retardation of 238u and 232th decay chain radionuclides in long island and connecticut aquifers abstract knowledge of the ability of an aquifer to retard the groundwater transport of toxic or radioactive ions can be inferred from the analysis of groundwater for the radionuclides of the 238u and 232th decay chains groundwaters of varying chemical composition were analyzed from wells in long island new york and connecticut aquifer lithologies are arkose quartz sandstone granite and glacial drift adsorption k1 and desorption k2 coefficients for ra and pb were calculated using 222rn activity as a measure of the supply of other recoil nuclides laboratory tests of the validity of this assumption were made by measuring the flux of 224ra and 222rn from aquifer solids the ratio k 1 k 2 is the distribution coefficient k which is effectively equal to r the retardation factor the average value of k for ra is 6 102 in long island aquifers and 5 104 in connecticut the distribution coefficient for pb is 104 in long island and 105 in connecticut results from this and other studies reveal a strong dependence of retardation on ph o 2 and ionic strength that tends to overwhelm any dependence of retardation on lithology

liquefaction evidence for strong earthquakes of holocene and latest pleistocene ages in the states of indiana and illinois usa abstract sand and gravel filled clastic dikes of seismic liquefaction origin occur throughout much of southern indiana and illinois nearly all of these dikes originated from prehistoric earthquakes centered in the study area in this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the holocene and at least one during the latest pleistocene the recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects but some have been recognized only by geotechnical testing at sites of liquefaction most paleo earthquakes presently recognized lie in indiana but equally as many may have occurred in illinois studies in illinois have not yet narrowly bracketed the age of clastic dikes at many sites which sometimes causes uncertainty in defining the causative earthquake but even in illinois the largest paleo earthquakes probably have been identified prehistoric magnitudes were probably as high as about moment magnitude m 7 5 this greatly exceeds the largest historic earthquake of m 5 5 centered in indiana or illinois the strongest paleo earthquakes struck in the vicinity of the concentration of strongest historic seismicity elsewhere paleo earthquakes on the order of m 6 7 have occurred even where there has been little or no historic seismicity both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back calculating prehistoric magnitudes methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere

on the geologic structure at the epicenter of the 1886 charleston south carolina earthquake the study focuses on evidence of cenozoic faulting in the epicentral area of the 1886 charleston south carolina earthquake and its connection with mesozoic structure the seismic data consist of several reflection profiles collected near summerville south carolina in the period 1975 1983 reprocessing of the data reveals an extensive early mesozoic extensional basin approximately 20 km in width between summerville and charleston the basin is delineated by the geometry of reflections that image early mesozoic volcanic and sedimentary rocks and by positive magnetic and gravity anomalies cenozoic compressional reactivation of mesozoic extensional faults is imaged in the interior of the basin the northwestern boundary of the basin is marked by a sharp gradient in the magnetic field folded cretaceous and tertiary atlantic coastal plain sediments in association with diffractions and truncated reflections from the early mesozoic section at four locations along this magnetic gradient indicate that the northwestern basin boundary is faulted instrumentally located earthquakes are clustered at the location of the faults imaged in the interior of the basin and in proximity to the northwestern basin margin modeling of magnetic and gravity data indicates that the upper crust beneath the seismically imaged structural basin is composed largely of mafic rocks to a depth of at least 4 km we propose that the charleston earthquake occurred due to compressional reactivation of a mesozoic fault in a localized zone of intense early mesozoic continental rifting

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

three dimensional geometry of the reelfoot blind thrust implications for moment release and earthquake magnitude in the new madrid seismic zone mapping of the reelfoot blind thrust using portable array for numerical data acquisition panda seismicity suggests that it is a complex fault that changes its geometry along strike the thrust appears to be bounded to the north by an east trending strike slip fault the southern end of the thrust is defined by seismicity and does not terminate at a known transverse fault the northern portion of the thrust steepens at shallow levels forming a listric concave upward shape in cross section the southern segment of the thrust is interpreted to flatten near the top of the precambrian basement although some segmentation of the blind thrust is observed from the mapping of 3 km wide strips of seismicity oriented perpendicular to the fault it does not appear to be significant enough to prevent rupture along its entire length the area of the blind thrust 1301 km 2 coupled with several estimates of displacement in the 7 february 1812 event is used to determine the moment released during the event the values of m 0 range from 6 8 10 26 to 1 4 10 27 dyne cm with preferred values between 6 8 10 26 and 8 7 10 26 dyne cm similar calculations for an earthquake in a d 1450 yield a moment release of 1 0 10 27 dyne cm computed moment magnitude for the 7 february 1812 event ranges from m w 7 2 to 7 4 with preferred values between m w 7 2 and 7 3 the moment magnitude for the a d 1450 event is computed as m w 7 3 these values for the magnitude of the 1812 earthquake are lower than previous estimates based on historical records of shaking however this does not imply a lowered seismic risk in the new madrid seismic zone as site effects in the mississippi embayment may significantly amplify the ground motion caused by earthquakes of a given magnitude

transport of u and th series nuclides in a baltic shield watershed and the baltic sea the transport of th ra and 210 pb from a continental source region and through an estuarine environment was investigated unlike previous studies here both short and long lived nuclide data were obtained for river inputs river water and estuarine waters the mire rich kalix river drainage basin was chosen as a typical northern shield area because this river may represent typical waters flowing into the arctic and northern seas groundwaters from bedrock and glacial tills have comparable th isotope concentrations and do not exhibit significant th isotopic shifts relative to host rocks the extensive peat deposits of the basin receive groundwater discharges and concentrate th and u but not ba and ra which cause high 230 th 232 th ratios in mire waters however mire outflows do not have a significant impact on th and ra isotopic compositions of the river overall weathering characteristics for the basin are obtained from the river data the 230 th 232 th 228 ra 226 ra and 226 ra ba river ratios are comparable to those of source rocks consistent with similar release rates of these nuclides from u th and ba bearing minerals river ratios of 230 th 238 u ar and 226 ra 238 u ar are 1 so that th and possibly ra are accumulating in the weathering regions and the weathering profile is still evolving low 228 ra 232 th ar and 226 ra 230 th ar ratios indicate that th is preferentially retained over ra river 234 th 238 u ar ratios are greater than 230 th 238 u ar ratios and suggest that in systems where river inputs are well characterized these ratios can be used to calculate th transit times through the watershed filtration data indicate that although a dominant fraction of the th is transported in the river on particles the rest is almost entirely carried by colloids the kalix river discharges into the baltic sea model calculations for the transport of th and ra isotopes in the baltic sea show that the high ratios of 234 th 238 u ar found here reflect long th residence times relative to particle scavenging of 50 d the water column 232 th budget is dominated by eolian inputs the 226 ra concentrations may be higher than those of water inflows with 60 derived from underlying sediments a greater fraction of 228 ra is derived from sediments to balance the decay of 228 ra within the water column during the 35 yr residence time of water in the baltic the baltic 228 ra 226 ra ar ratios which are relatively constant over a range of salinities are fortuitously similar to those of the river inflows

time scale and conditions of weathering under tropical climate study of the amazon basin with u series the rio solimoes amazonas amazon river and its major tributaries have been analyzed for u series nuclides 238 u 234 u 230 th 226 ra disequilibria have been measured in the dissolved 0 2 lm as well as bed sands u series disequilibria are closely related to major and trace element compositions and therefore reflect elemental fractionation during chemical weathering moreover while the dissolved load records present day weathering suspended particles integrate the erosion his tory over much longer time scales 100 ka lowland rivers are characterized by long time scales of chemical erosion p100 ka result ing in a high weathering intensity moreover exchange between suspended particles and the dissolved load may explain the u series signature for these rivers by combining u series and pb isotopes in suspended particles we show that erosion in the rio madeira basin occurred as a multi step process whereby the pristine continental crust was eroded several hundreds of ma ago to produce sediments that have then been integrated in the cordillera by crustal shortening and are currently eroded in contrast recent erosion of a pristine crust is more likely for the rio solimoes amazonas 10 ka the suspended particles of the rivers draining the andes solimoes ama zonas madeira suggest time scales of weathering ranging between 4 and 20 ka this indicates that suspended particles transported by those rivers are not stored for long periods in the andean foreland basin and the tropical plain the sediments delivered to the ocean have resided only a few ka in the amazon basin 6 3 1 ka for the rio amazonas at obidos nevertheless a large fraction of the sediments coming out from the andes are trapped in the foreland basin and may never reach the ocean erosion in the andes is not operating in steady state u series systematics shows unambiguously that rivers are exporting a lot more sediments than predicted by steady state erosion and that is a consequence of soil destruction greater than production by relating this observation to the short time scales of weathering inferred for the andes a few ka it appears that the erosion regime has been recently perturbed resulting in high denudation rates a possible explanation would be the increase in precipitation less than 5 ka proposed by recent paleoclimatic studies our results indicate that erosion responds rapidly to high frequency climatic fluctuations

chemical multi isotopic li b sr u h o and thermal characterization of triassic formation waters from the paris basin this work reports chemical and isotope data and temperature estimates for seven water samples collected from triassic formations in the paris basin in france four samples were collected in the central part of the basin saline waters and three were collected at the edge of the basin near the recharge zone dilute waters the saline waters collected from the chaunoy and champotran boreholes have high salinities around 120 g l and very similar chemical and isotopic compositions the saline water sample from the la torche borehole has much higher salinity 168 g l and significantly different isotope characteristics the chemical geothermometers applied to these fluids from the centre of the basin give temperature values ranging between 80 and 100 c the fresh water samples collected at the edge of the basin have very different chemical and isotopic compositions these dilute water samples santenay and ch teauroux are shallow with colder temperatures of around 45 to 50 c the study of uranium activity ratios for these triassic formation waters allows us as a first approximation to estimate a mean apparent fluid circulation velocity of around 0 2 m yr which corresponds to a mean age slightly higher than 1 my for waters sampled in the chaunoy champotran and la torche fields in the centre of the basin the multi isotope characterization of triassic formation waters shows that our data are in agreement with literature values as concerns traditional isotope systematics delta18o deltad 87sr 86sr li and b isotope signatures in the centre of the paris basin are in a good agreement with a fluid signature derived mainly from water rock interactions involving clastic rocks with water essentially resulting from a seawater derived brine endmember diluted by meteoric waters the data reported in the present work for li and b isotopes could be used as a reference for future studies to characterize sandstone formation waters

modelling of contaminant migration in a chalk aquifer abstract a numerical model is formulated and used to investigate chloride migration in the chalk aquifer beneath effluent lagoons to the north of royston hertfordshire uk the aquifer is characterised as a dual porosity medium in which lateral advection and hydrodynamic dispersion are dominant in the fissure system whereas molecular diffusion is dominant in the chalk matrix the galerkin finite element method is used to solve the equations of flow and transport in the fissure system a recurrence relationship is found which permits the coupling to the fissure model of a truncated series approximation to the analytical solution for one dimensional diffusion in the surrounding porous matrix the combined model has been calibrated using data collected between 1975 and 1979 and predictive simulations have been performed for the period from 1979 to 1986 the results are compared with data collected in 1986 the model is found to produce acceptable estimates of the spread of the chloride plume the value of the model and the causes and potential implications of the observed model errors are discussed

large scale erosion rates from in situ produced cosmogenic nuclides in european river sediments abstract we have calculated long term erosion rates of 20 100 mm kyr from quartz contained 10be in the bedload of middle european rivers for catchments ranging from 102 to 105 km2 these rates average over 10 40 kyr and agree broadly with rock uplift incision and exhumation rates historic soil erosion rates and erosion rates calculated from the measured sediment loads of the same rivers moreover our new erosion rate estimates correlate well with lithology and relief however in the regen neckar loire and meuse catchments cosmogenic nuclide derived erosion rates are consistently 1 5 4 times greater than the equivalent rates derived from measured river loads this may be due to the systematic under representation of high magnitude low frequency transport events in the gauging records which cover less than a century alternatively the discrepancy may derive from spatially non uniform erosion and preferential tapping of deeper sections of the irradiation profile a third explanation relates the high cosmogenic nuclide derived erosion rates to inheritance of an elevated pleistocene erosion signal uncertainties associated with the cosmogenic nuclide derived erosion rate estimates are not greater than the potential errors in conventional estimates therefore the cosmogenic nuclide approach is an effective tool for rapid catchment wide assessment of time integrated rates of bedrock weathering and erosion and we anticipate its fruitful application to the quaternary sedimentary record

transport of radionuclides in an unconfined chalk aquifer inferred from u series disequilibria abstract u series disequilibria measured in waters and rocks from a chalk aquifer in france have been used as an analog for long term radionuclide migration drill core samples from a range of depths in the vadose zone and in the saturated zone as well as groundwater samples were analyzed for 238 u 234 u 232 th and 230 th to determine transport mechanisms at the water rock interface and to quantify parameters controlling the migration of radionuclides isotope measurements in rocks were done by tims whereas 234 u 238 u and 230 th 232 th activity ratios in water samples were measured by multi collector icp ms both depletion and enrichment in 234 u relative to 238 u were observed in carbonate rock samples resulting from chemical weathering in the unsaturated zone and calcite precipitation in the zone of water table oscillation respectively the correlation between 230 th 232 th activity ratios and 87 sr 86 sr ratios found in the chalk samples indicates that thorium is mainly contained in a minor silicate phase whose abundance is variable in chalk samples water samples are all characterized by 234 u 238 u 1 resulting from recoil effect of 234 th groundwaters are characterized by a more radiogenic signature in 87 sr 86 sr than the rocks moreover 230 th 232 th activity ratios in the waters are lower than in the rocks and increase with distance from the water divide which suggests that th transport is controlled by colloids formed during water infiltration in the soil a 1 d transport model has been developed in order to constrain the u series nuclide transport considering a transient behavior of radionuclides in the aquifer and a time dependent composition for the solid phase this model permits a prediction of the time scale of equilibration of the system and an estimation of parameters such as weathering rate distribution coefficients and recoil fractions retardation factors of 10 35 and from 1 10 4 to 2 10 5 were predicted for u and th respectively and can be used to predict the migration of radionuclides released as contaminants in the environment at the scale of our watershed 32 km 2 a characteristic migration time from recharge to riverine discharge of 200 600 yr for u and 0 2 3 7 myr for th was obtained

magnitudes and locations of the 1811 1812 new madrid missouri and the 1886 charleston south carolina earthquakes we estimate locations and moment magnitudes m and their uncertainties for the three largest events in the 1811 1812 sequence near new madrid missouri and for the 1 september 1886 event near charleston south carolina the intensity magnitude m i our preferred estimate of m is 7 6 for the 16 december 1811 event that occurred in the new madrid seismic zone nmsz on the bootheel lineament or on the blytheville seismic zone m i is 7 5 for the 23 january 1812 event for a location on the new madrid north zone of the nmsz and 7 8 for the 7 february 1812 event that occurred on the reelfoot blind thrust of the nmsz our preferred locations for these events are located on those nmsz segments preferred by johnston and schweig 1996 our estimates of m are 0 1 0 4 m units less than those of johnston 1996b and 0 3 0 5 m units greater than those of hough et al 2000 m i is 6 9 for the 1 september 1886 event for a location at the summerville middleton place cluster of recent small earthquakes located about 30 km northwest of charleston

the importance of colloids and mires for the transport of uranium isotopes through the kalix river watershed and baltic sea the importance of colloids and organic deposits for the transport of uranium isotopes from continental source regions and through the estuarine environment was investigated in the mire rich kalix river drainage basin in northern sweden and the baltic sea ultrafiltration techniques were used to separate uranium and other elements associated with colloids 10 kd and 3 kd from solute uranium and provided consistent results and high recovery rates for uranium as well as for other elements from large volume samples uranium concentrations in 0 45 m filtered kalix river water samples increased by a factor of 3 from near the headwaters in the caledonides to the river mouth while major cation concentrations were relatively constant 234 u 238 u ratios were high 234 u 770 1500 throughout the basin without showing any simple pattern and required a supply of 234 u rich water throughout the kalix river a large fraction 30 90 of the uranium is carried by 10 kd colloids which is compatible with uranium complexation with humic acids no isotopic differences were found between colloid associated and solute uranium within the baltic sea about half of the uranium is removed at low salinities the proportion that is lost is equivalent to that of river derived colloid bound uranium suggesting that while solute uranium behaves conservatively during estuarine mixing colloid bound uranium is lost due to rapid flocculation of colloidal material the association of uranium with colloids therefore may be an important parameter in determining uranium estuarine behavior mire peats in the kalix river highly concentrate uranium and are potentially a significant source of recoil 234 u to the mirewaters and river waters however mirewater data clearly demonstrate that only small 234 u 238 u shifts are generated relative to inflowing groundwater a simple box model of uranium accumulation in peat and transport through the mire that is compatible with the mire data demonstrates that with efficient removal of uranium from solution only small shifts in 234 u 238 u ratios can be generated in mirewater uranium the measurements and model calculations show that mirewaters are not the primary source of the uranium in the river bedrock groundwaters with high 234 u 238 u ratios and uranium concentrations must be the dominant source of riverine uranium

depositional cycles in a lower cretaceous limestone reservoir onshore abu dhabi u a e abstract the upper reservoir zone of the lower cretaceous kharaib formation 46 54 m thick in the studied wells is regarded as the upper portion of a third order depositional sequence comprising higher order cycles whereas the third order sequence interpretation is clearly supported by the upward shoaling trend of the reservoir zone relationships defining the component cycles have not previously been documented and are the focus of the present study core descriptions from four wells in a single oilfield reveal little evidence of facies changes or trends of facies patterns indicative of high frequency depositional cycles cycle boundaries could possibly be represented by the repetitive pattern of coarse beds rudstone and floatstone 0 1 2 m thick commonly having sharp basal contacts and gradational upper contacts with enclosing packstone to wackestone because the coarse beds do not appear correlative between wells however we prefer the alternative interpretation that they reflect episodic storm events which locally redistributed detritus sourced from a patchwork of low relief lithosomes across the flat surface of the epeiric kharaib platform lagoon although the existence of high order eustatic fluctuations during upper kharaib deposition is well established low amplitude variations in water depth may not have touched down on the sea floor to significantly affect sediment textures in contrast with the dominant storm signal reservoir sub zones used for production operations but previously suggested to be fourth order parasequence sets are defined by dips in porosity log profiles reflecting thin approximately 1 m intervals of increased stylolite frequency these boundaries are thus diagenetic in character but their correlation over tens to hundreds of kilometers indicates an underlying depositional control we suggest that the link between sea level and diagenesis is depositional clay content which facilitates stylolitic dissolution profiles of bulk rock alumina analyses in the studied cores show subtle indications of higher clay content at the sub zone tops much greater clay peaks mark the third order sequence boundaries resulting in the dense very low porosity zones above and below the studied reservoir zone and the increased stylolite frequency in the upper and lower several meters of the zone possible factors promoting clay influx across a carbonate shelf during falls in sea level include increased stream gradients and more humid climate

seismic activity of the san francisco bay region moment magnitude m with objective confidence level uncertainties are estimated for felt san francisco bay region earthquakes using bakun and went worth s 1997 analysis strategy for seismic intensity observations the frequency magnitude distribution is well described for m 5 5 events since 1850 by a gutenberg richter relation with a b value of 0 90 the seismic moment rate m yr since 1836 is 2 68 1018 n m yr 95 confidence range 1 29 1018 n m yr to 4 07 1018 n m yr the seismic moment rate since 1850 is nearly the same m yr in the 56 years before 1906 is about 10 times that in the 70 years after 1906 in contrast m yr since 1977 is about equal that in the 56 years before 1906 80 1 14 of the plate motion moment accumulation rate is available for release in earthquakes the historical m yr and the portion of the plate motion moment accumulation rate available for release in earthquakes are used in a seismic cycle model to estimate the rate of seismic activity in the twenty first century high and low rates of future seismic activity are both permissible given the range of possible seismic cycle recurrence times t and the uncertainties in the historical m and in the percentage of plate motion available for release in earthquakes if the historical seismic moment rate is not greater than the estimated 2 68 1018 n m yr and the percentage of the plate motion moment accumulation available for release in earthquakes is not less than the estimated 80 then for all t the rate of seismic moment release from now until the next 1906 sized shock will be comparable to the rate from 1836 to 1905 when m 6 1 2 shocks occurred every 15 to 20 years

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

seismicity of california s north coast at least three moment magnitude m 7 earthquakes occurred along california9s north coast in the second half of the nineteenth century the m 7 3 earthquake on 23 november 1873 occurred near the california oregon coast and likely was located on the cascadia subduction zone or within the north american plate the m 7 0 earthquake on 9 may 1878 was located about 75 km offshore near the mendocino fault the surface wave magnitude m s 7 0 earthquake on 16 april 1899 was located about 150 km offshore within the gorda plate there were at least three m 7 north coast earthquakes in the 35 years before 1906 two m 7 earthquakes in the 20 years after 1906 no m 7 earthquakes from 1923 until 1980 and four m 7 earthquakes since 1980 the relative seismic quiescence after 1906 for m 7 earthquakes along california9s north coast mimics the post 1906 seismic quiescence in the san francisco bay area for m 6 earthquakes the post 1906 relative quiescence did not extend to lower magnitudes in either area the 18 april 1906 earthquake apparently influenced the rate of occurrence of m 7 north coast earthquakes as it apparently influenced the rate of m 6 earthquakes in the san francisco bay area the relative seismic quiescence along the california north coast region after 1906 should be taken into account when evaluating seismic hazards in northwest california

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

a pulse in the planet regional control of high frequency changes in relative sea level by mantle convection abstract an explanation for high frequency cycles of sea level in non glacial times has remained elusive despite more than two centuries of research since lavoisier9s seminal observations were published in 1789 in the development of seismic stratigraphy in the 1970s putatively global high frequency changes in relative sea level vail third order cycles were attributed to an unknown eustatic mechanism prompting a search for mesozoic ice ages over the last decade a regional mechanism of sea level control has been developed from studies of the sedimentary record in high quality oil industry data these geological studies have supported the geophysical prediction that significant regional control of sea level is exercised by mantle induced vertical motions of the earth9s surface these vertical motions can occur over time intervals from several tens of million years to less than a million years with amplitudes of tens of metres or more even at the shorter intervals the vertical motions are not confined to regions with major hotspots there are two related controls of surface vertical motion evolution of mantle convection cells and pulsing flow within each cell the effects are evident in the sedimentary record of north atlantic basins mantle convection provides an alternative regional mechanism to eustatic control for explaining medium frequency to high frequency sea level cycles

natural radionuclide mobility and its influence on u th pb dating of secondary minerals from the unsaturated zone at yucca mountain nevada abstract extreme u and pb isotope variations produced by disequilibrium in decay chains of 238u and 232th are found in calcite opal chalcedony and mn oxides occurring as secondary mineral coatings in the unsaturated zone at yucca mountain nevada these very slowly growing minerals mm my 1 contain excess 206pb and 208pb formed from excesses of intermediate daughter isotopes and cannot be used as reliable 206pb 238u geochronometers the presence of excess intermediate daughter isotopes does not appreciably affect 207pb 235u ages of u enriched opal chalcedony which are interpreted as mineral formation ages opal and calcite from outer younger portions of coatings have 230th u ages from 94 6 3 7 to 361 3 9 8 ka and initial 234u 238u activity ratios ar from 4 351 0 070 to 7 02 0 12 which indicate 234u enrichment from percolating water present day 234u 238u ar is 1 in opal chalcedony from older portions of the coatings the 207pb 235u ages of opal chalcedony samples range from 0 1329 0 0080 to 9 10 0 21 ma increase with microstratigraphic depth and define slow long term average growth rates of about 1 2 2 0 mm my 1 in good agreement with previous results measured 234u 238u ar in mn oxides which pre date the oldest calcite and opal chalcedony range from 0 939 0 006 to 2 091 0 006 and are 1 in most samples the range of 87sr 86sr ratios 0 71156 0 71280 in mn oxides overlaps that in the late calcite these data indicate that mn oxides exchange u and sr with percolating water and cannot be used as a reliable dating tool in the u poor calcite samples measured 206pb 207pb ratios have a wide range do not correlate with ba concentration as would be expected if excess ra was present and reach a value of about 1400 the highest ever reported for natural pb calcite intergrown with opal contains excesses of both 206pb and 207pb derived from rn diffusion and from direct recoil from u rich opal calcite from coatings devoid of opal chalcedony contains 206pb and 208pb excesses but no appreciable 207pb excesses observed pb isotope anomalies in calcite are explained by rn produced excess pb the rn emanation may strongly affect 206pb 238u ages of slow growing u poor calcite but should be negligible for dating fast growing u enriched speleothem calcite

anomalous clastic wedge development during the sevier laramide transition north american cordilleran foreland basin usa new high resolution regional correlation and isopach maps provide evidence that 1 laramide style deformation began as early as ca 77 ma in central utah and 2 rapid 208 km m y 1 and extensive 400 km progradation of a clastic wedge was facilitated by reduced subsidence during the transition from sevier to laramide style deformation this study defi nes three campanian alluvialto marine clastic wedges that traversed 200 400 km eastward across the utah colorado segment of the cordilleran foreland basin wedges a and c are thicker successions with rising trajectory shoreline stacking patterns blackhawk formation and lower castlegate sandstone bluecastle tongue and rollins sandstone that refl ect relatively slow overall progradation 50 81 km m y 1 of narrow 10 20 km wide wave dominated shorelines in contrast wedge b consists of lower volume successions with a fl at to falling shoreline stacking pattern middle castlegate sandstone sego sandstone neslen formation corcoran and cozzette members of the iles formation that suggests rapid progradation 208 km m y 1 of embayed 60 80 km wide mixed energy wave and tide infl uenced shore lines wedges a and c prograded 200 250 km in more than 3 m y whereas wedge b prograded 340 400 km in 2 m y 170 km m y 1 the anomalously extensive wedge b is unique in the utah colorado segment because of its long extent rapid progradation rate dominance of tidally infl uenced facies long transit transgressions regressions and low accommodation nested sequence architecture stratigraphic relationships indicate development of wedge b coeval with both sevier and laramide style deformation in utah assuming a constant sediment supply the extensive 300 400 km sheet like amalgamated wedge wedge b may have been caused by 1 reduced subsidence driven by a fl exural interference pattern whereby two short wavelength 200 km fl exural profi les are superimposed during the uplift of both basement cored and thin skinned thrust belt 2 an increase in or eastward migration of dynamic subsidence during tectonic transitions associated with slab fl attening or rollback i e long wavelength fl exure or 3 reduced subsidence due to short wavelength fl exural interference augmented by the reduction or migration of long wavelength fl

234u 238u activity ratios in freshwaters as tracers of hydrological processes the strengbach watershed vosges france abstract 234u 238u and 87sr 86sr isotopic ratios as well as major and trace u ba sr rb element concentrations were analyzed in dissolved loads of the strengbach stream vosges france in order to constrain the sources of u isotopes 234u 238u to river waters the variations of the 234u 238u activity ratios along the stream indicate a clear dependence between the 234u 238u activity ratios of the surface waters and the different types of rocks forming the watershed with near equilibrium values for the waters draining granites and high 234u 238u disequilibria 1 4 for those flowing over carbonates the high 234u 238u disequilibria are related to a supply of 234u enriched groundwaters located within the carbonate rocks the 234u 238u activity ratios of the waters at the outlet of the catchment collecting the sources of the stream on the granitic lithology decrease from 1 02 to 0 96 when the discharge of the stream increases such a tendency requires mixing between a water body enriched in 234u which weathered the granitic bed rock at secular equilibrium and a water with a 234u 238u activity ratio below unity representing a mobilization of u from material that has already been weathered comparison of the geochemical characteristics of waters collected during the year and those collected during a flood event reveals the involvement of two different weathered end members depending on the hydrological conditions during the year the dissolved u transported by the river originates from bed rock and deep horizons of the weathering profile whereas a significant part of u during the flood event is supplied by superficial horizons of soils probably complexed by organic colloids these results outline the potential of 234u 238u activity ratios to investigate hydrological processes and emphasize that their use as tracers of rock weathering should be made cautiously

sequence analytical approach to the upper kimmeridgian lower tithonian storm dominated ramp deposits of the boulonnais northern france a landward time equivalent to offshore marine source rocks an interdisciplinary approach based on high resolution physical stratigraphy biostratigraphy organic matter analysis and clay mineralogy has been applied to the mixed siliciclastic carbonate kimmeridgian tithonian deposits of the boulonnais north western france these rocks are the age equivalents of some of the offshore marine source rocks of the north sea and were deposited in an overall storm dominated homoclinal ramp setting which may represent one of the most shore proximal sediments of this age cropping out in north western europe comparison with data from the yorkshire dorset lorraine and aquitaine areas allows the discrimination of three major transgressive regressive sediment packages with disconformities of interregional extent 1 from the baylei zone to top eudoxus zone 2 from the autissiodorensis zone to base scitulus zone 3 from the upper scitulus zone to the pectinatus zone the lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the eudoxus zone and the top of the autissiodorensis zone formed by high frequency relative sea level variations during the periods of maximum transgression of the platform the latter disconformity the p1 nodule bed reflects a major tectonically induced reorganization of the north west european intrashelf sedimentary basin characterized by a shift in both the location of the main depocentre and the sources of sediment production

uranium series disequilibrium in river sediments and waters the significance of anomalous activity ratios abstract samples of river water suspended and bottom sediments from the fenland catchment system draining into the wash u k have been analysed for the longer lived u th series radionuclides 238u 234u 230th and 232th the aim of this work was to assess the effects of open system phase transfer on the u series disequilibria observed in the river waters and sediments and to investigate the controls exerted on this phase transfer by the hydrological regime two important aspects of the u series radionuclide mobilisation in this modern river system have been observed 1 u series radionuclides are in a continuous state of flux between river sediments and river water and 2 u sorption on sediment particles is seasonably variable sequential extraction of whole sediments revealed that the u series isotopic characteristics of the ion exchangeable organic bound carbonate amorphous fe mn oxyhydroxides and crystalline fe mn oxides are controlled to a significant degree by the acquisition of u isotopes from the aqueous phase during summer when surface run off and river discharges are generally low the u isotope acquisition by sediment particles results in anomalously high234u 238u activity ratios 1 this is of importance for studies which rely upon the isotopic and elemental separation of u series radionuclides in the weathering system i e mass balance weathering rate and sediment yield assessments

the 16 may 1909 northern great plains earthquake abstract the largest historical earthquake in the northern great plains occurred on 16 may 1909 our analysis of intensity assignments places the earthquake location 48 81 n 105 38 w close to the montana saskatchewan border with an intensity magnitude m i of 5 3 5 4 observations from two seismic observatories in europe give an average m s value of 5 3 the 1909 earthquake is near an alignment of epicenters of small earthquakes in montana and saskatchewan and on strike with the mapped hinsdale fault in montana thus the 1909 earthquake may have occurred on a 300 km long seismically active fault which could have seismic hazard implications for the region particularly for the hydraulically emplaced earth filled fort peck dam constructed in the 1930s on the missouri river in northeast montana

simulation of earthquake ground motions in the eastern united states using deterministic physics based and site based stochastic approaches abstract earthquake ground motion recordings are scarce in the central and eastern united states ceus for large magnitude events and at close distances we use two different simulation approaches a deterministic physics based method and a site based stochastic method to simulate ground motions over a wide range of magnitudes drawing on previous results for the modeling of recordings from the 2011 m w 5 8 mineral virginia earthquake and using the 2001 m w 7 6 bhuj india earthquake as a tectonic analog for a large magnitude ceus event we are able to calibrate the two simulation methods over this magnitude range both models show a good fit to the mineral and bhuj observations from 0 1 to 10 hz model parameters are then adjusted to obtain simulations for m w 6 5 7 0 and 7 6 events in the ceus our simulations are compared with the 2014 u s geological survey weighted combination of existing ground motion prediction equations in the ceus the physics based simulations show comparable response spectral amplitudes and a fairly similar attenuation with distance the site based stochastic simulations suggest a slightly faster attenuation of the response spectral amplitudes with distance for larger magnitude events and as a result slightly lower amplitudes at distances greater than 200 km both models are plausible alternatives and given the few available data points in the ceus can be used to represent the epistemic uncertainty in modeling of postulated ceus large magnitude events

a new method for u th pa ra separation and accurate measurement of 234u 230th 231pa 226ra disequilibria in volcanic rocks by mc icpms abstract a new method for the chemical separation and mc icpms measurements of u th pa ra disequilibria in volcanic samples from a single sample aliquot is presented the accuracy and precision of our techniques is assessed by replicate analyses of the synthetic u and th isotope standards irmm 184 and irmm 35 and the secular equilibrium rock standards bcr 2 w 2a and tml a measure of true sample reproducibility including the errors related to sample processing and the chemical separation is obtained from analysis of multiple digestions of the rock standards 234u 238u 230th 238u 231pa 235u and 226ra 230th activity ratios on ten separate dissolutions of usgs rock standard bcr 2 for example reproduce to 0 4 1 4 1 1 and 2 4 2 sd respectively all elements u th pa ra are separated from a single spiked sample aliquot and the elemental concentrations are measured on the same solutions as the isotopic compositions analytical artefacts from determination of elemental and isotopic concentrations on different sample aliquots due to sample heterogeneity are therefore avoided in addition our new chemical separation protocol is time efficient and allows for rapid processing of volcanic samples with less than 25 fg of pa and ra

the sequence of moderate size earthquakes at the junction of the ligurian basin and the corsica margin western mediterranean the initiation of an active deformation zone revealed a new seismically active zone is found in the southern part of the ligurian basin 80 km west of corsica western mediterranean the activity began in february 2011 with a foreshock ml 4 and a mainshock ml 5 3 5 days later followed by numerous aftershocks we first analyze the fore and mainshock in detail we compare the results obtained using classical methods linear location in a 1d medium and focal mechanisms from p and s polarities and new approaches non linear location in a 3d medium and waveform modeling for determining the seismic moment and the focal mechanism both methods provided similar results for location depth in the range of 6 13 km and focal mechanisms which reveal reverse faulting with nodal planes oriented n s and ne sw we then locate 27 of the aftershocks in the 3d model and find a 10 km long ne sw alignment with a depth between 7 and 16 km in 2012 and 2013 three other moderate size events ml 3 8 4 and 4 5 occurred and confirm that this zone is still active the epicentral area is located in the oceanic domain of the ligurian basin from analysis of the bathymetry and high resolution multi channel seismic profiles no morphologic anomaly at surface and no inherited fault in the shallow 4 km depth were imaged which suggest that no significant deformation occurred in the area since 5 ma thus the structure s activated during the 2011 2013 sequence remain unknown in light of these results we point out a notable difference on both sides of the ligurian basin the northern margin close to the alpine chain suffered strong earthquakes and large cumulated deformation since 5 ma while the southern margin close to the corsica sardinia continental block is poorly deformed since 5 ma

relative sea level change and carbon isotopes data from the upper jurassic oxfordian of central and southern europe studies on cretaceous pelagic limestones have shown a close correspondence between putative sea level curves and the carbon isotope profile suggesting a possible relationship between the two phenomena such a relationship could relate to shelf sea area governing the global burial rate of organic carbon which in turn controls the 13c 12c ratio of dissolved inorganic carbon in the oceanic reservoir in order to see whether or not this relationship might be of more general applicability the major mid oxfordian jurassic transgression is documented to zonal level and appropriate carbon isotope data are presented although the applicability of ammonite zonation to the mid oxfordian is problematic on a regional scale a clear 13c excursion is present in the trunsversariurn zone which is coincident with regional overstep and or evidence of shoreline retreat and or evidence of bathymetric deepening in europe and elsewhere the use of the carbon isotope curve as a proxy for shelf sea area or relative sea level is worthy of further exploration

eustatic curve for the middle jurassic cretaceous based on russian platform and siberian stratigraphy zonal resolution we have used the stratigraphy of the central part of the russian platform and surrounding regions to construct a calibrated eustatic curve for the bajocian through the santonian the study area is centrally located in the large eurasian continental craton and was covered by shallow seas during much of the jurassic and cretaceous the geographic setting was a very low gradient ramp that was repeatedly flooded and exposed analysis of stratal geometry of the region suggests tectonic stability throughout most of mesozoic marine deposition the paleogeography of the region led to extremely low rates of sediment influx as a result accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations the central part of the russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the jurassic and cretaceous the biostratigraphy of the russian platform provides the basis for reliably determining age and eustatic events the mesozoic section of the central part of the russian platform is characterized by numerous hiatuses in this study we filled the sediment gaps left by unconformities in the central part of the russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions such as northern siberia although these sections reflect subsidence the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled so the subsidence rate can be calculated and filtered from the stratigraphic data we thus have compiled a more complete eustatic curve than would be p ssible on the basis of russian platform stratigraphy alone relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the russian platform for determining paleowater depth we developed a model specifically designed for this region based on paleoecology sedimentology geochemistry and paleogeography the curve describes a series of high frequency eustatic events superimposed on longer term trends many of the events identified from our study can be correlated to those found by haq et al 1988 and other sea level studies from other parts of the world but there are significant differences in the relative magnitudes of events because the eustatic curve resulting from this study is based on a stable reference frame the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins basins and other active regions

strong ground motion inferred from liquefaction caused by the 1811 1812 new madrid missouri earthquakes peak ground accelerations pgas in the epicentral region of the 1811 1812 new madrid missouri earthquakes are inferred from liquefaction to have been no greater than 0 35 g pga is inferred in an 11 380 km2 area in the lower mississippi valley in arkansas and missouri where liquefaction was extensive in 1811 1812 pga was inferred by applying liquefaction probability curves which were originally developed for liquefaction hazard mapping to detailed maps of liquefaction by obermeier 1989 the low pga is inferred because both a shallow 1 5 m deep water table and a large moment magnitude m 7 7 earthquake were assumed in the analysis if a deep 5 0 m water table and a small magnitude m 6 8 earthquake are assumed the maximum inferred pga is 1 10 g both inferred pga values are based on an assumed and poorly constrained correction for sand aging if an aging correction is not assumed then the inferred pga is no greater than 0 22 g a low pga value may be explained by nonlinear site response soils in the study area have an average v s 30 of 220 15 m s a low inferred pga is consistent with pga values estimated from ground motion prediction equations that have been proposed for the new madrid seismic zone when these estimates are corrected for nonlinear soil site effects this application of liquefaction probability curves demonstrates their potential usefulness in paleoseismology

on the modified mercalli intensities and magnitudes of the 1811 1812 new madrid earthquakes we reexamine original felt reports from the 1811 1812 new madrid earthquakes and determine revised isoseismal maps for the three principal mainshocks in many cases we interpret lower values than those assigned by earlier studies in some cases the revisions result from an interpretation of original felt reports with an appreciation for site response issues additionally earlier studies had assigned modified mercalli intensity mmi values of v vii to a substantial number of reports that we conclude do not describe damage commensurate with intensities this high we investigate several approaches to contouring the mmi values using both analytical and subjective methods for the first mainshock on 02 15 lt december 16 1811 our preferred contouring yields m 7 2 7 3 using the area moment regressions of johnston 1996 for the 08 00 lt on january 23 1812 and 03 45 lt on february 7 1812 mainshocks we obtain m 7 0 and m 7 4 7 5 respectively our magnitude for the february mainshock is consistent with the established geometry of the reelfoot fault which all evidence suggests to have been the causative structure for this event we note that the inference of lower magnitudes for the new madrid events implies that site response plays a significant role in controlling seismic hazard at alluvial sites in the central and eastern united states we also note that our results suggest that thrusting may have been the dominant mechanism of faulting associated with the 1811 1812 sequence

evaluation of pleistocene groundwater flow through fractured tuffs using a u series disequilibrium approach pahute mesa nevada usa abstract groundwater flow through fractured felsic tuffs and lavas at the nevada national security site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at pahute mesa to help evaluate fracture flow and matrix water exchange we have determined u series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces breccia zones and interiors of unfractured core the u series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium series decay chain due to preferential mobilization of 234 u relative to 238 u and u relative to th samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays silica fe mn oxyhydroxides and zeolite intact core interiors and breccia fragments were sampled in bulk in addition profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture matrix water exchange samples of rock matrix have 234 u 238 u and 230 th 238 u activity ratios ar closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix greater u mobility was observed in welded tuff matrix with elevated porosity and in zeolitized bedded tuff samples of brecciated core were also in secular equilibrium implying a lack of long range hydraulic connectivity in these cases samples of discrete fracture surfaces typically but not always were in radioactive disequilibrium many fractures had isotopic compositions plotting near the 230 th 234 u 1 1 line indicating a steady state balance between u input and removal along with radioactive decay numerical simulations of u series isotope evolution indicate that 0 5 to 1 million years are required to reach steady state compositions once attained disequilibrium 234 u 238 u and 230 th 238 u ar values can be maintained indefinitely as long as hydrological and geochemical processes remain stable therefore many pahute mesa fractures represent stable hydrologic pathways over million year timescales a smaller number of samples have non steady state compositions indicating transient conditions in the last several hundred thousand years in these cases u mobility is dominated by overall gains rather than losses of u

mobility of u series nuclides during basalt weathering an example from the deccan traps india abstract u series disequilibria have been measured by tims and mc icp ms in dissolved phases and suspended sediments of the main basaltic rivers from the deccan trap region india for dissolved phases 234u 238u 230th 238u and 226ra 238u range between 1 11 and 1 28 between 0 03 10 2 and 1 35 10 2 and between 0 02 and 0 16 respectively for suspended particles 234u 238u 230th 238u and 226ra 238u range from 0 95 to 1 1 from 1 23 to 1 59 and from 0 1 to 0 47 respectively 230th 238u and 234u 238u systems show direct links with indices of weathering the data also indicate possible redistributions between the solid and aqueous phases and indicate that erosion processes do not presently operate at steady state because present day physical erosion rates are higher than expected 100 400 mm ka versus 40 mm ka for a steady state process for the narmada and the tapti basins models assuming either discrete or continuous particle leaching yield timescales for chemical erosion of 40 90 ka in contrast with basins located in northern latitudes erosion in the deccan basins does not appear to have been significantly disturbed during the last glaciation 234u 238u disequilibria in the dissolved phase of large rivers world wide are also explored and two key factors are highlighted in this study the dissolution of carbonates releasing dissolved u at secular equilibrium and the silicate weathering rate estimated at the scale of the watershed in particular a positive correlation is found between dissolved 234u 238u and basaltic weathering rates for the deccan that could reflect a key role of physical erosion since for silicate monolithological basins chemical erosion rates are primarily controlled by physical erosion rates for basins with mixed lithology dissolved organic matter also plays a key role in the preferential release of 234u from silicate minerals 234u 238u ratios in rivers therefore reflect a mixture between u released by carbonate dissolution and 234u preferentially released from silicate minerals located in high physical erosion and peat areas

deaggregation of probabilistic ground motions in the central and eastern united states abstract probabilistic seismic hazard analysis psha is a technique for estimating the annual rate of exceedance of a specified ground motion at a site due to known and suspected earthquake sources the relative contributions of the various sources to the total seismic hazard are determined as a function of their occurrence rates and their ground motion potential the separation of the exceedance contributions into bins whose base dimensions are magnitude and distance is called deaggregation we have deaggregated the hazard analyses for the new usgs national probabilistic ground motion hazard maps frankel et al 1996 for points on a 0 2 grid in the central and eastern united states ceus we show color maps of the geographical variation of mean and modal magnitudes m m and distances d d for ground motions having a 2 chance of exceedance in 50 years these maps are displayed for peak horizontal acceleration and for spectral response accelerations of 0 2 0 3 and 1 0 sec we tabulate m d m and d for 49 ceus cities for 0 2 and 1 0 sec response thus these maps and tables are psha derived estimates of the potential earthquakes that dominate seismic hazard at short and intermediate periods in the ceus the contribution to hazard of the new madrid and charleston sources dominates over much of the ceus for 0 2 sec response over 40 of the area for 1 0 sec response over 80 of the area for 0 2 sec response d ranges from 20 to 200 km for 1 0 sec 30 to 600 km for sites influenced by new madrid or charleston d is less than the distance to these sources and m is less than the characteristic magnitude of these sources because averaging takes into account the effect of smaller magnitude and closer sources on the other hand d is directly the distance to new madrid or charleston and m for 0 2 and 1 0 sec response corresponds to the dominating source over much of the ceus for some cities in the north atlantic states short period seismic hazard is apt to be controlled by local seismicity whereas intermediate period 1 0 sec hazard is commonly controlled by regional seismicity such as that of the charlevoix seismic zone

a study of uranium and thorium series isotopes in chalk groundwaters of lincolnshire u k a groundwater investigation is described in which uranium and thorium series radionuclides are applied to the study of the hydrogeologically well documented lincolnshire chalk aquifer system of north lincolnshire england the dominance of eh in controlling the uranium content of groundwaters is discussed and the 230th234u activity ratio used as an indicator of the speciation of uranium in highly reduced waters the 230th234u activity ratio approaches unity suggesting that the uranium in solution is behaving similarly to thorium in the 4 valence state in the oxidised environment the higher uranium content groundwaters exhibit lower 234u238u activity ratios a model of mixing young low 234u238u activity ratio fissure waters with old high 234u238u activity ratio pore waters is discussed but rejected it is considered that preferential dissolution of 234u in the lower rate weathering regimes produces the observed relationship between uranium content and activity ratio a method of in situ rn random release factor determination is suggested however the calculated values for rn are disproportionately high for a fissure flow system this along with evidence of a radium depleted aquifer matrix indicates that radium is being mobilised and transported from the pore water system to the fissure system and subsequently adsorbed by clay minerals lining the chalk fissures

the behavior of u and th series nuclides in groundwater groundwater has long been an active area of research driven by its importance both as a societal resource and as a component in the global hydrological cycle key issues in groundwater research include inferring rates of transport of chemical constituents determining the ages of groundwater and tracing water masses using chemical fingerprints while information on the trace elements pertinent to these topics can be obtained from aquifer tests using experimentally introduced tracers and from laboratory experiments on aquifer materials these studies are necessarily limited in time and space regional studies of aquifers can focus on greater scales and time periods but must contend with greater complexities and variations in this regard the isotopic systematics of the naturally occurring radionuclides in the u and th decay series have been invaluable in investigating aquifer behavior of u th and ra these nuclides are present in all groundwaters and are each represented by several isotopes with very different half lives so that processes occurring over a range of time scales can be studied table 1 within the host aquifer minerals the radionuclides in each decay series are generally expected to be in secular equilibrium and so have equal activities see bourdon et al 2003 in contrast these nuclides exhibit strong relative fractionations within the surrounding groundwaters that reflect contrasting behavior during release into the water and during interaction with the surrounding host aquifer rocks radionuclide data can be used within the framework of models of the processes involved to obtain quantitative assessments of radionuclide release from aquifer rocks and groundwater migration rates the isotopic variations that are generated also have the potential for providing fingerprints for groundwaters from specific aquifer environments and have even been explored as a means for calculating groundwater ages view this table table 1 radionuclides important in groundwater studies the highly fractionated nature of the

seismic moment assessment of earthquakes in stable continental regions iii new madrid 1811 1812 charleston 1886 and lisbon 1755 summary the sizes of three major or great historical earthquakes are reassessed using the isoseismal area regression tools developed in parts i and ii of this study of stable continental region scr seismicity the earthquakes are 1811 new madrid central united states and its following sequence 1886 charleston coastal south carolina and 1755 lisbon oceanic intraplate off the continental shelf of portugal the analysis confirms the large size of these events and for the first time places constraints on the uncertainty of their seismic moment release because of the exceptionally low seismic wave attenuation of eastern north america ena a separate north american regression of seismic moment on isoseismal area was developed additionally the unknown western extents of the new madrid isoseismal areas were calibrated with the patterns of the m 6 3 6 6 1843 and 1895 earthquakes application of part ii analysis procedures with these corrections yields new madrid size estimates expressed as moment magnitude of m 8 1 0 31 for the 1811 december 16 m 7 8 0 33 for the 1812 january 23 and m 8 0 0 33 for the 1812 february 7 principal events the charleston earthquake s magnitude decreases from m 7 4 to m 7 3 0 26 after compensation for the effect of coastal plain sediments on its inner isoseismals intensity regressions for lisbon are calibrated against the isoseismal pattern of the nearly co located m 7 8 1969 st vincent earthquake which in this case increases the predicted size of lisbon from m 8 4 to m 8 7 0 39 these size estimates are supported by data from independent phenomena extent and severity of liquefaction the maximum distance of induced landslides and for lisbon tsunami wave amplitudes estimated source parameters are controlled by crustal or lithospheric temperature which governs the depth extent of brittle faulting using estimated continental and oceanic geotherms viable fault lengths are 30 80 km for charleston 120 180 km for 1811 new madrid and 180 280 km for lisbon for average displacements of 2 4 m 8 11 m and 10 14 m respectively and for average static stress and strain drops at the estimated seismic moments of this study the 1811 new madrid and the 1755 lisbon events are respectively the largest known scr and oceanic lithosphere earthquakes

estimating locations and magnitudes of earthquakes in eastern north america from modified mercalli intensities we use 28 calibration events 3 7 m 7 3 from texas to the grand banks newfoundland to develop a modified mercalli intensity mmi model and associated site corrections for estimating source parameters of historical earthquakes in eastern north america the model batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathrm mmi 1 41 1 68 times mathbf m 0 00345 times delta 2 08 mathrm log delta end document where is the distance in kilometers from the epicenter and m is moment magnitude provides unbiased estimates of m and its uncertainty and if site corrections are used of source location the model can be used for the analysis of historical earthquakes with only a few mmi assignments we use this model mmi site corrections and bakun and wentworth s 1997 technique to estimate m and the epicenter for three important historical earthquakes the intensity magnitude m i is 6 1 for the 18 november 1755 earthquake near cape ann massachusetts 6 0 for the 5 january 1843 earthquake near marked tree arkansas and 6 0 for the 31 october 1895 earthquake the 1895 event probably occurred in southern illinois about 100 km north of the site of significant ground failure effects near charleston missouri manuscript received 14 march 2002

three dimensional flow and trace metal mobility in shallow chalk groundwater dorset united kingdom abstract the three dimensional groundwater flow and the hydrogeochemical regime have been determined in the bere stream valley north dorset downs southern england the dual porosity characteristics of the portsdown chalk have been established using geophysical and hydrochemical borehole logging chemical properties have been established using major and trace element analyses of depth samples and groundwaters the study site is located at the unconfined confined boundary of the chalk aquifer where it is overflowing in the observation boreholes the chalk dips locally at about 5 m km to the south east under palaeogene confining beds and three distinctive flow horizons may be recognised the chalk groundwater is of ca hco 3 type and three separate geochemical groundwater zones were also determined with depth having different oxygen levels and trace element characteristics 1 a shallow o 2 rich zone with around 80 dissolved o 2 and low trace element concentrations 2 a mixing and transition zone with significant concentrations of trace elements and high trace metal concentrations at its base manganese 29 g l nickel 55 g l cadmium 146 g l and zinc 214 g l 3 a deeper zone with depleted oxygen 5 20 dissolved o 2 and with longer water residence times shown by higher mg ca and k na ratios as well as higher sr and f the groundwater geochemistry in the chalk aquifer is dominated by incongruent reactions with the fine grained carbonate sediments which release trace element impurities to the water some of the metals are co precipitated with mn and fe oxide phases on fissure surfaces whilst producing a purer calcite during subsequent recrystallisation to purer iron and manganese oxides on fissure surfaces under specific geochemical and hydrodynamic conditions trace metals are released into the fissure water the results demonstrate the need to monitor quality stratification and the changes in the groundwater baseline chemistry in areas close to the redox boundary which in the dual porosity chalk is likely to be a diffuse zone with exchange between oxygen poor matrix waters and more oxic water flowing through the fissures

modelling the baseline geochemistry of groundwater in a chalk aquifer considering solid solutions for carbonate phases the chalk aquifer of champagne france baseline geochemistry has been determined using a solid solution approach for the modelling of calcite dissolution the water rock interactions are modelled by the speciation code chess from field data and ca mg and sr aqueous concentrations in groundwater the stoichiometries of solid solutions are defined in each stratigraphic unit of the chalk aquifer from bulk geochemistry and chalk mineralogy of samples taken from boreholes the initial mineralisation of water at the bottom of the unsaturated zone and the characterisation of the theoretical evolution of groundwater chemistry along the flow lines associated with incongruent calcite dissolution are calculated from this approach

weathering rates from top to bottom in a carbonate environment abstract this study investigates u series sr isotopes major and trace elements in a chalk aquifer system located in eastern france soil and rock samples were collected along depth profiles down to 45 m in four localities as an attempt to investigate the weathering processes in the soil the unsaturated zone and the saturated zone of the aquifer interstitial water was extracted from soils and rocks by a centrifugation technique u series offer a powerful tool to calculate weathering rates because the relative mobility of the u and th isotopes can be precisely measured and it does not require the determination of a reference state as in other approaches as expected the data show very large mobile element depletion in the soil with large 230 th excess relative to 238 u while the rocks show more limited but not insignificant mobile element depletion the u series data have been used to constrain weathering rates based on a 1 d reactive transport model weathering rates in the near surface are about 10 100 times faster than at depth however when integrated over the depth of the cores including the unsaturated and the saturated zones this underground weathering represents more than 30 of the total weathering flux assuming congruent dissolution of carbonates the 234 u 238 u ratios in interstitial water are consistent with solid samples showing 234 u depletion near the surface and an excess 234 u at depth a leaching experiment performed on chalk shows that the excess 234 u in natural waters percolating through carbonate rocks results both from preferential 234 u leaching and direct recoil in the interstitial water a new approach was used to derive the recoil ejection factor based on bet measurements and the fractal dimension of chalk surface consideration of preferential leaching and recoil allows a more accurate modeling of weathering rates

residence time of chalk groundwaters in the paris basin and the north german basin a geochemical approach the comparative geochemical and isotopic study of confined and unconfined chalk groundwaters of the paris basin and the n german basin proves a significant chemical evolution during groundwater flow from the recharge zones to the deep confined aquifer different time dependent geochemical parameters have been tested as dating tools cation ratios sr2 ca2 mg2 ca2 n no 3 noble gas contents as paleotemperature indicators ne ar kr xe radiogenic he 13c 14c 18o 2h 3h cation ratios and 13c show the importance of incongruent dissolution processes in the chalk aquifer water rock interactions were taken into account in a multi step dissolution model to determine radiocarbon groundwater ages the oldest waters in the confined part of the paris basin chalk with maximum 14c ages of 14 000 a b p contain pleistocene recharge components as can be shown by a stable isotope depletion and noble gas temperatures significantly lower than in recent groundwaters chalk waters at the lagerdorf site in northern germany show a distinct stratification with respect to residence times and hydrochemistry

seasonal progression of uranium series isotopes in subglacial meltwater implications for subglacial storage time abstract the residence time of subglacial meltwater impacts aquifer recharge nutrient production and chemical signals that reflect underlying bedrock substrate but is inaccessible to direct observation here we report the seasonal evolution of subglacial meltwater chemistry from the 2011 melt season at the terminus of the athabasca glacier canada we measured major and trace analytes and u series isotopes for twenty nine bulk meltwater samples collected over the duration of the melt season this dataset which is the longest time series record of 234 u 238 u isotopes in a glacial meltwater system provides insight into the hydrologic evolution of the subglacial system during active melting meltwater samples measured from the outflow were analyzed for 238 u 222 rn and 234 u 238 u activity conductivity alkalinity ph and major cations subglacial meltwater varied in 238 u and 222 rn from 23 to 832 ppt and 9 to 171 pci l respectively activity ratios of 234 u 238 u ranged from 1 003 to 1 040 with the highest 238 u 222 rn and 234 u 238 u activity values occurring in early may when delayed flow basal meltwater composed a significant portion of the bulk melt from the chemical evolution of the meltwater we posit that the relative subglacial water residence times decrease over the course of the melt season this decrease in qualitative residence time during active melt is consistent with prior field studies and model predicted channel switching from a delayed distributed network to a fast channelized network flow as such our study provides support for linking u series isotopes to storage lengths of meltwater beneath glacial systems as subglacial hydrologic networks evolve with increased melting and channel network efficiency

erosion timescales derived from u decay series measurements in rivers the relative importance of the factors influencing weathering of continental rocks has been a topic of debate for the last few decades the principal reasons are the lack of reliable proxies for chemical weathering and the difficulty in constraining actual physical denudation rates in this study 234u 238u 230th 238u and 226ra 238u were measured by tims and by mc icp ms in the dissolved and suspended loads of rivers from the mackenzie basin northwest territories canada the data show a complementary nature between 234u 238u 230th 238u in the dissolved and suspended loads while 226ra is characterized by a more complex behavior modeling of fractionation of u series nuclides in the particulate matter and the corresponding dissolved phase permits us to constrain the duration of chemical erosion for the suspended load currently sampled in the watershed 9 28 10 ka as well as the rates of release of u series nuclides the results also imply significant recent changes of chemical erosion rates and underline the impact of the last glaciation on current continental fluxes of northern latitude rivers such as the mackenzie river

comment on athabasca valles mars a lava draped channel system jaeger et al reports 21 september 2007 p 1709 presented images of the athabasca valles channel system on mars and asserted that the observed deposits are composed of thin fluid lavas however all the features they described are secondary and postdate the surface by many millions of years as documented by structural relationships with small young impact craters

introduction to u series geochemistry during the last century the earth sciences underwent two major revolutions in understanding the first was the recognition of the great antiquity of the earth and the second was the development of plate tectonic theory these leaps in knowledge moved geology from its largely descriptive origins and established the modern quantitative earth sciences for any science and particularly for the earth sciences time scales are of central importance until recently however the study of time scales in the earth sciences was largely restricted to the unraveling of the ancient history of our planet for several decades earth scientists have used a variety of isotope chronometers to unravel the long term evolution of the planet a fuller understanding of the physical and chemical processes driving this evolution often remained elusive because such processes occur on time scales 1 105 years which are simply not resolvable by most conventional chronometers the u series isotopes however do provide tools with sufficient time resolution to study these earth processes during the last decade the earth sciences have become increasingly focused on fundamental processes and u series geochemistry has witnessed a renaissance with widespread application in disciplines as diverse as modern oceanography and igneous petrology the uranium and thorium decay series contain radioactive isotopes of many elements in particular u th pa ra and rn the varied geochemical properties of these elements cause nuclides within the chain to be fractionated in different geological environments while the varied half lives of the nuclides allows investigation of processes occurring on time scales from days to 105 years u series measurements have therefore revolutionized the earth sciences by offering some of the only quantitative constraints on time scales applicable to the physical processes that take place on the earth the application of u series geochemistry to the earth sciences was thoroughly summarized in 1982

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

major earthquakes recorded by speleothems in midwestern u s caves historic earthquakes generated by the new madrid seismic zone represent some of the largest recorded in the united states yet prehistoric events are recognized only through deformation in late wisconsin to holocene age near surface sediments liquefaction monoclinal folding and changes in river meanders in this article we show that speleothems in caves of southwestern illinois and southeastern missouri may constitute a previously unrecognized recorder of large earthquakes in the u s midcontinent region the timing of the initiation and regrowth of stalagmites in southwestern illinois and southeastern missouri caves is consistent with the historic and prehistoric record of several known seismic events in the u s midcontinent region we conclude that dating the initiation of original stalagmite growth and later postearthquake rejuvenation constitutes a new paleoseismic method that has the potential for being applied to any region around the world in the vicinity of major seismic zones where caves exist use of this technique could expand the geographical distribution of paleoseimic data document prehistoric earthquakes and help improve interpretations of paleoearthquakes

in situ radionuclide transport and preferential groundwater flows at ineel idaho decay series disequilibrium studies uranium and thorium decay series disequilibria in groundwater occur as a result of water rock interactions and they provide site specific natural analog information for assessment of in situ long term migration of radionuclides in the far field of a nuclear waste disposal site in this study a mass balance model was used to relate the decay series radionuclide distributions among solution sorbed and solid phases in an aquifer system to processes of water transport sorption desorption dissolution precipitation radioactive ingrowth decay and recoil isotopes of u 238u 234u th 232th 230th 228th 234th ra 226ra 228ra 224ra and rn 222rn were measured in 23 groundwater samples collected from a basaltic aquifer at the idaho national engineering and environmental laboratory ineel idaho the results show that groundwater activities of th and ra isotopes are 2 4 orders lower than those of their u progenitors which average 1 35 0 40 dpm 238u l with 234u 238u ratios of 1 6 3 0 222rn activities range from 20 to 500 dpm l modeling of the observed disequilibria places the following constraints on the time scale of radionuclide migration and water rock interaction at ineel 1 time for sorption is minutes for ra and th time for desorption is days for ra and years for th and time for precipitation is days for th years for ra and centuries for u 2 retardation factors due to sorption average 106 for 232th 104 for 226ra and 103 for 238u 3 dissolution rates of rocks are 70 to 800 mg l y 4 ages of groundwater range from 10 to 100 years contours of groundwater age as well as spatial patterns of radionuclide disequilibria delineate two north south preferential flow pathways and two stagnated locales relatively high rates of dissolution and precipitation and recoil of 222rn occur near the groundwater recharging sites as well as in the major flow pathways decay of the sorbed parent radionuclides e g 226ra and 228ra on micro fracture surfaces constitutes an important source of their daughter 222rn and 228th activities in groundwater

controls on stable isotope profiles in the chalk aquifer of north east norfolk uk with special reference to dissolved sulphate groundwater samples were collected at a site in n norfolk uk comprising a borehole penetrating upper chalk and piezometers open within the overlyinf glacial deposits and intervening weathered putty chalk the samples were analyzed for 18o water 34s and 18o so4 and 13c hco3 as well as major ions variations in solute concentration and isotopic composition with depth were found to be caused by limited groundwater circulation at the site and incomplete flushing of old groundwater the isotopic data prove the existence of a mineralized palaeowater at depth which has undergone so4 reduction and is being slowly modified by mixing with recent groundwater circulating at a shallow depth in a more transmissive chalk horizon one measured 18o h2o value of 8 25 vsmow represents the lightest value reported for the norfolk chalk aquifer and is evidence for a component of late pleistocene recharge trapped at depth the wide range of observed isotope ratios at the site e g 34s and 18o so4 between 7 8 to 27 8 cdt and 5 2 to 20 0 ovsmow respectively demonstrates the importance of vertical stratification of solutes and the implications this has for interpreting spatial hydrochemical surveys of groundwater

chemical weathering in the drainage basin of a tropical watershed nsimi zoetele site cameroon comparison between organic poor and organic rich waters abstract this study deals with the weathering processes operating at the scale of a small catchment nsimi zoetele cameroon and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters samples of river spring and groundwaters from nsimi zoetele were filtered through membranes of decreasing pore size 0 22 m 0 025 m or 300 000 da 5000 da to separate colloidal fractions from the truly dissolved one major and trace elements and dissolved organic carbon doc were analysed in each fraction two kinds of waters can be distinguished in the catchment clear and coloured waters clear waters exhibit low concentrations of major and trace elements and doc elements are carried in these solutions in a true dissolved form except al and rare earth elements rees by contrast the higher abundances of al fe and trace elements in coloured waters are controlled by the colloidal fraction thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi hydroxide which are major minerals in the weathered soil for coloured waters the aqueous speciation of ca mg cu fe al la and th was calculated taking into account the complexes with humic acids speciation calculations for cu fe al la th show a strong complexation with humic acids in good agreement with the results of the filtration experiments by contrast although filtration experiments show a strong control of major cations by organic matter for example 75 for ca speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements this discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure finally both filtration experiments and speciation calculations show that organic matter plays an important role in natural doc rich waters organic acids increase significantly the dissolution rates of silicates and oxi hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment

an evaluation of paired δ18o and 234u 238u 0 in opal as a tool for paleoclimate reconstruction in semi arid environments abstract authigenic opal deposits are widespread in semi arid and arid environments and often contain high uranium concentrations that facilitate high precision dating by u series and u pb geochronology however despite their ubiquity and utility for placing temporal constraints on surficial processes the potential for authigenic opal deposits to be used as archives of past climate variability remains largely unexplored compared with more frequently used authigenic carbonate deposits here we investigate the potential for authigenic opal deposits to provide records of paleoclimate and paleohydrologic variability through the development of a combined record of uranium 234 u 238 u 0 and oxygen 18 o isotope variability using in situ ion microprobe methods on opal deposits from pinnacles national park california that precipitated from approximately 16 to 3 ka pinnacles opal 234 u 238 u 0 suggests a moderate decrease in net infiltration from the early to middle holocene coincident with the timing of increasing aridity inferred from sierra nevada lake records while pinnacles opal 18 o indicates a relative increase in subtropical storms at the same time a shift to more north pacific sourced storms commenced after 5 ka coincident with the easing of aridity in northern california and increased storminess in the sierra nevada as indicated by lake sediment records these results suggest that useful insights about past hydrologic change can be gleaned from authigenic opal deposits and that these deposits have the potential to enhance the spatial and temporal coverage of paleoclimate reconstructions in regions where other archives might be scarce however further study of the influence of water in opal on 18 o variability and additional in situ analysis of 18 o variability on longer lived opal deposits with uniform growth histories are necessary to verify the controls on this potential proxy similarly further investigation into short term and spatial variability in 234 u 238 u sw will improve qualitative and quantitative applications of 234 u 238 u 0 in authigenic opal deposits enhancing our ability to use this promising new paleoclimate archive

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

global implications of lower to middle eocene sequence boundaries on the new jersey coastal plain the icehouse cometh wedocumentninelower middleeocenesequencesonthenewjerseycoastalplainand comparethemwithglobal d 18 oandhaqetal records earlyeocenehiatusesdonotmatch d 18 ochanges anditisunlikelythattheyaretheresultofglacioeustasy consistentwithan ice free early eocene early middle eocene 49 43 ma evidence for a link between sequencesand d 18 oisequivocal andthepresenceoflargeicesheetsisuncertain beginning in the late middle eocene 43 42 ma concomitant increases in planktonic and benthic d 18 o records coincide with the timing of hiatuses on the new jersey coastal plain and a change from carbonate dominated to siliciclastic dominated sedimentation these represent the development of the antarctic ice cap and the beginning of the icehouse world of the 14 sequences predicted by haq et al for this interval 9 are resolvable on the new jersey margin and the other 5 appear to be combined with others we conclude that although ice volume changes controlled sequences since at least 42 ma mechanisms for sea level change prior to then are still not fully understood

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

processes controlling 234u and 238u isotope fractionation and helium in the groundwater of the st lawrence lowlands quebec the potential role of natural rock fracturing abstract the goal of this study is to explain the origin of 234 u 238 u fractionation in groundwater from sedimentary aquifers of the st lawrence lowlands quebec canada and its relationship with 3 he 4 he ratios to gain insight regarding the evolution of groundwater in the region 234 u 238 u activity ratios or 234 u 238 u act were measured in 23 groundwater samples from shallow quaternary unconsolidated sediments and from the deeper fractured regional aquifer of the becancour river watershed the lowest 234 u 238 u act 1 14 0 01 was measured in ca hco 3 type freshwater from the quaternary shallower aquifer where bulk dissolution of the carbonate allows u to migrate into water with little 234 u 238 u isotopic fractionation the 234 u 238 u act increases to 6 07 0 14 in na hco 3 cl type groundwater preferential migration of 234 u into water by recoil is the underlying process responsible for this isotopic fractionation an inverse relationship between 234 u 238 u act and 3 he 4 he ratios has been observed this relationship reflects the mixing of newly recharged water with 234 u 238 u act close to the secular equilibrium and containing atmospheric tritiogenic helium and mildly mineralized older water 14 c ages of 6 6 kyrs with 234 u 238 u act of 6 07 and large amounts of radiogenic 4 he in excess of the steady state amount produced in situ the simultaneous fractionation of 234 u 238 u act and the addition of excess 4 he could be locally controlled by stress induced rock fracturing this process increases the surface area of the aquifer matrix exposed to pore water from which produced 4 he and 234 u can be released by recoil and diffusion this process would also facilitate the release of radiogenic helium at rates greater than those supported by steady state u th production in the rock consequently sources internal to the aquifers could cause the radiogenic 4 he excesses measured in groundwater

uranium isotopes in soils as a proxy for past infiltration and precipitation across the western united states the intermittent presence of large pleistocene lakes in the southwestern interior of north america a region that is now a semi arid desert suggests repeated oscillations between profoundly different climatic conditions the origin of these shifts is still unresolved due to inconsistencies in existing climate proxy data for example pollen lake levels and oxygen isotopes in speleothems to resolve the inconsistencies in the water balance over the last 10 to 60 kyr we use uranium isotopic variations in secondary soil minerals to quantify net infiltration and precipitation along a north south transect in western north america we show that winter infiltration increased by 30 to 100 percent and precipitation by a lesser amount in the valleys of the great basin and mojave deserts between 60 and 26 ka this increase in infiltration and precipitation preceded the last glacial maximum lgm and the timing of most lake highstands in the region by 5 to 10 kyr respectively suggesting a possible last precipitation maximum lpm that coincided with a minimum in winter insolation subsequent decreases in infiltration and precipitation after the lgm can be reconciled with the timing of lake highstands if colder summer temperatures due to a minimum in summer insolation reduced lake evaporation the soil records combined with a range of proxy data suggest that seasonal insolation is the long term driver for large shifts in both precipitation and surface water variability in the region

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

differences in attenuation among the stable continental regions 1 there are systematic differences in the attenuation of damaging earthquake ground motions between different stable continental regions scrs seismic intensity and weak motion data show that the attenuation in seismic waves for eastern north america ena is less than for india africa australia and northwest europe if ena ground motion attenuation relations are used in seismic hazard models for other scrs as is commonly done then the estimated ground motions and resulting hazard may be too large if an attenuation model that averages observations from ena and the other scrs is used to estimate the magnitudes of large historical earthquakes in ena as is the case for recent estimates of m for the 1811 1812 new madrid missouri and the 1886 charleston south carolina events then the magnitude estimates for these events will be too large as will be the resulting hazard

234u 238u activity ratios of dissolved uranium in groundwaters from a jurassic limestone aquifer in england abstract uranium contents and234u 238u activity ratios have been determined for groundwaters from the lincolnshire limestone artesian aquifer in eastern england changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone the western part of the aquifer closest to recharge is dominated by oxidising groundwaters which then enter a reducing zone towards the east where there is an abrupt decrease in eh and the chlorinity of the groundwaters begins to increase uranium contents in the oxidising zone range from 0 7 to 3 4 g kg 1 and234u 238u activity ratio of this dissolved uranium is close to unity the equilibrium value the uranium content decreases abruptly when the grounwaaters enter the reducing zone averaging 0 04 g kg 1 east of the oxidation reduction barrier simultaneously with the decrease in uranium content there is an increase in234u 238u activity ratio and this ratio increases to a maximum within 7 km of the oxidation reduction barrier this increase in activity ratio is attributed to enhanced234u solution due to234th recoil from uraniferous fissure surfaces east of the oxidising zone the activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to234th recoil from the oolith surfaces however the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium 234th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium bearing surfaces in the process of oolith cementation

kinetics of incongruent dissolution of carbonates in a chalk aquifer using reverse flow modelling s u m m a r y water rock interactions are major processes that control the solute transfer from natural or anthropo genic sources in aquifers in carbonate aquifers these water rock interactions are mainly characterised by the incongruent dissolutions of carbonates the in situ quantification of these reactions is few studied in the present paper we provide a new quantification of the kinetic rates of simultaneous incongruent dissolution of composite carbonate and dolomite in a chalk aquifer the approach is based on a mass balance model used to calculate the rates of mineral dissolution and precipitation along a 500 m to 4 km flow path starting at the groundwater divide line the groundwater transfer times between the groundwater divide line and the wells are calculated thanks to flow and transport modelling used in a backward particle tracking mode the uncertainties on porosity dispersivity and transmissivity are taken into account the rates are found ranging between 1 5 10 a5 and 1 5 10 a4 mol c5 chalk l a1 w yr a1 for the composite carbonate dissolution between 1 0 10 a7 and 3 0 10 a6 mol dolomite l a1 w yr a1 for the dolomite dissolution and between 1 0 10 a5 and 1 5 10 a4 mol calcite l a1 w yr a1 for the calcite precipitation the results highlight the importance of physical and geological properties of the aquifer

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

internally consistent pattern of seismicity near charleston south carolina an improved velocity model for the meizoseismal area of the 1886 charleston earthquake was used to relocate current seismicity which showed marked separation into clusters the relocated hypocenters and composite focal plane solutions were compared with available geophysical data to interpret their tectonic significance and possible association with the 1886 earthquakes there is a distinct velocity discontinuity at a depth of about 10 km where vp increases from 5 9 to 6 45 km s the relocated hypocenters and composite focal plane solutions delineate two main source zones lying at different depths the shallower zone at 4 to 8 km depth and collinear with the ashley river is herein named the ashley river seismogenic zone the composite focal plane solution suggests reverse faulting on a steeply dipping northwest striking fault with the southwest side upthrown this zone is also associated with aeromagnetic and gravity anomalies the deeper zone at 9 to 13 km suggests a right slip on a fault extending n26 e from east of ravanel to jedburg a distance of more than 25 km and dipping steeply to the west northwest its location and extent are similar to the so called woodstock fault examination of geomorphic data suggests that there may be some ongoing tectonic uplift and subsidence in the area the inferred p axes from fault plane solutions are oriented s60 w firsthand accounts of the 1886 earthquakes suggest that two source areas were active in 1886 and the months that followed i postulate that the two zones of current seismicity are coincident with the 1886 source areas

the transport of u and th series nuclides in sandy confined aquifers a comprehensive evaluation of the transport of u th ra and rn nuclides of the 238 u and 232 th decay series in an unconfined sandy aquifer long island ny was conducted groundwater data are compared with results of a theoretical transport model of weathering of aquifer grains and interaction with surface coatings to establish relationships between the concentrations of the radionuclide activities in the water and flow line distance the data provide estimates for geochemical parameters including weathering rates and chemical reactivities in both the vadose zone and the aquifer a theoretical treatment of the transport is presented that considers the reaction between the water and a reactive surface layer it is found that a model with chemical exchange between the surface layer and the water for all species is not valid and that the effects of saturation and irreversible precipitation of th is required the water table shows a relatively wide range in u activities the only element in the u th series for which vadose zone input is significant in the aquifer high weathering of u and recoil inputs of 234 u to the water occur in the upper 3 m of the vadose zone while lower weathering and removal of u from the water occur below the deeper aquifer has variable 238 u activities that can be accounted for by input from the vadose zone and is not a result of non conservative behavior the isotopic composition of u is shown to be directly related to the recoil rate relative to the weathering rate the wide range of 238 u in the aquifer waters is a reflection of diverse vadose zone inputs showing that dispersive mixing is not a dominant effect the higher values of 234 u in the aquifer reflect the recoil weathering input ratios from within the aquifer where the weathering rate is lower than the vadose zone both high u activities and high 234 u values cannot be obtained in the vadose zone or within reasonable flow distances in the aquifer radium isotopes are found to be in exchange equilibrium with the surface layer 224 ra 228 ra and 226 ra have comparable activities throughout the aquifer in the vadose zone the dominant input of ra to groundwater is weathering and recoil as found elsewhere the 222 rn in the water is a large fraction 5 of the rn produced in the aquifer rock this cannot be due to ra precipitation onto surface coatings in the aquifer as supported by present weathering with th in exchange equilibrium with the surface layer it is found that th is saturated in the waters under oxidizing conditions so that the weathering input is irreversibly precipitating onto surfaces however it is shown that under somewhat reducing conditions th activities are much higher and the th u ratio in the solution is approximately that of the rock we propose that under oxidizing conditions the source of rn is a surface coating enriched in 232 th and 230 th this th was precipitated in an earlier phase during rapid dissolution of readily weathered phases that contain 10 of the u th inventory of the rock with the associated u carried away in solution therefore the previously precipitated 230 th and 232 th produce daughter nuclides in the surface coating which are the dominant contributors of ra and rn to the ground water in particular rn is provided by very efficient losses by diffusion or recoil from the surface coating this then does not require recent large recoil losses from the parent rock or the presence of nanopores in the rock the first data of both long lived 232 th and short lived 234 th and 228 th in ground water is reported the th isotope activities indicate that desorption kinetics are slow and provide the first estimate based on field data of the th desorption rate from an aquifer surface the mean residence time of th in the surface coating is 3000 y while in the water it is 1 h ra is in partition equilibrium with the aquifer surface layer however the strong fixation of th on surface coatings is very susceptible to changes in oxidation state as is shown by a comparison of two adjacent aquifers this makes it difficult to define with certainty the retentive characteristics in natural systems in general it is shown that the distributions of naturally occurring nuclides can be used to calculate values for transport parameters that are applicable to the transport of anthropogenic nuclides

uranium series isotopes in river materials insights into the timescales of erosion and sediment transport abstract the uranium series isotope signatures of the suspended and dissolved load of rivers have emerged as an important tool for understanding the processes of erosion and chemical weathering at the scale of a watershed these signatures are a function of both time and weathering induced fractionation between the different nuclides provided appropriate models can be developed they can be used to constrain the residence time of river sediment this chronometer is triggered as the bedrock starts weathering and the inferred timescale encompasses the residence time in the weathering profile storage in temporary sediment deposits e g floodplain and transport in the river this approach has been applied to various catchments over the past five years showing that river sediments can reside in a watershed for timescales ranging from a few hundreds of years iceland to several hundreds of thousands of years lowlands of the amazon various factors control how long sediment resides in the watershed the longest residence times are observed on stable cratons unaffected by glacial cycles or more generally climate variability and human disturbance shorter residence times are observed in active orogens andes or fast eroding recently glaciated catchments iceland in several cases the residence time of suspended sediments also corresponds to the time since the last major climate change the u series isotope composition of rivers can also be used to predict the river sediment yield assuming steady state erosion is reached by comparing this estimate with the modern sediment yield obtained by multi year sediment gauging it is clear that steady state is seldom reached this can be explained by climate variability and or human disturbance steady state is reached in those catchments where sediment transport is rapid iceland or where the region has been unaffected by climate change and or human disturbance u series are thus becoming an important tool to study the dynamics of erosion

the mechanism of 234u238u activity ratio enhancement in karstic limestone groundwater departamento de petrologia e metalogenia universidade estadual paulista campus de rio claro unesp sao paulo

baseline geochemical conditions in the chalk aquifer berkshire u k a basis for groundwater quality management the chalk aquifer is the most important british aquifer and is also important over much of northern europe aquifer protection requires a sound knowledge of the baseline conditions and how these might vary or have varied with time this detailed geochemical study of a representative area of chalk in berkshire u k includes a consideration of several components 1 the inputs from the atmosphere 2 the interstitial water of the soil and the unsaturated zone 3 the interstitial water in the confined and unconfined sections of the aquifer and 4 the saturated mainly fissure flow along the hydraulic gradient which forms an important water supply of the thames valley region atmospheric inputs form an important source of some elements but the dominant chemical characteristics of the chalk groundwater are acquired during percolation through the soil and the upper unsaturated zone during saturated flow downgradient the chemistry is modified mainly by incongruent reactions of the carbonate matrix and by redox reactions and only to a minor extent by exchange reactions and mixing with residual saline connate water the incongruent reaction of carbonate results in a marked increase in the mg ca ratio and the sr and 13c contents of the groundwater with increased residence time oxygen concentrations are reduced mainly by oxidation of fe2 and the onset of reducing conditions allows dissolved fe2 to increase and rapid denitrification to occur the salinity profile through the confined chalk confirms that residual connate water up to one fifth sea water concentration still remains at depth and this accounts for some salinity increase in the confined groundwater resulting from fissure water pore water diffusional exchange timescales for groundwater movement have been established using tritium radiocarbon and indirectly using inert gas ratios and stable isotope ratios on balance it is concluded that all abstracted water is of holocene age although inert gas temperatures indicate cooler climatic conditions for recharge for some of the confined groundwater the implications for development and aquifer protection are discussed especially the prospect of natural in situ denitrification problems of fe solubility and the recognition of groundwater of different maturities