relation between depositional environment and the elemental composition of early diagenetic siderite early diagenetic siderites from marine and fresh water depositional environments are characterized by distinctive compositional trends siderite from fresh water environments is often relatively pure i e greater than 90 mol feco sub 3 and commonly attains end member composition siderite from marine environments however is always extremely impure and has extensive substitution of mg up to 41 mol and to a lesser extent ca up to 15 mol for fe in the siderite lattice in addition marine siderite generally contains less mn and has a higher mg ca ratio than fresh water siderite this compositional variation appears to result from differences in the chemistry of early marine and meteoric pore waters inasmuch as early marine pore waters generally have a higher mg sup 2 ca sup 2 ratio and contain less mn sup 2 and fe sup 2 and more ca sup 2 and mg sup 2 than meteoric waters

clustering of fracture orientations using a mixed bingham distribution and its application to paleostress analysis from dike or vein orientations abstract the clustering and classification of fracture orientations are important in rock mechanics and in brittle tectonics the latter of which includes the paleostress analysis of extension fractures hosting dikes or mineral veins here we present an unsupervised clustering method for the orientations of extension fractures using mixed bingham distributions the method not only detects the elliptical clusters and girdles made by the poles to such planar features but also determines the appropriate number of those groups by means of bayesian information criterion bic without a priori information the method was tested with artificial data sets and successfully detected the assumed groups when the clusters had little overlaps however clusters with the common maximum concentration orientation and large aspect ratios were distinguished provided that their minimum concentration orientations were separated by a large angle our method separated two stress states from natural data from a miocene dike swarm in sw japan the method also evaluated the probabilities of the stresses to form each of the dike

comparing discontinuity orientation data collected by terrestrial lidar and transit compass methods terrestrial lidar light detection and ranging and a transit compass were used separately to collect discontinuity orientation data at an abandoned quarry in the vicinity of claytor lake dam southwest of christiansburg virginia dips software program was used to process the data obtained by the two methods stereonet plots of orientation data generated by the dips program were used to determine the principal discontinuity sets present at the quarry statistics provided by the dips program were compared to evaluate the variability of discontinuity orientation data between the two methods the purpose was to evaluate the reliability of lidar derived data by comparing it with manually collected data and to investigate whether the two datasets yield similar discontinuity orientations results of the study show that both data sets are able to identify bedding and two other joint sets however one gently dipping joint set identified by the manually collected data is either under represented or missing from the lidar data possible factors influencing this difference in the two datasets include 1 shadow zone related to sampling bias 2 patch size and 3 spatial variation of discontinuity orientations we suggest a protocol for minimizing the influence of these factors on discontinuity mapping by the lidar method

early diagenetic pyrite morphology in a mudstone dominated succession the lower jurassic cleveland ironstone formation eastern england abstract diagenetic pyrite in the mudstones and ironstones of the lower jurassic cleveland ironstone formation of eastern england exhibits two distinct morphologies framboidal pyrite commonly associated with organic matter and euhedral pyrite associated with detrital clay pellets these two morphologies are mutually exclusive in occurrence framboidal pyrite is present in clay rich mudstones ooidal ironstones apatite rich units and some silt rich mudstones euhedral pyrite is present in silt rich and sand rich mudstones 34s isotopic analysis of six samples of pyrite suggests that both types of pyrite morphology precipitated during early diagenesis from porewaters with open access to overlying sea water although both probably acted as sites for continued pyrite precipitation during burial it is proposed that framboidal pyrite precipitated from iron dominated porewaters at sites of sulfide supply i e in the region of organic matter as a result of bacterial sulfate reduction where locally sulfide production rates were high enough for porewaters to reach supersaturation with respect to fes euhedral pyrite also precipitated from iron dominated porewaters but sulfide production rates from organic matter was such that fes saturation was not reached at the sites of sulfide production instead euhedral pyrite was precipitated directly from porewater when fes2 saturation was reached the control over pyrite morphology was probably the amount and reactivity of the organic matter within the deposited sediments the sand rich mudstones contained less reactive organic matter due to clastic dilution and deposition in shallower environments with o2 rich bottom waters the ironstones and apatite rich units were deposited under very low sedimentation rates and as a result organic matter contents were very low and iron reduction dominated early diagenesis which inhibited sulfate reduction the presence of minor framboidal pyrite within these units however suggests that sulfide reduction took place in micro environments during early diagenesis

infiltrated clays in fluvial jurassic sandstones of reconcavo basin northeastern brazil abstract fluvial sandstones and conglomerates of the sergi formation a jurassic unit of reconcavo basin northeastern brazil contain significant amounts of interstitial detrital clays which are interpreted as the product of early mechanical infiltration developed in an arid semi arid environment within such an environment the lowered water table allowed muddy waters of episodic runoff to infiltrate through the coarse alluvium concentrating the clays in the upper phreatic zone near the sources of influent seepage petrographic textures considered to be typical of mechanically infiltrated mi clays are herein presented using examples from the sergi formation these textures include 1 ridges and bridges 2 geopetal fabrics 3 loose aggregates 4 anisopachous coatings of tangentially accreted lamellae cutans 5 massive aggregates and 6 shrinkage patterns developed during diagenesis in addition their detrital aspect as revealed by sem observations and the presence of impurities in the interior of the clay aggregates were also used as evidence for the interpreted origin of the clays in most hydrocarbon reservoirs in the sergi formation the clays described in this paper are among the main controls on porosity and permeability distribution commonly zones with maximum clay concentration are the main internal permeability barriers within the sergi formation reservoirs

a technique for identifying structural domain boundaries at the ekati diamond mine over 10 000 discontinuity orientations from various sources at the ekati diamond mine in northern canada were collected and amalgamated into a common database a new technique in which structural domains were determined in the area of three closely spaced active pits by quantitatively comparing stereonets from different regions was developed the frequencies of discontinuity poles plotting in orientation windows on stereonets were determined and compared using a correlation coefficient to quantify the degree of similarity between different stereonets structural boundaries between regions were established wherever their associated stereonets display low correlation coefficients the technique was able to determine boundaries in the vertical direction as well as radially in a number of pie shaped zones extending around the kimberlite pipes

role of glacial arctic ocean ice sheets in pleistocene oxygen isotope and sea level records abstract a comparison of the oxygen isotope signal in deep sea benthic foraminifera with the record of glacio eustatic sea level for the last 160 000 years reveals that the amplitude of the benthic 18 o records predicts more continental ice volume than appears to be reflected in lowered sea level stands these differences between the benthic 18 o ice volume estimates and radiometrically dated records of eustatic sea level are consistent with the presence of a large floating arctic ocean ice mass during glacial intervals the presence of an arctic ocean ice sheet during glacial intervals may account for the two climatic modes observed in oxygen isotope records which span the entire pleistocene the early pleistocene 1 8 to 0 9 myr b p interval is characterized by low amplitude high frequency 18 o fluctuations between glacial and interglacial periods while the late pleistocene 0 9 myr b p to present is characterized by large amplitude low frequency 18 o changes these two climatic modes can be explained by the initiation of earth orbital conditions favoring the co occurrence of glacial period arctic ocean ice sheets and large continental ice sheets approximately 900 000 years before present

comprehensive characterization and clustering of orientation data a case study from the songta dam site china abstract the quantitative description of orientation data in rock masses is fundamental for understanding the engineering geological properties of rock masses however the features of joint orientation distributions are still not easy to describe in practical projects orientation data are randomly distributed in a rock mass and its poles are also randomly distributed on a stereonet the delineation of orientation data on the stereonet is difficult but the density of poles on the stereonet indicates some characteristics of joint geometric patterns which will influence the mechanical and hydraulic properties of rock masses considering the nonlinear distribution of poles density fractal geometry is introduced to describe the orientation data in this study accordingly a framework combining the idea of fractal geometry graphic display and the schmidt upper hemisphere equal area projection plot is proposed for comprehensive characterization of orientation data the monofractal and multifractal descriptions have been used to delineate the orientation data and a fractal indicator is proposed for the dispersion of orientation data in addition the identification and delineation of joint sets with similar orientations are discussed and the optimal method is recommended finally the methods proposed in this study were further applied to a real data set collected from a survey at the dam site of the songta hydropower station china

deformation mechanisms and stability analysis of undermined sedimentary rocks in the shallow subsurface abstract the deformation mechanisms and the stability of an undermined sedimentary rock layers were studied using the numerical model flac itasca 2006 specifically validated for such configurations the lowermost stratum in a sequence of successive layers is modeled as multi fractured voussoir beam boundary conditions material properties and geometrical constraints for the numerical modeling were chosen to reflect rock mass properties that are characteristic to sedimentary rock masses a series of ordered models spanning over a representative range is presented the indeterminacy parameters of the voussoir beam model are determined using non linear regression of the numerical results over a dimensionless space the results show that the thickness coefficient of the compressive arch n formed within the deflecting beam is non uniform at the abutment na ranges from 0 3 to 0 4 inversely proportional to beam stiffness at the mid span nm ranges from 0 4 to 0 5 snap trough failure of the beam occurs for beams of normalized composite stiffness en

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

controls on the accumulation of coal and on the development of anastomosed fluvial systems in the cretaceous dakota formation of southern utah alluvial strata of the cretaceous dakota formation of southern utah are part of a transgressive systems tract associated with a foreland basin developed adjacent to the sevier orogenic belt these strata contain valley fill deposits anastomosed channel systems and widespread coals the coals constitute a relatively minor part of the dakota formation in terms of sediment volume but may represent a substantial amount of the time represented by the formation the coals are separated by clastic units up to 20 m thick the stratigraphically lowest clastic unit of the dakota formation lies above an unconformity cut into jurassic rocks incised valleys associated with the unconformity are up to 12 m deep two discrete episodes of valley fill sedimentation are recognized including a lower sandstone unit with conglomerate layers and an upper discontinuous coal bearing unit after the valleys filled the area became one of low relief where extensive mires formed peat accumulation was interrupted at least three times by deposition of clastic sediment derived from the west the clastic units consist of sandstone mudstone or heterolithic ribbon bodies stacked tabular sandstones and laminated mudstones and contain minor coal beds less than 0 35 m thick ribbon bodies are 1 9 m thick and 15 160 m wide have pronounced basal scours and are filled with both lateral and vertical accretion deposits an anastomosed channel complex is suggested by the large number of coeval channels of varying dimensions the variation in the structure and grain size of channel fills and the presence of abundant tabular sandstones interpreted as crevasse splays although some sandstone bodies have well developed lateral accretion surfaces the overall ribbon geometry indicates that mature meandering streams were not well developed this is in contrast to modern anastomosed systems which are commonly thought to be a transitional morphology caused by avulsion of a meander belt to a new position on its floodplain rather than being a transitional channel pattern related to river avulsion the anastomosed channels of the dakota formation may have formed part of a large inland delta that episodically invaded widespread mires the mires developed during periods when clastic influx was reduced either by high rates of subsidence close to the thrust belt or by deflection of rivers by emergent thrusts

empirical methods to estimate the strength of jointed rock masses abstract the ultimate strength and deformation of jointed rock mass are important parameters that designers look for in selecting sites for foundations of civil and mining engineering structures in rocks in the field it is extremely difficult to stress a rock mass to its ultimate failure stress consequently the field tests are performed up to a certain predefined stress level it is shown in this study that the results of these tests can be used to arrive at the ultimate strength of the rock mass a large number of uniaxial compressive strength ucs tests were conducted on the specimens of jointed block mass having various combinations of orientations and different levels of interlocking of joints four dominating modes of failure were observed the strength and the tangent elastic modulus values of the mass for a specific failure mode when plotted on the deere miller classification chart are found to follow an empirical straight line indicating strong correlation between them using the gradient of this empirical line correlations have thus been suggested to assess the ultimate strength of the jointed rock mass the findings of the study have been verified by applying it to estimate the ultimate rock mass strength of nine rock types from few dam sites in the lower himalayas the ultimate strength obtained by the present methodology is compared with that obtained through the q classification system it is concluded that reasonably good estimates on field strength of jointed rocks are possible by using the correlations suggested in this study

sulphur isotope geochemistry of pyrite from the upper cretaceous marshybank formation western interior basin abstract variations in the texture and sulphur isotopic composition of pyrite in the upper cretaceous marshybank formation are linked to depositional environment abundant framboidal and lesser euhedral pyrite precipitated in offshore marine rocks moderate quantities of pyrite also crystallized in brackish coastal plain rocks however in contrast to marine pyrite coastal plain pyrite is dominantly euhedral in texture reflecting direct precipitation from a porewater with a relatively low dissolved sulphide concentration in the marine rocks pyrite 34s values range from 35 7 to 27 4 avg 4 8 canyon diablo troilite cdt pyrite within carbonate concretions hosted in these marine rocks has a similar isotopic composition 49 8 to 10 6 cdt however isotopic values are often highly variable within individual concretions as a result of the heterogeneous nature of sulphate reduction and pyrite formation within marine sediments pyrite in coastal plain rocks is characterized by relatively high 34s values 4 2 to 35 5 avg 13 2 cdt while the overlying sideritized conglomerates have the lowest 34s values reported for cretaceous rocks from the western interior basin of north america 49 8 to 41 7 cdt very low 34s values which are only observed in the marine rocks are indicative of microbial sulphate reduction and pyrite formation in a sulphate replete i e open system higher 34s values up to 18 which were obtained for both the marine and coastal plain rocks are indicative of progressive pyrite crystallization in a sulphate limited i e closed system such conditions are expected in marine sediments as burial occurs and in brackish i e low sulphate sediments pyrite with very high 34s values 18 is common in the coastal plain rocks these high values are the result of influx of 34s enriched residual sulphide derived from overlying marine units a minor amount of 34s enriched pyrite is also present within and proximal to marine sedimentary unit h which was deposited at the same time as the coastal plain rocks we hypothesize that porewater containing 34s enriched residual sulphide flowed from the coastal plain and along unit h into the marine sediments thus producing anomalously high 34s pyrite

depositional environments and sequence stratigraphy of paralic glacial paraglacial and postglacial upper ordovician siliciclastic deposits in the murzuq basin sw libya abstract the application of sequence stratigraphy methods to glaciogenic deposits is more problematic than in normal paralic deposits because changes in the relative sea level are strongly influenced by an interplay between glacial advance and retreat and concomitant isostatic loading and rebound of the continental shelf the study of outcrop and subsurface sections of the upper ordovician glaciogenic melaz shuqran and the mamuniyat formations murzuq basin sw libya yielded important information on understanding changes in the relative sea level related to glacier movements three depositional sequences were recognized depositional sequence one ds 1 corresponds to the entire melaz shuqran formation that was bounded below by subglacial erosion surface i e sequence boundary sb formed during glacier advance into shallow water areas this surface correlates with a transgressive surface ts in deep water areas and records an initial rise in the relative sea level owing to glacier advance and loading of the continental shelf transgression occurred due to the slower rate of eustatic sea level fall than the isostatic loading the transgressive systems tract tst comprises shoreface sandstones and offshore mudstones diamictites with ice rafted debris further rise in relative sea level was associated with glacial retreat which resulted in sediment starvation in deep water areas and the formation of a condensed section these deposits represent glacial depositional systems the highstand systems tract hst comprises prograding deltaic deposits which was formed when the rate of sediment supply exceeds the rate of relative sea level rise the hst deposits represent paraglacial depositional systems depositional sequence two ds 2 corresponds to the lower and middle part of the mamuniyat formation and is bounded below by deep erosional surface sb that cuts into ds 1 as an incised valley which was formed during glacial advance across the continental shelf incision occurred due to the faster rate of eustatic sea level fall than the rate of isostatic loading glacier retreat and the concomitant rise in relative sea level resulted in the deposition of braided fluvial sediments in a lowstand systems tract lst and tide dominated estuarine sediments in a tst these deposits represent glacial depositional systems the hst sediments represent prograding foreshore to shoreface deposits which were formed when the rate of sediment supply exceeded the rate of relative sea level rise these deposits represent paraglacial depositional systems depositional sequence three ds 3 corresponds to the upper part of the mamuniyat formation and is bounded below by an erosional surface sb that was formed as a result of isostatic rebound associated with relative sea level fall ds 3 lst comprises gilbert type deltaic conglomeratic sandstones grading upwards into sandstones subsequent relative sea level rise during the late ordovician resulted in deposition of shoreface tst sandstone further rise in the relative sea level resulted in sediment starvation in deep water areas and the formation of thin hardground layer i e condensed section that marks the upper boundary of late ordovician deposits this study provides predictive model for the spatial and temporal distribution of ancient glaciogenic depositional facies that may have important implications in hydrocarbon explorations

distribution of diagenetic alterations in glaciogenic sandstones within a depositional facies and sequence stratigraphic framework evidence from the upper ordovician of the murzuq basin sw libya abstract the spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the upper ordovician glaciogenic quartzarenite sandstones in the murzuq basin sw libya which were deposited during the haritanian glaciation when the basin was laying along the continental margin of gondwana eogenetic alterations encountered include i replacement of detrital silicates mud matrix and pseudomatrix by kaolinite in paraglacial tide dominated deltaic in foreshore to shoreface highstand systems tract hst and in post glacial gilbert type deltaic lowstand systems tract lst sandstones particularly below the sequence boundaries sb kaolinite formation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline ii cementation by calcite 18 o vpdb 3 1 to 1 1 and 13 c vpdb 1 7 to 3 5 and mg rich siderite in the paraglacial tide dominated deltaic and foreshore to shoreface hst sandstones in the glacial tide dominated estuarine transgressive systems tract tst sandstones and in the post glacial shoreface tst sandstones is interpreted to have occurred from marine pore waters iii cementation by mg poor siderite which occurs in the post glacial gilbert type deltaic lst sandstones and in the paraglacial tide dominated deltaic and foreshore to shoreface hst sandstones is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline iv pervasive cementation by iron oxides has occurred in the glacial shoreface offshore tst sandstones and post glacial shoreface tst sandstones immediately below the maximum flooding surfaces mfs which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor v formation of grain coating infiltrated clays mainly in the glacial fluvial incised valley lst sandstones and in the post glacial gilbert type deltaic lst sandstones as well as less commonly in the paraglacial foreshore to shoreface hst sandstones and in the tide dominated deltaic hst sandstones below the sbs mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial fluvial incised valley lst sandstones post glacial gilbert type deltaic lst sandstones and glacial shoreface tst sandstones in which early carbonate cements are lacking illite chlorite and albitized feldspars which occur in small amounts are most common in the glacial tide dominated estuarine tst sandstones and paraglacial shoreface hst sandstones this study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir quality evolution in glacial paraglacial and post glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

investigation of the permeability anisotropy of 2d fractured rock masses abstract a hydro geometric anisotropy factor is derived for better correlation with the permeability anisotropy of field scale fractured rock masses the hydro geometric anisotropy factor considers the orientation length spacing and hydraulic aperture properties of a discrete fracture network numerical simulations are carried out by using a pipe network method which simulates the fractures as connected and directed pipes obeying darcy s law to validate the correlation between the hydro geometric anisotropy factor and the permeability anisotropy of fracture networks fracture patterns from simple to complex with a scale of 10 m by 10 m are generated to study the effects of different fracture distributions on the hydro geometric anisotropy of fracture networks and thus on the permeability anisotropy it is found that the aperture size and distribution have a significant effect on the permeability anisotropy that affects the main permeable direction of the fracture networks the permeability anisotropy varies following a power relation with the change of the intersection angle between two fracture sets varying the number and length ratio of the fracture sets also alters the permeability anisotropy in all fracture patterns the hydro geometric anisotropy factor gives an accurate correlation with the permeability anisotropy an anisotropic conductivity index is further defined to evaluate the directional hydraulic connectivity of the fracture system based on this approach the permeability anisotropy of a fracture network system can be quickly assessed through the correlation with the hydro geometric anisotropy factor and the anisotropic conductivity index

sequence stratigraphic distribution of diagenetic alterations in coal bearing paralic sandstones evidence from the rio bonito formation early permian southern brazil linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations and hence of reservoir quality a study of the coal bearing alluvial deltaic estuarine and shallow marine sandstones of the rio bonito formation early permian parana basin southern brazil reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework calcite dolomite siderite kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries transgressive and maximum flooding surfaces and is systematically distributed within lowstand transgressive and highstand systems tracts diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite detectable in resistivity wire line logs concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries particularly in the transgressive systems tract meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries transgressive and maximum flooding surfaces favoured the formation of grain rimming siderite the results of this study are relevant to the exploration of coal bed methane and other coal bearing reservoirs where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments

characteristics of weathering zones of granitic rocks in malaysia for geotechnical engineering design tropical climatic conditions cause severe weathering to rock masses resulting in thick weathering profiles consisting of different weathering zones with complex characteristics feasible geotechnical engineering design requires a detailed understanding of the characteristics of each weathering zone a typical weathering profile is usually characterized by field scale observation and geological study this paper presents the characteristics of weathering zones of various granitic rocks in the south of malaysia this region has a tropical climatic condition the study was carried out in four active quarries located in johor province malaysia and forty sections were investigated in the study areas a typical granitic weathering profile was characterized based on the geological and structural parameters i e joint characteristics corestone occurrence rock soil ratio mass homogeneity color of rock and discoloration at joints surfaces the profile includes common zones ranging from fresh to residual soil however two subzones are introduced based on corestone boulder occurrence in the highly weathered and completely weathered zones this study based on detailed field observations at the mentioned quarries followed by analysis presents an amalgamated picture of weathering zones in granitic profiles of a tropical region like malaysia moreover it is believed that the characterization of the typical weathering profile allows further classification of generally complex weathered rock masses for a specific geotechnical engineering design

global carbon isotopic events associated with mass extinction and glaciation in the late ordovician mass extinctions and glacioeustatic sea level changes in the lower part of the hirnantian final stage of the ashgill are accompanied by shifts in marine stable isotope compositions previously published stable isotope changes have been used to identify the onset and demise of the gondwana glaciation and to suggest relationships between biotic changes and carbon cycling within the oceans however the existing isotopic data set had limitations because it was derived from ordovician low latitude settings and from carbonates or organic carbon in separate areas we report new data from ordovician high latitude carbonates and demonstrate parallel shifts in organic and carbonate 13c from baltica brachiopod shells from a high palaeolatitude periglacial setting in argentina have elevated 13c values similar to those described previously from low latitude sites the new data demonstrate that the positive hirnantian 13c excursion previously only recognised from low palaeolatitude areas was widespread and probably global in extent the poor preservation state of the brachiopods unfortunately prevented the determination of a reliable oxygen isotopic value from the same material preliminary carbon isotopic data from thermally immature organic matter from estonia provide the first indication of a synchronous shift in organic and inorganic 13c in sediments from the same basin this work provides new data of critical importance for constraining models of end ordovician palaeoceanography and climate change

hydrogeology of a complex champlain sea deposit quebec canada implications for slope stability the thick sequences of marine clayey deposits which blanket the st lawrence lowlands in south eastern canada are highly susceptible to landslides with 89 of the population of the province of que