post oligocene river incision southern sierra madre occidental mexico the sierra madre occidental of western mexico consists of a granitic basement covered by oligocene ignimbrites that define a reference surface from which to estimate late cenozoic river incision a 90 m grid digital elevation model was used to characterize contemporary topography and interpolate the late oligocene surface of the ignimbrite plateau from a surface fit to the highest points in the relatively undissected uplands between major river valleys long term river incision rates calculated from the difference between this reference surface and longitudinal profiles of 11 rivers that flow toward the tepic zacoalco rift zone range from about 0 01 to 0 2 mm year 1 river profiles of this region also show evidence of river capture driven by flexural uplift along the flank of the rift zone river profile concavity values in the sierra madre occidental range from 0 22 to 0 63 a range similar to that reported previously for a wide range of environments in contrast the empirically constrained ratio of exponents in the stream power model of river incision m n ranges from 0 44 to 0 52 close to the expected theoretical value of 0 5 the wider range of observed values may illustrate how can differ from the driving values of m n in non steady state bedrock river systems

modelling karst denudation on a synthetic landscape this contribution presents the results of a numerical study of karst denudation on limestone plateaux the landscape evolution model used incorporates not only long range fluvial and short range hill slope processes but also large scale chemical dissolution of limestone surfaces the relative efficiencies of fluvial and chemical processes are of equal importance to the landscape evolution of a plateau dropping to sea level along an escarpment while fluvial processes have an impact confined mostly to river channels the karst denudation process is more uniform removing material also from the plateau surface the combined effect of both processes results in a landscape evolution almost twice as effective as the purely erosional evolution of an insoluble landscape

inversion of fluvial channels for paleorock uplift rates in taiwan the transient response of erosion to changes in rock uplift rate leads to the preservation of rock uplift history in the long profiles of rivers however extracting this information is nontrivial as changes in channel steepness are the result of both spatial and temporal changes in rock uplift rate as well as other factors such as climate and rock type we exploit an analytical linear solution for river channel profile evolution in response to erosion and tectonic uplift to investigate the rock uplift history of taiwan the analytical approach allows us to solve the linear inverse problem efficiently extracting rock uplift as a function of space and time from digital elevation data we assess the potential of fluvial topography to resolve rock uplift rates using three approaches 1 a synthetic resolution test 2 analysis of the forward model to demonstrate where in space and time the fluvial topography constrains rock uplift rate and 3 interpretation of the model resolution matrix furthermore the potential to analyze large data sets reduces the influence of stochastic processes such as landslides small scale river network reorganization and also local lithological variability in taiwan our analysis suggests that current rock uplift rates exceed erosion rates across much of the island and that there has been an increase in rock uplift rates since 0 5 ma across the central range

flexural constraints on the denudation of assymetric mountain belts the regional excavation of metamorphic rocks from mid and lower crustal levels is the consequence of erosion driven denudation of mountain belts that are in permanent isostatic equilibrium if the erosion process occurs at different rates in different parts of a topographically asymmetric mountain belt then the flexural properties of the lithosphere need to be considered in order to describe the features of the isostatic rebound such a situation is given in plateaulike mountain ranges which are likely to erode only at their steeply sloping edges whereas erosion on top stagnates this paper investigates the flexural isostatic response of a plate that is unloaded due to the continuous retreat of an erosional escarpment the isostatic response is tested for two limiting model cases 1 for a plate with a broken edge and 2 for a continuous plate with variable flexural rigidity it is shown that for both cases the rate of topography development on the exposed plate is not linear with the retreatrate of the escarpment this feature is utilized to predict the nature of the subsequent erosion of the newly formed topography and ultimately of the denudation of the plate geological limitations of the theoretical model and its relevance to plateaulike topographies in southern africa and the eastern highlands of australia are then discussed in these areas the origin of the apparently cyclic rebound forces creating stairlike topography at their continental margins and the old age of their present surface topography has previously been unexplained within the presented model these features can be explained satisfactorily two important conclusions may be drawn 1 the distance of flexural swells from great escarpments and the origin of subsequent stair like topographies may be explained by simple flexural considerations 2 the flexural rebound forces uplifting a plate exposed by a retreating escarpment are cyclic excavation times of metamorphic rocks under such mountain belts may therefore be prolonged not only by the nature of erosion of their initial topography but also by the nature of the subsequent isostatic rebound and ultimately their denudation history

tectonic and climatic controls on asymmetric half graben sedimentation inferences from 3 d numerical modeling the tectono sedimentary evolution of asymmetric extensional systems driven by the activity of major normal faults or detachments associated with footwall exhumation is often characterized by a sequence of slower faster and ultimately again slower subsidence rates in the center of hanging wall half grabens during their synkinematic and postkinematic evolution we have studied this specific evolution by the means of 3 d stratigraphic numerical modeling that accounts for the variability of the sediment and water flux combined with climatic and sea level variations and sediment compaction the model setup is constrained by observations from the pannonian back arc basin of central europe our modeling predicts the formation of low order tectonic and higher order sea level and climate driven transgressive regressive sedimentary cycles furthermore we model and analyze the autocyclic nature of the depositional systems retrograding prograding cycles are visible on the proximal flank of the half grabens by their different spatial and temporal expressions while depocenters record large water depth variations linked to the specific and episodic activity of normal faults and their migration with time the application to a system of multiple half grabens in the pannonian basin which are activated in different locations at different times and with different kinematics demonstrates a complex interplay between direct sediment sourcing and the sediments ability to bypass trapping subbasins and paleo reliefs created by eroded footwalls

controls on erosional retreat of the uplifted rift flanks at the gulf of suez and northern red sea the gulf of suez and red sea rifts are currently bordered by large asymmetric uplifts that are undergoing erosion we find that the amount and timing of erosion vary systematically along the strike of the margin and have been controlled by variations in the prerift stratigraphy the prerift strata are composed of cliff forming eocene cretaceous carbonates overlying the easily eroded cretacous cambrian nubian sandstone this lithologic succession promotes scarp retreat of the sedimentary section followed by dissection of the underlying basement the prerift section thins from over 2000 rn at the northern end of the rift to less than 400 rn at its junction with the red sea thus at the northern part of the gulf of suez the nubian sandstone is minimallyexposed and the carbonates form a scarp at the rift border fault farther south undercutting of the carbonates by erosion of the sandstone has resulted in scarp retreat the escarpment cuts diagonally away from the border fault and is over 100 km inland from the border fault at the southernmost gulf of suez the amount of retreat varies inversely with the sediment thickness exposure and erosion of basement are initiated by the retreat of the escarp ment and the depth of erosion as indicated by fission track ages increases with distance from the escarpment these observations are explained by a model in which erosion along the gulf of suez is initiated as rift flank uplift becomes sufficiently large to expose the friable sandstones undercutting of the escarpment and exhumation of basement has been propagating northward and westward for at least 20 m y the average rate of scarp retreat has been 6 km m y and the along strike propagation of the erosion has been 12 km m y the diachronous erosion of the the rift flanks at the gulf of suez highlights the importance of distinguishing between the timing of uplift and of erosion both thermochronometric and stratigraphic data primarily indicate the timing of erosion which may differ significantly from the timing of the uplift that initiates it they must be interpreted carefully to avoid erroneous conclusions about rift tectonics

postglacial topographic evolution of glaciated valleys a stochastic landscape evolution model the retreat of valley glaciers has a dramatic effect on the stability of glaciated valleys and exerts a prolonged influence on the subsequent fluvial sediment transport regime we have studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model the model incorporates a stochastic process to represent deepseated landsliding non linear diffusion to represent shallow landsliding and an approximation of the bagnold relation to represent fluvial sediment transport it was calibrated using field data from several recent surveys within british columbia canada we present ensemble model results and compare them with results from a deterministic linear diffusion model to show that explicit representation of large landslides is necessary to reproduce the morphology and channel network structure of a typical postglacial valley our model predicts a rapid rate of fluvial sediment transport following deglaciation with a subsequent gradual decline similar to that inferred for holocene time we also describe how changes in the model parameters affect the estimated magnitude and duration of the paraglacial sediment pulse

the timing of uplift volcanism and rifting peripheral to the red sea a case for passive rifting prior to the formation of the red sea the northeastern afro arabian continent had low relief and was largely below sea level from the late cretaceous to the early oligocene the events leading to the formation of the red sea followed the sequence 1 alkaline volcanism and rifting beginning about 30 32 ma affecting a narrow linear zone in the continent 2 rotational block faulting and detachment faulting well underway by 25 ma 3 gabbro and diorite magmatism andesite to rhyolite volcanism and fine grained nonmarine sedimentation in the rift between 20 and 25 ma 4 fine grained marine sedimentation in the rift as the early shelves started to subside in the middle miocene and 5 uplift of the adjacent continents about 3 km and subsidence of the shelves about 4 km between 13 8 and 5 ma the youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the proterozoic arabian shield that range in age from 13 8 to 568 ma the youngest of these ages coupled with the present high relief along the arabian escarpment and published heat flow measurements indicate that 2 5 4 km uplift has occurred in the last 13 8 m y the sequence volcanism rifting followed by uplift leads to our adoption of a passive mantle model for rift origin models that require uplift to create the rift are rejected because of the late uplift we advocate a model of lithospheric extension caused by two dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere it is acknowledged that traction models could explain the observed data but they imply a rigid static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions neither requirement is necessary in the extension model the rift starts with mechanical extension in a narrow zone of lithosphere between 25 32 ma in our model the thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis once partially melted rocks formerly part of the continental lithosphere join the upwelling asthenosphere resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge the resulting density decrease explains the uplift we think that the red sea began as a consequence of changing plate geometries resulting from the collision of india and eurasia after the collision the segment of the owens fracture zone north of the carlsberg ridge became locked forcing the northeast corner of afro arabia to rotate with the indian plate away from the rest of africa

response of glacial landscapes to spatial variations in rock uplift rate 1 the response of glaciated landscapes to rapid rock uplift driven by tectonic convergence is an important often neglected aspect of proposed interactions between plate tectonic processes and climate change rivers typically respond to more rapid rock uplift in part through increasing channel gradients in contrast the glacial buzzsaw hypothesis suggests that glaciers can erode as quickly as the fastest rock uplift rates 6 10 mm yr without any increase in mean elevations however it has not been established how this is achieved we examined moving window maps swath and longitudinal profiles hillslope relief and hypsometry for glacierized and formerly glacierized basins in areas of spatially variable rock uplift rate in the southern alps new zealand and around nanga parbat pakistan to determine whether glaciers have a specific response to rapid rock uplift the response of these glaciated landscapes to rapid rock uplift 6 10 mm yr comprises 1 modest steepening of the longitudinal profiles in smaller glaciated basins 2 maintenance of shallow downvalley slopes in larger glaciated basins 30 km2 southern alps 100 km2 nanga parbat 3 development of tall headwalls and 4 steepening of the basin as a whole dominated by hillslope lengthening around nanga parbat headwalls several kilometers high constitute 50 of the basin relief at rapid rock uplift rates although glaciers can incise the valley floor swiftly they cannot prevent headwalls from reaching exceptional heights the associated increase in mean distance between cirque heads i e a decrease in drainage density causes regional mean elevation to rise with increasing rock uplift rate however this is much less than the changes in elevation expected in unglaciated ranges

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

the coupling of mixed rossby gravity waves with diabatic heating during the trmm kwajex field campaign composite dynamic and thermodynamic structures of mixed rossby gravity mrg waves are presented with their coupling with diabatic heating and moisture sources sinks using tropical rainfall measuring mission kwajalein experiment trmm kwajex field campaign data a significant departure of convectively coupled waves from dry waves exists in the phases of wave component maximum low level wind convergence is accompanied by midtropospheric divergence and upper tropospheric convergence that is preceded by increase of moisture in the boundary layer these phases correspond to surface turbulent transport shallow and midlevel convections that cause moistening and heating of the lower and middle troposphere they are followed by deep convection with maximum heating centered in the upper troposphere the deep convective heating evolves to stratiform like upper tropospheric heating and lower tropospheric cooling that precedes the quick demise of convection such a structure on convectively coupled mrg waves is summarized by four phases which sheds lights on how tropical waves are coupled with convective processes in all their phases

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

incorporating 3 d parent nuclide zonation for apatite 4he 3he thermochronometry an example from the appalachian mountains the ability to constrain km scale exhumation with apatite 4he 3he thermochronometry is well established and the technique has been applied to a range of tectonic and geomorphic problems however multiple sources of uncertainty in specific crystal characteristics limit the applicability of the method especially when geologic problems require identifying small perturbations in a cooling path here we present new 4he 3he thermochronometric data from the appalachian mountains which indicate significant parent nuclide zonation in an apatite crystal using la icpms measurements of u and th in the same crystal we design a 3 d model of the crystal to explore the effects of intra crystal variability in radiation damage accumulation we describe a numerical approach to solve the 3 d production diffusion equation using our numerical model and a previously determined time temperature path for this part of the appalachians we find excellent agreement between predicted and observed 4he 3he spectra our results confirm this time temperature path and highlight that for complex u and th zonation patterns 3 d numerical models are required to infer an accurate time temperature history in addition our results provide independent and novel evidence for a radiation damage control on diffusivity the ability to exploit intra crystal differences in 4he diffusivity i e temperature sensitivity greatly increases the potential to infer complex thermal histories

fluvial landsculpting and the fractal dimension of topography abstract quantitative models of landform development can help us to understand the evolution of mountains and regional topography and the effects of tectonic motions and climate on landscape including its fractal geometry this paper presents a general and powerful three dimensional model of fluvial erosion and deposition at hill to mountain range scale the model works by accumulating the effects of randomly seeded storms or floods precipitons that cause diffusional smoothing then move downslope on digital topography grids that erode portions of elevation differences that transport a slope limited amount of eroded material and that deposit alluvium when their sediment carrying capacity is exceeded the iteration of these simple and almost linear rules produce very complicated simulated landscapes demonstrating that complex landscapes do not require complex laws each process implemented in the model is affected differently by changes in horizontal scale erosion a scale free process roughens topography at all wavelengths this roughening is balanced by diffusive processes scaling as 1 l 2 at short wavelengths and deposition scaling scaling as 1 l 2 at long wavelenghts such a mixture of scale free and scale dependent processes can produce multifractal behavior in the models the fractal dimension of the model topography is much more sensitive to climatic variables than to tectonic uplift landscape evolution may be fractal but it does not seem to be chaotic analysis of topography of areas in southern arizona using variograms shows approximately fractal behavior with mean fractal dimension around 2 2 2 3 departures from an exact fractal relatioship imply that the topography is in detail multifractal the fractal dimension at short wavelengths is less than that at long wavelengths this variation could either be caused by the relative strengths of diffusive and erosional processes shaping the topography or a result of changes in climatic or tectonic conditions still preserved in the landscape

late quaternary alluvial fans and paleosols of the kangra basin nw himalaya tectonic and paleoclimatic implications abstract the paper describes late quaternary pedosedimentary sequences of the alluvial fans from the kangra basin of nw himalayas for tectonic and paleoclimatic implications in the proximal part of the kangra basin three coalescing alluvial fans namely rait rihlu fans 65 km2 kangra fans 200 km2 and palampur fans 170 km2 from west to east evolved due to reactivation of longitudinal and transverse faults and climatic changes during the late quaternary the fans are characterised by subsidence of rait rihlu fans uplift of kangra fans and tilting of palampur fans the thick 90 m pedosedimentary sequences exposed along the rivers characterise the dominant formative processes over the fans the stream flow sediments dominate the rait rihlu fans whereas the debris flow sediments dominate the kangra and palampur fans the fan sequences are also marked by the formation of strongly developed paleosols on loess l1 l3 loess paleosols and weakly developed paleosols on fluvial deposits in response to the tectonics and climate change in nw himalayas formation of the loess in proximal and distal settings of the alluvial fans is related to the cool dry climates during the advance of glaciers in the adjoining areas at 78 ka 44 ka 30 ka and 20 ka when climate was approaching towards the last glacial maxima field characters micromorphology grain size and clay minerals of these loessic deposits suggest strong pedogenesis of the loess during a warm humid climate after the retreat of glaciers in the nw himalayan region and are likely related to marine isotope stages mis4 5 in proximal and mis2 3 in distal the loess paleosols show some degree of syndepositional pedogenesis in upper horizons and are accretionary in nature weakly expressed pedogenic features in fluvial and debris flow deposits suggest rapid sedimentation over unstable surfaces related to the reactivation of main boundary thrust mbt and other regional faults

reduction of long term bedrock incision efficiency by short term alluvial cover intermittency fluctuations of the sediment volume stored in mountain channels are driven by stochastic variations of discharge and sediment supply and can inhibit bedrock incision if sediment thickness is too large here i study how this short term stochasticity propagates into the long term reduction of bedrock incision efficiency the cover effect at geological time scales i introduce a new numerical model that resolves sediment transport and bedrock incision at daily time scales and is run for thousands of years it incorporates 1 a transport threshold and daily stochastic variations in water discharge and sediment supply 2 a freely evolving channel width and slope and 3 an explicit treatment of alluvial thickness variations and corresponding bed incision reduction for typical mountain river conditions the model predicts that alluvial cover oscillates between complete and negligible incision reduction in this intermittent regime the long term cover effect is mainly set by the fraction of time spent in full cover and the present day extent of alluvial cover is not representative of long term dynamics the long term integrated cover effect law differs strongly from proposed theoretical and experimental models and it is controlled by sediment supply stochasticity rather than the details of cover development at the hydraulic time scale model results also suggest that steady state channel configuration always depends on sediment supply rate while being never limited by transport capacity or strictly detachment limited these results point out that discharge and sediment supply stochasticity should not be considered less important than the intricate details of incision laws to model long term bedrock channel dynamics

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

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

structural control on drainage network and catchment area geomorphology in the dead sea area an evaluation using remote sensing and geographic information systems in the wadi zerka ma in catchment area jordan the geology of jordan is characterized by fault systems with three major trends 1 nw se the oldest 2 wnw ese and 3 nnw sse the youngest the drainage network of the wadi zerka ma in catchment area located in the middle of the dead sea rift parallels these structural orientations a regional transtensive fault with embedded normal faults bounds the lower and middle part of the catchment area the topographic profile of the zerka ma in river exhibits two major knickpoints where it crosses two major embedded normal faults the second major knickpoint developed as a result of the dramatic lowering of the lisan lake water level a lake that pre dates the dead sea the decreased water level triggered river incision into the clastic sandstone units of wadi zerka ma in we performed a morphotectonic analysis study to investigate how the rock structures control the drainage network and the catchment area geomorphology according to the transverse topographic symmetry factor t the catchment area is highly asymmetric the major basin asymmetry trend is se oriented parallel to the oldest set of fault systems the catchment area displays a convex hypsometric curve indicating a very recent stage in the geomorphologic cycle our study indicates that the lisan lake catchment area shrinkage and structures growth controlled and shaped the wadi zerka ma in catchment area geomorphology the combined use of a geographic information system gis and remote sensing was shown to be very efficient in unraveling the evolution of the drainage network and catchment area geomorphology

understanding the gravity response variability of sedimentary basins using forward stratigraphic modelling abstract it is accepted that gravity inversions are non unique and that multiple models will fit the data equally well over sedimentary basins this implies that gravity anomalies can be equally well explained by sedimentary strata with constant densities over a highly heterogeneous basement or by highly heterogeneous sedimentary strata over a constant density basement while both scenarios minimise the difference between the predicted and observed gravity signal neither are geologically plausible in this work we explore stratigraphic modelling as a new parameterisation for gravity models by using a process based numerical simulation to generate the sedimentary basins density models we seek to focus only on geologically plausible models we then study the variability of the sedimentary strata s gravity response i e the range of possible geophysical signatures to stratigraphic parameter changes results from a study of a 2d section in the northern carnarvon basin the northwest shelf of australia emphasize that even when the stratigraphic models are trialled using a wide range of input parameters the simulated gravity response still has a limited variability when compared to model results generated using other parameterisations lastly our results provide insights into the global sensitivity of the gravity response highlighting the sedimentary and stratigraphic parameters that most affect the geophysical signal allowing for a discussion of the geologic and stratigraphic controls of the sedimentary basin s gravity response

three dimensional numerical modeling of eustatic control on continental margin sand distribution abstract eustasy constitutes a key control on continental shelf accommodation along with tectonism the combined effect of these processes influences relative sea level which is thought to regulate the location of facies stratigraphic architecture and distribution of sediment to basin margins here we used a nonlinear diffusion based numerical stratigraphic forward model to investigate the impact of the eustatic curve we ran two models one using a eustatic curve derived from the new jersey margin u s a and the other a base case with no eustatic variation but which were otherwise identical we conclude that changing the eustatic curve resulted in a 0 9 difference in cumulative deep water 200 m sand volumes between models this is because the no eustatic variation model resulted in deep water sand delivery events with magnitudes similar to those observed in the eustatic model which were due to the delta becoming fixed at the shelf edge and the subsequent temporary suspension of avulsive processes in the eustatic model maximum deep water sand accumulation occurred during short term sea level falls but peak sand delivery was not well related to the amplitude of the sea level fall itself further examination of the relationship between rates of relative sea level and deep water sand delivery show a poor correlation r 2

the effect of rift shoulder erosion on stratal patterns at passive margins implications for sequence stratigraphy abstract numerical modelling indicates that the erosion of uplifted rift flanks at passive margins has a profound effect on offshore stratigraphic patterns flexural uplift due to isostatic rebound in response to erosion extends far into the basin and causes uplift of the shelf as a result the contemporaneously deposited sedimentary wedge displays a characteristic offlap pattern when the rift shoulder is largely eroded onlap promoting mechanisms related to cooling of the lithosphere enable sediments to onlap onto the basin margin the initial offlapping and subsequent onlapping strata form one complete second order depositional sequence comprising a shelf margin transgressive and highstand systems tract the modelling inferences are in broad agreement with stratal patterns and basin geometries observed on the u s east coast the southeastern brazilian and southeastern australian passive margins and the transantarctic mountains ross sea shelf system the initial offlaps caused by erosion of rift shoulders have important implications for the deriviation of eustatic signals from coastal onlap patterns

pattern and tempo of great escarpment erosion extensive geological geophysical structural and geochronological data suggest that the locations of great escarpments bordering passive margins are exceptionally stable and are probably determined by crustal structure together the data do not support the established paradigm of ongoing significant and parallel escarpment retreat rather thermochronologic data and sedimentary sequences in ocean basins suggest that initial tectonically controlled rift escarpments undergo rapid and significant erosion only during the earliest stages of seafloor spreading development of stable passive margin escarpments follows this period of intense erosion escarpments increase in sinuosity as embayments retreat more rapidly than interfluves measurements of 24 escarpments suggest that sinuosity and the rate at which it increases depends upon the location of maximum uplift the geometry of the preescarpment drainage system and margin age all data suggest that the location of passive margin escarpments does not change significantly over time

erosional control on the dynamics of low convergence rate continental plateau margins s u m m a r y over the last decade thermomechanical models have revealed the control of both tectonics and erosion on the morphology of continental plateaus margins however unravelling the specific effects of these two coupled processes has been difficult in practice here to assess the control of erosion we investigate the dynamics of the eastern and the northern borders of the tibetan plateau which are characterized by a low convergence rate and a steep topographic escarpment adjacent to the sichuan and tarim basins respectively thermomechanical modelling of continental lithosphere coupled with fluvial denudation reveals that important crustal deformation with large scale horizontal displacements can occur without any convergence as a response to mass transfer due to gravitational collapse and to erosional unloading these processes are sensitive to crustal structure geothermal gradient as well as surface erosion at a timescale of several million years our results suggest that this denudation triggered deformation exerts a primary control on the evolution of those plateau margins by counterbalancing the mass removal due to erosion and stabilizing the topographic escarpment this finding supports a possible explanation for the morphology of the longmen shan eastern tibet in which the paradoxical combination of persistent high topographic gradients close to the foreland and low convergence rates can be related to the influence of erosion on deformation patterns

numerical modelling of combined erosion and weathering of slopes in weak rock due to various decay processes associated with weathering the stability of artificial slopes in weak rocks may be affected well within their envisaged engineering lifetime conceptually the decay following the initial stress release after excavation can be described as a process seeking equilibrium between weathering and erosion the extent to which such an equilibrium is actually reached influences the outcome of the weathering erosion decay process as well as the effects that the decay has on the geotechnical properties of the exposed rock mass and thus ultimately the stability of slopes affected by erosion and weathering this paper combines two conceptual models for erosion and weathering and derives a numerical model which predicts the resulting slope development this can help to predict the development of a slope profile excavated in a weak rock in time and can be extended with the addition of strength parameters to the weathering profile to enable prediction of slope stability as a function of time copyright 2011 john wiley sons ltd

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

andean growth and monsoon winds drive landscape evolution at sw margin of south america abstract in the atacama desert the driest place on earth located at the subduction margin of the andes the landscape evolves very slowly and changes in tectonic or erosion processes remain for a long time in the memory of topography at latitude 19 30 s a threshold between exoreic and endoreic drainage regimes is clearly associated with the latitudinal gradient imposed by the modern monsoon carrying humidity from the atlantic and disposed obliquely over catchments draining the andes to the pacific we summarize the geomorphic geological and climatic data in the threshold area we then use these data to constrain numerical experiments of drainage evolution data and experimental results are consistent with the development of a flat low energy morphology close to sea level interrupted at 10 ma by tectonic uplift prevailing to the present suggesting trench ward relief growth by incorporation of the coastal atacama region to the andes mountain belt

possible flexural accommodation on the eastern edge of the altiplano in relation to focussed erosion in the rio la paz drainage system it has been proposed that erosional unloading by focused incision can be accommodated by flexural rebound which in turn potentially exerts a positive feedback on erosion this paper presents morphometric data from the la paz drainage basin in the bolivian andes to illustrate the effects of such a feedback mechanism between erosion and crustal bending the rio la paz is a prominent system with the headwaters on the altiplano and a trunk stream segment that cuts across the cordillera real thereby connecting large portions of the altiplano with the amazon basin the flexural feedback model explains why all drainages beyond the watershed disperse their waters to the altiplano it also provides an explanation for the presence of the highest peaks just next to the location where the la paz river cuts into the bedrock across the cordillera real

fluvial incision into bedrock insights from morphometric analysis and numerical modeling of gorges incising glacial hanging valleys western alps france bedrock gorges incising glacial hanging valleys potentially allow measurements of fluvial bedrock incision in mountainous relief using digital elevation models topographic maps and field reconnaissance we identified and characterized 30 tributary hanging valleys incised by gorges near their confluence with trunk streams in the romanche watershed french western alps longitudinal profiles of these tributaries are all convex and have abrupt knickpoints at the upper limit of oversteepened gorge reaches we reconstructed initial glacial profiles from glacially polished bedrock knobs surrounding the gorges in order to quantify the amount of fluvial incision and knickpoint retreat from morphometric analyses we find that mean channel gradients and widths as well as knickpoint retreat rates display a drainage area dependence modulated by bedrock lithology however there appears to be no relation between horizontal retreat and vertical downwearing of knickpoints assuming a postglacial origin of these gorges our results imply high postglacial fluvial incision 0 5 15 mm yr 1 and knickpoint retreat 1 200 mm yr 1 rates that are however consistent with previous estimates numerical modeling was used to test the capacity of different fluvial incision models to predict the inferred evolution of the gorges results from simple end member models suggest transport limited behavior of the bedrock gorges a more sophisticated model including dynamic width adjustment and sediment dependent incision rates predicts present day channel geometry only if a significant supply of sediment from the gorge sidewalls 10 mm yr 1 is triggered by gorge deepening combined with pronounced inhibition of bedrock incision by sediment transport and deposition

a 1 d mechanistic model for the evolution of earthflow prone hillslopes 1 in mountainous terrain deep seated landslides transport large volumes of material on hillslopes exerting a dominant control on erosion rates and landscape form here we develop a mathematical landscape evolution model to explore interactions between deep seated earthflows soil creep and gully processes at the drainage basin scale over geomorphically relevant 10 3 year timescales in the model sediment flux or incision laws for these three geomorphic processes combine to determine the morphology of actively uplifting and eroding steady state topographic profiles we apply the model to three sites one in the gabilan mesa california with no earthflow activity and two along the eel river california with different lithologies and varying levels of historic earthflow activity representative topographic profiles from these sites are consistent with model predictions in which the magnitude of a dimensionless earthflow number based on a non newtonian flow rheology reflects the magnitude of recent earthflow activity on the different hillslopes the model accurately predicts the behavior of earthflow collection and transport zones observed in the field and estimates long term average sediment fluxes that are due to earthflows in agreement with historical rates at our field sites finally our model predicts that steady state hillslope relief in earthflow prone terrain increases nonlinearly with the tectonic uplift rate suggesting that the mean hillslope angle may record uplift rate in earthflow prone landscapes even at high uplift rates where threshold slope processes normally limit further topographic development

reconstructing ancient topography through erosion modelling one of the main aims of geomorphology is to understand how geomorphic processes change topography over long time scales over the last decades several landscape evolution models have been developed in order to study this question however evaluation of such models has often been very limited due to the lack of necessary field data in this study we present a topography based hillslope erosion and deposition model that is based on the watem sedem model structure and works on a millennial time scale soil erosion transport and deposition are calculated using slope and unit contributing area the topography is iteratively rejuvenated by taking into account modelled erosion and deposition rates thereby simulating topographic development backwards in time a first attempt has been made to spatially evaluate the model using detailed estimates for historical soil erosion and sediment deposition volumes obtained from an augering campaign in a small catchment in the belgian loess belt the results show that the model can simulate realistic soil redistribution patterns however further research is necessary in order to deal with artificial flaws that cause routing problems and significantly influence results common problems and issues related to this type of backward modelling are also discussed

an analysis of cotswold topography insights into the landscape response to denudational isostasy we have used the nextmap britain digital terrain model dtm to determine the lithospheric response to erosional unloading and the contribution of tectonics in the form of elastic plate flexure to the cotswold scarp and vale landscape the calculations take into account lithology variations and along strike changes in escarpment retreat we show that flexural rock uplift as a result of erosional unloading varies spatially and may contribute up to 50 of the relief in the cotswold region this is supported by morphometric analysis of concavity and steepness for 66 longitudinal river profiles that drain the scarp and dip slope of the escarpment viscoelastic plate models suggest that the uplift is initially rapid up to 8 m ka 1 and essentially complete within 50 ka these initial rates are compatible with an early post anglian incision rate inferred from the thames terraces the staircase terrace pattern suggests however that there have been a number of denudational isostatic events each associated with a climate cycle finally the analysis reveals an inherited proto landscape that has a subdued relief when compared with the modern dtm such a relief is consistent with an early extension of the river thames through the vale of moreton to the north of the present day cotswold hills

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

the role of climate driven chemical weathering on soil production climate plays an important role in controlling rates of weathering and weathered regolith production regolith production functions however seldom take climate parameters into account based on a climate dependent weathered regolith production model at low denudation rates relative regolith thicknesses are less sensitive to changes in precipitation rates while at high denudation rates small changes in climatic parameters can result in complete stripping of hillslopes this pattern is compounded by the long residence times and system response times associated with low denudation rates and vice versa as others have shown the transition between regolith mantled and bedrock slopes is dependent on the ratio of denudation to production here we further suggest that this is itself a function of precipitation rate and temperature we suggest that climatic parameters can be easily incorporated into existing soil production models and that such additions improve the predictive power of soil production models

cenozoic vertical motions of the catalan coastal ranges ne spain the role of tectonics isostasy and surface transport 1 we analyze the cenozoic topographic evolution of the catalan coastal ranges ne spain and the role of fault activity erosion sedimentation and isostasy in controlling uplift and subsidence a forward numerical model constrained by an extensive geological and geophysical data set is used to examine the temporal and spatial record of cenozoic vertical motions we show that the effect of isostasy erosion and sedimentation is as important as the contribution of fault deformation to the topography of the catalan coastal ranges the model predicts that paleogene topography generation by thrusting was compensated by erosion up to 1 3 km and isostatic subsidence up to 1 2 km resulting in a 1 2 1 9 km high mountain range by the end of compression 29 ma during the neogene strong tectonic subsidence related to normal faulting and the consequent flexural uplift of 0 7 1 2 km surface erosion as much as 1 6 2 3 km and sedimentation up to 4 5 km led to the present landscape configuration extension rates along the barcelona fault controlled flexural uplift and in combination with erosion and sedimentation processes led to the migration of the topographic maximum of the prelitoral range toward the easternmost ebro basin

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

modeling the effects of bed topography on fluvial bedrock erosion by saltating bed load abrasion by saltation is an important mechanism of fluvial incision into bedrock sklar and dietrich 2004 introduced an abrasion model in which the erosion rate of an approximately planar bed is linearly dependent on the kinetic energy transferred by the vertical velocity of saltating grains however most bedrock floored channels exhibit topographic variations that yield deviations from a planar surface referred to as bed topography observations show that bed topography affects erosion here the saltation abrasion model is extended for a nonplanar bed a several centimeter high bump transverse to the flow is repeated every 50 cm the kinetic energy of grain impacts is calculated in two ways 1 impact velocity normal to bed topography and 2 vertical impact velocity by comparing the latter case with the planar model it is possible to isolate the effects of topography on the interception of saltation trajectories incorporating bed topography changes erosion in three ways first erosion is 10 to 1000 times faster depending upon transport stage and grain size enhanced erosion results from both the interception of grains by topography and the increased kinetic energy transfer associated with high angle impacts on the stoss side of bumps second erosion increases monotonically with transport stage whereas maximum erosion occurs at low to intermediate transport stage with a planar bed third erosion decreases monotonically with grain size whereas maximum erosion occurs with intermediate sized grains with a planar bed although the model is highly simplified results show that bed topography should be considered when simulating erosion of bedrock

abrupt changes in the rate of andean plateau uplift from reversible jump markov chain monte carlo inversion of river profiles abstract knowledge of the rate of surface uplift of the central andean plateau provides important boundary conditions for regional geodynamic models and paleoclimate reconstructions here we present a fully nonlinear inverse method to extract the rock uplift history of the central andean plateau from the cotahuasi river and its tributaries our approach is based on an analytical solution to the stream power model that relates elevation to rock uplift history under the assumptions of constant climatic conditions in space and time and spatially invariant rock uplift we use a bayesian framework that allows us to quantify the full state of knowledge of model parameters i e uncertainties trade offs the erosional efficiency defines the landscape response time and this must be determined using independent data therefore using thermochronometric data from the cotahuasi ocona canyon which record rapid fluvial incision at 13 10 ma we calibrate our results to infer a rock uplift history for the north central andean plateau we infer a pulse of rock uplift between 25 and 10 ma at rates as high as 0 25 km my however the rock uplift rate inferred during this pulse is not as high as is predicted if the central andean plateau grew as a result of loss of unstable lithospheric mantle therefore our results are more consistent with models requiring gradual uplift of the central andean plateau

soil production on a retreating escarpment in southeastern australia the functional dependence of bedrock conversion to soil on the overlying soil depth the soil production function has been widely recognized as essential to understanding landscape evolution but was quantified only recently here we report soil production rates for the first time at the base of a retreating escarpment on the soil mantled hilly slopes in the upper bega valley southeastern australia concentrations of 10 be and 26 al in bedrock from the base of the soil column show that soil production rates decline exponentially with increasing soil depth these data define a soil production function with a maximum soil production rate of 53 m m y under no soil mantle and a minimum of 7 m m y under 100 cm of soil thus constraining landscape evolution rates subsequent to escarpment retreat the form of this function is supported by an inverse linear relationship between topographic curvature and soil depth that also suggests that simple creep does not adequately characterize the hillslope processes spatial variation of soil production shows a landscape out of dynamic equilibrium possibly in response to the propagation of the escarpment through the field area within the past few million years in addition we present a method that tests the assumption of locally constant soil depth and lowering rates using concentrations of 10 be and 26 al on the surfaces of emergent tors

field measurements of the energy delivered to the channel bed by moving bed load and links to bedrock erosion 1 impact driven fluvial erosion is directly related to the energy delivered to the channel bed by moving bed load using a novel protocol we have measured this energy in four mountain streams in austria and switzerland similar to bed load transport rates the energy delivered to the bed displays large scatter over several orders of magnitude even for a constant discharge we found that only a small fraction 1 of the total energy available to the stream is delivered to the bed and can be used for erosive work empirical predictive equations can be defined for specific sites but there is large site to site variability prediction of energy delivered to the bed using the saltation abrasion model of bedrock erosion only provides the observed trends when measured bed load transport rates are used as input using an empirical transport law calibrated to the conditions at one of the study streams leads to overprediction of delivered energies by more than 2 orders of magnitude this overprediction decreases with increasing discharge and thus at high discharges better predictive results are obtained we find a correlation between the channels bed slope or characteristic grain sizes of the channel bed and the fraction of energy delivered to the bed of the total energy available to the stream this observation provides a tentative link between fundamental fluvial incision processes to the stream power model family that has widely been used to model fluvial bedrock incision in landscape evolution simulations

late cenozoic flexural deformation of the middle u s atlantic passive margin despite the century long recognition of regional epeirogeny along the middle atlantic passive margin relatively few studies have focused on understanding postrift uplift mechanisms here we demonstrate that epeirogenic uplift of the central appalachian piedmont and subsidence of the salisbury embayment represent first order flexural isostatic processes driven by continental denudation and offshore deposition our results show that regional epeirogenic processes present on all atlantic type passive margins are best resolved by specific stratigraphic and geomorphic relationships rather than topography a simple one dimensional geodynamic model constrained by well dated baltimore canyon trough coastal plain and lower susquehanna river piedmont stratigraphy simulates flexural deformation of the u s atlantic margin the model represents the passive margin lithosphere as a uniformly thick elastic plate without horizontal compressive stresses that deforms flexurally under the stress of strike averaged vertically applied line loads model results illustrate a complex interaction among margin stratigraphy and geomorphology the isostatic response to denudational and depositional processes and the modulating influence of exogenic forces such as eustasy the current elevation with respect to modern sea level of fluvial terraces and correlative coastal plain deposits or unconformities is successfully predicted through the synthesis of paleotopography eustatic change and margin flexure results suggest that the middle u s atlantic margin landward of east coast magnetic anomaly is underlain by lithosphere with an average elastic thickness of 40 km flexural rigidity d 4 1023 n m the margin experiences an average long term denudation rate of approximately 10 m m y and the piedmont has been flexurally upwarped between 35 and 130 meters in the last 15 m y long term isostatic continental uplift resulting from denudation and basin subsidence resulting from sediment loading are accommodated primarily by a convex up flexural hinge physiographically represented by the fall zone our results elucidate an inherent danger in using topography alone to constrain late stage passive margin deformation mechanisms only through careful synthesis of field stratigraphic and geomorphic elements such as fluvial terraces coastal plain deposits and offshore stratigraphy can age control be extended from the offshore depositional setting to the erosionally dominated continent this study demonstrates that despite a relatively subdued topography the middle u s atlantic margin experiences progressive flexural isostatic deformation similar to that proposed for high relief margins characterized by great escarpments thus margin topographic diversity remains a function of other factors such as lithospheric composition and or structure supracrustal stratigraphy and structure degree of drainage integration drainage divide migration and climate

experimental study of bedrock channel alluviation under varied sediment supply and hydraulic conditions 1 channel incision into bedrock plays a critical role in mountain landscape evolution a bed that is completely alluviated cannot undergo incision as a result incision driven by the collision of bedload grains and bedrock requires transport at below capacity conditions for example where the bed is partially covered by alluvium in a mechanistic model of bedrock incision it is important to have a formula describing the relationship between the bedload transport rate and the degree to which the bed is covered by sediment the purpose of this work is to understand the mechanisms underlying the degree of bed exposure in bedrock rivers by means of an experimental study a number of experiments with various hydraulic and morphological bed conditions were performed in order to characterize this model here we focus on planar bedrock beds with some roughness the results suggest that the sediment supply channel slope hydraulic bed roughness the degree of areal coverage and thickness of antecedent gravel in the channel as well as the presence of boulders in the channel are major factors controlling bedrock exposure for sufficiently low ratios of sediment supply to transport capacity it was found that bedrock roughness can play a role in determining the degree of bedrock exposure for higher sediment ratios on the other hand the composite roughness associated with grain roughness bars and or antidunes dominates so that the underlying bedrock roughness no longer affects the degree of exposure of the bed for lower bed slopes i e less than 0 015 based on our experimental setting bedrock exposure decreases more or less linearly with increasing values of the ratio of sediment supply rate to capacity rate for higher bed slopes i e more than 0 015 there is a range of lower values of the ratio of sediment supply rate to capacity rate where a bedrock surface becomes fully exposed without any alluvial deposit for a given bedrock roughness this range expands solely with increasing slope regardless of shear stress within the upper range of values of the ratio of sediment supply to capacity rate a linear relationship between the degree of bedrock exposure and this supply to capacity ratio still prevails the addition of model boulders can be viewed as very high hydraulic bed roughness to the channel has been found to suppress the overexposure of bedrock and so restore a linear relation between the degree of exposure and the ratio of sediment supply rate to capacity rate formulations for estimating bedrock exposure as a function of sediment supply to capacity ratio under different river channel characteristics are proposed a linear relation between the degree of alluvial cover and the ratio of sediment supply rate to capacity rate is a previously proposed model the present study expands the result for other cases including runaway alluviation some landscape evolution models assume an abrupt shift between fully exposed bedrock and complete alluviation whereas others assume the linear relation the present study shows that both formulations are valid under different settings of river characteristics

numerical modeling of spatially variable precipitation and passive margin escarpment evolution abstract passive margin escarpments are long lasting landforms which can remain steep and high over tens of millions of years precipitation variability has seldom been considered as a contributor to passive margin escarpment evolution however large and distinct variability in precipitation rates with elevation is observed in mountainous landscapes we assess the potential impacts of spatially variable precipitation on passive margin escarpment evolution with a numerical model that couples a simple elevation dependent precipitation rule with the cascade surface processes model and a simple flexural uplift model modeled topography is more sensitive to the elevation of the precipitation maximum than to the effective elastic thickness of the lithosphere if precipitation is maximized at the escarpment crest the escarpment decreases in elevation slope and proximity to the coast more rapidly than if precipitation is focused at low elevations low elevation precipitation maxima contribute to increasing escarpment slope over time and preservation of a high elevation escarpment using tropical rainfall measuring mission trmm precipitation radar data we establish precipitation elevation relationships at high elevation passive margins across the tropics and document the occurrence of patterns similar to those included in our model despite uncertainty as to the robustness of precipitation patterns and the simplified tectonic and geomorphic framework of our model we conclude that spatial variability in precipitation is a potentially significant contributor to passive margin escarpment evolution

large scale geomorphology classical concepts reconciled and integrated with contemporary ideas via a surface processes model linear systems analysis is used to investigate the response of a surface processes model spm to tectonic forcing the spm calculates subcontinental scale denudational landscape evolution on geological timescales 1 to hundreds of million years as the result of simultaneous hillslope transport modeled by diffusion and fluvial transport modeled by advection and reaction the tectonically forced spm accommodates the large scale behavior envisaged in classical and contemporary conceptual geomorphic models and provides a framework for their integration and unification the following three model scales are considered micro meso and macroscale the concepts of dynamic equilibrium and grade are quantified at the microscale for segments of uniform gradient subject to tectonic uplift at the larger meso and macroscales which represent individual interfluves and landscapes including a number of drainage basins respectively the system response to tectonic forcing is linear for uplift geometries that are symmetric with respect to baselevel and which impose a fully integrated drainage to baselevel for these linear models the response time and the transfer function as a function of scale characterize the model behavior numerical experiments show that the styles of landscape evolution depend critically on the timescales of the tectonic processes in relation to the response time of the landscape when tectonic timescales are much longer than the landscape response time the resulting dynamic equilibrium landscapes correspond to those envisaged by hack 1960 when tectonic timescales are of the same order as the landscape response time and when tectonic variations take the form of pulses much shorter than the response time evolving landscapes conform to the penck type 1972 and to the davis 1889 1899 and king 1953 1962 type frameworks respectively the behavior of the spm highlights the importance of phase shifts or delays of the landform response and sediment yield in relation to the tectonic forcing finally nonlinear behavior resulting from more general uplift geometries is discussed a number of model experiments illustrate the importance of fundamental form which is an expression of the conformity of antecedent topography with the current tectonic regime lack of conformity leads to models that exhibit internal thresholds and a complex response

erosional dynamics flexural isostasy and long lived escarpments a numerical modeling study erosional escarpments are common features of high elevation rifted continents fission track data suggest that these escarpments form by base level lowering and or marginal uplift during rifting followed by lateral retreat of an erosion front across tens to hundreds of kilometers previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat in this study we present a nonlinear two dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long term retreat of a rift generated escarpment the model represents topography as a grid of cells with drainage networks evolving as water flows across the grid in the direction of steepest descent the model accounts for sediment production by weathering fluvial sediment transport bedrock channel erosion and hillslope sediment transport by diffusive mechanisms and by mass failure numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift model results suggest that the necessary and sufficient conditions for long term escarpment retreat are 1 incising bedrock channels in which the erosion rate increases with increasing drainage area so that the channels steepen and propagate headward 2 a low rate of sediment production relative to sediment transport efficiency which promotes relief generating processes over diffusive ones 3 high continental elevation which allows greater freedom for fluvial dissection and 4 any process including flexural isostatic uplift that helps to maintain a drainage divide near an escarpment crest flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift of all the above conditions high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor

evolution of the santa cruz mountains california through tectonic growth and geomorphic decay i describe a strategy for modeling a specific large scale topographic feature that recognizes the discrepancy between tectonic and geomorphic scales and allows for important feedbacks between these processes in the geomorphic model the largest channel in each 4 4 km cell is explicitly treated the channel incision being driven by a stream power rule hillslopes internal to each cell respond rapidly to incision of the local channel prompting their treatment in the model as steady state forms i present analytic expressions for the local relief which is controlled by the local channel incision rate and rate constants associated with the dominant hillslope process either diffusive or landsliding initial conditions include any preexisting topography and a lightly etched a channel network the model is illustrated using the santa cruz mountains california i show that an earlier hypothesis that the santa cruz mountains are due to advection of topography past an uplift source related to a restraining bend in the san andreas fault remains viable when more specific geomorphic processes are considered the local tectonics are represented by crustal thickening necessitated by conservation of mass in the bend right lateral translation of crust with respect to the bend and flexural response to the distributed load the model produces reasonable geographic and statistical distributions of topography using rates of tectonic and geomorphic processes that are within the range of those measured locally this argues that this restraining bend is a long lived feature of the san andreas fault the slightly higher crest and shorter length of the southern santa cruz mountains may potentially be explained by slightly faster slip of the crust west of the fault with respect to the bend than of that to the east deflection is minimal beneath these relatively small mountains disallowing the interesting feedback of erosionally driven uplift the predicted pattern of exhumation could be used to guide the search for fission track sites that could aid in the testing of the model

spatial variability of 10be derived erosion rates across the southern peninsular indian escarpment a key to landscape evolution across passive margins abstract the persistence of significant topography in ancient tectonically inactive orogenic belts remains one of the outstanding questions in geomorphology in southern peninsular india the impressive topographic relief of the western ghat mountains in tectonic quiescence since at least ca 65 ma has raised important questions concerning the long term mechanism of topographic evolution quantifying the distribution of erosion in space and time is critical to understanding landscape evolution although the long term erosion rates are reasonably well known the short term erosion rates and the relative importance of factors controlling erosion in southern peninsular india are less well constrained we present a new suite of catchment averaged and local erosion rates using in situ produced 10be concentrations in river sediments and exposed bedrock samples in southern peninsular india catchment averaged erosion rates vary from 9 6 0 8 m ma 1 in the highlands to 114 3 13 8 m ma 1 on the escarpment side bedrock erosion rates range from 2 4 0 2 m ma 1 in the ridge top to 143 4 25 4 m ma 1 in active channel beds of the highlands catchment averaged erosion rates derived from the across escarpment westward draining catchments are significantly higher than those derived from the eastward draining over highland catchments the difference indicates that long term down wearing of the highland proceeds at lower rates than in the escarpment zones catchment averaged erosion rates are moderately correlated with mean hillslope angles and local relief whereas they are strongly correlated with catchment averaged channel steepness index this suggests that topographic steepness is the major control on the spatial variability of erosion while strong rainfall gradient is of minor importance in this area 10be derived average erosion rates in highlands are consistent with previous long term erosion rate estimated from thermochronometry these results collectively point to large scale steady state topography only decaying slowly with time steady state likely reflects the balance between erosion and isostatically driven uplift of the southern peninsular india

an incision wave in the geologic record alpujarran corridor southern spain almeria abstract the term incision wave was coined in the 1990s to describe wave like patterns of stream incision propagating through numerically modeled bedrock channel river systems an incision wave consists of a crest where available stream power is greatest and where vertical incision is most rapid the crest is flanked by limbs where there is less available stream power and where vertical incision rates are slower farther away from the crest available stream power is less and incision rates are slower than in the limbs modeling results suggest tectonically induced base level fall triggers incision waves that propagate upstream through bedrock stream networks however it has recently been postulated that the equation underpinning incision wave models cannot realistically simulate river systems this paper provides field geological evidence supporting the hypothesis that tectonically induced base level fall triggers incision waves that propagate through bedrock stream networks for tens of kilometers mid and late pleistocene alluvial morphostratigraphy in the rio andarax drainage basin southeast spain is interpreted to indicate that patterns of paleo stream power were controlled by an incision wave in the conceptual model proposed in this paper the signature of an incision wave in the rio andarax drainage network is recorded by the contrasting morphostratigraphy of oxygen isotope stage 8 ois8 time landforms at the crest of the incision wave during ois8 there is no record of a paleoalluvial level because available stream power exceeded critical stream power and streams were incising vertically the crestal area is flanked by ois8 time strath terraces which record the position of the two limbs of the incision wave farther upstream ois8 time alluvial fills mark an area unaffected by the incision wave during oxygen isotope stage 2 ois2 and or oxygen isotope stage 1 ois1 sediment availability in the rio andarax catchment was low and the pattern of relative stream power was threshold like rather than wave like differences in the manifestation of the incision wave during ois8 vs during ois2 and or ois1 indicate that climate and sediment availability can control how incision waves propagate through fluvial systems

a synthetic stratigraphic model of foreland basin development the processes of erosion and deposition must be included in foreland basin models to predict correctly basin geometry and stratigraphy we present a synthetic stratigraphic model of the development of nonmarine foreland basins that predicts progressive geometry topography and facies patterns in the model steady crustal shortening occurs according to a wedgethickening model erosion and deposition follow a diffusive process and the lithosphere is compensated elastically erosion and deposition are controlled by the transport coefficients r of the diffusion equation for a range of thrust velocities and lithospheric rigidities transport coefficients are of order 102 103 m yr in the mountain belt these values are much higher than those derived from the study of scarp degradation in the sedimentary basin transport coefficients of order 104 m2 yr are appropriate and are compatible with previous studies of fluvial and deltaic deposition rapid thrusting results in a narrow underfilled basin while slow thrusting results in a wide overfilled basin in addition by varying the erosional and depositional transport coefficients while holding other parameters constant we generate both overfilled and underfilled basins these results suggest that changes in the rate of thrust loading the climate or the source rock lithology can create stratigraphic signatures that have been interpreted to record viscoelastic relaxation of the lithosphere clearly to understand either the long term behavior of the lithosphere or to interpret orogenic history from preserved foreland strata the manner in which a basin was filled must be considered we apply the model to the evolution of the modern sub andean foreland and find that an erosional transport coefficient of 3000 m2 yr and a depositional transport coefficient of 20 000 m2 yr successfully predict the observed basin geometry

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

impact of hillslope derived sediment supply on drainage basin development in small watersheds at the northern border of the central alps of switzerland abstract this paper explores the effects of hillslope mobility on the evolution of a 10 km 2 drainage basin located at the northern border of the swiss alps it uses geomorphologic maps and the results of numerical models that are based on the shear stress formulation for fluvial erosion and linear diffusion for hillslope processes the geomorphic data suggest the presence of landscapes with specific cross sectional geometries reflecting variations in the relationships between processes in channels and on hillslopes in the headwaters the landscape displays parabolic cross sectional geometries indicating that mass delivered to channels by hillslope processes is efficiently removed in the trunk stream portion the landscape is i v shaped if the downslope flux of mass is balanced by erosion in channels i e if mass delivered to channels by hillslope processes is efficiently removed and ii u shaped if in channel accumulation of hillslope derived material occurs this latter situation indicates a non balanced mass flux between processes in channels and on hillslopes information about the spatial pattern of the postglacial depth of erosion allows comparative estimates to be made about the erosional efficiency for the various landscapes that were mapped in the study area the data suggest that the erosional potential and sediment discharge are reduced for the situation of a non balanced mass flux between processes in channels and on hillslopes these findings are also supported by the numerical model indeed the model results show that high hillslope mobility tends to reduce the hillslope relief and to inhibit dissection and formation of channels in contrast stable hillslopes tend to promote fluvial incision and the hillslope relief increases the model results also show that very low erosional resistance of bedrock promotes backward erosion and steepening of channel profiles in headwaters beyond that the model reveals that sediment discharge generally increases with decreasing erosional resistance of bedrock but that this increase decays exponentially with increasing magnitudes of fluvial and hillslope mobilities very high hillslope diffusivities even tend to reduce the erosional potential of the whole watershed it appears that besides rates of base level lowering factors limiting sediment discharge might be the nonlinear relationships between processes in channels and on hillslopes

transport slopes sediment cover and bedrock channel incision in the henry mountains utah 1 field data from channels in the henry mountains of utah demonstrate that abundant coarse sediment can inhibit fluvial incision into bedrock by armoring channel beds the cover effect we compare several small channels that share tributary junctions and have incised into the same sedimentary bedrock unit navajo sandstone but contain differing amounts of coarse diorite clasts owing to the spatial distribution of localized sediment sources bedrock channels that contain abundant clasts diorite rich have steeper longitudinal slopes than tributaries of these channels with smaller drainage areas and less sediment diorite poor the diorite poor tributaries have incised more deeply to lower average slopes and have more reach scale slope variability which may reflect bedrock properties longitudinal sediment sorting and incision at lower sediment supply diorite rich channels have less bedrock exposed and smoother longitudinal profiles than diorite poor channels we find that 1 coarse sediment can mantle bedrock channel beds and reduce the efficiency of incision validating the hypothesized cover effect in fluvial incision models 2 the channel slope needed to transport the sediment load can be larger than that needed to erode bedrock suggesting that the slope of incising bedrock channels can become adjusted to the sediment load 3 when abundant sediment is available transport capacity rather than thresholds of motion can be dominant in setting bedrock channel slope and 4 cover effects can be important even when moderate amounts of bedrock are exposed in channel beds

discharge discharge variability and the bedrock channel profile long term bedrock incision is driven by daily discharge events of variable magnitude and frequency with ineffective events below an incision threshold we explore theoretically how this short term stochastic behavior controls long term steady state incision rates and bedrock channel profiles combining a realistic frequency magnitude distribution of discharge with a deterministic detachment limited incision model in which incision rate is a power function of basal shear stress above a critical shear stress our model predicts a power law relationship between steady state slope and drainage area consistent with observations the exponent of this power law is independent of discharge mean and variability while the amplitude factor which controls mountain belt relief is a power law function of mean runoff with an exponent of 0 5 and a complex function of runoff variability in accordance with evidence that incision occurs between 6 and 20 of time in rapidly incising rivers 1 mm yr our model predicts that channel steepness is virtually insensitive to runoff variability runoff variability can only decrease channel steepness for very slow incision rates and or weak lithologies the relationship between channel steepness and incision rate is always a power law whose exponent depends on the channel cross sectional geometry and runoff variability this contradicts models neglecting discharge stochasticity in which the steepness incision scaling is set by the incision law exponent our results suggest that changes in climate variability cannot explain an increase in bedrock incision rates during the late cenozoic within the context of a detachment limited model

landscape response to climate change insights from experimental modeling and implications for tectonic versus climatic uplift of topography we present the results of an experimental investigation of the concurrent action of tectonic uplift and climate variation on relief evolution we designed an experimental apparatus that allows the study of erosion of laboratory scale topographies that evolve under given uplift and rainfall rates for constant uplift and rainfall rates the experimental topography evolves toward a statistical steady state defined by a mean elevation constant with time starting from such a steady state and keeping the input uplift rate constant a subsequent change in the rainfall rate yields a change in the mean elevation of the landscape to a new equilibrium elevation an increase in precipitation yields a lower mean steady state elevation whereas for a decrease in precipitation the surface is uplifted we define this phenomenon as a climatically induced surface uplift as opposed to a tectonically induced surface uplift the climatically and tectonically induced surface uplifts correspond to different dynamics of denudation so that it is theoretically possible to differentiate between the climatic or tectonic causes of surface uplift from records of output sediment fluxes

modelling landscape evolution in the waipaoa catchment new zealand a phenomenalogical approach landscape evolution models require detailed strength measurements which are difficult to obtain for large areas we offer an alternative phenomenalogical approach to modelling landscape evolution one that requires few input parameters the phenomena are hills channels floodplains knickpoints and coastal floodplain the model is demonstrated on the highly erodible waipaoa catchment in new zealand a digital elevation model is simulated every thousand years from 63000 bp through to present day there is good agreement between predicted and observed terrace heights and also good agreement between predicted and observed knickpoint locations suggesting the phenomenalogical approach is indeed representing the main drivers of landscape evolution in the waipaoa catchment

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

experimental study of knickpoint and longitudinal profile evolution in cohesive homogeneous material a series of experiments were conducted in homogeneous bedrock to study knickpoint and longitudinal profile evolution knickpoints are created by successive drops in base level which simulate intermittent uplift channel morphology and flow characteristics vary systematically along a knickpoint reach as the knickpoint lip is approached width decreases but depth velocity and bottom shear stress increase as a result knickpoints are rapidly destroyed through the process of 1 knickpoint replacement and 2 subsequent knickpoint inclination knickpoint replacement consists of two morphologically distinct erosional reaches the knickpoint face below the knickpoint lip which decreases in slope and an incising reach above the knickpoint lip which increases in slope knickpoint replacement is a significant process in the evolution of knickpoints in homogeneous bedrock within experimental limits this study supports the notion that knickpoints do not undergo parallel head ward retreat in homogeneous bedrock given intermittent uplift except in those possible cases of extensive and pervasive bedrock jointing only the erosional sediment transport discontinuity above the knickpoint is developed in cohesive sediments below the knickpoint a steep bedrock channel slope low sediment load and rapid decrease in grain size of sediment load preclude development of the aggradational sediment transport discontinuity knickpoint evolution can be characterized by three general models parallel retreat replacement and inclination these models are based on the following criteria within the knickpoint reach 1 relationship between bottom shear stress 0 and critical shear stress needed to initiate motion c 2 nature of the bed load transport discontinuities and 3 spatial variability of bedrock resistance to fluvial erosion

transform margins development controls and petroleum systems an introduction this paper provides an overview of the existing knowledge of transform margins including their dynamic development kinematic development structural architecture and thermal regime together with the factors controlling these this systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock seal rock and reservoir rock distribution expulsion timing trapping style and timing and migration patterns the paper then introduces individual contributions to this volume and their focus supplementary material location table and map of specific transform examples structural elements of the romanche transform margin and glossary of terms used in this article is available at https doi org 10 6084 m9 figshare c 3276407 gold open access this article is published under the terms of the cc by 3 0 license this volume shows dynamic linkage between new transform margin research and increasing transform margin exploration it offers a critical set of predictive tools via an understanding of the mechanisms involved in the development of play concept elements at transform margins and their controlling factors our introduction to this volume reviews the current knowledge of the transform margins focusing on their dynamic development kinematic development structural architecture thermal regimes and petroleum systems the last part of this paper introduces the contributions to this volume

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

sediment and rock strength controls on river incision into bedrock recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply challenging the common assumption that incision rate is simply proportional to stream power our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits maximum erosion rates occur at a critical level of coarse grained sediment supply where the bedrock is only partially exposed fine grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate furthermore we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief

evaluation of bed load transport formulae using field evidence from the vedder river british columbia abstract bed load transport formulae have not been tested extensively over medium spatial and temporal scales the lack of such testing is undoubtedly due to a paucity of field data available for testing at these scales extensive transport morphologic and discharge data available for a 10 year period along an 8 km study reach of the vedder river british columbia are used to test the predictive capabilities of bed load transport formulae at medium scales the transport data were obtained using the morphologic approach which is based on the premise that changes in channel morphology reflect the transfer of sediment such transport estimates can be made over larger spatial and temporal scales than is possible using traditional measurement techniques this study focuses on evaluating the original and revised versions of the bagnold stream power formula the meyer peter and muller formula and a stream power correlation overall the formulae are found to underpredict gravel transport rates for the vedder river the discrepancy is particularly pronounced in 1982 1983 and 1987 1990 which are periods during which significant dredging occurred dredging activity may have loosened the bed structure or resulted in a disequilibrium morphology thereby increasing sediment movement analysis is undertaken to assess how the use of mean daily discharge vs 15 min increment discharge series affects transport predictions results show that only the meyer peter and muller formula is particularly sensitive to which discharge series is used in calculations modification of the shields parameter is found to significantly affect transport predictions although it cannot explain alone the discrepancies between field data and calculated results predictions of total deposition in the study reach are well within an order of magnitude for all equations the bagnold type formulae and the meyer peter and muller formula do not capture the relatively even distribution of deposition along the study reach surprisingly the simple stream power correlation captured this downstream pattern of deposition cumulative distributions of predicted bed load transport are found to be most realistic for the original and revised bagnold formulae results of this study do not suggest that one particular formula is consistently preferred

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

sedimentary fills and sensitivity analysis of deep lacustrine facies in multi segment rift basins insights from 3d forward modeling abstract this article presents a series of stratigraphic forward simulations of deep lacustrine sedimentary fills of continental multi segment rift basins these models integrate basin filling with the evolution of the extrabasinal catchment area and relate tectonism and precipitation fluctuations to changes in lake level and sediment supply the models reproduce the physical processes acting on the whole depositional environment from the site of erosion in the catchment area to deposition deep in the basin and capture the complexity and variability of lacustrine rift basins results from these simulations show 1 both extremely arid and extremely high precipitation conditions are not favorable for the development of a large proportional volume of deep lacustrine facies in rift basins 2 an increase of basin subsidence rate or a decrease of erosion rate in the source area increases both the proportional volumes of deep lacustrine sediment contained within the total rift fill and sand rich sediment contained within deep lacustrine facies 3 the development of deep lacustrine facies is more sensitive to basin subsidence and source erosion under very high precipitation conditions and 4 under various scenarios of basin subsidence and source area erosion the proportion and style of deep water sand accumulation is shown to be insensitive to climate conditions our simulations shed light on deep lacustrine fills in lacustrine rift basins and deepen the understanding of the influences of different conditions of evaporation precipitation from arid to humid subsidence rates e g reflecting end member processes of continental extension and erosion rates e g reflecting varying bedrock terranes within the catchment which help predict favorable conditions for the development of lacustrine source rocks and deep water hydrocarbon reservoirs

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

mean bedrock to saprolite conversion and erosion rates during mountain growth and decline abstract weathering and associated atmospheric co2 consumption are thought to increase during the erosion of uplifting mountain ranges but the effect of enhanced erosion on weathering is still the subject of active debate we explore the possibility that erosion heterogeneity in uplifting landscapes significantly impacts the temporal relationships among mean uplift erosion and weathering using a 3d landscape evolution model applied to a synthetic surface with different uplift and climate scenarios although we do not strictly simulate the weathering outflux of the mountain we analyze the weathering response through the evolution of the mountain mean saprolite production rate and compare it to the mountain mean erosion rate through time the parametrical analysis shows that the temporal relationship between the mean erosion and saprolite production rates depends mainly on the ratio of the maximum saprolite production rate and the uplift rate wm u we explore two end members 1 when wm u 1 which corresponds to mountain ranges under a hot and humid climate the mean erosion and saprolite production rates vary at the same rate during the uplift and after once the uplift is stopped when the uplift is stopped the mean saprolite production increases and then decreases locally at different times this heterogeneity induces an overall decrease in the mean saprolite production rate 2 when wm u

controls on the erosion of the continental margin of southeast brazil from cosmogenic 10be in river sediments abstract the atlantic ocean coast region of southeast brazil contains two coast parallel mountain ranges the serra do mar and serra da mantiqueira generated by tectonic activity pulses tens of millions years after the main continental rift event occurred around 120 ma although the short term erosion rates for the region are established the relative importance of the factors controlling erosion is poorly constrained we combine new and published catchment averaged erosion rates n 48 using in situ produced 10be concentrations in quartz from river sediments to establish the regional erosion pattern the river catchments are i escarpment topography ii high altitude low relief and iii mixed topography which record how escarpment fronts are migrating inland ocean facing coastal escarpment catchments of the serra do mar e 18 53 m ma can be eroded approximately twice as fast as continent facing escarpment catchments in the serra do mar and serra da mantiqueira e 7 24 m ma the correlation between the normalized channel steepness index ksn and slope angle indicates that river incision and hillslope erosion processes combine to maintain the high relief the serra do mar catchments define a mean slope angle threshold indicating that landslides are the dominant erosional process when slope angles in excess of 30 tectonic activity is low and plays no significant role in driving erosion a first order relationship between erosion rate and precipitation temperature across the region implies that climate plays a key role in soil production river incision and in triggering erosional processes although the high topographic relief is a pre condition for the occurrence of significant erosion the climatic condition is the outlining factor of the regional variation in erosion rates

the influence of rifting on escarpment migration on high elevation passive continental margins 1 using numerical models that couple surface processes flexural isostasy faulting and the thermal effects of rifting we show that fault bounded escarpments created at rift flanks by mechanical unloading and flexural rebound have little potential to survive as retreating escarpments if the lower crust under the rift flank is substantially stretched in this configuration a drainage divide that persists through time appears landward of the initial escarpment in a position close to a secondary bulge that is created during the rifting event at a distance that depends on the flexural rigidity of the upper crust moreover the migration of the escarpment to the secondary bulge occurs when the pre rift topography dips landward otherwise the evolution of the escarpment is guided by the pre existing inland drainage divide to illustrate this new mechanism for the evolution of passive margins we study the examples of southeastern australia and southeastern brazil we propose that a pre existing inland drainage divide with rift related flank uplift can produce the double drainage divide observed in southeastern australia on the other hand we conclude that it is possible that the serra do mar escarpments on the southeastern brazilian margin originated as a secondary flexural bulge during rifting that persisted through time in both cases the retreating escarpment scenario is unlikely and the present day margin morphology can be explained as resulting from rift related vertical motions alone without requiring significant post rift rejuvenation

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

consolidation and break up of the south american platform in southeastern brazil tectonothermal and denudation histories the different tectonic stages that occurred at the end of the proterozoic and during the phanerozoic have an important bearing on the tectonothermal history of the south american platform and its consolidation geochronological data u pb monazite 40ar 39ar whole rock and apatite fission track analysis from precambrian rocks of the southeastern brazilian coastline permit the modeling of a long term thermal history of the crust and constrain variable denudation rates using these data a temperature time diagram reflects a period of accelerated exhumation during the end of the brasiliano orogeny followed by long stability and reactivation of the platform during the rifting phase of the south atlantic ocean u pb zircon and monazite blocking temperature of ca 650 c data from a series of igneous bodies suggest that a tangential and transpressional tectonic regime occurred between 625 and 610 ma during the following escape tectonics between 610 and 590 ma the exhumation process indicates cooling rates of ca 12 c ma 40ar 39ar biotite ages between 540 and 510 ma ca 300 c and a corrected fission track age on apatites 100 c of 480 ma indicate an exhumation event related to block tectonics with huge vertical displacement along shear zones a long stabilization phase with low exhumation and cooling rate around 0 25 c ma was recorded from the cambro ordovician to the mesozoic at 65 ma an acceleration of the exhumation through denudation and reworking of the south american surface with cooling rate of 1 5 c ma is observed the uplift of the mantiqueira and serra do mar mountain ranges along the southeast brazilian coastline works as a climatic barrier provoking lateral erosional processes causing long term scarp retreat combined with intense but progressive denudation towards the continent a denudation of 2 5 to 4 km was calculated for such processes this lateral retreat of escarpments and flexural response can provide important insights regarding marginal isostatic uplift and the evolution of offshore sedimentary basins of southeast brazil