the interplay of dynamic topography and eustasy on continental flooding in the late paleozoic abstract global sea level change can be inferred from sequence stratigraphic and continental flooding data these methods reconstruct sea level from peri cratonic and cratonic basins that are assumed to be tectonically stable and sometimes called reference districts and from spatio temporal correlations across basins however it has been understood that long wavelength typically hundreds of km and low amplitude

mean age of oceanic lithosphere drives eustatic sea level change since pangea breakup abstract the atlantic and indian oceans and the oceanic part of the antarctic plate have formed at the expense of panthalassa as a result of pangea breakup over the last 180 myr this major plate reorganization has changed the age vs surface distribution of oceanic lithosphere and has been a likely driver of sea level change assuming that the age surface structure of panthalassa has remained similar to the present day global distribution from 180 ma to present and using the isochron patterns preserved in the newly formed oceans we model resulting relative sea level change we find a first slower phase of sea level rise by 90 to 110 m culminating between 120 and 50 ma followed by a faster phase of sea level drop we show that this result is not strongly sensitive to our hypothesis of constant mean age of panthalassa for which much of the information is now erased due to subduction when the effects of oceanic plateau formation and ice cap development are added the predicted sea level curve fits remarkably well the first order variations of observed sea level change we conclude that the changes in mean age of the oceanic lithosphere varying between 56 and 62 0 2 myr which are simply the expression of the wilson cycle following pangea breakup are the main control accounting for 70 of first order changes in sea level

stratigraphical and δ13c records of permo carboniferous platform carbonates south china responses to late paleozoic icehouse climate and icehouse greenhouse transition abstract little attention has been focused on the stratigraphical imprints of the late paleozoic ice age on the equatorial eastern paleo tethys an integrated study of biostratigraphy microfacies and stable carbon isotope stratigraphy was carried out on pennsylvanian middle guadalupian carbonates of the gongchuan section in the bama platform south china it records seven cooling and two warming pulses in the pre kungurian interval comparing with ice proximal stratigraphical records and far field indirect proxies in lower latitudes a kungurian negative 13 c excursion from 4 4 at the base of the kungurian to 1 6 recorded only in the subequatorial belt is documented here it is followed by a global positive 13 c trend reaching 5 3 near the cisuralian guadalupian boundary seven third order shallowing upward cycles are reported for the first time from the kungurian succession the duration of each cycle is estimated to ca 1 myr these cycles are interpreted as being of glacioeustatic origin and mainly driven by long period modulations of obliquity 1 2 myr under major p co 2 decreasing condition this interpretation is supported by recent climate ice sheet modeling and cenozoic glaciation studies which argue that astronomical forcing will be amplified by large magnitude perturbations in the carbon cycle when only localized ice centers persist our results emphasize the need for integration of sedimentological and paleoclimatological proxies in elucidating the dynamics of the deglacial phases of the late paleozoic ice age

on estimating crystal shape for crystal size distribution analysis abstract the accurate determination of three dimensional crystal habit long intermediate short axis is a requirement to enable correct stereological conversion of 2d crystal size measurements to true 3d crystal size distributions csds in this contribution we introduce a database and spreadsheet program which provides an objective estimate of true crystal habit from raw 2d measurements the database compares the sample s 2d measurements with 2d shape curves for random sections through 703 different habits the output gives the five best match curves and corresponding crystal habits based on a least squares fit between sample and database the minimum sample size required to give good shape estimates from 2d data is tested using random runs of sections through known shapes with different population densities at minimum 75 crystal sections are required to robustly determine crystal habit for csd measurements if crystals are tabular in shape with more acicular shapes requiring a minimum of 250 sections suggesting a sample size of 250 sections to be used for shape determination in natural examples where the true 3d shape is unknown the crystal habit of the best match shape can then be used to provide a more robust csd analysis which in turn can be used to investigate magmatic processes with more certainty

the development of subgrain misorientations with strain in dry synthetic nacl measured using ebsd abstract the development of subgrain boundary misorientations with strain in dry synthetic nacl polycrystals deformed at elevated temperature has been investigated using electron backscattered diffraction ebsd at low natural strains up to 0 5 average misorientations of subgrain boundaries increase with strain and a power law relationship exists between strain and average misorientations the average misorientations are strongly influenced by grain orientation suggesting that the misorientation strain relationship may also be texture dependent in materials with high plastic anisotropy like nacl a slight grain size dependency of the average misorientations was observed the results indicate that with suitable calibration average subgrain boundary misorientations may offer a method for estimating the strain accommodated by dislocation creep in nacl and thus perhaps in other geological materials although current theories for polycrystalline plasticity imply that misorientations may also depend on stress in some situations

misorientation analysis and the formation and orientation of subgrain and grain boundaries in contrast to the behaviour of individual grains both inter and intra granular boundaries within rocks have received much less attention however many geological processes particularly during deformation e g yielding dislocation creep recrystallisation superplasticity and various fracture mechanisms and petrophysical properties depend to some extent on the nature of boundaries present in a rock in this contribution we consider the role of intergranular and intragranular crystal boundaries a precise characterisation of such boundaries depends on defining the crystallographic and dimensional orientations of the boundary and the misorientation between the adjacent regions i e grains subgrains etc separated by the boundary although several theoretical descriptions of boundary configuration are available practical precision is lacking and approximations are necessary we describe two specific approximations for boundary formation and orientation obtained using the sem electron channelling technique the first is a geometrical interpretation of electron channelling patterns ecp in terms of the likely formation and orientation of the intervening boundary the second considers the misorientation between adjacent regions across a boundary this involves a model which assumes a simple geometrical relationship between crystal slip systems responsible for the rotation and misorientation between adjacent regions and the formation and orientation of the resulting boundary these approximations are capable of a identifying trends in the dispersion of crystallographic directions during deformation b identifying active slip systems c calculating the relative schmid factors for each crystal slip system and therefore the most likely system to be activated d modelling synthetic misorientations and predicting the crystal slip systems and boundary configurations to be expected and e comparing real data with synthetic models our analyses are illustrated via natural examples of dynamic recrystallisation in quartzite and a theoretical simulation of the behaviour of an individual quartz grain during deformation

river channel changes in the rhone delta france since the end of the little ice age geomorphological adjustment to hydroclimatic change and natural resource management abstract this study provides a representative example of a river affected by artificial width contraction and consequent bed incision in a context of sea level rise geomorphological adjustment in the rhone catchment since the final stage of the little ice age has been induced by hydroclimatic change and human disturbances these adjustments are examined to highlight the response of two sand bed distributary channels of the rhone delta by using methods such as sedimentological evidence historical sources planimetric resurvey repeated longitudinal and cross profiling and hydraulic data the geomorphological and hydraulic responses to channel changes are characterised and their consequences assessed it is shown that the reduction of sediment yield is a combined effect of a decrease of flood frequency sediment dredging and building of dams on the rhone river and its tributaries the combination of decreased catchment sediment yield artificial width contraction increased stream power and boundary shear stress is the cause of channel incision of the rhone river in the coastal zone the increase of the rhone river s stream power has facilitated the transport of sediment down to the subdeltas engineering works designed to stabilise the planform and to limit overbank flooding caused 1 channel entrenchment thus 2 the destabilization of infrastructure e g bridges quays along the river 3 the lowering of the phreatic water table in the floodplain which in turn induced 4 soil salinization change in salt wedge position eventually the channelization led to 5 an increase of the flood hazard and risks because although more rare the inundations have become more destructive however the contribution of the large flood events is negligible in terms of progressive channel in filling because of their low frequency finally no relation exists between the vertical adjustment of the rhone channel through entrenchment and relative sea level which rose at a rate of up to 2 mm year 1 during the 20th century clearly natural resource management in particular engineering activities were the main cause of the river channel changes that occurred during the last century

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

using dendrogeomorphology and 137cs and 210pb radiochronology to estimate recent changes in sedimentation rates in kushiro mire northern japan resulting from land use change and river channelization abstract the purpose of this study is to describe the history of sediment deposition that has been occurring for several decades along the margins of the kushiro mire into which the kuchoro river drains the dendrogeomorphic technique was used to examine an even aged forest and adventitious roots to assess short term 20 years deposition rates and the frequency of heavy rainfall events for medium 40 years and long term 100 years deposition rates radiochronological analyses using 137 cs and 210 pb were also conducted several instances of high deposition rates caused by flooding events during the last 20 years were identified from the analysis of adventitious roots the average sedimentation rate from 1963 to the present estimated from the 137 cs study is over 1 3 cm year using the 210 pb dating method based on a cfcs model which considered the organic matter content appropriate to wetland sediment three deposition rates in the last 60 years were estimated 2 0 cm year from 1981 to 2000 8 9 cm year from 1975 to 1981 and 0 14 cm year from 1939 to 1975 the analysis of environmental radionuclides indicated that the greatest sedimentation rates occurred in the years 1975 to 1981 when the kuchoro river was extensively channelized and flood and or precipitation events occurred this suggests that land use development and channelization introduced a large amount of sediment into the marginal areas of wetland through the drainage system and this was deposited on top of the peat soil

the geomorphic evolution and sediment balance of the lower rhone river southern france over the last 130 years hydropower dams versus other control factors article i nfo atthe end of thelittleice age lia agriculturalpractices and successive phasesof channel management involv ing embankments and dams however the respective roles of these various control factors in modifying sedi ment storage and channel stability are often difficult to identify the aim of this paper is to determine the main factors that have driven morphological changes over the past 130 years on the 120 km long downstream reach of the rhone river a gis based analysis of maps and aerial photographs available since 1860 coupled with chrono stratigraphic data on the river s alluvial deposits has enabled quantification of sediment storage and erosion in different morphological units changes measured include riverbed incision narrowing of the main channel in relation with accumulation of fine sediments along the channel margins and reduction of sed iment input at the mouth on the basis of local and reach scale sediment balances we show that these changes are synchronous with engineering works carried out at the end of the nineteenth century and beginning of the twentieth century a period that coincided with a decline in river sediment inputs largely generated by human activities the early stabilisation of mountain slopesresulting from a decline inrural agriculture rural exodus re forestation and engineered torrent control has had a much greater impact in geomorphically transforming the rhone than dams and gravel mining the major identified causes of river destabilisation in the world this calls for caution in the all too common and wholesale attribution of declining sediment budgets of european rivers

sedimentology and sequence stratigraphy of a pronounced early ordovician sea level fall on baltica the bjorkasholmen formation in norway and sweden abstract the bjorkasholmen formation consists of interbedded carbonates shales and glauconitic beds and is characterized by heavy bioturbation and few preserved sedimentary structures the unit shows five facies shale glauconitic packstone and three predominantly mud dominated carbonate facies carbonates and shales are arranged in small scale deepening upward cycles a minimum of fourteen of these small scale cycles are recognized in the bjorkasholmen formation they are arranged in stacks of 3 to 5 forming a total of four medium scale cycles separated by decimeter thick shale units based on the predominance of mud rich facies the succession is interpreted to have been deposited in an overall tranquil setting during one mayor sea level fall and subsequent initial rise of third order time estimates suggest that the 14 small scale cycles fall into the milankovitch band of precessional forcing and the overriding medium scale cycles likely represent short eccentricity the sequence stratigraphic interpretation shows that the bjorkasholmen formation is characterized by falling stage lowstand and initial transgressive systems tracts consequently the contact between the bjorkasholmen and the underlying alum shale formation represents the basal surface of forced regression the maximum regressive surface is defined by a hiatus in the oland sections and by shallow marine packstones within mud rich distal ramp carbonates in norway the top of the bjorkasholmen formation represents a flooding surface at the base of the transgressive systems tract a comparison of time equivalent successions worldwide suggests that the bjorkasholmen formation represents a tectonically enhanced lowstand with two overriding short term milankovitch eustatic signals although deposition of the bjorkasholmen formation coincides with the initiation of a foreland basin in the caledonides of norway it remains unclear how these tectonic movements may have lead to the widespread bjorkasholmen lowstand during the early ordovician it is suggested in this study that a combination of compressional forces from avalonia and the caledonian margin may have acted in concert to produce an uplift of larger parts of the baltica plate for a time span of approximately 0 5 myr

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

tectonostratigraphic evolution of the eastern algerian margin and basin from seismic data and onshore offshore correlation abstract the eastern algerian basin part of the western mediterranean domain is a back arc basin resulting from the se drift of the lesser kabylia block gave rise to continental extension and birth of a new oceanic domain we aim here to define the structure and tectonostratigraphic evolution of this basin and the adjoining continental margin indeed the absence of wells and the lack of published mcs data kept this area mostly unknown the crustal architecture down to the moho and seismo stratigraphy of the sedimentary infill are detailed emphasizing particularly the pre messinian series by combining a new set of offshore deep penetrating seismic conventional mcs sections and wide angle seismic data because no well exist offshore we realized new field descriptions of the late oligocene and miocene deposits on land and propose onshore offshore extrapolation and age correlations the pre messinian series display four main units pmsu1 to 4 above which messinian units are consistent with stratigraphic models already proposed for the mediterranean basin the deep basin displays units as old as the omk oligo miocene kabyle series on land the basement is shaped by conjugate transcurrent faults striking n120 n40 forming a series of rhombic troughs resulting from transtensional tectonics the coeval e w extension and nw se stretching of the continental crust suggest a radial opening of the algerian basin during late oligocene lower miocene followed by a progressive uplift of the upper margin after the collision of lesser kabylia with africa besides steep slope of the eastern algerian margin downward flexure of the oceanic basin near the margin toe and growth of s dipping thrusts within the margin evidence a significant quaternary stress inversion overall this study highlights the complex stress evolution of the east algerian margin since oligocene times as evidenced by significant upward downward vertical motions and crustal extensional compressional successions we summarize this evolution into three main stages 1 rifting including sea floor spreading at late oligocene burdigalian in the context of back arc 2 collision between alkapeca blocks and africa at 17 ma and post rift sag basin infill till late tortonian to messinian and 3 inversion of the margin and development of flexural basins at quaternary times

criteria for the recognition of salt pan evaporites layered evaporites can accumulate in 1 ephemeral saline pans 2 shallow perennial lagoons or lakes and 3 deep perennial basins criteria for recognizing evaporites deposited in these settings have yet to be explicitly formulated the characteristics of the ephemeral saline pan setting have been determined by examining eight holocene halite dominated pans salt pans and their deposits marine and non marine from the u s mexico egypt and bolivia these salt pans are typified by alternating periods of flooding resulting in a temporary brackish lake evaporative concentration when the lake becomes saline and desiccation which produces a dry pan fed only by groundwater the resulting deposits consist of alternating layers millimetres to decimetres of halite and mud the layers of halite are characterized by 1 vertical and horizontal cavities rounded crystal edges and horizontal truncation surfaces due to dissolution during flooding 2 vertical chevrons and cornets grown syntaxially on the bottom during the saline lake stage 3 halite cements overgrowths and euhedral cavity linings and disruption of layering into metre scale polygons produced during the desiccation stage the muddy interbeds are characterized by displacive growth of halite during the desiccation stage immediately below the surface of the pan the halite layers are matured by repeated episodes of dissolution and diagenetic crystal growth this results in porous crusts with patches of chevron and cornet crystals truncated by dissolution clear diagenetic halite cement and internal sediment these layers of mature halite closely resemble the patchy cloudy and clear textures of ancient halite deposits holocene salt pans are known to cover thousands of square kilometres and cap halite deposits hundreds of metres thick so they are realistic models for ancient evaporites in scale e g permian salado formation of new mexico texas which preserves many primary salt pan features

phanerozoic transgressions and regressions on the continents a quantitative approach based on areas flooded by the sea and areas of marine and continental deposition

an assessment of sediment transport processes in the lower mekong river based on deposit grain sizes the cm technique and flow energy data abstract the lower mekong river has been an important research topic for at least 15 years notably in the fields of hydrology fluvial geomorphology and the impact of dams recent papers refer mostly to the impact of the lancang chain of hydroelectric dams constructed on the chinese section of the river among the pending scientific questions are 1 the upstream downstream variations in the concentration and yield of suspended sediment and 2 the relative importance of sand in the total yield the general consensus among the scientific community is that the relative importance of sand in suspended load is not the main scientific concern despite its extensive presence in the mekong river channel as noted by geomorphologists and despite its extreme importance for the stability of the delta shoreline in viet nam this paper contradicts the general consensus its objective is to present new information on the processes of sand transport in the lower mekong channel imagery field observations sampling on the river banks and grain size analysis of sand deposits have been carried out between chiang sean downstream of the chinese border and the delta the c m image technique served to discriminate between the various transport processes bedload and different types of suspension this technique helps in understanding the changing processes responsible for downstream sediment transfer in river channels the results of this study are the following 1 discrepancies in the values of annual suspended sediment load detected by different gauging stations have not yet been satisfactorily explained the cm image technique indicates that grain size and the quantity of sand transiting in suspension vs bedload vary from upstream to downstream 2 these upstream downstream differences may be related to the energy of floods energy helps to explain longitudinal variations in the relative importance of the different modes of transport and serves to distinguish between bedload graded and uniform suspension and wash load 3 the mekong is seen as a river carrying mostly silt and clay however the results suggest that sand plays a major role in downstream sediment transfer during floods this result is in line with the large amounts of sand present in the channel its relative importance in the total yield must be reassessed as suggested by walling 2005 2008 as may be expected the role of sand in the stability of the delta shoreline is of prime importance

palaeoenvironmental changes at col des tribes montagne noire france a reference section for the famennian of north gondwana related areas we present detailed biostratigraphy based on conodonts and palaeoenvironmental trends deduced from microfacies and conodont abundance through the famennian late devonian at col des tribes montagne noire france the succession is characterized by micritic limestones deposited in settings oscillating between mid to outer ramp facies contain poor fauna widely dominated by nektonic organisms this section is complete and one of the most conodont rich for the famennian of the north gondwana related area the upper kellwasser event frasnian famennian boundary and the hangenberg devonian carboniferous boundary have been lithologically identified they are characterized by decimetre thick black dysoxic to anoxic argillaceous sediments the condroz and annulata events although not materialized by lithological changes have been positioned due to the precise stratigraphy the first event occurred during the deposition of condensed ferruginous facies griotte limestones and the second event during the deposition of micrites barren of benthic fauna the combination of information from both facies and conodont biofacies changes allows a general sea level curve through the entire famennian for north gondwana to be proposed for the first time at col des tribes the general trend is a slight deepening upwards from triangularis to trachytera zones then a pronounced shallowing upwards trend from upper trachytera to praesulcata zones this curve correlates with the well known reference curve from euramerica concerning the late famennian trachytera to praesulcata zones there are some discrepancies in minor cycles which can be explained by tectonical phenomena at the onset of the edification of the variscan belt in europe

discrimination of local and global effects on upper mississippian stratigraphy illinois basin u s a abstract interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics eustasy tides and climate on upper mississippian middle chesterian stratigraphy in the tectonically active tide dominated illinois basin the cross sections show that five mixed carbonate siliciclastic high frequency sequences in the bethel through glen dean formations can be correlated around the outcrop belt through areas with very different subsidence histories the sequence boundaries are marked by paleosols and incised valleys and can be correlated basin wide within a framework of distinctive marker beds because of its updip position lowstand systems tracts are not preserved in the illinois basin the transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open marine skeletal limestone shallow marine shale and heterolithic siliciclastic tidal flat deposits the maximum flooding surface mfs for the sequences is picked at the base of the deepest water limestone facies highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal flat facies the basin wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea level changes rather than local tectonics or autogenic processes the sequences were likely produced by moderate to high amplitude 30 100 m fourth order 400 ky glacio eustatic sea level changes driven by the transition from the greenhouse conditions of the early mississippian to the icehouse conditions of the late paleozoic the lateral extent and frequency of component parasequences suggests that they were likely produced by fifth order sea level changes 10 100 ky the sequences may be bundled into third order composite sequences but the third order signal is obscured by the magnitude of the fourth order sea level changes a feature typical of ice house stratigraphies the sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the cincinnati arch and the more rapidly subsiding basin interior episodes of high and low differential subsidence occurred every two to three sequences these subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences the occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the appalachian orogenic belt to the east even in this tectonically active setting however it is the eustatic signal that generates basin wide mappable stratigraphic sequences

the spatial variability of overbank sedimentation on river floodplains abstract river floodplains are important landforms and information on rates and patterns of overbank sediment deposition is essential for understanding their development such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models the use of bomb derived 137cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved this approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques the study reported uses 137cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five british lowland rivers attention is given both to the overall reach and to more detailed investigations of small areas the observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved which include the floodplain microtopography and morphology the relationship between the grain size composition of deposited sediment and sedimentation rate is also considered

recent morphological channel changes in a deltaic environment the case of the rhone river france abstract channel morphological changes were measured at two sites within the rhone delta along the main channel of the rhone river over one century results show an average erosion rate of 2 8 mm year 1 during the 20th century and decreasing to

seismic reservoir characterization in resource shale plays stress analysis and sweet spot discrimination surface seismic data have proven to be an invaluable asset for organizations producing hydrocarbons from unconventional resource plays initially a primary benefit of surface seismic was the ability to locate and avoid drilling into zones with faults fractures and karsting which adversely affected the ability to complete the well successfully more recent advances in prestack seismic data analysis yield attributes that appear to be correlated to formation lithology rock strength and stress fields knowledge and proper utilization of these attributes may prove valuable in the optimization of drilling and completion activities

the evolution of the calabrian arc evidence from paleomagnetic and gps observations abstract the present day arcuate shape of the calabrian arc has been accomplished during neogene and early pleistocene by large and opposite vertical axis rotations along the two arms of the arc clockwise cw rotations have been systematically registered in sicily and calabria whereas counterclockwise ccw rotations were measured in southern apennines such opposite vertical axis rotations ceased in the uppermost part of the lower pleistocene about 1 ma ago along almost the entire calabrian arc and are not observed in the present day gps velocity field the end of the calabrian arc bending during the quaternary marks a decrease in the efficiency of the tectonic processes related to the long lived subduction of the ionian slab which caused the halting of the back arc opening in the southern tyrrhenian sea

pattern of orogenic rotations in central eastern sicily implications for the timing of spreading in the tyrrhenian sea new palaeomagnetic data from upper triassic to pliocene sediments reveal that in eastern sicily a major 70 clockwise cw rotation took place between oligocene and late tortonian time followed by a further 30 cw rotation results from central sicily are less coherent they show 44 83 post oligocene cw rotation local 14 post late tortonian counterclockwise ccw rotation and 25 post mid pliocene cw rotation we interpret the larger cw rotation observed in eastern sicily as related to a more internal palaeogeographical position with respect to central sicily our results complement pre existing data from the northwestern sicily carbonates and indicate that all the internal carbonate nappes coherently rotated by c 100 cw during tectonic emplacement implying a west to east increase of shortening in the sicilian maghrebian belt in sicily compressive deformation started during the langhian i e just after the deposition of the upper oligocene upper burdigalian numidian flysch turbidites therefore the age of the older 70 palaeomagnetic rotation synchronous to the thrusting is constrained to occur between the langhian and late tortonian furthermore by considering a maximum possible rotation rate of 20 ma 1 we infer that cw rotation started in sicily in langhian serravallian times between 15 16 and 11 12 ma ago the 100 cw rotation observed in pre orogenic strata from the whole of sicily is mirrored by 80 orogen scale ccw rotations characterizing the internal southern apennines palaeomagnetism therefore shows that during orogenesis the southern apennines and the sicilian maghrebides rotated in a saloon door fashion synchronous to back arc spreading of the southern tyrrhenian sea consequently our palaeomagnetic data suggest that the southern tyrrhenian back arc basin started to spread during langhian serravallian times from 15 16 to 11 12 ma significantly earlier than the late tortonian age 8 ma suggested so far by oceanic drilling data

floodplains permafrost cottonwood trees and peat what happened the last time climate warmed suddenly in arctic alaska abstract we use the stratigraphy of floodplains on alaska s north slope to describe how tundra watersheds responded to climate changes over the last 15 000 calibrated years bp 15 cal ka bp two episodes of extremely rapid floodplain alluviation occurred during the pleistocene holocene transition one between 14 and 12 8 cal ka bp and the other between 11 5 and 9 5 cal ka bp these aggradation episodes coincided with periods of warming in summer when cottonwood populus balsamifera l expanded its range peatlands became established and widespread thermokarst occurred the two aggradation episodes were separated by a period of floodplain incision during the younger dryas under cooler and possibly drier conditions at times of increasing summer warmth melting permafrost and enhanced precipitation probably triggered widespread mass wasting on hillslopes that overwhelmed the capacity of streams to transport sediment downstream and rapid floodplain aggradation resulted after peatlands became widespread in the early holocene rivers slowly incised their valley fills because major pulses of sediment input were limited to times of rapid thaw and increasing moisture many floodplains on the north slope have been effectively decoupled from upstream hillslopes for much of the past 15 000 years our findings a confirm the sensitivity of arctic watersheds to rapid warming in summer b emphasize the importance of hillslope mass wasting in landscape scale responses to climate change and c suggest that the presence of peatland on this arctic landscape today has raised its geomorphic response threshold to climate warming compared to what it was 14 000 years ago

sedimentation in the riparian zone of an incising river this paper focuses on one aspect of riparian zone change associated with channel incision it presents information on sedimentation within the riparian zone of the river garonne france derived from both historical and contemporary sources the riparian zone investigated is morphologically complex containing a remnant island and cut off channel information drawn from historical and contemporary sources permits the reconstruction of channel planform and cross profile change as well as an assessment of changes in riparian zone sedimentation rates and patterns very significant changes are identified over the last 50 years a change from a multiple thread to single thread channel planform high rates of riparian zone sedimentation of the order of 0 5 to 2 5 cm a 1 clear spatial patterns in over bank sedimentation reflecting topographic and vegetational variations and flood event magnitude and a reduction in morphological and vegetational diversity through the period which is expected to continue as the zone is transformed into an increasingly homogeneous sediment sink copyright 2001 john wiley sons ltd

gypsum anhydrite transformations in messinian evaporites of central tuscany italy abstract the messinian succession of tuscany central italy contains three evaporitic units among the several exposed evaporitic lithofacies only selenitic gypsum precipitated directly from evaporating brines all the other facies nodular microcrystalline gypsum gypsarenites and gypsum laminites despite their macroscopic differences display the same petrographic textures indicating that they are the product of dehydration of gypsum to give anhydrite which has been successively rehydrated to secondary gypsum these secondary facies show an entire array of textures ranging from cloudy ameboid xenotopic with anhydrite relics to idiotopic without anhydrite relics that are here interpreted as a sequence of progressive stages of rehydration the presence of completely hydrated petrofacies at the core of nodules which display a less hydrated rim suggests that these rocks have undergone at least two cycles of a dehydration rehydration process this interpretation is supported by the presence of satin spar veins that are replaced by microcrystalline gypsum satin spar itself is considered to be a by product of anhydrite hydration the first dehydration rehydration event affected the entire gypsum deposit producing a completely hydrated idiotopic facies together with satin spar veins the second affected only veins fractures and the rims of nodules turning the first generation of satin spar and idiotopic gypsum into cloudy ameboid gypsum sedimentary structures typical of sabkha environments indicate for the youngest formation that the first dehydration and rehydration process occurred syndepositionally the preservation of primary gypsum facies only at sites with condensed sections indicate for the oldest two formations that the first dehydration event occurred upon burial this event has been estimated to have occurred in the earliest pliocene after the early pliocene dehydration was favored even at shallow depths due to an increased heat flow related with the emplacement of local crustal magmatic bodies rehydration possibly occurred when these formations were uplifted and exposed to ground and or meteoric water the volterra basin has undergone alternating subsidence and uplift events that can account for two dehydration rehydration processes at least also driven by alternating circulation in the tectonic fractures of fresh and salty water the latter derived from dissolution of messinian halite

microstructural evolution of deformation modified primary halite from the middle triassic rot formation at hengelo the netherlands the microstructure of halite from the subhorizontal bedded main rot evaporite member at hengelo the netherlands akzo well 382 depth interval of 420 460 m was studied by transmitted and reflected light microscopy of gamma irradiation decorated samples primary microstructures compare favourably with those found in recent ephemeral salt pans large blocky fluid inclusion poor halite grains and elongated chevrons are interpreted to have formed in the saline lake stage while void filling clear halite is interpreted to have formed during the desiccation stage of the salt pan in addition in all layers the grains are rich in deformation related substructures such as slip bands and subgrains indicating strains of a few percent the study of gamma irradiation decorated thin sections shows that the main recrystallization mechanism is grain boundary migration grain boundary migration removes primary fluid inclusions and produces clear strain free new grains differential stresses as determined by subgrain size piezometry were 0 45 0 97 mpa the deformation of the salt layers is probably related to cretaceous inversion in the area

reducing uncertainty in characterization of vaca muerta formation shale with poststack seismic data the late jurassic early cretaceous vaca muerta vm formation in the neuquen basin has served as an important source rock for many of the conventional oil and gas fields in argentina with the interest in developing and exploiting shale resources in the country many companies there have undertaken characterization of the vm formation in terms of the elements of shale plays among other characteristics shale plays can be identified based on the total organic carbon toc content better toc leads to better production however there is no way of measuring it directly using seismic data and it can be estimated only indirectly considering the influence of toc on compressional and shear velocities and density geoscientists have attempted to compute it using the linear or nonlinear relationship it might have with p impedance understanding the uncertainty in using such a relationship for characterizing the vm formation a different approach has been followed for characterizing it because a linear relationship seems to exist between gamma ray gr and toc in addition to p impedance gamma ray is another parameter of interest for characterizing the vm formation using p impedance and gr volumes a bayesian classification approach has been followed to obtain a reservoir model with different facies based on toc and the associated uncertainty with it as the first step different facies were defined based on the cutoff values for gr and p impedance computed from well log data then gaussian ellipses were used to capture the distribution of data in a crossplot of gr versus p impedance next 2d probability density functions pdfs were created from the ellipses for each of the facies combining these pdfs with gr and p impedance volumes different facies were identified on the 3d volume poststack model based inversion was used to compute the p impedance volume and the probabilistic neural network pnn approach was used to compute gr volume derived p impedance and gr volumes correlated nicely at blind wells on the 3d volume which gave confidence in the characterization of the vm formation an overlay of the discontinuity detail in terms of curvature lineaments on the determined toc content at the level of interest helps in obtaining a more complete picture which is useful for the planning of horizontal wells

heterogeneous deformation and texture development in halite polycrystals comparison of different modeling approaches and experimental data modeling the plastic deformation and texture evolution in halite is challenging due to its high plastic anisotropy at the single crystal level and to the influence this exerts on the heterogeneity of deformation over halite polycrystals three different assumptions for averaging the single crystal responses over the polycrystal were used a taylor hypothesis a self consistent viscoplastic model and a finite element methodology the three modeling approaches employ the same single crystal relations but construct the polycrystal response differently the results are compared with experimental data for extension at two temperatures 20 and 100 degreesc these comparisons provide new insights of how the interplay of compatibility and local equilibrium affects the overall plastic behavior and the texture development in highly anisotropic polycrystalline materials neither formulation is able to completely simulate the texture development of halite polycrystals while at the same time giving sound predictions of microstructural evolution results obtained using the finite element methodology are promising although they point to the need for greater resolution of the individual crystals to capture the full impact of deformation heterogeneities c 2003 elsevier b v all rights reserved

the mediterranean water body in the late messinian interpreting the record from marginal basins on sicily the stratigraphic record of climatic and palaeoceanographic changes in the mediterranean during the late messinian is controversial on sicily sedimentary facies show a steady transgression suggesting that sub basins were hydrodynamically linked to a larger water body here we test this hypothesis using strontium isotope studies from messinian materials collected from a range of sites in the caltanissetta basin of central sicily the strata include a regionally regressive first cycle of early mid messinian age and a younger transgressive second cycle these cycles are separated by an inter regional unconformity which may be correlated with base level low stand in the mediterranean 87 sr 86 sr ratios for all first cycle gypsum fall within the expected global marine composition 0 70891 0 70897 all second cycle analyses fall within a grouping of significantly lower values 0 70868 0 70878 a surprisingly tight but discrepant grouping for data collected from shells of a brackish water fauna and from gypsum analyses from these different second cycle materials are statistically indistinguishable these results indicate that the strontium isotopic composition of waters from different sub basins on sicily are indistinguishable regardless of salinity during the late messinian therefore these basins must have mixed with a larger homogenized reservoir which we infer was the ancestral mediterranean thus circum mediterranean basins may indeed chart regional palaeoceanographic and climatic events by the end of messinian times the base level of the mediterranean was within the range of the world9s oceans but the water body probably had a distinctly different but internally homogeneous strontium isotopic composition

use of multi proxy flood records to improve estimates of flood risk lower river tay scotland abstract proxy flood records from sediment stacks in floodplain palaeochannels provide an opportunity to extend short instrumental records and thus improve current estimates of flood risk the bloody inches a meander cutoff on the lower river tay scotland has been infilling with flood deposits since c 1761 agricultural flood embankments locally breach with flows 850 m3 s 1 introducing silts into the palaeochannel and extensively fail with flows 1200 m3 s 1 which deposit sand repeated cores at the site up to 1 4 m in depth consistently reveal sand rich flood units in the upper section of the core 137cs dating enables these units to be correlated with clusters of floods in the post 1950 discharge record sand units in the lower part of the profile are correlated with major floods from 1814 onwards using a 210pb based chronology these dates are independently corroborated by flood marks inscribed on smeaton s bridge in perth 15 km downstream estimates of historic high flows back to 1814 can also be recovered from these flood stage levels at smeaton s bridge when combined with the 48 year long flow record these historic floods yield an augmented pot series extending back to 1847 using a relatively high threshold of 1361 m3 s 1 and the generalised pareto distribution to model this pot series estimates of the 50 100 and 200 year floods are 1875 2250 and 2050 m3 s 1 respectively these results provide independent and robust confirmation of the flood risk at perth using the standard statistical procedures advocated in the flood estimation handbook if successfully replicated at other sites radiometric dating of sediment stacks in palaeochannels provides a new technique to further advance palaeohydrology and the recovery of historic floods

influence of structural anisotropy on creep of rocksalt from simla himalaya india an experimental approach abstract the influence of structural anisotropy on time dependent deformation creep of rocksalt from shali formation precambrian himachal pradesh india was investigated to analyze the differential mobility of rocksalt body in nature the effect of structural anisotropy orientation of bedding planes with respect to the compression axis on the compressive strength yield strength modulus of elasticity failure strain and yield strain of rocksalt has been analyzed on cubic samples 5 5 5 cm3 to collect the basic input for the purpose of creep of rocksalt time dependent compression of cubic samples perpendicular parallel and oblique to bedding planes were subjected to constant stresses equal to 30 40 50 60 70 75 and 80 of their uniaxial compressive strengths for presenting analogous situation of variable stressing of rocksalt caused by over laying rocks and tectonic stresses the results of experimental deformation reveal the strong control of structural anisotropy on development of instantaneous strain transient strain steady state strain and accelerated strain however the influence of structural anisotropy on deformation of rocksalt decreases with increment in stress levels at higher stress level creeps the control of structural anisotropy on deformation became negligible the progress of time dependent deformation occurs due to evolution of minute tensile and shear crack arrays in proportions at lower stress creep the development of tensile crack arrays and shear crack arrays is assisted by structural anisotropy however at higher stress levels the creep of rocksalt is facilitated by reduction in tensile crack arrays and domination of shear crack arrays resulting in shearing where the anisotropic rocksalt exhibits isotropic behaviour thus the mobility of rocksalt bodies is dependent on characteristic of structural anisotropy and stress conditions

the brittle ductile transition in a deformation mechanism map for halite abstract the brittle ductile transition in rock deformation has been studied extensively but is still poorly quantified progress in our understanding of this and other transitions in mechanical behavior and deformation mechanisms is facilitated by use of deformation mechanism maps a preliminary deformation mechanism map for halite is presented based on shear experiments at room temperature 22 c over the range of normal stress up to 350 mpa and average shear strain rates between 10 to 10 6 s 1 the map illustrates that transitions in mode of failure mechanical behavior and dominant deformation mechanism which often are referred to collectively as the brittle ductile transition do not necessarily coincide the analysis also suggests that the transition from dominantly cataclastic to crystal plastic deformation mechanism fields is adequately described by the distinct and independent mechanism field of semi brittle flow

architecture and evolution of calciclastic marginal slope fans of the ordovician carbonate platform in the yijianfang outcrop of the bachu area west tarim basin the ordovician carbonate platform at the yijianfang outcrop of the bachu uplift region in the western tarim basin contains four types of genetic facies associations developed in the calciclastic slope fan depositional system an olistostrome zone fan channels lobes and a marginal slope the olistostrome zone is characterized by olistoliths and slump fans whereas the fan channels and lobes are further divided into proximal and distal facies the marginal slope deposits constitute the background sedimentation in which the calciclastic slope fans are intercalated from proximal to distal parts of the fan channels and lobes their scale gradually becomes smaller and the size and sorting of grains become finer and better respectively analysis of the stratigraphic framework indicates that the fans formed in the lower strata of the upper ordovician lianglitage formation in four high frequency sequences i e pss1 pss4 field paleocurrent measurements indicate northeast southwest depositional strike for the early platform margin of the lianglitage formation sediments in the calciclastic slope fans were derived from the platform margin and evolution of the calciclastic slope fans was generally progradational from pss1 to pss2 and then continuously retrogradational from pss2 to pss4 the calciclastic slope fans in the outcrop area are not reservoir prone rocks but interpretation on these fans can provide useful information about potential hydrocarbon reservoirs along the platform margin the p wave velocity s wave velocity and density variations in each genetic facies may be used to identify the subsurface calciclastic slope fan depositional system

quantitative model of the growth of floodplains by vertical accretion a simple one dimensional model is developed to quantitatively predict the change in elevation over a period of decades for vertically accreting floodplains this unsteady model approximates the monotonic growth of a floodplain as an incremental but constant increase of net sediment deposition per flood for those floods of a partial duration series that exceed a threshold discharge corresponding to the elevation of the floodplain sediment deposition from each flood increases the elevation of the floodplain and consequently the magnitude of the threshold discharge resulting in a decrease in the number of floods and growth rate of the floodplain floodplain growth curves predicted by this model are compared to empirical growth curves based on dendrochronology and to direct field measurements at five floodplain sites the model was used to predict the value of net sediment deposition per flood which best fits in a least squares sense the empirical and field measurements these values fall within the range of independent estimates of the net sediment deposition per flood based on empirical equations these empirical equations permit the application of the model to estimate of floodplain growth for other floodplains throughout the world which do not have detailed data of sediment deposition during individual floods copyright 2000 john wiley sons ltd

human induced sedimentation patterns of a channelized lowland river channelization of the severely polluted odra and vistula rivers in poland induced intensive accumulation of fine grained deposits rich in organic matter and heavy metals these sediments have been identified in vertical profiles in a narrow zone along river banks both in groyne created basins and on the floodplain grain size organic matter zinc zn lead pb copper cu content and cesium 137 137cs was used for sediment dating and stratigraphy and chemistry have been diagnostic features for these deposits named industrial alluvium in the most polluted river reaches stabilized by bank reinforcements and groynes 2 m thick slack water groyne deposits are composed of uniform strata of polluted silts with organic matter content over 10 zn content over 1000 mg kg and average cu and pb over 100 mg kg the average rate of sediment accretion in groynes is higher than on the floodplain and reaches 5 cm yr stratification which appears at higher levels in the groyne fields and on the levees reflects a change from in channel to overbank deposition and is typified by dark layers separated by bright sandy and less polluted strata stratified 4 m thick sediment sequences have been found in groyne fields of incised river reaches the average rate of sediment accretion in these reaches is of the order of 5 cm yr in stable and relatively less polluted river reaches vertical accretion organic deposits are finely laminated and the average rate of deposition amounts to a few millimeters per year investigations indicate that groyne construction favors conditions for long term storage of sediments at channel banks for this reason groynes should be considered as structures that efficiently limit sudden release of sediment associated heavy metals stored in channels and in floodplains of the historically polluted rivers copyright 2014 john wiley sons ltd

creep of rocksalt abstract a review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates included in the summary are discussions of a microstructures induced during steady state creep b creep rupture of rocksalt c experiments associated with project salt vault and more recent field studies and d brine migration a representative steady state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics while the mechanical behavior of rocksalt is probably better understood than for all other rock types further investigations especially on load path stress history and creep rupture are clearly mandated furthermore additional investigations of brine migration and of bench and field scale deformations are needed the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock mass response

accelerated overbank accumulation after nineteenth century river regulation works a case study on the maros river hungary abstract in the nineteenth century the meandering rivers of the carpathian basin were extensively regulated and their large up to 100 km wide floodplains were confined by artificial levees on the narrow 0 5 4 km artificial floodplains confined by these levees overbank sedimentation has become the dominant geomorphological process resulting in rising floodplain levels during the last century the maros river is an extreme example of this process as it carries a significant amount of suspended sediment 4 6 10 6 m 3 y and because its lowland reach was drastically shortened by cutoffs resulting in bed scour and an increased sediment load simultaneously a flood embankment system was constructed reducing the floodplain width by 70 80 the resulting accelerated overbank sediment accumulation increases the flood hazard along the river the aim of this study is to determine the spatial and temporal pattern of overbank sediment accumulation on the artificial floodplain of the lower maros river over the last 150 years and to identify its influencing factors the lateral slope of the protected natural floodplain was projected towards the present day channel allowing the volume m 3 and rate cm y of overbank sedimentation to be calculated using digital terrain modelling dtm changes in the rate of sedimentation were determined by pollen analysis the studied reach was divided into five sections based on the rate of aggradation i the distal surface of the alluvial fan where no sedimentation was measured only incision ii the original front of the alluvial fan 1 0 0 4 cm y iii the recently formed secondary alluvial fan 1 4 0 3 cm y iv the low lying floodplain 0 4 0 2 cm y and v the outlet unit 2 0 0 5 cm y the aggradation rate was slower on elevated forms such as the pre regulation natural levee 0 2 cm y and greater on the low lying floodplain 0 6 cm y the greatest accumulation rate 1 3 2 4 cm y was measured in cutoffs the sedimentation rate was high during the regulation period 1 9 2 4 cm y but later decreased to 0 5 0 9 cm y the rate of aggradation was determined by the width height and slope conditions of the floodplain the impoundment of the main river and the land use in the area

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

rheological behaviour of synthetic rocksalt the interplay between water dynamic recrystallization and deformation mechanisms abstract the ductile deformation of rocks in nature can be greatly enhanced by the presence of water part of the water induced weakening of rocks at depth may come from fluid assisted deformation or recrystallization mechanisms that are absent in dry rocks in this study we investigate the effect of water on the rheological behaviour of rocksalt we focus on quantification of the contribution of individual deformation and recrystallization mechanisms to deformation we also aim to calibrate a flow law that incorporates the effect of all the relevant microphysical processes and hence more accurately describes the flow of rocksalt in nature for this purpose the mechanical behaviour and microstructural evolution of synthetic rocksalt samples that are similar except for differences in water content determined using ftir analysis are investigated the samples are deformed to natural strains of 0 07 0 46 at 50 mpa confining pressure strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c resulting in flow stresses of 7 22 mpa the flow stress of samples with a water content below 5 ppm dry is higher than that of samples with a water content of 9 46 ppm wet at all strains under the investigated conditions the difference in flow stress can be explained as due to the operation of only work hardening dislocation creep without dynamic recrystallization in the dry material versus combined dislocation and solution precipitation creep plus fluid assisted grain boundary migration in the wet material the results allow us to calibrate a flow law for wet rocksalt that incorporates the effects of solution precipitation creep and fluid assisted grain boundary migration the results also suggest that strain localization in natural rocksalt is more likely to be localized due to fluid infiltration and associated rheological weakening than due to progressive removal of strain hardening substructure by grain boundary migration

sedimentary record of late neoproterozoic rifting in the nw tarim basin china abstract upper neoproterozoic sediments which have been exhumed in the nw tarim basin china comprise a 600 900 m thick non marine to marine synrift succession that reveals an early phase of extension this study presents new data from two measured and interpreted stratigraphic sections near aksu and wushi the synrift succession unconformably overlies high grade metamorphic basement and consists of the non marine sugaitebulake fm and the marine qegebulake fm the sugaitebulake fm is characterised by a basal alluvial fan conglomerate that passes upwards into fluvial and lacustrine facies sandstones and siltstones the stratigraphic position of the basal unconformity and the thickness of the basal conglomerate is locally variable which reflects the formation of small isolated depocentres during the onset of extension in addition to a pre existing topography the sugaitebulake fm also contains a series of concordant extrusive basalts which record episodic volcanism and together with the fluvial and lacustrine facies indicate the development of the rift system and the growth interaction and linkage of extensional faults the conformable qegebulake fm is characterised by foreshore to intertidal facies dolomites that contain abundant stromatolites representing a basin wide marine transgression and the rift climax stage this synrift sequence is shown to correlate with a similar succession in nw australia and corresponds to at least partial separation of the tarim block from east gondwana during the latest neoproterozoic to early palaeozoic

the influence of water on deformation microstructures and textures in synthetic nacl measured using ebsd abstract wet nacl with 10 15 ppm water shows weakening behaviour compared with dry nacl containing

suspended sediment and 137cs fluxes during the exceptional december 2003 flood in the rhone river southeast france abstract at the beginning of december 2003 one of the biggest floods for at least 150 yr was recorded on the rhone river in the lower part of the river the peak flood reached 11 000 m 3 s 1 the geomorphological and radioecological consequences of such an event were investigated downstream all the nuclear installations by using measured and calculated fluxes and the total export of suspended sediment and associated 137 cs results pointed out the major role played by large floods in the annual suspended sediment load as 3 70 10 6 tons of silts 0 85 10 6 tons of sands and 0 84 10 6 tons of clays were transferred towards the coastal environment nevertheless these solid loads were found to be lower than those expected as regards the liquid discharge reached during this event and suggested that previous floods that occurred on the river and on its main tributaries during the last decade have probably led to the removal of available sediment from the channels and their banks besides the 137 cs activity measured within the suspended load was estimated at 14 9 0 4 bq kg 1 which is a level characteristic of the suspended sediments from the rhone catchment area and demonstrated that nuclear installations located along the rhone valley did not significantly contribute to any increase in 137 cs activity in the water during the flood the total 137 cs particulate export amounted to 77 17 gbq and was mainly associated with the silt fraction that contributes to around 70 of the total 137 cs export

use of fallout 137cs in investigations of overbank sediment deposition on river floodplains abstract river floodplains have been recognised as important sinks for storing suspended sediment and associated contaminants mobilised from the upstream catchment however information on contemporary rates of overbank sedimentation is difficult to obtain using conventional methods measurements of the 137cs content of floodplain sediments provide an alternative approach to obtaining estimates of medium term rates ca 40 years of overbank sediment deposition the 137cs approach requires only a single site visit and minimum sample preparation furthermore it is capable of providing information on spatial patterns of sediment deposition on floodplains which is needed to improve our understanding of the processes involved in overbank flow and sediment deposition this paper reviews the basis for using 137cs measurements in floodplain sedimentation studies and presents improved procedures for interpreting 137cs profiles in floodplain sediments and for obtaining estimates of sedimentation rates from single measurements of the total 137cs inventories of bulk sediment cores the results obtained from a case study undertaken on the floodplain of the river stour dorset uk are presented

deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive eocene oligocene rocksalt from eyvanekey plateau and garmsar hills central iran abstract microstructural processes in mylonitic shear zones from extrusions of eocene oligocene rocksalts from garmsar hills and eyvanekey plateau central iran are described and analyzed the halite samples were studied by transmitted light microscopy of gamma irradiated thin sections subgrain size palaeopiezometry of polished and chemically etched samples and texture measurements by electron backscatter diffraction ebsd the studied shear zones are thin using published flow laws the strain rate in the fine grained mylonites is about 10 10 l s which is in a good agreement with earlier in situ measurements on glacier salt flow rate

multiple sulfur isotope records at the end guadalupian permian at chaotian china implications for a role of bioturbation in the phanerozoic sulfur cycle abstract a recent study on quadruple sulfur isotopes 32s 33s 34s and 36s of sedimentary pyrite suggested that the end guadalupian extinction was caused by shoaling of the sulfidic deep water this scenario is based on the assumption that sulfur isotopic compositions of pyrite from hosting sediments were controlled by benthos activities thus by the redox conditions of the sedimentary environments nonetheless the relationship between the sulfur isotope records and redox conditions reconstructed from litho and bio facies are poorly known in order to examine the effect of bioturbation in sediments quadruple sulfur isotopic compositions of sedimentary pyrite from the end guadalupian succession in chaotian south china were analyzed black mudstones of deep water facies immediately below the extinction horizon have consistently high 33s values of ca 0 079 clearly suggesting a sulfate reduction in the anoxic water column our new data are consistent with the emergence of a sulfidic deep water mass prior to the end guadalupian extinction the upwelling of the toxic deep water may have contributed to the extinction in contrast shallow marine bioclastic limestones with burrows deposited under oxic conditions have negative 33s values this anomalous isotopic signal indicates the mixing of two distinct types of pyrite one generated during the sulfate reduction in an open system and the other in a closed system we interpret that bioturbation supplied sulfate in the sediments and promoted sulfate reduction and in situ sulfide precipitation within the sediments the negative 33s values of oxic sediments in chaotian are inconsistent with the previous model and demonstrate that the sedimentary sulfur cycle associated with bioturbation was more complicated than previously thought our study also implies that more generally the role of bioturbation in increasing seawater sulfate concentration in the phanerozoic may have been overestimated in the previous studies because bioturbation may have enhanced sulfide burial or sulfur output from the oceans

temperature dependent grain boundary migration in deformed then annealed material observations from experimentally deformed synthetic rocksalt abstract grain boundary migration between strained substructured grains and newly appearing strain free grains has been observed during static in situ annealing of pre deformed rocksalt in the sem with increasing temperature t the migration velocity increases and the character of grain boundary migration changes as temperature increases there is an increase in the length of individual migrating boundary segments that move at similar rates in addition the frequency of migrating boundaries that form traces of a 100 boundary plane of at least one of the crystals involved increases and moving grain boundaries between new and old grains change from highly irregular to smooth straight boundaries at the same time there is a decrease in the influence of the substructure of pre existing strained grains on the grain boundary movement resultant microstructures reflect these changes at 325 350 c the deformed then annealed microstructure is characterized by very irregular grain boundaries a high abundance of 5 50 m scale remnants of old substructured grains within new grains giving a poikilitic microstructure at 350 400 c grain boundaries often exhibit elongate embayments into the strained grains and most remnants of old strained grains are located at former grain boundaries at 400 c grain boundaries between new and old strained grains are straight to smoothly curved the grain boundary velocity observations are explained by the effect of temperature on mobility coupled with local driving force variations additionally at low annealing temperature impurity solute drag and driving force variations are influential while at high temperature the anisotropy in grain boundary energy with crystallographic orientation becomes more important transferring the knowledge from our experiments to geological samples enables us to recognize and interpret similar microstructures in rocks thereby making it is possible to relate microstructural characteristics to the pre annealing and post deformational annealing history

the effect of rock fabric on p wave velocity distribution in amphibolites abstract this study presents contribution to the laboratory investigation of elastic properties and rock fabric of amphibolites p wave velocity was determined on four spherical samples prepared from a shallow borehole core the measurement was conducted in 132 directions under various conditions of hydrostatic pressure up to 400 mpa the rock fabric was investigated by image analysis of thin sections that enabled precise determination of grain size modal composition and shape parameters of rock forming minerals laboratory measurement of p waves revealed pseudoorthorhombic symmetry of rock fabric in amphibolites studied this symmetry reflects rocks macro and microfabric maximum p wave velocity corresponds to the macroscopically visible stretching lineation minimum p wave velocity is oriented perpendicular to the foliation plane the average grain size is the main microstructural factor controlling mean p wave velocity

lower palaeozoic unconformities in an intracratonic platform setting glacial erosion versus tectonics in the eastern murzuq basin southern libya the stratigraphic record of the eastern murzuq basin has been importantly influenced by deformation resulting in angular and or deeply erosional unconformities though the overall context is intracratonic major transgressive events and the ordovician glaciation are nevertheless documented allowing the delineation of tectonic eustasy or climate driven unconformities lower palaeozoic key events and related unconformities that characterize the north gondwana platform have therefore a signature in the eastern murzuq basin the basement cover unconformity also known as the infra tassilian surface truncates all the deformed and metamorphosed lower cambrian and older rocks above is a middle cambrian to lower ordovician megasequence murizidie and hasawnah fms which is in turn truncated by an intra ordovician angular unconformity this megasequence is unconformably overlain by a middle ordovician hawaz fm to silurian tanzzuft and akakus fms megasequence which includes the upper ordovician glaciogenic unit mamuniyat fm bounded at the base by a polygenic glacial erosion surface showing corrugated glacial lineations tillites and glaciotectonic structures the middle ordovician to silurian megasequence is finally truncated by a base devonian angular unconformity overlain by fluvial sandstones regarding the possibility that those fluvial deposits may be as younger as late devonian in the eastern murzuq basin based on palaeoflora the so called caledonian unconformity might be here a much younger mid eifelian surface and the occurrence of the lower devonian tadrart fm is questioned the upper ordovician glacial erosion surface which is sometimes referred to as the taconic unconformity usually truncates middle ordovician strata in the murzuq basin but reaches significantly deeper stratigraphic levels in places that have been previously involved in the intra ordovician deformation event in the murizidie southeastern murzuq basin the infra tassilian surface the intra ordovician unconformity and the upper ordovician glacial erosion surface amalgamate together here an estimate of the glacial erosion depth cannot be derived from the stratigraphic hiatus beneath the glacial incision the main part of which relate to the intra ordovician tectonic event the upper ordovician climate related glacial erosion surface is not a valid unconformity for a sequence hierarchy framework of the lower palaeozoic although it presents most of the physical attributes of tectonic driven unconformities

historical levels of heavy metals and artificial radionuclides reconstructed from overbank sediment records in lower rhone river south east france trace metals cu cd cr ni pb zn hg and artificial radionuclides cs 137 am 241 pu 238 and pu239 240 were investigated in overbank sediments located in inter embankment areas of the lower rhone river enrichment factors ef and anthropogenic factors af were calculated to estimate the level of contamination in these sediment storages the results show that in the studied sites co ni and sc display low ef values and are mainly from lithogenic origin for the other studied trace metals a great variability of sedimentary record is observed significant anthropogenic enrichment was highlighted at a particular site that undergoes fluvial inputs occurring in the last 50 years lead is the element with the highest ef values ef 13 followed by cd ef 11 cu ef 5 hg ef 7 and zn ef 2 temporal variations of pb cd and hg show a maximum in the 1960 s and a decreasing trend afterward maximum enrichment of artificial radionuclides were observed in sediment deposit during the period 1960 1990 when maximum liquid releases from nuclear activities occurred these results indicate that despite the high energy conditions and the generally sandy nature of the riverbank sediments significant anthropogenic enrichments were observed in some areas of sediment accumulation in the lower rhone river these enrichments are however relatively low compared to some other rivers in france and europe due to the important suspended sediment discharge in this river in particular during strong floods which dilutes the anthropogenic inputs of contaminant c 2011 elsevier ltd all rights reserved

modelling flood hydraulics and overbank deposition on river floodplains this paper outlines a numerical model for the prediction of floodplain inundation sequences overbank deposition rates and deposit grain size distributions the model has two main components first a simplified hydraulic scheme which predicts floodwater flow depths and velocities and second a sediment transport element which employs a mass balance relation describing suspended sediment dispersion by convective and diffusive processes and sediment deposition as a function of particle settling rates these relationships are solved numerically on a finite difference grid that accurately replicates the complex topographic features typical of natural river floodplains the model is applied to a 600 m reach of the river culm devon u k using data derived from a range of field and laboratory techniques continuous records of river stage and suspended sediment concentration provide the model s upstream boundary input requirements these are supplemented by measurements of the in situ settling characteristics of the suspended sediment load the model s sediment transport component is calibrated with the aid of a dataset of measured overbank deposition amounts derived from flood events over a 16 month period the model is shown to predict complicated floodwater inundation sequences and patterns of suspended sediment dispersion and deposition which are largely a product of the complex topography of the floodplain these results compare favourably with observations of overbank processes and are an improvement over those of previous models which have employed relatively simple representations of floodplain geometry 1997 by john wiley sons ltd

high frequency eustatic sea level changes during the middle to early late ordovician of southern jordan indirect evidence for a darriwilian ice age in gondwana abstract the middle to early late ordovician hiswah and dubaydib formations in southern jordan provide a well constrained sedimentary record of 4th and 3rd order relative sea level change along the northern tectonically quiescent subpolar gondwana continental margin cyclic deposition occurred on a wave and storm dominated microtidal shelf dominated by shoreface and offshore transition zone facies cycles are commonly bounded by amalgamated bounding surfaces sb ts or sb mfs and are characterised by stacked transgressive systems tracts tsts the small facies dislocation across key sequence bounding surfaces indicates a 15 50 m change in relative sea level fourth order sequences are hypothesized to be paced by the long eccentricity 405 kyr cycle and consequently 3rd order sequences are calculated to be 1 2 m y and 2 4 m y long these correlate with the global eustatic sea level curve in comparison with mesozoic and cenozoic sequence stratigraphical data we conclude that the 1 2 m y cycles correspond with long obliquity cycles predominant in icehouse conditions and the 2 4 m y cycles with the long eccentricity cycle predominant during greenhouse conditions we propose a darriwilian ice age during which orbitally induced cold snaps caused the expansion and amalgamation of small medium scale ice sheets the reduced size of the correlative positive carbon isotope excursion compared to that in the hirnantian may indicate that the darriwilian ice sheets only reached the sea in a few places the absence of glacio terrestrial deposits of middle ordovician age is most likely due to subsequent glacial erosion during repeated ice advances up to and including those in the hirnantian the existence of darriwilian ice sheets is consistent with zooplankton province distributions that indicate a polar front at 40 s during the ice age it is likely that polar ice existed throughout the ordovician

the importance of high resolution monitoring in erosion and deposition dynamics studies examples from estuarine and fluvial systems abstract erosion and deposition processes lie at the centre of geomorphological explanation but progress in understanding has been limited by a lack of appropriate high resolution monitoring methodologies which permit detection of erosion and deposition dynamics this paper presents a case for monitoring erosion and deposition at high temporal resolutions and uses hypothetical approaches supported by example erosion and deposition events and analyses drawn from estuarine and fluvial systems the paper first presents testable hypotheses to demonstrate the complexity of possible event combinations sequences and juxtapositions for the erosion driving forces which underpin the need for high resolution monitoring second it summarises recent improvements to the photo electronic erosion pin peep automatic erosion and deposition monitoring system including the novel concept of thermal consonance timing tct which is particularly promising because it helps to define the timing of nocturnal events and through the entire hydrograph third example results are discussed from high resolution monitoring of bank erosion at a tidal site at burringham on the river trent in northern england tidal banks are revealed to be much more dynamic than previous conventional monitoring has indicated a key result is that because the high resolution approach allows erosional and depositional activity to be assigned to specific periods of tidal inundation it becomes possible for the first time routinely to produce event based erosion 36 mm h 1 and deposition rates 4 5 and 8 4 mm h 1 such rate determinations are potentially very useful in the field validation of sedimentological and geomorphological models including grain settling and resuspension theory fourth through a longer term of aggregated daily data a striking 2 week cycle of deposition and erosion emerges which correlates most strongly with spring neap tidal cycling but is moderated by wind stress effects sediment was deposited on the bank relatively quickly over 4 5 days but then removed by erosion rather slowly over 9 10 days fifth the dangers of low resolution monitoring are illustrated by comparing the daily peep data set with a series resampled at a lower 14 day frequency to simulate the information generated by conventional resurvey methodologies the low frequency series failed adequately to represent the cyclicity mean range variability and trend of bank elevation changes and without this dynamics information rate and process definition is very difficult largely because of self concealing activity sixth a useful advance is illustrated by the fluvial erosion sequence for the river wharfe n england this shows how tct can generate rare and important results with the definition of the precise time of an erosion event within the hydrograph bank retreat here occurred very quickly after initial inundation and within 4 h of the flow peak information which can be used to define thresholds for entrainment e g critical shear stresses such high resolution monitoring helps to unravel some of the erosional effects of complex sequences combinations and juxtapositions of similar or different forcing events finally high resolution approaches have been adopted worldwide for fluvial estuarine mudflat and canal systems but considerable potential exists for their development and use in these and other contexts e g gully hillslope beach and dune environments to improve understanding and modelling of geomorphological processes more widely

relating natural heterogeneities and rheological properties of rocksalt new insights from microstructural observations and petrophyisical parameters on messinian halites from the italian peninsula abstract the importance and economic interest of rocksalt as well as its influence on tectonics and applicative purposes such as mining hydrocarbons extraction and nuclear waste storage are well known careful characterization of physical and chemical properties of rocksalt is fundamental as the rocksalt behavior may influence its potential use for applicative purposes mechanical and rheological properties of rocksalt have been extensively studied in the past however the role of natural heterogeneities within rocksalt and their effect on salt rheology have not been investigated quantitatively here we present a comprehensive salt facies study on messinian rocksalt from several italian sites volterra basin tuscany caltanissetta basin sicily and crotone basin calabria four salt facies end members have been identified and analyzed by optical analyses the main facies defining characteristics resulted to be the primary salt crystal abundance crystal size roundness and orientation as well as the clay inclusion contents three out of four facies were placed on an evolutionary path from an immature with respect to the deformation history to a mature rocksalt so we observed with increasing rocksalt maturity a progressive disappearing of primary crystal remnants increasing crystals elongation and iso orientation and decreasing in crystal size this trend has been confirmed by differential stress calculation from subgrain size through seismic waves velocity measurements and uniaxial compressive runs specific salt facies were tested results of the investigations demonstrate that the facies parameters have a distinct influence on the rocksalt petrophysical parameters like p and s waves velocity dynamic and static young modulus elastic limit and strain at peak finally this study allowed to suggest the subdivision of volterra s salt sequence in three different units that have been subjected to variable deformation degree in response to the different salt characteristics

constraining paleo latitude of a biogeographic boundary in mid panthalassa fusuline province shift on the late guadalupian permian migrating seamount abstract the guadalupian paleo atoll limestone iwato formation in sw japan was primarily formed in low latitude mid panthalassa and was later tectonically accreted to south china japan margin during the jurassic the present biostratigraphic study clarified that the iwato formation consists of 5 biostratigraphical intervals i e four fusuline assemblage zones assemblage zones 1 to 4 and a barren interval on the top assemblage zones 1 to 4 correspond to the neoschwagerina craticulifera zone n margaritae zone yabeina globosa zone and lepidolina multiseptata zone of the conventional tethyan fusuline stratigraphy respectively the present study newly clarified the following significant aspects of paleobiogeography of the permian fusulines as to the extinction of large tested taxa in the latest guadalupian 1 the long unknown stratigraphic relationship was documented for the first time between the yabeina dominant interval and the overlying lepidolina dominant one within a single limestone unit 2 the occurrence of lepidolina cf kumaensis kanmera the unique last runner of large tested fusuine was detected for the first time in mid oceanic paleo atoll limestones 3 with respect to the northbound migration history of the paleo seamount capped by the iwato formation the development of the two coeval fusuline biogeographic territories in the low latitude panthalassa i e the yabeina territory on the south and the lepidolina territory on the north was confirmed 4 the paleo latitude of the biogeographic boundary between the yabeina and lepidolina territories is constrained around 12 in the southern hemisphere on the basis of the latest geomagnetic data from the same limestone this new approach utilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo latitude data is applicable to other cases in different time space co ordinates and of other fossil groups for constraining position of ancient biogeographic boundaries within lost oceanic domains of deep past

stable lead isotopes contaminant metals and radionuclides in upper hudson river sediment cores implications for improved time stratigraphy and transport processes radionuclide stable lead isotope and trace metal analyses on fine grained sediment cores collected along a 24 mile reach of the upper hudson river were used to establish temporal trends of contaminant loadings to establish stable lead isotopes as an additional stratigraphic tool and as tracers for resolving particle transport fluxes over periods of decades very large contaminant inputs of cd sb pb and cr were evident in the sediment record one potential large source for these metals was from a pigment manufacturing facility in glens falls ny the total range in stable lead isotope ratios observed in well dated cores from about 15 miles downstream of the potential metal inputs was large e g maximum difference in 206 pb 207 pb is 10 and characterized by four major shifts occurring in the 1950s 1960s 1970s and 1980s the temporal trend in 206 pb 207 pb has been used to establish precise dating of a sediment core from 24 miles further downstream the large magnitude and abrupt shifts in stable lead isotope ratios preserved in upper hudson sediment cores provide a way to significantly improve dating models based only on radionuclide analyses cadmium lead and antimony were identified as quite sensitive tracers of upper hudson sediments due to the magnitude of contamination and the lack of significant additional downstream sources of these contaminant metals metal measurements in a pair of sediment cores located 24 miles apart were used to constrain relative fluxes of sediment entering the river between the two coring locations with sediment sections deposited between the early 1960s and the late 1970s in these two cores suggesting that 3 4 times more sediment entered the river between the two coring sites than was transported from upstream these dilution factors agree very well with estimates based on suspended sediment measurements during a flood event in april 1994 and with estimates based on mechanistic model of suspended sediment transport between 1977 and 1992 d 2003 elsevier science b v all rights reserved

importance of geomorphology and sedimentation processes for metal dispersion in sediments and soils of the ganga plain identification of geochemical domains abstract the ganga plain one of the largest alluvial plains of the earth is under severe environmental stress due to rapid industrial and urban development and exploding population growth disposal of industrial and urban wastes and the ignorance of their management have resulted severe environmental problems especially metal pollution in the present study an attempt is made to understand the transport and dispersion processes of metal contaminants in sediments and soils in kanpur unnao industrial region of the ganga plain the significance of geomorphology and monsoon rain is assessed in determining the distribution of contaminated sediments in this area three regional geomorphic surfaces t0 t1 and t2 are identified each with its characteristic river channel patterns and sediment distribution system which influence the dispersion and accumulation of the metal contaminants the sediment and water distribution regime depends on the nature of geomorphic features and character of the river channels geomorphic features sedimentation processes the nature of the river channels and distribution of excess rain water of the monsoon season have given the bases to delineate five geochemical domains in the study area each geochemical domain is an independently operating system with its own geomorphic and geochemical characters chemical parameters e g ph metal concentrations and dispersion of metal contaminated sediments and soils vary from domain to domain in comparison to reference values each domain exhibits its own enrichment of elements namely the loni river domain has high contents of c org cd cr zn the ganda nala domain of c org cu cr the ganga river domain of c org cr cu pb sn zn the sewage network domain of c org cd cr cu pb ni sn zn and the pandu river domain of c org cd cu ni zn patterns of changes in metal concentrations from one monsoon year to the other and in different seasons of a monsoon flood cycle are also domain specific each geochemical domain exhibits its own degree of metal enrichment in sediments and soils by anthropogenic activities and physico chemical processes identification of geochemical domains with their specific physico chemical processes in the fluvial system of the ganga plain will certainly help in assessing the environmental problems and land contamination of this region

amplitudes of late pennsylvanian glacioeustasy the late paleozoic is well documented as a time of significant continental glaciation but the extents of the glaciation and attendant glacioeustasy are not well constrained because precise amplitudes of eustasy are difficult to extract from the stratigraphic record in this paper we use preserved relief on ancient subaerial exposure surfaces of large algal bioherms to demonstrate directly that late pennsylvanian glacioeustasy reached minimum amplitudes of 80 m and probably exceeded 100 m upper paleozoic algal bioherms accreted predominantly during sea level falls but also during sea level rises and highstands and were capable of remarkably rapid growth rates eustatic amplitudes in excess of 100 m approach amounts documented for the pleistocene and place constraints on models for gondwanan ice volume climate dynamics and potential character and magnitude of glacioclimatic fluctuations

dynamic recrystallization of wet synthetic polycrystalline halite dependence of grain size distribution on flow stress temperature and strain abstract it is often observed that dynamic recrystallization results in a recrystallized grain size distribution with a mean grain size that is inversely related to the flow stress however it is still open to discussion if theoretical models that underpin recrystallized grain size stress relations offer a satisfactorily microphysical basis the temperature dependence of recrystallized grain size predicted by most of these models is rarely observed possibly because it is usually not systematically investigated in this study samples of wet halite containing 10 ppm water by weight were deformed in axial compression at 50 mpa confining pressure the evolution of the recrystallized grain size distribution with strain was investigated using experiments achieving natural strains of 0 07 0 12 and 0 25 at a strain rate of 5 10 7 s 1 and a temperature of 125 c the stress and temperature dependence of recrystallized grain size was systematically investigated using experiments achieving fixed strains of 0 29 0 46 and one to a strain of 0 68 at constant strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c yielding stresses of 7 22 mpa the microstructures and full grain size distributions of all samples were analyzed the results showed that deformation occurred by a combination of dislocation creep and solution precipitation creep dynamic recrystallization occurred in all samples and was dominated by fluid assisted grain boundary migration during deformation grain boundary migration results in a competition between grain growth due to the removal of grains with high internal strain energy and grain size reduction due to grain dissection i e moving boundaries that crosscut or consume parts of neighbouring grains at steady state grain growth and grain size reduction processes balance yielding constant flow stress and recrystallized grain size that is inversely related to stress and temperature evaluation of the recrystallized grain size data against the different models for the development of mean steady state recrystallized grain size revealed that the data are best described by a model based on the hypothesis that recrystallized grain size organizes itself in the boundary between the grain size sensitive solution precipitation and grain size insensitive dislocation creep fields application of a piezometer calibrated using the recrystallized grain size data to natural halite rock revealed that paleostresses can vary significantly with temperature up to a factor of 2 5 for t 50 200 c and that the existing temperature independent recrystallized grain size stress piezometer may significantly underestimate flow stresses in natural halite rock

organic matter accumulation of the wufeng longmaxi shales in southern sichuan basin evidence and insight from volcanism abstract the wufeng longmaxi formations wf lm fms in the sichuan basin are sets of graptolite bearing shale strata containing high frequency bentonite layers in order to investigate the influence of volcanism on the organic matter om accumulation in shales detailed observations of several typical profiles and wells were performed also analyses including total organic carbon toc contents and mineral compositions were conducted on 126 shale and 5 bentonite core samples major and trace element analyses were conducted on the selected 25 shale and 5 bentonite samples in the wf lm fms of well lu a results show that wf and lm1 4 members are the bentonites concentrated sections while lm5 6 are the bentonites relatively concentrated sections and no bentonite is found in lm7 9 members the high potassium k content of bentonites have the typical characteristics of intermediate acid calcium alkaline volcanic rocks such as andesite and dacite which probably originated from intraplate collision or volcanic arc structural backgrounds related to the collision belt of the cathaysia block to the yangtze block productivity indicators p content excess si p al cu al and ni al in the wf and lm1 3 members are all significantly higher than those in the lingxiang lx and lm4 5 members the higher biological productivity during the ordovician silurian o s transition was attributed to the massive and intensive volcanism the fertilization by volcanic ash brought abundant biologically relevant nutrient elements n p si fe and al into the ocean thus triggering the phytoplankton bloom and enhancing primary biological productivity all the redox condition indexes moef uef nief vef mo toc corg p and u th positively correlate with toc content during the o s transition the intensive and massive volcanic eruptions triggered global cooling sea level changes late ordovician mass extinction and primary productivity increases thus promoting anoxic and possibly intermittently euxinic bottom conditions in addition the deposited bentonite layers had a strong capacity for oxygen isolation volcanism should be considered when modeling the om accumulation of the wf lm shales

frasnian upper devonian integrated facies analysis magnetic susceptibility and sea level fluctuations in the nw algerian sahara changes in the palaeoenvironment are investigated in two representative frasnian sections of the nw algerian sahara integrating sedimentology and magnetic susceptibility ms the ben zireg section is characterized by condensed and ferruginous calcareous deposits in the south marhouma section the sedimentation rate is high dominated by muddy nodular limestones with several hypoxic shale intervals in both sections sediments were mostly emplaced on pelagic outer ramps below the limit of storm wave base evolving through time from proximal to distal setting investigations of the temporal evolution of facies and ms data permit a first estimate of the local sea level trends in nw algeria these trends match the overall long term rise of sea level recognized worldwide from frasnian zone 5 upwards noteable positive excursions of the sea level curve related to the semichatovae transgression as well as to the late frasnian transgression prior to the late kellwasser event can be established in this area although the sharp regression of sea level at the upper kellwasser level can be confirmed from our data no particular trend is depicted at the transition of conodont zones frasnian zones 12 13 where the presence of the lower kellwasser level has not yet been clearly recognized

paleoclimate reconstruction during the messinian evaporative drawdown of the mediterranean basin insights from microthermometry on halite fluid inclusions 1 data constraining the paleoenvironmental conditions during the messinian evaporative drawdown of the mediterranean basin are still conflicting here we present a comprehensive paleoclimatic reconstruction during messinian halite deposition from several italian sites we performed fluid inclusion analyses to define better both the composition of the mediterranean water body and the paleotemperatures of the messinian brine during halite crystallization we measured homogenization temperatures on 218 primary all liquid fluid inclusions in messinian halite from the volterra crotone and caltanissetta evaporite basins these measurements provided mean homogenization temperatures of 17 18 c with a range between 10 11 c and 28 29 c which should be close to the sst of the mediterranean sea during halite deposition the occurrence of major elements such as cl na mg s ca and k within the halite fluid inclusions together with the presence of minerals such as pentahydrite polyhalite and ca k and mg sulfates indicates that these salt bodies originated from mainly marine water taking into account both the present day annual sst of the mediterranean sea around the sampling sites which ranges between 18 and 20 c and the lower latitude of the mediterranean basin during the messinian salinity crisis our homogenization temperatures point to a colder climate during the messinian halite deposition compared to the present interglacial climate stage this conclusion is consistent with halite deposition during a late miocene glacial interval tg12

sediment characteristics floods and heavy metal pollution recorded in an overbank core from the lower reaches of the yangtze river overbank sediments contain abundant information about floods paleoenvironmental changes and recent pollution history of a river basin for the purpose of understanding modern overbank sediments and their environmental significance this multidisciplinary study sampled a core from the overbank and a short core from the overbank outcrop at nanjing in the lower reaches of the yangtze river the overbank deposit comprises fine grained discontinuous strata including silt sandy silt silty sand and sand layers field and laboratory observations indicated that the overbank sediment contained a series of layers of sandy silt coupled with thin silty sand layers each a few millimeters thick which formed muddy layers that were dozens of centimeters thick between the muddy layers were coarser sand layers grain size analyses 137cs dating and heavy metal measurements contained information on flood events and pollution history over the past 60 years the coarser sand layers corresponded with severe floods in 1954 and 1983 between the two severe floods the study area experienced an overbank building stage from the 1990s to the early 2000s the overbank sedimentation rate declined reflecting human activities especially the dams in the yangtze river basin that trapped more sediment the average heavy metal concentrations in the overbank sediments are higher than the background levels for suspended sediment in the yangtze river heavy metals in overbank sediments were assessed by enrichment factors and sediment quality assessment values for freshwater sediment cr and ni values were high especially from the early 1980s to the early 2000s the impacts of floods economic development and environmental management on these heavy metal variations were discussed

progress problems and prospects an overview of the guadalupian series of south china and north america abstract the guadalupian epoch is marked by the formation of the pangean supercontinent global sea level change rifting and drifting of the cimmerian continents formation of large igneous provinces and dramatic biotic changes a high resolution biostratigraphic chemostratigraphic and high precision geochronologic framework of this critical transition is fundamental to understanding these events extensive studies of the latest cisuralian and guadalupian series in both south china and north america reveal the same conodont lineages but the conodont interval zones based on jinogondolella within the guadalupian series are slightly diachronous high precision u pb geochronological studies ca id tims method calibrate the base of the guadalupian series base roadian at 273 01 0 14 ma a previously reported age from an ash bed overlying the emeishan flood basalts 259 51 0 21 ma is adopted for the guadalupian lopingian boundary glb based on recently published geochronology and bayesian age modeling from the guadalupian series the base of the capitanian is constrained at 264 28 0 16 ma and the base of the wordian is interpolated to be 266 9 0 4 ma the illawarra reversal is of early middle wordian age both north america and south china possess a distinct negative 13ccarb excursion of 3 5 at the latest kungurian and early roadian lk er cie which coincides with the early stages of a significant 3rd order sea level rise the large end guadalupian 13ccarb negative excursion may have been affected by post depositional diagenesis or a warming event associated with the emeishan volcanism the 87sr 86sr ratios in both regions declined from the latest kungurian to the late capitanian but have different ratios and reveal several fluctuations in the middle guadalupian measured 18oapatite values suggest that the delaware basin was 3 4 c cooler than the eastern yangtze block analysis of a new high resolution database of marine taxa indicates only a minor pre lopingian diversity drop from 261 04 ma to 259 98 ma which coincides with the peak emeishan volcanism the widely perceived end guadalupian mass extinction in north america is evidently masked by and possibly an artefact of a stratigraphic truncation effect due to rapid lithofacies changes from limestone to laminated evaporites with the closure of the west texas basins

high resolution evaluation of recent bank accretion rate of the managed rhone a case study by multi proxy approach abstract we determined the sedimentation rates near a managed embankment on the lower rhone for the second half of the twentieth century this was carried out using a combination of chronological indicators 137 cs 241 am dendrochronology and archived data and sedimentological measurements a high resolution chronological sequence has emerged from these data sets the average annual sedimentation rate of 14 cm has increased progressively over the last 50 years and at a much faster rate than observed elsewhere on this river this is probably due to a combination of factors such as the size of the river abundance and coarse texture of the solid load and local impact of river engineering works we also studied hydrological and sedimentological characteristics for a number of flood events

use of the geochemical record preserved in floodplain deposits to reconstruct recent changes in river basin sediment sources abstract the geochemical record preserved in overbank floodplain deposits is used in combination with a composite fingerprinting technique and the chronology provided by 137 cs dateable horizons to reconstruct recent changes in sediment sources in the exe and severn basins uk composite fingerprints for discriminating potential source materials are identified from a suite of properties including heavy metals trace metals and cation bases these fingerprints are then compared with those of historical floodplain deposits using a numerical sediment mixing model relative contributions from distinct spatial sources characterised in terms of the devonian carboniferous and permian geological sub areas of the exe and the ordovician silurian devonian carboniferous permian and triassic jurassic sub areas of the severn are shown to fluctuate over the recent past in response to intrinsic e g the occurrence of extreme hydrologic events and extrinsic e g anthropogenic disturbance associated with land use change controls the potential for fingerprint property transformation in association with floodplain storage is assessed and the scope for further research using fingerprinting to reconstruct longer term sediment sources is discussed

the magnitude of late paleozoic glacioeustatic fluctuations a synthesis a comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the carboniferous and permian and that at least eight distinct phases can be recognized facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20 25 m and occasionally as much as 60 m took place throughout the early mississippian tournaisian a widely recognized glacial period middle mississippian mid chadian through holkerian shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10 25 m a decrease that matches well with the paucity of coeval glacial deposits late visean asbian through mid brigantian glacioeustatic fluctuations of 10 50 m record the initial phases of ice accumulation in advance of the widespread mid carboniferous glacial event the latest mississippian earliest pennsylvanian mid brigantian through langsettian was a time of widespread glaciation and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40 100 m although middle pennsylvanian duckmantian through asturian glacial deposits are present in eastern australia paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m glacioeustatic fluctuations of as much as 100 120 m have been widely reported from late pennsylvanian earliest permian stephanian through mid sakmarian successions in north america an increase that corresponds to the growth of large ice sheets across much of gondwana and the accumulation of ice in the northern hemisphere incision and facies juxtaposition in early middle permian mid sakmarian through kungurian successions in eastern australia indicate that glacioeustatic fluctuations of 30 70 m occurred during the waning stages of major glaciation erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in australia suggests that eustatic fluctuations of 10 60 m occurred during the final stages of glaciation in the middle to late permian roadian through capitanian but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature this review demonstrates that far field cyclic successions record changing glacial conditions in gondwana that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice that carboniferous permian glacioeustasy was more variable than previously recognized and that generalizations from short temporal intervals are probably not representative of the late paleozoic ice age as a whole although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study