late cretaceous cenozoic fracturing in lofoten north norway tectonic significance fracture mechanisms and controlling factors abstract the lofoten ridge is a fault controlled basement horst residing between mesozoic basins on the north norwegian passive margin this major horst and the adjacent offshore basin bounding normal faults formed during stages of rifting from the permian jurassic to the early cenozoic well exposed heterogeneous nw se striking brittle fracture sets have been studied onshore at moskenes in the western lofoten islands this area provides an excellent frame for understanding onshore offshore fault fracture correlations and passive margin evolution as inferred from high quality offshore seismic data the fracture sets at moskenes exhibit geometric and kinematic variability i e systematic bisecting conjugate fractures parallel extensional fractures and anastomosing relay stepping shear fractures an incremental nw se oriented 1 compressive stress axis and a ne sw oriented 3 was inferred from the attitudes of the conjugate fracture sets the different fracture sets are interpreted to have formed in isolation and or in a progression through time as precursory parallel mode i or conjugate fractures mode ii and or more complex anastomosing shear fracture sets mode iii due to varying boundary stress conditions as controlling factors and not by mechanical weaknesses in the host rock whether parallel conjugate or anastomosing fractures formed depended on the initial spacing of precursory fractures the timing of development of complementary fractures and on the evolving strain stress conditions in terms of a north atlantic passive margin stress field the nw se trend of the heterogeneous fractures in western lofoten is roughly parallel to the late cretaceous early cenozoic regional extension directions but oblique to that of the permian jurassic a switch of the extension direction from wnw ese in the permian jurassic to nnw sse in the late cretaceous may have initiated multiple reactivations and e g right lateral shearing along ene wsw striking master faults producing a block internal nw se 1 in western lofoten alternatively the fractures formed by reactivation of transfer fault zones between nne ssw right stepping normal faults a third possibility is origin by cenozoic ridge push forces creating neotectonic fractures as a substitute to inversion structures and arc shaped domes on the mid norwegian margin farther south

late quaternary benthic foraminifera and deep water paleoceanography in the south china sea abstract recent and late quaternary deep sea benthic foraminifera in the south china sea scs have been quantitatively studied in order to approach some disputable questions about the glacial deep circulation of the pacific from the paleoceanographic records of a marginal sea for example whether or not there existed the north pacific deep water npdw during glacials based on the quantitative data of deep sea benthic foraminiferal faunas from sixty six surface sediment samples of the scs a q mode factor analysis indicates that the globocassidulina subglobosa assemblage the astrononion novozealandicum and bulimina aculeata assemblages and the eggerella bradyi assemblage are associated with the intermediate water mass iwm deep water mass dwm and the deep water below ccd in the scs respectively the factor assemblages resulted from surface sample data were then applied to the quantitative analysis of late quaternary deep sea benthic foraminifera in eight cores from the scs and western pacific the results show a generally increased contribution of the dwm assemblage relative to that of the iwm assemblage during glacials which implies that the influence of the dwm increased and that of the iwm decreased in the scs and western pacific however there were two major deep water paleoceanographic changes during the late quaternary 1 the deep sea carbonate dissolution of the scs and western pacific was intensified during 18 0 stages 4 5 evidenced by the higher arenaceous calcareous ratios of benthic foraminifera and relative abundance of eggerella bradyi 2 the influence of the pacific dwm above 2500 m greatly increased during the last glacial maximum lgm inferred from the increased abundances of the pacific dwm benthic foraminiferal assemblage as compared to those of the pacific iwm and pacific bottom water mass assemblages in the western pacific particularly the water in which favocassidulina favus was distributed could not enter the scs since the lgm meanwhile the great changes had taken place in the dwm of the scs during the lgm reflected in the occurrence of a clearly cooled and ventilated dwm and the replacement of a novozealandicum and b aculeata assemblages by b aculeata melonis barleeanum assemblage at water depths of 1000 2500 m these significant changes during the lgm may be related to the formation of the npdw

modern distribution patterns of planktonic foraminifera in the south china sea and western pacific a new transfer technique to estimate regional sea surface temperatures abstract we present 30 new planktonic foraminiferal census data of surface sediment samples from the south china sea recovered between 630 and 2883 m water depth these new data together with the 131 earlier published data sets from the western pacific are used for calibrating the simmax 28 transfer function to estimate past sea surface temperatures this regional simmax method offers a slightly better understanding of the marginal sea conditions of the south china sea than the linear transfer function fp 12e which is based only on open ocean data however both methods are biased toward the tropical temperature regime because of the very limited data from temperate to subpolar regions the simmax formula was applied to sediment core 17940 from the northeastern south china sea with sedimentation rates of 20 80 cm ka results revealed nearly unchanged summer temperatures around 28 c for the last 30 ky while winter temperatures varied between 19 5 c in the last glacial maximum and 26 c during the holocene during termination 1a the winter estimates show a younger dryas cooling by 3 c subsequent to a temperature optimum of 24 c during the bolling allerod estimates of winter temperature differences between 0 and 100 m water depth document the seasonal variations in the thickness of the mixed layer and provide a new proxy for estimating past changes in the strength of the winter monsoon

comparative micromorphology of two late pleistocene paleosols in the paris basin summary the micromorphology of two late pleistocene paleosols in the paris basin st pierre les elbeuf and bois du moulin were studied in order to characterize their pedogenic and sedimentary processes and to reconstruct and interpret the pedosedimentary history and climate of each profile the micromorphological observations of greatest interpretive value were the types of clayey and silty textural accumulations argillans and siltans pedality and porosity of lesser value were papules bioactivity and concretions during the last interglacial period on both profiles developed a sol brun lessive comparable to those developed during the holocene with the onset of cold conditions of the last glaciation the two differentiate pedologically and sedimentologically at elbeuf in the seine valley we observe colluviation of silts and the development of grey forest soils with strong textural degradation under cold and moderately dry local conditions at moulin on the plateau the grey forest phase is very weak and probably brief and is followed by a marked phase of churning and eluviation of silt conditions were wetter than in the valley such that the upland position protected the profile from colluvial truncation the advantages of micromorphology in interpreting pedo sedimentary sequences is discussed

p wave velocity in granulites from south india implications for the continental crust abstract p wave velocities v p were measured in 160 high grade metamorphic rocks from the south indian granulite terrain sgt the wide variations observed in the v p of charnockites and gneisses could be due to the complex prograde and retrograde metamorphic histories of the two major rock types of the sgt the velocity density relation showed distinct trends for charnockites and gneisses initial stages of retrograde metamorphism in charnockites significantly affected their magnetic properties however its effect on velocity and density is not diagnostic contrasting physical properties on either side of the palghat cauvery p c shear zone lends support for the contention that the p c shear zone is a major paleosuture the laboratory mean v p of the rocks from the northern sgt are comparable with the mid crustal dss velocity in the adjacent granite greenstone terrain ggt suggesting that the ggt is possibly underlain by a felsic granulite basement the physical properties of the high grade metamorphic rocks from sgt are significantly lower than that of the lower crust the physical properties and tectonic considerations show that the granulites of south india may not be of lower crustal origin and hence not representative of the lower crust as generally thought a simplified two layer crustal model with a predominantly felsic granulite upper crust and a mafic granulite lower crust is suggested for the sgt

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

a new tectono magmatic model for the lofoten vesteralen margin at the outer limit of the iceland plume influence the early eocene continental breakup was magma rich and formed part of the north atlantic igneous province extrusive and intrusive magmatism was abundant on the continental side and a thick oceanic crust was produced up to a few m y after breakup however the extensive magmatism at the voring plateau off mid norway died down rapidly northeastwards towards the lofoten vesteralen margin in 2003 an ocean bottom seismometer profile was collected from mainland norway across lofoten and into the deep ocean forward inverse velocity modeling by raytracing reveals a continental margin transitional between magma rich and magma poor rifting for the first time a distinct lower crustal body typical for volcanic margins has been identified at this outer margin segment up to 3 5 km thick and 50 km wide on the other hand expected extrusive magmatism could not be clearly identified here strong reflections earlier interpreted as the top of extensive lavas may at least partly represent high velocity sediments derived from the shelf and or fault surfaces early post breakup oceanic crust is moderately thickened 8 km but is reduced to 6 km after 1 m y the adjacent continental crystalline crust is extended down to a minimum of 4 5 km thickness early plate spreading rates derived from the norway basin and the northern voring plateau were used to calculate synthetic magnetic seafloor anomalies and compared to our ship magnetic profile it appears that continental breakup took place at 53 1 ma 1 m y later than on the voring plateau consistent with late strong crustal extension the low interaction between extension and magmatism indicates that mantle plume material was not present at the lofoten margin during initial rifting and that the observed excess magmatism was created by late lateral transport from a nearby pool of plume material into the lithospheric rift zone at breakup time

a crustal study off lofoten n norway by use of 3 component ocean bottom seismographs abstract twenty four 3 component ocean bottom seismographs obs were used in august 1988 in a combined seismic refraction and reflection study off lofoten n norway the purpose of the experiment was to map the crustal structure from the continental shelf to the oceanic crust off lofoten the very high data quality is demonstrated by the strong p wave and shear wave reflections as well as converted waves from the moho observed on the continental shelf these arrivals are observed continuously from near vertical to wide angle incidence very high seismic sea floor velocities in this area 3 1 km s to 5 1 km s indicates absence or very thin sequences of mesozoic sediments the 5 1 km s refractor coincides with the base cretaceous reflection interpreted from the multichannel reflection data the crystalline continental crust is here divided in layers with velocities of 6 0 km s 6 4 km s and 6 8 km s respectively on the seaward side of the escarpment tertiary sediments varying in thickness from 1 0 1 5 km are situated on top of a 1 5 2 0 km thick layer of flood basalt containing seaward dipping reflectors a layer with velocity of 6 7 km s is observed above the lower crust which in this area is found to have a velocity as high as 7 3 km s these high velocities indicate that the crust in this area is of oceanic origin or alternatively the high velocity layer in the lower crust might represent a magmatic body underplating highly thinned and intruded continental crust seven obss were deployed in the area that was covered by landward flowing basalt deposited during the early eocene breakup between norway and greenland the survey was partly performed to investigate whether this method can be used to map structures below the basalt which is impenetrable with conventional seismic reflection techniques the obs data contain considerable information about structures below the flood basalt pre opening sediments up to 4 0 km thick are indicated below the 1 0 2 5 km thick landward flowing basalt the velocities of the crystalline portion of the crust are found to be similar to those observed under the continental shelf 6 0 6 8 km s which implies that the crust east of the escarpment is of continental origin the crystalline crust is strongly thinned in this area showing a minimum thickness of about 6 km the depth to the moho increases from about 15 km in the western part of the area to about 26 km on the continental shelf the success of the obs survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and potentially in other areas where highly reflective surfaces make the reflection technique inefficient

compositional and metamorphic controls on velocity and reflectivity in the continental crust an example from the grenville province of eastern quebec we present velocity and density data for a suite of gabbros and metagabbros over a range of metamorphic grades from subgreenschist to the eclogite facies most of these rocks have a mesocratic protolith with overlapping bulk chemistry ranges providing an opportunity to investigate the systematics of mineralogy and physical properties across a wide range of metamorphic grades with minimal compositional variation in addition more mafic gabbros in the eclogite facies were also investigated in order to take into account variations in the extent of transformation of gabbro to eclogite controlled by bulk chemistry the physical properties data are used as the basis for a first order crustal model composed of granitic anorthositic and gabbroic components the objective of constructing the crustal model is to evaluate the relative contribution of compositional variation and metamorphism to the velocity density and reflectivity structure of the continental crust the model suggests that in the upper crust if fracture porosity is neglected composition dominates the velocity and density structure while in the middle and lower crust composition and metamorphism play equally important roles simulations designed to predict potential reflection coefficient size distributions for the various bulk chemistries and mineralogies in the crustal model indicate step increases in the potential for large reflection coefficients that are dominantly controlled by metamorphic grade step increases in reflectivity are predicted between the lower and upper amphibolite facies and between incompletely and completely eclogitized metagabbros in the eclogite facies we also consider several alternative mixing models which account for the effects of one of the three lithologic components occurring as isolated bodies rather than perfectly mixed with the other two components these models indicate a reduction of the potential for large reflection coefficients by as much as 50 emphasizing the importance of the degree of mixing for crustal reflectivity

micromorphology of atlantic rankers on the coast of northern portugal summary the micromorphological examination of atlantic rankers on the coast of northern portugal shows the importance of alternating phases of landscape stability and instability during the genesis of the profiles archaeological artifacts and marine deposits allow the dating of these events recent pedogenesis is characterized by the formation of a microgranular structure and the illuviation of amorphous organic matter remnants of an older leached phase in the gelfa section reflect an initial weakly base desaturation stage during historical times the soil was buried under eolian sands

shear wave velocities anisotropy and splitting in high grade mylonites shear wave velocities have been measured for 10 high grade granulite and upper amphibolite facies mylonites from the snowbird tectonic zone canada at various pressures up to 600 mpa in order to explore the kinematic significance of shear wave splitting in the lower crust at 600 mpa vs anisotropy ranges from 11 in amphibolitic mylonites to 2 in granulite facies pyroxene bearing and tonalitic mylonites hornblende bearing granitic mylonites display intermediate vs anisotropy 6 7 vs anisotropy is lower than vp anisotropy in hornblende rich mylonites whereas vs anisotropy is higher than vp anisotropy in feldspar rich mafic tonalitic granitic and diatexitic mylonites shear wave splitting is pronounced in rocks displaying strong s wave anisotropy in most of the high grade mylonites studied the polarization direction of the first arrival vs1 corresponds to the extension lineation x when propagation is parallel to y perpendicular to lineation and parallel to foliation or to the y direction when propagation is parallel to x for all other propagation directions the polarization direction of vs1 is oblique to the x y and z directions therefore it may be difficult to infer the structural implications of shear wave splitting in lower continental crustal shear zones if one does not know 1 the orientation of the propagation and fast vibration directions with respect to in situ lineation and foliation and 2 the lattice preferred orientation of in situ rock forming minerals

essai d interpretation des transferts sous forme figuree dans les podzols du quebec meridional a partir de l etude micromorphologique des profils abstract in the podzolic soils of southern quebec the migration of clay silt and even fine sand particles results in the formation of various kinds of accumulations and organizations which develop during the podzolization process the internal morphology of the accumulations is characterized by a coarse layered structure often irregular and presenting evidence of microerosion and also by their weak orientation and birefringence these accumulations do not integrate within the matrix and they are present in a large volume of soil with no clear lower boundary the horizons which form below the podzolic b horizons in the profiles developed in well sorted coarse sands contain accumulations of clay particles mixed with organic matter and or sesquioxides as coatings on the grains or agglomerates between the grains in the loamy sandy tills there is an horizon with silty caps which grades into a lamellar horizon at depth in the loamy tills the voids of the fragic horizon are partly blocked with accumulations of unsorted material

pliocene pleistocene stable isotope and paleoceanographic changes in the northern south china sea abstract based on the stable isotopic analysis of planktonic and benthic foraminifers from ocean drilling program core 1148 of the northern south china sea scs pliocene pleistocene isotope stratigraphy and events have been reconstructed the benthic foraminiferal 18o record shows that the pacific intermediate water had a greater influence upon the scs or the pacific deep water above 2600 m was warmer before 3 2 ma than at present after that the benthic 18o conspicuously increased during the 3 2 2 5 ma period in correspondence to the formation of the northern hemisphere ice sheet whereas the planktonic 18o signal suggests a stepwise overall decrease of sea surface temperature during the 2 2 0 9 ma period compared to the equatorial pacific records the decrease in planktonic globigerinoides ruber 13c during the 3 2 2 2 ma period is particularly striking suggesting that fertility of surface water increased noticeably according to the modern 13c distribution of g ruber in the northern scs it is inferred that the east asian winter monsoon strengthened during this interval afterwards there were several conspicuous decreases of g ruber 13c at 1 7 1 3 0 9 0 45 and 0 15 ma bp that is about every 0 4 ma suggesting that the east asian winter monsoon became episodically stronger this is confirmed by changes in relative abundance of planktonic foraminifer species neogloboquadrina dutertrei a typical east asian winter monsoon proxy the deep water 13c of the scs is close to that of the pacific but lighter than that of the atlantic implying that the pattern of deep water originating mainly from the atlantic and through the pacific entering the scs existed at least since the early pliocene after 1 4 ma the benthic 13c signal decreased conspicuously but with a periodicity of 100 ka suggesting that the deep water ventilation of the scs was reduced probably corresponding to a decrease of the north atlantic deep water and or further isolation of the scs deep basin from the pacific during glaciations

deep sea benthic foraminifera and biogenic opal glacial to postglacial productivity changes in the western equatorial pacific the accumulation rate of benthic foraminifera in deep sea sediments is strongly correlated with the productivity of the surface ocean core tops from diverse deep sea settings straddling different export production levels are used in this study for the calibration between the organic carbon flux to the seafloor jsf flux and the benthic foraminifera accumulation rate bfar the correlation can be used to reconstruct organic carbon flux to the seafloor in the past and hence the productivity of past oceans these results are compared with the accumulation rates of carbonate and biogenic opal in the sediments it is found that biogenic opal is more sensitive to productivity changes in the modern ocean than is carbonate the appropriate equations are derived for the equatorial pacific using core material fromeurydice erdc indomed inmd andpleiades plds expeditions these equations are then applied to two selected time horizons in sediments from the ontong java plateau a western equatorial pacific pelagic depth transect the last transition lt and the last glacial lg it is found that productivity was higher during the last glacial relative to the late holocene by a factor between 1 6 and 2 during the last transition productivity was intermediate between glacial and recent values we do not see any corresponding increase in the rates of accumulation of carbonate or biogenic opal during the last glacial this observation questions the importance of ocean productivity as the main controlling factor of carbonate and biogenic opal accumulation rates back through geological time

crustal structure and composition of the southern foothills metamorphic belt sierra nevada california from seismic data the foothills metamorphic belt is an accreted terrane consisting of paleozoic and mesozoic metamorphic rocks that separates the great valley from the sierra nevada batholith in northern and central california until recently the only available geophysical data for this area were reconnaissance refraction surveys and gravity and magnetic data new insights into the structure of the deep crust are provided by the interpretation of a seismic reflection profile cc 2 acquired in 1984 by the u s geological survey at the southern end of the foothills metamorphic belt our interpretation is constrained by a new seismic velocity model derived from coincident microearthquake data earthquake hypocenters that occur at unusually great depths of 12 to 30 km make the data set particularly useful for obtaining deep crustal velocity information the velocity model shows velocities of 5 2 to 6 3 km s 1 for the upper 12 km of the crust and 6 7 to 6 8 km s 1 from 12 km to an estimated moho at 32 km the upper crustal velocities correspond to metamorphic rocks and serpentinites of the foothills metamorphic belt as well as to diorites and granodiorites of the sierra nevada batholith while the lower crustal velocities are interpreted to represent intermediate to mafic granulites the majority of the earthquake hypocenters as well as a 6 7 km s 1 layer in the velocity model corresponds in depth to thick zones of west dipping midcrustal reflections that may represent major shear zones formed during the late jurassic nevadan orogeny or synbatholithic ductile shear zones that accommodated crustal extension associated with batholith intrusion these reflections are truncated updip by an inferred subvertical contact that coincides with the western edge of the sierra nevada batholith and the southward trace of the bear mountains fault zone the updip truncation of midcrustal shear zones and high lower crustal velocities indicate that strike slip faulting and magmatic underplating can be important processes during the docking and welding of an accreted terrane

crustal structure and erosion of the lofoten vesteralen shelf northern norwegian margin abstract the norwegian continental shelf has been through several rift phases since the caledonian orogeny early cretaceous rifting created the largest sedimentary basins and early cenozoic continental breakup between east greenland and europe affected the continental shelf to various degrees the lofoten vesteralen shelf is located off northern norway bordering the epicontinental barents sea to the northeast and the deep water lofoten basin to the west an ocean bottom seismometer hydrophone obs survey was conducted over the shelf and margin areas in 2003 to constrain crustal structure and margin development this study presents profile 8 03 located between the islands of lofoten vesteralen and the shelf edge the wide angle seismic data were modeled using forward inverse raytracing to build a crustal velocity depth transect gravity modeling was used to resolve an ambiguity in seismic moho identification in the southwestern part results show a crustal thickness of 31 km significantly thicker than what a vintage land station based study suggested profile 8 03 and other obs profiles to the southwest show high sedimentary velocities at or near the seafloor increasing rapidly with depth sedimentary velocities were compared to the velocity depth function derived from an obs profile at the barents sea margin tied to a coincident well log where there is little erosion results from this profile and the crossing profile 6 03 breivik et al 2017 indicate three major erosion episodes late triassic early jurassic tentatively mid cretaceous late cretaceous early cenozoic and a minor late glacial erosion episode off vesteralen

structural evolution of an a type subduction zone lofoten rombak area northern scandinavian caledonides the climactic phase of the caledonian orogeny in scandinavia involved collision of the baltic and greenland cratons in late ordovician to silurian time we infer that the collision resulted in large scale subduction of the leading edge of the baltic craton beneath an andean type greenland continental margin deep erosional levels in the lofoten rombak area norway sweden 69 n permit direct examination and evaluation of the structural evolution of a continental or a type subduction zone the early stages of collision involved en bloc underthrusting of the continental margin to depths of at least 30 km during this process deformational effects in the lower plate were restricted to its upper few hundred meters ultimately en bloc a type subduction should be limted by buoyancy effects as convergence continued the lower plate became involved in a series of imbricate thrusts with the same vergence as the intial subduction zone the temporal and spatial relationships between these basement involved thrusts are similar to those observed in foreland fold and thrust terrains field and geophysical data bearing on lower plate behavior elsewhere in the caledonldes and in other collisional orogens suggest that the structural features observed in the lofoten rombak area may be generally characteristic of a type subduction in continent continent collisional settings

a micromorphological examination of two alpine soil chronosequences southern norway the micromorphological characteristics of young alpine soils 230 years old from two chronosequences in norway are examined lenticular and alveolar microstructures together with matrix granules suggest that cryic processes are operative in subsurface ae b c horizons organic matter accumulation decomposition and incorporation are evident in surface l f ah horizons whereas hydration of biotite and translocation of silt and fine sand sized mineral particles organic material and sesquioxides seem major processes in subsurface ae b horizons consideration of depth related differences of quantitative micromorphological data has allowed assessment of the intensity of these pedogenic processes chronofunctions are constructed for each soil horizon from the quantitative data this approach allows soil development at the two sites to be assessed in a temporal context steady state conditions do not appear to be attained within the 230 years available for soil development at these sites

neogene and quaternary paleoceanographic changes in the southern south china sea site 1143 the benthic foraminiferal record deep sea benthic foraminiferal assemblages from ocean drilling program odp site 1143 located in the southern south china sea scs were investigated to evaluate the relationship between faunal composition patterns and paleoceatiographic changes during the last 6 million years late miocene to holocene we used multivariate statistics correspondence analysis to analyze carbon flux related changes in assemblage composition of benthic foraminifers additional proxies for carbon flux and deep water ventilation include delta 13 c records of epifaunal cibicidoides wuellerstoifi and infaunal uvgefina peregrina var dirupta and melonis pompilioides benthic foraminiferal accumulation rates bfarss diversity indices and relative abundances of indicator species we observe three significant benthic faunal changes in the southern south china sea during the last 6 million years strong fluctuations in bfar and relative abundance of productivity indicator species between glacial and inter glacial stages after the mid pleistocene revolution mpr at approximately 0 9 ma indicating stronger seasonal carbon flux fluctuations are accompanied by the extinction of such species as stilostomella spp increases in carbon flux indicator species are coupled with an overall deer ease in benthic foraminifer diversity around 3 0 ma in the late pliocene this may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength c 2004 elsevier b v all rights reserved

crustal structure of the lofoten vesteralen continental margin off norway abstract by compiling wide angle seismic velocity profiles along the 400 km long lofoten vesteralen continental margin off norway and integrating them with an extensive seismic reflection data set and crustal scale two dimensional gravity modelling we outline the crustal margin structure the structure is illustrated by across margin regional transects and by contour maps of depth to moho thickness of the crystalline crust and thickness of the 7 km s lower crustal body the data reveal a normal thickness oceanic crust seaward of anomaly 23 and an increase in thickness towards the continent ocean boundary associated with breakup magmatism the southern boundary of the lofoten vesteralen margin the bivrost fracture zone and its landward prolongation appears as a major across margin magmatic and structural crustal feature that governed the evolution of the margin in particular a steeply dipping and relatively narrow 10 40 km wide moho gradient zone exists within a continent ocean transition which decreases in width northward along the lofoten vesteralen margin to the south the zone continues along the voring margin however it is offset 70 80 km to the northwest along the bivrost fracture zone lineament here the moho gradient zone corresponds to a distinct 25 km wide zone of rapid landward increase in crustal thickness that defines the transition between the lofoten platform and the voring basin the continental crust on the lofoten vesteralen margin reaches a thickness of 26 km and appears to have experienced only moderate extension contrasting with the greatly extended crust in the voring basin farther south there are also distinct differences between the lofoten and vesteralen margin segments as revealed by changes in structural style and crustal thickness as well as in the extent of elongate potential field anomalies these changes may be related to transfer zones gravity modelling shows that the prominent belt of shelf edge gravity anomalies results from a shallow basement structural relief while the elongate lofoten islands belt requires increased lower crustal densities along the entire area of crustal thinning beneath the islands furthermore gravity modelling offers a robust diagnostic tool for the existence of the lower crustal body from modelling results and previous studies on and off shore mid norway we postulate that the development of a core complex in the middle to lower crust in the lofoten islands region which has been exhumed along detachments during large scale extension brought high grade lower crustal rocks possibly including accreted decompressional melts to shallower levels

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

late quaternary upwelling intensity and east asian monsoon forcing in the south china sea foraminifera from two cores off eastern vietnam and the northwestern philippines where modern summer and winter monsoon driven upwelling occurs in the south china sea respectively were analyzed to evaluate the changes in paleoproductivity and upper water structure over the last 220 000 yr we observed enhanced organic carbon flux and a shoaled thermocline when upwelling intensified off eastern vietnam during interglacial ages and off the northwestern philippines during glacial ages this indicates that the east asian summer monsoon increased while the winter monsoon decreased during interglacial ages particularly the upwelling reached a maximum off eastern vietnam during late marine isotopic stage mis 5 and off the northwestern philippines during mis 2 implying that the summer monsoon decreased gradually since mis 5 while the winter monsoon displayed an opposite trend the variations in upwelling proxies exhibit a distinct cyclicity with frequencies near 41 000 yr and 23 000 yr off eastern vietnam in contrast to a strong frequency peak near 100 000 yr off the northwestern philippines we suggest that the east asian summer monsoon has been forced by changes in solar insolation associated with precession and obliquity while ice volume forcing is probably a primary factor in determining the strength and timing of the east asian winter monsoon but with less important insolation forcing

planktonic benthonic foraminiferal ratios modern patterns and tertiary applicability abstract the abundance of planktonic specimens in foraminiferal assemblages was determined in numerous bottom samples from inner neritic to deep oceanic depths along the atlantic margin of the northeastern united states the results augment previous studies in other areas that have shown a general increase in percentage of planktonic specimens in total foraminiferal bottom assemblages as water depth increases the patterns found in this area of complex shelf bathymetry and hydrography illustrate the influence on the planktonic benthonic percentages of water depth distance from shore different water mass properties and downslope movement of tests in high energy areas the patterns found in the 661 samples from the atlantic margin were compared with results from 795 stations in the gulf of mexico pacific ocean and red sea the relative abundance of planktonic specimens and water depth correlates positively in all open oceanic areas even though taxonomic composition and diversity of the faunas from different areas is variable the variation of planktonic percentages in bottom samples within most depth intervals is large so that a precise depth determination cannot be made for any given value however an approximate upper depth limit for given percentages can be estimated for open ocean environments a decrease in planktonic percentages is seen in the lower salinity and higher turbidity coastal waters of the gulf of maine planktonic percentages intermediate between the lower values in the less saline coastal waters and the higher values in the normal open oceanic conditions occur in the transitional area between the gulf of maine and the open marine atlantic ocean to the east similarly lowered values in another area of restricted oceanic circulation occur in the high salinity clear but nutrient poor waters of the gulf of aqaba off the red sea a comparison of the similarity of modern planktonic percentage values to those found in earlier tertiary assemblages was made to confirm the usefulness of this measure in the fossil record in some stratigraphic sections in upper paleocene and lower eocene strata of the eastern gulf coastal plain water depths inferred from trends and values of planktonic percentages consistently match paleobathymetry constructed from physical stratigraphic characteristics and paleogeographic relationships

simultaneous high p t measurements of ultrasonic compressional and shear wave velocities in ichino megata mafic xenoliths their bearings on seismic velocity perturbations in lower crust of northeast japan arc 1 simultaneous measurements of ultrasonic compressional vp and shear wave velocities vs were conducted under pressures and temperatures representative of the lower crust on five mafic xenoliths derived from the northeast japan arc crust for comparison with the observed seismic heterogeneity of the lower crust of the northeast japan arc the velocity deviations dvp and dvs of the xenoliths were calculated using the average reference vp 6 61 0 1 km s and vs 3 76 0 1 km s the dvp and dvs values of the xenoliths at 700 c and 0 8 gpa are 0 8 and 1 2 for hornblende gabbro 4 8 and 4 0 for hornblende pyroxene gabbro 0 9 and 1 5 for amphibolite 2 5 and 1 7 for pyroxene amphibolite and 0 9 and 5 6 for hornblendite respectively we compared the velocity perturbations in the lower crust determined by seismic tomography with dvp and dvs of the xenoliths using vp vs vp vs deviation diagrams on the basis of our measurements we suggest that 1 the seismically high vp and vs regions beneath the tobishima basin consist of hornblende pyroxene gabbro 2 hornblende gabbro is a predominant rock type beneath the dewa hills and ou backbone range 3 the low velocity anomalies beneath the active volcano areas may be caused by the existence of partial melts of hornblende gabbro and 4 the low vp and high vs regions beneath the kitakami mountains consist of quartz plagioclase bearing rocks our data demonstrate that the seismic heterogeneity in the lower crust of the northeast japan arc reflects variations in rock composition and temperature that are related to the regional geological history

factors influencing the distribution of subantarctic deep sea benthic foraminifera campbell and bounty plateaux new zealand abstract we investigate the combination of environmental factors that influence the distribution patterns of benthic foraminiferal tests 63 m in a topographically varied region crossed by both the subtropical and subantarctic fronts south east of new zealand seafloor sample sites extending from outer shelf 50 m to abyssal 5000 m depths are bathed by five different water masses and receive phytodetritus from subtropical subantarctic and circumpolar surface water masses eight mappable associations are recognised by q mode cluster analysis of the benthic foraminiferal census data similar associations are identified using cluster analysis based solely on the presence or absence of species canonical correspondence analysis and a correlation coefficient matrix were used to relate the faunal data to a set of environmental proxies these show that factors related to water depth especially decreasing food supply with increasing depth are the most significant in determining the overall foraminiferal distribution other contributing factors include surface water productivity and its seasonality bottom water ventilation energetic state of the benthic boundary layer and resulting substrate texture and bottom water carbonate corrosiveness three shallow water associations 50 700 m dominated by cassidulina carinata trifarina angulosa globocassidulina canalisuturata gavelinopsis praegeri and bolivina robusta occur in coarse substrates on the continental shelf and on the crests and upper slopes of four seamounts under well oxygenated high energy regimes and high food input three mid bathyal to upper abyssal associations 500 3300 m dominated by alabaminella weddellensis c carinata and epistominella exigua occur in biopelagic sandy mud beneath a region of strongly seasonal food supply with their composition influenced by total food flux ventilation oxygen minimum zone and bottom current strength an unusual lower bathyal association 1200 2100 m dominated by t angulosa and ehrenbergina glabra occurs in a belt of coarser sandy substrate that runs along the crest of the submarine plateaux slopes beneath the strongly flowing subantarctic front related currents a deep abyssal association 3500 5000 m dominated by nuttallides umbonifer and globocassidulina subglobosa occurs on the abyssal plain beneath oligotrophic lower circumpolar water south east of the subantarctic front and is strongly influenced by the cold carbonate corrosive conditions the faunal composition of this subantarctic region is most similar to adjacent southern new zealand but with the addition of a few significant antarctic elements e g e glabra globocassidulina crassa

flin flon belt seismic anisotropy elastic symmetry heterogeneity and shear wave splitting laboratory measurements of compressional and shear wave velocities and shear wave splitting have been carried out on a set of upper greenschist lower amphibolite facies of metasediments and metavolcanics and plutonic rocks from two ductile shear zones in the flin flon belt ffb of the trans hudson orogen tho selected metamorphic rocks vary in composition from felsic to mafic test sites with outcrops of sheared metamorphic rocks were correlated with a series of inclined seismic reflectors possibly extending from the midcrust and intersecting a well mapped shear zone at the surface determination of the lithological and physical properties of highly deformed metamorphic rocks is essential for proper interpretation of the nature of observed seismic reflectors to investigate the anisotropic properties of the rocks compressional velocity was measured at confining pressure up to 300 mpa in three mutually orthogonal directions aligned with respect to visible textural features in addition on selected

seismic anisotropy inferred from wide angle reflections off lofoten norway indicative of shear aligned minerals in the upper mantle abstract data from six three component ocean bottom seismographs situated on a 175 km long profile on the continental shelf off lofoten northern norway have been modelled using 2 d seismic ray tracing and p and s wave velocity models for the upper mantle are presented a dipping structure about 10 km below the moho causes strong p and s reflections as well as p to s conversions this upper mantle reflection might be related to a possible seaward dipping master fault and or the presence of partially hydrated peridotite the modelling of these arrivals reveals significant seismic anisotropy in the upper mantle the maximum p wave anisotropy is inferred to be in excess of 15 the maximum s wave anisotropy in the order of 5 10 and the axis of the fast velocity is inferred to be inclined at least 45 from the horizontal the strong anisotropy for p waves indicates that its cause is related to alignment of minerals we postulate that the inferred steep inclination of anisotropic minerals might be a result of shearing along faults and fractures during post caledonian extensional episodes it must be emphasized however that it cannot be excluded that more complicated anisotropic models with other geological implications can also explain the observations satisfactorily the study demonstrates the importance of incorporating s waves in analysis of seismic data because the strong p wave anisotropy would not have been discovered without the constraints given by the s waves

foraminiferal responses to major pleistocene paleoceanographic changes in the southern south china sea a detailed age model for core 17957 2 of the southern south china sea was developed based on delta 18 o coarse fraction magnetostratigraphy and biostratigraphy for the last 1500 kyr the delta 18 o record has clear similar to 100 kyr cycles after the mid pleistocene revolution mpr at the entrance of marine isotopic stage mis 22 planktonic foraminifera responded to the mpr immediately showing the increased sea surface temperature sst and dissolution after the mpr benthic foraminifera did not respond to it until the brunhes matuyama boundary since the mpr the depth of thermocline gradually became shallower until miss 6 5 this major change within miss 6 5 was also reflected in the decreased ssts and increased productivity and deep water mass thus two major pleistocene paleoceanographic changes were found one was around the mpr the other occurred within miss 6 5 which speculatively might be ascribed to the reorganization of surface and deep circulation possibly induced by tectonic forces

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

pedology of soils within the spray zone of the victoria falls zimbabwe abstract six profiles were sampled in the victoria falls national park zimbabwe in order to investigate the influence of the abundant spray of the falls on the pedogenesis in the otherwise semi arid environment depending upon the thickness of the alluvium soils developed in the sediment with variable admixture of basalt gravel or practically directly on the underlying karroo plateau basalt layer those near the gorge are subject to a continuous spray during most of the year the more remote ones get only the natural precipitation chemical mineralogical and micromorphological analyses indicate that the parent material is a more dominant factor determining chemical mineralogical and micromorphological characteristics than precipitation the main active process is bioturbation phytolites and sponge spicules are abundant in most profiles basalt derived laumontite is observed in thin sections and in the silt fraction weathering of the basalt gravel is limited although pedogenesis has been active for at least 50 100 ka a subdivision of enaulic c f related distribution patterns is proposed

relict mountain slope deposits of northern portugal facies sedimentogenesis and environmental implications this paper deals with the formation processes and the palaeoenvironmental significance of relict slope deposits located on the uppermost part of the north portugal mountains for this purpose seven key sites representative of the different lithofacies have been selected and analysed in detail the data show that three main dynamic processes are responsible for the emplacement of regional fossil slope deposits runoff debris flows and dry grain flows the ubiquity of these processes and the lack of frost related features or landforms do not support the existence of severe pleistocene climates in this part of the lberian peninsula as postulated by previous work pedological data gathered at one of the study sites show that a subalpine environment was probably present at 700 800 m altitude between 29 and 14 kyr using data from the pyrenees mountains a 6 5 to 12 c depression in mean annual temperature has been tentatively postulated for this pleniglacial period copyright 2003 john wiley sons ltd

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

structural effects of the crust on the geoid modelled using deep seismic sounding interpretations summary according to the theory of isostasy the earth has a tendency to deform its surface in order to reach an equilibrium state the land uplift phenomenon in the area of the fennoscandian shield is thought to be a process of this kind the geoid as an equipotential surface of the earth s gravity field contains information on how much the earth s surface departs from the equilibrium state in order to study the isostatic process through geoidal undulations the structural evects of the crust on the geoid have to be investigated the structure of the crust of the fennoscandian shield has been extensively explored by means of deep seismic sounding dss the data obtained from dss are used to construct a 3 d seismic velocity structure model of the area s crust the velocity model is converted to a 3 d density model using the empirical relationship that holds between seismic velocities and crustal mass densities structural evects are then estimated from the 3 d density model the structural evects computed from the crustal model show that the mass deficiency of the crust in fennoscandia has caused a geoidal depression twice as deep as that observed from the gravimetric geoid it proves again that the crust has been isostatically compensated by the upper mantle in other words an anomalously high density upper mantle must exist beneath fennoscandia

pore pressure and oceanic crustal seismic structure summary marine refraction studies during the past decade have found considerable lateral variability in the seismic properties of the upper basaltic regions of the oceanic crust in many localities compressional and shear wave velocities are quite low at the top of the basalt section and velocities increase rapidly with depth it is concluded that pore pressure may be at least in part responsible for the low upper crustal velocities and contribute significantly to the lateral variability this is supported by compressional and shear wave velocity measurements as functions of confining pressure and pore pressure for basalt from the juan de fuca ridge and dolerite from the samail ophiolite oman within the oceanic crust regions of overpressure and underpressure will possess anomalous velocities the magnitude of which will depend upon the porosity and the deviation of the pore pressure from hydrostatic the influence of pore pressure on velocities is expected to diminish with depth and is unlikely to be significant at lower crustal depths where porosity is extremely low of significance poisson s ratio is shown to be dependent on pore pressure as well as confining pressure at constant confining pressure poisson s ratio increases with increasing pore pressure thus overpressured regions within the upper oceanic crust are likely to have relatively high poisson s ratios as well as low compressional and shear wave velocities

geo tectonic framework of the himalaya of n pakistan in the karakorum range there is a structurally complicated cretaceous are comprising the kohistan sequence on its northern side the northern suture consists of a mega melange and is bounded to the s by tightly folded pillow bearing volcanics and sediments to the s the kohistan plutonic belt consists of southwards a early foliated and late post tectonic tonalites and diorites b aplites and pegmatites up to 30 of rock volume c basic dykes up to 10 m thick d the chilas complex a stratiform cumulate body over 300 km long and 8 km thick chromite layered dunites gabbros and norites with a low pressure granulite facies mineral fabric of tectonic origin e an amphibolite belt with a complex mixture of other rocks and f the jijal complex a 200 km 2 tectonic wedge of high pressure granulites and chromite layered dunites cumulate graded units in the chilas complex show that it is folded by an isoclinal anticline f 1 the mid upper crust of the are is folded by a 50 km half wavelength f 2 syncline the whole kohistan sequence with its two phases of isoclinal folds was tilted during himalayan collision so that the structures are now subvertical the southern suture main mantle thrust has a wedge of glaucophane schists the indian plate contains a basement of psammites and schists intruded by cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales

distribution of recent benthic foraminifera along continental slope of the sunda shelf south china sea the distribution of live rose bengal stained and dead benthic foraminiferal distribution 150 mu m was investigated in sediment surface samples 0 1 cm from the winter upwelling region off borneo on the continental slope of the sunda shelf and from the continental slope of southern vietnam shelf the benthic foraminiferal faunas of both areas are highly diverse h s 2 91 4 25 for living and 4 01 4 38 for dead a canonical correspondence analysis proved that bathyal assemblages are most strongly influenced by the decreasing rates of organic carbon flux with increasing water depth resulting in a pronounced depth related succession of assemblages correlation between estimated c org flux and factor 1 loadings of the cca for modem dead foraminiferal assemblages is very good r 2 0 96 thus a local transfer function y 5 0289x 6 8142 for estimating paleo c org flux rates from the down core samples has been successfully developed for the continental slope of the sunda shelf four benthic foraminiferal biofacies were recognised within the studied depth ranges upper bathyal biofacies siphotextularia foliosa cibicidoides robertsonianus well supplied and well oxygenated middle bathyal biofacies uvigerina auberiana nuttallides rugosus located within the oxygen minimum zone uppermost lower bathyal biofacies lagenammina difflugiformis uvigerina peregrina and lower bathyal biofacies paratrochammina challengeri parrelloides bradyi from the relatively well oxygenated but food limited environment c 2009 elsevier b v all rights reserved

determination of poisson s ratio from pre critical wide angle seismic reflection data from the babel project summary the pre critical wide angle seismic reflection data collected during the babel survey using multireceiver spreads contain high amplitude p wave and modeconverted s wave reflected arrivals the two phases can be partially separated and their signal to noise ratio emphasized by exploiting the multifold nature and the increased sensitivity of velocity analysis afforded by these data to produce zero offset corrected stacked sections using these sections a method has been developed to derive estimates of poisson s ratio by optimizing the cross correlation of p wave and s wave arrivals and hence to constrain petrological models of the crust sampled by these data although the apparently high degree of temporal and spatial resolution of reflected arrivals that are visible within the stacked sections must be reduced to achieve a satisfactory degree of correlation robustness the results shed some light on crustal petrology and concur with existing estimates of poisson s ratio for the baltic shield

lower crustal seismic velocities from lofoten vesteralen north norway abstract the archipelago of lofoten vesteralen comprises archaean and proterozoic rocks in granulite or amphibolite facies the area is characterised by a large gravity anomaly 120 mgal and thin crust c 25 km and it has been suggested that it represents a deep section into the continental crust compressional and shear wave velocities have been measured in the laboratory on over 70 samples from the area most of them to 0 4 gpa confining pressure velocity profiles are then deduced for sections of the crust assuming a restored horizontal moho and it is shown that upper and lower crustal divisions of approximately 5 9 6 2 km s 1 and 6 5 6 6 km s 1 can be recognised which are similar to those found on seismic refraction lines in scandinavia the velocities of the lofoten granulites are however higher than the velocities observed on the lofoten seismic refraction experiment possible reasons for this including the opening of cracks at low pressure retrograde metamorphism the interpretation of the refraction data or major tectonic dislocation are explored

shear waves from three component ocean bottom seismographs off lofoten norway indicative of anisotropy in the lower crust summary data from four three component ocean bottom seismographs obs situated on a 145 km long profile on the rost high on the continental shelf off lofoten northern norway have been modelled using 2 d seismic ray tracing and a p and s wave velocity model along the profile is presented the s wave model has been obtained from a study of the high quality horizontal component data a vp vs ratio of 1 95 2 15 is found in the sedimentary layers on the rost high these high values are consistent with shaly sediments which are identified in dredged bedrock samples south of the rost high a considerably lower vp vs ratio ca 1 6 is estimated for the sediments which can be attributed in part to a higher degree of compaction in the deepest sediments and in part to a more sandy lithology in the upper and middle crystalline crust a vp vs ratio of 1 75 is obtained strong s reflections and p to s conversions at the moho are observed on all four instruments and the modelling of these arrivals indicates that the s wave velocity in the lower crust varies with angle of incidence from 3 5 km s 1 vp vs 1 95 at vertical incidence to 4 0 km s 1 vp vs 1 7 at 60 70d this angle of incidence dependent s wave anisotropy the order of 10 per cent is consistent with some horizontal or subhorizontal layering in the lower crust

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

foraminiferal isotopic evidence for monsoonal activity in the south china sea a present lgm comparison abstract the relationship between planktonic and benthic foraminiferal stable isotope values and oceanographic conditions and factors controlling isotopic variations are discussed on the basis of oxygen and carbon isotopic analyses of 192 modern surface and last glacial maximum lgm samples from the south china sea scs the harmonic variation of benthic 18o in surface sediments with water depth and temperature implies that the temperature is the main factor influencing benthic 18o variations planktonic 18o fluctuates with sea surface temperature sst and salinity sss the n s temperature gradient results in planktonic 18o decreasing from the northeast to the south cool saline waters driven by the winter monsoon are interpreted to have been responsible for the high 18o values in the northeast scs the east asian monsoons not only bring nutrients into the south china sea and maintain high nutrient concentration levels at the southwestern and northeastern ends which cause depleted 13c both in planktonic surface and benthic bottom samples but also reduce planktonic benthic 18o differences the distribution of 18o and 13c in the surface and lgm samples are strikingly similar indicating that the impact of sst and sss has been maintained and nutrient inputs mainly from the northeastern and southwestern ends have been controlled by monsoons since the lgm comparisons of the modern and lgm 18o indicate a difference of about 3 6 c in bottom water temperature and a large surface to bottom temperature gradient during the lgm as compared to today

transitional continental oceanic structure beneath the norwegian sea from inversion of surface wave group velocity data summary we have analysed the fundamental mode of love and rayleigh waves generated by 12 earthquakes located in the mid atlantic ridge and jan mayen fracture zone using the multiple filter analysis technique we isolated the rayleigh and love wave group velocities for periods between 10 and 50 s the surface wave propagation paths were divided into five groups and average group velocities calculated for each group the average group velocities were inverted and produced shear wave velocity models that correspond to a quasi continental oceanic structure in the greenland norwegian sea region although resolution is poor at shallow depth we obtained crustal thickness values of about 18 km in the norwegian sea area and 9 km in the region between svalbard and iceland the abnormally thick crust in the norwegian sea area is ascribed to magmatic underplating and the thermal blanketing evect of sedimentary layers maximum crustal shear velocities vary between 3 5 and 3 9 km s 1 for most paths an average lithospheric thickness of 60 km was observed which is lower than expected for oceanic type structure of similar age we also observed low shear wave velocities in the lower crust and upper mantle we suggest that high heat flow extending to depths of about 30 km beneath the surface can account for the thin lithosphere and observed low velocities anisotropy coeycients of 1 5 per cent in the shallow layers and 7 per cent in the upper mantle point to the existence of polarization anisotropy in the region

lateral variations in tectono magmatic style along the lofoten vesteralen volcanic margin off norway abstract the 400 km long passive continental margin west of the lofoten vesteralen archipelago off northern norway links the volcanic rifted voring margin and the sheared w barents sea margin multi channel seismic reflection profiles supplemented with crustal velocity gravity and magnetic anomaly data are used to outline the regional setting and main tectono magmatic features a well defined along strike margin segmentation comprising three segments characterized by distinct crustal properties structural and magmatic styles sediment thickness and post opening history of vertical motion is revealed the margin segments are governed by changes in fault polarity on late jurassic early cretaceous border faults and are separated by coeval cross margin transfer zones which acted as persistent barriers to rupture propagation and reflect the trend and character of older structural heterogeneities the transfer zones spatially correlate to small offset early opening oceanic fracture zones implying a structural inheritance from one rift episode to another culminating with lithospheric breakup at the paleocene eocene transition the pre seafloor spreading margin structural evolution is governed by the older predominantly late jurassic early cretaceous structural framework however the margin also provides evidence for mid and late cretaceous extension events that are poorly understood elsewhere off norway furthermore the lofoten vesteralen post breakup subsidence history contrasts with the adjacent margins reflecting breakup in thicker crust and a diminishing volume of high velocity lower crust emplaced during breakup