the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications the main aim of this paper is to review middle permian through middle triassic continental successions in european secondly areas of middle late permian sedimentation the permian triassic boundary ptb and the onset of triassic sedimentation at the scale of the westernmost peri tethyan domain are defined in order to construct palaeogeographic maps of the area and to discuss the impact of tectonics climate and sediment supply on the preservation of continental sediment at the scale of the western european peri tethyan basins the upper permian is characterised by a general progradational pattern from playa lake or floodplain to fluvial environments in the northern variscan belt domain areas of sedimentation were either isolated or connected to the large basin which was occupied by the zechstein sea in the southern variscan belt during the late permian either isolated endoreic basins occurred with palaeocurrent directions indicating local sources or basins underwent erosion and or there was no deposition these basins were not connected with the tethys ocean which could be explained by a high border formed by corsica sardinia palaeorelief and even parts of the kabilia microplate the palaeoflora and sedimentary environments suggest warm and semi arid climatic conditions at the scale of the whole study area an unconformity more or less angular is observed almost everywhere between deposits of the upper permian and triassic except in the central part of the germanic basin the sedimentation gap is more developed in the southern area where in some basins upper permian sediment does not occur the large sedimentary supply erosion and or lack of deposition during the late permian as well as the variable palaeocurrent direction pattern between themiddle late permian and the early triassic indicate a period of relief rejuvenation during the late permian during the induan all the intra belt basins were under erosion and sediment was only preserved in the extra belt domains the northern and extreme southern domains in the northern domain the central part of the germanic basin sediment was preserved under the same climatic conditions as during the latest permian whereas in the extreme southern domain it was probably preserved in the tethys ocean implying a large amount of detrital components entering themarinewaters mesozoic sedimentation began in the early olenekian the ephemeral fluvial systems indicate arid climatic conditions during this period three distinct areas of sedimentation occur a northern and southern domain separated by an intra belt domain the latter accumulated sediments during the early middle permian and experienced erosion and or no deposition conditions between the middle late permian and the beginning of mesozoic sedimentation dated as anisian to hettangian at the top of the lower triassic another tectonically induced more or less angular unconformity is observed the hardegsen unconformity which is dated as intra spathian and is especially found in the north european basins this tectonic activity created new source areas and a new fluvial style with marine influences at the distal part of the systems during the anisian and ladinian continental sedimentation was characterised by a retrogradational trend in other words the fluvial system evolved into fluvio marine environments attesting to a direct influence of the tethys ocean in the southern and northern domains both at the end of the olenekian spathian and during the anisian the presence of palaeosols micro andmacrofloras indicate less arid conditions throughout this domain

the continental rift system of the rhinegraben structure physical properties and dynamical processes abstract the geophysical investigation of the continental rift system of the rhinegraben by various methods has progressed to such a stage that details of structure physical properties and seismic activity and relations between these features can be recognised differences in the nature of the crust mantle boundary inside and outside the graben proper seem to be a typical property of continental rifts asymmetries of structure seismic activity temperature in the crust and physical properties in the lithosphere are an important clue to the understanding of rift dynamics these asymmetries indicate that the formation of the rift cannot be explained by the updoming of an asthenolith alone but that taphrogenesis took place in the foreland of the continent continent collision in the alpine mediterranean zone a number of future key experiments is proposed

a mechanical and thermal model for the evolution of the williston basin the williston basin is a large circular intracratonic basin containing over 4 km of sediments ranging in age from cambrian to tertiary data on seven formations from over 1300 wells in montana south dakota and north dakota were used to determine the shape of the basin over time by assuming that the lithosphere behaves like an elastic plate on a fluid substrate the shape of the basin could be closely matched using a point load the match was improved by adding the equation of a plane to the equation for elastic deformation before fitting the model to the data the planar adjustment allows for the effects of regional sedimentation or erosion or eustatic sea level changes the mechanical modeling indicates that the elastic strength of the lithosphere in this area has generally increased from the ordovician to the present the geometrical center of the basin migrated less than 20 km over 450 m y the direction and magnitude of tilt of the plane removed from the data is related to tectonic events in western north america the increasing deflection of the basin over time can be explained by a simple thermal model which would explain the thickening of the lithosphere consisting of conductive cooling of a hot region in the lithosphere depths to formations in a single well differ from the subsidence predicted by the elastic model with regional tilt removed because of global sedimentation events and the development in the mesozoic of a foreland thrust basin of which the williston basin became part the mechanical and thermal models constrain possible initiating mechanisms for this basin the thermal modeling and the absence of volcanics in the stratigraphic column rule out a shallow crustal heat source neither wrench faulting nor crustal stretching were likely to have been significant in the formation of the williston basin

geological and mechanical study of argillaceous north sea chalk implications for the characterisation of fractured reservoirs abstract argillaceous chalk intervals from the north sea are characterised by matrix permeabilities lower than 0 2 md and therefore they are defined as tight chalks hence fracture networks within these chalks are of major importance to predict fluid flow and reservoir or seal behaviour this study aims to understand the geological parameters controlling the chalk petrophysical and mechanical properties using the outcrop analogue of the cenomanian chalk at cap blanc nez northern france sedimentological petrographic and petrophysical analyses were performed and show that the combination of the depositional environment and diagenetic imprint control the microtexture non carbonate content is ranging from 5 to 40 within the studied samples and is critical for the diagenetic imprint the fracture behaviour of the chalk was studied using a mechanical stratigraphy approach throughout the 70 m thick succession where a transition between lower cenomanian argillaceous chalk and middle upper cenomanian pure chalk is exposed twenty two mechanical units are distinguished and the amount of fractures crosscutting initiating and terminating on mechanical interfaces quantified manual scanlines show that fracture spacing ranges from 17 to 232 cm mechanical interfaces are associated with lithological heterogeneities with strong microtextural contrasts related to the non carbonate content and or degree of cementation the mechanical units are thus defined either by deposition or diagenesis the fracturing behaviour of about 10 m homogeneous pure chalk interval units defined as dfz densely fractured zones differs significantly from the rest of the succession large sigmoidal shaped fractures are confined to those intervals and a dense fracture network developed because of their plastic behaviour clay layers are able to accommodate part of the stress whereas homogeneous pure chalk show a more brittle behaviour

scaling properties of normal fault populations in the western corinth graben greece implications for fault growth in large strain settings abstract a variety of one dimensional and two dimensional map techniques of fractal analysis have been employed to investigate the scaling properties of the dominant wnw trending normal fault population of the western corinth graben in central greece to assess possible constraints on fault geometry during fault growth the data have been compiled separately from the northern and southern domains of the graben which have experienced differing amounts of finite strain based on power law distributions of the fault throw the applied extension is estimated at 30 and 22 for the northern and southern domains respectively however the fault spacing and fault length populations in both domains obey similar power law relationships these conclusions are also supported by maximum throw vs trace length data which demonstrate that the faults in the northern domain have systematically higher values for the slip to length ratios than those in the southern domain it is proposed that the corinth graben has reached fracture saturation that is the fault spacing stops evolving and displacement increases rather than faults lengthening to accommodate the increasing extension this growth process consistent with throw distributions along individual faults may be explained either in terms of a stress feedback mechanism or by the mechanical interaction between the wnw trending normal faults with a set of nne trending transverse faults

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

subsidence of the paris basin we discuss the main results of a systematic quantitative analysis of the subsidence of the paris basin made on 100 wells backstripping techniques with decompaction as well as sea level and water depth corrections are used to derive tectonic subsidence curves in the absence of water and sediment loading assuming local as well as regional compensation a best fitting sea level variations curve is derived for the deepest central part on the basis of the resulting tectonic subsidence curve the adopted amplitude of the regression since upper cretaceous is 330 m the spatial and temporal distribution of tectonic subsidence is reconstructed and discussed it is shown that rigidity of the lithosphere with an adopted 50 km flexural parameter plays a significant role these results are then quantitatively interpreted in terms of the lithospheric stretching model this interpretation is reasonable provided it is made in terms of volumetric subsidence over the whole basin because of the thermal conduction and the rigidity low pass filtering effects the subsidence can be explained if the axial zone was thinned during permo triassic by a factor of about 1 3 with respect to the adjacent lithosphere it is shown that either the initial altitude was more than 500 m above sea level or the lower part of the lithosphere was lost at the beginning of the permo triassic phase of extension resulting in a rapid uplift of several hundreds of meters the similarity of the permo triassic initiating extensional phase with active continental rifting is shown

reconstruction of low temperature 100 c burial in sedimentary basins a comparison of geothermometer in the intracontinental paris basin abstract the thermal evolution of sediments in the shallowest part of sedimentary basins is challenging to investigate as most of the geothermometers are at their application limits this is typically the case of the callovian oxfordian claystones at the eastern border of the paris basin a recent 2000 m deep well penetrated the entire jurassic and triassic sedimentary series and permitted coring of sediments never reached by previous drilling in this part of the basin thanks to the use of several independent geothermometers apatite fission track thermochronology fluid inclusion microthermometry clay mineralogy and sedimentary organic matter evolution the burial history of the mesozoic series has been reconstructed modeled and calibrated using kinetic algorithms relevant to the various paleothermometers used in addition to these conventional methods an innovative approach was developed using the temperature dependence of the magnetic mineral assemblage within clay rich sediments mageval thermal modeling indicates that the callovian oxfordian and the lower triassic experienced maximum burial temperatures of 50 5 c and 90 10 c respectively i e about 25 c higher than present day this temperature offset implies the erosion of several hundred meters of sediments which depending on the thermal flux and conductivity considered most likely constituted upper cretaceous chalk deposits falling sea level resulted in the exposure and subsequent dismantling of the chalk cover at the beginning of cenozoic times the eastern border of the basin was then subjected to slow erosion and discrete tectonic deformation

keuper stratigraphic cycles in the paris basin and comparison with cycles in other peritethyan basins german basin and bresse jura basin abstract high resolution sequence stratigraphy of the keuper paris basin is used to establish correlations between the basin centre evaporite series and the basin margin clastics series the high resolution correlations show stratigraphic cycle geometries the keuper consists of five minor base level cycles whth occur in the upper portion of the scythian carnian major base level cycle and the lower part of the carnian liassic major base level cycle the maximum relative rate of subsidence for the base level fall phase of the scythian carnian major cycle occurs in the eastern part of the paris basin during the base level rise phase of the carnian liassic major cycle the area of highest rate of subsidence shifted westwards and northwards this shift records the first occurrence of an independent paris basin which was no longer merely the western margin of the german basin two phases of tectonic movement influenced evaporite sedimentation and sequence geometries by creating areas of subsidence where halite could accumulate the second within the marnes irisees superieures induced a general westward and northward tilt of the basin concurrent migration of depocentres to the west and north produced an intra marnes irisees superieures truncation comparison of the stratigraphic records of the paris basin and of other triassic peritethyan basins german basin bresse jura basin and south east basin reveals numerous similarities the coastal onlap curve of the german keuper aigner and bachmann 1992 exhibits many similarities with the sequence evolution of the paris basin but the triassic succession is more complete in the german basin and more cycles are observed the major difference between these two basins during the keuper is that the marnes irisees inferieures minor base level cycle does not occur in the german basin in the bresse jura basin the major difference concerns the lettenkohle one minor base level cycle is recorded in the paris basin while no cycle is observed in the bresse jura basin

structural sequences and styles of subsidence in the michigan basin subsidence in the michigan basin produced 5 km of sedimentation over a period of more than 200 m y during paleozoic time utilizing well log correlations and constrained by compaction corrections and estimates of paleobathymetry we recognize four different styles of subsidence in the basin trough shaped regional tilting narrow basin centered and broad basin centered subsidence began as a trough shaped northerly extension of the illinois basin during late cambrian to early ordovician time this was followed by narrow basin centered subsidence in early to middle ordovician time basin centered subsidence ceased for 30 m y during long wavelength 1000 km eastward tilting in middle to late ordovician time a pattern incompatible with thermal contraction subsidence models basin centered subsidence resumed in silurian time but with a broader distribution a second episode of narrow basin centered subsidence occurred in latest silurian through middle devonian time and was replaced by broad basin centered subsidence at the end of middle devonian time the geometry of upper devonian and younger paleozoic deposits suggests another eastward tilting event but results remain inconclusive due to erosion of strata and uncertainties in their paleobathymetry in addition to these subsidence patterns two distinct unconformity styles are present basin wide and marginal erosion there is no evidence for significant basin centered unconformities as predicted by purely thermal mechanisms a history of episodic subsidence reactivations is interpreted as the result of a stress induced crustal weakening mechanism for the narrow basin centered subsidence whereas broad basin centered subsidence is interpreted as thermal contraction related to lower crustal attenuation during the narrow subsidence episodes recently proposed dynamic topography related to initiation of ordovician subduction provides a driving mechanism for long wavelength eastward tilting together with a temporal correlation to appalachian tectonism these mechanisms provide a plate tectonic framework for the history of the michigan basin

sea level variations global sedimentation rates and the hypsographic curve sea level changes during the neozoic have been estimated by two different methods the first involves measuring the amount of present day land area which was flooded during the past and using the present day hypsographic curve to estimate the amount of sea level rise necessary to produce this flooding the second involves the estimation of the changing volume of mid oceanic ridges through time and estimating sea level changes after having allowed for isostatic adjustment a difference in sea level of 170 m is obtained from the two methods for the cretaceous 80 100 m y b p this is equivalent to a difference in continental flooding of 24 mm 2 using the present day hypsographic curve we attempt to explain this difference firstly by allowing for the fact that the present day ocean basins have more sediment in them than did the cretaceous ocean basins this produces a sea level change in the opposite direction to that produced by the reduction in mid ocean ridge volume since the cretaceous secondly we suggest another large factor in producing the difference is that the present day hypsographic curve is not the correct one to use when studying sea level stands in the cretaceous present day average continental heights are closely related to continental areas accepting this principle if continents are joined together in the past their average height must be greater and so their hypsographic curve must be steeper a given sea level rise would produce less continental flooding during times of continental aggregation than it would today

lower paleogene denudation of upper cretaceous cover of the morvan massif and southeastern paris basin france revealed by aft thermochronology and constrained by stratigraphy and paleosurfaces abstract low temperature thermochronology data have been acquired from outcrop samples from the southeastern edge of the paris basin morvan they provide indications about the former sedimentary cover its denudation and about inversion tectonics in the paris basin apatite fission track data acquired on variscan granites and triassic sandstones reveal that the basement was subjected to temperatures of about 70 10 c during the late cretaceous we suggest that the peak temperature was generated by an upper cretaceous sedimentary cover of low thermal conductivity chalk additional stratigraphic sedimentological paleogeographic paleoweathering and continental paleosurface data support the reconstruction of this chalk paleocover and of its erosion this former blanketing sequence was removed during the early paleogene regional inversion episode which affected the southern edge of the basin intensively and was related to far field compression between europe and africa this study shows that i for the se border of the intracontinental paris basin kilometer scale vertical deformation occurred ii the sedimentary sequences of the paris basin covered considerably larger areas than the present contours of the sediment fill iii paleoweathering and erosion processes later removed the sedimentary cover rather quickly

numerical models of a subsidence mechanism in intracratonic basins application to north american basins summary mckenzie s model of sedimentary basin evolution and its modification widely used in geophysics sometimes fails to explain discrepancies between predicted and observed values of extension thinning and subsidence of the earth s crust as for the north sea we develop a numerical model of sedimentary basin evolution based on the mechanism suggested by lobkovsky in the course of rifting accompanied by thinning of lower parts of the lithosphere the roof of the underlying asthenosphere moves upward the material of the mantle lifts and partially melts owing to the reduction of pressure the density difference between the melt and the crystalline skeleton results in the filtration of the lighter melt and its accumulation in the form of a magmatic lens due to changed p t conditions the material of the lens undergoes the gabbro eclogite phase transformation the resultant anomalously heavy eclogite lens sinks in the surrounding material this induces a viscous flow changing the surface topography and forming a sedimentary basin we construct a 2 d numerical model describing a viscous flow induced by subsidence of a heavy body and compute changes of surface topography to compute the flow we employ the galerkin spline approach with modifications allowing for density discontinuities and time dependence of the phase transformation we apply the model to the cases of the illinois michigan and williston basins the computed and tectonic subsidence curves agree well for these cases the proposed model is compatible with the seismic structure of the crust and upper mantle below these basins the model is also consistent with gravity data the approach is applicable to other intracratonic basins

oxygen isotopes of marine mollusc shells record eocene elevation change in the pyrenees abstract constraining paleoaltimetry of collisional orogens is critical to understand the dynamics of topographic evolution and climate tectonics retroactions here we use oxygen stable isotope record on oyster shells preserved in marine foreland deposits to examine the past elevation of the pyrenees during the eocene our approach is based on the comparison with the paris basin an intracratonic basin not influenced by orogenic growth the finding of a shift of 1 5 between 49 and 41 ma indicating more negative 18oc in the south pyrenean foreland is interpreted to reflect the inflow of river water sourced from higher elevation in the pyrenees to test this and provide paleoelevation estimate we adopt a morphologic hydrological model accounting for the hypsometry of drainage basin our best fitting model shows that the pyrenees rose up to 2000 m this indicates that the pyrenees reached high elevation in the eocene thus providing new critical constraints on their long term orogenic development 18o of marine mollusc shells are proved potentially attractive for paleoelevation studies especially for mountain belts where elevated continental surfaces have not been preserved

the evolution of the lorraine evaporite basin implications for the chemical and isotope composition of the triassic ocean abstract during the upper triassic times about 75 m of halite with minor anhydrite was deposited in the lorraine basin samples of halite and sulfates were systematically collected from a borehole intersecting the sequence the chemical evolution of the original brine was investigated by x ray microanalysis of primary inclusions trapped in halite the original brines were of the na mg k ca cl type being consistent with the mineral association of halite and minor anhydrite their solute content can be reproduced by evaporation of present day ocean composition in an open basin however some modifications are required the inflow of a small excess of cacl 2 into the basin 1 2 to 1 9 of the total recharge is required to explain the low so 4 values analyzed in fluid inclusions the same inflow helps to explain more satisfactorily the low na and high cl contents the back reaction of the brine with previous ca sulfate that forms polyhalite could explain the low and variable k values analyzed the excess of ca with respect to present day seawater and the formation of so 4 poor evaporite sequences is the rule rather than the exception in the geological record we have not been able to assess the ultimate origin of the ca excess in the basin nevertheless the great variation of the so 4 content within short vertical distances centimeter scale suggests that these variations are due to processes taking place within the evaporite basin rather than to changes in the composition of the ocean at a global scale the isotopic composition of sulfur and oxygen was determined using samples of sulfates from the same borehole the 34 s values of 21 samples analyzed show a narrow variation 34 s 15 5 0 4 the 18 o values of eight samples analyzed show a wider range of variation 18 o 13 0 1 1 none of the processes which modify the values such as sulfate reduction or additional sulfate sources continental recycling of sulfates from the margins were clearly identified the values of 34 s sw 15 7 to 14 5 and 18 o sw 13 7 to 12 2 for the sulfate dissolved in the triassic ocean explain the values of the sulfates interbedded in the halite of the lorraine basin and most analyses reported in the literature

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

luminescence dating of the niederweningen mammoth site switzerland abstract luminescence dating is used to further constrain the so far controversial age of the mammoth site at niederweningen switzerland gamma spectrometric analyses reveal the presence of radioactive disequilibria in the uranium decay chain in most of the samples but these cause only minor uncertainties in the age estimates the major uncertainty is actually related to the problem of estimating the average water content for the whole burial time nevertheless even considering these problems involved with dose rate determination the dating results clearly indicate that the peat is significantly younger than early wurmian in contrast to some previous assumptions together with the results of radiocarbon dating and pollen analyses the luminescence ages point to a correlation of the mammoth peat with interstadial conditions during the early part of the middle wurmian at around 45 ka ago

discriminating between tectonic and eustatic controls on the stratigraphic record in the paris basin the quantification of tectonic and eustatic factors in the control of the sedimentary record is one of the main questions in sedimentary basin dynamics we propose two methods allowing i 3d measurement of accommodation at basin scale and ii to decipher between local 10 100 km wavelength and basin scale accommodation the local signal is necessarily of tectonic origin the basin scale signal is of both eustatic and large tectonic origin the measurement of accommodation requires a high resolution time lines calibrated in ages sequence stratigraphy on well logs and biostratigraphy on cores b decompacted lithologies well logs and c palaeodepth palaeoaltitude sedimentology and well logs application of these methods to the intracratonic paris basin during the lias early jurassic suggests a tectonic origin for the 1 5 myr stratigraphic cycles with basin scale flexure during transgressive half cycles and 10 100 km uplift of basement units during regressive half cycles

effect of the thermal gradient variation through geological time on basin modeling a case study the paris basin many studies investigated the thermal modeling of the paris basin for petroleum interests during the 1970s most of the softwares developed by oil companies or research centers were based on the assumption of a constant thermal gradient in order to take into consideration the variation of the thermal gradient during basin evolution we developed the thermo s visual basic 1d program we applied our model to twenty boreholes located along a cross section roughly running ew over 150 km in the center of the paris basin the numerical results were calibrated with organic matter maturity data thermo s simulates the amount of heat provided to the sedimentary organic matter the heat parameter simulated shows lateral variation along the cross section it decreases from rambouillet to trou aux loups boreholes 87 66 mw m2 at about 100 km more to the east whereas the heat flux value simulated is 73 mw m2 in st loup borehole the mean thermal gradient calculated for liassic horizons at 87 my for the rambouillet well is 50 4 c km this value is similar to previously published results by integrating the calculation of the thermal gradients and conductivities related to the burial of each stratigraphic sequence our approach points out variations in the thermal regimes the sedimentary organic matter som has been subjected to through geological time

thermal evolution of the intracratonic paris basin insights from 3d basin modelling abstract the thermal evolution of the paris basin pb has been widely studied using 1d 2d and more rarely 3d thermal models it is well documented that the pb experienced higher temperatures in the past compared to what is currently observed however a quantitative analysis of the main processes and parameters that affect the temperature distribution at the basin scale and over time is still not available in this study through basin modeling which accounts for the main processes of the thermal evolution of sedimentary basins we analyze and quantify the role of the different geological mechanisms by discriminating the causes of abnormal temperatures during the late mesozoic this is done with a 3d basin model built from base moho to present day topography using the temisflow basin modelling software the model includes thermal processes within an evolving upper crust defined by three main structural domains each crustal sector presents radiogenic heat production conductivity and thickness values which are used as input parameters to reproduce the paleo and present day basal heat flow variations observed in the basin the model calculates heat flow through time in both crust and sedimentary column where the crust is coupled with the geological evolution of the basin this approach allows estimating the eroded thickness during the main tertiary uplift event and therefore the maximum temperature in the late cretaceous the model is constrained by different types of paleo thermo chronometers and by 52 wells that are regionally distributed over the entire basin resulting in a new regional thermal history of the pb the amount of missing section in the cretaceous chalk which mainly affected the eastern part of the basin is increased by up to 500m compared with previous studies and constitutes the key controlling factor of the temperature evolution this new regional thermal history of the paris basin may be important for further analysis of the hc generation from the lower jurassic toarcian source rock and bring new insights into the geothermal potential of the basin

relationship between eustatic sea level changes and basement subsidence geohistory reconstructions based on well data provide a direct and quantitative method of estimating basement subsidence geohistories in addition to responding to rates of sediment accumulation and to local and regional subsidence mechanisms also reflect eustatic sea level changes we have determined quantitatively that component of subsidence that is common to a worldwide set of wells after compensating for the response of the crust to sedimentation we find some correlations between the global rate of subsidence and low frequency changes in the height of eustatic sea level as determined from the stratigraphic interpretation of seismic data these results suggest that basement subsidence data which are independent of the techniques used previously may be used to re ognize variations in eustatic sea level however we are unable to determine the size of the eustatic sea level excursions because of difficulties in determining and separating variations in lithospheric rigidity thermal subsidence and sediment supply independent of tectonic subsidence and sea level variation we compare subsidence curves in an empirical fashion with published eustatic sea level curves thus avoiding the application of geologic models involving crustal properties we cannot quantify geohistory analysis is also a powerful means of studying subsidence on a regional scale and so of deducing the regional tectonic history we illustrate this point by subsidence maps through time for the north sea

from a mountain belt collapse to a sedimentary basin development 2 d thermal model based on inversion of stratigraphic data in the paris basin abstract the thermal mineralogical and mechanical behaviour of the lithosphere determines the genesis and evolution of sedimentary basins subsidence amplitude geometry of sediment bodies sedimentary processes using the large stratigraphic database available for the paris basin we constrain the lithosphere thermal evolution thickness and rigidity as well as the mechanism that gave birth to this wide intracontinental basin the thermal subsidence calculated with a two dimensional thermal model is adjusted to the estimated tectonic subsidence by optimization of three parameters extension profile crustal thickness profile and average mantle heat flow the best fits for the paris basin lithosphere are obtained for a mantle heat flow of 23 mw m 2 and for an elastic thickness lower than 20 km preferred value te 5 km two mechanisms for the origin of the basin subsidence have been tested a pure extensional collapse of the variscan belt and a delamination of the mantle lithosphere at the end of carboniferous it appears that in both cases inverted extension factors are large in the range 1 2 1 85 in the first case and in the range 1 0 1 85 in the second case both cases involve the presence of a thick variscan crustal wedge and a mountain belt elevation of 1500 3500 m located in the paris basin centre the maximum extensional rates are obtained in the centre part of the basin in addition lithospheric delamination at around 300 ma allows for both crustal and mantle melting in agreement with the widespread existence of permian bimodal magmatism in france at the end of extension the basin centre kept a high elevation of about 1000 m before subsiding around 40 my later below sea level

successive post variscan stress fields in the french massif central and its borders western european plate comparison with geodynamic data abstract structural analysis and particularly microtectonic methods have made it possible to define the different stages of brittle deformation of the massif central basement and the surrounding sedimentary cover from the end of the hercynian orogeny to the end of the tertiary during the stephanian a compressional tectonic regime prevailed regional faults appeared or were react vated reactivation as a result of initial n s compression becoming nw then e w these regional strike slip faults caused local extension which led to the formation of small coal bearing basins this compressional regime which marked the end of the formation of pangea was followed by a series of extension episodes permian triassic extension oscillating around n s e w to nw se extension in the early and middle jurassic and finally n s to ne sw extension in the late jurassic to cretaceous the normal faults formed during these episodes strongly influenced the distribution of emerging continents and sedimentary basins from the campanian 75 ma to the present the convergence of africa and eurasia involved the distribut on of stresses in the west european plate several tectonic episodes are distinguished in the massif central during the eocene approximately n s compression predominated general e w extension in the late eocene oligocene resulted in grabens with general northerly strike mainly in the centre of the massif central and on its east and southeast borders lastly compression varying from nw se to e w in the north and south of the massif central prevailed during the alpine orogenic phase at the end of the miocene these successive stages of brittle deformation are interpreted in the context of the evolution of the west european plate and its displacement in relation to the african plate the correspondences between the major geodynamic periods and the distribution of stresses over the west european continent are noted as well as the problems which remair to be resolved

parameterized rift development and upper mantle anomalies abstract the evolution of rift zones is studied by comparing some of their parameters parameters are e g the regional and axial values and the amplitudes of topography bouguer and free air gravity anomalies the study includes the rhine graben baikal east africa afar the red sea hon graben godawari rift and others we attempt to recognize trends e g with age the most interesting results are 1 1 the grouping into two famillies of rift zones which we call continental and oceanic 2 2 the decay of the negative axial bouguer anomaly with age toward zero while the oceanic trend overshoots zero 3 3 the rise and fall of the regional altitude of the rift shoulders with age or time although the approach is crude and involves some problems the results are encouraging they can be explained plausibly with an isostatic model of a hot low density front rising through the lower lithosphere and causing uplift doming and rifting of the crust and giving the characteristic gravity anomalies at the same time

effects of finite rifting times on the development of sedimentary basins abstract most thermo mechanical models for the development of sedimentary basins have assumed that the rifting responsible for the formation of the basin occurred instantaneously and have examined the post rift development of the basin this assumption greatly simplifies the mathematical treatment but is not in accord with what is found in nature where 10 to 50 m y rifting events commonly accompany the formation of sedimentary basins and continental margins the effects of a finite rifting time on the development of sedimentary basins are examined using an analytic technique which allows an arbitrary rifting history in both time and space and which considers the effects of both vertical and horizontal heat transfer this technique allows the thermal structure of the lithosphere to be calculated throughout the rifting event and thus permits the subsidence history and surface heat flow of the developing basin to be traced the effect of a finite duration extension event is that heat is lost during rifting increasing the syn rift subsidence at the expense of the post rift lateral heat flow which was not included in previous studies of the effect of finite rifting times has a significant effect on the subsidence history distribution of sediments and thermal history in particular the post rift subsidence is decreased by more than 25 for a 20 m y rifting event and by more than 10 15 for a rifting event as short as 10 m y this will significantly decrease the subsidence rates in the post rift stage and implies that inferences concerning the structure development and thermal history of the basin derived from using curves to interpret backstripped subsidence can be greatly in error variations in syn rift sediment accumulation and lithospheric thermal structure at the end of rifting resulting from different rifting histories can interact with other factors such as the flexural response of the lithosphere to sediment loading to affect the final width of the basin the total amount of sediments that accumulate and the basin stratigraphy

tectonics and sedimentation in a paleo mesoproterozoic rift sag basin espinhaco basin southeastern brazil abstract sedimentologic paleogeographic stratigraphic structural and tectonic studies in a paleo mesoproterozoic metasedimentary succession espinhaco megasequence southeastern brazil indicates deposition in a rift sag basin four basin evolution stages are recognized prerift rift transitional and flexural the four stages can be represented by six unconformity bounded tectonosequences the unconformities are recognized in the field and mappable even on a regional scale the prerift and rift stages of the espinhaco basin were filled by products of continental depositional systems the prerift stage probably represents the first product of the rifting process before the development of the half grabens that characterize the rift stage during the rift stage mechanical subsidence due to lithospheric stretching was predominant and led to episodic rising of the depositional base level as a result the basin fill is characterized by coarsening upward intervals paleocurrent patterns indicate that block tilting and half graben subsidence uplift controlled sediment dispersion the first marine incursion within the espinhaco basin marks the change in the subsidence regime of the basin the evolution of the transitional and flexural stages was probably controlled by thermal subsidence due to thermal contraction of the lithosphere during cooling the transitional stage was characterized by relatively low subsidence rates higher subsidence rates and a consequent sea level rise characterize the flexural stage of the espinhaco basin in which three second order transgressive progradational sequences can be recognized

clay mineralogical and geochemical expressions of the late campanian event in the aquitaine and paris basins france palaeoenvironmental implications campanian sediments from two french sedimentary basins were studied using clay mineralogy and stable isotope 13c and 18o geochemistry in order to investigate the late campanian event the clay fraction of the campanian sediments from the tercis les bains section aquitaine basin and from the poigny borehole paris basin is mainly composed of smectite this background sedimentation was however interrupted during the upper campanian in the two basins by a substantial increase in detrital inputs including illite kaolinite and chlorite at tercis les bains and illite at poigny this detrital event resulting from the enhanced erosion of nearby continental areas triggered by increasing runoff has also been recognized in the tethys and south atlantic oceans it coincided with a global negative carbon isotope excursion the late campanian event lce carbon isotope stratigraphy was used to correlate the two basins with previously studied sections from distant areas spectral analysis of the bulk 13c from tercis les bains suggests a duration of ca 400 kyr for a pre lce negative excursion and ca 800 900 kyr for the lce sensu stricto the detrital event as characterized by clay mineralogy spans the interval that comprises the pre lce and the lce with a duration of 1 3 myr intensification of continental erosion during the lce may have resulted either from the late campanian polyplocum regression and or from a regional tectonic pulse that triggered the emersion of previous submerged shelf areas and the increase of silicate erosion as the lce seems to be recorded at a large geographic scale it is proposed here that enhanced chemical weathering and an associated decrease in atmospheric pco2 levels could have contributed to the long term late cretaceous cooling trend

three dimensional accommodation analysis of the keuper of the paris basin discrimination between tectonics eustasy and sediment supply in the stratigraphic record abstract during the keuper the paris basin was an intracratonic sedimentary basin filled by continental deposits using paleo environmental isopach and paleo altitude maps we estimate the variations of accommodation rate at the scale of stratigraphic minor hemi cycle 1 3 ma an analysis of the short and long wavelength accommodation variations allows us to assess the relative influence of tectonics eustasy and sediment supply on the stratigraphic record our data suggest a pattern of subsidence along three trends e w in the carnian e w to nne ssw in the norian and ne sw in the norian rhaetian during the keuper the paris basin accurately records the different phases of the opening of the tethys ocean associated with a rotation of the extension direction the norian cycle could thus reflect the intraplate stresses in a transitional period between the triassic and the liassic

post variscan evolution of the lithosphere in the rhine graben area constraints from subsidence modelling in the area of the cenozoic rhine rift system crustal and lithospheric thicknesses range between 24 and 35 km and 60 and 120 km respectively this rift system transects the deeply truncated variscan orogen and superimposed permo carboniferous wrench induced troughs and late permian and mesozoic thermal sag basins at the time of its westphlian consolidation the variscan orogen was probably characterized by 45 60 km deep crustal roots that were associated with its rheno hercynian saxo thuringian saxo thuringian bohemian and bohemian moldanubian sutures all of which are transected by the cenozoic rhine rift system during the stephanian early permian wrench induced disruption of the variscan orogen subducted lithospheric slabs were detached causing upwelling of hot mantle material during the resulting thermal surge partial delamination and or thermal thinning of the continental mantle lithosphere induced regional uplift at the same time the variscan orogenic roots were destroyed and crustal thicknesses reduced to 28 35 km in response to the combined effects of mantle derived melts interacting with the lower crust regional erosional unroofing of the crust and on a more local scale by its mechanical stretching towards the end of the early permian the potential temperature of the asthenosphere returned to ambient levels with this regional long term thermal subsidence of the lithosphere commenced controlling the development of a new system of late permian and mesozoic thermal sag basins however the evolution of these basins was repeatedly overprinted by minor short term subsidence accelerations that reflect the build up of far field stresses related to rifting in the tethyan and atlantic domains comparison of observed and modelled subsidence curves suggests that in the area of the rhine rift system the lithosphere had equilibrated with the asthenosphere at the end of the cretaceous at depths of 100 120 km before it became thermally destabilized again by cenozoic rifting and plume related magmatism modelled subsidence curves indicate that by the end of early permian times the thermal thickness of the remnant mantle lithosphere ranged between 10 and 50 km in areas that were later incorporated into mesozoic thermal sag basins this corresponds to mid permian thermal lithosphere thicknesses of 40 80 km the geological society of london 2004

the permo carboniferous saar nahe basin south west germany and north east france basin formation and deformation in a strike slip regime the permo carboniferous saar nahe basin in south west germany and north east france formed at the boundary between the rhenohercynian and saxothuringian zones within the variscan orogen where non marine sediments were deposited in a narrow structurally controlled basin the basin has an asymmetrical geometry perpendicular to the south hunsruck fault however there is a lack of growth of the sediment pile into the fault and isopach maps show the depocentre always located adjacent to the south hunsruck fault but migrating towards the north east with time this pattern is typical of a strike slip basin indicating that the south hunsruck fault was a dextral strike slip fault during sedimentation tectonic subsidence curves indicate that during the middle devonian to early carboniferous the basin subsided due to thermal relaxation of the lithosphere a change to very rapid subsidence at the start of the westphalian continued until late in the autunian this was due to mechanical subsidence associated with strike slip movement on the south hunsruck fault towards the end of subsidence in the saar nahe basin the grenzlager volcanics introduced a thermal pulse into the crust leading to thermal cooling and relaxation of the lithosphere

basin scale thermal and fluid flow histories revealed by carbonate clumped isotopes δ47 middle jurassic carbonates of the paris basin depocentre the reconstruction of past diagenetic conditions in sedimentary basins is often under constrained this results from both the analytical challenge of performing the required analyses on the minute sample amounts available from diagenetic mineral phases and the lack of tracers for some of the diagenetic parameters the carbonate clumped isotopes thermometry 47 opens new perspectives for unravelling the temperatures of diagenetic phases together with the source of their parent fluids two parameters that are otherwise impossible to constrain in the absence of exploitable fluid inclusions here is reported the study of a large number of sedimentary and diagenetic carbonate phases from middle jurassic reservoirs of the paris basin depocentre by combining detailed petrographic observations with a large number of 47 data n 45 on a well documented paragenetic sequence including calcite and dolomite burial cements the data reveal carbonate crystallization at temperatures between 29 c and 98 c from fluids with 18owater values between 7 and 2 in response to the progressive burial and uplift of the paris basin throughout 165 myr of basin evolution coupled to the time temperature evolution previously estimated from thermal maturity modelling these temperatures allow determining the timing of four successive cementation episodes the overall dataset indicates a history of complex water mixing with a significant contribution of hypersaline waters from the triassic aquifers migrated upward along faults during the cretaceous subsidence of the basin subsequent large scale infiltrations of meteoric waters induced a dilution of these pre existing brines in response to the paris basin uplift in the tertiary overall the data presented here allow proposing an integrated approach to characterize the cementation events affecting the studied carbonate reservoir units based on temperature oxygen isotope composition and salinity of the parent fluids as well as on petrographic grounds this article is protected by copyright all rights reserved

subsidence of the paris basin and its bearing on the late variscan lithosphere evolution a comparison between plate and chablis models abstract in this study two different models for the lithospheric thermal evolution are used to predict the long term subsidence of the paris basin the plate or chablis models have a constant temperature or constant heat flow at the base of the lithosphere these boundary conditions yield a different thermal relaxation time for a given equilibrium lithospheric thickness the final thermal steady state does not depend on the boundary condition fixed at the base of the lithosphere the thermal evolution of the lithosphere is computed taking into account temperature and pressure dependent thermal characteristics metamorphism in the crust top crustal erosion and phase transition in the mantle spinel garnet the long term tectonic subsidence of the paris basin constrains the mesozoic thermal evolution of the lithosphere and the amplitude of the initial thermal anomaly the chablis model including the effects of spinel garnet phase transition predicts present day lithospheric thickness in better agreement with observation than the plate model the chablis model involves a basal heat transfer of 37 mw m2 similar to the value beneath oceanic plates the long term subsidence of the paris basin obviously results from the decay of a thermal anomaly initiated during late variscan times we first assume that at 300 ma the lithosphere was less than 150 km thick and the thickened crust started returning to its present thickness 35 km by uniform lithospheric extension the subsidence data can be explained by short stephano autunian as well as long stephano triassic lasting extension these hypotheses both implicitly refer to extensional collapse of the variscan belt however the evolution of the variscan belt from 350 to 300 ma may have involved almost no crustal thickening but an anomalously thin lithosphere ca 55 km the corresponding thermal evolution of the lithosphere is computed using the chablis model with an initially high heat transfer of 61 mw m2 at the base of the base of the lithosphere at 280 ma this heat transfer is tuned to 40 mw m2 leading to lithospheric cooling from 280 to 30 ma which can also explain the paris basin subsidence for the short lasting extension hypothesis the late variscan lithospheric evolution predicted with the chablis model yields paleogeography magmatism and retrograde p t t paths in good agreement with those reported from areas around the paris basin conversely the plate model does not allow mantle melting during the end of carboniferous and permian times the long lasting extension hypothesis does not explain the paleogeographic evolution the timing of magmatism and retrograde p t paths showing isothermal decompression the hypothesis with a strong lithospheric delamination cannot be ruled out however it is less plausible than the extensional collapse hypothesis

teleseismic p wave image of crust and upper mantle structure beneath the valles caldera new mexico initial results from the 1993 jtex passive array teleseismic p wave relative arrival time data collected from a temporary array during the 1993 jemez tomography experiment jtex have been inverted to image velocity anomalies beneath the valles caldera in northern new mexico instruments were deployed in two 30 km long profiles one of 8 and one of 9 stations these profiles crossed the caldera trending at azimuths of n46 w and n60 e respectively two dimensional teleseismic relative arrival time inversion of the 1993 data set supplemented with data from an overlapping 1987 profile confirms the existence of a mid crustal low velocity region 30 beneath the valles caldera in the depth range of 8 to 13 km below sea level with about a 6 km horizontal extent this feature is interpreted to be the seismic expression of the remnant magma chamber a shallow low velocity anomaly beneath san antonio mountain coincides with the region of highest thermal gradient values in the caldera a lower crust upper mantle low velocity anomaly is imaged but is not as well constrained due to the limited length of the profile we tentatively correlate this anomaly with the thermal effects of basaltic magmas ponded at the crust mantle boundary

the evolution of the pannonian depression romanian sector as derived from subsidence and heat flow data abstract a quantitative analysis of subsidence sedimentation and thermal evolution of the romanian sector of the pannonian depression is presented based on subsidence data from 75 boreholes uniformly distributed over the study area and on heat flow data the hydrocarbon generation window for neogene sedimentary formations is also estimated borehole heat flow and crustal thickness data support an extension of the lithosphere of 0 40 the excess heat in lithosphere was estimated to be 15 30 mw m 2 the result of lithospheric material ascending during extension the lithosphere thickness is at least 15 20 greater than the 65 75 km currently estimated by steady state conduction models in the case of the badenian 16 5 13 ma sarmatian 13 11 5 ma and early pannonian 11 5 5 1 ma formations conditions for hydrocarbon generation are fulfilled in certain areas

overview of the subsurface structural pattern of the paris basin france insights from the reprocessing and interpretation of regional seismic lines abstract the study presents the methodology used by the french geological survey brgm for the building reprocessing and interpretation of selected regional seismic lines in the paris intracratonic basin france the 14 constructed e w and n s regional transects represent a total of 2 516 km length and are based on the merge of 240 seismic single profiles recorded by petroleum operators between 1971 and 1995 the regional lines have been selected to cross the main oil fields of the paris basin as well as high potential areas for oil exploration a first difficulty was to recover the raw data necessary to build up the regional transects the signal reprocessing harmonization and merge of the single seismic lines constituent of the regional transects are then described these operations represent the cornerstone of the study we put the emphasis on the primary static corrections as the targeted structures are commonly spatially associated with large seismic velocity variations in the upper cretaceous chalk and tertiary sedimentary cover the interpreted regional transects definitely give complementary information to the existing studies which generally lack seismic and therefore structural data we give an overview of the main structural and geometrical features of the paris basin inversion structures major unconformities as well as permo carboniferous basins we also describe the structural pattern and show the close relationships between the faults geometry the faults density and the geological evolution of the paris basin we distinguish 1 few large scale polyphase faults with a variscan origin representing the first order structural frame of the paris basin 2 monophase normal faults with strike slip features representing the subsurface prolongation of cenozoic grabens cropping out in the neighbourhood 3 deep normal faults sealed by the base calcareous dogger sequence related to the permo liassic extensional tectonic regime this large scale view of the paris basin has highlighted several potential exploration targets