assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

a multiproxy approach to reconstructing sea surface conditions using coral skeleton geochemistry 1 we use elemental ratio mg ca sr ca u ca and ba ca and oxygen isotope data from a porites lutea coral head collected from offshore amedee island new caledonia 22 29 s 166 28 e to assess the degree to which changes in these geochemical variables reflect variations in sea surface conditions we have assessed the robustness of each geochemical proxy by comparing 25 years 1992 1968 of monthly geochemical variations with a local record of sea surface temperature sst and with the appropriate 1 by 1 grid box from a global gridded sst data set we conclude from our comparison that the most consistent proxies of monthly sst variations at this site are 18o r2 0 84 p 0001 and sr ca r2 0 84 p 0001 the fidelity of the coral based sr ca sst proxy was assessed via calibration verification exercises at new caledonia and rarotonga the paleoclimate accuracy of the coral sr ca sst technique is judged to be robust and the precision of the technique is estimated to be 0 3 0 5 2 based on the calibration verification exercise in contrast monthly variations in mg ca and u ca ratios are only moderately correlated with monthly sst variations r2 0 55 p 0001 for mg ca and r2 0 47 p 0001 the strength of the correlation between sst and mg ca and u ca varies as a function of time suggesting that variations in these ratios are not a simple function of sst variations this variability in goodness of fit between u ca sst and mg ca sst may ultimately limit the use of these ratios as coral paleothermometers averaging or stacking individual proxy sst records sr ca mg ca and u ca to generate a composite proxy sst record does not necessarily improve the proxy record if the signal to noise ratio in each proxy is highly variable for example stacking of sr ca mg ca u ca records at new caledonia produces a proxy sst time series that has greater standard error than the individual sr ca sst time series cf ordinary least squares standard error of 1 16 c versus 0 86 c ba ca variations have little correlation with sst sr ca mg ca or u ca variations at new caledonia in conclusion variations in oxygen isotopic composition of seawater calculated by removing the sr ca based temperature component of the 18o signal agree reasonably well with observed variations in sea surface salinity especially at the interannual timescale

two dimensional nonlinear diffusive numerical simulation of geomorphic modifications to cinder cones the temporal evolution of simple landforms such as cinder cones by nonlinear diffusive processes is studied through the use of a new 2d numerical model using well established and accurate numerical mathematics and high resolution digital elevation models dems extending 1d profile nonlinear diffusion analyses used in cinder cone hillslope and fault scarp evolution studies we have implemented a 2d numerical model with a spatially and temporally varying sediment transport rate coefficient scaled nonlinearly by the ratio of local slope to critical slope the high accuracy and efficient numerical implementation are documented in the paper and the matlab toolkit developed is used to solve for the developmentof an initial 2d cone form first we examine the nonlinear transport rule and suggest a refinement that accounts explicitly for flux at threshold slopes we find that the maximum diffusion necessarily introduced in the numerical model to avoid infinite rates at the critical slope controls the final morphology especially approaching steady state secondly solving the landscape evolution problem in 2d enables a natural accounting for sediment flux convergence or divergence in the profile thirdly the boundary behavior of a given landscape element controls much of what happens in that domain and so we allow for arbitrary flux magnitude or elevation boundary conditions fourthly landscapes are heterogeneous in their surface cover and so we allow for spatially and temporally varying transport rate k and we permit an arbitrary vertical displacement field within the model domain to test the new formulation for the nonlinear term the effect of variable diffusivity k and the numerical schemes implemented we apply the model to cinder cones built on the flanks of mount etna in 2001 and 2002 2003 we explore the effects of dem resolution with data from the 2001 cone and the utility of spatially variable diffusivity to explain the variation in erosion measured by differencing repeat light detection and ranging lidar surveys gathered in 2004 and 2007 over the 2002 2003 cone complex copyright 2013 john wiley sons ltd

evaluating fluvial terrace riser degradation using lidar derived topography an example from the northern tian shan china abstract the morphological degradation of fluvial terrace risers provides a constraint to terrace chronology in this study we morphologically date the terrace risers along the kuitun river on the north flank of the tian shan china and subsequently discuss possible relationships between terrace formation and the past regional climate changes and tectonic activity of the dushanzi fault related fold to do this 159 topographic profile swaths of terrace risers were extracted from lidar derived dem and were analysed to determine a range of best fitting morphological ages through monte carlo simulation a locally applicable sediment transport coefficient diffusivity was calibrated as 5 5 1 6 m 2 ky given the morphological age of the t1 t2 riser and its independently known age taking this calibrated coefficient we estimate age ranges of 11 6 3 4 ka 6 5 1 4 ka 5 3 1 1 ka and 4 2 1 2 ka for terraces t3 t4 t5 and t6 respectively under the assumption that the age of the riser is close to the abandonment age of the lower surface these new terrace ages combining climate proxy records from the oxygen isotope curve from the guliya ice cap and paleoearthquake events in the dushanzi fault related fold suggest that tectonic activity may be an important factor in the formation of lower terraces within the growing anticlines while in more extensive areas beyond anticlines climate changes controlled the main deposition and incision events in the present study area and thus terrace formation of t1 t3

the illusion of diffusion field evidence for depth dependent sediment transport soil covered upland landscapes are common in much of the habitable world and our understanding of their evolution as a function of different climatic tectonic and geologic regimes is important across a wide range of disciplines erosion laws direct quantitative study of the processes shaping earth s surface and form the basis of landscape evolution modeling but are based on limited field data here we use in situ produced cosmogenic 1 0 be and 2 6 al concentrations from granitic saprolite to quantify an exponential decline in soil production with increasing soil thickness for a new field site in point reyes california results are similar to soil production functions from two different previously studied field sites and are used with extensive measurements of soil thickness to quantify depth integrated sediment transport flux plots of calculated sediment fluxes against the product of soil depth and hillslope gradient provide the first field based evidence that soil transport is a nonlinear depth dependent function data from all sites suggest that the widely used linear diffusion equation is only appropriate for shallow gradient convex up regions while the depth dependent transport law is more broadly applicable quantifying both the mobile soil thickness and landscape morphology is therefore critical to understanding how landscapes evolve

fire and the evolution of steep soil mantled landscapes recent burns in the western united states attest to the signif icant geomorphic impact of fire in mountainous landscapes yet we lack the ability to predict and interpret fire related erosion over millennial time scales a diverse set of geomorphic processes is often invoked following fire the magnitude of postfire erosional processes coupled with temporal variations in fire frequency dic tate the extent to which fires affect sediment production and land scape evolution in the oregon coast range several models for long term rates of soil production and transport have been tested and calibrated although treatment of fire related processes has been limited following recent fires in the oregon coast range we observed extensive colluvial transport via dry ravel localized bed rock emergence due to excess transport and talus like accumula tion in adjacent low order valleys soils exhibited extreme but dis continuous hydrophobicity and no evidence for rilling or gullying was observed using a field based data set for fire induced dry rav el transport we calibrated a physically based transport model that indicates that soil flux varies nonlinearly with gradient the post fire critical gradient 1 03 which governs the slope at which flux increases rapidly is lower than the previously estimated long term value 1 27 reflecting the reduction of slope roughness from in cineration of vegetation by using a high resolution topographic data set generated via airborne laser swath mapping we modeled the spatial pattern of postfire and long term erosion rates postfire erosion rates exceed long term rates which average 0 1 mm yr 21 by a factor of six and subtle topographic variations generated local patches of rapid postfire erosion commonly 1 mm yr 21 our sim ulations indicate that fire related processes may account for 50 of temporally averaged sediment production on steep hillslopes our analysis provides a mechanistic explanation for the coincident early holocene timing of increased fire frequency and regional ag gradation in oregon coast range drainage basins given the sen sitivity of steep hillslopes to fire driven transport changes in cli mate and fire frequency may affect soil resources by perturbing the balance between soil transport and production

microdistribution of mg ca sr ca and ba ca ratios in pulleniatina obliquiloculata test by using a nanosims implication for the vital effect mechanism the mg ca ratio within foraminiferal calcareous tests shells is widely used to reconstruct past seawater temperature however recent studies reported that the organic components within a test affect the mg ca distribution in this study we have measured the mg ca sr ca and ba ca ratios within the planktonic foraminifera pulleniatina obliquiloculata by using a nanosims secondary ion mass spectrometer sims which has excellent spatial resolution 1 m and allows us to compare the distribution of chemical compositions with that of the organic components element compositions show banding distributions composed of alternately higher and lower values of those elemental ratios the mg ca ratios previously considered to be mainly controlled by calcification temperature show larger variations than the values expected from the seawater temperature at the habitat depth of p obliquiloculata comparison of the elemental distribution with the test microstructure reveals that the bands of high mg ca and sr ca ratios correspond with layers of the organic components such coincidence suggests that the organic components strongly affect the mg ca and sr ca ratios within a test in spite of the heterogeneous distribution temperature estimated from the averaged mg ca ratio within a test is consistent with seawater temperature at the habitat depth of p obliquiloculata indicating that whole mg ca ratio of foraminiferal test may be useful as paleotemperature proxy in contrast to the mg ca ratio the heterogenity in ba ca ratio which previously has been considered to be mainly controlled by the ambient seawater composition is not fully matched with the layers of the organic compositions although the organic components concentrate ba other unknown factors appear to also cause heterogenity in ba incorporation

age and duration of the emeishan flood volcanism sw china geochemistry and shrimp zircon u pb dating of silicic ignimbrites post volcanic xuanwei formation and clay tuff at the chaotian section abstract the age and duration of the emeishan basalts sw china remain poorly constrained largely due to the severe thermo tectonic overprinting of the ar ar system and failure to obtain zircon separates from erupted basalts in an attempt to solve this problem geochemical analyses and shrimp zircon u pb dating have been carried out on rare felsic ignimbrite in the uppermost of the emeishan lava succession the xuanwei formation which immediately overlies the emeishan basalts and a clay tuff at the middle late permian boundary at the chaotian section clastic rocks of the lowermost xuanwei formation group 1 in eastern emeishan large igneous province lip have a geochemical affinity to the emeishan felsic volcanic rocks whereas the overlying sediments group 2 are compositionally more akin to mafic components of the emeishan traps this is the reverse of volcanic sequence of the central emeishan lip where the felsic extrusives sit above predominant mafic rocks it is likely that the clastic rocks are water transported sediments resulting from erosion of the volcanic rocks in the center of the emeishan lip this interpretation is further supported by the general agreement between the age of the lowermost xuanwei formation 257 4 ma 260 5 ma and that of the silicic ignimbrite 263 4 ma and the clay tuff at the middle late permian boundary at chaotian 260 5 ma these ages interpreted as the termination age of the emeishan volcanism are indistinguishable within error from the middle late permian boundary age 260 4 0 4 ma and the main stage 259 262 3 ma of the emeishan volcanism inferred from dating of mafic and alkaline intrusions in the emeishan lip all these suggest that the emplacement of the emeishan volcanism took place over a very short interval moreover the temporal link and geochemical analyses suggest that the chaotian clay at the middle late permian boundary was genetically related to the emeishan silicic volcanism this together with the fact at that both the emeishan basalts and the chaotian clay rest on the maokou formation leads us to infer that the emeishan basalt was emplaced at the middle late permian boundary in this sense the emeishan volcanism can be regarded as a boundary event and its age is presumed at 260 ma although more precise dating is required both stratigraphic correlation and chronologic data presented in this paper lend supports to the notion that the emeishan volcanism was one of likely causes of the end guadalupian mass extinction

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

sediment transport by dry ravel 1 dry ravel is a general term that describes the rolling bouncing and sliding of individual particles down a slope and is a dominant hillslope sediment transport process in steep arid and semiarid landscapes during fires particles can be mobilized by the collapse of sediment wedges that have accumulated behind vegetation on a daily basis particles may be mobilized by bioturbation and by small landslides experiments on a dry ravel flume indicate that a basic expression of the momentum equation predicts the distance traveled by particles propelled down a rough surface this equation is further elaborated to produce a nonlinear slope dependent transport equation for dry ravel that represents the rate at which sediment crosses a contour width of slope sediment traps installed on two hillslope transects near santa barbara california measured the flux from dry ravel initiated by bioturbation and the data support the form of the equation additionally a physical model based on the infinite slope stability analysis is proposed for the initiation of dry ravel by landsliding the analytical result from this model is supported by experiments and field data reported by others

fitting degradation of shoreline scarps by a nonlinear diffusion model the diffusion model of degradation of topographic features is a promising means by which vertical offsets on holocene faults might be dated in order to calibrate the method we have examined present day profiles of wave cut shoreline scarps of late pleistocene lakes bonneville and lahontan it may be assumed that these scarps were initially at least as steep as the angle of repose offsets range from 1 to 12 m and present slope angles range from 9 to 29 a parameter called apparent diffusion age defined as half the mean square horizontal extent of the slope function of each profile is plotted as a function of scarp offset the points show a clear trend of apparent age increasing nearly linearly with offset if linear diffusion held and scarps were initially vertical apparent diffusion age would be the same for all the shoreline profiles the increasing trend can only partly be explained by nonvertical initial scarp slope and therefore the rate of transport of material downslope must increase significantly faster than a linear law in the range of slopes spanned by the data the transport law must become linear at small slope to reduce scatter between profiles with varying ambient slopes the transport law adopted for the purpose of dating is k0 1 5s2 where s is local slope the transport coefficient k0 is correlated inversely with fan slope suggesting that there is a dependence on the particle size distribution a table is included that allows easy application of the model to scarps with simple initial shape

computer simulation models of scoria cone degradation abstract long term erosional modifications of the relatively simple morphology of scoria cinder cones are ideally suited for study by field and computer simulation methods a series of temporally distinct cones in the san francisco and springerville volcanic fields of arizona provides the foundation for documenting the degradational evolution of scoria cones in a semi arid climate progressive changes due to erosion are illustrated by the systematic decrease with increasing age of various morphometric parameters including scoria cone height cone height width ratio hco wco crater depth width ratio and slope angle for example holocene latest pleistocene cones in the san francisco field have a mean hco wco value of 0 178 0 041 a mean maximum slope angle of 29 7 4 2 and a mean average slope angle of 26 4 7 3 whereas the group of pliocene cones have values of 0 077 0 024 20 5 5 8 and 8 7 2 7 respectively comparative morphology of scoria cones is a potentially useful dating tool for mapping volcanic fields in order to better understand the degradational modifications of these volcanic landforms we have developed a numerical approach to simulate the surficial processes responsible for the erosion of a typical scoria cone the simulation algorithm can apply either a linear diffusion equation model or a model with a nonlinear transport law using a finite difference formulation the simulation operates upon a three dimensional scoria cone input as a matrix of elevation values utilizing both field and model results the correlation between changing hco wco value cone age and computer time step was expressed graphically to derive comprehensive values of the transport or diffusion coefficient df for both volcanic fields for the san francisco volcanic field df had a calculated value of 21 4 m2 kyr for the linear model and 5 3 m kyr for the nonlinear model while for the springerville volcanic field df had a calculated value of 24 4 m2 kyr for the linear model and 6 3 m kyr for the nonlinear model

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

small crater modification on meridiani planum and implications for erosion rates and climate change on mars a morphometric and morphologic catalog of 100 small craters imaged by the opportunity rover over the 33 5 km traverse between eagle and endeavour craters on meridiani planum shows craters in six stages of degradation that range from fresh and blocky to eroded and shallow depressions ringed by planed off rim blocks the age of each morphologic class from 50 200 ka to 20 ma has been determined from the size frequency distribution of craters in the catalog the retention age of small craters on meridiani planum and the age of the latest phase of ripple migration the rate of degradation of the craters has been determined from crater depth rim height and ejecta removal over the class age these rates show a rapid decrease from 1 m myr for craters 1 ma to 0 1 m myr for craters 10 20 ma which can be explained by topographic diffusion with modeled diffusivities of 10 6 m2 yr in contrast to these relatively fast short term erosion rates previously estimated average erosion rates on mars over 100 myr and 3 gyr timescales from the amazonian and hesperian are of order 0 01 m myr which is 3 4 orders of magnitude slower than typical terrestrial rates erosion rates during the middle late noachian averaged over 250 myr and 700 myr intervals are around 1 m myr comparable to slow terrestrial erosion rates calculated over similar timescales this argues for a wet climate before 3 ga in which liquid water was the erosional agent followed by a dry environment dominated by slow eolian erosion

evaluation of oxygen isotope and mg ca ratios in high magnesium calcite from benthic foraminifera as a proxy for water temperature oxygen isotope ratios 18o and mg ca ratios in organically produced calcium carbonate calcite and aragonite by marine species have been used as proxies for paleotemperature the relationship between the components of large benthic foraminiferal tests high magnesium calcite and seawater temperature has been little investigated yet we conducted culture experiments using two species of reef dwelling large benthic foraminifera under six temperature conditions 21 30 c we selected the perforate species calcarina gaudichaudii and the imperforate species amphisorus kudakajimensis both of which are host to algal symbionts for the experiments the results indicated the significant correlation of mg ca ratios c gaudichaudii and a kudakajimensis and 18o c gaudichaudii with temperature the test weight of both species showed temperature dependency with maxima at 27 c or 29 c and subsequent decline at 30 c after correction for the contribution of the initial tests which can be calculated from the weight ratios of the initial and cultured tests the relationships of the mg ca ratios and 18o to temperature were obtained with the least squares best fit method as follows c gaudichaudii t 18 5 4 52 18oc 18osw a kudakajimensis t 25 0 4 96 18oc 18osw and c gaudichaudii and a kudakajimensis mg ca 2 85 t 81 20 we concluded that species specific calibration is unnecessary for mg ca temperature relationship although it is necessary for 18o related to the different calcification mechanisms of imperforate a kudakajimensis and perforate c gaudichaudii species

accurate estimation of sea surface temperatures using dissolution corrected calibrations for mg ca paleothermometry 1 paired 18o and mg ca measurements on the same foraminiferal shells offer the ability to independently estimate sea surface temperature sst changes and assess their temporal relationship to the growth and decay of continental ice sheets the accuracy of this method is confounded however by the absence of a quantitative method to correct mg ca records for alteration by dissolution here we describe dissolution corrected calibrations for mg ca paleothermometry in which the preexponent constant is a function of size normalized shell weight 1 for g ruber 212 300 m mg ca ruber 0 025 wt 0 11 e0 095t and b for g sacculifer 355 425 m mg ca sacc 0 0032 wt 0 181 e0 095t the new calibrations improve the accuracy of sst estimates and are globally applicable with this correction eastern equatorial atlantic sst during the last glacial maximum is estimated to be 2 9 0 4 c colder than today

the age of lathrop wells volcanic center an 40ar 39ar dating investigation the sup 40 ar sup 39 ar age spectrum analyses of basalt whole rock and partially degassed sanidine xenocrysts for the lathrop wells volcanic center nevada yield eruption ages of 77 3 plus minus 6 0 and 76 6 plus minus 4 9 ka 2 sigma for the ql sub 1 and ql sub 2 flows respectively basaltic samples were analyzed in four to six replicate runs and yield normally distributed plateau ages miocene ash flow tuff xenoliths were collected from the basaltic units with the majority of samples coming from the ql sub 2 the sanidines from the ql sub 2 xenoliths yielded apparent plateau ages n 10 ranging from 69 plus minus 17 to 309 plus minus 11 ka with a strong cluster n 6 at approximately 77 ka because the diffusion dimension of sanidine is approximated by the physical crystal size cracking of the sanidine following the development of an argon concentration profile may result in complex argon age spectra experimental studies exploring the natural and laboratory argon systematics of degassed sanidine reveal that crystal breakage and hf acid etching lead to anomalously old apparent ages these new ages for the ql sub 1 and ql sub 2 flows are analytically indistinguishable and agree well with published eruption ages determined by sup 3 he and sup 36 cl cosmogenic surface exposure dating methods we conclude that the ql submore 1 and ql sub 2 flows are temporally equivalent additionally the agreement between our eruption ages for these units and the published 76 plus minus 20 ka ital zreda ital et al 1993 sup 36 cl exposure age for the lathrop wells scoria cone qs sub 3 suggests that the cone may be temporally equivalent to the ql sub 1 and ql sub 2 flows we believe the simplest and most reasonable interpretation is that the volcanic center is monogenetic copyright 1999 american geophysical union less

degradation of 100 m scale rocky ejecta craters at the insight landing site on mars and implications for surface processes and erosion rates in the hesperian and amazonian rocky ejecta craters recs at the interior exploration using seismic investigations geodesy and heat transport insight landing site on elysium planitia mars provide constraints on crater modification and rates for the hesperian and amazonian the recs are between 10 m and 1 2 km in diameter and exhibit five classes of preservation class 1 represents pristine craters with sharp rims and abundant ejected rocks from classes 2 to 5 rims become more subdued craters are infilled and the ejecta become discontinuously distributed high resolution imaging science experiment digital elevation models indicate a maximum depth to diameter ratio of 0 15 which is lower than pristine models for craters of similar size the low ratio is related to the presence of a loosely consolidated regolith and early stage eolian infill rim heights have an average height to diameter ratio of 0 03 for the most pristine class the size frequency distribution of recs plotted using cumulative and differential methods indicates that crater classes within the diameter range of 200 m to 1 2 km are separated by 100 to 200 myr smaller craters degrade faster with classes separated by 100 myr rim erosion can be entirely modeled by nonlinear diffusional processes using the calculated timescales and a constant diffusivity of 8 10 7 m 2 year for craters 200 to 500 m in diameter diffusion models only partly capture depth related degradation which requires eolian infill depth degradation and rim erosion rates are 10 2 to 10 3 m myr respectively the rates are consistent with relatively slow modification that is typical of the last two epochs of martian history

distribution and occurrence of ge and related trace elements in sphalerite from the lehong carbonate hosted zn pb deposit northeastern yunnan china insights from sem and la icp ms studies abstract the rapid increase in the economic importance of germanium ge is driving further study of its geological cycle and the factors controlling its concentration in minerals the emerging la icp ms analytic technique is playing a significant insight into the geochemical characteristics of sphalerite in this study la icp ms and sem analyses were carried out aiming to constrain the substitution mechanisms of ge and related trace elements and to trace the evolution of hydrothermal fluids la icp ms element mapping and sem study showed that no ge bearing micro minerals are observed in the lehong deposit all spot analysis data indicate notable binary correlations between cu and ge and between ag and sb which suggests that the coupled substitutions are 3zn2 2cu ge4 and 2zn2 ag sb3 additionally the monovalent elements i e cu and ag approximately equal to the sum of all trivalent and tetravalent elements thus we consider that the monovalent cations may provide the charge balance in all of the coupled substitutions responsible for incorporating a wide range of trivalent and tetravalent cations especially in sn sb and ge in sphalerite at lehong the trace elements in sphalerite from two hydrothermal stages in the lehong deposit differ significantly early red brown sphalerite is more enriched in fe ge cu sb and ag than late yellow brown sphalerite suggesting that trace elements in sphalerite may have the potential to record the evolution of hydrothermal fluids early sphalerite is rich in fe and ge simultaneously which points toward coupled behavior of fe and ge in situ la icp ms data from sphalerite at lehong show that the cu contents in all samples are nearly double those of ge copper enriched in early sphalerite is an essential factor to promote the substitution of ge which results in the coupling of fe and ge in sphalerite during the evolution of hydrothermal fluids in addition sphalerite at depth is more enriched in mn ge cu and cd than shallow sphalerite there is a clear upward trend among mn ge cu and cd in sphalerite with increasing depth at lehong this relationship may be applied for exploration targeting

rapid analysis of high precision sr ca ratios in corals and other marine carbonates a method for rapid determination of high precision sr ca ratios in scleractinian corals is presented using an inductively coupled plasma atomic emission spectrophotometer samples are corrected for instrument drift using a reference solution similar to the approach used for analysis of stable isotopes using gas source mass spectrometry further correction for variation of the sr ca ratio with ca concentration is accomplished using internal standards the precision once all corrections have been made is better than 0 1 relative standard deviation 1 for samples of similar ca concentration and better than 0 2 for samples with variable ca concentrations this method increases the sample throughput by approximately a factor of 20 relative to thermal ionization mass spectrometry and significantly reduces instrument and per sample costs comparison of sr ca data for a coral from the galapagos islands with an instrumental temperature record shows excellent agreement and demonstrates the potential for application of this technique to samples of modern and fossil scleractinian corals and other marine carbonates including foraminifera

morphometry of scoria cones and their relation to geodynamic setting a dem based analysis abstract the morphometry of a great number of scoria cones belonging to volcanic fields of various geodynamic settings has been measured and analyzed addressing the question whether there is a relation between the prevalent cone shape in a given field and the geodynamic setting of the field itself morphometric analysis was carried out on freely downloadable digital elevation models dems the accuracy of the used dems and the associated error in scoria cone morphometry were determined by cross comparing high resolution lidar derived dems usgs ned tinitaly dem and aster gdem the 10 m tinitaly 01 and usgs ned dems are proven to be suitable for scoria cone morphometry whereas aster gdem can be used reliably for cones with volume greater than 30 10 6 m 3 according to a detailed morphometry of all scoria cones we propose that the cones related to subductional setting show relatively higher values of h c o w co and lower values of w cr w co than the cones related to extensional setting the detected differences can be imputable to peculiar eruption dynamics resulting in slight but systematic changes in shape and differences in lithological and sedimentological characteristics that govern post eruptive erosion to constrain the pathway of scoria cone erosion the detected morphometric changes were also interpreted using a simple linear degradation model utilizing the obtained simulation results the inferred initial cone base and the age of scoria cones we calculated a diffusion coefficient k for several dated cones which are related to the prevalent climate our results despite the high error associated allow to assess the median k for all volcanic fields due to the complexity of the factors behind it is not easy to understand if the prevalent shape characterizing a certain volcanic field is due mainly to sin eruptive or post eruptive mechanisms however our distinction between the two main geodynamic settings may be the first step to decipher these factors

geological features and origin of the huize carbonate hosted zn pb ag district yunnan south china abstract the huize zn pb ag district in the sichuan yunnan guizhou zn pb ag metallogenic region contains significant high grade zn pb ag deposits the total metal reserve of zn and pb exceeds 5 mt the district has the following geological characteristics 1 high ore grade zn pb 25 wt 2 enrichment in ag and a range of other trace elements ge in ga cd and tl with galena sphalerite and pyrite being the major carriers of ag ge cd and tl 3 ore distribution controlled by both structural and lithological features 4 simple and limited wall rock alteration 5 mineral zonation within the orebodies and 6 the presence of evaporite layers in the ore hosting wall rocks of the early carboniferous baizuo formation and the underlying basement fluid inclusion and isotope geochemical data indicate that the ore fluid has homogenisation temperatures of 165 220 c and salinities of 6 6 12 wt nacl equiv and that the ore forming fluids and metals were predominantly derived from the kunyang group basement rocks and the evaporite bearing rocks of the cover strata ores were deposited along favourable specific ore controlling structures the new laboratory and field studies indicate that the huize zn pb ag district is not a carbonate replacement deposit containing massive sulphides but rather the deposits can be designated as deformed carbonate hosted mvt type deposits detailed study of the deposits has provided new clues to the localisation of concealed orebodies in the huize zn pb ag district and of the potential for similar carbonate hosted sulphide deposits elsewhere in ne yunnan province as well as the sichuan yunnan guizhou zn pb ag metallogenic region

hillslope evolution by nonlinear creep and landsliding an experimental study landscape evolution models are widely used to explore links between tectonics climate and hillslope morphology yet mecha nisms of hillslope erosion remain poorly understood here we use a laboratory hillslope of granular material to experimentally test how creep and landsliding contribute to hillslope erosion in our experimental hillslope disturbance driven sediment transport rates increase nonlinearly with slope due to dilation driven gran ular creep and become increasingly episodic at steep slope angles as creep gives way to periodic landsliding we use spectral analysis to quantify the variability of sediment flux and estimate the slope dependent transition from creep to landsliding the power spec trum of sediment flux steepens with hillslope gradient exhibiting fractal 1 f scaling just below the creep landsliding transition by evolving the experimental hillslope under fixed base level boundary conditions we demonstrate how disturbance driven transport gen erates hillslope convexity the transient evolution is consistent with numerical predictions derived from a recently proposed nonlinear transport model as initially steep hillslopes are lowered rapidly by landsliding before slopes decay slowly by creep dominated transport

influences of coral genotype and seawater pco2 on skeletal ba ca and mg ca in cultured massive porites spp corals abstract coral skeletal ba ca is a proxy for seawater ba ca used to infer oceanic upwelling and terrigenous runoff while mg2 is implicated in the control of coral biomineralisation we cultured large individuals 12 cm diameter of 3 genotypes of massive adult porites spp corals over a range of seawater pco2 to test how atmospheric co2 variations affect skeletal ba ca and mg ca we identified the skeleton deposited after a 5 month acclimation period and analysed the skeletal ba ca and mg ca by secondary ion mass spectrometry skeletal mg ca varies significantly between some duplicate colonies of the same coral genotype hampering identification of genotype and seawater pco2 effects coral aragonite seawater ba ca partition coefficients kd ba ca do not vary significantly between duplicate colonies of the same coral genotype we observe large variations in kd ba ca between different massive porites spp coral genotypes irrespective of seawater pco2 these variations do not correlate with coral calcification photosynthesis or respiration rates or with skeletal kd mg ca or kd sr ca seawater pco2 does not significantly affect kd ba ca in 2 genotypes but kd ba ca is significantly higher at 750 atm seawater pco2 than at 180 atm in 1 p lutea genotype genotype specific variations in kd ba ca between different porites spp could yield large errors 250 in reconstructions of seawater ba when comparing ba ca between corals analysis of fossil coral specimens deposited at low seawater pco2 may underestimate past seawater ba ca and ocean upwelling freshwater inputs when compared with modern specimens but the effect is small in comparison with the observed difference between coral genotypes

nonlinear slope dependent sediment transport in cinder cone evolution sediment flux on transport limited hillslopes is well known to vary nonlinearly with slope diverging as the angle of stability is approached to date however no study has validated the precise form of the nonlinear slope dependent transport model over geologic time scales in a non steady state landform in this paper we show how cinder cones can be used to validate the nonlinear transport model using lathrop wells cinder cone in nye county nevada as a type example cinder cones are well suited for this purpose because they can be radiometrically dated and their angles of stability can be constrained by measurement of subsurface contacts between primary fallout and overlying colluvial deposits reworked from upslope forward model results with a generalized nonlinear transport model characterized by diffusivity and nonlinear exponent n show that the evolution of the cone rim and base are most sensitive to while the cone midpoint is most sensitive to n analyses of the full cone shape therefore permit the two model parameters to be independently inferred if the cone age and angle of stability are independently known results for lathrop wells imply that n 2 in the generalized nonlinear transport model which is consistent with roering et al 9s 1999 widely used form of that model

altervalent substitution of sodium for calcium in biogenic calcite and aragonite abstract sodium concentrations in biogenic caco3 are several thousands of parts per million and on a molar basis na is among the most abundant constituent minor element in these carbonates nevertheless the chemical form of na in caco3 is not well constrained we used synchrotron x ray spectroscopy to identify the dominant molecular host sites for na in biogenic calcite and aragonite precipitated by corals bivalves and foraminifera we also used the k edge x ray absorption near edge structure to investigate the chemical environment of na in biogenic calcium carbonates and identify the altervalent substitution of na into ca sites in the lattice structures of calcite and aragonite minor cation and anion concentrations in biogenic caco3 suggest that the principal substitution mechanism involves charge compensation through the creation of co32 vacancies the mostly homogeneous na concentrations in the skeletal microstructures of the various biota we examined indicate that environmental and biological controls such as temperature skeletal microstructure and calcification rates have only minor influences on skeletal na concentrations a decrease of na ca ratios with increasing age of foraminiferal shells picked from a quaternary sediment core indicates progressive release of na which suggests that structurally substituted na in biogenic caco3 is readily leached during burial diagenesis whereas the sediment that undergo diagenesis release some na back to the water column sodium co precipitation in biogenic caco3 serves as a potential sink of na for the ocean

on the fidelity of shell derived δ18oseawater estimates article i nfo 18 oseawater a robustproxyforsurfacesalinity we assessthe fidelity of shell derived 18 oseawater estimates for the surface dwelling foraminifer globigerinoides ruber white using an atlantic meridional coretop transect spanning basin scale temperature and salinity gradients shell derived and observed 18 oseawater values are well correlated r 2 0 77 but a large systematic bias is observed shell mg ca ratios are significantly elevated above values expected from observed and isotopic calcification temperatures in the saline subtropical gyres of both hemispheres this temperature independent shell mg ca ratio variability termed excess mg ca i s highly correlated with surface salinity r 2 0 77 and the observed salinity dependence 27 4 is much higher than indicated by culture studies 6 2 our coretop data are used to develop new atlantic basin temperature and salinity calibration equations that are accurate 1 1 c and 0 20 respectively precise r 2 0 82 and 0 81 respectively and verifiable using previously published data these results are valid for the relatively high salinities of the subtropical atlantic 35 5 37 3 we discover that inclusion of other published data from lower salinity regions b35 indicates little or no excess mg ca taken together these results point to a strongly non linear positive salinity effect on shell mg ca ratios that significantly affects the accuracy of sst and 18

post eruptive sediment transport and surface processes on unvegetated volcanic hillslopes a case study of black tank scoria cone cima volcanic field california abstract conical volcanic edifices that are made up from lapilli to block bomb pyroclastic successions such as scoria cones are widespread in terrestrial and extraterrestrial settings eruptive processes responsible for establishing the final facies architecture of a scoria cone are not well linked to numerical simulations of their post eruptive sediment transport using sedimentological geomorphic and 2d fragment morphology data from a 15 ky old scoria cone from the cima volcanic field california this study provides field evidence of the various post eruptive sediment transport and degradation processes of scoria cones located in arid to semi arid environments this study has revealed that pyroclast morphologies vary downslope due to syn eruptive granular flows along with post eruptive modification by rolling bouncing and sliding of individual particles down a slope and overland flow processes the variability of sediment transport rates on hillslopes are not directly controlled by local slope angle variability and the flank length but rather by grain size and morphological characteristics of particles such as shape irregularity of pyroclast fragments and block lapilli ratio due to the abundance of hillslopes degrading in unvegetated regions such as those found in the southwestern usa granulometric influences should be accounted for in the formulation of sediment transport laws for geomorphic modification of volcanic terrains over long geologic time

how long is a hillslope hillslope length is a fundamental attribute of landscapes intrinsically linked to drainage density landslide hazard biogeochemical cycling and hillslope sediment transport existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope area scaling where the hillslope domain transitions into the fluvial domain here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model dem based on flow directions calculated using pixel aspect until reaching the channel network defined using recently developed channel extraction algorithms through comparisons between these measurement techniques we show that estimating hillslope length from plots of topographic slope versus drainage area or by inverting measures of drainage density systematically underestimates hillslope length in addition hillslope lengths estimated by slope area scaling breaks show large variations between catchments of similar morphology and area we then use hillslope length relief structure of landscapes to explore nature of sediment flux operating on a landscape distinct topographic forms are predicted for end member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient because our method extracts hillslope profiles originating from every ridgetop pixel in a dem we show that the resulting population of hillslope length relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes we find that across a broad range of sites across the continental united states topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient

modulation and daily banding of mg ca in orbulina universa tests by symbiont photosynthesis and respiration a complication for seawater thermometry the mg ca composition of calcium carbonate tests shells secreted by planktonic foraminifera is increasingly being employed to estimate past seawater temperatures and reconstruct paleocean and climate records spanning hundreds of thousands of years we show using two high resolution microanalysis techniques that the final chamber of the planktonic foraminifera orbulina universa typically comprises between three and six paired low and high mg growth bands the number and spacing of these bands is consistent with a diurnal origin modulated by changing ph within the foraminiferal microenvironment due to the day night photosynthesis respiration cycle of algal symbionts the amplitude of mg ca variation within individual tests and across many daily growth bands cannot be accounted for by seawater temperature in the shallow euphotic zone habitat of o universa our results indicate the mg ca composition of calcite precipitated by o universa in nature is strongly influenced by diurnal changes in the biological activity of algal symbionts and the host foraminifer this brings into question the fundamental premise often made in applying mg ca palaeoseawater thermometry that the mg ca composition of foraminiferal calcite is determined by seawater temperature and whether the mg ca composition of other planktonic species that are more widely used for palaeoseawater thermometry are subject to similar influences 2004 elsevier b v all rights reserved

germanium geochemistry and mineralogy abstract germanium is enriched in the following geologic environments 1 1 iron meteorites and terrestrial iron nickel 2 2 sulfide ore deposits particularly those hosted by sedimentary rocks 3 3 iron oxide deposits 4 4 oxidized zones of ge bearing sulfide deposits 5 5 pegmatites greisens and skarns and 6 6 coal and lignitized wood in silicate melts ge is highly siderophile in the presence of native iron nickel otherwise it is highly lithophile among silicate minerals ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz in deposits formed from hydrothermal solutions ge tends to be enriched mostly in either sulfides or in fluorine bearing phases it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites greisens and skarns in sulfide deposits that formed from solutions having low to moderate sulfur activity ge is concentrated in sphalerite in amounts up to 3000 ppm sulfide deposits that formed from solutions having higher sulfur activity allowed ge to either form its own sulfides particularly with cu or to substitute for as sn or other metals in sulfosalts the ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids or is due to the incorporation of ge from the country rocks particularly from those containing organic material germanium bonds to lignin derivative organic compounds that are found in peat and lignite accounting for its common concentration in coals and related organic material germanium is precipitated from water together with iron hydroxide accounting for its concentration in some sedimentary and supergene iron oxide deposits it also is able to substitute for fe in magnetite in a variety of geologic environments in the oxidized zone of ge bearing sulfide deposits ge is concentrated in oxides hydroxides and hydroxy sulfates sometimes forming its own minerals it is particularly enriched in some iron and manganese bearing oxides and hydroxides including goethite up to 5300 ppm and hematite up to 7000 ppm

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

the coordination of mg in foraminiferal calcite the mg ca ratio of foraminiferal calcite is a widely accepted and applied empirical proxy for ocean temperature the analysis of foraminifera preserved in ocean sediments has been instrumental in developing our understanding of global climate but the mechanisms behind the proxy are largely unknown analogies have been drawn to the inorganic precipitation of calcite where the endothermic substitution of mg for ca is favoured at higher temperatures however evidence suggests that foraminiferal mg incorporation may be more complex foraminiferal magnesium is highly heterogeneous at the sub micron scale and high mg areas coincide with elevated concentrations of organic molecules na s and other trace elements fundamentally the incorporation mode of mg in foraminifera is unknown here we show that mg is uniformly substituted for ca within the calcite mineral lattice the consistency of mg specific x ray spectra gathered from nano scale regions across the shell test reveals that the coordination of mg is uniform the similarity of these spectra to that produced by dolomite shows that mg is present in an octahedral coordination ideally substituted for ca in a calcite crystal structure this demonstrates that mg is heterogeneous in concentration but not in structure the degree of this uniformity implies the action of a continuous mg incorporation mechanism and therefore calcification mechanism across these compositional bands in foraminifera this constitutes a fundamental step towards a mechanistic understanding of foraminiferal calcification processes and the incorporation of calcite bound palaeoenvironment proxies such as mg

arsenopyrite pyrite association in an orogenic gold ore tracing mineralization history from textures and trace elements laser ablation inductively coupled plasma mass spectrometry la icp ms spot analysis and element mapping coupled with high resolution focused ion beam scanning electron microscopy fib sem imaging has been performed on au hosting sulfides from a proterozoic orogenic gold deposit tanami gold province north central australia gold distribution patterns in the arsenopyrite pyrite assemblage which probably crystallized toward the end of the au forming event suggest a process of initial scavenging of au into arsenopyrite and subsequent remobilization of that au following brittle fracture gold expelled from the sulfide lattice during the remobilization event is reconcentrated around the margins of the same arsenopyrite grains and within swarms of crosscutting microfractures the distribution of pb bi and ag closely mimic au indicating that these elements were also reconcentrated preservation of oscillatory zonation patterns for co ni sb se and te in arsenopyrite imply however that no significant degree of sulfide recrystallization took place residual concentrations of invisible gold in grain centers are 5 ppm in arsenopyrite and 1 ppm in coexisting pyrite the presence of submicron sized pores is suggestive of a fluid driven process rather than solid state diffusion micron scale 2 10 m remobilized gold is accompanied by fine particles 200 nm 2 m and nanoparticles 200 nm of gold the extensive variation of au concentrations within single arsenopyrite grains underlines the significance of textures when using trace element data to understand how gold ores evolved

variability in magnesium carbon and oxygen isotope compositions of brachiopod shells implications for paleoceanographic studies abstract this study presents the carbon oxygen and magnesium isotope compositions of two modern brachiopods terebratalia transversa and frieleia halli and one fossil specimen 2 3 ma terebratula scillae the aim of this study is to investigate the variability of these isotopic compositions and to evaluate the potential of brachiopods as a proxy of past seawater 26mg values the two investigated brachiopod shells present the same range of 26mg variation up to 2 this variation cannot be ascribed to changes in environmental parameters temperature or ph as has been previously observed the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater in contrast the 26mg value of the primary layer is comparable to that of the secondary calcite layer value in both t scillae and t transversa negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions these trends can be explained by kinetic effects linked to changes in growth rate during the brachiopod life the innermost calcite layer of t transversa is in isotopic equilibrium for both oxygen and magnesium and could therefore be the best target for reconstructing past 26mg values of seawater

syn eruptive morphometric variability of monogenetic scoria cones according to wood s model morphometric parameters such as slope angle can provide valuable information about the age of conical volcanic edifices such as scoria cones assuming that their initial slopes range from 30 to 33 measured manually on topographic maps and assuming that their inner architectures are homogenous this study examines the morphometric variability of nine young a few thousand years old small volume scoria cones from tenerife canary islands using high resolution digital elevation models in order to assess their slope angle variability because of the young age and minimal development of gullies on the flanks their morphometric variability can be interpreted as the result of syn eruptive processes including 1 pre eruptive surface inclination 2 vent migration and lava outflow with associated crater breaching and 3 diversity of pyroclastic rocks accumulated in the flanks of these volcanic edifices results show that slope angles for flank sectors differ by up to 12 among the studied volcanoes which formed over the same period of time this range greatly exceeds the 2 3 indicated by wood the greater than expected original slope range suggests that use of morphometric data in terms of morphometry based relative dating and detection of erosional processes and settings must be done with great care or detailed knowledge about absolute ages and eruption history especially in field scale morphometric investigation

trace and minor elements in sphalerite from base metal deposits in south china a la icpms study laser ablation icp mass spectroscopy has been used to investigate the geochemistry of sphalerite in a range of nine zn pb deposits in south china the deposits which are of different ages and belong to different metallogenic provinces have been assigned to the following genetic types skarn hetaoping luziyuan syngenetic massive sulphide dabaoshan laochang and bainiuchang and mississippi valley type huize mengxing niujiaotang based on the features of the ore even though their origin is heavily debated based on other criteria the giant jinding deposit is considered separately sphalerite from each genetic class of deposit shows a distinct chemical signature sphalerite from the skarn deposits is characterised by elevated lattice bound concentrations of co and mn the distal character of these skarn systems is reflected by the low in content of sphalerite the three syngenetic massive sulphide deposits feature sphalerite strongly enriched in in sn and ga whereas the deposits of mvt type are typically enriched in ge cd tl and as these divergent characters are reflected in absolute element abundances as well as in element ratios time resolved depth profiles for sphalerite from the chinese deposits confirm the presence of elements such as co in ge ga and cd in solid solution but the dataset expands the understanding of sphalerite mineral chemistry by also indicating that other elements whose ability to enter the crystal structure of sphalerite has been previously debated ag sn tl sb may also be in solid solution sphalerite is a refractory mineral and trace element analysis of sphalerite shows promise as a tracer of ore genesis even in overprinted ores systematic work on larger sample suites may help define the geochemical signature of different metallogenic epochs in regions as geologically complex as south china and help resolve the mechanism by which many of the debated ore deposits were formed

mg coordination in biogenic carbonates constrained by theoretical and experimental xanes abstract incorporation of magnesium into biogenic calcium carbonate is widely used to infer the conditions of mineral growth from a mineralogical perspective the dominant chemical environment of mg and whether mg replaces calcium by ideal substitution in biogenic caco3 are still debated however here we show that energy positions and resonance features in experimental and theoretical xanes spectra can be used to identify the dominant molecular host site in all biogenic calcite which is produced by foraminifera corals bivalves and brachiopods the local environment of mg indicated that it is incorporated primarily as a structural substitute for calcium in the crystal lattice but in aragonitic coral and bivalves a pronounced effect of the organic fraction or disordered phases was observed these differences among caco3 polymorphs suggest that physicochemical parameters affect the final composition of biogenic calcite but in aragonite secreting organisms there may be physiological controls on mg concentrations in biogenic aragonite

detecting short term evolution of etnean scoria cones a lidar based approach the 2001 and 2002 2003 flank eruptions on mount etna italy were characterized by intense explosive activity which led to the formation of two large monogenetic scoria cones one from each eruption on the upper southern flank of the volcano continuous monitoring of etna especially during flank eruptions has provided detailed information on the growth of these cones they differ in genesis shape and size a set of high resolution 1 m digital elevation models dems derived from light detection and ranging lidar data collected during four different surveys 2004 2005 2006 and 2007 has been used to map morphology and to extract the morphometric parameters of the scoria cones by comparing lidar derived dems with a pre eruption 1998 10 m dem the volume of the two scoria cones was calculated for the first time comparison of the lidar derived dems revealed in unprecedented detail morphological changes during scoria cone degradation in particular the morphologically more exposed and structurally weaker 2002 2003 cone was eroded rapidly during the first few years after its emplacement mainly due to gravitational instability of slopes and wind erosion

high temporal resolution mg ca and ba ca records in modern porites lobata corals 1 secondary ion mass spectrometry sims was used to determine mg ca and ba ca variations across two skeletal structures the fasciculi and the centers of calcification cocs in two porites lobata corals of different linear extension rates from oahu hawaii both corals exhibit large mg and ba heterogeneity which is not related to sea surface temperature sst or composition higher concentrations of ba occur in the fasciculi and higher mg in the cocs of the slowly extending coral compared to the fast growing coral mg and ba concentrations are significantly higher in the cocs of both corals compared to the fasciculi trace element variations may reflect changes in the calcifying fluid composition or changes in skeletal trace element incorporation regressions between mg ba and sr reported in a prior publication indicate that the skeletal incorporation of each element is affected by a different factor or combination of factors smoothed sims records of ba ca variations across the fasciculi of the fast growing coral follow the seasonal trend predicted from sst and expected seawater chemistry variations smoothed sims mg ca records do not correlate with sst indicating that sims mg ca records cannot be used to estimate past ssts

evaluation of morphometry based dating of monogenetic volcanoes a case study from bandas del sur tenerife canary islands morphometry based dating provides a first order estimate of the temporal evolution of monogenetic volcanic edifices located within an intraplate monogenetic volcanic field or on the flanks of a polygenetic volcano two widely used morphometric parameters namely cone height width ratio hmax wco and slope angle were applied to extract chronological information and evaluate their accuracy for morphometry based ordering based on these quantitative parameters extracted from contour based digital elevation models dems two event orders for the bandas del sur in tenerife canary islands were constructed and compared with the existing k ar paleomagnetic and stratigraphic data the results obtained suggest that the commonly used hmax wco ratio is not reliable leading to inappropriate temporal order estimates while the slope angle gives slightly better results the overall performance of such descriptive parameters was however generally poor i e there is no strong correlation between morphometry and age the geomorphic morphometric mismatches could be the result of 1 the diversity of syn eruptive processes i e diverse initial morphologies causing geomorphic morphometric variability 2 contrasting edifice specific degradation that depends partly upon the inner facies architecture of the volcanic edifices 3 various external environmental controls e g tephra mantling from pyroclastic density currents unrelated to the edifice evaluated and 4 differences in the scale resolution of input data the observed degradation trend and changes in morphometric parameters over time do not support a simple degradation model for monogenetic scoria cones volcanoes

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

evolution of the bonneville shoreline scarp in west central utah comparison of scarp analysis methods and implications for the diffusion model of hillslope evolution abstract wave cut pluvial shoreline scarps are ideal natural experiments in hillslope evolution because the ages of these scarps are often precisely known and because they form with a range of heights alluvial textures and microclimates i e orientation previous work using midpoint slope methods on pluvial scarps in the basin and range concluded that scarp evolution is nonlinear and microclimatically controlled the purpose of this study was to further examine the influence of scarp height texture and microclimate in an attempt to calibrate a nonlinear model of scarp evolution to do this over 150 profiles of the bonneville shoreline in the adjacent snake and tule valleys west central utah were collected and analyzed by fitting the entire scarp profile to diffusion equation solutions taking into account uncertainty in the initial scarp angle in contrast to previous studies this analysis revealed no evidence for nonlinearity or microclimatic control to understand the reason for this discrepancy we undertook a systematic study of the accuracy of each scarp analysis method the midpoint slope inverse method was found to yield biased results with systematically higher diffusion ages for young tall scarps the slope offset method is unbiased but has limited resolution because it requires many scarp profiles to yield a single diffusion age a method that incorporates the full scarp profile and uncertainty in the initial scarp angle was found to be the most accurate technique the application of the full scarp method to the bonneville shoreline supports the use of a linear diffusion model for scarps up to 20 m in height scarp orientation had no discernable effect on diffusivity values soil texture was found to have a weak but significant inverse relationship with diffusivity values

an overview of biomineralization processes and the problem of the vital effect biomineralization links soft organic tissues which are compositionally akin to the atmosphere and oceans with the hard materials of the solid earth it provides organisms with skeletons and shells while they are alive and when they die these are deposited as sediment in environments from river plains to the deep ocean floor it is also these hard resistant products of life which are mainly responsible for the earth s fossil record consequently biomineralization involves biologists chemists and geologists in interdisciplinary studies at one of the interfaces between earth and life leadbeater and riding 1986 biomineralization refers to the processes by which organisms form minerals the control exerted by many organisms over mineral formation distinguishes these processes from abiotic mineralization the latter was the primary focus of earth scientists over the last century but the emergence of biogeochemistry and the urgency of understanding the past and future evolution of the earth are moving biological mineralization to the forefront of various fields of science including the earth sciences the growth in biogeochemistry has led to a number of new exciting research areas where the distinctions between the biological chemical and earth sciences disciplines melt away of the wonderful topics that are receiving renewed attention the study of biomineral formation is perhaps the most fascinating truly at the interface of earth and life biomineralization is a discipline that is certain to see major advancements as a new generation of scientists brings cross disciplinary training and new experimental and computational methods to the most daunting problems it is however by no means a new field the first book on biomineralization was published in 1924 in german by w j schmidt schmidt 1924 and the subject has continued to intrigue a dedicated community of scientists for many years until the early 1980s the field was known as

the influence of climate and microclimate aspect on soil creep efficiency cinder cone morphology and evolution along the eastern mediterranean golan heights although hillslope evolution has been subject to much investigation for more than a century the effect of climate on the morphology of soil mantled hillslopes remains poorly constrained in this study we perform numerical simulations of volcanic cinder cones in the golan heights eastern mediterranean to estimate soil transport efficiency across a significant north south gradient in mean annual precipitation 1100 to 500 mm we use the initial cinder cone morphology constrained by stratigraphy the modern hillslope form surveyed with sub meter accuracy and the eruption age based on 40ar 39ar chronology to predict the best fit value of the soil transport coefficient diffusivity based on a nonlinear transport model our results indicate that the best fit diffusivity k varies from 1 to 6 m2 ka 1 among the five cinder cones in our field area diffusivity k values vary systematically with precipitation and hillslope aspect specifically k is higher on south facing drier hillslopes and decreases with mean annual precipitation we interpret this climate dependency to reflect vegetation driven variations in apparent soil cohesion which increases with root network density and attenuation of rain splash and overland flow erosion which increases with vegetative ground cover to assess how vegetative root mass and ground cover vary with precipitation and aspect we quantified the spatial distribution of ndvi normalized difference vegetation index from aster satellite images and observed spatial variations that correlate with our calibrated values of k analysis of previously studied cinder cones in the usa can be used to extend our framework to arid domains this endeavor suggests a humped relationship between k and precipitation with maximum diffusivity at mean annual precipitation of 400 600 mm copyright 2017 john wiley sons ltd

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient

low magnesium calcite produced by coralline algae in seawater of late cretaceous composition abstract shifts in the mg ca ratio of seawater driven by changes in midocean ridge spreading rates have produced oscillations in the mineralogy of nonskeletal carbonate precipitates from seawater on time scales of 108 years since cambrian time skeletal mineralogies of anatomically simple organisms functioning as major reef builders or producers of shallow marine limestones have generally corresponded in mineral composition to nonskeletal precipitates here we report on experiments showing that the ambient mg ca ratio actually governs the skeletal mineralogy of some simple organisms in modern seas coralline algae produce skeletons of high mg calcite 4 mol mgco3 we grew three species of these algae in artificial seawaters having three different mg ca ratios all of the species incorporated amounts of mg into their skeletons in proportion to the ambient mg ca ratio mimicking the pattern for nonskeletal precipitation thus the algae calcified as if they were simply inducing precipitation from seawater through their consumption of co2 for photosynthesis presumably organic templates specify the calcite crystal structure of their skeletons in artificial seawater with the low mg ca ratio of late cretaceous seas the algae in our experiments produced low mg calcite 4 mol mgco3 the carbonate mineral formed by nonskeletal precipitation in those ancient seas our results suggest that many taxa that produce high mg calcite today produced low mg calcite in late cretaceous seas

influence of lithology on hillslope morphology and response to tectonic forcing in the northern sierra nevada of california 1 many geomorphic studies assume that bedrock geology is not a first order control on landscape form in order to isolate drivers of geomorphic change e g climate or tectonics yet underlying geology may influence the efficacy of soil production and sediment transport on hillslopes we performed quantitative analysis of lidar digital terrain models to examine the topographic form of hillslopes in two distinct lithologies in the feather river catchment in northern california a granodiorite pluton and metamorphosed volcanics the two sites separated by 2 km and spanning similar elevations were assumed to have similar climatic histories and are experiencing a transience in landscape evolution characterized by a propagating incision wave in response to accelerated surface uplift c 5 ma responding to increased incision rates hillslopes in granodiorite tend to have morphology similar to model predictions for steady state hillslopes suggesting that they adjust rapidly to keep pace with the incision wave by contrast hillslopes in metavolcanics exhibit high gradients but lower hilltop curvature indicative of ongoing transient adjustment to incision we used existing erosion rate data and the curvature of hilltops proximal to the main channels where hillslopes have most likely adjusted to accelerated erosion rates to demonstrate that the sediment transport coefficient is higher in granodiorite 8 8 m2 ka 1 than in metavolcanics 4 8 m2 ka 1 hillslopes in both lithologies get shorter i e drainage density increases with increasing erosion rates

trace elements of indium bearing sphalerite from tin polymetallic deposits in bolivia china and japan a femto second la icpms study abstract indium bearing tin polymetallic base metal deposits in japan toyoha ashio and akenobe china dulong and dachang and bolivia potosi huari huari bolivar and porco were studied using femto second laser ablation icpms fsla icpms and epma analyses for major and minor elements in sphalerite paying special attention to in concentrations sphalerite is a principal mineral in these tin polymetallic deposits and a broad range of in concentration is measured in the ores there are distinct differences in mode of occurrence of the sphalerite and the distribution of in the highest in concentration up to 18 wt occur as a zn in mineral within black sphalerite zones in an oscillatory zoned sphalerite from the huari huari deposits additionally jamesonite from the huari huari deposit also contains anomalous in values ranging from several hundreds to thousands g g sphalerite from the toyoha and the other bolivian deposits are characterized by oscillatory and chemical zoning whereas those from akenobe and the chinese deposits are represented by homogeneous distribution of in the 1000in zn values of sphalerite are in good agreement with those of the ore grade for each of the selected tin polymetallic deposits indicating that sphalerite is the principal host of in the in bearing sphalerite principally involves the combined coupled substitutions 2zn2 cu in3 3zn2 cu ag sn4 and 3zn2 2cu sn4 the first of these is apparent in sphalerite from huari huari and bolivar whereas the second is prominent in sphalerite from toyoha ashio potosi porco and dachang akenobe and dulong sphalerite features the dominant coupled substitution of 2zn2 cu or ag in3 owing to their poor sn content occasionally sub micron inclusions of minerals such as stannite and pb sb bearing sulfides can occur in sphalerite contributing to high cu sn and high ag contents respectively the observed correlations of each element in the in cu ag sn bearing sphalerite can be proposed as a fundamental reason for the indium enrichment related to sulfur rich oxidized magmatism in addition the ag content in sphalerite is considered a possible indicator of formation depth which ranges from plutonic to subvolcanic environments

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

morphometric and morphological development of holocene cinder cones a field and remote sensing study in the tolbachik volcanic field kamchatka article i nfo the evolution of landscape over time is a central aspect of geological paleogeographical and geomorphological studies volcanic features like cinder cones offer the opportunity to monitor the processes and development of the landscape cinder cones are perhaps the simplest and most common volcanic landforms in the world morphological and morphometric study of cinder cones has proven an efficient tool for determining their relative dates and the erosional processes affecting them the extensive kamchatka volcanic province russian far east with its large tolbachik cinder cone field is an excellent case study for spatial and temporal classification and calibration of changes in morphometric values with time we show how the morphological and morphometric values of the monogenetic cinder cones measured in the field and by digital elevation models can be used to validate their age and erosional processes field data were gps measurements of cinder cones formed at the tolbachik 1975 1976 eruption and of holocene cinder cones erosion processes on the cinder cones and lava flows were identified and evaluated for every studied cinder cone morphometric parameters were assessed on the basis of remotely sensed data and digital elevation model morphometric measurements were taken of cone height and slope and average axis diameter and the height width ratio was obtained the comparison of morphometric parameters calculated from aster dem and topographic map clearly supports the concept of relative morphometric dating as the most recent cinder cones are always associated with the highest slopes and h w ratio the measured morphometric values of the recent tolbachik cinder cones are valuable benchmark data for determining erosion rates such as the measured values for the paricutin cone in mexico after the 1943 eruption the variability of the morphometric values of the recent cinder cones is due to their lithological coarse composition a comparison with the older cinder cones in the area shows that the climatic conditions of the kamchatka peninsula and the slow development of vegetation cover determine a high rate of erosion and rapid change in the morphometric values as compared to published values for other volcanic fields

soil creep and convex upward velocity profiles theoretical and experimental investigation of disturbance driven sediment transport on hillslopes the movement of unconsolidated materials near the earth s surface is often driven by disturbances that occur at a range of spatial and temporal scales the nature of these disturbances ranges from highly variable such as tree turnover to periodic and predictable such as frost heave or creep to explore the effect of probabilistic disturbances on surface processes we formulated a granular creep model with analogy to rate process theory rpt used for chemical reactions according to the theory individual particles must be energized to a height greater than adjacent particles in order for grain dilation and transport to occur the height of neighbouring particles which is akin to activation energy in chemical reactions varies with slope angle such that energy barriers get smaller in the downslope direction as slopes steepen when slopes approach the friction limited angle of repose the height of energy barriers approaches zero and grains ow in the absence of disturbance an exponential function is used to describe the probability distribution of particle excitation height although alternative distributions are possible we tested model predictions of granular dynamics in an experimental sandpile in the sandpile acoustic energy serves as the disturbance agent such that grains dilate and shear in response particle velocities are controlled by the frequency of energy pulses that result in grain displacement using tracer particles we observed a convex upward velocity pro le near the surface of the sandpile consistent with predictions of our rpt based velocity model in addition we depth integrated the velocity model to predict how ux rates vary with inclination of the sandpile and observed non linear ux gradient curves consistent with model predictions by varying the acoustic energy level in the experimental sandpile we documented changes in the rate of grain movement similar changes in modelled velocities were achieved by varying the exponent of the particle excitation probability distribution the general agreement between observed and modelled granular behaviour in our simple laboratory sandpile supports the utility of rpt based methods for modelling transport processes e g soil creep frost heave and till deformation thus enabling us to account for the probabilistic nature of disturbances that liberate sediment in natural landscapes copyright 2004 john wiley sons ltd

correlation of homogenization temperatures of accessory minerals from sphalerite bearing deposits and ga ge model temperatures abstract the ga ge ratio in sphalerite can be related to the temperature of the initial fluids from which the sphalerite grew after mixing with various amounts of fluids from different origins the extent of mixing of the two fluids can be qualitatively derived from the pressure corrected homogenization temperature which represents the temperature after mixing of the fluids and the ga ge temperatures of sphalerite which indicates the temperature of the hot metal bearing initial fluids different temperature information strongly indicate that mixing of fluids did occur prior to sulphide formation

scarp degraded by linear diffusion inverse solution for age under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation a procedure is developed to invert a scarp profile to find its diffusion age diffusion age having dimension length 2 is the product of diffusivity times chronological age the second moment of scarp slope grows linearly with age this fact together with an assumption about initial scarp shape allows the inverse determination of diffusion age age found assuming a vertical initial scarp is termed apparent age any nonvertical initial scarp profile has a nonzero initial apparent age true diffusion age differs from apparent age by a fraction of scarp offset squared the inverse procedure applied to synthetic data yields the following rules of thumb evidence of initial scarp shape has been lost when apparent age reaches twice its initial value if a scarp is formed by two events the inversion gives their offset weighted mean age with an error that is a fraction of offset squared a scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age after scarps of two fault traces have diffused to appear as one the error in inferred age may be as large as half the apparent age variation of apparent age along strike would indicate multiple fault traces the simplicity of scarp profile measurement and this inversion makes profile analysis attractive if linearity of the flow law time for a free face to be reduced to the angle of repose and variation of diffusivity with climate and material could be established profile analysis would become a reliable dating technique

mg ca sr ca and stable isotopes in modern and holocene protothaca staminea shells from a northern california coastal upwelling region this study explores the potential of intertidal protothaca staminea shells as high resolution geochemical archives of environmental change in a coastal upwelling region mg ca and sr ca ratios were analyzed by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms at sub weekly temporal resolution in shells growing 1 mm per month growth patterns of a modern p staminea shell from humboldt bay california collected in december 1999 made it possible to infer a lifespan from 1993 to 1998 growth hiatuses in the shell may have excluded records of extreme events mg ca ratios appeared to be partly controlled by water temperature the correlation coefficient between temperature and mg ca was r 0 71 in one of four growth increments significant year to year differences in the sensitivity of mg ca to temperature in p staminea could not be explained however sr ca ratios appeared to be more closely related to shell growth rate oxygen isotopes measured at 2 week temporal resolution in the same shell did not show a clear relation to local temperature in summer possibly because temperatures were higher and less variable at the king salmon mudflat where the shell was collected than in the main channel of humboldt bay where water properties were monitored negative shell 13c values 0 5 marked spring and summer coastal upwelling events the mg contents of p staminea midden shells dated to 3 ka and 9 ka were significantly lower than in the modern shell this may have resulted from degradation of a mg rich shell organic matrix and precluded quantitative interpretation of the older high resolution records elevated 13c values in the 3 ka shell suggested that the individual grew in highly productive or stratified environment such as a shallow coastal embayment or lagoon

fault slip rates and initiation age based on diffusion equation modeling wasatch fault zone and eastern great basin models of the evolution of fault scarp morphology provide time elapsed since slip initiated on a faulted surface and may therefore provide more accurate estimates of slip rate than the rate calculated by dividing scarp offset by the age of the ruptured surface to accomplish this task linear and nonlinear models of sediment transport are calibrated from the morphology of lake bonneville shoreline scarps and fault scarps formed by multiple surface rupturing earthquakes along the wasatch fault zone wfz profile modeling of scarps formed by several events distributed through time is done using a constant slip rate csr solution and yields a value of a 1 2 slip rate diffusivity time elapsed since slip initiated on a fault is determined by establishing a value for and measuring total scarp offset csr nonlinear modeling 0 2 8 1 1 m2 kyr wfz of faults along the west slope of the oquirrh mountains indicates a slip rate of 0 1 mm yr since 50 to 65 ka which is corroborated by cosmogenic dating 10be 26al age 75 ka the slip rate along the west flank of the stansbury mountains varies from 0 04 to 0 2 mm yr for time frames of 10 to 100 ka with the most recent rupture on the northern portion of the fault zone 10 ka scarp analysis of the southern end of the nephi segment wfz suggests either temporal clustering or variable slip rate as indicated by differences in the short term 1 3 mm yr for 4 3 ka versus long term 0 4 mm yr for 70 ka slip rates

evaluation of linear and nonlinear sediment transport equations using hillslope morphology abstract although some simple erosive processes like soil creep or tillage redistribution may be satisfactorily described by linear diffusive equations the complexity of erosion phenomena requires the use of more complete nonlinear equations roering et al roering j j kichner j w dietrich w e 1999 evidence for nonlinear diffusive transport on hillslopes and implications for landscape morphology water resour res 35 853 870 have proposed a single test based on the relationship between the curvature and gradient of a hillslope rather then using a linear diffusion equation nevertheless this test based on steady state conditions is not complete as it is shown in this work with a counter example the hillslope profile used by roering et al roering j j kichner j w dietrich w e 1999 evidence for nonlinear diffusive transport on hillslopes and implications for landscape morphology water resour res 35 853 870 fig 2 can be generated either by a linear diffusion equation under transient conditions or a nonlinear diffusion equation under steady state conditions additional information on the soil profile changes would give a more complete interpretation of the hillslope evolution

gopher bioturbation field evidence for non linear hillslope diffusion it has generally been assumed that diffusive sediment transport on soil mantled hillslopes is linearly dependent on hillslope gradient fieldwork was done near santa barbara california to develop a sediment transport equation for bioturbation by the pocket gopher thomomys bottae and to determine whether it supports linear diffusion the route taken by the sediment is divided into two parts a subsurface path followed by a surface path the first is the transport of soil through the burrow to the burrow opening the second is the discharge of sediment from the burrow opening onto the hillslope surface the total volumetric sediment flux as a function of hillslope gradient is found to be qs cm3 cm 1 a 1 176 dz dx 3 189 dz dx 2 68 dz dx 34 dz dx 0 4 this result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport a one dimensional hillslope evolution program was used to evolve hillslope profiles according to non linear and linear diffusion and to compare them to a typical hillslope the non linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section copyright 2000 john wiley sons ltd

foraminiferal magnesium in globeriginoides sacculifer as a paleotemperature proxy foraminiferal magnesium shows increasing promise as a paleothermometer but the accuracy and precision are limited by biases introduced by partial dissolution salinity variations mg rich gametogenic calcite and contaminant phases we improved cleaning methods and reduced errors introduced by partial dissolution by sampling from well preserved cores in the equatorial atlantic and the caribbean sea with different dissolution histories all cores reveal a synchronous 25 increase in mg ca from the stage 2 3 boundary to the holocene core top indicating that dissolution is not a controlling factor modern temperatures estimated from core top mg ca are 24 5 25 0 c equal to mean annual water temperatures at 50 100 m we estimate that sea surface temperature increased by 2 6 c 1 3 from the last glacial maximum to the holocene holocene values were comparable to those during isotope stage 5e our data indicate that biases from contaminant phases and partial dissolution can be reduced this paleothermometer holds promise if uncertainties introduced by salinity variations and gametogenic calcite can be constrained

a biological origin for climate signals in corals trace element vital effects are ubiquitous in scleractinian coral skeletons 1 laser ablation icp ms was used to analyze mg sr and u at fine hundreds of microns and seasonal spatial scales in the reef coral porites and the non photosynthetic deep sea corals lophelia oculina and desmophyllum tropical corals display strong seasonal correlations between mg sr and u even when normal cycles are perturbed by unknown factors an inverse relationship between mg and u is a universal feature of all the corals but is much larger in deep corals despite stable environmental conditions this correlation originates from two aragonitic skeletal types mg rich opaque centers of calcification and u rich large translucent crystals the mg rich material probably precipitates rapidly and corresponds to materials strongly deficient in 18o and 13c compared to isotopic equilibrium combined these observations imply that varying proportions of the two skeletal types may account for most of the temperature or climate signal in tropical corals as well as anomalous vital effects

characterization of mg ca distributions in planktonic foraminifera species by electron microprobe mapping 1 the distribution of mg ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping species include several that are commonly used for estimation of past seawater temperatures globigerinoides ruber g sacculifer neogloboquadrina incompta synonym of n pachyderma dex n dutertrei and g truncatulinoides each of the investigated species displays large variations in mg ca composition within individual tests however the pattern of mg ca variation is notably different between symbiont bearing and symbiont free species in symbiotic species cyclic mg ca compositional banding occurs that is characterized by narrow 1 3 m high mg ca typically 8 11 mmol mol bands intercalated between broader low mg ca typically 1 5 mmol mol bands this factor of 2 3 difference equates to an apparent calcification temperature change of 10 c or more such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of mg ca into the tests of symbiont bearing species these vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures symbiont free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column

mesozoic plutons of the yidun arc sw china u pb geochronology and hf isotopic signature abstract the yidun arc is a triassic volcanic arc located between the songpan garze fold belt and the qiangtang block southwest china to constrain the age of a number of the major granitic plutons from the yidun arc laser ablation icp ms u pb analysis of zircon was conducted hafnium isotope data was also acquired through laser ablation multicollector icpms analysis of zircon with the aim of gaining insight into the age and nature of the source region of the plutons three age groups have been identified from seven granite samples early middle triassic 245 to 229 ma late triassic 219 to 216 ma and cretaceous 105 to 95 ma hafnium analysis shows the triassic granites to have negative and variable e hf values and mesoproterozoic 1 6 ga depleted mantle model ages which is interpreted to reflect derivation from an isotopically heterogeneous largely crustal source the cretaceous granite shows higher and less variable e hf values and slightly younger model ages 1 3 ga and is interpreted to be derived from melting of a more homogeneous crustal source a depleted mantle model age of 1 5 ga is calculated from the pooled triassic and cretaceous samples the source region for these magmas may be tentatively correlated with mesoproterozoic material of the yangtze craton which has been suggested to underlie the yidun arc however further work is necessary to demonstrate this suggestion