structurally controlled hydrothermal dolomites in albian carbonates of the ason valley basque cantabrian basin northern spain abstract shallow marine carbonate sedimentation dominated during the albian in the western part of the basque cantabrian basin in northern spain forming the large ramales platform this platform originated on a less subsiding tectonic block facing deeper and more subsiding areas to the south and east which were created by tectonic activity in the basin fracture related hydrothermal dolomites hosted in these albian carbonates are well exposed in the ason valley area mapping in the studied area revealed several dolomite bodies related to main faults that cut the stratification almost at right angles the bodies show a vertical development along fault strike up to 900 m thick from which kilometre scale branches expand following the stratification dolomitization is pervasive and independent of the limestone facies main dolomite facies are fine replacive sucrosic and saddle petrography c o and sr isotopes and fluid inclusion analysis support a polyphase hydrothermal dolomitization at fluid temperatures between 75 c and 240 c and highly variable salinity of up to 22 wt nacl fine dolomite replaced limestone first and then sucrosic and saddle dolomites replaced part of the first dolomite and cemented newly created fracture porosity together with different calcite cements zebra dolomites and hydroclastic breccias are products of this later stage burial analysis of the host rock supports maximum burial temperatures of 80 c and intense tectonic activity from the albian to turonian with a latest albian peak subsidence albian stretching of the crust and subsequent ascent of the isotherms in the area is suggested to have produced sufficient heat to the dolomitizing fluids the structural analysis indicates a strong transtensional tectonic activity in the studied area during albian to turonian time with the creation of an overstep between w e trending and n s trending faults fluids moved from subsiding areas to fractured uplifted parts of the ramales platform enhanced by diapiric activity

radiometric slope correction of synthetic aperture radar images the brightness in a sar image is affected by topographic height variations due to 1 the projection between ground and image coordinates and 2 variations in backscattering coefficient with the local scattering geometry this paper derives a new equation for 1 i e the radiometric slope correction based on a calibration equation which is invariant under a coordinate transformation an algorithm is described to obtain the slope correction from a sar interferogram which also enables retrieval of the full scattering geometry since the sar image and interferogram are derived from the same data set there is no need to match the image with the calibration data there is also no need for phase unwrapping since the algorithm only uses the fringe frequencies a maximum likelihood estimator for the fringe frequency is analyzed and the algorithm is illustrated by processing ers 1 sar data the example demonstrates that the spatial resolution and calibration error are adequate for most applications

microbial sulfate reduction in deep sea sediments at the guaymas basin hydrothermal vent area influence of temperature and substrates abstract microbial sulfate reduction was studied by a 35 s tracer technique in sediments from the hydrothermal vent site in guaymas basin gulf of california mexico in situ temperatures ranged from 2 7 c in the overlying seawater to 120 c at 30 cm depth in the hydrothermal sediment sulfate reduction was measured in intact cores of hydrothermal sediment at 3 20 35 50 70 and 90 c the maximum rates of sulfate reduction were found in the upper 0 2 cm of the sediment and ranged from 32 nmol cm 3 d 1 at 90 c to 1563 nmol cm 3 d 1 at 70 c the rates of sulfate reduction rapidly decreased with depth in the upper 0 10 cm of the sediment and the maximal depth integrated rate 0 10 cm was 70 3 mmol so 4 2 m 2 d 1 at 70 c in comparison the sulfate reduction rate in nonhydrothermal sediment from the vent area was 0 85 mmol m 2 d 1 at the in situ temperature of about 3 c the high subsurface rates of sulfate reduction in the hydrothermal vent area was attributed to an enhanced local substrate availability in slurries of hydrothermal sediment incubated at 10 120 c microbial sulfate reduction extended to 102 c and different temperature groups of microbial sulfate reducers had optimum temperatures at around 34 70 and 80 88 c the overall temperature response of thermophilic sulfate reduction was similar in hydrothermal sediment sampled at different sites addition of short chain fatty acids and yeast extract to the sediment slurries stimulated sulfate reduction rates at all incubation temperatures no sulfate reduction was detected in the temperature range from 102 120 c microbial rather than thermochemical sulfate reduction could be a possible source of h 2 s in sulfide deposits with formation temperatures at about 100 c

terrain influences in sar backscatter and attempts to their correction synthetic aperture radar sar images reveal radiometric image distortions that are caused by terrain undulations the authors present the results of a study extracting and investigating the various components of these terrain influences an imaging model is set up for the geometric rectification of the sar image and for a reconstruction of the imaging geometry a prerequisite for the setup of this model is the use of a digital elevation model eight different geometric parameters are derived and investigated for their influence on grey value variations in the geocoded sar image image grey value variations of three major land use classes forest agricultural land and urban suburban areas are examined empirical models of the sar backscatter variations are used to describe the relations between image grey values and various geometric parameters

multi model radiometric slope correction of sar images of complex terrain using a two stage semi empirical approach practical approaches for the implementation of terrain type dependent radiometric slope correction for sar data are introduced radiometric slope effects are modelled as the products of two models the first is a simple physical model based on the assumption of a uniform opaque layer of isotropic scatterers which is independent of terrain type frequency and polarization it accounts for the slope induced variation in the number of scatterers per resolution cell the second is a semi empirical model which accounts for the variation in scattering mechanisms dependent on terrain type frequency and polarization palsar fbd l band hh and hv polarization data are used at two test sites in brazil and fiji results for the brazilian area which has slopes up to 25 show that remaining slope effects for the multi model case are much smaller than 0 1 db for all land cover types this is much better than the best single model approach where remaining slope effects can be very small for forests but be as large as 1 77 db for woodland in hh polarization results for the fiji area which has different vegetation types are very similar the potential large improvement using this multi model approach in the accuracy of biomass estimation for transparent or open canopies is discussed it is also shown that biomass change on slopes can be systematically under or overestimated because of associated change in scattering mechanism

lead isotope study of zn pb ore deposits associated with the basque cantabrian basin and paleozoic basement northern spain a total of forty three galena samples from syngenetic and epigenetic pb zn mineralizations emplaced in the lower cretaceous basque cantabrian basin and paleozoic basement of the cinco villas massif in the western pyrenees have been analyzed for pb isotopic composition galena from sedex mineralizations hosted in carboniferous clastic rocks in the cinco villas massif display an homogeneous lead isotopic signature 206pb 2044pb 18 43 207pb 204pb 15 66 208pb 204pb 38 69 suggesting a single lead reservoir these values are slightly more radiogenic than lead from other european hercynian deposits possibly reflecting the influence of a more evolved upper crustal source underlying paleozoic sediments are proposed as lead source for the cinco villas massif ores analyses from twenty six galena samples from the four strata bound ore districts hosted in mesozoic rocks reveal the existence of two populations regarding their lead isotopic composition galena from the western santander districts e g reocin is characterized by more radiogenic isotope values 206pb 204pb 18 74 207pb 204pb 15 67 208pb 204pb 38 73 than those from the central and eastern districts troya legorreta central and western vizcaya 206pb 204pb 18 59 207pb 204pb 15 66 208pb 204pb 38 73 in all districts the most likely source for these mineralizations was the thick sequence of lower cretaceous clastic sediments the existence of two separate lead isotopic populations could be the result of regional difference in the composition of the basement rocks and the clastic sediments derived of it or different evolution histories in both sub basins isotopic ratios indicate an increase in crustal influence as the age of the ores decreases

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

sar observations and modeling of the c band backscatter variability due to multiscale geometry and soil moisture the effect of the multiscale surface geometry on the sensitivity of c band synthetic aperture radar sar data to soil moisture is studied the experimental data consist of c band sar images of an agricultural site including fields with various combinations of three distinct roughness components from small to large scale the backscatter variability due to surface roughness has been analyzed the effect of random roughness associated with soil clods is never less than 2 db and the effect of a row pattern can be as strong as 10 db in addition the periodic drainage topography induces a backscatter variability due to soil moisture variation and drainage relief the results indicate that airborne c band sar data cannot be easily inverted into soil moisture data however with ers 1 or radarsat data at an incidence angle of about 20 degrees the effect of random and periodic roughness can be reduced to about 2 db if the look angle is less than 50 degrees

geologic evolution of the yukon river implications for placer gold abstract the greatest placer potential in northwest canada lies in preglacial drainage systems the largest placer gold deposits are associated with pliocene pre glacial fluvial gravels of the dawson range in particular klondike plateau of west central yukon the abundance and or the lack of gold concentration in this area were controlled by the ability of the streams to aggrade in response to changes caused by extensional faulting in the tintina trench differential uplift and regional denudation gold bearing gravels in the northern and eastern slopes of the dawson range are found in low order tributaries of the pre glacial south flowing yukon river glaciation played an important role in masking and changing the direction of drainage and creating new channels in this region the earliest known drainage changes relate to late miocene formation of the tintina trench and early pliocene uplift of the st elias mountains prior to these events the yukon river drained south into the gulf of alaska initial regional glaciation 2 6 2 9 ma diverted the southward drainage toward the northwest becoming part of the kwikhpak river in alaska the present yukon river drainage basin is about 27 5 larger than the ancestral kwikhpak river basin the evolution of the river is described here in three stages 1 drainage in pre late miocene 2 drainage in early pliocene and 3 drainage after earliest pliocene glaciation

fluid inclusion technique for determining maximum temperature in calcite and its comparison to the vitrinite reflectance geothermometer theory laboratory experiments and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating and therefore some homogenization temperatures t h record a temperature close to the maximum reached by the rock this characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature t peak to test this hypothesis we have compiled fluid inclusion t peak mean random vitrinite reflectance r m and present day t peak from 46 diverse geologic systems that have been at t peak from 10 4 to 10 6 yr present t peak ranged from 65 to 345 c t h modes and means ranged from 59 to 350 c and r m data ranged from 0 4 to 4 6 spanning the temperature and thermal maturity range associated with burial diagenesis hydrothermal alteration and low grade metamorphism plots of t h and t peak data for systems thought to be currently at maximum temperature demonstrate close agreement between t h and present t peak in sedimentary basins although caution should be applied the relation suggests that t h of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature this study also compares t h to mean random vitrinite reflectance r m to offer further support for the use of t h as a measure of t peak and to provide a better understanding of r m t h correlates well with r m and results in a curve similar to r m vs t peak calibrations determined by other workers the strong correlation correlation coefficient r 0 93 between t peak and r m in these systems suggests that maximum temperature is the major control on thermal maturation

track of fluid paleocirculation in dolomite host rock at regional scale by the anisotropy of magnetic susceptibility ams an example from aptian carbonates of la florida northern spain the present study aims to apply the ams method anisotropy of magnetic susceptibility at a regional scale to track the fluid circulation direction that has produced an iron metasomatism within pre existing dolomite host rock the urgonian formations hosting the zn pb mineralizations in la florida cantabria northern spain have been taken as target for this purpose sampling was carried out in addition to ferroan dolomite host rock enclosing the zn pb mineralizations in dolomite host rock and limestone to make the comparison possible between magnetic signals from mineralized rocks where fluid circulation occurred and their surrounding formations ams study was coupled with petrofabric analysis carried out by texture goniometry scanning electron microscopy sem observations and also shape preferred orientation spo statistics sem observations of ferroan dolomite host rock illustrate both bright and dark grey ribbons corresponding respectively to fe enriched and pure dolomites spo statistics applied on four images from ferroan dolomite host rock give a well defined orientation of ribbons related to the intermediate axis of magnetic susceptibility k2 for ams data two magnetic fabrics are observed the first one is observed in ferroan dolomite host rock and characterised by a prolate ellipsoid of magnetic susceptibility with a vertical magnetic lineation the magnetic susceptibility carrier is fe rich dolomite these features are probably acquired during metasomatic fluid circulations in fe rich dolomite host rock c axes are vertical as a rule 0001 planes i e planes perpendicular to c axes are isotropic with respect to crystallographic properties so the magnetic anisotropy measured in this plane should reflect crystallographic modification due to fluid circulation this is confirmed by the texture observed using the sem consequently ams results show a dominant ne sw elongation interpreted as the global circulation direction and a nw se secondary elongation that we have considered as sinuosities of the fluid trajectory the second type of magnetic fabric is essentially observed in the limestone and characterised by an oblate form of the ellipsoid of magnetic susceptibility a horizontal magnetic foliation and mixed magnetic susceptibility carriers it is interpreted as a sedimentary fabric

removal of terrain effects from sar satellite imagery of arctic tundra synthetic aperture radar sar images of the earth s terrestrial surface contain geometric and radiometric image effects which are caused by varying terrain elevation and slope the radiometric effects tend to mask signal variations caused by other physical variables such as soil moisture and surface vegetation type which are known to influence sar backscatter signals as a result raw sar images are of limited use in classifying surface vegetation type or quantifying the spatial distribution of soil moisture in regions of terrain relief the authors present a technique for removing radiometric terrain effects from sar images image correction was carried out in two steps first an existing modeling package was used in combination with digital elevation data in order to map the raw image pixels onto a geodetic coordinate system thereby removing the geometric portion of the image distortion radiometric effects were then removed with the aid of a backscatter model which treats the reflected radiation as a combination of diffuse lambertian and specular components parameters in the backscatter model were determined by comparing two c band sar images of a test area in a region of arctic tundra which were taken from ascending and descending orbit tracks of the ers 1 satellite the ascending and descending images displayed reductions in pixel value variance of 30 and 13 respectively after processing direct comparison of the two test area images reveals a dramatic improvement in image similarity after processing

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

mineralogy paragenesis and mineral zoning of the west fork mine virburnum trend southeast missouri asarco9s west fork mine the newest mine in the viburnum trend began production in 1985 and reached full production in 1988 although significant mineralogical and paragenetic studies have been performed on the other ore deposits of the viburnum trend no attempt has been made to correlate these studies with mineral zoning patterns the distinct mineral zoning present at the west fork mine provides a unique opportunity to relate mineral paragenetic sequence to mineral zoning the present study concentrated on the main ore horizon m bed which is composed of four north south trending linear metal zones which together consist of an inner zone of colloform iron and zinc sulfides bordered outward by zones of disseminated iron and zinc sulfides and fringed by outermost zones of galena that also overprint the inner zone principal metallic sulfides in the ores at the west fork mine are pbs galena zns sphalerite and wurtzite and fes 2 pyrite and marcasite paragenetic sequence and metal zoning show that the ore forming fluids migrated initially through the inner zone where zns was deposited and subsequently traveled outward depositing fes 2 followed by pbs the presence of rapidly deposited colloform zns and fes 2 and bladed galena in the central fe zn zone indicates that ore fluids which deposited the sulfides in the central zone were more saturated with respect to metal sulfides outer layers of the colloform zns bodies in the fe zn zone are characterized by an abundant complex intergrowth of sphalerite and wurtzite schalenblende x ray analysis indicates that the wurtzite within the schalenblende inverted to sphalerite thereby producing pseudomorphous sphalerite after wurtzite because wurtzite is the sulfur deficient form of zns it can be postulated that sulfur fugacities were low at the end of the main stage of zinc sulfide deposition subsequent increase in sulfur fugacity during the main stage of iron deposition caused inversion of wurtzite to sphalerite interlayered pyrite and marcasite are evidence that the ore fluids during the main stage of deposition were oscillating above and below a ph of 5 minerals subsequently deposited in the outer zones were precipitated more slowly from fluids that were relatively depleted in metals the distinct differences in ore character between the metal zones may well be a result of multiple fluids separate fluids may have been channelized each fluid representing a zone or may have mixed through time the results of this study are not compatible with ore deposition from a single fluid source

a 900 k y record of strath terrace formation during glacial interglacial transitions in northwest china the timing of the development of strath terraces with respect to climatic variability remains equivocal previous studies attribute strath terrace formation to glacial or interglacial climates or to variations in sediment and water fluxes that cause lateral erosion followed by vertical incision a chronology of strath terrace formation spanning similar to900 k y has been generated on the basis of loess paleosol couplets and paleomagnetic thermoluminescence and radiocarbon dating of strath terraces in the qilian shan of northeastern tibet repetitive stratigraphic and geomorphic patterns on each terrace indicate that they formed during glacial interglacial transitions long term bedrock incision rates and inferred rock uplift rates appear steady and unrelated to strath formation over the past 900 k y

sulfur and lead isotope systematics implications for the genesis of the riopar zn fe pb carbonate hosted deposit prebetic zone se spain abstract the zn fe pb deposits of the riopar area prebetic zone se spain are hosted by dolostones that replace berriasian to valanginian upper jurassic lower cretaceous limestones mineralization consists of hypogene sphalerite marcasite and galena and supergene calamine zones the hypogene ores are associated with a saddle dolomite gangue the ore bodies occur as discordant and stratiform lenses ore cemented breccias cm to mm wide veins and veinlets disseminations and stylolite porosity filling within the host dolomites the main ore controls include stratigraphy and or lithology tectonics faults fractures and breccias and availability of metals and sulfur the morphologies and epigenetic character of the hypogene ore bodies are consistent with the classification of this mineralization as a mississippi valley type mvt deposit the ga ge geothermometer in sphalerite yielded a temperature range of 194 252 c which represents the temperature of the source region of the ore solution this value is comparable to the temperature obtained in the ore deposition site 159 15 c from the 34s geothermometer in sphalerite galena pairs this similitude points to a hydrothermal fluid that did not cool down significantly during flow from the fluid reservoir area to the precipitation site 34s values of base metal sulfides 7 5 to 3 5 are consistent with thermochemical reduction of triassic sulfate seawater and or derived from dissolution of evaporites by interaction with organic compounds e g hydrocarbons methane which reduced sulfate to sulfide in the deposition site the lead isotope ratios 206pb 204pb 18 736 18 762 207pb 204pb 15 629 15 660 208pb 204pb 38 496 38 595 of galena suggest that pb and probably other metals as zn is derived from continental crustal rocks on the other hand these relations points to a unique metal source probably derived from the paleozoic basement rocks the relationship between bedding parallel stylolites dolomitization sulfide precipitation and alpine tectonic affecting the mvt ore suggests a relative timing range for the mineralization in the riopar area of 95 20 ma upper cretaceous tertiary the sulfide mineralization and the associated dolomitization are thus explained by the contribution of two fluids that mixed in different proportions during dolomitization and mineralization i a fluid probably derived from cretaceous seawater saturating mesozoic sediments fluid a characterized by being dilute and initially low temperature which should have contained organic rich compounds in the ore deposition site e g hydrocarbons and ch4 dissolved gas and ii a high salinity hydrothermal brine fluid b rich in both metals and sulfate circulated through the paleozoic basement during the pre ore dolomitizing stage the fluid phase was dominated by the diluted fluid fluid a fluid b whereas in a later fluid pulse the proportion of the high salinity fluid increased fluid a

zinc and sulfur isotope variation in sphalerite from carbonate hosted zinc deposits cantabria spain we studied zinc and sulfur isotopes and the chemical composition of sphalerite samples from picos de europa aliva mine and sphalerite and hydrozincite samples from la florida mine two carbonate hosted mississippi valley type mvt deposits located in northern spain despite being close they are hosted in carbonatic rocks of different ages lower carboniferous and lower cretaceous respectively the two generations of sphalerite at picos de europa show different 66zn values stage 1 sphalerite 0 24 per mil and stage 2 sphalerite from 0 75 to 0 08 per mil both generations also differ in the sulfur isotope composition stage 1 has 34s 6 6 and stage 2 has 34s 0 9 to 2 9 per mil and the chemical composition stage 1 sphalerite compared to stage 2 sphalerite is significantly enriched in pb as mn sb slightly enriched in ag ni and cu and depleted in co ga tl te ge and sn we suggest that zn isotope fractionation was controlled predominantly by ph and t changes high zn isotope values reflect rapid precipitation of sphalerite from higher temperature acidic fluids that carried zn mostly as chloride species after interaction with carbonate rocks while lower zn isotope values most likely resulted from a longer precipitation process from fluid at higher ph and decreasing t that carried dominantly zn sulfide species at la florida sphalerite samples show light 66zn depleted signatures with 66zn values from 0 80 to 0 01 per mil mostly between 0 80 and 0 24 per mil and 34s values from 10 7 to 15 7 per mil without any relationship between the 66zn and 34s values here the variation in zn isotope values is interpreted as related to mixing of fluids from two reservoirs the zn was carried by a single deep seated and higher t 250 320 c fluid and precipitation took place after mixing with a connate s rich fluid in a system with mh2s mzn2 as a result of change in ph t and zn predominant species the light 66zn accompanied by heavy 34s values resulted from fractionation of zn aqueous sulfides at near neutral ph and decreasing t hydrozincite samples show much heavier 66zn values 0 21 to 0 33 per mil consistent with fractionation during supergene processes

genesis of the mississippi valley type zn pb deposit of san vicente central peru geologic and isotopic sr o c s pb evidence the san vicente zn pb ore deposit is situated 300 km east of lima in central peru within the upper triassic lower jurassic carbonate platform pucara group at the western margin of the brazilian shield production during the last 20 years and present reserves exceed 12 million tons of ore assaying about 12 percent zn and 1 percent pb sphalerite and galena the only ore minerals occur as lens shaped bodies generally parallel to the bedding within the 1 400 m thick pucara sequence three ore bearing dolomite units occur the ore lenses are bound to dolomitized tidal flat and lagoon facies with cryptalgal lamination and evaporite molds and to adjacent oolithic grainstones of barrier facies strontium carbon oxygen and sulfur isotope geochemistry was carried out on consecutive crystallization generations the results obtained display systematic trends the 87 sr 86 sr ratios range between 0 7077 and 0 7084 the first generations display values very similar to those of upper triassic lower jurassic ocean water later generations are slightly enriched in radiogenic strontium the degree of enrichment in radiogenic strontium is low compared to other mississippi valley type deposits the delta 18 o values range between 6 and 10 per mil pdb and the delta 13 c values between 2 and 1 per mil pdb the late crystallization generations are enriched in the light isotopes of oxygen and carbon compared to the first generations the sulfur isotope ratios of sphalerite are relatively homogeneous ranging between 9 9 and 13 0 per mil a trend to lighter sulfur isotope ratios with advancing diagenetic stage can also be recognized the san vicente lead zinc deposit formed during burial diagenesis the temperatures indicated by sulfur isotope geothermometry 75 degrees 92 degrees c would be consistent with temperatures reached at a burial depth of about 2 to 3 km this might have been reached by the end of the jurassic a model based on abiogenic reduction of sulfates at or near the ore site and the introduction of a zinc and lead bearing basinal brine characterized by strontium isotope ratios slightly higher than contemporaneous seawater and highly radiogenic lead is favored the association of the orebodies with peritidal facies with abundant sulfate molds is important evidence favoring the existence of two separate reservoirs for sulfur and metals leaching of detrital material derived from precambrian upper crust from the brazilian shield would explain both strontium and lead isotope ratios

marble hosted sulfide ores in the angouran zn pb ag deposit nw iran interaction of sedimentary brines with a metamorphic core complex the angouran zn pb ag deposit zanjan province nw iran is located within the central sanandaj sirjan zone of the zagros orogenic belt the deposit has proven and estimated resources of 4 7 mt of sulfide ore at 27 7 zn 2 4 pb and 110 g t ag and 14 6 mt of oxidized carbonate ores at 22 zn and 4 6 pb it is hosted by a metamorphic core complex that is unconformably overlain by a neogene volcanic and evaporite bearing marine to continental sedimentary sequence the sulfide orebody precursor to the significant nonsulfide ores is located at the crest of an open anticline at the contact between neoproterozoic to cambrian footwall micaschists and hanging wall marbles 40ar 39ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid mid miocene exhumation of the metamorphic basement 20 ma and yield an upper age constraint for mineralization the fine grained sulfide ore is massive replacive often brecciated clearly postmetamorphic and dominated by fe poor sphalerite with minor galena pyrite anhydrite quartz muscovite dolomite and rare calcite sphalerite contains na ca cl brine inclusions 23 25 mass total dissolved solids with homogenization temperatures of 180 70 c fluid inclusion chemistry na k li ca mg cl br ore geochemistry s and pb isotope data suggest that the angouran sulfide ore formed by the interaction of modified strongly evaporated miocene seawater and the lithotypes of an exhumed metamorphic core complex minor contributions of metals from miocene igneous rocks cannot be excluded mineralization occurred in a collisional intra arc setting with high heat flow probably during the transition from an extensional to a compressional regime the angouran deposit may represent a new type of low temperature carbonate hosted zn pb ore that is distinct from mississippi valley type and sedimentary exhalative deposits

low temperature sulphate reduction biological versus abiological sulphate is considered to have been a major source of sulphide in strata bound and stratiform base metal sulphide deposits many of these deposits however appear to have been formed at moderate temperatures 200 c which poses the question by what mechanism s was sulphate reduced to sulphide two modes of reduction have been established experimentally 1 catalysis by sulphate reducing bacteria which at present is only known to occur below ca 100 c and 2 abiological reduction by ferrous iron or organic matter which has only been clearly shown above ca 250 c several attempts have been made to demonstrate abiological reduction below 200 c and some new data are presented here although the results do not exclude the possibility that such a reaction may be geochemically significant there has been no unequivocal demonstration of nett sulphide formation from sulphate at these temperatures recent studies of the microbiology of hydrothermal regions have opened up the prospect of bacterial sulp

genetic implications of trace element distributions in carbonate and non carbonate phases of limestones and dolostones from western cantabria spain abstract fe zn sr ba and pb contents are reported for carbonate and non carbonate clay fractions of lower cretaceous limestones and dolostones from western cantabria spain increases in the zn contents of both carbonate and non carbonate fractions are observed in association with the calcite dolomite transformation suggesting that the dolomitising fluids were probably enriched in this element relationships between regional geochemical trends for some elements zn in the carbonate fraction and zn ba and pb in non carbonate fraction the paleogeography of the area during the aptian and albian and the geographical positions of the localities studied lead to the conclusion that the dolomitising fluids originated from adjacent basinal mud rocks stable isotope and fluid inclusion data support this hypothesis

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

controls on carbonate platform evolution on active fault blocks the lower cretaceous castro urdiales platform aptian albian northern spain abstract four contrasting carbonate sequences developed in a tectonically active extensional setting in the lower cretaceous aptian albian castro urdiales platform of north spain the four carbonate phases p1 p4 early aptian late aptian earliest albian and early late albian respectively are identified across the platform to basin transition on the basis of sedimentary geometries and internal facies patterns they are vertically separated by four incipient drowning events d1 d4 middle aptian aptian albian boundary early albian and late albian the first carbonate stage p1 corresponds to a low relief carbonate platform characterized by widespread shallow marine depositional environments with a nearly flat organization the second platform stage p2 developed as a rimmed carbonate platform the third carbonate stage p3 evolved from a low relief aggradational platform substage a to a progradational offlapping platform substage b and back to a backstepped aggradational rimmed platform substage c responding to changes in differential subsidence and carbonate production at the beginning of the albian the castro urdiales carbonate platform was broken up by extensional tectonic movements with formation of fault blocks bounded by ne sw and nw se trending faults on the crests of uplifted blocks meteoric processes were active whereas grabens and half grabens acted as channel conduits for terrigenous rich deposits subsidence rates increased during the late early albian late albian the crests of rotated blocks formed paleohighs that nucleated small residual carbonate platforms carbonate stage p4 that were surrounded by deeper water basins this study suggests that the evolution of carbonate platform sequences in the lower cretaceous of castro urdiales was primarily controlled by changes in accommodation space which were most likely driven by intraplate stresses related to extension in the north spanish continental margin during the opening of the north atlantic drowning events in the castro urdiales platform coincide with major crises of cretaceous carbonate production worldwide suggesting that regional tectonism and global oceanic changes interacted to cause phases of platform demise

contrasts among bidirectional reflectance of leaves canopies and soils the apparent brightness of a natural surface depends on the characteristics and direction of incident radiation surface radiative properties and the direction from which the surface is viewed the bidirectional reflectance distribution functions brdf for soils vegetation canopies and individual leaves have common features that arise from an anisotropic diffuse scattered component as well as specular reflections from irregular surfaces the diffuse scattered component however tends to dominate canopy and soil brdf s where as specular reflection tends to dominate leaf brdf s in this paper simple models are presented for predicting soil and canopy brdf s and predicted results are compared with some measurements this effort represents an attempt to illustrate the important features that cause observed brdf s the results of the models are compared with a simple three coefficient empirical equation that may be easier to invert than the causitive models so that radiation measurements can be used to obtain surface features some brdf measurements from corn and soybean leaves provide a contrast for canopy and soil distributions and also provide needed leaf properties that are important to vegetation canopy models the knowledge of soil canopy and leaf brdf s is combined into a single model called cupid to predict the resultant brdf of complex natural surfaces

long term stability of global erosion rates and weathering during late cenozoic cooling reports that the geological record of erosion indicates a fourfold increase in global sedimentation rates during the past 5 million years merited a global explanation explanations offered include an increased rate of mountain formation and global cooling now jane willenbring and friedhelm von blanckenburg reanalyse original data sets and use ocean records of beryllium isotope ratios to obtain an indirect measure of past erosion rates and rock weathering they find no clear evidence either for an increase in global erosion or for a pulse of weathered material in the oceans during the past 12 million years they suggest that cenozoic global cooling must have some other cause and the mountain building that did occur had little effect on erosion or weathering flux globally accelerated uplift and global cooling have been suggested as possible causes for a fourfold increase in global sedimentation rates and by inference in erosion rates or weathering fluxes during the past 5 million years here proxy evidence is provided that indicates stable weathering fluxes in the late cenozoic era it is proposed that processes different from an increase in denudation caused cenozoic global cooling over geologic timescales co2 is emitted from the earth s interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial this balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions1 changes in this balance have been attributed to changes in topographic relief where varying rates of continental rock weathering and erosion1 2 are superimposed on fluctuations in organic carbon burial3 geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation1 2 4 widespread observations of a recent 0 5 myr fourfold increase in global sedimentation rates require a global mechanism to explain them4 5 6 accelerated uplift and global cooling have been given as possible causes2 4 6 7 but because of the links between rates of erosion and the correlated rate of weathering8 9 an increase in the drawdown of co2 that is predicted to follow may be the cause of global climate change instead2 however globally rates of uplift cannot increase everywhere in the way that apparent sedimentation rates do4 10 moreover proxy records of past atmospheric co2 provide no evidence for this large reduction in recent co2 concentrations11 12 here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record13 as evidence we recast the ocean dissolved 10be 9be isotope system as a weathering proxy spanning the past 12 myr ref 14 this proxy indicates stable weathering fluxes during the late cenozoic era the sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean we conclude that processes different from an increase in denudation caused cenozoic global cooling and that global cooling had no profound effect on spatially and temporally averaged weathering rates

the origin of a mississippi valley type deposit in the viburnum trend southeast missouri petrologic and isotopic studies of the base metal sulfide mineralization in the buick mine have established the following paragenesis an early stage of fine grained pyrite and marcasite replaced the dolostone host rock the iron disulfides and dolostone were replaced by sphalerite during the main stage of sphalerite precipitation delta 34 s sp 16 5 to 19 0ppm following the sphalerite two main stages of galena were precipitated a cuboctahedral stage delta 34 s gn 21 3 to 10 0ppm during which galena replaced dolostone and sphalerite and grew in vugs in the dolostone and in the sphalerite and a cubic stage delta 34 s gn 10 5 to 0 9ppm the two stages of galena precipitation were separated by a period during which the main stage of sphalerite and the cuboctahedral galena were partially dissolved and bladed marcasite delta 34 s mc 2 3 to 4 1ppm was precipitated and followed by a period of mild etching of the cubic galena minor amounts of pale sphalerite delta 34 s sp 14 0 to 16 5ppm were then precipitated white and colorless rhombs of dolomite were precipitated at the same time as some of the main stage of sphalerite the cubic galena and the pale sphalerite after the pale sphalerite was precipitated chalcopyrite quartz and siegenite were precipitated followed by calcite and finally kaolinite the paragenetic and textural data for both galena and sphalerite in the buick mine strongly suggest that these minerals were precipitated and dissolved repetitively during ore formation similar textural evidence for galena reported by other workers for different mines in the viburnum trend implies that repetitive precipitation and dissolution of galena was probably an important process during the formation of the entire viburnum trend fluid inclusions in late quartz crystals coprecipitated with chalcopyrite have filling and freezing temperatures within the ranges reported for sphalerite from other parts of the viburnum trend demonstrating that the ore forming solutions in the viburnum trend were probably at temperatures in the range 105 degrees to 141 degrees c assuming a maximum pressure correction of about 11 degrees c and were extremely saline containing about 4 0 to 5 0 molal chloride consideration of typical chemical analyses of fluid inclusions from other mississippi valley type deposits suggests that the maximum likely concentration of dissolved co 2 in the ore forming solutions was about 0 05 molal at these concentrations the ore forming solutions that travelled to the site of deposition could have had ph9s about two units less than neutral and still have been in equilibrium with dolomite or calcite the ranges of sulfur and lead isotopic compositions of galena from the buick mine are very similar to those established by earlier studies of the old lead belt and adjacent subdistricts however the correlation of isotopically lighter sulfur with more radiogenic lead is much stronger for the viburnum trend suggesting that galena was precipitated from many solutions each of which carried lead and sulfur together and had different lead and overall sulfur isotopic compositions the textural paragenetic and isotopic data for the buick mine cannot be easily explained either by a sulfate reduction model in which sulfate was reduced by organic matter or methane or mixing models in which base metals and reduced sulfur were transported separately to the site of deposition instead the data strongly support a reduced sulfur model for ore formation according to which the base metals were transported together with reduced sulfur as h 2 s in the same solutions to the sites of deposition the reduced sulfur model is also supported by a theoretical calculation of the solubilities of galena and sphalerite which demonstrate that low but economically significant concentrations of lead or zinc could have been transported as chloride complexes together with equivalent concentrations of reduced sulfur at temperatures of 100 degrees to 150 degrees c and ph9s of one to two units less than neutral and could have been precipitated by ph increases cooling or dilution at the sites of deposition

refining the pre industrial atmospheric pb isotope evolution curve in europe using an 8000 year old peat core from nw spain abstract pb pollution has existed for several millennia and remains relevant today by using peat cores as environmental archives it is possible to reconstruct this long history on a regional scale this is a significant contribution to the findings from ice core records the only other archive recording purely atmospheric additions without information that allows linking and comparison between sites regionally within europe and elsewhere our ability to make coherent global models of the natural pb cycle and anthropogenic forcing of this cycle is limited in this respect the characteristics of the pb pre pollution aerosol ppa are important to define globally we characterize for the first time a ppa in southern europe with pb 0 78 0 86 g g 1 net pb accumulation rates of 0 032 0 030 mg m 2 y 1 and a 206 pb 207 pb signature of 1 25470 0 02575 this ppa pb isotope signature is more radiogenic than that found thus far in western and northern europe spain is a historically important mining site using three isotope plots and a pool of potential pb isotope signatures a detailed source appointment of both natural and anthropogenic pb sources was made we found evidence of saharan aridification and its termination 4400 bp and or agricultural signals and strong local control from rock and soil of the pb ppa human impact is first recorded at 3210 bp but does not exceed 50 of deposited pb until 3005 bp mines in se spain dominate early pb pollution history at this site during the rise of roman rule contributions come from mines in n nw and sw spain with no strong indication of other european mining activities in medieval and industrial times local contributions to the peat bog are reduced

radiometric correction of c band imagery for topographic effects in regions of moderate relief the combined effects of topography slope look angle and aspect on c band synthetic aperture radar sar data on the radiometric quality of sar images in a region of moderate relief are examined a correction method was used to attenuate the change of illumination across the swath due to the antenna pattern ground data were integrated into the analysis using a digital terrain model dtm correction functions based on the cosine of the incidence angle were applied to the thematic classes and to the grouped classes in order to reduce the effects related to topography it was found that it is possible to eliminate part of the radiometric variations created by moderate topographic relief after the corrections were applied a reduction was noted of the variance in the radiometric values of the spectral signatures of the cover types which ranged between 3 03 and 9 47 depending on the correction function used

flattening gamma radiometric terrain correction for sar imagery enabling intercomparison of synthetic aperture radar sar imagery acquired from different sensors or acquisition modes requires accurate modeling of not only the geometry of each scene but also of systematic influences on the radiometry of individual scenes terrain variations affect not only the position of a given point on the earth s surface but also the brightness of the radar return as expressed in radar geometry without treatment the hill slope modulations of the radiometry threaten to overwhelm weaker thematic land cover induced backscatter differences and comparison of backscatter from multiple satellites modes or tracks loses meaning the asar palsar sensors provide state vectors and timing with higher absolute accuracy than was previously available allowing them to directly support accurate tie point free geolocation and radiometric normalization of their imagery given accurate knowledge of the acquisition geometry of a sar image together with a digital height model dhm of the area imaged radiometric image simulation is applied to estimate the local illuminated area for each point in the image ellipsoid based or sigma naught 0 based incident angle approximations that fail to reproduce the effect of topographic variation in their sensor model are contrasted with a new method that integrates terrain variations with the concept of gamma naught 0 backscatter converting directly from beta naught 0 to a newly introduced terrain flattened 0 normalization convention the interpretability of imagery treated in this manner is improved in comparison to processing based on conventional ellipsoid or local incident angle based 0 normalization

on the growth of colloform textures a case study of sphalerite from the galmoy ore body ireland abstract colloform textures have been described from many of the world9s sulphide ore deposits and involve formation of distinct microcrystalline layers these textures provide information related to sequential stages of ore formation yet their mechanism of growth is poorly understood this study has analysed a series of colloform samples from the galmoy zn pb mine ireland results indicate that the growth sequence is not always intuitive and layers that appear stratigraphic upon cursory observation may not be the crystal preferred orientation cpo of discrete colloform layers abruptly switches between different orientation axes examination of the same layers using in situ laser sulphur isotope analysis reveals equally striking changes in 34 s signature between end member bacteriogenic 25 and hydrothermal 10 sources although these results combined with petrographic observation allow the determination of a probable growth history there is no correlation between shifting cpo and 34 s signature trace element analysis reveals changes in trace element sequestration between colloform layers cadmium and chlorine rich layers correspond to a hydrothermal sulphur source whereas iron rich layers correspond to a bacteriogenic sulphur source in the absence of alternative mechanisms we suggest that the most likely factors influencing cpo changes are temperature and degree of supersaturation during two fluid mixing

late cenozoic climate change paces landscape adjustments to yukon river capture late cenozoic cooling and changes in glacial interglacial cycle tempo are thought to increase global rates of erosion starting 3 million years ago ma bedrock rivers set rates and patterns of erosion in most landscapes but constraints on river response to late cenozoic climate change remain elusive here we determine cosmogenic isotope and luminescence ages of well preserved bedrock terraces along the fortymile river yukon river basin to reconstruct an 5 myr history of fluvial adjustment to late cenozoic climate and yukon river headwater capture at 2 6 ma post capture yukon river downcutting lowered the fortymile river outlet forcing subsequent bedrock incision throughout the fortymile basin in two pulses from 2 4 to 1 8 ma and at 1 ma these pulses of incision disrupted longer intervals of slow river channel sedimentation under near consistent climate forcing from 4 8 to 2 4 ma and from 1 8 to 1 ma the fortymile river delivers sediment to the bering sea where provenance and accumulation rate changes since 4 3 ma match observed variations in incision our results link alluviation and incision to late cenozoic climate steadiness and change respectively and support the hypothesis that climate forced changes in precipitation and runoff fundamentally control the pace of river incision and landscape erosion increased river incision and landscape erosion can be attributed to late cenozoic cooling changes in hydroclimate according to cosmogenic isotope and luminescence ages of a sequence of bedrock terraces in the yukon river basin

correction of sar imagery for variation in pixel scattering area caused by topography the radiometric correction of synthetic aperture radar sar imagery for topographically induced changes in the pixel scattering area is examined the relative significance of ground slope in the range and azimuth directions is compared and a widely used correction factor based on the sin of the local radar incidence angle is shown to be sufficiently accurate the importance of performing this correction in slant range rather than ground range is demonstrated

seasonal and short term variability of multifrequency polarimetric radar backscatter of alpine terrain from sir c x sar and airsar data signatures of glaciated and ice free areas were analyzed from polarimetric sar data at c l and p band and single polarization x band data the data base includes an airsar scene from june 25 1991 and sir c x sar images from april and october 1994 srl 1 and srl 2 acquired over the high alpine test site o spl uml tztal in austria the environmental conditions were different at the time of the three experiments ground measurements meteorological observations and backscattering modeling are the basis for interpreting the backscattering signatures seasonal differences are due mainly to the presence or absence of snow and due to changes of its properties short term variations of snow conditions can be monitored at c and x band for unglaciated areas the surface roughness has a dominant influence on backscattering in all seasons the dependence of the mean backscattering and correlation coefficients on the incidence angle was analyzed spectral and depolarization ratios and the magnitude of the hhvv correlation coefficient were selected as components of the multidimensional feature vector for studying the target separability good separability was found between the accumulation and ablation areas on the glaciers whereas on ice free areas the dominance of surface roughness limits the discrimination of different surface types short term variations of backscattering have significant impact for the classification of accumulation and ablation areas on glaciers as verified by comparisons with field data

characterization of forests in western sayani mountains siberia from sir c sar data abstract this paper examines the use of space borne radar data to map forest types and logging in the mountainous western sayani area in central siberia l and c band hh hv and vv polarized images from the shuttle imaging radar c instrument were used in the study techniques to reduce topographic effects in the radar images were investigated these included radiometric correction using illumination angle inferred from a digital elevation model and reducing apparent effects of topography through band ratios forest classification was performed after terrain correction utilizing typical supervised techniques and principal component analyses an ancillary data set of local elevations was also used to improve the forest classification map accuracy for each technique was estimated for training sites based on russian forestry maps satellite imagery and field measurements the results indicate that it is necessary to correct for topography when attempting to classify forests in mountainous terrain radiometric correction based on a digital elevation model improved classification results but required reducing the synthetic aperture radar resolution to match the digital elevation model using ratios of synthetic aperture radar channels that include cross polarization improved classification and had the advantages of eliminating the need for a digital elevation model and preserving the full resolution of the synthetic aperture radar data

a signature of transience in bedrock river incision rates over timescales of 10 4 10 7 years measured rates of river incision into bedrock are commonly interpreted as proxies for rates of rock uplift see refs 1 and 2 for example and indices of the strength of climatic forcing of erosion over time see refs 3 and 4 for example this approach implicitly assumes that river incision rates are in equilibrium with external forcings over a wide range of timescales here we directly test this assumption by examining the temporal scaling of bedrock river incision from 155 independent measurements of river incision compiled from 14 sites of these sites 11 exhibit a negative power law dependence of bedrock river incision rate on measurement interval a relationship that is apparent over timescales of 10 4 10 7 years and is independent of tectonic and geomorphic setting thus like rates of sediment accumulation rates of river incision into bedrock exhibit non steady state behaviour even over very long measurement intervals non steady state behaviour can be explained by episodic hiatuses in river incision triggered by alluvial deposition if such hiatuses have a heavy tailed length distribution regardless of its cause the dependence of incision rate on measurement interval complicates efforts to infer tectonic or climatic forcing from changes in rates of river incision over time or from comparison of rates computed over different timescales

a latest pliocene age for the earliest and most extensive cordilleran ice sheet in northwestern canada abstract the klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive cordilleran ice sheet cis in nw north america new terrestrial cosmogenic nuclide tcn burial ages indicate this gravel was emplaced 2 64 0 20 0 18 ma 1 coupled with previously interpreted paleomagnetic stratigraphy this numerical age constrains the timing of the earliest cis to the late gauss chron and provides a minimum age for the upper white channel gravel a significant placer gold source in the yukon this implies the first cis glacial maximum pre dates the maximum extent of the laurentide ice sheet indicating that during the initial stages of northern hemisphere glaciation the most extensive glaciers were present in the relatively cold and high elevation northern cordillera our results verify the cis as a likely source of persistent coeval ice rafted debris in the northern pacific and suggest that the first cis formed as a response to the establishment of the northern pacific halocline and emergence of the 41 ka obliquity cycle during the plio pliocene transition

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

genetic implications of regional and temporal trends in ore fluid geochemistry of mississippi valley type deposits in the ozark region fluids extracted from aqueous fluid inclusions in epigenetic gangue and ore minerals record the migration of huge volumes of highly saline fluids throughout the stratigraphic section of the ozark region the extracted fluids share many similarities regionally but there are significant temporal differences which define two geochemically distinct end member ore forming fluids that we refer to as the viburnum trend main stage or viburnum trend type and the tri state type viburnum trend type fluids are enriched in potassium and are associated only with deposits close to the basal lamotte sandstone the main stage octahedral galena ore of the viburnum trend and much of the old lead belt ore is thought to be derived from this type of ore fluid galena deposited by viburnum trend type fluids contains less radiogenic lead than galena deposited by tri state type fluids sulfides deposited by viburnum trend type fluids also contain isotopically heavier sulfur and significant amounts of copper cobalt nickel and silver tri state type fluids have a low potassium content when compared with viburnum trend type fluids and are characteristic of deposits where ore forming fluids migrated through large volumes of carbonate rock these fluids are thought to have formed the ore deposits of the tri state northern arkansas and central missouri districts the cubic galena stage ore of the viburnum trend and the many trace occurrences of sphalerite throughout the ozark region galena deposited by tri state type fluids has more radiogenic lead and the sulfides have isotopically lighter sulfur than sulfides deposited by viburnum trend type fluids a systematic south to north increase of potassium in the tri state type fluids suggests that they migrated from a southerly source such as the arkoma basin possible explanations for the origins of these two end member fluids include 1 a single parent brine evolved into two distinct fluids due to reactions with geochemically distinct aquifers during migration 2 the two distinct fluids reflect normal fluid evolution within a single source basin of a bittern and of later halite dissolution and 3 the viburnum trend and tri state type brines migrated to southeast missouri from two different source basins our data does not preclude any of these possibilities however the geochemical similarity of the viburnum trend end member fluid to a bittern may be accounted for by water rock modifications of the brine during migration other evidence strongly supports a southerly source for the ore forming brines thus limiting possible sources for the viburnum trend type fluid to the arkoma and or black warrior basins of the ouachita foreland trough viburnum trend type fluid flow was probably funneled northward through basal sandstones within the reelfoot rift and water rock modifications occurring there may have resulted in its unique geochemistry

radiometric correction of airborne radar images over forested terrain with topography radiometric correction of radar images is essential to produce accurate estimates of biophysical parameters related to forest structure and biomass we present a new algorithm to correct radiometry for 1 terrain topography and 2 variations of canopy reflectivity with viewing and tree terrain geometry this algorithm is applicable to radar images spanning a wide range of incidence angles over terrain with significant topography and can also take into account aircraft attitude antenna steering angle and target geometry the approach includes elements of both homomorphic and heteromorphic terrain corrections to correct for topographic effects and is followed by an additional radiometric correction to compensate for variations of canopy reflectivity with viewing and tree terrain geometry the latter correction is based on lookup tables and enables derivation of biophysical parameters irrespective of viewing geometry and terrain topography we evaluate the performance of the new algorithm with airborne radar data and show that it performs better than classical homomorphic methods followed by cosine based corrections

fluid inclusion and s c o pb isotope study of pb zn cu ag hydrothermal veins from central and northern portugal metallogenic implications abstract the pb zn cu ag hydrothermal veins from central and northern portugal occur in two distinct districts aveiro moinho da pena carvalhal palhal and telhadela and braganca ferronho vale da madre estevais and olgas the ore veins are composed by sulfides galena sphalerite chalcopyrite pyrite several quartz generations in both districts and dolomite as a gangue mineral in the aveiro district palhal and telhadela a mineralogical fluid inclusion and s c o pb isotopic study was carried out on ore mineralization with the aim to explain its genesis and metallogenic evolution aqueous fluids of h2o cacl2 or h2o nacl cacl2 in composition were identified in both districts the th tmi evolution starts with fluids of medium temperature 250 oc and low to moderate salinity 1 eq wt nacl in the aveiro district and 0 5 eq wt in the braganca district evolving to lower temperatures 250 to 100 oc and higher salinity for the aveiro district 20 eq wt nacl and lower salinity 4 eq wt nacl for the braganca district fluids of high salinity 20 eq wt nacl were trapped during the final stage at temperatures below to 100 c a mixing magmatic and meteoric fluid explained the wide negative values range of 34s measured for the samples from the aveiro district high positive 34s values measured on samples collected from the braganca district confirm a seawater source the c and o stable isotope measured on dolomite and calcite show a 13c depleted source for both carbonates pointing to a carbon source s related to the organic matter oxidation the pb isotope data confirm an uranogenic and a thoriogenic source the pb zn ore deposits from the aveiro and braganca districts are related to episodes of fluid circulation in the upper crust during late to post variscan period the lack of spatial and temporal relationship with magmatic episodes and the presence of basinal and superficial origin fluids support this idea

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

carbon and oxygen isotopic covariations in hydrothermal calcites isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes 1 mixing between two different fluids which leads to the precipitation of calcite 2 mixing between fluid and rock a calcite precipitation due to fluid rock interaction b secondary alteration of primary calcite by interaction with a subsequent fluid the models are derived from mass balance equations a distinction among the three mixing processes can be made on a 13c vs 18o diagram which places important constraints on the genesis of hydrothermal mineralization the variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock temperature and dissolved carbon species owing to significant temperature dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid the mixing processes may be distinguished by telltale patterns of isotopic data in 13c vs 18o space in particular caution must be exercised in postulating the fluid mixing as the cause for mineral deposition this is demonstrated for hydrothermal pb zn deposits in the western harz mountains germany a positive correlation between 13c and 18o values is observed for calcites from the bad grund deposit in the upper harz two sample profiles through calcite veins show similar correlations with the lowest values at the center of the veins and the highest values at the vein margins because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike it is assumed that a fluid rock interaction is responsible for the observed correlation and thus for the precipitation of calcite a deep seated fluid is inferred with a 13c value of 7 and a 18o value of 10 as well as h2co3 as the dominant dissolved carbon species precipitation temperatures of the calcites are estimated to be about 280 170 c quite different isotopic distributions are observed for calcites from the st andreasberg deposit in the middle harz an alteration model is suggested based mainly on the isotopic distribution through a calcite vein in addition to a primary fluid which has the same isotopic composition as that in the bad grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides an evolved hco 3 dominant subsurface fluid with 13c about 20 15 and 18o 0 is deduced to alter the primary calcite at low temperatures of 70 40 c

epigenetic dolomitization and the origin of xenotopic dolomite texture abstract xenotopic texture which is commonly observed in pre cenozoic rocks is defined here as a mosaic of anhedral crystals with irregular or curved intercrystalline boundaries and usually undulatory extinction xenotopic dolomite texture is similar in appearance to neomorphic limestone textures idiotopic dolomite texture euhedral to subhedral crystals with straight intercrystalline boundaries contrasts with xenotopic texture and is commonly observed in both cenozoic and more ancient dolomites texture may be controlled by the temperature at which crystals grow crystal growth theory predicts that at low temperature a smooth crystal surface is energetically favored and atoms are added to crystal faces layer by layer with dislocations acting as nucleation sites this results in faceted crystals and euhedral to subhedral crystal mosaics above a critical roughening temperature crt a rough surface is energetically favored surface nucleation does not require dislocations and atoms are randomly added to the crystal surface resulting in nonfaceted growth and an anhedral crystal mosaic it is hypothesized that a critical roughening temperature exists for dolomite above 50 c xenotopic dolomites are produced by dolomitization of limestone and or neomorphic recrystallization of dolomite at elevated temperature above the crt after burial idiotopic dolomites are produced below the crt by near surface processes and are occasionally produced above crt if growth inhibiting effects of the solution or impurities stabilize crystal faces calcite has a crt below 25 c and therefore develops anhedral crystal mosaics characteristic of neomorphic texture both at near surface and at elevated temperatures synthetic xenotopic dolomite was produced in the laboratory at 250 c and 300 c by dolomitization of aragonite and calcite skeletal fragments and by recrystallization neomorphism of nonstoichiometric cenozoic dolomites xenotopic dolomite resulted from the metamorphic recrystallization of the idiotopic hueco dolomite permian texas near the marble canyon intrusion at temperatures between 350 c and 600 c hydrothermal dolomitization of periclase calcite marble near the intrusion also resulted in a xenotopic texture xenotopic dolomite in the galena group ordovician wisconsin was produced by neomorphism of a preexisting dolomite during the emplacement of lead zinc sulfides at temperatures between 80 c and 227 c in the trenton limestone ordovician michig n xenotopic dolomite replaced limestone during the migration of hot 50 c fluids along fracture systems xenotopic dolomite was not observed in cenozoic dolomites that were subjected to temperatures near surface values only

strontium isotopic evidence for the origin of barites and sulfides from the mississippi valley type ore deposits in southeast missouri several barites from the lead barite district contain between 1 170 and 1 633 ppm sr their 87 sr 86 sr ratios range from 0 7098 to 0 7118 in contrast to the values of 0 7082 to 0 7089 for the host carbonate rocks four galenas from the viburnum mine in southeast missouri provide a rb sr age of 392 or 21 m y and an initial isotopic composition of 0 7104 or 0 0004 indicating the period of mineralization to be early devonian modified journal abstract

diagenesis of celestite in quartz geodes from the basque cantabric basin northern spain evidence from sulphur and strontium isotopes

ore depositional process in the navan zn pb deposit ireland the navan zn pb deposit in ireland is hosted by a lower carboniferous carbonate dominated sedimentary sequence in excess of 97 percent of the ore is hosted by a courceyan shallow water succession termed the pale beds the ore occurs as complex strata bound tabular lenses often dislocated by faulting and truncated by a submarine erosional slide structure above this surface unconformity lies the economically minor but genetically important conglomerate group ore hosted by a complex debris flow termed the boulder conglomerate timing constraints on the mineralization can be defined by the relationship to the erosion surface and style of mineralization suggesting a late chadian or early arundian age approximately 345 ma the bulk of the ore formed below the erosion surface in the semilithified to lithified pale beds ore the mineralogy of the economic ores is relatively simple being dominated by sphalerite and galena in a 5 1 ratio pyrite and marcasite are present in subordinate amounts in the majority of the pale beds ore but dominate the conglomerate group ore and the pale beds ore immediately below the erosion surface particularly lens 2 1 gangue minerals are dominated by calcite dolomite and barite the morphology of the mineralization reflects subsea floor emplacement the orebody occurs as numerous strata bound horizons ranging from intense high grade massive sulfides to lower grade sulfide layers separated by barren limestone in all cases there is strong evidence for tectonic disruption during ore deposition sulfides were dominantly deposited as open space growth and replacement of host rock open space textures include dendritic skeletal stalactitic internal sediment geopetal and coarse bladed forms the general absence of coarse euhedral cavity lining textures or substantial collapse brecciation suggests that large cavities were not present prior to mineralization replacement textures range from delicate pseudomorphs of biodasts to more destructive granular styles sulfide sulfur isotope analyses exhibit two dominant groupings of delta 34 s from around 23 to 5 and 0 to 15 per mil respectively and a third minor grouping around 32 to 28 per mil at least two sources of sulfur are invoked values around 23 to 15 per mil are considered to be the result of bacteriogenic reduction of lower carboniferous seawater sulfate approximately 20ppm with a characteristic fractionation around 35 to 45 per mil away from sulfate this is the most common range of delta 34 s in the deposit values around 8 to 15 per mil are interpreted to be hydrothermal sulfide transported with the metal bearing fluid mixing of these two components is inferred from the isotopic data and trends in the mineral paragenesis barite has a mean of delta 34 s 21 or 2 per mil which falls within the range generally recognized for lower carboniferous seawater sulfate we consider that contemporaneous seawater sulfate was the dominant source of sulfur in the barite at navan implying that seawater accessed the pale beds at the time of mineralization

carbonate depositional sequence development on active fault blocks the albian in the castro urdiales area northern spain the aptian to lowermost albian carbonate platform of castro urdiales cantabria northern spain was broken up by extensional tectonic movements shortly after the beginning of the albian block faulting characterized this rifting episode the effects of which waned during the albian in crestal locations tilting of the fault blocks caused the subaerial exposure of parts of the older platform resulting in intense karst diagenesis differential subsidence of the blocks controlled the development of a crestal residual carbonate platform arenillas which was surrounded by deeper water on both sides seven unconformities related to platform exposure and karstification are identified on the arenillas platform and form the basal boundaries of seven depositional sequences s1 s7 on the platform lowstand systems tract deposits consist of breccias filling caves and grainstones and debris flow deposits filling incised canyons transgressive plus highstand systems tracts consist of rare marls plus shallow water rudistid coral and chondrodontid limestones in the basin the unconformities are erosional surfaces at the base of resedimented limestones marls or sandy or silty siliciclastics lowstand systems tracts transgressive plus highstand systems tracts in this setting consist of marls and hemipelagic marly limestones tectonism is believed to be the main control on sequence formation and only a few sequence boundaries e g the base of s6 in the upper albian inflatum zone can be correlated with eustatic events

geology and geochemistry of the reocin zinc lead deposit basque cantabrian basin northern spain the reocin zn pb deposit 30 km southwest of santander spain occurs within lower cretaceous dolomitized urgonian limestones on the southern flank of the santillana syncline the reocin deposit is one of the largest known strata bound carbonate hosted zinc lead deposits in europe the total metal endowment of the deposit including past production and remaining reserves is 62 mt of ore grading 8 7 percent zn and 1 0 percent pb the epigenetic mineralization consists of sphalerite and galena with lesser marcasite and trace pyrite with dolomite as gangue microprobe analyses of different generations of dolomite revealed nonstoichiometric compositions with various amounts of iron up to 14 mol of feco3 replacement of host dolomite open space filling of fractures and cementation of breccias derived from dissolution collapse are the principal types of ore occurrence detailed cross section mapping indicates a stratigraphic and structural control on the deposit a stratiform morphology is present in the western part of the orebody capa sur whereas mineralization in the eastern part is highly discordant but strata bound barrendera stratigraphic studies demonstrate that synsedimentary tectonic activity related to the rifting of the north atlantic bay of biscay was responsible for variation in sedimentation presence of unconformities including paleokarsts local platform emergence and dolomitization along the n60 fault trend in the reocin area two stages of dolomitization are recognized the first stage is a pervasive dolomitization of the limestone country rocks that was controlled by faulting and locally affected the upper part of the aptian and the complete albian sequence the second dolomitization event occurred after erosion and was controlled by karstic cavities this later dolomitization was accompanied by ore deposition and locally filling of dolomite sands and clastic sediments in karstic cavities the circulation of hydrothermal fluids responsible for sulfide deposition and the infilling of karst cavities were broadly contemporaneous indicating a post albian age vitrinite reflectance data are consistent with previously measured fluid inclusion temperatures and indicate temperatures of ore deposition that were less than 100 c carbon and oxygen isotopic data from samples of regional limestone host rock dolostone and ore stage dolomite suggest an early hydrothermal alteration of limestone to dolostone this initial dolomitization was followed by a second period of dolomite formation produced by the mixing of basinal metal rich fluids with local modified seawater both dolomitization events occurred under similar conditions from fluids exhibiting characteristics of basinal brines the 34s values of sulfides are between 1 8 and 8 5 per mil which is consistent with thermochemical sulfate reduction involving organic matter as the main source of reduced sulfur galena lead isotope compositions are among the most radiogenic values reported for zn pb occurrences in europe and they are distinct from values reported for galena from other basque cantabrian deposits this suggests that a significant part of the lead was scavenged from the local underlying asturian sediments the stratigraphic and structural setting timing of epigenetic mineralization mineralogy and isotopic geochemistry of sulfide and gangue minerals of the reocin deposit are consistent with the features of most of mississippi valley type ore deposits

the null hypothesis globally steady rates of erosion weathering fluxes and shelf sediment accumulation during late cenozoic mountain uplift and glaciation at the largest time and space scales the pace of erosion and chemical weathering is determined by tectonic uplift rates deviations from equilibrium arise from the transient response of landscape denudation to climatic and tectonic perturbations we posit that the constraint of mass balance however makes it unlikely that such disequilibrium persists at the global scale over millions of years as has been proposed for late cenozoic erosion we synthesize weathering fluxes global sedimentation rates sediment yields and tectonic motions to show a remarkable constancy in the pace of earth surface evolution over the last 10 ma and support the null hypothesis that global rates of landscape change have remained constant over this time period despite global climate change and mountain building events this work undermines the hypothesis that increased weathering due to mountain building or climate change was the primary agent for a decrease in global temperatures

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur