a geochemical perspective and assessment of leakage potential for a mature carbon dioxide enhanced oil recovery project and as a prototype for carbon dioxide sequestration rangely field colorado measurements of co2 and ch4 soil gas concentrations and gas exchange with the atmosphere at a large scale co2 enhanced oil recovery eor operation at rangely colorado united states allowed assessment of the microseepage potential shallow and deep soil gas concentrations and direct transport of co2 and ch4 complemented by carbon isotopes have demonstrated an estimated microseepage rate to the atmosphere of approximately 400 t ch4 yr from the 78 km2 area of the rangely field preliminary estimates of deep sourced co2 losses are in the range of 170 to less than 3800 t yr several holes as much as 9 m deep for nested sampling of gas composition stable carbon isotopic ratios for co2 and ch4 and carbon 14 measurements on co2 indicate that deep sourced co2 microseepage loss was detected methanotrophic oxidation of microseeping ch4 to co2 in soils demonstrates significant contribution to soil gas co2 in high ch4 flux areas necessitating a revision of the estimated direct co2 microseepage rate to less than 170 t yr over the rangely field an evaluation of produced water quality from pre co2 eor to 1999 demonstrates an increase in some parameters particularly of ca2 and hco3 indicating dissolution of ferroan calcite and ferroan dolomite in the weber formation inverse computer modeling suggested carbonate mineral sequestration was possible within the constraints of evolution of produced water quality x ray analyses of well scales however do not support the presence of significant mineral sequestration instead modeling indicates that the bulk of the co2 that has been injected since 1986 is sequestered as dissolved co2

tectono sedimentary evolution of the bowland basin n england during the dinantian the bowland basin is a ne sw trending sedimentary basin lying between the askrigg bowland high to the n and nw and the central pennine high to the se the basin was initiated in late devonian tournaisian times sediment thickness and facies variations within the dinantian succession show marked asymmetry on both a basin wide and intra basin scale as a result of approximate nw se to n s extension across normal faults thickening of the sedimentary sequence from ne to sw over much of the basin resulted from fault controlled extension along the se margin of the basin with downthrow to the nw giving the basin a half graben character extension occurred in two distinct episodes marked by basin wide debris flow and sedimentary slide slump deposits during the late chadian early arundian the simple half graben became modified by a series of ne sw trending antithetic and nw se trending transfer faults associated with local unconformities and marked lateral thickness and facies variations this interval marks the transition from carbonate ramp to slope sedimentation and a temporary halt in carbonate supply to the basin the second episode of extension the late asbian early brigantian marks the break up of the northern basin margin ending major carbonate deposition within the basin reactivation of these structures at the end of the carboniferous created the ribblesdale fold belt as a result of nw se to n s compression transpression application of this research to areas surrounding the bowland basin has led to the recognition of additional shelf basins the orientation of which suggests control by normal and transfer fault systems discussion and

the bristol mendip foreland thrust belt the thrusts and associated fold structures of the bristol mendip area are interpreted in terms of a thin skinned piggy back foreland thrust belt of variscan age with dominant northward transport strike normal balanced sections and compatible strike parallel sections have been constructed to illustrate the 3 d geometry of the linked thrust system north south shortening of c 20 km 40 is calculated from deformed and restored strike normal sections a thick and extensive thrust wedge of pre old red sandstone basement in the west of the area is responsible for culminations expressed at the surface as the mendip periclines uplifted culminations permit erosion to lower stratigraphic levels in the west and south of the area strike parallel sections and a hanging wall cut off map indicate that the majority of thrusts in the area are mainly oblique ramps rather than simple frontal and lateral ramps or flats the en echelon pattern of the mendip periclines may be related to the oblique ne climb of two of these thrusts the angle of frontal ramp climb through the dinantian stratigraphy is generally low and this explains the presence of numerous klippen of lower on upper carboniferous rocks whilst suggesting that certain thrust sheets were much more extensive than present outcrops indicate early pre thrusting movement on basement lineaments in the variscan foreland created uplifts angular unconformities and a predominance of n s structures in the north of the area

dawsonite formation in the beier sag hailar basin ne china tuff a natural analog for mineral carbon storage abstract we determined the rock types the authigenic minerals the paragenetic sequence and the origin of dawsonite in pyroclastic rocks from the yimin formation of beier sag in the hailar basin china dawsonite a diagenetic mineral is thought to result from a large influx of co 2 and therefore this system represents a natural analogue for in situ mineral carbon storage the studied host rocks are mainly tuffs tuffaceous sandstones which now contain up to 70 vol authigenic carbonates including dawsonite ankerite and siderite the initial alteration of the tuffs yielded minor siderite kaolinite illite and mixed illite smectite then formed as product phases dawsonite and quartz subsequently precipitated in response to co 2 influx apparently coupled to feldspar and perhaps kaolinte dissolution dawsonite reaches a maximum 25 vol of the bulk rock mass balance suggests that this co 2 influx was coupled to the external import of sodium and export of sio 2 ankerite and additional siderite precipitated during the late stage alkaline diagenesis the carbon isotope values of the dawsonite are in the range 4 1 to 2 2 indicating the magmatic origin of the co 2 vitrinite reflectance and thermal gradient constraints suggest that the dawsonite at this location formed at a temperature of 75 c

stable isotope and radiocarbon balances of two tibetan lakes sumxi co longmu co from 13 000 bp hydrologic and climatic changes in western tibet since 13 000 bp are inferred from mineralogical and isotopic analyses of lacustrine sediments from the sumxi longmu co basin the interpretation is based on isotope data from the modern system carbon isotope chemistry is complex because of the presence of old limestones on the watershed sediments contain detrital and authigenic calcites the proportions of which are quantitatively estimated by x ray diffractometry stable isotope contents of the authigenic calcite are reconstructed from mass balance equations the high 13c contents up to 6 are attributed to an enhancement of calcite precipitation from water surface during freezing periods the 18o content is related to residence time and evaporation the validity of 14c dates obtained from different types of material is discussed our record in good agreement with paleobiological data from the same material shows the sudden establishment of wet warm conditions at 10 000 bp which culminated at 7500 6000 bp after a brief reversal event at 7900 bp maximum aridity for the whole holocene is recorded at 4300 bp

oxygen and carbon isotope trends and sedimentological evolution of a meromictic and saline lacustrine system the holocene medicine lake basin north american great plains usa abstract the succession of sedimentary subfacies in the medicine lake basin south dakota usa documents numerous changes in total dissolved solids tds lake level and the nature and stability of meromixis during the holocene the lake formed about 10 6 ka b p when coarse clastics and massive fine grained muds were deposited in a well mixed freshwater system subsequently the lake became saline and meromictic depositing a finely laminated unit composed of variegated and gray muds organic facies gypsum and aragonite laminae phototrophic bacterial plate communities bpc at the chemocline were significant producers of pelagic organic matter relatively high lake levels at least 10 m higher than today but saline and meromictic conditions predominated through the early to mid holocene at the end of this phase lake level dropped and stable meromixis was disrupted sands and massive or banded muds were deposited in sublittoral areas and benthic microbial communities bmc spread over the lake replacing bpcs as the predominant microbial producers when lake level rose again massive and laminated units were deposited under less saline conditions another pronounced episode of low lake level and high salinity followed the most recent sediments are sapropels massive or banded muds and littoral sands the 18o record from authigenic aragonite shows more positive values during the arid mid holocene interval with an abrupt increase at the end of this period followed by generally more negative values during the cooler and wetter late holocene the small range of 18o values 3 suggests that the lake was well buffered against high frequency climatic cycles probably as a result of groundwater modulation we postulate that meromixis and the type of photosynthetic microbial communities dominating the basinal region of the lake system either bpcs or bmcs exerted major controls on the carbon cycle and consequently on the development of isotopic trends linking 13c and 18o values more negative 13c values during the early and mid holocene are interpreted as a consequence of the predominance of 12c enriched microbial carbon from bpcs examples of both covariant and inverse covariant isotope trends between 13c and 18o values occur in the medicine lake record inverse covariant trends characterize long periods of stable meromixis when bpcs predominate over bmcs we hypothesize that well developed water stratification caused by greater influx of relatively 18o depleted freshwater induces higher productivity at the chemocline and consequently more positive 13c values in the precipitated carbonates unstable phases of meromixis or holomictic conditions are characterized by a predominance of bmcs or other biogenic producers over bpcs and a number of other factors combine to promote covariant trends the medicine lake record is consistent with the paleoclimatic interpretation for the northern great plains of a more arid early and middle holocene followed by an abrupt transition to a relatively cooler and wetter late holocene the sedimentary succesion in medicine lake documents a much more fluctuating and abrupt climate behavior than suggested by the vegetation paleorecord and suggest a late holocene climate punctuated by arid episodes

the maryport fault the post caledonian tectonic history of southern britain in microcosm the maryport fault forms part of the faulted southern margin of the northumberland solway basin seismic reflection data reveal a complex history of repeated fault reactivation large oblique normal displacements on the fault controlled early carboniferous extensional basin development subsequently variscan basin inversion was accompanied by partial reversal of the fault in permian and mesozoic times renewed oblique normal displacements strongly influenced basin subsidence further partial reverse displacement occurred as the solway basin was again inverted probably in mid tertiary times in response to alpine compression the maryport fault is most unusual therefore in providing direct evidence of the principal post caledonian tectonic events in southern britain

variscan inversion within the cheshire basin england carboniferous evolution north of the variscan front abstract a comprehensive seismic reflection and borehole database over the whole of the cheshire basin has allowed examination of the carboniferous succession beneath a thick permo triassic cover construction of a seismic sequence stratigraphy involving the recognition of unconformity bounded packages has allowed the examination of the control by tectonics of sedimentation within the pre permo triassic of the cheshire basin the carboniferous has been divided into two unconformity bound megasequences i e dinantian ms10 0 and namurian westphalian ms20 0 these are deformed by a hitherto unknown series of variscan structures interpretation of these structures has allowed assessment of the variscan orogeny in this area of the variscan foreland considerable variscan inversion in the area exists 100 150 km north of the variscan fold thrust front and is suggested to illustrate the effects of predominantly e w directed compression especially to the north of the northern apex of the adjacent midlands microcraton compression occurred during two late carboniferous pulses of thrusting

properties and origin of a very fine grained kaolinitic lacustrine deposit the rosebrook member of the miocene bunyan formation is a highly kaolinitic clay rock of lacustrine origin it is ultra fine grained plastic and of high cation exchange capacity cec of 20 33 c mol kg 1 of clay fabrics observed optically and by transmission electron microscopy tem indicate significant post depositional consolidation and localized shear failure sedimentation and tem analyses confirm its very fine grain size which is consistent with the relatively high cec tertiary soils and weathering profiles in the catchment of lake bunyan developed under relatively moist and cool conditions some were gibbsitic with kaolinite and smectite clay minerals highly weathered soils oxisols on basalt under modern high rainfall environments in the region are dominated by gibbsite and kaolinite these and other highly weathered soils in the region formed on a range of parent rocks have high proportions of very fine grained kaolinite in their subsoils such materials are likely to have been abundant in the catchment of lake bunyan during the miocene and would have contributed very fine grained kaolinite directly to the lake by sedimentation however the unusually high proportion of kaolinite in the rosebrook member and its euhedral crystal form suggest that some of its features developed diagenetically

paleomagnetic evidence for tectonic rotations in the variscan mountain belt a critical review of devonian and carboniferous paleomagnetic results from the hercynian basement of western and central europe reveals large rotations their geographic distribution suggests a tectonic origin for large scale curved structures such as the ibero armorican arc or the variscan v together with a coherence of the hercynian domain with time geodynamic models which can have produced the observed rotation pattern are discussed it appears that lateral compression due to the accommodation of continental collision as in the india asia convergence is a plausible mechanism although variscan and himalayan mountain belts have different characteristics

evidence of an imbricate crustal thrust belt in the southern british variscides contributions of southwestern approaches traverse swat deep seismic reflection profiling recorded through the english channel and the celtic sea the southwestern approaches traverse swat seismic reflection profiles recorded through the celtic sea and the english channel provide unexpected data concerning notably the deep structure of the irish and south british variscan crust one of the most significant results is the recognition of prominent deep southerly dipping reflectors regarded as large scale foreland directed variscan thrusts which constitute in the southern innermost zones a crustal stacking wedge the resulting overthickened crust may have induced the petrogenesis of the cornubian granitic batholith by an anatectic melting process the roots of this crustal duplex are not imaged on the swat lines because of their subsequent assimilation by the more recent layering of the present day lower crust upward the deep crustal ramps are assumed to flatten out and to join a roof thrust which acts as a major midcrustal decoupling zone not revealed by the swat profiles and which underlies the thick devonian allochthonous high strained units of cornwall northward this shallow northerly verging shear zone is overstepped by the tintagel antithetic back thrusts which are closely related to deeper northward dipping basement faults considered as caledonian features southward the imbricate crustal thrust unit is overridden by the lizard ophiolitic suture which appears as a 8 km thick gently southerly dipping sheared zone crosscuttting the entire crust and rooting deep beneath the present day moho its hanging wall is constituted by the channel cadomian block characterized by an almost seismically featureless upper crust which is not involved in the main variscan thrust stacking northward the imbricate thrust unit is delineated by a moderately southerly dipping ramp which penetrates straight down into the upper crust without any evidence of an intervening flat lying decollement level this frontal ramp emerges along a broadly 110 n trending discontinuous thrust front located above the northern downfaulted margins of the munster ireland and pembroke wales devonian basins the swat deep seismic data relate the overall variscan crustal shortening undergone by the south british domain to an oblique converging process involving a continental shelf pinched between the rigid allochthonous channel block and the northern autochthonous foreland this crustal shortening occurred during a carboniferous intracontinental collisional context subsequent to the closure and the obduction of a small oceanic crust floored basin lizard

influence of localised igneous activity on cleat dawsonite formation in late permian coal measures upper hunter valley australia abstract stable 13 c and 18 o and radiogenic 87 sr 86 sr isotopic data have been used to investigate the origin of cleat dawsonite naalco 3 oh 2 in the late permian wittingham coal measures of the upper hunter region in the sydney basin new south wales the 13 c pdb values have a narrow range 1 7 to 2 4 with an average of 0 3 suggesting a magmatic source for the carbon in contrast 18 o smow values have a wide range 13 6 to 19 8 and decrease systematically with decreasing distance from a major intrusion this systematic variation reflects establishment of localised hydrothermal cells water rock interaction between fluids associated with these hydrothermal cells and rb poor volcaniclastic detritus in the coal measures produced mantle like 87 sr 86 sr 0 705032 to 0 706464 in the dawsonite

shear zones as a new type of palaeostress indicator this paper proposes that shear zones act as palaeostress indicators in much the same way as brittle faults several hundred shear zones from both the limbs of the variscan langland mumblcs anticline south wales are treated using the graphical and numerical methods of fault slip analysis estimated palaeostress directions derived from shear zones are characterized by greater scatter than where brittle faults are used as stress indicators an important reason for this is the fact that on some shear zones the direction of maximum shear stress slip lineation is not perpendicular to the line of s c intersection as a consequence the use of slip lineations produces better solutions than cases where the slip direction is inferred as a line perpendicular to the s c intersection the filtering of data to reduce the scatter in the results produces insignificant improvement and is considered unnecessary

petrography carbonate mineralogy and geochemistry of thermally altered coal in permian coal measures hunter valley australia abstract carbonate minerals commonly occur in coals of many ages and from a utilisation viewpoint can be deleterious several studies have been undertaken of the carbonates in the permian coals of the hunter valley australia but few studies use a multi technique approach for this study a combined petrographic geochemical and mineralogical approach was used to determine the distribution and residence of carbonate minerals in coal that had been intruded by a dyke the dominant carbonate assemblages comprise primary siderite in inertinite rich microlithotypes and secondary calcite ankerite dolomite dawsonite in vitrinite rich microlithotypes the secondary carbonates were found in both the aureole of heated coal and also in an unheated mine face sample it is believed that the secondary carbonate minerals precipitated from magma derived fluids percolating through the coal following the emplacement of the intrusions the textures and distribution of the secondary carbonate minerals suggest that the temperature and pressure of the fluids may be just as important in developing fractures near dykes particularly those that have multiple phases of geometries cleat mineralogy and coal textures as direct heating from the intrusion the partitioning of primary siderite with inertinite and secondary carbonates with vitrinite indicates that it can be reasonably expected that there would be a partitioning of minerals in various density fractions derived from float sink tests and consequently a partitioning of elements with inertinite rich fractions containing elevated fe levels and vitrinite rich fractions containing elevated ca mg and al this partitioning has implications for the behaviour of the coal during washing and combustion and the composition of combustion products

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

transpressive duplex and flower structure dent fault system nw england abstract revised mapping along the dent fault northwest england has improved the resolution of folds and faults formed during variscan late carboniferous sinistral transpression a nne trending east down monocline comprising the fell end syncline and taythes anticline was forced in carboniferous cover above a reactivated precursor to the dent fault within the lower palaeozoic basement the taythes anticline is periclinal due to interference with earlier acadian folds the steep limb of the monocline was eventually cut by the west dipping dent fault the hangingwall of the dent fault was dissected by sub vertical or east dipping faults together forming a positive flower structure in cross section and a contractional duplex in plan view the footwall to the dent fault preserves evidence of mostly dip slip displacements whereas strike slip was preferentially partitioned into the hangingwall faults this pattern of displacement partitioning may be typical of transpressive structures in general the faults of the taythes duplex formed in a restraining overlap zone between the dent fault and the rawthey fault to the west the orientations of the duplex faults were a response to kinematic boundary conditions rather than to the regional stress field directly kinematic constraints provided by the dent and neighbouring variscan faults yield a nnw sse regional shortening direction in this part of the variscan foreland

separation of multiple stress events by fault striation analysis an example from variscan and younger structures at ogmore south wales the study of minor structures in carboniferous and triassic sedimentary rocks at ogmore by sea bridgend reveals that the observed microstructures are the consequence of successive brittle deformation events age relationships can be deduced from sets of structures consisting of conjugate faults oblique slip faults tension gashes and stylolites from which deductions can be made about the orientations of principal stresses corresponding to pre and post triassic events the demonstrable polyphase tectonic history at ogmore and the occurrence of large numbers of striated faults at four sites allow the opportunity of testing a newly proposed strategy for palaeostress analysis from striated faults with complex stress histories the new technique based on the statistical procedure of cluster analysis involves the sorting of fault slip data into coherent dynamic setsasa preliminary stage of formal stress inversion the fault sets separated using this technique yield stresses which are similar to those deduced from field observations four stress configurations are distinguished of which two are pre triassic in age correlations with previously derived stresses are discussed

early magmatic phase in the oslo rift and its related stress regime abstract the earliest magmatic rocks in the oslo graben consist of a complex of sills and dykes intermediate to felsic syenites termed maenaites and basic camptonites intruded into cambrian and lower ordovician pre rift sediments no volcanism appears to be associated with this intrusive phase the sill intrusions are regional in extent and can be found in all parts of the oslo graben except in the north samples from six maenaite sill occurrences dated by the rb sr method yielded late carboniferous ages ranging from 304 to 294 ma these ages place the sill intrusions in the same evolution phase as the proto rift asker group sediments interpreting the sill complex as a paleostress indicator and applying the tectonic model for the sill forming mechanism the deviatoric stress in the crust at the time of intrusion is found to be compressive at the level of the sills and shallower in contrast the succeeding evolution of the oslo graben was dominated by tensile deviatoric stress the timing of the incipient magmatic event in the oslo graben and its state of deviatoric compressive stress support the concept that the oslo rift developed initially in response to the build up foreland compressional stresses in conjunction with the hercynian orogeny there is no evidence for an early pre rift crustal doming stage

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

interaction between faulting and sedimentation during dinantian extension of the solway basin sw scotland the ene wsw trending north solway fault acted as a northern marginal fault to the solway basin during dinantian sedimentation structural sedimentological and diagenetic relationships suggest syn sedimentary dinantian movement was dip slip and normal a later carboniferous phase of dextral transtension is also indicated allokinetic deformation features increase in abundance and intensity towards the north solway fault their presence and nature being strongly facies dependent syn sedimentary fault deformation of the hanging wall sediments also increases towards this fault both distributed and localized shearing characterizes these early faults and is thought to be related to the water content of beds at the time of deformation local minor thrusting and reverse fault movement also occurred within the sediments during basin extension due to dextral transtensional movement on the north solway fault n s and nw se trending faults appear to show no evidence for syn sedimentary dinantian movement and are interpreted as the products of 9hercynian9 basin shortening and mesozoic basin formation

deep to shallow lacustrine evaporites in the libros gypsum southern teruel basin miocene ne spain an occurrence of pelletal gypsum rhythmites abstract a number of non marine evaporite units composed of primary gypsum were deposited in saline lakes that developed in the southern teruel basin ne spain during the miocene in the basin depocentre a continuum of lacustrine evaporite lithofacies influenced by the activity of organisms is displayed the libros gypsum was deposited in a deep lake in which water stratification became unstable with progressive shoaling rhythmites composed of laminae of pelletal gypsum and laminae of very fine lenticular gypsum crystals mixed with siliceous microorganisms formed in addition to gypsum turbidites intraformational gypsum breccias and slump structures the pelletal laminae originated from the faecal activity of animals crustaceans ingesting gypsum crystallites in the lake water during episodes of maximum evaporation whereas the laminae of very fine lenticular gypsum mixed with microorganisms accumulated during episodes of relative dilution in the wide marginal zones of the basin the libros gypsum unit consists of massive to thin bedded bioturbated gypsum and thin bedded clotted gypsum which formed in intermediate to very shallow palustrine water depths the bioturbated gypsum lithofacies were produced by the action of diverse organisms presumably worms and coleopterans and chironomid larvae to a lesser extent the massive lithofacies precipitated in very shallow water and the thin bedded lithofacies formed in shallow to deeper settings the thin bedded clotted gypsum is a relatively deep facies that may have diverse origins e g bioturbation compaction disruption of soft sediments and early diagenesis there is a well developed metre scale cyclicity in the marginal lake sequences which is not observed in the inner lake deposits this suggests a depth control in the various lacustrine subenvironments to record cyclic evaporitic processes the isotopic composition of the gypsum indicates early sulphate reducing bacterial activity in the bottom of the lake and suggests that the sulphate was derived from the chemical recycling of triassic evaporites of the country rocks

cenozoic evolution of continental humidity and paleoenvironment deduced from the kaolinite content of oceanic sediments abstract the distribution of detrital kaolinite in cenozoic sediments of the atlantic and west pacific oceans has been used to reconstruct the variations of the continental humidity and associated paleoenvironmental factors five stages have been recognized 1 1 during the late oligocene chattian c 30 m y p21 and np24 increased kaolinite content at every site marked an increase of global humidity 2 2 during the early miocene aquitanian c 20 m y n5 n6 and nn2 nn3 increasing continental aridity is deduced from low kaolinite contents in the atlantic ocean and philippine sea 3 3 during the middle miocene langhian c 14 m y n10 n12 and nn5 nn6 increased kaolinite contents at most of the sites marked a further increase of global humidity which was especially important at low latitudes in africa 4 4 during the late miocene tortonian c 10 m y n16 and nn10 nn11 kaolinite content and inferred continental humidity increased toward high latitudes but decreased toward low latitudes especially off tropical africa where it marked the development of arid conditions 5 5 during the late pliocene piacenzian c 3 m y nn15 nn16 kaolinite content and humidity increased again toward high latitudes while these conditions decreased again toward low latitudes emphasizing the latitudinal climatic zonation periods of increasing humidity show good correlation with the development of polar ice locally volcanism tectonic activity oceanic circulation and migration of lithospheric obliterated the climatic significance of clay mineral associations which therefore express complementary aspects of the continental and marine paleoenvironments

pedogenic evidence of urmia lake s maximum expansion in the late quaternary abstract the urmia lake recession and the resulting increase in vast barren area around it has been rapid in recent decades and thus has attracted attention of environmentalists and geoscientists alike however evidence for its different strandlines and the largest extension of the lake during the late quaternary has not been reported yet the principal goals of the current research were to figure out pedological evidence of its maximum expansion during the late quaternary and mapping out the different strandlines along the western shores of urmia lake over time thirty two soil pedons at different landscape positions geomorphic surfaces and distances from urmia lake were studied during autumn in 2013 and 2014 micromorphological and mineralogical studies were performed for some diagnostic horizons results showed along the transect under study three different entities diagnostic of the lake s history 1 lithological discontinuities 2 saline lacustrine sediments 3 buried soils however almost 2 km from the closest pedon to the lake no evidence of saline playa sediments were detected based on previous chronology results from urmia lake which indicated high lake levels with very low salinity since about 180 ky bp the sediments of this part of the study area were considered to have been deposited at the same period of time indicating a maximum expansion of urmia lake during the late quaternary the current results demonstrate that soil pedons which were situated at various distances from urmia lake denote different stages of the lacustrine evolution along with the distance from the lake the development of soils increases due to a longer and more intensive impact of pedogenic processes on the topstratum the overall soil system becomes more mature the study of buried soils and their comparison to upper non buried soils revealed that in some cases the buried soils were more evolved than their upper soils or vice versa through these observations the periods of exposure to soil forming processes after each sedimentation period was detected and schematic diagrams illustrating periods of highstands and lowstands recessions of urmia lake were reconstructed this study demonstrates that even though multiple episodes of lake recession were apparent the level of urmia lake increased during hydroclimatic events conducive to lake expansion which affected the soil evolution due to several fluctuations during the late quaternary

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

a late pleistocene long pollen record from lake urmia nw iran abstract a palynological study based on two 100 m long cores from lake urmia in northwestern iran provides a vegetation record spanning 200 ka the longest pollen record for the continental interior of the near east during both penultimate and last glaciations a steppe of artemisia and poaceae dominated the upland vegetation with a high proportion of chenopodiaceae in both upland and lowland saline ecosystems while juniperus and deciduous quercus trees were extremely rare and restricted to some refugia hippophae rhamnoides constituted an important phanerophyte particularly during the late last glacial period a pronounced expansion in ephedra shrub steppe occurred at the end of the penultimate late glacial period but was followed by extreme aridity that favoured an artemisia steppe very high lake levels registered by both pollen and sedimentary markers occurred during the middle of the last glaciation and late part of the penultimate glaciation the late glacial to early holocene transition is represented by a succession of hippophae ephedra betula pistacia and finally juniperus and quercus the last interglacial period eemian slightly warmer and moister than the holocene was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern european pollen sequences

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

late miocene stratigraphy palaeoecology and palaeogeography of the tabriz basin nw iran eastern paratethys abstract the tabriz basin is located in nw iran within the collision zone of the arabian and eurasian plates its upper miocene and pliocene basin fill termed lignite beds and fish beds can provide detailed insights into the neogene environments and processes during a time of intense tectonics and volcanism however a modern re evaluation of the lignite beds and fish beds is lacking here we present fission track ft data from the northern hinterland of the tabriz basin upper red formation and from the fish beds which support previous age assumptions for the upper red formation but together with the new biostratigraphic data point to an older stratigraphic age for the lignite and fish beds than previously thought lignite beds 11 6 10 0 ma fish beds 10 0 7 5 ma furthermore we describe for the first time the fossil fish and ostracod fauna and the diatom assemblages from both the lignite beds and fish beds all fossil groups are characterized by the occurrence of freshwater and brackish forms additional marine euryhaline taxa appear among the fishes and diatoms it can be assumed that the lignite and fish beds represent deposits of a lacustrine to euryhaline late miocene lake urmia during the initial state of the tabriz basin subsidence and that the ancient lake was located farther to the east and in a higher altitude than the present day lake urmia the fossil assemblages indicate a new palaeogeography for the late miocene of the study area with temporary connections between the tabriz basin and the southern caspian sea perhaps via an ancient araks river passage

the driving forces behind the caspian sea mean water level oscillations closed basins such as the caspian sea rapidly respond to variations in atmospheric and geological events this study has been conducted to deduce the role of natural and anthropogenic influences on the caspian sea mean water level fluctuations for the period of 1998 2005 it is recognized that climate is the primary mechanism of the caspian sea mean water level variations based on the relatively small differences of the caspian sea hydrologic budget residuals and the caspian sea mean water level fluctuations this is further supported by the similarity in water level variations of the caspian sea with those of lake van and lake urmia on the other hand the caspian sea needed to lose some of its water to attain water balance equilibrium in 2000 and 2001 the year 2000 showed anomalous seismic activity particularly in the southwestern part of the caspian sea two significant earthquakes with magnitudes of 6 8 and 6 5 mw occurred on november 25 2000 the focal mechanisms of these earthquakes and numerous aftershocks indicated normal faulting and therefore caused the caspian sea lake level to decline in 2000 the contribution of submarine mud volcano eruptions to the caspian sea lake level could be insignificant based on the comparison of water budget residuals and the mean water level variations neither crustal deformation based on the gps measurements nor the offshore oil and natural gas production activities in the caspian sea are responsible for noticeable changes to the level of the caspian sea

lacustrine sedimentation in the diapir controlled miocene bicorb basin eastern spain abstract the miocene bicorb basin is a small elongated basin developed by normal faulting of a thick jurassic cretaceous carbonate succession and subsequent diapirism of upper triassic mudstones and evaporites the basin fill comprises a sequence over 650 m thick formed by two units the lower alluvial unit consists of a complex alternation of conglomerates sandstones mudstones and minor lacustrine limestones the upper unit comprises marginal alluvial and lacustrine deposits in which seven lacustrine facies associations have been distinguished the inner lacustrine deposits comprise mudstones and carbonates with minor evaporitic deposits at the northeast and southwest basin edges alluvial inputs led to the development of delta and fan delta environments where sandstone and conglomerate deposits dominate the latter stages of the lake evolution are represented by an expansive thick limestone sequence which close to the nw fault bounded margin pass laterally to breccias the hierarchical arrangement of the upper unit shows five different orders of sequences the first order sequence defines a major vertical trend of lake expansion whereas three second order sequences are linked to major flooding expansion episodes all these sequences are related to the tectonic evolution of the diapir metre scale third and fourth order sequences and fifth order sequences which consist of finely laminated rhythmite deposits probably record climatically forced processes the diapir graben system evolution and the climatic variations have exerted major controls on the sequential arrangement and evolution of the lacustrine system both factors have also strongly influenced the changes in the gastropod assemblages

dawsonite cement in the triassic lam formation shabwa basin yemen a natural analogue for a potential mineral product of subsurface co2 storage for greenhouse gas reduction abstract the origin and permeability effects of carbonate cement blamed for poor reservoir quality in the upper triassic turbidite sandstones of the lam formation in yemen have been investigated using petrography x ray diffraction stable isotopes fluid inclusions and thermodynamic modelling in order of growth in the sandstone the carbonate cements include ferroan calcite dawsonite naalco3 oh 2 ferroan dolomite and siderite ferroan dolomite is the most abundant cement there is an inverse correlation between permeability and total carbonate cement volume supporting the earlier assertion that carbonate cements are the main control on reservoir quality in these sandstones ferroan calcite replaced and was sourced by marine limestone rock fragments that are abundant in the turbidite sandstone the later cements were probably also at least partly sourced from the marine limestone rock fragments stable isotope data from ferroan calcite ferroan dolomite and siderite show that diagenesis occurred in formation water with oxygen isotopes typical of closed system diagenesis and that only minor organic derived carbon dioxide was involved in diagenesis dawsonite while not common as a diagenetic mineral in sandstones has recently been suspected of being a routine consequence of co2 storage in the subsurface for greenhouse gas reduction in the lam formation dawsonite found at concentrations of up to 8 vol of the rock grew at the expense of detrital feldspar minerals under conditions of elevated partial pressure of carbon dioxide isotopic data show that dawsonite grew in the presence of carbon dioxide with a 13c value of about 4 to 2 this is distinctly different from the carbon isotope ratio of the gas phase carbon dioxide now present in the sandstone 27 which had an organic source rock origin the dawsonite 13c data probably represent a mixture between carbonate from detrital marine limestone rock fragments and carbon dioxide from a moderately negative source possibly of magmatic or basement origins dawsonite may thus be the result of a mass influx of deep e g magmatic carbon dioxide that pushed the lam formation into the dawsonite stability field at the expense of albite

devonian extensional tectonics versus carboniferous inversion in the northern orcadian basin the old red sandstone middle devonian orcadian basin was formed as a consequence of extensional collapse of the caledonian orogen onshore study of these collapse basins in orkney and shetland provides directions of extension during basin development the origin of folding of old red sandstone sediments that has generally been related to a carboniferous inversion phase is discussed syndepositional deformation supports a devonian age and consequently some of the folds are related to basin formation large scale folding of devonian strata results from extensional and left lateral transcurrent faulting of the underlying basement spatial variation of extension direction and distribution of extensional and transcurrent tectonics fit with a model of regional releasing overstep within a left lateral megashear in nw europe during late caledonian extensional collapse later inversion probably during the upper carboniferous is characterized by e w to ne sw contraction it induced reactivation of extensional faults as thrusts development of small scale folds and thrusts and right lateral transcurrent movement of the major faults such as the great glen and walls boundary faults

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

mineral dating of mantle derived co2 charging and its application in the southern songliao basin china abstract the timing of mantle derived co2 charging in sedimentary basins is the basis for studying co2 sandstone interactions and co2 oil interactions in general the time of the volcanic eruption near the co2 gas reservoir is considered to be the time of mantle derived co2 charging however this approach is not suitable for hydrocarbon bearing basins that have experienced multiple volcanic events in this paper using dawsonite bearing sandstones contained in an oil bearing co2 gas and oil reservoir in the southern songliao basin as the object of the study on the basis of paragenetic sequence and fluid inclusions we establish a mineral dating method for determining the time of mantle derived co2 charging in this method the mineral used for dating is dawsonite which is formed under a high co2 partial pressure and records the migration and aggregation of mantle derived co2 in geologic history by interpreting the dawsonite bearing sandstone in the southern songliao basin we find two hydrocarbon charges and one co2 charge and that the mantle derived co2 charging occurred slightly later than or quasi simultaneously with the second hydrocarbon filling combining the currently known time of hydrocarbon reservoir formation and the time of tectonic fracture development we deduce that the mantle derived co2 formed the dawsonite in the southern songliao basin at the end of the cretaceous end of the mingshui period and the beginning of the paleogene

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

reactive transport simulation study of geochemical co2 trapping on the tokyo bay model with focus on the behavior of dawsonite abstract a long term up to 10 ka geochemical change in saline aquifer co 2 storage was studied using the toughreact simulator on a 2 dimensional 2 layered model representing the underground geologic and hydrogeologic conditions of the tokyo bay area that is one of the areas of the largest co 2 emissions in the world in the storage system characterized by low permeability of reservoir and cap rock the dominant storage mechanism is found to be solubility trapping that includes the dissolution and dissociation of injected co 2 in the aqueous phase followed by geochemical reactions to dissolve minerals in the rocks the co 2 water rock interaction in the storage system mainly in the reservoir changes the properties of water in a mushroom like co 2 plume which eventually leads to convective mixing driven by gravitational instability the geochemically evolved aqueous phase precipitates carbonates in the plume front due to a local rise in ph with mixing of unaffected reservoir water the carbonate precipitation occurs extensively within the plume after the end of its enlargement fixing injected co 2 in a long geologic period dawsonite a na al carbonate is initially formed throughout the plume from consumption of plagioclase in the reservoir rock but is found to be a transient phase finally disappearing from most of the co 2 affected part of the system the mineral is unstable relative to more common types of carbonates in the geochemical evolution of the co 2 storage system initially having formation water of relatively low salinity the exception is the reservoir cap rock boundary where co 2 saturation remains very high throughout the simulation period

end carboniferous fold thrust structures oxfordshire uk implications for the structural evolution of the late variscan foreland of south central england interpretation of commercial seismic reflection data from the west of banbury south central england has provided information on the late carboniferous structural evolution of the oxfordshire syncline end carboniferous structures are preserved in the footwall of the main basin bounding faults of the permo triassic worcester graben restoration of major pre triassic normal faults has allowed reconstruction of earlier compressional structures in contrast to the wnw ese trend of structures to the south in the variscan foreland fold thrust belt major faults and folds in oxfordshire are approximately n s trending the structures seen to deform westphalian d stephanian aged sequences on the seismic profiles are a combination of steep 30 40 dip fault bounded uplifts and less dominant thin skinned tectonics apparently showing transport to the east in the south some thin skinned structures are present and in the north cover sequences are uplifted in a narrow zone of deformation on reactivated basement faults the amount of shortening also changes along strike from c 1600 m in the south to c 950 m in the north reactivation of major basement faults with differential basement shortening accounts for the main structures localized detachment in the young and weak sediments close to the palaeo land surface explains the thin skinned structures seen on some of the seismic lines these end carboniferous structures in oxfordshire and structures in the malvern abberley hills represent the structural limits of a large n s striking intra stephanian uplift in the late variscan foreland it is suggested that the structures formed during a discrete phase of intra stephanian e w directed regional shortening prior to the final phase of movement in the variscan belt

salt lakes a discussion of processes influencing palaeoenvironmental interpretation and recommendations for future study abstract the observed state of a salt lake system reflects the interaction of groundwater runoff surface water porewater and sediments aeolian transport and chemical and biological reactions these processes in turn affect the lacustrine biota the sediment composition deposition diagenesis deflation and re deposition and the geomorphic features of the salt lake the interactive processes thereby control the deposition and preservation of the palaeoenvironmental record in salt lakes consequently considerable understanding of these processes is required to recover palaeoclimatic and palaeoenvironmental detail from the sedimentary record during the recent sleads workshop participants recognized several key discipline research needs and herein make recommendations for future salt lake research covering 1 hydrology and hydrochemistry 2 geomorphology and stratigraphy 3 mineralogy isotopes and trace metals and 4 biology

linkage and evolution of conjugate strike slip fault zones in limestones of somerset and northumbria conjugate strike slip fault zones that cover metre scale areas at beadnell northumbria and kilve somerset were initiated as conjugate vein arrays early conjugate faults are linked by the propagation of one fault that eventually by passes the other fault a model for the development of strike slip faults is presented using fault and vein geometries and the position of damage zones with respect to the master faults as an indication of the propagation direction this model includes the evolution of networks from 1 the initial random development of vein arrays to 2 the isolated development of several unconnected conjugate fault segments that pass into vein arrays through 3 the intersection of a conjugate set of master faults and linkage with minor antithetic faults and the formation of new vein arrays with extensional geometries after a linked network of faults is established to 4 breaching of intersection points by dominant faults and finally 5 the propagation towards oversteps that are breached to form a through going fault the geometry of the active structures simplifies with time as strain is localised along the master fault but the complexities are preserved in the fault walls

palaeo stress fields in the variscan foreland during the carboniferous from microstructural analysis in the british isles abstract north of the variscan front the carboniferous series of the british isles is affected by mainly n s trending folds which are almost perpendicular to this e w oriented front flat and unconformable overlying permian strata demonstrate a variscan age for the deformation a microtectonic survey made in dinantian and to a lesser extent namurian calcareous layers has revealed two successive events according to chronological criteria the first event maximum stress e w trending led to the formation of n s folds with local reorientation in the vicinity of major pre existing faults this compression may have been active since the namurian it pre dates a second compressional event orientated n s which is related to the final emplacement of the variscan nappes

great salt lake and precursors utah the last 30 000 years sediment cores up to 6 5 m in length from the south arm of great salt lake utah have been correlated radiocarbon ages and volcanic tephra layers indicate a record of greater than 30 000 years a variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation these include acoustic stratigraphy sedimentologic analyses mineralogy geochemistry major element c o and s isotopes and organics paleontology and pollen the results indicate that prior to 32 000 year b p an ephemeral saline lake playa system was present in the basin the perennial lake which has occupied the basin since this time rose in a series of three major steps the freshest water conditions and presumably highest altitude was reached at about 17 000 year b p the lake remained fresh for a brief period followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present great salt lake the lake remained at low elevations and divided at times into a north and south basin until about 8 000 year b p since that time with the exception of two short rises to about 1290 m the lake level has remained near the present elevation of 1280 m

climatically induced lake level changes at lake van turkey during the pleistocene holocene transition sediment core k10 from lake van eastern turkey provides a continuous varve record back to 14 570 calendar years b p before present 1950 the longest unbroken and non floating lake varve sequence yet described the underlying sediment is unvarved and hard changes in the aragonite calcite ratio the presence of protodolomite and magnesite in certain profile sections the annual record of the sedimentation rate the water content of the sediment the concentrations of organic carbon and opal and the texture of the sediments from this core provide a record of the lake level history the new chronology enabled us to redate the old pollen profile van zeist and woldring 1978a b and to establish an accurate timescale for the reconstructed lake level change carbon 14 dates show that the highest lake terrace corresponds to high lake level at around 19 000 years b p during the last glacial 70 m above its present level before 15 000 years b p the lake must have been completely dry marking a reduction of lake level by 500 m in maximum 4000 years beginning at 14 600 years b p and ending at 12 040 years b p the lake level recovered by 250 m to fall again during the next 1400 years by 10 600 years b p the lake began to rise and reached following another regression between 9000 and 8100 years b p the holocene highstand by about 7500 years b p dropping to today s level at about 3000 years b p

petrology and isotopic geochemistry of dawsonite bearing sandstones in hailaer basin northeastern china abstract the co2 gas reservoir sandstones in the hailaer basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of co2 the origins of dawsonite and co2 in these sandstones were studied by petrographic and isotopic analysis according to the paragenetic sequence of the sandstones dawsonite grew later than co2 charging at 110 85 ma the dawsonite 18o value is 7 4 smow and the calculated 18o values of the water present during dawsonite growth are from 11 4 to 9 2 smow this combined with the nahco3 dominated water linked to dawsonite growth suggests meteoric water being responsible for dawsonite growth the 13c values of gas phase co2 and the ratios of 3he 4he of the associated he suggest a mantle magmatic origin of co2 rich natural gas in hailaer basin dawsonite 13c values are 5 3 to 1 5 average 3 4 and the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite are 11 4 to 7 3 these c isotopic values are ambiguous for the dawsonite c source from the geological context the timing of events together with formation water conditions for dawsonite growth dawsonite possibly grew in meteoric derived water atmospherically derived co2 maybe or at least the dominant c source for dawsonite it seems that there are few relationships between dawsonite and the modern gas phase of co2 in the hailaer basin

chemistry of the ordovician and silurian greywackes of the snowy mountains southeastern australia an example of chemical evolution of sediments with time abstract the ordovician quartz rich greywackes of the snowy mountains region are essentially mixtures of two components these are quartz and clay minerals the chemistry of any rock is largely determined by its proportions of clay minerals so that there is a strong negative correlation between si and those elements other than si contained in clay minerals elements that occur only in feldspar but not in clay minerals that is ca na sr and pb have a low and variable concentration these four elements have even lower abundances in the silurian greywackes deposited in basins on a basement of the ordovician rocks this is interpreted to have resulted from a further cycle of chemical weathering that acted on ordovician source rocks to produce the silurian detritus in a similar fashion the ordovician rocks are thought to have formed by weathering of more feldspar rich sedimentary rocks at the margins of the lachlan fold belt two episodes of chemical weathering are therefore recognised the first produced the feldspar poor ordovician rocks the second acted on part of these to form the almost feldspar free silurian strata in both cases ca na sr and pb were lost as feldspars were converted to clay minerals

continental scale magmatic carbon dioxide seepage recorded by dawsonite in the bowen gunnedah sydney basin system eastern australia abstract dawsonite naalco3 oh 2 is widespread as a cement replacement and cavity filling in permo triassic sedimentary rocks of the bowen gunnedah sydney basin system eastern australia the origin of dawsonite in these rocks was studied by petrographic and stable isotope analysis dawsonite d13c pdb values range from 4 0 to 4 1 and are remarkably consistent throughout the bowen gunnedah sydney basin system these values indicate either a marine carbonate or magmatic source for carbon in the dawsonite a magmatic carbon source is considered more likely on the basis that 1 evidence of and the cause for widespread marine carbonate dissolution in the sedimentary successions are not apparen 2 dawsonite is widespread in both marine and nonmarine facies 3 the region has been the site of major igneous activity 4 other dawsonite deposits of similar carbon isotopic composition are linked to igneous activity and 5 magmatic co2 accumulations are known in parts of the bowen gunnedah sydney basin system the timing of igneous activity in the bowen basin constrains the timing of dawsonite formation in the bowen gunnedah sydney basin system to the tertiary consistent with textural relationships which indicate that dawsonite formed late during the burial history of the permo triassic sequences the distribution and interpreted origin of dawsonite implies magmatic co2 seepage in the bowen gunnedah sydney basin system on a continental scale

the sedimentology of flint clay abstract flint clay is kaolinitic mudstone that distinctively differs from widely known shale in lithology genesis and economic uses flint clay is described as a fine grained compact non fissile essentially monomineralic kaolinitic rock that breaks with a conchoidal flinty fracture has almost no natural plasticity and resists slaking it is valuable as a refractory raw material but is also geologically interesting because of its sedimentology unique in some respects which is emphasized in this report although not particularly abundant in sedimentary rocks flint clay is worldwide in geographic occurrence flint clay is interpreted as having been a product of very early diagenesis a diagenesis that occurred mainly during accumulation of parent aluminum silicate material rather than dominantly after its deposition and consolidation the classical concept of diagenesis the depositional environment typically was non marine paludal or fluviatile at a time of local crustal stability within the environment and climate typical of coal measures diagenetic reactions producing flint clay were dominated by desilication partial removal of iron alkaline and alkali earths producing a mud that had the composition of kaolin followed by crystallization or recrystallization of the digested sediment into interlocking crystals of kaolinite which is rather well ordered crystallographically where leaching of silica and potassium did not progress far some illite may have persisted with the kaolinite elsewhere more intense desilication of the flint clay sediment produced diaspora or less commonly boehmite flint clay is an intermediate member of the flint clay facies which landward from marine shale includes non marine plastic semi plastic semi flint and flint clay with commonly associated diaspora or boehmite sedimentologically associated with it is also sandy flint clay sandstone sporadic coal carbonaceous clay pyrite tripolitic chert and cherty conglomerates it is doubtful that the process of resilication of high alumina minerals produced commercial deposits of flint clay

late quaternary lake level record from northern eurasia lake records from northern eurasia show regionally coherent patterns of changes during the late quaternary lakes peripheral to the scandinavian ice sheet were lower than those today but lakes in the mediterranean zone were high at the glacial maximum reflecting the dominance of glacial anticyclonic conditions in northern europe and a southward shift of the westerlies the influence of the glacial anticyclonic circulation attenuated through the late glacial period and the westerlies gradually shifted northward such that drier conditions south of the ice sheet were confined to a progressively narrower zone and the mediterranean became drier the early holocene shows a gradual shift to conditions wetter than present in central asia associated with the expanded asian monsoon and in the mediterranean in response to local monsoon type circulation there is no evidence of mid continental aridity in northern eurasia during the mid holocene in contrast the circum baltic region was drier reflecting the increased incidence of blocking anticyclones centered on scandinavia in summer there is a gradual transition to modern conditions after ca 5000 yr b p although these broad scale patterns are interrupted by shorter term fluctuations the long term trends in lake behavior show a clear response to changes in insolation and glaciation

holocene sedimentology of hypersaline lake urmia northwestern iran abstract a limnogeological expedition examined the sedimentary record of lake urmia one of the world s largest saline lakes located in a tectonically active arid intermontane plateau in northwestern iran near the cradle of western civilization lake urmia resembles the great salt lake u s a in many respects of morphology water chemistry and sediments the present lake area is about 5000 km 2 shallow 8 12 m and a perennial sodium chloride sulfate system 22 salts high resolution 3 5 khz seismic profiles show morphological relicts from a desiccation playa phase buried below only a few meters of sediments from lacustral phases in places around the deeper areas the lake floor is not smooth but covered with mounds aligned in prevailing current directions these are erosional relicts rather than bioherms sediments comprise aragonite chemical precipitates fecal pellet sands detrital clayey muds thin aragonite crusts oolites various gypsum types and occurrences of dolomite in peripheral areas organic matter characteristic of the present shorelines is not preserved at depth in basinal areas piston cores up to 6 m long penetrated a holocene sequence of hypersaline facies with laminated aragonite fecal pellet muds and bottomed in a playa mudflat facies with central gypsiferous muds and marginal terrigenous to dolomitic muds preliminary radiocarbon and pollen analyses suggest a playa stage prior to 9000 yr b p with saline lake deposition in a cool arid climate from 9000 to 7500 yr b p higher energy facies prevailed in a shallow saline lake and since then present day saline environments have persisted with evidence of numerous second order water level fluctuations the preliminary results suggest a lake system out of phase with north african and some other middle eastern lakes

geologic co2 storage in arkosic sandstones with cacl2 rich formation water abstract the feasibility of geologic co2 storage in deeply buried arkosic sandstones has been tested using high temperature high pressure short term laboratory experiments and long term numerical simulations with co2 saturated solution rich in cacl2 these conditions mimic the conditions found today in the eocene reservoir sandstones of depleted oilfields in the dongying sag bohai bay basin china experiments at 100 c and 150 c and pco2 of 4 mpa were conducted on sandstones rich in k feldspar and albite without anorthite during the experiments calcite and kaolinite precipitated while albite and k feldspar partly dissolved ca2 in formation water is shown to be critical for mineral trapping of co2 the continuous dissolution of k feldspar and albite at a slow rate for a long time period can prolong duration time of calcite precipitation and increase geologic co2 storage capability by mineral trapping addition of nacl kcl and mgcl2 can prolong the dissolution time of k feldspar and albite and precipitation duration of calcite it also increased the mass of sequestered co2 by mineral trapping the process of geologic co2 storage can be divided into 3 stages in stage i calcite precipitates rapidly and geologic co2 storage is dominated by solubility trapping within 100 years stage ii lasts up to 300 years in the solution without nacl kcl and mgcl2 and 900 years with addition of nacl kcl and mgcl2 into the solution the precipitation rate of calcite decreases abruptly and the mass of mineral trapping of co2 increases with increasing time because dissolution of k feldspar and albite causes decrease of ca activity and prolongs calcite precipitation time the geologic co2 storage is dominated by mineral trapping in stage iii reactions reach equilibrium and the mass of geologic co2 storage reaches the maximum the calculated mass of co2 by mineral trapping in sandstones of the es4x to es3z in the dongying sag is about 3 61gt

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

palaeomagnetic investigations in the hercynian mountain belt of central europe abstract the palaeomagnetism of sediments and volcanics of middle devonian to early carboniferous age has been studied in the hercynian realm of the vosges harz and franconian forest france and germany after appropriate cleaning characteristic directions of natural remanent magnetization nrm have been determined which are considered to be of pretectonic origin according to rock magnetic and structural geological evidence a mean palaeopole for the devonian rocks in the areas investigated was determined at 29 7 n and 9 0 e the site latitude derived from the devonian rocks agrees very well with that observed in great britain and britanny the significant difference in longitude between our devonian poles and the other european data may be due to an anticlockwise rotation of central europe with respect to the northern hercynian foreland the carboniferous rocks yield a mean palaeopole at 41 7 n and 340 4 e matching the carboniferous part of the european polar wander path a fold test within carboniferous greywackes from the harz mountains proves a pre folding origin of the nrm of these rocks however this stable magnetization direction indicates local or regional tectonic displacement our results do not support any major latitudinal motions of continental segments in central europe during the hercynian orogeny the palaeozoic palaeomagnetic data from the vosges franconian forest harz britanny and central massif can be used to interpret the hercynides in terms of a large scale shear belt

genesis of authigene carbonate minerals in the upper cretaceous reservoir honggang anticline songliao basin a natural analog for mineral trapping of natural co2 storage abstract dawsonite naalco 3 oh 2 as a trace mineral of co 2 is abundant in the upper cretaceous reservoir of the honggang anticline southern songliao basin petrologic and isotopic geochemical characteristics have been investigated by a polarizing microscope a scanning electron microscope sem x ray diffraction xrd cathode luminescence cl fluid inclusions and carbon oxygen isotopic analysis the diagenetic sequence indicated that dawsonite late generation microcrystalline quartz late generation kaolinite late generation calcite and ankerite was formed after co 2 flooding meanwhile as a function of analysis on carbon oxygen isotope the mantle magmatic co 2 provided a carbon source for the precipitation of dawsonite late generation calcite and ankerite the three kinds of carbonate minerals mentioned earlier grew in a progressively evolved condition using a basic thermodynamic fraction equation the total quantity of natural co 2 captured by dawsonite bearing sandstones per cubic meter was calculated to be 99 51 kg

controls on co2 fate and behavior in the gullfaks oil field norway how hydrogeochemical modeling can help decipher organic inorganic interactions oil degradation in the gullfaks field led to hydrogeochemical processes that caused high co2 partial pressure and a massive release of sodium into the formation water hydrogeochemical modeling of the inorganic equilibrium reactions of water rock gas interactions allows us to quantitatively analyze the pathways and consequences of these complex interconnected reactions this approach considers interactions among mineral assemblages anorthite albite k feldspar quartz kaolinite goethite calcite dolomite siderite dawsonite and nahcolite various aqueous solutions and a multicomponent fixed pressure gas phase co2 ch4 and h2 at 4496 psi 31 mpa reservoir pressure the modeling concept is based on the anoxic degradation of crude oil irreversible conversion of n alkanes to co2 ch4 h2 and acetic acid at oil water contacts these water soluble degradation products are the driving forces for inorganic reactions among mineral assemblages components dissolved in the formation water and a coexisting gas at equilibrium conditions the modeling results quantitatively reproduce the proven alteration of mineral assemblages in the reservoir triggered by oil degradation showing 1 nearly complete dissolution of plagioclase 2 stability of k feldspar 3 massive precipitation of kaolinite and to a lesser degree of ca mg fe carbonate and 4 observed uncommonly high co2 partial pressure 61 psi 0 42 mpa at maximum the evolving composition of coexisting formation water is strongly influenced by the uptake of carbonate carbon from oil degradation and sodium released from dissolving albitic plagioclase this causes supersaturation with regard to thermodynamically stable dawsonite the modeling results also indicate that nahcolite may form as a co2 sequestering sodium carbonate instead of dawsonite likely controlling co2 partial pressure

gas water rock interactions in frio formation following co2 injection implications for the storage of greenhouse gases in sedimentary basins to investigate the potential for the geologic storage of co2 in saline sedimentary aquifers 1600 t of co2 were injected at 1500 m depth into a 24 m thick sandstone section of the frio formation a regional brine and oil reservoir in the u s gulf coast fluid samples obtained from the injection and observation wells before co2 injection showed a na cacl type brine with 93 000 mg l total dissolved solids tds at near saturation with ch4 at reservoir conditions following co2 breakthrough samples showed sharp drops in ph 6 5 5 7 pronounced increases in alkalinity 100 3000 mg l as hco3 and fe 30 1100 mg l and significant shifts in the isotopic compositions of h2o dissolved inorganic carbon dic and ch4 geochemical modeling indicates that brine ph would have dropped lower but for the buffering by dissolution of carbonate and iron oxyhydroxides this rapid dissolution of carbonate and other minerals could ultimately create pathways in the rock seals or well cements for co2 and brine leakage dissolution of minerals especially iron oxyhydroxides could mobilize toxic trace metals and where residual oil or suitable organics are present the injected co2 could also mobilize toxic organic compounds environmental impacts could be major if large brine volumes with mobilized toxic metals and organics migrated into potable groundwater the d 18 o values for brine and co2 samples indicate that supercritical co2 comprises 50 of pore fluid volume 6 mo after the end of injection postinjection sampling coupled with geochemical modeling indicates that the brine gradually will return to its preinjection composition

a geological study of lake van eastern turkey lake van is a lake with a volume of 607 km3 and a maximum depth of 451 m in a tectonically active zone in eastern anatolia it may be divided into three physiographic provinces lacustrine shelf sublacustrine slope and lake basin the shelf is largely made up of submerged fluvial valleys and alluvial plains as evidenced by the local occurrence of karst like topography buried leveed river valleys and sediment wedges interpretable as relict deltas the shelf and basinal deposits are characterized by an alternating succession of well stratified and chaotically reflecting layers consisting of turbidites and slump deposits respectively this thick sequence of unconsolidated to consolidated sediments is underlain by a paleozoic metamorphic or upper cretaceous limestone basement

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

mineralogical and geochemical consequences of the long term presence of co2 in natural reservoirs an example from the springerville st johns field arizona and new mexico u s a abstract the springerville st johns co2 field in eastern arizona and western new mexico is one of more than a dozen gas fields developed within the colorado plateau and southern rocky mountain region extensive travertine caco3 deposits record a long history of co2 migration and leakage to the atmosphere the oldest travertine deposits may have formed during the initial filling of the co2 reservoir when groundwaters exsolved co2 upon reaching the surface the youngest travertine deposits are associated with springs on the floor of the little colorado river valley but travertine deposition appears to be insignificant today older deposits occur up to 325 m above the valley floor geologic relationships suggest travertine deposition began in the late pleistocene after volcanic activity ended at 0 3 ma most of the caco3 could have been derived from dissolution of the underlying limestones and dolomites interactions between the reservoir fluids and rocks were observed in core samples from one of the intervals that produced dry gas these reactions resulted in the dissolution of carbonate cements and detrital feldspars and the formation of dawsonite and kaolinite geochemical simulations suggest that the dawsonite could have been deposited when the co2 fugacity reached 20 bars and that the kaolinite formed as the co2 fugacity decreased corrosion of drill pipe by acidic waters and a pronounced hco3 anomaly above the co2 reservoir provide evidence of a continuing flux of co2 from depth co2 storage occurs primarily as dissolved carbonate species and as gas accumulations only a small percentage of the co2 was sequestered in secondary minerals

computer simulation of co2 trapped through mineral precipitation in the rose run sandstone ohio abstract equilibrium path of reaction and kinetic modeling of co2 brine mineral reactions in the rose run sandstone one of ohio s deep saline aquifers was conducted in order to investigate the factors that are likely to influence the capacity of this formation to trap injected co2 as solid carbonate mineral phases equilibrium modeling was applied to investigate the impact of temperature pressure mineralogy brine composition and co2 fugacity on mineral dissolution and precipitation the amount of co2 sequestered and the form of sequestration path of reaction and kinetic modeling were used to evaluate intermediate products and reaction progress as a function of time as well as to investigate the impact of brine to rock ratio the results of equilibrium modeling demonstrate that dissolution of albite k feldspar and glauconite and the precipitation of dawsonite and siderite are potentially very important for mineral trapping of co2 according to the path of reaction and kinetic modelling the stability of carbonate rocks is controlled by the brine to rock ratio the ph of the system the fugacity of co2 and the kinetic rate of dissolution in kinetic modeling with a brine to rock ratio of 1 25 reactive surface area of 10 cm2 g 10 mpa f co 2 and 12 porosity 1 5 2 g of co2 per kg of reacted rock significant quantities 10 40 g of carbonate minerals were precipitated from both the sandstone and mixed rock assemblages the rose run sandstone has the potential to store co2 over millennia as a negatively buoyant aqueous solution and ultimately as immobile carbonate minerals

pollen and clay mineral assemblages of a late miocene lacustrine sequence from the northwestern ethiopian highlands a unique pollen spore flora from a lacustrine deposit overlying an 8 myr old basalt flow on the northwestern ethiopian highlands is described a total of 126 pollen taxa is recorded the pollen flora presents strong characteristics of a lowland rainforest and lacks the diagnostic elements of upland forests the gymnosperms podocarpus and juniperus in east africa the commonest savanna element that characterizes the pollen diagrams from east africa the gramineae is very weakly represented the pollen spore diagram which is constructed from 20 selected taxa shows six distinct developments of the palaeovegetation during the deposition of the lake beds semi quantitative evaluation of the distribution of three diagnostic clay minerals shows developments parallel to that of the microflora kaolinite and illite are dominant in the humid pollen zone and an increase of smectite towards the end of the sedimentation period seems to agree with the observed general aridity trends in the clay mineral assemblages of equatorial zones towards the end of the miocene the flora most probably predates the late cenozoic global cooling and the mediterranean desiccation the northerly presence of lowland rainforest type vegetation as suggested by the composition of the chilga palaeoflora as recent as the latest miocene is of great interest for the phytogeographic evolution of the continent

structural synthesis of s staffordshire uk implications for the variscan evolution of the pennine basin the presence of strata of westphalian a to possibly stephanian age in south staffordshire located at the southern margin of the pennine basin provides a rare control on the timing of late carboniferous deformation in central england during westphalian a c times sedimentation in south staffordshire was controlled by thermal subsidence with a superimposed influence of synsedimentary normal and reverse faulting alkaline basic igneous activity occurred during westphalian c times synchronous with uplift of the southern margin of the pennine basin uplift culminated during westphalian c d times in a phase of variscan inversion along basement lineaments and the development of a regional unconformity renewed subsidence and deposition of a relatively thick sedimentary sequence of westphalian d to possibly stephanian age was followed by a final phase of variscan deformation comprising possibly two pulses of uplift tilting and erosion observations presented for south staffordshire in conjunction with studies from other parts of the pennine basin indicate a complex interrelationship between rifting thermal subsidence and variscan basin inversion pulses of n s extension and e w to nw se compression are interpreted as the product of regional strike slip deformation superimposed upon a regime of thermal subsidence alkaline igneous activity is considered to be the product of mantle partial melting in response to limited decompression due to transtensional displacements on crustal thickness faults

the late holocene climate change vegetation dynamics lake level changes and anthropogenic impacts in the lake urmia region nw iran two short 100 and 175 cm long sediment cores from the southwestern corner of lake urmia provide a record of vegetation dynamics lake level changes and the role of climate and humans in shaping the landscape around lake urmia over the last 2550 years relatively low values of arboreal pollen ap and substantial values of artemisia pollen from 2550 to 1500 cal bp indicate the prevalence of steppe vegetation and relatively arid climate in the area however a prominent peak of riella spores may indicate a short lived lake level rise for the period 1900 2000 cal bp the next period 1500 550 cal bp is characterized by substantial rise in ap particularly quercus and a sharp decline of artemisia chenopodiaceae amaranthaceae and wetland pollen types suggesting the expansion of oak forests under a rather moist climate and or a decline in agro sylvo pastoral practices in the area agricultural activity in the area can be inferred from sporadic occurrences of vitis ricinus and juglans pollen from the beginning of the record the rise of saline habitat pollen types between 1100 and 800 cal bp along with increased values of magnetic susceptibility and organic matter suggest a lower water level and the subaerial exposure of saline mud flats which could favour the re colonization of chenopods and other halophytes around the margins of the lake thus the medieval climatic anomaly seems to be warmer than present in the lake urmia region from 450 to 150 cal bp the decline in quercus and high values of artemisia along with higher lake levels and high magnetic susceptibility values could be associated with the little ice age since 500 cal bp quercus and riella steadily decline and fade out towards the surface of the core whereas pollen types attributable to steppe and desert vegetation increase a prominent increase in organic matter in the uppermost part of the record could be associated with a lower lake level and the expansion of wetland vegetation in the recent past our findings suggest that the regional forest coverage in the highlands of zagros and azerbaijan has reached its minimum during recent decades while urmia s lake level dropped dramatically increasing its water salinity most likely as a function of extensive anthropogenic activities and general climate aridification c 2015 elsevier ltd and inqua all rights reserved

petrological record of co 2 influx in the dongying sag bohai bay basin ne china abstract dawsonite occurs in sandstones of the fourth member of the shahejie formation dongying sag bohai bay basin northeastern china the paragenesis sequence formation temperatures carbon dioxide co2 and aqueous medium origin of dawsonite from the binnan area were studied to understand the formation of dawsonite as a possible mechanism for mineral trapping of co2 in carbon capture and storage ccs programs the petrological and geochemical characteristics of the dawsonite bearing sandstones were identified using polarizing microscope examination scanning electron microscope x ray fluorescence x ray diffraction and stable isotopic analyses the paragenesis sequence of the authigenic minerals are mainly quartz overgrowth early stage calcite a ferrocalcite dawsonite late stage calcite b ankerite siderite the carbon and oxygen isotope compositions of dawsonite reveal that 13c values of dawsonite range from 2 27 to 3 50 indicating inorganic co2 the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite range from 7 2 to 1 6 suggesting that co2 originated mainly from degassing of mantle derived magmas and partly from thermal decomposition of carbonate rocks as supported by regional magmatic activities rifting and observation of carbonate during drilling in well bin76 the 18o values of dawsonite vary from 17 2 to 19 8 and the calculated 18o values of h2o in isotopic equilibrium with dawsonite range from 2 1 to 0 4 the mixed aqueous medium was mainly connate water influenced by magmatic activities and meteoric water influx during the formation of dawsonite according to oxygen isotope data the formation temperatures of dawsonite in the binnan area range from 77 c to 95 c which are consistent with the estimated paleo temperatures 79 c to 85 c indicating that the dawsonite formed at the late stage of the diagenetic phase

a new variscan deformation map of england and wales collections of bedding orientations from subareas of 550 km 2 are used to define bedding fabrics from the variscan fold belt and foreland in england and wales the bedding fabrics constructed from data taken from published geological maps 1 50 000 scale are analysed in terms of the scheidegger watson orientation tensor the calculated eigenvalues of the orientation tensor define the average structural trends including the best fit fold axis for each subarea the eigenvectors of the tensor allow the original sedimentary fabrics to be distinguished from those modified by deformation the progressive tectonic modification of these fabrics leads to the concept of fabric evolution paths and the extent of the modification is expressed by a deformation parameter although it is emphasised that this parameter is not solely a function of finite strain magnitude its variation is represented on a map which brings out different degrees of variscan tectonic modification of bedding fabrics this map delineates a variscan bedding fabric front corresponding to the northern boundary of a zone of pervasive and strong deformation in the foreland this new analysis allows the variation of variscan trends to be mapped and the significance of these trends to be quantified in terms of deformation magnitude 1999 elsevier science b v all rights reserved

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