reinterpretation of late quaternary sediment chronology of lake biwa japan from correlation with marine glacial interglacial cycles a review of published stratigraphic records of pollen sediment grain size diatoms and organic matter composition from lake biwa japan identifies four pre holocene episodes of milder climate increased surface runoff and enhanced aquatic productivity indicating intervals of warmer and wetter conditions which are interpreted as being interglacial correlation of these episodes to times of marine interglacial periods revises the age scale of the lake biwa sediment sequence which has been based on fission track dating the revised chronostratigraphic scale proposes an age of ca 430 000 yr b p for the base of the 250 m thick t bed instead of the former age of ca 700 000 yr b p

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

a penultimate glacial monsoon record from hulu cave and two phase glacial terminations oxygen isotope records of three stalagmites from hulu cave china extend the previous high resolution absolute dated hulu asian monsoon record from the last to the penultimate glacial and deglacial periods the penultimate glacial monsoon broadly follows orbitally induced insolation variations and is punctuated by at least 16 millennial scale events we confirm a weak monsoon interval between 135 5 1 0 and 129 0 1 0 ka prior to the abrupt increase in monsoon intensity at asian monsoon termination ii based on correlations with both marine ice rafted debris and atmospheric ch 4 records we demonstrate that most of marine termination ii the full rise in antarctic temperature and atmospheric co 2 and much of the rise in ch 4 occurred within the weak monsoon interval when the high northern latitudes were probably cold from these relationships and similar relationships observed for termination i we identify a two phase glacial termination process that was probably driven by orbital forcing in both hemispheres affecting the atmospheric hydrological cycle and combined with ice sheet dynamics

tracing the cambro ordovician ferrosilicic to calc alkaline magmatic association in iberia by in situ u pb shrimp zircon geochronology gredos massif spanish central system batholith abstract u pb geochronological study of zircons from nodular granites and qtz diorites comprising part of variscan high grade metamorphic complexes in gredos massif spanish central system batholith points out the significant presence of cambro ordovician protoliths among the variscan migmatitic rocks that host the late carboniferous intrusive granitoids indeed the studied zone was affected by two contrasted tectono magmatic episodes carboniferous variscan and cambro ordovician three main characteristics denote a close relation between the cambro ordovician protholiths of the prado de las pozas high grade metamorphic complex strongly reworked during the variscan orogeny and other cambro ordovician igneous domains in the central iberian zone of the iberian massif 1 geochemical features show the ferrosilicic signature of nodular granites they plot very close to the average analysis of the metavolcanic rocks of the ollo de sapo formation iberia qtz diorites present typical calc alkaline signatures and are geochemically similar to intermediate cordilleran granitoids 2 both qtz diorite and nodular granite samples yield a significant population of cambro ordovician ages ranging between 483 and 473 ma and between 487 and 457 ma respectively besides 3 the abundance of zircon inheritance observed on nodular granites matches the significant component of inheritance reported on cambro ordovician metagranites and metavolcanic rocks of central and nw iberia the spatial and temporal coincidence of both peraluminous and intermediate granitoids and specifically in nodular granites and qtz diorite enclaves of the prado de las pozas high grade complex is conducive to a common petrogenetic context for the formation of both magmatic types tectonic and geochemical characteristics describe the activity of a cambro ordovician arc back arc tectonic setting associated with the subduction of the iapetus tornquist ocean and the birth of the rheic ocean the extensional setting is favorable for the generation emplacement and fast rise of subduction related cold diapirs supported by the presence of typical calc alkaline cordilleran granitoids contemporary with ferrosilicic volcanism

thermal and mechanical structure of the central iberian peninsula lithosphere abstract the central iberian peninsula spain is made up of three main tectonic units a mountain range the spanish central system and two tertiary basins those of the rivers duero and tajo these units are the result of widespread foreland deformation of the iberian plate interior in response to alpine convergence of european and african plates the present study was designed to investigate thermal structure and rheological stratification in this region of central spain surface heat flow has been described to range from 80 to 60 mw m 2 highest surface heat flow values correspond to the central system and northern part of the tajo basin the relationship between elevation and thermal state was used to construct a one dimensional thermal model mantle heat flow drops from 34 mw m 2 duero basin to 27 mw m 2 tajo basin and increases with diminishing surface heat flow strength predictions made by extrapolating experimental data indicate varying rheological stratification throughout the area in general in compression ductile fields predominate in the middle and lower crusts and lithospheric mantle brittle behaviour is restricted to the first 8 km of the upper crust and to a thin layer at the top of the middle crust in tension brittle layers are slightly more extended while the lower crust and lithospheric mantle remain ductile in the case of a wet peridotite composition discontinuities in brittle and ductile layer thickness determine lateral rheological anisotropy tectonic units roughly correspond to rheological domains brittle layers reach their maximum thickness beneath the duero basin and are of least thickness under the tajo basin especially its northern area estimated total lithospheric strength shows a range from 2 5 10 12 to 8 10 12 n m 1 in compression and from 1 3 10 12 to 1 6 10 12 n m 1 in tension highest values were estimated for the duero basin depth versus frequency of earthquakes correlates well with strength predictions earthquake foci concentrate mainly in the upper crust showing a peak close to maximum strength depth most earthquakes occur in the southern margin of the central system and southeast tajo basin seismicity is related to major faults some bounding rheological domains the duero basin is a relative quiescence zone characterised by higher total lithospheric strength than the remaining units

sequence stratigraphy of the palaeozoic welsh basin the timing and extent of unconformities in the welsh basin are investigated using rock preservation curves derived from outcrop stratigraphic logs four basin wide unconformities occur focussed in late precambrian late tremadoc pusgillian early ashgill and mid devonian times these bound three megasequences equating with newly defined lithostratigraphic units the dyfed gwynedd and powys supergroups less extensive unconformities bound 18 component sequences the majority of the sequence boundaries reflect a component of tectonic or volcanotectonic activity rather than a pure eustatic sea level change the megasequence boundaries are attributed to late precambrian to early cambrian onset of rifting to form a passive margin tremadoc onset of subduction with intra arc then back arc extension late caradoc end to subduction and late early devonian collisional deformation the megasequences and controlling events can be tentatively matched with other basins on the avalonian margin more generally this study shows that sequence analysis is feasible in onshore basins lacking well and seismic data and that the global eustatic interpretation of sequence stratigraphy is only partially applicable to active margin basins

paleozoic cambrian through devonian anoxitropic biotopes berry w b n wilde p and quinby hunt m s 1989 paleozoic cambrian through devonian anoxitropic biotopes palaeogeogr palaeoclimatol palaeoecol 74 3 13 the oxygen poor to denitrified waters of modern oceans provide an analog for open ocean conditions which contained the early paleozoic graptolite biotope certain euphausiids other zooplankton and fish as demonstrated in the eastern tropical pacific are found concentrated in and about denitrified waters the boundary zone between oxic and denitrified waters show intense organismal growth due to the increased chemical availability of nutrients as reduced nitrogen compounds such waters are areally limited in the present cold and well ventilated modern ocean the distribution patterns showing attraction to low or oxygen depleted waters anoxitropy in these modern open marine faunas suggest that early paleozoic plankton and nekton preserved in lithofacies formed under low oxygen or anoxic coditions could have been similarly attracted to the more extensive ancient denitrified and anoxic waters the major paleozoic faunal groups in order of their occupation of the niche include agnostid and olenid trilobites graptoloid graptolites styliolinids thin shelled bivalves small orthocone nautiloids and early ammonoids the expansion of low oxygen to anoxic waters across the shelves during warm climates in the early paleozoic may be correlated with major evolutionary radiations in the graptolites and possibly in the early ammonites

preliminary report on the geochemistry and mineralogy of the nod glas and related sediments ordovician of wales preliminary results are reported of geochemical and mineralogical studies on the nod glas sediments of caradoc age clingani linearis biozones in wales results are based on sampling at three localities in north wales together with a coeval section in south wales data have been obtained for 21 elements by icpaes and for organic c s and ignition loss xrd analysis has provided semi quantitative data on abundances of muscovite 2 m 1 quartz albite and chlorite mean values of k 2 o organic c s cu zr and ba are higher in the nod glas than in adjacent strata while fe 2 0 3 mno mgo cao and p 2 0 5 are lower analogy with the chemical composition of modern sediments reinforces the interpretation of the nod glas as being deposited under dysaerobic to anaerobic bottom conditions there is considerable variation in composition between different nod glas sections analysis of mineral chemical relationships shows some consistencies for example chlorite shows significant positive correlations with the heavier transition elements mn to zn as well as with li and mg presumably due to enrichment by adsorption of these elements onto subsequently recrystallized smectites other relationships are less consistent organic c is correlated with muscovite where it is probably held in interlayer sites as a relic from a smectite precursor and sometimes also with albite inconsistencies between the sections in mineral element interrelations may be due to diagenetic metamorphic changes

diatom biostratigraphy of lake baikal during the past 1 25 ma new results from bdp 96 2 and bdp 99 drill cores abstract detailed diatom zonation in the lake baikal holostratotype section bdp 96 2 is extended over the interval 0 85 1 25 ma and compared with diatom assemblage composition from the new bdp 99 drill core interglacial diatom assemblages at these two sites over 220 km apart are of similar composition and the same complete and continuous succession of diatom zones is observed in both drill cores over the 0 800 ka interval we propose a correlation of baikal diatomaceous intervals with the marine oxygen isotope stratigraphy and with european climato stratigraphic divisions of the early pleistocene we then use the diatom succession in bdp 96 2 to demonstrate evidence for disconformity in bdp 99 and to establish an approximate age model for this section diatom assemblages characteristic of the top of the matuyama reversed polarity interval and the upper part of the jaramillo normal polarity subchron are not found in the bdp 99 section below the disconformity boundary the lack of diatom zones corresponding to the mis 21 27 of the marine oxygen isotope stratigraphy in bdp 99 section suggests that the estimated age span of missing sediment interval in bdp 99 is ca 150 160 ka the unusual diatom assemblage of cosmopolitan species during mis 33 in both bdp 96 2 and bdp 99 drill core sections is indicative of abrupt ecological changes in the time interval 1 12 1 08 ma

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

high resolution carbon isotope stratigraphy of the basal silurian stratotype dob s linn scotland and its global correlation since its designation as the global stratotype section and point gssp for the base of the silurian system the choice of dob9s linn southern scotland has received criticism due to the difficulties of relating its well constrained graptolite biostratigraphy to shallow water sequences elsewhere kerogen samples from across the ordovician silurian boundary interval at dob9s linn have yielded carbon stable isotope signatures consistent with those recorded elsewhere in particular showing a clear positive 13 c excursion in the terminal ordovician the architecture of the 13 c curve from dob9s linn enables very high resolution stratigraphic subdivision and direct correlation between the deep water dob9s linn section and time equivalent carbonate shelf deposits an integrated stratigraphic scheme using isotope stratigraphy and biostratigraphy of graptolites conodonts and shelly faunas has been constructed this direct correlation shows that the shallow water successions including the former stratotype candidate at anticosti island are generally incomplete with hiatuses related to the rapid sea level changes during the hirnantian stage this confirms and greatly increases the global utility of dob9s linn as a boundary stratotype

paleolithic cultures of mis 3 to mis 1 in relation to climate changes in the central japanese islands abstract the pattern of latest pleistocene climate changes reconstructed on the basis of sediment cores from lake nojiri is one of the most detailed and reliable reconstructions in japan the climate changes over the last 72 ka can be compared directly with those recorded at upper paleolithic and incipient jomon sites on the basis of a revised age model for the lake nojiri sediment cores and the revised 14c dates calibrated after intcal09 fossil bones of megafauna from the tategahana site beside the lake have been placed ca 53 37 ka cal bp in the relatively warm temperate climate of the early mis 3 part of the tategahana site was interpreted as a kill and butchery site although the presence of the big game hunters is still uncertain as so far there is no reliable archaeological evidence in the japanese archipelago dating back to the middle paleolithic the number of paleolithic sites increased suddenly after 38 ka cal bp around lake nojiri this seems to coincide with the timing of the migration of homo sapiens into the japanese archipelago the climate had been gradually cooling toward the last glacial maximum lgm however the area around lake nojiri in the late mis 3 seems to have been a suitable place for the subsistence of hunter gatherers backed blade industries ca 29 20 ka cal bp point tool industries ca 22 19 ka cal bp and microblade industries 20 16 ka cal bp were characteristic of the late upper paleolithic the number of sites around lake nojiri decreased significantly during the lgm at the end of the lgm an abrupt change of vegetation from subarctic conifer forest to deciduous broadleaf forest had occurred around 14 ka and human activities became prominent around lake nojiri as shown by the linear relief pottery group ca 15 13 ka cal bp the number of sites seems to have decreased slightly during the younger dyras cooling event patterns of human occupation around lake nojiri show the influence of global and local climate changes

integrated upper ordovician graptolite chitinozoan biostratigraphy of the cardigan and whitland areas southwest wales to help calibrate the emerging upper ordovician chitinozoan biozonation with the graptolite biozonation in the anglo welsh historical type basin the graptolite bearing caradoc ashgill successions between fishguard and cardigan and at whitland sw wales have been collected for chitinozoans in the cardigan district finds of armoricochitina reticulifera within strata referred to the clingani graptolite biozone morrisi subzone together with accessory species indicate the fungochitina spinifera chitinozoan biozone known from several ordovician sections in northern england that span the base of the ashgill series tanuchitina bergstroemi eponymous of the succeeding chitinozoan biozone has tentatively been recovered from strata of pleurograptus linearis graptolite biozone age in the cardigan area the t bergstroemi biozone can also be correlated with the type ashgill series of northern england chitinozoans suggest that the widespread welsh basin anoxic oxic transition at the base of the nantmel mudstones formation in wales traditionally equated with the caradoc ashgill boundary is of cautleyan or younger ashgill age in the cardigan area in the broadly time equivalent graptolite rich whitland section also in sw wales two baltoscandian chitinozoan biozones and a subzone have been recognized again using accessory species namely the spinachitina cervicornis biozone the fungochitina spinifera biozone and the armoricochitina reticulifera subzone the new chitinozoan data provide a more precise means of correlation between the whitland and cardigan successions and suggest that the normalograptus proliferation interval of the whitland section is at least partly attributable to the dicellograptus morrisi subzone of the dicranograptus clingani biozone rather than equating with the overlying pleurograptus linearis biozone

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

the physics of explosive volcanic eruptions edited by j s gilbert and r s j sparks geological society special publication no 145 geological society london 1998 186 pp isbn 1862390207 us 98 59 00 members us 48 29

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

late caradoc graptolitic faunal gradients across the iapetus ocean late caradoc graptolite assemblages across the iapetus ocean in wales and scotland became progressively more disparate despite the narrowing of the ocean we compare faunal distributions in continuous sections from opposite sides of iapetus at whitland in south wales and hartfell score in the southern uplands of scotland a comprehensive graptolite range chart is given for each the graptolite assemblages from the clingani biozone are subdivided into a lower ensigraptus caudatus subzone and upper dicellograptus morrisi subzone at both localities though the faunas differ in detail higher in the sequence the distinctive scottish linearis biozone fauna is not recognizable at whitland its presumed equivalent being a fauna dominated by variable morphotypes of the genus normalograptus this suggests that environmental gradients depth and or temperature were changing more rapidly than the geography significantly the subsequent inception of limestone deposition at whitland was approximately contemporaneous with widespread replacement of black mudstones by oxic bioturbated sediments elsewhere in the welsh basin and in scotland this was possibly a response to an early phase of cooling prior to the end ordovician glaciation in wales the claimed hiatus at the caradoc ashgill boundary may rather reflect biofacies variation

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

climate deduced diatom changes elucidated in a sediment core tkn2004 of the late pleistocene takano formation in nagano central japan

a revision of ordovician series and stages from the historical type area this paper is a revision of the standard chronostratigraphy of the ordovician of the historical type area in england and wales the revision is a response to the need for more precise definitions of series and stages especially for practical international correlation in some cases this has entailed moving horizons for series bases away from those in the classical sections the scheme will be used as the standard for a forthcoming revision of the correlation chart of the british ordovician system the ordovician is divided into five series tremadoc arenig llanvirn caradoc and ashgill the llanvirn is extended to include part of the classical llandeilo series which is included within it as a stage where stage subdivisions of standard series have not yet been defined as in the tremadoc they are proposed in this paper however bancroft s fine stadial divisions of the caradoc which have been criticized for their brevity and local utility are combined into four new stages which will have wider application the former caradoc subdivisions are retained as substages for the purposes of regional correlation

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

a pre hirnantian late ordovician interval of global cooling the boda event re assessed facies analysis suggests that the early mid ashgill late ordovician boda event of fortey and cocks fortey r a cocks l r m 2005 late ordovician global warming the boda event geology 33 5 405 408 was an episode of global cooling not of warming as they proposed limestones are widely developed at this level from mid latitude to high latitude commonly interrupting thick ordovician successions of fine clastic sediments bryozoan carbonate mud mounds in a laterally extensive cool water carbonate belt along the high palaeolatitude margin of w gondwana are associated with glacial diamictites and grew during glacial lowstand with sea ice prior to the hirnantian glaciation from high to mid palaeolatitudes contemporaneous cool water carbonates with mud mounds including stromatactis both in gondwana and in baltica developed in mid outer ramp settings during regression in the dominantly clastic welsh basin of avalonia phosphatic facies on an iapetus facing carbonate ramp indicate upwelling cold waters down ramp yet up ramp coralliferous algal limestones suggest warm surface waters we propose that the late ordovician cool water carbonates developed in response to global cooling and expansion of gondwanan terrestrial and sea ice that lowered eustatic sea level and on the w gondwanan shelf reduced or shut down fluvial clastic input previously poorly circulated salinity stratified oceans that had restricted benthic dispersal in mid low latitudes were replaced by thermohaline ocean circulation that oxygenated bottom waters and dispersed benthic faunas an earlier caradoc carbonate interval in low mid palaeolatitudes that shares many facies characteristics with the ashgill cool water limestones and correlates with a widely recognised isotope excursion is interpreted as indicating an earlier global cooling episode

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

fluctuations in the east asian monsoon over the last 144ka in the northwest pacific based on a high resolution pollen analysis of images core md01 2421 abstract a high resolution pollen analysis of images core md01 2421 45 83 m from the northwest pacific off central japan was used to clarify the vegetation history of central japan over the past 144 ka an age model was constructed using the oxygen isotope stratigraphy of benthic foraminifera 12 accelerator mass spectrometry ams 14c datings and two tephra layers with known eruption ages the pollen temperature index t p 1 0 0 t w t c t w where tw is the sum of temperate taxa and tc the sum of subalpine taxa values were high during 129 119 115 100 82 76 53 49 and 15 0 ka cool temperate broad leaved forests developed during the high tp periods and subalpine conifer forests grew during the low tp periods the tp fluctuated synchronously with summer insolation at 36 n where the core was collected during periods with abundant cryptomeria or sciadopitys 120 118 115 89 78 70 and 4 0 3 ka the east asian summer monsoon was stronger and the annual precipitation was greater in central japan than at present 2000 vs 1500 mm fluctuations in the sea surface temperature sst calculated from the oxygen isotopes of foraminifera in core md01 2421 and changes in the strength of the summer monsoon were synchronous the sst was determined by the currents passing over the core site rather than by the strength of summer insolation northward movement high sst of the kuroshio current which is under the influence of the summer okhotsk high pressure was strong near the summer insolation minima when precipitation was high particularly around 116 94 and 71 ka thus the strengths of both summer insolation and the east asian summer monsoon have determined the vegetation history of central japan for the last 144 ka

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

correlation for the lower palaeozoic the global correlation standards now agreed for the ordovician and silurian systems and partly so for the cambrian system are summarized correlation of the international series and stages with the traditional and revised british series and stages is reviewed as well as with those in north america laurentia

rare earth element geochemistry of upper ordovician cherts from the southern uplands of scotland caradoc and ashgill radiolarian cherts and siliceous mudstones from the southern uplands preserve primary rare earth element ree signatures which are comparable to those of more recent deposits from continental margin settings this is incompatible with the widely held view of these rocks as open ocean deposits incorporated in an accretionary prism and reinforces the model of deposition on an extensional continental margin the ree signatures can be used as fingerprints to differentiate between some of the fault bounded formations within the area they indicate the provenance of the mud grade siliciclastic material in these distal hemipelagites and are comparable with published ree data on grey wackes in the same successions this detailed analysis of the ree patterns in lower palaeozoic cherts demonstrates the usefulness of this approach in ancient orogens

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site

upper ordovician δ13corg chemostratigraphy k bentonite stratigraphy and biostratigraphy in southern scandinavia a reappraisal a pioneer 13corg study through the upper sandbian and katian upper ordovician succession in the rostanga 1 drill core in the classical geological outcrop area at rostanga in southernmost sweden produced a wealth of new carbon isotope data which are useful for local and regional correlations among the upper ordovician positive 13c excursions the guttenberg gice waynesville saunja whitewater moe paroveja and hirnantian hice isotopic carbon excursions are recognized but the kope rakvere 13c excursion is missing suggesting a stratigraphic gap all these isotopic excursions are tied closely to biostratigraphy especially graptolite biostratigraphy and in the case of the waynesville saunja and whitewater moe excursions for the first time anywhere in the world the rostanga gice 13corg curve from the upper sularp shale shows a striking similarity to that of the katian gssp in oklahoma suggesting the potential of trans atlantic correlation based on a projection from the katian gssp the previously poorly constrained position of the base of the katian in southern sweden appears to be in the uppermost sularp shale in strata of the upper diplograptus foliaceus zone previous interpretations of the relations between k bentonite successions in southern scandinavia are somewhat revised and the kinnekulle k bentonite is recognized for the first time in scania based on new radiometric dates this very prominent and widespread ash bed appears to be slightly older than the deicke and millbrig k bentonites in eastern north america

high resolution correlation of anglo welsh middle to upper ordovician sequences and its relevance to international chronostratigraphy abstract continuously fossiliferous sections in south wales and shropshire spanning the base of the upper ordovician permit precise correlation of the nemagraptus gracilis biozone a horizon currently under scrutiny for the selection of a global stratotype section and point gssp using graphic correlation we have compiled a new composite global standard for the middle upper ordovician which shows that the first occurrence of the key graptolite n gracilis is not everywhere of the same age appearing earlier in north american successions than it does in britain species of dicellograptus by contrast appear to be almost synchronous in their first appearance the status and correlation of standard british biozones through the llandeilian caradoc interval based on graptolites and trilobites are revised suitable sections for the definition of bases of biozones are proposed if the base of the n gracilis biozone is accepted internationally as the base of the upper ordovician this biozone being coincident with the base of the caradoc series there are sections suitable for its precise definition in the british succession

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

a diatom record for the past 400 ka from lake biwa in japan correlates with global paleoclimatic trends abstract detailed diatom records from a 140 m sediment core with a time resolution of approximately 1000 1500 yr were obtained from lake biwa to examine possible correlations between diatom concentrations and paleoclimatic changes during the last approximately 400 ka in the sediments the diatom assemblages are generally dominated by planktonic diatoms the diatom stratigraphy is characterized by four zones with distinctly higher concentration values and 12 horizons with low concentration values diatom records from the 140 m core and another core indicate that these changes were not local phenomena but occurred throughout the lake basin comparison of diatom concentration records with pollen records from lake biwa sediments indicates that higher diatom concentrations represent warmer and wetter climatic conditions and that lower concentrations represent colder and drier climatic conditions comparison of diatom records from lake biwa with marine oxygen isotopic records shows that the number of peaks and their relative amplitudes are similar in both profiles therefore peaks and drops in diatom concentration profile might correlate with most oxygen isotopic events this finding indicates that during approximately the last 400 ka the changes in diatom concentration represented as diatom productivity in lake biwa correlate closely with global paleoclimatic changes at the scale of the milankovitch cycle precession cycles of 23 and 19 ka and that diatom concentration was higher during warm events and lower during cold or cooling events

estimation of temperature change and of gas age ice age difference 108 kyr b p at vostok antarctica air trapped in ice core bubbles provides our primary source of information about past atmospheres air isotopic composition 15n 14n and 40ar 36ar permits an estimate of the temperature shifts associated with abrupt climate changes because of isotope fractionation occurring in response to temperature gradients in the snow layer on top of polar ice sheets a rapid surface temperature change modifies temporarily the firn temperature gradient which causes a detectable anomaly in the isotopic composition of nitrogen and argon the location of this anomaly in depth characterizes the gas age ice age difference age during an abrupt event by correlation with the d or 18o anomaly in the ice we focus this study on the marine isotope stage 5d 5c transition 108 kyr b p a climate warming which was one of the most abrupt events in the vostok antarctica ice isotopic record petit et al 1999 a steplike decrease in 15n and 40ar 4 from 0 49 to 0 47 possibly a gravitational signal due to a change in firn thickness is preceded by a small but detectable 15n peak possibly a thermal diffusion signal we obtain an estimate of 5350 300 yr for age close to the model estimate of 5000 years obtained using the vostok glaciological timescale our results also suggest that the use of the present day spatial isotope temperature relationship slightly underestimates but by no more than 20 15 the vostok temperature change from present day at that time which is in contrast to the temperature estimate based on borehole temperature measurements in vostok which suggests that antarctic temperature changes are underestimated by up to 50 salamatin et al 1998

a sequential back arc and foreland basin thrust duplex model for the southern uplands of scotland thrust imbrication of ordovician and silurian submarine fan sequences overlapping pelagic deposits in the southern uplands has been interpreted in terms of an accretionary prism formed above a nw directed subduction zone structural features invoked to support accretion are not definitive and could be explained in terms of a thin skinned thrusting model new palaeocurrent and compositional evidence from llandeilo to mid llandovery age turbidites in the northern part of the southern uplands proves interdigitation of sediments with strongly contrasting petrography turbidites derived from the south contain significant quantities of fresh andesitic detritus whereas those from the north form more mature quartz rich formations this implies a back arc situation the turbidites being deposited in a basin with a relatively mature continental landmass to the north and a rifted continental fragment containing an active volcanic arc to the south oblique collision of the opposing continental margins of the iapetus ocean during the llandovery caused the cessation of subduction underthrusting of the southern margin initiated a se propagating thrust stack which deformed the back arc basin sequence and may eventually have ramped over the eroded and faulted remains of the volcanic arc a southward migrating foreland basin formed ahead of the rising thrust stack and is now represented by the late llandovery hawick group and wenlock sequences mid to end silurian sinistral strike slip resulted from oblique collision and produced a transpressional regime during which reactivation of deep seated structures allowed the intrusion of lamprophyre dykes and granites

stratigraphical and palaeoecological importance of caradoc upper ordovician graptolites from the cardigan area southwest wales graptolites from more than 60 horizons in the basinal caradoc succession of southwest wales between fishguard and cardigan allow recognition of the multidens clingani and linearis biozones the biostratigraphy permits recognition of major differences in the sedimentary rock sequence north and south of structures associated with the fishguard cardigan fault belt the penyraber mudstone formation disconformably overlying the fishguard volcanic group llanvirn is partly of multidens biozone age it is succeeded south of the newport sands fault by the cwm yr eglwys mudstone formation of clingani to linearis biozones age north of the fault the cwm yr eglwys mudstone formation is replaced laterally by the northwards thickening sandstone turbidite dominated dinas island formation clingani and linearis biozones graptolite stratigraphical distribution indicates that dicranograptus clingani occurs only rarely within the caudatus subzone of the clingani biozone and that climacograptus antiquus s l also does not range above the lower part of the clingani biozone the first occurrence of dicellograptus morrisi within the upper clingani biozone confirms its value as a marker for the morrisi subzone and is associated with the first occurrences of diplacanthograptus dorotheus and normalograptus minimus dicellograptus flexuosus used to indicate the morrisi subzone elsewhere occurs throughout the clingani biozone in the cardigan area the linearis biozone is recognized by climacograptus tubuliferus oxic bottom conditions in early and early mid caradoc times largely precluded the influx of or preservation of graptolite faunas in the penyraber mudstone formation anoxic mudstones of the cwm yr eglwys mudstone and dinas island formations preserve graptolite assemblages of 21 and 26 species signalling strong open marine influences which persisted in this area until late caradoc times this contrasts with the shelfal faunas in the whitland area south pembrokeshire where the late caradoc is dominated by low diversity normalograptus dominated assemblages

faunal evidence for oceanic separations in the palaeozoic of britain the faunal criteria for the recognition of the relative separation of old continents are 1 the contrast between shallow not deep water faunas off opposite shorelines 2 the recognition of deeper water facies surrounding the edges of continents and 3 the recognition of the disposition of ancient climatic belts these criteria are defined and used to assess the relative position of the various parts of what is now britain in the palaeozoic the iapetus ocean is well characterized by faunal differences from the cambrian until the lower ordovician but from caradoc times onwards these differences dwindle until by the latest silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds in the early ordovician s british faunas are comparable with those from bohemia france and elsewhere to the s indicating connection with gondwanaland and these faunas differ from those in the baltic area a distribution which we attribute to a true ocean tornquist9s sea between n and s europe tornquist9s sea probably closed in the upper ordovician and from ashgill times onwards the s british and baltic faunas remained similar during the middle and late silurian there is evidence of increasing faunal distinction between britain the baltic area and north america on the one hand and southern europe and gondwanaland on the other indicating an opening rheic ocean which appears to have persisted until late carboniferous times

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

the pusgillian stage in wales in northern enland and in southern scotland the pusgillian stage is related to the stratigraphical ranges of selected trilobite species and to the standard graptolite zonal scheme thus characterized it can be recognized in rocks of shelly facies at localities in the northwest southeast and south central berwyn hills of north wales and possibly in the llandeilo area of south wales but does not seem likely to be developed in any rocks of graptolitic facies in wales modified journal abstract

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

ordovician graptolite biostratigraphy in the welsh basin a review ordovician graptolite biostratigraphy in wales is crude compared with that of the silurian and is in need of refinement especially by detailed collecting from suitable sections and consequent taxonomic work this has been done in parts of the arenig llandeilo and lower caradoc successions there is particular potential for subdivision of and improvement in the correlation of the llanvirn series and the gracilis linearis biozones but there is little prospect of much new and detailed information from the upper tremadoc or ashgill series

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

graptolites in british stratigraphy 697 taxa of planktonic graptolites are recorded and their stratigraphical ranges are given through 60 biozones and subzones in the ordovician and silurian strata of england wales and scotland in the first such stratigraphical compilation for great britain since the synthesis of elles wood 1901 1918