discriminating fluid source regions in orogenic gold deposits using b isotopes abstract the genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions however there is considerable debate as to the ultimate source of these fluids and the metals they transport tourmaline is a common gangue mineral in orogenic gold deposits it is stable over a very wide p t range demonstrates limited volume diffusion of major and trace elements and is the main host of b in most rock types we have used texturally resolved b isotope analysis by secondary ion mass spectrometry sims to identify multiple fluid sources within a single orogenic gold ore district the loulo mining district in mali west africa hosts several large orogenic gold ore bodies with complex fluid chemistry associated with widespread pre ore na and multi stage b metasomatism the gara deposit as well as several smaller satellites formed through partial mixing between a dilute aqueous carbonic fluid and a hypersaline brine hydrothermal tourmaline occurs as a pre ore phase in the matrix of tourmalinite units which host mineralization in several ore bodies clasts of these tourmalinites occur in mineralized breccias disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation tourmalines show a large range in 11 b values from 3 5 to 19 8 which record a change in fluid source between paragenetic stages of tourmaline growth pre mineralization tourmaline crystals show heavy 11 b values 8 19 8 and high x site occupancy na ca 0 69 1 apfu suggesting a marine evaporite source for hydrothermal fluids syn mineralization and replacement phases show lighter 11 b values 3 5 to 15 1 and lower x site occupancy 0 62 0 88 apfu suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments the large overlapping range in isotopic compositions and a skew toward the opposing population in the 11 b data for both tourmaline groups reflects continual tourmaline growth throughout mineralization which records the process of fluid mixing a peak in 11 b values at 8 largely controlled by tourmalines of syn to post ore timing represents a mixture of the two isotopically distinct fluids this paper demonstrates that b isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems the importance of b as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes b isotope analysis a powerful tool for testing the level of source region variability in these fluids and by extension that of metal sources

a brine interface in the salton sea geothermal system california fluid geochemical and isotopic characteristics data from 71 geothermal production intervals in 48 wells from the salton sea geothermal system ssgs indicate that fluids in that system cluster into two distinct populations in terms of their salinity and their stable isotopic compositions the distinctive hot hypersaline brine typically 20 wt total dissolved solids for which the ssgs is known is overlain by a cooler 260 c fluid with distinctly lower salinity typically 10 wt total dissolved solids hypersaline brines have high and rather consistent 18o shifts produced by water rock interaction and have a very narrow range in d values low tds fluids on the other hand show a wide range in both d and 18o production of both types of fluid from closely spaced geothermal wells in many regions of the ssgs indicates that a relatively sharp salinity interface exists over much of the field the fluid interface typically cross cuts sedimentary bedding but is consistently found where reservoir temperatures are approximately 260 c at these temperatures hypersaline brines have densities of approximately 1 0 gm cm3 while the low tds fluids have densities as low as 0 85 gm cm3 this stable density stratified interface acts as a barrier to convective heat and mass transfer in the ssgs isolating the hypersaline reservoir from overlying dilute fluids a lithologic cap implied by previous ssgs models is unnecessary in such a stratified system since heat and mass transfer across the interface must occur by slow conductive diffusional and interface mixing processes regardless of local permeability

late holocene lacustrine chronology and archaeology of ancient lake cahuilla california freshwater lakes existed intermittently in the salton trough of southern california during the late holocene the lakes formed north of the subaerial colorado river delta whenever the colorado river flowed west into the trough instead of south to the gulf of california water filled the trough to a maximum altitude of 12 m stratigraphy radiocarbon dates and supplementary evidence document four lacustral intervals of lake cahuilla between a d 700 and 1580 archaeological sites are associated with the 12 m shoreline and their occupation correlates with these lacustral intervals

saline brines and metallogenesis in a modern sediment filled rift the salton sea geothermal system california u s a the salton sea geothermal system ssgs is the site of active hydrothermal metamorphism and metallogenesis in the delta of the colorado river which partially fills the salton trough rift zone at the head of the gulf of california growth of the delta across the rift has isolated the northern part of the salton trough since the pleistocene forming the evaporative salton sea basin whose sediments host the ssgs more than 70 commercial geothermal wells including a 3 2 km deep research borehole drilled as part of the salton sea scientific drilling project sssdp are yielding a wealth of new data from this system within the ssgs active greenschist facies metamorphism is occuring at temperatures 365 c at only 2 3 km depth by reaction of nacakfemncl brines with the deltaic and lacustrine pilo pleistocene sediments two kinds of base metal ore mineralization occur at depth stratabound diagenetic fe sulfides and epigenetic vertical veins containing fezncupb sulfides and fex oxides the vein mineralization occurs as two types an older reduced carbonate sulfide assemblage and a modern oxidized silicate hematite sulfide assemblage the earlier assemblage formed at temperatures up to 100 c higher than the ambient temperatures measured in the wells today implying that cooler oxidized fluids have displaced hot reduced fluids a sharp interface between shallow fluids containing 12 wt tds and deep hypersaline brines containing 15 27 wt tds exists in the ssgs the deeper hypersaline brines are rich in base metals fe 1500 ppm mn 1000 ppm zn 500 ppm whereas the overlying lower salinity fluids contain less than 100 ppm each of fe mn and zn the modern silicate hematite sulfide vein assemblage is precipitating where the two fluids appear to be mixing the two fluid types also have distincty different 18o and d relations the shallow lower salinity fluids have only partially exchanged oxygen with deltaic and lacustrine host rocls the deep hypersaline brines have exchanged oxygen extensively at 250 c with the deltaic sediments d values of the hypersaline brines are typically lighter than either the lower salinity fluids or the modern evaporating groundwaters occupying the salton trough implying a different source for the original fluids the high salinities of the geothermal brines are derived from a combination of evaporation of fossil lakewaters groundwater dissolution of shallow lacustrine evaporites and subsurface hydrothermal metamorphism of buried lacustrine evaporites episodic filling and desiccation of the closed salton sea basin has allowed cold saline brines to form and percolate down into the sedimentary section in some wells anyhydrite meta evaporites and interbedded solution collapse breccias occur at 1 km depth the anyhydrite contains fluid inclusions that are saturated in halite at their homogenization temperatures of 300 c recording the hydrothermal dissolution of bedded salt based on sr and pb isotopic data and whole rock chemical data the source of the metals in the hypersaline brines is from leaching of the host sediments however the origin of reduced s for ore mineralization remains an enigma 34s values for vein sulfides cluster uniformly around zero per mil implying that an isotopically homogeneous source of reduced sulfide exists in the brines it is possible that the vein sulfides receive a constribution from a magmatic s source movement and mixing of brines of different chemistry and oxidation states play a major role in ore genesis our model envisages an early stage in which a deep brine pool accumulated at depth in the sedimentary section by partial section by partial evaporation of basin and dissolution of bedded salts intrusion of rift related basaltic magma into the base of the sedimentary caused heatingand fracturing of the sediments resulting in precipitation of the carbonate sulfide veins during pore fluid expulsion heating also caused a diapir of the hypersaline brine to rise and displace colder less saline shallower pore fluids this brine intrusion was accompanied by pervasive and extensive mineralization as this diapir cooled it began to move downward drawing in shallow more oxidized fluids and causing the formation of the modern silicate hematite sulfide vein ore zone

slope and rainfall effects on the volume of sediment yield by gully erosion in the souar lithologic formation tunisia abstract the souar lithologic formation in semi arid tunisia is undergoing severe gully erosion which is threatening soil and water resources soil conservation strategies have focused more on terracing than on gully control techniques since the contribution of gully sediment yield in the overall soil loss from watersheds is unknown the paper reports investigations into the sediment yield provided by head cut as well as sidewall floor erosion of first order gullies on gentle and steep slope catchments underlined by the souar lithologic formation we measured mean field sediment volumes evacuated by different headward reaches of 10 and 9 gullies located on gentle and steep slope catchments respectively two equations between the length of the gully head cutting and the corresponding volume of evacuated sediment were established the treatment with a geographic information system arc view of air photographs of six flights from 1952 to 2000 allowed the calculation of the volume of sediment provided both by head cutting and gully sidewalls floor erosion through the following up of gully extension in eight catchments during the five periods separating the dates of these flights total gully erosion was on average 1 66 m3 ha 1 year 1 for the gentle slopes and 5 603 m3 ha 1 year 1 for the steep slopes sidewalls floor contribution in total erosion was on average 81 5 for the gentle slopes and 77 8 for the steep slopes we found out that the mean annual rainfall resulting from 40 mm daily rainfall threshold explained better the variation of annual head cutting sediment yield for these five periods than any other annual rainfall resulting from lower daily rainfall thresholds two equations between these two variables were established both for gentle and steep slope catchments

factors controlling sediment yield from small intensively cultivated catchments in a temperate humid climate abstract data on sediment yield from 26 small cultivated catchments 10 10 000 ha in central belgium were collected based on sedimentation rates in small flood retention ponds area specific sediment yield varies from 0 4 to 20 6 t ha 1 year 1 for catchments ranging from 7 to 4873 ha various catchment properties were analysed in order to understand this large variation in sediment yield catchment area alone explains 64 of the observed variance in area specific sediment yield although no other parameter could explain more it is concluded that catchment area is not a valid parameter to link with sediment yield overall catchment geomorphology e g presented by the hypsometric integral is much more important in controlling sediment yield the lack of data however made this not very clear a multiple regression model including three morphological catchment properties is a valuable tool to predict total sediment yield t year 1 from catchments in central belgium this model has an efficiency of 0 81 furthermore it was concluded that the within catchment spatial distribution of parameters for instance slope steepness is very important but difficult to obtain one single representative value the use of spatially distributed erosion and sediment delivery models is therefore necessary accurate sediment yield data like the one presented in this study however are needed to validate these models

the palaeoproterozoic boron deposits in eastern liaoning china a metamorphosed evaporite abstract we have carried out a field study of the palaeoproterozoic borate deposits of eastern liaoning province china the borates are hosted within mg silicate and mg carbonate rocks and have previously been interpreted as either skarns or metamorphosed volcanogenic exhalative deposits the deposits contain textures that are compatible with a sedimentary origin of the borates and there is a lack of the associated mineralization that is characteristic of magnesian skarns in addition preliminary boron isotope data indicate that the boron within the borates was not derived from the footwall rocks that have been proposed as the source of the skarn fluids a purely exhalative model can be dismissed on the basis of geochemical arguments and comparison with modern environments which show that borates are too soluble to precipitate directly from hydrothermal fluids the geology and field relationships show a number of similarities with recent non marine evaporite settings and young continental rifts in arid environments we conclude therefore that the liaoning deposits are metamorphosed evaporites in which the boron was originally present as primary evaporite borate minerals this model places the liaoning borates in the same category as the majority of other economic borate deposits in the world

assessment of gully erosion in eastern ethiopia using photogrammetric techniques abstract eastern ethiopia is severely affected by soil erosion as it is revealed by the commonly occurring deep and wide gullies these gullies are dynamically expanding into agricultural lands at an alarming rate they are also the chief sources of sediment causing siltation of lakes that are valuable sources of both drinking and irrigation water in the alemaya and harar areas a quantitative assessment of gully dynamics and the associated soil loss and a prognosis of areas susceptible to further gullying were deemed crucial aerial photographs from two different dates 1966 and 1996 with approximate scales of 1 45 000 were used to study the development and dynamics of gullies as indicated by volume changes between the two dates they were digitized at a pixel size of 20 m digital elevation models dem with grid widths of 20 and 2 m were derived from stereo image pairs separately gully breaklines and borderlines were measured for the identified gully systems gully profiles were positioned at regular intervals of 20 m along the gully length giving rise to gully sections that are portions of a gully between neighbouring profiles gully volume was computed for every gully section soil loss was estimated from the computed gully volumes using soil bulk density it showed that soil loss per unit of gully surface is very high 1 7 tons m 2 of gully surface over the 30 years time period indicating the severity of gully erosion in the subcatchment there was significant agreement between breakline measured and field measured gully depth and width for selected points this is an indication of the potential of the method for reliable gully volume estimation and hence quantification of soil loss due to gully erosion the possibility of predicting hill slope areas susceptible to further gullying based on the topographic attributes such as specific contributing area and local slope from an interpolated detailed dem with 2 m resolution was tested it was found that wetness index alone or a combination of the wetness index and the compound topographic index at the threshold values established in literature would give better results as viewed from better connectivity of flow lines and higher conformity of the predicted susceptible areas to natural gully headcut and expansion in a landscape reality

an assessment of land use and other factors affecting sediment loads in the rio puerco watershed new mexico abstract rapid channel erosion in the rio puerco watershed of northwest new mexico has been attributed to land use climate changes and internal channel adjustments the objectives of this study were to assess 1 the impacts of land uses on sediment load 2 the quantitative relationships between land use and sediment load and 3 the effectiveness of different erosion control methods the impacts of land uses on sediment load were assessed via hypotheses that holding other erosion related variables constant sediment load correlates positively with grazing intensity and with density of unpaved roads and correlates negatively with the number of erosion control treatments we calculated the average annual sediment load for 17 subbasins of 0 67 17 97 km 2 by comparing sediment accumulation at two points in time mid 1960s and 1999 behind intact sediment retention structures we assessed land use via grazing records and measurements of unpaved roads generated from aerial photographs soil characteristics vegetation and physical factors were quantified for each subbasin using 18 variables for each subbasin we employed mallow s c p as a selection criterion we used six statistical models including multiple regression and principal components analysis to determine inherent mathematical relationships between significant independent variables and sediment load the results indicate that sediment load does not correlate with grazing intensity except in small relatively low relief basins with fewer bedrock exposures however this interpretation may be compromised by the low quality of data available to quantify grazing sediment load is highly sensitive to the presence of unpaved roads which serve as high gradient channelized conduits of water and sediment during storms sediment load does not correlate with erosion control except in the subset of small relatively low relief subbasins that also proved sensitive to grazing intensity overall the statistical analyses suggest that the impact of land uses on sediment load can be assessed using the data available although physical factors appear more significant than land use in producing high sediment loads in the rio puerco subbasins historical erosion control techniques as implemented in the rio puerco watershed prove largely ineffective against accelerated sediment loads because they have not been appropriately implemented or maintained

genesis of native copper lodes in the keweenaw district northern michigan a hybrid evolved meteoric and metamophogenic model the keweenaw peninsula of northern michigan is well known for early diagenetic sulfide dominant sediment hosted stratiform copper mineralization hosted mainly by basal siltstone shale units of the nonesuch formation in the white pine district and later native copper lodes hosted mainly by flow top breccias and amygdaloidal portions of flood basalts and interbedded conglomerates of the stratigraphically lower portage lake volcanics the native copper mineralization is generally attributed to downdip burial metamorphism of the host strata an alternative model is proposed here involving a complementary influx of evolved meteoric water elevated in salinity and progressively equilibrating with its aquifers similar to the fluid which formed the white pine mineralization this model has several advantages over the metamorphogenic model alone it would provide the salinity by dissolution of evaporites and moderately oxidizing conditions as a result of hematitization i e reddening of coarse continental rift sediments necessary for copper transport and the evolved meteoric water would have been an important cupriferous brine owing to the leaching of trace amounts of copper from the voluminous aquifers further reduction of the evolved fluid would also explain the updip deposition of native copper in association with dehematitized pumpellyite and chlorite dominant i e reduced hydrothermal mineral assemblages at the same time this influx of meteoric water from highlands adjacent to the keweenaw rift basin would have provided a mechanism to move the deep seated hot dense ore brine upward along the aquifers of the portage lake volcanics on its ascent from deep portions of the rift basin the gravity driven evolved meteoric brine would have mixed with the fluid generated by burial metamorphism to form a hybrid evolved meteoric metamorphogenic oreforming hydrothermal brine

near channel versus watershed controls on sediment rating curves predicting riverine suspended sediment flux is a fundamental problem in geomorphology with important implications for water quality land and water resource management and aquatic ecosystem health to advance understanding we evaluated environmental and landscape factors that influence sediment rating curves srcs we generated srcs with recent total suspended solids tsss and discharge data from 45 gages on 36 rivers throughout the state of minnesota usa watersheds range from 32 to 14 600 km2 and represent distinct settings regarding topography land cover and geologic history rivers exhibited three distinct src shapes simple power functions threshold power functions and peaked or negative slope functions we computed src exponents and coefficients describing the steepness of the relation and the tss concentration at median flows respectively in addition to quantifying watershed topography climate hydrology geology soil type and land cover we used lidar topography to characterize the near channel environment upstream of gages we used random forest models to analyze relations between src parameters and attributes of the watershed and the near channel environment the models correctly classify 78 of src shapes and explain 37 60 of variance in src parameters we find that src steepness exponent is strongly related to near channel morphological characteristics including near channel relief channel gradient and presence of lakes along the local channel network but not to land use in contrast land use influences tss concentrations at moderate and low flow these findings suggest that the near channel environment controls changes in tss as flows increase whereas land use drives median and low flow tss conditions

quantitative analysis of factors controlling sediment yield in mountainous watersheds abstract sediment and turbidity are primary causes of impaired river ecosystems remedial action for these impairments requires the identification of their sources and controlling factors this paper examines the combined effects of watershed complexity in terms of land use and physiography on the specific sediment yield of the upper du river watershed 8973 km2 in china the land use composition land use pattern morphometric variables and soil properties of the watershed were calculated at the subwatershed scale and considered to be potentially influential factors because these watershed characteristics are highly codependent a partial least squares regression plsr was used to elucidate the linkages between the specific sediment yield and metrics composed of 19 selected watershed characteristics the first order factors were identified by calculating the variable importance for the projection vip the results revealed that the land use composition and land use pattern exerted the largest effects on the specific sediment yield and explained 65 2 of the variation in the specific sediment yield a set of physiographic indices was also found to have a large effect on the specific sediment yield and explained 17 7 of the observed variation in the specific sediment yield the following are the dominant first order factors of the specific sediment yield at the subwatershed scale the areal percentages of agriculture and forest patch density value of the shannon s diversity index contagion value of the hypsometric integral and saturated soil hydraulic conductivity the watershed size exerted a substantial effect on the sediment delivery ratio sdr the vip values also suggested that the shannon s diversity index contagion and hypsometric integral are important factors in the sdr with a readily available digital spatial database and rapid developments in geographic information system gis technology this practical and simple plsr approach could be applied to a variety of watersheds

natural and anthropogenic controls on soil erosion in the internal betic cordillera southeast spain soil erosion in southeast spain is a complex process due to strong interactions between biophysical and human components significant progress has been achieved in the understanding of soil hydrological behavior despite the fact that most investigations were focused on the experimental plot scale although experimental plots allow exploring the effect of multiple biophysical and anthropogenic factors they provide limited insights in the combined effect of all factors acting together at the landscape scale in this study area specific sediment yields ssy have been estimated based on the volume of sediment trapped behind 36 check dams in the southeast of spain low ssy values were reported mean 1 40 t ha 1 year 1 median 0 61 t ha 1 year 1 ssy variability could be explained for 67 by catchment characteristics such as drainage area soil characteristics land cover average catchment slope and annual rainfall the low ssy values are probably caused by the agricultural abandonment that occurred over the past decades and allowed the recovery of natural vegetation furthermore our results suggest that the soils have eroded in the past to such an extent that nowadays not much sediment is detached by overland flow due to residual enrichment of clay and stones also sediment is to a large extent trapped locally in the catchment as indicated by the negative relationship between ssy and catchment area c 2011 elsevier b v all rights reserved

variability of dry sediment bulk density between and within retention ponds and its impact on the calculation of sediment yields monitoring sediment yields from catchments is important for assessing overall denudation rates and the impact of environmental change one of the methods used to assess sediment yield is by quantifying sedimentation rates in reservoirs lakes or small ponds before reliable sediment yield values t ha 1 a 1 can be computed from such sedimentation records the measured sediment volumes need to be converted to sediment masses using representative values of the dry sediment bulk density in textbooks simple relations predicting dry sediment bulk density from sediment texture time since deposition and hydrologic condition are presented in this study 13 small flood retention ponds in central belgium were sampled to reveal the variability in dry sediment bulk density and to test the commonly used relations to predict dry sediment bulk density dry sediment bulk density varies not only between the selected ponds 0 78 1 35 t m 3 but also within individual ponds coefficient of variation at 95 per cent ranges from 7 to 80 per cent the observed variability can be attributed primarily to the hydrologic condition of the retention pond and also to sediment texture the existing relations are not a reliable predictor for the observed dry bulk densities because they are primarily based on sediment texture thus when using volumetric sedimentation data from small ponds with varying hydrologic condition to predict sediment yield existing relations predicting dry sediment bulk density cannot be applied instead frequent and dense sampling of sediments is necessary to calculate a representative value of the dry sediment bulk density copyright 2001 john wiley sons ltd

brine history indicated by argon krypton chlorine bromine and iodine analyses of fluid inclusions from the mississippi valley type lead fluorite barite deposits at hansonburg new mexico argon krypton chlorine bromine and iodine were measured in a homogeneous population of high salinity hydrothermal fluid inclusions from the tertiary age mississippi valley type mvt lead fluorite barite deposits at hansonburg new mexico to establish new types of evidence for the history of both the fluid and the major dissolved salts noble gases and halogens in fluid inclusions containing 10 10 10 9 l of brine cl 3 molal were analyzed by laser microprobe noble gas mass spectrometry lmngms on neutron irradiated samples the concentrations of36ar 4 7 10 8 molal and84kr1 8 10 9 molal in the fluid inclusions are equal to those of fresh surface waters in equilibrium with air at approximately20 5 the mole ratios ofbr cl 1 2 10 4 andi cl 1 2 10 6 are among the lowest measured in any natural waters similar to those of modern brines formed by dissolution of permian nacl bearing evaporites in southeast new mexico 40ar 36ar ratios 600 are twice that of air and indicate that the fluid inclusions had excess radiogenic40ar 1 4 10 5 molal when trapped the amount of excess40ar appears to be too large to have been acquired with cl by congruent dissolution of halite bearing evaporites and possibly too small to have been acquired with pb by congruent dissolution of granitic basement rocks with proterozoic kar ages from thelmngms data combined with published pb and s isotope data we infer the following sequence of events in the history of the hansonburg mvt hydrothermal brine 1 the brine originated as relatively dilute meteoric water and it did not gain or lose atmospheric ar or kr after recharge 2 the originally dilute fluid acquired the bulk of its cl and sulfate in the subsurface after recharge by dissolving halite bearing permian marine evaporites 3 the high salinity brine then acquired most of its pb and excess radiogenic40ar from interactions with aquifer rocks other than evaporites possibly clastic sedimentary rocks or basement rocks with phanerozoic kar ages and 4 the brine deposited fluorite without having boiled or degassed

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

geostatistical approaches for incorporating elevation into the spatial interpolation of rainfall this paper presents three multivariate geostatistical algorithms for incorporating a digital elevation model into the spatial prediction of rainfall simple kriging with varying local means kriging with an external drift and colocated cokriging the techniques are illustrated using annual and monthly rainfall observations measured at 36 climatic stations in a 5000 km 2 region of portugal cross validation is used to compare the prediction performances of the three geostatistical interpolation algorithms with the straightforward linear regression of rainfall against elevation and three univariate techniques the thiessen polygon inverse square distance and ordinary kriging larger prediction errors are obtained for the two algorithms inverse square distance thiessen polygon that ignore both the elevation and rainfall records at surrounding stations the three multivariate geostatistical algorithms outperform other interpolators in particular the linear regression which stresses the importance of accounting for spatially dependent rainfall observations in addition to the colocated elevation last ordinary kriging yields more accurate predictions than linear regression when the correlation between rainfall and elevation is moderate less than 0 75 in the case study q 2000 elsevier science b v all rights reserved

hillslope runoff processes and models abstract hillslope hydrology is concerned with the partition of precipitation as it passes through the vegetation and soil between overland flow and subsurface flow flow follows routes which attenuate and delay the flow to different extents so that a knowledge of the relevant mechanisms is important in the 1960s and 1970s hillslope hydrology developed as a distinct topic through the application of new field observations to develop a generation of physically based forecasting models in its short history theory has continually been overturned by field observation thus the current tendency particularly among temperate zone hydrologists to dismiss all hortonian overland flow as a myth is now being corrected by a number of significant field studies which reveal the great range in both climatic and hillslope conditions some recent models have generally attempted to simplify the processes acting for example including only vertical unsaturated flow and lateral saturated flows others explicitly forecast partial or contributing areas with hindsight the most complete and distributed models have generally shown little forecasting advantage over simpler approaches perhaps trending towards reliable models which can run on desk top microcomputers the variety now being recognised in hillslope hydrological responses should also lead to models which take account of more complex interactions even if initially with a less secure physical and mathematical basis than the richards equation in particular there is a need to respond to the variety of climatic responses and to spatial variability on and beneath the surface including the role of seepage macropores and pipes which call into question whether the hillside can be treated as a darcian flow system

human impact on sediment fluxes within the blue nile and atbara river basins a regional assessment of the spatial variability in sediment yields allows filling the gap between detailed process based understanding of erosion at field scale and empirical sediment flux models at global scale in this paper we focus on the intrabasin variability in sediment yield within the blue nile and atbara basins as biophysical and anthropogenic factors are presumably acting together to accelerate soil erosion the blue nile and atbara river systems are characterized by an important spatial variability in sediment fluxes with area specific sediment yield ssy values ranging between 4 and 4935t km 2 y statistical analyses show that 41 of the observed variation in ssy can be explained by remote sensing proxy data of surface vegetation cover rainfall intensity mean annual temperature and human impact the comparison of a locally adapted regression model with global predictive sediment flux models indicates that global flux models such as the art and bqart models are less suited to capture the spatial variability in area specific sediment yields ssy but they are very efficient to predict absolute sediment yields sy we developed a modified version of the bqart model that estimates the human influence on sediment yield based on a high resolution composite measure of local human impact human footprint index instead of countrywide estimates of gnp capita our modified version of the bqart is able to explain 80 of the observed variation in sy for the blue nile and atbara basins and thereby performs only slightly less than locally adapted regression models 2012 elsevier b v

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

a meta analysis of soil erosion rates across the world abstract over the last century extraordinary efforts have been devoted to determining soil erosion rates in units of mass per area and time under a large range of climatic conditions and land uses and involving various measurement methods we undertook a meta analysis of published data from more than 4000 sites worldwide the results show that there is extraordinarily high variability in erosion rates with almost any rate apparently possible irrespective of slope climate scale land use land cover and other environmental characteristics however detailed analysis revealed a number of general features including positive relationships of erosion rate with slope and annual precipitation and a significant effect of land use with agricultural lands yielding the highest erosion rates and forest and shrublands yielding the lowest despite these general trends there is much variability that is not explained by this combination of factors but is related at least partially to the experimental conditions our analysis revealed a negative relationship between erosion rate and the size of the study area involved significant differences associated with differing measurement methods with direct sediment measurement yielding the lowest erosion rates and bathymetric radioisotope and modeling methods yielding the highest rates and a very important effect of the duration of the experiment our results highlight that when interpreting erosion rates the experimental conditions involved must be taken into account even so the data suggest that only order of magnitude approximations of erosion rates are possible and these retain a very large degree of uncertainty consequently for practical purposes such as calculation of global sediment budgets empirical equations are not a substitute for direct measurements our results also show that a large proportion of the experiments have been short term less than 3 years which reduces dramatically the reliability of the estimated erosion rates given the highly non normal behavior of soil erosion time dependency despite the efforts already made more long term measurement experiments need to be performed especially in regions of the world that are under represented in global datasets in addition protocols need to be established for standardizing the measurement methods and reporting the results to enable data to be compared among diverse sites

metamorphosed plio pleistocene evaporites and the origins of hypersaline brines in the salton sea geothermal system california fluid inclusion evidence abstract the salton sea geothermal system ssgs occurs in plio pleistocene deltaic lacustrine evaporite sediments deposited in the salton trough an active continental rift zone temperatures up to 365 c and hypersaline brines with up to 26 wt tds are encountered at 1 3 km depth in the sediments which are undergoing active greenschist facies hydrothermal metamorphism previous models for the origins of the na ca k cl brines have assumed that the high salinities were derived mainly from the downward percolation of cold dense brines formed by low temperature dissolution of shallow non marine evaporites new drillcores from the central part of the geothermal field contain metamorphosed bedded evaporites at 1 km depth consisting largely of hornfelsic anhydrite interbedded with anhydrite cemented solution collapse shale breccias fluid inclusions trapped within the bedded and breccia cementing anhydrite homogenize at 300 c identical to the measured downhole temperature and contain saline na ca k cl brines some of the inclusions contain up to 50 vol halite sylvite and carbonate crystals at room temperature and some halite crystals persist to above 300 c upon laboratory heating the data are consistent with the trapping of halite saturated na ca k cl fluids during hydrothermal metamorphism of the evaporites and accompanying solution collapse of interbedded shales we conclude that many of the salt crystals in inclusions are the residuum of bedded evaporitic salt that was dissolved during metamorphism by heated connate fluids therefore the high salinities of the salton sea geothermal brines are derived in part from the in situ hydrothermal metamorphism and dissolution of halides and caso 4 from relatively deeply buried lacustrine evaporites this fact places important constraints on modeling fluid flow in the ssgs as brines need not have migrated over great distances the brines have been further modified to their present complex na ca k fe mn cl compositions by on going sediment metamorphism and water rock interaction

drivers of erosion and suspended sediment transport in three headwater catchments of the mexican central highlands quantifying suspended sediment exports from catchments and understanding suspended sediment dynamics within river networks is important especially in areas draining erodible material that contributes to the siltation of downstream reservoirs and to the degradation of water quality a one year continuous monitoring study of water and sediment fluxes was conducted in three upland subcatchments 3 0 9 3 and 12 0 km2 located within the cointzio basin in the central volcanic highlands of mexico michoacan state two subcatchments generated high sediment exports i e huertitas 900 1500 t km 2 y 1 and potrerillos 600 800 t km 2 y 1 whereas the third subcatchment was characterized by a much lower sediment yield i e la cortina 30 t km 2 y 1 such disparities in subcatchment behaviours were associated with the presence of severely gullied areas in huertitas and potrerillos rather than with rainfall erosivity indices an adapted classification of hysteretic patterns between suspended sediment concentration ssc and discharge was proposed because 42 of flood events contributing to 70 of sediment export were not discriminated by the classical clockwise anticlockwise typology this new classification allowed the identification of relationships in the hydrosedimentary responses of successive floods a stream transport capacity limit was also detected during hydrograph recession phases overall hydrosedimentary processes proved to be seasonally dependent sediment export was repeatedly limited by the stream transport capacity during the first part of the rainy season whereas a channel minimum erosivity threshold was frequently reached at the end of the season

tectonic forcing of evolution and holocene erosion rate of ravines in the marginal ganga plain india abstract understanding the processes of ravine formation and estimates of specific sediment yields ssy of these regions help in formulating mitigation policies significantly upto now in the ganga plain the work done on ravine formation erosion and ssy estimates has been speculative here utilizing i high resolution digital elevation models dems prepared from real time kinematic rtk survey and cartosat images of ravined zones and ii luminescence chronology we provide the first estimate of ssy from the ravines the results indicate that ssy in the marginal ganga plain mgp ravines may range between 600 100 t km 2 yr and 1600 200 t km 2 yr the correspondence between the orientations of fractures and that of first order ravine suggests that the ravine growth is genetically related to extensional stress regime of the peripheral forebulge further the clay sedimentology indicates that besides regional tectonics action of swelling clays may have accelerated development of the badlands the geomorphic relationship between the length of ravined catchments and incision in the trunk channels indicates that the river incision associated base level change is not playing an overarching role in the ravine formation in the mgp

inferring erosional resistance of bedrock units in the east tennessee mountains from digital elevation data measures of local relief regional relief and slope were calculated from digital elevation models dems for 50 bedrock units in the ridge and valley and blue ridge provinces of tennessee each of these measures was normalized and the three were then averaged to produce the erosional resistance index eri bedrock units with higher eri values include coarse clastics intermediate clastics and metaplutonics units with lower values include shales limestones limestones plus dolostones and carbonates plus fine clastics dolostones tend to have intermediate values the calculated eri values were compared with subjective ratings by a geologist with decades of field experience in east tennessee generally the agreement between the two ratings was good the most glaring exception being several shales with improbably high eri values these turned out to be thin units cropping out beneath very hard sandstones allowing them to stand higher and steeper than would otherwise be possible a systematic method for detecting such erroneously high eri values is suggested inspection of a drainage map superimposed on the geology map shows that in a given area streams tend to flow on rock units with the lowest eri values in addition statistical analysis shows that bedrock units with the lowest eri values are on average almost three times closer to the nearest stream and six times as likely to have streams flowing on them than are units with highest values further the effect of eri on stream location is strongest for streams with drainage areas between 1 and 30 km2 thus small streams appear to be subject to greater lithologic control than are larger streams

paleocurrent evidence for lateral displacement of the pliocene colorado river delta by the san andreas fault system southeastern california more than 600 paleocurrent measurements from fluvial paleochannels of the early colorado river delta plain preserved in the palm spring formation in the fish creek vallecito fcv section of southern california indicate that the fcv section was on the gulf of california southeastern flank of the delta plain as recently as 2 8 ma these measurements imply 130 km of tectonic translation to the northwest since 2 8 ma which can be accounted for by the displacement histories of baja california and component faults of the san andreas system stratigraphic data from the fcv section and other neogene localities when plotted on a palinspastic base indicate 1 marine transgression of a narrow gulf of california rift basin and bouse embayment site of modern lower colorado river by 5 5 ma and 2 uplift of the bouse embayment initiation of the lower colorado river and southward progradation of the delta to essentially its present position by 4 ma

use of floodplain sediment cores to investigate recent historical changes in overbank sedimentation rates and sediment sources in the catchment of the river ouse yorkshire uk abstract floodplain sediment cores collected from seven sites in the catchment of the river ouse in yorkshire uk have been used to provide information on recent historical changes in both rates of overbank sedimentation and sediment sources the environmental radionuclides 137 cs and unsupported 210 pb have been used to establish chronologies for each core and to estimate average sediment accumulation rates for the last ca 30 and 100 years respectively average sedimentation rates for the individual cores ranged from 0 11 to 1 04 g cm 2 yr 1 in all but one case the estimates of average sedimentation rate during the last ca 30 years for the individual cores are broadly similar to those for the last ca 100 years suggesting that overbank sedimentation rates have been essentially uniform over the longer time period composite fingerprints based on a combination of geochemical and mineral magnetic properties and a numerical mixing model have been used to investigate downcore changes in sediment source in the case of source type most of the cores reflect a primarily topsoil source although there have been periods with increased contributions from subsoil channel bank sources within the ouse basin in general the period commencing in the late 19th and early 20th century and extending through to the 1960s was characterised by increased contributions from topsoil sources however contributions from subsoil channel bank sources have increased over the last few decades the source tracing results relating to sediment contributions from the three main geological topographic zones are in broad agreement with the proportion of the area of the catchment underlain by each rock type temporal variations in the contributions from the three geological topographic zones vary from site to site but for the lower reaches of the river ouse contributions from areas underlain by permian and triassic rocks which mainly outcrop in the vale of york have increased since the turn of the century the changes in sediment source identified are probably a reflection of changes in land use and management and possibly changes in climate these results enable estimates of contemporary suspended sediment fluxes and sources to be placed into a historical context and provide a means of considering the likely impact of potential future changes in land use and climate in the study basin

a gis based approach for gully erosion susceptibility modelling using bivariate statistics methods in the ourika watershed morocco gully erosion is an important environmental issue with severe impacts this study aimed to characterize gully erosion susceptibility and assess the capability of information value infval and frequency ratio fr models for its spatial prediction in ourika watershed of the high atlas region of morocco these two bivariate statistical methods have been used for gully erosion susceptibility mapping by comparing each data layer of causative factor to the existing gully distribution weights to the gully causative factors are assigned based on gully density gullies have been mapped through field surveys and google earth high resolution images lithofacies land use slope gradient length slope aspect stream power index topographical wetness index and plan curvature were considered predisposing factors to gullying the digitized gullies were randomly split into two parts sixty five percent 65 of the mapped gullies were randomly selected as training set to build gully susceptibility models while the remaining 35 cases were used as validation set for the models validation the results showed that barren and sparse vegetation lands and slope gradient above 50 were very susceptible to gully erosion the roc curve was used for testing the accuracy of the mentioned models the analysis confirms that the fr model auc 80 61 shows a better accuracy than infval model auc 52 07 the performance of the gully erosion susceptibility map constructed by fr model is greater than that of the map produced by infval model the findings proved that gis based bivariate statistical methods such as frequency ratio model could be successfully applied in gully susceptibility mapping in morocco mountainous regions and in other similar environments the produced susceptibility map represents a useful tool for sustainable planning conservation and protection of land from gully processes

active ore formation at a brine interface in metamorphosed deltaic lacustrine sediments the salton sea geothermal system california the salton sea geothermal system is an area of active hydrothermal metamorphism of pliocene to pleistocene deltaic lacustrine and evaporitic sediments deposited in a modern continental rift zone temperatures up to 365 degrees c hypersaline metalliferous brines with up to 26 wt percent total dissolved solids and active base metal ore formation accompany low pressure greenschist and amphibolite facies metamorphism at depths less than 3 2 km drill cores recovered by the salton sea scientific drilling project shed new light on the nature and origin of ore formation in the eastern portion of the salton sea geothermal system base metal ore mineralization occurs in vertical fractures that comprise the major form of fluid permeability at 1 to 3 km in the modern geothermal system type 1 veins are dominated by carbonate contain pyrrhotite and other sulfides are completely sealed and occur in wall rock showing minimal alteration fluid inclusion data indicate that they were deposited under a thermal gradient much higher than that now found in the eastern part of the system type 2 veins are dominated by silicates and hematite are permeable and occur in wall rocks showing pervasive chloritization and epidotization fluid inclusion data indicate that they are forming now from the geothermal brines under the modern thermal gradient fluid inclusions record an apparent steep progressive salinity increase in the vein systems in the upper 2 km of the system however fluid production data from salton sea geothermal wells indicate that reduced metalliferous hypersaline brine averaging 23 wt percent total dissolved solids is overlain by more oxidized metal poor fluid averaging 5 wt percent total dissolved solids a sharp interface exists between the fluids at 1 to 2 km paralleling the 250 degrees c isothermal surface a model is developed for type 2 vein ore formation involving mixing at the interface between the two fluids magmatic intrusion induces fracturing heating and the expulsion of reduced connate fluids to cause early type 1 vein mineralization following the rising thermal front deep hypersaline brine rises diapirically and mixes with overlying fluids in vertical fractures transecting the ascending interface forming type 2 veins the hypersaline brine rises to a level of density temperature stabilization causing pervasive greenschist metamorphism of the host sediments the diapir then begins to cool and descend shallow oxidized brine is drawn in as the hypersaline brine descends promoting late stage hematite in type 2 veins the eastern salton sea geothermal system presently appears to be in this latter mode of cooling and retrograde brine descent ore formation in the system is caused by the coincidence of transaxial entry of a major river into an active rift zone deposition of metal bearing deltaic sediments to form a closed basin sedimentary environment episodic lacustrine evaporite formation and injection of heat and elements by rift related magmatic intrusions at depth the presence of an upwelling brine diapir in the system may be analogous to conditions immediately prior to the exhalation of metalliferous fluids that formed stratiform fe zn pb cu sulfide and oxide deposits in paleorift zone environments

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

sediment yield variability in spain a quantitative and semiqualitative analysis using reservoir sedimentation rates an existing dataset of area specific sediment yield ssy for 60 catchments in spain that was retrieved from sediment deposition rates in reservoirs avendano salas c sanz montero e rayan c gomez montana 1997 sediment yield at spanish reservoirs and its relationship with the drainage basin area in proceedings of the 19th symposium of large dams florence 1997 icold international committee on large dams pp 863 874 reveals that catchment area alone explains only 17 of the variability in ssy in this study an attempt to explain the remaining variability in ssy was made using a quantitative and a semiqualitative approach for 22 catchments during a field survey the 22 selected catchments were characterised by topography vegetation cover lithology shape and the presence of gullies in the broad vicinity of the reservoir this information was used to develop a factorial scoring index model that provides a fairly accurate and reliable prediction of ssy a classical multiple regression model using climatic topographic and land use properties derived from regional datasets could not explain as much variance as the qualitative index model nor did it appear to be as reliable the same conclusion could be drawn when using the corine soil erosion risk map of southern europe the low prediction capability of the multiple regression models and the corine soil erosion risk map could be attributed mainly to the fact that these methods do not incorporate gully erosion and that the land cover data are not a good representation of soil cover both variables have been shown to be of great importance during the field surveys future assessments of ssy could be quickly and efficiently made using the proposed factorial scoring index model in comparison with other models which demand more data the index model offers an alternative prediction tool d 2002 elsevier science b v all rights reserved

anhydrite bearing rocks from the rožna district moldanubian zone czech republic high grade metamorphosed exhalites several types of anhydrite bearing rocks have been found in the amphibolite facies metamorphosed rocks at the north eastern margin of the moldanubian zone anhydrite either forms monomineralic bands up to 40 cm thick or occurs in the form of disseminated grains in surrounding calc silicate gneiss together with feldspar scapolite amphibole pyroxene epidote and pyrite the isotopic composition of sulphur 34s 30 6 to 32 3 and strontium 87sr 86sr 0 70797 to 0 70781 in anhydrite may indicate a marine source of sulphate the isotopic ratio of strontium is in the same range as that of metamorphosed strata bound barite sulphide ores which have been previously described in the same area the 34s values of coexisting pyrite range from 21 4 to 22 5 the 34sanhydrite pyrite corresponding to the metamorphic temperature of 600 to 660 c in contrast to many submarine exhalative deposits the oxygen isotopic compositions of anhydrite 18o 9 3 to 10 2 are lighter than that of barite 18o 10 4 to 13 8 this indicates that the both minerals are not in isotopic equilibrium therefore it is probable that anhydrite and barite from the ro na district were deposited from fluids that contained different proportions of seawater and hydrothermal fluids or from hydrothermal fluids that underwent variable extent of oxygen isotope exchange with seafloor rocks the 13c values in calcite 13c 17 2 to 18 7 from anhydrite bearing rock are lower than those in distant marbles as graphite is absent in anhydrite and calcite bearing rocks impoverishment in the 13c isotope cannot be attributed to the graphite carbonate isotopic exchange during metamorphism it is proposed that low 13c values in carbonates are caused by pre metamorphic oxidation of organic matter in course of hydrothermal processes anhydrite and anhydrite bearing calc silicate gneiss from the north eastern part of the moldanubian zone are interpreted to be the high grade metamorphosed analogue of anhydrite rich exhalites commonly found in submarine exhalative hydrothermal deposits

sediment yield from irregularly shaped gullies located on the fortuna lithologic formation in semi arid area of tunisia the fortuna geological formation dated from the late oligocene to early miocene is mainly composed of friable sandstone gully erosion on this substratum is developing complex shaped gullies where bank processes are as important as head advance by cutting and bed deepening by vertical incision for irregularly shaped gullies quantitative information on gully erosion rates as related to gully head extension are scarce because bank active sides take many forms presumably depending on topography climate and lithology our field cross section measurements of 4 gullies developed in the fortuna formation 2 located on a steep slope area 15 and the other two on a gentle slope 9 have shown that the geometry of these gullies is far from a conical gully shape these field measurements were used to calculate gully reaches geometry and volume variation no direct relationships between gully volume and length could be established for these gullies in the fortuna formation nevertheless since both gully top view area and maximum top width are increasing as the gully reach length increases relationships could be established between maximum top width and their equivalent width defined as the ratio between gully reach top view area and its length then gully volume length relationships could be established for each of the 5 maximum bank full widths studied on the two gentle and two steep slope gullies for any maximum top width the gully volume length relationship was found to be not unique but the volume is increasing linearly up to the 15 m and 45 m distance from the gully head and then logarithmically for steep and gentle slope gullies respectively the linear and logarithmic equations coefficients were also found to be a function of gully maximum top width these equations were then used to quantify gully sediment yields related to gully shape evolution for eight gullies tributaries of as sahsafa wadis for this purpose the top view areas and lengths of these eight gullies were digitized and monitored on rectified air photographs of 1962 1974 and 2000 using a geographic information system arc view half of these gullies were located in an area with a gentle slope gradient and the other half with steep slope gradient the average gullies length variation for the whole study period 1962 2000 were 11 74 and 10 32 whereas the average top view areas variation was 23 57 and 29 4 for gentle and steep slope gullies respectively gullies volume changes during the periods 1962 1974 and 1974 2000 were then derived from the variation of gullies length and top view areas photo measurements on these 8 tributaries using the relationships established from the four measured gullies on gentle slopes the average gully sediment yields during 1962 1974 and 1974 2000 periods were 3 98 and 2 28 m3 ha 1 year 1 respectively on steep slopes these values are 4 82 and 2 47 m3 ha 1 year 1

calc silicate mineralization in active geothermal systems detailed study of the calc silicate mineralogy in the cerro prieto geothermal system was used to demonstrate examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc silicate assemblages in general there is a close correlation between calculated and observed fluid compositions calculated fugacities of o 2 at about 320 degrees c in the cerro prieto geothermal system are about five orders of magnitude less than those at the nearby salton sea geothermal system this observation is consistent with the occurrence of fe super 3 rich epidotes and andradite garnets in the latter system and the presence of prehnite at cerro prieto modified journal abstract

sediment yield in africa abstract several studies have compiled and analysed measured contemporary catchment sediment yield sy t km 2 y 1 values for various regions of the world although this has significantly contributed to our understanding of sy africa remains severely underrepresented in these studies the objective of this article is therefore 1 to review and compile available sy data for africa 2 to explore the spatial variability of these sy data and 3 to examine which environmental factors explain this spatial variability a literature review resulted in a dataset of sy measurements for 682 african catchments from 84 publications and reports representing more than 8340 catchment years of observations these catchments span eight orders of magnitude in size and are relatively well spread across the continent a description of this dataset and comparison with other sy datasets in terms of spatial and temporal distribution and measurement quality is provided sy values vary between 0 2 and 15 699 t km 2 y 1 median 160 t km 2 y 1 average 634 t km 2 y 1 the highest sy values occur in the atlas region with sy values frequently exceeding 1000 t km 2 y 1 also the rift region is generally characterised by relatively high sy values while rivers in western and central africa have generally low sy values spatial variation in sy at the continental scale is mainly explained by differences in seismic activity topography vegetation cover and annual runoff depth other factors such as lithology catchment area or reservoir impacts showed less clear correlations the results of these analyses are discussed and compared with findings from other studies based on our results we propose a simple regression model to simulate sy in africa although this model has a relatively low predictive accuracy 40 it simulates the overall patterns of the observed sy values well potential explanations for the unexplained variance are discussed and suggestions for further research that may contribute to a better understanding of sy in africa are made

global calibration of ecological models for planktic foraminifera from coretop carbonate oxygen 18 abstract a global dataset of coretop planktic foraminiferal 18oc is combined with a global database of seawater 18ow observations and ocean climatologies to determine robust optimum parameters for an ecological model for six commonly measured species and varieties these parameters consist of the temperature ranges optimum temperatures depth habitat and the amount of secondary calcification for globigerinoides ruber white g ruber pink neogloboquadrina pachyderma l n pachyderma r globigerinoides sacculifer and globigerina bulloides this approach produces ecological models and temperature ranges consistent with previous work and manages to reproduce the coretop oxygen 18 carbonate values remarkably well the standard error of modelled values of coretop calcite globally and for all species is 0 53 compared to an error of 1 2 when assuming annual average mixed layer equilibrium calcite

the cow as a geomorphic agent a critical review cows are important agents of geomorphological change on the uplands heavy grazing compacts the soil reduces infiltration increases runoff and increases erosion and sediment yield however light and moderate grazing have effects that are much less significant in riparian zones grazing decreases erosional resistance by reducing vegetation and exposing more vulnerable substrate trampling directly erodes banks thus increasing turbulence and consequent erosion future studies should be framed within the hydroclimatological edaphic and geomorphological dimensions of the areas being studied so that controlling variables may be more readily isolated we believe that both empirical studies and deterministic modeling can provide insights as to the effects of grazing on geomorphology

dynamics of fluid inclusion alteration in sedimentary rocks a review and discussion abstract fluid inclusions represent small volumes of interstitial fluids in crystal imperfections flaws during crystal growth and or deformation the entrapped fluids are commonly believed to preserve information on the composition pressure and temperature of fluid inclusion formation and later diagenetic alterations it is now known that fluid inclusions can be dynamic structures responsive to thermal and tectonic stresses by plastic and brittle deformation of the entrapping mineral wall these dynamic responses may include both morphologic and volumetric changes a comparison of measured fluid inclusion homogenization temperatures with sample burial depths for diagenetic studies from around the world show a strong positive correlation this correlation suggests that fluid inclusion stretching which results in increased homogenization temperatures is a common phenomenon associated with burial diagenesis burial diagenesis shifts and spreads the measured homogenization temperatures towards maximum burial conditions confining mineralogy shape size and composition of the fluid inclusions are important factors in determining the mode and degree of fluid inclusion deformation stretching classical fracture mechanics theory of predicts that plastic and brittle deformation of the surrounding mineral crystall will occur with burial and that annealing retrograde stretching of the strain in the inclusion walls will not occur in low temperature regimes experimental theoretical and field studies all indicate that fluid inclusions will react dynamically to burial diagenesis by increases in measured homogenization temperatures with increased burial it is suggested that this relationship can be selectively used to help determine the approximate maximum thermal exposures experienced by a sedimentary rock

meta evaporite sequence exhalative chemical sediments and associated rocks in the proterozoic willyama supergroup south australia implications for metallogenesis abstract the willyama supergroup comprises proterozoic meta sedimentary and meta igneous rocks in western new south wales and eastern south australia and contains the giant broken hill pb zn ag deposit in addition to numerous small stratiform stratabound and vein mineral deposits new lithological geochemical and fluid inclusion data from the olary block west of broken hill suggest the presence of former evaporite rocks now metamorphosed to a variety of chemically and mineralogically unusual lithologies these evaporite rocks overlie relatively oxidised strata and are in turn overlain by reduced graphite bearing pelites rocks of sodic composition abound represented by albite quartz rich rocks calcite actinolite epidote garnet clinopyroxene inferred to represent metamorphosed analcime rich strata of felsic volcaniclastic provenance with variable proportions of carbonates for example calcite dolomite trona and shortite these rocks are interspersed with potassic rocks possibly also with an evaporitic origin in addition to normal clastic meta sediments the presence of halogen rich minerals in a distinctive mineral assemblage hypersaline fluid inclusions pseudomorphic voids and minerals after gypsum and carbonate in addition to tourmalines with isotopically light boron isotopes is interpreted as evidence for a non marine evaporite parent rock for portions of the olary block types of mineral occurrences in the olary block form a continuum between chemical sediments formed by the exhalations of hydrothermal fluids to intrasediment deposits inferred to have been formed due to the chemical changes imposed on these and or diagenetic fluids during their passage through the sedimentary pile disseminated stratabound pyrite including cobaltian types and chalcopyrite extend along strike for many kilometres and are interpreted to have formed by a diagenetic mechanism the presence of massive sulphide bearing strata iron formations barite tourmalinite and manganiferous rocks are typical of chemical sediments derived from hot spring sources the olary block meta evaporites have similar whole rock compositions to tertiary analcime rich rocks of the green river formation wyoming these new data imply that portions of the adjacent broken hill block may also comprise meta evaporites for example the quartz albite rich strata of the thackaringa group and the calcsilicates of the lower broken hill group and that the disseminated cobaltian pyrite mineralisation in the thackaringa group may not be of exhalative origin

analysis of factors determining sediment yield variability in the highlands of northern ethiopia in many developing countries sustainable land management and water resources development are threatened by soil erosion and sediment related problems in response to such threats there is an urgent need for improved catchment based erosion control and sediment management strategies the design and implementation of such strategies require data on erosion rates and understanding of the factors that control the delivery of sediment through the catchment system in this study reservoir sedimentation and corresponding catchment attribute data were used to investigate the major factors controlling sediment yield variability in a mountainous dryland region of northern ethiopia sediment yield data were acquired for representative 11 catchments above reservoirs geomorphological and anthropogenic catchment attributes were extracted for each reservoir from different sources including digital elevation models satellite images and field surveys different statistical analyses such as pearson s correlation principal components and multiple regression were implemented to analyze the relationship between sediment yield and catchment characteristics and to determine the major factors controlling the variability of sediment yield the results show that terrain form gully erosion surface lithology and land cover explain most of the variability in sediment yield among the catchments the implications of the results for relevant management intervention targeted at ameliorating the major causative factors of erosion are also outlined

fe zn cu pb mineralization in the salton sea geothermal system imperial valley california the salton sea geothermal system is an area of active metamorphism in a plio pleistocene deltaic sedimentary sequence within it hypersaline brines containing up to 250 000 ppm total dissolved solids and temperatures up to 365 degrees c are causing incipient sulfide and oxide mineralization we have made a detailed analysis of ore mineralization in two boreholes drilled to depths of up to 2 500 m in this system major ore minerals observed are in order of decreasing abundance pyrite hematite sphalerite chalcopyrite pyrrhotite marcasite and galena the associated nonore minerals are mainly calcite quartz epidote anhydrite adularia and chlorite ore mineralization can be divided into three main types diagenetic sulfide mineralization occurring at depths less than 760 m and temperatures less than 250 degrees c consists of fine grained stratiform iron sulfides occurring as cement in sandstone and as disseminations and bands in shale metamorphic sulfide mineralization occurring at depths greater than 760 m and temperatures greater than 250 degrees c includes the progressive development of porphyroblastic pyrite with increasing depth and temperature its replacement by other fe cu zn pb sulfides at depths greater than 1 220 m and its decomposition into skeletal aggregates at depths greater than 1 525 m concurrent with hornfelsic recrystallization of the host sediments vein and related pore filling ore mineralization is of two contrasting types hematite silicate sulfide or sulfate and sulfide carbonate or silicate the first type occurs in open porous veins in single vertical zones at least 220 m thick in each borehole the second type occurs in veins that are generally sealed and occur in relatively thin scattered vertical intervals in both boreholes thermodynamic analysis indicates that the modern reservoir brines are near equilibrium with the hematite silicate sulfide or sulfate vein assemblage at 300 degrees c with ph 5 4 and log a sub o 2 30 reactions between hematite pyrite and iron bearing silicates chlorite epidote probably control the redox state of the present brines calculated metal chloride complex solubilities for fe zn pb and cu agree well with brine analyses hematite pyrite and chalcopyrite are supersaturated galena and sphalerite are undersaturated in the modern brines the phase relations of the presently sealed sulfide carbonate or silicate veins require that earlier fluids if formed at the same temperature and ph had to be more reduced and sulfur rich than the present slightly oxidized sulfur poor brines contrasting fluid redox states may be caused by a late lateral or fault controlled influx of more oxidized surficial waters lack of acid alteration implies boiling has not occurred to produce the oxidized fluids early formed diagenetic iron sulfides are commonly replaced by later cu pb zn sulfides and iron oxides and enveloped and resorbed by veins acting as nuclei and sources of s and fe for later mineralization precipitation probably occurs when seismic or hydraulic fracturing allows the metal rich sulfur poor brines to interact with earlier pyrite sulfur in the host rocks thus the geothermal system as presently explored is best classified as an incipient stratabound sulfide deposit that is being overprinted by hydrothermal and metamorphic processes

the santa rita gold deposit in the proterozoic paranoa group goias brazil an example of fluid mixing during ore deposition abstract the santa rita gold deposit central goias brazil is hosted by middle to upper proterozoic carbonate pelite sequences of the paranoa group that have been metamorphosed in the greenschist facies the ore is contained in pyrite bearing quartz carbonate veins the mineralization is structurally controlled by wnw ese high angle faults and fractures resulting from the reactivation of older ne sw lineaments pyrite is the sole sulphide and it shows growth zones enriched in co ni and as up to 4 wt hydrothermal alteration zones are enriched in co ni and as and are characterized by diffuse albitization carbonatization silicification and pyritization a fluid inclusion study on quartz from pyrite bearing quartz carbonate veins led to the identification of two fluids 1 a highly saline co 2 n 2 rich aqueous fluid with halite and sylvite daughter minerals and 2 a co 2 n 2 rich aqueous fluid with moderate salinity the two fluid types occur in the same quartz domain and display great variation in the degree of filling and notable dispersion of the microthermometric data on heating all the inclusions decrepitate between 200 and 300 c raman spectrometry detected high concentrations of n 2 in the gas phase with a co 2 n 2 molar ratio between 1 and 19 and a small proportion of ch 4 up to 2 mole the simultaneous entrapment of compositionally variable fluids in the system h 2 o co 2 n 2 nacl kcl allow us to propose a mechanism of heterogeneous trapping the entrapment may result from the mixing of a high salinity fluid h 2 o nacl kcl system with a carbonic fluid h 2 o co 2 n 2 system produced by the devolatilization process of carbonate and phyllitic host rocks considering the absence of spatially and temporally related igneous activity and the low p t regional metamorphism in the paranoa group the brines are inferred to result from leaching of evaporites occurring in the lower part of the paranoa lithostratigraphic column gold was probably initially transported as an aucl 2 complex t 300 c low ph moderate o 2 pyrite field stability as temperature decreased below 290 c the switch over process would lead to the predominance of au hs 2 in the fluid pyrite precipitated in this temperature interval the oscillatory zoning of the as co ni bearing pyrites indicates episodic fluctuation of the fluid composition such changes in fluid composition are favoured by a mechanism of fluid mixing by intermittent supplies in the hydrothermal system the proposed mechanism of heterogeneous trapping of two separate fluids in the system h 2 o co 2 n 2 nacl kcl and the resulting changes in the physicochemical conditions caused by the fluid mixing appears as a conspicuous process for the santa rita hydrothermal fluid evolution a model based on the existence of a proterozoic geothermal system involving the regional thermal gradient is proposed

buried rhyolites within the active high temperature salton sea geothermal system abstract previously unrecognized pulses of rhyolite volcanism occurred in the salton trough between 420 8 ka and 479 38 ka 2 based on high spatial resolution u pb zircon geochronology presently these rhyolite lavas tuffs and shallow subvolcanic sills are buried to depths between 1 6 and 2 7 km at ambient temperatures between 200 and 300 c and are overprinted by propylitic to potassic hydrothermal alteration mineral assemblages consisting of finely intergrown quartz k feldspar chlorite epidote and minor pyrite alteration resistant geochemical indicators whole rock nd isotopes zircon oxygen isotopes reveal that these rhyolites are derived from remelting of morb type crust that was chilled and hydrothermally altered by deep circulating hydrothermal waters u pb zircon dating confirms the presence of bishop tuff in well state 2 14 at 1 7 km depth approximately 5 km ne of the geothermal wells that penetrated the buried rhyolites these results indicate accelerated subsidence towards the center of the salton trough increasing from 2 2 mm a to 3 8 mm a based on these results the present day salton sea geothermal field is identified as a focus zone of episodic rhyolitic volcanism intense heat flow and metamorphism that predates present day geothermal activity and holocene volcanism by at least 400 ka

revisiting the hypsometric curve as an indicator of form and process in transport limited catchment hypsometry has historically been used as an indicator of geomorphic form of catchments and landforms yet there has been little work aimed at relating hypsometry to landform process and scale this paper uses the siberia catchment evolution model to explore linkages between catchment process and hypsometry siberia generates results that are qualitatively and quantitatively similar to observed hypsometric curves for physically realistic parameters however we show that not only does the hypsometry reflect landscape runoff and erosion process but it is strongly dependent on channel network and catchment geometry we show that the width to length ratio of the catchment has a significant influence on the shape of the hypsometric curve though little on the hypsometric integral for landforms dominated by fluvial sediment transport the classic strahler mature hypsometric curve is only generated for catchments with roughly equal width and length narrow catchments show a hypsometric curve more similar to strahler s monadnock form for landscapes dominated by diffusive transport the simulated hypsometric curve is concave down everywhere this being consistent with curves reported for some example catchments in france because the transition between diffusive dominance to fluvial is scale dependent with larger catchments exhibiting greater fluvial dominance then the hypsometric curve is a scale dependent descriptor of landforms experimental results for simulated landforms from a small scale rainfall erosion simulator are reported it is shown that siberia yields satisfactory fits to the data confirming its ability to predict the form of the hypsometric curve from a simple model of geomorphic processes 1998 john wiley sons ltd

prograde phase relations in the state 2 14 well metasandstones salton sea geothermal field california seventy five core samples of medium to fine grained metasandstones from the state 2 14 borehole were studied petrologically and mineralogically to evaluate compositional variations of geothermal minerals and prograde metamorphic reactions three distinct metamorphic zones are defined based on the appearance of index minerals with increasing grade they are 1 chlorite calcite chl cc zone at depths between 610 and 2480 m 2 biotite bt zone between 2480 and 3000 m and 3 clinopyroxene cpx zone between 3000 and 3180 m all of the studied metasandstones at depths greater than 906 m contain epidote ep and quartz qtz with or without albite ab characteristic assemblages ep qtz ab are 1 chl cc k feldspar ksp phengitic muscovite for the chl cc zone 2 bt chl ksp anhydrite anh and bt act chl for the bt zone and 3 diopsidesalite act bt oligoclase actinolitic hornblende for the cpx zone epidote exhibits a compositional variation ranging from 0 11 to 0 42 xfe fe fe al many amphibole grains of the clinopyroxene zone show patchy or lamellar intergrowths of both actinolite and actinolitic hornblende on a scale less than a few tens of micrometers these amphiboles show distinct compositional discontinuities such as in al2o3 contents 2 7 4 8 wt and fe fe mg ratios 0 41 0 55 the cpx zone samples thus mark the transition from the greenschist to amphibolite facies other important secondary phases include rutile or anatase depths 940 m peristerite 1235 m and mn salite 2484 m the observed assemblages and compositions of minerals are chemographically interpreted utilizing an epidote projection in the simple system al2o3 k2o mgo cao sio2 h2o co2 reactions for the appearance of index minerals are elucidated in a qualitative t xco2 diagram the results indicate that l the compositions of chl and bt are highly variable depending on the bulk composition however chl in the chl cc zone becomes enriched in mg with increasing depth 2 bt forms by a discontinuous reaction ksp chl cc bt ep qtz h2o co2 hence the first appearance of bt is greatly affected by the fluid composition 3 the hydrothermal fluid in equilibrium with the analyzed assemblages is very low in xco2 0 03 and 4 the absence of wairakite and prehnite is attributed to the high fo2 values of the salton sea geothermal system

geochemical survey of medium temperature geothermal resources from the baja california peninsula and sonora mexico abstract waters from hot springs and deep wells from cerritos in the northern baja california peninsula and deep wells from the riito zone sonora state were studied in order to classify medium temperature geothermal resources to be exploited in nw mexico geochemical characteristics of san felipe and punta estrella coastal springs indicate the mixing of seawater and meteoric components with secondary leaching of evaporates reservoir temperatures for both zones were estimated up to 225 c mixing of high portions of seawater 80 wt with local waters could be the origin for the puertecitos coastal spring with a reservoir temperature estimation of 195 c the el coloradito coastal spring is composed of meteoric water with a reservoir temperature of 127 c the formation of thermal manifestations along the baja california coast could be related to the heating up of convecting seawater along extensional tectonic structures as observed for submarine hydrothermal vents at the gulf of california and along the east pacific rise volcanic steam heated waters with a reservoir temperature of 135 c were found at the valle chico inland springs from the baja california peninsula deep fluids from the riito zone originated by evaporation of infiltrated waters with similar characteristics to those located in the mexicali valley reservoir temperature of 192 and 126 c are estimated for the riito deep wells er 1b er and r 1 respectively the riito artesian wells m 1 m 2 and m 4 indicate reservoir temperatures from 109 to 118 c isotopic data define the artesian wells as typical surface water or shallow groundwater from the mexicali valley the cerritos deep fluids of the mexicali valley show a close chemical and isotopic relationship to the adjacent cerro prieto reservoir fluids suggesting a similar origin and a possible connection of both aquifer systems conductive cooling of cerro prieto discharge fluids could originate the cooler cerritos system 130 c according to the reservoir temperature estimations electricity could be generated at san felipe punta estrella and riito zones using conventional or binary cycle while the direct application of fluids in heat pumps and industrial processes is feasible for the other sites

fluid inclusion evidence for immiscibility in magmatic differentiation abstract after a brief review of recent work on melt inclusions in diamond and in normal magmatic environments the nature of the fluid inclusion evidence for various stages of magmatic immiscibility is summarized during magmatic differentiation by crystal fractionation from originally low volatile content silicate melts yielding normal plutonic rocks through hydrous silicate melts yielding pegmatites to late stage water rich fluids yielding quartz veins and ore deposits the composition of the residual liquid changes drastically in some geologic environments this change in composition of the residual liquid may be continuous with no phase change in the fluid part of the system under most natural conditions however it is far more likely to have one or more stages in the evolution during which globules of a separate new immiscible fluid phase exsolve the term immiscibility is used here in its more general sense to refer to the existence at equilibrium of two or more non crystalline polycomponent solutions fluids differing in properties and generally in composition i believe that the great bulk of the magmatic inclusions that are being studied today have come about through the intervention of one or more such stages of immiscible fluid separation i e magmatic differentiation by fluid immiscibility examples include silicate melt dense co2 fluid silicate melt sulfide melt silicate melt silicate melt silicate melt low density vapor i e vesiculation and as presented in more detail in this paper various stages of silicate melt hydrous saline melt aqueous fluid co2 fluid immiscibility generally only parts of these stages are recorded by the trapping of fluid inclusions and the interpretation of the inclusion record is commonly ambiguous and difficult particularly that stage between hydrous silicate melts and the hydrous saline melts and aqueous solutions responsible for many ore deposits the ambiguity results mainly from problems of inclusion origin and nonrepresentative trapping within any given individual inclusion thus the probability of trapping of only one vs various amounts of two immiscible fluids or of trapping solid phases along with the fluid present severe difficulties in addition there is the almost universal superposition of various stages of trapping of fluids within any given sample these problems can only be approached by very careful petrography and analysis of optimum material combined with field data and experimental p v t x studies of pertinent systems completely unequivocal statements of the course of evolution of the fluids in such natural systems may never be possible

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis