quaternary compound incised valley in a microtidal environment roussillon continental shelf western gulf of lions france abstract a buried system was observed using seismic data along the northern side of the roussillon coastal plain and inner shelf western gulf of lion mediterranean sea far from the nearest agly and tet rivers it was interpreted as an example of a compound type which is subject to controversy a core 60 meters long was obtained on the sandy beach barrier between sea and lagoon approximately on the axis of the basal surface of erosion mapped from seismic data and long core logs obtained previously on the coastal plain in the lower part of the core 64 m to 26 m b p s l the main estuarine muddy silt facies and thin levels of fluvial gravels intercalated in the mud suggest that successive cycles of base level and sea level falls and rises were recorded this interpretation is confirmed by pollen diagrams showing several successive warming periods during climatic changes differentiated as interglacial phases recorded by the estuarine muds owing to these correlated data we can attest that this incised valley system is of a compound type every vertical succession of fluvial gravels and estuarine muddy silts represents a fundamental depositional sequence typical of the simple model of wave dominated incised valley filling truncated at the top by a subsequent base level fall several depositional sequence remnants are stacked upon each other the chronostratigraphic benchmark is based on microforaminiferal biomarkers which indicate that the time period covered by the successive phases of base level and sea level cycles extends from mis 16 about 600 000 years b p to mis1 present day the exact correlation of base level and sea level cycles with identified climate cycles remains partly approximate but the cycles which contain well known plant associations are quite reliable the internal geometry of the incised valley system based upon high resolution seismic data shows that the lateral migration of the successive phases of incision and filling explains both the preservation of several cycles and the incomplete preservation of the typical facies due to the reworking of the upper part of all individual depositional sequences eustasy is the dominant controlling factor and differential subsidence an important factor on the mid and outer shelf has a reduced impact at this location the preservation of the compound system depends upon the variable maximum depth of erosion reached at each maximum sea level lowstand we propose that different interglacial conditions took place in the drainage basins rather than differences in the lowstand sea level values the transverse shape of the incisions with lateral terraces and deeper channels combined with a continuous lateral shift of the successive incisions also contributed to preservation the lateral shifting is partly due to a normal fault and substratum tilting and partly to the oceanic regime

3d architecture of lowstand and transgressive quaternary sand bodies on the outer shelf of the gulf of lion france abstract a restricted area 700 km 2 of the outer continental shelf in the gulf of lions western mediterranean sea has been surveyed in detail in order to reconstruct the 3d architecture of large quaternary sand bodies that are exceptionally well preserved in the western part of the rho ne delta data sources include digital very high resolution seismic swath bathymetry and some shallow cores in two dimensions the seismic data display a complex superposition of alternating seismic units consisting of high and low angle prograding clinoforms corresponding to high and low energy environments the combination of faunal and grain size analysis from shallow cores geometry of sedimentary bodies showed that these two types of seismic facies can be attributed respectively to upper shoreface and prodelta c settings despite a similar geometry in 2d it appears that the prograding sand units have very different 3d geometries lateral extent direction of progradation with respect to the paleoshorelines implying different sedimentary processes at least two major sand units have shore parallel orientations and can be mapped along the entire study area the mechanism responsible for the formation of these sand bodies seems similar to that described for many sharp based sand bodies from the stratigraphic record especially in the western interior seaway their isolated position on the shelf being related to forced regressions in contrast some other sand units have lobate shapes with divergent directions of progradation and limited lateral extent they are often overlying fluvial incisions and they pinch out landward it is still not clear whether they are related to some allocyclic or autocyclic processes like shifting of delta c lobes as observed on the texas coast the very high resolution and high quality of the seismic data have enabled us to characterise the three dimensional architecture of small scale sedimentary bodies the study has pointed out the variability of depositional processes and has given an insight on reservoir characteristics 1998 elsevier science ltd all rights reserved

effect of mineralogy and pedoclimatic variations on ni and cr distribution in serpentine soils under temperate climate abstract part of the soils occurring in the serpentinite szklary massif sw poland have developed in quaternary under temperate climate on the parent rock not affected by chemical weathering in studied parent ultrabasite ni occurs in cr magnetite up to 0 96 wt of nio forsterite up to 0 55 wt of nio iddingsite up to 0 99 wt of nio and serpentine up to 0 55 wt of nio while cr is bounded with cr magnetites up to 21 77 wt of cr 2 o 3 and clinochlores up to 1 68 wt of cr 2 o 3 cr magnetites are highly resistant to weathering while other primary minerals more susceptible to weathering release parts of ni and cr which are trapped in authigenic phases the latter however contain less ni and cr than corresponding primary minerals clayous matrix 0 37 wt of nio and 0 08 wt of cr 2 o 3 smectites 0 30 wt of nio and 0 07 wt of cr 2 o 3 and mixture of oxy hydroxides and clay minerals 0 36 wt of nio and 0 14 wt of cr 2 o 3 at the mineral scale smectite plays an important role in the trapping of ni at the profile scale ni and cr are moderately diluted upwards the soil profile and cr is generally less mobile than ni the soil formed in szklary is chemically different than the analogous serpentine soils occurring more to the south in europe french massif central vosges mountains and ligurian apennines nw italy the difference is due to participation of fluvioglacial material produced by quaternary continental glaciacion in poland however similar vertical relative variations of ni and cr were found in all compared soils in spite of differences in parent rock composition allogenic contaminations and degree of soil development comparison with other well drained pedons located in similar uphill positions shows a climatic control of the cr and ni vertical distribution in serpentine soils humid mountainous variant of temperate climate induces leaching of mg and subsequent lack in smectite neoformation which lead to the release of ni ni is less mobile in the colder and dryer climate of poland moreover some primary minerals which are generally considered as not stable under soil conditions olivine serpentine and chlorite are still present even in the a horizon of the studied polish pedon their resistance is due to slower rates of weathering related to the climate but also due to former hydrothermal processes affecting the parent rock fabric

previously unknown mineral nanomineral relationships with important environmental consequences the case of chromium release from dissolving silicate minerals risk assessments that take into account the formation of environmentally dangerous hexavalent chromium in cr containing mine tailings and associated soils and sediments require an understanding of the occurrence and speciation of cr in silicate minerals and glasses silicates are more soluble and generally more susceptible to weathering than the refractory mineral chromite the principal ore mineral of cr studies at the nanoscale using a combination of advanced sample preparation via microtoming and focused ion beam techniques in combination with state of the art analytical transmission electron microscopy and electron diffraction reveal the occurrence of chromite nanoparticles held within clinochlore and lizardite grains in chromitite ore an igneous cumulate consisting primarily of chromite from the black thor chromium deposit in northern ontario canada and the mistake mine fresno county california u s a respectively nanoscale examinations of altered chromitite ore samples from the black thor deposit after dissolution experiments in sulfuric acid bearing solutions of ph 2 5 show that clinochlore alters to amorphous silica depleted in chromite nanoparticles this observation suggests the release of chromite nanoparticles rather than cr 3 aqueous species during the weathering of chromite bearing silicate minerals this will in turn have an impact on the environmental behavior of cr 3 and its potential oxidation to cr 6 the formation of cr 6 aq species in this case will require either the initial dissolution of the nanoparticles or the oxidation of cr 3 species on the surface of the nanoparticles either process being a rate limiting step in the formation of cr 6 aq species

rise and fall of the southern santa cruz mountains california from fission tracks geomorphology and geodesy the santa cruz mountains are closely associated with a left bend along the right lateral san andreas fault the loma prieta area on the northeast side of the san andreas consists of fault bounded blocks that rise along active deeply rooted reverse and oblique slip faults six samples from a transect across this area yield concordant apatite fission track ages averaging 4 6 0 5 ma these ages date the time of cooling below 110 c and suggest that about 3 km of unroofing has occurred over the last 4 6 m y allowing for current elevations of about 1 km this suggests an average uplift rate of the order of 0 8 mm yr over the last 4 6 m y to further define the extent and distribution of this young uplift we used morphometric analyses of the youthful topography of the area steep drainage slopes and high local relief indicate that the area northeast of the san andreas forms a well defined zone of high uplift in contrast the region on the southwest side of the san andreas is characterized by broad upwarping and folding more subdued topography old fission track ages and mean quaternary uplift rates of 0 1 0 4 mm yr geodetic data 1906 san francisco earthquake and subsequent strain transients 20 years of interseismic deformation 1989 loma prieta earthquake and 2 years of post loma prieta earthquake strain show that the southern santa cruz mountains repeatedly rise and subside through a complex sequence of bay area deformation events an additional deformation element that involves reverse slip averaging 2 3 mm yr along the foothills thrust system must occur to explain the longer term uplift pattern in the loma prieta area since the late pliocene the asymmetry in deformation on opposite sides of the san andreas probably reflects the contrasting rock types on opposite sides of the fault the influence of preexisting structures and the interaction with neighboring faults of the san andreas system

marine ferromanganese oxide a potentially important sink of light chromium isotopes abstract marine ferromanganese oxides are widely distributed in oxic marine sediments and are a sink for a range of metal elements derived from seawater their potential as a sink of chromium cr isotopes has yet to be investigated and may have important implications for our understanding of the cr isotope system in this study we reported cr isotope data of modern oceanic fe mn crusts for the first time the 53cr values of the surface scrapings of the fe mn crusts from the central north pacific seamounts range from 0 85 to 0 15 with an average of 0 42 0 34 2 n 11 which are lower than published data from pacific seawater 0 53 1 43 with an average of 0 79 these results reveal preferential removal of light cr isotopes from seawater into fe mn crusts with an isotopic fractionation 53cr 53crfe mn crust 53crseawater estimated from 2 3 to 0 7 averaging at ca 1 2 we suggest that such significant negative isotopic fractionation may have been reached through adsorption of dissolved cr vi oxyanions in the oxic water column onto the surface of mn oxide phases during the precipitation of fe mn crusts however our modelling results imply that the deposition of mn oxide sediments would make insignificant contribution to elevation of the global seawater average 53cr value

properties of iron oxides in some new caledonian oxisols abstract oxisols from two toposequences of new caledonia formed from peridotite consist essentially of fe oxides goethite hematite maghemite these fe oxides were characterized by their mineralogy crystal size and morphology al substitution thermal behaviour and dissolution kinetics in 6 m hcl at 25 c in one toposequence the samples were free of hematite goethite only at 1050 m above sea level whereas at lower altitudes hematite was also present al substitution was generally low due to the low al content of the peridotite except in gibbsitic samples on rocks somewhat higher in al the surface areas of goethite and hematite ranged between 50 and 150 m 2 g 1 dithionite extractable ni and cr were between 0 2 and 2 2 ni and 0 3 and 2 3 cr the hematite containing samples tended to be higher in cr and lower in ni whereas the opposite held for samples containing goethite only maghemites had a low unit cell size 8 31 8 32 instead of 8 34 8 35 a which was attributed to al substitution dehydroxylation temperature of goethites was weakly correlated with al substitution dissolution kinetics could be described by a linear form of a modified first order reaction with one straight line for samples containing goethite only and two lines for samples containing goethite plus hematite

variations of redox conditions in the atmosphere and yangtze platform during the ediacaran cambrian transition constraints from cr isotopes and ce anomalies abstract the ediacaran cambrian transition was characterized by the evolution from ediacaran soft body to cambrian skeletal organisms and fluctuations of the marine carbon cycle marine redox changes should have played an essential role in both ecological and environmental evolutions however temporary changes and spatial distribution of redox conditions in the ediacaran cambrian oceans remain elusive and highly debated in this study we analyzed chromium cr isotope and cerium ce anomaly profiles in carbonates from the upper ediacaran lower cambrian dengying and zhujiaqing formations at the xiaotan section south china in an attempt to provide new insights helping unravel earth s surface redox changes during the ediacaran cambrian transition our results show that these carbonates record generally positive 53crauth values up to 1 15 with fluctuations and prominent negative ce anomalies ce ce values down to 0 35 implying a broad increase in oxygenation in the atmosphere and the inner shelf of the yangtze platform during the ediacaran cambrian transition the first appearance and subsequent diversification of the cambrian animals may have benefited from this oxygenation event the pronounced fluctuations of 53crauth and 13ccarb values can be explained by episodic oxidation of a deep water doc pool in a stratified water column across the chemocline through upwelling releasing light carbon isotopes and organic matter bound isotopically unfractionated cr iii into shallow waters

lowstand shorefaces transgressive incised shorefaces and forced regressions examples from the viking formation joarcam area alberta abstract in the joarcam beaverhill lake area of alberta there are three long 40 km narrow 5 km sandbodies in the late albian viking formation they are surrounded by offshore open marine mudstones and have previously been interpreted as offshore bars however the sandbodies are both underlain and overlain by erosion surfaces joarcam is the only field with abundant cores and the sandbody shows a sandier upward and coarsening upward succession all three fields have recently been reinterpreted in the literature as lowstand shoreface deposits but the order in which they formed remains controversial our well log cross sections suggest that the lindbrook shoreface was the first to form at a time of maximum lowstand of sea level it was truncated as sea level began to rise and the lindbr ok transgressive surface of erosion tse has been traced into the erosion surface that underlies joarcam joarcam can therefore be interpreted as a shoreface incised during a pause in an overall transgression both the lindbrook and joarcam shorefaces appear to be truncated by the regressive surface of erosion rse that underlies beaverhill lake this suggests that beaverhill lake is the youngest of the shorefaces and implies a second major fall of relative sea level the lowstand shorefaces tend to be thinner because of reduced accommodation space during sea level fall they tend to prograde farther beaverhill lake about 23 km because of abundant sediment supply at lowstand but consist largely of sandstone directly overlying the rse at beaverhill lake the shoreface sediments prograded at least 10 km before any mud in the offshore to shoreface transition was preserved by contrast the transgressive shorefaces tend to be thicker because of accommodation space created during transgression however they tend not to prograde so far joarcam up to 13 km possibly because of reduced supply of sediment to the shoreface during transgression the two proposed episodes of lowering of relative sea level are tentatively correlated with the two separate valley incisions documented at crystal about 90 km to the southwest these incisions represent type 1 sequence boundaries but the boundaries are not continuous regressive surfaces of erosion from crystal to the joarcam beaverhill lake area in both cases the falling stage rses have been eroded by the subsequent tses these tses are the only surfaces preserved between the incised valleys and the lowstand shorefaces

serpentine geology links to water quality and heavy metals in sediments of a stream system in central queensland australia serpentinite soils common throughout the world are characterized by low calcium to magnesium ratios low nutrient levels and elevated levels of heavy metals yet the water quality and heavy metal concentrations in sediments of streams draining serpentine geology have been little studied the aim of this work was to collect baseline data on the water quality for both wet and dry seasons and metals in sediments at 11 sites on the marlborough creek system which drains serpentine soils in coastal central queensland australia water quality of the system was characterized by extremely hard waters 555 698 mg l as caco3 high dissolved salts 684 1285 mg l ph 8 3 9 1 and dissolved oxygen often 110 saturation cationic dominance was mg na ca k and for anions hco3 cl so4 al cu and zn in stream waters were naturally high and exceeded australian and new zealand environment and conservation council guidelines conductivity displayed the highest seasonal variability decreasing significantly after wet season flows there was little seasonal variation in ph which often exceeded regional guidelines stream sediments were enriched with concentrations of ni cr co and zn up to 35 21 10 and 2 times the world average for shallow sediments respectively concentrations for ni and cr were up to 60 and 16 times those of the relevant interim sediment quality guidelines low trigger values respectively the distinctive nature of the water and sediment data suggests that it would be appropriate to establish more localized water quality and sediment guidelines for the creek system for the water quality parameters conductivity cu and zn and possibly cr and cd also and for sediment concentrations of cd cr and ni

a new system for acquisition and processing of very high resolution seismic reflection data a new digital seismic data acquisition system and accompanying software have been developed by ifremer to replace the analog equipment commonly used in very high resolution less than 1 m shallow marine seismic reflection surveys the acquisition part based on a hewlett packard 9000 microcomputer is capable of sampling rates of up to 15 khz for one channel signal processing and image processing can be performed either during the survey by the acquisition computer or after the survey with a software system that runs on a sun workstation the system has been developed for the specific requirements of coastal studies understanding of the sediment layers in such studies requires a vertical resolution of around 1 m in the top 10 m of sediment this system has been successfully used for the study of subtidal sand waves off the cherbourg peninsula france the results which revealed the internal structure of sand waves from about 3 m to 8 m high correlated well with synthetic seismograms that were create

impact of relative sea level and rapid climate changes on the architecture and lithofacies of the holocene rhone subaqueous delta western mediterranean sea abstract the modern rhone delta in the gulf of lions nw mediterranean is a typical wave dominated delta that developed after the stabilization of relative sea level following the last deglacial sea level rise similar to most other deltas worldwide it displays several stacked parasequences and lobes that reflect the complex interaction between accommodation sediment supply and autogenic processes on the architecture of a wave dominated delta the interpretation of a large set of newly acquired very high resolution seismic and sedimentological data well constrained by 14c dates provides a refined three dimensional image of the detailed architecture seismic bounding surfaces sedimentary facies of the rhone subaqueous delta and allows us to propose a scenario for delta evolution during the last deglaciation and holocene the subaqueous delta consists of parasequence like depositional wedges a few metres to 20 30 m in thickness these wedges first back stepped inland toward the nw in response to combined global sea level rise and overall westward oceanic circulation at a time when sediment supply could not keep pace with rapid absolute eustatic sea level rise at the younger dryas preboreal transition more rapid sea level rise led to the formation of a major flooding surface equivalent to a wave ravinement surface after stabilization of global sea level in the mid holocene accommodation became the leading factor in controlling delta architecture an eastward shift of depocentres occurred probably favoured by higher subsidence rate within the thick messinian rhone valley fill the transition between transgressive backstepping geometry and regressive prograding geometry para sequences resulted in creation of a maximum flooding surface mfs that differs from a classical mfs described in the literature it consists of a coarse grained interval incorporating reworked shoreface material within a silty clay matrix this distinct lithofacies results from condensation erosion which appears as an important process even within supply dominated deltaic systems due to avulsion of distributaries the age of the mfs varies along strike between ca 7 8 and 5 6 kyr cal bp in relation to the position of depocentres and climatically controlled sediment supply the last rapid climate change of the holocene the little ice age 1250 1850 ad had a distinct stratigraphic influence on the architecture and lithofacies of the rhone subaqueous delta through the progradation of two deltaic lobes in response to changes in sediment supply linked to rapid climate changes and to anthropic factors the rhone delta evolved from wave dominated to fluvial dominated and then wave dominated again

paleo sea levels reconsidered from direct observation of paleoshoreline position during glacial maxima for the last 500 000 yr the drastic climatic changes which characterise the cooling trend of the last few million years of earth history led to variations in eustatic sea level that had tremendous impact on the geology and ecology of continental margins reconstructing a sea level curve back in time is not an easy task observations of shoreline positions are always a local measurement of relative sea level that needs to be corrected from the effect of tectonic and thermal subsidence sediment loading compaction and glacio hydro isostasy extensive studies have been done for the last deglaciation and for the last 100 000 yr cycle but very few studies deal with position of sea level during earlier cycles simply because conditions are very rarely favourable for the preservation of such witnesses the shelf of the golfe du lion western mediterranean reveals a unique record of shoreline paleopositions during glacial maxima of at least the last five circa 100 kyr glacial interglacial cycles in fact it is the entire glacial deltaic lobe of up to 50 m thick from delta front or shoreface to prodelta that has been preserved in place and which provides direct and independent constraints for relative sea level minima we measure a relative sea level of 112m 128 134 246 and 262 m for mis 2 6 8 10 and 12 respectively after corrections taking into account postdepositional movement of strata subsidence we find that sea level dropped to a depth of 102 6 m during the last three glaciations mis2 mis6 mis8 but reached exceptionally low values of more than 150 10 m during the preceding glaciations mis10 and mis 12 at about 340 and 434 kyr bp this general time framework and sedimentological interpretation has been confirmed by preliminary results from two deep drillings during the promess cruise july 2004 which validate our methodology however no detailed and absolute datings of such witnesses are available so far so that we cannot prove that these levels are the lowest ever reached during each glacials but they correspond undoubtedly to the last preserved shoreface before rapid sea level rise we also suggest that the abrupt change in sea level maxima might be the overprint of 400 kyr orbital periodicity cycles last but not least these results prove that the golfe du lion is indeed a unique laboratory to study paleoclimates and sea level variations on a larger time scale further work is needed for a complete glacio hydro sedimento isostatic modelling of each sequence and each glacial to further constraint local sea level versus global sea level and quantify in particular the relative effect of glacio hydro isostatic effect which differ according to ice sheet extend but also of erosion sedimentation isostatic effect erosion on land and deposition on the outer shelf and slope

very high resolution seismics as a tool for sequence stratigraphy applied to outcrop scale examples from eastern tyrrhenian margin holocene pleistocene deposits three eastern tyrrhenian continental margin areas with very different depositional and tectonic settings were analyzed using single channel very high resolution reflection seismics coupled with sea floor sampling fourth and fifth order depositional sequences derived from quaternary glacio eustatic processes are now buried at shallow depths within the continental shelf the sequences have been reconstructed in detail with great lateral continuity the tectonic setting did not influence the development of high order sequences which are probably synchronous at a global scale within these sequences it has been possible to recognize all the systems tracts hypothesized by sequence stratigraphy models confirming that this method does not depend upon time or scale the geom try of depositional sequences is strongly dependent on sedimentation rate i e on the distance from sources local factors such as transport pattern variations caused by sea level changes paleotopography of the transgressed surface characteristics of feeding hydrographic nets and interactions with bioconstructions must be considered because they play an important role in the geometrical development of depositional sequences in high order depositional sequences lowstand systems tracts are volumetrically predominant highstand and transgressive systems tracts seem to be linked to point sources because they have a three dimensional 3 d geometry on the contrary lowstand systems tracts are related to linear sources parallel to the shelf break they cause the progradation of the whole margin so that they form the margin structure almost entirely

a regional scale study of chromium and nickel in soils of northern california usa abstract a soil geochemical survey was conducted in a 27 000 km 2 study area of northern california that includes the sierra nevada mountains the sacramento valley and the northern coast range the results show that soil geochemistry in the sacramento valley is controlled primarily by the transport and weathering of parent material from the coast range to the west and the sierra nevada to the east chemically and mineralogically distinctive ultramafic um rocks e g serpentinite outcrop extensively in the coast range and sierra nevada these rocks and the soils derived from them have elevated concentrations of cr and ni surface soil samples derived from um rocks of the sierra nevada and coast range contain 1700 10 000 mg kg cr and 1300 3900 mg kg ni valley soils west of the sacramento river contain 80 1420 mg kg cr and 65 224 mg kg ni reflecting significant contributions from um sources in the coast range valley soils on the east side contain 30 370 mg kg cr and 16 110 mg kg ni lower cr and ni concentrations on the east side of the valley are the result of greater dilution by granitic sources of the sierra nevada chromium occurs naturally in the cr iii and cr vi oxidation states trivalent cr is a non toxic micronutrient but cr vi is a highly soluble toxin and carcinogen x ray diffraction and scanning electron microscopy of soils with an um parent show cr primarily occurs within chromite and other mixed composition spinels al mg fe cr chromite contains cr iii and is highly refractory with respect to weathering comparison of a 4 acid digestion hno 3 hcl hf hclo 4 which only partially dissolves chromite and total digestion by lithium metaborate libo 3 fusion indicates a lower proportion of chromite bound cr in valley soils relative to um source soils groundwater on the west side of the sacramento valley has particularly high concentrations of dissolved cr ranging up to 50 g l 1 and averaging 16 4 g l 1 this suggests redistribution of cr during weathering and oxidation of cr iii bearing minerals it is concluded that regional scale transport and weathering of ultramafic derived constituents have resulted in enrichment of cr and ni in the sacramento valley and a partial change in the residence of cr

origin and mobility of hexavalent chromium in north eastern attica greece abstract an integrated framework that is comprised of field surveys of groundwater surface water and soils laboratory process experiments and hydrologic and geochemical modeling is used to identify the origin anthropogenic versus geogenic sources fate and transport of hexavalent cr in tertiary and quaternary deposits of oropos plain in greece groundwater and soils were analyzed in may 2008 and exhibited considerable cr concentrations mineralogical analysis and micro xrf analysis of the heavy soil fractions metallic components showed cr bearing phases like chromites cr silicate phases with positive correlation between si al fe and cr soil concentrations column experiments showed the cr vi desorption ability of soils e g concentration of 20 g l 1 was detected after the application of 50 mm of rain the groundwater model simulated the variability of cr concentrations emanating from both anthropogenic and geogenic sources successfully using rate constants obtained from the laboratory experiments e g 4 24 nm h 1 for serpentine soil and 0 77 nm h 1 for soil in alluvial deposits the mineralogical and geochemical results support a geogenic origin for cr in soils and groundwater of oropos plain while modeling results suggest that contaminants transported by asopos river have affected only the upper layers of the subsurface in the vicinity of the river the framework can be used to establish background concentrations or clean up levels of cr contaminated soils and groundwater

oxygenation variations in the atmosphere and shallow seawaters of the yangtze platform during the ediacaran period clues from cr isotope and ce anomaly in carbonates abstract the late neoproterozoic era witnessed a significant oxygenation in earth s surface in line with the naissance and diversity of early animals however detailed variations of the oxygenation during this period remain controversial chromium isotope in ancient carbonates has shown its ability to trace the oxygenation history of the atmosphere hydrosphere system in this study we analyzed cr isotope and ce anomaly data of carbonates from the ediacaran doushantuo and dengying formations in the yangtze gorges area south china in order to reconstruct oxygenation variations in the atmosphere and shallow seawaters of the yangtze platform during the ediacaran period after evaluating and excluding detrital and diagenetic effects well preserved 53crauth signatures were obtained post marinoan carbonates record slightly positive 53crauth values 0 18 0 43 and slightly negative ce anomaly suggesting generally oxidizing conditions in the atmosphere with po2 over 1 pal and in shallow seawaters of the yangtze platform during the post marinoan phase which may have been related to the diversity of early ediacaran organisms shuram wonoka correlative carbonates are characterized by the fluctuations of 53crauth values 0 25 to 0 97 and a significant negative 13c excursion which may have resulted from partial oxidation of the large deep water doc reservoir under enhanced oxidative weathering conditions this process released 13c depleted carbon into dic pool and isotopically unfractionated cr iii into water columns the latter of which immediately precipitated by adsorption onto the detrital materials meanwhile an increase in local anoxia and even euxinia in the intrashelf basin of the yangtze platform driven by enhanced microbial sulfate reduction and the resultant h2s possibly limited regional biological evolution during this phase late ediacaran carbonates record elevated 53crauth values 0 40 0 96 together with the decreasing trend in ce ce values indicating a more oxygenated environment in the atmosphere and shallow seawaters of the yangtze platform during the late ediacaran phase which may have been beneficial to the diversification of late ediacaran animals

occurrence of hexavalent chromium in ground water in the western mojave desert california abstract about 200 samples from selected public supply domestic and observation wells completed in alluvial aquifers underlying the western mojave desert were analyzed for total dissolved cr and cr vi because cr vi is difficult to preserve samples were analyzed by 3 methods chromium vi was determined in the field using both a direct colorimetric method and epa method 218 6 and samples were speciated in the field for later analysis in the laboratory using a cation exchange method developed for the study described in this paper comparison of the direct colorimetric method and epa method 218 6 with the new cation exchange method yielded r 2 values of 0 9991 and 0 9992 respectively total dissolved cr concentrations ranged from less than the 0 1 g l detection limit to 60 g l and almost all the cr present was cr vi near recharge areas along the mountain front ph values were near neutral dissolved o 2 concentrations were near saturation and cr vi concentrations were less than the 0 1 g l detection limit chromium vi concentrations and ph values increased downgradient as long as dissolved o 2 was present however low cr vi concentrations were associated with low dissolved o 2 concentrations near ground water discharge areas along dry lakes chromium vi concentrations as high as 60 g l occurred in ground water from the sheep creek fan alluvial deposits weathered from mafic rock derived from the san gabriel mountains and cr vi concentrations as high as about 36 g l were present in ground water from alluvial deposits weathered from less mafic granitic metamorphic and volcanic rocks chromium iii was the predominant form of cr only in areas where dissolved o 2 concentrations were less than 1 mg l and was detected at a median concentration of 0 1 g l owing to its low solubility in water of near neutral ph depending on local hydrogeologic conditions and the distribution of dissolved o 2 cr vi concentrations may vary considerably with depth samples collected under pumping conditions from different depths within wells show that cr vi concentrations can range from less than the 0 1 g l detection limit to 36 g l in a single well and that dissolved o 2 concentrations likely control the concentration and redox speciation of cr in ground water

geometry lateral variability and preservation of downlapped regressive shelf deposits eastern tyrrhenian margin italy the shelf of the eastern tyrrhenian margin changes substantially in width shelf break depth and sea floor steepness over relatively short distances largely due to marked lateral changes in geologic structure remnants of late pleistocene prograded coastal deposits are locally preserved on the middle and outer parts of this complex shelf through the authors studies of these prograded deposits they recognize two major controls on the distribution lateral extent thickness and preservation potential first prograded downlapped deposits formed only where the physiographic shelf break was deeper than the lowstand shoreline thus providing accommodation space for the lowstand deposits second the proximity and relative size of sediment sources and the local coastal dispersal system influenced the geometry of the deposit mid shelf and shelf margin bodies composed of seaward steepening downlapping reflectors were deposited as thin to thick continuous prograding sheets over an irregular eroded shelf surface and onto the shelf edge during the last fall and lowstand of sea level a dearth of sediment at the end of lowstand conditions led to a switch from deposition to erosion during sea level rise shoreface erosion produced a major marine erosional ravinement surface landward of the 120 m isobath and much and in many places all of the downlapping depositmore was removed preservation of downlapping deposits is largely a function of their thickness thick continuous deposits are common on the shelf edge whereas on the mid shelf only thin remnants are preserved locally where depressions or morphologic steps were present in the shelf surface less

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

chromium fluxes and speciation in ultramafic catchments and global rivers abstract the role of ultramafic rock weathering in global chromium cr budgets and how these may be linked to changes in earth s climate over geological time was investigated by compiling dissolved cr speciation and fluxes in i 73 of the worlds large rivers representing 35 of global river discharge to oceans and in ii an ultramafic catchment putah creek watershed in the california coast range mountains usa weathering of ultramafic rocks creates ideal conditions for cr release and redox cycling alkaline river water draining ultramafic catchments is naturally enriched in cr up to 582 nmol l chromium concentrations increase with the extent of rock water interaction as indicated by correlations with mg and hco3 concentrations and ph whereas cr cycling depends on the availability of electron donors and acceptors e g fe ii organics mn iii iv oxides thus dissolved cr is exported from ultramafic watersheds as both the soluble hexavalent cr vi species mgcro4 cro42 and also as trivalent cr iii species croh co3 22 cr oh 3 the latter cr iii species were previously thought to have low solubility ultramafic catchments have higher area normalized cr and major ion fluxes for a given runoff when compared to global rivers and may thus have a disproportional impact on global cr budgets long term carbon cycling and moderation of the earth s climate over million year timescales riverine export fluxes of cr are linearly correlated with fluxes of ca mg and alkalinity in both ultramafic catchments and global rivers this suggests that silicate weathering is a key control on cr fluxes and that major element weathering fluxes may be a useful proxy for estimating cr and other trace element fluxes globally present day riverine dissolved cr fluxes to oceans are spatially variable and estimated to be 1 7 109 mol yr three times higher than previously reported however when geochemical reactions in estuaries are considered riverine cr fluxes may be lower throughout earth history cr weathering fluxes also may have varied with changes in the global distribution of ultramafic rocks cr concentrations in continental rocks or climactic conditions e g atmospheric co2 levels or runoff such variation should be considered when interpreting both modern and past cr seawater isotopic compositions and residence times

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

palynology of the northwestern mediterranean shelf gulf of lions first vegetational record for the last climatic cycle palynology has been performed for the first time on late quaternary sediments of the gulf of lions the aim is both to tighten the chronology of seismic profiles in the region and to elucidate the vegetation of southern france during the last climatic cycle four cores taken on the shelf mostly record marine isotope stages mis 1 and 2 and part of mis 3 and mis 5 the latter sediments might have been preserved in a paleodepression on the emergent shelf between the rhone and the herault rivers it would explain their preservation against transgression and regression erosions of more recent stages this study also provides a synthesis of palynological continental data collected during the last 40 years in southern europe preliminary comparisons made between the latter and new marine data demonstrate that refugia of picea and abies existed in southern france during mis 3 and mis 2 the dynamics of artemisia deciduous quercus and corylus abies and finally fagus is also reconstructed for the last deglaciation first results obtained in the gulf of lions confirm and complete that synthesis

late quaternary deltaic lowstand wedges on the rhone continental shelf france abstract shallow seismic profiles on the rhone continental shelf have shown the existence of stacked progradational lowstand wedges on the outer shelf accumulated during late quaternary glacioeustatic lowstands the wedges are bounded by sharp to erosional sequence boundaries and onlap onto the middle shelf the thickness of individual wedges attains 50 meters at the shelf edge where they are sheared by slumping the wedges exhibit well developed progradational clinoforms episodically interrupted by internal unconformities on which there is a downward shift of the succeeding clinoforms these represent small scale in the order of a few meters falls in sea level during the quaternary eustatic cycles the durations of the stable highstand conditions appear to have been too brief to permit the regressive highstand tract to prograde to the outer shelf therefore the shelf edge builds up entirely with lowstand wedges

seismic stratigraphy of the deglacial deposits of the rhone prodelta and of the adjacent shelf abstract in order to achieve a synthesis of the stratigraphic organization of the deglacial deposits of the inner middle shelf in front of the rhone delta plain we merged high resolution mini sparker and sparker and very high resolution chirp and mud penetrator seismic data into a single seismic database thus the merged seismic database improves the lateral correlation between eastern and western parts separated by the rhone incised valley deposits as a result the interpretation of seismic units in relation to local and global environmental changes was refined the deglacial deposits rest on a basal erosional discontinuity capping a complex of pleistocene prograding wedges the identified units make up transgressive and highstand systems tracts and are bounded by flooding surfaces the main flooding surfaces are 1 the transgressive surface d200 which forms the lower boundary of the deglacial deposits and 2 the maximum flooding surface which forms the boundary between the transgressive and highstand systems tracts regarding the data set the study area is divided into three parts depending on the stacking pattern and main control factors in the western area the units present an aggradational stacking pattern and the rate of sediment supply and dynamic conditions seems coupled with glacio eustacy role on sedimentary units building and evolution in the central area the units present an overall backstepping pattern mainly controlled by glacio eustacy in the eastern area the units present an aggradational stacking pattern and both the glacio eustacy and rate of sediment supply have an important role the lower parasequence of the transgressive systems tract u200 is due to the reworking of wurmian terraces above the parasequence u300 is a transgressive body formed during a rapid sea level rise the two upper parasequences are interpreted as ancestral coastal systems with a backstepping pattern the first coastal system u400 is due to a decrease in the rate of sea level rise that occurred during the younger dryas the second coastal system u500 may be due to a similar event or to an increased rate of sediment supply during a constant sea level rise finally the highstand systems tract is composed of three units i unit u601 located to the west and interpreted as a subaqueous delta ii iii units u600 and u610 located to the east and interpreted as prograding deltaic lobes

ecological implications of pedogenesis and geochemistry of ultramafic soils in kinabalu park malaysia abstract in sabah malaysia ultramafic rock outcrops are widespread totalling 3500 km 2 one of the main outcrops in the tropical zone and predominantly of the peridotite type however strongly serpentinised peridotite is also locally common particularly along fault lines in the mt kinabalu area this study aimed to determine the extent of chemical variation in ultramafic soils in relation to the degree of serpentinisation and the weathering intensity and consequent potential ecological implications linked to resulting soil chemical fertility it was hypothesized that young soils and soils derived from bedrock with a significant degree of serpentinisation strongly differ from typical geric ferralsols and result in soil chemistries with more adverse properties to plant life e g low availability of the essential nutrients n p k and ca and high concentrations of potentially phytotoxic mg and ni ultramafic soil diversity linked to the age of the soil or the degree of serpentinisation would thus be a main factor of plant diversity and distribution the diverse topography of kinabalu park ultramafic soils present between 400 and 2950 m asl has given rise to high pedodiversity with the broad overall ultramafic soil types being i deep laterite soils geric ferralsols ii moderately deep montane soils dystric cambisols with mor humus iii shallow skeletal soils at high altitude eutric cambisols hypermagnesic and iv bare serpentinite soils hypereutric leptosols hypermagnesic at low altitude 200 700 m asl leptosols on serpentinite and eutric cambisols have the most extreme chemical properties in the whole kinabalu park area both with very high mg ca molar quotients with either high available ni cambisols or high ph leptosols these soils host specific and adapted vegetation high level of endemism that tolerates geochemical peculiarities including ni hyperaccumulators geric ferralsols present far less chemical constraints than hypermagnesian cambisols soils to the vegetation and host a tall and very diverse rainforest not so different than that on non ultramafic soils it therefore appears that altitude soil age and degree of bedrock serpentinisation are the main determining factors of soil properties the qualifier ultramafic alone is not sufficient to define soil geochemical and ecological conditions in the kinabalu park area probably more than in any other ultramafic region in the world

synchrotron based speciation of chromium in an oxisol from new caledonia importance of secondary fe oxyhydroxides in new caledonia the weathering of ultamafic rocks under a tropical climate has led to the residual accumulation of trace elements in lateritic soils widely dominated by fe oxyhydroxides the speciation of trace elements such as cr ni and co in these oxisols remains a major subject of interest regarding mining and environmental issues we have assessed the speciation of chromium in the upper part of an oxisol by combining bulk and spatially resolved chemical analyses epma and sem eds with synchrotron based spectroscopic data exafs and xanes epma indicates that the main hosts for chromium in the bedrock sample are the silicates forsterite enstatite and lizardite hosting of chromium in these easily weatherable mineral species could lead to a significant loss of this element upon weathering however total analyses of major elements indicate only a slight depletion of cr together with an immobility of fe and al and drastic losses of si and mg after the weathering of the bedrock such a low mobility of chromium is likely related to its significant incorporation in goethite and hematite formed after the weathering of fe 2 bearing primary silicates this efficiency of secondary fe oxyhydroxides at immobilizing chromium is demonstrated by quantitative analysis of exafs data that indicates that these mineral species host between 67 and 75 wt of total cr compared to the 18 to 22 wt of total cr hosted by chromite in addition sem observation and sem eds analyses performed on the oxisol samples also show some evidence for chemical weathering of chromite chromite could then represent a past and or present source of chromium upon extended tropical weathering of the studied oxisol rather than a stable host these results emphasize the importance of secondary fe oxyhydroxides compared to cr spinels on chromium hosting in oxisols developed upon tropical weathering of ultramafic rocks although the trapping mechanism of chromium mainly corresponds to incorporation within the structural network of goethite and hematite sorption reactions at the surface of these mineral species could also be involved in such a process in addition considering their potential oxidative reactivity that can generate cr 6 or enhance the chemical weathering of chromite the occurrence of mn oxides could significantly modify the behavior of chromium upon weathering these considerations indicate that further studies are needed to assess the actual potential of chromium release from oxisols developed upon weathering of ultramafic rocks under a tropical climate

stratral architectures of late quaternary regressive transgressive cycles in the roussillon shelf sw gulf of lions france abstract a seismic and sequence stratigraphy scheme of the southwestern area of the gulf of lions shelf nw mediterranean basin is presented through the analysis of high resolution seismic profiles obtained with a minisparker system and calibrated with published seismic and core data of the adjacent languedoc area the observed stratigraphic architecture records the repetition of four regressive transgressive cycles which constitute high frequency depositional sequences dss regressive intervals dominate the generation of shelf sedimentary architecture within regressive intervals the identification of progressively shallower clinoforms from proximal to distal in a downdip direction constitutes a strong indicator of the occurrence of forced regressions this stratigraphic pattern documents the preservation of potential sand prone reservoirs encased within widespread regressive wedges and directly connected with organic matter rich muds as distally there is no sharp basal contact between the two the unusual preservation of pre last glacial maximum transgressive deposits is attributed to the combined influence of previous shelf topography and dominant wave regime the most significant transgressions were recorded by shallow water deposits in distal middle and proximal locations distal and proximal deposits develop over relatively steep surfaces which caused slower transgressions and favoured the generation of wave dominated coastal deposits in contrast middle deposits show moderate development over a smooth shelf profile as a consequence of rapid shoreline translation the analysis of spatial changes of regressive transgressive cycles provided important information about the nature of shelf processes and about the relative significance of regressive versus transgressive intervals within each individual ds whose development was led by recent high frequency sea level cycles dominance of 120 ka cycles would imply that transgressive deposits represent a partial record of glacial interglacial transgressions dominance of 20 ka cycles is not favoured by the fact that the preservation of quaternary deposits is apparently limited on the shelf

natural cr vi contamination of groundwater in the cecina coastal area and its inner sectors tuscany italy a detailed hydrogeochemical study of groundwater in the cecina coastal plain livorno province italy and its inner sectors was undertaken in 2008 as chemical analyses carried out on groundwater since 2006 have revealed cr vi concentrations of up to 49 g l well above the permissible limit of 5 g l ophiolite outcrops are present throughout the study area and their fragments likely represent a significant portion of the existing multilayered aquifer skeleton waters delivered by the serpentinite outcrops have a typically mg hco3 composition whereas those of the coastal plain are prevailingly of the ca mg hco3 type with significant mg contents significant no3 contamination characterises the studied coastal plain and an interesting negative correlation exists between cr vi and both no3 and so4 deriving from the widespread use of nh4 2so4 as a farm fertilizer chromium speciation calculations carried out using the eq3nr code reveal that the prevailing cr vi species in solution is cro4 2 however cacro4 and mgcro4 neutral complexes represent significant percentages up to 42 these findings suggest that the mobility and consequently the bioavailability of cr vi can be significantly enhanced by these neutral complexes which are not considered to be affected by adsorption desorption processes the cr vi source investigated by means of the mg sio2 molar ratio seems to be represented mainly by mg bearing minerals of the chlorite group petrographic observations confirm the occurrence of this mineral group the interaction between rainwater and the local serpentinite rock was simulated at different p text co 2 and p text o 2 conditions by reaction path modelling using the eq3 6 software package p text o 2 was varied in accordance with the assumption that redox conditions are determined in part by no3 results are in good agreement with experimental data on spring waters and subordinately with data on some coastal plain groundwater which plot in a rather wide p text co 2 and p text o 2 field although the dissolved cr content is mostly of natural origin fertilization may affect its fate

small rivers contribution to the quaternary evolution of a mediterranean littoral system the western gulf of lion france abstract along the mediterranean coasts and the atlantic french coast former and actual research programs focused on major river systems estuaries and deltas characterized by a last glacial relative sea level lowstand and incision and a well developed sedimentary incised valley infilling deposited during the following sea level rise and highstand this paper presents the preliminary results of a program focused on a particular area of the gulf of lion coast with a thin sedimentary cover over the substratum and only minor rivers with non apparent and important sedimentary contribution during the late quaternary the results show that in this area the best pliocene to actual sedimentary record is preserved the paper rests on the analysis of an extensive database of recent high resolution and very high resolution seismic reflection lines and previously published core data seismic data show that a major complex of paleovalleys connected with the orb aude and agly rivers is preserved on the inner shelf and adjacent coastal plain on the inner shelf the separated incised valleys merged in a unique broad and shoreparallel incision dipping southward at the southward extremity the incision turns eastward and seaward the basal surface of this incision extends seawards under six to seven late quaternary depositional sequences preserved on the mid and outer shelf the infilling of the complex of paleovalleys is characterized by aggrading deposits attributed to periods of relative sea level rise transgressive systems tracts organized into several subunits bounded by internal discontinuities locally deeply incising the discontinuities are amalgamated surfaces including successive sequence boundaries indicative of phases of relative sea level falls merged with transgressive surfaces indistinct tidal and wave ravinement surfaces the subunits are the part of late quaternary depositional sequences preserved in estuarine environments they are the lateral equivalents of landward fluvial terraces and seaward coastal and prodeltaic deposits on the shelf using borehole dataset the underlying and eroded deposits below the basal unconformity are correlated with pliocene deposits outcropping landward in the hinterland the top of the incised valleys complex is capped by the last glacial lowstand surface of erosion 18 ky b p reworked by the postglacial transgressive surface ts dissociated near the shoreline into a tidal and a wave ravinement surfaces above the ts the very high resolution vhr seismic data in the lagoons the tidal channels and cores reveal in details the stratigraphic architecture of the deposits at the base a small wedge constitutes the postglacial transgressive systems tract tst locally thinning in the areas distant of the sediment point sources the tst is capped by a flat surface of wave reworking maximum flooding surface or mfs prolongating under the leucate lagoon and merging offshore at the seafloor boreholes and vhr seismic lines trough the coastal barrier and in the lagoon show that the shoreline probably migrated far landward at the end of the transgression when the rate of sea level rise decreased strongly the shoreline migrated seaward and prograding and aggrading sandy material with landward muddy lateral equivalent facies deposited early highstand systems tract hst above the mfs offshore fine material deposited as a sigmoidal blanket of mud originating in part from the north east and rhone river under oceanic circulation equivalent to a subaqueous prodelta subsequently the modern beach barrier built up by wave reworking of the early hst this new study of the western part of the gulf of lion inner shelf and littoral illustrates an incised valley complex and thus presents the best preserved example of the sedimentary record of the effects of the relative sea level changes during the pliocene to actual period for the first time the land to sea transition is preserved and the late quaternary depositional sequences are in a great part observed the last post glacial deposits present a simplified but very different organisation compared to a record front of the adjacent rhone river consequently a synthesis is now possible

post glacial persistence of turbiditic activity within the rhone deep sea turbidite system gulf of lions western mediterranean linking the outer shelf and the basin sedimentary records emplacement of post glacial turbidites is commonly controlled by rapid changes in sea level or by seismicity on the continental rise of the gulf of lions western mediterranean an aseismic area we identified turbiditic beds deposited during the rising stage and highstand of sea level swath bathymetry sediment cores in situ cone penetrating tests cptu heavy mineral associations and radiocarbon dating determined the source composition distribution and age of the turbiditic beds turbidites are composed of homogeneous to positively graded silts to medium sand with quartz up to 90 shell debris and shelfal benthic faunas their distribution on the sea floor is very patchy and controlled by abundant inherited erosional bedforms their source is found in relict regressive sands at the outershelf their deposition occurred just after the onset of the post glacial sea level rise and the concomitant sediment starvation of the rhone deep sea turbiditic system until recently whilst canyons are fed with sand by strong seasonal hydro sedimentary dynamics on the outershelf the emplacement of post glacial turbidites is not controlled by sea level changes but probably by the periodic flushing of the canyons our study revealed that this low energy aseismic margin undergoes significant transport of sand down to the base of slope during the sea level rise and the holocene highstand

shoreface migrations at the shelf edge and sea level changes around the last glacial maximum gulf of lions nw mediterranean the bourcart herault canyon interfluve in the gulf of lions nw mediterranean was the site of very high sedimentation up to 2 5 m kyr around the last glacial maximum due to the vicinity of major fluvial systems that fed the shelf edge shoreface deposits and offshore muds deposited during each glacial interglacial 100 kyr cycle created a repeated motif with high angle and low angle clinoforms on seismic profiles new detailed morphological sedimentological and paleo environmental data constrained by 14c dating allow us to propose a scenario for the evolution of this critical area between 46 and 15 cal kyr bp the major seismic sequence s5 formed as a forced regression during the overall sea level fall between mis 3 and mis 2 can be sub divided into several prograding units which indicate that relative sea level changes were punctuated by intervals of increased fall or slow down or even stillstand similarly the onset of sea level rise was marked by steps during which wave cut terraces formed and can be tracked all around the gulf of lions three stillstands or slow downs of sea level change are identified and dated by deposits found at 90 m relative sea level 21 cal kyr bp 110 115 m rsl 18 17 cal kyr bp and 98 105 m rsl before 15 9 cal kyr bp cementation of beach rocks that now form eroded pinnacles culminating at 90 m occurred during the 21 kyr stillstand the position of relative sea level during the maximum lowstand is not known but should be deeper than 115 m periods of increased northwesterly winds favoured transport of coarser sediment at the shelf edge in relation with deep water cascading this created a distinct sandy interval during the period of heinrich event 2 around 24 cal kyr bp at the origin of amplitude anomaly on very high resolution seismic data the increased sea level rise around 15 cal kyr bp resulted in an abrupt decrease of sedimentation

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

redox condition in the nanhua basin during the waning of the sturtian glaciation a chromium isotope perspective abstract the neoproterozoic oxygenation event noe is often considered to be synchronously and possibly causally associated with the cryogenian glaciations reconstructing early cryogenian redox conditions is therefore essential for understanding the onset of the noe we analyzed cr isotope compositions 53cr as well as major and rare earth element ree concentrations of the banded iron formations bifs in the basal fulu formation of the xiajiajiang section nanhua basin which are thought to have been deposited during the waning stage of the sturtian glaciation strongly positively fractionated authigenic 53cr values were obtained after detrital correction ranging from 0 64 to 1 22 and averaging at 0 91 0 40 2 n 10 or after detrital evaluation 0 71 this suggests extensive oxidative cr cycling occurred at the earth s surface and implies that the po2 was probably higher than 1 pal during this period the lack of ce anomalies 0 90

weathering and transport of chromium and nickel from serpentinite in the coast range ophiolite to the sacramento valley california usa abstract a soil geochemical study in northern california was done to investigate the role that weathering and transport play in the regional distribution and mobility of geogenic cr and ni which are both potentially toxic and carcinogenic these elements are enriched in ultramafic rocks primarily serpentinite and the soils derived from them 1700 10 000 mg cr per kg soil and 1300 3900 mg ni per kg soil in the coast range ophiolite chromium and ni have been transported eastward from the coast range into the western sacramento valley and as a result valley soil is enriched in cr 80 1420 mg kg 1 and ni 65 224 mg kg 1 compared to median values of u s soils of 50 and 15 mg kg 1 respectively nickel in ultramafic source rocks and soils is present in serpentine minerals lizardite antigorite and chrysotile and is more easily weathered compared to cr which primarily resides in highly refractory chromite mg fe2 cr3 al fe3 2o4 although the majority of cr and ni in soils are in refractory chromite and serpentine minerals the etching and dissolution of these minerals presence of cr and ni enriched clay minerals and development of nanocrystalline fe hydr oxides is evidence that a significant fractions of these elements have been transferred to potentially more labile phases

sedimentary sequences in the gulf of lion a record of 100 000 years climatic cycles abstract the wide continental shelf of the gulf of lion up to 70 km has been the object of numerous investigations since the early days of oceanography yet the question of sequences duration the mechanisms of deposition and factors implied remained unanswered a study of a very dense grid of very high resolution vhr seismic reflection sparker data associated with surficial cores both collected by ifremer between 1992 and 2001 on the outer shelf and upper slope offshore of sete in the languedoc region gives a new insight into these issues analysis of the 3d geometry of the sedimentary record reveals a basic depositional pattern consisting of a pair of horizontally juxtaposed and downlapping prisms prism pi with low angle clinoforms results obtained from integrating lithology palynology micropaleontology seismic stratigraphy stratigraphic simulation support the hypothesis that the basic depositional pattern records a 100 000 years glacioeustatic interglacial glacial cycle as previously suggested by aloisi aloisi j c 1986 sur un modele de sedimentation deltaique contribution a la connaissance des marges passive these de doctorat d etat universite de perpignan 162 pp prisms pi corresponds to deposition at high sea level and prisms pii to deposition during low sea level at glacial maxima five sequences of paired prisms capped by five major erosion surfaces have been identified and modelled showing that the corresponding glacioeustatic cycles the last five cycles at least are recorded on the shelf of the western part of the gulf of lion

sedimentary architecture of a plio pleistocene proto back arc basin wanganui basin new zealand the sedimentary architecture of active margin basins including back arc basins is known only from a few end members that barely illustrate the natural diversity of such basins documenting more of these basins types is the key to refining our understanding of the tectonic evolution of continental margins this paper documents the sedimentary architecture of an incipient back arc basin 200 km behind the active hikurangi subduction margin north island new zealand the wanganui basin wb is a rapidly subsiding plio pleistocene sedimentary basin located at the southern termination of the extensional back arc basin of the active central volcanic region tvz the wb is asymmetric with a steep thrust faulted outer arc ward margin and a gentle inner craton ward margin it contains a 4 km thick succession of plio pleistocene sediments mostly lying offshore composed of shelf platform sediments it lacks the late molasse like deposits derived from erosion of a subaerial volcanic arc and basement observed in classical back arc basins detailed seismic stratigraphic interpretations from an extensive offshore seismic reflection data grid show that the sediment fill comprises two basin scale mega sequences 1 a pliocene 3 8 to 1 35 ma sub parallel regressive bpre growthq sequence that overtops the uplifted cratonward margin above the reverse taranaki fault and 2 a pleistocene 1 35 ma to present divergent transgressive bsyn growthq sequence that onlaps i the craton ward high to the west and ii uplifted basement blocks associated with the high angle reverse faults of the arc ward margin to the east along strike the sediments offlap first progressively southward mega sequence 1 and then southeastward mega sequence 2 with sediment transport funnelled between the craton and arc ward highs towards the hikurangi trough through the cook strait the change in offlap direction corresponds to the onset of arc ward thrust faulting and the rise of the axial ranges at ca 1 75 ma resulting in 5100 5700 m of differential subsidence across the fault system sedimentation has propagated south to southeast ward over the last 4 myrs at the tip of successive back arc graben volcanic arcs and the associated thermally uplifted parts of the north island following the southward migration of the hikurangi subduction margin subsidence occurred by mantle flow driven flexure the result of active down drag of the lithosphere by locking of the hikurangi subduction interface and sediment loading the wb is considered to be a proto back arc basin that represents the intermediate stage of evolution of an epicratonic shelf platform impacted by active margin processes

chromium isotopes in marine hydrothermal sediments abstract hydrothermal chromium cr cycling contributes to marine cr inventories and their cr isotopic composition yet cr isotope effects associated with this cycling remain poorly documented here we determine the distribution isotopic composition and diagenetic mobility of cr in hydrothermal sediments from the distal flank of the south east pacific rise sepr dsdp site 598 we find that cr is primarily associated with the metalliferous iron oxyhydr oxide and detrital components of the sediment 0 4 3 6 mg kg 1 whereas cr concentrations are much lower in the dominant carbonate phase 80 cr from the sediment relative to fe we propose this loss is tied to oxidation of authigenic cr iii to cr vi followed by diagenetic remobilization and efflux from the sediment pile the bulk 53cr composition of the sepr sediments is isotopically light 0 24 to 0 57 0 05 and the authigenic 53cr is as light as 1 2 0 2 we argue that this light cr isotopic composition results from the partial reduction of oxic seawater bearing cr vi by hydrothermal vent fluids enriched in fe ii aq diagenetic oxidation of the reactive cr pool by mn oxides and loss of cr vi from the sediment may further deplete the sediment in 53cr during diagenesis the 53cr composition of the detrital cr fraction of the sediment average 53cr composition 0 05 0 04 falls within the igneous silicate earth ise range revealing that detrital cr delivered to this region of the pacific ocean is unfractionated and has carried a relatively constant 53cr composition over the last 5 7 million years together our results show that light 53cr compositions in hydrothermal sediments are imparted through a combination of processes previously overlooked in the marine cr biogeochemical cycle and that the 53cr composition of such sediments may provide a rich source of information on paleo marine redox conditions

inside the head and tail of a turbulent gravity current gravity currents are an important buoyancy driven flow in environmental geophysical and industrial settings turbulence and mixing is commonplace in these flows but is typically overlooked in theoretical models and predictions sher woods j fluid mech vol 784 2015 pp 130 162 have quantified the velocity and density structure in turbulent gravity currents by combining high quality experimental data with new theory their insights are set to stimulate significant advances in the area

cr vi occurrence and geochemistry in water from public supply wells in california hexavalent chromium cr vi in 918 wells sampled throughout california between 2004 and 2012 by the groundwater ambient monitoring and assessment priority basin project gama pbp ranged from less than the study reporting limit of 1 microgram per liter g l to 32 g l statewide cr vi was reported in 31 percent of wells and equaled or exceeded the recently established 2014 california maximum contaminant level mcl for cr vi of 10 g l in 4 percent of wells cr vi data collected for regulatory purposes overestimated cr vi occurrence compared to spatially distributed gama pbp data ninety percent of chromium was present as cr vi which was detected more frequently and at higher concentrations in alkaline ph 8 oxic water and more frequently in agricultural and urban land uses compared to native land uses chemical isotopic tritium and carbon 14 and noble gas data show high cr vi in water from wells in alluvial aquifers in the southern california deserts result from long groundwater residence times and geochemical reactions such as silicate weathering that increase ph while oxic conditions persist high cr vi in water from wells in alluvial aquifers along the west side of the central valley results from high chromium in source rock eroded to form those aquifers and areal recharge processes including irrigation return that can mobilize chromium from the unsaturated zone cr vi co occurred with oxyanions having similar chemistry including vanadium selenium and uranium cr vi was positively correlated with nitrate consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return

quantifying subsidence and isostatic readjustment using sedimentary paleomarkers example from the gulf of lion passive margins are characterised by an important tectonic and thermal subsidence which favours a good preservation of sedimentary sequences this sedimentation in turn enhances the subsidence because of loading effects we present here a direct method based on sedimentary markers seen on seismic data to evaluate total subsidence rates from the coast to the outer shelf and to the deep basin in the gulf of lion from the beginning of massive salt deposition up to present day the last circa 6 ma with minimal theoretical assumptions on the shelf the pliocene quaternary subsidence shows a seaward tilt reaching a rate of 240 m ma 15 m ma at the shelf break 70 km from the present day coastline i e a total angle of rotation of 0 88 0 16 ma we were also able to measure and quantify for the first time the isostatic rebound of the outer shelf due to the messinian salinity crisis msc this value is very high and reaches up to 1 3 km of uplift during the crisis around the herault sete canyon heads around 1 8 km ma on the slope we also find a seaward tilting subsidence from km 90 to km 180 with a measured angle of 1 41 from 180 km to the deepest part of the basin the total subsidence is then almost vertical and reaches 960 m ma 40 m ma during the last 5 7 ma 0 25 ma in the deepest part of the basin the subsidence is organised in three compartments that seem related to the very deep structure of the margin during the opening of the liguro provencal basin these very high total subsidence rates enable high sedimentation rates along the margin with sediments provided by the rhone river flowing from the alps which in turn enable the detailed record of climate evolution during pliocene quaternary that make of the gulf of lion a unique archive

analysis and direct numerical simulation of the flow at a gravity current head part 1 flow topology and front speed for slip and no slip boundaries direct numerical simulations are performed of gravity current fronts in the lock exchange configuration the case of small density differences is considered where the boussinesq approximations can be adopted the key objective of the investigation is a detailed analysis of the flow structure at the foremost part of the front where no previous high resolution data were available for the simulations high order numerical methods are used based on spectral and spectral element discretizations and compact finite differences a three dimensional simulation is conducted of a front spreading along a no slip boundary at a reynolds number of about 750 the simulation exhibits all features typically observed in experimental flows near the gravity current head including the lobe and cleft structure at the leading edge the results reveal that the flow topology at the head differs from what has been assumed previously in that the foremost point is not a stagnation point in a translating system rather the stagnation point is located below and slightly behind the foremost point in the vicinity of the wall the relevance of this finding for the mechanism behind the lobe and cleft instability is discussed in order to explore the high reynolds number regime and to assess potential reynolds number effects two dimensional simulations are conducted for reynolds numbers up to about 30 000 for both no slip and slip i e shear stress free boundaries it is shown that although quantitative reynolds number effects persist over the whole range examined no qualitative changes in the flow structure at the head can be observed a comparison of the two dimensional results with laboratory data and the three dimensional simulation provides evidence that a two dimensional model is able to capture essential features of the flow at the head the simulations also show that for the free slip case the shape of the head agrees closely with the classical inviscid theory of benjamin

accessory chromium spinels their coexistence and alteration in serpentinites abstract accessory chromium spinel occurring in serpentinites is usually altered the extent of this alteration and its relationship to alteration processes such as serpentinization and metamorphism is not defined complicating the use of altered spinel as a petrogenetic indicator here the relationship between different alteration processes and spinel alteration is evaluated in terms of accessory chromium spinel occurring in serpentinites of progressive metamorphism in the eastern central alps two coexisting cr spinels were identified i e an altered fe rich cr spinel i with cr al and an fe poor cr spinel ii with al cr which exsolved a cr fe 3 phase and which resisted alteration alteration of cr spinel i is evident from decreasing al mg and cr values with a trend leading to ferrite chromite trend a an enrichment in cr trend b related to co 2 in the serpentinizing fluid indicated by the presence of carbonate talc or tremolite is superimposed to a alteration is a decomposition of the spinel structure caused by the dissolution of mg al and cr during serpentinization dissolution of cr is favored in a reduced environment whereas reprecipitation occurs under locally oxidizing conditions indicated by the presence of co 2 sio 2 detected in spinel is a relative measure of the degree of alteration metamorphism up to amphibolite facies recrystallized and homogenized preexisting spinel phases to various degrees whether or not and to what extent a spinel alters depends on its fe content fe 2 stabilized in the octahedral site high cfse is responsible for an inverse and less stable spinel structure fe rich spinels cr spinel i are therefore readily subjected to alteration whereas fe poor spinels cr spinel ii are resistant to alteration during the serpentinization processes

sand bodies at the shelf edge in the gulf of lions western mediterranean deglacial history and modern processes abstract the outer continental shelf of the gulf of lions is covered by thick mainly regressive sand deposits a combination of seismic sedimentological and geochronological methods allows us to demonstrate that a veneer of transgressive sand bodies few m to less than 1 m thick reworks these deposits they take the form of sand ridges and transverse dunes that formed at different periods in fact the low gradient outer shelf of the gulf of lions displays a complete record of deglacial history including not only transgressive deposits that formed during sea level rise but also bedforms that still evolve under episodic high energy events that occur under more highstand conditions core lithology 14 c dates and regional sea level curve suggest that the formation of the sand ridges was favoured during a period of deceleration of sea level rise such as during the younger dryas event the dunes are part of a mobile carpet here u160 the deposition of this marine sand veneer is possibly related to the interplay between different factors that trigger the turning on off for bottom currents sand deposition transport on the outer shelf in fact the sands appear to have been reworked intermittently due to high energy conditions in shallow water depth currents wave regime and wind driven circulation as well as they form current ridges superimposed to the transgressive deposits in the westernmost part of the studied area at the bourcart canyon s head

precipitation and dissolution of chromite by hydrothermal solutions in the oman ophiolite new behavior of cr and chromite chromite is a typical refractory igneous mineral precipitated from mafic magmas at relatively high temperatures chromites commonly occur in sedimentary metamorphic and metasomatic rocks where they are interpreted as relics of an igneous phase and serve as the source of cr for low temperature cr bearing minerals we present evidence for the nucleation of chromite within hydrothermal solutions we have found minute euhedal chromite grains enclosed by uvarovite ca cr garnet in a diopsidite metasomatically replacing the layered gabbro of the oman ophiolite the uvarovite shows oscillatory concentric zoning in terms of cr no cr cr al and the chromite is embedded only in the high cr no zones of the uvarovite another diopsidite replacing peridotite in the underlying upper mantle section contains xenocrystic chromite which is partly dissolved this suggests that a hydrothermal solution collected cr by partial to total dissolution of chromite within the upper mantle and precipitated chromite along with high cr no uvarovite within the lower crust upsection the metasomatic agent involved was a co2 so2 and cl bearing hydrothermal solution containing appreciable silicate components that could carry cr possibly as a complex the hydrothermal chromite is similar in chemistry to that commonly found in igneous rocks e g cr no 0 8 mg mg fe2 0 1 0 2 tio2 0 3 wt and fe3 cr al fe3 up to 0 3 but its cr no is clearly different from that of mantle chromite 0 6 0 7 in peridotites and chromitites from the oman ophiolite the results from this study suggest that a hydrothermal origin is possible for chromites in ultramafic rocks that have experienced fluid activity assuming that there is sufficient chromite at the fluid source

influence of ultramafic rocks and hot springs with travertine depositions on geochemical composition and baseline of soils application to eastern central greece abstract ultramafic rocks and hot springs which occur on almost every continent of our planet lead to enriching concentration to several elements including some potentially toxic ones to the soil groundwater fauna and flora and subsequently are posing potential risks to human health a geochemical and mineralogical soil survey was undertaken in eastern central greece an area characterised by the presence of ultramafic rocks of ophiolite complexes and hot springs with thermogenic travertine depositions the research aimed to investigate their influence on soil mineralogy and geochemistry and to establish the soil geochemical baseline values one hundred four soil samples were collected from 74 sites at depths of 0 25 cm and 25 50 cm they were found to be enriched in ca 5 17 fe 3 72 mg 2 08 co 28 mg kg cr 252 mg kg cu 32 mg kg and ni 267 mg kg relative to the median values of both greek and european soil and upper continental crust factor analysis revealed three main factors controlling the soil chemical composition reflecting the influence of ultramafic rocks ni co cr and fe pedogenesis processes ba al and k and thermogenic travertine deposits ca and sr all the factors showed a significant spatial correlation with the geological features within the study area geochemical baselines were estimated for three sub areas based on the three controlling factors revealed by the multivariance statistical analysis and spatial data calculating only one baseline value based on the total dataset would lead to incorrect baseline values for several elements the outcome of the present research could be used in future studies at regions with similar geological features i e serpentine soils and hot springs depositions providing a comparative example concerning the concentrations of several elements including some potentially toxic ones to the soil their host mineral phases and a scientific approach for setting pragmatic geochemical baseline values for pollution assessment

3 d process modelling of ancient storm dominated deposits by an event based approach application to pleistocene to modern gulf of lions deposits abstract a new numerical model was developed for 3 d characterization of deposits generated by storms along clastic coasts away from major rivers it is based on the assumption that the preserved sedimentary heterogeneities result mainly from a succession of deposits generated during both fair weather periods and major events storms in our case hydro sedimentary processes are first modelled during these major storms i transport parallel and transverse to the coast of suspended sediment by the strongest unidirectional currents littoral drift and downwelling currents ii sea bed erosion due to shear stress generated by unidirectional and wave induced oscillatory currents iii deposition of sediment fair weather deposits are modelled by an average deposition process the results of the numerical model i e the description of the sedimentary deposits are multi lithologic in three dimensions and with a flexible vertical resolution the latter is one of the main strengths of the model because the vertical description of the deposits can be adapted to the duration and extent of the simulation in order to save computation time very precise results definition of less than 1 mm can be obtained at a small time scale for storms lasting several hours to several days and reservoir scale results at a longer time scale the numerical model was applied to the gulf of lions which is located off the southern french coast in the north western mediterranean first present day storm deposits are simulated in order to validate the storm process modelling then sedimentary deposits formed over several thousands of years during the pleistocene are simulated in order to validate the sediment deposit modelling the model results fit well with observations and validate the approach of simulating the shelf deposits and their associated sedimentary heterogeneities at reservoir scale with an event and process based method this innovative approach seems promising for providing future geological models with realistic petrophysical properties

quaternary stratal architecture of the barcelona prodeltaic continental shelf nw mediterranean abstract the barcelona continental shelf is part of a 6 20 km wide canyon bounded shelf located off the city of barcelona ne spain this study integrates newly acquired high resolution single channel seismic reflection profiles and available lithological information of the barcelona shelf to describe its late quaternary architecture and the role of global glacio eustatic fluctuations and local factors in its development four major sequence boundaries are identified throughout the seismic dataset they are tentatively correlated with the four last 4th order 100 120 ka high amplitude late quaternary glacio eustatic lowstands most of the stratigraphic record is formed by falling stage systems tracts with forced regressive deposits which confers a general progradational vertical stacking pattern transgressive systems tracts are represented by continuous units confined directly off river sources and on previously eroded surfaces stillstand deposits are difficult to recognize in the available dataset the uppermost seismic unit corresponds to the holocene shore parallel besos and llobregat joint prodelta affected by the prevailing south westward circulation the general architecture of the late quaternary barcelona shelf deposits is determined by global glacio eustatic cycles however the lateral variability of the seismic units depends largely on local factors such as i the position of sediment sources essentially the llobregat river ii differential subsidence and especially sediment compaction iii erosive processes such as canyon incision mass wasting or wave base dynamics and iv underlying geomorphic restrictions

detailed architecture of a compound incised valley system and correlation with forced regressive wedges example of late quaternary tet and agly rivers western gulf of lions mediterranean sea france abstract quaternary incised valley systems are usually characterized by the preservation of a single valley fill attributed to the last post glacial period moreover there are very few cases of correlation between incised valley system developed on inner shelf and sedimentary units observed on the mid to outer shelf mainly forced regressive wedges the roussillon shelf in the western part of the gulf of lion is a particular example of preserved quaternary compound incised valley system also characterized by a direct correlation with the forced regressive lowstand wedges on the mid outer shelf high resolution seismic data and a borehole 60 m deep located on the beach barrier permit an accurate study of the geometry and lithology of the system six imbricated and more or less preserved incised valleys and valley fills are observed up to the inner to mid shelf the key surfaces associated to the incised valleys are correlated to the boundaries of the forced regressive wedges they are assumed to be reworked surfaces at the borehole location only few thin layers less than 1 m thick of coarse grain and or floating pebbles are observed and should correspond to preserved fluvial lowstand deposits reworked under marine influence the valley fills are mainly composed of estuarine muddy silts from ams 14c age dating it is inferred that the uppermost incised valley system is younger than 45 ky cal bp based on those observations the six preserved incised valley systems are assumed to be controlled by the last six 4th order sea level cycles 100 ky of the middle to late quaternary the paleo topography of the underlying plio quaternary deposits controls the compound incised valley system location the deep topography of the messinian erosionnal surface is a controlling factor at a lower degree the partial preservation of the successive valley fill is attributed not only to the differential subsidence but also to the lateral migration of each incision and to the hydrodynamic regime

inertial oscillations on the continental shelf of the gulf of lions observations and theory abstract observations in the gulf of lions northwestern mediterranean sea in summer have shown that gusts of wind lasting a few days generate transient upwellings and inertial motions oscillations at the inertial frequency were observed in current meter data near the shore and at a frequency 10 greater in the temperature data vertical coherences in current meter data show a strong baroclinic mode at frequencies greater than inertial frequency a simple one dimensional two layer transient model suggests that these motions are associated with two different physical processes the first process describes the local response of the ocean to meteorological forcing the second is associated with the propagation of long internal waves generated in the transient phase of the geostrophic adjustment process as suggested by the model the direction of propagation of the internal waves is computed from current and temperature data measured at one point and it is found that the shore is the source zone

sedimentary evolution of overlapped sand bodies in terrestrial faulted lacustrine basin insights from 3d stratigraphic forward modeling abstract terrestrial faulted lacustrine basins usually have large variabilities in structural subsidence and multiple river sources the facies in such basins are thus characterised by frequently changed facies and complex relationship of overlapped sand bodies e g liaoxi depression of liaodong bay bohai sea china therefore it s a great challenge to quantitatively describe evolution of sand bodies and their overlap relationship in this study a three dimensional stratigraphic forward model is used to solve this problem which is corrected according to well log data after the parameter optimization was verified against borehole strata thickness and lithology this model had a thickness error within 8 and the lithology distribution agreed with the well data as a whole four evolution phases of the shahejie 3 formation were recognised through the modeling in the first phase the lake level rose and the eastern fan delta sand developed in the second phase the fan delta sand scaled up and the braided river delta front sand developed at a small scale in the third phase the lake level shifted from falling to rising the fan delta sand further expanded the scale and the braided river delta developed at a large scale sands on both sides overlapped at a large scale in the fourth phase the lake level rose the lake basin expanded and lake shale was the main lithology in the study area from the sedimentary evolution of es3 formation sand overlapped in the third stage in 39 75 ma two parts of the sand body began to overlap and reached largest scale in 39 6 ma which was approximately 10 km 2 both then retrograded to a separation in 39 ma when the overlap ended coupling stratigraphic forward simulation with uncertainty quantification allowed us to estimate the influence of each stratigraphic parameter on sand overlap fluvial discharge appears to be the most influential parameter while the initial bathymetry and lake level variations exert a minor to moderate impact

timing of tectonic emplacement of the ophiolites and terrane paleogeography in the hellenides the timing of tectonic emplacement of the ophiolites is analyzed in the four oceanic terranes of the hellenides h2 h4 h6 h8 the criteria for this analysis are based on a the post emplacement sedimentary cover or intrusive rocks b the syn emplacement tectonostratigraphic formations and c the youngest rocks involved in the structure of the autochthon and the allochthon unit in each case the timing becomes younger towards the more external tectonic units of the hellenides with i late eocene oligocene age in the external ophiolite belt of the pindos cyclades oceanic terrane h2 ii late jurassic early cretaceous age in the internal ophiolite belt of the vardar axios oceanic terrane h4 iii post liassic pre late jurassic age in the ophiolites of lesvos circum rhodope oceanic terrane h6 and iv pre late jurassic age in the ophiolites of volvi eastern rhodope terrane h8 an ophiolite obduction model can be applied with the ophiolitic nappes always emplaced on top of pre alpine continental terranes with mesozoic shallow water carbonate platforms the geometry of the continental terranes drifting during the mesozoic within the tethys ocean controls the number and dimensions of the tethyan oceanic basins where a continental terrane dies out the two adjacent oceanic basins merge into one larger basin this seems to be the case of the pelagonian terrane h3 which is terminated north of skopje where the pindos oceanic basin h2 merges with the vardar axios oceanic basin h4

chromium geochemistry in serpentinized ultramafic rocks and serpentine soils from the franciscan complex of california weathering of ultramafic rocks and serpentinites in the franciscan complex of california produces serpentine soils containing high concentrations of cr as well as other potentially toxic elements including ni co and mn chromium concentrations in serpentine soils from jasper ridge biological preserve in the central coast range are as high as 4 760 mg kg 1 nearly three times greater than the serpentinite protolith 1800 mg kg 1 chromium containing minerals within the bedrock include chlorite 0 3 cr wt enstatite 0 4 cr wt augite 0 7 cr wt chromite 10 8 cr wt magnetite 8 2 10 3 cr wt and an ultra fine grained mixture of spinel and a silicate phase containing 13 3 cr weight percent chromium concentrations in serpentine soil profiles fluctuate between 1 725 to 4 760 mg kg 1 and do not correspond to variations in soil ph organic carbon or electrical conductivity the enrichment and variability of soil cr is directly related to the modal abundance and weathering of chromite cr magnetite and the spinel silicate mixture by comparison cr silicates account for

scaling analysis of multipulsed turbidity current evolution with application to turbidite interpretation deposits of submarine turbidity currents turbidites commonly exhibit upward fining grain size profiles reflecting deposition under waning flow conditions however more complex grading patterns such as multiple cycles of inverse to normal grading are also seen and interpreted as recording deposition under cycles of waxing and waning flow such flows are termed multipulsed turbidity currents and their deposits pulsed or multipulsed turbidites pulsing may arise at flow initiation or following downstream flow combination prior work has shown that individual pulses within multipulsed flows are advected forward and merge such that complex longitudinal velocity profiles eventually become monotonically varying although transition length scales in natural settings could not be predicted here we detail the first high frequency spatial vertical streamwise and temporal measurements of flow velocity and density distribution in multipulsed gravity current experiments the data support both a process explanation of pulse merging and a phase space analysis of transition length scales in prototype systems the point of merging corresponds to the transition in any deposit from multipulsed to normally graded turbidites the scaling analysis is limited to quasi horizontal natural settings in which multipulsed flows are generated by sequences of relatively short sediment failures 10 km sequences of breaches or where pulsing arises from combination at confluences of single pulsed flows such flows may be responsible for the pulsing signatures seen in some distal turbidites 100 km from source

late pleistocene holocene history of a tectonically active segment of the continental margin nekor basin western mediterranean morocco abstract in active basins tectonics can segment the continental shelf and control its stratigraphic architecture and physiography segmentation can explain the local evolution and morphology of the continental shelf because of sea level variations local tectonic segmentation and hydrodynamic processes here we investigate the tectonically active morocco continental margin southern alboran sea using high resolution seismic profiles and multibeam bathymetric data the active faults bounding the transtensive nekor basin triggered the segmentation of the shelf into three sectors showing different subsidence rates a western sector corresponding to an extensive fault relay a central sector corresponding to the subsiding al hoceima bay and an eastern sector corresponding to the footwall of the trougout senestral normal fault results show that the staircase morphology of the shelf corresponds to successive submarine terraces at the shelf edge st1 mid shelf st2 and inner shelf st3 around 110 m 80 m and 40 to 20 m deep respectively the terraces correspond to the top of prograding wedges seaward and are erosive landward they are correlated with stillstand from the last glacial maximum to the holocene highstand above the terraces sub aqueous dune fields are interpreted as degraded and deposited during the post glacial transgression in the central sector typical delta front seafloor undulations on the shelf and crescent shaped bedforms at the head of marine incisions on the upper slope denote a fluvial influence during the holocene seismic stratigraphy analysis revealed the preservation of six seismic units bounded by polygenic regional unconformities s1 s2 s3 s4 and s5 based on comparison with other mediterranean margins s1 to s5 are attributed to 4th order maximum regressive surface we discuss the local preservation of the system tracts as a function of the vertical motion and the physiography of this tectonically active domain this study provides useful clues for future local paleo seismic analysis and to advance our understanding of sedimentary processes in active areas

geochemistry and geobiology of a present day serpentinization site in california the cedars ultra basic ph 11 12 reducing 656 to 585 mv groundwater springs discharging from serpentinized peridotite of the cedars ca were investigated for their geochemistry and geobiology the spring waters investigated were of meteoric origin however geochemical modeling suggests that there were two sources of groundwater a shallow source with sufficient contact with the cedars peridotite body to be altered geochemically by serpentinization and a deeper groundwater source that not only flows through the peridotite body but was also in contact with the marine sediments of the franciscan subduction complex fsc below the peridotite body we propose that the groundwater discharging from lower elevations gps1 and cs1 reflect the geochemistry of the deeper groundwater in contact with fsc while groundwaters discharging from springs at higher elevations ns1 and bsc were a mixture of the shallow peridotite only groundwater and the deeper groundwater that has been in contact with the fsc cell densities of suspended microbes within these waters were extremely low in the ns1 and bsc spring fluids cell densities ranged from 10 2 to 10 3 cells ml while suspended cells at gps were lower than 10 cells ml however glass slides incubated in the bsc and gps1 springs for 2 3 weeks were colonized by cells with densities ranging from 10 6 to 10 7 cells cm 2 attached to their surfaces all of the springs were very low 1 m in several essential elements and electron acceptors e g nitrate ammonium sulfate and phosphate required for microbial growth which is not uncommon at sites of continental serpentinization gases rich in n 2 h 2 and ch 4 were exsolving from the springs the stable carbon isotope value 13 c ch4 68 0 6 and the ch 4 c 2 10 3 of methane and other gaseous hydrocarbons exsolving from ns1 were typical of microbially sourced methane whereas the isotope values and the ch 4 c 2 of bsc and cs1 springs were more enriched in 13 c and had ch 4 c 2 10 3 suggesting a mixture of microbial and non microbial methane the concentrations of aromatic compounds and ethane propane iso and n butane were well described by simple physical mixing between the aromatic and alkane poor shallow groundwater and the relatively aromatic and alkane rich groundwater that flows through both the peridotite and the fsc suggesting that these aromatic and alkane compounds originated in the deeper fsc groundwater and are not produced in the shallow peridotite only groundwater the aromatic compounds most probably originated from the diagenesis degradation of organic matter in the marine sediments below the peridotite body while the gaseous alkanes may have multiple sources including thermal degradation of the organic matter in the marine sediments below the peridotite body and possibly by abiogenic reactions occurring within the peridotite body this geochemical study demonstrates the complexity of the cedars and the possible sources of hydrocarbons at continental sites of serpentinization

direct imaging of coupled dissolution precipitation and growth processes on calcite exposed to chromium rich fluids abstract recent increases in industrial activity have resulted in elevated chromium cr pollution in the natural environment from the degradation of concrete and the leakage of water from landfills or mine waste the release of toxic chromate ions into the environment could have harmful consequences methods for cr removal are therefore becoming increasingly important to control the release of this highly toxic metal into the environment this study examines how chromate cro42 can be incorporated into a new stable solid phase at a dissolving calcite surface to study the relationship between solutions containing chromate and calcite we performed two series of time lapse atomic force microscopy afm experiments to identify calcite dissolution and growth rates in the presence of chromate in addition we conducted complementary experiments in a stirred flow through reactor to determine the amount of cr removal from solution all experiments were performed at room temperature and under a constant initial ph in the range 6 12 during the afm experiments we observed calcite dissolution via etch pit formation and propagation in the presence of chromate nanoparticles of a new phase nucleated and grew at the calcite surface by a coupled dissolution precipitation process in experiments with concentrations above 10 ppm cr or at ph 10 and higher we observed many nanoparticle precipitates while precipitates were rarely observed at lower concentrations of cr at ph 10 5 the precipitates covered the calcite surface this partly passivated further calcite dissolution an observation confirmed by the low amounts of cr removal measured in the flow through experiments scanning electron microscopy analysis demonstrated that cr was associated with the precipitates indicating that cr could be captured from solution and trapped in solid nanoparticles in the presence of calcite however the passivation of the calcite surface by a new precipitate may eventually slow down cr sequestration

anoxic oxidation of chromium naturally occurring cr vi has been ascribed to terrestrial cr iii oxidation by mn di oxides generated through reaction of mn ii with molecular oxygen o 2 however hydrogen peroxide h 2 o 2 is a potential oxidant of cr iii that may form in serpentinization high h 2 low o 2 systems where chromite i e the main mineralogical source of cr iii is abundant accordingly here we evaluate h 2 o 2 and chromite interactions in serpentinization systems to determine pathways of cr iii oxidation that alters the current paradigm of o 2 dependent oxidation field observations support that metastable h 2 o 2 and cr vi are present in serpentinization related fluids relatively absent of o 2 further laboratory experiments demonstrate and support that h 2 o 2 is a kinetically facile oxidant of chromite especially under alkaline conditions which provides a variety of alternative means by which cr vi may be generated and supplied to the oceans not directly linked to atmospheric o 2 thus cr iii oxidation pathways and their influence on the cr isotopic record must account for anoxic cr iii oxidation in serpentinization systems as well as a variety of h 2 o 2 induced cr iii oxidation pathways that may occur in both terrestrial and marine systems

nickel isotope fractionation during tropical weathering of ultramafic rocks abstract although ni isotopes have been shown to be significantly fractionated in terrestrial samples their use in continental environmental studies has not yet been evaluated the present study focuses on an ultramafic um massif barro alto goias brazil because such areas are naturally rich in ni we present developed lateritic weathering profiles the goal of the study is to evaluate the potential of using ni isotopes in environmental continental studies by combining its isotopic signature with mineralogy in order to better understand the geochemical cycling of ni in um settings during weathering as such ni isotope values were measured in samples from the barro alto um complex in the main stages of the lateritic weathering profile of um rocks including bedrock ores saprolitic and lateritic samples and soil the mineralogical composition of the samples with a focus on the different ni bearing minerals was also determined to decipher the potential links between isotopic fractionation and weathering dynamics isotopic signatures 60 ni from the natural ni geochemical cycle include bedrock samples 60 ni 0 28 0 08 ore samples saprolitic and lateritic 60 ni from 0 60 to 0 30 and soil samples 60 ni from 0 19 to 0 02 an overall trend of heavier isotope depletion was observed in the solid phase during weathering 60 ni soil bedrock 0 47 the mineralogical results were consistent with the literature and showed that the mineralogy of the lateritic part and soil was dominated by fe oxides whereas clay minerals were the primary ni phase scavengers in the saprolitic part of the profile thus the formation of ni bearing clay minerals and fe oxides appeared to lead to depletion in heavier isotopes which indicates preferential export of heavy isotopes in the dissolved phase this result is consistent with isotopic signatures measured in the exchangeable pool of the solid phase 60 ni exch total up to 0 47 and ni isotopes appear to be a promising tracer to better understand the biogeochemical ni cycling on the earth s surface

recent sedimentary events in the western gulf of lions western mediterranean abstract analysis of very high resolution data 3 5 khz profiles and em12d acoustic imagery collected during the calmar catalono languedocian margin cruise 1997 highlighted the occurrence of two very recent but previously unknown erosional sedimentary events on the continental rise between the rhone fan and the pyreneo languedocian ridge these events preserved as unconformable very thin lobes observable on acoustic imagery but not on 3 5 khz echo soundings relate to erosional processes linked to near bottom currents that seem to characterize the holocene hydrodynamical conditions in the deep gulf of lions they follow a pleistocene regime when gravity sedimentation dominated on the gulf of lions margin either through aggradational turbidite deposition rhone fan and pyreneo languedocian ridge or through remobilization of sediments by regional mass movements processes

sedimentary response to climate and sea level changes during the past 400 ka from borehole prad1 2 adriatic margin 1 borehole prad1 2 was drilled in 186 m water depth on the upper slope of the central adriatic in the frame of profiles across mediterranean sedimentary systems promess1 european union funded project the borehole penetrated 71 2 m through a stratigraphic interval characterized by subparallel seismic reflections and uniform seismic units according to an age depth model based on several independent proxies including foraminifera and nannoplankton stratigraphy 18o curves and magnetostratigraphy the cored interval records marine isotope stages and substages mis from mis1 to the top of mis11 thus encompassing the past 370 ka prad1 2 therefore represents an unprecedented continuous record through the last four glacial interglacial cycles from a proximal continental margin setting where depositional sequences are typically composed of progradational units these progradational units record dominantly interglacial intervals mis5 mis7 and mis9 and appear composed of thicker highstand deposits hst formed during interstadials and thinner forced regression units fsst deposited during stadials above distinctive downward shift surfaces the development of thicker highstand deposits with a distinctively thicker bottomset reflects enhanced shore parallel advection any time sea level rise leads to the drowning of the adriatic shelf triggering the formation of dense water and vigorous cyclonic circulation this advection mechanism persisted in each cycle throughout the early phases of the sea level fall but progressively decreased as sea level fall proceeded approaching the maximum lowstand position when most of the shelf became exposed relative sea level falls punctuating interglacials within each 100 ka cycle were thus accompanied by a dearth in sediment flux on the outer shelf the alternation of hst and fsst progradational wedges with markedly different thickness and downlap geometry of their bottomsets is the most evident stratigraphic signature within each 100 ka depositional cycle of the impact on the shelf of higher frequency 20 ka sea level cycles and concomitant supply fluctuations

magnitude and timing of episodic sea level rise during the last deglaciation a succession of elevated ridge deposits on the south florida margin was mapped using high resolution seismic and side scan sonar imaging in water depths ranging from 50 to 124 m the ridges are interpreted to be subtidal shoal complexes and paleoshorelines eolian dune or beach formed during the last sea level transgression oolitic and skeletal grainstones and mixed skeletal peloidal ooid packstones were recovered using a research submersible all of the grains are of shallow water or intertidal origin and both marine and nonmarine cements were identified formation and preservation of these features are attributed to episodic and rapid changes in the rate of the deglacial sea level rise at the onset of the termination 1a 18o excursion this high resolution record of sea level change appears to be related to deglacial processes operating on submillennial time scales and supports increasing evidence of rapid episodic fluctuations in ice volume climate and ocean circulation patterns during glacial interglacial transitions

chromium isotope systematics in the connecticut river abstract limited constraints on cr isotope fractionation during weathering and river transport is currently a gap in our understanding of the chromium cr isotope system which is an emerging proxy in environmental and paleoenvironmental studies here we investigate cr mobility and isotope fractionation from the temperate connecticut river usa including cr concentrations and isotopic compositions of river water suspended particles riverbed sediments and weathering profiles the 53cr values of the connecticut river water range from 0 17 to 0 92 which are similar to or higher than the weathered rocks in the catchment 0 08 to 0 29 we find seasonal variations in dissolved 53cr values in some but not all tributaries suggesting that dissolved 53cr is not a simple function of seasonality but may also be influenced by sub catchment heterogeneity in lithology in contrast to dissolved cr we found consistent seasonal difference in suspended cr concentration and 53cr suspended 53cr is 0 1 higher than the unfractionated bse in the fall 0 01 0 13 but indistinguishable from the bse in the spring 0 11 to 0 00 the suspended cr concentration is also lower in the spring and with higher al mn fe concentrations the lower suspended cr concentration and 53cr in spring may be linked to increased silicate and oxide load with depleted cr due to stronger hydrological flux building from our dataset there is not a consistent correlation with climate zones in a compilation of 53cr and cr concentration data from river water and weathering profiles suggesting that climate is not a dominating factor controlling cr isotopic behavior during weathering suggesting that other factors e g local catchment conditions and dissolved organic matter may also be responsible for the observed river water 53cr variability

shallow gas off the rhone prodelta gulf of lions sediment cores acquired in 2004 off the rhone prodelta show consistent anomalous methane concentrations of up to 87 440 ppm methane compositional and isotopic data support a biogenic origin although there are a few sites that show strongly depleted delta c 13 values 53 o pdb suggesting a mixed source for the gas biogenic and thermogenic anomalous methane concentrations samples with more than 90 ppm are discussed and integrated with organic carbon data sedimentary rates and adcp profiles highest gas concentrations were found directly off the river mouth 20 40 m water depth and where the ifremer models point to the thickest accumulation 2 m in response to the rhone flood event in areas unaffected by the high flux of organic matter and rapid thick flood deposition or in between flood events the conditions for methanogenesis and gas accumulation have not been met in these areas the physical and biological reworking of the surficial sediment may effectively oxidize and mineralize organic matter and limit bacterial methanogenesis in the sub surface we propose that in the rhone prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial c 2006 elsevier b v all rights reserved

late quaternary sedimentation and high resolution sequence stratigraphy of the east texas shelf the shelf margin deltas of the area show a complex pattern of progradation and aggradation that varies from one delta to the next this complexity is due predominantly to the different response of systems with different sediment supplies to fifth order eustatic fluctuations before we understood these autocyclic effects attempts at relating seismic stratigraphic changes to the oxygen isotope curve our proxy for sea level change were unsuccessful

pulse propagation in turbidity currents submarine turbidity currents are a key mechanism in the transportation of clastic sediments to deep seas such currents may initiate with a complex longitudinal flow structure comprising flow pulses for example by being sourced from retrogressive sea floor slope failures or acquire such structure during run out for example following flow combination downstream of confluences a key question is how far along channel pathway complex flow structure is preserved within turbidity currents as they run out and thus if flow initiation mechanism and proximity to source may be inferred from the vertical structure of their deposits to address this question physical modelling of saline flows has been conducted to investigate the dynamics of single pulsed versus multi pulsed density driven currents the data suggest that under most circumstances individual pulses within a multi pulsed flow must merge therefore initiation signatures will only be preserved in deposits upstream of the merging point and may be distorted approaching it downstream of the merging point all initiation signals will be lost this new understanding of merging phenomenon within multi pulsed gravity currents broadens our ability to interpret multi pulsed turbidites

subseafloor stratigraphic profiling and soil classification from piezocone tests a case study in the gulf of lion nw mediterranean sea we show the results provided by piezocone tests in determining the stratigraphic profile and the soil classification of two drilling sites in the outer shelf and the upper slope of the gulf of lion prgl2 and prgl1 respectively correlations with grain size data indicate that sleeve friction can be used for profiling fine grained sediments site prgl1 whereas cone tip resistance is the most adequate for sequences made of alternations of coarse and fine grained intervals site prgl2 normalized cone resistance and friction ratio proved to be also appropriate for soil stratigraphy as it depicts trends in the coarse fraction of the tested soil silts and clays present in similar proportions at site prgl1 responded to piezocone testing as pure clays usually do consequently classical soil classification methods resulted in erroneous interpretation of these sediments as clays whereas classification of the heterogeneous deposits at prgl2 was consistent with the grain size when tied to a high resolution seismic reflection profile the stratigraphy interpreted from the piezocone profile matches with the main seismic sequences and discontinuities defined from seismic stratigraphy analysis graded bedding also matches with cone tip resistance and sleeve friction data

late pleistocene holocene sediments on the spanish continental shelves model for very high resolution sequence stratigraphy abstract sequence stratigraphy analysis of high resolution seismic profiles geopulse uniboom and 3 5 khz of late pleistocene holocene sediments has been carried out on five sectors of the spanish continental margin four types of depositional settings are distinguished in these sectors 1 low subsident ramps alboran margin cadiz gulf 2 high subsident 2m kyr ramps alicante valencia 3 ria type morphology on the atlantic passive margin ria de muros and 4 fault scarp morphology systems with subsidence balearic margin a type 1 sequence is interpreted in all these sectors being composed of lowstand systems tract transgressive systems tract and highstand systems tract this conforms to the basic concepts of sequence stratigraphy and each systems tract correlates with a particular part of the last eustatic hemicycle characteristic shelf features such as terraces terraces with beach deposits and progradational sediment wedges evidence a complex stacking of lesser sub sequences in all the systems tracts which must be related to very short period sea level stillstands and fall we propose a very high resolution sequence stratigraphy model in which the last sea level hemicycle is punctuated by p cycles 4500 years which give rise to the neo glacial events h cycles 2200 950 years and c cycles 500 50 years these cycles interact with each other thus establishing the placing of the high and low sea levels this attention to detail 1 explains sedimentary evolution on both the shelf and upper slope during late pleistocene holocene time 2 illustrates some departures from the classical sequence stratigraphy model and 3 also demonstrates that the late pleistocene holocene eustatic curve is not one simple transgression but is modulated by three differing period cycle groups below the milankovitch band our model is delimited by fluctuating sea level during pleistocene holocene times such features should be identifiable on any continental margin however localized features occur due to subsidence and continental shelf morphology which determ ine the location and depth of sedimentary bodies generated in each eustatic cycle

geometry lateral variation and preservation of downlapping regressive shelf deposits eastern tyrrhenian sea margin italy abstract the shelf of the eastern tyrrhenian sea margin changes substantially in width shelf break depth and sea floor steepness over relatively short distances largely owing to pronounced lateral changes in subsurface geologic structure remnants of late pleistocene prograded coastal deposits are locally preserved on the middle and outer parts of the shelf we recognize two major controls on the distribution lateral extent thickness and preservation potential of these prograded deposits first prograded downlapping deposits formed only where the physiographic shelf break was deeper than the lowstand shoreline thus providing accommodation space for the lowstand deposits second the proximity and relative size of sediment sources and the local coastal dispersal system apparently infl enced the geometry of the deposit midshelf and shelf margin bodies composed of seaward steepening downlapping reflectors were deposited as thin to thick continuous prograding sheets over an irregular eroded shelf surface and onto the shelf edge during the latest fall and lowstand of sea level decreased sedimentation at the end of this lowstand resulted in net erosion during sea level rise shoreface erosion created a major marine erosional ravinement surface landward of the 120 m isobath and much of the downlapping deposits were removed preservation of these downlapping deposits is largely a function of their thickness thick continuous deposits are common on the shelf edge whereas on the midshelf only thin remnants are preserved locally where depressions or morphologic steps were present in the shelf surface

phase relationship between sea level and abrupt climate change direct traces of past sea levels are based on the elevation of old coral reefs at times of sea level high stands however these measurements are discontinuous and cannot be easily correlated with climate records from ice cores in this study we show a new approach to recognizing the imprint of sea level changes in continuous sediment records taken from the continental slope at locations that were continuously submerged even during periods of sea level lowstand by using a sediment core precisely synchronized with greenland ice cores we were able to recognize major floods of the mediterranean continental shelf over the past 270 kyr during the last glacial period five flooding events were observed at the onset of the warmest greenland interstadials consistent correspondence between warm climate episodes and eustatic sea level rises shows that these global flooding events were generated by pronounced melting of the northern hemisphere ice sheets due to rapid intensification of atlantic meridional overturning circulation the method described in this study opens a new perspective for inter hemi spheric synchronization of marine climate records if applied in other continental margins from the southern hemisphere or the equatorial regions c 2009 elsevier ltd all rights reserved

late pleistocene holocene deposits of the rhone inner continental shelf france detailed mapping and correlation with previous continental and marine studies very high resolution seismic data acquired on the rhone continental shelf were used to address the detailed morphology of late pleistocene and post glacial units from 18 000 yr bp to the present two groups of units can be distinguished 1 lower units that are mainly the product of variations in relative sea level they comprise the last pleistocene regressive deposits made of alluvial sheets u0 u1 and above transgressive deposits that can be divided into backstepping transgressive units u3 and u4a deposited during the landward retreat of the river mouth and transgressive units u4b u4c laid down during the inundation of the shelf a prograding littoral lagoon system u5 u6 indicating a fluctuation during the rise in sea level caps the transgressive units this work has emphasized the complexity of these depositional environments mainly related to a river system situated near the current petit rhone 2 upper units that make up the recent rhone delta and correspond to the current highstand systems tract hst developed since the stabilization of relative sea level seven prodeltaic lobes have been identified u7 u13 two of them are bilobate u7 and u8 and date from a period when the delta was split as a result of the fluviatile system being progressively divided into several channels other prodeltaic lobes u9 u10 are stacked in front of the distributary s outlet recording several periods of outflow the results show a strong correlation with studies on land the distribution of recent prodeltaic lobes was constrained by canalization of the rhone river to prevent the effects of climatic crises or other natural disasters

buried sandbodies within present day estuaries atlantic coast of france revealed by very high resolution seismic surveys abstract studies of sandbanks within estuaries and macrotidal bays are critical for management of those coastal environments where human activity concentrates they are also excellent analogues of reservoirs new very high resolution vhr seismic profilers are now available for studying at the outcrop resolution scale sandbodies in very shallow water we present here a vhr seismic study constrained by vibrocores repetitive bathymetric surveys and radiocarbon dating which provide evidence of buried sandbodies in mixed tide and wave influenced estuaries of the french atlantic coast the three selected buried sandbodies are chosen because they are located at various water depths and have different internal architecture and outer shape they include 1 a very shallow water around 2 m under low tide elongated nearshore sandbody emplaced during the last centuries 2 a 6 to 7 m deep elongated nearshore sandbody dated to 2965 30 bp and 3 sandwaves lying around 17 m of water depth over the top of a large rounded shape sandbody dated to 5260 30 bp deepest 6 and 17 m sandbodies are interpreted as remnants of lower sea levels and thus transgressive sandbodies all those sandbodies are buried under estuarine mud which have been mainly emplaced during the last millenium such major sedimentary transition from basal sand to upper mud is assumed to record a major environmental change in relation to both natural infilling of estuaries climate change and increasing human activities anthropogenic perturbations are however believed to be the most important factor they have mainly consisted of land reclamation and are responsible for 1 rapid infilling of tidal bays 2 tidal prism and tidal current energy decreases and 3 deposition of muddy sediments upon sandbodies

compound incised valley characterization by high resolution seismics in a wave dominated setting example of the aude and orb rivers languedoc inner shelf gulf of lion france a branch of a time calibrated late quaternary compound incised valley complex is investigated using high and very high resolution seismic data the incised valley system is confined on the inner shelf and entrenched parallel to the shore in unconsolidated pliocene deposits the infilling of the incised valley system comprises three sigmoidal bodies dipping progressively downstream representing depositional sequences the lowermost sequences are less well preserved at their downstream extremity and the whole system is both aggrading and prograding older pleistocene late quaternary sequences could be preserved under the coastal plain individual sequences are closely similar to the classic model of a microtidal incised valley fill nevertheless the central estuary bay basin muds are seen to interfinger locally with high energy deposits that represent potential reservoirs the properties prograding and aggrading architecture and occurrence of high energy deposits and preservation of these compound incised valley fill deposits are attributed to general glacio eustatic cycles and local atmospheric and oceanic regime and proximity of the hinge line conditions data acquisition strategy is a determining factor to interpret such systems

pedogeochemical characteristics of chromite in a paddy soil derived from serpentinites abstract chromite is a primary cr bearing mineral in serpentinitic soil therefore these soils generally contain a high concentration of cr which causes a potential risk to human health after cr is mobilized by chromite weathering into the environment this study examined the micromorphological characteristics of chromite and identified chromite weathering as a source of cr in a paddy soil profile derived from serpentinites in eastern taiwan the soil samples were tested by partitioning cr in the bulk soil and measuring the element composition in the chromite the fractionation of cr in all soil horizons was performed using a selective sequential procedure sse the sse results demonstrated that the original cr was primarily fixed in the recalcitrant minerals of the serpentinitic soils however labile cr fractions were also clearly observed in the soils during chemical weathering cr iii was released from hydrolysis in chromite under the submergence of the pedon whereas cr vi examined using xanes spectra was absent in the soils the micromorphological observation using polarized light microscopic and sem bse images indicated that chromite was altered which corresponded to the increase of labile cr toward the surface soil in the chromite grain cr decreased with the increase of fe and decrease of al mn mg and zn during pedogenesis chromite acted as a source of cr through dissolution in the pedon

corundum cr muscovite rocks at o briens zimbabwe the conjunction of hydrothermal desilicification and lil element enrichment geochemical and isotopic evidence monomineralic domains of chlorite corundum and cr muscovite coexist over a kilometer scale within ultramafic schists of the harare greenstone belt 2 73 ga this exotic lithological association includes the conjunction of some of the most aluminous al2o3 88 wt and potassic k2o 10 wt rocks known the paragenetic sequence developed from chlorite corundum corundum diaspore cr muscovite variably overprinted both the corundum and chloritite domains terminal stages were marked by sporadic production of andalusite quartz and finally margarite

terrestrial 10 be and electron spin resonance dating of fluvial terraces quantifies quaternary tectonic uplift gradients in the eastern pyrenees the 120 km longt et river flows out of the pyrenees to the mediterranean by displaying a mappable sequence of quaternary alluvial units between the pleistocene frontal moraines of the high range and the offshore sedimentary depocentres its 1400 km 2 watershed is well suited to quantifying gradients of topographic uplift five main generations of terrace treads had previously been inferred from constrasts in regolith weathering features but here we present the first radiometric age constraints based on 15 esr sediment burial ages covering the full sequence and 3 vertical tcn age profiles restricted to three mid sequence terraces analytically robust results were obtained for the oldest and uppermost terrace t5 esr age 1099 179 ka for t3b esr age 374 47 ka mis 10 and for t2 esr age 174 44 ka mis 6 these results are consistent with the contrasts in weathering grade of the deposits the tcn profiles only yielded minimum exposure ages but provided precise post depositional denudation rates for the fluvial terrace treads the land to sea geometry of the chronosequence also provided clues about valley incision rates in response to topographic uplift during the last 1 ma based on a critical review of similar data obtained for other mediterranean and atlantic watersheds in the pyrenees the full regional correlation reveals that post orogenic topographic uplift was substantial and relatively uniform throughout the entire mountain range patterns and magnitudes suggest a shared probably subcrustal driving mechanism of neogene and quaternary mountain growth with only subsidiary influence from isostasy and climatic forcing