the paleogeography of paleozoic and mesozoic storm depositional systems a reply we welcome discussion of our paper on the paleogeography of storm systems but can demonstrate that the major points raised in duke s discussion were considered and discussed already in our original text let s take his points in turn 1 alternative mechanisms for formation of hummocky stratification duke objects to some of the alternative modes of origin which we suggested as possibilities only one of these dealt with stratification within dome dunes readers familiar with mckee s 1979 p 98 102 his figs 57 and 58 work should not experience any difficulty observing similarities between bedding in the upper part of dome dunes and hummocky stratification we did not state that the large angle stratification at the core of the dome dune was hummocky stratification and duke s remarks

sea ice leads in the arctic ocean model assessment interannual variability and trends sea ice leads in the arctic are important features that give rise to strong localized atmospheric heating they provide the opportunity for vigorous biological primary production and predicting leads may be of relevance for arctic shipping it is commonly believed that traditional sea ice models that employ elastic viscous plastic evp rheologies are not capable of properly simulating sea ice deformation including lead formation and thus new formulations for sea ice rheologies have been suggested here we show that classical sea ice models have skill in simulating the spatial and temporal variation of lead area fraction in the arctic when horizontal resolution is increased here 4 5 km in the arctic and when numerical convergence in sea ice solvers is considered which is frequently neglected the model results are consistent with satellite remote sensing data and discussed in terms of variability and trends of arctic sea ice leads it is found for example that wintertime lead area fraction during the last three decades has not undergone significant trends

japan sea a pull apart basin abstract recent field work in the hokkaido central belt and marine geology studies along the eastern margin of japan sea in addition to previously published data lead us to propose a new model of opening of the japan sea the synthesis of both on land and offshore structural data gives new constraints about the structural evolution of the system the rhombohedral shape of the japan basin and the particular tectonic behaviour of the margins on both east and west sides can be explained by an early eo oligocene rifting of a pull apart basin accommodated along two large right lateral shear zones east of korea and west of northeast japan and sakhalin it is followed during upper oligocene lower miocene by the main opening of the japan basin as a mega pull apart then a back arc spreading probably related to the subduction process induced the creation of the yamato and tsushima basins at the end of lower miocene and in middle miocene clockwise rotation of southwest japan larger than 20 or major bending of honshu mainland deduced from paleomagnetic studies is unlikely at this time since 1 or 2 my b p to present compression prevails along the eastern margin of the japan sea the generation of marginal basins as pull apart basins along intracontinental strike slip faults is a mechanism which has been proposed by other authors concerning the south china sea the question then is whether the fragmentation of the asiatic continent is an intracontinental deformation related process as proposed here or a subduction related one

a sea ice lead detection algorithm for use with high resolution airborne visible imagery the detection of leads or cracks in sea ice is critical for the derivation of sea ice freeboard from altimetric measurements of sea ice elevation we present an approach for lead detection in sea ice using high resolution visible imagery from airborne platforms we develop a new algorithm i e the sea ice lead detection algorithm using minimal signal sildams that detects clouds extracts leads and classifies ice types within leads from airborne visible imagery cloud detection is based on an assessment of local variances of pixel brightness across image scenes and where available coincident altimetric measurements are used to confirm suspected cloudy scenes the lead extraction step computes affine time frequency distributions minimal signal for the red green and blue channels of each image the transformed outputs are combined to take advantage of three channels simultaneously finally lead pixel geolocations are extracted using a set of uniform thresholds for ice typing including open water thin ice and gray ice within leads along each flight line sildams was tested using data from the digital mapping system dms dms digital photographs represent the highest resolution 10 cm visible imagery available over sea ice and were collected during nasa operation icebridge sea ice flights in the antarctic and the arctic in 2009 and 2010 respectively we demonstrate that sildams has a high lead detection capability of 99

sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

palaeoproterozoic rifting and formation of sulphide deposits along the southwestern margin of the svecofennian domain southern sweden abstract a mineralized palaeoproterozoic volcanic sequence has been identified southwest of vetlanda in southern sweden the sequence which is defined as the froderyd group is surrounded by 1 78 ga granitoids and may be considered as the southernmost segment of svecofennian crust in sweden the froderyd group has a bimodal geochemical character and is dominated by pillow basalts and associated gabbros but rhyolites thin intercalations of marble and stratiform sulphide ores do also occur the carbonate intercalations and the stratiform sulphide ores are interpreted as submarine exhalites formed syngenetically with the volcanic activity the mafic rocks have a typical mid ocean ridge basalt geochemistry with flat rare earth elements patterns the lead isotopic compositions of the mafic rocks and the associated stratiform sulphide ores support such a close affinity to juvenile sources with mantle character in contrast the rhyolites display more evolved geochemical signatures and isotopic patterns and are interpreted to represent remelted products of slightly older sialic crust a model for the formation of the froderyd group is presented suggesting rifting along a continental margin which may have occurred in the final stage of the svecofennian crust forming period

mineralogically mature sandstones in accretionary prisms abstract plate tectonic interpretations of sandstone composition are made in the hope that detrital framework modes of sandstone suites provide information about the tectonic setting of basins of deposition and associated provenances dickinson et al 1983 the underlying assumption that provenance tectonics are directly associated with tectonics of depositional and post depositional sedimentary settings is not however universally true as sandstones from two contemporary accretionary prism complexes nias island indonesia and barbados west indies illustrate mineralogically immature sandstones rich in feldspar and volcanic lithic fragments are expected in such tectonic settings but both nias island and barbadian sandstones are mineralogically very mature dominated by quartz in b th cases this discrepancy between inferred and actual tectonic setting has been explained by postulating that sands from a provenance petrogenetically unrelated to the arc trench system e g continental or recycled orogen sands have been introduced into the accretionary prism by sedimentary or tectonic processes sandstones which are transported sedimentologically or tectonically across the boundaries of sedimentary tectonic provinces and which therefore occur in tectonic settings petrogenetically unrelated to the tectonics of the sediment source area are important components of at least some active accretionary complexes the possibility of trans boundary sedimentary and or tectonic transport must be allowed for in making plate tectonic interpretations based on sandstone petrog aphy especially in reconstructions of ancient orogenic belts

effect of surface roughness on bidirectional reflectance of antarctic snow the angular pattern of sunlight reflected by snow is altered by surface roughness which in the interior of antarctica is usually in the form of meter scale longitudinal erosional features sastrugi whose axes align with the direction of strong winds the bidirectional reflectance distribution function brdf changes over the course of a day as the solar azimuth changes relative to the sastrugi axis the normalized brdf or anisotropic reflectance factor r was measured at south pole station from a 22 m tower at 600 660 and 900 nm wavelengths the r pattern was similar at the three wavelengths it probably varies little from 300 to 900 nm measurements were made at solar zenith angles 0 from 67 to 90 over the full range of viewing zenith angle r azimuth angle between sun and view and azimuth angle between sun and sastrugi sas variation of r with sas was notable sastrugi oriented perpendicular to the solar beam cause a reduction of the forward peak and sastrugi at an oblique angle cause r to lose its symmetry about the solar azimuth however the effects of sastrugi are mostly restricted to large viewing zenith angles so remote sensing of albedo and atmospheric properties can be carried out accurately without knowledge of sastrugi height and orientation if only near nadir views are used this recommendation is opposite that for observations of broken clouds over dark surfaces for which large r is preferred a parameterization of r is developed valid for viewing angles r 50 sastrugi can cause a reduction of the snow albedo by altering the angle of incidence and by trapping of photons for the small sastrugi of the antarctic plateau the albedo is unaffected at visible wavelengths but can be reduced by a few percent at near infrared wavelengths when the sun is low

a review of gold mineralization styles in finland a wide range of styles of gold mineralization has been recognized in finland including orogenic metamorphosed epithermal skarn or epigenetic ironstone hosted intrusion related nonskarn massive sulfide hosted paleoplacer and placer deposits gold production in the past was principally as a byproduct from the mining of paleoproterozoic base metal massive sulfide deposits this situation has changed during the last decade with the closure of some base metal mines and the commencement of production from recently discovered gold only deposits gold mineralization occurred during distinct episodes of crustal evolution in finland several late archean greenstone belts in the karelian craton in eastern and northern finland contain orogenic gold deposits dated at about 2 75 to 2 70 ga suggesting a coherent and pervasive tectonic and metallogenic event in the paleoproterozoic low grade the main accretionary stage of the svecofennian orogeny in finland culminated with metamorphism and deformation between 1 89 and 1 86 ga during that time intrusion related au cu mineralization took place in both syntectonic porphyry stocks and their wall rocks in and close to the archean proterozoic margin orogenic gold mineralization took place at or slightly after the metamorphic peak throughout the svecofennian domain possibly also overprinting massive sulfide and intrusion related occurrences it is notable that the largest orogenic deposits are located within discrete plutons rather than hosted by supracrustal sequences this may be a consequence of the rheological contrasts between plutons and the supracrustal lithologies the paleoproterozoic lapland domain in the northern part of the country records a protracted and complicated evolution involving multiple episodes of rifting magmatism sedimentation and alteration culminating at around 1 9 ga with the collision of the karelian craton the svecofennian fold belt to the south and the kola craton to the north these deformational events led to orogenic gold mineralization throughout the proterozoic greenstone belts of northern finland at about 1 89 to 1 86 ga during and soon after the peak of metamorphism and deformation skarnlike or epigenetic ironstone hosted deposits were also formed during the orogeny in the western and southwestern parts of the lapland domain probably somewhat later at around 1 86 ga the most favorable sites for mineralization are regionally extensive zones of early albitization that predate gold mineralization the deposition of molasselike sediments during the terminal stages of the svecofennian orogeny and weathering of both orogenic and syngenetic sulfide mineralization also prior to 1 8 ga produced placer accumulations now paleoplacers in the conglomerates of the uppermost formation of the central lapland greenstone belt placer deposits of controversial origin and provenance have also been worked for many years in the glaciofluvial sediments of northernmost finland the areas with greatest potential for the discovery of new orogenic gold deposits in finland are the late archean and paleoproterozoic greenstone belts in eastern finland and lapland respectively some fe cu au skarns or epigenetic ironstone hosted deposits have been mined in the past and there may be potential for the discovery of larger iron oxide copper gold systems in the western central lapland greenstone belt for intrusion related nonskarn mineralization the most promising areas are close to the raahe ladoga suture and the potential for additional metamorphosed and deformed epithermal mineralization exists in the tampere schist belt the significant number of gold occurrences already known in these areas highlights the potential for new discoveries

estimation of sea ice thickness distributions through the combination of snow depth and satellite laser altimetry data 1 combinations of sea ice freeboard and snow depth measurements from satellite data have the potential to provide a means to derive global sea ice thickness values however large differences in spatial coverage and resolution between the measurements lead to uncertainties when combining the data high resolution airborne laser altimeter retrievals of snow ice freeboard and passive microwave retrievals of snow depth taken in march 2006 provide insight into the spatial variability of these quantities as well as optimal methods for combining high resolution satellite altimeter measurements with low resolution snow depth data the aircraft measurements show a relationship between freeboard and snow depth for thin ice allowing the development of a method for estimating sea ice thickness from satellite laser altimetry data at their full spatial resolution this method is used to estimate snow and ice thicknesses for the arctic basin through the combination of freeboard data from icesat snow depth data over first year ice from amsr e and snow depth over multiyear ice from climatological data due to the nonlinear dependence of heat flux on ice thickness the impact on heat flux calculations when maintaining the full resolution of the icesat data for ice thickness estimates is explored for typical winter conditions calculations of the basin wide mean heat flux and ice growth rate using snow and ice thickness values at the 70 m spatial resolution of icesat are found to be approximately one third higher than those calculated from 25 km mean ice thickness values

response of shallow marine carbonate facies to third order and high frequency sea level fluctuations hauptrogenstein formation northern switzerland abstract facies patterns in shallow marine carbonates of the hauptrogenstein formation of northern switzerland middle bajocian to early bathonian reflect small changes in sea level third order sea level fluctuations calculated from large scale facies patterns alternations of marl and carbonate dominated sedimentary units on the level of members and subsidence show two phases of sea level rise and fall in the late bajocian and a relative sea level rise in the early bathonian most of the sedimentary rocks were produced during phases of relative rise and highstand of sea level no periods of emergence during lowstands are preserved sea level changes of a higher order have been analyzed by facies changes at the outcrop scale thin shallowing up parasequences 0 5 6 m thick have been correlated across platform ramp and offshore sedimentary environments in each of these environments carbonates react differently to sea level fluctuations relative rises in sea level are represented by non deposition and biogenic sediments periods of stable or slightly falling sea level are dominated by oolitic sediments 1 in the offshoal environment marl layers at the base of thin shallowing up units are covered by increasingly proximal tempestites 2 in the ramp environment oblique stratified oolitic and bioclastic grainstones are bounded by marine flooding surfaces 3 on the platform marine flooding surfaces are overlain by beds deposited under moderate energy conditions coral beds oncoid beds platform tempestites which are in turn covered by high energy oblique stratified oolitic grainstones such parasequences deposited in response to small scale high frequency sea level changes can be correlated over distances of more than 100 km a model for evolution and response of carbonate facies to sea level changes is presented

influence of the atlantic inflow and mediterranean outflow currents on late quaternary sedimentary facies of the gulf of cadiz continental margin abstract the late quaternary pattern of sedimentary facies on the spanish gulf of cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the atlantic inflow currents flowing southeastward across the cadiz shelf toward the strait of gibraltar an inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10 20 m that extends deeper and obliquely down paleo valleys as a result of southward down valley flow a mid shelf holocene mud facies progrades offshore from river mouth sources but atlantic inflow currents cause extensive progradation along shelf toward the southeast increased inflow current speeds near the strait of gibraltar and the strong mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf at the outer shelf edge and underlying the mid shelf mud and inner shelf sand facies is a late pleistocene to holocene transgressive sand sheet formed by the eustatic shoreline advance the late quaternary pattern of contourite deposits on the spanish gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges coincident with the northwestward decrease in outflow current speeds from the strait there is the following northwestward gradation of contourite sediment facies 1 upper slope sand to silt bed facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins by comparison the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean outflow current the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies radiocarbon ages verify that the inner shelf shoreface sand facies sedimentation rate 7 1 cm kyr mid shelf mud facies maximum rate 234 cm kyr and surface sandy contourite layer of 0 2 1 2 m thickness on the cadiz slope 1 12 cm kyr have deposited during holocene time when high sea level results in maximum water depth over the gibraltar sill and full development of the atlantic inflow and mediterranean outflow currents the transgressive sand sheet of the shelf and the mud layer underlying the surface contourite sand sheet of the slope correlate respectively with the late pleistocene sea level lowstand and apparent weak mediterranean outflow current

an interlinked system of folds and ductile shear zones late stage svecokarelian deformation in the central fennoscandian shield finland abstract the svecokarelian deformation of the karelian and svecofennian provinces in finland involved four main phases isoclinal folding and associated thrusting were the main processes of d 1 which was followed by more open folding in d 2 subsequent deformation was localized during d 3 and d 4 this paper focuses on the late stage d 4 svecokarelian deformation that created most of the ductile shear zones in the central fennoscandian shield and was the last penetrative deformational event to affect the entire palaeoproterozoic domain deformation during d 4 occurred approximately from 1 85 1 80 ga and left a greater imprint in the rocks than has commonly been supposed the shear zones formed during d 4 are referred to collectively as the finlandia shear system the karelian province is composed of archaean basement and its autochthonous allochthonous palaeoproterozoic sedimentary cover svecokarelian tectonics split the basement into separate complexes the rheological properties of which differed markedly from those of the adjacent proterozoic supracrustal units on the northern and southern margins of the archaean complexes folding with steep e w trending axial surfaces was the main response to d 4 deformation whereas on the eastern and western margins of the complexes the response to d 4 was the development of sinistral and dextral shear zones trending ne sw and nw se respectively on a large scale these areas of folding and of shearing form an interlinked system the changes from one style of deformation to the other being gradual the principal d 4 elements in the area of juvenile svecofennian crust are folds with e w trending axial surfaces

contribution of detrital materials from the yukon river to the continental shelf sediments of the bering sea based on the electron spin resonance signal intensity and crystallinity of quartz abstract bering sea sediments contain detrital materials from the yukon river these materials may contain records of past climate changes in the arctic area such as the melting of glaciers around the drainage basin of the yukon river which help to understand hydrological cycle in this area in the bering sea however the spatial extent and pattern of the detrital materials supplied from the yukon river is not yet fully understood here we developed a method to identify clay to sand sized detrital materials derived from the yukon river based on electron spin resonance esr intensity of the e 1 center and the crystallinity of quartz we then estimated the spatial pattern of quartz contributed by the yukon river on the bering sea shelf by applying the method to core top samples from the continental shelf and slope of the eastern bering sea the results showed a large contribution of sand sized quartz from the yukon river to wide areas of the continental shelf and slope whereas contributions of clay to silt sized quartz from the yukon river were small except on the northeastern shelf these spatial distribution patterns suggest that sand sized quartz was repeatedly reworked and transported by processes such as storm surges to the outer continental shelf whereas the clay to silt sized quartz on the northeastern shelf was supplied as suspended materials directly from the yukon river

proterozoic tectonic evolution and late svecokarelian plate deformation of the central baltic shield the continental crust of the central baltic shield evolved by accretion towards the west during the svecokarelian orogeny 1700 2200 ma ago the following features are consistent with a plate tectonic mechanism involving subduction of oceanic crust below an archean craton in the east flysch sediments with serpentinite masses and pillow lavas linear high grade metamorphic zones island arc type volcanic belts and late tectonic batholiths with porphyry type cu mo deposits semi consolidated new crust was affected by late svecokarelian deformation dn after 1850 ma nne trending folds with crenulation cleavage were overprinted on older structures together with associated nw trending ductile transcurrent shear zones that curve the fn folds into gentle s and z shapes the late tectonic batholiths intruded partly at the same time as and partly after the dn deformation

nature of the early proterozoic outokumpu assemblage eastern finland abstract the 1970 ma old outokumpu assemblage consists of serpentinites gabbro and mafic metavolcanites with pelagic and chemogenic sediments lying in the early proterozoic 2200 1950 ma karelides of eastern finland its formation occurred after the development of the jatulian 2200 2000 ma quartzite dominated shelf sediments and prior to the deposition of the kalevian flysch the outokumpu assemblage has been compared to an ophiolite and though the lithologies are all present sheeted dykes excepted the internal stratigraphy suggests otherwise the mafic metavolcanites have a more depleted chemistry than n morb and were erupted into shallow water along with the deposition of pelagic shales carbonates and chemogenic sediments including metalliferous exhalites ultramafic sills intruded these rocks at a later stage prior to rapid subsidence and flysch deposition the recently discovered jormua ophiolite complex may constitute part of the depositional basement to the outokumpu assemblage and the kalevian flysch which formed over stretched crust in an ensialic basic

sea ice freeboard and thickness in the ross sea from airborne icebridge 2013 and satellite icesat 2003 2008 observations

arctic sea ice freeboard retrieval with waveform characteristics for nasa s airborne topographic mapper atm and land vegetation and ice sensor lvis data from an icebridge arctic campaign on april 20 2010 with the airborne topographic mapper atm and the land vegetation and ice sensor lvis in operation on the same airplane were used in this study atm and lvis lidar waveforms were fitted with gaussian curves to calculate pulsewidth peak location pulse amplitude and signal baseline for each waveform the centroid skewness kurtosis and pulse area were also calculated received waveform parameters such as pulsewidth pulse amplitude pulse area skewness and kurtosis show coherent response to variations of geophysical features along an atm or lvis profile these parameters combined with elevation were used to identify leads in sea ice freeboard calculation the relationship between these parameters and sea ice freeboard and surface features were studied by comparing the parameters with atm and lvis derived freeboard and coincident digital mapping system images which have been used to classify sea ice surface types such as leads thin ice gray ice and thick ice an elevation bias of more than 16 cm peak to peak as a function of laser scanner azimuth was found in the atm data and an empirical correction was applied this correction will improve the atm shot to shot freeboard significantly the newly derived atm freeboard was compared with the current icebridge idcsi2 freeboard product at national snow and ice data center nsidc and the freeboard derived from lvis data over the studied area the mean freeboard is 0 540 pm 0 091 m for the idcsi2 at nsidc 0 496 pm 0 062 m for the atm after empirical elevation correction and 0 509 pm 0 048 m for the lvis

8 precambrian geodynamics and ore formation the fennoscandian shield abstract compared with present day global plate tectonics archaean and palaeoproterozoic plate tectonics may have involved faster moving hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle this scenario also fits with the complex geodynamic evolution of the fennoscandian shield from 2 06 to 1 78 ga when rapid accretion of island arcs and several microcontinent continent collisions in a complex array of orogens was manifested in short lived but intense orogenies involving voluminous magmatism with a few exceptions all major ore deposits formed in specific tectonic settings between 2 06 and 1 78 ga and thus a strong geodynamic control on ore deposit formation is suggested all orogenic gold deposits formed syn to post peak metamorphism and their timing reflects the orogenic younging of the shield towards the sw and west most orogenic gold deposits formed during periods of crustal shortening with peaks at 2 72 to 2 67 1 90 to 1 86 and 1 85 to 1 79 ga the ca 2 5 to 2 4 ga ni cu pge deposits formed both as part of layered igneous complexes and associated with mafic volcanism in basins formed during rifting of the archaean craton at ca 2 5 to 2 4 ga svecokarelian ca 1 89 to 1 88 ga ni cu deposits are related to mafic ultramafic rocks intruded along linear belts at the accretionary margins of microcratons all major vms deposits in the fennoscandian shield formed between 1 97 and 1 88 ga in extensional settings prior to basin inversion and accretion the oldest cyprus type deposits were obducted onto the archaean continent during the onset of convergence the pyhasalmi vms deposits formed at 1 93 to 1 91 ga in primitive bimodal arc complexes during extension of the arc in contrast the skellefte vms deposits are 20 to 30 million years younger and formed in a strongly extensional intra arc region that developed on continental or mature arc crust deposits in the bergslagen uusimaa belt are similar in age to the skellefte deposits and formed in a microcraton that collided with the karelian craton at ca 1 88 to 1 87 ga the bergslagen uusimaa belt is interpreted as an intra continental or continental margin back arc extensional region developed on older continental crust iron oxide copper gold iocg deposits are diverse in style at least the oldest mineralizing stages at ca 1 88 ga are coeval with calc alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to continental arcs or to magmatic arcs inboard of the active subduction zone younger mineralization of similar style took place when s type magmatism occurred at ca 1 80 to 1 77 ga during cratonization distal to the active n s trending subduction zone in the west possibly interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore formation finally the large volumes of anorthositic magmas that characterize the sveconorwegian orogeny formed a major concentration of ti in the sw part of the sveconorwegian orogenic belt under granulite facies conditions about 40 million years after the last regional deformation of the sveconorwegian orogeny between ca 930 and 920 ma

early proterozoic deposition and deformation at the karelian craton margin in southeastern finland abstract the margin of the karelian craton underwent complex though not chaotic deformation during the svecokarelian orogeny the resultant structural sequence can be subdivided into an early phase that involved translation of thrust nappes and recumbent folds verging towards the craton and a younger phase having more zonal and upright structures these latter include nw trending ductile shear zones associated with widespread pluton emplacement and later n trending faults and shear zones having substantially vertical displacements these features are interpreted in terms of a relative increase in vertical crustal stresses resulting from gravitational and thermal disequilibrium in the overthrust archaean basement despite this structural complexity two distinct depositional provinces are recognized in north karelia separated by a major thrust zone the more easterly hoytiainen province is a narrow essentially intracratonic feature containing locally derived archaean and proterozoic detritus an early phase of chemogenic and pelitic deposition with sporadic tholeiitic volcanism was followed by an influx of coarse clastic detritus largely deposited from turbidity currents within a prograding submarine fan the province apparently records deposition in a transtensional en echelon system of basins initiated near the craton margin at about 2 1 ga in contrast the savo province is largely allochthonous and includes the distinctive outokumpu assemblage commonly interpreted as a remnant of lower proterozoic oceanic crust provenance for the bulk of the overlying metasediments remains problematical although local evidence for deposition on archaean basement exists if an accretionary margin context is considered several potential niches for savo province deposition can be found that appear to satisfy constraints imposed by both isotopic data relating to provenance and the sequence and geometry of svecokarelian deformation

provenance stratigraphic architecture and hydrogeologic influence of turbidites on the mid ocean ridge flank of northwestern cascadia basin pacific ocean abstract the northwestern edge of cascadia basin north pacific ocean is unusual because late pliocene to holocene turbidites lap onto juvenile oceanic crust of the juan de fuca ridge subsidence of the ridge flank combines with irregular westward progradation of the turbidite facies to create a stratigraphic section that coarsens and thickens upward the sand provenance is mixed individual turbidity currents have funneled into the area through several shelf slope and abyssal floor conduits including vancouver valley juan de fuca channel barkley canyon and nitinat canyon local bathymetric blockage deflection and reflection of flow paths by basement relief remobilization by intrabasinal submarine slides and debris flows episodic channel switching and sporadic overbank flooding have combined to produce erratic recurrence intervals for the turbidity currents only the tallest basement highs have remained isolated from turbidite deposition during the last 500 000 years spatial and temporal differences in sediment accumulation are important because they modulate the three dimensional responses of compaction and consolidation those changes in physical properties govern where and when hydraulic communication with the underlying basement shuts down the basal hemipelagic layer of cascadia basin transforms to an effective hydrologic seal seepage rates 1 mm yr once the sediment basalt interface is buried by 100 150 m of strata rapid accumulation of turbidites therefore accelerates the hydrogeologic conversion of igneous basement from open to sealed

detrital modes in a late miocene wedge top basin northeastern calabria italy compositional record of wedge top partitioning abstract the composition and stratigraphic relations of sandstones and associated conglomerates derived from erosion of the northern calabrian terranes provide important constraints for paleotectonic and paleogeographic models of the neogene wedge top depozone evolution of the southern italy foreland basin system after onset of continental collision in the southern italy orogenic belt during late oligocene to early miocene the calabrian arc drifted northeastward accreting over the adria lithosphere during mid to late miocene time since the tortonian the northern calabrian terranes represented an uplifted thrust belt in which along its leading edge tectonic subsidence was responsible for accumulation of a thick tortonian to quaternary succession dominantly siliciclastic up to 3300 meters thick deposited in the wedge top depozones rossano and crotone basins sandstone assemblages have a homogeneous quartzofeldspathic composition in the rossano and crotone basins characterized by a compositional trend through time in response to regional tectonics evolution of the basins fill occurred during 1 serravallian tortonian 2 late tortonian to early messinian and 3 late messinian detritus shed into those basins was derived mainly from terranes within the strongly deformed sila mountains allochthon which was one of the principal structural elements of the nearby northern calabrian terranes consisting of hercynian plutons intruding paleozoic cambrian to carboniferous metasedimentary host rocks and locally having a sedimentary cover of mesozoic longobucco group or early miocene paludi unit clastics low to medium grade metamorphic and minor plutonic grain types metamorphiclastic petrofacies represent the main detritus in the earliest serravallian tortonian sedimentation that accompanied progressive flexural bending of the western margin of the foreland basin system tortonian to early messinian time was characterized by isolation of the mediterranean region from the global marine realm leading to evaporite sedimentation in the foreland in addition to intense regional and local tectonics compositional response to those events was a marked increase in sedimentary detritus sedimenticlastic petrofacies related to cannibalization of early messinian evaporite successions after the evaporitic events within the basins and the gradual re establishment to the normal marine conditions sandstone detrital modes are characterized mainly by a return of the serravallian tortonian compositional modes i e metamorphic plutoniclastic petrofacies the post evaporitic sedimentation corresponds to a major tectonic rearrangement on both rossano and crotone basins related to extrusion and inversion of the basal portion of the serravallian tortonian sequences in the intermediate zone to form an intervening ciro structural high in the crotone basin during late messinian deposition of the carvane conglomerate records an abrupt sudden arrival of distinctive sedimentary containing clasts of detritus of reddish limestone marl quartz arenite siltstone and chert derived from mesozoic to tertiary basinal sequences of the southern apennines domains i e sicilide complex terranes detrital mode evolution of the inner portions of the late miocene southern italy foreland basin system was in response to abrupt tectonic partitioning due to continuation of accretionary processes rapid uplift of mid crustal blocks and the superposition of wrench tectonics

the vaasa migmatitic complex svecofennian orogen finland buildup of a lp ht dome during nuna assembly tectonic evolution of the paleoproterozoic vaasa migmatitic complex vmc in the central part of the svecofennian accretionary orogen is deciphered using aeromagnetic and gravity maps deep seismic

pan arctic lead detection from modis thermal infrared imagery polynyas and leads are key elements of the wintertime arctic sea ice cover they play a crucial role in surface heat loss potential ice formation and consequently in the seasonal sea ice budget while polynyas are generally sufficiently large to be observed with passive microwave satellite sensors the monitoring of narrow leads requires the use of data at a higher spatial resolution we apply and evaluate different lead segmentation techniques based on sea ice surface temperatures as measured by the moderate resolution imaging spectroradiometer modis daily lead composite maps indicate the presence of cloud artifacts that arise from ambiguities in the segmentation process and shortcomings in the modis cloud mask a fuzzy cloud artifact filter is hence implemented to mitigate these effects and the associated potential misclassification of leads the filter is adjusted with reference data from thermal infrared image sequences and applied to daily modis data from january to april 2008 the daily lead product can be used to deduct the structure and dynamics of wintertime sea ice leads and to assess seasonal divergence patterns of the arctic ocean

archaean proterozoic transition geochemistry provenance and tectonic setting of metasedimentary rocks in central fennoscandian shield finland the central part of the fennoscandian shield in finland is composed of the palaeoproterozoic svecofennian domain and the archaean karelian craton with a palaeoproterozoic allochthonous and autochthonous cover a cryptic suture separating these areas and another tentative suture dividing the svecofennian into central and southern parts have been proposed the chemical composition of sedimentary rocks n 300 within the study area including the effects of palaeoweathering hydraulic sorting depositional environment and post depositional processes have been studied in order to delineate sediment source components the main proposed source components for the archaean sedimentary rocks are weathered 3 0 3 2 ga greenstone granite ttg and local 2 7 ga sources autochthonous 2 2 1 9 ga cover rocks were mainly derived from a mixture of chemically weathered palaeosol 2 2 2 35 ga sedimentary rocks derived from the palaeosol and mafic dykes and plateau volcanics mainly 2 2 2 1 ga although in places locally derived non weathered archaean sources dominated archaean crust and 2 0 1 92 low k bimodal rocks from a primitive island arc are the proposed source for the allochthonous western kaleva cover rocks these formed in a subsiding foredeep during initial collision from orogenic detritus in the same oblique collision zone the central svecofennian sedimentary rocks can be divided into local arc derived rocks 1 89 ga and older 1 91 ga rocks from a mixture of western kaleva sources and a 1 91 2 0 ga mature island arc active continental margin source rifting followed by increased subsidence during initial collision in the ne and subsequent arc reversal caused rapid erosion from the mountain belt exposing diverse source compositions as seen in the large variation of th sc 2 0 5 and deposition into an oblique hinterland basin further developing into a subduction related foredeep mature greywackes from the southern svecofennian in the study area resemble passive margin sediments with a source dominated by inferred alkaline affinity complexes and archaean rocks less mature rocks also occur and had sources dominated either by island arc active continental margin rocks or local picritic rocks in the sedimentary record the archaean proterozoic transition up to 2 1 ga was dominated by input of mainly mafic plateau type volcanic contribution to the archaean detritus palaeoproterozoic sediments having a crustal component 2 1 ga show higher th sc th cr and lower sm nd and eu eu relative to the archaean rocks but locally low th cr ratios complicate the situation ba depletion relative to k rb and th is a characteristic feature of the sedimentary rocks of the central fennoscandian shield indicating high amounts of ba lost from the clastic record during 2 3 1 9 ga and further recycled back to the mantle forming a subduction component and an enriched mantle component ba depletion seems to have been especially characteristic of chemical weathering during 2 35 2 2 ga under co2 rich and low o2 atmosphere whether this strong ba depletion is characteristic of the archaean proterozoic transition and quiet supercontinent stages in general remains to be determined

stratigraphy and sedimentology of fault controlled backstepping shorefaces middle pliocene of crotone basin southern italy abstract the middle pliocene sedimentary succession of the crotone basin in the calabria peloritani terrane southern italy was deposited during extensional tectonism dominated by a system of horst and half grabens the studied succession spartizzo lagoonal clays and scandale shallow marine deposits is up to 250 m thick and represents a barrier lagoon system that spans a tectonically controlled transgressive phase the succession is internally organised into six higher frequency cycles 20 80 m thick most of these cycles are formed by transgressive lagoonal deposits separated from the overlying regressive shoreface units by a wave ravinement surface lowstand fluvial deposits were recognized locally at the base of the last cycle the shoreface units are up to 50 m thick and typically consist of a coarsening upward succession of isolated to amalgamated hummocky cross strata that merge upwards into swaley and trough cross strata ne trending synsedimentary normal faults strongly controlled the deposition and enhanced subsidence and thickness expansion within the half graben basins

precambrian metallogeny related to tectonics in the eastern part of the baltic shield abstract the bulk of the eastern baltic shield is underlain by archaean continental crust composed of three segments with varying tectonic settings the kola peninsula province consists of granulite gneiss terrain with fe ni cu deposits greenstone belts with ni cu bif and ree deposits a highly deformed volcanic sedimentary basin with kyanite deposits and late archaean gabbroanorthosite intrusions hosting fe ti v ores the karelian province is a typical granite greenstone belt terrain the greenstone belts were formed during the lopian orogeny 2 9 2 6 ga in tectonic environments resembling rifts and island arcs they contain ni cu and massive pyrite deposits with cu mineralizations and bif deposits late orogenic granites host mo cu mo deposits of the porphyry type the belomorian province is a region of granulite gneiss and granite greenstone belt terrains reworked tectonically and metamorphically during the lopian and svecofennian orogenies 2 0 1 75 ga which involved continent continent collision here muscovite and rare metals muscovite pegmatite deposits are related to svecofennian igneous and metamorphic processes in the early proterozoic the main metallogenic events were associated with intracontinental rift structures of the karelian stage 2 5 2 0 ga in the kuolajarvi vetrenny poyas zone and the monchegorsk fedorova pana toundri zone and of the svecofennian stage 2 0 1 8 ga in the pechenga imandra varzuga zone the above mentioned zones contain major ni cu pge and ti deposits hosted by layered intrusions 2 45 2 35 ga and gabbro wehrlites 2 0 1 9 ga and cu and au mineralizations hosted by metavolcanic rocks epicontinental sediments of the jatulian group 2 2 2 0 ga in a slightly deformed within plate basin contain cu cu co and schungite deposits the early proterozoic svecofennian province is represented by the ladoga belt only metamorphic zoning thrusts deformation and granite gneiss domes developed and some cu cu zn fe ti w and graphite mineralizations formed there the tectonic setting of the ladoga belt is interpreted as that of a deformed shelf deposit on a rifted and passive continental margin in addition to this an abortive continental rift belt with rapakivi granite intrusions 1 65 1 55 ga developed along the southern boundary of the baltic shield sn and sn cu zn fe deposits and fluorite and rare metal mineralizations are associated with these granites

sedimentology stratigraphy and reservoir properties of an unconventional shallow frozen petroleum reservoir in the cretaceous nanushuk formation at umiat field north slope alaska numerous oil and gas accumulations exist in the brooks range foothills of the national petroleum reserve in alaska npra we use cores and well logs from 12 abandoned legacy wells at umiat field near the southeastern boundary of the npra to characterize the sedimentology and stratigraphy of unconventional shallow frozen reservoirs in sandstones of the cretaceous albian cenomanian nanushuk formation the nanushuk formation at umiat has five facies associations offshore and prodelta lower shoreface upper shoreface delta front and delta plain three stratigraphically distinct regionally extensive nanushuk formation depositional systems at umiat contain several potential petroleum reservoirs the lower nanushuk formation including a reservoir interval known informally as the lower grandstand primarily consists of marine mudstone and shoreface sandstones the middle nanushuk formation is dominantly deltaic and contains a second major reservoir interval in the informal upper grandstand sandstone both the upper grandstand and lower grandstand are regressive the transgressive upper nanushuk formation contains an additional potential reservoir interval in shoreface sandstones of the informal ninuluk interval the primary reservoir intervals at umiat field are upper shoreface and delta front sandstones in the upper grandstand and lower grandstand where increased sorting and decreased bioturbation in high energy depositional environments affect overall permeability and permeability anisotropy

shallow marine turbiditic sandstones juxtaposed with deep marine ones at the eastern margin of the niigata neogene backarc basin central japan abstract at the eastern margin of the niigata neogene backarc basin two kinds of turbiditic sandstones were concurrently deposited i e deep marine turbiditic sandstones in the west area and shallow marine turbiditic sandstones in the east area the deposition took place in the upper part of the lower pliocene kawaguchi formation data based on sedimentological and heavy mineral analyses revealed that these sandstones were both supplied from the east but from different source rocks through different routes sedimentary structures of the east shallow marine sandstones mimic those of the bouma sequence except for the poor development of the massive sandstones and the existence of finer grained thin parallel lamination in the lowermost part of some sandstone beds these sandstones were supplied from the coastal area and transported offshore through many small feeder channels sedimentary structures of these sandstones seem to suggest the existence of shallow marine turbidity currents such turbidity currents might have occurred under such specific paleogeographic or tectonic conditions as backarc basins with relatively steep and narrow shelves

palaeoproterozoic intraplating exposed by resultant gravity overturn near kiruna northern sweden abstract the tectonic history of the kiruna area is reexamined on the basis of four newly available digitised geophysical maps a literature survey and some first hand field observations a basement complex of archaean gneisses was unconformably overlain by a palaeoproterozoic sequence of metabasalt andesite and keratophyric porphyries with interstratified tuffs and sediments the cover was then detached from its basement by an orogeny with a northerly tectonic grain a pile of ductile nappes separated by mylonites in the east pushed westward an imbricate fold thrust belt that may have decoupled over an evaporite unit of regional extent conglomerates and quartzites accumulated in a foredeep migrating in front of a wedge of emergent thrusts the allochthonous cover then developed a vertical north trending foliation in high t low p conditions as it foundered among buoyant diapirs of remobilised granitoid basement the near constant lateral spacing of the centres of these diapirs their mushroom shapes and the absence of contemporaneous volcanic rocks suggest that these diapirs rose in the solid state the region continued to distort episodically even after diapir emplacement ductile shear zones evolved through vein systems to faults as the region cooled and was uplifted before the cambrian the youngest fault movements clearly displace 9000 years old glacial deposits post or late orogenic plutons in the kiruna area appear to be contemporaneous with syn svecofennian plutons further south we therefore suggest reinstating the label svecokarelian for the orogeny in the kiruna area heat advected by melts from the mantle is invoked to account for the archaean basement risking in two convective stages the first as porphyritic lavas the second as solid state diapirs melts rose rapidly and erupted before the svecokarelian orogeny while the slower diapirs ended it we attribute the current southwestern dip of the diapir zone to extension of svecokarelian crust before the svecofennian magmatic arc was built above it

the accretionary svecofennian orogen insight from the babel profiles abstract the babel profiles b c 1 7 form a 1200 km long nearly continuous cross section through the svecofennides the near vertical marine reflection profiles display a wide range of crustal structures that can be associated with both the accretionary svecofennian orogeny 1 96 1 75 ga and the following subjotnian and jotnian rift stages 1 65 1 11 ga the svecofennian accretionary orogeny took place when a number of micro plates with island arc affinities and surface expression of a large archipelago accreted to the continental karelian plate some of the accreting terranes seem to have had older cores that have acted as crustal indentors during the collision babel profiles 3 and 4 image a series of collisional terrane boundaries between karelian continental margin savo arc sa and central finland arc cfa in the north the karelian margin has been both over and underthrust by the savo arc cfa comprises a folded thrust package on top of a continental nucleus and the savo arc the associated subduction zone and accretionary prism are interpreted to lie to the south underneath the bothnian basin area where prominent ne dipping lower to middle crustal reflections are found along babel profiles 1 and 4 an oblique collision of the central finland arc and the continent resulted in the development of the strike slip fault on the young hot savo arc babel profiles 1 6 7 and c image the internal architecture of the southern and central finland arcs the unusually thick crust 55 60 km hosts unreflective high density mafic intrusions acting as a crustal indentor a highly reflective antiform structure developed on the southern side of it southern finland arc complex sfa is an imbrication structure comprising stacked slices of arc related crust on an older continental nucleus bergslagen nucleus prior to the collision the sfa suffered from gravitational collapse during which the crust was thinned profile b images the architecture of the central and southern swedish svecofennides the sormland terrane sob is interpreted as the accretionary prism of the southern finland arc squeezed between the svecofennian collage in the north and the advancing continent to the south the southern continent island arc is characterised by ne dipping crustal reflections and moho offsets as well as step wise increasing thickness of the crust after the final collision large volumes of mantle derived material intruded the crust as large mushroom shaped plutons they are interpreted as the heat source for the tib magmatism in southern and western scandinavia

archean proterozoic collision boundary in central fennoscandia revisited abstract archean proterozoic ap collision boundary in central fennoscandia is a complex collage of archean basement rocks its paleoproterozoic supracrustal cover rocks and svecofennian 1 93 1 78 ga supracrustal and plutonic rocks the apparent steep nature and complexity of the ap boundary has led to contradictory tectonic models varying from arc continent collision via back arc closure to accretion of arc terranes along a strike slip shear zone we present new geochronology data from detrital zircons combined with whole rock geochemical and sm nd isotopic data on paleoproterozoic sedimentary and volcanic rocks across the boundary to revise its nature the 2 06 ga siilinjarvi volcanic complex and associated turbidites with an inferred deposition age at 2 1 2 06 ga are part of the cover sequence the siilinjarvi volcanic rocks derive from both plume oib and sub continental lithospheric mantle sclm magma sources and are often contaminated by the archean crust the sahara suite sedimentary cover rocks are derived from local 1 95 1 92 ga bimodal volcano plutonic source which source also explains the common age population found in younger sedimentary rocks the nalantojarvi suite psammites with maximum depositional ages of 1 97 1 93 ga are continental slope to deep water sediments deposited at the continental margin contemporaneous mafic magmatism seen as lavas and dykes show a change from sclm dominated present east to asthenospheric depleted mantle dm dominated present west melts the interpretation of the nalantojarvi suite as cover rocks of the lower plate indicates that the archean crust continues at least 50 km more to the west than thought earlier parautochthonous sedimentary rocks from salahmi eastern kansanneva and loutemaki with maximum depositional ages at 1 92 1 91 ga are inferred as collision related foredeep deposits from local sources both the lampaanjarvi suite and pyhajarvi suite sedimentary rocks have deposited at 1 89 1 88 ga or later whereas the lampaanjarvi suite rocks are dominated by a local source and the pyhajarvi suite rocks derive from a mixture of older sediments and 1 89 1 88 ga granitoids at least two tectono metamorphic stages separated with a major unconformity can be differentiated in the study area the early deformation and metamorphic stage in the nalantojarvi suite has occurred before the intrusion of the late to post collisional pyroxene granitoids at 1 88 ga the pyhajarvi suite sedimentary rocks have been deposited after the intrusion of these granitoids between 1880 and 1875 ma and then subsequently deformed and metamorphosed at 1875 ma we propose a tectonic model where the continental breakup occurred at 2 1 2 06 ga followed by a new spreading within the pre existing passive margin at 1 98 1 93 ga during initial continent arc collision the subducted slab steepened strongly at high angle subduction ceased rapidly and finally detached and shallow slab breakoff occurred at 1 92 1 91 ga followed subsequently by ophiolite obduction and a formation of a foreland fold and thrust belt mantle crust decoupling of the archean lithosphere occurred and a crocodile jaw formed where the arc rocks are partly buried beneath the bounding archean continent similar features have been recorded in other ap collision zones which could indicate that the buoyant nature of the archean lithosphere combined with denser paleoproterozoic lithosphere may be a general cause for decoupling of archean crust and mantle during arc continent collision in paleoproterozoic

the nature of the proterozoic cambrian transition in the northern amadeus basin central australia abstract the nature and completeness of the rock record is vital in determining whether evolution across the proterozoic cambrian boundary was episodic or explosive this study documents the nature of the neoproterozoic cambrian transition within the arumbera sandstone of the northern amadeus basin central australia and demonstrates an erosional surface close to this major stratigraphic boundary we are not able to recognise major facies differences between the largely unfossiliferous lower units i and ii and the rich trace fossil bearing beds of units iii iv horizons above and below the purported neoproterozoic cambrian transition were traced laterally and searched for both trace and body fossils in an attempt to locate a local boundary between the neoproterozoic and cambrian a single nonconformity bound sedimentary cycle above the major erosional surface dividing arumbera ii and iii is recognised the lowest sedimentary cycle of arumbera iii is devoid of trace fossils but at correlative levels in the ooraminna sub basin this horizon bears elements of the ediacara fauna reported for the first time herein we therefore suggest that contrary to previous studies the neoproterozoic cambrian transition is not coincident with the widespread seismic reflector but in areas of more complete sedimentation actually lies above it this study also presents new stratigraphic ichnological and palaeontological information from the neoproterozoic cambrian transition in central australia identifies areas of potentially continuous sedimentation and provides a basis for correlation of the arumbera sandstone with other neoproterozoic cambrian successions within australia and beyond

quantitative subsidence uplift analysis of the bajo segura basin eastern betic cordillera spain tectonic control on the stratigraphic architecture the bajo segura basin is located in the eastern betic cordillera at present connected with the mediterranean sea to the east it has a complete stratigraphic record from the tortonian to the quaternary which has been separated into six units bounded by unconformities this paper is concerned with the northern edge of the basin controlled by a major strike slip fault the crevillente fault zone cfz where the most complete stratigraphic successions are found the results obtained summarised below are based on an integrated analysis of the sedimentary evolution and the subsidence uplift movements unit i early tortonian is transgressive on the basin basement and is represented by ramp type platform facies organised in a shallowingupward sequence related to tectonic uplift during the first stages of movement along the cfz unit ii lower late tortonian consists of shallow platform facies at bottom and pelagic basin facies at top forming a deepening upward sequence associated with tectonic subsidence due to sinistral motion along the cfz unit iii middle late tortonian is made up of exotic turbiditic facies related to a stage of uplift and erosion of the southern edge of the basin unit iv upper late tortonian consists of pelagic basin facies at bottom and shallow platform facies at top defining a shallowing upward sequence related to tectonic uplift during continued sinistral movement on the basin bounding fault units v latest tortonian messinian and vi pliocene pleistocene p p consist of shallowing upward sequences deposited during folding and uplift of the northern margin of the basin no definitive evidence of any major eustatic sea level fall associated with the messinian salinity crisis has been recorded in the stratigraphic sections studied q 2001 elsevier science b v all rights reserved

uncertainties in ice sheet altimetry from a spaceborne 1064 nm single channel lidar due to undetected thin clouds in support of the ice cloud and land elevation satellite icesat ii mission this paper studies the bias in surface elevation measurements caused by undetected thin clouds the icesat ii satellite may only have a 1064 nm single channel lidar onboard less sensitive to clouds than the 532 nm channel the 1064 nm channel tends to miss thin clouds previous studies have demonstrated that scattering by cloud particles increases the photon path length thus resulting in biases in ice sheet elevation measurements from spaceborne lidars this effect is referred to as atmospheric path delay this paper complements previous studies in the following ways first atmospheric path delay is estimated over the ice sheets based on cloud statistics from the geoscience laser altimeter system onboard icesat and the moderate resolution imaging spectroradiometer modis onboard terra and aqua second the effect of cloud particle size and shape is studied with the state of the art phase functions developed for modis cirrus cloud microphysical model third the contribution of various orders of scattering events to the path delay is studied and an analytical model of the first order scattering contribution is developed this paper focuses on the path delay as a function of telescope field of view fov the results show that reducing telescope fov can significantly reduce the expected path delay as an example the average path delays for fov 167 rad a 100 m diameter circle on the surface caused by thin undetected clouds by the 1064 nm channel over greenland and east antarctica are illustrated

depositional controls on mudstone lithofacies in a basinal setting implications for the delivery of sedimentary organic matter deep water mudstones from ancient epicontinental settings are significant repositories for organic matter but the detailed temporal variations of and controls on the abundance and type of organic matter om is little studied using micro petrographic and geochemical data from late mississippian mudstones of the widmerpool gulf uk the processes that delivered fine grained sediment to this basin during a glacioeustatic sea level cycle are interpreted from detailed lithofacies analysis seven primary lithofacies are identified from core which show specific and systematic variations in total organic carbon toc content and bulk carbon isotope composition of organic material 13corg during sea level highstands thin bedded carbonate bearing mudstones are the dominant facies deposited contain up to 6 6 toc average 4 6 1 3 and have mean 13corg of 28 5 0 9 during phases of lower sea level thin bedded silt bearing clay rich mudstones with up to 4 1 toc average 2 3 0 8 mean 13corg 28 2 1 0 were interbedded with more organic lean graded silt bearing mudstones and sand bearing silt rich mudstones average toc 1 7 0 6 derived from turbidity currents the latter mean 13corg 26 2 0 7 are closely linked to significant proportions of terrestrial plant material while some rare plant debris and sand bearing mudstones produced from debris flows have more than 7 0 toc and 13corg 26 0 the 13c values of wood fragments ranged from 27 1 to 24 0 and therefore the 13corg is interpreted as a function of the ratio of marine and terrestrial organic matter more negative values in the carbonate bearing and the clay rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material the data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea level stages marine om was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial om was delivered by sediment density flows variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine om organic rich mudstones preserved in these marine basins are potential hydrocarbon source rocks especially as unconventional shale gas reservoirs detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source rock potential of basinal mudstones and of fine grained organic rich sediments in general

thin fine grained storm layers in a muddy shelf sequence an example from the lower jurassic in the stenlille 1 well denmark thin storm sand layers are a characteristic feature of many sandy shelf sequences while little evidence of storm layers is preserved in muddy shelf deposits where bioturbation is often total the present study shows that storm generated depositional processes governed sedimentation in a muddy shelf environment the studied sequence is dominated by blackish mudshale and silt streaked mudshale with thinner intervals of pale fine grained heterolithic sandstone it represents the lower jurassic fjerritslev formation in the eastern part of the danish basin and has been studied in four cores from the stenlille 1 well within the muddy outer shelf association four sedimentary facies and 14 types of laminae 0 5 10 mm thick may be distinguished most of the laminae share the characteristics of graded bedding erosive bases and occasional fading ripples with storm layers of sand grade the structures indicate that the mudshale laminae formed by settling of the suspension load carried by storm generated currents this kind of episodic deposition of fine grained storm layers may be common though rarely preserved in outer shelf environments

late holocene sediment accumulation on the northern california shelf oceanic fluvial and anthropogenic influences the late holocene sedimentary record of the northern california continental shelf archives the combined influences of fluvial and oceanic mechanisms of land to ocean sediment flux and provides perspective on the cumulative impacts of major floods and land use change in the drainage basin during historical time piston cores collected on the shelf 50 150 m water depths off the eel and klamath rivers were analyzed to identify lithologies indicative of depositional processes over the past 5 k y and dated using 137cs and 14c methods to resolve spatial patterns in sediment accumulation rates sediment accumulation rates averaged over the past several millennia display along and across shelf gradients that reflect interactions between the shelf flow field and antecedent tectonically produced topography the highest rates 3 6 mm yr 0 4 0 8 g cm2 yr are associated with structural lows on the middle shelf whereas the lowest rates 0 2 0 6 mm yr 0 03 0 05 g cm2 yr occur at structural highs and at the shelf edge this accumulation pattern is spatially coincident with postglacial sediment thicknesses on the shelf and with depocenters that form on shorter time scales in response to oceanic flood events the sediment column exhibits an upward fining sequence consistent with increased bypass of river silt and clay as delta plains progressively filled during the holocene transgression sedimentary event beds indicative of major river floods including two probable hyperpycnal discharges of the eel river within the past 1 k y are preserved stratigraphic evidence of accelerated sediment delivery to the shelf during historical time in the form of increased burial of fluvial mud relative to fine grained sand is superimposed on this natural record this change is concordant with the regional history of forest clearing and related land use practices in the watershed after the early 1800s and appears to record the combined impacts of timber harvesting and several extreme floods after ca a d 1950

geochemical characterisation of a polyphase deformed altered and high grade metamorphosed volcanic terrane implications for the tectonic setting of the svecofennides south central finland abstract the virtasalmi metavolcanic belt forms part of the early proterozoic svecofennide terrane in central finland the preserved supracrustal lithologies 40 of the assemblage have undergone extensive synvolcanic hydrothermal alteration polyphase regional ductile deformation low pressure regional polyphase metamorphism to granulite facies with subsequent amphibolitisation and extensive emplacement of a synkinematic i type plutonic suite despite these overprinting events three chemically distinct suites of metatholeiites and one suite of coeval coarser grained intrusive lithologies are recognized and their petrogenesis resolved primary igneous geochemistry is preserved mainly by the hfses and cr and ni variable major and lil element mobility is demonstrated significant differences in geochemistry are reflected in different metamorphic assemblages between suites preservation of vesicular pillow lavas indicate subaqueous extrusion of the three metatholeiitic suites trace element geochemistry indicates that suite i compositions are controlled by low pressure fractional crystallization in contrast suite iii amphibolite compositions are controlled by batch partial melting with limited modification by open system fractional crystallization these differences in fractionation history point to the evolution of these two main suites within distinct upper crustal magmatic plumbing systems also differences in more hyg less hyg element and other incompatible element ratios point to derivation of suites i and iii by different degrees of partial melting from different heterogeneous mantle source regions coeval eruption of these suites indicates that variations in source geochemistry and melting processes reflect spatial rather than temporal differences the volumetrically smaller suite ii comprises lava flows and pillowed units that are interlayered with but have a more depleted chemistry than the other suites marked variation in cr and ni contents within a narrow range of zr contents in individual flows in subgroups iia 1 and iia 2 and marked tio 2 enrichment in subgroup iib suggests that the more depleted character of this suite is due to fractional crystallisation and crystal settling in high level magma chambers suite iv amphibolites comprise a number of small intrusive bodies that are emplaced within the volcanic pile they are coarser grained than the enveloping amphibolites and are interpreted as tectonised relics of high level magma chambers and or sills emplaced into the coeval metavolcanic assemblage they have a depleted geochemistry and there is textural and geochemical evidence to suggest a partial cumulate origin similarities in fractionation histories suggest that suite iv intrusions are cogenetic with suites i and ii enrichment in incompatible elements particularly nb demonstrates that the virtasalmi metatholeiites are not related to supra subduction zone magmatism all the amphibolites are within plate basalts or e type morbs with similar compositions known today from a range of tectonic settings however the interlayering of e morb metavolcanic rocks with marbles and voluminous fine grained clastic metasediments is more likely to indicate an intracratonic rift passive margin geotectonic setting subsequent deformation and metamorphism of the volcanics and syn kinematic calc alkaline intrusives are interpreted as accretion at a destructive margin the latter was most probably a continental calc alkaline arc various crustal levels of which are now exposed in the study area

freeboard snow depth and sea ice roughness in east antarctica from in situ and multiple satellite data in october 2003 a campaign on board the australian icebreaker aurora australis had the objective to validate standard aqua advanced microwave scanning radiometer amsr e sea ice products additionally the satellite laser altimeter on the ice cloud and land elevation satellite icesat was in operation to capture the large scale information on the sea ice conditions necessary for satellite validation the measurement strategy was to obtain large scale sea ice statistics using extensive sea ice measurements in a lagrangian approach a drifting buoy array spanning initially 50 km x 100 km was surveyed during the campaign in situ measurements consisted of 12 transects 50 500 m with detailed snow and ice measurements as well as random snow depth sampling of floes within the buoy array using helicopters in order to increase the amount of coincident in situ and satellite data an approach has been developed to extrapolate measurements in time and in space assuming no change in snow depth and freeboard occurred during the period of the campaign on the floes surveyed we use buoy ice drift information as well as daily estimates of thin ice fraction and rough ice vs smooth ice fractions from amsr e and quikscat respectively to estimate kilometer scale snow depth and freeboard for other days the results show that icesat freeboard estimates have a mean difference of 1 8 cm when compared with the in situ data and a correlation coefficient of 0 6 furthermore incorporating icesat roughness information into the amsr e snow depth algorithm significantly improves snow depth retrievals snow depth retrievals using a combination of amsr e and icesat data agree with in situ data with a mean difference of 2 3 cm and a correlation coefficient of 0 84 with a negligible bias

hummocky cross stratification like structures and combined flow ripples in the punta negra formation lower middle devonian argentine precordillera a turbiditic deep water or storm dominated prodelta inner shelf system abstract turbidity current and storm induced deposits may exhibit similarities in particularly when the latter is laid down by a combination of oscillatory and unidirectional flows recent progress in facies analysis helps to discriminate the sedimentary effects of oscillatory from unidirectional components of the flow on the basis of detailed analysis of sedimentary facies strata geometry and palaeocurrent data the present study reinterprets the punta negra formation pnf lower middle devonian argentine precordillera previously considered as a depositional system of deep water as a storm dominated prodeltaic shelf depositional system in the sandstone beds of the pnf planar low angle and undulating laminations with weakly asymmetric hummocky and swaley bedforms combined flow ripples accretionary hummocky cross stratification like hcs like and anisotropic hcs like suggest the action of oscillatory currents combined with unidirectional currents in forming the deposits different hypotheses on the origin of the oscillatory currents have been examined the most convincing interpretation is that the oscillatory component of the velocity is attributed to storm induced waves the palaeocurrent data indicate offshore current directions suggesting that the unidirectional flow was a gravity induced bottom current inverse grading at the base and overlying normally graded divisions of the sandstone beds testify to waxing waning behaviour of the depositional flows interbedding of sedimentary structures undulating laminations low angle and parallel laminations and combined flow ripples in the lower and intermediate divisions of the beds indicate fluctuations of flow velocity this organisation of the sedimentary structures permits association of the unidirectional component with hyperpycnal bottom currents the terrestrial origin of the hyperpycnal flows is suggested by the abundance of terrestrial plant remains the mineralogical and textural immaturity of the sandstone composition and the relative scarcity of bioturbation which was likely controlled by fresh water input and a high rate of sedimentation storm influenced hyperpycnal flows generated subaqueous channelised forms at the mouth of the river deltas which later filled with sand at the distal end of the channelised forms lobe shaped sandstone beds were deposited evolving distally into thin sandstone beds alternating with sandy mudstone

long lived lree mobility in the cratonic rift and foredeep to foreland sedimentary cover at the western margin of the karelia province abstract the western margin of the karelia province of the fennoscandian shield consists of archean crust covered by remnants of paleoproterozoic c 2 5 1 9 ga metasedimentary rocks the study area in the eastern part of the margin shows 2 3 2 1 ga cratonic sedimentation followed by 2 1 2 05 ga rift sedimentation and c 1 91 1 92 ga foredeep to foreland sedimentation related to continent arc continent collision extreme lree mobility loss up 95 of la is recorded by many samples from these units monazite bastnasite and in some cases allanite have been the prealteration lree host phases in the lree depleted samples monazite was altered to th silicates with variable loss of the lree the remaining part of which was incorporated in th poor monazite the depositional age of the sedimentary units was studied by dating la mc icpms detrital zircon grains and the age of lree mobility by dating monazite and xenotime and by whole rock sm nd modeling the maximum deposition age of the foredeep to foreland basin is 1 91 1 92 ga based on detrital zircon data and the minimum age of the main foliation in the study area is 1 87 1 86 ga based on the younger age limit of late to post tectonic xenotime and the ages of few probable metamorphic zircons coeval bastnasite with xenotime in a lree enriched sample suggests that this was also one important stage of lree mobility monazite crystallizations have occurred 1 76 1 78 ga ago while the rb sr whole rock data suggest that the closure of this isotope system took place 1732 21 ma ago the sm nd modeling gives ages at 0 4 1 0 ga for lree depletion the sm nd age of 412 27 ma can be considered as the age of the latest major lree depletion event we propose that alkali bearing oxidizing fluids started to form in the cratonic sequences due to diagenetic reactions maybe as early as 2 3 2 1 ga alkalinity of fluids was later increased by interaction with alkaline 2 05 ga source materials before and during the c 1 91 1 92 ga foredeep to foreland basin stage basin inversion and metamorphic crystallization occurred at 1 91 1 87 ga episodes of fluid migration at 1 78 1 73 ga and afterwards were focused along fracture zones and in microfracture networks the 0 4 ga stage is the most prominent of the

arctic sea ice freeboard from altika and comparison with cryosat 2 and operation icebridge satellite radar altimeters have improved our knowledge of arctic sea ice thickness over the past decade the main sources of uncertainty in sea ice thickness retrievals are associated with inadequate knowledge of the snow layer depth and the radar interaction with the snow pack here we adapt a method of deriving sea ice freeboard from cryosat 2 to data from the altika ka band radar altimeter over the 2013 14 arctic sea ice growth season altika measures basin averaged freeboards between 4 4 cm and 6 9 cm larger than cryosat 2 in october and march respectively using airborne laser and radar measurements from spring 2013 and 2014 we estimate the effective scattering horizon for each sensor while cryosat 2 echoes penetrate to the ice surface over first year ice and penetrate the majority 82 3 of the snow layer over multiyear ice altika echoes are scattered from roughly the midpoint 46 5 of the snow layer over both ice types

internal waves vs surface storm waves a review on the origin of hummocky cross stratification hummocky cross stratification hcs is considered a diagnos tic structure of surface storm activity at the shoreface offshore transition however the origin of hcs is still debated laboratory experiments have not yet reproduced it and direct observations on the continental shelves do not exist most hydrodynamic interpretations invoke pure oscilla tory flows unidirectional dominated combined flows and oscillatory dominated flows but they all share the assump tion of hcs to reflect the combined action of surface storm waves and related currents within this context of uncertain ties internal waves gravity waves propagating along the pycnocline provide an alternative mechanism to explain the origin of hcs internal waves breaking on the shelf create episodic high turbulence events and induce upslope and downslope currents as well as oscillatory flows at the depth where the pycnocline intersects the sea floor in this scenario both the oscillatory and the unidirectional components needed for hcs to form are not necessarily linked to surface storm waves but can occur at various depth as far and near there is a pycnocline where internal waves can form

facies characteristics and depositional models of highly bioturbated shallow marine siliciclastic strata an example from the fulmar formation late jurassic uk central graben abstract an extensive core database from the late jurassic fulmar formation illustrates the practicalities of facies analysis and depositional modelling in highly bioturbated heterolithic shallow marine siliciclastic strata twelve major sedimentary facies 1 12 are defined on the basis of lithology grain size visually estimated sand silt content and the presence or absence of primary sedimentary structures ichnofabric characteristics are also defined and have proved to be not always facies specific for purposes of depositional modelling the 12 facies types are resolved into six facies associations a f each representative of distinct shoreline shallow marine environments from these associations three broad depositional models have been constructed storm influenced shoreface model 1 bioturbated shoreface model 2 and a speculative bioturbated shelf model model 3 stratigraphical and palaeontological criteria suggest that models 1 and 2 are shoreline attached sedimentological data indicate that they occur as end members to a spectrum of shoreline settings constrained by incident wave energy bands for shorefaces subject to significant storm influence well preserved event beds occur seaward of the upper shoreface in the bioturbated shoreface model however the lower shoreface and adjacent shelf deposits are characterized by intense infaunal reworking the bioturbated shelf model displays no clear evidence of shoreline connection with the resultant facies often exhibiting highly abundant siliceous sponge spicules together with other open marine indicators such as belemnites and rare ammonites unlike the shoreface sand bodies which received sediment from basin margin fluvial systems shelf sand bodies in the fulmar formation are more likely to have been intrabasinally sourced along relay ramps or other forms of transfer zone this sediment may have undergone a long transit residence period on the shelf prior to eventual burial in hanging wall depocentres strongly influenced by zechstein salt withdrawal this study demonstrates that an ichnofabric approach as opposed to one of simple ichnodiversity is highly significant with respect to the description and modelling of highly bioturbated shallow marine siliciclastic strata in the fulmar formation ichnofabric analysis is capable of providing sensitive information on fluctuations in depositional energy levels water depth sedimentation rates erosion rates substrate consistency and dissolved oxygen levels evidence of these fluctuations is often apparent at intra facies scale but would largely go unnoticed using a conventional sedimentological approach to data gathering based on ichnodiversity at best depositionally significant changes in ichnofabric may occur without any significant change in ichnodiversity ichnofabric analysis also plays an important role in the hierarchical assessment of key stratal surfaces for purposes of sequence stratigraphic modelling

a 5 year satellite climatology of winter sea ice leads in the western arctic the distribution of openings leads and polynyas in polar sea ice is not well known this study estimates the large scale distribution and variability of leads in the arctic of the western hemisphere in winter using a 5 year record of defense meteorological satellite program thermal and visible band imagery the occurrence density and orientation of leads are derived from gridded maps made at 10 day intervals their mean value and interannual seasonal and monthly variabilities are estimated lead densities are observed to be highest in early winter decreasing 20 from november through april the highest densities are observed in the central canada basin and the lowest are in the east siberian sea there is limited interannual variability in the positions of maximum and minimum densities preferred lead orientations are identified as generally north south in the beaufort sea sector and east west in the east siberian sea sector with transitional orientations in the intermediate area the mean distributions of lead density and orientation are observed to be associated with large scale mean fields of ice divergence and shear respectively

the origin and preservation of a major hurricane event bed in the northern gulf of mexico hurricane camille 1969 cores collected from mississippi sound in the gulf of mexico were studied using 210 pbxs and 137 cs geochronology x radiography granulometry and a multi sensor core logger our results indicate the presence of a widespread sandy event layer that we attribute to hurricane camille 1969 an initial thickness of more than 10 cm is estimated from the cores which is large compared to the time averaged apparent accumulation rate of 0 29 0 47 cm y 31 physical and biological post depositional processes have reworked the sandy layer producing a regional discontinuity and localized truncation and resulting in an imperfect and biased record of sedimentary processes during the storm the oceanographic and sedimentological processes that would have produced an event bed during hurricane camille are simulated using a series of numerical models i e 1 a parametric cyclone wind model 2 the swan third generation wave model 3 the adcirc 2d finite element hydrodynamic model and 4 a wave current bottom boundary layer model that is coupled to transport and bed conservation equations trans98 the simulated bed ranges from 5 cm to over 100 cm within a tidal channel near the barrier islands seaward of the islands the bed is more than 10 cm in thickness with local variability the magnitude and local variability of the storm bed thickness are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barriers 2002 elsevier science b v all rights reserved

characteristics and geological setting of synkinematic svecokarelian granitoids in southern finland abstract synkinematic granitoids are the predominant component of the svecokarelian crust their zircon u pb ages vary from 1900 to 1860 ma mainly 1890 1870 ma being roughly similar to those of mafic plutonic rocks and metavolcanic rocks synkinematic granitoids occur as distinct plutons in schist belts and also form the granitold complex of central finland with a total area in excess of 35 000 km2 the granitoids in schist belts occur as concordant plutons although locally they have cross cutting contacts and they crystallized soon after the peak of major regional deformation and metamorphism but before younger deformation phases they are composed of granodiorites tonalites and trondhjemites composite plutons are often zoned with gabbro diorite tonalite and or trondhjemite at their margins and with granodiorite and less commonly granite at their centres the granitoid complex of central finland is composed of a vast number of intrusions ranging in composition from gabbro to granite the granite intrusions comprising large parts of the complex coarse grained granitoids and polyphase deformation are common major minerals of the synkinematic granitoids are plagioclase potassium feldspar quartz biotite and hornblende typical accessories are sphene apatite magnetite and zircon whole rock analyses of 143 granitoids from throughout southern finland show calc alkaline characteristics with variable sio2 high na2o k2o and a cnk below 1 1 initial 87sr 86sr ratios are low the granitoid complex of central finland has higher feo mgo and k2o na2o than the granitoids in schist belts irrespective of silica content the synkinematic granitoids have the geological and geochemical characteristics of phanerozoic i type granitoids and are cogenetic with mafic plutonic rocks intrusion of these latter evidently caused major remelting in the lower crust giving rise to granitoid magmas so that a variable mixing of mantle derived and crustal magmas is probable according to nd isotopes studies archaean material was insignificant in the source of the granitoids except near the border zone of the archaean craton this indicates rapid recycling of material newly derived from the mantle geochemical features of the granitoid complex may also reflect a thicker crust in central finland than in surrounding areas during the generation of the granitoids many characteristics of the synkinematic granitoids strongly suggest a subduction related origin however the similarity in isotopic ages and lack of obvious linear trends in distribution of rock types combined with evidence for a minor older crustal component in their source indicates that the processes were not identical to those operating at modern continental margins

major palaeoproterozoic shear zones of the central fennoscandian shield abstract employing two recently studied crustal scale shear zones as type examples this paper summarizes the major palaeoproterozoic svecokarelian shear tectonics of the central fennoscandian shield and demonstrates that this part of the shield was not as stable during the svecokarelian orogeny as commonly assumed the collision of the svecofennian island arc with the karelian continent first created numerous nw se trending folds and thrusts of stages d1 and d2 which were then modified by successive shearing during stages d3 and d4 stage d3 built up a system of n s trending shear zones here named the savolappishearsystem the type example of which is the hirvaskoski shear zone this is a dextral strike slip shear zone at least 150 km long and 10 30 km wide characterized by blastomylonitic fault rocks and various structures such as hook folds z folds and sheath folds associated with the principal displacement zone synthetic riedel shears and pinnate shears the traces of the axial planes of f3 en echelon folds deviate 15 30 anticlockwise from the plane of the principal displacement zone other members of the savolappi shear system are the pajala shear zone in northern sweden and the russian north karelia shear zone in the east stage d4 created a conjugate shear system called the finlandia shear system the type example of which is the oulujarvi shear zone this is a ne sw trending sinistral strike slip shear zone more than 250 km long and 20 30 km wide across its southwestern end it is composed of a ne sw trending principal displacement zone synthetic riedel shears and pinnate shears with antithetic riedel shears in a nw se direction typical fault rocks within these shears are s c mylonites the axial plane traces of f4 folds of all scales diverge by 20 40 clockwise from the plane of the principal displacement zone the kuopio shear zone is a conjugate nw se trending counterpart of the oulujarvi shear zone as a whole the finlandia shear system forms a conjugate network of nw se and ne sw trending shear zones which occupies most of the northern and central fennoscandian shield

an early proterozoic ophiolite the jormua mafic ultramafic complex northeastern finland abstract the 1 96 ga old jormua complex comprises a fault bounded unit 2 5 20 km in the centre of the kainuu schist belt at the eastern margin of the early proterozoic svecokarelides the complex was dismembered and metamorphosed to lower amphibolite facies during the svecokarelian orogeny in the intact complex the basal unit was formed by serpentinites the middle unit of mafic dykes and the uppermost extrusive unit of basaltic pillow lavas gabbroic rocks are present as intrusive bodies in the serpentinites and narrow interdyke screens within the dyke unit trondhjemitic rocks occur as minor segregations in the gabbroic rocks or as cross cutting narrow dykes in the mafic dyke unit the dyke unit is locally composed exclusively of subparallel metabasalt and metadolerite dykes in places interdyke metagabbro and serpentinite screens are abundant well preserved chilled margins are common and many dykes are split and intruded by younger dykes the chemical composition of the serpentinites indicates derivation from harzburgitic dunitic mantle peridotites the gabbroic rocks which represent obvious tholeiitic cumulates show extreme differentiation similar to gabbros of the high ti ophiolites and gabbros dredged from present midocean ridges in chemistry the trondhjemitic rocks are close to granitic rocks from mid ocean ridges and high ti ophiolites the similar chemical composition of the dykes and lavas of the complex indicates that they are cogenetic both being tholeiitic metabasalts with chondrite normalized ree patterns ranging from slightly lree depleted to slightly lree enriched ones compared with modern rocks the jormua metabasalts most closely resemble transitional midocean ridge basalts it is suggested that the jormua complex and related mafic ultramafic bodies in eastern finland originated as divergent margin ophiolites concomitantly with the break up of the archaean craton in the extensional stage of the svecokarelian orogeny which culminated in the opening of a major ocean after 1 97 ga the tectonic emplacement of these ophiolites into their present locations occurred in connection with thrusting during the compressional stage of the orogeny about 1 9 ga ago

cloud cover from high resolution scanner data detecting and allowing for partially filled fields of view we present a new technique for obtaining cloud cover and determining clear sky radiances using high resolution infrared scanner data the technique which can be automated uses the spatial structure of the ir radiance field to identify radiances associated with fields of view that are either free of clouds or completely covered by clouds drawn from one or more distinct layers as the method uses only infrared radiances it should provide equally good results for both daytime and nighttime observations the approach is particularly suited for determining clear sky radiances over oceans from which sea surface temperature might be derived in addition for single layered systems the cloud cover fraction for a given region may be obtained from the clear sky radiance the completely cloud covered radiance and the mean radiance for the region for such systems the separation of completely covered from partially covered fields of view allows an estimate of the errors associated with commonly used threshold techniques for determining cloud cover these errors are in general shown to be highly sensitive to the applied threshold and to depend on the cloud areal size distribution in addition unlike the spatial coherence method described here histograms and correlations of visible and ir radiances as proposed for archiving information on cloud cover may fail to reveal the layered structure of cloud systems furthermore the high local structure observed for the visible radiances of regions that appear to be completely cloud covered makes it impossible to obtain reliable estimates of the cover from visible radiances alone

the boambolo formation a silurian prograding fan delta sequence in southeastern new south wales australia abstract the silurian sandstones and gravels of the boambolo formation are subdivided into six descriptive lithofacies each of which is diagnostic of a particular set of hydrodynamic conditions of deposition analysis of the vertical sequence of hydrodynamic conditions together with limited lateral facies variability information has permitted interpretation of this formation in terms of a prograding fan delta model within this broad model it has been possible to recognise deposits of current dominated quiet shelf delta front shoreface back beach pond and braided river environments an overall coarsening upward trend from shale dominated facies at the base of the formation to mixed sandstone and gravel at the top reflects the upward transition from low to high energy environments superimposed on this trend in the submarine portion of the formation are six secondary coarsening upward cycles representing establishment progradation and abandonment of migrating delta front lobes in the coarse terrestrial portion of the formation debris flow deposits are either absent or volumetrically insignificant with even the coarsest gravels diameters up to 15 cm believed to be traction current deposits

modern shallow water graded sand layers from storm surges bering shelf a mimic of bouma sequences and turbidite systems abstract a sequence of graded sand layers interbedded with mud extends offshore over 100 km from the yukon delta shoreline across the flat shallow 100 kin such shallow water graded layers off lobate deltas may be distinguished from similar deep water turbidites by 1 the predominance of trough cross lamination perhaps resulting from wave oscillation effects in the proximal part of the system and 2 gradation to common shallow marine fossils bioturbation and storm lag layers n distal areas

surface roughness characterizations of sea ice and ice sheets case studies with misr data this work is an examination of potential uses of multiangular remote sensing imagery for mapping and characterizing sea ice and ice sheet surfaces based on surface roughness properties we use data from the multi angle imaging spectroradiometer misr to demonstrate that ice sheet and sea ice surfaces have characteristic angular signatures and that these angular signatures may be used in much the same way as spectral signatures are used in multispectral classification three case studies are examined sea ice in the beaufort sea off the north coast of alaska the jakobshavn glacier on the western edge of the greenland ice sheet and a region in antarctica south of mcmurdo station containing glaciers and blue ice areas the misr sea ice image appears to delineate different first year ice types and to some extent the transition from first year to multiyear ice the misr image shows good agreement with sea ice types that are evident in concurrent synthetic aperture radar sar imagery and ice analysis charts from the national ice center over the jakobshavn glacier surface roughness data from airborne laser altimeter transects correlate well with misr derived estimates of surface roughness in antarctica ablation related blue ice areas which are difficult to distinguish from bare ice exposed by crevasses are easily detected using multiangular data

uraniferous bitumen nodules in the talvivaara ni zn cu co deposit finland influence of metamorphism on uranium mineralization in black shales in the central part of the fennoscandian shield the talvivaara ni zn cu co deposit hosted by palaeoproterozoic metamorphosed black schists contains low uranium concentrations ranging from 10 to 30 ppm the talvivaara black schists were deposited 2 0 1 9 ga ago and underwent subsequent metamorphism during the 1 9 1 79 ga svecofennian orogeny anhedral uraninite crystals rimmed by bitumen constitute the main host of uranium u pb secondary ion mass spectrometry dating indicates that uraninite crystals were formed between 1 878 17 and 1 871 43 ma during peak metamorphism rare earth element patterns and high th content average 6 38 wt in disseminated uraninite crystals indicate that u was concentrated during high temperature metamorphism 400 c the formation of bitumen rims around uraninite may be explained by two distinct scenarios a a transport of u coincident with the migration of hydrocarbons or b post metamorphic formation of bitumen rims through radiolytic polymerization of gaseous hydrocarbons at the contact with uraninite

new constraints for the source characteristics deposition and age of the 2 1 1 9 ga metasedimentary cover at the western margin of the karelian province abstract the paleoproterozoic cover sequence at the 100 150 km wide western margin of the archean karelian province is dominated by deep water lower and upper kaleva metasediments we present here an interpretation of sm nd isotope and geochemical data on 36 samples tims multi grain u pb zircon analyses on nine samples and ca 100 sims analysis of detrital zircon grains from four upper kaleva and one lower kaleva samples the lower kaleva is characterized by autochthonous parautochthonous lithologically heterogeneous metaturbidites showing common enrichment in quartz all the analysed detrital zircons are of a local neoarchean source but tdm variation up to 2 4 ga combined with geochemical data indicate abundant mixing of paleoproterozoic mafic material presumably from 2 1 ga plateau lavas and dykes in most of the lower kaleva samples the upper kaleva is dominantly allochthonous with tectonically enclosed fragments of ophiolite bodies and it is characterized by lithological and geochemical isotopic homogeneity geochemical isotopic and detrital zircon data favour material derived from an orogenic domain comprising both archean and proterozoic units followed by effective mixing during the transport the archean zircon grains 25 are mostly neoarchean the paleoproterozoic grains lack zircons at 2 5 2 2 ga and plot dominantly 92 between 1 92 and 2 05 ga the indicated maximum deposition ages vary from 1 95 1 94 ga to 1 92 ga the main source area proposed is the himalaya type lapland kola orogen now in the northeast which experienced mountain building and erosion at 1 95 1 91 ga the western margin of the karelian province shows evidence of rifting and lithosphere thinning from 2 1 to 1 95 ga but it is still under debate whether the craton breakup occurred at 2 06 ga in a volcanic or later at 1 95 ga in a non volcanic margin setting one hypothesis is that the onset of collision in the northeast changed plate motion and lead to a new spreading within the pre existing passive margin at 1 97 1 95 ga thus both a volcanic margin at 2 06 ga and a non volcanic margin at ca 1 95 ga could have been operated at the western margin of the karelian province

opening and closing of sea ice leads digital measurements from synthetic aperture radar the coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques an algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar sar digital images the pair of images is classified into leads and ice correcting for variation in brightness with range displacements are determined automatically on a regular 2 km grid on a 100 km square scene by cross correlation an algorithm groups together cells which cover a lead event the lead area change is estimated for each cell group by counting lead pixels before and after deformation all positive changes are summed to obtain the amount of opening and all negative changes give closing errors are estimated by comparison with area changes determined from manually digitized lead boundaries and are about 0 2 of the area of the scene for comparison the measured opening and closing are in the range of 1 to 3 of the scene area in ice models the openings and closings of leads are parameterized in terms of the large scale deformation sar allows us to study these parametric relations by giving us access both to direct observations of opening and closing and to detailed kinematic data from which to estimate the mean deformation in this image pair for which the deformation is nearly pure shear we find relatively small amounts of opening and closing consistent with previous observations and with parameterizations in most models the large values of opening and closing predicted by the poisson gauss kinematic model are not in evidence

genesis of palaeoproterozoic iron skarns in the misi region northern finland sodic alteration is widespread in palaeoproterozoic greenstone and schist belts of the northern fennoscandian shield in the misi region that forms the easternmost part of the perapohja schist belt several small magnetite deposits show intimate spatial relationships with intensely albitised gabbros raising the possibility that regional sodic alteration released iron which was subsequently accumulated into deposits two of these magnetite deposits raajarvi and puro display a typical paragenesis as follows from oldest to youngest 1 diopside 2 actinolite tremolite magnetite chlorite biotite and 3 serpentine hematite chlorite mass balance calculations suggest that significant amounts of fe ca mg k cu v and ba were lost and na and si gained during the albitisation of the gabbro at near constant al ga ti and zr significant amounts of si ca fe and na were enriched in the formation of skarn related to magnetite deposits fe and v leached from country rocks deposited during the skarn alteration and formed the vanadium rich iron deposits while cu passed through the system without significant precipitation due to low sulphur fugasity variations in na ca mg k and ba contents reflect the composition of the infiltrating fluid during alteration conventional heating freezing measurements and proton induced x ray emission pixe analyses of the fluid inclusions related to actinolite tremolite magnetite stage alteration indicate that the fluids that caused the alteration and the fe mineralisation were complex oxidised highly saline h2o co2 fluids that contained high amounts of na ca k fe and ba as well as elevated concentrations of cu zn and pb the oxygen isotope thermometry suggest that temperature during the fe mineralisation stage was between 390 and 490 c calculated 18ofluid values of 6 1 9 8 smow and 13c values of calcites in the ores and skarns were between 7 7 and 10 9 pdb and most likely reflect admixture of 13c depleted possibly magmatic fluids with the marble wall rocks that show 13ccalcite values of 13 pdb the sims u pb data on the zircons in the albitised gabbro next to the raajarvi and puro deposits suggest that intrusion of the gabbro took place at 2123 7 ma and was accompanied by the formation of diopside skarn the tims data on the metasomatic titanites related to sodic alteration yielded ages of 2062 3 and 2017 3 ma iron was probably stripped from the mafic country rocks by sodic alteration between 2123 and 2017 ma driven by repeated brine influxes subsequently the metal rich brine was focused by a fault system and the iron was precipitated from this fluid by a combination of wall rock reaction fluid mixing and a drop in the temperature

volume characteristics and element transfer of fenite aureoles a case study from the iivaara alkaline complex finland abstract fenitization in granodioritic rocks has been investigated taking the iivaara alkaline complex finland as a case study five main fenitization reactions responsible for the transition from a granodioritic precursor mineral assemblage to a syenitic or even cancrinite syenitic mineral assemblage of the fenites are set up an assessment of element transfer and volume change associated with each of these reactions indicates a general volume loss of about 20 due to fenitization high activities of na ca mg and fe as well as a low h2o co2 ratio in the fenitizing fluid phase are indicated si which is the main component released from the precursor rock was redistributed within the aureole and formed pyroxene dominated mineral assemblages in a reaction with the fenitizing fluid these vein type pyroxenites can be found cross cutting all fenite types compositional data of aegirine augite in the fenites reveal disequilibria and feldspar compositions point to minimum temperatures for the production of fenites with syenitic compositions of 660 c and also indicate fast cooling a sr isotope characterization of the fenites allows assessment of minimum fluid rock weight ratios in the fenite aureole of 0 023 2 3 the element transfer scheme developed in this study is applicable to other localities since many aureoles formed in granitic to granodioritic host rocks have petrographic characteristics similar to the iivaara fenites

decadal variations of sea ice thickness in the amundsen bellingshausen and weddell seas retrieved from icesat and icebridge laser altimetry 2003 2017

accretion tectonism in the proterozoic svecokarelides of the baltic shield the duality of early middle proterozoic terranes in the baltic shield reflects fundamental differences in history between coeval mobile belts and the manner of their interaction the karelides formed on a continent ocean transcurrent margin in which offsets developed as arcs and back arc basins on stretched continental crust at least one back arc basin was obducted onto the continental margin preserved as an allochthonous terrane in the karelian nappe pile remnant arc fragments form accreted exotic terrane in pohjanmaa the svecofennides developed as a succession of island arcs while the site of subduction moved south and successive extinct arcs were accreted onto the archean craton arc terrane impingement affected deformation style in the karelides which changed from one of major horizontal translation to one dominated by major dextral wrench faults analogies can be drawn with the phanerozoic evolution of the northeast pacific margin

multiply deformed paleoproterozoic foreland fold and thrust belt in northern fennoscandia the peripheral kuusamo belt as a key example abstract the central lapland belt clb perapohja belt pb and kuusamo belt kb form an important part of northern fennoscandia and record ca 700 ma 2 5 1 8 ga of precambrian tectonic processes the 2 5 2 1 ga sedimentary volcanic successions in these belts form a basin wide surfaces with a wide lateral continuum tidal influenced shallow epeiric sea setting dominated at 2 4 2 1 ga followed by a continental breakup and subsequent formation of a passive margin at 2 1 ga the collisional evolution 1 93 1 76 ga started with an e w locally nw se and ne sw compressional phase d1 1 93 1 90 ga that resulted in at least 600 km long and in part over 300 km wide e vergent lapland foreland fold and thrust belt ftb the kb is the best preserved example of this ftb and shows e vergent imbricated structures in the east and e vergent out of sequence thrusting in the west the southern part of the kb has been affected by n s shortening d2 seen as upright to slightly inclined open to tight f2 folds and as oval shaped dome and basin structures the d3 overprinting causes folding with nw se trending spaced foliation in less competent rocks and parallel folds and faults in orthoquartzites the d4 ne sw trending overprinting deformation is characteristic for the high grade areas of the kb and is seen in outcrop to map scale tight folding in general the easternmost peripheral part of the e vergent lapland foreland ftb formed upon non stretched archean basement is only moderately affected by the later deformation events in the stretched part of the archean basement the earlier rift structures have facilitated the n s shortening and the d2 structures dominate the map pattern the d3 due to a sw ne shortening shows strong strain partitioning and localized deformation after prolonged heating the archean basement started to act ductile and long wavelength crustal scale ne sw trending d4 folds formed the metamorphic zonation in the kb from greenschist facies in the south to medium pressure amphibolite facies in the north is explained by a major d4 anticlinorium wavelength 70 100 km

tide and storm dominated sand ridges on a muddy shelf cottage grove sandstone upper pennsylvanian northwestern oklahoma approximately 20 sandstone ridges of the cottage grove sandstone encased in shale and mudstone can be identified from subsurface control within a 504 mi2 1 305 km2 study area in northwestern oklahoma the sandstone ridges range in width from 0 6 to 2 5 mi 1 to 4 km and in length form 2 5 to more than 18 6 mi 4 to more than 30 km maximum sandstone thickness is about 100 ft 30 m the sandstone ridges trend generally northeast southwest oblique to present structural strike the sandstones show an overall fining upward trend unlike many reported shelf deposits a general vertical facies sequence from an axial core on a sand ridge consists of 1 mudstone basal 2 wavy bedded sandstone shale 3 alternating massive sandstone containing sy metrical oscillation ripples and flaser bedded and horizontally bedded sandstone with herringbone cross stratification and 4 wavy bedded sandstone shale which grades into the mudstone facies above a fossiliferous packstone grainstone facies also occurs as thin sheets in some sandstone ridges as well as interridge areas the cottage grove sandstone ridges were deposited in a shelf environment inferred depositional processes include reworking by tidal surge and ebb winnowing of ridge crests by wave action during storms and perhaps episodic delivery of sediment to the shelf by storm induced currents the fining upward trend in the sandstone bodies suggests deposition in a transgressive setting the characteristics and inferred processes of the cottage grove sandstone bodies are consistent with an origin similar to modern shoreface detached sand ridges

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

evaluation of ssm i and amsr e sea ice concentrations in the antarctic spring using kompsat 1 eoc images to evaluate sea ice concentrations sics from the special sensor microwave imager ssm i and advanced microwave scanning radiometer eos amsr e we observed sea ice with the 6 m resolution panchromatic electronic optical camera eoc sensor onboard the korea multi purpose satellite 1 kompsat 1 a total of 68 cloud free eoc images were obtained across the antarctic continental edges from september to november 2005 sea ice types in the eoc images were classified into white ice w gray ice g and dark gray ice d and then compared with ssm i and amsr e sics spatiotemporal standard deviation of passive microwave sic proved useful in selecting temporally stable and spatially homogeneous sics to overcome the diurnal variation of sea ice in the analysis of data from multiple satellites in the antarctic spring the eoc sic of w g showed the best fit to ssm i sic calculated by the nasa team nt algorithm mean difference of 2 3 and rmse of 3 2 whereas that of w g d showed the best fit to amsr e sic calculated by the nt2 algorithm mean difference of 0 3 and rmse of 1 4 it is concluded that the ssm i nt algorithm responds to young ice in addition to the ice types a and b whereas the amsr e nt2 algorithm detects ice type c and thin ice as well the 4 7 difference of sics between amsr e and ssm i was attributed to the enhanced detection of ice type c 2 1 and thin ice 2 6 of the amsr e nt2 algorithm

tectonic styles of early proterozoic ore deposition in the fennoscandian shield the early proterozoic metallogenic events of the fennoscandian shield are connected with two major stages of crustal evolution the karelian continental development 2 5 2 1 ga and the svecofennian orogeny 2 0 1 75 ga the karelian continental development was dominated by deposition of terrestrial sediments and tholeiitic volcanism on archaean crust a tensional regime probably associated with a mantle plume and partial melting of the upper mantle culminated in the generation of an ene wsw trending rift zone which was intruded by tholeiitic magma 2 44 ga ago some 15 layered igneous bodies hosting cr pge ni cu and fe v ti deposits are known in the kemi suhanko and koillismaa belts these mafic ultramafic bodies originally formed either several lopoliths or one single layered igneous complex with a minimum length of 260 km nw se and nnw sse trending dolerite dykes intruded the rifted and attenuated archaean crust 2 25 2 0 ga ago preceding ocean opening the coeval ne sw trending dolerite dykes in the northern part of the shield are interpreted as manifestation of an aulacogen the failed arm of a triple armed rift system oceanic crust is preserved in 1 96 ga old ophiolite complexes the cu co zn ni and cr contents of the outokumpu type deposits derive from hydrothermal leaching of oceanic crust and were discharged together with chemogenic cherts and carbonates from ascending hydrothermal fluids on the seafloor above fissure vents in the northern part of the shield rifting and probably ocean opening resulted in the formation of the layered tholeiitic sedimentary complex of the petsenga ni cu district intruded by mineralized mafic ultramafic magma the age of this event is poorly constrained the basin was subsequently closed and continental collision of the kola suture was accompanied by southward obduction of the lapland granulite belt on the archaean crust during the svecofennian orogeny the divergent continental margin was converted into an active margin early subduction of oceanic crust produced oceanic island arcs intruded by 1 93 1 9 ga old tonalites and trondhjemites subsequent subduction of oceanic crust generated 1 9 1 87 ga old continental island arcs associated with massive sulphide cu zn pb ag au deposits the island arcs were accreted to the archaean crust in a concave belt containing the ore districts of kiruna skellefte vihanti pyhasalmi aijala orijarvi and bergslagen bimodal volcanic suites with felsic calc alkaline and mafic tholeiitic volcanites are attributed to rifting of the overriding plate above subduction zones ni cu deposits in synorogenic 1 9 1 87 ga old mafic ultramafic intrusions occur in linear fault controlled belts at the margin of the archaean crust the generation of ni bearing tholeiitic to komatiitic magma is explained by partial melting of the mantle wedge above the early subduction zone magma differentiation and magma upwelling along transcurrent faults on the continental margin sulphur was probably assimilated from the supracrustal wall rocks 1 89 1 87 ga old early svecofennian granitoids are associated with porphyry type cu mo au deposits widespread late svecofennian s type 1 84 1 75 ga granitic magmatism generated minor mo u w sn and ree deposits emphasis is laid on the importance of geotectonic models as a basis for further exploration in the fennoscandian shield

fluvial coastal nearshore and shelf deposition in the upper proterozoic to lower cambrian addy quartzite northeastern washington abstract quartzose and lesser argillaceous strata of the approximately 1300 m thick upper proterozoic to lower cambrian addy quartzite of northeastern washington record shelf coastal and continental sedimentation on an actively subsiding relatively young passive margin the lower 400 to 500 m of the addy quartzite was deposited immediately following the initiation of subsidence in a wave dominated coastal and eventually storm dominated shelf environment this sequence records relative sea level rise that culminated in high stand conditions these sediments grade upwards into approximately 150 m of fluvial strata that record progradation of terrestrial environments during a period of relative sea level fall and a regional low stand the upper 700 m of the addy quartzite fines upwards from nearshore to shallow marine dominated sediments into shelf dominated deposits this sequence marks the reestablishment of net sea level rise the overall fining upwards trend displayed by the addy quartzite indicates that regional subsidence of the newly formed passive margin was one of the most important factors controlling addy sedimentation however variation seen in this trend throughout the addy quartzite indicates that rates of sea level rise associated with subsidence fluctuated and occasionally even reversed causes for the variation are inferred to be related to variations in subsidence rates and sediment supply textural and compositional data suggest addy detritus was derived from relatively proximal recycled sedimentary source terranes and more distal continental crystalline terranes

the tampere schist belt structural style within an early proterozoic volcanic arc system in southern finland abstract the central part of the narrow e w trending tampere schist belt comprises volcanic and sedimentary rocks of low metamorphic grade surrounded by intrusive rocks and migmatites the first folding event with subvertical axial surfaces and originally subhorizontal fold axes dominates the structure of the belt well preserved primary structures indicate a major e w trending syncline in the northern part of the belt with minor upright open to tight synclines and anticlines in the limb areas f 1 fold axes in the limbs have been rotated towards the steeply to vertically plunging stretching lineation dextral f 2 folds with subvertical e w to ne sw striking s 2 crenulation cleavage and steeply plunging fold axes overprint penetrative s 1 schistosity subhorizontal dextral shear is inferred from the d 2 structures d 3 kinking and fracturing is restricted to narrow nw se to n s trending zones the shear zone between the schists and the migmatites to the south is a south dipping thrust or reverse fault with uplift of the higher grade rocks in the northern part of the tampere schist belt another major fault is postulated both shear zones were formed at a late stage of progressive d 1 deformation on the basis of these structures and published sedimentological geochemical and isotopic data the tampere schist belt is interpreted as an upper part of a thrust sheet within a forearc of an ancient volcanic arc system the vergence of structures suggests subduction toward the present south

provenance of early proterozoic and archaean metasediments in finland a smnd isotopic study abstract sm nd isotopic analyses of early proterozoic and archaean clastic metasediments from finland are presented they have been used to calculate crustal residence ages and to constrain the sedimentary provenance the mean crustal residence age t dm for the svecofennian metagreywackes in the tampere schist belt is 2 22 ga which is about 0 3 ga in excess of the assumed stratigraphic age this indicates that the bulk of the sediments were eroded from newly formed crust their major source was most likely svecofennian orogenic material mixed with a small amount of archaean derived detritus the precursors of many granitoids in the svecofennian terrain also had similar short crustal residence times the kalevian metasediments which were deposited 2 05 1 9 ga ago on the edge of the archaean craton in eastern and northern finland have a mean t dm of 2 41 ga which is 0 4 0 5 ga more than the inferred stratigraphic age hence their source was on average older than that of the svecofennian metasediments investigated but definitely not purely archaean neither could crust similar to the bulk of the 1 9 ga old svecofennian terrain have been the only source various sources contributed at least locally but the bulk of the sedimentary material probably had a common provenance major sources consistent with existing isotopic data could have been 2 1 ga old jatulian rocks the c 2 0 ga old granulite belt in northern finland and or the svecokarelian early orogenic arc terrain mixed with archaean derived nd the method and data do not allow a distinction to be made between the possible alternatives the t dm model ages for two analysed archaean metasediments are slightly over 3 ga which is about 0 3 ga in excess of their assumed stratigraphic age thus providing no evidence for crust much older than 3 ga in this area

arctic sea ice leads from advanced very high resolution radiometer images a large number of advanced very high resolution radiometer avhrr images from throughout 1989 are analyzed to determine lead characteristics the units of analysis are square 200 km cells and there are 270 such cells in the data set clouds are masked manually leads are determined from images of the potential open water a scaled version of the surface temperature or albedo that weights thin ice by its thermal or brightness impact the lead fraction is determined as the mean the monthly mean lead fraction ranges from 0 02 in winter to 0 06 in summer in the central arctic and is near 0 08 in the winter in the peripheral seas a method of accounting for lead width sampling errors due to the finite sample areas is introduced in the central arctic the observed mean lead width for a threshold of 0 1 ranges from 2 or 3 km near the resolution of the instrument in the winter to 6 km in the summer in the peripheral seas it is about 5 km in the winter width distributions are often more heavily weighted in the tail than exponential distributions and are well approximated by a power law the along track number density power law n aw b has a mean exponent of b 1 60 standard deviation 0 18 and shows some seasonal variability mean floe widths in the central arctic are 40 to 50 km in the winter dropping to about 10 km in the summer for floes the power law has a mean exponent of 0 93 and exhibits a clearer annual cycle lead orientation is determined with a method based on the direction of maximum extent

sedimentary evidence of a cambro ordovician orogenic event in the northwestern himalaya abstract the late proterozoic early paleozoic sequence of the tethys himalaya provides evidence of an orogenic episode close to the cambrian ordovician boundary late pan african event pre middle cambrian sediments were deposited on a terrigenous tidal flat gradually passing upward to a peritidal carbonate platform the succession shows an overall transgressive trend which is reproduced at smaller scale by second and third order coarsening upward cycles terminated by the landward shift of carbonate facies during highstands of sea level sandstone petrography suggests a passive continental margin setting for this part of the sequence in middle cambrian times the carbonate platform underwent gradual drowning and outer shelf slope shales with intercalated tuffaceous material erupted from a nearby immature volcanic arc were deposited the shales are overlain by basinal turbidites attesting to the growth of a sandstone lobe enclosed in lobe fringe siltstones in the middle ordovician unconformable alluvial fan conglomerates and braid plain sandstones derived from uplifted sedimentary sequences indicate erosion of a newly formed orogenic belt comparison with early paleozoic and recent counterparts allows to interpret the cambro ordovician sedimentary evolution in terms of foreland basin development the thermal subsidence of a passive margin temporarily reduced by the passage of a peripheral bulge was enhanced strongly by flexural downwarping towards a subduction zone collision of a buoyant continental margin at the trench hampered subduction rapid uplift ensued with formation of a foreland fold thrust belt shedding sedimentary detritus into the adjacent molasse basins

heightened north pacific storminess during synchronous late holocene erosion of northwest alaska beach ridges a progradational regime of falling sea level and or high sediment input has produced extensive beach ridge plains in northwest alaska during the last 4000 yr eleven chukchi sea beach ridge complexes oriented at various angles to wind fetch provide a cumulative history of longshore transport and erosion archaeological and geological upper limiting radiocarbon ages n 59 allow correlations between depositional units on seven beach ridge complexes progradation started 4000 yr b p at nearly all complexes as eustatic sea level stabilized two disconformities or truncations are found on most of the complexes providing time parallel storm horizons dated at 3300 1700 and 1200 900 14c yr b p between 1700 and 1200 14c yr b p most of the complexes prograded indicating the predominance of less stormy conditions modern synoptic patterns that produce chukchi beach ridge erosion are linked to northerly shifts in north pacific storm tracks the regionwide beach ridge erosional truncations correlate with records of glacier expansion heightened precipitation evident in tree rings stream flooding and shelf deposits reworked by storm surges

icesat observations of arctic sea ice a first look 1 analysis of near coincident icesat and radarsat imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings containing thin ice or open water in the sea ice cover as well as to surface relief of old and first year ice the precision of the elevation estimates measured over relatively flat sea ice is 2 cm using the thickness of thin ice in recent openings to estimate sea level references we obtain the sea ice freeboard along the altimeter tracks this step is necessitated by the large uncertainties in the sea surface topography compared to that required for accurate determination of freeboard unknown snow depth introduces the largest uncertainty in the conversion of freeboard to ice thickness surface roughness is also derived for the first time from the variability of successive elevation estimates along the altimeter track overall these icesat measurements provide an unprecedented view of the arctic ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint of 70 m

hummocky cross stratification like structures in deep sea turbidites upper cretaceous basque basins western pyrenees france hummocky cross stratification is a sedimentary structure which is widely interpreted as the sedimentary record of an oscillatory current generated by energetic storm waves remobilizing surface sediment on the continental shelf sedimentary structures named hummocky cross stratification like structures similar to true hummocky cross stratification have been observed in the turonian senonian basque flysch basin south west france the bathymetry 1000 to 1500 m suggests that the observed sedimentary structures do not result from a hydrodynamic process similar to those acting on a continental shelf the morphology of these three dimensional structures shares similarities with the morphology of hummocky cross stratification despite a smaller size the lateral extent of these structures ranges from a few decimetres to many decimetres they consist of convex up domes hummock and concave up swales with a non erosive base four types of hummocky cross stratification like geometries are described they occur in association with structures such as climbing current ripple lamination and synsedimentary deformations in the basque flysch hummocky cross stratification like structures are only found in the tc interval of the bouma sequence hummocky cross stratification like structures are sporadic in the stratigraphic series and observed only in few turbidite beds or bed packages this observation suggests that hummocky cross stratification like structures are linked genetically to the turbidity current but form under a very restricted range of parameters these structures sometimes show an up current upslope migration trend antidunes in the described examples they could result from standing waves forming at the upper flow interface because of kelvin helmholtz instability

feasibility of sea ice typing with synthetic aperture radar sar merging of landsat thematic mapper and ers 1 sar satellite imagery ers 1 synthetic aperture radar sar and landsat thematic mapper tm images were acquired for the same area in the beaufort sea april 16 and 18 1992 the two image pairs were colocated to the same grid 25 m resolution and a supervised ice type classification was performed on the tm images in order to classify ice free nilas gray ice gray white ice thin first year ice medium and thick first year ice and old ice comparison of the collocated sar pixels showed that ice free areas can only be classified under calm wind conditions 10 m s 1 based on the backscattering coefficient alone this is true for pack ice regions during the cold months of the year where ice free areas are spatially limited and where the capillary waves that cause sar backscatter are dampened by entrained ice crystals for nilas two distinct backscatter classes were found at 17 db and at 10 db the higher backscattering coefficient is attributed to the presence of frost flowers on light nilas gray and gray white ice have a backscatter signature similar to first year ice and therefore can not be distinguished by sar alone first year and old ice can be clearly separated based on their backscattering coefficient the performance of the geophysical processor system ice classifier was tested against the landsat derived ice products it was found that smooth first year ice and rough first year ice were not significantly different in the backscatter domain ice concentration estimates based on ers 1 c band sar showed an error range of 5 to 8 for high ice concentration regions mainly due to misclassified ice free and smooth first year ice areas this error is expected to increase for areas of lower ice concentration the combination of c band sar and tm channels 2 4 and 6 resulted in ice typing performance with an estimated accuracy of 90 for all seven ice classes