metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

fibrous clay mineral formation and soil evolution in aridisols of northeastern patagonia argentina recent studies of soil landscape relationships in northeastern patagonia identified fibrous clay minerals in calcic and petrocalcic horizons developed on old fluvio glacial plains called rodados patagonicos rp the objectives of this study were i to evaluate the occurrence of fibrous clay minerals in the arid soil environment and ii to establish the relationship between the soil properties and degree of the calcic horizon development including the age of the soils containing fibrous clay minerals in extra andean patagonia the soil studied were calciargids natrigypsids and petrocalcids located at elevations of 50 70 and 130 m a s l respectively the soils are polygenetic where the clay mineralogy is related to the age of the pedogenetic periods that affected the formation of geomorphic surfaces in the surface horizons illite proved to be the dominant clay mineral and was slightly altered to interstratified illite smectite and smectite an older pedogenic episode was identified in argillic and calcic horizons in which smectite was prevalent the following soil formation period was recorded in calcic and calcic gypsic horizons appearing in the upper limit of the rp in these horizons palygorskite is the dominant clay mineral pedogenetic carbonate was qualified as lowmg calcite indicating that during its precipitation the mg 2 activity increased in the soil solution favoring the smectite palygorskite transformation the soil environment favorable for this transformation was the textural transition between the fine materials of sub surface horizons and the coarsest deposit of rp where temporary waterlogging occurred the petrocalcic horizons and their re transported fragments represent the oldest pedogenetic period where sepiolite was the dominant clay mineral during the calcretization processes the sepiolite was precipitated from the soil solution following the formation of palygorskite fluorite was identified in the petrocalcic horizon and its association with calcite and sepiolite indicated a successive precipitation of these minerals under alkaline conditions during evaporation processes 2007 elsevier b v all rights reserved

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

mineralogical and geochemical discrimination of the occurrence and genesis of palygorskite in eocene sediments on the northeastern tibetan plateau palygorskite is a widely used indicator of semiarid to arid environments in paleoclimate studies in this study we present detailed mineralogical and geochemical investigations exploring the genesis of palygorskite found in eocene fluvial sediment in the northern qaidam basin on the northeastern tibetan plateau the presence of two types of palygorskite is revealed based on their crystallinity characteristics and distinctive rare earth element ree patterns in the coexisting clay fraction well crystallized palygorskite samples are characterized by remarkably negative ce anomalies and obvious middle rare earth element enrichment poorly crystallized palygorskite samples generally exhibit positive ce anomalies and less pronounced middle rare earth element enrichment which resemble those of nonpalygorskite bearing clay samples given the presence of an overall oxidized fluvial sedimentary environment we attribute the well crystallized palygorskite which has textures comprising long interwoven fibers to direct precipitation i e neoformation occurring within a reducing environment during early postdepositional processes while the poorly crystallized palygorskite which is characterized by short club shaped single crystals originates as catchment delivered detritus these poorly crystallized palygorskites occur mostly in 49 5 47 0 ma and are accompanied by decreasing kaolinite content increasing chlorite content and abundant xerophytic spore pollen from the qaidam basin and its neighboring xining basin collectively these evidences suggest that a less humid climate followed after the early eocene climate optimum

reply to vogt s comments on the paper fibrous clay mineral formation and soil evolution in aridisols of northeastern patagonia argentina by p j bouza m simon j aguilar h del valle and m rostagno

comments on the paper fibrous clay mineral formation and soil evolution in aridisols of northeastern patagonia argentina by p j bouza m simon j aguilar h del valle and m rostagno

a new formation process for calcic pendants from pahranagat valley nevada usa and implication for dating quaternary landforms abstract it has been assumed that soil pendants form in a similar manner as stalactites in which innermost laminae are the oldest and outer laminae are the youngest this study presents a new interpretation for soil pendant development pahranagat valley nevada pendants contain features indicating continued precipitation through time at the clast pendant contact implying that the oldest deposits are not always found at the pendant clast contact as other studies have assumed these features include a void at the clast pendant contact where minerals such as calcium carbonate silica and or fibrous silicate clays precipitate in addition fragments of the parent clast and detrital grains are incorporated into the pendant and are displaced and or dissolved and result in the formation of sepiolite this study indicates that pendants are complex open systems that during and after their formation undergo chemical changes that complicate their usefulness for dating and paleoenvironmental analyses

structure chemistry and origins of gypsum crusts in southern tunisia and the central namib desert gypsum crusts are broadly defined as accumulations at or within about 10 m of the land surface from 0 10m to 5 0 m thick containing more than 15 by weight gypsum caso4 2h2o and at least 5 0 by weight more gypsum than the underlying bedrock the deposits are often but not invariably consolidated owing to cementation by gypsum the crusts are found in many of the world s deserts where mean monthly potential evaporation exceeds mean monthly precipitation throughout the year using structural fabric and textural criteria three main types of crust may be distinguished 1 bedded crusts found either at or beneath the land surface which are made up of discrete horizontal strata up to 0 10 m thick each showing a gradation in gypsum crystal size from less than 50 m at the top to more than 0 50 mm at the base 2 subsurface crusts of which there are two forms one made up of large lenticular crystals up to 0 50 m in diameter the desert rose crusts and the other a mesocrystalline form with gypsum crystals up to about 1 0 mm in diameter and 3 surface crusts which are subdivided into columnar powdery and cobble forms all of which are made up of predominantly alabastrine gypsum crystallites less than 50 m in diameter in southern tunisia and the central namib desert bedded crusts are found around ephemeral lakes and lagoons they are characterized by size graded beds gypsum contents of 50 80 by weight and comparatively high concentrations of sodium potassium magnesium and iron they are interpreted as shallow water evaporites which accumulate when saline pools evaporate to dryness desert rose crusts or croutes de nappe generally contain 50 70 by weight gypsum and have higher sodium concentrations than the second subsurface form texturally they are characterized by poikilitic inclusion of clastic material within large lenticular crystals they are interpreted as hydromorphic accretions which precipitate in host sediments at near surface water tables through the evaporation of groundwater the second form of subsurface crust the mesocrystalline often occurs in close association with the various surface forms unlike the hydromorphic crusts they are not restricted to low lying terrain they are characterized by gypsum contents reaching 90 by weight and have a close chemical and textural similarity to columnar surface crusts this mesocrystalline form represents an illuvial accumulation the surface forms excluding the bedded crusts are exhumed examples at various stages of solutional degradation subsurface precipitation of gypsum from meteoric waters containing salts leached from the surface results in displacive gypsum accumulation in the soil zone in southern tunisia the gypsum is derived from sand and dust deflated from evaporitic basins in the central namib salts dissolved in fog water are the most likely source where other salts are present differential leaching may form two tiered crusts calcrete gypsum or gypsum halite if rainfall is sufficient to mobilize the less soluble salt yet insufficient to flush the more soluble gypsum crust genesis is restricted to arid environments and if their susceptibility to post depositional alteration is acknowledged they can provide valuable palaeoclimatic indicators

the benthic cycle of copper evidence from sediment trap experiments in the eastern tropical north pacific ocean abstract the benthic fluxes of 24 elements and components are calculated from sediment trap fluxes and sediment accumulation rates at manop sites h and m in the eastern tropical north pacific ocean in this paper we focus our discussion on our data for copper benthic flux estimates for copper are 0 7 and 1 4 nmol cm 2 yr at h and m respectively these results compare well with estimates from another trap deployment in the galapagos and modeling of pprewater and water column concentration data by other authors partitioning of near bottom cu flux indicates that the two sites receive similar amounts of primary cu flux flux from upper water column and resuspended cu flux only the site located on the east pacific rise site m shows any input of hydrothermal cu at site m 35 of the near bottom flux is due to some source other than primary resuspended or hydrothermal flux we speculate that dissolved cu from the sediments is readsorbed onto particles near the bottom at this site sequential leaching of trap material indicates that the flux of cu associated with organic matter using an operational definition ranges from 56 to 84 of the trap material this fraction of the total cu increases with depth in the water column probably through scavenging

true tracks undertracks and eroded tracks experimental work with tetrapod tracks in laboratory and field abstract to be able to distinguish between true tracks undertracks and tracks altered by erosion is of great importance in tetrapod track ichnotaxonomy this paper reports three experimental approaches to the study of undertracks using the footprints of an emu dromaius novaehollandiae experiment 1 describes successive horizontal sections down through a plaster cast of an emu footprint emplaced in soft mud revealing a steady downward decrease in the area of the track particularly the length this is the result of the movements of the trackmaking limb during impact forward swing of the body and final kick off experiments 2 and 3 describe vertical sections cut through footprints emplaced in packages of layered coloured cement admixed with water to produce different consistencies firm and semi fluid after hardening the cement block was serial sectioned vertically and removal of a lightly cemented layer gave access to two undertrack bedding plane views successive undertracks downward show an increase in horizontal dimensions and decrease in vertical topography of the structure representing gradual degradation of the track anatomy with depth in experiment 3 the true track at the tracking surface was deformed by collapse and flow of the substrate after withdrawal of the foot in this case the undertracks that were formed in layers subjacent to the foot reproduced the morphology of the foot more faithfully than did the true track

sedimentological and geoenvironmental evaluation of the coastal area between al khowkhah and al mokha southeastern red sea republic of yemen the increasing anthropogenic activities e g constructing touristic resorts have led to notable changes in the yemeni red sea coastal regions in this context recent sediments have been investigated to infer possible natural and man induced processes on these coastal areas the target area lies between longitudes 43 13 43 30 e and latitudes 13 15 13 55 n it extends about 90 km along the coastline as a part of the tihama plain geomorphologically it forms a long curved stretch with pronounced headlands embayments and bays generally it is covered by recent sediments wadi lagoon beach and spit deposits along with sabkha coastal dunes and mangrove textural studies reveal that most of the studied sediments are mainly poorly to moderately sorted and are composed mainly of sandy fractions with few gravel and mud mostly bimodal with minor unimodal patterns the igneous granites as well as basic basalt andesite and andesitic pyroclastics and acidic dacite and rhyolite volcanic rocks of tertiary age which are exposed to the east of the study area are believed to be the source of pyroxenes amphiboles epidotes biotite sphene zircon tourmaline and rutile in a decreasing order of abundance moreover smectite kaolinite chlorite illite and palygorskite are the predominant clay minerals mainly of detrital origin the total carbonate content fluctuates from 37 41 lagoon sediments to 53 74 sabkha sediments the high amount of sea grasses which covers the tidal flat zone and relates to the fine grained sediments accounts for the high organic matter content the mineralogy of the source rocks has controlled the general distribution of major elements fe mg na k and mn in the beach sediments in such sediments the concentrations of the heavy metals cu zn cd ni pb and co may reflect the sediment pollution using different approaches the enrichment factors efs of the trace metals for most samples reveal values that are greater than 1 referring to three groupings which are moderate to moderately severe zn cu and mn minor to moderate pb and co and zero to minor cd and ni enrichment the efs for pb cd ni and co metals 5 especially in al khowkhah abu zahr moushij zahari ruays yokhtol and mokha localities are possible of anthropogenic contributions

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

resolving miss conceptions and misconceptions a geological approach to sedimentary surface textures generated by microbial and abiotic processes the rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone siltstone and mudstone bedding planes in recent years an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition resulting in their classification as microbially induced sedimentary structures or miss research into miss has developed at a rapid rate resulting in a number of misconceptions in the literature here we attempt to rectify these miss misunderstandings the first part of this paper surveys the stratigraphic and environmental range of reported miss revealing that contrary to popular belief there are more reported miss bearing rock units of phanerozoic than precambrian age furthermore miss exhibit a pan environmental and almost continuous record since the archean claims for the stratigraphic restriction of miss to intervals prior to the evolution of grazing organisms or after mass extinction events as well as claims for the environmental restriction of miss appear to result from sampling bias in the second part of the paper we suggest that raised awareness of miss has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features by introducing the umbrella term sedimentary surface textures of which miss are one subset we suggest a practical methodology for classifying such structures in the geological record we illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata resultant interpretations microbial or non microbial should be couched within a reasonable degree of uncertainty this approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current miss lexicon it is hoped that this new terminology will reduce the number of overly sensational and misleading claims of miss occurrence and permit the means to practically separate initial observation from interpretation furthermore this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone informing the search for true miss in earth s geological record and potentially on other planetary bodies such as mars

organic rich and manganese sedimentation during the cenomanian turonian boundary event in the outer carpathian basins a new record from the skole nappe poland abstract upper cenomanian lower turonian strata in the splawa section of the skole nappe outer carpathians poland provide a detailed palaeoenvironmental record of the oceanic anoxic event oae 2 from a deep water basin below the ccd at the northern margin of the western tethys the oae 2 succession consists of black parallel laminated radiolarian shales enriched in organic matter of mainly marine origin toc up to 8 organic carbon isotope variations together with microfossil datum events allowed to correlate the studied organic rich facies with other black shale successions along the outer carpathians and other areas of the western tethys the mean values of sedimentation rate 3 5 5 5 mm kyr and organic matter accumulation rate 0 5 g m2 year calculated for the oae 2 interval in the outer carpathian basins are comparable to the values from other deep water marginal basins in the western tethys the average redox sensitive trace metal contents and their enrichment factors indicate water column anoxia in the outer carpathian basins intensified during the interval of the largest shift in 13c values the periods of bottom anoxia were interrupted by intervals of variable eh conditions with sedimentation of hemipelagic green shales including poor agglutinated foraminiferal assemblages an increase in productivity of organic and siliceous plankton during the oae 2 is documented based on increased values of silica and barium enrichments this closely corresponds to an interval of the largest positive stable carbon isotope excursion related to the beginning of the largest sea level rise linked with intensive coastal upwelling extremely low sedimentation rate or even hiatuses and the increase in deep water circulation causing basin oxygenation resulted in precipitation of two ferromanganese layers their formation was related to changes in hydrodynamic conditions at the basin floor expressed by precipitation of fe mn carbonates some chemical indices seem to suggest that the primary metal enrichments could be related to hydrothermal activity however the concentrations of some elements show also on hydrogenic to diagenetic influences in these metalliferous sediments the precipitation of these fe mn sediments was probably synchronous with the manganese enrichment across the c t transition recorded in other western tethyan basins and in the adjacent epicontinental seas

the geomorphic influences of beaver dams and failures of beaver dams abstract uncounted millions of beaver ponds and dams existed in north america prior to european contact and colonization these ponds acted as sediment traps that contained tens to hundreds of billions of cubic meters of sediment that would otherwise have passed through the fluvial system removal of beavers by overtrapping in the 16th 19th centuries severely reduced their number and the number of ponds and dams dam removal altered the fluvial landscape of north america inducing sediment evacuation and entrenchment in concert with widespread reduction in the wetlands environments partial recovery of beaver populations in the 20th century has allowed reoccupation of the entirety of the pre contact range but at densities of only one tenth the numbers nevertheless modern beaver ponds also trap large volumes of sediment in the high hundred millions to low billions of cubic meters range failure of beaver dams is a more common phenomenon than often assumed in the literature during the past 20 years numerous cases of dam failure have been documented that resulted in outburst floods these floods have been responsible for 13 deaths and numerous injuries including significant impacts on railway lines

geochemistry of calcic horizons in relation to hillslope processes southern india abstract the study concerns chemical and mineralogical properties of calcic horizons in relation to their physical environment such as position in the soil profile and the terrain the carbonates were calcitic in upslope positions but dolomite was abundant in valley sites the content of fluorine increased downslope the distribution of the composition in the terrain indicates a sequential precipitation of calcite dolomite and fluorite from soil water and groundwater as the water flows downslope to discharge areas carbonates in vertisols formed from the more basic charnockites were of the low mg calcite type while dolomite occurred only in entisols and alfisols formed from biotite hornblende gneisses manganese in calcic horizons increased as the groundwater level was approached black intercalations in laminated petrocalcic horizons contained elevated concentrations of mn k al and si this may indicate periods of higher soil moisture and clay formation the presence of low mg calcitic carbonates overlying dolomitic ones in valley sites is likely to be due to deposition of calcite rich material from upslope the amount of soil eroded from upslope positions was between 0 2 and 2 m in four investigated profiles

where does the time go assessing the chronostratigraphic fidelity of sedimentary geological outcrops in the pliocene pleistocene red crag formation eastern england it is widely understood that earth9s stratigraphic record is an incomplete record of time but the implications that this has for interpreting sedimentary outcrop have received little attention here we consider how time is preserved at outcrop using the neogene quaternary red crag formation england the red crag formation hosts sedimentological and ichnological proxies that can be used to assess the time taken to accumulate outcrop expressions of strata as ancient depositional environments fluctuated between states of deposition erosion and stasis we use these to estimate how much time is preserved at outcrop scale and find that every outcrop provides only a vanishingly small window onto unanchored weeks to months within the 600 800 kyr of crag time much of the apparently missing time may be accounted for by the parts of the formation at subcrop rather than outcrop stratigraphic time has not been lost but is hidden the time completeness of the red crag formation at outcrop appears analogous to that recorded in much older rock units implying that direct comparison between strata of all ages is valid and that perceived stratigraphic incompleteness is an inconsequential barrier to viewing the outcrop sedimentary stratigraphic record as a truthful chronicle of earth history supplementary material further details of the regional geology and specific information on outcrops are available at https doi org 10 6084 m9 figshare c 4561001

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

dinosaurs of great britain and the role of the geological society of london in their discovery ornithischia completing our survey of british non avian dinosaurs we here review the ornithischians of britain heterodontosaurids are present in the lower cretaceous lulworth formation of dorset and a few earlier possible records imply a long presence in the region of this clade britain9s thyreophoran record is rich and includes the earliest well represented taxon scelidosaurus as well as middle jurassic stegosaurs and ankylosaurs including a reasonably good cretaceous record of polacanthids and nodosaurids cretaceous stegosaurs are known only from fragmentary remains but the proposal that stegosaurs were present as early as the rhaetian is rejected among british iguanodontian ornithopods the possible dryosaurid callovosaurus is the oldest global record whereas the proposed synonymy of cumnoria with camptosaurus requires confirmation iguanodon has become a taxonomic dumping ground for assorted iguanodontians and is in need of revision most of the british species referred to this genus are almost certainly not closely allied to the neotype species i bernissartensis and require new generic names fragmentary remains suggest the early presence of hadrosaurids in britain the only british record of marginocephalia the wessex formation skull roof named yaverlandia bitholus appears not to belong to this clade but seems to be from a maniraptoran theropod

pedogenic and early diagenetic processes in palaeogene alluvial fan and lacustrine deposits from the sado basin s portugal abstract the palaeogene deposits of the sado basin were deposited in a continental basin that shows a typical pattern with alluvial fans system in the margins of the basin passing towards distal areas of mudflat facies where in some areas the installation of shallow water bodies favoured the development of palustrine conditions the deposits of this basin vary form coarse conglomerates and sandstones to palustrine carbonates these sediments were affected by pedogenesis and early diagenetic processes that promoted important modifications on their primary features these modifications have been studied by the analyses of four profiles developed on proximal middle and distal fan deposits and the fourth one on lacustrine deposits the overall analyses of the sedimentological pedogenic diagenetic features and their relationships indicate that three main processes took place throughout the basin soil formation palygorskite neoformation and dolomitization soil formation processes led to illuviation of clays and carbonate precipitation mostly around roots pedogenic carbonates increase towards distal areas whereas hydromorphic features are present throughout the basin palygorskite neoformation was partially diagenetic being maximum in proximal areas and palustrine deposits this neoformation is attributed to the percolation of alkaline mg rich soil and groundwaters through smectitic rich sediments promoting important clay transformation dolomitization was an early diagenetic process that occurred mainly in carbonate rich deposits of distal and lacustrine environments as a result of the increasing mg ca ratio of the percolating groundwaters in all these processes there has been a close spatial and temporal interplay between pedogenesis and diagenesis driven by the chemistry of soil particles and groundwaters

geomorphological implications of engineering bed sediments by lotic animals abstract recent developments in zoogeomorphology in combination with the increasing interest of ecologists in ecosystem engineering by organisms initiated considerable research on the impact of running water i e lotic animals and other organisms on fluvial bed sediments and the transport of solids this research provided multiple evidence from field and laboratory observations and experiments that many species among mammals amphibians fish insects crustaceans mollusks and worms engineer bed sediments of running waters with diverse mechanistic tools thereby perturbing or consolidating the sediments in many types of running waters across continents seasons habitat types particle sizes and discharge levels baseflow vs flood furthermore many animals modify the bed sediment engineering by plants algae larger macrophytes riparian vegetation modeling effects of bioturbating lotic animals across species and relatively simple environmental conditions in mesocosms provided highly significant results p range

biogenic β fabric features in the hard laminated crusts of the mersin and adana regions southern turkey and the role of soil organisms in the formation of the calcrete profiles abstract this paper describes fabric features and their distribution in the calcretes and emphasizes the role of soil organisms in the formation of the calcrete profiles quaternary calcretes are common in the mersin and adana provinces occurring as powdery nodular tubular fracture infill and various forms of crusts the stable isotope values indicate calcrete development under semi arid climatic conditions and a pedogenic origin biogenic or fabric constituents are abundant in the hard laminated crust these are the rhizoliths alveolar septal structures needle fiber calcites calcified filaments spherical calcite bodies microcodium and vadose calcrete pisoliths rhizoliths have mainly formed by the petrification of roots and often contain cellular cortex structures the alveolar septal structure comprises root voids separated by a micritic wall or a bundle of tangentially oriented calcite needles needle fiber calcite is common in the hard laminated crust as monocrystalline rods and polycrystalline needles monocrystalline rods are smooth and small

remarkable preservation of brain tissues in an early cretaceous iguanodontian dinosaur it has become accepted in recent years that the fossil record can preserve labile tissues we report here the highly detailed mineralization of soft tissues associated with a naturally occurring brain endocast of an iguanodontian dinosaur found in c 133 ma fluvial sediments of the wealden at bexhill sussex uk moulding of the braincase wall and the mineral replacement of the adjacent brain tissues by phosphates and carbonates allowed the direct examination of petrified brain tissues scanning electron microscopy sem imaging and computed tomography ct scanning revealed preservation of the tough membranes meninges that enveloped and supported the brain proper collagen strands of the meningeal layers were preserved in collophane the blood vessels also preserved in collophane were either lined by or infilled with microcrystalline siderite the meninges were preserved in the hindbrain region and exhibit structural similarities with those of living archosaurs greater definition of the forebrain cerebrum than the hindbrain cerebellar and medullary regions is consistent with the anatomical and implied behavioural complexity previously described in iguanodontian grade ornithopods however we caution that the observed proximity of probable cortical layers to the braincase walls probably resulted from the settling of brain tissues against the roof of the braincase after inversion of the skull during decay and burial

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

fibrous clay minerals in the soils of namaqualand south africa characteristics and formation abstract palygorskite or sepiolite containing soils occur at elevations up to 1000 m in gently sloping landscapes formed by aeolian sands or by strongly eroded pedisediments overlying the namaqualand metamorphic complex the unconsolidated sands are in various stages of calcretization most of the soils are sandy shallow non saline with a ph ranging between 7 2 and 8 2 carbonate contents are low but increase towards the calcretized horizons most of the carbonates appear in the form of nodules in the clay fractions palygorskite or sepiolite dominate and are accompanied by illite and non expanding 14 a minerals or mixed layer minerals dta tga and chemical analysis indicate that the sepiolite is fe rich and contains organic material trapped within its channels the highest concentrations of the fibrous clay minerals commonly occur in the bottom horizons it is postulated that they formed pedogenically from silica released by silicates and mg derived from mg rich carbonates introduced by aeolian accretion this hypothesis is supported by a decrease in mg ca of the carbonates with soil depth another possible mg source considered is sea spray soil water extract compositions are not compatible with fibrous clay mineral stability electron micrographs of sepiolite clays suggest alteration into sheet clay minerals

dinosaur landscape interactions at a diverse early cretaceous tracksite lee ness sandstone ashdown formation southern england abstract an assemblage of dinosaur footprints is reported from the lower cretaceous berriasian valanginian ashdown formation of east sussex southern england the ichnofauna is concentrated around a 2 m thick stratigraphic marker the lee ness sandstone where recent cliff retreat has revealed 85 recognisable footprints attributable to 13 morphotypes many of which bear high fidelity skin impressions the newly identified morphotypes mean that this tracksite hosts one of the most diverse dinosaur ichnoassemblages in the well documented mesozoic record of britain recording the activity of theropod ornithopod thyreophoran and possibly sauropod tracemakers most of the footprints were emplaced on a single floodplain mudstone horizon beneath a fluvial crevasse splay sandstone where preservation was favoured by cohesive sediment and a prolonged interval of sedimentary stasis during which trackways could be imparted the sedimentological context of the trackways reveals evidence of interactions between dinosaurs and the riverine landscape that they inhabited including the development of microtopographies around footprints which impacted invertebrate burrowing activity and evidence for dinosaur wading below the bankfull level of small meandering channels and oxbow lakes modern analogue suggests that the large dinosaurs may have played a significant role as zoogeomorphic engineers within the ancient floodplain setting but the imperfect translation of sedimentary environment to sedimentary rock means that geological evidence for such is ambiguous

micromorphology clay mineralogy and geochemistry of calcic soils from western thar desert implications for origin of palygorskite and southwestern monsoonal fluctuations over the last 30 ka abstract the thar desert with intense aeolian activity and calcrete formation is one of the hottest arid regions of the world little is known about the formation of calcic soils with a large amount of palygorskite in the western thar in this study we have used microscopy sub microscopy clay mineralogy and geochemistry of three calcic soils from western thar to understand the pedogenesis in response to fluctuating southwestern monsoon over the last 30 ka thin sections of the soils show a dominance of weakly developed pedofeatures with powdery to well indurated pedogenic calcium carbonate that influenced weathering of primary mineral grains sub microscopy of the calcretes shows a large amount of fibrous palygorskite in pore spaces of micritic and sparitic nodules xrd of the total clay

paleosols in late moscovian carboniferous marine carbonates of the east european craton revealing great calcimagnesian plain paleolandscapes abstract late paleozoic strata commonly include lithologic cycles cyclothems driven by sea level fluctuations that repeatedly flooded and exposed broad expanses of epeiric shelves such successions commonly with multiple unconformities are well documented in permo pennsylvanian sedimentary successions but remain less understood in the east european craton eec part of the euramerican continental shelf rim this study documents unconformities and paleosols from the podolskian to myachkovian middle pennsylvanian epeiric carbonate succession of the eec and explores the non actualistic soil types landscapes and the character and density of vegetation in this pennsylvanian calcimagnesian dryland environment thin mostly 1 m paleosols developed at seven successive unconformities consist of an upper terrestrial clay layer or topclay a crust of beta calcrete beneath the topclay and a weakly karsted substrate limestone with rare rhizocretions solution pits and small 3 m deep karst sinkholes are rare nontruncated topclays commonly consist of two layers in situ clayey epipedons and resedimented terrestrial clays the latter are interpreted as playa sediments the myachkovian unconformities of the northernmost localities studied near arkhangelsk lack beta calcrete and root traces and the limestone beneath these unconformities is sepiolitized in podolskian paleosols of the southern moscow basin the topclays are predominantly palygorskitic the myachkovian paleosol clays are smectitic illitic with occasional chlorite admixture the majority of late moscovian paleosols surveyed formally conform to lithic rendollic haplocalcids within the aridisol class or rendzic calcic leptosols a detailed study of a representative podolskian paleo pedon reveals development of shallow soil carbonate low alumina bases and ba sr ratios enhanced mn and sr presence of soil gypsum and opal and a characteristic peak in magnetic susceptibility all suggesting a semiarid to arid pedogenic environment the palygorskite clay of this paleo pedon retains 1 1 1 5 of connate organic matter in the form of covalently bound organomineral complexes and is fulvate dominated resembling organic matter from extant dryland soils the palygorskitic composition of podolskian topclays and shallow 30 cm pedogenic carbonates is interpreted to reflect hot well drained semidesert conditions with precipitation less than 300 mm yr the transition from palygorskitic to smectitic soil clays across the podolskian myachkovian boundary apparently deeper soil carbonate and an increase in the degree of karstification record a general increase in humidity such that annual precipitation may have exceeded 300 400 mm the available data reconstruct the great calcimagnesian plain landscapes formed during low sea level supposedly glacial phases across tens of thousands of square kilometers of the eec this non actualistic system apparently lacked a fluvial network and was covered by uniform soils and playas the primary productivity of this early 310 305 ma old dryland ecosystem inferred from high toc and rhizogenic beta calcretes was not markedly different from present day steppe or savanna grasslands and semideserts in the northernmost outcrops surveyed near arkhangelsk drier conditions probably limited colonization by higher plants the available data open a hidden chapter in the paleozoic evolution of terrestrial ecosystems which is not recorded by paleobotany and urges modifications in the concept of low productivity character of pre miocene dry landscapes

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

inorganic geochemical indicators of glacial interglacial changes in productivity and anoxia on the california continental margin abstract evidence from sediments in cores collected from within the present oxygen minimum zone omz 600 1200 m on the central and northern california margins record several episodes during the last interstadial ois 3 ca 60 24 ka of deposition of laminated sediments containing elevated concentrations of several trace elements indicative of anoxic conditions e g mo ni zn and cu the presence of abundant well preserved organic matter as well as lack of bioturbation and the presence of elevated concentrations of mo and other trace elements all support the theory that the omz in the northeastern pacific ocean was more intense possibly anoxic at several times during the late pleistocene sediments of all ages in cores from the southern california margin contain elevated concentrations of mo suggesting that this area has always had higher rates of sulfate reduction than either the central or northern california areas most of the ba in sediments in all cores collected on the upper continental slope 200 2700 m off california and southern oregon is derived from detrital clastic material and this source did not change much in time however the amount of biogenic ba did vary with time and these variations closely follow the temporal variations in organic c corg mass accumulation rate using ba and corg mass accumulation rates as proxy variables for productivity all cores show that organic productivity under the california current upwelling system was highest during ois 3 and the holocene and lowest during the last glacial interval lgi ca 24 10 ka all paleoproductivity proxy variables indicate that the southern california area has always experienced higher productivity than other areas under the california current at least over the last 50 ky

sr ba in barite a proxy of barite preservation in marine sediments abstract the observation by bertram and cowen j mar res 55 1997 577 593 that the strontium content of marine barite decreased from the water column to the deep sea floor suggested that the sr ba ratio in barite was sensitive to barite dissolution following this observation we have investigated the potential of using the sr ba ratio in barite as a proxy of barite preservation by separating barite crystals from sediment cores collected at different water depths in the equatorial pacific and in the southern ocean our investigations do not reveal significant downcore variations in the sr ba ratios during the holocene period in the two basins and up to a few hundred thousand years in the equatorial pacific however a comparison of the mean sr ba ratios in individual cores suggests that the sr ba ratios in barite decrease with increasing water depth a feature that could be related to dissolution of barite crystals during settling to the deep sea floor and or at the sediment water interface if confirmed the sr ba ratios in barite could be used to infer the intensity of barite dissolution and the state of preservation of barite crystals in sediments such information could be employed usefully in paleoproductivity reconstructions for the purpose of distinguishing between productivity and dissolution signals affecting barite distributions in marine sediments

incomplete but intricately detailed the inevitable preservation of true substrates in a time deficient stratigraphic record true substrates are defined as sedimentary bedding planes that demonstrably existed at the sediment water or sediment air interface at the time of deposition as evidenced by features such as ripple marks or trace fossils here we describe true substrates from the silurian tumblagooda sandstone of western australia which have been identified by the presence of the surficial trace fossil psammichnites the examples are unexpected because they have developed along erosional internal bounding surfaces within a succession of cross bedded sandstones however their seemingly counterintuitive preservation can be explained with reference to recent advances in our understanding of the time incomplete sedimentary stratigraphic record ssr the preservation of true substrates seems to be an inevitable and ordinary result of deposition in environments where sedimentary stasis and spatial variability play important roles we show that the true substrates developed during high frequency allogenic disturbance of migrating bedforms forcing a redistribution of the loci of sedimentation within an estuarine setting and subsequently permitting an interval of sedimentary stasis during which the erosional bounding surfaces could be colonized these observations provide physical evidence that supports recent contentions of how sedimentary stasis and the interplay of allogenic and autogenic processes impart a traditionally underestimated complexity to the chronostratigraphic record of geological outcrop

hylaeosaurus polacanthus and the systematics and stratigraphy of wealden armoured dinosaurs two genera of armoured dinosaurs ankylosauria are present in the lower cretaceous wealden beds of england polacanthus owencan be distinguished from hylaeosaurus mantell on the basis of significant differences in the pectoral girdle hindlimb and dermal armour a comprehensive review of the dinosaurs from the wealden series of england and contemporary basins of western europe adds further evidence of a biologicalseparation between lower wealden hastings beds containing hylaeosaurusarmatus and upper wealden faunas wealden group of the isle of wight containing polacanthus foxii and nearly equivalent units in belgium france germany and spain

remineralization of particulate authigenic trace metals in the middle atlantic bight implications for proxies of export production abstract samples collected by time series sediment traps deployed in the middle atlantic bight were studied to better understand the formation and preservation of particulate authigenic forms of trace metals cu ni ba that hold potential to serve as proxies in the sedimentary record of past changes in the flux of biogenic detritus sinking from the surface ocean into the deep sea export production particulate biogenic and authigenic phases are extremely labile as evidenced by the observation that as much as 70 of the particulate fluxes of organic carbon and of certain metals cu ni and mn and up to 25 of the particulate fluxes of authigenic ba and of opal collected by sediment traps are released rapidly into solution during the time period between particle collection and trap retrieval further remineralization on the seabed reduces concentrations of authigenic cu and ni in surface sediments below the limit of detection approximately 80 of authigenic ba is remineralized during early diagenesis on the seabed much more than is expected for conditions of high sediment mass accumulation rate that exist in the study area extensive remineralization during early diagenesis combined with large corrections required to remove the aluminosilicate contribution to the concentrations of cu ni and ba in sediments preclude the successful use of down core profiles of these trace metals to reconstruct past changes in export production of the middle atlantic bight similar problems are likely to plague paleoproductivity reconstructions in other ocean margin regions or wherever high fluxes of aluminosilicate phases occur

reconstructing the ocean carbon system variation during the last 150 000 years according to the antarctic nutrient hypothesis in this study the vostok ice core co2 record and the 13c difference between the deep atlantic and pacific a p are used in combination with model simulations to analyze the history of the ocean carbon pump and the sources of atlantic deep water during the last 150 kyr it is assumed that the mechanism by which the glacial atmospheric co2 decreased is an increase in the ratio of antarctic net carbon production to upwelling in that region results from a wide range of circulations and antarctic net carbon productions input into a 14 box ocean atmosphere model show that similar distributions of phosphate 13c atmospheric co2 content and surface versus deep radiocarbon age are produced once the following parameters are fixed 1 the ratio of net carbon production to upwelling in the antarctic region 2 the ratio of northern component water to antarctic bottom water input into the atlantic and 3 the total upwelling into the low latitude surface waters therefore rather arbitrary circulations and antarctic net production values can be used to map model simulated geochemical properties as a function of these parameters decrease in atmospheric co2 and atlantic to pacific 13c difference are calculated from the model for constant low latitude upwelling and these are mapped as a function of the ratios 1 and 2 above the isolines of these two geochemical properties tend to be orthogonal and one can position any pco2 a p pair on an overlay of the two maps this is done for coeval ice core co2 and marine sedimentary 13c data for the last 150 kyr one finds that the history of the antarctic carbon pump efficiency varies with the same pattern as that of the atmospheric co2 the fraction of northern component water entering the atlantic tends to vary with the same shape function as the global marine 18o curve

history and bibliography of the study of fossil vertebrate footprints in the british isles supplement 1973 1983 abstract this paper supplements the history and bibliography of british fossil vertebrate footprints published by sarjeant in 1974 it discusses additional published accounts of these trace fossils issued during the period prior to 1973 and provides a resume of new discoveries and descriptions made during the decade 1973 1983 important among the former are a record of a hitherto unnoticed scottish carboniferous find reports of footprints found by the rev w lister and h c beasley in the triassic rocks of statffordshire a possible record of dinosaur footprints from the lowest cretaceous of wiltshire a more definite instance from the lower cretaceous of surrey and a rather dubious one from ulster new discoveries include a first report of dinosaur footprints from buckinghamshire and accounts of major footprint finds in the triassic sediments of south wales the purbeck formation of dorset and the wealden beds of east sussex and the isle of wight also the first record of dinosaur footprints from the scottish jurassic new information concerning vertebrate footprints from the triassic of shropshire and new conclusions on the taxonomy of the triassic footprints from south wales are presented

the cow as a geomorphic agent a critical review cows are important agents of geomorphological change on the uplands heavy grazing compacts the soil reduces infiltration increases runoff and increases erosion and sediment yield however light and moderate grazing have effects that are much less significant in riparian zones grazing decreases erosional resistance by reducing vegetation and exposing more vulnerable substrate trampling directly erodes banks thus increasing turbulence and consequent erosion future studies should be framed within the hydroclimatological edaphic and geomorphological dimensions of the areas being studied so that controlling variables may be more readily isolated we believe that both empirical studies and deterministic modeling can provide insights as to the effects of grazing on geomorphology

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

advective excess ba transport as shown from sediment and trap geochemical signatures abstract we report the results of a geochemical study of sediment and trap material major and trace elements zr ba rare earth elements and th were analyzed on bulk sedimentary material collected along the ne atlantic margin our aim is to test the widespread use of ba barite as a proxy for paleoproductivity in a continental margin area this environment is of great interest because atmospheric oceanic exchanges are important in sediments the geochemical signatures remain close to an upper crust reference with flat shale normalized rare earth elements patterns and constant elementary ratios the calculated biogenic fraction of ba or excess ba 20 45 remains lower than the excess ba record in trap material 80 99 the evolution of the geochemical signature along the margin reflects variable dilution of a detrital post archean australian shale like component by a biogenic carbonaceous seawater derived component the trap material displays a wide range of variation in its trace element content e g ba 150 3000 ppm zr 2 100 ppm except for the abyssal site which is characterized by constant signature in the two other sites all of the trace element contents increase with water depth and present pronounced seasonal changes at each sampled water depth the amount of excess ba also increases in the deepest traps and its evolution throughout the year mimics the change of the other analyzed trace elements in contrast its relationships with particulate organic carbon are not obvious in term of fluxes two periods of enhanced excess ba fluxes are observed 1 excess ba flux increases with the detrital like elements like th especially during winter and 2 excess ba flux is enhanced without any change for the other trace elements during spring to explain the first case a supply through lateral advection is proposed such transient input of significant excess ba flux will have a great impact on the yearly averaged estimation of the export production indeed only the second case reflects a bloom in the biological productivity of the water column and must be taken into account in a mean calculation of the export production finally a normalization of the excess ba by detrital like element like th will help to discriminate between a real increase of the excess ba due to local productivity change high excess ba and high excess ba th ratio 10 000 and any input due to advection process high excess ba but low excess ba th ratio

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

barium accumulation in the arabian sea controls on barite preservation in marine sediments in this study a new sequential extraction technique is used to investigate the particulate barium ba phases in sediments from the arabian sea to determine the processes controlling ba accumulation in marine sediments the total solid phase ba concentration in arabian sea surface sediments increases with water depth from 200 ppm at 500 meters below sea surface mbss to 1000 ppm at 3000 mbss the sedimentary ba composition consists of three major fractions barite ba incorporated in aluminosilicates and ba associated with mn fe oxides accumulation of barite which is the most important ba fraction in sediments located below 2000 mbss increases gradually with water depth the ba al ratio of the terrigenous fraction varies significantly across the arabian basin as the result of differences in grain size and provenance of the terrigenous sediment ba associated with mn oxides is a relatively minor fraction compared with bulk ba concentrations and it only accumulates in well oxygenated sediments below the present day oxygen minimum zone the water depth dependent accumulation of barite in the arabian sea is not related to the continuous formation of barite in settling organic particles or ba scavenging by mn oxyhydroxides but is primarily controlled by differences in ba preservation upon deposition a good correlation between the barite saturation index and the barite accumulation rate in the upper 2000 m of the water column may indicate that the degree of barite saturation of the bottom water is the main environmental factor regulating the burial efficiency of barite organic matter degradation bioturbation diagenetic mn cycling and the crystallinity of the accumulating barite may play additional roles copyright 2001 elsevier science ltd

settling barium fluxes in the arabian sea critical evaluation of relationship with export production abstract time series measurement of biogenic and barium fluxes was made using nine sediment traps deployed in the western central and eastern part of the arabian sea with the objective of evaluating barium as a proxy for surface ocean productivity our observations show a strong linear correlation between baexcess fluxes and biogenic opal and organic carbon corg fluxes indicating a biogenic origin of particulate ba however the correlation between biogenic and baexcess fluxes is remarkably strong in areas of uniform productivity like the central arabian sea when compared to regions of episodic productivity the processes that precipitate particulate ba appear to be less active during periods of high biogenic flux a large discrepancy is documented between the export flux calculated from the barium based algorithm francois r honjo s manganini s j ravizza g e 1995 biogenic barium fluxes to the deep sea implications for paleoproductivity reconstruction global biogeochemical cycles 9 289 303 and from corg fluxes sarnthein m winn k duplessy j c fontugne m r 1988 global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years paleoceanography 3 361 399 at different depths however 35 increase in ba fluxes and a concomitant increase in ba corg ratios are documented between 919 and 2002 m water depth in the western arabian sea this increase may be due either to barite formation within the fecal pellets of mesozooplankton thriving at deeper levels or to scavenging of ba by mn oxyhydroxides manganese oxyhydroxides seem to act as a prominent scavenging phase for particulate ba when the mnexcess content in the settling particles exceeds 200 ppm especially in the western and central arabian sea where in situ precipitation of mn oxides is reported the estimated preservation efficiency of ba in the arabian sea sediments ranges between 50 and 61 this is two fold higher than the global average suggesting that ba may be a promising proxy for paleoproductivity estimation

reconstruction of paleo particulate organic carbon fluxes for the campbell plateau region of southern new zealand using the zinc content of sponge spicules 1 the zinc concentration of siliceous sponge spicules was determined from spicules recovered from four sediment cores spanning the last 160 kyr from the campbell plateau region southeast of new zealand zinc si results showed little difference between holocene and glacial aged spicules an increase in zn si was observed for core y14 where zn si peaked at about 0 6 mol mol during marine isotope stages 5a 5b to better understand the role carbon export has on sponge zn si we explored the strong relationship observed between surficial sediment particulate organic carbon poc and the zn si of sponge silica and related this to sediment trap poc flux estimates conversion of the zn si records to benthic poc fluxes suggests that there has been little change in the amount of poc reaching campbell plateau sediments over the past 30 kyr these results suggest that surface productivity over the campbell plateau has remained relatively low over the past 160 kyr and suggests that glacial productivity was not significantly higher than the present day finally this work reveals that living marine sponges appear to act as the biological equivalents of moored sediment traps recording the flux of poc to the seafloor by archiving zinc associated with sinking poc in the growing silica skeleton

ankylosaurian dinosaur palaeoenvironmental associations were influenced by extirpation sea level fluctuation and geodispersal abstract more species of nodosaurid ankylosaurians than ankylosaurid ankylosaurians have been found in marine sediments and some previous quantitative studies of global dinosaur occurrences provide support for an association between nodosaurids and marine depositional environments we compiled a dataset of global ankylosaurian occurrences and found that the geographic distribution of marine ankylosaurian occurrences is regionally biased with 54 of records stemming from western north america in the cretaceous a time of regional highstands in sea level and epicontinental flooding coupled with differential extirpation of ankylosaurian subclades inhabiting the western interior basin wib within the western interior basin we found little statistical support for an association between ankylosaurian subclades and palaeoenvironment in a chronological context only the albian cenomanian transgressive regressive cycle had statistical support for an overabundance of nodosaurids in marine environments compared to ankylosaurids the apparent overabundance of nodosaurids relative to ankylosaurids in marine sediments in the western interior basin overall cannot be decoupled from the extirpation of north american ankylosaurids during the cenomanian and the subsequent absence of ankylosaurids in north america during the turonian to early campanian prior to the immigration of asian ankylosaurine ankylosaurids the north american ankylosaurian record highlights the difficulty in interpreting habitat preferences in the context of a shifting seaway regional extinctions and intercontinental dispersals

particulate barium fluxes in the ross sea we present particulate barium data collected using sequencing sediment traps in the ross sea region of the southern ocean data were collected in 1991 92 1994 95 and 1996 98 from two separate field programs samples were collected at 200 m depth and 75 m above the seafloor 450 765 m depth ba fluxes in the shallow traps at all sites are uniformly low and the barium to organic carbon ba corg ratios in these traps typically agree within a factor of two both spatially and temporally deeper trap fluxes are as much as an order of magnitude larger than shallow trap fluxes in addition the ba corg ratio in the deeper traps varies by more than an order of magnitude with the ratio decreasing with increasing rates of organic carbon flux increases in the deeper trap fluxes may result from horizontal transport of material from other regions of the ross sea resuspension of previously deposited sediment and increases in biogenic ba formation with depth data presented here and within the contemporary literature lead us to speculate that much of the biogenic ba may be formed in the water column at depths greater than 200 m also the factor of 10 range in the ba corg ratio in combination with the depth dependence of biogenic barium formation leads us to conclude that biogenic barium formation may depend on the rate at which particles sink independent of the causal mechanism the variations in this ratio imply that using an algorithm that relates barium export to carbon export may be imprudent in regions of highly variable carbon flux

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

controls on the genesis of some high fluoride groundwaters in india india has an increasing incidence of fluorosis dental and skeletal with some 62 million people at risk high fluoride groundwaters are present especially in the hard rock areas south of the ganges valley and in the arid north western part of the country the phenomenon is related to groundwater with residual alkalinity ca2 hco3 fluoride concentrations are governed by adsorption equilibria and by fluorite solubility evapotranspiration leads to a precipitation of calcite a lowering of ca activity and increase in na ca ratios and this allows an increase in f levels in southern india mg seems to be controlled by dolomite while sepiolite and palygorskite are mg sinks in rajasthan but may then release f under alkaline conditions the latter two minerals are probably also important sources and sinks for f in the hydroxy positions the increase in the extent of sodic soils as a result of irrigation is a contributing factor to the increasing incidence of fluorosis remedial measures including addition of gypsum and rainwater harvesting are needed even in areas where the sodicity does not cause structural problems in the soil

particulate manganese dynamics in gulf stream warm core rings and surrounding waters of the n w atlantic manganese has been measured in size fractionated paniculate matter profiles obtained by large volume in situ filtration of the upper 1000 m of the n w atlantic as part of the warm core rings experiment wcre in 1982 environments sampled included warm core rings wcr 82b and 82h the entrainment zone at the edge of these rings the slope water surrounding rings and the gulf stream gs and sargasso sea ss from which the rings formed manganese concentrations ranged from 10 pmol kg 1 to 10 000 pmol kg 1 with the extreme values observed in the quasi isolated core waters of wcr 82b and in a tongue of shelf water at the periphery of wcr 82b respectively the majority of the mn was in the 1 53 m particle size fraction and most mn was probably close to 1 m in size mn showed no correlation with major biogenic phases indicating that formation by local biological processes was not an important source instead most paniculate mn present in the waters sampled originated in reducing sediments at the continental margin a manganese budget for the quasi isolated core waters of wcr 82b between february and june 1982 showed that most mn removal was by the aggregation of the small mn oxyhydroxide particles into fecal material followed by sedimentation calculations show that wcrs cause offshore particulate mn transports from the continental margin between 66 w and cape hatteras of 8 5 104 to 14 104 mol d 1 with most derived from the continental shelf only 4 of the shelf derived mn becomes entrained into wcrs and the rest is left to disperse in the slope water or enter the circulation of the gulf stream the wcr induced offshore mn transports may account for a large fraction of the mn flux to sediments on the continental slope and upper continental rise

elephants and extinct relatives as earth movers and ecosystem engineers abstract modern african elephants affect habitats and ecosystems in significant ways they push over trees to feed on upper branches and often peel large sections of bark to eat these destructive habits sometimes transform woody vegetation into grasslands systems of elephant trails may be used and re used for centuries and create incised features that extend for many kilometers on migration routes elephants digging in search of water or mineral sediments may remove several cubic meters of sediments in each excavation wallowing elephants may remove up to a cubic meter of pond sediments each time they visit water sources accumulations of elephant dung on frequented land surfaces may be over 2 kg per square meter elephant trampling digging and dust bathing may reverse stratigraphy at archeological localities this paper summarizes these types of effects on biotic geomorphic and paleontological features in modern day landscapes and also describes several fossil sites that indicate extinct proboscideans had very similar effects such as major sediment disturbances

barium cycling in the north pacific implications for the utility of ba as a paleoproductivity and paleoalkalinity proxy benthic incubation chambers have been deployed in a variety of geochemical environments that provide a comprehensive geochemical framework from which to address issues related to ba geochemistry and the use of ba as a paleoproxy first order budgets for barium show that in the equatorial pacific present rates of ba rain and benthic remobilization are nearly in balance indicating that the rate of net accumulation is negligible and is clearly much less than the average for the holocene thus any paleoproxy algorithms built on the assumption of steady state are questionable in contrast budgets for sediments in the southern california borderland indicate much higher burial efficiencies in the range of 50 80 the ba alkalinity alk flux ratio is found to be remarkably constant throughout the environments studied and is indistinguishable from the deep water ratio used for paleoceanographic reconstructions however the ba organic carbon remobilization ratio is not constant combined these results do not indicate a simple first order direct link between ba and alkalinity remobilization via organic carbon oxidation however the similarities in the ba and alkalinity source functions conspire to maintain the ba alk ratio near the global water column average this latter observation provides promise for the use of the ba ca ratio in benthic foraminifera as a paleocirculation tracer

ecosystem engineers and geomorphological signatures in landscapes abstract biogeomorphologists study the roles of biota in landscape formation and decay ecologists interested in ecosystem engineering study environmental change caused by biota and the consequences for the engineer other organisms and ecological processes the interface is geomorphological change an interface both are aware of but study somewhat independently and differently interaction and integration among the two fields is the goal of this special issue here i take an ecological perspective of geomorphological change caused by ecosystem engineers in patches within landscapes that i hope can help facilitate this goal i ask the following general questions when will an ecosystem engineering species create a geomorphological signature in a landscape what in qualitative terms is such a signature how can the signature be estimated and how long will it last what engineer attributes and ecological factors will determine signature change what creates complications how do the answers inform whether or not life leaves a geomorphological signature to attempt answers i develop a provisional general theory of ecosystem engineering signatures that draws on and integrates a geomorphological foundation of balance between formation and decay landscape patch dynamics a general framework for ecosystem engineering and empirical studies i treat a landscape engineering signature as the balance of rates of formation f and rates of decay d across patches whose ratio value f d can be transformed 1 intermediate 1 or untransformed

avulsion mechanisms on the okavango fan botswana the control of a fluvial system by vegetation a study of the avulsion of a major distributory channel on the alluvial fan 22 000 km2 in area of the okavango river in northern botswana has revealed that channels serve as arterial systems distributing water which sustains large areas of permanent swamp the channels are vegetatively confined a primary channel defined here as a channel which receives water and sediment directly from the fan apex aggrades vertically as a result of bedload deposition the rate of aggradation increases downchannel and may exceed 5 cm yr 1 in the distal reaches rapid aggradation is associated with a decline in flow velocity this initiates a series of feedback mechanisms involving invasion of the channel by aquatic plants which trap floating plant debris further reducing flow rate and causing the channel water surface to become elevated thereby increasing rate of water loss from the channel accelerating blockage and aggradation the channel ultimately fails enhanced water loss from the channel promotes the growth of flanking swamp vegetation which confines the failing channel increased flow through the swamp erodes pre existing hippopotamus trails producing a secondary channel system which overlaps but does not connect directly to the failing reach of the primary channel the region of failure of the primary channel migrates upstream accompanied by headward propagation of the secondary channel system the swamp distal to the failed primary channel dessicates and is destroyed by peat fires secondary channels are stable and not prone to blockage comparison with avulsions described in other river systems indicates that the influence of plants in the okavango river system is exceptionally strong

the alkali soils of the middle niger valley origins formation and present evolution in niger republic the regional development of irrigation along the river niger is confronted with a large extent of alkali soils for a sound management of the irrigated area it appears necessary to understand the present evolution of these alkali soils the study of one of these areas located on the liptako bedrock reveals a concentric soil distribution within a zone of brown soil with abrupt textural change and alkaline in depth stagnic solonetz appears a ring of brown steppe soils cambic calcisol around zones of alkali soils solonetz these alkali soils are not saline but their soil solution is more concentrated than in brown steppe soils the abrupt boundary between the brown steppe soils and the alkali soils is related with morphological and geochemical changes resulting from calcite and fluorite precipitation in the soil solution the detailed study of this contact demonstrates the current transformation of alkali soils into brown steppe soils therefore it appears that soil alkalization is no longer in process on the terraces of the river niger the formation of brown steppe soils and alkali soils may be explained by the juxtaposition of two contrasted hydrological regimes in a former pond this hypothesis is supported by aerial pictures and microscopic observations it is also consistent with a recent study of the hydrology of sahelian ponds and with considerations on the chemical quality of the runoff

gopher bioturbation field evidence for non linear hillslope diffusion it has generally been assumed that diffusive sediment transport on soil mantled hillslopes is linearly dependent on hillslope gradient fieldwork was done near santa barbara california to develop a sediment transport equation for bioturbation by the pocket gopher thomomys bottae and to determine whether it supports linear diffusion the route taken by the sediment is divided into two parts a subsurface path followed by a surface path the first is the transport of soil through the burrow to the burrow opening the second is the discharge of sediment from the burrow opening onto the hillslope surface the total volumetric sediment flux as a function of hillslope gradient is found to be qs cm3 cm 1 a 1 176 dz dx 3 189 dz dx 2 68 dz dx 34 dz dx 0 4 this result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport a one dimensional hillslope evolution program was used to evolve hillslope profiles according to non linear and linear diffusion and to compare them to a typical hillslope the non linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section copyright 2000 john wiley sons ltd

a new species of polacanthus ornithischia ankylosauria from the lower cretaceous of sussex england the first specimen of the ankylosaur genus polacanthus from the mainland barremian of southeast england is described as polacanthus rudgwickensis sp nov polacanthus rudgwickensis is larger than polacanthus foxii and there are significant differences in the dermal armour the tibia and caudal vertebrae of the two species polacanthus foxii appears to be restricted at present to the isle of wight with one specimen from southwest england whilst polacanthus rudgwickensis is only known from sussex this geographical distribution the palaeobiological implications and possible sexual dimorphism are discussed for this genus

depositional environment of a kimmeridgian carbonate black band akkuyu formation south western turkey the upper jurassic akkuyu formation of south western turkey consists of pale coloured carbonate facies but includes a peculiar black band at its base in order to characterize the depositional environment of this level a sedimentological organic and inorganic geochemical study was performed on 30 samples three units are distinguished unit 1 consists of black marlstones very rich in organic carbon 22 30 with hi hydrogen index values around 600 the organic matter is an amorphous homogeneous material even at nanoscopic scale this unit is also characterized by a very high concentration of v 1000 p p m and a 13corg value around 26 5 unit 2 shows thin bedded black limestones with chert layers its organic content varies from 2 to 6 as in unit 1 the hi values are uniformly high 600 and gas chromatography shows a high quantity of hopanes the v concentration is also high 400 p p m the unit has a high sr ca ratio an organic carbon isotopic ratio close to 28 7 and diffuse nanoscopically amorphous organic material that is closely associated with pyrite unit 3 corresponds to the white limestones overlying the black band this calcitic facies is almost devoid of organic carbon 0 1 the 13corg values are similar to those of unit 1 25 5 to 26 deposition occurred in a basinal environment surrounded by a carbonate platform primary productivity was high but not exceptional terrestrial organic inputs were scarce bottom waters were probably euxinic during the deposition of unit 1 the presence of both hopane rich and sulphur rich nanoscopically amorphous organic matter may be the result of strong sulphate reducing bacterial activity coupled with low amounts of iron this led to intense vulcanization of the organic matter and thus good preservation with the onset of unit 2 deposition environmental conditions became less extreme perhaps because of cooler water temperatures finally the depositional conditions became oxic leading to the accumulation of pale coloured organic poor limestones of unit 3

impacts of flamingos on saline lake margin and shallow lacustrine sediments in the kenya rift valley abstract studies of modern holocene and pleistocene sediments around saline to hypersaline alkaline lake bogoria and lake magadi show that evidence of flamingo activity in marginal areas of these lakes is nearly ubiquitous flamingos produce discrete structures such as webbed footprints 9 cm long 11 cm wide and nest mounds 30 cm wide 20 cm high and they also extensively rework sediments in delta front delta plain and shoreline areas large 0 5 2 cm in diameter pinched bubble pores and ped like mud clumps are formed by the trampling and churning of wet clay rich sediments in these settings flamingo nest mounds although superficially similar to some thrombolite mounds are typically internally structureless unless formed on pre existing sediments that preserve internal structures the flamingo mounds consist of a dense packed oval shaped core a surrounding body of packed sediment and an external layer with a ped like texture of clumped mud the nests may contain open holes from roots or feather shafts incorporated into the nest and or burrows produced once the nests are abandoned in areas with high densities of flamingos lake margin sediments may be preferentially compacted particularly at breeding sites and become resistant to subaerial erosion and the effects of transgressive ravinement on time scales ranging from seasons to tens of thousands of years the relatively well compacted nest mounds and associated sediments also contribute to the stability of delta distributary channels during regressive transgressive cycles and can lead to the minor channelization of unconfined flows where currents are diverted around nest mounds pleistocene exhumed surfaces of relatively well indurated lake margin sediments at lake bogoria and lake magadi that are interpreted as combined regressive and transgressive surfaces flooding surface sequence boundary preserve evidence of flamingo activities and are overlain by younger porous lacustrine silts that preserve large bubble pores produced by flamingos

mechanism of palygorskite formation in the red clay formation on the chinese loess plateau northwest china abstract the morphological characteristics and microstructures of the authigenic palygorskite occurring with smectite and carbonate minerals in the late miocene red clay formation on the chinese loess plateau have been investigated with the powder x ray diffraction xrd scanning electron microscopy sem and high resolution transmission electron microscopy tem the xrd results indicate that the red clay sediments contain quartz feldspar calcite dolomite illite kaolinite chlorite palygorskite and smectite and sem analyses show that palygorskite is a common component delicate palygorskite fibers radiate from the margins of platy smectite suggesting a pedogenic origin during the weathering of pre existing smectite a process that involved intense dissolution of the smectite and an adjustment in its structure moreover palygorskite occurs as coatings pore fillings and pore bridging cements among dolomite rhombs suggesting that the fibrous palygorskite was formed by a direct dolomite precipitation from pore fluids mostly after dolomite crystallization there is evidence to show that these two mechanisms took place synchronously in the red clay formation and that the two processes are related under alkaline conditions with high ph 8 0 fluids rich in magnesium magnesium ions occupy the interlayer positions in the smectite and this results in a misfit between the mg octahedral sheet and the smectite layer thereby allowing interaction between the magnesium ions and smectite layers and a reorganization of the structure to form palygorskite then with this kind of palygorskite as a crystal nucleus more palygorskite grows through a direct chemical deposition process according to previous studies the red clay sediments experienced a steady dry warm climate with periods of high rainfall and evaporation the warm climate would have increased the rate of weathering of minerals and subsequently enhanced the ions content and ph in the soil solutions during dry periods this soil environment is favorable for smectite transformation and palygorskite deposition this study has improved our understanding of the environmental and paleoclimatic changes during the time that palygorskite formed in the arid soils of the chinese loess plateau

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores

on the first partial skull of an ankylosaurian dinosaur from the lower cretaceous of the isle of wight southern england the specimen is identified as the partial cranium of a nodosaurid ankylosaur ornithischia thyreophora on the basis of the presence of bone which is fused to the dorsal surface of the skull and has secondarily closed the upper temporal fenestrae the only unequivocally nodosaurid material recovered from the isle of wight to date comes from wealden facies and has been referred to the genus polacanthus it is considered highly probable that this new skull is referable to the same genus despite having undergone abrasion through post emergence water rolling the skull and cranial walls have proved to be relatively informative of the general anatomy of the braincase and the neural and vascular anatomy of this part of the head the anatomy of the braincase of most ankylosaurs with the notable exception of the juvenile specimens of the ankylosaurid pinacosaurus is surprisingly poorly known despite the relative abundance of cranial material in north american and asian collections the cranial neural and vascular anatomy is well shown in this specimen and enables the first detailed description of nodosaurid endocranial structures the general form of the brain can be outlined from the structure of the endocast and the principal lobes can be identified the majority of the cranial nerves have been identified and a significant component of the associated vascular system is also visible in most respects the endocast shows a neural anatomy which is common to that known in most dinosaurs when compared to their nearest relatives the ankylosaurid ankylosaurs euoplocephalus the nodosaurid endocranial cast shows a more pronounced cerebral flexure a forebrain which is broader and more expanded dorsally and a more prominent cerebellum although there is no evidence for a floccular lobe there are minor differences in the arrangement of the cranial nerves and the dorsal portions of the vascular system are better shown because of erosion the olfactory lobes of this specimen of cf polacanthus are not preserved and cannot be compared to those of ankylosaurid ankylosaurs the latter are unusual in the strong separation of the lobes reflected in the divergent olfactory stalks this feature may be associated with the very complex passages within the nasal region of the skull which are lacking in the nodosaurids described to date

the glaciogenic origin of the pleistocene calcareous dust in argentina on the basis of field mineralogical textural and geochemical analyses calcareous dust occurs in argentina as layers and pockets closely associated with pleistocene deposits and periglacial features from southernmost patagonia to at least the mendoza precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper pleistocene deposits between 51 s and 33 s and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment all observations and analyses lead us to conclude that 1 the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic 2 the dust was carried by southeasterly antarctic winds and 3 it was deposited over most of southern and central argentina field observations geomorphic evidence and radiocarbon dates suggest that the dust was deposited during several pleistocene glacial episodes