palaeohydrology fires and vegetation succession in the southern baltic during the last 7500 years reconstructed from a raised bog based on multi proxy data we present the first 7500 yr long multi proxy record from a raised bog located at the southern baltic coast poland testate amoebae plant macrofossils pollen and microscopic charcoal were used to reconstruct environmental changes in pomerania northern poland kaszuby lakeland from a 7 m thick peat archive of st zki bog dated 5500 bc ad 1250 we obtained a record of proxies representing different spatial scales regional vegetation changed simultaneously with local vegetation and testate amoebae showed a pattern of change similar to that of pollen and plant macrofossils on the basis of the combined proxies we distinguished three hydroclimatic stages moist conditions 5500 3450 bc drier conditions with regionally increased fires up to 600 bc and again moist conditions from 600 bc onward during the drier interval a first climatic shift to wetter conditions at 1700 bc is indicated by regional pollen as the replacement of corylus by carpinus and locally by e g the increase of hyalosphenia elegans and mire plants such as sphagnum sec cuspidata furthermore we observed a correlation since 600 bc among the re expansion of carpinus after a sudden decline ca 950 bc increased peat accumulation increase of hyalosphenia species and fewer fires suggesting lower evapotranspiration and a stable high water table in the bog fagus started to expand after ad 810 gradually replacing carpinus which was possibly due to a gradually more oceanic climate though we cannot exclude human impact on the forests peat accumulation determined by radiocarbon dating varied with bog surface wetness the hydroclimatic phases found in st zki peatland are similar to moisture changes recorded in other sites from poland and europe this is the first detailed record of hydroclimatic change during the holocene in the southern baltic region so it forms a reference site for further studies on other southern baltic bogs that are in progress

holocene vegetation and hydroclimatic dynamics in se lithuania implications from a multi proxy study of the cepkeliai bog abstract due to the scarcity of reliable palaeoecological and climatic proxy records from the eastern baltic covering the holocene there has been increased interest for multi proxy studies in the region to detect local to regional environmental changes the cepkeliai wetland complex se lithuania provides an uninterrupted holocene sediment sequence which is used here to reconstruct palaeoenvironmental history in the southern part of the eastern baltic high resolution lithological loi magnetic susceptibility palaeobotanical pollen plant macrofossil tree rings isotopic 14c and geochemical data were employed to reconstruct the peculiarities of vegetation and hydroclimate dynamics as well as to discuss results in a local to regional context temporal lags of environmental reactions to holocene climatic warming were recorded both in lithostratigraphical and biostratigraphical data thus confirming regional significance of this phenomenon a deep meso to eutrophic basin influenced by high surface runoff and surrounded by early boreal forest existed at the site until about 11 300 cal bp thereafter immigration of thermophylous taxa such as ulmus since 10 700 10 800 cal bp corylus since 10 400 10 300 cal bp tilia and quercus after 9500 cal bp as well as changes in the limnic environment point to an amelioration of the environmental situation i e to a predominance of a warm and dry climatic regime instability of palaeobotanical and lithological records suggests that environmental anomalies of the early holocene occurred at about 11 200 11 000 cal bp 10 600 10 300 cal bp and 8200 7800 cal bp these anomalies are thus contemporaneous with the pronounced climatic shifts i e dry and cool intervals known at the continental scale an expansion of picea was facilitated by the 8200 7800 cal bp climatic shift whereas early establishment of alnus glutinosa suggests an onset of a wet interval 10 200 cal bp which was previously unknown in the area the stepwise lowering of the water table noted at about 7300 7200 and 6600 6700 cal bp with the termination of the lake phase and change to telmatic environment after 6100 cal bp proves the positive reaction of the site to the dry climatic reversals of the middle holocene following the decay of the broad leaved thermophilous forest after 4500 cal bp a cold climatic reversal favored the formation of a diverse mosaic like vegetation which was then replaced by homogenous pinus picea vegetation after 3400 cal bp the climatic and site specific factors have been playing a leading role in the development of the site whereas signals of human interference remain negligible

construction of a pluton evidence from an exposed cross section of the searchlight pluton eldorado mountains nevada a top to bottom cross section of the searchlight pluton is exposed in a large tilt block in the colorado river extensional corridor of southern nevada hornblende barometry and geologic relations indicate that the pluton was about 10 km thick extending from approximately 3 to 13 km depth the pluton is stratified with about 2 km of fine grained quartz monzonite below the roof 2 km of granite in the center and 6 km of coarser more mafic quartz monzonite at the bottom the lower unit has a pronounced magmatic foliation that was subhorizontal prior to tilting contacts between the units are gradational over a few centimeters to about 20 m geometry field relations and elemental and isotopic data suggest that the three units mark the terminal stages of evolution of magma that filled a very thick magma chamber the upper unit formed as a solidification front that migrated downward from the roof and the middle unit granite and the lower unit represent complementary segregated melt and crystal rich cumulate thus the dominant part of the pluton appears to have solidified in monotonic fashion from more or less uniform magma that was compositionally similar to the upper unit the basal quartz monzonite and the lower part of the granite enclose widely scattered synplutonic hornblende gabbro and diorite pods that range from centimeter to kilometer scale these rocks are commonly fine grained and formed as quenched mafic melts they are isotopically distinct from the main sequence and represent discrete injections into the magma chamber the mafic magmas were contaminated by but did not strongly affect the main sequence magma the nd and sr isotopic compositions of the main sequence magma are intermediate between those of regional crust and enriched mantle derived basalts like those represented by the mafic pods this suggests that the principal magma was a hybrid with about 60 mantle component and thus the pluton represents both addition to and internal reorganization of the crust

episodic intrusion internal differentiation and hydrothermal alteration of the miocene tatoosh intrusive suite south of mount rainier washington the miocene tatoosh intrusive suite south of mount rainier is composed of three broadly granodioritic plutons that are manifestations of ancestral cascades arc magmatism tatoosh intrusive suite plutons have individually diagnostic characteristics including texture mineralogy and geochemistry and apparently lack internal contacts new ion microprobe u pb zircon ages indicate crystallization of the stevens pluton ca 19 2 ma reflection pyramid pluton ca 18 5 ma and nisqually pluton ca 17 5 ma the stevens pluton includes rare statistically distinct ca 20 1 ma zircon antecrysts wide ranging zircon rare earth element ree hf u and th concentrations suggest late crystallization from variably evolved residual liquids zircon eu eu hf covariation is distinct for each of the reflection pyramid nisqually and stevens plutons although most tatoosh intrusive suite rocks have been affected by weak hydrothermal alteration and sparse mineralized veins cut some of these rocks significant base or precious metal mineralization is absent at the time of shallow emplacement each of these magma bodies was largely homogeneous in bulk composition and petrographic features but prior to final solidification each of the tatoosh intrusive suite plutons developed internal compositional variation geochemical and petrographic trends within each pluton are most consistent with differential loss of residual melt possibly represented by late aplite dikes or erupted as rhyolite from crystal rich magma crystal rich magma that formed each pluton evidently accumulated in reservoirs below the present level of exposure and then intruded to a shallow depth assembled by episodic intrusion the tatoosh intrusive suite may be representative of midsized composite plutonic complexes beneath arc volcanoes

extreme rainfalls in eastern himalaya and southern slope of meghalaya plateau and their geomorphologic impacts this paper presents the detailed rainfall characteristics of 3 key areas located in the eastern monsoon india the margin of darjeeling himalaya the margin of bhutanese himalaya and the cherrapunji region at the southern slope of meghalaya upland all these areas are sensitive to changes but differ in annual rainfall totals 2000 4000 mm 4000 6000 m and 6000 23 000 mm respectively and in the frequency of extreme rainfalls therefore the response of geomorphic processes is different also due to various human impact in the darjeeling himalaya the thresholds may be passed 2 3 times in one century and the system may return to the former equilibrium at the margin of western bhutanese himalaya in 1990s the clustering of three events caused an acceleration in the transformation and formation of a new trend of evolution especially in the piedmont zone in the cherrapunji of meghalaya region in the natural conditions the effects of dozens of extreme rainfalls every year were checked by the dense vegetation cover after deforestation and extensive land use the fertile soil was removed and either the exposed bedrock or armoured debris top layer protect the surface against degradation and facilitate only rapid overland flow a new sterile system has been formed

late quaternary paleoclimate in the eastern mediterranean region from stable isotope analysis of speleothems at soreq cave israel abstract the eastern mediterranean continental paleoclimate during the past 25 000 years was determined by a high resolution petrographic stable isotopic and age study of speleothems from soreq cave israel 18o 13c trends indicate that all speleothems older than 7000 yr formed under conditions that differ from those of today the period from 25 000 to 17 000 yr b p was characterized by the highest 18o and 13c values which indicate deposition at temperatures of 12 16 c annual rainfall of 300 450 mm and vegetation typical of a mixed c3 c4type from 17 000 to 10 000 yr b p deglaciation in northern europe 18o values dropped progressively correlative with warming 2 3 c and a gradual increase in precipitation a simultaneous decrease in 13c gives a range expected for c3 type vegetation this period also shows significant 18o and 13c spikes which are correlatable with global events e g heinrich events and the younger dryas stade the speleothems that grew between 10 000 and 7000 yr b p have a unique petrography showing irregular thin laminae of various colors and much detritus they have the lowest 18o corresponding to 1000 mm rain coupled with the highest 13c caused by flooding events which stripped the soil cover from 7000 to 1000 yr b p conditions became closer to those of today this study demonstrates that global events which were recognized in northern europe and north africa are also evident in the eastern mediterranean and are reflected principally by large changes in the rainfall rate

late pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at crater lake oregon abstract rhyodacite tephra and three lavas erupted 27 ka interpreted to be early leaks from the climactic magma chamber of mount mazama contain ubiquitous resorbed crystals antecrysts that were recycled from young granodiorite and related plutonic rocks of the same magmatic system the shallow composite pluton is represented by blocks ejected in the 7 7 ka climactic eruption that formed crater lake caldera plagioclase crystals in both rhyodacite and granodiorites commonly have cores with crystallographically oriented fe oxide needles exsolved at subsolidus conditions at least 80 of plagioclase crystals in the rhyodacite are antecrysts derived from plutonic rocks other crystals in the rhyodacite notably zircon also were recycled sims 238 u 230 th dating indicates that zircons in 4 granodiorite blocks crystallized at various times between 20 ka and 300 ka with concentrations of analyses near 50 70 110 and 200 ka that correspond to periods of dacitic volcanism dated by k ar u th ages of zircon from a rhyodacite sample yield similar results no analyzed zircons from the granodiorite or rhyodacite are pre quaternary zircon minimum ages in blocks from different locations around the caldera reflect ages of nearby volcanic vents and may map the distribution of intrusions within a composite pluton survival of zircon in zircon undersaturated hydrous magma and of fe oxide needles in plagioclase suggests that little time elapsed from entrainment of antecrysts to the 27 ka eruption of the rhyodacite the 27 ka rhyodacite is an example of young silicic magma that preserved unstable antecrysts from a known source early during growth of a large high level magma chamber in contrast the voluminous 7 7 ka climactic rhyodacite pumice is virtually lacking in zircon indicating dissolution of any granodioritic debris in the intervening period mineralogical evidence of assimilation may be destroyed in hot vigorously growing silicic magma bodies such as ultimately produced the climactic eruption of mount mazama

lake level and groundwater level changes in the lake gosciąz area poland palaeoclimatic implications lake gosci z is located in the zone of the maximum extent of the last ice sheet distinct lake terraces and deposits related to the lateglacial transgression do not exist detailed examination of annually laminated sediments and landforms revealed three phases of higher water level and storage represented by shore features by littoral deltaic and bog deposits and by higher rates of lacustrine deposition in the pelagic zone holocene lake transgressions at c 8 4 7 7 ka 2 5 2 3 ka and less distinct at 5 4 ka bp coincide with phases of higher flood frequency in poland and glacial advances in the alps because of sedimentation isolation from groundwaters encroachment by peatland and drainage of the lake lake volume during the last 12 ka diminished by as much as 70 and current water level fluctuations of about 1 2 m can change water storage by 20 25

the response of flood plain ecosystems to the late glacial and early holocene hydrological changes a case study from a small central european river valley abstract we use a range of environmental variables to explore the possible drivers influencing the biota especially the composition of aquatic invertebrates during the younger dryas yd and early holocene eh in different river valley sites a well developed meandering river and the confluence zone of headwater streams using pollen macrofossil cladoceran and chironomid as well as geochemical and lithological data as proxies for environmental factors i e water depth and temperature we attempt to show that these different sites display similar hydroclimatic signals especially floods the geochemical records in the studied valley are correlated with environmental factors such as the evolution of the vegetation the intensification phase of slope processes and fluvial activities cladocerans and chironomids potentially play important roles in the recognition of flood episodes in the study sites and any shift in their diversity and especially the co occurrence of planktonic sediment associated cladocerans with rheophilic chironomids could be valuable indicators of floods and flow episodes the variable changes in water levels at the sites reconstructed by the cladoceran based water depth model were positively associated with changes in lithophilic elements k na al mg and ti sio2 biog ter and fe mn and our estimates of the paleohydraulic parameters for the study sites are generally consistent with changes in the composition of aquatic invertebrates the recorded yd floods appear to be synchronous regardless of the size and the different geological and geomorphological settings of each part of the river catchment our investigation demonstrates that flood magnitude increases in the downstream direction along the valley the common increases in the water level at all study sites from the grabia river valley are significant from 12 400 to 12 200 and from 11 900 to 11 800 cal bp and are comparable with those from elsewhere in poland and europe

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

stable isotopes of holocene calcareous tufa in southern poland as paleoclimatic indicators abstract the isotopic composition of oxygen in freshwater calcareous tufa seems to be a sensitive indicator of past climatic changes results of measurements of c 18 o and c 13 c in tufa samples dated with the 14 c method are used to reconstruct holocene climatic changes in southern poland values of c 18 o obtained on tufa samples from four sites raclawka rzerzu nia trzebienice sieradowice representing different hydrodynamic conditions of tufa sedimentation seem to form a selfconsistent series these values with some simplifying assumptions concerning the course of tufa sedimentation were therefore used to estimate mean annual temperatures in the interval ca 9500 2000 yr b p when the resulting curve of thermal changes in southern poland is compared with changes of deposition and erosion of tuffaceous sediments and with results of other methods of reconstruction of paleoclimate in central europe a reasonable agreement among the different specific methods is seen

rare earth element 87 sr 86 sr and 143 nd 144 nd compositions of cenozoic orogenic dacites from baja california northwestern mexico and adjacent west texas evidence for the predominance of a subcrustal component dacitic lavas and ignimbrites were examined from seven localities that span the entire 700 km width of the mid to late cenozoic magmatic arc of northwestern mexico and adjacent west texas these rocks have remarkably similar ree patterns that are parallel in the heavy ree and have modest negative eu anomalies samples from three localities including baja california the sierra madre occidental and the chihuahuan basin and range have initial 87sr 86sr between 0 7044 and 0 7050 and nd near 0 0 1 0 these dacites are isotopically similar to associated basalts and they show no systematic isotopic variation that is correlated with age or composition of the basement there is no evidence that magmas parental to these dacites interacted significantly with continental crust samples form three other localites in the basin and range vary in initial 87sr 86sr from 0 7051 to 0 7070 and nd from about 1 to 2 the composition of these rocks reflects contamination of the parental magmas by relatively small amounts of precambrian crust collectively the dacites of this study show much less isotopic variation than do mesozoic granitoids farmer and depaolo 1983 and late cenozoic olivine tholeiites hart 1985 from similar transects of the western united states the distinctive source region for the magmas parental to the mexican dacites was relatively uniform isotopically but it was enriched in lil and hfs elements beneath the eastern basin and range

change in the frequency of extreme events as the indicator of climatic change in the holocene in fluvial systems abstract the transformation of natural systems of climatic origin in the holocene may be realised by a change in the type of extreme events or by a change in their frequency or by both the rapid warming at the younger dryas preboreal transition exemplifies a parallel drop in frequency and a change in the type of events several wetter phases of the holocene are characterised by rises in frequency of various types of extreme rainfalls the fragmentary records of events in the fluvial and slope systems coincide with smoothed variations in stable ecosystems and shifts of ecotonal zones such as tree line and lake levels

gas driven filter pressing in magmas most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less the buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization and this process of gas driven filter pressing assists the crystallization differentiation of magmas for gas driven filter pressing to be effective the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt these conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs gas driven filter pressing thereby adds fractionated melt to magma bodies gas driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons this process could also account for the production of voluminous crystal poor rhyolites

slope deposits as an indicator of anthropopressure in the light of research in central poland abstract results of research on neo holocene slope covers uncovered at archaeological sites in central poland are described in this paper geoarchaeological investigations have been undertaken in the ner river basin distinctive archaeological relicts of human activity document periods of intensive activity of human societies artefacts included within deposits play a very important role in correct recognition of the chronology of covers and ecofacts for reconstructions of environmental evolution the origin and development of slope covers have been correlated with anthropogenic changes of the natural environment two main phases of acceleration of slope processes have been recognised dated to the middle bronze age and to the late roman period slope deposits have been classified as deluvia deluvial slope wash deposits or colluvial deposits their features are most typical for deluvial sands and if they contain more humic matter for soil deluvia the deluvial covers have been deposited as an effect of moderately intensive slope wash processes accumulation of slope deposits has resulted from natural processes initiated by human impact during periods of intensive settlement and economic activity the slope cover sediments are the source for recognition of intensity of human impact and of economic activity of ancient societies and for distinct phases of hiatuses of settlement development the possibility of archaeological and palaeogeographical interpretations based on research on slope covers at archaeological sites is presented

reconstruction of hydrological changes between 7000 and 3000 bp in the upper and middle vistula river basin poland rhythmic fluctuations in the hydrological regime are demonstrated based on a review of records sensitive to relative climatic stability between 7000 and 3000 bp in the upper and middle parts of the vistula river basin central europe in the fluvial deposits and landforms these variations are very clear phases of higher flood frequency are dated 6600 6000 5500 4750 4500 4100 and 3250 3000 bp these phases coincide very well with sparse information on landslides data on high lake levels in the early subboreal phases of forest ecosystem transformation and finally the reaction of human cultures to these changes their rhythmicity correlates well with records from the alps and the alpine foreland but poorly with those from scandinavia this may be explained by changes in the zonal pattern of air mass circulation among the causes of the humid phases it is the frequency of volcanic eruptions which should be taken into consideration

late glacial and early holocene lake level fluctuations in ne poland tracked by macro fossil pollen and diatom records abstract late glacial and early holocene vegetation history and lake level fluctuations in ne poland were described based on high resolution plant macrofossils analyses and records of pollen diatoms and radiocarbon dates the development of lake kojle perty began in the allerod gi 1c cooling during the younger dryas gs 1 led to the development of communities of heliophyte herbaceous plants palaeobotanical and lithostratigraphical records demonstrate that abrupt climate changes at approximately 11 600 and 9450 cal bp resulted in distinct changes in the vegetation and water level of lake kojle perty climate warming in the younger dryas holocene transition 11 600 cal bp caused the development of the terrestrial vegetation dominated by cold deciduous forest betula and appearance of thermophylious aquatic plants typha latifolia najas marina and ceratophyllum demersum a gradual decrease in the lake level since 11 200 cal bp is evident from the appearance of plants from shallow lake environments potamogeton natans and hippuris vulgaris the low water levels since 10 700 cal bp resulting from increased temperature and evaporation caused the development of peat on limnic sediments the dry and warm climatic phase with lowest lake level in the lakes of ne poland were coeval with the expansion of temperate deciduous forests corylus and ulmus that commenced at approximately 10 500 cal bp a distinctive increase in lake levels at approximately 9450 cal bp is suggested by the development of rush plants such as cladium mariscus and aquatic plants such as najas marina chara sp and nuphar lutea in the shallow parts of lake kojle perty the increased lake levels correspond with the expansion of alnus glutinosa in north east ne poland our reconstructions of the vegetation development and lake level changes align with results from other studies in the region

shrimp u pb dating of the preeruption growth history of zircons from the 340 ka whakamaru ignimbrite new zealand evidence for 250 k y magma residence times the whakamaru group ignimbrites are products of one of the largest caldera forming eruptions from the central taupo volcanic zone new zealand ca 340 ka imaging of zircons separated from low silica rhyolite pumice from whakamaru group ignimbrite reveals a complex magmatic crystallization history some grains contain resorbed cores cores and rims of individual zircons were dated using the sensitive high resolution ion microprobe due to the high u contents of the zircons 206 pb count rates were sufficiently high to obtain 206 pb 238 u ages with precisions of 5 10 1 s using longer than usual 206 pb count times and this has allowed zircon core and rim ages to be distinguished zircon rim and outer growth zone ages range from within 1 s error of the eruption age to 449 20 ka whereas zircon cores produced ages to 608 20 ka indicating magmatic residence times exceeding 250 k y for some zircons the data are consistent with a prolonged evolution of the magma system over hundreds of thousands of years involving magma replenishment and mixing with residual phases of older silicic magma chambers in addition to crystal fractionation processes prior to eruption the study has shown that 206 pb 238 u dating using high resolution ion microprobe can be used to determine zircon preeruptive growth histories in quaternary lavas and pyroclastic rocks

allerod younger dryas lake temperatures from midge fossils in atlantic canada remains of freshwater midges are abundant in lake sediments and their species distributions are closely related to the surface water temperature of lakes their distributions thus provide a powerful tool for paleoclimatology the distribution of species in a core from splan pond in atlantic canada indicates that there were abrupt transitions in late glacial temperatures between warm and cold states the transitions are correlative with the well known warm allerod and cold younger dryas events in europe these data thus confirm the inference from palynological data that these events affected regions on both sides of the atlantic

younger dryas flood events a case study from the middle warta river valley central poland the weichselian late glacial sequence composed of younger dryas overbank deposits and the allerod younger dryas organic rich series from the warta river valley central poland were studied within a project including sedimentological criteria analysis of aquatic invertebrates cladocerans and chironomids remains and diatoms the well dated sequence of events on the floodplain mainly due to the determination of the age of in situ riparian forest provided a basis for a reconstruction of local conditions of palaeofloods in a wide context of global climatic changes at the weichselian decline the flash floods were largely affected by catchment topography forest destruction in response to the younger dryas cooling and permafrost reappearance the floods have been detected as the causative factors in a river style change

present day events and the evaluation of holocene palaeoclimatic proxy data abstract reconstruction of holocene climatic changes should be based on correlation of proxy data representing various sediment facies and ecosystem characteristics in addition to long term fluctuations in such data various extreme events such as downpours floods and slope failures whose type and frequency fluctuate in time have also been recorded events may reflect global regional or local changes examples from poland are used to illustrate general principles the observation of present day processes and their erosional or deposition effects linked with proxy indicators from the past should help in interpretation of environmental changes in the holocene and to inferences about the causative mechanisms

natural transformation of the romoty paleolake ne poland during the late glacial and holocene based on isotopic pollen cladoceran and geochemical data abstract romoty is the name of a sediment profile from the overgrown lake located in elk lakeland ne poland the sediment core which is 8 4 m in length documents the development of the reservoir since the melting of dead ice and formation of the lake basin i e before 13 000 years bp until it became overgrown with plants the characteristics of the sediments changed from mineral deposits on the bottom silty sands to biogenic deposits consisting of dark olive calcareous detritus gyttja and light calcareous gyttja with increasing carbonate content and to peat in the upper part based on the data chemical stable isotopes subfossil cladocera remains pollen we have distinguished three main stages of the evolution of romoty paleolake the first stage includes the formation of the lake basin in the late glacial and early holocene preboreal the second stage is characterized by the harmonic natural development of the romoty paleolake from the boreal to subboreal this stage coincides with a period of climatic warming and biogenic sediments accumulated in this reservoir at that time the third stage concerns the disappearance of the lake in the late holocene subatlantic the lake conditions declined and the reservoir completely filled with sediments and has transformed into a mire the characterization of each stage involves a description of environmental conditions occurring in the romoty paleolake particularly the cladocera community the chemical composition the temperature and trophy of the water the water level the nature of bottom sediments and the plants occurring in the reservoir and its surroundings the lowest water temperature occurred in the late glacial and preboreal periods since the boreal period gradual warming is observed and is expressed through a positive trend in both 18 o and 13 c and changes in both cladocera and plant compositions the lake was deepest at the beginning of the holocene as a result of dead ice melting supply of melt water lowering of the lake bottom and or increased precipitation change in atmospheric circulation the water level fell during the atlantic period additionally the cladoceran and non pollen palynomorph data indicate low trophy followed by an increase in the mesotrophic state human impact was documented only by a low occurrence of pollen grains of cerealia in the youngest sediments subatlantic period suggesting a low penetration by human groups of the area near the romoty paleolake

a multiproxy study of younger dryas and early holocene climatic conditions from the grabia river paleo oxbow lake central poland abstract a multi proxy reconstruction of water depth temperature and precipitation inferred from cladocera chironomidae and pollen assemblages has been obtained from wierczyna paleo oxbow central poland during the younger dryas yd and early holocene results suggest that the yd was relatively cold and comprised two main phases the first ca 12 500 12 000 cal yrs bp is characterized by a continental climatic regime and a decrease in winter temperatures and precipitation but an increase in spring summer precipitation the second phase ca 12 000 11 500 cal yrs bp was more mild with a variable continental climate an increase in summer and winter temperature a lengthening of the growing season and increased annual precipitation the reconstructed water level generally follows changes in spring and summer precipitation and length of growing season the frequency and timing of hydroclimatic oscillations at wierczyna show strong similarities to records from other sites in europe this confirms that oxbows and valley mire ecosystems respond to rapid climate change during the yd and early holocene this study therefore brings new insights into the effects of climate changes on river environments especially during the yd we also discuss the limitations of water depth temperature and precipitation reconstructions inferred from the studied biotic assemblages

time scales of pluton construction at differing crustal levels examples from the mount stuart and tenpeak intrusions north cascades washington deciphering the magmatic history of continental magmatic arcs in general and the growth history of individual intrusions in particular is key to understanding the complex history of magma generation segregation and transport that define the dynamics of crustal growth we utilize high precision u pb geochronology to resolve a detailed magmatic history from two composite intrusions the 2 4 kbar mount stuart batholith and the 7 10 kbar tenpeak pluton emplaced in the cretaceous north cascades arc this temporal framework provides a way to evaluate models of pluton growth that explain common features of intrusions such as concentric compositional zoning and internal magmatic contacts u pb zircon crystallization ages were obtained from 12 samples of the mount stuart batholith and 8 samples of the tenpeak intrusion representing the range of compositional diversity and geographical extent these dates indicate that the mount stuart batholith was constructed over a 5 5 m y time period that was punctuated by four intervals of high magma flux the durations of the high flux periods are short a few hundred thousand years relative to the duration of the batholith the consistent pattern of magmatic fabrics and the lack of distinct contacts in the batholith may be explained by the juxtaposition of melt rich and mush zones with subtle contacts between mineralogically and texturally similar tonalite and time transgressive magma fabrics in contrast the tenpeak intrusion was constructed over a 2 6 m y time period with magma influx distributed throughout the intrusive history and texturally distinct magma bodies the tenpeak intrusion lacks distinct age domains which suggests that any magma reservoir was smaller in size and potentially more ephemeral although the distinct age domains and discrete compositional and textural phases indicate that pluton growth occurred incrementally neither pluton bears resemblance to a purely end member incremental growth model whereby a pluton is constructed from hundreds to thousands of discrete magma pulses that have little if any interaction in particular ages from the youngest domain of the mount stuart batholith indicate that a melt rich magma reservoir of 520 km 3 existed over a 170 90 k y time span

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

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