strike slip tectonics in the sw barents sea during north atlantic rifting swaen graben northern norway this study uses high quality three dimensional 3 d seismic data to investigate the occurrence of strike slip faults in the swaen graben sw barents sea the swaen graben is divided into two principal sub basins ssb1 and ssb2 the along strike and along dip displacement variations and scale relationships are analyzed for forty two 42 faults the displacement profiles for these faults are complex in the swaen graben showing clear evidence for polycyclic fault growth and marked syn sedimentary activity the observed variations in the displacement profiles indicate complex along strike segmentation linkage and mechanical interactions at distinct structural levels along dip displacement minima indicate fault reactivation by dip linkage importantly geometric evidence for strike slip faulting in the swaen graben includes the presence of extensional horsetail splay faults positive flower structures and minor transfer faults this study shows that the faults in the swaen graben developed under extensional regimes during late jurassic to early cretaceous rifting and were reactivated by regional stresses during the late cretaceous the two principal strike slip faults in the swaen graben reveal sinistral movement and are linked at a shallow depth by minor transfer faults at a relay zone our work further demonstrates the occurrence of late mesozoic strike slip movements in the sw barents sea which were induced by regional tectonics halokinesis and fault block rotation importantly strike slip faulting in the region extends perhaps into the cenozoic interacting with extension during the north atlantic rifting

exxon global cycle chart an event for every occasion the basic premise of the recent exxon cycle chart that there exists a globally correlatable suite of third order eustatic cycles remains unproven many of the tests of this premise are based on circular reasoning the implied precision of the exxon global cycle chart is not supportable because it is greater than that of the best available chronostratigraphic techniques such as those used to construct the global standard time scale correlations of new stratigraphic sections with the exxon chart will almost always succeed because there are so many exxon sequence boundary events from which to choose this is demonstrated by the use of four synthetic sections constructed from tables of random numbers a minimum of 77 successful correlations of random events with the exxon chart was achieved the existing cycle chart represents an amalgam of regional and local tectonic events and probably also includes unrecognized miscorrelations it is of questionable value as an independent standard of geologic time

erosion of biofilm bound fluvial sediments sediment grains in rivers are often bound together and stabilized by bacterial films experiments and mathematical models show that sediments bound by biofilms behave like a single elastic membrane that can rip catastrophically if the river flows fast enough

estuarine clay mineral distribution modern analogue for ancient sandstone reservoir quality prediction the spatial distribution of clay minerals in sandstones which may both enhance or degrade reservoir quality is poorly understood to address this clay mineral distribution patterns and host sediment properties grain size sorting clay fraction abundance and bioturbation intensity have for the first time been determined and mapped at an unprecedentedly high resolution in a modern estuarine setting ravenglass estuary uk results show that the estuary sediment is dominated by illite with subordinate chlorite and kaolinite although the rivers supply sediment with less illite and significantly more chlorite than found in the estuary fluvial supplied sediment has been locally diluted by sediment derived from glaciogenic drift deposits on the margins of the estuary detailed clay mineral maps and statistical analyses reveal that the estuary has a heterogeneous distribution of illite chlorite and kaolinite chlorite is relatively most abundant on the northern foreshore and backshore and is concentrated in coarse grained inner estuary dunes and tidal bars illite is relatively most abundant as well as most crystalline and most fe mg rich in fine grained inner estuary and central basin mud and mixed flats kaolinite has the highest abundance in fluvial sediment and is relatively homogenous in tidally influenced environments clay mineral distribution patterns in the ravenglass estuary have been strongly influenced by sediment supply residence time and subsequently modified by hydrodynamic processes there is no relationship between macro faunal bioturbation intensity and the abundance of chlorite illite or kaolinite based on this modern analogue study outer estuarine sediments are likely to be heavily quartz cemented in deeply buried burial temperatures exceeding 80 to 100 c sandstone reservoirs due to a paucity of clay grade material 0 5 to form complete grain coats in contrast chlorite enriched tidal bars and dunes in the inner estuary with their well developed detrital clay coats are likely to have quartz cement inhibiting authigenic clay coats in deeply buried sandstones

stochastic velocity inversion of seismic reflection refraction traveltime data for rift structure of the southwest barents sea we present results from an active source onshore offshore seismic reflection refraction transect acquired as part of the petrobar project petroleum related studies of the barents sea region the 700 km long profile is oriented nw se coincident with previously published multichannel seismic reflection profiles we utilize layer based raytracing in a markov chain monte carlo mcmc inversion to determine a probabilistic velocity model constraining the sedimentary rocks crystalline crust and uppermost mantle in a complex tectonic regime the profile images a wide range of crustal types and ages fromproterozoic craton to paleozoic to early cenozoic rift basins and volcanics related to eocene continental breakupwith greenland our analyses indicate a complex architecture of the crystalline crust along the profile with crystalline crustal thicknesses ranging from43 kmbeneath the varanger peninsula to 12 kmbeneath the bjornoya basin assuming an original post caledonide crustal thickness of 35 km in the offshore area we calculate the cumulative thinning factors along the entire profile the average factor along the profile is 1 7 0 1 suggesting 211 243 km of extension consistent with the amount of overlap derived from published plate reconstructions local factors approach 3 where bjornoya basin reaches a depth of more than 13 km volcanics carbonates salt diagenesis and metamorphism make deep sedimentary basin fill difficult to distinguish from original pre rift crystalline crust and thus actual stretching may in places exceed our estimates

subduction and eduction of continental crust major mechanisms during continent continent collision and orogenic extensional collapse a model based on the south norwegian caledonides during continental collision in the middle silurian the thickness of the lithosphere under the caledonides of s norway was doubled by subduction of the western margin of baltica including the western gneiss region under laurentia crustal rocks of the baltic plate reached sub moho depths of near 100 km or more as inferred from the presence of coesite in eclogites isostatic calculations indicate an average elevation of the mountain chain of about 3 km at this stage the subducted lithosphere experienced vertical constrictional strains as a result of slab pull by its heavy and cold root eduction of the deeply buried crustal material was initiated by decoupling of the thermal boundary layer in the subducted lithosphere isostatic rebound resulted in very rapid uplift 1 2 mm yr 1 and the deep crust was exhumed mainly by tectonic extensional stripping over a period of 30 40 myr the eduction was probably related to a rolling hinge footwall uplift mechanism and the early high pressure coaxial fabrics were overprinted by extensional simple shear as the deep crust reached middle and upper crustal levels the model explains the present day normal crustal thickness under the exhumed deep rocks without necessarily invoking large scale lateral flow of material in the lower crust or igneous underplating

clay coated sand grains in petroleum reservoirs understanding their distribution via a modern analogue abstract clay coated grains can inhibit ubiquitous porosity occluding quartz cement in deeply buried sandstones and thus lead to anomalously high porosity a moderate amount of clay that is distributed as grain coats is good for reservoir quality in deeply buried sandstones being able to predict the distribution of clay coated sand grains in petroleum reservoirs is thus important to help find and exploit anomalously good reservoir quality here we have adopted a high resolution analogue approach using the ravenglass estuary marginal shallow marine system in nw england u k extensive geomorphic mapping grain size analysis and bioturbation intensity counts were linked to a range of scanning electron microscopy techniques to characterize the distribution and origin of clay coated sand grains in surface sediment our work shows that grain coats are common in this marginal shallow marine system but they are heterogeneously distributed as a function of grain size clay fraction and depositional facies the distribution and characteristics of detrital clay coated grains can be predicted with knowledge of specific depositional environment clay fraction percentage and grain size the most extensive detrital clay coated grains are found in sediment composed of fine grained sand containing 3 5 to 13 0 clay fraction associated with inner estuary tidal flat facies thus against common convention the work presented here suggests that in deeply buried prospects the best porosity might be found in fine grained clay bearing inner tidal flat facies sands and not in coarse clean channel fill and bar facies

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

regional tectonic interpretation of image enhanced gravity and magnetic data covering the mid norwegian shelf and adjacent mainland abstract gravity and magnetic field data covering mid norway and the norwegian sea were processed in order to enhance tectonic features on various scales the local features were subjected to an unconventional processing technique involving a non linear adaptive wallis filter designed to enhance the smallest wave lengths when compared with recent structural information derived from seismic data the processed gravity and magnetic maps show the main structural trends major fault zones and basin boundaries thus proving their worth for regional tectonic mapping previously undetected nw se trending offshore crustal lineaments are revealed a landward prolongation of the bivrost lineament appears to continue subparallel towards proterozoic shear zones below the caledonian nappes in the rana area either along the western margin of the transscandinavian granite porphyry belt or the nw se trending mala skelleftea tectonic zone a large lineament is also observed as a landward prolongation of the surt lineament indicating a relationship with the storsjon edsbyn deformation zone a major deep crustal shear zone in the precambrian of sweden a slightly increased seismic activity which is possibly related to the present ridge push force is observed along parts of the previously unknown transfer zones combined gravity and magnetic modelling indicates a low crustal thickness in the northwesternmost part of the voring basin between the surt and the jan mayen lineaments the lack of correlation between the gravity and the magnetic patterns observed on the residual field maps suggests the presence of a shallow curie isotherm situated above or within the uppermost basement

sticky stuff redefining bedform prediction in modern and ancient environments the dimensions and dynamics of subaqueous bedforms are well known for cohesionless sediments however the effect of physical cohesion imparted by cohesive clay within mixed sand mud substrates has not been examined despite its recognized influence on sediment stability here we present a series of controlled laboratory experiments to establish the influence of substrate clay content on subaqueous bedform dynamics within mixtures of sand and clay exposed to unidirectional flow the results show that bedform dimensions and steepness decrease linearly with clay content and comparison with existing predictors of bedform dimensions established within cohesionless sediments reveals significant over prediction of bedform size for all but the lowermost clay contents examined the profound effect substrate clay content has on bedform dimensions has a number of important implications for interpretation in a range of modern and ancient environments including reduced roughness and bedform heights in estuarine systems and the often cited lack of large dune cross sets in turbidites the results therefore offer a step change in our understanding of bedform formation and dynamics in these and many other sedimentary environments

abrasion of detrital grain coating clays during sediment transport implications for diagenetic clay coats abstract detrital grain coating clay minerals have been identified as precursors of diagenetic grain coating clay minerals that inhibit quartz cementation and preserve good reservoir quality properties in deeply buried sandstone reservoirs between initial and final deposition detrital grain coats are likely to be affected by sediment transport processes to date it has not been demonstrated that detrital grain coating clays are able to survive sediment transport flume experiments simulating open channel flow conditions were performed using sediments from the ravenglass estuary cumbria uk where the distribution and characteristics of modern detrital grain coating clays is well established scanning electron microscopy and automated mineralogy techniques were employed to study the sediment before and after transport to determine the stability of the detrital grain coating clays the experimental results show that detrital grain coating clays are still present after sediment transport in turbulent flows with velocities up to 0 5 m s 1 the stability of the detrital grain coating clays was enhanced by 1 high initial clay coat coverage 2 turbulence characteristics of the flow and 3 entrapment of the detrital grain coating clays in bedforms this work documents the first quantifiable evidence that estuary derived detrital clay coats are routinely preserved after sediment transport clay coat rich estuarine sediments can therefore act as the source of clay coated grains found in cleaner estuarine sandstones and may even survive transport out into open marine settings

detrital clay grain coats in estuarine clastic deposits origin and spatial distribution within a modern sedimentary system the gironde estuary south west france

long lived fault zones and their influence on the tectonic development of the southwestern barents sea the southwestern barents sea shows a complicated network of fault complexes and systems with various geometrical and genetic characteristics trend relation to basement reactivation fault plane geometry and regional significance using these parameters a classification of the fault complexes has been made and a correlation to onshore faults has been attempted the area is subdivided into several fault blocks separated by deep seated zones of weakness first and second class fault systems these are reactivated in connection with later mesozoic movements in the area and have acted as foci of strain so leaving the central area of the blocks relatively strain free a third class of fault systems is of local significance and reflects deformation limited to the interior of the fault blocks

facies associations detrital clay grain coats and mineralogical characterization of the gironde estuary tidal bars a modern analogue for deeply buried estuarine sandstone reservoirs abstract estuarine tidal bar sandstones are complex reservoir geobodies commonly exploited by the oil and gas industry in order to better predict the reservoir potential of these geobodies this study provides a modern day reservoir analogue describing tidal bars in the inner and outer gironde estuary from the microscopic to the macroscopic scale the originality of this work lies in the multi scale study of modern estuarine tidal bars based on numerous piston cores extracted in a high energy environment this work demonstrates that these tidal bars are composite sedimentary bodies made up of individual reservoir sand units separated by thick muddy layers their vertical facies associations and internal architectures are controlled by local hydrodynamic variations and seasonal river influxes detrital clay grain coats are notably characterized using a portable and handheld mineral spectrometer from the base to the top of the tidal bars x ray diffraction and electron microscopes reveal that these coats are mainly composed of di octahedral smectite illite chlorite and kaolinite associated with other components such as diatoms or pyrite the best reservoir geobodies are those with the minimum clay permeability barriers at the macro and mesoscale an optimum coated grain content and clay fraction volume is also needed for generating authigenic clay coatings and inhibiting quartz overgrowth these conditions are met within the tidal sand bars of the outer estuary funnel that are expected to be the best reservoir geobodies in deeply buried sandstones

a new mississippian biozonal scheme for the finnmark platform norway palynostratigraphic integration of exploration wells 7128 4 1 and 7128 6 1 abstract a new biozonal scheme for the mississippian succession in the finnmark platform offshore norway is presented palynological analysis of exploration wells 7128 4 1 and 7128 6 1 that penetrated the billefjorden group allow integration of all of the mississippian palynological data from the region providing better age constraint and correlation of the sedimentary successions on the finnmark platform two new biozones and three subzones are described in ascending stratigraphic order the granulatisporites granulatus biozone mid to late visean consisting of the potoniespores delicatus subzone mid visean the monilospora mutabilis subzone late visean and the convolutispora vermiformis subzone late visean and the tripartites vetustus biozone late visean the new biozones are correlated to the carboniferous miospore biozones of western europe based on first and last occurrences of selected taxa

deformation of the baltic continental crust during caledonide intracontinental subduction views from seismic reflection data deep seismic profiling in norway and sweden provides documentation of the amount and style of deformation of the baltic crust in response to caledonian intracontinental subduction the seismic data demonstrate that the preserved caledonide allochthon in central scandinavia is 15 to 20 km thick considerably greater than the 2 to 5 km predicted from surface geologic data much of the thickness of allochthonous rocks results from imbrication of the baltic basement within a thin skinned style thrust complex seismic data across the skardora antiform one of the basement windows in the central caledonides indicate that the window represents an antiformal stack of thrust sheets involving basement and cover rocks these data suggest that many of the basement windows in the scandinavian caledonides may result from similar thrust culminations and that the basement windows do not expose autochthonous baltic basement documentation of the response of the baltic crust during intracontinental subduction provides new constraints on reconstructions of the scandinavian caledonides and insights into the style of deformation occurring in other collisional orogens

improved imaging and analysis of chlorite in reservoirs and modern day analogues new insights for reservoir quality and provenance abstract chlorite is a key mineral in the control of reservoir quality in many siliciclastic rocks in deeply buried reservoirs chlorite coats on sand grains prevent the growth of quartz cements and lead to anomalously good reservoir quality by contrast an excess of chlorite for example in clay rich siltstone and sandstone leads to blocked pore throats and very low permeability determining which compositional type is present how it occurs spatially and quantifying the many and varied habits of chlorite that are of commercial importance remains a challenge with the advent of automated techniques based on scanning electron microscopy sem it is possible to provide instant phase identification and mapping of entire thin sections of rock the resulting quantitative mineralogy and rock fabric data can be compared with well logs and core analysis data we present here a completely novel quantitative evaluation of minerals by scanning electron microscopy qemscan sem energy dispersive spectrometry eds methodology to differentiate quantify and image 11 different compositional types of chlorite based on fe mg ratios using thin sections of rocks and grain mounts of cuttings or loose sediment no other analytical technique or combination of techniques is capable of easily quantifying and imaging different compositional types of chlorite here we present examples of chlorite from seven different geological settings analysed using qemscan sem eds by illustrating the reliability of identification under automated analysis and the ability to capture realistic textures in a fully digital format we can clearly visualize the various forms of chlorite this new approach has led to the creation of a digital chlorite library in which we have co registered optical and sem based images and validated the mineral identification with complimentary techniques such as x ray diffraction this new methodology will be of interest and use to all those concerned with the identification and formation of chlorite in sandstones and the effects that diagenetic chlorite growth may have had on reservoir quality the same approach may be adopted for other minerals e g carbonates with major element compositional variability that may influence the porosity and permeability of sandstone reservoirs

anomalously high porosity and permeability in deeply buried sandstone reservoirs origin and predictability porosity and permeability generally decrease with increasing depth thermal exposure and effective pressure however a significant number of deep 4 km approximately 13 000 ft sandstone reservoirs worldwide are characterized by anomalously high porosity and permeability anomalous porosity and permeability can be defined as being statistically higher than the porosity and permeability values occurring in typical sandstone reservoirs of a given lithology composition and texture age and burial temperature history in sandstones containing anomalously high porosities such porosities exceed the maximum porosity of the typical sandstone subpopulation major causes of anomalous porosity and permeability were identified decades ago however quantification of the effect of processes responsible for anomalous porosity and permeability and the assessment of the predictability of anomalous porosity and permeability occurrence in subsurface sandstones have rarely been addressed in published literature the focus of this article is on quantification and predictability of three major causes of anomalously high porosity 1 grain coats and grain rims 2 early emplacement of hydrocarbons and 3 shallow development of fluid overpressure grain coats and grain rims retard quartz cementation and concomitant porosity and permeability reduction by inhibiting precipitation of quartz overgrowths on detrital quartz grains currently prediction of anomalous porosity associated with grain coats and grain rims is dependent on the availability of empirical data sets in the absence of adequate empirical data sedimentologic and diagenetic models can be helpful in assessing risk due to reservoir quality such models provide a means to evaluate the effect of geologic constraints on coating occurrence and coating completeness required to preserve economically viable porosity and permeability begin page 302 in a given play or prospect these constraints include thermal history and sandstone grain size and composition the overall effect of hydrocarbon emplacement on reservoir quality is controversial it appears that at least some cements quartz and illite may continue to precipitate following emplacement of hydrocarbons into the reservoir our work indicates that integration of basin modeling with reservoir quality modeling can be used to quantify prior to drilling the potential impact of hydrocarbon emplacement on porosity and permeability the best case scenario for significant reservoir quality preservation due to fluid overpressure development is in rapidly deposited tertiary or quaternary sandstones our models suggest that significant porosity can be preserved in sandstones that have experienced continuous high fluid overpressures from shallow burial depths the models also indicate that the potential for porosity preservation is greatest in ductile grain rich sandstones because compaction tends to be the dominant control on reservoir quality in such rocks the case for significant porosity preservation associated with fluid overpressures in pre tertiary basins however is more problematic because of the complexities in the history of fluid overpressure and the greater significance of quartz cementation as a potential mechanism of porosity loss

magmatic activity during the breakup of greenland eurasia and fluid flow in stappen high sw barents sea abstract a great deal of magmatic activity was recorded along the northern atlantic margins during the cenozoic opening of the norwegian greenland seas this work uses a recently acquired two dimensional seismic reflection dataset to characterize magmatic rocks and fluid flow features on the western margin of stappen high hard kicks are positive seismic high amplitude anomalies related to igneous rocks in the subsurface while soft kicks are negative high amplitude anomalies interpreted as fluid related anomalies the hard kicks are the most prominent anomalies in the study area and they are distributed in a n s zone that is coincident with the trend of the stappen high the hard kicks include extrusive and intrusive rocks such as lava flows dykes and volcanic sills the sills have saucer bowl transgressive tabular and convex geometries extrusive igneous rocks and other deeply seated volcanic sills are buried to a depth of greater than 3000 ms soft kicks are bright spots and enhanced reflections found close to angular unconformities channels clinoforms and canyons hydrothermal vents and vertical clusters of soft kicks gas charged sediments are evidence of vertically focused fluid flow in the study area this work finds that large scale magmatic edifices recorded in other northern atlantic margins are also present in the study area as volcanoes volcanic plateaus and cascade transgressive sills volcanic rocks in stappen high were emplaced during the late eocene oligocene and early pliocene delimiting the areas into a southern part that is magma rich and a northern hydrocarbon rich province

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

an inverse method for determining lithospheric strain rate variation on geological timescales abstract inverse theory is used to calculate the strain rate variation as a function of time needed to fit observed subsidence patterns within extensional sedimentary basins no a priori information concerning either the duration of rifting or the total strain is required the method is one dimensional but can be generalised for use with two and three dimensional data conventional kinematic modelling of such basins normally assumes that lithospheric stretching is instantaneous or that the strain rate during a rifting period of known duration is constant the scheme is tested on a variety of synthetic data and applied to subsidence data from the dolomites northern italy linear error analysis combined with random and systematic noise tests show that variations in strain rate are significant and well resolved in the dolomites inverse calculations produce good fits to the data yielding total strains and durations of lithospheric stretching that are consistent with geological constraints calculated strain rates are not constant but vary between 10 18 10 15 s 1 information concerning spatial and temporal strain rate variation will provide important constraints for dynamic models of lithospheric deformation

frequency distribution of geologically determined slip rates for normal faults in the western united states short term and long term slip rates are contrasted for 18 well studied faults in the basin and range and rio grande rift provinces over periods ranging from 3000 to 4 000 000 yr the intrinsic variability of the 62 interval slip rates on these normal faults is assessed by normalizing the long term slip rate of each fault to 0 1 mm yr the cumulative density function of the grouped data predicts that given a mean net slip rate of 0 12 mm yr extreme slip rates with 10 and 5 probability of exceedance are 0 51 and 0 92 mm yr respectively these slip rates are considerably higher than those chosen by an expert panel for the pajarito fault new mexico which has a long term mean slip rate of ca 0 12 mm yr

continuation of the caledonides north of norway seismic reflectors within the basement beneath the southern barents sea abstract the offshore continuation of the caledonides to the north of norway is poorly understood and the seismic signature of these rocks is unknown indeed the seismic signature of basement rocks is in general poorly documented from conventional seismic data this paper discusses an area in the southern barents sea the gjesvaer low where inferred caledonian basement rocks have been studied from conventional seismic data the gjesvaer low which has not been described previously as a separate structural element is defined on image processed gravity data the main processing steps were directional filtering and principal component analysis the interpretation of the low as a feature within the inferred basement rocks is based on well data the calculated depth to magnetic basement seismic signature and velocities in addition two dimensional gravity modelling shows that density variations within the basement rocks may explain the observed gravity anomaly although the following model may be simplistic distinct seismic reflectors within the low may be interpreted as originating from tectonic boundaries within a thrust system in the most likely evolutionary scenario the gjesvaer low and the south western part of the nordkapp basin are interpreted as having been formed as continuous caledonian structures whose continuity has survived until the present subsequent late palaeozoic erosion may have removed more than 10 km of caledonian rocks in the area of the low carboniferous rifting reactivated the caledonian structures and the south western nordkapp basin was formed the nordkapp basin which was decoupled from the gjesvaer low in carboniferous times subsided while the low was again eroded

third order depositional sequences controlled by synsedimentary extensional tectonics evidence from upper triassic carbonates of the carnian prealps ne italy the upper triassic platform margin deposits of the carnian prealps fail to show the succession of the two global sea level lowerings predicted for the norian and rhaetian by the haq global sea level curve in both cases a relative sea level rise occurs a discrepancy that can be explained by an increase in tectonically controlled subsidence a consequence of the plate scale rifting in the nw tethys gulf preceding oceanic spreading in the jurassic pulses of tectonic subsidence followed by relative quiescence are capable of generating depositional sequences similar in gross geometry and duration to the third order eustatic cycles of haq et al the late triassic part of the exxon global sea level curve partly derived from correlatable strata within the same palaeogeographical domain is likely to reflect pulses of tectonically induced subsidence rather than eustatic sea level changes

offshore prolongation of caledonian structures and basement characterisation in the western barents sea from geophysical modelling this study interprets the potential field of the western barents shelf at a crustal scale and characterises the basement underlying the deep basins in the southwestern barents sea comparing potent

patterns of basement structure and reactivation along the ne atlantic margin a lineament pattern on the ne atlantic margin is discussed illustrated by gravity and magnetic images in the norwegian sea and reviewed in the context of onshore field evidence while most possible fault trends exist three major sets predominate a ne sw left stepping lineament set defines the gross geometry of the margin while interposing northerly trends impose a rhomboidal geometry at a variety of scales the margin is segmented by nw se transfer zones sometimes involving significant offsets the principal trends are primarily a function of mesozoic cenozoic plate wide extensional stress fields certain proterozoic and caledonian lineaments were however opportunistically reactivated according to the extension direction caledonian ne sw orogen oblique shears typified by the more trondelag fault zone were reactivated via jurassic strike slip or oblique slip and were further exploited during cretaceous early cenozoic extensional episodes leading to continental break up jurassic e w extension may also have reactivated n s faults existing in the basement or generated in duplex systems between the ne sw shears precambrian and caledonian basement lineaments striking at a low angle to the extension direction probably predisposed the formation of major transfer zones

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

seismic interpretation and characterization of anhydrite caprocks in the tromso basin sw barents sea abstract the origin of anhydrite caprocks found in many evaporite basins is currently under debate existing models in the literature for anhydrite formation include rotated stratigraphic layering rotated crestal caprock and diagenetic anhydrite in this work we interpret high quality 2d seismic reflection data to understand the processes associated with anhydrite caprock formation our study focuses on anhydrite caprock formation in the tromso basin which represents one of several underexplored salt basins in the arctic we use well log data and seismic stratigraphic as well as seismic attribute analyses to characterize the anhydrite layers associated with salt diapirs our results reveal that the anhydrite layers are high amplitude reflections at the crests which are often found close to the seabed and lateral caprocks on the flanks of salt diapirs a third class of anhydrite layers is folded faulted and boudinaged intrasalt stringers encased by the salt diapirs lateral caprocks in the tromso basin are formed in response to rotated crestal caprock failure the crestal caprocks are secondary in origin occur at shallow depths and are formed as insoluble residues from the dissolution of halite by the ingress of basinal fluids into the tops of diapirs anhydrite stringers or floaters originate from tectonic related multi dimensional salt flow salt diapirs in the tromso basin are associated with varied anhydrite caprocks their formation cannot be fully explained using a single model our work demonstrates from seismic reflection data the occurrence of caprock events that formed progressively on the flanks of salt diapirs due to local folding

seismo and neotectonics in finnmark kola peninsula and the southern barents sea part 1 geological and neotectonic framework abstract as a background for assessing the seismo and neotectonics of the finnmark kola peninsula region emphasis has been directed towards the lineament framework involving a careful examination of digital landsat tm imagery integrated with a variety of data sets ranging from geophysics and digital elevation models to microtectonics based on a detailed field structural control of many of the multiphase lineaments in this 70 000 km2 area of the northeastern part of the fennoscandian shield as well as microscopic investigation of the fault mylonites and breccias five principal lineament sets were distinguished of the nw se polyphasal megafractures the murmansk shear zone carries geological and isotopic evidence of an archaean tectonothermal history and demarcates an important terrane boundary lineaments irrespective of their trends were classified according to their significance in the regional geological framework some lineaments are clearly associated with gravity and aeromagnetic anomalies and probably extend to deep crustal levels quite a few of the prominent faults within lineament zones were reactivated in post glacial times in one area in finnmark core drilling through a se dipping post glacial reverse fault has confirmed its listric shape at depth earthquake focal mechanisms for this same fault are presented in the second part of this dual contribution

fault kinematics and localised inversion within the troms finnmark fault complex sw barents sea abstract the areas bounding the troms finnmark fault complex are affected by complex tectonic evolution in this work the history of fault growth reactivation and inversion of major faults in the troms finnmark fault complex and the ringvassoy loppa fault complex is interpreted from three dimensional seismic data structural maps and fault displacement plots our results reveal eight normal faults bounding rotated fault blocks in the troms finnmark fault complex both the throw depth and displacement distance plots show that the faults exhibit complex configurations of lateral and vertical segmentation with varied profiles some of the faults were reactivated by dip linkages during the late jurassic and exhibit polycyclic fault growth including radial syn sedimentary and hybrid propagation localised positive inversion is the main mechanism of fault reactivation occurring at the troms finnmark fault complex the observed structural styles include folds associated with extensional faults folded growth wedges and inverted depocentres localised inversion was intermittent with rifting during the middle jurassic early cretaceous at the boundaries of the troms finnmark fault complex to the finnmark platform additionally tectonic inversion was more intense at the boundaries of the two fault complexes affecting middle triassic to early cretaceous strata our study shows that localised folding is either a product of compressional forces or of lateral movements in the troms finnmark fault complex regional stresses due to the uplift in the loppa high and halokinesis in the tromso basin are likely additional causes of inversion in the troms finnmark fault complex

cyclic carbonate sedimentation in the upper triassic dachstein limestone austria the role of patterns of sediment supply and tectonics in a platform reef basin system abstract factors that controlled the deposition of i peritidal lofer cycles on a carbonate platform and ii platform margin reef slope deposits have been deduced at localities in the austrian alps the steinernes meer and hochkonig massif these locations are part of an entire late triassic platform reef basin system that is preserved with most original stratigraphic relationships intact platform lofer cycles shallow upward from a subtidal grainstone through a variety of intertidal dolomitic mudstones to a supratidal weathering horizon soil lofer cycles show random non hierarchical stacking patterns limited lateral continuity varied progradation directions complete shoaling 98 of cycles and very low stratigraphic completeness only 1 20 exponential frequency distributions of cycle thickness suggest random aperiodic cycle deposition rather than regular deposition in response to regular eustatic sea level oscillations sediments in the adjacent reef complex record storms and the lateral migration of sand shoals and stromatolite capped banks not sea level fluctuations and intermittent subaerial exposure on the basis of these observations in contrast to many previous interpretations lofer cycles are interpreted to be mostly autocycles formed within a tidal flat island system by lateral migration of wide low emergent banks separated by shallow subtidal areas preservation potential of individual cycles is thought to have been low reworking was almost certainly very important in this system extensional regional tectonics in the late triassic exerted a long term control over the development of the tidal flat island system on the platform top and appears to have left a tectonic overprint in lofer cycle successions differential subsidence of individual platforms across the region is suggested by substantial regional thickness variations 1200 3000 m in the norian rhaetian platform carbonates of the northern calcareous alps two important tectonic deepening events in the steinernes meer section almost caused platform drowning and correlate with a lowermost rhaetian transgression in the western tethys many other tectonic events may have gone unrecorded on the platform within a 716 m thick measured succession of lofer cycles intervals of enhanced paleokarst development nd stacked intertidal to supratidal beds are present with 20 75 m vertical spacing these platform units are interpreted to represent prolonged periods in which greater areas of the platform were occupied by intertidal to supratidal sediments these units correlate with thick units of debris flows on the reef slope what may be tectonic highstands the result of a vertical tectonic movement are recorded as packstone to grainstone deposition on the reef slope a holistic model driven by aperiodic fault controlled downdropping resulting in switching loci of sediment export patterns from a continuously operative subtidal carbonate factory the reef complex best explains vertical facies patterns in the platform and reef slope successions it is not a static sea level model although thi d fourth and fifth order eustasy is not required the model could explain the sporadic occurrence of shallowing up cycles in the adjacent kossen basin late triassic eustatic sea level fluctuations were ineffective in controlling sedimentation as a result of the processes described above

biofilm origin of clay coated sand grains the presence of clay sized particles and clay minerals in modern sands and ancient sandstones has long presented an interesting problem because primary depositional processes tend to lead to physical separation of fine and coarse grained materials numerous processes have been invoked to explain the common presence of clay minerals in sandstones including infiltration the codeposition of flocculated muds and bioturbation induced sediment mixing how and why clay minerals form as grain coats at the site of deposition remains uncertain despite clay coated sand grains being of paramount importance for subsequent diagenetic sandstone properties we have identified a new biofilm mechanism that explains clay material attachment to sand grain surfaces that leads to the production of detrital clay coats this study focuses on a modern estuary using a combination of field work scanning electron microscopy petrography biomarker analysis and raman spectroscopy to provide evidence of the pivotal role that biofilms play in the formation of clay coated sand grains this study shows that within modern marginal marine systems clay coats primarily result from adhesive biofilms this bio mineral interaction potentially revolutionizes the understanding of clay coated sand grains and offers a first step to enhanced reservoir quality prediction in ancient and deeply buried sandstones

spatial and temporal distribution of microbially induced sedimentary structures a case study from siliciclastic storm deposits of the 2 9 ga witwatersrand supergroup south africa abstract microbially induced sedimentary structures miss arise from the interaction of microbial mats with the physical sedimentary dynamics of shallow marine settings the structures occur in siliciclastic deposits of paleo archean age to modern where they record biostabilization and baffling trapping and binding of photoautotrophic microbenthos in the brixton formation witwatersrand supergroup south africa erosional remnants and pockets wrinkle structures and oscillation cracks include carbon and pyrite rich filament like textures that resemble modern trichomes of cyanobacteria c isotope ratios of 22 0 1 indicate potential photoautotrophy the miss occur at the turning points of regression transgression and are restricted to a specific sedimentary facies characterized by 2 20 cm thick fine sandstone beds predominantly composed of quartz the sandstone beds display ripple marks which record moderate hydraulic reworking this spatial and temporal distribution of miss in the brixton formation is consistent with occurrences of those structures in comparable environments throughout earth history