estimating long term cliff recession rates from shore platform widths coastal cliff erosion is a problem in many coastal areas however often only very limited data are available to quantify the rates of recession for the development of coastal management strategies in the soft flysch deposits of the waitemata group auckland new zealand coastal cliffs are associated with shore platforms two models exist for the profile evolution of shore platforms and associated cliffs the first suggests that an equilibrium profile develops in response to erosive processes and this profile subsequently migrates landward the second model suggests that the seaward margin of the shore platform is relatively static and the profile extends landward through a combination of cliff recession and platform lowering physical simulations and field measurements for mudstone and limestone lithologies indicate that the second model is more likely for soft flysch deposits a eustatic sea level curve for the weiti estuary auckland suggests that up to 7120f70 years have been available for shore platform development since sea level reached the present seaward margins of shore platforms shore platform widths were measured using gps at two sites in waitemata group rocks the north shore of auckland and the southern side of the tawharanui peninsula north auckland the long term cliff recession rates estimated from shore platform widths 1 4f0 1 to 14 3f0 1 mm y 1 are consistent with the lower end of the average range of cliff top and face recession rates published for waitemata group rocks using different methods 11 75 mm y 1 and in agreement with cliff base recession estimates 3 5 mm y 1 shore platform widths were qualitatively related to the rock mass characteristics of the associated cliffs and therefore platform widths could provide a method of identifying regions of potential hazard d 2005 elsevier b v all rights reserved

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

long term fluvial incision rates and postglacial river relaxation time in the french western alps from 10be dating of alluvial terraces with assessment of inheritance soil development and wind ablation effects studying river long profile development as a response to tectonic and climatic controls requires reliable age dating of paleo profile remnants preserved as river terraces cosmic ray exposure cre dating often represents the only method available to date river terraces but the interpretation of cosmogenic nuclide concentrations is complicated by pre depositional inheritance and post depositional disturbance of the terrace deposits through pedogenesis and surface inflation or deflation here we use cosmogenic 10be measurements to date alluvial terraces in the french western alps in order to estimate river incision rates and to infer river response to climatic fluctuations and tectonic forcing we assess inheritance by constructing 10be concentration vs pebble depth profiles and use a monte carlo technique to estimate terrace ages we find that inheritance is negligible on all terraces enabling us to date terraces as young as 5 ky terraces that predate the last glaciation experienced intense pedogenesis and wind ablation which led to significant scatter in the 10be concentrations of surface samples we assess these effects using a model of 10be ingrowth and show that the oldest cre ages of surface clasts are close to the probable terrace age we study two catchments which have undergone varying degrees of glacial disruption the buech river experienced variations in runoff and sediment flux during the last glaciation as well as occasional ice dammings of its outlet its upper terraces record incision rates averaged over 190 ky of 0 8 mm yr consistent with denudation rates estimated in the surrounding areas and suggesting long term stability of river incision rates climatic forcing is well documented for the drac river which was repeatedly dammed by glaciers during cold periods its postglacial incision history was triggered by an 800 m drop in base level following ice dam disappearance long profile development by knickpoint propagation explains the time lag of 2 5 ky between this base level drop and terrace abandonment upstream as well as subsequent peak incision rates of 6 cm yr followed by a gradual decrease in incision rates the present knickpoint location 55 km upstream from the glacial damming site enables us to calculate a fluvial response time of 15 20 ky controlled by knickpoint propagation rates of several meters per year within the drac river

structure and tectonics of the upper cenozoic puerto rico virgin islands carbonate platform as determined from seismic reflection studies the puerto rico virgin islands carbonate platform was deposited over an area of 18 000 km2 from early oligocene to holocene on top of an inactive and subsiding cretaceous earliest oligocene island arc regional single channel and multichannel seismic reflection lines presented in this study provide the first information on the regional stratigraphy and structure of this platform that has previously been known mainly from onshore stratigraphic sections of a relatively small 2250 km2 portion of the platform exposed by late neogene tectonic uplift along the north coast of puerto rico seismic reflection lines are used to map the thickness of the carbonate platform strata and to correlate this thickness with onshore outcrop and well data from northern and southern puerto rico st croix u s virgin islands and the saba bank limestone thickness variations from a little over 2 km to almost zero are used to subdivide the puerto rico virgin islands platform into five distinct carbonate provinces 1 north puerto rico area including the onshore exposures 2 virgin islands area 3 st croix and saba bank area 4 south puerto rico area and 5 mona passage area carbonate thickness and structural information from each area are used to test five previously proposed models for the deformation and vertical movements of the platform the most prominent feature of the platform in the puerto rico virgin islands area is a large east west trending arch the northern limb of this arch exhibits a smoother more uniform dip than the steeper more abruptly faulted southern limb the core of the arch is responsible for the exposure of arc basement rocks on puerto rico the origin of this arch which occurs over a 300 km wide area is best explained by north south shortening and arching caused by interaction at depth of subducted slabs of the north america and caribbean plates other important evidence for this model can be found in the benioff zones observed in the earthquake profiles loading of the caribbean plate results in downward flexing of the north america plate and causes the 4 km subsidence of the carbonate platform north of puerto rico

actively evolving microplate formation by oblique collision and sideways motion along strike slip faults an example from the northeastern caribbean plate margin abstract the pattern of folding faulting and late quaternary coral reef uplift rates in western and central hispaniola haiti and dominican republic suggest that the elongate gonave microplate a 190 000 km2 area of the northeastern caribbean plate is in the process of shearing off the caribbean plate and accreting to the north american plate late cenozoic transpression between the southeastern bahama platform and the caribbean plate in hispaniola has inhibited the eastward motion of the northeastern corner of the plate transpression is manifested in western and central hispaniola by the formation of regional scale folds that correspond to present day anticlinal topographic mountain chains continuous with offshore anticlinal ridges areas of most rapid quaternary uplift determined from onland coral reefs 125 ka and younger coincide with the axial traces of these folds offshore data suggest recent folding and faulting of the seafloor onshore reef data do not conclusively require late quaternary folding but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the northwest peninsula of haiti 0 37 mm yr to to the central part of the coast of western haiti 0 19 mm yr to the south central part of western haiti 0 mm yr formation of the 1200 km long enriquillo plantain garden walton fault zone as a bypass strike slip fault has isolated the southern edge of the gonave microplate and is allowing continued unimpeded eastward motion of a smaller caribbean plate past the zone of late neogene convergence and quaternary uplift of coral reefs in hispaniola offshore seismic reflection data from the jamaica passage the marine strait separating jamaica and haiti show that the enriquillo plantain garden fault zone forms a narrow but deep active fault bounded trough beneath the passage the active fault is continuous with active faults mapped onshore in western haiti and eastern jamaica the bathymetric deep is present because the jamaica passage fault segment represents a 50 km wide transtensional left step of the fault trace between haiti and jamaica onshore satellite imagery and field observations suggest that the enriquillo plantain garden fault forms a continuous trace extending from central hispaniola east of lake enriquillo dominican republic to the westernmost end of the southern peninsula of haiti the regional lineament corresponds to a recent fault scarp in quaternary alluvium of the clonard pull apart basin in the central part of the southern peninsula of haiti and suggests that at least this part of the lineament has undergone recent slip calmus 1983 has suggested a total offset of 30 50 km of the enriquillo plantain garden fault zone in the southern peninsula of haiti using the apparent offset of lithologic units seismic reflection data from lake enriquillo document recent deformation of quaternary lake sediments where the lineament crosses the lake leveling of the crest of a late holocene coral reef and associated algal tufa around lake enriquillo demonstrate late holocene vertical movement and tilting in a 1500 m wide zone parallel to the fault trend lateral offset is difficult to show in the enriquillo valley area because of rapid recent sedimentation into the valley the pattern of inactive strike slip faults and fold belts of cenozoic age in cuba and the yucatan basin suggest that two elongate microplates were sheared off the proto caribbean plate and accreted to the north american plate by a similar process in paleocene and eocene times age of terminal deformation in western central and eastern cuba is consistent with southeastward younging and migration of arc collision the similarity of the size and sequence of events in cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas

effects of terrain smoothing on topographic shielding correction factors for cosmogenic nuclide derived estimates of basin averaged denudation rates estimation of spatially averaged denudation rates from cosmogenic nuclide concentrations in sediments depends on the surface production rates the scaling methods of cosmic ray intensities and the correction algorithms for skyline snow and vegetation shielding used to calculate terrestrial cosmogenic nuclide production while the calculation of surface nuclide production and application of latitude altitude and palaeointensity scaling algorithms are subjects of active research the importance of additional correction for shielding by topographic obstructions snow and vegetation is the subject of ongoing debate the derivation of all additional correction factor for skyline shielding for large areas is still problematic one important issue that has yet to he addressed is the effect of the accuracy and resolution of terrain representation by a digital elevation model dem on topographic shielding collection factors topographic metrics scale with the resolution of the elevalion data and terrain smoothing has a potentially large effect on the correction of terrestrial cosmogenic nuclide production rates for skyline shielding for rough high relief landscapes the effect of terrain smoothing call easily exceed analytical errors and should be taken into account here we demonstrate the effect of terrain smoothing on topographic shielding correction factors for various topographic settings and introduce an empirical model for the estimation of topographic shielding factors based on landscape metrics copyright c 2008 john wiley and sons ltd

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

investigating the complex interface where bedrock transforms to regolith abstract the interface where bedrock transforms to regolith is not planar but rather has a roughness that varies with the scale of observation the complexity of this surface is manifested in both element depth and fragment size depth distributions and may sometimes be related to the longitudinal profiles of watershed streams the fractal nature of the bedrock regolith interface means that the interface has a thickness which is 20 m in two ridgetop examples from pennsylvania and puerto rico such weathering thicknesses modeled as a function of one dimensional fluid flow are affected by the balance between rates of weathering and erosion one dimensional models are consistent with weathering advance rates that vary with equilibrium solubility and porefluid velocities and not reaction kinetics however fluid flow is not strictly downward and one dimensional permeability of regolith changes as particle size and bulk density changes with depth thus both downward and lateral flow occurs especially at reaction fronts where reactions change permeability the rate of weathering advance is therefore affected by the 3 dimensional distribution of reaction zones that affect permeability across the watershed quantitative models of such phenomena over a range of spatial and temporal scales are needed

linking geomorphology weathering and cation availability in the luquillo mountains of puerto rico abstract we explored the links between geomorphology weathering and cation availability across the most common forest types and geologic provinces in the el yunque national forest puerto rico our goal was to connect the controls on primary mineral supply to soil with stocks of plant available cations we established a network of 216 soil profiles comprising toposequences ridges slopes and valleys in three forest types colorado palm and tabonuco on two parent rock types quartz diorite and volcaniclastic in a factorial design the landscape underlain by quartz diorite is divided into lower slopes that are eroding rapidly in response to renewed uplift in the last 5 ma and those above a regional knickpoint where remnant landforms are eroding more slowly quartz diorite derived soils 0 80 cm below the knickpoint have lost significantly less calcium ca magnesium mg and potassium k relative to parent material 80 65 and 57 respectively than those above it which have lost 95 81 and 83 p 90 of all base cations relative to parent material while geology and geomorphology exert the most control on the degree of soil weathering as measured by total soil cation loss relative to parent material exchangeable cations are influenced by geologic biologic and meteoric factors tabonuco forests have significantly higher exchangeable cation stocks 0 80 cm than colorado forests even in the 500 700 m elevation zone where the two forest types are not correlated with elevation p 0 02 0 005 and 0 002 for ca mg and k respectively forest type explains 30 of the variance in exchangeable mg and k stocks but only 10 of the variance in exchangeable ca quartz diorite derived soils below the knickpoint have 2 more exchangeable ca than those above it and within that rapidly eroding region sites closest in elevation to the knickpoint have 2 more again the isotopic composition of bulk soil and exchangeable strontium suggests that the high ca stocks below and near the knickpoint are mostly derived from primary mineral weathering whereas above the knickpoint exchangeable ca is supplied by atmospheric deposition these data demonstrate that regional uplift lithology weathering atmospheric inputs and forest communities combine to shape cation availability across the luquillo landscape and we hypothesize that similar interactions are important in other montane tropical forests

does decreasing paraglacial sediment supply slow knickpoint retreat in four rivers in western scotland for which there is a well constrained record of relative base level fall the rate of postglacial bedrock erosion is quantifi ed by measuring the concentration of in situ cosmogenic 10be on strath terraces downstream of headward retreating knickpoints along channel gradients in 10be exposure age show two distinct trends upstream younging and constant age which we interpret as diagnostic of knickpoint retreat and diffusive transport limited incision respectively we show that bedrock channel incision and regional formation of strath terraces began shortly after deglaciation ca 11 5 ka and that knickpoint retreat rates peaked in the early to mid holocene erosion rates have since decreased by two orders of magnitude converging in the late holocene to low rates independent of stream power per unit channel area we infer this regional slowing in postglacial knickpoint retreat to be the result of the depletion of paraglacial sediment supply over the holocene leading to a defi ciency in tools for bedrock erosion our results imply that episodes of major fl uvial erosion may be in tune with glacial cycles and that sediment depletion following glacial interglacial transitions may be an important cause of bedrock erosion rate variations in rivers draining glaciated landscapes

a tem and microprobe study of a two perthite alkali gabbro implications for the ternary feldspar system an unusual magmatic three feldspar syenogabbro occurs 3 m inside the contact of the klokken gabbro syenite stock it contains plagioclase mesoperthite and cryptoperthite together with a low temperature symplectite intergrowth textural relationships have been investigated by cathodoluminescence bulk chemistry by microprobe and exsolution microtextures and intracrystalline boundaries by tem the mesoperthite has a bulk composition around or26ab52an22 well outside accepted limits of ternary feldspar solid solution it is a mainly coherent lamellar intergrowth of sodic andesine and orthoclase with incipient mtwinning the cryptoperthite bulk composition around or61ab33an6 is a coherent lamellar intergrowth of orthoclase and sodic low oligoclase the compositions of the exsolved phases have been estimated the meso and cryptoperthite crystals have sharp boundaries with each other

the hemispherical asymmetry in the martian polar caps an energy balance model is used to study the behavior of co2 ice on mars the effect of the solar zenith angle dependence of albedo is to lengthen co2 ice lifetimes at the poles hemispherical asymmetries in cloud and dust abundance could result in the survival of seasonal co2 ice through summer in the south and not in the north in agreement with observations co2 ice observed in the summertime polar cap in the south could be of recent origin although a permanent co2 polar cap cannot be ruled out

correction of in situ cosmogenic nuclide production rates for geomagnetic field intensity variations during the past 800 000 years we present integrated relative production rates for cosmogenic nuclides in rock surfaces which take into account reported variations of the geomagnetic field intensity during the past 800 000 yr the calculations are based on the model simulating cosmic ray particle interactions with the earth s atmosphere given by masarik and beer simulation of particle fluxes and cosmogenic nuclide production in the earth s atmosphere j geophys res 104 d10 12099 12111 1999 corrections are nearly independent on altitude between sea level and at least 5000 m the correction factors are essentially identical for all stable and radioactive cosmogenic nuclides with half lives longer than a few hundred thousand years at the equator integrated production rates for exposure ages between 40 000 to 800 000 yr are 10 to 12 higher than the present day values whereas at latitudes 40 geomagnetic field intensity variations have hardly influenced in situ cosmogenic nuclide production correction factors for in situ 14c production rates differ from those of longer lived nuclides they are always smaller than 2 because the magnetic field intensity remained rather constant during the past 10 kyr when the major fraction of the 14c extant today was produced

increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides we quantify the difference between the human caused sediment yield and the natural rates of soil production and bedrock erosion in a now largely deforested tropical highland the present day rate of soil loss in the upper mahaweli catchment sri lanka is calculated by using suspended river load fluxes these data provide spatially averaged sediment yields of 130 2100 t km 2 yr 1 local rates of soil loss from agricultural plots on hillslopes are as high as 7000 t km 2 yr 1 by comparison natural rates of sediment generation as determined by measuring cosmogenic 1 0 be in quartz from sediments and soils are only 13 30 t km 2 yr 1 the natural rates presented here provide a benchmark against which recent erosion rates determined by various sediment gauging techniques can be referenced in the sri lankan highlands these results suggest that soil is now being lost 10 100 times faster from agriculturally utilized areas than it is being produced

determination of predevelopment denudation rates of an agricultural watershed cayaguas river puerto rico using in situ produced 10be in river borne quartz accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities to model global geochemical cycles and to examine interactions among climate weathering and uplift we present a simple approach to estimate predevelopment denudation rates using in situ produced cosmogenic 10be in fluvial sediments denudation processes in an agricultural watershed cayaguas river basin puerto rico and a matched undisturbed watershed icacos river basin were compared using 10be concentrations in quartz for various size fractions of bed material the coarse fractions in both watersheds bear the imprint of long subsurface residence times fine material from old shallow soils contributes little however to the present day sediment output of the cayaguas this confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the cayaguas basin and suggests that pre agricultural erosional conditions were comparable to those of the present day icacos

lithological and fluvial controls on the geomorphology of tropical montane stream channels in puerto rico an extensive survey and topographic analysis of five watersheds draining the luquillo mountains in north eastern puerto rico was conducted to decouple the relative influences of lithologic and hydraulic forces in shaping the morphology of tropical montane stream channels the luquillo mountains are a steep landscape composed of volcaniclastic and igneous rocks that exert a localized lithologic influence on the stream channels however the stream channels also experience strong hydraulic forcing due to high unit discharge in the humid rainforest environment gis based topographic analysis was used to examine channel profiles and survey data were used to analyze downstream changes in channel geometry grain sizes stream power and shear stresses results indicate that the longitudinal profiles are generally well graded but have concavities that reflect the influence of multiple rock types and colluvial alluvial transitions non fluvial processes such as landslides deliver coarse boulder sized sediment to the channels and may locally determine channel gradient and geometry median grain size is strongly related to drainage area and slope and coarsens in the headwaters before fining in the downstream reaches a pattern associated with a mid basin transition between colluvial and fluvial processes downstream hydraulic geometry relationships between discharge width and velocity although not depth are well developed for all watersheds stream power displays a mid basin maximum in all basins although the ratio of stream power to coarse grain size indicative of hydraulic forcing increases downstream excess dimensionless shear stress at bankfull flow wavers around the threshold for sediment mobility of the median grain size and does not vary systematically with bankfull discharge a common characteristic in self forming threshold alluvial channels the results suggest that although there is apparent bedrock and lithologic control on local reach scale channel morphology strong fluvial forces acting over time have been sufficient to override boundary resistance and give rise to systematic basin scale patterns copyright 2010 john wiley and sons ltd

should quaternary sea level changes be used to correct glacier elas vegetation belt altitudes and sea level temperatures for inferring climate changes abstract changes in the altitudes of glacier snowlines elas and the altitudes of montane vegetation belts vbas measure quaternary climatic change an accepted correction to such changes by deducting the amount of contemporary sea level fall is wrong since the air displaced by the ice sheets approximately fills the space left by the falling sea level and so there is no overall downward movement of the troposphere this also causes a reduced cooling at the lowered sea level relative to that at the former inter glacial sea level about 1 c at the las glacial maximum which reduces the discrepancies previously noted by others between terrestrial and marine estimates of sea level cooling the change in temperature is indicated by the product of the ela or vba lowering and the environmental lapse rate elr prior estimates of ela 900 135 m and elr 6 0 1 c km 1 would indicate a cooling of 5 4 c at interglacial sea level and 4 4 c at glacial sea level although glacial period elrs are not known reliably established ela corrections for local epeirogenic uplift or subsidence are appropriate

the quebradillas limestone miocene pliocene northern puerto rico and tectonics of the northeastern caribbean margin the uppermost formation of the limestone belt of northern puerto rico is herein redesignated the quebradillas limestone a type section is established within the original type locality north of the town of quebradillas as here redefined the quebradillas limestone consists of a limestone sequence overlying the uppermost amphistegina algal limestone of the aymamon limestone along highway 2 north of the town of quebradillas the formation consists of three types of limestone biomicrite which form the basis for subdividing the formation into three members the lower member consists of globigerine biomicrite and is 16 m thick in many areas the lower member contains thin beds of oyster shells and shell fragments inter bedded within marl both the matrix of the oyster bearing beds and the marl are rich in planktonic foraminifers the middle member is essentially operculinoides biomicrite and is slightly amphistegina algal biomicrite and its thickness is estimated to be 44 4 m the threefold subdivision has been recognized throughout the outcrop belt of the formation from the west coast of the island eastward to barceloneta it probably applies to the easternmost outcrops as well the quebradillas aymamon boundary is an erosional unconformity between the two formations the globigerine limestone of the lower member of the quebradillas fills solution cavities in the uppermost aymamon and in places the upper aymamon shows marked relief most of the quebradillas is pliocene in age although part of the lower member may be latest miocene the quebradillas limestone is a regressive sequence the lower member represents a lower neritic to upper bathyal environment the middle member an outer shelf environment and the upper member a forereef subtidal and intertidal beach environment the upper member is veneered by what appears to be a paleosol which in turn is overlain by quaternary eolianite marginal marine and marine deposits the quebradillas is not limited to only the onshore coastal area of the island but extends northward into the puerto rico trench above a water depth of 5 000 m the quebradillas covers an area of at least 4 000 km 2 on the southern slope of the trench and the total area could be as much as 9 000 km 2 seismic and dredge sample data suggest that the quebradillas consists of the same facies offshore as in both outcrop and one well onshore the presence of widespread quebradillas in the puerto rico trench has important tectonic implications for regional studies of both the puerto rico trench and the northern caribbean region

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

effects of a tectonically triggered wave of incision on riverine exports and soil mineralogy in the luquillo mountains of puerto rico we document the long term response of a tropical mountain stream to tectonics and show how this response exerts a first order spatial control on the delivery of weatherable minerals to forest soils in its catchment these minerals in turn affect nutrient availability and biogeochemical cycles the luquillo mountains is a rainforest covered isolated massif on puerto rico island instead of displaying typical concave up long profiles of most mountain streams the rivers draining the southern flank of these mountains display a systematic downstream increase in gradient using concentrations of in situ produced cosmogenic 10be in quartz from river sediments we find that the downstream steepening is due to the propagation of an erosion wave along the rivers from the coastal plain upstream toward the headwaters decreased 10be concentration along the steepened reaches knickpoint faces or knickzones results from faster denudation of the valley sides around the steepened reaches the upper portions of the steepened reaches knickpoint lips cluster in elevation around the altitude of a flat lying dissected surface traceable around the luquillo mountains inspection of similar platforms over other parts of puerto rico and in the surrounding seas suggests that the dissected surface is an uplifted shore platform formed in the early pliocene 4 my ago upstream of the knickpoints rivers possess alluvial reaches still graded to this uplifted platform they represent relict profiles of the rivers that once drained an island that was surrounded by the now uplifted platform we conclude that the knickpoints initiated when the platform started to rise above the caribbean sea the knickpoints then started propagating upstream defining the front of a slow moving wave of erosion 10be derived catchment scale denudation rates measured above and below the knickpoints indicate a 30 210 increase in denudation associated to the passage of the knickpoints mineralogical analysis of the soils show that soils upstream of the knickpoints overlie deeply depleted saprolite and only contain recalcitrant minerals whereas soils downstream of the knickpoints experience an input of fresh weatherable minerals this influx considerably increases nutrient availability porder et al 2015 in a forest where atmospheric inputs are otherwise the main source of nutrients mcdowell et al 1990 zarin and johnson 1995 pett ridge 2009

quantification of the transient response to base level fall in a small mountain catchment sierra nevada southern spain 1 we integrated optically stimulated luminescence dating and 10be cosmogenic nuclide measurements to quantify short to medium term 102 104 years catchment dynamics and response to active tectonics in the 27 km2 rio torrente catchment sierra nevada southern spain rapid base level fall has triggered knickpoint migration up both trunk and tributary channels resulting in two distinct geomorphic zones 1 a steep lower catchment with concordant rates of hillslope erosion and channel incision over both short 100 years 5 8 mm yr 1 and medium 12 ka 5 1 mm yr 1 timescales and 2 a low relief soil mantled upland topography with uniformly low bedrock and hillslope erosion rates 0 05 0 02 mm yr 1 the uniformity of erosion in this upland surface indicates that catchment topography was previously in steady state rapid river incision below the channel knickpoints has resulted in the development of steep landslide dominated hillslopes that are essentially tracking the incising channel the magnitude of base level fall required to generate these steep hillslopes is 100 m at least 50 m of this base level fall occurred during the past 21 ka these steep hillslopes are eroding back into the low angled upland surface at a much slower rate than the channel knickpoint consequently the trunk channel knickpoint has already reached the catchment headwaters while hillslopes continue to adjust to the new base level indicating that the channel profile will regain equilibrium form long before hillslopes thus hillslopes are the limiting factor for the duration of landscape transience in this small mountain catchment

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

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

three phase tectonic evolution of the northern margin of puerto rico as inferred from an integration of seismic reflection well and outcrop data abstract integration of seismic reflection well and outcrop data from the oligocene pliocene puerto rico virgin islands platform prvi platform north of puerto rico indicates that three major tectonic phases characterize this seismically active region within the north america caribbean plate boundary zone tectonic phase 1 cretaceous to eocene formation and sedimentary infilling from a southern source area into a forearc basin formed between down to the north normal faults near the present day coast of puerto rico and an outer arc ridge near the present day shelf break tectonic phase 1 concluded the last volcanic arc activity in puerto rico produced by the subduction of oceanic crust of the north america plate beneath the caribbean arc system formation of the outer arc high defining the northern limit of this elongate basin may have been related to the accretion of off scraped sedimentary rocks beneath the northern margin of puerto rico in a manner similar to that observed in active arcs the end of tectonic phase 1 is related to initial collision between the caribbean arc and the bahama carbonate platform tectonic phase 2 oligocene to pliocene formation of a 1600 m thick northward thickening prvi platform predominately formed by carbonate rocks this phase started with a period of non deposition and erosion resulting in an latest eocene oligocene unconformity the base of the prvi platform is formed by a 400 m thick middle to late oligocene basal siliciclastic sequence that prograded northward across the forearc basin depositional thicknesses of sedimentary layers deposited during phase 2 are controlled by two large arches the nnw trending guajataca arch appears to have formed as the result of tectonic activity in the mona passage area the northeast trending san juan arch cannot be related to any adjacent structure or plate boundary feature onlap relations between carbonate rocks of the platform and both arches suggest that the arches were most active in the period from middle oligocene to early miocene rocks deposited during tectonic phase 2 are surprisingly devoid of faults and folds given their central position within the north america caribbean strike slip plate boundary zone that is known from regional studies to have been active throughout the deposition of the platform rocks tectonic phase 3 pliocene to holocene northward tilting of the prvi platform submerged the northern edge of the platform to a depth of 4 km and elevated the southern edge of the platform to several hundred meters above sea level on puerto rico northward tilting of this area occurred on the northern limb of a large arch or anticline formed parallel to the long axis of the island of puerto rico and its shelf areas the arch formed in response to a post pliocene convergence between the north america and caribbean plates

atmospheric scaling of cosmogenic nuclide production climate effect 1 absorption of cosmic rays by atmospheric mass varies temporally due to a redistribution of atmospheric pressure by ice sheets during glaciations the compression and expansion of the atmosphere due to cooling and warming and changes in katabatic winds near large ice masses these atmospheric processes can result in changes in production rates of cosmogenic nuclides which when integrated over long exposure durations may result in 0 to 5 adjustments in site production rates depending on location combining a ccm3 model with imbedded ice sheets for 20 ka we show that production rates changes relative to today are greatest at high elevations 6 7 at 5 km altitude due to atmospheric compression from decreased temperature production rates at specific times for sites near ice sheet margins can be reduced more than 10 due to a combination of katabatic winds draining off the ice sheet margins and atmospheric cooling nunatak settings may be significantly affected by the climate effect due to persistent glacial atmospheric conditions atmospheric variability may explain some of the disparities among cosmogenic nuclide production rate calibrations

investigation of in situ weathering of quartz diorite bedrock in the rio icacos basin luquillo experimental forest puerto rico abstract the rio icacos basin in puerto rico is the site of the highest measured chemical solute fluxes for a catchment on granodiorite this is partly attributable to high annual rainfall 4300 mm high average temperature 23 c and moderate relief the bulk of these fluxes is contributed by dissolution of plagioclase and amphiboles in zones of partially weathered rock 0 5 1 5 m thick underlying saprolite these zones are characterized by systems of onion skin rindlets each 3 10 cm thick in which porosity development is dominated by weathering of plagioclase to kaolinite fe bearing aluminosilicate minerals hornblende augite and biotite persist in the weathered rock after plagioclase has weathered to completion but hornblende and augite disappear between the porous rindlet systems and saprolite a new watershed scale solute mass balance corroborates earlier studies and yields an overall reaction stoichiometry that closely resembles complete weathering of the rock except quartz and biotite to kaolinite and fe3 oxides our findings indicate that steady state assumptions are reasonable and useful in studying weathering at this site estimated steady state sediment yields based on net solute fluxes and average bedrock composition of 3 24 10 9 to 3 60 10 9 kg m 2 s 1 are smaller than measured values indicating that sediment generation is currently accelerated with respect to steady state however sediment generation has recently been closer to steady state since weathering within the rindlet systems occurs on multiple fronts moving upward and downward two new steady state conceptual models are developed to account for 1 multiple parallel weathering fronts and 2 differential rates of advance of weathering fronts due to porosity development based on these models in situ weathering rates for plagioclase at two sample locations of 2 7 10 15 and 5 0 10 15 mol na g 1 s 1 are calculated values comparable to bet surface area normalized rates of 2 7 10 16 to 5 0 10 15 mol na m 2 s 1