basin morphology and seismic stratigraphy of lake kotokel baikal region russia the basin of lake kotokel located along the eastern shore of lake baikal russia has attracted several scientific projects to investigate the climate vegetation and lake history throughout the late pleistocene and holocene however little was known about its basin structure and sediment architecture echo sounding and 3 5 khz single frequency sub bottom profiling were used to decipher the basin morphology and seismic stratigraphy to a depth of approximately 50 m the bathymetric map shows a very shallow lake of 4 m mean water depth and an almost flat lake bottom a distinct elongated small sized depression of up to 12 m water depth between the north western coast and a small island developed along an nw se oriented fault line a total of 46 km of seismic profiles crossing the lake along 12 transects shows that the bottom sediments consist of three different facies which accords to previously analyzed core sequences several distortions of sediment layers at various sites indicate tectonically induced impact which resulted in up to 3 m vertical offsets of sediment packages at local sites the offsets indicate a probably still active fault along the western shoreline of the lake soft gyttja of the upper 6 m does not show distortions and may have obscured potential younger tectonic activity the sediments date to the late pleistocene small updoming features along the boundary between layers i and ii may be assigned to degassing processes or to seismic activity river channel fills along the north eastern coast are indicative of a lower lake level prior to 15 ka bp the sediment stratigraphy indicates that suitable coring sites for paleoclimate studies are only located in the southern part of the basin where almost undisturbed sediments can be expected

radiocarbon based carbon source quantification of anomalous isotopic foraminifera in last glacial sediments in the western north pacific a previous study interpreted extremely 13c depleted excursions of planktonic and benthic foraminifera in last glacial sediments 17 500 to 25 400 cal years b p of the core retrieved from off shimokita peninsula and off hokkaido japan as evidence for periodic releases of methane arising from the dissociation of methane hydrate to better understand the formation process of the 13c depleted excursions we conducted high resolution natural radiocarbon measurements and biogeochemical analyses we found highly depleted 13c excursions ranging from 10 2 to 1 6 and 6 8 to 1 6 in planktonic and benthic foraminifera respectively most of the foraminiferal tests in these horizons were brown most likely as a result of postdepositional alteration reflecting the formation of authigenic carbonate on the surface of tests these alterations were also supported by high levels of mg calcite and the acid leaching test for anomalous foraminifera to evaluate the carbon sources in the altered foraminifera tests we quantified the relative contributions of 14c free methane derived carbon sources to the formation of authigenic carbonates in foraminifera with depleted 13c excursions using a coupled mass balance isotopic model 14c c and 13c 12c the radiocarbon ages of both planktonic and benthic 13c depleted foraminifera were approximately 600 to 2000 years older than those of normal tests from nearby horizons the relative contributions of authigenic carbonates derived from the methane oxidizing process reached to 22 wt for planktonic foraminifera and 15 wt for benthic foraminifera the 13c values of methane calculated from the mass balance model were between 29 and 68 for planktonic foraminifera and between 40 and 108 for benthic foraminifera consistent with 13c values reported for thermogenic and abiogenic methane in global methane hydrate reservoirs these data consistently suggest that methane related drastic environmental change occurred in the horizons that included 13c anomalies this study provides important information for interpreting geological records of the methane hydrate instability associated with climate

holocene climate variations retrieved from gun nuur lake sediment core in the northern mongolian plateau our pollen based climate reconstruction shows that both temperature and moisture were low during the early holocene from 10 000 to 8000 cal a bp and gradually climbed from 8000 to 6000 cal a bp the last 6000 years have been generally warm and wet with high amplitude fluctuations the high moisture conditions for the past 6000 years are not only corroborated by high arboreal pollen non arboreal ap nap trees and shrubs over herbs pollen ratio and high pollen concentration but also by high organic matter content and diatom data we suggest that lower winter insolation and remaining ice covers in the early holocene might have slowed down temperature rise in the continental interiors and that the resulted low temperature might have suppressed regional evaporation that was a major water vapor source for precipitation at the same time icemelt water injection into the north atlantic ocean might have also suppressed water vapor supplies to the downwind areas including the northern mongolian plateau

biogenic silica record of the lake baikal response to climatic forcing during the brunhes abstract this work presents a detailed orbitally tuned biogenic silica record of continental paleoclimate change during the brunhes chron the brunhes matuyama boundary lies within the warm isotopic stage 19 in baikal and the boundaries between eight lithological cycles correspond to terminations in the marine oxygen isotope record the high amplitude and resolution of climatically driven changes in biosi content in lake baikal sediments permits tuning of almost every precessional cycle during the brunhes and reveals the structure of interglacial stages for example the last three interglacial stages mis 5 7 and 9 clearly consist of five substages a b c d e corresponding to precessional insolation peaks abrupt and intense regional glaciations in siberia during substages 5d and 7d were driven by extreme insolation minima during substage 9d cooling was more gradual in response to more moderate forcing the impact of strong glaciation is also observed in the middle of stage 15 where full glacial conditions appear to have lasted for over 30 000 yr during substages 15d 15c and 15b marine oxygen isotopic stage 11 appears to be the warmest period during the brunhes in the lake baikal record with at least three substages a new hypothesis is presented regarding the response of the lake baikal biosi record to insolation forcing based on the mechanism controlling modern diatom blooms biogenic silica production is hypothesized to be dependent on changes in the heat balance of the lake and consequently on changes in the thermal structure of the water column this mechanism is also sensitive to short term sub milankovich cooling events such as the mid eemian cooling the montaigu event during substage 5c and a cooling which appears to be analogous to the montaigu event during substage 9c the continuity of the lake baikal paleoclimate record its sensitivity to orbital forcing and its high resolution make it an excellent candidate for a new paleoclimatic stratotype section for continental asia

the last glacial maximum and late glacial environmental and climate dynamics in the baikal region inferred from an oxygen isotope record of lacustrine diatom silica abstract the last glacial maximum and late glacial environmental and climatic variability in the baikal region southern siberia russia has been studied in a sediment sequence from lake kotokel located 2 km east of lake baikal using the oxygen isotope composition of diatom silica 18 o diatom the purification of diatom frustules involved the process of trimethylsilylation which has been shown to be suitable for preparation of diatoms for oxygen isotope analysis the lake kotokel 18 o diatom record presented here spans intervals from about 24 6 to 22 9 ka bp further referred to as last glacial maximum and 16 7 11 5 ka bp further referred to as late glacial displaying variations in the oxygen isotope composition between 26 7 and 31 2 overall high 18 o diatom values of about 29 to 31 during the two investigated intervals characterize a strongly evaporative lake system in a dry environment and suggest a lower than present lake level due to enhanced evaporation the lake kotokel diatom isotope record is roughly in line with the 60 n summer solar insolation pointing to a linkage to broader scale climate change but displays weaker reaction to short term climatic oscillations i e bolling allerod or younger dryas the climate warming at 14 3 ka bp is marked by negative spikes in the 18 o diatom record due to isotopically low melt water input from the mountainous hinterland

tracing seafloor methane emissions with benthic foraminifera in the baiyun sag of the northern south china sea changes in the concentrations of atmospheric greenhouse gases are an important part of the global climate forcing the hypothesis that benthic foraminifera are useful proxies of local methane emission from the seafloor has been verified on sediment cores by numerous studies the calcium carbonate caco3 content and the high resolution carbon and oxygen isotope composition of the benthic foraminifera from the core 08cf7 from the northeastern shenhu gas hydrate drilling area in the baiyun sag of the northern south china sea were analyzed and the benthic foraminifera s evidence for methane release from gas hydrate decomposition are presented here for the first time two rapid obvious carbon isotope negative excursions were observed in the oxygen isotope stage boundaries 5d 5c and 6 5e penultimate deglaciation about 130 ka of the cold to warm climatic transition period the largest negative value of 13c is about 2 95 and the whole change of carbon and oxygen isotope is strikingly similar and is in consonance with the atmospheric methane concentration recorded by the vostok ice core and the carbon isotopic record from lake baikal combining these results with the analysis of the geological conditions of the study area and the fact that gas hydrate exists in the surrounding area it can be concluded that the carbon isotope negative excursions of the benthic foraminifera in the northern south china sea are associated with methane release from gas hydrate decomposition due to deglacial climate warming by recording the episodes of massive gas hydrate decomposition closely linked with the northern hemisphere temperatures during major warming periods the new 13c record from the baiyun sag provides further evidence for the potential impact of gas hydrate reservoir on rapid deglacial rises of atmospheric methane levels

columbia river flood basalts from a centralized crustal magmatic system the columbia river basalt group in the northwestern united states derived from flood basalt eruptions that occurred 16 million years ago exhibits variability in geography and trace element geochemistry that has led to a number of proposed magma origins however the geochemical variability can be explained by a relatively simple model in which magma is derived from a mantle plume that assimilated continental crust in a centralized magma system the columbia river basalt group in the northwestern united states1 comprising about 230 000 cubic kilometres of rock exhibits unusual patterns in lava distribution geochemistry and its apparent relationship to regional tectonics consequently there is little consensus on the origin of its magmas2 3 4 5 6 7 8 9 10 11 12 here we examine the isotopic ratios of sr nd pb and os and trace element abundances in columbia river basalts the results suggest that most of the lava was produced when magma derived from a mantle plume assimilated continental crust in a central magma chamber system located at the boundary between the north american craton and the accreted terranes of idaho and oregon other related basalts are the product of mixing between the mantle plume and different types of regional upper mantle magma was then transported over a wide region by an extensive network of dykes a process that has been identified in other flood basalt provinces as well13 interactions of the plume with surrounding upper mantle and of mantle derived magmas with regional crust provide a relatively simple6 7 9 14 15 model to explain the more unusual features of the main phase columbia river basalts

laccolithic as opposed to cauldron subsidence emplacement of the eastern mourne pluton n ireland evidence from anisotropy of magnetic susceptibility the structural evolution and emplacement of the eastern mourne pluton was investigated using anisotropy of magnetic susceptibility ams measurements carried out on 112 oriented block samples and structural data from the host rocks from these new data cauldron subsidence as the emplacement mechanism is disputed and evidence for an alternative laccolithic style model involving inflation is presented this includes deflection and uplift of host rock bedding close to contacts and the magnetic fabric pattern which has a gentle dome geometry even close to contacts the magnetic lineations usually plunge down dip near the external margins but otherwise have a general ssw nne trend that diverges northward this suggests a northward directed inflow direction the model for the emplacement of the eastern mourne pluton is a laterally fed laccolith emplaced south to north the eastern margin is interpreted as a faulted contact facilitating the inflation of an asymmetrical breached laccolith

vegetation and climate dynamics during the holocene and eemian interglacials derived from lake baikal pollen records abstract the last interglacial li and holocene changes in annual precipitation p ann the mean temperature of the warmest t w and coldest t c month and the moisture index were reconstructed from continuous pollen records from lake baikal the holocene core 52 31 n 106 09 e presented in this study was recovered from a depth of 355 m in the 25 km wide underwater buguldeika saddle separating the southern sub basin of lake baikal from its central sub basin the biome reconstruction shows that tundra and steppe biomes have highest scores during ca 15 000 13 300 cal years b p and that taiga becomes a dominant vegetation type after ca 13 300 cal years b p our quantitative reconstruction indicates an onset of relatively warm and wet conditions soon after ca 10 000 cal years b p the warmest and wettest climate with t w 16 c p ann 480 mm and 0 9 1 has been reconstructed for ca 9000 7000 cal years b p in the lake baikal region this interval is characterized by the appearance and spread of hunter communities kitoi culture consistently a hiatus in the regional archaeological record 4900 4200 years b c or 6850 6150 cal years b p coincides with the interval of a major climate deterioration which followed the climatic optimum an attempt to find a relationship between the archaeological record and a spread of steppe and meadow communities in the lake baikal region demonstrates that despite a long habitation of the area the human impact on vegetation was local rather than regional and likely did not affect the pollen record from lake baikal the reconstructed peaks in the steppe biome scores during the last 9000 years are consistent with short one to five hundred year episodes of weak pacific summer monsoon supporting our interpretation that the holocene vegetation changes around lake baikal are associated with large scale circulation processes controlling regional water balance rather than with human activities thus our study proves the suitability of lake baikal pollen data for the reconstruction of natural vegetation and climate dynamics through the whole period from the onset of the li to the present comparison of the recent and the last interglacial suggests that the holocene climatic optimum was less pronounced e g lower summer and winter temperatures and annual precipitation sums than that of the li on the other hand pollen records demonstrate that the holocene forest phase already lasts some thousand years longer than that of the li the interglacial vegetation dynamics derived from the lake baikal pollen records can be satisfactorily explained by reconstructed changes in summer and winter temperatures and in available moisture the interglacial vegetation around lake baikal is dominated by the boreal forests which are associated with a generally warm and wet climate the high sea level associated with decreased ice volume appears to have had a greater impact on the siberian environments during the last and the recent interglacial than the direct effect of lower than present winter insolation reconstructed changes in the winter temperature correlate well with changes in the sea level and global ice volume while the summer temperatures derived from the lake baikal pollen records track changes in the summer insolation

response of lake baikal ecosystem to climate forcing and pco2 change over the last glacial interglacial transition abstract the 13 c record of total organic carbon in the lake baikal core bdp 93 2 over the last glacial interglacial transition shows remarkable correlation with atmospheric co 2 fluctuations and the negative isotopic shift of 3 5 4 in response to the global increase in paleo p co 2 level with rapid evolution of the lake baikal carbon cycle from full glacial to full interglacial modes however the p co 2 signal in the baikal 13 c sedimentary organic matter is inundated by the basin wide productivity signal in the holocene the baikal diatom abundance record as a paleotemperature proxy lags behind the gisp2 ice core 18 o temperature proxy record by ca 1 ka possibly reflecting the response time of the baikal ecosystem to major climatic transitions there is no lag associated with the pronounced younger dryas cooling however suggesting a different forcing mechanism with a short response time for this abrupt climatic event in continental interior asia the phase difference observed between the diatom abundance and 13 c proxies in lake baikal core bdp 93 2 suggests their independent responses to different forcing mechanisms further justifying their importance for paleoclimate reconstructions from lake baikal records

productivity cycles in lake hovsgol nw mongolia during the last 1 ma and the age model of the hdp 04 drill core record abstract repetitive patterns in the records of total organic carbon toc total nitrogen tn and 13 c org observed in the lake hovsgol sediment section from hdp 04 drill core reflect past changes in productivity of lake hovsgol and in the isotopic composition of the lake s carbon pool lake hovsgol productivity proxy signals are interpreted to represent the response of the hovsgol lacustrine system to glacial interglacial cycles of the pleistocene this interpretation is supported by the apparent orbitally forced pattern in the toc tn and 13 c org records of the past 250 ka in the bdp 96 2 drill core from neighboring lake baikal the intervals with independent age control such as the radiocarbon dated last glacial interglacial transition and the paleomagnetic reversals make it evident that productivity proxy signals are reliable indicators of past cold to warm and warm to cold climate transitions as seen from the agreement with the pattern of global climate change in marine 18 o records the brunhes matuyama reversal during the mis 19 interglacial coincides with a distinct peak of toc and tn in the hovsgol record similar to the signal during the holocene interglacial by contrast the upper jaramillo reversal in the lake hovsgol record occurs in a diatom free calcareous interval characterized by minima in toc tn and by a glacial type range of 13 c org values in both lake baikal and lake hovsgol records peaks in toc and tn contents help distinguishing past interglacials and interstadials and isotopically heaviest 13 c org values help identify past glacial intervals an age model for the hdp 04 drill core section is proposed based on recognizing the repetitive patterns in lake hovsgol productivity and lithologic records as regional paleoclimate cycles of middle to late pleistocene absolute dates and diatom biostratigraphic correlation ties to the lake baikal record are used as key controls in the proposed age model the interval 81 24 m in the hdp 04 sediment section below the major unconformity is correlated to mis 27 through late mis 13 whereas the upper 24 m of the hdp 04 section is suggested to have recovered the sedimentary record of late mis 7 to mis 1

hybridization and the petrogenesis of composite intrusions the dyke at an cumhann isle of arran scotland the composite dyke at an cumhann arran consists of a central unit of quartz feldspar porphyry flanked by narrow marginal dolerites containing xenocrysts of quartz plagioclase and alkali feldspar identical to the phenocrysts in the porphyry the chemistry of the marginal dolerites indicates that they formed by the crystallization of a hybrid magma produced at depth by the incorporation of the porphyritic acid magma in a basic liquid during the intrusion of the hybrid magma flow caused a differential distribution of the xenocrysts across the initial basic dyke subsequent intrusion of the quartz feldspar porphyry magma along the still unconsolidated centre of the basic dyke produced the wide central unit a similar origin is proposed for other composite intrusions of the same type in the region whilst it is unlikely that the coexistence of the highly contrasting magmas necessary for the formation of these intrusions is entirely coincidental there is little likelihood that the two liquids were related as members of the same fractionation series

evidence from lake baikal for siberian glaciation during oxygen isotope substage 5d abstract the paleoclimatic record from bottom sediments of lake baikal eastern siberia reveals new evidence for an abrupt and intense glaciation during the initial part of the last interglacial period isotope substage 5d this glaciation lasted about 12 000 yr from 117 000 to 105 000 yr b p according to correlation with the specmap isotope chronology lithological and biogeochemical evidence of glaciation from lake baikal agrees with evidence for the advance of ice sheet in northwestern siberia during this time period and also with cryogenic features within the strata of kazantzevo soils in southern siberia the severe 5d glaciation in siberia was caused by dramatic cooling due to the decrease in solar insolation as predicted by the model of insolation changes for northern asia according to milankovich theory coupled with western atmospheric transport of moisture from the open areas of northern atlantic and arctic seas which became ice free due to the intense warming during preceeding isotope substage 5e other marine and continental records show evidence for cooling during 5d but not for intense glaciation late pleistocene glaciations in the northern hemisphere may have begun in northwestern siberia

tectonics and magma dynamics coupling in a dyke swarm of iceland abstract to study the dynamics of dyke and fissure swarms in iceland we analyse the distribution of the dykes across the tertiary alftafjordur dyke swarm and that of open fissures and faults across the active krafla fissure swarm within these narrow 5 to 10 km wide and long length width ratio 10 swarms deformation is accommodated both by tectonics and magmatism the dyke swarm built during the westward regional tilting of the host rock lava pile the populations of dykes suggest that a characteristic thickness at about 3 m is involved during dyking dykes show a quasi periodic distribution across the swarm and form clusters spaced by about 2 5 km the analysis of the fissure distribution in the krafla volcanic system reveals a cluster spacing of about half of that of the dyke clusters we discuss the potential origins of these features as a result of magma dynamics host rock properties and tectonics clustering possibly reflects the intrinsic mechanical response to stretching of the upper levels of the brittle crust we propose a three dimensional model of dyke swarms in which magma likely migrates laterally within the upper crust from igneous centres where high magmatic supply rates locally perturb the regional stress field

metal organic associations in sediments i comparison of unpolluted recent and ancient sediments and sediments affected by anthropogenic pollution abstract the concentrations of 19 trace elements were determined by plasma emission spectrometry in organic fractions organic solvent extractables soluble humics protokerogen and kerogen concentrates separated from various recent and ancient sediments mangrove sediments algal mats oil shales phosphorites as well as sediments polluted by industrial metal emissions rhine river port pirie smelter effluent often the organic constituents were found to be enriched in trace elements especially b v mn co ni cu zn as mo ag cd sb hg and pb up to more than three orders of magnitude compared to the bulk sediments indicating the importancesof organic substances with respect to transport and fixation of trace elements within sediments the formation of metal organic associations was found to reflect the environment of deposition marine to terrestrial as well as diagenetic transformations recent to ancient against an unpolluted natural background increasing metal pollution led to increasing metal potake by organic substances especially for b cr fe co cu zn as cd and pb

crustal assimilation during turbulent magma ascent ata new isotopic evidence from the mull tertiary lava succession n w scotland assimilation of crustal rocks with concomitant fractional crystallisation afc is a well documented phenomenon in many igneous suites but geochemical evidence from the tertiary mull lava succession suggests that in these magmas crustal contamination occurred by a distinctly different mechanism lavas from the lower half of the mull plateau group mpg can be divided into two broad sub types high 8 mgo basalts with elevated ba and k and lower mgo 8 basaltic hawaiites with lower ba and k the lower crust and most of the upper crust beneath mull is probably of lewisian age the sr nd and pb isotope compositions of local lewisian crustal samples yield the following ranges 87sr 86sr 0 71002 0 72348 143nd 144nd 0 51045 0 51058 and 206pb 204pb 14 0 14 6 ten lavas have also been analysed and yield the following ranges 87sr 86sr 0 7028 0 7042 143nd 144nd 0 51214 0 51230 and 206pb 204pb 15 1 17 9 however within this range it is predominantly the more primitive mafic compositions with elevated mg ba and k that show the lowest nd and pb and the highest sr isotope values modelling of these isotopic results in conjunction with major and trace element data show that 1 contamination by lewisian lower crustal material does occur 2 that the process involved was not one of assimilation with concomitant fractional crystallisation afc the proposed contamination process is one whereby the hottest most mgo rich magmas have assimilated acidic partial melts of lewisian lower crust during turbulent ascent ata through thin poorly connected dyke and sill like magma chambers the chemical composition of the contaminated lavas can be modelled successfully through addition of 5 acidic lewisian crust to an uncontaminated lava in contrast the more evolved magmas which probably fractionated at sub crustal levels were either not hot enough to molt significant amounts of crust or did not ascend turbulently because of their higher viscosity and so are less contaminated with crust

water level changes in lake baikal siberia tectonism versus climate relative changes in the level of lake baikal amounting to hundreds of meters in quaternary time are well documented data presented here show that tectonic displacements of the lake outlet or former shoreline features are entirely sufficient to explain these relative lake level changes in contrast the morphology and hydrology of the lake make its level hydrologically insensitive to climate change available evidence indicates that throughout the past several hundred thousand years lake baikal was a dilute through flowing lake controlled by the level of its outlet on the basis of geologic data alone climatic effects on lake level whatever their magnitude are difficult to separate from those caused by active rift tectonism however consideration of 1 the hydrologic budget of the lake and 2 the configuration of the outlet suggests that potential lake level fluctuations due solely to climate change were less than about 2 m

petrology and geochemistry of the loch ba ring dyke mull n w scotland an example of the extreme differentiation of tholeiitic magmas the loch ba ring dyke in the tertiary igneous central complex of mull n w scotland is composed predominantly of a banded rhyolitic welded tuff the rhyolite contains numerous inclusions of dark aphanitic rock the textural relationships between the different rocks indicate rapid violent and intimate mixing during emplacement of the dyke the dark glassy component varies continuously from basaltic andesite to andesite dacite and rhyolite these glasses are enriched in feo and depleted in mgo at a given sio2 content in comparison to other tholeiitic highly differentiated volcanic rocks the rhyolite contains an average of 4 phenocrysts and is associated with the mineral assemblage plagioclase an32 to an21 sanidine or50 60 hedenbergite fayalite magnetite ilmenite apatite zircon mineral aggregates involving either plagioclase hedenbergite ilmenite or plagioclase fayalite magnetite are common but aggregates containing fayalite and hedenbergite together are scarce the dark glassy components are either phenocryst free or contain less than 0 2 phenocrysts the main phenocrysts associated with the dark glasses are plagioclase an65 an30 high calcium clinopyroxene ranging continuously from augite to pure hedenbergite pigeonite magnetite ilmenite and rare apatite zoning in minerals is generally weak or absent the plagioclase feldspar high calcium clinopyroxenes and pigeonites have similar compositional ranges to the minerals observed in the middle and upper zones of the skaergaard intrusion the mineral compositions are systematically related to sio2 content and mg number of the glasses the data demonstrate that mineral compositions and assemblages similar to the skaergaard form from silica rich andesitic to rhyolitic liquids the various mafic glasses are interpreted to have been derived from a zoned magma chamber underlying an upper layer of rhyolitic magma differentiation is attributed to fractional crystallization of the observed mineral assemblages causing sio2 enrichment and feo depletion however glasses with less than 57 sio2 have unusual compositions with very low mgo and p2o5 as well as variable al2o3 and tio2 their peculiarities could be explained by andesitic magmas assimilating cumulate mineral aggregates precipitated from more differentiated dacite and rhyolite magmas the bulk compositions of these cumulates have high feo low sio2 and negligible mgo and p2o5 it is suggested that the high density of the mineral aggregates containing fayalite hedenbergite magnetite and ilmenite caused them to settle through the zoned chamber to be assimilated by high temperature less differentiated magmas

srndpb isotopic evidence for crustal contamination in the rhum intrusion abstract sr nd and pb isotope ratios measured on cumulates from the eastern layered series els of the rhum intrusion indicate that the rhum magma chamber was contaminated by upper crustal amphibolite facies lewisian gneiss this is in marked contrast to the skye main lava series of skye which shows extensive contamination by lower crustal granulite facies lewisian gneiss 3 the amount of contamination involved was about 7 cryptic sr isotope profiles through the els show that contamination was extremely variable and may be controlled by mixing between fractionated contaminated magma and periodic injections of primitive magma into the chamber

compositional similarities of non solvent extractable fatty acids from recent marine sediments deposited in differing environments abstract five recent sediment samples from a variety of north american continental shelves were analyzed for fatty acids fas in the solvent extractable solex lipids as well as four types of non solvent extractable nonex lipids the nonex lipids were operationally defined by the succession of extraction procedure required to recover them the complete procedure included i very mild acid treatment ii hf digestion and iii saponification of the sediment residue following exhaustive solvent extraction the distribution pattern and various compositional parameters of solex fas in the five sediments were divided into three different groups indicating the difference of biological sources and also diagenetic factors and processes among the three groups of samples nevertheless the compositions of the corresponding nonex fas after acid treatment were surprisingly very similar this was also true for the remaining nonex fa groups in the five sediment samples the findings implied that most of the nonex fas reported here are derived directly from living organisms it is also concluded that a large part of nonex fas are much more resistant to biodegradation than we have thought so that they can form the large percentage of total lipids with increasing depth of water and sediments

two contrasting styles of interaction between basic magmas and continental crust in the british tertiary volcanic province some of the magmas that were extruded to form the 59 ma early plateau forming basalt dominated floods in the british tertiary volcanic province mixed with small amounts of sialic melt during their uprise through the continental crust while others underwent concomitant fractional crystallization and crustal assimilation magma batches of the first group originated in the uppermost asthenosphere and mostly ponded at the moho where they crystallized fractionally to form a basalt benmoreite suite the major element compositions of members of this series show that they underwent negligible further fractional crystallization between the moho and the surface nevertheless they paused long enough during their uprise to dissolve their high pressure phenocrysts and in many cases to mix with small amounts of acid melt from lower crustal granulite facies archaean lewisian leucogneisses basalts and tholeiitic andesites of the second group outcrop locally at the base of the lava piles in mull and skye their major element compositions show that they equilibrated within the upper third of the crust under conditions approximating to anhydrous 1 atm cotectic equilibria most of these lavas are in sw mull where proterozoic moine metasediments form the uppermost crust the major and trace element and isotopic compositions of the sw mull basal lavas show that they assimilated substantial amounts of moine metasediments progressively as they fractionated within the upper crust pb isotope data reveal that before their final upper crust evolution some of the sw mull basal lavas had already mixed with small amounts of lower crust acid melts

the lipid chemistry of an interfacial sediment from the peru continental shelf fatty acids alcohols aliphatic ketones and hydrocarbons a sample of the sediment water column interface which lies on the continental shelf under the peru upwelling regime has been examined for fatty acids fatty alcohols ketones and hydrocarbons fatty acids were the most abundant compound class ranging from c12 c24 with 16 0 as the major component 765 5 g g dry sediment the alcohols were dominated by 3 7 11 15 tetramethylhexadeca 2 en ol phytol with even chain n alcohols in the range c14 c20 the ketones consisted of c37 c39 di and tri unsaturated alken 2 ones and alken 3 ones both alkanes and alkenes were present in the hydrocarbon fraction the alkanes ranging from c13 c20 and comprising both straight chain and isoprenoid compounds the alkenes consisting of isomeric pairs of c25 branched trienes and tetraenes the data indicate that the organic content has been contributed very largely from marine sources probably mainly from phytoplankton and bacteria showing little terrigenous influence the presence of labile compounds such as polyunsaturated fatty acids with two to six double bonds implies that the sediment has undergone very little diagenetic alteration and the lipids are probably largely unchanged from the state in which they actually reached the sediment they may therefore serve as a useful baseline in assessing diagenesis in older sediments where diagenetic transformations are more advanced

evidence for an early proterozoic crustal province in the north atlantic region published sm nd data for the ketilidian belt of greenland the rockall bank in the north atlantic and the islay inishtrahull block of the british isles are used to suggest the existence of a single early proterozoic crustal province in the north atlantic region with a crustal formation age of c 1 96 ga the three sub provinces also have similar metamorphic histories as documented by sr and pb isotope data they probably represent one or more island arcs which were accreted to the laurentian craton 100 ma later in the 1 85 to 1 75 ga ketilidian laxfordian orogeny a line of suture between the archaean craton and early proterozoic accreted terranes is tentatively proposed

authigenic rhodochrosite from a gas hydrate bearing structure in lake baikal early diagenetic carbonates are rare in lake baikal siderite fe carbonate concretions in the sediments were discovered only recently here we discuss the first finding of rhodochrosite concretions mn carbonate discovered in the near bottom sediments of the gas hydrate bearing seepage structure st petersburg 2 in the deep water environment of the central baikal basin the crystal lattice of rhodochrosite contains iron and calcium substituting to manganese based on pore water geochemistry and of 13c values of rhodochrosite 23 3 and 29 4 carbon dioxide 3 8 to 16 1 and methane 63 2 to 67 8 we show that carbonate crystallization most likely occurred during microbial anaerobic oxidation of organic matter and that part of the oxygen making up the rhodochrosite seems to be derived from the 18o rich water released from dissociating gas hydrates

isotopic evidence for the incorporation of methane derived carbon into foraminifera from modern methane seeps hydrate ridge northeast pacific the presence of modern methane seeps at hydrate ridge offshore oregon provide an opportunity to study the influence of methane seeps on the ecology and geochemistry of living foraminifera a series of cores were collected from the southern summit of hydrate ridge in 2002 samples were preserved and stained to determine the 13c composition of three species of live stained and dead benthic foraminifera uvigerina peregrina cibicidoides mckannai and globobulimina auriculata specimens were examined under light and scanning electron microscopy sem and exhibit no evidence of diagenesis or authigenic carbonate precipitation individual living foraminifera from seep sites recorded 13c values from 0 4 to 21 2 indicating the isotopic influence of high methane concentrations average 13c values calculated from single specimens range from 1 28 to 5 64 at seep sites and 0 81 to 0 85 at a control off seep site two distinct seep environments distinguished by the presence of microbial mats or clam fields were studied to determine environmental influences on 13c values individual foraminifera from microbial mat sites exhibited more depleted 13c values than those from clam field sites we interpret these differences as an effect of food source and or symbiotic microbes on foraminiferal carbon isotopic values acting to magnify the negative 13c values recorded via the dic pool no statistical difference was found between 13c values of live vs dead specimens this suggests that authigenic carbonate precipitation did not play a dominant role in the observed isotopic compositions however a few dead specimens with extremely negative 13c composition 12 do indicate potential evidence for an authigenic influence on the recorded 13c composition

asymmetric late pleistocene glaciations in the north basin of the baikal rift russia new morphological sedimentological and radiocarbon data of quaternary deposits from the northern baikal rift document at least three extensive late pleistocene glaciations at 50 ka 40 35 ka and 26 13 ka respectively during these periods valley glaciers advanced from the high rift shoulders 2500 m down to the present day coast of lake baikal 456 m in places the glaciers advanced beyond the present day shoreline into the lake basin as indicated by large moraines exposed in steep cliffs along the lakeshore furthermore stratigraphic relations between lacustrine sequences and glacial deposits as well as 14 c ages of two palaeo shorelines 10 and 4 m above the present lake level show that the last and the penultimate glaciations were followed by relative lake highstands these land based observations document a significant influence of late pleistocene glaciations on the sedimentary development of this lacustrine rift basin the northern baikal rift is characterized by an asymmetric half graben geometry that controls river drainage and sedimentation this asymmetry greatly influenced the development and spatial distribution of pleistocene glaciers on both rift margins on the western flank tilted fault blocks parallel to the rift served as topographic barriers for valley glaciers advancing toward the lake basin only in two locations glaciers could reach the present day coast on the eastern rift flank in contrast structure and drainage conditions allowed the development of numerous consequent streams providing thoroughfares and space for recurrent valley glaciations thus the glaciers on the eastern flank could advance beyond the present day lakeshore into the lake basin in numerous locations these observations indicate that asymmetric rift structure in combination with the effects of global cooling were the important controls on the pleistocene glacial development of the baikal rift

atmospheric impacts and ice core imprints of a methane pulse from clathrates in relation to arctic warming the possible occurrence of methane hydrate degassing events has attracted an increasing interest in recent years we evaluate the atmospheric impact of rapid and massive emissions of methane and how they are imprinted in ice core records by combining for the first time models of atmospheric chemistry and trace gas transport in firn different emission characteristics as well as climatic conditions present pre industrial glacial are considered the d isotopic signatures characterizing stable isotopologues of methane dch3 and 13 ch4 are also analysed our results suggest little effect of clathrate degassing on the main methane oxidant oh radicals due to the relatively short atmospheric lifetime of methane the simulated clathrate induced perturbations last for less than a century this time scale is comparable to or shorter than the duration of air bubble closure in polar ice sheets as a consequence rapid methane perturbations in the atmosphere are strongly smoothed in ice core records this smoothing mostly depends on the snow accumulation rate at the site of ice core drilling we propose a methodology to identify a potential clathrate degassing event in ice core records continuous ch4 records from high accumulation rate sites could allow to decipher short time scale events d do f ch 4 should reveal a typical lying s shape at high accumulation rate sites reflecting the combined effects of the clathrate source signature negative excursion and subsequent oh fractionation in the atmosphere positive excursion the amplitude ratio of the negative and positive dd swings recorded in greenland and antarctica under similar accumulation rate conditions could also indicate the latitude of a clathrate degassing event

is the colonsay west islay block of sw scotland an allochthonous terrane evidence from dalradian tillite clasts in the scottish caledonides context the colonsay west islay terrane has seemed anomalous and therefore likely to be allochthonous new studies suggest however that its basement is not necessarily exotic but represents the missing early proterozoic link between greenland and scandinavia recent interpretations of the scottish mainland deformation history imply that the age of the grampian events there resembles that of the late proterozoic deformation previously identified in the colonsay group cover succession reconnaisance studies of dalradian tillite provenance suggest that the colonsay west islay basement was a source of dalradian sediment and perhaps floored that basin there is therefore less reason now to regard the colonsay west islay terrane as allochthonous and recent hypotheses of its tectonic emplacement being the cause of the grampian orogeny should be viewed with caution

ams radiocarbon analyses from lake baikal siberia challanges of dating sediments from a large oligotrophic lake abstract a suite of 146 new accelerator mass spectrometer ams radiocarbon ages provides the first reliable chronology for late quaternary sediments in lake baikal in this large highly oligotrophic lake biogenic and authigenic carbonate are absent and plant macrofossils are extremely rare total organic carbon is therefore the primary material available for dating several problems are associated with the toc ages one is the mixture of carbon sources in toc not all of which are syndepositional in age this problem manifests itself in apparent ages for the sediment surface that are greater than zero however because most of the organic carbon in lake baikal sediments is algal autochthonous in origin this effect is limited to about 1000 500 years which can be corrected at least for young deposits the other major problem with dating lake baikal sediments is the very low carbon contents of glacial age deposits which makes them extremely susceptible to contamination with modern carbon this problem can be minimized by careful sampling and handling procedures the ages show almost an order of magnitude difference in sediment accumulation rates among different sedimentary environments in lake baikal from about 0 04 mm year on isolated banks such as academician ridge to nearly 0 3 mm year in the turbidite depositional areas beneath the deep basin floors such as the central basin the new ams ages clearly indicate that the dramatic increase in diatom productivity in the lake as evidenced by increases in biogenic silica and organic carbon began about 13 ka in contrast to previous estimates of 7 ka for the age of this transition holocene net sedimentation rates may be less than equal to or greater than those in the late pleistocene depending on the site this variability reflects the balance between variable terrigenous sedimentation and increased biogenic sedimentation during interglaciations the ages reported here and the temporal and spatial variation in sedimentation rates that they imply provide opportunities for paleoenvironmental reconstructions at different time scales and resolutions

role of precursory less viscous mixed magma in the eruption of phenocryst rich magma evidence from the hokkaido komagatake 1929 eruption during the 1929 activity of hokkaido komagatake volcano the plinian eruption of a phenocryst rich andesite was preceded by a small eruption of more mafic magma formed by magma mixing a similar eruption sequence has been reported for some other eruptions pallister et al 1996 venezky and rutherford 1997 suggesting that eruption of a mixed magma is a precursor of phenocryst rich magmas for the purpose of understanding the tapping processes of the phenocryst rich magma chamber we investigated the temporal variation in the erupted magma and estimated the viscosity and density of the end member and mixed magmas with constraints drawn from petrography for the precursory mixed magma we estimate 33 4 vol phenocrysts andesitic dacitic melt composition 3 wt h2o content and temperature of 1040 c in comparison for the climactic silicic end member magma we estimate 48 3 vol phenocryst high silica rhyolitic melt 3 wt h2o and temperature of 950 c respectively the mafic end member magma which was not erupted is thought to be an almost aphyric basaltic andesitic magma based on mass balance calculation of the phenocryst content the proportion of the mafic end member magma component in the mixed magma was calculated to be 20 40 wt on the basis of these data we estimate magma viscosities of 103 9 106 9 and 102 0 pa s for the mixed silicic end member and mafic end member magmas respectively the calculated density differences among these magmas are inconsequential when possible errors are considered we calculate the minimum excess pressure required for dike propagation to be 31 mpa for the silicic end member magma and 8 mpa for the mixed magma using the estimated viscosity and dike propagation model of rubin 1995 if we assume that excess pressure is limited by the wall rock strength of the magma chamber excess pressure retainable in the magma chamber is less than ca 20 mpa this suggests that the mixed magma was able to ascend to the surface without freezing whereas the viscous silicic end member magma could not the formation and precursory eruption of the mixed magma are therefore effective and necessary initiation processes for the phenocryst rich viscous magma eruption

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

deglacial methane emission signals in the carbon isotopic record of lake baikal changes in the concentrations of atmospheric greenhouse gases constitute an important part of global climate forcing here we present the first continental evidence for climatically caused changes in a methane gas hydrate reservoir the organic carbon stable isotope record from lake baikal during the past 130 000 years registers regular emissions of isotopically light carbon by the occurrence of distinct negative shifts of 3 5 at every major orbitally forced cold to warm climatic transition during the past 130 000 years including marine oxygen isotope stage boundaries 6 5e 5d 5c 5b 5a and 2 1 we conclude that these emissions were associated with decomposition of sedimentary clathrates widespread in the baikal basin among potential hypotheses to account for these methane episodes the most probable appears to be hydrate dissociation due to deglacial warming of lake water we estimate that as much as 12 33 tg of methane could have been released with each episode by recording the systematically recurring episodes of massive methane clathrate decomposition closely linked with the northern hemisphere temperatures during major orbital warmings the new baikal 13c record provides further evidence for the potential involvement of clathrate reservoir in rapid deglacial rises of atmospheric methane levels

orbital forcing of continental climate during the pleistocene a complete astronomically tuned climatic record from lake baikal se siberia abstract a new composite bdp 96 biogenic silica record over the entire pleistocene was generated by splicing bdp 96 1 and bdp 96 2 drill cores from lake baikal crosschecked against a similar record from a nearby bdp 98 drill core a new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of september perihelia this target is derived from analysis of regional climate proxy responses during the holocene the last interglacial and around paleomagnetic reversals by resolving virtually every precessional cycle during the pleistocene the new age model represents a major improvement compared with previously reported lake baikal timescales the astronomically tuned ages of the pleistocene paleomagnetic reversals are consistent with published dates the minimal tuning approach we used precession only has also aligned high signal power in a narrow obliquity band confirming the strong presence of orbital forcing there are also strong ca 100 ka scale cycles but these are not aligned with the orbital eccentricity despite the location of lake baikal in a continental interior that is highly sensitive to insolation forcing the tuned biogenic silica record reveals a consistent phase difference of 32 ca 4 ka relative to insolation in the obliquity band an inherent lag embedded in a continental proxy record not driven by global ice volume is an intriguing finding another new observation is that long term changes in sedimentation rates in lake baikal appear to be related to the amplitude of orbital forcing both amplitudes and sedimentation rates undergo significant changes during mis 24 mis 19 interval corresponding to the middle pleistocene transition with potential for linking continental and marine climato stratigraphies the new baikal record serves a new benchmark correlation target in continental eurasia as an alternative to june 65 n insolation and odp correlated timescales

getting granite dikes out of the source region whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow various formulations are developed for a viscous fluid at temperature t sub m intruding a growing crack in an elastic solid the initial solid temperature equals t sub m at the source and decreases linearly with distance from the source if t sub m is the unique freezing temperature of the fluid dike growth is initially self similar and an essentially exact solution is obtained if t sub m is above the solidus temperature the solution is approximate but is designed to overestimate the distance the dike may propagate the ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness perhaps more intuitively one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus necessary for dikes to propagate far into subsolidus rock it is concluded that for reasonable material properties and source conditions most basalt dikes will have little difficulty leaving the source region but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus while these results can explain why granitic dikes are common near granitic plutons but rare elsewhere the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes nonetheless these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies

paleoenvironmental proxy records from lake hovsgol mongolia and a synthesis of holocene climate change in the lake baikal watershed abstract here we discuss paleoenvironmental evolution in the baikal region during the holocene using new records of aquatic diatom and terrestrial vegetation changes from hovsgol mongolia s largest and deepest lake we reconcile previous contradictory baikal timescales by constraining reservoir corrections of ams dates on bulk sedimentary organic carbon synthesis of the holocene records in the baikal watershed reveals a northward progression in landscape vegetation changes and an anti phase behavior of diatom and biogenic silica proxies in neighboring rift lakes in lake baikal these proxies appear to be responsive to annual temperature increases after 6 ka whereas in lake hovsgol they respond to higher precipitation runoff from 11 to 7 ka unlike around lake baikal warmer summers between 6 and 3 5 ka resulted in the decline not expansion of forest vegetation around lake hovsgol apparently as a result of higher soil temperatures and lower moisture availability the regional climatic proxy data are consistent with a series of 500 yr time slice holocene gcm simulations for continental eurasia our results allow reevaluation of the concepts of the holocene optimum and a maximum of the asian summer monsoon as applied to paleoclimate records from continental asia

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

insolation regime in siberia as a major factor controlling diatom production in lake baikal during the past 800 000 years abstract a unique diatom biostratigraphy of the brunhes chron in lake baikal revealed by detailed studies of pelagic diatom paleo assemblages indicates that dramatic changes in insolation during the past 800 ka bp produced surprisingly rapid diatom speciation and extinctions the orbitally tuned age model allows the diatom assemblages to be compared with individual marine isotopic stages and substages during the brunhes most of the interglacial periods are characterized by explosive speciation and appearances of new pelagic planktonic diatom species in contrast most of the glacial periods are characterized by spectacular extinctions three broad periods characterized by different degrees of stability in the pelagic diatom assemblages are distinguished during the brunhes chron in the lake baikal sedimentary record mis 19 15e mis 15a 11 and mis 9 5 these periods are apparently associated with the long term changes in the amplitude of precessional insolation variations examination of individual interglacial periods further reveals the sensitivity of the baikal ecosystem to the regional energy balance virtually every precessional insolation peak during the early brunhes is characterized by a unique and peculiar paleo assemblage for the first time the siliceous microfossil record has demonstrated such a high degree of sensitivity to insolation forcing of regional climate despite the dramatic changes in the pelagic plankton driven by extreme climatic changes diatoms never went fully extinct during any glacial period although greatly or completely renewed during each subsequent interglacial the pelagic diatom assemblage still managed to return dominated by the new baikal endemic species the diatom assemblage observed in modern lake baikal despite being mostly endemic has formed during the past 50 100 ka and is therefore rather young these results demonstrate the remarkable capacity of this large freshwater system to sustain the dynamic stability on the large time scales

diagenesis of free and bound lipids in terrestrial detritus deposited in a lacustrine sediment recent sediments from an oligotrophic lake loch clair having uniform organic input for 2000 yr show changes in lipid abundance and composition with increasing depth attributed to diagenesis stability of free lipids decreases in the order n alkanes alkan 2 ones sterols n alkanoic acids n alkanols n alkenoic acids diagenetic loss of shorter chain homologues is complete within 400 yr stabilisation of bound relative to free lipids increases the proportion of the former with sediment age and reduces loss of shorter chain bound homologues in an eutrophic lake cross mere shorter chain free and bound sedimentary lipids show increased abundance compared with loch clair the relative importance of higher input of shorter chain lipids derived from aquatic detritus and slower initial diagenesis due to the anoxic hypolimnion as causative factors for this difference between lake types cannot yet be assessed

vegetation response in the southern lake baikal region to abrupt climate events over the past 33calkyr abstract we reconstructed vegetation changes and fire events in the southern lake baikal region over the past 33 cal kyr using a sediment core from the buguldeika saddle southern lake baikal to examine vegetation response to past short term climate variations herbs such as artemisia and asteraceae were dominant just before the last glacial maximum lgm low pollen accumulation rates pars with little herb pollen indicate sparse herbaceous vegetation cover during the lgm picea expanded after the bolling interval suggesting expansion of riparian areas and shrub alnus rapidly increased during the following allerod interval abies and pinus subgen haploxylon began to increase at the beginning of the holocene and pinus subgen diploxylon has been highly dominant since the middle holocene the vegetation change after the lgm is similar to that from other sites in the lake baikal region but the responses to short term climate events are pronounced fluctuations in herb elements and vegetation cover as indicated by the par correspond to the younger dryas yd cooling event the decline in the par and increase in herb taxa were remarkable at the beginning of the yd but larix and picea trees were distributed in river valleys near lake baikal in the latter half the rapid expansion of betula and artemisia following frequent fires in the early holocene may have been in response to the 8 2 cal ka bp cooling event from these findings the southern lake baikal region including the selenga river basin may possibly have been more sensitive than other parts of the region to abrupt climate changes

challenges in constructing the age model for the lake baikal cores during the last glacial interglacial transition the response to m a grachev

high resolution records of methane hydrate dissociation odp site 893 santa barbara basin abstract sediment records from odp site 893 santa barbara basin have documented brief negative carbon isotopic excursions in the late quaternary in planktonic and benthic foraminifera these excursions were interpreted as evidence of major releases of methane from the marine hydrate reservoir affecting the entire water column and likely reaching the atmosphere these carbon isotopic excursions are further recorded in the 13c values and concentration of lipid biomarkers of marine methanotrophs in the basin three previously described carbon isotopic excursions are re examined during this study at a resolution of every 3 7 years the original isotopic excursions were sampled at a resolution of once every 50 70 years examination using light microscopy and environmental scanning electron microscopy esem indicates that specimens in this study are in excellent condition with no apparent evidence of postdepositional diagenesis or alteration of the foraminiferal shells alternative hypotheses to account for these conspicuous carbon isotopic excursions include postdepositional carbonate diagenesis of the excursion intervals and changes in surface ocean productivity and carbon export to the sediments in this study we further test the hypothesis that these excursions record the primary signal of methane in the water column by intensive analyses of the previously described carbon isotopic excursions all four carbon isotopic excursions studied are associated with interstadial warming in the basin time periods that are associated with shifts in the benthic foraminiferal assemblages toward low oxygen fauna at high resolution 13c excursions appear very brief 5 10 years duration and within this time planktonic and benthic species record a significant shift in 13c composition planktonics to 3 and benthics to 6 excursion events are synchronous in benthic and planktonic species within the resolution of these records in one interval studied 37 5 ka the bulk organic carbon 13c records a 1 negative shift in concert with the carbon isotopic excursion in benthic and planktonic foraminifera consistent with a carbon isotopic shift of photosynthetically derived marine organic carbon we suggest that alternate explanations invoking changes in productivity and or postdepositional alteration of these intervals cannot account for the entire magnitude of the carbon isotopic excursion nor the diversity of evidence presented here thus methane hydrate destabilization remains a compelling hypothesis to explain the conspicuous 13c excursions observed in odp site 893 and similar late quaternary excursions described elsewhere

the genesis ascent and emplacement of the northern arran granite scotland implications for granitic diapirism integrated structural and petrological data are used to trace the evolution of the northern arran coarse granite during the latter stages of its ascent and its emplacement structural analysis of the aureole of the granite suggests that it rose as a single body of magma which is confirmed by petrological data during its ascent the pluton intersected the downward dipping limb of an existing synform refolding and displacing it upward to form a concentric or rim synform this direct evidence of vertical displacement of the country rocks confirms that the pluton is a diapir diapiric ascent was permitted by a reduction in wall rock viscosity and hence viscous drag forces on the pluton aided by heat loss due to crystallization during ascent most of the deformation within the aureole can be attributed to ascent of the pluton the early rim synform is overprinted by flattening strains and faulting caused by in situ radial expansion which represents the ultimate evolution of a diapiric body the final shape of the pluton is determined by inhomogeneous deformation of the aureole which is partly controlled by pre existing faults

lipid biogeochemistry in the laurentian trough ii changes in composition of fatty acids sterols and aliphatic hydrocarbons during early diagenesis abstract interfacial sediments of the 300 m deep laurentian trough contained 3 2 11 1 2 6 2 0 4 2 4 0 2 0 5 mg g 1 oc of fatty acids unresolved hydrocarbons ucm sterols and resolved aliphatic hydrocarbons respectively reflecting a 46 93 loss relative to settling particles intercepted at 150 m depth a further 22 66 lipid loss was observed between 0 3 and 35 cm depth in the sediments lipid accumulation efficiencies in the top 3 cm sediment inventory averaged 21 29 of water column fluxes and indicated a clear reactivity trend pheopigments sterols fatty acids total lipids resolved hydrocarbons ucm however within each lipid class marine derived components were as highly reactive as pheopigments whereas terrestrial compounds behaved akin to the ucm extremely labile marine lipids that were enriched in settling particles such as pristane 24 methylcholesta 5 22e dien 3 ol and heneicosahexaene were quickly lost near the sediment water interface only moderately reactive components 16 0 16 1 fatty acids squalene and the more stable 22 0 and 24 0 acids fichtelite and ucm persisted deep enough to preserve the geographical trends observed for rapidly settling particles i e predominance of terrestrial and petrogenic compounds at a landward site and prevalence of marine lipids at a station located 120 km further seaward the preferential decay of marine components continued with depth in the cores resulting in similar residual lipid patterns at 35 cm depth however each site could still be discriminated clearly by its fatty acid and hydrocarbon composition in situ sedimentary processes such as the vertical distribution of bacteria and the production of coprostanol were also recorded in the lipid composition of these deep coastal sediments

the structure and development of the baikal rift depression abstract the baikal rift depression located in southeastern siberia is one of the best investigated intra continental rift structures in the world in addition to being the site of comprehensive studies by russian geo scientists for decades the baikal depression is now the subject of new international investigations using advanced technical means and technologies the present paper summarizes the principal results concerning the morphostructure of the baikal rift the stratigraphy of the cenozoic deposits and the stages of the baikal depression development based on cross sections which exhibit the impact of both tectonic and climatic processes the development of the baikal depression occurred through two stages i the pre crypto rift stage of the late cretaceous eocene and ii active rifting of the oligocene recent the second stage is divided into several steps and substeps separated by tectonic phases formation of the baikal rift zone appears to be related to the indo eurasian plate collision related to a model of passive rifting the uplifted shoulders of the depression have a complex morphostructure overlain by cenozoic deposits which are thin and restricted in area the near marginal zones of the rift are largely defined by the system of longitudinal blocks of different width surfaces of the blocks are inclined either to the uplifted shoulder of the rift bound by listric faults typical for western edges of the depression or to the axis of the depression cenozoic deposits on the blocks consist of accumulative plains composed primarily of thick lacustrine sequences

ridge plume interaction in the north atlantic and its influence on continental breakup and seafloor spreading development of the rifted continental margins and subsequent seafloor spreading in the north atlantic was dominated by interaction between the iceland mantle plume and the continental and oceanic rifts there is evidence that at breakup time a thin sheet of particularly hot asthenospheric mantle propagated beneath the lithosphere across a 2500 km diameter region this event caused transient uplift massive volcanism and intrusive magmatism and a rapid transition from continental stretching to seafloor spreading subsequently the initial plume instability developed to an axisymmetric shape with the 100 km diameter central core of the iceland plume generating 30 40 km thick crust along the greenland iceland faeroes ridge the surrounding 2000 km diameter region received the lateral outflow from the plume causing regional elevation and the generation of thicker and shallower than normal oceanic crust we document both long term 10 20 ma and short term 3 5 ma fluctuations in the temperature and or flow rate of the mantle plume by their prominent effects on the oceanic crust formed south of iceland lateral ridge jumps in the locus of rifting are frequent above the regions of hottest asthenospheric mantle occurring in both the early history of seafloor spreading when the mantle was particularly hot and throughout the generation of the greenland iceland faeroes ridge the northern north atlantic is a classic example of continental breakup above a thermal anomaly in the mantle created by a mantle plume the most obvious consequence of this was the generation of huge volumes of basaltic magmas by partial melting of the mantle at the time of continental breakup white mckenzie 1989 most of this magma bled up to the crust where the majority perhaps 60 80 was frozen in the lower crust while the rest was extruded as lava flows and pyroclastic deposits often after undergoing fractionation in crustal magma chambers if the extrusion rates are sufficiently high lava flows may form extensive sub horizontal flood basalts extending across the continental hinterland on rifted continental margins the extrusive lavas are typically expressed as seaward dipping reflector sdr sequences that are readily identifiable on seismic reflection profiles all these features have been found along more than 2 500 km of the rifted continental margins in the northern north atlantic on both the european and the greenland sides furthermore the mantle plume that gave rise to the thermal anomaly in the mantle is still going strong lying beneath iceland at the present day the northern north atlantic is therefore an excellent natural laboratory in which to investigate the interplay between rifting and magmatism because the history of rifting is well recorded from the time of continental breakup in the early tertiary to the seafloor spreading at the present day magnetic anomaly field reversals during the tertiary were frequent and south of iceland there are few large fracture zones in the oceanic crust so the seafloor spreading magnetic anomalies contain a clear record of the rifting history throughout the ocean basin there have also been several well constrained wide angle seismic surveys of the continental margins on both sides of the atlantic e g barton white 1997b smallwood et al 1999 korenaga et al 2000 often with coincident drilling penetrating the volcanic rocks so both the structure of the rifted margins and the timing of the igneous activity are well known in this paper we examine the interaction between the mantle plume and rifting first of the continental lithosphere to form the present continental margins and subsequently of the oceanic lithosphere to form the mid ocean ridge and the land mass of iceland smallwood white rift plume interaction 3

possible origin of n alkanes with a remarkable even to odd predominance in recent marine sediments abstract n alkane distributions with a remarkable even to odd predominance c16 c24 were found in marine surface sediments the previously proposed diagenetic reduction of the corresponding n fatty acids could not be considered as a source for these n alkane based on a comparison of compositional features of n alkane n fatty acid and n alcohol distributions carbon isotope analyses and other geochemical parameters the data indicate that the even predominant n alkanes were derived directly from marine bacteria

molecular and isotopic abundances of long chain n fatty acids in open marine sediments of the western north pacific abstract molecular abundance and compound specific carbon isotope ratios of long chain n fatty acids lcfas ranging from c20 to c30 are reported for open marine sediments of the western north pacific a positive correlation r2 0 94 is observed between total organic carbon toc and lcfa concentrations although the toc concentrations varied from 0 34 to 2 62 wt in dry sediment the relatively uniform ratio of lcfas to toc 0 74 0 12 mg gc is similar to that of the central pacific reported by ohkouchi et al ohkouchi n kawamura k kawahata h taira a 1997 latitudinal distributions of terrestrial biomarkers in the sediments from the central pacific geochim cosmochim acta 61 1911 1918 and in a core sample from the tropical central pacific by prahl et al prahl f g muehlhausen l a lyle m 1989 an organic geochemical assessment of oceanographic conditions at manop site c over the past 26 000 years paleoceanography 4 495 510 on the other hand lcfa concentrations in riverine and estuarine sediments are apparently higher than in open marine sediments carbon isotopic compositions of individual lcfas in open marine sediments are similar 26 1 for n c24 and n c26 being more enriched in 13 c than bay and riverine sediments by up to 6 terrestrial c3 higher plants commonly have a 13 c value of 26 in bulk organic carbon and because lipid components including fatty acids are known to be depleted in 13 c by several per mil compared to bulk organic matter this study indicates that the open marine sedimentary lcfas are not derived from normal terrestrial c3 higher plants rather the isotopic composition is consistent with a mixed source of c4 and c3 terrestrial higher plants and or marine organisms low carbon preference index cpi values of the lcfas and the isotopic difference between the northern and southern samples suggest that the lcfas of this study are likely to be related to marine primary productivity even though lcfas have often been used to infer a terrestrial higher plant input to marine sediments

an organic carbon isotopic record of glacial postglacial change in atmospheric pco2 in the sediments of lake biwa japan a 12 m piston core of sediment from lake biwa japan provides a high resolution record of sedimentary organic matter accumulation over the pleistocene holocene transition organic carbon concentrations are generally 1 2 in sediments deposited since 15 kyr ago c n ratios indicate that the organic matter is predominantly from aquatic production a shift in organic carbon isotopic composition from 21 to 25 occurs over the glacial postglacial boundary changes in lake productivity organic matter preservation sources of organic matter and water temperature can be eliminated as probable causes of the observed organic carbon isotopic shift annual overturn of lake waters and rapid dissolution of biogenic carbonates maintain equilibrium between atmospheric co2 and dissolved co2 in this lake the isotopic composition of organic matter buried in the sediments of lake biwa consequently appears to record the shift in atmospheric pco2 from 200 ppm to 280 ppm which occurred at the pleistocene holocene transition

high time resolution ams 14c data sets for lake baikal and lake hovsgol sediment cores changes in radiocarbon age and sedimentation rates during the transition from the last glacial to the holocene abstract high time resolution 14 c dating of lake baikal sediment cores indicates negative and positive anomalies of calculated linear sedimentation rate lsr 1 1 and 35 6 cm ka respectively during the period of climate transition from the last glacial to holocene the timing of the lake baikal apparent lsr anomalies is consistent with that of the changes in the atmospheric radiocarbon concentration 14 c during younger dryas rapid cooling event 14 c dating of lipids in the lake baikal surface sediments revealed that the sources of sedimentary lipids were different in each basin in the northern basin of lake baikal the 14 c age of total lipids from the surface sediment 4 0 14 c ka was found to be older than that of toc 1 6 14 c ka by contrast the 14 c age of total lipids in the southern basin was younger than that of the toc by ca 0 7 3 0 ka in the lake hovsgol sediment cores ages of the main lithologic boundaries during the last glacial interglacial transition were estimated based on new 14 c data sets toc concentration in the cores started to rapidly increase at 13 8 0 3 14 c ka at the base of the basinwide finely laminated layer deposited during bolling allerod the base of the layer diatomaceous mud corresponds to the end of younger dryas event 10 6 0 1 14 c ka

the blackstones bank igneous complex geochemistry and crustal context of a submerged tertiary igneous centre in the scottish hebrides the blackstones bank located about 60 km wsw of the isle of mull in western scotland is a submarine plutonic complex in the british tertiary igneous province geochemical and isotopic analysis of gabbros microgabbros and basic dykes shows that the magmas interacted strongly with crustal rocks during their emplacement the isotopic signature of the contaminated tertiary intrusions shows no evidence of any interaction with archaean basement despite the location of the blackstones complex to the west of the great glen fault instead the blackstones rocks have crustal signatures resembling the proterozoic basement and cover rocks of western islay it is therefore inferred that early proterozoic crust extends to the west of the great glen fault at this point on the scottish continental shelf in addition the occurrence of similar isotopic signatures in tertiary igneous rocks east of the loch gruinard fault confirms that early proterozoic basement extends under the grampian block of mainland scotland when combined with published evidence from the rockall bank the new data constrain the location of an archaean proterozoic crustal suture with a wnw trajectory which cuts across the continental shelf of northwest britain

pre eruptive magma mixing in ash flow deposits of the tertiary rum igneous centre scotland the northern marginal zone of the rum igneous centre is a remnant of an early caldera and its infill it is composed of intra caldera breccias and various small volume pyroclastic deposits overlain by prominent rhyodacite ash flow sheets of up to 100 m thickness the ash flows were fed from a feeder system near the caldera ring fault and intrusive rhyodacite can locally be seen grading into extrusive deposits a variety of features suggest that the ash flows were erupted from a magma chamber that contemporaneously hosted felsic and mafic magmas i chilled basaltic inclusions in rhyodacite ii formerly glassy basaltic to andesitic enclaves with fluid fluid relationships iii feldspars with thick reaction rims enclosed in the basaltic to andesitic inclusions yet with cores chemically resembling those of the rhyodacite iv trace element compositions of the rhyodacite and the mafic enclaves form a mixing line between the end member rhyodacite and basalt compositions additionally textural and chemical features in the rhyodacite feldspar phenocrysts are consistent with magma mixing v feldspars with resorption embayments cutting through internal zonation of the crystals vi complexly zoned crystals with sieve textured zones that are overgrown with euhedral zones vii oscillatory zonation of feldspar phenocrysts in the rhyodacite showing sharp increases in anorthite an 10 followed by gradual decrease in an content an 4 this evidence points to eruption of ash flows from a felsic magma chamber that was periodically replenished by injection of mafic magma diffusional mixing between the two magmas was permitted by temperature and compositional differences but was slow due to the contrast in viscosities and densities the fe ti p enriched basic magma that replenished the chamber was degassing on entering the lower temperature environment and soon equilibrated thermally followed by chemical exchange between the two end member magmas this process formed hybrid andesite enclaves enriched in trace elements beyond that caused by simple mixing implying trace element diffusion in addition to bulk mixing eruption was caused by replenishment with and degassing of the basic magma and the chamber partially evacuated while the process of hybridisation was underway the erupted products record magma mixing by chamber replenishment blending of two magmas and elemental exchange in the magma chamber and also physical mingling in the eruptive conduit

geological implications from geochemical and isotopic studies of upper cretaceous and lower tertiary igneous rocks around the northern rockall trough major trace rare earth element geochemistry and isotopic data have been obtained for offshore igneous rocks from around the northern rockall trough ne atlantic ocean most comprise basalts derived from the sub rockall hebridean asthenospheric mantle but subcontinental lithospheric mantle generated the phono tephrites of rosemary bank and melting of upper crust was responsible for the peraluminous dacites of well 163 6 1a crustal contamination of the lavas around the rockall trough suggests that the lewisian islay rockall bank basement terrane boundary crosses the trough and passes between george bligh and rockall banks basalts representing uncontaminated mantle derived material are scarce but the available data indicate that the cretaceous basalts of rosemary bank and anton dohrn have higher 206 pb 204 pb ratios than the younger palaeocene lavas of rockall bank the hebrides shelf and well 163 6 1a implying significant geographic and or temporal changes in mantle composition

a model that helps explain sr isotope disequilibrium between feldspar phenocrysts and melt in large volume silicic magma systems feldspar phenocrysts of silicic volcanic rocks are commonly in sr isotopic disequilibrium with groundmass in some cases the feldspar is more radiogenic and in others it is less radiogenic several explanations have been published previously but none of these is able to accommodate both senses of disequilibrium we present a model by which either more or less radiogenic feldspar or even both within a single eruptive unit can originate the model requires a magma body open to interaction with biotite and feldspar bearing wall rock magma is incrementally contaminated as wall rock melts incongruently biotite preferentially melts first followed by feldspar such melting behavior which is supported by both field and experimental studies first contaminates magma with a relatively radiogenic addition followed by a less radiogenic addition feldspar phenocrysts lag behind melt groundmass of volcanic rock in incorporating the influx of contaminant thus resulting in sr isotopic disequilibrium between the crystals and melt the sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process this model is testable by isotopic fingerprinting of individual feldspar crystals for a given set of geologic boundary conditions specific core to rim sr isotopic profiles are expectable moreover phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history initial results of sr isotopic fingerprinting of sanidine phenocrysts from the taylor creek rhyolite are consistent with the model more tests of the model are desirable

black sea lake reservoir age evolution since the last glacial hydrologic and climatic implications abstract chronologies of sediments that document the last glacial history of the black sea lake are hampered by issues relating to reservoir age regulated by basin hydrology reservoir ages represent a tool that could potentially be used to better understand the response of black sea lake hydrology to climate change therefore deciphering reservoir age evolution is crucial both for better constraining the basin chronological framework and for providing new insights into our understanding of black sea lake hydrology by tuning a meaningful new high resolution geochemical dataset obtained from core md04 2790 to a climate reference record here we propose a reliable chronology spanning the last 32 kyr bp the chronology is compared to a large ams radiocarbon dataset n 51 pairs of calendar and radiocarbon ages allowed us to compute reservoir ages and to then reconstruct a high resolution quantitative reservoir age record for the last glacial history of the black sea lake the main factor controlling reservoir ages in lakes is the hard water effect hwe which is regulated by basin hydrology therefore changes in the reconstructed reservoir age record have been qualitatively interpreted in terms of the hydrologic responses of the black sea lake to climate change our results allowed us to determine periods of complete isolation or outflow for the black sea lake during heinrich event 2 he2 and during the last glacial maximum lgm the basin was strictly isolated whereas prior to he2 and during he1 it outflowed into the marmara sea following the onset of the bolling allerod factors other than the hwe are thought to have influenced the reservoir age preventing conclusive interpretations we also determined an undocumented to date phase of black sea lake stratification during the full glacial he2 and lgm our results indicate that reservoir age is a powerful tool for investigating and better understanding past hydrologic changes in lakes and inland seas

the north atlantic igneous province stratigraphy tectonic volcanic and magmatic processes the north atlantic igneous province has been the subject of extensive scientific investigation over the past thirty years with a wide field of knowledge being accumulated recently recognition of the potential role of large igneous provinces in affecting ocean and atmosphere systems and biotic evolutionary pathways has lead to increased interest in this province this has been further stimulated by the expansion in the search for oil and gas in mesozoic and tertiary sediments along the ne atlantic margin an improved understanding of the interaction between igneous and sedimentary processes is vital for the identification of potential hydrocarbon resources the regions covered include continental margin norway east and west greenland the faroe shetland basin and the faroe islands themselves the papers in this book contain new data and interpretations of north atlantic igneous province magmatic processes rift evolution tectonics stratigraphy chemostratigraphy biostratigraphy seismic and isotope stratigraphy and sediment dispersal many of the papers adopt a multidisciplinary approach to tha analysis and interpretation of complex volcanic and sedimentary sequences these new data and the reviews and compilations of existing data provide the reader with access to current research directions in north atlantic igneous province geology

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

the stability and the abrupt ending of the last interglaciation in southeastern siberia abstract paleoproductivity records from lake baikal indicate that the last interglaciation in southeastern siberia lasted ca 12 000 yr from 127 000 to 115 000 yr b p was punctuated by a climatic oscillation about 120 000 yr ago and ended abruptly with a rapid onset of regional glaciation during marine isotope substage mis 5d the siberian equivalent of the mis 5e 5d transition appears to lead the post eemian cold pulses in europe and in the central north atlantic by 5000 to 8000 yr the baikal record also registers a pronounced cold event during early mis 5c which correlates with the montaigu event in pollen records from france in siberia the climatic deterioration during the mis 5d was a full scale glacial pulse unlike the short moderate cooling during the montaigu event

deep ventilation of lake baikal waters due to spring thermal bars increase of density due to mixing cabbeling instability in a spring thermal bar in lake baikal results in the sinking of cold surface water t 3 2 3 4 c w 0 3 cm s 1 below the profile of tmd this density increase generates forced convection and subsequent movement of cold water along the underwater slope to maximum depths cooling of deep and near bottom waters caused by forced convection is compensated during other seasons of the year by eddy heat flux directed toward the bottom on a long term basis vertical temperature profiles in deep waters remain constant

magma ascent along a major terrane boundary crustal contamination and magma mixing at the drumadoon intrusive complex isle of arran scotland the composite intrusions of drumadoon and an cumhann crop out on the se coast of the isle of arran scotland and form part of the larger british and irish palaeogene igneous province a subset of the north atlantic igneous province the intrusions shallow level dykes and sills comprise a central quartz feldspar phyric rhyolite flanked by xenocryst bearing basaltic andesite with an intermediate zone of dark quartz feldspar phyric dacite new geochemical data provide information on the evolution of the component magmas and their relationships with each other as well as their interaction with the crust through which they travelled during shallow crustal emplacement the end member magmas mixed isotopic evidence shows that both magmas were contaminated by the crust prior to mixing the basaltic andesite magma preserves some evidence of contamination within the lower crust whereas the rhyolite mainly records upper crustal contamination the highland boundary fault divides arran into two distinct terranes the neoproterozoic to early palaeozoic grampian terrane to the north and the palaeozoic midland valley terrane to the south the drumadoon complex lies within the midland valley terrane but its isotopic signatures indicate almost exclusive involvement of grampian terrane crust therefore although the magmas originated at depth on the northern side of the highland boundary fault they have crossed this boundary during their evolution probably just prior to emplacement

muted climate variations in continental siberia during the mid pleistocene epoch the large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 mis 12 and mis 11 spanning the interval between about 480 and 380 kyr ago has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period with consequences for global ice volume sea level and the global carbon cycle1 2 3 4 the extent of the change is intriguing because orbital forcing is predicted to have been relatively weak at that time5 here we analyse a continuous sediment record from lake baikal siberia which reveals a virtually continuous interglacial diatom assemblage a stable littoral benthic diatom assemblage and lithogenic sediments with interglacial characteristics for the period from mis 15a to mis 11 from about 580 to 380 kyr ago from these data we infer significantly weaker climate contrasts between mis 12 and 11 than during more recent glacial interglacial transitions in the late pleistocene epoch about 130 to 10 kyr ago for the period from mis 15a to mis 11 we also infer an apparent lack of extensive mountain glaciation

hydrothermal petroleums from yellowstone national park wyoming u s a abstract in yellowstone national park oil is actively discharging with thermal waters at several widely separated thermal areas samples from two locations were studied petroleum from calcite springs occurs as vapor condensates in steam vents detailed geochemical analyses show a complex origin for the petroleum fluid deeply buried hydrothermally altered sedimentary rocks are believed to have contributed a high temperature pyrolysate consisting largely of polynuclear aromatic hydrocarbons and heterocyclic compounds shallow sedimentary rocks which are also hydrothermally altered have contributed large amounts of aromatic and polar compounds as well as minor amounts of hydrocarbons the permian phosphoria formation is suggested as a likely source rock for the bulk of the oils autochthonous pyrolysates and lipids from thermally altered surface and near surface bacterial and land plant debris have also been introduced to the vents the latter may have been introduced by downward percolating meteoric water the oil from rainbow springs is a highly paraffinic low s crude oil depleted in light hydrocarbons unlike the calcite springs samples the oil from rainbow springs is believed to have originated from a single sedimentary source rock with little or no hydrocarbon contributions from surface biota the oil contains a unique molecular marker assemblage that suggests both gymnosperm and angiosperm input and places the age of the source unit in the tertiary consideration of the local stratigraphy and water temperatures limits the probable source zone to the eocene aycross formation an intra volcanic lacustrine mudstone calculation of deep water temperatures indicates that this unit is exposed to thermal waters in an extensive near surface aquifer such conditions are consistent with the widespread surface manifestations and biomarker kinetic models consideration of the petroleum chemistry and regional hydrodynamics indicates that the yellowstone park oils did not migrate into the park from distant sources the chemical data are also inconsistent with the oils being generated and trapped prior to tertiary volcanism at both calcite springs and rainbow springs oil generation appears to be contemporaneous and is attributed to thermal alteration of relatively shallow sedimentary rocks by hydrothermal fluids

petrogenesis and tectonic implications of two types of liaoji granitoid in the jiao liao ji belt north china craton abstract two types of granitoid monzogranite and granodiorite are recognized within the paleoproterozoic liaoji granitoids of the jiao liao ji belt jljb in the hupiyu and simenzi areas north china craton we conducted zircon u pb geochronological geochemical and hf isotopic analyses of these granitoids zircon u pb dating indicates an emplacement age of 2180 14 ma for the monzogranite hupiyu granitoids and ages of 2130 24 and 2173 11 ma for the fangjiaweizi and dadingzi granodiorites at simenzi respectively the hupiyu monzogranite samples are enriched in zr ga and y and depleted in nb and ti low nb y ratios and high zr saturation temperatures 849 884 c indicate that the hupiyu monzogranites have an affinity with a2 subtype granitoids the fangjiaweizi and dadingzi granodiorites have high sr y and low k2o na2o ratios indicating an affinity with adakitic rocks geochemical compositions and wide variation in ehf t values suggest that the monzogranites and granodiorites were derived from thinned and thickened lower crust respectively and that magmatism was accompanied by input of mantle material this study represents the first identification of pre tectonic adakitic rocks in the jljb the assemblage of pre tectonic a2 type granitoids and adakitic rocks indicates a continental back arc basin as the initial tectonic setting of the jljb these new data combined with results of previous studies support an arc continent collision model for the jljb

timing and duration of volcanism in the north atlantic igneous province implications for geodynamics and links to the iceland hotspot abstract we combine new and published 40 ar 39 ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing duration and distribution of volcanic activity during construction of the north atlantic igneous province we use these ages together with volume estimates of erupted magmas and their cumulates to calculate melt production rates for the early tertiary flood basalts of east greenland and the faeroes islands the lavas lie at opposite ends of the greenland iceland faeroes ridge the postulated iceland hotspot track and record volcanic activity leading up to during and following continental breakup between greenland and europe dominantly basaltic but also alkalic and picritic magmas were erupted from beneath thick continental lithosphere simultaneously at 61 ma from baffin island to the western and eastern margins of greenland to the faeroe islands and the western british isles a roughly circular area 2000 km in diameter volcanic activity was increasingly intermittent by 57 56 ma but at 56 1 0 5 ma the average melt production rate increased by more than an order of magnitude over previous levels from 3000 km 3 km of rift my coinciding with continental rifting and shallow decompressional melting of the mantle that fed subaerial volcanic activity along most of the eastern margin of greenland and its complement on the northwestern european margin offshore abnormally thick oceanic crust was produced along the line of plate separation the upper part of this crust comprises seismically imaged seaward dipping subaerially erupted lavas by 50 ma eruption rates had diminished drastically and volcanic activity had narrowed to a much restricted portion of the east greenland margin at the western end of the greenland iceland ridge that subsequently connected in an age progressive trend to present hotspot activity in southeastern iceland the startup mantle plume head and tail model with moderate excess temperature t 100 c and active upwelling best explains the time space and compositional aspects of volcanism in this province

lake baikal record of continental climate response to orbital insolation during the past 5 million years the sedimentary record of biogenic silica from lake baikal in south central siberia suggests that this region of central asia was impacted by two major cooling episodes at 2 8 to 2 6 and 1 8 to 1 6 million years ago the spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records in the baikal record the 41 000 year obliquity cycle is particularly strong from 1 8 to 0 8 million years ago variance in the 100 000 year eccentricity band increases during the past 0 8 million years the expected precession frequency of 23 000 years is highest during the past 400 000 years the modulation of the predicted 23 000 and 41 000 year insolation forcing by the 100 000 and 400 000 year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the eurasian continental interior as well as in tropical and high latitude ocean sites

sr and nd isotope evidence for successive crustal contamination of slieve gullion ring dyke magmas co armagh ireland the palaeogene slieve gullion igneous centre in southern armagh northern ireland consists of a layered central intrusive complex surrounded by a prominent and slightly older ring dyke that intrudes both lower palaeozoic sedimentary rocks and the caledonian newry granodiorite pluton 452 ma the ring dyke comprises two major rock types porphyritic felsite and porphyritic granophyre we analysed both ring dyke lithologies both types of country rock and a local palaeogene basalt dyke sample for sr and nd isotopes trace element and whole rock data for this suite suggest that there are two distinct groups of both felsite and granophyre one si rich and one si poor most likely representing two magmas from a zoned chamber and their mushy chamber wall equivalents mcdonnell et al 2004 isotope data show the low si rocks to be higher in radiogenic sr than the high si rocks which is inconsistent with a simple afc scenario of increasing sediment assimilation with higher degrees of differentiation however using morb type basalt as a starting composition the low si ring dyke rocks can be modelled through afc with lower palaeozoic sedimentary rock as the contaminant the decreasing 87 sr 86 sr trend from low si to high si dyke rocks in turn represents a second stage of contamination selective assimilation of the most fusible portions of newry granodiorite which is lower in radiogenic sr than the local sedimentary rocks appears to be the most plausible solution the sr and nd data are consistent with a at least a two stage contamination history during upper crustal residence and storage whereby fractionating magmas of basaltic and intermediate composition are contaminated by local sedimentary rocks giving rise to rhyolite magmas that experience additional shallow contamination by newry granodiorite and b a zoned rhyolite magma chamber where high si magma is stored in the upper part of the chamber where crystallization and crustal contamination are most extensive

quantitative reconstruction of the last interglacial vegetation and climate based on the pollen record from lake baikal russia changes in mean temperature of the coldest t c and warmest month t w annual precipitation p ann and moisture index were reconstructed from a continuous pollen record from lake baikal russia the pollen sequence con01 603 2 53 57 n 108 54 e was recovered from a 386 m water depth in the continent ridge and dated to ca 130 114 8 ky bp this time interval covers the complete last interglacial li corresponding to mis 5e results of pollen analysis and pollen based quantitative biome reconstruction show pronounced changes in the regional vegetation throughout the record shrubby tundra covered the area at the beginning of mis 5e ca 130 128 ky consistent with the end of the middle pleistocene glaciation the late glacial climate was characterised by low winter and summer temperatures t c 38 to 35 c and t w 11 13 c and low annual precipitation p ann 300 mm however the wide spread of tundra vegetation suggests rather moist environments associated with low temperatures and evaporation reconstructed 1 tundra was replaced by boreal conifer forest taiga by ca 128 ky bp suggesting a transition to the interglacial taiga dominant phase lasted until ca 117 4 ky bp e g about 10 ky the most favourable climate conditions occurred during the first half of the li p ann reached 500 mm soon after 128 ky bp however temperature changed more gradually maximum values of t c 20 c and t w 16 17 c are reconstructed from about 126 ky bp conditions became gradually colder after ca 121 ky bp t c dropped to 27 c and t w to 15 c by 119 5 ky bp the reconstructed increase in continentality was accompanied by a decrease in p ann to 400 420 mm however the climate was still humid enough 0 9 to support growth of boreal evergreen conifers a sharp turn towards a dry climate is reconstructed after ca 118 ky bp causing retreat of forest and spread of cool grass shrub communities cool steppe dominated the vegetation in the area between ca 117 5 ky and 114 8 ky bp suggesting the end of the interglacial and transition to the last glacial mis 5d shift to the new glaciation was characterised by cool and very dry conditions with t c 28 to 30 c t w 14 15 c p ann 250 mm and 0 5

a re evaluation and spatial analysis of evidence for a younger dryas climatic reversal in beringia abstract an objective classification of paleoclimatic proxies from 75 lake and peat records is used to re evaluate data quality and inferred climatic patterns in beringia during the younger dryas mapped data reveal coherent but spatially complex regional patterns suggesting the younger dryas was characterized by 1 cooling in southern alaska eastern siberia and portions of northeastern siberia and 2 uniform to warmer than present conditions through most of central alaska northeastern siberia and possibly the russian far east and northern alaska the beringian patterns correspond to distinctive large scale climatic forcings although in some locations further modified by more local influences such as topography general circulation models and modern synoptic climatology provide a conceptual framework for exploring possible mechanisms responsible for the observed changes forcings and associated climatic responses consistent with the proxy data include 1 lowered sea surface temperatures in the north atlantic and pacific reducing temperature and precipitation in eastern siberia 2 intensified aleutian low and lowered sea surface temperatures causing cooler summers and higher winter precipitation in southern alaska 3 stronger pacific subtropical high and an eastward shift of the east asian trough reducing summer temperatures in southern alaska and causing relative warmth in northeastern siberia and 4 strong high pressure system producing warm dry conditions in interior alaska

the new bdp 98 600 m drill core from lake baikal a key late cenozoic sedimentary section in continental asia abstract the new 600 m drill core bdp 98 from the academician ridge of lake baikal recovered a continuous sedimentary record of the past 10 ma the entire section is represented by lacustrine sediments which gradually change from distal deltaic facies at the bottom of the section to fine undisturbed hemipelagic sediments of the upper 300 m interval the entire 10 ma lacustrine section contains abundant diatoms thus allowing extension of plio pleistocene diatom and biogenic silica records into the miocene above the matuyama gauss paleomagnetic reversal boundary the bdp 98 record contains clearly delineated glacial interglacial lithologic cycles below this boundary the diatom signal is quite different average diatom contents are higher and variations are of lower amplitude although most likely paleoclimatic in origin these variation presumably reflect past changes in the moisture regime of southeast siberia under conditions of warm subtropical climate during the miocene and early middle pliocene the continuous bdp 98 drill core which covers the hiati present in the composite continental sections of the baikal region is a key section for reconstructing the neogene quaternary climatic evolution of continental asia the bdp 98 section also places several important time constraints on the rifting history of lake baikal by providing reliable correlation of lithological and physical properties of the drill core sediments with calculated positions of the acoustic reflection boundaries interpreted from multichannel seismic studies the lithologic composition indicates that on the stable block of academician ridge where the bdp 96 and bdp 98 drill sites are located acoustic reflection boundaries are not associated with major erosional events but instead result from changes in sediment density and composition several lithologic indices further suggest that significant changes have occurred in the physics and chemistry of lake baikal waters affecting the carbonate equilibrium and oxygen regime of baikal

a precise u pb zircon age for the inishtrahull syenitic gneiss county donegal ireland smd zircon fractions from the deformed alkaline igneous complex on inishtrahd county donegal ireland yield near concordant u pb ages of 1779 3 ma interpreted as dating the igneous crystallization of the gneiss9s precursor sm nd depleted mantle model ages range from 1912 ma to 1978 ms the similarity of the model ages and the crystallization age indicates that the protoliths were derived from a depleted mantle source essentially uncontaminated by older crust the isotopic data confirm previous tentative correlations of the inishtrahull rocks with those of islay in southwestern scotland archaean crust is apparently absent from this region consistent with recent models placing a southern limit on the archaean along the line of the great glen fault zone pre caledonian orthogneisses in scotland and ireland south of the great glen fault zone have generally been correlated with the late archaean lewisian complex of northwestern scotland e g wilkinson 1907 mccallien 1930 bowes hopgood 1975 dixon et al 1990 although aftalion max 1987 concluded that the lewisian was absent from the annagh division gneisses of north mayo ireland there are now several lines of evidence to suggest that archaean crust may be absent southeast of the great glen fault zone e g fitches et al 1990 daly 1990 halliday et al 1985 a large area of pre caledonian basement here termed the rhinns complex is thought to be present within the fault bounded colonsay west islay block fig 1 bentley et al 1988 fitches et al 1990 marcantonio et al 1988 which extends from colonsay in

tectonic significance of the highland boundary fault scotland none of the major roles assigned to the highland boundary fault such as a transcurrent fault with an orogen parallel sinistral displacement of several hundred kilometres or terrane boundary are confirmed the highland boundary fault can be traced ne sw across scotland for 240 km and defines the northern margin of the midland valley except for small outliers of late palaeozoic rocks on the nw side it separates the highland border ophiolite and dalradian rocks of neoproterozoic early ordovician age grampian terrane to the nw from late silurian early carboniferous rocks midland valley terrane to the se the present highland boundary fault is a steep nw dipping post early devonian reverse fault that probably terminates sw of bute stratigraphical and provenance links and palaeostress data limit post early devonian lateral displacement to

the magmatic plumbing of the submarine hachijo nw volcanic chain hachijojima japan long distance magma transport 1 recent geophysical observations on basaltic composite volcanoes in izu bonin arc reveal the process of long distance lateral magma transport within arc crust to clarify a long distance magma transport system of the basaltic arc volcano from geological and petrological aspects we investigated 20 km long submarine volcanic chains hachijo nw chain and hachijo kojima chain and cones on the northeastern slope ne edifices as well as subaerial satellite cones nested hachijo nishiyama volcano in the northern izu arc front basalts from hachijo nw chain have more primitive composition than those from other edifices the composition of the hachijo nw chain basalts is controlled by fractional crystallization while plagioclase accumulation occurred in ne edifices and subaerial satellite cones trace element and isotopic characteristics indicate that the same basaltic primary magma is involved in all sections of the volcano this leads us to consider that magma was transported long distances between the nishiyama volcano and the hachijo nw chain primitive magma was laterally transported nnw for at least 20 km in the middle to lower crust 10 20 km deep from nishiyama volcano with only minimal crustal level modifications and formed hachijo nw chain on the other hand magmas experienced crystal fractionation and accumulation at shallow magma chamber beneath nishiyama volcano seems to have been transported in a short distance 5 km and formed ne trending edifices and subaerial satellite cones the long distance magma transport seems to be controlled by a regional extensional stress regime while short distance transport may be controlled by local stress regime affected by load of main volcanic edifice

basin structure and tertiary magmatism on skye nw scotland the emplacement of igneous material into upper crustal rocks of sedimentary basins is likely to be strongly controlled by the geometry of the pre existing basin structures these controls are investigated using examples from the tertiary igneous complexes of skye part of the sea of hebrides basin of nw scotland the basin consists of an array of half graben related to se dipping normal faults these pre volcanic mesozoic structures are traced near the igneous complexes using geological relationships preserved unconformably beneath the widespread basaltic lava fields the unconformity represents a period of cretaceous uplift and denudation of the basin and its flanks entirely pre dating the tertiary volcanism of nw scotland this unconformity seals stratigraphically the major basin faults preserving field relationships that permit the tracing of these faults in the country rocks to the tertiary intrusions the major camasunary fault is separated from the raasay fault via a series of minor graben linked by a series of steep nw se trending faults that transfered mesozoic displacements between the principal fault strands a broad range of igneous material of various compositions was intruded into part of the mesozoic sea of hebrides basins and their flanks during palaeocene times different emplacement styles and different structural controls are found the major gabbroic centres do not appear to be controlled by upper crustal structures having been emplaced into the footwalls of major faults however minor synmagmatic displacements on the basin faults may have been sufficient to generate dilatational sites in these footwall positions thereby facilitating emplacement in contrast the granitic melts have been emplaced as sheets and domed into the sediments and overlying lava pile reactivating segments of the basin fault network doming occurred from an array of sills the stratigraphic levels of which can be reconstructed using structural relationships preserved in the roofs and walls of the intrusions the sill levels and their transgressive forms are strongly related to inferred mesozoic basin structures the major fold structures of tertiary age in southern skye are interpreted as accommodating granitic emplacement rather than crustal shortening the nw se mesozoic transfer fault trend appears to have strongly influenced the segmentation of the granite domes these interpretations are illustrated using field relationships mapped in the vicinity of the coire uaigneich granophyre it is concluded that although the higher parts of the basin faults were reactivated to facilitate the doming of granitic intrusions the deeper levels of the mesozoic faults show no evidence of substantial reactivation

post glacial history of siberian spruce picea obovata in the lake baikal area and the significance of this species as a paleo environmental indicator abstract the relative abundances of siberian spruce picea obovata and total arboreal pollen in pollen spectra from the lake baikal region and calculation of a steppe forest vegetation index place constraints on the past climatic conditions related to permafrost summer temperatures precipitation and soil moisture availability here we review the data on picea pollen in sub recent spectra the present day distribution of picea obovata and sedimentary records from a number of sites to arrive at a coherent picture of evolution of regional vegetation since the late glacial the expansion of siberian spruce along with steppe vegetation dates back to the undivided bolling allerod interval when this species became dominant in arboreal vegetation steppe landscapes persisted in a large part of the lake baikal watershed prior to 9 2 9 ka when the expansion of arboreal vegetation took place following the younger dryas which seems to have had little effect on regional vegetation and peat accumulation the role of siberian spruce steadily declined until 8 6 6 8 ka in the late holocene the abundance of p obovata rarely exceeded the present day ratio of ca 2 total arboreal pollen departures towards higher picea abundance and higher steppe forest index at ca 6 5 and 3 2 5 ka in selenga delta area appear to reflect periods with decreased temperatures and higher moisture availability in the southern part of the lake baikal watershed

active hydrate destabilization in lake baikal siberia abstract in this paper we present new seismic and heat flow data that show the base of the hydrate stability zone bhsz in lake baikal to be locally characterized by abnormal variations in depth with distinct regions of deeper than normal and regions of shallower than normal bhsz these variations are related to strong lateral variations in heat flow and occur in close association with important rift basin faults areas of shallow bhsz are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor we infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre existing hydrates in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the bhsz it thus seems that present day hydrate dissociation in lake baikal is modulated by the tectonic activity in the rift rather than by climatically controlled changes in lake level or water temperature

assimilation of felsic crust by basaltic magma thermal limits and extents of crustal contamination of mantle derived magmas basaltic magma is the most widely used probe of mantle chemistry and structure chemical characterization of the sources for mantle derived magma is possible only after quantitative evaluation of possible contamination by crustal wall rocks the most commonly invoked contamination mechanisms are the combined processes of crustal assimilation and magmatic fractional crystallization afc because of the energetic link between these processes predicting assimilation and crystallization progress requires modeling both heat and mass transfer in the magma country rock system using the melts software package we modeled isenthalpic heat balanced afc between two common types of basaltic magma and several types of felsic crust at 1 kbar our simulations show that during the early stages of isenthalpic afc the ratio of rates of assimilation to crystallization r may be substantially greater than one 2 0 2 7 allowing assimilation of a mass of country rock up to 5 18 of the initial magma mass with only 3 7 crystallization the second stage of afc beginning with plagioclase and or pyroxene saturation is characterized by lower r 0 5 1 0 the initial high r stage results from suppression of crystallization associated with the change in magma composition as assimilation progresses under certain conditions even small degrees of crystallization of olivine alone coupled with cooling of the magma can accommodate relatively large amounts of crustal assimilation and cause large shifts in isotopic and trace element geochemical indices with little differentiation