shear stress in the graphitization of carbonaceous matter during the low grade metamorphism from the northern parang mountains south carpathians implications to graphite geothermometry abstract low grade metamorphic rocks from the northern parang mountains south carpathians were examined to infer the temperature of metamorphism and to obtain new data to study the applicability of the geothermometers relying on the graphite crystallinity to rocks that underwent different shear stress conditions there were analyzed samples of graphitic carbonaceous matter bearing rocks that exposed dissimilar degrees of strain for which the temperature of metamorphism was calculated using the graphite geothermometers based on the lattice parameter c0 determined through x ray diffractometry and based on the peak area ratio of the first order raman spectrum the temperature was also inferred from the chemical composition of the chlorite and from the fe mg partitioning between chlorite and chloritoid the mineral chemistry being determined through electron microprobe analyses the results obtained have shown i differences of up to more than 150 c between vicinal strained and less strained zones when applying the geothermometers based on the graphite crystallinity and ii considerable discrepancies between the temperatures calculated based on the graphite crystallinity and those based on the chlorite and chloritoid chemical compositions these inconsistencies are most likely caused by the fact that the calibration of the graphite geothermometers considers temperature as being exclusively responsible for enhancing the degree of graphite crystallinity and therefore these graphite geothermometers should be adjusted accordingly by introducing a correction factor that quantifies the degree of strain of the samples analyzed in order to obtain more accurate results

channel incision evolution and potential recovery in the walla walla and tucannon river basins northwestern usa we evaluated controls on locations of channel incision variation in channel evolution pathways and the time required to reconnect incised channels to their historical floodplains in the walla walla and tucannon river basins northwestern usa controls on incision locations are hierarchically nested a first order geological control defines locations of channels prone to incision and a second order control determines which of these channels are incised channels prone to incision are reaches with silt dominated valley fills which have sediment source areas dominated by loess deposits and channel slopes less than 0 1 area 0 45 among channels prone to incision channels below a second slope area threshold slope 0 15 area 0 8 did not incise once incised channels follow two different evolution models small deeply incised channels follow model i which is characterized by the absence of a significant widening phase following incision widening is limited by accumulation of bank failure deposits at the base of banks which reduces lateral channel migration larger channels follow model ii in which widening is followed by development of an inset floodplain and aggradation in contrast to patterns observed elsewhere we found the widest incised channels upstream of narrower reaches which reflects a downstream decrease in bed load supply based on literature values of floodplain aggradation rates we estimate recovery times for incised channels the time required to reconnect to the historical floodplain between 60 and 275 years restoration actions such as allowing modest beaver recolonization can decrease recovery time by 17 33 per cent published in 2007 by john wiley sons ltd

cretaceous to cenozoic thermal evolution of the southwestern south carpathians evidence from fission track thermochronology abstract the southwestern south carpathian orogen is composed of various nappe complexes which were assembled during the cretaceous cenozoic orogeny these are from footwall to hangingwall 1 the danubian nappe complex including a cadomian variscan basement 2 the arjana and severin units with jurassic to early cretaceous rift and oceanic sequences and 3 the getic nappe complex with variscan continental basement fission track ft thermochronology on apatite zircon and sphene from samples collected from various units of the south carpathians in conjunction with field constraints and previous geochronology is used to characterise the alpine tectonic events and to restore the pattern and amount of exhumation since the cretaceous zircon from the flysch unit and the danubian liassic cover sequence yields ft ages around 200 ma suggesting cooling of the rift flanks prior to the opening of the severin rift zircon and sphene from the getic and danubian basement units yield ft ages averaging 110 ma and indicating cooling under 240 c of the basement contemporaneous with or postdating thrusting apatite ft ages display a decreasing age trend from the hangingwall 65 ma to the footwall units 30 ma the age data and corresponding horizontal confined track length distributions suggest that exhumation of the nappe pile occurred in two stages the first is related to the late cretaceous nappe stacking and the second one to the final thrusting of the south carpathians onto the top of the moesian platform apatite ft ages along major brittle wrench faults indicate reheating above ca 120 c during fluid flow associated with fault re activation during oligocene and neogene times thus shear zone rocks experienced a higher temperature overprint during cenozoic time than rocks of the unaffected nappe pile temperatures of hydrothermal flow along these zones decreased below 100 c progressively starting with the late oligocene early miocene when the area began to override the moesian platform

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

natural levee formation along a large and regulated river the danube in the national park donau auen austria abstract we investigated overbank deposition and natural levee formation along the danube east of vienna based on airborne laserscan data als combined with historical information the analyses of equally spaced cross sections hypsographic curves and point elevations revealed the significance of the distance from the river bank the floodplain width and the floodplain flow situation inflow outflow sections for the spatial variability of sediment deposition deposition was high near the banks natural levee formation in wide floodplain sections and in inflow areas the overall pattern was modified by the presence of side channels and the micro relief of the floodplain from the derived sedimentation rates averaged for the past 120 years over the reach of about 11 0 mm yr 1 at the natural levee and about 0 3 mm yr 1 at the flood protection dyke we can estimate an overbank deposit rate of 416 000 m 3 yr 1 for the entire free flowing reach between river km 1921 and 1880 that is between 18 and 20 of the annual transported suspended load an analysis of historical cross sections showed that there was no natural levee along the riverbanks shortly after the regulation about 100 years ago we thus assume that natural levee formation is a consequence of the danube regulation in the late 19th century under natural conditions overbank deposition was balanced and limited by side erosion and lateral channel migration after stabilization of the banks the overbank deposits were not eroded and distinct natural levees formed these levees will develop and grow further and affect flood protection and floodplain ecology we discuss the interplay between floodplain deposition and lateral bank migration under the concept of dynamic equilibrium

controls on links between geomorphical and surface sedimentological variability aitutaki and maupiti atolls south pacific ocean abstract isolated carbonate platforms and atolls occur throughout the geologic record from archean to present although the roles of sea level change tectonics and sediment supply on large scale changes in stratigraphical architecture of these systems are relatively well understood the details of the nature and controls on sedimentological variability between and within individual geomorphic elements on platforms and atolls are less well constrained the purposes of this study are 1 to describe compare and contrast geomorphological and sedimentological characteristics of surficial holocene sediments from two south pacific atolls aitutaki and maupiti representing different physical and chemical oceanographic settings and 2 to explore possible causes for sedimentological heterogeneity by contrasting the patterns with those present on other platforms and regions both atolls include annular shelf edge reef systems with a red algal rim and reef flat flanked lagoonward by reef sand aprons up to 1 500 m wide these aprons consist of moderately sorted coarse sand and gravel with an abundance of halimeda coral and red algal fragments broadly sediments become finer and better rounded away from margins water depths increase abruptly inboard of these reef sand aprons into platform interiors with depths up to 25 m maupiti and 9 m aitutaki although patch reefs dot these lagoons sediment is commonly poorly sorted with bimodal and polymodal size distributions and includes a mix of whole and fragmented skeletal grains peloids and ooids mud and fine sand are abundant up to 80 on maupiti 85 on aitutaki the occurrence of peloids fine ooid sand and oolitically laminated skeletal grains on maupiti atoll as previously documented on aitutaki is consistent with interpretations of the impact of elevated regional ocean total alkalinity ta and ph levels in this part of the pacific on these wave dominated atolls open ocean waves impinging on the platform margins generate currents that transport sediment from the reef across the sand apron and towards the platform interior unlike the tide dominated platforms of the bahamas however weak tides preclude strong daily agitation and circulation so ooids do not grow large and mud and fine sand transported into the atoll interiors is sequestered there in the interiors both sediment produced in situ and fine allochthonous sediment are more influenced by biological processes than by physical transport processes so bioturbated muddy sand is most common collectively the comparative analysis provides actualistic process based conceptual models for the nature and controls on variability of shelf margin reef and reef apron systems and platform interiors within and among atolls

tertiary tectonic evolution of the external south carpathians and the adjacent moesian platform romania depth interpreted seismic sections of the getic depression foredeep paleostress indicator data and analysis of outcrop to regional scale structures are integrated to derive the tectonic evolution of the south carpathians moesian platform area following late cretaceous and older orogenic phases the south carpathians moesian platform area underwent strike slip deformation with ne sw oriented compression and nw se tension in paleogene to early burdigalian times tensional deformation is recorded which led to the opening of wsw ene to e w trending extensional basins in the late burdigalian ne sw oriented contraction took over causing the oblique inversion of preexisting extensional structures during sarmatian times nw se and slightly younger n s trending compression caused the activation of mainly nw se dextral strike slip faults and in the frontal areas south directed thrusting the nw se direction of extension determined for paleogene to early burdigalian times is hardly compatible with presently accepted models of substantially continuous dextral wrenching between the intra carpathians units to the north of the south carpathians and the moesian platform to the south in contrast we have demonstrated dextral transpressive to transtensional movements within an e w trending corridor from the late burdigalian to late sarmatian which are compatible with available models

evolution of 2 1 layered silicates in low grade metamorphosed liassic shales of central switzerland white mica from the liassic black shales and slates in central switzerland was analysed by transmission electron microscopy tem and electron microprobe to determine its textural and compositional evolution during very low grade prograde metamorphism samples were studied from the diagenetic zone anchizone and epizone t 100 450 c phyllosilicate minerals analysed include illite smectite i s phengite muscovite brammallite paragonite margarite and glauconite textural evolution primarily is towards larger more defect free grains with compositions that approach those of their respective end members the smectite to illite transformation reduced the amounts of the exchange components sik 1al 1 mgsial 2 and fe3 al 1 these trends continue to a lesser degree in the anchizone and epizone correlations between the proportion of smectite in i s and the composition of i s indicate that smectite layers may contain a high layer charge illite in i s bears a compositional resemblance to macrocrystalline phengite in some samples but is different in others paragonite first appears in the upper diagenetic zone or lower anchizone as an interlayer deficient brammallite and it may be mixed with muscovite on the nanometre scale owing to the small calculated structure factor for paragonite muscovite superstructures conventional x ray powder diffraction cannot distinguish between mixed layer structures and a homogeneous compositionally intermediate solid solutions however indirect tem evidence shows that irregularly shaped domains of na and k rich mica exist below 10 nm subsequent coarsening of domains at higher grades produced discrete paragonite grains at the margins of muscovite crystals or in laths parallel to the basal plane of the host muscovite margarite appears in the epizone and follows a textural evolution similar to paragonite in that mixtures of margarite paragonite and muscovite may initially occur on the nanometre scale however no evidence of interlayer poor margarite has been found

eastern alpine tectono metamorphic evolution constraints from two dimensional p t t modeling we use two dimensional 2 d p t t modeling to constrain the thermal and rheological aspects of different scenarios for the late mesozoic and cenozoic tectonic evolution of the eastern alps inferred from excellent data sets from the tauern window tw models invoking subduction of the south penninic sp oceanic lithosphere during thrusting and subsequent erosion of the austro alpine aa upper plate nappe stack are inconsistent with the observed thermal evolution within the aa and penninic units in these models predictions for the aa peak thermal conditions are lower than observed after exhumation and cooling to midcrustal levels and subduction of the continental middle penninic mp block the aa undergoes a phase of renewed heating to almost the previous peak temperatures simultaneously the penninic units experience a phase of heating upon subduction followed by cooling after onset of subduction of the north penninic np basin the model predictions are inconsistent with the observed nearly isothermal uplift path of the sp after subduction and cannot explain observed inverted metamorphic peak conditions in the deeper aa amphibolite facies down to the higher penninic unit greenschist facies a model with the beginning of subduction of the sp occurring after crustal thickening of the aa and subsequent return to normal crustal thicknesses is compatible with the p t t data in this model peak temperature conditions are higher in the aa followed by a phase of strong cooling in the aa upper plate with the onset of underthrusting this model also explains successfully nearly isothermal exhumation of the mp and inverted metamorphic peak conditions in the deeper aa material accreted to the hanging wall from the oceanic crust sp experiences a phase of cooling during ongoing subduction of oceanic lithosphere and begins to heat up to its thermal climax after the subduction of trailing continental lithosphere the subsequent pt path of the penninic units strongly depends on the timing and rates of underthrusting by the foreland observed pt paths in the mp within the tw require continuous subduction of the np and the trailing european foreland under the exhuming mp block documented rapid cooling in the final uplift phase of the penninic units in the tw requires exhumation rates up to approximately 4 mm yr predictions of slightly elevated present day geothermal gradients in the tw area are consistent with available heat flow data as a result of mesozoic rifting followed by late mesozoic crustal thickening of the aa paleorheological reconstructions are characterized by a contrast between relatively strong oceanic lithosphere and adjacent weak continental lithosphere predicted decoupling of weak continental and oceanic lithosphere during subsequent subduction of the penninic units can explain observed late cretaceous crustal extension in the aa units in terms of gravitational spreading ongoing subduction leads to an overall strength increase due to underthrusting of cool oceanic lithosphere whereas subduction of continental lithosphere causes a strength decrease in the upper levels of the lithosphere continuous crustal thickening and relaxation of the depressed isotherms reduce the strength of the lower lithospheric mantle beneath the central orogen further enhanced by rapid late stage uplift predictions for the present day rheological structure of the eastern alps support the existence of a strong upper crustal layer two wedge shaped strong upper mantle layers to the north and the south of the orogen and a weak upper mantle underlying the central orogen

water table fluctuations near an incised stream walnut creek iowa abstract incised channels are common features in many agricultural watersheds but the effects of channel incision on riparian water table conditions have been poorly documented in this study we evaluate the water table fluctuations in the floodplain near an incised stream walnut creek iowa and investigate the roles that channel incision and variable recharge play in modifying the water table configuration in the floodplain groundwater flows from higher landscape positions towards walnut creek under hydraulic gradients that were steepest near the upland floodplain contact and in the near stream riparian zone annually water table fluctuations on the floodplain were greatest in wells located 30 m from the creek midway between the creek and upland water levels monitored continuously during a runoff event indicated that bank storage was confined to a narrow zone adjacent to the channel a steady state one dimensional analytical model was developed to describe the shape of the water table surface near an incised stream and evaluate how variable groundwater recharge and channel bed lowering has affected the shape of the water table surface results from this study have implications for managing the riparian buffers of incised streams with successful establishment dependent upon matching buffer vegetation to riparian water table conditions

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

exhumation in a convergent orogen the western tauern window unroofing of the western tauern window involved both low angle detachment faulting brenner fault and enhanced footwall erosion contemporaneous with upright antiformal folding this combination reflects orogen parallel e w extension during continued n s alpine convergence new fission track ages establish the relative chronology of folding and faulting and demonstrate that displacement was not always accommodated on the same surface during exhumation some units migrated from the footwall to the hanging wall of the main detachment fault due to the interplay between folding and faulting the region can effectively be divided into 3 distinct domains 1 the penninic units of the western tauern window were always in the footwall to the fault with maximum exhumation in the core of the dome due to folding and erosion 2 the lower austroalpine unit north of the tauern window was first part of the hanging wall to the brenner fault at a later stage this unit was exhumed by a further 4 5 km as part of the footwall to a more discrete through going fault the silltal fault 3 the middle and upper austroalpine units west of the tauern window were always within the hanging wall exhumation of the footwall from an initial depth of 25 km led to a transition in mechanical behaviour the curviplanar folded ductile shear zone marking the boundary to the tauern window was eventually transected by a more planar discrete brittle fault silltal fault with unit 2 now in the footwall along which the pre existing mylonites were passively exhumed to the surface

very low grade metamorphism of the taveyanne greywacke glarus alps switzerland detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic eocene oligocene taveyanne greywacke of the glarus alps eastern switzerland presented data indicate an increase of metamorphic grade from zeolite facies to prehnite pumpellyite and pumpellyite actinolite facies low grade outcrops contain laumontite minor corrensite and pumpellyite assemblage type 1 whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite type 2 prehnite pumpellyite al white mica type 3 a single outcrop shows pumpellyite actinolite facies type 4 from the zeolite to prehnite pumpellyite pumpellyite actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain 1 mm in type 1 to a few millimetres in type 2 and to a whole thin section in type 3 metamorphic p t conditions were determined by a combination of chlorite thermometry fluid inclusion and vitrinite reflectance data peak temperatures range from 170 190d c for zeolite facies to 270 310d c for prehnite pumpellyite and pumpellyite actinolite facies for the higher temperature range pressures of 2 3 kbar are derived indicating a geothermal gradient of 24 32d c km 1 the well constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed the best correspondence to the temperatures determined here is for the cathelineau calibration in addition in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites

caesium 137 in sandy sediments of the river loire france assessment of an alluvial island evolving over the last 50 years recent sedimentological and morphological evolution of an island in the river loire france was investigated using the 137cs method this study describes the morphological adjustment of the island in the last 50 years which corresponds to the increased bed incision of this sandy multiple channel environment because of among other things the increase in sediment extraction up to 1995 the results show that some 137cs can be retained by sandy particles potentially in clay minerals forming weathering features included in detrital sand grains from a morphological perspective significant lateral erosion can be observed in the upstream part of the island while a weak lateral accretion occurs in its downstream section data about 137cs and aerial photographs show that the morphology of the island margins has undergone significant changes leading to a lateral migration while the centre of the island has remained relatively stable or is slowly eroding the migration of the island depends on 1 the withdrawal of inherited preincision morphological units such as levees or the development of new units such as a channel shelf 2 water and sediment supply from surrounding channels during flood events 3 preferential sediment trapping 20 mm year 1 from the presence of riparian vegetation on the bank of the secondary channel that is subject to narrowing the sedimentological and morphological response of the island in the context of incision of the loire river bed is expressed mainly by lateral migration and secondarily by a low vertical adjustment

experimental investigations of blueschist greenschist transition equilibria pressure dependence ofal2o3 contents in sodic amphiboles a new geobarometer

sedimentary facies of bora bora darwin s type barrier reef society islands south pacific the unexpected occurrence of non skeletal grains abstract barrier reefs when encircling small islands have been comparatively little noticed by voyagers but they well deserve attention in their structure they are little less marvelous than atolls and they give a singular and most picturesque character to the scenery of the islands they surround darwin 1842 p 2 sediment sampling revealed six modern sedimentary facies in the barrier reef system around the volcanic island of bora bora including mixed skeletal packstone peloidal packstone halimeda rich packstone to grainstone coralgal grainstone wackestone and mudstone whereas sediments rich in corals and coralline algae are abundant on reefs and carbonate shoals mud rich sediments with mollusks and foraminifera occur in deep lagoons 15 40 m carbonate mud is composed largely of aragonite needles probably derived from codiaceans like halimeda and coccoliths in moderate abundances despite the proximity to a volcanic island the content of siliciclastics in the sediments is low 10 on average which is a consequence of the absence of permanent water courses in addition to skeletal grains non skeletal grains cemented fecal pellets aggregates occur in high abundance 30 50 in shallow lagoons 5 m on the eastern side of bora bora this observation opposes the widely held concept that non skeletal carbonate grains are abundant on platforms from the atlantic ocean but virtually missing in recent indo pacific reefs and carbonate platforms in bora bora non skeletal grains and aggregates apparently form in warm shallow 5 m moderately agitated areas with relatively low sedimentation rates in addition early cementation is probably favored by elevated alkalinity and ph in surface waters in this part of the south pacific in the same area some 900 km to the southwest of the study area ooids and peloids have recently been discovered in the shallow lagoon of aitutaki cook islands more occurrences of abundant non skeletal grains probably exist in the indo pacific region however too few locations have been systematically studied a comparison of the new bora bora data with other modern reefs and platforms shows that sediment occurrence and distribution exhibits basic patterns in that marginal areas are dominated by coarse grained coralgal sediment whereas lagoons and platform interiors are characterized by mollusk foram halimeda and non skeletal grains and fines still grain abundances may vary significantly among locations and again suggest the need for more studies in order to fully understand the factors controlling occurrence and distribution of modern sediments

very low temperature metamorphism of shales from the diablo range franciscan complex california new constraints on the exhumation path we have determined illite crystallinity coal rank percent 2m 1 white k mica polytype and phase assemblages for shales and shale matrix melange from various areas in the diablo range additional information concerning metamorphic conditions and fluid composition was derived from stable isotope work and fluid inclusion measurements this study presents new constraints on the pressure temperature evolution of the franciscan units from the diablo range several shales indicate a lower pressure possibly higher temperature overprint on the peak pressure assemblages peak pressure assemblages include jadeitic pyroxene sodic amphibole lawsonite aragonite and phengite reactions which indicate a lower pressure possibly higher temperature overprint are the transition from aragonite to calcite the formation of albite from jadeitic pyroxene quartz the compositional gradient from phengite to muscovite in white k mica and the transition from sodic to calcic amphibole the assemblage albite calcic amphibole lawsonite and chlorite found in a single shale from pacheco pass indicates the transition from blueschist to greenschist facies conditions we suggest that this transition occurred at a pressure and temperature of 5 8 kilobars and 300 350 c fluid inclusion data from post kinematic quartz veins from the mount hamilton area support the idea of a lower pressure possibly higher temperature metamorphic event pressure temperature conditions of trapping early h 2 o and ch 4 rich fluids were 4 5 kilobars and 230 c geothermal gradients for the transition from blueschist to greenschist facies and the formation of early fluid inclusions are estimated to be 14 c km illite crystallinity for all areas indicates diagenetic to high grade anchizonal conditions coal ranks are between 1 6 and 2 5 mean ro these estimates are not consistent with metamorphic conditions deduced for two different shale assemblages from pacheco pass suggesting that illite crystallinity and coal rank are retarded poor illite crystallinity is thought to result from small coherent scattering domain sizes along c of white k mica crystals rich in a phengite component dalla torre et al 1994a in press the exact cause of the retardation of coal rank is not clear the high pressure in the diablo range may have affected the maturation of organic matter our results imply that coal rank data from high pressure terranes must be interpreted with caution if used as an absolute paleothermometer

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

event sequence and sediment exhaustion in the lower panuco basin mexico abstract although large tropical river systems transport the majority of the world s runoff and sediment few studies have examined the dynamics of suspended sediment transport in this setting this includes mexico which contains two of the larger river basins draining into the gulf of mexico this study provides a detailed analysis of discharge q and suspended sediment transport dynamics for the lower panuco basin 98 227 km2 of eastern mexico including the lower moctezuma lower tamuin and panuco rivers daily values of discharge and suspended sediment concentration ssc are examined for three stations spanning from the late 1950s to early 1990s although the panuco is a large basin the relationship between discharge and suspended sediment concentration represents a departure from the oft reported study by heidel trans am geophys union 37 1956 56 instead of sediment lagging discharge the sediment wave precedes discharge by an average of 1 7 days displaying pronounced clockwise positive hysteresis this may be due to the sources of runoff and sediment which are derived primarily in the lower reaches of the basin because of precipitation patterns geology and basin morphometry the distinct differences in lithology between the tamuin and moctezuma basins which join in the coastal plain to form the rio panuco allow the influence of geologic setting to be considered q ssc relations display positive hysteresis where the sediment is derived from erodible tertiary shale deposits in the moctezuma basin in contrast q ssc relations in the rio tamuin which transports less suspended sediment because of its karstic setting are more linear due to these relations being dependent on the entrainment of bed material consideration of the sequence of events during the rainy season suggests that much of the hillslope derived sediment is flushed through the system by early events which would occur because of exhaustion of hillslopes sediments q ssc relations are increasingly linear during later events in the rio panuco which is likely due to these events transporting a higher proportion of sediment entrained from the channel this is manifest by a reduction in lead times as the number of days between peak ssc and peak q for early and late events significantly decreases from 2 6 to 0 9 respectively large events 750 m3 s in the latter part of summer and early fall having high suspended sediment concentrations could be due to the replenishment of hillslope sediments or due to the contribution of sediment from source areas that were not previously exhausted the findings from this study are likely common to most drainage systems having seasonal bimodal streamflow regimes whereas the seasonal signature of q ssc relations is likely enhanced in those settings where agriculture is a major component of the landscape

vitrinite reflectance and shear induced graphitization in orogenic belts a case study from the kandersteg area helvetic alps switzerland vitrinite reflectance vr is an important indicator of incipient metamorphism and it is generally assumed that temperature and to a lesser degree time are the two main variables the role of stress in vr is controversial and will be addressed in this study in the kandersteg area north of lake oeschinen four different helvetic tectonic units are present comprising mainly limestones marls and greywackes of mesozoic and lower tertiary age vr rr rmax rmin and illite crystallinity ic were determined from a very steep section at elevations between 1700 and 2900 m a s l in general rr rmax and ic increase from tectonically higher to lower units i e from upper diagenetic 2 3 to 4 5 rr to upper anchizonal conditions 3 4 to 5 6 rmax several samples contain in addition to coaly fragments abundant semigraphitized and graphitized particles that are believed to be of authigenic origin transitional matter showsrmax values ranging from 7 to about 11 and rmin of 1 3 3 4 optical graphite showsrmax of about 15 16 and rmin of 1 6 1 8 there is good textural evidence that tectonic deformation has played a major role in the development of these strongly coalified particles the first tiny needle like crystals of graphitic material occur within narrow shear zones transecting the rock matrix the beginning of graphite formation parallels the onset of plastic deformation and dynamic recrystallization of quartz elevated vitrinite reflectance rmax and bireflectance values are found near thrust planes where simple optical observation on quartz grain morphology indicates an increase in strain intensity it appears that frictional heating associated with thin shear zones may have been responsible for the formation of authigenic graphite in the kandersteg samples

cretaceous to miocene thrusting and wrenching along the central south carpathians due to a corner effect during collision and orocline formation field studies in the romanian south carpathians longitude 22 5 to 24 2 e and latitude 45 2 to 45 6 n demonstrate 1 cretaceous top to ne shearing parallel to the present strike of the thrust system connected with coaxial flattening within the generally northwest dipping foliation 2 paleogene ductile brittle dextral wrenching e w compression 1 87 15 and basin formation petrosani basin along the cerna jiu fault system 3 large scale miocene dextral wrenching along the northern margin of moesia 1 143 16 and 4 probably pliocene early pleistocene n s compression 1 205 25 we discuss the tectonics of the south carpathians stressing the corner effect of the moesian foreland promontory during convergence and formation of the carpathian orocline up to the late early cretaceous subduction of oceanic crust was active between europe moesia on one side and east carpathia rhodopia on the other side collision and intracontinental deformation occurred during the late early and late cretaceous the pinning of the thrust front at the western tip of moesia and the foreland recess north of it caused superposition of thrusting and wrenching during collision and lateral translation tangential stretching during orocline formation and spreading into the recess further convergence during the early tertiary resulted in dislocation of the previously welded east carpathian rhodopian and moesian fragments along the cerna jiu fault system and the further northeast translation of the western segment the intramontane petrosani basin opened as a northeasterly propagating transient pull apart structure along the cerna jiu fault system which acquired a curved northwesterly convex transtensional trace due to the shape of the moesian promontory tightening of the carpathian orocline and or rearrangement of the microplate geometry during the formation of the pannonian basin system led to large scale dextral wrenching along the northern margin of moesia pliocene n s compression reflects final shortening in the carpathian system before ongoing convergence between europe and africa was transferred to the mediterranean rotation of material lines around the moesian corner is corroborated by paleomagnetic studies

channel and landscape dynamics in the alluvial forest mosaic of the carmanah river valley british columbia canada abstract the highly diverse shifting mosaic of forest patches of an alluvial forest within the carmanah river valley on the west coast of vancouver island british columbia was studied to examine the hydrogeomorphic disturbance regime that structures it we used a landscape scale analysis to quantify historical channel migrations and changes in the extent of specific forest types this gis based analysis using a 70 year aerial photographic record was complemented by field based research thirty eight plots containing 4509 trees were sampled for forest structure age and elevation above the contemporary channel these data including a vegetation chronosequence spanning over 500 years were used to examine channel and landscape dynamics our findings support a general conceptual model that describes cycles of patch development and destruction in unconfined alluvial forests of the pacific coastal ecoregion over the past century carmanah river has eroded nearly 30 of the alluvial forest in this study area and approximately 65 over the past 500 years at least 80 of the 2007 channel was forested area within the past 70 years younger landforms were disturbed more frequently than mature forest patches which suggest that as biogeomorphic succession progresses the likelihood of future disturbance decreases estimated half lives of landforms ranged from 24 years for pioneer bars to over 1500 years for old growth terraces years of regional high magnitude floods resulted in a net loss of floodplain forest area indicating that disturbance was climate driven in this pluvial watershed whereby rain events result in flood disturbance that converted forests to channel these events initiate a subsequent course of vegetation succession and geomorphic development and often result in the deposition of large wood that modifies the channel environment and contributes to channel avulsion and further hydrogeomorphic disturbance the composition of the landscape is a reflection of the balance between the disturbance rate and successional development we also observed a relationship between landscape composition and watershed size specifically the ratio of mature to developing alluvial forests was higher in this smaller watershed compared to larger watersheds in the region results imply that larger flood events predicted to occur with climate change may change the disturbance regime of floodplain forests and alter landscape composition

experimental study on the pressure dependence of vitrinite maturation we conducted the first systematic experiments over a pressure range of 0 5 to 20 0 kbar at temperatures of 200 to 350 c and run durations of 2 4 and 7 days to investigate the influence of pressure on vitrinite reflectance the data indicate that applied pressure lowers vitrinite reflectance the suppression appears to be stronger under wet than under dry conditions in addition high pressure favors liptinite preservation at temperatures 300 c whereas at the same temperature range yet at low pressure liptinite is decomposed our data fit an empirical rate equation which expresses rr as a function of pressure temperature and time the derived equation satisfactorily describes our experiments and enables extrapolations to geological timescales values of rr calculated for a pressure of 0 5 kbar are remarkably consistant with previous numerical pressure independent models a literature review shows that previous experimental data and field observations are inconsistent regarding the effect of pressure on vitrinite maturation this and some previous studies suggest that vitrinite maturation is suppressed by increased pressure whereas other workers regarded pressure as having little influence on the rate of coalification we suggest that original virinite composition experimental design and natural environment tectonic regime play important roles regarding the effects of pressure on vitrinite maturation interpretation of geothermal histories of sedimentary rocks based on vitrinite reflectance data must therefore include evaluation of the pressure otherwise vitrinite reflectance data from high pressure terranes should be interpreted with caution if used as a quantitative paleogeothermometer

age and significance of core complex formation in a very curved orogen evidence from fission track studies in the south carpathians romania abstract twenty four new zircon and apatite fission track ages from the getic and danubian nappes in the south carpathians are discussed in the light of a compilation of published fission track data a total of 101 fission track ages indicates that the getic nappes are generally characterized by cretaceous zircon and apatite fission track ages indicating cooling to near surface temperatures of these units immediately following late cretaceous orogeny the age distribution of the danubian nappes presently outcropping in the danubian window below the getic nappes depends on the position with respect to the cerna jiu fault eocene and oligocene zircon and apatite central ages from the part of the danubian core complex situated southeast of this fault monitor mid tertiary tectonic exhumation in the footwall of the getic detachment while zircon fission track data from northwest of this fault indicate that slow cooling started during the latest cretaceous the change from extension getic detachment to strike slip dominated tectonics along the curved cerna jiu fault allowed for further exhumation on the concave side of this strike slip fault while exhumation ceased on the convex side the available fission track data consistently indicate that the change to fast cooling associated with tectonic denudation by core complex formation did not occur before late eocene times i e long after the cessation of late cretaceous thrusting core complex formation in the danubian window is related to a larger scale scenario that is characterized by the nnw directed translation followed by a 90 clockwise rotation of the tisza dacia block due to roll back of the carpathian embayment this led to a complex pattern of strain partitioning within the tisza dacia block adjacent to the western tip of the rigid moesian platform our results suggest that the invasion of these southernmost parts of tisza dacia started before the late eocene i e significantly before the onset of miocene age rollback and associated extension in the pannonian basin

exhumation of the danubian nappes system south carpathians during the early tertiary inferences from kinematic and paleostress analysis at the getic danubian nappes contact abstract a detailed kinematic study based on the analysis of brittle structures combined with a description of structures in the adjacent foredeep allows for the definition of three major tectonic episodes during the late cretaceous tertiary evolution of the central part of the south carpathians following middle cretaceous and older orogenic phases the first tectonic event that affected the studied area was a late cretaceous nnw sse oriented contraction which led to the final major emplacement of the danubian and getic nappes during the paleogene early miocene an extension event induced rapid exhumation of the danubian units leading to the formation of large normal faults dipping towards both the foreland and the hinterland this extension together with dextral rotation of the south carpathians around the western corner of the moesian platform allows for the ne ward movement of the internal continental blocks with respect to the foreland platforms in the late miocene e ward translation of the internal south carpathians units with respect to the moesian platform was accommodated through a large scale e w oriented strike slip corridor within the south carpathians the general paleogene early miocene ne to e ward rotation and the late miocene e ward translation of the rhodopian fragment allowed for the accommodation of roll back and contraction taking place in the east carpathians

thermal effects of exhumation of a metamorphic core complex on hanging wall syn rift sediments an example from the rechnitz window eastern alps the removal of overburden by tectonic processes displaces the rock masses and their temperature with respect to the surface consequently high cooling rates and increased heat flow have been reported from rapidly exhuming terrains previous studies were mainly focused on the greenschist and amphibolite facies tectono thermal evolution of the footwall a two dimensional numerical thermal model presented in this study concentrates on the thermal history of the hanging wall and the footwall blocks and evaluates the variation of the near surface heat flow above an evolving metamorphic core complex based on structural thermobarometric and geochronological constraints from the rechnitz core complex of the eastern alps the modelling suggests that rapid movement along the extensional fault took place between 22 and 17 ma during this period the heat flow reached values of 140 150 mw m 2 in the hanging wall in a 10 15 km wide zone parallel to the fault trace the increased heat flow caused the high coal rank in the miocene syn rift sediments deposited on the hanging wall apatite fission track geochronology of the thermally overprinted sedimentary deposits gives the time at which the bottom of the syn rift sediment pile passed through 110oc 13 6 0 9 ma the vitrinite reflectance data rr 0 67 1 04 suggest significant burial of the margin of the hanging wall at the time of core complex formation considering the coal rank data and the thermal conductivity of the sedimentary deposits by modelling of the organic maturation we calculate syn rift early middle miocene burial of the hanging wall margin of the rechnitz core complex to be 1100 1600 m this value shows the importance of the post middle miocene erosion of the region which was related to the inversion of the pannonian basin 1998 elsevier science b v all rights reserved

sediments from fringing reefs of reunion island indian ocean abstract on reunion island fringing reefs comprise the following physiographical zones from the open sea landwards outer sandy spread spur and groove zone reef flat backreef zone sixty two samples collected from the various zones have been analyzed by using correspondence factor analysis to determine variations in sediment composition and grain size five sediment facies and three foraminiferal subfacies can be recognized on the basis of component composition and three sediment types can be defined using the grain size data alcyonaria terrigenous fine sand facies and calcarina subfacies occur in the outer sandy spread whereas foraminiferal coarse sand facies characterizes the spur and groove system the outer margin of the reef flat exhibits coral coralline algal and coral molluscan coarse sand facies and the inner part of the reef flat exhibits a coral terrigenous mediumsand facies the whole reef flat also presents a miniacina subfacies the backreef area displays a coral coralline algal medium sand facies and a marginopora textularia subfacies factor axes seem to reflect physiographical or hydrodynamical gradients

spatial and temporal variability in sedimentation rates associated with cutoff channel infill deposits ain river france floodplain development is associated with lateral accretion along stable channel geometry along shifting rivers the floodplain sedimentation is more complex because of changes in channel position but also cutoff channel presence which exhibit specific overflow patterns in this contribution the spatial and temporal variability of sedimentation rates in cutoff channel infill deposits is related to channel changes of a shifting gravel bed river ain river france the sedimentation rates estimated from dendrogeomorphic analysis are compared between and within 14 cutoff channel infills detailed analyses along a single channel infill are performed to assess changes in the sedimentation rates through time by analyzing activity profiles of the fallout radionuclides 137cs and unsupported 210pb sedimentation rates are also compared within the channel infills with rates in other plots located in the adjacent floodplain sedimentation rates range between 0 65 and 2 4 cm a1 over a period of 10 to 40 years the data provide additional information on the role of distance from the bank overbank flow frequency and channel geometry in controlling the sedimentation rate channel infills lower than adjacent floodplains exhibit higher sedimentation rates and convey overbank sediment farther away within the floodplain additionally channel degradation aggradation and bank erosion which reduce or increase the distance between the main channel and the cutoff channel aquatic zone affect local overbank flow magnitude and frequency and therefore sedimentation rates thereby creating a complex mosaic of sedimentation zones within the floodplain and along the cutoff channel infills last the dendrogeomorphic and 137cs approaches are cross validated for estimating the sedimentation rate within a channel infill

decoding the mechanism of formation in marine ooids a review abstract ooid shoals sedimentary structures consisting of carbonate grains are often used as proxies to explore changes in seawater chemistry over earth history despite their importance as contributors to the global carbonate budget and as paleo environmental indicators for water depth ph temperature and water energy the mechanism of formation of these concentric sub spherical concretions of tangentially or radially arranged aragonite or calcite crystals is still the subject of intense debate unlike oncoids whose microbial origins are well acknowledged ooids are traditionally viewed as abiotic grains mainly produced in suspension by agitated warm waters that are supersaturated with respect to caco3 yet there is considerable evidence including geochemical bio signatures and detection of viable microbes capable of mineralization and biofilm production and degradation to suggest otherwise the emergence of new and sophisticated technologies reveals that the level of microbial diversity of these sedimentary grains exceeds that of some microbialite systems these findings have refined our understanding of ooid genesis and ooid accretion processes and argue toward microbial mediation both as a direct result of metabolic activities inducing changes in the environment conducive to precipitation and by a passive mechanism in which mucilaginous extracellular polymeric substances eps act as a template for mineral nucleation furthermore new developments in the field indicate that carbonate mineralization in marine ooids occurs through sequential precipitations that involve an amorphous calcium carbonate phase acc which some argue are of biotic origins herein we discuss the most relevant theories of ooid formation including some of the early pioneering studies that laid the groundwork for new theories attempting to decode the origins of these controversial grains

orogen parallel extension in the southern carpathians a structural study including a kinematic analysis based on sense of shear criteria recorded in fault rocks is combined with fission track dating a two stage alpine tectonic evolution is proposed for the major tectonic units which constitute the southern carpathians of the parang mountains area upper cretaceous top to the sse nappe stacking was followed by wsw ene orogen parallel extension in the eocene top to the ene shearing in lower greenschist facies mylonites from the eastern part of the danubian window parang mountains is associated with a low angle detachment at the base of the brittlely deformed getic nappe the getic detachment below the dome shaped getic detachment east dipping at the eastern termination of the danubian window the danubian units were rapidly exhumed hence the eastern part of the danubian window represents a greenschist facies core complex as a working hypothesis it is proposed that this orogen parallel stretch was originally n s oriented and that it formed when the rhodopean fragment which includes the getic and supragetic nappes moved northward into an oceanic embayment past the western margin of moesia this eocene extension was part of a process of oroclinal bending in the area of the southern carpathians and their continuation into the balkan mountains extension was followed by about 50o clockwise rotation of the southern carpathians associated with dextral wrenching along the northern boundary of moesia and compression in the moldavides of the eastern carpathians 1998 elsevier science b v all rights reserved

heating during thrust faulting in the rocky mountains friction or fiction abstract measurement of the levels of organic maturation below and within shear zones of thrust faults in the rocky mountains has revealed no general thermal metamorphism that can be attributed to faulting with the exception of very localized areas with few exceptions the vitrinite reflectance values obtained are in the range expected if the maximum level of organic maturation was produced as a result of increasing temperature during progressive burial accompanying sedimentation only at marias pass evidence has been found to suggest additional maturation as a result of post orogenic burial below the thrust sheets anomalously high vitrinite reflectances obtained from the lewis thrust mcconnell thrust coleman thrust and two unnamed thrusts are restricted to very narrow films immediatly adjacent to or within the shear zone which considering any reasonable thermal conductivity indicates elevated temperatures were very short lived the anomalously high vitrinite reflectances within these films when compared to laboratory heated coals suggest temperatures in the order of 350 650 c were locally generated during faulting such high temperatures are considered to have been generated during stick slip faulting at macro asperities or at ramps on the fault plane where local and possibly transient high frictional stresses existed the absence of evidence for extensive frictional heating supports previous arguments that stable sliding and or low frictional stress must exist during thrusting

vitrinite and vitrinite like solid bitumen reflectance in thermal maturity studies correlations from diagenesis to incipient metamorphism in different geodynamic settings abstract vitrinite reflectance vr is a useful and reliable parameter to monitor the level of organic matter maturation from the immature stage to graphite additionally vr is a useful and essential tool in modelling the temperature maturation time path huminite vitrinite bearing sedimentary and meta sedimentary rocks can be used to reconstruct the thermal history of basins or orogenic terranes throughout their geological history the usefulness of vr evidently depends on the presence of huminite vitrinite phytoclasts however pre upper silurian rocks and many organic rich marine rocks e g sapropelic sediments lack of huminite vitrinite particles furthermore vitrinite is sparse in carbonate sediments however the presence of bitumen in rocks lacking type iii kerogen provides a valuable aid via its reflectance vitrinite like solid bitumen reflectance vlbr and or solid bitumen reflectance br to fulfil the above described tasks that vr enables this study presents basically a relationship between br vlbr and vr for various types of geodynamic settings and over the largest possible range of maturation levels so that vlbr may be used as a substitute for vr whereas the effort to correlate vr with br is not novel it is the first time that the vr br correlation is re judged discriminating bitumen from vlb moreover for the first time the correlation is established for various geodynamic settings the investigated geological contexts are 1 sedimentary basins e g the saar ruhr ohio west virginia and petrosani basins 2 metasedimentary terranes occurring as inverted basins in orogenic belts e g from the subalpine molasse helvetic austroalpine and danubian nappe systems and having suffered from very low to low grade metamorphism from anchizone to greenschist facies 3 metasedimentary terranes e g slates and schists from the franciscan and alpine belts that were subducted at anchizone to blueschist facies conditions and 4 metasedimentary rocks affected by contact metamorphism together the frequent geological settings are referred and most of the earth geothermal conditions and heat fluxes considered despite temperature pressure and heating time also heat flow gradient dependences cannot be ignored

sediments of the almost atoll aitutaki cook islands south pacific abstract modern sedimentary facies in the shallow platform interior of the almost atoll of aitutaki cook islands is significant because abundant non skeletal grains have been discovered in this pacific location and also in some adjacent carbonate platforms abundant non skeletal carbonate grain occurrences have been classically placed in the western atlantic and the arabian persian gulf but not in the indo pacific realm in order of decreasing abundance non skeletal grains in aitutaki include peloids aggregate grains and ooids peloids are largely cemented fecal pellets and their occurrence is controlled by the occurrence of mollusk and crustacean producers in the interior platform ooids which are characterized by thin and irregular cortices and aggregate grains appear to be more common at the platform margin in environments of somewhat elevated depositional energy in general high alkalinity in this part of the south pacific seems to be another precondition of non skeletal grain formation the fine grain size fraction reaches an abundance of 70 in the platform interior average 41 5 and is largely of skeletal origin based on the quantitative analysis of texture and composition of samples two groups of sediment types may be distinguished including coralgal grainstones and packstones that occur at the platform margin as well as peloidal and mixed skeletal peloidal wackestones and packstones in the platform interior these two types may be further differentiated into eight sedimentary facies including 1 peloidal wackestone 2 peloidal packstone 3 mud rich skeletal peloidal packstone 4 skeletal peloidal packstone 5 skeletal peloidal grainstone 6 coralgal packstone 7 coralgal grainstone and 8 coralgal aggregate grainstone sediment texture is correlated with water depth which is considered a good proxy for depositional energy considerable bathymetric overlap exists however between sedimentary facies also facies distribution in the platform interior appears to be fragmentary rather than being characterized by laterally extensive units these observations have to be considered when using sedimentary facies distribution in modern reefs and carbonate platforms as models for ancient systems in the fossil record

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

pore networks in holocene carbonate sediments abstract permeabilities of holocene carbonate sediments from florida and the bahamas determined for 74 samples by water flow rates in a variable head permeameter range from 0 6 to 57 000 millidarcies porosities range from 40 to 78 percent these parameters are related to depositional texture as follows table the muddiest sediments i e the finest grained have the highest porosities but lowest permeabilities this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks even as young as pleistocene high porosity and low permeability in sediments show a strong correlation with percentage of fines 62 m from capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 m in diameter at least after drying measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation the calculated rates would require excessive time to produce the degree of cementation seen in late pleistocene rocks of florida and the bahamas the amounts of rainfall and evaporation are the most important factors in the degree of cementation

recent sedimentary facies of isolated carbonate platforms belize yucatan system central america abstract distribution of recent sedimentary facies is significantly different in four closely spaced isolated carbonate platforms off the coasts of belize and yucatan se mexico these differences are largely controlled by variations in submarine topography which are likely the result of differential subsidence and karstification from platform to platform a variety of depositional styles and patterns is found in platform interiors that developed during the same holocene sea level rise composition and texture of surface sediment samples were used to define four major sediment types and to distinguish nine depositional environments within the platforms facies maps are based on analysis of 454 sediment samples and high resolution satellite imagery glovers reef is characterized by a circular facies distribution the nearly continuous reef margin is composed of a coral red coralline algae halimeda grainstone mixed nonskeletal peloidal skeletal wackestones and packstones are present in shallow lagoon parts 5 m water depth behind the margin the deep interior from 5 to 18 m water depth is characterized by mollusk foram halimeda wackestones with over 860 patch reefs of coral red algae halimeda mollusk packstones lighthouse reef also has a coral grainstone and coral red algae halimeda grainstone rim but the facies distribution in the interior is strongly asymmetrical the 8 m deep eastern lagoon is floored by mollusk foram halimeda wackestones and packstones the 3 m deep western lagoon has the mixed peloidal skeletal wackestone to grainstone facies a linear trend of coalescing patch reefs and skeletal grainstone facies separates the two lagoons banco chinchorro is similar to lighthouse reef inasmuch as facies distribution patterns of the interior are strongly asymmetrical mollusk foram halimeda wackestones grainstones are present in eastern lagoon areas whereas shallow 5 m western parts of the lagoon are composed of mixed peloidal skeletal grainstones packstones and wackestones most of turneffe islands is protected on the east by lighthouse reef accordingly turneffe has a narrower reef and skeletal grainstone rim than the other two platforms restricted interior lagoons are up to 8 m deep and are enclosed by wide mangrove rims and surface sediments dominated by halimeda rich wackestone rich in organic matter coral patch reefs are absent in contrast the unprotected northernmost part of turneffe has a wide reef and grainstone rim and the open lagoon area consists of mollusk foram halimeda wackestones packstones with abundant patch reefs

sedimentation and sediment accretion in michigan coastal wetlands u s a abstract sediment transport and accretion rates were studied for three different types of coastal wetlands of lake michigan u s a a forested intradunal wetland cranberry bog no 1 near stevensville michigan displayed sediments in the form of detritus and exported them very little sedimentary material entered by streamflow these features of bottom land wetlands were confirmed by radioisotope studies on cores which showed low accretion rates of 210 pb the mass fluxes were found to range from 0 01 to 0 2 g cm 2 yr 1 the equivalent linear growths are 0 5 9 0 mm yr 1 the suspended material from this wetland entered a filling shrub bog lake complex known as cranberry bog no 2 a considerable fraction of the incoming sediments were retained in this intradunal basin wetland this was confirmed via radioisotope studies with cores showing higher accretion rates than in the bottom land wetland the river delta wetland at pentwater michigan had little sediment trapping ability large amounts of water and suspended materials entered this riverine wetland but no annual average removal was found radioisotope studies of cores at selected locations within this system showed little or no accretion in stream channels and normal accumulation of organic material in non channel areas no net annual effect on water quality of the streams as they discharged to lake michigan was found storm events caused no notable import or export of suspended material presumably the sand substrate in the vicinity of all three wetlands caused runoff events to be mediated by subsurface flow through this porous soil these three sand based coastal wetlands appear to have little net effect on suspended solids the 210 pb method proved more valuable than 137 cs because of the small depth of occurrence of the latter isotope interpretation of isotope profiles required information on acid fraction soluble profiles results are expressed in terms of mass units since compaction of cores distorts the linear accretion rate delayed transfers of radionuclides appear to have occurred perhaps as a result of integration of atmospheric inputs by the watersheds the total activities of 210 pb and 137 cs are well correlated which indicates particle trapping efficiency as the primary factor for affecting accumulation of both isotopes

modern fringing reef carbonates from equatorial se asia an integrated environmental sediment and satellite characterisation study abstract fringing reefs of se asia may conservatively comprise 30 of the world s coral reef area but remain almost unstudied white 1987 tomascik et al 1997 this study provides insights into the primary sedimentological and early alteration characteristics of an isolated fringing reef system kaledupa hoga from the tukang besi archipelago se asia a combined multispectral satellite imagery field and petrographic study allowed for the generation of an environmental facies map which acts as a model for the distribution of primary sedimentological characteristics in relation to the primary environmental facies the islands of the tukang besi archipelago are mesotidal 71 accuracy when compared with field and sedimentary data with the exception of the reef crest and reef slope that commonly have widths on a sub imaging resolution although field and satellite imagery observations reveal ten environmental facies sedimentological characterisation results in a lower number of distinctive categories due to the similarity of many deposits foreshore backshore and bare intertidal deposits are distinctive and are composed of reef derived material that has been reworked shorewards seagrass associated facies all show some fine silt clay sized material

heavy mineral distributions of maastrichtian deposits from the haţeg basin south carpathians tectonic and palaeogeographic implications abstract this study represents the first extensive investigation of source areas of the maastrichtian continental deposits of the ha eg basin using heavy mineral associations the heavy mineral associations consist of garnet hematite magnetite ilmenite rutile staurolite kyanite epidote apatite titanite tourmaline and zircon the general pattern indicates different source areas with contrasting metamorphic grades for the northern and southern parts of the basin the sediments of the northern and central sectors of the basin show a high proportion of garnet staurolite and kyanite and a low proportion of epidote suggesting an amphibolite facies metamorphic source which is compatible with the lithology of the getic upper plate on which the basin formed the samples with abundant amphibolite facies heavy mineral components have high proportions of magnetic fe ti oxides with complex exsolution intergrowth features these oxides belong chiefly to the hematite ilmenite solid solution series and indicate a high grade metamorphic and or igneous source area in the south the heavy mineral spectra change to epidote rich evidence of exhumation and erosion of the greenschist metamorphic rocks of the danubian lower plate during updoming and core complex formation the study shows that for the northern and central parts of the basin the getic plate is the main source for the sediments during the maastrichtian time due to increasing relief in the hinterland and exhumation of the lower plate the danubian unit fed the basin as recorded in the sediments situated along sibisel and r ul b rbat valley

holocene ooids of aitutaki atoll cook islands south pacific although oolitic sands are widespread throughout the phanerozoic carbonate rock record and they are abundant in some modern shallow marine carbonate systems recent ooids have not been recognized from any locality in the pacific basin on aitutaki atoll cook islands south pacific oolitic sands occur in water depths of 2 1 6 3 m within the lagoon and less abundantly on shallower reef aprons most ooids are between 150 and 300 m in diameter have between 1 and 25 concentric to irregular laminae and occur with peloids and skeletal grains cortical laminae include mg calcite crystals with radial tangential and random orientations the occurrence and distribution of oolitic sands on aitutaki are facilitated by a convergence of hydrodynamic and chemical factors wave driven currents combined either with flow separation over a sharp increase in depth at the reef apron lagoon interface or with oceanward flow in the lee of islands serve to transport ooids without flushing them from the system here ph alkalinity and carbonate supersaturation are at some of the highest levels in the tropical pacific the restricted occurrence of holocene oolitic sands in areas of the pacific and atlantic basins with elevated ph and total alkalinity reflects the importance of carbonate saturation thresholds in limiting the spatial distribution of these sands in modern shallow marine settings these recent examples are consistent with interpretations of the importance of these variables in determining the distribution abundance and cortical mineralogy of oolitic sands throughout the phanerozoic stratigraphic record of carbonate accumulation

unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates carbonate sequence stratigraphy is founded on the principle that changes in relative sea level are recorded in the rock record by the accumulation of sediment with relative water depth dependent attributes while at the scale of a shelf to basin transect facies clearly arrange by water depth the relation blurs for depths 40 m the most vigorous zone of carbonate production the reason for this change in behaviour is two fold firstly in shallow water the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution secondly facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers remote sensing imagery field observations and hydrodynamic models for two reef rimmed shore attached carbonate platforms in the red sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation considered together however the predictive power of the two variables rises significantly the results demonstrate it to be an oversimplification to assume a direct link between palaeo water depth and depositional diversity of subtidal lithofacies while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone while the size distributions of facies extents in the two focus areas follow power laws no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported the work is relevant for the interpretation of metre scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies

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 chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

floodplain sedimentation quantities patterns and processes this paper presents the result of measurements of floodplain sedimentation using sediment traps the study was carried out on two embanked floodplains along the rivers rhine and meuse in the netherlands during a 3 day flood in january 1993 raster maps of sediment accumulation were made by interpolating the measurements from the traps using block kriging the sediment maps show clear patterns in sediment accumulation together with the estimated interpolation errors average sediment accumulation ranges between 0 57 and 1 0 kg m 2 high sediment accumulation is found on the levees 4 kg m 2 or more and on low lying areas 1 6 kg m 2 sediment accumulation decreases with distance from the main channel the sedimentation patterns are related to floodplain topography and sediment transporting mechanisms sediment transport by turbulent diffusion as well as by convection can be recognized also flood duration and the process of sediment settling out in ponding water in closed depressions are important the applied method allows comparison of the results with raster based sedimentation models

solid bitumen in calcite veins from the natih formation in the oman mountains multiple phases of petroleum migration in a changing stress field abstract solid bitumen in calcite veins in natih limestone on the southern flank of the jebel akhdar anticline provide evidence for at least two previously unrecognized petroleum migration events in the oman mountains we present field observation of bituminous calcite veins combined with microscopy using highly polished thin sections this allows imaging of solid bitumen in reflected light and study of its microstructural context in transmitted light straight and en echelon black impregnated bedding normal natih a calcite veins strike 110 they formed as one of the earliest structures in an extensional stress regime at the end of cretaceous turonian santonian either by flexure of the arabian plate wasia aruma break or by subsidence during subduction the veins always contain planar arrays of small during the first migration event microfracturing during obduction of the semail ophiolite and emplacement of the hawasina thrust sheets in santonian campanian times formed pathways for oil into the veins mosaic type solid bitumen formed during further vein growth it has a higher solid bitumen reflectance br r 3 40 3 76 combined with a high optical anisotropy compared to the underlaying thermally overmature natih b source rock br r 3 10 3 14 the higher reflectance of mosaic type solid bitumen is interpreted to result from deformation and does not reflect maximum burial temperatures which are inferred to have been about 225 c the second migration event is indicated by low reflective homogeneous type solid bitumen with palaeotemperatures br r 0 86 0 92 about 145 c lower than maximum burial it occurs along pressure solution seams which cross cut the veins showing that this is the latest event in the paragenetic sequence interpreted to have formed after lateral intraformational oil migration from the active natih oil kitchen located approximately 40 km sw of the study area during doming and uplift of the oman mountains in oligocene to pliocene times

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

very low grade metamorphic evolution of pelitic rocks under high pressure low temperature conditions nw new caledonia sw pacific the p t gradient in a late eocene low t high p metamorphic belt in northern new caledonia increases from sw to ne metapelites in the pumpellyite prehnite and blueschist zones contain lawsonite mg carpholite fe stilpnomelane and fe glaucophane thermodynamic calculations indicate a progression of metamorphic conditions from less than 0 3gpa and 250 c in a kaolinitebearing rock in the sw up to 1 5gpa and 410 c in a lawsonite glaucophane bearing sample in the ne of the diahot terrane through a multi method investigation of phyllosilicates organic matter and fluid inclusions we demonstrate that the evolution of organic matter and illite crystallinity depends strongly on the evolution of the p t path with time in addition we show that the illite muscovite b cell dimension provides a robust estimate of maximum pressure reached in low temperature domains with polyphase metamorphic histories despite subsequent hightemperature low pressure events fluid inclusion study reveals an isothermal decompression in the diahot terrane

correlation of very low grade data to calibrate a thermal maturity model in a nappe tectonic setting a case study from the alps abstract vitrinite and bituminite reflectance data xrd studies on clay minerals radiometric data and geochemical data have been used to investigate metamorphism of very low and low grade sediments from the lower austroalpine and south penninic nappes in the oberhalbstein valley central alps numerical maturity modelling methods are calibrated with petrological structural and new geochronological data to reconstruct temperature histories even in nappe tectonic settings the combination of low grade data and maturity modelling shows that the duration of peak temperature metamorphism plays an important role in the alteration of organic matter vitrinite reflectance vr often does not correlate with other low grade parameters but in the oberhalbstein equilibrium between the different parameters is evident because heating near the peak conditions for more than 20 ma took place it is proposed to use the comparison to evaluate equilibrium conditions for the temperature parameters in general in addition from petrological work and vr modelling the pressure conditions are estimated the results yield an eroded overburden of 6 1 km and a temperature gradient of 30 2 c km 1 at the base of the nappe stack pressure conditions of 4 1 kbar are determined and therefore no evidences for a high pressure event the main heating is dated between 90 and 70 5 ma and is attributed to nappe stacking in the upper crust

on the interpretation of shallow shelf carbonate facies and habitats how much does water depth matter abstract many stratigraphic studies of ancient shallow water carbonate platforms focus interpretation on the primacy of changes in accommodation inferred by assuming a direct and deterministic link between depositional facies and water depth the purpose of this study is to test this assumption explicitly and quantitatively by exploring relations between substrate type classified on the basis of both habitats and facies and the water depth at which they occur on a modern well studied shallow rimmed shelf margin gis analysis of digital benthic habitat and bathymetry maps of the shallow 8 m south florida shelf illustrate that most substrate types occur across a range of water depths similarly at greater water depths habitats and facies are more constrained more dominance of one class more deterministic with generally decreasing dominance more diversity at shallower water depths at a scale of shelf to basin transects facies and habitats clearly are related to water depth yet on this narrower 10 km shallow shelf margin at the scale of this study water depth and habitats and facies are not uniquely related or linked this general lack of correspondence between bottom type and water depth may be a manifestation of landscape disequilibrium a state in which habitats and facies do not fully reflect ambient environmental conditions perhaps recording the influence of rapid change in sea level alternatively it may reflect the impact of variables other than water depth although more general consequences of these results for other depositional settings remains to be evaluated they do emphasize the fact that variables other than bathymetry may significantly influence the ecological and sedimentologic attributes of depositional surfaces they do allow for the quantification of some of the potential uncertainties inherent in the interpretation of analogous ancient platforms and can serve to focus future observations on the causes and consequences of vertical and lateral heterogeneity in ancient stratigraphic sequences

modeling oil generation with time temperature index graphs based on the arrhenius equation the time and depth of oil generation from petroleum source rocks containing type ii kerogens can be determined using time temperature index tti graphs based on the arrhenius equation activation energies e and frequency factors a used in the arrhenius equation were obtained from hydrous pyrolysis experiments on rock samples in which the kerogens represent the range of type ii kerogen compositions encountered in most petroleum basins the e and a values obtained were used to construct graphs that define the beginning and end of oil generation for most type ii kerogens having chemical compositions in the range of these standards activation energies of these standard kerogens vary inversely with their sulfur content the kerogen with the highest sulfur content had the lowest e value and was the fastest in generating oil whereas the kerogen with the lowest sulfur content had the highest e value and was the slowest in generating oil these standard kerogens were designated as types iia b c and d on the basis of decreasing sulfur content and corresponding increasing time temperature requirements for generating oil the summation tti arr values determined graphically with these type ii kerogen standards in two basin models were compared with a computer calculation using 2000 increments the graphical method came within 3 of the computer calculation as type ii kerogens are the major oil generators in the world these graphs should have wide application in making preliminary evaluations of the depth of the oil window in exploration areas

dolomitization of quaternary reef limestone aitutaki cook islands six holes were drilled to depths of 30 69 m in the shallow lagoon of aitutaki in the southern cook islands one hole encountered pervasively dolomitized reef limestones at 36 m subbottom depth which extended to the base of the drilled section at 69 3 m this hole was drilled near the inner edge of the present barrier reef flat on the flank of a seismically defined subsurface ridge both the morphology and biofacies indicate that this ridge may represent an outer reef crest mineralogy porosity and cementation change in concert downhole through three zones zone 1 0 9 m is composed of primary skeletal aragonite and calcite with minor void filling aragonite and magnesian calcite cement of marine phreatic origin zone 2 9 36 m is composed of replacement calcite and calcite cement infilling intergranular intragranular mouldic and vuggy porosity stable isotopes mean 18o 5 4 pdb for carbonate d 50 smow for fluid inclusions support the petrographic evidence indicating that sparry calcite cements formed in predominantly freshwater carbon isotope values of 4 0 to 11 0 for calcite indicate that organic matter and seawater were the sources of carbon zone 3 36 69 3 m is composed of replacement dolostone consisting of protodolomite with on average 7 mol excess caco3 and broad and weak ordering x ray reflections at 2 41 and 2 54 a the fine scale replacement of skeletal grains and freshwater void filling cements by dolomite did not significantly reduce porosity stable isotopes mean 18o 2 6 0 pdb for dolomite maximum d 27 smow for fluid inclusions and chemical composition indicate that the dolomite probably formed from seawater although formation in the lower part of a mixed freshwater seawater zone with up to 40 freshwater contribution cannot be completely ruled out the carbon 13c 2 7 and magnesium were derived from seawater low temperature hydrothermal iron hydroxides and associated transition metals occur in void space in several narrow stratigraphic intervals in the limestone section that was replaced by dolomite the entire section of dolomite is also enriched in these transition metals the metals dispersed throughout the dolostone section were introduced at the time of dolomitization by a different and later episode of hydrothermal circulation than the one s that produced the localized deposits near the base of the section the primary reef framework is considered to have been deposited during several highstands of sea level following partial to local recrystallization of the limestone a single episode of dolomitization occurred both tidal and thermal pumping drove large quantities of seawater through the porous rocks and perhaps maintained a wide mixing zone however the isotopic geochemical and petrographic data do not clearly indicate the extent of seawater mixing

causes of planform stability of a low energy meandering gravel bed river cher river france abstract for at least two centuries the lateral mobility of the meandering reaches of the cher river france has been very low this article aims to identify the main causes of this behavior two not mutually exclusive explanatory hypotheses are proposed under the first hypothesis the natural mechanisms of loop migration would have been inhibited or blocked by the presence of bank protections under the second hypothesis a decrease in the frequency and or intensity of morphogenic hydrological events since the nineteenth century would have reduced the frequency of bedload mobilization and or reduced the capacity of the river to erode its banks to test these hypotheses the diachronic evolution of the planform was reconstituted at different time scales using a gis and field surveys morphological transformations were characterized and quantified eroded and vegetated areas length of eroded banks rates of bank retreat and the critical discharges of bedload mobilization and of lateral erosion were estimated engineering works in the riverbed were identified and when possible dated the results show that meander morphodynamics have been highly constrained and disrupted by engineering works probably for over a century however the meanders still have noticeable potential for bedload mobility and lateral erosion and hence for self restoration

spatial hydrogeomorphological influences on sediment and nutrient deposition in riparian zones observations from the garonne river france abstract this paper investigates the influence of geomorphological setting on riparian zone sedimentation within a reach of the river garonne france during three major floods the sampling design was stratified to reflect landforms constructed by fluvial processes e g floodplain lateral benches islands side channels and point bars observed sedimentation varied significantly with flood event planform context landform type and associated vegetation cover and in some cases with sample location within the landform lowest sedimentation was associated with the flood with the smallest peak discharge peak sediment concentration and sediment load sites under natural riparian vegetation experienced higher sedimentation than poplar plantations sites on concave outer banks received less sedimentation than those on convex inner banks sedimentation on floodplain sites and higher benches was lower than on low benches point bars and side channels there was considerable interdependence among these patterns reflecting the underlying geomorphological forms and processes meandering rivers tend to evolve through erosion of concave banks and deposition on convex banks point bar features tend to be built along convex banks whilst concave banks are eroded into higher floodplain and bench features as a result concave banks tend to be bordered by higher riparian margins that are less frequently flooded than convex banks where river margins are developed for agriculture the higher less frequently flooded sites are preferentially selected analyses of the quantity calibre nutrient and carbon content of the deposited sediment reveal further significant relationships which reflect the geomorphological structure of the riparian zone sediment particle size coarsens in locations with higher amounts of sedimentation the quantities of total organic carbon toc total organic nitrogen ton and total phosphorus tp all increase as the quantity of deposited sediment increases the concentration of toc and ton also increased significantly with an increase in the percentage of silt plus clay in the deposited sediments based upon the above observations a conceptual model is proposed which considers the spatial pattern in riparian zone sedimentation according to riparian morphology and flood magnitude the implications of channel incision for the functioning of the model are also discussed

metamorphic evolution of a very low to low grade metamorphic core complex danubian window in the south carpathians the danubian window characterized by diagenetic to low greenschist facies conditions at a high thermal gradient is evidently of great interest for methodological studies because high metamorphic thermal gradient conditions during low grade metamorphism have received little attention so far the general increase in metamorphic grade from sw to ne in the danubian window is indicated by mineral parageneses studies as well as by illite kubler index ki measurements and organic matter reflectance omr for the first time this study distinguishes between metamorphic conditions related to jurassic ocean floor cretaceous nappe stacking post collisional accommodation and syn kinematic getic detachment metamorphism and cooling after oligocene exhumation the occurrence of the prehnite pumpellyite facies in the severin cosustea units in the southeastern area is the result of cretaceous metamorphism remnants of ocean floor metamorphism prevailed the highest pressure is constrained by the upper stability limit of prehnite to be at around 4 0 kbar the danubian units situated within the diagenetic zone were not below 200 8c due to epidote formation the ki omr and mineral data indicate diagenetic conditions assuming temperatures between 200 and 250 8c pressures between 1 8 and 2 6 kbar were calculated using kinetic and numerical maturity models orogenic collisional cretaceous peak pressure conditions of 4 0 1 0 kbar are found in the danubian nappes not altered by a subsequent syn detachment metamorphic overprint highest temperatures in chloritoid schists and epidote hornblende bearing mylonites have been inferred for samples from the northern border of the danubian window between 300 and 400 8c along a synto post detachment retrograde pressure path post dating the chloritoid formation the occurrence of clinozoisite chlorite quartz suggests temperatures 300 8c in the northwest while the association andalusite quartz and biotite muscovite indicates temperatures between 370 and 400 8c at 3 5 kbar in the northeast it is demonstrated that the slope of the regression lines between ki and omr data gives valuable qualitative information about the relative magnitudes of p and t the slope of the regression line for the danubian window samples indicates normal heat flow conditions during nappe stacking and hyperthermal conditions during the formation of the getic detachment high thermal gradient conditions can easily be explained by partly isothermal decompression during the getic detachment event the elevation of the geotherm being caused by crustal thinning and rapid exhumation of the danubian units probably also a higher heat flux prevailed at the end of the getic detachment at a time when the retrograde chloritoid decomposition reactions took place documenting late stage ht greenschist facies metamorphism from siegesmund s fugenschuh b froitzheim n eds tectonic aspects of the alpine dinaridecarpathian system geological society london special publications 298 281 315 doi 10 1144 sp298 14 0305 8719 08 15 00 the geological society of london 2008 location of the study area and

historical geomorphic analysis 1932 2011 of a by passed river reach in process based restoration perspectives the old rhine downstream of the kembs diversion dam france germany the old rhine downstream of the kembs diversion dam is one of the largest by passed river reaches in the world 50 km it offers a unique opportunity to study the morphological effects of by passing and address physical and ecological restoration approaches in regulated rivers we conduct a space time analysis of channel adjustment over a period of 80 years 1932 to 2011 we examine planform changes from aerial photographs erosional and depositional patterns from vertical profiles sediment sizes within the active channel and the new established floodplain and we date riparian vegetation encroachment results show that the old rhine exhibited rapid response to the completion of the by passing scheme in the 1950s with a 26 narrowing in median active channel width between 1956 and 2008 from vegetation encroachment on dewatered channel margins mostly groyne fields the narrowing was accompanied by overbank fine sediment deposition 1 5 cm y 1 aggradation since 1950 as well as slight bed degradation 0 7 cm y 1 since 1950 we found no downstream propagation of active channel narrowing over time nor propagation of bed degradation the channel was already significantly adjusted prior to the diversion scheme following the nineteenth century river straightening and groyne construction by passing dewatering mainly provided new pioneer habitat for synchronous vegetation establishment and promoted channel stability by decreasing sediment transport owing to peak flow reduction the morphological budget calculated over the past 20 years estimated a downstream output for coarse sediments at 16 000 m3 y 1 with 80 originating from bed degradation and 20 from bank erosion without significant inputs from upstream the present day morphodynamics remain sensitive to changes because of dynamic bed armouring 2 1 this retrospective analysis permits us to discuss management strategies for altered rivers recommended activities are gravel reintroduction with particle sizes finer than the armoured river bed to enhance sediment transport and promote form dynamism under current flood magnitudes this should be coupled with river widening to allow for complex depositional patterns that benefit ecological habitats these actions should not be implemented without prior analysis of local sediment transfer processes based on in situ experiments and modelling

linking danube river activity to alpine ice sheet fluctuations during the last glacial ca 33 17 ka bp insights into the continental signature of heinrich stadials abstract offshore archives retrieved from marine lacustrine environments receiving sediment from large river systems are valuable quaternary continental records in the present study we reconstruct the danube river activity at the end of the last glacial period based on sedimentological mineralogical and geochemical analyses performed on long piston cores from the north west black sea margin our data suggest that the danube river produced hyperpycnal floods throughout the ca 33 17 ka period four main periods of enhanced danube flood frequency each of 1 5 3 kyr duration are recorded at ca 32 5 30 5 ka equivalent to the first part of heinrich stadial hs 3 at ca 29 27 5 ka equivalent to greenland stadial 4 at ca 25 3 23 8 ka equivalent to hs 2 and at ca 22 3 19 ka based on mineralogical and geochemical data we relate these events to enhanced surface melting of the alpine ice sheet ais that covered 50 000 km2 of the danube watershed at the last glacial maximum lgm our results suggest that i the ais growth from the inner alps to its lgm position in the northern alpine foreland started from ca 30 5 ka ended no later than ca 25 3 ka and was interrupted by a melting episode ca 29 27 5 ka ii the ais volume drastically decreased from ca 22 3 to 19 ka as soon as summer insolation energy at the ais latitude increased and iii hss strongly impacted the ais mass balance through enhanced summer surface melt this together with evidence of severely cool winters and the rapid expansion of sea ice in the north atlantic implies strong seasonality in continental europe during stadials

organic petrographic investigations of the kupferschiefer in northern germany abstract results of an organic petrographic study of the kupferschiefer zechstein upper permian in northern germany are presented because vitrinite occurs only sporadically in this black shale the random reflectance r r of a relatively high reflecting vitrinite like variety of bituminite was measured as a maturity parameter and the problems connected with this procedure were investigated the main organic component is bituminite generally with an abundance of more than 90 sporomorphs and algae are relatively scarce inertinite is usually a trace component and vitrinite is present only in some samples taken close to the coast of the zechstein sea migrabitumen also occurs in small amounts in a few samples the range of the bituminite reflectance values is often considerable and depends on rank anisotropy particle size porosity and shearing interpretation of the reflectance values is made difficult by differences of up to 0 4 r r between layers within the kupferschiefer hydrothermal alteration may also be present the difference between the reflectance of the light and normal varieties of bituminite disappears between 0 9 and 1 2 r r bituminite behaves in a way very similarly to vitrinite during coalification their reflectance is identical between 2 and 4 r r below 2 r r the reflectance of bituminite is lower than that of vitrinite linear regression curves valid up to 4 r r were calculated for r max versus r r and for r r versus r max taking certain limitations into consideration bituminite reflectance may be used as a coalification parameter

a new petrogenetic grid for low grade metabasites abstract we have used internally consistent thermodynamic data to present calculated phase equilibria for the system na2o cao mgo al2o3 sio2 h2o ncmash in the range 0 500 c and 0 1 10 kbar involving the phases anorthite glaucophane grossular heulandite jadeite laumontite lawsonite paragonite prehnite pumpellyite stilbite tremolite wairakite zoisite with excess albite clinochlore quartz and pure water average activity terms derived from published mineral chemical data were included for clinochlore glaucophane prehnite pumpellyite tremolite and zoisite the new petrogenetic grid delineates stability fields and parageneses of common index minerals in zeolite prehniteactinolite prehnite pumpellyite pumpellyite actinolite blueschist and greenschist facies metabasites the stability fields of mineral assemblages containing prehnite pumpellyite epidote actinolite albite chlorite quartz were analysed in some detail using activity data calculated from five specific samples for example the prehnite actinolite facies covers a p t field ranging from about 220 to 320 c at pressures below 4 5 kbar the transition from the prehnite actinolite and pumpellyite actinolite to greenschist facies occurs at about 250 300 c at 1 3 kbar and at about 250 350 c at 3 8 kbar p t fields of individual facies overlap considerably due to variations in chemical composition

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

calibration and testing of an empirical chloritoid chlorite mg fe exchange thermometer and thermodynamic data for daphnite a compilation of literature data on the fe mg composition of coexisting chlorite and chloritoid from metapelites metamorphosed at various p t conditions shows that the logarithm of the fe mg partitioning lnkd varies linearly with the inverse of temperature from about 2 4 at 300 c to about 1 3 at 600 c in contrast no trend was observed with pressure and the molar volumes of mg and fe chlorite end members suggest that the pressure dependence of lnkd is not significant therefore the chloritoid chlorite mg fe exchange reaction is a potential thermometer and has been empirically calibrated using the analyses of 112 chloritoid chlorite pairs from 28 different localities temperatures estimated using the chl cld thermometer were checked against independent estimates for 20 samples not involved in the calibration beni mzala window morocco and the results are in fair agreement with independent temperature estimates however the analytical uncertainties and errors are too large to obtain reliable temperature estimates for extremely mg rich or fe rich compositions the chl cld thermometer is unreliable at xmg cld 0 8 at 700 c and xmg cld 0 9 at 300 c using the results of the empirical calibration we calculated new thermodynamic data for daphnite implementing these data it becomes possible to estimate t and p conditions of metamorphism for the invariant chlorite chloritoid quartz aluminosilicate assemblage that is widespread in low grade metapelites these estimates appear to be relevant only in the stability field of kyanite whereas the uncertainties on the calculated pressure conditions are very large in the stability field of kaolinite and pyrophyllite

flow and sediment dynamics in the vegetated secondary channels of an anabranching river the loire river france this study investigates the hydrological and sedimentological mechanisms occurring in the vegetated secondary channels of an anabranching river affected by incision the loire river france during and after flood events that occurred between 2000 and 2003 observations and measurements were performed on a vegetated secondary channel located in the study site of brehemont 790 km downstream the source morphological changes and sediment dynamics were analysed using low elevation airborne photographs topographic and bathymetric surveys and scour chains the hydraulic behaviour of the channel was also analysed by measurements performed on flow velocity and direction during different flood stages in order to quantify the influence of woody vegetation on flow resistance the roughness of bands of trees was determined from measurements performed on the field the impact of the disruption of armour layers on bedload pulses the variation of sedimentary processes during a single flood event and the fixation of bedforms by vegetation are all identified as key processes influencing the behaviour of the study channel topographic surveys demonstrate that sediment dynamics is substantial in the upstream part of the channel and that sediment budgets are different according to the temporal scale considered moreover an asymmetrical behaviour of the secondary channel is demonstrated reduced quantities of sediment deposited and preserved in the vegetated zones contrast with material by passing observed in the third order channels flow velocity and direction measurements indicate that these parameters vary according to the water level and to the morphological units of the channel pools riffles vegetated areas during low flows scouring and export of particles from the secondary channel are a consequence of reduced sediment supply from the main channel of the loire river for these water levels sedimentation occurs in pools where velocity and turbulence decrease whereas third order channels are subjected to erosion during high discharges large quantities of sediment available in the main channel feed the temporary stores formed by riffles and bars in the secondary channel the vegetated area located in the downstream part of the secondary channel deflects current trickles at low discharges and decreases flow velocity during high water levels the sedimentary accretion observed in this area exerts a feedback on flow and sedimentary processes d 2005 elsevier b v all rights reserved

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

low temperature low pressure metamorphism of mn rich rocks in the lienne syncline venn stavelot massif belgian ardennes and the role of carpholite low grade mn rich metamorphic rocks of the lienne syncline western part of the venn stavelot massif belgian ardennes have been re examined to evaluate the petrological significance of carpholite proper mn2 al2 si206j 0h 4 metamorphic p t conditions of these rocks are estimated to be 300 q 1 2 kbar which is in accordance with the exclusive occurrence of carpholite in low p rocks such as hydrothermal environments elsewhere carpholite of the lienne syncline exclusively occurs in quartz rich segregations its composition is close to end member thermodynamic calculations confirm that carpholite is a stable phase at low pressure low temperature conditions in contrast to ferro and magnesiocarpholite which are high pressure minerals no information is available on the high p behaviour of carpholite the occurrence of carpholite is partly closely associated with spessartine bearing country rocks or carpholite is altered to assemblages with spessartine sudoite chlorite muscovite and paragonite spessartine in these rocks contains minor amounts of hydrogarnet component h 4 si h 4 0 03 0 06 the presence of carpholite spessartine assemblages in these low p rocks is in contrast to high pressure metamorphic rocks from other areas where parageneses such as fem magnesiocarpholite chloritoid or magnesiocarpholitechlorite kyanite occur the appearance of carpholite ga rnet assemblages in low p mn rich rocks can be explained by contrasting phase relations because of a high mn mg partition coefficient between the minerals under consideration in rhodochrosite bearing veins in the lienne syncline nearly complete replacement of carpholite by spessartine and chlorite is due to the continuous reaction carpholite rhodochrosite quartz spessartine chlorite h2o co 2 which defines a very low xco in the temperature range under consideration it is suggested that spessartine possibly containing some hydrogarnet component during prograde metamorphism at low pressure becomes stable at a temperature of 300 c

syn and post collisional heat flow in the cenozoic eastern alps the heat flow evolution of a continental collisional zone is exemplified by the eastern alps heat flow maps for the syn collision oligocene syn extrusion early middle miocene and post extrusion late miocene recent stages are presented and are discussed in relation to the orogenic evolution continental collision during paleogene time was characterized by extremely low heat flow 150 mw m2 a few hundred kilometers south of it the former was a result of crustal thickening and of thermal blanketing due to rapid sedimentation and nappe stacking the latter was caused by slab break off and magmatic activity the early middle miocene syn extrusion stage was characterized by rapid exhumation of metamorphic core complexes tauern and rechnitz windows and by magmatic activity styrian basin both mechanisms caused extremely high heat flow 200 mw m2 in contrast the orogenetic front remained cold thereafter magmatic activity ended and uplift rates decreased thus late miocene heat flow is characterized by low to moderately high values heat flow values 75 mw m2 were restricted to the transition zone of the pannonian basin characterized by thinned crust and to the tauern window area recent temperature data indicate a subtle post miocene increase in heat flow

patterns of floodplain sediment deposition along the regulated lower roanoke river north carolina annual decadal centennial scales abstract the lower roanoke river on the coastal plain of north carolina is not embayed and maintains a floodplain that is among the largest on the mid atlantic coast this floodplain has been impacted by substantial aggradation in response to upstream colonial and post colonial agriculture between the mid eighteenth and mid nineteenth centuries additionally since the mid twentieth century stream flow has been regulated by a series of high dams we used artificial markers clay pads tree ring dendrogeomorphic techniques and pollen analyses to document sedimentation rates amounts over short intermediate and long term temporal scales respectively these analyses occurred along 58 transects at 378 stations throughout the lower river floodplain from near the fall line to the albemarle sound present sediment deposition rates ranged from 0 5 to 3 4 mm y and 0 3 to 5 9 mm y from clay pad and dendrogeomorphic analyses respectively deposition rates systematically increased from upstream high banks and floodplain to downstream low banks reaches except the lowest reaches conversely legacy sediment deposition a d 1725 to 1850 ranged from 5 to about 40 mm y downstream to upstream respectively and is apparently responsible for high banks upstream and large wide levees along some of the middle stream reaches dam operations have selectively reduced levee deposition while facilitating continued backswamp deposition a gis based model predicts 453 000 mg of sediment is trapped annually on the floodplain and that little watershed derived sediment reaches the albemarle sound nearly all sediment in transport and deposited is derived from the channel bed and banks legacy deposits sources and regulated discharges affect most aspects of present fluvial sedimentation dynamics the lower river reflects complex relaxation conditions following both major human alterations yet continues to provide the ecosystem service of sediment trapping