ice moraine and landslide dams in mountainous terrain we review recent work on ice moraine and landslide dams in mountainous terrain thus complementing several comprehensive summaries on glacier dams in intracontinental and arctic areas of low relief we discuss the roles of tectonic and climatic forcing on ice moraine and landslide dam formation and sudden drainage and focus on similarities and differences between their geomorphic impacts on confined valleys drained by steep bedrock and gravel bed rivers despite numerous reported failures of natural dams in mountain belts throughout the world their relevance to long term dynamics of mountain rivers remains poorly quantified all types of dams exert local base level controls thus trapping incoming sediment and inhibiting fluvial bedrock incision pervasive geomorphic and sedimentary evidence of outburst events is preserved even in areas of high erosion rates suggesting that sudden dam failures are characterized by processes of catastrophic valley floor aggradation active channel widening and downstream dispersion of sediment during which little bedrock erosion seems to be achieved we find that in the absence of direct evidence of former dams a number of similarities among the geomorphic and sedimentologic characteristics of catastrophic outburst flows may give rise to ambiguous inferences on the dam forming process this is especially the case for tectonically active mountain belts where there is ample and comparable potential for the formation and failure of ice moraine landslide and polygenetic dams concomitant with climatic oscillations or earthquake disturbance hence the palaeoclimatic implications of erroneously inferring the cause of dam formation may be significant we recommend that future research on natural dams in mountainous terrain addresses a climate and earthquake controlled systematics in the pattern of formation and failure b quantification of response of mountain rivers to catastrophic outburst events and their concomitant process sequences c elaboration of a comprehensive classification of natural dams in mountainous terrain with special attention to polygenetic dams d physical based modelling of dam formation failure and routing of water and sediment outbursts and e quantitative controls on the contribution of natural dams to sediment budgets in mountainous terrain

central arctic surface ocean environment during the past 80 000 years stable oxygen and carbon isotope and sedimentological paleontological investigations supported by accelerator mass spectrometry 14 c datings were carried out on cores from north of 85 degrees n in the eastern central arctic ocean significant changes in accumulation rates provenance of ice rafted debris ird and planktic productivity over the past 80 000 years are documented during peak glacials i e oxygen isotope stages 4 and 2 the arctic ocean was covered by sea ice with decreased seasonal variation limiting planktic productivity and bulk sedimentation rates in early stage 3 and during termination i major deglaciations of the circum arctic regions caused lowered salinities and poor oxygenation of central arctic surface waters a meltwater spike and an associated ird peak dated to similar to 14 12 14 c ka can be traced over the southern eurasian basin of the arctic ocean this event was associated with the early and rapid deglaciation of the marine based barents sea ice sheet a separate termination ib meltwater event is most conspicuous in the central arctic and is associated with characteristic dolomitic carbonate ird this lithology suggests an origin of glacial ice from northern canada and northern greenland where lower paleozoic platform carbonates crop extensively out

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

geophysical investigations of the geology and structure of the pangushan tieshanlong tungsten ore field south jiangxi china evidence for site selection of the 2000 m nanling scientific drilling project sp nlsd 2 abstract the pangushan tieshanlong tungsten ore field located in the center of southern jiangxi province eastern nanling region contains many granitic plutons both exposed and concealed and hosts numerous tungsten polymetallic ore deposits despite many previous geological studies the deep geology and structure of the field are poorly known because few geophysical measurements have been undertaken in this study we carried out a variety of geophysical measurements including gravity magnetic field detection magnetotelluric sounding mt and high resolution seismic reflection to better outline the nature of the ore field and to aid in site selection for the 2000 m nanling scientific drilling project sp nlsd 2 to be carried out by the chinese sinoprobe program four granitic intrusives the tangcun pangushan huangsha and bai e plutons crop out independently at the surface but were found to be parts of a large batholith at depth the tangcun composite pluton which at the surface consists chiefly of caledonian granite and minor early yanshanian intrusive material was found to be chiefly early yanshanian granite concealed beneath the lower part of the caledonian granite the bai e pluton initially decreases in size with depth and then expands as it merges with the major batholith the pangushan and huangsha plutons are domes on the inferred batholith four granitic magma channels and a considerable number of faults have been identified due to its favorable geological conditions the top of the pangushan pluton is predicted to be the best candidate for ore prospecting it is basically a granite cupola with many cross cutting and parallel faults in addition it is characterized by a high gravity anomaly a high magnetic anomaly and locally a low electrical resistivity anomaly

glacial lake vitim a 3000 km3 outburst flood from siberia to the arctic ocean abstract a prominent lake formed when glaciers descending from the kodar range blocked the river vitim in central transbaikalia siberia glacial lake vitim evidenced by palaeoshorelines and deltas covered 23 500 km2 and held a volume of 3000 km3 we infer that a large canyon in the area of the postulated ice dam served as a spillway during an outburst flood that drained through the rivers vitim and lena into the arctic ocean the inferred outburst flood of a magnitude comparable to the largest known floods on earth possibly explains a freshwater spike at 13 cal ka bp inferred from arctic ocean sediments

late quaternary paleoenvironmental records from the western lena delta arctic siberia abstract the three main lena delta terraces were formed during different stages of the late quaternary while only the first floodplain terrace is connected with active deltaic processes the second and third terraces which dominate the western part of the delta are erosional remnants of arctic paleolandscapes affected by periglacial processes the landscape dynamics of the second and the third terraces and their relationship to each other are of particular importance in any effort to elucidate the late quaternary paleoenvironment of western beringia multidisciplinary studies of permafrost deposits on the second terrace were carried out at several sites of the arga complex named after the largest delta island arga muora sise the frozen sediments predominantly consist of fluvial sands several tens of meters thick radiocarbon dated from 52 to 16 kyr bp these sands were deposited under changing fluvial conditions in a dynamic system of shifting river channels and have been additionally modified by synsedimentary and postsedimentary cryogenesis later thermokarst processes affected this late pleistocene fluvial landscape during the lateglacial and the holocene in addition eolian activity reworked the fluvial sands on exposed surfaces at least since the lateglacial resulting in dune formation in some areas contrary to the arga complex the third terrace is mainly composed of polygenetic alluvial and proluvial ice rich permafrost sequences ice complex deposits radiocarbon dated from 50 to 17 kyr bp which cover older fluvial sand units luminescence dated to about 100 50 kyr bp paleoecological records reflect tundra steppe conditions that varied locally depending on landscape dynamics during the marine isotope stage mis 4 and 3 periods and a persistent change to shrub and arctic tundra during lateglacial and holocene periods the study results indicate a continuous fluvial sedimentation environment for the laptev sea shelf in the region of the second lena delta terrace during the late pleistocene and confirm the presence of a dynamic channel system of the paleo lena river that flowed at the same time as the nearby subaerial ice complex deposits were being formed

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

late quaternary megafloods from glacial lake atna southcentral alaska u s a abstract geomorphic stratigraphic geotechnical and biogeographic evidence indicate that failure of a pleistocene ice dam between 15 5 and 26 ka generated a megaflood from glacial lake atna down the matanuska valley while it has long been recognized that lake atna occupied 9000 km2 of south central alaska s copper river basin little attention has focused on the lake s discharge locations and behaviors digital elevation model and geomorphic analyses suggest that progressive lowering of the lake level by decanting over spillways exposed during glacial retreat led to sequential discharges down the matanuska susitna tok and copper river valleys lake atna s size 50 ka duration and sequential connection to four major drainages likely made it a regionally important late pleistocene freshwater refugium we estimate a catastrophic matanuska megaflood would have released 500 1400 km3 at a maximum rate of 3 106 m3 s 1 volumes for the other outlets ranged from 200 to 2600 km3 and estimated maximum discharges ranged from 0 8 to 11 3 106 m3 s 1 making lake atna a serial generator of some of the largest known freshwater megafloods

constraining the timing of the most recent cataclysmic flood event from ice dammed lakes in the russian altai mountains siberia using cosmogenic in situ 10be ice dammed lakes were repeatedly formed in intermontane basins in the russian altai mountains throughout the pleistocene these cataclysmic outburst floods caused by ice dam failures were documented as earth9s largest flood waves by other geoscientists using in situ 10 be we successfully dated surfaces of flood associated boulders located in a former lake basin and downvalley from a former ice dam our precise surface exposure ages suggest that all boulders were associated with the most recent out of a number of cataclysmic floods that occurred at 15 8 1 8 ka the field location of the boulders implies that they were deposited by the largest late pleistocene flood that drained the chuya katun lake completely following initial dam failure a published reconstruction of the late glacial paleoenvironment in the vicinity of the former ice dam indicates that dam failure was likely a result of climatically induced downwasting of glaciers the failure of the ice dam provides more evidence for the timing of widespread warming during the late glacial in southern russia this flooding event in the headwaters of the ob river coincides with a freshwater peak as recorded in isotopic records of the kara sea and the arctic ocean

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

a multiproxy approach to reconstruct the environmental changes along the eurasian continental margin over the last 150 000 years abstract sediment cores located along the eurasian continental margin arctic ocean have been studied to reconstruct the environmental changes in terms of waxing and waning of the barents kara sea ice sheets atlantic water inflow and sea ice distribution over the last 150 kyr the stratigraphy of the cores is based on stable oxygen isotopes ams 14 c and paleomagnetic data we studied variations in marine and terrigenous input by a multiproxy approach involving direct comparison of sedimentological and organo geochemical data extensive episodes of northern barents sea ice sheet growth during marine isotope stages mis 6 and 2 have been supported by at least subsurface atlantic water inflow moisture bearing storms low summer insolation and minimal calving of ice ice advance during mis 4 was probably restricted to the shallow shelf between mis 4 and mis 2 large ice sheet fluctuations correspond to contemporary laurentide surging events and indicate short term climatic changes in the arctic ocean as has been recorded in lower latitudes in contrast in low precipitation areas in eastern eurasia glacial activity was rather limited only distinct ice rafted debris ird input during termination ii and early mis 3 reflects severe glaciations on the northern severnaya semlya margin during mis 6 and mis 4 we conclude that 1 oscillations of ice sheets are less frequent along the eastern eurasian margin than in areas with continuous moisture supply like the western eurasian margins and that 2 major fluctuations of the kara sea ice sheet during the last 150 kyr apparently followed the major interglacial glacial mis 5 4 and mis 7 6 transitions rather than the precession 23 kyr and the tilt 41 kyr cyclicity of the earth s orbit as observed for the scandinavian sis and the svalbard ice sheets respectively mangerud j jansen e landvik j y 1996 late cenozoic history of the scandinavian and barents sea ice sheets in solheim a riis f elverhoi a faleide j j jensen l n cloetingh s eds impact of glaciations on basin evolution data and models from the norwegian margins and adjacent basins global and planetary chance special issue 12 pp 11 26 surface and or subsurface atlantic water masses coupled with seasonally ice free conditions penetrated continuously to at least the franz victoria trough during the last 150 kyr however sustained periods of open water were largely restricted to substages 5 5 5 1 and the holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter mom signals of periodic open water conditions along the northern margin of severnaya semlya are of less importance higher production of foraminifera probably due to atlantic water inflow occurred between 38 and 12 14 c kyr and corresponds to periodic atlantic water advection penetrating into the arctic ocean however marine organic proxies indicate a continuous decrease of surface water productivity from the western to the eastern eurasian continental margin due to a more extensive sea ice cover over the last 150 kyr

paleohydrology of late pleistocene superflooding altay mountains siberia cataclysmic flooding is a geomorphological process of planetary significance landforms of flood origin resulted from late pleistocene ice dammed lake failures in the altay mountains of south central siberia peak paleoflows which exceeded 18 x 10 6 cubic meters per second are comparable to the largest known terrestrial discharges of freshwater and show a hydrological scaling relation to floods generated by catastrophic dam failures these seem to have been earth9s greatest floods based on a variety of reconstructed paleohydraulic parameters

instability of the atlantic overturning circulation during marine isotope stage 3 variations in the strength of the atlantic meridional overturning circulation amoc were involved in the occurrences of dansgaard oeschger d o events during marine isotope stage 3 mis3 the stability of the amoc to north atlantic freshwater perturbations is studied using a comprehensive climate model under mis3 boundary conditions an amoc stability diagram constructed from a series of equilibrium freshwater perturbation experiments reveals a highly nonlinear dependence of amoc strength on freshwater forcing the mis3 baseline state is remarkably unstable with respect to minor perturbations the global climate signal associated with a change in amoc strength is consistent with a transition from an interstadial to a stadial state including an annual mean surface air temperature drop of 8 k in central greenland we suggest that minor freshwater perturbations in the hydrologic cycle e g related to ice sheet processes had the potential to trigger d o type climate shifts associated with a threshold in the atmosphere ocean system

repeated megafloods from glacial lake vitim siberia to the arctic ocean over the past 60 000 years abstract cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation whether such events have also characterized previous deglaciations is not known arctic marine cores hint at megafloods prior to oxygen isotope stage ois 2 but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in eurasia and north america here we present the first well constrained terrestrial megaflood record to be linked with arctic archives based on cosmogenic nuclide exposure dating and optically stimulated luminescence dating applied to glacial lake sediments a 300 m deep bedrock spillway and giant eddy bars 200 m high we reconstruct a history of cataclysmic outburst floods from glacial lake vitim siberia to the arctic ocean over the past 60 000 years three megafloods have reflected the rhythm of eurasian glaciations leaving traces that stretch more than 3500 km to the lena delta the first flood was coincident with deglaciation from ois 4 and the largest meltwater spike in arctic marine cores within the past 100 000 years isotope event 3 31 at 55 5 ka the second flood marked the lead up to the local last glacial maximum and the third flood occurred during the last deglaciation this final 3000 km3 megaflood stands as one of the largest freshwater floods ever documented with peak discharge of 4 0 6 5 million m3s 1 mean flow depths of 120 150 m and average flow velocities up to 21 m s 1

geochemical evidence from coesite bearing jadeite quartzites for large scale flow of metamorphic fluids in a continental subduction channel abstract metamorphic fluids produced by dehydration of subducting crust transport mass and energy at the slab mantle interface in subduction channels it is commonly assumed that fluid flow is significant in oceanic subduction channels but insignificant in continental subduction channels this assumption is challenged by a combined study of whole rock geochemistry mg and o isotopes zircon u pb ages and trace elements in coesite bearing jadeite quartzites from the dabie orogen china although the target samples were collected from different outcrops in an area of 50 km2 zircon u pb dating yields similar discordia lines with not only consistent upper intercept ages of 1 9 2 0 ga but also consistent lower intercept ages of 224 235 ma this indicates the same paleoproterozoic protolith and the same triassic metamorphism for these jadeite quartzites the o isotope analysis of mineral separates and whole rock yields variable 18o values from 6 3 to 9 4 indicating involvement of supracrustal components except for one outlier at 0 43 all the other rocks give variable 26mg values from 0 16 to 0 61 much higher than normal mantle values the whole rock mg isotopes show significant positive correlations not only with mgo contents but also with rb la rb gd and rb nb ratios but a negative correlation with na2o contents these observations indicate that the middle paleoproterozoic protolith of jadeite quartzites was weathered to produce a kind of sedimentary rocks in a passive continental margin and then underwent significant metasomatism by metamorphic fluids with high 26mg values during the continental subduction in the triassic the metamorphic fluids were produced by the breakdown of biotite in the metasedimentary rocks during their subduction to subarc depths for ultrahigh pressure metamorphism they would have acquired their geochemical compositions not only from the biotite breakdown but also through leaching reaction with the ttg provenance in view of the spatial occurrences of the target samples the metamorphic fluids would have flowed inside the continental subduction channel on a large scale this is the first report of the large scale fluid flow in the continental subduction zone and therefore demonstrates that fluid flow can be significant in continental subduction channels

paleogeography and quaternary terrace sediments and complexes intermontane basins of prebaikalia southeastern siberia russia abstract several large lake stages interspersed by cycles with low water levels and exposed areas with erosion are recorded in prebaikalia depressions from the upper eopleistocene neotectonic activities were responsible for water level changes and ingression of lake waters into river valleys at the end of the eopleistocene the lake regime was transformed and finally replaced by a river two blocks of different elevation associated with sediment aggregates of the upper vii iv and low iii i terraces can be distinguished in the terrace complex the upper terraces were formed in a limnic environment and the lower terraces formed in a prevailing river environment with subordinate lacustrine conditions

late quaternary sedimentation history of the lena delta abstract core and outcrop analysis from lena mouth deposits have been used to reconstruct the late quaternary sedimentation history of the lena delta sediment properties heavy mineral composition grain size characteristics organic carbon content and age determinations 14c ams and ir osl are applied to discriminate the main sedimentary units of the three major geomorphic terraces which form the delta the development of the terraces is controlled by complex interactions among the following four factors 1 channel migration according to the distribution of 14c and ir osl age determinations of lena mouth sediments the major river runoff direction shifted from the west during marine isotope stages 5 3 third terrace deposits towards the northwest during marine isotope stage 2 and transition to stage 1 second terrace to the northeast and east during the holocene first terrace deposits 2 eustasy sea level rise from last glacial lowstand to the modern sea level position reached at 6 5 ka bp resulted in back filling and flooding of the palaeovalleys 3 neotectonics the extension of the arctic mid ocean ridge into the laptev sea shelf acted as a halfgraben showing dilatation movements with different subsidence rates from the continent side differential neotectonics with uplift and transpression in the siberian coast ridges are active both likely have influenced river behavior by providing sites for preservation with uplift in particular allowing accumulation of deposits in the second terrace in the western sector the actual delta setting comprises only the eastern sector of the lena delta 4 peat formation polygenetic formation of ice rich peaty sand ice complex was most extensive 7 11 m in thickness in the southern part of the delta area between 43 and 14 ka bp third terrace deposits in recent times alluvial peat 5 6 m in thickness is accumulated on top of the deltaic sequences in the eastern sector first terrace

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

long history of pre wisconsin ice age cataclysmic floods evidence from southeastern washington state abstract cataclysmic ice age floods in the pacific northwest began as early as 1 5 2 5 ma on the basis of an evaluation of surface exposures and recent borehole studies within southeastern washington field evidence suggests at least two episodes of pre wisconsin i e 130 ka glacial outburst flooding a middle pleistocene flood is identified by normal magnetic polarity calcrete capped deposits that yield maximum th u age dates from 200 to 400 ka the deposits with reversed polarity are correlated to early pleistocene 780 ka floods while exposures of pre wisconsin deposits are limited because of erosion and or burial the record of earlier pleistocene flooding is preserved within giant flood bars these bars show incremental growth representing a composite from cataclysmic floods deposited intermittently through the pleistocene in one giant flood bar up to 100 m thick deposits interpreted as matuyama age indicate that the bar had grown to half its present height by 780 ka furthermore matuy