tertiary tectonics of the border ranges fault system chugach mountains alaska deformation and uplift in a forearc setting the border ranges fault system brfs locally separates supracrustal upper cretaceous tertiary rocks of the cook inlet matanuska valley forearc basin on the peninsular terrane from metamorphosed cretaceous subduction complex rocks of the chugach terrane to the south this 5 to 10 km wide zone of concentrated deformation along the inboard edge of southern alaska s accretionary prism has suffered a protracted history beginning with its inception as a megathrust by early cretaceous time and continuing into early tertiary time when it was transected by a system of steeply arcward dipping normal and dextral slip faults based on detailed geologic mapping structural analysis metamorphic mineral assemblage data and k ar and fission track geochronology the tertiary history of displacements along a central part of this forearc fault system has been divided into several phases of deformation these include a paleocene phase of regional uplift of the forearc basin together with block faulting along the brfs to rapidly uplift and subaerially expose low grade metamorphic rocks of the subduction complex upper cretaceous valdez group within 15 ma of their inferred underplating at deep structural levels of the accretionary prism continued normal separation faulting along the brfs in late paleocene early eocene time to further uplift the subduction complex was recorded by deposition of a syntectonic alluvial fan system chickaloon formation across the brfs and along the southern margin of the forearc basin a third mid eocene increment of normal separation faulting along the brfs juxtaposed greenschist facies fabrics of early eocene age in the subduction complex against the chickaloon formation this latter uplift event predated intrusion of early late eocene 43 48 ma zircon fission track minimum ages felsic dikes into the present terrane bounding fault and was accompanied by no more than a few tens of kilometers of dextral slip faulting along the brfs a conclusion that does not accord with recent suggestions for thousands of kilometers of displacement along that fault system in early middle tertiary time based on paleomagnetic data field observations in the study area indicate that the great oroclinal bend of southern alaska is postearly eocene and possibly prelate oligocene in age a final period of deformation in middle to late tertiary time was marked by periods of minor north south contraction of the forearc basin and by local reverse slip reactivation of earlier faults fission track age data on apatite indicate rapid cooling and probably uplift of both subduction complex and adjacent parts of the forearc basin in miocene time 17 24 ma episodic uplift of the subduction complex either locally by normal separation faulting along its backstop or by a more regional uplift also affecting the adjacent forearc basin overlapped in time or closely followed discrete pulses of large scale sediment underplating along the gulf of alaska subduction margin this coincidence suggests that major pulses of sediment underplating along southern alaska s convergent margin may have led to isostatic uplift of its critical taper accretionary prism an uplift that was in part accommodated by normal separation faulting along its mechanical backstop

holocene palaeoclimates from peat stratigraphy macrofossil proxy climate records from three oceanic raised bogs in england and ireland quantified analyses of plant macrofossil remains have been made from three profiles of peat from raised bogs spanning a distance of 425 km from western ireland to northern england the reconstructed vegetation of each profile is related to changing bog surface wetness bsw and since the bogs are ombrotrophic these bsw changes are interpreted in terms of changing climate using age depth models based on a total of 49 radiocarbon dates a number of wetter and drier phases are identified and phase shifts to wetter and or cooler climates are defined prominent coincident changes to wetter conditions are dated in at least two of the profiles to ca 4400 4000 1750 1400 and 1000 cal bp and in all three profiles at 3200 2750 2350 2250 and around 700 cal bp these phases are related to proxy climate changes in other terrestrial data sets from northwest europe and a broad degree of synchroneity is demonstrated

the formation and evolution of the barrier islands of inhaca and bazaruto mozambique abstract the barrier islands of inhaca and bazaruto are related to the extensive coastal dune system of the mozambican coastal plain south east africa optically stimulated luminescence osl dating of key stratigraphic units indicates that accretion of sediment within these systems is episodic both islands appear to have been initiated as spits extending from structural offsets in the coastline superposition of significant quantities of sediment upon these spits during subsequent sea level highstands formed the core of the islands which were anchored and protected by beachrock and aeolianite formation at least two distinct dune building phases occurred during marine oxygen isotope stage mis 5 tentatively attributed to marine transgressions during sub stages 5e and 5c although some localized reactivation of dune surfaces occurred prior to the holocene large quantities of sediment were not deposited on either island during the low sea levels associated with mis 2 significant dune building and sediment reworking occurred immediately prior to and during the holocene though it is not clear whether these processes were continuous or episodic significant erosion of the eastern shoreline of bazaruto suggests that it is far less stable than inhaca and may suffer further large scale erosion a model is presented for the formation of barrier islands along the mozambican coastal plain

miocene recent sediment flux in the south central alaskan fore arc basin governed by flat slab subduction the cook inlet in south central alaska contains the early oligocene to recent stratigraphic record of a fore arc basin adjacent to a shallowly subducting oceanic plateau our new measured stratigraphic sections and detrital zircon u pb geochronology and hf isotopes from neogene strata and modern rivers illustrate the effects of flat slab subduction on the depositional environments provenance and subsidence in fore arc sedimentary systems during the middle miocene fluvial systems emerged from the eastern western and northern margins of the basin the axis of maximum subsidence was near the center of the basin suggesting equal contributions from subsidence drivers on both margins by the late miocene the axis of maximum subsidence had shifted westward and fluvial systems originating on the eastern margin of the basin above the flat slab traversed the entire width of the basin these mud dominated systems reflect increased sediment flux from recycling of accretionary prism strata fluvial systems with headwaters above the flat slab region continued to cross the basin during pliocene time but a change to sandstone dominated strata with abundant volcanogenic grains signals a reactivation of the volcanic arc the axis of maximum basin subsidence during late miocene to pliocene time is parallel to the strike of the subducting slab our data suggest that the character and strike orientation of the down going slab may provide a fundamental control on the nature of depositional systems location of dominant provenance regions and areas of maximum subsidence in fore arc basins

phases of soil erosion derived colluviation in the loess hills of south germany in south germany soil erosion is as old as farming and dates back to early neolithic times its sedimentary products form thick colluvial and alluvial sediment bodies in all drainage basins numerous local studies exist but the extrapolation of findings from local case studies to a regional scale has been problematic here a graphical approach is used for frequency analysis of existing data a frequency distribution for optical dates on colluvial sediments from the beginning of agriculture until 1200 ad was constructed by 1 representing the optical ages by gaussian distributions and 2 summing all the single curves the resulting graph clearly shows phases of increased colluviation during periods of stronger human impact a first significant increase occurred during the bronze age during the iron age roman period and at around 800 ad distinct maxima appear in the distribution and highest frequencies are present towards the end of the analysed period at around 1100 ad conclusions that can be drawn from such an approach are limited by sampling bias and other factors but for the analysed period and on a regional and long term scale colluviation seems to have been mainly triggered by intensity of land use climatic fluctuations are of only secondary importance rainfall events that were sufficiently erosive to produce colluvial sediments occurred throughout the agricultural periods the limiting factor for colluvium production was sensitivity of the landscape to erosion and this is a result of land use d 2002 elsevier science b v all rights reserved

long term fore arc basin evolution in response to changing subduction styles in southern alaska detrital zircon u pb and fission track double dating and hf isotopes from the mesozoic and cenozoic strata in the southern alaska forearc basin system reveal the effects of two different modes of flat slab subduction on the evolution of the overriding plate the southern margin of alaska has experienced subduction of a spreading ridge ca 62 50 ma and an oceanic plateau ca 40 0 ma when a subducting spreading ridge drives slab flattening our data suggest that after the ridge has moved along strike retro arc sediment sources to the forearc become more predominant over more proximal arc sources spreading ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent thin sedimentary strata in the forearc basin when a subducting oceanic plateau drives slab flattening our data suggest that basin catchments get smaller and local sediment sources become more predominant crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that combined create topography and increase rock exhumation rates consequently the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation the cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages this study demonstrates the merit of double dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large scale tectonic processes in magmatic regions

holocene river development and environmental change in upper wharfedale yorkshire dales england this paper provides the first radiometrically dated evidence of holocene alluvial landform development in upper wharfedale yorkshire dales four river terraces are identified terraces 1 and 2 are closely linked to late devensian and early holocene environmental change with gravel reworked from local glacial and periglacial sources prior to cementation by carbonate rich waters u series dating of cement provides age estimates for cementation of between ca 5 1 7 4 kyr bp for terrace 1 and ca 3 6 8 0 kyr bp for terrace 2 u series dating of tufas overlying terraces 1 and 2 produced ages of ca 4 2 4 5 kyr bp and ca 2 1 2 2 kyr bp respectively and provide upper age limits for terrace formation terrace 3 marks a change in sediment calibre supply and sedimentation style and 14c dating suggests that the principal source of fine grained material may be agricultural expansion in the yorkshire dales from ca ad 600 1350 cal yr bp radiocarbon dates indicate that terrace 4 was deposited from the eleventh century with initiation of the contemporary floodplain between the fifteenth and seventeenth centuries ad both these lowest units contain sediments contaminated with heavy metals as a result of mining activities within the catchment the evidence presented in this study is comparable to that of research undertaken in upland environments elsewhere in northern and western britain thereby adding to the corpus of information currently available for evaluating the fluvial geomorphological response to climate and vegetation change during the holocene copyright 2000 john wiley sons ltd

optical dating of a scroll bar sequence on the klip river south africa to derive the lateral migration rate of a meander bend problems are often encountered in accurately establishing the rates of processes associated with river channel change in this study optical dating was used to obtain the lateral migration rate of an abandoned meander bend on the klip river eastern free state south africa five samples were collected by augering along a transect across an approximately 200 m wide scroll bar sequence on the inner meander bend and an additional sample was collected from the channel fill of the related oxbow lake optically stimulated luminescence osl ages were derived for each sample using the single aliquot regenerative dose protocol on small aliquots of quartz incomplete bleaching was evident in some of the samples and thus the appropriate statistical analysis was performed using the finite mixture model for the scroll bar samples and the minimum age model for the channel fill sample the ages calculated were in the correct chronological order for the depositional sequence which was formed over the last 1000

surface lowering of limestone pavement as determined by cosmogenic 36cl analysis determination of the rate and total amount of limestone pavement surface lowering is a critical issue in developing models of regional landscape change in limestone terrain erratic capped pedestals have frequently been used for this purpose but problems concerning definition and measurement of pedestal height and the absence of a secure timeframe for erratic emplacement have resulted in conflicting interpretations we have used cosmogenic 36cl to establish the emplacement age of erratic boulders and the total amount of pavement surface lowering at sites in northwest england since erratic emplacement at 17 9 ka the limestone pavement has been lowered by 22 45 cm average 33 10 cm assuming lowering was continuous although indicating some spatial heterogeneity the results contrast with earlier reported values based on the measurement of pedestal heights and inferred age for deglaciation we consider that changes in climate and the character and duration of regolith covers to have been important influences in promoting surface lowering it is argued that nivation chemical and mechanical snow related processes associated with several cool cold periods is likely to have played an important role in surface lowering complicating factors associated with surface lowering thickness and longevity of snow and regolith covers are identified but as yet cannot be quantified copyright 2012 john wiley sons ltd

age and origin of clayey silt brickearth in west london england the loamy brickearth deposits overlying coarse cold climate kempton park lynch hill and taplow gravels of the r thames in west london are dated by thermoluminescence and mineralogical comparisons with loesses of three known ages although much of the brickearth resembles loess it often contains more sand or clay than typical loess and the mineralogical studies suggest that even the coarse silt 16 63 m fraction is rarely similar in composition to any known english loess the thermoluminescence measurements suggest that most of the brickearth on the taplow and lynch hill gravels was deposited in the late devensian whereas that on the park gravel is mainly flandrian it is suggested that the latter is mainly floodloam whereas the earlier brickearth is a mixed aeolian sediment derived from various local sources in and close to the thames valley

late quaternary coastal evolution and aeolian sedimentation in the tectonically active southern atacama desert chile abstract analyses of aeolianites and associated dune surficial carbonate and marine terrace sediments from north central chile 27 54 s yield a record of environmental change for the coastal southern atacama desert spanning at least the last glacial interglacial cycle optically stimulated luminescence dating indicates phases of aeolian dune construction at around 130 111 98 77 69 and 41 28 ka thin section and stable carbon and oxygen isotope analyses suggest a predominantly marine sediment source for the three oldest dune phases aeolianites appear to have accumulated mainly from tectonically uplifted interglacial marine sediments that were deflated during windier and or stormier intervals bedding orientations indicate that sand transporting winds varied in direction from s ese during mis 5e and wnw ese during mis 5c 5a winds from the southeast quadrant are unusual today in this region of the atacama suggesting either major shifts in atmospheric circulation or topographic airflow modification thin section evidence indicates that the aeolianites were cemented by two phases of vadose carbonate tentatively linked to wetter periods around 70 and 45 ka tectonic uplift in the area has proceeded at an average rate of 305 542 mm kyr 1 the study illustrates the complexity of understanding onshore offshore sediment fluxes in the context of late quaternary sea level fluctuations for an area undergoing rapid tectonic uplift

luminescence dating of loess palaeosol sequences and coversands methodological aspects and palaeoclimatic implications abstract of the terrestrial archives loess palaeosol sequences provide a most complete record of climatic change this may be compared with the marine oxygen isotope stratigraphy and may help in the reconstruction of past atmospheric circulation patterns numerical chronometry of loess palaeosol sequences has generally been based on correlation of variations in climatic proxies such as magnetic susceptibility and particle sizes with marine isotopic data such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time this review presents a brief survey of the present status methodology outstanding problems and interpretational aspects of luminescence techniques and discusses the import of luminescence ages on global land sea correlations statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence recent luminescence dating studies on closely spaced samples also lead to a similar inference luminescence ages imply high variability in loess sedimentation rates this conflicts with the assumption made in some current attempts to correlate loess records with marine records of almost constant particle fluxes a review of source proximal coversand deposits of northwest europe is also presented evidence of the onset of coversand deposition at 15 ka with a peak in accretion during the younger dryas and subsequent minor reactivation episodes is discussed

quartz and polymineral luminescence dating of japanese loess over the last 0 6 ma comparison with an independent chronology there are only a few luminescence dating studies of loess sediments in japan but interleaved with these deposits are many well described tephras of known age based on 14c and fission track analysis these independent age controls provide an opportunity to test the reliability of loess luminescence ages this study provides such a comparison at two sites in central honshu the largest island in the japanese archipelago samples were collected from sequences of interleaved volcanic tephra and loess deposited on a middle pleistocene river terrace in the niigata prefecture and on an early to middle pleistocene dissected fluvial surface at in the tochigi prefecture honshu equivalent doses de were estimated from fine grains 4 11 m using both polymineral ir osl and post ir blue osl and quartz blue osl the blue stimulated luminescence signals could be represented by up to three exponentially decaying components only the most light sensitive of these components was used in the final de estimation almost all the estimates of de from polymineral ir osl are smaller than those from polymineral post ir blue osl and quartz blue osl whereas the latter two are in good agreement the blue light stimulated luminescence ages using the most light sensitive component are shown to be in good agreement with the independent control up to 500 ka although the ir osl signals underestimate the known age a simple laboratory fading test is found empirically to correct for this underestimation we conclude that the most rapidly blue stimulated luminescence signals from quartz extracted from our loess samples give reliable ages and that future loess dating studies should concentrate on these signals

optical dating of tufa via in situ aeolian sand grains a case example from the southern high plains usa abstract precipitated carbonates commonly termed tufas or travertines maybe of considerable utility for palaeoenvironmental reconstruction their potential however for such reconstruction is commonly limited by difficulties associated with their absolute age control attempts to date such deposits via uranium series techniques have been complicated by their chemically open behaviour here we describe an alternative approach to date tufa deposits associated with ephemeral saline lake basins from the southern high plains usa we have optically dated sand grains of a mixed aeolian fluvial spring fed origin as the integrating dosimeter we assume that the grains are fully resetting prior to their incorporation into the tufa deposits and employ a time dependent disequilibrium dosimetric model to account for the build up of uranium series daughter products the approach was applied to a set of four samples with known stratigraphic association we obtained stratigraphically sensible optical ages ranging from 78 8 to 56 4 ka these data are consistent with existing palaeoenvironmental models of regional recharge

a 7500 year peat based palaeoclimatic reconstruction and evidence for an 1100 year cyclicity in bog surface wetness from temple hill moss pentland hills southeast scotland analyses of plant macrofossils peat humification and testate amoebae were used to reconstruct a proxy climate record spanning the last 7500 years from an ombrotrophic bog temple hill moss in southeast scotland the plant macrofossil data were subjected to detrended correspondence analysis dca which modelled effectively the significant wet shifts within the record a mean water table depth transfer function was applied to the testate amoebae data to provide quantifiable changes the three proxy records show coherent phase changes which are interpreted as variability in past effective precipitation two tephra horizons glen garry and lairg a were used in conjunction with radiocarbon dates to construct an age depth model producing a robust geochronology from which a time series was calculated the palaeoclimatic reconstruction identified major wet shifts throughout the holocene with specific events occurring around cal 6650 5850 5300 4500 3850 3400 2800 2450 1450 1350 and 250 150 bp spectral analysis of the plant macrofossil dca and colorimetric humification data produced a millennial scale periodicity of 1100 years the same periodicity has also been found in a palaeoclimatic reconstruction from a site in cumbria walton moss and may be linked with millennial scale periodicities found in oceanic palaeoclimatic records

anomalous clastic wedge development during the sevier laramide transition north american cordilleran foreland basin usa new high resolution regional correlation and isopach maps provide evidence that 1 laramide style deformation began as early as ca 77 ma in central utah and 2 rapid 208 km m y 1 and extensive 400 km progradation of a clastic wedge was facilitated by reduced subsidence during the transition from sevier to laramide style deformation this study defi nes three campanian alluvialto marine clastic wedges that traversed 200 400 km eastward across the utah colorado segment of the cordilleran foreland basin wedges a and c are thicker successions with rising trajectory shoreline stacking patterns blackhawk formation and lower castlegate sandstone bluecastle tongue and rollins sandstone that refl ect relatively slow overall progradation 50 81 km m y 1 of narrow 10 20 km wide wave dominated shorelines in contrast wedge b consists of lower volume successions with a fl at to falling shoreline stacking pattern middle castlegate sandstone sego sandstone neslen formation corcoran and cozzette members of the iles formation that suggests rapid progradation 208 km m y 1 of embayed 60 80 km wide mixed energy wave and tide infl uenced shore lines wedges a and c prograded 200 250 km in more than 3 m y whereas wedge b prograded 340 400 km in 2 m y 170 km m y 1 the anomalously extensive wedge b is unique in the utah colorado segment because of its long extent rapid progradation rate dominance of tidally infl uenced facies long transit transgressions regressions and low accommodation nested sequence architecture stratigraphic relationships indicate development of wedge b coeval with both sevier and laramide style deformation in utah assuming a constant sediment supply the extensive 300 400 km sheet like amalgamated wedge wedge b may have been caused by 1 reduced subsidence driven by a fl exural interference pattern whereby two short wavelength 200 km fl exural profi les are superimposed during the uplift of both basement cored and thin skinned thrust belt 2 an increase in or eastward migration of dynamic subsidence during tectonic transitions associated with slab fl attening or rollback i e long wavelength fl exure or 3 reduced subsidence due to short wavelength fl exural interference augmented by the reduction or migration of long wavelength fl

a high resolution late glacial isotopic record from hawes water northwest england understanding of the impact of past climate change on the terrestrial environment requires the development of quantitative palaeotemperature indicators that can be readily measured at closely spaced stratigraphic intervals a high resolution oxygen isotopic record from hawes water lancashire uk reveals a degree of climatic instability that is greater than that recognised in previous isotopic studies of sites from the atlantic margin of northwest europe four oscillations in the late glacial interstadial before the onset of the younger dryas stadial are marked by sharp negative excursions in the 18o record of the carbonate sediments and accompanied by marked changes in chironomid populations and the pollen record the oscillations are interpreted as cold events they correlate with events recognised in marine and lacustrine temperature proxy records as well as the isotopic record from the greenland ice cores results suggest that there has been a significant change in lake water composition since the late glacial but it is argued that the hawes water isotopic record constrained by the results of a study of carbonate precipitation in the modern lake provides a quantitative record of late glacial temperature change the 7 c maximum temperature difference inferred from the isotopic data from the interstadial optimum to the younger dryas stadial and the magnitude of individual oscillations compare well with estimates from terrestrial coleopterid and marine diatom sea surface temperature records all are significantly greater than the independently calibrated 4 2 c change documented from a chironomid record from south scotland such differences need to be resolved if the impacts of climatic events are to be fully understood

equatorial kelvin waves generated in the western tropical pacific ocean trigger mass and heat transport within the middle america trench off costa rica sequences of correlated seafloor temperature current velocity and acoustic backscatter events recorded at ocean drilling program odp sites at 4300 m depth in the middle america trench have been inferred to result from tidally induced turbidity currents generated in the vicinity of the 3300 m deep sill at the southern end of the trench new data from the borehole observatories extend the temperature records to 11 years november 2002 to december 2013 and confirm the highly episodic nature of the events we present satellite altimetry data and ocean circulation model results to show that event timing is correlated with intraseasonal kelvin wave motions in the equatorial pacific the observed temperature events had a mean 1 standard deviation occurrence interval of 61 24 days which spans the periods of the first two baroclinic modes lag times between peak bottom water temperatures at the odp sites and the passage of eastward propagating kelvin wave crests at locations in the eastern equatorial pacific are consistent with the time for mode 1 waves to propagate to the southern end of the trench at a mean phase speed of 2 0 m s 1 findings indicate that kelvin wave currents augment tidal motions in the vicinity of the sill triggering turbidity currents that travel northwestward along the trench axis at mean speeds of 0 1 m s 1 we conclude that mode 1 or possibly mixed mode 1 and mode 2 baroclinic kelvin waves generated by large scale atmospheric processes in the western tropical pacific lead to heat and mass transport deep within middle america trench in the eastern tropical pacific

mire development pathways and palaeoclimatic records from a full holocene peat archive at walton moss cumbria england plant macrofossil data have been used to identify the successive mire communities occupying both central and marginal locations in the walton moss peatland complex during the last 10 500 years the reconstructed pathways of mire development indicate that early holocene fen and fen carr communities were succeeded by species indicative of deep mire water tables and oligotrophic conditions the character of the fen bog transition fbt is compared with similar records of peatland development from britain and scandinavia and with independent climate data for the early holocene the pseudohochmoor of central europe is suggested as an approximate modern analogue for the dry pioneer oligotrophic mire type and alternative explanations for its presence are explored the first major increase in ombrotrophic sphagna occurred at c 7800 cal bp overlying sphagnum peats provide a continuous record of climate change inferred from fluctuations in raised mire surface wetness the proxy palaeoclimate record reconstr

revised chronostratigraphy of the kenai group from 40ar 39ar dating of low potassium bearing minerals cook inlet basin alaska thirty seven tephra beds primarily from coal partings in the sterling and beluga formations were successfully dated by the 40ar 39ar method providing a new and revised understanding of the chronostratigraphy of late tertiary strata within cook inlet basin meticulous sample preparation multiple analyses and statistical evaluation of the data were required for these low k plagioclase and hornblende bearing tephras dating of subsurface core material provides the first subsurface to outcrop tie in cook inlet between well 212 24 in the beluga river unit and deposits in the clam gulch diamond creek and fox creek areas the new 40ar 39ar chronostratigraphic framework place the age of upper part of the kenai group strata between 4 6 and 9 4 ma and support the 8 ma interpretation of the boundary between the homerian and clamgulchian paleobotanical stages the 49 ma age from core data in pioneer unit suggests the tyonek formation is older than previously thought or that these units belong to an older form

a review of tectonics and sedimentation in a forearc setting hellenic thrace basin north aegean sea and northern greece abstract exposure of the forearc region of the north aegean sea greece offers insight into evolving convergent margins the sedimentary fill of the thrace basin during the late eocene to oligocene time provides a record of subduction driven processes such as growth of magmatic arcs and construction of accretionary complexes this large sediment repository received sediment from two sources the southern outboard basin margin reflects the active influence of the exhumed accretionary prism e g pindic cordillera or biga peninsula while the northern inboard margin records the effect of the magmatic arc in the rhodope region the forearc basin sedimentary fills shoal upward into shallow marine strata but are dominated mainly by deep marine facies the depositional trend and stacking pattern are dominated by progradational patterns this trend which is observed in both basin margins is related to tectonic deformation rather than sea level fluctuations additional evidence for this tectonic uplift comes from the backstripping analysis the accretionary complex provided material into the forearc basin this material was transported northeast and formed a sand rich turbidity system that evolved upslope into shallow marine deposits stratigraphic data indicate that this turbidity system exhibits a successive landward inboard migration of the depocenter provenance data utilizing sandstone petrography conglomerate clast composition and bulk rock geochemistry suggest that this system reflects an increased influx of mafic material into the basin volcanic arc derived material was transported south and east and accumulated in deep marine settings both stratigraphic and provenance data indicate a seaward outboard migration of the basin depocenter and a significant increase in felsic detritus into the forearc

equivalent dose determinations for polymineralic fine grains using the sar protocol application to a holocene sequence of the chinese loess plateau abstract a single aliquot regenerative dose sar protocol involving stimulation of the same disc with an infra red laser diode followed by blue leds was applied to polymineralic fine grains infra red stimulated luminescence irsl and post ir optically stimulated luminescence osl ages are presented for a series of 19 fine grain 4 11 m samples taken from a loess section duowa in the western chinese loess plateau there are significant differences between the equivalent doses and thus the ages for the irsl and post ir osl measurements three potential explanations are investigated incomplete bleaching prior to deposition thermal transfer of charge and initial sensitivity change the question regarding which sequence of ages ir or post ir osl is correct if either is not resolved although the 19 post ir osl ages yield more consistent results it is proposed that the double sar protocol employed may not be correctly monitoring the sensitivity changes relating to either or both natural signals

climatic and sea level controls on late quaternary eolian activity on the agulhas plain south africa abstract located at the interface between the temperate westerly and sub tropical climate systems south africa s winter rainfall zone wrz is a key location in understanding late quaternary atmospheric circulation dynamics inactive eolian deposits in the wrz comprising pan fringing lunette and coastal dunes were investigated to establish their depositional ages and utility as paleoenvironmental indicators the resulting optical luminescence chronology reveals episodic lunette accretion at 60 000 45 000 yr 12 000 13 000 yr 2800 2600 yr 1200 yr and episodes of lunette and coastal dune accretion on the agulhas plain are temporally distinct reflecting differing fundamental controls on their activity comparisons to previously published data also reveal that the lunettes differ in age from more ancient coastal eolianites lunette deposition is asynchronous between locations reflecting the topographic and hydrological setting of the individual pans in near coastal settings with limited surface recharge lunette accretion appears to be at least partially controlled by sea level induced changes in groundwater levels those pans with more significant surface recharge particularly from fluvial systems may produce less ambiguous paleoenvironmental records with pan status more strongly reflecting regional hydrological conditions lunette orientation is indicative of strong westerly winds during both the pleistocene and holocene lunette accretion would have been promoted by reduced on shore moisture transport during the summer months enhancing rainfall seasonality such conditions would have been promoted by increased continentality as the agulhas bank was exposed during low sea level stands

new osl dating of uk loess indications of two phases of late glacial dust accretion in se england and climate implications windblown dust deposits or loess locally known in the uk as brickearth blanket many parts of southern england outside the limits of the british and irish ice sheet the best studied loess exposures occur in kent southeast england where the deposits are believed to be late glacial in age new sedimentological evidence is presented for phases of accretion with two distinct units a calcareous brickearth exhibiting periglacial cryoturbation and a non calcareous massive brickearth optically stimulated luminescence osl dating has been applied to chemically isolated modal quartz silts to derive a chronology for sediment accretion and to better understand the palaeoclimatic significance of these deposits

characteristics of 4 day oscillations trapped by the juan de fuca ridge current meter observations from different studies along the crest of the juan de fuca ridge have been combined to show new features of the relatively large broad spectral peak centered near a period of about 4 days the coherence range of the 4 day oscillations has been extended to the extreme ends of the ridge and the trapped waves appear to propagate northward along the entire length of the ridge at about 1 m s spectral amplitudes are about double on the south end compared to the north end and a recent model for bottom trapped subinertial waves over topography shows this may be due to variations in ridge width allen and thomson 1993 new observations show coherence between temperatures and currents near the south cleft vent field and suggest 4 day oscillations can play a major role in the local advection of hydrothermal plumes these observations combined with earlier results demonstrate that 4 day oscillations are a significant ridge trapped feature and they suggest that other ridges may be important in transmitting energy over much longer distances

age limit and age underestimation using different osl signals from lacustrine quartz and polymineral fine grains as part of a systematic palaeohydrological reconstruction of lake level fluctuations during the last glacial maximum a transect of cores from ancient lake xinias in centra greece has already been studied with respect to pollen sediment and mineral magnetic analyses the chronology was based on c 14 ams dating of terrestrial plant macrofossil remains from peat and clayey peat palaeogeog palaeoclimatol palaeoecol 158 2000 65 this site thus provides an opportunity for the comparison of fine grain optically stimulated luminescence osl ages of water lain sediments with an independent chronology we present here infrared ir post ir blue and blue osl characteristics of the fine grain sediments from lake xinias and a preliminary comparison with independent ages the equivalent doses based on the ir results are about 40 of those based on post ir blue stimulation which in turn are 10 15 below those based on quartz osl we discuss the ages derived from the 3 signals in terms of the independent chronology and draw conclusions about initial bleaching of the quartz and feldspar components and the reliability of the post ir blue signal as a chronometer c 2003 elsevier science ltd all rights reserved less

paleomagnetism of eocene volcanic rocks talkeetna mountains alaska previous paleomagnetic studies of eocene rocks deposited in the talkeetna mountains on the northern edge of the combined peninsular wrangellia and alexander terranes the southern alaska superterrane sas yield a paleolatitude of 76 n while late cretaceous rocks on the southern edge of the sas record a 32 n paleolatitude at face value these drastically different paleolatitudes imply that wrangellia moved 44 to the north in only 20 m y requiring a northward component of velocity of about 24 cm yr alternatively the discrepancy might be explained by postulating an unrecognized tectonic boundary separating the two localities allowing different emplacement ages we have tested the unrecognized tectonic boundary hypothesis allowing post eocene emplacement of the sas by sampling eocene volcanic rocks deposited near the southern edge of the sas in the talkeetna mountains our data set comprises measurements from 97 oriented cores collected from 26 lava flows and two tuffs distributed over a distance of 50 km a primary remanence is indicated by positive fold tests and penecontemporaneous intrusion tests age control is provided by nine new k ar whole rock age determinations ranging from 38 8 to 53 6 ma the mean paleomagnetic pole calculated for this study is not significantly different from the pole derived from the eocene flows to the north and gives a paleolatitude of 78 thus ruling out the hypothesis of an unrecognized suture accommodating major post eocene displacement this result has prompted a reevaluation of the data which suggest rapid movement including the precision of the age control the adequacy of averaging of secular variation and the possibility of sedimentary inclination error the bulk of the evidence suggests northward displacement from lower latitudes however the error limits are such that the dramatic velocities previously postulated are not required

late quaternary dune accumulation along the western margin of south africa distinguishing forcing mechanisms through the analysis of migratory dune forms abstract the west coast of south africa is situated at a critical location between temperate and subtropical oceanic and atmospheric circulation systems and palaeoenvironmental proxies from this region have the potential to elucidate issues concerning variations within these systems over glacial interglacical cycles while semi arid climates have hindered the preservations of organic proxies a variety of aeolian bedforms have been analysed in an effort to improve our understanding of environmental change in the region optically stimulated luminescence measurements of 51 samples from 15 reticulate dune sites along the west coast have enabled the identification of phases of aeolian activity as well as periods of relative geomorphic stability combined with data derived from previous studies of the region s sediment accumulating deposits and other palaeoenvironmental proxies periods of increased windiness are identified at 16 24 30 33 43 49 and 63 73 ka from approximately 17 12 ka decreasing transport capacity resulted in the stabilisation of the west coast s dune fields during the holocene altithermal 4 8 ka despite reduced wind strength increased aridity resulting from higher temperatures and a reduced influence of moisture bearing westerly systems appears to have trigged widespread remobilisation of the region s dune fields the combination of ages from a variety of dune forms with different development mechanisms and comparisons with a range of proxy data sources have allowed for an enhanced interpretation of the region s aeolian archives moving beyond simple correlations between dune activity and aridity

thermochronology in southeast alaska and southwest yukon implications for north american plate response to terrane accretion abstract this study presents the first comprehensive dataset of low temperature thermochronology from 43 bedrock samples collected north of the active yakutat north american plate boundary our apatite and zircon u th he and fission track data reveal the cooling history of the inboard wrangellia composite terrane that is dominated by rapid cooling after late jurassic to early cretaceous arc magmatism followed by very little cooling and exhumation until today deformation resulting in rock exhumation due to the collision of the yakutat microplate is spatially very limited 20 30 km and is concentrated mainly in the chugach prince william terrane and rocks near the border ranges fault focused exhumation from greater depths of ca 10 km with very high rates 5 km myr is localized at the syntaxis region starting ca 10 ma and shifted south through time the rapid exhumation rates are explained by the development of strong feedbacks between tectonically driven surface uplift and erosion which started already before glaciation of the area the shift in the location towards the south is a consequence of continuous readjusting between tectonics and climate which is changing on local and global scales since the late miocene

optical dating of holocene sediments from a variety of geomorphic settings using single grains of quartz this paper presents an improved method for the optical dating of holocene sediments from a variety of geomorphic settings we have measured the equivalent dose de in individual grains of quartz using green laser light for optical stimulation and have simulated the de distributions for multiple grain synthetic aliquots using the single grain data for 12 samples of known independent age we show that application of a minimum age model to the single grain and small 10 grain aliquot de data provides the most accurate estimate of the burial dose for nine of the samples examined 3 aeolian 5 fluvial and 1 marine the weighted mean de as obtained using the central age model gives rise to burial age overestimates of up to a factor of 10 for these nine samples whether single grains small aliquots or large 100 grain aliquots are used for the other three samples two aeolian and one fluvial application of either the minimum age model or the central age model to the single grain small aliquot and large aliquot de data yields burial ages in accord with the independent age control we infer that these three samples were well bleached at the time of deposition these results show that heterogeneous bleaching of the optical dating signal is commonplace in nature and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition we also show that grains sensitive to infrared ir stimulation can give rise to low de values which will result in significant underestimation of the burial dose and hence of the age of deposition we demonstrate that use of a modified single aliquot regenerative dose protocol incorporating ir stimulation prior to green light stimulation deals effectively with contamination by ir sensitive grains we conclude that application of the modified protocol to single grains or small aliquots of quartz using the lowest de population to estimate the burial dose is the best means of obtaining reliable ages for holocene sediments from a wide range of depositional environments d 2003 elsevier b v all rights reserved

infra red stimulated luminescence dating of holocene reworked silty sediments abstract infra red stimulated luminescence irsl ages are reported for holocene colluvial lacustrine and alluvial sediments and late glacial loess for colluvial sediments irsl ages concur with independent ages age overestimation occur in the case of very poorly bleached sediments such as young less than 2000 years floodloams for which a high suspended sediment load was deduced from sedimentation rates and actually observed floods age underestimates are observed for late glacial loess probably due to inadequate preheat procedures

cooling history of the st elias syntaxis southeast alaska revealed by geochronology and thermochronology of cobble sized glacial detritus

investigations into the potential effects of pedoturbation on luminescence dating much effort has been focussed on understanding the luminescence properties of natural minerals to achieve a reliable accurate and precise dating technique however some field related aspects such as the influence or effect of post depositional disturbance on luminescence dates are as yet underexplored in the case of pedoturbation depending on its intensity the rate of sedimentation and unit thicknesses potentially the whole sedimentary record at a site can be affected this may lead to distorted osl chronologies and erroneous sediment burial ages pedoturbation can result in sediment mixing and or exhumation that affect luminescence both at the bulk and single grain level effects of these two principle processes on luminescence ages are examined using standard multigrain and single grain protocols high resolution sampling of surface gopher mounds was used to determine the efficiency of bio exhumation in resetting luminescence signal results show this is an inefficient mechanism for onsite sediment bleaching the effects on luminescence signal of bio mixing were explored by comparing a sample collected from within a krotovina infilled burrow to an adjacent undisturbed sample results show the difficulties in identifying pedoturbated samples at the single aliquot level and the possible inaccuracies in using the lowest palaeodose values to calculate osl ages where pedoturbation of samples is suspected use of probability plots of palaeodoses data is recommended from these plots it is proposed that only data falling within a normal distribution centred on the peak probability be used to calculated osl ages and to mitigate problems arising from pedoturbation

cascades of dense water around the world ocean dense water overflow off continental shelves cascading is one of the contributing processes of shelf deep ocean exchange and of topical interest to climate studies and nutrient fluxes dense water originating from cooling evaporation freezing and salinization on a shallow shelf spills over the shelf edge and may develop as near bottom gravity current or an intermediate depth intrusion it is difficult to observe in nature due to its intermittent character this paper provides an extensive inventory of observed cases of water cascades around the world ocean summarises their locations and individual properties and provides statistics of the identified cases the search for cascading was carried out using oceanographic databases and a literature review this study identified 61 confirmed cases world wide including 25 cases in the arctic seas 12 at mid latitudes seven in sub tropical and tropical regions and 17 off the antarctic shelves eighteen cascades had not been reported before we analyze a set of numerical parameters of dense water cascades allowing us to quantify compare and contrast the properties of water cascades the overall average density contrast between the confirmed cascades and ambient water is 0 37 kg m3 it can be as much as 2 kg m3 on some arctic shelves frequently initiated by strong cooling at the surface cascades often remain colder through the descent thus supplying the deep ocean with colder and fresher water in non dimensional variables the data from all climate zones fit well to a unique curve which represents a relationship between a cascade s internal structure and the parameters describing its forcing on average the down slope volumetric flux provided by dense water cascades is estimated as 0 05 to 0 08 sv per 100 km of shelf edge regional terms arctic antarctic north atlantic ocean barents sea mediterranean sea skagerrak tasman sea sea of okhotsk

new constraints on the age of the last ice sheet glaciation in nw england using optically stimulated luminescence dating optically stimulated luminescence osl has been used to date silts interpreted as either primary or colluviated loess deposited in karstic depressions at three sites on the carboniferous limestone of nw england two of the ages presented here constrain the onset of the last late devensian ice in this region to later than ca 27 2 ka and the other two date initial deglaciation prior to ca 19 2 ka in the morecambe bay area and ca 17 2 ka in the karst of the yorkshire dales while these ages are broadly consistent with existing estimates from lacustrine and speleothem evidence they offer the tightest constraints yet published on the presence of the last ice sheet from northern england copyright 2009 john wiley sons ltd

in situ measurements of velocity structure within turbidity currents 1 turbidity currents are thought to be the main mechanism to move 500 000 m3 of sediments annually from the head of the monterey submarine canyon to the deep sea fan indirect evidence has shown frequent occurrences of such turbidity currents in the canyon but the dynamic properties of the turbidity currents such as maximum speed duration and dimensions are still unknown here we present the first ever in situ measurements of velocity profiles of four turbidity currents whose maximum along canyon velocity reached 190 cm s two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year long deployment

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

alternating asymmetric topography of the alaska range along the strike slip denali fault strain partitioning and lithospheric control across a terrane suture zone contrasting lithospheric strength between terranes often results in the concentration of strain and deformation within the weaker material dramatic alternating asymmetric topography of the central and eastern alaska range along the active denali fault is due to contrasting lithospheric strength between terranes and a suture zone controlled by fault location with respect to the irregular boundary of a relatively stronger terrane backstop highest topography and greatest neogene exhumation in the central alaska range occur on the concave side of the arcuate denali fault yet to the north and on the convex side of the fault in the eastern alaska range the denali fault largely lies along a mesozoic suture zone between two large composite terranes yukon and wrangellia composite terranes yct and wct but the mckinley strand of the fault cuts across an embayment of weaker suture zone rocks alaska range suture zone arsz within the irregular southern boundary of the yct hines creek fault deformation and uplift of the alaska range is driven by slip and partitioning of strain along the denali fault occurring preferentially in weaker rocks of the arsz against the stronger yct where the yct lies well north of the mckinley strand deformation is primarily to the north of the fault eastern alaska range where the yct is close to the fault deformation is primarily to the south central alaska range while the trace of the mckinley strand approximates a small circle two restraining bends mckinley and hayes pinned equidistant from the ends of this strand localize uplift and exhumation

estuarine versus transient flow regimes in juan de fuca strait 1 residual currents in juan de fuca strait are observed to switch between two fundamental states estuarine and transient the estuarine regime which prevails roughly 90 of the time in summer and 55 of the time in winter has a fortnightly modulated three layer structure characterized by strong 50 cm s 1 outflow above 60 15 m depth moderate 25 cm s 1 inflow between 60 and 125 m depth and weak 10 cm s 1 inflow below 125 10 m depth rotation increases the upper layer depth by 40 m on the northern side of the channel and upwelling favorable coastal winds augment inflow in the bottom layer by as much as 5 cm s 1 rotation combined with modulation of the estuarine currents by tidal mixing in the eastern strait leads to fortnightly variability in the along channel velocity and cross channel positioning of the core flow regions transient flows which occur roughly 10 of the time in summer and 45 of the time in winter are rapidly evolving horizontally and vertically sheared reversals in the estuarine circulation generated during poleward wind events along the outer coast major events can persist for several weeks force a net inward transport and give rise to an o 10 km wide surface intensified o 100 cm s 1 inflow along the southern olympic peninsula boundary of the strait this olympic peninsula countercurrent is typically accompanied by an abrupt decrease in salinity indicating that it is a buoyancy flow originating with low density water on the northern washington shelf

eocene volcanism above a depleted mantle slab window in southern alaska the caribou creek volcanic fi eld lies along the continent side edge of forearc basin rocks in south central alaska and consists of over 1000 m of shallow dipping basalt and andesite lavas with minor mafi c pyroclastic deposits dacite and rhyolite lavas along with shallow intrusions form dome complexes with associated pyroclastic deposits that overlie and crosscut the basalt and intermediate lavas the basalts are tholeiitic and strongly depleted in the light rare earth elements la yb 0 18 1 5 with concentrations of high fi eld strength elements e g zr hf ti y similar to mid ocean ridge basalt and with variable enrichment in fl uid mobile elements e g cs ba and pb intermediate and felsic rocks show enrichment in the rare earth elements and fl uid mobile elements plus rb and k but retain low la yb ratios 0 48 3 6 a few andesite and dacite samples are strongly depleted in the heavy rare earth elements and are geochemically similar to adakites e g sr y up to 52 ten 40 ar 39 ar ages for the caribou creek volcanic rocks range from 49 4 2 2 to 35 6 0 2 ma an adakite like tuff beneath the other volcanic rocks yields an age of 59 0 0 4 ma caribou creek basalts were derived from mid ocean ridge like depleted mantle that was emplaced beneath the southern margin of alaska through a slab window following spreading ridge subduction caribou creek volcanism was coeval with oblique subduction oroclinal bending and right lateral strike slip faulting in south central alaska all of which could have induced crustal extension to allow adiabatic melting of the depleted mantle reservoir to form basaltic magmas the basalts then evolved by fractional crystallization with moderate to high degrees of assimilation of jurassic arc basement rocks to form the intermediate and felsic magmas enrichment of the basaltic parent magmas in fl uid mobile elements occurred by contamination from the jurassic arc rocks and or by contamination with metasomatic mantle remnant from preceding subduction high heat fl ow through the slab window induced partial melting of garnet bearing mafi c parts of the jurassic arc basement to form the adakite like rocks the caribou creek volcanic rocks demonstrate that slab windows can directly infl uence magmatism inboard of accretionary prism and forearc basin settings given a suitable deformation regime e g crustal extension and that the infl uence of a slab window on continental margin magmatism can be long lived 20 m y

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

the yakutat terrane dramatic change in crustal thickness across the transition fault alaska we present new constraints on the crustal structure of the yakutat terrane and evidence of the role of the transition fault in southern alaska the yakutat terrane south of yakutat bay includes crystalline crust that is 24 27 km thick overlain by sedimentary units that are 4 5 7 5 km thick the yakutat terrane crustal thickness and velocity structure are consistent with an oceanic plateau origin the southern edge of the yakutat terrane is bounded by the transition fault which is imaged as a near vertical fault zone 1 km wide the transition fault is coincident with a dramatic change in moho depth from 32 km for yakutat oceanic plateau crust to 11 5 km for pacific ocean crust occurring over a horizontal distance of 0 5 km there is no evidence for underthrusting of the pacific ocean crust beneath the yakutat terrane at the transition fault we argue that the yakutat terrane formed on the kula or farallon plate and was later juxtaposed next to younger pacific ocean crust by the transition fault

thermoluminescence dating of late devensian loesses in southern england scattered across southern england are many isolated deposits of loess like material1 a few such as that at pegwell bay in kent are highly calcareous and unweathered but most have been reworked by fluvial or colluvial processes there is good stratigraphical evidence for a few pre devensian loesses also in kent but dating of more recent loess has so far been based on indirect evidence much work has been done on the pegwell bay loess as it is the most extensive truly aeolian loessic deposit in britain kerney2 compared the late devensian deposits in the isle of thanet and at pegwell bay with similar deposits in holland and belgium where radiocarbon dates have been obtained for interstadial deposits correlation of the east kent deposits with these in northern europe indicates that the loesses in kent were formed between 30 000 and 14 000 yr ago i report here dates for six of the more recent deposits in southern britain from the scilly isles to kent the dates have been obtained on the loess itself using a recently developed thermoluminescence tl dating technique3 4 and confirm the ages as being late devensian

near inertial motions over a mid ocean ridge effects of topography and hydrothermal plumes we investigate the spatial structure of near inertial motions in the vicinity of the endeavour segment of juan de fuca ridge approximately 48 n 129 w in the northeast pacific ocean on the basis of time series current and water property data collected from september 1984 to september 1987 near inertial motions are ubiquitous features of the 2200 m water column with root mean square rms current speeds comparable to those of the dominant m2 tidal currents within the lower 1000 m of the water column where most of the observations were obtained near inertial oscillations have rms current speeds of o 1 cm s and vertical isotherm displacements of o 10 m the fluctuations are confined to the frequency band 0 966 1 079 f f is the local coriolis parameter and have characteristic event durations of 1 week although the spectra of subsurface motions are dominated by the blue shifted superinertial band significant spectral peaks are found also in the subinertial and inertial frequency bands marked alteration of the near inertial current amplitudes occurs over two well defined depth zones within the study region within the 200 m zone immediately above the 2100 m ridge crest current amplitudes are amplified by a factor of 1 2 1 7 because of bottom reflection and or scattering of the downward propagating energy evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross slope rotation of the near inertial current ellipses with increased proximity to the top of the ridge reflection would occur at grazing angles of less than 1 and would be associated with surface generated waves originating at distances of over 100 km from the observational site in contrast to the enhanced amplitudes immediately above the top of the ridge near inertial currents within the 1600 to 1800 m depth range undergo pronounced attenuation and frequency alteration amplitude attenuation is especially pronounced for motions in the superinertial band and may arise through critical layer absorption of downward propagating waves as they encounter increased vertical shear in the background flow the increased shear is most likely associated with buoyancy induced flow formed by the extensive hydrothermal plume emanating from vent sites in the axial valley along the ridge crest but it could also be related to bottom trapped oscillations over the steep ridge topography near inertial motions are estimated to have vertical coherence scales of the order of 10 100 m while horizontal coherence scales exceed the 50 km separation between the mooring locations minimum vertical and horizontal coherences are found for the depth zone 1600 1800 m while maximum correlation occurs for near bottom motions immediately above the crest of the ridge weak near inertial motions are observed within the 100 m deep axial valley

rivers turned to rock late quaternary alluvial induration influencing the behaviour and morphology of an anabranching river in the australian monsoon tropics abstract late quaternary alluvial induration has greatly influenced contemporary channel morphology on the anabranching gilbert river in the monsoon tropics of the gulf of carpentaria the gilbert one of a number of rivers in this region has contributed to an extensive system of coalescing low gradient and partly indurated riverine plains extensive channel sands were deposited by enhanced flow conditions during marine oxygen isotope oi stage 5 subsequent flow declined probably associated with increased aridity however enhanced runoff recurred again in oi stages 4 3 65 50 ka aridity then capped these plains with 4 7 m of mud a widespread network of sandy distributary channels was incised into this muddy surface from sometime after the last glacial maximum lgm to the mid holocene during a fluvial episode more active than the present but less so than those of oi stages 5 and 3 this network is still partly active but with channel avulsion and abandonment now occurring largely proximal to the main gilbert flow path a tropical climate and reactive catchment lithology have enhanced chemical weathering and lithification of alluvium along the river resulting in the formation of small rapids waterfalls and inset gorges features characteristic more of bedrock than alluvial systems thermoluminescence tl and comparative optically stimulated luminescence osl ages of the sediments are presented along with u th ages of pedogenic calcrete and fe mn oxyhydroxide oxide accumulations they show that calcrete precipitated during the late quaternary at times similar to those that favoured ferricrete formation possibly because of an alternating wet dry climate intense chemical alteration of the alluvium leading to induration appears to have prevailed for much of the late quaternary but probably due to exceptional dryness not during the lgm the result has been restricted channel migration and a reduced capacity for the channel to adjust and accommodate sudden changes in bedload consequent avulsions have caused local stream powers to increase by an order of magnitude inducing knickpoint erosion local incision and the sudden influx of additional bedload that has triggered further avulsions the gilbert river while less energetic than its pleistocene ancestors is clearly an avulsive system and emphasizes the importance in some tropical rivers of alluvial induration for reinforcing the banks generating nickpoints reworking sediment and thereby developing and maintaining an indurated and anabranching river style

rock uplift at the transition from flat slab to normal subduction the kenai mountains southeast alaska abstract the process of flat slab subduction results in complex deformation of overlying forearcs yet how this deformation decays with distance away from the zone of underthrusting is not well understood in south central alaska flat slab subduction of the yakutat microplate drives shortening and rock uplift in a broad coastal orogenic belt defined limits of the zone of underthrusting allow testing how orogenesis responds to the transition from flat slab to normal subduction to better understand forearc deformation across this transition apatite u th he low temperature thermochronometry is used to quantify the exhumation history of the kenai mountains that are within this transition zone measured ages in the northern kenai mountains vary from 10 20 ma and merge with the exhumation pattern in the chugach mountains to the northeast where high exhumation occurs due to flat slab related deformation in the southern kenai mountains however ages increase to 30 50 ma across a transition near seward alaska above the zone from flat slab to normal subduction these ages are relatively old in comparison to ages determined in other studies in southern alaska and suggest minimal exhumation furthermore transitions in topographic expression of the coastal orogen also occur at the margin of yakutat underthrusting these observations suggest that either deformation associated with flat slab subduction requires tens of kilometers to decay with distance away from the zone of underthrusting or that orogenesis in the kenai mountains is driven by a distinct tectonic cause a potential driver of deformation is underplating of thick sediments specifically the surveyor submarine fan along the aleutian megathrust analogous to the tectonic mechanism responsible for the emergence of the kodiak island forearc if correct this may represent a recent tectonic transition in the region given the minimal exhumation of the rugged kenai mountains despite the presence of an erosion conducive glacial climate

late quaternary sea level changes of the persian gulf abstract late quaternary reflooding of the persian gulf climaxed with the mid holocene highstand previously variously dated between 6 and 3 4 ka examination of the stratigraphic and paleoenvironmental context of a mid holocene whale beaching allows us to accurately constrain the timing of the transgressive highstand and regressive phases of the mid to late holocene sea level highstand in the persian gulf mid holocene transgression of the gulf surpassed today s sea level by 7100 6890 cal yr bp attaining a highstand of 1 m above current sea level shortly after 5290 4570 cal yr bp before falling back to current levels by 1440 1170 cal yr bp the cetacean beached into an intertidal hardground pond during the transgressive phase 5300 4960 cal yr bp with continued transgression interring the skeleton in shallow subtidal sediments subsequent relative sea level fall produced a forced regression with consequent progradation of the coastal system these new ages refine previously reported timings for the mid to late holocene sea level highstand published for other regions by so doing they allow us to constrain the timing of this correlatable global eustatic event more accurately

geochronology and eruptive history of the katmai volcanic cluster alaska peninsula abstract in the katmai district of the alaska peninsula k ar and 40ar 39ar ages have been determined for a dozen andesite dacite stratocones on the arc front and for 11 rear arc volcanoes 10 of which are monogenetic tied to mapping and stratigraphic studies our dating emphasized proximal basal lavas that rest on basement rocks in order to estimate ages of inception of each polygenetic cone oldest among arc front cones is alagogshak volcano 690 43 ka succeeded in the holocene by the active mount martin cone mount mageik consists of four overlapping subedifices basal lavas of which give ages of 93 71 and 59 ka and holocene the three small prehistoric cones of trident volcano yield ages of 143 101 58 and 44 ka falling mountain and mount cerberus dacite domes near the 1912 novarupta vent are related compositionally to the trident group and give ages of 70 ka and 114 ka mount katmai which underwent caldera collapse in 1912 consists of two subedifices that overlapped in space and time and is the only arc front center here to include basalt and rhyolite one cone began by 90 ka the other by 47 ka snowy mountain also consists of two contiguous cones which started around 200 and 171 ka respectively the younger remaining active into the holocene devils desk the only mafic cone on the arc front was short lived at about 245 ka in the rear arc 1 mount griggs produced mafic to silicic andesite in several episodes between 292 ka and the holocene 2 the savonoski river cluster includes a pliocene dacite dome and five small mafic cones 390 88 ka 3 gertrude creek cone 49 8 sio2 yields an age of 500 ka and 4 the saddlehorn creek cluster includes five pliocene basalt to andesite remnants eruptive volumes were reconstructed permitting estimates of average eruption rates for edifice lifetimes since the mid pleistocene total volume erupted along the arc front here is 210 47 km3 and in the rear arc 39 6 km3 of which mount griggs alone accounts for 35 5 km3 most productive has been mount katmai at 70 18 km3 yielding a rate of 1 km3 kyr followed by mount mageik 0 33 km3 kyr and mount griggs 0 3 km3 kyr since 50 ka

vertical structure and temporal evolution of an anticyclonic eddy in the balearic sea western mediterranean 1 an anticyclonic eddy in the balearic sea western mediterranean was described using data from a mooring line deployed at the northern slope of mallorca island at about 900 m deep its surface signature was investigated using sea surface height and sea surface temperature images the eddy which lasted around 1 month modified the thermohaline characteristics and the currents of the entire water column levantine intermediate waters usually resident in the region were displaced by colder and fresher western mediterranean intermediate waters associated with the eddy along slope main currents toward ne were completely reversed at 500 m and significantly deviated at 900 m interestingly near bottom velocities were found to be systematically larger than those at intermediate depths furthermore during the eddy velocities reached values up to 26 cm s at the bottom 5 times larger than the bottom average speed the recurrence of the phenomenon was explored with an eddy detection tool applied to satellite observations results indicated that anticyclonic eddies are common structures in the balearic current

optically stimulated luminescence osl dating of loessic sediments and cemented scree in northwest england optically stimulated luminescence osl dates are reported for silts and very fine sands believed to be loessic sediments from northwest england at three sites loessic sediments were initially interpreted as primary aeolian deposits and at two other sites as loess incorporated into the matrix of cemented scree however the results of osl dating indicate a more complex pattern of accumulation than originally hypothesized and have prompted reconsideration of these materials whatever the process es and underlying cause s it is evident that significant amounts of soil erosion occurred on the limestone uplands earlier than previously thought all but one of the ages fall entirely within the holocene period and suggest that these deposits contain reworked rather than primary loess four of the five sites are characterized by non gaussian dose distributions and consequently equivalent doses have been estimated using a range of appropriate age models the implications of differences in the ages derived f

plate tectonics and basin subsidence history tectonic setting exerts fi rst order control on basin formation as refl ected in basin subsidence history while our approach ignores the effects of fl exural loading and eustatic sea level change consistency of backstripped subsidence histories i e with local loading effects of sediment removed suggests consistent tectonic driving mechanisms in each tectonic setting with the possible exception of forearc basins based on published subsidence curves and open fi le stratigraphic data we show the subsidence characteristics of passive margins strike slip basins intracontinental basins foreland basins and forearc basins passive margin subsidence is characterized by two stages rapid initial synrift subsidence and slow post rift thermal subsidence with increasing subsidence rates toward the adjacent ocean basin subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings but the former is generally slower longer lived and lacks initial subsidence long lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents basins associated with strike slip faults are usually short lived with very rapid subsidence changes in local stress regimes as strike slip faults evolve and migrate over time coupled with three dimensional heat loss in these small basins likely explain this subsidence pattern foreland basin subsidence rates refl ect the fl exural response to episodic thrust loading resultant subsidence curves are punctuated by convex up accelerating segments forearc basins have the least consistent subsidence patterns subsidence histories of these basins are complex and may refl ect multiple driving mechanisms of subsidence in forearc settings second order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings the effects of eustatic sea level change may also explain some deviations in curves for many of these settings subsidence histories are suffi ciently distinctive to be used to help determine tectonic setting of ancient basin deposits

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

structure and variability of the denmark strait overflow model and observations we report on a combined modeling and observational effort to understand the denmark strait overflow dso four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution the observations reveal the mean path of the dense water as well as the presence of strong barotropic flows energetic variability and strong bottom friction and entrainment a regional sigma coordinate numerical model of interbasin exchange using realistic bottom topography and an overflow forced only by an upstream reservoir of dense fluid is compared with the observations and used to further investigate these processes the model successfully reproduces the volume transport of dense water at the sill as well as the 1000 m descent of the dense water in the first 200 km from the sill and the intense eddies generated at 1 3 day intervals hydraulic control of the mean flow is indicated by a region supercritical to long gravity waves in the dense layer located approximately 100 km downstream of the sill in both model and observations in addition despite the differences in surface forcing both model and observations exhibit similar transitions from mostly barotropic flow at the sill to a bottom trapped baroclinic flow downstream indicating the dominant role of the overflow in determining the full water column dynamics

sediment gravity flows triggered by remotely generated earthquake waves recent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the cascadia subduction zone of the pacific northwest we analyzed seafloor temperature pressure and seismic signals and of video stills of sediment enveloped instruments recorded during the 2011 2015 cascadia initiative experiment and seafloor morphology our results led us to suggest that thick accretionary prism sediments amplified and extended seismic wave durations from the april 11 2012 mw8 6 indian ocean earthquake located more than 13 500 km away these waves triggered a sequence of small slope failures on the cascadia margin that led to sediment gravity flows culminating in turbidity currents previous studies have related the triggering of sediment laden gravity flows and turbidite deposition to local earthquakes but this is the first study in which the originating seismic event is extremely distant 10 000 km the possibility of remotely triggered slope failures that generate sediment laden gravity flows should be considered in inferences of recurrence intervals of past great cascadia earthquakes from turbidite sequences future similar studies may provide new understanding of submarine slope failures and turbidity currents and the hazards they pose to seafloor infrastructure and tsunami generation in regions both with and without local earthquakes

the crustal structure of the wrangellia terrane along the east glenn highway eastern southern alaska recently acquired seismic refraction data from eastern southern alaska provide new information on the structure and composition of the wrangellia and adjacent terranes the data comprise a 160 km long refraction profile along the east glenn tok cutoff highway that was collected as part of the u s geological survey s multidisciplinary trans alaska crustal transect program the upper 3 km of the wrangellia terrane and associated rocks is characterized by low compressional wave velocities vp 1 9 3 3 4 6 5 6 km s 1 and high velocity gradients common to most onshore seismic refraction profiles there is also clear seismic expression of the west fork fault system as a steep down to the southwest fault that separates the peninsular terrane to the southwest and the metamorphic complex of gulkana river to the northeast in contrast no seismic expression occurs for the paxson lake fault which separates the wrangellia terrane from the metamorphic complex of gulkana river adjacent to the denali fault within the wrangellia terrane two high velocity bodies vp 6 6 km s 1 occur in the upper crust one of these extends to 10 km depth and correlates with a late paleozoic dioritic complex suggesting that the wrangellia terrane is at least 10 km thick in this part of alaska from 5 to 23 km depth the crust appears seismically homogeneous with velocity increasing from vp 6 2 to vp 6 6 km s 1 beneath this level the crust is less well resolved although evidence exists for a low velocity zone between 23 and 26 km and a possible southwest dipping interface at 35 km no identifiable mantle refraction or reflection is observed possibly indicating a crust as thick as 55 km the relatively low seismic velocities in the upper 23 km of the crust compare favorably with laboratory measured velocities on pelitic schists and intermediate composition plutonic rocks granites and granodiorites both of which are recognized in wrangellia we interpret the seismic velocities to indicate that silicic to intermediate composition rocks are important constituents of the basement of this part of wrangellia geologic evidence indicates that the alaskan part of the wrangellia terrane is a paleozoic and mesozoic island arc our seismic evidence indicates it may have been built mostly on continental crust as opposed to the fragment of wrangellia from vancouver island which was probably built on oceanic crust

thermoluminescence dating and geochemistry of loessic deposits in southeast england the results of a thermoluminescence tl dating and geochemical survey of loessic deposits in southeast england involving sampling at 26 localities demonstrate that the loessic deposits appear to be the product of at least three depositional phases of aeolian silt during the late pleistocene namely 10 25 ka bp 50 125 ka bp and 170 ka bp the majority of localities sampled date to the late devensian but isolated pockets of older material were found throughout the area the majority of the samples analysed were of decalcified material the results of geochemical analyses of major oxide and trace element concentrations indicate the uniformity of material and suggest a common provenance

slow and delayed deformation and uplift of the outermost subduction prism following ets and seismogenic slip events beneath nicoya peninsula costa rica abstract two odp cork ocean drilling program circulation obviation retrofit kit borehole hydrologic observatory sites deployed in 2002 at the toe of the subduction prism off nicoya peninsula costa rica were visited in december 2013 the five years of seafloor and formation fluid pressure data collected since the previous visit include clear signals associated with an episodic tremor and slip ets event off the coast of nicoya peninsula in 2009 and a mw 7 6 subduction thrust earthquake beneath the peninsula in 2012 formation pressure anomalies associated with the ets event are similar to ones observed following ets events observed previously here as well as ones following very low frequency earthquake swarms within the nankai accretionary prism off southwestern japan positive and negative impulsive transients in the hanging wall and foot wall of the subduction thrust respectively suggest contractional and dilatational strain generated by local slip propagating up the thrust fault beneath the outermost prism in the case of the 2009 event the transients occurred roughly two weeks after the initiation of slip observed at gps sites along the adjacent coast at the same time a decrease in seafloor pressure at the prism site relative to the subducting plate was observed indicating concurrent uplift of the prism of 1 2 cm other events at the prism toe following ets events closer to the coast are seen in 2006 2007 2008 2010 and 2011 the time between the initiation of ets slip constrained by gps and the onset of the prism toe transients suggest up dip rupture propagation along the seaward part of the subduction thrust at rates of a few km day in the case of the 2009 event the slip at the prism toe c 11 cm estimated from the 1 2 cm uplift and the local dip on the decollement 6 is roughly a factor of 5 greater than the slip further landward estimated from gps data by dixon et al in press in other cases slip at the toe is less or unresolvable similar uplift and formation fluid pressure transients occurred two days after the 2012 nicoya thrust earthquake then episodically unrelated to aftershocks every 1 3 weeks over the next few months slip rates at the prism toe estimated from the magnitude and duration of these and ets related uplift events are roughly 5 cm day such rates are much too slow for tsunamigenesis or seismogenesis total slip of the outermost prism after the 2012 earthquake determined from the uplift accumulated until the end of the observation period and the estimated local fault dip is roughly 75 cm a significant fraction of the seismogenic slip of the mw 7 6 earthquake itself a maximum of over 3 m negative steps in formation pressure are observed at both the prism and subducting plate sites simultaneous with the 2012 thrust earthquake the sign of these steps is inconsistent with the contractional deformation predicted by an elastic fault dislocation model with slip limited to the seismogenic zone highly compliant low shear modulus sediment below the decollement or very low stress deformation along splay faults may be responsible for the co seismic dilatation observed in the outermost prism and incoming plate

late quaternary stratigraphy and luminescence geochronology of the northeastern mojave desert abstract the chronology of the holocene and late pleistocene deposits of the northeastern mojave desert have been largely obtained using radiocarbon ages our study refines and extends this framework using optically stimulated luminescence osl to date deposits from valjean valley silurian lake playa red pass and california valley of particular interest are eolian fine silts incorporated in ground water discharge gwd deposits bracketed at 185 140 and 20 50 ka alluvial fan deposits proved amenable for osl by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy lacustrine sand in spits and bars also yielded acceptable osl ages these osl ages fill gaps in the geochronology of desert deposits which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate this study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the mojave desert sediments from previously undated landforms can be more accurately placed within correct geologic map units

old crow tephra across eastern beringia a single cataclysmic eruption at the close of marine isotope stage 6 abstract old crow tephra is the largest and most widespread quaternary eruption presently known in eastern beringia its major and trace element geochemistry fe ti oxides and stratigraphic and paleoecological context indicate that it is the result of a single cataclysmic eruption the proximal region may well have experienced tephra fallout from small eruptions just prior to or after the old crow event but there is no evidence to indicate that the distal area was affected we recalculate the glass fission track age at 124 10 ka which coupled with stratigraphic and paleoenvironmental reconstructions indicates that deposition occurred prior to development of the last interglacial boreal forest which suggests a latest marine isotope stage mis 6 age the bulk tephra volume erupted is estimated by three different approaches that are in broad agreement at 200 km 3 but this result must be considered as tentative given the poor controls on definition of isopachs over such a large area the source caldera although presently unrecognized is located in the eastern aleutian arc possibly at or near the emmons lake volcanic center

flow processes and sedimentation in contourite channels on the northwestern south china sea margin a joint 3d seismic and oceanographic perspective abstract 3d seismic data from the northwestern south china sea margin coupled with the quantification of oceanographic processes and morphological results were used to infer three dimensional flow processes and in turn sedimentation in contourite channels contour currents resulting from the northern pacific deep water npdw ccs flowing through the bends of contourite channels around a topographic high lead to an imbalance in the transverse direction around the bend between three competing forces i e upslope directed coriolis forces versus downslope directed centrifugal and pressure gradient forces the interface deflection of npdw ccs by coriolis pressure gradient and centrifugal forces yields a helical flow cell consisting of upper return flows directed downslope and basal flows orientated upslope ekman boundary layers at the base and flow interface are also likely present leading to flows in the downslope direction the helical flow cell in the bulk of contour currents and ekman boundary layers constitute a coriolis force induced helical flow circulation which we suggest promoted asymmetric intra channel deposition i e downslope deposition versus upslope erosion forcing contourite channels to consistently migrate in an upslope direction such coriolis force induced helical flow circulation is evidenced by occurrence of volumetrically significant overbank deposits along downslope margins and by asymmetric channel cross sections with steepened channel walls and truncation terminations along upslope margins it exhibits subcritical flow conditions represented by internal froude numbers estimated as 0 04 to 0 19 and is sufficiently deep to spill out of the studied contourite channels yielding overbank deposits along downslope flanks of the contourite channels

late glacial early holocene slope deposits on the swiss plateau genesis and palaeo environment abstract on the swiss plateau glacial and glaciofluvial sediments deposited during mis 2 are widespread they are generally overlain by younger sediments of different origin mainly related to periglacial and slope wash processes depending on their genesis and composition 3 types of slope deposits can be distinguished which are classified as units 1 2a and 2b unit 1 is characterized by its wide spatial occurrence and a constant thickness of 40 60 cm high silt contents and a sharp lithological discontinuity to the lying sediments generally forming the parent material for the ah and al horizons of the luvisols unit 2 represents erosion rills filled up with loess loam and some gravel based on stratigraphic assumptions the formation of unit 1 has been tentatively attributed to the younger dryas optical stimulated luminescence and radiocarbon dating of unit 2 indicate morphodynamic activity during the early holocene up to 7 5 ka suggesting an open landscape this scenario is in conflict with the established notion that reforestation in middle europe took place during the bolling allerod warm period in order to explain this apparent contradiction for the younger dryas to early holocene environment we suggest a continental climate with dry summers and drought stress on the vegetation in combination with very cold winters and deep soil frost at the pleistocene holocene transition caused by the orbital precession maximum after 7 5 ka with the spread of oceanic woodland and reduced seasonal contrasts the landscape stabilized and soils developed

environmental dose rates and radioactive disequilibrium from some australian luminescence dating sites abstract determination of geological archaeological ages by luminescence dating requires the measurement of the rate of delivery of radiation dose from the sample and its environment for all age determinations it is necessary to assess whether the dose rate has been constant during the time that the dose has been accumulating and to make allowance for it if it was not we report here results from a number of australian sites to illustrate the information that can be found about element concentrations about their distribution and about dose rates tests for radioactive disequilibrium form part of these measurements such tests take the form of comparison of independent measurements of dose rates and or individual elements in general there is little or no evidence for disequilibrium in aeolian dune systems even when the age of the system exceeds 500 ka however disequilibrium has been found in several sites subject to wet conditions

holocene sea levels last glacial maximum glaciomarine environments and geophysical models in the northern irish sea basin uk newly acquired geological records from the isle of man reveal intercalated intertidal and terrestrial sediments that record a relative sea level rise from ca 3 86 m in the early holocene up to a mid holocene maximum between ca 6 6 and 4 5 cal kyr bp at ca 2 25 m when compared with similar marine records from elsewhere in the northern irish sea basin the sea level data confirm a strong north south trend in glacioisostatic loading but little east to west difference in loading this pattern results from the central northern sectors of the british ice sheet over scotland strongly influencing the glacioisostatic downwarping throughout the northern irish sea basin differential ice thicknesses over the irish sea the lake district and ireland did not cause perturbations of local glacioisostatic signatures the holocene marine data in the central irish sea record a slow termination of global eustatic sea level rise during the early holocene geophysical predictions of relative sea level partially constrained by the holocene rsl observations but extrapolated to the last glacial maximum show the potential for shallow marine conditions in the central irish sea basin and in northeast ireland between ca 21 0 16 0 cal kyr bp however glaciomarine deposits in northeast ireland suggest the model relative sea level predictions are too low and require increased ice loading or a thinner lithosphere to generate extra glacioisostatic depression at the time of deglaciation furthermore predicted deglacial relative sea level for northeast ireland does not match the geological record highlighting complex ice margin ocean interaction during deglaciation on the isle of man where glacioisostatic loading is of a similar magnitude to that across northeast ireland the presence of grounded ice inhibited marine incursion during early deglaciation but the occurrence of glaciolacustrine conditions along the ice margin as it moved northwards supports model predictions that relative sea level fell below present during the late glacial early holocene due to rapid glacioisostatic rebound

a wild boar dominated ungulate assemblage from an early holocene natural pit fall trap cave shaft sediments in northwest england associated with the 9 3 ka bp cold event a highly unusual pit fall ungulate assemblage dominated by wild boar sus scrofa was recovered during the recent exploration of a cave shaft in the upland karstic landscape of northwest england both the opening of the cave shaft to the surface and its infilling by clastic sediments are attributable to accelerated landscape erosion associated with the 9 3 ka bp climatic deterioration evidence that wild boar had died in winter or spring suggests that their deaths relate to the prolonged periods of annual snow cover experienced by the uplands of northwest england during the 9 3 ka bp event the dominance of wild boar in the pit fall assemblage is explained by the snow pack concealing the open shaft and turning it into a baited trap for wild boar whenever it contained carrion wild boar bones splintered and chewed by wild boar demonstrate carrion cannibalism human presence is attested by slight butchery to an aurochs bos primigenius how mesolithic people adapted to climate change associated with the 9 3 ka bp event is a subject well worth pursuing

source fingerprinting loess deposits in central asia using elemental geochemistry with bayesian and glue models abstract the provenance of loess deposits in central asia is largely unexplored accordingly the goals of this research were to test and compare the performance of two different models generalized likelihood uncertainty estimation glue and a bayesian model for quantifying the uncertainty in source apportionment estimated for 46 target loess samples collected in the ili basin in eastern central asia model performance was evaluated using goodness of fit gof mean absolute fit maf and virtual mixtures vm in combination with root mean square error rmse and mean absolute error mae our dataset comprised 132 surficial samples collected from three potential sources comprising river alluvium n 29 sand dunes n 35 and topsoils n 68 all samples were analysed for elemental geochemistry six geochemical properties co er y ga dy and pb were selected in a composite fingerprint which classified 83 of the samples from the three source categories correctly based on both models source contributions to the loess samples were in the following order topsoils river alluvium sand dunes based on the gof and maf tests both models were accurate in predicting measured tracer concentrations in the loess samples the bayesian model was slightly more accurate mean rmse 1 6 mean mae 1 8 than the glue mean rmse 5 0 mean mae 4 7 model in predicting known source contributions overall our results provide confirmation that application of source fingerprinting with elemental geochemistry and uncertainty modelling techniques is useful for identifying the provenance of loess sediments in arid and desert environments

environments of deposition paleocurrents and provenance of tertiary deposits along kachemak bay kenai peninsula alaska abstract grain size distributions and sedimentary structures of tertiary strata along kachemak bay indicate a variety of inchannel and overbank fluvial facies a markov analysis indicates cyclicity of these facies probably caused by repeated and regular channel migration during subsidence fossils indicate a cool temperate climate and probable freshwater deposition paleocurrent directions and sandstone composition suggest a metamorphic and sedimentary clastic provenance during homerian time with the addition of pyroclastics during clamgulchian time the homerian stage beds represent facies of braided meandering streams whereas the clamgulchian stage beds represent facies of meandering streams these streams flowed westward and northwestward from the chugach kenai mountains onto wooded low gradient alluvial plains

luminescence chronology of non glacial sediments in changeable lake russian high arctic and implications for limited eurasian ice sheet extent during the lgm a 10 5 m core from changeable lake in the severnaya zemlya archipelago just north of the taymyr peninsula intersects ca 30 cm of diamicton at its base interpreted as a basal till because the upper 10 13 m of this core consists of non glacial sediments a maximum numeric age for these non glacial sediments would provide a clear lower limit to the timing of the last glaciation in the area of changeable lake radiocarbon 14c dating of several materials from this core yielded widely scattered results consequently we applied photonic dating to sediments above the diamicton the experimental single aliquot regenerative sar dose fine grain method was applied to two samples using the double sar approach with one exception these fine grain sar results and the results of application of the sar method to sand sized quartz grains from two samples at ca 9 95 m and ca 10 05 m depth are discrepant with age estimates from the multi aliquot infrared photon stimulated luminescence ir psl method applied to fine grains multi aliquot ir psl dating of 10 samples produces ages increasing monotonically from ca 4 ka at 2 m to 53 4 ka at 9 97 m these self consistent multi aliquot ir psl ages along with limiting 14c ages of 47 ka at ca 10 m provide direct evidence that glacial ice did not advance over this lake basin during the last glacial maximum and thus delimit the northeastern margin of the barents kara sea ice sheet to somewhere west of this archipelago the last regional glaciation probably occurred during marine isotope stage mis 4 or earlier copyright 2004 john wiley sons ltd

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

observations of long duration episodic bottom currents in the middle america trench evidence for tidally initiated turbidity flows 1 benthic flow in the middle america trench off the pacific coast of costa rica is examined using time series from a single point acoustic current meter moored 21 m above bottom at 4386 m depth at the southern end of the trench from november 2005 to april 2007 in addition to significant 0 1 m s 1 tidal currents the instrument recorded a series of 12 episodic northwestward along trench flow events of roughly monthly duration event velocities often exceeded 0 25 m s 1 and were contemporary with enhanced acoustic backscatter intensity events ended with a rapid 1 day reversal to southeastward flow and reduced backscatter seafloor temperature records from two nearby ocean drilling program odp borehole observatory sites reveal that the flow events were accompanied by a steady rise in bottom water temperature temperatures dropped abruptly to background values at the end of each event the event timing generally tracked the envelope of the tidal current modulation on the basis of the november 2002 to february 2009 borehole observatory temperature records the events had a mean duration of 40 20 days and were separated by a between event interlude of 30 25 days findings indicate that the episodic flows were likely rotationally modified autosuspending turbidity currents initiated by tidal current resuspension of sediments above the shoaling trench floor to the southeast of the mooring site suspended particles in the turbidity currents are estimated to range from 0 0003 to 0 006 of the current by volume results suggest that tidally induced turbidity currents may be common to steep well mixed regions of the deep ocean adjacent to sediment rich continental margins

thermoluminescence dating of the british coversand deposits abstract coversand deposits thought to be of lateglacial age are found in britain in north lincolnshire south west lancashire and central east anglia a comprehensive dating study of them using thermoluminescence tl techniques is currently underway in an attempt to link the british coversand deposits to the european coversand chronology initial results from four of the british coversand sites sampled are presented the 26 tl dates from 14 samples show that in lincolnshire aeolian deposition took place from 12 5 ka to i1 ka cessation of the initial sand deposition was synchronous with this in lancashire but sand deposition occurred significantly earlier in east anglia the upper layers of aeolian sand in lancashire are much younger and are attributed to holocene reworking on the basis of these dates lincolnshire and lancashire coversand deposition occurred at a similar time to the younger coversand ii whilst east anglian coversand deposition coincided with the younger coversand i phase in the european coversand chronology

a holocene calcrete from north yorkshire england implications for interpreting palaeoclimates using calcretes glacial gravels of late devensian dimlington stadial age 26 000 13 000 years bp at west tanfield north yorkshire england have been cemented by carbonate rich solutions to produce a strongly indurated calcrete horizon the low mg cements occur as drusy spar needle fibres alveolar septal structures micrite and micropinnacles indicative of vadose zone cementation some complex pore partition structures attributed to precipitation along meniscus films also occur these partitions separate air dominated and water dominated microenvironments of the vadose zone the abundance of vadose fabrics shows that the accumulation is not a groundwater calcrete in addition much of the carbonate appears to have been precipitated by biological mediation carbon and oxygen isotopic data suggest that the carbonate did not form as a result of freezing as has been suggested for some arctic soil carbonates the pollen history of the area since the devensian suggests that this calcrete precipitated at low temperatures this contrasts with widely reported occurrences of calcrete in soils of hot arid or semi arid regions and suggests that palaeo calcretes should not be used as absolute palaeoclimatic indicators the unusual occurrence albeit localized of a thick calcrete under a cool and wet climate probably reflects the well drained nature of the gravels the abundance of caco3 as limestone clasts in the gravel and a high degree of biological activity beneath a forest cover which created a local environment favouring carbonate precipitation