u pb and pb pb zircon ages for arc related intrusions of the bolu massif w pontides nw turkey evidence for late precambrian cadomian age we present new u pb and pb pb radiometric age data from two tectono stratigraphic units of the regionally extensive bolu massif in the w pontides fragment n turkey a structurally lower unit sunnice group is cut by small meta granitic intrusions whereas the structurally higher unit com prises meta volcanic rocks ca surtepe fm cut by meta granitic plutons tullukirisand kapokaya plutons u pb single crystal dating of zircons from the kapokaya pluton yielded a concordant cluster with a mean 238 u 206 pb age of 565 3 1 9 ma zircons from the tullukirispluton affected by pb loss gave a 207 pb 206 pb age of 576 6 ma age late precambrian small meta granitic intrusions cutting the sunnice group yielded a less precise 207 pb 206 pb age of 262 19 ma early permian the older ages from the bolu massif confirm the existence of latest precambrian arc magmatism related to subduction of a cadomian ocean we infer that the bolu massif represents a fragment of a cadomian active margin cadomian orogenic units were dispersed as exotic terranes throughout the variscan and tethyan orogens and the bolu massif probably reached its present position prior to latest palaeozoic time our dating results also confirm that nw turkey was affected by hercynian magmatism related to subduction of palaeotethys as inferred for other areas of the pontides

40ar 39ar age constraints on cretaceous fossil bearing formations near the china north korea border abstract abundant mesozoic terrestrial plant fish and invertebrate fossils have been discovered from the lishugou formation and the underlying xiaolin formation in the eastern liaoning province of ne china since the 1970s these discoveries have great potential for substantially increasing our knowledge on the evolution of paleoecosystems and paleoenvironments in east asia however previous geological and geochronological studies for these fossil bearing formations are rare because the fossil outcrops are near the border between china and north korea here we present robust 40ar 39ar ages of 99 9 0 4 ma for one sample from the lishugou formation and 109 1 0 2 ma and 122 4 0 2 ma for two samples from the upper and lower parts of the xiaolin formation from dandong city liaoning china our new age data indicate that the lishugou and xiaolin formations were deposited contemporaneously with the jiufotang formation from the classic jehol outcrops in western liaoning therefore our results provide an accurate age calibration for the fossils discovered from the liaodong peninsula and suggest that the hypothesis of the jehol migration should be reappraised

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

late middle pleistocene interglacial deposits at upper strensham worcestershire england pleistocene deposits containing the disarticulated skeleton of a mammoth and associated faunal and floral remains were discovered in july 1990 at upper strensham worcestershire the environmental evidence from the fauna and flora together with limited geological evidence indicates that the deposits accumulated within a low energy fluvial environment with a surrounding marsh and restricted tree cover on or close to the floodplain the patchy occurrence of trees in a species rich grassland is discussed and the climatic significance of the fauna and flora is considered the strensham site lies within the valley of the river avon which is known to contain at least five altitudinally distinct river terraces the deposits at strensham lie beneath a terraced surface that cannot be accommodated within the existing framework of terrace development in the valley and evidence is presented which may suggest that these deposits form a previously unrecognised fluvial unit the strensham member of the avon valley formation amino acid age estimates from shells taken from the fossiliferous sediments of the strensham member suggest a correlation with oxygen isotope stage 7 this correlation suggests that the temperate deposits at this site should be correlated with the temperate phase recorded at marsworth buckinghamshire and stoke goldington in the vafley of the great ouse journal of quaternary science

geochemistry and u pb protolith ages of eclogitic rocks of the asis lithodeme piaxtla suite acatlan complex southern mexico tectonothermal activity along the southern margin of the rheic ocean recent data indicating that the piaxtla suite acatlan complex southern mexico underwent eclogite facies metamorphism and exhumation during the devono carboniferous suggest an origin within the rheic ocean rather than the iapetus ocean the asis lithodeme piaxtla suite consists of polydeformed metasediments and eclogitic amphibolites that are intruded by megacrystic granitoid rocks u pb zircon data indicate that the metasediments were deposited after c 700 ma and before intrusion of c 470 420 ma quartz augen granite the metasedimentary rocks contain abundant mesoproterozoic detrital zircons c 1050 1250 ma and a few zircons in the range of c 900 992 and c 1330 1662 ma their geochemical and sm nd isotopic signature is typical of rift related passive margin sediments derived from an ancient cratonic source which is interpreted to be the adjacent mesoproterozoic oaxacan complex megacrystic granites were derived by partial melting of a c 1 ga crustal source similar to the oaxacan complex amphibolitic layers exhibit a continental tholeiitic geochemistry with a c 0 8 1 1 ga source t dm age and are inferred to have originated in a rift related environment by melting of lithospheric mantle in the ordovician this rifting may be related to the early ordovician drift of peri gondwanan terranes e g avalonia from gondwana and the origin of the rheic ocean

cambrian ordovician depositional sequences in the middle east a perspective from turkey abstract in southern turkey taurus chain or taurides and southeastern turkey border folds of the arabian plate nearly complete cambrian to ordovician successions are preserved four major sedimentary sequences are defined according to the main transgressive events and the subsequent shelf progradations these sequences allow us to link the turkish mostly distal lower palaeozoic detritals to the more proximal arabian formations in spite of contrasting facies the lower palaeozoic development is outlined through four successive steps defined in southern turkey 1 initiation of a cratonic platform regime terreneuvian i e earliest cambrian depositional sequence 1 with fluviatile conglomerates and red bed sediments associated with volcanics 2 development of a stable marine platform late terreneuvian to early ordovician depositional sequences 2 and 3 including widespread but diachronous middle cambrian carbonates and subsequent storm dominated detritals 3 tectonic instability middle ordovician leading to a new palaeogeography on the gondwana platform with the differentiation of a sag basin bedinan qasim depocenter lower part of depositional sequence 4 and 4 glaciation latest ordovician upper part of depositional sequence 4 identified by glaciomarine deposits forming the hirnantian glacial record this thick 2000 m detrital succession records a first order long term subsidence driven cambrian to ordovician transgressive trend and includes second order sequences reflecting interactions between global eustasy and tectonic instability on a larger scale the identification of recurrent sequence stratigraphic features with similar trends in the cambrian ordovician successions on the arabian platform implies that a former location of the taurus domain cannot be situated in the present day eastern mediterranean area but should lie directly north of the arabian platform this location places southern turkey at the junction between the north african segment of the gondwana siliciclastic shelf to the west present day coordinates and the eastern arabian segment in good agreement with mixed faunal signatures from both areas primary control of the tectonostratigraphic development of southern turkey during the lower palaeozoic may be a forced evolution from arc platform to rift drift transitions cordilleran model that has migrated progressively eastwards from the avalonian domain along the northern gondwana margin to the arabian domain throughout the lower palaeozoic

early palaeozoic rift related magmatism in variscan europe fragmentation of the armorican terrane assemblage early palaeozoic bimodal rift related magmatism is widespread throughout much of the variscides of europe it is traceable from the polish sudetes to nw iberia granitic plutonism generally predates cambro ordovician bimodal magmatism in the n bohemian massif this early palaeozoic granitic plutonism was generated by partial melting of cadomian basement whereas contemporaneous alkali granites with a mantle component are typical of the nw iberian massif silurian devonian mafic magmatism in the n bohemian massif massif central and nw iberian massif is partly preserved as obducted ophiolites compositional diversity displayed by cambro ordovician mafic magmatism can be accounted for by interaction between a spreading centre and an upwelling mantle plume this indicates that combined tensional forces and mantle plume convection assisted the early palaeozoic dispersal of terranes from the n gondwana margin continued fragmentation resulted in development of an archipelago of related terranes separated by a network of seaways and formation of oceanic crust

palynostratigraphy of some pleistocene deposits in the western alps a review in the alps interglacial and interstadial deposits are rarely preserved due to the intense erosive effect of glaciers in the valleys fortunately some outcrops and cored sequences located in the field area ranging from lyon to evian provided sedimentary profiles datable by palynostratigraphy in a highly documented geomorphological context an overview of several palynological sequences studied in this large area is proposed and their position in a general chronostratigraphical pattern is discussed particular attention is paid to palynostratigraphical evidence whose relevance is tested with systematic comparisons with long reference european pollen sequences spanning several glacial cycles minimum ages are suggested for non glacial episodes corresponding to the deposits studied

climatic reconstruction in europe for 18 000 yr b p from pollen data an improved concept of the best analogs method is used to reconstruct the climate of the last glacial maximum from pollen data in europe in order to deal with the lack of perfect analogs of fossil assemblages and therefore to obtain a more accurate climate reconstruction we used a combination of pollen types grouped according to plant phenology and present climate constraints rather than pollen percentages for each individual taxon the distribution of pollen taxa into plant functional types pfts is aimed to reflect the vegetation in terms of biomes which have a wider distribution than a species the climatic variables are then calibrated on these pfts using an artificial neural network technique the use of pfts allowed us to deal with situations where pollen assemblages have only partial modern analogs the method is applied to the glacial steppic vegetation in europe using 15 pollen records north of the pyrenees alps line the reconstructed temperatures were lower than today 30 10 degrees c for the temperature of the coldest month t c and 12 3 degrees c far the annual mean t ann south of that line t c and t ann anomalies were respectively 15 5 degrees c and 10 5 degrees c the available moisture index and annual precipitation were also lower than present 60 20 north of mediterranean sea 800 100 mm for precipitation in italy and greece the available moisture was 20 lower with a precipitation anomaly of ca 600 200 mm southward the moisture index was close to that at present 20 and precipitation was lower 300 300 mm c 1998 university of washington

origin of the rheic ocean rifting along a neoproterozoic suture the rheic ocean is widely believed to have formed in the late cambrian early ordovician as a result of the drift of peri gondwanan terranes such as avalonia and carolina from the northern margin of gondwana and to have been consumed in the devonian carboniferous by continent continent collision during the formation of pangea other peri gondwanan terranes e g armorica ossa morena northwest iberia saxo thuringia moldanubia remained along the gondwanan margin at the time of rheic ocean formation differences in the neoproterozoic histories of these peri gondwanan terranes suggest the location of the rheic ocean rift may have been inherited from neoproterozoic lithospheric structures formed by the accretion and dispersal of peri gondwanan terranes along the northern gondwanan margin prior to rheic ocean opening avalonia and carolina have sm nd isotopic characteristics indicative of recycling of a juvenile ca 1 ga source and they were accreted to the northern gondwanan margin prior to voluminous late neoproterozoic arc magmatism in contrast sm nd isotopic characteristics of most other peri gondwanan terranes closely match those of eburnian basement suggesting they reflect recycling of ancient 2 ga west african crust the basements of terranes initially rifted from gondwana to form the rheic ocean were those that had previously accreted during neoproterozoic orogenesis suggesting the rift was located near the suture between the accreted terranes and cratonic northern gondwana opening of the rheic ocean coincided with the onset of subduction beneath the laurentian margin in its predecessor the iapetus ocean suggesting geodynamic linkages between the destruction of the iapetus ocean and the creation of the rheic ocean

centennial scale vegetation dynamics and climate variability in se europe during marine isotope stage 11 based on a pollen record from lake ohrid abstract to better understand climate variability during marine isotope stage mis 11 we here present a new centennial scale resolution pollen record from lake ohrid balkan peninsula derived from sediment cores retrieved during an international continental scientific drilling program icdp campaign our palynological data augmented by quantitative pollen based climate reconstructions provide insight into the vegetation dynamics and thus also climate variability in se europe during one of the best orbital analogues for the holocene comparison of our palynological results with other proxy data from lake ohrid as well as with regional and global climate records shows that the vegetation in se europe responded sensitively both to long and short term climate change during mis 11 the chronology of our palynological record is based on orbital tuning and is further supported by the detection of a new tephra from the vico volcano central italy dated to 410 2 ka our study indicates that mis 11c 424 398 ka was the warmest interval of mis 11 the younger part of the interglacial i e mis 11b 11a 398 367 ka exhibits a gradual cooling trend passing over into mis 10 it is characterized by considerable millennial scale variability as inferred by six abrupt forest contraction events interestingly the first forest contraction occurred during full interglacial conditions of mis 11c this event lasted for 1 7 kyrs 406 2 404 5 ka and was characterized by substantial reductions in winter temperature and annual precipitation most notably it occurred 7 ka before the end of mis 11c and 15 ka before the first strong ice rafted debris event in the north atlantic our findings suggest that millennial scale climate variability during mis 11 was established in southern europe already during mis 11c which is earlier than in the north atlantic where it is registered only from mis 11b onwards

insect evidence for environmental and climate changes from younger dryas to sub boreal in a river floodplain at st momelin st omer basin northern france coleoptera and trichoptera the st omer area is a rapidly subsiding basin in which long sequences of weichselian and holocene sediments are preserved a core 21 m long extracted from near st momelin about ten km north of st omer has been analysed for insect fossils four faunal units smi 1 to smi 4 are described based on changes in both coleopteran and trichopteran assemblages the basal faunal unit smi 1 includes many cold adapted species and is attributed to the younger dryas chronozone the transition to holocene sedimentation was abrupt faunal units smi 2 to smi 4 are attributable to the holocene they lack all the cold adapted species found in the basal sediments and in their place are insect assemblages very similar to the present day fauna in this region this sequence spans the period from the pre boreal to the sub boreal faunal unit smi 2 includes insects from the pre boreal the boreal and most of the atlantic periods this fauna was fairly sparse and made up largely of species living in freshwater habitats the faunal unit smi 3 includes the insect assemblages from the late atlantic to sub boreal periods this fauna was much more diverse and indicated a river meandering across its floodplain and bordered by a mature forest at a time when the climate was warmer than that of the present day this chronostratigraphical sequence of events is supported by 14c dates and by lithological data thermal climatic conditions have been quantified using the mutual climatic range method during the younger dryas period smi 1 tmax the mean july temperature was in the region of 10 c and tmin the mean temperature of january february was close to 11 12 c after the sudden climatic amelioration at the start of the holocene smi 2 to smi 4 tmax probably fluctuated throughout the early holocene between 16 c to 19 c and tmin between 0 c to 5 c figures that are close to those of the present day this climatic history is compared with others in northern europe

the importance of along margin terrane transport in northern gondwana insights from detrital zircon parentage in neoproterozoic rocks from iberia and brittany abstract detrital zircons from late neoproterozoic rocks of the peri gondwanan cadomian belt of sw iberia and north armorican domain of brittany record neoproterozoic ca 860 550 ma palaeoproterozoic ca 2300 1800 and archaean ca 3300 2600 ma u pb ages the absence of mesoproterozoic zircons suggests that these terranes evolved in a peri w african realm this is in contrast to other western european terranes that preserve mesoproterozoic zircons and are likely to have evolved in a peri amazonian realm such a contrast in detrital zircon populations coupled with the presence of mesoproterozoic zircons in the ordovician armorican quartzite deposited in a peri african platform is interpreted to record along margin terrane transport the change in provenance suggests that subduction was replaced by transform faults that juxtaposed amazonia derived terranes against w africa derived terranes to form the avalonia and armorica microcontinents subsequent extension along the margin resulted in the birth of the rheic ocean and the outboard drift of avalonia

early and middle pleistocene vegetation history of the medoc region southwest france pleistocene deposits together with their pollen plant macrofossil foraminiferal dinoflagellate and coleopteran remains from five sites along the atlantic coast of the medoc peninsula are described and discussed sediments making up the negade formation are shown to have been laid down under either estuarine or lagoonal conditions when closed quercus pinus tsuga canadensis regional woodland existed comparison with plant records from the netherlands indicates that these deposits are most likely attributable to either the early pleistocene bavel interglacial marine oxygen isotope stage mis 31 or an interglacial of the waalian mis 37 49 or tiglian mis 63 79 in addition clays assigned to the argiles du gurp sensu stricto were similarly deposited in either an estuary or lagoon which subsequently was cut off from the sea a freshwater lake with vegetation dominated by azolla filiculoides then developed this was succeeded by reedswamp and an organic mud termed lignite in the corresponding french stratigraphical records formed regional quercus abies woodland was replaced by one with pinus dominant and pterocarya a minor component comparison with plant records from france and other parts of europe suggest that the clays and organic mud might be correlated with the holsteinian praclaux interglacial mis 11c copyright 2003 john wiley sons ltd

superposed hercynian and cadomian orogenic cycles in the ossa morena zone and related areas of the iberian massif polyphase ductile deformation and metamorphism in the ossa morena zone of the iberian massif are related to a complex evolution including two major tectonothermal episodes of cadomian late proterozoic to early cambrian and hercynian age middle to late paleozoic petrological structural and geochronological data attest to a number of tectonic episodes in the 620 480 ma interval the model presented for this orogeny comprises stages of volcanic arc generation backarc extension tectonic inversion crustal thickening and cratonization in an andean type continental margin the hercynian cycle began in the early paleozoic with episodes of continental rifting orogenic events occurred in the 390 300 ma interval and affected both the cadomian basement which was heterogeneously reworked and overprinted and the paleozoic cover hercynian regional metamorphism was generally of low grade high pressure assemblages and thermal domes developed locally and were related to subduction and late extensional events the geodynamic model proposed for the cadomian and hercynian orogenies and the correlation with comparable areas from pre mesozoic massifs elsewhere in western europe account for the geodynamic scenarios that drove the fate of cadomian terranes

neoproterozoic cambrian synsedimentary magmatism in the central iberian zone spain geology petrology and geodynamic significance petrographic geochemical and field studies in low grade metamorphic areas ciudad rodrigo hurdes sierra de gata domain crhsg central western spain show that neoproterozoic lowermost cambrian series in the central iberian zone ciz record two kinds of provenance sources including 1 detrital material derived from recycled orogens and 2 a cadomian coeval juvenile contribution that governs their isotopic signature evidence of magmatism contemporaneous with neoproterozoic cambrian sedimentation is provided by the presence of coherent massive volcanic rocks metabasalts metaandesites and metarhyolites volcaniclastic shales sandstones conglomerates and breccias the appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession reinforces this evidence although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity some of them display calc alkaline affinity different trace element ratios such as sm nd nb yb and ta yb suggest a magmatic evolution in the same tectonic setting the geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the neoproterozoic lowermost cambrian successions in the ciz in particular the relatively high end t values and the high range of f sm nd ratios are consistent with an active margin during the neoproterozoic early cambrian the existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks all of these traits favour a geodynamic model in which the iberian cadomian segment represented in the ciz would have been part of an active northern margin of gondwana with an associated magmatic arc and related basins during neoproterozoic lower cambrian times a proposed link between the ossa morena and the central iberian zones might account for late cadomian pull apart basins developed on both sides of the magmatic arc sharing the same scenario and involving similar magmatic activity during the neoproterozoic cambrian transition

early ordovician orogenic event in galicia nw spain evidence from u pb ages in the uppermost unit of the ordenes complex new u pb data zircon monazite and rutile obtained from rocks of the uppermost allochthon in the variscan belt of nw spain indicate that the hangingwall to the suture includes an allochthonous unit with a pre variscan tectonothermal evolution this evolution is characterised by an early ordovician 498 500 ma bimodal magmatism followed almost immediately 493 498 ma by a barrovian style metamorphism up to the granulite facies the metamorphism subsequent to the igneous intrusions requires convergence and crustal thickening in order to generate the barrovian facies pattern shown by the lithologies of the uppermost allochthon the almost coeval magmatism and metamorphism and the chemistry of the metabasites suggest an accretionary complex probably related to a volcanic arc as the most probable setting for the origin of the uppermost unit the implications of the existence of early ordovician convergent plate boundaries are discussed in the context of gondwana laurentia avalon interactions

continental mafic magmatism of different ages in the same terrane constraints on the evolution of an enriched mantle source the antigonish highlands nova scotia are within the avalon terrane of the northern appalachians and contain four distinct episodes of rift related magmatism neoproterozoic cambrian middle ordovician and late devonian all four magmatic suites are composed of basalts and subordinate crustally derived felsic rocks the mafic rocks of these suites which do not appear to be significantly contaminated by continental crust display similar geochemical and sm nd isotopic characteristics consistent with an enriched mantle source that was metasomatically enriched prior to the oldest rifting event probably between 0 8 and 1 1 ga these data also imply that the avalonian crust and its subcontinental lithospheric mantle remained coupled during four magmatic events because the earliest phases of magmatism occurred when avalonia was located along the gondwanan margin and the latest phases after avalonia accreted to laurentia the coupling of crust and mantle in the antigonish highlands suggests that the migration of avalonia did not completely detach its lithospheric mantle from its crustal cover this study demonstrates the importance of comparing magmatism of different ages in the same terrane

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

evolution of late neoproterozoic to early paleozoic tectonic elements in central and southeast european alpine mountain belts review and synthesis abstract late neoproterozoic to early paleozoic cadomian tectonic elements are widespread in the southeastern alpine mediterranean mountain belts with discontinuous exposure extending from the alps to the menderes massif in turkey the sequences include voluminous plutonic island and continental arc successions some ophiolites of variable late neoproterozoic and cambrian to early ordovician ages high to medium grade metamorphic sequences and subordinate metasediments geological and geochronological data suggest that these cadomian elements partly experienced tectonothermal activity including metamorphism and magmatism between ca 650 and 600 ma followed by further i and s type plutonism in an andean type continental margin setting ca between 570 and 520 ma subsequently a major rift zone developed which resulted in continental stretching and subsequent formation of a back arc basin which is dated as late cambrian rifting is followed by oceanic spreading which commenced ca at the cambrian ordovician boundary possibly in a back arc setting this tectonic scenario suggests that alpine mediterranean cadomian tectonic elements were accreted to gondwana during early cadomian events ca 600 650 ma subsequently they were likely part of a long lasting outer subduction zone of gondwana at the margin of a panthalassa type ocean during late neoproterozoic iii and cambrian due to back arc spreading continental pieces started to split off from gondwana ca at the cambrian ordovician boundary

the climate in western europe during the last glacial interglacial cycle derived from pollen and insect remains using the pollen sequence of la grande pile xx france we review problems with the application of transfer functions in paleoclimatic reconstructions one of them is to find modern analogues for the herbaceous vegetation of the cold periods we propose a method to distinguish between steppes and tundra vegetations for which the moderns are only partial analogues of the glacial periods another method to solve these problems is based on constraining by insect remains the two methods provide coherent reconstructions the results are also compared with other paleodata there is a good correlation with the six cold heinrich events between 70 and 15 ka b p a cooling event during the eemian period marked by high percentages of taxas at about 125 ka b p needs still to be correlated with high resolution ocean and ice cores

an attempt at correlation between the velay pollen sequence and the middle pleistocene stratigraphy from central europe abstract long continuous lacustrine sequences constitute on the continent a precious tool for coupling the long term continental environmental changes with deep sea and ice core records using the count from the top method moreover they can contribute to long distance correlation on the continent itself and thus help to classify discontinuous sedimentary records palynostratigraphical correlation is proposed here between the velay long sequence and the late middle pleistocene series from central europe with special attention to temperate episodes the similarities between the praclaux and the holsteinian interglacial suggest that they are both contemporaneous with marine isotopic stage mis 11 even if absolute dates are still divergent the evidence of two major warm periods with an interglacial type of vegetation between the holsteinian and the eemian is confirmed by the velay record

early ordovician continental break up in variscan europe ndsr isotope and trace element evidence from bimodal igneous associations of the southern massif central france abstract the high grade marvejols group and the low grade albigeois cevennes sedimentary sequence contain bimodal igneous rocks of early ordovician age which are representative of a widespread thermal event in the european variscides comparison of their nd sr isotope and trace element characteristics provides additional evidence for their origin in an ensialic extensional setting as an alternative to the back arc model proposed by previous authors we propose that these associations record a continental break up episode unrelated to contemporaneous subduction in this model the widespread early paleozoic bimodal magmatism marks the birth of a mid european oceanic arm we propose that the break up was controlled by both transtensional processes and mantle plume activity high grade associations such as the marvejols group and low grade bimodal associations such as the albigeois cevennes might be regarded as representing opposite rifted passive margins the northern marvejols type margin was involved in a late ordovician silurian subduction like process with hp ht metamorphism in contrast the southern albigeois cevennes margin remained largely unaffected possibly as part of the overriding plate of the subduction zone pseudo calc alkaline signatures unrelated to subduction processes may occur in magmatic rocks associated with continental break up episodes in this case negative nb anomalies are produced by the addition of crustal components enriched in th and lree relative to nb this inferred alternative origin of nb anomalies has important bearing on the paleogeodynamic settings based on geochemical data

zircon u pb geochronology of paragneisses and biotite granites from the sw iberian massif portugal evidence for a palaeogeographical link between the ossa morena ediacaran basins and the west african craton

first evidence of in situ eemian sediments on the high plateau of evian northern alps france implications for the chronology of the last glaciation a 2 m profile of organic sediments interbedded between two tills was taken from the evian high plateau at hameau de maravant 860 m a s l haute savoie western alps france pollen plant macrofossils and insect remains were used to reconstruct the local palaeoenvironment which consisted of a moss and carex mire surrounded by a dense abies and picea mixed forest pollen and macrofossil data indicate that this peat layer was deposited at the end of the eemian interglacial the lower till should therefore be assigned to the penultimate glaciation and the upper till to the maximum extent of the rhone glacier during the wurm a comparison of the results with previous studies carried out in the geneva area and other alpine valleys has yielded a detailed reconstruction of the past fluctuations of the rhone glacier 1 a first early lower wurmian advance reaching the region around lyon 2 a subsequent retreat of ice 3 a second moderate readvance restricted to the surroundings of geneva followed by a final deglaciation a continuous lacustrine sequence has been obtained from the nearby roseire peat bog 890 m a s l pollen and radiometric results show the establishment of a former palaeolake during the upper pleniglacial probably before ca 22 450 850 cal years bp thus implying that the high plateau was ice free from that time these new data appear to suggest that the maximal extension of the rhone glacier occurred prior to the last glacial maximum ois 2 and according to a well documented geomorphological context probably during the lower wurmian pleniglacial

middle pleistocene deposits at la cote val de lans isere department france plant macrofossil palynological and fossil insect investigations plant macrofossils pollen and spores and coleoptera remains were analysed from high altitude lacustrine interglacial deposits collected from la cote val de lans isere western french alps the investigation concentrated on the second half of the temperate stage locally called the la cote interglacial stage palaeoecological palaeoenvironmental and quantitative climatic reconstructions for the termination of the interglacial period and the onset of cold conditions are presented because the different fossils were affected in varying ways by taphonomic processes they provide a range of complementary data about the palaeoenvironment and illustrate the importance of multi disciplinary studies as conditions became cooler at the end of the temperate stage the lake levels fluctuated and the water s trophic status changed the occurrence of pterocarya and the dominance of abies support a correlation with the temperate holsteinian stage oxygen isotope stage 11 at the top of the core an interstadial event characterised by pinus picea and betula is represented this could have occurred either directly after the la cote interglacial stage or the event may have occurred during the following cold la bourns stage after a hiatus the climate fluctuations represented at the end of the la gate interglacial stage in the val de lans basin prompt comparisons with the end of the eemian stage late pleistocene and suggest that such oscillations are characteristic for the end of temperate stages an understanding of the changes represented here aids the evaluation of present trends as we possibly enter the final phases of the holocene stage sites of this age and located at this altitude are rare in europe therefore it is proposed that the la cote site should be considered as a high altitude alpine parastratotype for the holsteinian stage in western europe c 2000 elsevier science b v all rights reserved

geological constraints on the paleozoic tectonic evolution of tectonostratigraphic terranes in the iberian massif abstract the presence of oceanic paleozoic sequences in the iberian variscan fold belt is used to identify and separate suspected exotic terranes from a reference iberian autochthon terrane which constitutes the greater part of it in this paper the relevant data characterizing the pre accretionary evolution of the paleozoic iberian terranes are presented as well as the available evidence concerning the accretionary process itself emphasis is placed on the analysis of the sedimentary igneous and structural expression of the major events which affected the iberian terranes before during and after their amalgamation the main conclusions of such an analysis may be summarized as follows 1 a recognition of rift and passive margin stages in all the iberian massif terranes during the early paleozoic 2 b late paleozoic accretion of the exotic terranes to the iberian autochthon via a long and complex process variscan orogeny which involved initial subduction underneath the latter and eventual obduction followed by oblique collision of a promontory the iberian autochthon northwestern margin with a northwestern continental block this latter process could account for the large scale crustal imbrication shown by the northern branch of the orogen coeval with predominant strike slip faulting in the southern branch as well as with the formation of the typical arcuate shape of this orogenic belt major present uncertainties relate to the palinspastic provenance of continental suspect terranes and their correlation with similar units in other circum atlantic paleozoic orogens a discussion and speculations on this subject are dealt with in the final section of this paper

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

space and time in the tectonic evolution of the northwestern iberian massif implications for the variscan belt recent advances in geochemical studies of igneous rocks isotopic age data for magmatism and metamorphism quantitative pressure temperature p t estimates of metamorphic evolution and structural geology in the northwestern iberian massif are integrated into a synthesis of the tectonic evolution that places the autochthonous

the lacustrine deposits of fornaci di ranica late early pleistocene italian pre alps stratigraphy palaeoenvironment and geological evolution an interdisciplinary investigation of the pleistocene clay succession of fornaci di ranica italian pre alps aimed to reconstruct the palaeoenvironmental history and its chronostratigraphic position and to consider the implications for the quaternary evolution of the southern alpine borderland near the early middle pleistocene transition a detailed survey of quaternary deposits in boreholes and exposed sections provided a complete record of the basin the most complete core was analyzed for palynology and magnetic properties plant macrofossils were obtained by flotation pollen and spectrometric analysis allowed a precise stratigraphic placement of a moose antler and braincase kept in museum collections the basin originated from fluviatile obstruction of a tributary valley cut into bedrock the basal deposits formed as a terrestrial hydromorphic soil under a dense tsuga forest zone rnc 1 the overlying palustrine gyttja shows a marked forest withdrawal with a climatic signature zone rnc 3 followed by a re establishment of mixed conifer forests zones rnc 4 6 the occurrences of pollen of cold adapted taxa saxifraga oppositifolia type saxifraga stellaris type larix are the oldest so far known south of the alps and suggest that mean summer temperature was near or even below the thermic tree limit high herb diversity partially represented by tall forbs characterizes this zone a further increase of the water table can be assumed in zones rnc 4 and rnc 5 since pollen of aquatic plants increases the find of larix decidua l cones demonstrates the existence of the european larch in the early pleistocene of the alps previously not identified at the species level after the serio river had reached the maximum quaternary aggradation the lake was rapidly filled up with turbiditic sediments the identification of cervalces latifrons johnson 1874 by azzaroli palaeantogr italica 71 1979 48 was confirmed pollen spectra obtained from clay fragments preserved in the braincase allowed us to constrain the stratigraphic position of these fossil remains in the lower palustrine portion of the sequence pollen and moose palaeoecology corroborate the reconstruction of a boreal landscape the succession of fornaci di ranica is attributed to the late early pleistocene on the basis of the following elements i the occurrence of an acme pollen zone of tsuga with carya and pterocarya ii the low representation of cedrus iii the biochronology of cervalces latifrons iv normal fossil magnetic polarity interpreted as part of the jaramillo subchron on the basis of correlations with other studied sections from the same region and finally v indications from the regional geological evolution the basin deposits spanned the final stage of a temperate period and the subsequent transition to a cold phase during the jaramillo subchron or the cobb cryptochron the basin originated by fluvioglacial aggradation triggered by glaciation in the northern part of the serio river catchement the lake succession may represent an episode of marked increase of polar ice volume related to mis 36 30 or 28 the correlation with the leffe sequence also suggests that cold climate conditions inferred for pollen zone rnc 3 did not occur earlier in the early pleistocene of this region

the middle pleistocene deposits of waverley wood pit warwickshire england a complex of channels underlying the baginton lillington gravel baginton formation at waverley wood quarry warwickshire is described fossil pollen and plant macrofossils coleoptera ostracoda mollusca and mammalia are described from the channel fill deposits consideration of all the evidence allows the identification of four separate stages of channel fill which largely occurred under a cool temperate climate at the top of channel 2 evidence for a cold continental climatic episode can be recognised suggesting that the whole complex was deposited under a fluctuating climate at the end of a temperate stage at two levels in the channels human artefacts were recovered confirming the presence of palaeolithic people in warwickshire during the deposition of the sediments amino acid geochronology suggests an age within the cromerian complex stage for the channels the small vertebrate and molluscan faunas indicate that the deposits are no older than the latter part of the cromerian complex stage of east anglia the regional stratigraphic significance of the waverley wood succession is outlined

a multi proxy study of holocene lake development lake settlement and vegetation history in central ireland stratigraphical investigations geomorphological mapping and diatom plant macrofossil and pollen analyses were undertaken in and around two lakes in central ireland to establish correlations between changes in lake conditions and catchment vegetation throughout the holocene similar investigations of an adjacent mire reveal early holocene changes in lake level and area the palaeoecological data show high correlations related to variations in lake depth and area catchment vegetation type organic inputs and trophic status catchment scale deforestation is gradual and occurs through the bronze and the iron ages and the construction of a crannog in the early medieval period seventh century ad appears to be associated with a widespread increase in deforestation and mixed agriculture in the catchment both pollen and plant macrofossils suggest that one of the crannogs was used for crop storage in addition to domestic and any other activities in the early to middle holocene similarities in the proxy data appear to be climatically driven through changing lake levels and areal extent whereas the later holocene record is clearly dominated by anthropogenic changes within the catchment and the construction of crannogs in the lakes the advantages of combining multi proxy indicators of lake hydroecology with the vegetation record are illustrated

rissian eemian and wurmian coleoptera assemblages from la grande pile vosges france abstract the grande pile peat bog sequence is one of the few west european sites that cover the entire time span of the last major climatic cycle 140 000 years a recent program of coring has provided material for insect analysis the aim of this palaeoentomological study is to interpret the environmental and climatic evolution from the end of the rissian glaciation to the holocene using subfossil coleoptera the studied samples yielded 394 taxa of coleoptera half of them identified to species level 19 of which do not belong to the present day french fauna the large number of taxa suggests a wide variety of habitats and provides much detailed palaeoecological evidence for the period studied the lowermost sediments of the sequence corresponding to the end of the rissian glaciation were deposited under very cold conditions in a tundra environment this is succeeded by a forest period in which two cool interludes of grassland environment occur although these periods are decidedly poor in tree dependent coleoptera they do not contain any really cold adapted taxa they divide the forest phase into three periods the first one corresponding to the eemian interglacial shows an early stage in which the beetle fauna is characterized by species dependent on deciduous trees a later stage in which this fauna is mixed with many conifer dependent elements some of which e g platypus oxyurus suggest warmer and perhaps wetter climatic condition than today the two later woodland periods yielded coleopteran assemblages rather similar to those recorded in the second part of the eemian i e with both deciduous and conifer dependent taxa there is some evidence to suggest that these two periods were slightly cooler than the eemian proper marked climatic deterioration becomes obvious in the upper half of the sedimentary sequence attributed to the last glacial period wurm with the reappearance of tundra beetle assemblages sediment and insect evidence suggest that the climate was extremely cold and continental at la grande pile at about 30 000 b p a comparison of the insect analysis with previous palynological works enables precise correlation between the results provided by these two independent approaches however large numbers of running water coleoptera in the forest periods replaced by standing water coleoptera in cold periods raise questions concerning the lacustrine origin of the sedimentation at la grande pile

inherited arc signature in ediacaran and early cambrian basins of the ossa morena zone iberian massif portugal paleogeographic link with european and north african cadomian correlatives abstract geochemical data from clastic rocks of the ossa morena zone iberian massif show that the main source for the ediacaran and the early cambrian sediments was a recycled cadomian magmatic arc along the northern gondwana margin the geodynamic scenario for this segment of the avalonian cadomian active margin is considered in terms of three main stages 1 the 570 540 ma evolution of an active continental margin evolving oblique collision with accretion of oceanic crust a continental magmatic arc and the development of related marginal basins 2 the ediacaran early cambrian transition 540 520 ma coeval with important orogenic magmatism and the formation of transtensional basins with detritus derived from remnants of the magmatic arc and 3 gondwana fragmentation with the formation of early cambrian 520 510 ma shallow water platforms in transtensional grabens accompanied by rift related magmatism these processes are comparable to similar cadomian successions in other regions of gondwanan europe and northwest africa ediacaran and early cambrian basins preserved in the ossa morena zone portugal and spain the north armorican cadomian belt france the saxo thuringian zone germany the western meseta and the western high atlas morocco share a similar geotectonic evolution probably situated in the same paleogeographic west african peri gondwanan region of the avalonian cadomian active margin

pleistocene deposits at stoke goldington in the valley of the great ouse uk at stoke goldington in the valley of the great ouse in buckinghamshire a river terrace at a height of about 7 m above the floodplain is underlain by fluvial sediments representing climatic fluctuations in the late middle pleistocene near the base of the succession at a level only 1 m above the modern floodplain a fossil assemblage including pollen plant macrofossils molluscs insects and ostracods provides evidence for the local development of herb rich grassland under temperate climatic conditions the fossil record amino acid racemisation ratios and uranium disequilibrium dating all suggest deposition of this material during oxygen isotope stage 7 the deposits containing the temperate assemblage are immediately overlain by typical cold climate gravels of the great ouse these have been subjected to a later cut and fill episode with the fill accumulating in cool climatic conditions the cut and fill episode was succeeded by aggradation forming the overlying terrace surface amino acid racemisation ratios indicate that the fill was emplaced and the terrace surface created during or after oxygen isotope stage 5 1996 john wiley sons ltd

contiguous rather than discrete paleozoic histories for the avalon and meguma terranes based on detrital zircon data upper ordovician lower devonian strata of the meguma terrane in the canadian appalachians contain zircon populations including an important mesoproterozoic zircon population 1 0 1 4 ga similar to those in coeval strata of avalonia and strongly suggest contiguous rather than discrete histories for these terranes throughout the paleozoic that these terranes were juxtaposed throughout the early paleozoic is indicated by the absence of a cambrian ordovician accretionary event the lack of intervening suture zone ophio litic units and the similarity of avalonian and meguma basement nd isotope signatures in early paleozoic igneous suites as avalonia had accreted to laurentia baltica by the early silurian these data suggest that the meguma terrane like avalonia resided along the same northern margin of the rheic ocean at that time these conclusions have implications for reconstructions of the northern gondwanan margin in the early paleozoic and imply that the silurian devonian acadian orogeny in maritime canada occurred in an andean type setting and was not related to collision of the meguma terrane with the laurentian margin

middle to late paleozoic acadian orogeny in the northern appalachians a laramide style plume modified orogeny the laramide orogeny of the western united states is proposed as a modern analogue for the silurian devonian acadian orogeny and subsequent diachronous voluminous short lived magmatism and basin formation in the northern appalachians shallowing of the benioff zone accounts for several enigmatic features associated with plate convergence in the northern appalachians including 1 wenlockian ludlovian termination of arc related magmatism in the avalon terrane followed by a period of relative magmatic quiescence from 395 to 380 ma and 2 diachronous migration of the acadian deformation front from ca 415 ma in the southeast to ca 370 ma in the northwest extending more than 600 km into the continental interior the flattening of the subduction zone is attributed to overriding of a plume by the convergent margin which may explain 1 the abrupt termination of magmatic quiescence by 380 370 ma and voluminous felsic magmatism and production of plume related lamprophyres in the southeast meguma terrane as the plume thermally eroded the oceanic lithosphere causing melting of the lower crust 2 late devonian regional high temperature low pressure metamorphism in the meguma terrane related to the thermal anomalies above a plume 3 synchronous devonian emplacement of meguma gold deposits and associated siderophile elements possibly derived from fluid circulation above an ascending plume 4 rapid late devonian uplift and erosion of as much as 10 km due to dynamic uplift over a plume 5 migration of magmatism to the north avalon terrane cobequid highlands so that plume related carboniferous magmatism occurred in and around the carboniferous permian maritimes basin 6 the high density lens at the base of the crust beneath the maritimes basin the product of plume derived underplated mafic rocks and 7 a subsidence mechanism for formation of the maritimes basin by cooling of a decapitated plume head