frasnian famennian biotic crisis undervalued tectonic control the prime cause of the late devonian kellwasser crisis culminating in a mass extinction event near the frasnian famennian f f boundary remains conjectural nevertheless rapid sea level fluctuations of uncertain origin during tectono eustatic highstand paired with repeated oceanic anoxia and climatic changes are usually thought at present to be one of the main immediate triggers the cathles hallam model of stress induced changes in plate density accompanying rapid rift formation furnishes an alternative for understanding the enigmatic sudden eustatic variations in the non glacial time late devonian tectonic extension causing rifting and volcanicity appears to be strongly marked in several regions of eurasia particularly in kazakhstan and eastern laurussia all larger devonian continents were more or less tectonically affected a subtle record of this tectonic rearrangement is implied even for distant and apparently quiet carbonate platforms in local extensional block faulting and tilting hydrothermal mineralisation geochemical anomalies and localized blooms of siliceous biota interpreting the late frasnian regressive transgressive pattern in terms of the cathles hallam tectono eustatic model two major rifting events are hypothesized one at about the beginning of the rhenana zone and a second principal pulse in the late linguiformis zone that encompassed the f f transition developing the veimarn milanovsky scenario of the global extensional pulse it is assumed that the key endogenous factors were related to episodic super plume activity the tectonically triggered changes climaxed in thermal and nutrient pulses and induced the stepdown ecosystem destabilization observed in the f f bio crisis minor cometary strike s might have eventually participated in this prolonged multicausal environmental stress mainly due to additional thermal shocks but perhaps effective on a regional scale only

alpine orogenic p t t deformation history of the catena costiera area and surrounding regions calabrian arc southern italy the nappe edifice of north calabria revised with insights on the tyrrhenian apennine system formation 1 the nappe structured belt of calabria constitutes the eastward termination of the southern branch of the alpine mediterranean belt that delimits the northern edge of the africa plate contrasting hypotheses for the origin and tectonic significance of the north calabrian nappe edifice have been proposed and kinematic data from north calabria have been used to support different interpretations of the alps apennines linkage and the polarity of the tethyan subduction in the apennine region we reconstruct the architecture of the north calabria nappe edifice through a multidisciplinary approach which integrates structural investigations with metamorphic thermobarometry and 40ar 39ar geochronology results from this study indicate that north calabria consists of a tertiary nappe stack resulting from superimposed top to the west extensional shearing late oligocene to middle miocene in age onto a previously structured top to the east compressional belt eocene to oligocene in age this study also documents that the top to the west extensional tectonics was achieved by means of regionally sized extensional detachment fault systems stretching apart and translating as allochthonous fragments the previously accreted units thinning operated by top to the west extensional detachment tectonics also resulted in the direct juxtaposition of non alpine or slightly alpine metamorphosed units upper plate complex onto the previously exhumed deep seated portions of the orogenic wedge metamorphosed under blueschist facies metamorphic conditions lower plate complex these findings support a new tectonic scenario for the orogenic history of north calabria which may be adequately framed within the tertiary apennine tyrrhenian system evolution

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

floating lids on large mid ocean spreading center magma chambers a discussion rosencrantz and nelson 1982 have concisely presented arguments in favor of the hypothesis that lids overlying ocean ridge magma chambers are supported by flotation of the lid on magma of equal or higher density i concur that given the highly fractured nature of oceanic crust the lids to oceanic magma chambers can only be supported by flotation regardless of the width of the magma chamber in their quantitative analysis rosencrantz and nelson implicitly made two assumptions on the shape of the magma chamber and therefore on the nature and density of the lid and on the nature and therefore the density of the contents of the magma chamber it is important to realize that in a situation in which either one of these assumptions is thought not to hold the acceptance of the flotation hypothesis places severe constraints on other properties of the situation the problem is raised in the light of the archean ocean ridge model of sleep and windley 1982 fig 3 in the same issue of journal of geology but is of general relevance given our ignorance concerning magma chambers there have been several suggestions for the shape of ocean ridge magma chambers in situations where permanent magma chambers are thought to exist sleep 1975 rosendahl 1976 and dewey and kidd 1977 envisaged a magma chamber narrowing upwards with a triangular cross section and a relatively flat base hereafter this shape is referred to as an inverted funnel from their work on the samail ophiolite in oman pallis

microbially mediated carbonates in the holocene deposits from sarlieve a small ancient lake of the french massif central testify to the evolution of a restricted environment both the mineralogy and facies of lacustrine bio induced carbonates are controlled largely by hydrological factors that are highly dependent upon climatic influence as such they are useful tools in characterizing ancient lake environments in this way the study of the sedimentary record from the small ancient sarlieve lake limagne massif central france aims to reconstruct the hydrological evolution during the holocene using petrographical mineralogical and geochemical analyses the fine grained marls mainly calcitic display numerous layers rich in pristine ca dolomite with small amounts of aragonite which are clearly autochthonous as these minerals are rather unusual in the temperate climatic context of western europe the question arises about their forming conditions and therefore that of the lacustrine environment ca dolomite prevails at the base of the sequence as a massive dolomicrite layer and in the middle part it builds up most of the numerous laminae closely associated with organic matter scanning electron microscope observations reveal the abundance of tiny crystals tens to hundreds of nanometres mainly organized as microspheres looking like cocci or bacilli such a facies is interpreted as resulting from the fossilization of benthic microbial communities by dolomite precipitation following organic matter consumption and extracellular polymeric substance degradation these microbial dolomites were precipitated in a saline environment as a consequence of excess evaporation from the system as is also suggested by their positive 18o values the facies sequence expresses the following evolution i saline pan i e endorheic stage with a perennial lowstand in lake level boreal to early atlantic periods ii large fluctuations in lake level with sporadic freshening of the system atlantic iii open lake stage sub boreal and iv anthropogenic drainage sub atlantic

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

limits to quantifying climate driven changes in denudation rates with cosmogenic radionuclides abstract the hypothesis that climate change significantly modifies the denudation history of an orogen can be tested by reconstructing catchment wide denudation histories cosmogenic radionuclides measured in sediment deposits of known age e g a sequence of fluvial terraces offer one approach for quantifying catchment wide paleo denudation rates we present a numerical model and two case studies that evaluate the utility of this technique for reconstructing different denudation histories the concentration of cosmogenic beryllium 10 10 be is calculated for a sequence of sediments produced from climate driven variations in the mean denudation rate of a drainage basin at sea level and high latitude the model accounts for the nucleonic and muonic production and decay of 10 be as sediment is eroded and stored in deposits of different ages two scenarios for different climate driven denudation histories are considered 1 a sinusoidal variation in the input denudation rate with free parameters of periodicity 23 41 100 kyr amplitude 0 1 0 5 1 0 and mean denudation rate 0 01 0 1 1 0 mm yr 1 2 a climate driven denudation history based on oscillations of a global benthic foraminiferal oxygen isotope 18 o record over the last 2 myr results from both scenarios suggest cosmogenic radionuclides measured in a system with high denudation rates 0 5 mm yr 1 longer periodicity 100 kyr and low amplitude have the highest potential for reconstructing climate driven paleo denudation rates unfortunately the high denudation rates preferred in the theoretical consideration are not suitable for paleo denudation rate determination due to overprinting of nuclides accumulated during denudation by post depositional decay and irradiation hence a compromise between the capability to determine changes in paleo denudation rates and the determination of true denudation rates has to be accepted application of the model to previous data sets from northwest europe and southwest north america produce a good agreement but highlight the need for future work to consider how geomorphic processes e g landsliding respond to climate change and influence catchment wide denudation rates in addition other climate proxies than the benthic foraminiferal 18 o record should be used for specific sample locations

formation of uppermost oceanic crust the uppermost portion of oceanic crust extrusive basalts underlain and fed by diabasic dikes represents the chilled roof zone or lid to mid oceanic spreading center magma chambers this rigid lid forms and evolves through a steady state process of flexure subsidence and internal rotation all occurring within a couple of kilometers of the spreading axis the lid accommodates lateral spreading with dikes emplaced along a unique axis dikes tap underlying magma to feed overlying flows basalts accumulating along the axis of the lid load the lid which responds by flexing down and away from the intrusive axis this subsidence affects lid structure in the following ways emplaced dikes are tilted away from and basalt flows are tilted toward the intrusive axis lid subsidence and section rotation extend the base of the lid more rapidly at the axis than elsewhere consequently dikes preferentially intrude at the existing axis to maintain existing axis shape and relative position through continued spreading loading and flexure of the lid plus faster accretion at the base of the lid as a result of lid rotation cause the lid to be uplifted distal to the axis this creates flanking marginal highs and generates extension structures fissuring and faulting flanking and paralleling the loading extrusive axis the crustal structure and geometry produced by this process is compatible with structure and topography observed at present day mid oceanic spreading centers and with structure observed in ophiolites particularly the bay of islands ophiolite

late quaternary palaeoclimate in the savannas of south america the paper reviews late quaternary palynological evidence from eight sites in the savannas of northern south america the sites reviewed are lake valencia 10 n carajas 6 s aguas emendadas 15 s crominia 17 s salitre 19 s lagoa de serra negra 18 s lagoa santa 20 s and lagoa dos olhos 20 s four of the sites show evidence for a climate more humid than at present from ca 36 ka bp to ca 22 18 ka bp maximum dryness was reached at 14 ka to 10 5 ka bp at lake valencia there was an increase in moisture from 8 8 ka bp at lake valencia and from 7 ka bp in central brazil the presence of charcoal indicates human impact from ca 8 6 ka bp 1997 john wiley sons ltd

the development and application of a database of radiocarbon dated holocene fluvial deposits in great britain abstract this paper reports on the development of a british database of 14c dated holocene fluvial units over the last 15 years since its inception in 1989 the database has undergone substantial expansion refinement and improvement together with considerable methodological development so that today it serves as a powerful research tool for investigating the spatial and temporal dynamics of holocene river development and flooding in great britain the improved analytical method is here applied to the currently existing database by examining datasets of 14c dated fluvial units from river basins that lie within and beyond the limits of late devensian glaciation this analysis indicates how the contrasted conditions in these two types of river environment have to an extent led to divergent records of flooding in response to holocene climate and land use change however even in the contrasting sedimentary records of upland glaciated and lowland unglaciated river basins six corresponding episodes of increased flood frequency are identified at c 5730 c 3540 c 2730 c 2280 c 660 and c 570 cal bp these represent widespread common responses from british river systems to large scale changes in climate the method of database construction and analysis outlined and demonstrated in this paper could be readily adopted in other parts of the world to improve our understanding of holocene river behaviour at the continental and global scale

palaeozoic sequences and evolution of the calabrian peloritan arc southern italy three palaeozoic sequences belonging to three different basins crop out in the calabrian peloritan arc their age covers the time span from middle cambrian to early carboniferous the sequences comprise terrigenous volcanic and carbonate rocks and show low grade metamorphism the basement is of pre middle cambrian age crops out in the calabrian peloritan arc and was metamorphosed prior to the opening to the palaeozoic basins the palaeozoic basins existed no later than the middle carboniferous with inferred maximum crustal extension in the cambro ordovician by devonian time the tectonic regime was compressional overall with middle devonian island arc type volcanic activity that continued until the closure of the basins approximately 330 myr the palaeozoic sequences experienced low pressure greenschist facies metamorphism and continuing subduction controlled the variscan tectonogenesis with 280 myr island arc type intrusive magmas subduction ceased and late stage 280 270 myr granitic magmas were emplaced during continental collision the crustal sector carrying the palaeozoic basins is interpreted as comprising fragments of an active continental margin one of the several microplates located at the southern margin of the euro asia continent which faced a large at least 1500 km in width ocean basin

the augen gneisses of the peloritani mountains ne sicily granitoid magma production during rapid evolution of the northern gondwana margin at the end of the precambrian abstract the medium to high grade polymetamorphic basement rocks of the peloritani mountains northern sicily include large volumes of augen gneiss of controversial age and origin by means of a geochemical and shrimp zircon study of representative samples the emplacement age of the original granitoid protoliths of the augen gneisses and the most likely processes and sources involved in that granitoid magmatism have been determined u pb dating of three samples from widely spaced localities in the peloritani mountains yielded igneous protolith ages of 565 5 545 4 and 545 4 ma respectively these late ediacaran early cambrian ages are much older than was previously assumed on geological grounds and are typical of the peri gondwanan terranes involved in the geodynamic evolution of the northern gondwana margin at the end of the avalonian cadomian orogeny major and trace element compositions and sr nd isotopic data in combination with zircon inheritance age patterns suggest that the granitoid protoliths of the sicilian and coeval calabrian augen gneisses were generated by different degrees of mixing between sediment and mantle derived magmas the magmas forming the ca 545 ma inheritance rich granitoids appear to have had a significant contribution from partial melting of paragneiss that is the dominant rock type in the medium to high grade peloritanian basement the closeness of the inferred deposition age of the greywacke protoliths of the paragneisses with the intrusion age of the granitoids indicates rapid latest precambrian crustal recycling involving erosion burial metamorphism to partial melting conditions and extensive granitoid magmatism in less than ca 10 ma

petrogenesis of contrasting hercynian granitoids from the calabrian arc southern italy abstract the granitoids of the southern calabrian arc have been investigated for whole rock and phase chemistry zircon typology ree sr and nd isotopes two distinct granitoid associations which are related in time and partly in space are present a calc alkaline one and a peraluminous one the prevailing calc alkaline association is compositionally expanded sio2 48 70 and biotite dominated with tonalites and granodiorites as predominant rock types the peraluminous association is compositionally restricted sio2 67 76 and contains two mica al silicates distinct peraluminous typologies occur also as core facies within the calc alkaline types all granitoids are ilmenite bearing the cittanova cn villa s giovanni vsg and capo rasocolmo cr peraluminous granites display zircon typology ree patterns srt 51 to 113 and ndt values 8 5 to 4 6 at 290 ma suggesting a dominantly quartzofeldspathic metasedimentary source in more detail the cn types and the cr vsg types require heterogeneous and different sources the calc alkaline granitoids display very variable ree patterns cen 25 227 and ybn 3 5 18 5 in the tonalites granodiorites and variable age corrected ndt values 8 5 to 0 25 whereas sr values vary little 82 to 93 thus in terms of ndt srt covariation the data points define a vertical array which is inconsistent with a model involving crustal contamination by mantle derivatives a more viable mechanism seems to be the melting of hydrous and heterogeneous mafic lower crust and or basic underplate producing distinct magma batches evolving independently crustal contamination mingling and fractionation processes may all have contributed to the observed geochemical variations within the granitoids the peraluminous granodiorites occurring within the serre and capo vaticano multipulse calc alkaline plutons exhibit isotopic ratios ndt 6 11 to 0 33 and srt 93 to 97 which are similar to those of the calc alkaline host rocks suggesting a possible genetic link geologic and geochemical data indicate a continental collision setting for this plutonic activity the magmas were produced during late thickening to exhumation phases following collision and moderate crustal overthickening and were emplaced subsequently during a short time span a mantle contribution should have favoured melting which affected various sectors of the continental crust

establishing sediment budgets for two small lowland agricultural catchments in the uk sediment budgets have been established for two small 4 km2 lowland agricultural catchments by using 137cs measurements sediment source fingerprinting and more traditional monitoring techniques to quantify the individual components of the budget the gross and net erosion rates for the fields on the catchment slopes were estimated using 137cs measurements within selected fields which encompassed a representative range of slope angles slope lengths and land use these estimates were extrapolated over the entire catchment using a simple topographically driven soil erosion model terrain based gis tbgis superimposed on a dem to derive catchment average gross and net erosion rates suspended sediment yields were measured at the catchment outlets and sediment source fingerprinting techniques were used to establish the relative contributions from the catchment surface subsurface tile drains and eroding channel banks to the sediment yields in channel and wetland storage were quantified using both direct measurements and 137cs measurements the sediment budgets established for the catchments highlighted the importance of subsurface tile drains as a pathway for sediment transfer accounting for ca 60 and 30 of the sediment output from the two catchments erosion from channel banks contributed ca 10 and 6 of the sediment output from the two catchments although the suspended sediment yields from these catchments were considered high by uk standards ca 90 t km 2 year 1 the sediment delivery ratios ranged between 14 and 27 indicating that a major proportion of the mobilised sediment was stored within the catchments in field and field to channel storage were shown to be of similar magnitude but storage of sediment in the channel system and associated wetlands was relatively small representing 5 of the annual suspended sediment yield

from sedimentary records to sediment budgets multiple approaches to catchment sediment flux this paper reviews the traditional approach to sediment budget studies in geomorphology new approaches and more specifically the potential impact of new methodological advances each component of the budget is discussed including the spatial and volumetric estimations of erosion deposition and storage and the precision and accuracy of flux rate estimation examples are used from recent work in germany the netherlands and the uk and include the pedogenic approach to erosion estimation remote sensing lidar geophysics and sediment based dating techniques for flux rate estimation the precision and accuracy of catchment sediment flux estimates based upon sediment storage is not only dependant upon volumetric accuracy but also on the precision and accuracy of sediment dating in this area there has been a revolution with direct sediment dating techniques tl osl esr freeing budget studies from the constraints and biases of radiocarbon of particular importance is the use of cosmogenic nuclides for dating but which can also be used to derive long term erosion rates but only using a steady state assumption finally a tentative initial application of the sediment budget approach to pleistocene terrace staircase in unglaciated basins is discussed it is argued that only now do we have the techniques available to be able to produce accurate sediment budget estimations at spatial scales greater than that of zero order basins and over time periods greater than that covered by direct observations

overlapping rift zones at the 5 5 s offset of the east pacific rise a seabeam and magnetometer survey of the pacific nazca plate boundary around 5 5 s mapped a nontransform offset whose geology and kinematics seem typical of a whole class of structures formed where fast spreading rises are laterally offset for distances less than the width of a subaxial magma chamber though the spreading center is abruptly displaced by 15 km right laterally there is no trace of strike slip faulting instead the ends of two 100 km long axial volcanic ridges veer 15 toward each other and overlap for more than 20 km in this overlapping region between 5 22 s and 5 32 s accretion of the upper oceanic crust by dike injection and eruption is partitioned between two adjacent and parallel rift zones with oblique and one sided spreading a continuous but dog legged magma chamber is inferred to underlie both rift zones and an intervening 9 km wide volcano studded basin a strong magnetic signature from the crust which accreted around this oblique chamber identifies the trace of the offset on the adjacent rise flank in the past 0 5 106 years the southern axial ridge has propagated north at 40 mm yr 55 of the spreading half rate

time space relationships among structural and metamorphic aureoles related to granite emplacement a case study from the serre massif southern italy tectonic and thermal perturbations related to emplacement of granodiorite in the upper continental crust have been investigated in the late hercynian basement exposed in southern calabria italy here the structural aureole is marked by the presence of a major rim fold adjacent to the intrusive contact for a length of at least 20 km geometrical analysis of the structural aureole and related foliations lineations and crenulations reveals that the perturbed zone is at least 3000 m wide and characterized by an open synform trending nearly parallel to the intrusive contact this pattern is compatible with a laccolith like mode of magma emplacement related to the accretion of the pluton that shouldered weak phyllitic and slaty wall rocks the metamorphic aureole about 1800 m wide is characterized by biotite cordierite and andalusite that appear sequentially in spotted schists and hornfelses approaching the intrusive contact the peak assemblage equilibrated between 535 and 590 c at pressures between 175 and 200 mpa confirmed by al in hornblende barometry on granodiorite microstructural analysis allowed the inference of a time lag between the thermal and tectonic perturbations with the aid of thermal modelling it was possible to quantify the time required to reach the peak temperature at a distance from the intrusive contact where cordierite spots and andalusite porphyroblasts clearly overprint crenulations this estimate represents the time limit to accomplish deformation in the inner portion of the aureole and thus indicates a minimum strain rate of 4 10 14 s 1 within the country rocks during granodiorite intrusion

detrital zircon and micropalaeontological ages as new constraints for the lowermost tectonic unit talea ori unit of crete greece the talea ori unit is the lowermost known tectonic unit of crete and the most external part of the hellenides its stratigraphy ranges from late carboniferous to oligocene and outcrops of the lower part are only known in the talea ori mountains central crete in this area a black sandstone at the base of the galinos beds thought to be the oldest formation contains zircons which were dated using the single grain evaporation method the majority of these grains yielded late carboniferous ages variscan while a small group yielded early proterozoic ages the age distribution of these zircons suggests that at the carboniferous permian boundary not much of the older north gondwanan basement was exposed and that a river system carried detrital material from the variscan belt towards the forming neotethyan rift additionally higher up in the stratigraphy benthic foraminifers miliolids were found in clasts from a conglomerate which was so far thought to be of early triassic age epting m kudrass h r leppig u schaffer a 1972 geologie der talea ori kreta n jb geol palaont abh 141 259 285 these miliolids belong to the species hoyenella inconstans michalik j jendrejakova o borza k 1979 some new foraminifera species of the fatra formation uppermost triassic in the west carpathians geol carpath 30 1 61 91 thus attributing a late triassic carnian norian maximal age to this conglomerate the carbonate platform from which the miliolids bearing clasts come is not known the presence to the north of a continuous hemipelagic record from the carboniferous to the triassic phyllite quartzite and tripali units attributed to the palaeotethys realm allows the talea ori unit and its lateral equivalents the ionian zone to be assigned to the westward continuation of the cimmerian block and therefore to the northern margin of the east mediterranean neotethys ocean

a buried volcano in the calabrian arc italy revealed by high resolution aeromagnetic data 1 aeromagnetic data collected between the aeolian volcanoes southern tyrrhenian sea and the calabrian arc italy highlight a wnw ese elongated positive magnetic anomaly centered on the capo vaticano morphological ridge tyrrhenian coast of calabria characterized by an apical subcircular flat surface results of forward and inverse modeling of the magnetic data show a 20 km long and 3 5 km wide magnetized body that extends from sea floor to about 3 km below sea level the magnetic properties of this body are consistent with those of the medium to highly evolved volcanic rocks of the aeolian arc i e dacites and rhyolites in the calabria mainland widespread dacitic to rhyolitic pumices with calc alkaline affinity of pleistocene age 1 0 7 ma are exposed the tephra falls are related to explosive activity and show a decreasing thickness from the capo vaticano area southeastward the presence of lithics indicates a provenance from a source located not far from capo vaticano the combined interpretation of the magnetic and available geological data reveal that 1 the capo vaticano wnw ese elongated positive magnetic anomaly is due to the occurrence of a wnw ese elongated sill 2 such a sill represents the remnant of the plumbing system of a pleistocene volcano that erupted explosively producing the pumice tephra exposed in calabria and 3 the volcanism is consistent with the aeolian products in terms of age magnetic signature and geochemical affinity of the erupted products the results indicate that such volcanism developed along seismically active faults transversal to the general trend of the aeolian arc and calabria block in an area where uplift is maximized 4 mm yr such uplift could also be responsible for fragmentation of the upper crust and formation of transversal faults along which seismic activity and volcanism occur

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

mid ordovician u pb ages of porphyroids in the peloritan mountains ne sicily palaeogeographical implications for the evolution of the alboran microplate petrographic geochemical and geochronological work on a metavolcanic suite interbedded in a metapelitic sequence of the palaeozoic basement in the peloritan mountains sicily is used to contribute to a better understanding of the pre variscan geodynamic evolution of the former alboran microplate major and trace element data show that the volcanic suite consists of two main groups an intermediate unit of andesites and dacites with volcanic arc affinity and a felsic porphyroid unit of rhyolites with peraluminous composition isotope dilution thermal ionization mass spectrometry u pb analyses for single and multigrain zircon fractions from four samples of the felsic porphyroids yield results that are tightly clustered on or near concordia giving caradoc ages in the range of 456 452 ma the consistent morphological characteristics and oscillatory zoning of the zircons indicate single stage magmatic crystallization xenocrystic zircon grains with ages of 1150 and 2015 ma indicate that these rocks were developed upon a cratonic basement with grenvillian and transamazonian components hence supporting a peri gondwanan origin from the combined evidence we conclude that this portion of the alboran microplate formed as a mid ordovician volcanic arc in a sector of the peri gondwanan terranes that was affected by a tectonothermal caradoc event

floating lids on large mid ocean spreading center magma chambers we suggest that the volcanic lids or carapaces lava and sheeted dikes overlying mid oceanic magma chambers float on underlying magma estimated porosites of mor volcanics and dikes are large enough to reduce the overall density of the lid to values less than the density of underlying magma floating these lids eliminates the difficulty of mechanically maintaining relatively thin brittle lids over large magma chambers at mid oceanic spreading centers

a combined radiometric and mineral magnetic approach to recent geochronology in lakes affected by catchment disturbance and sediment redistribution abstract as a result of empirical testing of 210 pb dating models in a wide variety of lakes we conclude that there are many situations where despite major changes in sedimentation rates as a result of lake or catchment disturbance the crs constant flux model provides a sound basis for establishing recent chronology factors which may complicate or vitiate the assumptions of the model include short water residence time bioturbation for which we propose a modified dating model discontinuous or disturbed sedimentation sediment resuspension and shifts in sediment source in the case of the last three processes we illustrate ways in which the problems can be identified and evaluated using mineral magnetic measurements we propose an evaluative approach to 210 pb dating projects with emphasis on independent dating evidence on tests of internal consistency and on the use of data from several correlatable cores

an approximation of the sediment budget of the lower mississippi river prior to major human modification a sediment budget is constructed for the lower mississippi river prior to the introduction of most human modifications components of the budget are derived from historical data including mississippi river commission hydrographic survey maps for the period from 1877 to 1924 a quantitative estimate of major sediment sources sinks and storage locations in the lower mississippi valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short term channel storage than in longer term overbank storage the budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated the magnitude and variability of these sediment budget components are discussed the results of the study suggest that prior to modifications the river was aggrading over much of its length

geomorphic and pedogenic evolution in coastal sediments central california abstract studies of soil chronosequences on marine terraces facilitate the use of terraces for tectonic and paleoclimatic interpretation however many areas on the california coast have received substantial eolian deposits after pedogenesis began so do not qualify as chronosequences these areas are worthy of study because they are widespread coastal landscape features and they enable us to interpret pedogenic and geomorphic processes in sandy regolith the objective of this study was to use soil and deep regolith morphology and chemistry to interpret pedogenic and geomorphic evolution on a sequence of four marine terraces san luis obispo county california the terraces are numbered 1 2 3 and 4 from oldest to youngest the eroded terrace platforms have been tentatively dated at 560 420 or 480 320 and 120 ka respectively the sand deposits on each platform may be considerably younger the amount of land surface dissection and the depth of stream incision increase with increasing terrace age and elevation morphological features suggest that the soils xeropsamments on terrace 4 haploxerolls on terrace 3 on the two youngest terraces are well drained and their morphological development is typical of soils in eolian sand deposits morphological and chemical features of the basal regolith contrast with those of the soils clay fe oxides and opaline silica were deposited by groundwater flow above the bedrock platform above the shoreline angle where the deep regolith receives additional groundwater from higher terraces redoximorphic features have developed gray mottles are larger more common and more distinct in the basal regolith of progressively older terraces erosion has removed much of the overburden on terraces 2 and 1 and soils epiaqualfs on terrace 2 epiaqualfs on terrace 1 have developed in what was once deep regolith the landscape soils and deep regolith show an evolution of processes whereby the path and direction of water movement through the regolith is controlled first by terrace morphology and stratigraphy then by the development of pedogenic features in the soil and deep regolith and by terrace dissection

use of fallout pb 210 measurements to investigate longer term rates and patterns of overbank sediment deposition on the floodplains of lowland rivers the potential for using fallout unsupported pb 210 210pb measurements to estimate rates of overbank sediment deposition on the floodplains of lowland rivers is explored a model which distinguishes the contribution from direct atmospheric fallout and the catchment derived input associated with the deposition of suspended sediment has been developed to interpret the fallout pb 210 inventories at floodplain sampling sites and to estimate average sediment accumulation rates over the past 100 years the approach has been successfully used to estimate rates of overbank sedimentation on the floodplains of the rivers culm and exe in devon u k a detailed investigation of the pattern of longer term sedimentation rates within a small reach of the floodplain of the river culm indicated a range of deposition rates between 0 07 and 0 59 g cm 2 a 1 which was in close agreement with estimates of current sedimentation rates obtained using sedimentation traps

miocene thrusting in the eastern sila massif implication for the evolution of the calabria peloritani orogenic wedge southern italy abstract alpine orogens in the central mediterranean region have revealed the concomitance of crustal extension in back arc domain and crustal shortening in frontal domain quantitative data of deformation in the frontal orogenic wedges are necessary to understand how the shortening extension pair evolves in terms of structures orogenic transport timing and exhumation rate this paper deals with kinematics and ages of the frontal thrust systems of the calabria peloritani arc italy exposed in the eastern sila massif we first present structural fieldwork onshore and offshore well log data and new apatite fission track aft thermochronology then we describe the structural architecture of the studied area as an ene verging stacking of thrust sheets involving basement units and syn orogenic sediments the aft study documents that thrust sheets entered the partial annealing zone from 18 ma to 13 ma this early middle miocene thrusting phase was coeval with exhumation of high pressure low temperature metamorphic rocks in the hinterland of the orogen coastal chain area mainly driven by top to the w extensional tectonics opposite kinematic shear senses contractional top to the e and extensional top to the w and different exhumation rates slow in the frontal more rapid in the hinterland are framed in a tectonic scenario of a critically tapered orogenic wedge during the eastward retreating of the apennine slab

sediment characteristics and sedimentations rates of a small river in western central brazil the purpose of this study is to characterise the alluvial sediments and to quantify sedimentation rates of a small river system the ribeirao do torto in central western brazil the study area provides an excellent opportunity to examine the effect of land use on sedimentation rates in the region for the first time and thus contributes to understanding sediment transport processes into water reservoirs silting 137cs 210pb and 14c dating techniques were used to estimate natural sedimentation rates and those associated with land use development complementary use of physical and chemical analyses of the sediments and contained anthropogenic materials revealed that sedimentation dynamics had varied over time natural sedimentation rates are more than ten times lower than in the period since the mid 1950s for the alluvial system of the ribeirao do torto the results indicated that human impact had accelerated the sedimentation dynamics which resulted in higher sediment quantities and sand content and changes of sediment sources the variation of sedimentation rates may reflect also several other factors e g natural fluctuation in flow energy or geomorphologic changes within the alluvial system however the multiple dating techniques and supplementary interpretation employed in this study show the potential use of radionuclides and soil sediment parameters to identify changes in sedimentation rate stream energy and sediment characteristics in floodplains

late holocene environmental change in the howgill fells northwest england abstract new data from chapel beck in the southwest howgill fells combined with existing data support the identification of three phases of extensive hillslope gullying after 2200 between 1250 700 and after 500 cal bp examination of cumulative probability density function cpdf plots of the distribution of calibrated radiocarbon dates confirms the identification of these phases there are differences in the spatial distribution of geomorphic activity between these phases with the c 2200 1800 cal bp episode limited to the western howgill fells in comparison the 1250 700 and post 500 cal bp episodes are more widespread cross region phenomena and affected the more remote central fells pollen and geochemical data reveal several phases of increased human activity in these uplands with small scale temporary clearances during the late bronze age early iron age and more substantial clearances during the late iron age and romano british times 2300 1500 cal bp and these were followed by woodland expansion and decline in human activity during both the mid to late iron age and the period after the roman withdrawal from britain after 1500 cal bp the final substantial woodland clearances occurred from c 1100 900 cal bp after which there has been little woodland recovery a range of pollen sites across the howgill fells indicate that there is spatial variability in the level of human activity and impact iron age romano british woodland clearances appear to have affected the west of the region more than the remote central valleys whereas the later 1100 900 cal bp woodland reduction affected the entire region this pattern is similar to that identified from the geomorphology and demonstrates the importance of pollen sites that record local palaeo vegetation information and the significance of using a series of sites to explore intra regional variability in the vegetation history we suggest that human activity is a critical factor in mediating the late holocene geomorphic record but climate and particularly individual storms are the trigger mechanism responsible for erosion and incision on hillslopes and within the wider fluvial system palaeoclimate data humification and plant macrofossil from peat deposits at archer moss identify shifts to wetter conditions c 3100 2700 2400 1700 1300 1100 and after 650 cal bp and probably reflect increases in summer wetness of these the 2400 1700 1300 1100 and post 650 cal bp wetter phases coincide with increased geomorphic activity and perhaps encouraged incision on hillslopes rendered more susceptible to erosion by the activities of people