weichselian land sea interactions western norway norwegian sea abstract six major weichselian glacier expansions including the younger dryas are recorded in western norway three of the advances reached the continental shelf while the others were restricted to the coastal areas during the upper weichselian glacial maximum 18 20 ka there was an ice free corridor between the british and the scandinavian ice sheets in the northern north sea more or less complete deglaciation of southern norway seems to have happened some time around 90 and 70 ka large parts of the norwegian sea were at least seasonally open with influx of atlantic surface water in periods through isotope substage 5d to stage 4 possibly also during a short time interval close to the 2 3 boundary a small area in the southeastern norwegian sea was ice free all these influxes of atlantic water seem to correlate to periods with interstadial conditions in western norway during times with the most extensive continental glaciations there are no traces of any influx of atlantic surface water the western norwegian glacial record and the norwegian sea surface circulation record seem to vary with a ca 20 ka cycle during the weichselian this indicates a dominance of the precessional orbital forcing between the ca 100 ka interglacial glacial interglacial cycle

back arc with frontal arc component origin of triassic karmutsen basalt british columbia canada the largely basaltic 4 5 6 2 km thick middle to upper triassic karmutsen formation is a prominent part of the wrangellian sequence twelve analyses of major and minor elements of representative samples of pillowed and massive basalt flows and sills from queen charlotte and vancouver islands are ferrotholeiites that show a range of 10 2 3 8 mgo as normalized h2o and co2 free and related increases in tio2 1 0 2 5 zr 43 147 ppm and nb 5 16 ppm other elemental abundances are not related simply to mgo distinct groupings are evident in al2o3 na2o and cr but considerable scatter is present in feo feo 0 9fe2o3 and cao some of the variation is attributed to alteration during low rank metamorphism or by seawater including variation of ba rb sr and cu but high field strength elements sc ti y zr and nb as well as cr ni cu and rare earth elements ree s were relatively immobile ree s show chondrite normalized patterns ranging from light ree depleted to moderately light ree enriched on eleven discriminant plots these analyses fall largely into or across fields of within plate basalt wip normal or enriched mid ocean ridge tholeiite morb and island arc tholeiite iat karmutsen basalts are chemically identical to the stratigraphically equivalent nikolai greenstone of southern alaska and yukon territory these data and the fact that the karmutsen rests on sicker group island arc rocks of paleozoic age suggest to us that 1 1 the basal arc after minor carbonate shale deposition underwent near axial back arc rifting as e g the mariana arc rifted at different times 2 2 the karmutsen basalts were erupted along this rift or basin as arc rift tholeiitite and 3 3 after subsequent deposition of carbonates and other rocks and jurassic magmatism a large fragment of this basalt sediment covered island arc was accreted to north america as wrangellia the major and minor elemental abundances of karmutsen basalt is modeled by first mixing primitive arc magma with enriched basaltic liquid derived either from garnet peridotite or metasomatized mantle followed by fractionation of olivine pyroxenes plagioclase and spinel

sedimentology and stratigraphy in the cave hamnsundhelleren western norway the stratigraphy in hamnsundhelleren is as follows a basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the laschamp excursion 43 47 000 yr bp angular blocks bones and clay above this are 14c dated to the alesund interstadial 28 38 000 yr bp another stadial laminated clay following the alesund interstadial includes a palaeomagnetic excursion correlated with lake mungo 28 000 yr bp the newly discovered hamnsund interstadial above this consists of frost weathered clay and scattered angular blocks it is 14c dated to 24 500 yr bp on bones mixed into the alesund interstadial the hamnsund interstadial is succeeded by another stadial laminated clay and then a late glacial holocene mixture of bones and blocks in hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice free ice covered cycle have been identified i ice free phase deposition of bones and frost weathered blocks ii subaerial ice dammed lake phase sand or silt deposited in a lateral glacial lake iii subglacial ice dammed lake phase cave closed by ice deposition of till debris flows and laminated clay d ice plugged phase cave is plugged by frozen lake water and or glacial ice no deposition

mesozoic cenozoic deformation in the canadian cordillera the record of a continental bulldozer abstract a possible mesozoic cenozoic trajectory for the north american craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path and from westward movement of the craton based on the assumption that africa has been the least mobile continent geographically since the latest paleozoic during each of five time intervals that span 220 million years the craton trajectory had a different vector each vector appears to be reflected in the canadian cordillera by the dominant style and orientation of structures formed during that interval for much of the past 220 million years the meridionally oriented western margin of the pangea laurasia north america plate has been the site of arc magmatism where weak arc back arc lithosphere sandwiched between strong ocean floor and craton lithospheres at times coupled across convergent or transform plate boundaries focused and recorded strain when the craton apparently moved due westward between 180 160 ma and 120 60 ma the dominant structures formed then record orogen normal compression and were accompanied by orogeny structures formed during the earlier episode are mainly in the eastern and interior cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin in the later episode compressional structures span the entire cordillera which emerged as a tectonic and physiographic entity before and between these intervals when the craton apparently moved mostly northwestward mainly geological and paleomagnetic considerations indicate some terranes moved southward sinistrally relative to the craton after 60 ma southwestward movement of the craton was concurrent with large northward dextral strike slip faults that disrupted the newly established ancestral cordillera the coincidence between the age of structures that record dominant orogen normal compression at times when the craton apparently moved due westward and orogen parallel displacements when the craton had either northward or southward components of motion suggests the craton acting as a continental bulldozer was the primary driver of cordilleran deformation and orogenesis

palaeomagnetic excursions recorded in mid weichselian cave sediments from skjonghelleren valderoy w norway abstract anomalous single component palaeomagnetic directions in laminated clay silt sediments in the non karstic skjonghelleren cave w norway are interpreted to record two high resolution but incomplete records of geomagnetic field excursions a depositional non distorted origin of magnetization carried by ultra fine magnetite maghemite grains has been inferred from field evidence redeposition experiments and magnetic fabric properties the sediments deposited sub glacially between 56 ka to 12 ka determined by consistent isotope ages obtained from bones and travertine the youngest excursion

tectonic history of the eastern edge of the alexander terrane southeast alaska rocks exposed west of the coast plutonic complex in southern southeast alaska form an imbricate thrust belt that overprints the tectonic boundary between two of the largest allochthonous crustal fragments in the north american cordillera the insular and intermontane composite terranes in the alexander terrane insular composite terrane lower paleozoic metavolcanic and metasedimentary rocks descon formation and dioritic plutons are unconformably overlain by lower devonian clastic strata karheen formation these rocks are overlain locally by upper triassic basalt rhyolite and marine clastic strata hyd group upper jurassic and lower cretaceous metavolcanic and metasedimentary strata of the gravina sequence unconformably overlie the alexander terrane the gravina sequence forms a structural package over 15 km thick and records intermittent arc volcanism along the eastern edge of the alexander terrane the gravina sequence is structurally overlain by upper paleozoic and lower mesozoic metamorphosed basaltic strata marble and argillite alava sequence and locally by lower paleozoic supracrustal rocks and orthogneiss kah shakes sequence together these constitute the taku terrane which we correlate with the intermontane composite terrane local unconformity of gravina sequence strata over the alava sequence demonstrates that the gravina sequence overlapped an earlier structural boundary between the intermontane and insular composite terranes the rocks were deformed in the mid cretaceous by west vergent thrusting that was was broadly coeval with arc magmatism deformation involved emplacement of west directed thrust nappes over the structurally intact and relatively unmetamorphosed alexander terrane basement mid cretaceous tonalite granodiorite and quartz diorite intrude rocks of the thrust belt and are locally affected by the deformation mid cretaceous deformation occurred during two episodes that were contemporaneous with the emplacement of large sill like plutons older structures record ductile southwest vergent folding and faulting regional metamorphism and development of axial planar foliation the second generation structures developed during the later stages of southwest directed thrust faulting which juxtaposed rocks of contrasting metamorphic pressures and temperatures structural stratigraphic and geochronologic data indicate that the two phases of regional thrusting in southeast alaska occurred between 113 ma and 89 ma rocks in the western part of the thrust belt were uplifted regionally by 70 ma deformation involved the collapse of a marginal basin s and a magmatic arc and overprinted the older tectonic boundary between the insular composite terrane and the late mesozoic western margin of north america at that time the intermontane composite terrane contractional deformation along the length of the thrust belt was broadly coeval with arc magmatism and thus records intra arc tectonism late paleocene to early eocene igneous activity and extensional deformation subsequently affected the thrust belt

the gravina sequence remnants of a mid mesozoic oceanic arc in southern southeast alaska fragments of upper jurassic to lower cretaceous volcanic and basinal strata constitute the gravina belt in southeast alaska in the ketchikan area the gravina belt is made up of two lithotectonic units the lower unit consists of coarse marine pyroclastic and volcaniclastic strata mafic flows breccia and fine grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite the volcanic rocks are characterized by tholeiitic arc basalts lack felsic volcanic strata and overlie upper triassic and older strata of the alexander terrane augite and or hornblende bearing porphyritic rocks are common and locally intrude the alexander terrane basement where they are thought to represent the intrusive equivalents of lavas within the section age constraints for the volcanic unit based on structural and stratigraphic relations with adjacent units are late middle to late jurassic the gravina belt upper unit consists of fine to coarse grained turbidites and related conglomeratic channel fill deposits the basinal rocks unconformably overlie permian and triassic rocks of the taku terrane and remnants of the lower volcanic part of the gravina sequence which overlie the alexander terrane the conglomerate units contain mostly volcanic and plutonic lithic clasts some of which yield pb u zircon ages of 154 158 ma the predominance of pyroclastic deposits interbedded with massive flows tuff breccia and argillaceous turbidites and the lithologic and chemical composition of the volcanic rocks indicate a submarine volcanic arc setting for the gravina sequence the basinal pyroclastic rocks are inferred to have been shed from submarine stratovolcanos during the late jurassic epiclastic rocks were deposited as submarine fans derived in part from erosion of a magmatic arc the presence of fine grained tuffaceous turbidites implies ongoing but distant volcanism the pyroclastic and volcaniclastic rocks represent remnants of a late jurassic oceanic arc constructed on a composite basement consisting of the alexander and taku terranes the strata accumulated in an intra arc basin on the eastern edge of the alexander terrane the volcanic and basinal rocks were deformed during a major mid cretaceous intra arc contractional event in conjunction with the emplacement of a distinctly younger arc related plutonic suite

comment on u pb and hf isotope analysis of detrital zircons from mesozoic strata of the gravina belt southeast alaska by yokelson et al 2015

geometric test for late cretaceous paleogene intracontinental transform faulting in the canadian cordillera the tintina trench northern rocky mountain trench tt nrmt fault zone and the fraser river straight creek fr sc fault zone are separate en echelon concentric small circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the canadian cordillera from the outboard part of a tectonic collage of accreted foreign terranes in the south into the north american preaccretionary continental margin in the north most of the 450 km of right hand slip on the tt nrmt fault zone was transformed southward during the late cretaceous and paleocene into oblique convergence in the southern canadian rockies the remainder probably comprising less than 100 km was transformed southwestward during early and middle eocene time via a zone of distributed shear and east west crustal stretching into right hand slip on the en echelon fr sc fault zone these interpretations based on regional systematic mapping of geologic structures are in conflict with interpretations of paleomagnetic measurements that call for more than 1000 km of post mid cretaceous right hand displacement along the general locus of the tt nrmt fault zone involving foreign terranes and the parts of north america to which they had been accreted this paradox must be resolved

the metallogeny of late triassic rifting of the alexander terrane in southeastern alaska and northwestern british columbia a belt of unusual volcanogenic massive sulfide vms occurrences is located along the eastern margin of the alexander terrane throughout southeastern alaska and northwestern british columbia and exhibits a range of characteristics consistent with a variety of syngenetic to epigenetic deposit types deposits within this belt include greens creek and windy craggy the economically most significant vms deposit in alaska and the largest in north america respectively the occurrences are hosted by a discontinuously exposed 800 km long belt of rocks that consist of a 200 to 800 m thick sequence of conglomerate limestone marine clastic sedimentary rocks and tuff intercalated with and overlain by a distinctive unit of mafic pyroclastic rocks and pillowed flows faunal data bracket the age of the host rocks between anisian middle triassic and late norian late late triassic this metallogenic belt is herein referred to as the alexander triassic metallogenic belt the vms occurrences show systematic differences in degree of structural control chemistry and stratigraphic setting along the alexander triassic metallogenic belt that suggest important spatial or temporal changes in the tectonic environment of formation at the southern end of the belt felsic volcanic rocks overlain by shallow water limestones characterize the lower part of the sequence in the southern and middle portion of the belt a distinctive pebble conglomerate marks the base of the section and is indicative of high energy deposition in a near slope or basin margin setting at the northern end of the belt the conglomerates limestones and felsic volcanic rocks are absent and the belt is composed of deep water sedimentary and mafic volcanic rocks this northward change in depositional environment and lithofacies is accompanied by a northward transition from epithermal like structurally controlled discontinuous vein and pod shaped pb zn agba cu occurrences with relatively simple mineralogy to sulfosalt enriched vms occurrences exhibiting characteristics of vein diagenetic replacement and exhalative styles of mineralization and finally to cu zn co au occurrences with larger and more clearly stratiform orebody morphologies occurrences in the middle of the belt are transitional in nature between structurally controlled types of mineralization that formed in a shallow water near arc setting to those having a more stratiform appearance formed in a deeper water rift basin setting the geologic setting in the south is consistent with shallow subaqueous emplacement on the flanks of the alexander terrane northward the setting changes to an increasingly deeper back or intra arc rift basin igneous activity in the alexander triassic metallogenic belt is characterized by a bimodal suite of volcanic rocks and a previously unrecognized association with mafic ultramafic hypabyssal intrusions immobile trace and rare earth element ree geochemical data indicate that felsic rocks in the southern portion of the belt are typical calc alkaline rhyolites which give way in the middle of the belt to peralkaline rhyolites rhyolites are largely absent in the northern part of the belt throughout the belt the capping basaltic rocks have transitional geochemical signatures radiogenic isotope data for these rocks are also transitional basalts and gabbros end 4 9 and 87sr 86sr initial at 215 ma 0 7037 0 7074 together these data are interpreted to reflect variable assimilation of mature island arc crust by more primitive melts having the characteristics of either mid ocean ridge morb or intraplate within plate basalts wpb the ore and host rock geochemistry and the sulfosalt rich mineralogy of the deposits are strikingly similar to recent descriptions of active sea floor hydrothermal white smoker systems in back arcs of the southwest pacific ocean these data in concert with existing faunal ages record the formation of a belt of vms deposits and occurrences in a propagating intra to back arc rift tectonic setting during the late triassic a modern analogue having similar tectonic and metallogenic features is the southward projection of the lau basin from the active sea floor hydrothermal vents of the valu fa ridge to the taupo volcanic zone of the north island new zealand

geology of the duncan canal shear zone evidence for early to middle jurassic deformation of the alexander terrane southeastern alaska the duncan canal shear zone central southeastern alaska disrupts and penetratively deforms devonian pennsylvanian and upper triassic strata of the lexander terrane the deformation is interpreted to have occurred within a regime of right lateral shear during early or middle jurassic time clastic and volcanic rocks correlated with the upper jurassic and lower cretaceous strata of the gravina belt lack the fabrics characteristic of the deformed alexander terrane strata and are inferred to unconformably overlie the shear zone deformational fabrics of mid cretaceous age observed in the gravina rocks locally truncate and deform the shear zone strata dextral strike slip faults of late cretaceous and or tertiary age that disrupt and modify fabrics of the shear zone are interpreted to accommodate some of the displacement observed on the clarence strait fault the duncan canal shear zone extends southward to the mosman inlet region on etolin island where it projects beneath jura cretaceous gravina strata in duncan canal and mosman inlet the shear zone evolved within the alexander terrane and does not coincide with any recognized terrane boundaries since the duncan canal shear zone is restricted to the currently exposed eastern margin of the alexander terrane the shear zone is interpreted to reflect deformation along the eastern margin of the alexander terrane

geochronology of augen gneiss and related rocks yukon tanana terrane east central alaska using several isotopic techniques we have determined the ages of selected metamorphic rocks in the yukon tanana terrane ytt of east central alaska u pb zircon data from an augen gneiss body in the big delta quadrangle indicate that the granitoid protolith of the gneiss was intruded 341 3 m y ago lower intercept age an upper intercept age of 2 136 31 m y indicates an inherited early proterozoic component in these zircons this inheritance age is substantiated by a sm nd whole rock model age of 2 09 0 08 b y from the big delta augen gneiss body detrital zircons from quartzitic wall rocks to this body were also derived from an early proterozoic 2 1 to 2 3 b y old crustal source s zircons from three other augen gneisses occurring in an east west belt which extends into the southern yukon territory canada have similar mississippian and early proterozoic intercept ages a rb sr whole rock isochron from widely separated bodies of augen gneiss has an age of 333 26 m y and an initial 87 sr 86 sr ratio of 0 728 0 002 confirming the mississippian intrusive age for the protolith the high initial 87 sr 86 sr ratio further indicates an old crustal component in these rocks a rb sr mineral isochron 115 4 m y k ar data from hornblende and micas 128 to 107 m y and u pb data from sphene 134 m y from augen gneiss and related rocks are similar to many k ar ages in this region and confirm the occurrence of an early cretaceous thermal event u pb ages of zircons from three metavolcanic units in the ytt suggest that extrusion of the protoliths of these rocks occurred 360 380 m y ago scatter in the data is caused by ubiquitous inheritance and multiple lead loss events significant devonian mississippian igneous activity 380 340 m y took place in the ytt followed by one or possibly two metamorphic episodes mississippian and cretaceous as yet no early proterozoic source rocks for the paleozoic magmas have been identified in the ytt but rocks of similar early proterozoic ages occur to the east and south in the northwest territories and british columbia canada

reinterpretation of lower mesozoic rocks on the chilkat peninsula alaska as a displaced fragment of wrangellia the southern chilkat peninsula is underlain by low grade metamorphic rocks consisting of a thick unit of greenstone in part of carnian age that is locally overlain by an attenuated section of calcareous sedimentary rocks and chart of latest carnian to late norian age and a thick flysch unit of jurassic and or cretaceous age the triassic part of this sequence has previously been inferred to be part of the taku terrane however its lithology age fossils and regional distribution indicate that it is probably a sliver of wrangellia that was offset from the eastern alaska range to its present position by at least 350 km dextral displacement on the denali fault

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

extent and dynamics of the scandinavian ice sheet during oxygen isotope stage 3 65 000 25 000 yr b p the climate of the middle weichselian glaciation marine oxygen isotope stage 3 ois 3 a relatively mild period compared to the glacial maxima of ois 4 and ois 2 consisted of long warm interstades punctuated by brief cold excursions that grew colder and more frequent with time the ois 4 ice sheet is generally thought to have persisted throughout ois 3 but evidence from dated ois 3 interstadial deposits suggests that it was swiftly reduced to small remnants which only briefly expanded and retreated only 30 000 years ago the deteriorating climate initiated a sustained ice advance leading toward the final glacial maximum of ois 2 dynamic ice sheet models support the existence of a prolonged ice free interval during ois 3 induced perhaps by low precipitation due to extensive sea ice cover offshore

tidal hydrodynamics and fine grained sediment transport on the radial sand ridge system in the southern yellow sea abstract the large radial sand ridge rsr system located in the southern yellow sea off the jiangsu coast is characterized by a radial current field and high suspended sediment concentrations sscs significant rectilinear currents are present over the northern sand ridge area whereas rotary currents prevail over the southern area the transition between the two being dominated by a locally generated trapped wave observations undertaken in 2006 and 2007 indicate a seasonal pattern in the ssc and associated dynamic characteristics the results of a calibrated hydrodynamic model show that the m2 tide dominates the rsr area the maximum tidal amplitude in the core region close to land being approximately 2 m an amphidromic point is located some distance north of the rsr off the abandoned yellow river mouth 121 686 e 34 6 n specifically the eulerian and lagrangian residual currents flow southward in both summer and winter whereas the stokes drift is directed southward in the north and northward in the south moreover in deep water the lagrangian residual current is mainly determined by the eulerian residual current whereas it is strongly influenced by the stokes drift in shallow water the seasonal variation in the residual current in the southern yellow sea is a good indicator for the location of the yellow sea warm current yswc in both summer and winter measurements show that a ssc peak appears off the abandoned yellow river delta in response to the strong currents and plentiful supply of fine grained sediment from coastal erosion another ssc peak lying close to the north branch of the changjiang river mouth is related to the abundant suspended sediment supplied by the river seasonal variations in ssc are observed in the study area maximum average values and widest diffusion from land occurring in winter this being contrasted by minimum mean values in summer sensitivity experiments demonstrate that the main factor influencing the distribution of ssc is the tide while river discharge wind and wave effects are small and very localized to explain the seasonal variation in ssc the role of hydrodynamics initial conditions and temperature are tested in the model the results show that the hydrodynamics play a significant role whereas the initial conditions only have a minor regional influence temperature on the other hand is also shown to greatly influence the seasonal variation in ssc because of substantial changes in the viscosity of the water and the erosion shear stress the modeled results are used to calculate sediment fluxes which are shown to be consistent with the lagrangian residual current pattern while wind waves can significantly change the fluxes in winter bed elevations change substantially on a monthly time scale in general the deep channels are undergoing erosion while the shallow ridges and coastal tidal flats are accreting the net sediment transport being directed towards the coastal tidal flat and the changjiang yangtze river subaqueous delta

quaternary glaciations in southern fennoscandia evidence from southwestern norway and the northern north sea region abstract based on records from the northern north sea and southern norway quaternary fennoscandian glaciations are described and discussed maximum glaciation defined as the presence of shelf edge glaciation an ice stream flowing out of the norwegian channel and most likely an ice divide over the central part of fennoscandia sweden gulf of bothnia occurred for the first time in the late cenozoic at ca 1 1 myr the fedje glaciation this glaciation was followed by a ca 600 kyr period with at least two glaciations with ice extension somewhat larger than the younger dryas event in the region the first maximum glaciation of the bruhnes chron was during isotope stage 12 and was followed by repeated maximum glaciations within each of the light isotopic stages until stage 2 during the weichselian the southwestern part of the fennoscandian ice sheet reached maximum position three times sometime between 22 and 28 37 and 50 and 60 and 80 ka limited glaciations probably occurred during stadials between the early and middle weichselian interstadials between 500 ka and 1 1 myr and most likely also prior to 1 1 myr deep norwegian sea ice rafted detritus ird records reflecting contributions from several different ice sheets fennoscandian barents sea iceland and greenland each with large variations in history of ice extent to their respective margins yet to some degree they reflect the glaciation of the northern north sea region with an increasing ird input around 1 1 myr and a relatively low input of north sea components during some cycles around the b m boundary maximum glaciations occurred during insolation minima in the earlier part of the middle pleistocene however not all such minima are reflected by maximum glaciation in southern parts of fennoscandia the relatively poor chronological control and non continuous character of the data on weichselian interstadials stadials precludes a clear relationship to atmospheric changes recorded in greenland ice cores as well as to precession and or obliquity cycles in insolation

middle and late weichselian devensian glaciation history of south western norway north sea and eastern uk data from eastern england scotland the northern north sea and western norway have been compiled in order to outline our current knowledge of the middle and late weichselian glacial history of this region radiometric dates and their geological context from key sites in the region are presented and discussed based on the available information the following conclusions can be made i prior to 39 cal ka and most likely after ca 50 cal ka scotland and southern norway were extensively glaciated most likely the central north sea was not glaciated at this time and grounded ice did not reach the shelf edge ii during the time interval between 29 and 39 ka periods with ameliorated climate including the alesund sandnes and tolsta interstadials alternated with periods of restricted glaciation in scotland and western norway iii between 29 and 25 ka maximum weichselian glaciation of the region occurred with the fennoscandian and british ice sheets coalescing in the central north sea iv decoupling of the ice sheets had occurred at 25 ka with development of a marine embayment in the northern north sea v between 22 and 19 ka glacial ice expanded westwards from scandinavia onto the north sea plateau in the tampen readvance vi the last major expansion of glacial ice in the offshore areas was between 17 5 and 15 5 ka at this time ice expanded in the north western part of the region onto the maloy plateau from norway and across caithness and orkney and to east of shetland from the moray firth the norwegian channel ice stream ncis which drained major parts of the south western fennoscandian ice sheet was active at several occasions between 29 and 18 ka

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

evolution of the yukon tanana terrane evidence from southeastern yukon territory the yukon tanana terrane ytt in southeastern yukon consists predominantly of a mid paleozoic volcanic plutonic arc assemblage built on continental crust the ytt had experienced strong deformation and metamorphism by late triassic time by mid cretaceous the metamorphic complex and late triassic clastic rocks derived from it were imbricated with middle and upper paleozoic ophiolitic sheets the ytt differs markedly from adjacent parts of the north american continental margin in both its depositional and tectonic histories the composition and tectonic history of the ytt is comparable to that of the kootenay and barkerville terranes of southern and central british columbia from which the ytt may have been displaced

detrital cave sediments record late quaternary hydrologic and climatic variability in northwestern florida usa abstract detrital sediment in florida s usa submerged cave systems may preserve records of regional climate and hydrologic variability however the basic sedimentology mineralogy stratigraphic variability and emplacement history of the successions in florida s submerged caves remains poorly understood here we present stratigraphic mineralogical and elemental data on sediment cores from two phreatic cave systems in northwestern florida usa on the dougherty karst plain hole in the wall cave hitw and twin cave water flowing through these caves is subsurface flow in the apalachicola river drainage basin and the caves are located just downstream from jackson blue 1st magnitude spring 2 8 m3 s 1 discharge sedimentation in these caves is dominated by three primary sedimentary styles i ferromanganese deposits dominate the basal recovered stratigraphy which pass upsection into ii poorly sorted carbonate sediment and finally into iii fine grained organic matter gyttja deposits resolving the emplacement history of the lower stratigraphic units was hampered by a lack of suitable material for radiocarbon dating but the upper organic rich deposits have a punctuated depositional history beginning in the earliest holocene for example gyttja primarily accumulated in hitw and twin caves from 5500 to 3500 cal yr bp which coincides with regional evidence for water table rise of the upper floridian aquifer associated with relative sea level rise in the gulf of mexico and evidence for invigorated drainage through the apalachicola river drainage basin gyttja sediments were also deposited in one of the caves during the bolling allerod climate oscillation biologically these results indicate that some floridian aquatic cave stygobitic ecosystems presently receive minimal organic matter supply in comparison to prehistoric intervals the pre holocene poorly sorted carbonate sediment contains abundant invertebrate fossils and likely documents a period of enhanced limestone dissolution and cave formation speleogenesis during lower paleo water levels further work is still required to a determine whether precipitation of the ferromanganese deposits is inorganically or biologically mediated b temporally constrain the emplacement history of the primary sedimentary styles and c determine the full geographic extent of these sedimentary signals however these preliminary observations suggest that sedimentation in the inland underwater caves of northwestern florida is related to quaternary scale hydrographic variability in the apalachicola river drainage basin in response to broader ocean and atmospheric forcing

ancient continental margin assemblage in the northern coast mountains southeast alaska and northwest canada geologic relations indicate that quartz rich metasedimentary rocks in the northern coast mountains separate strata to the east that belong to the stikine terrane from strata to the west of the alexander wrangellia and taku terranes the quartz rich rocks structurally overlie western terranes along a mid cretaceous thrust fault and are overlain structurally originally stratigraphically by strata of the stikine terrace these rocks are interpreted to be a continental margin assemblage that belongs to the yukon crystalline terrane u pb and nd isotopic data indicate that the metasedimentary rocks were shed from a source terrane consisting at least in part of proterozoic rocks

lagrangian trajectories residual currents and rectification process in the northern gulf of california abstract considering a semi implicit approximation of the coriolis terms a numerical solution of the vertically integrated equations of motion is proposed to test the two dimensional numerical model several experiments for the calculation of euler stokes and lagrange residual currents in the gulf of california were carried out to estimate the lagrangian residual current trajectories of particles were also simulated the applied tidal constituents were m2 s2 k2 n2 k1 p1 and o1 at spring tides strong tidal velocities occur in the northern half of the gulf in this region of complex geometry depths change from a few meter in the northern shelf zone to more than 3000 m in the southern part in the archipelago region the presence of islands alters amplitude and direction of tidal currents producing a rectification process which is reflected in a clockwise circulation around tiburon island in the lagrangian residual current the rectification process is explained by the superposition of the euler and stokes residual currents residual current patterns show several cyclonic and anticyclonic gyres in the northern gulf of california numerical experiments for individual and combinations of several tidal constituents revealed a large variability of lagrangian trajectories

late quaternary land sea interactions fennoscandia and svalbard the nordic seas abstract glaciation curves from western spitsbergen northern norway and western norway for the entire last interglacial glacial cycle are presented despite uncertainties due to chronology and discontinuous sedimentary records it seems safe to conclude that there were five major weichselian glacier expansions in western norway so far only three expansions have been recorded in western spitsbergen the weichselian maximum occurred during lower to middle weichselian in western spitsbergen as opposed to the upper weichselian maximum extent for the scandinavian ice sheet episodes of intrusion of relatively warm surface water into the norwegian sea correlate with interstadial conditions in western norway the lower weichselian maximum ice extent in western spitsbergen on the other hand probably occurred during a prolonged period of at least seasonally open water conditions far north in the norwegian sea suggesting that this was the major precipitation source the upper weichselian glaciers in spitsbergen probably failed to grow to a comparable size due to lack of precipitation as the entire norwegian sea probably was ice covered year round throughout most of stage 2 these observations suggest that there is a ca 20 ka interval between glaciations in western norway and a ca 40 ka interval in western spitsbergen this may reflect milankovitch cyclicity but both geological and climatological arguments against this supposition

mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations abstract theories associated with flow in the vicinity of headlands and sandbanks together with proposed mechanisms for sandbank formation and maintenance are reviewed to exemplify water and sand movement around a sandbank on a tidally dominated shelf tidal currents in the vicinity of a headland associated linear sandbank are described these data are integrated with sedimentological information on bedforms and grain size distributions the sandbank under detailed investigation the scarweather sands is located along the northern coastline of the bristol channel uk which is an area susceptible to high energy inputs the maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the atlantic ocean but the area is 460km from the shelf break detailed observations are presented from 11 long term current meter stations located within 10km of the sandbank currents are described in terms of residual water circulation shallow water harmonics and tidal ellipse characteristics bedload transport paths are inferred from the distribution of bedforms grain size and m2 m4 tidal current interactions transport vectors are predicted from near bed current meter observations combined with empirically derived formulae it is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance the results of the present study are thought to be applicable directly to headland associated sandbanks elsewhere it is shown on the basis of theoretical considerations that the pattern of residual water movement and possibly sand transport around this sandbank could be extended to continental shelves on a global basis

structural and geochronologic relations along the western flank of the coast mountains batholith stikine river to cape fanshaw central southeastern alaska abstract geologic and u pb geochronologic studies in central southeastern alaska provide constraints on the mid cretaceous to mid tertiary deformation west of the coast mountains batholith the ne dipping sumdum and fanshaw faults record the w directed emplacement of the ruth assemblage yukon tanana terrane and taku terrane over the subjacent gravina belt and alexander terrane ductile fabrics of the sumdum fanshaw fault system truncate early formed foliation and thrust faults in albian and older gravina belt strata u pb age data from syn and post tectonic plutons suggest that deformation was ongoing at 92 9 3 0 ma but had mostly ceased by 90 ma the sumdum fanshaw fault system marks the tectonic boundary between the alexander wrangellia terrane and inboard yukon tanana and stikine terranes and lies within a thrust belt that extends from southern alaska to northern washington mid cretaceous structures are truncated to the east by ne dipping ductile fabrics of the coast shear zone sheet like paleocene tonalites were emplaced into and deformed within the shear zone undeformed mid eocene dikes cross cut the tonalites kinematic relations in the coast shear zone suggest a complex displacement history that includes both east side up reverse and west side up normal shear the shear zone probably accommodated the collapse of overthickened crust developed during mid cretaceous shortening

geology of the western flank of the coast mountains between cape fanshaw and taku inlet southeastern alaska the western flank of the coast mountains batholith between cape fanshaw and taku inlet is underlain primarily by jura cretaceous strata of the gravina belt pre permian permian and triassic strata of the taku terrane and mid proterozoic to upper paleozoic rocks of continental margin affinity the continental margin rocks include mid proterozoic to lower paleozoic quartzite and marble of the tracy arm assemblage mid paleozoic metavolcanic and subordinate metasedimentary rocks of the endicott arm assemblage and upper paleozoic quartz rich metaturbidites and metaconglomerate of the port houghton assemblage we suggest that these three assemblages are correlative with components of the yukon tanana terrane which underlies a large region of yukon and eastern alaska rocks of the gravina belt taku terrane and yukon tanana terrane are juxtaposed along west vergent thrust faults of mid cretaceous age and are internally deformed and disrupted along latest cretaceous to early eocene dip slip and possibly strike slip shear zones these rocks and structures together with mid cretaceous to eocene plutons of the coast mountains batholith separate rocks of the alexander wrangellia terrane to the west from rocks of the stikine terrane to the east mid cretaceous thrust faults in the area belong to a system of thrusts that form the inboard margin of the alexander wrangellia terrane from central alaska to northwestern washington the continental margin rocks in the northern coast mountains may be part of the in situ north american margin that has been overthrust by the stikine and adjacent terranes alternatively these rocks may have 1 rifted from and then returned to the north american margin 2 moved 800 km along left lateral or right lateral faults from elsewhere along the north american margin or 3 originated near a continent other than north america

sedimentary processes and depositional environments in glaciated fjord systems evidence from nordfjord norway abstract fjords situated in past or present glacial regimes represent important repositories between land masses source systems and the open oceans sink systems newly collected topas high resolution seismic profiles from the previously glaciated nordfjord system on the west coast of norway reveal sedimentary processes and depositional environments within fjords in more detail than before the seismic data show that the fjord basins are characterised by a well laminated lower unit that is overlain by acoustic transparent lensoidal bodies we infer the lower unit which is up to 350 m thick to be composed of glacimarine sediments the transparent bodies represent up to 0 25 km 3 large slide debrites that comprise 14 c yr bp c 15 000 cal yr bp during the last deglaciation the entire nordfjord system was ice free for a short time period before the 1000 year long younger dryas readvance halted the main fennoscandian deglaciation and over ran the eastern part of nordfjord in contrast to the last glacial maximum we suggest that the sediments in the ice covered fjord basins were preserved during younger dryas the rapid isostatic adjustments accompanying the withdrawal of the younger dryas ice sheet promoted conditions for failures we relate the identified nordfjord slide bodies to this paraglacial environment this implies that the acoustic well laminated glacimarine fjord unit has been deposited in about 2000 yr and that sediment rates as high as 20 cm yr have existed during deposition

proterozoic zircon from augen gneiss yukon tanana upland east central alaska u th pb analyses of zircons from an ortho augen gneiss body in the yukon tanana upland of east central alaska yield strong evidence for the presence of early proterozoic material in this area u pb data define a chord that intersects concordia at about 2 300 and 345 m y we consider two interpretations 1 the protolith was intruded during the proterozoic and was subsequently metamorphosed in the paleozoic or more likely 2 the protolith was intruded in the paleozoic and incorporated material of proterozoic age an sm nd model age of about 1 900 m y on a whole rock sample of augen gneiss is additional evidence for the presence of proterozoic material in the gneiss k ar and u th pb dating of mica and sphene respectively reveal that younger thermal events occurred at least as recently as 110 m y ago

tidal velocity asymmetries and bedload transport in shallow embayments abstract tidal circulation can cause a net transport of sediment when the tidal velocity is asymmetric about a zero mean flood or ebb dominant and the sediment transport rate is related nonlinearly to velocity the relationship between tidal elevation and velocity is elucidated here to permit determination from tide gauge data and sediment transport relations whether tidal asymmetry needs to be considered as a mechanism for net sediment transport in the embayment of interest a relationship between elevation and velocity in a shallow water nonlinear system is derived through the continuity equation and shown to be significantly different than the linear relation finite difference numerical solutions of the one dimensional shallow water nonlinear equations are compared to the continuity relation and are in agreement especially toward the landward end of the channel tide gauge data collected at the landward end of the embayment are most useful for predicting velocity asymmetries throughout a major portion of the embayment channel the ratio of flood to ebb bedload transport and its relation to an asymmetric tidal elevation has been determined for both the linear relation between elevation and velocity and the nonlinear relation results show that the ratio of flood to ebb bedload transport as calculated from the nonlinear relation between elevation and velocity is similar to the flood to ebb ratio calculated from the linear relation because of offsetting effects

structural evolution of an arc basin the gravina belt in central southeastern alaska the upper middle jurassic lower cretaceous gravina belt lies along the eastern margin of the alexander terrane in southeastern alaska this group of turbidites and mafic to intermediate volcanic rocks was deformed during mid to late cretaceous time during the closing of a basin of unknown size between the alexander terrane on the west and the stikine terrane to the east therefore structures of gravina belt rocks largely reflect the final accretion and subsequent transport of the alexander terrane six geologic transects across the central gravina belt southern mitkof island to northern douglas island define a structural history that includes 1 syndepositional soft sediment folding and faulting possibly in conjunction with block tilting and extension 2 tight to isoclinal folding or thrust faulting with formation of a slaty cleavage s1 striking 330 3 local coaxial refolding with formation of crenulation cleavage s2 4 development of domainal crenulation folds and cleavage s3 oriented at a large angle to the margin of the belt 5 intrusion of tonalitic plutons around 90 ma and 6 right lateral strike slip displacement on faults oriented 330 finite strain measurements on sedimentary rocks suggest the belt was at least twice its present width normal to the foliation before deformation subhorizontal margin parallel fold axes margin parallel slaty cleavage and margin perpendicular stretching lineations suggest orthogonal contraction of the gravina basin assuming that oblique plate convergence was not decoupled along strike slip faults after contractional deformation strike slip faults indicate dextral displacement probably of the order of several tens of kilometers of the alexander terrane with respect to the terranes to the east domainal crenulation folds and cleavages at a high angle to the margin of the belt suggest that the change in convergence directions occurred while the rocks presently at the surface could still plastically deform this kinematic interpretation of structures is consistent with changes in plate motions engebretson et al 1985 before 100 ma the convergence directions between the kula and north america plates were at a high angle to the continental margin whereas after 100 ma convergence directions were at a small angle to the continental margin in addition after 100 ma the kula north america and not the farallon north america convergence direction is most compatible with a n s principal paleostress orientation derived from inversion of strike slip fault data this relationship suggests that it may have been the kula plate that drove northward transport of the alexander terrane along the margin of north america

a multiproxy approach to reconstruct the environmental changes along the eurasian continental margin over the last 150 000 years abstract sediment cores located along the eurasian continental margin arctic ocean have been studied to reconstruct the environmental changes in terms of waxing and waning of the barents kara sea ice sheets atlantic water inflow and sea ice distribution over the last 150 kyr the stratigraphy of the cores is based on stable oxygen isotopes ams 14 c and paleomagnetic data we studied variations in marine and terrigenous input by a multiproxy approach involving direct comparison of sedimentological and organo geochemical data extensive episodes of northern barents sea ice sheet growth during marine isotope stages mis 6 and 2 have been supported by at least subsurface atlantic water inflow moisture bearing storms low summer insolation and minimal calving of ice ice advance during mis 4 was probably restricted to the shallow shelf between mis 4 and mis 2 large ice sheet fluctuations correspond to contemporary laurentide surging events and indicate short term climatic changes in the arctic ocean as has been recorded in lower latitudes in contrast in low precipitation areas in eastern eurasia glacial activity was rather limited only distinct ice rafted debris ird input during termination ii and early mis 3 reflects severe glaciations on the northern severnaya semlya margin during mis 6 and mis 4 we conclude that 1 oscillations of ice sheets are less frequent along the eastern eurasian margin than in areas with continuous moisture supply like the western eurasian margins and that 2 major fluctuations of the kara sea ice sheet during the last 150 kyr apparently followed the major interglacial glacial mis 5 4 and mis 7 6 transitions rather than the precession 23 kyr and the tilt 41 kyr cyclicity of the earth s orbit as observed for the scandinavian sis and the svalbard ice sheets respectively mangerud j jansen e landvik j y 1996 late cenozoic history of the scandinavian and barents sea ice sheets in solheim a riis f elverhoi a faleide j j jensen l n cloetingh s eds impact of glaciations on basin evolution data and models from the norwegian margins and adjacent basins global and planetary chance special issue 12 pp 11 26 surface and or subsurface atlantic water masses coupled with seasonally ice free conditions penetrated continuously to at least the franz victoria trough during the last 150 kyr however sustained periods of open water were largely restricted to substages 5 5 5 1 and the holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter mom signals of periodic open water conditions along the northern margin of severnaya semlya are of less importance higher production of foraminifera probably due to atlantic water inflow occurred between 38 and 12 14 c kyr and corresponds to periodic atlantic water advection penetrating into the arctic ocean however marine organic proxies indicate a continuous decrease of surface water productivity from the western to the eastern eurasian continental margin due to a more extensive sea ice cover over the last 150 kyr

two phase evolution of accretionary margins examples from the north american cordillera abstract the coast mountains orogen southeastern alaska and the salmon river suture zone western idaho record the accretion of oceanic crustal fragments to the north american cordilleran margin structural elements associated with these boundaries include a western accretion related thrust belt and steeply dipping post accretionary shear zone the shear zones the coast shear zone southeastern alaska and western idaho shear zone idaho are steeply dipping crustal scale structures characterized by steep isotopic and geophysical gradients the presence of syndeformational tabular calc alkaline tonalitic plutons concordant with shear zone fabrics locally preserved dextral strike slip indicators and pervasive down dip mineral and elongation lineations are consistent with an intra arc transpressional origin for both structures in addition to strike slip translation the structures accommodated exhumation of high pressure moderate temperature metamorphic rocks within the thrust belt to the west and moderate pressure high temperature batholithic rocks to the east similarities between the structures in alaska and idaho suggest that the observed two stage history of underthrusting of accreting crustal fragments followed by modification by intra arc transpressional shear zones is a common tectonic process our analysis implies that recognition of processes active during the accretion of crustal fragments to continental or cratonal margins is commonly inhibited by post accretion deformation and provides insight into lower crustal processes presently operative under modern strike slip accretionary boundaries in addition the intra arc transpressional shear zones e g the coast and western idaho shear zones are structures that could have accommodated paleomagnetically determined large magnitude transcurrent displacements

marine caves on off signals for glaciations abstract a marine cut cave situated above the highest postglacial sea level in western norway contains a 15 m thick sediment sequence showing a repetitive pattern of glacial and non glacial sediments three periods of continental glaciation with underlying intervening and overlying ice free periods are recorded the glaciogenic sediments consist of laminated silts and clays deposited in an ice dammed lake the ice free periods are represented by blocky beds where the blocks are weathered from the cave ceiling by frost shattering speleothem fragments are found in the upper three of the blocky beds vertebrate bones in the upper two the sediments range in age from ca 80 90 ka to the present the last ice free period the alesund interstadial is dated to around 30 ka bp such repetitive sequences are rare in formerly glaciated regions due to glacial erosion but surveying of several caves in western norway suggests that they might be quite common in caves

tectonic framework of the upper paleozoic and lower mesozoic alava sequence a revised view of the polygenetic taku terrane in southern southeast alaska fragments of upper paleozoic and lower mesozoic metavolcanic and metasedimentary sequences of the taku terrane are exposed discontinuously along a narrow belt in southeast alaska and form a distinct lithostratigraphic package in the ketchikan area called the alava sequence crinoidal and argillaceous marble carbonaceous phyllite argillite mafic flows pillow breccia pyroclastic tuff and quartzite characterize the sequence these strata are unconformably overlain by upper jurassic to lower cretaceous fine to coarse grained epiclastic rocks of the gravina sequence the upper paleozoic part of the alava sequence may be correlative with the yukon tanana terrane whereas the middle and upper triassic portion of the alava sequence may represent a metamorphic vestige of the stikine terrane both parts are now exposed on the western flank of the coast plutonic complex in contrast with their correlatives to the east these relations suggest that the stikine and alexander terranes were juxtaposed prior to deposition of the gravina sequence the western boundary between rocks of north american affinity and allochthonous ensimatic crustal fragments of the alexander and wrangellian terranes lies west of the coast plutonic complex

detrital zircon geochronology of the taku terrane southeast alaska u pb geochronologic studies have been conducted on 60 detrital zircon grains from permian and triassic metasandstones of the taku terrane in central southeast alaska the resulting ages are mainly in the range 349 387 ma with five additional grains that yield probable ages ranging from 906 to 2643 ma these ages are similar to the ages of detrital zircons in carboniferous and older rocks of the yukon tanana terrane which lies directly east of the taku terrane in contrast these ages are different from the ages of detrital zircon grains in the alexander terrane to the west the data are accordingly consistent with models in which the taku terrane is a western component of the stikine and yukon tanana terranes and that this crustal fragment is separated by a fundamental tectonic boundary from rocks of the alexander and wrangellia terranes to the west

paleomagnetic correlations between scandinavian ice sheet fluctuations and greenland dansgaard oeschger events 45 000 25 000 yr b p abstract two paleomagnetic excursions the skjong correlated with the laschamp about 41 000 gisp2 yr b p and the valderhaug correlated with the mono lake about 34 000 gisp2 yr b p have been identified in stratigraphic superposition in laminated clay deposited in ice dammed lakes in three large caves in western norway during both periods the margin of the scandinavian ice sheet advanced and reached the continental shelf beyond the outermost coastline the mild 4000 yr long alesund interstade when the coast and probably much of the hinterland were ice free separated the two glacial advances the two paleomagnetic excursions have also been indirectly identified as increased fluxes of 36cl and 10be in the grip ice core greenland this article presents a correlation between ice margin fluctuations of the scandinavian ice sheet and the stratigraphy of grip gisp cores using the paleomagnetic excursions and the 36cl and 10be peaks and thus circumventing the application of different dates or time scales some of the fluctuations of the scandinavian ice sheet were of the allerod younger dryas type in the sense that its margin retreated during mild interstades on greenland and readvanced during cold stades however some fluctuations were apparently not in phase with the greenland climate

quaternary regional evolution based on karst cave geomorphology in picos de europa atlantic margin of the iberian peninsula abstract alpine caves have attracted considerable geomorphological paleoenvironmental and hydrogeological interest since climate glaciations relief uplift fluvial incision and karst aquifer control their evolution in the atlantic margin of the iberian peninsula picos de europa mountains is among of the most important karst areas of the world containing some of the deepest caves explored today in addition these mountains represent a reference site for the study of the last glacial cycle in the sw of europe this work aims to reconstruct the pliocene quaternary evolution of this region based on geomorphological and geochronological research u th and al be carried out in four alpine caves cave geomorphological mapping evidences that 12 km of studied caves are made up of 47 vadose canyons and shafts 45 phreatic epiphreatic conduits organised in six cave levels and 7 breakdown modified passages their deposits are characterized by speleothems including flowstones that represent ancient cave pavements fluvial terrace deposits with allochthonous clasts slackwater deposits related to cave floods and debris deposits produced by breakdown one 26al 10be burial age indicates a minimum age of 2 1 0 5 ma for the caves origin allowing estimation of the mountain uplift at 0 15 0 25 mm a 1 since the late pliocene twenty eight new 234u 230th ages and another six previous speleothem ages give ages ranging from mis 8 to 1 the speleogenetic model comprises six phases of regional evolution phase 1 main development of cave levels with se directed phreatic flow in the nw of picos de europa in a karst partially or totally covered by the detrital permian mesozoic cover presently eroded phase 2 erosion of the permian mesozoic cover and onset of vadose conditions before 260 ka in a karst affected by fluvial captures phase 3 cave infill during 220 145 ka probably caused by the erosion of stephanian detrital outcrops phase 4 erosion of cave infill during 125 45 ka phase 5 apparent pause in the speleothem formation during 45 25 ka related to dry and cold regional conditions phase 6 reactivation of the speleothem precipitation since 25 ka regional climate fluvial incision and the ancient presence of detrital outcrops at the surface appear to have been the main factors that controlled the cave evolution and regional geomorphological evolution throughout pliocene and quaternary times

petrology and tectonic significance of augen gneiss from a belt of mississippian granitoids in the yukon tanana terrane east central alaska an approximately east west trending belt of porphyritic peraluminous granitoids metamorphosed and deformed to augen gneiss is exposed for 400 km across the yukon tanana terrane this belt consists of compositionally texturally and isotopically similar concordant intrusions of augen gneiss in the big delta eagle and tanacross quadrangles of east central alaska in the fiftymile batholith of west central yukon territory and in two batholiths in the offset part of the yukon tanana terrane northeast of the tintina fault in southeastern yukon territory chemical analyses of augen gneiss from widely separated localities within the big delta intrusion suggest that the various samples are related by crystal fractionation comparison of major and trace element data from concordant layers of augen poor gneiss and aplitic gneiss with similar data from adjacent augen gneiss suggests that the layers represent co magmatic sills of more highly differentiated filter pressed melt similarities between elemental abundances particularly those of rare earth elements in augen gneiss from the large bodies in the big delta eagle and tanacross quadrangles alaska and southeastern yukon territory suggest a common origin for these bodies the peraluminous composition of the gneiss its high initial 87 sr 86 sr ratio and high th concentration indicate that the augen gneiss protolith contains a large component of crustal material geochronologic studies of augen gneiss in east central alaska and southeastern yukon territory indicate a mississippian intrusive age and an early proterozoic age for the crustal component the augen gneiss bodies were intruded late in a middle paleozoic volcanic plutonic episode and they may represent a deeply eroded continental magmatic arc regional amphibolite facies metamorphism and mylonitization may have occurred late during the tectonic episode that resulted in intrusion of the porphyritic granitoid protoliths

regionally extensive mid cretaceous west vergent thrust system in the northwestern cordillera implications for continent margin tectonism the intermontane insular superterrane boundary zone represents a fundamental crustal boundary separating the two largest allochthonous crustal fragments in the north american cordillera structural stratigraphic and geochronologic relations along this boundary indicate that substantial west vergent compression and concomitant crustal thickening occurred there in mid cretaceous time this orogenic zone extends for more than 1200 km along strike length between southern southeast alaska and northern washington in southern southeast alaska and northwest british columbia rocks of the insular superterrane were imbricated along a series of west to southwest vergent thrust faults in northern washington and southwestern british columbia a wide zone encompassing the margins of the two superterranes as well as numerous intervening smaller fragments was shortened principally along west vergent thrusts known geologic relations do not discriminate among existing tectonic models that explain the origin of the mid cretaceous thrust system

comparison between predicted and observed physical features of sandbanks a linear stability analysis has been carried out to investigate the influence of parameters like tidal current depth and coriolis force on sand bank formation the applied analytical model allowed the computation of the horizontal wave number corresponding to the fastest initial growth rate of seabed form perturbations sandbank wavelength and the angle between the crest of the sandbank and tidal current direction were also obtained the experiments show an exponential decay of this angle for increasing values of tidal currents at a particular depth the sand bank wavelength grows almost linearly with the velocity we compared these theoretical results with observations of sandbank features in several geographic areas persian gulf the gulf of korea gulf of california and the north sea the results show that all observed sand bank wavelengths and angles are in very close agreement with the calculated theoretical curves

glacial origin for cave rhythmite during mis 5d c in a glaciokarst landscape picos de europa spain abstract laminated slackwater deposits have been identified in many karst caves related to fluvial and lacustrine sedimentation however sedimentological evidence rarely supports a glacial origin for these deposits which was proposed by previous studies the torca la texa shaft is located in a glaciokarst area that comprises numerous slackwater type deposits piled up in fining upward sequences a basal sandy erosive layer and millimeter sized laminated rhythmite with interbedded flowstone characterize these sequences fining upward layers of carbonate silt clay and minor quartz sand deposited in flooded conduits define the rhythmite lamination the presence of allochthonous minerals indicates that the rhythmite sediment comes from the glacial erosion of nearby carbonate mountains two 234u 230th radiometric ages dated the rhythmite deposits around 109 and 95 ka coinciding with relative cold periods included in the mis 5d c these cold periods were marked by a high annual seasonality immediately after the glacial local maximum extension in agreement with a varve type deposit the combination of these sedimentological mineralogical geomorphological and paleoclimate information indicates that the rhythmite should be introduced into the studied cave during the summer melting of the glaciers which produced the recharge of the karst aquifer triggering cave floods in addition punctual glacier collapses would also have their imprint in the slackwater sequences with thicker coarser and erosive sand deposits and the spring blocking by glaciers may have promoted floods inside the cave therefore the studied rhythmite can be interpreted as glacial varves decanted during the relatively cold climate conditions