sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

investigating fossil hydrothermal systems by means of fluid inclusions and stable isotopes in banded travertine an example from castelnuovo dell abate southern tuscany italy southern tuscany italy hosts geothermal anomalies with associated widespread co2 gas rich manifestations and active travertine deposing thermal springs geothermal anomalies have been active since the late miocene and have led to the formation of widespread late miocene pleistocene travertine deposits and meso and epithermal mineralizations this study investigates the travertine deposit exposed in the castelnuovo dell abate area of southern tuscany here a fissure ridge type travertine deposit and its feeding conduits currently filled with banded calcite veins i e banded travertine represent a spectacular example of fossil hydrothermal circulation in the peripheral area of the exploited monte amiata geothermal field the castelnuovo dell abate travertine deposit and associated calcite veins were analysed to establish the characteristics of the parent hydrothermal fluids and the age of this circulation the focus of the study was on fluid inclusions rarely considered in travertine studies but able to provide direct information on the physico chemical characteristics of the original fluid uranium thorium geochronological data provided further constraints on the 1 age of tectonic activity 2 age of the hydrothermal circulation and 3 evolution of the monte amiata geothermal anomaly results indicate that brittle deformation nw and se trending normal to oblique slip faults was active during at least the middle pleistocene and controlled a hydrothermal circulation mainly characterized by fluids of meteoric origin and as old as 300 350 ka this is the oldest circulation documented to date in the monte amiata area the fluid chemical composition is comparable to that of fluids currently exploited in the shallow reservoir of the monte amiata geothermal field therefore suggesting that fluid composition has not changed substantially over time these fluids however have cooled by about 70 c in the last 300 350 ka corresponding to a cooling rate of the monte amiata geothermal area of about 20 c 100 ka 1

processes and rates of recent holocene basin filling in an active transform margin santa monica basin california continental borderland abstract santa monica basin an inner basin of the california continental borderland is a deep margin basin presently receiving sediments under high sea level conditions since the slowing of the last transgression the basin has been receiving primarily suspended load contributions with rare turbidites except in the most headward parts of the two principal canyons one turbidite found throughout the basin was laid down about 200 years bp and was probably deposited by a turbidity current generated by mass movement of slope sediments in the slope apron adjacent to the major active canyons similar basin wide events have occurred throughout holocene time at intervals of about 500 1000 years and these represent the effects of big earthquakes major floods or other exceptional happenings not commonly recorded in historic time except for these exceptional events the basin has received fine clastic sedimentation derived from the mainland rivers and transported by nepheloid plumes near bottom and in the surface mixed layer biogenic carbonate and organic carbon input from areas of high productivity fed by upwelling is masked by the fine detrital influx over the major fans by dilution from the rain of particulates from the major surface and near bottom turbid plumes that pass over the basin center a maxima of carbonate and organic content occurs in the basin floor sediments most distant from the combined diluting effects of these two major detrital inputs the basin slope fan and shelf bank top sediments are differentiated on the basis of mean particle size and skewness changes in sand and silt content are related to the pattern of the prevailing surface and near bottom water circulation with their reservoirs of fine suspended particulates the principal process removing the fine particles from the surface plumes is biological filtering and pelleting sedimentation rates of major sediment components show that near bottom nepheloid plumes are trapped by the closed deep basin and their load settles out as the turbid waters circle over the central basin floor sedimentation rates vary from 40 80 cm 1000 years average sediment delivery is about 106 tons but exceptional floods can deliver several fold more sediment at 10 30 year intervals

clay fabric of selected submarine sediments fundamental properties and models abstract clay fabric of selected mississippi delta sediment and a red clay from the eastern equatorial pacific is related to void ratio and depth of burial relatively high void ratio naturally consolidated delta sediment is characterized by a fabric of randomly oriented domains and short linking chains with particles in edge to face and face to face contacts lower intermediate void ratio sediment showed greater particle to particle packing but a consistent predominance of randomly oriented domains with a few chains and a slight development of larger domains than observed in the high void ratio sediment the deeply buried very low void ratio sediment has highly oriented domains and thin long voids the red clay sample is characterized by flocs connected by long linking chains and a very hi h void ratio domains and turbostratic type clay fabric are characteristic of high porosity high void ratio mississippi delta sediments highly oriented domains and long chains are diagnostic of the deeply buried very low porosity delta muds the clay fabric of natural undisturbed samples was compared with laboratory remolded samples for comparison with models suggested by earlier researchers observations using the transmission electron microscope tem support the proposed fabric models for remolded sediment selected samples were studied using the scanning electron microscope sem tentative clay fabric models for undisturbed submarine sediment are proposed and related to void ratios

an offshore eddy in the california current system part ii surface manifestation abstract ship and satellite observations taken over the last thirty years show that mesoscale patterns of sea surface temperature sst in the california current system are consistently found throughout the year and usually occur in approximately the same geographical locations typically these patterns are more pronounced in fall winter than in spring summer the temporal and spatial characteristics of these persistent feature were examined with satellite infrared ir measurements during winter 1980 1981 in january 1981 a ship surveyed the vertical structure of several physical chemical and biological parameters beneath one of these sst features centered near 32 n 124 w the surface ir pattern had a length scale of 200 km and a time scale of about 100 days it disintegrated following the first two storms of the winter season motion studies of the pattern in late october indicated an anticyclonic rotation with maximum velocities of 50 cm s 1 at 50 km from the axis of rotation as a unit the pattern advected southward with an average speed of 1 cm s 1 thermal fronts determined from the satellite imagery were strongest 0 4 c km 1 along the rim of the pattern and were advected anticyclonically with the pattern their length scales were 20 30 km in the along front direction and less than 10 km wide the hydrographic data revealed a three layer structure beneath the surface pattern a 75 m deep surface layer a cold core region from 75 to 200 m depth and a warm core eddy extending from 250 to 1450 m the anticyclonic motion of the surface layer was caused by a geostrophic adjustment to the surface dynamic height anomaly produced by the subsurface warm core eddy the ir pattern observed from space reflects the horizontal structure of the surface layer and is consistent with a theoretical model of a mean horizontal sst gradient perturbed by a subsurface density anomaly ship of opportunity sst observations collected by the national marine fisheries are shown to resolve mesoscale patterns for december 1980 the sst pattern near 32 n 124 w represented a 2 c warm anomaly compared with the 20 year mean monthly sst pattern

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

effects of biological activity on the entrainment of marine sediments nowell a r m jumars p a and eckman j e 1981 effects of biological activity on the entrainment of marine sediments mar geol 42 133 153 the effects of animal tracks and fecal pellet production on the critical entrainment velocity of marine sediments were examined experimentally laboratory measurements in a free surface seawater flume were made using three sediment sizes effects of three species of polychaetes and two species of bivalves were tested boundary shear velocity was calculated from the mean velocity profile in the logarithmic region of the boundary layer measurements were made with a hot film anemometer tracking doubled the boundary roughness and decreased the critical entrainment velocity by 20 ambient or free sediments were more easily entrained than fecal mounds which were restrained from movement by mucous adhesion between the fecal coils isolated pellets such as those egested by amphicteis scaphobranchiata transported readily as bedload over a cohesive sediment surface

common trace element characteristics of crustal and mantle derived k rich magmas at mt amiata central italy rare earth and other trace element data are reported for k rich mafic inclusions and siliceous lavas from mt amiata southern tuscany italy which form an almost complete mixing series as a result of magmachamber replenishment despite a wide range of sio2 contents 48 67 wt most of the rocks are equally enriched in light ree 200 300 and heavy ree 10 15 relative to chondritic values whereas intermediate ree are slightly less abundant in the lavas compared with the inclusions eu shows negative anomalies eueu 0 49 0 70 that are most pronounced in the lavas the compatible elements cr v sc and co are found to behave like sr ba and most major elements as they show a distinct inverse correlation with sio2 while cs follows na and li and markedly increases with sio2 however k and a number of other predominantly incompatible elements viz rb zr la ce yb lu nb y hf th and u display surprisingly little or no variation and all of the rocks have unusually high concentrations of many of these elements based on arguments that mixing in the magma chamber was not accompanied by significant selective enrichment of certain elements these chemical characteristics are attributed to the end members which can be identified as a silica saturated tuscan type magma and a primitive silica undersaturated roman type magma of the high k series it is tentatively suggested that the different sources in the lower crust and upper mantle from which the end member magmas are thought to originate were metasomatized by the same fluids prior to melting

in situ cone penetration tests at the active dashgil mud volcano azerbaijan evidence for excess fluid pressure updoming and possible future violent eruption active mud volcanism is a global phenomenon that represents a natural hazard by self igniting eruptions and the continuous emission of methane gas in both marine and continental settings mud domes are often found in compressional tectonic settings such as the caucasus orogenic wedge dashgil mud volcano the most prominent of 200 features in azerbaijan has erupted vigorously in historic times for several years we have observed variations in the activity of dashgil dome including transients in methane flux build up of extrusive mud cones on the main feature and flexural polygonal cracks adjacent to the main crater lake and new mud cones in spring 2007 we carried out in situ cptu cone penetration testing with pore pressure measurement experiments in the crestal area of dashgil our data suggest that the central portion of the crater lake which hosts the conduit for gas and possible mud ascent shows both low sediment shear strength 5 20 kpa and excess pore fluid pressures between 15 and 30 kpa supra hydrostatic at 1 m sub bottom depth in situ cone resistance as a measure for undrained shear strength is as low as 150 kpa in the conduit whereas the mud is found rather stiff in all other testing locations 300 700 kpa probably a result of deeply buried shales of the maikop formation parts of which now liquefy and ascend pore pressure is low in the centre of the conduit probably because of rapidly migrating gas it increases to 30 kpa at the lake bottom and deep flank then decreases upslope on the lake flank and reaches hydrostatic values at the crater rim from the overpressured region beneath the fluid filled crest of dashgil dome combined with the other observations we suspect to currently witness an ongoing period of updoming the presence of sintered mudstones from explosive eruptions in 1908 and 1928 and most likely before suggests that a similar violent activity may occur in the near future

depositional models for fine grained sediment in the western hellenic trench eastern mediterranean sediment in tectonically active topographically restricted settings of the western hellenic arc eastern mediterranean consists primarily of clayey silt and silty clay failure of metastable sediment temporarily stored on relatively steep slopes is triggered by earthquake tremors and eustatic oscillations redeposition of these materials by gravitative transport has resulted in markedly different lithofacies from site to site most piston cores include three late quaternary stratigraphic units that can be correlated with sections in other parts of the eastern mediterranean numerous radiocarbon age determinations enhance the correlation seven fine grained sediment types are identified in cores from eight distinct depositional environments some muds are closely related to specific environments slump and debris flow deposits on slope and high relief environments or to time well laminated mud during the latest pleistocene mid holocene or to both uniform and faintly laminated muds restricted to trench basins turbiditic and hemipelagic muds are common throughout the study area mud distribution patterns correlate closely with calculated sedimentation rates we propose two depositional models for these sediments the first emphasizes downslope transformations resulting in progressively reduced flow concentration during transport from slump and debris flow turbidity current low density turbidity current or turbid layer mechanisms the distal end member deposits settling from low concentration flows are thick rapidly emplaced fine grained uniform muds closely associated with faintly laminated muds these were ponded in flat trench basin plains planktonic and terrigenous fractions in the turbiditic finely laminated and uniform muds record mixing of materials of gravitative and suspension origin during redeposition this sequence prevails under conditions of minimal stratification of water masses as characterized by the present mediterranean in the second model developed for conditions of well developed water mass stratification well laminated rather than uniform mud prevails as the end product of low concentration flows these very finely laminated and graded muds record particle by particle settling from detached turbid layers concentrated along density interfaces they include material from turbid layers complemented by the normal rain of pelagic material stratification barriers resulted in region wide distribution of such deposits in both slope and trench environments

a new mechanism for seaward dispersion of midshelf sediments silt to sand size particles may be transported across middle continental shelves by currents forced by the radiation stress of variable amplitude swell with the passage of each group of waves of sufficient amplitude for the high waves in the group to resuspend bottom sediments there is a seaward bias in the return of sediments to the seafloor over a storm season with the passage of many wave groups the net seaward sediment displacement may be 1 5 km

depositional mechanisms of deep sea coarse clastic sediments cap enrage formation quebec cambro ordovician cap enrage deep sea sediments consist of six main facies 1 coarse conglomerates 2 graded stratified cross bedded fine conglomerates 3 dispersed pebbly sandstones 4 liquefied pebbly sandstones 5 ungraded cross bedded fine conglomerate and pebbly sandstones 6 massive sandstones facies 1 and coarser parts of facies 2 beds have unimodal grain orientations in bedding with unimodal a axis imbrications finer facies 2 beds have unimodal or bimodal grain orientations in bedding with bimodal up and downstream a axis imbrications facies 3 4 and 6 beds have unimodal bimodal or random grain orientations in bedding the a axis imbrications vary as follows mainly bimodal for facies 3 bimodal or unimodal for facies 4 and dominantly unimodal for facies 6 facies 5 beds result from fractional reworking of previous deposits by strong bottom currents velocities 70 125 cm s dilute spillover flows all other facies were deposited mostly from concentrated clast dispersions

chemical composition of thermal springs cold springs streams and gas vents in the mt amiata geothermal region tuscany italy abstract a geochemical study of thermal and cold springs stream waters and gas emissions has been carried out in the mt amiata geothermal region the cold springs and stream waters do not seem to have received significant contribution from hot deep fluids on the contrary the thermal springs present complex and not clearly quantifiable interactions with the hot fluids of the main geothermal reservoir the liquid dominated systems in the mt amiata area like most of the high enthalpy geothermal fields in the world are characterized by saline nacl fluids the nature of the reservoir rock carbonatic and anhydritic and its widespread occurrence in central italy favor a regional circulation of ca sulfate thermal waters which discharge from its outcrop areas waters of this kind which have been considered recharge waters of the known geothermal fields dilute disperse and react with the deep geothermal fluids in the mt amiata area preventing the use of the main chemical geothermometers for prospecting purposes the temperatures obtained from the chemical geothermometers vary widely and are generally cooler than temperatures measured in producing wells other thermal anomalies in central italy apart from those already known might be masked by the above mentioned circulation a better knowledge of deep fluid chemistry could contribute to the calibration of specific geothermometers for waters from reservoirs in carbonatic rocks

effects of cone tip roughness in situ stress anisotropy and strength inhomogeneity on cpt data interpretation in layered marine clays numerical study abstract this paper explores the effects of cone tip roughness factor soil in situ stress ratio and strength non homogeneity on cone tip resistance in three layer clay deposits aiming at presenting a general cpt data interpretation framework to extract soil layered profiles and strengths large deformation finite element ldfe analysis has been carried out simulating continuous penetration of the standard cone penetrometer from the seabed surface with the consideration of cone tip roughness factor in situ stress ratio and soil strength non homogeneity within a practical range in the ldfe analyses a thin relatively stiff or soft clay layer was interbedded in a uniform or nc clay deposit with various strength ratios between two successive layers and thickness ratios of the thin layer to the cone diameter explored the results have shown that the noted factors have significant influence on net cone penetration resistance in stratified deposits these influences in the layered deposits were found to be similar in magnitude to those on the cone limiting resistance in a single clay layer leading to the resultant influence on a thin layer correction factor for cone penetration resistance minimal this was confirmed by the evidence of the evolving soil flow mechanisms around the cone tip therefore the design charts and formulas developed for a smooth cone in uniform three layer soils are applicable for delineating layer boundaries and interpreting the undrained shear strength of each identified layer for a partially rough cone in three layer non homogeneous clay deposits however the cone tip roughness factor was shown to have an influence in the layer boundary identification especially for the cone penetration from a stiff layer to a soft layer

sites of river derived sedimentation in the ocean most of the world9s rivers have discharged sediment on wide continental shelves and in estuaries since the last rise in sea level in most cases sediments are thus trapped on these areas and are not deposited on the now relict submarine fans oceanward of these rivers the conclusions are based on remote sensing on data in the literature on present sedimentation rates on the shelves and the submarine fans and on river sediment discharges for the 22 rivers studied these submarine fans will remain cut off from their fluvial sources until the shelves and estuaries are filled and sediments can bypass these areas the time required to fill these shelves and estuaries ranges from 2 600 to 3 400 yr for the ganges brahmaputra to 1 to 1 2 m y for the yenisei ob for most river systems sea level will change before shelves and estuaries are filled with sediments

transtensional shear zones controlling volcanic eruptions the middle pleistocene mt amiata volcano inner northern apennines italy terra nova 00 1 10 2010 abstract the mt amiata volcano is characterized by the sw ne alignment of the eruption centres as well as other italian pleistocene volcanoes we carried out a structural and kinematic analysis in a broad stripe comprehending the eruption centres and the substratum towards ne and sw the results point out that a transtensional left lateral brittle shear zone affects the pre neogene substratum the middle pleistocene volcanic rocks and the late pleistocene travertines this transtensional structure is active since the early pliocene it controlled the location of the eruption centres through pull apart structures thus providing the deep structural channels for the uprising of magma to the surface the mt amiata volcano represents a key study area to investigate the pleistocene to present relationships between tectonics and magmatism in the tyrrhenian area

comment on recurrence of volcanic activity along the roman comagmatic province tyrrhenian margin of italy and its tectonic significance by f marra j taddeucci c freda w marzocchi and p scarlato

sb hg ore deposit distribution controlled by brittle structures the case of the selvena mining district monte amiata tuscany italy abstract this paper deals with the tectonic control on the hydrothermal system that gave rise to sb hg ore deposits in the monte amiata area that was one of the most relevant mining district for the exploitation of mercury in italy the study area selvena mining district is located in southern tuscany inner northern apennines one of the most important mineralized area in the western mediterranean region southern tuscany was severely affected by middle late miocene low angle normal faults later dissected by pliocene pleistocene faults coeval magmatism late miocene pleistocene and hydrothermal activity pliocene present the selvena mining district is located south of middle pleistocene monte amiata volcanic complex our structural and kinematic study is based on the integration among fieldwork borehole and mine data the results highlight two pleistocene holocene left lateral transtensional shear zones linked by normal faults defining a coeval pull apart structure here the sb hg mineralization transported by meteoric hydrothermal fluids mainly is particularly diffuse and concentrated in the cataclasites and in damage zones of the normal faults furthermore a widespread mineralization also occurs in the cataclasites of miocene low angle normal faults mine evidence suggests that ore bearing fluids percolated through structural conduits located along the fault planes and resulting parallel to the intermediate stress axis geological structures and ore deposit distribution are related to a single hydrothermal circuit with meteoric water channelled to depth through conduits parallel to the intermediate stress axis of the transcurrent shear zones then hydrothermal fluids mainly ascended through the almost vertical deformation zones located at the intersection between normal and strike slip faults thus hydrothermal fluids permeated also the middle late miocene cataclasites this study shed light on the relationships between geological structures and mineralization in southern tuscany and underlines the importance to investigate mine areas to understand hydrothermal fluids path

estimation of the undrained shear strength of adapazari fine grained soils by cone penetration test abstract a comprehensive study to determine the undrained shearing resistance of fine grained soils by the use of cone penetration test cptu was carried out on the thick fluvial sediments of the plain of adapazari turkey the soundings were performed adjacent to geotechnical boreholes for comparison eighty three undisturbed samples of low intermediate and high plasticity were procured in the process which were classified and tested in unconsolidated undrained triaxial uu conditions in the laboratory the cone resistance sleeve friction and pore water pressure values recorded along the length of undisturbed sampling were averaged to obtain characteristic values it is known that the empirical formulae to interpret cpt readings use cone factors nk nkt and nke which can be highly variable this can lead to unacceptable error levels in the assessment of undrained shear strength su nevertheless it was noticed in this study that the undrained strengths estimated by employing the traditional relationships for cpt came out quite close to the values measured in the laboratory if soil classes are taken into account since soil sampling is not done in the cone penetration test by default classification of the soil is attempted by the use of the soil type behavior index ic this study showed that the error margins for su values measured in the laboratory and inferred from cpt are considerably reduced by using the soil type behavior index ic to determine soil behavior type specific cone factors

an offshore eddy in the california current system part iv plankton distributions abstract the distribution of plankton across a warm core eddy system in the california current 400 km off point conception california was studied in january 1981 the eddy system about 150 km in diameter at the 7 c isotherm was made up of a 75 m thick surface layer a cold core region extending from 75 m to about 200 m and a warm core eddy below 200 m extending to at least 1450 m casts for the vertical distribution of chlorophyll phaeophytin and integrating zooplankton net tows were taken at 37 stations located about 20 km apart on two orthogonal transects across the eddy system vertical distributions of microplankton were determined on one section from the eddy center to beyond the eastern edge integrated chlorophyll phaeophytin values were highest to the north and east of the eddy system across the system itself there was only a small increase of values near the center asymmetrical distributions of maximum concen current water was being entrained into the center of the eddy system from the northeast dinoflagellates were numerically the most important member of the microplankton especially in the deep chlorophyll maximum zooplankton distributions indicated the intermingling of warm and cool water species throughout at least the upper 200 m of the eddy system some cold water species were as abundant inside the system as outside to the north and east their numbers were much reduced in a band surrounding the system where warm water species were most abundant the presence of species characteristic of different water types throughout the region of the eddy system provides an indication of the mixing that had occurred since the system originally formed the biological data together with the physical and chemical results indicate the importance of frontal boundary processes and lateral entrainment of surrounding water into the eddy system in determining the character and productivity of such systems

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

field measurements of shear strength of an underconsolidated marine clay abstract this paper presents the observations of cone penetration testing cpt in situ vane shear testing and undrained triaxial testing of underconsolidated marine clay in the craney island dredged material management area cidmma norfolk va comparison of vane shear measurements taken during 1981 1983 to cpt measurements taken during 1993 indicates a change in undrained shear strength both the vane shear and cone penetration resistances are lowest at the mid heights of the clay layers and the excess pore water pressures are highest at the mid height of the clay layers indicating that the clay layer is underconsolidated

a simple model of flow sediment organism interaction abstract previous models of organism sediment interaction have been limited primarily to eddy diffusion type mixing while such models are useful in interpreting some stratigraphic records they cannot be expected to provide mechanistic insights into the diversity of interactions among sedimentary processes organism activities and boundary layer flows to provide a more general formulation capable of dealing with all three types of processes in concert a simple discrete time markov model is generated this version of the model deals explicitly only with particulate and not liquid phases the initial formulation is a two compartment ergodic model of deposit feeding particle selection by deposit feeders results in incorporation of the selected particles into fecal pellets and fecal pellet disaggregation completes the cycle particles which are more strongly selected or which are incorporated into more robust pellets thus spend more time and reach higher relative concentration in the fecal pellet compartment the next level of complexity is achieved by adding burial from the free sediment non fecal pellet compartment this model predicts that particles which are more strongly selected or incorporated into more robust fecal pellets will have greater residence times in surficial sediments both pellets and free sediments before they become part of the stratigraphic record and will therefore achieve higher concentrations in surficial sediments than will less preferred particles the full flow sediment organism system is reached by adding the potential for lateral advection of particles the probability of such advection is allowed to differ between pellets and free sediments increasing selection and robustness of fecal pellets then can either increase or decrease relative concentration and residence time of a given particle type in surficial sediments the model thus provides a means of explaining differences in stratigraphic patterns among materials deposited simultaneously it also suggests that deposit feeder selection may increase the average age i e time since initial deposition of surficial sediments by maintaining preferred particle types near the surface selection may likewise control the texture of surficial sediments in a manner which is easily confused with purely physical sorting parameters which require careful measurement in testing these simple predictions are selectivity by deposit feeders probability of selection rate of fecal pellet breakdown under realistically simulated conditions probability of pelletal disaggregation differential erodibilities of pellets versus free sediments relative probabilities of lateral advection and rates of burial of free sediments versus pelletized sediments probabilities of burial

geochronological study of the monte amiata lavas central italy k ar and fission track age measurements were performed on lava samples of monte amiata volcano central italy which is formed by a sequence of lava flows and lava domes ranging in composition from trachybasalts to high sio2 quartzlatites

transport processes deduced from geochemistry and the void ratio of surface core samples deep sea sagami bay central japan abstract sagami bay is a deep water foreland basin with an average sedimentary rate of approximately 0 1 g cm 2 year it is an appropriate area to study for better understanding of sedimentary processes in a setting with a high sedimentation rate seven multiple core samples 30 50 cm thick were obtained from sagami bay four of the core samples were taken from the tokyo submarine fan system tokyo canyon floor tokyo fan valley and its levee the distal fan margin two samples were obtained from the sakawa fan delta and the adjacent topographic high the remaining one was from an escarpment of the sagami submarine fault variations in chemical composition can be recognized at every coring site they show two different sediment sources the sediments of the tokyo submarine fan system and those from sakawa fan delta further there are differences in chemical composition between canyon floor and levees even within the tokyo submarine fan system the results suggest that the sedimentary process is strongly controlled not by vertical particle settling but by a hyperpycnal flow process the proxies obtained from the core samples do not reflect conditions in the water column immediately overlying the sea floor rather they are controlled by conditions on the adjacent continental shelf or and shallow basins which are the areas of primary accumulation

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

hybrid character and pre eruptive events of mt amiata volcano italy inferred from geochronological petro geochemical and isotopic data abstract a new geochronological and geochemical study was carried out to better constrain the petrogenesis and eruptive history of monte amiata a large pleistocene trachydacitic volcano of southern tuscany previous studies suggested a magma mixing origin between calc alkaline silicic melts from the tuscan magmatic province tmp and potassic mafic melts like those found in the roman magmatic province rmp two eruptive episodes the first at ca 300 kyr the second at ca 200 kyr were distinguished from the few available ages however both the involvement of a rmp like melt as mafic end member and the timing of volcanic activity remained to be ascertained the k ar ages obtained on plagioclase sanidine and glass separated from mt amiata volcanic rocks demonstrate the sanidine is the most suitable phase for k ar dating sanidine yields ages of 304 293 kyr for the basal trachydacitic unit btc 298 280 kyr in the domes unit dlc and unexpected older ages of 312 308 kyr for the more mafic summit lava unit oll a careful re examination of the literature ages together with those obtained in this study shows that they tend to a common age of ca 300 kyr whatever the volcanic unit we interpret this as a reset of the k ar chronometer in response to a consequent recharge of the silicic magma reservoir by hot mafic melts this recharge most probably triggered the first volcanic eruption of mt amiata magmas in our model we suppose an initially chemically stratified magma chamber the input of deep hot mafic melts reset the crystals clock and probably allowed the eruption of the huge amount of trachydacitic crystal mush we propose that the controversial btc unit could have emplaced during a non explosive eruption if we consider either pre eruption passive degassing or extrusion of the trachydacites as magmatic foam first pb isotopic data of mafic enclaves from the trachydacitic units together with major and trace elements and new sr and nd data support the magma mixing as the dominant process at the origin of the mt amiata volcanic rocks the similar lile hfse ratios evidenced in this contribution between the magmatic enclaves of mt amiata and rmp volcanic rocks together with their comparable sr nd and pb isotopic compositions definitively argue for the involvement of a rmp like melt in the mixing the mt amiata is thus indisputably a hybrid volcano between tmp and rmp in terms of petrogenesis and ages

behaviour of trace elements during magmatic processes in the crust application to acidic volcanic rocks of tuscany italy abstract plio quaternary acidic rock suites from three volcanic centres of tuscany italy san vincenzo roccastrada and monte amiata are composed predominantly of rhyolitic and rhyodacitic ignimbrites the rocks are characterized by distinct enrichments particularly of k and rb and display considerable compositional differences among the various volcanic centres the volcanic rocks of roccastrada and most of s vincenzo were probably generated by partial melting of metapelitic rocks from the paleozoic basement of tuscany leaving a residue composed of biotite cordierite and quartz and sometimes plagioclase or garnet the enrichment of k and related elements can be attributed to selective contamination by fluids the other volcanic rocks including trachytes of mt amiata have also been affected by interaction with an upper mantle component probably k rich basaltic rocks a similar petrogenetic model can be applied to the granodiorite pluton of mt capanne elba which belongs to the same magmatic cycle since the variation trends observed in the tuscany volcanic rocks are similar to those reported from many acidic plutons it appears that crustal anatexis accompanied by interaction with upper mantle components has frequently played an important role in the genesis of the granitic rocks

mineral weathering in trachydacitic derived soils and saprolites involving formation of embryonic halloysite and gibbsite at mt amiata central italy abstract mount amiata is a volcano that has been extinct for 200 ka it is located in southern tuscany central italy and is composed largely of trachydacitic rocks the soils of mt amiata show a dark carbon rich a horizon that overlies a slightly structured bw horizon or directly a very thick saprolite which at a depth of about 3 m still maintains some ellipsoidal cores of coherent material mineral weathering in two of these soils one under beech and the other under chestnut was studied in detail the mineralogy of the parent rock consists predominantly of volcanic glass with phenocrysts of feldspar principally k feldspar biotite and pyroxene the main weathering products are an embryonic form of halloysite and gibbsite while allophane is usually absent or occurs in minor amounts sem evidence indicates that the clay minerals form directly from the weathering of volcanic glass in an environment where si is preferentially depleted in relation to al in the saprolite an anomalous situation is observed where optically fresh ferromagnesian minerals are thickly coated by clay particles whereas the surfaces of the glass and feldspar grains are relatively much cleaner however the ferromagnesian minerals are also much more heavily colonised by fungal hyphae and it is proposed that this results in the preferential deposition or flocculation of colloidal suspensions which translocate from higher positions in the weathering profile

comment on borgia a mazzoldi a brunori c a allocca c delcroix c micheli l vercellino a grieco g 2014 volcanic spreading forcing and feedback in geothermal reservoir development amiata volcano italia j volc geoth res 284 16 31 abstract borgia et al 2014 illustrated an active volcanic spreading model for the amiata volcanic area southern tuscany italy although at first glance the model may appear appealing this is not fully supported by the available data and the paper does not take into account their discussion accordingly the supposed negative consequences of the borgia et al 2014 model on both contamination of shallow water and geothermal exploitation can likely be regarded as speculative

physical processes and fine grained sediment dynamics coast of surinam south america abstract the prograding holocene mud wedge between the amazon and orinoco rivers in the trade wind belt of northeastern south america provides a modern day example of muds accumulating under moderate wave energy conditions gigantic shore attached mudbanks 10 km 20 km composed partly of thixotropic fluid mud gel front this coast every 30 60 km to form a buffer to wave attack and a temporary storage for fine grained sediments this mesotidal coast tide range 2 0 m with gentle offshore slope 0 0006 allows the exposure twice a day of extensive tidal flat deposits which are backed by mangrove swamps on a well developed chenier plain complex field experiments were conducted in surinam du ing 1975 and 1977 to provide new information on process form relationships in this interesting but unusual muddy environment simultaneous measurements of waves currents tide elevation suspended sediment concentration and variations in mud density show that soft intertidal and subtidal muds are suspended at both tide and wave frequency suspended sediment concentrations typically exceed 1 000 mg l at the surface as incoming solitary like waves partially disperse fluid mud into overlying water on a falling or rising tide redeposition of mud may occur near time of high tide the strong attenuation of shallow water waves by these muds provides conditions that are favorable for further sedimentation high concentrations of suspended fluid mud together with solitary like waves from the northeast throughout the year can lead to extraordinarily high net sediment transport rates in the nearshore zone calculations based on solitary wave theory and on data obtained from this study indicate that 15 65 106 m3 of mud can move along shore each year without involving breaking waves the concept of radiation stress and a nearshore circulation cell or bedload transport farther offshore outside the zone of wave dominance wind driven currents and the guiana current combine to transport muds to the northwest consistent with the observed direction of mudflat migration

initial investigations of the soft clay test site at bothkennar this paper presents findings from a wide range of in situ tests and laboratory investigations of the soft silty clay at bothkennar many of which were undertaken prior to the purchase of the site the soft clays at bothkennar are unusual in being remarkably uniform compared to other similar deposits in the uk this is thought to result from their deposition under rather stable estuarine conditions during the period 8500 6000 years before present bp thus apart from the presence of a highly laminated zone in the south east corner the soft clay is generally consistent across the site with many engineering properties increasing linearly with depth in contrast with many other soft clays the bothkennar clay has high effective strength parameters and high undrained strength the site appears to be ideal for a wide range of research and the presence of the highly laminated zone only enhances its potential cet article presente les resultats d une grande variete d essais in situ et en laboratoire de l argile

piezocone testing in underconsolidated clay this paper describes the results of piezocone testing that was carried out in underconsolidated soft marine clay in osaka bay the obtained profiles of the tip resistance and the pore water pressure were quite different from those for clay strata of normally consolidated state it was apparent that a different approach is needed to interpret the test results for underconsolidated clay the dissipation tests with the piezocone were performed at different elevations and indicated the excess pore water pressures remaining in the stratum the depth profile of excess pore pressure of underconsolidated clay is of special importance to the understanding of the degree of consolidation of the stratum an effort was made in this paper to assess the excess pore pressures remaining in the clay based on the piezocone data obtained during penetration an examination was made of available piezocone data of similar marine clays of both normally consolidated and underconsolidated states based on this a method was propos

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

un courant d eau continu peut il generer des turbidites resultats d experimentations analogiques abstract the arenite pelite or limestone marl alternations of turbiditic sequences are today considered as resulting from quasi instantaneous turbidite flows separated by long relatively calm periods i e background sedimentation during which marls or pelites are deposited this is the classical interpretation of the turbidity concept considering the frequent incoherency of the sequences as well as the presence of silts in the sometimes normally graded pelites we propose an alternative explanation for the origin of turbiditic deposits which emphasizies the continuous nature of turbidity flows rather than alternating mechanisms we therefore carried out experiments involving the reproduction of turbidites in a tank for the first time the turbiditic alternation of arenitic and pelitic facies has been formed from a continuous unidirectional current rather than from the intermittent currents usually used in previous experiments the arenite pelite alternations were produced by introducing a given quantity of sediment into the continuous flow at various stages the basin i e the tank occasionally undergoes turbiditic pulsations whereas the supplying current remains completely continuous the turbidity of the water current increases rapidly after sediment addition and decreases very slowly until all the sediment is deposited the procedure was repeated several times at lengthening intervals and with various quantities of sediment arenites and pelites were deposited in spite of the constancy of the current this situation corresponds well to that in a river in which the sediment load variations are controlled by variations in floods which subsequently enter the basin these experiments therefore demonstrate that turbidites can form under fluviatile type conditions the facies discontinuities within turbidites need not reflect drastic systematic variations in turbid flows but could result from turbidity variations within a continuous turbid flow because rivers are the main carriers of sediments from the continents to the basins they could be the cause of the turbidite formation such conditions could explain many sequential aberrations within turbidites such as intrasequence erosion pelitic laminae within ripple foresets and the high proportion of silts in the pelites between the turbiditic sequences these pelites should not be considered as background sedimentation but as the product of a genuine turbid flow such as that which produced the coarse deposits this model leads to significant modification of the sequence interpretation of turbiditic basins which will be much more linked to drainage systems rather than to a particular geodynamic context

origin of siltstones glacial grinding versus weathering siltstones are unusual rocks they are mainly made up of quartz glacial grinding is considered by some authors to be the main or even the only process generating silt this is supported by 1 the presence of silt in basal tills from present ice caps and above all 2 by the volumetric importance of quaternary loess however ancient glaciogenic sediments contain only a little silt scattered in the matrix of tillites or forming thin intercalations in pro and periglacial deposits these siltstones represent less than 5 of the total volume of upper proterozoic and upper ordovician glaciogenic sequences of west africa on the other hand silt is abundant in weathering profiles of tropical equatorial and mediterranean zones this silt is generated by splitting of minerals mainly quartz inherited from the parent rock quartz grains are partly dissolved in situ and their fragments cemented by iron oxi hydroxides in tropical and equatorial zones and by calcite in mediterranean zones silt is particularly abundant in tropical soils comprising up to 50 75 secondary dissolution of the iron or calcite matrix induces disaggregation of these soils and the release of silt which is later reworked and concentrated by wind or running water weathering processes and especially those operating in tropical zones are the main phenomena generating silt glacial grinding would generate only a little silt a large part of the material of quaternary loess may be derived from glacially reworked weathering profiles

recurrence of volcanic activity along the roman comagmatic province tyrrhenian margin of italy and its tectonic significance 1 the roman comagmatic province rcp developed along the nw se striking extensional tyrrhenian margin of italy since middle pleistocene and includes ultrapotassic small eruptive centers and large volcanic districts by means of a review and statistical analysis of a large data set of radiometric ages we demonstrate that in the rcp major eruptive cycles occurred at different volcanic districts almost simultaneously and with an almost constant recurrence time our analysis started with the alban hills volcanic district where a detailed 40ar 39ar chronology of the eruptive cycles has been recently achieved and then extended to include a database of 264 radiometric ages of the rcp volcanics published since 1980 statistical treatment of the data set shows a marked non poissonian behavior of volcanic activity through the whole magmatic province with climax of each major eruptive cycle occurring simultaneously at the different districts approximately every 48 kyr the concomitant eruption of many volcanic districts spreading over a 250 km long chain implies a control mechanism acting at a regional scale after discussing the possible relationship between tectonics sea level changes and volcanic activity we hypothesize that constant rates of slab retreat during middle pleistocene could have been a key factor controlling the rate of magma upwelling and the major cycles of recharge of the magma chambers as a working hypothesis we propose that the duration of the cycles may be related to 1 progressive weakening of the crust due to magma underplating or 2 cyclic injection of convective plumes into the mantle wedge

experimental investigation of silt formation by static breakage processes the effect of temperature moisture and salt on quartz dune sand and granitic regolith weathering simulations carried out using a climatic cabinet have demonstrated that diurnal temperature and humidity variations typical of those occurring in warm desert environments are ineffective in causing static breakage of quartz dune sand and polymineralic regolith sand grains wetting and drying combined with temperature variations was also found to be a relatively ineffective weathering process these results suggest that crack tip processes are insignificant where mineral grains are not subject to static loading sodium sulphate weathering was found to cause slight damage to quartz dune sand grains and major damage to first cycle regolith grains feldspars and mica in the regolith sands were more susceptible to salt action than quartz salt weathering of the regolith sands produced substantial quantities of silt in the size range typically found in natural loess deposits

geochemical characteristics of the south tuscany italy volcanic province constraints on lava petrogenesis abstract three suites of volcanic rocks from radicofani mts cimini and mt amiata south tuscany italy were analyzed for major and trace element contents and sr isotopic composition all samples are silica saturated hypersthene normative and some are peraluminous samples from radicofani and the less evolved mts cimini samples have high mg numbers 74 5 66 3 consistent with the fosteritic rich nature of their olivine phenocrysts and high bulk rock abundances of ferromagnesian trace elements all samples are highly enriched in light ree 150 315 chondrites compared to heavy ree 9 15 chondrites and have negative eu anomalies eu eu 0 92 0 44 87 sr 86 sr ratios are high and variable radicofani 0 7137 0 7150 mts cimini 0 7128 0 7138 mt amiata 0 7119 0 7131 a distinctive feature of the radicofani samples is that with decreasing age the rocks increase in k2o content but decrease in la ce these south tuscany rocks have geochemical characteristics of the calc alkaline and alkaline series namely in addition to the high k rb cs ba and lree contents they have high ratios of incompatible elements relative to the high field strength ions such as ti zr hf nb and hree when compared to an estimated primitive mantle composition in general the geochemical characteristics of south tuscany volcanics are consistent with mixing between crustal derived material and mantle derived magma the mantle derived component was unusually rich in radiogenic sr and incompatible elements and had geochemical features similar to basic lavas of the high k series in the roman province

biological activity and associated sedimentary structures in hebble area deposits western north atlantic abstract biological and sedimentologic samples along with x radiographs of sediment slabs were taken from box cores in the hebble area 4700 m on the lower continental rise of nova scotia these data suggest that this bottom region is influenced by periods of strong near bottom currents which erode and physically transport sediments these high periods alternate with periods of weaker flow biogenic reworking of sediments by an active benthic infauna dominates particle transport during low flow conditions

grain size relationship between suspended matter originating in the gironde estuary and shelf mud patch deposits abstract the grain size variations of the elementary fraction without aggregates of gironde suspended matter during its transfer to the shelf were analyzed and compared with those of the surficial sediment of the west gironde mud patch located between water depths of 30 and 70 m which is considered as a preferential deposition area for estuarine suspended matter sm the results made it possible to show that two processes complicate the relationships between the estuary and the shelf a biogenic contribution identified as early as at the gironde outlet corresponding to a mode at 15 20 m in the sm of the turbid plume and an inorganic contribution of a fine grained fraction coming from sandy shelf deposits corresponding to micas with a mode at 50 60 m and settling on the inner part of the mud patch the nourishment of the western and deeper part of this mud patch by estuarine suspended matter is derived from the benthic nepheloid layer in terms of grain size distribution this supply is characterized by the 7 5 m mode which is typical of particulate matter originating in the gironde estuary