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

a stagodontid mammal from the mid cretaceous of france confirms the euramerican distribution of early marsupialiforms abstract the global palaeobiogeography of early marsupialiform mammals is still poorly understood due to a meagre fossil record outside western north america here two isolated teeth of a marsupialiform mammal from the lowermost upper cretaceous lower cenomanian of southwestern france are described and referred to stagodontidae a dentally specialized group whose unambiguous members are so far known exclusively from the upper cretaceous of north america the occurrence of stagodontids in europe represents additional evidence of faunal exchanges between the two landmasses during the latest albian early cenomanian interval around 100 million years ago and shows that early mid cretaceous marsupialiforms were more widely distributed than previously thought

exceptionally fast growth rate of 100 yr old tufa big soda lake nevada implications for using tufa as a paleoclimate proxy large tufa mounds 3 m tall with a basal circumference of 5 m have been discovered on the margin of big soda lake nevada usa these tufa mounds are rooted at a maximum of 4 m below the current lake surface and are actively forming from groundwater seepage which can be seen emanating from the top of the tufa mounds big soda lake is a volcanic crater lake whose water level is maintained exclusively by groundwater the age of the tufa mounds is well constrained because prior to the development of the newlands irrigation project in 1907 the water level was 18 m lower than the current lake level the vertical columnar nature of the tufa mounds indicates that they formed under the lake and not subaerially thus the tufa mounds are 100 yr old and have grown at a rate 30 mm yr stable oxygen and carbon isotope analyses of tufa carbonate compared to isotopic analyses of groundwater and lake water and hydrochemical data indicate that the fluids responsible for their precipitation are a simple mixture of modern groundwater and lake water and do not reflect a recent climate signature the exceptionally fast growth of the tufa mounds indicates that large tufa deposits may form almost instantaneously in geologic time given this potential for rapid growth and the fact that variations in isotopic compositions of tufa deposits have been interpreted in terms of changes in paleoclimate and changes in the composition of recharge water over thousands of years care should be taken when trying to determine the significance of variations in isotopic or chemical compositions of tufas that may have been caused by mixing with groundwater

oxygen and carbon isotope trends and sedimentological evolution of a meromictic and saline lacustrine system the holocene medicine lake basin north american great plains usa abstract the succession of sedimentary subfacies in the medicine lake basin south dakota usa documents numerous changes in total dissolved solids tds lake level and the nature and stability of meromixis during the holocene the lake formed about 10 6 ka b p when coarse clastics and massive fine grained muds were deposited in a well mixed freshwater system subsequently the lake became saline and meromictic depositing a finely laminated unit composed of variegated and gray muds organic facies gypsum and aragonite laminae phototrophic bacterial plate communities bpc at the chemocline were significant producers of pelagic organic matter relatively high lake levels at least 10 m higher than today but saline and meromictic conditions predominated through the early to mid holocene at the end of this phase lake level dropped and stable meromixis was disrupted sands and massive or banded muds were deposited in sublittoral areas and benthic microbial communities bmc spread over the lake replacing bpcs as the predominant microbial producers when lake level rose again massive and laminated units were deposited under less saline conditions another pronounced episode of low lake level and high salinity followed the most recent sediments are sapropels massive or banded muds and littoral sands the 18o record from authigenic aragonite shows more positive values during the arid mid holocene interval with an abrupt increase at the end of this period followed by generally more negative values during the cooler and wetter late holocene the small range of 18o values 3 suggests that the lake was well buffered against high frequency climatic cycles probably as a result of groundwater modulation we postulate that meromixis and the type of photosynthetic microbial communities dominating the basinal region of the lake system either bpcs or bmcs exerted major controls on the carbon cycle and consequently on the development of isotopic trends linking 13c and 18o values more negative 13c values during the early and mid holocene are interpreted as a consequence of the predominance of 12c enriched microbial carbon from bpcs examples of both covariant and inverse covariant isotope trends between 13c and 18o values occur in the medicine lake record inverse covariant trends characterize long periods of stable meromixis when bpcs predominate over bmcs we hypothesize that well developed water stratification caused by greater influx of relatively 18o depleted freshwater induces higher productivity at the chemocline and consequently more positive 13c values in the precipitated carbonates unstable phases of meromixis or holomictic conditions are characterized by a predominance of bmcs or other biogenic producers over bpcs and a number of other factors combine to promote covariant trends the medicine lake record is consistent with the paleoclimatic interpretation for the northern great plains of a more arid early and middle holocene followed by an abrupt transition to a relatively cooler and wetter late holocene the sedimentary succesion in medicine lake documents a much more fluctuating and abrupt climate behavior than suggested by the vegetation paleorecord and suggest a late holocene climate punctuated by arid episodes

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

dramatic local environmental change during the early eocene climatic optimum detected using high resolution chemical analyses of green river formation stromatolites abstract the eocene green river formation represents a system of lakes that covered parts of what is now wyoming colorado and utah and captures the early eocene climatic optimum eeco 52 50 million years ago or ma the warmest period of the cenozoic era and a period associated with very high levels of atmospheric co2 lakes especially closed basin lakes can respond dramatically to environmental change because of their sensitivity to precipitation and evaporation in this study stromatolites from the rife bed of the green river formation are used as fine scale records of terrestrial paleoenvironmental change during a global hothouse climate and to investigate how the environmental dynamics within the lake system affected the growth of stromatolites the stromatolites are composed of branching microdigitate columns laminated on the 10 100 m scale laminae are grouped in cm scale layers that alternate between calcite fan micritic and mixed microstructures the fan layers are depleted in 18o na and mg ca the micrite layers in contrast are comparatively enriched in 18o na and mg ca the 13c and 18o are strongly positively correlated suggesting the stromatolites formed in a closed basin lake consistent with the regional stratigraphy additionally clumped isotope analyses provide the first quantitative values for water temperatures in lake water from the green river formation 35 c for micrite layers and 28 c for fan layers changes in 18o and sodium ion concentration are likely related to periods of evaporation and recharge and thus can be used to estimate lake volume change during stromatolite growth two models one using sodium ion concentrations in a conserved system the other using rayleigh fractionation and mixing equations to explain changes in oxygen isotopes converge upon similar results for lake volume changes revealing multiple episodes of meter scale lake level rise and fall during the accretion of the 30 cm thick stromatolite because of the broad flat bathymetry of the lake such lake volume and depth changes would have been accompanied by shoreline shifts on the order of tens of kilometers while the stromatolites were actively growing challenging the view of a single stromatolite paleoenvironment in the lake therefore the fan microfabric interpreted here as abiogenic in nature formed in cooler waters when the lake was deeper possibly below a thermocline in contrast the micrite microfabric for which there is evidence of biogenicity formed when the lake was shallow and warm the alternation between biogenic and abiogenic microfabrics present in the rife bed stromatolites is hypothesized to result from dramatic changes in lake level influencing the microbiology and chemistry of the waters in which the stromatolites formed indicating that stromatolite growth can occur under disparate conditions and therefore does not necessarily represent a single facies

anthropogenic influences on the input and biogeochemical cycling of nutrients and mercury in great salt lake utah usa abstract despite the ecological and economic importance of great salt lake gsl little is known about the input and biogeochemical cycling of nutrients and trace elements in the lake in response to increasing public concern regarding anthropogenic inputs to the gsl ecosystem the us geological survey usgs and us fish and wildlife service usfws initiated coordinated studies to quantify and evaluate the significance of nutrient and hg inputs into gsl a 6 decrease in 15n observed in brine shrimp artemia franciscana samples collected from gsl during summer time periods is likely due to the consumption of cyanobacteria produced in freshwater bays entering the lake supporting data collected from the outflow of farmington bay indicates decreasing trends in 15n in particulate organic matter pom during the mid summer time period reflective of increasing proportions of cyanobacteria in algae exported to gsl on a seasonal basis the c n molar ratio of pom in outflow from farmington bay decreases during the summer period supportive of the increased activity of n fixation indicated by decreasing 15n in brine shrimp and pom although n fixation is only taking place in the relatively freshwater inflows to gsl data indicate that influx of fresh water influences large areas of the lake separation of gsl into two distinct hydrologic and geochemical systems from the construction of a railroad causeway in the late 1950s has created a persistent and widespread anoxic layer in the southern part of gsl this anoxic layer referred to as the deep brine layer dbl has high rates of so 4 2 reduction likely increasing the hg methylation capacity high concentrations of methyl mercury ch3hg median concentration 24 ng l were observed in the dbl with a significant proportion 31 60 of total hg in the ch3hg form hydroacoustic and sediment trap evidence indicate that turbulence introduced by internal waves generated during sustained wind events can temporarily mix the elevated ch3hg concentrations in the dbl with the more biologically active upper brine layer ubl brine shrimp collected during the summer fall time periods contained elevated hg concentrations median concentration 0 34 mg kg dry weight dw relative to samples collected during the spring median concentration

plio pleistocene lacustrine stromatolites from lake turkana kenya morphology stratigraphy and stable isotopes abell p i awramik s m osborne r h and tomellini s 1982 plio pleistocene lacustrine stromatolites from lake turkana kenya morphology stratigraphy and stable isotopes sediment geol 32 1 26 a sequence of fossil stromatolites from lake turkana in kenya was examined for 51so and 513c content these stromatolites ranging in age from holocene 10 000 yrs b p to middle pliocene 3 m y showed a variety of growth forms from oncolitic columnar layered to bulbous heads the stromatolites used in our study contain filamentous blue green algae of one morphological type and rare coccoids thus the stromatolites are considered biogenic the stable isotope ratios for oxygen and carbon indicate changing climatic conditions ranging from a cool wet climate prior to ca 1 9 m y to much drier warmer conditions around 1 4 m y followed in turn by a somewhat cooler and wetter climate at the end of the pleistocene

evaporation induced 18o and 13c enrichment in lake systems a global perspective on hydrologic balance effects growing pressure on sustainable water resource allocation in the context of global development and rapid environmental change demands rigorous knowledge of how regional water cycles change through time one of the most attractive and widely utilized approaches for gaining this knowledge is the analysis of lake carbonate stable isotopic compositions however endogenic carbonate archives are sensitive to a variety of natural processes and conditions leaving isotopic datasets largely underdetermined as a consequence isotopic researchers are often required to assume values for multiple parameters including temperature of carbonate formation or lake water delta o 18 in order to interpret changes in hydrologic conditions here we review and analyze a global compilation of 57 lacustrine dual carbon and oxygen stable isotope records with a topical focus on the effects of shifting hydrologic balance on endogenic carbonate isotopic compositions through integration of multiple large datasets we show that lake carbonate delta o 18 values and the lake waters from which they are derived are often shifted by 10 parts per thousand relative to source waters discharging into the lake the global pattern of delta o 18 and delta c 13 covariation observed in 70 of the records studied and in several evaporation experiments demonstrates that isotopic fractionations associated with lake water evaporation cause the heavy carbon and oxygen isotope enrichments observed in most lakes and lake carbonate records modeled endogenic calcite compositions in isotopic equilibrium with lake source waters further demonstrate that evaporation effects can be extreme even in lake records where delta o 18 and delta c 13 covariation is absent aridisol pedogenic carbonates show similar isotopic responses to evaporation and the relevance of evaporative modification to paleoclimatic and paleotopographic research using endogenic carbonate proxies are discussed recent advances in stable isotope research techniques present unprecedented opportunities to overcome the underdetermined nature of stable isotopic data through integration of multiple isotopic proxies including dual element c 13 excess values and clumped isotope temperature estimates we demonstrate the utility of applying these multi proxy approaches to the interpretation of paleohy droclimatic conditions in ancient lake systems understanding past present and future hydroclimatic systems is a global imperative significant progress should be expected as these modern research techniques become more widely applied and integrated with traditional stable isotopic proxies c 2015 elsevier ltd all rights reserved

factors affecting 14c ages of lacustrine carbonates timing and duration of the last highstand lake in the lahontan basin abstract two processes contribute to inaccurate 14c age estimates of carbonates precipitated within the lahontan basin nevadacalifornia low initial 14c c ratios in lake water reservoir effect and addition of modern carbon to calcium carbonate after its precipitation the mast reliable set of 14c ages on carbonates from elevations 1310 m in the pyramid and walker lake subbasins indicate that lakes in all seven lahontan subbasins coalesced 14 200 14c yr b p forming lake lahontan lake lahontan achieved its 1330 m highstand elevation by 13 800 14 c yr b p and receded to 1310 m by 13 700 14c yr b p calculations based on measured carbonate accumulation rates of the amount of time lake lahontan exceeded 1310 and 1330 m 500 and 50 yr are consistent with this chronology the timing of the lake lahontan highstand is of interest because of the linkage of highstand climates with proximity to the polar jet stream the brevity of the lahontan highstand is interpreted to indicate that the core of the southern branch of the polar jet stream remained only briefly over the lahontan basin

geomorphic controls on lacustrine isotopic compositions evidence from the laney member green river formation wyoming oxygen isotope values from lacustrine carbonate in the laney member of the green river formation wyoming exhibit a sudden basinwide 6 upsection decrease in 18 o at ca 49 ma 40 ar 39 ar geochronology constrains the duration of the isotopic shift to 200 000 years this change coincides with a sudden change in lake type from balancedfi lled in the lower laclede bed to overfi lled in the upper laclede bed as well as an increase in the proportion of calcitic 80 calcite out of total carbonate by x ray diffraction xrd samples from 32 to 73 the 18 o shift is correlatable through several locations across the greater green river basin and also coincides with a previously observed shift to less radiogenic 87

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

shoreline fluctuations of lake hayk northern ethiopia during the last 3500years geomorphological sedimentary and isotope records abstract this paper presents a stratigraphical and geomorphological analysis supported with geochronological dating aiming to reconstruct the late holocene lake level fluctuations and paleohydrological history of lake hayk this lake 23 km 2 in surface is located in the eastern side of the northern ethiopia highlands at an altitude of around 2000 m above sea level along the northern margin of the lake which is mainly characterized by steep rocky slopes the studied succession consists of colluvial and stromatolitic deposits along the southern margin which is characterized by a wide coastal plain drained by the main watercourse feeding the lake the ankarka river the study deposits are mainly palustrine deltaic and fluvial in origin geomorphological and sedimentological data integrated with a radiocarbon chronology highlighted that during the last 3500 years the lake was affected by three main highstand phases which occurred at about 3250 3000 2600 950 and 650 160 cal yrs bp respectively these highstands are documented by aggradation of siliciclastic systems both along the southern and northern margins whereas isotope data highlight that most of the stromatolitic deposits developed during phases of intense evaporation this peculiar feature could be differently explained i stromatolite growth was triggered by rapid lacustrine rises but mainly occurred during the long lasting lacustrine falls ii stromatolite developed during tectonic induced transgressions which occurred during phases of intense evaporation despite the possible effects of local tectonics the lake hayk record shows a good correlation with those of several late holocene lakes of east africa lakes naivasha tanganyika victoria turkana abhe ziway shala bosumtwi and abyiata highlighting that it can be considered as a suitable climatic proxy for late holocene time span in particular by both siliciclastic and stromatolitic deposits occurring in the uppermost part of the sedimentary succession record high frequency oscillations which have been ascribed to three main droughts that occurred during the little ice age these droughts were previously documented only in lake naivasha and lake victoria

stromatolites in walker lake nevada great basin usa record climate and lake level changes 35 000 years ago abstract walker lake is a closed basin remnant of the large pleistocene glacial lake lahontan system that has experienced multiple high amplitude 100 200 m changes in water level over the past 40 000 years in response to changes in climate a laminated carbonate stromatolite composed of varying proportions of calcite fans and micrite was collected from a paleoshoreline located at approximately 58 m above present lake level radiocarbon dating revealed that the stromatolite spans approximately 2000 years of growth from 35 227 to 33 727 calibrated years before present ybp a time period during which paleolake level is not well constrained distinct laminae were drilled along the growth axis and the resulting powders were collected for clumped isotope analyses to generate formation temperatures lake water temperatures during stromatolite formation from which 18 o water was calculated results indicate that the stromatolite experienced an initial increase in temperature and water 18 o values followed by a decrease in both during the course of accretion the resulting temperature and isotopic data were input into a rayleigh distillation model for lakewater evaporation in order to estimate the magnitude of lake level and volume fluctuations over the course of accretion modeling results reveal a lake level decrease between 8 1 and 15 6 m followed by an increase of between 4 3 and 8 8 m during the course of stromatolite growth the results of this study indicate that walker lake experienced significant lake volume change over the course of 2000 years perhaps as a response to precipitation changes driven by fluctuations in the polar jet stream and accompanying changes in regional climate and or evaporation induced changes in lake level these results add to a growing body of research indicating that stromatolites and other lacustrine tufas represent a detailed and extensive terrestrial archive that can potentially be used to reconstruct the timing and magnitude of climate change

shoreline tufa and tufaglomerate from pleistocene lake bonneville utah usa stable isotopic and mineralogical records of lake conditions processes and climate shoreline carbonate deposits of pleistocene lake bonneville record the conditions and processes within the lake including the evaporative balance as well as vertical and lateral chemical and isotopic gradients tufas swash zone and tufaglomerates cemented subaqueous colluvium or beachrock on multiple well developed shorelines near the silver island range utah also present an opportunity to examine physicochemical lake processes through time three shorelines are represented by carbonate deposits including the 23 20 ka stansbury stage 15 14 5 ka bonneville stage and 14 5 14 ka provo stage mean 18ovsmow values of all three shorelines are statistically indistinguishable 27 1 when a few bonneville samples of unusual composition are neglected however differences in primary carbonate mineralogy indicate that the correspondence is an artefact of the different fractionation factors between calcite or aragonite and water second in order to sustain a much smaller shallower lake during the colder stansbury stage the climate must have also been relatively dry third 18o values in tufa are higher than tufaglomerate by 0 5 consistent with greater evaporative enrichment of lake water in the swash zone fourth mean 13c values for the provo stansbury and bonneville shorelines 4 4 5 0 and 5 2 respectively show that carbon species were dominated by atmospheric exchange with the variations produced by differences in the oxidation of organic matter comparisons of shoreline carbonates with deep lake marls of the same approximate age indicate that shoreline carbonate was much higher in 13c and 18o values both 2 5 during bonneville time whereas isotopic differences were minor both 1 in stansbury time in particular the bonneville stage may have sustained large vertical or lateral isotopic gradients due to evaporative enrichment effects on 18o values in contrast the lake during the much shallower stansbury stage may have been well mixed differences in the primary mineralogy stansbury and bonneville aragonite calcite provo calcite aragonite reflect profound differences in lake chemistry in terms of open versus closed basin lakes the establishment of a continuous outlet during provo time probably reduced the mg2 ca2 ratio of lake water curiously regardless of primary mineralogy tufaglomerate cements are enriched in na and cl and depleted in mg2 relative to capping tufa of the same age this probably reflects vital or kinetic effects in the swash zone tufa we suspect that abiotic effects may have been important in the dark pore space of developing tufaglomerate where the absence of light suppressed photosynthesis copyright 2005 john wiley sons ltd

replacement of aragonite by quasi rhombohedral dolomite in a late pleistocene tufa mound great salt lake utah u s a abstract fabric preserving quasi rhombohedral dolomite forms as cement and replacement of aragonite in a tufa mound 2 m thick on the western shoreline of the great salt lake the rounded crystals range in size from 5 to 20 m in diameter crystal faces are not pitted and have numerous sharp edged steps and kinks the quasi rhombohedral forms are the result of crystal growth phenomena and not of post crystallization dissolution microprobe analyses n 92 of the dolomite yield an average 46 mole mgco3 in agreement with the 44 to 45 mole mgco3 content determined from x ray diffraction 30 8 2 position of the 104 peak the great salt lake dolomite is poorly ordered with relative ordering of 28 5 and a reflection ratio of 0 9503 compared to a well ordered standard dolomite the great salt lake dolomite has the poorest ordering of any natural dolomite recorded to date more than half of the electron microprobe analyses show elevated sr abundance indicating that dolomite formed in a rock buffered diagenetic system where much of the bicarbonate and ca were supplied by dissolution of aragonite and mg from the lake water preservation of the tufa fabric by dolomite was accomplished by the closely related dissolution of aragonite and precipitation of dolomite in a fluid undersaturated with respect to aragonite and supersaturated with respect to ca rich dolomite formation of spheroids might reflect a high growth rate from a high alkalinity fluid that was undersaturated with respect to other carbonate minerals maintenance of this growth rate might have been aided by the ca enrichment and cation disordering of the precipitating dolomite phase and the large surface area of a sphere compared to that of an inscribed rhomb

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

reassessment of carbonate ages by dating both carbonate and organic material from an etosha pan namibia stromatolite evidence of humid phases during the last 20ka abstract previous research on lacustrine stromatolites from etosha pan in namibia obtained ages on carbonate close to or beyond the limits of radiocarbon dating these ages suggested that the basin was likely not subject to extensive flooding during the last ca 40 ka this study shows that ams radiocarbon ages for the carbonate of a stromatolite from poacher s point are 15 21 ka older than ages for organic material in the stromatolite structure calibrated ages range from 30 to 40 ka for carbonate and 3 19 ka for the organic residue the new ages together with petrographic and isotopic data for the stromatolite have provided important new information on past flooding of etosha pan including evidence of prolonged lacustrine conditions during the holocene climatic optimum

δ13c δ18c covariance as a paleohydrological indicator for closed basin lakes the relationship between 18o and 13c in a closed basin lake is a function of hydrological change vapor exchange lake productivity and total co2 or carbonate alkalinity concentration covariance of 18o and 13c usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer on shorter time scales however certain subtleties in the use of the 13c 18o covariance as a hydrology history indicator must be recognized the covariant trend may not be found in hyper alkaline lakes because of the insensitivity of 13c to lake volume changes for less alkaline closed basin lakes covariance of 13c 18o will result from relatively rapid increase or decrease of lake volume with the rapid decrease condition giving rise to heavy and narrow ranged isotopic values for both 13c and 18o due to the coupled evaporation productivity effect when the lake volume remains stable as is the case for an over flowing open lake poor 13c 18o covariance will ensue due to the effect of vapor exchange with the atmosphere we have used the measured 13c 18o covariance in carbonate sediments of mono lake california to deduce paleo hydrological and lake water alkalinity and salinity variations and found the results in consonance with holocene lake level history derived from the 18o and other information

the rise and fall of lake bonneville between 45 and 10 5 ka a sediment core taken from the western edge of the bonneville basin has provided high resolution proxy records of relative lake size change for the period 45 1e10 5 calendar ka hereafter ka age control was provided by a paleomagnetic secular variation psv based age model for blue lake core bl04 4 continuous records of d 18 o and total inorganic carbon tic generally match an earlier lake level envelope based on outcrops and geomorphic features but with differences in the timing of some hydrologic events states the stansbury oscillation was found to consist of two oscillations centered on 25 and 24 ka lake bonneville appears to have reached its geomorphic highstand and began spilling at 18 5 ka the fall from the highstand to the provo level occurred at 17 0 ka and the lake intermittently overflowed at the provo level until 15 2 ka at which time the lake fell again bottoming out at w14 7 ka the lake also fell briefly below the provo level at w15 9 ka carbonate and d

petrography and characterization of microbial carbonates and associated facies from modern great salt lake and uinta basin s eocene green river formation in utah usa

carbonate deposition pyramid lake subbasin nevada 4 comparison of the stable isotope values of carbonate deposits tufas and the lahontan lake level record abstract in this paper the fundamental importance of changes in hydrologic balance and hydrologic state on the 18o and 13c values of water and dissolved inorganic carbon dic in lakes of the lahontan basin is illustrated abrupt changes in 18o and 13c values of carbonate deposits tufas from the pyramid lake subbasin nevada coincide with abrupt changes in lake level and hydrologic state minima in lake level at 26 000 15 500 and 12 000 yr b p are associated with relatively heavy 18o and 13c values maxima in the lake level record at 14 000 and 10 500 yr b p are associated with relatively light 18o and 13c values we believe that the correlation between maxima and minima in the lake level and 18o records reflect the fundamental effect of lake level dynamics on the 18o value of lake water evaporation increases the 18o value of lake water whereas streamflow discharge and on lake precipitation decrease the 18o value variation in the 18o value of lake water therefore indicates change in the hydrologic balance increases in 18o accompany decreases in lake volume and decreases in 18o accompany increases in lake volume covariance of 13c and 18o indicates that change in 13c values of dic also accompany change in lake volume we offer the hypothesis first put forward by j a mckenzie that change in the productivity photosynthesis respiration balance is responsible for much of the observed variation in 13c most great basin lakes including lake lahontan experienced changes in hydrologic state during the late wisconsin when a lake becomes hydrologically open the residence time of water decreases the greater the rate of spill the greater the volume of evaporated 18o enriched water removed from the spilling lake and the more negative the 18o value of water remaining in the spilling lake the concentration of dic as well as the concentrations of photosynthesis limiting nutrients e g phosphorus nitrogen silica molybdenum decrease as spill increases increasing rates of spill therefore lead to overall decreases in photosynthetic rates relative to respiration rates and as a consequence the 13c values of dic become more negative

pulses of carbon dioxide emissions from intracrustal faults following climatic warming carbon capture and geological storage represents a potential means of managing atmospheric carbon dioxide levels an analysis of a 135 000 palaeorecord shows that pulses of carbon dioxide leakage from a natural reservoir in utah are associated with episodes of glacial unloading

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

contributions to the solute and isotopic groundwater geochemistry antelope island great salt lake utah abstract the 110 km2 antelope island is predominantly composed of precambrian gneiss similar to rocks in the wasatch range 32 km to the east three types of island groundwater systems have been identified on the basis of aquifer composition and dissolved solute content the systems include ground waters which discharge from either crystalline or sedimentary rocks sedimentary groundwater systems contain ground water which is either na cl rich or poor all island ground water has anomalously high na cl or so24 concentrations when compared with ground waters that issue from similar bedrock in nearby areas island groundwater systems may be statistically distinguished from each other and from other ground water in the region the solute chemistry of island ground water cannot be accounted for by the simple dissolution of aquifer minerals and the water does not plot along fault controlled thermal water precipitation or parent aquifer precipitation cl so 2 4 mixing lines discharge elevations and cl so 2 4 also rule out mixing with residual salts from paleo lake bonneville or brines of the great salt lake for most island ground water tritium values 40 tritium units tu suggest that island groundwater systems are primarily recharged from modern meteoric water stable isotopic 2h and 18o data plot along an evaporation line which indicates that recharge water contains a component of evaporated great salt lake water temporal variations in spring discharges tritium concentrations and discharge temperatures of less than 20 c indicate short flow paths and shallow circulation excess cl and so2 4 concentrations are attributed to the deposition of aerosols of wind blown dust from nearby evaporate deposits and sea spray sulfur isotope data suggest contributions to crystalline systems of reduced sulfur from nearby smelter or other industrial plumes

paleoclimatic significance of lacustrine microbialites a stable isotope case study of two lakes at torres del paine southern chile article two patagonian lakes studied here lago sarmiento and laguna amarga are located within the orographic rain shadow formed to the east of the southern patagonian ice field in the andes range major thrombolite colonies are present in lago sarmiento whereas widespread stromatolites occur in laguna amarga based on the characterization of the hydrologic system of these two lakes together with an estimation of the isotopic balance and an analysis of the equilibrium conditions between the water and biologically induced carbonates it is concluded that the microbialites of lago sarmiento are better suited as paleotemperature indicators than those of laguna amarga lago sarmiento thrombolites contain unique carbonate mineral species in which carbonate precipitation occurs close to isotopic equilibrium and where the variation in water temperature controls fractionation of the stable oxygen isotope the results indicate that at 1215 cal yr bp the level of the lake was at 85 m a s l with a temperature close to 9 3 c was at 82 m a s l at 600 cal yr bp with a temperature close to 8 5 c this coincides with the timing of the northern hemisphere medieval warming period at 183 cal yr bp the level of the lake was at 80 m a s l with a cooler temperature close to 7 7 c representing a colder period coinciding with the timing of the little ice age lia an interesting outcome of this study is that it reinforces the idea that the 13 c signal in carbonate deposits can be an effective tool in distinguishing between inorganic and biologically induced precipitation

lacustrine cave carbonates novel archives of paleohydrologic change in the bonneville basin utah usa records of past changes in lake levels and lake water isotopic composition in closed basins provide key insights into past variations in the hydrological cycle however these records are often limited by dating precision and temporal resolution here we present data from lacustrine cave carbonates a previously unexplored class of carbonates that comprise a promising new archive of past hydrologic changes in the bonneville basin of the northeastern great basin usa these dense carbonates precipitated within caves crevices and other protected spaces flooded by lake bonneville during its highstand in the last glacial period we report on deposits in cathedral and craners caves located 50 km apart at similar elevations approximately 100 m above the modern great salt lake and almost 200 m below lake bonneville s highstand shoreline carbonates from the two caves show similar chronologies mineralogical transitions isotopic compositions and uranium concentrations these findings suggest that lacustrine cave carbonates record changes in lake level and in the isotopic composition and chemistry of lake water importantly the deposits can be precisely dated by u th methods providing the first records of lake bonneville s water balance changes tied to precise u th ages close agreement between paired u th and calibrated 14 c ages in the deposits suggests a minimal o200 a carbon reservoir effect in the lake and allows 14 c dating to be used for age control in portions of the deposits less suitable for u th dating we use ages for the onset and cessation of lacustrine cave carbonate deposition to offer new constraints on past changes in lake level and the carbonate saturation state of lake water we also present precisely dated high resolution oxygen and uranium isotope records from the deposits within a first phase of deposition reflecting the lake s transgression between 26 and 18 ka our isotopic data suggest a large influx of freshwater during heinrich stadial 2 a hiatus in deposition beginning at 18 270 3 ka may be the result of freshening related to the lake s overflow calcite deposition resumes at cathedral cave at 16 470 2 ka suggesting that basin overflow had ceased by this time and that the lake s calcite saturation state had increased andd 18 o values increase markedly after 15 9 ka consistent with drying at this time these data imply that the lake s deglacial regression began well before the bolling warming cessation of this second phase of deposition at 14 770 2 ka coincident with the bolling warming may reflect the lake s drop below cathedral cave s elevation a final stage of aragonite deposition between 13 8 and 13 6 ka differs from the underlying facies and may not reflect deposition from lake waters filling the cave

great salt lake utah microbialite δ13c δ18o and δ15n record fluctuations in lake biogeochemistry since the late pleistocene extensive lacustrine microbialite deposits exposed along the shores of great salt lake gsl utah preserve a rich continental paleoenvironmental record newly reported microbialite carbon and oxygen stable isotope ratios in carbonate nitrogen isotope ratios in organic matter and organic matter radiocarbon ages archive paleolake hydrological and biogeochemical changes from the late pleistocene through the holocene positive correlations between 18o and 13c in 15 7 6 cal ka microbialite carbonate are consistent with a hydrologically closed basin lake with fluctuations in volume chemistry and associated changes in lake primary production the 15n of microbialite bulk organic matter 5 18 versus air shows that the balance between nitrogen fixation and assimilation of dissolved inorganic nitrogen has varied significantly inverse 18o and 13c correlations in combination with high 15n in some carbonate deposits may imply periods of higher salinity and stable lake stratification similar to modern gsl conditions we compare our c and o data sets with pleistocene lake bonneville carbonate stable isotope records and demonstrate progressive development of spatially isolated hydrological basins during the shift to warmer and drier conditions in the holocene

introduction to seamount special section this special section is the outcome of a symposium held at the lamont doherty geological observatory november 17 19 1982 on the origin and evolution of seamounts the topic for the symposium arose from the realization that although there is now a wealth of new ideas on the geology geophysics and geochemistry of the ocean floor the study of seamounts has been relatively neglected despite their great importance to plate tectonics one of the most interesting features of the ocean floor is the large number of small volcanoes or seamounts usually these features are circular in plan view and have a sharp summit there has been extensive debate in the literature about the significance of the different morphological types of seamounts a traditional view has been that flattopped seamounts e g guyots formed as a result of subaerial erosion when the volcanoes were above sea level seamounts covered by fringing reefs or sediments e g atolls on the other hand are believed to have formed when the original volcanic foundation subsided below sea level

stromatolite lamination frequency walker lake nevada implications for stromatolites as biosignatures lamination in stromatolites considered some of the oldest fossils on earth is commonly interpreted to record the periodic response of a microbial community to daily seasonal or perhaps yearly environmental forcing but the inability to date ancient stromatolites precludes an understanding of the lamination formation processes we use high resolution 14c dating of holocene stromatolites from walker lake nevada united states to construct a record of lamination rate over the course of accretion laminae formed with a period of 5 6 1 6 yr lamination at the base of the structure 1 6 2 8 1 9 yr lamination in the middle and 4 5 0 8 yr lamination at the top of the laminated portion the predominant 4 6 yr periodicity indicates that lamination formation is likely more closely related to regional climate forcing e g el nino southern oscillation versus the typical diurnal or seasonal changes in microbial mats traditionally assumed for most ancient stromatolites thus generalizations regarding the influence of microbial mats on stromatolite lamination and the use of stromatolites as biosignatures need careful consideration

an alkaline lake in the late paleozoic ice age lpia a review and new insights into paleoenvironment and petroleum geology abstract the ca 300 ma fengcheng formation in the junggar basin of nw china is reported to develop a rare alkaline lake soda lake in this study based on an expanded literature survey and new insights from geological and geochemical data the development of this ancient alkaline lake resulted from a convergence of favorable paleotectonic paleogeographic and paleoclimatic conditions a detailed characterization of the alkaline lake includes evidence for a ph of 9 0 indicated by 15n data average 18 4 the presence of alkali minerals such as trona and shortite globular bacteria like fossils low contents of clay minerals organic and inorganic geochemistry indicating high salinity strongly reducing conditions and hydrothermal activity and a complete sedimentary evolution sequence of an archetypal alkaline lake the studied lake deposit is presented as the first such deposit worldwide to generate a large oil reserve thus allowing scientific insights to be gained into the controls on hydrocarbon generation in alkaline lakes the alkaline lacustrine source rocks have high contents of organic matter favorable organic matter type abundant oil and poor natural gas multiple phases of hydrocarbon generation and high hydrocarbon volumes the genesis and development of this alkaline lake were controlled jointly by evaporation and volcanic hydrothermal activity however some aspects of this type of lake remain unclear and future work should explore the integrated evolution of biological climatic petroleum geology systems with respect to alkaline lakes and their associated deposits and their coupling research with worldwide event then namely glacial episode iii of the late paleozoic gondwanan glaciation our data suggest that the fengcheng formation is a well preserved archive of late paleozoic ice age lpia geology and geochemistry around 300 ma

carbonate microbialites and hardgrounds from manito lake an alkaline hypersaline lake in the northern great plains of canada abstract manito lake is a large perennial na so 4 dominated saline to hypersaline lake located in the northern great plains of western canada significant water level decrease over the past several decades has led to reduction in volume and surface area as well as an increase in salinity the salinity has increased from 10 ppt to about 50 ppt tds this decrease in water level has exposed large areas of nearshore microbialites these organogenic structures range in size from several cm to over a meter and often form large bioherms several meters high they have various external morphologies vary in mineralogical composition and show a variety of internal fabrics from finely laminated to massive in addition to microbiolities and bioherms the littoral zone of manito lake contains a variety of carbonate hardgrounds pavements and cemented clastic sediments dolomite and aragonite are the most common minerals found in these shoreline structures however calcite after ikaite monohydrocalcite magnesian calcite and hydromagnesite are also present the dolomite is nonstoichiometric and calcium rich the magnesian calcite has about 17 mol mgco 3 ams radiocarbon dating of paired organic matter and endogenic carbonate material confirms little or no reservoir affect although there is abundant evidence for modern carbonate mineral precipitation and microbialite formation most of the larger microbialites formed between about 2300 and 1000 cal bp whereas the hardgrounds cements and laminated crusts formed about 1000 500 cal bp

great salt lake and precursors utah the last 30 000 years sediment cores up to 6 5 m in length from the south arm of great salt lake utah have been correlated radiocarbon ages and volcanic tephra layers indicate a record of greater than 30 000 years a variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation these include acoustic stratigraphy sedimentologic analyses mineralogy geochemistry major element c o and s isotopes and organics paleontology and pollen the results indicate that prior to 32 000 year b p an ephemeral saline lake playa system was present in the basin the perennial lake which has occupied the basin since this time rose in a series of three major steps the freshest water conditions and presumably highest altitude was reached at about 17 000 year b p the lake remained fresh for a brief period followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present great salt lake the lake remained at low elevations and divided at times into a north and south basin until about 8 000 year b p since that time with the exception of two short rises to about 1290 m the lake level has remained near the present elevation of 1280 m

14 c and th u dating of pleistocene and holocene stromatolites from east african paleolakes during recent humid episodes stromatolites were built along paleolake margins some 60 m above the modern water level of lakes natron and magadi southern gregory rift valley three generations of stromatolites are observed the more recent ones frequently covering pebbles and boulders eroded from the older ones the youngest one yielded 14c ages ranging from approximately 12 000 to 10 000 yr b p their 13c values 2 6 suggest isotopic equilibrium between the paleolake total inorganic dissolved carbon and the atmospheric co2 thereby lending credence to the reliability of the 14c an initial 230th232th ratio in the detrital component was determined by thu measurements on the 14c dated stromatolites using this value a 230th234u chronology for the older stromatolites was calculated ages of 240 000 and 135 000 10 000 yr were obtained for the first and second generations respectively a humid episode apparently characterized eastern africa during each glacial interglacial transition 18o and 13c measurements on stromatolites when compared to values on modern waters and carbonates provide paleohydrological information long residence time of the paleolake waters and less seasonally contrasted regimes are inferred

lake carbonate δ18o records from the yukon territory canada little ice age moisture variability and patterns abstract a 1000 yr history of climate change in the central yukon territory canada is inferred from sediment composition and isotope geochemistry from small groundwater fed seven mile lake recent observations of lake water 18 o lake level river discharge and climate variations suggest that changes in regional effective moisture precipitation minus evaporation are reflected by the lake s hydrologic balance the observations indicate that the lake is currently 18 o enriched by summer evaporation and that during years of increased precipitation when groundwater inflow rates to the lake increase lake water 18 o values decrease past lake water 18 o values are inferred from oxygen isotope ratios of fine grained sedimentary endogenic carbonate variations in carbonate 18 o supplemented by those in carbonate and organic 13 c c n ratios and organic carbon carbonate and biogenic silica accumulation rates document changes in effective moisture at decadal time scales during the early little ice age period to present results indicate that between ad 1000 and 1600 effective moisture was higher than today a shift to more arid climate conditions occurred after ad 1650 the 19th and 20th centuries have been the driest of the past millennium temporal variations correspond with inferred shifts in summer evaporation from marcella lake 18 o a similarly small stratified alkaline lake located 250 km to the southwest suggesting that the combined reconstructions accurately document the regional paleoclimate of the east central interior comparison with regional glacial activity suggests differing regional moisture patterns during early and late little ice age advances

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

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

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

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

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

fluvial tufa evidence of late pleistocene wet intervals from santa barbara california u s a abstract past pluvials in the western united states provide valuable context for understanding regional hydroclimate variability here we report evidence of conditions substantially wetter than today from fluvial tufa deposits located near zaca lake santa barbara county california that have been dated by radiocarbon 14c and infra red stimulated luminescence irsl two successions of tufa deposition occur within a small catchment that drains miocene monterey formation bedrock 1 a fluvial deposit 0 0 5 m thick 200 m in extent that formed along a narrow valley below a modern spring and 2 a perched deposit 10 m higher 2 m thick 15 m in extent irsl and radiocarbon dating of the perched carbonates suggest at least two episodes of carbonate growth one at 19 4 2 4 1 through 17 8 2 8 1 ka and another at 11 9 1 5 1 ka verified with a charcoal 14c age of 10 95 0 12 2 cal ka bp the relationship between the perched and fluvial spring deposits is inferred to represent a drop in the water table of more than 10 m associated with a transition from a wet climate in the late glacial to a dry holocene today the wet period indicated by the perched tufa deposit between 19 4 and 17 8 ka is relatively consistent with other california climate records both north and south of zaca lake however tufa growth ca 12 to 11 ka demonstrates wet conditions occurred as far south as zaca lake during the younger dryas event in contrast to climate records farther south in lake elsinore that indicate a drying trend through this interval a small shift north in the average position of the winter season storm track could explain wet winters at zaca while at the same time generating dry winters at lake elsinore 275 km southwest of zaca if true these data indicate that rather small latitudinal shifts in the average winter season storm track can produce large changes in regional hydroclimate