cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

measuring alluvial fan sensitivity to past climate changes using a self similarity approach to grain size fining death valley california the effects of climate change on eroding landscapes and the terrestrial sedimentary record are poorly understood using mountain catchment alluvial fan systems as simple analogues for larger landscapes a wide range of theoretical studies numerical models and physical experiments have hypothesised that a change in precipitation rate could leave a characteristic signal in alluvial fan sediment flux grain size and down system fining rate however this hypothesis remains largely untested in real landscapes this study measures grain size fining rates from apex to toe on two alluvial fan systems in northern death valley california usa which each have well exposed modern and ca 70 ka surfaces and where the long term tectonic boundary conditions can be constrained between them these surfaces capture a well constrained temporal gradient in climate a grain size fining model is adapted based on self similarity and selective deposition for application to these alluvial fans this model is then integrated with cosmogenic nuclide constraints on catchment erosion rates and observed grain size fining data from two catchment fan systems to estimate the change in sediment flux from canyon to alluvial fan that occurred between mid glacial and modern interglacial conditions in a fan system with negligible sediment recycling an approximately 30 decrease in precipitation rate led to a 20 decrease in sediment flux and a clear increase in the down fan rate of fining supporting existing landscape evolution models consequently this study shows that small mountain catchments and their alluvial fan stratigraphy can be highly sensitive to orbital climate changes over 105 year timescales however in the second fan system it is observed that this sensitivity is completely lost when sediment is remobilised and recycled over a time period longer than the duration of the climatic perturbation these analyses offer a new approach to quantitatively reconstructing the effects of past climate changes on sedimentation using simple grain size data measured in the field this article is protected by copyright all rights reserved

pleistocene deglaciation chronology of the amery oasis and radok lake northern prince charles mountains antarctica abstract the east antarctic ice sheet is the largest ice mass on earth with a capacity to raise global sea level by up to 65 m as the lambert glacier amery ice shelf drainage system is the largest to reach the coast of antarctica quantifying its evolution over the quaternary is a vital component in developing an understanding of the antarctic response to future climate change here we present a deglaciation chronology based on 10 be and 26 al in situ cosmogenic exposure ages of the northern prince charles mountains which flank the lambert glacier amery system and that records the progressive emergence of mcleod massif and radok lake basin from beneath the mac robertson land lobe of the east antarctic ice sheet the exposure ages monotonically decrease with both decreasing altitude and increasing proximity to the amery ice shelf at the antarctic coast exposure ages from the crests of mcleod massif near the edge the amery ice shelf and from fisher massif 75 km further inland each at 1200 m above sea level are 2 2 0 3 and 1 9 0 2 ma respectively suggesting their continuous exposure above the ice sheet at least since close to the plio pleistocene boundary an extensive plateau at 800 m altitude on mcleod massif above battye glacier records the massif s increased emergence above the ice sheet surface at about between 880 and 930 ka ago indicating 400 m of ice volume reduction in the mid pleistocene correcting these apparent ages for a reasonable choice in erosion rate would extend this event to 1 15 ma a period identified from prydz bay odp core 1167 when sedimentation composition alters and rates decrease 10 fold exposure ages from boulder mantled erosional surfaces above and beyond the northern end of radok lake at 220 m range from 28 to 121 ka independent of choice of model interpretation to explain this age spread the most recent major reoccupation of radok lake by battye glacier ice occurred during the last glacial cycle moraine ridges at the lower altitude of 70 125 m were deposited during the final withdrawal of battye glacier ice from the lake basin between 11 and 20 ka ago this new chronology indicates that the highest amery oasis peaks have not been overridden by the mac robertson land lobe of the east antarctic ice sheet for at least the past 2 ma since this time we document 3 major periods of regional reduction in ice sheet volume at 1 1 ma during the last glacial cycle 120 to 30 ka and through the last glacial maximum 20 to 10 ka that resulted in an overall 1000 m of ice lowering in the battye glacier radok lake region

oxygen isotope zonation and alteration in the northern noranda district quebec evidence for hydrothermal fluid flow volcanic rocks of the new vauze norbec area central noranda volcanic complex consist of andesites and rhyolites that have been chemically and isotopically altered by synvolcanic semiconformable alteration processes including spilitization chloritization silicification and epidote quartz alteration andesites have whole rock delta 18 o values of 1 9 to 9 7 per mil those with megascopic mineralogical evidence of hydrothermal alteration have ones of 5 1 to 9 7 per mil rhyolites also show a broad range in delta 18 o values 4 4 to 13 7 per mil all of the volcanic rocks are either enriched or depleted in 18 o with respect to fresh rhyolite 8ppm or fresh andesite 6ppm a marked upward stratigraphic increase in delta 18 o values and the strata bound occurrence and regional zoning of alteration minerals provide evidence of district scale hydrothermal alteration these alteration patterns formed under the conditions of an increasing thermal gradient and a downward decrease in water rock ratio controlled by the cooling of the flavrian lake synvolcanic intrusion

origin of glacial fluvial landforms in the azas plateau volcanic field the tuva republic russia role of ice magma interaction the basaltic azas plateau volcanic field is located in the tuva republic of the russian federation the area was glaciated multiple times and the field is characterized by the formation of subglacial volcanoes called tuyas but subaerial volcanoes and lava fields also exist a combined study of remote sensing and field observations in the vicinity of the tuyas in the southeastern azas plateau volcanic field identified landforms that are best explained by the jokulhlaup hypothesis the landforms include elongated hills paleochannels and butte and basin topography these landforms are hypothesized to have formed by both erosion and deposition caused by high energy water streams the triggering for the hypothesized jokulhlaups was either melting of ice by subglacial volcanism and or destabilization of ice dammed subglacial reservoirs the age estimation of the flood events is difficult but they probably occurred during the ice ages of the quaternary as late as in the middle late pleistocene

simulation of snow shielding corrections for cosmogenic nuclide surface exposure studies abstract snow cover reduces cosmogenic nuclide production rates in bedrock corrections for snow cover can be more than 10 in mountainous mid latitude regions where many glacial chronologies have been constructed using cosmogenic nuclide surface dating of landforms most published snow corrections use historic climate data of limited duration that are not likely to reflect adequately the full range of snow conditions over the time of exposure we present a model for describing the impact of snow burial on long term exposure histories of landforms the model applies an energy balance approach to snowpack evolution and incorporates both historic and long term climate proxy data attenuation of cosmogenic fast neutrons is modeled alternatively as a simple exponential decrease with increased shielding or as a thin surface layer with constant production followed by an exponential decrease with increasing depth the choice of attenuation model has little effect on the modeled results for the cairngorms but will have a more significant effect in regions characterized by thinner less dense snowpacks spatial variability in snow cover is modeled as a function of elevation only ignoring local variability in snow accumulation as a result of slope aspect wind redistribution and local topography thus model results reveal general spatial and temporal trends in snow shielding effects rather than site specific corrections applications to data from the cairngorm mountains of scotland show that the constant plus exponential cpe production rate depth profile reduces but does not eliminate snow shielding effects under present day conditions snow at 900 m in the cairngorm mountains reduces average production rates by 6 using the cpe profile and 9 with the exponential profile ep long term climate simulations from 15 5 ka through today produce larger snow shielding effects mainly because they predict an increased proportion of precipitation as snowfall during the younger dryas at 900 m this long term simulation reduces average cosmogenic isotope production rates by 12 cpe and 14 ep these results indicate that snow shielding corrections based on historic climate records may be a potential source of systematic error in midlatitude mountainous regions

fractal dimensions of diamictic particle size distributions simulations and evaluation it has been proposed that deformation tills have fractal particle size distributions reflecting scale invariant debris comminution processes numerical simulations however show that fractal dimensions m typical of deformation tills can be produced by the mixing of gaussian parent populations analogous to the mechanical mixing of coarse medium and fine grained sorted sediments the simulated distributions have high r2 values 0 98 and narrow 95 confidence limits indicating that fractal analysis cannot distinguish diamictons that have been created by shearing from those formed by other mechanisms such as the mixing of preexisting sediments the fractal dimensions of diamictons reflect the relative amounts of coarse and fine material in the distribution but are not uniquely diagnostic of particular genetic processes

fragmentation model of the grain size mix of sediment supplied to basins abstracta key factor in the downstream dispersal and fractionation of sediment is the grain size distribution of sediment supplied by upstream catchments modeling of the grain size distribution of modern bedload in the main trunk channels of tectonically uplifting catchments including the sediment at their outlets and the weathering products of a range of bedrock lithologies in southern italy and sicily reveals fractal dimensions of 2 3 2 7 similar to the fractal dimension of many natural materials undergoing fragmentation we examine the impact of changing statistical properties of the grain size distribution of the sediment supply in simulating grain size trends in sedimentary basins model simulations show a marked movement of the gravel front and patterns of progradation and retrogradation in basin stratigraphy these grain size trends and sedimentary architectures are generated simply by variations in the grain size mix of the sediment supply without variations in base level or sediment discharg

from grain size to tectonics 1 regional grain size trends in fluvial successions can reveal important information regarding the dynamics of sediment routing systems self similar solutions for down system grain size fining have recently been proposed to explore how key variables such as the spatial distribution of deposition sediment discharge and sediment supply characteristics control spatial distribution of grain size in fluvial successions over time scales of 104 106 years we explore the sensitivity of these solutions to changes in key variables and assess their applicability to ancient fluvial successions several sensitivity analyses are presented to investigate the relative control of the key model variables on the spatial pattern of down system grain size fining in fluvial successions sensitivity analyses demonstrate that 1 an increase in the initial value of sediment discharge to a basin causes a decrease in the rate of grain size fining in fluvial successions an effect that becomes nonlinear for large values of initial sediment discharge 2 a short wavelength high amplitude subsidence regime generates a greater rate of down system grain size fining and a long wavelength lower amplitude subsidence regime generates a lesser rate of down system grain size fining in fluvial successions and 3 an increase in the spread of grain sizes in the sediment supply generates a greater rate of down system grain size fining we apply this modeling technique to grain size data sets collected from two time surfaces within conglomerates of the upper eocene montsor fan succession of the pobla basin spanish pyrenees these data sets exhibit approximately self similar grain size distributions further the observed increase in down system grain size fining associated with smaller depositional system lengths provides support for the application of self similar solutions to fluvial successions by applying these solutions to carefully collected grain size data from fluvial successions we are able to relate explicitly the initial grain size supplied to the system the spatial distribution of subsidence and the sediment discharge into the basin to the rate of grain size fining in fluvial successions this method thus offers a powerful means of elucidating sediment routing system dynamics over time

pebble abrasion during fluvial transport experimental results and implications for the evolution of the sediment load along rivers 1 in actively eroding landscapes fluvial abrasion modifies the characteristics of the sediment carried by rivers and consequently has a direct impact on the ability of mountain rivers to erode their bedrock and on the characteristics and volume of the sediment exported from upland catchments in this experimental study we use a novel flume replicating hydrodynamic conditions prevailing in mountain rivers to investigate the role played by different controlling variables on pebble abrasion during fluvial transport lithology controls abrasion rates and processes with differences in abrasion rates exceeding two orders of magnitude attrition as well as breaking and splitting are efficient processes in reducing particle size mass loss by attrition increases with particle velocity but is weakly dependent on particle size fragment production is enhanced by the use of large particles high impact velocities and the presence of joints based on our experimental results we extrapolate a preliminary generic relationship between pebble attrition rate and transport stage c where fluvial shields stress and c critical shields stress for incipient pebble motion this relationship predicts that attrition rates are independent of transport stage for c 3 and increase linearly with transport stage beyond this value we evaluate the extent to which abrasion rates control downstream fining in several different natural settings a simplified model predicts that the most resistant lithologies control bed load flux and fining ratio and that the concavity of transport limited river profiles should rarely exceed 0 25 in the absence of deposition and sorting

glacial interglacial climate changes recorded by debris flow fan deposits owens valley california abstract it is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy basin sediments produced by catchment alluvial fan systems may record past climate over a variety of timescales and could offer unique information about how climate controls sedimentation unfortunately there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals here we examine 35 debris flow fan surfaces in owens valley california that record deposition throughout the past 125 000 years during which climate has varied significantly we show that the last full glacial interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits these flows transported finer sediment during the cooler glacial climate and became systematically coarser grained as the climate warmed and dried we explore the physical mechanisms that might explain this signal and rule out changes in sediment supply through time instead we propose that grain size records past changes in storm intensity which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates this is supported by an exponential clausius clapeyron style scaling between grain size and temperature and also reconciles with climate dynamics and the initiation of debris flows the fact that these alluvial fans exhibit a strong sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing finally our findings highlight the importance of threshold controlled events such as storms and debris flows in driving erosion and sedimentation at the earth s surface in response to climate change

downstream fining in a network of gravel bedded rivers a network based routing model is used to determine how spatial variations in sediment supply influence rates of downstream fining in a small watershed in central pennsylvania gravel of a specified size distribution and lithology is supplied to the network at zero order basins once in transport the total sample weight and moments of the grain size distribution are modified according to empirical functions of transport distance contributions from each zero order basin are summed to determine the total population of sizes and lithologies at any location in the study area resistant quartz sandstone ridges supply sediment an order of magnitude larger than other lithologies because these ridges occur primarily in the basin headwaters spatial variations in supply strongly influence rates of downstream fining model calculations indicate that spatial variations in supply alone account for over 80 of the decrease in mean grain size along the main channel

modeling weathering pathways and processes of the fragmentation of salt weathered quartz chlorite schist 1 the relationship between the rate of rock breakdown and environmental and geological factors must be understood in order to establish the conditions under which weathering limits erosion in this study qualitative and quantitative models of the rock fragmentation process are fitted to previously published data obtained from laboratory salt weathering trials of quartz chlorite schist weathering was modeled as a combination of 1 a fragmentation event that fragments the parent particle into a number of daughter particles while preserving mass and 2 a fracture probability that determines the probability that a fragmentation event will occur in a given time period we show that observations of the complex breakdown of salt weathered schist are consistent with model assumptions of a simple fracture geometry model and an increase in fracture probability with time for the fragmentation geometry the best fit to the experimental data was achieved by assuming that each fragmentation event involves splitting of the parent particle into two daughter fragments of equal volume for the fragmentation rate the data could best be described with a fracture probability and hence the weathering rate that increased linearly with time this paper shows that it is possible to use a physically based fragmentation model to infer the process of fragmentation for individual particles using a time evolving particle size distribution for the weathering rock fragments

origin of fluvial grain size trends in a foreland basin the pocono formation on the central appalachian basin abstract a widely recognized phenomenon of modern and ancient river systems is downstream decrease in grain size over the past two decades theoretical formulations observations of modern rivers flume studies and numerical models have significantly increased our understanding of sediment transport in mixed grain size river systems these have established that downstream fining in modern and ancient rivers can be attributed to a combination of selective sorting abrasion rate and accumulation rate however no detailed multiple grain size sediment transport model has been used to address how much subsidence rate sediment flux water discharge hydraulic geometry and the mechanics of sediment transport influence grain size distribution and facies belt development in ancient fluvial systems we have combined the results of recent empirical and theoretical studies with a multiple grain size sediment transport model midas to test the sensitivity of downstream fining trends to those controlling mechanisms our results demonstrate that subsidence and sediment feed rate are the most important mechanisms controlling downstream fining trends in a foreland basin if the evolution of hydraulic geometry is known to illustrate the application of this result we have replicated the textural trends of the mississippian upper pocono formation and burgoon sandstone of pennsylvania this methodology can be applied to constrain plausible values of accumulation and subsidence rate for ancient alluvial deposits and enhances our ability to interpret paleohydraulic conditions from such facies in a foreland basin

fluvial archives a valuable record of vertical crustal deformation abstract the study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms but also for identifying the nature of crustal deformation and its history in recent decades geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens here we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions the effects of horizontal deformation are not addressed channel long profiles have received considerable attention in the literature and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady state characteristics then we review the literature dealing with the transient response of rivers to tectonic perturbation through the production of knickpoints propagating through the drainage network inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories finally we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes as well as the erosional imprint of tectonic forcing sedimentary deposits such as fluvial terrace staircases are also considered as a classical component of tectonic geomorphology we show that these studies have recently benefited from rapid advances in dating techniques allowing more reliable reconstruction of incision histories and estimation of incision rates the combination of progress in the understanding of transient river profiles and larger more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace profile correlation i e extrapolation of local data to entire profiles finally planform changes in fluvial systems are considered at the channel scale in alluvial rivers and regional level in terms of drainage reorganisation examples are given of how numerical modelling can efficiently combine with topographic data to shed new light on the dis equilibrium state of drainage systems across regional drainage divides

sediment routing controls on sandstone bulk petrographic composition and texture across an ancient shelf example from cretaceous western interior basin utah and colorado u s a

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

the functioning of sediment routing systems using a mass balance approach example from the eocene of the southern pyrenees abstractsediment routing systems link source regions undergoing erosion with depositional sinks and involve a volumetric or mass budget understanding how these source to sink systems function is key to stratigraphic prediction but estimation of their surface sediment discharges and depositional fluxes on geological time scales is a challenging problem we recognize a paleosediment routing system from the geological record in the mid late eocene escanilla formation and time equivalents of the tectonically active wedge top region of the southern pyrenees by mapping the 200 km long fairway of the escanilla sediment routing system we obtain the sediment budget and grain size fractionation of three time intervals each of 2 5 2 6 m yr duration over the time period 41 6 33 9 ma four thousand cubic kilometers of sediment sourced principally from two feeder systems in the high pyrenees was deposited in a period of 7 7 m yr the positions of moving boundaries characterized by rapid reduction in the perc

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

surface exposure dating reveals mis 3 glacial maximum in the khangai mountains of mongolia abstract this study presents results from geomorphological mapping and cosmogenic radionuclide dating 10be of moraine sequences at otgon tenger 3905 m the highest peak in the khangai mountains central mongolia our findings indicate that glaciers reached their last maximum extent between 40 and 35 ka during marine oxygen isotope stage mis 3 large ice advances also occurred during mis 2 at 23 and 17 16 ka but these advances did not exceed the limits reached during mis 3 the results indicate that climatic conditions during mis 3 characterized by a cool wet climate with a greater than today input from winter precipitation generated the most favorable setting for glaciation in the study region yet glacial accumulation also responded positively to the far colder and drier conditions of mis 2 and again during the last glacial interglacial transition when precipitation levels increased viewed in context of other pleistocene glacial records from high asia the pattern of glaciation in central mongolia shares some features with records from southern central asia and ne tibet i e ice maxima during interstadial wet phases while other features of the mongolian record i e major ice expansion during the mis 2 insolation minimum are more in tune with glacier responses known from siberia and western central asia

micromechanics of quartz sand breakage in a fractal context from a quaternary science perspective sand sized quartz as well as silt sized quartz is often acknowledged as final products of glacial abrasion through different evolution mechanisms this view challenges the existence of any universal comminution process which may relate the formation of detrital quartz sand and silt the contribution of grain size energy input and crystalline integrity in the scale of quartz crushability has long been the matter of much debate the present empirical work examines the micromechanics of sand to silt size reduction in the quartz material a series of grinding experiments was performed on leighton buzzard lower greensand using a high energy agate disc mill analogous conditions to glacial abrasion are provided due to the combined abrasion between grains asperity tips and also between grains and rotating smooth tungsten carbide pestle simulation of discontinuous grain breakage allowed the examination of grains crystalline defects to enable an objective assessment of micromechanics of size reduction measurements of particle and mode size distribution fractal indexes and micro morphological signatures were made the crushing approach was probed through varied grinding times at a constant energy input as well as varied energy inputs at constant grinding time breakage pathway was inspected via laser diffraction spectroscopy and transmission light microscopy results suggested that the grain breakdown is not necessarily an energy dependent process non crystallographically pure amorphous quartz sand and silt are inherently breakable materials through a fractal breakdown process results also revealed that the internal defects in quartz are independent from size and energy input

transformation of tectonic and climatic signals from source to sedimentary archive sedimentary rocks reflect past tectonic and climatic events numerical simulations suggest that changes in precipitation and in the rate of tectonic uplift affect the grain size and the distribution of sediments deposited downstream

glaciers and climate in pacific far ne russia during the last glacial maximum a combined geomorphological physical model approach is used to generate three dimensional reconstructions of glaciers in pacific far ne russia during the global last glacial maximum glgm the horizontal dimensions of these ice masses are delineated by moraines their surface elevations are estimated using an iterative flowline model and temporal constraints upon their margins are derived from published age estimates the equilibrium line altitudes elas of these ice masses are estimated and glgm climate is reconstructed using a simple degree day melt model the results indicate that during the glgm ice masses occupying the pekulney kankaren and sredinny mountains of pacific far ne russia were of valley glacier and ice field type these glaciers were between 7 and 80 km in length and were considerably less extensive than during pre lgm phases of advance glgm ice masses in these regions had elas of between 575 22 m and 1035 41 m above sea level corresponding to an ela depression of 350 740 m relative to present data indicate that in the pekulney mountains this ela depression occurred because of a 6 48c reduction in mean july temperature and 200 mm a 1 reduction in precipitation relative to present thus reconstructions support a restricted view of glgm glaciation in pacific far ne russia and indicate that the region s aridity precluded the development of large continental ice sheets copyright 2011 john wiley sons ltd

geomorphology of subglacial volcanoes in the azas plateau the tuva republic russia abstract the azas plateau volcanic field is located in the tuva republic of the russian federation the compositions of the azas plateau volcanics include low viscosity trachybasalt and basanite volcanic edifices of middle late pleistocene age are widely distributed in the southeastern part of the volcanic field there are subglacial volcanoes among the volcanic edifices and their formation coincided with extensive ancient glaciations in the region the dominant subglacial volcanoes in the area are tuyas the general shapes of the tuyas flat tops with steep sides are due to eruptions into meltwater lakes and confinement of ice walls and effusive subaerial eruptions of basaltic lavas there are also non flat topped subglacial volcanoes and at least one subaerial volcanic edifice in the area degradation appears to have modified the primary shapes of the tuya edifices and such processes seem to include failures of over steepened slopes gully formation due to stream runoff and debris flows cirque valley glaciation and modification by rock glaciers the estimated thicknesses of the ice sheets covering the subglacial volcanoes during their eruptions range 300 600 m on average

stable vegetation and environmental conditions during the last glacial maximum new results from lake kotokel lake baikal region southern siberia russia abstract this paper presents a new decadal resolution fossil pollen record from lake kotokel 52 47 n 108 07 e 458 m a s l and provides a reconstruction of the last glacial maximum lgm vegetation and environments in the study area during this interval of globally harsh climate lake kotokel is situated close to the eastern shoreline of lake baikal in the boreal forest zone of southern siberia the analysed 190 cm long section 6 of the bottom core ktk10 ktk10 6 consists of compact undisturbed greenish grey to dark grey slightly laminated silty clay indicating continuous lacustrine sedimentation throughout the lgm period ca 26 8 19 1 cal ka bp the age model is supported by 11 calibrated ams dates the results of pollen analysis and pollen based biome reconstruction show that steppe and tundra vegetation composed of grasses and various herbs dominated ca 26 8 19 1 cal ka bp occurrence of conifer tracheids and stomata throughout the record together with small quantities of boreal conifer and broadleaf tree and shrub taxa pollen suggests the presence of single trees or small forest stands in the lake vicinity most likely in the river valleys application of the biomisation method and the resulting numerical scores of the most characteristic biomes steppe tundra and cold deciduous forest show minor fluctuations signifying stability of the regional vegetation cover during the analysed lgm interval in contrast to the regional biomes the local environmental indicators demonstrate greater sensitivity of the lake system to decadal and century scale climate variability the highest pollen percentages of ranunculaceae representing littoral meadow vegetation communities are registered ca 23 8 23 4 cal ka bp this and an increase in coarse grained sand particles together with slightly increased total inorganic carbon tic values representing calcite in the ktk10 6 sediment provide evidence of a much shorter than present distance between the coring site and the shoreline and a reduced lake area in line with a drier than present lgm climate a general stability of the grassland vegetation in the study region ca 26 8 19 1 cal ka bp and relatively constant total organic carbon toc values support the hypothesis that this productive vegetation could stably serve as a perennial food resource for large populations of herbivores thus providing favourable environments for the local hunter gatherers inhabiting the lake baikal region during the lgm interval

mechanisms of loess sized quartz silt production and their relative effectiveness laboratory simulations the production of loess sized quartz silt is frequently ascribed to glacial grinding mechanisms in this study a series of laboratory simulations was set up the purpose of which was to demonstrate that a range of geomorphic mechanisms are capable of producing silt under laboratory conditions the geomorphic mechanisms investigated were aeolian abrasion fluvial comminution glacial grinding salt weathering and frost weathering the results confirmed that under laboratory conditions all of these mechanisms were capable of producing silt the relative effectiveness of these mechanisms at producing silt under laboratory conditions was then calculated in order to provide a starting point for a consideration of their potential effectiveness within the natural environment these results indicate that fluvial and aeolian activity are highly effective at producing quartz silt over short time periods in a dust storm of four days duration 287 g of silt could potentially be produced from every kilogram of sand entrained while fluvial comminution in a turbulent fluvial environment could potentially produce 900 g of silt from every kilogram of sand entrained within 32 h over longer periods of time the glacial grinding and weathering mechanisms represent more continuous and hence more effective silt producing mechanisms although it is realised that the relative importance of each silt producing mechanism will differ spatially and temporally due to differences in climate relief geology and geomorphic history the findings from this work do have implications for the genesis of loess deposits they demonstrate that glacial and cold weathering processes are not solely responsible for fine particle formation and that efficient silt producing mechanisms can operate within a variety of environments under suitable conditions weathering together with episodic contributions from aeolian and fluvial mechanisms could be responsible for a considerable proportion of global quartz silt production

the nature and controls on downstream fining within sedimentary links abstract at scales of 100 to 102 km grain size change in gravelly alluvial systems is characterized by punctuated downstream fining significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends using a new set of surface grain size data eighteen such links along two canadian gravel bed rivers are examined negative exponential functions are found to be most appropriate for describing within link grain size changes development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate examination of within link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope the predictive value of this relation is limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information however as previously noted for alluvial fans although for different reasons channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between link length and diminution rate the validity of the derived relation cannot be tested for want of a suitable data set several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers and it is argued that this may be typical of sedimentary links fining rate must then be a function of the efficiency with which sorting processes operate and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links

volumetric budget and grain size fractionation of a geological sediment routing system eocene escanilla formation south central pyrenees the supply of sediment and its characteristic grain size mix are key controls on depositional facies and stratigraphic architectures in sedimentary basins consequently constraints on sediment caliber budgets and fl uxes are a prerequisite for effective stratigraphic prediction here we investigate a mid to late eocene 41 6 33 9 ma sediment routing system in the spanish pyrenees we derive a full volumetric sediment budget weighted for grain size fractions partitioned between terrestrial and marine depositional sectors and we quantify sediment fl uxes between depocenters the paleo sediment routing system was controlled by syndepositional thrust tectonics and consisted of two major feeder systems eroding the high pyre nees that supplied a river system draining parallel to the regional tectonic strike and that ultimately exported sediment to coastal shallow marine and deep marine depo centers we show signifi cant changes in both the volume and grain size distribution of sediment eroded from the pyrenean mountain belt during three different time intervals in the mid to late eocene which controlled the characteristics of stratigraphy preserved in a series of wedge top basins the time averaged sediment discharge from source areas increased from 250 km 3 m y to 700 km 3 m y over the 7 7 m y interval investigated this temporal increase in sediment supply caused major westward progradation of facies belts and led to substantial sediment bypass through the terrestrial routing system to the initially marine jaca basin the grain size mix measured as size fractions of gravel sand and fi ner than sand also changed over the three time intervals integration of volumetric and grain size information from source to sink provides an estimate of the long term grain size distribution of the sediment supply comprising 9 gravel 24 sand and 67 fi ner than sand the techniques and concepts used in the escanilla study can profi tably be applied to paleo sediment routing systems in other tectonic and climatic settings and to catchments with a range of bedrock lithology and vegetation this will promote a better generic understanding of the dynamics of source tosink systems and provide a powerful tool for forward stratigraphic modeling the sediment routing system approach has the potential to contribute strongly to new models of sequence stratigraphy

the size distribution of pyroclasts and the fragmentation sequence in explosive volcanic eruptions in an explosive eruption the atmospheric column dynamics depend strongly on the mass fraction of gas in the erupting mixture which is fixed by fragmentation in the volcanic conduit at fragmentation gas present in vesicular magmatic liquid gets partitioned between a continuous phase separating magma clasts and a dispersed phase in individual bubbles within the clasts as regards flow behavior it is the former continuous gas phase which matters and we show that its amount is determined by the fragment size analysis of 25 fall deposits and 37 flow deposits demonstrates that ash and pumice populations follow a power law size distribution such that n the number of fragments with radii larger than r is given by n r d d values range from 2 9 to 3 9 and are always larger than 3 0 in fall deposits d values for pyroclastic flow deposits are systematically smaller than those of fall deposits we show that at fragmentation the amount of continuous gas phase is an increasing function of the d value large d values cannot be attributed to a single fragmentation event and are due to secondary fragmentation processes laboratory experiments on bubbly magma and on solid pumice samples demonstrate that primary breakup leads to d values of 2 5 0 1 and that repeated fragment collisions act to increase the d value a model for size dependent refragmentation accounts for the observations we propose that in a volcanic conduit fragmentation proceeds as a sequence of events primary breakup releases a small amount of gas and is followed by fragment collisions due to refragmentation and decompression both the mass and volume fractions of continuous gas increase the final d value and hence the mass fraction of continuous gas at the vent depends on the time spent between primary fragmentation and eruption out of the vent

the formation of silt material for terrestrial sediments particularly loess and dust abstract there are certain controls which operate to demarcate the nature and size range of quartz particles in terrestrial detrital sediments the particles fall into discrete and definable populations which are separated by tanner gaps quartz sand nature is determined largely by a eutectic like reaction which takes place in the original igneous rock this reaction delivers a fine mix of quartz and feldspar units which on weathering deliver quartz sand the formation of quartz silt is more contentious it appears that silt production is essentially controlled by the presence in larger quartz particles of moss defects crystalline defects introduced into the quartz structure by earlier events e g the high low displacive transformation in cooling quartz there appear to be two modes in airborne quartz particles which have been called large dust and small dust the larger mode is the loess mode around 20 60 m and the smaller mode falls into the classification with high level long travel dust mode around 2 6 m the quartz in small dust is around the same size as the clay mineral agglomerate particles cma which form a considerable proportion of high level dust clouds the cma particles form from lake deposits the size is controlled by the openness of the packing in the lake sediments this can be demonstrated by a simple monte carlo model

similarity solutions for fluvial sediment fining by selective deposition 1 current models for downstream sediment sorting by selective deposition generally perform well at describing observed sorting data however since most were developed initially for application to modern rivers they are typically formulated in terms of hydraulic and bed surface variables that are not readily measurable in the sedimentary record moreover their algebraic complexity obscures some of the underlying simplicity of the segregation process here we show how a pair of hydraulically based sorting models developed by parker et al can be reformulated with minimal loss of accuracy in terms of the size distribution of the supplied sediment and the downstream depositional mass balance by invoking constant dimensionless shear stress within either the gravel or sand regimes reach scale short term details of hydraulics and sediment transport are summarized via a pair of dimensionless relative mobility functions one for gravel and one for sand our approach yields simplified similarity solutions in which the long term longitudinal grain size distribution of the substrate and the relative mobility functions can be collapsed into self similar forms in which only local mean and standard deviation of sizes in transport are used as scaling parameters the formulation we propose offers a simple means to explore the impact of controlling variables on fining profiles and can be easily incorporated in long term basin scale numerical stratigraphic models avoiding the necessity of modeling the details of hydraulics and sediment transport the model involves a minimum number of physically based parameters the numerical values of which can be determined from the spatial distribution of rate of deposition dimensionless shear stress and the coefficient of variation of the supply gravel or sand size distributions

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

extensive glaciation in transbaikalia siberia at the last glacial maximum abstract successively smaller glacial extents have been proposed for continental eurasia during the stadials of the last glacial period leading up to the last glacial maximum lgm at the same time the large mountainous region east of lake baikal transbaikalia has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations we have applied cosmogenic 10be exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region based on eighteen exposure ages from five moraine complexes we propose that large mountain ice fields existed in the kodar and udokan mountains during oxygen isotope stage 2 commensurate with the global lgm these ice fields fed valley glaciers 100 km in length reaching down to the chara depression between the kodar and udokan mountains and to the valley of the vitim river northwest of the kodar mountains two of the investigated moraines date to the late glacial but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post lgm glacial history in addition to the lgm ice fields in the highest mountains of transbaikalia we report geomorphological evidence of a much more extensive ice cap type glaciation at a time that is yet to be firmly resolved

late pleistocene and holocene vegetation and climate records from lake kotokel central baikal region abstract climatically driven late pleistocene and holocene vegetation changes were reconstructed based on pollen records from the sediments of lake kotokel and cheremushka bog located on the eastern shore of lake baikal the described paleoenvironmental record has higher resolution than records collected from lake baikal and unites individual events identified in prior studies of bottom and onshore cores remarkable shifts in landscapes and expansions of index plants are as follows forest tundra and or forest steppe landscape with birch spruce artemisia and poaceae prevailed at ca 50 25 14 c kyr bp tundra and or steppe vegetation dominated by artemisia and poaceae was typical for the last glacial maximum the expansion of shrub birch and willow occurred at ca 15 5 14 c kyr bp two peaks of spruce expansion at ca 47 5 42 4 14 c kyr bp karginian time and at ca 14 5 13 ka bolling allerod warm intervals suggest that the condition were more humid than today a slight increase in artemisia at ca 11 10 5 14 c kyr bp 13 12 ka was indicative of the younger dryas event an expansion of birch forests with fir at ca 12 6 4 ka suggests higher humidity the currently dominant scots and siberian pine forests with birch expanded since 6 4 ka

lithological controls on hillslope sediment supply insights from landslide activity and grain size distributions the volumes rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems moreover hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations however there are very few detailed field studies characterising hillslope sediment supply as a function of lithology and delivery process here we present new empirical data from tectonically active areas in southern italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes landslides are the major source of hillslope sediment supply in this area and our inventory of 2800 landslides reveals that landslide sediment flux is dominated by small shallow landslides we find that lithology and rock strength modulate the abundance of steep slopes and landslides and the distribution of landslide sizes outcrop scale rock strength also controls the grain sizes supplied by bedrock weathering and influences the degree of coarsening of landslide supply with respect to weathering supply finally we show that hillslope sediment supply largely determines the grain sizes of fluvial export from catchments and that catchments with greater long term landslide rates deliver coarser material therefore our results demonstrate a dual control of lithology on hillslope sediment supply by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system

sediment transport model for the eocene escanilla sediment routing system implications for the uniqueness of sequence stratigraphic architectures abstract stratigraphic architectures are fundamentally controlled by the interplay at different temporal and spatial scales of accommodation and sediment supply modulated by autogenic responses of the sediment routing system and its constituent segments the flux and caliber of sediment supply is a function of climate catchment area and tectonics in the source regions and unraveling these forcing mechanisms from the observed stratigraphic architecture remains a key research challenge the mid to late eocene escanilla sediment routing system had its source regions in the south central pyrenean orogen northern spain and transported sediment from wedge top basins along tectonic strike to marine depocenters by constructing a volumetric budget of the sedimentary system it has been demonstrated that there were marked changes in the grain size distribution released from the sediment sources and also in the position of the gravel front across three 2 6 myr time intervals from 41 6 to 33 9 ma classical sequence stratigraphic interpretations would relate the movement of depositional boundaries such as the gravel front to changes of base level either in isolation or in combination with sediment supply herein we explore the possibility that the position of the gravel front was primarily driven by variability of grain size distributions released from the source regions as a result of changes in catchment uplift rate and or surface run off using a simple model of sediment transport that captures first order processes we simulate the lateral movement of gravel deposition in the proximal part of the escanilla sediment routing system movement of the gravel front is a function of both accommodation generation and the transport capacity of the sediment routing system we assume that the transport capacity is a linear function of the local slope and the water flux by assuming that the observed thickness of deposits is equivalent to the accommodation available during deposition we then use the stratigraphic architecture to constrain the change in catchment size and water flux over the three time intervals of the escanilla paleo sediment routing system multiple scenarios are investigated in order to find the most plausible tectonic and climatic history model results indicate that during the mid eocene there was an increase in catchment length and sediment flux most likely driven by tectonic uplift in the pyrenean orogen subsequent marked progradation of the gravel front during the late eocene was the consequence of reduced transport capacity due to a reduction in surface run off the latter model result is in agreement with records of pollen taxa that indicate increased climatic aridity in the late eocene the combination of a sediment transport model with a full sediment budget makes it possible to test the non uniqueness of these results