fault reactivation and structural inversion backarc and intraplate compressive deformations example of the eastern sunda shelf indonesia the tectonic evolution of the eastern sunda platform in indonesia is revealed by the study of seismic profiles and comprises three general tectonic periods during the cenozoic extension with graben infill from the paleogene to the early miocene a tectonically quiet period with only broad subsidence and a middle miocene recent period of folding inversion and thrusting these structures reveal changes in the intraplate stress field which was controlled by the changes in the boundary conditions of the plates collisions on the northern and eastern sides and interplate coupling southward along the java subduction zone inversions often occurred without reactivation of pre existing normal fault planes at the upper levels of these faults the factors controlling these deformations are discussed with special interest placed on the conditions for the potential reactivation of cohesionless normal faults inversion and reactivations were mostly controlled by the orientation of the pre existing fault planes in relation with the regional stress field and by the tectonic stress regime in a strike slip regime effective principal stresses 1 and 3 horizontal with 1 2 3 the optimum conditions for reactivation in isotropic rocks are pre existing faults that strike close to the potential two vertical conjugate failure planes the same mechanical properties as for pre existing fault prevail in such conditions strike slip movements and reverse strike slip movements and associated en echelon folds were generally observed in a compressive regime 1 and 2 horizontal with 1 2 3 typical steeply dipping normal faults are difficult to reactivate by slip movements we suggest that reverse slip movements occurred in the deeper levels of faults and were accommodated by flexure above the pre existing fault planes and the inversion of grabens the strongly inverted grabens are those whose orientation is perpendicular to the regional compression nevertheless with strong regional shortening large uplifts and thrust faults were observed with reactivation in the form of reverse or reverse strike slip movements along pre existing steeply dipping normal fault planes

tertiary uplift and inversion history in the north celtic sea basin and its influence on source rock maturity abstract tertiary uplift and basin inversion have been widely recognized in the area of the north celtic sea basin offshore ireland but the magnitude and timing of the various events have not been well documented an understanding of these events is important because recent basin history generally has a major influence on hydrocarbon source rock maturity levels a multi disciplinary approach was used to investigate the timing and nature of uplift in the north celtic sea basin involving seismic data interpretation well log correlation vitrinite reflectance measurement apatite fission track analysis and a cretaceous chalk group isopach and velocity study both regional uplift and compressive inversion can be interpreted to have occurred based on missing geological section compressive reactivation of earlier normal faults and basin centred uplift two tertiary erosion events are recognized a regional uplift in the palaeocene and compressive inversion characterized by basin doming and fault reversal probably associated with an oligo miocene phase of the alpine orogeny separating these was a period of basinal deposition in the eocene to oligocene a map of the magnitude of erosion generated as a result of the two events shows that the amount of uplift is quite variable in the northeast part of the basin where the later event was most severe uplift was as much as 1100 m reconstruction of the basin geometry before inversion together with thermal modelling at selected well locations suggests that upper jurassic source rocks reached maturity for oil generation only in the central portion of the basin whereas lower jurassic source rocks entered the gas window in much of the basin prior to tertiary uplift

development and hydrocarbon potential of mesozoic sedimentary basins around margins of north atlantic the late triassic early jurassic rift basins of iberia offshore eastern canada and the continental shelf of western europe are fragments of a formerly coherent northeast trending rift system that probably formed as a result of tensional stress between europe africa and north america the separation of europe north america and iberia was preceded by a late jurassic early cretaceous rifting phase that is clearly distinct from the earlier mesozoic rifting episode and was little influenced by it the two periods of rifting are separated by a middle jurassic relatively tectonically quiet period the distribution of hydrocarbon finds within the rift basin suggests that the best prospects are in areas where the two rifting episodes are superimposed lack of mature source r cks in the later mesozoic rift basins and an unfavorable temporal relationship between hydrocarbon generation and tectonic activity in the early mesozoic basins are proposed as explanations for the apparently poor hydrocarbon prospectivity of large areas of the mesozoic basins

syntectonic sedimentation rigs and fault reactivation in the coal measures of britain rigs are sediment bodies that occupy linear arcuate and ringed depressions in coal seam roofs and are interpreted as the sites of pools that formed on a peat surface the form of the rigs indicates that their origin is due to contemporary tilting of the peat surface during movement attributed to activity of a nearby contemporary fault subsequent movement ultimately led to the formation of a coal seam split at a later date the fault was reactivated but with a different sense of movement

statistical storm time examination of mlt dependent plasmapause location derived from image euv the location of the outer edge of the plasmasphere the plasmapause as a function of geomagnetic storm time is identified and investigated statistically in regard to the solar wind driver imager for magnetopause to aurora global exploration image extreme ultraviolet euv data are used to create an automated method that locates and extracts the plasmapause the plasmapause extraction technique searches a set range of possible plasmasphere densities for a maximum gradient the magnetic local time mlt dependent plasmapause results are compared to manual extraction results the plasmapause results from 39 intense storms are examined along a normalized epoch storm timeline to determine the average plasmapause l shell as a function of mlt and storm time the average extracted plasmapause l shell follows the expected storm time plasmapause behavior the results show that during the main phase the plasmapause moves earthward and a plasmaspheric drainage plume forms near dusk and across the dayside during strong convection during the recovery phase the plume rejoins the corotationally driven plasma while the average plasmapause location moves farther from the earth the results are also examined in terms of the solar wind driver we find evidence that shows that the different categories of solar wind drivers result in different plasmaspheric configurations during magnetic cloud driven events the plasmaspheric drainage plume appears at the start of the main phase during sheath driven events the plume forms later but typically extends further in mlt

structural analysis and kinematic evolution of the inverted central south celtic sea basin abstract the central south celtic sea basin shows excellent examples of tectonics and sedimentation relationships as evidenced by detailed geological interpretation of a local grid of seismic profiles these relationships together with balanced restored geological cross sections and block diagrams have been used to unravel the post variscan evolution of this part of the celtic sea basin three sedimentary mega sequences separated by two erosional surfaces have been recognized overlying a deformed palaeozoic basement in this area 1 permo triassic jurassic syn rift mega sequence sedimentation of the lowest part of this succession is strongly controlled by extensional faults whereas the rest of the sequence indicates much less fault control lateral extent of these rocks is also controlled by the disposition of the palaeozoic basement which appears as an elevation in the pembrokeshire ridge area where no sedimentation occurs 2 cretaceous post rift mega sequence 3 tertiary post rift mega sequence the cretaceous and tertiary successions are more extensive than permo triassic jurassic sediments covering the central south celtic sea basin and the pembrokeshire ridge the structural framework displayed by the syn rift and post rift sequences is very different thus the general structure beneath the jurassic cretaceous late cimmerian unconformity consists of a wsw ene trending fault system and related folds this resulted from an extensional phase which led to a sub basin compartmentalization of the area and a subsequent inversional event which caused significant reverse movement along previous extensional structures early cretaceous erosion was responsible for an important and unequal denudation the timing of the switch between extension and inversion cannot be determined due to early cretaceous erosion overlying the jurassic cretaceous unconformity cretaceous sediments are slightly deformed by broad anticlines formed during early tertiary mainly as a result of tightening of previous folds the tertiary sequence shows a subhorizontal disposition responsible for the present day smooth bathymetric relief of the south celtic sea basin

the permian to jurassic stratigraphy and structural evolution of the central cheshire basin new seismic reflection data reveal details of the permo triassic basin fill in the central cheshire basin the seismic stratigraphy indicates that the permian and triassic succession is far thicker than previously estimated seismic data and backstripping of the preserved permian to early jurassic sedimentary succession suggest that at least two phases of fault controlled subsidence occurred in early permian and early triassic times an intra triassic unconformity is seen on the seismic data near the top of the sherwood sandstone group this may equate with the hardegsen unconformity it is possible that this unconformity was generated by syn extensional regional uplift accompanying lithospheric thinning the gross morphology and location of the faults on the eastern margin of the cheshire basin are interpreted to be at least locally controlled by extensional re activation of a westwards dipping reverse fault possibly an extension of the pontesford linley lineament

salt as a fluid driver and basement as a metal source for stratiform sediment hosted copper deposits the source of copper for stratiform sediment hosted copper deposits is considered to be redbed clastics situated stratigraphically below the deposits however for one of the principal copper provinces in the world the zambian copperbelt there is insufficient thickness of redbeds to constitute a viable source numerical modeling demonstrates that high salinity sedimentary brines generated beneath a halite seal will develop convective hydrothermal plumes that penetrate through the redbeds deep into the crystalline basement despite its low permeability and regardless of the availability of cross stratal conduits this greatly expands the volume of the potential metal source for this style of ore deposit

petroleum seepages and impregnations in great britain abstract this paper documents 173 occurrences of surface petroleum seepages and impregnations in great britain a brief description is given of the seven main areas where they are found the descriptions range from pore fillings of bitumen to steady flows of oil and gas the principal areas in which seepages are found are as follows the orcadian basin of north east scotland the midland valley of scotland the flanks of the pennines the welsh borderlands cornwall the dorset coast of the wessex basin and the south eastern weald stratigraphically the seepages range from caledonide basement to holocene peat the principal sources for the petroleum are devonian oil shales orcadian basin carboniferous shales and coals midland valley pennines welsh borderlands devon and cornwall and the liassic wessex and wealden basins several anomalous seepages are recorded from welsh and scottish basement there are three clearly defined styles in which the seepages occur many are found where permeable carrier beds unconformably overlie impermeable basement around the margins of basins orcadian basin midlands carboniferous basin others are fault related especially in the wessex and wealden basins the seepages in the cornish tin mines are best explained as sourced from the culm series and drawn by the convective flow of connate waters into the thermal chimneys of the granite intrusions

transdimensional love wave tomography of the british isles and shear velocity structure of the east irish sea basin from ambient noise interferometry we present the first love wave group velocity and shear velocity maps of the british isles obtained from ambient noise interferometry and fully non linear inversion we computed interferometric inter station green s functions by cross correlating the transverse component of ambient noise records retrieved by 61 seismic stations across the uk and ireland group velocity measurements along each possible inter station path were obtained using frequency time analysis and converted into a series of inter station traveltime datasets between 4 and 15 seconds period traveltime uncertainties estimated from the standard deviation of dispersion curves constructed by stacking randomly selected subsets of daily cross correlations were observed to be too low to allow reasonable data fits to be obtained during tomography data uncertainties were therefore estimated again during the inversion as distance dependent functionals we produced love wave group velocity maps within 8 different period bands using a fully non linear tomography method which combines the transdimensional reversible jump markov chain monte carlo rj mcmc algorithm with an eikonal raytracer by modelling exact raypaths at each step of the markov chain we ensured that the non linear character of the inverse problem was fully and correctly accounted for between 4 and 10 seconds period the group velocity maps show remarkable agreement with the known geology of the british isles and correctly identify a number of low velocity sedimentary basins and high velocity features longer period maps in which most sedimentary basins are not visible are instead mainly representative of basement rocks in a second stage of our study we used the results of tomography to produce a series of love wave group velocity dispersion curves across a grid of geographical points focussed around the east irish sea sedimentary basin we then independently inverted each curve using a similar rj mcmc algorithm to obtain a series of one dimensional shear velocity profiles by merging all 1d profiles we created a fully three dimensional model of the crust beneath the east irish sea the depth to basement in this model compares well with that averaged from seismic reflection profiles this result is the first 3 dimensional model in the uk with fully quantified uncertainties it shows basin depths and basement structures and their concomitant uncertainties

structural and tectonic setting of the permo triassic basins of northwest europe abstract the permo triassic basins of nw europe formed by i late orogenic spreading of the variscan mountain belt eventually leading to ocean floor formation in the mid atlantic ii continental rifting propagating south from the arctic and iii thermal subsidence following carboniferous volcanic activity in the north sea spreading values in the northernmost north sea west of shetland and west and southwest of britain are relatively high but the sediments are dominantly continental the permo triassic rifting affected lithosphere thickened during caledonian and variscan orogenesis however subsidence associated with the arctic rifting together with global sea level changes allowed marine incursions into the north sea producing the large zechstein salt basins interference of the different basin formation mechanisms led to a complex three dimensional fault pattern and multidirectional extension across britain and the north sea this fault pattern formed the basic framework for subsequent jurassic and cretaceous basin formation

late mesozoic reactivation of variscan faults in the north celtic sea basin ireland abstract three major ene trending reactivated fault systems downthrow to the north west in the north western part of the north celtic sea basin they control the location of three mesozoic half grabens the location of the faults is determined by the underlying basement structures these are variscan in age although they exploit older caledonide trends comparison of the variscan structures identified in the area with regional structures suggests a series of imbricate thrust features these structures reactivated during the mesozoic controlled both the location and depositional histories of the half graben basins in the region

olivine dolerite intrusionsin the fastnet basin sills of olivine microgabbro and olivine dolerite 0 5 180 m thick intrude lower liassic hettangian sinemurian sediments in the fastnet basin a sw extension of the n celtic sea basin about lat 50 n long 10 w the evidence of 3 wells and 2300 km of seismic reflection profiles indicates 6 major sills and sill complexes and 3 possible igneous centres or plugs a high level sill may intrude lower cretaceous sediments and one plug apparently deforms cretaceous reflectors k ar ages on separated biotites from a thick sill intruding liassic sediments gave 170 4 ma bajocian this sill contains 30 olivine fo 70 73 20 clinopyroxene magnesian salite 45 plagioclase an 60 78 with accessory magnetite ilmenite edenitic hornblende ti phlogopite apatite zircon spinel in olivine and sulphides alteration to serpentine minerals chlorite sericitic mica and leucoxene is sporadic the magmatism in the fastnet province thus appears to have been active from the mid jurassic to the early tertiary related initially to the time of initial rifting between the european and american plates and subsequently to their final separation between greenland and rockall and associated thulean magmatism

the east irish sea basin from caterpillar to butterfly a thirty year metamorphosis in the thirty years since the award of the first licenses the east irish sea basin has emerged as a significant hydrocarbon province this paper first lists some of the occasionally almost arbitrary events that led to the first success in the basin the discovery of the morecambe field in 1974 an attempt is made to review progress over those thirty years in certain topics namely 1 stratigraphy 2 structure 3 sedimentology 4 diagenesis the platy illite problem and others 5 uplift and inversion 6 hydrocarbon sources and types 7 east irish sea basin analogues the paper concludes by summarizing the current state of knowledge 1995 represented the thirtieth anniversary of the first award of licences in the east irish sea basin eisb the twenty sixth anniversary of the drilling of the first wells and the twenty first anniversary of the discovery of the south morecambe field it is perhaps appropriate to look back on some of the crucial events of the last thirty years and on some of the earlier concepts and interpretations with a view to seeing how these last have progressed or been found wanting undoubtedly the biggest spur to exploration was the discovery in 1974 by the british gas corporation subsidiary hgb ltd of the south morecambe field how a fledgling organization came to discover this 5 tcf gas accumulation in its first venture is itself noteworthy key events that led to this discovery might be summarized as follows 1 the wish of the government in power in 1969 to foster a national presence in the exploration of british waters by allowing the then gas council to take 100 interests in eisb blocks 2 the readiness of the gas council to exploit this opportunity 3 the unwillingness of the council s main north sea partner to participate in the proposed application with its offer of a firm well 4 the unwillingness of other majors to join the application 5 the informal gift by gulf in 1973 of the logs of wells 110 8 1 and 2 on the basis of a gentleman s agreement that hgb would likewise make data available from any wells it

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

the sticklepath lustleigh fault zone tertiary sinistral reactivation of a variscan dextral strike slip fault dextral strike slip movement on the sticklepath lustleigh fault zone slfz is indicated by displacements of permian and older rocks previous authors have inferred that the main dextral movement which caused these displacements was post permian and noting the presence of small tertiary pull apart basins along the fault zone probably of tertiary age however the geometry of these early tertiary pull apart basins indicates sinistral rather than dextral strike slip movement we present an alternative model for the history of the sticklepath lustleigh fault zone summarized below 1 late variscan strike slip movement with a total displacement of up to 10 km produced the slfz and offset dextrally an earlier variscan thrust 2 extensional reactivation of this thrust led to rapid permo triassic subsidence in the crediton trough and a dextrally offset neighbour the hatherleigh outlier 3 approximately 6 km of early tertiary sinistral movement on the slfz produced small pull apart sedimentary basins and reduced the net dextral offset across the fault 4 in mid tertiary times minor dextral movements on the slfz may have produced reverse faulting on the margins of the tertiary basins

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

the tectonic evolution of the north celtic sea and cardigan bay basins with special reference to basin inversion abstract the morphology and structural evolution of the north celtic sea basin ncsb and cardigan bay basin cbb are in large part controlled by reactivation of basement features of caledonian and possibly variscan origin from earliest triassic until maastrichtian times sedimentation was almost continuous initially in a rapidly subsiding rift system and finally in a progressive passive sag phase at the onset of the alpine orogeny both basins experienced spectacular inversion along readily identifiable axes the inversion takes the form of a compressive reactivation and reversal of the pre existing growth faults and a broad regional upwarping of the cretaceous depocentre the amount of inversion varies depending on the location within the basin but values in excess of 1000 m are possible by utilising regional seismic data the timing of inversion can be estimated as occurring between maastrichtian and eocene times which correlates with the so called laramide pulse of the alpine orogeny

tertiary erosion magnitudes in the east midlands shelf onshore uk sonic velocities from the upper and middle chalk the kimmeridge clay the lias and the bunter sandstone were used to quantify apparent erosion i e amount of missing section in the welton 1 and cleethorpes 1 wells of the east midlands shelf onshore uk apparent erosion was determined with reference to sonic velocities in 150 wells the uk southern north sea area apparent erosion at cleethorpes 1 is estimated as 1 4 km from the kimmeridge clay lias and bunter sandstone and 1 6 km from the upper and middle chalk and at welton 1 as 1 6 km from the bunter sandstone and 1 7 km from the lias the consistency of results from the different units analysed increases confidence in the results with respect to compaction studies based on a single stratigraphic unit estimates of missing section in this study are generally greater than those previously published for the east midlands shelf but they are consistent with recent estimates from apatite fission track analysis

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

source rock burial history and seal effectiveness key facets to understanding hydrocarbon exploration potential in the east and central irish sea basins the timing of hydrocarbon generation from carboniferous source rocks and the lack of evapo rites within the triassic mercia mudstone group seal sequence have contributed significantly to the lack of exploration success in the triassic sherwood sandstone play of the central irish sea basin apatite fission track analysis afta combined with vitrinite reflectance data from the central irish sea basin and adjacent areas indicates that maximum burial and heating of the carboniferous section was achieved by the early cretaceous the long residence period for trapped hydrocarbons generated in the early cretaceous combined with the ineffectiveness of the mercia mudstone group seal caused by the absence of annealing halites and the presence of thief sandstones led to hydrocarbon loss through trap breaching during subsequent tectonic events in contrast maximum burial of carboniferous source rocks in the central east irish sea hydrocarbon province was achieved in the late cretaceous early tertiary giving a shorter residence period for generated hydrocarbons the combination of a short residence period and the presence of a halite bearing mercia mudstone seal sequence significantly improved hydrocarbon retention within the sherwood sandstone reservoir if traps were episodically breached during the late tertiary they were recharged by the inversion process which caused gas expansion spill from charged traps and lateral remigration of hydrocarbons updip the inversion related pressure drop also caused retrograde condensate dropout from gas accumulations to provide a supply of late condensate for preferential spill and remigration

deep crustal features of the celtic sea from complementary processing on the swat data complementary processing develop by bano 1989 including automatic extraction of reflections and migration of deep seismic data are applied to the swat south west approaches traverse deep seismic profiles in the celtic sea the automatic extraction of reflection gives a more reliable definition of the basement under the deep celtic sea basins using migration we derive a more accurate geometry of these basins

hydrocarbon prospectivity in the irish sea area insights from recent exploration of the central irish sea peel and solway basins abstract compared with the prolific success of the triassic play in the east irish sea basin eisb the lack of hydrocarbon discovery in neighbouring permo triassic basins of the irish sea has been an enigma however recent exploration of the peel solway and central irish sea basins has provided new insights into the geology of these basins and the controls upon hydrocarbon prospectivity in the irish sea area regional seismic interpretation suggests that 12 of the 15 exploration wells drilled in the basins adjacent to the eisb tested valid structural closures at top triassic reservoir level re evaluation of the irish sea petroleum system reveals that although effective reservoirs occur in the lower middle triassic ormskirk sandstone formation and evaporites in the middle upper triassic mercia mudstone group provide a regional top seal the major factor controlling hydrocarbon prospectivity is the limited presence of effective source rocks in the underlying carboniferous section a further control upon prospectivity is the timing of hydrocarbon migration from those areas where carboniferous source rocks were deposited and preserved the namurian basinal marine oil and gas prone shales which form the principal source of hydrocarbons for the triassic play in the eisb are restricted to an east west fairway extending from the eisb into the kish bank basin rocks of this age are absent from the peel and solway basins as a result of variscan uplift and erosion however palaeogeographical reconstructions based on well and outcrop data suggest that even if preserved the depositional environment was not conductive to the formation of marine oil and gas prone source rocks well and seismic data suggest that rocks of namurian age were not deposited in the central irish sea area which remained high during much of dinantian and namurian time potential source rock development in the central irish sea area is therefore limited to the westphalian section which is organically lean and dominated by intertinitic kerogens potential hydrocarbon traps in the central irish sea peel and solway basins formed largely as a result of early cretaceous tectonism and were subsequently modified by fault reactivation during tertiary uplift phases trap formation appears to postdate the most likely timing of hydrocarbon charge which this study suggests would have occurred in late triassic and jurassic time hydrocarbon entrapment in the eisb may have been favoured by limited early cretaceous uplift coupled with renewed hydrocarbon generation and re migration during early tertiary time it is concluded that the remaining prospectivity of the triassic play in the irish sea area is likely to be restricted to the proven play fairway within the eisb

discussion of energy dissipation and turbulent production in weak hydraulic jumps by e mignot and r cienfuegos fil romagnoli martin universidad nacional de rosario facultad de ciencias exactas ingenieria y agrimensura centro universidad rosario de investigaciones hidroambientales argentina consejo nacional de investigaciones cientificas y tecnicas argentina

investigation of two elemental error sources in boat mounted acoustic doppler current profiler measurements by large eddy simulations measurements of water discharge and flow velocities in riverine and tidal environments are commonly made with acoustic doppler current profilers adcps mounted on a moving boat this paper presents results of high resolution large eddy simulations les conducted to investigate two elemental error sources in adcp measurements from a moving boat one of these errors is due to the flow disturbance induced by the boat mounted adcp the other error is due to the lack of flow homogeneity in horizontal layers assumed by the adcp algorithm to compute orthogonal velocities from the measured radial velocities along the acoustic beams the first error is investigated by comparing les results for an undisturbed flow field with les results for a flow field disturbed by a boat mounted adcp the second error is investigated by comparing the velocities beneath the adcp simulated by les with virtual adcp velocities which are obtained by applying the adcp algorithm to les velocities data mined along the path of the acoustic beams of the virtual profiler the distribution of the reynolds stresses beneath the adcp estimated with the adcp algorithm from the virtual adcp velocity data are also compared with those obtained from the les solutions for both the undisturbed and adcp disturbed flows results show that the boat significantly disturbs the flow field and that the disturbed flow field is qualitatively different from the flow fields observed around an isolated adcp no boat

a two layer lithospheric compressional model for the tertiary uplift of the southern united kingdom reflection seismic records show that many of the mesozoic sedimentary basins of the southern united kingdom were compressed and uplifted inverted during the late cretaceous tertiary recent quantitative studies based on apatite fission track analysis and chalk porosity data show that uplift and erosion although concentrated in the inverted basins was regional and not limited to the recognized areas of crustal shortening inversion a two layer or heterogeneous model of lithospheric compression similar to two layer models of lithospheric extension may account for this pattern of uplift upper lithospheric shortening is accommodated by reverse movement on major reactivated extensional detachments causing inversion of pre existing basins pure shear shortening of the lower lithosphere is decoupled and may be laterally displaced from that in the upper lithosphere lower lithospheric shortening and thickening displaced from that in the upper lithosphere causes initial subsidence due to the submersion of cold dense lithosphere into the surrounding asthenosphere subsequent thermal re equilibration of the lower lithosphere may have generated the uplift without attendant crustal shortening witnessed by apatite fission track and chalk porosity data

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

evidence of synsedimentary tectonic movements in the triassic halite of cheshire during the triassic north west europe was subjected to tensional stresses which resulted in the formation of a complex system of rapidly subsiding grabens and wrench faulted basins this pattern of regional crustal extension which is part of the larger scale mesozoic break up of the pangean megacontinent is related to the triassic opening of the tethys ocean in southern europe and rifting in the arctic north atlantic and is a prelude to the jurassic opening of the southern north atlantic1 great thicknesses of generally continental sediments often with salt deposits accumulated in the triassic basins which were mainly avolcanic in western britain a complex series of fault bounded basins extended from the western approaches and channel area northwards to the irish sea and includes the worcester graben and the cheshire basin the present study of the halite formations in the cheshire basin shows evidence for penecon temporaneous fault movements these were a feature of triassic times but it is rare that such movements can be detected so precisely as is the case here

the control of basin evolution on patterns of sedimentation and diagenesis an example from the mississippian great orme north wales the mississippian north wales platform is located on the margins of the east irish sea basin and has been little studied over the last 30 years the exposed visean limestones provide new insights into the deposition porosity evolution distribution of dolomitization and pb zn and cu mineralization on the north wales carbonate platform this is of relevance to the characterization of fault related dolomite hydrocarbon reservoirs and age equivalent mississippi valley type mineral deposits in particular the study demonstrates the intimate relationship between sedimentation basin scale tectonism and post depositional fluid flux depositional cyclicity is marked with metre scale upward shallowing cycles in which pervasive marine and meteoric calcite cements occlude matrix porosity and syndepositional fractures consequently subsequent burial diagenetic replacive dolomitization is matrix selective and cements are primarily restricted to fractures seven phases of dolomite are defined based on texture and cathodoluminescence petrography with phases d1 d3 as the most volumetrically significant dolomite phases d0 d2 are matrix replacive cross cutting stratigraphy and locally fingering along beds for several metres dolomite phases d3 d7 are hosted by faults and fractures and also line vugs evidence of telogenesis is recorded where burial diagenetic products are post dated by calcite cements precipitated from meteoric fluids dolomitization probably occurred during the mississippian and continued into the pennsylvanian pb zn mineralization is also interpreted to have occurred during the pennsylvanian associated with variscan tectonism overall the north wales platform displays a more complex paragenesis than age equivalent platforms in the pennine basin owing to multiple phases of burial and exhumation the study demonstrates the importance of linking burial history to detailed field and petrographical data to understand and predict the spatial and temporal controls on diagenetic processes and products within syn and post rift sequences

solar and interplanetary sources of major geomagnetic storms dst 100 nt during 1996 2005 1 we present the results of an investigation of the sequence of events from the sun to the earth that ultimately led to the 88 major geomagnetic storms defined by minimum dst 100 nt that occurred during 1996 2005 the results are achieved through cooperative efforts that originated at the living with a star lws coordinated dataanalysis workshop cdaw held at george mason university in march 2005 on the basis of careful examination of the complete array of solar and in situ solar wind observations we have identified and characterized for each major geomagnetic storm the overall solar interplanetary solar ip source type the time velocity and angular width of the source coronal mass ejection cme the type and heliographic location of the solar source region the structure of the transient solar wind flow with the storm driving component specified the arrival time of shock disturbance and the start and ending times of the corresponding ip cme icme the storm driving component which possesses a prolonged and enhanced southward magnetic field bs may be an icme the sheath of shocked plasma sh upstream of an icme a corotating interaction region cir or a combination of these structures we classify the solar ip sources into three broad types 1 s type in which the storm is associated with a single icme and a single cme at the sun 2 m type in which the storm is associated with a complex solar wind flow produced by multiple interacting icmes arising from multiple halo cmes launched from the sun in a short period 3 c type in which the storm is associated with a cir formed at the leading edge of a high speed stream originating from a solar coronal hole ch for the 88 major storms the s type m type and c type events number 53 60 24 27 and 11 13 respectively for the 85 events for which the surface source regions could be investigated 54 63 of the storms originated in solar active regions 11 13 in quiet sun regions associated with quiescent filaments or filament channels and 11 13 were associated with coronal holes remarkably nine 11 cme driven events showed no sign of eruptive features on the surface or in the low corona e g no flare no coronal dimming and no loop arcade etc even though all the available solar observations in a suitable time period were carefully examined thus while it is generally true that a major geomagnetic storm is more likely to be driven by a frontside fast halo cme associated with a major flare our study indicates a broad distribution of source properties the implications of the results for space weather forecasting are briefly discussed

stratigraphic and structural analysis of the late palaeozoic mesozoic of ne wales and liverpool bay implications for hydrocarbon prospectivity interpretation of seismic lines from the offshore ne wales area has provided information on the structural and stratigraphic evolution of the southern part of morecambe liverpool bay basin wide megasequence boundaries are present between the dinantian and overlying sequences and between the upper carboniferous and permo triassic megasequences geological information obtained from seismic lines has been used to construct an e w geological cross section and a basin analysis summary chart for the ne wales cheshire onshore area stratigraphic interpretations have been considered in an assessment of the petroleum potential of the region the distribution of carboniferous oil and gas prone source rocks is a key element in predicting hydrocarbon accumulations source rock maturity may have been reached in the offshore area prior to a phase of inversion and uplift during tertiary times fault controlled hydrocarbon traps generated during triassic jurassic rifting were modified during tertiary inversion and new structures were generated

shelf sheet sand reservoir of the lower cretaceous greensand north celtic sea basin offshore ireland core and log data show that the marine early to middle albian a sand of the aptian to lower cenomanian greensand gault interval north celtic sea basin offshore ireland was deposited as an approximately tabular sand body in shelf water depths the a sand is the major reservoir interval at kinsale head and ballycotton gas fields the reservoir sandstone is bioturbated variably glauconitic shell rich and least muddy toward its provenance in a local area of the irish massif and finer grained southeastward into the basin thickness and coarseness of the a sand are related in part to distance from a narrow area of the paleoshore bathymetric control of sand thickness was superimposed on proximal distal trends specifically thick intervals are inferred to have be n deposited in shelf lows and thin zones were deposited over bathymetric highs the a sand was not deposited as a ridge sand and positive relief on the depositional sand body appears to have been minor deposition of the greensand occurred during thermal subsidence of the north celtic sea basin following early cretaceous rifting overall late early cretaceous to late cretaceous transgression was interrupted by progradation of the a sand probably caused by a relative drop in sea level forced regression the a sand sheet consists of several units within the central depositional basin three slightly coarsening upward units up to 15 m thick probably are the consequence of high frequency fluctuations in sea level during progradation the top of the a sand consists of a several m ter thick very glauconitic muddy sandstone to sandy mudstone the upper unit accumulated in deepening water following the maximum lowstand

deciphering the late paleozoic to mesozoic tectono sedimentary evolution of the northern bohemian massif from detrital zircon geochronology and heavy mineral provenance from permian to late cretaceous the northern bohemian massif experienced a complex intra plate tectono sedimentary evolution involving development of at least four generations of sedimentary basins in different settings we examine this protracted evolution using stratigraphic changes in sediment provenance analyzed through heavy mineral assemblages and u pb detrital zircon geochronology by laser ablation icp ms in permian jurassic and late cretaceous successions the provenance data point to multiple temporally evolving sources ranging from local e g the west sudetic island through more distant from elsewhere in the bohemian massif to exotic likely derived from baltica the latter is interpreted as a trace of now completely eroded late jurassic to early cretaceous basin that once covered the lusatian lausitz block and received the baltica derived detritus from northerly fluvial and deltaic depositional systems we suggest that fill of this basin was recycled into the bohemian cretaceous basin during progressive unroofing of the west sudetic island a time slice reconstruction of the paleogeographic and tectono sedimentary evolution of the northern bohemian massif is then developed to show that periods of basin development and deposition early permian late early permian to early triassic middle jurassic early cretaceous and late cretaceous were interrupted by major depositional gaps middle triassic early jurassic mid cretaceous and post early campanian the mesozoic depositional episodes resulted from reactivation of major nw se strike slip fault zones due to stress transfer from the north atlantic rift during jurassic to early cretaceous overridden by the far field effect of convergence of iberia africa and europe during late cretaceous

influence of epoch time selection on the results of superposed epoch analysis using ace and mpa data 1 the influence of the reference time selection when conducting a superposed epoch analysis is examined for intense geomagnetic storms at solar maximum the events were selected according to the minimum pressure corrected dst dst being less than 100 nt solar wind data from ace are used along with near earth data from the magnetospheric plasma analyzer mpa instruments on the los alamos national laboratory operated geosynchronous spacecraft numerous choices for the zero epoch time are used ranging from the storm sudden commencement ssc the peak of the ring current enhancement minimum dst slope to the time of the storm peak minimum dst value when doing superposed epoch analysis sea the choice of the time stamp can be very important for different choices different storm characteristics are evident in the averaged data in the superposed ace data we find that when using the ssc as a time reference the ssc related jump in solar wind parameters is very well defined but near the storm peak bz does not apparently follow the well known criteria for intense storms bz 10 nt for more than 3 h even though this criterion is met by most of the individual storms selected for this study when the zero epoch time is chosen near the storm peak the jump in solar wind parameters is less distinct and eventually lost but the criterion for bz is met regarding the mpa data there are certain parameters that require the choice of a specific epoch time in order to produce a systematic behavior in the sea analysis and others that are less sensitive to this choice of epoch time since they appear to be less distinct in their temporal and spatial location for instance the nightside and morningside hot ion density and temperature are main phase traits and a zero epoch time near the peak of the ring current enhancement is required to make these features distinct

sedimentary structures sorby and the last decade henry clifton sorby pioneered in the last century the description and especially the hydrodynamic interpretation of sedimentary structures together with their use as palaeocurrent indicators research completed since the last syntheses were published a decade ago shows that work along these lines continues to be necessary and relevant particularly as regards the physical explanation of structures and to present significant challenges and opportunities perhaps the most pressing needs are for a better understanding of 1 bedforms in gravels silts and carbonate sediments 2 tidal and especially sand wave bedding 3 hummocky and swaley cross stratification and 4 soft sediment and dewatering structures in turbidites many sedimentary structures present a little exploited opportunity to quantify process rates and define short time periods from the rock record

errors in acoustic doppler profiler velocity measurements caused by flow disturbance acoustic doppler current profilers adcps are commonly used to measure streamflow and water velocities in rivers and streams this paper presents laboratory field and numerical model evidence of errors in adcp measurements caused by flow disturbance a state of the art three dimensional computational fluid dynamic model is validated with and used to complement field and laboratory observations of flow disturbance and its effect on measured velocities results show that near the instrument flow velocities measured by the adcp are neither the undisturbed stream velocity nor the velocity of the flow field around the adcp the velocities measured by the adcp are biased low due to the downward flow near the upstream face of the adcp and upward recovering flow in the path of downstream transducer which violate the flow homogeneity assumption used to transform beam velocities into cartesian velocity components the magnitude of the bias is dependent on the deployment configuration the diameter of the instrument and the approach velocity and was observed to range from more than 25 at 5 cm from the transducers to less than 1 at about 50 cm from the transducers for the scenarios simulated

thermal and tectonic history of the east midlands shelf onshore uk and surrounding regions assessed by apatite fission track analysis apatite fission track analysis has been used to study the thermal and tectonic history of the east midlands shelf and surrounding areas of onshore uk apatites from outcrops of palaeozoic crystalline basement give fission track ages between 300 29 and 420 31 ma which are the oldest yet reported in the uk region and reflect the relative stability of this cratonic region mean track lengths in these samples are between 12 and 13 m namurian and triassic sandstones from outcrop give apatite fission track ages between c 100 and c 390 ma with mean track lengths generally between 10 and 12 5 m distributions of single grain ages and track lengths suggest that all samples have been annealed implying exposure to higher temperatures since deposition with maximum palaeotemperatures reached some time in the 50 80 ma range prior to the onset of cooling samples from five exploration wells show consistent patterns in which apatite fission track ages decrease sharply from around or just less than the stratigraphic age at near surface to values in the 50 80 ma range at depths of c 1 2 km present temperatures of c 40 70 c showing that the samples studied have all been exposed to higher temperatures single grain ages and track length data suggest that maximum palaeotemperatures were attained at or before c 60 ma subsequent cooling was protracted and the data are compatible with two phases in the early and mid tertiary palaeotemperature analysis suggests that palaeo geothermal gradients were similar to present values and that elevated palaeotemperatures were due to greater depth of burial with cooling due to subsequent uplift and erosion estimates of uplift and erosion vary from c 1 1 5 km on the east coast around the humber estuary to c 2 2 km in the east midlands and southern pennines compilation of palaeotemperature estimates from all samples analysed from the uk onshore region shows that mesozoic burial and tertiary uplift has affected a wide area and that uplift was due to broad scale regional warping with recognized inversion axes being areas where uplift and erosion were particularly pronounced or where younger sediments and or inverted basinal structures allow the identification of uplift and erosion the recognition of late cretaceous early tertiary unconformities across wide areas of northwest europe both onshore and offshore suggests that the regional uplift and erosion may have been far more widespread than previously recognized this has important implications for hydrocarbon exploration in northwest europe

global basin classification system a proposed system classifies sedimentary basins worldwide into specific as well as general categories the geologic history of each basin may be subdivided into cycles using three parameters basin forming tectonics depositional sequences and basin modifying tectonics sedimentary basins may be simple with one or two tectonic sedimentary cycles or they may be complex polyhistory basins with many different cycles and events there are eight simple cycle types in this classification which cover continental continental margin and oceanic areas the eight basic cycle types their depositional fills and tectonic modifiers have been given letter and number symbols so that the specific geologic history of each basin may be written as a formula these formulas may then e compared and similarities or differences between basins noted

dependence of emic wave parameters during quiet geomagnetic storm and geomagnetic storm phase times as electromagnetic ion cyclotron emic waves may play an important role in radiation belt dynamics there has been a push to better include them into global simulations how to best include emic wave effects is still an open question recently many studies have attempted to parameterize emic waves and their characteristics by geomagnetic indices however this does not fully take into account important physics related to the phase of a geomagnetic storm in this paper we first consider how emic wave occurrence varies with the phase of a geomagnetic storm and the sym h ae and kp indices we show that the storm phase plays an important role in the occurrence probability of emic waves the occurrence rates for a given value of a geomagnetic index change based on the geomagnetic condition in this study we also describe the typical plasma and wave parameters observed in l and magnetic local time for quiet storm and storm phase these results are given in a tabular format in the supporting information so that more accurate statistics of emic wave parameters can be incorporated into modeling efforts

diachronous variscan late orogenic collapse as a response to multiple detachments a view from the internides in france to the foreland in the irish sea