age and weathering status of granite tors in arctic finland 68 n abstract cold based ice along the fennoscandian glacial ice divide in northern finland allowed preservation of old landscape features because there was little or no movement at the ice land surface contact erosion was at a minimum and relict landscape features such as tors can be found we investigated two such granitic tors located at pyha nattanen 68 07 335 n 27 22 207 e 508 m asl and riestovaara 68 02 613 n 27 09 003 e 390 m asl in subarctic finland at pyha nattanen the sampling sequence included bedrock material and grus taken from within horizontal cracks which are so prevalent at the site as to make the tor resemble a stack of pancakes at riestovaara where the outcrop is more subdued in addition to bedrock and grus samples soil samples were also extracted from a pit dug in an embryonic soil forming on the bedrock surface based on cosmogenic nuclide dating both tors greatly predate recent glaciation the tor at pyha nattanen which is a more prominent landscape feature had longer minimum 10be and 26al apparent exposure ages 89 1 6 7 kyr and 69 6 6 4 kyr respectively than did the tor at riestovaara 55 8 4 5 kyr and 46 5 4 0 kyr respectively both of them are significantly older than the regional last deglaciation age indicating that both sites have survived multiple episodes of glaciation analyses of the 10be and 26al measurements in accordance with marine oxygen isotope records dsdp 607 indicate that the tors have undergone a minimum estimated total exposure burial durations of 997 kyr pyha nattanen and 858 kyr riestovaara and survived at least 14 16 episodes of glaciation weathering as measured by porosity determined with a microprobe was somewhat more advanced in the pyha nattanen granite samples than in the riestovaara granite however with both granites rock porosity did not change to a depth of 4 cm below the rock surface or vary by lichen cover noncovered surfaces indicating that weathering had progressed to a stage where recent lichen growth is overwhelmed by the long weathering history other measures of weathering including total elemental analyses did not detect significant differences among at a site samples perhaps because all samples are highly weathered and we did not have a sample of unweathered granite for comparison all samples rock grus and soil were within the grus weathering range as indicated by chemical weathering indices the soil forming adjacent to the tor at riestovaara exhibited only slight development despite the great apparent age of the landscape the regolith in which the soil is forming must therefore be much younger than the exposed bedrock and most likely represents a post deglaciation accumulation of grus spanning only the last 9 kyr

glacial dispersal train of paleozoic erratics central baffin island n w t canada a glacial dispersal train of erratics derived from paleozoic bedrock has been delineated stretching east northeast west southwest across central baffin island the lithologies of these erratics suggest a derivation from strata of member b of the ordovician ship point formation to the west which are presently either submerged or covered by quaternary sediment in the eastern part of foxe basin these paleozoic erratics were carried from foxe basin onto the baffin upland and the western edge of the davis highlands they can be inferred to have reached at least ekalugad fiord and the eastern part of home bay

subsurface flow in a soil mantled subtropical dolomite karst slope a field rainfall simulation study abstract soil and epikarst co evolve resulting in complex structures but their coupled structural effects on hydrological processes are poorly understood in karst regions this study examined the plot scale subsurface flow characteristics from an integrated soil epikarst system perspective in a humid subtropical cockpit karst region of southwest china a trench was excavated to the epikarst lower boundary for collecting individual subsurface flows in five sections with different soil thicknesses four field rainfall simulation experiments were carried out under different initial moisture conditions dry and wet and rainfall intensities 114 mm h 1 high and 46 mm h 1 low on average the soil epikarst system was characterized by shallow soil overlaying a highly irregular epikarst surface with a near steady infiltration rate of about 35 mm h 1 the subsurface flows occurred mainly along the soil epikarst interface and were dominated by preferential flow the subsurface flow hydrographs showed strong spatial variability and had high steady state coefficients 0 52 and 0 36 for high and low rainfall intensity events irregular epikarst surface combining with high vertical drainage capacity resulted in high threshold rainfall depths for subsurface flows 67 mm and 263 mm for initial wet and dry conditions respectively the above results evidenced that the irregular and permeable soil epikarst interface was a crucial component of soil epikarst architecture and consequently should be taken into account in the hydrological modeling for karst regions

oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the cretaceous valanginian campanian passive margin northern gulf of mexico an integrated sequence stratigraphic study based on outcrop core and wireline log data documents the combined impact of cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern gulf of mexico the diverse facies and abundant data of the comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting cretaceous platform development regional cross sections across the shoreline to shelf margin profile provide a detailed record of mixed carbonate siliciclastic strata for the hauterivian to lower campanian stages ca 136 to 80 ma the study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes three second order supersequences comprised of eight composite sequences are recognized in the valanginian barremian the aptian albian and the cenomanian campanian the valanginian barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting as well as variable rates of mid ocean ridge volcanism the aptian albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b the cenomanian campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d after which the platform evolved to a deep subtidal system consisting of anoxic dysoxic shale and chalk in the time surrounding oceanic anoxic event 2 each period of oceanic anoxia is associated with composite sequence maximum flooding termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain dominated facies and shallow subtidal to intertidal environments because they are products of eustacy and global oceanographic processes the three supersequences and most composite sequences defined in the south texas passive margin are recognizable in other carbonate platforms and published eustatic sea level curves

the subglacial thermal organisation sto of ice sheets abstract this paper examines ice sheet wide variations in subglacial thermal regime and ice dynamics using the landform record exposed on the beds of former mid latitude ice sheets the laurentide cordilleran fennoscandian and british irish ice sheets we compare the landform patterns beneath these former ice sheets to the flow organisation beneath parts of the contemporary antarctic ice sheet inferred from radarsat 1 antarctic mapping project ramp data the evidence preserved in the landform record and observed on contemporary ice masses can be grouped into four major ice dynamical components that collectively define the subglacial thermal organisation sto of ice sheets these ice dynamical components are frozen bed patches ice streams ice stream tributaries and lateral shear zones frozen bed patches appear at a wide range of spatial scales spanning four orders of magnitude in some areas frozen bed zones comprise large proportions of the bed e g near the ice divide in continental areas whilst in other areas they constitute isolated islands in areas dominated by thawed bed conditions ice streams narrow zones of fast flow in ice sheets that are otherwise dominated by slow sheet flow are also common features of quaternary ice sheets tributaries to ice streams flow at velocities intermediate between full ice stream and sheet flow and may divert ice drainage from one primary ice stream corridor to an adjacent one sharp lateral boundaries between landforms indicate sliding and non sliding conditions respectively these lateral boundaries represent important discontinuities in the glacial landscape and mark the location of shear zones between thawed bed ice streams and intervening frozen bed areas we use the landform evidence in the area around great bear lake canada to trace the evolution of an ice stream web through time demonstrating that frozen bed patches are integral components of this complex system we conclude that frozen bed patches are important for the stability of ice sheets because they laterally constrain and isolate peripheral drainage basins and their ice streams

short and long term delivery rates of meteoric 10be to terrestrial soils well constrained long term average meteoric 10be deposition rates are important when meteoric 10be is used as a chronometer or tracer of earth surface processes to constrain meteoric 10be delivery to terrestrial soils we estimate time integrated 10be deposition rates from meteoric 10be inventories measured in dated soils and compare these results to a new synthesis of short term measurements of 10be in precipitation comparison of these long term rates to short term measurements suggests that short term measurements likely predict long term meteoric 10be deposition rates within uncertainties of 20 in precipitation measurements it is possible to deconvolve the contribution of atmospherically produced primary meteoric 10be from recycled meteoric 10be delivered by terrestrial dust if a second isotope is measured that quantifies either the recycled or primary components of meteoric 10be deposition we use dust concentration dependent differences between 7be and 10be measurements to make new estimates of the recycled contribution to total meteoric 10be flux delivered to the earth s surface these dust corrected data show a strong linear dependence between precipitation amount and primary meteoric 10be flux concentrations of primary meteoric 10be in mid and low latitude precipitation vary predictably by latitude between 0 63 104 and 2 05 104 atoms cm3 of precipitation providing a first order estimate of primary meteoric 10be deposition for a given latitude and precipitation rate

paleoecology of a 90 000 year lacustrine sequence from fog lake baffin island arctic canada a 137 cm sediment core from fog lake a small upland basin that was not glaciated during the late wisconsinan reveals the following stratigraphic succession i basal diamicton ii laminated silts iii compacted dewatered gyttja iv stratified minerogenic sediments and v overlying gyttja units i iii and most of unit iv were deposited prior to the holocene unit v represents approximately the last 8000 14c years alternate luminescence dating techniques tl and irsl place unit iii in latter oxygen isotope stage ois 5 74 000 years bp a suite of 20 ams 14c dates suggests that much of the post ois 5 paleoenvironmental record is characterized by either extremely low continuous sediment accumulation or by one or more episodes of more rapid sedimentation diverse pollen and spore assemblages have concentrations that are unexpectedly high throughout the pre holocene sediments 10 000 grains cm 3 by comparison to the holocene 5000 grains cm 3 exceedingly low sediment accumulation rates appear to have resulted in the concentration of atmospherically derived pollen and spores diatom assemblages record the evolution of the lake s chemistry and past algal production several abrupt changes occurred synchronously in both the terrestrial and aquatic components of the system and these appear to represent ecological responses to pre holocene climatic variability the sediments of fog lake provide the first integrated paleoecological record older than holocene for a vast region of the canadian arctic thereby refining our understanding of long term arctic ecosystem ontogeny 2000 elsevier science ltd all rights reserved

subglacial carbonates constrain basal conditions and oxygen isotopic composition of the laurentide ice sheet over arctic canada subglacially precipitated carbonate crusts spccs formed on bedrock and till boulder surfaces adjacent to the barnes ice cap bic central baffin island arctic canada act as unique archives of laurentide ice sheet basal conditions uranium series dating of these features reveals that carbonate precipitation from subglacial meltwater occurred during the last glacial maximum lgm requiring warm based ice in the region at that time however the preservation of fragile spccs is unlikely beneath erosive warm based ice suggesting that the transition to subsequent cold based conditions took place shortly after the lgm and glacial erosion in the region occurred dominantly prior to the lgm the oxygen isotopic composition of the meltwater from which the spccs precipitated is indistinguishable from that of the debris rich bic basal ice 18 o 24 referenced to vienna standard mean ocean water but distinct from that of the overlying white pleistocene ice 18 o 35 demonstrating that spccs are reliable archives of the isotopic composition of only the basal ice of past ice sheets

carbonate platform margin architecture and its influence on cambrian ordovician reef shoal development tarim basin nw china abstract six types of carbonate platform marginal slope have been identified in the cambrian ordovician of tarim basin these include a progradational carbonate ramp platform a progradational carbonate rimmed platform an aggradational rimmed carbonate platform a retrogradational rimmed carbonate platform an aggradational margin on an isolated carbonate platform and a retrogradational margin on a submerged carbonate platform various platform margin architectures and reef shoal characteristics occur in different areas of the tarim basin a progradational carbonate ramp platform margin began in the early cambrian in the tarim basin a progradational rimmed platform margin developed in the middle cambrian time in the northern tarim basin whereas contemporaneously a progradational ramp platform margin developed in the southwestern and central tarim basin a retrogradational rimmed carbonate platform developed in the northern tarim basin whereas an aggradational rimmed carbonate platform occupied the central tarim basin in the early ordovician time an aggradational margin on an isolated platform and a retrogradational margin on a submerged platform developed mainly during the late ordovician in the central tarim basin platform margin slopes migrated continually throughout the cambro ordovician the broad platform area western tarim platform that occupied most of the northwestern and central tarim basin in the early cambrian time was split by an east west oriented shelf seaway that began to develop along the eastern and western margins of the platform in the early ordovician time and completely transected the platform by late ordovician time the resultant central tarim basin platform area was much reduced elongate east west around the central tarim paleo uplift and terminated eastward towards region of the late ordovician basinal deposition across the eastern tarim basin affected by platform margin structure climate and paleodepth algal reefs and shoals developed mainly in the cambrian and intraclastic shoals developed mainly in the early ordovician followed by reef building of framestone or bafflestone in the late ordovician

steep microbial boundstone dominated plaform margins abstract seaward progradation of several kilometers has been documented mostly for leeward margin low angle carbonate slope systems with a dominant platform top sediment source however steep and high relief margins fronting deep basins can also prograde and as such are somewhat perplexing characteristics of two prograding carboniferous examples provide a model which may apply elsewhere 1 outcrops in asturias northern spain serve as important analogs for 2 hydrocarbon reservoirs in steep sided isolated platforms of the north caspian basin kazakhstan such as tengiz seismic and well data from tengiz corroborate outcrop patterns for slope development showing progradation of up to 5 and more than 10 km respectively despite the high relief up to 600 m and steep 20 35 nature of these margins the two examples share a highly productive microbial boundstone factory extending from the platform break down the slope to nearly 300 m or more depth and a lower slope dominated by mega breccias and grain flow deposits derived from the margin and slope itself the broad depth range of microbial boundstone increases the potential for production during both lowstands and high stands of sea level and thereby facilitates progradation independent from platform top derived sediment rapid in situ lithification of the boundstone provides stability to the steep slopes but also leads to readjustment through shearing and avalanching what controls the microbial cement boundstone formation remains a debate but its presence is a key factor controlling the progradational geometry of these and possibly other margins this new model of slope shedding has implications for slope readjustment processes and resulting architecture sequence stratigraphic interpretation reservoir characterization and reservoir modeling especially the isotropic character of microbial boundstone will reduce the potential for coherent seismic reflections to develop and possibly invoke under certain stress regimes shattering and fracturing thereby generating significant non matrix permeability key considerations are the contrasts with the bahamian high stand shedding depositional model slope progradation rates that range from 450 to 1500 m my and net growth rates of in situ boundstone of 1000 m my comparable to or higher than accretion rates for metazoan skeletal reef growth

the imprint of time on canadian soil landscapes abstract the imprint of time on canadian soil landscapes reflects the strong influence of repeated quaternary glaciations with most soils having formed on late pleistocene glacial sediments and to a lesser extent holocene non glacial sediments soil chronosequences in these youthful landscapes seldom span the full holocene and have been documented principally in areas of coastal isostatic uplift and shoreline evolution as well as on recessional moraine sequences in the cordillera these chronosequences have placed quantitative constraints on rates of podzolization in environments ranging from coastal temperate rainforest to subarctic longer sequences involving soils and relict paleosols on pleistocene morainal and glaciofluvial surfaces in the central yukon territory record more complex legacies of pedogenesis and landscape evolution but with much coarser time control and many potentially confounding influences of climatic change and disturbance processes older weathered bedrock and regolith can make significant contributions to soil parent materials in several settings 1 in favoured locations where local conditions protected these materials from glacial erosion in southern canada 2 beyond the maximum limits of glaciation principally in northwestern canada and 3 in the arctic where cold based non erosive ice allowed preservation of these materials closer collaborations between pedologists and other quaternary scientists will be needed to ensure a more complete understanding of these complex pedogenic legacies in canadian landscapes

rapid glacial erosion at 1 8 ma revealed by 4he 3he thermochronometry alpine glaciation and river incision control the topography of mountain ranges but their relative contributions have been debated for years apatite 4 he 3 he thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern coast mountains of british columbia canada five proximate samples require accelerated denudation of the klinaklini valley initiating 1 8 0 2 million years ago ma at least 2 kilometers of overlying rock were removed from the valley at 5 millimeters per year indicating that glacial valley deepening proceeded 6 times as fast as erosion rates before 1 8 ma this intense erosion may be related to a global transition to enhanced climate instability 1 9 ma

changes in the silt and clay size mineralogy of sediments at ocean drilling program site 645b baffin bay site 645b ocean drilling program odp leg 105 was cored in 2010 m water depth off the eastern margin of baffin island a 279 m core was dated as extending back to ca 2 ma samples of sediment were analyzed for their silt and clay size mineralogy using x ray diffraction techniques constrained cluster analysis on these data defined three units which indicated that significant changes in mineralogies occurred at approximately 75 m below sea floor bsf ca 0 5 ma and 155 m bsf ca 1 15 ma these boundaries coincide closely with units ia ib and ib ii as designated in the odp shipboard reports and which were based on detrital carbonate and sand contents unit ii 1 2 2 ma is characterized by zero clay size calcite and high amounts of clay size smectite and silt size mica unit ib 0 5 1 15 ma is noteworthy for the first presence of clay size calcite high amounts of detrital dolomite and a peak in clay size kaolinite the uppermost unit ia 0 0 5 ma is characterized by consistently high value

unequal ice sheet erosional impacts across low relief shield terrain in northern fennoscandia abstract much previous work on late cenozoic glacial erosion patterns in bedrock has focussed on mountain areas here we identify varying impacts of ice sheet erosion on the low relief bedrock surface of the fennoscandian shield and examine the geological topographical and glaciological controls on these patterns we combine gis mapping of topographical hydrological and weathering data with field observations we identify and investigate areas with similar geology and general low relief that show different degrees of ice sheet erosional impact despite similar ice cover histories on two transects with a total area of 84 000 km2 across the northern fennoscandian shield we first establish patterns of glacial erosion and then examine why glacially streamlined areas exist adjacent to areas of negligible glacial erosion the northern transect includes two areas of exceptional glacial preservation the parkajoki area in sweden and the so called ice divide zone in finland each of which preserve tors and deep saprolite covers the southern transect overlapping in the northern part with the first transect includes areas of well developed glacial streamlining with bedrock areas stripped of loose material and barely any weathering remnants for both areas we firstly present contrasting indicators for ice sheet erosional impact streamlined and non streamlined inselbergs parallel and dendritic rectangular drainage patterns and the absence and presence of neogene weathering remnants this is followed by an investigation of factors that possibly influence ice sheet erosional impact ice cover history ice cover duration and thickness bedrock type and structure and topography we find that the erosional impact of the fennoscandian ice sheet has varied across the study area distinct zones of ice sheet erosion are identified in which indicators of either low or high erosion coexist in the same parts of the transects no direct impact of rock type on glacial erosion patterns was found but an indirect control appears clear bedrock geology and long term differential weathering and tectonic evolution determined the topography of the pre glacial landscape and these topographic differences subsequently influenced ice sheet dynamics and thereby partly controlled patterns of ice sheet erosion ice cover duration and former ice thickness were not significant controls on glacial erosion patterns extensive preservation of pre glacial relief through low glacial erosion is attributed to the maintenance throughout the pleistocene of divergent flow and frozen bed conditions in the fennoscandian ice sheet in contrast glacial streamlining and strong glacial erosion were caused mainly by acceleration of flow around major obstacles and flow towards major depressions on the ice sheet bed the relatively strong ice sheet erosion towards the gulf of bothnia is the result of a combination of favourable factors bedrock structure and river valleys aligned sub parallel to ice sheet flow and convergent ice flow towards the baltic

plio pleistocene climate evolution trends and transitions in glacial cycle dynamics abstract we describe the evolution of climate system dynamics by examining the climate response to changes in obliquity and precession over the last 5 3 myr in particular we examine changes in the shape of glacial cycles and the power of obliquity and precession response in benthic 18 o when the exponential trend in 18 o variance is removed its spectral power exhibits strong proportional responses to amplitude modulations in orbital forcing over most of the plio pleistocene precession responses correlate with modulations in forcing for the last 5 myr but 41 kyr response is sensitive to obliquity modulation only before 1 4 myr where responses are sensitive to modulations in forcing we demonstrate that glacial cycles are orbitally forced rather than being self sustained or paced by orbital changes the shapes of glacial cycles have several nonlinear properties which may be indicative of glacial interglacial differences in climate sensitivity or response time the saw tooth asymmetry of glacial cycles first appears shortly after the onset of major northern hemisphere glaciation and the relative duration of interglacial stages decreases at 1 4 myr collectively trends in the shape of glacial cycles and the sensitivity of 18 o to obliquity and precession are suggestive of major transitions in climate dynamics at approximately 2 5 and 1 4 myr but show no significant change associated with the appearance of strong 100 kyr cycles during the mid pleistocene transition

subglacially precipitated carbonates record geochemical interactions and pollen preservation at the base of the laurentide ice sheet on central baffin island eastern canadian arctic the mineralogy and isotopic compositions of subglacially precipitated carbonate crusts spccs provide information on conditions and processes beneath former glaciers and ice sheets here we describe spccs formed on gneissic bedrock at the bed of the laurentide ice sheet lis during the last glacial maximum on central baffin island geochemical data indicate that the ca in the crusts was likely derived from the subglacial chemical weathering ca bearing minerals in the local bedrock c and sr isotopic analyses reveal that the c in the calcite was derived predominantly from older plant debris the 18o values of the spccs suggest that these crusts formed in isotopic equilibrium with basal ice lis preserved in the barnes ice cap bic columnar crystal fabric and the predominance of sparite over micrite in the spccs are indicative of carbonate precipitation under open system conditions however the mean 18o value of the calcite crusts is 10 higher than those of primary lis ice preserved in the bic demonstrating that spccs record the isotopic composition of only basal ice palynomorph assemblages preserved within the calcite and basal bic ice include species last endemic to the arctic in the early tertiary the source of these palynomorphs remains enigmatic

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

accumulation rates from well dated late neogene carbonate platforms and margins abstract margins of large carbonate platforms isolated platforms and atolls are dynamic settings that both generate and accumulate sediments with the exceptions of modern platforms the rates of accumulation are often poorly constrained due to inadequate or unreliable subsurface age data a compilation is here presented of well dated late neogene ice house platform and margin accumulation for the interval from 7 to 2 ma the rates are grouped according to platform type and setting sea level effects and subsidence bathymetry control are the significant influences the six settings are 1 slow aggraded platform 2 partially drowned platform 3 fast aggraded platform 4 atolls 5 prograded margin and 6 periplatform mean rates are 10 to 20 m my for slow aggraded and partially drowned platforms 20 40 m my for atolls and a fast aggraded platform 40 m my for a current dominated prograded margin and 40 110 m my for most prograded and periplatform systems the maximum rates measured from the age depth plot are generally two to three times as high the mean accumulation rates and maximum rates are primarily related to the influence of sea level and to a lesser extent regional subsidence the shallow platforms and atolls are directly sea level controlled whereas the deeper margins are sea level influenced the platform top deposits have the lowest rates of accumulation 10 26 m my due to subaerial exposure and only intermittent flooding the deeper platform margins below lowstand base level are influenced by events on the shallow platform mainly to sediment production and offbank transport slope erosion and redeposition are also important prograded margins and periplatforms accept large volumes of allochthonous sediment and can have periods of extremely high 200 m my vertical accumulation separated by intervals of non deposition erosion or sediment bypass these data despite limitations provide some basic values for ice house carbonate accumulation and the relevant extrinsic controls the late neogene rates can help constrain the sediment dynamics of the carbonate platform and flank system data especially important for calibration of computer models and for the resultant reservoir attributes

10be distribution in soils from merced river terraces california abstract the distribution and residence time of cosmogenic 10 be in clay rich soil horizons is fundamental to understanding and modelling the migration of 10 be on terrestrial sediments and in groundwater solutions we have analyzed seven profiles of clay rich soils developed from terrace sediments of the merced river california the terraces and soils of increasing age are used to compare the 10 be inventory with a simple model of accumulation decay and erosion the data show that the distribution of 10 be varies with soil horizon clay content that the residence time of 10 be in these horizons exceeds 10 5 years and that to a rough approximation the inventory of 10 be in a thoroughly sampled soil profile fits the equation n q em 1 e where q is delivery rate e is erosion rate m is the concentration of 10 be in the eroding surface layer is the decay constant and t is the age of the depositional unit from which the soil has developed the general applicability of this model is uncertain and warrants further testing in well calibrated terrace sequences

the ombrina rospo plateau apulian platform evolution of a carbonate platform and its margins during the jurassic and cretaceous abstract in this paper we analyze the jurassic and cretaceous evolution of the buried northwards stretch of the apulia platform southern italy ombrina rospo plateau orp and adjacent adriatic basin exploration wells indicate that inner platform carbonate facies across the orp in the jurassic and lower cretaceous are capped along a subaerial exposure surface by oligocene miocene carbonates a nw trending intra platform basin casalbordino corridor was infilled with shallow to deeper water sediments in the late early to late cretaceous interval while platform margins were experiencing tectonic reactivation the orp to basin transitional belt formed a corner defining a nw and a ne margin the nw margin was essentially stationary a syn and early post rift platform toe bypass wedge formed when late hettangian sinemurian extension produced the platform basin relief export of platform material coupled with a halt of faulting made the platform slope profile continuous in the late early or early middle jurassic possibly across an ooidal rim late jurassic ellipsactinia coral reefs passed downdip into bioclastics the maiolica fm displays two cycles m1 m2 where m2 onlaps the slope built by m1 in the aptian with lithospheric arching a high angle fault rejuvenated the margin off this margin a narrow basin locked between the orp and a pelagic carbonate platform was largely infilled with turbidites sourced by the orp but the high hampered the dispersal of the sand fraction the ne margin displays prograding ooidal to bioclastic clinoforms middle and upper jurassic downlapping onto the rift basin in the lower cretaceous the platform recovered after a slow down of carbonate productivity m1 2 boundary the marne a fucoidi fm thickens at the toe of and seals a fault backstepping the margin further backstepping occurred 5 km platformwards along a cenomanian normal fault producing room for a rudist factory a retreating rocky shoreline sourced breccias while downdip the shallow water facies graded into the scaglia fm basin along a ramp like profile with low angle clinoforms merging with turbidites

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

isolated stationary carbonate platforms the middle triassic ladinian of the marmolada area dolomites italy as a result of a phase of extensional tectonics in the western tethyan region a horst and graben topography formed during the middle triassic ladinian in northern italy horsts were sites of shallow water carbonate sedimentation while pelagic and volcaniclastic sediments were deposited in the grabens two carbonate platforms approximately 500 m thick can be distinguished in the marmolada area of the dolomites the marmolada platform proper which covered an area of 6 km2 and the costabella platform which extended for about 12 km in a nw se direction and was about 3 km across the facies of these isolated platforms reflect the influence of storms from the sw windward platform margins were characterized by a marine sand belt of skeletal and aggregate grainstones with a dominant platform directed cross stratification the central portions of the platforms were occupied by supratidal sand cays which are made up of storm washovers leeward parts of the platforms are composed of shallow subtidal sand flat deposits laterally discontinuous reefs chiefly composed of various calcareous algae are developed at the outer margins of the platforms along windward margins reefs may form a belt several hundred metres wide along leeward margins their width is commonly reduced to some tens of metres foreslope talus breccias surround the platforms clinoform bedding showing basinward dips of 30 40 is typical of this facies belt which is approximately 2 km wide basinal sediments only some tens of metres thick are radiolarian micrites abundant sediment gravity flow deposits expand the basinal sequence at the toes of windward margins and were probably triggered by storm return flows synsedimentary faults striking both nne ssw and nw se separate the bedded platform limestones from flank deposits and reefs they account for the stationary nature of the platforms neptunian dykes show preferred nne ssw and e w trends sinistral displacements are associated with nw se trending faults depressions in the basins filled with red turbiditic pelagic sediments show n s trends and are probably compressional in origin the structural pattern may have resulted from oblique nw se oriented extension of the e w trending middle triassic graben zone of the dolomites in the ladinian of the dolomites the stationary platform type can be distinguished from a retrograding type whereas continuously prograding platforms apparently did not develop

humidity estimate for the middle eocene arctic rain forest the exquisite preservation of fossilized metasequoia trees that grew near 808n latitude during the middle eocene ca 45 ma in nunavut canada allowed for dd and d 18 o analyses of cellulose techniques previously restricted to wood 30 000 yr old from the isotopic results we determined that the middle eocene arctic atmosphere contained 23 the water found in the region s atmosphere today this water vapor contributed to a middle eocene greenhouse effect that insulated the polar region during dark polar winters

last glacial maximum ice sheet dynamics in arctic canada inferred from young erratics perched on ancient tors along standing debate regarding the reconstruction of former ice sheets revolves around the use of relative weathering of landscapes i e the assumption that highly weathered landscapes have not been recently glaciated new cosmogenic isotope measurements from upland bedrock surfaces and erratics along the northeastern margin of the laurentide ice sheet lis shed light on this debate 10 be and 26 al concentrations from three perched erratics yielding cosmogenic exposure ages of 17 11 ka are much lower than those measured in two unmodified highly weathered tors upon which they lie which yield cosmogenic exposure ages of 60 ka these findings suggest that non erosive ice covered weathered upland surfaces along the northeastern margin of the lis during the last glacial maximum these data challenge the use of relative weathering to define the margins of pleistocene ice sheets the juxtaposition of non erosive ice over upland plateaus and erosive ice in adjacent fiords requires strong gradients in basal thermal regimes suggestive of an ice stream mode of glaciation r 2003 elsevier science ltd all rights reserved

fossil biotas from the okanagan highlands southern british columbia and northeastern washington state climates and ecosystems across an eocene landscape the late early to early middle eocene okanagan highlands fossil sites spanning 1000 km north south northeastern washington state southern british columbia provide an opportunity to reconstruct biotic communities across a broad upland landscape during the warmest part of the cenozoic plant taxa from these fossil sites are characteristic of the modern eastern north american deciduous forest zone principally the mixed mesophytic forest but also include extinct taxa taxa known only from eastern asian mesothermal forests and a small number of taxa restricted to the present day north american west coast coniferous biome in this preliminary report paleoclimates and forest types are reconstructed using collections from republic in washington state usa and princeton quilchena falkland mcabee hat creek horsefly and driftwood canyon in british columbia canada both leaf margin analysis lma and quantitative bioclimatic analysis of identified nearest living relatives of megaflora indicated uppe

ice sheet erosion and the stripping of tertiary regolith from baffin island eastern canadian arctic abstract the erosion of glaciated regions and concomitant changes in ice sheet dynamics through the pleistocene are poorly documented the baffin island landscape which has been shaped by the foxe sector of the laurentide ice sheet lis contains a variety of glacial and proximal glaciomarine sedimentary archives spanning the pleistocene we examine these records to better understand when tertiary regolith was stripped from beneath the foxe sector of the lis till on the interior plateaux of the island in areas with scoured bedrock have low chemical index of alteration cia values low meteoric 10 be 10 be met concentrations and clay mineralogy consistent with erosion from an unweathered bedrock source however in some areas in between fiord onset zones more weathered till is present containing considerably higher cia values high 10 be met concentrations and secondary clay mineral weathering products implying that the till has persisted on the landscape and weathered during successive glaciations using these weathering signatures we analyze the coastal glaciogenic deposits of the clyde foreland formation cff at two sites for evidence of tertiary regolith removal from the interior of baffin island by lis erosion provenance indicators within the cff demonstrate that pleistocene lis ice flow lines across baffin island have remained generally constant the oldest cff glaciogenic unit likely representing one of the first if not the first lis advances across baffin island had high 10 be met concentrations at the time of deposition consistent with extensive regolith erosion evidence of notably weathered sediment is absent in all younger units suggesting that tertiary regolith was likely largely stripped from the interior of the island by 1 6 0 2 ma

a 600 year annual 10be record from the ngrip ice core greenland understanding the link between the sun and climate is vital in the current incidence of global climate change and 10be in natural archives constitutes an excellent tracer for this purpose as cosmic rays enter the atmosphere cosmogenic isotopes like 10be and 14c are formed variations in solar activity modulate the amount of incoming cosmic rays and thereby cosmogenic isotope production atmospherically produced 10be enters natural archives such as sediments and glaciers by wet and dry deposition within about a year of production 10be from natural archives therefore provides information on past solar activity and because these archives also contain climate information solar activity and climate can be linked one remaining question is to what degree 10be in natural archives reflects production and to what extent the local and regional environment overprints the production signal to explore this 10be was measured at annual resolution over the last 600 years in a greenland ice core measurement potentials for these samples benefited from the development of a new laboratory method of co precipitating 10be with niobium to diversify geographic location and archive media type a pioneer study of measuring 10be with annual resolution in varved lake sediments from finland was conducted with samples from the entire 20th century pathways of 10be into lake sediments are more complex than into glacial ice inferring that contemporary atmospheric conditions may not be recorded here it is shown for the first time that tracing the 11 year solar cycle through lake sediment 10be variations is possible results also show that on an annual basis 10be deposition in ice and sediment archives is affected by local environmental conditions on a slightly longer timescale however diverse 10be records exhibit similar trends and a negative correlation with solar activity cyclic variability of 10be deposition persisted throughout past grand solar minima when little or no sunspot activity was recorded 10be levels indicate that although solar activity has been high during the 20th century levels are not unprecedented in the investigated 600 years aerosol 10be 7be values indicate possible influence of stratosphere troposphere exchange on isotope abundance and the production signal

meteoric 10be in soil profiles a global meta analysis abstract in order to assess current understanding of meteoric 10 be dynamics and distribution in terrestrial soils we assembled a database of all published meteoric 10 be soil depth profiles including 104 profiles from 27 studies in globally diverse locations collectively containing 679 individual measurements this allows for the systematic comparison of meteoric 10 be concentration to other soil characteristics and the comparison of profile depth distributions between geologic settings percent clay 9 be and dithionite citrate extracted al positively correlate to meteoric 10 be in more than half of the soils where they were measured but the lack of significant correlation in other soils suggests that no one soil factor controls meteoric 10 be distribution with depth dithionite citrate extracted fe and cation exchange capacity are only weakly correlated to meteoric 10 be percent organic carbon and ph are not significantly related to meteoric 10 be concentration when all data are complied the compilation shows that meteoric 10 be concentration is seldom uniform with depth in a soil profile in young or rapidly eroding soils maximum meteoric 10 be concentrations are typically found in the uppermost 20 cm in older more slowly eroding soils the highest meteoric 10 be concentrations are found at depth usually between 50 and 200 cm we find that the highest measured meteoric 10 be concentration in a soil profile is an important metric as both the value and the depth of the maximum meteoric 10 be concentration correlate with the total measured meteoric 10 be inventory of the soil profile in order to refine the use of meteoric 10 be as an estimator of soil erosion rate we compare near surface meteoric 10 be concentrations to total meteoric 10 be soil inventories these trends are used to calibrate models of meteoric 10 be loss by soil erosion erosion rates calculated using this method vary based on the assumed depth and timing of erosional events and on the reference data selected

glacial variability over the last two million years an extended depth derived agemodel continuous obliquity pacing and the pleistocene progression abstract an agemodel not relying upon orbital assumptions is estimated over the last 2 ma using depth in marine sediment cores as a proxy for time agemodel uncertainty averages 10 ka in the early pleistocene 2 1 ma and 7 ka in the late pleistocene 1 ma to the present twelve benthic and five planktic 18 o records are pinned to the agemodel and averaged together to provide a record of glacial variability major deglaciation features are identified over the last 2 ma and a remarkable 33 out of 36 occur when earth s obliquity is anomalously large during the early pleistocene deglaciations occur nearly every obliquity cycle giving a 40 ka timescale while late pleistocene deglaciations more often skip one or two obliquity beats corresponding to 80 or 120 ka glacial cycles which on average give the 100 ka variability this continuous obliquity pacing indicates that the glacial theory can be simplified an explanation for the 100 ka glacial cycles only requires a change in the likelihood of skipping an obliquity cycle rather than new sources of long period variability furthermore changes in glacial variability are not marked by any single transition so much as they exhibit a steady progression over the entire pleistocene the mean variance skewness and timescale associated with the glacial cycles all exhibit an approximately linear trend over the last 2 ma a simple model having an obliquity modulated threshold and only three adjustable parameters is shown to reproduce the trends timing and spectral evolution associated with the pleistocene glacial variability

felsenmeer persistence under non erosive ice in the torngat and kaumajet mountains quebec and labrador as determined by soil weathering and cosmogenic nuclide exposure dating soil analyses and terrestrial cosmogenic nuclide exposure dating are combined and a conceptual model proposed to explain altitudinal weathering contrasts in high latitude highlands we show that summits in the torngat and kaumajet mountains were covered by ice during the last glacial maximum and that their felsenmeer cover probably survived multiple glaciation events for similar lithologies soils on felsenmeer covered summits are signigicantly more weathered than those below the felsenmeer limit displaying higher concentrations of crystalline iron amorphous aluminium and silicium extracted with oxalate secondary minerals such as gibbsite and kaolinite occur in felsenmeer soils whereas those formed in till lacked these secondary minerals 10be and 26al exposure ages for nine of ten samples from high elevation tors and autochthonous felsenmeer blocks range from 73 6 to 157 15 ka by contrast ages of 11 4 1 0 and 11 7 1 0 ka are measured for bedrock in the much lower saglek zone indicating extensive 3 m glacial erosion of this zone during late wisconsinan glaciation 26al 10be ratios demonstrate that exposure of the high elevation surfaces was interrupted during at least one cosmic ray shielding event by either ice or till cover in either case late wisconsinan glaciers could not have extensively eroded these surfaces five erratics dated above the saglek zone including one in the felsenmeer zone have exposure ages ranging from 11 6 1 0 to 13 6 0 7 ka this indicates that valley and high elevation ice persisted through the younger dryas chron and provides further evidence that the highlands were not nunataks during the late wisconsinan period

arctic north american seasonal temperatures from the latest miocene to the early pleistocene based on mutual climatic range analysis of fossil beetle assemblages late tertiary and early quaternary fossil beds in the arctic regions of north america have yielded abundant well preserved remains of plants and arthropods documenting the existence of coniferous forests in the high arctic latitudes nearly all of the beetle coleoptera specimens in these fossil assemblages represent extant species we have applied the mutual climatic range mcr method of paleotemperature analysis to fossil beetle assemblages from 11 sites to estimate mean summer t max and winter t min temperatures we found that arctic t min values during the latest miocene and pliocene were substantially warmer than they are today the mcr estimates therefore support the scenario derived from the paleobotanical data namely that arctic pliocene climates were far less continental several pliocene age assemblages from the high arctic yielded t max estimates 9 10 c warmer than modern values at the sites this is the same degree of warming required to allow coniferous forests to grow in the high arctic by 3 million years bp a cooling trend is marked in the paleobotanical and fossil beetle evidence from alaska all assemblages dating between 5 7 and 2 million years bp yielded calibrated t max values between 12 4 and 13 8 c regardless of location thus the insect fossil data support the theory that there was far less latitudinal gradation in temperatures during the late pliocene than there is today our reconstructions suggest regional climatic cooling especially winter temperatures began by at least 2 million years bp

timing and significance of maximum and minimum equatorial insolation variations in summer insolation at high northern latitudes on a timescale of 100 ka are very small thus a common belief is that the pronounced 100 ka glacial cycles are not directly linked to the very weak 100 ka insolation periodicity here we show analytically and numerically that the annual maximum and minimum of daily equatorial insolation has pronounced eccentricity periodicities with timescales of 400 ka and 100 ka as well as a pronounced half precession periodicity with timescale of 11 ka the timing of the maximum and minimum annual equatorial insolation may change around the equinoxes solstices alternating between the vernal and autumnal equinoxes summer and winter solstices where the time of the maximum minimum equatorial insolation may occur up to more than 1 month from the equinoxes solstices we also show that when considering the mean insolation of periods larger than 1 d the 11 ka periodicity becomes less dominant and it vanishes when the averaging period is half a year for the later case the maximum minimum may occur for any day in the annual cycle the maximum equatorial insolation may alter the timing and amplitude of the maximum surface temperature of the summer hemisphere and in this way may drastically affect the hadley circulation changes in hadley circulation affect the heat and moisture transport from low to high latitudes affecting the buildup of the high latitude northern hemisphere ice sheets

morphological indicators of structural control relative sea level fluctuations and platform drowning on present day and miocene carbonate platforms abstract the morphology of carbonate platforms may be influenced by tectonic activity and eustatic variations 3d seismic data and satellite imagery are used in order to investigate the morphological similarities between present day carbonates platforms east of borneo island and miocene carbonate platforms of the south china sea the morphological similarities exhibit platform fragmentation that could be caused by subtle faulting sufficient to drown reef rims platform contraction which is a result of back stepping of the reef margin during a relative sea level rise and polygonal patterns in internal lagoons described as mesh reefs in modern platforms and possibly interpreted as karst in miocene platforms vertical movements may trigger the formation of new geomorphological conditions that modify the distribution of coral growth with respect to the new hydrodynamic conditions in space and time these movements uplift and tilting reduce and localize the space necessary for the coral ecosystem explaining the contraction leading to drowning of parts of and ultimately the whole platform

large scale instabilities of the laurentide ice sheet simulated in a fully coupled climate system model 1 heinrich events related to large scale surges of the laurentide ice sheet represent one of the most dramatic types of abrupt climate change occurring during the last glacial here using a coupled atmosphere ocean biosphereice sheet model we simulate quasi periodic large scale surges from the laurentide ice sheet the average time between simulated events is about 7 000 yrs while the surging phase of each event lasts only several hundred years with a total ice volume discharge corresponding to 5 10 m of sea level rise in our model the simulated ice surges represent internal oscillations of the ice sheet at the same time our results suggest the possibility of a synchronization between instabilities of different ice sheets as indicated in paleoclimate records index terms 1827 hydrology glaciology 1863 1620 global change climate dynamics 3309 3344 meteorology and atmospheric dynamics paleoclimatology 5416 planetology solid surface planets glaciation citation calov r a ganopolski v petoukhov m claussen and r greve largescale instabilities of the laurentide ice sheet simulated in a fully coupled climate system model geophys res lett 29 24 2216 doi 10 1029 2002gl016078 2002

slope sedimentation associated with a vertically building shelf bone spring formation mescalero escarpe field southeastern new mexico mescalero escarpe field contains slope strata in the bone spring formation which provide insight into development of the northwestern shelf to the north and the delaware basin to the south during the leonardian permian the northwestern shelf grew vertically due to regional subsidence and cyclic sedimentation slope facies include 1 dolomitized peloid bioclast packstone 2 dolomite megabreccia 3 laminated dolomitic mudstone and 4 very fine grained sandstone oil is produced from peloid bioclast packstones and megabreccias stratigraphic relationships indicate carbonate sedimentation in slope and basinal environments contemporaneous with carbonate sedimentation on the shelf peloid bioclast packstones overlain by megabreccias are present at the toe of slope and dolomitic mudstones occur higher on the slope and deeper in the basin basinal sandstones are present between those carbonate strata seismic data show erosion and backstepping of the shelf margin correlative with megabreccia deposition at the toe of slope lithologic and stable isotope data suggest that erosion of the shelf took place in sea water depositional cycles are related to sea level cycles 1 during rapid sea level rises the shelf was flooded and carbonate sedimentation initiated sediment swept off the shelf formed peloid bioclast packstones at the toe of slope and dolomitic mudstones in other slope and basinal environments 2 as sea levelmore rise slowed or stopped the shelf approached sea level the shelf margin was eroded and debris flows transported eroded detritus to the toe of slope and megabreccias formed deposition of carbonate mud continued in adjacent environments 3 when sea level stayed still or dropped the shelf was at sea level or emergent and terrigenous sand was transported into the basin less

erosion rates in fennoscandia during the past million years abstract the widespread existence of cosmogenic nuclides accumulated in bedrock prior to the last glaciation demonstrates the limited erosional efficacy of the most recent fennoscandian and laurentide ice sheets yet the deeper history of erosion in these landscapes repeatedly blanketed by ice remains essentially unknown here we present the first comprehensive ice sheet wide analysis of cosmogenic 10be data n 953 from the fennoscandian landscape we find 64 of all sampled bedrock surfaces contain 10be inheritance including 85 of blockfields and tors and 50 of ice carved terrain in addition to 27 of ice transported boulders recent ice sheets scoured landscapes well beyond glacial troughs and nuclide inventories reveal a patchy legacy of erosional effectiveness that diminishes at high elevations such that 89 n 55 of bedrock samples retain inheritance above 1600 m we exploit this widespread nuclide inheritance in a markov chain monte carlo based inversion model to estimate long term erosion rates and surface exposure histories from 113 paired 10be 26al bedrock samples nuclide inventories with or without inheritance convey equally important information about the erosional effectiveness of the last ice sheet we define cosmogenic nuclide memory as the residence time of bedrock samples inside the nuclide production window 2 m depth where 80 of the total nuclide production occurs the cosmogenic nuclide memory is set by mean erosion rate and varies from 10 ka for samples eroded 2 m during the last glaciation to 1 ma for the slowest erosion rates we find that mean erosion rates are well constrained compared to the ratio of exposure to burial the inclusion of bedrock erosion in our computations thwarts the capacity to constrain surface exposure history or identify former nunataks from paired 10be 26al data ice carved surfaces reflect diverse erosion histories that are not straightforward to interpret from surficial morphology alone relative to the 10 mm kyr benchmark for polar ice masses we report point based mean erosion rates that vary by more than three orders of magnitude with glacial troughs and areal scour terrain eroding at 1 to 100 mm kyr blockfields at 0 8 16 mm kyr and tors at 0 8 7 7 mm kyr 5th 95th percentiles

wisconsinan refugia and the glacial history of eastern baffin island arctic canada coupled evidence from cosmogenic isotopes and lake sediments new data constrain the timing and character of glaciation of eastern baffin island arctic canada lake sediments radiocarbon dated to between 14 and 52 ka coupled to 10 be and 26 al exposure ages 35 ka from adjacent moraines and bedrock demonstrate that some coastal uplands remained above the limits of continental glaciation throughout oxygen isotope stage 2 at lower elevations exposure ages from a flight of distinct lateral moraines range from 10 to 35 ka and imply that low gradient outlet glaciers reached the outer coast during the late wisconsinan collectively these results reconcile terrestrial evidence for the presence of ice free refugia through the late wisconsinan with marine evidence for extensive outlet glaciers in the major fiords and bays of eastern baffin island

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

facies architecture and high resolution sequence stratigraphy of an upper cretaceous platform margin succession southern central pyrenees spain abstract excellent exposures of upper cretaceous santonian carbonate platforms on the northern flank of sant corneli anticline southern central pyrenees provide detailed information of facies architecture in both depositional strike and dip directions basic accretional units are differentiated by facies contrast across mappable surfaces these surfaces do not show clear evidence of subaerial erosion and are correlated basinward with bedding planes across which there are subtle changes in skeletal composition two types of basic accretional units have been identified based on bedding patterns internal facies architecture and skeletal composition 1 rudist buildups consist of a rudist and coral belt at the platform margin passing landward into a slender hippuritid lithosome locally overlain by a bioclastic blanket that passes basinward into bioclastic apron like clinobeds and into fine grained packstone wackestone 2 calcarenite wedges consist of yellow brown benthic foraminifer rich grainstones to grain dominated packstones with scattered rudist shells and small coral colonies passing basinward into mud dominated packstones to wackestones with variable siliciclastic content quartz sand to silt and clay rudist buildups and calcarenite wedges alternate although not rhythmically these changes in platform skeletal composition reflect changes in the dominant type of carbonate producing biota independently of the changes in accommodation both types of basic accretional units rudist buildups and calcarenite wedges form simple sequences and parasequences according to internal lithofacies arrangement and inferred sea level cyclicity cycles or paracycles high frequency sea level cyclicity fits in the milankovitch frequency band long term changes in accommodation governing aggradation progradation and backstepping of basic sequences and parasequences reflect tectonic influence rather than long term changes in eustatic sea level

absolute chronology for major pleistocene advances of the laurentide ice sheet we used a 26 al 10 be burial isochron method to date the glacial stratigraphic section in missouri usa that records the largest advances of the laurentide ice sheet this permits an improved comparison of terrestrial and marine records of glaciation the first recorded advance of the laurentide ice sheet reached 39 n near the extreme southern limit of north american glaciation 2 4 ma the next advance to this latitude took place near the beginning of the mid pleistocene transition 1 3 ma and three more took place from 0 75 to 0 2 ma there is no evidence that the laurentide ice sheet advanced south of 45 47 n between 2 4 and 1 3 ma this chronology 1 shows that north american continental glaciation postdated cordilleran alpine glaciation 2 is consistent with the hypothesis that both of these events were threshold responses to tropical cooling 3 is consistent with the hypothesis that the first advance of the laurentide ice sheet was glaciologically anomalous due to the presence of deformable preglacial regolith 4 is not consistent with the hypothesis that this deformable regolith persisted until the mid pleistocene transition and 5 indicates that the increase in global ice volume at the mid pleistocene transition was at least in part the result of a more extensive laurentide ice sheet

wisconsin and holocene δ18o variations barnes ice cap canada new 18o measurements on ice samples from barnes ice cap show a relatively large shift from about 23 in the blue ice that makes up the bulk of the ice cap to 38 in a basal layer of clean white ice this strongly suggests that the latter is of pleistocene age thus confirming an earlier interpretation based on less comprehensive data the shift between the pleistocene and holocene ice is attributed in part to the change in climate at the end of the pleistocene and in part to a decrease in elevation of the accumulation area of 700 m beneath the clean white ice there is a layer of dirty white ice with less negative 18o values this ice is believed to have been deposited during a climatically warm period in early to middle wisconsin time in addition however the less negative 18o values in it are in part attributed to fractionation at a time in the past when the basal ice was at the melting point and some of the water produced by pressure melting was lost through a permeable bed

plio pleistocene ice volume antarctic climate and the global δ18o record we propose that from 3 to 1 million years ago ice volume changes occurred in both the northern and southern hemispheres each controlled by local summer insolation because earth9s orbital precession is out of phase between hemispheres 23 000 year changes in ice volume in each hemisphere cancel out in globally integrated proxies such as ocean 18 o or sea level leaving the in phase obliquity 41 000 years component of insolation to dominate those records only a modest ice mass change in antarctica is required to effectively cancel out a much larger northern ice volume signal at the mid pleistocene transition we propose that marine based ice sheet margins replaced terrestrial ice margins around the perimeter of east antarctica resulting in a shift to in phase behavior of northern and southern ice sheets as well as the strengthening of 23 000 year cyclicity in the marine 18 o record

response of planktic foraminiferal size to late quaternary climate change 1 geographical size distribution within entire holocene foraminiferal assemblages is related to global environmental gradients such as temperature primary productivity and environmental variability this study demonstrates that these correlations are also recognizable in late quaternary assemblages from three locations in the south atlantic on temporal and latitudinal scales the size response to temporal paleoenvironmental changes during glacial interglacial cycles mimics the geographic holocene size variability the amplitude of size variability is directly related to the amplitude of the climatic fluctuations as shown by the stable size temperature relationship over time the documented changes in the assemblage size are caused by species replacement and intraspecific size variability the relative importance of these processes depends on the environmental setting species have been shown to reach their maximum size and abundance under certain optimum conditions and decrease in size if environmental conditions differ from these optima we confirm that late quaternary species sizes were largest at paleotemperatures identical to holocene ones

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

late cenozoic deep weathering patterns on the fennoscandian shield in northern finland a window on ice sheet bed conditions at the onset of northern hemisphere glaciation abstract the nature of the regolith that existed on the shields of the northern hemisphere at the onset of ice sheet glaciation is poorly constrained in this paper we provide the first detailed account of an exceptionally preserved deeply weathered late neogene landscape in the ice sheet divide zone in northern finland we mine data sets of drilling and pitting records gathered by the geological survey of finland to reconstruct regional preglacial deep weathering patterns within a gis framework using a large geochemical data set we give standardised descriptions of saprolite geochemistry using a variant of the weathering index of parker wip as a proxy to assess the intensity of weathering we also focus on mineral prospects and mines with dense pit and borehole data coverage in order to identify links between geology topography and weathering geology is closely linked to topography on the preglacial shield landscape of northern finland and both factors influence weathering patterns upstanding resistant granulite granite gabbro metabasalt and quartzite rocks were associated with fresh rock outcrops including tors or with thin fines values above 3000 and 4000 beneath valley floors developed along mineralised shear and fracture zones weathering penetrated locally to depths of 50 m and included intensely weathered kaolinitic clays with wip fines values below 1000 late neogene weathering profiles were varied in character tripartite clay gruss saprock profiles occur only in limited areas bipartite gruss saprock profiles were widespread with saprock thicknesses of 10 m weathering profiles included two discontinuities in texture materials and resistance to erosion between saprolite and saprock and between saprock and rock limited core recovery when drilling below the soil base in mixed rocks of the tana belt indicates that weathering locally penetrated deep below upper fresh rock layers such deep seated weathered bands in rock represent a third set of discontinuities incipient weathering and supergene mineralisation also extended to depths of 100 m in mineralised fracture zones the thin weathering crusts found extensively beneath till may represent types of early or middle pleistocene palaeosols we confirm that glacial erosion has been very limited

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

quaternary glacial and marine stratigraphy of the qivitu peninsula northern cumberland peninsula baffin island canada summary sediments exposed along the outer coast of the qivitu peninsula record the advances and retreats of glaciers in the fiords bordering the peninsula and accompanying sea level fluctuations during the quaternary seven main lithofacies and 21 subfacies are recognized based on texture color bed thickness and lateral extent internal structures and abundance of macrofossils in contrast to earlier work in the area the interpretation of lithofacies genesis using a model of fiord glaciomarine sedimentation suggests that all lithofacies are of marine or glaciomarine origin with no evidence of grounded ice extending seaward of the peninsula the abundance and diversity of benthic foraminifera in selected samples and in situ subarctic molluscs shows that relatively warm water was present along the east baffin island coast during several periods of extensive fiord glaciers analysis of upward facies transitions in 54 stratigraphic sections suggests that facies sequences are cyclical these sedimentation cycles are interpreted in terms of glacier sea level responses during glacial interglacial cycles detailed relative time control for the lithofacies sequence is provided by time dependent amino acid ratios on the common shell fragments in many stratigraphic units because the stratigraphic sequence is marked by significant unconformities due to relative sea level regressions near the end of each glacial sedimentation cycle amino acid ratios on molluscs contemporaneous with particular cycles are statistically similar and distinct from ratios for older and younger cycles thus although few stratigraphic units can be physically traced for more than 0 5 km aminozones based on groups of animo acid ratios allow chronocorrelation and relative dating of units in each sedimentation cycle the qivitu stratigraphic sequence is divided into two formations consisting of a total of seven members for which formal names are proposed sediments predating the two most recent interglacials are lithologically similar to later beds suggesting that events during these earlier periods were of the same character as those of later glacial interglacial cycles biostratigraphic evidence suggests that a relatively mild climate prevailed in this region during the clyde and ayr lake glaciations and intervening cape broughton aquatherm the quajon interstade is correlative with the marine sediments deposited near the end of the ayr lake glaciation rather than the cape broughton aquatherm soil horizons indicate regressions at the end of the cape broughton aquatherm and ayr lake glaciation and pollen assemblages suggest that the terrestrial climate may have been warmer than the present climate a reinterpretation of u series dates and amino acid ratios on shells suggests that the cape broughton aquatherm and earlier events predate marine oxygen isotope substage 5e the ayr lake glaciation may have occurred well before the major interglacial glacial transition in more temperate latitudes but evidence from ocean cores in the north atlantic and ice cores from greenland and devon island supports the interpretation of warm water incursions into baffin bay during this ice advance following substage 5e by inference relative sea level during the period following the ary lake glaciation was lower than present sea level and glacier extent was restricted no evidence of an exceptionally cold dry climate has been found however distal glaciomarine sediments in the upper coastal cliffs suggest a limited readvance of fiord glaciers prior to the holocene near the beginning of the holocene 10 000 yr b p warmer water extended into the area as relative sea level fell and subsequently rose again to 15 m about 8 200 yr b p pollen assemblages in peat horizons suggest that during the earliest holocene a climate milder than that of the present day existed local deposition of eolian and soliflucted sediment may indicat deteriorating climate in late holocene time

quaternary relief generation by polythermal glacier ice the juxtaposition of wet based erosive ice in valleys and cold based non erosive ice atop felsenmeer covered interfluve plateaus has generated relief in the torngat mountains of northeastern canada measurements of in situ terrestrial cosmogenic nuclide tcn concentrations from 31 bedrock sites coupled with soils and geomorphology indicate that erosion of the valleys has been 2 m during a single glacial interglacial cycle however on summit plateaus the long term over several glacial interglacial cycles erosion rate is 1 4 m ma 1 tcn ratios reveal that the exposure plus ice cover history retained on some summit surfaces probably spans more than 800 ka despite complete ice cover as recently as 11 ka a thermodynamic ice sheet model with a basal water calculation is used to calculate the sliding distance normalized by the duration of ice cover for the region we formulate a general glacial erosion rule for the torngat mountains which correlates tcn derived erosion rates for terrain once partially covered by cold based ice with modelled average ice basal sliding velocities erosion rates vary linearly with average sliding velocity by a glacial erosion coefficient of 5 10 7 due to the significant distribution of cold based ice cover in this high latitude region our estimates of net regional glacial erosion and glacial erosion coefficient are orders of magnitude lower than a previously published value copyright 2005 john wiley sons ltd

the late quaternary glaciations as the response of a three component feedback system to earth orbital forcing abstract a climatic feedback system previously described consisting of three prognostic nonlinear equations governing the mass of ice sheets the mass of marine and continental marginal ice and the mean ocean temperature is forced by a representation of the effects of external earth orbital variations with reasonable amplitudes for the eccentricity obliquity and precession forcing the free oscillatory solutions of major period near 100 kyr can be modified in a way that substantially agrees with the 18o derived observations of ice mass evolution in particular a proper structure variance spectrum and phase lock of the major variations are obtained over the last 400 kyr an analysis of the sensitivity of these results to variations in the model parameters and to random perturbations shows that the solution is robust for small changes in all but a few of the equation coefficients concomitant variability in the marine ice mass ocean temperature and net radiation at the top of the atmospher

estimate of three dimensional flexural isostatic response to unloading rock uplift due to late cenozoic glacial erosion in the western united states alpine glacial erosion may strongly influence mountain building through erosionally driven rock uplift and relief production in this paper i use a three dimensional model for the flexural isostatic response of the lithosphere to estimate the potential for late cenozoic erosionally driven rock uplift in the western united states specifically i present a map of the ratio of erosionally driven rock uplift to glacial erosion for this region this ratio depends on the magnitude of the flexural bending stresses that act to limit differential uplift the map is created by constraining the extent of pliocene quaternary alpine glacial erosion in the western united states and solving the three dimensional flexure equation for the resulting lithospheric deflection the map indicates that the magnitude of erosionally driven uplift depends sensitively on the size of the glaciated range and the presence of nearby glaciated ranges as a result regional scale patterns must be considered in order to correctly estimate local amounts of erosionally driven rock uplift the ranges in the western united states with the greatest ratios of uplift to erosion are the san juan mountains and the yellowstone plateau absaroka range because these are extensively glaciated and have glaciated ranges nearby in contrast the wind river range and sierra nevada have ratios of uplift to erosion that are only half as large these results identify which ranges likely underwent the greatest erosionally driven uplift and relief production and provide a widely applicable technique for modeling the flexural isostatic response to loading and unloading in three dimensions

simulating the mid pleistocene transition through regolith removal abstract quaternary 18o ice volume proxy records show a transition from high frequency small amplitude glacial cycles to low frequency large amplitude glacial cycles this reorganization of the climate system termed the mid pleistocene transition mpt is thought to reflect a change in land ice response to orbital forcing despite no significant change in orbital cycles during this period one potential explanation for the mpt proposes that gradual erosion of high latitude northern hemisphere regolith by multiple cycles of glaciation caused a transition in ice sheet response to external forcing here we explore this regolith hypothesis using a complex earth system model we show that simulating a transition from deformable sediment to crystalline bedrock produces an evolution in ice volume response similar to proxy reconstructions of the mpt the simulated change in ice volume response is due to a combination of climate and ice flow changes with crystalline bedrock producing thicker colder ice sheets that accumulate more snowfall and have a smaller ablation zone further experiments that include transient eccentricity amplifying co2 forcing show only small differences in ice response compared to those with orbital forcing only suggesting that cycles of co2 were not the primary cause of the mpt

selective glacial erosion on the norwegian passive margin glaciated passive margins display dramatic fjord coasts but also commonly retain plateau fragments inland it has been proposed recently that such elevated low relief surfaces on the norwegian margin are products of highly efficient and extensive glacial and periglacial erosion the glacial buzzsaw operating at equilibrium line altitudes elas we demonstrate here that glacial erosion has acted instead to dissect plateaus in western norway low relief surfaces are not generally spatially associated with cirques and do not correlate regionally with modern and last glacial maximum elas glacier dynamics require instead that glacial erosion is selective with low relief surfaces representing islands of limited pleistocene erosion deep glacial erosion of the coast and inner shelf has provided huge volumes of sediment 70 000 km3 largely resolving apparent mismatches 65 100 000 km3 between fjord and valley volumes and pliocene pleistocene sediment wedges offshore nonetheless as pleistocene glacial valleys and cirques are cut into preexisting mountain relief tectonics rather than isostatic compensation for glacial erosion have been the main driver for late cenozoic uplift on the norwegian passive margin

on the mid pleistocene transition to 100 kyr glacial cycles and the asymmetry between glaciation and deglaciation times 1 a mechanism is proposed for the mid pleistocene transition from a dominant periodicity of 41 kyr to 100 kyr in glacial oscillations the same mechanism is shown to also explain the asymmetry between the long glaciation and short deglaciation phases of each cycle since that transition versus the symmetry of the 41 kyr oscillations prior to the transition these features arise naturally within the framework of the sea ice switch glacial cycle mechanism of gildor and tziperman 2000 as a result of the gradual cooling of the deep ocean during the pleistocene this cooling results in a change of the relation between atmospheric temperature and the rates of accumulation and ablation of continentals ice sheets it is this latter change that leads to the activation of the sea ice switch and therefore to the initiation of the 100 kyr oscillations the gradual glaciation and rapid deglaciations during these oscillations occur because the mean value of the ice sheet ablation is not far from the maximum rate of snow accumulation during warm periods this proximity of mean ablation and maximum accumulation rates is shown to be also a consequence of the mid pleistocene gradual cooling of the deep ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 1620 global change climate dynamics 3309 1640 global change remote sensing 4267 oceanography general paleoceanography keywords climate dynamics glacial cycles mid pleistocene transition 100 kyr 41 kyr

the goldilocks dilemma big ice little ice or just right ice in the eastern canadian arctic our conceptions of the ne sector of the laurentide ice sheet lis at the last glacial maximum lgm have evolved through three major paradigms over the past 50 years until the late 1960s the conventional view was that the eastern canadian arctic preserved only a simple deglacial sequence from a lis margin everywhere at the continental shelf edge flint paradigm glacial geologic field studies began in earnest in this region in the early 1960s and within the first decade field evidence documenting undisturbed deposits predating the lgm led a pendulum swing to a consensus view that large coastal stretches of the eastern canadian arctic remained free of actively eroding glacial ice at the lgm and that the most extensive ice margins occurred early in the last glacial cycle this minimalist paradigm dominated until the late1980s when an expanded data set from shallow marine studies indicated lgm ice at least locally reached the continental shelf within the past decade the marine data coupled with new evidence from lake sediments and cosmogenic exposure dates on moraines and glaciated terrain in the eastern canadian arctic has led to a new paradigm that better reconciles the terrestrial and marine evidence collectively these lines of evidence indicate that all of southern baffin island was glaciated at the lgm but that some coastal uplands north of cumberland sound remained above the limit of actively eroding glacial ice even though outlet glaciers reached the continental shelf in front of most fiords and sounds the most plausible explanation for the observed glacial limits is that low gradient relatively fast moving outlet glaciers sliding on deformable sediments occupied marine embayments and fiords contrasting with slower moving ice frozen to its bed on the intervening crystalline terrain slow moving ice frozen to its bed would have had steeper surface gradients hence would have terminated inland from the coast this scenario is consistent with observations indicating high elevation coastal terrain remained unglaciated even though outlet glaciers reached the continental shelf lgm summer temperatures were apparently much lower than present as lakes in the ice free regions were permanently frozen

clay mineralogy chemical weathering and landscape evolution in arctic alpine sweden abstract the purpose of this research was to 1 characterize the clay mineralogy of soils in and adjacent to karkevagge a recently deglaciated valley in arctic sweden 2 document chemical weathering in a periglacial environment and 3 use the mineralogy to help explain landscape evolution soil samples were analyzed from 11 sites that differ in elevation parent material drainage slope and vegetation parent materials include residuum alluvium colluvium and glaciofluvial material derived from garnet mica schist plus in one locality a till of granitic origin x ray diffraction xrd was used to characterize the clay size fraction

permeability distribution and scaling in multi stages carbonate damage zones insight from strike slip fault zones in the tarim basin nw china abstract architecture and permeability of fault damage zones are important for understanding faulting mechanisms and fluid flow in fractured rocks nevertheless this understanding is often hindered by limited availability of data especially in the subsurface a comprehensive suite of cores logs and production data is here presented to unravel petrophysical properties and fracture characteristics of deep 6000 m ordovician limestones within strike slip fault zones of the tarim intracratonic basin nw china the results show that 1 the carbonate porosity is mainly secondary dissolution porosity and comprises low porosity 5 md and high porosity 8 2 fault damage zones are generally tight with fracture aperture

insights into the late cenozoic configuration of the laurentide ice sheet from 40ar 39ar dating of glacially transported minerals in midcontinent tills glacial sedimentary sequences in the north central united states record multiple advances of the laurentide ice sheet lis since 2 ma although the tills found in these sequences were deposited by southward flowing glacial lobes little information is available on the geometry of flow lines in the interior of the lis during any one glaciation and the provenance of glacial deposits older than the last ice advance is largely unknown systematic changes in the composition of midcontinent tills and other paleogeographic considerations however raise the possibility of significant shifts in the trajectory of flow lines feeding the lobes of the southwestern lis margin here we constrain till provenance using 40ar 39ar ages of individual hornblende and feldspar grains retrieved from tills representing several glaciations since 2 ma hornblende grains show 40ar 39ar ages that indicate erosion of paleoproterozoic 1 7 2 0 ga and late archean 2 5 ga rock sources whereas feldspar grains show a broad range of paleoproterozoic ages 1 4 2 4 ga dating of hornblende and feldspar minerals in single pebbles suggests that this latter distribution of ages is related to the greater sensitivity of feldspars to thermal resetting during minor tectonic events accordingly the range of 40ar 39ar ages for the predominant population of paleoproterozoic hornblende and feldspar grains in our samples is consistent with a source from terrains forming the churchill province of the canadian shield while the small population of archean age grains likely reflects a source from the southwestern tip of the archean superior province that crops out near the study area these results indicate that midcontinent tills were deposited by ice derived from the northwestern keewatin sector of the lis the nearly identical distribution of hornblende and feldspar ages in the till samples identifies the keewatin ice dome and the related ice flow to the midcontinent as long standing features of the lis throughout the late pliocene pleistocene glaciations

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

glacial erosion at the fjord onset zone and implications for the organization of ice flow on baffin island arctic canada abstract organized conduits of fast ice flow at the fringe of present and past ice sheets move the majority of ice from ice sheet interior to periphery these relatively narrow corridors play a critical role in feedbacks between landscape evolution and ice sheet dynamics here we combine bedrock 10 be concentrations with distribution of lakes on baffin island arctic canada to constrain the pattern of glacial modification at a fjord onset zone the region of increasing relief from the continental interior to the fjord head high lake density and a lack of 10 be inheritance in the valley bottom indicate significant glacial scouring for some duration of the last glacial cycle in contrast 10 be inheritance and a lack of lakes at higher elevations indicate a lack of glacial scour and only slight glacial modification despite the entire region being covered by the laurentide ice sheet during the last glaciation this pattern of glacial erosion at the fjord onset zone is similar to what is found in the outer fjords 100 km toward the last glacial maximum ice margin and indicates that ice flow becomes organized well inland from the fjorded coast the relief generating process of selective linear erosion occurs at the fjord onset zone and was responsible for evolving baffin island fjords even in the late quaternary

geochemical constraints on the regolith hypothesis for the middle pleistocene transition the transition from 41 to 100 kyr glacial cycles and concomitant increase in global ice volume 1 ma remain an enigmatic feature of late cenozoic climate here we examine the petrology mineralogy and geochemistry of the silicate fraction of tills spanning the past 2 ma from the north central united states to evaluate the hypothesis that this so called middle pleistocene transition mpt occurred by erosion of regolith and subsequent exposure of underlying canadian shield bedrock by the laurentide ice sheet these data indicate that late pliocene tills are depleted in crystalline lithologies unstable minerals and major element oxides derived from plagioclase and ferromagnesians and are enriched in kaolinite quartz iron oxides tio2bearing resistates and meteoric 10 be in contrast early and middle pleistocene tills show enrichment in crystalline lithologies stable minerals and major oxides derived from plagioclase and ferromagnesians and depletion in meteoric 10 be whereas late pleistocene tills show major element concentrations that are most similar to that of fresh shield bedrock marine isotope records of sr os and hf show significant changes around the mpt that are consistent with the removal of a regolith and the exhumation of fresh silicate bedrock these results indicate that ice sheets initially expanded on highly weathered bedrock and progressively exhumed a fresher rock source thereby supporting the hypothesis that a change in the composition of the substrate underlying ice sheets best explains the origin of the mpt d 2004 elsevier b v all rights reserved

sedimentation on a lower jurassic carbonate platform flank geometry sediment fabric and related depositional structures djebel bou dahar high atlas morocco abstract along the southern margin of the high atlas morocco carbonate platforms of lower jurassic age developed in a transtensional basin the south atlas trough complete exposure and preservation of the platform margin flank and basin of the djebel bou dahar allowed the subdivision of the slope into an upper mid and lower slope based on geometry sediment fabric and depositional structures at ca 50 m below the platform margin coral algal patch reefs and ooid sand shoals grade into the depositional slope the straight upper slope showing discontinuous bedding at angles up to 29 extends down to ca 250 m and consists mainly of poorly sorted mixtures of sand and gravel almost devoid of mud avalanching rockfall and shearing of the coarse gravelly sediment are the dominant processes readjusting the upper slope the middle and lower part of the slope profile extending down to ca 500 m below the margin is separated from the upper slope by a distinct slope break slope angles range from 19 near the slope break down to 4 8 where the slope merges with the basin plain the irregularly bedded mid slope is characterized by scouring and deposition of muddy sands and non cohesive gravelly debris flows sedimentation on the dominantly muddy concave upwards lower slope can be separated into evenly bedded shales muddy sands and mud free gravel sand mixtures deposited as debris sheets the results of this study emphasize the relationship between sediment fabric and the slope geometry of a carbonate platform flank the overall geometry internal heterogeneity and depositional structures are suggested to be strongly related to the original character of the sediment supplied to the djebel bou dahar platform flank

tectonic controls on carbonate platform evolution in southern papua new guinea passive margin to foreland basin the middle oligocene collision of the northern margin of the australian craton with a complex subduction system resulted in emplacement of a thrust mass and formation of a foreland basin that extended from the coral sea to the indian ocean the distribution of carbonate platform facies in southwestern papua new guinea reflects the transition from an eocene passive margin setting to the early stages of foreland basin evolution the initial basin configuration with terrigenous sedimentation confined to the proximal foredeep allowed carbonate deposition in the shallow environment adjacent to the peripheral forebulge subsequent southward migration of the basin resulted in a rapid increase in the area and thickness of carbonate platform deposition when the proximal foredeep became filled by detritus shed from the emerging orogen clastic sediments buried the platform and terminated carbonate deposition the history of the southern papua new guinea carbonate platform illustrates the paradox of carbonate deposition within the foreland basin whereby basin configuration initially encourages thick and extensive carbonate deposition but inevitably leads to terrigenous inundation and the demise of the carbonate platform

platform margins reef facies and microbial carbonates a comparison of devonian reef complexes in the canning basin western australia and the guilin region south china devonian reef complexes were well developed in western australia and south china but no detailed direct comparison has been made between reef building in the two regions the regions differ in several respects including tectonic stratigraphic and palaeoceanographic palaeogeographic settings and the reef building styles reflect minor differences in reef builders and reef facies similarities and differences between the two reef complexes provide insights into the characteristics of platform margins reef facies and microbial carbonates of both regions here we present a comparison of platform margin types from different stratigraphic positions in the late devonian reef complex of the canning basin western australia and middle and late devonian margin to marginal slope successions in guilin south china comparisons are integrated into a review of the reefal stratigraphy of both regions reef facies reef complex architecture temporal reef builder associations 2nd order stratigraphy and platform cyclicity in the two regions were generally similar where the successions overlap temporally however carbonate deposition began earlier in south china carbonate complexes were also more widespread in south china and represent a thicker succession overall platforms in the canning basin grew directly on precambrian crystalline basement or early palaeozoic sedimentary rocks but in south china carbonate complexes developed conformably on older devonian siliciclastic strata pre frasnian reef facies in south china had more abundant skeletal frameworks than in canning basin reefs of equivalent age and famennian shoaling margins containing various microbial reefs may have been more common and probably more diverse in south china however late devonian platform margin types have been documented more completely in the canning basin deep intra platform troughs deep depressions containing non carbonate pelagic sediments nandan type successions that developed along syndepositional faults characterize devonian carbonate platforms in south china but have no equivalent on the lennard shelf canning basin where inter reef areas were more shallow the south china platform to depression pattern was generally continuous from the lower to upper devonian indicating that many pre devonian tectonic features continued to exercise considerable effect through deposition localized fault controlled subsidence was an important factor in both regions but similarities in 2nd order aggradation progradation cycles suggest that eustasy was also an important control on the larger scale stratigraphic development of both regions

glacial and periglacial buzzsaws fitting mechanisms to metaphors the buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier equilibrium line altitudes elas irrespective of uplift rates rock type or pre existing topography here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and elas and whether the glacial system can produce low relief surfaces or limit summit heights plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited pre glacial relief summit heights may correlate with elas but no causal link need be implied as summit erosion rates are low cirque headwalls may not directly abut summits and on passive margins cirques are cut into pre existing mountain topography any simple links between elas and glacial erosion break down on passive margins due to topographic forcing of ice sheet growth and to the km scale vertical swaths through which elas have shifted through the quaternary glaciers destroy rather than create low relief rock surfaces through the innate tendency for ice flow to be faster thicker and warmer along valleys the glacial buzzsaw cuts down

the iberian middle jurassic carbonate platform system synthesis of the palaeogeographic elements of its eastern margin spain abstract during the middle jurassic the domain of the iberian and catalan coastal ranges of eastern spain was occupied by a system of fault controlled carbonate platforms that flanked the iberian massif to the east this platform system marked the transition between the shelves of the alpine tethys and the central atlantic ocean the palaeogeographic reconstruction of the iberian middle jurassic platform system is based on more than 199 surface sections and 37 wells from southwest to northeast eight main palaeogeographic elements with associated characteristic facies are recognized these represent a system of horsts and grabens in the southwest the internal castilian platform is characterized by the frequently dolomitized oolitic and restricted facies of the yemeda formation to the northeast the nw trending open marine carbonate environments of the external castilian and aragonese platforms were separated by the fault controlled el maestrazgo high that is characterized mainly by the dolomitized rafales formation the external castilian and aragonese platforms consist from bottom to top of the microfilament mudstones to wackestones of the el pedregal formation the bioclastic and oolitic grainstones to packstones of the moscardon formation and the domeno formation that reflects a return to an open marine low energy wackestone to mudstone facies locally containing patches of oolitic grainstones the highly subsiding tortosa platform represented by the sant blai cardo and la tossa formations is bounded by the dolomitic facies deposited on the el maestrazgo and the tarragona highs and by the catalan massif where no middle jurassic deposits have been recorded the open marine facies and condensed sections of the beceite strait separated the aragonese and tortosa platforms a regional stratigraphical gap spanning the upper callovian lamberti zone to the lower oxfordian cordatum zone is evident a system of northwest and northeast trending normal faults controlled thickness and facies distribution data from the iberian carbonate platform system indicate that expanded sections were not necessarily associated with open marine environments condensed and expanded sections are developed in open and restricted marine facies even on such palaeogeographic highs as the el maestrazgo high restricted and shallow marine environments occasionally developed in parts of the external castilian platform

the broughton trough on the continental shelf of eastern baffin island northwest territories bathymetric and seismic surveys of the trough across the continental shelf of baffin island at broughton island indicate that there were four stages in its development the first involved deposition of cretaceous and early tertiary marine sediments before and during formation of a graben associated with the opening of baffin bay with the uplift of baffin island extensive deltaic deposits at the distal end of the trough were laid down in the second stage these deposits are thought to represent the products of a river system raised much above grade flowing in the trough and the fiords to the southwest and depositing in a sea with a relative level 300 400 m below present in the third stage during pliocene pleistocene glaciation the proximal regions of the trough were eroded to more than 700 m below present sea level lateral moraines indicate the extension of ice to the edge of the continental shelf although the relatively small amount of erosion in the distal region suggests that the ice may have be

grus weathering mantles problems of interpretation abstract grus is an ill defined product of deep weathering of coarse grained rocks whose relationships to other weathering changes remain unclear this paper attempts to address this issue by reviewing a number of examples of coarse saprolites from a variety of climatic and topographic settings grus is the category of weathering mantle that possesses the following characteristics sand gravel 75 100 silt clay

increased terrigenous influx but no drowning palaeoenvironmental evolution of the tunisian carbonate platform margin during the late aptian during the aptian some carbonate platforms of the sub tropical realm for example on the northern tethys margin or in the gulf of mexico were affected repeatedly by severe perturbations in the carbonate production factory and drowning preferentially during global warming events such as the early aptian oceanic anoxic event 1a and a prominent mid late aptian warming interval these platform growth crises have been explained mainly by strongly increased coastal runoff for example siliciclastics and nutrients in combination with pronounced eustatic sea level rises in the last few years increasing evidence suggests that carbonate platforms of lower latitudes were generally less or even not affected by environmental perturbations during these events this raises the question as to the responsible factors that promoted platform growth or decline in different latitudinal areas in this study upper aptian middle gargasian to uppermost clansayesian inner tropical carbonate ramp deposits of the serdj formation at djebel serdj north central tunisia are studied in detail with regard to microfacies lithology biostratigraphy and chemostratigraphy these data allow reconstruction of the palaeoenvironmental evolution of the tunisian carbonate platform margin and investigation of its response to the prominent mid late aptian warming interval the unusually expanded 600 m thick serdj formation consists of limestones marlstones and siltstones suggesting deposition within mid ramp to inner ramp palaeoenvironments deposits of the mid late aptian are represented by quartz rich platform carbonates and siltstones probably resulting from increased coastal runoff on the tunisian shelf as a response to global warming and accelerated water cycling the siliciclastic input was accompanied by elevated nutrient levels as indicated by a partial decline in the abundance of oligotrophic biota and mass occurrences of orbitolines and green algae carbonate platform drowning during the mid late aptian as reported from the sub tropical realm has not been identified a comparison with other tropical river influenced platforms suggests that none of them drowned during the mid late aptian one important reason might be widespread arid to semi arid climatic conditions within lower latitudes during that time promoting platform growth due to comparably low nutrient runoff

modelling northern hemisphere ice volume over the last 3 ma the northern hemisphere ice sheet volumes over the last 3 ma were simulated using the lln 2 d model the forcings were both insolation and co2 concentration different atmospheric co2 scenarios were used because of a lack of co2 reconstruction over this remote past with constant co2 concentrations the simulated ice volume does not show any gradual increase as recorded in the marine sediments moreover its spectrum changes according to the chosen value of co2 when co2 is fixed at 220 ppmv the simulated ice volume is dominated by the similar to 100 ka period if a pre industrial co2 concentration of 280 ppmv is used the simulation is dominated by the similar to 41 ka period by using a linearly decreasing co2 concentration going from 320 ppmv at 3 ma bp to 200 ppmv at present the simulated changes in the power spectrum are in agreement with those obtained from the sedimentary records roughly before 1 ma bp the dominating period is similar to 41 ka afterwards the similar to 100 ka period becomes dominant this transition is accompanied by a gradual increase of the ice volume potential mechanisms for this transition are discussed using cyclic co2 fluctuations over the last 0 6 ma does not change significantly the spectral characteristics of the simulated ice volume but amplifies the amplitude of its variations c 1998 elsevier science ltd all rights reserved

palaeo ice streams in the foxe baffin sector of the laurentide ice sheet in this paper we describe mapping of palaeo ice streams in the foxe baffin sector of the laurentide ice sheet by means of geomorphological interpretation of high resolution satellite images our interpretations were guided by a glaciological inversion scheme aided by digital elevation models publicly available sonar surveys and field studies as a result we produced a map depicting the location geometry and relative temporal changes of palaeo ice streams and analysed their palaeoglaciological implications for the foxe baffin sector we conclude that in the period between the last glacial maximum and approximately 7 0 kyr bp the foxe baffin sector was largely drained by topographically controlled outlet glaciers and ice streams which were organized in a relatively stable pattern during this time large areas of melville peninsula and central baffin island were subject to cold based conditions between 7 0 and 6 0 kyr bp the foxe baffin sector collapsed catastrophically in the foxe basin after which its remnant portion became confined to baffin island during this collapse rapid successions of small transient ice streams occurred along wide loosely defined topographical corridors in two sectors of baffin island the presently available landform archive on emerged land is not sufficient to conclusively support the existence of fully scaled ice streams along the whole length of hudson strait as an alternative solution we propose that topographically controlled ice streams might have occurred along the deepest parts of hudson strait with attendant cold based ice zones on marginal areas and islands at the head of the strait

meteoric cosmogenic beryllium 10 adsorbed to river sediment and soil applications for earth surface dynamics abstract rainfall scavenges meteoric cosmogenic 10be from the atmosphere 10be falls to the earth s surface where it binds tightly to sediment particles in non acidic soils over the life span of those soils as such meteoric 10be has the potential to be an excellent geochemical tracer of erosion and stability of surfaces in a diverse range of natural settings meteoric 10be has great potential as a recorder of first order erosion rates and soil residence times even though this tracer was first developed in the late 1980s and showed great promise as a geomorphic tool it was sidelined in the past two decades with the rise of the sister nuclide in situ 10be which is produced at a known rate inside quartz minerals since these early days substantial progress has been made in several areas that now shed new light on the applicability of the meteoric variety of this cosmogenic nuclide here we revisit the potential of this tracer and we summarize the progress 1 the atmospheric production and fallout is now described by numeric models and agrees with present day measurements and paleo archives such as from rain and ice cores 2 short term fluctuations in solar modulation of cosmic rays or in the delivery of 10be are averaged out over the time scale soils accumulate 3 in many cases the delivery of 10be is not dependent on the amount of precipitation 4 we explore where 10be is retained in soils and sediment 5 we suggest a law to account for the strong grain size dependence that controls adsorption and the measured nuclide concentrations and 6 we present a set of algebraic expressions that allows calculation of both soil or sediment ages and erosion rates from the inventory of meteoric 10be distributed through a vertical soil column the mathematical description is greatly simplified if the accumulation of 10be is at a steady state with its export through erosion in this case a surface sample allows for the calculation of an erosion rate explored further this approach allows calculation of catchment wide erosion rates from river sediment similar to the approach using 10be produced in situ in contrast to the in situ 10be approach however these analyses can be performed on any sample of fine grained material even where no quartz minerals are present therefore this technique may serve as a tool to date sediment where no other chronometer is available to track particle sources and to measure earth surface process rates in soil suspended river sediment and fine grained sedimentary deposits

cosmogenic radionuclides from fiord landscapes support differential erosion by overriding ice sheets the interpretation of differentially weathered mountainous areas along the fringes of pleistocene ice sheets is fundamental for determining ice sheet behavior and thickness during the last glaciation two existing interpretations are either that highly weathered uplands remained as nunataks while freshly eroded troughs held outlet glaciers during the last glaciation or that uplands and lowlands were equally covered by ice but that it was differentially erosive as a function of its spatially variable basal thermal regime cosmogenic radionuclide measurements from 33 bedrock samples and 27 upland erratics from differentially weathered fi ord landscapes on northeastern baffi n island shed light on laurentide ice sheet lis dynamics and thickness tors on weathered upland surfaces have minimum 10 be ages between ca 50 and ca 170 ka n 12 whereas the majority of erratics perched in the uplands range from ca 10 to ca 13 ka n 14 indicating that the whole landscape was glaciated during the last glacial maximum lgm glacially sculpted bedrock n 7 near sea level refl ects the age of deglaciation and increasing amounts of isotopic inheritance in highelevation sculpted bedrock n 3 higher elevation intermediately weathered bedrock n 11 and highest elevation intensely weathered bedrock refl ect the weakening of erosive power as the ice sheet transitioned from fi ords to interfi ord plateaus cold based glaciation of uplands was contemporaneous with warm based glaciation in fi ords suggesting the presence of ice streams 26 al and 10 be concentrations measured in 10 bedrock samples indicate that tors have experienced a complex history of alternating periods of exposure burial and limited glacial erosion the paired isotope data reveal a minimum duration of burial of 80 500 k y presumably by cold based ice and indicate that the tors have an age of at least 150 580 ka these data together with other reconstructions of ice streams in the eastern canadian arctic suggest that ice streams were a large infl uence on northeastern lis dynamics throughout the late quaternary thus the northeastern lis was sensitively tied with north atlantic thermohaline circulation and abrupt climate change

conservative behavior of mg isotopes in massive dolostones from diagenesis to hydrothermal reworking abstract mg isotopes in syndepositional dolomite have been suggested to be a potential proxy for understanding seawater chemistry however it is argued that the 26mg values of dolomite could be complicated by the effects of early diagenesis and later hydrothermal activities further investigations into the behaviors of mg isotopes in dolomitization systems are needed to resolve this controversy in the present study we investigated early ordovician dolostones from the tarim basin including diagenetically altered dolomites hydrothermally altered dolomites and well preserved dolostones that precipitated in the slope margin and interior of a carbonate platform different types of dolomites bulk dolostone and limestone were sampled by microdrilling for analyses of c o mg isotope compositions and ree concentrations the dolostone 13c values match those of coeval seawater and the ree distribution patterns in the dolostones are comparable with those in the limestones indicating that the dolostones originated from syndiagenetic dolomitization the 26mg values of the various syndiagenetic dolomites that formed in the slope margin and interior of the carbonate platform are similar averaging approximately 2 06 0 20 no stratigraphic variability in the dolomite mg isotopes can be discerned which implies that the mg isotope compositions of the porewater were homogeneous during massive dolomitization and remained in equilibrium with seawater additionally the 26mg values of the altered dolostone do not show correlations with diagenetic and hydrothermal signals demonstrating that dolomite mg isotopes are insensitive to postdepositional alteration given these facts we propose that mg isotopes in dolostones have conservative behaviors during diagenesis and late stage hydrothermal reworking

radiogenic isotope records of quaternary glaciations changes in the erosional source and weathering processes variations of global and regional silicate weathering rates and paleo ocean circulation patterns are estimated by using radiogenic isotope records but the effects of changes in provenance are generally ignored here sediment provenance has been constrained through the use of ar ar ages for individual detrital minerals from the labrador sea which can be compared directly to the radiogenic isotope compositions from the same core material dramatic changes in the radiogenic isotope composition of north atlantic deep water through the quaternary period are shown to reflect discrete changes in both sources and weathering processes accompanying northern hemisphere glaciation changes in the different radiogenic isotope systems reflect the influence of source physical weathering and chemical weathering and not simply changes in the underlying weathering rate or ocean circulation patterns that are typically inferred

reorganization of ice sheet flow patterns in arctic canada and the mid pleistocene transition 1 evidence for the evolution of laurentide ice sheet lis basal thermal regime patterns during successive glaciations is poorly preserved in the geologic record here we explore a new approach to constrain the distribution of cold based ice across central baffin island in the eastern canadian arctic over many glacial interglacial cycles by combining till geochemistry and cosmogenic radionuclide crn data parts of the landscaped with geomorphic evidence for limited glacial erosion are covered by till characterized by high chemical index of alteration cia values and crn concentrations requiring complicated burial exposure histories till from regions scoured by glacial erosion have cia values indistinguishable from local bedrock and crn concentrations that can be explained by simple exposure following deglaciation crn modeling results based on these constraints suggest that the weathered tills were deposited by 1 9 to 1 2 ma and by that time the fiorded baffin island coastline must have developed close to its modern configuration as piracy of ice flow by the most efficient fiord systems resulted in a major shift in the basal thermal regime across the northeastern lis the resultant concentration of ice flow in fewer outlet systems may help explain the cause of the mid pleistocene transition from 41 to 100 kyr glacial cycles

aminostratigraphy of quaternary marine and glaciomarine sediments qivitu peninsula baffin island a complex sequence of cyclical marine and glaciomarine lithofacies exposed along the coastal lowlands of the qivitu peninsula was deposited during the marine transgressions and regressions that affected this area during repeated glaciation of the region multivariate analysis of amino acid ratios measured on shell fragments of the pelecypods hiatella arctica and myatruncata in the lithostratigraphic units provides a basis for their chronocorrelation through the use of informal regional aminostratigraphic units termed aminozones all but the oldest aminozones correspond with particular lithostratigraphic units deposited during transgressive regressive periods when relative sea level was higher than present sea level discriminant analysis shows total amino acid fraction allo iso ratios from either species are the best overall criteria for assigning a shell sample to a particular aminozone but free fraction allo iso ratios are more useful in the younger zones the distribution of ratios in lithostratigraph