three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

deficiencies in the diatom evidence for a pliocene reduction of the east antarctic ice sheet evidence for pliocene reduction of the east antarctic ice sheet eais has been inferred from the presence of pliocene planktic marine diatoms in tills of the sirius group now exposed along the slopes of the transantarctic mountains we highlight deficiencies in this diatom evidence for a pliocene reduction of the eais first we examine what diatom habitats are left behind by a retreating ice sheet in this case the fennoscandian ice sheet fis and find that diatoms should occur in planktic and benthic marine brackish water freshwater and terrestrial habitats we expect that during former reexpansions these diverse diatom assemblages were picked up by the advancing fis and deposited in tills this is shown to be the case and diatoms found in tills from sweden and finland reflect the many habitats over which the fis passed if there was a reduction of the eais during the pliocene followed by renewed glaciation diatoms from many different habitats should be found in the resulting tills of the sirius group this is not the case only marine planktic diatoms and a few freshwater forms are reported similarly vertical downsection distribution of diatoms in sirius group and fennoscandian tills differ while in the sirius group diatoms appear restricted to surface and near surface sediments in fennoscandia they are found throughout the tills such data do not support a pliocene reduction model for the eais

deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

bulk organic δ13c and c n ratios as palaeosalinity indicators within a scottish isolation basin microfossils in isolation basin sediments are frequently used to reconstruct sea level change but preservation problems and non analogue situations can limit their usefulness here we investigate the potential of stable carbon isotopes 13c and c n ratios from bulk organic matter as an alternative proxy of salinity within isolation basin sediments from a basin in northwest scotland within the holocene sediment 13c and c n are determined largely by the mean weighted values of the predominant source of the organic material analysis of modern materials and comparison with the diatom record shows that the marine parts of the sequence are dominated by high 13c and variable c n in the fresh water sequences the organic material is a mixture of both freshwater aquatic and terrestrial plant input that have relatively low 13c and high c n the application of 13c and c n ratios in the studied basin in general follow the environmental change recorded by the diatoms and shows the potential of bulk organic matter in the investigation of salinity change in isolation basins copyright 2005 john wiley sons ltd

tsunamigenic potential due to frontal rupturing in the sumatra locked zone abstract the sumatra subduction zone is one of the most seismically active subduction zones although there have been three m w 8 4 earthquakes in the region including the disastrous 2004 m w 9 2 sumatra andaman earthquake a 500 km long patch around mentawai islands is still locked and could produce a large megathrust earthquake if the rupture propagates to the subduction front as it most likely occurred during the 2004 earthquake it may lead to a devastating tsunami here we present high resolution reflection seismic data from the sumatra locked zone that shows the subduction interface down to 20 km depth the seismic data also show that the wedge is composed of two layers a shallow layer formed by mixed to landward vergent thrusts termed as pop ups and a deeper layer showing sub horizontal reflectors the lower layer is most probably formed by duplexes whose roof serves as a pseudo decollement for the mixed to landward thrust systems based on the seismic results we perform mechanical modeling in order to understand the formation of these structures and to retrieve the associated frictional properties we first show that the activation of the pseudo decollement requires 1 either a sudden increase of effective friction along the plate interface or an irregular geometry of the plate interface 2 a lower effective friction along the pseudo decollement than along the plate interface we then show that low effective frictional values 0 1 are required to reproduce the observed frontal structures the low effective friction along the pseudo decollement could either be due to the presence of a long term high pore pressure layer or to dynamic weakening associated with earthquakes since similar structures are present in the 2010 tsunami earthquake area we favor the dynamic weakening hypothesis according to the mechanical modeling if the next rupture propagates up to the toe rupturing the three most frontal pop up structures we could expect at least 5 5 to 9 2 m of frontal horizontal displacement and a frontal uplift of 2 to 6 6 m along the frontal thrusts this would amplify the uplift of the water column and as a consequence generate a large tsunami

diatoms in antarctic ice cores some implications for the glacial history of antarctica the presence of reworked pliocene and older marine microfossils in glacial tills of the sirius group suggests that these sediments were emplaced during the pliocene or later by glaciers riding up the eastern east antarctic slope of the transantarctic mountains this interpretation implies that there was considerable fluctuation in the size of the east antarctic ice sheet as recently as ca 3 ma here we test an alternate scenario eolian emplacement of the pliocene microfossils by comparing diatoms in the sirius group with diatoms in holocene and last glacial maximum ice from the dome c core from the central antarctic plateau since the diatoms in dome c ice are known to be eolian in origin we hypothesize that if the sirius diatoms are also eolian then the two antarctic sites dome c and the sirius group equally remote from the southern ocean will have the same exotic flora i e windblown diatoms from either a fresh water or marine source however whereas the dome c diatoms are predominantly fresh water those of the sirius are predominantly marine we conclude from these data that the sirius and dome c diatoms each reflect a different mode of emplacement and that the diatoms in the sirius till were not emplaced via wind transport this conclusion does not prove that the pliocene diatoms in the sirius till record a deglaciation and pliocene reglaciation of east antarctica but rather it removes an alternate mechanism eolian transport raised by those who oppose this scenario

the last interglacial glacial cycle in ne fennoscandia a nearly continuous record from sokli finnish lapland abstract boreholes from the sokli basin in finnish lapland have recovered a unique sequence of diamicts interlayered with fine grained sediments that are rich in fossils the diamicts are interpreted as till beds deposited by the fennoscandian ice sheet the fine grained intercalations seem to represent a series of warm stages that include one interglacial and three interstadials the interglacial is characterized by a mixed taiga pollen assemblage and corresponds to a distinct diatom gyttja bed the interstadials show progressively colder floras from open birch forest to arctic forest limit to shrub tundra their sediments comprise gyttja interlayered with wood and sand interstadial 1 sands grading into sandy gyttja interstadial 2 and sands overlain by laminated silt and clay interstadial 3 the interstadial 2 and 3 deposits are underlain by diamict and are interpreted as deglaciation sequences silts with a tundra pollen assemblage separate the interglacial and interstadial 1 deposits luminescence dating evidence indicates that the interglacial bed most probably represents the nw european mainland eemian interglacial marine isotope stage mis 5e the interstadial 1 2 and 3 deposits are tentatively correlated with the early weichselian brorup and odderade interstadials and an interstadial of middle weichselian age respectively mis 5c 5a and 3 respectively the correlation implies that the easternmost part of the ice divide zone of the fennoscandian continental ice sheet was deglaciated during part of mis 3

cool kaolins in finland we use d h and 18o 16o ratios to explore the age of kaolins on the fennoscandian shield sub cretaceous kaolins in southern scandinavia have isotopic compositions indicative of weathering under warm mean annual temperatures mats of 15 c deep kaolins on the shield surface in finland previously also have been regarded as products of humid tropical weathering of mesoproterozoic to eocene age new oxygen and hydrogen isotope ratios indicate however weathering by cool groundwater under mats of 13 15 c isotope ratios are also not consistent with deep 1 km burial by cover rocks indicating that a very old age for the weathering is unlikely palaeotemperatures are below cretaceous mats yet substantially above plio pleistocene mats comparisons with palaeotemperatures in n europe and around the arctic ocean indicate that the finnish kaolins developed on the shield surface in the palaeogene or alternatively miocene deep weathering was selectively developed in highly fractured shield rocks and took place in response to latest cretaceous and palaeogene uplift and after stripping of palaeozoic cover rocks the cool kaolins in finland indicate that previous routine attributions of kaolinitic weathering products in the geological record to humid tropical environments should be closely scrutinised

possible splay fault slip during the 1946 nankai earthquake this paper considers seafloor deformation associated with the 1946 nankai earthquake which occurred in the nankai trough subduction zone off the coast of southwest japan we note that recent high resolution determinations of the slip distribution assumed to be confined to the plate boundary result in a pronounced maximum in seafloor displacement midway between the coast of shikoku and the trough axis we show that this feature could be due to slip on a splay fault rather than the plate boundary such a model for the western part of the slip distribution is able to account for the main features of the tsunamigenic seafloor deformation obtained in previous studies with a maximum slip consistent with the plate convergent rate and history of earthquake recurrence at the nankai trough

on marine microfossil transport and pathways in antarctica during the late neogene evidence from the sirius group at mount fleming there are two extreme views of the evolution of the pliocene antarctic ice sheet dynamicists argue for ice sheet reduction and reexpansion on the basis of pliocene marine diatoms in a glacial deposit the sirius group that is widespread in the transantarctic mountains stabilists argue from other evidence that the antarctic cryosphere remained essentially constant in area and volume they propose marine diatom transport by eolian processes and emplacement into terrestrial glacial strata hence the inferred source area and transport mechanism of marine diatoms are of critical importance we tested the reduction hypothesis on an important outcrop of the sirius group at mount fleming south victoria land we observed very few unidentifiable marine diatom fragments in sirius group strata in contrast marine diatoms enclosed in a surface diamicton covering the sirius group were more abundant and identifiable our study further indicates that the sirius group at mount fleming was not deposited by the east antarctic ice sheet but rather by alpine ice originating on the transantarctic mountains on the basis of both data sets we infer that marine diatoms postdate sirius group deposition at mount fleming and that transport was by wind and we advance alternative scenarios for their source and transport pathways

diatoms of the mcmurdo ice shelf antarctica implications for sediment and biotic reworking abstract in the course of investigations of the origin of the mcmurdo ice shelf mis we analyzed diatoms in 59 sediment samples collected from its upper surface fragments of centric marine species most of which occur in the ross sea today were found in all samples but identifiable marine taxa dominated the total diatom flora in only two samples in contrast non marine diatoms are abundant and diverse in most mis samples these non marine species probably live in the numerous melt ponds which are distributed widely over the shelf surface during the warmest few weeks of each austral summer non marine diatoms are clustered in four assemblages which are probably related in a complex way to geographic position on the ice shelf sediment age local geochemical variations and seasonal blooms the presence of marine diatoms in mis sediments is consistent with isotopic evidence that the mis consists of frozen seawater and with debenham s hypothesis that transport of marine macrofossils to its surface is accomplished by freezing on at the base and upward movement through the shelf caused by surface melting the combined marine and non marine diatom floras of the mis suggest a new mechanism to explain mixed diatom floras and sediments observed in antarctic cores these composite floras and sediments may be introduced or reintroduced to the marine environment during austral summers by melt water streaming off the front of the mis or through crevasses additionally icebergs calved from the mis release theie load of mixed biota and sediment when they melt these observations may pertain to oher present and former antarctic ice shelves that are characterized by surface ablation and basal freezing

a machine learning based surrogate model of mars thermal evolution constraining initial conditions and parameters of mantle convection for a planet often requires running several hundred computationally expensive simulations in order to find those matching certain observables such as crustal thickness duration of volcanism or radial contraction a lower fidelity alternative is to use 1 d evolution models based on scaling laws that parametrize convective heat transfer however this approach is often limited in the amount of physics that scaling laws can accurately represent e g temperature and pressure dependent rheologies or mineralogical phase transitions can only be marginally simulated we leverage neural networks to build a surrogate model that can predict the entire evolution 0 4 5 gyr of the 1 d temperature profile of a mars like planet for a wide range of values of five different parameters reference viscosity activation energy and activation volume of diffusion creep enrichment factor of heat producing elements in the crust and initial temperature of the mantle the neural network we evaluate and present here has been trained from a subset of 10 000 evolution simulations of mars ran on a 2 d quarter cylindrical grid from which we extracted laterally averaged 1 d temperature profiles the temperature profiles predicted by this trained network match those of an unseen batch of 2 d simulations with an average accuracy of 99 7per cent

organic remains in finnish subglacial sediments abstract many sites in fennoscandia contain pre late weichselian beds of organic matter located mostly in the flanks of eskers it is a matter of debate whether these fragmentary beds were deposited in situ or whether they were deposited elsewhere and then picked up and moved by glacial ice the till mantled esker of harrinkangas includes a shallow depression filled with sand and silt containing for example several tightly packed laminar sheets of brown moss bryales remains it is argued that these thin peat sheets were transported at the base of the ice sheet or englacially and were deposited together with the silt and sand on the side of a subglacial meltwater tunnel subglacial meltout till subsequently covered the flanks of the esker near the receding ice margin information about the depositional and climatic environments was obtained from biostratigraphic analysis of the organic matter pollen spectra for the peat represent an open birch forest close to the tundra zone a thin diamicton beneath the peat contains charred pine wood recording the former presence of pine forests in western finland the unhumified extremely well preserved peat evidently originated during the final phase of an ice free period most probably the end of the eemian interglaciation it was redeposited in the esker by the last ice sheet reconstructions of the pleistocene chronology and stratigraphy of central fennoscandia that rely on such redeposited organic matter should be viewed with caution

early mis 3 glacial lake evolution ice marginal retreat pattern and climate at sokli northeastern fennoscandia lake development at sokli northern finland is traced through the analysis of diatoms and other siliceous micro fossils in a 2 meter thick minerogenic laminated clay silt deposit dated to the early part of marine isotope stage mis 3 fluctuating water levels and changes in lake extent depicted by the siliceous micro fossil record together with lithology suggest that an important part of the sediment sequence was deposited in a glacial lake the proxy based glacial lake evolution is tested using a digital elevation model and geomorphologic evidence including eskers dated to the early mis 3 tulppio interstadial at sokli despite the apparent ice dammed nature of the lake the sediment is relatively rich in fossils and there are limited signs of re deposition of older fossil material the siliceous micro fossil record together with data from other proxies previously analysed in the same sediment samples provides a coherent picture of past environmental changes around the sokli site this is most probably due to the sheltered position of the coring site in a lake embayment quantitative climate reconstructions based on the diatom record show mean july air temperatures as high as present day values at sokli and the temperature ranges indicated by the diatom record are in agreement with temperature reconstructions based on chironomids the position of sokli in the northeastern portion of the central area of the scandinavian glaciations and the northern retreat pattern implies that an important part of eastern fennoscandia was deglaciated during the early mis 3 warming event

modelling late cenozoic isostatic elevation changes in the barents sea and their implications for oceanic and climatic regimes preliminary results late cenozoic isostatic changes in the elevation of the barents sea are simulated using a numerical model isopach maps of the deposits off present day bear island and storfjorden troughs made earlier are used to calculate the thickness of sediment cover removed from the respective drainages basins at various time intervals during the last 2 3 ma results indicate that barents sea was subaerially exposed at 2 3 ma and major parts of it became submarine after 1 ma barents sea today receives around 40 of the warm and saline north atlantic waters flowing into the scotland greenland ridge and about half of the atlantic water entering the arctic ocean it thus has an important role to play in the present day ocean circulation pattern in the polar north atlantic region and water mass transformations that take place in the greenland iceland norwegian sea and the arctic ocean the effects of an uplifted barents sea on the oceanic regime and the arctic sea ice cover under the present day forcings fields are studied using the miami isopycnic coordinate ocean model preliminary results indicate that a subaerial barents sea causes an increased input of warm atlantic waters into the arctic ocean through the fram strait which results in warming of the atlantic water masses in the arctic ocean followed by a reduction in the sea ice cover the obtained findings can be used to explain the apparent discrepancy in the late cenozoic record of the sub arctic and arctic regions whereby fennoscandia iceland and greenland are envisaged to have been covered by major ice sheets during late pliocene whereas high arctic areas such as svalbard and ne greenland were apparently free of any major ice r 2002 elsevier science ltd all rights reserved

relief and saprolites through time on the baltic shield abstract the relief of basement rocks in high latitudes has most often been interpreted as the result of glacial erosion although over large areas its character of exhumed paleoplains has been known for a long time the relief in the precambrian basement of sweden has therefore been analysed in relation to remnants of late proterozoic and phanerozoic cover rocks most of the shield was exposed in the late proterozoic the end result was an extremely flat surface the primary peneplain it was covered by palaeozoic rocks which preserved this surface until re exposure as a sub cambrian surface it makes up the present scenery in large parts of eastern and central sweden the south swedish dome is a key area for the geomorphic analysis of the shield as it has palaeozoic cover rocks on its northern and eastern slopes and mesozoic rocks on its southern and western ones based on the experience from this area classification of the relief in the whole country and experiences from the tropics on relief evolution two theoretical schemes were constructed for a discussion of the relief differentiation the analysis of the relationship between relief saprolite and cover rocks through time led to the conclusion that the most important factor for the present relief differentiation is the time of exposure of the basement surface during the phanerozoic this has important applications for the evaluation of phanerozoic crustal movements as well as implications for the assessment of glacial erosion the approach is thought to be most valuable for comparative studies of shield geomorphology in general and with the laurentian shield in particular

reworked jurassic neogene calcareous nannofossils in the central arctic abstract over 130 different reworked calcareous nannofossil taxa ranging from the lower jurassic to the neogene are recorded in quaternary sediments from the central arctic ocean species with mesozoic and tertiary stratigraphic ranges occur together this suggests that the reworked specimens are not primarily derived from the local bedrock but are transported to the central arctic ocean from the surrounding shelves and landmasses sea ice provides a possible means of transport the reworked nannofossil assemblages in the arctic are a result of geologic and climatic developments in the source areas both during the time of their deposition and during their subsequent erosion and transportation in the quaternary only two specimens restricted to the lower jurassic were observed and none restricted to the middle and upper jurassic the lower cretaceous is represented by at least four species restricted to that interval together with other long ranging taxa the presence of micrantholithus speetonensis perch nielsen is the first record of this species outside northwest europe the other lower cretaceous species observed are all typical of temperate to high latitude assemblages of both the southern and northern hemispheres the nannofossils reworked from the upper cretaceous strata are the dominant component of the assemblages nephrolithus corystus wind is recorded in the northern hemisphere for the first time some of the distinctive high latitude species present in the southern hemisphere have not been observed in the arctic helioliths discoasters and sphenoliths indicate relatively warm surface water conditions in the arctic subarctic areas during the paleocene and eocene

prediction of thrusting sequences in accretionary wedges 1 the main objective is to determine the three stages of the life of a thrust in an accretionary wedge which are the onset of thrusting along its ramp the development with the construction of the relief and the arrest because of the onset of another thrusting event a simple kinematics is proposed for the geometry of the developing thrust fold based on rigid regions separated by velocity discontinuities along which work is dissipated according to the coulomb criterion the evolution of the thrust fold satisfies mechanical equilibrium and is optimized at every time of the three stages to provide the least upper bound in tectonic force according to the maximum strength theorem the development of the thrust or its arrest because of the initiation of another thrust is decided by selecting the event which leads to the least upper bound in tectonic force the approach is first validated by proving that the critical slope angle c for the classical triangular wedge is properly captured it is shown that a perturbation in the form of an extra relief in this perfectly triangular geometry leads to the onset of thrusting with the ramp or the back thrust outcropping either at the back or to the front of the perturbation respectively for a range of slope dip close to the critical angle c the study of normal thrust sequences from the rear to the front in the wedge toe reveals that weakening of the ramp accounted for by changing its friction angle from an initial to a smaller final value is necessary for each thrust to have a finite life span this life span is longer with a larger relief buildup for more pronounced weakening decreasing the decollement friction angle results in an increase in the number of thrusts in the sequence each thrust creating milder relief the normal sequence is ended with the first out of sequence thrust which occurs earlier for smaller weakening over the ramp the proposed methodology is partly used to construct an inverse method proposed to assess the likeliness for the transfer of activity from the active to the incipient thrust in a section of nankai s accretionary wedge the inverse method provides the initial friction angle over the incipient ramp and the final friction angle over the fully active ramp from the geometry of the corresponding thrusts and the topography it is shown that the friction angle over the incipient ramp is most likely to be larger then the one over the active ramp justifying a key hypothesis needed to predict discrete sequences of thrusting

ion microprobe uranium lead dating of zircons from the lappajarvi impact crater western finland the lake lappajarvi impact crater lies in paleoproterozoic svecofennian metasedimentary rocks on the western side of the central finland granitoid complex 1 9 ga two conflicting ages have been reported for the meteorite impact an age of 77 3 0 4 ma on the basis of ar ar whole rock data from impact melt samples and a paleomagnetic age of 195 ma during studies on impact crater indicator minerals at lappajarvi zircons with an atypical appearance were found in suevite boulders these zircons seemed to have been affected by impact shock metamorphism and it was considered that they would be good candidates for ion microprobe u pb dating allowing a new and independent age estimate for the impact event at lappajarvi four spot analyses on two black coated zircons plotted close to the upper intercept end of the concordia curve giving an approximate age of 1 8 ga for the source rock seventeen analyses were done on three dull zircon grains showing patchy impact related partial recrystallization most of these data fell fairly well on a single discordia line with intercept ages of 73 3 2 5 3 ma and 1854 2 5 1 ma however five of the data spots near the lower intercept end fell on the younger side of the line this was interpreted to indicate post impact loss of lead importantly the new ion microprobe u pb age of 73 3 f 5 3 ma is in a very good agreement with the previously reported ar ar age

glacier fluctuations equilibrium line altitudes and palaeoclimate in lyngen northern norway during the lateglacial and holocene based on lacustrine and morpho stratigraphical evidence from lyngen in troms northern norway 13 marginal moraines have been mapped in front of lenangsbreene in strupskardet moraines m1 m13 are inferred to represent glacier halts or advance readvance taking place during the lateglacial and holocene the presence of collapse depressions suggests that some of them were ice cored m1 m3 a chronological framework taking into account a combination of former shorelines and related glacier meltwater channels lichenometry and ams radiocarbon dated lacustrine sediments spanning the last 20 000 cal yr bp has been established the distal glacier fed lake aspvatnet was isolated from the sea c 10 300 cal yr bp and the lacustrine sediments have been investigated by use of loss on ignition loi magnetic susceptibility water content wet and dry bulk density dbd and the magnetic parameters anhysteretic remanent magnetization arm and saturation remanent magnetization sirm there is in general good agr

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

cenozoic erosion and sedimentation in the western barents sea abstract seismic reflection data and well logs are used to interpret cenozoic sedimentary environments in the south western barents sea using volumetric calculations and compaction trend analysis the cenozoic erosion and sedimentation rates have been quantified marine environments ranging from neritic to bathyal water depths dominated the southern barents sea during the late palaeocene at the palaeocene eocene boundary a southwards progradation commenced along the uplifted and eroded loppa and stappen highs during the early eocene to mid miocene sedimentation continued in the intracratonic basins as well as along the newly established continent ocean boundary in the embryonic northern norwegian greenland sea substantial erosion occurred on the westernmost margin particularly on the stappen high during this time interval in the mid miocene during a period of relative lowstand of sea level a system of lowstand fans was deposited west of the stappen high later a pronounced progradation of the shelf edge commenced during the mid miocene to late pliocene the shelf edge prograded between 20 and 40 km during the mid pliocene to early pleistocene the barents sea and adjacent land areas were uplifted a fluvial glaciofluvial drainage system developed on the continental shelf resulting in pronounced erosion there and very high sedimentation rates on the continental margin during the last 0 8 ma several large glaciations on the barents sea shelf proper have resulted in overdeepened troughs and high sedimentation rates at the continental shelfbreak and on the continental slope the overall cenozoic erosion varies spatially as well as temporally in the svalbard area close to 3 km of rocks have been eroded since the oligocene the same amount or more was eroded from the stappen high during the palaeocene and early neogene in the south western areas during the eocene mid miocene erosion occurred along the margin in addition the loppa high and adjacent areas served as sediment source areas during the late pliocene and pleistoncene the average erosion in the south western barents sea amounted to about 600 m erosion was greater in the south east than to the west and north and was more extensive where the former glacial ice streams had flowed

holocene climate of the kola peninsula evidence from the oxygen isotope record of diatom silica holocene climate variability was studied in a lake sediment record covering the last c 9000 years from lake chuna on the kola peninsula north west russia using the oxygen isotope composition of diatom silica 18odiatom the evaporation of the lake waters is likely to be minimal and thus the isotopic composition of the lake waters recorded by the 18odiatom reflects the isotopic composition of summer precipitation overall the 18odiatom signal seems to record a predominance of the polar arctic air mass bringing cold summer air temperatures immediately after the last glaciation and again after 4000 years to present time the atlantic maritime air mass is likely to have supplied warm summer rainfall especially in the mid holocene the pattern is broadly consistent with a quantitative pollen reconstruction from chuna lake which suggests higher mean july temperatures from deglaciation to 5500 years bp with a rather steep decline to lower temperatures after 4000 years bp our results support the general regional scenario of a mid holocene warm period deduced from the higher tree line vegetation changes and glacier fluctuations in fennoscandia however the 18odiatom record from the kola peninsula suggests a relatively cold early holocene with a gradual shift to warmer conditions to a maximum at around 5000 4000 years bp assuming that the modern precipitation temperature relationship has been constant throughout the holocene

the marine eemian of the baltic new pollen and diatom data from peski russia and pohja uhtju estonia several relatively well preserved last interglacial eemian marine oxygen isotope substage 5e ca 130 116 ka deposits containing marine diatom flora have been found in finland in addition to these finnish sites more numerous eemian mikulino marine deposits are known from the northwestern part of russia and from estonia two new clayey and silty deposits covered by till one at peski russia and the other pohja uhtju estonia were studied for pollen and diatom content at peski the deposit representing the eemian interglacial is 3 8 m thick the polyhalobous diatom flora in the corylus and carpinus zones indicates the maximum of the marine transgression during the climatic optimum later the increasing proportion of brackish water diatom flora indicates a lowering in the relative sea level and finally during a very late phase of the eemian the sharply increasing proportion of freshwater species indicates the isolation of the sedimentary basin from the eemian sea at pohja uhtju according to the pollen the eemian deposit is 3 5 m thick diatoms occur only in a layer 1 6 m thick which represents the period of corylus and carpinus zones and thus the period of the climatic optimum the brackish marine diatom flora consists mainly of littoral shallow water species although peski is situated at a higher altitude than pohja uhtju at present the diatom stratigraphy at peski indicates deeper and more saline conditions than at pohja uhtju during the eemian this probably is the result of variations in glacio isostatic rebound between these sites which can be accounted for by differences of the ice load during the final phase of the saalian glaciation copyright 2002 john wiley sons ltd

a siliceous microfossil view of middle eocene arctic paleoenvironments a window of biosilica production and preservation integrated ocean drilling program iodp expedition 302 the arctic coring expedition acex unearthed the most significant find of paleogene siliceous microfossils in nearly 2 decades 100 m of early middle eocene organic rich finely laminated sediments contain abundant marine and freshwater siliceous microfossils allowing intriguing insights into central arctic paleoenvironments during the start of cenozoic cooling largely endemic assemblages of marine diatoms and ebridians are preserved along with very high abundances of chrysophyte cysts the endogenously formed resting stage of freshwater algae an overall brackish environment is invoked but variations in group dominance suggest episodic changes in salinity stratification and trophic status with the backing of inorganic geochemistry we synthesize the sediment characteristics by hypothesizing an environmental model for the cooccurrence of these diverse siliceous microfossil groups we also report on initial insights into the composition of some of the laminations which may help explain the formation of this rich sediment archive

chronology of tertiary fan deposits off the western barents sea implications for the uplift and erosion history of the barents shelf abstract a combined biostratigraphic and seismic study was performed on three holes drilled in the western barents sea two holes penetrate the thick sedimentary wedge which forms a large fan located off a trough on the barents sea shelf the bjornoyrenna fan the study shows that the fan was built over a short time span in the late pliocene pleistocene mainly due to glacial erosion of the barents shelf region this contrasts earlier age assignments which concluded that fan deposition started in the oligocene the results have a major impact on the understanding of trough mouth fan formation and has important bearing on the history of the sedimentary basins of the barents shelf

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

diatoms in south pole ice implications for eolian contamination of sirius group deposits marine and nonmarine diatoms occur throughout a south pole ice core spanning the past 2000 yr similar diatoms occur in east and west antarctica at siple and taylor domes because there are no local diatom sources at these locations diatoms must have been carried by winds from coastal or extra antarctic sites our data demonstrate widespread historical eolian transport of diatoms to the antarctic ice sheets supporting the view that sirius group sediments were contaminated by late neogene diatoms long after they were deposited if so there is no reason to postulate a pliocene deglaciation event in east antarctica

origin of a crustal splay fault and its relation to the seismogenic zone and underplating at the erosional north ecuador south colombia oceanic margin 1 splay faults within accretionary complexes are commonly associated with the updip limit of the seismogenic zone prestack depth migration of a multichannel seismic line across the north ecuador south colombia oceanic margin images a crustal splay fault that correlates with the seaward limit of the rupture zone of the 1958 mw 7 7 tsunamogenic subduction earthquake the splay fault separates 5 6 6 km s velocity inner wedge basement rocks which belong to the accreted gorgona oceanic terrane from 4 to 5 km s velocity outer wedge rocks the outer wedge is dominated by basal tectonic erosion despite a 3 km thick trench fill subduction of 2 km high seamount prevented tectonic accretion and promotes basal tectonic erosion the low velocity and poorly reflective subduction channel that underlies the outer wedge is associated with the aseismic decollement thrust subduction channel fluids are expected to migrate upward along splay faults and alter outer wedge rocks conversely duplexes are interpreted to form from and above subducting sediment at 14 to 15 km depths between the overlapping seismogenic part of the splay fault and the underlying aseismic decollement coeval basal erosion of the outer wedge and underplating beneath the apex of inner wedge control the margin mass budget which comes out negative intraoceanic basement fossil listric normal faults and a rift zone inverted in a flower structure reflect the evolution of the gorgona terrane from cretaceous extension to likely eocene oblique compression the splay faults could have resulted from tectonic inversion of listric normal faults thus showing how inherited structures may promote fluid flow across margin basement and control seismogenesis

megathrust friction determined from mechanical analysis of the forearc in the maule earthquake area the seismogenic potential of a given fault depends essentially on its frictional properties and on the mechanical properties of the medium determining the spatio temporal variations of frictional properties is therefore a key issue in seismotectonics this study aims to characterize the friction on the south america megathrust in the 2010 mw 8 8 maule earthquake area from mechanical analysis of the forearc structure and morphology based on the critical taper theory we first show that the rupture area of the maule earthquake also shown to be locked in the interseismic period coincides with the stable part of the wedge in the surrounding area the wedge is critical a finding consistent with various evidence for active deformation there this is in particular true for the arauco peninsula area which seems to have arrested the maule earthquake s rupture to the south this observation lends support to the view that the seismic rupture is inhibited when propagating beneath a critical area the geometry of the critical portion of the wedge suggests a standard internal friction int 0 7 0 13 and a hydrostatic pore pressure within the wedge the effective friction beneath the critical outer wedge is estimated to be eff b 0 27 0 03 this could be related to intrinsically low friction minerals clay or high pore pressure along the megathrust we next use the limit analysis approach to constrain the variation of the effective friction along the megathrust based on the location and geometry of internal faulting within the forearc a low effective friction is found within the rupture area eff b 0 14 to explain the reactivation of thrust fault such as the santa maria updip of the coseismic rupture or the activation of normal splay faults downdip of the rupture area the low effective friction found there could reflect strong dynamic weakening

origin and evolution of a splay fault in the nankai accretionary wedge subduction zones are often characterized by wedge shaped sedimentary complexes called accretionary prisms that form when sediments are scraped off the subducting plate and added to the overriding plate large landward dipping thrust faults can cut through such a prism these faults known as megasplay faults 1 2 originate near the top of the subducting plate and terminate at the shallow landward edge of the prism1 3 4 5 6 megasplay faults have been the subject of numerous geological and geophysical studies4 5 6 7 8 9 10 11 12 13 14 15 but their initiation and evolution through time remains poorly constrained here we combine seismic reflection data from the nankai accretionary wedge with geological data collected by the integrated ocean drilling program iodp and find that the splay fault cutting this wedge initiated approx1 95 million years myr ago in the lower part of the prism as an out of sequence thrust oost after an initial phase of high activity the movement along the fault slowed down but uplift and reactivation of the fault resumed about 1 55 myr ago the alternating periods of high and low activity along the splay fault that we document hint at episodic changes in the mechanical stability of accretionary prisms

the baltic ice lake and yoldia sea stages based on data from diatom analysis in the central south eastern and eastern baltic abstract this paper is the first attempt to summarize the results of diatom analyses from sediments of late glacial and preboreal age in the central south eastern and eastern baltic the baltic ice lake deposits are poor in diatoms and amongst those present planktonic freshwater species dominate the yoldia stage sediments however are richer in diatoms and it is possible to recognize these sediments from changes in the composition of the diatom flora i e the occurrence of brackish marine and halophilous species the decrease in planktonic forms and the increase in periphytic ones

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

freshwater diatom influx in intertropical atlantic relationships with continental records from africa diatom assemblages from modern west african rivers and from lacustrine sediments subjected to deflation represent the present day sources of continental diatoms to the sea diatom productivity in large rivers is high especially for the genus melosira windblown diatoms derive mainly from the central and northern sahara summer dust plume where saline chloride water assemblages are widespread or from the southern edge of the sahara winter dust plume where melosira rich assemblages of dilute water predominate freshwater diatom peaks in atlantic cores may reflect 1 phases of increased river influx correlated with humid episodes on the continent or 2 phases of enhanced deflation and wind transport during arid episodes the single hypothesis for fine sediments from mid ocean sites genus melosira dominates the freshwater assemblages of many modern and fossil marine samples whatever the transport agent is therefore it is not an accurate paleoclimate indicator by itself but associated taxa may provide information on the environmental and geographical origin of the displaced diatoms this tentative approach shows that freshwater diatoms in atlantic cores may be a good tool for reconstructing paleoclimates and for establishing continent ocean correlations if species analyses are made and if the continental distribution of the taxa encountered is considered

stratigraphic evidence for eemian crustal movements and relative sea level changes in eastern fennoscandia abstract palaeobotanical data show that during the last or eemian interglacial the climate in northern europe was warmer than during the postglacial climatic optimum the main warm period of the eemian is identifiable in pollen and plant macrofossil analyses from the abundance of thermophilous species many of which grew in eemian time far beyond their flandrian northern limits these features typical of the eemian occurrences were found in the ollala interglacial site in haapavesi western finland the diatom flora together with the plant macrofossils showed a sequence from a marine to fresh water environment and thus the isolation of the sedimentary basin from the eemian sea as a consequence of glacio isostatic rebound the marine diatom flora was rich with many exotic species indicating a higher salinity than ever found in the postglacial marine deposits in this region together with some other finds the ollala interglacial deposits at about 116 117 m above the present sea level suggest that the general patterns of eemian and flandrian uplift were largely similar but that there were also differences in crustal deformations during these two interglacials the ice load during the maximum phase of each glaciation determines the amount of crustal downwarping but the deglaciation history and changes in the geographical distribution of the ice load during the melting phase are other important factors responsible for the shape of the land uplift regions

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

seismic slip propagation to the updip end of plate boundary subduction interface faults vitrinite reflectance geothermometry on integrated ocean drilling program nantro seize cores seismic faulting along subduction type plate boundaries plays a fundamental role in tsunami genesis during the integrated ocean drilling program iodp nankai trough seismogenic zone experiment nantro seize stage 1 the updip ends of plate boundary subduction faults were drilled and cored in the nankai trough offshore japan where repeated large earthquakes and tsunamis have occurred including the a d 1944 tonankai mw 8 1 earthquake samples were obtained from the frontal thrust which connects the deep plate boundary to the seafloor at the toe of the accretionary wedge and from a megasplay fault that branches from the plate boundary decollement the toe of the accretionary wedge has classically been considered aseismic but vitrinite reflectance geothermometry reveals that the two examined fault zones underwent localized temperatures of more than 380 c this suggests that frictional heating occurred along these two fault zones and implies that coseismic slip must have propagated at least one time to the updip end of the megasplay fault and to the toe of the accretionary wedge

in situ stress state in the nankai accretionary wedge estimated from borehole wall failures we constrain the orientations and magnitudes of in situ stress tensors using borehole wall failures borehole breakouts and drilling induced tensile fractures detected in four vertical boreholes c0002 c0001 c0004 and c0006 from nw to se drilled in the nankai accretionary wedge the directions of the maximum horizontal principal stress shmax indicated by the azimuths of borehole wall failures are consistent in individual holes but those in c0002 margin parallel shmax are nearly perpendicular to those in all other holes margin normal shmax constrained stress magnitudes in c0001 and c0002 using logged breakout widths combined with empirical rock strength derived from sonic velocity as well as the presence of the drilling induced tensile fractures suggest that the stress state in the shallow portion of the wedge fore arc basin and slope sediment formations is predominantly in favor of normal faulting and that the stress state in the deeper accretionary prism is in favor of probable strike slip faulting or possible reverse faulting thus the stress regime appears to be divided with depth by the major geological boundaries such as unconformities or thrust faults the margin perpendicular tectonic stress components in the two adjacent sites c0001 and c0002 are different suggesting that tectonic force driven by the plate pushing of the philippine sea plate does not uniformly propagate rather the stress field is inferred to be influenced by additional factors such as local deformation caused by gravitation driven extension in the fore arc and thrusting and bending within individual geologic domains

fluid pressure control on splay fault activation in accretionary prism based on the maximum strength theorem with application to the nankai wedge abstract the maximum strength theorem is applied to determine the pressure conditions in accretionary wedges responsible for the activation of splay faults sf this theorem based on the limit analysis developed in soil mechanics selects among several modes of deformation the one prevailing for a given pressure distribution it applies for frictional rock properties and for an arbitrary wedge geometry in particular the decollement is assumed here to be partitioned into two mechanically distinct regions the internal region being part of the seismogenic zone the considered modes of deformation include the activation of a thrust fold rooting on the decollement and outcropping anywhere on the topography this mode if close to the transition between the seismic and the aseismic region of the decollement is in competition with the sf which constitutes also a potential mode of deformation the dominance of the various modes of deformation is presented in stability maps in the plane spanned by the pressure ratios of the two regions of the decollement pore pressure divided by lithostatic pressure both referenced to the sea floor several maps are proposed for the particular case of the kumano transect of nankai wedge south west japan varying the sf pressure ratio the position of the sf root on the decollement with respect to the transition between the seismic and aseismic regions as well as the respective length of these two regions in addition these stability maps are suggesting various scenarios to explain the changes through time in the prevailing mode of deformation in an accretionary wedges for the kumano transect three scenarios could explain the observed deactivation of the sf one of them being the seaward migration of the decollement transition point

effect of increased shear stress along a plate boundary fault on the formation of an out of sequence thrust and a break in surface slope within an accretionary wedge based on numerical simulations abstract we investigated the effect on accretionary wedge structure of increased shear stress which describes the frictional sliding resistance along a decollement arising from an increase in material friction or reduction in pore pressure to clarify the nature of the effect we performed numerical simulations using two models a stable friction model and an increased friction model the stable friction model produced a low angle smooth surface slope and an in sequence thrust whereas the increased friction model produced a break in surface slope scarp and an out of sequence thrust ost that cuts through the thrust sheet the ost formed via the connection of segments of two adjacent thrusts and its formation resulted in a change in the thickening mode of the wedge from thrust sheet rotation and back thrust activity to underplating this contrast in thickening mode between the landward high friction zone and seaward low friction zone resulted in the formation of a clear break in slope as the landward zone is steeper than the seaward zone consistent with critical taper theory the subduction of a basement slice or seamount can produce similar structures arising from an increase in resistance to basal shear sliding however the distinctive structures arising in an accretionary wedge as a result of increased shear sliding resistance include a flat basal plane and absence of slope failure sediments beneath the ost these structural features are observed in accretionary wedges of the nankai trough off muroto japan the sunda strait and the barbados ridge

dem identification of macroscale stepped relief in arctic northern sweden abstract stepped relief is a characteristic feature of many upland areas on earth in this study we examine if stepped relief can be identified objectively by gis analysis of digital elevation models dems we specifically study the stepped relief landscapes of northern sweden comprising areas of contrasting topography in the mountainous northern scandes and on the inselberg plains of the precambrian basement east of the caledonides we mainly use hypsographic curves to examine the elevation distribution of the study areas and to identify palaeosurfaces peaks in the hypsographic curves are interpreted as palaeosurfaces while hypsographic minima are interpreted as breaks in slope separating these surfaces in the northern scandes where only patchy remnants of palaeosurfaces remain we use empirical cutoff values of slope angles to restrict palaeosurface areas to those identified in the field and in air photos in addition air photo and field mapping of glacially eroded areas is necessary to exclude glacially formed low relief surfaces such as valley floors these latter procedures introduce an unavoidable degree of subjectivity to the study our results indicate that in the northern scandes surfaces with an inclination of

late cenozoic erosion of the high latitude southwestern barents sea shelf revisited the southwestern barents sea has experienced profound erosion during the last 2 7 m y that has resulted in the development of a characteristic glacial morphology of the continental shelf and deposition of a several kilometer thick sediment fan along the western margin prograding into the deep sea in the period from ca 2 7 to 1 5 ma proglacial processes including fluvial and glaciofluvial erosion dominated for this period the total average erosion of the shelf was 170 230 m the average erosion rate was 0 15 0 2 mm yr and the average sedimentation rates on the fan were 16 22 cm k y subglacial erosion affected an area of 575 000 km 2 during the period from ca 1 5 to 0 7 ma total average erosion is estimated at 330 420 m for this interval and the average erosion rate was 0 4 0 5 mm yr average sedimentation rates were 50 64 cm k y during the last 0 7 m y glacial erosion mainly has occurred beneath fast flowing paleo ice streams topographically confined to troughs 200 000 km 2 the total average erosion is estimated at 440 530 m average erosion rate is 0 6 0 8 mm yr and average sedimentation rate on the continental slope is 18 22 cm k y the amount of erosion was mainly determined by the duration of the glaciations and the location velocity and basal properties of the ice streams in total glacial erosion of the troughs has been relatively high throughout the last 2 7 m y at 1000 1100 m for the banks erosion is inferred to have increased from ca 2 7 ma to a peak between 1 5 and 0 7 ma subsequently little erosion occurred in these areas which implies a total of 500 650 m of erosion compared with other high latitude areas our rates are among the highest so far reported this comparison also demonstrates that there have been large variations in the rate of sediment delivery to the glaciated continental margins

mid cenozoic tectonic and paleoenvironmental setting of the central arctic ocean drilling results from the integrated ocean drilling program s arctic coring expedition acex to the lomonosov ridge lr document a 26 million year hiatus that separates freshwater influenced biosilica rich deposits of the middle eocene from fossil poor glaciomarine silty clays of the early miocene detailed micropaleontological and sedimentological data from sediments surrounding this mid cenozoic hiatus describe a shallow water setting for the lr a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting a review of cenozoic tectonic processes affecting the geodynamic evolution of the central arctic ocean highlights a prolonged phase of basin wide compression that ended in the early miocene the coincidence in timing between the end of compression and the start of rapid early miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended however for much of the late paleogene and early neogene tectonic reconstructions of the arctic ocean describe a landlocked basin adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown

volcano tectonic setting of the intraplate pliocene holocene newer volcanic province southeast australia role of crustal fracture zones 1 the pliocene holocene newer volcanic province in victoria southeast australia is a wide volcanic field site of the most recent volcanic activity of australia the intraplate signature and the localization on the northern side of the southern ocean have been used in the past to ascribe the volcanic activity either to the presence of a mantle hot spot or to thermal anomalies inherited from the seafloor spreading that separated australia from antarctica during the gondwana breakup the spacing and distribution of groups of eruption points suggests the presence of a 32 km deep mantle thermal anomaly alignments of eruption points indicate a strong tectonic control on magma emplacement mainly along nw se mesozoic cenozoic structures and along n s palaeozoic and e w late cretaceous structures this volcano tectonic setting relates to the interference of the left lateral kinematics of the major n s trending faults associated with the tasman fracture zone and the extensional structures of the otway basin this interpretation is also coherent with stress in situ data and focal mechanisms of earthquakes shmax oriented n150 this interpretation enhances the role of the tasman fracture zone a major sinistral transform on the reactivation of transtensional structures and on triggering the magmatism of the newer volcanic province

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

transition of accretionary wedge structures around the up dip limit of the seismogenic subduction zone the nankai accretionary prism is divided into three segments outer and inner wedges and their transition zone these wedges reflect different aspects of wedge taper internal deformation and basal plate boundary fault the outer wedge is characterized by narrow critical taper internal deformation by in sequence fold and thrust and aseismic decollement the inner wedge represents a stable narrow taper weakly deformed internal structure and seismogenic plate boundary fault along its base the transition zone between the two wedges shows large critical taper with steep surface slope internal structure of out of sequence thrust and step down of decollement onto the sediment oceanic basement interface the trench slope break and oceanward margin of forearc basin is located around the landward edge of this transition zone these common aspects might be related to the lithification of both accreted and underthrust sediments and the resultant switch of the plate boundary fault deformation and lithification process recorded in exhumed on land melange of accretionary complexes suggest that the step down of the plate boundary decollement occurs around the up dip limit of seismogenic subduction zone

long term morphotectonic evolution in sweden abstract a morphotectonic interpretation of the relief of sweden is presented based on an analysis of the gross forms of the topography computer made topographic profiles covering 76 375 km have been examined together with contour maps new maps of relief and layers of height have also been used three main aspects considered are the relation between the surface of the precambrian basement and its cover rocks the erosional new surfaces developed in both caledonian basement and reexposed precambrian basement and the evolution of the valley pattern the analysis produced the following results the surface of the precambrian basement is a mosaic of old exhumed surfaces and new surfaces formed after erosion of the cover rocks the exhumed surfaces include 1 a sub jotnian surface mainly below cover rocks in downfaulted positions 2 the sub cambrian peneplain and 3 sub mesozoic etch surfaces block faulting was identified in relation to the different exhumed surfaces after the formation of the caledonides a post caledonian surface was cut across the caledonian basement and the precambrian basement with its cover the subsequent evolution of the swedish part of this surface has been traced through several new surfaces in stepped sequences and in relation to the exhumed surfaces five main denudation intervals are distinguished that result in characteristic relief they are preceded by intervals of orogeny uplift and faulting and followed by subsidence and or deposition of sedimentary strata the valley patterns the distribution of new and exhumed surfaces as well as remmants of cover rocks give some fundamental clues to where and when uplift and subsidence occurred historical geomorphology has mainly been based on theories of erosion cycles the relief of the cratons are difficult to fit exclusively into such a system the importance of long lasting covers and of exhumed surfaces have not been considered enough neither the movements of uplift and subsidence reconstruction of geomorphic events appears to be more important for understanding relief evolution than any model as every phase is unique the methods used in this study are worth testing within other cratons

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

geological record and reconstruction of the late pliocene impact of the eltanin asteroid in the southern ocean in 1995 an expedition on board the research vessel fs polarstern explored the impact site of the eltanin asteroid in the southern ocean the only known asteroidimpact into a deep ocean basin analyses of the geological record of the impact region place the event in the late pliocene 2 15 myr and constrain thesize of the asteroid to be 1 km the explosive force inferred for this event places it at the threshold of impacts believed to have global consequences and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events which are common on geological timescales

cenozoic erosion and the preglacial uplift of the svalbard barents sea region abstract the creation of the huge fans observed in the western barents sea margin can only be explained by assuming extremely high glacial erosion rates in the barents sea area glacial processes capable of producing such high erosion rates have been proposed but require the largest part of the preglacial barents sea to be subaerial to investigate the validity of these proposals we have attempted to reconstruct the western preglacial barents sea our approach was to combine erosion maps based on prepublished data into a single mean valued erosion map covering the whole western barents sea and consequently use it together with a simple airy isostatic model to obtain a first rough estimate of the preglacial topography and bathymetry of the western barents sea margin the mean valued erosion map presented herein is in good volumetric agreement with the sediments deposited in the western barents sea margin areas and as a direct consequence of the averaging procedures employed in its construction we can safely assume that it is the most reliable erosion map based on the available information by comparing the preglacial sequences with the glacial sequences in the fans we have concluded that 1 2 to 2 3 of the total cenozoic erosion was glacial in origin and therefore a rough reconstruction of the preglacial relief of the western barents sea could be obtained the results show a subaerial preglacial barents sea thus during interglacials and interstadials the area may have been partly glaciated and intensively eroded up to 1 mm y while during relatively brief periods of peak glaciation with grounded ice extending to the shelf edge sediments have been evacuated and deposited at the margins at high rates the interplay between erosion and uplift represents a typical chicken and egg problem initial uplift is followed by intensive glacial erosion compensated by isostatic uplift which in turn leads to the maintenance of an elevated and glaciated terrain the information we have on the initial tectonic uplift suggests that the most likely mechanism to cause an uplift of the dimensions and magnitude of the one observed in the barents sea is a thermal mechanism

high precision slip distribution of the 1944 tonankai earthquake inferred from tsunami waveforms possible slip on a splay fault abstract inversion of tsunami waveforms is a well established technique for estimating the slip distributions of subduction zone earthquakes with some of the most detailed results having been obtained for earthquakes in the nankai trough sw japan the present study although it uses a method and tsunami waveform data set almost identical to previous study aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami green s functions specifically we incorporated four improvements in the present study 1 we used a realistic plate model based only on seismic survey results and assumed it to be the fault plane of the 1944 tonankai earthquake 2 the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis 3 we included the effect of horizontal displacement of the ocean bottom on tsunami generation and 4 we performed a checkerboard resolution test as obtained in previous studies a zone of high slip 2 0 m was resolved off the shima peninsula however the more precise calculation of tsunami green s functions has revealed additional detail that was not evident in previous studies which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism while there was little or no slip near the trench axis in the eastern part of the rupture zone there was up to 1 5 m of slip resolved within 30 km of the trough axis in the western part along the coast of the kii peninsula this troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys furthermore it is also clear that the upper edge of the enshu fault off shima and atsumi peninsulas is consistent with the up dip limit of slip in the eastern part of our model we tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 tonankai earthquake and find that slip on this splay fault is also consistent with the data although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface we further suggest that the position of the enshu fault may be determined by the subduction of topographic highs and that such faults may have an important influence on the up dip rupture limit of the 1944 tonankai and potentially other subduction zone earthquakes

splay fault slip in a subduction margin a new model of evolution in subduction zones major thrusts called splay faults are thought to slip coseismically during large earthquakes affecting the main plate interface we propose an analytical condition for the activation of a splay fault based on force balance calculations and suggest thrusting along the splay fault is generally conditioned by the growth of the accretionary wedge or by the erosion of the hanging wall in theory normal slip on the splay fault may occur when the decollement has a very low friction coefficient seaward such a low friction also implies an unstable extensional state within the outer wedge finite element elasto plastic calculations with a geometry based on the nankai kumano section were performed and confirm that this analytical condition is a valid approximation furthermore localized extension at a shallow level in the splay hanging wall is observed in models for a wide range of friction coefficients from 0 to the value of internal friction coefficient of the rock here equals to 0 4 the timing of slip established for the splay fault branch drilled on nankai kumano transect suggests a phase of concurrent splay and accretionary wedge growth 2 ma to 1 5 ma followed by a locking of the splay 1 3 ma active extension is observed in the hanging wall this evolution can be explained by the activation of a deeper and weaker decollement followed by an interruption of accretion activation of a splay as a normal fault as hypothesized in the case of the tohoku 2011 earthquake can be achieved only if the friction coefficient on the decollement drops to near zero we conclude that the tectonic stress state largely determines long term variations of tightly related splay fault and outer decollement activity and thus influences where and how coseismic rupture ends but that occurrence of normal slip on a splay fault requires coseismic friction reduction

mineralogy and geochemistry of the clay fraction of till in northern finland abstract the mineralogy and geochemistry of the clay fraction of till in different moraine types and in different bedrock areas in northern finland have been studied moraine types include ground moraine rogen moraine pulju moraine sevetti moraine and kianta moraine the bedrock is composed of granite granite gneiss and mafic volcanite x ray diffraction differential thermal and thermogravimetric analyses transmission electron microscopy x ray fluorescence and atomic absorption spectrometry were used as analytical methods quartz feldspars and amphibole are the primary rock forming minerals occurring in nearly all the samples of each study area the clay minerals proper include kaolinite vermiculite swelling lattice vermiculite chlorite illite and mixed layer minerals kaolinite occurs most abundantly only in till in the kittilaarea where a preglacial weathering crust has been the source rock poorly crystalline or amorphous fe oxides also abound in till at kittila sodium ca and si have been depleted and al mg fe k ti p and trace elements have been enriched in the clay fraction compared with the fine fraction the contents of si k and na are higher in the granitic areas and the contents of cu co ni and zn are higher in the mafic volcanite areas preglacial weathering has led to the depletion of si mg ca k and na and to the enrichment of al fe ti p and trace elements in the clay fraction of till in the kittilaarea high base metal values in the inari area suggest the possibility of sulphide mineralizations there and high as values in the kittilaarea indicate au potential there the most important factors controlling the mineralogical and geochemical composition of the clay fraction of the tills in northern finland are the composition of the bedrock and the possible occurrence of an old weathering crust the final grain size composition of the tills and consequently the quantitative proportions of the different minerals are often related to the last glacial quarrying and sorting processes therefore the mineralogical composition of the tills is to a certain extent bound also to the respective moraine types

pleistocene marine deposits in the coastal areas of kola peninsula russia abstract on the basis of field data datings from both electron spin resonance and optically stimulated luminescence and micro and macrofauna in addition to presence of diatoms three late pleistocene marine units have been identified in the coastal areas of the kola peninsula the stratigraphically lowest sequence is correlated to the ponoi beds and the boreal transgression attributed to the marine isotope stages mis 5e to 5d in the white sea depression and to mis 5e to 5c in the barents sea thermophilic fauna and diatoms indicate normal water salinity and a water temperature above zero the second marine unit referred as the strel na beds can be correlated with the early weischselian transgression termed the belomorian transgression with low water salinity and a water temperature similar or colder than the present times belomorian transgressions are reliably detected in the white sea and are not clearly found in the barents sea the results obtained from the sediments of the ponoi and strel na beds indicate a continuously existing marine reservoir from 130 to 80 70 ka ago entire mis 5 in the white sea depression the early middle weichselian barents kara ice sheet invasion and its recession might have caused the glacioeustatic middle weichselian mis 3 transgression and the third late pleistocene marine sequence has been deposited in the regressing shallow cold sea with less saline waters the results help in the understanding of the history of late quaternary ice sheets in north eurasia and provide evidence for the debatable early and middle weichselian marine events

8786sr phytoplankton and the nature of the late cretaceous and early cenozoic arctic ocean abstract the arctic ocean s link to the lower latitude world ocean during the late cretaceous and early cenozoic is puzzling the tectonic development of the arctic ocean evidently included termination of the pacific arctic connection late in the cretaceous and the atlantic link was not significant until at least the eocene yet during the late cretaceous arctic ocean mollusks indicate that there was no more than partial restriction and late cretaceous and middle eocene phytoplankton species are the same in both the arctic and world ocean sr isotope ratios of fish associated with the phytoplankton are higher than that accepted as the world ocean s ratios for any time during this interval yet these high ratios do not indicate an isolated arctic basin the arctic was linked with the world ocean and the best evidence for this is the phytoplankton similarity but the location of the marine connection remains enigmatic

rapid forearc basin uplift and megasplay fault development from 3d seismic images of nankai margin off kii peninsula japan abstract offshore kii peninsula japan a large thrust within the overriding forearc the megasplay fault appears to move coseismically during great earthquakes 3d seismic images of the kumano forearc basin that overlies the megasplay correlated with iodp drilling data are a potential record of the history of large scale motion along this structure in the early quaternary uplift occurred in the southwest portion of the basin that may be a preliminary phase of motion along the megasplay more extensive landward tilting of the outer basin sediments across the seismic volume occurred over 300 kyr in the middle to late quaternary 1 3 1 ma this tilting event may represent the major period of motion along the megasplay that formed the modern fault geometry extensive normal faulting that cuts the forearc basin sediments clearly formed subsequent to the late quaternary tilting and in many cases offset the modern seafloor these faults may form either due to gravitational response to the uplift or as a by product of sediment underthusting these results suggest that the megasplay is a recently formed and transient structure and support the idea that out of sequence thrusts serving as the dominant structure for convergence driven shortening in a subduction zone may be short lived geologically but dominate a margin during these intervals

cenozoic microfossils in northern finland local reworking or distant wind transport abstract allochthonous cenozoic microfossils have been reported from late pleistocene lake and mire host sediments across an area of 30 000 km2 in northern finland two main groups of microfossils are recognised palaeogene marine diatoms silicoflagellates and ebridians that include taxa from around the time of the palaeocene eocene thermal maximum and pliocene to early pleistocene freshwater diatoms the presence of these microfossils has been regarded as evidence that eocene marine and late neogene freshwater sediments formerly existed on the shield surface both groups have been referred to frequently in reconstructions of the sea level tectonic and erosion history of the northern fennoscandian shield the questions raised by the presence of allochthonous cenozoic microfossils in northern finland are however strongly resonant of the debate over the biota origin and age of the pliocene sirius group in antarctica where competing hypotheses have been put forward of local deposition and reworking versus distant wind transport of marine diatoms from the continental shelf this review explores alternative origins for the allochthonous cenozoic microfossils in northern finland local reworking of palaeogene marine sediments during pleistocene glaciation is unlikely as no source rocks of palaeogene age are known from the shield surface or from surrounding sedimentary basins in the baltic and white sea moreover at all sites except akanvaara the marine diatom taxa cover wide age ranges and occur only as minor components in diatom assemblages that are dominated by quaternary freshwater taxa local reworking of pliocene pleistocene freshwater diatoms is however compatible with the widespread survival of pre pleistocene deep weathering although no in situ or unmixed ice rafted pliocene pleistocene lacustrine sediment has yet been found an alternative origin for the marine palaeogene microfossils by distant wind transport is proposed in this hypothesis palaeogene diatomites on the barents sea shelf were exposed to deep glacial and fluvioglacial erosion during the pliocene and early pleistocene and in low sea level stages of the middle and late pleistocene intense wind action acting on comminuted mudstones on outwash plains carried dust including microfossils into northern fennoscandia to be deposited by rain out in lakes and wetlands this material may have been later further recycled by glacial and meltwater transport and more localised wind action processes that also may help to account for the distribution of eemian marine diatoms well beyond eemian shorelines the distant wind transport hypothesis implies that the presence of marine palaeogene diatoms on the shield surface in northern finland cannot be regarded as vestiges of former marine sediments and so do not constrain the tectonic and geomorphic history of the northern fennoscandian shield in the cenozoic

holocene environmental history recorded in lake lyadhej to sediments polar urals russia an 1180 cm long core recovered from lake lyadhej to 68 15 n 65 45 e 150 m a s l at the nw rim of the polar urals mountains reflects the holocene environmental history from ca 11 000 cal yr bp pollen assemblages from the diamicton ca 11 000 10 700 cal yr bp are dominated by pre quaternary spores and redeposited pinaceae pollen pointing to a high terrestrial input turbid and nutrient poor conditions existed in the lake ca 10 700 10 550 cal yr bp the chironomid inferred reconstructions suggest that mean july temperature increased rapidly from 10 0 to 11 8 c during this period sparse treeless vegetation dominated on the disturbed and denuded soils in the catchment area a distinct dominance of planktonic diatoms ca 10 500 8800 cal yr bp points to the lowest lake ice coverage the longest growing season and the highest bioproductivity during the lake history birch forest with some shrub alder grew around the lake reflecting the warmest climate conditions during the holocene mean july temperature was likely 11 13 c and annual precipitation 400 500 mm the period ca 8800 5500 cal yr bp is characterized by a gradual deterioration of environmental conditions in the lake and lake catchment the pollen and chironomid inferred temperatures reflect a warm period ca 6500 6000 cal bp with a mean july temperature at least 1 2 c higher than today birch forests disappeared from the lake vicinity after 6000 cal yr bp the vegetation in the lyadhej to region became similar to the modern one shrub betula nana salix and herb tundra have dominated the lake catchment since ca 5500 cal yr bp all proxies suggest rather harsh environmental conditions diatom assemblages reflect relatively short growing seasons and a longer persistence of lake ice ca 5500 2500 cal yr bp pollen based climate reconstructions suggest significant cooling between ca 5500 and 3500 cal yr bp with a mean july temperature 8 10 c and annual precipitation 300 400 mm the bioproductivity in the lake remained low after 2500 cal yr bp but biogeochemical proxies reflect a higher terrestrial influx changes in the diatom content may indicate warmer water temperatures and a reduced ice cover on the lake however chironomid based reconstructions reflect a period with minimal temperatures during the lake history

lateglacial of lake onega contribution to the history of the eastern baltic basin abstract new stratigraphy data especially diatom analyses are presented from the area north of lake onega relevant to the discussion on possible lateglacial connection between the baltic sea and white sea following the deglaciation 12 000 11 000 years ago lake onega basin was occupied by a system of ice dammed lakes which drained to the lake ladoga basin when the ice retreated from the threshold leading to the white sea 11 000 years ago the water level dropped and since that the lake was controlled by its thresholds to the white sea and the baltic basin lake onega has remained distinctly above the sea level and no late weichselian sea connection existed between the white sea and baltic basins the marine diatoms frequently found in sediments are reworked older fossils as also suggested by some earlier workers lake onega drained to the white sea basin over the maselga threshold and also to lake ladoga between 11 000 and 10 000 radiocarbon years ago and to the white sea alone between 10 000 and 9500 years ago and the present outlet of lake onega river svir originated 9500 years ago

influence of patagonian glaciers on antarctic dust deposition during the last glacial period dust deposition over antarctica was much higher during the last glacial period but the causes of this flux remain unclear an analysis of the composition and age of glacial outwash sediments indicates that growth and decay of glaciers in patagonia may have influenced dust transport to antarctica at that time

timing and mechanisms of north atlantic cenozoic uplift evidence for mantle upwelling postrift domal uplift patterns are a distinct feauture of northern north atlantic margins on the basis of apatite fission track data offshore seismic stratigraphy geomorphology gravity and seismic tomography we argue that southern norway is characterized by predominantly neogene domal uplift currently available data suggest similar processes for other uplifted regions such as spitsbergen northern norway the british isles aad parts of east greenland