neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

giant carbonate mud mounds in the southern rockall trough seismic profiles sidescan sonar data bottom photography and sampling proved for the first time that there are giant carbonate mounds bioherms in the rockall trough the pelagia mounds on the northern porcupine bank are relatively isolated whereas most of the logachev mounds on the southeast rockall bank form a field of closely spaced contiguous mounds they are all found on the upper slope at depths between about 500 and 1200 m and as a result of this study about 500 have been mapped they have a variety of shapes and the larger ones are very steep sided up to 350 m high and 2 km wide at the base sediment samples show that the mounds consist of pale coloured muds mainly aragonite usually with live and or dead cold water corals at the seafloor and with buried dead corals coral thickets appear to be detected as a brush like signature on high resolution profiles and as a speckled pattern on high resolution sidescan sonar records shelly sands are found on the seabed between the mounds currents in the mound areas are strong enough to transport sands along slope as medium sized sand waves and to prevent pelagic deposition thus providing surfaces for initial coral settlement by the winnowing of fines to leave glacial dropstones and exposed rocks these observations show that the poleward directed upper slope current of the eastern north atlantic extends further south than hitherto known and that there is a southwesterly directed current on rockall bank there are waves on the logachev mounds with a wavelength of about 20 30 m that are thought to be moulded in carbonate muds by across slope directed internal tidal currents and or cascading currents mounds develop above erosional surfaces seen on seismic data the huge amount of carbonate mud seems to be produced by the rapid growth and breakdown of cold water corals living in a very favourable environment intermediate nepheloid layers formed upstream by the strong currents may provide the food source for the deep water suspension feeders conditions for giant mound growth require an ideal balance between current speed and sedimentation rate among other factors no evidence for the suggested link to methane seepage has been found so far

fold axis parallel extension in an arcuate fold and thrust belt the case of the helvetic nappes abstract the helvetic nappes of western switzerland are discussed as an example of an arcuate foreland fold and thrust belt in which active fold axis parallel stretching occurred fold axis parallel extension is recorded by 1 1 incremental strain data from pressure shadow fibres the significance of pressure shadow fibres for the determination of the deformation history of a region is discussed pressure shadows are used to quantify the amount of and to describe the distribution of fold axis parallel extension occurring in the helvetic nappes 2 2 the extension directions of conjugate systems of en echelon veins it is shown that an analysis of the geometry of conjugate vein systems can reveal a regional deformation pattern the relative age of the conjugate en echelon vein systems in the helvetic deformation history can be assessed the geometry of the conjugate sets relative to the local anisotropy plane is described and the significance of the preferred orientation of their extension directions is discussed 3 3 fold axis parallel sections a comparison of the regional distribution of the fold axis parallel strain with the shape of the helvetic nappes in fold axis parallel sections shows that the fold axis parallel strain cannot be related to the footwall topography of the nappes it is concluded that the fold axis parallel extension in the helvetic nappes was induced by a change of direction of overthrust shear this change occurred late in the deformation history and was superposed on the already formed nappes the changing direction of overthrust shear is the expression of an overall anticlockwise rotation going on in the overthrusting alpine nappe pile relative to the european plate a rotation which lead to the arcuate shape of the western alps

late palaeozoic to mesozoic kinematic history of the talas ferghana strike slip fault kyrgyz west tianshan as revealed by 40ar 39ar dating of syn kinematic white mica abstract the nw trending talas ferghana fault tff in kyrgyzstan central asia is one of the largest intracontinental strike slip faults in the world it extends over a distance of more than 2000 km from southern tourghai to western tarim and exhibits a maximum dextral offset of 200 km during the late palaeozoic to present the history of the fault provides important insights for the understanding of the evolution of southern central asia but remains poorly constrained due to lack of reliable geochronological data we present new ar ar ages and structural data from the kyrgyz west tianshan that elucidate the kinematic history of the tff in the palaeozoic and mesozoic 40ar 39ar ages on mylonitic white micas document a deformational history consisting of several episodes a late carboniferous age of 312 4 ma point to initiation of top to the south and dextral transpressional deformation during a metamorphic overprint in precambrian and palaeozoic rocks along the northern compartment of the tff the main phase of dextral motion along the entire fault occurred in the permian as suggested by minimum ages of 260 290 ma obtained at two different locations in the nw and central parts of the tff partial isotopic resetting occurred between 240 and 210 ma and younger ages of the ar ar mineral ages and structural data argue for a major phase of dextral shearing affecting the entire region from the west tianshan to mongolia in the late permian and leading to formation of almost equally spaced major nw trending dextral strike slip faults the uniform character of this deformation indicates that the process of amalgamation in this part of the caob ended prior to the late permian and central asia evolved as a single coherent continental block since that time

application of the rfφ technique to ellipitical markers deformed by pressure solution abstract the applicability of the r f technique of finite strain analysis to elliptical markers whose shape is modified by pressure solution is investigated variably oriented elliptical markers shortened by removing material from one or both sides in open and closed systems are compared to markers shortened homogeneously by the same amount for the models examined it was found that the r f technique correctly predicts the principal directions the initial marker axial ratio and the axial ratio of a circle deformed in a like manner interpretation of strain ratios in terms of percent shortening requires knowing how much volume was lost equations relating the strain ratio to percent shortening are given for both constant volume and volume loss deformation

estimation of viscosity contrast and finite strain from deformed elliptical inclusions a method of strain analysis is described which takes into account a possible competence difference between the strain markers and the rest of the rock using data consisting of the sectional shapes and orientations of groups of inclusions from conglomerate like rocks limits are placed on the possible effective viscosity contrast between the inclusions and the rock as a whole as well as on the bulk finite strain suffered by the rock these results are calculated using a computer program based on the theory for the deformation of elliptical cylinders the method can be considered an extension of the rf method but provides more information and involves less restrictive assumptions

strain and tectonic styles related to variscan transpression and transtension in the moravo silesian culmian basin bohemian massif czechoslovakia abstract progressive variscan development of the n s to nne ssw trending dextral wrench zone in the moravo silesian culmian basin on the eastern border of the bohemian massif resulted in the westphalian asturian transpression followed by transtension of the area the kinematics of the structures are indicated by three phase folding n s to nne ssw and e w stretching of rocks and eastward oriented thrust tectonics the estimated displacement based on strain analysis of conglomerates and folds can reach several tens of kilometers and important stretching up to 160 is due to the perpendicular extension transtension in the most ductile part of the zone

experimental folding and boudinage under pure constrictional conditions abstract constrictional folds are characterized by true fold axis parallel extension if the rock volume does not vary during deformation studies of such folds in experiments using plasticine layers of different apparent viscosity and power law exponent clearly indicate that fold axis parallel stretch may be accompanied by plastic elongation as well as boudinage of the competent layer characteristic aspects of the experimentally folded competent layers are 1 coeval development of folds and boudins 2 layer thickness not changing during deformation 3 layer parallel shortening in sections perpendicular to the fold stretching axis 4 enlargement of the initial thickness of the competent layer results in increasing fold wavelength and decreasing number of boudins the ratio of dominant wavelength to layer thickness of the constrictional folds can be described mathematically approximately by the equation developed for plane strain folding of power law materials

aragonite cycles diagenesis caught in the act organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession a record from the early pliocene of the maldives ocean drilling program odp leg 115 is presented containing precession and eccentricity cycles expressed as variable aragonite content additional sub milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval comparison with palaeo productivity indicators nannofossils chlorin total organic carbon suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity the coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment the observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on milankovitch and sub milankovitch scales diagenetically stable proxies for palaeo productivity such as nannofossil assemblage data were used to distinguish between palaeoclimate and diagenetic influences

the evolution of the porcupine and rockall basins offshore ireland the geological template for carbonate mound development the margins of the deep water sedimentary basins west of ireland contain a number of large clusters provinces of spectacular carbonate mounds and build ups these basins have a complex development history involving the interplay of rift tectonics thermal subsidence igneous activity and oceanographic variations the porcupine and rockall basins both rest upon thin continental crust the consequence of major rift episodes in permo triassic late jurassic and early cretaceous times phases of volcanism occurred in the early cretaceous and especially in the early cenozoic fluid flow within the basins is likely to have been controlled by the overall basin geometry and by the distribution and linkage of permeable strata with fault systems stratal surfaces and unconformities a number of regional unconformities controlled by both basin tectonic and regional oceanographic effects can be mapped and correlated throughout the porcupine and rockall basins the youngest of these unconformities c10 early pliocene can be traced throughout much of the nw european atlantic margin it forms the horizon on which virtually all the carbonate mounds in the basins develop suggesting a geologically instantaneous mound nucleation and growth event although the control on their development is uncertain the mound clusters show a spatial association with lithified strata buried contourite and deltaic deposits slope failure features and with the basin margins analysis of these relationships points to a combination of geological and oceanographic processes controlling mound initiation and growth

the problem of strain marker centers and the fry method abstract the fry method and its variants will underestimate finite strain when applied to strain markers deformed heterogeneously at marker scale despite homogeneous behavior at a population scale this difference results from the post deformation centers not coinciding with the original pre deformation centers the amount of error may rapidly approach 50 for small strains in ideal cases but is likely to be in the range of 20 30

a comparison of methods used in measuring finite strains from ellipsoidal objects abstract the available methods for measuring strains in two and three dimensions from passive ellipsoidal objects are compared in an attempt to determine the most useful and precise procedure for the structural geologist a comparison of data collection techniques showed that the use of thin orthogonally cut slabs or mylar overlays used with a monocomparater provides the most reproducible data lisle s theta curve and shimamoto and ikeda s algebraic methods provided the most precise and probably most accurate two dimensional data while miller and oertel s procedure and possibly dunnet s phase 5 program gave the best three dimensional results an examination of errors encountered in strain analyses suggests that all of the available methods give accurate orientations of the finite strain ellipsoid however the magnitudes of strain ratios show large variations that are dependent on the sample size and procedure used shimamoto and ikeda s method again proved to be the most precise giving reproducible results with as few as ten elliptical objects the samples used in the above comparison are part of a larger analysis of strains occurring in southeastern maine structural elements observed in four selected areas of avalonian belt rocks and the strain data collected suggest that the region has undergone at least three non coaxial deformations with d1 d2 d3

a 3d seismic study of the morphology and spatial distribution of buried coral banks in the porcupine basin sw of ireland an industrial 3d seismic data volume supplemented by high resolution 2d seismics was used to study part of a province of buried mound structures in the porcupine basin southwest of ireland these magellan mounds and their associated moat structures interpreted as scour marks were mapped semi automatically from time structure and isopach maps image analysis techniques such as a tophat transformation mathematical morphology were applied for feature extraction size measures of both mounds and moats were derived from the resulting maps and summarised by means of some descriptive statistics spatial variability in mound occurrence and characteristics was investigated comparison with other mound structures in the area allowed the magellan mounds to be identified as coral banks associated with the growth of cold water deep sea coral species such as lophelia pertusa l and madrepora oculata l mound growth clearly started in a single event confined in time and space bottom currents and oceanographic characteristics of the surrounding water masses influenced this sudden process and the further mound development however the analysis of the 3d seismic data set did not allow us to identify unambiguously the actual cause for the sudden mound start up the mounds appear to have formed a dense cluster of structures of moderate size which are significantly elongated in a n s direction they are associated with even more elongated moats implying a periodically reversing n s directed current influence a spatial density of one mound per km2 was measured which remains more or less constant over the area investigated mound width and cross sectional area and moat shape gradually change across the mound province due to spatially changing environmental conditions at the initial growth stages of the mounds and during their further development interplay between current regime and sedimentation

structural and strain analyses of the middle part of the talassian alatau ridge middle asia kirgizstan abstract the middle part of the talassian alatau ridge is composed of upper precambrian lower paleozoic greenschists the usunakhmatian sheet which were overthrust on unmetamorphosed rocks of nearly the same age the talassian and kumishtagian sheets three phases of deformation can be recognized in the usunakhmatian sheet the most intensive of which was the late silurian early devonian d 2 deformation in the usunakhmatian sheet the axis of maximum extension is subhorizontal and parallel to f 2 fold axes r xz varies from 2 4 to 7 5 and k from 0 03 to 1 75 flattening is widespread but the strain of many samples is nearly plane strain in the talassian sheet r xz varies from less than 1 8 to 4 4 and k from 0 to 0 35 r xz and k values increase near large faults r xz values determined by quartz and chert grains were found to be linearly related a three stage strain history is related to d 2 deformation the earliest was simple shear parallel to the axial surfaces of folds following this the fold and thrust system was transformed by pure shear with an orogen parallel axis of extension some minor increments of strain are locally represented by pressure shadows around pyrite crystals

deformed conglomerates and textural zones in the otago schists south island new zealand abstract the prehnite pumpellyite to greenschist facies rocks of the classic low grade otago schist terrane are subdivided into a number of textural zones based on the development of slaty cleavage and the appearance of segregation lamination in metagreywackes in this study conglomerates from fifteen localities have been studied in order to investigate the relationship between ductile strain and the sequence of textural zones strain measurements on lithic pebbles show a clear correlation between strain and textural zone ranging from around 40 shortening in tz iia with the development of slaty cleavage to more than 70 in tz iiia corresponding to the appearence of segregation lamination the much lower and more prolate strains of the quartzose pebbles compared to the corresponding lithic clasts may be explained by differential strain partitioning between clast and matrix microstructural evidence including well developed strain shadows and solution seams indicates that solution transfer was the dominant deformation mechanism the development of quartz segregation laminae in tz iii is due to three related processes the development of mica rich solution seams demarcating quartzo feldspathic microlithons the development of amalgamated and recrystallised strain shadow overgrowths on clastic grains and the formation rotation and disruption of early formed veins the large increase in strain from tz ii to tz iii is responsible both for increased segregation and for the rotation and flattening of segregation features into the foliation thus producing a segregation lamination large strains developed by solution transfer during the low grade metamorphism of greywackes will lead inevitably to segregated schists

the problem of shearing along axial plane foliations abstract the structural significance of axial plane foliations cannot be understood unless we make a distinction between rotation of the material plane foliation and rotation of the geometrically defined x y plane of the strain ellipsoid if the foliation rotates as a material plane at any stage of deformation then its final orientation will be different from that of the x y plane it is suggested that reorientation of foliation takes place by some combination of the formation of foliation e g recrystallization along the x y plane and passive rotation of the material plane foliation in the same continuous deformation the deviation between the foliation and the x y plane is then much less than 5 degrees however because of this deviation a considerable amount of shear strain may develop along the foliation the analysis thus explains how a foliation can be approximately parallel to the x y plane and yet be a plane of shearing

the seismogenic zone in the central costa rican pacific margin high quality hypocentres from an amphibious network transition from subduction of normal to thickened oceanic crust occurs in the central portion of the costa rican margin where large interplate earthquakes m 7 and abundant interseismic seismicity have been associated with subduction of bathymetric highs we relocated 1 300 earthquakes recorded for 6 months by a combined on and offshore seismological network using probabilistic earthquake relocation in a 3d p wave velocity model most of the seismicity originated at the seismogenic zone of the plate boundary appearing as an 18 dipping planar cluster from 15 to 25 30 km depth beneath the continental shelf several reverse focal mechanisms were resolved within the cluster the upper limit of this interseismic interplate seismicity seems to be controlled primarily by the overlying plate thickness and coherency which in turn is governed by the erosional processes and fluid release and escape at temperatures lower than 100 to 120 c along the plate boundary the downdip limit of the stick slip behaviour collocates with relative low temperatures of 150 to 200 c suggesting that it is controlled by serpentinization of the mantle wedge the distribution of the interseismic interplate seismicity is locally modified by the presence of subducted seamounts at different depths unlike in northern costa rica rupture of large earthquakes in the last two decades seems to coincide with the area defined by the interseismic interplate seismicity

pore networks in holocene carbonate sediments abstract permeabilities of holocene carbonate sediments from florida and the bahamas determined for 74 samples by water flow rates in a variable head permeameter range from 0 6 to 57 000 millidarcies porosities range from 40 to 78 percent these parameters are related to depositional texture as follows table the muddiest sediments i e the finest grained have the highest porosities but lowest permeabilities this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks even as young as pleistocene high porosity and low permeability in sediments show a strong correlation with percentage of fines 62 m from capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 m in diameter at least after drying measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation the calculated rates would require excessive time to produce the degree of cementation seen in late pleistocene rocks of florida and the bahamas the amounts of rainfall and evaporation are the most important factors in the degree of cementation

orogen parallel extension and oblique tectonics the relation between stretching lineations and relative plate motions many collisional orogens exhibit two distinct deformation phases the first and relatively early phase forms within an obliquely subducting continent and is characterized by regionally consistent stretching lineations subparallel to the orogen and to associated isoclinal and sheath folds second phase folds and stretching lineations develop during and after imbrication of the subducting plate into the overriding plate and they become progressively disharmonic with stretching lineations oriented perpendicular to the orogen structural morphology and stretching lineations indicate that a fundamental kinematic transition occurs as material is imbricated from footwall to hanging wall kinematic modeling based on modern oblique convergent boundaries and considerations of buoyancy forces suggest that only the relatively early structures reflect the relative plate motion but that the correspondence is not simple in particular the orientation of stretching lineations is a function of finite strain kinematics of deformation and angle of subduction and convergence and it will consistently underestimate the angle of oblique convergence second phase structures reflect isostatic emergence of the hanging wall and are independent of relative plate convergence examples are drawn from the south central canadian rockies the western alps the variscides of ireland and france and the himalaya

mobility and immobility of redox sensitive elements in deep sea turbidites during shallow burial during the first few tens of thousands of years after an organic rich turbidite is emplaced on an abyssal plain surficial oxidation of the unit occurs by downwards diffusion of bottom water o2 from work on piston cores it is known that a suite of redox sensitive elements form characteristic relocation peaks in such units around the deepest reaches upper few dm achieved by oxidation fossil oxic post oxic boundaries four individual turbidites now buried at depths of 130 230 m below seafloor mbsf obtained by odp leg 157 drilling on the madeira abyssal plain map have been investigated to determine the effects of burial diagenesis on these geochemical signals over 3 7 my porewater data indicate that post oxic conditions persist to around 130 mbsf on the map below which sulphate reduction predominates all four units have retained high total organic carbon corg contents 1 4 in their lower reaches despite the fact that bottom waters have previously oxidised this same organic matter in the turbidite tops to 0 2 the apparent inertness of the turbidite corg contrasts with the reactivity of organic matter observed in hemipelagic sediment from other odp investigations in all four cases low initial caco3 contents have been quantitatively removed along with corg oxidation with additional dissolution of carbonate by undersaturated bottom waters diagenetic fractions of the elements se cd sb tl and v are present in highly localised peaks and show no evidence of migration in different combinations the elements cu co ni and zn appear to have migrated over short 5 cm distances in thin mm dark coloured sulphide bands probably sourced by reduction of a mn oxyhydroxide host phase during early 70 ky burial two examples of local diagenetic pyritisation up to 20 wt fes2 are observed in the bodies of the two turbidites buried to 130 mbsf confirming that sulphate reduction is active at this level this diagenetic pyrite is associated with high concentrations of as and lesser enrichments of ni zn co se sb and possibly mo

carbonate budget of a cold water coral carbonate mound propeller mound porcupine seabight high resolution studies from the propeller mound a cold water coral carbonate mound in the ne atlantic show that this mound consists of 50 carbonate justifying the name carbonate mound through the last 300 000 years approximately one third of the carbonate has been contributed by cold water corals namely lophelia pertusa and madrepora oculata this coral bound contribution to the carbonate budget of propeller mound is probably accompanied by an unknown portion of sediments buffered from suspension by the corals however extended hiatuses in propeller mound sequences only allow the calculation of a net carbonate accumulation thus net carbonate accumulation for the last 175 kyr accounts for only 0 3 g cm2 kyr which is even less than for the off mound sediments these data imply that propeller mound faces burial by hemipelagic sediments as has happened to numerous buried carbonate mounds found slightly to the north of the investigated area

deformational and strain patterns of an intracontinental collision ductile shear zone an example from the higher garhwal himalaya the higher himalayan metamorphic belt of garhwal appears to have evolved in a major 15 20 km wide ne dipping ductile shear zone of the overthrust type due to intracontinental crustal shortening during cenozoic continental collision within the indian plate out of the four major distinct deformation phases the most widespread d2 deformation phase is marked by a prominent s2 foliation axial planar to the reclined and recumbent f2 folds a coaxial ne plunging l2 stretching lineation and syntectonic growth of index metamorphic minerals these deformational structures are developed during the sw directed d2 ductile shear deformation irrespective of the orientation of the s2 foliation and thrust zones regional strain patterns in quartzite of the lesser himalayan garhwal group beneath the main central thrust mct and the central crystalline zone using rf data on quartz clasts and aggregates reveal that the maximum values of finite strain es are attained within narrow mylonitic shear zones within the broad ductile shear zone during its progressive translation towards higher structural levels in late d2 and d3 deformation phases the shortening was accommodated by development of thrust sheets with the mct and jutogh thrust surfaces coinciding with zones of mylonite and maximum strain at higher levels ductile shear zones became compressional brittle ductile zones which resulted in the development of sw verging f3a and f3b folds during the southward migration of the thrust sheets in the lesser himalaya

carbonate mound development at the sw rockall trough margin based on high resolution tobi and seismic recording abstract in 2002 high resolution sidescan sonar images of a mound area at the sw rockall trough margin were recorded with the tobi deep towed sidescan sonar processed tobi images with a pixel resolution of 6 m provide a unique overview of the carbonate mound distribution and related sedimentary features around the mounds three morphologically distinct areas can be recognised on the tobi mosaic in area i between 500 and 600 m water depth upslope of the mounds giant sediment waves are found with wavelengths up to 500 m with wave crests of more than 10 km long and with an amplitude of up to 30 m reflected with a high backscatter on the tobi image area ii between 600 and 1000 m water depth along the upper margin flank is characterised by clustered and isolated carbonate mounds forming elongated ridges with an orientation perpendicular to the slope sedimentary structures such as flow ridges sediment waves local scouring at the foot of some mounds and draping of sediment around mounds indicate the influence of strong near bed currents oriented in two main current directions parallel to the margin as well as in a similar direction as the mound clusters the mound clusters are several kilometres long can be over 380 m high and are dissected by downslope directed channels on the tobi image the mounds appear as regions of high backscatter caused by the presence of cold water coral colonies on the sediment and by distinct shadows all mounds have their tops at a specific depth level 500 600 m water depth area iii between 900 and 1200 m water depth below the mounds is characterised by disturbed sediments with distinct slump scars and flow ridges 2d high resolution seismic profiling perpendicular and parallel to the slope across the mounds does in general not reveal strong internal reflectors within the mounds in contrast three strong reflectors can be observed in the sedimentary sequence underneath the mounds the upper reflector c10 of early pliocene age is an erosional unconformity above which most of the mounds and sediment waves seem to have developed the second erosional unconformity c20 of middle miocene age is formed by an apparent irregular surface that locally is dissected by some small faults reflectors c10 and c20 have been found in two different mound clusters in the mound area indicating that mound development possibly started after formation of reflector c20 the third reflector forms the acoustic basement which is locally dissected by some small faults that are located below the mounds at least two stages of mound formation are recognised on the seismic profiles

calibration of xrf core scanners for quantitative geochemical logging of sediment cores theory and application abstract on line analysis of split sediment cores by xrf core scanners has become increasingly popular in the past decade because it allows nondestructive extraction of near continuous records of element intensities from sediment cores with a minimum of analytical effort a disadvantage of xrf core scanning relative to conventional geochemical analysis is the problematic conversion of core scanner output to element concentrations the main reason for this long standing problem is the poorly constrained measurement geometry attributable to inhomogeneity of the specimens e g variable water content and grain size distribution irregularities of the split core surface and in some setups spatial variations in thickness of an adhesive pore water film which forms directly below a protective foil covering the core surface we propose a log ratio calibration model for xrf core scanners derived from a combination of xrf spectrometry theory principles of compositional data analysis and empirical evidence the log ratio calibration model provides accurate and precise predictions of sediment composition element concentrations from xrf core scanner output with a limited number of parameters namely 2 d 1 where d equals the number of chemical elements whose concentrations are to be estimated the model can accommodate the inherent non linearity of the relation between relative intensities and concentrations which is apparent from the fact that it provides unbiased estimates an immediate corollary of our results is that log ratios of element intensities which are related to log ratios of element abundances by a simple linear transformation provide the most easily interpretable signals of relative changes in chemical composition consistent use of log ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies the relative standard deviation precision of predicted element concentrations in core geob7920 is less than 2 stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens improved control over input errors and development of robust goodness of fit statistics allows xrf core scanning to be developed into a rigorous quantitative measurement technology the log ratio calibration equation derived in this study may be adapted to inter laboratory and inter instrument calibration as well

strains and structures associated with a terrane bounding stretching fault the melones fault zone central sierra nevada california abstract an examination of the structures total strains and rock types across the melones fault zone indicates that in the central sierra nevada this fault separates and locally imbricates two distinct terranes east of the fault a widespread early jurassic cleavage displays west northwest to northwest strikes and is associated with moderate to high strain intensities these structures form in jura triassic metasedimentary rocks in part derived from a continental source a weak northwest striking cleavage and low strain intensities occur west of the fault in lower jurassic volcanic rocks and upper jurassic slates and sandstones the fault zone itself consists of steep east dipping ductile brittle shear zones or stretching faults along which the early jurassic structures are transposed parallel to the jura cretaceous and fault related structures large flattening type strains are common in the fault zone and may be the result of heterogeneous strains developed when the shear zones bend around resistant blocks or by volume losses total strains in the eastern hanging wall reflect the superposition of fault related on older strains therefore stretching lineations in this hanging wall do not reflect directions of fault motion stretching lineations in the footwall and fault zone kinematic indicators in the fault zone and a small eastward jump in metamorphic grade suggest an east over west or reverse sense of movement no evidence for significant strike slip or oblique slip motion was found removal of footwall strains indicates that the jura cretaceous shortening across the fault was responsible for both the transposition of older structures east of the fault and the rotation of the fault to its present steep dips thus the melones fault is a large ductile brittle shear zone along which the eastern hanging wall merced river terrane moved to the southwest over the western footwall eastern foothills terrane

including strain data in balanced cross sections abstract almost all published balanced cross sections include cleaved and or strained rocks and may therefore violate the requirement that bed lengths and formation areas are preserved between undeformed and deformed states knowledge of distortions presence and type of cleavage and overprinting relations in poly deformed segments are necessary to define area changes related to volume loss strike elongation and poly deformation work in the southern and central appalachians has shown variation in structural complexity and changing deformation styles both along and across the thrust belt this necessitates separate treatment of individual sheets during balancing regions of little or no interstratal slip pinning points should be chosen for each thrust sheet and each fold strain in the sheet in external sheets where deformation intensity increases towards thrusts pin points should be back limb inflection points in intermediate and internal sheets where cleavage is approximately coeval with folding pin points should be at fold hinges where cleavage and strain are heterogeneously developed throughout a stratigraphic sequence a line length balance using massive relatively uncleaved beds e g knox group southern appalachians can be used as a basis for restoring the section unstraining of deformed layers given strain data and cleavage trajectories for individual thrust sheets provides line lengths and formation areas which can be fitted to the key bed of the undeformed section cleavages which partially or fully postdate folding indicate continued shortening in the thrust wedge and modify earlier pinning points in upper sheets these cleavages and poly deformed segments are difficult to restore as strain data are generally scarce in the metamorphosed internal thrust sheets

structural development during flysch basin collapse the fencemaker allochthon east range nevada abstract during mesozoic deformation in north central nevada a thick succession of triassic siliciclastic and hemipelagic carbonate strata that were deposited in a deep water basin shortened against and overrode penecontemporaneous shallow water carbonates and interbedded siliciclastics at the eastern margin of the basin initial rheologic contrasts developed between lithologic units during shallow pretectonic burial localized displacements within fine grained poorly cemented units and along lithologic boundaries changes in theology during low pressure and low temperature deformation led to more brittle conditions possibly due to fluid expulsion and subsequent displacements truncated bedding structures in triassic strata suggest that the w facing slope of the shelf to basin transition localized thrusting collapse of the basinal strata against strata of the basin margin and formation of a thrust at the shelf to basin transition demonstrate the ability of stratigraphic declivities and associated rheologic contrasts to buttress deformation and localize thrusting

thrust related strain gradients and thrusting mechanisms in a chevron folded sequence southeastern australia an e directed imbricate fan thrust system within a chevron folded monotonous quartz rich turbidite succession shows marked gradients in strain from the upper to lower parts of individual thrust sheets upper parts of thrust sheets show low to moderate strains xz strains 30 1 tight inclined chevron folds ila 30 with predominantly w dipping axial surfaces intense phyllitic cleavage with a strong down dip mineral stretching lineation and long curved tapering quartz pressure shadows on pyrite such differences in fold geometry the intensity of the cleavage and the geometry of quartz fibres in pressure shadows require thrust sheet emplacement to be synchronous with the internal deformation of sheets thrust sheets show a change from an approximately constant volume plane strain coaxial deformation in their upper parts to non coaxial high strain deformation with incremental i between those expected for pure shear and simple shear i e 0 i 5 45 in their basal parts observed geometries and intensities reflect partitioning of strain and deformation mechanisms within individual thrust sheet volumes both during the initiation and propagation of subsurface detachment faults and with their emplacement to shallower crustal levels strain softening related to chevron folding and more intense cleavage development within a 500 m basal zone has controlled the emplacement of these turbidite dominated thrust sheets transport and internal deformation of the thrust sheets did not involve gravitationally induced spreading but required either a push from the rear or some form of underthrusting

structure and development of giant carbonate mounds at the sw and se rockall trough margins ne atlantic ocean abstract high resolution seismic reflection profiling carried out in 1997 1999 showed that giant carbonate mounds occur between 500 and 1200 m water depth along both the se and sw margins of rockall trough the mounds rise 5 300 m above the surrounding seafloor and have diameters at their bases of up to 5 km buried mounds at relatively shallow depths below the seafloor are also found both individual and complex clusters of mounds can be recognized smaller and individual sometimes buried mounds are found at the upper slope on the sw rockall trough margin higher steeper and individual mounds are found deeper downslope 900 1100 m at the middle slope the mounds merge into a complex structure and form complex clusters with a very irregular upper surface and an apparent lack of internal reflectors 600 1000 m depth initial results of high resolution 3d seismic profiling at 30 m line spacing in august 2000 in two boxes of 750 m 14 5 km covering a small central part of the sw rockall trough mound area indicate two stages of mound development here the latest probably of pliocene holocene age this age based on the presence of a regionally recognizable unconformity below the mounds is also assumed for the mounds of the se rockall trough porcupine bank margin

regional structural and strain analyses of terranes in the western metamorphic belt central sierra nevada california abstract a comparison of total strains in 225 samples from the western metamorphic belt sierra nevada shows that strain types and intensities strongly depend on rock type greywackes and clast supported conglomerates are least strained whereas more intense strains occur in lapilli tuffs pebbly mudstones and slates large belts of volcanic rock record plane strain whereas nearby slate and greywacke sequences record flattening type strain suggesting that volume losses of 45 65 occurred in slates and 0 26 in greywackes lapilli tuffs record less than 11 volume loss the differences in volume loss and strain from one rock type to another require that discontinuities in total strain occur at most lithologic contacts independently of the lithologic control regional structural patterns and strain fields support the delineation of three terranes foothills merced river and northern sierra and two distinct domains western and eastern foothills terranes at these latitudes within the western metamorphic belt these terranes each bordered by large ductile shear zones differ in average strain intensity and orientation but not in strain type in the foothills terrane strain intensities decrease from moderate values in the western foothills terrane to low values in the eastern foothills terrane strain intensities in the study area are highest in the melones and bear mountains fault zones and in terranes east of the melones fault structures associated with regional deformation in each terrane do not extend far across terrane boundaries multiple generations of regionally developed structures are therefore rare in this part of the western metamorphic belt outside of fault zones we see one regionally developed cleavage in the foothills terrane a single but older cleavage in the merced river terrane and two still older cleavages in the northern sierra terrane however younger deformations may have reactivated and rotated older structures in adjacent terranes the timing and kinematics of the deformation in the foothills terrane suggest that faulting and rigid body rotations preceded pervasive shortening continued fault movement and rotation of faults to steep dips if orientations of ductile structures reflect plate motions structures in the merced river terrane suggest jurassic triassic orthogonal nne convergence whereas structures in the foothills terrane support late jurassic orthogonal ne convergence changing to oblique ene convergence about 150 ma ago

valemount strain zone a dextral oblique slip thrust system linking the rocky mountain and omineca belts of the southeastern canadian cordillera the valemount strain zone vsz a narrow zone of high orogen parallel op strain in pebble conglomerate of the late proterozoic miette group is the footwall expression of a thrust fault of the western edge of the rocky mountain belt marking the eastern limit of a wide zone of op fabrics distributed through the omineca crystalline and western rocky mountain belts of the southeastern canadian cordillera kinematic indicators from the vsz and the adjacent bear foot thrust zone show that both thrust and dextral displacement are associated with folding and thrust motion in the rocky mountains thereby linking the southern rocky mountain belt to the omineca belt by an oblique slip thrust regime that is tectonically unrelated to the southern rocky mountain trench transverse shortening of thrust sheets and subsequent distribution of op shear are invoked to explain the parallelism of stretching lineations and fold axes strain and kinematic data and the thrust belt geometry of the vsz suggest that op lineations are a product of a large amount of transverse shortening during slightly oblique a type subduction thus op lineations are not representative of relative plate motions between north america and accreted terranes but probably are a function of footwall buttressing of thrustmore sheets a mechanism that may be widely applicable to the internal zones of collisional orogens less

ability of the fry method to characterize pressure solution deformation abstract the applicability of the fry method to marker distributions deformed by pressure solution is examined four types of pressure solution deformation were modeled they differ by the spacing of the dissolution surfaces relative to the distance between marker centers the amount of volume loss and whether or not markers in contact with dissolution surfaces are dissolved completely the results show that the fry method correctly characterizes each type of deformation but without additional information such as the amount of volume loss it can be used only where the deformation is constant volume and where dissolution surfaces are more closely spaced than marker centers

finite strain patterns of nevadan deformation western klamath mountains california finite strain analyses of galice formation metagraywackes from the footwall block of the orleans fault western klamath mountains california show a dramatic increase in strain ratios structurally upward approaching the orleans fault r xz strain values range from less than 3 at a distance of 2 km from the fault to 6 5 adjacent to the fault strain ellipse orientations are relatively consistent x directions are commonly northwest southeast and subhorizontal and trend subparallel to the trace of the orleans fault finite strain ellipse orientations and the clockwise rotational strain recorded by microscopic kinematic indicators are both compatible with the interpretation of dextral oblique convergence on the orleans fault during the nevadan orogeny

strain refraction in layered systems abstract strain refraction across competence contrasts is presented as a simple model consisting of two components a homogeneous strain and a heterogeneous simple shear for newtonian materials the ratio of the layer parallel simple shear component in adjacent layers is the inverse of their viscosity ratio strong changes in ellipsoid size shape and orientation are predicted across viscosity contrasts the geological implications of strain refraction theory are considered within the context of the cleavage strain debate the particular relationships of relative competence and strain revealed by the refraction model may contribute to the problem of why cleavages of different morphologies in rocks of different lithologies and kinematic histories should appear to be subparallel to the xy planes of measured strain ellipsoids competent rocks should develop dominantly layer orthogonal strain and incompetent layers shear dominated deformation a variety of structural features ranging from cleavage refraction changing lineation orientations folds transected by cleavage changes from coaxial to non coaxial deformation and ramp flat fault geometry may be the result of stress and strain refraction in rocks

crack propagation sequence and pore fluid conditions during fault bend folding in the appalachian valley and ridge central pennsylvania bedding parallel bpv strike sv and cross fold cfv veins represent a sequence of polyphase fracturing during the development of a fault bend fold in lower paleozoic carbonate beds in the appalachian valley and ridge province pennsylvania brecciation and layer parallel shearing played important roles in the development of the earliest vein set bpv which propagated prior to folding fluid inclusions in calcite bpv are highly saline brines 23 4 wt naci trapped at conditions close to lithostatic p 180 mpa t 267 c while passing through the lower kink plane of a fault bend fold strike joints propagated in dolomitic beds located on the extensional side of neutral surfaces stylolitization of strike joint surfaces accompanied slip of the hanging wall up a ramp renewed extension upon passing through a second kink plane led to propagation of antitaxial sv along the stylolitized joints by the crack seal process slightly less saline fluids 22 4 wt naci were trapped in sv at fluid pressures 144 mpa and temperatures 217 c with the concurrent formation of lateral ramps the carbonates moved to the upper flat and were subjected to strike parallel extension as manifested by the propagation of antitaxial cfv due to further mixing of fresh waters the salinity of fluids forming cfv decreased 20 5 wt nacl with trapping conditions at p 116 mpa and t 179 c the fluid evolution path from bpv to cfv through sv shows a modest decrease in salinity with a sharp decrease in possible trapping pressures

factors affecting finite strain estimation in low grade low strain clastic rocks the computer strain analysis methods sape mrl and dtnnm have permitted the characterization of finite strain in two different regions with contrasting geodynamic scenarios 1 the talas ala tau tien shan kyrgyzs republic and 2 the somiedo nappe and narcea antiform cantabrian to west asturian leonese zone boundary variscan belt nw of iberia the performed analyses have revealed low strain values and the regional strain trend in both studied areas this study also investigates the relationship between lithology grain size and percentage of matrix and strain estimates the two methodologies used the results show that these methods are comparable and the absence of significant finite strain lithological control in rocks deformed under low metamorphic and low strain conditions

diagenetic processes in carbonate mound sediments at the south west rockall trough margin cold water coral covered carbonate mounds at the south west margin of the rockall trough form ridges several kilometres long and up to 380 m high piston cores obtained at three mound crests reveal the complex internal structure of the mound build up with alternating unlithified coral dominated intervals and lithified intervals the most recent lithified interval is covered by corals embedded in a fine grained matrix comprising ca 11 000 years of continuous mound evolution before this time 230th u dating shows the presence of several hiatuses in mound build up aragonitic coral material is absent or only present as mouldic porosity in the lithified intervals and coccoliths display widespread overgrowth downcore x ray fluorescence scanning computer tomography scan images and petrographic observations indicate different degrees of diagenetic alteration the upper boundary of the most recent lithified interval shows some erosional features but petrographic observations indicate that initial lithification of the sediments is not related to this erosive event or to long term non sedimentation but to earlier sub surface diagenesis organic matter oxidation and the subsequent lowering of the saturation state of the carbonate system drives dissolution of the unstable aragonitic coral skeletons depending on the openness of the system this can lead to precipitation of a more stable low magnesium carbonate a model is presented describing the sedimentary and diagenetic processes leading to the formation of lithified intervals

pencil structure and strain in weakly deformed mudstone and siltstone abstract weakly deformed mudstone and siltstone middle ordovician knobs formation of the appalachian valley and ridge province south western virginia u s a show strain dependent transitions between bedding fissility pencil structure and cleavage pencil structures are associated with a bulk inhomogeneous shortening deformation where minimum principal strain z ranges between 9 and 26 shortening assuming a plane strain and constant volume where strains are less bedding fissility dominates pencil fragments are defined by intersecting fracture sets subparallel to the pre existing bedding fissility and cleavage their long axes are both parallel to the bedding cleavage intersection and to the inferred y axis of the tectonic strain ellipsoid pencil development is considered to result from fracturing along both fabric anisotropies during weathering and post tectonic stress relaxation pencils show variations in size and shape depending on lithology grain size and composition degree of initial clay preferred orientation degree of cleavage development type of cleavage total bulk strain and degree of strain homogeneity their shape l w however is a direct measure of total y z strain since strain determinations from chlorite pressure fringes on framboidal pyrite within the pencil fragments give y z 0 913 0 019 l w pencil structure is therefore a potential strain marker in weakly deformed rocks

two types of ductile deformation regional metamorphic belt abstract the geometry of plastic strains of regional metamorphic rocks is divided into two types one is the uniaxial extension strain prolate and the other the biaxial shortening strain oblate from the plane strain simple shear to the uniaxial shortening geometry the uniaxial extension geometry is found in deformation of metamorphic rocks of the sambagawa ryoke kamuikotan and franciscan belts while the biaxial type is seen in deformation of the shimanto the alpine the appalachian and the caledonian metamorphic rocks the classification of the metamorphic belts by means of strain geometry and strain path is independent of the metamorphic facies series the difference in strain geometry of metamorphic belts is responsible mainly for the tectonic stress regime in metamorphism it is suggested that the biaxial type belongs to the collision type orogeny and the uniaxial type to the cordilleran type orogeny

the structure and the phyllosilicates chemistry crystallinity and texture of talas ala tau tien shan kyrgyz republic comparison with more recent subduction complexes abstract geological mapping and structural analysis of the talas ala tau tien shan kyrgyz republic have revealed a complex structure composed of folds with axial plane cleavage and thrust faults verging towards the ne the main structures of the range correspond to minor tertiary and carboniferous permian deformation superimposed on the main deformation event that took place during the baikalian orogeny the pervasive axial plane cleavage diminishes in penetrativity from the hinterland to the foreland in both the uzunakhmat and karagoin sheets the main thrusts developed phyllonitic shear related rocks on the hangingwall immediately above the thrust planes a crystal chemical study of the phyllosilicates growth during the baikalian deformation event along a cross section revealed changes in the crystallinity composition and lattice parameters of them the phyllosilicates present in the talas ala tau rocks were crystallized in very low grade metamorphic conditions that is below 300 c as indicated by their kubler index ki which decreases from sw towards the ne detailed tem study of the phyllosilicates reveals a clear textural difference at the lattice level between samples with higher or lower ki parameters there is also a clear difference in crystal chemical parameters ki and b and composition between the phyllosilicates growth in relation to the axial plane cleavage and the ones belonging to the thrust related phyllonites the first ones are more affected by the ferrimuscovitic vector than the phyllosilicates of phyllonites closer to the theoretical phengitic component huge ranges of values of phengitic content of micas at sample level are interpreted as the result of a decompression path from at least 8 kbar we propose a subduction geodynamic environment for the regional deformation and the origin of the phyllosilicates as they are similar to those obtained in more recent accretionary complexes

quaternary crusts on slopes of the mediterranean sea a tentative explanation for their genesis abstract quaternary deep sea crusts i e lithified omission surfaces are widespread on slopes and subsea relief features in the western and especially the eastern mediterranean sea the lithification is induced by the early precipitation of a magnesian calcite cement in the uppermost few centimetres of a calcareous ooze based on their thickness and degree of hardening the collected samples have been divided into three main types each of them corresponding to a different degree of lithification except in rare probably old crusts collected at water depths below 2000 2500 m and in infills of some sponge skeletons or in the case of inferred internal tension recrystallization and generally mineral alterations are very limited the precipitation mechanisms appear to be essentially physicochemically controlled and ions involved in cementation come from the seawater reservoir by means of an inward diffusion of solutions diffusion is enhanced by bottom currents these currents maintaining a low or zero rate of sedimentation moreover lithification also depends on the chemical characteristics of the seawater i e supersaturation with respect to low magnesian calcite and low contents of phosphates and dissolved organic matter which would inhibit crystal growth local factors and primary composition of the original sediment also appear to influence the speed of early lithification when conditions of lithification are favourable a few hundreds of years to a few thousand years at the most seem sufficient for the first two stages of lithification to be reached the submarine lithification was active during the last glacial episode and as exhibited by numerous samples especially towards the end of this period the previous cold stages were probably also episodes of efficient lithification this correlation with quaternary climatic cycles certainly reflects an intensification of thermohaline and bottom current circulations during periods of severe climatic conditions there is also some evidence of holocene and even present day crusts