the messinian event on the margin of the mediterranean sea in the nice area southern france abstract seismic reflection profiles have been used to map the messinian erosion surface and associated basin margin deposits on the continental margin off nice a palaeovalley extends seaward from the incised var palaeovalley mapped on land the lower part of this valley is filled by an acoustically incoherent unit with a flat top and steep slope into the basin this unit is interpreted as a coarse grained deltaic deposit that accumulated synchronously with the upper messinian evaporites in a ponded lake basin two submersible dives on strategic outcrops supported the interpretation of the seismic profiles we examined and sampled outcrops of probably early tertiary sandstones underlying the messinian erosion surface and of a fining up predominantly conglomeratic sequence that fills messinian channels on the continental slope and probably overlies the deltaic deposits these conglomerates pass up into early pliocene marls and have turbidite sedimentary structures these are prodeltaic deposits formed during the transgression at the end of the messinian based on seismic facies mapping sampling and submersible observations a palaeogeographic reconstruction of the area is proposed a basal erosion surface including the var palaeovalley represents extreme dessication of the western mediterranean and was followed by accumulation of the main messinian salt following this a lake was ponded in the ligurian basin with accumulation of evaporites and shales a gilbert type delta prograded into the basin from the var palaeovalley relative sea lake level lowering is estimated to be about 1200 m at this time there has been little faulting on the margin since the early pliocene transgression but there is estimated to have been about 800 m of flexural subsidence due to both thermal subsidence and water loading

detailed morphology of a small area on the nova scotian continental slope abstract a detailed bathymetric seismic and sidescan survey in a small area of the nova scotian continental slope reveals a complex surficial morphology on the upper slope large scale mass movements have left a steep 150 m escarpment below which a chaotic mass of debris has accumulated large coherent blocks of sediment up to 50 m thick lie within the debris resulting in the characteristically irregular relief of the upper slope in the midslope area the relief is less medium scale mass movements control the morphology resulting in a discontinuous system of hummocks and depressions with relief on the scale of tens of metres an erosive channel some 50 m deep and 1 km wide traverses the upper and middle slopes rapidly decreasing in depth and width below 800 m water depth where it crosses a broad depositional lobe the lobe is similar in profile and dimensions to the suprafan of a small submarine fan and is thought to have been deposited during an early stage in the channel development a small part of the study area shows a very smooth morphology and has been largely unaffected by mass movement processes analysis of piston cores suggests that slump and turbidity current activity ceased at the end of the wisconsinan an overall high sedimentation rate and sudden loading by turbidite deposition are likely causes of the mass movements the channel system is thought to be a young ungraded feature which is equilibrating through erosion and deposition at various points along its profile

soft sediment deformation in the shallow submarine slope off nice france as a result of a variably charged pliocene aquifer and mass wasting processes abstract along the ligurian slope near nice southeastern france a combination of natural and man made factors govern slope stability and contributed to a devastating tsunamigenic landslide near nice airport in 1979 based on a total of 72 gravity and kullenberg cores we characterise the architecture and facies of the subbottom sediment a total of six sedimentary facies types were observed three of which represent the pliocene holocene background sediment in the wider nice area while another three are associated with the 1979 landslide and tsunami the three primary facies types are soft silty clay clayey silt somewhat indurated silt sand interbeds and pliocene conglomerates underlying the former the three other facies are poorly sorted mass wasting deposits up to pebble size silt representing the finer fraction of the mobilised mass and a tsunami related bed into which plant debris and artefacts got amalgamated accompanying geotechnical results attest that significant strength variations exist when comparing measurements from the narrow shelf shelf break and shallow slope as well as the 1979 slide scar factors such as groundwater charging in the more permeable horizons further lower the effective stress and in places approach lithostatic above such permeable silt sand beds deformation of soft clay is observed suggesting that leaching of ions from the clay mineral surfaces and frayed edges also facilitates weakening and creep micro slumping and folding elevated water supply as well as hydraulic fracturing of the clayey sediment is further attested by pipes of cm diameter and several decimeters length which entrained very soupy mud in the shallowmost deposits in and landward of the slide scar we also observe remnants from the catastrophic deposition associated with the 2 3 m high tsunami wave triggered in 1979 as attested by amalgamated sea grass and artefacts based on our observations and measurements on core scale and earlier models based on in situ cptu we suggest that a significant part of the quaternary delta and slope apron deposits are prone to being mobilised without a large external trigger so that all in all a high risk for a landslide event of considerable size off nice international airport is identified

seismic evidence for a complex slide near the wreck of the titanic model of an instability corridor for non channeled gravity events abstract the continental rise southeast of the grand banks of newfoundland was surveyed many times during the last 8 years especially during the search area for the wreck of the titanic high resolution sidescan sonar images systeme acoustique remorque sar have shown an area characterised by complex surficial morphology referred to as in instability corridor new seismic reflection profiling has shown that the instability corridor is more extensive than was previously believed and that it is the expression of the distal part of a large sediment slide it consists of upslopedipping imbricated sediment blocks which are tens of metres thick and many kilometres in length downslope from the slide is an acoustically incoherent unit interpreted as comprising debris flow deposits which could represent the final phase of evolution of the slide the slide is blanketed by 5 10 m of younger sediment the upper part of this blanket has been recovered by coring and consists of foram ooze thin sandy turbidites and muddy beds with mudstone clasts radiocarbon dating and foram assemblages show that the upper metre of the core is late holocene in age with about eight resedimented beds forming in the last 4000 years these recent turbidity currents cut erosional furrows and refresh the pre existing steps of the slide three phases characterise the evolution of the instability corridor 1 the major event involving a giant slide of bedded sediments up to 100 m thick with a source probably on the steep continental slope of the grand banks 100 km to the north 2 a draping of normal continental margin terrigenous sediments and 3 erosion by one or a series of high density turbidity currents the giant slide created an instability corridor within which a number of channeled and non channeled events took place during the late holocene

oxygen and hydrogen isotope stratigraphy of the rustenburg layered suite bushveld complex constraints on crustal contamination new do values for plagioclase pyroxene and olivine and limited whole rock dd values are presented for samples from the rustenburg layered suite of the bushveld complex south africa in combination with existing data these provide a much more complete composite o isotope stratigraphy for the intrusion throughout the layered suite mineral do values indicate that the magmas from which they crystallized had do values that were about 7 1 that is 1 4 higher than expected for mantle derived magmas suggesting extensive crustal contamination more limited h isotope data suggest that the oh present within whole rocks regardless of the degree of alteration is of magmatic origin and not an alteration phenomenon there appears to be no systematic change in do value with stratigraphic height and this requires the contamination to have taken place in a staging chamber before emplacement of the magma s into the present chamber large amounts 30 40 of contamination by the lower to middle crust are needed to explain these do values which is in general agreement with previous estimates based on srand nd isotope data alternatively smaller amounts of contamination 20 by sedimentary rocks or their partial melts represented by the country rock can explain the data but it is not apparent how such material could have been present at the depth of the staging chamber in the lower to middle crust

messinian erosional and salinity crises view from the provence basin gulf of lions western mediterranean abstract though the late miocene messinian salinity crisis has been intensely researched along the circum mediterranean basins few studies have focused on the central part of the mediterranean basin and especially the pre salt deposits to improve our knowledge of the messinian events it is imperative to better understand this domain in this study we provide a more complete understanding of this central domain in the provence basin we were able to recognize a thick marine detrital series up to 1000 m derived from the messinian subaerial erosion which is partly prolongated in the distal part by b a thick unit of deep marine deposits up to 800 m prior to the evaporites c a thick presumed alternation of detritals and evaporites 1500 m below the mobile halite and d a two step transgression at the end of the messinian spatially we document the eroded shelf to the deep basin and from the western to the eastern parts of the gulf of lions and temporally we extend the interpretations from the early deposition of detritic sediments to the final sea level rise the results provide a new basis for discussion not only for the development of the messinian salinity crisis but also for the reconstruction of the subsidence history of the provence basin

magmatic metasomatism and formation of the merensky reef bushveld complex the rare earth element ree contents of pyroxenes and other minerals from the merensky reef and stratigraphically adjacent rocks of the atok section bushveld complex have been determined with the ion microprobe merensky reef clinopyroxene and orthopyroxene contain much higher and more variable concentrations of the ree than their cumulus counterparts in rocks several meters below the reef chondrite normalized merensky clinopyroxene ce contents vary from 10 to 90 for ce and from 4 to 17 for yb they also possess deep negative eu anomalies the eu anomalics being deeper for crystals having high ree contents and relatively shallow for pyroxenes with low ree contents similar compositional characteristics are displayed by cl rich apatite which is an accessory phase in the rocks interstitial pyroxene in cumulates above and below the reef also tends to have elevated ree contents and in general is not in equilibrium with coexisting cumulus minerals the melt from which the cumulus minerals crystallized falls within the compositional range of continental basalts that from which merensky and postcumulus pyroxenes crystallized is inferred to be much more highly enriched in ree than any normal tholeiitic or alkalic basalt despite their highly evolved nature in terms of the ree the merensky reef pyroxenes are not evolved in terms of major elements the decoupling of incompatible trace and major elements is best explained by a metasomatic process it is speculated that metasomatism involved upward percolation of hydrated silicate melt through and its reaction with the crystalline cumulate pile the fact that the rocks enriched in the platinum group elements are also those that show evidence for metasomatism suggests that these elements were also metasomatically redistributed

niveo aeolian sand deposition in subarctic dunes eastern coast of hudson bay quebec canada aeolian sand transport during winter and the snow free season was assessed quantitatively by direct year round field measurements along transects on the lee side of parabolic dunes in subarctic quebec in 1987 1988 niveo aeolian deposition was more important than aeolian sedimentation in three of the four study sites and contributed 75 of the total annual accumulation in exposed sites and 25 in protected forest sites the maximum depth of interstratified snow and sand deposits 3 5 m was recorded in march semi permanent snow lenses may persist longer than 2 years in the aeolian sediments after dissipation of snow 22 cm of sand as a maximum accumulated on the slipface of the most active dunes whereas only minor sand accumulation occurred in distant areas from active sand erosion wind driven sand was dispersed over 7 4 km2 in the whapmagoostui kuujjuarapik area the acumulation of snow and sand during the snow season together with spring thaw and collapse of the niveo aeolian deposit caused different types of injuries to trees especially in 1985 and 1987 when a maximum of torn branches was recorded over the last 10 year period

tectonic and sedimentary conditions necessary for the deposition of the messinian evaporite successions in the eastern mediterranean a simple 2d model abstract the existing literature shows that the only saline water source for the eastern mediterranean during the messinian was the atlantic ocean and that the sicily sill created a physical barrier between the eastern and western mediterranean higher than the physical barrier at the gibraltar sill between the western mediterranean and the atlantic ocean the presence of distinctive messinian subunits in the eastern mediterranean similar to those observed in the western mediterranean suggests the existence of a similar set of depositional processes across the entire mediterranean during the messinian salinity crisis the above statements impose two critical conditions the eastern mediterranean massive salt deposits must be older than their counterparts in the western mediterranean and the sicily gateway must have remained within a goldilocks zone during the deposition of the massive eastern mediterranean evaporites predominantly halite while the sea level in the western mediterranean would remain at the level of the sicily sill a simple 2 d model is developed which satisfies these conditions the model suggests that the eastern and western basin margins experienced a nearly synchronized gypsum deposition associated with the initial drawdown of the mediterranean level followed by re sedimentation in the deep basins of the terrigenous and early evaporite deposits as the drawdown intensified the synchroneity of evaporite deposition across the eastern and western basins broke down as the sicily gateway became largely subaerial during a period when the calabrian arc area experienced uplift associated with slab break off the sicily sill must have remained within a goldilocks zone to allow the right amount of saline water inflow into the eastern mediterranean so that evaporites massive halite could be deposited during this time the sea level in the western mediterranean was at the breach level of the sicily sill and still open to atlantic water influx thus no evaporite deposition took place there the model suggests that further restriction of the inflow occurred across the gibraltar region which became largely subaerial associated with the uplift of the gibraltar arc caused again by lithospheric slab break off similar to the sicily gateway the gibraltar gateway also remained within the goldilocks zone to allow the right amount of saline water inflow into the western mediterranean so that massive halite could be deposited the re opening of the gibraltar gateway re flooded the western mediterranean first then the eastern mediterranean allowing the deposition of a mixed evaporite siliciclastic unit followed by the transgressive sediments with distinctive brackish water lago mare fauna

a loess paleosol record of climate and glacial history over the past two glacial interglacial cycles 150 ka southern jackson hole wyoming abstract loess accumulated on a bull lake outwash terrace of marine oxygen isotope stage 6 mis 6 age in southern jackson hole wyoming the 9 m section displays eight intervals of loess deposition loess 1 to loess 8 oldest each followed by soil development our age depth model is constrained by thermoluminescence meteoric 10 be accumulation in soils and cosmogenic 10 be surface exposure ages we use particle size geochemical mineral magnetic and clay mineralogical data to interpret loess sources and pedogenesis deposition of mis 6 loess was followed by a tripartite soil thin loess complex soils 8 7 and 6 apparently reflecting the large climatic oscillations of mis 5 soil 8 mis 5e shows the strongest development loess 5 accumulated during a glacial interval 76 69 ka mis 4 followed by soil development under conditions wetter and probably colder than present deposition of thick loess 3 43 51 ka mis 3 was followed by soil development comparable with that observed in soil 1 loess 1 mis 2 accumulated during the pinedale glaciation and was followed by development of soil 1 under a semiarid climate this record of alternating loess deposition and soil development is compatible with the history of yellowstone vegetation and the glacial flour record from the sierra nevada

post glacial loess deposition in a montane environment south thompson river valley british columbia canada in the late wisconsinan the south thompson river valley british columbia was occupied by an ice dammed lake after the lake drained the exposed lacustrine silt became the source material for a holocene loess the purpose of this paper is to establish the stratigraphic depositional and geomorphic framework of loess occurring along the south thompson river valley immediately east of kamloops british columbia this montane environment of loess deposition was characterised by active slope and fluvial processes depositing sediments contemporaneously with the accumulation of loess the loess reaches an average of 4 m in thickness in the central part of the valley and thins towards the valley sides two tephras mount st helens y 3 4 ka and mount mazama 6 8 ka occur in the loess and are invaluable stratigraphic markers most of the loess was probably deposited between 8 2 ka and 3 4 ka a period coinciding with mid holocene increased summer temperatures and decreased precipitation in south central british columbia debris flows and small streams originating on the valley sides flowed out on to the loess depositing sand and gravel beds these deposits form a definite proximal distal relation across valley with the slope derived sediments decreasing and the loess increasing in thickness towards the centre of the valley the lactustrine silt particles were mobilised by diurnal mountain and valley gravity and canalised winds flowing within the south thompson valley an analysis of contemporary wind flow data was undertaken to provide a possible analogue for valley wind flows in the mid holocene

influence of orbital parameters on pleistocene loess deposition in central alaska few long proxy climatic records are available from terrestrial locations the isotope records of pleistocene climate change found in marine cores reflect worldwide ice volume and temperature changes forced by variations in the earth s orbital geometry comparable terrestrial records are rare loess wind deposited silt is perhaps the closest terrestrial analogue to marine sediments in that both result from more or less continuous deposition of fine grained sediment here we examine the hypothesis that mag netic susceptibility variations through loess sections reflect climate forcing we statistically tested cross correlations between high precision orbitally tuned marine oxygen isotope curves recording the past 250 000 yr bp and magnetic susceptibility profiles through a thick loess section in central alaska highly significant p 0 0001 correlations indicate strong thick palaeosols formed in arctic loess during early parts of interglacial periods correspond ing to isotope stages 7 and 5 thinner soils formed during interstadial events corresponding to early stage 7 and stage 3 autocorrelation and time series analysis of the loess data show spectral peaks at 125 000 41 000 and 23 000 yr bp showing for the first time that terrestrial orbital periodicities influenced and are recorded in proxy climatic data from terrestrial aeolian deposits at high latitudes

applied geomorphology and archaeological survey strategy for sites of pleistocene age an example from central alaska abstract the development of a survey strategy for archaeological sites of pleistocene age through the application of historical geomorphology is described geomorphic contexts in the northern foothills of the alaska range with potential for producing archaeological remains from the 30 000 12 000 bp interval were identified and subjected to exploratory testing contexts were selected on the basis of estimated age palaeotopographic setting and geomorphic history and included glaciofluvial outwash side valley fan alluvium loessic colluvium and primary frozen loess testing was eventually focused on formerly deflated terrace surfaces a potential source area for artifacts redeposited in the outwash or alluvium although the results of the exploratory testing were negative and archaeological sites in the region remain confined to loess deposits of the later late glacial 12 000 10 000 bp discoveries in other parts of beringia suggest that sites of earlier late glacial age 14 000 12 000 bp are also likely to be present in the foothills the application of historical geomorphology in surveys for early prehistoric sites is essential for effective use of available resources and for maximizing the significance of the results positive or negative

magnetostratigraphy and grain size record of the xijiadian fluviolacustrine sediments in east china and its implied stepwise enhancement of the westerly circulation during the eocene period in order to reveal the eocene westerlies evolution history 1053 paleomagnetic samples were collected and thermally demagnetized for the fluviolacustrine sediments at xijiadian hubei province east china fourteen normal and 14 reversed polarity zones are recognized for the section correlation of the resultant magnetic polarity column to the geomagnetic polarity time scale suggests that the section was generally continuous and spanned 56 4 37 1 ma with respect to the stable eurasian continent variations in magnetic declination of the section indicate no significant rotations supporting the earlier view that the south china block has experienced no significant rotation relative to eurasia since the late cretaceous provenance analysis suggests that the dominant fine sediments red beds of the xijiadian section were transported by wind into the study area grain size measurements indicate that the 20 m fraction and clay in the study area decreased from 56 4 to 50 7 ma and stepwise increased during 50 7 37 3 ma implying that the westerly circulation in the northern hemisphere weakened during 56 4 50 7 ma and stepwise strengthened during 50 7 37 3 ma in contrast the 20 63 m fraction mainly from nearby dust sources of the study area generally increased during 56 4 50 7 ma and stepwise decreased from 50 7 to 37 3 ma implying aridity in the study area strengthened during 56 4 50 7 ma and stepwise mitigated from 50 7 to 37 3 ma changes in global temperature during the eocene period probably played the primary role on evolutions of the westerly circulation in the northern hemisphere and of the arid conditions in the study area

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

seismic stratigraphy and structure of the east canadian continental margin between 41 and 52 n the seismic stratigraphy of the eastern grand banks continental margin is examined and a five fold division of the sedimentary sequence overlying basement is proposed oceanic basement of cretaceous age underlies the eastern part of the study area to the west continental basement ranging in age from late precambrian to jurassic underlies the grand banks the sediment units ranging in age from early cretaceous to recent have been dated by extrapolation of both commercial and dsdp drilling results from the grand banks and from the formerly conjugate iberian margin identification of oceanic magnetic anomalies in the newfoundland basin agrees with the proposed age of the two oldest early cretaceous units

hydrogen isotope composition of the merensky reef and related rocks atok section bushveld complex hydrogen isotope compositions of rocks from the bushveld complex at the atok mine have been determined to evaluate the relative importance of hydromagmatic and subsolidus hydrothermal processes for defining the geochemical characteristics of the merensky reef and adjacent rocks the rocks include mineralized pyroxenite and pegmatoid of the merensky reef as well as underlying and overlying pyroxenite norite and anorthosite cumulates from the merensky and bastard cyclic units of the upper critical zone the samples were chosen specifically because of the absence of deuteric alteration phases the water contents of all rocks including the pegmatoid are less than 0 26 wt percent and typically in the range 0 05 to 0 15 wt percent the major hydrous phase observable optically is phlogopite however there is not enough phlogopite in most samples to account for even these low water contents additional water is believed to be present either in solution in pyroxene or in submicroscopic phlogopite lamellae within pyroxene the upper critical zone rocks have relatively homogeneous hydrogen isotope compositions having delta d smow values in the range of 93 to 55 per mil there is a small but systematic difference in composition between pegmatoid and pyroxenite of the merensky reef avg delta d 65ppm and of the generally more leucocratic rocks elsewhere in the section avg delta d 79ppm within each lithology there is no relationship between isotopic composition and water content and the data cannot be rationalized in terms of simple mixing of light magmatic water with heavier meteoric crustal water the narrow range of the d h ratio of all the rocks suggests that their isotopic signatures were established under similar conditions this and the fact that different lithologies exhibit different isotopic compositions but possess the same mineralogy the rocks differ from each other mainly in modal abundances of the major phases are used to argue that their isotopic compositions could not have been imposed by subsolidus processes this contention is supported by the composition of merensky reef phlogopite the halogen contents of phlogopite do not vary with the crystal chemical factors known to influence their substitutional behavior phlogopite composition was in part controlled by its equilibration with an intergranular fluid of variable composition implying that there was no significant flow to homoginize pore fluid during subsolidus cooling in the massive rocks subsolidus circulation was therefore limited to large through going fractures the geochemical features of the merensky reef and adjacent rocks at atok were established during late stage solidification the hydrogen isotope data are consistent with a model involving addition of hydrous vapor to the merensky protoreef horizon this vapor originated from crystallization of the intercumulus melt below the reef and may also have included a small portion of water from the country rocks

mineral chemistry and stable isotope constraints on the magmatism hydrothermal alteration and related pge base metal sulphide mineralisation of the mesoarchaean baula nuasahi complex india the baula nuasahi complex on the southern flank of the singhbhum archaean nucleus in north eastern india exposes a series of mesoarchaean igneous suites these are 1 a gabbro anorthosite unit which is petrographically homogeneous although mineral chemistry data hint at a subtle eastward differentiation 2 a peridotite unit with three chromitite layers together with 3 a pyroxenite unit which display cumulate textures modal layering and for the peridotite unit differentiation trends in both mineralogy and mineral chemistry and 4 the bangur gabbro 3 1 ga which defines an oblong intrusion crosscutting the older igneous suites in the southern part of the complex with a curvilinear nw trending apophysis 2 km long and up to 40 m wide magmatic breccia comprising ultramafic and chromitite wall rock clasts in a gabbro matrix is exposed at the contact of the main bangur gabbro body and also forms the entire bangur gabbro apophysis concentrations of platinum group minerals pgms are found where the breccia contains abundant chromitite clasts and two types of platinum group element pge mineralisation are recognised type 1 pt 1 1 14 2 pd 0 1 2 1 ppm with an average pt pd 8 9 is a contact type mineralisation which occurs in the breccia at the contact between the bangur intrusion and its ultramafic host the pgms pt alloys isoferroplatinum and sulphides braggite malanite are enclosed by pyroxene and plagioclase reflecting a magmatic origin significant wall rock assimilation by the magma giving rise to the bangur gabbro is indicated by changes in pyroxene composition and by the presence of relicts of chromite from the host now altered to secondary ferritchromite in the contact zone type 2 pge mineralisation pt 0 3 1 6 pd 1 8 6 0 ppm with pt pd 0 5 3 0 is restricted to the breccia apophysis of the bangur gabbro where it occurs in the breccia matrix associated with an intense hydrothermal alteration which does not exist in the contact zone pgms pge arsenides tellurides bismuthides and antimonides and where present base metal sulphides bmss form intergrowths with hydrous silicates reflecting a hydrothermal origin oxygen isotope geothermometry documents the main stages of hydrothermal alteration within a decreasing temperature range between 700 1 000 and 500 600 c and oxygen hydrogen and sulphur isotopes show that the hydrothermal fluids were derived from the magma rather than an external source pervasive hydrothermal alteration in the breccia apophysis likely represents upward channelling of late magmatic fluids along a narrow near vertical subplanar conduit which led away from the main magma chamber we suggest that type 2 mineralisation was produced by late magmatic hydrothermal remobilisation and reconcentration of type 1 pge mineralisation and that the composition of the hydrothermal fluids controlled whether bmss were enriched along with the pgms

le canyon du var case study of a modern active proximal channel the var canyon and the continental slope along the french riviera were investigated using sar a new deeply towed high resolution side scan sonar and 3 5 khz subbottom profiler package later on a ground truth operation using the cyana submersible and kuellenberg cores provided in situ observations and samples the main characteristics of this area are the narrow shelf the steep continental slope and very coarse superficial materials during the pliocene an alluvial cone was built on the floor of a deep ria located at the present var alluvial plain this detritic cone overlies the messinian erosion surface it is totally submarine and formed by pudding stones conglomerates and marls since the early quaternary this large sedimentary body has been dismantled by gravity processes mass wasting debris flows turbidites the bed form at the head of the var valley 500 m depth is marked by an anastomosed network eroding the spurs that give the typical herringbone facies of the canyon s flanks downslope from this area begins a gravel wave field extending to a water depth of 2 100 m wavelength and height appear to be directly controlled by the topography downward and according to a break in the slope the sea floor is characterized by amore rhythmic alternance of gravel fields and mud fields to 2 400 m the muddy areas are always located on relatively high points of the sea bottom the significance of these bed forms will be discussed and related to the sedimentary processes which may have operated in this area less

discussion of geochemical evidence for the origin of late quaternary loess in central alaska in a recent paper muhs and budahn 2006 aim to test regional paleowind hypotheses put forth in the literature for the provenance of quaternary loess deposits in central alaska with geochemical evidence the experimental design of their study consists of a comparison and multilinear regression analysis mra of major element and rare earth element ree geochemistry between possible source sediment material along the yukon tanana and nenana rivers and the youngest loess units of three deposits near fairbanks alaska see their fig 2 such a study has been long overdue and we applaud their initiative however through this discussion letter we wish to address two points the first concerns the opposing hypotheses to be tested while the second concerns aspects of their experimental design muhs and budahn 2006 pp 324 325 set out to test the opposing hypotheses of northerly versus southerly paleowinds for the origin of quaternary loess in central alaska literature accounts of paleowind reconstructions are either based on sand dune orientations and sand sheet locations or loess deposits for both types of archives sand and loess the inferred paleowinds are presented by the authors as inconsistent and contradictory we argue that the platform on which this paper is set up i e north versus south is built from a misinterpretation and inaccurate representations of previous work referenced as supporting evidence furthermore temporal variability an important issue appears to be cast aside concerning aeolian sand deposits in the inner parts of central alaska hopkins 1982 and lea and waythomas 1990 conclude winds came from a northeasterly direction during the last glacial maximum muhs and budahn 2006 hypothesize p 324 from the occurrence of aeolian sands of early holocene age north of9the yukon river near the confluence of the porcupine river see froese et al 2005 and their fig 1 for location that winds must

salt tectonics and crustal tectonics along the eastern sardinian margin western tyrrhenian new insights from the metyss 1 cruise abstract the tyrrhenian sea is usually interpreted to be a neogene back arc basin that opened by continental rifting and oceanic spreading caused by the eastward migration of the apennine subduction system during miocene and pliocene times rifting of the southern tyrrhenian sea started first along the eastern sardinian margin during the middle to late miocene times including the messinian the metyss project aims at better constraining the relationships between crustal tectonics salt tectonics and sedimentation from messinian times to present day the metyss 1 cruise 2009 allowed to acquire about 1200 km of hr seismic reflection profiles along the eastern sardinian margin western tyrrhenian sea this data set clearly illustrates that this area has been highly dissected during the rifting stage by n s trending normal faults delineating ridges and basins as previously described the messinian seismic markers uu and mu locally display fan shaped stratal geometries but the mechanism responsible for such geometries salt tectonics or rifting has yet to be carefully deciphered we also mapped the spatial distribution of the mobile salt the highly variable thickness of the small confined salt basins may be related to the initial pre messinian basin geometry to the fact that salt deposition was syn rift or to salt movement southeastward salt tectonics is vigorous in unconfined basins and appears to have started early during the uu deposition more surprisingly our data demonstrate that some of the major faults have been significantly reactivated during the post rift period up to late quaternary time as shown by bathymetric scarps and associated debris flows moreover some of this post rift deformation can be evidenced within the plio quaternary sequence by a regional unconformity the post miocene deformation style varies greatly between different areas of the margin and can also be strongly influenced by the presence or absence of mobile messinian salt

the halogen geochemistry of the bushveld complex republic of south africa implications for chalcophile element distribution in the lower and critical zones solidification of the interstitial liquid the stratigraphic distribution halogen bearing minerals especially apatite are minor but ubiof s cu and the pge in the critical zone cannot readily be quitous phases throughout the bushveld complex interstitial apatite explained either by precipitation of sulfide as a cotectic phase or as is near end member chlorapatite below the merensky reef lower a function of trapped liquid abundance evidence from potholes and and critical zones and has increasingly fluorian compositions with the pge rich driekop pipe of the bushveld complex imply that increasing structural height above the reef main and upper zones migrating cl rich fluids mobilized the base and precious metal cl f variations in biotite are more limited owing to crystal chemical sulfides we suggest that the distribution of sulfide minerals and controls on halogen substitution but are also consistent with a the chalcophile elements in the lower and critical zones reflects a decrease in the cl f ratio with structural height in the complex general process of vapor refining and chromatographic separation of a detailed section of the upper lower zone to the critical zone is these elements during the evolution and migration of a metalliferous characterized by an upward decrease in sulfide mode from 0 01 cl rich fluid phase 0 1 to trace 0 001 cu tends to correlate with other incompatible elements in most samples whereas the platinum group elements pge can behave independently particularly in the critical zone the decrease in the cl f ratio of apatite in the

origin of phlogopite orthopyroxene inclusions in chromites from the merensky reef of the bushveld complex south africa about 30 of the chromite grains of variable sizes in a chromitite seam at the base of the merensky reef of the bushveld complex on the farm vlakfontein contain abundant composite mineral inclusions the inclusions are polygonal to circular with radial cracks that protrude into the enclosing chromite they vary from a few microns to several millimeters in diameter and are concentrated in the cores and mantles of chromite crystals electron backscattered patterns indicate that the host chromites are single crystals and not amalgamations of multiple grains na phlogopite and orthopyroxene are most abundant in the inclusions edenitic hornblende k phlogopite oligoclase and quartz are less abundant cl rich apatite rutile zircon and chalcopyrite are present at trace levels na phlogopite is unique to the inclusions it has not been found elsewhere in the bushveld complex other minerals in the inclusions are also present in the matrix of the chromitite seam but their compositions are different the mg mg fe2 ratios of orthopyroxene in the inclusions are slightly higher than those of orthopyroxene in the matrix k phlogopite in the inclusions contains more na than in the matrix the average compositions of the inclusions are characterized by high mgo 26 wt na2o 2 4 wt and h2o 2 6 wt and low cao 1 1 wt and feo 4 4 wt the 18o value of the trapped melt estimated by analysis of inclusion rich and inclusion poor chromites is 7 this value is consistent with the previous estimates for the bushveld magma and with the 18o values of silicate minerals throughout the reef the textural features and peculiar chemical compositions are consistent with entrapment of orthopyroxene with variable amounts of volatile rich melts during chromite crystallization the volatile rich melts are thought to have resulted from variable degrees of mixing between the magma on the floor of the chamber and na k rich fluids expelled from the underlying crystal pile the addition of fluid to the magma is thought to have caused dissolution of orthpyroxene leaving the system saturated only in chromite both oxygen and hydrogen isotopic values are consistent with the involvement of a magmatic fluid in the process of fluid addition and orthopyroxene dissolution most of the cr and al in the inclusions was contributed through wall dissolution of the host chromite dissolution of minor rutile trapped along with orthopyroxene provided most of the ti in the inclusions the na and k rich hydrous silicate minerals in the inclusions were formed during cooling by reaction between pyroxene and the trapped volatile rich melts

latest pleistocene increase in wind intensity recorded in eolian sediments from central alaska abstract a brief increase in wind intensity between ca 11 100 and 10 700 yr b p is recorded by a sharp increase in sediment grain size at eolian sections along the nenana river in central alaska this occurred at the same time as the younger dryas climatic reversal in northern europe and an increase in the vigor of atmospheric circulation recorded by greenland ice cores climatic fluctuations in high latitude areas during younger dryas time may reflect variations in the co2 content of the atmosphere

the late messinian salinity crisis and late miocene tectonism interaction and consequences on the physiography and post rift evolution of the gulf of lions margin the interpretation of rhone maritime seismic profiles and the accurate mapping of all the structural features affecting the miocene cover made it possible for us to develop herein a new structural model for the top of the eroded miocene of the gulf of lions platform late miocene extensional faults exerted a considerable structural control on the messinian erosion in particular mapping of transfer zones has shown that these structures controlled retrogressive erosion of the platform this late miocene extension could have been caused by gravity driven destabilization of the platform associated with base level lowering at the onset of the messinian salinity crisis

did the giant broken hill australia zn pb ag deposit melt abstract recent published research has proposed that some metamorphosed massive sulfide deposits including the broken hill deposit australia have partially melted here we discuss the evidence for and against this process the broken hill deposit is located in the curnamona craton within a rift in an apparent upward coarsening sequence of clastic metasediments into which paleoproterozoic mafic and felsic melts intruded the deposit was metamorphosed to granulite facies conditions 750 800 c and 5 6 kbar and was subjected to at least five periods of deformation at peak p t conditions a melt phase was produced in silicate rocks especially granitoids and psammopelites and in ore characterized by the systems cu as s ag pb s ag sb as s cu sb pb s sb as s cu sb s and fe as s however the proportion of minerals in these s bearing systems is insignificant 2 feo mno cao al 2 o 3 p 2 o 5 co 2 zns pbs fes feass feas 2 which is the most relevant system to broken hill ores p t conditions were never high enough to produce a melt phase in this system authors arguing for sulfide rock melting suggest that mn rich lithologies garnetite and quartz garnetite which are intimately associated with the pb rich ores at the broken hill deposit were produced by a reaction between mn rich sphalerite and aluminous wall rocks however to produce such rocks would require mn contents of sphalerite compositions that are unrealistically high and yet to be found in nature moreover the implication of the melt model is that wherever mn rich quartz garnetite and garnetite are found sphalerite should be located next to them this is clearly not the case the presence of polyphase sulfide inclusions within garnet in garnetite has also been considered by some in the literature to be sulfide melt inclusions with the implication that the enclosing garnet was a product of melting however we consider these sulfides to be products of hydrothermal processes during retrograde metamorphism it is impossible to form garnetite and quartz garnetite in rocks within the curnamona craton that formed at upper greenschist lower amphibolite facies conditions by partial melting p t conditions were too low we consider that the fe and mn component of garnetite and quartz garnetite are products of exhalation and inhalation at or near the sea floor and that these rocks are meta exhalites or meta inhalites some garnet rich rocks also formed by metasomatic processes throughout the protracted metamorphic history that affected the curnamona craton

the merensky reef at winnaarshoek eastern bushveld complex a primary magmatic hypothesis based on a wide reef facies the merensky reef on the winnaarshoek property in the central sector of the eastern limb of the bushveld complex belongs to what may be described as a wide reef facies in which platinum group element pge mineralization is largely contained within a relatively thick succession of medium grained nonpegmatoidal feldspathic orthopyroxenite bounded top and bottom by thin chromite stringers the wide reef merensky reef facies at winnaarshoek presents the opportunity to study subtle processes which could potentially be obscured or obliterated in the thinner reef facies found in many areas of the western limb especially in places where the reef zone contains a component of pegmatoidal orthopyroxenite at winnaarshoek a pegmatoidal feldspathic orthopyroxenite is developed below the lower chromite stringer and a second pegmatoidal orthopyroxenite is intermittently developed several centimeters above the upper chromite stringer in contrast to most occurrences in the western limb however both these pegmatoidal orthopyroxenites are only sporadically mineralized if at all in addition rather than being at the base of a feldspathic orthopyroxenite unit as is the case throughout most of the western limb the merensky reef at winnaarshoek occurs toward the top of a sequence of feldspathic orthopyroxenite despite the gross relative uniformity of the merensky reef on a property wide scale at winnaarshoek we demonstrate using underground channel samples that individual intersections spaced a matter of meters apart commonly display remarkable variations in grade distribution our study is based primarily on whole rock and mineral chemical profiles from drill cores through three separate and distinctive subfacies of essentially normal i e nonpothole reef one of the drill core intersections represents typical reef in which pge mineralization forms an upper reef extending from the upper chromitite stringer approximately 1 m into the underlying feldspathic pyroxenite and a much thinner lower reef centered on the lower chromitite stringer the other two drill core intersections represent extremes in terms of the vertical distribution of the pge one having mineralization confined to the immediate vicinity of the two chromitite stringers while the other is richly mineralized throughout the reef zone peaks in pge concentrations in all three intersections are coincident with the most primitive compositions of orthopyroxene plagioclase and chromite the dominant rock forming minerals whereas the cumulate layers below major pge peaks are the most evolved as indicated by mineral compositions and elevated whole rock incompatible element concentrations furthermore the lowest grade merensky reef intersection has the most chemically evolved footwall whereas the richest intersection has a relatively primitive footwall we consider the origin of the merensky reef in the context of its position as the culmination of a sequence of several pge mineralized chromite bearing layers in the upper critical zone and suggest that the regular upward variations in the chemistry of the chromitite from one layer to the next and the overall cyclicity are indicative of complex magma replenishment and mixing processes in the chamber we apply a model of lateral streaming of magma with chromite crystallization and consequent sulfide and platinum group mineral pgm precipitation resulting from magma mixing specifically the merensky reef cannot be properly interpreted outside the context of the sequence of successive events that evolved throughout the development of the upper critical zone genetic models also need to account for lateral facies variations in the reef

on the evolution of rifted continental margins comparison of models and observations for the nova scotian margin summary a model for the formation and evolution of rifted continental margins based on lithospheric extension during rifting and its thermal and mechanical consequences is proposed model predictions are then compared with geological and geophysical observations from a transect of the 185 ma old rifted margin off nova scotia through the scotian basin three kinematic models of the rifting process are discussed these are 1 the uniform extension model in which the amount of extension is uniform with depth but varies with position across the margin 2 the uniform extension and melt segregation model which has similar properties but also provides an explanation for the properties of the extended continental crust and its transition to oceanic crust by postulating that basaltic melt segregates from the asthenosphere and migrates to the crust and 3 the depth dependent extension model in which the first order consequences of rapidly changing rheological properties with depth in the lithosphere are included by decoupling the lithosphere into two zones with depth each of which undergoes differing amounts of extension these rift models predict the form of crustal and lithospheric thinning subsidence and temperature change once the amount of extension has been determined this is estimated from seismic measurements of present crustal thickness on the assumption that the crust had a uniform thickness equal to that currently measured in the adjacent continental region before rifting occurred rifting is also considered to occur instantaneously a time stepping thermo mechanical model is used to predict the cooling of rifted margin additional thermal contraction subsidence and its amplification by water and sediment loading thermal aspects are calculated using a finite difference model of time dependent conductive heat transport whereas regional isostatic response to loading is calculated by a finite element model the models are coupled because the temperature distribution is used to define a rheological lithosphere an elastic region with thickness that varies in time and space as the model evolves for flexural calculations in the mechanical model secondary coupling occurs through perturbations to the temperature field by sedimentary thermal blanketing and advection of heat during isostatic adjustment the model predictions of 1 sedimentary basin stratigraphy 2 moho position 3 free air gravity anomaly 4 age depth relations for deep exploratory wells and 5 subsidence and temperature histories agree well with observations from the scotian basin additional effects due to sedimentary and crustal radiogenic heat production lateral heat transport and the possible existence of a near surface brittle listric faulted region created during rifting are also considered it is concluded that a model in which rifting occurred by depth dependent extension and which includes a finite thickness for the rheological lithosphere radiogenic heat production in the sediments and crust and a brittle listric faulted crustal layer affords an accurate description of the first order processes that occur during rifting and evolution of this margin

150 000 years of loess accumulation in central alaska abstract the halfway house site in interior alaska is arguably the most studied loess deposit in northwestern north america the site contains a complex paleomagnetic and paleoenvironmental record but has lacked the robust chronologic control that would allow its full potential to be exploited detailed reexamination of stratigraphy paleomagnetics and tephrostratigraphy reveals a relatively complete marine isotope stage mis 6 to holocene record constrained by the old crow 124 10 ka vt 106 10 ka sheep creek klondike ca 80 ka dominion creek 77 8 ka and dawson ca 30 2 cal ka bp tephras we show two well developed paleosols formed during marine isotope stages mis 5e and 5a while mis 5c and 5b are either poorly represented or absent the new tephrostratigraphy presented here is the most complete one to date for the late pleistocene and indicates mis 5 sediments are more common than previously recognized a magnetic excursion within the sediments is identified as the post blake excursion 94 1 7 8 ka providing independent age control and adding to the increasing body of evidence that alaskan loess is a detailed recorder of variations of the earth s magnetic field over time a high resolution magnetic susceptibility profile placed into this new chronostratigraphic framework supports the hypothesis that wind intensity is the main variable controlling fluctuations in susceptibility correlation of the susceptibility record to global marine 18o records is complicated by highly variable accumulation rates we find the lowest rates of accumulation during peak warm and cold stages while abrupt increases are associated with periods of transition between marine isotope sub stages building on previous accumulation models for alaska surface roughness is likely a leading variable controlling loess accumulation rates during transitions and peak cold periods but the negligible accumulation during mis 5e and 5a suggests that loess production was exceedingly low negating the role of surface roughness this interplay of variables leads to optimal conditions for loess accumulation during transitions between isotope stages and to a somewhat lesser extent stadials and interstadials

sedimentary mechanisms and underlying tectonic structures of the northwestern mediterranean margin as revealed by comprehensive bathymetric and seismic surveys abstract the tectonic structures lithological contrasts and sedimentary processes of the northwestern mediterranean margin are revealed by a comprehensive survey including recently acquired seabeam and seismic profiling data mass wasting by gravity flow processes occurs over this entire area gravity slides are concentrated on the thick plio quaternary formations located in the interchannel areas they can lead to surprisingly steep walls and contribute to the widening of the canyons the contrasts between these superficial formations and the underlying neogene formations are morphologically well expressed the slide products sometimes directly observed as voluminous erratic blocks can seal the deep sea channels and cause their migrations areal extent of these slides can be very large especially with respect to the small size of the basin however the turbidity currents are the main gravity flow processes leading to the construction during the quaternary glacial epochs of the rhone deep sea fan and other sedimentary ridges they are responsible for the formation of particular bedforms such as circular depressions into the valley floors or sediment waves on the interchannel areas the wide extent of the gravity flow processes can be explained by the particular geological setting of this margin which is a mountainous borderland with steep slopes and rapid deposition of undercompacted sediments the general instability is favored by recent tectonic movements linked with the alpine setting and especially in the deepest areas by the lubricating effects of the underlying messinian salt layer under the loading effect of the sedimentary cover this salt layer crops out around the rhone deep sea fan as a peripheral belt of diapirs having shapes controlled by deep tectonic structures

the messinian salinity crisis past and future of a great challenge for marine sciences forty years after the image of the mediterranean transformed into a giant salty lake was first conceived the fascinating history of the messinian salinity crisis msc still arouses great interest across a large and diverse scientific community early outcrop studies which identified severe palaeoenvironmental changes affecting the circum mediterranean at the end of the miocene were followed by investigations of the marine geology during the 1950s to 1970s these were fundamental to understanding the true scale and importance of the messinian event now after a long period of debate over several entrenched but largely untested hypotheses a unifying stratigraphic framework of msc events has been constructed this scenario is derived mainly from onshore data and observations but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep mediterranean basins the msc was an ecological crisis induced by a powerful combination of geodynamic and climatic drivers which had a great impact on the subsequent geological history of the mediterranean area and on the salinity of the global oceans these changed the mediterranean s connections with both the atlantic ocean and the freshwater paratethyan basins causing high amplitude fluctuations in the hydrology of the mediterranean the msc developed in three main stages each of them characterized by different palaeoenvironmental conditions during the first stage evaporites precipitated in shallow sub basins the msc peaked in the second stage when evaporite precipitation shifted to the deepest depocentres and the third stage was characterized by large scale environmental fluctuations in a mediterranean transformed into a brackish water lake the very high resolution timescale available for some late miocene intervals in the mediterranean makes it possible to consider environmental variability on extremely short time scales including in some places annual changes despite this fundamental questions remain some of which could be answered through new cores from the deepest mediterranean basins improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal messinian succession for the first time the resulting data would allow us to decipher the causes of this extreme environmental change and its global scale consequences

transport of late pleistocene loess particles by katabatic winds during the lowstands of the english channel studies of the submerged pleistocene conglomerate cored and dredged in the english channel show that it resulted from the cementation of stony beaches under a loess blanket although the loess cover was later washed out by younger transgressions the northern limit of the conglomerate corresponds to the original offshore extension of the loess deposits compilation of offshore and onshore altitudes of the limits of these deposits shows that loess was deposited by low level wind fields never thicker than 200 m mapping surveys show that the present limits of loess are probably close to their original boundaries the past proximity of the british ice sheet the accumulation of dusty sediments coating north facing cliffs of brittany originating in the outwash of the british irish ice sheet and in the palaeo rivers of the english channel as well as the southeastward orientation of the palaeo winds deduced from particle size analysis and heavy minerals distribution suggest that large volumes of loess were transported by strong katabatic winds blowing from the northern ice covered regions towards brittany and normandy the existence of katabatic winds is also consistent with the drift of ice rafts that transported icelandic basalts now grounded in brittany and possibly with the orientation of homo neandertalensis shelters

sediment slides and turbidity currents on the laurentian fan sidescan sonar investigations near the epicenter of the 1929 grand banks earthquake the epicenter area of the 1929 grand banks earthquake on the continental slope south of newfoundland has been investigated using sea marc i a deeply towed midrange sidescan sonar with a 4 5 khz subbottom profiler shallow slides pass downslope into debris flows on the muddy continental slope east of the epicenter at the head of the eastern valley of the laurentian fan west of the epicenter arcuate slide scars cut undisturbed upper slope sediment and lead downslope to a lineated erosional seabed at a water depth of about 1600 m this erosional seabed passes into extensive fields of 100 m wavelength gravel waves situated on the broad irregular valley floor the gravel waves become better developed downslope and extend at least to water depths of 3000 m all these morphological features appear fresh on the sidescan sonograms suggesting that they date from the 1929 earthquake event and the distribution of slides corresponds to the area of instantaneous cable breaks in 1929 the upper limit of erosion on valley walls suggests that the 1929 turbidity current was less than 300 m thick timing of cable breaks downfan suggests that flow velocities were sufficient to rework gravel deposits into large bedforms during waning flow stages over elevated areas of the valley floor similar cross bedded coarse sands and gravels are common in ancient channel deposits

the rosa keystone dunes field the geoarchaeology and paleoecology of a late quaternary stabilized dune field in eastern beringia stabilized sand sheets and dunes hold a remarkable amount of information on paleoenvironmental conditions under which late quaternary landscapes evolved in northern subarctic regions we provide the results of a project focused on understanding the development of lowland environments and ecosystems including dunes and sand sheets which were critical habitat for early human occupations in subarctic regions our study area is the rosa keystone dunes field in the shaw creek flats of the middle tanana river basin interior alaska one of the oldest continuously occupied areas in north america 14 000 cal bp to present the disturbance regimes of reactivated dunes and associated forest fire cycles between 12 500 and 8800 cal bp fostered a unique early to mid successional mixed vegetation community including herbaceous tundra shrubs and deciduous trees this environment provided key habitats for large grazers and browsers significant resources for early hunter gatherer populations in central alaska aft

origin of last glacial loess in the western yukon tanana upland central alaska usa loess is widespread over alaska and its accumulation has traditionally been associated with glacial periods surprisingly loess deposits securely dated to the last glacial period are rare in alaska and paleowind reconstructions for this time period are limited to inferences from dune orientations we report a rare occurrence of loess deposits dating to the last glacial period 19 ka to 12 ka in the yukon tanana upland loess in this area is very coarse grained abundant coarse silt with decreases in particle size moving south of the yukon river implying that the drainage basin of this river was the main source geochemical data show however that the tanana river valley to the south is also a likely distal source the occurrence of last glacial loess with sources to both the south and north is explained by both regional synoptic scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the brooks range to the north and the alaska range to the south based on a comparison with recent climate modeling for the last glacial period seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources

holocene development of parabolic dunes in the central st lawrence lowland quebec abstract stabilized parabolic dunes in the central st lawrence lowland are oriented ne sw in the postulated direction of dune building winds coming from anticyclonic air circulation induced by the retreating laurentide ice sheet about 10 000 yr ago the eolian chronology reconstructed from several sections in mixed dune peatland environments indicates that postglacial plant colonization characterized by a fortuitous assemblage of arctic subarctic and boreal elements preceded dune formation during champlain sea regression around 10 000 yr b p confined peatlands and small forests were buried by eolian sands between 10 000 and 7500 yr b p under dry and temperate conditions this eolian episode lasted about 2500 14 c yr and ended when cyclonic air circulation similar to the present humid climatic regime was established following the breakup and disappearance of the laurentide ice sheet over hudson bay and peripheral areas dune stabilization through paludification of well drained eolian sands about 7500 yr b p suggests a major shift in climate toward wetter conditions that have been characteristic during most of the holocene in eastern north america minor eolian erosion induced by wildfire was recorded during late holocene time about 1250 yr b p anthropogenic perturbation logging and agriculture practice was also responsible for recent very local eolian activity

late quaternary slumps and debris flows on the scotian slope the scotian slope just west of verrill canyon was surveyed using the sea marc i deep towed sidescan sonar system high resolution seismic reflection profiles and 25 piston cores the generally smooth continental slope has a gradient of 2 5 it is crossed by 2 small valleys that are 1 km wide and 100 m deep much of the sea bed shows evidence of surficial sliding that removed 10 20 m of sediment and the slide scars give the sea bed a steplike morphology from the 600 m isobath to 1 800 m there extend 2 zones of disturbed sediment these disturbed zones have the rough surface and transparent acoustic character previously regarded as characteristic of debris flows but sidescan sonar images and cores suggest that they are principally rotational slide deposits with true debris flows at their distal limits streamlined erosional depressions near the downslope edge of the debris flows cut both the flow and sediment farther down slope these may have been produced by a turbidity current associated with the debris flows sorted coarse sand in piston cores provides further evidence of current activity this widespread sediment failure on relatively low slopes was probably the result of a large earthquake that can be dated from cores as occurring between 5000 and 12000 yr b p

morphology and microstructure of chromite crystals in chromitites from the merensky reef bushveld complex south africa the merensky reef of the bushveld complex consists of two chromitite layers separated by coarse grained melanorite microstructural analysis of the chromitite layers using electron backscatter diffraction analysis ebsd high resolution x ray microtomography and crystal size distribution analyses distinguished two populations of chromite crystals fine grained idiomorphic and large silicate inclusion bearing crystals the lower chromitite layer contains both populations whereas the upper contains only fine idiomorphic grains most of the inclusion bearing chromites have characteristic amoeboidal shapes that have been previously explained as products of sintering of pre existing smaller idiomorphic crystals two possible mechanisms have been proposed for sintering of chromite crystals 1 amalgamation of a cluster of grains with the same original crystallographic orientation and 2 sintering of randomly orientated crystals followed by annealing into a single grain the ebsd data show no evidence for clusters of similarly oriented grains among the idiomorphic population nor for earlier presence of idiomorphic subgrains spatially related to inclusions and therefore are evidence against both of the proposed sintering mechanisms electron backscatter diffraction analysis maps show deformation related misorientations and curved subgrain boundaries within the large amoeboidal crystals and absence of such features in the fine grained population microstructures observed in the lower chromitite layer are interpreted as the result of deformation during compaction of the orthocumulate layers and constitute evidence for the formation of the amoeboid morphologies at an early stage of consolidation an alternative model is proposed whereby silicate inclusions are incorporated during maturation and recrystallisation of initially dendritic chromite crystals formed as a result of supercooling during emplacement of the lower chromite layer against cooler anorthosite during the magma influx that formed the merensky reef the upper chromite layer formed from a subsequent magma influx and hence lacked a mechanism to form dendritic chromite this accounts for the difference between the two layers

late neogene evolution of the western south aegean volcanic arc sedimentary imprint of volcanicity around milos abstract the distribution and stratigraphy of volcanic rocks around the island of milos has been interpreted from seismic reflection profiles a consistent seismic stratigraphy can be recognised in the major basins which contain mostly hemipelagic to low energy gravitative sedimentation interrupted only locally by mass transport deposits despite the proximity to volcanic islands volcanic rocks have a distinctive rather incoherent acoustic signature and in places overlie stratified marine sediment their age is inferred from position relative to the messinian seismic marker and by correlation with volcanic episodes dated on land volcanic rocks underlie an area five times larger than the present outcrops of volcanic rocks on milos and adjacent islands the main phase of volcanism was of late pliocene age it locally overlies folded lower pliocene strata in places the volcanic rocks have been planed off by quaternary coastal erosion surfaces and have subsequently subsided at rates of 0 2 0 35 mm yr basin margins appear to have been generally stable probably as a consequence of the relatively shallow water depths volcano flank failure deposits do not appear to be a major component of the sedimentary architecture

reply to the discussion by f lagroix and s k banerjee of geochemical evidence for the origin of late quaternary loess in central alaska we thank f lagroix and s k banerjee 2006 for their interest in our recent paper and welcome this opportunity to clarify our thoughts on the issues they raise lagroix and banerjee 2006 state that we have misinterpreted past work on paleowinds of alaska and furthermore that considerations of temporal variability have been cast aside we believe that lagroix and banerjee 2006 have misinterpreted our statements about last glacial paleowinds versus early holocene winds in the yukon river valley we stated that hopkins 1982 and lea and waythomas 1990 presented a picture of northeasterly winds to explain eolian sand distribution over much of alaska during the last glacial period we then cited the yukon river example of froese et al 2005 holocene eolian sands on the north side of the river as an example of how paleowinds may have changed at the end of the last glacial period we stated the following muhs and budahn 2006 p 324 if the ages are maximum limiting estimates and if the sands were locally derived these deposits imply sand transporting winds from the south by the start of the holocene italics added for emphasis this statement coming after our summary of northeasterly paleowinds from hopkins 1982 and lea and waythomas 1990 was intended to show not a contradiction but a shift in winds from glacial to interglacial time furthermore we do not disagree with lagroix and banerjee 2006 that the deposits studied by froese et al 2005 could have come from the north derived from the porcupine river we qualified our statement about both the age and the source of the sands with the word if which emphasizes the uncertainty we had at that time and still have today until provenance studies are conducted the source or sources of eolian sand along the yukon river are purely speculative

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

erosional processes and paleo environmental changes in the western gulf of lions sw france during the messinian salinity crisis abstract current interpretation of the messinian salinity crisis msc involves partial desiccation of the mediterranean sea coupled with the deposition of thick evaporites in the deep basins new sets of seismic reflection profiles in the western part of the gulf of lions confirm the basinward extension of the messinian erosion and enable the mapping of distinctive seismic markers indicating the messinian erosional surface or messinian unconformity the basin margin detrital deposits and the deep evaporite sequence the geometrical relationship between these three elements and their relationship to the paleogeography of the margin during the msc provide new information about the evolution of the study area during the messinian the messinian erosional surface mes commonly correlated with the desiccation phase and the deposition of deep evaporites during the apogee of the event is generally interpreted as a subaerial feature in the gulf of lions it is a complex diachronic polygenic erosional surface observed at the base of the prograding plio quaternary sequence beneath the shelf and slope it extends downslope beneath the deep basin upper evaporites and the salt and possibly correlates conformably with the base of the so called deep lower evaporites the whole morphology of the mes reflects a buried drainage pattern supporting the interpretation of fluvial erosion driven by a substantial drop in sea level our results also suggest that large submarine gravity flows occurred prior to any significant accumulation of salt in the basin and prior to the upper evaporites consequently interbedded clastic deposits may partly account for the parallel reflectors of the lower evaporites since river erosion persisted throughout the msc the salt and upper evaporite units may also contain a large amount of detrital sediments the good quality of the new seismic data clearly reveals fan shaped messinian deposits in the downstream part of the main messinian valleys i e the nile var and spanish rivers the depositional scenarios generally involve a substantial sea level fall coupled with deltaic prodeltaic accumulations a chaotic seismic unit unit d filling messinian lows and extending beneath the salt within the study area is interpreted as a messinian clastic unit we propose a polyphase scenario of detrital fan deposition involving pre syn and post salt deposition in subaqueous subaerial environments in the gulf of lions a late miocene tectonic phase that affected the western shelf also played an important role in controlling a the pattern of the messinian fluvial network b the location of maximum erosion on the shelf and c the location of the detrital fan depocentre downslope

the munson nygren slide a major lower slope slide off georges bank the munson nygren slide is a large compound slide located between munson and nygren canyons below 1900 m depth on the continental slope off georges bank its structural and morphological features are recognized in high resolution seismic reflection profiles the slide comprises an axial trough which has a relief as great as 325 m and a width of 6 10 km the trough is flanked by displaced and disrupted strata for a total lateral extent of approximately 20 km and a downslope extent of at least 35 km the slide is unrelated genetically to the adjacent canyons and may postdate munson canyon there is evidence of plastic deformation at the base of the section subjected to sliding certain features of the slide complex resemble those seen in landforms on the laurentian rise and attributed by emery et al to the 1929 grand banks earthquake the munson nygren slide may have been triggered by a large earthquake in late pleistocene time or later destructional landforms associated with the slide are similar to those widely present along the lower slope off georges bank

generation and migration of coarse grained sediment waves in turbidity current channels and channel lobe transition zones large scale sediment waves composed of gravels and sands have been studied using deep water sidescan systems new data are presented from submarine channels off the canary islands and from canyon mouths off portugal data from other areas are briefly reviewed including a re interpretation of data from laurentian fan in order to summarise the varied morphology and setting of these bedforms coarse grained sediment waves are found in the proximal dominantly bypassing areas of deep water turbidite systems within canyons channels and channel lobe transition zones wave heights are in the region of 1 10 m and wavelengths are up to several hundred metres the distribution of waves and sparse sedimentological evidence from modern and ancient sediment wave fields suggests that initial transport and deposition of coarse sediment occurs within a high density turbidity current and not as a non newtonian debris flow in some cases the development of pronounced wave asymmetry and evidence of wave disruption and reworking suggests that the wave morphology is at least partially controlled by a later phase of low density turbidity flow grain size also appears to exert some control on wave morphology for example gravel rich waves have a greater height for the same wavelength than sand rich waves coarse grained sediment waves are often difficult to recognise on the seafloor because of reworking or burial by younger turbidity currents and are equally difficult to recognise in outcrop because of their large size

eolian deflation by ancient katabatic winds a late quaternary example from the north alaska range strong katabatic winds are frequently generated in glaciated mountain valleys of the alaska range by downglacier gravitational flow of chilled air stronger katabatic winds probably occurred during late quaternary time when glaciers were more extensive and such winds may have greatly influenced eolian sedimentation in nenana river valley and in most of adjacent teklanika river valley the entire 1 to 2 m thick eolian cap is postglacial in age and the beginning of loess deposition coincides almost exactly with rapid recession of late wisconsin ice previously deposited loess and bluff edge dunes were apparently deflated during the last glaciation between 25 000 and 12 000 yr b p loess deposition in these mountain valleys thus is exclusively an interglacial phenomenon glacial phases are characterized by deflation meteorological modeling of katabatic winds generated during the last glaciation predicts that paleowind velocities greatly exceeded the entrainment thresholds required for eolian deflation when both nenana river and teklanika river valleys are compared theoretical differences in the potential for generating katabatic winds and differences in valley physiography explain why pre holocene loess is preserved in downstream reaches of teklanika river valley and not nenana river valley the presence of strong katabatic winds in mountain valleys beyond former glacier limits has significant implications for late pleistocene paleoecology and archeology

the dust provenance and transport mechanism for the chengdu clay in the sichuan basin china the chengdu clay in the sichuan basin china was named by thorp and dye in 1936 the genesis dust provenance and transport mechanism for the chengdu clay however are still debated in the present work the chengdu clay and adjacent loess from the eastern tibetan plateau the chinese loess plateau and the qinling mountains were investigated the content and grain size distribution of quartz quartz 18o sm nd isotopic system rare earth elements and other trace element concentrations for the chengdu clay and its adjacent loess were analyzed based on comparison and spatial variation analysis the results confirm that the chengdu clay is of aeolian origin the dust provenance of the chengdu clay differs from those of the adjacent loess the chengdu clay is possibly of local origin and is transported by an ancient katabatic wind over a short distance during glacial and stadial periods the alluvial sediments in the northwestern sichuan basin are possibly the major sources of the chengdu clay there is little possibility of an effective aeolian transport bringing dust from the tibetan plateau the arid area in northwestern china or inner mongolia into the sichuan basin where it may be deposited to form the chengdu clay thus long range dust transport by the east asian winter monsoon the westerly jet or the tibetan plateau winter monsoon possibly plays a minor role in controlling the magnitude of the dust flux of the chengdu clay in the sichuan basin

beryllium 10 surface exposure dating of glacial successions in the central alaska range glacial landforms and outwash terraces in the nenana river valley reindeer hills and monahan flat in the central alaska range were dated with 60 10 be exposure ages to determine the timing of late pleistocene glaciation in the nenana river valley glaciation occurred at 104 180 ka lignite creek glaciation ca 55 ka healy glaciation and ca 16 ka carlo creek phase glaciers retreated in the reindeer hills and monahan flat by ca 14 ka and ca 13 ka respectively the carlo creek moraine is similar in age to at least six other moraines in the alaska range ahklun mountains and brooks range the new data suggest that post depositional geological processes limit the usefulness of 10 be methods to the latter part 60 ka of the late quaternary in central alaska ages on healy and younger landforms cluster well with the exception of riley creek moraines and monahan flat west sites where boulders were likely affected by post depositional processes copy right 2010 john wiley sons ltd supporting information may be found in the online version of this article

magnetoclimatology a test of the wind vigour model using the 1980 mount st helens ash abstract magnetic mineralogy is now commonly employed in the study of past climate changes but the underlying magnetoclimatological mechanisms are not fully understood many important instances have been reported where pedogenesis leads to magnetic enhancement warmer more humid conditions produce higher magnetic signals however significant exceptions occur wherein colder more arid conditions lead to higher magnetic content one suggested explanation for the latter is the so called wind vigour model in which glacial intervals are associated with stronger more frequent winds which are more efficient at entraining and transporting dense iron oxide particles this notion is tested here by determining the relevant magnetic properties of the ash produced by the 1980 eruption of mount st helens a clear exponential decrease of magnetic susceptibility with increasing distance from the vent is observed this supports the wind vigour concept at least in some environments as a viable alternative to the pedogenetic model of magnetoclimatology

large scale submarine rotational slumps and growth faults in the eastern mediterranean submarine slumps with areas of 1000 km2 and more disturb the continental margin of israel and nearby areas in them the plio quaternary silty clayey sediments up to 1 5 2 km thick are broken by shore parallel growth faults into 5 10 blocks which are generally rotated and tilted landward the faults flatten downward and become rooted in ridges formed by deformation of the underlying mobile messinian evaporite bearing series deformation is thin skinned and does not visibly extend to deeper levels slumping occurred only where a sufficiently thick overburden accumulated over a sufficiently well developed mobile substrate then gravitational instability developed and led to basinward sliding of the continental margin sediments over the messinian series which acted as a lubricant and a level of decollement the mobility of this series is probably caused by overpressured shale beds that are confined between the impervious evaporites this mechanism explains all the features of the slumps hitherto faults directly related to the slumps of the eastern mediterranean were not identified but since the region is tectonically active it is not possible to exclude the possibility that basinward sliding was triggered either by motion of minor underlying faults or by seismic shaking however it seems that even if this were the case slumping could be triggered only because the continental margin was anyhow gravitationally unstable or close to such a state therefore the gravitational instability was the main factor that controlled the deformation of the pliocene quaternary sediments the slumps of the eastern mediterranean resemble large scale slumps that are known from other passive continental margins in the world

halogens of bushveld complex south africa δ37cl and cl f evidence for hydration melting of the source region in a back arc setting abstract the bushveld complex is one of only a few layered intrusions anomalously enriched in chlorine this study presents the first chlorine stable isotope analyses of bushveld and associated rocks designed to constrain the source of bushveld cl most samples overlap the range of values for pristine morb and altered seafloor samples 37 cl 4 relative to sea water this contrasts with distal metasedimentary floor rocks 37 cl 0 with little evidence of contamination away from the marginal rocks the cl isotope composition and high cl f ratio is therefore a fundamental characteristic of the lower and critical zone magmas and not derived from infiltration from the country rock these results the high cl f ratio and the boninitic arc like character of bushveld magma are consistent with hydration partial melting of a depleted source in a subduction related setting with cl supplied either by the dehydration of a subducted slab with a heavy cl signature or an overridden wet mantle hotspot

the messinian of the nijar basin se spain sedimentation depositional environments and paleogeographic evolution abstract the reconstruction of the depositional events related to the messinian salinity crisis msc of the mediterranean is generally hampered by an incomplete stratal record in the circum mediterranean basins the sediments of the northern part of the nijar basin however provide an excellent and continuous record of late messinian sediments because features of severe erosion are lacking especially the successions of the deeper part of the basin had sufficient accommodation space to warrant ongoing deposition and may thus serve as a testing ground for existing hypotheses regarding the msc conformable contacts with the overlying pliocene and good correlation possibilities with the adjacent astronomically dated messinian of the sorbas basin provide the necessary age constraints the main body of evaporites in the nijar basin yesares formation has been affected by local dissolution and erosion prior to deposition of the latest messinian lago mare facies pelitic float breccias show textures indicating flowage and or mass transport and include slumped and slided stratal packets due to foundering of the mixed evaporitic clastic margin increased runoff of meteoric waters probably played an important role as these packet slides are perfectly sealed by the hyposaline lago mare strata field observations show that marginal sediments commonly classified as the terminal carbonate complex tcc are a lateral equivalent of the basinal yesares evaporites the latest messinian deposits feos formation are characterized by a sedimentary cyclicity related to fluctuating base levels consisting of chalky marly laminitic strata alternating with continental coarser clastic intervals despite considerable w e facies changes and indications for discrete tectonic events a persistent sequential pattern of eight lago mare cycles is present which are interpreted as precession controlled variations in regional climate instead of one major desiccation event in the latest messinian the repeatedly fluctuating water levels of the lago mare episode may have been the cause of the widespread vigorous erosion and canyon cutting in the lower evaporites abrupt non erosional contacts with the normal marine pliocene take place above the continental interval of the last lago mare cycle indicating that flooding took place during a period of lowered water levels the paleogeographic configuration of the nijar sorbas and vera basins has changed considerably during the messinian separation of the formerly interconnected basins is thought to have started in the late yesares times by tectonic uplift of the basement complexes in the latest messinian of the nijar basin two different coarse clastic supply areas can be distinguished which point to the partial emergence of the sierra cabrera and the cabo de gata block and activity of the sierra alhamilla and carboneras faults concerning the overall regional tectonic activity tectonics were probably also instrumental for the restoration of the atlantic gateway in the basal pliocene

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

stratigraphic simulations of the shelf of the gulf of lions testing subsidence rates and sea level curves during the pliocene and quaternary determining the relative importance of factors interacting to control stratigraphic organization is a key issue in sedimentology the pliocene quaternary chronostratigraphy on the gulf of lions platform is still poorly constrained giving rise to different interpretations of the evolution of its subsidence through time this paper examines the pliocene quaternary sedimentary filling of the gulf of lion s shelf with dionisos a numerical stratigraphic model our results show that a constant subsidence rate accurately reproduces the observed geometries whereas a varying subsidence rate reproduces them only if the acceleration of subsidence is limited at this time scale a third order eustatic curve is also reappraised a higher resolution curve built using d 18 o measurements gives a more realistic restitution of our stratigraphic markers finally the constant subsidence rate and sediment fluxes implied in these modellings are discussed relative to climate and local factors of sedimentation

direct sediment transfer from land to deep sea insights into shallow multibeam bathymetry at la reunion island abstract submarine canyon heads are key areas for understanding the triggering factors of gravity currents responsible for the transfer of detrital sediment to the deep basins this contribution offers a detailed picture of canyon heads off la reunion island with high resolution multibeam bathymetry in the water depth range of 4 220 m the present feeding of the cilaos turbidite system one of the largest modern volcaniclastic systems in the world is deduced from morphological and sedimentological interpretations of newly acquired data the study highlights small scale sedimentary features indicating hydrodynamic and sedimentary processes a direct connexion between the saint etienne river mouth and submarine canyons is evidenced by the complete incision of the shelf and the presence of canyon heads connected to the modern deltaic bar this direct connection supplied by river torrential floods cyclonic floods every two or three years suggests the continuity of high density fluvial flows to submarine gravity flows forming hyperpycnal flows in the canyon the initiation of secondary submarine gravity flows by storm waves large austral waves and cyclonic waves is also proposed for submarine canyons with large canyon heads developed in the surf zone from a sandy coastal bar bedforms in active canyon axis are considered as an indicator of the frequent activity of high density turbidity currents moreover a morphological record of last glacial and deglacial sea level variations is preserved and particularly the last glacial maximum sea level with the presence of small vertical cliffs observed in this bathymetric data which likely corresponds to a paleo shoreline or paleo reefs

partitioning behavior of chlorine and fluorine in the system apatite silicate melt fluid the partitioning behavior of cl among apatite mafic silicate melt and aqueous fluid and of f between apatite and melt have been determined in experiments conducted at 1066 to 1150 c and 199 205 mpa the value of dclapatite melt wt fraction of cl in apatite cl in melt 0 8 for silicate melt containing less than 3 8 wt cl at higher melt cl contents small increases in melt cl concentration are accompanied by large increases in apatite cl concentration forcing dclapatite melt to increase as well melt containing less than 3 8 cl coexists with water rich vapor that containing more cl coexists with saline fluid the salinity of which increases rapidly with small increases in melt cl content analogous to the dependency of apatite composition on melt cl content this behavior is due to the fact that the solubility of cl in silicate melt depends strongly on the composition of the melt particularly its mg ca fe and si contents once the melt becomes saturated in cl additional cl must be accommodated by coexisting fluid apatite or other phases rather than the melt itself because cl solubility depends on composition the cl concentration at which dclapatite melt and dclfluid melt begin to increase also depends on composition the experiments reveal that dfapatite melt 3 4 in contrast to cl the concentration of f in silicate melt is only weakly dependent on composition mainly on melt ca contents so dfapatite melt is constant for a wide range of composition the experimental data demonstrate that the fluids present in the waning stages of the solidification of the stillwater and bushveld complexes were highly saline the cl rich apatite in these bodies crystallized from interstitial melt with high cl f oh ratio the latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated

crustal contamination and fluid rock interaction during the formation of the platreef northern limb of the bushveld complex south africa the platreef is the main platinum group element pge bearing and contains some of the most important magmatic ore deposits yet discovered the intrusion covers an area of facies of the northern limb of the bushveld complex but unlike the merensky reef of the eastern and western limbs it is in direct roughly 65 000 km e g tankard et al 1982 and lies almost entirely within the bounds of the transvaal basin contact with the country rock mineral separate o values for samples from the upper zone and main zone of the northern limb fig 1 the layered igneous rocks the rustenburg layered suite sacs 1980 can be divided into eastern indicate crystallization from a well mixed already contaminated magma having a o value of 7 5 pyroxenes from the pyroxenites and western limbs of approximately the same size and a smaller northern limb the northern limb differs in facies of the platreef at sandsloot mine have o values that are up to 2 4 higher than pyroxenes from the upper and main several important aspects from the more well known eastern and western limbs e g van der merwe 1976 zones these differences can be explained by additional assimilation of up to 18 dolomite which is in contact with the intrusion at buchanan et al 1981 cawthorn et al 1985 eales cawthorn 1996 first the layered rocks show a this locality samples from the platreef that have plagioclase and pyroxene not in oxygen isotope equilibrium appear to have interacted pronounced transgression across the floor rocks from a with fluids during slow cooling quartz veins with granophyric level above the magaliesberg quartzite formation south margins have o values between 10 1 and 12 2 which of the town of potgietersrus across the whole pretoria suggest that the fluid that passed through the cooling platreef had group and the banded iron formations and dolomites a o value of 7 9 these data together with hydrogen isotope of the older chuniespoort group onto archaean granitic data from minerals and whole rock samples d of biotite 60 rocks fig 1 second the igneous layering shows an to 88 of the platreef suggest interaction with magmatic fluid apparent transgressive relationship with respect to the at low water rock ratios interaction of this fluid with the calcsilicate contact such that ultramafic rocks of the lower zone footwall rocks lowered their o values abut against the contact south of potgietersrus whereas to the north rocks forming the base of the intrusion are progressively higher in the stratigraphic succession of the

ancient and modern cold climate aeolian sand deposition a review although partly active aeolian sand sheets and dunes cover large areas in the zones of dis continuous permafrost little precise information is available about the influence of cold climate conditions on modern aeolian processes this means that palaeoenvironmental reconstructions in the stabilised mainly late pleistocene dune fields and cover sand regions in the sand belts of the european lowlands and the northern great plains of the usa and canada are necessarily still based on ancient evidence cold climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains glacial outwash plains till plains and lake shores the common parabolic and transverse dune forms resemble those observed in temperate regions although a variety of periglacial features has been identified in late pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces the nature of annual sedimentation cycles and the processes by which strata were deposited and or contorted but surprisingly little is known about the role of vegetation in the process of sand accumulation dunes are most informative with respect to reconstructions of past wind regimes which offer important data for verification of palaeoclimatic simulations

the enigmatic messinian pliocene section of cuevas del almanzora vera basin se spain revisited erosional features and strontium isotope ages abstract the cuevas del almanzora section was in the late seventies the focus of a discussion because of alleged continuous marine messinian to pliocene sedimentation however a discontinuity has been shown to exist in the shape of laminated strata including the late messinian brackish lacustrine lago mare biofacies more recently benson and rakic el bied 1991 concluded that the section is still one of the best biostratigraphic successions for the western mediterranean in which to document terminal miocene events but that it entirely has an early messinian age i e it antedates deposition of the main evaporites this paper presents strontium isotope ages indicating that the classic threefold division in an earlier marine messinian a lago mare and a pliocene interval sensu geerlings et al 1980 cita et al 1980 should be maintained moreover the sr isotopic composition of the euryhaline cyprideis ostracodes from the lago mare laminites is similar to those from central mediterranean basins this stresses the importance of late messinian water exchange between the vera basin and the then enclosed mediterranean it thus refutes the opinion of benson and rakic el bied 1991 that this interval is a local facies of no particular stratigraphic importance a time gap of up to 0 8 ma between the youngest marine strata of the messinian and the overlying pliocene provides a maximum timing for the duration of the messinian salinity crisis during which very little net sedimentation occurred compared to coeval deposits in for example the nearby nijar and sorbas basins in the cuevas section an inconspicuous and hitherto overlooked erosional gap has been observed this separates the lago mare marls from the pliocene marls more field observations have been made and are discussed in the light of existing interpretations in order to demonstrate the importance of more widespread erosion in the vera basin gypsum containing mass flow deposits filling up a late messinian palaeorelief in the garrucha area are shown to be derived from the basin these probably continue offshore as feeder channels related to a late messinian sea level fall a holistic approach of a key section thereby not overlooking the regional geology is a necessary step to be made before far reaching claims can be made about its interregional significance

plio pleistocene evolution of the var deep sea fan off the french riviera abstract the var deep sea fan was deposited during the pliocene and quaternary seaward progradation of the var delta within a steep sided flat floored basin formed during the messinian salinity crisis the prominent palaeo var canyon was cut on the slope at the same time following the early pliocene transgression var sediments were initially trapped in the coastal ria formed by sea level incursion of the head of the messinian valley by middle pliocene time gilbert type deltas had prograded to the break of slope modern coastline allowing coarse sediment to reach the basin quaternary coastal uplift and sediment supply from the glaciated alps resulted in a supply of coarse sediment to the fan by the braided var river throughout the quaternary even during sea level highstands such as the present in the earliest pliocene hemipelagic clays accumulated while coarse sediment was trapped in the var ria through the rest of the pliocene a leveed fan valley extended southward from the var canyon which periodically switched locations through avulsion to the east at about the beginning of the quaternary this eastward spillover channel became the main distributary and re occupation of the older south trending channels was blocked by rapid levee progradation and aggradation of mud waves by overbanking of turbidity flows on the var sedimentary ridge during the quaternary channel shifting to the north occurred the quaternary var fan has an unusually steep concave longitudinal profile compared with most passive margin fans the laurentian fan has a similar profile to the var both have a high levee and a gravel and pebble floored fan valley that is essentially a bypass zone compared with the aggradational channel levee systems with lower levees in most passive margin fans this is a consequence of the constant supply of coarse sand gravel and pebbles to the fan even during highstands of sea level the erosive capability of this coarse sediment in ignitive turbidity currents resulted in flushing out of the upper and middle fan valley system thick muddy turbidity currents probably resulting from slumping caused by canyon incision produced the prominent mud waves on the levee the concave longitudinal profile led to rapid sediment deposition at critical points in the valley system as a result of turbidity flow expansion this in turn promoted the development of a left hook in the valley system

hydrogeology and its effect on slope stability along the coastal aquifer of nice france abstract along the ligurian continental margin off nice western mediterranean a considerable portion of the sediments is affected by pore pressure transients resulting from groundwater charging by the nearby river var and also from leaching clay mineral bearing deposits which results in sensitive weak clays in 1979 the area suffered a tsunamigenic landslide that generated several casualties and material damage to the coastal zone the seafloor presently shows evidence for soft sediment deformation and pore water freshening in this paper we present the first comprehensive in situ pore pressure data set collected over space and time between 2006 and 2009 in a landslide prone area using piezometers ifremer brest france and dynamic cone penetrometers ff cptu marum bremen germany as well as a simple modelling approach we illuminate what governing factors control strength and pore pressure in marine slope sediments affected by the var aquifer our results attest i a strong link between pore pressure transients and local precipitation over a period of 11 months ii overpressure at levels where groundwater flow occurs coarse intervals containing sand and gravel and iii fluidised fractures and channels that indicate high pore pressures at least temporarily in essence seepage and repeated pore pressure fluctuations weaken the sediment effectively so that it cannot be ruled out that the currently stable portion adjacent to nice airport may fail in the near future

morphology and extension of the evaporitic structures of the liguro provencal basin new sea beam data abstract a multi beam echo sounder sea beam and continuous seismic profiling in the liguro provencal basin were used to determine the distribution and morphology of the salt domes in this region several areas were mapped on the scale of 1 25 000 having 10 m distant contour lines an analysis of the sea beam and seismic profile data has enabled a better understanding of the hypotheses concerning the phenomenon of halokinesis i e the influence of the sedimentary overload and the influence of tectonic activities in the area it will be demonstrated that the sediment cover in the delta regions of the rhone and var rivers has a negative influence on halokinesis in these areas no piercement structures can be seen deep level tectonic activity and the faulting of the area have a primary role in the halokinesis observed in the studied zones observed diapiric features are characteristic of the underlying layer and can be used as guides for geodynamic study of the basin

multiphased tectonic evolution of the central algerian margin from combined wide angle and reflection seismic data off tipaza algeria 1 the origin of the algerian margin remains one of the key questions still discussed in the western mediterranean sea due to the imprecise nature and kinematics of the associated basin during the neogene for the first time the deep structure of the maghrebian margin was explored during the spiral seismic survey in this work we present a n s transect off tipaza west of algiers a place where the margin broadens due to a topographic high khayr al din bank new deep penetration seismic profiles allow us to image the sedimentary sequence in the algerian basin and the crustal structure at the continent ocean boundary modeling of the wide angle data shows thinning of the basement from more than 15km in the continental upper margin to only 5 6km of oceanic type basement in the algerian basin and reveals a very narrow or absent transitional zone analysis of the deep structure of the margin indicates features inherited from its complex evolution 1 an oceanic type crust in the deep basin 2 similarities with margins formed in a transform type setting 3 a progressive deepening of the whole sedimentary cover and the thickening of the plio quaternary sediments at the margin foot coeval with 4 a downward flexure of the basement in the basin these features argue for a multiphased evolution of the margin including 1 an early stage of rifting and or spreading 2 a late transcurrent episode related to the westward migration of the alboran domain and 3 a diffuse plio quaternary compressional reactivation of the margin

lead isotopic disequilibrium between sulfide and plagioclase in the bushveld complex and the chemical evolution of large layered intrusions abstract the pb isotopic compositions of coexisting plagioclase and sulfide from the bushveld complex were determined by laser ablation multi collector icpms la mc icpms the samples are of the upper critical zone in the northeast corner of the complex and were collected from drill core and underground mine exposures all the rocks are fresh and exhibit no evidence for alteration weathering or disruption of the pb isotope systematics subsequent to the initial cooling of the intrusion furthermore individual plagioclase and sulfide crystals do not contain enough u to warrant correction for radiogenic in growth for these reasons the measured pb isotope ratios approximate the initial ones for plagioclase 207pb 206pb ranges from 0 98 to 1 02 and 208pb 206pb from 2 26 to 2 35 low 207pb 206pb and 208pb 206pb ratios characterize grain boundaries and partially annealed microcracks some of which contain minute fragments of sulfide and other phases and this accounts for most if not all the heterogeneity exhibited by individual samples real compositional differences exist however in plagioclase from different lithologic layers for example plagioclase 207pb 206pb values vary from 1 004 in norite beneath the merensky pyroxenite to 1 009 in the mineralized pyroxenite and 0 997 in overlying norite in most samples in which sulfide and plagioclase coexist the sulfide 207pb 206pb ratio is lower and 208pb 206pb ratio higher than the corresponding ones in plagioclase for example in a mineralized merensky reef sample average sulfide 207pb 206pb and 208pb 206pb ratios are 0 993 and 2 313 respectively while those in plagioclase are 1 000 and 2 292 in one sample the sulfide is extremely heterogeneous with 207pb 206pb and 208pb 206pb ratios as low as 0 84 and 2 12 in this particular sample the compositions must represent an isolated occurrence of addition of a young pb component the array of sulfide and plagioclase compositions requires multiple sources of pb at the time of crystallization or soon thereafter the disequilibrium between plagioclase and sulfide implies that some of the pb originated from the isotopically distinct country rocks and was introduced at temperatures at which the composition of sulfide but not plagioclase could be modified thus bushveld sulfide and to some extent plagioclase do not reliably record the initial pb isotopic composition s of the parent magma s

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

sediment transport processes at the head of halibut canyon eastern canada margin an interplay between internal tides and dense shelf water cascading abstract to investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin the bottom boundary layer quadrapod ralph was deployed at 276 m depth in the west halibut canyon off newfoundland during winter 2008 2009 two main sediment transport processes were identified throughout the deployment firstly periodic increases of near bottom suspended sediment concentrations ssc were recorded associated with the up canyon propagation of the semidiurnal internal tidal bore along the canyon axis carrying fine sediment particles resuspended from deeper canyon regions the recorded ssc peaks lasting less than 1 h were observed sporadically and were linked to bottom intensified up canyon flows 40 cm s 1 concomitant with sharp drops in temperature secondly sediment transport was also observed during events of intensified down canyon current velocities that occurred during periods of sustained heat loss from surface waters but were not associated with large storm waves high resolution velocity profiles throughout the water column during these events revealed that the highest current speeds 1 m s 1 were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow such flows had associated low ssc and cold water temperatures and are interpreted as dense shelf water cascading events channelized along the canyon axis sediment transport during these events was largely restricted to bedload and saltation producing winnowing of sands and fine sediments around larger gravel particles analysis of historical hydrographic data suggests that such gravity flows are not related to the formation of coastal dense waters advected towards the outer shelf that reached the canyon head rather the dense shelf waters appear to be generated around the outer shelf where convection during winter is able to reach the sea floor and generate a pool of near bottom dense water that cascades into the canyon during one or two tidal cycles a similar transport mechanism is likely to occur in other submarine canyons along the eastern canadian margin as well in other canyoned margins where winter convection can reach the shelf edge

the stampede tephra a middle pleistocene marker bed in glacial and eolian deposits of central alaska a deformed block of silt incorporated in a push moraine of the lignite creek drift of the nenana river valley in central alaska contains the 10 cm thick stampede tephra the silt block and tephra are folded sheared and cut by multiple fault planes and appear to have been entrained by a glacier and deformed by glaciotectonic processes while frozen the stampede tephra is also found in a paleosol preserved within a sequence of eolian sediments near the tanana river some 175 km to the northeast allowing direct tephrochronologic correlations between the depositional record of quaternary glaciations in the alaska range and eolian sediments in unglaciated central alaska the lignite creek drift predates deposits of the late wisconsin riley creek and penultimate healy glaciations but postdates the stampede tephra indicating that it dates to the middle quaternary and is not part of the tertiary nenana gravel formation