reinterpretation of the burmester core bonneville basin utah abstract initial interpretation of the sediments from the burmester core eardley et al 1973 geological society of america bulletin 84 211 216 indicated that 17 deep lake cycles separated by shallow lake and soil forming intervals occurred in the bonneville basin during the brunhes chron the last 780 10 3 yr our re examination of the core along with new sedimentological geochronological and paleontological data indicate that only four deep lake cycles occurred during this period apparently correlative with marine oxygen isotope stages 2 6 12 and 16 this interpretation suggests that large lakes formed in the bonneville basin only during the most extensive of the northern hemisphere glaciations

soil geomorphic research a selective overview abstract much soil geomorphologic research involves tracking the development of soils with time otherwise known as soil chronosequences most of these have been undertaken on landforms underlain by quaternary depsits of varying ages in general there is a predictable variation in both soil horizon sequence and amounts of constituents such as clay fe and caco 3 with time the rate at which these constituents accumulate in the soil is a function of parent material bioclimate and atmospheric dust influx and because of the latter soils in aridic regions can form at rapid rates profile properties can be used to estimate the ages of deposits and faulting events but the error on the estimated age can be 50 or greater the position of salt accumulations in soil profiles is one of the best indications of climatic change and these can be modelled to compare with various climatic parameters present and past profile characteristics due to pedogenic thresholds however can mimic those due to climatic change so close dating is necessary to differentiate the effects of both soil geomorphic data are essential to understand the origin of ancient paleosols in the sedimentary rock records but a major problem still is one of recognition of these features as soils and to separate the effects of pedogenesis from those of diagenesis

late quaternary environmental change in the bonneville basin western usa abstract excavation and analyses of small animal remains from stratified raptor deposits spanning the last 11 5 ka together with collection and analysis of over 60 dated fossil woodrat midden samples spanning the last 50 ka provide a detailed record of changing climate in the eastern great basin during the late pleistocene and holocene sagebrush steppe dominated the northern bonneville basin during the full glacial suggesting that conditions were cold and relatively dry in contrast to the southern basin which was also cold but moister limber pine woodlands dominated 13 11 5 ka indicating increased dryness and summer temperatures 6 7 c cooler than present this drying trend accelerated after 11 5 ka causing lake bonneville to drop rapidly eliminating 11 species of fish from the lake from 11 5 8 2 ka xerophytic sagebrush and shadscale scrub replaced more mesophilic shrubs in a step wise fashion a variety of small mammals and plants indicate the early holocene was 3 c cooler and moister than at present not warmer as suggested by a number of climatic models the diversity of plants and animals changed dramatically after 8 2 ka as many species disappeared from the record some of the upland species returned after 4 ka and great salt lake became fresh enough at 3 4 and 1 2 ka to support populations of utah chub

design criteria for laboratory measurements of low permeability rocks the advantages and limitations of two versions of the pulse technique for laboratory measurements of low permeabilities 10 16 to 10 24 m are discussed the transient pulse technique developed by brace et al 1968 is the preferred method because of the ease of data reduction the modified transient pulse technique developed by trimmer et al 1980 can be used when the assumptions inherent in the transient pulse technique are invalid the systematic error associated with the transient pulse technique is a function of the ratio of the effective sample pore volume to the reservoir volumes if this ratio is less than 0 25 then the error associated with the transient technique is less than 10 the modified transient pulse technique does not suffer from this systematic error criteria are also presented for optimizing the experimental configuration for measurement durations as well as ease of data reduction

history of quaternary offset and paleoseismicity along the la jencia fault central rio grande rift new mexico abstract the la jencia fault in the central part of the rio grande rift has a remarkable history of segmented movement during the late pleistocene and holocene after a long period of relative quiescence in the pleistocene movement on the reactivated fault created new scarps along five of its six segments movement occurred at varying intervals of several ka to more than 10 ka and at what appears to be decreasing recurrence intervals from the late pleistocene into the holocene surface rupturing has been in such a manner to fill in intervening unbroken segments of the fault and to produce continuous scarps along 30 km of the fault9s 35 km length many of the segments have scarps that show characteristic and statistically significant relations between their height and their maximum slope angle the holocene and upper pleistocene fault scarps were formed by prehistoric earthquakes having richter magnitudes of 6 8 to 7 1 estimated from two relations of earthquake magnitude to displacement and length of ground rupture and moment magnitudes of 6 6 to 6 7 estimated from one relation of magnitude to area of source rupture the geologic and pedologic evidence derived from trenching demands a minimum of five separate instances of faulting during the past 33 ka although as many as six such events are required if movement along different segments of the fault was not synchronous the average recurrence interval is about 7 5 ka in the former case and about 6 ka in the latter case although earthquakes of richter magnitude 6 or greater have not been felt in the rio grande rift in historic times the abundance of quaternary faults suggests that large earthquakes have been prevalent during the quaternary if these faults have histories of offset and paleoseismicity such as has been documented for the la jencia then the region may have a more significant potential for earthquake hazards than previously considered

quaternary palaeolakes in the evolution of semidesert basins with special emphasis on lake bonneville and the great basin u s a abstract this paper reviews attributes of quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts basin floor and basin closure morphometry have set limits on palaeolake sizes lake morphometry and basin drainage patterns have influenced lacustrine processes and water and sediment loads have influenced basin neotectonics information regarding inundated runoff producing and extra basin spatial domains is acquired directly from the palaeolake record including the littoral morphostratigraphic record and indirectly by reconstruction increasingly detailed hypotheses regarding lake bonneville the largest late pleistocene palaeolake in the great basin are subjects for further testing and refinement oscillating transgression of lake bonneville began about 28 ka the highest stage occurred about 15 ka and termination occurred abruptly about 13 ka a final resurgence of perennial lakes probably occurred in many subbasins of the great basin between 11 and 10 ka when the highest stage of great salt lake successor to lake bonneville developed the gilbert shoreline and when the russell shoreline formed 500 600 km away in the carson desert of the lake lahontan basin the highest post gilbert stage of great salt lake which has been one of the few permanent lakes in the great basin during holocene time probably occurred between 3 and 2 ka a set of eighteen general observations regarding geologic aspects of the palaeolake record in semidesert basins is helping to guide quaternary studies in the great basin

late pleistocene and early holocene rivers and wetlands in the bonneville basin of western north america abstract field investigations at dugway proving ground in western utah have produced new data on the chronology and human occupation of late pleistocene and early holocene lakes rivers and wetlands in the lake bonneville basin we have classified paleo river channels of these ages as gravel channels and sand channels gravel channels are straight to curved digitate and have abrupt bulbous ends they are composed of fine gravel and coarse sand and are topographically inverted i e they stand higher than the surrounding mudflats sand channels are younger and sand filled with well developed meander scroll morphology that is truncated by deflated mudflat surfaces gravel channels were formed by a river that originated as overflow from the sevier basin along the old river bed during the late regressive phases of lake bonneville after 12 500 and prior to 11 000 14c yr b p dated samples from sand channels and associated fluvial overbank and wetland deposits range in age from 11 000 to 8800 14c yr b p and are probably related to continued sevier basin overflow and to groundwater discharge paleoarchaic foragers occupied numerous sites on gravel channel landforms and adjacent to sand channels in the extensive early holocene wetland habitats reworking of tools and limited toolstone diversity is consistent with theoretical models suggesting paleoarchaic foragers in the old river bed delta were less mobile than elsewhere in the great basin

morphological analysis of the lake lahontan shoreline and beachfront fault scarps pershing county nevada abstract with the diffusion equation representation of landform evolution providing reference calculations quantitative comparisons between profiles of the high stand of lake lahontan presented here and profiles of the lake bonneville shoreline scarps analyzed elsewhere reveal that the two sets of scarps are nearly identical morphologically when care is exercised in the selection of profiles the lahontan high stand scarps are remarkably reproducible from one profile to the next highly suggestive evidence that the processes that have shaped and changed the shape of these landforms are correspondingly regular slope angle differences of only 2 are both discernible and interpretable features of these late quaternary landforms cut in weakly consolidated alluvium at a level of uncertainty of no more than 50 per cent the mass diffusivity of the lahontan high stand is the same as the lake bonneville shoreline 1 1 gkg 1 gkg 1 m 2 ka this result suggests that much can be learned about the ages of late quaternary fault scarps cut in weakly consolidated alluvium throughout the basin and range province from their morphology alone the beachfront fault scarps themselves truncated by lake lahontan in our study area are morphologically only slightly older 15 to 18 ka bp than the lahontan high stand 12 ka bp

an optimized scheme of lettered marine isotope substages for the last 1 0 million years and the climatostratigraphic nature of isotope stages and substages a complete and optimized scheme of lettered marine isotope substages spanning the last 1 0 million years is proposed lettered substages for marine isotope stage mis 5 were explicitly defined by shackleton 1969 but analogous substages before or after mis 5 have not been coherently defined short term discrete events in the isotopic record were defined in the 1980s and given decimal style numbers rather than letters but unlike substages they were neither intended nor suited to identify contiguous intervals of time substages for time outside mis 5 have been lettered or in some cases numbered piecemeal and with conflicting designations we therefore propose a system of lettered substages that is complete without missing substages and optimized to match previous published usage to the maximum extent possible our goal is to provide order and unity to a taxonomy and nomenclature that has developed ad hoc and somewhat chaotically over the decades our system is defined relative to the lr04 stack of marine benthic oxygen isotope records and thus it is grounded in a continuous record responsive largely to changes in ice volume that are inherently global this system is intended specifically for marine oxygen isotope stages but it has relevance also for oxygen isotope stages recognized in time series of non marine oxygen isotope data and more generally for climatic stages which are recognized in time series of non isotopic as well as isotopic data the terms stage and substage in this context are best considered to represent climatostratigraphic units and thus climatic stages and climatic substages because they are recognized from geochemical and sedimentary responses to climate change that may not have been synchronous at global scale

the 87sr 86sr ratios of lacustrine carbonates and lake level history of the bonneville paleolake system lakes in the bonneville basin have fluctuated dramatically in response to changes in rainfall temperature and drainage diversion during the quaternary we analyzed tufas and shells from shorelines of known ages in orderto develop a relation between 8 7 sr 8 6 sr ratio of carbonates and lake level which then can be used as a basis for constraining lake level from similar analyses on carbonates in cores carbonates from the late quaternary shorelines yield the following average 8 7 sr 8 6 sr ratios 0 71173 for the stansbury shoreline 22 20 1 4 c ka 1350 m 0 71153 for the bonneville shoreline 15 5 14 5 1 4 c ka 1550 m 0 71175 for the provo shoreline 14 4 14 0 1 4 c ka 1450 m 0 71244 for the gilbert shoreline 10 3 10 9 1 4 c ka 1300 m and 0 71469 for the modern great salt lake 1280 m these analyses show that the 8 7 sr 8 6 sr ratio of lacustrine carbonates changes substantially at low to mid lake levels but is invariant at mid to high lake levels sr isotope mixing models of great salt lake and the bonneville paleolake system were constructed to explain these variations in 8 7 sr 8 6 sr ratios with change in lake level our model of the bonneville system produced a 8 7 sr 8 6 sr ratio of 0 71193 very close to the observed ratios from high shoreline tufa and shell the model verifies that the integration of the southern sevier and beaver rivers with the bear and others rivers in the north is responsible for the lower 8 7 sr 8 6 sr ratios in lake bonneville compared to the modern great salt lake we also modeled the 8 7 sr 8 6 sr ratio of lake bonneville with the upper bear river diverted into the snake river basin and obtained an 8 7 sr 8 6 sr ratio of 0 71414 coincidentally this ratio is close to the observed ratio for great salt lake of 0 71469 this means that 8 7 sr 8 6 sr ratios of 0 714 for carbonate can be produced by climatically induced low lake conditions or by diversion of the upper bear river out of the bonneville basin this model result also demonstrates that the upper bear river had to be flowing into the bonneville basin during highstands of other late quaternary lake cycles carbonates from the little valley 130 160 ka and cutler dam 59 5 ka lake cycles returned 8 7 sr 8 6 sr ratios of 0 71166 and 0 71207 respectively and are too low to be produced by a lake without the upper bear river input

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

paleoclimatic implications of late pleistocene sediment yield rates for the bonneville basin northern utah abstract climate factors such as precipitation and temperature as well as climate driven geomorphic processes such as glaciation affect rates of erosion and the amount of sediment supplied from a drainage basin sediment yield thus sediment yield rates provide paleoclimatic implications although very little work has been published on ancient sediment yield rates late pleistocene lake bonneville utah idaho and nevada with its well documented lake level history and well preserved deltaic sequences provides a unique opportunity to estimate ancient sediment yield rates two end member delta systems coarse grained gravel classic gilbert type deltas and fine grained sand silt and clay deltas are exposed along the eastern margin of paleolake bonneville one example of each end member delta is examined in this study american fork and weber river deltas the established bonneville hydrograph can be used to determine time of deposition for a given package of sediments because these shoreline deltaic sediments were deposited in shallow water the geomorphic expressions of these deltas are well preserved and their sediment volumes can be determined river drainage basin area can be combined with time constraints and delta volumes to estimate sediment yield rates sediment yield rate estimates for the coarse grained american fork and fine grained weber river deltas are 478 m 3 km 2 yr 1 34 and 705 m 3 km 2 yr 1 15 respectively the similarity of these values is somewhat surprising due to the large difference in drainage basin sizes american fork 160 km 2 and weber river 3328 km 2 however this similarity suggests that precipitation may be the dominant control on sediment yield using sediment yield precipitation regression equations developed for similar modern basins in the southern alps of new zealand a first order approximation of paleoprecipitation is 1 6 m yr 14 for american fork delta and 1 9 m yr 7 for weber river delta these paleoprecipitation value are comparable to modern precipitation values of 0 4 1 5 m yr range of mean values over both drainage basins a maximum late pleistocene precipitation increase of 33 over the modern day value is suggested this is determined by the difference between the highest paleoprecipitation rate 1 9 m yr 7 of the weber river delta and the modern value 1 5 m yr previous climate models and this 33 paleoprecipitation increase suggest a maximum decrease in basin floor paleotemperature of approximately 13 c this paleotemperature decrease is consistent with previous estimates of late pleistocene temperatures using amino acid epimerization rates and periglacial wedges in the bonneville basin and adjacent areas these estimates suggest that although late pleistocene precipitation rates may have been slightly higher than present up to 33 higher late pleistocene temperature and evaporation rates were more important in the development of lake bonneville and associated glaciers

facies architecture and sequence stratigraphy of fine grained lacustrine deltas along the eastern margin of late pleistocene lake bonneville northern utah and southern idaho this study documents the effects of changing lake level limnostasy tectonics sediment yield and basin physiography on the facies architecture sequence stratigraphy and reservoir quality of three fine grained deltas deposited along the eastern margin of late pleistocene lake bonneville analysis of facies architecture indicates that the weber and spanish fork deltas were strongly wave modified because they were situated along openly exposed portions of the shoreline the bear river delta nestled in a relatively isolated northeast arm of the lake records both fluvial and wave processes these fine grained deltas were fed by low gradient rivers that drained large regions that were sparsely glaciated whereas other contemporaneous coarse grained gilbert deltas were fed by steep gradient rivers that drained local source areas that were strongly influenced by glaciers limnostasy tectonics and sediment yield were similar for all three fine grained deltas implying that the most influential forcing parameter on sequence stratigraphy is basin physiography basin physiography specifically ramp length and accommodation most strongly controlled the external and internal geometry of the lowstand systems tract of each delta potential hydrocarbon reservoir quality e g grain size and sorting is largely a product of drainage basin size and stream gradient relative differences in ramp lengths seemed to determine thickness and lateral continuity of delta front deposits relative differences in accommodation appeared to determine the internal geometry of the delta front deposits especially in the lowstand systems tract these deltas can serve as analogs for lacustrine exploration and production where many forcing parameters typically are unknown

fitting degradation of shoreline scarps by a nonlinear diffusion model the diffusion model of degradation of topographic features is a promising means by which vertical offsets on holocene faults might be dated in order to calibrate the method we have examined present day profiles of wave cut shoreline scarps of late pleistocene lakes bonneville and lahontan it may be assumed that these scarps were initially at least as steep as the angle of repose offsets range from 1 to 12 m and present slope angles range from 9 to 29 a parameter called apparent diffusion age defined as half the mean square horizontal extent of the slope function of each profile is plotted as a function of scarp offset the points show a clear trend of apparent age increasing nearly linearly with offset if linear diffusion held and scarps were initially vertical apparent diffusion age would be the same for all the shoreline profiles the increasing trend can only partly be explained by nonvertical initial scarp slope and therefore the rate of transport of material downslope must increase significantly faster than a linear law in the range of slopes spanned by the data the transport law must become linear at small slope to reduce scatter between profiles with varying ambient slopes the transport law adopted for the purpose of dating is k0 1 5s2 where s is local slope the transport coefficient k0 is correlated inversely with fan slope suggesting that there is a dependence on the particle size distribution a table is included that allows easy application of the model to scarps with simple initial shape

new evidence for an extended occupation of the provo shoreline and implications for regional climate change pleistocene lake bonneville utah usa abstract lake bonneville was a climatically sensitive closed basin lake that occupied the eastern great basin during the late pleistocene ongoing efforts to refine the record of lake level history are important for deciphering climate conditions in the bonneville basin and for facilitating correlations with regional and global records of climate change radiocarbon data from this and other studies suggest that the lake oscillated at or near the provo level much longer than depicted by current models of lake level change radiocarbon data also suggest that the lake dropped from threshold control much more rapidly than previously supposed these revisions to the lake bonneville hydrograph coupled with independent evidence of climate change from vegetation and glacial records have important implications for conditions in the bonneville basin and during the pleistocene to holocene transition

winter use of sea ice and ocean water mass habitat by southern elephant seals the length and breadth of the mystery understanding the responses of animals to the environment is crucial for identifying critical foraging habitat elephant seals mirounga leonina from the kerguelen islands 49 20 s 70 20 e have several different foraging strategies why some individuals undertake long trips to the antarctic continent while others utilize the relatively close frontal zones is poorly understood here we investigate how physical properties within the sea ice zone are linked to foraging activities of southern elephant seals ses to do this we first developed a new approach using indices of foraging derived from high temporal resolution dive and accelerometry data to predict foraging behaviour in an extensive low resolution dataset from ctd satellite relay data loggers ctd srdls a sample of 37 post breeding ses females were used to construct a predictive model applied to demersal and pelagic dive strategies relating prey encounter events pee to dive parameters dive duration bottom duration hunting time maximum depth ascent speed descent speed sinuosity and horizontal speed for each strategy we applied these models to a second sample of 35 seals 20 males and 15 females during the post moult foraging trip to the antarctic continental shelf between 2004 and 2013 which did not have fine scale behavioural data the females were widely distributed with important foraging activity south of the southern boundary front while males predominately travelled to the south eastern part of the east antarctica region combining our predictions of pee with environmental features sea ice concentration water masses at the bottom phase of dives bathymetry and slope index we found higher foraging activity for females over shallower seabed depths and at the boundary between the overlying antarctic surface water aasw and the underlying modified circumpolar deep water mcdw increased biological activity associated with the upper boundary of mcdw may provide overwintering areas for ses prey male foraging activity was strongly associated with pelagic dives within the antarctic slope front where upwelling of nutrient rich circumpolar deep water onto surface water may enhance and concentrate resources a positive association between sea ice and foraging activity was found for both sexes where increased biological activity may sustain an under ice ecosystem variability of the east antarctic sea ice season duration is likely a crucial element to allow air breathing predators to benefit from profitable prey patches within the pack ice habitat

swirling in the ocean immature loggerhead turtles seasonally target old anticyclonic eddies at the fringe of the north atlantic gyre abstract in a highly heterogeneous open ocean swirling oceanographic structures such as eddies drive ocean productivity and aggregate many predators including oceanic sea turtles during early life juvenile loggerhead turtles can spend more than a decade feeding on gelatinous zooplankton in the open ocean but the way they use mesoscale eddies is still poorly understood here we investigated the relationships between 1 the distribution and 2 the diving behaviour of immature loggerhead turtles of the north east atlantic and mesoscale eddies for this purpose 28 turtles were satellite tracked from the azores archipelago using the residence time rt analysis as a proxy to identify high use areas the tracks and dive data of the turtles as well as drifter trajectories were analysed in relation to eddy characteristics which include eddy radius amplitude type cyclonic vs anticyclonic lifetime and region inner core outer core periphery the turtles dispersed widely using many distinct high use areas although there were always more cyclones than anticyclones over the study region the individuals seasonally associated more with the inner cores of old anticyclonic eddies likely due to the higher productivity of decaying anticyclones the comparison between passive drifters and turtles movements showed an active swimming behaviour from the turtles rather than a passive advection through currents three dive types were identified and the one associated with the highest rt was characterized by dives of medium duration and depths in the inner cores of eddies this study is the first to highlight strong affinities of oceanic loggerhead turtles for old anticyclonic eddies around the azores suggesting a greater complexity of these warm core eddies that appear to be much more productive than cyclones

characterization of transport and water retention properties of damaged callovo oxfordian claystone in the context of the underground storage of radioactive waste the aim of this experimental study is to characterize the effect of damage on transport and water retention properties of callovo oxfordian cox argillite the originality of the study is to simultaneously investigate the pore size distribution water retention the dry effective and relative gas permeability and the gas breakthrough pressure gbp of damaged cox argillite these different properties are all relevant to characterizing the fluid transport ability of cox argillite results show that the damage has a significant impact on the properties of the cox argillite it induces a decrease in its water retention capacity and gbp and it increases its gas permeability and apparent porosity available to water owing to the creation of micro cracks another objective is to show which of these properties is the most suitable to detect early damage states in cox argillite with a potential use being to identify them in situ gbp appears to be the best detector of damage because of its sensitivity to damage even under high confinement pressures gas permeability could be a good indicator of damage as it increases significantly one or several orders of magnitude after the damage finally the water permeability curve is a poor indicator of cox argillite damage

age and paleoclimatic significance of the stansbury shoreline of lake bonneville northeastern great basin abstract the stansbury shoreline one of the conspicuous late pleistocene shorelines of lake bonneville consists of tufa cemented gravel and barrier beaches within a vertical zone of about 45 m the lower limit of which is 70 m above the modern average level of great salt lake stratigraphic evidence at a number of localities including new evidence from crater island on the west side of the great salt lake desert shows that the stansbury shoreline formed during the transgressive phase of late pleistocene lake bonneville sometime between about 22 000 and 20 000 yr b p tufa cemented gravel and barrier beaches were deposited in the stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m we refer to the fluctuations as the stansbury oscillation the stansbury oscillation cannot have been caused by basin hypsometric factors such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin or by changes in drainage basin size therefore changes in climate must have caused the lake level to reverse its general rise to drop about 45 m in altitude reducing its surface area by about 18 5000 km2 and later to resume its rise if the sizes of great basin lakes are controlled by the mean position of storm tracks and the jetstream which as recently postulated may be controlled by the size of the continental ice sheets the stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the laurentide ice sheet

integrated three dimensional interpretation of major concealed faults beneath mapleton utah county utah using gravity data supported with magnetic data abstract gravity and magnetic surveys were conducted to locate major concealed faults beneath mapleton utah county utah a developing city along the wasatch front 80 km south of salt lake city utah although the magnetic data are not as useful for this study due to cultural magnetic noise and logistical limitations in acquiring dense data sets these data do play a backup role in supporting the gravity data by helping to constrain the interpreted models of the major concealed faults data were collected at 196 stations and were processed using conventional techniques regional trends were calculated using trend analysis and residual data were modeled using self consistent iterative modeling ambiguities in the subsurface models were reduced by 1 incorporating data from previous geophysical surveys surface mapping trench studies aerial photos well data and earthquake data 2 integrating the gravity and magnetic data and 3 correlating the modeled cross sections along numerous selected profiles the modeled profiles and integrated three dimensional interpretation indicate that there are four major fault blocks beneath the mapleton area these fault blocks are bounded by a series of west dipping synthetic listric faults depths to the fault blocks range from

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

under stress permeability determination of the meuse haute marne mudstone abstract in the underground waste isolation projects such as the andra one in the site of bure the transport properties of the surrounding rock mass is of fundamental importance to measure very low permeability we use the modified version of the pulse test proposed by hsieh et al hsieh p a tracy j v neuzil c e bredehoeft j d silliman s e 1981 a transient laboratory method for determining the hydraulic properties of tight rocks i theory int j rock mech min sci geomech abstr vol 18 pp 245 252 which enables the intrinsic permeability k and the specific storage coefficient s s of rocks such as mudstone to be characterized in this paper the special effort performed on the laboratory apparatus design to ensure a good sensitivity of the rock response with respect to both parameters k and s s is presented in addition two parameters identification procedures are proposed the graphical method given by hsieh et al hsieh p a tracy j v neuzil c e bredehoeft j d silliman s e 1981 a transient laboratory method for determining the hydraulic properties of tight rocks i theory int j rock mech min sci geomech abstr vol 18 pp 245 252 and a parameter identification based on the solution of an inverse problem the efficiency of the apparatus design and the parameters identification procedures is then demonstrated though some pulse tests performed on the meuse haute marne mudstone

paleoshoreline geomorphology of boon tsagaan nuur tsagaan nuur and orog nuur the valley of lakes mongolia abstract we conducted a preliminary study of paleoshoreline features associated with boon tsagaan nuur tsagaan nuur and orog nuur lakes located in the gobi altai transition zone of the valley of lakes dolina ozor which stretches from central to western mongolia the paleoshoreline features were first identified on radarsat satellite sar imagery we investigated the features during the 1998 field season of the joint mongolian russian american archaeological expedition to the gobi altai region we identified paleoshorelines of multiple elevations in the field which are considered to be relict beach ridges and wave cut terraces other paleolake landforms include spits and gilbert type deltas these landforms are complex large and well established implying that the paleolakes were stable for extended periods the reconstructed paleolakes cover extensive areas of the valley floor implying that hydrological and climatic conditions were very different in the past paleolake expansions may have occurred under a variety of circumstances one hypothesis is that the high lake stands occurred during the wetter period corresponding to the oxygen isotope stage 3 prior to the last glacial maximum lgm during the warmest early holocene and the late holocene or during all these periods if low evaporation rates due to lower temperatures glacier meltwater and possibly increased precipitation are important factors then the expansions may have occurred during the terminal late glacial period after the last glacial maximum the greatly expanded lakes in the gobi altai could have significantly affected the quaternary human demography and migration in the region

the influence of oceanographic features on the foraging behavior of the olive ridley sea turtle lepidochelys olivacea along the guiana coast abstract the circulation in the western equatorial atlantic is characterized by a highly dynamic mesoscale activity that shapes the guiana continental shelf olive ridley sea turtles lepidochelys olivacea nesting in french guiana cross this turbulent environment during their post nesting migration we studied how oceanographic and biological conditions drove the foraging behavior of 18 adult females using satellite telemetry remote sensing data sea surface temperature sea surface height current velocity and euphotic depth simulations of micronekton biomass pelagic organisms and in situ records water temperature and salinity the occurrence of foraging events throughout migration was located using residence time analysis while an innovative proxy of the hunting time within a dive was used to identify and quantify foraging events during dives olive ridleys migrated northwestwards using the guiana current and remained on the continental shelf at the edge of eddies formed by the north brazil retroflection an area characterized by low turbulence and high micronekton biomass they performed mainly pelagic dives hunting for an average 77 of their time hunting time within a dive increased with shallower euphotic depth and with lower water temperatures and mean hunting depth increased with deeper thermocline this is the first study to quantify foraging activity within dives in olive ridleys and reveals the crucial role played by the thermocline on the foraging behavior of this carnivorous species this study also provides novel and detailed data describing how turtles actively use oceanographic structures during post nesting migration

ecosystem and paleohydrological response to quaternary climate change in the bonneville basin utah we report the results of a detailed paleoecological study of the bonneville basin covering the last 280 000 yr our study used fossil ostracodes and a sedimentological record obtained from the august 2000 glad800 drilling operation at great salt lake we analyzed 125 samples taken at 1 m intervals from site 4 gsl00 4 for ostracodes and other paleoecologic and sedimentologic indicators of environmental change multivariate analyses applied to the ostracode data and qualitative analyses of fossil and sedimentological data indicate an alternation between three major environments at the core site over the cored interval 1 shallow saline or hypersaline lakes 2 salt or freshwater marshes and 3 occasional deep freshwater lakes these environmental changes are consistent with shoreline studies of regional lake level fluctuations but provide considerable new detail on both the timing and environmental conditions associated with the various lake phases our age model using 14 c useries tephra and biostratigraphic chronologies allowed us to associate the core s record of regional paleohydrology with the marine oxygen isotope stages of global climate change the core contains continuous records for the last four glacial interglacial sequences salt freshwater marshes were common during the interglacials and deep freshwater conditions correspond with maximum global ice volume in ois 2 and before a maximum in global ice during ois 6 immediately following deep lake phases crashes in lake level from rapid desiccation resulted in the deposition of thick evaporite units our study suggests that the climate of the great salt lake catchment appears to have been drier during ois 6 than during ois 2 we compare our record of environmental change during ois 6 glaciation with other records from the western united states and find that the overall

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

accelerator mass spectrometer ams radiocarbon dating of pleistocene lake sediments in the great basin abstract pleistocene lake sediments in the great basin typically contain little organic carbon and thus are difficult to date reliably by conventional radioccarbon methods paleoenvironmental data are abundant in these sediments but are of limited value without adequate age controls with the advent of accelerator mass spectrometer ams radiocarbon dating it is now possible to date these paleolacustrine sediments ams dates were obtained on sediment cores from the bonneville franklin and lahontan basins in the bonneville basin the ams based chronology compares well with other chronologies constructed from dated shore zone features in the bonneville and franklin basins ams dates delimit unconformities not apparent by other means we found that dispersed organic carbon from sediments deposited during relatively freshwater intervals provided apparently reliable ams radiocarbon dates carbonate microfossils from the lahontan basin also produced results that appear reasonable while bulk carbonate yielded erroneous results

the mean flow field of the tropical atlantic ocean the mean horizontal sow eld of the tropical atlantic ocean is described between 20in and 20is from observations and literature results for three layers of the upper ocean tropical surface water central water and antarctic intermediate water compared to the subtropical gyres the tropical circulation shows several zonal current and countercurrent bands of smaller meridional and vertical extent the wind driven ekman layer in the upper tens of meters of the ocean masks at some places the sow structure of the tropical surface water layer as is the case for the angola gyre in the eastern tropical south atlantic although there are regions with a strong seasonal cycle of the tropical surface water circulation such as the north equatorial countercurrent large regions of the tropics do not show a signi cant seasonal cycle in the central water layer below the eastward north and south equatorial undercurrents appear imbedded in the westward sowing south equatorial current the antarcic intermediate water layer contains several zonal current bands south of 3in but only weak sow exists north of 3in the sparse available data suggest that the equatorial intermediate current as well as the southern and northern intermediate countercurrents extend zonally across the entire equatorial basin due to the convergence of northern and southern water masses the western tropical atlantic north of the equator is an important site for the mixture of water masses but more work is needed to better understand the role of the various zonal under and countercurrents in cross equatorial water mass transfer 1999 elsevier science ltd all rights reserved

late quaternary environmental changes in the upper las vegas valley nevada abstract five stratigraphic units and five soils of late pleistocene to holocene age crop out in dissected badlands on corn creek flat 30 km northwest of las vegas nevada and at tule springs nearer to las vegas the record is dominantly fluvial but contains evidence of several moister marsh forming periods the oldest unit b dates perhaps to the middle wisconsin and the more widespread unit d falls between 30 000 and 15 000 yr b p unit d therefore correlates with pluvial maximum lacustrine deposits elsewhere in the great basin standing water was not of sufficient depth or extent during either period to form lake strandlines between 14 000 and 7200 yr b p unit e standing surface water gradually decreased a trend also apparent in great basin pluvial lake chronologies during the same period groundwater carbonate cementation and burrowing by cicadas cicadae accompany the moist phase units after 7200 yr b p increased wind action decreased biotic activity and at least 25 m of water table lowering accompanied widespread erosion of older fine grained deposits based on pack rat midden and pollen evidence this coincides with major vegetation changes in the valley from sagebrush dominated steppe to lower mohave desertscrub

new insights in the french guiana continental shelf circulation and its relation to the north brazil current retroflection 1 moored current measurements carried out from 6 october 2003 to 18 february 2004 over the french guiana continental shelf are presented two contrasted situations have been evidenced in which the currents were either weak and oscillating during the first period from october to early december or strong and northwestward during the rest of the survey further analysis of these measurements in light of moderate resolution imaging spectroradiometer satellite images have revealed that these situations are mainly due to the motion of an outer shelf mesoscale feature the north brazil current nbc retroflection two other main results have also been evidenced in this survey 1 when the nbc retroflection occurs northwestward of the french guiana continental shelf part of the nbc climbs over the shelf slope and propagates to the inner shelf and 2 the guyana current does not persist throughout the year at a 22 m depth and below finally the location of the nbc retroflection has also a strong impact on the spread of the amazon plume over the french guiana continental shelf and is felt to have an influence on the nutrient supply in this region

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

correlation between long term pedogenic caco3 formation rate and modern precipitation in deserts of the american southwest abstract the rates of caco 3 formation in desert soils of the american southwest are highly variable and potentially useful in estimating the age of soil profiles the objective of this study was to examine the correlation between the long term rate of caco 3 formation ltr and modern mean annual precipitation map and temperature mat ltr is not significantly related to temperature but is linearly related to map ltr 0 0150 map 37 r 2 0 924 the slope of the regression is significantly different from 0 0 and is equivalent to a calcium concentration of 6 0 mg liter 1 in rainfall however the intercept term which suggests a lower limit of precipitation for caco 3 formation of 37 mm is not significantly different from 0 0 the ltr map relationship may be useful in estimating the age of soil profiles by the caco 3 method in the desert southwest

upper mantle viscosity derived from the difference in rebound of the provo and bonneville shorelines lake bonneville basin utah twenty four new field measurements of elevation of provo level and bonneville level shoreline terraces provide data for reanalysis of isostatic rebound in the lake bonneville basin analysis of the differential rebound between the provo shoreline maximum rebound of 43 m and the bonneville shoreline maximum rebound of 69 m requires that the latter be an equilibrium shoreline within the possible measurement errors the provo shoreline formed after the elastic lithosphere had attained at least 91 equilibration to the removal of the water load between the bonneville and provo shorelines within the errors the provo may also represent an equilibrium shoreline from the new data presented in this paper the best estimate of the upper limit of effective viscosity of the uppermost mantle assuming a half space model and a 2000 year time interval between the bonneville and provo shorelines is 2 1019 n s m 2 2 1020 p in addition comparison of shoreline rebound profiles for both shorelines with theoretical plate flexure models indicates that the mean flexural rigidity of the basin and range lithosphere in this region is 1 1023 n m or slightly less

latest pleistocene glacial and climate history of the wasatch range utah abstract the geologic record of mountain glaciation is one of the most sensitive archives of terrestrial climate change during the late quaternary period pleistocene glacial deposits are exceptionally well preserved in the great basin of north america where they are found in close proximity to shoreline deposits of coeval paleo lakes representing a unique opportunity to investigate paleoclimate change using both hydrologic systems mountain glaciers advanced across much of the wasatch range utah during the same general time interval when lake bonneville expanded in the adjacent bonneville basin here we present a range wide latest pleistocene glacial history for the wasatch range based on 22 new and 41 recalculated cosmogenic 10be surface exposure ages and reconstruct glaciers and climate for the last glacial maximum lgm and lateglacial periods our results indicate three distinct range wide phases of glaciation in the wasatch including the pinedale 1 ca 21 20 ka pinedale 2 ca 17 5 ka and pinedale 3 ca 15 ka our modeling results indicate that the pinedale 1 advance near the end of the global lgm was primarily driven by decreased annual temperatures with little to no change in precipitation as compared to modern wasatch glaciers appear to have reoccupied near maximum positions after the end of the lgm during the pinedale 2 responding to increased precipitation in concert with rising lake levels across western north america and then retreated from ice distal positions near ca 17 5 ka wasatch glaciers occupied recessional positions at approximately half their maximum lengths during pinedale 3 until ca 15 ka followed by rapid i e several millennia deglaciation our glacial chronologies establish that wasatch glaciers responded synchronously across the range to global and regional climate forcings during the latest pleistocene the new wasatch glacial chronology combined with global glacial chronologies and paleoclimate proxies from western north america suggest glacier change was driven by a combination of long term global temperature forcing as well as regional to local modifications in precipitation

an unsaturated hydro mechanical modelling of two in situ experiments in callovo oxfordian argillite abstract the unsaturated behaviour of callovo oxfordian argillite is investigated through the modelling of 2 in situ experiments the first test studies the influence of ventilation in a gallery on the hydro mechanical behaviour of the rock mass the second test consists in a gas injection in the rock mass from an experimental borehole a hydro mechanical model is described and used in the modelling of the experiments a review of the main hydro mechanical parameters of argillite is presented the numerical results highlight the need of a flow boundary condition reproducing the fluid transfers between the surroundings and the rock mass the influence of dissolved gas on the compressibility of the liquid phase is also emphasised

the composite nature of the provo level of lake bonneville great basin western north america abstract deposits of a transgressive phase lake bonneville stillstand or oscillation are found just below the elevation of the regressive phase provo shoreline at numerous exposures throughout the bonneville basin existence of these subprovo shoreline deposits provides a new explanation for the massive size of provo depositional and erosional landforms which can no longer be explained by a long stillstand at the provo shoreline provo coastal landforms are large because they are superimposed on subprovo landforms results also help to clarify divergent interpretations regarding the relative age of the provo shoreline and the number of times it was occupied by the water plane occupation of approximately the same level during both the transgressive and the regressive phase of lake bonneville may be coincidental or it may indicate that a bedrock sill controlled outflow at subprovo as well as provo time rise to the bonneville level could have occurred after massive slope failure plugged the outlet pass

cosmogenic 14c in carbonate rocks abstract the rate of in situ production of cosmogenic 14 co in limestone is 18 3 atom g caco3 year corrected to high latitude and sea level based on measurements of 14 co in limestone associated with the bonneville provo shoreline complex in utah in situ cosmogenic 14 co was separated cryogenically from co2 using 14 c dead co as a carrier for in situ cosmogenic 14 co this rate of production was used to estimate an age of 4360 1220 cal year b p for the last movement on the south oquirrh mountain fault zone in northern utah and an age of at least 10 600 900 years for the penultimate event of the pleasant valley fault in northern nevada

paleomagnetic investigation of the bonneville alloformation lake bonneville utah abstract paleomagnetic secular variation in a portion of the bonneville alloformation is compared with secular variation in lacustrine sediments in the mono basin california and with secular variation in lake lahontan sediments in the northwestern great basin the comparison places an age of about 18 000 yr b p and a span of 1000 to 3000 yr on part of a transgressive stage of lake bonneville near delta utah that is coeval with a wet period in the lahontan basin

large mid holocene and late pleistocene earthquakes on the oquirrh fault zone utah abstract the oquirrh fault zone is a range front normal fault that bounds the east side of tooele valley and it has long been recognized as a potential source for large earthquakes that pose a significant hazard to population centers along the wasatch front in central utah scarps of the oquirrh fault zone offset the provo shoreline of lake bonneville and previous studies of scarp morphology suggested that the most recent surface faulting earthquake occurred between 9000 and 13 500 years ago based on a potential rupture length of 12 to 21 km from previous mapping moment magnitude mw estimates for this event range from 6 3 to 6 6 in contrast our results from detailed mapping and trench excavations at two sites indicate that the most recent event actually occurred between 4300 and 6900 yr b p 4800 and 7900 cal b p and net vertical displacements were 2 2 to 2 7 m much larger than expected considering estimated rupture lengths for this event empirical relations between magnitude and displacement yield mw 7 0 to 7 2 a few short discontinuous fault scarps as far south as stockton utah have been identified in a recent mapping investigation and our results suggest that they may be part of the oquirrh fault zone increasing the total fault length to 32 km these results emphasize the importance of integrating stratigraphic and geomorphic information in fault investigations for earthquake hazard evaluations at both the big canyon and pole canyon sites trenches exposed faulted lake bonneville sediments and thick wedges of fault scarp derived colluvium associated with the most recent event bulk sediment samples from a faulted debris flow deposit at the big canyon site yield radiocarbon ages of 7650 90 yr b p and 6840 100 yr b p all lab errors are 1 a bulk sediment sample from unfaulted fluvial deposits that bury the fault scarp yield a radiocarbon age estimate of 4340 60 yr b p stratigraphic evidence for a pre bonneville lake cycle penultimate earthquake was exposed at the pole canyon site and although displacement is not well constrained the penultimate event colluvial wedge is comparable in size to the most recent event wedges charcoal from a marsh deposit which overlies the penultimate event colluvium and was deposited during the bonneville lake cycle transgression yields an ams radiocarbon age of 20 370 120 yr b p multiple charcoal fragments from fluvial deposits faulted during the penultimate event yield an ams radiocarbon age of 26 200 200 yr b p indirect stratigraphic evidence for an antepenultimate event was also exposed at pole canyon charcoal from fluvial sediments overlying the eroded free face for this event yields an ams age of 33 950 1160 yr b p providing a minimum limiting age on the antepenultimate event ages for the past two events on the oquirrh fault zone yield a recurrence interval of 13 300 to 22 100 radiocarbon years and estimated slip rates of 0 1 to 0 2 mm yr temporal clustering of earthquakes on the nearby wasatch fault zone in the late holocene does not appear to have influenced activity on the oquirrh fault zone however consistent with findings on the wasatch fault zone and with some other quaternary faults within the bonneville basin we found evidence for higher rates of activity during interpluvial periods than during the bonneville lake cycle if a causal relation between rates of strain release along faults and changes in loads imposed by the lake does exist it may have implications for fault dips and mechanics however our data are only complete for one deep lake cycle the past 32 000 radiocarbon years and whether this pattern persisted during the previous cutler dam and little valley deep lake cycles is unknown

thermoluminescence dating of fault scarp derived colluvium deciphering the timing of paleoearthquakes on the weber segment of the wasatch fault zone north central utah the timing of middle to late holocene faulting on the weber segment of the wasatch fault zone utah is constrained by thermoluminescence tl and radiocarbon age estimates on fine grained fault related colluvial sediments the stratigraphy in two trenches excavated across fault scarps is characterized by a stack of three colluvial wedges deposited in response to three separate faulting events the oldest of which buried a soil developed on a middle holocene debris flow thermoluminescence age estimates by the partial and total bleach methods and the regeneration method on fine grained colluvium from the trenches agree within 1 sigma and are concordant with the radiocarbon chronology a synthesis of the tl and 14c age estimates indicate that these three faulting events occurred sometime between 4500 and 3500 between 3200 and 2500 and between 1400 and 1000 years ago detailed investigation of a sequence of fine grained scarp derived distal colluvium shows that much of the sediment was deposited during 600 year intervals immediately after faulting the sedimentation rate of colluvium is inferred to increase shortly after faulting and tl dating of these sediments provides additional information to constrain the timing of faulting events

pluvial lakes in the great basin of the western united states a view from the outcrop abstract paleo lakes in the western united states provide geomorphic and hydrologic records of climate and drainage basin change at multiple time scales extending back to the miocene recent reviews and studies of paleo lake records have focused on interpretations of proxies in lake sediment cores from the northern and central parts of the great basin in this review emphasis is placed on equally important studies of lake history during the past 30 years that were derived from outcrop exposures and geomorphology in some cases combined with cores outcrop and core records have different strengths and weaknesses that must be recognized and exploited in the interpretation of paleohydrology and paleoclimate outcrops and landforms can yield direct evidence of lake level facies changes that record details of lake level fluctuations and geologic events such as catastrophic floods drainage basin changes and isostatic rebound cores can potentially yield continuous records when sampled in stable parts of lake basins and can provide proxies for changes in lake level water temperature and chemistry and ecological conditions in the surrounding landscape however proxies such as stable isotopes may be influenced by several competing factors the relative effects of which may be difficult to assess and interpretations may be confounded by geologic events within the drainage basin that were unrecorded or not recognized in a core the best evidence for documenting absolute lake level changes lies within the shore nearshore and deltaic sediments that were deposited across piedmonts and at the mouths of streams as lake level rose and fell we review the different shorezone environments and resulting deposits used in such reconstructions and discuss potential estimation errors lake level studies based on deposits and landforms have provided paleohydrologic records ranging from general changes during the past million years to centennial scale details of fluctuations during the late pleistocene and holocene outcrop studies have documented the integration histories of several important drainage basins including the humboldt amargosa owens and mojave river systems that have evolved since the miocene within the active tectonic setting of the great basin these histories have influenced lake levels in terminal basins many pre late pleistocene lakes in the western great basin were significantly larger and record wetter conditions than the youngest lakes outcrop based lake level data provide important checks on core based proxy interpretations we discuss four such comparisons in some cases such as for lakes owens and manix outcrop and core data synthesis yields stronger and more complete records in other cases such as for bonneville and lahontan conflicts point toward reconsideration of confounding factors in interpretation of core based proxies

the kuroshio extension bifurcation region a pelagic hotspot for juvenile loggerhead sea turtles satellite telemetry of 43 juvenile loggerhead sea turtles caretta caretta in the western north pacific together with satellite remotely sensed oceanographic data identified the kuroshio extension bifurcation region kebr as a forage hotspot for these turtles in the kebr juvenile loggerheads resided in kuroshio extension current kec meanders and the associated anti cyclonic warm core and cyclonic cold core eddies during the fall winter and spring when the kec water contains high surface chlorophyll turtles often remained at a specific feature for several months however in the summer when the kec waters become vertically stratified and surface chlorophyll levels are low the turtles moved north up to 600 km from the main axis of kec to the transition zone chlorophyll front tzcf in some instances the loggerheads swam against geostrophic currents and seasonally all turtles moved north and south across the strong zonal flow loggerhead turtles traveling westward in the kebr had their directed westward movement reduced 50 by the opposing current while those traveling eastward exhibited an increase in directed zonal movement it appears therefore that these relatively weak swimming juvenile loggerheads are not passive drifters in a major ocean current but are able to move east west north and south through this very energetic and complex habitat these results indicate that oceanic regions specifically the kebr represent an important juvenile forage habitat for this threatened species interannual and decadal changes in productivity of the kebr may be important to the species s population dynamics further conservation efforts should focus on identifying and reducing threats to the survival of loggerhead turtles in the kebr r 2006 elsevier ltd all rights reserved

dating quaternary fault scarps formed in alluvium using morphologic parameters abstract ages of fault scarps as well as those other types of transport limited slopes can be estimated by comparing their morphology with the morphology of scarps of known age age estimates are derived by fitting the scarp profiles to synthetic profiles generated using a diffusion equation or alternatively by classification using a linear discriminant function the usefulness of morphology derived age estimates depends on the relative importance of non age related morphologic variation data from more than 200 scarp profiles demonstrate that morphologic variation not related to scarp age can introduce significant uncertainties into morphology derived age estimates

chronology of lake bonneville 30 000 to 10 000 yr b p abstract 368 radiocarbon ages between 30 and 10 cal ka for samples collected from outcrops and shorelines from the lake bonneville basin have been compiled for this paper samples include 1 organic materials from sources outside the lake such as wood charcoal plant fragments from emergent aquatics and dispersed wetland organics and 2 carbonate materials deposited in the lake such as mollusk shells tufa charophyte debris ooids and marl in general organic materials provide rather than precise ages for lacustrine events but their interpretation is less complicated than interpretation of results from carbonate samples the data set shows evidence of contamination of different carbonate samples with both younger carbon and older carbon for example a radiocarbon reservoir at certain places within the lake during the middle transgressive phase accounts for ages of mollusk shells that are older than basal wood ages at similar altitudes the large number of ages permits an accurate reconstruction of the lake chronology conflicts between ages can be detected and reliable ages can be meaningfully integrated in interpretations if fewer ages were available the chronology might look simpler but its accuracy would be unknown

late quaternary faulting and thermoluminescence dating of the east cache fault zone north central utah the east cache fault zone ecfz the southernmost of five en echelon quaternary normal faults between the wasatch and teton faults displays evidence of two large paleoearthquakes in the last 15 000 years 15 ka stratigraphic data from a trench on the central segment of the ecfz are augmented with one radiocarbon date the regional radiocarbon chronology and 14 thermoluminescence tl age estimates of the 14 tl analyses performed by alpha analytic inc only 8 satisfied our criteria for statistical acceptability 20 per cent coefficient of variation 50 per cent extrapolation to residual tl level the tl age estimates broadly bracket the earlier faulting event at between 8 7 1 0 and 17 4 3 0 ka and the later event at between 2 5 0 5 and 8 7 1 0 ka one radiocarbon age further constrains the earlier event to be younger than 15 540 130 yr bp correlation of local quaternary deposits to the regional radiocarbon chronology provides indirect but more tightly limiting age constraints of ca 4 to ca 7 ka for the later event and ca 13 ka to 15 540 130 yr bp for the earlier event both events had small vertical displacements at the trench site 0 8 to 1 8 m but the cumulative net vertical tectonic displacement elsewhere is up to 4 2 m suggesrive of m s 6 9 to 7 1 paleoearthquakes single event displacements and the extent of fault scarps suggest that these two paleoearthquake ruptures were probably limited to the 20 kin long central segment of the east cache fault zone near logan utah the elapsed time since the most recent event on the central segment ca 4 to ca 7 ka is somewhat less than the estimated recurrence interval between the latest two paleoearthquake 8 6 3 0 ka however comparison of only a single poorly constrained recurrence interval with the elapsed time does not result in a confident assessment of future earthquake potential

linking foraging behaviour to physical oceanographic structures southern elephant seals and mesoscale eddies east of kerguelen islands in the southern ocean mesoscale features such as fronts and eddies have been shown to have a significant impact in structuring and enhancing primary productivity they are therefore likely to influence the spatial structure of prey fields and play a key role in the creation of preferred foraging regions for oceanic top predators optimal foraging theory predicts that predators should adjust their movement behaviour in relation to prey density while crossing areas with sufficient prey density we expect predators would change their behaviour by for instance decreasing their speed and increasing their turning frequency diving predators would as well increase the useful part of their dive i e increase bottom time thereby increasing the fraction of time spent capturing prey southern elephant seals from the kerguelen population have several foraging areas in antarctic waters on the kerguelen plateau and in the interfrontal zone between the subtropical and polar fronts this study investigated how the movement and diving behaviour of 22 seals equipped with satellite relayed data loggers changed in relation to mesoscale structures typical of the interfrontal zone we studied the links between oceanographic variables including temperature and sea level anomalies and diving and movement behaviour such as displacement speed diving duration and bottom time correlation coefficients between each of the time series were calculated and their significance tested with a parametric bootstrap we focused on oceanographic changes both temporal and spatial occurring during behavioural transitions in order to clarify the connections between the behaviour and the marine environment of the animals we showed that a majority of seals displayed a specific foraging behaviour related to the presence of both cyclonic and anticyclonic eddies we characterized mesoscale oceanographic zones as either favourable or unfavourable based on the intensity of foraging activity as identified by the behavioural variables our findings highlight the importance of mesoscale features for top predators behaviour and introduce a new approach for evaluating the importance to the seals of the origin and intensity of these features

eddies in the north brazil current retroflection region observed by geosat altimetry mesoscale fluctuations in the western tropical atlantic are analyzed in geosat altimetry sea surface height ssh and geostrophic velocity anomalies to investigate the role of eddies in the north brazil current nbc retroflection zone the detachment of anticyclonic eddies from the nbc retroflection is observed during november through january when the nbc retroflection into the north equatorial countercurrent necc weakens and finally breaks down these eddies are traced over more than 2 months between 50 and 60 w on their way toward the caribbean at average speeds of 15 cm s 1 in one case an apparent merger of two anticyclonic eddies occurs one detached from the retroflection zone and one detached from the necc cyclonic eddies are also observed but are generally less persistent mesoscale ssh variance just west of the retroflection increases by a factor of 2 from early summer to winter mainly because of the anticyclonic eddies interhemispheric water mass transfer associated with the eddy flux out of the nbc retroflection may amount to an average transport of 3 sv

bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum abstract lacustrine shoreline depositional features in the bonneville basin western north america were investigated to chronicle paleolake expansion and contraction in response to climate change based on stratigraphy sedimentology geomorphology and radiocarbon dating this study identifies multiple intermediate to large lake intervals during marine isotope stage 3 and the last glacial maximum timing and magnitude of the bonneville basin lake size change are compared with those of hemispheric scale climate change events reported from the greenland ice sheet southwestern north america winter precipitation and east asian monsoon 18 o records the amount of precipitation received by surface water systems in the bonneville basin appears to have increased significantly during the greenland stades throughout the last half of mis 3 and early mis 2 the lake also underwent rapid large amplitude oscillations during the last glacial maximum

stratigraphy and chronology of offshore to nearshore deposits associated with the provo shoreline pleistocene lake bonneville utah abstract stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of lake bonneville based on key marker beds and geomorphic position the deposits are interpreted to have accumulated during the period from the late transgressive phase through the overflowing phase into the regressive phase of the lake radiocarbon ages of sediments associated with the provo shoreline indicate that lake bonneville dropped rapidly from the provo shoreline at about 12 600 14c yr bp 15 000 cal yr b p the presence of one or more sand beds in the upper part of the provo aged marl indicates rapid lowering of lake level or storm events at the end of the provo episode an accurate understanding of the timing and nature of lake bonneville s climate driven regression from the provo shoreline is critical to correlations with records of regional and hemispheric climate change the rapid descent of the lake from the provo shoreline correlates with the decline of lakes lahontan and estancia and with the onset of the b o lling aller o d warming event

amino acid paleothermometry of quaternary ostracodes from the bonneville basin utah abstract unlike many other proxy climate recorders temperature dependent chemical reactions that take place in fossils are independent of paleoprecipitation changes and therefore allow paleotemperatures to be calculated uniquely in this study i use the extent of amino acid racemization in fossil ostracode shells to reconstruct the temperature history of the bonneville basin utah the enantiomeric composition d l ratios of 64 ostracode samples each comprising an average of 18 subsamples from 25 sites were analyzed by reverse phase hplc the effective diagenetic temperature edt for five intervals of the quaternary including the last full glacial period was calculated for two amino acids aspartic and glutamic acids errors associated with the edt calculations were derived using a monte carlo procedure age control was provided by both new and previously published ams 14 c luminescence tephra and amino acid geochronology the edt for the southern bonneville basin during the middle pleistocene interval from 620 150 ka oxygen isotope stages ois 16 6 was 5 7 1 5 c this compares with an edt of 10 9 1 3 c for the late holocene last 5 8 cal ka and a current mean annual temperature of about 9 4 c at nearby sites 40 n latitude the edt then decreased to 3 3 1 3 c for the interval from ois 6 2 150 12 cal ka during the last full glacial period 24 12 cal ka ois 2 the edt was 1 1 2 5 c or about 10 3 c lower than during the late holocene paleotemperatures this low suggest that reduced evaporation rather than increased precipitation could have accounted for the increased effective moisture and the growth of lake bonneville

transgressive stratigraphic record and possible oscillations of late pleistocene lake bonneville northern hogup mountains utah u s a abstract distinct mappable facies changes make the stratigraphic record of the shorezone of late pleistocene lake bonneville the most robust indicator for past lake level oscillations unfortunately clear stratigraphic evidence of transgressive and regressive deposits has been generally lacking new stratigraphic and chronological data within the lacustrine shorezone sediments of the hogup mountains of northwestern utah provide some of the best evidence yet for oscillations within the overall transgressive phase of the lake this study documents two previously unknown oscillations hereby named the lower hogup 22 cal ka and upper hogup 20 6 cal ka oscillations and provides further evidence for the previously proposed u2 oscillation 21 3 cal ka the study suggests that the water level of the lake changed dramatically up to 25 of the lake s total volume during the transgressive phase 30 15 cal ka with the additional oscillations documented in this study there are seven proposed oscillatory events during the transgressive phase of the lake these events likely correlate to rapid but short term regional climatic fluctuations during the broader climatic trends of the last glacial maximum however it is still unknown what specific climatic drivers are causing these oscillations and if these events can be correlated to other global climatic events

ages of travertine deposits in eastern grand canyon national park arizona abstract travertine deposits in eastern grand canyon national park arizona are inferred to have formed under conditions of effective wetness that were greater than present uranium series dating of 17 samples indicates that the deposits formed at about 15 000 71 000 111 000 171 000 and 338 000 yr b p intervals of travertine deposition are essentially contemporaneous with dated high paleolake levels montane glacial maxima and high paleowater table levels from several great basin localities

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

a revised chronology for the last pleistocene lake cycle in the central lahontan basin radiocarbon dates of plant materials from packrat middens in caves below the elevation of the last high stand of pleistocene lake lahontan in conjunction with radiocarbon dates of ancient archaeological materials provide evidence that the last high stand terminated before 12 070 yr b p this new information suggests that the last major fluctuation in the level of lake lahontan was approximately synchronous with those of lakes bonneville and russell and that these three lakes probably responded contemporaneously to the same regional paleoclimatic changes

chronology of latest pleistocene mountain glaciation in the western wasatch mountains utah u s a abstract understanding the timing of mountain glacier and paleolake expansion and retraction in the great basin region of the western united states has important implications for regional scale climate change during the last pleistocene glaciation the relative timing of mountain glacier maxima and the well studied lake bonneville highstand has been unclear however owing to poor chronological limits on glacial deposits here this problem is addressed by applying terrestrial cosmogenic 10be exposure dating to a classic set of terminal moraines in little cottonwood and american fork canyons in the western wasatch mountains the exposure ages indicate that the main phase of deglaciation began at 15 7 1 3 ka in both canyons this update to the glacial chronology of the western wasatch mountains can be reconciled with previous stratigraphic observations of glacial and paleolake deposits in this area and indicates that the start of deglaciation occurred during or at the end of the lake bonneville hydrologic maximum the glacial chronology reported here is consistent with the growing body of data suggesting that mountain glaciers in the western u s began retreating as many as 4 ka after the start of northern hemisphere deglaciation at ca 19 ka

geometry and kinematics of active normal faults south oquirrh mountains utah implication for fault growth the nnw striking south oquirrh mountains normal fault zone consists of four individual faults the individual faults are arranged in a right stepping pattern in the north and a left stepping pattern in the south forming a convex shaped fault zone in map view with the apex towards the hanging wall late quaternary fault activity is characterized by 2 0 4 5 m high discontinuous fault scarps developed in both late quaternary alluvium and bedrock the fault scarps in bedrock contain evidence of two large rupture events the last large earthquake occurred prior to the highstand of the bonneville lake cycle 15 ka based on cross cutting relationship between the bonneville shoreline and the fault scarp and on comparisons of fault scarp morphology cumulative displacement patterns inferred from range crest elevations bouguer gravity data in the adjacent basin and rotation of the subsidiary faults adjacent to the west mercur fault are similar to the pattern of displacements measured across late quaternary fault scarps that is the maximum displacement is near the apex of the convex shaped fault zone where the west mercur fault is located and then tapers off towards both ends of the fault zone fault traces that range from a few meters to tens of kilometers long are characterized by two dominant orientations strike n11 w and n43 w the two orientations are separated from each other by a statistically constant angle of 33 3 slip directions concentrate on a trend of s70 w for both groups of faults perpendicular to the average strike of the fault zone these data indicate that the geometry of the fault surfaces is non cylindrical and may be composed of self similar structural ridges and troughs of variable wavelength and amplitude that are elongated parallel to slip direction the relationships between fault geometry displacement and geomorphology in the south oquirrh mountains fault zone suggests a growth model of normal faults in which apex points on the convex shaped fault sections mark the nucleation points of primary faults secondary faults developed at the ends of the primary fault step into the footwall block as the fault zone grows laterally intersecting regions between two laterally growing fault zones are concave shaped in map view

a general method for morphologic dating of hillslopes morphologic dating of hillslopes is the determination of the age of a hillslope by its morphology current methods match the observed morphology with the morphology predicted by the diffusion equation model for hillslope evolution the morphologic dating method presented here requires no specific model for evolution but is only applicable to transport limited hillslopes on which the downslope debris flux is some scale and time independent function of slope angle if these conditions are met changes in morphology with scale e g height for a set of hillslopes of a fixed age are identical to changes in morphology with time for a hillslope of a fixed scale this fact provides the basis for a simple generally applicable method for morphologically dating such hillslopes with any initial morphology this new dating method may be applied to a wide variety of vegetated hillslopes in temperate humid regions and is an improvement over previous morphologic dating methods that relied on the diffusion equation model

cosmogenic nuclide and uranium series dating of old high shorelines in the western great basin usa closed basin pluvial lakes are sensitive recorders of effective moisture and they provide a terrestrial signal of climate change that can be compared to marine and ice records of glacial interglacial cycles although the most recent deep lake cycle in the western great basin at ca 16 ka has been studied intensively comparatively little is known about the longer term quaternary lacustrine history of the region lacustrine features higher than those of the most recent highstand have been discovered in many locations throughout the western great basin qualitative geomorphic and soil studies of shoreline sequences above the latest pleistocene level suggest that their ages increase as a function of increasing altitude the results of cosmogenic nuclide dating using chlorine 36 depth profiles from three sites in nevada walker lake columbus salt marsh and newark valley combined with uranium series and radiocarbon ages corroborate the geomorphic and soil evidence the 36 cl results are consistent with available 14 c ages and together indicate that the most recent highstands of all three lakes occurred ca 20 15 ka late in marine isotope stage mis 2 as shown by previous ages the 36 cl ages indicate that older lakes in all three basins reached highstands between 100 and 50 ka and most likely during mis 4 shorelines of this age are at about the same or higher altitudes as the younger mis 2 shorelines in those basins the 36 cl results combined with uranium series ages and one tephra correlation obtained on shorelines higher in altitude than those of mis 4 and 2 lakes suggest that there were also major lake highstands in the western great basin at ca 100 200 ka likely corresponding with mis 6 and during at least two older periods from these results we conclude that the preserved shorelines show an apparent decrease in maximum levels with time suggesting long term drying of the region since the early middle pleistocene

lake bonneville constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of bonneville provo and gilbert stage shorelines the deformed shorelines of the late pleistocene lake bonneville provide an excellent opportunity to analyze the response of the earth to surface loads of relatively short wavelengths 400 km and short duration 30 kyr recently revised estimates of the lake loading history and an expanded compilation of shoreline elevations for the bonneville 1550 m provo 1440 m and gilbert 1300 m shorelines have prompted us to reexamine the deflection the earth model we use is identical with that employed by nakiboglu and lambeck and consists of an elastic plate overlying a maxwell viscoelastic channel and a rigid base our calculation differs from that of nakiboglu and lambeck in two respects we used a significantly more detailed load model and we compared our results with observations from three distinct shorelines the lake elevation history spans 32 kyr in 18 piecewise linear segments the water load is computed at each time step from a digital terrain model 4 4 km cell size and a specified lake elevation we find that the use of three separate shorelines significantly reduces the acceptable region of parameter space the effective elastic lithospheric thickness is 23 2 km the mantle viscosity is 1 2 0 2 1020 pa s and the depth to a significant viscosity increase is no less than 300 km though it might be much more examination of the residual deflections differences between observed and computed shoreline elevations reveals a regional tilt down to the ne of 6 10 5 which we attribute to collapse of the peripheral bulge produced by the laurentide ice sheet

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

evidence for a shallow early or middle wisconsin age lake in the bonneville basin utah abstract relatively complete stratigraphic records of the bonneville cycle and of at least one and probably two earlier lacustrine are exposed along the bear river below cutler dam in northern utah between altitudes of 1290 and 1365 m in most exposures the unconformity between the bonneville alloformation and the underlying unit herein named the cutler dam alloformation is marked by slight erosional relief and by a weakly to moderately developed buried soil herein named the fielding geosol in truncated profiles the fielding geosol reaches a maximum of stage ii carbonate morphology wood from near the base of the cutler dam alloformation yielded a 14 c date of 36 000 yr b p beta 9845 alloisoleucine isoleucine aile ile ratios of sphaerium shells from the cutler dam beds average 0 15 0 01 in the total hydrolysate which is significantly greater than the average for sphaerium shells of bonneville age elsewhere in the basin therefore the cutler dam alloformation is older than 36 000 yr b p but much younger than deposits of the little valley lake cycle 140 000 yr b p which bear shells having significantly higher aile ile ratios the cutler dam alloformation along the bear river may be broadly correlative with marine oxygen isotope stages 4 or 3 fine grained fossiliferous marginal lacustrine facies of the cutler dam alloformation are exposed at altitudes near 1340 m and are probably the highest exposures of sediments deposited in the early or middle wisconsin lake in the bonneville basin

the santa rita fault zone evidence for large magnitude earthquakes with very long recurrence intervals basin and range province of southeastern arizona a discontinuous zone of subdued west facing fault scarps offset quaternary alluvium along 58 km of the western piedmont of the santa rita mountains south of tucson arizona scarps trend ne to n s and are 1 to 6 km basinward from the deeply embayed mountain front scarp heights range from 1 to 7 m and maximum scarp slope angles range from 3 to 9 5 a 6 m deep trench excavated in middle pleistocene and younger deposits exposed a high angle fault zone with about 3 5 m of total displacement estimated ages of faulted and unfaulted surfaces extent of degradation of piedmont scarps and stratigraphic relations exposed in the trench suggest an age of about 100 ka for the most recent surface rupture event units having well developed relict soils of late pleistocene age and older are faulted whereas units having weakly to moderately developed soils of latest pleistocene and holocene age are not offset morphologic fault scarp analyses suggest an age of 60 to 100 ka earthquake magnitude estimates derived using minimum and maximum seismic source moment calculations range from 6 4 to 7 3 one or more earlier surface rupture events are implied by significantly high scarp heights on mid pleistocene than on late pleistocene surfaces scarp heights on middle and early pleistocene surfaces are similar restricting faulting to post middle pleistocene time 200 to 300 ka stratigraphic relationships observed in the trench also suggest two fault displacement events tectonic landform analysis of the mountain front piedmont area implies several m y of inactivity along the range bounding fault system prior to these late quaternary displacements extremely long recurrent intervals between displacement events and reactivation of faulting after an interval of tectonic quiescence are typical of late quaternary fault behavior in southeastern arizona

early holocene great salt lake usa shorelines and surficial deposits including buried forest floor mats and organic rich wetland sediments show that great salt lake did not rise higher than modern lake levels during the earliest holocene 11 5 10 2 cal ka bp 10 9 c 14 ka bp during that period finely laminated organic rich muds sapropel containing brine shrimp cysts and pellets and interbedded sodium sulfate salts were deposited on the lake floor sapropel deposition was probably caused by stratification of the water column a freshwater cap possibly was formed by groundwater which had been stored in upland aquifers during the immediately preceding late pleistocene deep lake cycle lake bonneville and was actively discharging on the basin floor a climate characterized by low precipitation and runoff combined with local areas of groundwater discharge in piedmont settings could explain the apparent conflict between evidence for a shallow lake a dry climate and previously published interpretations for a moist climate in the great salt lake basin of the eastern great basin c 2015 university of washington published by elsevier inc all rights reserved

a new estimate of the global 3d geostrophic ocean circulation based on satellite data and in situ measurements abstract a new estimate of the global ocean 3d geostrophic circulation from the surface down to 1500 m depth surcouf3d has been computed for the 1993 2008 period using an observation based approach that combines altimetry with temperature and salinity through the thermal wind equation the validity of this simple approach was tested using a consistent dataset from a model reanalysis away from the boundary layers errors are less than 10 in most places which indicate that the thermal wind equation is a robust approximation to reconstruct the 3d oceanic circulation in the ocean interior the surcouf3d current field was validated in the atlantic ocean against in situ observations we considered the andro current velocities deduced at 1000 m depth from argo float displacements as well as velocity measurements at 26 5 n from the rapid mocha current meter array the surcouf3d currents show similar skill to the 3d velocities from the glorys mercator ocean reanalysis in reproducing the amplitude and variability of the andro currents in the upper 1000 m high correlations are also found with in situ velocities measured by the rapid mocha current meters the surcouf3d current field was then used to compute estimates of the atlantic meridional overturning circulation amoc through the 25 n section showing good comparisons with hydrographic sections from 1998 and 2004 monthly averaged amoc time series are also consistent with the rapid mocha array and with the glorys mercator ocean reanalysis over the april 2004 september 2007 period finally a 15 years long time series of monthly estimates of the amoc was computed the amoc strength has a mean value of 16 sv with an annual resp monthly standard deviation of 2 4 sv resp 7 1 sv over the 1993 2008 period the time series characterized by a strong variability shows no significant trend

updated cosmogenic chronologies of pleistocene mountain glaciation in the western united states and associated paleoclimate inferences abstract surface exposure dating with terrestrial cosmogenic nuclides tcns has become the primary method for determining numerical ages of pleistocene mountain glacial deposits and landforms in the conterminous western united states u s and in numerous other glaciated settings worldwide recent updates to models of tcn production and scaling warrant a reconsideration of published exposure ages of moraines of the last two pleistocene glaciations and associated paleoclimate inferences previously reported tcn exposure ages of moraines are recalculated here using newer production rates and scaling models for nuclides helium 3 3he beryllium 10 10be aluminum 26 26al and chlorine 36 36cl in most cases yielding significant differences from originally reported ages recalculated tcn exposure ages of moraines of the penultimate glaciation display a high degree of variability for individual landforms particularly toward the younger end of age distributions suggesting that exposure history is affected by moraine denudation and that older age modes provide the best estimate of the depositional age of these moraines oldest exposure ages of penultimate glaciation moraines are well aligned among mountain ranges across the western u s and yield a mean of 138 13 ka indicating that mountain glaciation occurred in step with global ice volume maxima during marine oxygen isotope stage 6 on average terminal moraines of the last glaciation date to 19 5 2 3 ka and correspond to the latter part of the global last glacial maximum lgm down valley recessional moraines representing prolonged glacial stabilizations or readvances to 75 of maximum lengths have a mean exposure age of 17 0 1 8 ka suggesting that these moraine positions were last occupied during heinrich stadial 1 evidence for multiple glacial culminations during the last glaciation is found in several mountain ranges and likely reflects at least two phases of late pleistocene climate an earlier phase when glaciers attained their maximum length in response to cooling during the lgm and a later phase when glaciers persisted at or readvanced to near maximum lengths in response to sustained cold temperatures and or increased precipitation

radiocarbon chronology of lake bonneville eastern great basin usa abstract lake bonneville occupied a series of connected topographically closed structural basins in the eastern great basin from about 30 ka to 12 ka the following synthesis of lake bonneville history is based on a critical evaluation of the stratigraphic and geomorphic contexts of 83 radiocarbon ages of a variety of samples including wood charcoal dispersed organic matter mollusk shells and tufa the lake began to rise from levels close to average holocene levels after about 28 ka by 22 ka it had transgressed approximately 100 m between 22 and 20 ka it regressed about 45 m in the stansbury oscillation and the stansbury shoreline was formed transgression after 20 ka proceeded in two phases a rapid phase from 20 to 18 ka and a slower phase from 18 to 15 ka the lake overflowed intermittently at its highest level the bonneville shoreline from about 15 to 14 5 ka then catastrophically dropped 100 m during the bonneville flood to the level of the provo shoreline which it occupied until about 14 ka subsequent closed basin regression was rapid and complete by 12 ka and was followed by a modest transgression to form the gilbert shoreline between 10 9 and 10 3 ka the lake bonneville record is an accurate proxy of the changing water balance in the bonneville basin during the late pleistocene although the nature of the climatic changes during this period are still uncertain

the amazon influenced muddy coast of south america a review of mud bank shoreline interactions the 1500 km long coast of south america between the amazon and the orinoco river mouths is the world s muddiest this is due to the huge suspended sediment discharge of the amazon river 106 754 tons yr 1 9 part of which is transported alongshore as mud banks mud bank formation is controlled by the physical oceanography of the continental shelf seaward of the amazon river mouth an initial seafloor storage area for much of the suspended sediment discharged from the river in this area rapid and sustained fluid mud concentration and trapping are associated with fresh water salt water interaction and estuarine front activity on the shelf due to the enormous amazon water discharge ca 173 000 m3 s 1 at obidos 900 km upstream of the mouth fluid mud is transported shoreward and then along the coasts of the guianas by a complex interaction of wave and tidal forcing and wind generated coastal currents the mud banks which may number up to 15 or more at any time are up to 5 m thick 10 to 60 km long and 20 to 30 km wide and each may contain the equivalent mass of the annual mud supply of the amazon as the banks migrate alongshore their interaction with waves results in complex and markedly fluctuating shorelines that are associated with space and time varying depositional bank phases and erosional inter bank phases bank zones are protected from wave attack as a result of wave energy dampening by mud and undergo significant albeit temporary coastal accretion accompanied by rapid mangrove colonization the dampening of waves in bank areas as they propagate onshore is accompanied by the shoreward recycling of mud commonly in the form of individual mud bars these bars progressively undergo desiccation and consolidation and thus constitute a major pathway for rapid and massive colonization by mangroves erosion by waves propagating across relatively mud deficient shoreface zones in inter bank areas can lead to muddy shoreline retreat rates of tens of metres to several kilometres over a few months to a few years accompanied by massive removal of mangroves notwithstanding the higher incident wave energy on inter bank shores inter bank shorefaces are permanently muddy due to the pervasive influence of the amazon muddy discharge inter bank and transitional bank to inter bank phases are associated with both periodic sandy chenier formation and extreme forms of rotation of rare headland bound sandy beaches the high mud supply from the amazon has been the overarching geological control on the quaternary evolution of the northeastern south american coast having led to the growth of a muddy shelf clinoform at the mouth of the amazon and more or less important progradation throughout this coast net progradation reflects an imbalance in favour of deposition during each mud bank inter bank cycle the high mud supply has presumably blanketed shelf sand deposited by smaller rivers during eustatic lowstand phases the shelf clinoform structure at the mouth of the amazon and the muddy coastal progradation throughout the coast of the guianas and into venezuela provide analogues of the geological record on muddy shorefaces

effect of far field slope on morphologic dating of scarplike landforms the principal finding of this paper is that the far field slope has a first order effect on model age determinations of scarplike landforms in weakly consolidated terrains observationally this can be demonstrated in two ways using the lake bonneville and lahontan shoreline scarps as separate and combined data sets use of the reduced scarp slope tan theta sub s minus b where theta sub s is the maximum scarp angle and b is the far field or fan slope instead of tan theta sub s alone as the measure of scarp slope measurably reduces separation between the two data sets induced by different average fan slopes for the two data sets and significantly reduces scatter in the slope offset plot for both the separate and combined data sets theoretically the argument can be put even more strongly at least within the range of linear and nonlinear diffusion models that the authors consider here together with a mathematical transformation of the empirical approach of r c bucknam and r e anderson when one correctly takes into account the far field slope one will basically get the same age determination no matter which of these models one uses conversely without accounting properly for the effect of far field slope one is virtuallymore guaranteed to get an erroneous age determination no matter which model is used less

lake bonneville fluctuations and global climate change lake bonneville the largest late pleistocene closed basin lake in the north american great basin fluctuated widely in response to changes in climate the geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water and stratigraphic studies of shore zone deposits provide evidence of millennial scale lake level fluctuations that had amplitudes of about 50 m between 30 and 10 ka falling lake events occurred at 21 18 5 19 17 5 16 15 5 14 13 and 10 ka radiocarbon years synchronously with the terminations of heinrich events h1 and h2 and other smaller scale iceberg rafting events a b c and younger dryas in the north atlantic ocean the lake bonneville results thus support other climate records that suggest that late pleistocene millennial scale climate change was global in extent the size and shape of the northern hemisphere ice sheets which determined the mean positions of storm tracks may have been the primary control on late pleistocene water budgets of great basin lakes

slip rate variations on faults in the basin and range province caused by regression of late pleistocene lake bonneville and lake lahontan late pleistocene regression of two large pluvial lakes lake bonneville and lake lahontan caused considerable lithospheric rebound in the basin and range province usa here we use finite element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes our results show that fluctuations in the volume of lake bonneville caused along strike slip variations on the wasatch normal fault with a pronounced slip rate increase on its northern and central parts during lake regression the response of normal and strike slip faults near the ring shaped lake lahontan depends on their location within the rebound area faults located in the centre of rebound show a slip rate increase during lake regression whereas strike slip faults at the periphery decelerate all slip rate variations are caused by differential stress changes owing to changing lake levels regardless of the individual fault response

reevaluation of holocene faulting at the kaysville site weber segment of the wasatch fault zone utah the 1978 kaysville utah trench excavated by swan and others 1980 across a large graben of the weber segment of the wasatch fault zone was reexcavated in 1988 to reevaluate the timing and nature of holocene faulting relogging of the trench reveals evidence for five or six faulting events younger than the provo phase of lake bonneville circa 13 000 14c years b p geometric reconstruction of net vertical offset in the last three events suggests a variation in coseismic vertical displacement at this site ranging from a net of 1 4 3 4 m per event the three latest faulting events occurred at shortly before 0 6 0 8 ka 2 8 0 7 ka and circa 3 8 7 9 ka earlier events cannot be directly dated because older graben fill sediments yielded thermoluminescence ages older than the time of deposition and some scarp derived colluvial wedges beneath the trench floor were not exposed the two younger faulting events we recognize at kaysville correlate reasonably well with faulting events on the same segment 25 km north near east ogden utah at circa 0 8 1 2 ka and 2 5 3 0 ka forman and others 1991 whereas the earlier kaysville event is significantly older than the earliest 3 5 4 0 ka event dated at east ogden the 3 5 4 0 ka ground rupture recognized at east ogden may have died out at a subsegment boundary between the two trench sites within the 61 km long weber segment

compound soil horizons with mixed calcic and argillic properties examples from the northern great basin usa abstract palaeosols between deposits of the last two deep lake cycles in the northern great basin have multiple carbonate engulfed horizons and compound calcic and argillic properties at depth they are difficult to explain pedogenetically because they bifurcate in places especially in basin centres where they are separated by sediments of a minor lake expansion of probable early wisconsinan age one sequence of processes can account for all phenomena two cycles of colluviation and synchronous admixture of loess particles were each succeeded by the formation of an argillic over a calcic horizon carbonate enrichment resulting from the later period of soil formation affected the buried older soil this led to welding of the two soils and the formation of a compound horizon carrying the argillic properties of the first and the calcic properties of the second pedogenic phase steady aeolian influx to the same soil surface the commonly invoked mechanism cannot explain the bifurcated palaeosols and is not needed to explain the welded ones