chemostratigraphy a method to improve interwell correlation in barren sequences a case study using onshore duckmantian stephanian sequences west midlands u k abstract chemostratigraphy has been applied to onshore duckmantian stephanian successions encountered in outcrop and penetrated by two boreholes from the west midlands u k these successions represent the onshore equivalents of the barren red measures which are important hydrocarbon bearing sequences in the southern north sea much is known about the onshore successions in terms of sedimentology mineralogy and provenance and thus they provide the ideal test for the validity of chemostratigraphy as a stratigraphic tool reliable inorganic geochemical data have been acquired from geochemical analyses of core sidewall core and cuttings samples with 19 elements being determined stratigraphic variations in elemental concentrations are compared with known variations in the mineralogical data the established lithostratigraphic units of the duckmantian stephanian intervals can also be recognized from the geochemical data and by using these data can be subdivided further this results in an independent chemostratigraphic correlation being established for the two boreholes which has been assessed statistically by discriminant function analysis from the geochemical and mineralogical data distinct changes in provenance are identified within the upper carboniferous successions the sediments of the coal measures were derived from a north westerly and westerly source caledonian whereas the etruria formation sediments came from the wales brabant massif the sediments having mixed caledonian and cadomian characteristics eventually these sediments were replaced by sediments from a southern hercynian source halesowen and salop formations

occurrence of palygorskite and sepiolite in upper paleocene middle eocene marine deep sediments of the lagonegro basin southern apennines italy paleoenvironmental and provenance inferences abstract a mineralogical and geochemical study of clay lithologies and a biostratigraphic analysis of the carbonates from the deep sea lagonegro basin southern apennines italy have been carried out to deduce in general the provenance of clay sediments and their paleoenvironmental conditions and particular to recognize the signature of the paleocene eocene climatic global warming the analysed succession comprising a wide stratigraphic interval of the sannio unit spanning between albian to the upper oligocene lower miocene is exposed near accettura and stigliano villages eighteen clay samples were analysed by xrd xrf sem tg dta their age was framed by biostratigraphic analyses carried out on carbonate sediments mineral assemblage of the clay sediments includes quartz carbonates calcite and dolomite feldspars plagioclase and k feldspars hematite randomly illite smectite mixed layers with a low illite percentage kaolinite discrete illite muscovite chlorite palygorskite and sepiolite the low illite percentage in randomly illite smectite mixed layers indicates low diagenetic conditions for the studied successions these features are unique for the cretaceous tertiary successions of the lagonegro domain and are particularly significant for the preservation of the native mineralogical assemblage useful to determine the provenance and paleoenvironmental conditions of the clayey sediments palygorskite and sepiolite are concentrated in the upper paleocene middle eocene stratigraphic interval and particularly in the upper part of the early eocene lower part of the middle eocene biozone of blow p 9 12 clay sediments rich in palygorskite and sepiolite show a higher p 2 o 5 amount and a lower kaolinite percentage compatible with warm and arid climatic conditions typical of the global warming event well recorded in the southern tethyan margin likely palygorskite and sepiolite formed in lagoonal environment in nearby carbonate platform margins and then they were transported into the lagonegro basin as indicated by the well developed habitus of palygorskite during the paleogene the lagonegro basin and the nearby carbonate platforms represented a key sector the southern paleodomains of the tethys the discovery of these minerals gives a contribution to the reconstruction paleoenvironmental conditions of the tethian paleo margin during the early middle eocene

paleoenvironmental changes during the late albian oceanic anoxic event 1d an example from the capacho formation southwestern venezuela abstract the late albian early cenomanian oceanic anoxic event 1d oae 1d 103 to 99 5 ma represents a global interval of enhanced organic carbon burial due to widespread oxygen deficiency in the water column and or increased primary productivity the biostratigraphy and geochemistry of organic rich sediments in the la grita member capacho formation in southwestern venezuela were studied to document the paleoenvironmental conditions that governed the deposition of this succession during oae 1d carbon isotope 13ccarb and 13ccorg chemostratigraphy and biostratigraphic constraints show that the la grita member spans the late aptian period rotalipora appenninica zone and that oae 1d is well recorded in this succession a prominent increase in total organic carbon toc values up to 10 is clearly recorded through the onset of oae 1d coinciding with a prominent change in overall redox sensitive proxies suggesting that the la grita member sediments accumulated under anoxic and possibly euxinic bottom water conditions in a partially restricted basin the detrital proxies suggest that the greenhouse climate prevailing during oae 1d induced significant acceleration of the hydrologic cycle and an increase in continental chemical weathering rates overall the carbon and oxygen isotope records toc contents as well as the detrital proxies show cyclic variation during the late albian stage these variations support the hypothesis that orbital forcing likely also modulated the equatorial monsoonal activity during the oae 1d

facies classification and patterns of lacustrine carbonate deposition of the barra velha formation santos basin brazilian pre salt abstract the lacustrine carbonate rocks of the giant pre salt oil fields in the santos and campos basins differ in a number of important aspects from classic lake deposits prior work has described distinctive and unusual features of deposition early diagenesis and reservoir quality with in these rocks that defy classification using established schemes in addition to their unusual textures debate continues as to how to interpret the vertical stacking pattern of facies a new facies classification scheme is proposed based on the relative abundance of three end member components mud micrite and clay minerals calcite spherulites and fascicular calcite shrubs although focused on the main textural and mineralogical features of the rocks as seen today the proposed scheme takes into account the relative contribution of depositional and early diagenetic components sediment mineralogy and the degree of dissolution application of this scheme offers insight into depositional conditions whilst also linking to reservoir quality basic elementary cycles can be defined using this classification in combination with the variation in the abundance of detrital grains and the chemical composition three possible models are suggested to interpret the origin of the basic cycle within the barra velha formation in the context of variation in climate lake level and water chemistry integration of data from different sources including petrographic core description and chemical data for the basic cycle offers improved process based understanding of metre scale facies patterns and provides a foundation for understanding larger scale vertical variations within and between unconformity bound sequences

composition and discrimination of sandstones a statistical evaluation of different analytical methods the discriminative power of four analytical approaches to sandstone composition is evaluated with respect to the separation of different formations and source areas the case study is cretaceous synorogenic sandstones litharenites from the eastern alps of europe which belong to four different formations and are derived from two source areas methods evaluated are light mineral analysis petrographic framework composition heavy mineral analysis major element xrf analysis and trace element xrf analysis the statistical parameters calculated percentages of well classified samples mahalanobis distance applying the logratio approach suggest that light mineral analysis has a significantly lower discriminative power than the other three methods taking into account the analytical expenditure for data acquisition trace element analysis appears to be the most efficient method for discrimination of at least the sandstone units examined although based on a single case study these results are interpreted to have a more general meaning with respect to sandstone discrimination based on composition concerning sandstone provenance trace element analysis provides a quick tool to estimate the discriminative potential of a sample suite i e the potential to discriminate between contrasting source areas if a provenance model already exists and discriminate functions between contrasting source areas are calculated trace element analysis is considered to be most efficient in correctly assigning an unknown sample to its source area these results cannot be extended to all kinds of sands and sandstones but they cast serious doubt on the belief that petrographic point count methods are the best approach to discriminate between sandstones

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

geochemical background in polluted river sediments how to separate the effects of sediment provenance and grain size with statistical rigour abstract defining anomalies from geochemical background is a principal step in anthropogenic contamination studies and environmental risk assessment and yet the complexity of processes affecting the composition of sediments makes this task extremely difficult we address grain size and sediment provenance as two parameters influencing the geochemistry of contaminated fluvial sediments we analysed 576 sediment samples from channels floodplains oxbow lakes and dam reservoirs of the morava river czech republic the geochemical data are compared with grain size and statistically processed using primary observations and log ratios an effective way to remove the grain size and provenance effect is to use enrichment factors calculated from least trimmed squares regression of pb zn cu and cr data vs normalizing ti which is sensitive to grain size based on empirical testing titanium proved more suitable for normalizing than did al and rb isometric log ratio coordinates of the pb zn cu and cr data show a strong misfit with those defined by the enrichment factors a log ratio approach considering just subcompositions of elements with similar geochemical behaviour provides much better results

element chemostratigraphy of the devonian carboniferous boundary a compositional approach abstract the devonian carboniferous d c boundary is a critical interval in the phanerozoic history which is associated with vigorous climatic perturbations continental glaciation global sea level fall and rapidly increased extinction rates in marine realms in many sections world wide these global changes left a marked lithological signature in particular the hangenberg black shale products of deep shelf anoxia and the overlying hangenberg sandstone sudden siliciclastic influx into predominantly carbonate depositional environments both layers bear a distinct geochemical signature even though either or both of these two lithologies are absent at many sections their correlative counterparts can be indicated by subtle geochemical markers we studied elemental geochemistry of fourteen d c boundary sections in six key areas across europe with the aim to select globally correlatable elemental proxy for the d c boundary analysis of raw log transformed geochemical data edxrf c p s units presenting the standard approach here indicates that concentrations of terrigenous elements al k rb ti and zr are mainly controlled by diluted ca carried by marine calcium carbonate in limestone facies and accordingly their variations can be related to carbonate production in the sea rather than to terrigenous input from continent nevertheless due to the relative nature of geochemical observations reliance solely on statistical processing of raw data might lead to incomplete picture of multivariate data structure and or biased interpretations for this reason the aim of this contribution is to discuss the logratio alternatives of the standard statistical methods which may better reflect the relative nature of the data for this purpose principal component analysis was employed to reveal main geochemical patterns and while the geochemical signature of the d c boundary was further analysed using q mode clustering that leads to predicative orthonormal logratio coordinates balances the comprehensive picture of the multivariate data structure provided by these statistical tools makes them a primary choice for exploratory compositional data analysis at the same time it turns out that the standard and compositional approaches have synergic effects this fact can be extensively used in further geochemical studies

numerical zonation of log suites and logfacies recognition by multivariate clustering zonation of well logs and the correlation of zones between wells are routine fundamental tasks in subsurface geological analysis objective numerical multivariate clustering is an effective procedure to simultaneously comprehend a suite of well logs and partition it into geologically meaningful zones and for identifying zone specific logfacies discrimination of zones and logfacies from log suites was established by a hierarchical clustering algorithm that defines clusters so that their within cluster dispersion is minimal logfacies are defined by an unconstrained analysis of unzoned data whereas the special requirements of the stratigraphic context of the zonation are observed by an adjacency constraint which prohibits merging individual depth levels or lower order clu ters if their members are not vertically contiguous two test cases one involving a succession composed of several alternating lithologies and the other entailing a uniform carbonate sequence with only subtle changes demonstrate the applicability and efficacy of the method in both cases the numerical zonation matched the manual lithostratigraphic division extremely well the geological validity of the numerically defined zones was also borne out by density neutron crossplots the unconstrained analysis successfully identified logfacies which are zone specific indicating that logfacies can serve as important leads for the recognition of reverse faults in boreholes and for interwell correlations

continental weathering and redox conditions during the early toarcian oceanic anoxic event in the northwestern tethys insight from the posidonia shale section in the swiss jura mountains abstract the geochemistry and mineralogy of organic rich sediments of the rietheim succession in northern switzerland were studied to evaluate the main impacts of the early toarcian oceanic anoxic event t oae 183 ma ago on the depositional environment in the nw tethys ocean the geochemical data obtained notably 13corg 13ccaco3 rock eval pyrolysis toccff support the hypothesis that the negative c isotope excursion at the onset of the t oae mainly reflects a major perturbation in the global carbon cycle rather than local environmental changes e g basinal restriction productivity rock eval pyrolysis and 13corg 15ntotal crossplots indicate that the organic matter was primarily of marine origin during the t oae and deposited in an epicontinental sea setting detrital proxies notably detritus index siliciclastic balance and ln al2o3 na2o suggest that the elevated pco2 levels and greenhouse climate prevailing during the t oae induced significant acceleration of the hydrologic cycle and an increase in continental chemical weathering rates redox sensitive proxies relative pyrite contents organic and sulfide balances v v ni ratios trace elements enrichment factors trace element toc co variation patterns and toc ptotal molar ratios indicate that the rietheim posidonia shale sediments accumulated under oxic to dysoxic bottom water conditions with more reducing conditions during the t oae anoxic and possibly euxinic these changes in redox conditions were probably induced by substantial thermohaline stratification driven by enhanced freshwater input and the recurrent influx of brackish arctic seawater into the nw tethys through the viking corridor in agreement with previous sedimentological and geochemical evidences from the nw tethys ocean in the studied succession such conditions were perhaps also responsible for sequestration of most of the regenerated p in the deeper water column by adsorption and or co precipitation into authigenic phases overall the major palaeoenvironmental changes documented in this study provide a robust example of earth s possible responses to the rapid onset of extreme greenhouse conditions

a standard analytic curve of potential temperature versus salinity for the western north atlantic abstract an algorithm is described for computing salinity as a continuous function of potential temperature for the western north atlantic the algorithm uses historical data compiled by worthington and melcalf 1961 for the deep western north atlantic and iselin 1936 for shallow and intermediate waters of the same region

sedimentary chemofacies characterization by means of multivariate analysis abstract multivariate statistical analysis is applied to geochemical data from three sections forming part of the stratigraphic record of the cerro pelado formation oligocene miocene in the central region of the falcon basin northwestern venezuela our main goal is introducing and testing a statistical protocol for the identification of chemofacies in the studied sections the first step involves data preparation and cleaning selection of relevant components convenient replacement of values below the detection limit and determination of outliers second a biplot analysis allows us to infer geochemical processes that can be interpreted from a paleoenvironmental point of view detrital association redox organic matter association and carbonatic association considering such geochemical associations a constrained cluster analysis is then carried out to determine the chemofacies for each section according to the compositional nature of geochemical data all statistical analysis is conducted within a log ratio analysis framework in addition robust statistical methods are considered for outlier detection and biplot representation in order to smooth the influence of potential outliers on the estimates

vertical motion in the gulf stream and its relation to meanders vertical motion at 700 m in the gulf stream main thermocline is computed using the adiabatic heat equation and a combination of data from inverted echo sounders and moored current meter measurements of t and u v at 400 700 1000 and 3500 m daily maps of all data on a regular grid were created using optimal estimation from these maps the tendency and advection terms in the heat equation were calculated the mapped vertical motions w agree well with w observed contemporaneously along isopycnal rafos float tracks strong events occur frequently within the gulf stream diagnosed vertical motions greater than 2 mm s 1 that persist for days are common occurring roughly every week within the 250 km mapped region upwelling and downwelling regions have horizontal scales of about 100 km both along and across stream case studies and animation elucidate the relationship between meander properties and the structure phasing and amplitude of the w fields typically the largest w is positioned near the steepest thermocline slope downwelling upwelling occurs entering exiting troughs strongest vertical motions occur in slowly propagating features and vertical motions are usually weaker for rapidly propagating features this observed dependence upon phase speed is opposite to predictions of recent kinematic and conceptual models the main contribution to observed w and the factor missing in those models is the existence of strong abyssal flow serving as a barotropic reference for the entire water column with a component which may flow orthogonal to the baroclinic front along sloping isopycnals the strongest vertical and cross frontal components are usually associated with slowly moving or stalled steep meanders associated with which abyssal cyclones or anticyclones have developed the vertical motion which is forced in these cases can significantly alter the vertical vorticity and or frontal strength through tilting of the strong vertical shear and of the strong vertical stratification vertical and cross frontal transports of 5 sv occur in steep meanders

mineral sources of aqua regia extractable base cations in scottish soils interpreted from cubist models trained with quantitative mineralogy data abstract the long term potential capacity for soils to deliver essential elements to plants and the soil solution is often assessed using aqua regia ar extractions and understanding specific mineral contributions to extracted element concentrations is central to the accurate interpretation of such data the objective of this study was to assess whether the supplying quantitative soil mineralogy data to the cubist machine learning algorithm could result in accurate prediction of ar extractable base cation concentrations naaqr mgaqr kaqr and caaqr and consequently facilitate the interpretation of meaningful mineral sources of these elements mineral concentrations were quantified in 191 soil samples collected by horizon from 96 sites across scotland these mineral concentrations together with ph and soil organic matter data were used to train cubist models for the prediction of log naaqr log mgaqr log kaqr and log caaqr yielding concordance correlation coefficients of 0 77 0 87 0 78 and 0 71 respectively when assessed by cross validation the dominant variables selected by cubist for the conditions of the models contrasted substantially between the four elements aligning with the independent nature of each base cation interpreted from compositional biplot analysis namely plagioclase concentrations were predominantly selected by cubist for log naaqr prediction chlorite concentrations for log mgaqr prediction dioctahedral mica concentrations for log kaqr prediction and ph for log caaqr prediction the selection of these variables is found to be geochemically appropriate for each element demonstrating how data driven methods can yield meaningful conclusions with respect to mineral sources of ar extractable elements in validating the utility of combining quantitative soil mineralogy data with the cubist machine learning algorithm on the relatively well characterised base cations future work can progress towards using similar approaches to define mineral sources of more challenging trace elements in new detail

role of pore fluids in the generation of seismic precursors to shear fracture a systematic study of temporal changes in seismic b values defined as the log linear slope of the earthquake frequency magnitude distribution has shown that large earthquakes are often preceded by an intermediate term increase in b followed by a decrease in the months to weeks before the earthquake1 the onset of the b value increase can precede earthquake occurrence by as much as 7 years a recently proposed fracture mechanics model of the earthquake source2 explains these temporal fluctuations in b in terms of the underlying physical processes of time varying applied stress and crack growth the model predicts two minima in b separated by a short lived maximum here we report the results of controlled laboratory deformation experiments done in simulated upper crustal conditions on both air dried and water saturated rock specimens as found in previous experiments3 5 shear fracture in dry specimens is characterized by a decline in b during anelastic deformation to a single minimum reached just before failure but in water saturated specimens when pore fluid volume is kept constant by servo control we also observe a second intermediate term b value minimum so reproducing the double b value anomaly predicted by the model2

quaternary tectonics and present stress tensor of the inverted northern falcon basin northwestern venezuela abstract the tertiary falcon basin in northwestern venezuela has a privileged position in the geodynamic puzzle of northwestern south america occurring in a region where several major plates caribbean south america and nazca and minor lithospheric blocks maracaibo bonaire and western colombia are interacting a combination of good exposures due to aridity and a near continuous sedimentary record in a now inverted basin helps to unravel the neogene and quaternary geodynamic evolution of this region a neotectonic and microtectonic investigation of the plio quaternary sedimentary rocks of the northern falcon basin reveals that this region is subject to a compressive to transpressive regime at present this regime is characterized by a nnw sse oriented maximum horizontal stress and a ene wsw trending intermediate or minimum horizontal stress as is confirmed by focal mechanism solutions this stress field is in agreement both with the nne directed extrusion of the maracaibo and bonaire blocks in western venezuela where the falcon basin is located and present day transpression along the caribbean south america plate boundary zone

palaeohydrology of the lower cretaceous pre salt lacustrine system from rift to post rift phase santos basin brazil abstract large oil accumulation discoveries in the last decade in the pre salt rock succession off the brazilian coast aroused renewed interest in carbonate reservoirs prompting several studies aiming at unravelling the conditions of formation of these rocks despite that there are still many gaps in the knowledge concerning environmental conditions of the deposition of the pre salt carbonates of santos basin located at the southeastern brazilian margin in this study we present and discuss a new suite of geochemical and biostratigraphic data of the lacustrine rift to post rift succession broadly correlated with itapema and barra velha formations of the santos basin whose deposition occurred in the aptian the integration of the petrographic biostratigraphic and geochemical data serves the ultimate purpose of the study which is to apply the new radiogenic strontium data as a proxy for the reconstruction of the evolution of the lake hydrology associated with the deposition of the carbonates of the itapema and barra velha formations these data are integrated into numerical models whose results bring new ideas on the general hydrologic conditions of the lake system and on its evolution through time the mass balance calculations indicate that two end members alone can account as potential sources of sr to the palaeolake a mafic and a felsic component respectively the latter likely contributed with significantly higher fluxes roughly one to two and up to four orders of magnitude higher than the former end member for most of the depositional history in order to generate the 87sr 86sr trends observed in the carbonate rocks finally the results obtained from the integration of the observations with the numerical models point to decreasing fluxes of water with time as contributed from both sources suggesting that the formation of the deposits became very likely constrained to progressively more evaporitic and alkaline lake waters these results also open up a new window into the environmental conditions of the interior gondwana continent immediately prior to the definitive opening of the south atlantic ocean

statistical modelling of compositional trends in sediments abstract trends in compositional diagrams are frequently used to describe and interpret the imprint of certain processes on sediment composition most of these trends are intuitive and hand drawn although a numerical description of compositional changes involved with these processes would allow for a quantitative assessment of the observed sediment compositions and the proposed processes this paper suggests a statistical approach to model compositional linear trends which allows for a mathematically rigorous description of changes in sediment composition related to a specific process or a combination of processes three case studies dealing with different aspects of the sedimentary cycle demonstrate the usefulness of the approach in the first example a modelled average global chemical weathering trend is used to calculate an appropriate measure for the degree of chemical weathering of the suspended load from some of the world s major rivers in the second example data on precipitation and relief from different watersheds are quantitatively related to the petrographic composition of fine grained sands from low order streams derived from these watersheds the third example is an attempt to quantify the interdependence of chemical sediment composition and grain size in the absence of chemical weathering superposition of individual compositional linear trends allows for modelling sediment composition in more complicated case studies although primarily a forward modelling approach it can be also used inversely and therefore has strong potential for tracing back the sediment forming processes in order to reconstruct the original source rocks of the sediment

resolving original signatures from a sea of overprint the geochemistry of the gungri shale upper permian spiti valley india abstract the geochemistry of black shales can faithfully record paleoenvironmental conditions however the original geochemical signatures are obscured by post depositional events such as diagenesis and weathering resolving the relative influence of these processes on the geochemistry of shales requires a combination of geochemical and chemometric chemical statistics approaches to data analysis that identify the sources of variance in major and trace element geochemistry the permian gungri shale kuling group at attargoo spiti valley himachal pradesh india is a gray to black shale capped unconformably by an iron rich pebble sand layer ferruginous layer marking ostensibly the permian triassic boundary high resolution analysis of the gungri at attargoo 3 cm intervals reveals a geochemical record complicated by low grade metamorphism diagenesis and modern weathering using multivariate chemometric techniques e g principal component analysis we identified variance in the geochemical record associated with the original detrital and depositional conditions we also identified 4 beds within the gungri that mark depositional events which may correlate to those identified in other pt sections e g guryul ravine kashmir identification of sources of variance allowed us to identify geochemical signatures that can be used for paleooceanographic reconstruction the attargoo section records a sequence of discrete events including transient iron enrichments attributed to euxinic depositional conditions and late diagenetic formation of siderite and regression condensation surfaces associated with pulsed transgression regression towards the uppermost permian our results show that chemometric analysis of geochemical data enables the resolution of paleoenvironmental conditions in shales impacted by post depositional alteration

determining geostrophic velocity shear profiles with inverted echo sounders it is known that vertical acoustic travel time round trip from the seafloor to the sea surface as measured by inverted echo sounders iess can be interpreted in terms of dynamic height this relationship is generalized and quantified in this paper for dynamic height di j integrated between a variety of pressure limits pi pj which span different portions of the main thermocline the generalized form of the di j relationships is nonlinear the conventional linear relationship is valid when the limits of integration span the entire main thermocline velocity and temperature records are shown to be highly correlated vertically indicating that the variability of the gulf stream and adjacent eddy field is dominated by the lowest baroclinic mode which is called a gravest empirical mode gem a parallel isotherms model is used to approximate the gem and to develop analytic expressions for the observed di j relationships in the gulf stream the analytic expressions represent the observations well with noise to signal variance ratios that are typically 1 using these new di j relationships the baroclinic velocity structure can be determined geostrophically by measuring the horizontal gradients with laterally separated measurements from iess baroclinic velocities determined from a two dimensional array of iess in the gulf stream during 1988 1990 agree with velocity shears directly measured by current meters the rms velocity difference between these two measurements of velocity shear at 400 dbar relative to 1000 dbar was 12 cm s 1 in the presence of typical currents of 50 cm s 1 ageostrophic motions at both mesoscale and submesoscale measured by the current meters but not by the iess contribute most of the velocity differences

uses and misuses of compositional data in sedimentology this paper serves two goals the first part shows how mass evolution processes of different nature become undistinguishable once we take a size limited noisy sample of its compositional fingerprint processes of exponential decay mass mixture and complementary accumulation are simulated and then samples contaminated with noise are extracted the aim of this exercise is to illustrate the limitations of typical graphical representations and statistical methods when dealing with compositional data i e data in percentages concentrations or proportions the second part presents a series of concepts tools and methods to represent and statistically treat a compositional data set attending to these limitations the aim of this second part is to offer a state of the art compositional data analysis this includes descriptive statistics and graphics the biplot ternary diagrams with confidence regions for the mean regression and analysis of variance models to explain compositional variability and the use of compositional information to predict environmental covariables or discriminate between groups all these tools share a four step algorithm 1 transform compositions with an invertible log ratio transformation 2 apply a statistical method to the transformed scores 3 back transform the results to compositions and 4 interpret results in relative terms using these techniques a data set of sand petrographic composition has been analyzed highlighting that finer sands are richer in single crystal grains in relation to polycrystalline grains and that grain size accounts for almost all compositional variability a stronger water flow river discharge favors mica grains against quartz or rock fragment grains possibly due to hydrodynamic sorting effects a higher relief ratio implies shorter residence times which may favor survival of micas and rock fragments relatively more labile grains

orbitally induced limestone marlstone rhythms in the albian cenomanian cismon section venetian region northern italy sedimentology calcareous and siliceous plankton distribution elemental and isotope geochemistry abstract a multidisciplinary study of the upper albian cenomanian portion of the cismon section venetian region northern italy was undertaken in order to characterize the cyclic alternations of carbonate rich and carbonate poor layers and to investigate their possible origin and cyclic patterns limestone semicouplets are characterized by abundant radiolarians and micarbs micron sized calcitic fragments common planktonic foraminifera strong bioturbation good oxygenation as expressed by the mn and v v ni parameters high si al ratio low k al in the absence of pyrite and organic matter the marlstone semicouplets are on the contrary frequently laminated rich in pyrite and organic matter with common fish remains in the absence of radiolarians the mn and v v ni parameters indicate that the marlstone deposition occurred in dysoxic to anoxic conditions which allowed the preservation of organic matter the low si al ratio and high k al ratio the latter related to abundant feldspars indicate that marlstones received a substantial contribution from a terrigenous source the abundance of biogenic silica suggests that during limestone deposition surface waters were rather fertile due to an efficient recycling of nutrients from deeper waters the enhanced fertility was coupled with an efficient current system at the welloxygenated sea floor which prevented the organic matter from accumulating during marlstone deposition surface waters were less fertile than in the limestone semicouplets but still within the mesotrophic spectrum as indicated by the presence of fertility index species among calcareous nannofossils whereas the bottom waters were oxygen depleted to accommodate fertility at the surface with stagnation at the bottom the scenario implies an enhanced stratification caused by an increase in freshwater runoff monitored by 18o depleted values in the meantime the water discharge supplied the nutrients to the surface waters necessary for the calcareous nannofossils to proliferate the cyclic organization of limestone marlstone couplets as revealed by power spectral analysis seems to represent climatic cycles the alternating conditions are 1 efficient mixing highly fertile surface and near surface waters and a well oxygenated seafloor to 2 enhanced water runoff or decreased evaporation or both and oxygen depleted bottom waters we suggest that this deterministic sedimentary cyclicity could be explained by periodic orbital climatic cycles in tune with the milankovitch cycles within this scenario the latest cenomanian bonarelli level is an exceptional event marked by a large positive 13c spike it is characterized by high to very high fertility conditions in surface waters caused by increased upwelling that engendered high nutrient levels in near surface waters the enhanced production of organic matter was in excess for the oxygen available at the bottom floor thus allowing the organic matter to accumulate in the sediments

chemostratigraphic correlation structure and sedimentary environments in the dalradian of the nw co mayo inlier nw ireland a thorough geochemical survey of the dalradian rocks in the nw mayo inlier has shown that each formation has a characteristic geochemical signature within regional geochemical trends that vary systematically with stratigraphic age this geochemical characterization enables correlation between geographically and tectonically isolated stratigraphic successions in the nw mayo inlier an almost complete succession of late proterozoic grampian appin and argyll group dalradian rocks structurally overlies earlier basement annagh division gneisses in structural blocks bounded by caledonian thrusts extensional low angle faults and steeply dipping faults grampian appin group relationships are better seen here than anywhere else in scotland or ireland but no tayvallich subgroup or southern highland group dalradian rocks are present comparison with chemostratigraphic data from scottish dalradian rocks reveals broadly similar chemical trends with time suggesting that the geological evolution of the dalradian took place in a related depositional environment probably an unbroken continental margin along the entire dalradian outcrop seen in both scotland and ireland

mineralogical geochemical and magnetic signatures of surface sediments from the canadian beaufort shelf and amundsen gulf canadian arctic mineralogical geochemical magnetic and siliciclastic grain size signatures of 34 surface sediment samples from the mackenzie beaufort sea slope and amundsen gulf were studied in order to better constrain the redox status detrital particle provenance and sediment dynamics in the western canadian arctic redox sensitive elements mn fe v cr zn indicate that modern sedimentary deposition within the mackenzie beaufort sea slope and amundsen gulf took place under oxic bottom water conditions with more turbulent mixing conditions and thus a well oxygenated water column prevailing within the amundsen gulf the analytical data obtained combined with multivariate statistical notably principal component and fuzzy c means clustering analyses and spatial analyses allowed the division of the study area into four provinces with distinct sedimentary compositions 1 the mackenzie trough canadian beaufort shelf with high phyllosilicate fe oxide magnetite and al k ti fe cr v zn p contents 2 southwestern banks island characterized by high dolomite k feldspar and ca mg loi contents 3 the central amundsen gulf a transitional zone typified by intermediate phyllosilicate magnetite k feldspar dolomite and al k ti fe mn v zn sr ca mg loi contents and 4 mud volcanoes on the canadian beaufort shelf distinguished by poorly sorted coarse silt with high quartz plagioclase authigenic carbonate and si zr contents as well as high magnetic susceptibility our results also confirm that the present day sedimentary dynamics on the canadian beaufort shelf is mainly controlled by sediment supply from the mackenzie river overall these insights provide a basis for future studies using mineralogical geochemical and magnetic signatures of canadian arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late quaternary climate and oceanographic changes keywords mineralogy elemental geochemistry magnetic properties surface sediment sediment provenance redox condition canadian beaufort shelf amundsen gulf

a multi proxy palaeolimnological record of the last 16 600 years from coastal lake kushu in northern japan abstract based on diatom aquatic pollen and non pollen palynomorph npp lake sediment microfacies and x ray fluorescence xrf analyses we define three main phases of lake basin development including a marshy phase ca 16 600 9400 cal yr bp lagoon phase ca 9400 5900 cal yr bp and freshwater lake phase since ca 5900 cal yr bp marine influence on the lake system linked to global sea level rise and the holocene marine transgression reached a maximum between ca 8000 and 6000 cal yr bp an increase of aulacoseira subarctica at 5530 cal yr bp marks the end of the holocene thermal optimum i e onset of middle holocene cooling in the study region our results further suggest that freshwater lake kushu had a significant effect on the initial habitation of rebun island by sedentary hunter gatherer populations the reconstructed onset of stable freshwater conditions ca 5100 cal yr bp coincided with the appearance of the earliest permanent settlements during the middle jomon culture phase ca 5000 4000 cal yr bp on the other hand there is evidence for human induced changes in the limnological conditions this includes enhanced sediment and nutrient input into lake kushu resulting in high eutrophication levels that caused strongly reduced diatom productivity and enhanced green algae growth which can be attributed to human activities apparently associated with the okhotsk ca 1450 950 cal yr bp and classic ainu ca 350 100 cal yr bp culture periods

cyclogenesis in the deep ocean beneath the gulf stream 2 dynamics strong cyclones in the deep ocean beneath the gulf stream have been observed during the period june 13 1988 to august 7 1990 near 68 w 37 n in data from the synoptic ocean prediction synop experiment these cyclones developed in association with the evolution of large amplitude quasi stationary meander troughs in the gulf stream it is likely that baroclinic instability is responsible for cyclone spin up the dynamical analysis of these cyclones indicates the process is analogous with atmospheric cyclogenesis from the perspectives of divergence and conservation of potential vorticity but not in terms of the density field evolution large positive vertical velocities in the thermocline over developing low pressure centers at 3500 m are consistent with convergence at depth and divergence in the upper ocean and with stretching of the lower water column and shortening of the upper water column the stretching of the lower water column accounts for the generation of positive relative vorticity there however the evolution of the density field in the oceanic case does not resemble the atmospheric case in the atmosphere density field adjustments in the air column above the low pressure center at the earth s surface are in the correct sense to account for decreasing pressure there in the ocean density field adjustments in the water column fail to account for the developing low pressure centers so sea surface height depressions must be responsible these depressions must have an approximate magnitude of 0 5 m depth over a 250 km horizontal extent the cyclone s diameter

can mn s redox cycling drive sedimentary dolomite formation a hypothesis abstract the formation of dolomite in modern peritidal environments is linked to the degradation of buried microbial mats with complexation of ca and mg by extracellular polymeric substances epss and alkalinity generation through organic carbon respiration facilitating the nucleation of dolomite precursors in the past two decades microbial sulfate reduction methanogenesis and methanotrophy have all been considered as potential drivers of the nucleation process but it remains unclear why dolomite formation could not also occur in suboxic sediments where abundant alkalinity is produced by processes linked to mn iv and or fe iii reduction coupled with the diffusion and reoxidation of reduced sulfur species here we report the interstitial occurrence of spheroidal aggregates of nanometer scale ca rich dolomite rhombohedra within suboxic sediments associated with remnant microbial mats that developed in the peritidal zone of the archipelago los roques venezuela multiple analytical tools including epma icp ms synchrotron based xrf and xrd and spatially resolved xanes microanalyses show that the dolomite cemented interval exhibits depleted bulk iron concentrations but is interstitially enriched in mn and elemental sulfur s0 manganese occurs in several oxidation states indicating that the dolomite cemented interval was the locus of complex biological redox transformations characterized by coupled mn and s cycling the tight correspondence between sedimentary mn and mgco3 concentrations further hints at a direct role for mn during dolomitization while additional studies are required to confirm its relevance in natural settings we propose a model by which coupled mn s redox cycling may promote alkalinity generation and thus dolomite formation in manner similar to or even more efficiently than bacterial sulfate reduction alone

geochemical investigation of the south wellesley island wetlands insight into wetland development during the holocene in tropical northern australia the south wellesley islands in the gulf of carpentaria northern australia were the recent focus of a palynological investigation which found vegetation change during the holocene was driven by coastal progradation and regional climate here we present new elemental data from x ray fluorescence core scanning which provides non destructive continuous and high resolution analysis from three wetlands across bentinck island the largest of the south wellesley islands elemental data and grain size analyses are combined with lead 210 210pb and accelerator mass spectrometry ams carbon 14 14c dates an open coastal environment was present 1250 cal a bp on the south east coast of bentinck island with sediment supply incorporating fluvial deposition and detrital input of titanium and iron from eroding lateritic bedrock prograding shorelines dune development and river diversion formed a series of swales parallel to the coast by 800 cal a bp forming the marralda wetlands wetlands developed at sites