effectiveness of natural riparian buffers to reduce subsurface nutrient losses to incised streams abstract perennial vegetation borders many incised perennial streams and rivers in southern iowa and is assumed to provide a natural riparian buffer against subsurface nutrient losses from shallow groundwater questions remain about the effectiveness of these systems near incised channels that cut through nutrient rich holocene alluvium underlying the riparian corridors in this study riparian groundwater nutrient concentrations were evaluated near an incised stream under four perennial land cover types common to southern iowa with the objectives to assess how groundwater quality differed by i distance away from an incised stream and ii perennial land cover type groundwater samples were collected from riparian wells installed 1 m 20 m and 40 m from an incised channel under four replicated land covers cool season grass warm season grass woods pasture on six occasions across the growing season results indicate that channel incision lowers water tables in the near stream zone and maintains more aerobic conditions but did not result in enhanced nitrogen mineralization or leaching to groundwater average concentrations of nitrate nitrogen phosphorus and dissolved organic carbon were 0 3 mg l 0 2 mg l and 6 mg l respectively with variations due mainly to land cover type and geomorphology study results suggest that nutrient losses from perennial buffers in the region do not greatly impact regional water n and p loads although average concentrations in riparian groundwater may exceed proposed stream nutrient criteria

holocene lake level trends in the rocky mountains u s a abstract the availability of water shapes life in the western united states and much of the water in the region originates in the rocky mountains few studies however have explicitly examined the history of water levels in the rocky mountains during the holocene here we examine the past levels of three lakes near the continental divide in montana and colorado to reconstruct holocene moisture trends using transects of sediment cores and sub surface geophysical profiles from each lake we find that mid holocene shorelines in the small lakes 4 110 ha were as much as 10 m below the modern lake surfaces our results are consistent with existing evidence from other lakes and show that a wide range of settings in the region were much drier than today before 3000 2000 years ago we also discuss evidence for millennial scale moisture variation including an abruptly initiated and terminated wet period in colorado from 4400 to 3700 cal yr bp and find only limited evidence for low lake stands during the past millennium the extent of low water levels during the mid holocene which were most severe and widespread ca 7000 4500 cal yr bp is consistent with the extent of insolation induced aridity in previously published regional climate model simulations like the simulations the lake data provide no evidence for enhanced zonal flow during the mid holocene which has been invoked to explain enhanced mid continent aridity at the time the data including widespread evidence for large changes on orbital time scales and for more limited changes during the last millennium confirm the ability of large boundary condition changes to push western water supplies beyond the range of recent natural variability

holocene water levels at rice lake ontario canada sediment pollen and plant macrofossil evidence four cores taken along a transect from the western basin and four cores from the middle basin of rice lake ontario provide evidence for shoreline transgression during the early holocene for low

uplift driven expansion delayed by middle holocene desiccation in lake winnipeg manitoba canada new findings of paleoenvironmental change in lake winnipeg southern manitoba reveal evidence of unexpectedly dry conditions from 7 5 to 4 ka 7500 to 4000 radiocarbon years before present with reduced lake area in the north and a desiccated lake basin in the south changes in extent of this large lake now 400 km long can be explained by a combination of 1 expansion due to postglacial differential uplift tilting and 2 lake area reduction due to drier climates associated with the former presence of dry grassland vegetation comparing lake areas sustainable by grassland climate with computed potential lake areas based on the assumption of open overflowing conditions we quantify the atmospheric moisture reduction represented by the middle holocene dry conditions this approach holds promise for calibrating regional models of climate change and exploring the effects of dry paleoclimates in other large lake basins such as the laurentian great lakes the ongoing postglacial tilting is of societal concern because it contributes to long term lakeshore erosion and to the decrease in discharge capacity of the inflowing flood prone red river in a populated region

little ice age aridity in the north american great plains a high resolution reconstruction of salinity fluctuations from devils lake north dakota usa the little ice age was an interval between about ad 1500 and 1850 characterized by advancing glaciers in mountainous regions of europe and western north america however it is unclear whether this cool moist period was truly global in extent or how it was manifested in other regions with different climatic controls a high resolution reconstruction of salinity fluctuations in devils lake north dakota based on fossil diatoms ostracode shell geochemistry and bulk carbonate geochemistry indicates that saline conditions prevailed throughout much of the recent past these results suggest an arid climate in the northern great plains throughout the little ice age and that during this interval climatic gradients between the great plains and regions to both the east and west may have been quite steep

late quaternary paleohydrology in the north american great plains inferred from the geochemistry of endogenic carbonate and fossil ostracodes from devils lake north dakota usa abstract devils lake north dakota is a closed basin lake in which water chemistry is responsive to hydrological changes making it a valuable resource for documenting paleoclimate conditions ostracode trace element and bulk carbonate geochemistry in a core are used to generate a 12 000 year record of salinity fluctuations the relative amounts of sr ca and ba in the bulk carbonate fraction can be linked mechanistically to changes in sediment mineralogy calcite aragonite and or solute chemistry whereas the elemental geochemistry of ostracode valves reflect solute chemistry associated minima in sr ca and maxima in mg ca in ostracode valves from the devils lake core may be due to aragonite mediation of sr chemistry during the precipitation of multiple mineral phases during more saline intervals the devils lake record can be divided into four hydrological periods on the basis of the geochemical proxies a 12 5 9 k y low salinity b 9 5 4 5 k y fluctuating saline conditions with a maximum at about 8 k y c 4 5 3 5 k y low salinity phase but probably not as fresh as at 12 5 9 k y d 3 5 k y present saline phase although generally less so than 9 5 4 5 k y however a large degree of variability characterizes the entire record suggesting the absence of long term climatic stability in this region

macrofossil and tree ring evidence for a long term forest succession and mid holocene hemlock decline abstract paludified dune fields in southern quebec provided a unique opportunity to analyze a mid holocene forest succession ranging from xero mesophilous forests to treed peatlands which registered the hemlock decline a major biostratigraphic event in eastern north america our fossil tree chronology established from 66 radiocarbon dates of tree stems indicates that white pine and hemlock were present at the study site about 6000 5700 yr b p hemlock reached a maximum 4900 4800 yr b p and then declined between 4600 and 3800 yr b p the species recovered around 3700 yr b p and then decreased when white pine and eastern latch dominated the site after 3000 yr b p and between 2600 and 2200 yr b p respectively tree ring signatures of fossil hemlocks suggest the continuous influence of biotic factors possibly insect defoliators throughout the record as shown by recurrent suppressed growth pattern microscopic examination of the hemlock fossil stems disclosed no evidence of fungal disease the hemlock decline was probably caused by regional posthypsithermal climatic changes toward moister conditions

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

climate change in southern illinois usa based on the age and δ13c of organic matter in cave sediments abstract matrix supported diamicton and uniform to laminated silty fine grained sediment deposited from about 42 500 to 27 600 cal yr b p under slackwater conditions nearly filled two caves in southwestern illinois at some point most of the sediment was flushed from the caves and from about 22 700 to 4000 cal yr b p floods deposited a drape of sandy and silty sediment on remnant slackwater successions cobbly alluvium and bedrock especially from 7700 to 4000 cal yr b p clay mineral analyses of the slackwater cave sediment reveal a provenance of chiefly petersburg silt a smectite and illite rich proglacial lacustrine unit present in the overlying illinois episode glacial succession today remnants of the ancient subterranean slackwater deposits nearly fill several secondary passages and in at least two locations cover a cobble mantled strath terrace 1 3 to 1 5 m above active stream channels slumping and sinkhole formation appear to have been important mechanisms for deposition of the ancient subterranean deposits slumping of these surficial deposits and associated vegetation can occur along the flanks of sinkholes in addition to sinkhole formation and enter caves however the finer organics some of them comminuted during transport into the caves become part of the cave alluvium this finer organic fraction is the modern analog of the humified organic matter disseminated in slackwater sediment dated in this investigation by radiocarbon methods twenty four 14c ages on humified organic matter provide chronologic control the 13c values of the organic matter reflect the proportion of c4 type to c3 type vegetation growing in and around swallets and sinkholes at the time of redeposition drought tolerant c4 type vegetation was more prevalent relative to c3 type vegetation from 42 500 to 31 200 cal yr b p compared to conditions from 28 800 cal yr b p to the present the 13c values are consistent with the results from other investigations of speleothems and organic matter from loessial paleosols

the magnitude of error in conventional bulk sediment radiocarbon dates from central north america abstract although the carbon reservoir problem with bulk sediment radiocarbon dates from lakes has long been recognized many synoptic studies continue to use chronologies derived from such dates for four sites in central north america we evaluate chronologies based on conventional radiocarbon dates from bulk sediment versus chronologies based on accelerator mass spectrometry ams radiocarbon dates from terrestrial plant macrofossils the carbon reservoir error varies among sites and temporally at individual sites from 0 to 8000 yr an error of 500 2000 yr is common this error has important implications for the resolution of precise event chronologies

buried soils in a perched dunefield as indicators of late holocene lake level change in the lake superior basin abstract a stratigraphic analysis of buried soils within the grand sable dunes a dune field perched 90 m above the southern shore of lake superior reveals a history of eolian activity apparently linked with lake level fluctuations over the last 5500 yr a relative rise in the water plane of the nipissing great lakes initially destabilized the lakeward bluff face of the grand sable plateau between 5400 and 4600 14 c yr b p this led to the burial of the sable creek soil by eolian sediments derived from the bluff face subsequent episodes of eolian activity appear to be tied to similar destabilizing events high lake levels may have initiated at least four and perhaps eleven episodes of dune building as expressed by soil burials within the dunes intervening low lake levels probably correlate with soil profile development which varies from the well developed sable creek spodosol catena to thin organic layers containing in place stumps and tree trunks paleoecological reconstructions available for the area do not imply enough climatic change to account for the episodic dune activity burial of soils by fine fraction sediments links dune building episodes with destabilization of the lower lake facing bluff which is rich in fines

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

holocene paleoenvironments in southeastern minnesota chasing the prairie forest ecotone this paper uses a multi proxy approach involving pollen plant macrofossils speleothem isotopes and alluvial history of streams to reconstruct the history of prairie expansion and contraction along the prairie forest border of southeastern minnesota usa early holocene forests were replaced by prairie along this border but eastward expansion of prairie stalled for 2000 yr when the prairie forest ecotone stabilized prairie invaded the area from the west 8000 9000 yr b p but mesic forest remained less than 100 km to the east until about 6000 yr b p changes in n 13 c values in speleothem calcite that reflect the rise of c4 grasses correlate well with the presence of c4 grass species identified in the plant macrofossil record periods of large floods correlate with speleothem evidence of dry summers increased cool season precipitation both resulting in less plant cover to absorb moisture and change to prairie vegetation fl 2002 elsevier science b v all rights reserved

evolution of eureka flat a dust producing engine of the palouse loess usa sedimentologic stratigraphic and pedologic evidence demonstrates that eureka flat ef a narrow 80 km long deflation plain in south central washington usa is the source for the thick and widespread loess of the palouse region located in the southern columbia plateau ef has been a depocenter for abundant clay to sand sized sediment derived from repeated glacial outburst floods that swept through the area during the pleistocene prevailing sw winds that were funneled across ef remobilized flood sediment into sand dunes sand sheets and loess an eolian sand sheet buried beneath 1 8 m of loess at the downwind end of ef attests to bioclimatically driven changes in the style of eolian deposition the depositional transition from sand sheet to loess is characterized by a change from wind rippled strata to structureless bimodal sand and silt with insect burrows and rhizoliths to unimodal sandy loess soil moisture and density of dust trapping vegetation control where sand dunes and loess accumulate up to 4 5 m of post lgm loess mantles the landscape adjacent to and downwind from ef some of the thickest loess deposits owe their origins to the sequestering of eolian sand particles by topographic traps such as the touchet river and its tributary valleys the removal of saltating sand from the eolian system promotes thick accumulation of loess downwind of topographic traps patterns of loess accumulation across the columbia plateau are identified on isopach maps of major pre and post lgm loess units and show that ef has been the major engine for the production of atmospheric dust and loess during both times

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

impact of the alluvial style on the geoarcheology of stream valleys abstract the extensive archeological record within river valleys provides an environment long favored for study by the archeologic community this record of human occupation varies with the alluvial style of the river resulting in each river valley having a unique archeological record controlled by three factors location of occupation sites preservation of those sites and recognition of the sites if problems of site preservation and recognition in a river valley can be recognized and addressed a better insight into settlement patterns and complex human environment interactions can result this study represents a synthesis of extensive published and secondary data sets pertaining to archaeology and alluvial geomorphology of the lower missouri red and mississippi rivers to examine the relationship of prehistoric site distribution with fluvial geomorphology the archeologic data are from published literature and government agencies the geomorphic data are from a variety of published and unpublished investigations including maps of alluvial geomorphology digital elevation models aerial photographs and topographic maps the data were input into spreadsheets and a gis for qualitative and quantitative analysis prehistoric human occupation of the narrow missouri valley floor is limited with only 0 061 recorded sites km2 additional sites are likely buried by thick vertical accretion sediment on the limited prehistoric portions of the floodplain and within alluvial colluvial fans along the valley margin non random preservation patterns such as the absence of sites from the youngest cultural period are attributed to shifts in settlement patterns in comparison to the lower missouri river valley prehistoric occupation of the lower red and mississippi rivers was much more extensive and the density of occupation was 0 274 sites km2 and 0 277 sites km2 respectively significant differences do exist in the age of sites and their relationship to different floodplain depositional environments many sites along the active meander belt of the red river were likely lost due to high rates of channel migration nevertheless intense occupation of paleo indian through caddoan groups assures that many significant sites have been preserved the wide valley and high rates of sedimentation suggest that many sites are likely buried particularly along natural levees flanking an older meander belt recorded sites are also present along streams that incise the terrace along the terrace margin and along small channels that cross the backswamp the spatial and temporal site distribution along the lower mississippi valley is distinct in comparison with the red river because the mississippi valley is wider the terraces are younger and less dissected and the floodplain has more relief and is not broadly inundated by floodwater with relatively low sediment concentrations most of the significant archaic through mississippian period floodplain sites are located along the surfaces of abandoned mississippi and distributary meander belts which aggraded above the adjacent backswamp and have rarely been influenced by flood sedimentation since abandonment abundant paleo indian through mississippian period sites are also widely distributed across undissected terraces only a few significant mississippian sites are present along the active meander belt and in the backswamp where flooding was common in comparison with the red river the archaeological record of the floodplain is less likely to be influenced by burial or erosion due to the mississippi river having lower rates of overbank sedimentation and channel migration respectively the variable alluvial styles of the lower missouri river lower red river and the lower mississippi river valleys presented varying opportunities and constraints to occupation and sustained settlement and resulted in widely varying archaeological patterns that are partly dependent upon the alluvial geomorphology

vertical distribution of total carbon nitrogen and phosphorus in riparian soils of walnut creek southern iowa abstract subsurface lithology plays an important role in many riparian zone processes but few studies have examined how sediment nutrient concentrations vary with depth in this study we evaluated concentrations of nutrients n c and p with depth in a riparian zone of the glaciated midwest a total of 146 sediment samples were collected from 24 cores that extended to a maximum depth of 3 6 m at eight sites in the riparian zone of walnut creek subsurface deposits were predominantly silt loam becoming coarser and more variable with depth nitrogen and carbon content ranged from

speleothem evidence for holocene fluctuations of the prairie forest ecotone north central usa carbon and oxygen isotopic trends from seven midwestern speleothems record significant offsets in the timing of middle holocene vegetation change interactions of dry pacific and moist gulf of mexico air masses maintained a sharp moisture gradient across iowa minnesota and wisconsin such that the arrival of prairie was offset by 2000 years between caves and pollen sites located only 50 km apart oxygen isotopes shift concomitantly with carbon in most cases although these changes are believed to represent increased evaporative enrichment of 18o prior to infiltration during the prairie period

loess record of dry climate and aeolian activity in the early to mid holocene central great plains north america thick holocene bignell loess sections provide new evidence for the timing of early to middle holocene aridity in the central great plains the immediate source of loess in these sections was dune fields just upwind based on thickness trends and grain size data thus periods of rapid loess accumulation indicate episodes of extensive dune activity under drier than present climate in typical bignell loess sections a thick zone of coarse textured loess with minimal pedogenic alteration is interpreted as a record of the most rapid sustained holocene loess accumulation optical ages indicate that loess in this zone was deposited beginning about 9000 10000 years ago at five study sites accumulation ended shortly after 6500 years ago at three sites but possibly earlier at the other two in two well dated sections the average rate of loess accumulation between 9000 10000 and 6500 years ago was about 1 6 3 5 times greater than in the late holocene thus we infer that the most extensive sustained holocene

responses of floods to holocene climatic change in the upper mississippi valley abstract dimensions of holocene relict channels and sedimentological characteristics of point bars associated with these relict channels were used to reconstruct a holocene history of long term changes in magnitudes of 1 58 yr floods in upper mississippi valley watersheds of southwestern wisconsin the reconstructed record of floods shows relatively large and persistent nonrandom departures from contemporary long term average flood magnitudes the flood history indicates climatic changes that are broadly similar to climatic changes indicated from fossil pollen in the same region the holocene floods ranged from about 10 15 larger to 20 30 smaller than contemporary floods of the same recurrence frequency large floods were characteristic between about 6000 4500 and 3000 2000 yr b p and during a brief interval after 1200 yr b p small floods were common between about 8000 6500 4500 3000 and 2000 1200 yr b p these fluvial responses were found to be closely associated with a long term episodic mobility and storage of sediments in the wisconsin watersheds during periods of relatively large floods relatively rapid lateral channel migration either reworked or removed extensive tracts of valley bottom alluvium in contrast during periods of relatively small floods relatively slow lateral channel migration is apparent and the channel and floodplain system appear to have been relatively stable

landscape evolution alluvial architecture environmental history and the archaeological record of the upper mississippi river valley abstract the alluvial fill in the upper mississippi river valley umv is a palimpsest of past landscapes environments and physical evidence of human life ways the valley has undergone significant changes in fluvial style during the time humans have occupied its landscapes including changes in channel pattern location of depocenters and sediment lithology remnants of late glacial braidplains that predate human presence in the upper midwest occur as sandy terraces and terrace fills a subsequent major change in alluvial architecture resulted from fundamental changes in seasonal water and sediment input that marked the end of glacial meltwater input into the valley about 12 4 ka 10 500 14c yr b p a shift to net transport of sandy bedload and storage of fine grained overbank sediment on the floodplain accompanied the change to an island braided channel pattern at that time the holocene channel belt has been significantly narrower and the zone of sediment storage is reduced relative to that of the late glacial river major holocene depocenters include alluvial fans and colluvial slopes floodbasins natural levees and fluvial fans at the junction of large tributaries climate models and paleobotanical and isotopic studies indicate that shifts in large scale patterns of atmospheric circulation and moisture transport into the mid continent of north america induced hydrologic and vegetation changes that strongly influenced flood frequency and magnitude the delivery of sediment from tributary basins and the evolution of the umv landscape understanding the alluvial architecture of the valley and the temporal spatial distribution of biotic environments and processes that have buried mixed altered or destroyed archaeological deposits is essential to develop strategies for sampling the valley for evidence of past human activity and for properly interpreting the archaeological record

postglacial climate in the st lawrence lowlands southern quebec pollen and lake level evidence abstract pollen and lake level data are used to reconstruct past climate changes in the st lawrence lowlands southern quebec past lake level changes are assessed from sedimentological pollen and macrofossil records from a single shallow water core from lac hertel which lies in the central part of the studied area three low lake level phases are recognised prior to 8000 7600 6600 and 4800 3400 cal bp the modern analogue method is applied to pollen data from seven well dated sites from the st lawrence lowlands and adjacent mountain areas constrained and unconstrained by lake level changes the reconstructed climate changes are congruent with the pattern of climate changes known from eastern north america a dry and cold late glacial episode due to the presence of pro glacial lakes and seas a rapid warming between 12 500 and 11 000 cal bp possibly caused by increasing summer insolation a dry period from 10 000 to 6500 cal bp a brief cooling between 9000 and 8000 cal bp possibly related to a summer cooling of arctic airmasses a temperature maximum around 8000 cal bp and finally a progressive decrease in summer temperature and an increase in winter precipitation over the 4500 last years these results show that it is possible to reveal seasonal patterns in climate by combining pollen and lake level data

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

inferring paleotemperature from the d h ratio of lacustrine organic matter abstract linking the d h d records of the kerogen from bulk organic matter in lake sediments to known temperature d of precipitation relationships may offer new possibilities in paleoclimate studies here we examine the hydrogen isotope ratio obtained from a radiocarbon dated lake core from wisconsin situated in the midwestern part of the united states to infer paleo surface temperatures paleotemperatures were estimated by converting the d values of the organic fraction to the d values of the lake water and by implication to that of local precipitation the temperature estimates show that the middle holocene from 7000 to 5000 years before present bp was warmer by about 3 c in general agreement with speleothem data from the midwestern united states our study shows the usefulness of the d h rations of kerogen from bulk sediment as a climate proxy that can compliment compound specific hydrogen isotope studies

pollen plant macrofossils and microvertebrates from mid holocene alluvium in east central iowa usa comparative taphonomy and paleoecology abstract pollen plant macrofossils and micromammals are commonly used in paleoecological interpretations but rarely are found associated because of distinctly separate taphonomic pathways into the fossil record the lilienthal local biota dating between 5920 60 and 6300 80 14 c b p is a rare exception as the site contains all three proxies juxtaposed in alluvium impounded upstream from a fossil log near the headwaters of mud creek east central iowa u s a a variety of taphonomic processes can strongly influence the composition of fossil assemblages this paper compares the taphonomic framework for each fossil group interprets the paleoecologic signal from each and then compares the three interpretations pollen and plant macrofossils are found in organic silts indicating deposition in a quiet water environment microvertebrates ordinarily occur in sand sized sediments and show evidence of fluvial transport despite these different pathways all lilienthal assemblages indicate that a largely closed mesic deciduous forest grew along mud creek in mid holocene time therefore a narrow north south ecotone must have existed between the forest and tall grass prairie biomes in eastern iowa this robust data set provides a detailed picture of the paleoecology and paleogeography of this past environment

middle holocene dry climate caused by change in atmospheric circulation patterns evidence from lake levels and stable isotopes sediment hiatuses detritus layers and inwashed terrestrial moss layers in five cores at crawford lake ontario canada show that the lake level was low between ca 4 8 and 2 ka 1 ka 1000 14 c yr b p this low level is attributed to a dry and warm climate which has also been documented at other sites in southern ontario southern michigan and southern wisconsin oxygen isotope 18 o values from authigenic marl show a negative shift of 2 4 from 9 to 11 4 vienna peedee belemnite between ca 5 and 2 ka enhanced evaporation under dry and likely closed basin conditions would lead to more enrichment in 18 o so we suggest that the trend to depleted 18 o indicates a significant change in the 18 o value of the source meteoric water the major moisture source for the great lakes region is the gulf of mexico from which the amount and seasonality of precipitation are affected by the interplay of air masses from the gulf of mexico and north pacific probably controlled by jet stream positions and storm tracks in the late middle holocene the isotopically heavy moisture from the gulf might have contributed less precipitation and or a higher proportion in winter months probably caused by more frequent eastward extension of dry pacific air depleted in 18 o this hypothesis implies that the 18 o values of paleoprecipitation in the middle holocene reflected moisture source history more strongly than paleotemperature

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

late holocene development of a floodplain along a small meandering stream northern quebec canada this paper describes the activity of a small meandering stream and the development of its floodplain during the last 4600 years calendar years bp in the northern boreal zone of quebec three trenches were excavated across the floodplain s full width and permitted the interpretation of morphosedimentary units in relation to modern analogs chronological controls within trenches was provided by the dendrochronological and radiocarbon dating of buried tree trunks from 4600 to 2900 cal bp and from 1000 to 120 cal bp the channel migrated and constructed its floodplain at very slow rates mostly because of low flow velocities vegetated streambanks and the cohesive texture of marine sediments reworked by the channel vertical accretion rates were extremely variable on the floodplain with high rates proximal to the modern channel and low rates over distal also older portions of the floodplain following a major channel shift meander cut off or avulsion around 2900 cal bp channel migration appears to have been constrained to a narrow zone adjacent to the modern channel within this constrained zone the migrating channel has reworked its own sediments leading to a marked unconformity between 2900 1000 cal bp it is thought that underlying marine sediments protrusions and perhaps the forested banks protected older alluvial sediments from being eroded during the last three millenniums our study shows that small boreal floodplains may contain in a very small area abundant and diversified archives of their evolution

paleoecology of a northern michigan lake and the relationship among climate vegetation and great lakes water levels abstract we reconstructed holocene water level and vegetation dynamics based on pollen and plant macrofossils from a coastal lake in upper michigan our primary objective was to test the hypothesis that major fluctuations in great lakes water levels resulted in part from climatic changes we also used our data to provide temporal constraints to the mid holocene dry period in upper michigan from 9600 to 8600 cal yr b p a shallow lacustrine environment characterized the mud lake basin a sphagnum dominated wetland occupied the basin during the mid holocene dry period 8600 to 6600 cal yr b p the basin flooded at 6600 cal yr b p as a result of rising water levels associated with the onset of the nipissing i phase of ancestral lake superior this flooding event occurred contemporaneously with a well documented regional expansion of tsuga betula pollen increased during the nipissing ii phase 4500 cal yr b p macrofossil evidence from mud lake suggests that betula alleghaniensis expansion was primarily responsible for the rising betula pollen percentages major regional and local vegetational changes were associated with all the major holocene highstands of the western great lakes nipissing i nipissing ii and algoma traditional interpretations of great lakes water level history should be revised to include a major role of climate

airflow terrain interactions through a mountain gap with an example of eolian activity beneath an atmospheric hydraulic jump the integration of atmospheric soundings from a fully instrumented aircraft with detailed sedimentary and geomorphic analyses of eolian features in the ferris dune field of south central wyoming lends insight into the manner in which topography interacts with airflow to modify eolian activity topographically modified airflow results in zones of airflow deceleration acceleration and enhanced atmospheric turbulence all of which influence the surface morphology and sedimentology extreme lateral confluence of prevailing airflow produces accelerated unidirectional winds these winds correlate with unusually continuous and elongate parabolic dunes that extend into a mountain gap windy gap persistently heightened winds produced at the entrance to windy gap have resulted in a concentration of active sand dunes that lack slipfaces common development of a strongly amplified atmospheric wave analogous to a hydraulic jump in the gap contributes to the formation of a variety of eolian features that mantle the surface of windy gap and the ferris dune field tail heightened unidirectional winds in this zone promote grain size segregation the formation of elongated and aligned sand drifts climbing and falling dunes elongate scour streaks and parabolic dunes that have low angle 20 sup 0 cross stratification deflation of bedrock and loose sediment has been enhanced in the zonemore of maximum turbulence beneath the hydraulic jump less

post glacial drainage basin evolution in the midcontinent north america implications for prehistoric human settlement patterns abstract the long term variation in archaeological site distribution in alluvial settings results from how changing environmental conditions and drainage basin evolution interplay with cultural needs and choices to configure site distribution these relationships are often believed synchronous with large scale climate and environmental changes research results within the white river valley drainage basin central indiana usa aimed to understand the fluvial and alluvial processes and chronology responsible for landform development and associated human settlement two long term processes characterized the white river since local deglaciation the first occurred between 18 ka local deglaciation and 6 ka when channel incision and erosion lateral migration processes dominated along the trunk the second occurred after 6 ka when cyclical intervals of overbanking levee formation and vertical accretion separated by intervals of flood plain stability characterized the white river floodplain because channel migration and lateral accretion processes predominated before 6 ka paleoindian and early middle archaic sites are unlikely to be preserved in the valley bottom conversely episodic terrace accretion process after 6 ka means that late archaic and woodland sites which occur in surface contexts on all terraces may also be common in buried or stratified floodplain contexts our data indicate that the modern distribution of archaeological sites in the valley is incomplete due to geomorphic processes our conclusions are relevant to other drainage networks because similar processes and chronologies occur elsewhere in the world

late holocene intensification of colds fronts in southern brazil as indicated by dune development and provenance changes in the sao francisco do sul coastal barrier abstract holocene coastal barriers from southern brazil present great geomorphological changes during their late stages of development in this study we investigate the holocene evolution of the sao francisco do sul sfs barrier through geomorphological heavy minerals and grain size analyses constrained by optically stimulated luminescence osl dating the sfs barrier stands out among the southern brazilian barriers due to its well preserved morphology with a parabolic dune belt in the seaward portion the progradation of the sfs barrier started at least 4914 478 years ago and had a pronounced morphodynamic shift around 1891 155 years ago this shift is characterized by episodic development of parabolic dunes migrating to nnw associated with sand coarsening and a marked variation in sediment provenance represented by the input of sands derived from local coastal watersheds southward from the sfs barrier this morphodynamic provenance shift resulted from the strengthening of sse winds and associated wave systems responsible for the northward alongshore drift implying intensification of cold fronts coupled with higher precipitation since 1891 155 years ago osl dating combined with grain size heavy minerals and geomorphological analyses allowed assessing the response of coastal barriers to the impacts of centennial to millenial climate events occurred during the late holocene reconstruction of the late holocene climate variability and associated impacts on coastal sedimentation is a key issue to evaluate the sensitivity of coastal barriers to future climate changes

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

isotopic evidence for younger dryas aridity in the north american midcontinent determining the impact of the younger dryas yd climate event on the unglaciated north american midcontinent has proved difficult due to a scarcity of suitable paleoclimate proxies here we present a well dated carbon isotope 13c record from a buried soil sequence in southwestern missouri which reveals a large isotopic excursion during the yd chronozone in this region of the modern prairie forest border the 13c signature of soil organic matter is a reliable indicator of past climatic change because 13c values are controlled primarily by the relative abundance of c3 and c4 plants which is tied to the environmental setting between ca 13 200 and 11 900 yr ago the abundance of c4 grasses increased by upwards of 50 of the total biomass indicating expansion of grassland most likely driven by increased aridity during this period environmental gradients in the midcontinent must have been very steep because at the same time that a c4 rich prairie existed in southwestern missouri spruce forests grew in iowa illinois and ohio

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

the origin and significance of boxwork clay coatings on dune sand grains from the nebraska sand hills usa abstract aeolian dune sands of late pleistocene to late holocene age in the nebraska sand hills are widely characterized by the development of partial clay coatings which form connected ridges and boxwork structures on the grain surfaces the proportion of sand grains with clay coatings typically shows considerable variability with depth in any given section distinct bands of sand enriched in fines are quite common especially just below the present or buried dune surfaces the morphology texture and mineralogical composition of clay coatings from two sites the merritt reservoir megabarchan and the dismal river ranch section have been investigated using a combination of sem x ray microanalysis xrd and coulter multisizer analysis in order to determine their mode of formation and environmental significance based on the analytical results and field observations it is concluded that the boxwork clay coatings formed in the vadose zone mainly as a result of precipitation and surface runoff induced infiltration of clay and very fine silt from the dune surface the main source of fines is concluded to be fine grained allochthonous aeolian dust derived principally from the high plains or more distal sources

isotopic composition of precipitation in central iowa abstract the isotopes of hydrogen and oxygen have been used extensively as indicators of groundwater age 3h and paleotemperature of groundwater recharge 18o 16o 2h 1h however comparisons of values in groundwater with those in recent precipitation are few this study describes and interprets the isotopic composition of precipitation in central iowa for the year 1992 an unusually mild winter driven by south westerly flow of the jet stream was followed by an unusually cool and predominantly dry summer that was caused by a persistent northwesterly flow in the upper atmosphere temperature was below normal 9 0 c precipitation was above normal 868 4 mm and was mostly derived from a gulf of mexico moisture source fifty one precipitation samples were collected from 37 events and analyzed for hydrogen and oxygen isotopes tritium activities ranged from 0 to 44 tritium units tu and the weighted mean 3h activity was 11 02 tu a value consistent with international atomic energy agency iaea data anomalously high 3h activities suggested input of technogenic 3h weighted mean values of 18o and 2h were 8 02 and 53 62 respectively and the equation of the local meteoric water line was 2h 9 26 18o 4 65 weighted mean 18o and 2h values from the gulf pacific moisture source 10 80 74 82 were more depleted than those ascribed solely to a gulf of mexico moisture source 7 24 47 39 seasonal differences in temperature primarily controlled these differences in isotopic composition

terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest ohio usa article i nfo article history received 7 may 2010 available online 21 february 2011 optically stimulated luminescence dated sand dunes and pleistocene beach ridges in northwest ohio are used to reconstruct landscape modification more than 5000 yr after deglaciation four of the osl ages 13 3 11 1 ka cluster around the younger dryas cold event five ages 10 8 8 2 ka cluster around the preboreal one young age 0 9 0 7 ka records more recent aeolian activity and one age of 15 1 13 1 ka dates a barrier spit in lake warren in northwest ohio both landscape instability recorded by aeolian activity and a vegetation response recorded by pollen are coeval with the younger dryas however the climate conditions during the preboreal resulting in aeolian activity are not recorded in the available pollen records from this we conclude that aeolian dunes and surfaces susceptible to deflation are sensitive to cooler drier episodes of climate and can complement pollen data younger dryas and preboreal aged aeolian activity in northwestern ohio coincides with aeolian records elsewhere in the great lakes region east of the prairie forest ecotone

intensity gradients and reversals in late glacial environmental change in east central north america abstract radiocarbon dated pollen sites from the allegheny plateau east and the till plains west document significant vegetational and climatic change between 15 000 and 9000 14 c bp south of the great lakes although limited by the problems of no analog vegetation pollen transfer functions tf and response surfaces rs quantify the climatic changes including a cold oscillation chronologically equivalent to the european younger dryas phase i before ca 13 000 14 c bp conditions across the region were similar january 20 to 16 c july 12 c rs or 19 c tf mean annual precipitation 80 to 90 cm year 1 phase iia between ca 13 000 and 11 000 14 c bp n s and e w climate gradients were initiated till plains temperatures increased by ca 8 c in january and by 8 c rs or 2 3 c tf in july plateau increases for january were 3 6 c and for july were 8 c rs or 1 2 c tf precipitation generally increased somewhat phase iib ca 11 000 to 10 000 14 c bp gradients became less pronounced the western sites show a climate reversal january drop of ca 5 to 2 c july drop to ca 1 2 c becoming more like the plateau sites which show a brief small fluctuation this is followed by an abrupt 10 to 20 cm year 1 reduction in precipitation january warming of ca 3 c and continued cooler julys phase iii after 10 000 14 c bp gradients similar to those of today developed the changes in phases iib and iii are probably linked to the drainage history of the great lakes and via that history to the changes on the european continent

a 130 000 year long pollen record from pittsburg basin illinois abstract pittsburg basin in south central illinois contains a sediment record extending from the present back to the end of the late illinoian glaciation when central illinois was covered with picea pinus forest during the last interglaciation a temperate deciduous forest more diverse than holocene quercus carya forest replaced the illinoian late glacial boreal forest prairie pollen types and the charcoal pollen ratio indicating fire frequency temporarily increased then forest with high juniperus percentages became dominant once more as the charcoal pollen ratio dropped after the last interglaciation the charcoal pollen ratio increased again and prairie and wetland surrounded pittsburg basin through the entire wisconsinan glacial age the area was still prairie in late wisconsinan time but with some picea and pinus during the holocene the region has been a mixture of prairie and quercus carya forest during the last interglaciation pittsburg basin was surrounded by vegetation different from that surrounding it during the present interglaciation rather than indicating substantial differences in climate between analogous phases of different glacial interglacial cycles this variation may be due to changes in fire frequency which could be caused by small changes in climate human activity or differences in soil

the anatomy of a climatic oscillation vegetation change in eastern north america during the younger dryas chronozone century scale climate changes reshaped circulation patterns over the north atlantic and adjacent regions during the last glacialto interglacial transition here we show that vegetation across eastern north america shifted dramatically at the beginning and end of the younger dryas chronozone ydc 12 900 11 600 cal yr b p when changes in ocean circulation rapidly cooled and then warmed the north atlantic sea surface on both the site specific scale and the continental scale vegetation changed only gradually during the millennia before 15 000 13 000 cal yr b p and after 11 000 9000 cal yr b p the ydc but climate changes ca 12 900 and 11 600 cal yr b p altered the vegetation on both spatial scales within centuries plant associations changed and some taxa rapidly migrated hundreds of kilometers 300 km within b100 yr in limited regions near the north atlantic coast abrupt cooling ca 12 900 cal yr b p resulted in a return to earlier vegetation types elsewhere however the vegetation patterns during the ydc were distinct from those of both earlier and later intervals they indicate abrupt non reversing seasonal temperature changes that were probably related to atmospheric circulation changes during the ydc rather than to the direct influence of north atlantic sea surface temperatures atmospheric circulation patterns during the ydc were unique within the last 21 000 yr because of a unique combination of climate controls insolation ice sheet extent and atmospheric composition were significantly different from their full glacial states even when the north atlantic returned to near full glacial conditions the ydc vegetation patterns demonstrate 1 rapid ecological responsiveness to abrupt climate change and 2 spatially varied patterns of ydc climate change r 2002 elsevier science ltd all rights reserved

the timing of regional lateglacial events and post glacial sedimentation rates from lake superior abstract we analyze both new and previously published paleomagnetic records of secular variation psv from lake superior sediment cores and compare these records to correlated rhythmite varve thickness records to determine post glacial sedimentation rates and to reassess the termination of glaciolacustrine varves in the basin the results suggest that offshore sedimentation rates have exhibited considerable spatial variation over the past 8000 years particularly during the mid holocene we attribute offshore mid holocene sedimentation changes to alterations in whole basin circulation perhaps precipitated by a greater dominance of the gulf of mexico air mass during the summer season nearshore bays are characterized by high sedimentation rates for at least 1000 years after varve cessation and during a period between around 4500 and 2000 cal bp after 2000 cal bp sedimentation rates subsided to earlier rates the increases between 4500 and 2000 cal bp are probably due to lake level fall after the nipissing ii highstand the older glaciolacustrine varve thickness records suggest that the influx of glacially derived sediment ended abruptly everywhere in the lake except near the lake nipigon inlets multiple sediment cores reveal 36 anomalously thick varves previously ascribed to the formation of the nakina moraine which were deposited just prior to varve cessation in the open lake the psv records support the observation that the cessation of these thick varves is a temporally correlative event occurring at 9035 170 cal bp calibrated years before 1950 ca 7950 8250 14 c bp this date would correlate to the eastern diversion of lake agassiz and glacial meltwater into lake ojibway

paleoenvironmental records of water level and climatic changes from the middle to late holocene at a lake erie coastal wetland ontario canada pollen and diatom assemblages and peat stratigraphies from a coastal wetland on the northern shore of lake erie were used to analyze water level and climatic changes since the middle holocene and their effects on wetland plant communities peat deposition began 4700 cal yr b p during the nipissing ii transgression which was driven by isostatic rebound at that time a diatom rich wild rice marsh existed at the site water level dropped at the end of the nipissing rise at least 2 m within 200 yr leading to the development of shallower water plant communities and an environment too dry for most diatoms to persist the sharp decline in water level was probably driven primarily by outlet incision but climate likely played some role the paleoecological records provide evidence for post nipissing century scale transgressions occurring around 2300 1160 700 and 450 cal yr b p the chronology for these transgressions correlates with other studies from the region and implies climatic forcing peat inception in shallow sloughs across part of the study area around 700 cal yr b p coincides with the little ice age these records considered alongside others from the region suggest that the little ice age may have resulted in a wetter climate across the eastern great lakes region

evidence for increased cool season moisture during the middle holocene isotopic analyses of three stalagmites from cold water cave northeast iowa united states reveal nearly identical 13 c trends from ca 7 to 2 ka however 18 o patterns differ by as much as 3 from 5 7 to 3 2 ka these disparate 18 o values reflect evaporative 18 o enrichment in meteoric water prior to infiltration suggesting that previously calculated temperatures based on a single cold water cave stalagmite overestimated middle holocene warming the coincidence of elevated middle holocene growth rates in the stalagmites with the lowest oxygen isotopic compositions indicates that the middle holocene was marked by a predominance of coolweather precipitation during a period of increased overall aridity

mapped plant macrofossil and pollen records of late quaternary vegetation change in eastern north america abstract macrofossil presence absence maps and isopoll maps in 3000 year intervals show how ranges and abundance maxima for 12 eastern north american tree and shrub taxa picea p glauca p mariana larix laricina abies balsamea tsuga canadensis pinus strobus p resinosa p banksiana betula papyrifera b alleghaniensis b series humiles have changed from the last glacial maximum to the present the macrofossil maps corroborate patterns shown by the isopoll maps and provide spatial detail and taxonomic resolution the macrofossils confirm the inference from pollen data that unglaciated southeastern north america was cooler during the last glacial maximum 18 and 15 ka than simulated by the cohmap experiments with the ncar ccm0 general circulation model the geographic distribution of macrofossil occurrences during the late glacial 12 and 9 ka indicate that migration lag of boreal species did not occur at regional to subcontinental scales and that pollen assemblages lacking modern analogs resulted from climate gradients lacking modern analogs early holocene 9 and 6 ka macrofossil maps show rapid northward expansion of tree species ranges into deglaciated regions the data also show modest contractions of northern range limits of temperate species and expansions of southern range limits of boreal species in response to cooling trends during the late holocene 3 and 0 ka comparison of modern macrofossil maps of nine of these taxa with corresponding range maps confirm that the macrofossils record the geographic ranges accurately comparison of the modern macrofossil maps with maps of tree growing stock volume shows that for some taxa abies tsuga macrofossil occurrences were most frequent in regions of maximum tree abundance comparison of modern isopoll maps with the modern range and growing stock volume maps indicate that in contrast to the macrofossil data the pollen data provide poorer resolution of range limits for most taxa but better indications of abundance maxima and minima within the ranges

ecosystem development following deglaciation a new sedimentary record from devils lake wisconsin usa abstract processes and rates of ecosystem development can be reconstructed using lacustrine sedimentary sequences but this approach often requires records that contain the start of primary succession most lakes in the upper midwestern u s were formed by glaciers at the end of the last ice age approximately 11 700 cal yr bp devils lake wisconsin is a rare example of a lake from this region whose sediments extend into the pleistocene and may include the last glacial maximum sediment magnetic geochemical pollen and charcoal records were generated from a 10 m core whose basal sediments may be 28 000 years old together with a previously published pollen record these proxies combine to reveal a history of long term climatic vegetative and geologic change during the late pleistocene to holocene we identify six sedimentary units that indicate a series of consecutive events rather than a predictable trajectory of ecosystem development at the site productivity in the lake was low during the late pleistocene and increased during the holocene as reflected by the sediment lithology which shows a sudden shift from glacial vivianite rich and organic poor clastic dominated sediments to holocene diatomaceous sapropels several important processes initiated around 17 000 cal yr bp including the onset of organic matter accumulation and fire in the terrestrial ecosystem however the post glacial landscape was not devoid of vegetation because pollen assemblages indicate that terrestrial vegetation likely a spruce tundra survived near the site a switch to a hardwood forest period during the holocene also led to a change in the fire regime with increased frequency of burning aquatic ecosystem productivity lagged terrestrial ecosystem productivity throughout the record nutrient cycling as recorded by sedimentary 15n was variable but not directional and appeared to be correlated with climate conditions early in the record and terrestrial ecosystem processes later in the record throughout the holocene magnetic mineral concentration decreased as productivity increased and the source of magnetic material shifted from almost exclusively lithogenic to approximately 50 derived from soil or biogenic sources magnetic grain size ambrosia pollen percentages and charcoal concentration increased and 15n decreased in the most recent part of the record due to anthropogenic influence in the region including agricultural activities

inland aeolian deposits of the iberian peninsula sand dunes and clay dunes of the duero basin and the manchega plain palaeoclimatic considerations abstract this paper describes the latest research on the geomorphological characteristics formation environment and chronology of the main inland aeolian deposits from the south eastern duero basin db and the manchega plain mp of the iberian peninsula similarities and differences between the aeolian deposits of these two locations are summarised wind deflation from the guadiana and jucar alluvial systems created the aeolian deposits of the mp these deposits are mainly composed of quartz sands however in the san juan alluvial plain mp there is a large extent of clay dunes formed by exposure to prevalent winds of seasonal playa lakes with salt and clay sediments in the db wind remobilisation of the small particles from quaternary terraces and tertiary arkosic sediments left aeolian deposits of quartz feldspar sands textural parameters of the aeolian deposits show large variations depending on the location and the original deposit thus in the db the aeolian sands derived from the deflation of fluvial sediments are better sorted and smaller in grain size than those created by the deflation of arkosic sediments morphologically simple and compound parabolic dunes u v forms hemicyclic lobate and elongate crescentic and linear dunes climbing dunes and blowout dunes have been recognized at both sites barchan and dome dunes are present only in the db while lunette lunette clay dunes are found only in the mp in both locations the large extent of aeolian sand sheets and the predominance of simple and compound parabolic dunes indicates the active role of sparse vegetation cover in the formation of this aeolian system in the db dunes were formed by southwest and west winds while in the mp the aeolian morphologies indicate that the prevalent winds were west and northwest the chronology of the dune deposits is being determined with luminescence tl osl dating and mass spectrometry analysis 14 c ams in this way the aeolian activity and stabilisation stages can be established the latter well marked in the db through soil a horizon development thus the main sand dune formation in the db and the eastern regions of the mp occurred between 13 5 and 7 ka bp during the cold and arid younger dryas episode and the early holocene the clay dunes of the mp accumulated mainly from 29 to 19 ka bp that corresponds with heinrich events he 3 and he 2 and the last glacial maximum however clay dunes were also formed between 13 5 and 7 ka bp in both locations there have been reactivations of some sand deposits in the recent holocene with maximum activity around 5 2 ka bp and 0 5 0 2 ka bp on the other hand three marked stages of stabilisation of the db aeolian system have been established with 14 c ams around 10 2 6 2 and 1 2 ka bp finally the main winds contributing to dune construction were also responsible for the deflation processes with the formation of erosional depressions

postglacial water level changes of a small lake in southern quebec canada sediment stratigraphy and palaeobotanical data from five cores were used to reconstruct the postglacial water level changes of a small lake in southern quebec the cores were taken along two transects from the centre of the lake to the margins lake level was relatively high before 11 000 cal bp when sedimen tation was characterized by the deposition of silty gyttja 13 000 cal bp and marl 13 000 11 000 cal bp from 11 000 to 7000 cal bp a sediment hiatus was indicated by the lack of two regional pollen zones between the marl and the overlying gyttja suggesting either nondeposition or erosion of the previously deposited sedi ments due to a low lake level the lake level was approximately 2 m lower than present on the basis of macrofossil assemblages a rise in the water level of about 1 m occurred around 7000 cal bp which was interrupted by a second lowering between 6100 and 4400 cal bp as indicated by a hiatus in the pollen stratigra phy during this low period the water level was at leas

thermoluminescence ages of loess and associated sediments in central nebraska usa abstract thick deposits of quaternary loess maximum 60 m more typically 20 30 m occur in the loess hills and south of the platte river in central nebraska a programme of field sampling and thermoluminescence dating has provided new age estimates for the younger aeolian stratigraphic units in the upper part of the sequence dates from aeolian sands below the gilman canyon formation at two sites indicated ages ranging from 64 7 to 48 5 ka providing a maximum age for this unit a date of 35 3 ka was obtained from near the top of a truncated gilman canyon sequence in one section but radiocarbon evidence from other sites suggests that slow accumulation of dust accompanied by pedogenesis and syn depositional reworking continued in some areas until at least 23 ka ago the gilman canyon formation is overlain by up to 25 m of grey peoria loess which accumulated between c 22 ka and 10 5 ka ago between c 10 5 ka and 9 ka ago the rate of dust accumulation decreased apparently due to a reduction in sediment supply from the great plains river valleys thereby allowing the widespread development of a soil the brady soil after 9 ka ago the rate of dust deposition again accelerated resulting in the accumulation of up to 5 m of bignell loess the main source of bignell loess was probably also the valleys of ephemeral great plains rivers during periods when the region experienced a drier climate than present dating evidence suggests that some time after 3 2 ka ago the rate of dust accumulation again slowed allowing development of the modern soil it is suggested that this change reflected a reduction in dust availability related to a change towards slightly wetter climate and associated changes in river regime

significance of δdkerogen δ13ckerogen and δ34spyrite from several permian triassic p tr sections for the first time we report d of kerogen dkerogen for three permian triassic p tr sequences hovea 3 perth basin western australia jameson land east greenland and lusitaniadalen spitsbergen we have compared dkerogen with 13c of kerogen 13ckerogen and 34s of total reduced inorganic sulfur tris essentially pyrite 34spyrite of all the sections and for one sample set with 13c of carbonate 13ccarbonate to establish i similarities between the sections and ii evaluate whether these signals are local and or global stable isotope shifts occur for all three sample sets either at the p tr transition western australia or coinciding with the marine ecosystem collapse spitsbergen and east greenland dkerogen reflects organic matter om kerogen type and is not sensitive to the low level of thermal maturation reliable palaeoenvironmental information in terms of the use of d can therefore only be obtained for the p tr transition from hydrogen compound specific isotope analyses csia of biomarkers nabbefeld et al 2010b the negative shifts in 13ccarbonate primary and 13ckerogen are attributed to the release of 13c depleted carbon into the atmosphere whereas the isotopic excursions in 34spyrite relate to palaeoredox changes however the global coincidence in timing of the shifts in dkerogen 34spyrite and 13ckerogen suggests a relation between the sulfur carbon and hydrogen cycles the negative shifts in 13ccarbonate primary are in general attributed to the release of 13c depleted source of carbon into the oceans and atmosphere whereas 13ckerogen can reflect the latter in certain cases but can also be superimposed by varying sources of om kerogen type isotopic excursions in 34spyrite relate to global changes in the palaeoredox conditions that affect sulfur cycling in the ancient seas

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

clearing up clouded waters palaeoenvironmental analysis of freshwater mussel assemblages from the green river shell middens western kentucky despite much progress in the analysis of middle and late archaic period c 6000 3000bp shell midden sites along the lower green river many issues remain unresolved one area of concern is the relationship between malacological and geoarchaeological data specifically archaeological mussel assemblages have been interpreted to suggest shallow swiftly flowing sections of river near the sites whereas geoarchaeological discussions have been interpreted to indicate a deep sluggish channel this apparent contradiction has contributed to discussions that question the traditionally presumed dietary role of the shellfish positing instead for example that shell could have been transported long distances in order to construct mortuary monuments in this paper we show that the notion of a contradiction between malacological and geoarchaeological data is false on the one hand an analysis of mussels from the haynes site 15bt11 supports a previous reconstruction of stream conditions based on malacological data from the nearby carlston annis site 15bt5 on the other hand geoarchaeological discussions have been misconstrued through literal interpretation of generalizations that apply at a broad geological scale supporting data especially from pre impoundment survey maps suggest that the stretches of river in question included suitable habitat for the mussel species that dominate the middens with this point of confusion resolved we plan subsequent research to expand the data base at haynes and other shell bearing sites focusing on overall palaeoenvironmental reconstruction taphonomic processes site distributions in relation to geomorphological contexts and dietary analysis

patterns of holocene climatic change in the midwestern united states the holocene pollen sequence in the minnesota area is asymmetric around the so called prairie period the early holocene is dominated by elm with pine in the north and the late holocene by oak the elm zone is interpreted as a manifestation of summer monsoonal rains enhanced by the milankovitch insolation maximum and the pine in the north is interpreted as a result of summer cooling near the retreating ice sheet as the summer insolation waned during the holocene its associated monsoonal rains from the caribbean moisture source lasted longer in the south northeastern iowa and southern wisconsin where the inferred mesic elm forest changed to prairie as late as 5000 yr b p compared to 8000 yr b p in minnesota and 9000 yr b p in the dakotas

hot acidic late permian seas stifle life in record time abstract the end of permian time 252 251 ma hosts the largest mass extinction in earth history yet events heralding this global catastrophe remain intensely disputed we present a chemostratigraphic marker the 187re 188os ratio which soars to unprecedented levels approaching the permo triassic boundary these ratios are tied to profound trace element changes and a precise re os time record at 252 ma preserved in black shales from east greenland and the mid norwegian shelf within a 36 meter shale section an 80 fold increase in re concentrations two fold for os signals seawater conditions that became increasingly inhospitable to life unwavering initial 187os 188os ratios of 0 6 preclude mafic volcanism and meteorite impact as the direct cause of late permian anoxia we argue that extraordinarily high 187re 188os ratios are the hallmark of simultaneously rising ocean temperature and acidity leading to loss of oxygen and the stifling of life in latest permian time

reconstruction of holocene lake level from diatoms chrysophytes and organic matter in a drainage lake from the experimental lakes area northwestern ontario canada abstract a paleolimnological study of lake level changes in lake 239 rawson lake a headwater lake in the experimental lakes area in northwestern ontario indicates large fluctuations have occurred over the holocene analyses are based on diatoms the proportion of chrysophyte scales to diatoms and organic matter content from near shore sediment cores quantitative estimates of lake level are based on a diatom inferred depth model that was developed from surficial sediments collected along several transects in lake 239 declines of 1 3 m occurred during the late holocene whereas declines of at least 8 m occurred during the more arid mid holocene these results provide the first substantive evidence of large declines in lake level in northwestern ontario during the mid holocene conditions during the mid holocene may provide a partial view of future conditions under increasing global temperatures

effects of storminess sand supply and the north atlantic oscillation on sand invasion and coastal dune accretion in western portugal holocene forested coastal dunes fringe the atlantic coast of western portugal mapping of dunes in the field and using air photographs shows a range of forms reflecting dominant northwest and westerly onshore wind regimes planting of maritime pine forests in the thirteenth and twentieth centuries was initiated because of sand invasion causing problems for human settlement and agriculture early holocene dunes have a well developed podsol and date to 9 7 and 8 2 ka suggesting at least some of these sands may have been emplaced during a global cooling event significant transgressive dune accretion at 2 2 and 1 5 ka implies abundant sand supply and strong onshore winds the most recent dune building period dates to ad 1770 1905 and coincides with a predominantly negative winter north atlantic oscillation index naoi accretion of dunes along the portuguese coast appears out of phase with dune development in southwest france which may reflect different atlantic storm tracks driven by changes in the domin

chemical signals for oxidative weathering predict re os isochroneity in black shales east greenland abstract re and os isotopes in shales are increasingly used for precise and accurate geochronology and for tracking rates of continental weathering in the geologic past moreover trace element compositions of organic rich shales reveal paleoredox conditions and properties of shale organic matter om useful for lithostratigraphic correlations chemical weathering alters the original shale composition and hence may compromise geologic interpretations based on geochemical data here we compare re os isotopes trace elements and om properties in correlative shales from outcrops and nearby drillcore to quantify the effects of weathering we define chemical parameters that distinguish weathered from pristine shale in samples that are macroscopically identical black shale from the ravnefjeld formation in east greenland yields disturbed re os isotope systematics for outcrop samples and highly precise re os isochron ages for drillcore geochemical data show that re os and common os are hosted in the organic matter rather than sulfides re and os both show mobility during weathering combined use of rock eval pyrolysis indices and sulfur contents documents oxidation of both om and pyrite thereby providing a valuable chemical criterion to assess invisible shale weathering further studies on chemically diverse shales will test the widespread application of these criteria as weathering indicators systematic differences in major and trace element content and kerogen quality between weathered and fresh shale samples are used to characterize and quantify weathering effects the character of the om in shales is most telling ravnefjeld data are compared with data from time correlative shales from the mid norwegian shelf georgiev et al 2011 hot acidic late permian seas stifle life in record time earth planet sci lett 310 389 400 to present a strategy for identification of re os isochroneity in advance of re os analytical work our recent compilation and comparison of upper permian shales from widely separated sequences on pangea s margins reveal exceptionally high re os ratios on a global scale we suggest upper permian shales may have significantly influenced the cenozoic e g eocene 187os 188os ratio of seawater on their exposure and weathering

wind regimes and aeolian transport in the great basin u s a abstract the modern great basin of the interior western united states is characterized by surface winds with considerable spatial and temporal variabilities wind records from the second half of the 20th century for 12 great basin localities analyzed with standard aeolian sediment transport methods developed elsewhere in the world reflect this complexity the drift potential dp for aeolian deposits is generally moderate dp 200 400 in the western great basin and weak dp 300 at the eastern edge of the great basin where the dominant prevailing wind direction is south southwesterly both dp and resultant drift direction rdd are consistent with synoptic meteorological observations of the evolution of cold fronts in the great basin meteorological observations show that effective winds to produce dunes are most commonly the result of late winter early spring cyclogenesis there has been considerable temporal variability of dp in the latter half of the 20th century most of the great basin has experienced decreasing wind strength since 1973 consistent with recent studies of wind strength in north america and elsewhere dune morphology matches both localized rdd and temporal variations in dp reasonably well in the great basin the results demonstrate that local topography can have an important influence on wind directionality thus providing a cautionary note on the interpretation of dune morphology in the paleoclimatic and stratigraphic record

timing and origin for sand dunes in the green river lowland of illinois upper mississippi river valley usa abstract the recent increase in dune studies in north america has been heavily focused in the great plains while less attention has historically been given to the dune fields east of the mississippi river here we report ages and suggest a potential sediment source for sand dunes in the green river lowland illinois which may provide a better understanding of the dynamic interactions between eolian glacial lacustrine and fluvial processes that shaped the landscapes of the upper midwest seven coherent optically stimulated luminescence ages osl or optical ages obtained from four sites suggest that major dune construction in the green river lowland occurred within a narrow time window around 17 500 ago this implies either an enhanced aridity or an episodic increase of sediment supply at 17 500 years ago or combination of the both contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the lake michigan lobe retreated from the area we propose that green river lowland dunes sand originated from the green bay lobe through the rock river specifically sediment supply increased in the rock river valley during drainage of glacial lake scuppernong which formed between 18 000 and 17 000 years ago when the green bay lobe retreated from its terminal moraine the lake drained catastrophically through the rock river valley providing glacial sediment and water to erode the preexisting sandy sediments throughout the remainder of the late pleistocene the laurentide ice sheet drained into larger more northerly glacial lakes that in turn drained through other river valleys therefore the dunes in the green river lowland formed only during the catastrophic drainage of glacial lake scuppernong but were stabilized through the remainder of the pleistocene this scenario explains the abrupt dune construction around 17 500 years ago and explains the lack of later dune activity up to the pleistocene holocene transition osl and radiocarbon ages also indicate that dunes were reactivated during the early middle and late holocene some eolian activation occurred within well defined dry intervals in the upper midwest suggesting that increased aridity may have been the primary driver in mobilizing sand however many ages do not correspond to drier periods in contrast to the relative coherency of the pleistocene osl ages from multiple study sites the holocene osl ages do not overlap from one site to another suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation in the holocene therefore we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the holocene the multiple periods of eolian activity during the holocene suggest a high potential for future sand activation in the region and these results are informative for environmental prediction and potential future mitigation

parent material influence on soil response to vegetation change southeastern minnesota u s a abstract soil morphology changes dramatically across the former transition from forest to grassland in the midwestern u s a that vegetation boundary shifted as a result of holocene climatic change and fire suppression following euroamerican settlement but the timescale of soil response to those vegetation changes and the factors that influence it are poorly known on steep colluvial slopes of southeastern minnesota mollisols with thick dark a horizons typically associated with grassland are found today under deciduous forest soils with much thinner and or lighter colored a horizons occur immediately up and downslope of the forest covered mollisols most of the soils with thick a horizons are not in topographic settings found to favor organic matter accumulation in other landscapes principal component analysis highlights important axes of textural and mineralogical variation among horizons of these soils often related to parent material properties soils with and without thick a horizons are separated along one principal component heavily loaded by high ph reflecting the presence of dolomite fragments in the hillslope sediment that soils with thick dark a horizons formed in stable c isotope analysis reveals that the mollisols with thick dark a horizons under forest had c input from vegetation with abundant c4 grasses in the past public land survey data also indicate replacement of grassland or savanna by forest since 1854 on colluvial slopes where forest covered mollisols occur today we propose that the soils with thick dark a horizons under forest today reflect a lagged response to vegetation change from grassland or savanna to closed forest their thick a horizons and some c4 derived organic matter may be preserved because dolomite weathering releases abundant ca and mg that favor aggregation and organic matter stabilization soils with thin a horizons just up or downslope may also have formed partly under grasses but have responded more quickly and or more substantially to vegetation change

late permian early triassic environmental changes recorded by multi isotope re os n hg data and trace metal distribution from the hovea 3 section western australia abstract the temporal coincidence between the late permian mass extinction lpme and the emplacement of siberian trap basalts suggests a causal link between the two events here we discuss stratigraphic changes of organic and inorganic including isotopic geochemical properties of marine sediments across the permian triassic boundary ptb in the hovea 3 core western australia a key ptb section in the southern neo tethys ocean these data are compared with published data from the meishan section southern china and from the opal creek section in western canada providing a view of tethys and panthalassa changes at the ptb trace metal and n isotopic data together with organic matter properties suggest that anoxic conditions were established prior to the lpme intensified close to the lpme and continued with photic zone euxinia into the early triassic for the hovea 3 section re os ages confirm changhsingian 253 5 1 4 ma deposition of the dated interval sampled immediately below the stratigraphic level characterized by major lithological and isotopic changes evaluation of re os n and hg elemental and isotopic data for hovea 3 suggests that anoxic conditions in the latest permian were generally unrelated to direct magmatic contributions a major increase in the initial os isotopic ratio of lower triassic shales suggest an 8 increase in the early triassic continental runoff based on moderately conservative assumptions for end members contributing os to the permian triassic ocean comparison to other ptb sections confirms a global signal of increasing re os ratios in the late permian and major and long lived changes in the isotopic composition of the post extinction ocean a distinct peak in hg concentrations carrying a volcanic isotopic signature also identified in other ptb sections likely represents a major pulse of siberian trap volcanism this hg peak in the hovea 3 section however is detected above the stratigraphic level containing multiple other widely recognized and more permanent geochemical changes therefore direct volcanic inputs to the permian triassic ocean likely post date the lpme in this western australian section

the structure of holocene climate change in mid latitude north america abstract a sequence of long term and rapid changes during the holocene appears in a network of 40 well resolved paleoclimate datasets from mid latitude north america including records of pollen inferred temperatures alkenone derived sea surface temperatures ssts lake level changes dust accumulation and lake isotopes from idaho to maine statistical analyses reveal that changes in insolation and the laurentide ice sheet explain 51 7 of the variance in the records especially multi millennial trends but peak rates of change indicate additional rapid changes at ca 10 8 9 4 8 3 7 0 5 5 5 2 4 7 2 1 and 0 9 ka step changes between 9 4 and 8 3 ka relate to ice sheet dynamics that warmed much of the region and changes at 5 5 ka were the largest since the demise of the ice sheet the shift at 5 5 ka initiated widespread cooling and increases in effective moisture which culminated in the coolest wettest millennia in most areas after 2 1 ka replicated evidence from multiple records also shows a spatially varied set of multi century fluctuations including 1 low temperatures and high effective moisture at 5 5 4 8 ka in the mid continent and 2 repeated phases of low ssts cool summers and drought superimposed upon long cooling moistening trends in eastern north american since 5 5 ka

up in the refrigerator geomorphic response to periglacial environments in the upper mississippi river basin usa abstract james c knox was best known for his work on holocene and historical changes in fluvial systems but he also had a long standing interest in the effects of late pleistocene periglacial environments on landscape evolution in parts of the upper mississippi river basin that were just outside the laurentide ice sheet margin or as knox put it up in the refrigerator knox and others in the quaternary community of the midwestern u s often suggested that hillslope erosion was accelerated under periglacial conditions so that glacial periods have had a dominant effect on the landscape we see today this paper reviews the evidence and reasoning supporting that view in a study area of the upper mississippi basin bordered on three sides by ice margins of the last glaciation including the wisconsin driftless area and adjacent landscapes sparse but compelling paleoecological data and relict ice or sand wedge polygons provide clear evidence for a cold climate and widespread permafrost around the peak of the last glaciation in highly dissected relatively high relief parts of the study area the loess and soil stratigraphy on ridgetops and the colluvial mantles on steeper slopes are best explained by highly effective hillslope erosion including solifluction during and just after the last glacial maximum knox used the post depositional truncation of a loess unit to quantify contrasting late pleistocene and holocene sediment yields from a small driftless area watershed while the late pleistocene yield indicates accelerated erosion it is still lower than modern sediment yields in many tectonically active or semiarid landscapes and it may reflect deposition of highly erodible loess as well as effects of periglacial conditions the views of knox and other midwestern geomorphologists on landscape evolution through glacial interglacial cycles were highly influenced by the work of robert v ruhe ruhe proposed that an episode of widespread erosion during and just after the last glacial maximum can explain enigmatic aspects of quaternary stratigraphy and the soil landscape on the iowan erosion surface a very low relief landscape of the study area ruhe s key evidence is still valid though it needs to be separated from an implausible model of landscape evolution interpretation of the iowan erosion surface and other low relief landscapes just outside the ice margin also requires recognition of the profound effect of eolian processes on those landscapes under periglacial conditions many new insights on landscape evolution in the study area could result from wider application of cosmogenic nuclide based methods to assess glacial interglacial changes in basinwide rates of erosion and residence time of soils just as important a need exists for much more field based characterization of hillslope fluvial and eolian sediments for comparison with those of modern permafrost regions and past periglacial environments in europe

patterns of holocene environmental change in the midwestern united states abstract four pollen sequences along a transect from north central iowa to southeast wisconsin reveal the distribution of prairie and forest during the holocene and test the use of pollen isopolls in locating the holocene prairie forest border prairie was dominant in central iowa and climate was drier than present from about 8000 to 3000 yr b p during the driest part of this period in central iowa 6500 5500 yr b p mesic forest prevailed in eastern iowa and wisconsin suggesting conditions wetter than at present prairie replaced the mesic forest about 5400 yr b p in eastern iowa but did not extend much farther east mesic forests were replaced in southern wisconsin and northern illinois about 5400 yr b p by xeric oak forests this change from mesic to xeric conditions at 5400 yr b p was widespread and suggests that the intrusion of drier pacific air was blocked by maritime tropical air from the gulf of mexico until the late holocene in this area

basin scale reconstruction of the geological context of human settlement an example from the lower mississippi valley usa abstract large river valleys integrate hydroclimatic change differently than smaller ones whereas sedimentary deposits in smaller valleys serve to record temporally short lived and or low amplitude hydrological and geomorphic responses larger valleys are relatively insensitive to changes at these scales however because of their size larger valleys archive sedimentary records of longer term geographically extensive flooding and climate related landscape evolution recent work in the upper tensas basin of the lower mississippi river valley usa demonstrates the utility of analyzing sediments from a large geomorphically and fluvially complex river basin as a proxy for significant climatic and landscape changes and their relation to human history a 6000 year sedimentary archive is used to explore the interplay between climate change landscape evolution and human responses to changing environmental parameters once the mississippi river basin stabilized following glacial retreat and deceleration of sea level rise the history of the river and its inhabitants was dominated by long periods of landscape stability punctuated by episodes of significant landform alteration modifications of the landscape are correlated with intervals of rapid climate change recorded in globally distributed multiproxy data sets periods of significant landscape instability and fluvial re adjustment are recorded for the periods ca 4800 3800 3000 2500 and 1000 800 cal bp these punctuations in the history of the lower mississippi valley are related to periods of major cultural transformation and suggest climate change plays a significant role in the long term history of human occupation in this river valley this research demonstrates how geoarcheology can provide information on human environmental relationships and long term landscape histories at temporal and spatial scales relevant to understanding cultural responses to climate change

unprecedented last glacial mass accumulation rates determined by luminescence dating of loess from western nebraska abstract a high resolution chronology for peoria last glacial period loess from three sites in nebraska midcontinental north america is determined by applying optically stimulated luminescence osl dating to 35 50 m quartz at bignell hill nebraska an osl age of 25 000 yr near the contact of peoria loess with the underlying gilman canyon formation shows that dust accumulation occurred early during the last glacial maximum lgm whereas at devil s den and eustis nebraska basal osl ages are significantly younger 18 000 and 21 000 yr respectively at all three localities dust accumulation ended at some time after 14 000 yr ago mass accumulation rates mars for western nebraska calculated using the osl ages are extremely high from 18 000 to 14 000 yr much higher than those calculated for any other pre holocene location worldwide these unprecedented mars coincide with the timing of a mismatch between paleoenvironmental evidence from central north america and the paleoclimate simulations from atmospheric global circulation models agcms we infer that the high atmospheric dust loading implied by these mars may have played an important role through radiative forcing in maintaining a colder than present climate over central north america for several thousand years after summer insolation exceeded present day values

a chronological framework for the holocene vegetational history of central minnesota the steel lake pollen record abstract paleorecords from minnesota and adjacent areas have often been used to evaluate large scale climatic processes in the mid continent of north america however most of these records are compromised by chronological flaws making problematic any comparisons with climatic interpretations based on other records e g gisp2 in greenland we report here a high resolution pollen record with a secure chronology constrained by 26 14 c dates on terrestrial macrofossils from steel lake central minnesota about 11 2 ka cal bp 11 000 calibrated yr before present the late glacial picea forest near steel lake was succeeded abruptly by pinus banksiana and or resinosa the pinus forest began to open 9 4 ka cal bp with the expansion of prairie taxa and a pine parkland or savanna prevailed until about 8 ka cal bp when quercus replaced pinus to become the dominant tree in the prairie areas for 4500 yr the close chronological control permits the correlation of key vegetational changes with those at other reliably dated sites in the eastern dakotas and in minnesota suggesting that the abrupt decline of the spruce forest was time transgressive from southwest to northeast during 2000 yr and that the development of prairie was time transgressive in the same direction over 2600 yr correlation of key pollen horizons at steel lake with those in the high resolution pollen profiles of elk lake ca 50 km northwest of steel lake suggests that the well known elk lake varve chronology for the early holocene is about 1000 yr too young

an exceptionally rich hyaena coprolites concentration in the late miocene mammal fossil site of la roma 2 teruel spain taphonomical and palaeoenvironmental inferences abstract the la roma 2 alfambra teruel spain late miocene vertebrate fossil site is characterised by a rich and unusual concentration of mammalian coprolites distributed along a band running in a nne ssw direction sub parallel to a fossil bone assemblage these coprolites contain residues that provide direct evidence regarding the diets of the organisms that produced them they contain a variety of inclusions such as small bone fragments pollen grains and fungal spores the bone fragments show evidence of heavy digestion including corrosion and rounded and highly polished fracture surfaces all the coprolites at the site are circular in section some of them showing two convex ends and others with both concave and convex sometimes pointed end their shape and size match the faeces produced by the extant spotted hyaena crocuta crocuta x ray diffraction analysis showed these coprolites to be mostly composed of calcium phosphate with small amounts of quartz and gypsum all these characteristics suggest that they represent the excreted remains of digested bones their size and morphology allow their attribution to the late miocene hyaenid lycyaena chaeretis the spatial distribution of the coprolites and the lack of tooth marks on the surface of the nearby fossil bones suggest that these elements were transported to their present positions from different places of origin by different water currents the palynological analysis of the coprolites suggests their makers lived in an open environment with relatively scarce vegetation and under relatively cool climatic conditions but where water was available pines were the dominant tree taxa but oak hazel and birch were also present

centennial to millennial hydroclimatic fluctuations in the humid northeast united states during the holocene paleoclimate records indicate that the hydroclimate of the northeast united states changed continuously during the holocene but the signals of multi century variations have been difficult to distinguish from local effects and noise systematic replication of the signals can help diagnose the patterns of change here we use ground penetrating radar gpr and sediment core analyses to extend and compare the regional network of lake level records we reconstruct the histories of two lakes in northeast pennsylvania which show that multi century hydrologic changes observed in coastal new england extended to the susquehanna river watershed correlations with isotopic and marine temperature records r 0 65 indicate that high temperatures coincided with low water at 4 9 3 8 and 2 8 2 0 ka widely recognized holocene events at ca 4 2 and 2 7 ka therefore may have shared similar ocean atmosphere dynamics in this region low water levels in pennsylvania from ca 5 5 4 9 ka however demonstrate that other multi century changes had different patterns at ca 5 5 ka anti phased inland and coastal hydrologic changes followed a sharp temperature decline and produced drought possibly as far inland as the great lakes the long term increase in water levels since then underscores that current pluvial conditions in the region probably lack a holocene precedent

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation

comparison of multiple proxy records of holocene environments in the midwestern united states we compare four emerging approaches to reconstructing holocene vegetation and climate from south of the glacial border in northeastern iowa united states pollen plant macrofossils carbon isotopic 13 c values from alluvial organic matter and carbon isotopic values in stalagmites from a nearby cave all show similar paleovegetational and paleoclimatic trends during the holocene pollen and plant macrofossils show a rapid change from forest to prairie about 6000 cal yr b p followed by a return of oaks to a presumably savanna like community about 3500 cal yr b p the 13 c values in alluvial organic matter and the percentage of c 4 plants both increase ca 6300 cal yr b p and then decrease in the last 3500 years in the cave 13 c values rise beginning at 6000 cal yr b p to a broad peak ca 4500 to 3000 cal yr b p and decrease thereafter pollen and plant macrofossils record the composition of the vegetation that produced the isotopic signals and verify c 3 c 4 interpretations based on the isotopic records we demonstrate that these methods are complementary but that any single method will provide an accurate reconstruction of past environments