source and origin of roxana silt and middle wisconsinan midcontinent glacial activity abstract thick roxana silt middle wisconsinan in central and southwestern illinois traditionally has been interpreted as loess derived from valley train deposits in the ancient mississippi river valley winters et al h a winters j j alford and r l rieck quaternary research 29 25 35 1988 recently suggested that the roxana was not directly related to glacial activity but was derived from sediment produced by increased shoreline and spillway erosion associated with a fluctuating ancestral lake michigan because 1 paleoenvironmental and paleohydrologic conditions inferred in the hypothesis are unlikely for a loess depositional system and 2 loess did not accumulate during late wisconsinan deglaciation under conditions similar to those hypothesized we suggest the hypothesis should be rejected roxana distribution suggests the major source was drainage from the upper mississippi river valley and variations in loess thickness in illinois can be explained by consideration of valley width depth orientation and postdepositional erosion tills in the headwaters region of the ancient mississippi drainage system in minnesota and wisconsin occur in the appropriate stratigraphic position and have colors and mineralogic compositions that suggest they could be the parent till of the roxana we believe a valley train source for thick roxana is most probable and urge continued consideration of middle wisconsinan glaciation in the upper great lakes area

effects of in situ biostimulation on iron mineral speciation in a sub surface soil abstract the in situ alteration of fe redox states in subsurface soils by bacteria otherwise known as bioreduction may play a key role in the immobilization of hazardous redox active metals such as u tc and cr the objective of this study was to characterize changes in fe mineralogy occurring in a subsurface soil as a result of biostimulation in order to evaluate the bioremediation potential of this approach biostimulation was achieved by injecting glucose into the soil through a small well next to a sampling well cores taken from the sampling well were analyzed by variable temperature 57 fe mossbauer spectroscopy results revealed that biostimulation resulted in an overall loss of fe from the system and major changes in the distribution of its oxide and oxyhydroxide mineral forms compared to the non biostimulated soil the spectral components assigned to goethite were greatly diminished in intensity in the samples that had been biostimulated whereas the hematite component was appreciably increased the fe ii fe iii ratio in the non oxide phase aluminosilicate clay minerals also increased indicating that the bioreduction processes in the soil also affected the redox state of fe in the constituent clay minerals

low temperature feldspar and illite formation through bioreduction of fe iii bearing smectite by an alkaliphilic bacterium abstract biogenic mineral assemblages that form from circumneutral microbial reduction of iron in smectite have been suggested as biosignatures in the geological record however mineralogical transformation of smectite mediated by microbes under extreme ph condition is still poorly known the objective of this study was to understand the reduction capacity of structural fe iii in iron rich smectite nontronite nau 2 by a novel anaerobic alkaliphile strain ccsd 1 isolated from the deep subsurface and associated mineralogical changes the experiments with ccsd 1 were conducted in a growth medium containing the electron shuttle anthraquinone 2 6 disulfonate aqds at ph 9 4 the fe ii concentration was monitored over the course of the experiment via wet chemistry and unreduced and reduced nontronites were characterized with x ray diffraction xrd and scanning and transmission electron microscopy sem and tem the results indicate that strain ccsd 1 utilizes proteinaceous substrates yeast extract and tryptone to reduce structural fe iii in smectite with the maximum reduction extent of 26 2 mineralogical analysis confirmed that biogenic plagioclase na ca feldspar and illite were formed after bioreduction our work shows that the interaction between alkaliphile and iron bearing smectite could account for low temperature feldspar and illite formation and these minerals may be used as biosignatures in sedimentary rocks

microbe clay mineral interactions clays and clay minerals are common components in soils sediments and sedimentary rocks and they play an important role in many environmental processes iron is ubiquitous in clays and clay minerals and its oxidation state in part controls the physical and chemical properties of these fine grained minerals the structural ferric iron in clay minerals can be reduced either chemically or biologically biological reductants include mesophilic and thermophilic microorganisms from diverse environments such as soils sediments sedimentary rocks and hydrothermal hot springs multiple clay minerals have been used for microbial reduction studies including dioctahedral smectiteillite series palygorskite chlorite and their various mixtures in natural soils and sediments all of these clay minerals are reducible by microorganisms under various conditions with smectite nontronite being the most reducible and illite the least the rate and extent of bioreduction depends on many experimental factors such as the type of microorganisms and clay minerals solution chemistry and temperature despite significant efforts current understanding of the mechanisms of microbial reduction of ferric iron in clay minerals is still limited whereas some studies have presented evidence for a solid state reduction mechanism others argue that the clay mineral structure partially dissolves when the extent of reduction is high this inconsistency may be related to several experimental conditions and their specific effects are discussed in this paper whereas past experiments have been largely conducted in well controlled laboratory systems recent efforts have attempted to transfer knowledge to the field to improve our understanding of more complex soil systems for better agricultural practices biologically reduced clay minerals are also important agents in remediating inorganic and organic contaminants in soil and groundwater systems this paper reviews the most recent developments and suggests some directions for future research

soils surficial geology and geomicrobiology of saline sodic wetlands north platte river valley nebraska usa abstract saline sodic wetlands along a 200 km stretch of the north platte river valley in western nebraska usa lie within an important agricultural region but their processes salt mineralogy and geomicrobiology have not previously been investigated putative anthropogenic salinization has long been a concern yet early historical accounts of widespread surface salts in the area have never been applied as comparative standards surface salts in the area originate from soil capillarity and surface evaporation thenardite na 2 so 4 and or mirabilite naso 4 10 h 2 o dominate depending on ambient conditions bloedite na 2 mg so 4 2 4 h 2 o halite nacl burkeite na 6 co 3 so 4 2 and calcite caco 3 are minor constituents historical accounts indicate that salts accumulated naturally long before euramerican settlement apparently as a result of rock water interaction in nearby volcaniclastic sediments of the brule formation ephemeral to permanent water holding basins in the wetlands contain na rich waters that vary widely in electrical conductivity as high as 159 ms cm and in ionic composition but local spring waters are extremely dilute basin floors exhibit a unique type of microrelief which appears to form by the filling of microlows with water and the dispersal of soil material therein by na followed by dewatering and collapse of the soil with drying illite dominates basin surface soils but smectite dominates at depth high soil ph available k and frequent wetting drying cycles in the wetlands suggest that in situ illitization may have occurred soil crusts and vesicular surface horizons are common as are upward increases in electrical conductivity the activity of sulfate reducing microbes forms prominent near surface horizons of sulfate reduction in saturated soils which retract or disappear entirely during dry episodes saline sodic wetland soils in the study area change on daily to seasonal scales cycles of surface salt development microbial activity and microrelief genesis are all controlled by regular wetting drying cycles and the interaction of ponded surface waters and shallow groundwaters relatively unique aspects of microbial ecology and surface processes make the soils important as geomicrobial reactors wherein important parts of hydrological and geochemical cycles occur

quaternary aminostratigraphy of mississippi valley loess five pleistocene loess units in the mississippi valley that contain terrestrial gastropod fossils are differentiated by amino acid ratios aile ile values in the total acid hydrolysate of the fossil terrestrial gastropods hendersonia occulta catinella and succinea late wisconsin peoria loess which has been independently dated by radiocarbon and thermoluminescence methods is identified by alle ile values in fossil gastropods which progressively increase from northern illinois to southern louisiana early to middle wisconsin roxana silt is characterized by alle ile values in hendersonia only slightly greater and values in catinella and succinea distinctly greater than those of the peoria loess aiie ile values in hendersonia suggest that the chinatown silt informal term in illinois and the loveland silt in arkansas are the same age independent geologic evidence suggests that they predate the sangamon last interglacial aile ile values in hendersonia from the sicily island loess informal term in louisiana indicate that it is significantly older than the loveland silt and the chinatown silt the oldest loess unit recognized by alle ile values in hendersonia from the mississippi valley is the county line silt informal term in illinois the study shows that amino acid ratios in fossil gastropods from loess are an extremely valuable relative age indicator and provide a means of long distance correlation of midcontinent loess deposits

clay mineral evolution changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4 567 ga of planetary evolution in our solar system reflect evolving tectonic geochemical and biological processes clay minerals were absent prior to planetesimal formation 4 6 billion years ago but today are abundant in all near surface earth environments new clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in earth s evolution notably the formation of a mafic crust and oceans the emergence of granite rooted continents the initiation of plate tectonics and subduction the great oxidation event and the rise of the terrestrial biosphere the changing character of clay minerals through time is thus an important part of earth s mineralogical history and exemplifies the principles of mineral evolution

vermiculations from karst caves the case of pertosa auletta system italy abstract unlike the spectacular speleothems that can often be found in numerous caves vermiculations are rather unassuming formations whose origin and evolution still subject of several heated debates in order to provide a quantitative basis for the understanding of the nature and evolution of vermiculations in karst environments the geochemical properties of one of the most important karst systems of southern italy the pertosa auletta cave were studied through a comprehensive approach which included elemental mineralogical and microscopy analyses the chemical element abundances mineral composition and microstructure of the vermiculations covering the entire range of morphologies and colours observed in the case study cave were investigated thus providing the first quantitative record of these traits the vermiculations presented exceptional diversity in their morphology colour chemical and mineral composition with it being due to exogenous determinants such as the deposition of stream sediments or organic matter as well as the development of photoautotrophic communities they were invariably composed of calcite associated to quartz as well as clays and other secondary minerals the formation of which may be biologically mediated this occurrence and the evidences of microbial activity observed through dissolution traces support the possible involvement of biogenic processes in vermiculation development

modern sangamon and yarmouth soil development in loess of unglaciated southwestern illinois abstract the thebes section in unglaciated southwestern illinois contains a well preserved 500 kyr loess paleosol sequence with four loesses and three interglacial soils various magnetic mineralogical and elemental properties were analyzed and compared over the thickness of soil sola these proxies for soil development intensity have the following trend yarmouth geosol sangamon geosol modern soil quartz plagioclase zr sr and tio 2 na 2 o ratios were most sensitive to weathering frequency dependent magnetic susceptibility and anhysteretic remanent magnetization greatest in a horizons also correspond well with soil development intensity neoformed mixed layered kaolinite expandables suggestive of a warm humid climate were detected in the sangamon and yarmouth soil sola clay illuviation in soils was among the least sensitive indicators of soil development differences in properties among interglacial soils are interpreted to primarily reflect soil development duration with climatic effects being secondary assuming logarithmic decreases in weathering rates the observed weathering in the sangamon geosol is consistent with 50 kyr of interglacial weathering oxygen isotope stage 5 compared to 10 kyr for the modern soil oxygen isotope stage 1 we propose that the yarmouth geosol in the central midwest formed over 180 kyr of interglacial weathering including oxygen isotope stages 7 9 and 11

mineral stimulation of subsurface microorganisms release of limiting nutrients from silicates abstract microorganisms play an important role in the weathering of silicate minerals in many subsurface environments but an unanswered question is whether the mineral plays an important role in the microbial ecology silicate minerals often contain nutrients necessary for microbial growth but whether the microbial community benefits from their release during weathering is unclear in this study we used field and laboratory approaches to investigate microbial interactions with minerals and glasses containing beneficial nutrients and metals field experiments from a petroleum contaminated aquifer where silicate weathering is substantially accelerated in the contaminated zone revealed that phosphorus p and iron fe bearing silicate glasses were preferentially colonized and weathered while glasses without these elements were typically barren of colonizing microorganisms corroborating previous studies using feldspars in laboratory studies we investigated microbial weathering of silicates and the release of nutrients using a model ligand promoted pathway a metal chelating organic ligand 3 4 dihydroxybenzoic acid 3 4 dhba was used as a source of chelated ferric iron and a carbon source to investigate mineral weathering rate and microbial metabolism in the investigated aquifer we hypothesize that microbes produce organic ligands to chelate metals particularly fe for metabolic processes and also form stable complexes with al and occasionally with si further the concentration of these ligands is apparently sufficient near an attached microorganism to destroy the silicate framework while releasing the nutrient of interest in microcosms containing silicates and glasses with trace phosphate mineral inclusions microbial biomass increased indicating that the microbial community can use silicate bound phosphate inclusions the addition of a native microbial consortium to microcosms containing silicates or glasses with iron oxide inclusions correlated to accelerated weathering and release of si into solution as well as the accelerated degradation of the model substrate 3 4 dhba we propose that silicate bound p and fe inclusions are bioavailable and microorganisms may use organic ligands to dissolve the silicate matrix and access these otherwise limiting nutrients

age genesis and paleoclimatic interpretation of the sangamon loveland complex in the lower mississippi valley u s a for more than a century the sangamon paleosol the sangamon has been an integral part of geologic and pedologic investigations in the central united states including the upper mississippi and lower missouri river valleys compositional pedologic micromorphologic stratigraphic and age data indicate that the prominent reddish paleosol developed in silt rich deposits of the lower mississippi valley from southernmost illinois to northwestern mississippi represents multiple periods of soil formation and is wholly or in part time equivalent to the sangamon of the central united states thermoluminescence data for localities where the sangamon developed in loess indicate that the primary period of loess deposition was from 190 to 130 ka oxygen isotope stage ois6 that loess deposition continued intermittently from 130 to 74 ka ois5 and that deposition was wholly or in part coeval with loveland loess deposition in the central united states beryllium 10 chemical and pedologic data indicate that in the lower mississippi valley 1 the sangamon represents a minimum time period of 60 80 k y 2 there were at least two periods of soil formation ca 130 90 ka and 74 58 ka ois4 and 3 rates of weathering and pedogenesis equaled or exceeded the net loess accumulation rate until at least 46 ka ois3 and resulted in development of a paleosol in the overlying basal roxana silt along a n s transect from southern illinois to western mississippi sangamon macroscopic characteristics as well as the micromorphology chemistry and mineralogy suggest a regional paleoclimate during periods of soil formation that 1 was warm to hot with a wider range in temperature precipitation and evapotranspiration than present 2 had seasonal to decadal or longer periods of drought and 3 had down valley southward trends of increasing temperature and precipitation and decreasing seasonality and variation in annual to decadal precipitation

exceptionally preserved microbially induced sedimentary structures from the ediacaran post glacial successions in the kimberley region northwestern australia abstract a set of exceptionally preserved microbially induced sedimentary structures miss is described from the post glacial yurabi formation of late ediacaran age in the kimberley region northwestern australia these miss comprise oriented grains bamboo leaf like cracks polygonal cracks worm like cracks sinuous cracks gas domes pyrite concentrated laminae and micrite laminae most of the yurabi miss are morphologically comparable with their ancient and modern counterparts micrometre or nannometre scale bacteria or biofilm like inorganic objects are detected from most miss and are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization oriented grains indirectly support microbial control on their accumulation both pyrite conformable laminae and micrite laminae suggest degradation and decay of original microbial mats upon diagenesis sinuous cracks were likely generated in a soft sediment deformation process whereas other sand cracks bamboo leaf like cracks worm like cracks polygonal cracks could have formed from sediment surface layer microbial organics shrinkage upon desiccation gas domes may have formed as the result of anoxic redox reactions and being filled with gases and sediments transported from below two proxies bedding plane coverage percentage and accumulative thickness of single miss bearing beds are developed to semi quantitatively evaluate miss abundance on bedding plane and vertical outcrop respectively the yurabi miss have substratum preference to fine sandstone facies and intertidal settings the yurabi formation yields the most abundant and diverse post glacial miss assemblages during the late ediacaran worldwide both kimberley and global fossil records indicate that miss may have proliferated in shallow marine ecosystems soon after the retreat of ediacaran gaskiers glaciation during late neoproterozoic

upper lower triassic stromatolite from anhui south china geobiologic features and paleoenvironmental implications abstract widespread stromatolites and other microbialite deposits characterize lower triassic marine successions worldwide this study documents a stromatolite deposit 1 1 m thick from the upper spathian lower triassic of the susong area south china the stromatolite comprises distinct laminated domes in the basal part and columns at the upper part dark laminae are loosely spaced and interlayered with thicker light colored laminae diffusive dark colored laminae are composed of peloidal micrite that grade locally into microclotted structures and yield copies of bacteria clump like and coccoid like spheroid aggregates the former are characterized by cloudy micrite nuclei rimmed by coarse grained euhedral sparry calcite crystals while the latter are comprised of solid calcite crystal nuclei coated with rather thin micrite envelopes the cloudy micrite nuclei resemble bacteria clump like structures observed in present day travertine both the coccoid like spheroids and bacteria clump like structures are surrounded by coarse grained euhedral calcite crystals suggesting a similar accretion mechanism both spherical structures therefore could be crucial in the accretion of the susong stromatolite the laminated microclotted structures are interpreted as the result of variation in timing of lithification relative to the timing of the decay of microbes micro analysis also unravels the common occurrence of authigenic micro quartz crystals in association with fe bearing illite clay minerals in the stromatolite columns their coalescing nature with each other together with the associated pyrite grains strongly support the formation of micro quartz crystals from microbial reduction of an fe bearing smectite precursor by sulfate reducing bacteria a comparison of the susong stromatolite with its counterparts from the upper lower triassic strata in dajiang south china reveals many similarities in stromatolite microstructures suggesting that a harsh euxinic anoxic environment resulting in the bloom of sulfate reducing bacteria most likely extended into the latest spathian in south china

ams radiocarbon age of the upper mississippi valley roxana silt abstract accelerator mass spectrometer radiocarbon ages of the roxana silt loess along the upper mississippi valley of wisconsin and minnesota indicate that loess sedimentation of the roxana silt occurred between about 55 000 and 27 000 14 c yr b p however due to local environmental controls the basal age at any given site may range from 55 000 to 35 000 14c yr b p the radiocarbon ages presented here are in agreement with previous radiocarbon ages for the roxana silt in its type area of west central illinois but indicate that long term sedimentation rates along the bluffline of the upper mississippi valley were very slow 4 8 cm 1000 yr compared to long term sedimentation rates along the bluffline of the type area 40 70 cm 1000 yr comparison of radiocarbon ages for midcontinent middle wisconsinan loess deposits indicates that sedimentation along the mississippi river valley may have preceded loess sedimentation along the missouri river valley by as much as 20 000 yr or that basal ages for middle wisconsinan loess along the missouri valley are erroneously young the bracketing ages for the upper mississippi valley roxana silt indicate that the mississippi river valley was receiving outwash sedimentation between 55 000 and 27 000 14c yr b p

evaluation of amino acid racemization epimerization dating using radiocarbon dated fossil land snails the relation between age and amino acid epimer ratios alloisoleucine isoleucine a i of holocene land snails was quantitatively evaluated through 14 c and amino acid analysis of 33 samples from fluvial and colluvial sediments and rodent middens in the northern negev desert of israel a i is strongly correlated with 14 c ages in fluvial and rodent midden deposits r 0 95 and 0 94 respectively permitting age estimates from a i ratios with precisions of 700 and 660 yr the correlation is weaker in colluvial deposits r 0 74 and age estimates from a i ratios are correspondingly less precise 1580 yr this probably results from delayed burial which exposes the shells to intense radiation on the desert surface because of the generally strong relation between age and a i amino acid epimerization analysis of individual shells can be used to identify mixed age deposits and to reconstruct species chronologies from mixed age deposits

summer monsoon response of the northern somali current 1995 preliminary results on the development of the northern somali current regime and great whirl during the summer monsoon of 1995 are reported they are based on the water mass and current profiling observations from three shipboard surveys of r v meteor and on the time series from a moored current meter and adcp array the monsoon response of the gw was deep reaching to more than 1000m involving large deep transports the northern somali current was found to be disconnected from the interior arabian sea in latitude range 4 n 12 n in both water mass properties and current fields instead communication dominantly occurs through the passages between socotra and the african continent from moored stations in the main passage a northward throughflow from the somali current to the gulf of aden of about 5 sv was determined for the summer monsoon of 1995

new insights on the loess paleosol quaternary stratigraphy from key sections in the u s midwest abstract three key quaternary loess paleosol sections were examined in the missouri valley iowa eustis ash pit nebraska and in the wittsburg quarry arkansas to gain insights into the sedimentation environment and climate change of the u s midwest four loess units are present separated by three well developed paleosols crowley s ridge loess oxygen isotope stage ois 8 is pre illinoian in age and is the oldest loess unit investigated a well developed paleosol interpreted as yarmouth soil ois 7 is found in this loess in all three sections overlying the yarmouth soil is loveland loess ois 6 which has been pedogenically altered by the sangamon soil ois 5 it has luvisolic properties but a more clayey pedogenic texture than modern luvisols and has no clear eluvial horizon the overlying roxana silt ois 4 is pedogenically altered at wittsburg and missouri valley the farmdale soil ois 3 is developed in the roxana silt based on pedogenic features we correlate this paleosol to that developed in the gilman canyon formation at eustis in missouri valley and eustis sections the paleosol has chernozemic properties and therefore the gleyic features observed at missouri valley are interpreted as later alterations overlying the farmdale soil is the widespread peoria loess ois 2

smectite dehydration its relation to structural development and hydrocarbon accumulation in northern gulf of mexico basin a comparison of clay diagenesis data obtained from a study of tertiary shales from the brazos colorado river system of texas the mississippi river system of louisiana and the niger river system of nigeria illustrates significant differences in temperature intervals over which smectite diagenesis occurs the threshold temperature required to initiate diagenesis ranges from about 160 f 71 c in mississippi river sediments to more than 300 f 150 c in the niger delta water expelled from smectite into the pore system of the host shale during the process of diagenesis may migrate out of the shale early or may be totally or partially trapped and released slowly through time in either situation the water can act as a vehicle for hydrocarbon migration p ovided hydrocarbons are present in a form and in sufficient quantities to be transported observations from the northern gulf of mexico basin indicate a close relation between buildup of high fluid pressure and the smectite illite transformation process abnormal pressures exert partial control on the type and quantity of hydrocarbons accumulated because pressure potential determines the direction of fluid flow and overpressuring partly controls the geometry of growth faults and related folds in basins where shale structures are the dominant type formed the depths to which growth faults can penetrate and the angle of dip that these faults assume at depth are largely dependent on fluid pressure in the sedimentary section at the time of faulting dips of some faults in texas have been observed to change abruptly within the interval of smectite diagenesis and some faults formed in the overpressured miocene and younger sections become beddingplane types at depths where the temperature is near that required for thermal generation of petroleum although these faults may be important for fluid redistribution in shallow sandstone shale sections they are a minor factor in moving hydrocarbons out of shale below the faults in much of the texas offshore area fluid movement upward through microfracture systems in the deeply buried overpressured section overlying and extending upward from fault trends in the sub tertiary section is proposed as a mechanism for flushing hydrocarbons from the deeper portion of the northern gulf of mexico basin this flushing process would be enhanced by smectite diagenesis because water derived from smectite that was trapped during basin subsidence would cause the flushing process to continue for longer periods of time and to extend to greater depths than could be attained if only remnants of original pore water were present shale tectonism is also the primary mechanism for structural development in the tertiary section of the niger delta however seismic data indicate that the rate of dip change of seaward dipping listric growth faults is commonly less than that observed in texas where dips as low as 10 15 can occur at depths as shallow as 10 000 15 000 ft 3 048 4 572 m syndepositional faults in nigeria are formed in sandstone shale sections where the clay composition of shale is primarily kaolinite and where little water of smectite diagenesis has been added to the pore system of the host sedimentary section subtle differences in structural styles in the tertiary sections of texas and nigeria are probably the result of differences in clay composition of the shaly sections being deformed

a 45 000 yr record of a tropical lowland biota the land snail fauna from cave sediments at coco ree jamaica the land snail fauna from cave sediments in wet tropical lowland forest in central jamaica was analyzed with regard to their implications for the biogeographic history of the late quaternary eight radiocarbon dates on the shells range from 600 to 45 000 yr b p and show a close relationship to amino acid epimer ratios d alloisoleucine l isoleucine or a i values a i values of individual shells indicate that the faunas span a continuous time sequence but that a significant mixture of ages occurs within each level of the cave sediments the chronologies of individual species were therefore determined by a i values of individual shells calibrated against radiocarbon ages the land snail fauna consists of 40 species all endemic to the island and shows remarkable stability over the span of time covered by the deposit indicating the continuous persistence of forest the much lower epimerization rate for the late pleistocene compared to the holocene indicates much cooler late pleistocene temperatures but this appears to have had little effect on the fauna many species that are presently endemic to restricted regions which include the area of the cave are present throughout the sequence no changes are detected at the last glacial maximum but some changes are seen in the holocene at 3000 4000 yr b p two species disappear from the sequence one lives nearby at present whereas the other presently has a distribution farther to the west the first records of one species in the sequence occurs at this time and for another species at ca 10 000 yr b p no extirpations of species occur at the site following european settlement relatively stable climatic gradients rather than climatic change may be an important cause of the evolution of faunas endemic to different parts of the island

smectite diagenesis pore water freshening and fluid flow at the toe of the nankai wedge the presence of low chloride fluids in the lowermost sediments drilled at ocean drilling program site 808 at the nankai accretionary wedge has been considered as prime evidence for long distance lateral fluid flow from depth here we re evaluate the potential role of in situ reaction of smectite s to illite i in the genesis of this low chloride anomaly this reaction is known to be occurring at site 808 with both the s content and s to i ratio in the mixed layer clays decreasing substantially with depth we show that the bulk of the chloride anomaly can generate by in situ clay dehydration particularly if pre reaction smectite abundances ai approach 10 15 of the bulk sediment the ai values however are not well constrained at ai values 10 15 an additional source of low cl fluid centered close to the decollement could be required thus there remains the important possibility that the observed low cl anomaly is a compound effect of both lateral flow and in situ smectite dehydration

aminostratigraphic correlation and geochronology of two quaternary loess localities central mississippi valley abstract amino acid epimeric aile ile values from terrestrial molluscs are used to define and correlate three aminozones in loess sequences exposed across the central mississippi valley in arkansas and tennessee three superposed aminozones are defined at wittsburg quarry arkansas primarily using aile ile values from total hydrolysates of the gastropod genus hendersonia peoria loess aile ile 0 07 0 01 roxana silt 0 14 0 02 and a third loess 0 28 0 06 loess units at wittsburg quarry can be correlated on lithologic characteristics eastward across the mississippi valley to the old river section near memphis tennessee however only one loess unit is fossil bearing peoria loess aile ile 0 05 at that section radiocarbon analyses of charcoal from the upper roxana silt ca 26 000 to 29 000 yr old and mollusc shell carbonate from the basal roxana silt ca 39 000 yr old are used to calibrate amino acid epimeric data for the central mississippi valley these data applied to the apparent parabolic kinetic model of r m mitterer and n kriausakul 1989 quaternary science reviews 8 353 357 suggest an illinoian 120 000 yr age for the third loess in the central mississippi valley that is correlative with part of the loveland loess in illinois and iowa

late pleistocene evolution of the lower mississippi river valley southern missouri to arkansas the mississippi river served as the principal conduit for meltwaters discharging from the southern margins of north american ice sheets the northern half of the mississippi river alluvial valley in missouri and arkansas can be subdivided into two distinct channel courses the western and eastern lowlands which are separated by crowleys ridge the eastern lowlands contain two entry points the bell city oran and thebes gaps the latter is a narrow bedrock gorge that contains the modern river this paper summarizes a model for evolution of channel courses in the western and eastern lowlands during the illinoian and wisconsin glacial stages for the western lowlands stratigraphic relations between loess units and subjacent fluvial deposits show that major continuous terrace surfaces or valley trains are illinoian or late wisconsin in age investigations of tributary valley fills further show the western lowlands were deeply incised during the early to middle wisconsin stage then aggraded during the late wisconsin stage to such an extent that tributary valleys were backfilled with slackwater deposits moreover analysis of loess thinning and fining trends shows that early to middle wisconsin roxana silt and the late wisconsin peoria loess covers on western lowlands valley trains were derived from deflation of valley trains in the eastern lowlands we conclude that the western lowlands were the primary mississippi river course during illinoian deglaciation but were abandoned shortly thereafter then episodically reoccupied during the late wisconsin stage for the eastern lowlands course valley trains of early to middle wisconsin age are not preserved with the exception of a small remnant where the mississippi river broke through a gap in the southern margins of crowleys ridge and reentered the western lowlands all valley trains in the eastern lowlands are late wisconsin age a series of discontinuous terrace surfaces in the bell city oran gap represent dissected remnants of the primary late wisconsin full glacial and early late glacial course of the mississippi river or combined mississippi and ohio rivers whereas younger continuous braided stream surfaces in the bell city oran and thebes gap courses represent valley trains of latest wisconsin and earliest holocene age hence the bell city oran gap was the primary course during the entire wisconsin stage and the thebes gap was permanently occupied in earliest holocene time as much as 5 m difference in elevation between successive late wisconsin terrace surfaces of the eastern lowlands indicates that valley trains were rapidly constructed incised and abandoned in response to fluctuations in the delivery of meltwater and outwash from the former ice margin moreover a variety of data indicates that deglacial meltwater floods were commonly of sufficient magnitude to overflow from the primary course in the bell city oran gap throughout the late wisconsin substage floodwaters overflowed into the western lowlands constructed a series of secondary valley trains and filled tributary valleys with slackwater deposits during the latest wisconsin stage perhaps in association with the drainage of glacial lake agassiz floodwaters overflowed into the western lowlands and broke through the thebes gap the charleston fan represents the initial deposits of the thebes gap course following deposition of a large crevasse splay at the western lowlands entrance that course was no longer active but flow was routed through the thebes gap during periods of high magnitude flooding until the bell city oran gap was abandoned and the thebes gap course was permanently occupied during earliest holocene time

illite and hydrocarbon exploration illite is a general term for the dioctahedral mica like clay mineral common in sedimentary rocks especially shales illite is of interest to the petroleum industry because it can provide a k ar isotope date that constrains the timing of basin heating events it is critical to establish that hydrocarbon formation and migration occurred after the formation of the trap anticline etc that is to hold the oil illite also may precipitate in the pores of sandstone reservoirs impeding fluid flow illite in shales is a mixture of detrital mica and its weathering products with diagenetic illite formed by reaction with pore fluids during burial k ar ages are apparent ages of mixtures of detrital and diagenetic end members and what we need are the ages of the end members themselves this paper describes a methodology based on mineralogy and crystallography for interpreting the k ar ages from illites in sedimentary rocks and for estimating the ages of the end members

microbial reduction of fe iii in illite smectite minerals by methanogen methanosarcina mazei abstract clay minerals are ubiquitous in soils sediments and sedimentary rocks and could coexist with methanogens in anoxic environments but whether or not methanogens can reduce structural fe iii in clay minerals other than smectite is not known the objective of this study was to understand the capability of a mesophilic methanogen methanosarcina mazei in reducing structural fe iii in illite smectite clay minerals and its potential role in inducing mineralogical changes bioreduction experiments were performed in batch systems where four different clay minerals nontronite nau 2 mixed layer illite smectite rar 1 and iscz 1 and illite imt 1 were exposed to m mazei in growth medium with and without anthraquinone 2 6 disulfonate aqds as electron shuttle the extent and rate of bioreduction were quantified via wet chemistry and mineralogical transformed by x ray diffraction and scanning and transmission electron microscopy our results demonstrated that m mazei was able to reduce structural fe iii in clay minerals with fe iii in smectite being the most reducible and illite the least aqds enhanced the reduction rate and extent the bioavailability of structural fe iii to m mazei was correlated to the smectite proportion in each clay mineral methanogenesis was inhibited by fe iii bioreduction possibly due to diversion of electrons from the methanogenesis pathway to structural fe iii in clay minerals bioreduction of fe iii in clay minerals induced formation of biogenic mixed layer illite smectite silica and vivianite these data collectively showed that mesophilic methanogen is capable of reducing structural fe iii in illite smectite minerals and of inducing a number of mineralogical changes

loess stratigraphy of the lower mississippi valley abstract loesses of the lower mississippi valley lmv are world famous sir charles lyell 1847 hilgard 1860 stafford 1869 call 1891 and mabry 1898 thought the lmv loess was a single water deposit although double submergence was noted by call 1891 and salisbury 1891 shimek 1902 and emerson 1918 recognized lmv loess as a wind deposit which came from the valley although wind deposited loess gained wide acceptance russell 1944a published his controversial theory of loessification which entailed weathering of backswamp deposits downslope movement and recharge by carbonates to form loess wascher et al 1947 identified three lmv loesses mapped distributions and strongly supported eolian deposition leighton and willman 1950 identified four loesses and supported eolian deposition as did krinitzsky and turnbull 1967 and snowden and priddy 1968 but krinitzky and turnbull questioned the deepest loess daniels and young 1968 and touchet and daniels 1970 studied the distribution of loesses in south central louisiana west et al 1980 and rutledge et al 1985 studied the source areas and wind directions which deposited the loesses on and adjoining crowley s ridge b j miller and co workers miller et al 1985 1986 miller and alford 1985 proposed that the loveland silt was early wisconsin rather than illinoian age and advanced the name sicily island loess they proposed the underlying loess was illinoian and advanced the name crowley s ridge we termed the loesses from the surface downward peoria loess roxana silt loveland sicily island loess crowley s ridge loess and marianna loess researchers agree that the surfical peoria loess is late wisconsin and the roxana silt is late to middle wisconsin but little agreement exists on the age of the older loesses pye and johnson 1988 proposed early wisconsin for the loveland sicily island mckay and follmer 1985 suggested this loess correlated with a loess under illinoian till clark et al 1989 agreed on crowley s ridge but suggested the loveland sicily island loess on sicily island was older mirecki and miller 1994 and millard and maat 1994 suggested an illinoian age for the loveland sicily island loess miller and co workers suggested as did pye and johnson 1988 an illinoian age for the crowley s ridge loess mckay and follmer 1985 suggested it correlated with a loess under kansan till stratigraphy indicates the marianna is the older of the five loesses researchers identified loess on both the east and west side of the lmv as well as on higher terraces within the valley many researchers assumed unaltered loesses were commonly yellowish brown and silts or silt loams west et al 1980 miller et al 1986 the nonclay fraction of unweathered lmv loesses was dominated by quartz followed corresponding author by carbonates mainly dolomites followed by feldspars and micas clays were dominated by montmorillonite followed by micaceous minerals kaolinite and vermiculite miller et al 1986 soils in the crowley s ridge loess are most developed followed by the soils in the loveland sicily island which are more developed than the modern soils in the peoria loess soils in the roxana and marianna loesses are least developed and the farmdale soil of the roxana is the weaker of the two miller et al 1986 there is certainly overlapping range in the degree of soil development in the various loesses

ocean atmosphere covariability in the western arabian sea abstract the western arabian sea exhibits strong spatial variability in sea surface temperature sst during the southwest monsoon with changes in sst that can exceed 5 c over 200 km exploration of satellite based and in situ data shows a strong connection between mesoscale sst features and changes in the atmospheric boundary layer the fundamental relationship is that of weak strong wind velocities overlying cold warm sst features there are also coherent changes in other near surface meteorological parameters such as the air sea temperature difference and relative humidity indicating changes in the stability of the planetary boundary layer over the mesoscale sst features these relationships are similar to those recently reported over the equatorial pacific tropical instability wave region this observed covariability of atmospheric boundary layer structure and sst results in variations of the surface heat and moisture fluxes latent heat flux is modified by changes in relative humidity principa

early diagenetic quartz formation at a deep iron oxidation front in the eastern equatorial pacific a modern analogue for banded iron chert formations the mechanisms of early diagenetic quartz formation under low temperature conditions are still poorly understood in this study we investigated lithified cherts consisting of microcrystalline quartz recovered near the base of a 420 m thick miocene holocene sequence of nannofossil and diatom ooze at a drill site in the eastern equatorial pacific ocean drilling program site 1226 precipitation seems still ongoing based on a sharp depletion in dissolved silica at the depth of the cherts also palaeo temperatures reconstructed from 18o values in the cherts are in the range of adjacent porewater temperatures opal a dissolution appears to control silica concentration throughout the sequence while the solution remains oversaturated with respect to quartz however at the depth of the sharp depletion in dissolved silica quartz is still saturated while the more soluble silica phases are strongly undersaturated hence precipitation of quartz was initiated by an auxiliary process a process previously observed to assist in the nucleation of quartz is the adsorption of silica on freshly precipitated iron oxides indeed a deep iron oxidation front is present at 400 m below seafloor which is caused by upward diffusing nitrate from an oxic seawater aquifer in the underlying oceanic crust sequential iron extraction showed a higher content of the adsorbed iron hydroxide fraction in the chert than in the adjacent nannofossil and diatom ooze x ray absorption near edge structure xanes spectroscopy revealed that iron in the cherts predominantly occurs in illite and amorphous iron oxide whereas iron in the nannofossil and diatom ooze occurs mainly in smectite mossbauer spectroscopy also indicated the presence of illite that is to 97 oxidized two possible mechanisms may be operative during early diagenetic chert formation at iron oxidation fronts 1 silica precipitation is catalysed by adsorption to freshly precipitated iron oxide surfaces and 2 porewater silica concentration is locally decreased below opal a and opal ct saturation allowing for precipitation of the thermodynamically more stable phase quartz this mechanism of chert formation at the iron oxidation front in suboxic zones may explain why early diagenetic microcrystalline chert only occurs sporadically in modern marine sediments it may also serve as a modern analogue for the deposition of much more abundant banded iron chert formations at the time of the great oxidation event around 2 4 ga bp which was probably the largest iron oxidation front in earth s history

reduction of structural fe iii in nontronite by thermophilic microbial consortia enriched from hot springs in tengchong yunnan province china abstract iron redox cycling provides one of the most important energy sources supporting microorganisms in terrestrial hot springs in order to understand microbial fe iii reduction processes in hot springs fe iii reducing bacterial consortia were successfully retrieved from seven acidic hot springs in tengchong county yunnan province china a temperature range from 40 6 c to 74 7 c and a ph range from 2 64 to 4 72 these fe iii reducing consortia were mainly composed of sulfate reducing bacteria srb including desulfotomaculum thermodesulfobacterium and desulfomicrobium and organic matter fermenting bacteria thermoanaerobacterium and thermoanaerobacter with each consortia having specific composition depending on the physio chemical conditions of the studied hot springs the obtained consortia were capable of dissimilatory reduction of fe iii in nontronite nau 2 ferruginous smectite with 20 8 to 29 8 reduction extent and initial reduction rate of 0 011 0 023 mm fe iii g nau 2 h these extents and rates were comparable to those by mesophilic fe reducers in the presence of electron shuttles both high temperature and the possible presence of electron shuttles in hot springs may have accounted for these observed high reduction extents and rates various secondary minerals formed during nau 2 bioreduction including fe sulfides and oxides silicates and silica in one spring illitization and kaolinization of smectite were observed suggesting that fe reducers play important roles in mineral transformation in geothermal environments

geopressured shale and sealing effect of smectite to illite transition ten shale samples of frio and vicksburg tertiary overpressured shales from brazoria and hidalgo counties texas were examined by transmission electron microscopy tem techniques initially illite and smectite with some mixed layer component are present in subparallel domains with smectite packets dominating and providing abundant dislocations for ion transport supplying avenues that contribute to local permeability as the transition proceeds illite packets grow within a shrinking matrix of smectite dislocations decrease and pathways for ion transport are restricted we suggest this development of illite packets and diminished ion transport causes loss of local permeability and a rise in the fluid pressure gradient as illite packets coalesce local permeabil ty is increasingly lost hydraulic continuity with the surface is further restricted and a more efficient geopressure seal is formed in both hidalgo and brazoria counties the base of normal hydropressure 0 465 psi ft or 10 5 kpa m coincides with the depth of onset of the smectite to illite transition geopressure greater than 0 7 psi ft 15 8 kpa m occurs at depths corresponding to 50 illite packets in brazoria county and 70 in hidalgo county in both cases 0 7 psi ft 15 8 kpa m geopressure occurs prior to the depth at which the transition ceases these relationships suggest that if the smectite to illite transition begins and proceeds to completion the development of coalescing illite packets during diagenesis will lead to increasing geopressure with the actual values of illite proportion and corresponding fluid pressure gradient determined by the local geologic setting

controls on palagonitization versus pedogenic weathering of basaltic tephra evidence from the consolidation and geochemistry of the keanakako i ash member kilauea volcano 1 on the summit of kilauea volcano incipient palagonitization and consolidation of vitric tephras from the 90 of the carbon is mantle derived we hypothesize that the palagonitized zones may denote the location of fossil steam vents similar to active vents exposed along circumferential faults on both the north and the south sides of the kilauea caldera elsewhere keanakako i tephras are weathering into pedogenic products that closely reflect modern environmental conditions under acidic soil conditions ph 6 0 tephra is undergoing dissolution with the development of opaline crusts on outcrop faces under more neutral soil ph 6 5 7 8 the pedogenic products reflect the degree of desilication of tephra mitigated by leaching dominantly smectite where mean annual rainfall is 50 cm yr and dominantly kaolinite allophane and or imogolite where rainfall exceeds 250 cm yr

analysis of the seismic origin of landslides examples from the new madrid seismic zone by analyzing two landslides in the new madrid seismic zone we develop an approach for judging if a landslide or group of landslides of unknown origin was more likely to have formed as a result of earthquake shaking or in aseismic conditions the two landslides analyzed are representative of two groups of land slides that previous research on the geomorphology and regional distribution of landslides in this region indicates may have been triggered by the 1811 1812 new madrid earthquakes slope stability models of aseismic conditions show that neither landslide is likely to have formed aseismically even in unrealistically high ground water conditions dynamic stability analysis using newmark s method shows that both slides probably would have experienced large inertial displacements during earthquake shaking similar to that which occurred in 1811 1812 these displacements are large enough that catastrophic failure is highly probable thus the stability analyses are consistent with other lines of evidence that these landslides formed as a result of strong earthquake shaking during the 1811 1812 earthquakes our analysis yields a general relationship between newmark landslide displacement earthquake shaking intensity and the critical acceleration of a landslide using this relationship we estimate the minimum shaking intensities required to trigger the types of landslides studied an mb 5 8 or m 5 9 earthquake is the lower bound threshold at zero epicentral distance that could trigger catastrophic movement of typical block slides in the new madrid seismic zone for earth flows mb 5 4 or m 5 3 is the threshold earthquake

historical developments and recent advances in amino acid geochronology applied to loess research examples from north america europe and china abstract amino acid geochronology provides important chronostratigraphic insight in the regional correlation and paleoclimatic evaluation of loess paleosol sequences in the midwestern us throughout western central and eastern europe and in china in general loess of the last four glacial cycles corresponding to marine oxygen isotope stages ois 2 4 6 8 and 10 respectively can be distinguished on the basis of alloisoleucine isoleucine a i ratios measured in fossil gastropod shells preserved in the loess the racemization reaction is much slower in older samples resulting in decreased temporal resolution in the midwestern us and europe it is not possible to confidently subdivide the last glacial cycle on the basis of aminostratigraphic data however in china where effective temperatures were higher during the late pleistocene loess above and below l1ss1 the ois 3 interstadial paleosol can be distinguished using amino acid racemization data with improvements in analytical methods multiple amino acid d l enantiomers are now being measured using reverse phase liquid chromatography aspartic acid racemizes at a higher rate than the traditionally measured alloisoleucine isoleucine diastereomers and can be measured more rapidly this development offers hope for better temporal resolution and enhanced stratigraphic subdivision of loess units than has been achieved previously

a study of the circulation and salinity budget of the arabian sea with an isopycnic coordinate ocean model abstract the evolution of surface circulation and salinity budget are studied with the open boundary version of the miami isopycnic coordinate ocean model micom that uses a global micom simulation as a boundary condition under climatological wind and thermodynamic forcing the model develops solutions that are in good agreement with the climatologically forced global micom results and with observations when the observed winds force the model interannual variability of the surface fields increases significantly however coalescence of the two large eddies off somalia in the end of the summer monsoon suggested in earlier observations does not occur in the model to identify what processes facilitate or restrict the merger a series of experiments was performed with modified model parameters and forcing fields the eddies coalesced when half slip rather than no slip boundary conditions were used in this case less positive vorticity was produced at the coast resulting in reduced blocking effect on the propagation of the southern eddy the socotra island which is submerged in the standard model hinders a northward movement of the great whirl leading to a stronger interaction between the eddies which results in their subsequent merging a more realistic coalescence occurs in an experiment where winds are held constant after reaching the peak summer value freshwater fluxes from the east and south are important for the salinity budget in the arabian sea where evaporation exceeds precipitation the only significant cross equatorial transport of low salinity water occurs in the upper 400 m in the model most of this water is advected below the surface mixed layer at the western boundary the strongest interaction between the mixed layer and the oceanic interior occurs during the summer in the coastal upwelling regions off somalia almost half of all upwelled water comes from depths between 100 and 200 m thus signifying the importance of mid depth circulation and water mass distribution for the surface processes

aminostratigraphic relations and age of quaternary deposits northern espanola basin new mexico abstract amino acid ratios of gastropods provide a useful basis for correlation and approximate dating of middle to late quaternary fluvial deposits from the northern espanola basin new mexico sparsely fossiliferous slackwater deposits in the rio chama rio grande floodplain were buried episodically by piedmont alluvium during periods of climatic change as the axial river system cut down 120 m during the past 620 000 yr alloisoleucine isoleucine alle ile ratios in the total hydrolysate and free fraction of amino acids in succinea and vallonia are strongly correlated with elevation ratios in succinea range from 0 01 to 0 79 in the total hydrolysate and from 0 00 to 1 15 in the free fraction for deposits that range in age from modern to 620 000 yr old amino acid ratios are tightly clustered for deposits that contain the 620 000 yr old lava creek b tephra layer demonstrating their utility for correlation and providing a calibration point for a local dating curve two 14c ages from younger deposits and limiting ages for erosion surfaces that lie above gastropod bearing units tend to support the validity of much of the curve combining the dating curve with the geologic constraints suggests that aggradation events separated by episodes of net incision occurred at about 620 000 310 000 70 000 170 000 40 000 95 000 15 000 yr ago after 19 000 yr ago and during two minor periods between 80 000 and 25 000 yr ago

quaternary paleoecology of the lower mississippi valley copyright c 1996 elsevier science b v all rights reserved in 1938 clair a brown published his classic paleobotanical discoveries from the tunica hills of southeastern louisiana indicating ice age plant migrations of more than 1100km brown collected fossils of both boreal trees such as white spruce picea glaucar and southern coastal plain plants from deposits mapped as the port hickey prairier river terrace by harold n fisk subsequent revisions of terrace mapping radiocarbon dating and paleoecological analysis reconciled browns conceptual and stratigraphic mixingr of these two ecologically incompatible fossil plant groups an older terrace 2 of sangamonian to altonian ager contains the warm temperate assemblage a younger terrace 1 of farmdalian woodfordian and holocene ager includes full glacial and late glacial remains of both boreal and cool temperate plants and a warm temperate suite of plants dates from the holocene interglacial new plant fossil localities with radiocarbon chronologies are now available from within the lower mississippi valley of missouri and arkansas as well as from the adjacent ozark plateaus the interior low plateaus of kentucky and tennessee and the bordering blufflands of tennessee mississippi and louisiana these studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by regional changes in climate glacial runoff and regime of the mississippi river

the volume transport of the somali current during the 1995 southwest monsoon abstract during the summer monsoon of 1995 two hydrographic and direct velocity sections were occupied over the continental shelf and slope off the coast of somalia in order to capture the flux of the western boundary current the first section was in early june just after the onset of the monsoon winds when no current was observed instead there was an anticyclonic eddy at the boundary with a small net northward transport of 3 5 1 5 sv the second section was occupied in mid september when a strong somali current was evident the resulting snapshot represents the only direct velocity section of the jet structure as it flows along the western boundary the strength of the somali current was 37 5 sv this is in general agreement with previous observations given the temporal variability of the current and represents a peak value according to contemporary model simulations the somali current of september extended far into shallow coastal waters of less than 200 m depth with speeds over 150 cm s 1 resulting in a considerable transport of 14 sv over the shelf northward flow of more than 10 cm s 1 penetrated to over 2000 m depth along the continental slope so that the subthermocline flux contributes another 13 sv to the total volume transport model simulations and satellite images of sea surface height illustrate that the somali current system exhibits large spatial variability on short timescales and thus differences in measured transports owe as much maybe more to the changing path of the current as to variability in its strength

a multi proxy palaeoecological and palaeoclimatic record within full glacial lacustrine deposits western tennessee usa the fulton section along the mississippi river in western tennessee usa is a 1 km continuous exposure 20 m vertically of quaternary fluvial and lacustrine deposits inset within eocene sediments and buried by thick loess fossiliferous slackwater lake sediments record maximum aggradation during the last two major glaciations with deposition between ca 190 140 ka and q1 24 18 14 c ka bp based on amino acid and radiocarbon chronology respectively during the onset of full glacial conditions ca 24 22 14 c ka bp a relatively permanent shallow lake environment is indicated by ostracodes aquatic molluscs and both pollen and macrofossils of aquatic plants by 21 8 14 c ka bp increasing emergent plants amphibious gastropods pomatiopsis and heavier d 18 o compositions suggest marsh like conditions in a periodically drying lake the surrounding uplands consisted of picea pinus woodlands mixed with cool temperate hardwoods e g quercus populus carya grasses and herbs more open conditions ensued ca 20 14 c ka bp with loess and slopewash gradually infilling the former lake by 18 14 c ka bp modern analogue analyses of ostracodes and palaeontological evidence imply a full glacial climate similar to today s mixed boreal zone in central minnesota usa about 98c cooler in mean annual temperature than present day western tennessee copyright 2009 john wiley sons ltd

monitoring the variations of the socotra upwelling system during the last 250 kyr a biogenic and geochemical approach abstract a combination of changes in the species composition of the radiolarian populations and in the sediment chemical composition content and mass accumulation rates of carbonate organic carbon and selected major and trace elements with special attention paid to ba is used to reconstruct the variations in upwelling activity over the last 250 kyr in the socotra gyre area somali socotra upwelling system nw indian ocean in the socotra gyre core md 962073 at 10 n the variations in upwelling intensity are reconstructed by the upwelling radiolarian index uri while the thermocline surface radiolarian index tsri testifies to productivity variations during non upwelling intervals despite an origin related both to marine and terrigenous inputs the geochemical records of organic carbon silica and trace elements ba p cu and zn normalized to al are controlled by the variations in surface paleoproductivity the data indicate a continuous increase in upwelling intensity during the last 250 kyr with a maximum activity within the mis 3 while high productivity periods in between the upwelling seasons occurred both during glacial and interglacial intervals a comparison of our data with published observations from another gyre of the somalian upwelling area located at 5 n in the somali gyre area shows differences regarding periods of upwelling activity and their geochemical imprint three hypotheses are proposed to explain these differences 1 changes in the planktonic community resulting in more silica rich deposits in the socotra gyre and more carbonate rich deposits in the somali gyre that are controlled by differences in the source water of the upwelling 2 a more important terrigenous input in the southern gyre and 3 a different location of the sites relative to the geographic distribution of the upwelling gyres and hydrologic fronts

influence of organic matter on smectite illitization a comparison between red and dark mudstones from the dongying depression china interactions between organic matter om and clay minerals have received considerable attention in previous studies the influence of om on smectite illitization has been analyzed primarily in simulation experiments rather than in diagenetic studies the present study explores the influence of om on smectite illitization during diagenesis thirty red and dark mudstone samples from the dongying depression were analyzed x ray diffraction xrd analyses revealed that the illite percentages in mixed layer illite smectite i s of both types of samples were dispersive above 3100 m and more convergent below this depth the stacking mode of i s in dark mudstones above 3100 m remained primarily at r0 r0 5 ordering with the average number of layers nave dispersively distributed between 2 and 4 5 in red mudstones the i s changed from the r0 to r0 5 mode with the nave increasing from 2 to 5 over this range the smectite illitization in dark mudstones was slower than that in red mudstones below 3100 m the i s stacking mode of dark mudstones changed from r0 5 to r3 ordering with the nave increasing sharply from 4 to 8 in red mudstones the i s displayed r1 5 and r3 ordering with the nave varying between 4 5 and 6 5 over this range the smectite illitization in dark mudstones accelerated rapidly whereas the process in red mudstones was retarded additionally the red mudstone samples contained little om whereas the dark mudstone samples contained abundant total organic carbon 0 17 4 43 thermo xrd near infrared nir as well as mid infrared mir spectroscopy analyses suggested that the om in dark mudstones exhibited a significant transition at 3100 m coincident with the illitization change above 3100 m the smectite illitization in dark mudstones was delayed due to the om pillar effect in the interlayer spaces of smectite below 3100 m the interlayer om became varied and desorbed discharging organic acid this led to the dissolution of smectite structural layers consequently illitization in the dark mudstone was accelerated this study revealed that the existence and occurrence of om could influence the smectite illitization in diagenesis further study on the interactions between om and clay minerals is needed to facilitate our understanding on the mechanism of smectite illitization as well as its geological applications

somali current rings in the eastern gulf of aden 1 new satellite based observations reveal that westward translating anticyclonic rings are generated as a portion of the somali current accelerates northward through the socotra passage near the mouth of the gulf of aden rings thus formed exhibit azimuthal geostrophic velocities exceeding 50 cm s are comparable in overall diameter to the width of the gulf of aden 250 km and translate westward into the gulf at 5 8 cm s ring generation is most notable in satellite ocean color imagery in november immediately following the transition between southwest boreal summer and northeast winter monsoon regimes the observed rings contain anomalous fluid within their core which reflects their origin in the equator crossing somali current system estimates of socotra passage flow variability derived from satellite altimetry provide evidence for a similar ring generation process in may following the winter to summer monsoon transition cyclonic recirculation eddies are observed to spin up on the eastern flank of newly formed rings with the resulting vortex pair translating westward together recent shipboard and lagrangian observations indicate that vortices of both sign have substantial vertical extent and may dominate the lateral circulation at all depths in the eastern gulf of aden

distinct influence of air sea interactions mediated by mesoscale sea surface temperature and surface current in the arabian sea abstractduring the southwest monsoons the arabian sea as develops highly energetic mesoscale variability associated with the somali current sc great whirl gw and cold filaments cf the resultant high amplitude anomalies and gradients of sea surface temperature sst and surface currents modify the wind stress triggering the so called mesoscale coupled feedbacks this study uses a high resolution regional coupled model with a novel coupling procedure that separates spatial scales of the air sea coupling to show that sst and surface currents are coupled to the atmosphere at distinct spatial scales exerting distinct dynamic influences the effect of mesoscale sst wind interaction is manifested most strongly in wind work and ekman pumping over the gw primarily affecting the position of gw and the separation latitude of the sc if this effect is suppressed enhanced wind work and a weakened ekman pumping dipole cause the gw to extend northeastward delaying the sc separation by 1 current wind i

desilication in archean weathering processes traced by silicon isotopes and ge si ratios abstract the influence of continental weathering on oceanic seawater compositions in the precambrian is poorly understood here we combine si isotopes and ge si ratios of a mesoarchean paleosol 2 95 ga and overlying shales as proxies for weathering processes and si mass transfer at the early earth s surface results show that as with modern soils neoformation of secondary clay minerals in the paleosol was associated with the fractionation of si isotopes and ge si ratios in response to chemical weathering and soil desilication furthermore the loss of fe bearing minerals most likely fe bearing smectites produced additional controls on si and ge mobility through the coupled dissolution and re precipitation of clay minerals under reductive conditions opposite fractionation behaviors are observed neoformed secondary clay minerals acted as a 28 si and ge sink whereas the leaching of fe bearing minerals released 28 si and ge into soil solutions an attempt to estimate 30 si and ge si signatures of released dissolved elements into soil solution provided 30 si and ge si signatures of about 0 1 and 1 4 mol mol respectively furthermore shales deposited shortly after paleosol formation display 30 si and ge si compositions that may be explained as mixtures of the recognized paleosol components the shale record suggests that weathering induced desilication and leaching of fe bearing minerals to a lesser extent might have been widely effective during the mesoarchean for the transfer of si from the continents to the hydrosphere comparison of si isotopes recorded in detrital sediments and chemical precipitates over time might thus provide a useful supplementary tool to decipher the impact of putative increases in continental weathering and desilication relative to changes in hydrothermal and continent derived solute inputs to ocean and ocean cooling

intraseasonal variability in the southwestern arabian sea and its relation to the seasonal circulation an analysis of topex poseidon altimeter data and in situ current and temperature data obtained between april 1995 and october 1996 from a moored array shows strong intraseasonal fluctuations in the southwestern arabian sea an oceanic region where the great whirl gw a predominantly wind generated very energetic anticyclone is present during the southwest monsoon fluctuation periods between 30 and 50 days up to 100 days during some years are observed in the 8 year altimetric dataset mostly during late summer and fall these fluctuations are largest in a 1000 km wide region off the somali omani and yemeni coasts north of 5 n suggesting a local generation mechanism the in situ data at different moorings show strong and coherent fluctuations that are characterized by southwestward phase propagation and northward energy propagation their periods range from 30 to 60 days and increase steadily from july 1995 to january 1996 in the first stage these periods are at and below the cut off period of freely propagating first baroclinic mode rossby waves but approach this theoretical limit later in the year instabilities of the flow in the transition region between the southern gyre and the gw are likely sources of these fluctuations

microorganism induced weathering of clay minerals in a hydromorphic soil abstract in order to improve the understanding of factors influencing weathering in hydromorphic soils the clay mineral and chemical compositions iron hydr oxides organic compounds and sr and nd isotopic compositions of hydromorphic soils on the banks of the liangzi lake hubei province south china were investigated the b horizon in the lower profile exhibits a distinct net like pattern with abundant short white veins within the red brown matrix their various 87sr 86sr and 143nd 144nd isotopic compositions showed only small variations of 0 7270 0 7235 and 0 51200 0 51204 respectively consistent with the composition of yangtze river sediments indicating that the soils were all derived from alluvium from the catchment the white veins contained notably more sio2 al2o3 tio2 and mobile elements relative to the red brown matrix while they both showed similar values for the chemical index of alteration of 86 7 and 87 1 respectively and displayed similar degrees of weathering the clay minerals in a ae and e horizons of the soil profile were illite kaolinite and mixed layer illite smectite these same three clay minerals comprised the white net like veins in the soil b horizon whereas only illite and kaolinite were observed in the red brown matrix iron hydr oxides in a ae and e horizons of the soil profile were hematite and goethite whereas in the red brown matrix of the b horizon they were hematite goethite and ferrihydrite different organic compounds were observed for the white vein and the red brown matrix in the soil b horizon an 18 2 fatty acid biomarker for fungi in the net like vein but not in the red brown matrix compared with the red brown matrix the white net like vein also clearly contained more mono unsaturated fatty acids which are sometimes associated with bacteria that have the capacity to reduce fe iii thus migration of iron and the formation of the net like veins involved the participation of biota during the hydromorphic pedogenesis process as ferrihydrite is usually formed with the assistance of biota redoximorphic processes will chemically affect phyllosilicates by changing their charge and fe iii in illite may serve as electron acceptor for fe iii reducing microorganisms this leads to an increase in negative charge in the illite structure which could be neutralized by electrostatic displacement of interlayer cations and adsorption of protons thereby promoting transformation of illite to mixed layer illite smectite and dissolution of the pre existing illite mineral our results suggest that microorganisms brought about iron leaching and dominated the alteration of clay minerals by redox processes and different mineral volumes formed in the net like b horizon of the hydromorphic soil were attributed to the microorganism induced weathering process

microbial mediation of authigenic clays during hydrothermal alteration of basaltic tephra kilauea volcano 1 highly altered glassy tephras within the active steam vents at kilauea volcano hawaii contain subsurface bacteria characterized by small 500 nm in diameter epicellular grains attached directly to the cell walls compositionally the grains were dominated by si al fe and k in a stoichiometry similar to a dioctahedral smectite the initial dissolution of glass which may in part have been microbiologically mediated served as the source for many of the elements sequestered into the biomineralized clays overlying the tephras are white crusts silica and calcite and green colored biofilms the biofilms comprise a filamentous likely cyanobacterial community coated with spherical 100 nm in diameter grains of amorphous silica directly attached to the sheaths individual precipitates can easily be resolved but quite often they coalesce forming a dense mineral matrix of amorphous silica for both the clays and silica the microbial surfaces are clearly sites for mineral nucleation and growth these observations imply that microbial biomineralization may be a significant process in the overall alteration of primary basaltic glass in active steam vent systems

microbially mediated iron redox cycling of subsurface sediments from hanford site washington state usa abstract iron bearing clay minerals are predominant in soils and sediments and they undergo oxidation reduction cycles as a result of natural processes such as wetting drying cycles and plant root respiration however the kinetics and mechanisms of multiple redox cycles of iron in clay rich sediments and consequences of such cycling on sediment properties are poorly understood the objective of this study was to understand how multiple redox cycles of fe in clay rich sediment affect the rate and extent of fe bioreduction and the physicochemical properties of the sediment a natural sediment sample containing fe bearing montmorillonite from hanford washington usa was size fractionated 2 0 to 0 5 m hanford c and 0 5 to 0 02 m hanford f and redox cycled for four times bioreduction was achieved utilizing geobacter sulfurreducens and re oxidization was performed with sparged air time course change of total fe ii was monitored to measure the rate and extent of fe iii bioreduction redox cycled sediments were characterized to determine the physicochemical changes both the initial rate and extent of bioreduction fluctuated across the four redox cycles but they ultimately decreased from 5 3 mol g 1 h 1 and 22 9 to nearly zero by the fourth cycle these fluctuation patterns were likely due to a combined effect of reductive dissolution of small poorly crystalline clay particles by 3 5 and clay mineral structural changes as evidenced by redox induced changes of aqueous chemistry surface area cation exchange capacity mineralogy and mossbauer parameters once these small poorly crystalline clay particles were dissolved structural fe in residual larger and more crystalline clay particles was largely reversible across additional redox cycles as revealed by mossbauer spectroscopy through the first three cycles

microbial dissolution of clay minerals as a source of iron and silica in marine sediments interactions between microbes and minerals have the potential to contribute significantly to the global cycles of various elements and serve as a link between the geosphere and life in particular the microbially mediated cycle of iron within marine sediments is closely tied to the carbon cycle the dissolved iron that serves as a nutrient is thought to be primarily drawn from well known pools of highly reactive bioavailable iron and iron complexes iron contained within the crystal lattice of clay minerals the most abundant materials found at the earth s surface is not thought to be part of this pool here we analyse the mineral composition of middle cambrian aged mudstones from the western united states we find intergrown mineral aggregates of quartz pyrite and calcite on the basis of mineral phase relationships and temperatures of crystallization derived from stable isotopes of oxygen we infer that mineral dissolution driven by microbes released iron and silica to the surrounding sediment pore waters and led to the subsequent precipitation of the observed minerals the microbial extraction of structurally coordinated fe3 from clay minerals after their deposition in marine sediments may liberate a fraction of iron previously considered unavailable and may be important in iron and silica cycling in marine sediments interactions between microbes and minerals are evident in modern global elemental cycles relationships between minerals in cambrian mudstones indicate that such interactions may have released otherwise unavailable mineral bound iron and silica into the ancient oceans

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

iron reduction through the tan green color transition in deep sea sediments mossbauer spectroscopic investigations of deep sea sediments from the peru basin revealed a prominent downcore increase of the bulk sediment fe ii fe iii ratio across the well known tan green color transition this increase occurs along a continuous gradient extending over a 3 cm zone at the two deep sea sites that we report remarkably constant values of the fe ii fe iii ratios above 11 2 89 2 and below 37 2 63 2 the iron redox transition zone delimit the gradient clearly a minor peak of diagenetic iron enrichment is manifest at the redox front this fe enrichment has accumulated in a redox cycle and amounts to 16 4 of the total fe at the peak maximum the data imply that 26 4 of the detrital iron has experienced in situ redox transition from fe iii to fe ii within the iron redox transition zone

low temperature illitization of smectite in the late eocene and early oligocene of the isle of wight hampshire basin u k variegated palaeosols which formed from weathering of clays silts and brackish to freshwater limestones are present in the late eocene early oligocene solent group of the hampshire basin southern u k the detrital clay mineral suite is dominated by illite and illite smectite with minor kaolinite and chlorite in pedogenically modified palaeosol and evaporitic lacustrine clay rich sediments the proportion of illite in the illite smectite is greater than in the non pedogenically modified sediments and where alteration is most intense kaolinite and chlorite are absent the smectite to illite transition has been investigated in the 0 5 m fraction by xrd analysis powder and oriented mounts thermogravimetry tg analytical sem and chemical analysis of fe2 modeling of xrd data reveals that the illite smectite is a mixture of compositions overall 60 95 illite r 0 with high rotational stacking disorder dehydroxylation occurs mainly at 500 c but also at higher temperatures indicating heterogeneous octahedral cation composition analytical sem and chemical analysis of fe2 indicate that the illite to smectite transition occurs through fe reduction in octahedral sites leading to increased layer charge coupled with k fixation the driving mechanism for what appears to be irreversible fe3 reduction is wetting reducing and drying oxidizing cycles in gley soil in which reoxidation of reduced fe is never complete

southward subsurface flow below the somali current the existence of a southward flowing current beneath the northern part of the seasonally reversing somali current is documented in a 2 year long time series of currents obtained at moored stations near 5 n about 30 km off the somali coast its mean annual transport in the layer 150 600 m amounts to about 5 106 m3 s the undercurrent has a pronounced seasonal cycle in phase with the near surface flow suggesting a close coupling to the monsoonal wind forcing with the spin up of the deepreaching northern somali gyre after the onset of the southwest monsoon the undercurrent is temporarily destroyed in the northern somali basin during june july but is re established in august the undercurrent does not reach 3 n but turns offshore north of that latitude

variability of the somali current system during the onset of the southwest monsoon 1979 abstract an array of six current meter moorings and several coastal temperature recorders was deployed on the shelf and continental slope off northern somalia from march to july 1979 a seventh mooring was placed near 2 s in addition four deep sea moorings were deployed for a period of one month in may june farther offshore already during the late northeast monsoon in march the somali current north of 5 n was flowing northeastward in the top 150 m underneath in the depth range 150 400 m a narrow southward undercurrent was observed from march to june after the first onset of the southwest monsoon which occurred around 5 may when winds shifted from easterly to southwesterly parallel to the coast the near surface temperatures on the shelf decreased immediately with no detectable phase difference between 6 and 10 n but no change was observed in the offshore circulation pattern the final monsoon onset around 10 june was characterized by a drastic increase in wind speeds and the establishment of a st

microbial reduction of fe iii in smectite minerals by thermophilic methanogen methanothermobacter thermautotrophicus clay minerals and thermophilic methanogens can co exist in hot anoxic environments including the continental subsurface geysers terrestrial hot springs and deep sea hydrothermal vent systems however it is unclear whether thermophilic methanogens are able to reduce structural fe iii in clay minerals in this study the ability of a thermophilic methanogen methanothermobacter thermautotrophicus to reduce structural fe iii in iron rich and iron poor smectites nontronite nau 2 and wyoming montmorillonite swy 2 and the relationship between iron reduction and methanogenesis were investigated m thermautotrophicus reduced fe iii in nontronite nau 2 and montmorillonite swy 2 with h2 co2 as substrate the extent of bioreduction was 27 for nontronite and 13 15 for montmorillonite anthraquinone 2 6 disulfonate aqds did not enhance the extent of bioreduction but accelerated the rate when methanogenesis was inhibited via addition of 2 bromoethane sulfonate bes the extent of bioreduction decreased to 16 for nau 2 and 9 for swy 2 these data suggest that fe iii bioreduction and methanogenesis were mutually beneficial the likely mechanism was that fe iii bioreduction lowered the reduction potential of the system so that methanogenesis became favorable and methanogenesis in turn stimulated the growth of the methanogen which enhanced fe iii bioreduction nau 2 was partly dissolved and high charge smectite and biogenic silica formed as a result of bioreduction

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

pre late wisconsinan pleistocene biota from southeastern michigan u s a abstract fossiliferous sediments underlie the late wisconsinan mill creek and fisher road tills at the mill creek site northwest of port huron michigan fragmentary remains of 5 fish and 11 mammal taxa occur with 39 taxa of molluscs 6 of ostracodes and a pine spruce pollen assemblage while the fish are wide ranging the mammals include distinctly northern elements such as dicrostonyx sp lemmus sp mictomys borealis and microtus xanthognathus the molluscs include a mixture of cold vertigo alpestris oughtoni and v modesta and warm lioplax sulculosa taxa none of the vertebrates have been found at michigan sub till sites before and lioplax is new to michigan fossil or living vertigo hannai is known only as a pleistocene fossil at present the age of the biota is indeterminate the stratigraphy indicates a middle wisconsinan or greater age a finite 14c age of 48 3 0 8 ka ql 1215 was later supplemented by a tl date of 57 9 ka but perhaps as old as 300 ka two clusters of amino acid allo isoleucine isoleucine values obtained from six genera of molluscs are interpreted to represent the co occurrence of early sangamonian aile ile values ranging from approximately 0 15 to 0 25 and illinoian aile ile values ranging from approximately 0 25 to 0 35 mollusc fossils at the mill creek site these results highlight the need for more reliable quaternary dating methods

reactive fe ii layers in deep sea sediments the percentage of the structural fe ii in clay minerals that is readily oxidized to fe iii upon contact with atmospheric oxygen was determined across the downcore tan green color change in peru basin sediments this latent fraction of reactive fe ii was only found in the green strata where it proved to be large enough to constitute a deep reaction layer with respect to the pore water o2 and no3 large variations were detected in the proportion of the reactive fe ii concentration to the organic matter content along core profiles hence the commonly observed tan green color change in marine sediments marks the top of a reactive fe ii layer which may represent the major barrier to the movement of oxidation fronts in pelagic subsurface sediments this is also demonstrated by numerical model simulations the findings imply that geochemical barriers to pore water oxidation fronts form diagenetically in the sea floor wherever the stage of iron reduction is reached provided that the sediments contain a significant amount of structural iron in clay minerals

sequential mineral transformation from kaolinite to fe illite in two brazilian mangrove soils abstract mangrove soils have peculiar chemical and physical conditions generated by the variable water salinity cyclic tidal changes and intense biological activity that produce complex clay suites in this study the crystal chemical characteristics of clay minerals from two mangrove soils were investigated in detail to further our understanding of the processes taking place the two brazilian mangroves are from zones of contrasting climatic type and continental sediment character 1 tropical wet climate area receiving highly weathered sediments braganca para state and 2 mild semiarid climate area supplied with a mixture of highly and moderately weathered sediments acarau ceara state the investigation of the 2 0 2 m and 4 ions abundant in the interstitial water superior fe rich illite contents in acarau mangrove compared to braganca mangrove are explained by high inputs of 2 1 clays from sediment source areas inland the above clay mineral reactions shed light on the role of clays and the interaction between minerals and biotic components in mangrove soils in addition these reactions may influence the cycle of major elements in coastal ecosystem surrounding mangroves

wind driven cross equatorial flow in the indian ocean abstractmeridional velocity mass and heat transport in the equatorial oceans are difficult to estimate because of the nonapplicability of the geostrophic balance for this purpose a steady state model is utilized in the equatorial indian ocean using ncep wind stress and temperature and salinity data from the world ocean atlas 2005 woa05 and argo the results show a somali current flowing to the south during the winter monsoon carrying 11 5 1 3 sv 1 sv 106 m3 s 1 and 12 3 0 3 sv from woa05 and argo respectively in the summer monsoon the somali current reverses to the north transporting 16 8 1 2 sv and 19 8 0 6 sv in the woa05 and argo results transitional periods are considered together and in consequence there is not a clear somali current present in this period model results fit with in situ measurements made around the region although argo data results are quite more realistic than woa05 data results

suggested terminology for quaternary dating methods abstract classification of quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods we recommend the use of the terms numerical age calibrated age relative age and correlated age to describe these levels we also classify dating methods by type into sideral isotopic radiogenic chemical and biological geomorphic and correlation methods the use of absolute is inappropriate for most dating methods and should be replaced by numerical the use of date should be minimized in favor of age or age estimate we recommend use of the abbreviations ka and ma for most ages calender dates can be used where appropriate and yr b p can be used for radiocarbon ages

an early triassic smithian stromatolite associated with giant ooid banks from lichuan hubei province south china environment and controls on its formation this study is partly supported by the 111 program of china b80210 two research grants from the state key laboratory of biogeology and environmental geology bgeg gbl11206 and state key laboratory of geological processes and mineral resources gpmr201302 china university of geosciences and two nsfc grants 41272023 41572091

in situ silicification of an icelandic hot spring microbial mat implications for microfossil formation transmission electron microscopy and energy dispersive x ray analysis revealed that filamentous phototrophic bacteria resembling chlorojlexus aurantiacus underwent rapid silicification in an icelandic hot spring microbial mat the mineralization associated with the cells occurred both extracellularly within and on the external sheaths of the bacteria and intracellularly within the cytoplasm the exceptional preservation of the bacterial sheaths is due to the presence of distinct mineral nucleation sites this results in the production of silica casts of the bacteria which bear a striking resemblance to microbial remains in ancient microfossil assemblages rcsumc les analyses par microscopie clectronique i transmission et par 1 6nergie dispersive des rayons x ont rcvcl6 que les bactkries filamenteuses phototrophes ressemblant b chlorojlexus aurantiacus ont subi une silicification rapide au sein d un tapis microbien de source therrnale en islande la mineralisation associee aux cellules se presente sous forme extracellulaire b l interieur de et sur la membrane externe des bacteries et sous forrne intracellulaire i l interieur du cytoplasme la preservation exceptionnelle de la membrane des bacteries est due b la presence de sites de nucleation minerale disperses le resultat est la production des moulages siliceux des bactkries affichant une resemblance remarquable avec les vestiges microbiens d anciens assemblages microfossiles traduit par la raaction fossil evidence of the earth s earliest biosphere shows that complex communities of microorganisms were abundant and well distributed throughout the precambrian era among the richest beds of microbial fossils are those found in the gunflint iron formation north of lake superior in canada barghoorn and tyler 1965 the early archaean apex chert of australia schopf and packer 1987 schopf 1993 and the riphean section of the anabar uplift in russia sergeev 1993 all ranging in age from 0 8 to 3 5 ga the distribution and types of microorganisms preserved as cellularly intact microfossils are remarkably similar to those in modern microbial mats in which organic rich layers formed by cyanobacteria and or other types of filamentous bacteria alternate with layers that are comprised of detrital inorganic sediment and authigenic mineral precipitates morse and mackenzie 1990 these benthic microbial communities are considered to be analogous and possibly homologous with those that were preserved billions of years ago as stromato

coupling of fe ii oxidation in illite with nitrate reduction and its role in clay mineral transformation abstract in pedogenic and diagenetic processes clay minerals transform from pre existing phases to other clay minerals via intermediate interstratified clays temperature pressure chemical composition of fluids and time are traditionally considered to be the important geological variables for clay mineral transformations nearly ten years ago the role of microbes was recognized for the first time where microbial reduction of structural fe iii in smectite resulted in formation of illite under ambient conditions within two weeks however the opposite process the oxidation of structural fe ii in illite has not been studied and it remains unclear whether or not this process would result in the back reaction e g from illite to smectite the overall objective of this study was to investigate biological oxidation of structural fe ii in illite coupled with nitrate reduction and the effect of this process on clay mineral transformation laboratory incubations were set up where structural fe ii in illite served as electron donor nitrate as electron acceptor and pseudogulbenkiania sp strain 2002 as mediator solution chemistry and gas composition were monitored over time mineralogical transformation resulting from bio oxidation was characterized with x ray diffraction and scanning and transmission electron microscopy our results demonstrated that strain 2002 was able to couple oxidation of structural fe ii in illite with reduction of nitrate to n 2 with nitrite as a transient intermediate this oxidation reaction resulted in transformation of illite to smectite and ultimately to kaolinite illite smectite kaolinite transformations this study illustrates the importance of fe redox process in mediating the smectite illite mineral cycle with important implications for fe redox cycling and mineral evolution in surficial earth environments

chronologic evidence for multiple periods of loess deposition during the late pleistocene in the missouri and mississippi river valley united states implications for the activity of the laurentide ice sheet abstract the loess stratigraphy of the mid continental u s is an important proxy record for the activity of the laurentide ice sheet in north america one of the most outstanding problems is deciphering the age of loess deposits in this area during the late pleistocene radiocarbon dating of snails and thermoluminescence dating of the fine silt fraction 4 11 m from loess at the loveland loess type section loveland iowa and a recent excavation at the pleasant grove school section madison county illinois provide new chronologic control on loess deposition in the mississippi missouri river valley chronology indicates that the loveland loess is illinoian in age 135 20 ka but is not correlative with the teneriffe silt which is dated to 77 8 ka concordant radiocarbon and thermoluminescence age estimates demonstrate that the roxana silt and a correlative loess in iowa the pisgah formation is probably 40 30 ka old these age estimates in conjunction with previous results indicate that there were four periods of loess deposition during the last 150 ka at 25 12 ka 45 30 ka 85 70 ka and at ca 135 20 ka this chronology of loess deposition supports the presence of both a late illinoian and early wisconsinan loess and associated soils thus there may be more than one soil in the loess stratigraphy of the mid continental u s with morphologies similar to the sangamon soil the last three periods of loess deposition may be correlative with periods of elevated dust concentrations recorded in the dye 3 ice core from southern greenland this is particularly significant because both areas possibly had the same source for eolian particles reconstructions of atmospheric circulation for glacial periods show a southerly deflected jet stream that could have transported dust from the mid continental usa to southern greenland lastly the inferred record of loess deposition is parallel to a chronology for deglaciation of the laurentide ice sheet deciphered from chronologic and stratigraphic studies of raised glacial and marine sediments in the hudson bay lowlands canada these chronologies indicate that the laurentide ice sheet was quite dynamic during the late pleistocene advancing and retreating across north america at least four times during the last 150 ka

mesoscale dynamics in the arabian sea and a focus on the great whirl life cycle a numerical investigation using roms the great whirl gw is a persistent anticyclonic mesoscale eddy that is observed seasonally in the arabian sea during a period embedding the 3 months of the southwest monsoon june july august at a quasi steady location its dynamics remain unclear despite it being one of the largest coherent vortices in the world ocean realistic regional numerical experiments using roms are performed to investigate the life cycle of the gw which is not well resolved by sparse available in situ measurements in the region using a set of sensitivity experiments and an accurate temporal characterization of the eddy properties including position radius depth and vorticity we i confirm the role of basin scale downwelling rossby waves in the gw generation ii clarify the role of the monsoonal strong anticyclonic wind in its maintenance and barotropization and iii suggest a connection between basin scale rossby wave dynamics and gw collapse

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

strong intraseasonal variability of meridional currents near 5 n in the eastern indian ocean characteristics and causes abstractthis paper reports on strong intraseasonal upper ocean meridional currents observed in the indian ocean between the bay of bengal bob and the equator and elucidates the underlying physical processes responsible for them in situ measurements from a subsurface mooring at 5 n 90 5 e reveal strong intraseasonal variability of the meridional current with an amplitude of 0 4 m s 1 and a typical period of 30 50 days in the upper 150 m which by far exceeds the magnitudes of the mean flow and seasonal cycle such prominent intraseasonal variability is however not seen in zonal current at the same location further analysis suggests that the observed intraseasonal flows are closely associated with westward propagating eddylike sea surface height anomalies sshas along 5 n the eddylike sshas are largely manifestations of symmetric rossby waves which result primarily from intraseasonal wind stress forcing in the equatorial waveguide and reflection of the equatorial kelvin waves at the eastern bou

on the origins of eogenetic chlorite in verdine facies sedimentary rocks from the gabon basin in west africa abstract the verdine facies clay assemblages are regularly encountered in shallow marine sediments of equatorial latitudes where fe of terrigenous origin is readily available there the 7 a fe rich green clay odinite of syn sedimentary origin commonly occurs previous findings suggested that odinite serves as a precursor of diagenetic chlorite whose importance in porosity conservation has been widely acknowledged the investigation of fe rich clays is therefore helpful to constrain the specific conditions and mechanisms which give rise to chlorite growth thus illuminating the history of early burial in this contribution we studied cretaceous sediments from the gabon coast where multiple sedimentary basins came into existence prior during and after the opening of the south atlantic analyzed core is siliciclastic and petroleum bearing stemming from the fluvio lacustrine deltaic environment recovered from depths of 1500 m tvd electron micro beam investigation coupled with x ray diffraction on the clay fraction and spectra fitting revealed odinite interstratified odinite chlorite o c and to a lesser extent illite chlorite smectite i c s and illite smectite occur as grain coatings and pore filling phases with a characteristic honeycomb texture embryonic chlorite emerges at the contact of odinite and o c flakes as a particulate authigenic mineralization formed from aluminosilicate and fe oxyhydroxide debris at sediment water interface odinite becomes intrinsically unstable possibly due to the activity of fe reducing bacteria or decaying organic matter creating a prevalently reducing environment that promotes fe reduction such condition facilitated a two step chlorite growth which first included a partial chloritization of odinite through the in situ solid state transformation of 7 a to 14 a layers then with increasing burial at peak diagenetic conditions 50 c 1 5 km depth odinite and o c both recrystallized to form eogenetic chlorite most likely following the ostwald ripening mechanism

multiple mineral horizons in layered outcrops at mawrth vallis mars signify changing geochemical environments on early mars abstract refined calibrations of crism images are enabling identification of smaller deposits of unique aqueous materials on mars that reveal changing environmental conditions at the region surrounding mawrth vallis through characterization of these clay sulfate assemblages and their association with the layered phyllosilicate units of this region more details of the aqueous geochemical history can be gleaned a stratigraphy including five distinct mineral horizons is mapped using compositional data from crism over ctx and hrsc imagery across 100s of km and from crism over hirise imagery across 100s of meters transitions in mineralogic units were characterized using visible near infrared vnir spectral properties and surface morphology we identified and characterized complex doublet type spectral signatures with two bands between 2 2 and 2 3 m at one stratigraphic horizon based on comparisons with terrestrial sites the spectral doublet unit described here may reflect the remnants of a salty evaporative period that existed on mars during the transition from formation of fe rich phyllosilicates to al rich phyllosilicates layered outcrops observed at mawrth vallis are thicker than in other altered regions of mars but may represent processes that were more widespread in wet regions of the planet during its early history the aqueous geochemical environments supporting the outcrops observed here include i the formation of fe3 rich smectites in a warm and wet environment ii overlain by a thin ferrous bearing clay unit that could be associated with heating or reducing conditions iii followed by a transition to salty and or acidic alteration phases and sulfates characterized by the spectral doublet shape in an evaporative setting iv formation of al rich phyllosilicates through pedogenesis or acid leaching and v finally persistence of poorly crystalline aluminosilicates marking the end of the warm climate on early mars the doublet type units described here are likely composed of clay sulfate assemblages formed in saline acidic evaporative environments similar to those found in western australia and the atacama desert despite the chemically extreme and variable waters present at these terrestrial saline lake environments active ecosystems are present thus these doublet type units may mark exciting areas for continued exploration important to astrobiology on mars

rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal bearing sediments offshore shimokita peninsula japan iodp site c0020 sediments recovered at integrated ocean drilling program iodp site c0020 in a forearc basin offshore shimokita peninsula japan include numerous coal beds 0 3 7 m thick that are associated with a transition from a terrestrial to marine depositional environment within the primary coal bearing unit 2 km depth below seafloor there are sharp increases in magnetic susceptibility in close proximity to the coal beds superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence we investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record using isothermal remanent magnetization irm thermal demagnetization anhysteretic remanent magnetization arm iron speciation and iron isotopes magnetic mineral assemblages in all samples are dominated by very low coercivity minerals with unblocking temperatures between 350 580 c that are interpreted to be magnetite samples with lower unblocking temperatures 300 400 c higher arm higher frequency dependence and isotopically heavy 56fe across a range of lithologies in the coal bearing unit between 1925 1995 mbsf indicate the presence of fine grained authigenic magnetite we suggest that iron reducing bacteria facilitated the production of fine grained magnetite within the coal bearing unit during burial and interaction with pore waters the coal peat acted as a source of electron donors during burial mediated by humic acids to supply iron reducing bacteria in the surrounding siliciclastic sediments these results indicate that coal bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time within the subsequent deep biosphere