sedimentology of the bondi main heavy mineral beach placer deposit murray basin southeastern australia abstract drilling and pit wall exposures at the southern end of the bondi main heavy mineral beach placer deposit provided access to the loxton parilla sands which are here divided into five lithofacies the depositional environment of each lithofacies is interpreted as shoaling zone breaker zone surf zone swash zone and backshore dune other units encountered include the duddo limestone loddon river group bookpurnong formation and shepparton formation the interpreted depositional environments for these units are respectively shallow marine fluvial shallow marine shelf and fluvio lacustrine a palaeogeographical model is presented which proposes that the bondi main deposit formed at the southern end of a north trending shoreline this shoreline was truncated to the south by the dundas tableland and is broadly analogous in its geomorphological setting to the modern geographe bay in western australia the deposit therefore appears to have formed in association with a heavy mineral trap at its southern end postdepositional weathering overprints include ferruginous mottling clay eluviation and possibly quartz fracturing and disaggregation the ferruginous mottles formed under spatially and temporally variable redoximorphic conditions with fe being derived from the weathering of fe bearing primary minerals particularly ilmenite postdepositional clays in the loxton parilla sands are interpreted as being derived from the overlying shepparton formation

modeling an exogenic origin for the equatorial ridge on iapetus abstract iapetus has a ridge along the equator that extends continuously for more than 110 in longitude parts of the ridge rise as much as 20 km above the surrounding terrains most models for the formation of this enigmatic ridge are endogenic generally requiring the formation of a fast spinning iapetus with an oblate shape due to the rotation speed many of these require specific scenarios and have constraining parameters in order to generate a ridge comparable to what is seen today an exogenic formation mechanism has also been proposed that the ridge represents the remains of an early ring system around iapetus that collapsed onto the surface thus far none of the models have conclusively identified the origin of the ridge in this study an exogenic origin for the ridge is assumed which is derived from a collapsing disk of debris around iapetus without invoking any specific model for the generation of the debris disk here we evaluate whether it is possible to generate a ridge of the size and shape as observed by simulating the impact of the collapsing debris using the cth hydrocode pi scaling calculations suggest that extremely oblique impact angles 1 10 are needed to add to ridge topography these extreme impact angles severely reduce the cratering efficiency compared to a vertical impact adding material rather than eroding it during crater formation furthermore material is likely to be excavated at low angles enhancing downrange accumulation multiple impacts from debris pieces will heighten this effect because infalling debris is predicted to impact at extremely low angles both of these effects might have contributed to ridge formation on iapetus the extreme grazing angles of the impacts modeled here decouple much of the projectile energy from the target and impact heating of the surface is not significant these models suggest that a collapsing disk of debris should have been able to build topography to create a ridge around iapetus

on the application of simple rift basin models to the south polar region of enceladus 1 the south polar terrain spt of saturn s moon enceladus is a mysteriously active region that exhibits intriguing tectonic signatures and widespread fracturing the central region of the nearly circular spt is depressed into the surface by a few hundred meters and bounded by a ring of cliffs roughly 1 km high in this study we investigate whether this depression and surrounding mountainous uplift is consistent with the morphology of terrestrial rift basins and the possibility that the spt could have formed during a tectonic event analogous to those of such rift basins on earth using three mechanical models of basin formation we compare our predicted topography of the spt with observed topography of the region the first of three models we consider assumes crustal stretching by factor b and predicts a basin depth of roughly 600 m closely matching previously published estimates of the depth at the spt models of extension and compression assuming an elastic response in the ice crust predict best fit mountain uplift of roughly 1820 m and 1130 m respectively our preferred model suggests that the icy shell in the spt has been stretched but the extension is partially balanced by compression along the edges of the basin leading to the uplift of the mountains along the boundary thereby implying that the spt may have a tectonic origin analogous to that of a terrestrial basin

cassini imaging science initial results on phoebe and iapetus the cassini imaging science subsystem acquired high resolution imaging data on the outer saturnian moon phoebe during cassini s close flyby on 11 june 2004 and on iapetus during a flyby on 31 december 2004 phoebe has a heavily cratered and ancient surface shows evidence of ice near the surface has distinct layering of different materials and has a mean density that is indicative of an ice rock mixture iapetus s dark leading side cassini regio is ancient heavily cratered terrain bisected by an equatorial ridge system that reaches 20 kilometers relief local albedo variations within and bordering cassini regio suggest mass wasting of ballistically deposited material the origin of which remains unknown

delayed formation of the equatorial ridge on iapetus from a subsatellite created in a giant impact 1 the great equatorial ridge on saturn s moon iapetus is arguably the most perplexing landform in the solar system the ridge is a mountain range up to 20 km tall and sitting on the equator of iapetus and explaining its creation is an unresolved challenge models of its formation must satisfy three critical observations why the ridge 1 sits exactly on the equator 2 is found only on the equator and 3 is thus far found only on iapetus we argue that all previously proposed models fail to satisfy these observations and we expand upon our previous proposal that the ridge ultimately formed from an ancient giant impact that produced a subsatellite around iapetus the orbit of this subsatellite would then decay once iapetus itself had despun due to tides raised by saturn until tidal forces from iapetus tore the subsatellite apart the resultant debris formed a transient ring around iapetus the material of which rained down on the surface to build the ridge by sequestering the material in a subsatellite with a tidally evolving orbit formation of the ridge is delayed which increases the likelihood of preservation against the high impact flux early in the solar system s history and allows the ridge to form on thick stiff lithosphere heat flow likely 1 mw m 2 required to support this massive load without apparent flexure this mechanism thus explains the three critical observations

seismic velocities from the barbados ridge complex indicators of high pore fluid pressures in an accretionary complex three wide aperture 0 5 km offset seismic profiles were shot perpendicular to the strike of the barbados ridge accretionary complex at 16 12 n line 465 14 23 n line 480 and 13 20 n line 484 to image the deep structure of the accretionary complex and obtain seismic velocity data velocity analyses on full fold common depth point cdp gathers were used to provide velocity depth functions at 1 km separation along each line to map the variation in velocity with depth and distance across the accretionary complex the sediments within the complex show consolidation increasing laterally with greater age of the complex as indicated by the increase in seismic velocity and the inferred decrease in porosity the velocity at the base of the wedge along line 480 is 2 4 km s at the toe the velocity at the wedge base at 60 km from the toe where the wedge thickness has increased from 1 8 km to 5 0 km has increased to greater than 3 0 km s however the velocities within the leading margins and within undeithrust sequences in each of the three sections are low as much as 1 0 km s less than velocities found in undeformed sedimentary sequences of equivalent thickness the low velocity regions are interpreted as sediments with high porosity where porosity is inferred to be high pore fluid pressures are also inferred to exceed hydrostatic and pore fluids actually support the increased lithostatic load produced by recent thrusting and thickening of the complex the correlation between the most rapidly thickened regions and the velocity anomalies suggests that a rapid rate of loading relative to the rate of pore fluid expulsion produced these overpressured sediments velocities in the underthrust sequences where the differences between loading histories of wedge sediments and the underthrust sequences are largest are sufficiently low to produce velocity inversions low velocities also occur in regions adjacent to the complex where the pore fluid pressures may be elevated by the pressure produced in the adjacent wedge west of the wedge in the forearc basin along line 480 and near a seismically imaged mud diapir velocities at a depth of 3 5 km below the seafloor are 0 5 km s less than what is expected in a more normal sedimentary section immediately seaward of the complex the deepest undeformed sequences have a velocity anomaly of 0 5 km s velocities remain low for at least 12 km seaward of the complex but they become closer to a more normal sediment section farther from the wedge

fluid flow in and around a mud volcano field seaward of the barbados accretionary wedge results from manon cruise a field of mud diapirs and mud volcanoes situated in the barbados trench at 13 50 n and extending along an old oceanic fracture zone mercurus was investigated during the manon cruise using both surface ship and nautile submersible sampling and measurements the entire zone from 13 50 n up to 14 20 n has an anomalously high heat flow which implies that fluids are drained into it from a segment of the accretionary wedge a few hundred kilometers wide two structures interpreted as diatremes atalante and cyclops expell large amounts of water and methane we propose that they were formed from the release of a light fluid when gas hydrates were dissociated in the sediment as the result of the circulation of warm fluid in the area however they expell only a small fraction of the incoming fluid implying that disperse flow is the dominant mode of expulsion in this area the chemoautotrophic communities on the surface of the structures rely mostly on sulfides submersible observations temperature measurements in the sediment and the chemistry of the pore fluid indicate that convection of seawater occurs within the first few meters of sediment through high permeability channels such as cemented carbonate conduits we propose that this convection is driven by the density difference between the pore fluid and seawater but fresh water released by the dissolution of shallow hydrates may also contribute this shallow convection may be a frequent process in cold seep environments

folding of oceanic lithosphere folding of the lithosphere just south of the bay of bengal appears as 1 undulations in acoustic basement topography and 2 as linear geoid undulations in the seasat altimeter data from the seasat data we find that the east west trending folds have wavelengths ranging from 130 to 250 km and clustering about 190 km the horizontal gravity disturbances due to the folds range in amplitude from 15 to 50 mgal elastic models of oceanic lithosphere have in the past been used to demonstrate the implausibility of lithosphere buckling or folding in response to compression these elastic models typically predict that compressive stresses of about 5 gpa are required to buckle oceanic lithosphere with an age comparable to that of the northeastern indian ocean 40 70 ma these stresses exceed the strength of lithospheric rock we use an elastic plastic model to show that oceanic lithosphere of this age should have a net compressive strength equal to about 12 of the elastic buckling stress we further demonstrate that loads approaching the net compressive strength cause the lithosphere to fold with a wavelength about 200 km i e the wavelength observed from seasat our results reinforce earlier speculation that this folding may be related to the himalayan orogeny

water flow in the barbados accretionary complex we present a simple analytic kinematic model of the barbados accretionary complex assuming a porosity depth law and deformation by pure vertical shear the model is applied to two sections a northern one with a 900 m thick basin sedimentary column near 16 n and a southern one with a 4 5 km thick one to the south this simple model is compatible with growth of the barbados accretionary complex since 50 ma assuming a constant subduction rate and a constant basin sedimentary column equal to the present one this conclusion is not affected by reasonable changes in the porosity depth law it suggests that the totality of the entering sedimentary column is either accreted or subcreted to the wedge the accretion velocity decreases dramatically with age and its variation should be taken into account in any quantitative model the average strain rates show remarkably different distributions between the two sections the thinner wedge having a much higher rate in a narrow area at the toe we then use the model to compute the sediment grains flow the fluid flow and their thermal effects these effects are small and do not exceed 5 of the heat flow in the absence of other internal flows in contrast the thermal effect of the burial of the slab can result in a lowering of the surface heat flow by as much as 40 the temperature at the base of the wedge on its arc side is close to 300 c on the southern section and half that amount on the northern one this high temperature could account for the absence of large earthquakes to the south and their presence to the north the amount of water discharged if collected by faults over the whole toe area is unable to account for some of the manifestations observed over the toe or seaward of the toe in the barbados area we suggest two possible other sources one for the southern section is the orinoco fan area the other for the northern section might be seismic pumping at the limit of the seismogenic zone along the backthrusts between the accretionary wedge and the forearc basin

a contraction model for the flattening and equatorial ridge of iapetus others have explained the excess flattening of iapetus by a model in which the moon formed at a high spin rate achieved isostatic equilibrium by very rapid interior heating caused by short lived radioactive isotopes slri and subsequently cooled locking in the excess flattening with respect to an equilibrium shape at its present spin rate here we propose an alternate model that does not require an unusually high initial spin rate or the slri the initial formation of iapetus results in a slightly oblate spheroid with porosity 10 radioactive heating by long lived isotopes warms the interior to about 200 k at which point it becomes ductile and the interior compacts by 10 while the 120 km thick exterior shell remains strong the shell must deform to match the reduced volume of the ductile interior and we propose that this deformation occurs along the equator perhaps focused by a thinner equatorial shell the final shape of the collapsed sphere matches the observed shape of iapetus today described as an oblate ellipse except along the equator where strain concentration forms a broad ridge to maintain this non equilibrium shape the thickness of the shell must exceed 120 km testing the equatorial focusing hypothesis will require a model that includes non linear processes to account for the finite yield strength of the thick lithosphere nevertheless we show that the stress in the lithosphere generated by the contraction of the interior is about 3 times greater than the stress needed to deform the lithosphere so some type of lithospheric deformation is expected

porosity of sediments in accretionary prisms and some implications for dewatering processes rapid dewatering largely through loss of porosity is one of the most striking changes affecting deformed sediments in accretionary prisms analysis of porosity from sample and seismic data confirms that porosity in accretionary prisms is significantly less than that in basinal strata of similar lithology more specifically the porosity depth gradient increases arcward across the prism until porosities less than 10 occur within a few kilometers of the surface in deeper parts of the prism dewatering and volume reduction occur not only during loss of porosity but also during dehydration and metamorphic reactions calculations involving volume change lead us to define a function which reflects total volume reduction the distribution of the relative intensity of dewatering within the prism can be calculated from the porosity contours and trajectories of sediment elements an initial attempt indicates that in the toe region the rate of dewatering is accelerated at depth relative to the basinal section and may be greatest near the base of the prism toward the rear of the prism the maximum rate of dewatering occurs at progressively shallower depths several lines of evidence suggest that in addition to gradual diffuse dewatering localized zones of strong dewatering are associated with zones of intense shear this model of shear dewatering based on critical state soil mechanics suggests that sediments adjacent to the basal decollement should be strongly dewatered

mineralogical and sub microscopic aspects of iron oxides in polygenetic oxisols from minas gerais brazil iron oxides are known to be useful paleo environmental indicators and their properties may give information about past and present circumstances of weathering and soil formation iron oxides from polygenetic oxisols developed on saprolites of metamorphic rocks soil saprolite sequences and on sediments soil sediment sequences from minas gerais brazil were studied by x ray diffraction mossbauer spectroscopy micromorphology and electron microscopy to establish the connection between their properties and circumstances of formation hematite and goethite are the only iron oxides found in the clay and silt fractions micromorphology and mineralogy indicated the presence of three genetically different forms of hematite and four forms of goethite xrd and mossbauer spectroscopy indicate that these forms have differences in mean coherence length mcl and al substitution in soil saprolite sequences hematite is mainly formed during saprolite formation while goethite formed mainly during soil formation microscopic hematite formed in the saprolite has low al substitution and uniform mcl in response to soil formation it diminishes to submicroscopic size and goethite is formed towards toposoils goethite formed in yellow surface soils reflects recent soil formation and has high al substitution hematites and goethites related to gley phenomena have low al substitution and large mcls different coexisting forms of either goethite or hematite point to varying pedo environments either in time corroborating the polygenetic nature of the studied soils or at micron scale

evaluating trace elements as paleoclimate indicators multivariate statistical analysis of late mississippian pennington formation paleosols kentucky u s a abstract the temporal and spatial distributions of trace elements in paleosols in relation to soil forming processes and climate have received little attention primarily due to their generally low concentrations 100 ppm and a fundamental lack of knowledge of their behavior in soil systems trace element concentrations of pennington formation paleosols spanning an 8 ma interval in the late mississippian chesterian were analyzed using linear and multivariate statistics of whole rock elemental data linear statistics of the elemental data set show that ti zr nb cs la hf ta w ce and th have the highest correlation through time with r values 0 75 nb served as the proxy trace element for comparison temporal trends in nb closely match trends in lessivage clay formation and accumulation by feldspar weathering mean annual precipitation map and chemical weathering map effectively controls soil hydrology and the accumulation of organic matter and clay map in conjunction with chemical we

friction of ice the frictional strength of ice seems to be well below that for all other rocks triaxial testing of cylinders of pure water ice containing a 45 inclined sawcut at temperatures of 77 t 115 k and confining pressures 0 1 p 250 mpa reveals the frictional laws 0 20 n 8 3 mpa for p 10 mpa and 0 55 n 1 0 mpa for p 5 mpa where and n are the shear and normal stresses on the sawcut surface friction is independent of t and over the one order of magnitude tested of average sliding velocity the sliding behavior is invariably stick slip examination of sliding surfaces shows only minor gouge development a curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength these results apply to models of near surface tectonic activity on jupiter s three large icy moons europa callisto and ganymede they indicate for example that a global expansion on ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 3 km

the distinction between ground water gley and surface water gley phenomena in tertiary paleosols of the ebro basin ne spain abstract in studies of paleosols the distinction iron segregation due to either surface water or ground water fluctuatins is hardly ever made recognition of subsequent hydromorphic phases is even more rare nevertheless such distinctions can be made and are very useful in determining the paleoenvironment in this study we demonstrate that subsequent stages of hydromorphism and their sequence can be recognized in paleogene paleosols of the ebro basin it appears that in these carbonate rich hydromorphic oils goethite iron segregations are due to ground water influence while hematitic segregations are due to surface water the preservation of original mineralogy in this case is due to absence of late diagenetic transformations the results contradict the thesis that red colours in such paleosols would be the result of the late diagenesis in the studied samples mottledcolour patterns frequently indicate fairly advanced soil formation although weathering of primary minerals is almost absent detailed study of colour patterns gives much additional information on the post depositional environment

geochemistry and spatial distribution of heavy metals in oxisols in a mineralized region of the brazilian central plateau abstract the majority of the soils of the central plateau of brazil are product of long time development over stable surfaces usually associated with erosion and re deposition cycles in this context to successfully study the geochemistry and spatial distribution of heavy metals it is essential to understand the geology as well as the geomorphology of the landscape and the properties of the metals related to their mobility the main objective of this work was to evaluate contents of naturally occurring heavy metals co cu mn ni pb and zn in some highly weathered tropical soils as related to their geochemistry geology and geomorphology additionally it was aimed to interpret the spatial distribution patterns of these metals and of major elements al fe ti and mg evaluating the association and taking the influence of the geology and geomorphology into consideration in geo referenced sites ranging from 480 to 1040 m in altitude samples were collected at two depths 0 20 and 60 80 cm ground sieved and prepared for analysis heavy metals and major element contents were determined by extraction with aqua regia descriptive statistics pearson correlation coefficients principal components analysis pca and spatial variability analyses were conducted and soil metal concentrations for the whole area were predicted by kriging interpolation a close association between pb zn and mn was observed using pca and pearson s correlation highest concentrations of pb zn and mn were determined in soils between 650 and 550 m altitude surrounding the dolomite massif hills and ambrosia and fagundes mineral deposits copper and fe were found to be geochemically associated with highest concentrations observed in soils formed from carbonaceous phyllite with quartzite layers cobalt and ni concentrations were associated with areas characterized geomorphologically as alluvial colluvial deposits at the lowest altitudes within the region although there is a marked dispersive action of tropical weathering on metal distribution in the region cu pb and zn were found spatially associated with their geological source this probably happens because of greater affinity of those metals to fe and mn oxides formed predominantly under tropical conditions and present in higher concentrations near to the sources of these heavy metals on the other hand both the low affinity of ni and co for these oxide minerals and the region s geomorphology allowed for their migration towards the drainage network to the regions of sediment accumulation at lower altitudes during the landscape s evolution

ridge formation and de spinning of iapetus via an impact generated satellite abstract we present a scenario for building the equatorial ridge and de spinning iapetus through an impact generated disk and satellite this impact puts debris into orbit forming a ring inside the roche limit and a satellite outside this satellite rapidly pushes the ring material down to the surface of iapetus and then itself tidally evolves outward thereby helping to de spin iapetus this scenario can de spin iapetus an order of magnitude faster than when tides due to saturn act alone almost independently of its interior geophysical evolution eventually the satellite is stripped from its orbit by saturn the range of satellite and impactor masses required is compatible with the estimated impact history of iapetus

fluid flow and mass flux determinations at vent sites on the cascadia margin accretionary prism fluid venting from the toe of the accretionary prism off oregon was measured in situ during a series of dives with dsrv alvin in 1987 and 1988 a benthic chamber was placed over active vent sites to sequentially collect samples of venting fluids and to make direct measurements of discharge rates calibrated flow meter measurements and flow rates determined from dissolved methane transfer indicate that discharge from two vent sites alvin 1428 and alvin 1900 ranges roughly between 100 and 500 l m 2 d 1 with the most reliable estimates falling in the range of 125 150 l m 2d 1 these rates imply subsurface advective flow on the order of 100 m yr 1 comparison of observed discharge rates with rates calculated for steady state expulsion supported by accretion related compaction indicates that the observed flow is greater than predicted flow by several orders of magnitude the disparity dictates that fluids are not derived locally but are transported laterally within the prism or that flow is not steady state and that individual vents are short lived features in the ongoing accretion process

compositions and sources of fluids in sediments of the peru subduction zone sediments of the middle to lower slope regions of the peru continental margin drilled during ocean drilling program odp leg 112 contain interstitial waters with chloride concentrations as low as 454 mm cl equivalent to 20 dilution of seawater with fresh water strontium isotope data suggest that two separate fluid regimes are present a northerly one in which fluids contain more radiogenic sr than seawater 87sr 86sr up to 0 70996 possibly originating from continental crust and a southerly regime where fluids contain sr less radiogenic than seawater 87sr 86sr down to 0 70722 and which are also enriched in ca2 and depleted in mg2 and 18o that appear to have interacted with oceanic basement o c and he isotopic data support these interpretations

effect of diagenesis on the sr o and c isotope composition of late cretaceous mollusks from the western interior seaway of north america evaluating the effects of diagenesis on the isotopic compositions of sr o and c in marine carbonates is critical to their use as proxies in reconstructing information on the salinity temperature and dissolved inorganic carbon of ancient oceans we have analyzed a series of samples of mollusk shells from the baculites compressus zone late campanian of the pierre shale of south dakota samples included outer shell material and septa of cephalopods collected inside and outside concretions preservation was evaluated using light microscopy scanning electron microscopy sem trace element analysis and x ray diffraction all of the material consists of aragonite based on x ray diffraction an sem preservation index pi was established based on comparison of the microstructure of the fossil material with that of modern nautilus excellent preservation pi 5 was characterized by well defined nacreous plates with discrete angular boundaries in contrast samples showing fused nacreous plates with indistinct boundaries were rated poor pi 1 87sr 86sr ratios vary with preservation and average 0 707648 000021 n 10 for excellent preservation pi 5 0 707615 000028 n 5 for good preservation pi 3 0 707404 000074 n 7 for fair preservation pi 2 and 0 707261 000053 n 8 for poor preservation pi 1 these data suggest that as the quality of the preservation declines the mean 87sr 86sr ratio decreases and the standard error of the mean increases oxygen and carbon isotope analyses of the same specimens also show decreases with preservation and 18o 13c and 87sr 86sr are well correlated suggesting that these tracers are all altered as the pi decreases the sr ca ratio increases as preservation decreases indicating that sr is added to the shell material during diagenesis in contrast mg ca shows no trend with preservation if the increasing sr concentration and decreasing 87sr 86sr of the shell material with decreasing preservation represents the addition of sr to the shell during diagenesis we calculate that the added sr had 87sr 86sr ranging from 0 707582 to 0 707032 potential sources of the added sr include older marine carbonates and weathering of volcanic ash layers present in the shale the mechanisms of alteration likely include epitaxial growth of strontianite on the original shell aragonite and isotopic exchange of c and o between alteration fluids and shell carbonate we conclude that sem preservation criteria are effective in screening shell material that records original isotopic values and that variations in sr o and c isotope composition in well preserved material can be used to assess paleoenvironmental parameters such as salinity and temperature our results also indicate that assessing preservation is a critical prerequisite to the determination of numerical ages of shell material using strontium isotope stratigraphy

geogenesis pedogenesis and multiple causality in the formation of texture contrast soils abstract coarse over fine vertical texture contrasts vtc are common in soils and weathering profiles in a variety of environmental settings including many where inheritance or surficial processes alone cannot account for them a multiple causality model is presented here which shows that texture contrasts can form in response to a combination of ubiquitous phenomena there are six key elements downward translocation by water erosional winnowing soil mixing by bioturbation the tendency for surface clay additions to be mobilized while subsurface clays are more likely to remain in place and biological facilitation of moisture flux no element alone is sufficient to create a vtc but not all are necessary in any given regolith the model is illustrated by application to case studies in the ouachita mountains arkansas ridgetops in eastern kentucky the lower coastal plain of north carolina and the upper coastal plain of east texas the implications for interpretation of soils paleosols and weathering profiles is that the presence of a textural contrast by itself does not connote any particular set of geogenic or pedogenic processs or controls texture contrasts may be geogenic pedogenic or both given the widespread occurrence of the mechanisms of the multiple causality model vertical texture contrasts are inevitable

holocene environmental history at the treeline in the northern apennines italy a micromorphological approach the aim of this work is to investigate paleoenvironment at treeline quotas through the help of soil micromorphology it also assesses how the micromorphological approach can provide information in paleoenvironmental studies where paleosols are available as proxy archives nine soil profiles are described across the treeline between 1723 and 1860 m on mt cusna slope 2121 m a s l northern apennines italy undisturbed samples from selected soil horizons are collected in kubiena boxes from field observations all the profiles appear to be composed of two main pedogenetic units the upper one composed of a recent soil of colluvial origin and the deeper one consisting of an underlying more developed buried paleosol thin sections give detailed information about the nature and the origin of both pedological units four principal phases of paleosol development are detected a first period of temperate climate with forest cover and contrasted seasons is followed by a phase of change and then by a successive decrease of forest cover in a last phase the soil experiences frost action under the effect of a colder climate the final deposition of colluvium seems to be very recent historical time moreover multiple colluvial layers are identified colluvial material of different origins could be identified as part of dismantled soils similar to the preexisting paleosol in conclusion with the help of soil micromorphology it is possible to assess the existence of past stable forest at least 100 m above the present treeline the micromorphological approach represents a powerful tool in multidisciplinary paleoenvironmental studies due to its high level of resolution in outlining the individual and successive phases of soil evolution

testing models for the formation of the equatorial ridge on saturn s moon iapetus via crater counting abstract iapetus s equatorial ridge visible in global views of the moon is unique in the solar system the formation of this feature is likely attributed to a key event in the evolution of iapetus and various models have been proposed as the source of the ridge by surveying imagery from the cassini and voyager missions this study aims to compile a database of the impact crater population on and around iapetus s equatorial ridge assess the relative age of the ridge from differences in cratering between on ridge and off ridge and test the various models of ridge formation this work presents a database that contains 7748 craters ranging from 0 83 km to 591 km in diameter the database includes the study area in which the crater is located the latitude and longitude of the crater the major and minor axis lengths and the azimuthal angle of orientation of the major axis analysis of crater orientation over the entire study area reveals that there is no preference for long axis orientation particularly in the area with the highest resolution comparison of the crater size frequency distributions show that the crater distribution on the ridge appears to be depleted in craters larger than 16 km with an abruptly enhanced crater population less than 16 km in diameter up to saturation one possible interpretation is that the ridge is a relatively younger surface with an enhanced small impactor population finally the compiled results are used to examine each ridge formation hypothesis based on these results a model of ridge formation via a tidally disrupted sub satellite appears most consistent with our interpretation of a younger ridge with an enhanced small impactor population

tectonics on iapetus despinning respinning or something completely different abstract saturn s moon iapetus is unique in that it has apparently despun while retaining a substantial equatorial bulge stresses arising from such a non hydrostatic shape should in principle cause surface deformation tectonics as part of a search for such a tectonic signature lineaments linear surface features on iapetus were mapped on both its bright and dark hemispheres lineament orientations were then compared to model stress patterns predicted for spin down from a rotation period of 16 5 h or less to its present synchronous period and for a range of lithospheric thicknesses many lineaments are straight segments of crater rimwalls which may be faults or joints reactivated during complex crater collapse most striking are several large troughs on the bright trailing hemisphere these troughs appear to be extensional and are distinctive on that hemisphere because the interior floors and walls of the troughs contain dark material globally no specific evidence of strike slip or thrust offsets are seen but this could be due to the age and degraded nature of any such features we find that observed lineament orientations do not correlate with predicted patterns due to despinning on either hemisphere the equatorial ridge was specifically excluded from this analysis and is considered separately modest evidence for preferred orientations 40 from north could be construed as consistent with respinning which is not necessarily far fetched assuming the rigidity of unfractured ice predicted maximum lithospheric differential stresses from despinning range from 1 mpa to 160 mpa for the elastic spheroid and thin lithosphere limits respectively although it is only for thicker elastic lithospheres that we expect a nonhydrostatic state to be maintained over geologic time against lithospheric failure the tectonic signature of despinning may have been obscured over time because the surface of iapetus is very ancient iapetus thick lithosphere may have inhibited the full tectonic expression of despinning or both several prominent lineaments strike e w and are thus parallel to the equatorial ridge though not physically close to it but a tectonic or volcanic origin for the ridge is highly problematic

nankai trough japan trench and kuril trench geochemistry of fluids sampled by submersible nautile abstract deep water samples collected during the kaiko project are often associated with biological communities located on geological structures favorable to fluid venting the evidence of fluid venting are the temperature anomalies the decrease in sulfate concentrations the content in methane and the lowc 1 c 2 c 3 ratio of light hydrocarbons because of large dilution by ambiant seawater during sampling it is difficult to compute the composition of the advected end member pore fluid part of this fluid should originate in the petroleum window i e at temperature about 60 c modeling the upward flow of water taking into account the anomalies of temperature measured on the seafloor and the geochemical anomalies leads to non steady state advection of the pore fluid the occurrence of a deep component in the fluid has implications for the geological and tectonic models of the subduction zones off japan

weathering trends and parent material characteristics of polygenetic oxisols from minas gerais brazil i mineralogy in geologically stable areas in the tropics climatic changes and geomorphic cycles give origin to polygenetic soils polygenesis involves new soil formation phases taking place on preweathered materials from previous phases resulting in soils with rather similar chemical and mineralogical properties polygenetic soils from minas gerais brazil were investigated with the purpose of distinguishing mineralogical aspects in relation to polygenesis the soil materials were studied by micromorphology and electron microscope and analyzed by xrd all soils are strongly weathered and even show weathered grains of ilmenite and quartz the soils show two phases of kaolinite formation pseudomorphs after mica and precipitation from solution and of accumulation of iron compounds desilication causes gibbsite formation from kaolinite occasionally even in the deep saprolite superposed processes can be due to progressively deeper weathering or to changes of the external environment

on a ring origin of the equatorial ridge of iapetus 1 most recent cassini observations by the imaging science subsystem iss showed that the third largest saturnian satellite iapetus has a curious ridge system exactly aligned with its equator porco et al 2005 because iapetus has a large hill sphere for the trapping of circum satellitary material a ring system might have been present during its formation a scenario is proposed to describe how the equatorial ridge system could have been produced by the collisional accretion of a ring remnant subsequent to the formation of the proto iapetus

geochemistry of the tenryu canyon deep sea fan biological community kaiko abstract the tenryu canyon deep sea fan biological community is characterized by both reduced and oxidized sediments in the immediate vicinity of the pore water vents the upper sediments in contact with the clams are reduced the organic matter is enriched in sulfur and inorganic sulfides fe cu zn are forming towards the outer fringes of the communities the sediment is oxidized and metals generally associated with ferro manganese oxides are concentrated several metals cd pb mo show distributions which are strongly influenced by the metabolism of the clam colony comparison of water and sediment geochemistry leads to the conclusion that there should be a downward flux of oxygenated seawater on the boundaries of the colony and an upward flux of chemically more reduced deep pore water at the location of the colony trace metals anomalies as well as 15n anomalies of organic matter may be useful to prospect for extinct venting areas in ancient subduction zones

formation of the bulge of iapetus through long wavelength folding of the lithosphere abstract previous models that attempted to explain the formation of the pronounced oblate shape of iapetus suggested that it was a preserved rotational bulge these models found that heating was provided by short lived radioactive isotopes that decayed rapidly and allowed the excess flattening of the lithosphere to be locked in by a thickening lithosphere but placed severe timing constraints on the formation of iapetus and its bulge here we show that finite element simulations with an elastic viscous plastic rheology indicate it is possible to form the bulge through long wavelength folding of the lithosphere of iapetus during an epoch of contraction combined with a latitudinal surface temperature gradient in contrast to models of a frozen rotational bulge heat generated by long lived radioactive isotopes warms the interior which causes porosity loss and forces iapetus to compact by 10 our simulations are most successful when there is a 30 k temperature difference between the pole and the equator tectonic growth of the bulge is not sensitive to the time scale over which the moon contracts and lithospheric thickness primarily controls whether a fold can form not fold wavelength in addition long term simulations show that when no stress is applied the mechanical lithosphere is strong enough to support the bulge with negligible relaxation over billion year time scales

alluvial fan and wetland interactions evidence of seasonal slope wetlands from the silurian of south central wales uk distal environs of the ludlow age trichrug formation from south central wales uk detail deposition on the outer fringe of an ephemeral debris flow dominated alluvial fan debrites and subordinate sheetflood deposits are interbedded with sporadic thin sandstone dominated heterolithic units deposited in shallow ephemeral ponds in the axial valley the latter slope wetland system fringed the permeable alluvial fan deposits being maintained by streamflow precipitation and ground water recharge a prolonged high water table is indicated by low chroma intervals interpreted as the result of gleying a variety of redoximorphic indicators including colour mottling and ferricrete concretions are evidence of iron mobilization and concentration associated with a seasonally fluctuating water table the slope wetlands were colonized periodically by skolithos generating organisms most likely to have been arthropods the widespread occurrence of redoximorphic indicators and ferricrete contrasts markedly with calcrete vertisols in penecontemporaneous continental deposits lower old red sandstone of the region it is likely that the alluvial fan toe area was the site of a wetland depression which maintained a high though fluctuating water table in contrast the alluvial channel reaches of the surrounding drainage network were significantly better drained with floodplains prone to wetting and drying and vertisol palaeopedogenesis

bromine and iodine in peru margin sediments and pore fluids implications for fluid origins at the peruvian convergent margin two distinct pore fluid regimes are recognized from differences in their cl concentrations the slope pore fluids are characterized by low cl concentrations but elevated br and i concentrations due to biogenic production the shelf pore fluids exhibit elevated cl and br concentrations due to diffusive mixing with an evaporitic brine in the slope pore fluids the br i and nh4 concentrations are elevated following bacterial decomposition of organic matter but the i concentrations are in excess of those expected based on mass balance calculations using nh4 and br concentrations the slope sediment organic matter which is enriched in iodine from oxidationreduction processes at the oxygenated sediment water interface is responsible for this enrichment the increases in dissolved i and the i enrichments relative to nh4 and br correlate well with sedimentation rates because of differential trapping following regeneration the pore fluid i br ratios suggest that membrane ion fiitration is not a major cause of the decreases in cl concentrations other possible sources for low cl water including meteoric water clathrate dissociation and or mineral dehydration reactions imply that the diluting component of the slope low cl fluids has flowed at least 1 km through the sediment the low bottom water oxygenation in the shelf is responsible for the low if any enrichment of iodine in the shelf sediments fluctuations in bottom water oxygen concentrations in the past however may be responsible for the observed variations in the sediment ibr ratios comparison of na cl and br cl molar ratios in the pore fluids shows that the shelf high cl fluid formed from mixing with a brine that formed from seawater concentrated by twelve to nineteen times and probably was modified by halite dissolution this dense brine located below the sediment sections drilled appears to have flowed a distance 500 km through the sediment

iapetus geophysics rotation rate shape and equatorial ridge iapetus has preserved evidence that constrains the modeling of its geophysical history from the time of its accretion until now the evidence is a its present 79 33 day rotation or spin rate b its shape that corresponds to the equilibrium figure for a hydrostatic body rotating with a period of 16 h and c its high equatorial ridge which is unique in the solar system this paper reports the results of an investigation into the coupling between iapetus thermal and orbital evolution for a wide range of conditions including the spatial distributions with time of composition porosity short lived radioactive isotopes slri and temperature the thermal model uses conductive heat transfer with temperature dependent conductivity only models with a thick lithosphere and an interior viscosity in the range of about the water ice melting point can explain the observed shape short lived radioactive isotopes provide the heat needed to decrease porosity in iapetus early history this increases thermal conductivity and allows the development of the strong lithosphere that is required to preserve the 16 h rotational shape and the high vertical relief of the topography long lived radioactive isotopes and slri raise internal temperatures high enough that significant tidal dissipation can start and despin iapetus to synchronous rotation this occurred several hundred million years after iapetus formed the models also constrain the time when iapetus formed because the successful models are critically dependent upon having just the right amount of heat added by slri decay in this early period the amount of heat available from short lived radioactivity is not a free parameter but is fixed by the time when iapetus accreted by the canonical concentration of 26al and to a lesser extent by the concentration of 60fe the needed amount of heat is available only if iapetus accreted between 2 5 and 5 0 myr after the formation of the calcium aluminum inclusions as found in meteorites models with these features allow us to explain iapetus present synchronous rotation its fossil 16 h shape and the context within which the equatorial ridge arose

the topography of iapetus leading side abstract we have used cassini stereo images to study the topography of iapetus leading side a terrain model derived at resolutions of 4 8 km reveals that iapetus has substantial topography with heights in the range of 10 km to 13 km much more than observed on the other middle sized satellites of saturn so far most of the topography is older than 4 ga neukum g wagner r denk t porco c c 2005 lunar planet sci xxxvi abstract 2034 which implies that iapetus must have had a thick lithosphere early in its history to support this topography models of lithospheric deflection by topographic loads provide an estimate of the required elastic thickness in the range of 50 100 km iapetus prominent equatorial ridge porco c c and 34 colleagues 2005 science 307 1237 1242 reaches widths of 70 km and heights of up to 13 km from their base within the modeled area the morphology of the ridge suggests an endogenous origin rather than a formation by collisional accretion of a ring remnant ip w h 2006 geophys res lett 33 doi 10 1029 2005gl025386 l16203 the transition from simple to complex central peak craters on iapetus occurs at diameters of 11 3 km the central peaks have pronounced conical shapes with flanking slopes of typically 11 and heights that can rise above the surrounding plains crater depths seem to be systematically lower on iapetus than on similarly sized rhea which if true may be related to more pronounced crater wall slumping which widens the craters on iapetus than on rhea there are seven large impact basins with complex morphologies including central peak massifs and terraced walls the largest one reaches 800 km in diameter and has rim topography of up to 10 km generally no rings are observed with the basins consistent with a thick lithosphere but still thin enough to allow for viscous relaxation of the basin floors which is inferred from crater depth to diameter measurements in particular a 400 km basin shows up domed floor topography which is suggestive of viscous relaxation a model of complex crater formation with a viscoplastic bingham rheology melosh h j 1989 impact cratering oxford univ press new york of the impact shocked icy material provides an estimate of the effective cohesion viscosity at 0 04 0 01 mpa 0 6 0 2 gpa s the local distribution of bright and dark material on the surface of iapetus is largely controlled by topography and consistent with the dark material being a sublimation lag deposit originating from a bright icy substrate mixed with the dark components but frost deposits are possible as well

the dark side of iapetus abstract this paper presents new photometric and spectrophotometric observations of the dark leading hemisphere of saturn s satellite iapetus spectrophotometry from 0 3 1 0 um may 1979 shows the dark hemisphere to be very red similar to a few asteroids and the moon but with no spectral features attributable to olivine or pyroxene near infrared spectrophometry in the regions 1 4 2 5 um may 1981 and 3 0 3 8 um february 1981 reveals water ice absorption bands probably resulting from the polar caps intruding onto the dark hemisphere the reflectance of iapetus is unlike that of carbonaceous chondrites or c type asteroids and most closely resembles the reflectance and low albedo of carbonaceous organic residue from the murchison c2 carbonaceous chondrite the murchison material has the same red slope and a probable spectral feature near 0 6 um seen in iapetus data three hypotheses for the formation of the dark hemisphere are discussed in light of the observational data the favored hypothesis is that debris from phoebe or other unknown outer satellites of saturn impacts the dark hemisphere of iapetus as poynting robertson drag causes the debris to spiral toward saturn the high velocity impacts preferentially remove ice from the satellite s surface causing enrichment of included carbonaceous material intrinsic to iapetus the reflectance of phoebe itself is significantly different from that of iapetus suggesting that relatively little phoebe debris lies on the dark hemisphere there remains the possibility that the impacting debris originates from another body of composition similar to the murchison residue and that this material is exposed on the surface of iapetus

mud volcano field seaward of the barbados accretionary complex a deep towed side scan sonar survey a 30 km2 diapiric field has been identified near 13 50 n up to 12 km seaward of the deformation front of the barbados accretionary complex using a deep towed side scan sonar with a 3 5 khz profiler we identified 31 different diapiric structures based on seismic stratigraphy we show that this field has been active for 200 000 years and that it is a transient feature triggered by the seaward propagation of the high pore fluid pressure associated with the decollement beneath the accretionary complex both basement and decollement in this area are anomalously shallow due to the presence of a n110 basement ridge the height of the diapirs above seafloor does not exceed 40 50 m and can be related to the pressure head of the mud below the decollement two types of structures are identified mud volcanoes and massively emplaced diapirs and ridges on the one hand enigmatic circular very flat mud pies and conical mounds on the other hand the second type of structures has steeper slopes and appears to be associated with very active venting as confirmed by a submersible exploration reported in a companion paper le pichon et al this issue b the venting results in the formation of a stiff carbonate crust and of large subsiding basins around the mud pies continuous active fluid expulsion through these structures indicates that an efficient piping system still connects them to the zone of anomalously high pore pressure below the protodecollement

constraints on yield strength in the oceanic lithosphere derived from observations of flexure summary the wavelength and amplitude of outer rises seaward of sub duction zones and arches surrounding islands and seamounts are used to parameterize flexure profiles in terms of the moment and curvature at the first zero crossing the data show the clear age dependence in the mechanical thickness of the lithosphere up to 60 100myr saturation of moment at large curvature is interpreted in terms of a depth dependent yield strength for the lithosphere using relations adopted from laboratory experiments of rock deformation a comparison of theoretical curves with observed moments indicates that old oceanic lithosphere has no long term strength below about 40 km depth with no difference between 100 and 165 myr old crust moderate axial loading forces 200 mpa can explain most variations in the moment curvature observations except in the case of the kuril trench which appears anomalous given the age of the crust regional tension causes greater variability in moment as compared to regional compression because of the greater slope in the brittle failure envelope under tension the observations point to a lithosphere weaker than the prediction from experimental deformation of rocks of the possible weakening mechanisms elevated pore fluid pressure on faults does not predict the correct age dependence and is incompatible with earthquake focal mechanisms our favoured explanation is that the activation energy q appropriate for ductile flow at geological strain rates is lower than the values derived from laboratory extrapolations of dry olivine data taken at high temperatures if recent oceanic geotherms are reliable q in the lower lithosphere must be lower than 100kcal mol 1 the method used here is most appropriate for trench profiles with curvatures greater than 10 7m 1 for lower curvatures such as along seamount profiles small errors in the curvature estimate cause large changes in rheological parameters

seawater sr isotope variation over the past 300 kyr and influence of global climate cycles the past 300 000 years have been characterized by glacial inter glacial fluctuations accompanied by glacio eustatic changes in sea level and changes in continental erosion arising from varying low latitude rainfall and river drainage here we use measurements of strontium isotopes in foraminifera and corals to place limits on variations in the sr isotope composition of sea water in response to these changing inputs we find small variations of about 20 p p m in the 87sr 86sr ratio which for the foraminiferal record seem to follow a cycle close to the 100 kyr periodicity seen for a number of other climate related phenomena these are superimposed on a general increase in87sr 86sr through the cenozoic to the present on short timescales these changes are likely to be controlled by variations in the global riverine sr flux and thus by weathering rates rather than in the hydrothermal sr flux at mid ocean ridges we show that transient variations over a 50 kyr timescale can be explained on the basis of the present day global drainage system in conjunction with the perturbations expected to accompany climate changes over the past 300 kyr

shapes of the saturnian icy satellites and their significance the sizes and shapes of six icy saturnian satellites have been measured from cassini imaging science subsystem iss data employing limb coordinates and stereogrammetric control points mimas enceladus tethys dione and rhea are well described by triaxial ellipsoids iapetus is best represented by an oblate spheroid all satellites appear to have approached relaxed equilibrium shapes at some point in their evolution but all support at least 300 m of global wavelength topography the shape of enceladus is most consistent with a homogeneous interior if enceladus is differentiated its shape and apparent relaxation require either lateral inhomogeneities in an icy mantle and or an irregularly shaped core iapetus supports a fossil bulge of over 30 km and provides a benchmark for impact modification of shapes after global relaxation satellites such as mimas that have smoother limbs than iapetus and are expected to have higher impact rates must have relaxed after the shape of iapetus was frozen

major and trace element and sr isotope constraints on fluid circulations in the barbados accretionary complex part 1 fluid origin abstract we measured the chemical and sr isotope compositions of vent and pore fluids and associated sediments from a diapiric field located near 13 5 n east of the deformation front of the barbados accretionary complex the two diapiric structures with the largest thermal anomalies and characterized by active fluid conduits exhibit the strongest chemical and 87 sr 86 sr variations these two diatremes atalante and cyclope also have low chloride contents and non radiogenic 87 sr 86 sr which may be explained by interaction between seawater and volcanic ash or with underlying oceanic crust in the central zone of the two structures 87 sr 86 sr varies little with depth which implies that fluid expulsion is at such a high rate that it is not affected by seawater 87 sr 86 sr the expelled fluids probably circulate along the decollement zone and ascend along faults which act as channels a deep component is probably located in the decollement zone whereas another component may be recirculated seawater the ascending fluid interacted with numerous materials causing dehydration of clay minerals and alteration of volcanic ash and or underlying oceanic crust to explain the low chloride contents of the atalante fluids gas hydrate decomposition yielding dilution of the fluid without modifying its sr isotope ratio needs to be superimposed on the mixing between seawater and the deep component the occurrence of gypsum in these two diatremes implies higher fluid temperatures and more intense activity at least temporarily to allow the deposition of such a mineral

mud diapirism and subcretion in the barbados ridge accretionary complex the role of fluids in accretionary processes mud diapirism has recently been recognized in several modern accretionary wedges it provides an important means of dewatering accretionary wedges and should be regarded as an important process for producing the melanges found in both modern and ancient accretionary terranes mud diapirism affects a large area of the barbados ridge accretionary complex the distribution of the mud diapirs appears to be primarily controlled by the presence of underconsolidated terrigenous submarine fan deposits that are being accreted to the complex the frequency of diapir occurrence decreases northward as the fan becomes thinner mud diapirs are absent from the very eastern most part of the complex formed from sediments accreted at its toe with the exception of a few mud volcanoes on the ocean floor in front of the complex the initiation of diapirism appears to be spatially coincident with the onset of subcretion or underplating of sediment to the base of the complex at a ramp between two levels of decollement it is proposed that the release of mud and pore water from the subcreted sediments is a direct or indirect cause of most of the mud diapirism in the accretionary complex there is a range of diapiric form dependent on the viscosity of the mud from mud volcanoes fed by low viscosity mud to higher viscosity mud ridges the diapirs in the eastern areas of the complex are generally mud volcanoes with narrow conduits feeding a surface mound mud ridges are prominent in the western parts of the complex this is interpreted as reflecting a general westward decrease in the fluid content of the accretionary complex bottom simulating seismic reflectors formed by gas hydrate are commonly developed in the areas of mud volcano occurrences the presence of the hydrate indicates that large volumes of methane are being generated at depth in these regions the generation of methane may be contributing to zones of overpressuring in the wedge methane may also be partly responsible for driving the diapiric material to the surface to form mud volcanoes ridges in the subducting oceanic crust beneath the accretionary complex locally enhance diapirism above their crests and southern flanks faults formed later in the development of the complex are more commonly associated with diapirism than those resulting from accretion at the toe of the wedge these later faults play an important role in controlling the sites of individual mud volcanoes chains of mud volcanoes and mud ridges

origins and implications of soil layering abstract layering is common in soils due to a variety of pedologic and geologic processes and has important consequences for the interpretation of soils and landscapes layering can derive from original sedimentary layering depositional upbuilding episodic surface erosion deposition and stability soil production by weathering vertical or lateral translocation bioturbation and various combinations of these complex and polygenetic models incorporate both geogenic and pedogenic processes and allow for physical and biological processes as well as both vertical and horizontal movements we review these conceptual frameworks and synthesize them into a vertical contrast model vcm for interpreting layered surficial materials the vcm incorporates a variety of geologic and pedologic processes which may create destroy enhance or obscure vertical contrasts the model is illustrated via application to sites in the ouachita mountains usa and northwest saxonian lowlands germany the examples illustrate the importance of a comprehensive pedogeomorphic interpretation of layering since neither standard stratigraphic or top down pedogenetic principles necessarily apply the examples also show that the same process can sometimes contemporaneously both create and destroy vertical contrasts

spatial variability of soil hydraulic conductivity along a tropical rainforest catena abstract we investigate the spatial variability of saturated hydraulic conductivity ksat along a tropical rainforest catena which consists of a typic kandiudult latossolo vermelho distrofico argissolico and plinthic hapludox latossolo amarelo distrofico tipico the former soil type extends from midslope to interfluve and has a high clay content throughout the profile whereas the latter soil type extends from the midslope to valley bottom and only has a high clay content at depths 90 cm we measured ksat along a transect at depths of 20 30 50 and 90 cm with a compact constant head permeameter ksat is not significantly different 0 10 between these soil types at any depth except for 90 cm ordinary and robust linear regression models with distance from the interfluve as in the independent variable showed no significant change in ksat as a function of topography loess regression showed some dependency of ksat on topography only at the 90 cm depth semivariograms showed no apparent spatial structure in ksat at distances 25 m for all depths we conclude that the strong topography dependence of soil types along this catena and hence primary soil attributes is not reflected in a similar dependence of ksat and tentatively attribute this lack of dependence to the overriding influence of bioturbation controlled macroporosity we outline a framework for detecting possible ksat topography relationships based on the distinction between bioturbation controlled nonstructural macroporosity and mineralogy controlled structural macroporosity

thin elastic shells with variable thickness for lithospheric flexure of one plate planets summary planetary topography can either be modelled as a load supported by the lithosphere or as a dynamic effect due to lithospheric flexure caused by mantle convection in both cases the response of the lithosphere to external forces can be calculated with the theory of thin elastic plates or shells on one plate planets the spherical geometry of the lithospheric shell plays an important role in the flexure mechanism so far the equations governing the deformations and stresses of a spherical shell have only been derived under the assumption of a shell of constant thickness however local studies of gravity and topography data suggest large variations in the thickness of the lithosphere in this paper we obtain the scalar flexure equations governing the deformations of a thin spherical shell with variable thickness or variable young s modulus the resulting equations can be solved in succession except for a system of two simultaneous equations the solutions of which are the transverse deflection and an associated stress function in order to include bottom loading generated by mantle convection we extend the method of stress functions to include loads with a toroidal tangential component we further show that toroidal tangential displacement always occurs if the shell thickness varies even in the absence of toroidal loads we finally prove that the degree one harmonic components of the transverse deflection and of the toroidal tangential displacement are independent of the elastic properties of the shell and are associated with translational and rotational freedom while being constrained by the static assumption degree one loads can deform the shell and generate stresses the flexure equations for a shell of variable thickness are useful not only for the prediction of the gravity signal in local admittance studies but also for the construction of stress maps in tectonic analysis

the development of deep soil processes in ancient kurgans of the north caucasus abstract in the past four thousand years luvisols with a clearly differentiated profile have developed on kurgans of the bronze age under beech and oak stands in humid climatic conditions of the foothills of the north caucasus the great height of the kurgans up to 10 m and their homogeneous composition the kurgans were constructed of chernozemic soil and are underlain by chernozem make it possible to study the direction and rate of pedogenetic and diagenetic processes acting at a considerable depth in these kurgans the profiles of luvisols are underlain by the carbonate illuvial horizon that has been shaped by illuviation processes acting for about 4000 years the major part of this horizon lies at the depths of 110 350 cm though carbonates penetrate as deep as 9 m along the deep earthworm burrows at this depth they occur within the noncalcareous mass of the lower part of the kurgans bodies and in the upper part of the underlying chernozem at the depth of 5 9 m in the kurgans and in the buried chernozem gypsum and iron pedofeatures nodules and red brown films on ped faces have appeared humus clayey infillings are present in some of the earthworm burrows at this depth the formation of such a deep profile with the carbonate illuvial gypsiferous and ferruginated horizons is related to the local bioclimatic conditions characterized by high precipitation and the growth of forest vegetation deep washing of the soil with atmospheric precipitation is combined with the manifestation of illuviation processes and alteration of the soil mass at a considerable depth the mineralization of humic substances and some alkalization of the soil mass also take place in the deep horizons however these processes may occur at different depths independently from the illuviation processes and can be attributed to the group of diagenetic processes

geochemical and biogeochemical observations on the biological communities associated with fluid venting in nankai trough and japan trench subduction zones we have studied the compositions and structure of the lamellibranchiacalyptogena sp associated with fluid venting in subduction zones off japan the gills of thecalyptogena are the habitat of symbiotic bacteria which develop owing to chemoautotrophy they most probably assimilate hydrogen sulfide methane and or carbon dioxide and reduce nitrogen the isotopic budget of methane uptake enables to establish the thermal diagenetic origin of the light hydrocarbons brought by the upwelling fluids the microscopic examination of thin sections of the bacteria enables to establish that their membranes are compatible with uptake of inorganic nutrients and to establish relations with the metabolism of archeobacteria

despinning and shape evolution of saturn s moon iapetus triggered by a giant impact abstract iapetus possesses two spectacular characteristics i a high equatorial ridge which is unique in the solar system and ii a large flattening a c 34 km inconsistent with its current spin rate these two main characteristics have probably been acquired in iapetus early past as a consequence of coupled interior rotation evolution previous models have suggested that rapid despinning may result either from enhanced internal dissipation due to short lived radioactive elements or from interactions with a sub satellite resulting from a giant impact for the ridge formation different exogenic and endogenic hypotheses have also been proposed but most of the proposed scenarios have not been tested numerically in order to model simultaneously internal heat transfer tidal despinning and shape evolution we have developed a two dimensional axisymmetric thermal convection code with a deformable surface boundary coupled with a viscoelastic code for tidal dissipation the model includes centrifugal and buoyancy forces a composite non linear viscous rheology as well as an andrade rheology for the dissipative part by considering realistic rheological properties and by exploring various grain size values we show that in the absence of additional external interactions despinning of a fast rotating iapetus is impossible even for warm initial conditions t 250 k alternatively the impact of a single body with a radius of 250 350 km at a velocity of 2 km s may be sufficient to slow down the rotation from a period of 6 10 h to more than 30 h by combining despinning due to internal dissipation and an abrupt change of rotation due to a giant impact we determined the parameters leading to a complete despinning and we computed the corresponding shape evolution we show that stresses arising from shape change affect the viscosity structure by enhancing dislocation creep and can lead to the formation of a large scale ridge at the equator as a result of rapid rotation change for initial rotation periods of 6 h

heat flow tectonics and fluid circulation at the toe of the barbados ridge accretionary prism detailed patterns of near surface tectonics and heat flow were investigated at two locations at the toe of the barbados ridge accretionary prism at the two locations in the thickly sedimented southern portion of the prism near 12 20 n and in the northern area drilled during ocean drilling program odp leg 110 near 15 32 n relative highs of heat flow were associated with zones of thrusting we attribute them to upward advection of water rising from the decollement along faults through the sediments in the odp area a significant heating plate effect from warm fluids flowing along the decollement and thrusts is required to account for the high regional heat flow this effect implies high rates of fluid flow at the decollement which can only be non steady state or would require massive lateral transport of fluids along strike

transient fluid flow through the toe of the barbados accretionary complex constraints from ocean drilling program leg 110 heat row studies and simple models thirty four sediment and mud line temperatures were collected from six drill holes on ocean drilling program odp leg 110 near the toe of the barbados accretionary complex when combined with thermal conductivity measurements from sediment cores and results from earlier surveys these data delineate the complicated thermal structure on the edge of this convergent margin heat flow values at the seafloor of 92 192 mw m sup 2 are 80 300 higher than those predicted by standard heat flow versus age models for oceanic crust but are compatible with earlier seafloor measurements made in this area at the same latitude heat flow tends to decrease downhole at four sites suggesting the presence of heat sources within the sediments these results are consistent with the flow of warm fluids through the complex along high permeability conduits including thrust faults the major decollement zone and sandy intervals simple calculations suggest that this fluid flow is transient occurring on time scales of tens of thousands of years fluid flow velocities along the decollement zone estimated with a simple thermal model are about 10 sup minus 7 m s 100 times faster than predicted by numerical steady state analyses the estimated maximum sediment permeability within the decollement zone which was basedmore on the above fluid flow velocity is about 10 sup minus 12 m sup 2 also 100 times higher that that calculated numerically high heat flow in the vicinity of 15 degree 30 prime n and not elsewhere along the deformation front suggests that the leg 110 drill sites may be situated over a prism water discharge zone with dewatering more active here than elsewhere along the accretionary complex less

interpretation of temperature measurements from the kaiko nankai cruise modeling of fluid flow in clam colonies during the kaiko nankai detailed submersible survey numerous measurements of the temperature gradient inside the sediment were performed on the deepest active zone of fluid venting which is situated on the anticline related to the frontal thrust using the ifremer t naut temperature probe operated from the submersiblenautile we thus obtained the temperature structure below different types of clam colonies associated with fluid venting we used the finite element method to model the thermal structure and fluid flow pattern of these vents and to determine the velocity of upward fluid flow through the colonies on a biological basis four types of clam colonies are defined each biological type has distinctive thermal characteristics and corresponds to a particular fluid flow pattern darcian flow velocity in the most active type of colony type a is of the order of 100 m a the total amount of fluid flowing through colonies in the studied area is estimated to be 200 m3 a 1 per metre width of subduction zone most of the flow is vented through type a colonies this value is more than one order of magnitude too high to be compatible with the amount of water available from steady state compaction of sediments in the whole wedge thermal arguments suggest that downwelling of seawater occurs around type a colonies and that seawater is then mixed with upcoming fluids at a depth of 1 or 2 metres furthermore finite element modeling shows that a salinity difference of a few parts per mil between the upcoming fluids and seawater is sufficient to drive convection around the colonies as water samples from a few vents indicate that the fluid source should actually be significantly less saline than seawater we propose that the very high fluid flows measured are a consequence of the dilution of the fluid of deep origin with seawater by a factor of 5 to 10

a simplified analysis of parameters controlling dewatering in accretionary prisms abstract one of the many dynamic geologic processes taking place at subduction zones is the compaction driven dewatering of seafloor sediments as they are accreted to the overriding plate the rate of dewatering is equal to the divergence of the sediment matrix velocity field this rate can be estimated analytically if simplifying assumptions are made about the geometry of the prism and motion of the sediments the analytical expression depends only on the sediment accretion velocity thickness of the accreted section prism taper angle and sediment porosity distribution a sensitivity analysis of the solution shows that the fluid production distribution is relatively insensitive to the sediment porosity distribution however the solution is very sensitive to the taper angle of the wedge high angle wedges expel almost all of the incoming water within 20 km while low angle wedges may retain a significant fraction of the incoming water for 50 or more kilometers thickness of the incoming section is also important dewatering of thin accreted sections is more concentrated near the toe of the wedge analyses of transects through the northern barbados makran vancouver and nankai accretionary prisms illustrate a range of dewatering rates and spatial distributions of dewatering

anthropic pedogenesis of purple rock fragments in sichuan basin china abstract considerable amounts of rock fragments are found in many purple soils developed from purple rocks in the sichuan basin of southwestern china we describe the effects of anthropic pedogenetic processes on purple rock fragments associated with soil amelioration by determining changes in rock fragment size distribution transformation of p and k of purple rocks into soils and the complexing of purple rock particles soil mineral particles with organic matter during anthropic pedogenesis of purple soils in sichuan basin of southwestern china the pedogenetic capacity of rock fragments can be expressed by the content of r 0 891 0 961 n 16 digging simulated by sieving and crop planting facilitate pedogenesis of purple rock fragments and their mineral nutrient transformations the soil mineral particles preserve 18 36 of the organic carbon added as corn straw the organic carbon is complexed after corn straw is mixed with

erosion sedimentation and pedogenesis in a polygenetic oxisol sequence in minas gerais brazil the geomorphic evolution of the south eastern brazilian landscape is attributed to climatic changes coupled with tectonic activity soils developed on the resulting surfaces are mainly deep polygenetic oxisols the combination of stable landscapes with continuously exposed soils and neo cenozoic graben zones episodically filled with sediments that may have undergone soil formation offers the possibility to unravel the history of the soils that are found at the present day surface soil sediment sequences in the southern part of the state of minas gerais brazil were investigated by micromorphology and mineralogy in order to understand the genesis of the soils erosion profile thinning weathering biological activity clay accumulation and iron translocation are the main soil forming processes imprinted in the various pedosedimentary layers strong weathering is shown by dissolution of quartz and weathering of ilmenite bioturbation is ubiquitous even in older and deeper buried layers clay accumulation is observed as illuviation and precipitation features which were micromorphologically differentiated accumulation and movement of iron are represented by gley and pseudogley features related to groundwater and surface water saturation processes these features and the layering of sediments and soils play key roles in understanding the evolutionary phases undergone by the soils and sediments as main soil formation episodes the graben fillings show two phases of clay formation and illuviation separated by a phase of ferralitization interrupted by various episodes of erosion the whole material was eventually overprinted by a phase of ferralitization and plinthite formation apart from water saturation these processes also appear to have acted on the soils of the stable areas not affected by tectonic activity but overprinting and erosion prevents recognition of the separate evolutionary phases

major cation gradients in dsdp interstitial waters the role of diffusive exchange between seawater and upper oceanic crust abstract interstitial water analyses from dsdp legs 1 53 were surveyed to identify sites at which the dominant process supporting gradients of major seawater cations is alteration of the underlying oceanic crust sites with thin sediment cover are generally without gradients sites with appreciable sediment accumulation are generally with gradients the transition is probably the result of cessation of convective circulation within the sediments a model is developed for the diffusive flux through an accumulating unreactive sedimentary layer supported by continued reaction within the crust the model is consistent with the observations provided that convection within the crust extends to depths 1 km and that convective flow within the sediments ends once 100 150 m of sediment accumulates the model suggests a steady state gradient inversely proportional to the sedimentation rate this dependence is apparent in the data however some variation in the reaction rate is also required fluxes of mg and na are systematically related to the flux of ca which because of its mobility serves as a tracer of hydrolysis of the basalt when the ca flux is low the mg flux serves as the principal sink for alkalinity produced during basalt hydrolysis when the ca flux is high the mg flux becomes diffusion limited and nabearing alteration phases must form the fluxes resulting from these alteration reactions exert little influence on either the chemistry of seawater or that of the upper crust

tectonic processes along the front of modern convergent margins research of the past decade at convergent margins oceanic crust descends beneath continental crust to form a complex crustal juncture this juncture begins at an ocean trench and can be followed deep into the earth as a zone of high seismicity created as the two crustal plates move past one another the places where oceanic crust descends into the earth known as subduction zones are highly dynamic features modern examples contain analogues for processes that created the now static remains of ancient margins exposed on land at the fronts of subduction zones where the descending oceanic crust is still relatively shallow exploration geophysical techniques can define the structure of sedimentary strata modern seismic reflection techniques can resolve 100 m intervals in the upper 2 6 km of a sedimentary section at trench depths drill cores of such sediment from trenches have been successfully recovered between about 0 5 and 1 2 km below the seafloor this review focuses on the advances in knowledge of the fronts of modern convergent margins where the structure and tectonic history can be so observed the review is in part historical because new findings of the past decade became increasingly difficult to explain without extensive modifi

major and trace element and sr isotope constraints on fluid circulation in the barbados accretionary complex part ii circulation rates and fluxes abstract 87 sr 86 sr ratios of pore fluids recovered from diapiric structures east of the deformation front of the barbados accretionary prism remain quasi constant from the surface to depths of 8 m the sr isotopic ratios are non radiogenic compared with seawater which implies that non local fluid was expelled at such a high rate that its sr isotopic composition was dominated by the source fluid and not by pore fluid or seawater chloride depletion recorded in the fluids corresponds to a five fold dilution in the deepest sample from the atalante diatreme this also strongly suggests upward flow the comparison of measured chloride contents and sr isotope depth profiles with theoretical values obtained using a steady state advection diffusive model gives some constraints on the fluid circulation rate in the two diatremes atalante and cyclope and in one mud diapir c the velocities are variable but the diatremes which have the largest thermal and chemical anomalies yield the highest estimated advection rates the fluid circulation rate in the centre part of the largest diatreme atalante 0 47 km 2 total surface is estimated at about 1 m yr the fluid flux from the deepest to shallowest levels of the atalante diatreme was estimated on the basis of the fluid circulation rate calculations fluid release is clearly favoured if active conduits are present as they are in the diatremes but not in the mud diapirs however even though this steady state advection diffusion model provides a rough estimation of flow rates modification of the fluid pressure and therefore fluid volume during earthquakes may superimpose large but transient fluid expulsions

ocean drilling program leg 112 peru continental margin part 2 sedimentary history and diagenesis in a coastal upwelling environment on the shelf and upper slope off peru the signal of coastal upwelling productivity and bottom water oxygen is well preserved in alternately laminated and bioturbated diatomaceous quaternary sediments global sea level fluctuations are the ultimate cause for these cyclic facies changes during late miocene time coastal upwelling was about 100 km west of the present centers along the edge of an emergent structure that subsequently subsided to form the modern slope the sediments are rich in organic carbon and intense microbially mediated decomposition of organic matter is evident in sulfate reduction and methanogenesis these processes are accompanied by the formation of diagenetic carbonates mostly ca rich dolomites and mg calcites the downhole isotopic signatures of these carbonate cements display distinct successions that reflect the vertical evolution of the pore fluid environment from the association of methane gas hydrates burial depth and low chloride interstitial fluids we suggest an additional process that could contribute to the characteristic chloride depletion in pore fluids of active margins release of interlayer water from clays without a mineral phase change the shelf sediments also contain a subsurface brine that stretches for more than 500 km from north to south over the area drilled the source of the brine remains uncertain although the composition of the oxygen isotopes suggests dissolution of evaporites by seawater