sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

grain size dependent concentration of cosmogenic 10be and erosion dynamics in a landslide dominated himalayan watershed for documenting recent or late quaternary erosion rates at the scale of a small watershed or even an entire mountain range the use of in situ terrestrial cosmogenic nuclides tcn such as 10be in river sediments has become widespread over the last decade in mountainous settings however landslides may induce a two fold complication in the cosmogenic nuclide budget first they may episodically deliver large amounts of sediment with low tcn concentrations to the river channel second they may generate a grain size concentration dependence in these sediments however studies that have explored grain size dependence in landslide dominated areas have reached differing conclusions and the underlying mechanisms remain poorly understood the present study focuses on the khudi khola river basin a small drainage basin in the central himalayas the area is characterized by steep slopes heavy rainfall and high sediment production rates importantly the watershed contains a large area of active landsliding in situ 10be was analyzed in sediments of grain sizes ranging from 75 m to 4 cm collected from five locations upstream downstream and in the small tributaries which drain the landslides in all sampling locations including those situated upstream of the landslides the finest grains 75 250 m are two to four times more concentrated in 10be than the largest clasts 4 7 mm we developed a numerical slope model which includes a low level of background soil erosion and episodic denudation from large mass wasting events we then introduced a coarsening of average grain size with soil depth to the model our simulation shows that the data available for this valley are compatible with a scenario in which landslides deliver coarse grains to the channel that are less concentrated in tcn and have deeper provenance best fit estimates of the model parameters suggest recurrence times of 3000 to 9000 years for a major landslide on the same slope and mean long term landslide denudation rates of 1 7 to 4 7 mm yr 1 a negative correlation between tcn concentration and grain size is also observed directly upstream and 5 km downstream of the landsliding area suggesting that nearly all of the sediment carried by the river is derived from ancient landslides while almost no sediment is supplied by erosion of soil mantled slopes despite these complications apparent denudation rates directly derived from the tcn concentrations and from previously published data in the region are all on the same order of magnitude around 2 mm yr 1 however a factor of three variability remains between the different studies depending on the location the year of sampling and the analyzed grain size fraction thus although tcn derived average denudation rates provide a useful first order estimate even in fast eroding terrains dominated by landslides caution should be applied when using quantitative results in such settings

flux and fate of small mountainous rivers derived sediments into the taiwan strait article i nfo high resolution chirp sonar profiles across the taiwan strait reveal a large silt sand dominated deltaic clinoform up to 50 m thick overlying the postglacial transgressive sea floor across the southeastern central and northern strait delta like configuration and internal depositional sequences indicate a northwestward progradation from western taiwan primarily from the choshui zhuoshui river grain size and mineral data confirm the sediment s taiwanese derivation the chirp profiles together with existing radiocarbon and geomagnetic dates suggest that the clinoform has formed over the past 10 kyr the estimated volume of 375 km 3 of sediment mainly sand and silt suggests a mean annual accumulation of 60 10 6 t yr presumably much of fine mud delivered by taiwanese rivers has been washed away by the local currents and escaped either northeastward into the southern okinawa trough or southward into the south china sea numerous shallow borings onshore over the central western taiwan coastal plain reveal an additional 350 km 3

erosion rates over millennial and decadal timescales at caspar creek and redwood creek northern california coast ranges comparing millennial scale denudation rates from cosmogenic nuclides with decadal scale sediment yields can shed light on erosional processes and on the effects of land use on sediment delivery to streams detailed measurements of sediment fluxes in the northern california coast ranges at caspar creek and redwood creek have provided estimates of physical erosion rates since 1963 and 1971 respectively we used cosmogenic 10 be to measure

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

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

exposure dating and validation of periglacial weathering limits northwest scotland periglacial weathering limits on two mountains in northwest scotland separate zones of contrasting exposure history exposure dating of bedrock below the weathering limits gives ages consistent with late devensian deglaciation but six out of seven samples from above the weathering limits give minimum exposure ages older than late devensian ice expansion these results suggest that mountain summits stood as nunataks above the last ice sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation trimming of frost debris during an ice sheet readvance or enhanced weathering prior to climatic warming during ice sheet downwastage the dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold based ice on mountain summits and erosive warm based ice at lower elevations although 26 al 10 be ratios for high level bedrock surfaces provide no evidence of prolonged static ice cover

watershed averaged denudation rates from cosmogenic 36cl in detrital magnetite abstract quartz is widely used as a target mineral for determining watershed averaged denudation rates because it is resistant to chemical weathering geologically widespread and has a well constrained 10be production rate however quartz is not available in many landscapes developed on mafic to intermediate igneous rocks this creates a need to develop new target minerals that are applicable in these environments magnetite is a common accessory mineral in many rock types without quartz and like quartz is resistant to chemical weathering here we evaluate magnetite s suitability as a target mineral by comparing denudation rates inferred from 36cl in magnetite to 10be in quartz at 12 watersheds in the sierra nevada region of california we find that magnetite and quartz produce denudation rates that are in broad agreement validating the use of magnetite the reproducibility between the two minerals is comparable to the reproducibility of measurements of 10be from repeat samples of quartz from a single catchment this level of variance is likely attributable to the stochastic nature of erosion and sediment supply in small mountainous watersheds

mineralogical geochemical and microbial investigation of a sulfide rich tailings deposit characterized by neutral drainage mineralogical geochemical and microbial characterization of tailings solids from the greens creek mine juneau alaska was performed to evaluate mechanisms controlling aqueous geochemistry of near neutral ph pore water and drainage core samples of the tailings were collected from five boreholes ranging from 7 to 26 m in depth the majority of the 51 samples 77 were collected from the vadose zone which can extend 18 m below the tailings surface mineralogical investigation indicates that the occurrence of sulfide minerals follows the general order pyrite fes 2 sphalerite zn fe s galena pbs tetrahedrite fe zn cu ag 12 sb 4 s 13 arsenopyrite feass and chalcopyrite cufes 2 pyrite constitutes 35 wt of the tailings mineral assemblage whereas dolomite camg co 3 2 and calcite caco 3 are present at 30 and 3 wt respectively the solid phase geochemistry generally reflects the mineral assemblage the presence of additional trace elements including cd cr co mo ni se and ti is attributed to substitution into sulfide phases results of acid base accounting aba underestimated both acid generating potential ap and neutralization potential np recalculation of ap and np based on solid phase geochemistry and quantitative mineralogy yielded more representative results neutrophilic s oxidizing bacteria nsob and so 4 reducing bacteria srb are present with populations up to 10 7 and 10 5 cells g 1 respectively acidophilic s oxidizing bacteria asob and iron reducing bacteria irb were generally less abundant primary influences on aqueous geochemistry are sulfide oxidation and carbonate dissolution at the tailings surface gypsum precipitation dissolution reactions as well as fe reduction below the zone of sulfide oxidation pore water ph values generally ranged from 6 5 to 7 5 near the tailings surface and from approximately 7 8 below the oxidation zone elevated concentrations of dissolved so 4 s 2 o 3 fe zn as sb and ti persisted under these conditions

a quantitative analysis for geomorphic indices of longitudinal river profile a case study of the choushui river central taiwan due to the plate movement is considerably slow the human history record is too short to register landscape change for such a long time scale however longitudinal river profile can display watershed landscape characteristics therefore this paper applies a quantitative analysis of geomorphic indices coupled with some mathematical models for the choushui river and its six tributaries including the gradient index and slope area relationship the abnormally high sl and sl k values indicated that a decreasing trend from lower to mid stream areas and south lishan fault was higher than north lishan fault on the upstream areas and the result of slope area relationship also indicated that the regression line of the upper and lower steam exhibit an obvious right shift nearby lishan fault could be explained by geodynamic models of active deformation in taiwan area this study also found that the abnormally high values of sl k were affected by river and fault intersecting to form a high angle or perpendicular and the abnormally low values of sl k were affected by river along with a fault or form a low angle but the channel of junda river along with lishan fault is opposite based on quantitative results of these geomorphology indices this study suggests that the important factor influencing landscape of the choushui river watershed is tectonic uplift

the erosion response to quaternary climate change quantified using uranium isotopes and in situ produced cosmogenic nuclides abstract studying how catchment erosion has responded to past climate change can help us better understand not only how landscape evolution operates but also predict the consequences of future climate change on soil resource availability recent years have seen the development of tools that allow a quantitative assessment of past changes in catchment erosion this work reviews the principles of the application of in situ produced cosmogenic nuclides and uranium isotopes to quantifying past erosion rates results highlight the role of periglacial processes and mass wasting in dictating how catchment erosion responds to climatic variability at the 10 kyr scale at the million year scale it is more difficult to untangle the role of climate and tectonics a strong coupling exists at the 10 kyr to 100 kyr scales between climatic cycles and the transfer time of regolith from source to sink this coupling reflects changes in sediment source that are either set by changes in vegetation cover at the catchment scale or by the storage of sediments on continental shelves at a larger scale although further analytical developments are required for these tools to reach their full potential existing works suggest that in the near future they will provide unprecedented quantitative insights on how soil and fluvial systems adapt to external perturbations climatic tectonic and or anthropic

late pleistocene and halocene sea level changes in japan implications for tectonic histories and mantle rheology abstract it is very important to separate the tectonic and glacial isostatic components in the observed holocene and late pleistocene sea level changes in tectonically active areas such as japan for studying tectonic processes and for constraining mantle rheology the separation can be achieved by considering the spatial dependence of the relative sea level on the geometry of the coastline around the site where sea level is evaluated in fact the relative sea level caused by the last deglaciation at sites in the embayment such as tokyo and osaka has a sea level curve with a high stand at mid holocene and that site situated on the tip of peninsula has a sea level curve culminating towards the present the geometric effect also causes the regional difference of the sea level variations in the late glacial phase in the japanese islands the regional difference of the predicted relative sea level is about 5 m at 6000 years ago 20 m at 10 000 years ago and 30 m at 18 000 years ago comparison between observations and predictions indicates that the observations at several sites in japan are consistent with the predicted sea level variations more systematic data is required for the period 18 000 years ago to the present in order to examine tectonic processes and mantle rheology

seismogenic faults along the major suture of the plate boundary deduced by dislocation modeling of coseismic displacements of the 1951 m7 3 hualien taitung earthquake sequence in eastern taiwan abstract research at plate boundaries generally focuses on the kinematics of plate motions the genesis of large earthquake and natural resources however often the present state of knowledge is still insufficient to reveal the details of such dynamic systems to define in more detail the dynamics of a major plate boundary fault the coastal range fault eastern taiwan we use seismologic and geodetic data to unravel its subsurface geometry and relevant fault behavior by recomputing the archive triangulation datasets 1917 1978 and using a dislocation algorithm we determine that it consists of three segments our model results are consistent with the observation of the 1951 m7 3 hualien taitung earthquake sequence that the southern two segments are both oblique slip faults with significant thrust components while the northern segment is a pure strike slip fault according to our model each segment has the potential to produce an earthquake larger than m7 however based on gps observations and seismic records slip on the southern segment may take the form of aseismic creep and multiple moderate earthquakes rather than large events with long recurrence interval as occur on the two more northerly segments with regard to the central segment the epicenter distribution of catalogued earthquakes occurring after 1951 reveals the presence of a seismic gap indicating that slip on this segment is predominantly coseismic with a correspondingly higher potential for large earthquakes in the future

the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment the study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape these measurements are done with in situ produced cosmogenic nuclides e g 10be 26al mostly in quartz from alluvial sediment cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the earth s surface they are produced within a characteristic depth scale of about 1 m which means that the measured concentrations record an integrated denudation history while material passed through this depth interval depending on the denudation rate the resulting integration time scales are 103 to 105 years and one obtains a robust long term estimate of natural denudation that is relatively insensitive to short term changes the last 10 years have seen significant research activity using these methods and an array of fascinating tectono geomorphologic and geochemical insights are emerging amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change a compilation of world wide denudation rates in non glaciated areas that however does not yet include some of the world s most active mountain belts has resulted in the following findings some of which have been unexpected 1 no obvious relationship between precipitation or mean annual temperature and total denudation is apparent 2 topographic relief alone does not result in high rates of denudation 3 denudation rates are high in areas of landscape rejuvenation that is triggered and controlled by tectonic activity faulting escarpment formation and retreat rifting surface uplift 4 rates of weathering using a combination of cosmogenic nuclides and zirconium normalised cation loss balances co vary primarily with physical erosion rates and much less with temperature or precipitation 5 in some areas of high land use short term rates from river load gauging exceed those from cosmogenic nuclides by several orders of magnitude which serves to highlight the severity of geomorphic change caused by human action in the future the control mechanisms over denudation will be determined on all spatial scales ranging from the single soil section to entire river basins the same analysis can be done back through time on well dated terraces lake records and marine sediment cores which is possible with 10be for the past 1 2 my the rates obtained will be used to develop a quantitative understanding of tectonic geomorphologic and geochemical landscape processes which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic climate and anthropogenic forcing

tectonic interpretations of holocene marine terraces east coast of coastal range taiwan abstract the east coast of the coastal range in taiwan is well known for its multiple holocene marine terraces and their very rapid uplift the study area extends from hualien to taitung over ca 150 km of coastline here we present some new data on the age and height of holocene marine terraces and we discuss their significance for holocene coastal tectonics the holocene marine terrace sequence is subdivided into a maximum of 10 steps the highest and oldest terrace mostly underlain by transgressive deposits represents the sea level position of the culmination of holocene sea level rise and reaches up to ca 80 m above sea level transgressive deposits are radiocarbon dated at several sites back to ca 13 000 yr bp the lower terraces are mostly erosional ones overlain by thin coral beds in situ less than 1 m thick and indicate successive lowering of relative sea level during the late holocene the uplift rate of the coast is very high ranging from 5 to 15 m ka three tectonic subregions a c are identified based on the pattern of marine terrace features and uplift rate the presence of many steps during holocene time implies that intermittent uplifts associated with large earthquakes at intervals of one thousand to several hundred years have repeatedly occurred in this coastal area but with different time and amount at each subregion the uplift of subregion a resulted from an onshore active fault milun fault causative faults for the uplift of the subregions b and c are not identified offshore active faults striking obliquely to the coastline appear to be causative faults

tectonic significance of holocene marine terraces in the coastal range eastern taiwan abstract well developed marine terraces on the coast of eastern taiwan between chengkung and hualien can be divided into three morphotectonic sectors 1 i chengkung kueian 2 ii shuilien and its vicinity 3 iii north of shuilien sector i displays at least five terrace levels and has undergone northward tilting and uplift the available 234 u 230 th and 14 c ages suggest that one of its holocene terraces rises to about 40 m and locally to 70 m above msl the average uplift rate for the holocene in this sector decreases northward from 9 10 mm yr to about 2 3 mm yr few traces of former shorelines or marine terraces higher than 5 m are found in sector ii north of shuilien in sector iii terrace elevation increases gradually and indicates an uplift rate of about 2 3 mm yr the uplift pattern agrees with geodetic data obtained between 1985 and 1988 the high uplift rates in sector i may represent compression and shortening of the northwestern corner of the philippine sea plate the low rates in sector ii may correlate with the region where the ryukyu trench meets the eastern coast of taiwan

spatial and temporal evolution of cu zn mine tailings during dewatering abstract the ruttan cu zn mine produced about 50 mt of fine grained tailings over 30 a since the closure of the mine in 2002 the tailings have been systematically dewatered through trenches draining into the open pit and underground workings this study evaluated the evolution of tailings that were underwater until 2002 and also tailings that had been exposed to oxidizing conditions for more than 20 a acid generation is dominated by the oxidization of the abundant pyrite and pyrrhotite comprising 25 wt of tailings with zn being mobilized from the sphalerite remaining after beneficiation of the ore little cu is being mobilized partly due to the armouring of remnant chalcopyrite by primary quartz and also by preferential absorption of cu rather than zn on secondary fe oxy hydroxides a very fine grained fraction of unoxidized sulfides is a likely cause of an initial pulse of acid generation and metal and so 4 2 release occurring at the onset of dewatering metals are temporarily attenuated from waters associated with the tailings either absorbed on fe oxy hydroxide precipitates or as evaporite hydroxy sulfate minerals at the surface of the tailings while some secondary phases are stable evaporites are only temporary metal sinks as they redissolve in wet weather conditions trace amounts of calcite provide little buffering capacity resulting in rapid acidification of pore and surface water the ph of pore water and shallow groundwater decreased first to the al oxy hydroxide buffer at 4 5 and then stabilized at values of 2 3 being controlled predominantly by the dissolution of solid fe oxy hydroxides the metal contents of the ground and surface water are still increasing but the ruttan lake reservoir that receives drainage water from the tailings is maintaining a constant composition

improving in situ cosmogenic chronometers new radiocarbon ages for sierra nevada deglaciation the first 10 be measurements from the laurentide terminal moraine and calculations based on paleomagnetic field strength have the potential to substantially improve the accuracy of cosmogenic age estimates specifically three new constraints apply to the interpretation of measured abundances of in situ produced cosmogenic 10be and 26al 1 a suite of minimum limiting radiocarbon dates indicates that the sierra nevada was deglaciated at least several thousand years earlier than assumed when nishiizumi et al 1989 first calibrated 10be and 26 al production rates based on polished bedrock surfaces in the range with retreat beginning by 18 000 cal yr b p and completed by 13 000 cal yr b p 2 concentrations of 10be in moraine boulders and glacier polished bedrock in new jersey show little variance 10 1 and can be used to calculate a preliminary 10be production rate integrated over the past 21 000 22 000 cal yr b p at 41 200 300 m altitude that is about 20 lower than currently accepted 3 calculations of the effect of past geomagnetic field strength variations on production rates suggest that the use of temporally averaged production rates may generate age errors of 20 however cosmogenic exposure ages can be corrected for this effect although the corrections currently are imprecise many previously reported late pleistocene 10be and 26al exposure ages are probably too young and are less accurate and less precise than implied by reported uncertainties the discrepancy between accepted production rates and those calculated from laurentide exposures when considered together with the sierran deglacial chronology and the model results suggest that correlations between cosmogenic and other numerical ages especially for brief events like the younger dryas and heinrich events will not be robust until temporal variations and the altitude latitude scaling of production rates are fully understood and quantified at levels comparable to current analytic uncertainties 3

quantifying rainfall controls on catchment scale landslide erosion in taiwan landslide erosion is a dominant hillslope process and the main source of stream sediment in tropical tectonically active mountain belts in this study we quantified landslide erosion triggered by 24 rainfall events from 2001 to 2009 in three mountainous watersheds in taiwan and investigated relationships between landslide erosion and rainfall variables the results show positive power law relations between landslide erosion and rainfall intensity and cumulative rainfall with scaling exponents ranging from 2 94 to 5 03 additionally landslide erosion caused by typhoon morakot is of comparable magnitude to landslide erosion caused by the chi chi earthquake mw 7 6 or 22 24 years of basin averaged erosion comparison of the three watersheds indicates that deeper landslides that mobilize soil and bedrock are triggered by long duration rainfall whereas shallow landslides are triggered by short duration rainfall these results suggest that rainfall intensity and watershed characteristics are important controls on rainfall triggered landslide erosion and that severe typhoons like high magnitude earthquakes can generate high rates of landslide erosion in taiwan copyright 2012 john wiley sons ltd

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

early holocene catastrophic mass wasting event and fan delta development on the hua tung coast eastern taiwan abstract landslides and debris flows rarely occurred during historical times in the tectonically active coastal range of eastern taiwan this topographic stability however contrasts greatly with the widespread existence of terraced alluvial fans and fan deltas on the hua tung coast which fringes the range this study focuses on the two largest fan terrace systems on the hua tung coast both of which consist of alluvial fans plane view areas up to 8 km 2 larger than their contributing catchments stratigraphic data show that both systems were in sandy wave dominated settings during de glacial times the systems were then disturbed by a catastrophic landslide debris flow event or events which brought enormous amounts of gravel facies gm into the systems deforming previously deposited marine sands facies sm and shallowing the seafloor the combined gm sm complex yields multiple radiocarbon dates ranging from 11 3 to 8 3 ka cal bp with a cluster around 8 6 ka cal bp this mass wasting event has been unique since the emergence of its contributing catchment 0 2 0 3 ma ago the low frequency of such an event could reflect the great resistance of rock mass in the source areas to weathering and erosion the common blockage of valley floors by giant boulder piles which limits channel incision and sediment transport could also increase the apparent stability of the mountain the trigger of landslides in the coastal range has been linked to large earthquakes additionally we propose that the great magnitude and duration of the observed early holocene event were caused by the contemporaneous prolonged rainfall and or high frequency of typhoons associated with the east asian summer monsoon maximum

tectonic and climatic controls of denudation rates in active orogens the san bernardino mountains california abstract the relative importance of climatic and tectonic factors in driving rates of denudation in mountain ranges has long been debated with both precipitation and rates of crustal uplift cited as first order controls in a variety of different mountainous settings few studies however have explicitly considered the influence of climatic and tectonic processes on denudation rates during the early stages of orogenesis using basin wide denudation rates derived from in situ cosmogenic 10 be and published modern precipitation rate data the significance of rainfall and snowfall on rates of denudation is evaluated for the san bernardino mountains california denudation rates vary between 52 mm ka 1 in the arid northern regions of the mountains and 2700 mm ka 1 in the more humid southern sector we select three basins where the influence of precipitation on denudation rates can be isolated from the effects of crustal uplift and find that there is no apparent relationship between denudation rates and precipitation denudation rates differ more than five fold on the opposing slopes of mill creek a valley bisected by a major splay of the san andreas fault and we propose that this denudation rate disparity can be best explained by variations in uplift rates across the fault the results suggest that crustal uplift is the mechanism that underpins the 50 fold variability in denudation rates we have measured in the san bernardino mountains but that this must be facilitated by sufficient precipitation to remove valley fill deposits

quantifying quartz enrichment and its consequences for cosmogenic measurements of erosion rates from alluvial sediment and regolith abstract in situ cosmogenic 26 al and 10 be record the residence time of quartz grains near the earth s surface and thus can be used to measure whole catchment erosion rates averaged over millennial time scales quartz is enriched in hillslope regolith by the dissolution of more soluble minerals thus its residence time will be longer than the regolith average it has been noted that this introduces a bias into erosion rate estimates derived from cosmogenic nuclide concentrations in regolith or alluvium geomorphology 27 1999 131 but the magnitude of this bias has not previously been measured the enrichment of quartz in regolith and the resulting bias in cosmogenic erosion rate estimates can be quantified using concentrations of immobile elements such as zirconium in bedrock and regolith here we show that the erosion rate bias introduced by regolith dissolution is less than 12 across 22 granitic catchments that span a wide range of temperate climates except in extreme weathering environments biases due to regolith dissolution will be a small component of the overall uncertainty in cosmogenic erosion rate measurements

iron isotope investigation of hydrothermal and sedimentary pyrite and their aqueous dissolution products abstract oxidative dissolution experiments were carried out on pyrite from multiple petrogenetic environments hydrothermal sedimentary and coal related nodules to investigate possible variations in the iron isotopic composition of pyrite and the products of pyrite dissolution the experimental materials were leached under carefully controlled abiotic conditions and a subset of leachates and starting materials from these experiments was analyzed for 56fe 54fe by multicollector icp ms bulk pyrite 56fe values relative to irmm 014 ranged from 0 1 to 1 3 with hydrothermal bulk pyrite values

erosional equilibrium and disequilibrium in the sierra nevada inferred from cosmogenic 26al and 10be in alluvial sediment we used cosmogenic 26 al and 10 be in stream sediment to measure landscape scale erosion rates for topographically diverse catchments at seven sierra nevada sites at three sites erosion rates and hillslope gradients are strongly correlated increasing with proximity to fault scarps and river canyons which appear to have accelerated local base level lowering rates and thus increased catchment erosion rates by up to 15 fold at four other sites far from fault scarps and river canyons erosion rates are much more uniform and less sensitive to average hillslope gradient our measurements show that contrasts in landscape erosion rates cannot be inferred from hillslope gradients alone because landscapes can evolve toward a state of erosional equilibrium in which steep and gentle slopes erode at similar rates

rare earth element resources in coal mine drainage and treatment precipitates in the appalachian basin usa abstract drainages from abandoned coal mines in the appalachian basin represent a potential source of rare earth elements and yttrium rey many of which are considered to be critical resources due to their use in electronics and batteries we report rey data from coal mine drainage cmd sites and precipitates from cmd treatment systems throughout pennsylvania most cmd discharges are enriched in total rare earth elements relative to concentrations expected in unaffected surface or ground waters generally by 1 4 orders of magnitude relative to the north american shale composite nasc which approximates the rock with which mine waters interact cmd waters generally show a pattern of enrichment in the middle ree including several identified as critical resources nd eu dy tb low ph discharges tend to have higher rey concentrations than circumneutral discharges and a precipitous drop in concentration around ph 6 6 suggests adsorption of rey in the mine water flow path at near neutral ph values treatment precipitates including fe oxy hydroxides ca mg lime slurries and si and al rich precipitates are enriched in rey relative to the average cmd discharge value by factors of 103 104 while the discharges and precipitates analyzed in this study did not overlap in space and time the overall rey pattern of the precipitates approximate those of the cmd but with a slight depletion in light rare earth elements the higher rey concentrations in precipitates from systems treating low ph discharges most likely reflects the generally higher rey concentrations in these discharges but this needs to be established through direct comparisons over multiple seasonal cycles we estimate that coal mine drainage outflows in the appalachian basin generate a total of about 538 metric tons of rey per year in a dissolved state with 83 of that from low ph

accumulation of terrestrial organic carbon on an active continental margin offshore southwestern taiwan source to sink pathways of river borne organic particles abstract sediment samples 213 sites collected from the tectonic active continental margin offshore southwestern taiwan were analyzed for grain sizes organic carbon nitrogen and carbon isotopic composition to obtain mass accumulation rate of terrestrial organic carbon and carbon budget to evaluate fate of terrestrial organic carbon from small mountainous rivers on the continental margin offshore southwestern taiwan terrestrial organic carbon accumulation rates range from 0 29 to 45 6 g c m 2 yr 1 with a total accumulation budget of 0 063 mt yr 1 which accounts for less than 13 of total river particulate organic carbon loads exported from the adjacent rivers the gaoping a k a kaoping erhjen and tsengwen rivers this low burial efficiency of terrestrial organic carbon demonstrated that a majority of river borne particles together with organic materials was moved away from the study area for the river borne particles from the gaoping river a pair of depocenters in the upper slope flanking the gaoping submarine canyon are the locations where the maximum tc org accumulation rate were observed which hold up to 45 0 016 mt yr 1 of the calculated accumulation found in the study region on the other hand the occurrence of higher fraction terrestrial organic carbon in the upper and middle gaoping submarine canyon suggests that a majority of particulate organic carbon of the gaoping river was transported directly into the deep sea basin through the gaoping submarine canyon our results demonstrated that active margin with narrow shelf and slope is not an efficient sink for the large amount of terrigenous organic carbon supplied by the small rivers but a transient environment for these river derived particles

effective attenuation lengths of cosmic rays producing 10be and 26al in quartz implications for exposure age dating we have measured cosmic ray produced 10be t 1 5 my and 26al t 0 72 my as functions of depth in a core of quartz sandstone bedrock collected in south victoria land antarctica these data were used to place limits on the exposure age and erosion rate of the exposed surface and to calculate the effective attenuation lengths of cosmic rays producing these nuclides these latter results indicate that the production attenuation length for 26al is comparable to that for 10be this suggests that the production ratio 26al 10be does not vary substantially with depth in a rock and that its value at the surface of exposed rock is not strongly affected by erosional losses allowing wider use of the ratio in determining exposure ages

effects of physical erosion on chemical denudation rates a numerical modeling study of soil mantled hillslopes article i nfo many biogeochemical and earth surface processes depend critically on chemical weathering the immediate products of chemical weathering are present as solutes and secondary minerals in groundwater soils and streams and form the nutritional foundation for terrestrial biogeochemistry chemical weathering also contributes to physical erosion by weakening bedrock and producing easily erodible regolith and as the primary long term sink for atmospheric co2 it modulates earth s long term climate via the greenhouse effect long term chemical denudation rates on soil mantled hillslopes can be estimated from cosmogenic radionuclide crn concentrations in soil borne quartz and the enrichment of a chemically inert tracer in soil relative to its parent bedrock a technique that inherently assumes steady physical erosion over the timescale of crn accumulation we present a numerical model that computes changes in soil mineralogy and crn concentrations under time varying physical erosion rates and we use this model to assess the accuracy of the crn based technique for estimating chemical denudation rates in non steady conditions our modeling results suggest that crn based estimates of chemical denudation rates closely resemble actual chemical denudation rates averaged over the timescale of crn accumulation even during large amplitude and long period oscillations in physical erosion rates for example this model predicts that when physical erosion rates fluctuate sinusoidally by 50 of their mean over any period in time crn based estimates of chemical denudation rates should differ from actual chemical denudation rates by less than 15 our model also implies that chemical denudation rates should approach zero both when physical erosion rates approach zero because soluble minerals become depleted in the soil and when physical erosion rates approach the maximum soil production rate because soil thickness approaches zero modeled chemical denudation rates thus reach a maximum at intermediate physical erosion rates if this relationship holds in nature it implies that in rapidly eroding regions further increases in physical erosion rates e g due to increases in tectonic uplift rates may not necessarily lead to faster chemical denudation on soil mantled hillslopes published by elsevier b v

attenuation length for fast nucleon production of 10be derived from near surface production profiles abstract we have measured the fast nucleon production of 10 be to depths of 2 37 m 659 g cm 2 in a granodiorite core of uniform density and composition from the mt givens pluton on the western side of the sierra nevada california at 37 14 7 n 118 53 7 w and 2286 m the data are well fit with a simple exponential decrease yielding an apparent attenuation length of 10 be production of 177 4 2 g cm 2 the shallowest data point is from a depth of 1 24 cm 3 45 g cm 2 and shows no indication of a near surface flattening of the radionuclide inventory and hence the 10 be production rate

late quaternary climatic controls on erosion rates and geomorphic processes in western oregon usa climate regulation of erosion in unglaciated landscapes remains difficult to decipher while climate may disrupt process feedbacks that would otherwise steer landscapes toward steady erosion sediment transport processes tend to erase past climate landforms and thus bias landscape evolution interpretations here we couple a 50 k y paleoenvironmental record with 24 10be derived paleo erosion rates from a 63 m thick sediment archive in the unglaciated soil mantled oregon coast range our results span the forested marine oxygen isotope stage mis 3 50 29 ka the subalpine mis 2 29 14 ka and the forested mis 1 14 ka to present from 46 ka through 28 5 ka erosion rates increased from 0 06 mm yr 1 to 0 23 mm yr 1 coincident with declining temperatures mean mis 2 erosion rates remained at 0 21 mm yr 1 and declined with increasing mis 1 temperatures to the modern mean rate of 0 08 mm yr 1 paleoclimate reconstructions and a frost weathering model suggest periglacial processes were vigorous between 35 and 17 ka while steady erosion is often assumed our results suggest that climate strongly modulates soil production and transport on glacial interglacial time scales by applying a cosmogenic paleo erosion model to evaluate 10be concentrations in our sedimentary archive we demonstrate that the depth of soil mixing which is climate dependent controls the lag time required for cosmogenic erosion rates to track actual values our results challenge the widely held assumption that climate has minimal impact on erosion rates in unglaciated midlatitude terrain which invites reconsideration of the extent to which past climate regimes manifest in modern landscapes

effects of long soil surface residence times on apparent cosmogenic nuclide denudation rates and burial ages in the cradle of humankind south africa in situ cosmogenic nuclides are an important tool for quantifying landscape evolution and dating fossil bearing deposits in the cradle of humankind coh south africa this technique mainly employs cosmogenic 10 beryllium be 10 in river sediments to estimate denudation rates and the ratio of 26 aluminium al 26 to be 10 al 26 be 10 to constrain ages of sediment burial here we use be 10 and al 26 concentrations in bedrock and soil above the rising star cave the discovery site of homo naledi to constrain the denudation rate and the exposure history of soil on the surface apparent be 10 derived denudation rates obtained from pebble to cobble sized clasts and coarse sand in soil on average 3 59 0 27 m ma and 3 05 0 25 m ma respectively are 2 3 times lower than the bedrock denudation rates on average 9 46 0 68 m ma in addition soil samples yield an average al 26 be 10 ratio 5 12 0 27 that is significantly lower than the surface production ratio of 6 75 which suggests complex exposure histories these results are consistent with prolonged surface residence of up to 1 5 ma in vertically mixed soils that are up to 3 m thick we conclude that the be 10 concentrations accumulated in soils during the long near surface residence times can potentially cause underestimation of single nuclide be 10 catchment wide denudation rates in the coh further burial ages of cave sediment samples that consist of an amalgamation of sand size quartz grains could be overestimated if a pre burial al 26 be 10 ratio calculated from the surface production is assumed

oxidative dissolution of hydrothermal mixed sulphide ore an assessment of current knowledge in relation to seafloor massive sulphide mining highlights seafloor massive sulphides vary in mineralogy and oxidise at different rates galvanic cells play a role in increasing dissolution rates sms deposits that have been inactive for some time may have lost economic value the geochemistry of oxidation products has potential to be an exploration tool potential for anthropogenic release of heavy metals during seafloor mining any risk needs addressing by the isa prior to the formation of mining regulations the weathering process of seafloor massive sulphide sms deposits can be considered analogous to weathering of terrestrial volcanogenic massive sulphides vms deposits however in the context of sms deposits the process occurs in chemically buffered waters of near neutral ph resulting in the formation of insoluble fe oxy hydroxide minerals including goethite and hematite as well as sulphates such as jarosite as a result of this precipitation it is commonly assumed that any sms deposit is unlikely to exhibit a significant loss of metals dissolution and release of heavy metals into the water column however galvanic interactions have never been considered in this seafloor context whilst they have already been shown to have the ability to increase dissolution significantly in terrestrial deposits if heavy metal release is not temporally balanced by precipitation of oxide phases there is the potential that these metal occurrences lose economic value this is specifically significant if there is an industrial focus on exploiting deposits associated with hydrothermal vents that have been inactive for some time not only this but the geochemistry of weathering products gossans that are formed have the potential to be used as tools for exploration furthermore it is unknown what impact galvanic coupling may have with regards to anthropogenic release of heavy metals during seafloor mining of deposits associated with either active or inactive vents disturbance of sediment plume generation and dewatering process this environmental impact needs to be addressed prior to the formulation of regulations for deep sea mining by the international seabed authority the present review examines our current understanding of oxidation and dissolution of a mixed sulphide ore bringing together lines of evidence from a range of literature sources based on this review different seafloor sulphide ore deposits will dissolve by oxidation and release a variety of different metals economic and or toxic all at different rates with galvanic cells playing a role by increasing dissolution rates while precipitation of oxide and oxy hydroxide phases will occur it is unknown in both a natural weathering and anthropogenic mining context whether heavy metal release including economic and toxic metals is temporally balanced by this precipitation and any subsequent adsorption based on our current understanding certain sites will be more predisposed to oxidation as a result of their mineralogy those containing significant pyrrhotite marcasite galena and secondary copper sulphides and or environment higher temperatures and oxygen concentrations lower ph s furthermore certain sites pose more of an environmental risk in terms of toxicity than others with arc related sms deposits associated with higher concentrations of as pb sb cd and hg and ultra mafic hosted sms deposits associated with high concentrations of co and ni the review highlights the need for subsequent studies that investigate the natural weathering process of seafloor sulphide ore deposits including how this process impacts their economic value and consequent geochemical signature of oxides that are produced over time moreover this review underlines the necessity for experiments to elucidate the oxidative dissolution of ore throughout any mining process

holocene tectonic uplift deduced from elevated shorelines eastern coastal range of taiwan abstract this paper is concerned with the tectonic trends that can be deduced from the holocene raised shorelines between ch eng kung and hsin she along a 65 km long coastal sector in the eastern coastal range of taiwan sequences of up to eight superimposed shorelines have been identified in a single section twelve new radiocarbon dates six of which were obtained by accelerator mass spectrometry of in situ marine samples up to 40 m in altitude have confirmed a holocene age however it is difficult to define clearly the upper marine boundary in the highest holocene coastal terraces which have been uplifted to 65 70 m but have been capped by and often also interfingered with alluvial deposits high uplift rates ranging from 2 5 3 0 to over 8 mm yr have been inferred along the coast providing evidence of differential uplift in some cases uplift movements appear to have occurred by steps probably spasmodically recurrence periods of fast uplifts seem to be of the order of at most 1000 yr this means that a new spasmodic movement may be imminent because the last displacement 4 6 m has been dated about 1000 yr bp

dating of pliocene colorado river sediments implications for cosmogenic burial dating and the evolution of the lower colorado river we applied cosmogenic 26 al 10 be burial dating to sedimentary deposits of the ancestral colorado river we compared cosmogenic burial ages of sediments to the age of an independently well dated overlying basalt flow at one site and also applied cosmogenic burial dating to sediments with less precise independent age constraints all dated gravels yielded old ages that suggest several episodes of sediment burial over the past 5 3 m y comparison of burial ages to the overlying 4 4 ma basalt yielded good agreement and suggests that under the most favorable conditions cosmogenic burial dating can extend back 4 5 m y in contrast results from other sites with more broadly independent age constraints highlight the complexities inherent in burial dating these complexities arise from unknown and complicated burial histories insufficient shielding postburial production of cosmogenic isotopes by muons and unknown initial 26 al 10 be ratios nevertheless and in spite of the large range of burial ages and large uncertainties we identify samples that provide reasonable burial age constraints on the depositional history of sediment along the lower ancestral colorado river these samples suggest possible sediment deposition and burial at ca 5 3 4 7 and 3 6 ma our calculated basinwide erosion rate for sediment transported by the modern colorado river 187 mm k y 1 is higher than the modern erosion rates inferred from the historic sediment load 80 100 mm k y 1 in contrast basinwide paleo erosion rates calculated from pliocene sediments are all under 40 mm k y 1 the comparatively lower denudation rates calculated for the pliocene sediment samples are surprising given that the sampled time intervals include significant pliocene aggradation and may include much incision of the grand canyon and its tributaries this conflict may arise from extensive storage of sediment along the route of the colorado river slower paleobedrock erosion or the inclusion of sediments that were derived preferentially from higher elevations in the watershed

rock to sediment slope to sea with 10be rates of landscape change abstract measurements of cosmogenic nuclides predominately 10be allow new insights into the ways in which and the rates at which sediment is generated transported and deposited over timescales ranging from 103 to 106 years samples from rock exposures are used to estimate erosion rates at points on the landscape whereas samples of fluvial sediment provide estimates of basin scale rates of denudation integrated over 104 km2 nuclide data show that hilltop bare rock outcrops erode more slowly than basins as a whole suggesting the potential for relief to increase over time as well drained outcrops grow higher more elaborate experiments and interpretive models provide insight into the distribution of hillslope processes including the bedrock to soil conversion rate which appears to increase under shallow soil cover and then decrease under deeper soils changes in average nuclide activity down slopes can be used to estimate grain speed over millennia suggesting for example that sediment o

mineral specific chemical weathering rates over millennial timescales measurements at rio icacos puerto rico abstract mineral weathering plays a prominent role in many biogeochemical and geomorphological processes it supplies nutrients to soils and streams accelerates physical erosion by weakening bedrock and producing easily erodible soil and modulates earth s long term climate by drawing down atmospheric carbon dioxide we calculate mineral specific chemical weathering rates at two field sites in the rio icacos catchment puerto rico by combining new mineral abundance measurements from quantitative powder x ray diffraction xrd with existing measurements of i soil production rates from cosmogenic nuclides ii chemical alteration of the regolith from x ray fluorescence xrf and iii dust deposition rates the central purpose of this paper is to show that combining measurements of cosmogenic nuclides with xrf based geochemistry and xrd based mineralogy can in favorable cases provide weathering rates of abundant soluble mineral phases in actively eroding terrain to an accuracy of better than 20 of the mean even in places with high dust deposition rates mineral weathering at our two field sites is dominated by plagioclase at rates of 3274 575 mol ha 1 yr 1 and 3077 541 mol ha 1 yr 1 followed by hornblende at 187 71 mol ha 1 yr 1 and 308 93 mol ha 1 yr 1 within the uncertainty of our data all weathering of these primary minerals occurs below the saprolite soil interface our measurements imply that kaolinite production in saprolite is roughly 1 3 times faster than kaolinite weathering in the soil our results are the first to show that field measurements of cosmogenic nuclides xrf xrd and dust fluxes can be combined within the geochemical mass balance method to quantify long term mineral weathering rates even in locations with high dust deposition rates this implies that the mass balance method can be a valuable tool for quantifying the effects of climate vegetation tectonics and other factors on weathering rates of individual mineral phases

a reactive transport model for marcellus shale weathering abstract shale formations account for 25 of the land surface globally and contribute a large proportion of the natural gas used in the united states one of the most productive shale gas formations is the marcellus a black shale that is rich in organic matter and pyrite as a first step toward understanding how marcellus shale interacts with water in the surface or deep subsurface we developed a reactive transport model to simulate shale weathering under ambient temperature and pressure conditions constrained by soil and water chemistry data the simulation was carried out for 10 000 years since deglaciation assuming bedrock weathering and soil genesis began after the last glacial maximum results indicate weathering was initiated by pyrite dissolution for the first 1000 years leading to low ph and enhanced dissolution of chlorite and precipitation of iron hydroxides after pyrite depletion chlorite dissolved slowly primarily facilitated by the presence of co2 and organic acids forming vermiculite as a secondary mineral a sensitivity analysis indicated that the most important controls on weathering include the presence of reactive gases co2 and o2 specific surface area and flow velocity of infiltrating meteoric water the soil chemistry and mineralogy data could not be reproduced without including the reactive gases for example pyrite remained in the soil even after 10 000 years if o2 was not continuously present in the soil column likewise chlorite remained abundant and porosity remained small if co2 was not present in the soil gas the field observations were only simulated successfully when the modeled specific surface areas of the reactive minerals were 1 3 orders of magnitude smaller than surface area values measured for powdered minerals small surface areas could be consistent with the lack of accessibility of some fluids to mineral surfaces due to surface coatings in addition some mineral surface is likely interacting only with equilibrated pore fluids an increase in the water infiltration rate enhanced weathering by removing dissolution products and maintaining far from equilibrium conditions we conclude from these observations that availability of reactive surface area and transport of h2o and gases are the most important factors affecting rates of marcellus shale weathering of the in the shallow subsurface this weathering study documents the utility of reactive transport modeling for complex subsurface processes such modelling could be extended to understand interactions between injected fluids and marcellus shale gas reservoirs at higher temperature pressure and salinity conditions

stratigraphic modeling of the western taiwan foreland basin sediment flux from a growing mountain range and tectonic implications abstract sediment flux signals from source to sink in foreland basins preserve a record of tectonics sea level and climate through erosion and sedimentation however longitudinal sediment transport often occurs in foreland basins thus removing part of the orogenic material flux from foreland basin records here we use mass balance calculation and stratigraphic simulations of sediment fluxes for the taiwan orogen to provide an order of magnitude estimate of how much orogenic material may bypass a foreland basin our results indicate a significant potentially more than 50 mismatch between sediment volume currently preserved in the basin and the amount of material presumably eroded from the orogen since the onset of collision in taiwan this suggests either a significant overestimation of average erosion rates over the period concerned with orogenic development of taiwan or it supports previous paleogeographic work suggesting that longitudinal sediment transport in the paleo taiwan strait served as a major bypass conduit of importance for the establishment of a steady state orogen we identify candidate submarine topography in the south china sea that may preserve taiwan s missing erosional mass

long term controls on soil organic carbon with depth and time a case study from the cowlitz river chronosequence wa usa abstract over timescales of soil development millennia the capacity of soils to stabilize soil organic carbon soc is linked to soil development through changes in soil mineralogy and other soil properties in this study an extensive dataset of soil profile chemistry and mineralogy is compiled from the cowlitz river chronosequence crc wa usa the crc soils range in age from 0 25 to 1200 kyr spanning a developmental gradient encompassing clear changes in soil mineralogy chemistry and surface area comparison of these and other metrics of soil development with soc properties reveal several relationships that may be diagnostic of the long term coupling of soil development and c cycling specifically soc content was significantly correlated with sodium pyrophosphate extractable metals emphasizing the relevance of organo metal complexes in volcanic soils the depth distributions of organo metals and other secondary weathering products including the kaolin and short range order sro minerals support the so called binary composition of volcanic soils the formation of organo metal complexes limits the accumulation of secondary minerals in shallow soils whereas in deep soils with lower soc content secondary minerals accumulate in the crc soils secondary minerals formed in deep soils below 50 cm including smectite allophane fe oxides and dominated by the kaolin mineral halloysite the abundance of halloysite was significantly correlated with bulk soil surface area and 14 c content a proxy for the mean age of soc implying enhanced stability of c in deep soils allophane an sro mineral commonly associated with soc storage was not correlated with soc content or 14 c values in crc soils we propose conceptual framework to describe these observations based on a general understanding of pedogenesis in volcanic soils where soc cycling is coupled with soil development through the formation of and fate of organo metal or other mobile weathering products this framework highlights interactions between soc and soil development which may be applicable to other soils where organic inputs interact with the products of chemical weathering

quantifying effects of deep and near surface chemical erosion on cosmogenic nuclides in soils saprolite and sediment cosmogenic nuclides in rock soil and sediment are routinely used to measure denudation rates of catchments and hillslopes although it has been shown that these measurements are prone to biases due to chemical erosion in regolith most studies of cosmogenic nuclides have ignored this potential source of error here we quantify the extent to which overlooking effects of chemical erosion introduces bias in interpreting denudation rates from cosmogenic nuclides we consider two end member effects one due to weathering near the surface and the other due to weathering at depth near the surface chemical erosion influences nuclide concentrations in host minerals by enriching or depleting them relative to other more or less soluble minerals this increases or decreases their residence times relative to the regolith as a whole at depth where minerals are shielded from cosmic radiation chemical erosion causes denudation without influencing cosmogenic nuclide buildup if this effect is ignored denudation rates inferred from cosmogenic nuclides will be too low we derive a general expression termed the chemical erosion factor or cef which corrects for biases introduced by both deep and near surface chemical erosion in regolith the cef differs from the quartz enrichment factor of previous work in that it can also be applied to relatively soluble minerals such as olivine using data from diverse climatic settings we calculate cefs ranging from 1 03 to 1 87 for cosmogenic nuclides in quartz this implies that ignoring chemical erosion can lead to errors of close to 100 in intensely weathered regolith cef is strongly correlated with mean annual precipitation across our sites reflecting climatic influence on chemical weathering our results indicate that quantifying cefs is crucial in cosmogenic nuclide studies of landscapes where chemical erosion accounts for a significant fraction of the overall denudation copyright 2012 john wiley sons ltd

interpreting erosion rates from cosmogenic radionuclide concentrations measured in rapidly eroding terrain a combination of numerical analysis and 10be concentrations measured in sediment samples from the high relief torrente catchment southern spain allows us to investigate the sampling requirements for determining erosion rates using cosmogenic nuclides in high relief landslide dominated terrain we use simple modelling to quantify the effect of particle spalling and or landsliding on erosion rates determined using a cosmogenic in situ produced isotope analytical results show that the cosmogenic nuclide concentration of a surface experiencing regular detachment of a grain or block may be considered to be in steady state and in situ erosion rates estimated when an appropriate number of spatially independent samples are amalgamated we present equations that enable calculation of the number of bedrock samples that must be amalgamated for the estimation of mean erosion rates on an outcrop experiencing regular detachment of a grain or chip of thickness l every t years our findings confirm that mean catchment erosion rates may be reliably estimated from 10be concentrations in fluvial sediment in high relief rapidly eroding terrain these catchment wide integrated erosion rates can be calculated where erosion is primarily accomplished through shallow 3 m landslides are the dominant mode of erosion only minimum erosion rates can be determined lastly we present erosion rate measurements from the torrente catchment that reveal variation of two orders of magnitude 0 03 1 6 m ka 1 quantifying the high degree of spatial variation in erosion rates expected within rapidly uplifting catchments copyright 2006 john wiley sons ltd

spatial variability of 10be derived erosion rates across the southern peninsular indian escarpment a key to landscape evolution across passive margins abstract the persistence of significant topography in ancient tectonically inactive orogenic belts remains one of the outstanding questions in geomorphology in southern peninsular india the impressive topographic relief of the western ghat mountains in tectonic quiescence since at least ca 65 ma has raised important questions concerning the long term mechanism of topographic evolution quantifying the distribution of erosion in space and time is critical to understanding landscape evolution although the long term erosion rates are reasonably well known the short term erosion rates and the relative importance of factors controlling erosion in southern peninsular india are less well constrained we present a new suite of catchment averaged and local erosion rates using in situ produced 10be concentrations in river sediments and exposed bedrock samples in southern peninsular india catchment averaged erosion rates vary from 9 6 0 8 m ma 1 in the highlands to 114 3 13 8 m ma 1 on the escarpment side bedrock erosion rates range from 2 4 0 2 m ma 1 in the ridge top to 143 4 25 4 m ma 1 in active channel beds of the highlands catchment averaged erosion rates derived from the across escarpment westward draining catchments are significantly higher than those derived from the eastward draining over highland catchments the difference indicates that long term down wearing of the highland proceeds at lower rates than in the escarpment zones catchment averaged erosion rates are moderately correlated with mean hillslope angles and local relief whereas they are strongly correlated with catchment averaged channel steepness index this suggests that topographic steepness is the major control on the spatial variability of erosion while strong rainfall gradient is of minor importance in this area 10be derived average erosion rates in highlands are consistent with previous long term erosion rate estimated from thermochronometry these results collectively point to large scale steady state topography only decaying slowly with time steady state likely reflects the balance between erosion and isostatically driven uplift of the southern peninsular india

relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the central alps of switzerland 1 a north south traverse through the swiss central alps reveals that denudation rates correlate with recent rock uplift rates in both magnitude and spatial distribution this result emerges from a study of in situ produced cosmogenic 10be in riverborne quartz in central alpine catchments as a prerequisite we took care to investigate the potential influence of shielding from cosmic rays due to snow glaciers and topographic obstructions to calculate a possible memory from last glacial maximum lgm glaciation and to identify a watershed size that is appropriate for systematic sampling mean denudation rates are 0 27 0 14 mm a for the alpine foreland and 0 9 0 3 mm a for the crystalline central alps the measured cosmogenic nuclide derived denudation rates are in good agreement with post lgm lake infill rates and are about twice as high as denudation rates from apatite fission track ages that record denudation from 9 to 5 ma in general denudation rates are high in areas of high topography and high crustal thickness the similarity in the spatial distribution and magnitude of denudation rates and those of rock uplift rates can be interpreted in several ways 1 postglacial rebound or climate change has introduced a transient change in which both uplift and denudation follow each other with a short lag time 2 the amplitude of glacial to interglacial changes in both is small and is contained in the scatter of the data 3 both are driven by ongoing convergence where their similarity might hint at some form of long term quasi steady state or 4 enhanced continuous quaternary erosion and isostatic compensation of the mass removed accounts for the distribution of present day rock uplift

new insights into holocene marine terrace development caused by seismic and aseismic faulting in the coastal range eastern taiwan abstract the coastal range in eastern taiwan which has resulted from arc continent collisions involves well developed holocene uplifted marine terraces along a 140 km long stretch of the coast this is the first study that unraveled the aseismic generation of marine terraces associated with coseismic uplift along the creeping fault we organized dems lidar mapping and field surveys to obtain detailed and systematic measurements of the inner and outer edges and wave cut platform elevations along thirty three stream profile transects allowing us to locate the bedrock profile spatial and temporal variations in the 14c age are characterized by an offlapping built feature of significant seaward younging trend of ages across the marine terrace caused by aseismic and coseismic uplift thus heights of the bedrock riser and platform are caused by coseismic large earthquake and aseismic plus moderate coseismic vertical deformations during a large earthquake cycle respectively this indicates that each terrace duration and paleoshoreline ages can be used to infer the recurrence interval and the timing of large earthquake events respectively results of the age of the paleoshoreline indicate six paleoseismic events at 8500 6300 4800 3400 1700 and 700 yr bp this implies that the chihshang creeping fault could be capable of producing large earthquakes greater than m7 at millennial time scales associated with larger coseismic deformations the creep faulting associated with seismic and aseismic uplift is a dominant process constraining the holocene marine terrace evolution

historical coseismic uplift on euboea island greece abstract in the aegean region it is usually accepted that uplift is confined to the southern areas near the outer island arc whereas subsidence prevails in the inner basin areas however we give evidence of elevated notches andlithophaga shells dated by ams14c showing that holocene coseismic uplift of the order of about a metre occurred in inner aegean areas too and affected parts of the coasts of north and central euboea island between 510 and 380 b c and also possibly between 1050 and 900 b c

patterns of landscape evolution on the central and northern tibetan plateau investigated using in situ produced 10be concentrations from river sediments abstract quantifying long term erosion rates across the tibetan plateau and its bordering mountains is of critical importance to an understanding of the interaction between climate tectonic movement and landscape evolution we present a new dataset of basin wide erosion rates from the central and northern tibetan plateau derived using in situ produced 10 be concentrations of river sediments basin wide erosion rates from the central plateau range from 10 1 0 9 to 36 8 3 2 mm kyr slightly higher than published local erosion rates measured from bedrock surfaces these values indicate that long term downwearing of plateau surfaces proceeds at low rates and that the landscape is demonstrably stable in the central plateau in contrast basin wide erosion rates from the kunlun shan on the northern tibetan plateau range from 19 9 1 7 to 163 2 15 9 mm kyr although the erosion rates of many of these basins are much higher than the rates from the central plateau they are lower than published basin wide erosion rates from other mountains fringing the tibetan plateau probably because the basins in the kunlun shan include both areas of low relief plateau surface and high relief mountain catchments and may also result from retarded fluvial sediment transport in an arid climate significantly higher basin wide erosion rates derived from the tibetan plateau margin compared to the central plateau reflect a relatively stable plateau surface that is being dissected at its margins by active fluvial erosion

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

landscape evolution of a bedrock peneplain on the southern tibetan plateau revealed by in situ produced cosmogenic 10 be and 21 ne article i nfo 10 be cosmogenic 21 ne low relief bedrock surfaces that occur at high altitude are a common feature of cenozoic mountain belts and have often been used to infer a significant amount of rock uplift after their generation at low elevation the timescale over which such surfaces can be preserved at high elevation and the rate at which they are modi fied by weathering and erosion are poorly known here we use cosmogenic 10 be and 21 ne to quantify the landscape evolution of a bedrock peneplain in southern tibet that occurs at an altitude of 5300 m the pe neplain is developed in cretaceous granitoids and jurassic metasediments of the northern lhasa block 90 e 31 n and originally had a minimum extent of 150 km east west and 75 km north south it has been dissected by small rivers that generated a few hundred meters of relief and formed additional bedrock sur faces of limited extent at lower elevation local denudation rates for the peneplain and the lower bedrock surfaces based on 10 be concentrations in grus samples and amalgamated quartz clasts cluster between

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

holocene sea level highstand and its implications for the vertical stability of panglao island southwest bohol philippines abstract emerged tidal notches in panglao island southwest bohol central philippines were used to investigate relative sea level changes during the holocene the elevation and profile of a laterally continuous notch were surveyed at 22 sites around panglao island the tidal notch documents higher than present mean sea level pmsl consistent with regional field observations and predictions for mid holocene time the reconstructed paleo shoreline elevations range from 0 to 1 6 m above pmsl exhibiting a general increase to the northeast the more protected part of the coast this lateral variation in the holocene paleo mean sea level msl along with changes in notch depth and profile suggests tilting of the island best explained by differential land movement last interglacial msl estimates by previous workers also show tilting to the southwest moreover the holocene notch data suggest segmentation of the island into several blocks that tilt consistently to the southwest suggesting the presence of faults lineations in aerial photographs trending northeast southwest confirm the presence of these faults these data indicate differential land movements during the holocene and late pleistocene calculated rates of uplift are 0 3 and 0 06 mm yr for the holocene and for the late pleistocene respectively these values relative to the high uplift rates from tectonically active regions imply that panglao is relatively vertically stable after accounting for tectonic tilting mid holocene sea level is estimated at approximately 0 3 0 6 m

marine deposits of late glacial times exposed by tectonic uplift on the east coast of taiwan abstract marine sediments deposited some 14 000 years ago when the sea level was between 80 and 100 m below the present sea level have been found exposed at about 17 m in altitude near tu lan on the east coast of taiwan this implies a minimum average uplift rate of 7 6 0 9 mm yr similar values of tectonic uplift are not uncommon on the eastern coastal range of taiwan such rates of tectonic uplift among the highest reported in the literature are of the same order as present day maximum glacio isostatic uplift rates

vertical crustal movements in eastern taiwan and their tectonic implications abstract leveling surveys along several routes and tidal observations at various points in eastern taiwan demonstrate rapid vertical crustal movements and they provide an effective means for monitoring the effects of collision between the philippine sea plate and the eurasian plate rapid elevation changes were detected in the southern section of the longitudinal valley repeated releveling along three routes since 1984 reveals that the coastal range was uplifted with respect to the longitudinal valley floor at a rate of about 3 0 cm yr this deformation is found to be confined within a very narrow zone along the east coast of taiwan two surveys 1984 and 1987 revealed that the coast is also undergoing uplift but at different rates from 0 cm yr to 3 5 cm yr the point of the most rapid uplift is located near 23 n and the rate generally diminishes towards the north the changes in rates may be controlled by the movements across faults tidal observations while providing a local datum show that uplift of the tidal station has occurred significant horizontal creep has been observed across many faults but rapid vertical creep as observed in the longitudinal valley is not very common

catchment scale denudation and chemical erosion rates determined from 10be and mass balance geochemistry mt lofty ranges of south australia abstract global biogeochemical cycles have as a central component estimates of physical and chemical erosion rates these erosion rates are becoming better quantified by the development of a global database of cosmogenic radionuclide 10 be crn analyses of soil sediment and outcrops here we report the denudation rates for two small catchments 0 9 km 2 in the mt lofty ranges of south australia as determined from 10 be concentrations from quartz sand from the following landscape elements 1 dissected plateaux or summit surfaces 14 10 1 61 t km 2 y 1 2 sandstone outcrops 15 37 1 32 t km 2 y 1 3 zero order drainages 27 70 1 42 t km 2 y 1 and 4 stream sediment which reflect a mix of landscape elements 19 80 1 01 t km 2 y 1 thus the more slowly eroding plateaux and ridges when juxtaposed with the more rapidly eroding side slopes are leading to increased relief in this landscape chemical erosion rates for this landscape are determined by combining cosmogenic denudation rates with the geochemical mass balance of parent rock soil and saprolite utilizing zirconium immobility and existing mass balance methods two different methods were used to correct for chemical weathering and erosion in the saprolite zone that is shielded at depth from crn production the corrected values are higher than uncorrected values total denudation of 33 24 or 29 11 t km 2 y 1 and total chemical erosion of 15 64 or 13 68 t km 2 y 1 thus according to these methods 32 40 of the denudation is taking place by chemical weathering and erosion in the saprolite below crn production depth compared with other similar areas the overall denudation and chemical erosion rates are low in most areas with sub humid climates and tectonic uplift physical erosion is much greater than chemical erosion the low physical erosion rates in these mt lofty range catchments in what is a relatively active tectonic setting are thought to be due to low rainfall intensity during the winter wet season which inhibits physical erosion such as land sliding and debris flows

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

the impact of local geochemical variability on quantifying hillslope soil production and chemical weathering soil mantled upland landscapes are widespread across the habitable world support extensive life and are the interface between the atmosphere hydrosphere and lithosphere but typically are not cultivated soil found across such landscapes fits the conceptual framework of a physically mobile layer derived from the underlying parent material along with some locally derived organic content the extent and persistence of these upland soils depend on the long term balance between soil production and erosion here we briefly review methods used to quantify the physical and chemical processes of soil production and erosion and revisit three granitic study areas in southeastern australia and northern california that enabled early quantification of the soil production function and topographic controls on chemical weathering we then present new major and trace element data from 2 m by 2 m pits dug at each field site to quantify local variability of zr concentrations and the chemical index of alteration cia weathering indices used to determine chemical weathering rates and extents in soils and saprolites using both new and previously published data we compare differences between local variability and regional as well as intersite variability of these important indices for each of the 2 m pits we collected 25 samples and found that the simple mean and the 2 standard deviation best describe the local variation in the data we also find that the variability in the 2 m pit data lies within variability observed in the same data from samples collected in individual soil pits across each of the field sites and that the differences between sites are consistent with previously published results these observations highlight the importance of quantifying local scale variability in studies that use similar multifaceted measurements to quantify hillslope soil production and erosion processes

cosmogenic nuclide evidence for low weathering and denudation in the wet tropical highlands of sri lanka 1 some of the lowest weathering and erosion rates in any mountain range in the world have been measured using cosmogenic nuclides in the steep humid tropical highlands of sri lanka the total preanthropogenic denudation rates were measured in creek sediments and soil samples from unperturbed rain forest sites bedrock from mountain crests and bedrock from inselbergs denudation rates are in the range of 5 30 t km 2 yr 1 2 11 mm ky 1 these rates average denudation over the last 50 250 ky weathering exports in rivers draining the mountainous central highlands show that silicate weathering rates are also low varying from 5 to 20 t km 2 yr 1 today 2 7 mm ky 1 but they represent a significant fraction of the total denudation all these observations run contrary to the conventional geomorphologic and geochemical wisdom that would predict rapid erosion for highlands of high relief temperatures and precipitation we speculate that the high relief in sri lanka represents the remnant of a geomorphic block that was uplifted during rifting at 130 ma or even earlier and that was reduced to the interior of the island by rapid receding of escarpments after continental breakup it is possible that throughout this history hillslopes where not exposing bare bedrock were protected by thick weathered profiles such clay rich layers would inhibit silicate weathering by shielding bedrock from weathering agents in the absence of landscape rejuvenation physical erosion rates are low and fresh mineral surfaces are not being supplied the observation that wet steep tropical highlands can have low rates of rock weathering and erosion has some potentially profound implications for the long term controls of atmospheric co2 budgets high temperature and precipitation which are much invoked though controversial agents for silicate dissolution and co2 drawdown become ineffective in promoting weathering in areas that are not tectonically active

paleoerosion rates from cosmogenic 10be in a 1 3 ma terrace sequence response of the river meuse to changes in climate and rock uplift abstract river borne quartz carries a cosmogenic nuclide memory that is a function of the catchment wide erosion rate this record may be preserved in fluvial deposits such as river terraces if the age of a terrace is independently known and transport time in the river system is relatively short then the upstream erosion rate at the time of terrace deposition can be determined we have used cosmogenic nuclides to date river terraces in the lower meuse catchment the netherlands and to obtain a 1 3 ma record of paleoerosion rates in a 104 km2 drainage basin comprising the ardennes mountains paleoerosion rates were uniform within the range of 25 35 mm ka from 1 3 to 0 7 ma after 0 7 ma erosion rates have increased progressively to late pleistocene values of around 80 mm ka around 0 7 ma both climatic and tectonic boundary conditions changed the amplitude and duration of climate cycles increased significantly resulting in long periods of sustained low temperatures in the meuse catchment in additio

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

comparison of dissolution under oxic acid drainage conditions for eight sedimentary and hydrothermal pyrite samples the abiotic oxidative dissolution behaviors of eight natural pyrite samples five sedimentary and three hydrothermal from various geological environments were compared under oxic conditions at ph 3 and 6 in a highly controlled batch reactor dissolution system the three sedimentary pyrite samples associated with coal had greater specific surface areas and also exhibited greater apparent dissolution rates and extent than the other two sedimentary and three hydrothermal samples under both ph conditions however after normalizing for surface area the dissolution rate constants for the different pyrite samples were similar the greatest difference was between the two non coal sedimentary pyrite samples pyrite morphology and the presence of trace metals could contribute to the differences in dissolution behavior as reflected in the normalized dissolution rates the sulfur iron ratio observed in the aqueous solution at ph 3 increased with time but was always less than 2 0 predicted from the stoichiometry of dissolution for all the pyrite samples during the 24 h experimental duration this can be explained by the disproportionation dissociation of thiosulfate an initial product of pyrite dissolution to elemental sulfur and sulfate which does not occur in a 1 1 ratio the results of this work indicate the importance of extracting and using the specific pyrite s relevant to particular mining areas in order to understand pyrite dissolution rates and the influence of environmental conditions on those rates

a model for the termination of the ryukyu subduction zone against taiwan a junction of collision subduction separation and subduction boundaries 1 the nw moving philippine sea plate psp collides with the eurasian plate eup in the vicinity of taiwan and at the same time it subducts toward the north along sw ryukyu the ryukyu subduction zone terminates against eastern taiwan while the ryukyu trench is a linear bathymetric low about 100 km east of taiwan closer to taiwan it cannot be clearly identified bathymetrically owing to the deformation related to the collision making the location of the intersection of the ryukyu with taiwan difficult to decipher we propose a model for this complex of boundaries on the basis of seismicity and 3 d velocity structures in this model the intersection is placed at the latitude of about 23 7 n placing the northern part of the coastal range on eup as psp gets deeper along the subduction zone it collides with eup on the taiwan side only where they are in direct contact thus the eurasian plate on the taiwan side is being pushed and compressed by the nw moving philippine sea plate at increasing depth toward the north offshore of northeastern taiwan the wedge shaped eup on top of the ryukyu subducting plate is connected to the eup on the ryukyu side and coupled to the nw moving psp by friction at the plate interface the two sides of the eup above the western end of the subduction zone are not subjected to the same forces and a difference in motions can be expected the deformation of taiwan as revealed by continuous gps measurements geodetic movement along the east coast of taiwan and the formation of the hoping basin can be understood in terms of the proposed model

patterns of denudation through time in the san bernardino mountains california implications for early stage orogenesis abstract basin averaged cosmogenic 10 be concentrations apatite u th he thermochronometry and incision into a dated palaeosurface constrain spatial and temporal variations in the rates of denudation experienced during the early stages of orogenesis in the san bernardino mountains california cosmogenic 10 be analysis measures denudation over intermediate 10 2 10 4 years time scales and records rates which decrease from a maximum of 2700 500 mm ka 1 in the south to a minimum of 52 5 mm ka 1 in northern catchments corresponding rates from u th he and incision into a dated palaeosurface measure long term 10 6 years denudation rates which decrease from between 1200 400 mm ka 1 in the south to a minimum of 30 20 mm ka 1 in the north the temporal consistency observed in the broad scale patterns of denudation rates probably results from the persistent imprint of the initial crustal architecture and drainage network these have maintained an influence on slope distributions and are thus fundamental factors controlling the gross patterns of denudation throughout the early stages of orogenesis where variations between the denudation rates measured over different time scales are apparent the intermediate term rates are found to be consistently greater than the long term with the increase being more pronounced around the fault bounded peripheries of crustal blocks relative to quiescent block interiors this provides empirical support for a model of mountain building whereby topographic development is dictated by the headward retreat of drainage systems that propagate away from zones of displacement our findings indicate that recent localised increases in denudation rates in young fault block orogens may be explained by a progressive denudational response to prior tectonic uplift rather than a consequence of climatic change

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

late holocene coseismic uplift on the hua tung coast eastern taiwan evidence from mass mortality of intertidal organisms abstract the evidence of coseismic uplift on the dynamic wave dominated hua tung coast fringing the active coastal range eastern taiwan has been equivocal due to complex controls by wave and terrestrial sediment over morphological and ecological systems of the coast this study by applying radiocarbon dating methods demonstrates coseismic uplift nature of the coast by finding synchronously killed intertidal organisms mostly boring shell jouannetia sp stranded at different sites of the coast with distinct physiographic characters based on these data together with evidence from wave cut notch sequences two coseismic uplift systems are recognized one centers around the northern middle part of the coast and yields events with uplift amounts of maximal 3 6 m and an average recurrence interval of at least several hundred years the most recent activity of this system influencing at least 70 km of coast occurred at 0 9 ka the earthquake generating this event also triggered extensive landslides debris flows in the region another system exemplified by the uplift associated with the 2003 cheng kung earthquake centers on the southern part of the coast and yields uplift of likely

coral reefs and sea level change abstract coral reefs provide significant evidence for former sea level positions because of their geological preservation and suitability for dating interpretation of this evidence presumes an understanding of reef geomorphology modern reef organism distributions and environmental factors influencing them fossil reef terraces formed during the last interglacial marine oxygen isotope mis substage 5e 128 116 ka are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level implying less extensive icesheets than at present an elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift recent compilations suggest elevations up to 8 9 m but incorporate few observations from reefs where the last interglacial is found below sea level oscillation of sea level during mis 5e has been interpreted from several sites with recent studies inferring rapid rise of several metres at the end of the interglacial these interpretations are at the limits to the precision with which corals can currently be dated and their palaeo water depths inferred it is not surprising that constraining last interglacial sea level changes within uncertainties of less than 1 2 m remains controversial considering sea level variations recognised between reef sites in the holocene and observed geographical variation in isostatic or flexural adjustments fossil coral reefs on uplifting margins also provide clear evidence for mis substages 5c and 5a and those on huon peninsula indicate fluctuations related to heinrich events mis 3 interpretations show considerable variability between sites with still greater uncertainties about sea level timing and elevation during previous interglacials future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties submerged reefs have already yielded important information about sea level rise during the last deglaciation coring around barbados and tahiti as well as on the huon peninsula has produced a broadly consistent picture of ice melt reflecting eustatic change since the last glacial maximum these studies have shown the sensitivity of reefs to rapid sea level rise associated with meltwater pulses with some reefs drowning while others back stepped integrated ocean drilling program iodp expeditions to tahiti and recently the great barrier reef extended these records but details of timing nature and impact of deglacial meltwater pulses remain elusive studies of holocene reefs have indicated different growth strategies some kept up with sea level while others caught up when sea level decelerated holocene sea level appears to have experienced a gradual rise up to present across the caribbean providing accommodation space for reefs to accrete vertically whereas in the indo pacific sea level has been near its present level since 7 ka with many reef flats emergent following a slight fall of sea level caused by ocean siphoning microatolls on reef flats provide perhaps the clearest evidence of past sea level position but in their absence novel biological or other sea level indicators are required to better constrain palaeo water depths there is an urgent need for further research from additional key reef locations not only to decipher processes driving past sea level change and its geographical variability but also to better understand how coral reefs will respond in the context of future sea level rise

new geomorphic data on the active taiwan orogen a multisource approach a multisource and multiscale approach of taiwan morphotectonics combines different complementary geomorphic analyses based on a new digital elevation model dem side looking airborne radar slar and satellite spot imagery aerial photographs and control from independent field data this analysis enables us not only to present an integrated geomorphic description of the taiwan orogen but also to highlight some new geodynamic aspects well known major geological structures such as the longitudinal valley lishan pingtung and the foothills fault zones are of course clearly recognized but numerous previously unrecognized structures appear distributed within different regions of taiwan for instance transfer fault zones within the western foothills and the central range are identified based on analyses of lineaments and general morphology in many cases the existence of geomorphic features identified in general images is supported by the results of geological field analyses carried out independently in turn the field analyses of structures and mechanisms at some sites provide a key for interpreting similar geomorphic features in other areas examples are the conjugate pattern of strike slip faults within the central range and the oblique fold and thrust pattern of the coastal range furthermore neotectonic and morphologic analyses drainage and erosional surfaces have been combined in order to obtain a more comprehensive description and interpretation of neotectonic features in taiwan such as for the longitudinal valley fault next at a more general scale numerical processing of digital elevation models resulting in average topography summit level or base level maps allows identification of major features related to the dynamics of uplift and erosion and estimates of erosion balance finally a preliminary morphotectonic sketch map of taiwan combining information from all the sources listed above is presented