gravity anomalies and segmentation of the continental margin offshore west africa the free air edge effect anomaly at passive continental margins provides constraints on the thermal and mechanical properties of the lithosphere in extensional regions like many margins the edge effect high offshore gabon west africa is located at the shelf break in the region of maximum sediment thickness gabon differs however from other margins in that the edge effect low is displaced from over the continental rise to the slope the origin of the low has been investigated by backstripping the sediments at the margin we have used the backstrip to calculate the amount of crustal thinning assuming airy isostasy such a model implies zero strength during rifting alternatively this amount of crustal thinning can be explained by a strong margin and a depth of necking that exactly balances the upward and downward forces that act on the crust during rifting we have developed a method which takes into account variations in the strength during rifting and the depth of necking to compute the thinning directly from the sediment backstrip the backstrip and the crustal thinning have been used to calculate the rifting gravity anomaly differences between the backstrip and the present day water depth give the geometry of the sediment load and hence the contribution to the gaavity anomaly of sedimentation by comparing the combined rifting and sedimentation anomaly to the observed free air gravity anomaly we have been able to constrain the flexural rigidity and equivalent elastic thickness te of the lithosphere during and after rifting the best fitting model is one in which the low is caused by a 125 km wide zone of relatively thin i e 15 km continental crust which was weak i e 0 te 10k during rifting and has remained so since then we speculate that the weak zone extends for 350 400 km along strike of the gabon margin and that passive margins may be highly segmented as regards their long term strength

the dykes and structural setting of the volcanic front in the lesser antilles island arc the orientations of dykes from many of the islands of the lesser antilles island arc have been mapped most of these dykes can be interpreted in terms of local or regional swarms derived from specific volcanoes of known age with distinct preferred orientations dykes are known from all cenozoic epochs except the palaeocene but are most common in pliocene miocene and oligocene rocks a majority of the sampled dykes are basaltic intrude volcaniclastic host rocks and show a preference for widths of 1 1 25 m locally dyke swarms dilate their hosts by up to 9 over hundreds of metres and up to 2 over distances of kilometres the azimuths of dykes of all ages show a general ne sw preferred orientation with a second nw se mode particularly in the miocene rocks of martinique the regional setting for these minor intrusions is a volcanic front above a subduction zone composed of three segments saba montserrat guadeloupe martinique st lucia grenada the spacing of volcanic centres along this front is interpreted in terms of rising plumes of basaltic magma spaced about 30 km apart this magma is normally intercepted at crustal depths by dioritic plutons and andesitic dacitic magma generated there plumes which intersect transverse fracture systems or which migrate along the front can avoid these crustal traps throughout its history the volcanic front as a whole has migrated episodically towards the backarc at an average velocity of about 1 km ma the local direction of plate convergence is negatively correlated with the local preferred orientation of dykes the dominant ne sw azimuth mode corresponds closely to the direction of faulting in the sedimentary cover of the backarc and the inferred tectonic fabric of the oceanic crust on which the arc is founded a generalised model of the regional stress field that controls dyke intrusion outside of the immediate vicinity of central volcanic vents is proposed in which the maximum horizontal stress parallels the volcanic front except in the northern segment where subduction of the barracuda rise perturbs the stress field there is also evidence of specific temporal changes in the stress field that are probably due to large scale plate kinematics

thermal effects of normal faulting during rifted basin formation 1 a finite difference model abstract a finite difference model is presented describing the thermal structure of a region undergoing fault controlled extension the model is two dimensional and time dependent we combine temperature changes resulting from conduction advection due to fault movements sediment blanketing and heat production cooling curves can be derived at chosen points in the area this study mainly investigates the effect of the extension rate on the thermal field which turns out to be very important 20 km of extension with extension rates of 0 2 2 0 and 20 mm yr yield maximum deviations in temperatures from the steady slate situation of 2 26 and 84 the sediment blanketing effect can even be reversed by variations in the sedimentation rates fast sedimentation leads to crustal cooling slow sedimentation to crustal heating the turning point value is lithology dependent and corresponds to 2 0 mm yr for shale 2 2 mm yr for clay and 1 4 mm yr for sand a sandstone will cause an increased cooling at both high and low velocities our modelling shows that footwall cooling during or immediately after a rifting event cannot be explained by the downwards movement of the adjacent relatively cold hanging wall consequently in areas where such a cooling is observed other cooling mechanisms must play an important role these can be phenomena like footwall uplift or the fading out of an older thermal anomaly

the dynamics of extensional sedimentary basins constraints from subsidence inversion on the continents sedimentary basins are generally formed by small amounts of lithospheric extension extension might cease because the lithospheric mantle has cooled and strengthened or because the driving force is removed in the former case a relationship should exist between the maximum strain rate during extension and the final stretching factor attained we explore how this relationship depends on the rheology of the lithospheric mantle and of the crust as well as on sedimentation and prior rifting events we also present strain rate information obtained by inverting subsidence data from a variety of sedimentary basins there is evidence of a systematic relationship between strain rate and stretching factor in each basin implying that lithospheric rheology is consistent with the rheology of olivine measured in laboratory experiments our data are difficult to explain if removal of the driving force governs the magnitude of stretching factors

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

central gulf of aden conjugate margins yemen somalia tectono sedimentary and magmatism evolution in hybrid type margins abstract magma rich and magma poor passive margins are generally studied separately yet the spatial evolution from one type to another is not well understood central gulf of aden margins are at the transition between these two types of margins based on new seismic data published wells and gravity data we determine seismic stratigraphy and structural patterns we map the distinct crustal domains continental ocean continent transition oct oceanic domains and propose a tectonic evolution of the yemeni and somalian conjugate margins in an oblique rifting context the most striking results are the significant segmentation narrowness and asymmetry of conjugate margins as well as the gradual eastward decrease in the intensity of magmatic activity of these hybrid type margins west of bosaso hami fracture zone bhfz the hami ahl medo segment presents magmatic type margin features in the distal yemeni margin related to the strong influence from the afar plume seaward dipping reflectors develop since the late syn rift stage 21 18 ma near the xiis al mukalla fracture zone conversely east of bhfz the bosaso sayhut margins segment is characterized by magma poor margins for which the exhumation stage is characterized by the unroofing of mantle along multiple detachment faults in the oct and shortly followed by diachronous volcanism 18 ma the central gulf of aden is affected by a major uplift during the final syn rift stage and up to oct formation this event is associated with the formation of erosional surfaces in the east and with gravitational deformation taking place on decoupling surfaces at the base of the syn rift sequence lower ghaydah fm that lead to the sliding of syn rift units on top of the exhumed mantle rocks in the oct

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

contrasting styles of rifting models and examples from the eastern canadian margin we present the results of a dynamical model of lithospheric rifting and rupture which show that a wide range of crustal thinning patterns across rifted passive margins can be produced by varying the steady state geotherm lithospheric composition dry versus wet materials and strain rate the basic mechanism of continental rupture is assumed to be passive rifting and necking we use a numerical thermomechanical model of lithosphere extension based on a finite element approach when plasticity is significant i e at lower temperatures or for harder materials deformation is unstable and thinning takes place abruptly over a narrow area conversely a progressive thinning across the margin is observed when creep is dominant i e in warm or ductile conditions cooling and associated hardening of the thinned area can occur during extension and cause the locus of extension to migrate laterally in these circumstances rupture is likely to take place asymmetrically along one edge of the thinned area producing a narrow margin and a very wide conjugate the eastern margins of canada and their conjugates across the north atlantic provide examples which cover this range of theoretical profiles the crustal thinning patterns inferred from deep seismic data and the duration of rifting compare well with model results we discuss also the constraints that these geodynamical models provide on such current issues as the seismic reflectivity of the lower crust or the location of the ocean continent boundary in wide areas supposedly underlain by 5 km thin continental crust

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

the 1975 1977 crisis of la soufriere de guadeloupe f w i a still born magmatic eruption on july 8 1976 eruptive activity broke out at la soufriere de guadeloupe f w i after about one year of increasing seismic activity seismic activity continued to increase until august 1976 reaching more than 1500 events a 200 fold increase over the preceding quiet period of a few years and an energy output of about 1017 ergs in a day a total of 26 major phreatic eruptions similar to the july 8 outburst took place during an eight months period the steam blasts that characterized the eruptions gave rise to particle and sometimes block charged plumes that deposited an estimated 106 m3 of solids the h2o rich gases emitted during the blasts presumably contained other gases h2s so2 co2 that were partly adsorbed on solid particles all material was erupted at temperatures of the order of 100 to 200 c the observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth and of abnormal variations of the geomagnetic field indicate a deep energy source for the phreatic eruptions a small proportion of the gases adsorbed on solid particles had a magmatic origin however most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system similar phreatic eruptions have occurred several times in recorded history in the case of la soufriere the origin of the phreatic eruptions is best described by an abnormal energy input versus steady state from a crustal magma chamber the occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system the abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption substantial improvement of the guadeloupe volcano observatory has followed the 1975 1977 crisis permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations

numerical modeling on the relationship between thermal uplift and subsequent rapid subsidence discussions on the evolution of the tainan basin existing evidence shows that an oligocene erosion event occurred on the northern continental margin of the south china sea and the tainan basin area might be at the center of this event followed by a rapid tectonic subsidence in the late oligocene and early miocene period the rapid tectonic subsidence is mainly thermal controlled and the effect of the yichu fault on the tainan basin is limited to the basin s eastern part we develop a 2 d thermal mechanical kinematic numerical model to explore the relationship between thermal uplift and subsequent rapid subsidence in the tainan basin our modeling indicates that the oligocene uplift erosion and subsequent rapid subsidence could be caused by a thermal event and the differential subsidence of the basement caused by thermal contraction can initiate the development of small faults however it also suggests that other mechanisms might be needed to jointly account for the observed erosions citation shi x h xu x qiu k xia x yang and y li 2008 numerical modeling on the relationship between thermal uplift and subsequent rapid subsidence discussions on the evolution of the tainan basin tectonics 27 tc6003 doi 10 1029 2007tc002163

some comments on two layer extensional models for the evolution of sedimentary basins simple extensional models that involve listric faulting in the brittle upper crust and plastic flow in the lower lithosphere have been shown to account for the subsidence history of various continental sedimentary basins and continental shelves in this paper we present structural evidence that extension in the continental lithosphere during rifting is not uniform we review evidence that the rifting process in major intracratonic rift basins is spasmodic rather than continuous that extension and subsidence within the rift during a tectonic phase is generally accompanied by uplift and erosion of the rift flanks that subcrustal heat input during rifting occurs over an area much broader than the rift proper and that there may be broad regional uplift before and or during rifting to explain the uplift of the flanks during rifting and their postrift subsidence we invoke two mechanisms subcrustal thinning by extension below the flanks and tilted major normal faults in the crust between graben and flanks the uplift and erosion of the flanks due to tilted faults probably do not significantly affect estimates of extension from subsidence analysis but uplift due to both sources can in certain cases be incorrectly attributed to regional uplift or doming we present a simplified analysis of the two layer extensional model for the elementary case in which extension is instantaneous and the crust is thinned by a different amount from the subcrustal lithosphere we provide a simple graphical method of data analysis to obtain the parameters that describe thinning of the crust and lithosphere during extension from the subsidence history application of this method to the central part of the pattani trough in the intracratonic gulf of thailand shows that extension and thinning of the lithosphere of a factor of 2 since late eocene can account for much of the subsidence history and the present day heat flow our analysis suggests that thinning of the crust in this area is 20 greater than thinning of the whole lithosphere assuming that none of the lithosphere is removed from the region of extension during rifting we show by simple geometric examples that a process of nonuniform extension implies that much greater thicknesses of sediment can be deposited in the center of a young basin than in the case of uniform extension of both crust and subcrustal lithosphere such an extensional process produces significant uplift of the flanks of the rift and as a result of erosion of the uplifted areas the effective cross sectional area of the basin can be increased by as much as 10 20 depending on the rate of erosion compared to the area that would have been created by a process of uniform extension finally we show that it may ultimately be possible to compute erosion rates from seismic cross sections of basins

basin modelling of the sw barents sea abstract the sw barents sea is an epicontinental platform consisting of n to nne oriented basins separated by basement highs the basins were formed during four distinct rift phases in the carboniferous late permian late jurassic early cretaceous and paleocene eocene progressive rifting culminated in continental breakup and seafloor spreading along the north atlantic axis approximately at 55 ma we present tectonic and thermal models of basin evolution along two seismic profiles crossing the sw barents sea the thermal and isostatic history of basins is constrained through time forward basin modelling based on an automated inverse basin reconstruction approach we estimate the effects of continental breakup and near margin processes magmatic underplating and sill intrusions on the thermal history and kerogen maturity below the vestbakken volcanic province basin models are calibrated against well data the results imply that both breakup and underplating alter the thermal and isostatic history of sediments along the margin the hydrocarbon potential of source rocks modelled along the margin suggests breakup has a permanent thermal effect on the present day sediments promoted by lateral heat flow while heat conduction by underplating is more diffuse inhibited to some degree by deeply buried low conductivity shales and limestones

flexural response of passive margins to deep sea erosion and slope retreat implications for relative sea level change we suggest that the magnitude of the early late oligocene eustatic fall as predicted from sequence stratigraphy has been overestimated because of flexural rebound along margins that was induced by late eocene to early oligocene erosional unloading the unloading of sediments from a continental margin during periods of deep sea erosion and slope retreat will be accompanied by some form of flexural rebound the magnitude and form of this rebound are controlled by 1 the amount of sediment removed from the margin and 2 the strength of the lithosphere at the time of sediment removal along margins with narrow continental shelves this rebound will induce a relative sea level fall resulting in a basinward shift in the shoreline and the predicted systems tracts will be similar to those expected for a eustatic fall in contrast rebound along wide continental shelves will not alter the position of the shoreline even though a relative sea level fall may be recorded across the outer shelf deep sea drilling and seismic reflection data from many margins support the interpretation of a late eocene to early oligocene 38 34 ma deep sea erosional event best developed along the continental slope and rise seismic reflection and drilling data also document a prominent canyon cutting event across the shelf during the early late oligocene 32 29 ma this event has been interpreted in terms of a large eustatic fall 150 m nevertheless there appears to be a correlation between late eocene to early oligocene deep sea erosion and the development or at least enhancement of unconformities across the shelf during the early late oligocene

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

evolution of the san jorge basin argentina the san jorge basin although small is the most important hydrocarbon producing basin in argentina remaining untested potential is high because of the presence of good source rock favorable structural complexity and multiple reservoirs reservoir quality is commonly low because of the highly tuffaceous sandstones the sedimentary fill of the basin is closely related to its tectonic history northwest southeast trending grabens formed and filled during a triassic and early jurassic early rift phase climaxing with a pervasive middle jurassic volcanic episode continued growth and filling of the basin occurred during a late jurassic earliest cretaceous late rift phase and cretaceous early and late sag phases late cretaceous early tertiary extension set up many of the present day structural traps along normal faults middle tertiary andean compression produced the narrow north south san bernardo structural belt which exhibits reversed movement on older normal graben bounding faults and on local low angle thrust faults marked early to middle tertiary erosion produced a significant unconformi y within cretaceous beds around basin margins origin of upper jurassic and lowermost cretaceous sedimentary fill is primarily lacustrine or fluvial in origin lacustrine organic rich black shales are fringed by oolitic and other limestones and fluvial deltaic sandstones derived mostly from the north a significant southern source of sand existed during the valanginian interbedded marine shales occur mostly to the west toward a presumed marine seaway connection to the northern magallanes basin middle to upper cretaceous sedimentary rocks sourced mostly from the north are mainly fluvial sandstone shale successions with some minor lacustrine influence reservoir quality glauconitic sands were deposited during a late cretaceous early tertiary marine incursion from the atlantic after development of a lower tertiary regional unco formity relatively undisturbed younger tertiary sediments completed the basin fill lower cretaceous lacustrine shales of the d 129 formation are the best source rocks yet identified however most hydrocarbon production occurs above the source in middle and upper cretaceous sandstones along the basin flanks the most obvious hydrocarbon emplacement mechanism is vertical migration along reactivated graben faults

thermo tectono stratigraphic forward modelling of the upper rhine graben in reference to geometric balancing brittle crustal extension on a highly viscous mantle abstract four structural cross sections through the central segment of the upper rhine graben urg were balanced by means of thermo tectono stratigraphic forward modelling ttsf modelling results were compared to geometric retro deformation of pre rift reference horizons applying line length and area balancing methods ttsf modelling with a deep necking level 20 km and or a high effective elastic thickness te 15 km yielded extension values similar to those of geometric balancing while modelling with shallower necking depths and or lower te yielded unrealistic high extension values a best fit of geometric balancing indicating 5 km rift orthogonal extension was reached by ttsf modelling with a te of 15 km and a pre rift necking depth of 29 km coinciding with the moho discontinuity this is compatible with a the geophysically mapped moho that does not shallow significantly beneath the central segment of the urg and its shoulders b seismicity indicating brittle elastic deformation of the entire crust and a seismic ductile deformation of the lithospheric mantle c compensation of crustal faults and shear zones in the crust mantle transition zone modelled time extension paths imply rifting during the middle eocene to early miocene a late miocene post rift stage and renewed rifting during the pliocene to recent apparent northward migration of extension in time is an effect of uplift processes which are not related to rifting correcting for these the extension history for the four cross sections becomes very similar suggesting plane strain deformation and rifting at very low strain rates of about 1 7 10 16 s 1 involving brittle elastic deformation of the crust and ductile deformation of the highly viscous high strength upper mantle that controls the position of the lithospheric necking level

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

cenozoic evolution of the eastern black sea a test of depth dependent stretching models abstract subsidence analysis of the eastern black sea basin suggests that the stratigraphy of this deep extensional basin can be explained by a predominantly pure shear stretching history a strain rate inversion method that assumes pure shear extension obtains good fits between observed and predicted stratigraphy a relatively pure shear strain distribution is also obtained when a strain rate inversion algorithm is applied that allows extension to vary with depth without assuming its existence or form the timing of opening of the eastern black sea which occupied a back arc position during the closure of the tethys ocean has also been a subject of intense debate competing theories called for basin opening during the jurassic cretaceous or paleocene eocene our work suggests that extension likely continued into the early cenozoic in agreement with stratigraphic relationships onshore and with estimates for the timing of arc magmatism further basin deepening also appears to have occurred in the last 20 myr this anomalous subsidence event is focused in the northern part of the basin and reaches its peak at 15 10 ma we suggest that this comparatively localized shortening is associated with the northward movement of the arabian plate we also explore the effects of paleowater depth and elastic thickness on the results these parameters are controversial particularly for deep water basins and margins but their estimation is a necessary step in any analysis of the tectonic subsidence record stored in stratigraphy

migration pathways of the late campanian and maastrichtian shallow facies ammonite sphenodiscus in north america abstract records of the ammonites sphenodiscus lobatus and s phenodiscus pleurisepta from the latest cretaceous gulf of mexico region the western interior seaway and the atlantic coast have repeatedly been used as a stratigraphic index for a maastrichtian age in recent years however high resolution biostratigraphy on north eastern mexican occurrences and its combination with other correlation tools such as sequence stratigraphy as well as a refined position of the campanian maastrichtian boundary led to a different interpretation regarding the age of the earliest sphenodiscus the wealth of data allows us to reconstruct their routes of dispersal over the north american continent migration appears to have been directed from south to north and is thus opposed to that of baculites ovatus dispersal of all three species is clearly related to changes in the maastrichtian sea level

high resolution conceptual hydrogeological model of complex basaltic volcanic islands a mayotte comoros case study we present a high resolution conceptual hydrogeological model for complex basaltic volcanic islands based on mayotte island in the comoros its geological structure and hydrogeological functioning are deduced from a large dataset geological mapping geophysics some forty new boreholes piezometric data hydraulic conductivity hydrochemical data etc we describe previously unknown deep cut and fill palaeovalleys the resulting conceptual geological and hydrogeological model of the island is very different from the hawaiian model in that it lacks a low elevation basal aquifer and dyke impounded high level aquifers it is closer to the canary islands model which has however not yet been described at a high resolution scale it does not have a continuous aquifer but rather a discontinuous succession of perched aquifers separated by aquicludes and aquitards this results more from the complex geological structure of the island which has experienced several phases of volcanism erosion and weathering than from its age but is also a result of the high resolution scale of the model high resolution conceptual modelling is now necessary to solve problems of applied geology and hydrogeology

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

groundwater and volcanoes examples from the azores archipelago groundwater at the azores archipelago is a strategic resource for the freshwater supply freshwater mineral and thermal water discharges occur in the archipelago and especially at the fogo and furnas volcanoes sao miguel these discharges provide data for case studies of groundwater chemistry from volcanic monitoring due to the stable composition of the sampled waters the mineral and thermal discharges are mainly of sodium bicarbonate types and present a large range of temperatures from cold springs to waters at about 90 c some boiling discharges have a sulfate dominated composition suggesting a steam heating mechanism geochemical studies on these mineral and thermal waters began in the 19th century data gathered since these earlier studies provide a baseline for ph temperature co2 and major element composition weekly measurements of ph and temperature also denote a rather stable behavior

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

the geodynamic province of transitional lithosphere adjacent to magma poor continental margins two different types of transitional lithosphere have been documented along magma poor rifted margins one consists of apparently subcontinental mantle that has been exhumed brit tlely deformed and serpentinized during late stages of rifting a second is thinned 10 km con tinental crust which in some cases is known to have been supported near sea level at least early in the rift history and thus is interpreted to reflect depth dependent extension in both cases it is typically assumed that oceanic crust forms at the time that the brittle continental crust is breached or soon thereafter and thus that transitional lithosphere has relatively limited width here three representa tive cases of transitional lithosphere are examined one in the newfoundland iberia rift and one at goban spur both exhumed mantle and one off the angola congo margin thin continental crust flanked seaward by apparently exhumed lower continental crust exhumed mantle considering the geological and geophysical evidence it appears that depth dependent extension riftward flow of weak lower continental crust and or upper mantle may be a common phenomenon on magma poor margins and that this can result in a much broader zone of transitional lithosphere than has hitherto been assumed transitional lithosphere in this wide zone may consist of subcontinental mantle lower continental crust or some combination thereof depending on the strength profile of the pre rift continental lithosphere transitional lithosphere ceases to be emplaced i e final break up occurs only when emplacement of heat and melt from the rising asthenosphere becomes domi nant over lateral flow of the weak lower lithosphere this model implies a two stage break up first the rupture of the brittle continental crust and second the eventual separation of the ductile sub continental lithosphere which is coincident with emplacement of normal oceanic crust well defined magnetic anomalies can form in transitional lithosphere that consists of highly serpenti nized exhumed mantle and such anomalies therefore are not diagnostic of oceanic crust where present the anomalies can be helpful in interpreting and dating the rifting history

heterogeneity of hydrodynamic properties and groundwater circulation of a coastal andesitic volcanic aquifer controlled by tectonic induced faults and rock fracturing martinique island lesser antilles fwi summary we conducted a multidisciplinary study to analyze the structure and the hydrogeological functioning of an andesitic coastal aquifer and to highlight the importance of faults and associated rock fracturing on groundwater flow a helicopter borne geophysical survey with an unprecedented resolution skytem was flown over this aquifer in 2013 tdem resistivity total magnetic intensity geological and hydrogeological data from 30 boreholes and two pumping tests were correlated including one which lasted an exceptional 15 months we demonstrate that heterogeneous hydrodynamic properties and channelized flows result from tectonically controlled aquifer compartmentalization along the structural directions of successive tectonic phases significant fracturing of the central compartment results in enhanced hydrodynamic properties of the aquifer and an inverse relationship between electrical resistivity and transmissivity basalts within the fractured compartment have lower resistivity and higher permeability than basalts outside the compartment pumping tests demonstrate that the key factor is the hydraulic conductivity contrast between compartments rather than the hydrodynamic properties of the fault structure in addition compartmentalization and associated transmissivity contrasts protect the aquifer from seawater intrusion finally unlike basaltic volcanic islands the age of the volcanic formations is not the key factor that determines hydrodynamic properties of andesitic islands basalts that are several million years old 15 ma here have favorable hydrodynamic properties that are generated or maintained by earthquakes faulting that result from active subduction beneath these islands which is superimposed on their primary permeability

testing inverse kinematic models of paleocrustal thickness in extensional systems with high resolution forward thermo mechanical models 1 reconstructing continental paleocrustal thickness is important for estimating tectonic accommodation constraining three dimensional basin geometry during early rifting phases of extensional margins and predicting the distribution of thick crustal sills that may block the global ocean and create restricted basins we test an inverse kinematic method for modeling paleocrustal thickness by inverting the final bulk crustal structure produced from high resolution thermo mechanical models of lithospheric extension the inverse kinematic method assumes pure shear includes simple rules based on geodynamic models and field observations and requires displacement boundary conditions and the prescription of a transition from rigid to nonrigid deformation the inverse pure shear method produces a history of bulk crustal thickness that closely matches the forward models provided that the width of the rift zone is narrow during the later phases of continental extension when crust undergoes hyper extension we also observe that the width and surface trace of large scale ls shear zones observed in the thermo mechanical models coincide with inflection points and large gradients in inverted nonrigid velocity field our results demonstrate that if displacement boundary conditions can be constrained and the transition from rigid to nonrigid deformation defines a narrow rift zone during hyper extension then relatively simple kinematic rules can be used to invert present day bulk crustal structure for paleocrustal thickness bulk lateral strain and aspects of upper crustal shear zone geometry from extensional systems with nonlinear rheology structures dominated by simple shear in the upper crust depth dependent extension and asymmetric crustal thinning

hydrological behaviour and modelling of a volcanic tropical cultivated catchment the hydrological behaviour of the cultivated f ef e catchment 17 8 ha on the tropical volcanic island of guadeloupe was studied to identify flow paths to quantify water fluxes and finally to build a lumped model to simulate discharge and piezometer levels the approach combined two steps an experimental step and a modelling step which covered two time scales the annual and the storm event scale the hydrological measurements were conducted over 2 years the f ef e catchment is characterized by heavy rainfall 4229 mm year 1 on permeable andosols the results showed that underground flow paths involved two overlapping aquifers and that the annual water balance in 2003 was shared among outflows of the deep aquifer 42 evapotranspiration 31 and streamflow 27 on the event scale the surface runoff coefficient ranges between 6 2 and 24 4 depending on antecedent dry or wet moisture conditions hortonian overland flow predominated over subsurface and saturation overland flow processes recharge of the shallow aquifer is mainly governed by a constant infiltration capacity of the andosols with depth in the vadose zone outflows of this shallow aquifer were the baseflow of the main stream and the recharge of the deep aquifer volcanic deposits at f ef e promoted the underground flow path and cultivated areas seemed to explain the high stormflow values relative to other tropical small catchments under rain forest a conceptual lumped model integrating runoff infiltration evapotranspiration and fluctuations of the two overlapping aquifers was developed the model has six parameters and was calibrated and validated on the hydrograph at the outlet and on the two piezometers of the shallow and the deep aquifers the results show fair to good agreement between measured and simulated variables and consequently the model was consistent with the main hydrological processes observed from experimental results in wet conditions resume d auteur

on the evolution of rifted continental margins comparison of models and observations for the nova scotian margin summary a model for the formation and evolution of rifted continental margins based on lithospheric extension during rifting and its thermal and mechanical consequences is proposed model predictions are then compared with geological and geophysical observations from a transect of the 185 ma old rifted margin off nova scotia through the scotian basin three kinematic models of the rifting process are discussed these are 1 the uniform extension model in which the amount of extension is uniform with depth but varies with position across the margin 2 the uniform extension and melt segregation model which has similar properties but also provides an explanation for the properties of the extended continental crust and its transition to oceanic crust by postulating that basaltic melt segregates from the asthenosphere and migrates to the crust and 3 the depth dependent extension model in which the first order consequences of rapidly changing rheological properties with depth in the lithosphere are included by decoupling the lithosphere into two zones with depth each of which undergoes differing amounts of extension these rift models predict the form of crustal and lithospheric thinning subsidence and temperature change once the amount of extension has been determined this is estimated from seismic measurements of present crustal thickness on the assumption that the crust had a uniform thickness equal to that currently measured in the adjacent continental region before rifting occurred rifting is also considered to occur instantaneously a time stepping thermo mechanical model is used to predict the cooling of rifted margin additional thermal contraction subsidence and its amplification by water and sediment loading thermal aspects are calculated using a finite difference model of time dependent conductive heat transport whereas regional isostatic response to loading is calculated by a finite element model the models are coupled because the temperature distribution is used to define a rheological lithosphere an elastic region with thickness that varies in time and space as the model evolves for flexural calculations in the mechanical model secondary coupling occurs through perturbations to the temperature field by sedimentary thermal blanketing and advection of heat during isostatic adjustment the model predictions of 1 sedimentary basin stratigraphy 2 moho position 3 free air gravity anomaly 4 age depth relations for deep exploratory wells and 5 subsidence and temperature histories agree well with observations from the scotian basin additional effects due to sedimentary and crustal radiogenic heat production lateral heat transport and the possible existence of a near surface brittle listric faulted region created during rifting are also considered it is concluded that a model in which rifting occurred by depth dependent extension and which includes a finite thickness for the rheological lithosphere radiogenic heat production in the sediments and crust and a brittle listric faulted crustal layer affords an accurate description of the first order processes that occur during rifting and evolution of this margin

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

salt diapir influenced shallow marine sediment dispersal patterns insights from outcrop analogs unique outcrop exposures of two salt diapirs a secondary salt weld and associated syndiapiric strata in northeast mexico offer an important perspective on salt influenced petroleum reservoirs by allowing recognition and description of salt related sandstone depocenters spectacular progressive unconformities and halokinetic sequences coupled with laterally continuous exposures permit accurate correlation and interpretation of syndiapiric units analysis of the syndiapiric upper cretaceous delgado sandstone member potrerillos formation delineates regional shoreline sediment dispersal locally impacted by diapiric relief and the distribution and internal character of salt diapir proximal sandstone depocenters sequence stratigraphic correlation defines striking relationships between highstand hst and transgressive systems tracts tst stratal thinning trends and salt diapir relief transgressive systems tract and highstand systems tract strata show thinning and lithofacies shoaling trends toward diapirs however the latter is more pronounced in the hst and occurs at a greater distance from salt diapirs within 1 2 km 0 6 1 2 mi sandstone depocenters roughly 0 5 1 0 km 0 3 0 6 mi wide and 0 5 0 2 km 0 3 0 1 mi thick are present in both tst and hst strata and consist of sandier shallower water facies however depocenters are better developed in tst strata as thicker stratigraphic sections on updip diapir margins we propose that sandstone depocenters formed by preferential sediment reworking and shelf ridge development on landward diapir margins during marine transgression elevated diapir relief and higher subsidence rates adjacent to salt diapirs likely enhanced this process additionally depocenters adjacent to el papalote diapir are smaller and contain deeper water facies than the age equivalent depocenters adjacent to el gordo diapir suggesting that it had higher broader sea floor relief

the groundwater resources and sustainable yield of cheju volcanic island korea hydrogeologic data of 455 water wells comprising geologic logs water qualities and aquifer test results are analyzed to determine hydrogeological characteristics water quality and sustainable yield of the groundwater resources of cheju volcanic island the groundwater of the island occurs in unconsolidated pyroclastic deposits and clinkers interbedded in highly jointed basaltic and andesitic rocks as high level basal and parabasal groundwater under unconfined conditions the total storage of groundwater is estimated at about 44 billion m3 the average transmissivity and specific yield of the aquifer are at about 0 34 m2 s 1 29300 m2 day 1 and 0 12 respectively the average annual precipitation is about 3 39 billion m3 of which 1 49 billion m3 equivalent to 44 0 of the total annual precipitation is recharged into aquifers with 0 638 billion m3 year 1 of runoff and 1 26 billion m3 year 1 of evapotranspiration based on a groundwater budget analysis the sustainable yield is estimated at about 0 62 billion m3 year 1 equivalent to 41 6 of annual recharge a low permeability marine sedimentary formation sehwari formation composed of loosely cemented sandy silt was recently found to be situated at 120 68 m below mean sea level if the said marine sediment is distributed as a basal formation of the freshwater zone of the island most of its groundwater will be of parabasal type so the marine sediment is one of the most important hydrogeological boundaries and groundwater occurrences in the area

a two dimensional inverse model for extensional sedimentary basins 2 application 1 we apply the two dimensional strain rate inversion algorithm described in the companion paper to five sedimentary basins located world wide this general algorithm makes no assumptions about the number duration or intensity of rifting episodes within a basin instead the distribution of strain rate is allowed to vary smoothly through space and time until the misfit between observed and predicted stratigraphy is minimized potentially important two dimensional effects such as lateral heat flow and elastic thickness have been incorporated in each case observed subsidence profiles can be automatically and accurately fitted the calculated distributions of strain rate are corroborated by independent information about the number and duration of rifting episodes peak strain rate estimates are comparable to present day measurements in actively extending basins such as the aegean sea and the basin and range province temporal and spatial strain rate patterns from a large number of sedimentary basins in diverse settings will help to constrain the dynamical evolution of thinning continental lithosphere in all five sedimentary basins the smallest acceptable misfit is achieved when the elastic thickness is less than 2 4 km this surprising result indicates that the lithosphere beneath sedimentary basins remain weak during and after rifting it also underscores the importance of inverting data sets so that the existence uniqueness and resolution of solutions can be analyzed our two dimensional approach is one small step toward a generalized three dimensional inverse model of sedimentary basins

evolution of deep water rifted margins testing depth dependent extensional models 1 a general understanding of rifted margins which form by thinning of the continental lithosphere exists nevertheless the exact form of thinning is unclear this debate has been stimulated by acquisition of dense seismic wide angle and deep reflection surveys from atlantic ocean margins a central issue concerns the way in which thinning changes with depth we have tackled this issue by developing a generalized inverse model this model attempts to fit subsidence and crustal thinning observations by varying strain rate as a function of time and space depth dependent thinning is permitted but we do not prescribe its existence or form here the algorithm is applied to six margins including two of the most contentious conjugate margins newfoundland iberia and brazil angola calculated strain rate histories predict thinning estimates which broadly match estimates inferred from normal faulting the eastern indian and beaufort sea margins formed by largely uniform lithospheric thinning in contrast the newfoundland iberian conjugate margins formed by a pattern of strongly depth dependent strain rate to account for the paucity of syn rift decompression melting of the underlying asthenosphere the lithospheric mantle close to oceanic continent transition must thin more slowly than the overlying crust this form of depth dependency is not common for example the brazil angolan conjugate margin could have formed by uniform lithospheric thinning provided thick layers of salt were deposited in a preexisting 400 m deep topographic depression depth dependent thinning is not required to account for rapid subsidence of presalt strata

two dimensional inverse modeling of sedimentary basin subsidence recently developed mathematical models of subsidence in extensional basins provide a good basis for forward modeling however the large number of parameters to be specified by the user makes it difficult not only to do the modeling itself but also to judge the meaning of the results we present a new method for automatic searching of the best fitting parameter set of a 2d basin formation model weighted goal functions are used in the minimization process by the inverse problem solver algorithm the nominal parameter set in the present case includes profiles of the crustal and subcrustal thinning factors and the level of lithosphere necking the method was tested on synthetic data with parameters that were perturbed beforehand with some restrictions the algorithms are capable of resolving such perturbations the inversion technique has been applied to two profiles crossing the dnieper donets basin ukraine the crustal thinning factors obtained argue for a scissors like style of basin opening high subcrustal thinning values are necessary in order to explain the abnormally thick carboniferous section in the basin these values should be treated as cumulative ones due to the currently unresolvable influence of other rifting related processes particularly phase transitions

maastrichtian climate productivity and faunal turnovers in planktic foraminifera in south atlantic dsdp sites 525a and 21 abstract stratigraphic faunal and isotopic analyses of the maastrichtian at dsdp sites 525a and 21 in the south atlantic reveal a planktic foraminiferal fauna characterized by two major events an early late maastrichtian diversification and end maastrichtian mass extinction both events are accompanied by major changes in climate and productivity the diversification event which occurred in two steps between 70 5 and 69 1 ma increased species richness by a total of 43 and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity the onset of the terminal decline in maastrichtian species richness began at 67 5 ma and the first significant decline in surface productivity occurred at 66 2 ma coincident maximum cooling to 13 c in surface waters and the reduction of the surface to deep temperature gradient to less than 5 c major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the maastrichtian between 200 and 400 kyr before the k t boundary surface and deep waters warmed rapidly by 3 4 c and cooled again during the last 100 kyr of the maastrichtian surface productivity decreased only moderately across the k t boundary species richness began to decline during the late maastrichtian cooling and by k t boundary time the mass extinction had claimed 66 of the species viewed within the context of maastrichtian climate and productivity changes the k t mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

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

contribution of correlation and spectral analyses to the regional study of a large karst aquifer charente france the purpose of the study is to demonstrate that correlation and spectral analyses can contribute to the regional study of a large karst aquifer an example is presented for the la rochefoucauld karst aquifer charente france different types of spatially distributed time series provide valuable spatio temporal information for the karst aquifer the available time series consist of the spring flow rates the flow rates at different locations in sinking streams the piezometric levels the electrical conductivity and temperature of the water the atmospheric pressure and the precipitation the analysis of the flow rates at the springs shows that the aquifer empties very slowly and has a large storage capacity hydrodynamic links were established between three of the four rivers flowing on the aquifer and the springs the results also demonstrate the important spatial heterogeneity of the aquifer and indicate that the most rapid flow occurs in the northern part of the aquifer hourly piezometric and electrical conductivity time series indicate that the transmissivity of the aquifer varies when some conductive channels become desaturated during the low water period the delays between the distributed recharge and the piezometric level between the localized river input and the flow rates at the springs and between the electrical conductivities in rivers and the main spring provide information on the travel times in the aquifer the observation of earth tides and barometric effects indicate that this apparently unconfined aquifer has a confined behaviour

theropod avian pterosaur and arthropod tracks from the uppermost cretaceous las encinas formation coahuila northeastern mexico and their significance for the end cretaceous mass extinction two unique localities that combine an unusual diversity of avian pterosaurian and dinosaur tracks as well as trails of arthropods were recently discovered by us in uppermost maastrichtian siliciclastic sediments of the las encinas formation in the mexican state of coahuila 40 km north of saltillo the trackway assemblages at amargos and rancho san francisco were produced by at least six different types of birds while trackways of azhdarchoid pterosaurs are rare only a single footprint was produced by a nonavian theropod a diverse ichnofauna of arthropod traces is also present in a different facies the tetrapod trackway assemblage was deposited during the very latest maastrichtian as indicated by an up to 2 5 m thick unit with abundant smectite spherules attributed to the chicxulub impact less than 8 5 m stratigraphically up section at amargos sphenodiscus pleurisepta is the last ammonite at amargos and may have crossed the cretaceous paleogene boundary

structure and hydrogeological functioning of an insular tropical humid andesitic volcanic watershed a multi disciplinary experimental approach summary the aim of the study is to establish an hydrogeological scheme of the structure and the functioning of andesitic volcanic systems in the insular and humid tropical context a watershed has been instrumented at fefe in guadeloupe french west indies in the lesser antilles to measure rainfall runoff and piezometric fluctuations between 2003 and 2006 given the heterogeneity of the volcanic deposits a multi disciplinary approach has been used a geological and an hydrogeological survey an hydrodynamic approach hydraulic tests and signal processing of hydrological time series and finally an hydrogeochemical approach major elements and some trace elements two main superposed aquifer respectively in aerial deposits and in recent nuees ardentes glowing ash and lava flows as well as the underlying aquiclude the highly weathered older substratum were identified at a local scale some hydrogeological heterogeneities internal to the aquifers were highlighted and related to a polyphased building up of the geological formations hydraulic relationships between the multi layered aquifers such as the confinement of the deep aquifer upstream of the basin were identified groundwater stream exchanges were characterised detailing various contributions of the shallow and the deep aquifers to stream and spring waters significant river losses were also observed at a global scale within such relatively permeable volcanic formations the aquifer recharge is about 85 of the annual effective rainfall for an average rainfall year the hydrogeological scheme appears to be coherent with a geological structure of cut and fill paleovalleys frequently observed in andesitic areas consequently groundwater drainage axis are mainly localised in recent nuees ardentes deposits whereas the inversion of relief characteristic of volcanic areas explains the non superposition of surface water and groundwater divides and both surface water losses and springs finally this work shows the highly heterogeneous hydrogeological processes occurring in volcanic formations of andesitic type it also shows the relationships between the geological structure and the hydrogeological functioning of such basins and proposes an affordable methodological approach to investigate such a hydrogeological context in depth

basinward transport of chicxulub ejecta by tsunami induced backflow la popa basin northeastern mexico and its implications for distribution of impact related deposits flanking the gulf of mexico ejecta bearing strata are present at the top of cretaceous foreland basin deposits throughout the la popa basin in northeastern mexico in the southeast part of the basin locally thick as much as 4 6 m ejecta rich conglomeratic strata occupy valley like features at a bathymetric break that separated maastrichtian upper shoreface from lower shoreface and prodelta depositional settings clast supported textures normally graded planar conglomerate sandstone couplets upcurrent dipping low angle cross laminae sparse paleocurrent data and transported fossils indicate deposition by south to southeast directed turbulent supercritical flow in the northwest part of the basin ejecta grains are present but less common in correlative deposits sediment ejecta and organisms were eroded from shoreward environments and transported basinward by backflow of run up surge s emplaced against the continent by one or several tsunami s high discharge supercritical offshore directed flow provides a mechanism for transport of voluminous ejecta bearing sediment and late maastrichtian marine organisms into deep water gulf of mexico settings

the volcanic activity of la soufriere of guadeloupe lesser antilles structural and tectonic implications abstract among observations made on la soufriere volcano guadeloupe to monitor its its activity are temperature measurements temperature of fumaroles hot springs ground surface and water inside two boreholes 80 and 90 m deep those measurements proved to be of prime importance in understanding mechanisms working in the volcano and governing its activity they lead with other observations such as self potential measurements and geochemical analysis of fumaroles and hot springs to a possible interpretation of phreatic activity rather different from the one retained earlier which was essentially based on seismic data in this model the magma reservoir is only in a stable state and in particular supplies heat at a constant rate to the overlying geological structures the cycle of volcanic activity and period of quiescence is interpreted as due to a cycle of clogging and reopening of the system of fractures transferring heat from a lower aquifer to an upper one and eventually to the atmosphere the model is discussed in regard of other geophysical observations in particular seismicity some inferences are made concerning a new phase of activity and suitable observations to predicit it

on the origins of band topography europa we use stereo derived topography of extensional bands on europa to show that these features can be elevated by 100 150 m with respect to the surroundings and that the positive topography sometimes extends beyond the band margins lateral variations in shell thickness cannot maintain the observed topography for timescales greater than 0 1 myr lateral density variations can maintain the observed topography indefinitely mean density contrasts of 5 and 50 kg m 3 are required for shell thicknesses of 20 and 2 km respectively density variations caused by temperature contrasts require either present day heating or that bands are young features 1 myr old stratigraphic analyses suggest that these mechanisms are unlikely the observation that bands form from ridges may be explained by an episode of shear heating on ridges weakening the ridge area and leading to strain localization during extension fracture porosity is likely to persist over myr timescales in the top one third to one quarter of the conductive part of the ice shell lateral variations in this porosity of order 20 are the most likely mechanism for producing band topography if the ice shell is thin 2 km porosity variations of 2 or less are required if the shell is thicker 20 km if the ice shell is thick lateral variations in salt content are a more likely mechanism warm ice will tend to lose dense low melting temperature phases and be buoyant relative to colder salt rich ice thus lateral density variations will arise naturally if bands have been the sites of either localized heating or upwelling of warm ice during extension

provenance of upper cretaceous paleogene sandstones in the foreland basin system of the sierra madre oriental northeastern mexico and its bearing on fluvial dispersal systems of the mexican laramide province sandstone petrography and detrital zircon u pb analysis of upper cretaceous paleogene sandstones in the foreland basin of the sierra madre oriental in northeastern mexico indicate long distance sediment transport from arc basement and thrust belt sources lying to the west northwest and south the basin fill termed the difunta group consists of sublitharenites litharenites feldspathic litharenites and lithic arkoses derived from mixed sources that included sedimentary rocks magmatic arc rocks and subordinate basement rocks six age populations comprise the detrital zircon content of the sandstones proterozoic 1900 900 ma early paleozoic 500 400 ma late paleozoic early triassic 288 235 ma jurassic 180 151 ma early cretaceous 150 111 ma and late cretaceous paleogene 110 54 ma these grains were derived from several arc terranes ranging in age from permian to paleogene in western mexico and the southwestern united states from sedimentary rocks and possibly interbedded tuffs of the sierra madre oriental orogen and from basement sources or their derivative sandstones of the southwestern united states the petrographic and geochronologic provenance data corroborate existing models for derivation of much foreland detritus from arc sources to the west identify the sierra madre orogen itself as an important source for sediment and these data modify the late cretaceous paleogene paleogeography of mexico to include a long orogen parallel fluvial system with headwaters in the southwestern united states the difference in average ages of the youngest grains in the sandstones and their inferred depositional ages is 10 5 m y indicating that the initial coarse fill of the foreland basin was derived from early laramide uplift and eastward arc migration in northwestern mexico and the southwestern united states

evolution of the newfoundland iberia conjugate rifted margins it is accepted that mildly extended sedimentary basins form by largely uniform thinning of continental lithosphere no such consensus exists for the formation of highly extended conjugate rifted continental margins instead a wide range of models which invoke differing degrees of depth dependent thinning have been proposed much of this debate has focussed on the well studied newfoundland iberia conjugate margins we have tackled the problem of depth dependency at this pair of margins in three steps first we have reconstructed water loaded subsidence histories by making simple assumptions about changes in water depth through time secondly we have used these reconstructed subsidence histories to determine the spatial and temporal variation of lithospheric strain rate an inversion algorithm minimizes the misfit between observed and predicted subsidence histories and crustal thicknesses by varying strain rate as a smooth function of distance across the margin depth through the lithosphere and geologic time depth dependent thinning is permitted but crucially our algorithm does not prescribe its existence or form given the absence of significant volumes of syn rift magmatism we have also applied a minimal melting constraint inverse modeling has yielded excellent fits to both reconstructed subsidence and crustal observations which suggest that rifting occurred from not vert similar 150 135 ma and at rates of up to 0 3 ma 1 strain rate distributions are depth dependent suggesting that lithospheric mantle thins over a wider region than the crust beneath highly extended parts of the margin crustal strain rates greatly exceed lithospheric mantle strain rates thirdly we have tested our strain rate histories by comparing the total horizontal extension with the amount of extension inferred from normal faulting patterns both values agree within error we freely acknowledge that there are important uncertainties in reconstructing the subsidence histories of deep water margins nevertheless stratigraphic records remain the only albeit imperfect means of determining how crust and lithospheric mantle thin through time and space

ammonite correlation of the uppermost campanian of western europe the u s gulf coast atlantic seaboard and western interior and the numerical age of the base of the maastrichtian

animated models of extensional basins and passive margins 1 we present animated models of the development of the san jorge north falkland and north sea extensional sedimentary basins and the orange pearl river mouth and voring passive continental margins these animations show the link between strain rate and subsidence and track both compaction and thermal development of the sediment pile calculations are based on a two dimensional inverse model for extracting the spatial and temporal variation of strain rate from stratigraphic profiles across extensional terrains this general algorithm requires no a priori assumptions about the number duration and intensity of the rifting episodes instead strain rate is allowed to vary smoothly through space and time until misfit between observed and predicted stratigraphy is minimized calculated 2 d and 1 d strain rate histories are corroborated by the number and duration of rifting episodes determined from independent stratigraphical and structural evidence the evolving temperature structure of the sediment pile is a function both of porosity which varies through time as compaction occurs and of heat flow into the base of the basin which is determined from the strain rate history we discuss the implications of the calculated strain rate histories for understanding the regional tectonic development of each basin and margin

flexural deformation due to amazon fan loading a feedback mechanism affecting sediment delivery to margins the uplift associated with the peripheral bulge engendered by sediment loads such as the amazon fan may provide a potential tectonic feedback mechanism that affects both coastal and fluvial depositional processes for example topographic and geologic maps of the brazilian margin document the existence of a drainage divide affecting coastal river networks that is spatially coincident with the location of the peripheral bulge predicted by our flexural modeling of the fan load while regions in close proximity to the fan load are depressed regions farther from the load are lifted i e peripheral bulge by 25 50 m which is sufficient to cause subaerial exposure of large portions of the shelf and modification of existing fluvial drainage networks furthermore our modeling results suggest that the development of the peripheral bulge may have deflected the sediment laden waters of the amazon river progressively southward through time this prediction is consistent with the existence of canyons off the amapa coast north of the present day amazon canyon and with the distribution of amazon fan sediments both of which suggest that the proto amazon river delivered sediment farther north along the coast however changing the location of sediment input into a basin also changes the shape of the cumulative sediment load and thus the resultant deformation this feedback between sediment loading and the peripheral bulge uplift modifies the spatial and temporal history of sediment delivery to the margin and provides a viable way to change base level without having to invoke glacial eustasy the efficiency of this feedback is dependent on the flexural wavelength and thus the strength of the lithosphere at the time of loading and the relative position of the sediment load with respect to the continental margin

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

the dynamics of rifting deformation of the lithosphere by active and passive driving forces summary the thermal and mechanical behaviour of the lithosphere during rifting is investigated using a two layer model for its rheology and different driving forces for the rift process the uppermost crustal layer is assumed to deform by brittle failure while the lower lithosphere including the lower crust is assumed to behave as a newtonian viscous fluid results of numerical modelling of the deformation flow and heat transport in the viscous layer are presented in which viscosity is a strong function of depth and temperature deformation of the upper brittle layer is complex and difficult to quantify thus deformation of this upper layer was approximated by a simple kinematic model in which the layer is thinned by an amount proportional to the amount of extension it experiences two fundamentally different driving forces were investigated they correspond to active rifting in which the litho sphere is thinned by an upwelling limb of a convection cell or mantle plume and to passive rifting or stretching of the lithosphere the results show that for zones of stretching which are wider than the thickness of the viscous layer thinning at all levels in the lithosphere can be described by a single parameter as in earlier stretching models this is not always true when the rift zone is narrow or near the edges of the rift zone initial subsidence due to isostatic and thermal changes during stretching slows as stretching progresses giving an exponential character to the rift stage subsidence active rifting is associated with thermal uplift in this case lithospheric deformation is confined to a narrow zone near the base of the lithosphere and thinning of the crust does not occur until the base of the lithosphere approaches that level the rate of lithospheric thinning and width of the rift zone depend on the convection velocities in the underlying asthenosphere and on the viscosity depth gradient near the lithosphere asthenosphere boundary also contributing to the elevation changes during rifting are dynamic stresses which result from the flow these dynamic affects may significantly modify the uplift or subsidence of the rift zone another important process which results from viscous flow is the generation of secondary convection in the upwelling asthenosphere ths will further thin the lithosphere and can cause depth dependent stretching in which the lower lithosphere is thinned more than the upper lithosphere both of these properties of the flow dynamic stresses and secondary convection critically depend on absolute values of viscosity and so are not well constrained at present the model results presented here exhibit the degree of complexity which results from viscous flow in the lower lithosphere and which is matched by the wide variety of observations on rifting

a two dimensional inverse model for extensional sedimentary basins 1 theory 1 a simple two dimensional inverse model for extracting the spatial and temporal variation of strain rate from extensional sedimentary basins is described our starting point is a forward model which allows basin stratigraphy to be calculated from any given strain rate distribution this forward model includes potentially important effects such as flexural rigidity and the two dimensional conduction advection of heat conversely inverse modeling determines strain rate variation by minimizing the misfit between predicted and observed patterns of basin subsidence no a priori assumptions about the number duration or intensity of rifting episodes are necessary instead strain rate is allowed to vary smoothly throughout time and space an important restriction is that vertical lines remain vertical but this restriction can be relaxed if deemed necessary we have successfully inverted different synthetic sedimentary basin geometries which were generated by forward modeling sensitivity analysis and noise tests demonstrate that strain rate patterns can be recovered with confidence the relationship between stratigraphic misfit and elastic thickness shows that usually an upper limit but not a lower limit for elastic thickness can be retrieved our general approach is applicable to any extensional sedimentary basin including highly extended passive margins and it should be regarded as the stepping stone to more sophisticated two dimensional and three dimensional inverse modeling in the companion paper we apply our algorithm to a set of phanerozoic extensional sedimentary basins located worldwide

influence of water fugacity and activation volume on the flow properties of fine grained anorthite aggregates 1 to specify quantitatively the effect of pressure and water weakening on the flow strength of feldspar we performed triaxial creep experiments in a gas deformation apparatus at temperatures of 1000 1150 c confining pressures of 100 450 mpa and axial stresses of 10 400 mpa resulting in strain rates of 6 10 7 to 3 10 3 s 1 dense samples with a grain size of 3 m were prepared by hot isostatic pressing of anorthite glass powder hydrous samples contain about 0 33 0 14 wt h2o and dry specimens 0 0005 0 02 wt h2o the estimated residual glass content of wet samples is 2 vol samples deformed by grain boundary diffusion controlled creep at low stresses and dislocation creep at stresses 150 mpa we estimate an activation volume of v 24 cm3mol 1 for anhydrous samples deforming in diffusion creep for wet samples deformed in hydrous conditions with varying buffers fixing oxygen fugacity the activation volume is about 38 cm3 mol 1 creep rate of hydrous anorthite aggregates depends on water fugacity raised to a power of r 1 0 0 3 suggesting hydrolysis of oxygen bonds considering the effect of activation volume and water fugacity on extrapolation of constitutive laws to conditions prevailing in the continental lower crust viscosities of hydrous feldspar aggregates increase by a factor of 3

high resolution heat flow density in the lower congo basin 1 heat flow density hfd has been derived in the lower congo basin from 293 conventional probe measurements 424 oil exploration data and about 1 000 000 bottom simulating reflector bsr values each set of data provides independent estimates of temperature gradients associated with specific uncertainties and geographic distributions but a statistical comparison in overlapping domains shows a relatively good consistency in situ conductivity has been measured in conventional surveys and estimated from rock composition and porosity in oil exploration boreholes in the deep offshore measurements and estimates are consistently low and increase significantly toward the shelf domain thermal conductivity does not change significantly in the interval between the water bottom and the bsr and can be estimated from the surface measurements to provide an inference of hfd the combined sets of hfd in the lower congo basin cover the overall domain of the continental margin and a part of the oceanic domain high resolution imaging of the bsr by three dimensional 3 d seismic studies provides in addition good quality nominal resolution of 500 m in the deep offshore at short length scales on the order of kilometers large variations of hfd from 30 to 140 mwm 2 exist above salt diapirs and canyons related to heat refraction on the other hand no small scale effect related to fluid flow has been detected although active venting is known at larger length scale hfd in the deep offshore is different on both sides of the congo submarine channel 54 8 mwm 2 to the north and 48 12 mwm 2 to the south which are also characterized by different basin tectonic styles at the margin scale hfd is significantly different in the oceanic domain 42 3 mwm 2 the deep continental offshore 52 10 mwm 2 and the continental shelf 65 15 mwm 2 a progressive reduction of the radiogenic heat contribution in the extended continental crust is the more likely the cause of these differences mantle heat flow below the continental margin is consequently high compared to that expected 15 mwm 2 for old shields such as congo

understanding the thermal evolution of deep water continental margins areas of exploration for new hydrocarbons are changing as the hydrocarbon industry seeks new resources for economic and political reasons attention has turned from easily accessible onshore regions such as the middle east to offshore continental shelves over the past ten years there has been a marked shift towards deep water continental margins 500 2 500 m below sea level in these more hostile regions the risk and cost of exploration is higher but the prize is potentially enormous the key to these endeavours is a quantitative understanding of the structure and evolution of the thinned crust and lithosphere that underlie these margins

automated thermotectonostratigraphic basin reconstruction viking graben case study we present a generic algorithm for automating sedimentary basin reconstruction automation is achieved through the coupling of a two dimensional thermotectonostratigraphic forward model to an inverse scheme that updates the model parameters until the input stratigraphy is fitted to a desired accuracy the forward model solves for lithospheric thinning flexural isostasy sediment deposition and transient heat flow the inverse model updates the crustal and mantle thinning factors and paleowater depth both models combined allow for automated forward modeling of the structural and thermal evolution of extensional sedimentary basins the potential and robustness of this method is demonstrated through a reconstruction case study of the northern viking graben in the north sea this reconstruction fits present stratigraphy borehole temperatures vitrinite reflectance data and paleowater depth the predictive power of the model is illustrated through the successful identification of possible targets along the transect where the principal source rocks are in the oil and gas windows these locations coincide well with known oil and gas occurrences the key benefits of the presented algorithm are as follows 1 only standard input data are required 2 crustal and mantle thinning factors and paleowater depth are automatically computed and 3 sedimentary basin reconstruction is greatly facilitated and can thus be more easily integrated into basin analysis and exploration risk assessment

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

age and depositional environment of the dinosaur graveyard at las aguilas southern coahuila ne mexico abstract here we provide a detailed description of the upper campanian sediment succession at las aguilas southern coahuila northeastern mexico including the first absolute age dating for this interval paleoenvironmental reconstructions and taphonomic observations on the abundant dinosaur remains at the locality stratigraphic investigations of the dinosaur bearing succession at the las aguilas vertebrate fossil area near porvenir de jalpa reveal a diverse vertebrate assemblage including dinosaurs crocodilians and turtles new findings in adjacent sites include eusuchian crocodylomorphs four different kinds of turtles dromaeosaurids lambeosaurines pterosaurs and elasmosaurid plesiosaurs strontium isotope measurements on fossil oyster shells provide an absolute age of 73 1 ma for the lower part of the las aguilas section the locality is thus of late campanian age the vertebrate invertebrate and plant materials as well as the sediment structures observed in a 50 m thick predominantly siliciclastic succession of the cerro del pueblo formation suggest deposition in an extensive delta plain environment the facies succession indicates a short termed cyclicity of limnic brackish and shallow marine environments during the late campanian early maastrichtian cerro del pueblo formation with numerous layers containing dinosaur fossil remains resumen aqui damos una descripcion detallada de la sucesion de sedimentos del campaniano superior en las aguilas sur de coahuila noreste de mexico incluyendo la primera datacion absoluta para este intervalo reconstrucciones paleoambientales y observaciones taxonomicas sobre la abundancia de restos de dinosaurios en la localidad investigaciones estratigraficas de los estratos con dinosaurios en el area fosilifera de las aguilas cerca de porvenir de jalpa revelan un ensamblaje vertebrado diverso incluyendo dinosaurios cocodrilos y tortugas nuevos descubrimientos en sitios adyacentes incluyen crocodylomorfos eusuquios cuatro diferentes tipos de tortugas dromaeosauridos lambeosaurinos pterosaurios y plesiosaurios elasmosauridos mediciones de isotopos de estroncio en conchas de ostiones fosiles proveen una edad absoluta de 73 1 millones de anos para la parte inferior de la seccion de las aguilas la localidad es por lo tanto de edad campaniana tardia el material de vertebrados invertebrados y de plantas asi como las estructuras sedimentarias observadas en una sucesion predominantemente siliciclastica de 50 m de la formacion cerro del pueblo sugieren una depositacion en un ambiente de una extensa planicie deltaica la sucesion de facies indica una ciclicidad de periodo corto de ambientes limnicos estuarinos y marinos someros durante el campaniano tardio maastrichtiano temprano de la formacion cerro del pueblo con numerosos estratos conteniendo fosiles de dinosaurios palabras clave las aguilas sucesion de dinosaurios campaniano superior ambientes deposicionales formacion cerro del pueblo coahuila

crustal structure a key constraint on the mechanism of ultra high pressure rock exhumation abstract the distribution of ultra high pressure uhp metamorphic rocks demonstrates that burial to 100 km and rapid exhumation 1 cm a 1 of continental crust is a normal part of early 10 ma continental collision currently there is no comprehensive model for this fundamental tectonic process that also satisfactorily explains the upper crustal structures resulting from early collisional uhp rock exhumation characteristic features requiring explanation include structural domes that are cored by uhp nappes associated medium to high pressure nappes displaying a distinct pressure gap overlying lower grade rocks including suture zone ophiolites and coeval foreland directed thrust faults and syn exhumation normal faults we present a geodynamical model involving crustal burial and exhumation in a subduction channel below an accretionary wedge competition between down channel shear traction and up channel buoyancy forces expressed as the exhumation number e controls burial and exhumation leading to rapid up channel flow when e 1 exhuming uhp material forms a nappe stack and structural dome as it penetrates and destabilises the overlying wedge driving thrusting and extension this solution is compelling because it explains both the geology and the petrology of the tso morari and other uhp complexes and because it demonstrates that pulse like buoyant exhumation from deep in the subduction channel creates observed upper crustal structures this places constraints on the exhumation mechanism and provides a test of alternative models other proposed mechanisms such as continuous circulation in a lithospheric scale wedge or overpressured subduction channel predict different types of upper crustal structures and are therefore unsatisfactory explanations for early collisional exhumation of uhp terranes

integrative analysis of a lacustrine carbonate reservoir kambala field cabinda angola the presalt lacustrine rift basins of west africa are the continued focus of exploration and development in this prolific petroleum province kambala field produces from the barremian aptian lacustrine carbonates of the toca formation source rocks are the rich lacustrine shales of the bucomazi formation toca carbonates were deposited along major shorelines and around islands in large lake systems reservoir studies provide the necessary models and analogs to guide exploration and evaluation efforts the toca reservoirs in kambala field have been subdivided into two units the lower toca is characterized by limestones and cherty dolomites which range texturally from high energy ooid and oncoid grainstones and packstones to lower energy ostracod wackestones and marls the upper and lower toca are separated by a unit of middle bucomazi shale the upper toca is composed of thin beds of low energy facies and thick porous carbonate units which are pervasively dolomitized kambala field sits over a northwest southeast trending basement high the field is bounded by intense faulting on the west and dips gently to the northeast the faults on the eastern side are more widely spaced and have less throw than the ones on the west seismic amplitude maps on the upper toca show markedly highermore amplitudes on the western and southern edges of the field the high seismic amplitudes and intense faulting generally correlate with the zone of porous dolomite less

an arbitrary lagrangian eulerian formulation for creeping flows and its application in tectonic models summary this paper presents and analyses numerical techniques developed to investigate viscoplastic stokes flows within a model of lithospheric deformation in particular the techniques are related to a subduction model of compressional orogens the driving mechanism in the model corresponds to the near rigid convergence and subduction of one mantle lithosphere beneath another in plane strain and this boundary condition forces flow in an overlying viscoplastic model crust the numerical techniques use the arbitrary eulerian lagrangian formulation in which flows with free surfaces and large deformation are computed on an evolving eulerian finite element grid that conforms to the material domain a regridding algorithm allows the associated lagrangian motion and fields to be followed and in addition coupled back to the eulerian calculation of the flow mass flux boundary conditions are used so that the effects of erosion and deposition by surface processes and mass loss by subduction can be included in the model calculation the evolving model crustal layer is flexurally compensated using a general elastic beam formulation the applicability of the numerical techniques to problems ranging from accretionary wedges to crustal and lithospheric scale deformation is discussed simple flows a linear viscous subduction model a whirl flow and a quasi convection model are used to show that the mass conservation regridding and surface tracking errors are small the broader applicability of the modelling techniques is reviewed

frontier exploration in the south atlantic structural prospectivity in the north falkland basin seismic stratigraphic analysis of the continental shelf north of the falkland islands confirms that it is dissected by a significant extensional fault system that broadly defines the north falkland basin the basin comprises a series of extensional subbasins that developed during two distinct rift episodes analysis of structural styles shows that while extension occurred predominantly on a series of planar normal faults with changes in rift polarity in northern areas the southern portion of the basin has listric faults that sole out along preexisting thrusts after rifting the basin largely underwent postrift thermal subsidence with the passive infill of remnant topography however evidence exists for at least two uplift events affecting the postrift sediments the earlier period of uplift tilted the basin to the south resulting in the formation of a southerly prograding forced regressive wedge the later episode of uplift tilted the basin northward resulting in truncation of earlier strata and minor compressional reactivation and inversion in southernmost parts of the basin the later tilting allows for the possibility that the original rift system once extended across the falkland islands although the lack of well control does not permit a comprehensive assessment of hydrocarbon plays the seismic data do at least demonstrate the trapping potential of the basin interpreted structural and depositional styles found within the prerift synrift and postrift sequences are similar to those found in proven hydrocarbon provinces such as the north sea and the gulf of suez the success or failure of the frontier hydrocarbon province thus is likely to depend upon factors other than structural ones

shale tectonic processes field evidence from the parras basin north eastern mexico abstract major decollements located within buried overpressured shale commonly develop in thrust fronts accretionary prisms and sedimentary deltas controlled by gravity tectonics in seismic data it is possible to observe only large scale deformation of what is commonly designed as mobile shale but the precise geometry and the dynamic evolution of these bodies remains poorly understood it is often difficult to define if we are dealing with ductile or brittle deformation and to understand the role of the fluids in time and space during deformation for this reason large scale outcrops were studied in the parras basin mexico which makes possible a direct observation of the shale tectonic processes this work suggests changes in space and time of the deformation processes which occurred within the shale formation hosting the decollement distributed deformation was observed within the shale formation hosting the decollement compared to more localized deformation above also a change of the rheology of the shale over time occurred progressively toward brittle processes in the whole sedimentary pile xrd and microscopic studies have shown that diagenetic processes are favored in the shear zones of penetrative deformation leading notably to reverse gradient of illitization the isotopic analysis of cements in veins and the study of associated fluid inclusions have shown that fluid dynamics also evolved during time showing notably evidence for widespread fluid migration issued from rocks located below the decollement during the beginning of the deformation progressively the tectonic system located above the decollement tends to be preserved from fluid migration coming from below the decollement and to be influenced only by local fluid migration closed system

a comparison of the moho interpreted from gravity data and from deep seismic reflection data in the northern north sea summary we present the results of gravity modelling of the nsdp 84 deep seismic reflection profiles in the northern north sea the moho depths inferred from forward modelling of marine bouguer gravity anomalies from independent inversion of free air gravity anomalies derived from satellite altimetry and from deep seismic reflection profiling are in good mutual agreement this agreement suggests that the moho discontinuity interpreted from seismic reflection data corresponds to a major jump in density and therefore is likely to represent not only the geophysical but also the petrological boundary between the continental crust and the upper mantle in spite of the significant lateral heterogeneity of the crystalline basement below the northern north sea area as documented by seismic reflection profiling the average density contrast between the basement and the upper mantle is interpreted to show rather little variation this is not true for the deepest part of the viking graben where the nature of the lower crust and upper mantle may have been changed by magmatic processes accompanying the graben formation a relationship between the degree of crustal extension and the volume of magmatic intrusion into the lower crust is tentatively supported by our results