brittle tectonic evolution along the western margin of south africa more than 500 myr of continued reactivation abstract the brittle structural history of western south africa has been investigated by remote sensing and field studies to build a conceptual scheme for its 500 ma long evolution paleostress tensors were computed from a significant fault slip dataset and a relative geochronological succession of brittle deformation events was established this was aided by separating in time faulting events through the usage of cretaceous weathering horizons silicified fluvial deposits paleosols and 77 54 ma olivine melilitite plugs as time markers the oldest features recognized formed during four compressional episodes assigned to the neoproterozoic pan african evolution this history is expressed by sub vertical conjugate fracture sets and fits well the inferences derived from remote sensing the greatest compressive direction rotated from nw se to nne ssw and finally to almost e w a subsequent ene wsw oriented extensional episode is associated with the local effects of the opening of the atlantic ocean and was followed by a second ca e w extensional episode linked to the well acknowledged mid cretaceous 115 90 ma event of margin uplift a late santonian 85 83 ma nw se compressive paleostress deformed the late cretaceous sequences and was in turn followed firstly by a renewed episode of ne sw extension and later by ca nne ssw late maastrichtian 69 65 ma shortening the latter is broadly coeval with the emplacement of the gamoep magmatic suite a phase of wnw ese cenozoic extension is assigned to the extensional phase recorded in the okawango delta interpreted as reflecting propagation of the east african rift system into southern africa no stress tensor was computed for the present day wegener anomaly stress field oriented nw se however in situ stress measurements were used to perform slip tendency analysis which indicates that under the currently existing stress conditions wnw ese and nnw sse striking faults are critically stressed and are the most likely reactivated in agreement with the present seismicity

plate tectonic development of the south west indian ocean a revised reconstruction of east antarctica and africa a revised sequence of reconstructions for east antarctica relative to africa is generated from published seafloor spreading and fracture zone anomalies these date from the cretaceous tertiary boundary to the late jurassic and lead to a revised predrift reconstruction for east and west gondwanaland euler pole 1 67 s 35 99 e rotation angle 53 43 this reconstruction derived wholly from marine data places east antarctica adjacent to the lebombo mountains and south of and subparallel to the sabi acid volcanic suite supporting the postulate that these rocks represent mesozoic plate boundaries this refit implies that part of the coastal plain of mozambique is underlain by oceanic or very highly extended continental crust the reconstruction is supported by the alignment of 1 the cape fold belt with its antarctic equivalents and 2 the western limit of pan african reactivation of the mozambique mobile belt with the western limit of the sverdrupfjella metamorphic suite antarctica initially moved along a transform fault lying immediately east of and subparallel to the lebombo mountains the eastern face of the tugela cone the southeastern face of the falkland plateau in its reconstructed position and the eastern flank of the agulhas plateau in its reconstructed position at m10 time a triple junction formed near the tip of the falkland plateau implying that the oldest lineated magnetic anomalies in the eastern weddell sea associated with this triple junction cannot predate m10 at m2 time the mozambique ridge rifted from the astrid ridge in a ridge jump episode such an event may also explain the presence of magnetic anomalies in the southern mozambique basin gunnerus ridge conrad rise and del cano rise are all tectonically associated with the madagascar ridge

kimberlite u th he dating links surface erosion with lithospheric heating thinning and metasomatism in the southern african plateau documenting the surface response to processes at depth is a central challenge in continental tectonics kimberlites bear an unusual record of both surface and deep processes through their downrafted crustal clasts pipe erosion levels and mantle xenolith suites here we combine new apatite u th he ahe data from four south africa kimberlites ranging in emplacement age from ca 143 ma to ca 74 ma with a wealth of other geologic information from the pipes to resolve the timing patterns and causes of erosion across 200 km of the southern african plateau comparison of the ahe dates with the kimberlite eruption ages constrains a strong regional unroofing pulse ca 117 90 ma which was most intense from ca 100 to 90 ma this unroofing phase is synchronous with warming thinning and metasomatism of the mantle lithosphere recorded by xenocrysts and peridotite xenoliths within these same kimberlites these thermochemical changes could be related to still deeper dynamic mantle processes our ahe data appear to directly document the erosional response to surface uplift induced by these various events the ahe results also detect as much as 1 5 km of cenozoic unroofing that is spatially centered on a proposed mid tertiary paleotributary to the orange river suggesting drainage patterns as the cause our results not only tightly refine the surface history of the interior of the southern african plateau but show that kimberlite ahe dating can tie cratonic erosion phases with contemporaneous thermochemical changes in the mantle and thereby point to causative links

where is my sink reconstruction of landscape development in southwestern africa since the late jurassic abstract quantifying the rates and timing of landscape denudation provides a means to constrain sediment flux through time to offshore sedimentary basins the late mesozoic evolution of drainage basins in southern africa is poorly constrained despite the presence of several onshore and offshore sedimentary basins a novel approach has been developed to calculate the volume of material eroded since the late jurassic at different time steps by constructing structural cross sections and extrapolating thicknesses of eroded material using different assumptions the calculated volumes of material eroded from southwestern africa range from 2 52 106 km3 11 3 km of vertical thickness removed to 8 87 105 km3 4 0 km of vertical thickness removed for the southward draining systems alone the calculated removal of 7 81 105 2 60 105 km3 of material is far greater than the volumes of sediment recorded in offshore sedimentary basins 268 500 km3 reconstruction of the drainage systems using geomorphic indicators and clast provenance of the uitenhage group as well as extrapolated surface exposure ages indicate the southern draining systems were active from the late jurassic with coeval activity in axial and transverse drainage systems the calculated volumes are tied to published apatite fission track aft dates to constrain the changes in exhumation rate through time using multiple scenarios which indicate a significant amount of early cretaceous exhumation up to 1 26 106 km3 equivalent to 5 70 km of vertical thickness for the first time this has permitted long term landscape evolution to be used to support the interpretation that some of the missing sediment was deposited in sedimentary basins on the falkland plateau as it moved past southern africa during the early cretaceous this implies that in this instance the sinks are separated from their source areas by 6000 km

testing the applicability of morphometric characterisation in discordant catchments to ancient landscapes a case study from southern africa the ancient landscapes south of the great escarpment in southern africa preserve large scale geomorphological features despite their antiquity this study applies and evaluates morphometric indices such as hypsometry long profile analysis stream gradient index and linear areal catchment characteristics to the gouritz catchment a large discordant catchment in the western cape spatial variation of morphometric indices were assessed across catchment trunk rivers and subcatchment scales the hypsometric curve of the catchment is sinusoidal and a range of curve profiles are evident at subcatchment scale hypsometric integrals do not correlate to catchment properties such as area circularity relief and dissection and stream length gradients do not follow expected patterns with the highest values seen in the mid catchment areas rock type variation is interpreted to be the key control on morphometric indices within the gouritz catchment especially hypsometry and stream length gradient external controls such as tectonics and climate were likely diminished because of the long duration of catchment development in this location while morphometric indices can be a useful procedure in the evaluation of landscape evolution this study shows that care must be taken in the application of morphometric indices to constrain tectonic or climatic variation in ancient landscapes because of inherited tectonic structures and signal shredding more widely we consider that ancient landscapes offer a valuable insight into long term environmental change but refinements to geomorphometric approaches are needed

cenozoic deformation of the south african plateau namibia insights from planation surfaces abstract passive margins and associated inland areas display complex vertical displacements that have been abundantly described offshore but much less so onshore due to erosion planation surfaces are ubiquitous markers inland that can be used as a proxy both climatic conditions and changes in vertical displacements induced by both short faults and long tilting flexure wavelength deformations we propose 1 a synthetic typology of the planation surfaces driven by a genetic process weathering versus mechanical erosion and 2 a method to use these surfaces to map short and long wavelength deformations this methodology was applied to the namibian margin and inland plateau to quantify the cenozoic deformation the results show that the namibian margin was affected by bulging during the oligocene and by an e w to nw se extension during the late miocene and pliocene the bulge is parallel to the shoreline with a wavelength of 300 km and an amplitude up to 500 m after investigating the available deformation processes we propose that an increase in the spreading rate along the mid oceanic ridge during the oligocene generated this bulging the vertical displacement is partially maintained afterwards via isostasy because of mass loss generated by scarp retreat a minimum average rate of scarp retreat of 5 km myr was calculated which is high compared to the rates estimated in other places in the world we ascribe this high value to the prior intense weathering period indeed the alteration largely degraded the bedrock and facilitated the formation of the subsequent scarp this study also reveals that the high reliefs of the damara domain existed before the cenozoic induced by a reactivation of the damara structures

agulhas plateau sw indian ocean new evidence for excessive volcanism a new set of seismic reflection and refraction lines has been interpreted regarding the basement and crustal structure of the southern agulhas plateau a large number of extrusion centres were identified lava flows dip away from those extrusion centres and form subparallel stratified sequences we interpret those extrusion centres as the result of excessive volcanism in course of the separation of the southern agulhas plateau from the maud rise since the sedimentary layers appear to be little affected by the volcanism that episode obviously ceased before onset of sedimentation in late cretaceous times we have not found evidence for continental fragments within overthickened predominantly oceanic crust we therefore propose that the agulhas plateau belongs to the world wide suite of large igneous provinces lip of predominantly oceanic origin

on the tectonic origin of iberian topography the present day topography of the iberian peninsula can be considered as the result of the mesozoiccenozo ic tectonic evolution of the iberian plate including rifting and basin formation during the mesozoic and compression and mountain building processes at the borders and inner part of the plate during the tertiary followed by neogene rifting on the mediterranean side and surface processes acting during the quaternary the northern central part of iberia corresponding to the geological units of the duero basin the iberian chain and the central system shows a mean elevation close to one thousand meters above sea level in average some hundreds of meters higher than the southern half of the iberian plate this elevated area corresponds to i the top of sedimentation in tertiary terrestrial endorheic sedimentary basins paleogene and neogene and ii planation surfaces developed on paleozoic and mesozoic rocks of the mountain chains surrounding the tertiary sedimentary basins both types of surfaces can be found in continuity along the margins of some of the tertiary basins the bouguer anomaly map of the iberian peninsula indicates negative anomalies related to thickening of the continental crust correlations of elevation to crustal thickness and elevation to bouguer anomalies indicate that the dierent landscape units within the iberian plate can be ascribed to dierent patterns 1 the negative bouguer anomaly in the iberian plate shows a rough correlation with elevation the most important gravity anomalies being linked to the iberian chain 2 most part of the so called iberian meseta is linked to intermediate elevation areas with crustal thickening this pattern can be applied to the two main intraplate mountain chains iberian chain and central system 3 the main mountain chains pyrenees and betics show a direct correlation between crustal thickness and elevation with higher elevation crustal thickness ratio for the central systemvs the betics and the pyrenees other features of the iberian topography namely the longitudinal pro le of the main rivers in the iberian peninsula and the distribution of present day endorheic areas are consistent with the tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the late neogene and the quaternary some of the problems involving the timing and development of the iberian meseta can be analysed considering the youngest reference level constituted by the shallow marine upper cretaceous limestones that indicates strong dierences induced by i the overall tertiary and recent compression in the iberian plate responsible for dierences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and ii the eect of neogene extension in the mediterranean margin responsible for lowering several thousands of meters toward the east and uplift of rift shoulders a part of the recent uplift within the iberian plate can be attributed o sostatic uplift in zones of crustal thickening

applicability of thin or thick skinned structural models in a region of multiple inversion episodes southern south africa abstract the deformation of the cape fold belt has been attributed to repeated structural reactivation of a mega detachment from the late proterozoic to the mesozoic 650 65 ma through the integration of onshore cross sections with observations from the offshore mesozoic extensional system this study evaluates the applicability of the mega detachment model regional scale cross sections through the permian triassic cape fold belt reveal that it comprises two main structural domains a northern domain dominated by northward verging and asymmetric folds and a southern domain comprising a series of approximately 8 km wavelength box folds the genesis of these box folds is attributed to motion on underlying high angle 45 reverse faults this variation between north and south in the fold belt is reflected by a similar variation in extensional geometry of the mesozoic normal faults as revealed by subsurface data the normal faults demonstrate a progressive increase in dip from 24 in the north to 60 in the south features commonly attributed to thin and thick skinned tectonic models are observed in both domains therefore it is not appropriate to describe the observed deformation as one of the two end members in addition the structures are inferred to have undergone at least two stages of inversion irrespective of dip this is not predicted by either end member model

fission track dating of phosphate minerals and the thermochronology of apatite several phosphate minerals have been investigated for their usefulness in geochronology and thermochronology by the fission track method of these apatite ca5 po4 3 f cl oh has proved pre eminently suitable for this purpose for reasons discussed below apatite was one of the first minerals amongst many others to be investigated for fission track dating by fleischer and price 1964 and has subsequently become by far the most important of all the minerals used for dating by this method the usefulness of apatites for fission track dating arises from their near universal tendency to concentrate uranium within their structure at the time of crystallization and their widespread occurrence in all of the major rock groups price and walker 1963 first recognized the possibility that the accumulation of radiation damage tracks in natural minerals from the spontaneous nuclear fission of 238u within their lattices could be used for geological dating they also demonstrated that a simple chemical etching procedure served to enlarge these fission tracks to optical dimensions so that they could be observed and measured under an ordinary optical microscope price and walker 1962b 1963 this simple procedure quickly opened the way for a wide range of nuclear particle track studies in natural minerals and glasses e g fleischer et al 1975 the most important of which was fission track dating fleischer et al 1964 also showed that spontaneous or fossil fission tracks provided an explanation for various anomalous etch pits in apatite which had puzzled crystallographers over many years the essence of a fission track age determination involves measuring the number of tracks that have accumulated over the lifetime of the mineral along with an estimate of the amount of uranium that is present knowing the rate of spontaneous fission decay a geological age can be calculated detailed

calcite twin analysis in syntectonic calcite cape fold belt south africa implications for fold and cleavage formation within a shallow thrust front abstract lithologies of two formations in the frontal ranges of the cape fold belt south africa host synorogenic calcite precipitated at low metamorphic grade during the end permian deformation of this gondwana wide orogen the calcite crystals are mechanically twinned and this deformation is linked to both folding and the formation of an axial planar cleavage with associated extensional veins twinning strain analysis reveals a complex rotational synfolding history in the upper thin layered prince albert formation twinned calcite within the fold preserves two unique strain events the primary shortening strain fabric is layer parallel and transport parallel north south the shortening strain overprint 5 82 is layer normal and plunges steeply to the northeast these results are inconsistent with a flexural slip folding mechanism by contrast a homogeneous syn cleavage stress strain field is recorded in the underlying massive thick bedded dwyka tillite analyses of calcite twins in clast hosted syn cleavage fibrous calcite and rare limestone clasts define a sub horizontal n s shortening and sub horizontal e w extension the intermediate axis e 2 is vertical and preserves shortening 5 3 the extension axis e 3 is horizontal and parallel to the clast tension gash fracture plane these deformed syn cleavage calcite materials provide an independent constraint to the debate about contemporaneous stress strain fields associated with folding and formation of an axial planar cleavage

predicting and testing continental vertical motion histories since the paleozoic abstract dynamic topography at the earth s surface caused by mantle convection can affect a range of geophysical and geological observations including bathymetry sea level change continental flooding sedimentation and erosion these observations provide important constraints on and test of mantle dynamic models based on global mantle convection models coupled with the surface plate motion history we compute dynamic topography and its history for the last 400 ma associated with pangea assembly and breakup with particular focus on cratonic regions we propose that burial unroofing histories of cratons inferred from thermochronology data can be used as a new diagnostic to test dynamic topography and mantle dynamic models our models show that there are currently two broad dynamic topography highs in the pacific and africa for the present day earth that are associated with the broad warm structures i e superplumes in the deep mantle consistent with previous proposals of dynamical support for the pacific and african superswells our models reveal that pangea assembly and breakup by affecting subduction and mantle upwelling processes have significant effects on continental vertical motions our models predict that the slave craton in north america subsides before pangea assembly at 330 ma but uplifts significantly from 330 ma to 240 ma in response to pre pangea subduction and post assembly mantle warming the kaapvaal craton of africa is predicted to undergo uplift from 180 ma to 90 ma after pangea breakup but its dynamic topography remains stable for the last 90 ma the predicted histories of elevation change for the slave and kaapvaal cratons compare well with the burial unroofing histories inferred from thermochronology studies thus supporting our dynamic models including the development of the african superplume mantle structure the vertical motion histories for other cratons can provide further tests of and constraints on our mantle dynamic models

recalibrating the breakup history of sw gondwana u pb radioisotopic age constraints from the southern cape of south africa abstract syn rift deposits often provide the only means to determine the chronology of rift initiation and evolution however the earliest syn rift packages deposited in jurassic cretaceous rift basins that formed during the breakup of sw gondwana are poorly understood because they are deeply buried beneath overlying passive margin sequences the exhumed remnants of several such rift basins are exposed in the southern cape of south africa and contain the suurberg and uitenhage groups which are predominantly continental taphrogenic fossiliferous strata interbedded with volcaniclastics here we present the first robust u pb chronostratigraphic framework for these groups by dating zircon in nine pyroclastic and five resedimented volcaniclastic deposits using laser ablation inductively coupled plasma mass spectrometry la icpms to further improve the precision and accuracy of the results we utilize chemical abrasion thermal ionisation mass spectrometry ca tims on four selected samples minimizing the effects of pb loss and further constraining depositional uncertainties we thereby show that the suurberg group was deposited rapidly during the emplacement of the karoo large igneous province in the early jurassic and likely predates the main phase of rifting whereas the uitenhage group was deposited over a prolonged 40 ma period beginning in the early jurassic and continuing into the early cretaceous the uitenhage group records two phases of rifting an initial jurassic episode that roughly coincides with the separation of east and west gondwana and is contemporaneous with widespread volcanism in sw gondwana and a subsequent period of renewed rifting during the early cretaceous opening of the south atlantic and initiation of the agulhas falkland transform this framework illustrates the complexity of long lived rift basin sedimentation and highlights the importance of high resolution chronostratigraphy when investigating and integrating the tectonic palaeogeographic and palaeontological records from the final stages of a unified sw gondwana

melting ice sheets 400 000 yr ago raised sea level by 13 m past analogue for future trends abstract marine isotope stage mis 11 was possibly the longest 423 000 362 000 yr ago and warmest interglacial of the entire quaternary period this resulted from a special arrangement of earth s orbital parameters similar to the present interglacial mis 1 suggesting that mis 11 provides an analogue for future natural climate forcing and sea levels although precise documentation of mis 11 sea level history is therefore crucial especially considering additional impetus from anthropogenic warming the maximum mis 11 sea level remains highly contentious estimates from onshore indicators have ranged from below present sea level to about 20 m resulting from uncertainties in reliability of sea level indicators estimates of their subsequent displacement by vertical crustal motion and in dating we used a clear and unambiguous sea level indicator interface between subtidal and intertidal deposits in well exposed regressive raised shoreline deposits along south africa s southern coast the coast is stable in terms of tectonic setting and falls within a zone of low predicted glacio isostatic adjustment gia and low sensitivity for plausible model parameters the sea level indicators were directly dated using thermally transferred optically stimulated luminescence tt osl which gave a mean age of 390 ka corresponding with mis 11 we determined a precise maximum elevation of 14 m for the mis 11 sea level indicator which corrected for minor crustal uplift and gia yielded a eustatic sea level of 13 m 2 m the complete mis 11 transgressive regressive shoreline succession is preserved and the wave cut platform extends 950 m inland from the present shoreline indicating a prolonged highstand we have also documented sea level fluctuations during mis 11 including an earlier lower highstand close to present sea level which may explain the lower elevation range of some previous estimates at one locality mis 11 deposits form a sea cliff against which mis 5e sediments at an elevation of 6 2 m abut the 13 m mis 11 sea level tallies with total melting of the greenland and west antarctica ice sheets regarded as most susceptible to melting our data predict notably higher sea levels in the future regardless of anthropogenic influence on climate

the chronology and tectonic style of landscape evolution along the elevated atlantic continental margin of south africa resolved by joint apatite fission track and u th sm he thermochronology atlantic type continental margins have long been considered passive tectonic settings throughout the entire postrift phase recent studies question the long term stability of these margins and have shown that postrift uplift and reactivation of preexisting structures may be a common feature of a continental margin s evolution the namaqualand sector of the western continental margin of south africa is characterized by a ubiquitously faulted basement but lacks preservation of younger geological strata to constrain postrift tectonic fault activity here we present the first systematic study using joint apatite fission track and apatite u th sm he thermochronology to achieve a better understanding on the chronology and tectonic style of landscape evolution across this region apatite fission track ages range from 58 3 2 6 to 132 2 3 6ma with mean track lengths between 10 9 0 19 and 14 35 0 22 m and mean u th sm he sample ages range from 55 8 31 3 to 120 6 31 4ma joint inverse modeling of these data reveals two distinct episodes of cooling at approximately 150 130ma and 110 90ma with limited cooling during the cenozoic estimates of denudation based on these thermal histories predict approximately 1 3 km of denudation coinciding with two major tectonic events the first event during the early cretaceous was driven by continental rifting and the development and removal of synrift topography the second event during the late cretaceous includes localized reactivation of basement structures as well as regional mantle driven uplift relative tectonic stability prevailed during the cenozoic and regional denudation over this time is constrained to be less than 1 km

detecting young slow slipping active faults by geologic and multidisciplinary high resolution geophysical investigations a case study from the apennine seismic belt italy 1 the southern apennines range of italy presents significant challenges for active fault detection due to the complex structural setting inherited from previous contractional tectonics coupled to very recent middle pleistocene onset and slow slip rates of active normal faults as shown by the irpinia fault source of a m6 9 earthquake in 1980 major faults might have small cumulative deformation and subtle geomorphic expression a multidisciplinary study including morphological tectonic paleoseismological and geophysical investigations has been carried out across the extensional monte aquila fault a poorly known structure that similarly to the irpinia fault runs across a ridge and is weakly expressed at the surface by small scarps warps the joint application of shallow reflection profiling seismic and electrical resistivity tomography and physical logging of cored sediments has proved crucial for proper fault detection because performance of each technique was markedly different and very dependent on local geologic conditions geophysical data clearly 1 image a fault zone beneath suspected warps 2 constrain the cumulative vertical slip to only 25 30 m 3 delineate colluvial packages suggesting coseismic surface faulting episodes paleoseismological investigations document at least three deformation events during the very late pleistocene 20 ka and holocene the clue to surface rupturing episodes together with the fault dimension inferred by geological mapping and microseismicity distribution suggest a seismogenic potential of m6 3 our study provides the second documentation of a major active fault in southern italy that as the irpinia fault does not bound a large intermontane basin but it is nested within the mountain range weakly modifying the landscape this demonstrates that standard geomorphological approaches are insufficient to define a proper framework of active faults in this region more in general our applications have wide methodological implications for shallow imaging in complex terrains because they clearly illustrate the benefits of combining electrical resistivity and seismic techniques the proposed multidisciplinary methodology can be effective in regions characterized by young and or slow slipping active faults

cretaceous reactivation and intensified erosion in the archean proterozoic limpopo belt demonstrated by apatite fission track thermochronology abstract cratons are generally assumed to be regions of long lasting tectonic stability in particular the study of the phanerozoic exhumation history of cratons has been largely hampered by the scarcity of suitable stratigraphic controls onshore this fact is even more pronounced in terranes lacking mesozoic or younger penetrative structural fabrics and metamorphic overprinting our study in the limpopo belt shows that modern apatite fission track thermochronology provides a hitherto unavailable perspective in the study of these rocks and has profound implications for the crustal evolution of the zimbabwe craton apatite fission track data from 35 samples taken along two transects in the southern edge of the zimbabwe craton and in the central zone of the limpopo belt suggest that extensive regions experienced kilometer scale exhumation in two discrete events as recently as the cretaceous the first occurred at around 130 ma and the second at around 90 ma basin subsidence and sedimentation loads on the mozambique margin support the timing of these events and provide strong indications of the source and pathways for the eroded material further the results indicate that young and old surfaces in a geomorphological sense may be structurally juxtaposed in regions of high elevation in zimbabwe this is contrary to early ideas of surface chronologies based on summit accordances or invoking pediplanation

climate control on early cenozoic denudation of the namibian margin as deduced from new thermochronological constraints abstract the processes that control long term landscape evolution in continental interiors and in particular along passive margins such as in southern africa are still the subject of much debate e g braun 2018 although today the namibian margin is characterized by an arid climate it has experienced climatic fluctuations during the cenozoic and yet to date no study has documented the potential role of climate on its erosion history in western namibia the brandberg massif an erosional remnant or inselberg provides a good opportunity to document the cenozoic denudation history of the margin using the relationship between rock cooling or exhumation ages and their elevation here we provide new apatite u th sm he dates on the brandberg inselberg that range from 151 12 to 30 2 ma combined with existing apatite fission track data they yield new constraints on the denudation history of the margin these data document two main cooling phases since continental break up 130 myr ago a rapid one 10 c myr following break up and a slower one 1 2 c myr between 65 and 35 ma we interpret them respectively to be related to escarpment erosion following rifting and continental break up and as a phase of enhanced denudation during the early eocene climatic optimum we propose that during the early eocene climatic optimum chemical weathering was important and contributed significantly to the denudation of the namibian margin and the formation of a pediplain around the brandberg and enhanced valley incision within the massif additionally aridification of the region since 35 ma has resulted in negligible denudation rates since that time

new constraints on the age of the opening of the south atlantic basin abstract detailed high quality marine total field magnetic data recently acquired over parts of the south atlantic ocean off the southwestern margin of south africa display a pattern of well defined nw se striking linear magnetic anomalies that can be traced with confidence over distances 150 km the magnetic anomalies are interpreted to be m series seafloor spreading anomalies m9 to m11 which are consistent with the initiation of seafloor spreading at approximately 135 ma late valanginian early hauterivian seafloor spreading models indicate a more rapid 44 mm yr initial spreading phase between m11 and m4 m5 followed by slower 29 mm yr spreading from m4 m5 to m0 this two rate spreading model also matches m series anomalies previously reported over the conjugate south american margin offshore argentina where the rates are slightly breaks in the continuity of the linear anomaly pattern observed in map view are oriented approximately ne sw and are considered sites of possible fracture zones one such discontinuity which we have termed the cape lineament cl marks a significant change in crustal character and cretaceous depositional history as revealed by gravity data and seismic reflection data respectively crust nw of the cl in the orange basin is characterized by greater thickness and the presence of seismically imaged seaward dipping reflectors sdrs whereas se of the cl the crust has a more normal oceanic thickness and sdrs are either absent or more limited in areal extent magnetic gravity and seismic data were combined to develop a crustal model of the south african margin north of the cl that includes a a region of rifted attenuated continental crust landward of magnetic anomaly g b a 60 80 km wide zone of substantially intruded underplated thin continental crust overlain by sdrs between anomalies g and m11 and c a 90 km wide zone of thick oceanic crust associated with a wide intrusion zone and smoother seafloor spreading magnetic anomalies that thins progressively to normal oceanic crustal thickness at the seaward edge of the overlying sdrs south of the cl the change in crustal character from attenuated continental crust to normal thickness oceanic crust occurs over a much shorter distance of approximately 35 40 km possibly indicating the diminished influence of magmatic material although linear magnetic anomalies are observed both nw and se of cl anomalies to the se display a better correlation with those predicted by our seafloor spreading model we have successfully reconstructed the positions of the african and south american margins south of 32 s at m11 time i e 135 ma using a new rotation pole at 38 86 n 31 46 w this pole applies only to the southernmost margins of the austral segment where m11 is observed further north at this time the margins are undergoing non rigid deformation that includes both crustal extension and magmatic underplating

a global scale plate reorganization event at 105 100 ma abstract a major plate reorganization is postulated to have occurred at approximately 100 ma however this reorganization has received limited attention despite being associated with the most prominent suite of fracture zone bends on the planet and many other geological events we investigate tectonic events from the period 110 to 90 ma and show that the reorganization occurred between 105 and 100 ma was global in scale and affected all major plates seafloor evidence for plate motion changes is abundant during this period with either fracture zone bends or terminations preserved in all ocean basins long lived eastern gondwanaland subduction ended along a 7000 km long section of the margin while elsewhere around the proto pacific rim subduction continued and there is evidence that compressional stresses increased in the overriding plates thrusting in western north america transpression and basin inversion in eastern asia and development of the present day andean style margin along western south america occurred contemporaneous with the development of an extensional regime in eastern gondwanaland basin instability in africa and western europe further demonstrates that lithospheric stress regime changes were widespread at this time considering the timing of the reorganization and the nature of associated plate boundary changes we suggest that eastern gondwanaland subduction cessation is the most likely driving mechanism for the reorganization subduction is the dominant driver of plate motion and therefore this event had the potential to strongly modify the balance of driving forces acting on the plates in the southwestern proto pacific and neighboring plates whereby producing widespread changes in plate motion and continental lithospheric stress patterns we propose that major changes in ridge trench interaction triggered the cessation of subduction the progressive subduction of two closely spaced perpendicular mid ocean ridges at the eastern gondwanaland subduction zone to the east of australia and new zealand respectively resulted in very young crust entering the trench and we suggest that by 105 100 ma there was insufficient negative buoyancy to drive subduction finally we propose that the plume push force of the bouvet plume that erupted near the african antarctic south american triple junction contributed to plate motion changes in the southern atlantic region

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

first evidence for onshore marine isotope stage 3 aeolianite formation on the southern cape coastline of south africa abstract the southern cape coast of south africa boasts an impressive suite of plio pleistocene aeolian dune deposits aeolianite previous research has shown that in this region onshore dune accumulation was generally focused around interglacial sea level highstands with the locus of coastal dune accumulation shifting onto the adjacent continental shelf during glacial sea level lowstands here using new luminescence dating results we present the first evidence for preserved onshore glacial age dunes specifically on the robberg peninsula a rocky headland 28 km east of knysna two phases of aeolianite formation are identified corresponding to early 45 60 ka and late 35 30 ka marine isotope stage mis 3 subsequently during the holocene all substantive dune accumulation occurred between 10 2 and 7 0 ka forming cliff fronting dunes and filling the limited accommodation space on the headland including an archaeological rock shelter combining these ages with bathymetric data we infer that this distinct onshore glacial age aeolianite record reflects 1 restricted accommodation space during sea level highstands 2 a regional narrowing of the continental shelf and 3 liberation of sediments lying on a prominent 45 to 60 m offshore terrace which would have been exposed during mis 3 this demonstrates that despite broad regional scale trends in the timing of coastal aeolian activity driven by commonalities in relative sea level trends and climate distinct local variations in late quaternary coastal evolution can be identified this is ascribed to local controls on preservation accommodation space and sediment supply shoreline position and antecedent offshore sediment supplies such findings may have wider implications for interpretations of site context resource availability at several notable coastal archaeological sites and more broadly suggest that local offshore or onshore geologic contexts can at times assume greater influence on a preserved coastal aeolianite record than the regional scale trends in sea level and climate

strong rocks sustain ancient postorogenic topography in southern africa the cape mountains of southern africa exhibit an alpine like topography in conjunction with some of the lowest denudation rates in the world this presents an exception to the often cited coupling of topography and denudation rates and suggests that steep slopes alone are not sufficient to incite the high denudation rates with which they are commonly associated within the cape mountains slope angles are often in excess of 30 degrees and relief frequently exceeds 1 km yet be 10 based catchment averaged denudation rates vary between 2 32 0 29 m m y and 7 95 0 90 m m y we attribute the maintenance of rugged topography and suppression of denudation rates primarily to the presence of physically robust and chemically inert quartzites that constitute the backbone of the mountains be 10 based bedrock denudation rates on the interfluves of the mountains vary between 1 98 0 23 m m y and 4 61 0 53 m m y the close agreement between the rates of catchment averaged and interfluve denudation indicates topography in steady state these low denudation rates in conjunction with the suggestion of geomorphic stability are in agreement with the low denudation rates 20 m m y estimated for southern africa during the late cenozoic by means of cosmogenic nuclide thermochronology and offshore sedimentation analyses accumulatively these data suggest that the coastal hinterland of the subcontinent may have experienced relative tectonic stability throughout the cenozoic

tectonic subsidence history and thermal evolution of the orange basin the orange basin offshore southwest africa appears to represent a classical example of continental rifting and break up associated with large scale transient volcanism the presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension we present results of a combined approach using subsidence analysis and basin history inversion models our results show that a classical uniform stretching model does not account for the observed tectonic subsidence moreover we find that the thermal and subsidence implications of underplating need to be considered another departure from the uniform stretching model is renewed sub crustal thinning and linked to that uplift in the cenozoic that is necessary to reproduce the observed phases of erosion and the present day depth of the basin the dimension of these events has been examined and quantified in terms of tectonic uplift and sub crustal thinning based on these forward models we predict the heat flow evolution not only for the available real wells but also for virtual wells over the entire study area finally the hydrocarbon potential and the temperature evolution is presented and shown in combination with inferred maturation of the sediments for depth intervals which comprise potential source rocks 2009 elsevier ltd all rights reserved

linking source and sink evaluating the balance between onshore erosion and offshore sediment accumulation since gondwana break up south africa abstract the geomorphic origin and evolution of the tectonically unique interior highland of southern africa the kalahari plateau and its flanking low lying coastal planes remain largely unresolved because of a lack of regional quantitative analyses of its uplift and erosion history here we focus on the southern cape south africa and link onshore denudation based on new apatite fission track thermochronology results to offshore sediment accumulation using abundant well data and a seismic reflection profile we attempt to relate source and sink in order to resolve some first order issues concerning timing of the exhumation and development of the topographic features of southern africa the volume of sediment accumulated off south africa s south coast is calculated using 173 wells and a seismic reflection profile a total uncompacted sediment volume of 268 500 km3 accumulated off south africa s south coasts since 136 ma in the outeniqua and southern outeniqua basins accumulation volumes and rates were highest in the early cretaceous 48 800 104 km3 at 8150 km3 ma from 136 to 130 ma and 57 500 104 km3 at 5750 km3 ma from 130 to 120 ma and mid late cretaceous 83 700 104 km3 at 3200 km3 ma from 93 to 67 ma volumes and accumulation rates were lowest for the early mid cretaceous 47 400 104 km3 at 1750 km3 ma from 120 to 93 ma and the cenozoic 31 200 104 km3 at 450 km3 ma from 67 to 0 ma although our analysis shows that the accumulated volume of offshore sediments does not match the calculated volume of onshore erosion as quantified through apatite fission track thermochronology e g tinker j h de wit m j brown r 2008 mesozoic exhumation of the 439 southern cape south africa quantified using apatite fission track thermochronology tectonophysics doi 10 1016 j tecto 2007 10 009 the timing of increased sediment accumulation closely matches the timing of increased onshore denudation this suggests that the greatest volumes of material were transported from source to sink during two distinct cretaceous episodes and that the processes driving onshore denudation decreased by an order of magnitude during the cenozoic

passive margin evolution and its controls on natural gas leakage in the southern orange basin blocks 3 4 offshore south africa using a 2d seismic dataset that covers part of the southern orange basin offshore south africa we reconstructed the geological evolution of the basin this evolutionary model was then used to investigate the occurrence of natural gas within the sedimentary column and the distribution of gas leakage features in relation to the observed sedimentary and tectonic structures developed in the post rift succession since the early cretaceous the cretaceous succession has been subdivided into five seismic units the highest sedimentation rates occur within the barremian aptian unit c1 and the turonian coniacian unit c3 two cenozoic units t1 and t2 have been distinguished these show a sudden decrease in sedimentation rate for the whole of the cenozoic three phases of gravitational tectonics with two late cretaceous phases of mass movement in the northern study area and cenozoic slumping in the southern study area have been related to sedimentation rates sea level changes paleoenvironmental evolution and regional tectonics the occurrence of natural gas leakage follows a coast parallel distribution within the study area in the near shore part at water depths shallower than 400 m massive gas chimneys penetrate through the sediment layers and reach the near surface within an intermediate narrow band between 300 and 500 m water depth the gas migrates more diffusely through sub vertical faulted cretaceous sediments while in the outer part of the basin through the cretaceous and cenozoic gravitational wedges only very few signs of gas accumulation and migration can be seen along the faults a conceptual model has been established with the aptian source rock generating gas in the outer part of the basin this source rock underlies the cenozoic wedge in the south and the thick cretaceous wedge in the north and is a postulated source for the natural gas within the sedimentary column this thermogenically generated gas does not migrate directly through the gravitational faults and the above lying sediments but moves buoyancy driven up dip along stratigraphic layers to escape through the sediments to the sea floor in the inner shelf area

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

global miocene tectonics and regional sandstone style uranium mineralization abstract the formation of sandstone style uranium deposits are significantly controlled by the latest tectonic uplift events especially those generated in an open system by the infiltration of meteoritic water this study explores the spatiotemporal relationship between global miocene tectonics and sandstone style uranium deposits to evaluate the link between tectonic uplift and metallogenic ages in general modern landforms were shaped by diverse global tectonic events that began in the middle and late miocene this includes the formation of continental scale faults and fold belts including the uplift of the three broadly contemporaneous ranges the alpine himalayan belt the cordillera and the east african rift these events were accompanied by intense magmatic activity as well as an increase in the spreading rates of oceanic ridges and higher sedimentation rates in the pacific indian and atlantic oceans modern global climate patterns are a direct consequence of these miocene tectonic events studies on sandstone style uranium deposits report that though their stratigraphic ages extend from the proterozoic to the cenozoic they notably occur from the late mesozoic to the neogene uranium mineralization ages are concentrated between 20 and 0 1 ma clustering mainly in the miocene although remobilizations are known to have occurred subsequently some even in the holocene global tectonics in the miocene between 20 and 5 ma resulting in the regional uplift of mountain ranges and continental tilts may have exerted significant control over the migration directions of uranium bearing fluids that formed these sandstone style uranium deposits climate patterns in the miocene specifically subtropical high pressure belts on both sides of the equator controlled the creation of arid and semi arid areas creating characteristic rainfall patterns which would also have influenced the spatial distribution of these uranium deposits thus the spatiotemporal characteristics of most sandstone style uranium deposits in the world were controlled by global tectonics in the miocene that uplifted mountain ranges and tilted continents generating subtropical high pressure belts and the asian high pressure region in addition to new ideas adding greater research value to the study of global sandstone style uranium mineralization this paper also provides a new exploration indicator for sandstone style uranium deposits

geological and soil maps of the palaeo agulhas plain for the last glacial maximum abstract the south african cape south coast is bordered by one of the broadest continental shelves in africa the agulhas bank inshore shelf and presently exposed coastal plain make up the palaeo agulhas plain pap though our area of study extends beyond this limit and as far inland as the first mountain belt quaternary sea levels have been significantly lower than at present for 90 of the pleistocene exposing a terrestrial ecosystem on what is now the submerged shelf the presently drowned component makes up 94 of the total area of the pap past work has hypothesised a contrast in character of this submerged landscape when compared to the subaerial environment here we assimilate newly acquired geophysical and geological datasets to produce geological and soil maps from the last glacial maximum on a scale of 1 750 000 covering an area of 55 000 km three broad geomorphic zones are defined including the western section from cape agulhas to cape infanta the central section from cape infanta to knysna and the eastern section extending eastward of knysna we demonstrate that mesozoic sedimentary deposits crop out near the surface on this current swept shelf and soils derived from siltstone and shale bedrock are prominent when the coast is up to 64 km distant from the modern shoreline at its maximum point beyond this weathered limestone dominates the substrate sequences on the agulhas bank we show that the submerged landscape was a unique terrestrial environment and that there is no exact modern day analogue in the region other than a small 70 km2 area located at the edge of the agulhas plain near cape agulhas and map major contrasts in the geological topographic and edaphic nature of the landscape from the onshore to the offshore the expansion of this plain is coupled with exaggerated floodplains meandering shallowly incised rivers and wetlands the submerged shelf is dominated by fertile soils compared to the dissected onshore belt and extensive calcareous dunefields extending up to 10 km inland from their associated palaeoshorelines covered much of the emergent shelf sedimentary bedforms may have obstructed or slowed drainage as suggested by leached palaeosols and carbonate mixing observed in petrographic thin sections and grain mounts the data show a low relief plains landscape which contrasts strongly to the topographically complex contemporary coastal foreland

sequence stratigraphy and ichnology of early cretaceous reservoirs gadvan formation in southwestern iran abstract the siliciclastic gadvan formation from abadan plain southwestern iran is highly bioturbated and allows relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high resolution sequence stratigraphic framework relying on the sedimentary and ichnological characteristics the siliciclastic succession is divided into two facies associations a wave dominated offshore shoreface complex and a tide river influenced delta the first includes facies that have been deposited in shelf offshore upper offshore lower shoreface and upper middle shoreface environments the latter includes facies that have been deposited in prodelta and delta front integrated ichnologic and sedimentologic studies of the gadvan formation allow distinction between prodelta and delta front and open marine deposits with the identification of maximum flooding and ravinement surfaces as bounding surfaces of the stratal units detailed analysis on systematic changes in the stacking pattern cycle thickness cycle type and facies proportion are made eight ichnocoenoses could be differentiated in the studied sections the positions of the ichnocoenoses within genetically related stratal units genetically related ichnocoenoses indicate three large scale cycles ds1 to ds3 from oldest to youngest the cyclical nature of the gadvan formation is attributed to low amplitude eustasy in greenhouse conditions formed under interaction of eustatic high frequency cycles and longer term tectonically driven sea level variations during the long term transgressive sea level trend of the early cretaceous stratigraphic architectural style of sequences ds1 to ds3 which includes scarce evidence of lowstand deposits partial or total truncation of the hst and predominance of thick transgressive deposits is remarkably similar to long term transgressive sea level trend of the early cretaceous across the arabian plate this study suggests a more relatively seaward position of the siliciclastic successions of the gadvan formation of abadan plain than the mesopotamian basin upper zubair formation equivalent in western iraq and kuwait which would be concordant with the prevailing view of an easterly prograding coastline across the arabian plate this study reveals important sedimentological and ichnological features and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical significance of trace fossil assemblages that can be readily compared or translated to analogous depositional systems worldwide the ichnological analysis is based on cores and can be especially applied to evaluate the applicability of current ichnological models to the study of cretaceous reservoirs of western iraq kuwait and western saudi arabia

sediment deposits in the cape basin indications for shifting ocean currents the benguela current system running off southwest africa is one of the world s largest upwelling regions the current has strongly influenced sedimentary features on the continental margin to unravel its development seismic stratigraphy tied to drilling results from ocean drilling program leg 175 sites 10851087 was established four units southern cape basin scb 1 to scb 4 were defined for the cenozoic sediments the upper unit scb 1 1 5 ma characterized by continuous high amplitude reflectors represents global cooling and glacial interglacial cycles unit scb 2 14 ma distinguished by low amplitude reflections is associated with the onset of the upwelling system and establishment of the modern circulation pattern in the cape basin slump scarps are concentrated along the middle and upper shelf slope suggesting they are caused by a combination of mass movements triggered by bottom currents and slope instabilities because of increased deposition associated with the upwelling a westward extension and or movement of upwelling filaments is interpreted from the observed seaward shift of scarp locations with time erosion associated with stronger currents probably thinned unit scb 2 in the south the two lower units scb 3 and scb 4 56 ma probably represent material eroded from the shelf break and deposited during a major oligoceneearly miocene regression that is consistent with a significant uplift of southern africa the basal reflector scb d of unit scb 4 is associated with the prominent reflector d or l described in previous publications

evidence of a widespread paleo pockmarked field in the orange basin an indication of an early eocene massive fluid escape event offshore south africa abstract the detailed interpretation and seismic attribute analysis of 2d and 3d seismic reflection data sets revealed the presence of a distinct seismic horizon displaying circular and elongated depressions in early eocene sediments along the northwestern slope of the orange basin on the southwest african margin their occurrence within a single seismic horizon indicates a contemporaneous formation process we interpret the depressions as paleo pockmarks which occur as single pockmarks predominantly nne ssw aligned pockmark trains and coalescing elongated pockmarks the paleo pockmarked surface covers an area of 2800 km 2 and has been mapped by integrating the 3d dataset with industrial 2d seismic grids the spatial and temporal occurrence of the paleo pockmarks is associated to two episodes of rapid sedimentation during the late maastrichtian to paleocene comprising fine grained shelf eroded material we propose that they were formed during the early eocene by the seepage of both 1 overpressured pore fluids from disequilibrium compaction of upper maastrichtian sediments and 2 thermogenic gas from underlying cretaceous mature source rocks we show that the location of the pockmarks is controlled by the underlying faults system of the paleo slope the paleocene eocene transition is known for its series of hyperthermal events characterized by negative excursions of the carbon isotope curve the early eocene widespread event of fluid and thermogenic gas escape identified in this work can be an example of the type of carbon release processes occurring in hydrocarbon prone sedimentary basins during this time

evolution of the glorieuses seamount in the sw indian ocean and surrounding deep somali basin since the cretaceous abstract little is known about the geological history of the glorieuses seamount including basic information about its age and origin related to the regional evolution of the southern tip of the somali basin this study focused on describing and reconstructing the long term stratigraphic evolution of the glorieuses seamount sw indian ocean to identify the mechanisms that have occurred through time to finally shape the emerged modern islands distinct terrace levels currently submerged along the flanks of the seamount and surrounding seamounts have already been interpreted as resulting from successive carbonate development and back stepping episodes over the last 62 myr new isotopic and biostratigraphic dating on the flanks of the seamount coupled with sequence stratigraphic interpretation of seismic profiles acquired in the adjacent basin provide new constraints for the late cretaceous and cenozoic vertical evolution of the seamount topped by carbonate platforms and sedimentation in the surrounding deep basin even if starved steep slopes prevent a straightforward source to sink continuity between the platform and the basin domains our findings propose a consistent chronostratigraphic framework for the identified seismic markers and sequences in the deep basin and discuss a long term geological model that includes the main driving factors behind deposition volcanic events subsidence vs uplift phases climate and hydro dynamism changes and their quantitative impact on the evolution of the isolated carbonate sedimentary system our results show that i the glorieuses volcanic seamount emerged from two successive late cretaceous magmatic pulses firstly during the turonian then during the maastrichtian ii at least two potential uplift phases are recognized during the tertiary paleogene and or the eocene and tortonian iii basinal sedimentation recorded an abrupt change probably related to major regional hydro dynamical changes in late eocene times in the western indian ocean iv the export of sediments from the platform towards the basin numerous gravity flow processes is strongly enhanced after the mid miocene and is probably linked to the onset of the asian monsoon winds and bipolar circulation finally the glorieuses seamount although located in the vicinity of the comoros islands appears to have a much longer history and is geologically more comparable to the nearby seychelles this long term study has enabled us to associate the glorieuses seamount with the sse nnw madagascar seychelles alignment rather than with the comoro hot spot evolution

topographic growth around the orange river valley southern africa a cenozoic record of crustal deformation and climatic change we reconstruct the history of topographic growth in southern africa on both sides of the orange river valley from an integrated analysis of erosion surfaces crustal deformation and climate change first we propose an inventory of erosion surfaces observed in the study area and classify them according to their most likely formative process i e chemical weathering or mechanical erosion among the various land units observed we define a new class of landform the pedivalley which corresponds to a wide valley with a flat erosional floor in the orange river valley we mapped three low relief erosion surfaces each bevelling a variety of lithologies the oldest and most elevated is 1 a stripped etchplain evolving laterally into 2 a stepped pediplain bearing residual inselbergs 3 a younger pediplain later formed in response to a more recent event of crustal deformation these are all cenozoic landforms the etchplain is associated with a late palaeocene to middle eocene weathering event and the two pediplains are older than the middle miocene alluvial terraces of the orange river landscape evolution was first driven by slow uplift 10 m ma followed by a second interval of uplift involving a cumulative magnitude of at least 200 m this event shaped the transition between the two pediplains and modified the drainage pattern a final phase of uplift magnitude 60 m occurred after the middle miocene and drove the incision of the lower terraces of the orange river climate exerted a major control over the denudation process and involved very humid conditions responsible for lateritic weathering followed by more arid conditions which promoted the formation of pedivalleys collectively these produce pediplains

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

reconstruction of the southwestern african continental margin by backward modeling abstract as the evolution of the southwestern african passive continental margin and in particular the vertical movements in this area are still a matter of debate this study aims to quantify the past vertical movements by reconstructing the paleobathymetric evolution of the southwestern african margin during the post rift phase to quantify the vertical movements inferred from paleobathymetries different subsidence components that have affected the passive continental margin are calculated and interpreted with respect to the generating processes our investigation takes advantage of information on the present day sedimentary thicknesses and the crustal configuration along the sw african margin by using this detailed information and modeling backward in time we attempt to separate different subsidence components such as the load induced subsidence and the thermal subsidence for different time intervals during the post rift phase calculating the amounts of each subsidence component and subtracting them from the present day configuration yields paleobathymetries which are interpreted with respect to the evolution of the southwestern african passive margin these restored paleobathymetries for different time steps during the post rift phase indicate spatial and temporal variations of vertical movements including phases of seafloor uplift as a result our investigation allows to give minimum estimates of the vertical movements that have occurred during the post rift phase in addition to predominant subsidence about 1000 m of seafloor uplift are deduced for the northern and southern parts of the sw african margin quantifying the amounts of vertical movements cannot finally clarify the generating processes behind these movements but the timing and magnitude of seafloor uplift indicate a deep mantle mechanism

sediment supply to the orange sedimentary system over the last 150 my an evaluation from sedimentation denudation balance the south african plateau is bordered by passive margin basins preserving the terrigeneous sediment produced during onshore erosion as such these basins potentially provide a record of the variation in onshore elevation and relief over time here we bring new constraints on the uplift and erosion of the southern african plateau over the last 150 ma from the perspective of the stratigraphic architecture of these basins we review published data to quantify the terrigeneous supply eroded in the drainage area and preserved in the basins the novel aspect of our approach is the integration of the evolution of the whole domain in sedimentation i e not only the platform as well as the onshore eroding region along the south african and namibian atlantic margins we determined the long term signal of sedimentary supply at the 10 ma scale from 3d mass balance calculations comparing sedimentary volumes deduced from offshore isopach maps with a particular attention to associated uncertainties on one hand and denudation volumes deduced from thermochronology data on the other we show that in this case the volumes of denudation and of sediments preserved in the basin are consistent both in total and incremental amount the latter is therefore a reliable estimation of the denudation in the associated continental domain subject to certain assumptions such as the drainage area over time the long term signal of sedimentary supply of the south african and namibian atlantic margins shows that the major part of the denudation occurred during the post rift lower cretaceous and the upper cretaceous and subsequently decreased this is not the expected behavior for the simple relaxation of topography acquired during rifting that would show a progressive decrease of the sediment supply over time this suggests a significant rejuvenation of relief during the upper cretaceous 50 ma after the rifting event if erosion is directly linked to elevation or relief variation this implies 2 generations the first before break up i e before 130 ma presumably during rifting and the second during the upper cretaceous

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

a revised position for the rotated falkland islands microplate the early stages of transform margin formation are associated with crustal fragmentation and block rotation the restricted size of the resultant microcontinental blocks precludes palaeogeographical reconstructions and reliable estimations of the amount of rotation they can undergo an example considered here is the falkland plateau this is located adjacent to the agulhas falkland fracture zone and its westernmost province is the falkland islands microcontinent the position of the plateau and the islands prior to gondwana break up remains contentious this study integrates seismic reflection and gravity data to propose a revised position of the falkland islands microcontinent constrained by 1 the presence of a mega decollement controlling the gondwanide orogen described north of the falkland islands and underneath south africa and the outeniqua basin and 2 the similar architecture of fault networks mapped north of the islands and in the northernmost outeniqua basin this revised position requires a re evaluation of the timing and rate of rotation of the falkland islands microcontinent and affects the expected crustal architecture adjacent to the islands our model yields rotation rates between 5 5 and 8 ma 1 and two potential times for rotation and predicts more unstretched crust beneath the basin east of the falkland islands than previous models

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

neoproterozoic to early cambrian crustal evolution of the pan african saldania belt south africa abstract the saldania belt forms part of a system of neoproterozoic mobile belts that surround and weld older cratons on the african continent it is a poorly exposed low grade orogenic belt composed of a number of inliers unroofed in mega anticlinal hinges of the permo triassic cape fold belt along the southern tip of africa deformed meta volcanosedimentary units are contained within tectonostratigraphic terranes separated by deep rooted sinistral dextral strike slip fault zones which display evidence of prolonged reactivation sedimentary rocks and volcanics of the boland terrane malmesbury group lower kango group and gamtoos group are considered to be distal facies of rift successions overlying the mid proterozoic crystalline basement on the southwestern edge of the kalahari craton these lithologies have been deposited in semi pull apart basins that formed in response to the breakup of rodinia and progressive opening of the proto atlantic adamaster ocean from 780 750 ma fragments of juvenile pan african crust with wpb morb characteristics occur in the bridgetown formation swartland terrane malmesbury inlier and attest to ocean floor spreading in this belt the thick turbidite successions of the swartland and tygerberg terranes malmesbury group reflect deeper water conditions and were deposited partly on oceanic crust in an evolving ocean continental margin basin marked by increasing sea levels and reduction of continental freeboard reversal of spreading and closing of the adamastor ocean possibly initiated by the opening of iapetus occurred in the period 600 570 ma although this movement vector caused sinistral transpressional reactivation of the gariep and saldanian margins there is no proper collision orogen developed in the saldania belt the bridgetown formation represents the suture between the southern rifted margin succession of the kalahari craton and a poorly developed southern orogenic belt represented in part by the swartland and tygerberg terranes this geosuture is similar to that of the south atlantic which formed in the analogous gariep belt between 575 and 543 ma multiphase s i and a type granites of the cape granite suite intruded the saldania belt in a pervasive transpressive regime between 550 and 510 ma comparing well with the timing of peak metamorphism collision in the gariep belt 545 ma the absence of a proper collisional orogen and the strongly developed northwesterly structural grain in the saldania belt seem to suggest that the cape granite suite was generated in a strike slip regime a discrepancy of approximately 50 ma between the age of the collision granites of the dom feliciano belt and cape granite suite suggests that they are genetically unrelated similarities in structural styles magmatism and dated events between the saldania ross delamarian chain of orogens however indicate a common history the evolution of this chain and that of the gariep damara dom feliciano belts can be accommodated in a single plate tectonic model of simultaneous sinistral transpressive subduction driven by the rifting of laurentia from south america and opening of the iapetus ocean loading and depression of the western and southern kalahari craton margin by thrust stacks of the late neoproterozoic orogens led to the formation of syn to post orogenic peripheral foreland basins such as those represented by the nama and vanrhynsdorp groups lowering of sea level and increased continental freeboard deposition of the unconformity based upper kango group and possibly the molassic franschhoek formation occurred in intra orogen pull apart basins which possibly developed between 530 and 510 ma in the saldania belt

the african landscape through space and time it is generally accepted that cenozoic epeirogeny of the african continent is moderated by convective circulation of the mantle nevertheless the spatial and temporal evolution of africa s basin and swell physiography is not well known here we show how continental drainage networks can be used to place broad constraints on the pattern of uplift through space and time first we assemble an inventory of 710 longitudinal river profiles that includes major tributaries of the 10 largest catchments river profiles have been jointly inverted to determine the pattern of uplift rate as a function of space and time our inverse model assumes that shapes of river profiles are controlled by uplift rate history and modulated by erosional processes which can be calibrated using independent geologic evidence e g marine terraces volcanism and thermochronologic data our results suggest that modern african topography started to develop 30 myr ago when volcanic swells appeared in north and east africa during the last 15 20 myr subequatorial africa was rapidly elevated culminating in the appearance of three large swells that straddle southern and western coasts our results enable patterns of sedimentary flux at major deltas to be predicted and tested we suggest that the evolution of drainage networks is dominated by rapid upstream advection of signals produced by a changing pattern of regional uplift an important corollary is that with careful independent calibration these networks might act as useful tape recorders of otherwise inaccessible mantle processes finally we note that there are substantial discrepancies between our results and published dynamic topographic predictions

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

from source to sink in central gondwana exhumation of the precambrian basement rocks of tanzania and sediment accumulation in the adjacent congo basin apatite fission track aft and u th he ahe thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated 1000 m a s l but low relief tanzanian craton coeval episodes of sedimentation documented within adjacent paleozoic to mesozoic basins of southern tanzania and the congo basin of the democratic republic of congo drc indicate that most of the cooling in the basement rocks in tanzania was linked to erosion basement samples were from an exploration borehole located within the craton and up to 2200 m below surface surface samples were also analysed aft dates range between 317 33 ma and 188 44 ma alpha ft corrected ahe dates are between 433 24 ma and 154 20 ma modelling of the data reveals two important periods of cooling within the craton one during the carboniferous triassic 340 220 ma and a later less well constrained episode during the late cretaceous the later exhumation is well detected proximal to the east african rift 70 ma thermal histories combined with the estimated geothermal gradient of 9 c km constrained by the aft and ahe data from the craton and a mean surface temperature of 20 c indicate removal of up to 9 2 km of overburden since the end paleozoic the correlation of erosion of the craton and sedimentation and subsidence within the congo basin in the paleozoic may indicate regional flexural geodynamics of the lithosphere due to lithosphere buckling induced by far field compressional tectonic processes and thereafter through deep mantle upwelling and epeirogeny tectonic processes

uplift history of a transform continental margin revealed by the stratigraphic record the case of the agulhas transform margin along the southern african plateau the south and southeast coast of southern africa from 28 s to 33 s forms a high elevated transform passive margin bounded to the east by the agulhas falkland fracture zone affz we analysed the stratigraphic record of the outeniqua and durban thekwini basins located on the african side of the affz to determine the evolution of these margins from the rifting stage to present day the goal was to reconstruct the strike slip evolution of the agulhas margin and the uplift of the inland high elevation south african plateau the agulhas transform passive margin results from four successive stages 1 rifting stage from late triassic to early cretaceous 200 134 ma punctuated by three successive rifting episodes related to the gondwana breakup 2 wrench stage 134 131 ma evidenced by strike and dip slip deformations increasing toward the affz 3 active transform margin stage 131 92 ma during which the falkland malvinas plateau drifts away along the affz with an uplift of the northeastern part of the outeniqua basin progressively migrating toward the west 4 thermal subsidence stage 92 0 ma marked by a major change in the configuration of the margin onset of the shelf break passive margin morphology two main periods of uplift were documented during the thermal subsidence stage of the agulhas margin 1 a 92 ma short lived margin scale uplift followed by a second one at 76 ma located along the outeniqua basin and 2 a long lasting uplift from 40 to 15 ma limited to the durban thekwini basin this suggests that the south african plateau is an old upper cretaceous relief 90 70 ma reactivated during late eocene to early miocene times 40 15 ma

u th he thermochronometry constraints on unroofing of the eastern kaapvaal craton and significance for uplift of the southern african plateau the timing and causes of the 1 0 km elevation gain of the southern african plateau since paleozoic time are widely debated we report the first apatite and titanite u th he thermochronometry data for southern africa to resolve the unroofing history across a classic portion of the major escarpment that encircles the plateau the study area encompasses 1500 m of relief within archean basement of the barberton greenstone belt region of the eastern kaapvaal craton titanite dates are neoproterozoic apatite dates are cretaceous with most results clustering at ca 100 ma thermal history simulations confirm mesozoic heating followed by accelerated cooling in mid to late cretaceous time the lower temperature sensitivity of the apatite u th he method relative to previous thermochronometry in southern africa allows tighter constraints on the cenozoic thermal history than past work the data limit cenozoic temperatures east of the escarpment to 35 c and appear best explained by temperatures within a few degrees of the modern surface temperature these results restrict cenozoic unroofing to less than 850 m and permit negligible erosion since the cretaceous if substantial uplift of the southern african plateau occurred in the cenozoic as advocated by some workers then it was not responsible for the majority of post paleozoic unroofing across the eastern escarpment significant mesozoic unroofing is coincident with large igneous province activity kimberlite magmatism and continental rifting within and along the margins of southern africa compatible with a phase of plateau elevation gain due to mantle buoyancy sources associated with these events

denudation along the atlantic passive margin new insights from apatite fission track analysis on the western coast of south africa apatite fission track aft data from two traverses across the great escarpment of the western coast of south africa are used to reconstruct the tectonic evolution and denudation history of this sector of the atlantic passive margin fission track ages range between 180 and 86 ma modelling of this data identifies two distinct cooling events the first event between 160 and 138 ma is recorded only by the rocks above the escarpment in the karoo area and is tentatively linked to post karoo magmatism 180 ma thermal relaxation the second between 115 and 90 ma results instead from a tectonically induced denudation episode responsible for the removal of up to 2 5 km of crust across the coastal zone in front of the escarpment and less than 1 km on the elevated interior plateau based on these results it is suggested that the cretaceous is the time when most of the elevated topography of southern africa was generated with only a minor cenozoic contribution

long term controls on continental scale bedrock river terrace deposition from integrated clast and heavy mineral assemblage analysis an example from the lower orange river namibia abstract establishing relationships between the long term landscape evolution of drainage basins and the fill of sedimentary basins benefits from analysis of bedrock river terrace deposits these fragmented detrital archives help to constrain changes in river system character and provenance during sediment transfer from continents source to oceans sink thick diamondiferous gravel terrace deposits along the lower orange river southern namibia provide a rare opportunity to investigate controls on the incision history of a continental scale bedrock river clast assemblage and heavy mineral data from seven localities permit detailed characterisation of the lower orange river gravel terrace deposits two distinct fining upward gravel terrace deposits are recognised primarily based on mapped stratigraphic relationships cross cutting relationships and strath and terrace top elevations and secondarily on the proportion of exotic clasts referred to as proto orange river deposits and meso orange river deposits the older early to middle miocene proto orange river gravels are thick up to 50 m and characterised by a dominance of karoo supergroup shale and sandstone clasts whereas the younger plio pleistocene meso orange river gravels 6 23 m thick are characterised by more banded iron formation clasts mapping of the downstepping terraces indicates that the proto gravels were deposited by a higher sinuosity river and are strongly discordant to the modern orange river course whereas the meso deposits were deposited by a lower sinuosity river the heavy minerals present in both units comprise magnetite garnet amphibole epidote and ilmenite with rare titanite and zircon grains the concentration of amphibole epidote in the heavy minerals fraction increases from the proto to the meso deposits the decrease in incision depths recorded by deposit thicknesses above strath terraces and the differences in clast character size and roundness and type between the two units are ascribed to a more powerful river system during proto orange river time rather than reworking of older deposits changes in provenance or climatic variations in addition from proto to meso orange river times there was an increase in the proportion of sediments supplied from local bedrock sources including amphibole epidote in the heavy mineral assemblages derived from the namaqua metamorphic complex this integrated study demonstrates that clast assemblages are not a proxy for the character of the matrix and vice versa because they are influenced by the interplay of different controls therefore an integrated approach is needed to improve prediction of placer mineral deposits in river gravels and their distribution in coeval deposits downstream

new angles on south atlantic opening existing models of relative motion between the south america and africa plates significantly misrepresent the azimuth of lower cretaceous seafloor spreading in the south atlantic ocean an improved model is derived from fits of fracture zones magnetic reversal anomalies and the edges of a rifted large igneous province at the northeast georgia rise and agulhas plateau an absolute date for this rifting event is not known but by assuming least change in spreading rates during magnetic chron c34 rifting can be estimated to have occurred at 100 ma this modelling demands a plate divergence history that involves diachronous opening of the south atlantic consistent with published estimates of the ages of breakup from sedimentary basins on the south american and african passive margins the diachronous opening lasts approximately 40 million years during which time it must be accommodated by significant intracontinental deformation a reconstruction using the intra c34 rotation also illustrates the earliest possibility for direct deep water connection between the central and south atlantic oceans one further consequence of this model is that a total reconstruction derived from it and closure of the central atlantic between north america and africa suggests that the venezuelan and gulf of mexico basins may be conjugates formed during the earliest opening of the central atlantic and not separate marginal basins

an integration of magnetic gravity and seismic data in evaluating the algoa basin in the eastern cape province of south africa for stratigraphic and structural geodynamics the algoa basin is a hydrocarbon potential basin which lies off the southern continental margin of south africa along the coastal region of port elizabeth area with both onshore and offshore components despite the continued consensus on the basin s hydrocarbon potential both its structural and stratigraphic geodynamics are still not well documented in this study gravity data constrained by borehole data was modelled to reveal onshore subsurface geology whereas the seismic sections were used for offshore in addition magnetic data was used to delineate magnetic zones and lineaments the onshore magnetic results show the localised occurrence of large scale geologic bodies with high and positive anomalies forming bounding rims coincidental with the edges of the basin the average depths to the top of the shallowest and deepest magnetic sources were estimated from the power spectrum to be approximately 0 4 0 6 km and 9 5 km respectively the onshore bouguer gravity map is characterised by a gravity low zone over the basin s sediment where it attains its lowest value over the depocentre 2 d gravity modelling results along five profiles show that the basin comprises of two to three v shaped sub basins of shallow crustal depth with sediment thickness of up to 4 6 km the models also revealed discontinuity in sediment units confirming the diachronous nature of the uitenhage group analyses of offshore seven seismic sections show that the stratigraphic sequence consists of diachronous geological units which are characterised by displacements forming a series of minor and major faults complementary to onshore gravity models seismic sections also shows relatively shallow vertical extension to the paleozoic crustal basement between 1 3 and 5 3 km

post breakup evolution of the namibian margin constraints from numerical modeling abstract the namibian margin evolution started 130 myr ago after the breakup between south america and southern africa today it shows specific features i an elevation and a bathymetry about 1000 m higher than the surrounding areas ii a significant sediment supply during the late cretaceous following the first sedimentary peak that occurred during rifting and just afterwards and iii a long term progradation since the mid cretaceous this present configuration results in couplings between several processes and the inherited structure we constrained this evolution using a numerical simulation applied both onshore and offshore integrating different couplings i a thermal adjustment of a lithosphere driven by conductivity ii a flexural isostasy and iii the loading unloading effects of surface matter transfer three processes were investigated rock uplift a change in the erosion efficiency and a sea level fall the results were compared to some pertinent observations made on the namibian margin such as the vertical displacements the sediment transfers the denudation and the stratigraphic architecture in the marginal basin in each simulation rift related reliefs were rapidly relaxed resulting in an exponentially decreasing denudation and sediment accumulation sixty myr after the breakup we simulated an additional uplift an increase in the transfer efficiency of the sediment and a sea level fall the subsidence increased by loading inducing a new progradational trend nonetheless the three types of events differed in the duration of this progradation trend the larger the additional uplift the longer the progradation the transfer efficiency increase and sea level fall only resulted in a transient progradation trend from these results we suggest that the post rift evolution of the namibian margin was associated during the upper cretaceous to the rejuvenation of its continental relief triggered by a climate change during the turonian and by a slow long term rock uplift during the cenozoic