neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

mesozoic cover over northern england interpretation of apatite fission track data whether a significant thickness of mesozoic cover rocks once rested upon the palaeozoic rocks which form the structural highs of the english lake district and the northern pennines is a subject of long debate which has been revived recently by apatite fission track analysis afta studies evidence from adjacent basins suggests that 1200 1750 m of mesozoic cover was probably formerly present on the highs prior to cenozoic erosion higher estimates c 3000 m of cover thickness based on such fission track derived palaeotemperatures result from underestimation of early cenozoic surface temperatures and from not allowing for the relatively low thermal conductivity of the eroded cover rocks for similar reasons apatite fission track estimates of eroded cover rocks elsewhere in britain may also prove to be overestimates

national geohazards mapping in europe interferometric analysis of the netherlands abstract the launch of copernicus the largest earth observation program to date is significant due to the regular reliable and freely accessible data to support space based geodetic monitoring of physical phenomena that can result in natural hazards in this study wide area interferometric synthetic aperture radar insar capability is demonstrated by processing 435 copernicus sentinel 1 c band sar images may 2015 may 2017 using the intermittent small baseline subset isbas method to produce a wide area map wam covering 53 000 km2 of the netherlands belgium and germany the isbas wam contains over 19 million measurements achieving a ground coverage of 94 the retrieval of measurements over soft surfaces i e agricultural fields forests and wetlands was crucial due the dominance of non urban land cover a statistical analysis of the velocities reveals that intermittently coherent measurements in rural areas can provide reliable additional deformation information with a very high degree of confidence 5 which spatially correlates to known deformation features associated with compressible soils infrastructure settlement peat oxidation gas production salt mining and underground and opencast mining the spatial distribution of deformations concurs with independent data sources such as previous persistent scatterer interferometry psi deformation maps models of subsidence and settlement susceptibility and quantitatively with gps measurements over the groningen gas field remotely derived deformation products with near complete spatial coverage provide a powerful screening tool for mitigation and remediation of geological and geotechnical issues to help in the protection of assets property and life the isbas wam demonstrates that routine generation of such products on a continental scale is now theoretically achievable given the establishment of the copernicus programme and the development of state of the art insar methods such as isbas

thermal history of the rio muni west africa ne brazil margins during continental breakup abstract we document the thermal record of breakup of the conjugate rio muni west africa and ne brazil margins using apatite fission track analysis vitrinite reflectance data and stratigraphic observations from both margins these results permit determination of the timing of four cooling episodes and the temperature of samples at the onset of each episode all samples are interpreted to have experienced higher temperatures in the geological past due to i elevated basal heatflow palaeogeothermal gradient in rio muni 1 well decaying from 58 c km during the mid cretaceous to 21 5 c km in the late cenozoic and ii progressive exhumation from formerly greater burial depth a well constrained history of changing palaeogeothermal gradient allows for much more precise quantification of the thickness of eroded section exhumation than if a constant heatflow is assumed cooling episodes identified from the palaeotemperature data at 110 95 ma both margins and 85 70 ma rio muni only coincide with major unconformities signifying respectively the cessation of rifting breakup and compressional shortening that affected the african continent following the establishment of post rift sedimentation drift the interval between these separate unconformities is occupied by allochthonous rafts of shallow water carbonates recording gravitational collapse of a marginal platform the rift shoulder uplift that triggered this collapse was enhanced by local transpression associated with the obliquely divergent ascension fracture zone and thermal doming due to the coeval st helena and ascension plumes the data also reveal a c 45 35 ma cooling episode attributed to deep sea erosion at the onset of eo oligocene ice growth and a c 15 10 ma episode interpreted as the record of miocene exhumation of the west african continental margin related to continent wide plume development integration of thermal history methods with traditional seismic and stratigraphy based observations yields a dynamic picture of kilometre scale fluctuations in base level through the breakup and early drift phases of development of these margins major unconformities at ocean margins are likely to represent composite surfaces recording not only eustasy but also regional plate margin generated deformation local intra basinal reorganization and the amplifying effect of negative feedbacks between these processes

the continental margin of central east greenland in relation to north atlantic plate tectonic evolution the east greenland continental margin is inferred to have formed in three stages during the tertiary evolution of the adjacent north atlantic ocean the east greenland basaltic volcanism occurred over a period of 2 3 ma which was just prior to the probable date of onset of seafloor spreading in the early eocene shortly before magnetic anomaly 24b 52 ma the associated coastal flexure is interpreted as marking the edge of a zone of stretched and thinned continental crust beneath the inner denmark strait shelf and jan mayen microcontinent this represents a short lived rifting phase just prior to break up according to the evolutionary model the initial break up produced the margins south of the faeroe transform fault 68 5 n and north of the jan mayen fracture zone 72 n but in the intervening region the microcontinent remained attached to east greenland after break up the outer shelf of denmark strait formed from anomalously thick oceanic crust complementary to the iceland faeroe ridge the blosseville kyst margin 68 5 n to 70 n was initiated after anomaly 20 time 42 ma as the jan mayen microcontinent started to separate from greenland with spreading on both sides the new split occupied the line of the pre existing coastal dyke swarm and flexure the liverpool land margin 70 n to 72 n was also initiated at this time but the main separation of the northern part of the microcontinent only commenced after anomaly 7 time 26 ma when a single spreading axis was relocated west of the microcontinent it is suggested that the blosseville lavas subsided during deposition by loading and slight crustal stretching doming occurred near kangerdlugssuaq at the time of break up otherwise the topography of the lavas remained subdued until the relocation of the spreading axis at 26 ma after which the main regional uplift took place

the mountains of north east greenland are not remnants of the caledonian topography a comment on pedersen et al 2012 tectonophysics vol 530 531 p 318 330 abstract pedersen et al 2012 suggest that the present day mountains in north east greenland represent remnants of the original caledonian topography modified during early rifting and that the area has undergone slow steady exhumation since 250 ma they base this hypothesis on inverse modelling calibrated by new apatite fission track data from samples of exposed caledonian basement however apatite fission track data on their own register only cooling and must be integrated with geological evidence to reveal episodes of reheating reflecting re burial the well documented geological record of north east greenland shows that the caledonian mountains were obliterated as topographic features during the late palaeozoic and provides clear evidence of a history involving episodic post caledonian exhumation and re burial the high grade metamorphic basement was at great depth during the devonian and was exhumed to the surface before being reburied by up to 2 km of upper carboniferous and younger sediments these sediments were then partially removed during renewed early middle jurassic exhumation that led to the formation of a low lying landscape which eventually subsided and was buried below a km thick cover of middle jurassic and younger sediments this cover was then partially removed during later phases of uplift and exhumation that eventually led to the formation of the present day relief in post jurassic times the geological record in east greenland is incompatible with the idea of slow steady exhumation since the caledonian orogeny

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

the denudation history of the onshore continental margin of se brazil inferred from apatite fission track data a suite of 68 new apatite fission track analysis results from the onshore rift margin in southeast brazil are presented some of the results reflect resetting related to the eruption of the parana continental flood basalt 130 ma and four others are directly related to late cretaceous magmatism 80 ma the majority of the results were obtained from precambrian basement rocks and sediments from the parana basin the fission track ages broadly increase inland from 60 90 ma on the coastal plain to 300 ma in the continental hinterland the track length distributions show a characteristic trend being negatively skewed at the coast and showing increasing bimodality inland except for the oldest samples which are more unimodal these trends do not reflect rift related heating and resetting but are the result of protracted denudation since the opening of the south atlantic the results are consistent with more than 3 km of exhumation on the coastal plain but little more than 1 km in the hinterland the topographic morphology in the northern region of the study area is complex and is clearly influenced by structure and bedrock lithology for the region further south model calculations of the isostatic response to the denudation suggest that isostatic rebound makes a minor contribution to the long wavelength topography unless the flexural rigidity is more than 1025 n m in this case the initial elevation of the rift margin would need to be 2 5 km in order to accommodate the amount of denudation inferred from the fission track data however it is possible that the effective flexural rigidity varies across the margin becoming greater in the continental interior alternatively the broad scale wavelength topography may be the result of magmatic underplating related to the parana continental flood basalt event if so estimates of the volume of magma generated would need to be revised upward by as much as a factor of 5

thermochronologic constraints on ore formation at the gays river pb zn deposit nova scotia canada from apatite fission track analysis fission tracks in detrital apatites from the cambro ordovician metasedimentary basement in the vicinity of the carboniferous hosted gays river pb zn deposit nova scotia provide a record of final

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

distribution timing and causes of andean deformation across south america the andean orogeny in south america has lasted over 100 ma it comprises the peruvian incaic and quechuan phases the nazca and south american plates have been converging at varying rates since the palaeocene the active tectonics of south america are relatively clear from seismological and global positioning system gps data horizontal shortening is responsible for a thick crust and high topography in the andes as well as in se brazil and patagonia we have integrated available data and have compiled four fault maps at the scale of south america for the mid cretaceous late cretaceous palaeogene and neogene periods andean compression has been widespread since the aptian the continental margins have registered more deformation than the interior for the peruvian phase not enough information is available to establish a tectonic context during the incaic phase strike slip faulting was common during the quechuan phase crustal thickening has been the dominant mode of deformation to investigate the mechanics of deformation we have carried out 10 properly scaled experiments on physical models of the lithosphere containing various plates the dominant response to plate motion was subduction of oceanic lithosphere beneath continental south america however the model continent also deformed internally especially at the margins and initial weaknesses

mesozoic exhumation of the southern cape south africa quantified using apatite fission track thermochronology southern africa s topography is distinctive an inland plateau of low relief and high average elevation is separated from a coastal plane of high relief and low average elevation by a steeply dipping escarpment the origin and evolution of this topography is poorly understood because unlike high plateaus elsewhere its development cannot be easily linked to present day compressional plate boundary processes understanding the development of this regional landscape since the break up of gondwana is a first order step towards resolving regional epeirogenesis we present data that quantifies the timing and extent of exhumation across the southern cape escarpment and coastal plane using apatite fission track analysis afta of 25 outcrop samples and 31 samples from three deep boreholes kw1 67 sa1 66 cr1 68 outcrop fission track aft ages are cretaceous and are significantly younger than the stratigraphic ages of their host rocks indicating that the samples have experienced elevated paleotemperatures mean track lengths vary from 11 86 to 14 23 m the lack of cenozoic apatite ages suggests that major cooling was over by the end cretaceous the results for three boreholes situated seaward south of the escarpment indicate an episode of increased denudation in the mid late cretaceous 100 80 ma an earlier episode of increased denudation 140 120 ma is identified from a borehole north of the escarpment thermal modelling indicates a history involving 2 5 3 5 km of denudation in the mid late cretaceous 100 80 ma at a rate of 175 to 125 m ma the aft data suggest that less than 1 km of overburden has been eroded regionally since the late cretaceous 80 ma at a rate of 10 to 15 m ma but do not discount the possibility of minor in relative amplitude episodes of uplift and river incision through the cenozoic the reasons for rapid denudation in these early and mid cretaceous episodes are less clear but may be related to epeirogenic uplift associated with an increase in mantle buoyancy as reflected in two punctuated episodes of alkaline intrusions e g kimberlites across southern africa and contemporaneous formation of two large mafic igneous provinces 130 and 90 ma flanking its continental margins because cenozoic denudation rates are relatively minimal epeirogenic uplift of southern africa and its distinct topography cannot be primarily related to cenozoic mantle processes consistent with the lack of any significant igneous activity across this region during that time

meso cenozoic morphotectonic evolution of southern norway neogene domal uplift inferred from apatite fission track thermochronology apatite fission track aft thermochronology of precambrian and paleozoic basement samples from southern norway reveals a post paleozoic exhumation history related to offshore mesozoic and cenozoic extensional basin development the data indicate two major phases of rapid exhumation a first mesozoic phase started in the triassic 220 ma in the east and south of the study area and migrated to the west where jurassic 160 ma ages of exhumation predominate a second event is indicated by thermal history modeling of aft ages and track length distributions it is inferred to be neogene in age initiated at about 30 ma and it produced a domal pattern of aft isochrons which follow present day topographic elevation youngest aft ages 100 ma are encountered at sealevel in the inner fjords near the areas of highest topography ages increase radially outward to the mountain peaks and the coastlines forward modeling of age elevation patterns suggests that mesozoic geothermal gradients were 10 15 c km higher than the present value of 20 c km during the triassic and jurassic a total of 1 3 3 5 km of overburden was removed from the study area assuming a 30 c km geothermal gradient for that period we attribute this to rift margin erosion as a result of erosional base level lowering and flank uplift as evidenced by thick continental clastic sequences deposited in triassic jurassic half grabens in the north sea basins we propose that 1 5 2 5 km of neogene exhumation were a result of late stage domal uplift this is supported by basinward dipping pre neogene strata in the basins surrounding southern norway and the infill of a 1 to 2 km thick neogene sediment wedge containing various internal unconformities domal uplift probably started in the late oligocene may have been amplified in the pliocene and was overprinted by plio pleistocene glacial erosion maximum neogene tectonic uplift is estimated at approximately 1 1 5 km radially decreasing outward to a value 500 m near the shoreline neogene domal uplift is coincident with oligocene and pliocene plate reorganizations in the north atlantic similar neogene domes are found around the norwegian greenland sea i e svalbard and the barents sea northern norway east greenland suggesting a regional tectonic cause the onset of neogene uplift postdates major volcanism and continental breakup by 25 m y and predates plio pleistocene glaciations its origin is possibly a combination of induced mantle convection resulting in thermal erosion of the lithosphere and the operation of intraplate stresses

scales of transient convective support beneath africa beneath sub equatorial africa there is convincing evidence for a gigantic slow velocity anomaly within the lower mantle that is inferred to be a thermochemical superplume here we define the spatial and temporal pattern of uplift across the northern edge of this putative superplume by analyzing stratal geometries and stacking velocities of neogene sedimentary rocks these marine deposits are imaged on a dense grid of seismic reflection profiles that straddle the southwest african coastal shelf inverse modeling of stacking velocity profiles demonstrates that there have been at least two significant phases of uplift a post pliocene uplift event increases from 0 to 500 m elevation over a distance of 1000 km in close agreement with geophysical estimates of the present day variation of dynamic topography an earlier phase of uplift occurred in middle oligocene time ca 30 35 ma ago we propose a two stage development of epeirogeny in which a middle oligocene phase of uplift may be related to initiation and growth of the african superplume post pliocene denudation records rapid 100 250 m ma vertical motions generated by upper mantle convection which vary on length scales of 500 1000 km our results support the existence of a convective circulation system that has operated on different temporal and spatial scales beneath the african plate

late mesozoic to early cenozoic components of vertical separation across the more trondelag fault complex norway abstract low temperature apatite fission track aft data from two horizontal transects across the more trondelag fault complex mtfc and along the coast of the fosen peninsula have defined a complicated series of structural blocks whose exhumation to temperatures cooler than the uppermost apatite partial annealing zone paz occurred during a broad mesozoic to cenozoic time span the 100 million year cooling difference between the innermost and outermost blocks indicates they were subjected to very different exhumation pathways track length histograms and inverse model results also suggest that significant differences in thermal histories are present over very short horizontal distances in conjunction with the offshore geological evidence the aft data and models strongly suggest that the innermost zones of the mtfc underwent between 2 and 4 km of structurally controlled net vertical rock column uplift subsidence following latest cretaceous time and potentially much of the tertiary as well the up to the east down to the west relative offset at the norwegian margin is interpreted in terms of a flexed nearly broken lithospheric plate architectural model for late mesozoic and tertiary scandes mountain building whose driving force was likely dominanted by erosionally induced loading unloading at the margin

continental lithospheric thinning and breakup in response to upwelling divergent mantle flow application to the woodlark newfoundland and iberia margins abstract depth uniform stretching is not the dominant deformation process for thinning continental lithosphere leading to breakup it cannot explain the observed depth dependent lithosphere stretching and mantle exhumation at rifted continental margins depth dependent lithosphere thinning in which stretching of the lower crust and lithosphere mantle greatly exceeds that of the upper crust has been observed at many non volcanic and volcanic rifted continental margins including conjugate margin pairs passive continental margins show a paucity of brittle deformation in the upper crust during continental lithosphere thinning leading to breakup and sea floor spreading initiation a new model of rifted continental margin formation has been developed that assumes that deformation and thinning of continental lithosphere leading to breakup occurs in response to an upwelling divergent flow field within continental lithosphere and asthenosphere and that this deformation evolves into sea floor spreading the new model successfully predicts depth dependent stretching of continental margin lithosphere for both non volcanic and volcanic margins and mantle exhumation at non volcanic margins both of which are observed but are not explained by existing depth uniform continental lithosphere stretching models the new model provides a balance of extensional strain supplies an explanation for the paucity of synrift brittle deformation and offers a simple transition from prebreakup lithosphere thinning to sea floor spreading the observed diversity of rifted continental margin structure and width of the ocean continent transition can be explained by variability in the form of the upwelling divergent flow field the new upwelling divergent flow model of continental lithosphere thinning leading to continental breakup successfully predicts the observed bathymetry and margin geometry for the most recent segment of sea floor spreading initiation in the woodlark basin in the western pacific and the observed bathymetry and free air gravity anomaly for the newfoundland and iberian margins

morphotectonic evolution of rifted continental margins inferences from a coupled tectonic surface processes model and fission track thermochronology we use a numerical model to study the topographic evolution and erosional history of rifted continental margins the model combines a kinematic description of lithospheric extension tectonic model with a surface processes model that includes short range hillslope and long range fluvial transport the tectonic model predicts the evolution of the lithospheric temperature and strength elastic thickness distribution as well as the tectonic uplift through time this is input into the surface processes model which calculates the degradation of topography and associated isostatic rebound modeled denudation histories across the margin are used to predict apatite fission track age and length patterns modeling results indicate that depending on the adopted parameters an uplifted rift flank should degrade by erosion within 50 100 m y without significant retreat of the topographic elevation maximum the development of an escarpment system at rifted continental margins is in itself not an indication of tectonic rift flank uplift but results from the existence of a high elevation interior plateau erosional base level lowering as a consequence of rifting and regional isostatic response to erosion of the margin however apatite fission track thermochronology reveals that the areas seaward of the escarpment at a number of rifted margins have been exhumed from several kilometers depth such amounts of denudation cannot be accommodated with isostatic rebound alone and require additional tectonic uplift of the rift flanks modeling of apatite fission track patterns suggests that fission track thermochronology dates the onset of rapid erosion which coincides with the initiation of strong relief i e initiation of rifting fission track ages which are younger than the age of rifting thus cannot be unambiguously interpreted as excluding prerift uplift the timing of margin uplift can be established only by careful track length analysis and integration with regional stratigraphic data the model is applied to the saudi arabian red sea margin and the southeastern australian highlands where it is constrained by present day topography and apatite fission track data as well as seismic and gravity data for the saudi arabian red sea margin synrift regional plateau uplift with a magnitude of approximately 1 km is inferred possibly as a result of asthenospheric upwelling flexurally induced tectonic uplift of the rift flank with a magnitude of 2 km is superimposed on this regional uplift the relatively high elevation of the southeastern australian highlands their steep front and the relatively high amounts of erosion suggest that apart from mesozoic synrift flexural uplift tertiary rejuvenation of topography has occurred possibly as a result of renewed lithospheric thinning and underplating the low elevation of the australian interior would inhibit the evolution of a major escarpment in the absence of such renewed uplift

long term stratigraphic evolution of atlantic type passive margins a numerical approach of interactions between surface processes flexural isostasy and 3d thermal subsidence the thermal and flexural evolution of passive margins is impacted by the un loading effects of erosion sedimentation processes which in turn affect their relief and sediment accumulation these complex couplings are recorded by the stratigraphic trend of the associated sedimentary basins which is controlled by the balance between sediment accumulation subsidence and eustasy our objective is to constrain the relative contribution of the factors controlling the mechanical response of the lithosphere and the efficiency of the surface processes on parameters such as the denudation accumulation and uplift subsidence history and long termstratigraphic trends the novel aspect of our approach is to integrate the evolution of both domains in erosion and in sedimentation using state of the art modeling of the flexure of the lithosphere including the surface processes erosion sedimentation and the thermal evolution as well as concepts in sequence stratigraphy we investigated numerically the post rift evolution of passive margins testing the influence of the lithosphere s initial geometries thermal states and stretching profiles as well as the efficiency of the surface processes in all simulations the initial flexural rift shoulder is eroded away within 10 to 20 myr in the following stages the sedimentary supply and the evolution of the margin are mostly controlled by the flexural response to the thermal relaxation of the isotherms by cooling and the un loading mass transfer at the surface both the sediment accumulation controlled by relief relaxation and the subsidence rates decrease exponentially with time the evolution of their relative values forms a regressive transgressive sequence we show that variations in the efficiency of the surface processes may impact the uplift subsidence histories and the long term stratigraphic trend within the same range of magnitude as lithospheric parameters such as pre rift crust thickness or depth dependency of stretching the initial crustal thickness is then determinant in the denudation accumulation history whereas the margin width will impact the uplift subsidence history the second most depth of necking and effective elastic thickness are critical mostly during the initial phase of the margin history syn and immediate post rift whereas bulk sediment density and lithosphere thickness become critical in the late post rift

post breakup burial and exhumation of passive continental margins seven propositions to inform geodynamic models despite many years of study the processes involved in the post breakup development of passive margins remain poorly understood integration of apatite fission track analysis afta and stratigraph

post breakup tectonics in southeast brazil from thermochronological data and combined inverse forward thermal history modeling the continental margin of southeast brazil is elevated onshore tertiary basins and late cretaceous paleogene intrusions are good evidence for post breakup tectono magmatic activity to constrain the impact of post rift reactivation on the geological history of the area we carried out a new thermochronological study apatite fission track ages range from 60 7 1 9 ma to 129 3 4 3 ma mean track lengths from 11 41 0 23 mm to 14 31 0 24 mm and a subset of the u th he ages range from 45 1 1 5 to 122 4 2 5 ma results of inverse thermal history modeling generally support the conclusions from an earlier study for a late cretaceous phase of cooling around the onshore taubate basin for a limited number of samples the first detectable period of cooling occurred during the early tertiary the inferred thermal histories for many samples also imply subsequent reheating followed by neogene cooling given the uncertainty of the inversion results we did deterministic forward modeling to assess the range of possibilities of this tertiary part of the thermal history the evidence for reheating seems to be robust around the taubate basin but elsewhere the data cannot discriminate between this and a less complex thermal history however forward modeling results and geological information support the conclusion that the whole area underwent cooling during the neogene the synchronicity of the cooling phases with andean tectonics and those in ne brazil leads us to assume a plate wide compressional stress that reactivated inherited structures the present day topographic relief of the margin reflects a contribution from post breakup reactivation and uplift

rapid south atlantic spreading changes and coeval vertical motion in surrounding continents evidence for temporal changes of pressure driven upper mantle flow the south atlantic region displays 1 a topographic gradient across the basin with africa elevated relative to south america 2 a bimodal spreading history with fast spreading rates in late cretaceous and eo oligocene and 3 episodic regional uplift events in the adjacent continents concentrated in late cretaceous and oligocene here we show that these observations can be linked by dynamic processes within earth s mantle through temporal changes in asthenosphere flow beneath the region the topographic gradient implies westward pressure driven mantle flow beneath the basin while the rapid spreading rate changes on order 10 million years require significant decoupling of regional plate motion from the large scale mantle buoyancy distribution through a mechanically weak asthenosphere andean topographic growth in late miocene can explain the most recent south atlantic spreading velocity reduction arising from increased plate boundary forcing associated with the newly elevated topography but this mechanism is unlikely to explain the late cretaceous tertiary spreading variations as changes in andean paleoelevation at the time are small we propose an unsteady pressure driven flow component in the asthenosphere beneath the south atlantic region to explain the late cretaceous tertiary spreading rate variations temporal changes in mantle flow due to temporal changes in regional mantle pressure gradients imply a correlation of horizontal and vertical motions we find that this prediction from our models agrees with geologic and geophysical observations of the south atlantic region including episodes of passive margin uplift regional basin reactivation and magmatic activity

post break up tectonic inversion across the southwestern cape of south africa new insights from apatite and zircon fission track thermochronometry the south west african margin is regarded as an example of a passive continental margin formed by continental rifting following a phase of lithospheric extension and thinning recent attention focused on this margin has included theoretical modelling studies of rift processes plate kinematic studies of the opening geometry and timing and empirical studies focused on documenting the crustal structure and offshore sedimentary record here we examine the onshore geomorphic and tectonic response to rifting and breakup with a specific focus on the sw cape of south africa we present 75 new apatite and 8 new zircon fission track analyses from outcrop samples and onshore borehole profiles along the western margin of south africa the data are used to derive robust thermal histories that record two discrete phases of accelerated erosional cooling during the early cretaceous 150 130 ma and late cretaceous 100 80 ma respectively both periods of enhanced erosion are regional in extent involved km scale erosion and extend well inland of the current escarpment zone albeit with spatially variable intensity and style the late cretaceous episode is also expressed more locally by tectonic reactivation and inversion of major faults causing km scale differential displacement and erosion the new aft data do not exclude the possibility of modest surface uplift occurring during the cenozoic but they restrict the depth of regional cenozoic erosion on the western margin to less than c 1 km the inferred pattern and chronology of erosion onshore is consistent with the key features and sediment accumulation patterns within the offshore orange and bredasdorp basins it is suggested that the late cretaceous event was triggered by a combination of regional dynamic uplift augmented along the western margin and in the sw cape by local tectonic forces arising from dextral displacement of the falkland plateau along the falkland agulhas fracture zone

cenozoic uplift of nuussuaq and disko west greenland elevated erosion surfaces as uplift markers of a passive margin remnants of a high plateau have been identified on nuussuaq and disko central west greenland we interpret the plateau as an erosion surface the summit erosion surface formed mainly by a fluvial

late cretaceous reactivation of major crustal shear zones in northern namibia constraints from apatite fission track analysis abstract namibia s passive continental margin records a long history of tectonic activity since the proterozoic the orogenic belt produced during the collision of the congo and kalahari cratons in the early proterozoic led to a zone of crustal weakness which became the preferred location for tectonism during the phanerozoic the pan african damara mobile belt forms this intraplate boundary in namibia and its tectonostratigraphic zones are defined by ductile shear zones where the most prominent is described as the omaruru lineament waterberg thrust oml wt the prominance of the continental margin escarpment is diminished in the area of the central and northern zone of the damara belt where the shear zones are located this area has been targeted with a set of 66 outcrop samples over a 550 km long 60 km broad coast parallel transect from the top of the escarpment in the south across the damara sector to the kamanjab inlier in the north apatite fission track age and length data from all samples reveal a regionally consistent cooling event thermal histories derived by forward modelling bracket this phase of accelerated cooling in the late cretaceous maximum palaeotemperatures immediately prior to the onset of cooling range from ca 120 to ca 60 c with the maximum occurring directly south of the omaruru lineament because different palaeotemperatures indicate different burial depth at a given time the amount of denudation can be estimated and used to constrain vertical displacements of the continental crust we interpret this cooling pattern as the geomorphic response to reactivation of basement structures caused by a change in spreading geometry in the south atlantic and south west indian oceans

formation of the steer s head geometry of sedimentary basins by differential stretching of the crust and mantle if the lithospheric mantle is stretched over a wider region than the crust postrift stratigraphic onlap will occur at basin margins giving rise to a steer s head geometry space problems are avoided by making the total amount of extension in the lithospheric mantle equal to that in the crust the predicted pattern of onlap agrees well with that observed if the lithospheric mantle is stretched over a fractionally wider region than is the crust thus extensive stratigraphic onlap can be produced easily without recourse to sea level rise or flexural rigidity

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

synchroneity of cratonic burial phases and gaps in the kimberlite record episodic magmatism or preservational bias abstract a variety of models are used to explain an apparent episodicity in kimberlite emplacement implicit in these models is the assumption that the preserved kimberlite record is largely complete however some cratons now mostly devoid of phanerozoic cover underwent substantial phanerozoic burial and erosion episodes that should be considered when evaluating models for global kimberlite distributions here we show a broad temporal coincidence between regional burial phases inferred from thermochronology and gaps in the kimberlite record in the slave craton superior craton and cratonic western australia a similar pattern exists in the kaapvaal craton although its magmatic deposition and erosion history differs in key ways from the other localities one explanation for these observations is that there is a common cause of cratonic subsidence and suppression of kimberlite magmatism another possibility is that some apparent gaps in kimberlite magmatism are preservational artifacts even if kimberlites occurred during cratonic burial phases the largest uppermost portions of the pipes would have been subsequently eroded along with the sedimentary rocks into which they were emplaced in this model kimberlite magmatism was more continuous than the preserved record suggests implying that evidence for episodicity in kimberlite genesis should be carefully evaluated in light of potential preservational bias effects either way the correlation between burial and kimberlite gaps suggests that cratonic surface histories are important for understanding global kimberlite patterns

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

denudational history along a transect across the drakensberg escarpment of southern africa derived from apatite fission track thermochronology 1 the denudational history of a 500 km long transect across the drakensberg escarpment on the high elevation passive margin of se africa is quantified on the basis of thermal history modeling of apatite fission track data for 15 deep borehole samples supplemented by an additional 10 outcrop samples a minimum of 4 5 km of denudation since formation of the margin 130 myr ago is estimated for the coastal zone with a marked early cretaceous episode of accelerated denudation broadly coincident with continental breakup samples from the swartberg borehole sw 1 67 located 30 km seaward of the present position of the drakensberg escarpment indicate a total depth of denudation of 3 1 1 2 km since 91 myr with a phase of accelerated denudation of 2 1 0 9 km at a mean rate of 95 43 m myr between 91 and 69 myr samples from the ladybrand borehole la 1 68 west of the lesotho highlands indicate 1 7 0 5 km of denudation since 78 myr with a phase of accelerated denudation at 82 43 m myr from 78 to 64 myr average denudation rates declined to about 10 m myr during much of the tertiary although the apatite fission track data do not provide any direct constraints on the denudational history of the lesotho highlands interpolation between the two boreholes constrained by geological evidence and extrapolated in situ produced cosmogenic 36cl derived denudation rate estimates suggests a pattern of denudation compatible with numerical modeling studies of escarpment evolution involving rapid river incision seaward of a preexisting inland drainage divide these patterns of denudation are incompatible with constant retreat of the drakensberg escarpment from an initial position near the present coast we suggest that the drakensberg escarpment formed by rapid post breakup river incision seaward of a preexisting drainage divide located just east of the present escarpment location and became pinned at this divide with subsequent retreat rates of only 100 200 m myr

palaeocene recent plate boundaries in the ne atlantic and the formation of the jan mayen microcontinent abstract breakup and sea floor spreading between greenland and eurasia established a series of new plate boundaries in the north atlantic region since the late palaeocene a conventional kinematic model from pre breakup to the present day assumes that eurasia and greenland moved apart as a two plate system however new regional geophysical datasets and quantitative kinematic parameters indicate that this system underwent several adjustments since its inception and suggest that additional short lived plate boundaries existed in the ne atlantic among the consequences of numerous plate boundary relocations is the formation of a highly extended or even fragmented jan mayen microcontinent and subsequent deformation of its margins and surrounding regions the major oligocene plate boundary reorganization and microcontinent formation might have been precluded by various ridge propagations and or short lived triple junctions ne and possibly sw of the jan mayen microcontinent from the inception of sea floor spreading 54 ma to c18 40 ma our model implies a series of failed ridges offshore the faeroe islands a northern propagation of the aegir ridge ne of the jan mayen microcontinent and a series of triple junctions and or propagators in the southern greenland basin

evidence from apatite fission track analysis for the post devonian burial and exhumation history of the northern highlands scotland abstract devonian and older rock samples from outcrops in the northern scottish highlands have undergone protracted cooling since they reached palaeotemperatures of 110 c or more in the late palaeozoic to early mesozoic the results not only suggest that the northern highlands region has experienced kilometre scale exhumation since the late palaeozoic but also that devonian and possibly permo carboniferous sedimentation was probably more extensive than current outcrop patterns would imply a permian outcrop sample from the minches basin reached a maximum palaeotemperature of 70 90 c prior to the onset of cooling in the early tertiary while data from devonian and older samples suggest an acceleration in the rate of cooling in the early tertiary the magnitude of early tertiary palaeotemperatures on the mainland adjacent to the inner moray firth imf indicate similar amounts of tertiary exhumation to those derived from compaction analyses for the imf however to the west the magnitude of tertiary cooling cannot be solely ascribed to exhumation and a contribution of heating due to hydrothermal effects and or elevated heat flow associated with the tertiary igneous complex may also need to be invoked

anatomy of a modern marine sabkha in a rift valley setting northwest gulf of california baja california mexico abstract an extensive sabkha 100 by 20 km 62 by 12 mi caps holocene siliciclastic tidal flats along the coast of baja california in the northwest gulf of california structural trough this sabkha bounded on the west by alluvial fans is a complex of sand flat saline mud flat gypsum halite pan and supratidal mud flat subenvironments the sand flat transitional between the fans and the sabkha consists of horizontally to wavy laminated sand washed onto the flats by sheetfloods from the fans under upper flow regime conditions the sand flat passes into saline mud flats characterized by massive mud crowded with discoidal gypsum crystals grown within the sediment destroying the layering this intrasediment growth of gypsum is driven by evaporative pumping of brine from a shal ow subsurface brine body a gypsum pan occupies a wide shallow depression within the saline mud flat after storm flooding either marine or meteoric the pan becomes a temporary saline lake with an algal mat overgrowing a siliciclastic storm layer precipitation of gypsum needles from the open lake brine and bottom growth of gypsum prisms produce a gypsum layer that mimics the algal mat topography evaporation of the lake leads to 1 vadose diagenetic growth of gypsum that distorts and polygonally disrupts the gypsum layers 2 deposition of a surface halite layer in the center of the pan these layered pan deposits are the evaporites of the sabkha seaward of the saline mud flats are supratidal mud flats underlain by millimeter thick laminites with deep prism cracks sheet cracks an scattered gypsum discoid crystals pervasive mud cracking during long periods of nondeposition completely disrupts layering creating a massive arid soil a beach ridge separates this sabkha complex from the burrowed and ripple cross laminated intertidal sediments end of article last page 460

thermal and tectonic evolution of the falkland islands implications for hydrocarbon exploration in the adjacent offshore region apatite fission track and vitrinite reflectance data combine to suggest that the falkland islands experienced three discrete episodes of heating and cooling during the phanerozoic each of which can be related to major changes in the plate tectonic setting of the islands combined with published data from the adjacent offshore areas the results provide unique insights into the behaviour of the region during the phases of convergent and divergent tectonic movements that have affected the region since the permian initial cooling of the falkland islands in the late permian was initially restricted to west falkland and was the result of differential uplift and erosion of west falkland relative to east falkland coinciding with d2 gondwanian deformation subsequent early jurassic cooling of both east and west falkland was associated with plume related thermal uplift preceding the separation of east and west gondwana and the development of the falkland plateau basin the falkland islands experienced renewed heating during the mesozoic probably due to increased burial suggesting that the offshore basins originally extended onto the present onshore region late cretaceous early tertiary cooling of the falkland islands was contemporaneous with the development of a transpressional plate boundary along the southern margin of the falkland plateau resulting in erosion of the islands that were situated on a flexural forebulge

interpreting data dispersion and inverted dates in apatite u th he and fission track datasets an example from the us midcontinent abstract new apatite u th he ahe and apatite fission track aft data were acquired for cratonic basement samples from an 80 m span of drillcore in northeastern kansas the short depth interval over which the samples were collected indicates that they should have undergone thermal histories that would be indistinguishable using low temperature thermochronometry techniques individual ahe dates from four samples range from 99 to 464 ma three samples yield dates 300 ma higher eu 39 113 ppm and substantial data dispersion uncorrelated with eu and grain size these apatites have strong and variable eu zonation aft dates for five samples range from 242 to 291 ma the sample with the highest eu apatites and oldest ahe dates yields the youngest aft results these results are inverted with ahe dates distinctly older than the corresponding aft date we explore both the causes of data dispersion and the overall compatibility of this cratonic dataset we find that geologically reasonable thermal histories can 1 explain the distribution of the moderate eu ahe data when accounting for the influence of radiation damage grain size and eu zonation on apatite he diffusivity 2 reproduce the observed dispersion in the high eu ahe data when using a viable range of eu zonation and grain size and 3 explain the aft data for the same samples the ahe and aft data are mutually consistent and viable thermal histories successfully predict the observed pattern of older ahe than aft dates for the high eu apatites together these results suggest that appropriately accounting for the known controls on apatite he diffusivity can explain the observed dispersion and inverted ahe and aft results in some thermochronometry datasets a range of ahe dates should be especially common in cratonic data because small differences in apatite he diffusivity are amplified by the thermal histories that typify cratonic settings we use these results to develop some guidelines for interpreting dispersed ahe datasets first date eu and date grain size correlations should be evaluated and if these patterns occur they can be used to better resolve the thermal history second for samples that yield inexplicably large dispersion of ahe dates uncorrelated with eu and crystal size the appropriate strategy is either to reject these samples from the suite used for thermal history interpretation or to acquire additional data to help decipher the significance of the age distribution

episodic burial and exhumation of the southern baltic shield epeirogenic uplifts during and after break up of pangaea cratons are conventionally assumed to be areas of long term stability however whereas precambrian basement crops out across most of the baltic shield palaeozoic and mesozoic sediments rest on basement in southern sweden and thus testify to a complex history of exhumation and burial our synthesis of published stratigraphic landscape analysis and new apatite fission track analysis data reveals a history involving five steps after formation of the extremely flat sub cambrian peneplain 1 cambrian to lower triassic rocks accumulated on the peneplain interrupted by late carboniferous uplift and exhumation 2 middle triassic uplift removed the palaeozoic cover along the south western margin of the shield leading to formation of a triassic peneplain with a predominantly flat relief followed by deposition of upper triassic to lower jurassic rocks 3 uplift that began during the middle jurassic to earliest cretaceous caused denudation leading to deep weathering that shaped an undulating hilly relief that was buried below upper cretaceous to oligocene sediments 4 early miocene uplift and erosion produced the south smaland peneplain with scattered hills 5 early pliocene uplift raised the miocene peneplain to its present elevation leading to reexposure of the sub cretaceous hilly relief near the coast our results thus provide constraints on the magnitude and timing of episodes of deposition and removal of significant volumes of phanerozoic rocks across the southern portion of the baltic shield late carboniferous middle triassic and mid jurassic events of uplift and exhumation affected wide areas beyond the baltic shield and we interpret them as epeirogenic uplifts accompanying fragmentation of pangaea caused by accumulation of mantle heat beneath the supercontinent early miocene uplift affected north west europe but not east greenland and thus likely resulted from compressive stresses from an orogeny on the eurasian plate early pliocene uplift related to changes in mantle convection and plate motion affected wide areas beyond north east atlantic margins

formation uplift and dissection of planation surfaces at passive continental margins a new approach the usefulness of large scale low relief high level landscapes as markers of uplift events has become a subject of disagreement among geomorphologists we argue that the formation of low relief surfaces over areas of large extent and cutting across bedrock of different age and resistance must have been guided by distinct base levels in the absence of other options the most likely base level is sea level we have analysed west greenland landscapes in a recent study by combining the cooling history from apatite fission track analysis afta data with the denudation history from landscape analysis and the stratigraphic record an important difference between our approach and that of classical geomorphology is that we now have the ability to document when thick sections of rocks have been deposited and then removed the present day high level plateau in west greenland is the remnant of a planation surface that was formed by denudation that lasted c 20 million years during which up to 1 km of cover was removed after maximum burial at the eocene oligocene transition here we present additional afta data to show that the planation surface is the end product of cenozoic denudation even in basement areas and argue that phanerozoic sediments most likely of cretaceous palaeogene age must have been present prior to denudation the planation surface was offset by reactivated faults and uplifted to present day altitudes of up to 2 km the uplift occurred in two late neogene phases that caused incision of valleys below the planation surface and their subsequent uplift we therefore find that the elevated and deeply dissected plateau is evidence of episodic post rift uplift that took place millions of years after cessation of sea floor spreading west of greenland we suggest that other margins with similar morphology may also be characterized by episodic post rift uplift unrelated to the processes of rifting and continental separation rather than being permanently uplifted since the time of rifting as is commonly assumed copyright 2009 john wiley sons ltd

low temperature phanerozoic history of the northern yilgarn craton western australia abstract the phanerozoic cooling history of the western australian shield has been investigated using apatite fission track aft thermochronology aft ages from the northern part of the archaean yilgarn craton western australia primarily range between 200 and 280 ma with mean confined horizontal track lengths varying between 11 5 and 14 3 m time temperature modelling of the aft data together with geological information suggest the onset of a regional cooling episode in the late carboniferous early permian which continued into late jurassic early cretaceous time present day heat flow measurements on the western australian shield fall in the range of 40 50 mw m 2 if the present day geothermal gradient of 18 2 c km 1 is representative of average phanerozoic gradients then this implies a minimum of 50 c of late palaeozoic to mesozoic cooling assuming that cooling resulted from denudation the data suggest the removal of at least 3 km of rock section from the northern yilgarn craton over this interval the perth basin located west of the yilgarn craton contains up to 15 km of mostly permian to lower cretaceous clastic sediment however published u pb data of detrital zircons from permian and lower triassic basin strata show relatively few or no grains of archaean age this suggests that the recorded cooling can probably be attributed to the removal of a sedimentary cover rather than by denudation of material from the underlying craton itself the onset of cooling is linked to tectonism related to either the waning stages of the alice springs orogeny or to the early stages of gondwana breakup

the thermal history of the eastern officer basin south australia evidence from apatite fission track analysis and organic maturity data the eastern officer basin in south australia contains a neoproterozoic to devonian succession overlain by relatively thin 500 m permian mesozoic and tertiary deposits within the basin fill there are several major unconformities representing uncertain amounts of erosion three of these surfaces are associated with regional deformational events regional unconformities formed between 560 and 540 ma petermann ranges orogeny approximately 510 490 ma delamerian orogeny 370 300 ma alice springs orogeny 260 150 ma and 95 40 ma afta results from 13 samples of neoproterozoic cambrian and permian sedimentary rocks in five wells giles 1 manya 2 5 and 6 and lake maurice west 1 show clear evidence for a number of distinct thermal episodes results from all samples are consistent with cooling from the most recent thermal episode beginning at some time between 70 and 20 ma maastrichtian miocene afta results from giles 1 indicate at least two pre cretaceous thermal episodes with cooling beginning between 350 and 250 ma carboniferous permian and between 210 and 110 ma late triassic albian results from manya 2 5 and 6 and lake maurice west 1 show evidence for at least one earlier higher temperature event with cooling from elevated paleotemperatures beginning between 270 and 200 ma late permian to late triassic these episodes can be correlated with other cooling erosional events outside the study area and the afta derived paleotemperatures are consistent with kilometre scale erosion for each of the episodes identified integration of the afta data with organic thermal maturation indicators mpi in the manya and giles 1 wells suggests that the cambrian and neoproterozoic successions in the northern part of the study area reached peak maturation prior to the permian while limited data from lake maurice west 1 allows peak maturation to have occurred as young as the late permian to late triassic thermal episode revealed by afta the approach outlined in this study is relevant to all ancient basins as it emphasises the importance of understanding events associated with neighbouring regions the thermal history of the officer basin as with most other ancient basins has been strongly affected by significant tectonic events throughout its history even though younger deposits are not preserved in the basin itself the recognition of these younger events and the implications of these events for the depositional history is important as it allows identification of the best regions for preservation of early generated hydrocarbons and in some cases suggests areas where generation of hydrocarbons could have occurred more recently than previously thought

rift to post rift evolution of a passive continental margin the ponta grossa arch se brazil low temperature thermochronology was applied at the brazilian passive continental margin in order to understand and reconstruct the post rift evolution since the break up of southwestern gondwana thermochronological data obtained from apatite fission track analysis of neoproterozoic metamorphic and paleozoic to mesozoic siliciclastic rocks as well as mesozoic dikes and alkaline intrusions from the ponta grossa arch provided ages between 66 2 1 3 and 5 9 0 8 ma these data clearly indicate a post rift reactivation during late cretaceous and paleogene times integrating the results of older thermochronological studies the reactivation of the southeastern brazilian margin could be described in three main phases related to the rift to post rift evolution of se brazil furthermore the spatial distribution of age data indicates the presence of two age groups a ne age group ne of curitiba with ages around 20 ma and a sw age group curitiba and nw with ages of around 50 ma the change of ages follows the nw se trending sao jeronimo curiuva fault zone that can be traced offshore into the southern end of the santos basin within the santos basin this lineament ends up to the salt occurrence in the south and seams to play a major role in the structural evolution of the santos basin and the rio grande rise sedimentological studies in the santos basin evidenced that the transport direction changed in miocene from wnw to wnw nnw during the oligocene and earlier the sediments were transported mainly from southeastwards to the direction of the curitiba area into the santos basin within the miocene an additional transport direction from an area north of curitiba developed

post rift reactivation of the onshore margin of southeast brazil evidence from apatite u th he and fission track data abstract on the continental margin of southeast brazil there is good geological evidence for post rift tectonic reactivation in the form of onshore tertiary basins up to 800 m deep and cretaceous to paleocene alkaline intrusive bodies at the surface with the aim of constraining the mesozoic and cenozoic exhumation history of this region we present new apatite u th he ages on basement samples which one of us previously used for apatite fission track aft analysis the new he ages range from 115 5 2 2 ma to 47 0 6 4 ma whereas the aft ages range from 330 3 22 ma to 64 5 3 ma inverse thermal history modelling of all the data provides more detail on the post rift cooling history than do the aft data alone furthermore models incorporating radiation damage effects on he diffusion produce thermal histories that are more consistent with independent geological evidence than models without these effects the results imply that only a few samples record an early cooling phase around the time of opening of the south atlantic ocean the new u th he data also imply a late cretaceous phase of exhumation between 90 and 60 ma subsequently the region underwent slow cooling i e erosion rate two or three samples seem to indicate a period of rapid cooling during the neogene although this is at the limit of resolution of the methods the post rift cooling phases imply exhumation from depths between 2 and 5 km this activity we attribute to compression in the south american plate between the andean subduction zone and the mid atlantic ridge in southeast brazil compression acted on a crust that was thermally or mechanically susceptible to reactivation during the late cretaceous deformation in the study area was of regional extent whereas during the tertiary it concentrated along pre existing shear zones of the precambrian brasiliano orogeny

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

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

development of the continental margins of the labrador sea a review abstract the labrador sea is a small oceanic basin that developed when the north american and greenland plates separated an initial period of stretching in early cretaceous time formed sedimentary basins now preserved under the continental shelves and around the margins of the oceanic crust the basins subsided thermally during late cretaceous time and a second episode of tectonism took place during latest cretaceous and early paleocene time before the onset of sea floor spreading in mid paleocene time around the northern labrador sea davis strait and in southern baffin bay voluminous picrites and basalts were erupted at and shortly after the commencement of sea floor spreading volcanism occurred again in early eocene time at the same time as sea floor spreading commenced in the northern north atlantic farther southeast along the labrador and southern west greenland margins oceanic crust is separated from continental crust by highly stretched but non magmatic transition zones which developed before sea floor spreading a complex transform zone which developed during sea floor spreading in late paleocene and early eocene time separates continental and oceanic crust along the baffin island margin the greenland and labrador ocean continent transitions are asymmetric across the only available conjugate cross sections however a cross section through the labrador margin farther north resembles the greenland cross section in the conjugate pair more than it does the labrador cross section of this pair consideration of the geological history of the area suggests that the non magmatic transition zones may have formed by slow extension of a few millimetres per year through a period of 53 ma during cretaceous and early paleocene time

reply to the mountains of north east greenland are not remnants of the caledonian topography a comment on pedersen et al 2012 in this reply we comment on the issues raised by japsen chalmers and green japsen et al 2013 the mountains of north east greenland are not remnants of the caledonian topography a comment on pedersen et al 2012 tectonophysics we find that new vitrinite reflectance measurements from one location in the region may suggest a more complicated post caledonian evolution than proposed by pedersen et al 2012 for the southernmost part of the studied area overall however we cannot reconcile our aft data set with a complete obliteration of the topography in late paleozoic times followed by episodic post caledonian exhumation and re burial as suggested by japsen et al 2013

rapid erosion of the southern african plateau as it climbs over a mantle superswell we present new sedimentary flux data confirming that a large pulse of erosion affected the southern african plateau in the late cretaceous and is likely to be related to a major uplift episode of the plateau this short phase of erosion i e less than 30 myr in duration has commonly been difficult to reconcile with a mantle origin for the plateau anomalous uplift given its size the rise of the african superplume is likely to have lasted much longer here we demonstrate by using a simple model for fluvial erosion that tilting of the continent as it rides over a wide dynamic topography high cannot only cause rapid uplift of the plateau but also trigger continent wide drainage reorganization leading to substantial denudation in a relatively short amount of time the amplitude and short duration of the sedimentary pulse are best reproduced by assuming a strong erodibility contrast between the karoo sedimentary and volcanic rocks and the underlying basement we also present a new compilation of paleoclimate indicators that shows a transition from arid to very humid conditions approximately at the onset of the documented erosional pulse suggesting that climate may have also played a role in triggering the denudation the diachronism of the sedimentary flux between the eastern and western margins of the plateau and the temporal and geographic coincidence between the uplift and kimberlite eruptions are however better explained by our tilt hypothesis driven by the migration of the continent over a fixed source of mantle upwelling