the organic and mineral matter contents in deposits infilling floodplain basins holocene alluviation record from the klodnica and osobloga river valleys southern poland the work examines the timing and environmental conditions of floodplain sedimentation in the valleys of the upland klodnica and piedmont osobloga rivers in the upper odra river basin a distribution of 52 14c ages shows relatively high floodplain sedimentation at the late glacial holocene transition more stable floodplain environments since the early in the klodnica valley and middle holocene in the osobloga valley and a gradual increase in floodplain deposition in the late holocene since 3 4 kyr bp organic matter om and mineral matter mm fluctuations were correlated with variables responsible for the activation of erosion i e vegetation changes human impact and hydrological events as well as factors affecting the local record of sedimentation i e valley morphology hydrologic conditions and episodes of local erosion a clear relationship is shown between an increase in alluviation and climate or human induced extension of unforested areas the deposition of mineral rich sediments increases rapidly during periods characterized by non arboreal pollen values exceeding approximately 8 in pollen diagrams on the other hand the results obtained do not confirm significant interactions between holocene changes in forest composition and alluviation despite the settlement of agrarian groups the sedimentary record of human activity in the osobloga catchment is very poor during the neolithic and early bronze age a large scale alluviation of the osobloga and klodnica valleys was initiated during the settlement of people of the lusatian culture from the middle bronze age and escalated in the early middle ages and modern times the deposition of products of soil erosion was limited to between ca 1 9 1 2 kyr bp probably due to demographic regression during the migration period comparison of om mm fluctuations with phases of increased fluvial activity does not show a relationship between holocene wetter phases and catchment sediment yield sedimentary episodes in the upper odra basin also show a low degree of correlation with the probability density curve of the 14c ages the results obtained in the klodnica and osobloga valleys indicate a strong to moderate correlation between the spatial distribution of the study sites and the origin of mm rich deposits but a weak correlation between the spatial distribution of the study sites and toc content such a pattern suggests that om mm fluctuations relate predominantly to the changes in sediment yield although morphological conditions have a significant impact on the capture potential of sedimentary basins during phases of alluviation additionally high om content is not a simple function of an increase in wetness of the sedimentary environment on the other hand hydrologically conditioned hiatuses as well as erosion episodes impoverish the sedimentary record complicating the consideration on the geochronology of deposits and making it difficult to calculate reliable accumulation rates however they do not reduce the value of om mm fluctuations as an indicator of alluviation events for a preserved series of sediments

magnitude scale and quantification of earthquakes despite various shortcomings the earthquake magnitude scale is one of the most fundamental earthquake source parameters to be used for catalogs although use of a uniform scale is desirable it is not always possible because of changes in instrumentation the data reduction method and the magnitude formula the station distribution etc as a result various magnitude scales have been developed and are currently in use recent developments in seismometry and earthquake source theories provide more quantitative source parameters than the magnitude in order to maintain continuity and uniformity of the data it is important to relate these magnitude scales and the new parameters in view of this importance relations between different magnitude scales are examined with an emphasis on the difference in the period of the waves used for the magnitude determination use of several magnitude scales determined at different periods provides a convenient method for characterizing earthquakes the moment magnitude can be used to quantify both shallow and deep earthquakes on the basis of wave energy radiated and provides a uniform scheme

the alternative interpretation of chronology of flood events in the mid warta river valley record of early holocene alluviation in the kolo basin central poland abstract the detailed research of organic deposits with remains of riparian forest dated to the allerod younger dryas transition undertaken at the ko min las site enables the discussion of the evolution of river system and flood events in the kolo basin central poland results of former studies showed the intense accumulation of silty sandy overbank deposits during the younger dryas results of recent research in the ko min las site including results of 14c dating of organic deposits indicate significant increase of flooding in the early holocene in consequence this interpretation indicates the existence of a meandering river pattern during allerod and younger dryas and the development of a multichannel river system in the early holocene in the kolo basin including the mid warta river

age limits on the late quaternary evolution of the upper loire river abstract the loire river is one of the largest rivers in europe draining a basin area of southern france which exceeds 100 000 km 2 despite its significance the loire remains poorly studied and has a very limited amount of chronological control on the deposited sedimentary record of fluvial activity these factors coupled with the availability of a set of 10 radiocarbon dates on younger c

tracking holocene glacial and high altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments lake blanc huez western french alps holocene palaeoenvironmental evolution and glacial fluctuations at high altitude in the western french alps are reconstructed based on a multiproxy approach within lake blanc huez 2550 m a s l drainage basin the combination of seismic profiling 3 5 khz piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the holocene over the last 9700 years the holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal bp during the early holocene the organic lacustrine facies reflects reduced glacial activity in the catchment this major glacial retreat seems to result from solar forcing and high summer insolation after 5400 cal bp lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion suggesting a progressive transition to wetter climatic conditions this climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations characterizing the beginning of the neoglacial period both colder temperature and humid climate induced significant glacier advance since 4700 cal bp over this global trend three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern westerlies regimes across the north atlantic and western europe they are dated from 8700 to 7000 4700 to 2500 and 1200 to 200 cal bp these wetter phases drastically contrast with periods of reduced glacial activities dated from the early bronze age ca 3870 3770 cal bp the iron age ca 2220 2150 cal bp the roman period ca ad115 330 and the medieval warm period ca ad760 1160 in addition these dryer periods are associated with mining activities at high altitude

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

preservation potential for late quaternary river alluvium valley sequences of late quaternary alluvial units reflect alluvial preservation as well as alluvial production factors effects of lateral channel migration incision aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets cartographically dated and model data based on lateral channel migration well mapped and dated late quaternary valley unit surveys and composite age frequency plots for dated alluvial units and flood sediments despite much expectable variation between sites and the complex effects of river activity combinations a common characteristic of the data sets examined is the significance of preservation factors lateral migration tends to eliminate older units as it creates new alluvial deposits whereas incision may lead to the preferential preservation of older units beyond the incision slot aggradational environments are likely to preserve more complete records although simultaneous lateral migration may eliminate possibly repeatedly the upper parts of alluvial units the common pattern of inset and incised streams within pleistocene and early holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley floor units is necessarily at the expense of reprocessing earlier ones floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials thus limiting the preserved record of earlier events in light of these censoring effects of river activities the sequence of preserved late quaternary units within uk sequences is reconsidered it is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive copyright 2003 john wiley sons ltd journal of quaternary science

the mediaeval warm period drought recorded in lake huguangyan tropical south china the geochemistry of dated sediment cores from lake huguangyan 21o9 n 110o17 e tropical south china reveals distinct stratigraphical patterns in total organic and inorganic carbon toc tic biogenic silica bs and total nitrogen tn over the past 1400 years in this hydrologically closed lake tic variations may reeect changes in the precipitation evaporation ratio which controls the evaporative enrichment of carbonate toc bs and tn in the sediment are proxy indicators of lake productivity and nutrient input which we believe are linked to local precipitation high tic content correlates with low concentrations of toc bs and tn and indicates two drought episodes dated to ad 670 760 and ad 880 1260 in the sediments of lake huguan gyan local historical chronicles support these data suggesting that the climate of tropical south china was dry during the mediaeval warm period mwp and wet during the little ice age lia the detected mwp drought is temporally correlated with evidence for lower precipitation on the guliya china and quelccaya peru ice caps and with increased salinity in moon lake us great plains

palynofacies analysis of the late holocene san nicolas terrace of the cauca paleolake and paleohydrology of northern south america abstract the detailed palynofacies analysis of the late holocene laminated succession of the san nicolas terrace in the middle cauca valley northern colombia is interpreted as the product of sedimentation in a lacustrine to fluvial dominated setting radiocarbon analyses reveal that the succession was deposited between 3500 and a few hundreds of years with sedimentary rates in excess of 600 cm ka the milimetric laminae and the high frequency fluctuations in the content of the palynodebris of terrestrial origin i e the high altered ligno cellulosic debris amorphous organic matter ratio together with diatoms typical of fluvial conditions such as aulacoseira granulata do suggest an intermittent and continuous hydrological and biological connectivity with the cauca river akin to a varzea lacustrine environment drier to wetter conditions appear to occur moving upward in the succession this might reflect regional precipitation conditions all along the cauca valley and the southern migration of the intertropical convergence zone

trends and controls of holocene floodplain sedimentation in the rhine catchment article i nfo holocene floodplain sedimentation in the rhine catchment is controlled by human and climate impacts intricate river behaviour modifies the fluvial response to the external impacts making cause effect analysis difficult especially on large spatial scales to better understand the relative importance and interdependencies of external and internal controls temporally resolved floodplain sedimentation rates are established using three different methods i floodplain storage studies on the trunk stream ii depth age analysis of overbank deposits from different parts of the catchment and iii cumulative frequency distributions of 14 c ages from floodplain deposits from various parts of the catchment the applied methodology strongly differs with the available temporal resolution and the size of the corresponding catchment all three methods show a strong increase in sedimentation rate for more recent periods that can be linked to increasing human impact evidences for climate impacts and intricate river behaviour are less clear and hindered by insufficient temporal resolution of the currently available data

influence of late holocene alluviation on the degradation of peat forming wetlands as exemplified by the lower reach of the osobloga river valley southern poland

how tides and river flows determine estuarine bathymetries abstract for strongly tidal funnel shaped estuaries we examine how tides and river flows determine size and shape we also consider how long it takes for bathymetric adjustment both to determine whether present day bathymetry reflects prevailing forcing and how rapidly changes might occur under future forcing scenarios starting with the assumption of a synchronous estuary i e where the sea surface slope resulting from the axial gradient in phase of tidal elevation significantly exceeds the gradient in tidal amplitude an expression is derived for the slope of the sea bed thence by integration we derive expressions for the axial depth profile and estuarine length l as a function of and d the prescribed depth at the mouth calculated values of l are broadly consistent with observations the synchronous estuary approach enables a number of dynamical parameters to be directly calculated and conveniently illustrated as functions of and d namely current amplitude u ratio of friction to inertia terms estuarine length stratification saline intrusion length flushing time mean suspended sediment concentration and sediment in fill times four separate derivations for the length of saline intrusion li all indicate a dependency on d 2 f u u o uo is the residual river flow velocity and f is the bed friction coefficient likely bathymetries for mixed estuaries can be delineated by mapping against and d the conditions li l however the length of saline intrusion in a funnel shaped estuary is also sensitive to axial location observations suggest that this location corresponds to a minimum in landward intrusion of salt by combining the derived expressions for l and li with this latter criterion an expression is derived relating di the depth at the centre of the intrusion to the corresponding value of uo this expression indicates uo is always close to 1 cm s 1 as commonly observed converting from uo to river flow q provides a morphological expression linking estuarine depth to q with a small dependence on side slope gradients these dynamical solutions are coupled with further generalised theory related to depth and time mean suspended sediment concentrations as functions of and d then by assuming the transport of fine marine sediments approximates that of a dissolved tracer the rate of estuarine supply can be determined by combining these derived mean concentrations with estimates of flushing time ft based on li by further assuming that all such sediments are deposited minimum times for these deposition rates to in fill estuaries are determined these times range from a decade for the shortest shallowest estuaries to upwards of millennia in longer deeper estuaries with smaller tidal ranges

a 7000 year environmental history and soil erosion record inferred from the deep sediments of lake pavin massif central france a 14 m long sedimentary sequence core pav12 was collected in the deepest part of lake pavin a maar lake located in the french massif central the pav12 sedimentary sequence documents the lake s environmental evolution since its formation 7000 years ago the relationships between the catchment s vegetation cover erosion processes and changes in trophic status were shown using a multi proxy characterization of mineral and organic fractions supported by palynological data the record shows a succession of lithological units starting at the base with volcanoclastic material corresponding to the early stage of lake pavin the deposition of organic rich and diatomaceous sedimentary units above volcanoclastic material indicates an evolution toward a pristine lacustrine state the late holocene environmental history of this lake is marked by two tipping points reflecting major environmental disturbances at ca 4000 cal bp and after the deposition of erosive mass wasting deposits mwds at 1350 cal bp ce 600 and 650 cal bp ce 1300 the upper unit of core pav12 which corresponds to the past 700 years indicates that one of these mwds was likely the driving force behind a major limnological change marked by a shift in redox sensitive elements i e current meromictic lacustrine state the palynological diagram indicates a forested catchment where woodland clearances and agro pastoral activities have remained limited except over the last 700 years these findings suggest restricted human impact within the watershed compared to other regional archives the reconstruction of the lake pavin erosion record determined from titanium and red amorphous particle fluxes highlights phases of enhanced erosion at ca 6 5 5 5 4 1 3 8 3 5 2 8 2 6 1 6 1 4 cal kyr bp and during the little ice age lia a comparison between this erosion record palaeoenvironmental archives from western europe and palaeoclimatic data supports an atlantic signal driving precipitation patterns over lake pavin at centennial to millennial timescales the influence of local human activities even on a small scale cannot be completely discounted as their impact on erosional processes may be amplified in a steep catchment such as that found in lake pavin

historical seismicity of peninsular india abstract well documented historical earthquake data from 1340 to 1983 has been analyzed and reported in this work so as to understand the seismicity and associated phenomena of peninsular india it has been the belief among earth scientists that the peninsular shield is aseismic as the region attained stability long ago however the earthquake at koyna 10 december 1967 bhadrachalam 13 april 1969 broach 23 march 1970 hyderabad 30 june 1983 etc altered this concept and it has now widely accepted that seismic activity is still continuing on a mild scale as such a need has arisen to take into consideration historical as well as recent seismological data to study the seismic status of peninsular india using the well known frequency magnitude relation of gutenberg and richter 1954 an attempt has been made to derive a and b and the ratio a b the values as obtained for peninsular india are 4 4 0 85 and 5 17 which are typical of moderately active zones the world over recurrence periods of earthquake magnitude 6 75 and 7 0 are calculated to be 21 and 35 yr respectively further the historical seismicity correlates well with the protocontinents such as dharwar aravalli and singhbhum in the peninsular shield it is observed that seismicity in a broad sense is defined by the protocontinents with low intracontinental seismicity while the lineaments and rift valleys are from zones of moderate seismicity

soil erosion in small catchments of the quercy region southwester france during the holocene erosion rates in two small catchments of the quercy region southwestern france calculated from colluvial deposits trapped in karstic depressions show a progressive increase during the holocene rates lower than 0 2 t ha 1 yr 1 have been found for the period that covers the beginning of the holocene to the early iron age the soils buried in the depressions testify to the permanence of a forest cover until the late neolithic and to its replacement by a herbaceous vegetation during protohistorical times probably as a consequence of forest clearance and increased grazing by cattle after the early iron age erosion increased significantly and the mean rate reached 0 8 t ha 1 yr 1 before mediaeval times the associated coarse grained crudely stratified colluvium is thought to reflect ploughing of the surrounding fields erosion rate increased up to c 1 3t ha 1 yr 1 during mediaeval and modem times

the relation between climate and river processes landforms and deposits during the quaternary abstract the extent to which river processes and morphology are dependent on climate is an old question when looking at large time scales climatic cyclicity seems to coincide with alternating events in fluvial development however the shorter the time scales at which fluvial development is considered the more it is difficult to find a close correspondence with climate evolution ultimately it appears that the response time of river processes to climatic change may restrict the sensitivity of the fluvial systems to adapt to short climatic oscillations the impact of climate on fluvial systems is largely transferred to these systems by the climate determined soil cohesion and peak discharges the latter factors are especially related to vegetation cover and permafrost conditions finally a number of basin characteristics are discussed that demonstrate that fluvial systems are not completely controlled by climate

changes in sediment flux and storage within a fluvial system some examples from the rhine catchment the rhine river system can look back on a long history of human impact whereas significant anthropogenic changes to the river channel started only 200 years ago the impacts of land use have been felt for more than 7500 years here we review results from several case studies and show how land use change and climate impacts have transformed the fluvial system we focus on changes in sediment delivery pathways and slope channel coupling and show that these vary in time and depend on the magnitude of a rainfall event these changes must be accounted for when trying to use sediments as archives of land use change and climatic impacts on fluvial systems for example human impact is recorded in slope deposits only as long as rainfall intensity and runoff generation do not exceed the threshold for gullying similarly climatic impacts are only recorded in alluvium when both the landscape is rendered sensitive by human activities e g deforestation and rainfall thresholds for gullying are exceeded copyright 2003 john wiley sons ltd

the wet little ice age recorded by sediments in huguangyan lake tropical south china abstract although temperature decreased in a similar trend in many regions around the word during the little ice age lia the reconstructed humidity is remarkably different from region to region the precipitation history during the lia is poorly understood as compared to the temperature history in tropical south china in this study a sediment core with a length of 117 5 cm was recovered in the central part of huguangyan lake in tropical south china total organic carbon toc total nitrogen tn inorganic carbon ic and non residual strontium sr were analyzed at approximately 1 cm intervals to study the regional precipitation changes during the lia generally sr containing minerals are sensitive to chemical weathering which is dominated by the precipitation in tropical south china thus the non residual sr in huguangyan sediments can be used as an indicator of precipitation changes which is also verified by the downcore variations of toc tn and ic in huguangyan lake the non residual sr correlated positively with toc and tn but negatively with ic in the sediment profile toc tn ic and the non residual sr jointly demonstrated a wet period from ad 1500 to 1750 which corresponds to the lia coincidently both the total solar irradiance tsi and northern hemisphere temperature have the lowest values between ad 1500 and 1750 over the past millennium therefore the wet lia in tropical south china was most likely caused by the low solar irradiation during the lia the low solar irradiation likely resulted in the decrease of the northern hemisphere temperature which weakened the intensity of the east asian summer monsoon easm and synchronously moved the north edge of the asian summer monsoon southward leading to an increase in the precipitation in tropical south china

petrographic and geochemical study of organic matter in surficial laminated sediments from an upwelling system mejillones del sur bay northern chile a study of recent laminated sediments accumulated in the oxygen minimum zone of mejillones bay northern chile shows that the organic matter is autochthonous and deposited under varying oceanographic conditions sedimentary units dominated by light laminations have low values of total organic carbon total nitrogen and sulphur and chaotoceros content coupled with high values of yellow amorphous organic matter these were deposited under conditions of low primary productivity favoring the recycling of the major part of metabolizable organic matter in the water column and the accumulation only of non metabolizable organic matter in the bottom sediments in contrast a unit rich in dark laminations with high values of total organic carbon total nitrogen and sulphur shows high values of brown and black aom and chaetoceros content this sedimentary unit reflects increased flocculation of organic particles during a period of high productivity and fast transit of organic material through the column water thus diminishing the recycling of metabolizable organic matter and its accumulation with non metabolizable organic matter in the sediments finally a unit characterized by presence of both light and dark laminations was formed by abrupt alternations of the two oceanographic states described previously

robust chronologies for landform development obtaining chronological control for geomorphological sequences can be problematic due to the fragmentary and non sequential nature of sediment and landform archives the robust analysis of 14c ages is often critical for the interpretation of these complicated sequences this paper demonstrates a robust methodology for the 14c dating of geomorphological sequences using a case study from the lower ribble valley northwest england the approach adopted incorporates using greater numbers of ages targeting plant macrofossils obtaining replicate measurements from single horizons to assess the extent of reworking and the use of bayesian approaches to test models of the relative order of events the extent of reworking of organic materials and space time dynamics of fluvial change means that it is critical that chronological control is sufficiently resourced with 14c measurements as a result bayesian approaches are increasingly important for the evaluation of large data sets assessing the conformability of relative order models informed by interpretation of the geomorphology can identify contexts or materials that are out of sequence and focuses attention on problem materials reworking and errors in interpretation outlier ages these relative order models provide a framework for the interrogation of sequences and a means for securing probability based age estimates for events that occur between dated contexts this approach has potential value in constraining the sequence of geomorphological development at scales that vary from individual sites to a catchment or region furthering understanding of forcing and change in geomorphological systems copyright 2008 john wiley sons ltd

salt wedge dynamics lead to enhanced sediment trapping within side embayments in high energy estuaries off river coves and embayments provide accommodation space for sediment accumulation particularly for sandy estuaries where high energy in the main channel prevents significant long term storage of fine grained material seasonal sediment inputs to hamburg cove in the connecticut river estuary usa were monitored to understand the timing and mechanisms for sediment storage there unlike in freshwater tidal coves sediment was primarily trapped here during periods of low discharge when the salinity intrusion extended upriver to the cove entrance during periods of low discharge and high sediment accumulation deposited sediment displayed geochemical signatures consistent with a marine source numerical simulations reveal that low discharge conditions provide several important characteristics that maximize sediment trapping first these conditions allow the estuarine turbidity maximum etm to be located in the vicinity of the cove entrance which increases sediment concentrations during flood tide second the saltier water in the main channel can enter the cove as a density current enhancing near bed velocities and resuspending sediment providing an efficient delivery mechanism finally higher salinity water accumulates in the deep basin of the cove creating a stratified region that becomes decoupled from ebb currents promoting retention of sediment in the cove this process of estuarine enhanced sediment accumulation in off river coves will likely extend upriver during future sea level rise

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

a seismic hazard map of india and adjacent areas abstract we have produced a probabilistic seismic hazard map showing peak ground accelerations in rock for india and neighboring areas having a 10 probability of being exceeded in 50 years seismogenic zones were identified on the basis of historical seismicity seismotectonics and geology of the region procedures for reducing the incompleteness of earthquake catalogs were followed before estimating recurrence parameters an eastern united states acceleration attenuation relationship was employed after it was found that intensity attenuation for the indian region and the eastern united states was similar the largest probabilistic accelerations are obtained in the seismotectonic belts of kirthar hindukush himalaya arakan yoma and the shillong massif where values of over 70 g have been calculated

a carbon storage perspective on alluvial sediment storage in the rhine catchment abstract floodplains are important sinks in terms of the sediment and carbon flux in fluvial systems despite the large amount of detailed geomorphological studies which include measurements on total organic carbon little is known of the coupling of long term carbon and sediment flux and on the amount of carbon storage in floodplains therefore the influence of the sedimentary facies in fluvial systems was investigated based on a statistical analysis of 1948 organic carbon measurements in different parts of the rhine catchment the analysis allows to develop a conceptual carbon budget model of fluvial systems which was coupled with a holocene alluvial sediment budget to estimate the holocene sequestration rates of carbon storage in floodplains averaged over the rhine catchment the sedimentary carbon sequestration ranges between 3 4 to 25 4 g m 2 yr 1 with more reasonable values between 5 3 to 17 7 g m 2 yr 1 compared to the recent particulate carbon export these values are in the same order of magnitude but somewhat smaller indicating that approximately the same amount of the exported carbon may be stored in floodplains however compared to sedimentary carbon sequestration rates obtained elsewhere the presented values are at the lower limit corresponding to the lower mean holocene soil erosion and floodplain accumulation rates

bulk composition of sedimentary organic matter used in palaeoenvironmental reconstructions examples from the tropical belt of south america and africa abstract the organic matter of lake sediments contains information that allows for the reconstruction of past environmental and climatic changes the elemental composition and isotopic characteristics of sedimentary organic matter enable discrimination between allochthonous vegetal matter from within the catchment and autochthonous phytoplanktonic and fixed algae components this approach makes it possible to distinguish between the inputs of organic matter from c 3 vs c 4 type land plants sedimentary records from south america and africa provide examples of applications of organic bulk composition in palaeoenvironmental reconstructions the records from two african lakes show that during the last glacial maximum lgm the distribution of c org n org 13 c pairs indicates the dominance of organic material having a c 4 terrestrial origin these inferences are supported by pollen analysis which indicates opening up of the forest at both sites consistent with drier climatic conditions than present the record from siberia lake bolivia ca 3000 m altitude shows that during the lgm the sedimentary organic matter is dominated by the phytoplanktonic fraction as indicated by the c org n org 13 c pairs the petrographic analyses show that this material is not well preserved suggestive of drier conditions consistent with interpretations from the pollen record the beginning of the holocene is marked by a shift from a scattered c 4 signal to one with a greater terrestrial c 3 and aquatic phytoplanktonic influence these results indicate climatic amelioration towards more humid and warmer climatic conditions leading to forest development in the lake catchment together with increasing lake levels conducive to greater phytoplankton production these conditions persisted during the holocene as shown by the c org n org 13 c pairs in all lakes with a terrestrial c 3 signal predominating at the carajas and siberia lakes only dom helvecio lake shows a different pattern during the beginning of the holocene in the distribution of c org n org 13 c pairs this pattern indicates that the sedimentary organic material is dominated by c 4 terrestrial material coming from savanna expansion in the lake catchment during a period of relative aridity in central brazil

late glacial and early holocene environmental changes affecting the shallow lake basin of la narce du beage ardeche massif central france abstract the sedimentary sequence of la narce du beage basin is one of the few natural archives covering the last 18 ka cal bp in the french massif central this paper focuses on the palaeoecological reconstruction of environmental and climatic changes affecting this shallow periglacial lake from the late glacial to the early holocene after field surveys and geophysical mapping two cores cores a and d were extracted and dated plant macrofossils pollen non pollen palynomorphs npps and diatom assemblages were compared within the cores to study vegetation temperature ph water level and ice cover changes through time during the oldest dryas 18 14 75 ka cal bp climatic conditions were the coldest with a short ice free season allowing the development of periphytic diatoms only ecologically comparable to arctic ones a cold and dry steppe landscape exposed to severe erosion comprised an herbaceous and shrub flora e g artemisia chenopodiaceae helianthemum ephedra hippophae juniperus animal presence is suggested by coprophilous fungi periphytic diatoms and allochtonous pollen cedrus underline windy conditions and the possible erosion of neo formed soils then during the bolling allerod interstadial 14 75 12 7 ka cal bp the ice free season increased and some trees shrubs salix betula and juniperus established locally within open grasslands during the younger dryas 12 7 11 7 ka cal bp cooler conditions favoured steppe taxa again helianthemum achillea artemisia caryophyllaceae ranunculaceae and erosion increased the ice cover on the lake prevailed even if the conditions were not as cold as during the oldest dryas during the preboreal 11 7 10 ka cal bp isoetes echinospora and i lacustris developed in the eulittoral zone of the lake which was surrounded by a swamp forest with betula nana and b pubescens pinus sylvestris betula pendula corylus avellana and trees from the quercetum mixtum rapidly established in the uplands occurrences of gaeumannomyces and xylomyces fungi both phytopathogens on broadleaved trees and decreasing herb values indirectly hint at a close forest canopy at the beginning of the boreal 10 ka cal bp aquatic and semi aquatic taxa developed on open water due to longer ice free seasons diatoms micro algae alisma plantago aquatica potamogeton typha the final terrestrialization towards a mire occurred as a consequence of the holocene warming and related to water chemistry changes acidification eutrophication

sensitivity of west and central european river systems to environmental changes during the holocene a review abstract sediment deposition in floodplains is an essential part of the sediment dynamics of a catchment these sediment dynamics can vary largely on a holocene time scale under the influence of driving forces such as land use and climatic variations in this paper we review the holocene floodplain sediment deposition history of rivers in west and central europe with special attention to the influence of climate and land use variability during the early holocene preboreal to atlantic period most floodplains were rather stable with limited floodplain aggradation after this initial phase of relative stability sedimentation rates increase during the middle and late holocene with often the most important deposition phase during the last 1000 to 2000 a the start of the increase in sedimentation varies spatially with an earlier start in the west france germany then in the east poland belarus ukraine while there are also local differences between regions which are settled early e g loess regions compared to later settled regions the sedimentation history of most floodplains can be linked to the local land use history while influence of climatic variations on floodplain aggradation is often reported to be of minor importance processes related to bedload are often reported to be more influenced by climatic events relationships between the driving forces and the sediment history are mainly based on synchronicity and there is seldom proof for a direct causal relationship future research should focus on a system based approach integrating the floodplain deposition in the entire sediment dynamics which includes also erosion colluvial deposition and export main research questions that need further attention include integration of system based concepts like landscape connectivity and buffering effects and also the assessment of the individual contribution of land use changes and climatologic variations on the sediment dynamics detailed sediment budget studies combined with modeling studies can make an important contribution to the understanding of floodplain sediment dynamics

pollen analysis of a long upper pleistocene continental sequence in a velay maar massif central france abstract a new 20 m sequence is presented which is based on 279 spectra derived from a coring at le bouchet lake massif central france the vegetational history of this region is described back to the end of the last interglacial ribains interglacial the two preglacial early glacial forested interstadials st geneys 1 and st geneys 2 are evidence for the first time in the massif central in spite of the altitude of the site 1200 m they suggest a quite temperate vegetation with the same mesophilous character as during the holocene the pleniglacial appears to be threefold with two cold episodes lower and upper pleniglacial divided by a long complex period of moderate climatic improvement the vegetation history of this mountain region is compared with that evidenced for the same period on the basis of the sequence of les echets at a lower altitude 267 m botanical and climatic inferences are discussed

salinity intrusion in estuaries abstract one dimensional time averaged solutions are examined for salinity intrusion in estuaries with a breadth variation bl x n and a depth variation h x m where x is the distance from the head of the estuary these solutions emphasize the importance of the rate of change of cross sectional area in determining salinity distribution assuming a constant longitudinal dispersion coefficient dx d the salinity distribution is shown to be highly dependent on the dimensionless parameter v u1 x1 d with u1 the velocity of the fresh water flow at position x1 where the estuary is effectively at oceanic salinity this parameter v is equivalent to the flushing number f introduced by arons and stommel 1951 for the case of an estuary of rectangular cross section for eight estuaries comparisons are made between calculated and observed salinity distributions where for each estuary the value of d in the calculated distribution was chosen to produce the best agreement with the observed distribution

quantification and regulation of organic and mineral sedimentation in a late holocene floodplain as a result of climatic and human impacts taligny marsh parisian basin france quantification in grams per metres squared per year of the sediment accumulation in a flood plain marsh located in the southwestern parisian basin showed that there is no close relationship between the accumulation of organic matter om and mineral matter mm during the late holocene and provided an accurate view of the distinct yield and storage conditions of both sediment components endogenic om accumulation in peaty sediments is not related to the climate but to felling of the alder forest and its substitution by cyperaceae and paludal taxa in the marsh iron age and middle ages mm accumulation expresses mainly the sediment yield on the slopes determined by landuse during an initial phase from the late neolithic to the early middle ages land use change from crop cultivation to pastureland possibly related to climate deterioration led to a decrease in the sediment yield during a second phase since the early middle ages the considerable development of crop cultivation over pasturing even during periods of climate deterioration such as the little ice age led to a sharp increase in sediment yield however although sediment yield was high the hydrodynamics in the fen did not favour particle retention thus since the neolithic yield and storage of om and mm sediment have been marked by human activities initially with high climatic stress but since the middle ages without significant climatic stress

saline intrusion in partially mixed estuaries abstract restricting interest to partially mixed estuaries earlier studies of tidally averaged linearised theories relating to the vertical structure of salinity and velocities accompanying saline intrusion are extended to take account of tidal straining and associated convective overturning the applicability of these theories is evaluated by reference to a single point numerical model in which the time varying cycle of depth averaged tidal current amplitude u and a temporally and vertically constant saline gradient sx are specified this model highlights the importance of convective overturning in counteracting unstable density structures introduced by tidal straining by omitting overturning in the model results agree closely with linearised theoretical derivations however incorporating overturning substantially increases tidally averaged surface to bed differences for both residual currents u and salinity s the vertical structure of tidal currents is a maximum and hence the effect of tidal straining in shallow macro tidal estuaries the propagation of tidal elevations and currents remains insensitive to saline intrusion in partially mixed estuaries the applicability of the model was evaluated by simulation of recent measurements by rippeth et al j phys oceanogr 31 2001 2458 to explore the generality of estuarine responses the model was run for a wide range of values of saline intrusion lengths l and water depths d additional sensitivity analyses were made for changes in u and bed stress coefficient k response frameworks are shown for u s potential energy anomaly work done by bed friction and internal shear rates and efficiency of saline mixing and ratios of relative mixing by diffusion to overturning by equating the rate of mixing associated with vertical diffusion with river flow q an expression for saline intrusion length l d 2 k u u o uo river flow velocity was derived this formulation agrees with an earlier derivation based on flume tests and showed reasonable agreement with observed values in six estuaries eight cases however in funnel shaped estuaries axial migration of the intrusion introduces major variations in d u and uo thereby complicating the application of the above expression for l moreover the time lag involved in the adjustment of l to changes in u and q may explain much of the complexity encountered in the observations

probabilistic seismic hazard macrozonation of tamil nadu in southern india abstract the south indian state of tamil nadu in the peninsular shield is a zone of low to moderate seismic activity with a sparse historical record of significant earthquakes the current intensity based zoning adopted by the indian seismic code stipulates an effective peak ground acceleration pga of either 0 10 or 0 16 g for different parts of the state for the maximum considered earthquake mce and the service life of a structure in the current study probabilistic seismic hazard contour maps for tamil nadu and the union territory of pondicherry in terms of the ground motion parameters pga and spectral accelerations at 0 1 0 5 and 1 0 sec for 2 5 and 10 probabilities of exceedance in a 50 yr period have been produced hazard computations have been performed over a grid of sites covering the territory at an interval of 0 2 a comprehensive earthquake catalog has been compiled for the region extending between 2 and 20 7 n latitude and 68 and 88 e longitude and spanning 950 yrs the hazard maps are produced by suitably accounting for epistemic uncertainty in the hazard computations within a logic tree framework incorporating parameters such as different probabilistic hazard analysis methods classical cornell mcguire and zone free approaches catalog completeness estimation methods maximum cutoff magnitude and ground motion predictive equations for shallow crustal intraplate environments the hazard maps are compared to the zoning prescribed by the seismic code the current estimations show that the potential seismic hazard in considerable parts of the state is underestimated by the broad zoning adopted by the indian standards

late quaternary changes in ecosystems and carbon cycling on mt kenya east africa a landscape ecological perspective based on multi proxy lake sediment influxes abstract the degree to which different lakes within a landscape respond coherently in unison to external drivers such as climate change and soil development is uncertain presentation of multi proxy geochemical and palaeoecological data from individual lakes in the form of fluxes minimizes distortions resulting from variable sedimentation rates and changes in sediment composition we use the accumulation rates of magnetic minerals total organic c and n terrestrial and aquatic biomarkers graminoid epidermis pollen green algae diatoms and diatom c in four small lakes situated between 2350 and 4595 m a s l on the ne flank of mt kenya east africa to reconstruct changes in c cycling over the last 38 ka the results conflict with earlier models of landscape and lake development showing 1 that glacial interglacial changes in vegetation cannot be interpreted as simple altitudinal shifts in the modern vegetation belts and 2 that limnological changes were not coherent rapid variations in climate water level erosion and nutrient input overwhelmed long term successional trends in lake sedimentation and c accumulation since the last glacial maximum the results also reveal previously unrecognized features of the palaeoenvironmental record such as the rapid degradation of organic matter in diatoms and the occurrence of a productive fire prone montane grassland during the highly seasonal monsoonal climate of the lateglacial and early holocene

variations of the amazonian rainforest environment a sedimentological record covering 30 000 years abstract two cores css 2 and css 10 were collected from two lakes situated in the carajas area 6 35 s 49 30 w that show different stages of silting up the results of geochemical and petrographic organic analyses backed up by 14 c radiometric dating lead to a reconstruction of the variations in the hydrological regime of these lakes over the last 30 000 years evidence is revealed for a period of drying up characterized by a sedimentary hiatus between 22 000 and 13 000 14 c years bp followed by a period of refilling between 13 000 and 11 000 14 c years bp 15 400 12 900 cal years bp the latter interval is primarily characterized by a mainly clastic sedimentary input rich in quartz kaolinite and iron hydroxides leading on to the authigenic formation of siderite this type of sedimentation implies the erosion of the small catchment basin during periods of transition between arid and humid climatic regimes from 8000 to 4000 14 c years bp 8900 4500 cal years bp as well as from 2700 to 1500 14 c years bp 2780 1360 cal years bp special hydrological conditions prevailed they are characterized in the sedimentary record by the presence of micro laminae containing wood charcoal interlayered with sponge spicule material this interlamination reflects the rapid alternation of dry and humid periods a comparison with the results obtained by pollen analysis shows that sedimentological indicators once filtered for strictly local effects can provide a full record of the regional scale variations in the environment

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

how to obtain earthquake ground motions for engineering design abstract the earthquake ground motions that ultimately are selected for engineering design depend chiefly on the criticality of a site or structure and the engineering analyses that are to be performed several key steps are necessary in this selection process they are 1 a reconnaissance to understand the hazards and obtain preliminary earthquake ground motions 2 decisions on the application of deterministic or probabilistic methods 3 selection of appropriate motions for requirements in design 4 consideration of thresholds at which motions become significant for engineering and 5 decisions on specifying appropriate earthquake ground motions for sizes of earthquakes distances from sources the structures sites and testing to be done this paper presents five tables that show steps for evaluating these factors and for enabling the investigator to specify earthquake ground motions appropriate for engineering design

relationships between organo mineral supply and early diagenesis in the lacustrine environment a study of surficial sediments from the lac du bouchet haute loire france the relationships between organo mineral composition and early diagenetic processes in surface 50 cm sediments from the lac du bouchet haute loire france are presented parallel pore water studies reveal downcore increases in dissolved organic carbon inorganic carbon and ch4 illustrating the dominant methanogenetic degradation but also highlighting regions of enhanced degradation due to sulphate reduction confirmed by solid phase sulphur and pyrite distributions three sedimentary facies are observed ia 0 25 cm where the majority of compaction and degradation of the organic matter by diagenesis occurs in the absence of any significant change in the type of organic material or sedimentation rate ib 25 40 cm characterised by an increased grain size and diatom abundance ii below 40 cm whose base dates at 2500 350 bp i e within the sub atlantic shows high organic carbon contents and large grain size autochthonous amorphous organic matter is the dominant petrographical organic component whereas pedogenetic allochthonous amorphous organic matter is slightly enriched in facies ii and ia this is coincident with the disappearance of the spores and pollen and suggests a greater continental runoff from the surrounding basin at these times proportions of kaolinite chlorite and illite content do not vary greatly indicating that the detrital input has not changed significantly over the last 2500 years downcore decreases in the sial curve proxy for biogenic silica parallel those of total organic carbon suggesting the dissolution of solid phase silica over time the anthropogenic deforestation and consequent greater nutrient runoff into the oligotrophic lake encouraged an increased production of diatoms around 30 cm the increased sedimentation rate at the beginning of the sub atlantic facies ii as a result of greater continental runoff due to installation of present climatic conditions enhanced the preservation of the organic material by reducing the dia genetic effects and by increasing the proportion of diagenetically inert and relatively resistant organic matter these findings underline the critical role that bulk sedimentation rate and the nature of organic matter play in the final determination of sediment composition both in terms of input and in post depositional degradation

seismogenesis in the stable continental interiors an appraisal based on two examples from india characteristics of two recent moderate earthquakes from india 1993 killari mw 6 1 and 1997 jabalpur mw 5 8 are presented in this paper to illustrate the influence of geologic and tectonic setting on the nature of seismicity in stable continental regions scrs the killari event which occurred in the middle of a cratonic region of low background seismicity long recurrence interval and poorly developed neotectonic features may be qualified as a common type of scr event this earthquake is also characterized by a shallow focal depth and a long sequence of aftershocks in contrast the jabalpur earthquake shows a spatial association with a well defined tectonic structure with significant background seismicity a remarkable feature of this earthquake is its deep focus not commonly observed in scr seismicity this event was associated with fewer aftershocks unlike most other scr earthquakes analogous events are found in other shield regions as well based on their general characteristics a broad classification of moderate scr earthquakes is attempted here two broad groups have been identified in this study 1 a set of deep focus earthquakes that are related to intracratonic paleorifts and 2 shallow focus earthquakes associated with discrete faults in the less deformed precambrian terrains a synthesis of earthquake data from different geologic environments will improve our understanding of the seismogenesis in the shield regions 1999 elsevier science b v all rights reserved

the oxbow sedimentary subenvironment its value in palaeogeographical studies as illustrated by selected fluvial systems in the upper odra catchment southern poland research was conducted in valleys of sinuous rivers that drain medium high mountain foreland basin and upland areas where loose quaternary deposits predominate the cyclic pattern determined for deposits of the oxbow sedimentary subenvironment in the upper odra basin can be expressed as a few alternative sequences the best developed cycle occurring on a relatively high level of probability is represented by the unilateral transition from channel to overbank deposits and upwards bilateral oscillations between overbank and biochemical as well as biochemical and slope deposits in the first stage oxbow filling processes are usually determined by autocyclic factors resulting from spatial relations between abandoned channels and the active channel as a consequence overbank and or biochemical sediments usually overlie channel deposits later allocyclic processes could easily dominate autocyclic processes in these cases overbank slope and late holocene alluvial fan deposits were delivered to oxbow

sensitivity analysis of seismic hazard for the northwestern portion of the state of gujarat india we test the sensitivity of seismic hazard to three fault source models for the northwestern portion of gujarat india the models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years these recurrence intervals imply that large earthquakes occur on one of these faults every 266 533 years similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the new madrid region in the central united states if one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults the peak ground accelerations pga horizontal and 1 hz spectral acceleration ground motions 5 damping are greater than 1 g over a broad region for a 2 probability of exceedance in 50 years hazard level these probabilistic pgas at this hazard level are similar to median deterministic ground motions the pgas for 10 in 50 years hazard level are considerably lower generally ranging between 0 2 g and 0 7 g across northwestern gujarat ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals these higher ground motions are mainly caused by the application of intraplate attenuation relations which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies for sites in bhuj and ahmedabad magnitude m 7 3 4 earthquakes contribute most to the pga and the 0 2 and 1 s spectral acceleration ground motion maps at the two considered hazard levels d 2004 elsevier b v all rights reserved

tidal variations of flow convergence shear and stratification at the rio de la plata estuary turbidity front 1 intratidal variability of density and velocity fields is investigated at the turbidity front of the rio de la plata estuary south america current velocity and temperature salinity profiles collected in august 1999 along a repeated transect crossing the front are analyzed horizontal and vertical gradients stability of the front convergence zones and transverse flow associated to the frontal boundary are described strong horizontal convergence of the across front velocity and build up of along front velocity shear were observed at the front in the proximity of the front enhanced transverse or along front flow created jet like structures at the surface and near the bottom flowing in opposite directions these structures persisted throughout the tidal cycle and were advected upstream downstream by the flood ebb current through a distance of 10 km during peak flood the upper layer flow reversed from its predominant downstream direction and upstreamflow occupied the entire water column outside the peak flood two layer estuarine circulation dominated changes in density field were observed in response to tidal straining tidal advection and wind induced mixing but stratification remained throughout the tidal cycle this work demonstrates the large spatial variability of the velocity field at the turbidity front it provides evidence of enhanced transverse circulation along the frontal boundary and reveals the importance of advective and frictional intratidal processes in the dynamics of the central part of the estuary

late holocene erosion in nw anatolia from sediments of lake manyas lake ulubat and the southern shelf of the marmara sea turkey abstract this paper deals with modern and ancient sedimentation in fresh water lakes and the marine shelf of the southern marmara region nw anatolia turkey most of the information has been obtained from monitoring of suspended load discharged into two lakes manyas and ulubat in the last 45 years and from 8 to 11 m thick lacustrine sediments in addition to radiocarbon dated shelf sediments this allows a holistic approach to the drainage basin denudation over time the results show that the sedimentation rates in the lakes were low 0 22 cm year 1 from 4000 to 2000 years bp and then they increased 0 29 cm year 1 up to sub recent times and reached 0 44 cm year 1 in the last century it is suggested that deforestation created high rates of sedimentation in the basins and or strong denudation of the region during the late holocene this study also shows that for shallow freshwater lakes the calculation of sedimentation rates must include fine particles lost by the outlets and coarse grained bed load deposited on their shores in addition a high rate of sedimentation has been created by short but repetitive intense depositions during the last century particularly during the last 45 years the rate of sedimentation or denudation has increased dramatically in nw turkey the two world wars and mismanagement of the land had important local effects by increasing deforestation and resulting in the present erosive conditions

major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator lagoa do caco ne brazil sediment samples collected along a 6 m core drilled in the deepest part of the lagoa do caco ne brazil have been investigated in order to determine source s and degradation conditions of the organic matter om with special emphasis on paleoenvironmental implications bulk organic geochemistry rock eval pyrolysis c n determination 13c and 15n measurement and petrography combined with sedimentological evidence and radiocarbon dates allowed to identify four major intervals documenting major environmental changes that occurred during the last 20 000 years the first interval dating back to the end of the last glacial maximum lgm contains well preserved om derived from higher plants this material was most probably produced in an ephemeral palustrine system and rapidly buried by sands this level is thought to have been deposited under relatively arid climate conditions associated with strong but episodic rainfalls between 19 240 and 17 250 cal years bp the climate appears to have been more humid and seasonality more pronounced as suggested by the presence of a permanent lake after a drastic environmental change dating back to 17 250 cal years bp the sediment became truly lacustrine with restricted mineral input and highly degraded higher plant derived organic matter after that a stepwise improvement in the preservation of om occurred as revealed by several pronounced shifts in the rock eval tps2 signal these changes could document abrupt climatically driven changes during the late glacial finally around 5610 cal years bp environmental conditions approaching those prevailing today were established minor climatic changes during the holocene were probably buffered by a high water table which might explain the lack of paleoenvironmental fluctuations

extension of the lac du bouchet palaeomagnetic record over the last 120 000 years a high resolution profile of the palaeomagnetic variations recorded in the upper 20 m of the lac du bouchet sedimentary sequence has been reconstructed from several parallel mackereth and livingstone type cores inter core correlations were established by comparing individual core profiles of magnetic susceptibility individual records of af cleaned directions were then stretched to a common depth scale and merged the mean record was then filtered and smoothed in order to reduce the background noise accelerator radiocarbon determinations and pollen analyses show that the sequence covers the last interglacial glacial cycle back to ca 120 kyr b p and allow to perform a depth to time transformation there is a noted absence of widely divergent directions back to 90 kyr b p it is estimated that the recorded signal a pdrm signal represents the geomagnetic input signal attenuated by about 19 it follows that the excursions reported for the laschamp and olby lavas if they existed at all must have been of rather short duration two durable excursions appear in narrow diameter sections at the base of three independent cores b c and d while a reverse to normal transition is possibly documented in the lowermost meter core d this part of the sequence is dated from the recognition of major climatic events related to the 18 o isotopic stages defined in the oceanic record between 116 and 95 kyr this introduces the possibility of new excursions at ca 104 and 95 kyr i e immediately after the recovery of normal polarity documenting the end of the blake event

factors affecting the accumulation of organic rich deposits in a modern avulsive floodplain examples from the cumberland marshes saskatchewan canada since the 1870s the saskatchewan river at the cumberland marshes east central saskatchewan canada has been undergoing progradational avulsion resulting in development of a 500 km2 avulsion belt the avulsion belt consists of an unstable network of active and abandoned channels splays and floodbasins some containing small shallow lakes fine grained deposits of varying total organic content toc are currently accumulating within floodbasins inside adjacent to and outside the avulsion belt the toc of these deposits depends on factors that control the amount of siliciclastic sediment received by floodbasins five factors that affect toc content are identified distance from an active channel position relative to the avulsion belt presence of alluvial ridges changes in local channel activity and developmental stage of avulsion a channel to basin trend of increasing toc is present at many locations reflecting greater suspended sediment loads received by near channel areas and locations within the avulsion belt generally accumulate sediment with lower toc than those adjacent to or outside the belt alluvial ridges locally act as barriers to floodbasin deposition and channel abandonment reduces suspended sediment to adjacent floodbasins both of which increase toc of sediment finally as avulsion wanes less siliciclastic sediment is distributed throughout the avulsion belt resulting in increased toc in the geological record such fine grained avulsion deposits are likely to appear as intervals of mudrock between thin beds of coal or carbonaceous shale formed from organic rich sediment deposited between avulsion events a succession that is common in many ancient alluvial strata

past hydrological events reflected in the holocene fluvial record of europe abstract a comprehensive database of radiocarbon dated fluvial units in great britain poland and spain has been compiled to investigate the relationship between environmental change flooding and holocene river dynamics following the methodology recently developed by macklin and lewin macklin m g lewin j 2003 river sediments great floods and centennial scale holocene climate change journal of quaternary science 18 101 105 radiocarbon dates in fluvial sequences that coincide with a modification in sedimentation rate or style have been highlighted allowing geomorphologically significant changes in holocene river activity to be identified data analysis has been undertaken at both national and sub national scales and on catchments of different size type and land use history multiple phases of higher flood frequency characterized by accelerated erosion and sediment deposition on floodplains are recognized and compared with a range of climate proxies the relative and varying roles of climate and land use on river dynamics are considered and the value of the database for reconstructing past hydrological events as well as for predicting river response to future environmental change is assessed

a record of late holocene environmental change from southern new england usa article i nfo article history received 28 march 2011 available online 31 august 2011 analyses of a sediment core from little pond located in the town of bolton massachusetts provide new insights into the history of environmental and ecological changes in southern new england during the late holocene declines in organic content and peaks in the abundance of isoetes spores indicate reduced water depth at 2900 2600 2200 1800 and 1200 800 calibrated years before present cal yr bp generally consistent with the timing of dry conditions in records from elsewhere in the northeastern united states the little pond pollen record features little change over the last 3000 yr indicating that the surrounding vegetation was relatively insensitive to these periods of drought the 1200 800 cal yr bp dry interval however coincides with increased abundance of castanea pollen suggesting that the expansion of castanea in southern new england may have been influenced by late holocene climatic variability

cumulative probability functions and their role in evaluating the chronology of geomorphological events during the holocene cumulative probability functions cpfs for large numbers of radiocarbon age determinations are increasingly being used by scientists as a methodology to discern environmental histories while the recent compilation of regional databases of the radiocarbon dating control for fluvial sediment sequences has been beneficial for identifying gaps in knowledge and stimulating new research there are a number of problems that critically undermine the use of these cpfs as sensitive hydroclimatic proxies i the cpf method is underpinned by the assumption that each radiocarbon measurement is a true age estimate for a point in time whereas each measured age in fact forms a scatter around the true age of the sample ii calibration of radiocarbon ages is responsible for much of the structure in cpfs and compounds the problem of scatter and smears the chronological control iii the databases incorporate multiple types of environmental changes differing chronological relationships between the 14c measurements and the dated events with pre dating dating or post dating chronological control each displaying variable length temporal lags all mixed together in the same analysis and iv the radiocarbon ages from individual case studies need to be more robustly tested before being incorporated into regional databases all these factors negate the value of cpfs as sensitive proxies of environmental change because peaks in probability for individual radiocarbon measurements are likely to be an incorrect estimate for the age of a geomorphological event and this problem is compounded by combining probabilities for multiple unrelated events in this paper we present a critical analysis of cpfs and their interpretation before suggesting alternative approaches to analysing radiocarbon geochronologies of geomorphic events which include i bayesian age modelling of river terrace development ii developing regional databases that test specific geomorphic hypotheses iii bayesian age modelling of palaeoflood records and iv analysis of sedimentation rates copyright 2011 john wiley sons ltd

probabilistic seismic hazard estimation for peninsular india peninsular india 10 0 n 28 0 n 68 0 e 90 0 e is one of the oldest and seismically most stable landmasses of the indian plate recent seismic history however shows that more than five damaging earthquakes with magnitudes greater than mw 6 0 have occurred in this region highlighting the importance of seismic hazard assessment for the region this article estimates the probabilistic seismic hazard associated with peninsular india with a zoneless approach incorporating the observed seismic activity and known geological characteristics of the region the seismicity parameters for hazard assessment have been estimated incorporating com pleteness criteria for various spans of the catalog data the spatial and temporal variations of seismic activity have been modeled using different source models seis mic source zones for the region have been defined on the basis of large scale geo logical features which are used for assigning the maximum possible earthquake potential due to the poorly known attenuation characteristics of the study region three appropriate attenuation models have been used for the estimation of ground motion parameters hazard maps for peninsular india have been developed using a convolution scheme based on weighting and incorporating various uncertainties in volved while modeling different parameters the comparison of the probabilistic seismic hazard map developed herein with the hazard map specified in the indian standards shows that the design parameters in the indian standards may significantly underestimate the seismic hazard in some regions of peninsular india

late holocene paleoenvironmental changes in northeast brazil recorded by organic matter in lacustrine sediments of lake boqueirao northeast brazil represents a key area in terms of holocene environmental changes in south america due to its distinct semi arid climate at near equatorial latitudes as well as to a wetter early and middle holocene paleoclimate in comparison with other south america regions which also experienced a reduced monsoon at that time we studied the lacustrine sediments of lake boqueirao which is located at 5 s latitude on the brazilian atlantic coast it is directly influenced by displacement of the intertropical convergence zone itcz a short 1 m core boqc0701 was collected at a 7 5 m water depth during a seismic survey organic matter om geochemical rock eval total organic carbon toc hydrogen index hi oxygen index oi and petrographical studies allowed us to distinguish five sedimentary intervals during the last 3 kyrs phase e 3000 to 2050 cal yr bp presents the largest toc hi and oi fluctuations in the entire core the most probable cause of these variations is a great instability in the lake level during this period phase d 2050 to 1830 cal yr bp is marked by an increase in sedimentation rate and a higher contribution from a well preserved om with an algal origin this was interpreted as a higher and more stable lake level during phase c 1830 to 1550 cal yrs bp low hi and high oi indicate the input of more oxidized degraded and detrital om reflecting a lower lake level in phase b 1550 to 1470 cal yr bp the om quality and quantity hi and toc indicate an algal contribution during phase a 1470 to 570 cal yr bp the high stability of the proxies may be due to a deep environment where om fluctuations are strongly buffered these changes in lake level can be compared with other tropical south america high resolution records a correspondence seems to exist between phases of low enso cool north atlantic ocean and boqueirao wet phases we did not encounter this same pattern during the last 1050 years during which the 1050 570 cal yrs bp interval was generally wet although probable fluctuations are buffered in our proxies while the north atlantic was warm mann et al 2009 a prolonged dryness occurred in lake boqueirao from 570 cal yrs bp until recent decades this phase corresponds to the little ice age characterized by a cooler north atlantic ocean mann et al 2009 these data indicate that the teleconnection pattern between the tropical atlantic enso and northeast brazil rainfalls has changed in the past

use of seismotectonic information for the seismic hazard analysis for surat city gujarat india deterministic and probabilistic approach surat the financial capital of gujarat india is a mega city with a population exceeding five millions the city falls under zone iii of the seismic zoning map of india after the devastating 2001 bhuj earthquake of mw 7 7 much attention is paid towards the seismic microzonation activity in the state of gujarat in this work an attempt has been made to evaluate the seismic hazard for surat city 21 170 n 72 830 e based on the probabilistic and deterministic seismic hazard analysis after collecting a catalogue of historical earthquakes in a 350 km radius around the city and after analyzing a database statistically deterministic analysis has been carried out considering known tectonic sources a further recurrence relationship for the control region is found out probabilistic seismic hazard analyses were then carried out for the surat region considering five seismotectonic sources selected from a deterministic approach the final results of the present investigations are presented in the form of peak ground acceleration and response spectra at bed rock level considering the local site conditions rock level peak ground acceleration pga and spectral acceleration values at 0 01 s and 1 0 s corresponding to 10 and 2 probability of exceedance in 50 years have been calculated further uniform hazard response spectrum uhrs at rock level for 5 damping and 10 and 2 probability of exceedance in 50 years were also developed for the city considering all site classes these results can be directly used by engineers as basic inputs in earthquake resistant design of structures in and around the city

lacustrine organic fluxes and palaeoclimatic variations during the last 15 ka lac du bouchet massif central france to assess the influence of climatic changes on organic lacustrine sedimentation two cores recovered from the centre of the lac du bouchet were studied by petrographical palynofacies and geochemical methods only core ldb h was used for estimation of the organic fluxes the variation of these fluxes with climo stratigraphic periods showed low organic fluxes during the lateglacial an increase at the beginning of the holocene a minimum at the end of the atlantic period resulting from the climatic cooling and a maximum at the end of the sub boreal related to the installation of the present climatic conditions

petrographical and geochemical study of modern lacustrine sedimentary organic matter lagoa do caco maranao brazil relationship between early diagenesis organic sedimentation and lacustrine filling abstract lagoa do caco is an equatorial lake in northeast brazil where the inter tropical convergence zone itcz enters the south american continent and so at a key position for deciphering quaternary climatic variation preliminary results have shown that the sedimentary organic matter om in the lake records the shifts in the itcz since the last glacial maximum the nature and fate of the om have been determined by studying surface sediments and potential om sources we present here the results of organic petrographic and rock eval pyrolysis assessments of the biological origin and preservation state of the om in modern sediments from two deep transects of the lake the results led us to understand how an oligotrophic lake has accumulated 6 m of om rich sediment during the last 20 kyr palaeoenvironmental studies have shown that the lake level fluctuated during this time our results explain the influence of lake bathymetric variation on early diagenesis and enable interpretation of the corresponding sedimentary om record which is dependent on the bathymetric variation

palynofacies as useful tool to study origins and transfers of particulate organic matter in recent terrestrial environments synopsis and prospects palynofacies analysis is based on transmitted light microscope study of organic constituents isolated and concentrated by acid and basic digestions published results of studies of present day terrestrial environments show that two complementary approaches successfully characterize particulate organic matter om from palynofacies analyses the first method is based on the identification and the quantification of some typical particles optical markers according to their origin i e aquatic or terrestrial their nature i e biogenic anthropogenic fossil and or their formation i e biodegradation combustion oxidation the second approach is based on the use of binary or ternary diagrams in order to define petrographical signatures from the relative proportions of significant organic constituents this approach can be used for tracking i changes in om composition during humification in soil profiles ii transport of reworked terrestrial particles iii diagenesis of peaty deposits or iv weathering of geological substratum the more advanced approach is based on the use of some predefined optical markers and their optical signatures to establish the relation between the om compositions palynofacies and their depositional environments in addition this kind of study aims to define a modern frame of reference that can be applied in paleoenvironmental reconstructions this paper combines a bibliographic review with previously unpublished data from palynofacies analyses the aim is to present some applied examples illustrating 1 the main approaches developed for characterization of the particulate om in surficial deposits and 2 the study of om transfers in terrestrial geosystems

bathymetric influences on the estuarine equilibrium length and adjustment time abstractlinear theories are extended to enable investigations of how exponentially convergent width and sloping bottom affect the sensitivity of estuarine equilibrium length and adjustment time this study focuses on the response to river forcing and considers a regime dominated by gravitational circulation but the results are generalizable for a range of forcing and bathymetric profiles the predicted equilibrium length and adjustment time compare favorably with numerical solutions from a width averaged model the main findings are that 1 convergent width and sloping bottom reduce the sensitivity of equilibrium length to river forcing the sensitivity is governed by a dimensionless parameter that measures the degree of width and depth changes sampled by the intrusion length hence the sensitivity is not a constant in a system but varies with forcing when discharge increases a shortened estuary experiences less bathymetric changes over its intrusion the sensitivity therefore increases progressively

past hydrological events reflected in holocene history of polish rivers abstract a database of 335 radiocarbon dates from holocene fluvial sediments in poland has been compiled each sample is characterized by 25 parameters all samples were grouped into one of 7 regions characterized by hydrological regime and one of 8 depositional environments statistical analysis was used to enhance the palaeoenvironmental data and 17 phases may be distinguished 10 of which have a distinct sharp peak abandoned paleochannels 149 dates clearly reflect the major wetter phases of the holocene an opposite picture is presented by overbank aggradation 86 dates connected mainly with expansion of agriculture preliminary correlations are made on peat bog records changes in vegetation lake water level rates calcareous tufa and speleothems growth landslides phases and debris flow phases these show many convergences explained by climatic fluctuations during the holocene

natural and anthropogenic channel pattern changes in the mid mountain valley during the late glacial and holocene polish uplands the purposes of this study are to describe the channel patterns of the czarna nida river quantitatively and to determine the factors that have had the greatest influence on the development of these patterns among the factors considered were natural climatic and anthropogenic prehistoric metallurgy river development was examined with a focus on valley floor formations channel geometry changes and depositional changes river widths and channel patterns were measured on aerial photographs and longitudinal profiles were prepared from topographic maps within the bottom of the valley in a single morphological level a row of inserts of various ages appears these inserts were formed by the river of different development of the channel macromeanders late glacial multichannel systems early holocene subatlantic small meanders holocene general tendencies of the late glacial and holocene erosion accumulation cycle are related to the well known principles for valleys of central europe and described in numerous studies they encompass dissection from the turn of the younger pleniglacial and late glacial younger dryas straightening and braiding of channels as well as holocene phases of intensified fluvial activity in the czarna nida river valley distinct traces of higher fluvial activity linked with development of prehistoric iron metallurgy in the roman period were recognised