the sediment beneath each water mass using statistical and graphical methods it was found that sediment beneath the high velocity antarctic bottom water in the bottom of the channel exhibits the coarsest mean size poor sorting and a large percent of coarse silt left as a lag deposit sediment beneath the overlying low velocity north atlantic deep water is marked by fine mean size good sorting no coarse silt and a large percent of fine silt sediment beneath the intervening transition zone is characterized by fine t mean size moderate sorting largest percent fine silt and a small lag component of coarse silt the methods developed for delineating bottom currents in the vema channel may be applied to a wide range of benthic oceanographic settings as well as the geologic record in order to examine relative paleovelocity fluctuations of major bottom currents

decoupling of δ13cσco 2 and phosphate in recent weddell sea deep and bottom water implications for glacial southern ocean paleoceanography

notes on southern ocean hydrography sea ice and bottom water formation abstract the southern ocean circulation and sea ice distribution is briefly described the formation of extremely cold bottom water in the weddell sea and its relation to the floating ronne filchner ice shelves is discussed it is shown that a concentrated swift eroding bottom current with anomalous low 18 o ratio transports the cold and dense ice shelf water from the shelf towards large depths comments are made on possible implications of this process for the large scale deep water circulation and for the interpretation of sediment cores

age and granite association of skarn w mineralization at niutangjie district south china block abstract numerous w sn deposits are developed in the south china block with the majority related to the yanshanian jurassic to cretaceous granites a smaller number of deposits have been found associated with kwangsian middle paleozoic granites the largest of which is the niutangjie skarn w deposit the niutangjie deposit is spatially associated with two suites of granites the unmineralized yuechengling biotite and two mica granites have zircon u pb ages of 427 1 2 9 ma and 427 5 3 5 ma respectively whereas the mineralized niutangjie muscovite granite yields a younger age of 421 0 1 5 ma u pb dating of cassiterite coexisting with scheelite from the niutangjie muscovite granite indicates a mineralization age of 420 8 8 0 ma consistent with the age of the host rock the unmineralized yuechengling biotite granites have a cnk ratios of 0 97 1 16 and show characteristics of both i type and s type granites in contrast the mineralized niutangjie muscovite granites are s type granites with a cnk ratios of 1 12 1 72 and have higher sio2 contents and rb sr ratios and lower nb ta zr hf and k rb ratios than the unmineralized yuechengling biotite granites geochemical differences together with zircon hf isotopic compositions indicate that the relatively fractionated mineralized niutangjie muscovite granites were generated by partial melting of proterozoic meta sediments whereas the unmineralized yuechengling biotite granites were derived from partial melting of proterozoic meta sediments with subordinate meta igneous rocks the unmineralized yuechengling two mica granites have similar geochemical characteristics to the mineralized niutangjie muscovite granites but their relatively small volumes and lack of exploration may explain why the yuechengling two mica granites have not so far been found to be mineralized similarly the larger volume and more highly fractionated nature of the mesozoic yanshanian mineralized granites may explain the greater abundance of w sn mineralization associated with these rocks compared to the paleozoic kwangsian granites

post miocene disconformities and paleoceanography in the atlantic sector of the southern ocean abstract the magnetostratigraphy and biostratigraphy of 166 islas orcadas piston cores in the atlantic sector of the southern ocean reveal disconformities in the sedimentary record which are attributed to bottom current erosion the hiatus frequency as a function of water depth reveals both shallow erosion by circumpolar deep water cdw and deep erosion by antarctic bottom water aabw the post miocene history of erosion by both bottom currents is delineated by analysis of areal and temporal fluctuations of hiatus frequency erosion by cdw caused disconformities on the maud rise astrid ridge indian antarctic ridge scotia sea and islas orcadas rise the shallow disconformities increased in frequency and size from 4 0 to 1 0 ma with two periods of distinctly widespread disconformities from 5 5 to 4 5 ma and 2 5 to 1 5 ma after 1 0 ma the frequency and extent of the hiatuses decreased erosion by aabw caused disconformities in the weddell abyssal plain argentine basin and through a narrow conduit in the south sandwich basin downstream from the bullard fracture zone the deep disconformities increased in frequency and size from 4 5 to 5 0 ma 3 5 to 4 0 ma and from 1 0 to 2 5 ma after 1 5 ma the frequency and extent of hiatuses decreased fluctuations in hiatus frequency are consistent with results of a similar study in the southeast indian ocean and may be correlated with paleoceanographic events southern ocean cooling and possible re establishment of the west antarctic ice sheet and fringing ice shelves at 4 3 3 5 ma was accompanied by increased aabw and cdw activity the formation expansion of the northern hemisphere ice sheets at 2 5 3 0 ma resulted in a decrease in aabw velocity and was accompanied by increased cdw activity both deep and shallow bottom currents increased in velocity during the late matuyama chron 2 0 1 5 ma as a result of antarctic cooling after 1 0 ma however the frequency and extent of shallow and deep hiatuses was reduced and the modern extent of hiatuses is the lowest within the post miocene