the medieval climate anomaly in the iberian peninsula reconstructed from marine and lake records abstract selected multi proxy and accurately dated marine and terrestrial records covering the past 2000 years in the iberian peninsula ip facilitated a comprehensive regional paleoclimate reconstruction for the medieval climate anomaly mca 900 1300 ad the sequences enabled an integrated approach to land sea comparisons and despite local differences and some minor chronological inconsistencies presented clear evidence that the mca was a dry period in the mediterranean ip it was a period characterized by decreased lake levels more xerophytic and heliophytic vegetation a low frequency of floods major saharan eolian fluxes and less fluvial input to marine basins in contrast reconstruction based on sequences from the atlantic ocean side of the peninsula indicated increased humidity the data highlight the unique characteristics of the mca relative to earlier the dark ages da ca 500 900 years ad and subsequent the little ice age lia 1300 1850 years ad colder periods the reconstruction supports the hypothesis of trouet et al 2009 that a persistent positive mode of the north atlantic oscillation nao dominated the mca

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

glacial interglacial variablity in the benguela upwelling system spatial distribution and budgets of organic carbon accumulation 1 modern sedimentary total organic carbon toc content as a proxy for surface water export production was mapped on the shelf and on the upper continental slope of the benguela upwelling system using 137 core tops shelf maxima in toc can be correlated with maxima in surface water productivity on the slope high toc contents are observed offshore from sites of strong modern upwelling estimates of modern toc mass accumulation rates mar show that approximately 85 of the total is accumulating on the shelf toc mar were calculated mapped and budgeted for the holocene and for the last glacial maximum lgm using 19 sediment cores from the continental slope during the lgm centers of deposition and production have migrated offshore with respect to their holocene positions toc accumulation on the continental slope was approximately 84 higher during the lgm than during the holocene possibly reflecting enhanced productivity the toc distribution patterns and sediment echo sounding data suggest that undercurrents strongly influence the sedimentation off namibia winnowing and focusing result in great lateral heterogeneity of sedimentation rates and sediment properties individual cores therefore do not necessarily reflect general changes in export production these results highlight the need for detailed regional studies based on a large number of sediment cores for highly heterogeneous high productivity areas in order to derive general statements on total fluxes

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

hydrogen index and carbon isotopes of lacustrine organic matter as lake level indicators abstract optical and geochemical techniques were applied to organic matter of late quaternary sediments from lakes victoria and rukwa east africa variations in total organic carbon toc and hydrogen content expressed as hydrogen index hi can be related to known changes in lake level and used to identify periods of very low water or subaerial exposure in basinal sequences toc and hi both decline as an exposure surface is approached mainly due to the selective removal of unstable components by bacterial respiration and inorganic oxidation inert organic material of very low hi is typically concentrated at the overlying transgression surface the carbon isotopic composition of the particulate organic matter tends to be less negative in sediments associated with exposure surfaces although weathering may be partially responsible isotopic variations are mainly due to changes in the relative importance of material from plants using c4 photosynthesis such as grasses and sedges growing around the shore and on the exposed lake muds and of material from planktonic algae and terrestrial c3 plants

new late jurassic to early cretaceous paleomagnetic results from north china and southern mongolia and their implications for the evolution of the mongol okhotsk suture

an oceanic model for lithological and faunal changes tested on the silurian record a model for oceanic cycles is presented the cycles are expressed as changes between more humid low latitude and cooler high latitude climates p episodes and dryer low latitude and warmer high latitude climates s episodes the cyclicity may be self regulating through changes in the co 2 storage capacity of the deep ocean due to temperature changes and through changes in the oceanic input and output of dissolved carbonate the model permits over 30 predictions regarding observable changes in both deep water and shelf lithologies and variations in the abundance diversity and extinction rate of planktic and benthic faunas sedimentary changes involve fluctuations in the rate of clay deposition and carbonate production the advance and retreat of carbonate deposition on the shelf edge the timing of oolite reef and black shale formation and changes between oxic and anoxic deep water faunal effects include both iterative evolution and intermittently widespread taxa lazarus taxa these predictions agree well with changes observed in well known sequence of wenlock and ludlow age as well as changes seen in selected older and younger sequences

timing of deglaciation and postglacial environmental dynamics in nw iberia the sanabria lake record abstract the multiproxy study sedimentology geochemistry and diatoms of sediment cores from sanabria lake 42 07 30 n 06 43 00 w 1000 m a s l together with a robust 14c chronology provides the first high resolution and continuous sedimentary record in the region extending back the last 26 ka the development of a proglacial lake before 26 cal ka bp demonstrates the onset of deglaciation before the global last glacial maximum similarly to other alpine glaciers in southern european mountains rapid deglaciation occurred at the beginning of the greenland interstadial gi 1e bolling 14 6 cal ka bp following a short lived episode of glacier re advance 14 4 14 2 cal ka bp gi 1d a climatic improvement at 13 9 cal ka bp suggests the glaciers retreated from the lake basin during the gi 1c another glacier reactivation phase occurred between ca 13 0 12 4 ka starting earlier than the onset of gs 1 younger dryas rapid deglaciation during the early holocene 11 7 10 1 cal ka bp was followed by a period of higher river discharge 10 1 8 2 cal ka bp after 8 2 ka the holocene is characterized by a general decreasing trend in humidity punctuated by the driest phase during the mid holocene ca 6 8 4 8 a wetter interval between 4 8 and 3 3 cal ka bp and a relatively decline of rainfall since then till present with a minor increase in humidity during some phases ca 1670 1760 of the little ice age discrete silt layers intercalated in the organic rich holocene deposits reflect large flooding events of the tera river ca 10 1 8 4 7 5 6 2 5 7 5 6 4 6 4 2 3 7 3 3 3 1 2 7 2 5 and 2 0 cal ka bp their synchronicity with a number of cold and humid events described in the atlantic demonstrates a strong control of nw iberian climate by north atlantic dynamics at centennial millennial scale comparison with western mediterranean records points to similar regional dynamics during the holocene although modulated in the nw iberian peninsula by the stronger atlantic influence

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

palaeoclimatological and palaeolimnological records from fossil midges and tree rings the role of the north atlantic oscillation in eastern finland through the medieval climate anomaly and little ice age abstract hydrological changes and air temperature variability are reconstructed from the sediments of lake pieni kauro eastern finland during the medieval climate anomaly mca and little ice age lia using transfer functions derived from midge insecta nematocera based calibration models the reconstructions are compared with a regional tree ring chronology and sediment physical properties are determined to track depositional changes an objective of the study is to examine the long term relationship between the north atlantic oscillation nao and climate temperature precipitation our results show that the mca was characterized by warm and dry summer conditions which were accompanied by changes in the sediment magnetic susceptibility values most likely representing major forest fires during the tree ring indicated mca megadrought however the midge based stream flow reconstruction shows increased values during the mca thus implying enhanced spring floods after snowy winters during the lia the tree ring data indicate that a generally wetter climate prevailed during summers but the stream flow reconstruction indicates less snowy winters in the terms of long term climatology the present results show support to the concept that the nao has a positive correlation between winter precipitation and annual temperature and a negative correlation between summer precipitation in eastern finland thus the results may serve as important background data for global change assessments

solar and proxy sensitivity imprints on paleohydrological records for the last millennium in west central europe this paper presents a lake level record established for the last millennium at lake saint point in the french jura mountains a comparison of this lake level record with a solar irradiance record supports the hypothesis of a solar forcing of variations in the hydrological cycle linked to climatic oscillations over the last millennium in west central europe with higher lake levels during the solar minimums of oort around ad 1060 wolf around ad 1320 sporer around ad 1450 maunder around ad 1690 and dalton around ad 1820 further comparisons of the saint point record with the fluctuations of the great aletsch glacier swiss alps and a record of rhone river floods from lake bourget french alps give evidence of possible imprints of proxy sensitivity on reconstructed paleohydrological records in particular the great aletsch record shows an increasing glacier mass from ad 1350 to 1850 suggesting a cumulative effect of the little ice age cooling and or a possible reflection of a millennial scale general cooling until the mid 19th century in the northern hemisphere in contrast the saint point and bourget records show a general trend toward a decrease in lake levels and in flood magnitude anti correlated with generally increasing solar irradiance

assessment of peat quality by molecular and bulk geochemical analysis application to the holocene record of the chautagne marsh haute savoie france although it is primarily constituted in general from a limited variety of local plants peat is however sensitive to physicochemical changes in the medium in particular those induced by hydrological fluctuations the present study aims at confronting the information on peat quality provided by various families of biochemical components lipids lignin sugars especially in order to check the validity of a new organic matter om quality indicator the r400 index directly drawn from rock eval pyrolysis this parameter which is deduced from the sole s2 pyrolysis peak is extremely robust the chautagne marsh located between the le bourget lake and the rhone river lies in a key situation for recording lake level variations and rhone river floods all along its holocene filling the study was conducted on a 6 m long core which comprises 4 m of peat under 66 cm of pedogenetically altered om rich sediment classical rock eval pyrolysis revealed few qualitative and quantitative om changes with total organic carbon toc values close to 50 and hydrogen index values around 300 350 mg hc g 1toc in the peat the r400 parameter remains practically unchanged in the upper unit affected by pedogenesis it fluctuates however all along the peaty unit together with a progressive downward decrease ascribable to diagenesis molecular analyses show that samples with high r400 values are richer in sugars and in slightly oxidized lignin these results support the idea that the r400 parameter can be used as an indicator of om preservation since om preservation is mostly controlled by the water table in peat the chautagne marsh records hydrological fluctuations such as those of the le bourget lake water level all along the holocene

holocene climate variability as reflected by mid european lake level fluctuations and its probable impact on prehistoric human settlements abstract a data set of 180 radiocarbon tree ring and archaeological dates obtained from sediment sequences of 26 lakes in the jura mountains the northern french pre alps and the swiss plateau was used to construct a holocene mid european lake level record the dates do not indicate a random distribution over the holocene but form clusters suggesting an alternation of lower and higher climatically driven lake level phases they provide evidence of a rather unstable holocene climate punctuated by 15 phases of higher lake level 11 250 11 050 10 300 10 000 9550 9150 8300 8050 7550 7250 6350 5900 5650 5200 4850 4800 4150 3950 3500 3100 2750 2350 1800 1700 1300 1100 750 650 cal bp and after 1394 ad a comparison of this mid european lake level record with the gisp2 polar circulation index pci record the north atlantic ice rafting debris ird events and the 14 c record suggests teleconnections in a complex cryosphere ocean atmosphere system correlations between the gisp2 pci the mid european lake level the north atlantic ird and the residual 14 c records suggest that changes in the solar activity played a major role in holocene climate oscillations over the north atlantic area

first paleomagnetic data for the new siberian islands implications for arctic paleogeography abstract in this paper we present new paleomagnetic and paleontological data from the ordovician and silurian carbonate rocks of kotelny island the anjou archipelago and from the ordovician turbidities of bennett island the de long archipelago it is assumed that both archipelagos belong to the nsi new siberian islands terrane a key tectonic element in the arctic region ages of the studied rocks have been established by paleontological data and lithological correlations our new data on conodonts combined with those from previous studies of ordovician and silurian fauna indicate a biogeographic similarity between the shelves of the siberian paleocontinent and the nsi in the early paleozoic three new paleomagnetic poles for the nsi 48 9 n 13 8 e a95 18 1 for 475 ma 45 5 n 31 9 e a95 11 0 for 465 ma and 33 7 n 55 7 e a95 11 0 for 435 ma fall between the south eastern part of central europe and the zagros mountains the similarity of paleomagnetic directions from kotelny and bennet islands confirms that both the anjou and de long archipelagos belong to the same terrane calculated paleolatitudes indicate that in ordovician silurian times this terrane has been located between 30 and 45 possibly in the northern hemisphere based on this observation we suggest a linkage between the nsi and the kolyma omolon superterrane comparison of apparent polar wander paths apwps of the nsi siberia and other cratons terranes suggests that the nsi drifted independently we demonstrate that the structural line between svyatoy nos peninsula and great lyakhovsky island is the continuation of the kolyma loop suture on the arctic shelf and expect that the continuation of the south anyui suture is to be found east of the nsi

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

early silurian paired δ13ccarb and δ13corg analyses from the midcontinent of north america implications for paleoceanography and paleoclimate abstract paired 13ccarb and 13corg samples from well preserved marine carbonates of the wayne formation in central tennessee were analyzed to test a previously proposed model of relative changes in atmospheric pco2 during the well known ireviken early wenlock positive carbon isotope 13ccarb excursion our investigation provides the first detailed 13corg stratigraphy through this interval and documents a negative excursion in 13corg associated with the positive 13ccarb excursion this is consistent with the notion that the ireviken positive 13ccarb excursion was associated with elevated global temperatures that began during an icehouse greenhouse transition although our data are consistent with predictions made by the silurian oceanographic model jeppsson l 1990 an oceanic model for lithological and faunal changes tested on the silurian record j geol soc lond 147 663 674 a link to global changes in atmospheric pco2 remains tenuous until it can be shown that the 13corg trends shown herein can be reproduced globally

tripartite climate reversal in central europe 5600 5300 years ago abstract the history of variations in water level of lake constance as reconstructed from sediment and pollen analysis of a sediment sequence from the archaeological site of arbon bleiche 3 shows an abrupt rise in lake level dendrochronologically dated to 5375 yr ago 5320 yr relative to ad 1950 this event paralleled by the destruction of the neolithic village by fire provoked the abandonment of this prehistoric lake shore location established in the former shallow bay of arbon bleiche and was the last of a series of three episodes of successively higher lake level the first occurring at 5600 5500 cal yr b p the dendrochronologically dated rise event was synchronous with an abrupt increase in atmospheric 14 c this supports the hypothesis of an abrupt climate change forced by varying solar activity moreover the three successive episodes of higher lake level between 5600 and 5300 cal yr b p at arbon bleiche 3 coincided with climatic cooling and or changes in moisture conditions in various regions of both hemispheres this period corresponds to the mid holocene climate transition onset of the neoglaciation and suggests inter hemispheric linkages for the climate variations recorded at arbon bleiche 3 this mid holocene climate reversal may have resulted from complex interactions between changes in orbital forcing ocean circulation and solar activity finally despite different seasonal hydrological regimes the similarities between lake level records from lake constance and from jurassian lakes over the mid holocene period point to time scale as a crucial factor in considering the possible impact of climate change on environments

palynology organic geochemistry and carbon isotope analysis of a latest ordovician through silurian clastic succession from borehole tt1 ghadamis basin southern tunisia north africa palaeoenvironmental interpretation abstract palynological and palynofacies analyses combined with organic carbon isotope measurements have been performed on terminal ordovician through silurian clastic sediments from the north african margin of gondwana southern tunisia a first carbon isotopic signal 13corg from gondwanan silurian sedimentary sequences is presented showing interesting correlation with existing coeval isotopic curves from other areas changes in lithology palynofacies characteristics palynomorph diversity carbon isotope developments and organic geochemistry parameters appear to be all causally linked and to reflect changes in palaeoceanographic conditions in particular the detailed chronostratigraphic correlation and the observed similarities in patterns of carbon isotopic developments and palyno and litho facies changes through the study section has permitted to identify the supposedly global earliest wenlock ireviken event and late ludlow lau event isotopic excursions for the first time in high latitude gondwana this confirms that these excursions were linked to global changes in the oceanic system the present results suggest that from rhuddanian to early wenlock times an extended period of black shale deposition occurred over the north african gondwanan margin progressively transgressing from basin palaeodepressions to basin palaeohighs palynofacies and organic geochemistry support a coastal upwelling promoted productivity increase during this interval associated to a decrease in diversity of the marine microplanktonic communities the earliest wenlock strong positive isotopic shift appears associated with this protracted period of massive black shale deposition and thus of organic carbon burial on continental platforms located in high latitude settings this could well explain the apparent paradox between excessive carbonate deposition simultaneous to a carbon isotopic shift towards lighter values observed in low palaeolatitude localities laurentia and baltica the strong distinct isotope excursion occurring in late ludlow times is possibly linked to the well know lau event evidence for extensive organic carbon burial is lacking to explain this strong excursion some significant changes in the marine palynomorph communities are recorded in connection to the increase in stable isotope values 13corg additionally a strong correlation between abundance of terrestrially derived palynomorphs miospores and 13corg development is recorded which seems to support increased clastic input from a terrestrial source

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes

variability in the δ13c of lower palaeozoic palynomorphs implications for the interpretation of ancient marine sediments abstract we have analyzed the stable carbon isotope ratios of various organic walled microfossils preserved in marine sediments of silurian and devonian age the aim of this study is to determine the amplitude of isotopic fractionations among the different extinct palynomorph groups twenty six samples of marine palynomorphs have 13c values in the range 30 0 to 26 3 whereas two samples likely of terrestrial origin tracheids and woody tissue have the highest 13c values 24 8 and 23 3 among six sediments that only contain marine palynomorphs three show 13c variations of 0 8 1 0 and 2 5 respectively whereas the others do not show significant difference in the presence of fragments of woody tissue mixed with the marine plankton these internal isotopic variations may reach about 4 the bulk 13c values of organic matter in these ancient marine sediments are interpreted as average values which integrate in addition to chemical characteristics of surface waters e g co2 aq source and species dependent isotopic compositions the possible occurrence of such 13c heterogeneities at the scale of a sediment sample could result at least from three kinds of material fluxes 1 autotroph and heterotroph elements from the water column 2 oceanic current and river inputs and 3 selective molecular preservation related to specific biochemical structures

erosion in mediterranean mountain landscapes during the last millennium a quantitative approach based on lake sediment sequences iberian range spain abstract land degradation and soil erosion are key environmental problems in mediterranean mountains characterized by both a long history of human occupation and strong seasonality of hydrological regimes experimental monitored catchments have identified main controlling factors on erosion dynamics but because of the short time span of the instrumental measurements they do not integrate the complete temporal and spatial variability of these environments to obtain some long term series of mediterranean landscape evolution we propose a novel strategy based on multi proxy analyses of lake sediments aimed to quantify sediment delivery and erosion dynamics karstic lakes in the iberian range central spain provide an opportunity to reconstruct the depositional evolution of the watersheds and to evaluate the response to both the variable anthropogenic impacts and climate forcings during the last 1000 years the most significant periods of increased sediment delivery 26 483 t km yr 1 in the iberian range sites took place during the 15th 16th and 18th 19th centuries as a result of large land use changes and land clearing positive synergies between increasing human population and more humid periods led to peaks in sediment deliver during some phases of the little ice age recent changes associated with the rural exodus and land abandonment during mid 20th century are more clearly shown in larger watersheds by decreased sediment delivery to the lakes due to the re vegetation of the landscape 6 200 t km yr 1 this new integrated approach based on long term lake sequences provides a longer perspective of erosion processes in mediterranean watersheds and validates the main factors identified in monitoring surveys land cover and surface formations erodibility in both settings lakes and experimental catchments most sediment delivery occurs during flooding events measured and reconstructed values show comparable large ranges underlying the punctuated nature of sediment dynamics in mediterranean landscapes at decadal and centennial scales

multicentury glacier fluctuations in the swiss alps during the holocene subfossil remains of wood and peat from six swiss glaciers found in proglacial fluvial sediments indicate that glaciers were smaller than the 1985 reference level and climatic conditions allowed vegetation growth in now glaciated basins an extended data set of swiss glacier recessions consisting of 143 radiocarbon dates is presented to improve the chronology of glacier fluctuations a comparison with other archives and dated glacier advances suggests 12 major recession periods occurring at 9850 9600 93008650 85508050 77007550 74506550 61505950 57005500 52004400 43003400 28002700 21501850 14001200 cal yr bp it is proposed that major glacier fluctuations occurred on a multicentennial scale with a changing pattern during the course of the holocene after the younger dryas glaciers receded to a smaller extent and prolonged recessions occurred repeatedly culminating around 7 cal kyr bp after a transition around 6 cal kyr bp weak fluctuations around the present level dominated after 3 6 cal kyr bp less frequent recessions interrupted the trend to advanced glaciers peaking with the prominent little ice age this trend is in line with a continuous decrease of summer insolation during the holocene

sequestration of 12c in the deep ocean during the early wenlock silurian positive carbon isotope excursion abstract marine carbonates from three biostratigraphically well dated silurian sections from the mid continent of north america were analyzed for carbon isotopic 13 c carb study the early wenlock positive carbon isotope excursion ireviken excursion is recorded in three sections from tennessee iowa and ohio with values of 4 5 this global shift in the carbon isotopic ratio of marine waters began during a protracted extinction event ireviken event that spanned the llandovery wenlock boundary although several oceanographic models have been developed to account for the coincident changes in lithology biology and carbon isotope stratigraphy during this interval of the silurian their proposed causal connections among glaciation oceanography primary productivity and the global carbon cycle remain a matter of debate this investigation provides carbon isotopic and lithologic evidence that the ireviken excursion occurred during a time of relatively oligotrophic conditions a third order transgressive regressive cycle and increased carbonate production throughout the mid continent of north america the ireviken excursion is recorded in relatively pure carbonate sequences and is immediately preceded by a significant unconformity in each of the measured sections it is proposed that the ireviken excursion was the product of sequestration and burial of 12 c in deep water as a result of altered deep ocean circulation

high resolution late silurian correlations between gotland sweden and the broken river region ne australia lithologies conodonts and isotopes high resolution correlations partly with a precision better than 10 ka are achieved between late ludfordian sequences on gotland sweden on baltica and a section cog through the coral gardens formation along the broken river northeastern australia on gondwana despite these sections having been on different palaeocontinents facing different oceans the interval is characterised by rapid very large faunal isotopic and lithologic changes lithologies are remarkably similar in the two areas consisting of in order from below marls with thin limestone beds flaggy limestones oncoidal crinoidal limestone oncoidal marls terrigenous clastics silty clay mudstone sandstone oolite and cliff gorge forming limestones further independent correlation dates several of the lithological changes as coeval the 813 c excursion in whole rock carbonates is one of the three largest ones known during the phanerozoic the increase in delta c 13 is very similar in the two areas from below 1 parts per thousand to c 9 parts per thousand vpdb though two gotland samples yielded 9 71 parts per thousand and 10 54 parts per thousand the corresponding cog interval included fewer carbonate layers than needed to definitely exclude that this difference is due to a lack of suitable rocks for sampling compared with the lithologies and the delta c 13 curves the conodont faunas display some divergence but key taxa permit precise correlations for much of the studied interval the conodont assemblages change stepwise from very diverse in the polygnathoides siluricus zone to a low diversity fauna dominated markedly by a single taxon upper icriodontid subzone returning abruptly to a comparatively diverse ozarkodina snajdri zone fauna a method resembling graphic correlation in some respects is used to propose a similarly high resolution correlation through a longer interval for future testing c 2006 elsevier b v all rights reserved less

high altitude varve records of abrupt environmental changes and mining activity over the last 4000 years in the western french alps lake bramant grandes rousses massif abstract two twin short gravity cores and a long piston core recovered from the deepest part of proglacial lake bramant grandes rousses massif french alps under and overlying a large slump identified by high resolution seismic profile allow the investigation of holocene natural hazards and interactions between human activity and climatic changes at high altitude annual sedimentation throughout the cores glacial varves is identified on photographs itrax high resolution continuous microfluorescence x and cat scan computerized axial tomography analyses and is supported by 1 the number of dark and light laminations between dates obtained by radionuclide measurements 137cs 241am 2 the correlation of a slump triggered by the nearby ad 1881 allemond earthquake msk intensity vii and of a turbidite triggered by the ad 1822 chautagne regional earthquake msk intensity viii 3 the number of laminations between two accelerator mass spectrometry ams 14c dates and 4 archaeological data in lake bramant dark layers are coarser contain less detrital elements but more neoformed elements and organic matter content these darker laminations result from calm background sedimentation whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt traces of mining activity during the roman civilization apogee ad 115 330 and during the early bronze age 3770 3870 cal bp are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the nw alps warmer climate during the bronze age in this part of the alps is suggested by 1 two organic deposits 4160 3600 cal bp and 3300 2850 cal bp likely reflecting a lower lake level and smaller glaciers and 2 evidence of a different vegetation cover around 2500 m a s l the onset of clastic proglacial sedimentation between 3600 3300 cal bp and since 2850 cal bp is synchronous with periods of glacier advances documented in the alps and high lake levels in west central europe this major change in proglacial sedimentation highlights the development of a larger st sorlin glacier in the catchment area of lake bramant

palaeoenvironmental interpretation of microphytoplankton diversity trends in the cambrian ordovician of the northern sahara platform abstract analysis of vertical fluctuations in assemblage diversity and relative abundances of microphytoplankton morphological classes permits palaeoenvironmental reconstructions of the cambrian ordovician stratal sequences in the hassi r mel area north central algeria and northern rhadames basin southern tunisia abundance fluctuations of acritarch morphological classes and assemblage diversity appear to be related to changes in depositional facies the present palaeoenvironmental interpretation is primarily based on a comparison with microphytoplankton distributional trends in modern depositional environments where possible the observations are tested against palaeoenvironmental information derived independently from previous lithostratigraphical macropalaeontological and petrographical studies of the formations investigated the present data support the following palaeoenvironmental scenario during late cambrian times relatively shallow water neritic conditions prevailed throughout the study area with evidence for a more proximal environment in southern tunisia in the early tremadoc open marine offshore conditions characterized the central algerian region but a shallower water setting is indicated for southern tunisia during the late arenig llanvirn interval an open marine offshore setting is envisaged for the southern tunisian region with more proximal conditions prevailing in the algerian hassi r mel area during the entire ashgill an essentially restricted marine environment was established throughout the study area some stratigraphically important acritarch species e g acanthodiacrodium angustum appear to be facies sensitive the recognition of palaeoecological control on microphytoplankton distribution has important consequences on the biostratigraphic application of these microfossils

origin sequence stratigraphy and depositional environment of an upper ordovician hirnantian deglacial black shale jordan the upper ordovician succession of jordan was located 60 s less than 100 km from the hirnantian ice sheet margin new graptolite dates indicate glaciation ended in jordan in the late hirnantian persculptus biozone the succession records two glacial advances within the ammar formation and the subsequent deglaciations organic rich black shales batra formation form part of the final deglacial transgressive succession that in filled an existing low stand glacial continental shelf topography the base of the black shale is coincident with the maximum flooding surface during transgression interfluves and sub basin margins were breached and black shale deposition expanded rapidly across the region the top of the black shales coincides with peak highstand the expanding puddle model sensu wignall for black shale deposition adapted for the peri glacial setting provides the best explanation for this sequence of events we propose a hypothesis in which anoxic conditions were initiated beneath the halocline in a salinity stratified water column a fresher surface layer resulted from ice meltwater generated during early deglaciation during the initial stages of marine incursion nutrients in the monimolimnion were isolated from the euphotic zone by the halocline increasing total organic carbon toc and 13corg up section indicates the organic carbon content of the shales was controlled mainly by increasing bioproductivity in the mixolimnion the strakhov model mixolimnion nutrient levels were sustained by a continual and increasing supply of meltwater derived nutrients modulated by obliquity changes in high latitude insolation anoxia was sustained over tens to hundreds of thousands of years the formation of black shales on the north gondwana shelf was little different to those observed in modern black shale environments suggesting that it was the nature of the ordovician seas that pre disposed them to anoxia

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

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

climatic variability in the northwestern alps france as evidenced by 600 years of terrigenous sedimentation in lake le bourget cores recovered from periglacial lake le bourget deep basin northwestern alps were investigated to examine the ine uence of the little ice age lia on terrigenous lacustrine sedimentation growing glaciers in the regional watershed induced catastrophic rhone river e oods and major undere ow deposits in the deep basin during the early e fteenth the sixteenth and the mid eighteenth centuries the lia is characterized by a decrease in deposition from intere ows from ad 1550 to 1740 and an increase in deposition from undere ows from ad 1550 to 1800 on one hand spectral analyses of the laminations in intere ow deposits reveal 4 5 years cyclicities from ad 1440 to 1550 as well as 7 8 and 13 14 years cyclicities from ad 1740 to 1870 on the other hand spectral analyses of a clay mineral ratio ree ecting undere ow deposits highlight 45 50 years cyclicities from ad 1550 to 1800 these pluriannual decadal and pluridecadal periods are typical of the north atlantic oscillation nao a nao like period in our data would be a consequence of periodical variations in rainfall and snow accumulation during late autumn and winter over lake le bourget s watershed

recent climatic and anthropogenic imprints on lacustrine systems in the pyrenean mountains inferred from minerogenic and organic clastic supply vicdessos valley pyrenees france high resolution seismic profiling has been combined with geochemical analyses of both watershed samples and five lacustrine cores retrieved from two natural lacustrine basins of glacial origin lake majeur and lake sigriou 1630 m a s l and 1995 m a s l respectively eastern french pyrenees identifying specific minerogenic and organic markers of autochthonous and allochthonous supply data allow documenting past climatic and anthropogenic pressures over the past century the lacustrine sediment of lake majeur has been essentially composed of algae drastically contrasting with the natural sedimentary infill of the basin mainly resulting from soil erosion from the mid late holocene since ad 1907 the lake majeur has been used for hydroelectricity production human induced lake level regulations affecting up to 37 of the lacustrine surface have increased by fourfold the accumulation rate of the lake and favoured water enrichment rubidium abundance within the lacustrine sediments of the two lakes reflects the mid late holocene palaeohydrology after dam construction in ad 1907 greater quantities of rubidium found in lake majeur sedimentary infills indicate drier climatic periods such as from ad 1975 to ad 1982 during which water reservoirs were particularly in demand inversely before the dam was built rubidium fluctuations were correlated with wetter conditions and hydrological events were recorded as sandy layers deposited by canyon reactivation synchronous with european climatic deterioration phases we notably document that the mediaeval climate anomaly was interrupted by some humid periods dated c ad 940 ad 1080 ad 1100 and ad 1250 we also date the onset of the little ice age c ad 1360 and identify that this period was wetter after c ad 1500

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

a quick and low cost technique to identify layers associated with heavy rainfall in sediment archives during the anthropocene long term records are needed to investigate the impact of extreme events inthe current framework of global change sedimentary reconstruction with ahigh resolution remains difficult without conducting expensive destructiveand or time consuming analyses in this study high resolution ct scan profiles 0 6 mm resolution were used to investigate their potential for detecting flood deposits induced by heavy rainfall events this method was applied to a sediment core dated with fallout radionuclides covering 120 year period collected in a pond draining a small forested catchment french massif central central france between 1960 and 2017 28 layers were deposited seventy six percent of these deposits were correlated to the occurrence of heavy rainfall 50 mm recorded during one or two consecutive days the remainder of the deposits detected with the computer tomo graphy ct scanner n 5 were not correlated to weather events they mainly occurred in response to landscape management operations for example afforestation works as a result of the major 1999 storm this period was indeed characterized by an increase in the delivery of137cs enriched sediment demonstrating a greater topsoil contribution to sediment during majorforest management operations the intensity of detrital layers has significantly decreased throughout time after a major land use change that tookplace in 1948 and land abandonment the frequency of heavy rainfall anassociated detrital deposits has nevertheless increased by 60 and 75 respectively between the years 1960 and 2017 these results outline the potential of ct scan for reconstructing long term flood deposits associated with heavy precipitation

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

climate palaeohydrology and land use change in the central iberian range over the last 1 6 kyr the la parra lake record a multiproxy study of a 7 m long sedimentary sequence from lake la parra 39 50 948 1 52 1014 m a s l supported by 11 14c ams and 210pb 137cs dates provides a robust high resolution hydrological and environmental variability record for the last 1600 years of the las torcas sinkhole complex in the central iberian range the succession of depositional environments in lake la parra sinkhole is controlled by both changes in the regional water table and by the balance between sedimentary input through ephemeral creeks and in lake production of carbonates and organic matter although synergetic links with climate are likely phases of increased sediment delivery to the lake at c ad 500 700 c ad 1000 ad 1450 1500 ad 1550 650 and since 1700 till recent times are driven primarily by human impact in the watershed prior to c ad 300 the sinkhole was dry then became a lake at the end of the roman period ad 350 when the doline was flooded and it has not dried out during the last 1600 years moderate

reconstructing historical seismicity from lake sediments lake laffrey western alps france sediment archives from a mountain lake are used as indicators of seismotectonic activity in the grenoble area french western alps 45n sedimentological analysis texture and grain size characteristics exhibits several layers resulting from instantaneous deposits in lake laffrey six debris flow events up to 8 cm thick can be attributed to slope failure along the western flank of the basin dating with 210 pb and 137 cs gamma counting techniques and the reconnaissance of historical events provide a constrained age depth model over the last 250 years five of such debris flow deposits could be related to historical earthquakes of msk intensities greater than vi over an area of 60 km one debris flow deposit triggered at the beginning of the last century can be related to an historical landslide possibly triggered by the artificial regulation of the lake level

quantitative palynofacies analysis as a new tool to study transfers of fossil organic matter in recent terrestrial environments classical palynofacies method which consists in an organic concentrate microscopic qualitative observation after mineral phase dissolution is commonly used in order to study sedimentary organic matter in the present study we develop a new quantitative palynofacies method that allows organic particles mass concentrations to be determined in studied samples this method was developed to help quantify the input of fossil organic matter fom into modern environments as a result of sedimentary rocks weathering studied samples were collected from different pools like bedrocks weathering profiles soils and riverine particles in an experimental watershed le laval this watershed overlying callovo oxfordian marls 1 km in area is located near digne alpes de haute provence in france in addition to palynofacies techniques rock eval 6 pyrolysis and al2o3 content measurements inductively coupled plasma emission spectrometry were carried out on the samples obtained results show that this quantitative palynofacies method is suitable for fom studies in modern environments and fom particles are quantified in the different pools results also give evidence that fom alteration depends on the type of weathering but also on the kind of organic particles soil formation under vegetation resulting from the bio chemical weathering lead to fossil organic particles concentration losses that do not exceed 30 elsewhere mechanical weathering appears extremely fast and has no qualitative or quantitative influence on the observed fom particles which feeds directly into riverine stocks fom appears to be very resistant to weathering processes this highlights its occurrence into supergene pools and then into carbon cycle quantitative palynofacies analysis is a new method adapted to a such study but can also be applied to other palynological paleoenvironmental or archeological studies

considering lacustrine erosion records and the de ploey erosion model in an examination of mountain catchment erosion susceptibility and precipitation reconstruction reconstruction of paleo precipitation can provide an insight into past climate and precipitation de ploey et al 1995 presents a highly simplified erosion equation to consider precipitation and erosion susceptibility this empirical model allows estimation of total precipitation and erosion susceptibility across a range of catchment characteristics including catchment area slope elevation vegetation cover and when limited catchment or meteorological data is available the presented study tests the de ploey equation using dated lacustrine records of catchment soil deposition both spatially and temporally the objective is to examine the de ploey equation s ability and efficiency in reconstructing past long term precipitation using sedimentological parameters the erosion susceptibility factor is described as a black box value by de ploey et al 1995 this research unravels the erosion susceptibility variable identifying it to change spatially and temporally according to precipitation vegetation cover and composition the extent of tree establishment across the catchment total lacustrine deposition and geochemical signatures in the archive calculation of the erosion sustainability variable and it s use within the de ploey erosion equation illustrate a reconstruction of an indicative mean annual precipitation and erosion susceptibility change over the recent period 100 years

carbon isotope event markers through the wenlock pridoli sequence at ohesaare estonia and priekule latvia abstract the ohesaare borehole in the northern part of the silurian baltic gulf penetrates shallow and deep shelf marlstones limestones and dolostones the priekule borehole in the deep shelf belt of the basin was drilled through marlstones and graptolitic mudstones most of the successions except the upper part are characterized by a high sr ca ratio close to marine calcites suggesting good preservation of carbonate material conodont alteration indices are low 1 2 carbon isotopes were measured using whole rock samples in the ohesaare core section two distinctive 13 c positive excursions were established one in the early wenlock riccartonensis and low rigidus ellesae standard graptolite zones 4 2 and the second in the late wenlock nassa zone 4 6 before and after the latter there are also intervals with low 13 c values the first just above the lundgreni zone 1 8 and another in the ludensis perhaps reaching into nilssoni zone 3 8 in the priekule section the early wenlock 13 c peak is well represented 3 1 but in the late wenlock early ludlow 13 c values show little variation from 2 0 to 1 in this section a high peak of 13 c values 5 9 was determined in the nova beds correlated with the topmost gorstian and lowermost ludfordian ludlow the carbon isotope positive excursions show good correlation with lows of the global sea level curve and with most of the biotic and supposed climatic events glaciation ocean state

hydrocarbon biomarkers thermal maturity and depositional setting of tasmanite oil shales from tasmania australia this study represents the first geological and organic geochemical investigation of samples of tasmanite oil shale representing different thermal maturities from three separate locations in tasmania australia the most abundant aliphatic hydrocarbon in the immature oil shale from latrobe is a c19 tricyclic alkane whereas in the more mature samples from oonah and douglas river low molecular weight n alkanes dominate the extractable hydrocarbon distribution the aromatic hydrocarbons are predominantly derivatives of tricyclic compounds with 1 2 8 trimethylphenanthrene increasing in relative abundance with increasing maturity geological and geochemical evidence suggests that the sediments were deposited in a marine environment of high latitude with associated cold waters and seasonal seaice it is proposed that the organism contributing the bulk of the kerogen tasmanites occupied an environmental niche similar to that of modern sea ice diatoms and that bloom conditions coupled with physical isolation from atmospheric co2 led to the distinctive isotopically heavy 13c values 13 5 to 11 7 for the kerogen 13c data from modern sea ice diatoms 7 supports this hypothesis isotopic analysis of n alkanes in the bitumen 13 5 to 31 suggest a multiple source from bacteria and algae on the other hand the n alkanes generated from closed system pyrolysis of the kerogen 15 are mainly derived from the preserved tasmanites biopolymer algaenan the tricyclic compounds mean 8 both in the bitumen and pyrolysate have a common precursor they are consistently enriched in 13c compared with the kerogen and probably have a different source from the n alkanes the identification of a location where the maturity of the tasmanite oil shale approaches the oil window raises the possibility that it may be a viable petroleum source rock

high resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake lake le bourget northwestern alps france abstract lake le bourget is a deep peri alpine glacial lake originating from the last glacial the wurm the lake has amassed over 250 m of sediment since the last glacial maximum two seismic sparker surveys on the lake revealed the glacial and post glacial sedimentary infill the depth and the morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface the density of the seismic grid and the high resolution of the data even at greater depths allowed a detailed study of the sedimentary processes and of their evolution throughout the deglaciation five main seismic facies characterise the basin fill they are interpreted as glacial deposits glacio lacustrine sediments proglacial lacustrine fans alluvial fan deltas and authigenic lacustrine drape these occur as a suite of deposits associated with the major lake tributaries and are the result of major changes in sediment supply and style of discharge into the lake the three dimensional facies associations within the basin fill document the history of the basin and its catchment area since the onset of the deglaciation

assessing mechanisms of environmental change palynological signals across the late ludlow silurian positive isotope excursion δ13c δ18o on gotland sweden abstract the silurian is characterised by strong environmental changes as indicated by several pronounced positive 13c and 18o excursions the mechanisms responsible for these isotopic shifts are a matter of much debate the purpose of the present study is a quantitative high resolution evaluation of the palynomorph distribution across the late ludlow ludfordian isotope excursion on gotland marine and terrestrial palynomorphs have been chosen as palaeoenvironmental indicators because they are widely distributed and exceptionally well preserved moreover the combined analysis of marine and terrestrial palynomorphs allows the reconstruction of contemporaneous palaeoenvironmental change in the marine and terrestrial realms to correlate our results with the carbon isotope stratigraphy we have sampled only localities with published isotope data from diagenetically unaltered brachiopod shells our results show that fluctuations in the composition of the acritarch assemblages are closely correlated with the stable isotope development low abundances of acritarchs occur in times of high stable isotope values and vice versa indicating that an increase in marine productivity cannot have been the reason for the positive 13c excursion the results are in good agreement with climatic models for the silurian assuming alternating humid and arid climatic conditions in low latitudes times of high stable isotope values correspond to arid climatic conditions in low latitudes with low input of terrestrial nutrients resulting in impoverished acritarch and conodont communities whereas times of low stable isotope values correlate with humid climate high nutrient input and abundant and diverse acritarch communities the major change in acritarch communities took place during the increase of the stable isotope values after hemipelagic planktonic or nektonic organisms graptolites conodonts have been affected this indicates that environmental changes connected with the stable isotope excursion first affected deeper water settings and later the photic zone the absolute abundance of terrestrial spores closely mirrors the marine 13c and 18o development showing that both the marine and the terrestrial realm were synchronously affected by the climatic changes the high abundance of spores during the isotope excursion might be explained by increased aeolian input

fluctuations in epeiric sea carbonate production during silurian positive carbon isotope excursions a review of proposed paleoceanographic models positive excursions in the carbon isotopic ratio of marine carbonates 13ccarb are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains the notion that high 13ccarb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings what is surprising is that major positive carbon isotope excursions during the silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas in fact silurian 13ccarb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally this discrepancy has sparked considerable debate among silurian carbon isotope specialists but has offered a valuable opportunity to re examine the intricate connections among nutrients primary productivity carbonate sedimentology and the global carbon cycle in the lower paleozoic here we consider several sedimentological and geochemical features of one of these silurian positive carbon isotope 13ccarb excursions and discuss the broader implications of current silurian 13ccarb models to the interpretation of lower paleozoic carbonate sequences

δ13c records across the late silurian lau event new data from middle palaeo latitudes of northern peri gondwana prague basin czech republic abstract during the late silurian the prague basin was located in middle southern latitudes in contrast to palaeocontinents positioned in tropical and subtropical latitudes like baltica no reefs are developed which is in accordance with the predicted cooler water the prague basin represents a relatively restricted and shallow rift basin with a complex tectonic history sections in different palaeoenvironments have been studied to document the most prominent silurian stable carbon isotope excursion recorded during the late silurian ludfordian lau event from this part of peri gondwana deeper water deposits of the kopanina formation investigated in the present study were deposited on the slope to basin transition near the kosov volcanic centre in the western part of prague basin the sediments are developed as an alternation of dark partly laminated limestones and marls with an increase of the limestone marl ratio in the upper part of the succession a pronounced positive carbon isotope excursion starts in the neocullograptus kozlowskii graptolite and in the upper polygnathoides siluricus conodont zone the maximum of the shift is observed in the lower part of an interval characterised by the ananaspis fecunda cyrthia postera community the maximum values scatter around 8 which represent the highest values reported hitherto from the prague basin in low latitudes often a decrease of 13c values towards deeper water settings is reported in contrast in the present study the 13c values of about 8 are much higher than those recorded from the contemporaneous shallow water sections studied in the classical muslovka and po ary quarries the most reasonable explanation is the presence of stratigraphical gaps in the shallow parts of the basin as indicated by karstification these gaps were caused by a sea level drop another effect of this sea level fall was a strongly reduced sedimentation of the cephalopod limestone facies around volcanic and tectonic elevations

a weathering hypothesis for glaciation at high atmospheric pco2 during the late ordovician new paired carbonate and organic carbon isotope analyses from nevada usa together with a consideration of the effects of mountain building and ice sheet coverage of the continents on atmospheric pco2 lead to a new hypothesis for the cause of the late ordovician glaciation we suggest that the taconic orogeny which commenced in the late middle ordovician caused a long term decline in atmospheric pco2 through increased weatherability of silicate rocks ice sheet growth was triggered when pco2 decreased to a threshold of 10 present atmospheric level and proceeded by positive ice albedo feedback in the midst of glaciation atmospheric pco2 began to rise as continental silicate weathering rates declined in response to coverage of weathering terrains by ice sheets at first this enhanced greenhouse effect was overcompensated for by ice albedo effects ultimately however atmospheric pco2 reached a level which overwhelmed the cooling effects of ice albedo and the glaciation ended the isotope results can be interpreted to indicate that atmospheric pco2 rose during the glaciation consistent with other proxy information although alternative interpretations are possible the large positive carbonate isotope excursion observed in late ordovician rocks around the world is explained as the expected response to increased carbonate platform weathering during glacioeustatic sea level lowstand rather than as a response to increased organic carbon burial

new middle cambrian and middle ordovician palaeomagnetic data from siberia llandelian magnetostratigraphy and relative rotation between the aldan and anabar angara blocks abstract whether siberia was a coherent tectonic unit throughout the phanerozoic or whether significant rotations occurred in early palaeozoic times between the anabar angara and aldan blocks is still a matter of debate addressing this problem a detailed palaeomagnetic study of sections of mid cambrian and llandeillian age has been carried out along the river lena river maya river kulumbe and river stolbovaya with a total of 403 collected hand samples a section of llandeilian age was also investigated on the russian platform near st petersburg the studied rocks are carbonates or fine grained terrigenous sediments of reddish and greyish colors stepwise thermal demagnetization experiments reveal a rather simple directional behavior in most samples after removal of a secondary magnetizations at low to intermediate temperatures a high temperature component is isolated which is carried by magnetite and or hematite positive reversal tests and fold tests clearly demonstrate the primary character of the latter component while only reversed polarity directions are obtained in the lower two thirds of the llandeilo six magnetozones of normal polarity are found in the upper llandeilo which mark the end of the moyero reverse superchron together with previously published paleomagnetic data our new results show rather systematic difference in declinations of 20 between the aldan and anabar angara blocks this argues in favor of a relative rotation between these two blocks with an euler pole of rotation located at latitude 62 n and longitude 117 our interpretation is further supported by existing results from deep sounding seismic experiments yielding a very similar pole of rotation

quantitative estimates of temperature and precipitation changes over the last millennium from pollen and lake level data at lake joux swiss jura mountains abstract this paper presents quantitative climate estimates for the last millennium using a multi proxy approach with pollen and lake level data from lake joux swiss jura mountains the climate reconstruction based on the modern analogue technique indicates warmer and drier conditions during the medieval warm period mwp mwp was preceded by a short lived cold humid event around ad 1060 and followed by a rapid return around ad 1400 to cooler and wetter conditions which generally characterize the little ice age lia around ad 1450 solar sporer minimum the lia attained a temperature minimum and a summer precipitation maximum the solar maunder minimum around ad 1690 corresponded at joux to rather mild temperatures but maximal annual precipitation these results generally agree with other records from neighbouring alpine regions however there are differences in the timing of the lia temperature minimum depending on the proxy and or the method used for the reconstruction as a working hypothesis the hydrological signal associated with the mwp and lia oscillations at lake joux may have been mainly driven by a shift around ad 1400 from positive to negative nao modes in response to variations in solar irradiance possibly coupled with changes in the atlantic meridional overturning circulation

new paleomagnetic paleolatitudes for the omulevka terrane of northeast russia a comparison with the omolon terrane and the eastern siberian platform abstract paleomagnetic measurements were made on samples from silurian devonian carboniferous and permian aged rocks from the omulevka terrane northeast russia the omulevka terrane is a fragment of continental margin that forms a major component of the kolyma omolon superterrane a superterrane that constitutes the core of northeast russia all samples were collected from sites along the taskan river and all showed a very strong secondary overprint and in some cases more than one with detailed thermal demagnetization a component of magnetization that decayed towards the origin when viewed as an orthogonal plot was commonly present and showed better clustering of magnetization directions in stratigraphic coordinates all of the sites sampled were tilted but none had enough variation in bedding attitude to perform fold tests comparing data between localities was used as a pseudo fold test and indicates that in all but one case the characteristic remanent magnetization found represents a magnetization acquired very early in the history of the rock interpretation of these data in terms of both virtual pole positions and paleolatitude changes with time shows that the omulevka terrane and the adjacent omolon terrane were together at low latitudes in silurian and devonian time and until late devonian their latitude was consistent with them being closely related to the siberian craton between devonian and permian times the paleolatitudes of the terranes decreased and when compared with equivalent reference paleolatitudes for the nearby siberian platform show a clear latitudinal separation from permian to jurassic time the omulevka and omolon terranes move steadily northwards reducing the relative latitudinal separation from siberia by late jurassic to early cretaceous time the observed and equivalent siberian paleolatitudes are identical indicating the accretion of the kolyma omolon superterrane to the eastern siberian continent

palaeoenvironmental studies in nw iberia cantabrian range vegetation history and synthetic approach of the last deglaciation phases in the western mediterranean abstract at the north western limit of the mediterranean basin in the mediterranean oceanic transition zone the multidisciplinary study of two palaeolakes villaseca and la mata province of leon provides data on the last deglaciation the juxtaglacial lakes were formed during a deglaciation phase of the last cold stage weichselian wurm estimated from the regional and pyrenean chronological data between circa 48 ka and 32 ka ka 1000 years ago their drainage occurred circa 17 ka and 15 ka respectively during the definitive glacial retreat phases these results provide evidence for a glacial maximum extension preceding the global last glacial maximum lgm and an early deglaciation comparisons with the pyrenean data show that in the most important glacial basins of the pyrenean cantabrian range glaciers were still present at middle elevation circa 18 20 ka the final deglaciation did not happen until around 16 ka during the period 48 13 3 ka along the pyrenean cantabrian range three stages can be distinguished in the deglacial processes between circa 48 and 32 ka the deglacial retreats were contemporaneous with d o events 12 to 6 between circa 32 ka and 18 ka major sedimentary modifications were rare two of them are synchronous with d o 4 and 3 a glacial readvance also occurred during this period along the pyrenean cantabrian range between 18 and 17 ka major sedimentary changes and an increase in the 18o records of the ngrip ice core record are synchronous between 15 and 13 3 ka glacial retreats and sedimentary changes are synchronous with the climatic improvement observed from the end of the oldest dryas to the end of the bolling allerod period these correspondencies suggest relationships between the deglacial processes in the western mediterranean and the palaeoenvironmental events in the north atlantic region during the last glacial interglacial transition during the full glacial period the pollen data indicates dominant steppic environments the oldest dryas was not a constant cooling phase and from around 15 5 ka the pollen data indicates a slight warming during the holocene until circa 2040 cal bp mixed oak forests developed and pine was a prominent component of the cantabrian landscape then the forests were destroyed due to mining agriculture and fire and this favoured the extension of heathland

carbon isotope geochemistry and palaeontology of neoproterozoic to early cambrian siliciclastic successions in the east european platform poland a well preserved stratigraphic record of the organic carbon isotopic composition across the precambrian cambrian transition has been obtained from a sequence of entirely detrital rocks underlying the lublin slope east european platform poland the observed 13 c pattern for organic carbon is comparable to isotope data determined for coeval carbonate platform sequences elsewhere these results underline the truly global nature of these secular variations within the carbon cycle during the terminal proterozoic and early cambrian largely independent of host lithology and facies the direct combination of micropalaeontological and geochemical results from sedimentary organic matter allows a detailed interpretation of the isotope record as probably caused by secular changes in the net balance of burial and erosion rates of repositories of organic carbon furthermore these variations appear to be directly correlatable with changes in the diversity and abundance of the biota and radiation extinction events

the sedimentary response to a pioneer geo engineering project tracking the kander river deviation in the sediments of lake thun switzerland human activities such as river corrections and deviations lake level regulations and installations of hydropower plants affect and often strongly modify natural processes in lacustrine systems in 1714 the previously bypassing kander river was deviated into peri alpine lake thun this pioneering geo engineering project the first river correction of such dimensions in switzerland doubled the water and sediment input to the lake in order to evaluate the sedimentary consequences of the kander river deviation the lacustrine sediments were investigated using a combined approach of high resolution 3ae5 khz reflection seismic data and sediment cores maximum length 2ae5 m the significance of this study is increased by the possible hazard represented by ammunition dumped into the lake from 1920 to 1960 and by the recent installation of a gas pipeline on the lake floor in 2007 2008 the first 130 years after the river deviation were dominated by an extremely high sediment input which led to the frequent occurrence of subaquatic mass movements slope failures primarily occur due to rapid sediment accumulation but were occasionally triggered in combination with earthquake induced shocks and lake level fluctuations after 1840 massmovement activity and sedimentation rates decreased due to a reduced sediment input as the kander river adjusted to its new base level and to a smaller degree by further engineering of the kander river bed and gravel withdrawal at the kander delta a further consequence of the kander river deviation is that the shores around lake thun have been more frequently affected by flooding due to the increased water input in the time span from 1850 to 2006 six historically and or instrumentally documented flood events could be correlated to flood turbidites in the sediment cores this study demonstrates the significant usefulness of lacustrine sediments not only in archiving natural hazards and human impact but also in assessing the consequences of future anthropogenic interventions on lacustrine systems

the silurian of gotland sweden facies interpretation based on stable isotopes in brachiopod shells the silurian of gotland sweden consists of 440 m of carbonate deposits repeatedly uniform sequences of micritic limestones and marls are interrupted by complex structured reefs and by adjacent platform sediments generally the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated the carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than to paleotemperature carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions consequently the facies succession on gotland results from global paleoclimatic conditions changes in terrigenous input due to different rates of weathering and freshwater runoff rather than sea level fluctuations control the carbonate formation of the silurian on gotland

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

north western alps holocene paleohydrology recorded by flooding activity in lake le bourget france abstract a 14 m long piston core was retrieved from lake le bourget nw alps france in order to provide a continuous record of flooding events of the rhone river during the holocene the selection of the coring site was based on high resolution seismic profiling in an area with limited mass wasting deposits and accumulated proximal rhone river inter and underflow deposits the age depth model of this core is based on i 14 ams radiocarbon dates ii radionuclide dating 137cs and iii the identification of historical data flood events eutrophication of the lake the sedimentary record dates back to 9400 cal bp and includes a thin mass wasting event deposited around 4500 cal bp a multi proxy approach was used to track the evolution and origin of clastic sedimentation during the holocene in order to identify periods of higher hydrological activity in the catchment area spectrophotometry was used to detect fluctuations in clastic supply and the study of clay minerals especially the illite crystallinity index allowed locating the main source area of fine grained clastic particles settling at the lake after flood events this dataset highlights up to 12 periods of more intense flooding events over the last 9400 years in lake le bourget and shows that the main source area of clastic particles during this period is the upper part of the arve river drainage basin this part of the catchment area drains several large glaciers from the mont blanc massif and fluctuations in rhone river flood supply in lake le bourget is interpreted as resulting essentially from mont blanc glacier activity during the holocene the comparison of clastic sedimentation in lake le bourget with periods of increasing land use and periods of alpine glacier and mid european lake level fluctuations suggest that the core ldb04 clastic record in lake le bourget is a continuous proxy of the holocene hydrological history of the nw alps

pollen based reconstruction of holocene land cover in mountain regions evaluation of the landscape reconstruction algorithm in the vicdessos valley northern pyrenees france long term perspectives on climate and human induced shifts in plant communities and tree line in mountains are often inferred from fossil pollen records however various factors such as complex patterns of orographic wind fields and abundant insect pollinated plants in higher altitudes make pollen based reconstruction in mountain regions difficult over the last decade the landscape reconstruction algorithm lra a model based approach in reconstruction of vegetation has been successfully applied in various parts of the globe however evaluation of its effectiveness in mountain ranges is still limited the present study assesses the extent to which the lra approach helps quantify the local changes in vegetation cover at vicdessos valley in northern french pyrenees as a case study in the study area well dated sediment cores are available from eight bogs and ponds 6 113 m in radius located above the current tree line we first use a simple simulation experiment to evaluate the way how pollen records from landscape islands mountain tops and plateaus would represent local vegetation and to clarify important factors affecting the lra based reconstruction in a mountainous region this study then uses pollen records from these sites and vegetation and land cover data both within a 50 km radius around the vicdessos valley and within a 2 km radius from each site for evaluation of the reveals and love based reconstruction of the regional and local plant cover respectively in the lra approach the land cover data are complied for coniferous trees broadleaved trees and non forested areas from the corine and historical maps in three time windows 1960 1970 1990 2000 and 2000 2013 major findings are as follows 1 accuracy of the regional vegetation estimates affects the reliability of the lra based reconstruction of vegetation within a 2 km radius use of the corine data as input to the love model improves reliability of the results over the use of the reveals based estimates of regional vegetation this implies that a systematic selection of pollen data only from sites above the tree line is problematic for estimating regional vegetation and thus the entire lra process 2 selection of the dispersal models for pollen transport i e the langrangian stochastic model vs gaussian plume model does not affect significantly the lra based estimates at both the regional and local scales in the study area 3 the lra approach improves the pollen based reconstruction of local vegetation compared to pollen percentage alone in northern pyrenees although further empirical and simulation studies are necessary our results emphasize the importance of site selection for the lra based reconstruction of vegetation in mountain regions

late holocene nao and oceanic forcing on high altitude proglacial sedimentation lake bramant western french alps comparison of glacially derived clastic inputs in high altitude proglacial lake bramant western french alps with measured north atlantic oscillation winter naow index reveals an inverse correlation between ad 1884 and 1968 at the pluridecadal timescale 20 25 years this reflects periodical variations in snow accumulation over lake bramant catchment area partly influencing the glacier mass balance in the watershed further comparisons with reconstructed naow index since ad 1500 highlight spatial and temporal variations of the pluridecadal naow influence on this alpine climate especially at the end of the little ice age in addition wavelet analysis of continuous proxies of clastic sedimentation over the last 4150 years indicates significant pluridecadal variability at frequencies compatible with the nao 30 years while periods centered at 60 70 years could also be linked to the north atlantic ocean atmosphere internal variability atlantic multidecadal oscillation amo the influence of the n

tectonic setting of the plutonic belts of yakutia northeast russia based on 40ar 39ar geochronology and trace element geochemistry samples from plutonic belts and individual intrusions in the sakha republic yakutia northeastern russia were analyzed using 40ar 39ar geochronology and trace element geochemistry four phases of activity were identified a subduction event along the southwest margin of the kolyma omolon superterrane with apparent ages of ca 160 140 ma a superposed collisional event dated at 143 138 ma a subduction event along the northern margin of the superterrane dated at 130 123 ma with a slightly older to contemporaneous extensional event to the west and intrusions associated with east west extension between 106 and 92 ma these phases are interpreted to represent 1 subduction under and 2 accretion to asia of kolyma omolon followed by local extension 3 subduction along the northern edge of this superterrane and 4 regional extension following closure of the south anyui suture and or the start of subduction associated with the okhotsk chukotka volcanic belt

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

biostratigraphy taxonomic diversity and patterns of morphological evolution of ordovician acritarchs organic walled microphytoplankton from the northern gondwana margin in relation to palaeoclimatic and palaeogeographic changes abstract acritarchs the fossilizable resting cysts of phytoplanktonic algal protists are the dominant component of marine organic walled microfossils in the palaeozoic the majority of acritarchs show strong similarities with dinoflagellate cysts in morphological and biogeochemical features as well as distributional patterns in the sediments the production of these organic walled microfossils and their distribution and survivorship in the sediments were controlled by differences in ecological tolerances and life cycle autecology of the planktonic parent organisms calculation of evolutionary rates and development of a detailed diversity curve at specific level form the basis for discussing the influence of global palaeoenvironmental perturbations on the evolution of organic walled microphytoplankton in northern gondwana during latest cambrian through ordovician times the potential of acritarchs for biostratigraphic correlation at the regional scale northern gondwana domain is much improved by our detailed revision of distributional patterns of 245 acritarch taxa the most important cambro ordovician acritarch bio events are short periods of diversification which also correspond to introduction of morphological innovations observed in latest cambrian and earliest tremadoc late tremadoc early arenig basal llanvirn and latest ashgill and an important extinction phase in the early caradoc overall acritarch diversity increased from the basal ordovician up to the middle llanvirn then declined in the early and middle caradoc during ashgill times the assemblages are poorly diversified at the generic level as a result of a combined effect of sea level drawdown and onset of glacial conditions but no major extinction event is observed in connection with the end ordovician biotic crisis the peak in acritarch diversity during middle ordovician times appears to be correlated to maximum spread of palaeogeographical assembly acritarch dynamics appear largely uncorrelated to second order sea level oscillations the primary abiotic controls on acritarch evolution were palaeogeographical and the associated palaeoceanographic changes especially during middle ordovician and the end ordovician palaeoclimatic shift the acritarch fossil record provides important information on the evolution of oceanic primary producers however the relationships between acritarch diversity oceanic productivity and evolution of invertebrate animals are proving much more complex than previously thought in particular the hypothesis of a causal relationship between changes in acritarch diversity and metazoan evolution in the palaeozoic is not supported by our data

use of lacustrine sedimentary sequences as indicators of holocene glacial history banff national park alberta canada abstract bottom sediments from three lakes in the canadian rocky mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of holocene glacial histories analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non glacial sediment sources sedimentary histories of the three lakes are similar suggesting that they record regional glacial climatic forcing rather than localized events and thus that they may be useful in reconstructing holocene glacial history lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500 7000 yr b p with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr b p possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr b p sometime after 4000 yr b p sedimentation rates and glacial sediment output began to rise again reaching approximately present levels by 2750 2650 yr b p and have not since returned to low mid holocene levels in detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr b p sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr b p and have remained very high since if the lake sediments are interpreted as a proxy record of upvalley glacial activity they allow the development of a glacial chronology which is at once generally consistent with and more complete and easily datable than the surficial glacial record

geology of the east siberian sea russian arctic from seismic images structures evolution and implications for the evolution of the arctic ocean basin 1 the kinematics and history of the opening of the amerasia basin are closely linked to the geology of the wide shelves surrounding the arctic ocean in this context multichannel seismic reflection data from the virtually unexplored shelf of the east siberian sea russian arctic are discussed in combination with potential field data three seismic marker horizons were defined and mapped their ages were linked to main tectonic and regional events and to onshore findings the data reveal that there is no continuation of the large rift basins from the laptev shelf onto the east siberian shelf and there are no indications for the previously defined several hundred kilometers wide blagoveshchensk basin the east siberian shelf is best described as an epicontinental platform that synsedimentarily subsided continuously since late cretaceous times with stronger subsidence to the northeast resulting in the formation of a large depocenter some form of extensional transtensional stresses affected the area and created relatively small ese wnw striking basins within this depocenter these basins are filled with 6 km thick late cretaceous to tertiary sediments the general dip of the platform of the east siberian shelf toward the northeast may be explained by dip slip movements along a major transform fault that is proposed by the rotation model for the opening of the amerasia basin for the evolution of small sag shaped basins within the east siberian depocenter we suggest a link to the opening of the eurasia basin instead of to the opening of the makarov basin

silurian δ13c stratigraphy a view from north america three positive shifts in 13 c are recognized in well dated carbonate successions in north america and can be confidently correlated with shifts in the baltic region by using conodont and graptolite zonations the 13 c excursions reach distinct peaks of 3 to 4 at the ends of the amorphognathoides and siluricus conodont zones and within the ludensis graptolite zone the three events are associated with the most significant extinction horizons in the silurian and occur near clastic carbonate transitions that mark eustatic or oceanographic changes the magnitudes of the two oldest 13 c peaks compare well with the baltic region however the end siluricus excursion reaches far greater values of as much as 11 in sweden likely reflecting local modification of the global seawater signature

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

palaeogeography and 10be exposure age chronology of middle and late pleistocene glacier systems in the northern pyrenees implications for reconstructing regional palaeoclimates abstract we present constraints on the chronology palaeogeography and palaeoclimatic implications for western europe of middle and late pleistocene glaciation in the ariege catchment north eastern pyrenees based on 37 cosmogenic 10 be exposure ages obtained from moraines and glacially scoured bedrock exposures we have dated six regional glacial stades the chronology emphasises several conclusions that are new to the region i in the pyrenees the global lgm occurred several thousands of years after the maximum ice extent of the wurmian glaciation ii almost full glacier extent occurred again during the global lgm but only in the eastern pyrenees iii valley glaciers such as in the ariege trunk valley attained lengths of 25 km during the oldest dryas stadial the cosmogenic exposure ages additionally provide the first direct evidence of 10 km scale fluctuations of ice front positions during the late pleistocene glacial cycle probably at the time of marine isotope stage 3 as well as rare insights into middle pleistocene ice margin positions compared with existing evidence of glacial palaeogeography in other catchments of the pyrenan range the data also reveal a sharp contrast in relative ice extent between the glacierized catchments of the eastern pyrenees ariege carol malniu tet where wurmian mie and lgm ice fronts reached similar positions and the rest of the range where ice fronts at the time of the mis 2 and global lgm palaeotemperature minima lagged far behind the wurmian mie terminal moraines we ascribe this non uniform behaviour among catchments to non uniform palaeoclimatic conditions along the strike of the pyrenees a range of palaeoenvironmental proxies reviewed in the literature highlight a sharp difference in sea surface temperatures between the warmer western mediterranean and the cooler bay of biscay the consequences of such an e w temperature gradient on weather patterns during the global lgm are compatible with a strengthening of mediterranean low pressure systems particularly the semi permanent balearic low generating greater precipitation over the eastern pyrenees compared to atlantic weather systems further west

the direction correction tilt test an all purpose tilt fold test for paleomagnetic studies abstract the tilt or fold test in paleomagnetism is used to infer whether paleomagnetic remanence was acquired before or after tectonic tilting while several tilt test formulations have been proposed none fully satisfies the requirements of statistical validity applicability to all bedding geometries and ease of use this paper introduces the direction correction dc test which examines the relationship between the paleomagnetic site mean directions and their corresponding bedding tilt corrections the dc test is similar to mcfadden s correlation test because both test whether or not the site directions contain information about the bedding tilts however the dc test gives greater weight to sites with greater counter bedding the dc test is similar to watson s numerical tilt tests because they determine the degree of untilting which gives optimal concentration of site directions however the dc test uses analytical rather than numerical methods graphical output aids the researcher in recognizing problem sites using both real and simulated data the dc test is demonstrated to be more discriminating than other tilt test formulations for all bedding geometries the simulations show that the power of the tilt test is inversely proportional to the 95 confidence interval 95 of the overall mean as a rule of thumb paleomagnetists should attempt to sample sufficient sites to obtain an 95 less than 1 6 of the bedding attitude difference