sediment delivery after a wildfire we use a record of sedimentation in a small reservoir within the cerro grande burn area new mexico to document postfire delivery of ash other fine grained sediment carried in suspension within floods and coarse grained sediment transported as bedload over a five year period ash content of sediment layers is estimated using fallout 137 cs as a tracer and ash concentrations are shown to rapidly decrease through a series of moderate intensity convective storms in the first rainy season after the fire over 90 of the ash was delivered to the reservoir in the first year and ash concentrations in suspended sediment were negligible after the second year delivery of the remainder of the fine sediment also declined rapidly after the first year despite the occurrence of higher intensity storms in the second year fine sediment loads after five years remained significantly above prefire averages deposition of coarse grained sediment was irregular in time and was associated with transport by snowmelt runoff of sediment stored along the upstream channel during short duration summer floods coarse sediment delivery in the first four years was strongly correlated with snowmelt volume suggesting a transport limited system with abundant available sediment transport rates of coarse sediment declined in the fifth year consistent with a transition to a more stable channel as the accessible sediment supply was depleted and the channel bed coarsened maximum impacts from ash and other fine grained sediment therefore occurred soon after the fire whereas the downstream impacts from coarse grained sediment were attenuated by the more gradual process of bedload sediment transport

late guadalupian to lopingian permian carbon and strontium isotopic chemostratigraphy in the abadeh section central iran abstract the abadeh section well exposed in the hambast valley in central iran has long been one of the most extensively studied sections because of its continuous carbonate dominated strata from lower permian to lower triassic however biostratigraphy and correlation with the equivalent sequences in other regions remain controversial in this paper both carbon isotope excursion 13 c carb and strontium isotope ratio 87 sr 86 sr based on bulk carbonate samples have been measured to serve as chemostratigraphical proxies to estimate the three different chronostratigraphical boundaries in the lopingian at the abadeh section including the permian triassic event pteb the guadalupian lopingian glb and the wuchiapingian changhsingian boundaries wcb these three boundaries are important for understanding the marine biological evolution around this critical interval based on the 13 c excursions the rising trend of 87 sr 86 sr and the value around 0 7073 and the occurrence of microbialite beds the permian triassic event boundary bed 25 at the meishan section is suggested at 0 5 m below the base of the main microbialite bed the glb is suggested at 46 5 m based on the position of the minor 13 c carb negative depletion coupled with the values between 0 7069 and 0 7070 of 87 sr 86 sr and its beginning point of the rising trend which is above the lowest value 0 7068 of 87 sr 86 sr ratio in the paleozoic the relationship between section thickness and their high resolution depositional age projecting age is interpolated for the whole lopingian using locally weighted regression scatter plot smoother lowess of strontium isotopic ratio based on the negative 13 c excursion and the value 0 7072 of 87 sr 86 sr ratio the wcb is estimated at 1 m above the lithologic boundary between unit 6 and unit 7 much lower than the boundary defined by previous conodont biostratigraphy but similar to other index fossils this boundary is projected as ca 254 6 ma in 87 sr 86 sr age projecting model and is close to zircon u pb dating age from south china

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

a giant late archean lake system the meentheena member tumbiana formation fortescue group western australia abstract the 2720 ma old meentheena member of the tumbiana formation fortescue group is a 30 50 m thick succession of alternating siliciclastic and limestone beds that crop out intermittently over a distance of 680 km across the pilbara craton western australia limestones of the member consist of flat pebble intraformational conglomerate oolite grainstone calcisiltite and calcilutite siliciclastics consist of shale siltstone and sandstone and many of these are tuffaceous sedimentary structures include abundant symmetrical ripples ripple cross stratification desiccation cracks teepee structures and planar to wavy lamination the member is superficially similar in appearance wherever it crops out however the correlation of individual beds and units over distances greater than 15 km is problematic there are no regional marker beds radiometric ages from tuffaceous units young to the west by a few million years four lithofacies are defined a flat pebble conglomerate b ripple cross laminated oolite grainstone c planar to wavy laminated calcilutite calcisiltite and d shale siltstone stromatolites are found in all three of the limestone facies evaporites are rare and include halite pseudomorphs the four lithofacies are generally found in a vertical succession that characterizes a lithofacies association and reflects a deepening upward succession associations may not have all four lithofacies but do reflect the same deepening upward pattern the uppermost portions of shale siltstone facies commonly contain symmetrical ripples and desiccation cracks indicating subaerial exposure measured sections contain as many as 25 of these parasequences indicating fluctuating water levels limestone lithology and facies commonly change abruptly laterally at the meter and greater scale and vertically centimeter to meter scale the sedimentary structures differences and abrupt changes in lithofacies patterns the inability to correlate confidently between regions and the differences in age from east to west suggest a complex diachronous depositional system of fluctuating water levels in separate bodies of water the limestone is dominated by sedimentary structures indicative of shallow water within wave base however it is devoid of evidence of any tidal influence possibilities for depositional environments include a tideless sea or a lacustrine system 87sr 86sr values from limestone differ from known archean marine carbonates ree patterns are decidedly non marine as well a lacustrine system is favored for the meentheena member based on sedimentary structures the abruptness of lithologic and facies changes the facies association lateral gradation into fluvial deposits the inability to correlate many units and beds for more than a few to several kilometers geochemical data stromatolites and comparisons with younger lacustrine basins as well as marine successions there is no single line of evidence that unequivocally establishes a lacustrine origin however multiple lines of evidence are collectively consistent with a lacustrine origin the meentheena member would therefore represent the oldest known carbonate rich lacustrine system which we call the meentheena lakes system

deep water anoxia over the frasnian famennian boundary la serre france a tectonically induced oceanic anoxic event the frasnian famennian f f transition is well exposed in the basinal setting of la serre montagne noire france where oxygen deficient conditions prevailed in bottom environments in this paper we study the f f transition using inorganic geochemistry notably major elements redox sensitive and or sulphide forming trace metals and productivity proxies the results are compared with published data concerning the la serre section other f f sections and other geological formations also deposited in basinal settings the very high enrichment in redox and productivity tracers indicates that anoxic conditions prevailed across the f f boundary and that surface productivity was intense such deep water restricted conditions coupled with high productivity occurred in various places in late devonian oceans recycling alone cannot account for the intense nutrient supply and therefore the most probable source was via land runoff we discuss the eovariscan episode of uplift that stimulated rock weathering and hence long term nutrient supply to the seas

gully morphology hillslope erosion and precipitation characteristics in the appalachian valley and ridge province southeastern usa this study investigates gully erosion on an east tennessee hillslope in a humid subtropical climate the study area is deeply gullied in ultisols acrisol according to the world reference base for soil with thirty years of undisturbed erosional history with no efforts to correct or halt the erosion the objectives are 1 to examine how different gully morphologies channel sidewall and interfluve behave in response to precipitation driven erosion and 2 to identify an appropriate temporal scale at which precipitation driven erosion can be measured to improve soil loss prediction precipitation parameters total accumulation duration average intensity maximum intensity extracted from data collected at an on site weather station were statistically correlated with erosion data erosion data were collected from erosion pins installed in four gully systems at 78 locations spanning three different morphological settings interfluves channels and sidewalls kruskal wallis non parametric tests and mann whitney u tests indicated that different morphological settings within the gully system responded differently to precipitation p 0 00 for channels and sidewalls regression models relating erosion and precipitation parameters retained antecedent precipitation and precipitation accumulation or duration r2 0 50 p 0 00 for channels r2 0 28 p 0 00 for sidewalls but precipitation intensity variables were not retained in the models for interfluves less than 20 of variability in erosion data could be explained by precipitation parameters precipitation duration and accumulation including antecedent precipitation accumulation were more important than precipitation intensity in initiating and propagating erosion in this geomorphic and climatic setting but other factors including mass wasting and eolian erosion are likely contributors to erosion high correlation coefficients between aggregate precipitation parameters and erosion indicate that a suitable temporal scale to relate precipitation to soil erosion is the synoptic time scale this scale captures natural precipitation cycles and corresponding measurable soil erosion

the 4 d microgravity method for waterflood surveillance a model study for the prudhoe bay reservoir alaska forward and inverse gravity modeling is carried out on a suite of reservoir simulations of a proposed water injection in the prudhoe bay reservoir alaska a novel surveillance technique is developed in which surface gravity observations are used to monitor the progress of a gas cap waterflood in the reservoir at 8200 ft 2500 m depth this cost effective method requires that high precision gravity surveys be repeated over periods of years differences in the gravity field with time reflect changes in the reservoir fluid densities preliminary field tests at prudhoe bay indicates survey accuracy of 5 10 gal can be achieved for gravity data using a modified lacoste romberg g type meter or scintrex cg 3m combined with the navstar global positioning system gps forward gravity modeling predicts variations in surface measurements of 100 gal after 5 years of water injection and 180 250 gal after 15 years we use a constrained least squares method to invert synthetic gravity data for subsurface densi

ni isotope fractionation during sorption to ferrihydrite implications for ni in banded iron formations abstract a major decline in marine methanogen populations during the late archaean eon has been proposed as a driver for the great oxidation event goe at 2 4 ga konhauser et al 2009 nature 458 750 753 recently hypothesized that a dramatic decrease between 2 7 and 2 4 ga in the concentration of dissolved ni an essential nutrient for methanogens may have been responsible for the decline to test that hypothesis ni stable isotopes a novel proxy for methanogen ni limitation will be applied to the late archaean paleoproterozoic rock record in the future possibly through analysis of banded iron formations bifs in order to facilitate interpretation of those data we investigated the fractionation of ni stable isotopes during sorption to synthetic ferrihydrite which was likely the primary precipitating phase during bif deposition via bench top experiments the observed fractionations for adsorption and coprecipitation experiments were indistinguishable and averaged 60 58nidissolved sorbed 0 35 0 10 1 sd light ni sorbed parallel linear trends in isotope compositions of dissolved and sorbed ni as a function of fraction of ni sorbed indicate an equilibrium isotope effect with rapid and continuous exchange between dissolved and sorbed ni additionally we observed fractionation of 60 58nidissolved sorbed 0 23 0 07 1 sd in experiments in which ferrihydrite had been aged for up to 30 days and had partially transformed to goethite and hematite thus the fractionations in all of our experiments are the same within uncertainties although our simple system differs from archaean seawater our results suggest that ferrihydrite precipitating to form bifs may always have been offset by a constant fractionation from coexisting dissolved ni in seawater

climate change and the episodicity of sediment flux of small california rivers abstract we studied the streamflow and sediment flux characteristics of the 20 largest streams entering the pacific ocean along the central and southern california coast extending for 750 km from monterey bay to just south of the u s mexico border drainage basins ranged in area from 120 to 10 800 km2 with headwater elevations ranging from 460 to 3770 m annual streamflow ranged from 0 to a maximum of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 1 times 10 9 end document m3 yr for the santa clara river in 1969 with a

estimation of pore pressure change in a compacting reservoir from time lapse seismic data abstract an approach is developed to estimate pore pressure changes in a compacting chalk reservoir directly from time lapse seismic attributes it is applied to data from the south east flank of the valhall field the time lapse seismic signal of the reservoir in this area is complex despite the fact that saturation changes do not have an influence this complexity reflects a combination of pressure depletion compaction and stress re distribution throughout the reservoir and into the surrounding rocks a simple relation is found to link the time lapse amplitude and time shift attributes to variations in the key controlling parameter of initial porosity this relation is sufficient for an accurate estimation of pore pressure change in the inter well space although the time lapse seismic estimates mostly agree with reservoir simulation unexplained mismatches are apparent at a small number of locations with lower porosities less than 38 the areas of difference between the observations and predictions suggest possibilities for simulation model updating or a better understanding of the physics of the reservoir

sensitivity of time lapse seismic data to pore pressure changes is quantification possible time lapse seismic data have contributed to increased reservoir knowledge and improved hydrocarbon recovery mainly by monitoring changes in fluid saturation seismic signatures of pore pressure changes have been less commonly reported although some observations such as large depletion magnus field and secondary effects such as associated gas out of solution shiehallion field and geomechanical effects in the reservoir and overburden ekofisk valhall and hthp fields have been made quantification of the pore pressure changes from seismic data has rarely been performed to date

human impact on land ocean sediment transfer by the world s rivers abstract land ocean transfer of sediment by rivers is a key pathway for material transfer on earth contemporary data on the sediment loads of rivers provide clear evidence of significant recent changes in the sediment fluxes of several rivers in response to human impact the key drivers of increased sediment loads include land clearance for agriculture and other facets of land surface disturbance including logging activity and mining although programmes for soil conservation and sediment control can result in reduced sediment loads the trapping of sediment by dams represents the dominant cause of reduced loads this influence is currently assuming increasing importance at the global scale any attempt to link these drivers to changes in the global land ocean sediment flux must take account of the aggregation and buffering effects that operate in larger basins which can cause damping and even removal of signals of increasing flux within the upstream basin and complicate the link between upstream and downstream response to human impact further work is required to provide a precise quantitative assessment of the human impact on global land ocean sediment fluxes and the net effect of increasing and decreasing fluxes particular attention must be paid to the temporal perspective and the variation of impact trajectories in different areas of the globe and for river basins of different sizes

exploring the effect of meso scale shale beds on a reservoir s overall stress sensitivity to seismic waves abstract intra reservoir sub seismic shale beds with a thickness range from 1 10 m are present in most clastic reservoirs they are often studied to investigate their effect on fluid flow and reservoir performance here it is found that shales with such thicknesses can also strongly affect the effective elastic wave behaviour of the composite reservoir particularly when observed with frequent time lapse surveys more specifically for reservoirs experiencing pressure depletion the effective impedance of the reservoir interval is usually expected to harden however our results indicate that shales can reduce this hardening effect or perhaps unexpectedly soften the overall impedance the overall in situ stress sensitivity of the reservoir is reduced below that predicted from taking laboratory core plug measurements of sand stress sensitivity alone these predictions are based on a combination of geomechanical and pressure diffusion phenomena that are in turn controlled by the shale thickness permeability and the mechanical properties as sub seismic shale layers of approximately 1 m thickness take less than three months to pressure equilibrate whilst thicker shale layers of 10 m can take over 20 years in the context of repeated seismic surveying our predictions require accurate knowledge of the shale properties and statistics and hence a good description of the sedimentology based on our default property values it appears that reduced or anomalous stress sensitivity is likely to be more important for 4d projects with frequent acquisitions of 3 12 months but is of less concern when seismic is repeated on conventional time periods of every 5 10 years the critical set of parameters required to carry out accurate calibration of these predictions is not yet fully available from published literature

comparison of geomechanical deformation induced by megatonne scale co2 storage at sleipner weyburn and in salah geological storage of co2 that has been captured at large point source emitters represents a key potential method for reduction of anthropogenic greenhouse gas emissions however this technology will only be viable if it can be guaranteed that injected co2 will remain trapped in the subsurface for thousands of years or more a significant issue for storage security is the geomechanical response of the reservoir concerns have been raised that geomechanical deformation induced by co2 injection will create or reactivate fracture networks in the sealing caprocks providing a pathway for co2 leakage in this paper we examine three large scale sites where co2 is injected at rates of 1 megatonne y or more sleipner weyburn and in salah we compare and contrast the observed geomechanical behavior of each site with particular focus on the risks to storage security posed by geomechanical deformation at sleipner the large high permeability storage aquifer has experienced little pore pressure increase over 15 y of injection implying little possibility of geomechanical deformation at weyburn 45 y of oil production has depleted pore pressures before increases associated with co2 injection the long history of the field has led to complicated sometimes nonintuitive geomechanical deformation at in salah injection into the water leg of a gas reservoir has increased pore pressures leading to uplift and substantial microseismic activity the differences in the geomechanical responses of these sites emphasize the need for systematic geomechanical appraisal before injection in any potential storage site

trace element and stable c o and radiogenic sr isotope geochemistry of stromatolitic carbonate rocks of the mesoarchaean pongola supergroup implications for seawater composition abstract the mesoarchaean pongola supergroup hosts one of the oldest well preserved stromatolitic carbonate successions major and trace element geochemistry along with c o and sr isotopic analyses of three stratigraphic sections of stromatolitic carbonate rocks were undertaken in order to infer the depositional environment and to unravel the chemical characteristics of contemporaneous seawater the carbonate rocks consist mainly of dolomite and to a lesser extent ankerite their variable sr concentrations of 95 to 450 mg kg are interpreted as resulting from early to late dolomitization of metastable carbonates aragonite and or high mg calcite facies control and calcitization during meteoric diagenesis 18o values range from 19 6 to 12 0 vpdb and reflect recrystallization of carbonates caused by high water rock interactions during diagenesis and metamorphism a 13c value of 2 5 vpdb was measured in carbonate samples least affected by alteration and we suggest that it approximates the composition of dissolved inorganic carbon in coeval seawater the samples display variable 87sr 86sr isotopic ratios from as low as 0 708 to 0 777 these ratios are considerably higher than those expected in archaean open ocean water masses buffered by hydrothermal interaction with the mantle we interpret the highly radiogenic sr isotopic ratios in some carbonate samples to reflect isotopic exchange with radiogenic sr from siliciclastic volcaniclastic components in the samples and fluids from clay rich layers intercalated with the carbonates the least radiogenic sr isotopic ratio may approximate the mixed isotopic composition of seawater in the epicontinental basin and of riverine freshwater draining the kaapvaal craton the dolomitic carbonate samples show shale normalized rare earth element and yttrium distribution patterns that resemble those of modern ocean water with positive lasn gdsn and ysn anomalies superchondritic y ho ratios a small negative cesn anomaly and depleted light rare earth elements relative to the heavy rare earth elements these anomalies are not as pronounced as expected for an open marine setting which together with the sr isotopic results support a more restricted setting with riverine input and fluctuations in marine ingressions a convex upward shale normalized rare earth element and yttrium pattern is probably a result of several factors including organic matter complexation and element fractionation during estuarine mixing the small negative cesn anomaly may suggest small amounts of free oxygen in shallow waters due to local oxygenic microbial activity

transvaal supergroup carbonates implications for paleoproterozoic δ18o and δ13c records abstract the paleoproterozoic interval is characterized by the first evidence for incontrovertibly free oxygen in the ocean atmosphere system in this study carbonates from the transvaal group the silverton lucknow rooinekke and particularly the duitschland formations were analyzed for isotopes of carbon oxygen and strontium in order to constrain models dealing with the patterns of seawater evolution although the trace element data showed variable alteration of the carbonate samples selected samples with a lesser degree of alteration yielded interpretable results the best measured 87sr 86sr isotope value of 0 7031 at 2 35 ga ago fits well with the published curve for precambrian seawater confirming that paleoproterozoic budget of sr was dominated by input from continental sources during the paleoproterozoic times carbonates with 13c values of about 10 are known to have been present worldwide and they have been studied also during this research the observation that in the duitschland formation such high isotope values and normal marine values were both present within a single formation indeed within its single beds suggested that the large spread of 13c values reflects local or regional rather than global phenomena the oxygen isotope data show a large spread of values from 3 to 16 while their corresponding 13c signals are almost unchanged over this entire range with the lucknow and silverton formations clustering around 10 and the rooinekke formation around 2 the duitschland formation has a bimodal distribution with both 13c populations present the last formation also contains samples with 18o as low as 20 particularly in the vicinity of the bushveld intrusive body these highly 18o depleted samples show homogenization of 13c values towards 5 modelling suggests that the trends could have resulted from post depositional alteration by basinal fluids at near surface to about 50 c temperatures in a rock buffered system the duitschland formation samples particularly at duitschland farm the locality closest to the bushveld complex were then further altered at temperatures up to about 80 c in response to this intrusion

fragmentation and dispersal of komatiitic pyroclasts in the 3 5 3 2 ga onverwacht group barberton greenstone belt south africa the 3 5 3 2 ga onverwacht group of the barberton greenstone belt south africa contains thick sequences of komatiitic tuff lapilli tuff and lapillistone representing proximal to distal volcanic settings volcaniclastic komatiites in the southern part of the belt include 1 areally extensive sheets of silicified massive to normally graded ash and accretionary lapilli interpreted as pyroclastic fall deposits and 2 thick widespread carbonatized beds of lapilli and minor ash deposited by subaqueous sediment flow and pyroclastic fallout lithofacies 1 clasts are aphyric and poorly to nonvesicular implying rapid quench rates and fragmentation primarily through magma water contact low water magma ratios initial melt fracturing through minor volatile exsolution and high magma fluxes were probably the main factors that enabled the production of buoyant eruption columns and widespread ash distribution these tuffs were generated during vent shoaling in water that was probably

estuarine abandoned channel sedimentation rates record peak fluvial discharge magnitudes abstract fluvial sediment deposits can provide useful records of integrated watershed expressions including flood event magnitudes however floodplain and estuarine sediment deposits evolve through the interaction of watershed marine sediment supply and transport characteristics with the local depositional environment thus extraction of watershed scale signals depends upon accounting for local scale effects on sediment deposition rates and character this study presents an examination of the balance of fluvial sediment dynamics and local scale hydro geomorphic controls on alluviation of an abandoned channel in the salinas river lagoon ca a set of three sediment cores contained discrete flood deposits that corresponded to the largest flood events over the period of accretion from 1969 to 2007 sedimentation rates scaled with peak flood discharge and event scale sediment flux but were not influenced by longer scale hydro meteorological activities such as annual precipitation and water yield furthermore the particle size distributions of flood deposits showed no relationship to event magnitudes both the responsiveness of sedimentation and unresponsiveness of particle size distributions to hydro sedimentological event magnitudes appear to be controlled by aspects of local geomorphology that influence the connectivity of the abandoned channel to the salinas river mainstem well developed upstream plug bar formation precluded the entrainment of coarser bedload into the abandoned channel while salinas river mouth conditions open closed in conjunction with tidal and storm surge conditions may play a role in influencing the delivery of coarser suspended load fractions channel adjacent sediment deposition can be valuable records of hydro meteorological and sedimentological regimes but local depositional settings may dominate the character of short term interdecadal signatures

a new sea floor gravimeter a new reservoir management application uses precise time lapse gravity measurements on the sea floor to detect seawater infiltration in offshore natural gas fields during production reservoir models for the north sea troll field predict gravity changes as large as 0 060 mgal within a 3 5 year period we have constructed and deployed a new instrument the rovdog remotely operated vehicle deployed deep ocean gravimeter system for this application because the measurements must be relocated accurately within 3 cm we required a gravimeter which could be handled by an rov and placed atop sea floor benchmarks we have built an instrument based upon the scintrex cg 3m land gravimeter motorized gimbals level the gravimeter sensor within a watertight pressure case precision quartz pressure gauges provide depth information a shipboard operator remotely controls the instrument and monitors the data the system error budget considers both instrumental and field measurement uncertainties the instrument prototy

post fire hydrological response and suspended sediment transport of a terraced mediterranean catchment in july 2013 a wildfire severely affected the western part of the island of mallorca spain during the first three post fire hydrological years when the window of disturbance tends to be more open the hydrological and sediment delivery processes and dynamics were assessed in a representative catchment intensively shaped by terracing that covered 37 of its surface area a nested approach was applied with two gauging stations covering 1 2 km2 and 4 8 km2 built in september 2013 that took continuous measurements of rainfall water and sediment yield average suspended sediment concentration 1 503 mg l 1 and the maximum peak 33 618 mg l 1 were two orders of magnitude higher than those obtained in non burned terraced catchments of mallorca this factor may be related to changes in soils and the massive incorporation of ash into the suspended sediment flux during the most extreme post fire event 50 mm of rainfall in 15 minutes reaching an erosivity of 2 886 mj mm ha 1 h 1 moreover hysteretic counter clockwise loops were predominant 60 probably related to the increased sensitivity of the landscape after wildfire perturbation though the study period was average in terms of total annual precipitation even higher in intensities minimal runoff 2 and low sediment yield 6 3 t km 2 y 1 illustrated how the intrinsic characteristics of the catchment i e calcareous soils terraces and the application of post fire measures limited the hydrosedimentary response despite the wildfire impact

runoff and erosion processes after a forest fire in mount carmel a mediterranean area in the mediterranean forest area of israel fires increase runoff and sediment yield rates relative to undisturbed forested land the september 1989 fire covered an area of 4 km2 in the main recreation area of mount carmel a typical mediterranean forest area the lithology is chalk and limestone and about 40 of the burnt area has steep slopes exceeding 30 three study plots were established in burnt and unburnt areas plots were located on 100 300 m2 areas with different slope exposures runoff and sediments were collected after each storm by a collector system a hydrometric station was established draining an area of 1 km2 in the burnt zone rainfall was measured by two recorders and several rain gauges at the experimental sites in the first rainfall season after the fire runoff and sediment yield were 500 and 100 000 times higher respectively in the burnt areas rainfall intensity is a dominant factor in runoff and sediment yield rates in the measured basin total runoff in the first year was 1 6 revegetation recovery of the area was rapid as shown by the results from the second season runoff decreased by one order of magnitude from an average of 10 mm to 1 5 mm sediment yield decreased by two orders of magnitude from 1200 g m 2 to 10 g m 2 the third season 1991 1992 was an exceptionally rainy year and therefore runoff and sediment yield increased but to less than in the first year runoff and sediment yield are related to vegetation cover rainfall intensity soil properties slope steepness and exposure and fire intensity logging activities after fire increase sediment yields through its effects on vegetation cover and soil fire severity increases the potential for erosion

a warm or a cold early earth new insights from a 3 d climate carbon model abstract oxygen isotopes in marine cherts have been used to infer hot oceans during the archean with temperatures between 60 c 333 k and 80 c 353 k such climates are challenging for the early earth warmed by the faint young sun the interpretation of the data has therefore been controversial 1d climate modeling inferred that such hot climates would require very high levels of co2 2 6 bars previous carbon cycle modeling concluded that such stable hot climates were impossible and that the carbon cycle should lead to cold climates during the hadean and the archean here we revisit the climate and carbon cycle of the early earth at 3 8 ga using a 3d climate carbon model we find that co2 partial pressures of around 1 bar could have produced hot climates given a low land fraction and cloud feedback effects however such high co2 partial pressures should not have been stable because of the weathering of terrestrial and oceanic basalts producing an efficient stabilizing feedback moreover the weathering of impact ejecta during the late heavy bombardment lhb would have strongly reduced the co2 partial pressure leading to cold climates and potentially snowball earth events after large impacts our results therefore favor cold or temperate climates with global mean temperatures between around 8 c 281 k and 30 c 303 k and with 0 1 0 36 bar of co2 for the late hadean and early archean finally our model suggests that the carbon cycle was efficient for preserving clement conditions on the early earth without necessarily requiring any other greenhouse gas or warming process

the effects of wildfire on the sediment yield of a coastal california watershed the occurrence of two wildfi res separated by 31 yr in the chaparral dominated arroyo seco watershed 293 km 2 of california provides a unique opportunity to evaluate the effects of wildfi re on suspended sediment yield here we compile discharge and suspended sediment sampling data from before and after the fi res and show that the effects of the postfi re responses differed markedly the 1977 marble cone wildfi re was followed by an exceptionally wet winter which resulted in concentrations and fl uxes of both fi ne and coarse suspended sediment that were 35 times greater than average sediment yield during the 1978 water year was 11 000 t km 2 yr we suggest that the combined 1977 1978 fi re and fl ood had a recurrence interval of greater than 1000 yr in contrast the 2008 basin complex wildfi re was followed by a drier than normal year and although suspended sediment fl uxes and concentrations were signifi cantly elevated compared to those expected for unburned conditions the sediment yield during the 2009 water year was less than 1 of the post marble cone wildfi re yield after the fi rst postfi re winters sediment concentrations and yield decreased with time toward prefi re relationships and continued to have signifi cant rainfall dependence we hypothesize that the differences in sediment yield were related to precipitationenhanced hillslope erosion processes such as rilling and mass movements the millennialscale effects of wildfi re on sediment yield were explored further using monte carlo simulations and these analyses suggest that infrequent wildfi res followed by flincrease long term suspended sediment fl markedly thus we suggest that the current approach of estimating sediment yield from sediment rating curves and discharge data without including periodic perturbations from wildfi res may grossly underestimate actual sediment yields

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

an insightful parametrization for the flatlander s interpretation of time lapsed seismic data an approximation is developed that allows mapped 4d seismic amplitudes and time shifts to be related directly to the weighted linear sum of pore pressure and saturation changes the weights in this relation are identified as key groups of parameters from a petroelastic model and include the reservoir porosity this dependence on groups of parameters explains the inherent non uniqueness of this problem experienced by previous researchers the proposed relation is of use in 4d seismic data feasibility studies and inversion and interpretation of the 4d seismic response in terms of pore pressure and water saturation changes a further result is drawn from analysis of data from the north sea and west africa which reveals that the relative interplay between the effects of pore pressure and saturation changes on the seismic data can be simplified to the control of a single spatially variant parameter cs cp combining these results with those from published literature we find that cs cp 8 appears to be a generality across a range of clastic reservoirs with a similar mean porosity using this cs cp value an in situ seismic scale constraint for the rock stress sensitivity component of the petroelastic model is constructed considering this component carries the largest uncertainty

gravity fields and the interpretation of volcanic structures geological discrimination and temporal evolution abstract a review of gravity data reflecting shallow concealed structures on volcanoes demonstrates that valuable information may be derived on the geological development of such structures and on the dynamic evolution of active volcanoes to a first approximation all recorded examples of anomalous gravity fields associated with volcanoes are concentric with and have sources that lie within the volcanic edifice positive anomalies with wavelengths less than 20 km and amplitudes up to ca 30 mgal characterise mainly basaltic volcanoes from various tectonic settings and are caused by a relatively dense intrusive complex magma body which contrasts with its surroundings either because the body is more mafic than average or more likely because near surface previously erupted materials are uncompacted negative anomalies with wavelengths up to 100 km and amplitudes up to ca 60 mgal occur over much larger volcanic calderas many of which have erupted highly silicic pyroclastic ash and pumice uncompacted silicic caldera infill with a possible contribution from low density magma bodies is responsible for the observed anomalies there is some evidence for a continuum of gravity anomaly types that corresponds to the geological evolution of volcanic systems generally from primitive rift or subduction related basaltic andesite to mature high level silicic calderas repeated microgravity observations over active volcanoes enable magma movements variations in magma input and changes in magma density to be monitored closely dynamic modelling of volcanic systems is providing new evidence on the behaviour of concealed magma bodies and could have considerable potential for predicting eruptive events

are changes in time lapse seismic data due to fluid substitution or rock dissolution a co2 sequestration feasibility study at the pohokura field new zealand seismic methods are commonly used to monitor the subsurface when carbon dioxide co2 is injected into a reservoir besides fluid saturation and pressure changes co2 water mixtures may cause rock alteration in this petrophysical study we compare the elastic property changes due to fluid replacement and those due to mineral dissolution for carbonate cemented sandstones at the pohokura field new zealand we quantify the effects of fluid substitution from fully brine to fully supercritical co2 saturation and carbonate cement dissolution on the seismic signatures of the reservoir rocks by combining laboratory results petrographic analyses and geophysical well log data we conclude that elastic property changes due to mineral dissolution are significantly greater than those due to fluid substitution alone the northern part of the pohokura field has coarser grained sandstones which experience the largest changes in wave speeds our hypothesis is that these changes result from carbonate cement dissolution in the presence of co2 water sandstone reactions if time lapse seismic data were to be acquired in this field the northern area could show p wave velocity reductions of up to 20 and a 131 7 increase in seismic amplitude from a brine saturated rock to an altered fully co2 saturated rock in comparison the southern part of the field where sandstones are mostly fine grained we expect a p wave velocity decrease of 6 if such dissolution process took place finally we show that the elastic properties of the reservoir rocks can be described with the constant cement model the model is used to predict that the dissolution process reduces the volume of grain contact cement on average from 2 5 to 1 75 of the total rock mineral volume our analysis suggests that changes to the rock frame which includes carbonate minerals cannot be ignored for a co2 injection scenario

evolution of the composition of seawater through geologic time and its influence on the evolution of life abstract the redox state of the surface environment of the early earth is still controversial and a detailed and quantitative estimate is still lacking we carried out in situ analyses of major trace and rare earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea deposits in order to eliminate secondary carbonate and contamination of detrital materials and to estimate the redox condition of seawater through time based on the ce content and anomalies of the carbonate minerals at given parameters of atmospheric co2 content pco2 and ca content of seawater we calculated the oxygen contents of shallow and deep seawater respectively the results show that the oxygen content of the deep sea was low and constant until at least 1 9 ga the oxygen content of shallow seawater increased after 2 7 ga but fluctuated it became quite high at 2 5 and 2 3 ga but eventually increased after the phanerozoic in addition the calculation of a high pco2 condition shows that seawater was more oxic even in the archean than at present suggesting a relatively low pco2 through geologic time our detailed calculations from compositions of carbonate minerals in three gorge area south china show a low oxygen content of seawater after the snowball earth until the late ediacaran an increase in the late ediacaran and a significant decrease around the precambrian cambrian and nemakit daldynian tommotian boundaries these variations were possibly caused by global regression and dissolution of methane hydrates

critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires received 26 february 2004 revised 15 september 2004 accepted 5 november 2004 published 22 january 2005 1 increased erosion is a well known response after wildfire to predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles as this soil property is temperature dependent a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required in this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures 40 550 c for 1 hour results were obtained for four replicates of soils derived from three different types of parent material granitic bedrock sandstone and volcanic tuffs in general the relation between critical shear stress and temperature can be separated into three different temperature ranges 275 c which are similar to those for water repellency and temperature the critical shear stress was most variable 1 0 2 0 n m 2 for temperatures 2 0 n m 2 between 175 and 275 c and was essentially constant 0 5 0 8 n m 2 f or temperatures 275 c the changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire

erosion thresholds and suspended sediment yields waipaoa river basin new zealand characteristics of the suspended sediment load in the waipaoa river new zealand and in two of its tributaries mangatu and te arai rivers are examined for evidence of different dominant erosion processes in the basins upstream different shapes of the suspended sediment concentration water discharge relations lead to differences in long term average yield event yield magnitude frequency relations and relative importance of large flows and rare events in the mangatu river frequent runoff events 2 1 are relatively more important to the long term yield 11 540 t km yr half of the long term average load is transported by events with return periods less than 1 year and there is little evidence of an erosion threshold limitation on sediment supply this is consistent with the predominance in the mangatu basin of hillslope erosion processes that involve scour by surface and channelized runoff particularly gully erosion this contrasts with the te arai river where sediment concentration tends to be much lower at low and moderate flows frequent runoff events transport less of the long term yield 4600 t km 2 yr than do rarer large magnitude flood events event sediment yields are an order of magnitude lower during events with subannual return periods and half of the long term average load is transported during events with a return period of 2 years some of these characteristics appear to result in part from two populations of runoff events in the te arai basin nonetheless they are consistent with field evidence that most of the sediment supplied to the te arai stream network is generated by shallow landslides which are activated once a rainfall threshold is exceeded

landslides on coastal sage scrub and grassland hillslopes in a severe el nino winter the effects of vegetation conversion on sediment delivery during the 1997 1998 el nino record rainfall triggered 150 shallow landslides within a 9 5 km2 area near santa barbara cal ifornia they were studied to analyze the sediment delivery to val ley floors from landslides in coastal sage scrub and converted grasslands the conversion of coastal sage to grasslands primarily to provide pasturage for cattle is common in the region and the landscape s response may affect water quality reservoir infilling and debris flow hazards we explore the relationship between lateral root reinforcement and landslide volume by developing a slope stability analysis that incorporates root cohesion along the sides of the failure the stability analysis correctly predicts an inverse re lationship between landslide volume and hillslope angle in the sage the volumes of failures in the grasslands do not vary systemati cally with slope and are generally smaller than those in the sage from aerial photograph analysis and field mapping we find that there are 22 9 failures per square kilometer in the grasslands com pared to 13 2 failures per square kilometer in the sage despite the lower failure density in the coastal sage greater failure volumes and longer transport distances delivered more sediment to valley floors with a specific volumetric flux of 2 8 3 10 2 m 3 m 1 for this el nino compared to 1 73 10 2 m 3 m 1 in the grasslands we con clude that the conversion from vegetation with stronger and deeper roots coastal sage to vegetation with weaker and shallower roots grass has caused a pulse of increased landsliding in the grasslands because the soils are currently too thick for the prevailing root reinforcement we suggest that over time soils in the grassland hollows will become thinner as the evacuation by landslides is re peated until the landsliding rate declines to balance the soil sup plied from local colluvium production and diffusive processes upslope

deriving effects of pressure depletion on elastic framework moduli from sonic logs we have developed a method to determine the effect of pore pressure depletion on elastic framework moduli by utilizing sonic logs from wells drilled at different locations through a reservoir at varying depletion stages this is done by first inverting the sonic logs for elastic framework bulk and shear moduli thus carefully removing pressure dependent fluid effects by crossplotting these elastic framework moduli against an increase in net stress which is directly related to depletion we derive the stress sensitivity of the elastic framework moduli we found that the observed stress sensitivity was consistent with time lapse seismic results and that the sensitivity derived from the sonic logs was much smaller than predicted by hydrostatic measurements on core samples this method is applicable to depletion scenarios in mature fields and can be used both for modelling and inverting time lapse seismic data for effects of pore pressure depletion on seismic data

impact of historic land use change on sediment delivery to a chesapeake bay subestuarine delta historic land use in the chesapeake bay drainage basin induced large fluxes of fluvial sediment to subestuarine tributaries stratigraphic and palaeoecologic analyses of deltaic deposits may be used to infer changes on the landscape but are not sufficient to quantify past sediment supply when viewed as an inverse boundary value problem reconstruction of the sediment supply function may be achieved by combining deltaic sedimentation chronologies with an equation governing delta progradation we propose that the diffusion equation is appropriate for simulating delta progradation and obtaining the sediment supply function provided a suitable diffusion constant d can be determined three new methods for estimating d are presented for the case of estuarine deltas when the inverse boundary value technique was applied to otter point creek a tidal freshwater delta at the head of bush river in upper chesapeake bay d values ranged from 3763 to 6199 m2 a 1 delta growth simulations showed a 1740 1760 initial pulse a 1760 1780 erosive redistributive interval a 1780 1920 growth period and a 1920 present erosive redistributive era coupling of simulated delta elevations with an empirical plant habitat predictive equation allowed for comparison of predicted versus actual relative habitat areas also the model yielded reconstructed watershed erosion rates and stream suspended sediment concentrations that could be useful for development of water quality regulations copyright 2001 john wiley sons ltd

gravimetric monitoring of gas production from the troll field four surveys of relative gravity and depth measurements have been conducted over the troll field since gas production began in 1996 precision in gravity intrasurvey repeatability measured as standard deviation has improved from 26 gal to 4 5 gal in two surveys in 2002 and 2005 the scatter of 74 station depth differences standard deviation has improved to 1 0 cm with modeled subsidence removed for the same two surveys subsidence of up to 3 cm is observed above the thickest reservoir of troll east between 2002 and 2005 time lapse gravity shows a general slight average increase in troll east 95 confidence for the interval centered at 5 2 4 4 gal which is likely caused by edgewater influx one gravity station close to troll a shows a 9 gal gravity increase indicating 2 2 m water rise repeated logging in a nearby well indicates 2 8 m rise these two observations agree within uncertainty bounds gravity decrease in troll west is explained by oil production and a downward moving gas oil con

the early paleozoic carbon cycle a review of o c sr and s isotope trends for the entire phanerozoic shows that the present day values of isotope signals are similar to those at the proterozoic termination the sharp rise in 87sr 86sr since 65 ma has been attributed to an uplift and subsequent metamorphism and erosion associated with the himalayas and tibet this orogenic evolution has been postulated to have influenced the global organic and inorganic carbon cycles and climate as well a similar large scale orogeny the pan african event also dominated the neoproterozoic vendian times and the similarity of modern and neoproterozoic isotope values for seawater may therefore have had a comparable tectonic cause in this contribution we present the results of a numerical model of the coupled c alkalinity s sr cycles suggesting that the early paleozoic from early cambrian to late devonian evolution of sr o c and s seawater isotope signals could have been the consequence of progressive oxidation of a large reduced carbon reservoir exhumed during the pan african orogeny the 18o measured in brachiopod shells is used as a forcing of the model postulating that any change in the oxygen isotopic composition of seawater is the result of a disequilibrium in the organic carbon subcycle through the coupling of the oxygen isotopic and carbon cycles the calculated 13c 87sr 86sr and 34s are in good agreement with the data as is the reasonable calculated history for atmospheric pco2 and its relation to global climate

post fire thin debris flows sediment transport and numerical modelling the creation of a hydrophobic layer in the soil during res in semi arid environments inhibits the in ltration of rainfall this leads to increased rates of runoff and associated sediment transport when the hydrophobic layer is deposited beneath the soil surface a perched water table develops which may cause thin 1 2 cm hillslope failures that are distinguishable from features caused by rilling and sheet ow evidence for these failures was observed after a re near santa barbara california the amount of sediment eroded from some hillslopes was substantial with 290 kg of sediment per metre width of hillslope delivered to the valley oor the mechanics of these failures are examined with a numerical model that incorporates a stability analysis with subsurface ow routing along a typical hillslope pro le the model correctly predicts the location of the failures as well as the rainfall amount necessary to trigger them copyright 2003 john wiley sons ltd

tectonic controls on atmospheric climatic and biological evolution 3 5 2 4ga abstract this paper presents a speculative scenario for the evolution of the earth s surface environment and biological community 3 5 2 4 ga based on the geologic record and its interpretation available geologic evidence suggests that the earth s climate before 3 2 ga was hot probably 60 73 c as a result of a co 2 and ch 4 greenhouse the early biological community was probably dominated by anoxygenic photosynthetic thermophiles cyanobacteria if they evolved before 3 1 ga would have struggled to survive at such high temperatures as a result the atmosphere contained extremely low levels of o 2 and 33 s shows wide departures from 0 indicating mass independent fractionation of s isotopes in the upper atmosphere this hot early climate collapsed 3 1 3 0 ga due to growth of large new blocks of continental crust cratons the weathering of which resulted in the depletion of atmospheric co 2 and eventual drawdown of ch 4 due to formation and rainout of methane aerosols cooling may have culminated in glaciation about 3 0 2 9 ga this climatic catastrophe and attendant changes in atmospheric composition drove a major biological revolution 3 0 2 7 ga characterized by the emergence of new low temperature taxa including cyanobacteria and their spread throughout surface environments at the expense of extreme thermophiles including methanogens during a period of general tectonic stability 3 0 2 7 ga the earth s surface was characterized by overall clement conditions with temperatures 2 after 2 75 ga and by 2 7 ga surface temperatures had returned to 60 c cyanobacteria were again suppressed o 2 production waned and atmospheric mass independent fractionation is again indicated by extreme variations in 33 s these conditions persisted perhaps intermittently until about 2 5 2 4 ga when weathering and erosion of vast new blocks of continental crust formed about 2 65 2 6 ga caused the second and probably last collapse of a 60 c surface climate broad tectonic climatic and biological events 3 5 2 9 ga are remarkably parallel to those of the late archean and paleoproterozoic 2 75 2 2 ga and neoproterozoic 1 0 0 50 ga these 500 myr long cycles of greenstone volcanism and crustal generation climatic and atmospheric instability and biological innovation reflect the long term interaction of the tectonic atmospheric climatic and biological components of the earth s surface system they suggest that the evolution of the earth s interior expressed through its control on the formation of large blocks of continental crust has influenced atmospheric composition and climate which in turn have provided a fundamental control on the timing and directions of biological evolution throughout earth history

gravity changes and natural gas extraction in groningen gravity observations made over the groningen gasfield from 1978 onwards are available the existing gravity data were reanalysed and a new survey was carried out the observed gravity changes obtained during four surveys spanning an 18 year period were compared with the gravity effect due to natural gas extraction computed from the reservoir model and the production data the random error in the gravity values is small enough to detect the effect of gas extraction after a few years up to 2 gal year the trends obtained from observed and calculated gravity changes agree well within their expected error margins after statistical data snooping due to the inadequate measurement set up of the previous surveys systematic errors present in the gravity data hampered the use of this data for refinement of the reservoir and the production models however with improved gravity monitoring in particular a very systematic network set up and well calibrated instruments this should now be feasible by using the network analysis from the 1996 measurements for the planning of a network in space and time most of the current problems can be avoided

coupling fine particle and bedload transport in gravel bedded streams abstract fine particles in the silt and clay size range are important determinants of surface water quality since fine particle loading rates are not unique functions of stream discharge this limits the utility of the available models for water quality assessment data from 38 minimally developed watersheds within the united states geological survey stream gauging network in california usa reveal three lines of evidence that fine particle release is coupled with bedload transport first there is a transition in fine particle loading rate as a function of discharge for gravel bedded sediments that does not appear when the sediment bed is composed of sand cobbles boulders or bedrock second the discharge at the transition in the loading rate is correlated with the initiation of gravel mobilization third high frequency particle concentration and discharge data are dominated by clockwise hysteresis where rising limb discharges generally have higher concentrations than falling limb discharges these three observations across multiple watersheds lead to a conceptual model that fine particles accumulate within the sediment bed at discharges less than the transition and then the gravel bed fluidizes with fine particle release at discharges above the transition discharge while these observations were individually recognized in the literature this analysis provides a consistent conceptual model based on the coupling of fine particle dynamics with filtration at low discharges and gravel bed fluidization at higher discharges

oxygenation of the earth s atmosphere ocean system a review of physical and chemical sedimentologic responses abstract the great oxidation event goe is one of the most significant changes in seawater and atmospheric chemistry in earth history this rise in oxygen occurred between ca 2 4 and 2 3 ga and set the stage for oxidative chemical weathering wholesale changes in ocean chemistry and the evolution of multicelluar life most of what is known about this important event and the subsequent oxygenation history of the precambrian earth is based on either geochemistry or data mining published literature to understand the temporal abundance of bioelemental sediments bioelemental sediments include iron formation chert and phosphorite which are precipitates of the nutrient elements fe si and p respectively because biological processes leading to their accumulation often produce organic rich sediment black shale can also be included in the bioelemental spectrum thus chemistry of bioelemental sediments potentially holds clues to the oxygenation of the earth because they are not simply recorders of geologic processes but intimately involved in earth system evolution chemical proxies such as redox sensitive trace elements cu cr v cd mo u y zn and ree s and the ratio of stable isotopes 56fe 53cr 97 95mo 98 95mo 34s 33s in bioelemental sediments are now routinely used to infer the oxygenation history of paleo seawater the most robust of these is the mass independent fractionation of sulfur isotopes mif which is thought to have persisted under essentially anoxic conditions until the onset of the goe at ca 2 4 ga since most of these proxies are derived from authigenic minerals reflecting pore water composition extrapolating the chemistry of seawater from synsedimentary precipitates must be done cautiously paleoenvironmental context is critical to understanding whether geochemical trends during earth s oxygenation represent truly global or merely local environmental conditions to make this determination it is important to appreciate chemical data are primarily from authigenic minerals that are diagenetically altered and often metamorphosed because relatively few studies consider alteration in detail our ability to measure geochemical anomalies through the goe now surpasses our capacity to adequately understand them in this review we highlight the need for careful consideration of the role sedimentology stratigraphy alteration and basin geology play in controlling the geochemistry of bioelemental sediments such an approach will fine tune what is known about the goe because it permits the systematic evaluation of basin type and oceanography on geochemistry this technique also provides information on how basin hydrology and post depositional fluid movement alters bioelemental sediments thus a primary aim of any investigation focused on prominent intervals of earth history should be the integration of geochemistry with sedimentology and basin evolution to provide a more robust explanation of geochemical proxies and ocean atmosphere evolution

long term erosional responses after fire in the central spanish pyrenees 2 solute release abstract studies were conducted for 8 years to determine the effect of fire on solute losses from abandoned fields found on the slopes of the pyrenees mountains in spain solute release played a key role in loss of materials from eroding slopes and may account for up to 60 of these losses the objective of the research was to examine long term solute losses caused by fire that occurred during the first month following burning after this initial surge caused by the increase in surface runoff the loss of solutes was very low during the 8 year study period calcium was the major element lost the measured effect of fire on solute release was negligible in comparison to other semiarid and humid environments

suspended sediment behavior in a coastal dry summer subtropical catchment effects of hydrologic preconditions abstract variation in fluvial suspended sediment discharge behavior is generally thought to be the product of changes in processes governing the delivery of sediment and water to the channel the objective of this study was to infer sediment supply dynamics from the response of suspended sediment behavior to antecedent hydrologic factors the salinas river california is seasonally active moderately sized and potentially susceptible to lasting impacts of hydrologic event history because of aridity high discharge variability and in channel terminating flows forty five years of suspended sediment data from the lower salinas and 80 years of hydrologic data were used to construct hydrologic descriptors of basin preconditioning and to test the effects of these preconditions on suspended sediment behavior hydrologic precondition factors including change in mean daily discharge and increasing elapsed time since the last moderate discharge event 10 20 times mean discharge q mean were found to have significant positive effects on discharge corrected fine suspended sediment concentrations conversely increased elapsed time since the last low discharge event 0 1 0 4 times q mean and the sum of low flow conditions over interannual time scales were found to cause significant negative trends in fine suspended sediment concentration residuals suspended sand concentrations are suppressed by increased elapsed time after threshold discharges of 0 1 2 and 5 100 times q mean and increased low to no flow days over time scales from 1 to 2000 days current and previous year water yield and precipitation magnitudes correlate positively with sand concentration addition of fine sediment from lower salinas hillslope or channel sources on the rising limb of the hydrograph is the major mechanism behind an overall positive hysteretic pattern which was forensically supported by the annual occurrence of in channel suspended sediment deposition by early season channel terminating flows and by the flushing function of moderate hydrologic events found in this study the importance of hillslope and or channel fine sediment contributions proximal to the lower salinas are further highlighted by the lack of control exerted by upper subbasin water provenance on fine suspended sediment concentration while sand behavior is differentiated by upper basin water provenance investigation of suspension of bed sized sediment showed that the channel bed could exert significant effects on fine and sand sized suspended sediment dynamics but this mediation for fine sediment was most likely small in terms of decadal scale sediment budgets the magnitude of the effects of hydrologic variables on sediment dynamics remains uncertain but the factors identified here may play a significant role in water quality if not long term sediment flux to the ocean

tectonic control of chemical and isotopic composition of ancient oceans the impact of continental growth a numerical model that couples carbon sulfur strontium and atmospheric oxygen cycles is used here to explore the impact of continental growth on the long term or 10 8 yrs evolution of the isotopic composition of seawater three growth scenarios are tested big bang generation of continents shortly after the accretion of the earth and two more gradual scenarios with a major growth episode around the archean proterozoic boundary the corresponding 87 sr 86 sr delta 34 s and delta 13 c of seawater and the sizes of the respective crustal sedimentary reservoirs are calculated for each scenario and compared to the available data the gradual continental growth scenarios yield a better fit to the existing 87 sr 86 sr and delta 34 s isotope data for ancient seawater than does the big bang model and can be in agreement also with the measured seawater delta 13 c providing c org participates in carbon subduction flux over the earth history these scenarios also generate a progressive oxygenation of the ocean atmosphere system with a large po 2 rise coincident with and due to the major continental growth event around the archean proterozoic transition in accord with the geologic record that indicates a major oxidation event in the early proterozoic the advancing oxygenation of the planetary exogenic system may therefore be a consequence of tectonic evolution rather than of biological innovations such as the photosystem 2 the latter may have predated considerably the impact of oxygenation visible in the geologic record in contrast to the above isotope systematics the model does not approximate well experimental observations of large delta 18 o variations at 10 8 yrs time scales at least during the phanerozoic the reason for this discrepancy may depend on the model structure that permits large variations in the oxygen isotopic composition of seawater only on time scales of 10 9 yrs

temporal and spatial variations of sediment rating curves in the changjiang yangtze river basin and their implications the natural hydrologic regime of the changjiang yangtze river in china has been disturbed considerably by intensified human activities over the past five decades in this study sediment rating curves were analyzed based on monthly data of water discharge and suspended sediment concentration at stations in the upper yichang station middle hankou station and lower datong station reaches of the changjiang in different periods from 1955 to 2007 temporal and spatial variations of the sediment rating curves were analyzed with respect to the impact of human activities and watershed characteristics results indicate that human disturbances have had a substantial impact on sediment rating parameters with the magnitude of the impact related to the scale of the river sections as indicated by the sediment rating parameters the sediment transport regimes between the upper and the mid lower reaches differ significantly in particular the impoundment of the three gorges dam in 2003 changed the sediment transport regimes in the upper and mid lower reaches of changjiang into similar regimes characterized by a decrease in the sediment transport capacity of high water discharge furthermore the sediment rating curve at the datong station in 1955 1968 was applied to estimate the potential sediment load 1969 2007 in the absence of human influences the mean annual sediment deficit caused by human activities has increased from 80 mt yr 1969 1985 to 250 mt yr 2003 2007 this indicates that intensified human activities in the changjiang basin especially the construction of the three gorges dam have altered the natural sediment transport process and have thus become a dominant force in changjiang sediment delivery to the sea

sulfur and carbon isotope records from 1700 to 800 ma carbonates of the jixian section northern china implications for secular isotope variations in proterozoic seawater and relationships to global supercontinental events abstract this study is a comprehensive stable isotope survey of the marine carbonate dominated upper paleo to lower neoproterozoic stratigraphy of jixian county china carbonate associated sulfate cas was extracted and measured for 34 s cas using the same samples analyzed for 13 c carbonate this integrated proxy approach is a step towards a more comprehensive picture of secular variation in the composition of proterozoic seawater we specifically sampled marine carbonate intervals from the lower section of the chuanlinggou formation changcheng group ca 1700 ma to the top of the jingeryu formation qingbaikou group ca 800 ma 13 c carbonate values are mostly negative in the upper paleoproterozoic changcheng group with an ascending trend from 3 to 0 we observed variation of approximately 0 1 in the mesoproterozoic jixian group and positive values of 2 2 characterize the lower neoproterozoic qingbaikou group stratigraphic variations in 34 s cas are more remarkable in their ranges and magnitudes including conspicuously high values exceeding 30 in the three intervals at ca 1700 ma 1300 1100 ma and 1000 900 ma in the changcheng group 34 s cas values are typically higher than 25 with only a few values of less than 15 in contrast most of the data spanning from the mesoproterozoic tieling formation of the jixian group to the lower neoproterozoic jingeryu formation of the qingbaikou group are highly variable between 10 and 25 with some values exceeding 25 in the late paleoproterozoic 1700 1600 ma a 10 decrease in 34 s cas and 3 increase in 13 c carbonate are coincident with and likely related to the breakup of columbia a supercontinent that predated rodinia carbon and sulfur isotope data from the mesoproterozoic when global tectonic activity was comparatively weaker fall mostly in the ranges of 15 10 and 0 1 respectively but fluctuations of 20 for 34 s cas and 3 for the 13 c carbonate at ca 1450 1400 ma may reflect subduction and large scale magmatic activity in island arcs marking the end of columbia breakup from the late mesoproterozoic ca 1300 1100 ma to the early neoproterozoic ca 800 ma the 13 c and 34 s of seawater increased gradually with increasing variability most impressive are 34 s cas values that exceed 30 in two intervals at ca 1300 1100 ma and ca 1000 900 ma which may reflect the assembly and early breakup of rodinia although gaps in the record remain and studies of even higher resolution are warranted our results suggest that changes in paleoceanographic conditions linked to global tectonics strongly influenced the biogeochemical cycles of c and s furthermore periods of the proterozoic previously noted for their isotopic invariability show clear isotopic expressions of this tectonic activity

constraining the marine strontium budget with natural strontium isotope fractionations 87sr 86sr δ88 86sr of carbonates hydrothermal solutions and river waters we present strontium sr isotope ratios that unlike traditional 87sr 86sr data are not normalized to a fixed 88sr 86sr ratio of 8 375209 defined as 88 86sr 0 relative to nist srm 987 instead we correct for isotope fractionation during mass spectrometry with a 87sr 84sr double spike this technique yields two independent ratios for 87sr 86sr and 88sr 86sr that are reported as 87sr 86sr and 88 86sr respectively the difference between the traditional radiogenic 87sr 86sr normalized to 88sr 86sr 8 375209 and the new 87sr 86sr values reflect natural mass dependent isotope fractionation in order to constrain glacial interglacial changes in the marine sr budget we compare the isotope composition of modern seawater 87sr 86sr 88 86sr seawater and modern marine biogenic carbonates 87sr 86sr 88 86sr carbonates with the corresponding values of river waters 87sr 86sr 88 86sr river and hydrothermal solutions 87sr 86sr 88 86sr hydend in a triple isotope plot the measured 87sr 86sr 88 86sr river values of selected rivers that together account for not vert similar18 of the global sr discharge yield a sr flux weighted mean of 0 7114 8 0 315 8 the average 87sr 86sr 88 86sr hydend values for hydrothermal solutions from the atlantic ocean are 0 7045 5 0 27 3 in contrast the 87sr 86sr 88 86sr carbonates values representing the marine sr output are 0 70926 2 0 21 2 we estimate the modern sr isotope composition of the sources at 0 7106 8 0 310 8 the difference between the estimated 87sr 86sr 88 86sr input and 87sr 86sr 88 86sr output values reflects isotope disequilibrium with respect to sr inputs and outputs in contrast to the modern ocean isotope equilibrium between inputs and outputs during the last glacial maximum 10 30 ka before present can be explained by invoking three times higher sr inputs from a uniquely glacial source weathering of shelf carbonates exposed at low sea levels our data are also consistent with the weathering peak hypothesis that invokes enhanced sr inputs resulting from weathering of post glacial exposure of abundant fine grained material

sedimentary manganese metallogenesis in response to the evolution of the earth system abstract the concentration of manganese in solution and its precipitation in inorganic systems are primarily redox controlled guided by several earth processes most of which were tectonically induced the early archean atmosphere hydrosphere system was extremely o2 deficient thus the very high mantle heat flux producing superplumes severe outgassing and high temperature hydrothermal activity introduced substantial mn2 in anoxic oceans but prevented its precipitation during the late archean centered at ca 2 75 ga the introduction of photosystem ii and decrease of the oxygen sinks led to a limited buildup of surface o2 content locally initiating modest deposition of manganese in shallow basin margin oxygenated niches e g deposits in india and brazil rapid burial of organic matter decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the archean proterozoic transition concurrently a massive drawdown of atmospheric co2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused paleoproterozoic glaciations 2 45 2 22 ga the spectacular sedimentary manganese deposits at ca 2 4 ga of transvaal supergroup south africa were formed by oxidation of hydrothermally derived mn2 transferred from a stratified ocean to the continental shelf by transgression episodes of increased burial rate of organic matter during ca 2 4 and 2 06 ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere black shale hosted mn carbonate deposits in the birimian sequence ca 2 3 2 0 ga west africa its equivalents in south america and those in the francevillian sequence ca 2 2 2 1 ga gabon are correlatable to this period tectonically forced doming up attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric co2 drawdown causing glaciation on the neoproterozoic rodinia supercontinent tectonic rifting and mantle outgassing led to deglaciation dissolved mn2 and fe2 concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation during the sturtian glacial interglacial event ca 750 700 ma interstratified mn oxide and bif deposits of damara sequence namibia was formed the varangian marinoan ca 600 ma cryogenic event produced mn oxide and bif deposits at urucum jacadigo group brazil the datangpo interglacial sequence south china liantuo nantuo varangian event contains black shale hosted mn carbonate deposits the early paleozoic witnessed several glacioeustatic sea level changes producing small mn carbonate deposits of tiantaishan early cambrian and taojiang mid ordovician in black shale sequences china and the major mn oxide carbonate deposits of karadzhal type central kazakhstan late devonian the mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans during the early jurassic oae organic rich sediments host many mn carbonate deposits in europe e g urkut hungary in black shale sequences the late jurassic giant mn carbonate deposit at molango mexico was also genetically related to sea level change mn carbonates were always derived from mn oxyhydroxides during early diagenesis large mn oxide deposits of cretaceous age at groote eylandt australia and imini tasdremt morocco were also formed during transgression regression in greenhouse climate the early oligocene giant mn oxide carbonate deposit of chiatura georgia and nikopol ukraine were developed in a similar situation thereafter manganese sedimentation was entirely shifted to the deep seafloor and since ca 15 ma b p was climatically controlled glaciation deglaciation assisted by oxygenated polar bottom currents aabw nadw the changes in climate and the sea level were mainly tectonically forced

global change in the late devonian modelling the frasnian famennian short term carbon isotope excursions a model of the global biogeochemical cycles coupled to a energy balance climate model the combine model is used to identify the causes of two large n 13 c value excursions across the frasnian famennian f f boundary we test a scenario that links the sea level rise to stratification of the proto tethys ocean through the formation of warm saline deep waters in extended epicontinental seas even though this scenario can produce dysoxia below 100 m depth it fails to increase the global burial flux of organic carbon and thus seawater n 13 c values since stratification of the ocean leads to decreased productivity in surface waters several scenarios postulating a continental origin of the perturbations in the late devonian biogeochemical cycles are then tested we found that weathering of platform carbonates exposed during the early famennian sea level fall can account for a maximum positive shift in n 13 c value of 0 7x at the end of the sea level fall episode another 1 0x increase in n 13 c might originate from rapid spreading of vascular land plants near the f f boundary postulating that higher plants globally increased the weatherability of continental surface and that colonized continental area increased by 30 across the f f boundary finally the n 13 c excursion observed at the base of upper rhenana zone and the rapid increase of the carbon isotope ratios at the f f boundary require an increase of phosphorus delivery to the ocean by 40 coeval with the sea level rises once the calculated n 13 c values are in agreement with the measured data the combine model calculates a decrease in atmospheric pco2 from pre perturbation 2925 ppmv in the lower rhenana conodont zone to 1560 ppmv in the upper triangularis zone this decrease in pco2 is due to the increase in burial of organic matter during the kellwasser events and increased continental weatherability triggered by the spreading of continental vascular plants these changes occur within 4 million years the corresponding global climatic cooling reaches 4 4 c at the pole and 2 1 c at the equator f 2003 elsevier b v all rights reserved

denudation processes and rates in the transverse ranges southern california erosional response of a transitional landscape to external and anthropogenic forcing 1 quantification of denudation in the transverse ranges of california permits reconstruction of spatial and temporal variations in erosion that represent both the response and evolution of interacting hillslopes and channels on the southern front of the san gabriel mountains observational records of the infilling of debris basins and dams define twentieth century landscape erosion rates averaging 1 6 and 0 9 mm yr 1 respectively although all major sediment transport occurs during intense winter storms debris production on hillslopes is greatly enhanced by recurrent fires consequently in this populated region anthropogenic fires have augmented the natural erosion rates we perform a global inversion to estimate the role of precipitation intensity burned areas and local slope on catchment denudation rates after subtracting the effects of anthropogenic fires we estimate landscape denudation rates given natural fire ignition rates increased fire during the past century has augmented sediment production in debris basins by an average of 60 and individual basins show increases up to 400 to identify the dominant hillslope erosion processes the volumetric contribution of landslides was estimated using repeat aerial photographs for the same time interval over which the debris basins have been operative between 1928 and 1973 landsliding produced only 10 of the sediment in debris basins even in the long term when infrequent but volumetrically important landslides occur bedrock landslides appear to contribute a maximum of 50 to the long term landscape denudation previous mapping of soil slippage in the san dimas experimental forest within the san gabriel mountains rice et al 1969 rice and foggin 1971 indicates that shallow landsliding is likely to be the dominant modern hillslope erosion process when compared to incision rates derived from a fluvial shear stress model and to exhumation rates based on low temperature thermochronological data blythe et al 2000 modern natural erosion rates are comparable to denudation rates since the pliocene comparisons of modern erosion rates suggest that debris production on hillslopes and first order channels is directly dependent on vegetation cover and precipitation intensity for higher order channels drainage areas 2 km2 only major storms convey the sediments down valley during the past century some temporal decorrelation occurs between small scale and large scale catchments because hillslope produced sediment is stored in second order and higher channels until major storms mobilize it thus the larger fluvial network damps the episodic fire induced hillslope sediment pulses that occur within small watersheds at a longer temporal scale however uplift and denudation may have been sustained sufficiently long in much of the san gabriel mountains for the topography to reach a macroscale steady state in contrast to rapidly eroding 2 mm yr 1 ranges for which quantification of bedrock landsliding will approximate the sediment flux the san gabriel mountains occupy a niche of intermediate rates 0 1 1 0 mm yr 1 in which a broad suite of hillslope processes including shallow seated and deep seated landslides debris flows and wet and dry ravel contribute to the sediment flux

1500 years of lake sedimentation due to fire earthquakes floods and land clearance in the oregon coast range geomorphic sensitivity to floods during timber harvest period

holocene paleoecology of an estuary on santa rosa island california abstract the middle to late holocene history and early anglo european settlement impacts on santa rosa island california were studied through the analysis of sediments in a small estuarine marsh a 5 4 m long sediment core produced a stratigraphic and pollen record spanning the last 5200 yr three major zones are distinguishable in the core the lowermost zone 5200 to 3250 yr b p represents a time of arid climate with predominantly marine sediment input and high chenopodiaceae and ambrosia pollen values the intermediate zone 3250 yr b p to 1800 a d is characterized by greater fresh water input and high values for asteraceae and cyperaceae pollen and charcoal particles the uppermost zone 1800 a d to present documents the unprecedented erosion sedimentation and vegetation change that resulted from the introduction of large exotic herbivores and exotic plants to the island during anglo european settlement the identification of pollen grains of torrey pine pinus torreyana documents the persistence of this endemic species on the island throughout the middle to late holocene

reductions in fluvial sediment discharge by coastal dams in california and implications for beach sustainability abstract the long term sustainability of california s beaches depends on periodic deliveries of sand and gravel from coastal rivers and streams to assess the long term health of california s beaches this study characterized the current state of fluvial sediment delivery and quantified on a littoral cell basis the cumulative impacts of dams in decreasing annual discharge presently more than 500 dams impound more than 42 000 km2 or 38 of california s coastal watershed area flow modeling suggests that by diminishing flood hydrographs these dams have reduced the average annual sand and gravel flux to 20 major littoral cells by 2 8 million m3 yr or 25 in 70 of the streams considered in this study suspended sediment loads during equivalent discharge events have declined over the past three decades which indicates that dams have also significantly reduced downstream sediment supplies approximately 23 or 274 km of the 1193 km of beaches in california are downcoast from rivers that have had s

gravimetric monitoring of gas reservoir water influx a combined flow and gravity modeling approach knowledge of the magnitude and distribution of water influx can be essential for managing water drive gas fields geophysical fieldwide monitoring can give valuable information particularlyoffshorewherewellcontrolissparseand observationwellsareexpensive advancesintheaccuracyof seafloor time lapse gravimetry have made this method feasible it can quantify which areas are flooded providing information complementary to well monitoring production and 4d seismic data gravimetric monitoring may aid materialbalance calculations which are vital for assessing reservoirdrive mechanism and estimating initial and remaining gas volumes in addition it can constrain reservoir simulation models our goal is to produce better physical insight into typical density changes occurring in water drive gas fields andtheirassociatedsurface gravityresponse itisfeasibleto monitor displacement of gas by water in reservoirs that are only a few meters thick gravimetric monitoring can detect edgewater encroachment in early stages with current accuracy the method is applicable for gas reservoirs of modest size 210 8 m 3 in situ gas volume at medium depths 2k m

the impact of hydroclimate and dam construction on terrigenous detrital sediment composition in a 250 year santa barbara basin record off southern california abstract the recurrence and magnitude of southern california hydroclimate extremes are poorly resolved due to the relatively short duration

how earth s atmosphere evolved to an oxic state a status report the evolution of the earth s atmosphere is essentially the story of atmospheric oxygen virtually every realm of the earth sciences biology geology geochemistry oceanography and atmospheric science is needed to piece together an understanding of the history of oxygen over the past decade new data from these fields has shown that there were two significant increases in atmospheric o2 levels at around 2 4 2 3 and 0 8 0 6 billion years ago respectively throughout earth history oceanic sulfate concentrations appear to have increased in accord with greater o2 levels while levels of methane a strong greenhouse gas may have inversely mirrored o2 both oxic transitions occurred in eras characterized by bsnowball earthq events and significant disturbances in the carbon cycle perhaps associated with increases in o2 and losses of methane to understand what controlled the oxygenation of the atmosphere it is necessary to determine how o2 is consumed on geologic time scales through reaction with reductants released from the earth s crust and mantle there was apparently a long delay between the appearance of oxygenic photosynthesis and oxygenation of the atmosphere and a plausible explanation is that excess reductants scavenged photosynthetic o2 from the early atmosphere however a quantitative understanding of how and why o2 became abundant on our reducing planet is still lacking thus the study of the early atmosphere remains a frontier field with much to be discovered d 2005 elsevier b v all rights reserved

the paleozoic to mesozoic carbon cycle revisited the carbon isotopic composition of terrestrial organic matter 1 two thousand one hundred forty eight carbon isotope values for terrestrial organic matter plant fossils coal bulk terrestrial organic matter provide a proxy record for temporal changes in the global carbon cycle 13ctom 13ccarb and 13cco2 allow a full evaluation of carbon transfer in the atmosphere ocean system as well as between the marine and the terrestrial realm the temporal evolution of 13ctom parallels respective data sets from marine carbonate carbon thus reflecting the linkage between both reservoirs via atmospheric carbon dioxide on the basis of a comparison between measured and predicted isotope records for 13ctom changes in the carbon isotopic fractionation associated with plant metabolism are discernible this contradicts the notion of an invariable carbon isotopic fractionation associated with c3 plant metabolism in light of results from current plant growth experiments these changes are viewed as dependent on the atmospheric o2 co2 hence 13ctom might serve as a proxy signal for atmospheric composition

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

strontium isotope evolution of late permian and triassic seawater the 87sr 86sr values based on brachiopods and conodonts define a nearly continuous record for the late permian and triassic intervals minor gaps in measurements exist only for the uppermost brahmanian lower part of the upper olenekian and middle norian and only sparse data are available for the late permian these 219 measurements include 67 brachiopods and 114 conodont samples from the tethyan realm as well as 37 brachiopods and one conodont sample from the mid european middle triassic muschelkalk sea the late permian lower triassic interval is characterized by a steep 1 3 10 3 rise from 0 7070 at the base of the dzhulfian to 0 7082 in the late olenekian a rate of change comparable to that in the cenozoic in the mid triassic anisian and ladinian the isotope values fall to 0 7075 followed again by a rise to 0 7081 in the middle late norian the 87sr 86sr values decline again in the late norian sevatian and rhaetian to 0 7076 the sharp rise in the 87sr 86sr values during the late permian early triassic was coincident with widespread clastic sedimentation because of the paucity of tectonic uplifts the enhanced erosion may have been due to intermittent humid phases during mainly an arid interval coupled with the absence of a dense protective land plant cover following the mass extinction during the latest permian the apex of the 87sr 86sr curve at the olenekian anisian boundary coincides with cessation of the large scale clastic sedimentation and also marks the final recovery of land vegetation as indicated by the renewed onset of coal formation in the middle triassic the rising 87sr 86sr values from the middle carnian to the late norian coincide with the uplift and erosion of the cimmeride indosinian orogens marking the closure of the palaeotethys the subsequent rhaetian decline that continues into jurassic pliensbachian toarcian boundary on the other hand coincides with the opening of the vardar ocean and its eastern continuation in the izmir ankara ophiolitic belt samples from the upper muschelkalk are more radiogenic than the global trend this may reflect separation of the basin from the open ocean due to strong meteoric influx from a large land mass in the north the germanic basin became increasing brackish up section in the north and east but because of the high evaporation rates the salt content was not much reduced in the southern and central basin where a rich but increasingly endemic marine fauna survived

hydrological response of small watersheds following the southern california painted cave fire of june 1990 following the painted cave fire of 25 june 1990 in santa barbara california which burned 1214 ha an emergency watershed protection plan was implemented consisting of stream clearing grade stabilizers and construction of debris basins research was initiated focusing on hydrological response and channel morphology changes on two branches of maria ygnacio creek the main drainage of the burned area research results support the hypothesis that the response of small drainage basins in chaparral ecosystems to wildfire is complex and flushing of sediment by fluvial processes is more likely than by high magnitude debris flows during the winter of 1990 1991 35 66 cm of rainfall and intensities up to 10 cm per hour for a five minute period were recorded with a seasonal total of 100 of average normal rainfall average 63 cm year during the winter of 1991 1992 48 74 cm of rainfall and intensities up to 8 cm per hour were recorded with a seasonal total of 115 of normal even though there was moderate rainfall on barren saturated soils no major debris flows occurred in burned areas the winter of 1992 1993 recorded total precipitation of about 170 of normal annual average intensities were relatively low and again no debris flows were observed the response to winter storms in the first three years following the fire was a moderate but spectacular flushing of sediment most of which was derived from the hillslopes upstream of the debris basins the first significant storm and stream flow of the 1990 1991 winter was transport limited resulting in large volumes of sediment being deposited in the channel of maria ygnacio creek the second storm and stream flow was sediment limited and the channel scoured debris basins trapped about 23 000 m3 the majority coming from the storm of 17 20 march 1991 sediment transported downstream during the three winters following the fire and not trapped in the debris basins was eventually flushed to the estuarine reaches of the creeks below the burn area where approximately 108 000 m3 accumulated changes in stream morphology following the fire were dramatic as pools filled with sediment which greatly smoothed longitudinal and cross sectional profiles major changes in channel morphology occur following a fire as sediment derived from the hillslope is temporarily stored in channels within the burned area however this sediment may quickly move downstream of the burned region where it may accumulate reducing channel capacity and increasing the flood hazard ecological consequences of wildfire to the riparian zone of streams in the chaparral environment are virtually unknown but must be significant as the majority of sediment particularly gravel necessary for fish and other aquatic organisms entering the system does so in response to fires 1997 john wiley sons ltd

intra survey reservoir fluctuations implications for quantitative 4d seismic analysis during the time taken for seismic data to be acquired reservoir pressure may fluctuate as a consequence of field production and operational procedures and fluid fronts may move significantly these variations prevent accurate quantitative measurement of the reservoir change using 4d seismic data modelling studies on the norne field simulation model using acquisition data from ocean bottom seismometer and towed streamer systems indicate that the pre stack intra survey reservoir fluctuations are important and cannot be neglected similarly the time lapse seismic image in the post stack domain does not represent a difference between two states of the reservoir at a unique base and monitor time but is a mixed version of reality that depends on the sequence and timing of seismic shooting the outcome is a lack of accuracy in the measurement of reservoir changes using the resulting processed and stacked 4d seismic data even for perfect spatial repeatability between surveys a spatially variant noise floor is still anticipated to remain for our particular north sea acquisition data we find that towed streamer data are more affected than the ocean bottom seismometer data we think that this may be typical for towed streamers due to their restricted aperture compared to ocean bottom seismometer acquisitions even for a favourable time sequence of shooting and spatial repeatability importantly the pressure signals on the near and far offset stacks commonly used in quantitative 4d seismic inversion are found to be inconsistent due to the acquisition timestamp saturation changes at the boundaries of fluid fronts appear to show a similar inconsistency across sub stacks we recommend that 4d data are shot in a consistent manner to optimize aerial time coverage and that additionally the timestamp of the acquisition should be used to optimize pre stack quantitative reservoir analysis

a 560 year record of santa ana fires reconstructed from charcoal deposited in the santa barbara basin california microscopic charcoal from varved santa barbara basin sediments was used to reconstruct a 560 yr record a d 1425 to 1985 of santa ana fires comparison of large 3750 m2 charcoal with documented fire records in the santa barbara ranger district shows that high accumulations correspond to large fires 20 000 ha that occurred during santa ana conditions the charcoal record reconstructed a minimum of 20 large fires in the santa barbara region during the study period the average time between fires shows no distinct change across three different land use periods the chumash period apparently characterized by frequent burning the spanish early american period with nominal fire control and the 20th century with active fire suppression pollen data support the conclusion that the fire regime has not dramatically changed during the last 500 yr comparison of large charcoal particle accumulation rates and precipitation reconstructed from tree rings show a strong relationship between climate and fire history with large fires consistently occurring at the end of wet periods and the beginning of droughts

comparison of soil infiltration rates in burned and unburned mountainous watersheds steady state infiltration measurements were made at mountainous sites in new mexico and colorado usa with volcanic and granitic soils after wildfires and at comparable unburned sites we measured infiltration in the new mexico volcanic soils under two vegetation types ponderosa pine and mixed conifer and in the colorado granitic soils under ponderosa pine vegetation these measurements were made within high severity burn areas using a portable infiltrometer with a 0 017 m 2 infiltration area and artificial rainfall rates ranging from 97 to 440 mm h 1 steadystate infiltration rates were less at all burned sites relative to unburned sites the volcanic soil with ponderosa pine vegetation showed the greatest difference in infiltration rates with a ratio of steady state infiltration rate in burned sites to unburned soils equal to 0 15 volcanic soils with mixed conifer vegetation had a ratio burned to unburned soils of at most 0 38 and granitic soils with ponderosa pine vegetation had a ratio of 0 38 steady state infiltration rates on unburned volcanic and granitic soils with ponderosa pine vegetation are not statistically different we present data on the particle size distribution at all the study sites and examples of wetting patterns produced during the infiltration experiments published in 2001 by john wiley sons ltd