annual biogenic particle fluxes to the interior of the north atlantic ocean studied at 34 n 21 w and 48 n 21 w abstract in order to clarify the annual quality quantity and export processes of biogenic particles from the euphotic zone to the deep ocean interior an array of automated time series sediment traps were deployed for 1 year from 4 april 1989 to 17 april 1990 at 34 n 21 w and 48 n 21 w as part of the joint global ocean flux program jgofs north atlantic bloom experiment nabe three sediment traps with 13 time series sediment collectors were placed at both stations approximately 1 and 2 km below the surface and 0 7 km above the bottom they collected settling particles during 26 14 day intervals for 376 days with an 20 day hiatus in september october 1989 for changeover of the trap moorings the collection periods of the six traps were synchronized forming a spatio temporal matrix of 156 samples the annual mass flux at about 2 km deep during this experiment was 22 and 27 g m 2 y 1 at the 34 and 48 n stations consisting of biogenic particles with traceable quantities of lithogenic particle flux the spring particle bloom characterized by the sedimentation of particles relatively enriched by norg began in january at the 34 n station and in march at the 48 n station the bloom continued for 4 5 and 3 months and provided 62 and 50 of the annual biogenic particle mass flux at 2 km at the 34 and 48 n stations the surface bloom penetrated to the ocean interior within a few weeks with apparently accelerated settling speed at deeper layers the order of susceptibility of biogenic elements to mineralization while settling in the 0 7 1 km a b water column was from least to most resistant p norg corg si and ca the c n p ratio at 0 7 km a b was 154 18 1 at the 34 n station and 148 18 1 at the 48 n station

dissolution kinetics of biogenic silica and tentative silicon balance in the yellow sea the dissolution of biogenic silica bsio2 in coastal environments is important for marine productivity and essential to the global silicon cycle bsio2 dissolution experiments were performed using sediments from the yellow sea ys to explore the factors that influence bsio2 dissolution and to better understand the silicon cycle in the ys the results showed that the bsio2 content in surface sediments varied from 0 40 to 3 7 average 2 2 0 79 sio2 additionally the bsio2 content was higher in the central areas of the northern and southern ys and lower in the near shore area of the northern changjiang estuary the burial flux of bsio2 in surface sediments ranged from 0 12 mol m 2 yr 1 to 2 3 mol m 2 yr 1 and gradually decreased eastward from near shore to offshore continuous flow experiments showed that the solubilities of bsio2 in the ys sediments varied from 91 0 to 303 m si further the dissolution rate constant of bsio2 was 9 3 41 nmol g 1 h 1 which is 2 3 orders of magnitude lower than that of other marginal seas such as the arabian sea and scotia sea the structural incorporation of aluminum in bsio2 and the content of lithogenic minerals in sediments hindered bsio2 dissolution the silica budget of the ys was established the burial efficiency of bsio2 in the surface sediment was calculated to be 73 which accounts for 4 of the global balance and is much higher than that of the global ocean average because of its high sediment accumulation rate and much lower dissolution rate constant bsio2 was well preserved in the ys highlighting the important role of the ys in the global silicon cycle

calcretes at sequence boundaries in upper carboniferous cyclothems of the sydney basin atlantic canada abstract nodular and associated groundwater calcretes in coal bearing cyclothems of the sydney basin mark the boundary between underlying marginal marine and overlying alluvial deposits they are inferred to represent lowstand surfaces sequence boundaries the host sediments include both sand siltstones and palustrine limestones microfabrics of calcretes with detrital hosts show evidence of replacement displacement and shrinkage alpha fabrics suggesting that the calcretes formed under relatively arid conditions in contrast microfabrics of nodular calcretes with limestone hosts exhibit predominantly beta fabrics with root induced brecciation and subordinate shrinkage fabrics the calcretes and host limestones are inferred to have formed in topographic lows thick alluvial sediments with red calcic vertisols overlie the calcretes and formed within the transgressive systems tract under conditions of abundant sediment supply coals and associated hydromorphic palaeosols lie near the transgressive maximum and in the highstand systems tract the presence of calcareous palaeosols on lowstand surfaces suggests that the lowstands were times of relative climatic aridity

control of terrestrial stabilization on late devonian palustrine carbonate deposition catskill magnafacies new york u s a abstract upper devonian frasnian terrestrial strata of south central new york contain palustrine and lacustrine carbonate deposited within the well developed catskill clastic wedge succession these nonmarine limestone beds 8 50 cm thick were repeatedly subaerially exposed and subjected to pedogenic processes palustrine features include subaerial exposure surfaces with soil crusts pseudo microkarst and microkarst brecciation desiccation cracks horizontal planar and circumgranular cracks and rhizoliths lacustrine carbonate sedimentation was derived primarily from biogenically induced precipitation and from degradation of calcified charophyte stems and ostracodes these deposits accumulated in relatively shallow water depths probably 10 m the results of stable isotope analyses 13c 4 0 to 4 7o oo pdb 18o from 6 8 to 8 7o oo pdb reveal covariance between 13c and 18o values the high degree of covariance r 0 75 suggests that these late devonian carbonate lakes were hydrologically closed high rates of surface water productivity resulted in the heavier 13c values late devonian carbonate lakes developed as a result of landscape stabilization by the developing rhizosphere in addition plants of small to moderate stature functioned as clastic filters trapped terrigenous clastic sediment along lake margins and thereby permitted carbonate sedimentation to occur in a system otherwise dominated by terrigenous clastics these upper devonian lacustrine deposits contain the oldest recognized occurrence of palustrine facies the temporal distribution of palustrine carbonate deposits therefore appears limited to post silurian strata

records of the influence of deccan volcanism on contemporary sedimentary environments in central india deccan volcanism with a duration of 5 myr represents a major continental flood basalt province in which 2 million km3 of lavas were formed such voluminous and rapid volcanism in phanerozoic earth history has commonly been advanced as a cause for mass extinctions despite this significance few studies have attempted to understand the influence of continental flood basalt volcanism on contemporary sedimentary environments thin sedimentary sequences associated with the deccan volcanics i e the infra and inter trappean sequences offer an opportunity to assess the influence of deccan volcanism on contemporary sedimentary environments in central india the lameta formation mainly constitutes a well characterised regolith regionally consisting of calcretes and palustrine facies which may in places be associated with ephemeral sandy braided river and sheetflood facies an assessment of the influence of deccan volcanism on contemporary surficial environments reveals a an input of basaltic degradational products in the basal fluvial facies of the lameta formation b upward changes in facies assemblages from lacustrine palustrine to subaerial dominated followed eventually by burial by the first lavas locally c significant changes in the palaeoflow characteristics of fluvial channel facies respectively under and overlying the main calcareous regolith of the lameta formation d that most freshwater lacustrine taxa survived the initial effects of the deccan volcanism without undergoing any drastic change in addition to the role of constructional topography resulting from lava emplacement and associated surface uplift the mode of preservation of sedimentary packets significantly affects changes in the vertical motifs of coeval sedimentary sequences because of the problems of time resolution on 105 106 year time scales in the continental infra and inter trappean sequences detailed cause volcanism effect surficial environments relationships at the event level are not well understood also the lack of data from multiple stratigraphic levels of the inter trappean beds precludes any serious assessment of the directions and rates of changes that took place in co2 concentrations of the palaeoatmospheres of that period 65 3 myr

the importance of water column processes on the dissolution properties of biogenic silica in deep sea sediments i solubility abstract flow through experiments have been performed to study the thermodynamics of biogenic silica opal dissolution in deep sea sediments they were applied for the first time on sediment from the southern ocean van cappellen and qiu 1997a van cappellen and qiu 1997b we have extended the use of these experiments to other deep sea settings thereby covering a wide range of in situ silicic acid asymptotic concentrations casympt 200 to 900 mol l and biogenic opal content bsi 0 5 to 80 performing these experiments under in situ bottom temperatures allows for the comparison between experimental apparent solubilities and casympt concentrations low values of bsi apparent solubilities have been measured in the deepest sections of the multicores collected in the northeast atlantic 229 mol l and in the equatorial pacific 505 mol l they are only 10 to 20 higher than the in situ casympt concentrations this demonstrates a clear control of pore water silicic acid concentrations by the in situ apparent solubility of the bsi i e the solubility of bsi within a complex sedimentary matrix that includes important quantities of silicate minerals in regions where the percentage detrital percentage biogenic ratio is low the apparent solubility of the biogenic silica is close to that of in situ biogenic silica in the opposite case when the percentage detrital percentage biogenic ratio is high reprecipitation reactions induce strong interference on the dissolution properties of the opal both in situ and in flow through experiments in such a sedimentary matrix it is important to determine the appropriate opal solubility to be used in early diagenetic models i e the solubility of the biogenic silica just before deposition on the seabed this has been achieved by performing flow through experiments on sediment trap material from the north atlantic site comparison of apparent biogenic silica solubility measured by flow through experiments and the silicic acid concentrations measured in the cups of the sediment traps suggested that the solubility of biogenic silica that reaches the sediment water interface is not unique and varies spatially and temporally in fact it is the degree of coupling between surface waters and the sediment water interface that will control the aging of biogenic silica in the water column and hence the dissolution properties of the biogenic silica deposited at the sediment water interface all these results call for a strong improvement of biogenic silica early diagenetic models that should include not only a reprecipitation term that takes into account interaction with silicate minerals but also the existence of several phases of biogenic silica and thus that should operate in a non steady state mode to account for seasonal variations in the quality of deposited biogenic silica

influence of seasonal phytodetritus deposition on biogenic silica dissolution in marine sediments potential effects on preservation abstract the deposition of fresh phytoplankton detritus phytodetritus following phytoplankton blooms may influence biogenic silica bsi dissolution in marine sediments we studied bsi dissolution properties before during and after periods of phytodetritus deposition during time series field programs in the abyssal north atlantic the bengal project and on the west antarctic peninsula shelf the foodbancs project dissolution experiments performed by means of flow through reactors showed temporal variations in the dissolution properties of bsi in the sediment column after phytodetritus deposition this non steady state character of benthic silica dynamics is an important aspect of pelagic benthic coupling the last foodbancs cruise occurred after a phytodetritus deposition event and yielded high pore water dissolved silica dsi concentrations and dsi effluxes in the upper centimetres of the sediment column suggesting a rapid turnover of recently deposited siliceous material higher dissolution rates were measured in the phytodetritus rich sediments relative to surface sediments collected during previous seasons on earlier foodbancs cruises during the bengal project high dissolution rates were measured at depth in the sediment column only after a summer phytodetritus deposition event in the highly detrital sediment matrix of the abyssal north atlantic ocean resolution of increased dissolution rates and experimental artefacts of the flow through reactors can be difficult because of the low abundance of bsi depending on the sediment matrix bioturbation can play a crucial role in transporting fresh bsi particles to depth where dsi concentrations are close to experimentally determined bsi solubilities the potential impacts of such processes on bsi preservation are discussed we suggest that future models of bsi early diagenesis should include the rapid mixing of freshly deposited particles if we want to describe further the preservation of bsi in marine sediments

biogenic silica dissolution in sediments of the southern ocean i solubility abstract a stirred flow through reactor technique was used to determine silica solubilities in sediments collected with a multicorer in the indian sector of the southern ocean antares i cruise the results show that the apparent silica solubility in the cores may decrease increase or remain constant with depth the silica solubility profiles are best explained by the early diagenetic interactions between biogenic silica and soluble aluminum derived from detrital material by combining the solubility data with measured dissolved silica profiles it is shown that the variable asymptotic pore water silica levels in the cores cannot be explained solely by differences in silica solubility in sediments that experience a significant detrital input the simultaneous reprecipitation of dissolved aluminum and dissolved silica prevents water silicic acid from reaching saturation with the dissolving biogenic silica the principal oceanographic control on pore water silica build up in the cores studied is the ratio of the deposition fluxes of biogenic silica and detrital material solubility differences inherited from the biomineralization process in the surface waters do not appear to have a significant effect on the observed pore water silica levels

climate and vegetation changes 180 000 to 345 000 years ago recorded in a deep sea core off portugal a new high resolution combined marine proxy pollen sequence from the portuguese margin md01 2443 enables direct comparison of ocean and ice volume changes with vegetation development in south west iberia during marine isotope stages mis 7 8 and 9 changes in sea surface conditions on both orbital and millennial time scales are closely mirrored by forest extent indicating a coherence of climate variability between the north atlantic and south west iberia deglacial warming at the start of mis 7 and 9 was interrupted by incursions of subpolar water masses at the site accompanied by reversals in tree population expansion during mis 7e and 9e the close relationship in timing and amplitude between vegetation and offshore conditions broke down early forest collapse points to pronounced cooling and aridification on land which although not accompanied by a change in water masses at the portuguese margin appears to have coincided with abrupt decreases in atmospheric methane concentration recorded in antarctic ice cores the most extreme glacial conditions of mis 8 occurred during the early part followed by an interval of warmer conditions and tree population expansion similar to 263 ka this has sometimes been considered as indicating an early deglaciation but the data presented here show that it was distinct from termination iii which occurred later in line with milankovitch forcing a sub orbital oscillation in both isotopic and pollen records is observed at the end of mis 7 ca 184 ka which appears to be coeval with a recently identified sea level high stand c 2006 elsevier b v all rights reserved

epicontinental permian cretaceous seaways in central india the debate for the narmada versus godavari rifts for the cretaceous tertiary incursion abstract this study presents an overview of mesozoic transgressions that influenced the palaeogeography of central india and offers an analysis of the existing evidence for the interpretation of the depositional record of infra and inter trappean sequences these data are then used to understand the respective palaeogeographic settings of the narmada and the godavari master valleys leading to a reappraisal of the paths suggested thus far for a cretaceous tertiary k t seaway major rift related discontinuities have been subjected to reactivation episodes during the mesozoic these tectonic events caused the initiation of several pericratonic basins the riftogenic valley systems have been affected by transgressions from the western margin of india through the narmada valley and or from the eastern margin through the godavari valley however for the most part these continent scale valley systems have hosted mainly mesozoic fluviatile and lacustrine sediment successions besides a marine incursion from the west in the lower reaches of narmada valley is widely recognised on the basis of the late cretaceous bagh beds additionally the maastrichtian palaeogeography of these valley systems of central india have been strongly influenced by the uplift resulting from the thermo magmatic flux associated with the deccan volcanism this resulted in major topographic readjustments within the godavari and narmada tapti palaeovalleys resulting in turn in major basinal depressions as revealed from the reconstruction of the palaeo digital elevation model significantly removed from the eastern and western coastal margins of india isolated occurrences of marine biota such as foraminifera marine algae and palm fossils have been found in infra and inter trappean maastrichtian and danian sequences of central india their presence in these inland basins is enigmatic and three hypotheses have been proposed to explain the presence of marine environments in these basins a trans deccan strait connecting both the margins of india through pre existing rift systems b an 800 km long seaway through the narmada valley and c a marine incursion through the godavari valley this palaeogeographic analysis supports a marine incursion through the godavari rift and presents arguments against the other two

environmental control on concretion forming processes examples from paleozoic terrigenous sediments of the north gondwana margin armorican massif middle ordovician and middle devonian and sw sardinia late ordovician abstract concretions of various compositions are common in the paleozoic terrigenous successions of the north gondwana margin this study focuses on phosphatic p and siliceous si concretions present in some successions of the armorican massif nw france and sw sardinia w italy it shows that they consist of mudstones fine to very fine grained sandstones or shellbeds with a more or less abundant p cement and form a continuum between a phosphatic end member and a siliceous biogenic end member the p 2 o 5 contents are ranging from 0 26 to 21 5 and are related to apatite the sio 2 contents vary from 25 to 82 and are linked both to a terrigenous phase and to a biogenic silica phase concretions showing the lower p contents p 2 o 5 2 al 2 o 3 5 comparison with the surrounding sediments shows that all the concretions are enriched in chlorite and in middle rare earth elements la s gd s 0 12 0 72 and some of them in y up to 974 ppm rare earth elements more than 300 ppm and sr 260 880 ppm the concretions with highest biogenic silica concentrations are contained in the outer shelf sediments whereas the other concretions are present from the proximal part of the inner shelf to the outer shelf a genetic model in two stages is proposed during early diagenesis the dissolution of shells and degradation of organic matter progressively enrich the pore water in dissolved si ca and p when the suboxic zone is reached p precipitation begins leading to the formation of protoconcretions in shallow environments the relative permeability of sediments and the winnowing or reworking of the upper few centimetres by bottom currents allow for suboxic conditions to be maintained leading to p rich concretion formation in deeper environments the anoxic zone is reached more rapidly thereby preventing extensive phosphogenesis nevertheless in the protoconcretions the early p cement preserves pore spaces from compaction in the presence of biogenic siliceous particles the fluids are enriched in dissolved silica and diffuse towards the protoconcretions silica precipitation can thus occur later in the intergranular spaces

palustrine sedimentation and associated features grainification and pseudo microkarst in the middle miocene intermediate unit of the madrid basin spain abstract a rather thick sequence 50 75 m of lacustrine limestones forms the uppermost part of the intermediate unit middle miocene in the ne part of the madrid basin central spain a gradual change from distal alluvial to open lake facies is recorded in this area red mudstones passing vertically to strongly mottled limestones are typical of the transition from distal alluvial to marginal lake deposits a wide variety of facies occur in the marginal lacustrine facies association all of them showing pedogenic features e g root traces alveolar septal structures pseudo microkarst micrites and biomicrites are interpreted as open lacustrine deposits although not as strongly pedogenically modified as the marginal lacustrine facies they still show evidence of subaerial exposure the carbonate sequence was deposited in a low gradient shallow lake system in which slight fluctuations in the water level caused extensive emergence pedogenic processes affected most of the lake deposits but modification was more intense in the marginal facies biogenic activity and mechanical reworking at lake margins led to the formation of pedogenic diagenetic pseudo microkarst and peloidal and or intraclastic limestones

quantitative and qualitative relationships between planktonic diatom communities and diatom assemblages in sedimenting material and surface sediments in lake baikal siberia endemic planktonic diatoms are a major component of lake baikal sediments during interglacial periods to investigate how these diatom assemblages are altered during sediment formation quantitative plankton monitoring 1995 1998 was integrated with sediment trapping over 2 yr 1996 1997 in baikal s southern basin depth 1 400 m the traps consisted of both open 6 monthly and sequential 2 weekly collectors deployed throughout the water column sedimentation was seasonal with diatom species composition valve abundance and total dry mass reflecting changes in the planktonic communities sedimented assemblages were transmitted largely intact to the deepest traps 1 300 1 390 m some compositional blurring occurred from differential sinking rates and dissolution of diatom valves a rapid mass flux event of aulacoseira skvortzowii and a baicalensis was recorded in summer 1997 with particle sinking rates between 60 and 100 m d 21 and dry mass fluxes 5gm 22 d 21 although dissolution was evident for all species more delicate taxa were preferentially affected e g a skvortzowii vegetative cells and finesynedra species whereas nitzschia acicularis valves were almost entirely dissolved within the water column comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment with sedimentary diatom accumulation rates being only about 1 of trap deposition and plankton production rates dissolution was significant in explaining 5 30 of species variance between all taphonomic levels plankton trap samples and surface sediments results indicate that diatom based paleoclimatic records in lake baikal sediments could be improved and refined by taking taphonomic considerations into account

stable climate in india during deccan volcanism suggests limited influence on k pg extinction abstract large igneous provinces lips have been temporally correlated to mass extinctions throughout the phanerozoic including the emplacement of the deccan volcanic province dvp 66 3 65 6 ma in western and central india which has been invoked as either a cause or exacerbating factor in the cretaceous paleogene k pg extinction however relatively little is known about local paleoclimatic and paleoenvironmental responses to volcanism to investigate the dvp s role as a driver of local environmental change and to provide climatic background for known ecological shifts new inter basaltic paleosol profiles at the eastern edge of the dvp are used in conjunction with profiles from the literature to reconstruct paleoclimate and terrestrial environments before and after the k pg these profiles provide a novel opportunity to study the sediments within basalt flows before during and after a mass extinction event and in the midst of a lip emplacement event paleoclimate proxies and the floral humidity province proxy reflect little long term change in either climate or environment across the k pg with stable precipitation values and temperatures accompanied by a constant forest signal these interpretations are corroborated by macrofloral records and sedimentology from india which suggest some environmental turnover but generally support a forested fluvio lacustrine environment throughout the duration of volcanism our results support the possibility of rapid recovery times for terrestrial ecosystems during volcanism and suggest that while dvp eruptions may have exacerbated long term environmental perturbation the emplacement of the dvp is not likely to have caused the terrestrial mass extinction at the k pg boundary

a quantitative approach to soil occurrence in alluvial deposits and its application to the old red sandstone of britain palaeosols fossil soils are a major component of alluvial deposits in the geological record not only do these typically show considerable variations in their degrees of development within single formations but they also exhibit highly complex stratigraphic relationships with one another a simple quantitative approach to these variations is presented which provides a graphical means of assessing differences in soil palaeosol development within a sequence with calcic or petrocalcic horizons to illustrate the approach a range of palaeosols from the siluro devonian old red sandstone of britain are characterized in terms of the likely frequency and magnitude of depositional events which occurred during their formation in particular two alluvial suites from the manorbier area of south wales are analysed using this approach the technique should be widely applicable to other alluvial successions and provides a means of graphicallv presenting relationships between multiple palaeosols although the wide range of rates of formation of calcic and petrocalcic horizons precludes their use to provide narrow estimates of deposition rates

a benthic si mass balance on the congo margin origin of the 4000 m dsi anomaly and implications for the transfer of si from land to ocean to elucidate the origin of the silicic acid dsi anomaly observed along the 4000 isobath on the congo margin we have established a benthic si mass balance and performed direct measurements of biogenic silica bsio2 dissolution in the deep waters and in the sediments results strongly suggest that the anomaly originates from the sediments the intensity of dsi recycling is consistent with the degradation of organic matter as observed from si o2 ratios in the benthic fluxes compared to that ratio observed in the anomalies strong imbalances observed in both the si and c mass balances suggest that the biogenic matter that degrades and dissolves in these sediments near 4000 m does not come from pelagic sedimentation it is probably not coming also from the deep channel because observations were similar in the deep channel vicinity site d and further south far from its influence site c the composition of the sediments with an si c ratio close to that observed on continental shelves suggests that this matter is coming from downslope transport a first estimate of the magnitude of this flux at global scale close to 12 t mol si yr 1 suggests that it may be an important path for transferring si from land to ocean

lithofacies associations and stable isotopes of palustrine and calcrete carbonates examples from an indian maastrichtian regolith detailed information on semi arid palustrine carbonate calcrete lithofacies associations in a sheetwash dominated regolith setting is sparse this is addressed by studying the lower limestone of the lameta beds a well exposed maastrichtian regolith in central india the general vertical lithofacies assemblage for this unit comprises a basal calcareous siltstones and marls with charophytes ostracods and gastropods b buff micritic limestones associated in their upper parts with calcretized fissure fill sandstones c sheetwash as fissure fill diamictites and thin pebbly sheets locally developed over a few metres and d sandy nodular brecciated and pisolitic calcretes at the top the sequence is regressive with upsection filling of topographic lows by increased sheetwash lateral lithofacies change is marked but there are no permanent open water lake deposits in topographic lows close to the water table marshy palustrine or groundwater calcretes formed whereas on better drained highs brecciation and calcretization occurred prolonged exposure is implied suggesting that shrinkage was the main cause of brecciation evidence for rhizobrecciation and other biological calcrete fabrics is sparse contrasting with the emphasis on root related brecciation in many studies of palustrine lithofacies stable isotope d18o and d13c values are consistent with the palustrine limestones being fed from meteoric derived groundwater with a strong input of soil zone carbon there is overlap of both d18o and d13c values from the various palustrine and calcrete fabrics co occurring at outcrop this suggests that in groundwater supported wetlands conversion from palustrine carbonate to calcrete need not show isotopic expression as the groundwater source and input of soil zone carbon are essentially unchanged cretaceous tertiary d18o and d13c values from palustrine lithofacies and associated calcretes appear to be strongly influenced by the inherited values from lakes and wetlands hydrologically closed lakes and marine influenced water bodies tend to result in low negative palustrine d18o and d13c values during brecciation and calcretization the degree of isotopic inheritance depends on whether or not alteration occurs in waters that are different from those of the original water body or wetland marked biological activity e g rhizobrecciation or root mat development during calcretization may lower d13c values where c3 plants are abundant but in shrinkage dominated systems d13c values will be largely inherited from the palustrine limestones

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

cenozoic calcretes from the teruel graben spain microstructure stable isotope geochemistry and environmental significance in the teruel graben northeast spain laminar and nodular calcretes formed in a variety of cenozoic deposits ranging in age from palaeogene to pleistocene these calcretes developed in a relatively small area under the influence of the same highlands consequently differences in their microstructure and isotopic composition c and o must be related to differences in host rock climate vegetation and duration of development nine profiles developed in different sedimentary settings from proximal areas to lacustrine environments were studied to determine whether the microstructure and stable isotope composition changed during the cenozoic these characteristics might be used as indicators of the prevailing climate and vegetation and reveal any changes that occurred during this time most of the laminar calcretes studied are compound profiles that formed on hard substrates e g jurassic limestones or coarse detrital deposits e g palaeogene pliocene and plio pleistocene sandstones and conglomerates these profiles formed in proximal areas of the basin and also in fluvial terraces microstructures include biogenic features such as alveolar septal structures root tubes calcified root cells and calcified organic filaments underside coatings of micrite and fibrous vadose cements are common around gravel clasts on the other side spherulites are only preserved at the very top of the youngest calcretes nodular calcretes developed on fine detrital substrates e g on palaeogene miocene and pliocene red mudstones and sandy mudstones of distal alluvial and floodplain environments and in some places grade vertically into palustrine limestones the nodules consist of micrite and were elongated vertically show desiccation cracks and mottling micritic coatings some alveolar septal structures and root traces microcodium of type 1 occurs in both laminar and nodular calcretes but only in those of palaeogene age while calcified root cells microcodium of type 3 are seen in the pliocene calcretes the stable isotope composition covers a wide range 8 23 18o 4 29 pdb and 7 29 13c 3 42 pdb nodular laminar and palustrine facies occupy overlapped isotopic fields displaying an overall negative covariant trend location within the basin prevailing climate and density of vegetation are responsible for differences in isotope values the palaeogene samples show a wide range of values and are difficult to separate from the others however there is as significant change to lighter carbon values from the miocene to the pliocene profiles this change may be related to the cooler climatic conditions that prevailed during the pliocene and is reverse to the expected shift to heavier 13c values which is related to the increase of c4 vegetation that occurred in many areas of the world during the miocene or to the transit to the pliocene the formation of these calcretes seems to have occurred in semi arid conditions with prevailing c3 vegetation

biogenic flux of al to sediment in the central equatorial pacific ocean evidence for increased productivity during glacial periods we examined the flux of al to sediment accumulating beneath the zone of elevated productivity in the central equatorial pacific ocean along a surface sediment transect at 135 w as well as downcore for a 650 kyr record at 1 3 n 133 6 w across the surface transect a pronounced broadly equatorially symmetric increase in al accumulation is observed relative to ti with al ti ratios reaching values 3 4 times that of potential detrital sources the profile parallels biogenic accumulation and the modeled flux of particulate 234th suggesting rapid and preferential adsorptive removal of al from seawater by settling biogenic particles normative calculations confirm that most al is unsupported by the terrigenous fraction the observed distributions are consistent with previous observations of the relative and absolute behavior of al and ti in seawater and we can construct a reasonable mass balance between the amount of seawater sourced al retained in the sediment and the amount of seawater al available in the overlying column the close tie between al ti and biogenic accumulation as opposed to concentration emphasizes that biogenic sedimentary al ti responds to removal transport phenomena and not bulk sediment composition thus in these sediments dominated by the biogenic component the bulk al ti ratio reflects biogenic particle flux and by extension productivity of the overlying seawater the downcore profile of al ti at 1 3 n displays marked increases during glacial episodes similar to that observed across the surface transect from a background value near al ti of average upper crust the excursions in al ti are stratigraphically coincident with maxima in both bulk and caco3 accumulation and the excess al appears to not be preferentially affiliated with opaline or organic phases consistent with the similar behavioral removal of al and 234th the latter of which responds to the total particle flux the al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits these results collectively indicate that 1 al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater therefore the common tenet that al is dominantly associated with terrestrial particulate matter and the subsequent use of al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment needs to be reevaluated 2 the al ti ratio in biogenic sediment can be used to trace the productivity of the overlying water providing a powerful new paleochemical tool to investigate oceanic response to climatic variation 3 the close correlation between the al ti productivity signal and carbonate maxima downcore at 1 3 n suggests that the sedimentary carbonate maxima in the central equatorial pacific ocean record increased productivity during glacial episodes

diagenesis of flint and porcellanite in the maastrichtian chalk at stevns klint denmark abstract flint is common in many successions but since the nodules can be the result of a series of replacement and void filling processes their origin and broader paleo oceanographic significance can remain enigmatic this study addresses the origin of flint in the campanian maastrichtian chalk of denmark using the 450 m long stevns 1 core as a natural laboratory four types of siliceous nodules occur in the core porcellanite white flint white flint with a core of dark flint and dark flint all nodules consist mainly of microquartz with subordinate lutecite spherulitic chalcedony megaquartz and dolomite the lutecite replaces macrofossil fragments mainly bryozoans and shells microquartz replaces coccoliths and the chalcedony and megaquartz are pore filling the preservation of the external shape of bryozoans shells and coccoliths suggest that siliceous nodules were formed early by a one by one volume replacement of chalk values of 18osmow of microquartz and lutecite around 33 indicate temperatures of 15 17 c at the time of precipitation in contrast the 18osmow values of megaquartz indicate precipitation at temperatures up to 48 c the occurrence of chalcedony together with more stable and ordered megaquartz in irregular voids indicates that silica gel and or opal ct transformed to the quartz phases microquartz lutecite chalcedony and megaquartz through the dissolution precipitation process ostwald ripening these results motivate a conceptual model in which the replacement process was initiated by microbial decomposition of organic matter and took place during periods of low rate of or even stopped sedimentation which fixed the redox boundary and the microbial metabolic zones at a specific depth below the sea floor biogenic opal a incorporated in the sediment column below the sea floor was dissolved and precipitated at the redox boundary as silica gel and or opal ct possibly aided by sulfide oxidizing bacteria during burial the dissolution precipitation process transformed the silica gel and opal ct to the quartz phases the results of this study indicate that precipitation of the flint precursor can be controlled by a combination of an abundant biosiliceous source and high microbial activity in the sediments immediately below the seafloor flint is therefore likely to reflect deposition in a narrow interval at relatively shallow depths and therefore might be useful in studies of shallow water carbonates

a classification of rhizogenic root formed calcretes with examples from the upper jurassic lower cretaceous of spain and upper cretaceous of southern france reply abstract studies of fluvial sequences from the upper jurassic and lower cretaceous of the cameros basin spain and the upper cretaceous of the aquitaine basin france have revealed large numbers of calcrete profiles which have formed wholly or largely through the action of plant root calcification those from spain have formed by the calcification of root mats whereas those from france resulted from the accumulation of calcified root cells microcodium these root related rhizogenic calcretes developed in stages allowing developmental time series chronosequences to be identified contrasting with existing models for calcrete profile growth they provide unique examples where vegetation has been the dominant control on profile development and probably indicate specific vegetation types and palaeoecological settings the role of root activity in forming some quaternary calcretes is also discussed

sensitivity of the marine biospheric si cycle for biogeochemical parameter variations 1 a systematic quantitative assessment of the marine silicon cycle is presented based on a prognostic coupled water column sediment global biogeochemical ocean general circulation model hamocc the resulting tracer distributions are compared with a comprehensive marine si database of measurements the model parameters which govern the si cycle within the model world are optimized through a linear response model the functional relationships between the si cycle parameters and the si tracer distributions are derived from a series of sensitivity experiments addressing opal export production particle flux through the water column porewater chemistry and external biogeochemical forcing the most important parameters for a further quantitative improvement of the simulation are depth dependent opal dissolution kinetics a productivity dependent opal settling velocity a general change in maximum si uptake velocity vmaxopal and the clay as well as the si input from continental weathering the modeled si budget shows a larger global export production larger opal deposition rates onto the sediment surface and higher diffusive transports of porewater silicic acid into the open water column as estimated by treguer et al 1995

dehydroxylation and diagenetic variations in diatom oxygen isotope values abstract numerous studies have documented changes in the dissolution and reactivity of biogenic silica as it is transferred from the water column to sediment archives here we present the first experimental data that demonstrate a physical mechanism by which the oxygen isotope 18osil values of biogenic silica diatoms are altered during early diagenesis the 18osil value of diatom silica cultured at 19 3 c was 31 9 0 2 n 6 the same silica experimentally aged in an artificial seawater media at near silica saturation at 85 c had an average 18osil value of 27 1 0 6 n 20 the most significant change in the 18osil value was coincident with an initial reduction in the total silanol abundance indicating that the timing of dehydroxylation reactions in natural sedimentary environments is associated with diagenetic changes in the recorded 18osil values the rate of change in the experimental aging environment at 85 c was rapid with significant changes in both silanol abundance and 18osil values additionally the silica water fractionation relationship recorded by the experimentally aged samples approaches the equilibrium quartz water fractionation factor the linear rate law was used to estimate the timing of these changes in low temperature environments the initial and most significant change in silica reactivity and 18osil values is likely to occur on the order of 10 s of years at 4 c published silica water fractionation factors for sedimentary diatoms most likely represent a combination of growth and diagenetic environments and the 18o value of diagenetic water needs to be addressed when using 18osil values to reconstruct paleoceanographic and paleoenvironmental conditions

germanium silicon fractionation in a river influenced continental margin the northern gulf of mexico abstract in this study we have sampled the water column and sediments of the gulf of mexico to investigate the effects of high riverine terrigenous load and sediment redox conditions on the cycling of ge and si water column ge si ratios across the gulf of mexico continental shelf range from 1 9 to 25 mol mol which is elevated compared to the global ocean value of 0 7 mol mol the ge enrichment in the gulf of mexico seawater is primarily due to anthropogenic contamination of the mississippi river which is the main ge and si source to the area and to a smaller extent due to discrimination against ge during biogenic silica bsi production ge si 1 2 1 8 mol mol especially by radiolarians and siliceous sponges ge si 0 6 1 1 mol mol most sediment pore waters ge si 0 3 4 5 mol mol and sediment incubation experiments benthic flux ge si 0 9 1 2 mol mol indicate precipitation of authigenic phases that sequester ge from pore waters non opal sink this process appears to be independent of oxidation reduction reactions and suggests that authigenic aluminosilicate formation reverse weathering may be the dominant ge sink in marine sediments compilation of previously published data shows that in continental margins non opal ge burial flux is controlled by bsi supply while in open ocean sediments it is 10 100 times lower and most likely limited by the supply of lithogenic material we provide a measurement based estimate of the global non opal ge burial flux as 4 32 mmol yr 1 encompassing the 2 16 mmol yr 1 needed to keep the global marine ge cycle at steady state

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

laboratory analysis of dissolution effects on southern ocean polycystine radiolaria abstract laboratory analyses were conducted on siliceous microfauna in holocene and older interglacial samples from the southern ocean to determine dissolution effects on their skeletons examination of siliceous skeletons was made at regular intervals throughout the experiment no major differential dissolution was detected among the dominant southern ocean radiolarian species as only minor variations in relative abundance occurred with increasing degrees of silica dissolution dissolution rate is a function of age of the polycystine radiolaria with higher holocene rates than those registered in the interglacial sample these results serve to strengthen the premise that information about past southern ocean conditions can be reliably acquired from analysis of polycystine radiolarian assemblages preserved in marine sediments

pedogenic modification and structure evolution in palustrine facies as exemplified by the bembridge limestone late eocene of the isle of wight southern england abstract this paper considers the development and evolution of pedogenic structures within palustrine facies and their relationship with those of calcretes as exemplified by the bembridge limestone bl formation upper eocene of the isle of wight within this formation primary lacustrine facies mainly biomicrites have been modified by pedogenesis to varying degrees whilst such changes developed as part of an evolving continuum three structures are recognised to represent evolving stages in this process brecciated nodular clotted peloidal and peloidal ooidal structures a fourth structure laminar is sometimes intercalated with the other three and in places is seen to replace them they are particularly developed in the western outcrops of the formation which represent the palustrine fringes of the main lacustrine bodies the structures are thought to represent the progressive differentiation of the peloidal and ooidal elements from the original lacustrine sediment and appear to be a response to alternations of wetting and drying of the soil under fluctuating climatic conditions the vermiform fabric of the laminar structure is attributed to calcified root mats the general depletion in the heavy o and c isotopes of palustrine facies with respect to the original lacustrine ones is interpreted as being the result of repeated dissolution reprecipitation processes occurring during soil development the palustrine facies of the bl correlates well with an intermediate condition between semi arid and subhumid climates with extensive biological soil modification of freshwater carbonates

shrinkage and sediment supply control on multiple calcrete profile development a case study from the maastrichtian of central india multiple calcrete profiles of the mottled nodular beds form part of an extensive dinosaur bearing infratrappean regolith in central india the profiles have clear variations in the distribution of carbonate morphologies powdery nodular and sheet platy calcretes sheet calcrete is however distinctive and resembles to some extent a k horizon these calcretes are interpreted as having formed in the soil vadose zone profile development was governed mainly by the pattern and depth of shrinkage it is possible that the mature stage 3 to incipient stage 4 calcrete sheets of these shrinkage related profiles formed quite rapidly and certainly in no more than about 400 000 years prominent shrinkage cracking appears to have favoured quite rapid calcrete formation and associated rhizocretion formation was also likely to have been rapid a combination of climatic conditions carbonate availability and volcanism induced sediment starved conditions resulted in the development of a stack of fourteen calcrete profiles sediment starvation allowed most of the stratigraphic interval to be affected to some degree by calcareous pedogenesis this contrasts with other phanerozoic calcrete stacks where nodular carbonate typically occurs in discrete horizons caused by relatively higher sediment supply

biogenic silica and chert in the pacific ocean evidence for the dissolution of biogenic silica at the base of pelagic sections supports the hypothesis that much of the chert formed in the pacific derives from the dissolution and reprecipitation of this silica by hydrothermal waters as ocean bottom waters flow into and through the crust they become warmer initially they remain less saturated with respect to dissolved silica than pore water in the overlying sediments with the diffusion of heat dissolved ions and to some extent the advection of water itself biogenic silica in the basal part of the sedimentary section is dissolved upon conductively cooling these pore waters precipitate chert layers the most common thickness for the basal silica free zone 20 m lies below the most common height of the top of the chert interval above basement 50 m this mode of chert formation explains the frequent occurrence of chert layers at very shallow subbottom depths in pelagic sections of the pacific it is also consistent with the common occurrence of cherts 150 m above basement

imbalance in the carbonate budget of surficial sediments in the north atlantic ocean variations over the last millenium abstract fluxes contributing to the particulate carbonate system in deep sea sediments were investigated at the bengal site in the porcupine abyssal plain northeast atlantic deposition fluxes were estimated using sediment traps at a nominal depth of 3000 m and amounted to 0 37 0 1 mmol c m 2 d 1 dissolution of carbonate was determined using flux of total alkalinity from in situ benthic chambers is 0 4 0 1 mmol c m 2 d 1 burial of carbonate was calculated from data on the carbonate content of the sediment and sedimentation rates from a model age based on 14c dating on foraminifera 0 66 0 1 mmol c m 2 d 1 burial plus dissolution was three times larger than particle deposition flux which indicates that steady state is not achieved in these sediments mass balances for other components bsi 210pb and calculations of the focusing factor using 230th show that lateral inputs play only a minor role in this imbalance decadal variations of annual particle fluxes are also within the uncertainty of our average long term change in dissolution may contribute to the imbalance but can not be the main reason because burial alone is greater than the input flux the observed imbalance is thus the consequence of a large change of carbonate input flux which has occured in the recent past a box model is used to check the response time of the solid carbonate system in these sediments and the time to reach a new steady state is in the order of 3 kyr thus it is likely that the system has been perturbed recently and that large dissolution and burial rates reflect the previously larger particulate carbonate deposition rates we estimate that particulate carbonate fluxes have certainly decreased by a factor of at least 3 and that this change has occurred during the last few centuries

stable isotopic compositions of recent freshwater cyanobacterial carbonates from the british isles local and regional environmental controls recent 50 years old freshwater cyanobacterial carbonates from diverse environments streams lakes waterfalls throughout britain and ireland were analysed for their stable carbon and oxygen isotope compositions the mean 18o value of 5 9 pdb for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central britain 7 5 smow assuming a mean water temperature of 9 c the mean 18o of lake data 4 5 pdb is statistically different reflecting the effects of residence time and or variations in the oxygen isotopic composition of rainfall carbon isotopes have wide variations in both fluviatile and lake data sets 3 to 12 pdb these variations are principally controlled in the fluviatile samples by contribution of isotopically light soil zone carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution lake samples have the heaviest carbon isotope values reflecting a trend toward isotopic equilibrium between atmospheric co2 and aqueous hco 3 we infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information although the effects of stabilization and diagenesis on primary 18o values will need careful consideration primary carbon isotope compositions should be well preserved although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate

pore waters of the central pacific ocean nutrient results interstitial waters from the manop siliceous and calcareous ooze sites in the central pacific ocean were recovered by shipboard squeezing and centrifuging techniques and an in situ harpoon sampler the pore waters were analyzed for nutrients carbonate system species mn 2 ca 2 total alkaline earth metals and dissolved oxygen siliceous ooze site only in calcareous sediments the co 2 alkalinity po 4 3 and ca 2 results obtained from shipboard techniques are significantly different than those recovered in situ the other species measured as well as all of the data from the siliceous ooze site reveal no significant dependence on the method used to sample the pore water the relative changes in o 2 no 3 mn 2 alkalinity and co 2 indicate that respiration using o 2 no 3 and mno 2 as electron acceptors is the dominant reaction affecting the pore water species we develop a model which simulates the fate of pore water oxygen and nitrate and particulate organic carbon in sediments this model includes the effects of pore water diffusion oxygen and nitrate respiration sediment accumulation sediment mixing and changes in sediment porosity we observe that factor of 2 variations in the rates of sediment mixing and accumulation have only a minor effect on the pore water profiles the major factor controlling the pore water profiles is the flux of organic carbon across the sediment water interface we conclude that the large intra site variability observed in the interstitial water nitrate profiles is probably caused by small scale variations in the flux of organic material

dissolved al in and ce in the eastern indian ocean and the southeast asian seas in comparison with the radionuclides 210pb and 210po to carry out comparative geochemical investigation of refractory and reactive metals in different oceanic settings covering different s characteristics productivity dissolved oxygen profiles water and sediment discharge etc we have determined the vertical profiles of dissolved 0 04 m al in and ce as well as 210pb and 210po in the eastern indian ocean from 40 s in the southern ocean to 8 n in the bay of bengal and the southeast asian seas in the antarctic circumpolar region the concentrations of these refractory metals are very low presumably due to very low the atmospheric input and intensified scavenging resemblance in the vertical profiles of these metals is often seen in some other stations however there are also significant differences among their distributions for example in the magnitude of surface enrichment caused by the external input from eolian and fluvial coastal sources comparison of al distributions in surface waters with those of atmospherically derived 210pb suggests the relative importance of eolian input over fluvial coastal sources fluvial and coastal input appears to be insignificant for dissolved in but may be important for ce the mean residence time of al in the surface mixed layer was estimated to be 2 years which is similar to that of 210pb in the intermediate and deep waters the concentrations of each element vary with depth and location the range of variation is in the order of al ce in depending upon particle reactivity although dissolved al decreases along the water trajectory by particle scavenging variations of dissolved in and ce are relatively small which may be due to less scavenging for both elements compared with significantly high 4 pm dissolved ce throughout the water column in the bay of bengal dissolved al concentration remains low suggesting that it has higher affinity to particles and hence is scavenged by sinking particulate matter this is consistent with the observation that the dissolved al in the antarctic intermediate water aaiw decreases from 4 to 6 nm in the 30 s perth basin to 0 7 nm in the 10 s west australia basin along its trajectory using the chlorofluorocarbons cfcs ventilation age of aaiw fine 1993 the mean residence time of al in the intermediate and deep waters in the eastern indian ocean is estimated to be 17 yr approximately the same as that of 210pb 10 15 yr in the semiclosed basins of southeast asia the distributions of al in and ce are also very unique in the south china sea there is a strong sediment source for dissolved in and ce during the deepwater passage through the luzon strait

middle albian climate fluctuation recorded in the carbon isotope composition of terrestrial plant matter abstract this study presents the carbon isotopic record for terrestrial plant matter 13ctpm in the jinju formation gyeongsang basin korea during the middle albian the measured 13ctpm provides continuous high resolution temporal variations for reconstructing climate change during the middle albian which has previously been poorly understood we found that the 13ctpm variation mostly exceeds the isotopic variation of the contemporaneous atmospheric co2 indicating that the variation was primarily governed by climate change rather than atmospheric source the 13ctpm values corrected to modern atmospheric co2 show cyclic fluctuations 27 8 to 23 3 reflecting a temporal variation of water availability and or a related taxonomic turnover of plant communities in the hinterland of jinju lake based on a transfer function for estimating mean annual rainfall mar from the measured 13ctpm values the middle albian climate of the basin was found to vary from sub humid to humid conditions mar 500 1500 mm this variability suggests that albian climate change at middle latitudes occurred more frequently than previously interpreted the temporal increase in aridity observed in the basin 35 38 n has not been detected in the isotopic records of the cretaceous hokkaido section 42 45 n in japan this difference implies the possibility of a periodic northward shift or expansion of the northern hemisphere subtropical high pressure belt

lacustrine and palustrine facies in the bembridge limestone late eocene hampshire basin of the isle of wight southern england abstract the carbonate lake system represented by the late eocene bembridge limestone formation isle of wight southern england comprises two main facies lacustrine and palustrine these facies are arranged vertically in transgressive regressive cycles corresponding to a model of carbonate lakes of low gradient and fluctuating margins with extensive palustrine fringes these lakes developed in a coastal plain of limited relief where two paleogeographical domains predominate a lacustrine domain is represented in northern and eastern sections in the isle of wight by cycles representing upward passage from central lacustrine sub facies marl marly limestone through marginal lacustrine sub facies biomicrite to sub facies indicative of exposure brecciated nodular limestone a palustrine domain predominant in west wight is represented by a predominantly pedogenic palustrine facies with clotted peloidal to ooidal textures and some intercalated laminated laminar calcrete horizons within the pedogenic facies textures have evolved from those of unaltered biomicrites through clotted peloidal to dense ooidal to open ooidal textures a third domain developed in close geographical proximity to more saline waters is represented by gypsiferous lake margin facies found in north wight in which microlenticular gypsum developed post depositionally as a result of evaporation following subaerial sediment exposure in the lacustrine domain there appears to be an association between cyclicity and changes in base sea level reflecting a likelihood that the lakes were part of a paralic coastal plain complex with distal marine connections alternatively the cyclicity might have developed as a result of the alternation of wetter and drier climatic periods

fresh water carbonates from the lower freshwater molasse oligocene western switzerland sedimentology and stable isotopes abstract the lower freshwater molasse of western switzerland comprises a thick series of continental deposits of late oligocene early miocene age fresh water carbonates occur at two main horizons within this succession lower chattian palustrine carbonates calcaires inferieurs show a shallow fresh water fauna flora of ostracods and charophytes but display clear evidence of subaerial exposure in the form of glaebule pisoid formation circumgranular cracking rhizoliths and microkarstic cavities repeated desiccation led to locally intense modification by pedogenesis these horizons record the development of shallow ephemeral lakes at the northern margin of the swiss molasse basin stable isotope analyses were carried out on 46 calcite samples data from matrix and intraclasts reveal typical fresh water compositions 13c 5 to 7 5 18o 5 5 to 9 a weak co variant trend suggests deposition in hydrologically closed lakes although the range of 13c values recorded is also consistent with pedogenetic overprinting associated with subaerial exposure spar cements and vadose crystal silts display 13c compositions from 6 to 7 but show light 18o values from 10 to 11 recording formation from meteoric waters upper chattian carbonates calcaires d eau douce et dolomie include algal ostracodal laminites interpreted as profundal lake deposits as well as bioturbated shallow lake charophyte ostracod mudstones and wackestones sandy wackestones and white dolomite stable isotope analyses 20 calcites 2 dolomites show 13c values from 2 to 6 and 18o from 6 to 11 data for laminites and biomicrites plot in different fields variations in carbon isotopic composition may be attributable to higher organic productivity during high lake stands the laminites show heavier 13c values or to areal differences in the proportions of biogenic authigenic and detrital carbonate 13c values are generally higher in areas of greater detrital carbonate supply the heavier 18o values shown by the dolomites 13 c 3 18 o 0 to 1 suggest formation from evolved evaporitic lake waters these carbonates record deposition in an extensive possibly deeper lake complex subject to clastic input from the alps in the south

palaeoclimate and palaeovegetation in central india during the upper cretaceous based on stable isotope composition of the palaeosol carbonates abstract the oxygen isotope compositions of the pedogenic carbonates formed on the sediments of the lameta formation of central india during the upper cretaceous range from 6 7 to 8 9 estimates of the oxygen isotope composition of the soil water in equilibrium with the carbonates suggest average meteoric water composition of 8 this value is considerably lighter compared to the modern precipitation in central india 3 the lighter oxygen isotope composition can be explained in terms of cumulative effects of highly seasonal monsoon like climatic regime in a rain shadow zone and a more pronounced continental effect due to a bigger size of cretaceous india the carbon isotopic compositions of the lameta carbonates range from 7 1 to 10 7 with an average of 9 1 suggesting pedogenesis in soils dominated by c 3 type of vegetation the estimated average composition of the vegetation is about 3 enriched compared to the modern day c 3 vegetation this is probably due to atmospheric influence contributing about 15 of the total co 2 in the soil an analysis of this contribution using the model of cerling 1991 indicates that the partial pressure of co 2 in the late cretaceous atmosphere was 800 12 000 ppmv

stable isotopic results from paleosol carbonate in south asia paleoenvironmental reconstructions and selective alteration article i nfo we measured 18 o and 13 c values of paleosol carbonate nodules from a variety of sedimentary units in southern asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration paleosol carbonate nodules were collected from lower to upper cretaceous strata exposed in two locations in southern tibet and from lower to middle miocene strata in northern india and nepal additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values based on the implausibly low 18 o values 13 of most of the marine carbonate samples we interpret the 18 o values of the associated paleosol carbonate nodules as being reset and therefore unreliable for paleoenvironmental or paleoelevation reconstruction importantly the 18 o values of 13 c values of marine carbonate rocks fall within the expected primary

concentration of carbon dioxide in the late cretaceous atmosphere stable carbon isotope data from late cretaceous maastrichtian palaeosols in india are used to estimate the concentration of carbon dioxide in the late cretaceous atmosphere we show that the maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of co 2 this value agrees with an independently modeled value of co 2 in the late cretaceous atmosphere a low concentration of the greenhouse gas carbon dioxide in the maastrichtian atmosphere relative to concentrations in the earlier cretaceous is consistent with palaeotemperature information from terrestrial plant and marine fossils which suggest that the global climate cooled toward the end of the cretaceous period

pedogenic carbonates in texas stable isotope distributions and their implications for reconstructing region wide paleoenvironments abstract pedogenic carbonates are ubiquitous in paleosols through geologic history and have been widely used to speculate on paleoclimatic conditions during their formation they are widespread and well developed in large areas of texas a majority are of late quaternary age and have formed across a range of climatic conditions on various types of substrates to evaluate the usefulness of pedogenic carbonates as environmental indicators this study investigates regional scale trends in stable isotope compositions of pedogenic carbonates across approximately 900 km of texas the 13c values of 49 pedogenic carbonate profiles 182 analyses on various host strata e g limestone igneous rocks range from 10 6 to 0 7 v pdb most 13c values are evenly distributed between 9 and 1 and the 18o values range from 9 1 to 0 2 v pdb mainly between 6 and 2 there is no correlation between carbon and oxygen isotopic values r2 0 0002 pedogenic carbonates in the texas gulf coastal plains southern high plains and west texas exhibit higher 13c values than those in south and central texas which corresponds to the spatial change in vegetation between c4 dominated and c3 dominated plants the marked increase in 13c values of the pedogenic carbonates from the tertiary strata into the overlying quaternary strata confirms the invasion of a c4 biomass into the southern high plains since the early pliocene from east to west the 18o values of late quaternary pedogenic carbonates decrease gradually a trend that mimics the spatial variation of 18o values of modern meteoric water primarily due to the increased distance from the gulf of mexico source of most of the meteoric water in contrast to the regional trends the stable isotope values of some pedogenic carbonates developed on marine limestone and calcareous alluvium in central texas and south texas have isotopic signatures inherited from the host strata in addition some of the 13c values of pedogenic carbonate nodules in the gulf coastal plains have been affected by saline groundwater soil carbonates formed in the shallow parts of the profile such as petrocalcic horizons may have also been influenced by the atmospheric co2 nevertheless climatic trends are readily apparent in the isotopic data thus demonstrating their potential value in region wide paleoclimatic analyses

estimating rates of calcrete formation and sediment accretion in ancient alluvial deposits the use of calcrete horizons as a means of assessing rates of sediment accretion in ancient alluvial sequences is reviewed any attempt to use such horizons in quantifying ancient alluvial deposition must appreciate that accurate data on rates of formation of quaternary calcretes are limited such data show considerable variations in the rates and no reliable data exist at all for some calcrete types the abundance of calcretes in the geological record warrants a new initiative to improve our understanding oftheir origins and rates of formation

a review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction diatom silica frustules are a form of biogenic opal and contain oxygen isotopes that are being increasingly used in palaeoclimate studies frustules are comprised of an inner tetrahedrally bonded silica skeleton si o si with an outer hydrous layer the hydrous layer is freely exchangeable and must be removed prior to oxygen isotope measurement using oxidising reagents and or high temperatures analysis of the oxygen isotope composition of diatom silica requires samples that are almost pure diatomite since extraction techniques will liberate oxygen from all the components in the sediment there is a generally acceptable protocol involving chemistry sieving and settling techniques and more recently laminar flow separation recent studies of lacustrine diatoms have shown that even a small proportion of contaminant can have a significant influence on the oxygen isotope value all lake sediments require their own specific procedure and every sample must be scrutinised by microscopy to check for the level of contamination prior to analysis where sediment cannot be purified sufficiently a semi quantitative assessment of the diatom content can facilitate mass balance techniques when robust preparation methods are used diatom silica offers an important palaeoclimate proxy providing an additional complementary rather than an alternative host of oxygen isotopes in carbonates in lacustrine isotope studies it is often assumed but rarely proven that diatom silica form in isotope equilibrium and hence empirically derived palaeotemperature equations usually made in vitro can be used most studies lack the detailed investigation of contemporaneous materials from natural waters of the region under study to test these equations further investigations need to be conducted in order to understand the systematic relationship between temperature water isotope composition and diatom isotope composition to enable quantitative interpretation of the sediment record experiments to test for vital effects and inter specific differences have so far revealed little variation it is useful to know when and where the diatom silica is formed in the modern environment so details of diatom ecology are important in the interpretation of isotope data here we show that valuable palaeoclimate data can be gained from the oxygen isotope composition of diatom silica 18odiatom especially since diatoms are abundant in many lakes sensitive to climate variation where other hosts e g carbonates are absent to date the most successful studies have been conducted in areas where the 18odiatom registers changes in the oxygen isotope composition of the lake water rather than temperature which is then related to other aspects of climate in these studies the range of values obtained is often greater than the error introduced by contaminating materials

structure of a silica diagenetic transformation zone the gjallar ridge offshore norway three dimensional seismic data from the gjallar ridge were used together with x ray diffraction data scientific boreholes and wireline logs to analyse the seismic structure of a silica diagenetic transformation zone the following features were identified i an interval some 150 to 300 m thick that contains anomalously high amplitude reflections ii a strong reflection event at the top of this interval which cross cuts stratigraphy interpreted as the transformation boundary between opal a rich and opal ct rich sediment iii amplitude variations on stratigraphic reflections within the interval attributed to variations in the proportions of opal a and opal ct and iv a second deeper cross cutting reflection event within the interval interpreted as the transformation boundary between opal ct rich and quartz rich sediment the base of the interval containing the anomalously high amplitude reflections is interpreted as a stratigraphic reflection demarcating the base of the silica rich strata on a stratigraphic reflection within the interval of high amplitudes roughly circular regions of anomalously high amplitude with diameters of 0 8 to 2 5 km are separated by lower amplitude regions this pattern is similar to the cells previously identified at the opal a to opal ct transformation boundary and probably results from more complete transformation of opal a to opal ct all of these observations provide the first recognition from seismic data that silica diagenetic transformations are not always narrow boundaries represented by single cross cutting seismic reflection events as implied previously but can be heterogeneous and hundreds of metres in thickness as observed at outcrop

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

effect of trace metal limited growth on the postmortem dissolution of the marine diatom pseudo nitzschia delicatissima we investigated the effects of iron fe and copper cu limitations on biogenic silica bsio 2 dissolution kinetics of the marine diatom pseudo nitzschia delicatissima during a 3 week batch dissolution experiment the dissolution of this species was faster during the first week than thereafter modeling results from four dissolution models and scanning electron microcopy images suggested the successive dissolution of two phases of bsio 2 with two different dissolution constants micronutrient limitation during growth affected the respective proportion of the two phases and their dissolution constants after 3 weeks of dissolution frustules from micronutrient limited diatoms were better preserved than those of replete cells our results also confirm that micronutrient limited cells may export more si relative to n than replete cells and may increase the silicate pump this may not only be due to a higher degree of silicification of the live cells but also to a decoupling between the recycling of si and n during dissolution we suggest that a mechanistic understanding of the evolution of the dissolution constant during dissolution is needed this would improve the parameterization of dissolution in ecosystem models and ultimately their predictions on the amount of bsio 2 that dissolves in the photic zone and the amount of bsio 2 that is exported to the seafloor

caliche as a geological repository for atmospheric sulfate 1 recent studies demonstrate that important information on sulfur source oxidation pathway transport pattern and reaction kinetics of atmospheric oxidation of sulfur gases can be uncovered by measuring multiple isotope compositions of the oxidation product secondary atmospheric sulfate sas sas from earth s distant past however is rarely preserved in the rock records because of its high solubility and small quantity we report here from the measurement of 47 modern and fossil caliche samples that caliches contain variable amounts of carbonate associated sulfate cas and the 17o values of the cas range from 0 12 to 2 32 with most values higher than the background value of 0 05 for seawater sulfate indicating the presence of an sas component derived from the oxidation of sulfur gases by atmospheric ozone or related oxidants this study demonstrates that caliche a pedogenic carbonate common in the geologic record could serve as a repository for ancient sas

chert in the pacific biogenic silica and hydrothermal circulation abstract data on sections drilled by dsdp and odp in the pacific have been compiled for 187 sites 105 of which contain chert the spatial pattern of siliceous deposits in the pacific generally follows the pattern of biologic productivity there is some evidence that enhanced vertical diffusivity in the ocean during the eocene warm climate gave rise to siliceous deposits on and near bathymetric highs and basin margins the most common occurrence of chert is in eocene and older sections however cherts do occur in sections as young as 7 ma in the sites investigated over half of the youngest chert occurrences in sedimentary sections are within 150 m of basement nearly all the chert occurrences on crust younger than 60 ma are within 150 m of basement the deficit in heat flow over ocean crust younger than 60 ma is explained as the result of heat advection by hydrothermal waters circulating in the upper part of the ocean crust these waters appear to dissolve biogenic silica and deposit it as chert in the lower parts of sedimentary sections diffusion of these waters into the lower sediment section is enhanced by small scale faulting this faulting may be associated with intra plate stresses that develop during ridge jumps and reorientations of plate motion the relatively warm bottom waters of the early cenozoic may have also enhanced the dissolution of biogenic silica during hydrothermal circulation in the upper oceanic crust and basal sediment section

what controls opal preservation in tropical deep sea sediments measurements of opal preservation in deep sea sediment cores have been presented in three ways the opal concentration as a fraction of total dry weight opaltot the opal concentration normalized to calcite free dry weight opalcalcite free and me opal accumulation rate opal mar it is tempting to interpret changes in these indices as indicators of rates of biological production in past oceans based on theoretical constraints we argue that in typical tropical and subtropical sediments both opalcalcite free and opal mar reflect a significant artifact of dilution by other phases thus the band of high opalcalcite free in the equatorial pacific appears to be caused in large part by the high calcite in that region rather than by high opal productivity the best candidate for a reliable paleoproductivity proxy appears to be opaltot unfortunately present day opaltot data from tropical and subtropical regions show little or no systematic trend with the rain rate of opal pore water silica concentration data reveal that the apparent pore water opal solubility is not constant but correlates regionally with the rain rate of opal to the seafloor a model that treats opal as a single homogeneous phase with a single well defined solubility product predicts a strong dependence of opal concentration on rain rate in stark contrast to the data and a constant asymptotic pore water si two models representing opal as multiple heterogeneous phases with different solubilities are able to reproduce the observed asymptotic pore water si rain rate relationship but not the lack of rain rate trend in the opal concentration data only by assuming a systematic trend in the quality of opal i e the solubility as a function of opal production can we reproduce the observed pattern of opal preservation the implication of this study is that changes in opal preservation in the geologic record cannot simply be interpreted in terms of changes in surface ocean productivity until our understanding of opal diagenesis can be improved

the benthic silica cycle in the northeast atlantic annual mass balance seasonality and importance of non steady state processes for the early diagenesis of biogenic opal in deep sea sediments within the framework of the eu funded bengal programme the effects of seasonality on biogenic silica early diagenesis have been studied at the porcupine abyssal plain pap an abyssal locality located in the northeast atlantic ocean nine cruises were carried out between august 1996 and august 1998 silicic acid dsi increased downward from 46 2 to 213 m mean of 27 profiles biogenic silica bsi decreased from ca 2 near the sediment water interface to 1 at depth benthic silicic acid fluxes as measured from benthic chambers were close to those estimated from non linear dsi porewater gradients some 90 of the dissolution occurred within the top 5 5 cm of the sediment column rather than at the sediment water interface and the annual dsi efflux was close to 0 057 mol si m 2 yr 1 biogenic silica accumulation was close to 0 008 mol si m 2 yr 1 and the annual opal delivery reconstructed from sedimentary fluxes assuming steady state was 0 065 mol si m 2 yr 1 this is in good agreement with the mean annual opal flux determined from sediment trap samples averaged over the last decade 0 062 mol si m 2 yr 1 thus ca 12 of the opal flux delivered to the seafloor get preserved in the sediments a simple comparison between the sedimentation rate and the dissolution rate in the uppermost 5 5 cm of the sediment column suggests that there should be no accumulation of opal in pap sediments however by combining the bengal high sampling frequency with our experimental results on bsi dissolution we conclude that non steady state processes associated with the seasonal deposition of fresh biogenic particles may well play a fundamental role in the preservation of bsi in these sediments this comes about though the way seasonal variability affects the quality of the biogenic matter reaching the seafloor hence it influences the intrinsic dissolution properties of the opal at the seafloor and also the part played by non local mixing events by ensuring the rapid transport of bsi particles deep into the sediment to where saturation is reached

rapid post mortem maturation of diatom silica oxygen isotope values 1 oxygen isotope values of diatom silica 18odiatom are increasingly used as paleoclimate proxies however the magnitude and timing of post mortem alteration of 18odiatom values has been unclear in freshwater diatom silica from a human made pond in northern new mexico post mortem alteration of 18odiatom values occurs within one year of sediment burial diatom silica collected antemortem has an average 18odiatom value of 21 5 vsmow 1 3 n 23 whereas diatom silica from two sediment cores from the same freshwater environment records significantly higher 18odiatom values 28 9 0 8 n 13 the difference in ante and post mortem 18odiatom values indicate post mortem alteration of diatom silica oxygen that results in a 7 increase in 18o values this study demonstrates that 18odiatom values reach mature values within 0 5 years of frustule death initial diatom 18o values that record growing conditions are rapidly overwritten during silica maturation and the mature diatom 18o values approach isotopic equilibrium for quartz water the rapid post mortem alteration of diatom 18o values explains much of the disparate data regarding silica water fractionation for diatom silica and has a profound effect on the use of diatom silica 18o values as a paleoclimate proxy in lacustrine and marine environments

radiolarian assemblage as an indicator of environmental conditions in the marginal seas of the western north pacific abstract in this study we analyzed 45 surface sediment samples collected in the marginal seas of the western north pacific including the south china sea the east china sea and the philippine sea to investigate the radiolarian assemblages and their relationship with upper layer environmental conditions based on the results of q mode cluster analysis the radiolarian assemblages can be divided into four clusters corresponding to the north equatorial current assemblage north equatorial current bifurcation assemblage kuroshio south china sea assemblage and kuroshio east china sea assemblage winter sea surface temperature sstw winter sea surface salinity sssw and annual silicate concentration were the most significant environmental variables associated with the radiolarian assemblages among which sstw showed the highest correlation with the radiolarian fauna the significant influences of sstw and sssw suggested that the seasonal change of the north equatorial current kuroshio current system exerted a crucial effect on the abundance and distribution pattern of the radiolarian fauna

seasonal wetland carbonate sequences and dynamic catenas a re appraisal of palustrine limestones abstract palustrine carbonate cyclothems are compared directly to well documented peritidal carbonate cyclothems in the case of the latter the trend of increasing degree of exposure seen vertically through a cyclothem has been interpreted as due to the aggradation of the sediment surface relative to the semi diurnal tidal regime palustrine cyclothems also show similar increases in the degree of exposure and this is interpreted as the effect of sediment aggradation in a seasonal wetland regime the resulting changes in the drainage characteristic revealed in a palustrinc cyclothem reflect a type of seasonally variable catenary relationship referred to here as a dynamic catena this model explains the key features of palustrine cyclothems and suggests the importance of seasonal wetland environments in ancient continental settings

the oldest record of microbial caddisfly bioherms from the early cretaceous jinju formation korea occurrence and palaeoenvironmental implications abstract fossil microbial caddisfly bioherms have been recently discovered in the early cretaceous lacustrine deposits jinju formation at jahyeri korea the jahyeri deposits consist of shallow to marginal lake deposits in which medium to fine grained sandstone beds and silty mudstone beds are alternated and small scale wave ripples and polygonal desiccation cracks are common the microbial caddisfly bioherms occur on and within oolitic sandstone and are also covered by oolitic sandstone suggesting that the bioherms formed in shallow and turbulent water the depositional condition of jahyeri caddisfly bioherms is thus correspondent with the wave washed and well oxygenated biotope of modern lentic trichoptera by comparing the habitat size and shape of cases the composition of case building particles and case construction way it seems likely that the jahyeri caddisfly cases were those of the family leptoceridae the jahyeri microbial caddisfly bioherms are all that have been discovered throughout the jinju formation and the jahyeri bioherms are very small compared with the tall growth of the eocene little mesa bioherms the limited growth and occurrence of microbial caddisfly bioherms in the jinju formation might have resulted from the predominance of clastic deposition in the jinju lake the occurrence of jahyeri microbial caddisfly bioherms may reflect the development of a drought stage which resulted in a limited supply of clastic sediments into the jahyeri lake the jahyeri microbial caddisfly bioherms have common features with modern and tertiary microbial caddisfly bioherms in that the colonial caddis cases constructed bioherms in cooperation with a benthic microbial mat the similarity between the jahyeri microbial caddisfly bioherms and those from the tertiary and modern deposits suggests that the physical environments of microbial caddisfly symbiosis has changed little throughout the geologic time and space and thus indicates that the microbial caddisfly bioherms can be used to interpret paleohydrological conditions this finding is the first report of fossil microbial caddisfly bioherms in asia and represents the oldest occurrence of microbial caddisfly bioherms in the geological records

biogenic silica recycling in surficial sediments across the polar front of the southern ocean indian sector abstract the processes controlling preservation and recycling of particulate biogenic silica in superficial sediments must be understood before one uses biogenic silica as a proxy in paleooceanographic studies and in order to compute oceanic mass balances for silica in this respect the antarctic ocean is certainly a key region due to its high productivity and export of biogenic silica in order to quantify sedimentary fluxes and identify crucial processes that allow the preservation of biogenic silica pore water and solid phase silica profiles were performed on sediment cores from the southern ocean indian sector during the antares 1 cruise in combination with solubility data reported by van cappellen and qiu 1997a a process model representing the early diagenesis of silica was developed in this model a dependence with depth of the kinetic constant was introduced to allow the preservation of biogenic silica in sediment porewater undersaturated with respect to that phase using this steady state model it is proposed that a proportionality of the reactivity of the biogenic silica with its settling flux is necessary to explain the observed profiles it is then shown using this model that the preservation of biogenic silica is not a linear function of the deposited flux using a modified version of this model containing an explicit term of reprecipitation we hypothesize that reprecipitation alone cannot counterbalance dissolution and that its effect is certainly related to a decrease in either surface solubility or kinetics of dissolution

regional paleohydrologic and paleoclimatic settings of wetland lacustrine depositional systems in the morrison formation upper jurassic western interior usa abstract during deposition of the upper jurassic morrison formation water that originated as precipitation in uplands to the west of the western interior depositional basin infiltrated regional aquifers that underlay the basin this regional groundwater system delivered water into the otherwise dry continental interior basin where it discharged to form two major wetland lacustrine successions a freshwater carbonate wetland lacustrine succession formed in the distal reaches of the basin where regional groundwater discharged into the denver julesburg basin which was a smaller structural basin within the more extensive western interior depositional basin an alkaline saline wetland lacustrine complex lake t oo dichi formed farther upstream where shallower aquifers discharged into the san juan paradox basin which was another small structural basin in the western interior depositional basin these were both wetlands in the sense that groundwater was the major source of water input from surface and meteoric water was limited in both basins lacustrine conditions developed during episodes of increased input of surface water inclusion of wetlands in our interpretation of what had previously been considered largely lacustrine systems has important implications for paleohydrology and paleoclimatology the distal carbonate wetland lacustrine deposits are well developed in the morrison formation of east central colorado occupying a stratigraphic interval that is equivalent to the lower morrison but extends into the upper morrison formation sedimentologic paleontologic and isotopic evidence indicate that regional groundwater discharge maintained shallow hydrologically open well oxygenated perennial carbonate wetlands and lakes despite the semi arid climate wetland deposits include charophyte rich wackestone and green mudstone lacustrine episodes in which surface water input was significant were times of carbonate and siliciclastic deposition in scarce deltaic and shoreline deposits marginal lacustrine deposits include ooid and skeletal packstone grainstone siltstone and sandstone distal lacustrine units are skeletal mudstone wackestone microbialites and laminated siliciclastic mudstone differentiation between wetlands and distal lacustrine units is not always possible palustrine features magadi type chert mtc and evaporites record episodes of increased aridity and exposure farther upstream during deposition of the upper part of the brushy basin member the ancestral uncompahgre uplift imposed a barrier to shallow eastward flowing groundwater that discharged into the san juan paradox basin on the upstream side of the uplift this created the closed hydrologic setting necessary for development of an alkaline saline wetland lacustrine complex lake t oo dichi silicic volcanic ash delivered by prevailing winds from calderas west and southwest of the basin contributed to the pore water evolution in the sediments a distinctive lateral hydrogeochemical gradient reflecting increasing salinity and alkalinity in the pore waters altered the ash to a variety of authigenic minerals that define concentric zones within the basin the basinward progression of diagenetic mineral zones is smectite clinoptilolite analcime potassium feldspar albite the groundwater fed wetlands were shallow and frequently evaporated to dryness scarce laminated gray mudstone beds record distinct episodes of freshwater lacustrine deposition that resulted from intermittent streams that carried detritus well out into the basin

calcretes related to phreatophytic vegetation from the middle triassic otter sandstone of south west england carbonate cementation in the triassic otter sandstone of budleigh salterton sw england occurs in two distinct forms large vertical concentrically zoned cyclinders and thin subhorizontal sheets the former represent rhizocretions of the tap roots of phreatophytic plants which colonized bars and abandoned channels on a large braidplain the sheets represent cementation around ancient water tables the precipitation of the rhizocretions took place at least in part during the life of the plants and 13c and 18o values support the view that evapo transpiration induced carbonate precipitation palaeosol profiles are rare in the otter sandstone reflecting the geomorphological instability of the braidplain surfaces in contrast rhizocretionary and sheet calcretes which formed several metres below the active depositional surface are abundant because they had a high preservation potential

near surface shrinkage and carbonate replacement processes arran cornstone formation scotland a 47 m thick succession of conglomerates sandstones and mudstones of late devonian or early carboniferous age outcrops at fallen rocks in northeast arran western scotland it is defined here as the type section of the arran cornstone formation at numerous levels in the succession varieties of fissures and carbonate concretions formed during the accumulation of the formation the fissures opened as a result of drying shrinkage and were closed again either by filling with different sediment or by wetting and expansion of the fissure wall sediment carbonate concretions form complete beds discontinuous bedding concordant sheets or bedding discordant nodules or rods the rod cornstones these concretions formed close enough to the surface to be incorporated after erosion and redeposition as clasts into overlying beds the concretions were formed by growth of micrite mainly by replacement but shrinkage displacement played an important role in subsequently fracturing and reworking the micrite the micrite was also locally replaced by microspar and spar and this involved dissolution and precipitation no independent evidence of biological influence in any of these processes has been found

carbonate paleosol genesis in the plio pleistocene st david formation southeastern arizona abstract we use soil developmental criteria to interpret carbonate paleosol genesis in the plio pleistocene st david formation southeastern arizona our study of six paleosol sections indicates that pedogenesis varied during the time the st david formation was deposited as well as in different depositional environments paleosol features range from those common to modern well drained surface soils requiring long periods of stability to those indicating hydromorphic soil processes and cumulic pedogenesis differentiating these pedogenic processes helps to interpret carbon and oxygen isotope data vadose zone paleosols reflect paleoenvironment better than hydromorphic paleosols because the likelihood of detrital carbonate and ground water contamination is less the morphology and texture of paleosols that formed above the influence of the ground water table vadose are similar to those of nongravelly well drained quaternary soils developed in arid regions carbonate enriched zones are beneath clay rich carbonate depleted zones carbonate is disseminated in the matrix and is segregated into small 1 cm diameter nodules filaments and seams well developed carbonates are massive layers of increased clay accumulation have a higher ratio of fine to coarse or to total clay than overlying or underlying layers indicating that clay in these layers was probably translocated paleosols that formed within the influence of the ground water table hydromorphic have carbonate and clay accumulations unlike those found in modern well drained surface soils carbonate is segregated into large 2 10 cm diameter subspherical masses glaebules in a noncalcareous or weakly calcareous matrix layers of increased clay accumulation seldom have a genetic relation to zones of increased carbonate these clay rich layers lie above or below or correspond to the zones of carbonate aggregates

does burial diagenesis reset pristine isotopic compositions in paleosol carbonates abstract sedimentological study of early oligocene continental carbonates from the fluvial dagshai formation of the himalayan foreland basin india resulted in the recognition of four different types namely soil palustrine pedogenically modified palustrine and groundwater carbonates stable oxygen and carbon isotopic 18 o and 13 c analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep burial diagenesis complete isotopic homogenization does not occur 18 o and 13 c analyses of 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with 18 o of more robust bioapatite fossil vertebrate tooth phase show that dense micrites 70 carbonate invariably preserve the pristine 18 o value mean of 9 8 while altered carbonates show much lower 18 o value 13 8 such inhomogeneity causes large intra sample and intra soil profile variability as high as 5 suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains a simple fluid rock interaction model suggests active participation of clay minerals to enhance the effect of fluid rock ratio in local domains during diagenesis this places an upper limit of 70 micrite concentration above which the effect of diagenetic alteration is minimal careful sampling of dense micritic part of the soil carbonate nodules therefore does provide pristine isotopic composition and it is inappropriate as proposed recently to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis based on pristine 13 c value of 8 8 0 2 in soil carbonates an atmospheric co 2 concentration between 764 and 306 ppmv is estimated for the early oligocene 31 ma dagshai time these data show excellent agreement between two independent proxy records viz soil carbonate and marine alkenone and support early oligocene survival of the antarctic ice sheet

continental brackish and marine carbonates from the lower cretaceous of kolone barbariga istria croatia stratigraphy sedimentology and geochemistry abstract during the early cretaceous wide areas of the dinaric adriatic carbonate platform emerged for long periods the hauterivian barremian carbonates from kolone barbariga show a few typical examples of lacustrine facies with dinosaur bones and brackish palustrine facies the sequence of the platform is made for the most part by subtidal and intertidal limestones the bone levels are located in a large depression few meters deep in the uppermost hauterivian marine limestones the filling facies of this depression are made by oncolitic rudstones and algal boundstones which represent marginal lacustrine facies and by laminated limestones thin stromatolitic levels and distal fringes of rudstones which represent relatively open lacustrine facies the fossil content is characterized by rare charophyte stems ostracods gastropods and plant remains while typical marine fauna is absent at the hauterivian barremian boundary a major emersion event has been observed then a slow transgressive phase occurred the transgressive facies are primarily made by mudstones with ostracods charophytes and spirillina brackish and probably freshwater facies wackestones with ophtalmidiidae and rare dasyclad algae storm layers with gastropods and miliolids and breccia like dinoturbated beds wackstones packstones and very rich in dasyclad grainstones outcrop at the top of the section representing the maximum of the transgression trace elements content carbon and oxygen stable isotope analyses have been performed to aid the palaeoenvironmental interpretation in this geological setting barium seems to discriminate between brackish and freshwater facies the isotopic values of the marine carbonates appear to depend on early diagenetic processes meanwhile lacustrine facies seem to show a weak signal of the depositional environment

forced regressive shoreface sandstone from himalayan foreland implications to early himalayan tectonic evolution abstract sedimentology and sequence stratigraphic analysis of the 31 ma old marker white sandstone unit from the subathu sub basin nw himalayan foreland suggest it to be a forced regressive wedge frw formed during the transition from the marine subathu formation to the continental dagshai formation the frw is bounded between the surf diastem below and type 1 unconformity at the top and differs from rsme regressive surface of marine erosion occurring below bounded frws described from other classical coastal foreland settings correct identification of bounding surfaces of a frw has an important implication to the estimation of rate of relative sea level rsl fall a faster rate of rsl fall higher than the sedimentation rate has been postulated for the erosion of the lower shoreface and rsme using the logged thickness of the subathu dagshai transition zone including the white sandstone bounded between the surf diastem and unconformity available chronology and eustatic sea level fall 0 023 mm year at 31 ma a higher rsl fall than the sedimentation rate 0 07 mm year has been inferred during the deposition of the white sandstone petrography of sandstones and their sr and nd isotopic compositions indicate a major provenance switch over from dominant mafic ultramafic to metamorphic source from white sandstone 31 ma onwards attesting the link between hinterland tectonics provenance and forced regression the provenance switch over at 31 ma was earlier inferred to be driven by proto himalayan thrust propagation in the foreland using a simple isostatic model on the contrary a mechanism of accelerated surface uplift at a rate of 0 10 0 15 mm year is suggested for both provenance change and forced regression

regional to global correlation of lower cretaceous hauterivian barremian shallow water carbonates of the southern apennines italy and dinarides montenegro southern tethyan margin abstract we propose a high resolution regional to global scale correlation of two hauterivian barremian shallow water carbonate platform sections belonging to different palaeogeographic domains of the southern margin of the tethys these successions are now located more than 500 km apart and are represented by 137 m of core drilled at monte raggeto southern apennines italy and by 80 m of well stratified rocks cropping out in the podgorica mountains dinarides montenegro they display three superimposed orders of stratigraphic cyclicity defined by elementary cycles grouped into bundles and superbundles and attributed to orbitally induced composite sea level fluctuations elementary cycles are interpreted as the precession and the obliquity periodicities 20 40 ky while bundles and superbundles correspond to the short 100 ky and long 400 ky eccentricity cycles respectively as both the ratios between the elementary cycles and the bundles and between the bundles and the superbundles do not always reflect the classical 5 1 and 4 1 relationship the sedimentary record of both the studied sections is likely to include omission of bundles or their portion the general evolution of depositional and diagenetic facies the vertical change in thickness of the cyclic units and the interpretation of superbundles as small scale depositional sequences suggest that elementary cycles and their groups are superimposed on lower frequency environmental oscillations these display an upward transgressive regressive trend t rt of the facies and testify to larger scale variations of accommodation potential on the shelf t rts sequence stratigraphic interpretation of the superbundles as well as the common occurrence of the biostratigraphic dated hauterivian barremian boundary in the studied sections support the long distance regional correlation between the successions to be carried out on the 100 ky scale moreover by assuming the maximum flooding intervals of time equivalent superbundles as virtually isochronous intervals we have detected stratigraphic gaps of 1200 and 600 ky in the monte raggeto and in the podgorica mountains sections respectively both sections are formed of 10 complete superbundles each of them testifying to the 400 ky long eccentricity hence the monte raggeto and podgorica mountains successions represent a duration of at least 4 0 my in terms of elapsed time regardless of gaps within the stratigraphic record finally a correlation between the orbitally induced compared sections and both the 3rd order tethyan stratigraphic cycles and the global cycle chart is suggested our study confirms that cyclically organized shallow marine carbonate platform deposits controlled by orbitally induced sea level fluctuations represent a powerful tool for high precision regional and global correlations this can be of fundamental importance for quantification of sedimentary diagenetic and evolutionary processes as well as for the understanding of autocyclic versus allocyclic control on sequence development

antares i a biogeochemical study of the indian sector of the southern ocean abstract the first expedition of the antares program the french contribution to southern jgofs investigated the biology and the chemistry of the benthic environment and the water column in a region located between 60 s 72 e and 39 s 55 e in this special issue we present a detailed description of the transports of water masses across the polar front zone which are corroborated by chemical and microbial tracer studies a description of the sediment water interface bridging biological chemical and microbial studies and new insights into the diagenesis of biogenic silica

deciphering the history of hydrologic and climatic changes on carbonate lowstand surfaces calcrete and organic matter evaporite facies association on a palimpsest middle jurassic landscape from portugal abstract the unusual occurrence of calcretes and prominent organic matter in the middle jurassic lower bathonian serra de aire formation of the lusitanian basin of western portugal western iberian margin revealed a complex palimpsest exposure record here interpreted as reflecting hydrological changes caused by phases of emergence and immersion it serves as a potential model for understanding stratigraphic development at lowstand surfaces in carbonate successions the exposure dominated facies association grades upwards into peritidal and lagoonal limestones and the interval is assigned to the regressive peak of a transgressive regressive facies cycle 2nd order of the thick middle jurassic carbonate ramp succession the galinha quarry fatima region ne of lisbon a type section for this lowstand assemblage exhibits varied calcretes with black clasts interbedded with and grading into organic rich marly clayey seams and lenses locally with carbonate nodules carbonates with evaporite traces microbial laminites black clast and fenestral limestones some lithofacies are dolomitized the palynofacies contains phytoclasts associated with less refractory more prone to degradation components which suggests natural combustion pyrolysis wild fires the lowstand surface represents a low relief landscape with small depressions ponds bordering a more distal marginal littoral setting the partly subaerial and partly subaqueous settings were subjected to lengthy exposure and to fluctuating very shallow water bodies and water table coeval climatic regime was a seasonally dry wet one with dry semi arid phases dominating over the sub humid as shown by the combined record of intense calcrete development rhizogenic structures microbial mats brecciation desiccation evaporites and wild fire evidence however sea level rise caused changes to shallow sea water influenced restricted lagoonal peritidal settings comparisons and differences with modern and ancient coast marginal carbonates are made to provide a guide to the variability in such lowstand deposystems in the stratigraphic record

palaeoenvironments of the dinosaur bearing lameta beds maastrichtian narmada valley central india abstract the maastrichtian lameta beds of central india are intimately associated with the deccan lavas and are critical to determining upper cretaceous palaeoenvironments and palaeogeography of the area in the type jabalpur sub region four mappable units of the lameta beds are recognised the basal green sandstone is interpreted as a braided stream deposit the lower limestone characterised by brecciation and shrinkage cracks is interpreted as a sub aerially exposed palustrine flat with calcrete formation occurring on topographic highs of low relief plains the overlying mottled nodular beds exhibit a variable range of calcrete fabrics and morphologies including circum granular and linear cracks root casts and nodules these are interpreted as pedogenically modified sheet wash deposits of a semiarid alluvial plain the upper sandstone is a sheet flood deposit again pedogenically modified before arrival of the basal lava flows overall the lameta beds are considered to represent a regionally extensive maastrichtian regolith carbon and oxygen isotope analyses of calcareous components are entirely consistent with soil zone environments the 13c values are low typically 8 to 9 pdb demonstrating a strong input of carbon from the decay of terrestrial land plants calcrete 18o values are variable 5 to 10 pdb consistent with precipitation from meteoric water some of which was evaporatively modified in pools on the alluvial palustrine flat the lameta beds are well known for sauropod nesting sites and sedimentological analyses of these sites suggest that the animals selected topographic highs usually in marly or sandy soft sediment multiple nests with similar egg types probably indicate colonial nesting isotopic analyses of eggshell carbonate agree with earlier work suggesting that the sauropods ate a c3 plant food

biogenic silica dissolution in the oceans reconciling experimental and field based dissolution rates 1 on average 50 60 of diatomaceous opal produced in the euphotic zone redissolves within the upper 100 m of the water column high specific silica dissolution rates in the surface ocean contrast with order of magnitude lower values in deep sea sediments the lack of a mechanistic understanding of these large variations in dissolution kinetics is a major source of uncertainty in models of nutrient silicon cycling in the oceans here we show that the observed variability in biogenic silica reactivity is consistent with results of experimental dissolution studies differences in aluminum content and specific surface area of the diatom skeletons plus differences in temperature and degree of undersaturation all contribute to lowering silica dissolution rates in deep sea sediments relative to the euphotic zone when variations in these material and environmental properties are accounted for the predicted specific opal dissolution rate in average surface ocean water is over 2 orders of magnitude faster than the rate measured in recently deposited biosiliceous oozes of the southern ocean the predicted specific dissolution rate however is approximately 5 times higher than the value obtained from global estimates of the depth integrated dissolution rate and biogenic silica concentration in the upper water column this discrepancy likely reflects the inhibitory effect of protective organic coatings on fresh diatom shells in surface waters the experimental data further imply that aluminum incorporation in the silica matrix during biomineralization or after death of the organisms enhances the preservation efficiency of biogenic opal in marine sediments

microphyte pigments and resting spores at the water sediment interface in the subantarctic deep sea indian sector of the southern ocean during the antares i cruise april may 1993 in the indian sector of the southern ocean deep sea sediments were collected using a multiple gravity corer in the polar frontal zone pfz and frontal zone between crozet and kerguelen islands and in the permanently open ocean zone pooz south west of kerguelen and heard islands microphyte biomass indicators chl a b c and related phaeopigments measured by spectrofluorometry tests on natural fluorescence and detection of encysted diatoms observed by scanning electron microscopy sem were carried out on both sediment and overlying fluff whenever present evaluation of the phytoplankton biomass in the overlying surface water masses also was performed at each sampling station the phytoplankton biomass was on the whole very low and decreased from north to south 0 25 0 10 g 1 1 chl a with a maximum on the frontal zone whereas the sediment water interface of the southern sampling stations pooz was pigment enriched a consistent bioclastic fluffy layer was only present in the pooz stations up to 13 g 1 1 chl a 157 g 1 1 phaeo a biodeposition of this type was very thin or absent north of the pf polar front illustrating stronger advection in the northern part of the study area hydrodynamic studies of the crozet basin and the presence of benthic pennate coastal diatoms at the sediment interface of these northern stations further suggest increased advective activity in the north surficial sediments first 5 mm also were enriched with pigments in the pooz up to 0 15 g g 1 dw chl a 3 5 g g 1 dw phaeo a whereas in the pfz the chl a concentrations were insignificant pigment gradients in the sediments particularly well marked in the pooz indicate the absence of a secondary intense reworking such as bioturbation or resuspension nevertheless also in the pooz an unusual and well preserved megafaunal faecal cast was sampled and analysed sediments at southern stations 50 55 s 56 75 e 3600 4700 m depth were the most enriched with encysted microphytic cells mainly diatoms belonging to the genus chaetoceros this was related primarily to the presence of a fluffy layer composed mainly of well preserved detritic frustules of various diatom genera including robust nitzschia and thalassiosira as well as chains of delicate chaetoceros corethron and rhizosolenia well preserved coccoliths and silicoflagellates also were noticeable in the fluffs revival tests cultures on f2 medium initiated with samples from the water sediment interface were positive for the southern stations leading to low diversity diatom assemblages dominated by the genera chaetoceros and nitzschia

climatic and environmental indications of carbon and oxygen isotopes from the lower cretaceous calcrete and lacustrine carbonates in southeast and northwest china abstract carbon and oxygen isotopic ratios were determined from 100 lower cretaceous samples from four carbonate bearing facies in southeast se and northwest nw china for palaeoclimatic and palaeoenvironmental analyses the samples were interpreted as sediments within sublithofacies of distal alluvial ponds sf1 open shallow lakes sf2 littoral lakes sf3 and marshes sf4 results of analyses show in se china 13c values range between 5 0 and 3 0 with a negative trend through time and 18o values are all negative 19 3 7 4 in nw china 13c values range from 4 0 to 4 0 with periodic change and 18o values range between 18 0 and 1 5 both relatively heavy values and pronounced covariances of most 13c and 18o indicate semiarid climate and domination of closed brackish lakes marshes and ponds in nw and se china during the early cretaceous of them positive 13c 0 0 to 4 0 and relatively heavy 18o 5 0 to 1 5 values suggest interruptions of arid evaporation in intermittences of the early hauterivian in sw fujian of the middle aptian in west jiuquan basin of the late aptian in sw ordos basin and of the late aptian early albian in liupanshan basin in a short interval of the early aptian the hot and humid climate occurred in local sw zhejiang by high kaolinite content and in west jiuquan basin by warm flora could be an exception particularly extremely negative 18o values mainly 19 0 9 0 indicate relatively low temperature in se fujian in the berriasian barremian in liupanshan basin in the late aptian in sw ordos basin in the late albian and in west jiuquan basin in the mid late aptian which is supposed to attribute to the presence of 2500 m 4500 m in elevation more positive values and more covariance ratios of 13c and 18o in nw china than in se china and in mainland china than in america indicate a arider climate in former than in later probably attributing to the palaeogeography in distance to sea a tentative correlation of the early cretaceous 13c value excursion of calcretes shows a good compatibility between marine oaes and terrestrial carbonate sediments and between nw china and america continents implying a global response to carbon cycle in both marine and terrestrial environments the feature suggests the potential of global correlation and application of terrestrial calcrete 13c excursions in pre cenozoic