burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

effects of vegetation change on interrill runoff and erosion walnut gulch southern arizona during the past 100 years grassland has been replaced by shrubland in many parts of the american southwest the effects of this vegetation change on interrill runoff and erosion are investigated by performing field experiments on small and large runoff plots located on contemporary grassland and shrubland hillslopes in walnut gulch experimental watershed the experiments indicate that the vegetation change causes runoff and erosion to increase in interrill areas by decreasing resistance to overland flow decreasing runon infiltration increasing the spatial heterogeneity of the plant canopy and possibly increasing the susceptibility of the soil to frost action increased runoff and erosion result in stripping of the soil a horizon the formation of desert pavement in intershrub areas and the development of rills fines remain and accumulate only under shrubs where they form islands of fertility shrubs are able to regenerate in these islands but it is difficult for any plants to become established in intershrub areas consequently there is an increase in the spatial heterogeneity of soil resources and this spatial heterogeneity is self perpetuating increasing spatial heterogeneity of soil resources is considered to be characteristic of the process of desertification

gully incision as a key factor in desertification in an arid environment the negev highlands israel abstract gully incision has been eroding the alluvial sediments and loess soils deposited and developed along the valleys in the arid and semiarid regions of israel this phenomenon is critical in the arid regions of the negev highlands where the agricultural fields the main floral biomass and the areas which have the highest grazing value are limited to narrow valleys filled with redeposited loessial sediments the headcut migration and gully development in the region were studied between 1990 and 2001 in three representative drainage basins zipporim revivim and sekher during flood events the runoff penetrates the alluvial cover of the valleys forming vertical headcuts which gradually retreat up the valley the runoff is channeled into narrow gullies preventing the floodwater from spreading over the whole width of the valley the change in irrigation efficiency along the valleys is reflected in a sharp estimated drop of 70 90 in the floral biomass causing the reduction of the range value by 83 99 during the monitoring time interval 1990 2001 the linear gully retreat in the study area ranged between 12 3 and 250 m an average rate of 1 12 22 7 m year 1 for each gully head the process is accompanied by erosion of soil which has high agricultural and range value the total soil losses in these sites ranged between 800 and 9000 m3 at an average rate of 81 818 m3 year 1 for each gully head which is equivalent to 121 1227 mg year 1 during the monitoring period approximately 0 11 0 87 ha of land lost its agricultural and range value in each basin under study at an average rate of 0 01 0 079 ha year 1 since the byzantine period 1400 bp approximately 6 5 ha which is 10 of the land that had high agricultural and range value in the zipporim valley lost its value due to gully erosion no recovery effects of the gully channels were found in the nearby region the soil erosion is generated by a long term natural dynamic change in the soil rock ratio evolving within the drainage basins through time since the termination of the last glacial phase the loessic sediments originally deposited within the drainage basins during the late pleistocene glacial stage are being removed under the present holocene climate in several erosion stages this ongoing phenomenon is causing degradation of soil and biomass and is severely reducing the agricultural and range potential of the region these parameters indicate that an ongoing process of desertification is active in the arid environment of the negev highlands and is advancing in proportion to the headcut retreat rates in the region the soil erosion and headcut retreat have been active in the negev highlands for the last few millennia if these processes continue in the future the negev highlands region will lose its agricultural potential within a few millennia however the fact that the ancient inhabitants of the region implemented successful long term land conservation techniques already 3000 years ago implies that a sustainable land management policy can be adapted to the negev highlands as well as to other semi arid regions in the middle east

distribution of some biochemical compounds in the sediments of the bay of bengal abstract surficial sediment samples collected from the continental shelf and slope of the bay of bengal were studied for the distribution of organic carbon and its constituent fractions such as carbohydrates proteins amino acids and lipids organic carbon carbohydrates proteins amino acids and lipids content of the slope sediments were higher than those of the shelf sediments a positive correlation was observed between the organic carbon and the concentrations of the individual constituents carbohydrates constituted 30 50 of organic matter as compared with proteins 10 24 and lipids 1 91 4 28 the group composition of carbohydrates amino acids and lipids shows that residual carbohydrates combined amino acids and polar compounds respectively were the major components no relationship was observed between the concentrations of these compounds and the depth of the overlying water column the total caloric content of the sediments calculated from the above data varied from 11 33 68 46 cal g dry sediment carbonnormalized total carbohydrate yields indicate the presence of terrestrially derived carbohydrates

nari calcrete outcrop contribution to ancient agricultural terraces in the southern shephelah israel insights from digital terrain analysis and a geoarchaeological field survey a field survey revealed that byzantine and early arab ca 5th to 8th century c e agricultural systems in the semi arid region of the shephelah central israel were similar to runoff agricultural systems in the arid region of the negev southern israel this similarity led to the hypothesis that systems in the shephelah also function as runoff farms this hypothesis is not trivial since runoff values in semi arid regions are generally low due to intensive but short rainfall events and due to the presence of sink patches that absorb runoff on slope surface the aim of the current research is to examine whether runoff potential in a representative agricultural system in the shephelah is sufficient for sustaining runoff farming a geoarchaeological field survey and digital terrain analysis show that large nari calcrete outcrops on the footslopes generate high runoff values that improve water potential hydrological simulations and calculations show that 230 mm of direct rainfall generates a water potential equivalent to 300 mm of direct rainfall in view of these results it is reasonable to conclude that the presence of nari enabled runoff agricultural farming in the shephelah region even in drought years

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

glaciotectonised quaternary sediments at cape shpindler yugorski peninsula arctic russia implications for glacial history ice movements and kara sea ice sheet configuration the coastal cliffs of cape shpindler yugorski peninsula arctic russia occupy a key position for recording overriding ice sheets during past glaciations in the kara sea area either from the kara sea shelf or the uplands of yugorski peninsula polar urals this study on late quaternary glacial stratigraphy and glaciotectonic structures of the cape shpindler coastal cliffs records two glacier advances and two ice free periods older than the holocene during interglacial conditions a sequence of marine to fluvial sediments was deposited this was followed by a glacial event when ice moved southwards from an ice divide over novaya zemlya and overrode and disturbed the interglacial sediments after a second period of fluvial deposition under interstadial or interglacial conditions the area was again subject to glacial overriding with the ice moving northwards from an inland ice divide the age control suggests that the older glacial event could possibly belong to marine oxygen isotope stage mois 8 drenthe 300 250 ka and that the underlying interglacial sediments might be holsteinian 300 ka one implication of this is that relict glacier ice buried in sediments and incorporated into the permafrost may survive several interglacial and interstadial events the younger glacial event recognised in the cape shpindler sequence is interpreted to be of early to middle weichselian age it is suggested to correlate to a regional glaciation around 90 or 60 ka the cape shpindler record suggests more complex glacial dynamics during that glaciation than can be explained by a concentric ice sheet located in the kara sea as suggested by recent geological and model studies copyright 2003 john wiley sons ltd

runoff generation from successive simulated rainfalls on a rocky semi arid mediterranean hillslope runoff generation in a mediterranean carbonate rock environment the judaean mountains west bank and israel was studied by a 2 day sprinkling experiment on an 18 x 10 m 2 plot during the first day three spells of 24 1 mm h 1 12 3 mm 27 8 mm h 1 12 3 mm and 14 4 mm h 1 12 5 mm were applied almost saturating the runoff plot on the second day 20 h later two spells of 18 7 mm h 1 34 3 mm and 35 2 mm h 1 25 4 mm followed surface runoff was a combination of infiltration excess runoff from rocky portions of the plot and saturation excess runoff from areas covered by soil soil saturation was accelerated by lateral runoff from adjacent rocky areas once the plot was saturated 80 90 of the applied rainfall became surface runoff significantly different concentrations of chloride sulphate and nitrate ions in the sprinkled water on two successive days served as tracers during the second day a two component hydrograph separation pointed to the importance of shallow reservoirs playing active parts in runoff generation about 14 of the flow collected during the second day originated from water applied during the first day during the second day of sprinkling both water sources obviously mixed in saturated soil reservoirs and contributed in variable percentages to surface flow it is hypothesized that at least during high magnitude rainfall the steep rocky slopes investigated might be regarded as flood generating zones rather than areas of pronounced recharge into the underlying yarkon taninim aquifer

analysis of neutral monosaccharides in marine sediments from the equatorial eastern atlantic abstract in the samples analysed carbohydrate carbon constitutes from 3 0 to 5 8 wt of the total organic carbon no significant degradation of carbohydrates is observed with increasing depth in the sediment the major part of the carbohydrates appears to be derived from marine organisms variations in relative saccharide contributions with depth indicate changes in the composition of the microbial assemblages periods of increased primary productivity seem to be associated with the presence of cyanobacteria or marine algae characterized by relatively high contributions of xylose 6 o methyl mannose and 3 and or 4 o methyl mannose correlations between the alkenone unsaturation index u k 37 18 o and the relative contribution of glucoheptose indicate that higher sea surface temperatures are associated with a restricted contribution of bacterial saccharides

a pleistocene sand sea on the alaskan arctic coastal plain a ridge and thermokarst basin landscape that is strikingly portrayed in landsat winter imagery consists of large pleistocene dunes that have been modified by younger eolian activity and thermokarst processes this is the most extensive area of large stabilized dunes yet reported in the north american arctic the landscape is of particular interest because it has been proposed as a first order analog for martian fretted terrain recognition of the large dunes permits a new interpretation for linear and curvilinear trends visible in landsat summer imagery

sources and distribution of terrigenous organic matter delivered by the atchafalaya river to sediments in the northern gulf of mexico abstract suspended sediments ss from the atchafalaya river ar and the mississippi river and surficial sediment samples from seven shallow cross shelf transects west of the ar in the northern gulf of mexico were examined using elemental oc c n isotopic 13c 14c and terrigenous biomarker analyses the organic matter om delivered by the ar is isotopically enriched 24 5 and relatively degraded suggesting that soil derived om with a c4 signature is the predominant om source for these ss the shelf sediments display oc values that generally decrease seaward within each transect and westward parallel to the coastline a strong terrigenous c n 29 signal is observed in sediments deposited close to the mouth of the river but values along the remainder of the shelf fall within a narrow range 8 13 with no apparent offshore trends depleted stable carbon isotope 13c values typical of c3 plant debris 27 are found near the river mouth and become more enriched 22 to 21 offshore the spatial distribution of lignin in shelf sediments mirrors that of oc with high lignin yields found inshore relative to that found offshore water depth 10 m the isotopic and biomarker data indicate that at least two types of terrigenous om are deposited within the study area relatively undegraded c3 plant debris is deposited close to the mouth of the ar whereas more degraded isotopically enriched soil derived om appears to be deposited along the remainder of the shelf an important input from marine carbon is found at the stations offshore from the 10 m isobath quantification of the terrigenous component of sedimentary om is complicated by the heterogeneous composition of the terrigenous end member a three end member mixing model is therefore required to more accurately evaluate the sources of om deposited in the study area the results of the mixing calculation indicate that terrigenous om soil derived om and vascular plant debris accounts for 79 of the om deposited as inshore sediments and 66 of om deposited as offshore sediments importantly the abundance of terrigenous om is 40 higher in inshore sediments and nearly 85 higher in offshore sediments than indicated by a two end member mixing model such a result highlights the need to reevaluate the inputs and cycling of soil derived om in the coastal ocean

efficient preservation of young terrestrial organic carbon in sandy turbidity current deposits burial of terrestrial biospheric particulate organic carbon in marine sediments removes co2 from the atmosphere regulating climate over geologic time scales rivers deliver terrestrial organic carbon to the sea while turbidity currents transport river sediment further offshore previous studies have suggested that most organic carbon resides in muddy marine sediment however turbidity currents can carry a significant component of coarser sediment which is commonly assumed to be organic carbon poor here using data from a canadian fjord we show that young woody debris can be rapidly buried in sandy layers of turbidity current deposits turbidites these layers have organic carbon contents 10 higher than the overlying mud layer and overall woody debris makes up 70 of the organic carbon preserved in the deposits burial of woody debris in sands overlain by mud caps reduces their exposure to oxygen increasing organic carbon burial efficiency sandy turbidity current channels are common in fjords and the deep sea hence we suggest that previous global organic carbon burial budgets may have been underestimated

climate and surface properties hydrological response of small arid and semi arid watersheds abstract a positive relationship between annual rainfall and geomorphic processes runoff and erosion rates and environmental factors water regime soil and vegetation cover is often assumed for arid and semi arid areas with an annual rainfall in the range of 100 300 mm this assumption disregards the fact that changes along a climatic gradient at desert margins are not limited to purely climatic factors they are often accompanied by a parallel change in surface properties especially the relative extent of rocky or soil covered surfaces that differ greatly in their response to rainfall this raises the issue whether the change in surface properties along a climatic gradient enhances the assumed positive effects of rainfall increase or limits it the hypothesis advanced in this paper is that runoff generation and rate in arid and semi arid areas are primarily controlled by surface properties rather than by the absolute amounts of storm and annual rain amounts hydrological data collected at two instrumented watersheds located one in an arid rocky area and the second in a semi arid soil covered area support this hypothesis the implications of data obtained for runoff generation and flow continuity under changing climatic conditions are analyzed they point to the fact that the same regional climatic change may have different and even opposite effects on the hydrological response of different adjoining surface units this response is expected to be strongly controlled by the specific local surface conditions that prevailed in the area prior to the climatic change

sarcopoterium spinosum from mosaic structure to matrix structure impact of calcrete nari on vegetation in a mediterranean semi arid landscape abstract sarcopoterium spinosum l s p is a common type of dwarf shrub in the eastern mediterranean area this study focuses on the semi arid south western judean foothills shephelah in israel characterized by a hilly landscape with variable coverage of hard calcrete rock outcrops nari on chalk the following research questions were addressed 1 what is the effect of calcrete rock outcrops on s p and the spatial composition of the vegetative landscape 2 what are the landscape conditions in which s p dominates the vegetation 3 what is the spatial structure and occupation strategy of s p in relation to rocky and non rocky landscape surfaces a field study was conducted to measure visual surface coverage of five components s p shrub excluding s p and including other dwarf shrubs and trees annuals rock and bare soil the results show that rock an abiotic component plays an important role in the semi arid landscape of the research area when rocky coverage is more than 14 of the surface its presence contributes to high heterogeneity and advanced ecological niches and governs the appearance and distribution of biotic components such as s p and others among the studied components the relationship between rock and s p was found to be the strongest furthermore rock and s p seem to fill interchangeable functions as rock presence decreases s p distribution increases when rock coverage is less than 14 s p becomes the dominant landscape component covering 37 77 of the surface characterized by large patches with a high level of homogeneity along the entire slope our results show that the rock s p ratio controls changes in the landscape structure varying from stable heterogenic mosaic to stable homogeneous s p matrix

the relationship of massive ground ice and the late pleistocene history of northwest siberia abstract the stratigraphy and 18 0 composition of ground ice on the yamal gydan and taz peninsulas were investigated in order to provide new data concerning the existence or non existence of a late weichselian glaciation in northwestern siberia radiocarbon dates on organic horizons and on organics related to syngenetic ice wedge growth indicate that this area has not been glaciated for at least the past 30 000 years and was covered by mixed forests by 9000 years ago the preservation of mammoth remains 10 to 30 ka old suggest that this area probably formed an important refugium during the late weichselian

recurrent depletion of benthic oxygen with 4th order transgressive maxima in the cretaceous western interior seaway abstract a study was designed to investigate the relationship between depletion of benthic oxygen and 4th order sea level change within the cretaceous western interior seaway of north america three 4th order sea level change cycles were studied in strata belonging to the tropic shale and the tununk shale member of the mancos shale in utah these sedimentary deposits accumulated within prodeltaic environments in utah strata belonging to all three 4th order cycles exhibit evidence for depletion of benthic oxygen at times of peak 4th order transgression and development of condensed sections the evidence includes decreased intensities of bioturbation increased cr al ni al and zn al ratios and decreased mn fe ratios the data also suggest that depletion of benthic oxygen in the distal section preceeded that in the more proximal one and thus may reflect episodic expansion of an oxygen depleted water mass es from the pelagic to the prodeltaic environment of the seaway evidence for subsequent increases in benthic oxygen level with the onset of 4th order regressions is interpreted to reflect either aggradation of the seafloor above the oxygen poor water due to sediment accumulation or contraction of the oxygen depleted water mass from the prodeltaic part of the seaway or a combination of the two s organic c ratios of strata interpreted to have been deposited under conditions of depleted benthic oxygen are distinctly below 0 4 and thus were not useful for recognition of paleo oxygen levels in the prodeltaic environment this study highlights the importance of depletion of benthic oxygen as a mechanism for enhancing preservation of organic carbon in condensed sections on a hundred thousand year time scale our results underline the potential for source rock formation in similar prodeltaic deposits of other epicontinental seaways during periods of relatively high sea level and global depletion of benthic oxygen

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

late quaternary stratigraphy and soils of gydan yamal and taz peninsulas northwestern siberia abstract ground ice preserved in pleistocene deposits of northwestern siberia has been considered to have originated from either glacial ice sea ice or by segregation processes the sediments have been considered by other researchers to have various origins including glacial estuarine and alluvial thus considerable differences of opinion exist regarding the extent of glaciation in the region detailed analysis of six sections on yamal gydan and taz peninsulas provide a corpus of stratigraphic evidence confirming an estuarine alluvial origin for the sediments enclosing massive ice bodies radiocarbon and optically stimulated luminescence dates on parts of two sections permit an evaluation of the two dating methods 18o analysis confirms that contemporary ground ice averages 18 and can be significantly less negative while older ice generally has a composition between 19 and 24 soils in the area are all arctic brown inceptisols to tundra entisols types and show horizon deformation patterns associated with permafrost on comparing cox or cg horizon mineralogy with bw and ah horizons weathering sequences in these soils show weak transformations of illite and illite smectite to smectite vermiculite and chlorite

coupling between sedimentary dynamics early diagenetic processes and biogeochemical cycling in the amazon guianas mobile mud belt coastal french guiana coastal french guiana lies within the vast mobile mudbelt that characterizes much of the s american inner shelf downdrift of the amazon river approximately 15 20 of the amazon sediment outfall moves nw along the guianas in part as a series of 20 25 coastal mud waves seasonal studies of a representative migrating mudwave located between kourou and sinnamary french guiana demonstrate that diagenetic properties and biogeochemical cycling are closely coupled to sedimentary dynamics and the refluxing of reduced components between the seabed coastal facies and well oxygenated overlying water an unsteady two zone diagenetic regime is typically present in the shallow subtidal and low intertidal regions a surficial layer usually 0 5 1 m thick is nonsulfidic highly reactive and dominated by fe mn cycling this suboxic layer unconformably overlies more consolidated sediment in which net so42 reduction is often observed and contracts shoreward toward the mangrove fringe as sediments stabilize and become bioturbated the relatively stable intertidal flats are also sites of significant benthic primary production despite suboxic conditions over extensive intervals anaerobic remineralization rates are high co2 0 2 0 6 mm day 1 and often show little evidence of attenuation with depth integrated co2 fluxes are 20 235 mmol m 2 day 1 wet dry season average 120 far exceeding diffusive o2 fluxes into the bottom high reactivity 0 08 day 1 and low c n remineralization release ratios 5 3 of decomposing material imply fresh substrate of marine origin most reduced solid phase fe is present as nonpyritic authigenic fe minerals 20 fe ii is in pyrite and low sedimentary c s ratios 6 8 reflect the generally nonsulfidic conditions a broad range of tracers e g 234th t1 2 24 days 210pb t1 2 22 years seasonal cl profiles and nonsteady state diagenetic models of pore water concentrations and oxidant reductant relationships demonstrate that the upper 0 1 1 m of deposits are reworked and exchanged with overlying water on timescales of 10 days to seasonally thus the seafloor acts as a massive suboxic batch reactor entraining and processing reactive marine plankton regenerating fe mn oxides exchanging metabolites and nutrients with the oxygenated water column and generating suites of nonsulfidic authigenic minerals the apparent paradoxical properties of high remineralization rate low reductant content corg 630 mol g 1 and dominance of suboxic metal cycling are a direct consequence of frequent entrainment of highly reactive organic substrate and simultaneous regeneration of the major fe oxidants in oxygenated water the amazon guianas mobile mudbelt is a zone of extraordinarily intense sedimentary and biogeochemical recycling greatly exceeding stable coastal systems such as salt marshes in material exchange with the sea

recurrent anoxia recorded in shallow marine facies at zhangcunping western hubei china throughout the ediacaran to earliest cambrian abstract in order to reconstruct the redox history of surface seawater for ediacaran shallow marine facies on the yangtze platform as well as to understand its implications for geological events oxidation and phosphatization and early evolution of life we have conducted a systematic high resolution investigation on microfacies analyses pyrite morphology as well as sulfur and carbon contents in a continuous carbonate ediacaran cambrian succession drilled 407 core in the zhangcunping area of western hubei south china the framboidal pyrites and snav toc nav non acid volatile sulfur based redox reconstruction show a dynamic history of recurrent shallow marine anoxia the early aftermath of the marinoan glaciation cap dolomite to phosphorites was characterized by either absence of pyrite or dominated by large framboids low toc contents and phosphorite deposition as well as well preserved microfossils indicating a minor oxygenated dysoxic to oxic photic shallow marine ecosystem meanwhile the uppermost doushantuo and dengying formations were potentially fully oxygenated due to the lack of pyrites as well as low snav and toc contents correlating with macrofossil assemblages miaohe biota and ediacara biota found in western hubei a major oxygenated marine ecosystem can be outlined for the late ediacaran in addition a complicated diagenetic microfabric overprints the fine microstructure of microfossils preserved in phosphorites leaving remarkable taphonomic puzzles for future study

origin of the oligocene manganese deposit at obrochishte bulgaria insights from c o fe sr nd and pb isotopes abstract the large manganese mn deposit at obrochishte ne bulgaria is part of a cluster of similar early oligocene deposits located around present day black sea they collectively constitute the earth s second largest endowment of mn after the kalahari manganese field in africa we have employed a battery of isotopic techniques c o fe sr nd pb to help understand the genesis of this deposit carbon isotope data indicates that some sections of the mn ore layer have diagenetic mnco3 mineralization formed by reaction of mn oxides with organic carbon corg whereas other sections have mnco3 precipitated directly from the seawater column oxygen isotopes show that the high grade mn mineralization had seawater as the fluid source whereas some lower grade sections had a mix of ground water and seawater as fluid sources sr and nd isotope values of ore leachates also indicate that the mn deposition occurred in normal early oligocene seawater nd and pb isotope values suggest that the clastic host sediments were sourced from continental bedrock rather than younger arc volcanic rocks to the west iron isotope composition of the mn ore implies deposition in a redox stratified basin similar to the modern black sea with much of the fe sequestered in deep anoxic euxinic water as sulfides similar to the modern black sea most of the detrital fe was transferred from shallow oxic sediments into deep anoxic euxinic water by an iron shuttle and remobilized mn sequestered in the upper suboxic water layer however during the oligocene the iron shuttle operated intermittently due to the chemocline falling mostly below the shelf break thereby limiting the efficiency of the shuttle mechanism we propose a model for the lower oligocene strata in which intense weathering during the eocene weathering phase produced a thick lateritic crust on the southern european continent the drastic sea level drop at the end of the eocene initiated downcutting of streams through this weathered material transferring fe and mn oxides to the redox stratified western black sea here these oxides were partly or entirely dissolved in the suboxic mn oxides partly fe oxyhydroxides entirely dissolved and anoxic euxinic mn oxides entirely dissolved dissolved fe2 re precipitated water layers eventually fe was re precipitated as sulfide in the deep anoxic euxinic water while mn accumulated in the suboxic water layer transgression in the early oligocene brought this mn rich water onto the shallow shelf where it precipitated as mn oxide then converted to mn carbonates during early diagenesis some mn was also contributed by submarine groundwater discharge further transgression brought lower oxygen water onto the shelf and mn carbonate precipitated directly from the water column the findings from this work provide insights about the unique oligocene geochemical event in the region that lead to the formation of the 2nd largest cluster of mn deposits in the world

estimation of algal carbonate input to marine aragonitic sediments on the basis of xylose content the input of calcareous green algae to the 63 m fraction of bermuda shallow water carbonate sediments is estimated from combination of mineralogical and xylose data factors for the conversion of algal xylose into algal aragonite were obtained by the analysis of sedimentary remains of halimeda and by chemical oxidation of halimeda and penicillus major producers of the area under investigation application of these conversion factors to core samples generally showed good agreement with field observations thus allowing a distinction to be made between sediments with major algal or coral contributions

climate control of sulfate influx to lake hovsgol northwest mongolia during the last glacial postglacial transition constraints from sulfur geochemistry abstract changes in sulfur cycles in lake hovsgol northwest mongolia are discussed on the basis of total organic carbon toc total sulfur ts concentrations and stable sulfur isotope ratios 34 s in two sediment cores x104 and x106 covering the last glacial to the present correlation plots of toc and ts c s plots of the sediment cores indicate dissolved sulfate enrichment in sediment pore water and high sulfate reducing bacteria srb activity during the climate transition from the last glacial to postglacial period lg pg transition from ca 21 to 11 6 cal ka bp in addition positive shifts of 34 s values from 3 7 to 32 6 were observed during the lg pg transition these results suggest a large influx of 34 s rich dissolved sulfate into the lake during this period the 34 s rich dissolved sulfate may have accumulated on the shore wetlands and marshes of lake hovsgol during the last glacial period owing to the increase in atmospheric precipitation and lake level rise during the lg pg transition the 34 s rich dissolved sulfate may have been supplied from the shore to the lake increased sulfate influx during the lg pg transition has also been observed in a lake baikal sediment core our new sulfur geochemical data shows past environmental changes particularly moisture changes within continental asia during the climate transition

great salt lake and precursors utah the last 30 000 years sediment cores up to 6 5 m in length from the south arm of great salt lake utah have been correlated radiocarbon ages and volcanic tephra layers indicate a record of greater than 30 000 years a variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation these include acoustic stratigraphy sedimentologic analyses mineralogy geochemistry major element c o and s isotopes and organics paleontology and pollen the results indicate that prior to 32 000 year b p an ephemeral saline lake playa system was present in the basin the perennial lake which has occupied the basin since this time rose in a series of three major steps the freshest water conditions and presumably highest altitude was reached at about 17 000 year b p the lake remained fresh for a brief period followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present great salt lake the lake remained at low elevations and divided at times into a north and south basin until about 8 000 year b p since that time with the exception of two short rises to about 1290 m the lake level has remained near the present elevation of 1280 m

paleo cold seep activity in the southern south china sea evidence from the geochemical and geophysical records of sediments abstract over the past decade more than 30 cold seep sites have been reported along the continental slope of the south china sea scs these seep sites have all been located in the northern scs and no methane seepage has been discovered in the southern scs here we report on the analysis results of the geochemical and geophysical of the marine core sediments 58s collected from the southern continental slope of the scs we suggest that the sedimentary total sulfur ts total inorganic carbon tic 34scrs values of chromium reducible sulfur crs and carbonate 13ctic values of the bulk sediments coupled with the ratio of nrmaf60mt nrmaf80mt nrm can be used to trace the methane release events in a methane rich environment at least two methane release events were identified at depths of 5 5 6 2 m and 6 8 7 2 m moreover according to the characteristic of the ts toc and nrmaf60mt nrmaf80mt nrm ratio of sediments we suggest the methane flux has changed episodically this inference is supported by the occurrence of the strongly negative carbonate 13ctic values of bulk sediments and the positive 34scrs values which indicate the occurrence of anaerobic oxidation of methane aom and the location of a past or present sulfate methane transition zone smtz respectively ultimately these new data suggest that the combined geochemical and geophysical study of marine sediments provides a valuable tool with which to infer the temporal variations in methane seepage in a marine environment

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

scanning electron microscopy of pleistocene sands from yamal and taz peninsulas ob river estuary northwestern siberia coastal sediments in the ob river estuary of northwestern siberia are considered to have either glacial and or estuarine alluvial origins one school of thought argues for interconnected ice domes on the continental shelf that linked the fenno scandinavian and siberian ice grosswald thesis another school of thought argues for an estuarine alluvial origin danilov vtyermin thesis the key to solving the problem of the origin of these sediments lies in detailed stratigraphic oxygen 18 and scanning electron microscopic sem analysis of sediments both the stratigraphy and sem results support the hypothesis of very limited pleistocene glacial activity on yamal gydan and taz peninsulas the sem analysis points to a vast majority of rounded quartz grains with v shaped percussion microfractures and a great range of preweathered microtextures the sem microtextures support a fluvial origin for the sediments far removed from any glacial source a companion paper in this volume by fred michel discusses the 18o analysis of ground ice in the area

origin and diagenesis of carbohydrates in ancient sediments abstract neutral saccharides were determined quantitatively in acid hydrolysates of sediments ranging in age from tertiary to jurassic derived from varying depositional environments and with different diagenetic histories the present data show that intact saccharides can be identified and quantified in ancient sediments and that an increase in temperature has a profound effect on the quantity and quality of the saccharides present in diagenetically altered ssediments

differential responses of hillslope and channel elements to rainfall events in a semi arid area the degree of hydrological connectivity of hillslope elements in a semi arid climate was studied at the season and event timescales field data were obtained in rambla honda a medalus project field site situated in se spain on micaschist bedrock and with 300 mm annual rainfall the season timescale was assessed using correlation analysis between soil moisture and topographic indices the event timescale was studied by a quasi continuous monitoring of rainfall soil moisture runoff and piezometric levels results show that widespread transfers of water along the hillslope are unusual because potential conditions for producing overland flow or throughflow are spatially discontinuous and extremely short lived during extreme events runoff coefficients may be locally high ca 40 on slope lengths of 10 m but decrease dramatically at the hillslope scale 10 on slope lengths of 50 m two mechanisms of overland flow generation have been identified infiltration excess and local subsurface saturation from upper layers the former occurs during the initial stages of the event while the latter which is quantitatively more important takes place later and requires a certain time structure of rainfall intensities that allow saturation of the topsoil and the subsequent production of runoff hillslopes and alluvial fans function as runoff sources and sinks respectively permanent aquifers are lacking in rambla honda variable proportions of hillslope areas may contribute to flash floods in the main channel but their contribution to the formation of saturated layers within the sediment fill is very limited

early diagnesis of carbohydrates in the marine environment ii composition and origin of carbohydrates in skagerrak sediments abstract the distribution and composition of carbohydrates were determined for the upper 15 cm of four cores from the southern slope of the skagerrak high concentrations were found in the upper bioturbated layers rapidly decreasing at sediment depths 3 cm total contents appear to be controlled by bioturbation application of various biomarker criteria suggests that carbohydrates originated from terrestrial macroalgal and planktonic sources input from these sources might be by episodic events rather than by continuous sedimentation as can be hypothesised from the irregular occurrence of marine and terrestrial signals

geochemistry and extractable fe and al in cold temperature soils of northwestern siberia the concentrations of major minor and trace elements in three cryosols from north western siberia were analysed to determine profiles of geochemical uniformity element mobility and the release and build up of extractable fe and al the scope of this study involves weathering processes over all or part of the lateglacial to the holocene epoch 10 ka bp q1 in a cold environment the variability of hf content in the horizons is likely silica induced and accounts for much of the concentration variation in the other elements the slight increases of mobile to immobile elements in the b horizons indicate trivial downward movement within the profiles iron and al extracts were investigated to elicit information regarding profile age and palaeoclimate extractable fe and al show slight increases relative to the total concentrations in the soil sola ah bw horizons lattice fe decreases in the ah bw horizons as a result of weathering and production of sesquioxides over time increases of ferrihydrite in the ah horizons and in the parent material of some profiles may indicate perched water tables at some time in the past possibly as sustained yearly water levels in the active layer free iron fed relative to total fe increases in the ah bw horizons compared with the lower horizons where the oxidation potential is weaker low total fe reflects reworked felsic rich deltaic and shallow marine deposits from the permian to the early tertiary thereafter emplaced by episodic flooding of glacial meltwater from the arctic urals and or the kara sea ice sheet organically complexed al alp uniformly low in all soils nevertheless shows trends indicating some downward movement a rather unique occurrence in arctic tundra soils as indicated by the slow increase of oxihydrites it may not be realistic to estimate the age of a profile by its physical characteristics however it appears possible to determine broad age ranges from the isotopic composition of water in soils organic carbon concentrations between and within soil profiles indicate it may be more prevalent in tundra soil than previously thought and may also play a significant role in uploading co2 to the atmosphere as warming and microbial activity q2 progresses copyright 2009 john wiley sons ltd

pelagic and benthic sources of sedimentary carbohydrates in a shallow water environment kiel bight baltic abstract the carbohydrate fraction of two cores from kiel bight taken at 25 and 28 m water depth and spanning approximately the last 200 years was analysed for its constituent monomers grain size fractionation of the 25 m core indicated a close association of carbohydrates with the m fraction effects of bioturbation were noticeable down to a sediment depth of 8 cm from the carbohydrate composition the presence of macroalgal sugars is evident calculation of contributions from benthic sources results in a value of 73

geochemical relationships of late paleozoic carbon rich shales of the midcontinent usa a compendium of results advocating changeable geochemical conditions abstract previous studies have shown that pennsylvanian black shales of the midcontinent us possess a more complex geochemical history than was once thought vine and tourtelot econ geol 65 1970 253 and coveney and glascock appl geochem 4 1989 347 note that the widespread nature of metalliferous pennsylvanian black shales and the diverse geological environments across the midwestern us pose the likelihood that metals contained in the black shales are of complex origins detailed geochemical and statistical representations using characteristics of numerous black shale members have shown that water depth may not have been uniformly deep as previously inferred by numerous workers earlier suggestions that these black shales were associated exclusively with anoxic depositional conditions have been challenged by a more realistic theory of multifaceted fluctuating environmental conditions a wide range of major and trace element concentrations combined with widely varying characteristics and diverse types of organic matter indicate the presence of fluctuating geochemical settings the presumption is that numerous associated chemical reactions occurred syngenetically one geochemical index degree of pyritization dop suggests a dysaerobic to aerobic setting for many of the shales whereas some other geochemical proxies i e v v ni indicate punctuated episodes of bottom water anoxia schieber abstr programs geol soc am 33 6 2001 a102 notes that in some black shales pyrite enrichment due to intermittent organic reworking explains the high dop values once thought to equate with extreme euxinic depositional conditions it seems likely therefore that even during apparent euxinic periods as indicated by bulk geochemistry oxygen deprived events were apparently short lived the seemingly euxinic fingerprint as shown by geochemical characteristics may result through time averaging abstr programs geol soc am 33 6 2001 a102 of intermittent euxinic events providing a misleading indication of dominant euxinic conditions thus detailed microstratigraphic sampling is necessary to delineate short punctuated occurrences of intermittent sub oxic episodes the midcontinent pennsylvanian shales may reflect a complex array of bottom water oxygenation variations and water depth fluctuations in response to climatic and localized events hatch j r and leventhal j s 1992 relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas usa in meyers p a pratt l m nagy b eds geochemistry of metalliferous black shales chem geol 99 65 82 complicated by post depositional events appl geochem 4 1989 347 this research examines the previous exclusively anoxic origin for midcontinent pennsylvanian black shales from a geochemical perspective and offers an alternative supported by detailed statistical presentations with the hypothesis that events of anoxia were punctuated by short lived dysaerobic or even near oxic events

hypersulfidic deep biosphere indicates extreme sulfur isotope fractionation during single step microbial sulfate reduction coexisting dissolved sulfide and sulfate from hypersulfidic interstitial waters of a 380 m long sediment core show a large isotopic difference of up to 72 caused by in situ microbial sulfate reduction this is considerably larger than the assumed biological maximum of 46 derived from laboratory studies with pure cultures of sulfate reducing bacteria similar high fractionations inferred from sedimentary metal sulfides have been previously explained by a multistage process involving sulfide reoxidation and disproportionation of sulfur intermediates our data show that extreme isotopic differences between sulfate and the reduced sulfur species can also be generated during microbial single step fractionation this result indicates that the sulfate reducing communities and or their cellular metabolic activities in the deep biosphere may differ from those observed in near surface sediments or the water column

speciation and spatial distribution of solid phase iron in surface sediments of the east china sea continental shelf abstract speciation and reactivity characterization of solid phase fe in marine sediments are of significance to understanding its heterogeneous mineralogy and crystallinity the diagenetic cycling of fe and its regulating roles on many other elements in sediments in this study a combination of sequential and single step extractions was used for the determination of seven fe pools in surface sediments of the east china sea ecs continental shelf 1 carbonate associated fe fe ii carb plus acid volatile sulfide fe fe ii avs 2 easily reducible amorphous poorly crystalline fe oxides fe ox1 3 reducible crystalline fe oxides fe ox2 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u total fe fe t in the sediments is largely determined by terrestrial aluminosilicate particles as indicated by a great similarity of the fe t with that of the yangtze river and global riverine particulates the size of fe prs is found to be the largest pool followed by fe u fe ox2 fe mag fe ii avs carb fe ox1 and fe py the large fe prs may result from neoformation of fe rich clay minerals via reverse weathering and subsequent ageing the small sizes of fe ii avs carb and fe py pools is believed to be the result of low so 4 reduction due to generally low labile organic matter together with the oxic suboxic dynamic environments of the surface sediments the occurrence of fe ox1 fe ox2 and fe prs in the sediments is closely associated with the clay fraction as indicated by a high spatial correlation between the former and the latter highly reactive fe fe hr in the sediments is comparable to that in global marine sediments but apparently lower than in the yangtze river and global riverine particulates due probably to sequestration in the yangtze estuary the ratios of fe hr fe t fe pr fe t and fe u fe t in the ecs surface sediments consistently show more similarity to those in the yangtze river particulates than in the global continental margin or deep sea sediments the surface sediments maintain a high level of buffering capacity toward sulfidation suggested by a large fraction of highly reactive fe iii oxides fe iii hr in fe hr

flint workshop affiliation chronology technology and site formation processes at giv at rabbi east lower galilee israel abstract salvage excavations at the middle paleolithic flint workshop giv at rabi east lower galilee israel aimed at obtaining chronometric ages for the site s exploitation reconstructing the process of its formation and collecting an assemblage of diagnostic flint items for testing the conjectured connection with nearby qafzeh cave the excavations revealed two archaeological units the lower one directly overlaying the calcrete bedrock formation and separated from the upper one by a sterile layer of clay sediments the sequence of four osl ages fall within the time range of the levantine middle paleolithic and correspond to mis 6 and most of mis 5 the assemblage of flint artefacts included hundreds of levallois debitage items alongside bifacial fossiles directeurs of the lower paleolithic acheulian found mostly in the lower archaeological unit while parameters reflecting the degree of core exploitation i e size number of scars and amount of cortex support the hypothesized connection between the workshop and qafzeh cave osl dates suggest that the beginning of the workshop s existence predates that cave s occupation moreover the possibility that the upper archaeological unit in gre represents re deposited part of the original accumulation of flint artefacts reduces even more the likelihood of the connection between the workshop and the cave these results suggest that additional and more remote sites were probably involved in the workshop formation and allow for a variety of scenarios concerning acquisition and management of flint resources during the middle paleolithic in the lower galilee chronometric dates within the sequence of the middle paleolithic the indication of nearly in situ deposition of the lower archaeological unit alongside physical condition of different artefact groups suggest that the bifacial type fossils of the lower paleolithic acheulian may have been recycled by middle paleolithic hominids

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples