the mechanics of intersecting echelon veins and pressure solution seams in limestone abstract many studies that describe the formation of echelon vein arrays relate the causative stresses implicitly to the deformation reliant on simple shear kinematics such that the vein to array angle and the array width are the primary physical quantities in contrast we identify twelve physical quantities to describe echelon veins in two dimensions including coeval vein intersecting pressure solution seams a finite element method is used to reproduce vein shapes in linear elastic and elastic perfectly plastic model limestone model vein geometries are designed using values within the range of geometries measured from echelon veins at raplee anticline and comb monocline utah four physical quantities are significant for describing echelon vein shapes vein spacing vein array angle limestone elastic stiffness and closing of orthogonal pressure solution seams pressure solution seam closing influences the mechanical interaction between adjacent veins and for a range of conditions causes a nearly linear vein opening distribution triangular shapes and encourages straight vein propagation both of which approximate field measurements model results show that small spacing of veins with seams and large vein array angles promote straight vein traces in limestone with stiffness typical of laboratory measurements given the physical geologic conditions inferred from the burial history of the limestone strata

understanding the environmental impacts of large fissure eruptions aerosol and gas emissions from the 2014 2015 holuhraun eruption iceland abstract the 2014 2015 holuhraun eruption in iceland emitted 11 tg of so2 into the troposphere over 6 months and caused one of the most intense and widespread volcanogenic air pollution events in centuries this study provides a number of source terms for characterisation of plumes in large fissure eruptions in iceland and elsewhere we characterised the chemistry of aerosol particle matter pm and gas in the holuhraun plume and its evolution as the plume dispersed both via measurements and modelling the plume was sampled at the eruptive vent and in two populated areas in iceland the plume caused repeated air pollution events exceeding hourly air quality standards 350 g m3 for so2 on 88 occasions in reykjahli town 100 km distance and 34 occasions in reykjavik capital area 250 km distance average daily concentration of volcanogenic pm sulphate exceeded 5 g m3 on 30 days in reykjavik capital area which is the maximum concentration measured during non eruptive background interval there are currently no established air quality standards for sulphate combining the results from direct sampling and dispersion modelling we identified two types of plume impacting the downwind populated areas the first type was characterised by high concentrations of both so2 and s bearing pm with a high sgas spm mass ratio so2 g so 4 2 pm 10 the second type had a low sgas spm ratio

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

development of cleavage in limestones of a fold thrust belt in eastern new york abstract tectonic cleavage has developed in lower devonian limestones of the hudson valley fold thrust belt in new york state morphology and distribution of cleavage in these limestones is controlled by the amount of clay quartz matrix present and by strain only limestones with greater than 10 clay quartz matrix developed widespread cleavage x ray diffraction analyses indicate that the clay matrix was altered during deformation the width of the 001 illite peak in cleaved lime wackestone is less than that in uncleaved lime wackestone from the same stratigraphic level a minimum of 10 clay is necessary to provide interconnectivity between sites of dissolution and the free fluid system preliminary analyses of bulk chemistry indicate that calcite is removed from the local rock system during cleavage development supporting proposals that circulation of fluid through the rock plays a major role in the development of cleavage textural evidence suggests that both pressure solution and free face dissolution contribute to the removal of ions at grain boundaries cross cutting relations indicate that cleavage was initiated early during the development of the fold thrust belt but continued to develop during the late stages of folding

the 8 2 ka event from greenland ice cores we present a collection of high resolution chemistry and stable isotope records from the plateau of the greenland ice cap during the cold event 8200 yr ago using a composite of four records the cold event is observed as a 160 5 yr period during which decadal mean isotopic values were below average within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period four cores in north south and central greenland show differences at decadal and shorter timescales it is not yet clear if this represents significant spatial differences in response the results show clear evidence for colder temperatures and a decrease in snow accumulation rate however the changes in chemical concentrations for the ions looked at here are small suggesting only minor changes in atmospheric circulation for this event apart from the decrease in methane concentration greenland ice cores give only weak evidence for effects outside the north atlantic region

formation of quartz veins by local dissolution and transport of silica a simple model is proposed for the often thick quartz veins observed in the modum complex in southern norway the formation of these veins cannot easily be explained by silica imported by hot ascending fluids the proposed model has dissolution in the host rock adjacent to the veins as the source for silica the suggested process for vein formation is represented by a reaction diffusion equation and the process is studied in terms of a damkohler number estimates for the growth rate of quartz cement are derived the estimates for the growth rate can be used to constrain poorly known parameters of the vein formation process like for instance the degree of supersaturation in the host rock

sulphur dioxide particle and elemental emissions from mount etna italy during july 1987 sulphur dioxide emission rates were measured at mount etna italy during july 1987 while the volcano was undergoing relatively quiet activity the so2 flux averaged 930 587 1 mg d excluding 19 july when the flux was 3200 1730 1 mg d rising magma and or an influx of less degassed magma could explain the increased so2 flux the high so2 flux did not correlate with changes in observed volcanic activity this suggests that so2 monitoring may be useful as an indicator of shallow magmatic activity but not as a predictor of future eruptions of mount etna

tracking the sea level signature of the 8 2 ka cooling event new constraints from the mississippi delta 1 the ever increasing need for accurate predictions of global environmental change under greenhouse conditions has sparked immense interest in an abrupt century scale cooling around 8200 years ago with a focal point in the north atlantic and with hemispheric teleconnections despite considerable progress in the unraveling of this striking feature including a conceivable driving mechanism rapid drainage of proglacial lake agassiz ojibway and a resulting reduced strength of north atlantic thermohaline circulation several key questions remain unanswered one salient aspect concerns the total amount of freshwater released during this catastrophic event likely echoed by a near instantaneous eustatic sea level rise so far no attempts have been made to perform high resolution sea level studies that explicitly focus on this critical time interval here we present new data from the mississippi delta suggestive of abrupt sea level rise associated with the 8 2 ka event however the amount of sea level rise was likely less than 1 2 m corresponding to a meltwater volume of less than 4 3 1014 m3 values lower than estimates used by several recent studies

bay head deltas across the northern gulf of mexico back step in response to the 8 2 ka cooling event abstract estuaries along the northern gulf of mexico show rapid landward shifts in estuarine environments back stepping around 8200 cal yr bp paleogeographic maps of the estuaries based on seismic data and cores and constrained chronologically by radiocarbon dates depict bay head delta retreat in excess of 25 m yr during these events the sub aerial delta plain flooded to create sub tidal upper and middle bay environments abrupt sea level rise associated with the 8200 cal yr bp climate change event caused these estuaries and others around the world to reorganize abruptly in the northern gulf of mexico the sea level rise associated with the event was only 0 1 m over a sub decadal time period this rise was superimposed on a background decelerating rate of sea level rise of 1 0 0 5 m century the widespread bay head delta back stepping documented here may be an appropriate analog for possible abrupt future climate change in response to global warming it also shows that estuaries fringed by low gradient shorelines are highly sensitive to low amplitude and sudden sea level rise

grain size analysis of the neogene red clay formation in the pannonian basin the red clay is a significant deposit underlying the pleistocene loess paleosols sequence in the pannonian basin the sedimentary processes involved and the origin of the materials remain controversial in order to determine the depositional processes of the pliocene red clay formation we studied many red clay sections in hungary here we present results of grain size analyses of the red clay from representative sites in particular their grain size distribution is compared with that of typical pleistocene eolian loess paleosols as well as lacustrine and fluvial sediments it appears from the sedimentological data that the majority of the red clay is of a wind blown origin the red clay might be transported by weak westerly winds and has been modified by post depositional alteration

methane bubble growth in fine grained muddy aquatic sediment insight from modeling abstract methane ch 4 is the most abundant hydrocarbon and one of the most important greenhouse gases in the atmosphere ch 4 bubble growth and migration within muddy aquatic sediments are closely associated with sediment fracturing in this paper we present the modeling of buoyancy driven ch 4 bubble growth in fine grained muddy aquatic sediment prior to the beginning of its rise we designed a coupled mechanical reaction transport numerical model that enables a differential fracturing over the bubble front as it occurs in nature when the fracturing increment stays constant at the bubble head and subsides towards bubble tail during bubble growth we show that this differential fracturing over the bubble front controls the bubble shape and size temporal evolution and is significantly affected by the critical stress intensity factor of the muddy sediment the intercalated stages of elastic expansion and fracturing during the bubble growth shorten with time as the bubble approaches its terminal size prior to its ascent our simulations reveal a high asymmetry in the bubble shape growing with time with respect to its initial symmetric penny shaped configuration it was found that the bubble grows allometrically while the importance of the bubble surface area growth with time we also confirmed the earlier predictions about the inverted tear drop bubble cross section just prior to the beginning of its rise modeling of the terminal bubble characteristics will permit prediction of the delivery of gaseous methane from the sediment to the atmosphere via the water column

insights into crustal assimilation by icelandic basalts from boron isotopes in melt inclusions from the 1783 1784 lakagigar eruption abstract the boron isotope system has great potential for tracing alteration and assimilation in basaltic systems due to the very low concentrations of b in mantle derived melts and the strong isotopic contrast between the mantle and surface materials however variability in b concentrations and isotope ratios in basalts can also be interpreted to reflect inputs from enriched regions of the mantle as the extent of mantle heterogeneity with respect to boron remains poorly delineated we have determined boron concentrations and isotope ratios in fresh glassy plagioclase hosted melt inclusions and unaltered scoriaceous matrix glasses from four localities associated with the 1783 1784 lakagigar laki fissure eruption iceland boron concentrations range from 0 59 to 1 25 ppm in the melt inclusions and from 1 25 to 1 65 ppm in the matrix glasses while 11 b nbs 951 ranges from 7 8 to 16 5 in the melt inclusions and 10 5 to 16 9 in the matrix glasses in contrast to previous studies of boron in basaltic melt inclusions from other fissure swarms in iceland gurenko and chaussidon 1997 chem geol 135 21 34 the lakagigar melt inclusions display a significant range of boron concentrations and isotope ratios at constant k 2 o wt which is more consistent with b addition by assimilation of altered basalt than it is with mixing between depleted and enriched mantle sources assimilation of freshwater altered crustal materials at depth may impart a light 11 b signature such as that observed in the lakagigar melt inclusions and tephra host glasses considering boron concentrations and isotope ratios in the lakagigar glasses and previously studied altered icelandic basalts together with volatile equilibration depths of the lakagigar melt inclusions we propose that a mantle derived magmas formed beneath lakagigar assimilated 5 20 altered crust at a depth of 3 4 km or more probably during magma accumulation in sills formed at the boundaries of low density hyaloclastite layers and b the magma subsequently underwent extensive mixing and homogenization prior to eruption quite possibly within the magma chamber beneath the grimsvotn central volcano assimilating an additional 10 of altered crust at that time for a total of up to 30 crustal assimilation we hypothesize that volatiles including h 2 o co 2 s f and cl which were responsible for the majority of the considerable casualties attributed to the lakagigar eruption were added together with isotopically light b by assimilation of hydrothermally altered crustal materials

health hazards and disaster potential of ground gas emissions at furnas volcano sao miguel azores a health hazard assessment of exposure to soil gases carbon dioxide and radon was undertaken in the village of furnas located in the caldera of an active volcano a soil survey to map the area of soil gas flow was undertaken gas emissions were monitored at fumaroles and in eight houses and a preliminary radon survey of 23 houses in the main anomaly area was performed potential volcanic sources of toxic contamination of air food and water were also investigated and ambient air quality was evaluated about one third 41 ha of the houses were located in areas of elevated carbon dioxide soil degassing unventilated confined spaces in some houses contained levels of carbon dioxide which could cause asphyxiation mean indoor radon levels exceeded uk and us action levels in the winter months a tenfold increase in radon levels in one house over 2 h indicated that large and potentially lethal surges of carbon dioxide could occur without warning toxic exposures from the gaseous emissions and from contamination of soil and water were minimal but sulphur dioxide levels were mildly elevated close to fumaroles in contrast evidence of dental fluorosis was manifested in the population of the nearby fishing village of ribeira quente where drinking water in the past had contained elevated levels of fluoride the disaster potential of volcanic carbon dioxide in the area could also be associated with the hydrothermal system storing dissolved carbon dioxide beneath the village felt or unfelt seismic activity or magma unrest especially with a reawakening of explosive volcanic activity 30 probability in the next 100 years could result in an increase in gas flow or even a gas burst from the hydrothermal system a survey of all houses in furnas is advised as structural measures to prevent the ingress of soil gases including radon were needed in some of the study houses evaluations of the human hazards of volcanic gases should be undertaken in all settlements in volcanic and hydrothermal areas associated with soil gas emissions

stomatal response of swordfern to volcanogenic co2 and so2 from kilauea volcano 1 the experimentally determined relationship between atmospheric pco2 and plant stomata has been used to interpret large but transient changes in atmospheric composition such as may have resulted from the eruptions of flood basalt however this relationship has not been tested in the field i e in the vicinity of active volcanoes to examine the specific effects of volcanogenic emissions moreover the interpretation of paleoatmospheric pco2 from fossil stomatal data assumes that the stomatal response resulted solely from variation in pco2 and ignores the potential effect of outgassed so2 we hypothesize that volcanogenic so2 also has a significant effect on leaf stomata and test this hypothesis by measuring the stomatal index of the common swordfern nephrolepis exaltata in the plumes of the actively outgassing vents of kilauea volcano we find that compared to control locations stomatal index is lowest at sample sites in the plume of halema uma u crater where concentrations of both co2 and so2 are much higher than background however sites located directly in the plume of pu u o o where so2 levels are high but co2 levels are not also yield low values of stomatal index we propose that shifts in the stomatal index of fossil leaves may record transient atmospheric increases in both so2 and co2 such as may be caused by eruptions of flood basalts calculations of pco2 based on stomatal frequency are likely to be exaggerated

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

mechanics of the formation of orthogonal sets of solution seams and solution seams and veins and parallel solution seams and veins abstract commonly observed networks of pressure solution seams psss and psss and veins can be broken down to three basic assemblages orthogonal pss sets orthogonal pss vein sets and parallel pss vein sets we investigate stress distributions around psss idealized as localized volume reduction structures lvrss to identify the conditions for forming these three fundamental assemblages various geometries of lvrss are taken into account including elliptical lvrss with smooth flanks lvrss with triangular and rectangular asperities on their flanks and lvrss with overall irregular geometries such as columnar and conical shapes the modeling results indicate that if the first pss set has elliptical shapes with smooth flanks the conditions for generating the fundamental assemblages listed above are highly restrictive primarily due to relatively large average aspect ratios of psss as measured in the field which indicate lower stresses around psss as they grow however both laboratory and field observations have shown that pss surfaces are extremely rough we find that psss with relatively rough flanks and psss with overall irregular trace geometry such as sutured and zig zag or wiggly are much more favorable for generating the stresses for the formation of these fundamental structural assemblages based on a series of stress domain maps from our mechanical model we evaluated the stress strain and geometric conditions for the formation of each of the three assemblages it turns out that there are a wide variety of loading and geometric factors favoring the formation of a particular type of assemblage

late quaternary vegetation and climate changes in central texas based on the isotopic composition of organic carbon stable carbon isotope analysis of organic carbon in alluvial deposits and soils of three streams in central texas reveals significant shifts in the ratio of c3 to c4 plant biomass production during the past 15 000 yr these temporal changes in vegetation appear to be in response to changes in climate during the late pleistocene c4 plants comprised only about 45 to 50 of the vegetative biomass in this area suggesting that conditions were cooler and wetter than at any time during the past 15 000 yr the time between 11 000 and 8000 yr b p is interpreted as transitional between late pleistocene conditions and warmer and drier holocene conditions based on a slight increase in the abundance of c4 plant biomass during the middle holocene between approximately 6000 and 5000 yr b p mixed c3 c4 plant communities were replaced almost completely by c4 dominated communities indicating prairie expansion and warmer and drier climatic conditions by 4000 yr b p the abundance of c4 plant biomass decreased to levels similar to the early holocene transitional period suggesting a return to cooler and wetter climatic conditions no significant shift in the ratio of c3 to c4 productivity has occurred during the last 4000 yr except for a slight increase in the abundance of c4 plant biomass around 2000 yr b p the results of this investigation correlate well with other regional late quaternary climatic interpretations for central and north texas the southern plains region and with other portions of the great plains

the sea level fingerprint of the 8 2 ka climate event the 8 2 ka cooling event was an abrupt widespread climate instability there is general consensus that the episode was likely initiated by a catastrophic outflow of proglacial lakes agassiz and ojibway through the hudson strait with subsequent disruption of the atlantic meridional overturning circulation however the total discharge and flux during the 8 2 ka event remain uncertain we compute the sea level signature or fingerprint associated with the drainage of lakes agassiz and ojibway as well as the expected sea level signal over the same time period due to glacial isostatic adjustment gia in response to the late pleistocene deglaciation our analysis demonstrates that sites relatively close to the lakes including the west and gulf coasts of the united states have small signals due to the lake release and potentially large gia signals and thus they may not be optimal field sites for constraining the outflow volume other sites such as the east coast of south america and western africa have significantly larger signals associated with the lake release and are thus better choices in this regard

atmospheric dispersion environmental effects and potential health hazard associated with the low altitude gas plume of masaya volcano nicaragua masaya volcano 560 m a s l nicaragua re sumed its degassing activity in mid 1993 with the con tinuous emission of so 2 at rates increasing from 600 metric tons t day 1 7 0 kg s 1 in 1995 to 1800 t day 1 21 0 kg s 1 in 1999 the low altitude gas plume is typically blown westward by the prevailing wind across the masaya caldera and las sierras high lands which are at a higher elevation than the gas vent in this study the areal distribution of atmospheric so 2 concentrations was monitored within 44 km of the vent with a network of passive samplers measured so 2 air concentrations ranged from 2 to 90 ppbv in 1998 and from 2 to 230 ppbv in 1999 the data suggest that the volcanic emissions influenced air quality across a 1 250 km2 area downwind local topography exerts a strong control on plume dispersal and hilltops are particularly prone to fumigation and thus to high ambient so 2 lev els in a zone 22 km2 in size located within 15 km of the source the response of vegetation to sustained exposure to high atmospheric dose of volcanic so 2 and hf result ed in a strong reduction in the number of plant communi ties a transition zone of somewhat indefinite boundary surrounds the devastated zones and exhibits vegetation damage in the form of leaf injury in addition to the envi ronmental impacts of the volcanic emissions both short and long term public health hazards may exist in areas most exposed to the plume the harmful effects of the volcanic emissions on cultivated vegetation could be di minished by using windbreaks made of gas tolerant trees and shrubs such as eugenia jambos brosimum utile and clusia rosea the current gas crisis at masaya volcano provides an unique opportunity for investigating the at mospheric environmental and medical impacts of volca nic gases and aerosols

an early holocene sea level jump and delta initiation 1 early holocene sea level change controlled the evolution of clastic coastal depositional systems radiocarbon dated borehole cores obtained from three incised valley fill systems in asia changjiang song hong and kiso river record very similar depositional histories especially between about 9000 and 8500 cal bp sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period in addition large decreases in sediment accumulation rates occurred a sea level jump causes an estuarine system and its depocenter to move rapidly landward it is possible that the final collapse of the laurentide ice sheet accompanied by catastrophic drainage of glacial lakes at approximately 8500 cal bp caused such a jump the jump was followed immediately by a period of decelerated sea level rise that promoted delta initiation

the fractal geometry of some stylolites from the calcare massiccio formation italy stylolites are serrated surfaces that form by stress enhanced dissolution though their geometry and morphology reflects their formation and evolution only a few studies have attempted to quantify them here we present results indicating that stylolites in limestone of the calcare massiccio formation jurassic italy are fractal over 4 5 orders of magnitude in spatial bandwidth with an average fractal dimension obtained by spectral and scaled windowed variance analyses clustering at 1 47 some stylolites from the skene cambrian usa and tamar cenomanian israel formations are fractal over 3 orders of magnitude with fractal dimensions of 1 26 and 1 43 these values are high relative to other natural surfaces and reflect the jagged topography of the stylolites preliminary results indicate that the fractal dimension and power are constant throughout the stylolite surface and are not orientation dependent furthermore we show that stylolite contours are fractal too the grain size does not register in our analyses implying that the grain is not a cutoff between processes rather stylolite generating processes operate similarly below and above the grain size our results suggest that the geometry of these stylolites especially at long wavelengths may not be sensitive to the immediate fabric surrounding them

the effect of stylolite spacing on quartz cementation in the lower jurassic sto formation southern barents sea abstract the shallow marine lower jurassic quartz arenites of the sto formation in the southern barents sea comprise 1 intervals where dispersed detrital clay is absent and where the spacing between clay rich laminae that evolved into stylolites upon burial is exceptionally large up to several meters and 2 intervals where minor detrital clay matrix occurs clay laminae are very common and stylolite spacing is typically less than a centimeter point counting of thin sections and cathodoluminescence micrographs shows that quartz cement contents are far lower in the intervals where stylolite spacing is exceptionally large 4 11 versus 10 20 outside these intervals there is also a correlation between distance to nearest stylolite and volume of quartz cement samples located a centimeter or less from a stylolite contain 10 20 quartz overgrowths for distances of 3 20 cm quartz cement content is 4 10 and only 3 8 when the closest stylolite is more than 20 cm distant modeling of quartz cementation with the exemplartm diagenetic modeling program indicates that the observed trend of decreasing quartz cement abundance outwards from stylolites is not caused by variations in grain size degree of grain coating or content of quartz grains i e the trend is not due to more quartz surface area being available for overgrowth formation close to stylolites on the contrary the modeling suggests that the samples situated more than 20 cm from stylolites contain 5 8 less quartz cement than what would have been the case given a more normal stylolite abundance this study indicates that sandstones with exceptionally few clay rich or micaceous laminae and without clay or mica at individual grain contacts will be significantly less quartz cemented and more porous than other sandstones with similar temperature histories however such sandstones seem to be highly unusual on the norwegian continental shelf this suggests that exceptionally low abundance of stylolite precursors may be of only local importance for preserving reservoir quality at elevated temperatures and that it is normally not necessary to include stylolite spacing and distance to the nearest stylolite as variables in quantitative models of quartz cementation

pressure solution in chalk pressure solution residues in the cretaceous to paleocene chalk from the north sea area were studied to understand the pressure solution process and fluid flow residue seams reach lengths and thickness of more than 800 and 0 15 m 2625 and 0 5 ft respectively seams can present significant barriers to fluid flow because they have nannodarcy permeability and hold back large pressure differentials stylolite amplitudes decrease when they merge making it difficult to quantify volume loss measuring amplitudes allows volume loss estimates using a new dissolution ratio method the sum of the thicknesses of all residues is multiplied by the maximum amplitude to residue thickness ratio on average 30 mm 1 2 in of chalk had to be dissolved to produce a 1 mm 0 04 in thick residue the volume loss of chalk from flamborough averages about 50 and is 60 in the machar oil field united kingdom central graben the minimum fluid volume required to produce the volume loss in 1 unit volume of preserved chalk on the machar field is estimated to be 8000 unit volumes this and the stable isotopes of vein carbonates imply that the pressure solution process involved an open fluid system high illite content in mixed layered illite smectite and high illite crystallinity of clays in the pressure solution seams in the machar reservoir indicate high diagenetic maturity with implied temperatures in the range of 200 360c 392 680f which is greater than the present day reservoir temperature of 85c 185f the anomalously hot temperatures are interpreted to be produced by deep mineralizing fluids transported from the central graben the lack of abundant veining in the chalk and the large fluid volumes involved in the chalk dissolution suggest that this was an open pressure solution system

c4 plant productivity and climate co2 variations in south central texas during the late quaternary abstract a continuous record of organic carbon 13c from a buried soil sequence in south central texas demonstrates 1 strong coupling between marine and adjacent continental ecosystems in the late pleistocene as a result of glacial meltwater entering the gulf of mexico and 2 ecosystem decoupling in the holocene associated with a reduction of meltwater and a shift in global circulation patterns in the late pleistocene reduction in c4 plant productivity correlates with two well documented glacial meltwater pulses 15 000 and 12 000 14c yr b p indicating a cooler than present adjacent continental environment increased c4 production between 11 000 and 10 000 14c yr b p suggests that the younger dryas was a warm interval responding to the diversion of glacial meltwater away from the mississippi river with waning meltwater flow c4 productivity generally increased throughout the holocene culminating in peak warm intervals at 5000 and 2000 14c yr b p shifts in the abundances of c3 c4 plants through the late quaternary show no correlation to ecophysiological responses to atmospheric co2 concentration

three dimensional morphology and connectivity of stylolites hyperactivated during veining abstract the limestone of the palaeozoic jack formation in north queensland australia contains bedding parallel stylolites that locally increase in amplitude adjacent to calcite veins the veins formed in response to inhomogeneous strain locally superposed on the tightly folded strata stylolites were locally hyperactivated during vein formation and provided calcite for vein filling three dimensional reconstructions of the morphology of the stylolites based on detailed serial profiles demonstrate that the side faces of columnar stylolites form an interconnected fluid pathway through the rock the connective morphology defines a drainage network comprising highly tortuous major trunks of high amplitude side faces linked locally by minor pathways of variable amplitude the permeability pathway anastomoses in three dimensions making it impossible to image in two dimensions alone

in situ measurements of tropospheric volcanic plumes in ecuador and colombia during tc4 a nasa dc 8 research aircraft penetrated tropospheric gas and aerosol plumes sourced from active volcanoes in ecuador and colombia during the tropical composition cloud and climate coupling tc 4 mission in july august 2007 the likely source volcanoes were tungurahua ecuador and nevado del huila colombia the tc 4 data provide rare insight into the chemistry of volcanic plumes in the tropical troposphere and permit a comparison of so 2 column amounts measured by the ozone monitoring instrument omi on the aura satellite with in situ so 2 measurements elevated concentrations of so 2 sulfate aerosol and particles were measured by dc 8 instrumentation in volcanic outflow at altitudes of 3 6 km estimated plume ages range from 2 h at huila to 22 48 h downwind of ecuador the plumes contained sulfate rich accumulation mode particles that were variably neutralized and often highly acidic a significant fraction of supermicron volcanic ash was evident in one plume in plume o 3 concentrations were 70 80 of ambient levels downwind of ecuador but data are insufficient to ascribe this to o 3 depletion via reactive halogen chemistry the tc 4 data record rapid cloud processing of the huila volcanic plume involving aqueous phase oxidation of so 2 by h 2o 2 but overall the data suggest average in plume so 2 to sulfate conversion rates of 1 2 h 1 so 2 column amounts measured in the tungurahua plume 0 1 0 2 dobson units are commensurate with average so 2 columns retrieved from omi measurements in the volcanic outflow region in july 2007 the tc 4 data set provides further evidence of the impact of volcanic emissions on tropospheric acidity and oxidizing capacity

mineral growth in rocks kinetic rheological models of replacement vein formation and syntectonic crystallization abstract we model three cases of coupling between mineral growth kinetics and mechanical response of the rock i dispersed spherical crystals growing by replacement in a hydrostatically stressed elastic rock ii growth of veins or vein networks accommodated by viscous relaxation of surrounding rock and iii syntectonic crystallization in a rock undergoing bulk pure shear such models for the microscopic environment of mineral growth together with additional assumptions or knowledge about rheological behavior and aggregate geometry provide refined estimates of the behavior of a macroscopic volume element which could be combined with geochemical reaction transport models crucial in the models are the various consequences pressure solution creep fracturing of the local stress that is necessarily generated by mineral growth in rocks other than in pores in the first model the dispersed spherical crystals of mineral a are assumed to grow within a spherical volume of rock consisting of mineral b the mineralized zone mz itself embedded in elastic rock the macroscopic stress in the mz and the far field stress in the surrounding rock are uniform and hydrostatic mineral growth of the a crystals is driven by supersaturation with respect to mineral a is accommodated by replacement of b grains and leads to an expansion of the mz described by an infinitesimal strain the radial growth rate of a spherical crystal of mineral a with replacement of mineral b is da dt k a r tln a k b v 0 b k b v 0 b k a v 0 a where ka and kb are kinetic constants r is the gas constant t the temperature in kelvin and v0a and v0b are specific volumes reference saturation states of mineral a a 1 and host mineral b b 1 are specified at the far field hydrostatic stress 0 the microscopic environment of each crystal of a is modeled by a representative volume element rve consisting of a sphere of mineral a embedded in a spherical shell of mineral b in each rve stress is neither uniform nor hydrostatic the model links the local microscopic stress with the macroscopic stress in the mz and surrounding rock the second model refers to veins that make room for themselves by growing not to veins that form by cementation of previously opened or opening cracks if the growth of mineral a as propagating veins or as an interconnected vein network takes place by deformation and expansion of the mz with the deformation itself driven by the stress arising from the supersaturation driven growth the surrounding rock undergoes deformation and is treated as viscous the rate of growth in vein width w is dw dt 2 k a rtln a sv 0 a 1 m where m 16 kav0ac2 3b3 is the medium viscosity c is the vein radius and each vein is treated as centered in a spherical rve of radius b s is an effective tensile stress required for vein propagation for a vein network in which veins surround equant polyhedra of rock of radius b we set c b and drop the term in s for simplicity veins may also widen by replacement the ratio of vein widening by expansion to that by replacement is dw dt expansion dw dt replacement 3 b 16 3 b 16 k a v 0 a k b v 0 b k b v 0 b k a v 0 a both mechanisms of accommodation contribute equally when 3b 16kbv0b at higher viscosity replacement is dominant the incipient growth of a cylindrical crystal with circular cross section in a medium deforming in pure shear simulates syntectonic crystallization both dissolution and deformation of the host accommodate growth in the model the crystal tends to grow faster in the direction of maximum rate of extension in this direction the host mineral may either dissolve to accommodate growth or precipitate to form a pressure shadow accommodation by host dissolution is greatest in the direction of maximum rate of shortening

so2 and fine aerosol dispersion from the kilauea plume kau district hawaii usa proximal ground level assessment of sulfur dioxide gas and fine aerosol in the volcanic gas plume downwind from kilauea volcano indicates high levels of both species fine aerosol and so 2 data were collected in the kau district 37 74 km downwind from the eruption and at a nonexposed control site in hawi hawaii typical trade winds and effusive eruption occurred during sampling in august september 2003 ambient so 2 concentrations measured with diffusion tubes ranged from 6 to 34 ppbv and correlated negatively with altitude in contrast fine aerosol 0 3 m size concentrations measured with a cascade impactor ranged from 0 61 to 11 82 g m 3 and correlated positively with altitude we attribute decrease of so 2 with altitude to rapid oxidation as diurnal wind patterns blow the plume from oceanic terrain landward to more abundant oxidation sources aerosol increase with altitude likely reflects emission of h 2 so 4 from kilauea supplemented by oxidation of so 2 in atmospheric hydrosols kau residents are exposed to volcanogenic pollutants at concentrations that warrant concern for adverse health effects

pressure solution features in a shallow buried limestone abstract three distinct types of pressure solution features are found in the alpena limestone devonian michigan stylolites solution seams and fitted fabric texture the style of pressure solution is different in grainstones packstones and wackestones the difference is interpreted to be the result of preferential cementation of the grainstones well cemented grainstones typically have stylolites whereas solution seams and fitted fabric texture are more common in poorly cemented grainstones packstones and wackestones pressure solution occurs at e80 percent of the lithologic transitions this is probably due to competency contrasts between adjacent units that material dissolved at pressure solution surfaces is not locally reprecipitated is indicated by porous allochems which abut against stylolites and units of abundant intergranular pressure solution fitted fabric texture which lack cement the style of pressure solution in the alpena limestone and its relationship to cementation is also observed in the tuscarora quartz arenite silurian appalachian basin

modeling the growth of stylolites in sedimentary rocks stylolites are ubiquitous pressure solution seams found in sedimentary rocks their morphology is shown to follow two self affine regimes analyzing the scaling properties of their height over their average direction shows that at small scale they are self affine surfaces with a hurst exponent around 1 and at large scale they follow another self affine scaling with hurst exponent around 0 5 in the present paper we show theoretically the influence of the main principal stress and the local geometry of the stylolitic interface on the dissolution reaction rate we compute how it is affected by the deviation between the principal stress axis and the local interface between the rock and the soft material in the stylolite the free energy entering in the dissolution reaction kinetics is expressed from the surface energy term and via integration from the stress perturbations due to these local misalignments the resulting model shows the interface evolution at different stress conditions in the stylolitic case i e when the main principal stress is normal to the interface two different stabilizing terms dominate at small and large scales which are linked respectively to the surface energy and to the elastic interactions integrating the presence of small scale heterogeneities related to the rock properties of the grains in the model leads to the formulation of a langevin equation predicting the dynamic evolution of the surface this equation leads to saturated surfaces obeying the two observed scaling laws analytical and numerical analysis of this surface evolution model shows that the cross over length separating both scaling regimes depends directly on the applied far field stress magnitude this method gives the basis for the development of a paleostress magnitude marker we apply the computation of this marker i e the morphological analysis on a stylolite found in the dogger limestone layer located in the neighborhood of the andra underground research laboratory at bure eastern france the results are consistent with the two scaling regimes expected and the practical determination of the major principal paleostress from the estimation of a cross over length is illustrated on this example

the role of pressure solution seam and joint assemblages in the formation of strike slip and thrust faults in a compressive tectonic setting the variscan of south western ireland abstract the ross sandstone in county clare ireland was deformed by an approximately north south compression during the end carboniferous variscan orogeny the initial assemblage consists of mutually abutting orthogonal arrays of 170 oriented set 1 joints veins jvs and approximately 75 oriented set 1 pressure solution seams psss formed under the same stress conditions orientations of splay jvs and psss set 2 suggest a clockwise remote stress rotation of about 35 responsible for the contemporaneous shearing of the set 1 arrays among these nearly orthogonal strike slip faults the prominent set is sub parallel to set 1 jvs these faults are formed by the linkage of en echelon segments with broad damage zones responsible for right lateral offsets of hundreds of meters thrust faults with up to 30 m of offset initiate within shale horizons and follow either the psss in the sandstones or high angle shales within tilted sequences within the large thrust fault zones compartmentalised blocks of rocks are bounded by thrust faults segments with various dip angles strike slip and thrust faults are contemporaneous and owe their existence to initial weaknesses in the form of jvs and psss rather than by switching relative stress magnitudes and orientations associated with andersonian models of faults and related stress orientations

sun photometer and lidar measurements of the plume from the hawaii kilauea volcano pu u o o vent aerosol flux and so2 lifetime 1 aerosol optical depths and lidar measurements were obtained under the plume of hawaii kilauea volcano on august 17 2001 9 km downwind from the erupting pu u o o vent measured aerosol optical depths at 500 nm were between 0 2 0 4 aerosol size distributions inverted from the spectral sun photometer measurements suggest the volcanic aerosol is present in the accumulation mode 0 1 0 5 micron diameter which is consistent with past in situ optical counter measurements the aerosol dry mass flux rate was calculated to be 53 mg d 1 the estimated so2 emission rate during the aerosol measurements was 1450 mg d 1 assuming the sulfur emissions at pu u o o vent are mainly so2 not aerosol this corresponds to a so2 half life of 6 0 hours in the atmosphere

kaolin coating of stylolites effect on quartz cementation and general implications for dissolution at mineral interfaces abstract the deeply buried 4 km 160 c quartz rich sandstones of the middle jurassic garn formation in well 6507 7 1 offshore mid norway typically contain 20 30 quartz cement and only 3 9 porosity the exception is a less than 1 5 m thick interval at the top of the formation where quartz cement volumes typically drop to 8 16 and porosities are in the range 7 19 the uppermost part of the garn formation is not isolated from the rest of the formation by any type of impermeable barrier the sandstones are water filled indicating that the change in cementation does not correspond to a hydrocarbon contact and there are no significant changes in grain size grain coating abundance grain mineralogy or other factors that could give a lower quartz surface area for development of quartz overgrowths within the uppermost 1 5 m of the sandstones however in the samples from the less cemented interval illitization of authigenic kaolin is either not detectable or very restricted compared to deeper down in the cores where illitization of kaolin is usually complete we propose that the cause of reduced quartz cementation in the top of the garn formation may be the coating of stylolites developed from primary illitic clay rich and micaceous laminae with authigenic kaolin as quartz cementation proceeds and the authigenic kaolin rich rock adjacent to the stylolites is dissolved although we do not have evidence indicating that this may be a common phenomenon of major importance for preservation of reservoir quality our observations may help to unravel the mechanisms of quartz dissolution at stylolites specifically we suggest that the lack of significant surface charge on kaolin compared to illite and mica may lead to a reduced thermodynamic drive for quartz dissolution at kaolin quartz contacts similarly lack of dissolution at clean quartz quartz surfaces may be due to smaller and equal surface charges setting up oppositely directed electric fields that cancel each other whereas the positive surface charge of carbonate minerals may actually enhance the electric fields from negatively charged illitic clay and mica which may explain the extensive dissolution often seen at stylolites in limestones

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

are stylolites fluid flow efficient features abstract it sounds counter intuitive to consider contraction features such as stylolites as potential conduits for flow however this idea has grown since 1980 with geoscientists finding many examples principally in carbonate reservoirs where stylolites can be considered as fluid efficient features among others these features can be reactivated stylolites can generate positive porosity and permeability anomalies can drive corrosive fluids or can remain open in an overpressured system conversely stylolites can also be closed forever these impermeable stylolites can generate permeability anisotropy that may impact fluid movements stylolites require particular attention to evaluate whether they act as drains or as barriers to flow compartmentalisation we review some of the key studies of the past thirty years with a special attention to the most recent ones we end up considering their mechanical origin their nucleation and growth their past and present impact on reservoir properties and performances as key factors influencing the flow efficiency differentiation of these features this short review presents the latest theories and observations about stylolites with respect to the key factors aforementioned the authors support herein that a distinction should be made between processes occurring in the past and the present day impact the stylolite had on reservoir properties

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

sedimentary stylolite networks and connectivity in limestone large scale field observations and implications for structure evolution stylolites are rough surfaces formed by localized rock dissolution and prevalent in carbonates and other sedimentary rocks their impact on porosity and permeability and capacity to accommodate compactive strain are well documented this paper presents a meso scale field study on sedimentary stylolites in carbonates characterizing large scale distributions of stylolites including measurements conducted on longer than kilometer long stylolites our field study suggests that on large scales connections between stylolites become important since connectivity and also lack of connectivity are expected to play a significant role in strain accommodation and hydraulic rock properties we suggest that large scale analysis may require a new characterization scheme for stylolites populations based on their connectivity we therefore divide sedimentary stylolite populations into three end member types which are correlated with the three possibilities for percolation of such systems isolated stylolites with zero percolation connectivity long parallel stylolites with 2 dimensional percolation connectivity and interconnected stylolite networks with 3 dimensional percolation connectivity new statistical parameters and measures are devised and used to quantitatively characterize the different population types schematic mechanistic models are then offered to explain the evolution of the three end member connectivity classes in addition we discuss the effect on fluid flow of the different population types

extensional veins induced by self similar dissolution at stylolites analytical modeling abstract stylolites are surfaces of localized dissolution observed in rocks many stylolites share a common morphological feature the amount of dissolved rock in the center of the seam is proportional to the stylolite s length field observations demonstrate that stylolites can locally influence formation of veins the developed analytical model of the indirect solution of eshelby s transformation problem calculates the stress field within and around the stylolite the results suggest that growth of a stylolite with an elliptic dissolution pattern generates a local non uniform stress field in the host rock which is in turn accommodated by brittle mode i fracturing in the stylolite midsection further resulting in veins formation parametric analysis and qualitative comparison with anticrack model describing stress field within and around stylolite are conducted

an analysis of the roles of stress temperature and ph in chemical compaction of sandstones abstract chemical compaction also known as pressure solution involves dissolution along grain contacts and transport of solute to the adjacent pore space by diffusion the driving force for diffusion is a gradient in chemical potential therefore chemical compaction requires persistent gradients in chemical potential along grain contacts in order to drive diffusion continuously such gradients exist in porous rocks because of the heterogeneous distribution of stress over the grain surfaces the rate of chemical compaction depends on stress fluid pressure temperature and the composition of the pore fluid which itself depends on various processes that add or remove solute an alternative model of chemical compaction invokes the effect of sheet silicates on ph to account for localized dissolution of grains adjacent to stylolites or where sheet silicates are present along grain contacts in this model the rate of chemical compaction is independent of stress and fluid pressure depending only on temperature this model is untenable because the proposed mechanism cannot give rise to the persistent gradient in chemical potential required to drive diffusion however sheet silicates may increase the rate of chemical compaction because of their influence on dissolution and diffusion rates the development of anisotropic fabrics as a result of chemical compaction and the widespread occurrence of stylolites in carbonates as well as sandstones are inconsistent with the ph model and provide strong support for the role of stress in chemical compaction

rapid sea level rise and ice sheet response to 8 200 year climate event 1 the largest abrupt climatic reversal of the holocene interglacial the cooling event 8 6 8 2 thousand years ago ka was probably caused by catastrophic release of glacial lake agassiz ojibway which slowed atlantic meridional overturning circulation amoc and cooled global climate geophysical surveys and sediment cores from chesapeake bay reveal the pattern of sea level rise during this event sea level rose 14 m between 9 5 to 7 5 ka a pattern consistent with coral records and the ice 5g glacio isostatic adjustment model there were two distinct periods at 8 9 8 8 and 8 2 7 6 ka when chesapeake marshes were drown as sea level rose rapidly at least 12 mm yr 1 the latter event occurred after the 8 6 8 2 ka cooling event coincided with extreme warming and vigorous amoc centered on 7 9 ka and may have been due to antarctic ice sheet decay

the importance of sea level and climate change including changing wind energy on the evolution of a coastal estuary copano bay texas abstract 123 km of high resolution 2 d seismic lines and 6 sediment cores up to 16 m in length were collected from copano bay texas these data were used to examine the role of climate and sea level changes in the evolution of the bay paleogeographic maps of the bay were constructed to show how the bay evolved through time the overall transgression was punctuated by five environmental changes within copano bay over the past 9 6 ky the largest environmental change occurred at 8 2 ka when the bay head delta back stepped approximately 7 5 km as a result of a 0 4 1 2 m rapid rise in sea level with a well constrained model of how the bay changed through time textural data from the most continuous record of middle bay deposits was used to produce a proxy for wind strength over the last 8 2 ky our wind strength proxy reveals that copano bay experienced relatively tranquil winds during the early holocene followed by its windiest conditions from 5 2 to 4 1 ka and a return to more tranquil winds during the late holocene the wind strength proxy was compared with other published paleo climatic records for the region and a reasonable correlation was found between periods of higher wind energy and drier climate this study illustrates that despite their complex depositional systems and many sediment and water sources a system wide approach to studying an estuary can still be used to extract paleoclimate archives from estuarine deposits

a tem study of microstructures associated with solution cleavage in limestone abstract microstructures associated with clay filled seams in the scaglia rossa limestone from the umbria marche apennines italy were characterized with transmission electron microscopy tem in order to study one of the mechanisms that presently falls under the heading of pressure solution only seams that formed after lithification often called solution of spaced cleavage were examined although some observations supported suggestions that much of the clay in the solution cleavage seam could be authigenic this report focuses primarily on the limestone microstructures no evidence of plastic deformation could be observed around the seams with an optical microscope however the tem resolved dislocations concentrated within limited areas of single grains comparisons with experimentally deformed calcite microstructures and with computer simulations of tem dislocation contrast allowed further interpretation of the character and density of dislocations dislocation concentrations were frequently associated with voids and pits the pits and voids were usually elongate in a calcite dislocation slip plane and were interpreted as dissolution features these and other observations suggested that selective dissolution of localized dislocation tangles was responsible for solution cleavage formation similar microstructures associated with the stress corrosion cracking have been interpreted elsewhere as evidence of plastic strain enhanced heterogeneous dissolution further interpretations indicated that a solution cleavage surface grows laterally like a fracture tip

a 190 ky record of lithogenic grain size on the namibian slope forging a tight link between past wind strength and coastal upwelling dynamics abstract we inferred wind strength variations at the namibian coast and its effect on upwelling intensity over the last 190 ky by comparing grain size data and alkenone based sea surface temperatures ssts from one sediment core located on the upper slope off luderitz 25 6 s 13 38 e the wind strength proxy was defined by partitioning terrigenous grain size distributions gsds into two sub populations owing to a simple statistical model the fine poorly sorted component is assumed to include both fine aeolian dust and hemipelagic mud carried by rivers or winnowed from the shelf those two fractions are assumed to have been identically sorted during settling in the water column and are not distinguished by our approach the mode of the coarse well sorted sub population displays rapid high amplitude variations through time we ascribe a strictly aeolian origin to this component and consider that low altitude winds are able to carry coarse grained particles to the ocean as shown by grain size measurements of present dust material from the adjacent continent stuut j b w prins m a schneider r r weltje g j jansen j h f postma g 2002 a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic mar geol 180 221 233 variations in the coarse grained dust diameter are closely correlated with sst changes past ssts records from the namibian upper slope have been previously hypothesized as reflecting upwelling intensity combined with occasional injection of warm water from the angola dome we challenge this view in considering that past long term ssts variations are primarily induced by the wind strength and witness coastal upwelling intensity early mis 6 is the only period with evidences of warm poleward water intrusion at the core site the windiest conditions occurred during isotopic stages 3 and 4 the wind strength proxy defined in this study can be used confidently as an independent proxy for past upwelling intensity over the last two climatic cycles

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume