sedimentary characteristics and origin of the late pleistocene ice complex on north east siberian arctic coastal lowlands and islands a review abstract the origin of late pleistocene ice rich fine grained permafrost sequences ice complex deposits in arctic and subarctic siberia has been in dispute for a long time corresponding permafrost sequences are frequently exposed along seacoasts and river banks in yedoma hills which are considered to be erosional remnants of late pleistocene accumulation plains detailed cryolithological sedimentological geochronological and stratigraphical results from 14 study sites along the laptev and east siberian seacoasts were summarized for the first time in order to compare and correlate the local datasets on a large regional scale the sediments of the ice complex are characterized by poorly sorted silt to fine sand buried cryosols toc contents of 1 2 4 8 wt and very high ground ice content 40 60 wt absolute a second large constituent of the ice complex are large syngenetic ice wedges resulting in a total ice content of the ice complex of up to 80 vol ice complex deposits were mostly formed during the middle weichselian interstadial and or during the late weichselian stadial periods a conceptual model of nival lithogenesis of ice complex deposits was developed that integrates various other formation hypotheses a combination of various local and regional paleogeographical geological and paleoclimate conditions controlled the formation of ice complex sequences during the late pleistocene in northern east siberia they are chronologically and stratigraphically but not genetically equivalent to eurasian and alaskan loess deposits

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

constraints on magma ascent emplacement and eruption geochemical and mineralogical data from drill core samples at obsidian dome inyo chain california systematic chemical and mineralogical variability occurs in samples from drill holes through obsidian dome the conduit to the dome and a nearby associated feeder dike the drill hole samples from the margins of the conduit and most of the lower part of the dome are high ba low silica rhyolites they contain two populations of phenocrysts and represent commingled magmas whereas samples from the dike and upper parts of the dome are low ba higher silica rhyolites that do not reflect commingled magmas samples from the center of the conduit are low ba higher silica rhyolites that are only slightly mixed a major part of the variability within the drill core samples of the dome and conduit reflects the juxtaposition and commingling of two distinct magmas during their passage through the conduit

benthic foraminifera as palaeo sea ice indicators in the subarctic realm examples from the labrador sea baffin bay region abstract benthic foraminifera are found in a wide range of environments and may at times be one of few proxies available for the study of palaeoenvironmental conditions however the response of benthic foraminifera to changing sea ice conditions is not well understood this paper discusses benthic foraminifera as potential sea ice proxies with special emphasis on their use in shelf regions of the sub arctic realm four marine sediment records from the labrador sea baffin bay region serve as examples in all four records independent sea ice proxy will be used for testing the foraminiferal response to changing sea ice conditions this test suggests that 1 benthic foraminifera provide information on variations in sea ice cover but they are not direct proxies for sea ice cover and no true sea ice species has yet been identified 2 foraminifera mainly respond to the surplus of food often available at sea ice edges 3 dominance of agglutinated foraminifera may suggest corrosive bottom water conditions which may at times be linked to seasonal sea ice cover

central japan triple junction revisited we show that the two dimensional kinematic discussion of mckenzie and morgan s ttt type triple junction is not sufficient as it ignores the interaction of the sinking plates we derive a relation for the three dimensional existence of ttt triple junctions and show that it is satisfied at the unstable central japan triple junction we then use the geometry of the subducting pacific plate beneath the philippine sea and eurasian plates to show that the present situation did not hold before about 3 ma before that time the triple junction was probably located north of the present one and very close to the pole of relative motion finally we discuss the geological implications of this model

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

degassing of rhyolitic magma during ascent and emplacement the degassing history of a rhyolitic igneous system was documented from analyses of drill core samples through the extrusive and intrusive portions of obsidian dome and of surface samples of associated tephra the initial volatile composition of the inyo magma was estimated to be 4 0 wt h2o 500 ppm f 800 ppm cl and 80 ppm s retained volatile contents of glassy and crystalline samples reflect the effects of decompression and second boiling decompression is rapid and involves loss of water rich fluid until a close approach to lithostatic equilibrium is achieved second boiling is a slower process and produces a chlorine rich fluid some of which can be trapped during development of extremely fine crystallization textures nearly complete dewatering during decompression of surface extruded magma strongly undercools the system t 175 c suppressing crystallization and yielding glassy rhyolitic lava partial degassing of shallowly intruded magma permits pervasive crystallization even at high cooling rates the subvolcanic intrusive regime is the zone of maximum volatile release because second boiling is incomplete in extrusives and volatile bearing crystalline phases are stable in magma crystallized at greater depth

textural development of mixed finely porphyritic silicic volcanic rocks inyo domes eastern california magma mixing in silicic volcanic rocks of the inyo chain is manifest by bimodal mineral chemistry and distinctive banding defined by either variations in 1 glass color and chemistry or 2 microlite abundance within colorless glass bands composed of brown or microlite rich colorless glass are characterized by more mg rich mafic silicates and more calcic plagioclase than microlite poor colorless glass domains a rhyolitic and a dacitic mixing end member can be defined on the basis of this mineral distribution thermobarometry using the mineral assemblages unique to each end member indicates that prior to mixing the dacite was more oxidized and water rich than the rhyolitic magma determined mineral crystallization conditions compare favorably with experimentally derived phase equilibria for melts of broadly similar composition the spatial association of contrasting mineral assemblages with the flow banding in these rocks implies that the banding is a direct product of magma mixing it formed as either 1 volumes of the comingled magmas were immediately vented to the surface and quenched preserving domains of two distinct glass compositions or 2 bands of dacitic magma precipitated microlites when comingled with the rhyolitic magma in an attempt for the two magmas to approach equilibrium

linking the modern distribution of biogenic proxies in high arctic greenland shelf sediments to sea ice primary production and arctic atlantic inflow the eastern north coast of greenland is considered to be highly sensitive to the ongoing arctic warming but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability here we present a detailed investigation of 11 biogenic proxies preserved in surface sediments from the remote high arctic wandel sea shelf the entrance to the independence hagen and danmark fjords the composition of organic matter organic carbon c n ratios 13c 15n biogenic silica and ip25 and microfossil assemblages revealed an overall low primary production dominated by benthic diatoms especially at the shallow sites while the benthic and planktic foraminiferal assemblages underline the intrusion of chilled atlantic waters into the deeper parts of the study area the distribution of organic walled dinoflagellate cysts is controlled by the local bathymetry and sea ice conditions the distribution of the dinoflagellate cyst polarella glacialis matches that of seasonal sea ice and the specific biomarker ip25 highlighting the potential of this species for paleo sea ice studies the information inferred from our multi proxy study has important implications for the interpretation of the biogenic proxy signal preserved in sediments from circum arctic fjords and shelf regions and can serve as a baseline for future studies this is the first study of its kind in this area

holocene treeline history and climate change across northern eurasia radiocarbon dated macrofossils are used to document holocene treeline history across northern russia including siberia boreal forest development in this region commenced by 10 000 yr b p over most of russia forest advanced to or near the current arctic coastline between 9000 and 7000 yr b p and retreated to its present position by between 4000 and 3000 yr b p forest establishment and retreat was roughly synchronous across most of northern russia treeline advance on the kola peninsula however appears to have occurred later than in other regions during the period of maximum forest extension the mean july temperatures along the northern coastline of russia may have been 2 5 to 7 0 c warmer than modern the development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions including heightened summer insolation the demise of eurasian ice sheets reduced sea ice cover greater continentality with eustatically lower sea level and extreme arctic penetration of warm north atlantic waters the late holocene retreat of eurasian treeline coincides with declining summer insolation cooling arctic waters and neoglaciation

the penultimate interglaciation of northern russia abstract this paper presents new field and laboratory data combined with previously published materials on interglacial sediments underlying two upper tills of northern european russia and west siberia the emphasis is on the structure and chronometric data of marine strata with shells of boreal molluscs of cyrtodaria genus indicative of the atlantic marine invasion into these sedimentary basins during the late middle pleistocene another line of evidence for this time span is inferred from inter till terrestrial sequences in the european northeast with forest pollen spectra suggesting a climate much warmer than today the decisive correlation signal is provided by optically stimulated luminescence and electron spin resonance dates indicating mis 7 time and by the geological position of two interglacial formations between the first second and third from the surface glacial complexes the collected evidence disagrees with the model of the unique boreal transgression and confirms that saline atlantic water at least twice invaded northern russia during the last 250 kyears the sedimentary formations of the penultimate interglaciation can serve as a new intra regional stratigraphic marker for the northern pleistocene

ice dammed lakes and rerouting of the drainage of northern eurasia during the last glaciation during the quaternary period ice sheets centred over the barents and kara seas expanded several times onto mainland russia and blocked northflowing rivers such as the yenissei ob pechora and mezen large ice dammed lakes with reversed outlets e g toward the caspian sea formed south of these ice sheets some lakes are reconstructed from shorelines and lacustrine sediments others mainly from ice sheet configuration ice dammed lakes considerably larger than any lake on earth today are reconstructed for the periods 90 80 and 60 50 ka the ages are based on numerous optically stimulated luminescence osl dates during the global last glacial maximum lgm about 20 ka the barents kara ice sheet was too small to block these eastern rivers although in contrast to the 90 80 and 60 50 ka maxima the scandinavian ice sheet grew large enough to divert rivers and meltwater across the drainage divide from the baltic basin to the river volga and that way to the caspian sea climate modelling shows that the lakes caused lower summer temperatures on the continent and on the lower parts of the ice sheet the final drainage of the best mapped lake is modelled and it is concluded that it probably emptied within few months we predict that this catastrophic outburst had considerable impact on sea ice formation in the arctic ocean and on the climate of a much larger area c 2003 elsevier ltd all rights reserved less

sand veins and wedges in cold aeolian environments sedimentary structures formed by the progressive primary infilling of thermal contraction cracks with sand are termed primary sand veins and sand wedges in addition to simple vein or wedge shapes irregularities can be caused by sand veins branching from their sides and toes primary sand wedges form widely in sandy polar deserts locally in sandy areas of tundra and probably in seasonally frozen ground there are no unique criteria for distinguishing primary sand veins and wedges from sand veins and wedges of other origins identification of the former depends on the occurrence of distinctive features not always present and on evaluation of their lithofacies and palaeoenvironmental contexts care and caution are advocated in the use of ancient relict primary sand veins and wedges as quantitative palaeoenvironmental indicators because modern active wedge distribution is poorly known and hence inferred thermal climatic threshold values are questionable it is suggested that ancient relict primary sand wedges exceeding 2 m in depth and with well developed vertical lamination probably indicate the former occurrence of continuous permafrost whereas sand veins and narrow sand wedges frost cracks are potentially ambiguous as they may form not only in the active layer above and within continuous permafrost but also in seasonally frozen ground in non permafrost areas

the dynamic arctic research campaigns over the last decade have yielded a growing stream of data that highlight the dynamic nature of arctic cryosphere and climate change over a range of time scales as a consequence rather than seeing the arctic as a near static environment in which large scale changes occur slowly we now view the arctic as a system that is typified by frequent large and abrupt changes the traditional focus on end members in the system glacial versus interglacial periods has been replaced by a new interest in understanding the patterns and causes of such dynamic change instead of interpreting changes almost exclusively as near linear responses to external forcing e g orbitally forced climate change research is now concentrated on the importance of strong feedback mechanisms that in our palaeo archives often border on chaotic behaviour the last decade of research has revealed the importance of on off switching of ice streams strong feedbacks between sea level and ice sheets spatial and temporal changes in ice shelves and perennial sea ice as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi dome ice sheets recent advances in dating techniques and modelling have improved our understanding of leads and lags that exist in different arctic systems on their interactions and the driving mechanisms of change future arctic research challenges include further emphases on rapid transitions and untangling the feedback mechanisms as well as the time scales they operate on

a new type of active margin the convergent extensional margin as exemplified by the middle america trench off guatemala the results of dsdp legs 67 and 84 during which a transect of holes was drilled across the middle america trench off guatemala show no accretion at the front of that subduction zone since early eocene time the tectonic evolution of the trench includes extensional structure on the landward as well as the seaward trench slopes the guatemalan margin is proposed as the model of a new type of active margin the convergent extensional active margin ce margin

a comprehensive study of pumice formation and dispersal the cretaio tephra of ischia italy the cretaio tephra is a small volume 0 02 km3 pumice deposit on the island of ischia in italy it was erupted during historical time and is associated with a tuff ring dome complex extruded along a n s trending normal fault system bordering the east side of the mt epomeo resurgent block 14c ages of the deposit average 1860 a b p which is in agreement with the potsherds found in paleosols underlying and overlying the deposit the eruption sequence consists of 7 members most of these members are pumice fall deposits one is an ash and pumice fallout and another is a surge bed the tephra have a trachytic phonolitic composition all chemical characteristics including major and trace elements and sr isotope composition are homogeneous throughout the sequence the vesicularity of pumice clasts does not show any systematic change the erupted magma had the same amount of volatiles the same flux and vesicle growth behavior throughout the eruption sequence grain size analyses of 90 tephra samples representative of all the members at variable distance from the supposed vent have been processed using the sequential fragmentation transport theory in order to define the effects of eruptive fragmentation and subsequent transport on the particle sizes distribution four significant subpopulations have been identified and related to transport mechanisms

monitoring of helium and carbon isotopes in the western eger rift area czech republic relationships with the 2014 seismic activity and indications for recent 2000 2016 magmatic unrest abstract we report new data of the regional distribution pattern of total gas compositions as well as he and co2 isotopic compositions from 25 gas exhalations in the western eger rift and its surroundings additionally the first time series data from gas exhalations in a clay pit within the cheb basin cb are given at 21 degassing locations the first data were obtained 20 years ago from 7 locations within the degassing center cb and from 3 degassing sites belonging to the marianske lazn ml degassing center neon and argon isotope compositions were determined also co2 is the major component at all degassing sites the 13c values display a small range 1 7 to 5 1 and the 3he 4he ratios vary from 1 9 to 5 9 ra the highest 3he 4he ratios are found at locations along the pocatky plesna fault zone followed by the degassing site in the clay pit on the nova ves fault and the locations on the ml fault at the edge of the cb although gas flow and co2 concentrations in all degassing centers are very high the fractions of mantle derived helium are different with presently up to 94 in relation to the sclm 3he 4he of 6 32 ra in the cb up to 73 in the ml and up to 35 in the karlovy vary degassing center at the locations in the eastern part of the cb a clear progressive increase of the 3he 4he ratio has been observed since the first sampling campaigns there in 1993 and 1994 whereas at the other degassing sites the helium isotope ratio remained essentially the same the progressive increase of the 3he 4he ratio in the eastern part of the cb together with further short time increases up to 6 3 ra at one location bublak before both the 2000 and 2008 earthquake swarms indicate an ongoing magmatic process beneath this area which seems to be associated with the occurrence of seismicity the cb is located close to the nov kostel focal zone where since the beginning of our investigations four strong periods of seismicity with magnitudes 3 occurred the latest gas data confirm our earlier findings time series studies showed that in relation with seismic events decreased 3he 4he ratios were repeatedly observed due to admixed seismically released crustal helium presently the eastern part of the cb is the most active non volcanic region in the european cenozoic rift system with gas signatures similar to those found in free mantle derived gases from the east african rift system

quaternary glaciation in north western siberia new evidence and interpretation abstract the pleistocene history of north western siberia is hotly discussed by researchers as the extension and impact of ancient glaciers are subjected to major revision the representative object for this study is the siberian uval an upland at the right hand bank of the ob river the uval contains some stony debris and for a long time researchers considered it as a moraine of an ice sheet however the siberian uval represents a predominantly sandy 30 40 m river terrace its origin is associated with development of the river network ice floe drift tectonics and marine ingressions well developed paleosols in the terrace body add to the picture of the development the first paleosol was encountered at a depth of a few meters and two 14 c dates 25693 27748 cal bp soan 7550 and 34740 35440 cal bp beta 410187 confirm the soil formation as karga mis3 the second paleosol is in the center of undisturbed section of 30 40 m terrace and its 14 c dates 45 ka bp soan 7551 soan 7552 43 5 ka bp beta 410188 the warmer paleobotanical spectra obtained from it may suggest that the paleosol formed in the beginning of mis5 the stony debris either underlies or overlies the first paleosol and represents rare boulders and pebbles embedded in the top sandy part of the terrace the debris is a result of ice floe drift ancient glaciers developed only in the mountains surrounding northwestern siberia only and then the stony moraine material could be spread by river ice floe drift during the river floods and sea water ingressions extrapolations relying on the data obtained by study of modern glaciers in the mountains surrounding northwestern siberia as well of relics remained by ancient glaciers confirm this conclusion

an arctic perspective on dating mid late pleistocene environmental history to better understand pleistocene climatic changes in the arctic integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required not least for correlation to extra arctic records in this paper we discuss from an arctic perspective methods and correlation tools that are commonly used to date arctic pleistocene marine and terrestrial events we review the state of the art of arctic geochronology with focus on factors that affect the possibility and quality of dating and support this overview by examples of application of modern dating methods to arctic terrestrial and marine sequences event stratigraphy and numerical ages are important tools used in the arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes age control is commonly provided by radiocarbon luminescence or cosmogenic exposure ages arctic ocean deep sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition patterns in palaeomagnetic records and increasingly biostratigraphic data many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning recent advances in dating technology calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material i e foraminifera for c 14 and single grain luminescence however for much of the pleistocene there are still limits to the resolution of most dating methods consequently improving the accuracy and precision analytical and geological uncertainty of dating methods through technological advances and better understanding of processes are important tasks for the future another challenge is to better integrate marine and terrestrial records which could be aided by targeting continental shelf and lake records exploring proxies that occur in both settings and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers

late weichselian ice sheets in arctic and pacific siberia abstract interpretation of space images coupled with field data on glacial geomorphology and glacial geology of northern eurasia have provided compelling evidence for a continuous late weichselian ice sheet covering the entire arctic margin of the continent in addition to the scandinavian ice sheet three ice sheets of the same order the karan east siberian and beringian are identified within the major eurasian ice sheet also there is evidence and other considerations suggesting a former ice sheet in the sea of okhotsk ice spreading centers of the ice sheets were situated on the continental shelves off the siberian coasts thus we can term the ice sheets siberian so far the conventional stratigraphic approach to the problem of siberian glaciation has proven fruitless and yielded nothing but uncertainty while geomorphological studies have discovered a wealth of glacial landforms in arctic siberia it was these landforms and their spacing that made the existence of former siberian ice sheets evident the east siberian ice sheet rested on the shelves of the eastern laptev and east siberian seas and its flow was directed radially including up the yana and indigirka rivers the beringian ice sheet was grounded on the chukchi bering and beaufort sea shelves overriding the chukchi and seward peninsulas from the north and flowing through the bering strait it was continued by a thick floating ice shelf buttressed by the submarine aleutian commander ridge the okhotsk ice sheet was grounded on the okhotsk shelf specific gemorphic signatures of marine ice sheets the glacially cut corners have been identified on all promontories jutting out into the bering and okhotsk seas the beringian and okhotsk ice sheets are consistent with the results of deep sea drilling in the adjacent north pacific during leg 145 of d v joides resolution

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

normal faulting of the daiichi kashima seamount in the japan trench revealed by the kaiko i cruise leg 3 abstract a detailed topographic and geophysical survey of the daiichi kashima seamount area in the southern japan trench northwestern pacific margin clearly defines a high angle normal fault which splits the seamount into two halves a fan shaped zone was investigated along 2 4 km spaced 100 km long subparallel tracks using narrow multi beam seabeam echo sounder with simultaneous measurements of gravity magnetic total field and single channel seismic reflection records vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported the northern and southern extensions of the normal fault beyond the flank of the seamount were delineated materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount canyons observed in the upper landward slope terminate at the mid slope terrace which has been uplifted since start of subduction of the seamount most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern japan trench wall this survey was conducted on r v jean charcot as a part of the kaiko i cruise leg 3 in july august 1984 under the auspices of the french japanese scientific cooperative program

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

dinoflagellate cyst evidence for warm interglacial conditions at the northern barents sea margin during marine oxygen isotope stage 5 dinoflagellate cyst analysis has been conducted on a sediment core from the northern barents sea margin eastern arctic ocean to reconstruct sea surface conditions during marine oxygen isotope stage 5 cyst concentrations and composition of assemblages display a distinct variability reflecting deglacial warming and the onset of relatively warm interglacial conditions in early stage 5 dinoflagellate cyst assemblages of the last interglacial which corresponds broadly to substage 5e are comparable with those from recent sediments of the area but have lower abundances of cold water taxa such assemblages suggest that sea surface temperatures of the last interglacial were therefore at least as warm as today or even warmer after a distinct cooling relatively stable cold conditions with minor periods of surface water warming prevailed from mid substages 5d to 5b temperatures might have been similar in substages 5a and 5e but the different compositions of assemblages indicate a stronger stratification of surface waters probably owing to a larger meltwater supply in substage 5a these results are compared with previous studies on marine carbonate and calcareous microfossil records from the fram strait and yermak plateau area which show that the general view of a cold last interglacial in the eastern arctic ocean is untenable copyright 2001 john wiley sons ltd

erratum to severnaya zemlya arctic russia a nucleation area for kara sea ice sheets during the middle to late quaternary quaternary science reviews 25 21 22 2006 2894 2936 abstract quaternary glacial stratigraphy and relative sea level changes reveal at least four expansions of the kara sea ice sheet over the severnaya zemlya archipelago at 79 n in the russian arctic as indicated from tills interbedded with marine sediments exposed in stratigraphic superposition and from raised beach sequences that occur at altitudes up to 140 m a s l chronologic control is provided by ams 14c electron spin resonance green stimulated luminescence and aspartic acid geochronology major glaciations followed by deglaciation and marine inundation occurred during mis 10 9 mis 8 7 mis 6 5e and mis 5d 3 the mis 6 5e event associated with the high marine limit implies ice sheet thickness of 2000 m only 200 km from the deep arctic ocean consistent with published evidence of ice grounding at 1000 m water depth in the central arctic ocean till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively suggesting wet based ice cap advance followed by cold based regional ice sheet expansion local ice caps over highland sites along the perimeter of the shallow kara sea including the byrranga mountains appear to have repeatedly fostered initiation of a large kara sea ice sheet with exception of the last glacial maximum mis 2 when kara sea ice did not impact severnaya zemlya and barely graced northernmost taymyr peninsula

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

structure and stratigraphy beneath a young phreatic vent south inyo crater long valley caldera california an 861 m long hole has been cored on a slanted trajectory that passed directly beneath south inyo crater in the west moat of long valley caldera california the purpose of the hole was to investigate the magmatic behavior that led to surface deformation and phreatic activity during the 600 year old eruption of the inyo vent chain the hole was sited 216 m southwest of the crater passed beneath its center at a depth of 566 m and terminated 79 m northeast of the crater center at a depth of 810 m metamorphic basement was encountered at a depth of 779 m the volcanic and sedimentary sequence consists solely of post bishop tuff caldera fill including 319 m of moat basalt and 342 m of early rhyolite and is nearly 900 m thinner than in a unocal corporation well 900 m to the southeast apparently a major fault lies between the two holes and forms part of the western structural boundary of the caldera 3 4 km inboard of its topographic boundary breccia zones that intrude the caldera fill were intersected at 12 0 9 3 m and 1 2 0 8 m sw and 8 5 25 1 m ne of the crater center the largest breccia unit is symmetrically zoned from margins rich in vesicular rhyolite and locally derived rhyolite wall rock with most clasts 0 1 m to a center of up to 50 vol basalt with individual basalt clasts to 1 m in intersected length the basalt appears to be an early feeder for the moat basalt sequence the vesicular rhyolite is chemically distinct from both the rhyolite wall rock and previously recognized 600 year old inyo eruptives but matches fresh appearing pyroclasts in the crater ejecta this component of the breccia is therefore interpreted as representing juvenile magma that vesiculated and fragmented as it rose along the margins of an older basalt intrusion during this process wall rock fragments were ejected from depths extending to at least 800 m progression to a magmatic eruption was probably prevented by rapid influx of groundwater into the feeder the chemical data do not support the hypothesis that a single simple dike exists under the entire segment of the inyo chain that was active 600 years ago if such a dike exists it apparently tapped different magma chambers along its 10 km length the excess of surface extension over that needed to accommodate the intruded juvenile material may reflect the presence of a larger intrusion at depth below the level of fragmentation or the contribution of tectonic activity to the surface deformation

a sr isotopic comparison between thermal waters rocks and hydrothermal calcites long valley caldera california abstract the 87 sr 86 sr values of thermal waters and hydrothermal calcites of the long valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks five thermal waters display 87 sr 86 sr of 0 7081 0 7078 but show systematically lighter values from west to east in the direction of lateral flow we believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression all types of pre syn and post caldera volcanic rocks in the west and central caldera have 87 sr 86 sr m between about 0 7060 and 0 7072 and values for sierra nevada granodiorites adjacent to the caldera are similar sierran pre intrusive metavolcanic and metasedimentary rocks can have considerably higher sr isotope ratios 0 7061 0 7246 and 0 7090 0 7250 respectively hydrothermally altered volcanic rocks inside the caldera have 87 sr 86 sr m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites 0 7068 0 7105 occupy a midrange of values between the volcanic plutonic rocks and the sierran metamorphic rocks these data indicate that the long valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks reequilibration of sr isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill

petrology and emplacement dynamics of intrusive and extrusive rhyolites of obsidian dome inyo craters volcanic chain eastern california drilling at obsidian dome has provided continuous core samples of the distal and proximal portions of obsidian dome its conduit and an associated feeder dike both the dome and conduit are chemically and mineralogically zoned and consist of a finely porphyritic high ba low silica rhyolite occurring in the basal portion of the dome and margins of the conduit and a finely porphyritic low ba higher silica rhyolite occurring in the upper portion of the dome and center of the conduit the high ba rhyolite contains two distinct phenocrysts assemblages with two distinct compositions and represents mingled magmas the low ba rhyolite in the dome and conduit contains significantly fewer disequilibrium phenocrysts and is only slightly mingled the dike sampled at 600 m depth as well as a related tephra fall from obsidian dome vent are entirely low ba rhyolite that contain no evidence of magma mingling end members of the mingled magma calculated using two different methods are a 63 silica end member and a silicic end member identical in composition to the dike and tephra fall from obsidian dome vent this silicic end member was the first magma emplaced in the dike and comprised much or all of the first magma vented to the surface during formation of the obsidian dome vent when eruption rates were high magma mingling of mafic and rhyolite magmas occurred during formation of the conduit a comparison of the magma types at obsidian dome with the other 600 year old magma types in the inyo chain demonstrates that the finely porphyritic rhyolites at obsidian dome are similar to the finely porphyritic rhyolites at the other domes all of these originated by mingling of two end members the coarsely porphyritic rhyolites that occur at glass creek and deadman domes are distinctly different from the finely porphyritic rhyolites the two rhyolites can not be related by any fractionation scheme and could not have been in thermal or chemical equilibrium with each other these observations require considerable heterogeneity in the inyo domes magmatic system two possible interpretations of the chemical variation and emplacement sequence are explored in the first interpretation the chemical patterns observed in the surface and subsurface samples at obsidian dome are explained by differential draw up of magma from a stratified dikelike reservoir this differential draw up is the result of changing flow rates during the course of the eruption when the magma initially vented to the surface during the main part of the explosive phase flow rates were very high and the deepest layer of the reservoir was drawn into the conduit where magma mingling occurred during the subsequent effusive phase flow rates were low draw up depths were reduced and only magma from the uppermost layer in the reservoir erupted only slightly contaminated by earlier hybrid magma drawn up similar processes most likely occurred at the other inyo domes however the low ba rhyolite was less abundant and highly viscous coarsely prophyritic rhyolite was near the surface and drawn up as a late pluglike structure an alternate interpretation is that the dike initially consisted of heterogeneous magma domains and that the zonation observed in the conduit of obsidian dome and on the surface of the three inyo domes is the result of the tendency of less viscous magma to encapsulate more viscous magma during sustained flow in a conduit

glacial history and palaeo environmental change of southern taimyr peninsula arctic russia during the middle and late pleistocene abstract we here reconstruct a glacial and climate history of arctic nw siberia for the last 600 000 years based on the stratigraphy and chronology of 35 studied river sections on the southern taimyr peninsula from this stratigraphic mosaic we have identified four glacial events marked by tills glaciotectonics which are intercalated with mainly marine sediments deposited in proglacial settings during transitions from glacial conditions into subsequent interglacials interstadials the traces of early shelf based kara sea ice sheet ksis glaciations in marine isotope stages mis 12 14 and 8 are sparsely preserved but these ice advances are suggested to have terminated far south into the central siberian uplands as also was the case with the younger taz glaciation mis 6 the inception phase of the latter glaciation was complex with ice advancing into a proglacial marine basin both from the south putorana anabar uplands and the north the deglaciation leading into the karginsky interglacial mis 5e was marked by the development of the southernmost ice marginal zones imzs on the taimyr lowlands the urdakh and sampesa imzs the most recent late pleistocene glacial cycle is recorded by three successively smaller ksis advances from the kara sea shelf onto taimyr of which only the first during early zyryanka mis 5d reached south of the byrranga mountains with its maximum extent marked by the jangoda syntabul severokokorsky imz retreat of the ice margin during mis 5c b was accompanied by deposition of glaciomarine sediment in the proglacial basin and deposition of large successions of delta sediments in the foothills of the byrranga mountains reaching 100 m above present sea level the region north of the byrranga mountains was subjected to two subsequent ksis glaciations during mis 4 and mis 2 while the area south of the byrranga mountains transitioned to a terrestrial environment from the middle into the lower zyryanka as evidenced by deposition of fluvial aeolian and ice complex yedoma sediments

interpreting exposure ages from ice cored moraines a neoglacial case study on baffin island arctic canada 10be dating of moraines has greatly improved our ability to constrain the timing of past glaciations and thus past cold events however the spread in ages from a single moraine is often greater than would be expected from measurement uncertainty making paleoclimatic interpretations equivocal here we present 28 new 10be ages from ice cored neoglacial moraines on baffin island arctic canada and explore the processes at play in moraine formation and evolution through field observations and a numerical debris covered glacier model the insulating effect of debris cover modifies glacier lengths and results in the development of ice cored moraines over multiple advances and thousands of years although ice cores can persist for several millennia spatially variable ice core melt out contributes to moraine degradation and boulder destabilization making it likely that the 10be clock is reset on moraine boulders in these settings thus exposure ages from ice cored moraines must be interpreted with caution the oldest ages after excluding samples with inheritance provide the best estimates of initial moraine formation three baffin island moraines yield 10be ages suggesting formation at 5 2 4 6 and 3 5 ka respectively adding to a growing body of evidence for significant summer cooling millennia before the little ice age

the unique radar properties of silicic lava domes 1 silicic lava domes exhibit distinct morphologic characteristics at scales of centimeters to kilometers multiparameter radar observations capture the unique geometric signatures of silicic domes in a set of radar scattering properties that are unlike any other natural geologic surfaces backscatter cross section values are among the highest observed on terrestrial lava flows and show only a weak decrease with incidence angle cross polarization backscatter hv shows a unique behavior increasing with increasing wavelength circular polarization ratios are relatively high in the 0 3 0 95 range and increase with increasing wavelength field measurements of boulder size frequency distributions and microtopography indicate that silicic dome surfaces are among the roughest ever measured rms heights at a 1 m lateral scale range from 13 cm to 50 cm rms slopes at 1 m spacing range from 12 to 43 degrees modeling of the scattering behavior suggests it results from a combination of rough surface facet scattering and scattering from block edges that act as a random collection of dipoles the unusual wavelength dependence of the radar parameters appears to result from a higher component of edge scattering at large wavelengths producing for example higher cross polarized backscatter at p band 68 cm steep sided volcanic domes on venus superficially resemble terrestrial silicic domes in plan view gross morphology but few similarities remain when the radar scattering and three dimensional shapes of the features are compared the unique radar scattering properties suggest that such volcanic surfaces can be identified with multiparameter radar observations in future planetary radar missions and in active terrestrial volcanoes where dome development can represent serious hazards

glaciomorphological map of the russian federation abstract this is an overview of glacial features of the russian federation from the western border to the laptev sea in the form of an explanatory note to the map of ice marginal formations and ice limits 600 to 11 ka old attached is a generalized version of glaciomorphological map of the russian federation scale 1 2 500 000 compiled by geological research institute russian geological survey the principal purpose of the mapping is correlation of ice advances in different regions of glaciated russia possible paleogeographic and stratigraphic implications of the map pattern are discussed

three dimensional gravity modeling of the geologic structure of long valley caldera a 48 mgal gravity low coincides with long valley caldera and is mainly attributed to low density caldera fill gravity measurements by unocal geothermal have been integrated with u s geological survey data vastly improving gravity station coverage throughout the caldera a strong regional gravity trend is mainly attributed to isostasy a best fitting based on regional control of basement densities airy heiskanen isostatic model was used for the regional correction a three dimensional multiple unit gravity modeling program with iterative capabilities was developed to model the residual gravity the density structure of long valley caldera and vicinity was modeled with 22 discrete density units most of which were based on geologic units information from drill hole lithologies surface geology and structural geology interpretations constrain the model some important points revealed by the three dimensional gravity modeling are that 1 the volume of ejected magma associated with the bishop tuff eruption is greater than previously thought 2 the caldera structure is strongly influenced by precaldera topography and the extensions of major active faults 3 the main west ring fracture is coincident with the inyo domes mono craters fracture system 4 a relatively low density region probably underlies the caldera and 5 a silicic magma chamber may underlie devils postpile

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

nankai trough and the fossil shikoku ridge results of box 6 kaiko survey abstract seabeam mapping and detailed geophysical surveying have been conducted over the nankai trough where the fossil shikoku ridge is subducted below southwest japan the geometry of the oceanic lithosphere bending under the margin as well as the three dimensional structure of the accretionary prism have thus been determined in detail three 350 trending probably transform faults have been identified in the area of the survey they do not extend further south and appear to be limited to the last phase of spreading within the shikoku basin probably between 15 and 12 ma this last phase of spreading would then have been accompanied by a sharp change in spreading direction from east west to n 350 the two eastern transform faults limit a zone of reduced nankai trench fill of turbidites opposite to the tosa bae embayment this observation suggests that the tosa bae embayment actually results from this reduced supply of trench fill to the imbricate thrusting process the accretionary prism can be divided into three different tectonic provinces separated by continuous mappable thrusts the lower and upper main thrusts surface shortening is limited to the lower accretionary prism south of the upper main thrust umt whereas uplift with possible extension characterizes the prism above the umt deformation due to the relative plate motion mostly affects the lower accretionary prism south of the umt

magnetotelluric transect of long valley caldera resistivity cross section structural implications and the limits of a 2 d analysis twenty four magnetotelluric mt soundings have been collected in an east west profile across the center of long valley caldera the average station spacing is approximately 1 km and appears adequate to sample the important features of the upper crustal and deeper resistivity structures additional control on the shallowest resistivity is provided by a continuous profile of time domain electromagnetic soundings coincident with the western portion of the mt line our mt data set reveals numerous resistivity structures which illuminate the evolution and present state of the long valley system many of these have been quantified through two dimensional 2 d finite element modeling emphasizing the transverse magnetic tm mode important structural components include low resistivity layers 0 5 1 5 km deep under the eastern half of the caldera beneath the axial graben of the resurgent dome and under the west caldera moat most of this layering appears to lie in post caldera early rhyolite tuffs and the upp

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

physical rock properties in and around a conduit zone by well logging in the unzen scientific drilling project japan abstract the objective of the unzen scientific drilling project usdp is not only to reveal the structure and eruption history of the unzen volcano but also to clarify the ascent and degassing mechanisms of the magma conduit conduit drilling usdp 4 was conducted in 2004 which targeted the magma conduit for the 1990 95 eruption the total drilled length of usdp 4 was 1995 75 m geophysical well logging including resistivity gamma ray spontaneous potential sonic wave velocity density neutron porosity and fullbore formation microimager fmi was conducted at each drilling stage variations in the physical properties of the rocks were revealed by the well log data which correlated with not only large scale formation boundaries but also small scale changes in lithology such variations were evident in the lava dike pyroclastic rocks and breccias over depth intervals ranging from 1 to 40 m these data support previous models for structure of the lava conduit in that they indicate the existence of alternating layers of high resistivity and high p wave velocity rocks corresponding to the lava dikes in proximity to narrower zones exhibiting high porosity low resistivity and low p wave velocity these narrow low porosity zones are presumably higher in permeability than the adjacent rocks and may form preferential conduits for degassing during magma ascent

development and emplacement of the inyo domes magmatic suite california evidence from geological textural csd and geochemical observations of ash and lava the inyo domes magmatic system erupted 650 years ago in eastern california it is a series of three lava domes and associated pyroclastic rocks made up of phenocryst poor fp and phenocryst rich compositions cp we examined the chemical composition quantitative petrographic texture and geology of the ensemble the fp unit has considerable compositional variation that was produced by fractional crystallisation of feldspars and pyroxenes in a plexus of conduits and magma storage areas under or close to the inyo domes magmatic system there is no magmatic link with the synchronous north mono silicic eruption 20 km to the north the cp unit is compositionally more uniform and originated from a mushy feldspar cumulate formed in an earlier rhyolitic magma chamber the eruption started with the reactivation of a major fault which ruptured the surface initially the fault intersected a single hydrous magma source in the plexus and produced a pyroclastic eruption in the south other regions of the plexus to the north were rapidly co opted making further pyroclastic eruptions as the magmas became degassed lava domes started to form from fissures finally the cp magma source became reactivated by the injection of new magma felsic or mafic into the chamber the cp magma was forced out into a conduit of the fp unit where it formed a mixed unit im the quantity of the cp component increased until it dominated at this point the fp units were solid and the cp unit piled up to make the central knobs of the southern domes

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime

the taimyr peninsula and the severnaya zemlya archipelago arctic russia a synthesis of glacial history and palaeo environmental change during the last glacial cycle mis 5e 2 abstract we here suggest a glacial and climate history of the taimyr peninsula and severnaya zemlya archipelago in arctic siberia for the last about 150 000 years ka primarily it is based on results from seven field seasons between 1996 and 2012 to a large extent already published in papers referred to in the text and on data presented by russian workers from the 1930s to our days and by german colleagues working there since the 1990s although glaciations even up here often started in the local mountains their culminations in this region invariably seems to have centred on the shallow kara sea continental shelf most likely due to expanding marine ice shelves grounding there as a combined effect of thickening ice and eustatically lowered sea levels the most extensive glaciation so far identified in this region named the taz glaciation took place during marine isotope stage 6 mis 6 i e being an equivalent to the late saale illinoian glaciations it reached c 400 km southeast of the kara sea coast across and well beyond the byrranga mountain range and ended c 130 ka it was followed by the mis 5e karginsky eemian interglacial with an extensive marine transgression to 140 m above present sea level facilitated by strong isostatic downloading during the preceding glaciation during the latest zyryankan weichselian wisconsinan glacial cycle followed a series of major glacial advances the earliest and most extensive culminating c 110 100 ka mis 5d 5e also reached south of the byrranga mountains and its post glacial marine limit there was c 100 m a s l the later glacial phases around 70 60 ka and 20 ka terminated at the north taimyr ice marginal zone ntz along or some distance inland from the present northwest coast of taimyr they dammed glacial lakes which caused the taimyr river to flow southwards where to day it flows northwards into the kara sea the c 20 ka glacial phase contemporary with the maximum lgm glaciation in nw europe was this glacial cycle s least extensive one up here probably an effect of precipitation shadow caused by the major glaciations to the west from the kara sea shelf this advance only reached c 100 km inland over some limited parts of nw taimyr the severnaya zemlya islands were only locally glaciated at this time the lowlands south of the byrranga mountains have been a terrestrial mammoth steppe environment during the last c 50 ka and periglacial permafrosted sediments here have preserved excellent information on its megafauna and vegetation the latter according to new dna data had considerably more for grazing animals nourishing flowering plants growing than earlier pollen based grass dominated spectra have suggested

correlation of upper pleistocene sediments in northern west siberia abstract a geochronometric database comprising 121 optically stimulated luminescence and 59 radiocarbon dates plus u th date on peat from 24 key sections in northern west siberia is presented and discussed these data have been obtained during russian norwegian joint research for the past 15 years and are augmented by reports on radiocarbon dated mammoth carcasses in west siberia together they provide the basis for revising the regional stratigraphic scheme and for correlation to the european quaternary chronostratigraphy and marine oxygen isotope record the geochronologic correlation of sedimentary formations across west siberia involves classical stratotypes of fluvial shallow limnic and temperate marine sediments of the karginsky horizon ca 130 ka which was previously attributed to mis 3 the older kazantsevo marine formation is thus assigned a middle pleistocene age the uppermost glacial sedimentary complex containing glacial ice was deposited by shelf based ice sheets between ca 100 and 60 ka bp the postglacial pleistocene sediments are mostly ice bound loess like deposits and sink hole silts containing numerous mammoth carcasses that are radiocarbon dated to between ca 42 and 25 ka bp there are no traces of glacial activity on the siberian plains during mis 2 a period for which palaeoclimatic proxies suggest a cold and dry environment this synthesis indicates that the prior usage of the siberian correlation horizons of kazantsevo and karginsky as equivalents of the eemian and middle pleniglacial is stratigraphically invalid

hydrography and mollusc faunas of the baltic and the white sea north sea seaway in the eemian abstract palynologically dated mollusc and cirriped faunas from a region extending from the north sea through the baltic and karelia to the arkhangelsk region show that the hydrography of the baltic was very different from the holocene for 2 2 5 ka in the early eemian a seaway existed from the barents to the north sea through karelia until it was severed at the present continental watershed to the north of lake onega after this the ladoga onega trough remained an arm of the baltic for several millennia the benthic faunas are comparable to the holocene but their boundaries were displaced much further into the baltic notable differences from the holocene are the absence or rarity of the macoma balthica biocoenosis and the presence of cold portlandia dominated biocoenoses in karelia in the belt sea and western baltic winter sea surface temperatures and salinity were higher than now by ca 6 c and 15 and the distinctly brackish top layer was missing at the same time cold bottom water 2 5 c with a tendency to anoxia characterised the karelian arm of the baltic water exchange through this area was inhibited by the constriction to the north of lake onega and the basin and threshold bathymetry water transport through the white sea baltic seaway was too sparse to play an active role in the north atlantic surface circulation or climatic change in the region the high salinity and temperature in the belt sea and western baltic persisted throughout the eemian and are explained by wider and deeper passage from the north sea to kattegat wider straits through denmark higher salinity in the north sea higher evaporation as well as more dispersed fresh water supply the advection of oceanic water into the baltic culminated in the early eemian before the carpinus zone and probably resulted in an oceanic climate in the baltic region while at the same time cold winters produced cold bottom water in the karelian arm

helium isotope and gas discharge variations associated with crustal unrest in long valley caldera california 1989 1992 the onset of anomalous seismic activity in 1989 beneath mammoth mountain on the southwestern rim of the long valley caldera california was followed within approximately 4 months by a large increase in sup 3 he sup 4 he in vapor discharged from a fumarole on the north side of the mountain the helium isotopic ratio at this vent rose to a maximum of 6 7 r sub a in july 1990 and subsequently declined to values near 5 r sub a potential sources of the sup 3 he rich vapors include degassing of fresh magma degassing from fresh surfaces generated in newly fractured igneous rocks and volatile release from a sup 3 he rich gas chamber situated above previously emplaced intrusives the magnitude of the increase in helium isotopic composition from 3 8 to 6 7 r sub a the persistence of relatively high values 5 r sub a over a period of 3 years the increase in the flux of total he relative to gases in air saturated water and the increases in the rates of discharge of steam and gas from this fumarole indicate that magmatic intrusion did in fact begin in 1989 beneath mammoth mountain seismic activity and limited measurements of extensional deformation at the surface suggest that the depth of intrusion maymore be as shallow as 2 km consistent with the prompt appearance of increased sup 3 he sup 4 he ratios in the fumarolic gas and that the intrusive process may have persisted for approximately 1 year in contrast a similar combination of magmatic intrusion and anomalous seismic activity beneath the resurgent dome south moat region during the 1989 1991 period resulted in at most relatively small changes in sup 3 he sup 4 he in fumarolic discharge at the southern edge of the resurgent dome the more subdued response may result from a combination of greater intrusive depths and greater dilution of sup 3 he rich inputs to thermal fluid reservoirs in the shallow hydrothermal system in this area compared with mammoth mountain 60 refs 11 figs 4 tabs less

is northern honshu a microplate abstract seismic slip vectors along the japan trench the eastern margin of the japan sea and the sagami trough are compared with global relative plate motions rm2 minster and jordan 1978 to test a new hypothesis that northern honshu japan is part of the north american plate this hypothesis also claims that the eastern margin of the japan sea is a nascent convergent plate boundary kobayashi 1983 nakamura 1983 seismic slip vectors along the japan trench are more parallel to the direction of the pacific north american relative motion than that of the pacific eurasian relative motion however the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence seismic slip vectors and rates of shortening along the eastern margin of the japan sea for the past 400 years are also consistent with the relative motion between the north american and eurasian plates calculated there seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south kanto beneath which the philippine sea plate is subducting indicate two major directions one is the relative motion between the north american and philippine sea plates and the other that between the eurasian and philippine sea plates one possible interpretation of this is that the eastern margin of the japan sea may be in an embryonic stage of plate convergence and the jump of the north american eurasian plate boundary from sakhalin central hokkaido to the eastern margin of the japan sea has not yet been accomplished in this case northern honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates behaving as part of either the eurasian or north american plate another possibility is that the seismic slip vectors and crustal deformations in south kanto do not correctly represent the relative motion between plates but represent the stresses due to non rigid behaviors of part of northern honshu

depositional history of the north taymyr ice marginal zone siberia a landsystem approach the sediment landform associations of the northern taymyr peninsula in arctic siberia tell a tale of ice sheets advancing from the kara sea shelf and inundating the peninsula probably three times during the weichselian in each case the ice sheet had a margin frozen to its bed and an interior moving over a deforming bed the north taymyr ice marginal zone ntz comprises ice marginal and supraglacial landsystems dominated by thrust block moraines 2 3 km wide and large scale deformation of sediments and ice large areas are still underlain by remnant glacier ice and a supraglacial landscape with numerous ice walled lakes and kames is forming even today the proglacial landsystem is characterised by subaqueous e g deltas or terrestrial e g sandar environments depending on location altitude and time of formation dating results osl c 14 indicate that the ntz was initiated ca 80 kyr bp during the retreat of the early weichselian ice sheet and that it records the maximum limit of a middle weichselian glaciation ca 65 kyr bp during both these events proglacial lakes were dammed by the ice sheets part of the ntz was occupied by a thin late weichselian ice sheet 20 12 kyr bp resulting in subaerial proglacial drainage copyright c 2002 john wiley sons ltd

surface and subsurface facies architecture of a small hydroexplosive rhyolitic centre in the mesoproterozoic gawler range volcanics south australia abstract at menninnie dam south australia a drilling program has revealed a complete section through the subsurface feeder system and erupted products of a small hydroexplosive rhyolitic centre within the mesoproterozoic gawler range volcanics porphyritic rhyolite intruded near vertical faults in the palaeoproterozoic basement and at less than a few hundred metres depth interacted with fault hosted hot groundwater hydrofracturing of the wall rock occurred in advance of and at the margins of the rhyolitic intrusions the rhyolitic intrusions have peperitic margins and grade into discordant lithic rich pb facies the advancing fragmentation front intersected the palaeosurface triggering phreatic eruptions that deposited a poorly sorted lithic rich explosion breccia rhyolite then rose to the surface through the intrusive breccias and shallow seated magma water interaction occurred in the conduit within 800 m from the inferred source the products include muddy sandstone and pumice breccia at the end of the eruption rhyolitic lava was extruded in the form of a small dome the presence of contemporaneous pb zn ag mineralisation in the wall rocks suggests that an active hydrothermal system may have been involved in the formation of the menninnie dam hydroexplosive volcanic centre

late pleistocene and holocene vegetation and climate on the taymyr lowland northern siberia abstract pollen records from perennially frozen sequences provide vegetation and climate reconstruction for the last 48 000 14c years in the central part of taymyr peninsula open larch forest with alnus fruticosa and betula nana grew during the kargin middle weichselian interstade ca 48 000 25 000 14c yr b p the climate was generally warmer and wetter than today open steppe like communities with artemisia poaceae asteraceae and herb tundralike communities with dwarf betula and salix dominated during the sartan late weichselian stade ca 24 000 10 300 14c yr b p the statistical information method used for climate reconstruction shows that the coldest climate was ca 20 000 17 000 14c yr b p a warming allerod interstade with mean july temperature ca 1 5 c warmer than today occurred ca 12 000 14c yr b p the following cooling with temperatures about 3 4 c cooler than present and precipitation about 100 mm lower corresponds well with the younger dryas stade tundra steppe vegetation changed to betula nana alnus fruticosa shrub tundra ca 10 000 14c yr b p larch appeared in the area ca 9400 14c yr b p and disappeared after 2900 14c yr b p cooling events ca 10 500 9600 and 8200 14c yr b p characterized the first half of the holocene a significant warming occurred ca 8500 14c yr b p but the holocene temperature maximum was at about 6000 4500 14c yr b p the vegetation cover approximated modern conditions ca 2800 14c yr b p late holocene warming events occurred at ca 3500 2000 and 1000 14c yr b p a cooling little ice age took place between 500 and 200 14c yr ago

rhyolite intrusions in the intracaldera bishop tuff long valley caldera california abstract drilling of the long valley exploratory well on the resurgent dome in the long valley caldera revealed 300 m cumulative thickness of granophyric intrusions within the 1180 m thick 760 ka intracaldera bishop tuff the intrusions are aphyric to sparsely plagioclase phyric high silica high barium and low strontium rhyolites they resemble the lavas of the early rhyolite the first phase of post caldera volcanism a mean 40 ar 39 ar age of 590 17 ka from a part of a shallow intrusion is coeval with early rhyolite volcanism a second mean age of 454 17 ka from the same intrusion may reflect either younger early rhyolite activity with no external equivalent or hydrothermal resetting of the argon system hydrothermal alteration of the intrusions is characterized by introduction of quartz calcite and pyrite and formation of illite smectite high co 2 content of fluids apparently inhibited zeolite formation alteration varies locally within intrusions and intrusive groups and does not vary systematically with depth oxygen shows consistent depletion of the 18 o isotope from an initial magmatic composition of 6 0 to 8 5 to values ranging from 1 4 to 0 4 the constant oxygen isotope depletion most likely reflects alteration of intrusions due to local emplacement induced hydrothermal circulation rather than a caldera scale hydrothermal system in contrast 18 o depletion of the host bishop tuff increases regularly with depth except at an intrusive contact a pre early rhyolite geothermal gradient of approximately 70 c km was inferred this is substantially higher than the current gradient but substantially lower than expected for the case of a conductive regime over a shallow residual magma chamber either the intrusions were fed from a deep chamber or a cool hydrologic recharge regime was established early in caldera history the age thickness and suspected lateral extent of these shallow intrusions are such that emplacement of the intrusions rather than inflation of a shallow chamber is responsible for resurgence of the central long valley caldera similar intrusions occur in another well on the resurgent dome lv13 21 but not in wells located off the dome

structures and lithofacies of inferred silicic conduits in the parana etendeka lip southernmost brazil abstract extensive silicic units in the parana etendeka lip have been long interpreted as pyroclastic density currents rheomorphic ignimbrites derived from the messum complex in namibia in recent literature however they have been characterized as effusive lava flows and domes in this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at mato perso sao marcos and jaquirana cambara do sul areas in southern brazil inferred conduits are at least 15 25 m in width and the lithofacies include variably vesicular monomictic welded and non welded breccias in the margins to poorly vesicular banded spherulitic and microfractured vitrophyres in the central parts flat lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits large scale regional tectonic structures in southern brazil include the ne sw aligned porto alegre suture leao and acotea faults besides the antas lineament a curved tectonic feature accompanying the bed of antas river south of the antas lineament smaller scale nw se lineaments limit the exposure areas of the inferred conduits ne sw and subordinate nw se structures within this smaller scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub vertical banding in the widespread banded vitrophyre lithofacies upper lava flows display flat lying foliation pipe like and spherical vesicles and have better developed microlites petrographic characteristics of the silicic vitrophyres indicate that crystal poor magmas underwent distinct cooling paths for each inferred conduit area the vitrophyre chemical composition is defined by the evolution of trachydacitic dacitic vitrophyres with 62 65 wt sio 2 to rhyodacite and rhyolite with 66 68 wt sio 2 the more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions based on the documented lithofacies architecture we attribute the source of the silicic lava flows in the studied localities to tectonic controlled local conduits rather than pyroclastic density currents from distant vent areas

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

postglacial viability and colonization in north america s ice free corridor during the last glacial maximum continental ice sheets isolated beringia northeast siberia and northwest north america from unglaciated north america by around 15 to 14 thousand calibrated radiocarbon years before present cal kyr bp glacial retreat opened an approximately 1 500 km long corridor between the ice sheets it remains unclear when plants and animals colonized this corridor and it became biologically viable for human migration we obtained radiocarbon dates pollen macrofossils and metagenomic dna from lake sediment cores in a bottleneck portion of the corridor we find evidence of steppe vegetation bison and mammoth by approximately 12 6 cal kyr bp followed by open forest with evidence of moose and elk at about 11 5 cal kyr bp and boreal forest approximately 10 cal kyr bp our findings reveal that the first americans whether clovis or earlier groups in unglaciated north america before 12 6 cal kyr bp are unlikely to have travelled by this route into the americas however later groups may have used this north south passageway

trench triple junction off central japan preliminary results of french japanese 1984 kaiko cruise leg 2 abstract leg 2 of the french japanese 1984 kaiko cruise has surveyed the trench triple junction off central japan where the japan izu bonin and sagami trenches intersect the izu bonin trench is deeper than the japan trench and filled by a thick turbiditic series its anomalous depth is explained by the westward retreat of the edge of the northwestward moving philippine sea plate on the contrary to what happens in the japan trench horst and graben structures of the pacific plate obliquely enters the izu bonin trench suggesting that the actual boundary between these two trenches is located to the north of the triple junction the inner wall of the izu bonin trench is characterized in the triple junction area by a series of slope basins whose occurrence is related to the dynamics of this area the northernmost basin is overthrust by the edge of the fore arc area of the northeast japan plate the plate boundary is hardly discernible further east which makes it impossible to locate precisely the triple junction itself these features suggest that large intra plate deformation occurs there due to the interaction of the plates involved in the triple junction and the weak mechanical strength of the wedge shaped margin of the overriding plates

hydrothermal alteration and past and present thermal regimes in the western moat of long valley caldera abstract hydrothermal alteration in caldera fill early rhyolite and moat rhyolite was investigated in six western moat drillcores in long valley caldera with an emphasis on clay mineralogy in two of the cores examined a complete sequence was observed in argillic alteration of tuffaceous rocks progressing from smectite often with kaolinite to mixed layer illite smectite i s to illite with increasing depth portions of this sequence were observed in the other four drillcores lower permeability rhyolitic lavas typically showed much sparser clay alteration than tuffs in cores where alteration progressed through smectite to i s or illite the distribution of the clay minerals and of compositional and structural variation in the i s phases allowed estimation of pre existing alteration temperatures and thermal gradients i s and illite occurred at the shallowest depths and highest elevations in the shady rest sr core and comparable alteration occurred at progressively deeper levels in plv 1 and inyo 4 presently observed temperatures are well below preexisting temperatures at comparable depths in these three holes with the exception of the deeper portion of sr paleotemperatures in the zone of i s alteration in the sr hole 200 250 m depth were 65 c higher than at present with a thermal gradient at least twice the steep gradient existing there now in plv 1 temperatures near the base of the hole have declined even further than in sr despite the steep gradient currently observed in inyo 4 hydrothermal circulation somewhat cooler than that in sr and plv 1 occurred at one time in the deeper portion of the hole and the steep thermal gradient currently observed at shallower levels in inyo 4 may be the truncated remnant of a gradient that once continued to greater depth in mlgrap 1 hydrothermal circulation occurred previously near the base of the hole but at temperatures probably not far above present ones no evidence of high temperature alteration was observed in cores from mlgrap 2 or plv 2

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

evidence for 600 year old basalt and magma mixing at inyo craters volcanic chain long valley caldera california andesite inclusions are found within the vent areas of two 600 year old rhyolite domes in the inyo craters volcanic chain eastern california both domes lie within the present northwestern sector of 0 73 ma long valley caldera inclusion morphology indicates that they were partially molten and ductile during incorporation within coarsely porphyritic rhyolite the xenocryst assemblage within the inclusions plagioclase hornblende biotite quartz sanidine is identical to the phenocryst assemblage within the host rhyolite microprobe analyses of xenocrysts within the andesite inclusions show that they have compositions similar to phenocrysts in the host rhyolite these data suggest that the andesite inclusions are the result of mixing of the coarsely porphyritic rhyolite with a more mafic end member whole rock geochemistry of the inclusions generally supports a simple mixing model between the coarsely porphyritic rhyolite of the inyo domes and typical postcaldera mafic lavas found throughout the western caldera moat the inclusions provide the first evidence for involvement of basaltic magma in the 600 year old rhyolite eruptions of the inyo craters volcanic chain and suggest the possibility that the rhyolitic eruptions were initiated by injection of basalt into the lower part of the silicic magma system periodic thermal replenishment of the magmatic system through basaltic injection may explain the relatively high temperatures encountered in drill holes within the western caldera moat the inclusions further suggest that although rhyolite eruptions are statistically more likely from the inyo craters volcanic chain future basaltic eruptions cannot be ruled out

benthic foraminiferal and stable isotope evidence for a younger dryas style cold spell at the saalian eemian transition denmark abstract benthic foraminiferal and stable isotope studies of two borings from the island of anholt denmark reveal a continuous late saalian eemian sequence with an overall gradual warming interrupted by a short term temperature deterioration comparable with the younger dryas cold spell the sequence is correlated to the global deep sea stable isotope record based on environmental evidence given by foraminiferal faunas and stable isotopes the following environmental changes in the anholt cores can be attributed to the global variations 1 1 an interstadial phase the flakket interstadial which had a duration of about 1000 years is correlated to stable isotope event 6 01 2 2 the following cold spell the kattegat stadial spanning about 1000 years represents most of the interval between isotope events 6 01 and 6 0 3 3 a phase of rapid warming within about 1000 years bsotope events 6 0 and 5 53 4 4 a sea level change within the eemian between isotope events 5 53 and 5 51

middle pleistocene glaciations of the russian north abstract geological data on the pre eemian glaciations of northern russia including the latest results by the russian norwegian pechora project are synthesized in order to present evidence for comparison with other early glaciations around the arctic the bulk of evidence indicates that arctic and subarctic regions of european russia of western and central siberia during the middle pleistocene were at least 4 times covered by large ice sheets which advanced mainly from the shelf ice domes partly from fennoscandia and the putorana plateau ice accumulations in the ural mountains were insignificant and did not form any noticeable ice dispersal centres unlike the classical glaciated areas ice sheets of northern russia acted mainly on a soft perennially frozen substrate which was heavily glacitectonised the middle pleistocene ice sheets were much larger than the weichselian ones the fennoscandian ice dispersal centre was most active in northern european russia during the penultimate glaciation ois 6 when shelf centred ice domes were relatively weaker larger continental ice sheets were formed in preceding ice ages when kara sea ice dispersal centre dominated the lowland ice sheets reached their maximum extent at different stages from cromerian don glaciation in european russia to ois 8 in west siberia therefore the maximum ice limit is time transgressive in northern russia

surface deformation and shallow dike intrusion processes at inyo craters long valley california the inyo craters are the two largest of four phreatic craters that lie within a 2 5 km long 500 to 700 m wide n s trend of faults and fissures at the south end of the inyo volcanic chain in eastern california the alignment of these features with dike fed silicic volcanic centers of the same age a few kilometers to the north suggests that they were produced during intrusion of a dike at about 650 550 yr b p e w extension south of south inyo crater is ten to several tens of meters suggesting that the dike is at least that thick to understand how the faults and fissures developed we mapped and studied the fault and fissure pattern used a theoretical boundary element model to determine the surface strain profile above a shallow dike in a purely elastic medium and conducted physical model experiments of fault and fissure growth results of the field studies and experiments indicate that deformation develops according to the following sequence 1 extension fractures and perhaps other inelastic deformation develop immediately above the dike top and on the limbs of a shallow syncline which forms above the dike 2 fissures form along two parallel trends at the surface on opposite sides of the dike plane leaving a relatively unfractured region in between 3 dip slip movement on subsurface fractures and linkage of these fractures with surface fissures produces inward facing normal fault scarps that bound a nested graben above the dike experimental graben widths are up to several times narrower than predicted from the locations of theoretical strain maxima above a dilating crack in a linearly elastic medium this fact is apparently due to the growth of a zone of inelastic deformation above the experimental dike top in the subsurface if the ratio between the depth to the dike top and the distance between the outermost surface fissures at inyo craters is within the range of ratios measured experimentally then the depth to the dike top is between 250 m and several times that a slant hole drilled in the summer of 1987 by the department of energy office of basic energy sciences intersected three breccia bodies of possibly intrusive origin directly below the center of south inyo crater between 550 m and 610 m below the crater rim no intact juvenile igneous rock was intersected suggesting that the hole passed above the magma filled dike top perhaps passing through the zone of inelastic deformation which is inferred to exist from our model results

the mount perkins block northwestern arizona an exposed cross section of an evolving preextensional to synextensional magmatic system the steeply tilted mount perkins block northwestern arizona exposes a cross section of a magmatic system that evolved through the onset of regional extension new 4oar 39ar ages of variably tilted 0 90 o volcanic strata bracket extension between 15 7 and 11 3 ma preextensional intrusive activity included emplacement of a composite miocene laccolith and stock trachydacite dome complex and east striking rhyolite dikes related volcanic activity produced an 18 16 ma stratovolcano cored by trachydacite domes and flanked by trachydacite trachyandesite flows and 16 ma rhyolite flows similar compositions indicate a genetic link between the stratovolcano and granodioritic phase of the laccolith magmatic activity synchronous with early regional extension 15 7 14 5 ma generated a thick felsic volcanic sequence a swarm of northerly striking subvertical rhyolite dikes and rhyolite domes field relations and compositions indicate that the dike swarm and felsic volcanic sequence are cogenetic modes of magma emplacement changed during the onset of extension from subhorizontal sheets east striking dikes and stocks to northerly striking subvertical dike swarms as the regional stress field shifted from nearly isotropic to decidedly anisotropic with an east west trending horizontal least principal stress preextensional trachydacitic and preextensional to synextensional rhyolitic magmas were part of an evolving system which involved the ponding of mantle derived basaltic magmas and ensuing crustal melting and assimilation at progressively shallower levels major extension halted this system by generating abundant pathways to the surface fractures which flushed out preexisting crustal melts and hybrid magmas remaining silicic melts were quenched by rapid upper crustal cooling induced by tectonic denudation these processes facilitated eruption of mafic magmas accordingly silicic magmatism at mount perkins ended abruptly during peak extension 14 5 ma and gave way to mafic magmatism which continued until extension ceased

basement structure and implications for hydrothermal circulation patterns in the western moat of long valley caldera california detailed surface mapping subsurface drill hole data and geophysical modeling are the basis of a structural and hydrothermal model for the western part of long valley caldera six fault zones are recognized in the western caldera with dominant orientations of north northwest and northeast sub parallel to regional fault trends in the surrounding sierran basement the internal structural geometry of the cores of 12 exogenous domes inside and outside the caldera suggests that the domes erupted at the intersections of these principal fault trends rather than along the axis of a single dike gravity modeling and subsurface data from deep geothermal wells indicate that the floor of the caldera is segmented into a number of discrete fault blocks with varying offsets one of the northeast trending fault zones designated discovery fault in this paper appears to be part of the original sierran embayment that existed before caldera collapse recent hydrothermal alteration occurs along discovery fault strands and composite vertical offset of intracaldera volcanic units across the entire fault zone may be as much as 400 m field relationships geophysical interpretations and interpretaions of drill hole data suggest that this fault is a fundamental flaw in the western caldera the preexisting tectonic framework of the basement rocks controlled the configuration of the western caldera floor and through it the location of postcollapse eruptive centers these deep basement structures may also provide the high fracture density which controls circulation in the present geothermal system of long valley

severnaya zemlya arctic russia a nucleation area for kara sea ice sheets during the middle to late quaternary quaternary glacial stratigraphy and relative sea level changes reveal at least four expansions of the kara sea ice sheet over the severnaya zemlya archipelago at 79 degrees n in the russian arctic as indicated from tills interbedded with marine sediments exposed in stratigraphic superposition and from raised beach sequences that occur at altitudes up to 140 m a s l chronologic control is provided by ams c 14 electron spin resonance green stimulated luminescence and aspartic acid geochronology major glaciations followed by deglaciation and marine inundation occurred during mis 10 9 mis 8 7 mis 6 5e and mis 5d 3 the mis 6 5e event associated with the high marine limit implies ice sheet thickness of 2000m only 200km from the deep arctic ocean consistent with published evidence of ice grounding at similar to 1000m water depth in the central arctic ocean till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively suggesting wet based ice cap advance followed by cold based regional ice sheet expansion local ice caps over highland sites along the perimeter of the shallow kara sea including the byrranga mountains appear to have repeatedly fostered initiation of a large kara sea ice sheet with exception of the last glacial maximum mis 2 when kara sea ice did not impact severnaya zemlya and barely graced northernmost taymyr peninsula

the last ice sheet of the kara sea terrestrial constraints on its age abstract the ice dispersal features on the siberian mainland unanimously indicate that the last ice domes were positioned on the kara sea shelf and adjacent coastal plains the age of the last glacial maximum evokes much controversy the problem may be solved by sorting out the available radiocarbon dates both statistically and using geological common sense over 200 finite radiocarbon dates have been analysed 77 of the entire population represent sediments overlying the topmost till including dating the most reliable organics such as mammoth remains the rest of the dates 23 have been obtained from the underlying sediments mostly on materials readily prone to redeposition and contamination such as driftwood and shells the last culmination of the shelf ice sheet must have occurred beyond the range of the conventional radiocarbon method and after the last warm water sea transgression correlative to the eemian the early weichselian age for the last kara sea ice sheet is also supported by the lack of proglacial lacustrine sediments with finite radiocarbon dates in periglacial west siberia