origin of siderite concretions in microenvironments of methanogenesis developed in a sulfate reduction zone an exception or a rule abstract the mississippian shales from wardie scotland were deposited in a large normally brackish water basin they host siderite concretions with 13c values ranging from 3 5 to 12 1 which show that sulfate reduction and methanogenesis contributed to the production of bicarbonate fossils are found within each of the concretions suggesting that the decay of these organic remains provided a catalyst for concretionary growth the pore water was freshened which is indicated by the very negative 18o values from 12 8 to 4 7 many features indicate that the concretions are very early diagenetic precompactional precipitates the concretions are mostly homogeneous only a few exhibit complex concentric zoning the microstructure of the homogeneous concretions indicates a pervasive growth however their isotopic composition reveals a clear trend towards lighter 13c and 18o values from the center to the edge it is proposed that the concretions grew due to methanogenesis in microenvironments around large organic remains which acted as nuclei we suggest that this process may be one of the reasons for the very common occurrence of cements as mineral concretions not as disseminated precipitates along beds these microenvironments developed entirely within the sulfate reduction zone which resulted in the establishment of isotopic gradients in bicarbonate dissolved in the pore water across these microenvironments these gradients were caused by fast consumption of sulfate by the intensive oxidation of organic remains this resulted in the isotopic trends preserved in the homogeneous concretions the formation of the zoned concretions proceeded generally concentrically but detailed observations suggest that pervasive growth also contributed to their formation afterwards all the concretions were deeply buried probably within the oil window where late diagenetic phases crystallized mainly kaolinite quartz and sulfides

petrology chemistry and diagenesis of calcite concretions in silurian shales from central sweden calcite concretions in the lower silurian rastrites shale from central sweden were formed within 1 m depth of the seafloor micrite 1 4 m was formed initially but recrystallized into microspar 4 50 m and subsequently transformed into pseudospar 50 150 m skeletal calcite in the concretions and in the host shale has been replaced by microspar which is chemically similar to that occurring in the concretion body the 13cpdb values mostly between 2 and 2 suggest that carbonates were mainly derived from seawater some of the carbon within calcite was derived from the oxidation of organic matter recrystallization has resulted in increasingly negative 18 opdb values 7 to 4 3 whereas the 13c was not changed significantly

the central paratethys during oligocene as an ancient counterpart of the present day black sea unique records from the coccolith limestones abstract four isochronous oligocene coccolith limestone horizons from the carpathians were examined in order to reconstruct paleoceanographic conditions in the central paratethys the dominance of small and size uniform pyrite framboids the occurrence of low diversity dinoflagellate cysts and coccolithophorids and the presence of biomarker molecule 28 30 dinorhopane indicate that the water column was stratified with the upper water column being relatively well oxygenated but the bottom water being anoxic the latter is confirmed by the fine and consistent horizontal laminations in various parts of the basin scarcity of benthic organisms and their trace fossils the limestones exhibit typical marine 13c values but are significantly depleted in 18o and enriched in 87sr relative to contemporaneous ocean water these isotopic compositions result from a decreased salinity of the surface waters caused by an increased riverine input this is confirmed by the lack or impoverishment of planktonic foraminifers presence to abundance of goniodomid dinoflagellate cysts and massive occurrence of low diversity nannoplankton assemblages which indicates decreased salinities as low as 17 and high productivity in the upper water column these observations indicate that the limestones were formed during periods when connection of the central paratethys with the global ocean was limited which impeded water exchange causing the development of low salinity conditions of surface water and bottom water anoxia during the deposition of the oldest tylawa horizon primary productivity was enhanced and chemocline was positioned exceptionally high in the water column moreover decreased 13c values in both carbonates and organic matter of this horizon suggest that widespread methane venting took place in the basin during np23 all these data show that during the oligocene the central paratethys experienced similar conditions to those of the current black sea which can be used as a modern analogue especially for the tylawa horizon therefore the tylawa horizon can be perceived as a potential effect of future post depositional processes of coccolith marls analogous to those having been deposited in the black sea for 2 7 kyr

concretion morphologies reflecting diagenetic and epigenetic pathways abstract due to complex physicochemical processes concretions develop variable but distinctive morphologies reflecting the state of the sediment in subsequent stages of diagenesis and epigenesis they deserve a study and systematization in their own right at the same time concretional morphologies illustrate the effect of hierarchic self organization which is a basic element also in biological evolution

field relationships and stable isotope geochemistry of concretions from james ross island antarctica abstract early diagenetic precompactional concretions are abundant throughout the cretaceous tertiary marambio group larsen basin antarctica four distinct concretion types are recognised 1 spherical subspherical concretions 2 sheet concretions 3 fossil nucleated concretions and 4 concretionary burrow networks all concretion types have a micritic to microsparry variably non ferroan to ferroan calcite cement stable isotope analyses show a wide spread in both 18o and 13c 13c values are typically negative ranging between 3 38 and 39 15 o pdb usually 16 to 230 18o ranges between 1 28 and 13 81 pdb with most of the values between 5 and 10 the 13c signature is interpreted to represent carbon sourced from sulphate reduction and or methane oxidation with minor input from shell dissolution and is consistent with a shallow burial early diagenetic origin a single mudstone hosted concretion has a 18o composition indicative of precipitation of carbonate from seawater the low 18o signatures in the sandstone and siltstone hosted concretions are possibly due to early diagenetic modification of the pore water composition through volcaniclastic mineral dissolution reprecipitation reactions and perhaps through input of meteoric water concretion distribution is related to a changes in sedimentation rate and b the dominance of diffusion on concretion cementation

glaciation aridification and carbon sequestration in the permo carboniferous the isotopic record from low latitudes to evaluate the isotopic record of climate change and carbon sequestration in the late paleozoic we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from carboniferous through middle permian 359 260 ma strata we focus on the isotopic records from the u s midcontinent and the russian platform because these two regions provide well preserved marine fossils spanning a broad time interval both regions show a 18o increase at the mid carboniferous boundary ca 318 ma that roughly correlates with geologic evidence for an expansion of gondwanan glaciers only the russian platform record shows a 18o maximum during the glacial maximum in the asselian in contrast to a previous study korte c jasper t kozur h w and veizer j 2005 18o and 13c of permian brachiopods a record of seawater evolution and continental glaciation palaeogeogr palaeoclimatol palaeoecol 224 333 351 our data show no oxygen isotope evidence for glacial retreat in the early permian but instead show increasing 18o values related to aridification dissimilarity in the 18o trends for the epicontinental seas of north american and the russian platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater 18o values these results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western north america intermediate values in the midcontinent and high values in the sverdrup basin russian platform and northern spain nevertheless both u s midcontinent and russian platform records show a late serpukhovian minimum a sharp increase across the mid carboniferous boundary and a minimum centered on the kasimovian the correlative increase in brachiopod 13c and 18o values at the mid carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the permo carboniferous

lunar surface rock abundance and regolith fines temperatures derived from lro diviner radiometer data 1 surface temperatures derived from thermal infrared measurements provide a means of understanding the physical properties of the lunar surface the contrasting thermophysical properties between rocks and regolith fines cause multiple temperatures to be present within the field of view of nighttime multispectral data returned from the lunar reconnaissance orbiter lro diviner radiometer between 60 n s latitudes regolith temperatures are influenced by the presence of rocks in addition to factors such as the thermophysical properties of the regolith fines latitude and local slopes and radiative heating from adjacent crater walls preliminary comparisons of derived rock concentrations with lro camera images show both qualitative and quantitative agreement although comparisons of derived rock concentrations with circular polarization ratio radar data sets display general similarities there are clear differences between the two data sets in the relative magnitude and areal extent of rocky signatures several surface units can be distinguished based on their regolith temperature and rock concentration values and distributions including maria and highlands surfaces rocky impact craters rilles and wrinkle ridges dark mantled deposits and isolated cold surfaces rock concentrations are correlated with crater age and rocks are only preserved on the youngest surfaces or where steep slopes occur and mass wasting prevents mantling with fines the presence of rocky surfaces excavated by young impacts allows for the estimation of minimum regolith thickness from the size of the impact the derived rock concentrations confirm the presence of thicker regolith cover in the highlands and in locations of radar dark haloes

sedimentological significance of strain and sonic velocity anisotropy in fine grained turbiditic and hemipelagic deep sea sediments an example from the mississippi fan abstract in visually homogeneous and compositionally similar argillaceous sediment of the mississippi fan depositional processes turbiditic versus hemipelagic sedimentation are reflected in the anisotropy of strain as well as in sonic velocity the correspondence between the mode of deposition and anisotropy was observed in single beds as well as in entire depositional sequences in single beds the turbiditic part as opposed to the pelagic portion is characterized by an anisotropy within bedding and a comparatively low anisotropy between vertical and horizontal directions as current influence decreases anisotropy within bedding disappears while anisotropy in vertical versus horizontal directions increases because of rapid sedimentation the sediments are not influenced by bioturbation that would distort the primary fabric in depositional sequences the anisotropy pattern depends on the type of sequence in fining upward sequences anisotropy in vertical versus horizontal directions increases upsection and anisotropy within bedding is less frequent this pattern is explained by the decreasing influence of turbidity currents on sediment fabric and an increasing proportion of quietly accumulated hemipelagic deposits in coarsening upward sequences the inverse trends are found the general correspondence between trends in lithology and anisotropy only documents relative changes in the predominant depositional process within a specific fan sub environment on an absolute scale values of both types of anisotropy differ from site to site a clear pattern within the fan is found thus anisotropy determinations provide useful supplementary information for interpreting fan environments compaction generally leads to an increasing anisotropy but the relative differences in anisotropy between turbiditic and hemipelagic sediments are not significantly affected

interrelationships between porosity and other geotechnical properties of slowly deposited fine grained marine surface sediments wetzel a 1990 interrelationships between porosity and other geotechnical properties of slowly deposited finegrained marine surface sediments mar geol 92 105 113 the pore volume expressed as porosity or void ratio of fine grained marine deposits at the sediment surface 0 2 cm is closely related to other geotechnical properties such as liquid limit plastic limit compression index and specific surface area equations have been formulated for the interdependencies between 1 average porosity at the sediment surface n and liquid limit ll in 100 0 0378ll 0 43 0 0378ll 1 43 2 liquid limit ll and specific surface area sg ll 1 01 88 46 5 if ll 50 and 3 compression index c and void ratio at a stress of 0 01 mpa eo e o 3 352 exp col from the relationship between geotechnical properties and initial porosity the state of consolidation of surface sediments and the influence of bioturbation often lead to an increase in porosity 5 10 and compressibility up to 10 and a decrease in the overconsolidation ratio from 2 3 to about 1 at the sediment surface the interrelationship between initial porosity and physical properties can be explained by the dependence of the geotechnical properties on the electrostatic forces between the particles and the adsorbed water around them

recent shallow moonquake and impact triggered boulder falls on the moon new insights from the schrodinger basin shallow moonquakes are thought to be of tectonic origin however the geologic structures responsible for these moonquakes are unknown here we report sites where moonquakes possibly occurred along young lobate scarps in the schrodinger basin our analysis of lunar reconnaissance orbiter and chandrayaan 1 images revealed four lobate scarps in different parts of the schrodinger basin the scarps crosscut small fresh impact craters 1500 boulders associated with trails and bouncing marks their origins are largely controlled by recent impact events ejecta rays and secondary crater chains from a 14 km diameter impact crater traversed schrodinger and triggered significant boulder falls about 17 ma therefore a combination of recent shallow moonquakes and impact events triggered the boulder falls in the schrodinger basin

isotopic variations in dolomite concretions from the monterey formation california abstract isotopic analysis of dolomite concretions from the miocene monterey formation of california yields a covariance of 18o and 18c within every concretion analyzed the total range for all concretions in 18o smow is 27 3 to 33 6 the total range in 13c pdb is 10 2 to 10 8 variations of up to 3 6 in oxygen and 12 2 in carbon are encountered within a single concretion decreasing 18o is interpreted in terms of increasing temperatures of formation as the concretion grows during burial the claypool and kaplan 1974 model can be successfully used to interpret carbon isotope variations as the result of progressive concretion growth in the zones of microbial sulfate reduction microbial methane production and thermocatalytic decarboxylation monterey dolomite concretions are too rich in carbonate to have originated by simple cementation of initially porous sediment much of the originally diatomaceous sediment appears to have been replaced by dolomite isotopic zonation within one concretion is found to be complex suggesting nucleation at several sites which then grew together complex growth patterns may result from local variations in lithology and porosity during precipitation multiple sampling of several concretions at a single outcrop yields a more complete early diagenetic history than by sampling only one concretion isotopic diagenetic profiles inferred from the dolomite concretions are similar to those seen in deep sea drilling project cores where deep sea dolomitization is occurring today single samples from a concretion cannot reveal the range or the trend of the diagenetic reactions that have occurred multiple sampling of diagenetic carbonate concretions is clearly essential in determining the early diagenetic history from isotopic measurements

the internal structure of carbonate concretions in mudrocks a critical evaluation of the conventional concentric model of concretion growth abstract carbonate concretions have traditionally been viewed as forming concentrically through the progressive addition of carbonate to the outer edge of the growing concretion this conventional model of concretion growth is based mainly upon center to edge textural and geochemical trends that are consistent with concentric growth however a number of recent studies of concretions in mudrocks have documented complex zonation that is not compatible with the conventional concentric model in some cases complexly zoned concretions contain late stage cements that precipitated throughout the concretion body none of the center to edge relationships used to support the conventional concentric model exclude more complex modes of origin as concretions that fit the conventional model may be the exception rather than the rule high resolution petrographic analysis of concretions should always be used to characterize internal structure and mode of growth prior to interpretation of geochemical and textural data

constraints on the recent rate of lunar ejecta breakdown and implications for crater ages we present a new empirical constraint on the rate of breakdown of large ejecta blocks on the moon based on observations from the lunar reconnaissance orbiter lro diviner thermal radiometer we find that the rockiness of fresh crater ejecta can be quantified using the diviner derived rock abundance data set and we present a strong inverse correlation between the 95 th percentile value of the ejecta rock abundance ra 95 5 and crater age for nine craters with published model ages derived from crater counts on their continuous ejecta ra 95 5 decreases with crater age as age m y 0 46 this result implies shorter rock survival times than predicted based on downward extrapolation of 100 m crater size frequency distributions and represents a new empirical constraint on the rate of comminution of large rocks not previously analyzed experimentally or through direct observation in addition our result provides a new method for dating young lunar craters

shallow seismic activity and young thrust faults on the moon the discovery of young thrust faults on the moon is evidence of recent tectonic activity but how recent is unknown seismometers at four apollo landing sites recorded 28 shallow moonquakes between 1969 and 1977 some of these shallow quakes could be associated with activity on the young faults however the epicentre locations of these quakes are poorly constrained here we present more accurate estimates of the epicentre locations based on an algorithm for sparse seismic networks we found that the epicentres of eight near surface quakes fall within 30 km of a fault scarp the distance of the expected strong ground shaking from an analysis of the timing of these eight events we found that six occurred when the moon was less than 15 000 km from the apogee distance analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near apogee events within 60 km of a fault scarp occur at or near the time of peak compressional stresses when fault slip events are most likely we conclude that the proximity of moonquakes to the young thrust faults together with evidence of regolith disturbance and boulder movements on and near the fault scarps strongly suggest the moon is tectonically active shallow moonquakes detected at four apollo landing sites between 1969 and 1977 occurred during maximum stress and in close proximity to young faults suggesting that the moon is tectonically active according to reanalyses of the seismic data and tidal force modelling

global thrust faulting on the moon and the influence of tidal stresses lunar reconnaissance orbiter camera images reveal a vast globally distributed network of over 3200 lobate thrust fault scarps making them the most common tectonic landform on the moon based on their small scale and crisp appearance crosscutting relations with small diameter impact craters and rates of infilling of associated small shallow graben these fault scarps are estimated to be younger than 50 ma and may be actively forming today the non random distribution of the scarp orientations is inconsistent with isotropic stresses from late stage global contraction as the sole source of stress we propose that tidal stresses contribute significantly to the current stress state of the lunar crust orbital recession stresses superimposed on stresses from global contraction with the addition of diurnal tidal stresses result in non isotropic compressional stress and thrust faults consistent with lobate scarp orientations the addition of diurnal tidal stresses at apogee result in peak stresses that may help trigger coseismic slip events on currently active thrust faults on the moon

concretion morphology classification and genesis abstract a discussion of the most relevant morphological features of concretionary bodies and the different classifications and the criteria involved in these classifications is presented together with suggestions for improvements to the various classification schemes the meaning of syngenetic diagenetic and epigenetic related to the relative timing and environment of growth of concretionary bodies is also reviewed and discussed the replacement of mixed morphogenetic classifications which lead to conflicting results by classification categories based on textural features is proposed because the identification of the genetic environment of a concretionary body tells little about its history i recommend defining growth patterns in which the successive steps associated with changes in composition and or texture and the development of new structures are recorded a new path is presented that accounts for the contradiction between textural and isotope features which suggests respectively syngenetic and diagenetic or even epigenetic signatures this new path is characterized by the preservation of large porosities over very long time spans and down to depths that are somewhat greater than expected due to the inhibition of normal compaction caused by early overpressuring this overpressuring is the result of the development of hydraulic seals since approximately the syngenetic phase times the concepts of force of crystallization and displacive growth are also reviewed it is being suggested to discard some controversial interpretations of their actual importance for true concretionary displacive growth under epigenetic conditions in accordance with other authors the conclusion is reached that displacive growth is only possible if the shear strength of the host is very low and the stress field within the host is almost hydrostatic a new model the symcompactional concretionary growth model is proposed which explains how a concretionary body generally a nodule can grow while its host thins down by compaction this overpressured undercompacted model will be useful for the interpretation of an assemblage of features such as injection dikes hydraulic breccias cone in cone structures among others that are thought to be representative of the former presence of overpressured horizons these overpressured horizons could serve as detachment planes in paleotectonically active basins seals that could have controlled the movement of brines and hydrocarbons during the diagenetic evolution of the basin can also be assessed this is relevant for the identification of maturation conditions the potential development of secondary fracture permeability due to hydraulic fracturing in buried areas of the basin can also be evaluated based on the identification of formerly overpressured horizons in outcrops the origin of concretions is generally a geological puzzle clifton 1957

the geochemistry of concretions from the kimmeridge clay formation of southern and eastern england concretions from the kimmeridge clay formation are of three types calcareous concretions septarian calcareous concretions and pyrite calcite concretions and nodules which occur within different mudstone facies isotopic and chemical analysis of the concretionary carbonates indicate growth in the fe reduction sulphate reduction and decarboxylation zones the septarian concretions show a long and complex history with early initiation of growth and development spanning several phases of burial each often resulting in the formation of septaria growth apparently ceased in the transitional zone between the sulphate reduction and the methanogenesis zones very early growth in the fe reduction zones is also seen in one sample the non septarian concretions began growth later within the sulphate reduction zone and have had a simpler burial history while the pyrite calcite concretions show carbonate cementation in the sulphate reduction methanogenesis transition zone a ferroan dolomite calcite septarian nodule with decarboxylation zone characteristics also occurs development of concretions appears to be indirectly controlled by the sedimentation rate and depositional environment the latter determining the organic matter input to the sediments calcareous concretions predominate in swell areas and during periods of low sedimentation rate in the basins with poor organic matter preservation and deposition of calcareous mudstones pyrite calcite concretions occur in organic rich mudstones deposited under higher sedimentation rates in the basins while the ferroan dolomite nodule grew under very high sedimentation rates

chemical model for the origin of minor limestone shale cycles by anaerobic methane oxidation chemical and isotopic studies of jurassic carbonate concretions indicate an origin by anaerobic methane oxidation concretion growth occurred within the top 1 m of sediment in a thin zone where methane was consumed to stimulate a late rejuvenated phase of sulfate reduction similar chemical and isotopic characteristics are shown by diagenetic carbonate in several limestone shale sequences and an origin by anaerobic methane oxidation is proposed for these sequences also the evolution of isolated concretions into diagenetic limestones depends on the extent of and depth variations in carbonate supersaturation arising from anaerobic methane oxidation and the persistence of a reduced sedimentation rate or a depositional hiatus diagenetic limestones formed in this way can often be recognized by their association with a later pyrite phase that is more abundant and has more positive sup 34 s values than the adjacent shales

global survey of lunar wrinkle ridge formation times abstract wrinkle ridges are a common feature of the lunar maria and record subsequent contraction of mare infill constraining the timing of wrinkle ridge formation from crater counts is challenging because they have limited areal extent and it is difficult to determine whether superposed craters post date ridge formation or have alternatively been uplifted by the deformation some wrinkle ridges do allow determination to be made this is possible where a ridge shows a sufficiently steep boundary or scarp that can be identified as deforming an intersecting crater or the crater obliterates the relief of the ridge such boundaries constitute only a small fraction of lunar wrinkle ridge structures yet they are sufficiently numerous to enable us to obtain statistically significant crater counts over systems of structurally related wrinkle ridges we carried out a global mapping of mare wrinkle ridges identifying appropriate boundaries for crater identification and mapping superposed craters selected groups of ridges were analyzed using the buffered crater counting method we found that except for the ridges in mare tranquilitatis the ridge groups formed with average ages between 3 5 and 3 1 ga ago or 100 650 ma after the oldest observable erupted basalts where they are located we interpret these results to suggest that local stresses from loading by basalt fill are the principal agent responsible for the formation of lunar wrinkle ridges as others have proposed we find a markedly longer interval before wrinkle ridge formation in tranquilitatis which likely indicates a different mechanism of stress accumulation at this site

deep burial alteration of early diagenetic carbonate concretions formed in palaeozoic deep marine greywackes and mudstones bardo unit sudetes mountains poland carbonate concretions formed in bathyal and deeper settings have been studied less frequently than those formed in shallow marine deposits similarly concretions affected by catagenetic conditions have rarely been reported calcite concretions in deep marine mudstones and greywackes of the bardo unit sudetes mountains poland formed during early diagenesis and were buried to significant depths petrographic and geochemical elemental and stable c and o isotopic analyses document their formation close to the sediment water interface prior to mechanical compaction within the sulphate reduction zone and their later burial below the oil window although the concretions were fully formed during early diagenesis the effects of increased temperature and interaction with late diagenetic interstitial fluids can be discerned during maximum burial the concretions underwent thorough recrystallization that caused alteration of fabric and elemental and o isotope composition the initial finely crystalline cement was replaced by more coarsely crystalline sheaf like poikilotopic calcite in the concretions these large calcite crystals engulf and partially replace unstable detrital constituents the extremely low 18o values down to 21 2 vienna pee dee belemnite in the concretions are the result of the increased temperature in combination with alteration of volcanic glass both causing a significant 18o depletion of bicarbonate dissolved in the interstitial fluids recrystallization led to uniform o isotope ratios in the concretions but did not affect the c isotope signature the 13c values of the late diagenetic cements precipitated in the greywacke and in cracks cutting through concretions imply crystallization in the catagenetic zone and decarboxylation as a source of the bicarbonate these late diagenetic processes took place in a supposedly overpressured setting as suggested by clastic dykes and hydrofractures that cut through both concretions and host rock all of these features show how the effects of early and late diagenesis can be distinguished in such rocks

redistribution of rare earth elements during diagenesis of turbidite hemipelagite mudrock sequences of llandovery age from central wales

joint interaction with embedded concretions joint loading configurations inferred from propagation paths abstract the interaction between propagating joints and embedded concretions in a devonian black shale near seneca lake ny permits identification of the loading configurations responsible for two joint sets of different ages striking at nearly the same orientation the earlier set consists of systematic joints cut by later alleghanian joints of the appalachian plateau the later set consists of non systematic curving cross joints that abut these same alleghanian joints field evidence shows that concretions functioned as stiff inclusions in a compliant black shale as a consequence of this elastic contrast local perturbations in the remote stress field persisted around the concretions during burial tectonic deformation and exhumation these stress perturbations influenced joint propagation paths of both joint sets our conclusions about loading configurations are based on finite element modeling of the effect of the local stress perturbation on concretion modified joint propagation modeling shows that the local stress perturbation from a thermoelastic loading was responsible for deflecting cross joints away from concretions in a curved propagation path near the concretion this load configuration also led to arrest of cross joints before they penetrated the shale concretion interface at greater distances from the concretion the propagation path of cross joints was controlled by the contemporary tectonic stress field the interface between concretions and the surrounding shale was strongly bonded as indicated by the crossing of the interface by some of the systematic ene joints higher compressive stress levels within the concretions relative to the shale suppressed joint development in the concretion causing the arrest of those joints once they had driven across the interface and a short distance into the concretion numerical modeling shows that interface penetration by the systematic ene joints is consistent with a fluid load the same loading configuration postulated for the subsequent alleghanian joints the traces of the systematic ene joints align on opposite sides of concretions rather than curving toward the concretion as predicted by two dimensional models of the fluid load co planar traces are indicative of large planar joints propagating in plane around the concretion making it energetically inefficient for the crack front to curve as it enters the local stress perturbation near the concretion a fluid load for the systematic ene joints came from high pore pressure during the pre alleghanian stages of burial of the devonian catskill delta complex

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

constraints on deep moonquake focal mechanisms through analyses of tidal stress 1 a relationship between deep moonquake occurrence and tidal forcing is suggested by the monthly periodicities observed in the occurrence times of events recorded by the apollo passive seismic experiment in addition the typically large s wave to p wave arrival amplitude ratios observed on deep moonquake seismograms are indicative of shear failure tidal stress induced in the lunar interior by the gravitational influence of the earth may influence moonquake activity we investigate the relationship between tidal stress and deep moonquake occurrence by searching for a linear combination of the normal and shear components of tidal stress that best approximates a constant value when evaluated at the times of moonquakes from 39 different moonquake clusters we perform a grid search at each cluster location computing the stresses resolved onto a suite of possible failure planes to obtain the best fitting fault orientation at each location we find that while linear combinations of stresses and in some cases stress rates can fit moonquake occurrence at many clusters quite well for other clusters the fit is not strongly dependent on plane orientation this suggests that deep moonquakes may occur in response to factors other than or in addition to tidal stress several of our inferences support the hypothesis that deep moonquakes might be related to transformational faulting in which shear failure is induced by mineral phase changes at depth the occurrence of this process would have important implications for the lunar interior

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

how old are lunar lobate scarps 1 seismic resetting of crater size frequency distributions abstract previous studies have estimated the ages of lunar lobate scarps some of the youngest tectonic landforms on the moon based on the estimated life times of their fresh morphologies and associated small graben using crater degradation ages or via buffered and traditional crater size frequency distribution csfd measurements here we reexamine five scarps previously dated by binder and gunga 1985 with crater degradation ages to benchmark the evaluation of both the buffered and traditional csfd approaches for determination of absolute model ages amas at scarps both csfd methods yield similar ages for each individual scarp indicating that fault activity not only can be measured on the scarp itself but also in the surrounding terrain an indication that tectonic activity causes surface renewal both adjacent to and even kilometers distant from scarps size frequency variations in the regions surrounding the scarps are thus useful for studying the extent and severity of the ground motion caused by coseismic slip events during scarp formation all age determination approaches continue to indicate that lunar lobate scarps were active in the late copernican with some scarps possibly experiencing activity within the last 100 ma

the origin of neotectonics on the lunar nearside new observations of wrinkle ridges on the nearside maria of the moon display signs of ongoing ridge modification in association with the wrinkle ridges we observed an absence of superposed craters narrow 30 m lobate scarps and graben and thermal anomalies related to exposures of meter size blocks many of these active wrinkle ridge systems are well beyond the influence of mascon basins and unrelated to any global tectonic pattern nevertheless they spatially correlate with ancient deep seated dike intrusions on the lunar nearside revealed by gravity data analysis we propose that this active nearside tectonic system ants reflects ongoing reactivation of an ancient system related to offset antipodal effects from the south pole aitken basin

cyanobacterial mats from silurian black radiolarian cherts phototrophic life at the edge of darkness abstract remains of silicified microbial mats composed of benthic colonial coccoid cyanobacteria similar to modern entophysalidaceans and or pleurocapsaleans have been identified in lower silurian black radiolarian cherts from central and southwestern poland contrary to widespread views ascribing the genesis of such deposits to permanently anoxic deep water marine environments the abundance of benthic mats of phototrophic cyanobacteria suggests that the water mat interface must have been located at moderate depth most probably close to the limit of light penetration dysphotic zone depending on ambient sulfide levels the mats could intermittently perform anoxygenic psi or oxygenic psii photosynthesis thriving under anoxic oxic or dysoxic microaerophilic conditions the open marine offshore character of these cherts is consistent with their paleooceanographic location and with the presence of remains of such planktonic organisms as acritarchs radiolarians chitinozoans and graptolites entrapped by the cyanobacterial mats

diagenesis of upper jurassic concretions from the antarctic peninsula abstract early diagenetic calcite concretions are widespread in mudstone tuff sequences deposited in late jurassic oxygen deficient basins of the antarctic peninsula although obscured or destroyed in host rocks original components and sedimentary structures are well preserved in concretions in spite of significant mineralogical and geochemical change during growth early diagenesis led to a rapid and almost total variation in the mineralogy within the concretions independently of the original host lithologies siliceous particles were replaced by chlorite and zeolites in suboxic alkaline and moderately reducing conditions on the sea floor and in the first centimeters of burial these conditions also led to localized early formation of phosphate concretions pyrite developed subsequently because of high sulfide abundance in the sulfate reduction zone most calcite precipitation took place in the lower part of the sulfate reduction zone in a strongly alkaline environment where sulfide content had been lowered by pyrite precipitation in this stage the remaining siliceous elements were dissolved or replaced by calcite later diagenetic changes include enlargement of zeolites minor changes in clay minerals and the formation of calcite veins the wide range of 13c values in cement and vein calcite 1 47o oo and 20 23o oo pdb is explained by mixed carbon sources from organic matter oxidation and dissolution of calcareous shells the low 18o of calcite 2 34o oo to 19 72o oo pdb is the result of recrystallization in contact with high temperature diagenetic or hydrothermal fluids flushed through micro fractures in the concretions which also produced extensive vein formation

authigenic dolomites in the eocene oligocene organic carbon rich shales from the polish outer carpathians evidence of past gas production and possible gas hydrate formation in the silesian basin abstract eocene oligocene dolomite concretions and beds from the grybow and dukla units of the polish outer carpathians were studied these rocks occur in the organic carbon rich marine and fine grained deposits of hemipelagic or turbiditic origin mineralogic elemental and stable c and o isotopic composition of the dolomites was determined results indicate that the rocks were formed by precipitation of predominantly fe rich dolomite cement close to the sediment water interface prior to significant compaction the main source of bicarbonate for dolomite formation was bacterial methanogenesis as evidenced by the high 13c values up to 16 6 the main source of alkalinity was probably weathering of silicate minerals which might have also liberated ca and mg ions for the dolomites to form the distribution of these dolomites indicates that microbial methane production was widespread in the silesian basin moreover formation of some dolomites in the eastern part of the dukla unit was probably associated with gas hydrates as suggested by the elemental and oxygen isotopic composition of dolomitic matrix therefore the dolomites may serve as a proxy of areas where biogenic methane was produced where the rocks had high hydrocarbon potential and where hydrates could have existed detailed mineralogic and petrographic analyses allowed for the reconstruction of the diagenetic sequence and the evolution of pore fluids textural relationships between successive cement generations indicate that the central parts of the composite dolomite crystals experienced corrosion and that the latest ankerite cement filled the secondary intragranular cavities within those crystals this observation shows that reconstructions of pore fluid evolution based on core to rim analyses of such composite crystals may lead to wrong interpretations septarian cracks developed in the dolomites are often filled with multistage cements the earliest generations are ferroan dolomite and ankerite cements which precipitated within the cracks simultaneously to the ferroan dolomite and ankerite cements from the matrix of the dolomitic rocks which shows that septarian cracking occurred very early during the final stages of concretionary formation these cements were followed by the late diagenetic precipitates mainly quartz kaolinite and blocky calcite this calcite is commonly associated with bitumen which shows that it precipitated during or after oil migration in the decarboxylation zone

spatial distribution of carbon and oxygen isotopes in laterally extensive carbonate cemented layers implications for mode of growth and subsurface identification abstract carbonate concretions and laterally extensive cemented layers are common features in the prairie canyon member of the mancos shale at its type locality in western colorado stable isotope and petrographic data were obtained from these cemented zones in an attempt to determine 1 how the cemented layers form 2 whether or not they can be chemically correlated and 3 if it is possible to differentiate them from concretions in the subsurface the cement in both the layers and concretions consists of ferroan dolomite and lesser amounts of stoichiometric dolomite and ankerite samples for stable isotope analysis were drilled from 10 grids with a typical grid spacing of 10 cm10 cm gridded samples were obtained from two continuous cemented layers at several locations along the layers 2 3 m to 1 5 km apart on the same layer and from isolated and stratabound concretions taken together all the cements regardless of spatial position show a remarkably linear correlation r2 0 98 between 13c and 18o systematic center to edge decreases in both 13c and 18o occur in each of the cemented zones and are persistent over lateral intervals of at least 1 5 km the cores of the cemented zones have positive 13c values up to 10o oo pdb which result from incorporation of 13c enriched carbon during methanogenesis the edges of the cemented zones have negative 13c values down to 9o oo pdb which suggests incorporation of 13c depleted carbon from thermocatalytic decarboxylation reactions oxygen isotope paleothermometry indicates that precipitation may have started at moderate temperatures 25 c and ended at temperatures as high as 92 c the spatial distribution of the isotopic data in the cemented layers can be explained as resulting from the coalescence of stratabound concretions followed by growth above and below the coalesced concretions such growth may have occurred in a complex manner in which early cements precipitated throughout the thickness of the layer but were more abundant in the core zone given the lateral persistence of the pattern of isotopic variation in the cemented layers geochemical correlation of the layers may be possible in the subsurface in addition because laterally persistent cemented layers in the prairie canyon member exhibit patterns of isotopic variation different from concretions layers have a more asymmetrical vertical distribution it should be possible to distinguish between the two styles of cementation from subsurface core data alone

constraints on water transport and alteration in the oceanic crust from the isotopic composition of pore water the oxygen isotopic compositions of pore fluids from sediments of older oceanic crust commonly decrease with depth increases in calcium ion concentrations always accompany the 18o 16o decreases these changes are attributed principally to the alteration of basalts or alteration of volcanic ash in the sediments oxygen isotope material balance calculations suggest that 5 20 of the upper kilometer of basalt is altered at the time of subduction of the oceanic crust this corresponds to a flux of 18o into the oceanic crust of 2 3 1015 moles per million years evaluation of the oxygen and hydrogen isotope data from the pore fluids also suggests that the principal process of mass transfer in the sediments of older oceanic crust is diffusion convection of water in the basalts of the oceanic crust appears to continue until subduction

the physical mechanisms of deep moonquakes and intermediate depth earthquakes how similar and how different abstract we here review the characteristics of deep moonquakes dmq and conclude that they share many common features with certain categories of intermediate depth earthquakes namely the pressure temperature conditions where they occur their occurrence in highly localized nests their tendency to occur repeatedly at the same or nearly the same location and their distribution of sizes b values we thus explore various physical mechanisms proposed for earthquakes that might also explain deep moonquakes these include the possibility that there are partial melts or fluid phases in the lunar mantle that permit dmq to occur at pressures where ordinary brittle fracture is not possible the possibility that stress concentration increases tidal stresses at certain locations where moonquakes occur repeatedly and the possibility that dmq occur at relatively low stresses because rock strength is lowered by a fatigue process induced by the repetitive application of tidal stresses the similarities between dmq and terrestrial earthquakes imply that research focusing on the properties of both phenomena may help us understand the physical origins of both

apollo lunar seismic experiment final summary processing and initial analysis of the entire set of apollo lunar seismic data collected continuously from 1969 through 1977 have now been completed recent results include 1 better defined deep moonquake locations which appear to be bounded rather sharply between about 800 km and 1000 km depths with concentrations near both boundaries and 2 middle mantle 500 to 1000 km depth seismic velocities of vp 8 3 0 4 km sec and vs 4 6 0 2 km sec which are significantly higher than previous estimates and represent an increase of velocities from the upper mantle as opposed to a decrease in previous estimates

investigation of newly discovered lobate scarps implications for the tectonic and thermal evolution of the moon abstract using observations of lunar scarps in apollo panoramic camera photos binder and gunga 1985 tested competing models for the initial thermal state of the moon i e whether it was initially completely molten or if the molten portion was limited to a global magma ocean binder and gunga 1985 favored the concept of an initially molten moon that had entered into a late stage epoch of global tectonism since the start of the lunar reconnaissance orbiter mission thousands of new small lobate scarps have been identified across the lunar surface with high resolution images from the lunar reconnaissance orbiter camera lroc as such we selected spatially random scarps and reevaluated the fault dynamical calculations presented by binder and gunga 1985 additionally we examined the geometry and properties of these fault scarps and place better constraints on the amount of scarp related crustal shortening we found that these low angle thrust faults 23 have an average relief of 40 m and average depths of 951 m using crater size frequency distribution csfd measurements we derived absolute model ages for the scarp surfaces proximal to the trace of the fault and found that the last slip event occurred in the last 132 ma along with young model ages lunar lobate scarps exhibit a youthful appearance with their crisp morphologies which is indicative of late stage horizontal shortening in conclusion interior secular cooling and tidal stresses cause global contraction of the moon

evidence for recent and ancient faulting at mare frigoris and implications for lunar tectonic evolution abstract nearside basin related extensional tectonism on the moon was thought to have ended by about 3 6 billion years ago and mare basin localized contractional deformation ended by about 1 2 billion years ago lunar reconnaissance orbiter camera lroc high resolution 50 200 cm pixel images show the moon s surface in unprecedented detail and have enabled us to find many previously unidentified tectonic landforms forcing a re assessment of our views of tectonism in the maria the morphology and stratigraphic relationships of these newly identified populations of tectonic landforms imply a more complex and longer lasting history of deformation we selected mare frigoris as an ideal location to perform a mapping survey where excellent imaging conditions abundant tectonic landforms and restricted mascon allow us to unravel the mare s tectonic evolution similar to previous surveys we find that tectonism in the eastern portion of mare frigoris was controlled by ancient mascon induced flexure in the western portion however we identify a parallel set of ancient compressional wrinkle ridges across the mare that is inconsistent with an origin by mare basin centric mascon flexure or influence from the mare imbrium mascon instead our results imply an ancient regional non isotropic stress field over western mare frigoris we also identify young wrinkle ridges and show that they have likely been active within the last 1 billion years and some ridges as recently as within 40 million years finally we identify a 300 km long series of lobate scarps coincident with one of the shallow moonquakes recorded during apollo and use geodetic strain from the mapped global population of young lobate scarps to predict a level of seismicity consistent with the shallow moonquakes recorded during apollo in tandem with similarly young lobate scarps and small graben as well as recorded shallow moonquakes these young wrinkle ridges imply that some tectonism in and around mare frigoris has occurred in the geologically recent past and likely still continues today

carbonate concretions an ideal sedimentary host for microfossils microfossils extracted from carbonate concretions tend to be better preserved more abundant and diverse and more likely to retain delicate and fragile structures than those extracted from the surrounding rocks enhanced preservation correlates with early diagenetic concretion formation at or near the sediment water interface and with higher carbonate organic material and metallic cation content than in surrounding rocks early diagenetic growth is inferred by diverging sedimentary laminations and small scale sedimentary structures in fossiliferous carbonate concretions high initial concentrations of microorganisms or fecal pellets may commonly be responsible for incipient carbonate concretion growth excellent preservation is demonstrated by radiolarians and palynomorphs extracted from a carbonate concretion from the middle jurassic shelikof formation southern alaska

contrasting diagenetic histories of concretions and host rock lion mountain sandstone cambrian texas white elliptical calcite cemented concretion nuclei up to 2 m long contrast markedly in color composition and diagenetic history from more glauconite rich concretion rinds and from dark green glaucarenite host rocks concretion nuclei are placers of loosely packed trilobite carapaces and minor quartz and glauconite tightly cemented with an average of 58 calcite cement the nuclei are shell lag deposits that were cemented by calcite at the sea floor or after burial of a few meters concretion rinds composed of sub equal amounts of quartz and compactionally deformed glauconite have an average of only 32 cement which consists of minor quartz overgrowths and later pore occluding calcite cement the rinds underwent burial for several million years to tens of million years to depths of several hundred meters before they were cemented the host rock is predominantly glauconite with very minor quartz and calcite cement 87 sr 86 sr ratios of host rock calcite cement are variable 0 7084 to 0 7093 but the lowest value suggests precipitation during the middle ordovician in the absence of significant amounts of carbonate cement the host rock underwent complete dissolution of trilobite carapaces and maximum compaction with total loss of porosity through squashing of glauconite grains maximum burial during this stage was completed by the end of ordovician time carbon and oxygen isotopic values of calcite from 16 samples show no differences between concretion nuclei rinds and host rocks 13 c ranges from 2 2 to 2 9 pdb and probably reflects derivation of carbon from trilobite carapaces and other skeletal grains 18 o ranges from 4 6 to 6 2 pdb and reflects either the original composition of the cement and trilobites or the modification of original grains by meteoric dominated ground water

shallow subsurface growth and burial alteration of middle devonian calcite concretions abstract organic rich shale hosted septarian and nonseptarian calcite concretions in the middle devonian givetian hamilton group of central new york state formed early in the shallow subsurface as indicated by detailed petrography sem x radiographic lithologic geochemical and isotopic analyses 13ccarb values suggest that carbon was derived from microbial breakdown of organic matter in the sulfate reduction zone at subsurface depths of less than 10 m however strongly depleted 18o 7 to 10 pdb suggests much greater burial depths the sup 18o data appear to represent an altered isotopic signature as indicated by their narrow depleted range and petrographic evidence for recrystallization of concretion carbonate evidence of primary porosity in concretions during growth indicates that early stage diagenetic alteration occurred in an open marine phreatic environment that homogenized isotopic and geochemical signatures of metastable carbonate minerals the association of septarian calcite and bitumen along with the depleted 18o values suggests that late stage diagenesis was a result of migration of warm basin derived connate waters through the open system preburial condensation of sediments in younger stratigraphic units within the hamilton group possibly caused by increased winnowing bioturbation and erosional events during shallowing of the hamilton sea has generated stratigraphic variations in concretion lithology and shape within any given unit however variation in characteristics of concretions remains a primary function of their timing of growth versus burial compaction unlike cenozoic carbonate concretions in organic rich marine sediments that possess a dolomitic matrix no dolomite concretions were discovered in the hamilton group preliminary data suggest that restriction of calcite as the host mineral for early to middle paleozoic concretions may be controlled by elevated sulfate concentrations that inhibited dolomite precipitation and or primary secular variations in carbonate mineralogy

structure and evolution of the lunar procellarum region as revealed by grail gravity data gravity data show a rectangular pattern of narrow linear anomalies bordering the lunar procellarum region that are interpreted to be the frozen remnants of lava filled rifts and underlying feeder dykes the procellarum region is a broad area on the nearside of the moon characterized by low elevations and thin crust and largely covered by dark basalts that can be seen from earth with the unaided eye this structure has been interpreted as an ancient impact basin jeffrey andrews hanna et al use data from nasa s gravity recovery and interior laboratory grail mission to examine the subsurface structure of the procellarum they find that a pattern of narrow linear anomalies border the region interpreted to be the frozen remnants of lava filled rifts and underlying feeder dikes the discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are a part of this continuous set of quasi rectangular border structures with angular intersections the authors conclude that the procellarum was formed in response to thermal stresses produced by the differential cooling of the province relative to its surroundings coupled with magmatic activity driven by elevated heat flux the procellarum region is a broad area on the nearside of the moon that is characterized by low elevations1 thin crust2 and high surface concentrations of the heat producing elements uranium thorium and potassium3 4 the region has been interpreted as an ancient impact basin approximately 3 200 kilometres in diameter5 6 7 although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features here we use data from the gravity recovery and interior laboratory grail mission8 to examine the subsurface structure of procellarum the bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border procellarum and are interpreted to be the frozen remnants of lava filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism the discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in grail data to be a part of this continuous set of border structures in a quasi rectangular pattern with angular intersections contrary to the expected circular or elliptical shape of an impact basin9 the spatial pattern of magmatic tectonic structures bounding procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings coupled with magmatic activity driven by the greater than average heat flux in the region

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

mudrock hosted carbonate concretions a review of growth mechanisms and their influence on chemical and isotopic composition existing interpretations of cement textures and isotopic compositions may significantly under estimate the depth and duration of concretionary growth minus cement porosities can commonly under estimate depths of concretionary growth for some or all of the following reasons i cements might not passively replace host sediment porosity ii non cement carbonate phases such as replaced bioclastic carbonate can be significant iii sediment compaction models over estimate rates of porosity loss at shallow carbon isotope data from modern sediments show that dissolved carbonate in the methanogenic zone has a continuum of values from 30 to 15 and thus overlaps 13 c depleted values normally considered characteristic of sulphate reduction many concretions previously thought to have grown entirely during sulphate reduction may therefore have continued cementation during methanogenesis indicating a deeper and more prolonged cementation history the necessary carbonate supersaturation for concretionary growth could either occur throughout the porewaters the equilibrium model or be generated in situ by organic matter decay the local equilibrium model or created where external fluids are introduced the fluid mixing model

evidence of recent thrust faulting on the moon revealed by the lunar reconnaissance orbiter camera lunar reconnaissance orbiter camera images reveal previously undetected lobate thrust fault scarps and associated meter scale secondary tectonic landforms that include narrow extensional troughs or graben splay faults and multiple low relief terraces lobate scarps are among the youngest landforms on the moon based on their generally crisp appearance lack of superposed large diameter impact craters and the existence of crosscut small diameter impact craters identification of previously known scarps was limited to high resolution apollo panoramic camera images confined to the equatorial zone fourteen lobate scarps were identified seven of which are at latitudes greater than 60 indicating that the thrust faults are globally distributed this detection coupled with the very young apparent age of the faults suggests global late stage contraction of the moon

runoff and suspended sediment yields from an unpaved road segment st john us virgin islands unpaved roads are believed to be the primary source of terrigenous sediments being delivered to marine ecosystems around the island of st john in the eastern caribbean the objectives of this study were to 1 measure runoff and suspended sediment yields from a road segment 2 develop and test two event based runoff and sediment prediction models and 3 compare the predicted sediment yields against measured values from an empirical road erosion model and from a sediment trap the runoff models use the green ampt infiltration equation to predict excess precipitation and then use either an empirically derived unit hydrograph or a kinematic wave to generate runoff hydrographs precipitation runoff and suspended sediment data were collected from a 230 m long mostly unpaved road segment over an 8 month period only 3 5 mm of rainfall was sufficient to initiate runoff from the road surface both models simulated similar hydrographs model performance was poor for storms with less than 1 cm of rainfall but improved for larger events the largest source of error was the inability to predict initial infiltration rates the two runoff models were coupled with empirical sediment rating curves and the predicted sediment yields were approximately 0 11 kg per square meter of road surface per centimetre of precipitation the sediment trap data indicated a road erosion rate of 0 27 kg m 2 cm 1 the difference in sediment production between these two methods can be attributed to the fact that the suspended sediment samples were predominantly sand and silt whereas the sediment trap yielded mostly sand and gravel the combination of these data sets yields a road surface erosion rate of 0 31 kg m 2 cm 1 or approximately 36 kg m 2 year 1 this is four orders of magnitude higher than the measured erosion rate from undisturbed hillslopes the results confirm the importance of unpaved roads in altering runoff and erosion rates in a tropical setting provide insights into the controlling processes and provide guidance for predicting runoff and sediment yields at the road segment scale copyright 2006 john wiley sons ltd