variations in the surface texture of suspended quartz grains in the loire river an sem study statistical size distribution and scanning electron microscopic studies of suspended sand grains in the loire river at montjean france were carried out over a period of a year hydrological cycle to discern seasonal variations the sand fraction in suspension is better sorted during winter average mean 0 69 mm median 0 65 0 95 mm sorting value 1 1 1 35 and is dominated by quartzo feldspathic minerals during summer on the contrary this fraction is rich in mica minerals and is poorly sorted average mean 1 21 mm median 0 33 0 95 mm sorting value 1 4 2 0 the grain size of the coarser fraction shows a tendency to increase with river discharge up to an optimum discharge of about 1000 m3 s 1 and thereafter decreases scanning electron photomicroscopy of quartz grains from the suspended sand population indicates that both mechanical and chemical features occur the former conchoidal fractures mechanical fractures and breakage dominate in the samples collected near the water surface during winter floods and the latter solution pits vermicular features silica flowers neogene silica and diatoms in the samples from the bottom during low summer flows during summer chemical action takes place on sediments prior to or upon their deposition sediments that are resuspended during winter floods undergo mainly physical processes attrition abrasion mixed surface features are therefore observed during average and low river discharge inheritance of these surface features from the source area is however not completely excluded thus the history of quartz grains in suspension can be reconstructed from sem exoscopic studies therefore it can be proposed that the fluvial quartz grain surface textures result from a combination of alternating chemical and physical processes

calculations of weathering rate and soil solution chemistry for forest soils in the norwegian russian border area with the profile model abstract potential response of forest soils to s deposition in the norwegian russian border area in the surroundings of the pechenganikel smelters the major s emitters in northern europe has been assessed with the profile model the release rate of base cations due to weathering range from 0 05 to 0 28 kmol c ha yr in the 0 50 cm soil layer thus demonstrating the high sensitivity of the coarse and thin podzols studied calculated steady state bc al values are significantly lower than the presumed critical value of 1 which indicate possible negative effect on vegetation through soil acidification according to the model calculations future s deposition has to be very low in order to stop the ongoing acidification and prevent vegetation damage however model assumptions uncertainty in input data and critical chemical values applied implies that modelling results must be interpreted carefully

a new self organizing mechanism for deep focus earthquakes the mechanism of deep focus earthquakes has been a puzzle since their discovery almost 70 years ago1 2 because brittle fracture and frictional sliding at depths in excess of 100 200 km would require unrealistic rock strengths3 4 rock strength does increase with pressure but a few hundred mpa equivalent to 10 20 km depth suffices to inhibit most fracture and elevated temperature activates ductile mechanisms that operate at stresses less than the fracture stength a range of mechanisms has been proposed for deep earthquakes including plastic instabilities5 7 shear induced melting8 11 and instabilities accompanying recrystallization12 13 or polymorphic phase transformation14 23 each of these proposed mechanisms has exhibited certain inherent weaknesses see kirby22 for review and discussion here we report experimental observations of high pressure faulting of metastable mg2geo4 olivine as it undergoes incipient transformation to a spinel 24 25 structure we present a model in which this faulting arises from the generation propagation and linking up of spinel filled anticracks26 when applied to the olivine spinel transformation in the earth s mantle the anticrack model27 satisfactorily accounts for the similarities and differences between shallow and deep earthquakes and removes the problems associated with frictional sliding

imprints in silica grains induced during an open channel flow experiment determination of microtextural signatures during aqueous transport abstract the aim of this work is to identify and characterize microtextural signatures in silica glass grains used as analogous to quartz that are produced during aqueous transport at different flow velocities with variable sediment concentrations transport distances and time intervals to achieve this an open channel flow experiment was conducted with a mixture of sand and silica glass microspheres in varying conditions velocity from 0 67 to 1 4 m s duration 1 or 10 minutes distance 0 to 2 5 m and sediment concentration 60 or 80 experimental conditions were used to replicate natural phenomena such as river superficial velocity or coastal swash processes before the experiment the microsphere surfaces were imaged and clear of any microtextural imprint increasing velocity distance and sediment concentration exhibited a strong correlation with higher numbers of surfaces abundantly covered with microtextures of mechanical origin i e craters abrasion marks and v shaped percussion marks sem microphotographs of silica were analyzed and classified to provide examples of the specific microtextures produced during the open channel flow experiment the purpose of the experiment was to characterize surface microscopic signatures in quartz grains replicating hydrodynamic conditions of coastal and fluvial environments the results demonstrated a strong correlation between higher velocities and higher sediment concentrations and a larger presence of microtextural mechanical imprints in the grains analyzed thus demonstrating a clear relation between microtextural imprints and water flow modes these results have important implications for future microtextural works analyzing grain imprints and their relation to sediment transport types an example demonstrated here is that the higher presence of v marks could be used as an indicator of supercritical flow conditions

implications of quartz grain microtextures for onset eocene oligocene glaciation in prydz bay odp site 1166 antarctica abstract this paper presents the results of the scanning electron microscopic sem analysis of quartz grains from a selection of samples at site 1166 ocean drilling program leg 188 drilled site 1166 on the prydz bay continental shelf antarctica to document onset and fluctuations of east antarctic glaciation this site recovered upper pliocene holocene glacial sediments directly above cretaceous through lower oligocene sediments recording the transition from preglacial to early glacial conditions sem analysis of quartz grains at site 1166 was used to characterize the glacial and preglacial sediments by their diagnostic textures angular edges edge abrasion as well as arcuate to straight steps are the most frequent features in glacial deposits the highest frequency of grains with round edges is present in middle late eocene fluvio deltaic sands however angular outlines fractured plates with subparallel linear fractures and edge abrasion indicating glacier influence are also present preglacial carbonaceous mudstone and laminated gray claystone show distinctive high relief quartz grains and some chemical weathering on grain surfaces the results of the microtextural analysis of quartz grains are used to verify some critical periods of ice sheet evolution such as the transition from the east antarctic preglacial to glacial conditions on the continental shelf from middle late eocene to late eocene early oligocene time

a soil chronosequence in northwestern italy morphological physical and chemical characteristics abstract a chronosequence of soils developed on fluvial terraces dating from lower middle pleistocene to upper upper pleistocene was studied to identify the morphological physical and chemical soil properties most sensitive to soil development and to further test the usefulness of iron oxides as indicators of relative age a relative horizon distinctness rhd index and the buntley westin and hurst colour indices clearly reflected differences in soil development with age among physical characteristics clay content and aggregation obtained by comparison of clay dispersion before and after removal of cementing agents were most efficient in indicating differences in duration of pedogenesis cation exchange capacity as related to clay content was the chemical property most useful to distinguish soils of different terraces iron oxide ratios were again useful as indices of soil development

boulder deposits from large waves during the last interglaciation on north eleuthera island bahamas abstract seven boulders measuring 100 to 1000 m 3 are scattered along the coastal ridge of north eleuthera some are situated on ridge crests up to 20 m above present sea level the boulders were probably deposited during oxygen isotope substage 5e or 5d as shown by their stratigraphic setting and by amino acid racemization ratios d alloisoleucine l isoleucine ratios were determined for land snails and oolite of both marine and eolian origin was associated with the boulders like the boulders the probable source rocks exposed in the adjacent cliffs are composed of marine and eolian limestone of oolitic and peloidal composition the source beds are correlated with stage 9 or 11 the largest boulder is about 10 times the size of the largest holocene ones moved by waves in the area tsunamis are a reasonable possibility as a transporting mechanism of the pleistocene boulders however if deposited instead by storms during the last interglaciation the storms were of much greater intensity than those occurring in the region during the late holocene

microtextural characteristics of quartz grains transported and deposited by tsunamis and storms article i nfo the complex transport and depositional processes associated with tsunamis and storms and the peculiarities of local inundation present questions associated with the recognition and differentiation of the sedimentary signature of these events this work presents a study of quartz grains transported and deposited by tsunami and storm waves with the objective of identifying specific microtextural signatures caused by high energy marine inundations and to correlate them with their principal sedimentary sources in this empirical study 1150 quartz grains 78 samples and their microtextural signatures were observed analyzed and classified using scanning electron microscope photomicrographs the results suggest that although no specific microtextural signature is associated with high energy inundations there are strong increases in the percent age of fresh surfaces and percussion marks when compared with the potential source material moreover tsunami and storm grains present the greatest microtextural variance among all the grains analyzed never theless specific local conditions and sediment concentrations constrain the microtextural implications on tsunami or storm grains one laboratory experiment was designed to test microtextural implications in grains subjected to variable velocities sediment concentration and time the surface microscopic signature in quartz grains of high energy events further contributes to the development of more efficient sedimentological criteria to identify deposits associated with tsunami and storm events

dual phase mass balance modeling of small mineral particle losses from sedimentary rock derived soils abstract losses of small mineral particles can be a significant physical process that affects the elemental composition of soils derived from sedimentary rocks shales in particular contain abundant clay sized minerals that can be mobilized by simple disaggregation and solutional weathering is limited because the parent rock is composed primarily of recalcitrant minerals previously subjected to continental weathering here the dual phase mass balance model is employed to quantify losses of small mineral particles as water dispersible colloids wdcs from three previously studied soil profiles along a hill slope at the susquehanna shale hills critical zone observatory ssho wdcs were isolated from soil in the laboratory to determine their mineralogical and elemental compositions clay minerals dominated wdcs including illite vermiculite and chlorite inherited from the parent shale along with neoformed kaolinite quartz present in bulk soil was generally excluded from wdcs elements of low solubility and or bound in recalcitrant forms like rb in illite were employed in tracer ratios in the dual phase model aluminum ga and rb were enriched in wdcs and zr and hf were partially excluded six different combinations of elements into tracer ratios al zr ga zr rb zr al hf ga hf rb hf each yielded similar model results mass losses of wdcs were large ranging from 68 7 to 15 5 relative to soil parent material in different parts of the profiles mass losses via solution were smaller ranging from 7 2 to a gain of 6 1 in part of one profile losses of wdcs account for 90 of total mass loss surpassing chemical dissolution and therefore dominate the weathering portion of denudation at ssho zirconium concentrations were 97 158 ppm in the generally 1 m wdcs suggesting colloidal zr bearing phases model quantified losses of zr via wdcs were large with a median loss of 41 relative to parent material such losses indicate systematic underestimates of weathering by traditional mass balance that uses zr as an index element losses of ca mg and k via wdcs exceeded losses via solution countering assumptions of base cation losses primarily via mineral dissolution the results illustrate a geochemical fingerprint of physical weathering and the ability of the dual phase model to quantify that weathering process

parent material uniformity and degree of weathering in a soil chronosequence northwestern italy abstract the uniformity of the parent material and degree of weathering of the soils of a chronosequence developed during the pleistocene were investigated using optical microscopy x ray fluorescence and scanning electron microscopy sem techniques uniformity of the parent material was assessed by two criteria the ratios of resistant minerals and their specific elements in the heavy fraction s g 2 96 g cm 3 there was some variation between heavy mineral ratios but there was less variation between ratios from the chemical data and on this basis it was concluded that the parent material of each of the three soils in the sequence was uniform sem examination confirmed that the resistant minerals had remained unaltered although some ti bearing minerals showed some alteration the degree of chemical weathering as expressed by the ratio of mobile to non mobile elements and by parker s index increased from the youngest to the oldest soil

assessing parent material uniformity of a red and black soil complex in the landscapes abstract the distribution of red and black soil xeralfs xerolls associations in the monarto area south australia is complex and their genesis either being derived from a uniform parent material or a lithologic discontinuity is not known the objectives of this study were i to assess zr and ti bearing grains as minerals resistant to chemical weathering prior to employing zr and ti in determining parent material uniformity and ii to confirm whether pedological processes or a lithologic discontinuity may be responsible for the textural contrast within the red and black soil profiles scanning electron microscopy sem and energy dispersive x ray analysis edax were used to study chemical weathering and elemental composition of surfaces of zr and ti bearing grains x ray fluorescence xrf analysis was used to determine elemental concentrations in various soil fractions results showed that zr bearing grains consisted of only zircon having smooth clean surfaces which are characteristic of a mineral resistant to chemical weathering edax spectra confirmed that zr was a specific element to represent zircon suggesting its reliability to be used in assessing parent material uniformity on the other hand ti derived not only from minerals rutile anatase resistant but also from minerals ilmenite pseudorutile biotite susceptible to chemical weathering this limited the usefulness of ti as an index mineral for soil development studies except for zr ti ratio all other indicators of parent material uniformity i e depth distribution curves of zr and y in various fractions and y zr ratio showed no considerable inflection and variation with depth in a xeralf red soil this indicated the xeralf derived from a uniform parent material mica schists thereby texture contrast within a profile is due to pedological processes on the other hand depth distribution curves showed clear inflection and variation in xerolls black soils indicating soils developed from lithologic discontinuities so different trends in particle size fractions between 0 48 cm for ma5 and 0 59 cm for ma3 profiles compared to the underlying layers are due to parent material differences and not pedogenesis the presence of complex red and black soil association in the landscape is attributed to the difference in parent materials where the red soil developed from mica schist and the black soils from calcareous deposits

modification of heavy mineral assemblages in english coversands by acid pedochemical weathering summary weathering of non opaque heavy minerals in five english soil profiles developed in texturally homogeneous late devensian coversands has been investigated by spline interpolation of detailed mineral counts values for d90 90 mineral depletion derived from the splines suggest a depletion sequence that is generally applicable to moderately acid weathering of sediments apatite olivines amphiboles pyroxenes epidotes garnets more resistant minerals weathered minerals form three groups each of which is eliminated in an almost discrete stage weathering is accompanied by a characteristic developmental sequence of surface textures weathering rates of most of the silicate minerals are probably determined mainly by their fe2 contents effective surface areas and soil ph considerable variations in the depth and severity of weathering between profiles may reflect differences in vegetation histories heavy mineral weathering is related to soil chemistry to examine its implications for podzol genesis

extremely high energy wave deposits inside the great barrier reef australia determining the cause tsunami or tropical cyclone abstract a hydrodynamic approach is used to determine whether tsunami or cyclone generated waves were responsible for the deposition of fields of well imbricated rock boulders up to 290 tonnes along the coast of cairns inside the great barrier reef australia calculations of the overturning moments show that only tsunami are capable of moving such large boulders in this environment it is hypothesised that large tsunami 11 m have been able to penetrate the great barrier reef through wide 5 10 km 50 70 m deep passages between individual reefs three such passages each approximately 35 km apart and oriented in the same direction exist in the cairns region it is possible that these passages have funnelled and amplified palaeotsunamis the preferential location of eroded coral boulders up to 3 m in length on reef flats alongside these passages and their absence on other reefs throughout the region provide further evidence that extremely high energy waves have been able to penetrate the great barrier reef into the inner channel adjacent to the mainland carbon 14 ages of the coral boulders on these reef flats matches closely the ages of coral fragments pinned below the very large rock boulders along the coast these ages suggest that the cairns region has experienced large tsunami twice over the last millennium

element mobilization and redistribution under extreme tropical weathering of basalts from the hainan island south china abstract chemical weathering of rocks has substantial influence on the global geochemical cycle in this paper the geochemical profile of a well developed basalt weathering profile 15 m thick including soil saprolite semi weathered rock and fresh basalt on the island of hainan south china was presented the soil and saprolite samples from this profile are characterized by high al2o3 and fe2o3 concentrations up to 32 3 and 28 5 respectively the mineral assemblage is dominated by kaolinite fe oxides hydroxides and gibbsite or boehmite indicating extensive desilicate and ferrallitic weathering the acidic and organic rich environment in the soil horizon may have promoted elemental remobilization and leaching the strongest sio2 depletion and al2o3 enrichment at about 2 4 m deep indicate that the main kaolinite hydrolysis and gibbsite formation occurred near the soil saprolite interface the mild sr reconcentration at about 3 9 m and 7 1 m deep may be attributed to secondary carbonate precipitation mn oxides hydroxides precipitated at 6 1 m deep accompanied by the strongest enrichment of ba and co uranium is mildly enriched in the middle part about 7 1 m and 9 1 m deep of the weathering profile and the enrichment may have been caused by the decomposition of uranyl carbonates or the accumulation of zircon immobile element i e zr hf nb ta th and ti distributions at different depths are mainly controlled by secondary fe oxides hydroxides and follow the stability sequence of nb ta th zr hf ti the limited thickness 15 cm of the semi weathered basalt horizon at the rock regolith interface 15 28 m deep suggests that plagioclase and pyroxene are readily altered to kaolinite smectite and fe oxides under tropical climate the marked enrichment of transitional metals such as cu zn ni and sc along the rock regolith interface may have associated mainly with increasing ph values as well as the dissolution of primary apatite and formation of secondary phosphates our findings highlight the importance of secondary phosphates in the redistribution of transition metals and in the possible mg cu and ni isotopic fractionation under extreme weathering of basalt in tropic climate

a compositional approach to the reconstruction of geochemical processes involved in the evolution of holocene marine flooded coastal karst basins mljet island croatia abstract geochemical patterns in the environment are always the result of certain processes therefore it is essential to decipher a process to properly evaluate the environmental role and potential of chemical elements compounds this allows the distinction between natural and anthropogenic influence on elemental concentrations however if the compositional nature of geochemical data is neglected erroneous or misleading conclusions regarding the processes involved are probable in this study the reconstruction of depositional environments and processes through the holocene in two sediment cores obtained from submerged sinkholes located on the island of mljet croatia was performed by taking into account the compositional nature of geochemical mineralogical and grainsize data problems involving compositional data are always multivariate for example the concentration of a single element does not carry any interpretative information as only the ratios between elements do this has led to the discovery of a large number of geochemical proxies based on elemental ratios which describe certain environmental conditions and processes involved nevertheless some proxies have been found to be restricted to only some specific environments thus preventing them from being used in general therefore some kind of relation between different proxies is necessary to obtain final conclusions however when using simple elemental ratios those correlations cannot be obtained due to the nature of compositional data with a sequential binary partition of a compositional vector orthonormal log ratio olr coordinates proxies can be constructed when based on expert knowledge those proxies fully acknowledge the geochemical properties of the chosen elements with one major difference that the correlation between newly obtained variables is mathematically well grounded as a result the final conclusion is more accurate in this research geochemical proxies obtained as a representation in olr coordinates of the elements that are enriched compared to the local soil were used to perform principal component analyses it helped to unravel the evolution of sedimentary environments mineralogical xrd and heavy mineral data and grain size analyses supported the conclusions obtained based solely on geochemical data furthermore data analysis suggests that the proxies for redox conditions described in the literature should be used with caution as their use is somewhat limited

impact of glacial activity on the weathering of hf isotopes observations from southwest greenland abstract data for the modern oceans and their authigenic precipitates suggest incongruent release of hafnium hf isotopes by chemical weathering of the continents the fact that weathering during recent glacial periods is associated with more congruent release of hf isotopes has led to the hypothesis that the incongruency may be controlled by retention of unradiogenic hf by zircons and that glacial grinding enhances release of hf from zircons here we study the relationship between glacial weathering processes and hf isotope compositions released to rivers fed by land terminating glaciers of the greenland ice sheet as well as neighbouring non glacial streams the weathered source rocks in the studied area mostly consist of gneisses but also include amphibolites of the same age 1 9 ga hafnium and neodymium isotope compositions in catchment sediments and in the riverine suspended load are consistent with a predominantly gneissic source containing variable trace amounts of zircon and different abundances of hornblende garnet and titanite glacially sourced rivers and non glacial streams fed by precipitation and lakes show very unradiogenic nd isotopic compositions in a narrow range nd 42 8 to 37 9 hafnium isotopes on the other hand are much more radiogenic and variable with hf between 18 3 and 0 9 in glacial rivers and even more radiogenic values of 15 8 to 46 3 in non glacial streams although relatively unradiogenic hf is released by glacial weathering glacial rivers actually fall close to the seawater array in hf nd isotope space and are not distinctly unradiogenic based on their abundance in rocks and sediments and their isotope compositions different minerals contribute to the radiogenic hf in solution with a decreasing relevance from garnet to titanite hornblende and apatite neodymium isotopes preclude a much stronger representation of titanite hornblende and apatite in solution such as might result from differences in dissolution rates than estimated from mineral abundance the strong contrast in hf isotope compositions between glacial rivers and non glacial streams results mostly from different contributions from garnet and zircon where zircon weathering is more efficient in the subglacial environment a key difference between glacial and non glacial waters is the water rock interaction time while glacial rivers receive continuous contributions from long residence time waters of distributed subglacial drainage systems non glacial streams are characterized by fast superficial drainage above the permafrost horizon therefore the increased congruency in hf isotope weathering in glacial systems could simply reflect the hydrological conditions at the base of the ice sheet and glaciers with zircon weathering contributions increasing with water rock interaction time

multi proxy evidence for trans pacific tsunamis in the hawai ian islands abstract the origin of two sand layers buried in polol wetland on the northeast coast of the island of hawai i was investigated using a multi proxy approach including radiometric dating sedimentology geochemistry micropalaeontology palynology and historical records based on 210 pb 137 cs and pollen data the lower sand unit extending 250 to 350 m inland is attributed to the 1946 aleutian tsunami while the upper sand unit was laid down by the 1957 aleutian tsunami chronological information does not appear to support any link between these deposits and historical storm events furthermore sedimentological geochemical diatom and pollen results suggest deposition of marine and near beach sediments under high energy conditions typically associated with tsunami inundation this work presents the first conclusive sedimentary evidence for distantly generated tsunamis on the hawai ian islands opening the way for more comprehensive historical and palaeotsunami studies indeed a brief review of archaeological data suggests that the hawai ian coast may have experienced similar large magnitude events in the past from both local and distant sources

mineral weathering processes in podzolic soils on granitic materials and their implications for surface water acidification many areas where concern has arisen over the recent acidification of their surface waters contain podzolic soils developed upon granitic materials the mineral weathering processes in these soils are reviewed and the ways in which such processes could be altered by acid deposition are considered the most weatherable primary minerals are plagioclase feldspar biotite and fine grained dioctahedral mica and their decomposition which is mediated by organic acids leads to the formation of proto imogolite allophane vermiculite and smectite other clay minerals occurring in podzols such as kaolinite and halloysite as well as gibbsite are probably inherited from previous weathering cycles although a present day pedogenic origin should not be ruled out entirely the possibility is considered that the partial replacement of soil organic acids by mineral acids introduced through precipitation could bring about significant differences in mineral weathering leading to more acid soils with more dissolved ionic aluminium in soil and stream waters the weathering products involved in the mobilization of aluminium from podzols are likely to be proto imogolite allophane and hydroxy al interlayered vermiculite or smectite another possibility is that sand and silt sized plagioclase feldspars are more reactive than previously realized

clast mobility within boulder beaches over two winters in galicia northwestern spain abstract a micro drone was used to make low altitude flights over boulder beaches at laxe brava and oia in galicia northwestern spain flights were made in july 2012 may 2013 and spring 2014 high resolution digital terrain models and orthophotographs combined with gis mapping were used to monitor changes in the position of thousands of boulders maximum storm wave height was higher in the winter of 2013 2014 than in winter 2012 2013 and this was reflected in an increase in the proportion of the boulders that moved in the two winters from 17 to almost 48 at laxe brava and from 53 to almost 88 at oia the greater mobility of the boulders at oia can be attributed in part to their generally smaller size although there was considerable overlap between the size of boulders that moved and those that did not move within and between the two beaches there were mobile boulders in areas up to several metres above the high tidal level on both beaches and boulder transport in the shore normal and alongshore directions triggered some changes in the beach profiles particularly in the middle to upper parts of the beaches estimates of threshold transport conditions scaled to boulder mass breaker height and other variables suggested that all but the very largest boulders on the two beaches should have been mobile even during the summer months when the waves were much lower than in winter model over prediction can be attributed to a number of factors including constraints on movement imposed by surrounding boulders differences in boulder size and their effect on pivoting angles and on the degree to which boulders are exposed or sheltered from wave impact and difficulties in assigning appropriate values to model coefficients

phase transformations earthquakes and the descending lithosphere abstract the energy dissipated from metastable phase transformations is investigated in this paper in addition to the kinetic energy envisaged by randall at least two other major forms of energy latent heat and metastability energy are involved in a metastable phase transformation the seismic energy density for metastable phase transformation is of the order of 10 24 10 25 erg km 3 for most mantle silicates as an example an earthquake of magnitude m 7 5 would require only 0 01 0 03 or 0 04 km 3 of basalt olivine or pyroxene respectively undergoing metastable phase transformation earthquakes caused by both faulting and phase transformation mechanisms have been observed in high pressure laboratory experiments the energy density associated with a faulting mechanism appears to be four to five orders of magnitude less than that associated with metastable phase transformations of mantle silicates confirming theoretical expectations according to all of the thermal models for the descending lithosphere available in the literature metastable phase transformations almost certainly occur in the descending lithosphere enormous energies would be released suddenly in association with these metastable phase transformations thus earthquakes within the descending lithosphere at depths greater than 100 km may be induced by metastable phase transformations however metastable phase transformations in the descending lithosphere have little or an opposing effect on the tectonic engine driving the motion of plates into the mantle

the tsunami phenomenon abstract with human activity increasingly concentrating on coasts tsunamis from japanese tsu harbour nami wave are a major natural hazard to today s society stimulated by disastrous tsunami impacts in recent years for instance in south east asia 2004 or in japan 2011 tsunami science has significantly flourished which has brought great advances in hazard assessment and mitigation plans based on tsunami research of the last decades this paper provides a thorough treatise on the tsunami phenomenon from a geoscientific point of view starting with the wave features tsunamis are introduced as long shallow water waves or wave trains crossing entire oceans without major energy loss at the coast tsunamis typically show wave shoaling funnelling and resonance effects as well as a significant run up and backflow tsunami waves are caused by a sudden displacement of the water column due to a number of various trigger mechanisms such are earthquakes as the main trigger submarine and subaerial mass wastings volcanic activity atmospheric disturbances meteotsunamis and cosmic impacts as is demonstrated by giving corresponding examples from the past tsunamis are known to have a significant sedimentary and geomorphological off and onshore response so called tsunamites form allochthonous high energy deposits that are left at the coast during tsunami landfall tsunami deposits show typical sedimentary features as basal erosional unconformities fining upward and landward a high content of marine fossils rip up clasts from underlying units and mud caps all reflecting the hydrodynamic processes during inundation the on and offshore behaviour of tsunamis and related sedimentary processes can be simulated using hydro and morphodynamic numerical models the paper provides an overview of the basic tsunami modelling techniques including discretisation guidelines for appropriate temporal and spatial resolution as well as the nesting method furthermore the boussinesq approximation a simplification of the three dimensional navier stokes equations is presented as a basic theory behind numerical tsunami models which adequately reflects the non linear dispersive wave behaviour of tsunamis the fully non linear boussinesq equations allow the simulation of tsunamis e g in the form of n waves based on the various subtopics presented recommendations for future multidisciplinary tsunami research are made it is especially discussed how the combination of sedimentary and geomorphological tsunami field traces and numerical modelling techniques can contribute to derive locally relevant tsunami sources and to improve the assessment of tsunami hazards considering the individual pre history and physiogeographical setting of a specific region

localized polymorphic phase transformations in high pressure faults and applications to the physical mechanism of deep earthquakes earthquake mechanisms based on frictional instabilities are widely accepted for relatively shallow earthquakes such mechanisms in unmodified form are highly unlikely for deep earthquakes because of the expected high frictional shear stresses at depths of 300 700 km several alternative mechanisms have been proposed here i discuss a new type of shear instability observed in experiments on ordinary polycrystalline ice and polycrystalline tremolite by my colleagues and me these shear instabilities lead to rapid stress drops and sound emissions and have the following characteristics 1 a single sharp shear zone forms in the maximum shear stress orientation 2 confining pressure does not suppress the instability and under some conditions raising confining pressure pc lowers the differential stress at which it occurs 3 stress drops can occur repeatedly after reloading at about the same differential stress 4 the mean stress vs temperature conditions at which the instabilities occur in ice and tremolite place them in the fields of thermodynamic stability of ice ii and diopside talc respectively although i have not as yet confirmed the existence of these high pressure phases in the shear zones transformation in the shear zone is implicated because such shear instabilities do not occur in similar materials in which polymorphic phase changes do not occur reconstructive polymorphic phase changes localized along shear zones may be a general phenomenon in crystalline materials stressed non hydrostatically near transition boundaries moreover by analogy the reconstructive phase transformations that are thought to occur in deeply subducted lithosphere may lead to localized shear instabilities manifested by deep earthquakes and produce the observed double couple first motion distribution finally if this is the earthquake source mechanism in deeply subducted lithosphere then earthquakes should shut off when all of the polymorphic phase changes have occurred this may explain the maximum depth of earthquakes at about 680 km

weathering of the new albany shale kentucky usa i weathering zones defined by mineralogy and major element composition abstract comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks here minerals that release and fix major elements during progressive weathering of a bed of devonian new albany shale in eastern kentucky are documented samples were collected from unweathered core parent shale and across an outcrop excavated into a hillside 40 year prior to sampling quantitative x ray diffraction mineralogical data record progressive shale alteration across the outcrop mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange altered primary minerals include k feldspars plagioclase calcite pyrite and chlorite secondary minerals include jarosite gypsum goethite amorphous fe iii oxides and fe ii al sulfate salt efflorescence the mineralogy in weathered shale defines four weathered intervals on the outcrop zones a c and soil alteration of the weakly weathered shale zone a is attributed to the 40 a exposure of the shale in this zone pyrite oxidization produces acid that dissolves calcite and attacks chlorite forming gypsum jarosite and minor efflorescent salt the pre excavation active weathering front zone b is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt jarosite and minor goethite intensely weathered shale zone c is depleted in feldspars chlorite gypsum jarosite and efflorescent salts but has retained much of its primary quartz illite and illite smectite goethite and amorphous fe iii oxides increase due to hydrolysis of jarosite enhanced permeability in this zone is due to a 14 loss of the original mass in parent shale denudation rates suggest that characteristics of zone c were acquired over 1 ma compositional differences between soil and zone c are largely attributed to illuvial processes formation of additional fe iii oxides and incorporation of modern organic matter

mineral evolution of acid forest soils in the strengbach catchment vosges mountains n e france abstract sand silt and clay fractions were analysed to characterise different soil forming processes of two acid forest soils from the strengbach catchment on the northern slope a podzolic soil was formed on only slightly hydrothermally altered brezouard granite and on the southern slope was an acid brown soil derived from granite strongly influenced by hydrothermal activity during hydrothermal alteration the parent material of the acid brown soil became enriched in fine grained white mica simultaneously the rock became more coherent in dissolution voids of albite favourable conditions for the subsequent neoformation of smectite were created physical weathering during the quaternary period produced high amounts of clay by release of illite and smectite from coarser particles although soil conditions are favourable to podzolisation the hydrothermal decrease in al rich minerals results in lower amounts of poorly crystalline compounds and less intensively hydroxy al interlayered 2 1 phyllosilicates illite evolved partly into interstratified illite vermiculite an intrazonal acid brown soil was developed at this site on the less hydrothermally altered material clay percentages are lower and podzolisation developed as expected in the surface horizon illite smectite was derived from illite dissolution of minerals and production of poorly crystalline compounds were even enhanced by lateral accumulation of albite rich material

aluminium solubility controls in acid waters the need for a reappraisal abstract stability diagrams have been frequently used to demonstrate aluminium solubility controls in acidic stream and soil waters this paper shows that it is possible by this method to generate apparent controls using random numbers in place of stream chemistry data thermodynamic arguments demonstrate that a wide variety of reactions can produce relationships similar to al oh 3 solubility controls it is proposed that stability diagrams alone should be used with great caution in identifying aluminium solubility controls taking care that their axes are independent thermodynamic solubility calculations should be used with due scepticism supplementary investigations should be used where possible to identify phases precipitating or dissolving

micromorphological changes as an indicator of the transition from glacial to glaciofluvial quartz grains evidence from svalbard abstract the micromorphology of quartz grains in a sedimentary environment is determined by the transport mechanism and the nature of weathering both these aspects change during the transport history of grains thus important questions include how are quartz grains affected by possible changes in the transport medium and how quickly do the different micromorphological features develop or disappear the main goal of this study was to characterize the changes in the micromorphological features of quartz grains during the transition from a glacial to a glaciofluvial environment and to identify a set of diagnostic microtextures that can be used to distinguish between glacial and glaciofluvial quartz grains the samples came from the moraines of the bertilbreen and horbyebreen glaciers svalbard and from the sediments of glacier fed rivers in the forelands of these glaciers a total of 30 different micromorphological features was observed on 800 different quartz grains from 13 samples of glaciofluvial sediment and 3 samples of glacial sediment it was found that the frequency of rounded grains v shaped pits meandering ridges and cemented microblocks on glaciofluvial grains increased significantly with increasing length of fluvial transport whereas the frequency of angular grains straight steps straight and curved grooves adhering particles pitting and oriented etch pits decreased significantly different types of micromorphological features of quartz grains change with fluvial transport at different rates adhering particles after the first kilometer of fluvial transport straight steps and meandering ridges after the second kilometer of fluvial transport and v shape pits angular shape and straight grooves after the third kilometer of fluvial transport are reliable mechanical micromorphological features for distinguishing between glacial and glaciofluvial quartz grains

analysis of barrier island surface sediments by scanning electron microscopy abstract the analysis of quartz grain surface microtextures from a sedimentary environment where grain transport and depositional pathways were closely interconnected allowed insight into subtle microfeature alteration during movement between subenvironments four fire island new york and one montauk point beach sample were analysed principally through use of a checklist approach using 36 common surface features beach overwash floodtidal delta dune and inlet grains displayed similar surface features only the latter two samples displaying distinctive microtextural patterns the pattern of development of inlet grains was related to the application of higher shear stresses on the grains during transport in the shallow channel the results from dune grains testify to the effectiveness of aeolian transport mechanisms in rapidly altering existing features glacially derived microtextures altered by subsequent subaqueous action were prevalent but whether these glacial microfeatures are derived from the headland region montauk point or from a closer offshore glacial lobe source is not determined comparison of offshore lobe and adjacent sediments revealed contrasting surface and morphological differences statistical treatment of checklist data in binary form 1 0 using stepwise discriminant analysis proved workable but more rigorous testing is required to prove its relevance and use in deciphering raw textural data

the loess section at borden kent se england a 5 3m profile originally described as loess with a buried interglacial soil is reinterpreted from petrographic evidence and thermoluminescence dating as a holocene colluvial accretionary soil mineralogical analyses of coarse silt 16 63 m fractions suggest that most of the silty colluvium was derived from weathered thanet beds upslope though some loess was incorporated during the final depositional phase thin sections show that clay illuviation occurred penecontem poraneously with deposition of colluvium thermoluminescence properties suggest partial optical bleaching of the grains during rapid deposition which is consistent with a holocene colluvial origin

an 800 kyr record of dune emplacement in relationship to high sea level forcing cooloola sand mass queensland australia abstract the cooloola sand mass is a large coastal dune field situated in southeast queensland australia and is part of a much larger system of coastal dune fields including the world s largest sand island fraser island as well as moreton island and stradbroke island cooloola is characterised by a sequence of onlapping parabolic dune units that have been emplaced episodically over the pleistocene and holocene the tectonically stable coastline of se queensland is an ideal area to study the driving mechanisms of coastal dune development as sea level variability is driven primarily by glacial eustasy geomorphic and chronostratigraphic analyses have identified seven major periods of dune activity with the earliest phase of deposition occurring ca 800 ka subsequent periods of dune emplacement date to about ca 150 ka 110 ka 10 6 ka 5 3 5 ka ca 2 ka and 0 4 0 2 ka the holocene dune activity coincides with the last stages of post glacial marine transgression and suggests these large parabolic dunes formed in response to rising sea levels it is likely that this pattern is consistent through the pleistocene and the mis 5 interglacial period is also recorded for earlier events the large absolute errors on the ages make interpretation difficult there is a notable absence of osl ages dating to the last glacial maximum and no ages that are unambiguously associated with lowstand periods this is most likely because the coast would have been 60 km offshore of its current position during lowstands limiting sediment supply and wind energy at the modern coast these results provide strong evidence that coastal dune fields in se australia are predominantly emplaced during sea level rise as originally proposed in the cooper thom model

a comparative sem study on the micromorphology of glacial and nonglacial clasts with varying age and lithology preliminary research on striated clasts from a variety of depositional environments suggests that scanning electron microscopy sem of striated clasts of varying lithology in diamictons may prove useful in interpreting a glacial origin evaluating whether sem analysis of clasts from diamictons is an applicable technique to define a glacial origin requires a better understanding of the microfeatures occurring on glacial and nonglacial clasts we describe microtextures and surface characteristics for samples of quartzite granite limestone basalt chert pillow basalt and quartz pebbles collected from a variety of depositional environments our study suggests that it is possible to differentiate between glacial and nonglacial deposits based on frequency and morphology of diagnostic surface microfeatures observed on entrained clasts these microfeatures are best preserved and identified on competent and monomineralic samples e g quartzite chert limestone and poorly preserved on less resistant and p

the influence of mineralogy on weathering rates and processes in an acid sensitive granitic catchment abstract weathering in an upland catchment on granitic parent material has been studied by chemical and mineralogical analyses of soils long term weathering rates for base cations calculated from chemical analyses of the mineral horizons from soil profiles using zr as an internal immobile index element are among the smallest recorded for scottish soils 1 7 3 1 meq m 2 a 1 indicating that these soils are susceptible to acid deposition sodium is the base cation lost to the greatest extent from the soils due to weathering of plagioclase feldspar mainly in the coarse size fractions calcium is lost not only from plagioclase feldspar but also from hornblende grains of which show dissolution etch pits and denticulate surface features when examined by scanning electron microscopy weathering of hornblende present in basic inclusions in the granite is a significant weathering process in these soils a range of values for 87sr 86sr ratios in stream waters confirms the spatial variability of the material supplying ca to the streams the current weathering rate calculated from input output budgets to be 28 9 meq m 2 a 1 is much greater than the long term weathering rate but small compared to other catchments on similar parent material

geomorphological control on boulder transport and coastal erosion before during and after an extreme extra tropical cyclone extreme wave events in coastal zones are principal drivers of geomorphic change evidence of boulder entrainment and erosional impact during storms is increasing however there is currently poor time coupling between pre and post storm measurements of coastal boulder deposits importantly there are no data reporting shore platform erosion boulder entrainment and or boulder transport during storm events rock coast dynamics during storm events are currently unexplored here we use high resolution daily field data to measure and characterize coastal boulder transport before during and after the extreme northeast atlantic extra tropical cyclone johanna in march 2008 forty eight limestone fine medium boulders n 46 and coarse cobbles n 2 were tracked daily over a 0 1 km2 intertidal area during this multi day storm boulders were repeatedly entrained transported and deposited and in some cases broken down n 1 or quarried n 3 during the most intense days of the storm eighty one percent n 39 of boulders were located at both the start and end of the storm of these 92 were entrained where entrainment patterns were closely aligned to wave parameters these data firmly demonstrate rock coasts are dynamic and vulnerable under storm conditions no statistically significant relationship was found between boulder size mass and net transport distance graphical analyses suggest that boulder size limits the maximum longshore transport distance but that for the majority of boulders lying under this threshold other factors influence transport distance paired analysis of 20 similar sized and shaped boulders in different morphogenic zones demonstrates that geomorphological control affects entrainment and transport distance where net transport distances were up to 39 times less where geomorphological control was greatest these results have important implications for understanding and for accurately measuring and modelling boulder entrainment and transport coastal managers require these data for assessing erosion risk 2016 the authors earth surface processes and landforms published by john wiley sons ltd

loess in italy genesis characteristics and occurrence abstract there is currently a renewed interest in loess genesis and occurrence in italy well known loess profiles in northern italy have been re examined and previously unknown loess deposits in central and southern italy have been reported this work combines a meta analysis of published data with new data presented here for the first time to provide the state of the art on the spatial distribution characteristics genesis and deposition ages of loess in italy a database of 98 soil horizons from 91 soil profiles was created and made available it stores information on soils formed from loess or containing layers that show admixture of loess soil data include the source of information the topographic geomorphological and geological setting kind of parent material and land use main soil horizon properties as described in the field soil classification particle size distribution and chemical data loess is reported from almost all regions of italy it is generally pedogenized throughout the entire loess body and forms the parent material of deep and complex soil profiles the thickness of the loess deposits varies from a few decimeters to a few meters pedogenesis and local reworking partially change the original loess characteristics in this study we propose a set of parameters that help recognizing loess in soils particle size distribution and sorting geomorphological setting pedostratigraphic position shape of the grains under optical and scanning electron microscope sem and soil micromorphological characteristics the ages of the loess deposits range between 70 ka bp and 18 ka bp there are also a number of samples that have been dated to the holocene the meta analysis suggests that climate is not the only driver of loess deposition in italy geomorphological instability and human disturbance as well as the influence of saharan dust most likely played major roles too this study demonstrates that loess is much more widespread in italy than previously estimated yet further research on the spatial and temporal distribution of loess deposition across the mediterranean region is needed to better understand its genesis sources and trajectories periods of enhanced loess formation and the role of loess deposits in ecosystem functioning and resilience

scanning electron microscope study of zircons and rutiles from a podzol chronosequence at cooloola queensland australia summary a chronosequence of four soils derived from aeolian deposited sand at cooloola along the eastern coast of southern queensland has been studied to document predepositional and pedogenic changes in zircon and rutile grains in the fine sand fraction 53 125 m with increasing soil age the soils range in age from holocene typic quartzipsamment presently drifting sand to mid pleistocene spodic quartzipsamment 90 ka bp parent materials are moderately stratified sands with irregular depositional layers in places having high concentration of heavy mineral grains scanning electron microscopy was used to characterize grain surface microtexture by a semi quantitative method based on frequency of occurrence of ten classes of surface microtextures pedogenic changes were quantified and differences between horizons in the same profile between different profiles within the same horizon and between minerals were tested for significance using the 2 distribution zircon grains are less chemically weathered during pedogenesis than rutile possibly due to the higher iron content of the latter however zircons tend to show more features which can be associated with physical alteration rutile grains in the illuviated b2hs horizons of the troporthod and spodic quartzipsamments are more thickly coated with poorly crystalline iron and alumino silicate compounds compared with zircon grains and the presence of grain coatings does not seem to have prevented the surfaces of grains from developing solution pits with increasing age there is a preponderance of weathering features on grains of both minerals the presence of various shapes and surface microtextures on grains from the different soils suggests a multiple grain source for zircon and rutile and a complex predepositional history for these minerals nevertheless microtextural features of zircons and rutiles are valuable for the interpretation of the extent and nature of post depositional weathering

thermodynamic constraints on phase changes as earthquake source mechanisms in subduction zones abstract application of thermodynamic equations for phase transitions with a shock wave output from metastable to stable phases that are believed to occur in subduction zones indicates that while many show a volume reduction and thus may contribute to slab pull mechanisms of plate tectonics they do not satisfy criteria for the generation of shock waves of the reactions considered only one antigorite clinoenstatite forsterite talc satisfies the criteria and for this case the shock wave pressure is in fact less than the pressure calculated for the leading edge of the subduction zone this would imply that if the transition does occur under shock conditions in the subduction zone dilatational rather than compressional first motions for the associated earthquake are expected

mineral weathering in forest soils and its relevance to the preservation of the buried archaeological resource there is more woodland in britain now than for many centuries and considering many international climate change mitigation policies woodland cover both in britain and internationally is being promoted however neither the management of existing woodlands nor their expansion should be at the expense of important archaeological evidence due to the large number of known archaeological sites the large areas of land with uninvestigated archaeological potential and the expanding woodland cover suitable mitigation strategies need to be developed to allow preservation in situ of important sites an understanding of how woodland soils and the buried archaeological resource interact is therefore essential this paper utilises ongoing environmental research into the mineral weathering rates in forest soils and considers its application to artefact preservation the study concludes that soil water ph its movement and the saturation of dissolved ions in the soil solution are major factors determining both mineral and artefact longevity a simple guide to artefact longevity based on these properties is proposed and a geochemical model for predicting loss is tested these tools could be applied to any soil or individual horizon irrespective of land use

pedogenic processes and domain boundaries in a vertisol climosequence evidence from titanium and zirconium distribution and morphology abstract the occurrences of titanium ti and zirconium zr within eight vertisols formed in a climosequence on the upper beaumont formation of the texas gulf coastal plain were investigated in order to determine processes responsible for ti and zr redistribution during pedogenesis discontinuities defined by significant shifts in particle size distribution and the content in volume percent of zr are present at 160 to 260 cm depth in each pedon the discontinuities are interpreted to be functional boundaries i e physico chemical expressions of pedogenic domains between an upper soil domain dominated by open system pedogenesis and a lower more closed system domain dominated by chemical weathering the depth at which the functional boundary occurs is dependent on physical and hydrogeochemical influences which are largely a function of available water soil materials above the discontinuities are slightly coarser textured and enriched in zr whereas below the sediments are finer textured and have lower and more constant zr contents the zr is associated almost exclusively with zircon and zr contents correlate positively to the weight percent sand coarse silt with negligible zr present in the profile volume loss gain i e soil strain e a mass balance calculation that assumes zr or ti immobility during pedogenesis indicate ezr values nearly four times greater than eti large values of ezr within the upper soil domains are due primarily to sand and coarse silt additions to the vertisols and preclude use of zr as a basis of mass balance calculations in these soils despite its relative chemical stability by comparison ti is generally conserved within the clay rich soil profiles and is therefore better suited for mass balance calculations of volume change and mobile element translocation during pedogenesis

advantages of beachrock slabs for interpreting high energy wave transport evidence from ludao island in south eastern taiwan abstract powerful typhoons frequently affect eastern taiwan on dabaisha beach on the sw coast of ludao island a small volcanic island lying se off mainland taiwan the presence of numerous beachrock slabs provides evidence of the sediment transport capabilities of high energy waves generated by these storms with a well defined beachrock source from which the slabs were derived it is easy to differentiate clasts transported in run up or backwash flow based on their current position relative to the outcrop in order to estimate the wave generated flow velocities from the measured beachrock slabs the hydrodynamic equations for boulder transport by nandasena et al 2011 have been rearranged so that they are appropriate for this particular geomorphic setting where exposed in situ beachrock outcrops liberate clasts which may then be transported either by run up onto the beach or backwash flow onto adjacent reef platforms such settings are common on tropical coastlines with fringing coral reefs and beaches comprising mostly biogenic sediments in the dabaisha beach case the lowest flow velocities required to transport all measured beachrock slabs from their source outcrop to current positions are 2 18 3 16 m s for run up and 1 76 3 24 m s for backwash with a discussion of advantages and limitations on the use of beachrock clasts for interpreting wave behaviour this paper presents another proxy for studying high energy wave events that is highly suitable for certain carbonate rich coastlines

the role of trace minerals in chemical weathering in a high elevation granitic watershed estibere france chemical and mineralogical evidence we investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the pyrenees france the sites were located on glacial deposits derived from similar hercynian 300 ma granites characterized by the occurrence of zoned plagioclases and trace calcic phases epidote prehnite sphene apatite the surface waters at those sites show high ca na molar ratios 1 which could not be explained by the dissolution of the major plagioclase oligoclase present in the rocks the coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale the weathering of the trace calcic minerals which represent 1 of the total rock volume are responsible for more than 90 of the calcium export at the sites annual cationic fluxes 23 104 eq km2 yr calculated for the estibere watershed are among the highest reported for high elevation systems draining granitic rocks and 80 of this annual cationic flux can be attributed to the weathering of trace calcic phases calculations based on isotopic values 87sr 86sr go in the same direction except apatite the trace calcic phases appear to be mainly silicates thus the type of chemical weathering observed in the estibere watershed may have an influence on atmospheric co2 consumption by granite weathering however comparison with other watersheds draining granitic environments worldwide and with the two other sites in the pyrenees indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering e g high elevation catchments on glacial deposits other factors such as the date of glacial retreat the physical denudation rate the hydrological functioning of the watershed and the nature and structure of the soil cover are also important

role of shallow phase changes in the subduction of oceanic crust detailed studies of the seismicity of several subduction zones demonstrate that shallow dipping thrust zones turn to steeper angles at depths of about 40 kilometers an increased downward body force resulting from shallow phase changes in subducted oceanic crust may be the cause of this increased dip angle in addition the volume reduction associated with phase changes may produce sufficiently large stresses in neighboring rocks to cause the seismicity of the upper benioff zone

waves coastal boulder deposits and the importance of the pre transport setting the pre transport environment of a coastal boulder along with its shape size and density determines the height of wave required for it to be transported different forces act on sub aerial boulders as opposed to submerged boulders when struck by a wave boulders derived from joint bounded blocks on shore platforms predominantly experience lift force and require a wave of greater height to be transported than boulders in other environments no one equation is applicable to determine the height of palaeo waves responsible for depositing a field or ridge of imbricated coastal boulders a range of equations and their derivation is presented here which can be applied to the respective pre transport environment of a boulder such an approach is necessary when attempting to reconstruct the frequency and magnitude of past coastal wave hazards and for differentiating between tsunami and storm wave deposited boulder fields

pedogenic and geomorphic evolution of a buried dune palaeocatena at magilligan foreland northern ireland abstract field description and laboratory analyses of a complex stratigraphy recently exposed near magilligan point have elucidated the late holocene evolution of magilligan foreland n ireland a marine beach ridge palaeocatena passes northwards into a penecontemporaneous aeolian dune palaeocatena both include soils and peat filled depressions and are overlain by an aeolian dune sand a second dune sand is confined to the south of magilligan foreland the thickness of the decalcified zone of the palaeocatena varies from 0 4 m near the crest of the palaeodune to 2 m below its slopes the palaeodune core exhibits large scale cross stratification enclosing unusual small scale reverse flow cross stratified sets d 90 90 depletion values indicate similar weathering intensities in the palaeocatena and in the overlying sand but deeper weathering in the former a mineral stability sequence has been constructed and unweathered sand identified which indicates the original composition of the magilligan deposits inter profile differences in weathering rates are attributed to variations in local environments

the effect of weathering in the silt fractions on the apparent stability of chlorite in scottish soil clays abstract previous work on chloritic soils in scotland indicated that irrespective of soil type or drainage class the chlorite that was dominant in the clay fractions weathered only slightly showing little variation in amount with depth these soils have been investigated further by determination of the chlorite content in the silt fractions by a quantitative x ray diffraction technique in a dystric cambisol and a placic podzol the fine silt fractions 1 4 20 m contain much more chlorite than the coarse silt 20 75 m and in both fractions the amount of chlorite decreases towards the surface markedly so in the placic podzol it is suggested that chlorite is being dissolved out from the clay fractions but as chlorite is being broken down and transferred to finer particle size fractions this dissolution effect is being masked by the replacement of the clay fraction chlorite from the fine silt analysis of the total soils

sedimentology of rocky shorelines 2 shoreline megaclasts on the north shore of oahu hawaii origins and history abstract limestone megaclasts up to 96 t in weight rest on a coastal rock platform near sunset beach on the north shore of oahu hawaii they occur in seaward dipping imbricate clusters and as solitary clasts the rock platform is subject to large swell waves and very large waves associated with winter storms and tsunami a series of photographs covering the period from ca 1905 to 1996 show episodic rearrangement of megaclasts on the platform and the appearance of new megaclasts near the platform edge the largest solitary megaclast ca 96 t was emplaced on the platform between 1940 and 1950 possibly by the 1946 aleutian tsunami and has moved twice since then in ca 30 m jumps along two different trajectories larger clasts have been broken from the platform edge and emplaced on the platform only by very large wave events whereas formation and movement of smaller tabular clasts ca 30 40 t appear to be a continuously ongoing process on the surface of the rock platform partial detachment of clasts by marine erosion processes along joints and cracks in the limestone bedrock facilitates their complete detachment from both the platform edge and platform surface the larger numbers of megaclasts emplaced on the north and northwest sectors of the platform relative to other sectors are attributed to exertion of maximum wave power on these sectors due to a combination of steep slope and ramp like submarine topography

the assessment of chemical weathering rates within an upland catchment in north east scotland a study has been made of weathering in glendye an upland catchement of heather moorland underlain mainly by granite with some gneiss in north east scotland the concentrations of a range of elements and ions in precipitation and river water were measured over a twelve month period the total input and output of each element or ion was calculated the resulting balances show net outputs of all species except hydrogen ion large net outputs of silicon 38 5 kg ha 1 a 1 and bicarbonate 48 kg ha 1 a 1 indicate considerable chemical weathering a large net output of chloride 32 kg ha 1 a 1 indicates the importance of dry deposition of oceanic aerosols when this is allowed for the rate of output of elements due to weathering is si ca na mg k fe al these results were compared with the abundance of elements in bedrock and differential weathering ratios calculated these are compared with data from the hubbard brook study in new hampshire in both cases calcium is by far the most mobile element the relative importance of the atmosphere and of chemical weathering as sources of each element was calculated and the results compared with those of a study at wet sleddale in the lake district similar patterns emerge in both cases

development of a feldspar weathering index and its application to a buried soil chronosequence in southeastern england abstract an index of feldspar weathering ifw has been developed based upon the assignment of individual grains to weathering classes defined in terms of progressive changes in surface morphology identifiable under a polarising microscope the index was used to test the hypothesis that profiles of a buried paleosol developed on the higher terraces of the river thames in southeastern england are more weathered than those formed on lower and younger terrace surfaces ifwr ratio between the ifw of soil and parent material and ifwd difference between the ifw of soil and parent material values support a trend of increased weathering with assumed terrace age although the pattern is less clear and conclusive towards the base of the terrace sequence anomalies in the dataset can be attributed to a range of factors including the possible variable composition and structure of the feldspars the nature of the parent material samples and probable fluctuations in soil processes and environments over time notwithstanding these problems some of which are specific to the study reported here the technique and general approach clearly have more widespread potential for the semi quantitative comparison of the relative weathering statuses of soils

changes in the rate of release of ca and mg and normative mineralogy due to weathering along a 5300 year chronosequence of boreal forest soils changes in the normative mineralogy and chemical weathering rates elemental loss of ca and mg from the uppermost mineral soil horizon were determined at five forested sites in the boreal zone forming a chronosequence the sites were all located on the same glaciofluvial esker deposit well sorted sand over a distance of 27 km in the coastal region of the gulf of bothnia in finland and had estimated ages from 339 to 5276 years because of isostatic land uplift the region is continually emerging from the sea the rates of which are known allowing the age of current surfaces to be dated soil profile development progressed from gleyic arenosols youngest and nearest the coast through haplic arenosols to haplic podzols 3 oldest and furthest away from the coast elemental concentrations of soil 2 mm were determined using xrf and icp ms from a hot aqua regia digest normative mineralogy was determined using these data and a stoichiometric mineral distribution model weathering elemental loss rates were calculated using xrf concentrations and normative quartz as the conservative reference component quartz was increasingly enriched in the uppermost horizon with soil age commensurate with the loss of easily weathered minerals using quartz as the conservative component the mass residual fraction remaining in the uppermost soil horizon of the oldest soil was 0 27 0 35 and 0 57 respectively for biotite hornblende and anorthite which are important sources of ca and mg b e horizon ratios of hydrous aluminosilicate contents increased from 1 to 14 with soil age clearly indicating the increase in degree of podzolisation the losses of ca and mg increased with soil age but at a decreasing rate ca and mg losses for the youngest soil were respectively 3 3 and 1 8 mol m 2 corresponding values for the oldest soil were 10 6 and 10 5 mean rates of loss for the youngest soil were 10 and 5 mmol m 2 yr 1 for ca and mg respectively and corresponding values for the oldest soil were 2 mmol m 2 yr 1 for both ca and mg the loss of these base cations from the soil will have resulted in a lower acid neutralizing capacity and increased sensitivity of these soils to acidic deposition and represents a reduction in the soil reserve of important plant nutrients

geochemistry of soils of king george island south shetland islands west antarctica implications for pedogenesis in cold polar regions fine fractions of soils on the barton peninsula king george island west antarctica have been forming during the last 6000 yr since the last deglaciation texturally they are mostly composed of mineral and rock fragments with some volcanic ashes which are also indicated by geochemical compositions representing for the nonclay silicate minerals and low values of chemical index of alteration no significant changes are observed in major and trace element abundances such geochemical characteristics suggest that chemical weathering of bedrocks on the barton peninsula seems insignificant and that the soils are composed of physically weathered mineral and rock fragments which are mixed with eolian additions of volcanic ashes and patagonian dusts chondrite normalized rare earth element ree distribution patterns of the barton peninsula soils are slightly different from those of bedrocks indicating that the ree abundances and characteristics were influenced by eolian additions mixing calculations which mass balance the rees suggest that volcanic ashes blown from deception island were the major eolian contributor followed by atmospheric dusts sourced from patagonia south america even in the warmer and humid climatic conditions in the maritime antarctic region the chemical weathering of bedrocks appears to be insignificant probably due to the relatively short duration of weathering since the last deglaciation

sedimentation et fracturation de haute energie en milieu recifal tsunamis ouragans et cyclones et leurs effets sur la sedimentologie et la geomorphologie d un atoll motu et hoa a rangiroa tuamotu pacifique se abstract a longitudinal festoon fracture of the reef flat widened by slow biological and mechanical erosion transverse along the grooves divides the nw coral rim of rangiroa tuamotu se pacific into colossal blocks 15 10 5 m 1500 t the elaboration of these blocks can be attributed to the dislocation of the top of the reef flat by catastrophic events tsunamis or hurricanes typhoons in the sw and s pacific the shifting of these blocks mega boulders would necessitate a considerable amount of energy and at present we cannot decide which one of these phenomena was responsible various examples observed in the pacific are cited to illustrate abrupt changes in the sea level these could be attributed either to meteorological events hurricanes cyclones or typhoons or to seismic events of very high energy ground sea or tsunamis the reader is reminded of the different characteristics that these phenomena produce this study is mainly concerned with tsunamis especially the frequency of their occurrence energy and effects on the coasts of small oceanic islands hurricanes cyclones and typhoons roughly originate from the n ne and e whereas tsunamis originate from all directions except from se s and sw angle these very high energy events hurricanes and tsunamis seem then to be responsible for 1 the decreasing grain size of the coral rim sediments from the ocean to the lagoon through the range of colossal blocks smaller boulders scree gravels coarse and fine sands 2 the sedimentary accretion of the motu itself at each very high energy so called catastrophic event they are also responsible for the preservation of the two characteristic geomorphic forms of an atoll motu and hoa 3 finally the alternation motu hoa motu etc on the coral rim this alternation seems to result from the interaction between oceanic disturbances hurricanes or tsunamis and the water volume which must flow over the coral rim the transported material the reef flat and the angle of incidence between the swell and the coast during these catastrophic events

threshold height of coastal cliffs for collapse due to tsunami theoretical analysis of the coral limestone cliffs of the ryukyu islands japan abstract stability analyses were made for both gravity and wave induced collapses of coastal cliffs with a vertical failure surface to determine the threshold cliff height for tsunami induced collapses the models proposed in this study have two distinct parameters characterizing the cliff height calculations of the critical notch depth from these models show that gravity induced collapses occur on cliffs of any height whereas the threshold cliff heights for tsunami induced collapses are controlled by the height of the tsunamis the relation between the threshold cliff height and the tsunami height is represented by a power law function

hydrodynamic evolution from quartz microtextures of a beach ridge in qinghai lake china abstract beach ridges are landforms that exist on beach shorelines and can supply abundant information regarding palaeoenvironments to better understand the hydrodynamic processes of beach ridges a quartz microtexture analysis was carried out in this study the microtextural features of a total of 1063 quartz grains from seven beach ridge samples and eight reference samples from rivers a dune and a nearby beach were observed and analysed by scanning electron microscopy the qualitative and quantitative results suggest that the quartz microtextures of the beach ridge samples present more fresh surfaces and percussion marks than the river samples but less angularity the upper sequence samples from the beach ridge present higher values of fresh surfaces and percussion marks and lower dissolution than the lower sequence samples a cluster analysis shows that the hydrodynamic conditions of qinghai lake underwent pronounced changes from weak to strong and then to weak at the present time furthermore quantitative analyses indicate that the beach ridge and river sedimentary environments can be distinguished through the microtextural features of the 250 125 m size fraction however more grain size fractions should be observed and analysed to interpret the hydrodynamic conditions the quartz microtextural analysis of beach ridges may be an effective method reflecting the palaeohydrodynamic conditions

a seismological constraint on the depth of basalt eclogite transition in a subducting oceanic crust the oceanic crust primarily has a basaltic composition1 2 which must transform into eclogite on subduction of the oceanic crust beneath continents3 4 there has been a considerable debate about the role of the basalt eclogite transformation in driving lithospheric plate motion5 and in the thermal regieme of subducting plates6 how important this transformation is in tectonics critically depends on the depth of transformation which is affected by factors such as temperature7 8 bulk rock chemical composition2 water content9 and perhaps stress environment becuase it would be practically impossible to evaluate all these factors correctly we attempt here to constrain the transformation depth by a more direct seismological method

coastal erosion rates of lava deltas around oceanic islands abstract rates of coastal erosion are needed for planning purposes and to improve understanding of how the shelves of islands develop ultimately becoming submerged banks near shore submarine platforms created by erosion of lava deltas of known age provide an opportunity to quantify erosion rates and to investigate how those rates vary between different types and ages of lava flows as well as how they vary with wave climate we have compiled data on deltas formed during historical and holocene eruptions age 6 ka from both a and p hoehoe lava flows and from diverse localities azores and hawaiian islands and ascension island near shore platforms were interpreted from multibeam sonar bathymetric light detection and ranging lidar and historical sounding data from them we estimated time averaged shoreline retreat rates from the seaward distances between the modern coastlines and the submarine platform edges the 35 interpreted platforms have rugged dipping surfaces left behind by erosion with an average gradient of 5 range 2 10 eroded distance of 436 m 78 1119 m and depth of platform edge of 25 m 5 56 m to evaluate the latter depths we computed seabed orbital speeds due to surface waves at the platform edges depths of platform edges correlate only modestly with those speeds suggesting that platform surfaces have adjusted to wave conditions with a wide range of particle sizes and hence thresholds of motion the largest retreat distances 800 m are associated with platforms of the central azores islands which are exposed to higher waves however retreat rates are highly varied 0 08 12 5 m yr and weakly correlated with measures of wave power suggesting that waves are only a secondary influence given that lack of correlation we suspect that the main factor contributing to variability arises from varied cliff resistance to erosion blocks between joints in lava flows and hence resistance to erosion vary greatly in size from the thicker and less densely jointed a flows to the thinner and shell like layered lavas in p hoehoe flows

mass fluxes and clay mineral formation in soils developed on slope deposits of the kowarski grzbiet karkonosze mountains czech republic poland abstract weathering mineral formation and transformation processes along slopes are complex in cool mountainous regions undisturbed soil development with a strong vertical leaching element may abruptly change as a result of erosion accumulation lateral water fluxes and aeolian input we investigated soils in the eastern karkonosze mountains that have developed on silicatic slope deposits to date illite vermiculite and chlorite are the minerals that have been detected in the clay fraction although the climate and parent material should be favourable for the formation of smectites expandable phases were not verified so far we investigated if expandable phases could be detected and how they related to elemental fluxes along a short slope sequence 1142 1268 m a s l on the border between the czech republic and poland mass balance calculations indicated intensive mineral weathering together with a significant leaching of mg al ca and mn on the shoulder and foot slope positions in the middle zone which has a concave or undulating surface shape however the mass balances of several elements na k al p revealed a less pronounced leaching corresponding to a lower degree of podsolization and in some cases even accumulation at all sites mass balance calculations and detected soil minerals e g the increase in illite towards the surface together with an increase in al and k indicate some aeolian input kaolinite was detected in all soil horizons its concentration slightly increased towards the soil surface together with the pronounced leaching of ca part of kaolinite originates from plagioclase weathering besides being a weathering product of primary minerals part of the kaolinite is inherited from the parent material and probably is also due to aeolian input in all soils illite was being transformed into vermiculite and smectites through regularly interstratified illite smectite phases in addition the content of chloritic components which increases with depth indicated their concurrent weathering and transformation into smectites amphibole also may have acted as a source of smectites not all smectite is being actively formed in the soil most likely due to slope processes cover beds that affected even the subsoil some smectite has been transferred along the slope part of the smectite also seems to derive from the parent material active formation of expandable clay minerals is related to convex and planar landscape forms this relationship suggests intense element leaching inheritance from the parent material and cover bed mixing processes have contributed to the presence of smectite along the slope zones with predominant vertical transport shoulder foot slopes may repeatedly be interchanged with zones dominated by lateral transport undulating slope concave forms

extraordinary boulder transport by storm waves west of ireland winter 2013 2014 and criteria for analysing coastal boulder deposits abstract before and after photos of supratidal coastal boulder deposits cbd in the west of ireland show that storms in the winter of 2013 2014 transported boulders at elevations up to 29 m above high water and at inland distances up to 222 m among the clasts transported are eighteen weighing more than 50 t six of which exceed 100 t the largest boulder moved during those storms weighs a fairly astonishing 620 t the boulders moved in these recent storms provide pinning points for mapping storm wave energies on coasts their topographic positions mark elevations and distances inland reached by wave energies sufficient to dislocate those specific masses taken together the cbd data reveal general relationships that shed light on storm wave hydrodynamics these include a robust correlation inverse exponential between maximum boulder mass transported and emplacement height above high water the greater the elevation the smaller the maximum boulder size with a dependency exponent of about 0 2 times the elevation in metres there is a similar relationship although with a much smaller rate of change exponent 0 02 between boulder mass and distance inland which holds from the shoreline in to about 120 m coastal steepness calculated as the ratio of elevation to inland distance seems to exert the strongest control with an inverse power law relationship between maximum boulder mass and slope ratio the more gentle the topography the larger the moved boulders quantifying cbd dynamics helps us understand the transmission of wave energies inshore during high energy storm events the transported boulders documented here are larger than many of those interpreted to have been moved by tsunami in other locations which means that boulder size alone cannot be used as a criterion for distinguishing between tsunami and storm emplacement of cbd the biggest blocks up to 620 t are new maxima for boulder mass transported by storm waves we predict however that this record will not last long the 2013 2014 storms were strong but not extreme and there are larger boulders in these deposits that didn t move on this occasion bigger storms will surely move larger clasts and clasts at greater distances from the shoreline these measurements and relationships emphasise the extreme power of storm waves impacting exposed coastlines and require us to rethink the upper limits of storm wave energy at coasts

tidal current dominated depositional environments in the central northern yellow sea as revealed by heavy mineral and grain size dispersals abstract this study confirms that the fine sand sized detritus in the central northern yellow sea is chiefly derived by the yellow river and explains the holocene yellow river dispersal system and the preservation of transgressive deposits by heavy mineral and grain size analyses micas which are sensitive to hydraulic sorting offer an effective key for identifying the dispersal of holocene yellow river derived fine grained sediments the heavy mineral compositional changes are attributed to hydraulic sorting by different marine dynamics and various mixing with additional local transgressive deposits of miscellaneous provenance the effects of hydraulic sorting are dominated by holocene tidal currents and by foreshore waves during the rapid transgression respectively the former results in obvious enrichments of garnet and common stable species such as ti oxides tourmaline and titanite whereas the latter seems more remarkable for the compositional changes with further depletion of epidote actinolite tremolite and zoisite clinozoisite the central yellow sea mud deposit and the alongshore muddy zone off the southern liaodong peninsula are opposite to each other as a pair of structurally symmetric coalesced terminal lobes far away from the high energy strait between cape chengshan and changsan got the haiyang subaqueous clinoform as another terminal lobe is revealed by a heavy mineral index which represents an extremity of deposits accumulated by the modern yellow river derived sediments off the southwestern shandong coast a small mud patch is revealed roughly corresponding to the central regime of the amphidromic system of principal m2 constituent the tidal current dominated depositional pattern proposed here emphasizes the importance of time velocity asymmetry of tidal currents such a dynamic mechanism is primarily responsible for the dispersal of the modern yellow river derived sediments when they are entrained from the bohai sea to the south yellow sea through the bohai strait and the strait between cape chengshan and changsan got

correlation of sandstones using heavy minerals an example from the statfjord formation of the snorre field northern north sea correlation of sandstones using heavy minerals is dependent on the recognition and quantification of provenance sensitive parameters suitable criteria include ratios of minerals that have similar hydraulic and diagenetic behaviour and properties of populations of individual mineral species sandstones of the statfjord formation in the snorre field display marked variations in their heavy mineral assemblages although hydraulic and diagenetic processes have played some part in generating these variations major changes in the nature of the source material can be detected on the basis of heavy mineral ratio and varietal data these changes in sand provenance can be used to produce a detailed stratigraphic breakdown of the sequence and to correlate from well to well eleven heavy mineral zones have been recognised on the basis of variations in monazite zircon garnet zircon and rutile zircon ratios on the incoming of chloritoid and on the composition of garnet populations the marked changes in provenance result from the proximity of the depositional location to the hinterland and it is considered unlikely that the detailed correlation made in the snorre field area applies to statfjord sandstones in other parts of the northern north sea however there is evidence for some degree of allogenic control on the heavy mineral variations and therefore some events may have regional significance

composition and mineralogy of suspended sediment in the fluvio estuarine zone of the loire river france the fluvio tidal transition of suspended sediment in terms of mineralogy and composition in the loire river drainage basin the largest french river basin was investigated in the fluvial zone at montjean and in the tidal zone at mauves thouare for a complete seasonal cycle at montjean where the river experiences unidirectional flow the composition and mineralogy especially clays and clay minerals of river suspended material rsm are governed by the river discharge upstream contributions climatic conditions and microbiological activities however due to reversing tidal and river currents at thouare in the zone of tidal dynamics these relations are changed in the downstream direction sand and clay content in the rsm decrease while the silt content increases among clay minerals between these two observation stations montmorillonite remains constant kaolinite diminishes and the other minerals increase downstream combustible material organic and nitrate no3 contents in the rsm increase whereas the phosphate po43 and caco3 contents decline considerably during transport at the head of the tidal zone where the river flow encounters the tidal influence there is a relatively stationary water mass tidal slack where sands clays phosphate carbonate and silica are deposited by physical and chemical processes physical sedimentation takes place by simple gravitational deposition sands and by sorting and complicated differential settling clays chemical sedimentation takes place by precipitation calcite caco3 apatite ca5 po4 3 oh f cl coagulation of dissolved silica sio2 in connection with seasonal algal bloom and eutrophic events resume le bassin de la loire est le plus vaste bassin fluvial franqais il constitue un domaine de choix pour l etude des apports a l ocean la composition des matieres en suspension mes a eteetudiee sur un cycle saisonnier complet en deux endroits choisis afin de mettre en evidence les effets du principal changement de regime hydrologiyue du fleuve au passage du milieu fluvial au milieu fluvio estuarien soumis a la maree dynamique et donc depourvu d effet de salinite les variations des mes sont regies par les debits liquides les apports du bassin versant les conditions climatiques et les activites biologiques et microbiologiques dans la zone ou s exerce la maree dynamique le lien de ces variations avec celles de debit liquide fluvial est cependant tres perturbe entre les deux stations de mesure les teneurs en sables et argiles diminuent et ies silts augumentent la kaolinite diminue la montmorillonite se maintient constante les interstratifies et i illite croissent les matieres organiques les substances colloidales ainsi que les nitrates augmentent phosphates et carbonates decroissent ces phenomenes peuvent s interpreter ainsi le debit fluvial est contrecarre par le flot ou on observe aussi une zone d imrnobilite relative des masses deau l etale qui produit deux types de resultats dynamiques decantation accelerie des silts aprks attrition des sables triagregation sorting et sedimentation differentiklle des argiles chimiques precipitation de calcite d apatite de silice sous confrole biogeochimique saisonnier etiages algual bloom d ete succedant aux crues et aux apports detritiques d hiver

extreme water velocities topographical amplification of wave induced flow in the surf zone of rocky shores water velocities as high as 25 m s 21 have been recorded in the surf zone of wave swept rocky shores velocities more than twice the phase speed of the breaking waves with which they are associated how can water travel twice as fast as the waveform that initially induces its velocity we explore the possibility that the interaction of a wave with the local topography of the shore can greatly amplify the water velocities imposed on intertidal plants and animals experiments in a laboratory wave tank show that interactions between bores refracted by a prowlike beach can produce jets in which the velocity is nearly twice the bore s phase speed this velocity can be further amplified by a factor of 1 3 1 6 if the jet strikes a vertical wall this type of topographically induced amplification of water velocity could result in substantial spatial variation in wave induced hydrodynamic forces and might thereby help to explain the patchwork nature of disturbance that is characteristic of intertidal communities

faulting associated with the olivine to spinel transformation in mg2geo4 and its implications for deep focus earthquakes samples of metastable mg2geo4 olivine fail by faulting when loaded at temperatures where the incoherent nucleation and growth of spinel the stable phase just becomes possible at lower temperatures where the transformation is inhibited metastable olivine is ductile and strong while at higher temperatures where the transformation happens very quickly samples are ductile and weak microfaults that have just been created and have slipped very little contain only very fine grained spinel those that have slipped more contain a mixture of fine grained spinel and larger broken olivine fragments a new type of transformation microstructure that develops only under nonhydrostatic stress occurs in all specimens that failed the spinel nucleates on grain boundaries and on subgrain boundaries within olivine and grows as fine grained lens shaped bodies with a strong preferred orientation normal to maximum compression the correlation between the onset of transformation the new microstructure and the mechanical instability suggests a cause and effect relationship the grain size of the spinel within the microfaults suggests that these zones have superplastic properties in this case the instability should not be suppressed by increasing pressure as normal frictional processes are suppressed analogous conditions exist in down going slabs of lithosphere in the mantle and we postulate that the same mechanism that causes faulting in our samples operates in the mantle causing deep focus earthquakes

microtextural analysis of quartz grains of tsunami and non tsunami deposits a case study from tirua chile abstract in order to estimate the tsunami hazard it is essential to reliably identify and differentiate tsunami deposits from other high energy events like storms recently the microtextural analysis of quartz grain surfaces was introduced as a method to differentiate between tsunami and other deposits using tsunami deposits sampled from a bank profile of the tirua river central chile an area that was significantly affected by the 2010 and 1960 chile tsunamis we tested the microtextural analysis method for its capability to identify tsunami deposits a total of 815 quartz grain surfaces of two tsunami layers two non tsunami marsh sediment samples and three reference samples from nearby beach dune and river were analyzed using scanning electron microscopy sem we grouped the detected microtexture features into five microtextural families angularity fresh surfaces percussion marks adhering particles and dissolution features both the tsunami deposits and reference samples reveal high numbers of fresh surfaces and percussion marks thus there are no statistically significant differences between tsunami beach dune and river deposits in characteristics and abundances in all microtextural families our study indicates that the microtextural analysis of quartz grains may not be a suitable method to identify tsunami deposits in tirua chile due to local factors such as high numbers of inherited microtextures and the possible effects of the high amount of heavy minerals

zircon an immobile index in soils interpretation of any element s mobility in soils needs rigorous means of calculating losses or gains in relation to parent rock the first mass balance calculations were based on isoelement changes major elements during conversion of fresh rocks to weathered materials harrisson 1933 leneuf 1959 isovolumetric mass balance calculations were applied for the first t ime in 1955 to determine mass transfers in saprolite millot and bonifas 1955 since that time numerous works have been carried out on mass balance calculations in determining transfers during weathering brimhall and dietrich 1986 recently equations used to calculate volumetric changes and net mass gain or loss of mobile elements have been based on zirconium mostly from the mineral zircon the aim of the paper is to question the axiomatic immobility of zircon in soils and then to assess the limit of mass balance calculations in surficial weathering systems

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

thermoluminescence dating of the british coversand deposits abstract coversand deposits thought to be of lateglacial age are found in britain in north lincolnshire south west lancashire and central east anglia a comprehensive dating study of them using thermoluminescence tl techniques is currently underway in an attempt to link the british coversand deposits to the european coversand chronology initial results from four of the british coversand sites sampled are presented the 26 tl dates from 14 samples show that in lincolnshire aeolian deposition took place from 12 5 ka to i1 ka cessation of the initial sand deposition was synchronous with this in lancashire but sand deposition occurred significantly earlier in east anglia the upper layers of aeolian sand in lancashire are much younger and are attributed to holocene reworking on the basis of these dates lincolnshire and lancashire coversand deposition occurred at a similar time to the younger coversand ii whilst east anglian coversand deposition coincided with the younger coversand i phase in the european coversand chronology

rocky coasts their role as depositional environments abstract the role of rocky coasts as depositional environments has been generally neglected by rock and depositional coast workers although rock coasts can be hostile sedimentary environments they frequently host a variety of deposits consisting of mixes of boulders and megaclasts to sand and cobbles these deposits include pockets of sand and pebble trapped in topographic depressions or at the foot of scarps and cliffs isolated boulders pocket beaches trapped between headlands and sand to boulder beaches in shallow bays exposed to strong wave action the tectonic setting which is reflected in the degree of geological heterogeneity alongshore together with the wave regime and other elements of the morphogenic environment help to determine the amount and mobility of the sediment and consequently whether it plays an essentially abrasional or protectional role many beaches have a resistant rock foundation which will modulate their response to rising sea level and possibly increased storminess during this century wave refraction and temporal and spatial changes in sediment abrasional and protectional efficacy influence the development of crenulated planforms on coasts with a high degree of geological heterogeneity and possibly on more geologically homogeneous coasts with longshore variations in cliff height or in the amount of sediment theory suggests that these coasts may develop equilibrium planforms with uniform rates of erosion in bays and on headlands or they may undergo a series of cyclical transformations involving alternating increases and decreases in the depth of the bays relative to the headlands