sedimentology and isotope geochemistry of carnian deep water marl limestone deposits from the sicani mountains sicily environmental implications and evidence for a planktonic source of lime mud abstract the upper triassic halobia bearing marl limestone deposits from the sicani mountains sicily record the sedimentary evolution of the sicanian basin through the middle and late carnian time dark marls and interbedded grey calcilutites of julian age are characterized by abundant pyrite sparse bioturbation and negative carbonate carbon 13c values they accumulated in a basin with dominantly anoxic to dysaerobic bottom waters lower tuvalian dark grey pyritic marls and calcilutites which contain carbonate minerals with relatively high mn contents and widely fluctuating 13c signatures were deposited under dysaerobic conditions middle and upper tuvalian cherty limestones show intense bioturbation and nearly invariable positive 13c values around 2 for calcite they form a thick and monotonous succession accumulated in a deeper and more oxygenated basin the halobia bearing deposits preserve some calcareous nannoplanktonic forms the nannofossils varying in size from 7 to 32 m are significantly abundant in the cherty limestones pointing to a notable role of the calcareous nannoplankton as a source of carbonate mud in the deep water basins of the southern tethys during the late triassic time

controls of eustasy and diagenesis on the 238u 235u of carbonates and evolution of the seawater 234u 238u during the last 1 4 myr using a leaching protocol designed for the study of u isotopes in recent carbonates we measured the u isotope composition both 238 u 235 u and 234 u 238 u of modern and ancient corals n 6 a limestone and a dolostone as well as 43 shallow water carbonate sediments from the odp leg 166 site 1009 drill core on the slope of the bahamas platform although bulk corals record the seawater 238 u value within 0 02 differences of up to 0 30 in the 238 u of individual leachates suggest a control of the coral structure and a more positive 238 u 235 u ratio in the centers of calcification the drill core 238 u data shows that the 238 u 235 u ratio of shallow water carbonates is controlled mainly by 1 variations in sea level through the mixing of different amounts of platform derived sediments with 238 u 0 50 0 60 heavier than seawater and pelagic sediments with seawater like 238 u values 2 authigenic u enrichment via pore watercirculation and u reduction both on the platform and down to 5 m below the surface mbsf after deposition of the sediment and to a lesser extent by 3 early diagenetic processes i e carbonate dissolution and or recrystallization during sediment burial the global effect of these processes leaves the 238 u values of shallow water carbonates offset relative to that of seawater by carbonates sw 0 24 0 06 95 ci including all samples this shift can be used in seawater paleoredox reconstructions based on carbonates deposited on shallow water platform shelf and slope environments i e most of the carbonate sedimentary record prior to the mesozoic to account for the average effect of carbonate diagenesis assuming that the 238 u 235 u ratio of carbonate platform sediments directly records the seawater 238 u 235 u ratio would underestimate the extent of ocean seafloor anoxia by at least a factor 10 the rapid fluctuations in 238 u values due to sea level changes i is a factor that should be considered before interpreting 238 u variations as reflecting changes in oceanic paleoredox conditions and ii reinforces the need for statistically meaningful data sets the 234 u data suggest that the 234 u 238 u ratio of the seawater has remained within 20 of the modern seawater value during the last 1 1 4 myr furthermore we find that small scale 1 15 variations in seawater 234 u mirror sea level changes during the penultimate glacial interglacial period 140 to 200 ka thus confirming the record of lower 234 u sw during periods of low sea level stand and expanding it to at least the last two glacial interglacial events i e 0 23 ma such fluctuations in 234 u initial values should be taken into account when screening carbonate sediments u th ages on the basis of the initial 234 u 238 u ratios of the samples

discriminating between subglacial and proglacial lake sediments an example from the danischer wohld peninsula northern germany subglacial lakes are common features of contemporary ice masses however they are rarely identified in the geological record this is due to the difficulty in discriminating between subglacial and proglacial lake sediments a proglacial origin is typically preferred as the simplest explanation we hypothesise that numerous deposits currently interpreted to record proglacial lake sedimentation may actually have a subglacial origin here we try and find ways of distinguishing proglacial from subglacial lake sediments by investigating three sites along the danischer wohld peninsula northern germany which have been interpreted to record both proglacial and subglacial sedimentation we identify two major phases of ice activity and associated lake formation during the late weichselian glaciation 1 proglacial lake formation at 23 ka in front of the advancing baltic ice stream this lake was subsequently overridden and the sediments glaciotectonised as ice continued to advance to its maximum extent 2 retreat of ice back into the baltic basin at 19 ka and formation of a proglacial lake that persisted for 4 ka we suggest that subglacial lake activity may have occurred at two of the sites between 23 and 19 ka this is based on the presence of aggrading sediment deposits characterised by stratified laminated diamictons and interbedded tabular to channelized sorted sediments the juxtaposition of relatively undeformed waterlain sediment and subglacial till absence of glaciotectonic thrusting and folding or of fining coarsening successions and the geomorphic association with tunnel valleys to the south of the study area the style of sedimentation and deformation provided the greatest insight into the discrimination of proglacially vs subglacially deposited glaciolacustrine sediments the luminescence signal palaeodose distributions also offers a potentially powerful means of fingerprinting sediment transport pathways of young glacial systems

mineralogy early marine diagenesis and the chemistry of shallow water carbonate sediments abstract shallow water carbonate sediments constitute the bulk of sedimentary carbonates in the geologic record and are widely used archives of earth s chemical and climatic history one of the main limitations in interpreting the geochemistry of ancient carbonate sediments is the potential for post depositional diagenetic alteration in this study we use paired measurements of calcium 44ca 40ca or 44ca and magnesium 26mg 24mg or 26mg isotope ratios in sedimentary carbonates and associated pore fluids as a tool to understand the mineralogical and diagenetic history of neogene shallow water carbonate sediments from the bahamas and southwest australia we find that the ca and mg isotopic composition of bulk carbonate sediments at these sites exhibits systematic stratigraphic variability that is related to both mineralogy and early marine diagenesis the observed variability in bulk sediment ca isotopes is best explained by changes in the extent and style of early marine diagenesis from one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the fluid fluid buffered to one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the precursor sediment sediment buffered our results indicate that this process together with variations in carbonate mineralogy aragonite calcite and dolomite plays a fundamental and underappreciated role in determining the regional and global stratigraphic expressions of geochemical tracers 13c 18o major minor and trace elements in shallow water carbonate sediments in the geologic record our results also provide evidence that a large shallow water carbonate sink that is enriched in 44ca can explain the mismatch between the 44 40ca value of rivers and deep sea carbonate sediments and call into question the hypothesis that the 44 40ca value of seawater depends on the mineralogy of primary carbonate precipitations e g aragonite seas and calcite seas finally our results for sedimentary dolomites suggest that paired measurements of ca and mg isotopes may provide a unique geochemical fingerprint of mass transfer during dolomitization to better understand the paleo environmental information preserved in these enigmatic but widespread carbonate minerals

sedimentology of a glaciofluvial deposit at ekeby east central sweden abstract the ekeby site south of stockholm has been chosen to elucidate glaciofluvial sedimentation processes soon after the end of the younger dryas detailed lithofacies and grain size analyses of gravel sand and fine sediment sequences in a gravel pit reflect changes in the depositional environment four main facies assemblages have been distinguished the lowermost part of the sequence was probably deposited in a subglacial conduit environment the middle part of the sequence reflects a transition to a proglacial subaqueous environment the upper part of the latter sequence probably occurred during increased melting of the ice the sequence was then covered by beach gravel formed during the regression after the drainage of the baltic ice lake

overdeepened quaternary valleys in the eastern danish north sea morphology and origin abstract a system of 100 350 m deep overdeepened and buried valleys has been mapped in the eastern danish north sea individual valleys can be traced for several tens of kilometres and valleys generally begin and terminate abruptly a correlation to buried valleys onshore southwest denmark is possible the valleys post date glaciotectonic structures and are interpreted to be elsterian and possibly saalian in age the origin of valleys in the eastern danish north sea is explained by repeated cycles of sub glacial down cutting of meltwater channels and channel closure due to ice creep eventually producing deeply incised valleys glacial erosion may have been significant in cases where valleys are broad and shallow the origin of overdeepened quaternary valleys in general can be attributed to a combination of three end member processes i steady state drainage of meltwater ii catastrophic outbursts of meltwater and iii glacial erosion the main requirement for sub glacial valley formation is the presence of a melting ice sheet overlying a poorly consolidated substrate permeability variations of the substrate may produce subregional variations in the pattern of valley incision while pre glacial rivers faults or salt structures are of local importance only

the origin of deep buried channels of elsterian age in northwest germany buried channels cut to a depth of over 100m into the underlying substratum of north germany are almost exclusively of elsterian age evaluation of geophysical well logs in the hamburg area for the first time allows the construction of detailed longitudinal and transverse profiles it can be shown that an apparently chaotic infill known from borehole records in some cases is actually a regular sedimentary sequence fining from proximal to distal channel formation seems to have been the result of catastrophic meltwater release in the marginal parts of the ice sheet the channel infill reflects these episodic outbursts of meltwater during deglaciation the channel remnants became infilled with fine sediments the channels ceased to exist as morphologically detectable forms at the end of the holsteinian stage

the pre weichselian glaciations of north west europe abstract in north west europe no evidence has been found for glaciations older than the elsterian the elsterian seems to consist of at least two separate ice advances with a minor interval in between during the elsterian in the area south of the baltic sea over 400 m deep channels were cut into the underlying substratum by a combination of glacial erosion and meltwater activity the channels were active until the late elsterian and were subsequently filled with meltwater deposits and glaciolacustrine silt and clay during the saalian no comparative channels were being formed three different ice advances can be distinguished within the saalian the stratigraphical correlation of which is to be discussed no convincing evidence was found for any interglacial within the saalian sequence there are good reasons to assume that the ice advances were only separated from each other by minor ice free intervals

seismic stratigraphy of quaternary deposits in the north western baltic proper a pilot study abstract this investigation is a seismic reflection survey carried out in order to investigate the possible submarine younger dryas marginal moraines in the north western baltic proper the records do not show any indications of distinct marginal moraines in the northern part of the investigated area south of stockholm in the southern part of the area there are indications of marginal deposits though the distance between the profiling lines is too spacious to allow detection of the direction of these morphological features the age of the formation of the morphological features in the southern part of the investigated area is presently unknown the beginning of younger dryas is likely but allerod and the end of older dryas should also be considered possible two seismic till units were discovered in one section in the south eastern part of the investigated area an erosional channel was found in the same section which may indicate a stillstand of unknown age of the ice margin

14c ams measurements from the late weichselian part of the swedish time scale abstract accelerator mass spectrometry measurements on plant macrofossils from the older part of the swedish time scale a chronology spanning over the past 13 000 calendar years indicate a good agreement between varve years and calibrated ages tree rings u th between ca 10 500 and ca 12 000 calendar years bp around 12 000 varve years the varve radiocarbon discrepancies seem to reach a maximum while the u th radiocarbon differences increase steadily

nature and origin of ground ice sandhills moraine southwest banks island western canadian arctic the sandhills moraine is a late wisconsinan lateral moraine complex on southwest banks island the occurrence of ice ablation landforms ground ice slumps kettle lakes and catastrophic lake drainage in winter suggests the presence of substantial bodies of massive ground ice the distinctive hummocky topography of the sandhills moraine is thought to reflect partial melt out of this ice stratigraphic observations indicate that the ice is overlain irregularly and unconformably by glacigenic sediments notably pebbly clay till and or sandy gravels outwash while the ice itself possesses numerous and variable mineral inclusions faults and foliations petrofabric analyses indicate a strongly preferred orientation to the ice crystals it is suggested that these characteristics are best explained if the ground ice is interpreted as relict glacier ice

enhanced cenozoic chemical weathering and the subduction of pelagic carbonate the observed trend of increasing oceanic 87sr 86sr ratios during the late cenozoic led raymo et al 1 to propose that chemical weathering rates increased at this time as a result of enhanced weatherability of silicate rocks they suggested that this was due in turn to continential uplift primarily in the himalayas and the andes because weathering involves the reaction of silicates with atmospheric carbon dioxide considerations of changes in weathering rates must take into account the need to balance the global carbon cycle to maintain this balance on timescales greater than 106yr enhanced weathering requires an increased flux of co2 into the atmosphere2 without such an increased flux weathering rates could not increase and one is then forced to search for other explanations for the observed 87sr 86sr trend such as a changing riverine strontium isotope composition3 6 here i assume that the strontium isotope record does indeed reflect enhanced weathering in the late cenozoic but propose that its cause may have been an increased co2 flux arising from the recycling of pelagic sedimentary carbon at subduction zones since the jurassic sedimentary carbonate accumulation has shifted from primarily cratonic to primarily pelagic environments7 11 because sea floor spreading transports pelagic carbonate to and recycles it through metamorphic environments in subduction zones this shift to pelagic carbonate accumulation would provide the increased co2 flux needed to increase weathering rates12 13

carbonate deposition climate stability and neoproterozoic ice ages the evolutionary success of planktic calcifiers during the phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate ion concentration the saturation dependent preservation of carbonate in sea floor sediments before this buffering was primarily accomplished by adjustment of shallow water carbonate deposition to balance oceanic inputs from weathering on land neoproterozoic ice ages of near global extent and multimillion year duration and the formation of distinctive sedimentary cap carbonates can thus be understood in terms of the greater sensitivity of the precambrian carbon cycle to the loss of shallow water environments and co 2 climate feedback on ice sheet growth

the formation of gneisses in the southern east uralian zone a result of late palaeozoic granite ascent and emplacement abstract geochemical and radiogenic age data are incompatible with the idea that the gneiss complexes of the east uralian zone are microcontinental blocks that collided with the magnitogorsk island arc during the uralian orogeny field and microstructural data from the dzhabyk and suunduk complexes presented in this paper enable us to suggest an alternative model that interprets the gneisses as deformed margins of the batholiths of the uralian granite axis the gneisses have been formed from a granitic protolith by a continuous fabric transformation on a retrograde metamorphic path all structures in the gneisses can be assigned to the ascent and emplacement of batholiths in an active strike slip belt

coastal paleo environment and sea level change at macassa bay southern mozambique since c 6600 cal bp changes in holocene coastal paleo environment and sea level variations have been recorded in estuary sediments from macassa bay southern mozambique methods include analysis of fossil diatoms sediment stratigraphy mineral magnetic properties stable carbon and nitrogen isotope composition and carbon and nitrogen content the chronology based on six ams c 14 dates suggests a basal age of the sediment core of c 6600 cal bp calibrated years before present the multi proxy dataset implies two phases when the site was experiencing marine conditions and tentative sea level high stands 1 between c 6600 6300 cal bp which is contemporary with the last phase of the global transgression and the holocene climatic optimum and 2 between c 4700 1000 cal bp a period when sea level curves from the region suggest occasional minor sea level high stands between these phases c 6300 4700 cal bp the environment within the macassa bay estuary was less influenced by marine processes and studied proxies indicate a freshwater phase associated with relatively low sea levels after c 1000 cal bp a terrestrial environment prevailed at the site probably as a result of a combined effect of sea level lowering and high accumulation of organic peat within the estuary c 2011 elsevier ltd and inqua all rights reserved

environmental changes and human impact as recorded in a sediment sequence offshore from a viking age town birka southeastern sweden the viking age town of birka which existed between ad 750 and 975 on the island of bjorko in the malar archipelago of the baltic sea is known as the oldest centre used for large scale international trading in sweden birka had a strong defence town rampart hillfort and a water palisade studies of lithology and microand macroremains in a sedimentary sequence accumulated offshore from birka outside the water palisade revealed a stratigraphically distinct refuse stratum referred to as the birka layer we argue that the bulk material of the birka layer emanates from human activities in the town e g latrine cleanings cuttings of shore vegetation cleaning of ditches and storage areas and domestic animal dung organic remains from vegetation and animals deposited during activities on the ice offshore from the town e g winter markets may also have contributed to the composition the material constituting the birka layer started to accumulate after the construction of the protecting water pali

subglacial groundwater flow during the last glaciation in northwestern germany abstract reconstruction of groundwater flow in overpressured soft sediments overridden by the last weichselian ice sheet in northwestern germany about 18 000 ka b p based on numerical modelling reveals a complete reorganisation of groundwater dynamics as compared to the present system groundwater flow controlled by potentiometric surface high up in the ice sheet and by a steep hydraulic gradient at the glacier periphery was here up to 30 times faster than at present and a vertical flow component penetrated the entire thickness of quaternary sediments reaching some 200 m in places

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

aftermath of the end cretaceous mass extinction possible biogeochemical stabilization of the carbon cycle and climate in the aftermath of the cretaceous tertiary k t boundary event 65 m y ago pelagic carbonate productivity was greatly reduced for several hundred thousand years a decrease in carbonate productivity by a factor greater than 3 in the absence of some mechanism to remove excess carbonate from the ocean should have resulted in the accumulation of carbon and alkalinity in the oceans this would cause the atmospheric partial pressure of co2 to fall dramatically and the deep ocean to become fully saturated with respect to calcite evidence of such a period of highly calcite saturated oceans with low atmospheric pco2 in the earliest tertiary is lacking suggesting that ocean chemistry may have been buffered by some process or processes shallow water carbonate accumulation rates may depend in part on carbonate ion concentrations and thus shallow water carbonate deposition might act to stabilize ocean chemistry in the face of a dramatic reduction in pelagic productivity in our four box ocean model as the oceanic carbonate ion concentration rises in the face of diminished pelagic carbonate accumulation the shallow water carbonate accumulation rate increases compensating for the reduction in pelagic carbonate accumulation these model results indicate that the carbonate ion feedback on shallow water carbonate sedimentation may have acted to balance oceanic carbon and alkalinity budgets at the k t boundary and furthermore may have been a primary mechanism maintaining high shallow water carbonate accumulation rates prior to the jurassic onset of widespread pelagic carbonate accumulation

geologic history of seawater a magic approach to carbon chemistry and ocean ventilation abstract we explore the relationship between atmospheric o 2 and co 2 evolution and seawater chemistry with particular focus on the co 2 carbonic acid system and ocean ventilation over the phanerozoic eon using a coupled biogeochemical earth system model magic this model describes the biogeochemical cycles involving the major components of seawater ca mg na k cl so 4 co 2 hco 3 co 3 as well as components o 2 fe p organic c reduced s central to long term ecosystem productivity the magic calculations show that the first order input fluxes from weathering of continental rocks of ca mg and dissolved inorganic carbon dic to the ocean varied in a cyclical manner over the phanerozoic the cyclicity is mainly the result of the impact of changing atmospheric co 2 levels and hence temperature and runoff on these fluxes reflecting the nature of hothouse greenhouse high co 2 and warm versus icehouse low co 2 cool and continental glaciation conditions during the phanerozoic uptake of dic by seafloor basalt seawater reactions also varied in a corresponding fashion to the weathering fluxes the fluxes of ca mg dic and other seawater constituents removed in oceanic sinks were also calculated and hence with calculated inputs and outputs of seawater constituents the changes in seawater chemistry through phanerozoic time could be obtained seawater ph increased irregularly during the phanerozoic from just above 7 in the cambrian period approaching modern average values in the most recent several millions of years calcite saturation state also increased with decreasing age both ph and calcite saturation state trends exhibited a cyclic overprint of hothouse and icehouse environmental conditions dissolved sulfate changed in a cyclical manner reflecting mainly variations in weathering and accretion rates and redox conditions whereas dissolved potassium exhibited little variation in concentration using our standard model results for the chemistry of seawater and changes in atmospheric co 2 and o 2 as the basis for a series of sensitivity experiments we vary the ventilation rate of the global ocean and quantify the resulting changes in terms of processes such as net primary production organic carbon burial and oxidation pyrite weathering and sulfate reduction we use these preliminary results to discuss how changes in ocean ventilation affect atmospheric co 2 and o 2 and in turn exert changes in the sulfur organic carbon and inorganic carbon systems we postulate that periods of slow plate accretion rates associated with lower atmospheric co 2 vigorous deep water formation cooler drier climatic conditions and greater poleward temperature gradients are more likely to be associated with a strong thermohaline circulation and thus enhanced global ocean mixing conversely periods of higher accretion rates higher co 2 higher average global temperatures with more equable poleward gradients and higher sea levels resulting in extensive continental inundation would be more likely to be coincident with times of reduced mixing of the global ocean it is important to recognize that the scale of these changes depends on how major tectonic cycles controlling chemical weathering co 2 and temperature in turn affect nutrient supply global ocean productivity and global ocean thermohaline circulation the key to elucidating these changes lies in an understanding of the relationship between long term tectonic evolution which leads to changes in climate sea level and the global distribution of continental landmasses and the sedimentary environments they host and the circulation of the global ocean

high precision analysis of hydrous rhyolitic glass inclusions in quartz phenocrysts using the electron microprobe and inaa a high precision electron microprobe emp technique has been developed that is capable of analyzing major minor and trace element abundances si ti ai fe mn mg ca na k cl in hydrous rhyolitic glasses the technique was developed to characterize the chemical compositions of rhyolitic glass inclusions in phenocrysts that occur in layers of paleozoic altered volcanic ash the compositions of these inclusions serve as excellent chemical fingerprints of the altered volcanic ash layers for use in stratigraphic correlation the precision and reproducibility of the analyses is sufficientnot only to distinguish one altered volcanic ash layer from another on the basis of inclusion compositions but also to discern differencesin the compositions of different inclusions from the same layer a high precision instrumental neutron activation analytical inaa technique was also developed that is capable of measuring an additional suite oftrace elements e g sc co rb cs sr ba la ce sm eu tb yb lu zr hf ta in rhyolitic glass inclusions in quartz phenocrysts with excellent accuracy and precision after correcting for the presence of the host quartz the abundances of elements measured by the emp technique and the corrected abundances determined using the inaa technique are identical within analytical uncertainty thus demonstrating the internal consistency of the results

a magnetostratigraphic comparison between 14c years and varve years during the late weichselian indicating significant differences between the time scales a 14c dated magnetostratigraphy of absolute declination and inclination between 12500 and 10000 14c yr bp was recently developed for southern sweden recently also the swedish geochronological time scale based on c 11 500 annually deposited clay varves was connected with the present it should therefore be possible to compare the two chronologies with a reliable magnetostratigraphic record in an appropriate clay varve section we have found such a site within the middle swedish end moraine zone statistical correlations between the two independently dated time scales suggest that at 10500 10200 14cy r bp the varve chronology exceeds the 14c chronology by the order of 500 600 varve yr other correlations indicate that the difference between the two chronologies was less at 11000 14c yr bp and further correlations between the time scales at 12000 14c yr bp suggest that the difference between the chronologies increased steadily from 12000 to 10000 14c yr bp if these correlations are correct they imply that the 14c production rate increased steadily during the late weichselian

late cretaceous to recent tectonic evolution of the north german basin and the transition zone to the baltic shield southwest baltic sea abstract in this study we investigate the late cretaceous to recent tectonic evolution of the southwestern baltic sea based on a dense grid of seismic reflection profiles this area covers the baltic sea sector of the salt influenced north german basin and its transition to the salt free baltic shield across the tornquist zone the upper cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high resolution time structure maps of the main horizons i e the upper cretaceous tertiary and pleistocene the upper cretaceous and tertiary layers reveal numerous significant faults throughout the study area several of these faults propagate upwards across the unconsolidated pleistocene sediments and occasionally penetrate the surface the salt influenced north german basin reveals three major fault trends nw se n s and nne ssw several of these faults are located directly above basement sub salt faults and salt pillows the majority of these faults are trending n s to nne ssw and parallel the direction of the gluckstadt graben faults in the salt free tornquist zone we identify two major shallow fault trends which are nw se and ne sw the majority of these faults are located above basement faults following the direction of the tornquist zone we conclude that generally basement tectonics controls activation and trends of shallow faults if salt is present the ductile salt layer causes a lateral shift between the sub and supra salt faults major plate reorganisation related to the africa iberia europe convergence and the subsequent alpine orogeny caused reactivation of pre existing faults and vertical salt movement in the late cretaceous the change of stress orientation from ne sw to a nw se during neogene caused another phase of fault and salt tectonic reactivation we explain that the ice sheet loading and or present day stress field may have acted in combination causing the recent tectonics and upward extension of the faults

the 1989 1990 activity of etna magma mingling and ascent of h2oclsrich basaltic magma evidence from melt inclusions abstract the melt inclusions in olivine phenocrysts from basaltic tephra erupted by etna volcano during the 1989 1990 eruptive period were investigated for major elements cl and s by electron microprobe fluorine by pigme particule induced gamma ray emission and h 2 o by sims the results indicate the ascent of basaltic magmas with different k 2 o concentrations possibly related to different feeding dykes lk basaltic melt inclusions rich in cl s and h 2 o are trapped in olivine fo 84 from the 1990 tephra and represent the early crystallization stage their composition in major elements is quite similar to those of most of the historic and even pre etnean alkali basalts but significantly lower in k 2 o compared with the 1989 1990 lavas only scarce hk basaltic melt inclusions were observed in the outer rim fo 79 6 of reversely zoned olivine phenocrysts and correspond to late crystallization stage at low pressure high sulfur concentration s 0 3 wt is a general characteristic of the etnean basaltic magmas with h 2 o s ratio as high as 7 the volatile abundances of the etna primitive basalts were computed at 1 45 wt for h 2 o 0 17 wt for cl and 0 047 wt for f with a high cl f ratio close to 3 6 the 1989 lava samples with cl at 660 90 ppm and f at 770 30 ppm have suffered a significant cl loss the possible behaviour of the volatile phase as co 2 h 2 o even cl is discussed with h 2 o and chlorine late degassing and an active role of h 2 o during the lava fountaining activity

the origin and flux of icebergs released into the last glacial maximum northern hemisphere oceans the impact of ice sheet topography the precipitation fields of a palaeoatmospheric general circulation model are used to derive estimates of the geographical distribution and flux of icebergs from the laurentide fennoscandinavian and eastern siberian ice sheets at the last glacial maximum lgm the atmospheric model fields from lgm simulations using climap or peltier ice 4g ice orography were studied to test the sensitivity of the predicted flux the estimated northern hemispheric lgm iceberg flux is 3500 4000 km3 yr 1 of which about 60 issued directly into the north atlantic the iceberg flux from the st lawrence area is of similar significance to that issuing from hudson strait in all estimates both the north pacific and the arctic received substantial iceberg fluxes ca 700 km3 yr 1 with relatively minor differences occurring between the two ice sheet reconstructions apparent discrepancies between arctic deep sea core samples of ice rafted debris and our estimates of mean glacial iceberg flux may be ascribed to coastal trapping of bergs the existence of floating ice tongues or a rapid exit of icebergs from the arctic basin into the greenland sea through the fram strait copyright 2001 john wiley sons ltd

pleistocene glacial history of the nw european continental margin abstract in this paper new and previously published data on the pleistocene glacial impact on the nw european margin from ireland to svalbard between c 48 n 80 n are compiled the morphology of the glaciated part of the european margin strongly reflects repeated occurrence of fast moving ice streams creating numerous glacial troughs channels that are separated by shallow bank areas end moraines have been identified at several locations on the shelf suggesting shelf edge glaciation along the major part of the margin during the last glacial maximum deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55 n and northwards whereas the margin to the south of this is characterised by the presence of submarine canyons glaciation curves based primarily on information from the glacial fed fan systems that depict the pleistocene trends in extent of glaciations along the margin have been compiled these curves suggest that extensive shelf glaciations started around svalbard at 1 6 1 3 ma while repeated periods of shelf edge glaciations on the uk margin started with mis 12 c 0 45 ma the available evidence for mis 2 suggest that shelf edge glaciation for the whole margin was reached between c 28 and 22 14 c ka bp and maximum positions after this were more limited in some regions north sea and lofoten the last glacial advance on the margin has been dated to 15 13 5 14 c ka bp and by c 13 14 c ka bp the shelf areas were completely deglaciated the younger dryas loch lomond advance reached the coastal areas in only a few regions

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

variable isostatic uplift patterns during the holocene in southeast sweden based on high resolution ams radiocarbon datings of lake isolations the construction of a new highway between uppsala and mehedeby in northern uppland southeastern sweden has motivated extensive archaeological excavations to describe changes in shoreline configuration over time the isolation of nine lake basins has been interpreted from diatom analysis their isolation ages were determined from 45 ams radiocarbon dates five per site of terrestrial macrofossils mainly betula and alnus seeds the isolation ages and the corresponding altitudes indicate a complicated pattern of isostatic uplift during the late holocene neither the present day isobases nor those for the neolithic sea seem to explain their isolation ages and corresponding altitudes in relation to their geographic distribution since at least some of the lakes are situated in a relatively pronounced topographic landscape we are inclined to explain the observations as the result of small scale irregular uplift earthquakes are rare in the area at present suggesting short term tectonic activities along e

the holocene shore displacement of gastrikland eastern sweden a contribution to the knowledge of scandinavian glacio isostatic uplift the holocene shore displacement of gastrikland eastern sweden a contribution to the knowledge of scandinavian glacio isostatic uplift

a volume based approach to calculation of ancient carbonate accumulations abstract volumes of carbonate rocks are computed for mesozoic platforms over several orders of length scales reservoir to basin scale for millions of years time intervals the calculation is based on the restoration of depositional geometries by correlating genetic sequences and on the estimation of carbonate concentrations from core and well log data the interpolation yields the total amount of carbonate buried in a closed system and represents the net budget of production preservation of sedimentary carbonate for a given time interval over a defined area covering several depositional environments a three dimensional 3 d accumulation rate is obtained by dividing the total volume of carbonate rocks by the total surface over a time interval derived from biostratigraphic data estimates of such a carbonate accumulation rate for various jurassic and cretaceous platforms range from 8 to 67 m m yr errors in computing carbonate volumes are limited whereas an uncertainty is associated with the calculati

deglaciation holocene shore displacement and coastal settlements in eastern svealand sweden abstract detailed mapping of the clay varve sediments and stratigraphical analysis of isolated lake basins on the sodertorn peninsula have been undertaken as part of the research project eastern svealand development of the holocene landscape the varve studies have identified three distinctive stratigraphical units and indicate that deglaciation took place between 11 400 and 10 400 clay varve years bp initially recession of the ice margin was slow but subsequently it became more rapid study of 15 isolation basins has allowed a tentative shore displacement curve to be constructed for the area this curve is marked by varied rates of regression and possibly displays 3 litorina transgressions the curve suggests markedly different ages for the transgression events than those proposed by earlier authors and this is assessed in terms of curve construction and dating errors archaeological evidence indicates that coastal settlements changed their altitudinal location in response to changes in sea level this evidence supporting the data derived from isolation basins

extent and timing of the last glacial maximum lgm in britain and ireland a review the last glacial maximum lgm of marine isotope stage mis 2 is defined here as the period either of maximum global ice volume or in which major ice sheets reached their maximum extent both definitions lack clarity as there is no reason to suppose that maximum volumes or limits were reached simultaneously at either all ice sheets or around the margins of individual ice sheets here we review the traditional terrestrial limits of the biis british irish ice sheet examine developments in understanding the offshore record and attempt a redefinition of the extent and timing of the mis 2 maximum as a working chronological model the build up of the biis is assigned to after 35 32 ka the maximum to the period 27 21 ka and a more limited readvance after 19 ka as marginal oscillations driven by ice sheet dynamics appear to have characterised much of the advance and especially the retreat of the biis caution should be exercised in assigning climatic significance to the many identified ice limits or still stands while much of the terrestrial limit in britain remains relatively unaltered significant revision is required offshore around britain and ireland to portray an extensive ice advance to the shelf edge and a period when the biis was conjoined with the adjacent fenno scandinavian ice sheet although there appears to be a broad synchrony between the biis and other major ice sheets local controls have produced some variation in the timing of advance to and retreat from maximum limits for particular ice streams or lobes but much of the offshore limit remains very poorly age constrained consequently a key objective in future research should be to improve and refine the chronological control for all portions of the maximum margin of the biis and its subsequent retreat stages copyright 2010 john wiley sons ltd

on the formation of the tunnel valleys of the southern laurentide ice sheet abstract catastrophic releases of meltwater produced by basal melting and stored for decades in subglacial reservoirs at high pressure may have been responsible for eroding the broad deep tunnel valleys that are common along the margins of some lobes of the southern laurentide ice sheet we surmise that these releases began when the high water pressure was transmitted to the margin through the substrate the water pressure in the substrate at the margin would then have been significantly above the overburden pressure leading to sapping failure headward erosion of a conduit in the substrate piping could then tap the stored water resulting in the outburst in some situations development of a siphon may have lowered the reservoir below its overflow level thus tapping additional water following the flood the seal could have reformed and the reservoir refilled setting up conditions for another outburst order of magnitude calculations suggest that once emptied a subglacial reservoir could refill in a matter of decades the amount of water released during several outbursts appears to be sufficient to erode a tunnel valley we think that tunnel valleys are most likely to have formed in this way where and when the glacier margin was frozen to the bed and permafrost extended from the glacier forefield several kilometers back under the glacier as reservoirs would then have been larger and more common and the seal more robust and more likely to reform after an outburst

on the formation of the tunnel valleys of the superior lobe central minnesota abstract when considering the formation of tunnel valleys most researchers have appealed to basal melting as the primary source of water erosion of the tunnel valleys can then be accomplished by steady state drainage over a long period or by storage and subsequent catastrophic release however field relationships in a large system of tunnel valleys formed by the superior lobe in central minnesota indicate that another source of water must be considered the minnesota tunnel valleys are composed of individual segments 10 20 km long and the segments commonly terminate in subaerial outwash fans at recessional ice margin positions eskers associated with the tunnel valleys are also composed of short segments frequently beginning at moulin kames and terminating at the head of outwash fans the dominant source of the water responsible for tunnel valley formation was seasonal meltwater from the glacier surface that reached the bed through moulins and crevasses the apparent continuity of the valleys resulted from the headward development of the englacial drainage system during ice retreat

erosion and infill of new york finger lakes implications for laurentide ice sheet deglaciation a comprehensive seismic reflection profile investigation of the new york finger lakes has revealed the extent of bedrock erosion and nature of sediment fill beneath the lakes bedrock deepens to the south where gorgelike profiles have been eroded to as much as 304 m below sea level and infilled with up to 275 m of late quaternary age 14 ka sediment we propose a working hypothesis that invokes ice streaming and pressurized subglacial meltwater and sediment to account for regional geomorphology this working hypothesis is consistent with recent concepts of the collapse of continental ice sheets via ice streaming and the marine isotopic record for a meltwater spike at 13 14 ka the finger lakes may provide a critical testing ground for deglaciation models of the southern laurentide ice sheet because they contain a thick well preserved and now seismically defined record of the deglaciation process

quaternary stratigraphy of the fladen area central north sea a multidisciplinary study based on detailed stratigraphic investigations on a 200 6m long core bgs borehole no 81 26 from the fladen ground area british sector core material from the sleipner field norwegian sector and shallow seismic profiles between the core sites the following conclusions are drawn 1 the north sea was glaciated sometime during th elaterpart of matuyama reversed period a complete glacial interglacial glacial cycle is recorded in these sediments 2 in a period of marine sedimentation in the middle pleistocene a transgression regression cycle under boreal arctic regime is recorded 3 the fladen area has subsided between 0 9 and 0 6 m ka through the later parts of the quaternary 4 a major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81 26 this till which was deposited by ice moving from the southwest scotland probably represents a period when the scandinavian and british ice sheets coalesced in the north sea 5 based on the seismic data and the stratigraphy of the sleipner core an ice free open embayment dry land is favoured for the central north sea during the late weichselian 6 from the amino acid data it is shown that there has been an episodic style of sedimentation through the quaternary 7 of the investigated sediments which span the last 1 mill year ca 98 have been deposited under arctic to boreal arctic conditions

testing urey s carbonate silicate cycle using the calcium isotopic composition of sedimentary carbonates abstract carbonate minerals constitute a major component of the sedimentary geological record and an archive of a fraction of the carbon and calcium cycled through the earth s surface reservoirs for over three billion years for calcium carbonate minerals constitute the ultimate sink for almost all calcium liberated during continental and submarine weathering of silicate minerals this study presents 500 stable isotope ratios of calcium in precambrian carbonate sediments both limestones and dolomites in an attempt to characterize the isotope mass balance of the sedimentary carbonate reservoir through time the mean of the dataset is indistinguishable from estimates of the calcium isotope ratio of bulk silicate earth consistent with the urey cycle being the dominant mechanism exchanging calcium among surface reservoirs the variability in bulk sediment calcium isotope ratios within each geological unit does not reflect changes in the global calcium cycle but rather highlights the importance of local mineralogical and or diagenetic effects in the carbonate record this dataset demonstrates the potential for calcium isotope ratios to help assess these local effects such as the former presence of aragonite even in rocks with a history of neomorphism and recrystallization additionally 29 calcium isotope measurements are presented from odp ocean drilling program site 801 that contribute to the characterization of altered oceanic crust as an additional sink for calcium and whose distinct isotopic signature places a limit on the importance of this subduction flux over earth history

tectonic setting of late archean bimodal volcanism in the michipicoten wawa greenstone belt ontario the tectono stratigraphic relationships depositional environments rock associations and major and trace element compositions of the late archean 2744 2696 ma bimodal basalt rhyolite volcanic rocks of the michipicoten wawa greenstone belt ontario are compatible with an origin along a convergent plate margin that varied laterally from an immature island arc built on oceanic crust to a more mature arc underlain by continental crust this environment is similar to that of the cenozoic taupo kermadec tonga volcanic zone michipicoten basaltic rocks most of which are proximal deposits compositionally similar la yb n 0 63 1 18 to modern oceanic island arc tholeiites are interpreted as having formed along the largely submerged island arc voluminous michipicoten rhyolitic pyroclastic rocks la yb n 4 3 18 7 ybn 5 7 15 9 probably erupted subaerially from the continental arc with distal facies deposited subaqueously on the adjacent oceanic island arc and proximal facies deposited in subaeri

palaeogeographical changes in response to glacial interglacial cycles as recorded in middle and late pleistocene seismic stratigraphy southern north sea offshore stratigraphic records from the north sea contain information to reconstruct palaeo ice sheet extent and understand sedimentary processes and landscape response to pleistocene glacial interglacial cycles we document three major middle to late pleistocene stratigraphic packages over a 401 km2 area norfolk vanguard boreas offshore wind farm offshore east anglia uk through the integration of 2d seismic borehole and cone penetration test data the lowermost unit is predominantly fluviatile yarmouth roads formation marine isotope stage mis 19 13 including three northward draining valleys the middle unit swarte bank formation records the southernmost extent of tunnel valley fills in this area of the north sea providing evidence for subglacial conditions most likely during the anglian stage mis 12 glaciation the yarmouth roads and swarte bank deposits are truncated and overlain by low energy estuarine silts and clays brown bank formation mis 5d 4 smaller scale features including dune scale bedforms and abrupt changes in cone penetration test parameters provide evidence for episodic changes in relative sea level within mis 5 the landscape evolution recorded in deposits of mis 19 5 are strongly related to glacial interglacial cycles although a distinctive aspect of this low relief ice marginal setting are opposing sediment transport directions under contrasting sedimentary process regimes

pacific caco3 preservation and δ18o since 4 ma paleoceanic and paleoclimatic implications the pliocene pleistocene history of caco3 preservation in the central equatorial pacific is reconstructed from a suite of deep sea cores and is compared to fluctuations in global ice volume inferred from 18o records the results are highlighted by 1 a strong covariation between caco3 preservation and ice volume over 104 to 106 year time scales 2 a long term increase in ice volume and caco3 preservation since 3 9 ma demonstrated by a deepening of the lysocline and the carbonate critical depth 3 a dramatic shift to greater caco3 preservation at 2 9 ma 4 distinctive ice volume growth and caco3 preservation events at 2 4 ma which are associated with the significant intensification of northern hemisphere glaciation 5 a mid pleistocene transition to 100 kyr cyclicity in both caco3 preservation and ice volume and 6 a 600 kyr brunhes dissolution cycle superimposed on the late pleistocene glacial interglacial 100 kyr cycles caco3 preservation primarily reflects the carbonate chemistry of abyssal waters and is controlled by long term 106 year and short term 104 to 105 year biogeochemical cycling and by distinct paleoclimatic events we attribute the long term increase in caco3 preservation primarily to a fractionation of caco3 deposition from continental shelf to ocean basin and secondarily to a gradual rise in the riverine and glaciofluvial flux of ca on shorter time scales the fluctuations in caco3 preservation slightly lag ice volume fluctuations and are attributed to climatically induced changes in the circulation and chemistry of pacific deep water

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

glacial tunnel valleys and quaternary history of the outer scotian shelf high resolution seismic reflection data indicate the presence of huge sub surface channel networks on the outer nova scotian continental shelf channel axes extend to over 450 m below present sea level b s l channel walls average 2 3 km in width mechanisms capable of producing such channels include fluvial submarine canyon or glacial erosion considerable debate has focused on the positions of the tertiary quaternary t q and pleistocene holocene p h boundaries1 4 in this region and the relationship of the t q boundary to the unconformity at the base of the channel networks uncertainty also surrounds the extent of pleistocene ice sheets on the south east canadian continental margin4 7 here we present a new stratigraphy for the sable island region fig 1 based on seismic profiles with lithologic and biostratigraphic control provided by two strategically placed boreholes this strati graphic analysis establishes the positions of the t q and p h boundaries outside the valleys at 51 m and 220 m b s l respectively our analysis also implies that the large channel systems are tunnel valleys cut by a sub ice meltwater process under a pre to early wisconsinan ice sheet which extended close to the shelf edge

the impact of calcareous nannofossils on the pelagic carbonate accumulation across the jurassic cretaceous boundary abstract calcareous nannofossils were important producers of pelagic carbonates in mesozoic oceans in order to better understand the origin of mesozoic pelagic carbonates we studied upper jurassic to lower cretaceous sediments in the central atlantic ocean dsdp sites 105 367 534a with respect to their content of calcareous nannofossils the interval under investigation is characterized by a significant increase in the deposition of carbonate rich sediments a trend that goes along with the rapid radiation of calcareous nannofossils the assemblage composition and the size variation of common taxa were analyzed and subsequently the contribution of this phytoplankton group to the pelagic carbonate accumulation was calculated results reveal two long term changes of the nannofossil assemblage composition 1 the early tithonian coccolith assemblages are of low diversity watznaueria spp cyclagelosphaera spp zeugrhabdotus spp whilst the mid to late tithonian assemblage is dominated by nannoliths conusphaera mexicana polycostella beckmannii nannoconus spp and large sized watznaueria 2 the early berriasian is characterized by a shift from the late tithonian nannolith rich assemblage to a highly diverse coccolith assemblage morphometric studies of the placolith genus watznaueria show for all three dsdp sites large sized forms of this genus in the mid and late tithonian followed by a decrease of up to 2 m for the mean size in the earliest berriasian at dsdp site 105 the studied nannolith taxa show an increase in size during the mid tithonian to berriasian interval the records of both nannofossil carbonate estimates and the measured bulk rock carbonate reveal two periods of increase in the nannofossil carbonate record of dsdp site 105 a first significant increase of the carbonate accumulation is observed in the mid and late tithonian probably caused by mass occurrences of strongly calcified taxa c mexicana p beckmannii nannoconus spp watznaueria cf manivitae this interval is here named nannofossil calcification event nce the second carbonate maximum in the late berriasian is related to a rise in absolute abundances of nannofossils this peak is amplified by an overall increase of the sedimentation rate the calculated accumulation rates of nannofossils nannofossil carbonate and bulk rock carbonate for the late berriasian are on the same scale as values from recent ocean surface sediments a comparison of nannofossil carbonate values with the bulk rock carbonate content shows that on average only 27 of the total carbonate can be explained by our nannofossil carbonate estimates this discrepancy is most likely caused by the high amount of unidentifiable micrite and fragments of calcareous nannofossils other factors contributing to the error are possible inaccuracies in the determination of absolute abundances and nannofossil volume calculations the nce occurs during a long term sea level fall dry climate and presumed low pco 2 levels a decline in abundance of strongly calcified nannofossils coincides with the opening of the pacific atlantic seaway via central america which may have had a substantial impact on the palaeoceanographic situation in the central atlantic ocean these changes are here considered to have at least partly caused the shifts in abundance size and assemblage composition of calcareous nannofossils observed across the jurassic cretaceous boundary interval

buried and open tunnel valleys in denmark erosion beneath multiple ice sheets abstract tunnel valleys are large elongate and irregular depressions cut beneath the margin of former ice sheets they are generally believed to play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour their origin however remains poorly understood examination of newly collected danish hydrogeophysical and lithological data has revealed numerous systems of buried valleys 50 350 m deep and 0 5 4 km wide these valleys are similar to the open tunnel valleys found in the present day landscape infills comprise a variety of sediments often with subglacial clay till and meltwater deposits the incised substratum consists of limestone heavy paleogene clay sand and silt the tunnel valleys have preferred orientations and can be divided into several generations each ascribed individual ice advances or ice sheets occurring during multiple glaciations the processes forming the valleys appear to prefer pre existing open and buried valleys for the renewed erosion thus old subglacial erosion pathways have been re used several times and some of the present tunnel valleys may have been established in the middle or early quaternary or even earlier this valley re use effect causes apparently anastomosed valley systems to emerge in the data images the valleys were mainly eroded by meltwater supposed to have drained from subglacially stored reservoirs probably behind a frozen margin the water was most likely released in repeated jokulhlaups and flowed in relatively small channels on the floors of the tunnel valleys which gradually became ice filled with the lowering of the bed selective linear glacial erosion is also believed to have contributed to the erosion this however was most pronounced for the widest valleys and is supposed to have played a secondary role

stress indicators adjacent to buried channels of elsterian age in north germany tectonic and soil mechanics investigations of a strongly plastic clay miocene mica clay led to the detection of strain phenomena induced in connection with the formation of elsterian buried channels a microjoint system with randomly distributed fissures is thought to result from early elsterian dessiccation and frost crack formation it occurs frequently in the upper part of the clay horizon a younger joint system which is encountered throughout the entire clay body comprises macrojoints arranged in three joint sets the evidence strongly suggests that they were formed by gravitational and kinematic loading of the clay body by overriding ice the macrojoints display various secondary alterations such as slickensides escarpments shear zones erosive and pressure zones the formation of which is seen in context with the channel incision investigations into the genesis of these alterations indicate a strong horizontally orientated stress induction lateral to the channels which resulted in stiffness modulus anisotropy it has also caused a horizontal compression of the clay body which at that time was already consolidated through ice overburdening horizontal compression of the clay led to evorsion of pore water eroding clay particles from the joint walls lower water content of the clay in combination with increased dry unit weights are found adjacent to the channels today

the last interglacial glacial cycle in denmark abstract the stratigraphy of late pleistocene interglacial interstadial and stadial deposits in denmark shows radical alternation of marine and terrestrial environments within the last interglacial glacial cycle isotope stages 6 2 climatically dependent environmental changes eustatic and isostatic responses combined with the advance and retreat of glaciers are elements in a chronostratigraphic model for sw scandinavia the late saalian borglum margreteberg interstade isotope stage 6 was characterized by arctic to boreo arctic marine conditions and tundra vegetation the eemian interglaciation isotope substage 5e reflects high sea levels with boreo lusitanian marine faunas and dense temperate forests in the early weichselian brorup interstade isotope substage 5c boreal to boreo arctic seas with relatively low water level prevailed along with open forest vegetation the middle weichselian commenced with arctic seas accompanied by ice rafting and followed by major glacier cover possibly reaching eastern denmark karmoy ristinge goteborg i stade isotope stage 4 the bo older dosebacka hirtshals interstade isotope stage 3 witnessed boreo arctic conditions with ice rafting and the establishment of a park tundra vegetation during the later jaeren goteborg ii vennebjerg stade isotope stage 3 shelf ice appeared in high arctic kattegat and skagerrak along with surging glaciers in the baltic the middle weichselian isotope stage 3 ended with the sandnes mon gardslov interstade park tundra and boreo arctic seas prevailed the late weichselian jylland stade isotope stage 2 comprises complex stadial conditions with glacier advance and retreat the jylland stade peaked with the maximum extension of weichselian glaciers along the main stationary line equivalent to the frankfurt poznan glacial stage on the north european continent

a relict ice scoured erosion surface in the central north sea abstract the interpretation of shallow seismic records from the central north sea has revealed the existence of an irregular erosion surface within late pleistocene sediments a morphological study of this surface has identified two main types of relief 1 an irregular rough topography with depressions varying in depth from 1 to 6 m and in width from 25 to 300 m and 2 a much smoother topography with relatively few depressions on a palaeobathymetric map the rough topography extends from ca 110 to 160 m below sea level od while the smoother topography extends beyond the 160 m below od contour this surface is interpreted as an ice scoured erosional feature formed by the grounding of sea ice in a shallow shelf environment the stratigraphic position of the ice scoured surface shows it to be a relict late weichselian feature formed at ca 17 000 18 000 b p

the quaternary geology of the north sea basin the north sea is a shallow 50 400 m deep 500 km wide marine embayment that separates the uk from scandinavia and northern europe fig 1 this epicontinental shelf area has had a long and complex geological history with its present day structural configuration largely being the result of rifting during the jurassic early cretaceous followed by thermal subsidence glennie and underhill 1998 zanella and coward 2003 since the middle cenozoic the central graben region of the north sea basin has accumulated up to 3000 m of oligocene to holocene sediments which locally includes more than 800 m of quaternary sediments caston 1977 1979 gatliff et al 1994 although a detailed understanding of the depositional history recorded by this sedimentary succession is yet to be fully established these sediments preserve evidence for the advance and retreat of several ice sheets into the north sea from the adjacent landmasses at different times during the quaternary these ice masses not only resulted in periodic erosion but also made a significant depositional contribution to the infill of the basin

continental drift and phanerozoic carbonate accumulation in shallow shelf and deep marine settings knowledge of past rates of transfer of rock forming materials among the principal geologic reservoirs is central to understanding causes and magnitudes of change in earth surface processes over phanerozoic time to determine typical rates of global sediment cycling we compiled information on area volume and lithology of shallow water sediments by epoch for both terrigenous clastics and marine carbonates data on amounts of surviving continental terrigenous rock as opposed to deep oceanic and including terrestrial marginal marine and marine deposits exhibit positive age area trends wherein greatest areas and volumes of conglomerate sandstone and shale are represented by younger sequences global volumes of terrigenous clastic sediment yield a mean cycling rate of 0 00124 m yr similar to that determined for eurasian 0 00127 north american 0 00058 a b ronov 0 00352 t d cook and a w bally african 0 0017 and south american 0 0021 clastic sequences surficial erosion results in the mean destruction of 0 124 of terrigenous rock volume per million years of reservoir age in contrast surviving epicratonic and shelf margin carbonate sequences yield negative cycling rates of about 0 164 m yr surviving areas and volumes increase with sequence age that is the amount of limestone and dolostone preserved in shallow water settings increases back in time to maximal areal extents in the middle and upper cambrian mass age data on terrigenous clastic successions indicate generally constant rates of crustal erosion over phanerozoic time decrease in size of the shallow marine carbonate reservoir forward in time therefore suggests generally invariant rates of global limestone accumulation and a shift in sites of accumulation from shallow cratonic to deep oceanic settings over much of the past 540 m yr causes of this eon scale depositional translocation of carbonate sediment from shallowto deep marine settings cannot be satisfactorily linked to either changes in global sea level or the evolution of carbonate producing plankton because neither exhibits a pattern of unidirectional change in position or abundance since the early phanerozoic however tabulation of long term variation in areas of continental shelves from paleogeographic maps reveals a generally uniform decrease in low latitude 30 platform area with decreasing age over most of the phanerozoic moreover rate of change of low latitude shelf area km 2 m yr is almost exactly

a mechanism for brief glacial episodes in the mesozoic greenhouse 1 the mesozoic perhaps the longest period of warmth during the phanerozoic earth history has been repeatedly affected by short lived cold interludes lasting about one million years while the origin of these cold snaps has been classically attributed to a temporary atmospheric co2 drawdown quantified mechanisms explaining these instabilities of the carbon cycle are still lacking based on a climate carbon cycle model we show that the general demise of carbonate platforms accompanying these short lived cold interludes is a powerful mechanism capable of generating a fast atmospheric co2 decrease and a moderate sea level drop associated with ice sheet buildup the temporary nature of the carbonate production decline explains the relative short time of these cold events but makes it possible to account for ice sheet waxing and waning

moredalen a canyon in the fennoscandian shield and its implication on site selection for radioactive waste disposal in south eastern sweden abstract in south eastern sweden there are a number of canyon like valleys formed in precambrian bedrock composed of granites and vulcanites the canyons called kursu or kursu valleys are generally interpreted to be formed by glaciofluvial erosion they are all located above the highest post glacial shoreline an example of such a valley is moredalen this paper discusses a combined geological and geophysical investigation of moredalen with the aim to investigate possible reasons for the formation of such an unusual feature moredalen is a marked approximately 7 km long e w striking valley that cuts through a plateau c 140 m a s l coinciding with a late precambrian peneplain geomorphological features of this kind indicate certain characteristics of the bedrock that need to be considered during safety analysis of repositories for nuclear waste the distinct weakness zones along which the kursu valleys are formed create prominent transport paths for groundwater flows furthermore the zones may be potential hazards from a rock mechanical point of view this is emphasized by palaeozoic to mesozoic differential block faulting on both sides of the moredalen valley and neotectonic movements along the valley

island arc elements and arc related ophiolites abstract all major structural elements in island arc systems fore arc magmatic arc back arc basins and remnant arcs are potential ophiolite sources and those features that allegedly characterise ophiolites of ocean ridge origin sheeted dyke complexes mantling pelagic rocks hydrothermal metamorphism and associated mineralization can also arise within arc settings age relations are critical in the interpretation of arc related ophiolites remnants of oceanic lithosphere identified by a pre arc initiation age are restricted to fore arc magmatic arc and remnant arc elements as are ophiolite masses generated at the inception of underthrusting the latter apparently common in ancient fore arc terrains form in nascent arc systems in which the rate of role back of the subduction hinge exceeds the rate of convergence spreading occurs above a foundering slab resulting in some arc like compositional features in simple arc systems later ophiolitic rocks have formed either in the active back arc basin or the magmatic arc only those ophiolites that have resided within or very close behind magmatic arcs should show calcalkaline or arc tholeiite magmatic affinities or be intruded or overlain by these rocks volcanic derived sediment or pelagic material may mantle ophiolites from all arc settings but pelagic rocks will generally dominate in stratigraphic sequences above remnant arcs and on back arc basin floors except adjacent to the magmatic arc ophiolites generated at major ocean ridges are unlikely to be immediately overlain by sediment with a significant volcanic component whereas such detritus may lie directly on arc inception arc and back arc ophiolites some arc derived ophiolites are preserved in their original tectonic position others can be identified from their internal features their relationship to other tectonic elements and the nature of associated rocks

rare earth element contents of jurassic fish and reptile teeth and their potential relation to seawater composition anglo paris basin france and england the rare earth element ree chemistry of jurassic shelf seawater from western europe anglo paris basin was investigated by analyzing the fish and reptile teeth deposited in shallow to deeper water 200 m environments ree patterns in apatites are controlled by the host sediments vertebrate teeth sampled from the siliciclastic sediments calcareous sandstones and shales show flat shale normalized ree patterns that reflect the dominant influence of the continental source from which the ree were derived carbonate deposits protected from the clastic sources contain fish and reptile teeth whose ree patterns reflect more accurately the ree composition of the overlying water column the ree patterns are similar through the bajocian to the oxfordian and are characterized by a depletion in heavy rare earth element dy ybn 1 8 5 0 compared to modern seawater compositions dy ybn 0 8 0 9 the fractionations among hree in the jurassic seawater are more efficient than in modern oceans and increases with depth instead of decreasing these hree removal processes operated as early as the paleozoic and disappeared during the late cretaceous the fractionation of hree relative to lree is correlated with the increasing depth of the basin as indicated by two independent criteria that are the sedimentary structures and the oxygen isotope composition of coexisting brachiopods the dy ybn ratio of the marine biogenic phosphates can be used as a proxy of paleo water depths at the scale of a water mass ce anomalies ce in biogenic apatite bearing limestones are variable and systematically negative relative to modern surface seawater and bathonian values mean ce 0 63 0 10 weak ce anomalies during the callovian mean ce 0 21 0 09 suggest the onset of more reducing conditions this redox change coincided with an increase of seawater temperatures as suggested by the oxygen isotope compositions measured on the same teeth we speculated that the callovian low ce could result from a decrease in the po2 due to the warming of seawater

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

the history of quaternary sedimentation in the uk sector of the north sea basin reconnaissance seismic and sampling surveys have shown that up to 500 m of lower and early middle pleistocene deltaic sediments are preserved in the uk sector of the north sea the distributions of delta related facies record the progressive expansion of peripheral delta systems northwards across the southern north sea during the early pleistocene a late middle pleistocene unconformity is present throughout the uk sector and sedimentation above the unconformity was dominated by glacial erosional and depositional processes a complex system of deeply incised valleys was eroded during each of three regional middle and upper pleistocene glaciations and the valleys have been filled or partially filled by glaciolacustrine or glaciomarine and interglacial marine sediments the valleys of the earliest elsterian glaciation are up to 400 m deep in the southern north sea the saalian and weichselian valleys are commonly more than 100 m deep they are eroded through their contemporary tills nearshore but occur well beyond the limits of these tills offshore the origins of these valleys are attributed to a combination of fluvial subglacial and periglacial processes

glacial incisions indicating middle and upper pieistocene ice limits off britain from the recognition that major incisions formed at lowland or tidewater ice sheet margins during each of the last three glacial stages it is assumed that a standard quaternary stratigraphy is applicable to the deposits geophysically profiled on the continental shelf off britain ice limits for each glacial stadial can be mapped from the geographical distribution of the incisions during the next glacial stage major incisions will be downcut on the present continental shelf or coastal lowlands to some 350 m below the ambient surface this will have important environmental consequences regarding the long term burial of hazardous wastes

volatile contents of obsidian clasts in tephra from the taupo volcanic zone new zealand implications to eruptive processes obsidian clasts in 6500 20 000 year old rhyolitic tephra deposits from the taupo volcanic zone new zealand contain variable h2o 0 2 2 5 wt and ci 0 12 0 18 wt contents these are elevated compared to degassed obsidian from rhyolitic domes 0 1 wt h2o2 0 1 wt cl which quenched at the surface major and trace element compositions of obsidian from tephra deposits suggest that they are co genetic with associated pumice the clear glassy appearance of the obsidian their high h2o release temperatures and 18o of 7 show that the water is magmatic and was not absorbed into the obsidian after tephra deposition based on analysis of melt inclusions recent primary taupo volcanic zone rhyolitic magmas contain 4 3 wt h2o and 0 18 wt cl the obsidian in the tephra deposits therefore represents partially degassed quenched primary magma water and cl contents correlate in the obsidian suggesting that the magmatic cl partitioned into a h2o rich fluid phase during eruptive degassing the partitioning of cl between the water rich vapor phase and the residual magma can be modelled as open system rayleigh fractionation using a pre eruptive h2o content of 4 3 wt and burnham s 1979 water solubility model the pressure and depth of initial vesiculation of the taupo magma is calculated to occur at about 0 9 kbar or 3 5 km depth initial fragmentation assumed to occur at a vapor melt ratio of 3 1 began at 0 1 kbar or 500 m depth obsidian in most tephra deposits contains less than 1 wt h2o and are calculated to have formed at 0 1 kbar or 500 m depth therefore some obsidian in these tephra deposits may have formed from fragmented magma the variable water contents of obsidian fragments in a single deposit indicates that quenching occurred over a range of depths this and the strong alignment of microphenocrysts in obsidian suggests that fragmented magma was welded onto the conduit walls during eruption cooled to form obsidian then incorporated into the tephra the 2000 year old hatepe phreatoplinian tephra contains many obsidian fragments with 2 wt h2o the meteoric water which caused this eruption to be phreatomagmatic may have caused obsidian to quench at unusually great depths resulting in higher h2o contents

predicting sediment thickness on vanished ocean crust since 200 ma tracing sedimentation through time on existing and vanished seafloor is imperative for constraining long term eustasy and for calculating volumes of subducted deep sea sediments that contribute to global geochemical cycles we present regression algorithms that incorporate the age of the ocean crust and the mean distance to the nearest passive margin to predict sediment thicknesses and long term decompacted sedimentation rates since 200 ma the mean sediment thickness decreases from 220 m at 200 ma to a minimum of 140 m at 130 ma reflecting the replacement of old panthalassic ocean floor with young sediment poor mid ocean ridges followed by an increase to 365 m at present day this increase reflects the accumulation of sediments on ageing abyssal plains proximal to passive margins coupled with a decrease in the mean distance of any parcel of ocean crust to the nearest passive margin by over 700 km and a doubling of the total passive margin length at present day mean long term sedimentation rates increase from 0 5 cm ky at 160 ma to over 0 8 cm ky today caused by enhanced terrigenous sediment influx along lengthened passive margins superimposed by the onset of ocean wide carbonate sedimentation our predictive algorithms coupled to a plate tectonic model provide a framework for constraining the seafloor sediment driven eustatic sea level component which has grown from 80 to 210 m since 120 ma this implies a long term sea level rise component of 130 m partly counteracting the contemporaneous increase in ocean basin depth due to progressive crustal ageing

the extension of the late weichselian late devensian ice sheets in the north sea basin the distribution of large channel like features comprising weichselian devensian incisions in the western north sea provides evidence for a much larger extension of the last ice sheet than currently assumed morphological comparison of the incisions with those in north germany and poland reveals a striking similarity in shape and distribution the features on the north sea floor are interpreted as being formed by meltwater erosion within the margin of the ice sheet the widespread absence of weichselian devensian till in the area under consideration may be attributed to later erosion large scale reworking and redistribution of sediments is indicated by the complete sediment infill of the majority of the incisions

a late devensian ice free area and possible interglacial site on the isle of lewis scotland at the time of the last glacial maximum the last scottish ice sheet has been considered by some1 2 to have extended to the continental shelf edge fig 1a whilst others3 4 have suggested that there were ice free areas in northern scotland no radiocarbon dated strati graphical evidence has been published to support either interpretation we present here data from the isle of lewis establishing that the shelly deposits from the north of that island are of late devensian age but which also show that a late devensian ice margin lay across northern lewis leaving part of the island ice free a peat possibly of interglacial status has been found in the ice free area the last scottish ice sheet therefore did not pass beyond the outer hebrides and may not even have reached the north of the island chain this evidence is also of interest to the debate on the relative expansions of the northern and southern margins of the laurentide and scandinavian ice sheets at the last glacial maximum5 6 for it suggests a restricted glacial expansion of the northern margin of the last british ice sheet at the time of its greatest southerly extent

a sedimentation pattern in anglian marginal meltwater channels from suffolk england several infilled glacial meltwater channels of anglian age are described from se suffolk u k these channels are up to 4km long 150m wide and 8m deep they possess a consistent pattern of infill comprising glacifluvial sands and gravels overlain by subglacial water lain fine sands and silts these pass conformably upwards through thinly interstratified tills and sands into basal tills the channels were formed at the ice margin their sedimentary infill indicates overriding by the ice sheet and subsequent subglacial deposition

geobiology and palaeogenomics abstract geobiology is centered on interactions of the biosphere with the atmosphere hydrosphere and lithosphere in deep time geobiology has focused on critical intervals of change for earth and its biota such geobiological studies include data from palaeobiology geochemistry and sedimentary geology within an interdisciplinary framework palaeogenomics has a variety of research agendas and one of them is to understand the genes involved in key changes in the evolutionary history of life and when those genes and their interactions first evolved the combination of geobiology and palaeogenomic studies is a powerful approach which leads to a more fundamental understanding of how earth and life have changed through time for example linking palaeogenomic studies of biomineralization genes in modern organisms and when they first evolved in the cambrian with geobiological studies of the impact this had on the production of carbonate sedimentary facies such as encrinites and the development of the neritan ocean provides a unique perspective on how genes have shaped formation of the sedimentary record another component of the cambrian explosion the evolution of vertical bioturbation at the start of the cambrian has had significant effects on biogeochemical cycling and sediment production and provides an inviting target for future genomic studies the remaining phanerozoic includes a broad variety of evolutionary innovations which within a joint geobiological and palaeogenomic context can also be profitably studied in pelagic environments the genomic changes leading to evolution of the calcium carbonate biomineralized skeletons of coccolithophores contributed to the widespread deposition of carbonate sediment in deep settings and development in the mesozoic of the cretan ocean on land linking palaeogenomic studies of the genes that led to the palaeozoic evolution of lignin and their associated geobiological effects such as deposition of coal provide another example of the effects of genes upon development of the sedimentary record such work will ultimately provide a history of genomic change and the environmental factors that influenced it as well as how genomic change influenced environments

planktogenic eustatic control on cratonic oceanic carbonate accumulation data on mass age distributions and latitudinal limits of mesozoic cenozoic shelf carbonate on cenozoic deepening of the ccd in all major ocean basins and on the abundance of pelagic chalk in epicontinental carbonate sequences indicate that the primary locus of global limestone deposition has gradually shifted from shallow cratonic to deep oceanic settings since jurassic time this change is generally coincident with progressive emergence of continents during global regression as well as with taxonomic diversification of calcareous plankton and implicates one or both processes as the primary control on carbonate sediment partitioning between shallow and deep marine reservoirs widespread pelagic carbonate does not occur with phanerozoic ophiolite sequences until the late mesozoic and generally corresponds to origins of planktonic foraminifera and diversification of coccolithophorids similarly cratonic chalk is largely re stricted to cretaceous sections correlation of mesozoic cenozoic positions of t

mid pleistocene thin skinned glaciotectonic thrusting of the aberdeen ground formation central graben region central north sea this paper presents the results of a high resolution 2d seismic survey of mid pleistocene glaciogenic sediments in the central graben region of the central north sea sediments have undergone major glaciotectonic thrusting and folding associated with the repeated southerly advance of a mid pleistocene ice sheet the total observed length of the thrust stacked section is approximately 5 6 km comprising a series of discrete thrust slices which range in length from 700 m the basal detachment of the thrust complex occurs at a depth of ca 220 m below the sea bed within the upper aberdeen ground formation a thin skinned glaciotectonic model involving proglacial to ice marginal glaciotectonic thrusting followed by post tectonic deposition is proposed initial ice advance led to the over pressurizing of groundwater within a laterally extensive sand sheet in the upper aberdeen ground formation promoting the formation of a major decollement surface at the base of the developing thrust stack over pressurization of the groundwater system is thought to have occurred in response to rapid ice advance suggesting that the development of large scale thrust complexes may be associated with surge type behaviour the proposed model evidences complex dynamics of mid pleistocene ice sheets within the central north sea

late wisconsin landform distribution and glacier bed conditions in wisconsin abstract the late wisconsin laurentide ice sheet advanced across permafrost and reached its maximum extent in wisconsin between about 18 000 and 15 000 years ago deep permafrost persisted in southern wisconsin until about 14 000 years ago and in northern wisconsin until about 13 000 years ago we suggest that during maximum glaciation a zone about 5 km wide in the south and 20 km wide in the north along the margin of the late wisconsin glacier was frozen to its bed meltwater from farther behind the margin where the bed was at least locally thawed cut a series of closely spaced tunnel channels through the frozen bed zone these channels most likely formed episodically and they were the source for much of the meltwater stream sediment deposited in broad outwash plains beyond the ice margin frozen bed conditions near the margin also likely contributed to increased upward shearing of sediment and the accumulation of thicl supraglacial sediment in northern areas up ice from the frozen bed zone the glacier bed was at least locally thawed in a zone about 75 km wide extensive drumlin fields formed in the area of the bed that was thawed by about 13 000 years ago permafrost melted in northern wisconsin and thawed bed conditions probably extended to the ice margin throughout wisconsin and adjacent areas after about 13 000 years ago in northern wisconsin the glacier was sliding on its bed and forming drumlins out to the ice margin and thick supraglacial sediment no longer accumulated

holocene relative shore level changes and stone age palaeogeography of the parnu bay area eastern baltic sea the shore displacement and palaeogeography of the parnu bay area eastern baltic sea during the stone age were reconstructed using sedimentological and archaeological proxies and gis based landsc

reconstructing the dynamics of the north west european pleistocene ice sheets abstract the flow lines of the north west european pleistocene ice sheets can be reconstructed with the aid of fabric measurements and glaciotectonic investigations from this there is evidence for a more extensive saalian glaciation of the north sea area than previously assumed with regard to the weichselian different glaciological models can be tested against the field evidence deformable bed and instantaneous glaciation may be partially responsible for the observed phenomena however while at the end of the weichselian there was fast moving ice largely following the course of the baltic sea depression during the weichselian maximum conventional radial ice flow as envisaged by hughes et al 1981 was dominant directional evidence suggests that fast moving baltic ice was present during the late stages of the older and younger saalian glaciations however possibly as a result of isostatic effects it occupied a more southerly position than during the weichselian

the origin of major incisions within the pleistocene deposits of the north sea a seismic survey to resolve the geometry of major incisions within the upper pleistocene has been run over an area of 1600 km2 in the mid north sea twelve separate incisions have been identified ranging up to 5 km wide and 25 km long with incised depths from 100 to 350 m deposits categorised into four recurring types infill the incisions to form a flat sea bed the surveyed features are comparable to others widely found beneath the northern continental shelves and lowlands of europe asia and america such incisions have a similar range of sizes and shapes were cut during at least three separate periods in the pleistocene and are down cut into substrates of various lithologies ranging from precambrian to pleistocene in age the major incisions are believed to be the product of a singular mechanism the outburst of intra ice sheet lakes forming jokulhlaup plunge pools except for late stage hollow infills which have interglacial temperate deposits the incision infills are periglacial the former deposits are similar to the sediments accumulating in the present day bathymetric enclosed deeps such as the lambay deep and devil s hole found on continental shelves it is suggested that the enclosed deeps are large kettle holes which resulted from the thawing of ice formerly buried in the incision infills