geochemical characterization of the middle and late pleistocene alluvial fan dominated infill of the northern part of the weihe basin central china major reorganizations in climate and tectonic regime occurred in east asia during the pleistocene resulting in large scale environmental changes in this paper a detailed geochemical and mineralogical record of these changes is presented from a distal alluvial fan sedimentary sequence in the northern weihe basin we established that in addition to glacial interglacial variation there are three distinctly different units deposited over the past 1 m y these units are the result of variations in the overall tectonic regime in the northern weihe basin fine grained detrital minerals were predominantly delivered during colder climatic periods whereas evaporative minerals were dominantly deposited during the warmer interglacial periods probably as a result of strong seasonal contrast this compositional variation demonstrates the importance of climate control on hinterland erosion surface runoff chemical weathering and evaporation al normalized ratios of indicative major elements relative to average loess composition indicate important variations in sedimentary processes mostly related to sediment flux si enrichment is an index for past flooding events while fe enrichment just like k and ti reflects influx of clays in contrast ca and mn are strongly enriched throughout the core associated with the authigenic precipitation of carbonates especially during interglacial periods the lower 1000 690 ka and upper 330 0 ka units of the core are characterized by relative intense and frequent flooding which coincided with extensive ponding in the study area in the middle unit 690 330 ka increased salinity levels caused by evaporation as reflected in the high sr ca ratio and dolomite abundance led to increased carbonate precipitation simultaneously the increased influx of fine sediments indicates increased clay production in the source area as a result of a more intense summer monsoon strength after 600 ka 2017 elsevier b v

floodplain aggradation and pedogenesis in a semiarid environment alluvial valley fills in the upper republican river basin southwestern nebraska provide evidence for processes of aggradation and pedogenesis on semiarid cut and fill floodplains sheetflow deposition on unchanneled valley floors represents an important mechanism of valley aggradation sheetflow deposits contain parallel to sub parallel laminae and discontinuous lobate sedimentary structures rates of sediment deposition on cut and fill floodplains strongly determine the degree to which pedogenic features develop within aggrading alluvium three pedofacies common to semiarid alluvial deposits correspond with increasing aggradation rates 1 cumulic soils 2 multiple buried soils and 3 no pedogenic features radiocarbon age determinations from alluvial fills indicate that floodplain aggradation greater than approximately 0 5 cm year 1 limits soil formation this represents a threshold rate of pedogenic assimilation floodplain soils formed under aggradation rates lower than this exhibit a strong positive relationship between aggradation rate and total caco3 percent and a negative relationship between aggradation rate and organic carbon percent recognizing the associations between pedogenic sedimentologic features and floodplain aggradation rates can help interpret past rates of sediment transport storage and deposition

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

a 14 000 year sediment yield record from western germany based on annually laminated lake sediments the reconstruction of sediment yield data for the catchment of lake holzmaar 205 8 ha in the eifel mountains western germany is based on high resolution geochemical and physical analyses of an absolutely dated sediment record this technique provides flux rates of allochthonous minerogenic deposition for the last 13 840 years the pleistocene holocene transition is characterized by instable soils and vegetation caused by adjustment of the catchment to interglacial climatic conditions these instabilities are the reason for elevated mean sediment yields in the catchment of 16 t km 2 yr 1 until 9800 cal bp during most of the holocene erosive processes are insignificant and sediment yields are very low 1 5 t km 2 yr 1 since humans cleared the forests for agriculture and early industrial purposes the natural environment has been disturbed and sediment yields increased to mean values of 14 t km 2 yr 1 during the last 2750 years comparisons of reconstructions from the eifel area with similar data from southern sweden and with measured data from lakes reservoirs and monitoring sites suggest that quantitative reconstructions based on lake holzmaar sediments may be regarded as reliable despite uncertainties related to the methods of reconstruction applied

tributary trunk stream relations in a cut and fill landscape a case study from wolumla catchment new south wales australia at the time of european settlement of the south coast of new south wales australia in the mid nineteenth century river courses were discontinuous throughout wolumla catchment within a few decades of settlement intact valley fills had been transformed into incised channels along trunk streams this induced associated patterns of secondary incision into tributary valley fills three of the primary subcatchments in wolumla catchment became fully incised while an upland swamp and a floodout i e sand sheet deposits atop an intact valley floor remain in mid catchment of the fourth subcatchment of the 70 lower order tributaries which join the trunk streams in the four subcatchments 27 have incised 12 of which are discontinuously incised incision of tributary streams in wolumla catchment cannot be explained by subcatchment area and slope relations the position of the trunk stream channel within the valley floor trough is the key determinant of whether or not tributary streams have incised changes to river morphology since european settlement have altered the linkage of tributary streams to the trunk stream impacting directly on the within catchment transfer of water and sediment

long stored soil carbon released by prehistoric land use evidence from compound specific radiocarbon analysis on soppensee lake sediments compound specific radiocarbon c 14 analyses allow studying the fate of individual biomarkers in ecosystems in lakes with small catchments terrestrial biomarkers have the potential to be used fo

distinguishing allogenic from autogenic causes of bed elevation change in late quaternary alluvial stratigraphic records abstract allogenic and autogenic mechanisms both cause changes in the bed elevation of rivers and thereby influence the characteristics of alluvial stratigraphic records asrs allogenic forcing mechanisms can be grouped into five categories whose relative influence varies with timescale climate tectonism base level land use land cover and direct human modification of channels late quaternary asrs are influenced by the greatest range of allogenic forcing variables with climate among the most important autogenic mechanisms of bed elevation change are ubiquitous throughout fluvial systems and are always time transgressive autogenic bed elevation change propagates through drainage networks at predictable rates and results in a time space envelope within which its effects are capable of operating asrs that can be correlated over geographical areas large enough and time intervals small enough to exist outside this envelope most likely result from allogenic forcing this formulation represents a quantitative and geographic set of threshold criteria for distinguishing between autogenic and allogenic mechanisms over late quaternary timescales 10 2 to 10 5 years in tectonically stable regions climate change is the dominant allogenic mechanism and therefore the first order control on the morphology sedimentology pedologic characteristics and chronology of alluvial stratigraphic records that meet or exceed the threshold criteria for demonstrating allogenic causality

interaction between aggrading geomorphic surfaces and the formation of a late pleistocene paleosol in the palouse loess of eastern washington state abstract variable rates of loess deposition contributed to dramatic regional variation in a soil stratigraphic unit the washtucna soil in the palouse loess deposits in the channeled scabland of eastern washington state throughout most of the channeled scabland the morphology of the washtucna soil is that of a single buried soil but it bifurcates into two well developed and pedologically distinct buried soils in areas immediately downwind of the major source of loessial sediment regional loess stratigraphy confirms that the two well developed soils formed during the same interval of time during which only one soil formed in areas that are distal to loess source areas the variable and perhaps rapid rates of soil formation suggested by the stratigraphy resulted from an interaction between variable rates of loess deposition and the formation of superimposed calcic soils petrocalcic horizons with weak stage iv morphology formed as the zone of carbonate accumulation moved up into former a and cambic horizons that had been profusely burrowed by cicadas the development of cicada burrows in one phase of soil development that were subsequently engulfed by pedogenic carbonate under a rising land surface seems to have greatly accelerated the development of the petrocalcic horizons accelerated rates of formation of the petrocalcic horizons occurred when extrinsic pulses of loess deposition and intrinsic engulfment of burrowed horizons thresholds were exceeded stratigraphic evidence suggests that the soil formation that accompanied the rise in the land surface due to additional loess deposition may have occurred during the late wisconsin glaciation when giant glacial outburst floods in the channeled scabland triggered a new cycle of loess deposition

use of soils and colluvial deposits in analyzing tectonic events the southern arava rift israel abstract buried soils in colluvium units developed on downthrown fault blocks have been presumed to form during periods of tectonic quiescence this assumes however that all colluvial units on a fault scarp are tectonically induced particularly for a multiple event fault scarp to test this hypothesis we compared the colluvial stratigraphy and pattern of soil development on two non tectonic scarps terrace risers and a nearby multiple event fault scarp on the same alluvial fan surface both slopes developed under extremely and climatic conditions the colluvial stratigraphy and soil catenary relationship developed on terrace risers were found to be substantially different from those on the multiple event fault scarp the fault scarp colluvium contained several colluvial units separated by soils whereas only two colluvial units without buried soils were found on the terrace risers the colluvial units on the fault scarp were triangular in shape while those on the terrace riser were concave and overlapped up the slope cumulic soils indicating a continuous and low rate of deposition during pedogenesis were formed along the terrace riser in contrast buried soils indicating episodic deposition occurred on the downthrown block of the multiple event fault scarp accordingly the colluvial stratigraphy developed on the fault scarp can be viewed as a record of distinct tectonic events with no climatically controlled deposition the data indicate that soils and sedimentary stratigraphy can serve as useful indicators to distinguish terrace risers and single event fault scarps from multiple event fault scarps these indicators can be helpful in distinguishing phases of tectonic activity and in evaluating recurrence intervals on a multiple fault scarp

quantification of soil erosion rates related to ancient maya deforestation we used seismic and sediment core data to quantify soil erosion rates for the past 6000 yr in the closed catchment of lake salpeten in the tropical lowlands of northern guatemala the region was affected by ancient maya land use from before ca 1000 b c to a d 900 this period of human impact coincided with deposition in the lake of a detrital unit maya clay as much as 7 m thick that contrasts sharply with the relatively organic rich gyttja deposited both before and after maya occupation of the watershed the greatest soil loss with mean sustained values of 1000 t km2yr 1 occurred in the middle and late preclassic periods 700 b c to a d 250 associated with relatively low maya population densities soil erosion slowed during the period of maximum population density in the late classic period a d 550 830 indicating a decoupling between human population density and soil erosion rate the most rapid soil loss occurred early during initial land clearance suggesting that even low numbers of people can have profound impacts on lowland tropical karst landscapes

relative rates of peoria loess accumulation and pedogenic processes implications for paleoclimatic inference abstract where it is thick enough to extend below the surface soil profile the late wisconsinan peoria loess in the midcontinent of north america has characteristics suggesting relatively little syndepositional pedogenesis in these thicker sections the peoria loess below the surface soil profile commonly displays massive macroscopic structure low organic carbon content and retention of detrital carbonate grains late wisconsinan climatic conditions provide one potential explanation for these observations this paper considers two other non climatic explanations 1 loess accumulation was more rapid than carbonate dissolution or oc accumulation and 2 post depositional diagenesis has removed evidence of syndepositional pedogenesis the approach used is comparison of potential rates for pedogenic processes and loess accumulation even when wide ranges of controlling factors precipitation evapotranspiration and soil carbon dioxide levels are considered loess accumulation was probably too rapid at many sites for carbonate mineral dissolution to keep pace on the other hand data from modern tundra and boreal forest environments suggest that soil oc accumulation could have kept pace with loess deposition in many cases low oc contents observed in the loess today probably reflect post depositional oxidation climatic factors may provide partial or local explanations for the apparent minor extent of syndepositional pedogenesis but loess accumulation rates and diagenesis are key factors as well

climatic change and contemporaneous land use phases north and south of the alps 2300 bc to 800 ad fluctuations in the 14c curve and subsequent gaps of archaeological findings at 800 650 and 400 100 bc in western and central europe may indicate major climate driven land abandonment phases to address this hypothesis radiocarbon dated sediments from four lakes in switzerland were studied palynologically pollen analysis indicates contemporaneous phases of forest clearances and of intensified land use at 1450 1250 bc 650 450 bc 50 bc 100 ad and around 700 ad these land use expansions coincided with periods of warm climate as recorded by the alpine dendroclimatic and greenland oxygen isotope records our results suggest that harvest yields would have increased synchronously over wide areas of central and southern europe during periods of warm and dry climate combined interpretation of palaeoecological and archaeological findings suggests that higher food production led to increased human populations positive long term trends in pollen values of cerealia and plantago lanceolata indicate that technical innovations during the bronze and iron age e g metal ploughs scythes hay production fertilising methods gradually increased agricultural productivity the successful adoption of yield increasing advances cannot be explained by climatic determinism alone combined with archaeological evidence our results suggest that despite considerable cycles of spatial and demographic reorganisation repeated land abandonments and expansions as well as large scale migrations and population decreases human societies were able to shift to lower subsistence levels without dramatic ruptures in material culture however our data imply that human societies were not able to compensate rapidly for harvest failures when climate deteriorated agriculture in marginal areas was abandoned and spontaneous reforestations took place on abandoned land south and north of the alps only when the climate changed again to drier and warmer conditions did a new wide spread phase of forest clearances and field extensions occur allowing the reoccupation of previously abandoned areas spatial distribution of cereal cultivation and growth requirements of cerealia species suggest that increases in precipitation were far more decisive in driving crop failures over central and southern europe than temperature decreases

complex response of a midcontinent north america drainage system to late wisconsinan sedimentation abstract the geomorphic evolution of mud creek basin in eastern iowa u s a serves to illustrate how geomorphic influences such as sediment supply valley gradient climate and vegetation are recorded in the alluvial stratigraphic record sediment supply to the fluvial system increased significantly during the late wisconsinan through a combination of periglacial erosion and loess accumulation subsequent evolution of the holocene alluvial stratigraphic record reflects long term routing of the late wisconsinan sediment through the drainage basin in a series of cut and fill cycles whose timing was influenced by hydrologic response to change in climate and vegetation when viewed in a regional context the alluvial stratigraphic record appears to reflect a long term complex response of the flu ial system to increased sediment supply during the late wisconsinan hydrologic and sediment supply changes accompanying the spread of euroamerican agriculture to the basin in the 1800s dramatically upset trends in sedimentation and channel behavior established during the holocene

support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages lunar meteorites represent a more random sampling of lunar material than the apollo or luna collections and as such lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the lunar cataclysm hypothesis within the lunar meteorite breccias mac 88105 que 93069 dag 262 and dag 400 seven to nine different impact events are represented with 40ar 39ar ages between 2 76 and 3 92 billion years ago ga the lack of impact melt older than 3 92 ga supports the concept of a short intense period of bombardment in the earth moon system at approximately 3 9 ga this was an anomalous spike of impact activity on the otherwise declining impact frequency curve

impacts of pre vs postcolonial land use on floodplain sedimentation in temperate north america abstract this paper evaluates the relative importance of anthropogeomorphic sedimentation on floodplains in the mid latitudes of north america before and after the arrival of euroamericans geohistorical and geoarchaeological theories have emerged that have conflicts concerning the relative effectiveness of pre and postcolonial anthropogeomorphic change in north america many geoarchaeologists paleoecologists historians and cultural geographers have concluded that intensive precolonial land use resulted in substantially humanized landscapes prior to the arrival of colonists this presents a geomorphic paradox to fluvial geomorphologists and river restorationists who interpret buried floodplain soils as evidence of landscape stability evidence for these theories is reviewed from a geomorphic perspective while making distinctions between ecological and geomorphic change and recognizing spatial and temporal variability in some locations mid millennial land use generated erosion and floodplain sedimentation subsequent indigenous population declines and reductions in land use intensity may have been followed by precolonial geomorphic stability and pedogenesis an abandoned landscape hypothesis that floodplain soils developed on precolonial anthropogenic alluvium and were subsequently buried should be considered where indigenous populations and land use activities were high variability is also noted in postcolonial floodplain sedimentation many stratigraphic studies show that rates of sedimentation increased greatly after colonization in response to land clearance for agriculture timbering and mining an inventory of studies that document postcolonial floodplain sediment shows strong spatial patterns most studies of postcolonial sedimentation cluster in the eastern usa from the mid atlantic southward and in the mississippi valley from wisconsin to mississippi but many occurrences of mining sediment are scattered throughout the west few of the studies reviewed in the west document anthropogenic floodplain sediment from agriculture or logging although more thorough regional inventories could change that vast areas of temperate north america do not have historical deposits that are well represented in the scientific literature so assumptions that legacy sediment on floodplains is ubiquitous are ill founded spatial and temporal variations in pre and postcolonial floodplain sedimentation are complex and more research is needed to fill in the knowledge gaps

end permian 252 mya deforestation wildfires and flooding an ancient biotic crisis with lessons for the present abstract current large scale deforestation poses a threat to ecosystems globally and imposes substantial and prolonged changes on the hydrological and carbon cycles the tropical forests of the amazon and indonesia are currently undergoing deforestation with catastrophic ecological consequences but widespread deforestation events have occurred several times in earth s history and these provide lessons for the future the end permian mass extinction event epe 252 ma provides a global deep time analogue for modern deforestation and diversity loss we undertook centimeter resolution palynological sedimentological carbon stable isotope and paleobotanical investigations of strata spanning the end permian event at the frazer beach and snapper point localities in the sydney basin australia we show that the typical permian temperate coal forming forest communities disappeared abruptly followed by the accumulation of a 1 m thick mudstone poor in organic matter that in effect represents a dead zone hosting degraded wood fragments charcoal and fungal spores this signals a catastrophic scenario of vegetation die off and extinction in southern high latitude terrestrial settings lake systems expressed by laterally extensive but generally less than a few metres thick laminated siltstones generally lacking bioturbation hosting assemblages of algal cysts and freshwater acritarchs developed soon after the vegetation die off the first traces of vascular plant recovery occur 1 6 m above the extinction horizon based on analogies with modern deforestation we propose that the global fungal and acritarch events of the permo triassic transition resulted directly from inundation of basinal areas following water table rise as a response to the abrupt disappearance of complex vegetation from the landscape the 13 corg values reveal a significant excursion toward low isotopic values down to 31 a shift of 4 across the end permian event the magnitude of the shift at that time records a combination of changes in the global carbon cycle that were enhanced by the local increase in microbial activity possibly also involving cyanobacterial proliferation we envisage that elevated levels of organic and mineral nutrients delivered from inundated dead forests enhanced weathering and erosion of extra basinal areas together with local contributions of volcanic ash led to eutrophication and increased salinity of basinal lacustrine lagoonal environments we propose that the change in acritarch communities recorded globally in nearshore marine settings across the end permian event is to a great extent a consequence of the influx of freshwater algae and nutrients from the continents although this event coincides with the siberian trap volcanic activity we note that felsic intermediate volcanism was extensively developed along the convergent panthalassan margin of pangea at that time and might also have contributed to environmental perturbations at the close of the permian

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

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

preservation of titanosaur egg clutches in upper cretaceous cumulative palaeosols los llanos formation la rioja argentina abstract studies of the palaeobiology of titanosaur eggs are significantly more common than studies of titanosaur egg bearing strata nevertheless the latter provide significant insight into palaeoenvironmental conditions associated with the egg laying behaviour this study examines titanosaur egg bearing strata of the upper cretaceous los llanos formation la rioja argentina and relates them to the laying and preservation of titanosaur egg clutches los llanos formation is a predominantly sandstone succession throughout represented by palaeosol profiles five titanosaur egg clutches were recovered from the bw horizon of an inceptisol profile this palaeosol type named tama pedotype constitutes 69 of the entire succession by thickness rare planar and undulating lamination and cross stratification quartz grain surface microtextures and ventifacts are indicative of the interaction of fluvial aeolian processes of sedimentation during accumulation of the parent material on the distal part of a coalescent alluvial fan system bajada highly abundant root traces reddish colour clay coatings and calcium carbonate nodules testify that the tama pedotype had abundant vegetation cover and was developed in well drained conditions under the influence of a semiarid climate regime palaeosol horizons with exaggerated thickness and diffuse boundaries indicate a cumulative pedotype whereby the soil developed in response to continuous accretion via on going sedimentary processes morphological features of eggshells suggest that titanosaurs dug holes in the topographic surface to lay eggs thus palaeosols seem to have been putative areas for the laying of titanosaur eggs actually it is uncommon for palaeosols to constitute sites for the preservation of eggs since soils typically develop in response to long episodes of weathering however cumulative palaeosols can provide ideal conditions for egg burial and preservation in cumulative soils the residence time of an object within the weatherable thickness of a soil is reduced to 3 years thereby significantly increasing the long term preservation potential of eggs

channel fill and sheet flood facies sequences in the ephemeral terminal river gash kassala sudan abstract detailed facies analysis of the river gash fluvial sediments on two dimensional profiles across and along the main channel has revealed a number of facies and two distinct types of sequences channel fill and sheet flood sequences it seems that each sequence type is produced by specific depositional event and both sequences represent two end members for suite of mixed sequences the facies and sequences show rapid lateral variability and they merge and interfinger with each other they also show partial to complete modification due to subsequent floods and stage variation it seems that the thick sediments of the river gash in the kassala area were produced in two phases first by braided channel aggradation and lateral migration second by both channelized and unchannelized sheet flood deposition deposits of these two phases contribute to the sediments of the present day gash fluvial basin in the kassala area the gash sediments show some similarities and differences to those of ephemeral and low sinuosity braided streams the predominance of sheet flood deposits is consistent with the ephemeral flashy high flow regime in the river gash the non conformity of the river gash depositional style with the braided model of fluvial deposition may be due to this semi arid terminal flashy character which has control on the depositional processes and patterns

thermoluminescence and new 14c age estimates for late quaternary loesses in southwestern nebraska abstract loess of late quaternary age mantles most of nebraska south of the platte river valley at least five late quaternary loesses are recognized from oldest to youngest one or more undifferentiated pre illinoian loesses the loveland loess the gilman canyon loess which exhibits a well developed soil and rests unconformably on the sangamon soil the peoria loess capped by the brady soil and the bignell loess which is distributed discontinuously previous research shows that the loveland loess is illinoian the gilman canyon loess and peoria loess are wisconsin and the bignell loess is holocene we present here the first thermoluminescence tl age estimates and new 14 c ages for these late quaternary loesses at two key sections in southwestern nebraska the eustis ash pit and the bignell hill road cut tl age estimates from all samples collected from eustis ash pit and bignell hill were internally consistent tl and 14 c age estimates from these two sections generally agree and support previous age determinations the tl age estimate on loveland loess indicates deposition at 163 ka tl and radiocarbon age estimates indicate that gilman canyon loess believed to be deposited during the farmdale interstade first began to accumulate at about 40 ka the lower part of the gilman canyon loess is 36 ka at eustis and the middle of the unit is 30 ka at bignell hill the lower and upper parts of the peoria loess give age estimates of 24 ka and 17 ka respectively tl age estimates for deposition of the bignell loess are 9 ka near the base in agreement with radiocarbon age estimates and 6 ka immediately below the modern soil substantiating its holocene age comparisons of tl age estimates with 18 o and insolation curves which show loess deposition during interglacial and interstadial as well as glacial periods indicate that loess deposition on the great plains can occur under a variety of climatic conditions

episodes of vertical accretion and catastrophic stripping a model of disequilibrium flood plain development this paper describes flood plains formed episodically by vertical accretion along high energy laterally stable channels in southeastern australia overbank deposition gradually builds a flood plain of fine textured alluvium over a period of hundreds or thousands of years following which catastrophic erosion by a single large flood or a series of more moderate floods strips the flood plain to a basal lag deposit from which it slowly reforms this periodic destruction appears due to the progressive development of large levee banks and flood plain surfaces of highly variable relief as the levees and flood plain grow overbank flow is gradually displaced from the broad flood plain into the main channel and flood plain backchannels with a resulting concentration of erosional energy eventually high flows greatly exceed erosional thresholds and wholesale scour of the channel boundary and flood plain occurs vertical accretion flood plains at different stages of development result in a wide range of bankfull recurrence intervals even along the same river some of these flood plains are so infrequently flooded that they can be mistaken for terraces formed under a prior flow regime the almost random but catastrophic nature of this flood plain erosion means that sediment supply and transport are highly variable and probably impossible to predict this model of flood plain formation is seen as only part of a continuum of alluvial environments ranging from vestigial coarsegrained traction load flood plains along high energy rivers in narrow gorges to extensive low gradient flood plains in which alluvial stratigraphy is dominated by fine grained overbank deposition

glacier and lake level variations in west central europe over the last 3500 years on the basis of glacier and lake level records this paper attempts for the first time a comparison between high resolution palaeohydrological and palaeoglaciological data in west central europe over the past 3500 years a data set of tree ring width radiocarbon and archaeological data in addition to historical sources were used to reconstruct fluctuations of the great aletsch the gorner and the lower grindelwald glaciers in the swiss alps the three ice streams experienced nearly synchronous advances at c 1000 600 bc and ad 500 600 800 900 1100 1200 and 1300 1860 these glacier fluctuations show strong correspondence with lake level variations reconstructed in eastern france jura mountains and pre alps and on the swiss plateau this supports the hypothesis of climatically driven fluctuations historical data available for the period since ad 1550 reveal in detail various meteorological conditions behind the successive glacier advances however in agreement with the general trend shown by th

floodplains permafrost cottonwood trees and peat what happened the last time climate warmed suddenly in arctic alaska abstract we use the stratigraphy of floodplains on alaska s north slope to describe how tundra watersheds responded to climate changes over the last 15 000 calibrated years bp 15 cal ka bp two episodes of extremely rapid floodplain alluviation occurred during the pleistocene holocene transition one between 14 and 12 8 cal ka bp and the other between 11 5 and 9 5 cal ka bp these aggradation episodes coincided with periods of warming in summer when cottonwood populus balsamifera l expanded its range peatlands became established and widespread thermokarst occurred the two aggradation episodes were separated by a period of floodplain incision during the younger dryas under cooler and possibly drier conditions at times of increasing summer warmth melting permafrost and enhanced precipitation probably triggered widespread mass wasting on hillslopes that overwhelmed the capacity of streams to transport sediment downstream and rapid floodplain aggradation resulted after peatlands became widespread in the early holocene rivers slowly incised their valley fills because major pulses of sediment input were limited to times of rapid thaw and increasing moisture many floodplains on the north slope have been effectively decoupled from upstream hillslopes for much of the past 15 000 years our findings a confirm the sensitivity of arctic watersheds to rapid warming in summer b emphasize the importance of hillslope mass wasting in landscape scale responses to climate change and c suggest that the presence of peatland on this arctic landscape today has raised its geomorphic response threshold to climate warming compared to what it was 14 000 years ago

alluvial response to the paleocene eocene thermal maximum climatic event polecat bench wyoming u s a abstract the stratigraphic interval spanning the paleocene eocene thermal maximum in the northern bighorn basin wyoming shows changes in the alluvial record that can be tied to a high resolution climate record the complexity and stratigraphic spacing of paleosols change through the study section comparison to the climate record reconstructed from paleosols indicates the changes correspond to paleocene eocene thermal maximum climatic fluctuations in particular the middle of the section contains thick welded paleosols and thin avulsion deposits that link to times of well drained floodplains and lower mean annual precipitation stratigraphic intervals below and above the main part of the paleocene eocene thermal maximum interval correspond to times of less well drained floodplains and higher mean annual precipitation these strata contain thinner paleosols and thick avulsion deposits differences in paleosol complexity and spacing suggest that sediment flux to the depositional site varied in response to precipitation fluctuations associated with the paleocene eocene thermal maximum welded paleosols and thin avulsion deposits indicate reduced floodplain accretion during deposition of the middle of the paleocene eocene thermal maximum intervals with widely spaced paleosols indicate more rapid accretion we hypothesize that drier episodes associated with warming caused reduced vegetation in source areas and promoted erosion and increased sediment yield because precipitation was reduced much of that sediment was stored in upstream reaches of the fluvial system rather than moving to the depositional basin welded paleosols formed because of diminished sediment supply to the basin with a return to wetter conditions during the recovery phase of the paleocene eocene thermal maximum upstream water flux increased stored sediment moved to the basin and vertically spaced thinner paleosols developed the results demonstrate how vertical sections of alluvial paleosols can provide information on how climate fluctuated through time and how the fluvial system responded to climate change

holocene land use evolution and associated soil erosion in the french prealps inferred from lake paladru sediments and archaeological evidences a source to sink multi proxy approach has been performed within lake paladru 492 m a s l french prealps catchment and a six meter long sediment sequence retrieved from the central lacustrine basin the combination of minerogenic signal specific organic markers of autochthonous and allochthonous supply and archaeological data allows the reconstruction of a continuous record of past human disturbances over the last 10000 years the lacustrine sedimentation was dominated by autochthonous carbonates and the watershed was mostly forest covered however seven phases of higher accumulation rate soil erosion algal productivity and landscape disturbances have been identified and dated from 8400 7900 6000 4800 4500 3200 2700 2050 cal bp as well as ad 350 850 ad 1250 1850 and after ad 1970 before 5200 cal bp soil erosion is interpreted as resulting from climatic deterioration phases toward cooler and wetter conditions during the mid late holocene period erosion fluxes and landscape disturbances are always associated with prehistorical and historical human activities and amplified by climatic oscillations such changes in human land used led to increasing minerogenic supply and nutrients loading that affected lacustrine trophic levels especially during the last 1600 years in addition organic and molecular markers document previously unknown human settlements around lake paladru during the bronze and the iron ages

ephemeral stream processes implications for studies of quaternary valley fills abstract three unstable ephemeral stream channels arroyos which drain source areas that have high sediment yields ranging from predominantly sand arroyo calabasas to a mixture of sand silt and clay sand creek to largely silt and clay sage creek were resurveyed to provide data on the rates and mechanics of erosion and sedimentation processes during periods ranging from 14 to 22 yr channel morphology changed significantly erosion occurred through nickpoint recession and bank collapse but erosional reaches are separated by aggrading or stable channel reaches in general sediment that is eroded as the nickpoint recedes upstream is trapped in the widened channel downstream in this manner sediment is transported episodically out of these basins during a series of cut and fill cycles the manner by which the channels aggrade and the morphology of the aggraded stable channels are controlled by the sediment type the wide and shallow channel of arroyo calabasas is filled by vertical accretion of sand size sediment the narrow and deep channels of sage creek and sand creek are created by the lateral accretion of cohesive fine grained sediment the channel modification and the cut and fill episodes are dependent on high sediment yields and therefore they are independent of subtle climatic shifts cut and fill deposits that have been created in this manner should not be equivalent in age from basin to basin and therefore channel trenching and filling in the semiarid western united states during the holocene need not be synchronous

holocene alluvial stratigraphy in the upper susquehanna river basin new york abstract two alluvial terraces and the present flood plain were studied at two locations along the susquehanna and unadilla rivers in south central new york state they have formed since deglaciation and incision of the stream channels into the valley train deposits the higher terrace has noncumulative soil profiles with well developed color b horizons predominantly of silt loam and very fine sandy loam the terrace is weathered to a degree similar to nearby glacial outwash terraces that have caps of similarly textured sediments incision that produced the terrace occurred before 9705 130 yr b p the lower terrace is characterized by relatively thick vertical accretion deposits of silt loam that contain sequences of thin buried a color b and c horizons they were formed between about 3240 110 14c data of soil humin and 235 80 yr b p deposits above the 235 80 yr b p stratum are unweathered the soil stratigraphy and 14c dates of soil humin from buried a horizons are surprisingly well correlated between sites most sediments of the present flood plain have been deposited since 1120 80 yr b p incipient a horizons and oxidation of inherited organic matter in the subsoil are the only evidence of pedogenesis in the flood plain deposits that are older than 275 80 yr b p the most recent flood plain fill deposited since then is unaltered these youngest sediments of the flood plain along with the youngest veneer of vertical accretion deposits on the lowest terrace are associated with an increased rate of deposition largely attributable to clearing of the forests by settlers beginning in the late 1700s comparison of the alluvial stratigraphy with the radiocarbon dated pollen stratigraphy of southwestern new york miller 1973 reveals some apparent time correlations between alluvial events and vegetation changes this gives reason to speculate that climatic change or forest catastrophes such as disease or drought are causes of some of the alluvial events

pedogenesis by upbuilding in an extreme leaching and weathering environment and slow loess accretion south westland new zealand abstract soil formation is usually envisaged as acting from the surface downwards in many environments however the accumulation of sediment and soil formation are contemporaneous it is only where the rate of one process far exceeds the rate of the other that assumptions of topdown pedogenesis are appropriate the aspect of upbuilding pedogenesis that distinguishes it from topdown pedogenesis is that each increment of soil below the a horizon has experienced processes characteristic of all horizons above it this study examines the influence of upbuilding soil formation in a high rainfall environment of rapid soil formation and slow loess accretion an environment where upbuilding could have a noticeable influence on soil properties soils formed by topdown soil formation topdown soils are compared with soils formed in loess that accumulated from early last glaciation to the holocene upbuilding soils soils are compared in two environments alaquods on poorly drained terraces and placorthods or dystrochrepts on well drained moraine crests we have assumed that properties of the upbuilding soils inherited during the current topdown phase of pedogenesis beginning in the holocene are analogous to those in the topdown soils in this manner soil properties evolved during upbuilding are distinguished in well drained upbuilding soils on moraines subsoil organic carbon has mineralised so that profile trends are very similar to corresponding topdown soils upbuilding has enhanced weathering in subsoils which is reflected in lower ph lower total p and lower primary inorganic p than in topdown soil counterparts total p concentrations in upbuilding soils are much lower than unweathered loess and constant throughout the subsoil and there is almost no p in primary forms in contrast total p in c horizons of topdown soils reaches concentrations typical of the parent material and more than 30 of this is in a primary inorganic form the differences are attributed to each subsoil increment of upbuilding soils having been part of acid a and e horizons oxalate extractable fe and al data indicate that podzolisation was active during upbuilding poorly drained upbuilding soils on terraces have higher subsoil organic carbon inherited from former a or o horizons than comparable topdown soils buried a and o horizons inherited during upbuilding and preserved in the reducing conditions have acted as sinks for mobile al and now resemble podzolic illuvial bh horizons upbuilding through addition of loess to soils promotes a pedogenic pathway distinct from topdown pedogenesis consequently soil chronosequence studies that include soils on old loess mantled surfaces do not strictly satisfy the assumptions of soil chronosequences the nature and rate of soil processes inferred from these studies need revisiting the findings of this study are transferable to other environments where the rate of soil formation and sediment accumulation are comparable

recent land use and soil erosion history within a small catchment in connemara western ireland evidence from lake sediments and documentary sources abstract environmental magnetism elemental chemistry pollen macrofossil and radioisotopes were studied on top metre cores from ballydoo lough connemara western ireland to reconstruct the impact of changing farming practices on soil erosion in a lake catchment documentary evidence including detailed agricultural statistics gave an independent land use history over the period represented in the sediment record i e most of the last two centuries maximum soil erosion which involved unweathered coarse material as well as topsoil was associated with a rapidly rising rural population and increased arable activity during the early 19th century the great famine 1845 1847 halved the population but arable and especially pastoral farming quickly recovered and were maintained at a high level from the late 1850s until the late 1890s during this time the rate of soil erosion slowed down considerably and the contribution of coarse mineral material relative to topsoil declined erosion of peaty soils was less important as potato cultivation declined and the middle slopes of the catchment were no longer cultivated from the end of the 18th century to the 1970s sediment accumulation and erosion rates were less and progressive podzolisation occurred as pastoral and particularly arable farming declined the uppermost sediments record a sharp increase in soil erosion involving mainly organic rich soils from the upper slopes this increase is attributed to a sharp rise in livestock numbers especially sheep a feature of the pollen record is the high arboreal pollen representation 43 66 of total terrestrial pollen which consists mainly of secondary pollen it indicates a substantial input of pollen bearing organic detritus derived from peaty soils and peat cuttings in the catchment

how fast are soil forming processes in quaternary sediments of a tropical floodplain a case study in southeast brazil abstract floodplains are depositional features of a channel valley associated with a specific climatic and hydrologic regime of a drainage basin in tropical conditions sediments can be quickly weathered by soil forming processes and tend to obliterate pre existing sedimentary structures therefore the objective of many studies on floodplains is to identify and discuss such sedimentary features mostly those related to the morphology of channel deposits additionally a qualitative approach to identify aspects of pedological evolution in these environments has been attempted in few studies the purpose of this study was to interpret the intensity and the time of alluvial sediment weathering by pedogenetic processes in tropical humid conditions soil profiles were analyzed in different environments of deposition in the pardo river floodplain southeast brazil by accounting for sedimentary facies and pedological features supported by multi proxy data provided from geochemistry macro and micromorphology grain size total carbon total nitrogen 13 c isotopic analysis and 14 c osl optically stimulated luminescence dating based on the results we identified that pedogenetic features and soil horizon distributions were closely related to sediment architecture grain size and position in the floodplain in the pardo floodplain fluvic gleysols loamic and clayic with moderately to strongly developed structures were identified in overbank fine sediments fluvic cambisols clayic were found in abandoned paleomeanders fluvic cambisols loamic in sandy scrollbars gleyic acrisols clayic cutanic differentic in channel deposits which presented a 130 cm thick bt horizon with illuvial clay coatings and histosols fluvic with high contents of total carbon 11 9 and 26 8 in histic horizons in small scale avulsive systems deposits were dated to between 35 000 and 700 years bp 13 c isotopic data revealed a trend toward enriched values in older samples 14 21 in which c 4 plants dominated and a relative impoverishment of the values in more recent samples 26 9 to 27 9 this result was consistent with the tendency of the distribution of c 3 plants to increase over that of c 4 plants favored by the warmer and wetter climate since the upper holocene in this study a fluvic gleysol profile of

identification of facies models in alluvial soil formation the case of a swiss alpine floodplain this paper describes different conceptual facies models intervening in alluvial soil formation in the case of the sarine river floodplain a partially embanked floodplain situated in the northwest of the swiss alps alluvial soils are submitted to processes of deposition and erosion and exhibit various characteristics reflecting the composition and properties of the material transported moreover these processes of sedimentation and erosion vary in space and time and contribute thus to the heterogeneity of the whole floodplain system detailed analyses of the different soil layers permit a precise description of the variability and complexity of soil formation in addition the vertical succession of the horizons is useful to reconstruct the different natural or artificial events that occurred in this alluvial valley since the nineteenth century on a larger scale this study aims to contribute to floodplain management by identifying zones for restoration the investigation was undertaken using data from 109 auger borings carried out in the sarine river valley several morphological attributes of the different horizons and of the different profiles were first reduced in number and then grouped by a hierarchical agglomerative clustering profile factors were analysed by means of correlation analyses as well as other data summaries the results showed positive correlations between several factors particularly between the total profile thickness and the number of horizons found in the profile four facies models of alluvial soil formation are then proposed to illustrate and explain the variability of alluvial soil formation in the sarine floodplain finally these facies models are placed into the context of the sarine floodplain scale case according to the levels of organization of the alluvial system

lake belau and its catchment northern germany a key archive of environmental history in northern central europe since the onset of agriculture the environmental history since the onset of agriculture was reconstructed from sediments and soils in the catchment area of lake belau schleswig holstein northern germany the established chron

roman driven cultural eutrophication of lake murten switzerland abstract land cover transformations have accompanied the rise and fall of civilizations for thousands of years exerting strong influence on the surrounding environment soil erosion and the associated outwash of nutrients are a main cause of eutrophication of aquatic ecosystems despite the great challenges of water protection in the face of climate change large uncertainties remain concerning the timescales for recovery of aquatic ecosystems impacted by hypoxia this study seeks to address this issue by investigating the sedimentary record of lake murten switzerland which witnessed several phases of intensive human land use over the past 2000 years application of geophysical and geochemical methods to a 10 m long sediment core revealed that soil erosion increased drastically with the rise of the roman city of aventicum 30 ce during this period the radiocarbon age of the bulk sedimentary organic carbon oc increasingly deviated from the modeled deposition age indicating rapid flushing of old soil oc from the surrounding catchment driven by intensive land use enhanced nutrient delivery resulted in an episode of cultural eutrophication as shown by the deposition of varved sediments human activity drastically decreased towards the end of the roman period 3rd century ce resulting in land abandonment and renaturation recovery of the lake ecosystem from bottom water hypoxia after the peak in human activity took around 50 years while approximately 300 years passed until sediment accumulation reached steady state conditions on the surrounding landscape these findings suggest that the legacy of anthropogenic perturbation to watersheds may persist for centuries

lake sediments erosion and landscape change during the holocene in britain and ireland abstract lakes are excellent repositories of air borne and especially stream borne materials it has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products to these may be added a variety of palaeoecological indicators including pollen fungi sphagnum leaves and faunal remains pollen analysis in particular enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance grazing and crop cultivation radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right the use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 british and irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late holocene sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern scotland and have either no clear signs of human impact or only so towards the latter part of the holocene this pattern probably reflects a combination of factors including low population densities thin soils and the sealing effect of blanket peat in contrast all sites with accelerated erosion have indications of anthropogenic impact this is often prior to levels of increased sedimentation showing a delay in system response while the spread of dates for the start of the rise in sediment accumulation spans 6200 940 bp three clusters are evident at 5295 4970 4530 4235 and 2980 2810 bp radiocarbon inversions mostly reversals are evident for 18 sites no obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils including peats around a particular site were pushed beyond an erosional threshold sufficient to age the sediments deposited within the lakes it is hoped that improvements in data quality will allow the refinement of such exercises in the future and that lakes will be valued as repositories of long term landscape sensitivity

climatic implications of the late quaternary alluvial record of a small drainage basin in the central great plains four late quaternary alluvial fills and terraces are recognized in wolf creek basin a small 163 km2 drainage in the kansas river system of the central great plains two terraces were created during the late pleistocene the t 4 is a fill top terrace underlain by sand and gravel fill fill i and the t 3 is a strath terrace cut on the cretaceous dakota sandstone both fill ii early holocene and fill iii late holocene are exposed beneath the t 2 a holocene fill top terrace the t 1 complex consisting of one cut and three fill top terraces is underlain by fills iii and iv a poorly developed floodplain t 0 has formed within the past 1000 yr as valleys in wolf creek basin filled during the early holocene an interval of soil formation occurred about 6800 yr b p early holocene fill has been found only in the basin s upper reaches indicating that extensive erosion during the middle holocene removed most early holocene fill from the middle and lower reaches of the basin valley filling between 5000 and 1000 yr b p was interrupted by soil formation about 1800 1500 and 1200 yr b p as much as 6 m of entrenchment has occurred in the past 1000 yr holocene events in wolf creek basin correlate well with those in other localities in the central great plains indicating that widespread changes in climate along with adjustments driven by complex response influenced fluvial activity

late holocene paleoecology and sedimentary history of a small lowland catchment in central england a variety of paleoecological and sedimentary techniques were used to investigate the storage of sediment within a small lowland catchment during the holocene radiocarbon dating of vertically accreted floodplain deposits allowed the calculation of inorganic accumulation rates these rates show a dramatic increase in sediment deposition during the late bronze age and early iron age 2900 2300 yr b p due to deforestation and cultivation of the catchment slopes and resultant soil erosion the soils within the catchment were susceptible to structural damage surface waterlogging and slope wash erosion from the calculated increases in sediment storage estimates of catchment erosion were made which vary from around 20 to 140 tons km 2 yr 1 the study of alluvial chronology at this scale can provide unique information on the source areas of holocene floodplain sediments and provide long term erosion rates

fluvial landscape development in the southwestern kalahari during the holocene chronology and provenance of fluvial deposits in the molopo canyon the southern kalahari drainage network is in a key position to analyze spatiotemporal changes in the tropical easterly and the temperate westerly circulation over the southern african subcontinent however due to the prevailing aridity paleoenvironmental archives within the southwestern kalahari are sparse and often discontinuous hence little is known about holocene environmental change in this region this study focuses on reconstructing paleoenvironmental change from the timing and provenance of fluvial deposits located within the molopo canyon which connects the southern kalahari drainage to the perennial flow regime of the orange river to gain insight into temporal aspects of fluvial morphodynamics within the molopo canyon the entire variety of fluvial landforms consisting mainly of slope sediments alluvial fans and alluvial fills were dated using optically stimulated luminescence osl we additionally applied a provenance analysis on alluvial fill deposits to estimate potential sediment source areas source areas were identified by analyzing the elemental and mineralogical composition of tributaries and eolian deposits throughout the course of the lower molopo the results allow the first general classification of fluvial landscape development into three temporally distinct deposition phases in the southern kalahari 1 a phase of canyon aggradation associated with short lived and spatially restricted flash floods during the early to mid holocene 2 a phase of fan aggradation indicating a decrease in flood intensities during the mid to late holocene and 3 a phase of canyon aggradation caused by the occurrence of supra regional flood events during the little ice age we interpret the observed spatiotemporal deposition patterns to latitudinal shifts of the tropical easterly circulation in the early to mid holocene and the temperate westerly circulation in the late holocene however despite marked changes in the provenance and timing of fluvial deposits in the molopo canyon throughout the holocene our analysis did not detect a contribution of sediments originating from the kalahari interior to the deposition of alluvial fills these results suggest that the southern kalahari drainage remained endorheic and therefore disconnected from the orange river throughout the holocene

stable isotope distribution in maastrichtian vertebrates and paleosols from the haţeg basin south carpathians abstract located in the south carpathians in romania the ha eg basin contains a thick sequence of maastrichtian continental deposits yielding a rich dinosaur and mammalian fauna stable isotope analyses of both calcretes and dinosaur crocodilian and turtle remains from two localities tustea and sibisel were integrated in order to reconstruct environmental conditions during maastrichtian time and to gain further insights into the metabolism and behaviour of the vertebrates the large difference observed between the 18o and 13c of the eggshells and the surrounding mudstones as well as the preservation of the 9 difference between the oxygen isotope composition of the telmatosaurus eggshell and tooth enamel indicate that diagenesis has not significantly altered the primary isotopic signal the presence of smectite in the fraction less than 2 m and the preservation of dinosaur eggshell structure also indicate that diagenesis was not significant in the studied outcrops stable isotope compositions of both calcretes and phosphatic remains suggest warmer conditions during the deposition of the tustea sequence mean annual temperature of around 14 c than during the deposition of the sibisel sequence mean annual temperature of 10 c the intra tooth 18o patterns for zalmoxes and allodaposuchus show different magnitudes of isotopic variation with lower values for tustea and higher for sibisel the calculated 18obody water enrichment for kallokibotion bajazidi is similar to that found in living turtle taxa by contrast in the case of allodaposuchus the isotopic enrichment is higher than for recent taxa this suggests that for allodaposuchus the body water was less buffered by a watery environment which probably indicates more time spent outside water i e more terrestrial habit the 18o values for the teeth of telmatosaurus and zalmoxes are similar to those of allodaposuchus suggesting that at the investigated sites the body temperature of both dinosaurs was similar to that of the crocodile the isotopic composition of calcretes teeth and eggshells indicates a c3 vegetation and diet with 13c values between 27 and 29 pdb and the absence of large scale habitat partitioning between the dinosaurs

an example of rapid gully initiation and extension by subsurface erosion coastal san mateo county california abstract gully networks developed on coastal hillslopes in san mateo county california extended nearly 300 from 1941 to 1978 primarily by subsurface erosion in one drainage subsurface erosion expanded the gully network by 80 m nearly doubling the gully length from 1982 to 1987 intense gullying is restricted to areas underlain by members of the pliocene purisima formation a unit rich in unstable volcanic lithic fragments which weather to produce expansive smectite clays gully development proceeds through a sequence of lateral eluviation of clays near the base of the a horizon piping development of an open conduit in which erosion proceeds by turbulent concentrated flow tunneling and finally collapse of the tunnel roof exposing an open gully measurements made in one gully system during a 25 yr storm showed that the subsurface drainage network carried four times as much flow as the surface drainage net and had average suspended sediment concentrations an order of magnitude higher

sedimentology of a fine grained aggrading floodplain abstract historical land use changes accelerated both soil erosion and subsequent floodplain alluviation within the galena river basin wisconsin a cross valley transect in a low gradient downstream section of this watershed permitted documentation of the lateral and vertical sedimentological properties occurring during this aggradational phase mechanical and statistical analyses of 97 sediment samples reveal two dominant controls determining the resulting floodplain sedimentology firstly the initial fine grained loessial texture dominated the particle size of the early post settlement alluvium generally yielding fine textured sediments across the valley bottom further landscape de stabilization promoted upland gullying into coarser textured residuum below the loess with a concomitant particle size increase in the foodplain alluvium thus the resulting foodplain stratigraphy exhibits a coarsening upward sequence secondly distance from the stream channel exerts a strong control on overall sedimentological properties distal settings possess massive high clay content sediments usually with less than 1 sand samples become coarser and more stratified near the modern stream channel with channel fill facies containing approximately 20 sand in the upper sections the fine grained loessial sediment source affected numerous sedimentological properties of the deposited alluvium sorting correlates negatively with particle size because all particle sizes were entrained during large overbank floods dominance of silt in this loess mantled basin maintains the maintains the median of the particle size distribution within a fairly narrow range only the tails of the distribution vary and they are primarily controlled by the distance to the stream channel in distal settings the fine tail emerges whereas the coarse tail appears in the channel fill and proximal settings although all sediments were deposited in an overbank floodplain environment passega s cm diagrams erroneously indicate a pelagic depositional environment

use geopedological methods for the evaluation of sedimentation rates on river floodplains southern quebec canada abstract this article pertains to the fluvial dynamics of rivers in southern quebec in particular to the aggradation and pedogenetic processes observed in floodplains affected by periodic floods the frequency of flood events notably along the saint francois river and its main tributaries leads to fine materials being frequently deposited on floodplains and affected development of alluvial soils particle size and physical and chemical analyses have led to a better understanding of the dynamics involved in the formation of floodplains and the development of soils related to this fluvial environment also sedimentological analyses layer texture and thickness microstructure combined with radiocarbon dating 14c and isotopic methods 210pb 226rd enabled the determination of sedimentation rates along the floodplains the radiocarbon dating results obtained from the organic layers buried in alluvial soils show relatively variable ages i e between 2210 60 and 30 70 years bp the data gathered reveal an active overbank deposition which shows evidence of the high flood recurrence in many rivers of the basin it is estimated that the annual floodplain aggradation ranges from 1 0 to 7 6 mm yr 1 on average which causes increases in floodplain elevations vertical accretion the sedimentation rates obtained using the constant rate supply dating model 210pb show average values that range from 2 1 to 10 7 mm yr 1 also the presence of contaminated layers at the lower level 100 cm of the floodplains suggested an active sedimentation rates along the rivers affected by floods

loess of the upper mississippi valley driftless area abstract loess of the driftless area includes four distinct late quaternary lithostratigraphic units the wyalusing new loveland roxana and peoria formations erosion has removed parts or all of the pre late wisconsian loess at many sites these formations consist largely of loess and retransported loess that typically occurs on uplands terraces and valley margins in the region the oldest widespread formation probably 125 000 yr b p is here formally named the wyalusing formation the three younger formations correlate with the loveland probably 125 000 yr b p roxana 55 000 25 000 yr b p and peoria 25 000 12 000 yr b p loesses recognized elsewhere in the midcontinental united states the soil stratigraphic morphology of the wyalusing loveland and roxana peoria couplets appears to represent two distinct loess sedimentation sequences related to major expansion and contraction of the laurentide ice sheet during oxygen isotope stages 6 and 3 2 respectively the occurrence frequency of loess units is inversely related to age illustrating the erosional nature of the driftless area landscape the occurrence of four loess units at some sites in driftless area stratigraphic sections corroborates loess stratigraphy along the length of the mississippi valley where typically not more than four or five loess units are found and they represent only the late and middle pleistocene

organic matter processing and soil evolution in a braided river system traditionally braided river research has considered flow sediment transport processes and recently vegetation dynamics in relation to river morphodynamics however if considering the development of woody vegetated patches over a time scale of decades we must consider the extent to which soil forming processes particularly related to soil organic matter impact the alluvial geomorphic vegetation system here we quantify the soil organic matter processing humification that occurs on young alluvial landforms we sampled different geomorphic units ranging from the active river channel to established river terraces in a wandering braided river system for each geomorphic unit soil pits were used to sample sediment soil layers that were analysed in terms of grain size 2 mm and organic matter quantity and quality rock eval method a principal components analysis was used to identify patterns in the dataset results suggest that during the succession from bare river gravels to a terrace soil there is a transition from small amounts of external organic matter supply provided by sedimentation processes e g organic matter transported in suspension and deposited on bars to large amounts of autogenic in situ organic matter production due to plant colonisation this appears to change the time scale and pathways of alluvial succession bio geomorphic succession however this process is complicated by the ongoing possibility of local sedimentation which can serve to isolate surface layers via aggradation from the exogenic supply and erosion which tends to create fresh deposits upon which organic matter processing must re start the result is a complex pattern of organic matter states as well as a general lack of any clear chronosequence within the active river corridor this state reflects the continual battle between deposition events that can isolate organic matter from the surface erosion events that can destroy accumulating organic matter and the early ecosystem processes necessary to assist the co evolution of soil and vegetation a key question emerges over the extent to which the fresh organic matter deposited in the active zone is capable of significantly transforming the local geochemical environment sufficiently to accelerate soil development

holocene flood plain soil formation in the southern lower mississippi valley implications for interpreting alluvial paleosols holocene mississippi river flood plain soils in central louisiana provide important insights on alluvial pedogenesis in an aggradational setting insights that are useful for interpreting alluvial paleosols the flood plain soils are younger than ca 5400 yr b p and are grouped into two categories 1 meander belt and 2 backswamp soils meander belt soils are entisols inceptisols and alfisols developed on point bar ridges and natural levee crests they consist of 3 5 m thick brown silty and sandy moderately well drained profiles with multiple parent materials common yellow brown and gray mottles and a few iron and calcite nodules backswamp soils are vertisols formed in flood plain depressions away from active and abandoned mississippi river channels and consist of up to 10 m thick gray clayey poorly drained profiles that have abundant yellow brown mottles iron and calcite nodules gypsum accumulations and slickensides the thickness of the soils and the presence of multiple parent materials show that as the flood plain aggrades concurrent or alternating episodes of sedimentation and pedogenesis produce cumulative profiles profile thickness is more closely related to sediment accumulation rates than to the depth of chemical weathering and the cumulative nature of the soils explains the difficulty of recognizing discrete paleosol profiles in many ancient alluvial deposits comparisons of soils formed on the three youngest holocene mississippi river meander belts saucier and snead 1989 show that the soils record episodes of meander belt growth abandonment and relocation meander belt 1 soils form as the active meander belt develops and consist of either vertically stacked entisols or a single inceptisol the soils contain few calcite nodules and form over intervals of a few hundred years meander belt 2 soils are alfisols lack free carbonates and form over intervals of a few thousand years following meander belt abandonment and soil leaching meander belt 3 soils are alfisols or vertisols that contain common calcite nodules and the profiles are developed in 1 to 2 m of backswamp mud that overlies meander belt silt and sand the mud inhibits profile leaching and leads to poor drainage and calcite precipitation this change in soil hydrology complicates interpretations of the effects of time on meander belt soil development backswamp soils are strongly influenced by seasonal episodes of soil wetting and drying as demonstrated by the gray colors and the abundance of mottles nodules and slickensides in the soils the distribution of calcite nodules in the backswamp and meander belt soils is more closely related to seasonal water table position than to mean annual precipitation which suggests that not all calcic paleosols in ancient alluvial deposits represent semiarid or arid climates slickensides attest to seasonal rainfall but the composition of the backswamp soils primarily reflects source area lithology and depositional influences rather than the effects of chemical weathering in general these soils provide an incomplete record of the humid subtropical climate of louisiana although short term sediment accumulation rates decrease away from mississippi river channels the backswamp soils are not better developed i e more mature than the meander belt soils because poor drainage and slow but continuous sedimentation inhibits weathering collectively these observations suggest that flood plain soils that developed in aggradational settings such as that of the mississippi river flood plain are best suited for interpreting depositional and hydrologic histories of ancient alluvial deposits rather than paleoclimates

taphonomical and palaeoecological investigation of the late cretaceous maastrichtian tustea vertebrate assemblage romania haţeg basin insights into a unique dinosaur nesting locality abstract the tustea vertebrate locality at oltoane hill northwestern part of the ha eg basin romania has provided a rich and diverse assemblage of late cretaceous maastrichtian continental vertebrates more than 800 vertebrate fossils were recovered from this locality the isolated and associated remains represent 21 different taxa including amphibians turtles lizards snakes crocodyliforms pterosaurs dinosaurs and mammals the local assemblage is overwhelmingly dominated by dinosaurs with the rhabdodontid zalmoxes as the most abundant taxon the bonebeds that yielded this fossil material occur in a stacked series of mudstone calcrete units belonging to the middle member of the densus ciula formation the taphonomical investigations suggest that the tustea assemblage is made up of attritionally accumulated politaxic remains and that it is a parautochthonous assemblage with no evidence for significant bone transport or reworking according to the synthesis of all available field data two outstanding fossiliferous levels can be identified within the tustea locality where megaloolithus eggs and hadrosauroid hatchling material are preserved together recognized here as two superposed nesting grounds such co occurrence was considered controversial since there is a long standing and quasi general consensus that eggs of the megaloolithus oogenus were laid by titanosaurian sauropods we present several alternative scenarios to account for the co occurrence of telmatosaurus hatchling remains and megaloolithid eggs in the nesting horizons and explore these alternative hypotheses by weighing the arguments supporting or contradicting them the burden of evidence derived from our sedimentological taphonomical and palaeoecological investigations at tustea is still in favour of the autochthony of the hatchlings preserved within their own nesting grounds whereas there is no such support for a titanosaurian origin of the tu tea megaloolithid eggs

distribution of palaeosols and deposits in the temporal evolution of a semiarid fluvial distributary system bauru group upper cretaceous se brazil abstract the stratigraphic and sedimentological knowledge of the bauru group upper cretaceous se brazil is still generally insufficient and controversial a sedimentological and palaeopedological study allowed to interpret the south eastern portion of the bauru group according to the model of a fluvial distributary system this work has two objectives 1 to include palaeosols in the interpretation of a fluvial distributary system and 2 to give detailed information on the sedimentological and stratigraphic features of the se portion of the bauru group in order to support biostratigraphical taphonomic and palaeoecological studies in the south eastern portion of the bauru group three genetic stratigraphic units were described and interpreted here informally called lower intermediate and upper units the lower unit is constituted of muddy sandstone salt flat deposits and sandstone sheet deltas deposits and is interpreted as a basinal part of a fluvial distributary system the intermediate unit is formed of very fine to fine grained sandstone filled ribbon channel and sandy sheet shaped beds suggesting a distal or medial portion of a fluvial distributary system the upper unit does not match with the present models of the fluvial distributary system because mostly constituted of moderately developed well drained medium to fine grained sandstone palaeosols which testify pauses of sedimentation to the order of 104 years preserved features of sedimentary structures suggest that the parent material was formed by occasional catastrophic unconfined flows this unit may represent the most distal portion of a fluvial distributary system generated by retrogradation of the alluvial system due to aridification of the climate the upper unit may be interpreted also as proximal portion of fluvial distributary system if considering the coarser grained and the well drained palaeosols however the absence of channel deposits makes this interpretation unconvincing

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

ams radiocarbon dating of annually laminated sediments from lake holzmaar germany ams radiocarbon ages have been determined on terrestrial macrofossils selected from the annually laminated sediments of lake holzmaar germany the radiocarbon chronology of this lake covers the last 12 6 ka comparison of the radiocarbon dated varve chronology with tree ring data shows that an additional 878 years have to be added to the varve chronology the corrected c 14 varve chronology of holzmaar reaches back to ca 13 8 ka cal bp and compares favourably with the results from soppensee switzerland hajdas et al 1993 the corrected ages for the onset and the end of the younger dryas biozone are 11 940 cal bp and 11 490 cal bp respectively the ash layer of the laacher see volcanic eruption is dated at 12 201 224 cal bp and the ulmener tephra layer is dated at 10 904 cal bp

three decades of dating recent sediments by fallout radionuclides a review this paper reviews the 210pb dating programme carried out at the university of liverpool over a period of three decades since its inception by frank oldfield in the mid 1970s the work at liverpool

variation in radiocarbon ages of soil organic matter fractions from late quaternary buried soils radiocarbon dating of three organic matter fractions total humic acid and residue isolated from late quaternary buried soils of the central great plains reveals that there often are considerable differences among but no consistent order to the ages of fractions for late holocene soils the residue fraction or the total fraction generally produces the oldest age for late pleistocene soils however no fraction was consistently the oldest the absence of a consistent sequence of fraction ages is attributed to postburial contamination of soils when bulk samples from the same soil were split and sent to two laboratories different radiocarbon ages were usually obtained the variability in radiocarbon ages of soil organic matter confirms that caution should be taken when using radiocarbon ages obtained from different laboratories to make regional stratigraphic correlations

episodic holocene loess deposition in central nebraska abstract the mirdan canal section in central nebraska usa provides evidence for multiple episodes of holocene loess deposition in the central great plains this irrigation canal cut exposes more than 4 m of holocene sediment that overlies the late wisconsinan peoria loess the oldest holocene sediment is local slopewash that fills gullies but overlying beds are interpreted as holocene loess bignell loess three buried soil profiles occur within the holocene sediment and have yielded uncalibrated 14 c ages of 3010 yr bp uppermost buried soil and 8790 yr bp third buried soil from top a fourth buried soil yielded an age of 9330 yr bp and is correlated with the brady soil the bignell loess has a darker color slightly more organic matter more clay more coarse silt and sand less smectite and less volcanic glass than the underlying peoria loess the bignell loess is most plausibly interpreted as dust from local flood plains containing a mixture of reworked peoria loess and older silts with contrasting mineralogy episodes of loess deposition occurred in the early middle and late holocene probably during periods of dry climate but possibly also as a consequence of large erosive floods that made wind erodible sediment available on nearby flood plains

production sedimentation and isotopic composition of organic matter in lake ontario organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the rochester basin of lake ontario to evaluate their usefulness in reconstructing historic changes in lake productivity the greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events indicating that calcite precipitation is an effective mechanism for sedimenting organic matter carbon isotopes of organic matter were low prior to the onset of stratification increased to maximum values in late summer and then decreased following fall overturn this pattern is controlled mainly by the timing of stratification and primary productivity which preferentially removes 12co2 from the epilimnion the physiological effect of decreased carbon isotopic fractionation with decreasing supplies of co2 aq may have also contributed to increased 13corgc nitrogen isotopes showed a seasonal pattern opposite to that of carbon whereby 15n values were low during the summer stratified period and high for the remainder of the year seasonal variability in 15norgn probably reflects changes in the source of sedimented organic particles which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period a comparison of organic carbon accumulation rates and 13corgc between sediment cores collected in 1987 and 1993 1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters but will not change the 13corgc values all cores analyzed for 13corgc display the reproducible pattern of a progressive increase in the 19oos peaking in the early to mid 1970s and then decreasing to the present this pattern matches the historical trends of phosphorus loading to the basin suggesting that 13c of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column the 15n of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0 3ppt per decade and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment the increase in 15norgn reflects a combination of factors including early forest clearance by europeans increased sewering by municipalities after 1940 and increased nitrate utilization as productivity increased in the lower great lakes increased rates of denitrification in the central basin of upstream lake erie from the 1930s to the early 1970s may have also contributed to the rise in 15norgn values

climatic influence on sedimentology and geomorphology of the rio ramis valley peru abstract fluctuations in regional precipitation and in base level the level of lake titicaca trigger changes in fluvial erosion and deposition in the largest tributary valley of lake titicaca the rio ramis peru relationships between fluvial sedimentation and terrace formation demonstrate that large scale aggradational and downcutting events are associated with specific regional climatic events that have been previously documented in the lake titicaca basin and elsewhere on the altiplano five laterally extensive terrace tracts a through e are present within the valley downcutting of the ramis valley is correlative with base level lake titicaca level fall caused by a decrease in precipitation aggradation is correlative with base level rise during increasing precipitation sedimentary facies underlying the terraces record deposition in a large paleolake followed by deposition of both meandering and braided fluvial sediments the highest terrace in the valley e is underlain by a thick sequence of lacustrine strata that was deposited during an extremely wet period in the lake titicaca region that terminated at about 40 000 cal yr bp these lacustrine strata were subsequently downcut likely at a time of large drop in lake level resulting in a deeply incised valley the main phase of fluvial aggradation in the valley sediments underlying the d through b terraces was slow spanning about 25 000 years it occurred before during and after the last glacial maximum from before 35 140 790 cal yr bp until about 10 421 181 cal yr bp a time period that was mostly characterized in the lake titicaca basin by high precipitation rates and high base levels the aggradation resulted in almost 40 m of sediment accumulation in the valley and was followed by rapid about 2 000 years but episodic incision into the underlying fluvial sediments to form the c and b terraces as well as the erosional surface beneath the modern fill terrace a this erosional phase corresponded to several periods of local base level lake titicaca lowering between 10 241 181 and 1 668 76 cal yr bp the modern fill terrace has aggraded about 2 m above modern river level likely within the last 1 500 years

varves and mass movement deposits record distinctly different sedimentation dynamics since the late glacial lake szurpily northeastern poland the sedimentological and geochemical characteristics of sediments from lake szurpily northeastern poland can be used as a record of mass movement and climate dynamics since the allerod late glacial sediments suggest enhanced runoff conditions in the catchment after the retreat of the scandinavian ice sheet while holocene varved sediments are interrupted by mass movement deposits mmds we identified 85 thin 1 m thick mmd type 2 consists of auto and allochthonous material and represents multistage processes including erosion and deformation of underlying varved sediments rapid deposition of clastic material and redeposition of previously eroded varved sediments seismic activity or permafrost degradation was responsible for the deposition of mmd type 2 furthermore varve thickness variability suggests gleissberg and suess solar cycles before 850 bc when human impact was limited additionally 22 and 11 yr sunspot cycles are recognized in light dark laminae thickness ratios and reflect influences of solar irradiance on lacustrine productivity

climatic signals from loess soil sequences in the central great plains usa abstract late quaternary eolian deposits and buried soils in the central great plains are interpreted to reflect the fluctuation of climatic conditions under which they formed the loveland loess was deposited approximately between 500 and 100 ka within the loess are four zones of pedogenic carbonate accumulation after 416 35 ka before 260 25 ka around 193 22 ka and before 92 7 0 ka the pedogenic carbonate zones were probably formed under warm and dry conditions the moderately weathered barton sand at the barton section and the equivalent sandy silt ii at other sections deposited between 92 7 0 and 69 6 4 ka suggest windy probably warm and fluctuating moisture consitions a reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very low rate of loess deposition overlying the reddish pedocomplex is the sandy silt i probably a stratigraphic equivalent to the roxana silt dated at 40 30 ka in the central lowlands the gilman canyon formation 35 20 ka a thick cumulic loessial and organic matter rich pedocomplex developed under relatively moist and probably cool conditions the peoria loess was deposited at a very rapid rate under dry and cold conditions the brady soil 10 5 8 5 ka was formed under relatively warm and moist conditions the poorly weathered bignell loess was deposited during the warm and dry altithermal period 9 5 ka

sedimentological response to holocene climate events in the istron area gulf of mirabello ne crete this paper aims to reveal the depositional environment of istron and its sedimentological response to holocene climatic events the results of a multi disciplinary geoarchaeological research undertaken in the coastal area of istron northeastern crete provided information on the depositional environment and the palaeoenvironmental evolution of the area during the holocene detailed fieldwork and sampling by drilling cores in the coastal area provided samples for further analytical studies the identification of the stratigraphy and the distinction of sedimentological units provided evidence for landscape evolution of the coastal area changes of sedimentation rates determined by optical dating and sedimentological analysis were also correlated with holocene climatic phases

late holocene alluvial chronology and climate change in the central great plains abstract alluvium in one reach of the republican river valley south central nebraska dates to the holocene radiocarbon dating of fills underlying the two terraces in the valley reveals that entrenchment between 4500 and 3700 yr b p formed the high terrace subsequently alternating aggradation and stability occurred until sometime between 1800 and 1100 yr b p following another period of alluviation channel incision formed the low terrace general synchrony between this chronology and other late holocene fluvial chronologies of the central great plains suggests climatic control of fluvial activity the episodes of incision are tentatively correlated with different climate regimes illustrating the difficulty of attributing a given fluvial response to a particular direction of climatic change

erosion under climate and human pressures an alpine lake sediment perspective we review the scientific efforts over the last decades to reconstruct erosion from continuous alpine lake sediment records we focused both on methodological issues showing the growing importance of non destructive high resolution approaches xrf core scanner as well as progresses in the understanding of processes leading to the creation of an erosion signal in lakes we distinguish continuous records from event records both provide complementary information but need to be studied with different approaches continuous regionally relevant records proved to be particularly pertinent to document regional erosion patterns throughout the holocene in particular applying the source to sink approach event based approaches demonstrated and took advantage of the strong non linearity of sediment transport in high altitude catchment areas this led to flood frequency and intensity reconstructions highlighting the influence of climate change upon flood dynamics in the mountain the combination of different record types both in terms of location high vs low elevation sedimentology high vs low terrigenous contribution and significance local vs regional is one of the main outputs of this paper it allows the establishment of comprehensive histories of nw french alps erosion but also and consequently soil dynamics and hydrological patterns throughout the holocene we also discuss the influence of glacier dynamics one of the major agents of erosion in the alps a major feature is the growing human influence upon erosion at a local scale since at least the middle of the bronze age 3500 cal bp however and according to the regional record from lake bourget only few periods of rising erosion at local scales generated a regional record that can be discriminated from wetter climatic periods among them the period between 200 bce and 400 ad appeared to be marked by a generalised rise in human triggered erosion at local scales in the northern french alps this review highlights the importance of modern high resolution and interdisciplinary studies of lake sediments in order to better understand the complex relationships between humans climate and the earth system in general we strongly argue that regional integration of data is now required to move a step further such an integration is easier with cost and time effective methods as well as after a better definition of approaches and their limits this should lead to a stronger collaboration between paleo data producers and modellers in the near future

alluvial stratigraphic evidence for channel incision during the mediaeval warm period on the central great plains usa alluvial valley fills from tributaries to the upper republican river southwest nebraska usa provide soil and morpho stratigraphic evidence for an episode of channel incision that occurred between c 1100 and 800 1 4 cyr bp based on 11 new radiocarbon ages this local episode of channel incision correlates with other alluvial stratigraphic studies from the central great plains and demonstrates regionally synchronous fluvial behaviour proxy records of palaeohydrologic conditions in and around the great plains including lacustrine aeolian and geomorphological sources indicate that channel incision correlates with a multicentennial episode of common widespread drought temporally this drought episode corresponds to the period recognized in many regions as the mediaeval warm period mwp therefore this research demonstrates 1 a relationship in the semi arid central great plains between drought and increased fluvial incision and 2 a local regional geomorphic response to a particular episode of global climate change

late quaternary loess in northeastern colorado part i age and paleoclimatic significance loess in eastern colorado covers an estimated 14 000 km 2 and is the westernmost part of the north american midcontinent loess province stratigraphic studies indicate there were two periods of loess deposition in eastern colorado during late quaternary time the first period spanned ca 20 000 to 12 000 14 c yr b p ca 20 14 ka and correlates reasonably well with the culmination and retreat of pinedale glaciers in the colorado front range during the last glacial maximum the second period of loess deposition occurred between ca 11000 and 9000 14 c yr b p this interval may be holocene or may correlate with a hypothesized younger dryas glacial advance in the colorado front range sedimentologic mineralogic and geochemical data indicate that as many as three sources could have supplied loess in eastern colorado these sources include glaciogenic silt derived from the colorado front range and two bedrock sources volcaniclastic silt from the white river group and clays from the pierre shale the sediment sources imply a generally westerly paleowind during the last glacial maximum new carbon isotope data combined with published faunal data indicate that the loess was probably deposited on a cool steppe implying a last glacial maximum july temperature depression relative to the present of at least 5 6 c overall loess deposition in eastern colorado occurred mostly toward the end of the last glacial maximum under cooler and drier conditions with generally westerly winds from more than one source

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

holocene fluctuations of lake levels in the french jura and sub alpine ranges and their implications for past general circulation patterns temperature and precipitation variations reflected in lake level fluctuations in the french jura and pre alps during the last nine millennia are qualitatively assessed by reference to 1 climatic oscillations reconstructed in the alps and 2 modern processes behind alpine tree limit variations the summer season and mainly the late summer appears to have a deterministic impact on the holocene environment correlations between palaeoclimatic proxy data recorded in the north atlantic area from high and middle latitudes and climatic dynamics illustrated by the little ice age and the recent warming suggest 1 the existence of climatic oscillations due to varying solar activity superimposed on larger plurimillennial climatic trends and 2 that these minor climatic phases correspond with two main types of general circulation pattern alternating over western europe during the last six millennia the climatic deteriorations correspond with cooling at high latitudes inducing a stronger thermal grad

holocene alluvial fills in the south loup valley nebraska abstract four holocene alluvial fills are present in nebraska s south loup river valley fill iv the oldest and thickest was deposited between 10 200 and 4800 14c yr b p fill iii has an age of about 3000 14c yr b p fill ii is younger than 2100 and older than 900 14c yr b p and fill i is younger than 900 14c yr b p regional contemporaneity of valley alluviation in the eastcentral great plains suggests that climate has controlled long term sediment storage in the south loup river valley