fluid inclusions in salton sea scientific drilling project core preliminary results fluid inclusions 191 in calcite quartz k feldspar and epidote from l mm veinlets in cores and well cuttings from 604 2560 m homogenize from 217 to 500 c and vary widely in salinity suggesting a complex history of fluids surrounding these samples no daughter minerals were seen and no clathrates were recognized on freezing vapor rich inclusions under pressure presumably containing co2 and or ch4 were found from a wide range of depths suggesting that effervescence has occurred low salinity fluids 1 2 4 0 wt nacl eq were present as deep as 1939 m the data can be explained by a combination of processes such as thermal metamorphism of evaporites and other sediments and mixing of water from metamorphic dehydration reactions with partly evaporated colorado river water

geological geophysical and thermal characteristics of the salton sea geothermal field california abstract the salton sea geothermal field is the largest water dominated geothermal field in the salton trough in southern california within the trough local zones of extension among active right stepping right lateral strike slip faults allow mantle derived magmas to intrude the sedimentary sequence the intrusions serve as heat sources to drive hydrothermal systems we can characterize the field in detail because we have an extensive geological and geophysical data base the sediments are relatively undeformed and can be divided into three categories as a function of depth 1 low permeability cap rock 2 upper reservoir rocks consisting of sandstones siltstones and shales that were subject to minor alterations and 3 lower reservoir rocks that were extensively altered because of the alteration inter granular porosity and permeability are reduced with depth field permeability is enhanced by renewable fractures i e fractures that can be reactivated by faulting or natural hydraulic fracturing subsequent to being sealed by mineral deposition in the central portion of the field temperature gradients are high near the surface and lower below 700 m surface gradients in this elliptically shaped region are fairly constant and define a thermal cap which does not necessarily correspond to the lithologic cap at the margin of the field a narrow transition region with a low near surface gradient and an increasing gradient at greater depths separates the high temperature resource from areas of normal regional gradient geophysical and geochemical evidence suggest that vertical convective motion in the reservoir beneath the thermal cap is confined to small units and small scale convection is superimposed on large scale lateral flow of pore fluid interpretation of magnetic resistivity and gravity anomalies help to establish the relationship between the inferred heat source the hydrothermal system and the observed alteration patterns a simple hydrothermal model is supported by interpreting the combined geological geophysical and thermal data in the model heat is transferred from an area of intrusion by lateral spreading of hot water in a reservoir beneath an impermeable cap rock

thermal regime of the state 2 14 well salton sea scientific drilling project temperature logs were made repeatedly during breaks in drilling and both during and after flow tests in the salton sea scientific drilling project well state 2 14 the purpose of these logs was to assist in identifying zones of fluid loss or grain and to characterize reservoir temperatures at the conclusion of the active phase of the project a series of logs was begun in an attempt to establish the equilibrium temperature profile initially we were able to log to depths below 3 km but beginning in late may of 1986 it was impossible to log below about 1 8 km owing to casing failure our best estimates of formation temperature below 1 8 km are 305 5 c at 1890 m and 355 10 c at 3170 m for the upper 1 8 km the latest temperature log october 24 1986 using a digital slickline heat shielded downhole recording device was within a few degrees celsius of equilibrium as confirmed by a more recent log july 31 1987 to a depth of 1 km as in most other wells in the salton sea geothermal field there is an impermeable thermally conductive cap on the hydrothermal system this cap extends to a depth of more than 900 m at the state 2 14 well thermal conductivities of 19 samples of drill cuttings from this interval were measured at room temperature the conductivity values were corrected for in situ porosity as determined from geophysical logs and for the effects of elevated temperature thermal gradients decrease from about 250 mk m 1 same as degrees celsius per kilometer in the upper few hundred meters to just below 200 mk m 1 near the base of the conductive cap using one interpretation thermal conductivities increase with depth mainly because of decreasing porosity resulting in component heat flows that agree reasonably well with the mean of about 450 m w m 2 this value agrees well with heat flow data from shallow wells within the salton sea geothermal field a second interpretation in which measured temperature coefficients of quartz and carbonate rich rocks are used to correct thermal conductivity results in lower mean conductivities that are roughly constant with depth and consequently systematically decreasing heat flux averaging about 350 mw m 2 below 300 m this interpretation is consistent with the inference from fluid inclusion studies that the rocks in this part of the field were once several tens of degrees celsius hotter than they are now the age of this possible disturbance is estimated at a few thousand years

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

the heating duration and provenance age of rocks in the salton sea geothermal field southern california abstract 40ar 39ar step heating of single k feldspar crystals 500 g in a furnace with a low argon blank and accurate temperature control provide constraints on the thermal history of the salton sea geothermal field southern california estimates of 40ar loss from detrital k feldspars coupled with kinetic information gleaned from laboratory degassing of 39ar allow possible thermal histories to be evaluated samples from core and cuttings of sandstones from the state 2 14 landers 1 dearborn farms 1 magmamax 2 elmore 3 and sinclair 3 wells have been analyzed for this purpose no recent 40ar loss is recognized in any of the 17 crystals measured even for samples currently at temperatures greater than 275 c this observation suggests that the present temperature distributions in these wells have not been maintained for greater than 1000 years however aggregates 100 mg of two k feldspar samples do reveal recent 40ar loss from the state 2 14 well suggesting a time scale of 1000 to 5000 years for near peak thermal conditions these estimates of heating duration are broadly consistent with earlier results from thermal modelling but do not support interpretations that paleotemperatures were once hotter than present provenance ages span the tertiary through middle proterozoic but cluster at ages of 25 70 and 1250 ma these age peaks are very common k feldspar k ar ages in detachment terranes of southeastern california and southwestern arizona both drained by the colorado river this coincidence supports earlier suggestions that the sands of the salton trough were derived mainly from the colorado river unrealistically low apparent activation energies

borehole gravity measurements in the salton sea scientific drilling project well state 2 14 borehole gravity measurements over a depth range from 1737 to 1027 m and the vertical gradient of gravity above ground were measured at the salton sea scientific drilling program well state 2 14 uncorrected borehole gravimetric densities match values from gamma gamma logs indicating that the high densities seen in state 2 14 in the depth range 0 5 to 3 km extend for a few kilometers from the well the above ground gradient was found to be 4 1 micro gal m higher than expected correcting for this value increases the gravimetric density in the borehole combining the borehole gravity and estimated vertical gravity gradients on the surface they find that this densified zone coincides with much of a broad thermal anomaly that has been found to the northeast of the salton sea geothermal field

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

shallow drilling in the salton sea region the thermal anomaly during two shallow thermal drilling programs thermal measurements were obtained in 56 shallow 76 2 m and one intermediate 457 3 m depth holes located both onshore and offshore along the southern margin of the salton sea in the imperial valley california these data complete the surficial coverage of the thermal anomaly revealing the shape and lateral extent of the hydrothermal system the thermal data show the region of high thermal gradients to extend only a short distance offshore to the north of the quaternary volcanic domes which are exposed along the southern shore of the salton sea the central thermal anomaly has an arcuate shape about 4 km wide and 12 km long across the center of the anomaly the transition zone between locations exhibiting high thermal gradients and those exhibiting regional thermal gradients is quite narrow thermal gradients rise from near regional 0 09 c m to extreme 0 83 c m in only 2 4 km the heat flow in the central part of the anomaly is greater than 600 mw m2 and in the two local anomalies exceeds 1200 mw m2 the shape of the thermal anomaly is asymmetric with respect to the line of volcanoes previously thought to represent the center of the field with its center line offset south of the volcanic buttes there is no broad thermal anomaly associated with the magnetic high that extends offshore to the northeast from the volcanic domes the salton sea thermal anomaly can be described as three nested thermal features superimposed on the regional salton trough heat flux a broad region of elevated conductive heat flow with constant temperature gradients of about 0 1 c m a central anomaly of high 0 4 c m near surface gradients observed through a conductive thermal cap underlain by a nearly isothermal zone of hydrothermal circulation and two local anomalies with shallow temperature gradients as high as 0 8 c m superimposed on the central geothermal system these observations of the thermal anomaly provide important constraints for models of the circulation of the hydrothermal system thermal budgets based on a simple model for this hydrothermal system indicate that the heat influx rate for local hot spots in the region may be large enough to account for the rate of heat flux from the entire salton trough

preliminary studies on the geochemistry of the mahanadi river basin india water and suspended and bed sediments were collected during 1986 1987 for the two seasons and analysed to study the geochemistry of the mahanadi river basin which is one of the eight major drainage systems in india the water chemistry reflects the control exercised on weathering by the most abundant lithology namely the carbonates in the basin water composition is in equilibrium with dolomite kaolinite and chlorite xrd studies in suspended and bed sediments show the presence of dolomite kaolinite chlorite and minor quantities of montmorillonite the mahanadi annually delivers 15 74 106t of sediments to the bay of bengal which is high compared to its basin size the dissolved load dominates over physical load by a factor of 4 with 95 of the transport taking place in the monsoon season the basin is characterised by an erosion rate of 138 24 t km 2 yr 1 with a lowering rate of 0 31 mm yr 1 textural studies indicate that the bed sediments are relatively coarser grained than the suspended sediments due to reworking the sediments are finer downstream fe mn cu zn and pb concentrations in the sediments are higher compared to the other peninsular indian rivers eventhough mahanadi transports annually to the bay of bengal 10 of the total load by other indian rivers and its weathering in a complex geological terrain with rich mineral deposits controls to a larger extent the chemistry of the sediments in the bay of bengal

storage and release of fossil organic carbon related to weathering of sedimentary rocks abstract the biogeochemical carbon cycle which plays an undeniable role in global climate change is defined both by the size of carbon reservoirs such as the atmosphere biomass soil and bedrock and the exchange between them of various mineral and organic carbon forms among these carbon forms fossil organic carbon foc i e the ancient organic matter stored in sedimentary rocks is widely observed in modern environments but is not included in the supergene carbon budget using a digitized map of the world and an existing model of co 2 consumption associated with rock weathering we establish the global distribution of foc stored in the first meter of sedimentary rocks and a first estimation of annual foc delivery to the modern environment resulting from chemical weathering of these rocks results are given for the world s 40 major river basins and extended to the entire continental surface with a mean value of 1100 10 9 t mainly controlled by shale distribution the global foc stock is significant and comparable to that of soil organic carbon 1500 10 9 t the annual chemical delivery of foc estimated at 43 10 6 t yr 1 and controlled by the areal distribution of shales and runoff is of the same order of magnitude as the foc output flux to oceans chemical weathering of bedrock within the amazon basin produces one quarter of the total global flux of foc derived from chemical weathering and thus is expected to govern foc release on a global scale these results raise important questions concerning the role of foc in the modern carbon cycle as well as the origin and the budget of carbon in soils and rivers

transport mechanism for pb 210 cs 137 and pu fallout radionuclides through fluvial marine systems abstract pb 210 cs 137 and pu 239 240 sediment depth profiles in an anoxic unbioturbated estuarine depositional regime at the head of the saguenay fjord que exhibit a seasonally modulated component caused by pulsed inputs of silts and sands during high energy spring river discharge events superimposed on an ambient depositional pattern of finer grained clays and organic matter a precise sediment timestratigraphy has been determined by the inverse correlation of the pb 210 activity with the rate of river discharge during the period 1963 1976 the historical record of cs 137 and pu 239 240 sediment fluxes has been reconstructed through the normalization of fallout radionuclide activities to the excess pb 210 activity profile radionuclide flux geochronologies have been interpreted on the basis of a fluvial marine transport model which distinguishes between inputs due to direct adsorption of radionuclides onto particles in the water column and inputs resulting from the erosion of particle associated radionuclides from the drainage basin rate constants corresponding to residence times of one year for cs 137 and pu 239 240 in the water column and 1500 years for each radionuclide in the drainage basin provide reasonable agreement between the model and experimental results although there is some evidence for a slightly longer drainage basin residence time for plutonium both the threshold for the initial appearance of pu 238 derived from the atmospheric burnup of a snap 9a satellite reactor in 1964 and the magnitude of its isotopic dilution by drainage basin inputs of pu 239 240 are also in agreement with model predictions

the influence of drought and anthropogenic effects on groundwater levels in orissa india summary investigating the response of groundwater levels to the extreme weather events provides essential information for sustainable planning and management of water resources the aim of this study was to identify and quantify the groundwater level trend of the state orissa india to understand the forcing mechanism of droughts in conjunction with the anthropogenic pressure using the non parametric mann kendall statistical procedure the pre and post monsoon groundwater level records of 1002 monitoring stations during the period 1994 2003 were analyzed the results show that the drawdowns due to deficient rainfall during dry years high temperatures and anthropogenic pressure have not been recovered through the recharge in wet years however this study does not determine whether drought high temperatures or anthropogenic effects have had largest influence on the groundwater levels decline the cases of significant water table declines are higher in number than those expected to occur by chance in the pre monsoon season 59 of the monitoring stations experienced groundwater declines as against 51 in the post monsoon season for the study area as a whole this could be interpreted that the fluctuation is not a part of noise but that a signal is being identified further the trend result showed wide spatial and seasonal differences irrespective of seasons the consolidated rock formation that covers 80 of the geographical area experienced significant water table decline however the semi consolidated and unconsolidated formations experienced water table decline in the pre monsoon summer season only the vulnerable sites where the groundwater level declined significantly were identified so that recharge measures could be taken up

sediment transport of the godavari river basin and its controlling factors abstract the mean annual water flow and sediment transport of the godavari river are estimated to be 92 km 3 and 170 10 6 ton t respectively in terms of sediment transport and the rate of physical erosion 555 t km 2 yr 1 the position of the godavari would be ninth and fifth respectively among the world rivers geology of the basin is the main controlling factor of the sediment transport the sedimentary rocks located in the lower part of the basin and constituting 7 of the total basin area are responsible for 33 of the sediment load more than 67 of sediment load is silt and clay annual monthly and daily variations in sediment transport indicate that a few selected days in the hydrological year control the annual sediment budget our latest estimates are nearly twice that of our earlier values the presently available global estimates on sediment transport need to be re evaluated

uranium thorium and lead nuclides in a delaware salt marsh sediment natural isotopes of uranium 234 238 thorium 232 230 and lead 210 have been assayed in sediments from a lower delaware salt marsh uranium is concentrated in the top sections of the core and decreases with depth 3 to 1 d min 1 g 1 a significant proportion of this uranium has been authigenically extracted from seawater as demonstrated by an excess ratio of 234u 238u 1 03 1 14 thorium 232 is rather constant 2 4 4 7 parts 10 6 for all but one sample while the concentration of 230th is deficient with respect to its uranium parent in contrast to the deep sea the fixation of authigenic reduced uranium dominates over the scavenging of 230th in these tidal sediments excess 210pb shows an exponential decay over the length of the core and when corrected for a correspondingly significant exponential decrease in organic carbon and salt yields a sedimentation rate of 0 47 cm year 1 although this rate approximates the local apparent rate of sea level rise a lower limit for the rate of salt marsh accumulation the actual rate is higher suggesting net filling and acccretion of salt marshes the total integrated flux of 210pb to this and other salt marsh surfaces in the eastern u s is calculated to more often exceed the reported local atmospheric flux it appears that salt marshes may scavenge 210pb as other trace metals from flooding waters

fallout 210pb as a soil and sediment tracer in catchment sediment budget investigations a review increasing anthropogenic pressures coupled with climate change impacts on natural resources have promoted a quest for innovative tracing techniques for understanding soil redistribution processes and assessing the environmental status of soil resources among the different existing tracers the fallout component of the radioisotope lead 210 also termed unsupported or excess lead 210 pb 210 ex when referring to its presence in soil or sediment arguably offers the broadest potential for environmental applications due to its origin and relatively long half life for more than five decades pb 210 ex has been widely used for dating sediments to investigate sedimentation processes and since the 1990s to provide information on the magnitude of soil and sediment redistribution the aim of this review is to provide a comprehensive evaluation and discussion of the various applications of pb 210 ex as a tracer in terrestrial and aquatic environments with particular emphasis on catchment sediment budget investigations this paper summarizes the state of the art related to the use of this tracer the main assumptions the requirements including the need for accurate analytical measurements and for parallel validation and the limitations which must be recognised when using this fallout radionuclide as a soil and sediment tracer lessons learned and current and future research needs in the environmental and radiochronological application of pb 210 ex are also presented and discussed c 2014 elsevier b v all rights reserved

spatio temporal dynamics of heavy metals in sediments of the river estuarine system mahanadi basin india dynamics of heavy metals in the surface sediments of mahanadi river estuarine system were studied for three different seasons this study demonstrates that the relative abundance of these metals follows in the order of fe mn zn pb cr ni co cu cd the spatial pattern of heavy metals supported by enrichment ratio data suggests their anthropogenic sources possibly from various industrial wastes and municipal wastes as well as agricultural runoff the metal concentrations in estuarine sediments are relatively higher than in the river due to adsorption accumulation of metals on sediments during saline mixing while there is a decreasing trend of heavy metal concentrations towards the marine side the temporal variations for metals such as fe mn zn ni and pb exhibit higher values during monsoon season which are related to agricultural runoff higher elemental concentrations are observed during pre monsoon season for these above metals except ni at the polluted stations and for metals such as cr co and cd at all sites which demonstrate the intensity of anthropogenic contribution r mode factor analysis reveals that fe mn oxy hydroxide organic matter caco3 and textural variables factors are the major controlling geochemical factors for the enrichment of heavy metals in river estuarine sediment and their seasonal variations though their intensities were different for different seasons the relationships among the stations are highlighted by cluster analysis represented in dendrograms to categorize different contributing sites for the enrichment of heavy metals in the river estuarine system

influence of carbonates on the riverine carbon cycle in an anthropogenically dominated catchment basin evidence from major elements and stable carbon isotopes in the lagan river n ireland abstract investigation of anthropogenic versus natural controls of the carbon cycle in the lagan river revealed a strong influence of carbonates this was evident by increasing ph values along the river as well as isotopic compositions of the riverine dissolved inorganic carbon 13cdic that approached expected values for carbonate dissolution this predominant influence of carbonates existed despite their minor abundance of only 5 in this densely populated catchment basin and outlines their capacity of buffering anthropogenic influences and co2 turnover these effects should be even more pronounced in other rivers where carbonates occupy a larger proportion of the catchment basin geology other controls on the riverine carbon cycle were silicate weathering and respiratory turnover of organic material that originated mainly from anthropogenic inputs and increased the dic pool by up to 26 6 predominant natural controls on the lagan river carbon cycle changed to anthropogenic ones closer to the mouth before discharging into belfast lough a recently installed weir caused stagnant seawater to make up between 53 and 92 of the water mass poor vertical mixing caused o2 decreases and anaerobic sedimentary activity that resulted in methane production recently installed aerators at the sediment surface did not prevent ongoing methanogenesis this was documented by decreased pco2 and more 13c enriched dic values at the sediment water interface when compared to those of surface waters from the same sampling sites installations of such weirs in estuaries of other rivers may cause similar anoxic effects that influence their biogeochemistry

convective hydrothermal c02 emission from high heat flow regions abstract in addition to volatiles released from volcanoes the flux of co2 to the atmosphere from other sources e g metamorphism and subsurface magmatism represents an important aspect of the global carbon cycle we have obtained a direct estimate of the present day atmospheric co2 flux from convective hydrothermal systems within subaerial seismically active high heat flow regions geothermal systems of the salton trough california u s a and the taupo volcanic zone new zealand provide benchmarks for quantifying convective hydrothermal co2 fluxes from such regions co2 fluxes from the salton trough 109 mol yr 1 and the taupo volcanic zone 8 109 mol yr 1 were computed using data on convective heat flow and the temperatures and co2 concentrations of reservoir fluids the similarity in specific co2 flux 106 mol km 2 yr 1 from these two disparate geologic tectonic settings implies that this flux may be used as a baseline to compute convective hydrothermal co2 emission from other areas of high heat flow if this specific flux is integrated over high heat flow areas of the circum pacific and tethyan belts the total global co2 flux could equal or exceed 1012 mol yr 1 adding this flux to a present day volcanic co2 flux of 4 1012 mol yr 1 the total present day earth degassing flux could balance the amount of co2 consumed by chemical weathering 7 1012 mol yr 1

connecting the atlantic sector and the north pacific mt logan ice core stable isotope records during the holocene the role of el nino the 18o holocene of the mt logan ice core is very different from those of eastern arctic canada and greenland the large changes seen in logan dwarf even the largest change the cooling event 8200 years ago in the atlantic sector cores large changes in logan s 18o and d are related to the state of el nino as reflected by the quelccaya 18o series it is found that the lagged auto difference series of the ice core records from the agassiz ice cap greenland and the 23 site stack of paleotemperature records of kaufman et al kaufman ds schneider dp mckay np ammann cm bradley rs briffa kr et al 2009 recent warming reverses long term arctic cooling science 325 1236 produce highly significant matches to the mt logan 18o series these correspondences suggest a lag of 1200 years this lag time is what some models of the diffusive great ocean conveyor d goc predict for the average travel time from the north atlantic to the tropical eastern pacific monte carlo testing of the correlation

seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting imperial valley california plate boundary rifting between transform faults is opening the imperial valley of southern california and the rift is rapidly filling with sediment from the colorado river three 65 90 km long seismic refraction profiles across and along the valley acquired as part of the 2011 salton seismic imaging project were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock both first arrival travel time tomography and frequency domain full waveform inversion were applied to provide p wave velocity models down to 7 km depth the valley margins are fault bounded beyond which thinner sediment has been deposited on preexisting crystalline rocks within the central basin seismic velocity increases continuously from 1 8 km s sediment at the surface to 6 km s crystalline rock with no sharp discontinuity borehole data show young sediment is progressively metamorphosed into crystalline rock the seismic velocity gradient with depth decreases approximately at the 4 km s contour which coincides with changes in the porosity and density gradient in borehole core samples this change occurs at 3 km depth in most of the valley but at only 1 5 km depth in the salton sea geothermal field we interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the 2 km myr sedimentation rate the newly formed crystalline crust extends to at least 7 8 km depth and it is shallower and faster where heat flow is higher most of the active seismicity occurs within this new crust

rates of erosion and sedimentation in the mahanadi river basin india abstract the mahanadi river basin extends over an area of 1 42 105 km2 and discharges about 15 74 106 t of sediment to the bay of bengal the geology of the basin is mostly characterised by precambrian rocks of the eastern ghats rocks associated with the gondwana supercontinent and recent littoral deposits sampling was done to determine chemical erosion physical erosion and sedimentation rate in the basin carbonate rock weathering is the dominant control on the chemical composition of the river water there is a spatial and temporal variation in water and sediment flow the chemical erosion rate for individual elements at different sites has been established sedimentation rate determined by the 210pb isotope method in core samples gives rates of 5 08 to 20 39 mm year 1 this high sedimentation rate is attributed to local anthropogenic activities carried out in the basin

spatial and temporal variability of sediment and dissolved loads from two alpine watersheds of the lesser himalayas abstract estimation of sediment load from himalayan basins is of considerable importance for the planning designing installation and operation of hydro power projects including management of reservoirs in the present study an assessment of physical and chemical load sediment yield and erosion rate has been undertaken at eight different locations in the sainj and tirthan watersheds the analysis revealed that the maximum load was transferred during the monsoon season moreover the estimated average chemical erosion rate of the sainj 83 t km 2 yr 1 and tirthan 80 t km 2 yr 1 watersheds were higher than that of the indian average 69 t km 2 yr 1 representing all the rivers both watersheds were eroding physically and chemically at a faster rate than that of the world global average erosion rate 185 t km 2 yr 1 the flattish nature of the channels in some segments of these watersheds showed a lower transport of sediments where as the constricted segments having steep bed slopes increased the velocity of flow and the sediment transport rate these findings have important implications for water resource management in the context of sediments mobilization erosion channel management ecological functions and operation of the hydro power projects in the lesser himalayan region

trace element geochemistry of river sediment orissa state india abstract geochemical analyses of bottom sediment from rivers flowing through orissa state india indicated that trace element concentrations were extremely variable and commonly higher than crustal abundance the highest elemental concentrations were associated with the brahmani river followed by the baitarani and mahanadi rivers although all three rivers drain similar geology the brahmani river catchment is heavily industrialized and sediment collected downstream from industry confirms that anthropogenic activity influenced its chemical composition a similar pattern was observed in sediments collected downstream from towns in the mahanadi and baitarani catchments in both examples the clay size fraction was shown to be the most highly reactive component of the sediments comparisons between metal concentrations from the upper to lower stretches of the three river systems indicated no net accumulation downstream apparently trace elements discharged into the river system tend to be short lived in the water column rapidly settling out or becoming adsorbed into the bottom sediment although for much of the year the trace metals may remain locally incorporated as bottom sediment during monsoonal episodes where bedload transport can be significant the effects of pollution may expand over regional distances 1997 elsevier science b v

paleomagnetic record for the past 80 ka from the mahanadi basin bay of bengal abstract high resolution paleomagnetic investigations were performed on a 50 08 m long sediment core md161 20 from mahanadi basin bay of bengal core yielded reliable paleomagnetic results for top 20 m below seafloor mbsf which spans about 80 ka based on the analysis of rock magnetic data the core is subdivided into five distinct zones zone 1 and zone 2 cover top 20 mbsf and do not show any abrupt change in magnetic mineralogy concentration and grain size zones 3 and 5 show significant reduction in lf arm and sirm due to dissolution of magnetic minerals zone 4 shows moderate values of lf and sirm the low value of arm suggests that magnetic signal is mostly carried by magnetic grains in psd md state the paleomagnetic data for the top 20 mbsf show four prominent geomagnetic excursions at 9 mbsf 13 5 to 15 mbsf 16 3 mbsf and 18 to 18 2 mbsf the age depth relationship is established using stratigraphic correlation between well dated sedimentary core nghp 01 19b and the core md161 20 the ages of the observed excursions correspond to 18 to 20 ka 42 to 49 ka 54 to 57 ka and 69 to 70 ka the excursions at 42 to 49 ka 54 to 57 ka and 67 to 70 ka is similar to the known excursions the laschamp and the split norwegian greenland sea events ngs i and ngs ii the excursion at 18 20 ka is not observed globally and may be related to lithological sedimentological changes occurring during last glacial maxima lgm the virtual geomagnetic path vgp of laschamp excursion traces clockwise loop all excursions identified in present study fall in the periods of relatively low paleointensity

chemical weathering and associated co2 consumption in the mahanadi river basin india abstract chemical weathering of continents is one of the major geochemical processes which consumes atmospheric co2 and exerts a strong impact on the global climate the major ion chemistry of the mahanadi river basin one of the largest river basins in india is determined to investigate the sources of major ions and their spatio temporal variability chemical weathering rates and associated co2 consumption in the basin the results reveal that the ions in the basin are dominated by ca and hco3 the total dissolved solids 215 mg l 1 in monsoon and 270 mg l 1 in pre monsoon and total cation concentration 2367 eq in monsoon and 3214 eq in pre monsoon in the basin are relatively higher than the global average the dissolved loads in the basin are dominantly controlled by rock weathering particularly chemical weathering of silicates and carbonates the estimated chemical weathering rates based on the forward model are 44 94 t km 2 yr 1 in monsoon and 2 45 t km 2 yr 1 in pre monsoon with annual average chemical weathering rate of 23 7 t km 2 yr 1 the contribution of silicate weathering rates in the basin is 32 and 1 55 t km 2 y 1 during monsoon and pre monsoon period respectively the estimated co2 consumption rate associated with chemical weathering in the basin is 13 3 105 mol km 2 yr 1 during monsoon and 0 66 105 mol km 2 yr 1 during pre monsoon period with an average annual rate of 6 9 105 mol km 2 yr 1 which is higher than the global average the net rate of co2 consumption by silicate weathering is estimated to be approximately 4 78 105 mol km 2 yr 1 it is observed that the runoff and lithology are the major factors influencing chemical weathering in the basin however the basin elevation has a good negative correlation with chemical weathering rate

the salton sea scientific drilling project in march 1986 a research borehole called the state 2 14 reached a depth of 3 22 km in the salton sea geothermal system of southern california this was part of the salton sea scientific drilling project sssdp the first major i e multimillion dollar research drilling project in the u s continental scientific drilling program the principal goals of the project were to investigate the physical and chemical processes of a high temperature high salinity magmatically driven hydrothermal system the borehole encountered temperatures of up to 355 c and produced metal rich alkali chloride brines containing 25 wt of total dissolved solids the rocks penetrated exhibit metamorphism and ore genesis in action they show a progressive transition from unconsolidated lacustrine and deltaic sediments to hornfelses with lower amphibolite facies mineralogy accompanied by pervasive veins containing iron copper lead and zinc ore minerals the sssdp included an intensive program of rock and fluid sampling flow testing and downhole logging and scientific measurement the purpose of this paper is to introduce this special section of the journal of geophysical research on the sssdp to describe briefly the background of the project and the drilling and testing of the borehole to summarize the initial scientific results and to discuss how the lessons learned are applicable to future scientific drilling projects

chemical mass transfer modelling of ore forming hydrothermal systems current practise and problems abstract chemical mass transfer modelling is a numerical approach to predicting the progress of multicomponent fluid rock reactions in natural hydrothermal systems based on thermodynamic data for minerals and fluid species quantitative simulations of hydrothermal wall rock alteration and ore mineral deposition can be used to develop and test geological models for ore formation which are a basis for mineral exploration and resource assessment in practice the application of thermodynamic mass transfer modelling to specific ore forming systems faces two main problems even for the limiting assumption of local equilibration between fluids and minerals the first problem relates to the geometry of fluid rock interaction where the scheme of the model must be adjusted to the geological question of interest one dimensional reactor models defining reaction progress as a function of integrated fluid flux along a path through a chemically reactive rock do not necessarily provide a more realistic description of chemical mass transfer than simple titration models without temporal and spatial dimension because in most ore depositing systems the fluids are partially channelized by structures like veins or faults the efficiency of metal extraction at the ore deposition site is commonly determined by a sensitive balance between fluid focusing on one hand and wall rock reaction promoting ore mineral precipitation on the other an example of gold and scheelite mineralization associated with mesothermal quartz veins illustrates how ore deposition and alteration zoning parallel to the main fluid flow direction in partially channelized systems can be described by a two dimensional multibox model the second problem relates to the extent and quality of thermodynamic data explicit consideration of fe bearing silicate solid solutions is essential for predicting realistic mass balance in complex fluid silicate sulphide reactions associated with hydrothermal ore formation although a high level of internal consistency of multicomponent data sets has been achieved by simultaneous fitting of multiple thermodynamic and equilibrium measurements significant inconsistencies persist among the most comprehensive data compilations published for the three main groups of species relevant to hydrothermal ore deposits aqueous species in high temperature aqueous brines silicate oxide carbonate minerals including fe mg silicates and sulphur bearing minerals including sulphides and sulphates discrepancies between thermodynamic predictions and observed brine composition and mineral assemblages in the salton sea geothermal system suggest that the redox scale for rock forming silicates may be inconsistent with that of sulphides and aqueous s c o h species this analysis is preliminary but illustrates the importance of field testing of thermodynamic data particularly for hydrothermal conditions between 150 and 450 c which lie between the high temperatures of reliable equilibrium experiments among rock forming minerals 500 c and the low temperatures of many experiments defining the thermodynamics of aqueous species mostly

compositional order disorder and stable isotope characteristics of al fe epidote state 2 14 drill hole salton sea geothermal system epidote ca2fe3si3o12 oh ca2al3si3o12 oh is a common hydrothermal mineral in metasediments and veins at depths 900 m in the state 2 14 drill hole of the salton sea geothermal system the mole fraction of ca2fe3si3o12 oh in epidotes xps from this drill hole ranges from 0 11 to 0 42 and complex compositional zoning of octahedral fe3 and al is typical within single grains with increasing depth there is an overall but irregular decrease in the fe3 content of epidotes in metasandstones in most samples vein epidotes are more fe3 rich and exhibit a wider compositional range than metasandstone epidotes from the same depth octahedral fe3 in the m 1 sites in four epidotes evaluated by 57fe mossbauer spectroscopy ranges from 7 5 1 7 to 11 4 1 5 of the total iron the most ordered epidote formed in veins at 2618 m in the biotite zone this epidote has an ordering parameter 1 2xfe3 m 1 of 0 85 0 03 which corresponds to a calculated state of equilibrium order disorder at 390 60 c in close agreement with the probable downhole temperature of 340 c two epidote samples from the chlorite calcite zone 1420 m 265 c 1867 m 300 c are more disordered corresponding to calculated states of equilibrium order disorder of 450 c these data suggest that the analyzed epidotes from the chlorite calcite zone are in a metastable state of substitutional order disorder the measured value of depidote from 1420 m is 96 which is 5 6 lighter than epidotes from 1867 m depidote 90 2227 m depidote 91 and 2618 m depidote 90 when compared to the reservoir fluid from the december 1985 flow test the derived fractionation of hydrogen isotopes between epidote and the geothermal brine is 19 at 1867 m and 340 c this value is in accord with published experimental hydrogen isotope fractionations between iron rich epidote and aqueous electrolyte solutions therefore considering the complexity of the salton sea brine the isotopic temperature is similar to the inferred downhole temperature

erosion and sediment transport in the ganges river basin india abstract based on sampling of the entire region of the ganges basin chemical and sediment load supplied at various parts of the basin have been computed annual flux of materials from sub basin into the main basin and input to the hoogly estuary have been calculated and compared to major river systems of the world the total annual load at calcutta mouth of the river was calculated as 411 10 6 t 328 10 6 t sediment load 83 10 6 t chemical load erosion rate 549 t km 2 yr 1 is among the highest in this river system and controlling factors on a global scale such as basin area are discussed in detail annual decrease in basin elevation indicates a rapid process of denudation and such rates have a bearing on rates of shelf sediment accumulation

analysis of geophysical well logs obtained in the state 2 14 borehole salton sea geothermal area california a complete suite of conventional geophysical well logs was obtained in the upper part of a 3220 m deep borehole drilled into geothermally altered alluvial sediments on the southeastern edge of the salton sea in situ temperatures greater than 300 c and an inability to cool parts of the borehole by circulation limited the suite of logs run below 2000 m in depth to deep induction spontaneous potential un calibrated neutron natural gamma and temperature bottom hole temperature trends given by repeat temperature logs were extrapolated to undisturbed temperatures approaching 355 c at a depth of 3220 m geophysical logs obtained in the state 2 14 borehole indicate that neutron porosity gamma gamma and deep induction logs provide useful information on lithologic trends with depth the natural gamma log contains almost continuous high frequency fluctuations that obscure lithologic trends and that may be related to recent radioisotope redistribution and departure from radiometric equilibrium acoustic transit time logs give unrealistically low in situ compressional velocities ranging from 1 8 to 3 0 km s whereas acoustic waveform logs indicate that sediment compressional velocities range from less than 3 0 km s shallower than 1000 m in depth to almost 5 0 km s at depths greater than 2000 m analyses indicate that most log values lie between two lithologic end points an electrically conductive claystone with moderate neutron porosity but no effective porosity and an electrically nonconductive fully cemented siltstone that has small but finite porosity a limited number of clean sandstones depart from this trend geophysical logs from these sandstones indicate an effective porosity ranging from 5 to 14 and saturation with brines having equivalent nacl concentrations greater than 100 000 mg l depth averaged trends in neutron porosity and deep induction logs along with trends in acoustic velocity determined from acoustic waveform logs demonstrate that major changes in the properties of alluvial sediments occur within the depth range from 1200 to 1800 m although caliper logs were not obtained deeper than 2000 m resistivity values less than 10 ohm m at those depths probably correspond to borehole enlargements in production zones rather than local increases in effective porosity the transition in sediment properties indicated by the geophysical logs in the depth interval from 1200 to 2000 m apparently represents a detailed vertical profile of the transition from relatively unaltered clay minerals in alluvial sediments to electrically nonconductive alteration products such as epidote and feldspar