quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

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

mechanics of basin inversion abstract the long term consequences of rifting for the thermal state of the deep crust and upper mantle reflect in part cooling induced by the reduction in heat production in the attenuated lithosphere and heating due to the burial of this heat production beneath the basin provided that the heat production is largely concentrated in the upper half of the crust these factors result in significant increases in temperature at deep crustal and upper mantle levels because the moho depth is likely to be reduced in the long term limit of an isostatically balanced basin these same factors may lead to slight cooling or slight heating of the moho depending on the nature of the basin fill for a brace goetze lithospheric rheology i e a rheology governed by a combination of frictional sliding and power law creep significant long term lithospheric weakening up to 5 per kilometre of basin fill accompanies basin formation when the lower crust is initially relatively strong and the basin fill is characterised by appreciable heat production and low thermal conductivity in contrast initially weak lower crustal rheologies may result in long term lithospheric strengthening evidence for basin inversion in the geological record may therefore imply that heat production is strongly concentrated in the upper half of the crust and under normal continental thermal regimes the lower crust is strong

structure of lower carboniferous basins of nw ireland and its implications for structural inheritance and cenozoic faulting abstract the geometry of lower carboniferous basins across the northern part of ireland is characterised by a gradual change in polarity of structure from a predominantly southward dipping fault system in northern ireland through the lough allen basin and into a mainly northward dipping fault system of connemara in the southwest this polarity change is reflected in the emergence of northward facing uplifted footwall blocks such as at croagh patrick and the ox mountains in the southwest with southward facing blocks in the northeast despite these structural changes there is a great degree of along strike continuity of lower carboniferous structure strain and displacement with the system forming a link between comparable sized and coeval basins in northern england and scotland to the east and the canadian maritime provinces to the west the spatial distribution of carboniferous normal faults suggests that caledonian structure such as the fair head clew bay line plays an important role in the localisation of post caledonian strain although the reactivation of individual caledonian structures may be less common the terrain of the west of ireland is strongly influenced by major carboniferous faults offsetting the base carboniferous unconformity as opposed to previously suggested cenozoic normal faulting of a tertiary peneplain

representative elementary area of shale at the mesoscopic scale abstract the representative elementary area rea of two shales callovo oxfordian claystone and tournemire argillite that are actively studied in the framework of the deep disposal of radioactive waste have been estimated from two mineral maps by classical methods i e the box counting and statistical approaches and by different microstructural descriptors i e the two point probability function lineal path function percolation length and variogram the classical box counting method provides estimates of the rea size of the clay fraction in the range from 129 m to 441 m consistent with estimates obtained from the literature on other shales however these estimates show an extreme sensitivity to the chosen e threshold or error and a wide scatter thereby bringing the statistical homogeneity of both maps into question although the two point probability function and lineal path function infer lower bounds of the rea size these microstructural descriptors are relevant to demonstrate the microstructural anisotropy of both shales due to the alignment of nonclay grains parallel to bedding at the study scale the results from the two point probability function and variogram undoubtedly confirm that the tournemire mineral map is not statistically homogeneous with regard to its mineral composition this aspect it makes difficult to interpret the results and even questions the rea size determination of this particular map finally our set of results allow us to recommend the use of the two point probability function and variogram to preliminarily validate the statistical homogeneity of maps under study before calculating the rea size using conventional methods e g the box counting and statistical approaches

impact of in situ stress and fault reactivation on seal integrity in the east irish sea basin uk abstract despite having been affected by several stages of exhumation during the cretaceous and cenozoic the contemporary stress state of the east irish sea basin eisb is poorly characterised as the basin is mature in terms of exploitation of hydrocarbons future exploration beyond the conventional sherwood sandstone group reservoir triassic necessitates a greater understanding of the in situ stress field while proposed natural gas storage and carbon sequestration schemes also require detailed stress field information using petroleum well data the in situ stress field of the eisb has been characterised to assess the mechanical seal integrity a strike slip stress regime most likely prevails in the basin meaning the maximum horizontal stress shmax is the greatest of the principal stresses interpretation of stress orientation data suggests that shmax is oriented 152 12 consistent with mean stress orientations across the wider region associated with plate boundary forces some degree of structural control appears to influence the orientation of shmax with orientations locally aligned sub parallel to major permo triassic basin bounding faults fault reactivation risk is evaluated through modelling the pore pressure increase required to induce failure on pre existing faults vertical faults striking 30 from shmax are optimally oriented to become reactivated under elevated pore pressure conditions for any project relying on an element of fault seal for the containment of buoyant fluids at the average reservoir depth of 800 m pore pressure increase should be less than 3 3 mpa to avoid reactivating pre existing optimally oriented faults higher pressure increases would be required to initiate reactivation of faults with other orientations vertical faults striking perpendicular to shmax are least likely to become reactivated and in the absence of halite seal integrity would instead be limited by caprock strength and capillary entry pressure major faults affecting the basin have been analysed for their slip tendency ratio of shear to normal stress which provides an indication of their susceptibility to become reactivated although the analysis is limited due to lack of an accurate 3d representation of the fault network the results suggest that many of the fault orientations observed in the eisb exhibit high slip tendencies including n s striking faults to the north and west of the east deemster fault where the shmax orientation is nw se faults striking perpendicular to shmax such as the lagman fault are least likely to become reactivated due to higher normal stresses that inhibit frictional sliding while faults striking parallel or very close to shmax also exhibit low slip tendency as they are not subjected to significant shear stresses

palaeostress analysis a contribution to the understanding of basin tectonics and geodynamic evolution example of the permian cenozoic tectonics of great britain and geodynamic implications in western europe abstract microtectonic analysis in association with tectonic sedimentological observations enables us not only to define palaeostress tensors but also to date each of them such a study carried out in central and northeastern england and in southernmost wales has permitted us to point out several tectonic stages during the permian cenozoic period 1 inferred from syn sedimentary faulting in the late permian series the permian early triassic tectonic regime is characterised by a nnw sse oriented extension 2 during the late triassic to the early late jurassic an e w to ene wsw oriented extension was acting as suggested by syn sedimentary normal faulting in keuper lias and middle dogger sediments and post sedimentary normal faulting in oxfordian sediments 3 the following tectonic event probably started during the malm and was particularly active during the early cretaceous it was characterised by a n s to nne ssw oriented extension and was associated with an e w to wnw ese oriented strike slip tectonic regime transtension 4 a locally observed nw se oriented transpressional strike slip tectonic regime is thought to correspond to the laramide inversion phase of the middle paleocene 5 the later tectonic event is characterised by a n s oriented transpressional strike slip regime and affects a paleocene tholeiitic dyke cleveland dyke it is supposed to be synchronous with the so called eocene pyrenean to the early miocene helvetic compressional stages these paleostress tensors are compared with others defined in france the benelux countries and germany and are also collated to the tectonic evolution of oil basins assessed from geophysical analyses these comparisons raise discussions about the paleostress distribution within the geodynamic evolution of the west european shelf

spatially correlated anomalous 40ar 39ar age variations in biotites about a lithologic contact near simplon pass switzerland a mechanistic explanation for excess ar forty four biotite samples collected about a lithologic contact between pelite and amphibolite were analyzed for 40ar 39ar and demonstrate the importance of bulk ar diffusivity and system geometry factors not usually considered in the interpretation and collection of 40ar 39ar age data the resulting 40ar 39ar apparent ages range from 11 30 0 05 ma to 17 90 0 10 ma the ages and excess argon contents are spatially and lithologically correlated the pelite samples all yield ages clustering around 12 ma the age expected for cooling through biotite closure 360 c in this region of the alps ages in the amphibolite biotites are older showing a smooth trend between 15 ma at the contact with the pelite to 18 ma 34 cm from the contact this data shows that characterization of the ar closure age for biotite in a given system should not rest on a single sample as otherwise irresolvable differences in age between samples within the same outcrop can exist a generalized mechanistic model for excess argon is presented the presence or absence of excess ar depends on an intrinsic system parameter t the transmissive timescale which is the characteristic time for 40ar to escape through the local intergranular transporting medium itm to some sink for argon to prevent buildup of geochronologically significant excess 40ar t must be very short relative to the true closure age of the mineral a fortran code including radiogenic ar production diffusive loss of ar from biotite and bulk ar diffusion through the itm has been developed application of numerical modeling suggests that the time averaged effective bulk diffusivity deffar in the biotite amphibolite rock during early retrograde cooling is 2 2 1 0 10 8 m2 yr assuming steady state conditions the first such measurement available numerical modeling also provides information about the transmissivity and geologic history specific to the field site including a drop in deffar at 15 5 1 0 ma the timing of this drop is related to coincident rheological changes and the onset of rapid exhumation of the nappe stack

physical explanation of the formation and evolution of inversion zones and marginal troughs inversion zones are elongate structures some tens of kilometers wide and up to hundreds of kilometers long that have deformed in response to compression and produced topography inversion zones in the alpine foreland are mainly associated with mesozoic grabens and troughs and although very important in the geologic picture the conditions of their formation and evolution and their regional geologic significance are not entirely understood the internal structure of inversion zones is variable and depends on details in the pre inversion setting the inversion inducing stress field and the sedimentary fill however on a larger scale most inversion zones share certain principal observational features which sample the physical structure and the rheologic properties of the lithosphere and thereby provide an opportunity to test hypotheses of lithospheric rheology and dynamics the quantitative model presented in this paper explains how inversion zones and the associated marginal troughs are related to lithospheric zones of differential shortening and regional isostatic compensation of the induced topography

experimental mechanical compaction of reconstituted shale and mudstone aggregates investigation of petrophysical and acoustic properties of sw barents sea cap rock sequences abstract this study investigates petrophysical and acoustic properties of experimentally compacted reconstituted samples of seal sequences from the southwestern barents sea the aggregates were collected from drill cuttings of mudstone and shale formations of two exploration wells 7220 10 1 salina discovery and 7122 7 3 goliat field the washed and freeze dried samples were characterized for grain size distributions geochemical analyses and mineralogical compositions a total of 25 compaction tests 12 dry and 13 brine saturated were performed with a maximum effective vertical stress of 50 mpa the laboratory measurements demonstrated that petrophysical and acoustic properties of argillaceous sediments can change within a sedimentary basin and even within a given formation the results show that the collected aggregates from goliat field are compacted more compared to salina discovery the maximum and minimum compaction are measured in samples collected from snadd and fuglen formations respectively the final porosity of brine saturated specimens varies between 5 and 22 the ultrasonic velocity measurements depict that samples with the same porosity values can have a broad range of velocity values the resulting compaction trends in this study were compared to published compaction curves for synthetic mixtures of quartz and clay all compaction trends show higher porosity reduction than the silt fraction with 100 quartz comparison of experimental compaction result of each mudstone and shale aggregate with its corresponding acquired well log data helps to delineate the burial history and exhumation in the study area a net exhumation of 950 m and 800 m is estimated at salina and goliat wells respectively the outcomes of this study can provide insights for hydrocarbon prospect discovery in a pre mature sedimentary basin in terms of exploration and production and also for geological co2 storage sites the experimental results may provide information for well log and seismic interpretation basin modeling and seal integrity of investigated horizons

quantification of the factors controlling the presence of excess 40 ar or 4 he abstract a quantitative physical model is presented which includes the factors that control the presence or absence of internally derived excess 40ar or excess 4he in geological systems in particular the model incorporates the transport and partitioning properties of the rock surrounding the mineral of thermochronologic interest and illuminates the related effects on the amount of excess 40ar or 4he preserved in the system modeling of a simplified 1 d rock column bounded by an external sink for 40ar or 4he shows that a steady state excess 40ar or 4he profile develops the magnitude of which is determined by a system parameter called the transmissive timescale t the characteristic time required to reach this steady state depends upon t and the total local sink capacity tlsc wherein the important role of local matrix mineral and fluid phases is incorporated together these two system parameters t and tlsc determine the evolution of excess 40ar or 4he buildup within a system above the closure temperatures of all minerals involved an analytical expression for the 1 d system describing the evolution of excess 40ar or by analogy 4he in a particular potassium bearing or u th bearing mineral located at a distance l from an external sink has been derived empirically from model results 40 ar age equivalent l t t ar 2 1 exp 5 2 t t ar 1 tlsc ar local matrix minerals perhaps most notably quartz may act as important sinks for 40ar except in the most fluid rich systems where fluids dominate and thus are fundamental in controlling and limiting thermochronologically problematic excess 40ar in neighboring potassium bearing minerals in general the model provides a rigorous means of predicting excess noble gas content residence release and transport within the compositionally variable and thermally evolving crust

triassic jurassic development of the st george s channel basin offshore wales uk abstract isopach maps and backstripped tectonic subsidence plots from the triassic jurassic of the st george s channel basin reveal significant departures from current models of extensional basin development i rifting was highly protracted with discrete increments of crustal extension spanning ca 120 my ii substantial syn kinematic sediment on the footwalls of major faults records pure shear sub seismic scale deformation to have been important during regional triassic extension forward modelling of depth converted seismic interpretations is used to test the notion of combined pure and simple shear and to quantify the distribution of crustal extension between large and sub seismic scale faults the models indicate that triassic subsidence was generated by ca 2 5 km extension on major faults and 10 km extension by sub seismic scale faulting in fault bounded compartments jurassic extension was dominated by large scale faults whereas in the areas of overlap between major fault segments jurassic extension was taken up chiefly by sub seismic scale faulting comparison of measured vitrinite reflectance vr and vr modelled from heatflow history yielded by the forward models supports this scheme of episodic pure shear dominated extension this research highlights the inherent difficulty in using seismic interpretation in isolation from quantitative subsidence and or thermal history data to identify syn and post kinematic sedimentary sequences furthermore it provides an opportunity to more fully reconstruct mesozoic basin development in the west of uk area which in the cheshire central and east irish sea basins is largely precluded by erosion of post triassic strata

development of a novel image analysis procedure to quantify biological porosity and illuvial clay in large soil thin sections among other driving forces climate change may lead to significant modifications of soil properties through variations of the intensity and dynamics of a number of soil processes including the especially sensitive and ubiquitous processes of bioturbation and illuviation progress toward the quantification of these processes needs to be made as a first step in order to ascertain or predict the impact of climate change in this study we develop and validate through an exhaustive accuracy assessment a digital 2d image analysis method adapted to large soil thin sections leading to the quantification characterization and classification of pores and illuvial clay features considered diagnostic of bioturbation and illuviation respectively the need to consider large soil thin sections 14 x 6 cm stems from observations that areas from 684 mm2 to more than 5 000 mm2 are needed to obtain representative measurements of fragments of illuvial clay papules and porosity associated with earthworms respectively whereas the soil heterogeneity in thin sections of such a large size prohibits the use of classical global and colorimetric image analysis procedures we succeeded to quantify and characterize the porosity and illuvial clay features with accuracies as high as 96 for porosity and 92 for illuvial clay by carefully considering different levels of soil organization from aggregates to individual illuvial clay features quantification of the size and the shape of pores and of illuvial clay features makes it possible to develop morphological classifications distinguishing pores of biological origin earthworms or roots from others or clay coatings and infillings from papules all these data are particularly useful to better characterize underlying soil processes results suggest that the proposed methodology provides an accurate and representative quantification of biological porosity and illuvial clay features in large thin sections we argue that the use of this approach could be extended to study and quantify bioturbation and illuviation intensities at the profile scale

the representative elementary area rea in studies of quantitative soil micromorphology abstract a fundamental question to be answered for studies in quantitative micromorphology at varying scales is what is the minimum area on a soil thin section or block that is required to represent the pedofeature of interest based on its distribution in soil space this paper investigates the necessity of establishing a representative elementary area rea in the study of pedofeatures for quantitative analysis of pedofeatures it also proposes a means by which an absolute rea may be determined this was achieved by suggesting that the rea for voids on 3 5 4 7 cm soil thin sections is attained at the area where the measurements made on a parameter in three successive areas of measurements do not change 10 relative to the next greater area of measurement using this method the rea for void pedofeatures in the size range of 50 to 2000 m on 3 5 4 7 cm thin sections from silt loam agricultural soils of southern ontario was investigated the rea was achieved for total void area between 50 and 500 m in diameter in 99 97 of 98 of the thin sections whereas for total perimeter 97 95 of 98 of the sections achieved the rea the average rea between 50 and 500 m in diameter for total void area and perimeter was 5 09 and 5 00 cm 2 respectively the average rea between 500 and 2000 m for total void area and perimeter was 6 73 and 4 95 cm 2 respectively it is suggested that the rea determination should be performed in every quantitative soil micromorphological study in order that the parameter of interest is an adequate representation of that feature in soil space

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

palaeothermal and compaction studies in the mochras borehole nw wales reveal early cretaceous and neogene exhumation and argue against regional palaeogene uplift in the southern irish sea the north atlantic continental margins have been subject to widespread exhumation although the timing magnitude and causes of this uplift and erosion are debated exhumation is thought to be most severe across the irish sea basin system western uk and recent years have seen an increasing emphasis on the role of palaeogene underplating as the primary mechanism of uplift we present a study of palaeothermal and compaction data from the mochras borehole nw wales located near the presumed locus of exhumation mochras penetrated thick successions of lower jurassic and oligo miocene sediments our results indicate that both these successions experienced considerably deeper burial prior to early cretaceous and neogene exhumation respectively apatite fission track analysis afta and vitrinite reflectance data from the borehole reveal evidence for exhumation related cooling episodes beginning during the cretaceous 150 80 ma and cenozoic 50 0 ma regional afta results and stratigraphic constraints refine the timing estimates to the early cretaceous 120 115 ma and neogene 20 0 ma estimates of exhumation magnitudes during these episodes based on palaeothermal and compaction data are c 2 5 km and c 1 5 km respectively palaeothermal data provide no evidence for elevated palaeogene palaeotemperatures indicative of deeper burial and thus question the basis of palaeogene exhumation

natural restoration of soils on mine heaps with similar technogenic parent material a case study of long term soil evolution in silesian krakow upland poland abstract the study focused on the variability in properties and pedogenesis of soils located at post mining sites in the old industrial area in the silesian krakow upland southern poland the investigated sites were comparable in terms of zn pb mining history soil texture and climate but differed in duration of pedogenesis which started after the waste materials were accumulated and covered 30 70 100 and about 400 years of self restoration a wide spectrum of soil parameters including zn pb and cd contents dehydrogenase activity pores space and aggregate formation organic matter decomposition were studied by chemical and micromorphological image analyses with the aim of tracing the evolution of soils and checking if the results of image analysis could be integrated with results obtained by chemical and biological determinations stepwise progressive regression equations were obtained to establish the parameters that varied over time zn pb and cd contents exceeded several times permissible values in all soils studied the evolution of these soils was significantly different from each other during the process of self restoration of the soil the contents of organic carbon and total nitrogen available potassium and phosphorus including dehydrogenase activity increased with increasing age of soils pedogenesis resulted also in the increasing amounts of aggregates of small sizes which were set close to one another together with narrow pores which was able to store water a synchronisation between soil properties obtained by chemical biological and micromorphological analyses indicating their usefulness for the demonstration of temporal changes

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

crustal trace of a hot convective sheet the iceland plume has played an influential role in the evolution of the north atlantic ocean and margins over the past 60 m y it is believed that this plume formed at the conjunction of a tetrad of hot subvertical convective sheets the impingement of these hot sheets at the base of the lithospheric lid caused decompressional melting generating substantial quantities of high temperature magma that were injected into the cold overlying lid over the next 10 m y these sheets partly coalesced to form a crudely axisymmetric plume head here we analyze the lithospheric fingerprint of one of these hot convective sheets by forward and inverse modeling of densely sampled wide angle seismic data in conjunction with gravity observations we determined the three dimensional shape of magmatic underplating trapped within the lithosphere the injection of this melt into the lithosphere generated substantial permanent and minor transient uplift of earth s surface predicted and measured amounts of consequent denudation and sedimentation agree within error temporal variations in the patterns of deposition and oceanic circulation adjacent to the convective sheet show its evolution through time and space our results suggest that this linear sheet has probably been directly and indirectly responsible for cyclical events over 60 m y these events have 0 5 1 and 4 6 m y periodicities the existence of which may help to elucidate the dynamic behavior of convective sheets during and after impingement thus in particular circumstances surficial geological processes yield an indirect record of mantle convection and melt generation processes

micromorphological and x ray µct study of orthic humic gleysols under different management conditions abstract the aim of this study was to evaluate the spatial distribution of different void types and fe mn oxide segregations in the a and b horizons of three orthic humic gleysols from an uncultivated area and two long time experimental plots an unfertilized continuous maize plot and a fertilized maize oats alfalfa alfalfa rotation plot from woodslee ontario in view of the fact that numerous x ray ct studies have obtained diverse results in principal because of a different resolution of the analyzed ct imagery the utilization of standardized classes in the quantification of similar features e g soil pores seems necessary in order to obtain comparable results this x ray study performed on polished blocks is an example of how ct quantitative results related to volume and area of pores and fe mn oxide segregations can be interpreted in connection with micromorphological characterizations of thin sections of the same samples using typical micromorphological classes separated based on size and shapes of the analyzed features maximum pore volume values noticed in the ah horizon of the uncultivated soil and in the bg horizon of the soil from the rotation plot were considered an indication of a more favourable aero hydric regime in these soils compared to the soil from the continuous maize plot the lowest volumes of fe mn oxides were found in the same horizons porosity and pore morphology have a clear influence in the evolution of redox processes and implicitly in the formation of typical redoximorphic pedofeatures in gleysols the thin section analysis revealed that fe mn nodules and concretions as well as fe depletion areas were more frequent and better developed in the soil from the continuous maize plot than in the other soils it was concluded that the examination of the soil features from the perspective of defined size and shape groups may represent a basis for a standardized spatial characterization of soil and for the interpretation of certain pedogenetic processes

isostatic compensation of quaternary vertical crustal motions coupling between uplift of britain and subsidence beneath the north sea new data from offshore and onshore regions confirm the view that the quaternary uplift of britain and subsidence beneath the north sea are coupled mediated by lower crustal flow induced by the lateral pressure gradient caused by climate driven surface processes most measured onshore uplift rates in both upland and lowland localities are only applicable since the mid pleistocene revolution beforehand generally lower rates prevailed earlier oligocene pliocene phases of uplift and subsidence had typically even lower rates furthermore the western margin of the north sea depocentre was 200 km farther from the modern coastline of north east england in the earliest cenozoic complex isostatic adjustments occurred in response to the magmatism associated with the iceland mantle plume the contemporaneous land surface relative to the present day rock column in northern england was typically 1500 m od however this activity died out during the palaeogene the main effect of these events on the modern isostatic configuration was via the emplacement of thick mafic underplating which now constricts the mobile lower crustal layer explaining the late cenozoic ultra stability of ireland the evidence enables interpretations of the present day topography of britain as static caused by the iceland mantle plume or actively developing in response to plate motions or plate boundary forces to be excluded

measuring plume related exhumation of the british isles in early cenozoic times mantle plumes have been proposed to exert a first order control on the morphology of earth s surface however there is little consensus on the lifespan of the convectively supported topography here we focus on the cenozoic uplift and exhumation history of the british isles while uplift in the absence of major regional tectonic activity has long been documented the causative mechanism is highly controversial and direct exhumation estimates are hindered by the near complete absence of onshore post cretaceous sediments outside northern ireland and the truncated stratigraphic record of many offshore basins two main hypotheses have been developed by previous studies epeirogenic exhumation driven by the proto iceland plume or multiple phases of cenozoic compression driven by far field stresses here we present a new thermochronological dataset comprising 43 apatite fission track aft and 102 u th sm he ahe dates from the onshore british isles inverse modelling of vertical sample profiles allows us to define well constrained regional cooling histories crucially during the paleocene the thermal history models show that a rapid exhumation pulse 1 2 5 km occurred focused on the irish sea exhumation is greatest in the north of the irish sea region and decreases in intensity to the south and west the spatial pattern of paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies and the timing of uplift and exhumation is synchronous with emplacement of the plume related british and irish paleogene igneous province bipip prior to the paleocene exhumation pulse the mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long lived rifting history of the neighbouring offshore basins the extent of neogene exhumation is difficult to constrain due to the poor sensitivity of the ahe and aft systems at low temperatures we conclude that the cenozoic topographic evolution of the british isles is the result of plume driven uplift and exhumation with inversion under compressive stress playing a secondary role

the representative sample size in shale oil rocks and nano scale characterization of transport properties abstract the experimental determination of petrophysical properties for shale rocks is dependent on measurement techniques and often produces inconsistent results alternatively high resolution three dimensional imaging techniques coupled with image analysis and direct numerical simulations have been employed to estimate these parameters in shale samples nevertheless the application of these results at the core and reservoir scales are uncertain due to the limited size of imaged samples here focused ion beam milling and scanning electron microscope tomography is employed to study transport properties for the three upper layers of the bakken formation the representative size of each shale sample is characterized pore types their connectivities and pore size distributions are studied using high resolution micrographs and their implications to mass transport at the macro scale are discussed porosity and permeability of the samples are also calculated from three dimensional images and the results are compared to experimentally measured values at the core scale it is shown that the representative size of shale samples is dependent on the scale of analysis and could range from tens to hundreds of microns we found that the upper bakken layer is rich in clay and organic materials the dominant pore type is pores associated with organic matter and no connected porosity was observed in the preserved core samples in contrast the middle bakken layers upper and lower layers have about 1 connected porosity mainly as intraplatelet pores within clay aggregates and interparticle pores resulting in permeabilities between 4 and 30 d moreover comparison of pore types and modeled flow pathways suggests the presence of water wet connected pores in the middle bakken rocks whereas mainly oil wet pores are present in the upper bakken shale

multifractal analysis of discretized x ray ct images for the characterization of soil macropore structures a correct statistical model of soil pore structure can be critical for understanding flow and transport processes in soils and creating synthetic soil pore spaces for hypothetical and model testing and evaluating similarity of pore spaces of different soils advanced visualization techniques such as x ray computed tomography ct offer new opportunities of exploring heterogeneity of soil properties at horizon or aggregate scales simple fractal models such as fractional brownian motion that have been proposed to capture the complex behavior of soil spatial variation at field scale rarely simulate irregularity patterns displayed by spatial series of soil properties the objective of this work was to use ct data to test the hypothesis that soil pore structure at the horizon scale may be represented by multifractal models x ray ct scans of twelve water saturated 20 cm long soil columns with diameters of 7 5 cm were analyzed a reconstruction algorithm was applied to convert the x ray ct data into a stack of 1480 grayscale digital images with a voxel resolution of 110 microns and a cross sectional size of 690 690 pixels the images were binarized and the spatial series of the percentage of void space vs depth was analyzed to evaluate the applicability of the multifractal model the series of depth dependent macroporosity values exhibited a well defined multifractal structure that was revealed by singularity and renyi spectra the long range dependencies in these series were parameterized by the hurst exponent values of the hurst exponent close to one were observed indicating the strong persistence in variations of porosity with depth the multifractal modeling of soil macropore structure can be an efficient method for parameterizing and simulating the vertical spatial heterogeneity of soil pore space

modelling the plate driving mechanism this paper demonstrates how sub lithospheric loading gives rise to plate interior stresses and plate boundary forces the stressing of the lithosphere resulting from plume heads in the upper mantle hot spots from low density asthenospheric upwelling beneath ocean ridges and from dense subducting slabs has been modelled by finite element analysis it is first demonstrated how a sub lithospheric load exemplified by a sub continental plume head produces local deviatoric stress in the strong upper lithosphere within a plate interior region it is shown that a 500 km wide region of anomalous density averaging 8 kg m 3 between 100 km and 400 km depths gives rise to a deviatoric tension of 75 mpa in a 20 km thick strong layer forming the upper lithosphere above the deep buoyant load the large stresses in the strong layer are caused by the shear drag and excess pressure exerted by the buoyant load when such a stress system is cut across by a zone or plane of weakness then plate boundary forces and distant plate interior stresses are produced a weak zone beneath the crest is incorporated in a model of a normal ocean ridge and this yields a ridge push force of 2 5 10 12 nm 1 referenced to old ocean floor and deviatoric compression of about 40 mpa in old ocean floor a model of a ridge underlain by an anomalously low density upper mantle plume head yields a much larger ridge push force and large deviatoric compressions of nearly 100 mpa extend into the bordering continents subduction pull slab pull and trench suction of about 4 5 10 12 nm 1 is modelled for a 300 km deep slab separated from the overriding plate by a weak fault and collision pull is shown to result from downbulging lower lithosphere beneath collision mountain ranges

mid cenozoic post breakup deformation in the passive margins bordering the norwegian greenland sea abstract since the initial breakup of the norwegian greenland sea in early eocene time chron 24b 53 7 ma the conjugate passive margins have been subject to compression extension magmatism and broad uplifts and subsidence mid to late cenozoic compressional doming basin inversion and reverse faulting occurred predominantly offshore within the rheologically weak deep cretaceous depocenters on the norwegian margin the domes seem to have formed primarily in middle eocene to early oligocene and in early miocene while doming in the faroes rockall region developed in late paleocene to early eocene oligocene and mid to late miocene we suggest that the main driving force was plume enhanced ridge push a testable working hypothesis is that discrete phases of compression were associated with periods of high plume flux in addition the oligocene chron 13 35 ma change in plate motion appears to have generated local shear adjustments along pre existing basement weaknesses forming compressional structures in the overlying sedimentary section this change in plate motion was first manifest by significant extension between the sw barents sea and the conjugate nne greenland margin and led to spreading along the knipovitch ridge mid cenozoic extension and magmatism also preceded the development of the kolbeinsey ridge the associated separation of the jan mayen microcontinent from east greenland must have been strongly influenced by the position of the iceland plume center in addition to the change in extension direction with respect to initial breakup of the norwegian greenland sea in early eocene time the mid cenozoic extension and magmatism is a post breakup phenomena widely spaced areas of neogene uplift occurred along all bordering margins these enigmatic uplifted areas acted as nucleation sites for growth of ice caps and initiated large glacial deposits that built out on the adjacent shelves

accurate estimates of the spatial pattern of denudation by inversion of stacking velocity data an example from the british isles accurate measurement of the temporal and spatial variation of uplift and denudation would improve our understanding of the way in which mountain building and mantle convection modify the earth s surface here we show that inverse modeling of stacking velocity data from seismic reflection data sets is a potentially useful tool for obtaining spatially resolved denudation estimates along and across continental shelves unlike many techniques for measuring denudation our approach is not restricted to outcrop or borehole locations although it is important to calibrate results with other measurements of denudation we have inverted 2200 stacking velocity analyses from a dense network of two dimensional seismic reflection lines which surround the british isles this region was chosen because there is a well known signal of cenozoic uplift and denudation which is big enough to be detectable using our approach despite simplified assumptions about the way in which porosity varies with depth our offshore denudation estimates are consistent with outcrop patterns and accord with published denudation measurements furthermore stacking velocity estimates agree with measurements obtained by analyzing sonic velocity logs from selected boreholes a region encompassing the british isles has evidently undergone variable amounts of denudation during cenozoic times however significant denudation 1 5 km is concentrated in discrete areas such as off nw scotland and parts of the irish sea the magnitude of denudation changes significantly over short 10 km distances implying that differential uplift and erosion have been important factors in creating the present day denudation pattern

thermal history reconstruction using apatite fission track analysis and vitrinite reflectance a case study from the uk east midlands and southern north sea apatite fission track analysis afta is a method of obtaining ther mal history information in sediments in sections that have been hotter in the past afta provides estimates of maximum palaeotemperatures and the time at which a sedimentary section began cooling from maximum palaeotempera tures it is useful for studying the thermal history of sequences containing source rocks and can provide information critical to the understanding of the timing of oil generation integration of afta and vitrinite reflectance vr data allows a coherent thermal history framework to be established and a formal method of analysing palaeogeothermal gradients has been developed by combining afta and vr data this approach allows definition of the major facets of thermal history based on directly measurable parameters rather than on assumed values of palaeo heatflow and provides rigorous estimates of the amount of uplift and erosion the case study demonstrates the application of this approach to the east midlands shelf region here afta data have revealed an episode of maximum palaeotemperatures prior to cooling commencing at around 60 ma combined afta and vr data show that this cooling was due to kilometre scale early ter tiary uplift and erosion under near normal geothermal gradients our estimates of uplift and erosion are significantly greater than those of pervious workers and show that uplift and erosion was not restricted to the recognized axes of inversion but was regional in extent this has implications for the evolution of source rock maturity in this region and in other basins in around the uk where afta has indicated early tertiary heating and where the extent and amount of tertiary uplift and erosion may have also been underestimated by previous workers apatite fission track analysis afta tm is a method of obtaining thermal history information in sediments and is particularly useful for studying the thermal history of sequences containing hydrocarbon source rocks as well as providing estimates of maximum palaeotemperatures afta provides a direct estimate of the time at which a sedimentary section began cooling from its maximum palaeotemperature a key advantage over traditional geochemical methods in many situations this knowledge is critical to the understanding of the timimg of oil generation and migration in relation to trap formation information on the timing of maximum palaeotempera ture can also be of significant value in the interpretation of vitrinite reflectance vr data and combination of afta and vr data allows a consistent integrated thermal history interpretation the afta technique is applied most usefully in sedimentary sections which have been hotter in the past than they are at the present day it is therefore applicable to large regions of britain and the uk continental shelf that have been subject to deeper burial in the past or affected by other sources of heating the basis of the technique has

gravity and geomorphological evidence for a large crustal bulge cutting across brittany france a tectonic response to the closure of the bay of biscay abstract moho undulations from the analyses of the gravity anomalies over brittany computed by incorporating various improvements in the classical filtering technique have been compared with deep seismic refraction data by progressively low pass filtering the gravity anomalies with increasing cut off wavelengths some distinct new anomaly trends associated with deep structures have become prominent comparisons with heat flow and wide angle seismic reflection results confirm that the sources of these anomalies are located at the lowest part of the crust in brittany the image of the moho undulations reveals the presence of a prominent n130 moho downwarp cutting across the superficial geological trends on the surface this trend corresponds to an active topographic uplift and indicates that the deep crustal bulge is still building up this structure is bounded by n130 dextral faults that are known to accommodate the actual closure of the bay of biscay west of brittany this shortening is also at the origin of an east west oriented bulge previously mapped with the same technique this bulge limits and postdates the subsidence of mesozoic and cenozoic basins of the celtic sea

shear deformation and eclogite formation within granulite facies anorthosites of the bergen arcs western norway the anorthosites of the bergen arcs contain two distinct metamorphic mineral assemblages which are stable under different p t conditions a granulite facies assemblage which equilibrated at t 800 900 c p 10 kbar is defined by the minerals plagioclase al rich diopside cpx i garnet gnt i scapolite orthopyroxene dark brown hornblende this assemblage is linked by corona structures to a primary magmatic mineralogy where coexistence of olivine and plagioclase limits the maximum crystallization pressure of the anorthosites to 8 kbar at 1200 c the anorthosites are transected by a series of fine grained shear zones in which the granulite facies assemblage is replaced by an eclogite mineralogy defined by omphacite cpx ii jd40 50 garnet kyanite epidote clinozoisite phengite quartz amphibole with plagioclase sometimes remaining in the marginal parts mineral compositions indicate equilibration conditions for the eclogite paragenesis of t 700 800 c p 16 19 kbar a series of textural and mineralogical changes which can be observed as the strain increases into the shear zones demonstrates that the eclogite mineralogy is formed at the expense of the granulite facies minerals during the early stages of shear zone development the eclogite mineralogy defines a strong mylonitic fabric which again is truncated by centimetres thick secondary shear zones containing clasts of both granulite and eclogite minerals these latter fine grained ultramylonites may be connected to uplift of this deep seated complex the eclogite shear zones are highly oblique to the granulite structures indicating that the eclogite shear zones formed under a new stress regime rb sr dating shows that the granulite facies assemblage formed in sveconorwegian time or earlier while minerals from shear zones define ages around 400 ma indicating a caledonian formation of the eclogites this work demonstrates the critical role of deformation in triggering metamorphic reactions whether the shear stress also was important in stabilizing the eclogite assemblages is not clear from the available data

an algorithm to calculate the gravity anomaly of sedimentary basins with exponential density depth relationships we derive wavenumber domain expressions to calculate the gravity anomaly of a body with irregular bounding surfaces and an exponential density depth relationship we apply the method to sedimentary basins which commonly have this type of geometry and density distribution the mathematical formulation also allows the exponential density depth relationship to be measured from an arbitrary irregular surface rather than the top surface using this arrangement the gravity anomaly of exhumed sedimentary basins can be predicted if the amount of eroded section can be estimated the corresponding inverse algorithms are also derived examples of the use of the forward algorithms from the galicia interior basin and the central irish sea basin are used to illustrate these methods

variability in spatial distribution of mineral phases in the lower bowland shale uk from the mm to μm scale quantitative characterization and modelling the microstructure of a highly laminated lower bowland shale sample is characterized at the micron to millimeter scale to investigate how such characterization can be utilized for microstructure based modelling of the shale s geomechanical behavior a mosaic of scanning electron microscope sem back scattered electron bse images was studied mineral and organic content and their anisotropy vary between laminae with a high variability in fracturing and multi micrometer aggregates of feldspars carbonates quartz and organics the different microstructural interface types and heterogeneities were located and quantified demonstrating the microstructural complexity of the bowland shale and defining possible pathways for fracture propagation a combination of counting box dispersion covariance and 2d mapping approaches were used to determine that the total surface of each lamina is 3 to 11 times larger than the scale of heterogeneities relative to mineral proportion and size the dispersion approach seems to be the preferential technique for determining the representative elementary area rea of phase area fraction for these highly heterogeneous large samples supported by 2d quantitative mapping of the same parameter representative microstructural models were developed using voronoi tessellation using these characteristic scales these models encapsulate the microstructural features required to simulate fluid flow through these porous bowland shales at the mesoscale

40 ar 39 ar thermochronology using alkali feldspars real thermal history or mathematical mirage of microtexture the multiple diffusion domain mdd theory of ar loss based on the 40ar 39ar method has been used to obtain thermal histories over tens of millions of years in the range 500 c to near surface temperatures of alkali feldspars from slowly cooled geological environments and recovered in situ from sedimentary basins and geothermal systems it assumes that ar diffuses in nature over geological time from the same domains and by the same processes that control its diffusion during laboratory step heating experiments mathematically the model has many stringent requirements the domains must form at t above those being modelled and must remain unchanged during geological time and during step heating must not interact must occur in discrete size ranges sharing one simple geometrical shape contain no compositional gradients in 40k and release ar into an infinite reservoir we describe the nature of possible diffusion domains and the fast pathways for diffusion between them known to exist in alkali feldspars from direct electron microscopic observations and explore their time temperature evolution based on established phase behaviour both over geological time and during step heating strain controlled microtextures whose morphology is controlled by the minimization of coherency strain energy do not provide fast pathways for ar loss and behave as crystallographically complex but single domains for ar subregular dislocations may form over a range of t in some strain controlled intergrowths but in nature the majority form closed loops and do not provide pathways to the crystal surface deuteric microtextures cut across strain controlled microtextures and are composed of microporous subgrain and grain mosaics with many pathways and a wide spectrum of possible domain sizes and shapes the deuterically altered zones provide pathways for ar diffusion out of the crystal although some ar is retained in fluid inclusions all microtextures likely to define diffusion domains form below 500 c over a range of t and in slowly cooled rocks of times the most important involve fluid feldspar reactions which can reset ar and continue to surface t feldspars in geothermal systems and young sedimentary basins are subject to ongoing chemical and microtextural changes because the microtextures are metastable during step heating experiments in the t range over which most ar is released domains and pathways for rapid diffusion of ar between domains will be significantly modified during step heating particularly above 750 c when departures from a simple arrhenius diffusion law are most marked pre melting is likely to be an important cause of complexity in ar loss behaviour few if any of the requirements of the mdd model are met and we conclude that thermal histories cannot be obtained from alkali feldspars using this method

regional velocity depth anomalies north sea chalk a record of overpressure and neogene uplift and erosion a normal velocity depth trend for the upper cretaceous danian chalk group is determined by identifying interval velocity data that represent maximum burial in areas unaffected by overpressuring these data are derived from 845 wells throughout the north sea basin data from pelagic carbonate deposits on a stable plateau constrain the trend for shallow depths positive velocity anomalies relative to the trend are mapped along the western and eastern margins of the north sea basin and reflect regional neogene uplift and erosion of up to 1 km along the present day limit of the chalk a hiatus at the base of the quaternary increases in magnitude away from the basin center where a complete cenozoic succession is found this hiatus is consistent in size with the missing section estimated from chalk velocities when allowance is made for the quaternary reburial of the chalk negative velocity anomalies in the central and southern parts of the basin outline an area within which overpressures in the chalk exceed 10 mpa equivalent to a burial anomaly greater than 1 km relative to the normal trend the chalk pressure system is primarily dependent on overburden properties because retention of overpressure generated by the load of the upper overburden depends on the thickness and sealing quality of the lower overburden therefore the chalk is considered to represent a regional aquitard and the hydrodynamic model of long distance migration within the chalk is rejected the neogene uplift and erosion of the margins of the north sea basin and the rapid late cenozoic subsidence of its center fit into a pattern of late cenozoic vertical movements around the north atlantic

palaeogene alpine tectonics and icelandic plume related magmatism and deformation in northern ireland the cenozoic tectonic history of nw europe is generally attributed to some combination of three principal controlling factors north atlantic opening alpine collision and formation of the icelandic mantle plume using constraints from the high resolution tellus aeromagnetic survey of northern ireland we show that palaeogene tectonics can be attributed to approximately north south alpine related compression forming nnw sse trending dextral and ene wsw trending sinistral conjugate strike slip faults with the latter defined by kilometre scale displacements along reactivated caledonian or carboniferous faults this tectonism was however punctuated by pulsed magmatic intrusive and extrusive events including four distinct dyke swarms that are attributed to ne sw to east west directed plume related extension although this evidence shows for the first time that north south alpine compression was periodically overwhelmed by the dynamic stresses and uplift associated with pulsed mantle plume related deformation associated strike slip faulting may have controlled the locus of volcanic activity and central igneous complexes and the location of sedimentary depocentres

signature of cryptic sedimentary basin inversion revealed by shale compaction data in the irish sea western british isles 1 inversion is one of the most common modes of intraplate deformation and a primary mechanism of sedimentary basin exhumation the key criterion for identification of basin inversion is the contractional reactivation of extensional faults reverse displacement associated with inversion is focused along the upper segments of faults so the evidence for inversion may be removed in deeply exhumed basins we believe this is the case in the irish sea western british isles previous authors have attributed the severe exhumation of this basin to plume related uplift and have ruled out inversion as a cause of uplift we present a method for identifying tectonic inversion in a basin where exhumation has removed evidence of reverse displacement on the upper segments of faults we utilize compaction based mapping of erosion patterns recorded by anomalously high sonic velocities in upper triassic shales we show that the amount of section removed during exhumation in the irish sea varies between 1 3 and 3 3 km and that exhumation patterns are markedly heterogeneous neither the heterogeneity of exhumation nor its focusing over hanging wall blocks of major faults is consistent with solely plume related uplift and we believe that our results record cryptic basin inversion that is superimposed on epeirogenic exhumation some of which may be plume related the direct evidence for this inversion has been removed because erosion has proceeded beneath the null lines of reactivated faults and we propose erosion of reactivated fault segments as one of the major reasons why shortening is frequently underestimated in inverted basins

inverse modelling of extension and denudation in the east irish sea and surrounding areas abstract epeirogenic uplift and denudation are difficult to quantify because unlike basin subsidence they do not leave an unambiguous record in recent years much research has been focussed on calculating regional denudation from sonic velocity measurements from vitrinite reflectance profiles and from fission track analyses here we show that inverse modelling of the remnant stratigraphy within extensional sedimentary basins yields estimates of denudation within a corridor which crosses the british isles for a variety of reasons these estimates are minima but they do broadly agree with those determined by inversion of vitrinite reflectance profiles our results also demonstrate that denudation estimates from fission track analyses are meaningful a combined stratigraphic and thermal indicator approach should now be used to map denudation across different continents

quantification of vertical movement of low elevation topography combining a new compilation of global sea level curves and scattered marine deposits armorican massif western france a wide range of methods are available to quantify earth s surface vertical movements but most of these methods cannot track low amplitude 5 ma e g cosmogenic isotope studies vertical movements characteristic of plate interiors the difference between the present day elevation of ancient sea level markers deduced from well dated marine deposits corrected from their bathymetry of deposition and a global sea level gsl curve are sometimes used to estimate these intraplate vertical movements here we formalized this method by re assessing the reliability of published gsl curves to build a composite curve that combines the most reliable ones at each stage based on the potential bias and uncertainties inherent to each curve we suggest i that curves which reflect ocean basin volume changes are suitable for the ca 100 to 35 ma greenhouse period ii whereas curves that reflects ocean water volume changes are better suited for the ca 35 to 0 ma icehouse interval and iii that for these respective periods the fit is best when using curves that accounts for both volume changes we used this composite gsl curve to investigate the poorly constrained paleogene to neogene vertical motions of the armorican massif western france it is characterized by a low elevation topography a variscan basement with numerous well dated cenozoic marine deposits scattered upon it using our method we identify low amplitude vertical movements ranging from 66 m of subsidence to 89 m of uplift over that time period their spatial distribution argues for a preferred scale of deformation at medium wavelengths i e order 100 km which we relate to the deformation history of northwestern european lithosphere in three distinct episodes i a phase of no deformation between 38 and 34 ma that has been previously recognized at the scale of northwestern europe ii a phase of low subsidence between 30 and 3 6 ma possibly related to buckling of the lithosphere and iii a phase of more pronounced uplift between 2 6 ma and present which we relate to the acceleration of the africa apulia convergence or to enhanced erosion in the rapidly cooling climate of the pleistocene

using argon as a temporal tracer of large scale geologic processes abstract argon ar has proven to be one of the most useful elements in understanding the timing and duration of geological processes because of its chemical and physical properties ar is a particularly sensitive indicator of temperature variations associated with large scale geological events ar mobility in minerals is commonly described using solid state diffusion theory volume diffusion which has been used extensively to model diffusion profiles and closure temperatures in minerals because 40 ar is the radiogenic daughter product of radioactive 40 k and therefore occurs in many common rock forming minerals ar has been used effectively as a temporal tracer to understand a wide variety of geological phenomena ar isotopes have been applied with great success in three broad fields of earth science the origin and evolution of the earth s atmosphere the tectonothermal history of geologic terranes and the timing and duration of large scale tectonic events from ar isotopic data the earth s atmosphere is now known to be mainly secondary in nature although evolutionary models have undergone a recent paradigm shift due to geophysical evidence moving away from the earlier notion of a chemically layered upper and lower mantle to a whole earth mantle structure that may be chemically inhomogeneous although recent models are growing in sophistication by integrating additional information and measurements reflecting the behaviour of other noble gases through time the temporal evolution of the earth s atmosphere still remains ambiguous because measured compositions of ancient atmosphere are sparse and remain difficult to obtain 40 ar 39 ar thermochronology is one of the most commonly used tools in tectonothermal investigations because of the large range of ar closure temperatures recorded by various common k bearing minerals although more recent thermochronological models such as multidiffusion domain mdd modelling remain controversial the combination of 40 ar 39 ar thermochronology with both higher and lower temperature thermochronological methods utilizing other isotopic systems makes this an extremely versatile method of understanding the temperature time evolution of geologic regions recent developments involving the numerical modelling of ar diffusion coupled with the geodynamic modelling of orogens have led to new ways of estimating the timing and duration of a complete tectonic cycle of subduction and exhumation by applying these new methods to rocks from the bergen arcs in norway studies have shown that this cycle can be so rapid that the subducted and exhumed crust can remain relatively cool never achieving thermal equilibrium with its ambient environment throughout the entire process in summary the versatility of the 40 ar 39 ar dating method combined with the effective application of various techniques e g laser spot dating and step heating and a detailed understanding of the diffusional behaviour of ar has proven to be a powerful research tool in elucidating the timing and duration of many large scale earth system processes

an application of spectral image analysis to soil micromorphology 1 methods of analysis abstract digital images of polished soil sections were produced using an eikonix scanner 4096 detectors in a linear array separate images were collected in each of the red green and blue wavelengths of visible incandescent source light and in the blue wavelength for ultraviolet uv illumination these spectral data sets were registered displayed and analyzed as colour composite images with an easi pace spectral image analysis system visual identification and delineation of pedological features were based on their morphologies and colours this task was aided by the image enhancement capabilities of the system features classified included skeletal grains void space mottles organic material manganese concretions carbonates and depletion zones an interpretive colour code for image display of these classified soil features was proposed and implemented the percentages of the total image area occupied by each of these pedological features were derived from the final image classification

sedimentary basin inversion and intra plate shortening abstract sedimentary basin inversion the shortening of formerly extensional basins is accommodated mainly by compressional reactivation of extant faults and fractures across a wide range of scales as such inversion is a large scale manifestation of byerlee friction the dynamic criterion for fault reactivation governing the effective shear strength of the shallow crust basin inversion generates distinctive deformational architecture and it is implicated strongly in sedimentary basin exhumation as a principal source of horizontal stress inversion drives significant sedimentary porosity reduction and resultant fluid flow upper crustal deformation is critically dependent on fluid overpressure i e pore fluid pressures greater than would be calculated from a hydrostatic gradient and perhaps more than in any other tectonic setting overpressures are potentially large during sedimentary basin inversion this review therefore includes discussion of the role of fluid overpressure in inversion and the evidence for it collectively inversion has profound implications good and bad for the prospectivity of many petroliferous sedimentary basins thus recognizing the evidence for basin inversion quantifying its magnitude and understanding the mechanisms that accommodate inversion and other phenomena affected by it have become essential components of the basin analyst s remit

evidence for kilometre scale neogene exhumation driven by compressional deformation in the irish sea basin system simon p holford paul f green jonathan p turner gareth a williams richard r hillis david r tappin ian r duddy

inversion and exhumation of the st george s channel basin offshore wales uk the western uk basins of the irish sea have provided one of the best natural laboratories for investigating the causes and consequences of intracratonic uplift and erosion exhumation to date the emphasis has been on igneous underplating as the chief process driving their exhumation in this paper we demonstrate that tectonic inversion the shortening of formerly extensional basins and reactivation of their constituent faults dominated the exhumation of the st george9s channel basin offshore wales based on mapping of an extensive 2d seismic grid evidence is presented for at least two major inversion episodes in the late cretaceous and the neogene plus minor shortening during the eocene inversion was distinctly noncoaxial especially during the neogene when coeval transpression and transtension was focused at discrete bends and stepovers on the basin bounding st george9s bala and northwest flank faults that the principal mechanism driving these uplift episodes was inversion as opposed to igneous underplating is corroborated by analysis of thermal history data apatite fission track and vitrinite reflectance they reveal late cretaceous and neogene geothermal gradients that were comparable with that at the present day i e no significant increase in basal heat flow sonic velocity profiles logged in hydrocarbon boreholes constrain the minimum thickness of the eroded section which varies between c 1000 m in the centre and c 2240 m at the margins of the basin given the strength of evidence for tectonic inversion in the st george9s channel basin our favoured model invokes superimposition of the effects of inversion and igneous underplating to account for the complex exhumation history of the st george9s channel basin in particular and the western uk basins in general

evidence for post early eocene tectonic activity in southeastern ireland the role played by cenozoic deformation in denudation and landscape development in ireland has historically been difficult to assess because of the lack of widespread pre glacial cenozoic deposits onshore here we combine analysis of apatite fission track data and geomorphic observations to place constraints on the timing kinematics and magnitude of onshore deformation in southeastern ireland relationships between apatite fission track central age and elevation for samples from the wicklow and blackstairs mountains and tullow lowland suggest that these rocks record an exhumed apatite partial annealing zone which after cooling was dismembered by differential vertical displacements of up to several hundred metres we use inverted models of sample thermal history to show that samples across the region experienced very similar thermal histories up to and including a cooling event in late paleocene or early eocene time this effectively rules out strongly spatially heterogeneous denudation and implies that differential rock uplift occurred in post early eocene time the central age elevation relationships define at least three spatial domains with internally consistent apatite fission track data separated by known faults or topographic escarpments geomorphic analysis of these structures shows that patterns of catchment incision and sinuosity as well as the presence of antecedent drainage are best explained by differential vertical displacements at or near the domain boundaries the kinematics and magnitudes of these displacements are consistent with those implied by the apatite fission track results and are compatible with other examples of known cenozoic deformation from ireland and the adjacent continental margin