control of pre rift lithospheric structure on the architecture and evolution of continental rifts insights from the main ethiopian rift east africa we investigate the along axis variations in architecture segmentation and evolution of the main ethiopian rift mer east africa and relate these characteristics to the regional geology lithospheric structure and surface processes we first illustrate significant along axis variations in basin architecture through analysis of simplified geological cross sections in different rift sectors we then integrate this information with a new analysis of ethiopian topography and hydrography to illustrate how rift architecture basin symmetry asymmetry is reflected in the margin topography and has been likely amplified by a positive feedback between tectonics flexural uplift and surface processes fluvial erosion unloading this analysis shows that 70 of the 500 km long mer is asymmetric with most of the asymmetric rift sectors being characterized by a master fault system on the eastern margin we finally relate rift architecture and segmentation to the regional geology and geophysical constraints on the lithosphere we provide strong evidence that rift architecture is controlled by the contrasting nature of the lithosphere beneath the homogeneous strong somalian plateau and the weaker more heterogeneous ethiopian plateau differences originating from the presence of pre rift zones of weakness on the ethiopian plateau and likely amplified by surface processes the data provided by this integrated analysis suggest that asymmetric rifts may directly progress to focused axial tectonic magmatic activity without transitioning into a symmetric rifting stage these observations have important implications for the asymmetry of continental rifts and conjugate passive margins worldwide

sub aerial denudation of passive margins regional elevation versus local relief models abstract variations in denudation rates which are an important factor in the modification of the sub aerial topography of passive margins have frequently been modelled as being proportionate to regional elevation to be valid this assumption requires that mean slope gradient and the related property of local relief show a strong positive relationship to regional elevation since slope angle is a primary determinant of denudation rate analysis of the relationships between these variables based on the 1 250 000 scale topographic map coverage of southern africa demonstrates that regional modal elevation explains only 0 5 of the variance in mean sine slope gradient and only 0 14 of the variance in local relief measured over 15 15 areas these results demonstrate that regional elevation cannot be used to predict denudation rates for passive margins such as those of southern africa where a dissected coastal zone is separated from a high interior plateau by a major escarpment on the basis of a previous regression analysis relating local relief to sediment and solute transport by rivers the data for southern africa indicate denudation rates of 80 m ma 1 over much of the coastal zone and 1 across most of the elevated interior extrapolation of these results over geological time however necessitates either assumptions about the local relief of palaeotopography or independent evidence of long term denudation rates

morphodynamic evolution of the orb river languedoc france evidence of eustatic tectonic and climatic controls this study aims to reconstruct the cenozoic and pleistocene morphodynamic evolution of the orb a mediterranean river which crosses all the structural units of the south massif central border a geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations and reconstructing the palaeodrainage heavy minerals were used to reconstruct the main sedimentary palaeochannels since the messinian the successive orb longitudinal profiles show anomalies which can be caused by structure and by interactions between fluvial dynamics and tectonics evidence of volcanic heavy minerals on the faugeres mountains and in the upper pliocene deposits of the languedocian piedmont demonstrates that a north south flow took place during the upper pliocene nevertheless a palaeo orb existed at the place of the present course when the basaltic lava flows were spreading but headward erosion did not reach them until the upper pleistocene because the orb middle and high terraces do not contain volcanic minerals sourced from the escandorgue the successive orb longitudinal profiles show that headward erosion due to pleistocene low sea levels does not reach beyond beziers and that a tectonic hinge has functioned near the shoreline the non lithologic knickpoints are explained by the montagne noire and avant monts uplift up until the pleistocene a progressive continental uplift is necessary to explain the orb terraces staircase in the beziers district and the fluctuations of incision from upstream to downstream are due to laterally differential movements which are isostatic effects of thick regressive deposits on the gulf of lion shelf during the cold periods copyright 2008 john wiley sons ltd

rates and possible causes of neotectonic vertical crustal movements of the emerged southeastern united states atlantic coastal plain emerged pliocene and pleistocene shorelines and associated marine deposits were used to determine the magnitude and rate of vertical crustal movement during the past 3 m y in the united states atlantic coastal plain of south and north carolina on the basis of a new regional ostracode assemblage zonation planktic biostratigraphic data and radiometric data emerged marine deposits were determined to be primarily interglacial and can tentatively be correlated with hemispheric warm intervals in evidence from deep sea data the paleontologic evidence indicates a primary glacio eustatic component to the local sea level record and a secondary tectonic component net vertical uplift rates averaging 1 to 3 cm 1 000 yr but perhaps as high as 5 to 10 cm 1 000 yr are in evidence for the emerged coastal plain although details of the timing of regional rheological events remain obscure the trend of net uplift contrasts with general subsidence rates of about 2 to 4 cm 1 000 yr since the cretaceous in submerged parts of the continental margin near subsiding sedimentary troughs hydro isostatic crustal response to multiple deglaciation events may have periodically uplifted the coast but long term lithospheric flexural upwarping in response to sediment loading offshore is a more plausible mechanism to explain the present positions of shorelines above present mean sea level a eustatic sea level model is proposed for interglacial high stands of the past 3 0 m y

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

geomorphically driven late cenozoic rock uplift in the sierra nevada california geologists have long accepted that the sierra nevada california experienced significant late cenozoic tectonically induced uplift a flexural isostatic model presented here shows however that a large fraction of the primary evidence for uplift could be generated by the lithospheric response to coupled erosion of the sierra nevada and deposition in the adjacent central valley and therefore requires less tectonic forcing than previously believed the sum of range wide erosion and the resultant isostatic rock uplift would have lowered sierra mean elevation by 200 to 1000 meters since 10 million years ago and could also have increased summit elevations during the current period of relief production

erosion rates in and around shenandoah national park virginia determined using analysis of cosmogenic 10be we use cosmogenic 10be analysis of fluvial sediments and bedrock to estimate erosion rates 104 105 year timescale and to infer the distribution of post orogenic geomorphic processes in the blue ridge province in and around shenandoah national park virginia our sampling plan was designed to investigate relationships between erosion rate and lithology mean basin slope basin area and sediment grain size fifty nine samples were collected from a variety of basin sizes inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3 0 to 21 m my the area weighted mean erosion rate for single lithology basins in the park is 12 2 m my single lithology erosion rate ranges for fluvial samples are granite 7 0 to 20 m my metabasalt 3 8 to 21 m my quartzite 3 8 to 15 m my and siliciclastic rocks 5 2 to 15 m my multilithology basins erode at rates between 3 0 16 m my the shenandoah river basin 3305 km2 is eroding at 6 6 m my bedrock erosion rates range from 1 8 to 11 m my across all lithologies with a mean of 6 5 4 3 m my grain size specific 10be analysis of four samples showed no consistent trend of concentration with grain size cosmogenic analysis of bedrock and sediment from the shenandoah national park area allows us to speculate about why some parts of the appalachian mountains erode more slowly and some more rapidly overall it appears that steep drainage basins erode more rapidly than gently sloped basins climate and lithology may also influence basin scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite and granite dominated basins data are conflicting in regards to the evolution of relief over time analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins susquehanna river shenandoah national park region or at similar rates great smoky mountains providing a mechanism for growing relief at the scale of individual ridgelines however considering relief on a landscape or physiographic province scale by comparing erosion rates of the highlands versus the lowlands suggests that relief of the range as a whole is either steady or very slowly decreasing over multi millennial timescales the presence of significant erosion rate slope relationships negates a broad hackian view of the landscape because there is not uniform erosion across this landscape the aspect erosion rate and slope erosion rate relationships present in the shenandoah area suggest that the landscape is not fully adjusted to rock strength

on isostasy at atlantic type continental margins cross spectral techniques have been used to analyze the relationship between free air gravity anomalies and topography of approximately 100 profiles over the continental margins of eastern north america southwest africa and the coral sea lord howe rise the resulting admittance functions for these margins have been interpreted in terms of the flexure model of isostasy the relatively young coral sea lord howe rise margin is associated with the lowest value of the effective elastic thickness te 5 km while the relatively old eastern north american margin is associated with the highest value 10 te 20 km thus te appears to increase with the age of the margin these results which are consistent with flexure studies from the major ocean basins have been interpreted in terms of a simple model in which the flexural strength of the lithosphere increases with age the model suggests that a low rigidity plate or airy type model is most applicable early in rifting history while a high rigidity plate is more applicable later in margin evolution thus sediments at a margin initially load a relatively thin and hot plate while sediments later in margin evolution load a relatively thick and cold plate the model explains a number of features of the tectonic stratigraphic evolution of margins these include a change in flexural style from a narrow and deep basin to a broad and shallow basin coastal plain onlap and uplift in the continental interior furthermore the flexure model of isostasy contributes in a major way to observed free air gravity anomalies at continental margins in particular the model explains the existance of airy isostatic gravity anomalies at margins the amplitude and wavelength of these anomalies are a function of the sediment supply the type of mechanisms controlling sediment deposition up building and or out building and the thermal structure history and age of the margin

appalachian piedmont landscapes from the permian to the holocene abstract between the potomac and susquehanna rivers and from the blue ridge to the fall zone landscapes of the piedmont are illustrated for times in the holocene late wisconsin early miocene early cretaceous late triassic and permian landscape evolution took place in tectonic settings marked by major plate collisions permian arching and rifting late triassic and development of the atlantic passive margin by sea floor spreading early cretaceous erosion proceeded concurrently with tectonic uplift and continued after cessation of major tectonic activity atlantic outer continental shelf sediments record three major erosional periods 1 late triassic early jurassic 2 late jurassic early cretaceous and 3 middle miocene holocene the middle miocene holocene pulse is related to neotectonic activity and major climatic fluctuations in the piedmont upland the holocene landscape is interpreted as an upland surface of low relief undergoing dissection major rivers and streams are incised into a landscape on which the landforms show a delicate adjustment to rock lithologies the fall zone has apparently evolved from a combination of warping faulting and differential erosion since late miocene the periglacial environment of the late wisconsin and earlier glacial epochs resulted in increased physical erosion and reduced chemical weathering even with lowered saprolitization rates geochemical modeling suggests that 80 m or more of saprolite may have formed since late miocene this volume of saprolite suggests major erosion of upland surfaces and seemingly contradicts available field evidence greatly subdued relief characterized the early miocene time near the end of a prolonged interval of tropical morphogenesis the ancestral susquehanna and potomac rivers occupied approximately their present locations in early cretaceous time local relief may have been as much as 900 m and a major axial river draining both the piedmont and appalachians flowed southeast past baltimore the late triassic landscape was influenced by rift basin development streams drained into a hydrologically closed basin no through flowing rivers seem to have been present a limestone escarpment along the blue ridge may have existed as a consequence of a semi arid climate the permian may have been a time of himalayan like mountains and mountain glaciers streams and glaciers generally flowed southwest and west

isostatic uplift driven by karstification and sea level oscillation modeling landscape evolution in north florida isostatic uplift of tectonically stable passive margin lithosphere can preserve a record of paleo shoreline position by elevating coastal geomorphic features above the influence of nearshore wave activity conversely depositional ages and modern elevations of these features can provide valuable information about the uplift history of a region we present a numerical model that combines sea level oscillation subaerial exposure a precipitation karstification function and isostatic uplift to explore the dynamic geomorphic behavior of coastal carbonate landscapes over multiple sea level cycles the model is used to estimate ages of coastal highstand depositional features along the atlantic coast of north florida numerical simulations using current best estimates for pleistocene sea level and precipitation histories suggest ages for trail ridge 1 44 ma the penholoway terrace 408 ka and the talbot terrace 120 ka that are in agreement with fossil evidence in addition model results indicate that the rate of karstification void space creation or equivalent surface lowering rate within the north florida platform is 3 5 times that of previous estimates 1 m 11 2 k y vs 1 m 38 k y and uplift rate is 2 times as high as previously thought 0 047 mm yr vs 0 024 mm yr this process has implications for landscape evolution in other carbonate settings and may play an underappreciated role within the global carbon cycle

regolith residence time and the concept of surface age of the piedmont peneplain the common upland weathering profile on foliated metamorphic rocks on the appalachian piedmont between alabama and maryland includes a 50 cm 1 m thick clay rich soil b horizon over 10 20 m of saprolite the saprolite retains the volume fabric and structure of the underlying parent rock but has lost about one third of the mass of the parent rock where the saprolite is thickest beneath upland drainage divides those divides are of loow slope and relief the flatness of the piedmont drainage divides provides the appearance of a planation surface of accordant summits or peneplain i interpret this flatness to be the result of three active processes volume reduction during compaction of saprolite into soil loss of mass in dissolved solids draining the soil b horizon and loss of mass from the soil surface by erosion of clay size particles the cumulative effects of these upland processes are to convert saprolite into soil to limit soil thickness and residence time and to limit the age of the oldest residual soils on the surface this results in a continual lowering of the piedmont peneplain surface this interpretation is corroborated by evidence of topographic inversion of fluvial gravels since the miocene near the fall line study of baseflow dissolved solids draining piedmont basins indicates a minimum rate of saprolite production of about 4 m ma 1 this minimum rate of production near the fall line is less than the estimated rate of surface lowering and saprolite consumption during the late tertiary and quaternary periods of topographic inversion measurement of cosmogenic 10be inventories in two 15 20 mores of piedmont upland regolith indicate a minimum residence time of residual soil and saprolite of about 1 ma this indicates a possible maximum rate of saprolite production and erosion of about 20 m ma 1 using the best available evidence therefore the typical piedmont upland regolith has a residence time of between 1 and 5 ma residence times may not be the same everywhere and ages may vary systematically across the surface the geomorphic evidence of topographic inversion and similar regolith profiles in other humid temperate and tropical regions strongly suggests that production and removal of piedmont saprolite has been an ongoing quaternary process and that most of the piedmont regolith is significantly younger than 5 ma independent geophysical evidence suggests that the rate of uplift probably involving tilting of parts of the piedmont blue ridge and valley and ridge has averaged between 5 and 20 m ma 1 through the cenozoic

scale dependence of lithological control on topography bedrock channel geometry and catchment morphometry in western scotland abstract we propose that a scale dependent topographic signature of erodibility arises due to fluvial and glacial erosion acting on different parts of the landscape at different times for 14 catchments in western scotland we define three levels of substrate erodibility in order of decreasing resistance quartzite rocks nonquartzite rocks and zones of fault related fracture then using digital topographic and planimetric data coupled with field measurements we identify regression based scaling relationships between substrate erodibility and morphometric parameters at two spatial scales catchment scale morphometry shows a weak to variable relationship with substrate metrics overall erodibility can be inferred from catchment steepness indices i e channel steepness index and relief ratio but the existence of multiple exceptions could confound a more general application of this approach nonetheless major valley troughs trace fault zones and nonquartzite rocks leaving much of the higher and stee

post alleghanian unroofing history of the appalachian basin pennsylvania from apatite fission track analysis and thermal models results of apatite fission track analyses on 29 ordovician through permian sandstones from the appalachian basin in pennsylvania are presented ages range from 111 17 to 184 10 ma mean track lengths of 10 71 0 29 to 13 10 0 17 m with unimodal negatively skewed length distributions are indicative of slow cooling the data separate into two groups on an age versus mean length plot the younger group 111 144 ma is found in the structural depressions of the anthracite basin and the broad top basin and adjacent appalachian plateau the older group 144 184 ma is found in the structurally higher southwestern appalachian plateau and juniata culmination and adjacent central plateau fission track data suggest that the basin cooled slowly after the alleghanian orogeny with culminations cooling earlier than depressions cooling histories modeled from apatite fission track data with maximum temperatures constrained by vitrinite reflectance indicate cooling beginning soon after the alleghanian orogeny except in the juniata culmination which apparently experienced synorogenic cooling and unroofing during formation of the underlying duplex model cooling histories and available geologic information indicate that the foreland basin did not experience mesozoic reheating unroofing histories were modeled from fission track cooling histories using heat flow estimates and burial depths derived from vitrinite reflectance profiles the models suggest that the unroofing history of the appalachian basin in pennsylvania can be divided into three episodes an initial episode of relatively rapid cooling and unroofing late permian early jurassic is attributed to flexural rebound of the foreland in response to erosional removal of alleghanian topographic load initial unroofing rates are higher in eastern pennsylvania than in the west consistent with a flexural model an episode of little to no unroofing middle jurassic late oligocene began contemporaneously with the inception of drift at the atlantic continental margin at this time unloading of the orogen was replaced by subsidence and sedimentation on the new margin without flexural rebound the driving force for unroofing of the basin was removed and unroofing slowed greatly an episode of rapid unroofing over the full width of the basin occurred from the miocene to the present although the driving mechanism for unroofing at this time has not been identified it is consistent with increased sedimentation rates in the middle atlantic offshore basins for the same period

fluvial architecture and dynamics in rising mountain chains and related basins tectonic climatic influence and human impact the flag seqs fluvial archive group subcommission for european quaternary stratigraphy siena meeting

stratigraphy petrography and correlation of late cenozoic middle atlantic coastal plain deposits implications for late stage passive margin geologic evolution regional chronostratigraphic correlation of middle atlantic upper coastal plain and fall zone fluvial deposits long thought to represent the updip proximal facies of a well dated post oligocene marine sequence in the salisbury embayment remains incomplete in part because of the paucity of biostratigraphic data petrography based lithostratigraphic correlations provide an opportunity to extend age control present in downdip marine deposits updip to fluvial deposits thus establishing the means for a regional chronostratigraphic correlation previous stratigraphic studies in new jersey delmarva southern maryland virginia and the central appalachian piedmont are linked by a crucial sequence of fluvial deposits at the head of chesapeake bay here petrography based lithostratigraphic correlations demonstrate 1 late oligocene late miocene susquehanna river dominated polygenetic quartzose fluvial aggradation bryn mawr formation 2 pliocene heterolithic but quartz dominated fluvial terrace and alluvial fan deposition perryville formation 3 pliocene early pleistocene paleo delaware hudson river dominated lithic and feldspathic rich fluvial aggradation pensauken formation and 4 the initiation of estuarine conditions turkey point beds by early pleistocene time these results are synthesized to propose a new late cenozoic regional chronostratigraphic correlation and depositional history for the salisbury embayment the correlation elucidates a complex interaction between passive margin isostasy tectonics eustasy and sediment source

quaternary fluvial history of the delaware river new jersey and pennsylvania usa the effects of glaciation glacioisostasy and eustasy on a proglacial river system abstract fluvial glacial and estuarine deposits in the delaware valley record the response of the delaware river to glaciation sea level change and glacioisostasy during the quaternary incision following an early pleistocene glaciation created the present valley which is inset into a pliocene strath and fluvial plain middle and upper pleistocene and holocene deposits were laid down in this inset valley estuarine terraces in the lower valley and bayshore at 20 m probably marine isotope stage mis 11 8 m mis 5e and 3 m mis 5a or c and a fluvial deposit that correlates to offshore mis 3 marine deposits at 20 m are at elevations consistent with glacioisostatic models successive incisions during lowstands in the middle and late pleistocene lengthened deepened and narrowed the channel in the lower valley and shifted the channel westward in delaware bay during mis 2 glaciation from 25 to 18 ka the delaware was diverted to the hudson shelf valley by glacioisostatic tilting most glacial sediment was trapped in fluvial lacustrine valley fills north of the terminal moraine incision of the valley fill was accomplished during the early stage of rebound between 17 and 12 ka drainage to the delaware shelf was restored between 15 and 13 ka as the forebulge collapsed during incision multiple postglacial terraces formed where the valley was perpendicular to rebound contours and so was steepened and elevated northward and a single terrace formed where the valley paralleled the contours and there was no differential elevation or steepening about 65 of the original volume of mis 2 glacial sediment remains in the main valley and most of the eroded volume is in the channel in the lower valley beneath holocene estuarine fill little glacial sediment reached the delaware or hudson shelf overbank deposition on the lower postglacial terrace and modern floodplain spans the holocene the volume of holocene sediment in the estuary and bay yields a basinwide denudation rate of about 20 m my

deciphering continental breakup in eastern australia using low temperature thermochronometers 1 first order topographical features at high elevation passive margins have the potential to store information about the early stages of continental rifting which are usually lost in the sediment record in this study we present a new combination of apatite fission track and u th he analyses from two coast perpendicular traverses to decipher the time of formation and evolution of the escarpment at the southeastern australian margin a combination of inverse and forward modeling of the apatite fission track aft and he data indicates that the coast experienced a rapid denudational event starting at 110 10 ma at least 15 myr before seafloor spreading 85 ma in agreement with the hypothesis that rifting at magma poor margins evolves slowly thus the enhanced denudation is not related to the synbreakup base level drop but it may have been related to a thermally driven transient surface uplift considerations on isostatic flexure and rigidity of the lithosphere indicate that unless significant synrift brittle movements are assumed to have occurred along margin parallel faults that are no more visible the coast must have experienced a higher geothermal gradient than normal the evolution of the rest of the coastal plain may have taken up to 90 myr in agreement with numerical models of passive margins evolution the u th he ages across the coastal plain are consistent with an in place excavation scenario of a high rift shoulder and they rule out the possibility of a constant retreat of the escarpment aft he data from the plateau indicate that the highlands remained stable throughout continental breakup experiencing rates of erosion of 5 10 m myr since at least 200 ma

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

mid pliocene shorelines of the us atlantic coastal plain an improved elevation database with comparison to earth model predictions abstract for nearly a century the atlantic coastal plain acp of the united states has been the focus of studies investigating pliocene and pleistocene shorelines however the mapping of paleoshorelines was primarily done by using elevation contours on topographic maps here we review published geologic maps and compare them to paleoshoreline locations obtained through geomorphometric classification and satellite data we furthermore present the results of an extensive field campaign that measured the mid pliocene 3 3 2 9 ma shorelines of the atlantic coastal plain using high accuracy gps and digital elevation models we compare our new dataset to positions and elevations extracted from published maps and find that the extracted site information from earlier studies is prone to significant error both in the location and more severely in the elevation of the paleoshoreline we also investigate using geophysical modeling the origin of post depositional displacement of the shoreline from georgia to virginia in particular we correct the elevation of our shoreline for glacial isostatic adjustment gia and then compare the corrected elevation to predictions of mantle flow induced dynamic topography dt while a subset of these models does reconcile the general trends in the observed elevation of the mid pliocene shoreline local discrepancies persist these discrepancies suggests that either i the dt and gia models presented here do not capture the full range of uncertainty in the input parameters and or ii other influences such as sediment loading and unloading or local fault driven tectonics may have contributed to post depositional deformation of the mid pliocene shoreline that are not captured in the above models in this context our field measurements represent an important observational dataset with which to compare future generations of geodynamic models improvements in models for dt gia and other relevant processes together with an expanded geographically distributed set of shoreline records will ultimately be the key to obtaining more accurate estimates of eustatic sea level not only in the mid pliocene but also earlier in the cenozoic

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

fluvial terraces of the lower susquehanna river abstract fluvial terraces of the lower susquehanna river offer a unique opportunity to investigate the late stage geologic and geomorphic evolution of the u s atlantic passive margin petrography and elevation distinguish and provide a basis for correlation of two groups of terraces the upland terraces and lower terraces through the piedmont newark basin and great valley downstream correlation to dated upper coastal plain and fall zone fluvial deposits relative weathering and soil profile development characteristics establish terrace age upland terraces tg1 tg2 and tg3 middle to late miocene strath terraces 80 to 140 m above the present channel occur only along the piedmont reach they are underlain by unstratified texturally mature quartz dominated roundstone diamictons lower terraces qtg qt1 qt6 pliocene and pleistocene strath and thin aggradational terraces within 45 m of the present channel are underlain by stratified and unstratified texturally and compositionally immature sand gravel and pebbly silt terrace age and longitudinal profiles suggest complex interactions among relative base level long term flexural isostatic processes climate and river grade our model for terrace genesis requires the susquehanna river to attain and maintain a characteristics graded longitudinal profile over graded time for the u s atlantic margin we propose that straths are continually cut along this graded profile during periods of relative base level stability achieved by slow steady isostatic continental uplift acting in concert with eustatic rise change in an external modulating factor such as eustatic fall or climate change results in fluvial incision and subsequent genesis of strath terraces longitudinal profiles of lower susquehanna river terraces which converge at the river mouth diverge through the piedmont and reconverge north of the piedmont contrast with their hypothesized original concave up profiles progressive and cumulative flexural upwarping of the atlantic margin accounts for terrace profile deformation suggesting flexural isostasy as a first order regional deformation mechanism these results offer new interpretations of terrace age correlation and geologic significance that require modification of previous studies suggesting uplifted or anticlinically warped peneplains on the u s atlantic margin

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

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

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

geomorphic and tectonic forcing of late cenozoic warping of the colorado piedmont late cenozoic warping of the colorado piedmont involved interplay of tectonic forcing river erosion and isostatic response to erosion modeled erosional isostasy closely replicates the observed pattern of deformation but accounts for only about half its magnitude the remainder reflects tectonic rock uplift that increases southward across the piedmont likely reflecting proximity to the northward propagating rio grande rift this differential uplift triggered differential erosion concentrated on southern piedmont river systems particularly the arkansas river which led in turn to differential isostatic rock uplift focused on the arkansas drainage covariation of tectonic uplift erosion and isostatic compensation across the piedmont reflects a positive feedback between uplift induced erosion and erosion induced isostasy which has progressed to the point that isostatic uplift is approximately equal to the initial tectonic forcing

climatic impact on isovolumetric weathering of a coarse grained schist in the northern piedmont province of the central atlantic states the possible impact of periglacial climates on the rate of chemical weathering of a coarse grained plagioclase muscovite quartz schist has been determined for a small watershed near baltimore maryland the isovolumetric chemical weathering model formulated from the geochemical mass balance study of the watershed shows that the weathering front advances at a velocity of 9 1 m m y if the modern environmental parameters remain the same back through time however recent surficial geological mapping demonstrates that periglacial climates have impacted the area such an impact significantly affects two key chemical weathering parameters the concentration of co2 in the soil and groundwater moving past the weathering front depending upon the assumptions used in the model the rate of saprolitization varies from 2 2 to 5 3 m m y the possible impact of periglacial processes suggested by the chemical weathering rates indicates a need to reconsider theories of landscape evolution as they apply to the northern piedmont province of the mid atlantic states i suggest that from the late miocene to the present that the major rivers have become incised in their present locations this incision has enhanced groundwater circulation and chemical weathering such that crystalline rocks beneath interfluvial areas remain mantled by saprolite and the saprolite mantle has been partially stripped as periglacial conditions alternate with humid temperate conditions

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

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

neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates abstract the persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution in the eastern north american appalachians this question is manifest in the outstanding problem of whether topographic relief is in a quasi equilibrium state decaying slowly over many millennia or whether relief has increased during the late cenozoic here we present quantitative geomorphic data from the nonglaciated portion of the susquehanna river drainage basin that provide insight into these end member models analysis of channel profiles draining upland catchments in the northern valley and ridge appalachian plateau blue ridge and piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300 600 m elevation but not systematically associated with transitions from weak to resistant substrate cosmogenic 10 be inventories of modern stream sediment indicate that erosion rates are spatially variable ranging from 5 30 m myr above knickpoints to 50 100 m myr below knickpoints overall channel gradients normalized for drainage area scale linearly with catchment averaged erosion rates collectively regionally consistent spatial relationships among erosion rate channel steepness and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with 100 150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization channel response timescales imply that the onset of relative base level change predates 3 5 ma and may have begun as early as 15 ma we suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of north america during the neogene

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

testing eustatic curves based on baltimore canyon neogene stratigraphy an example application of basin fill simulation basin fill simulation techniques provide scientists in both research and exploration with an important new tool the researcher obtains a tool for investigating the interaction of the major controls on basin scale stratigraphy subsidence sediment supply and eustasy the explorationist gains a tool for better understanding the hydrocarbon potential of an area through integrating data from various sources and testing an interpretation for spatial and temporal consistency as a result a researcher or explorationist may be able to refine a basin interpretation to a degree that might not have been possible if he or she had considered only a present day rendering of the basin basin modeling can be divided into three major categories structural stratigraphic and rock fluid properties evolution structural and stratigraphic modeling can be conducted back through time using backstripping techniques all three types of modeling can be conducted forward through time using simulation techniques several modeling systems combine backstripping procedures to obtain basin geometries with forward simulation to predict rock and fluid properties each category of basin modeling has its advantages and limitations when used together these techniques complement one another in this paper we illustrate the benefits of combining stratigraphic modeling techniques by presenting a research oriented case study involving the neogene sediments of the baltimore canyon trough offshore new jersey we designed this case study to evaluate several published sea level curves stratigraphic backstripping and simulation techniques were used to model a dip oriented cross section for which present day stratigraphy is well documented each sea level curve was used in a separate modeling run comparing presently accepted and modeled stratigraphic patterns allowed us to draw conclusions about the different eustatic curves in the final section we present several ways in which basin fill simulation can address exploration problems

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

long term average mineral weathering rates from watershed geochemical mass balance methods using mineral modal abundances to solve more equations in more unknowns abstract the number of phases for which weathering rates can be determined by watershed geochemical mass balance is limited by the number of equations that can be constructed from elemental flux losses from the watershed and mineral stoichiometries mass balance studies of watershed weathering rates routinely use the flux losses of the six major cations sio 2 al na k mg and ca analyses of these species in water are common but following matrix algebraic methods limits the number of weathering rates that can be calculated to six for the brubaker run watershed located in the northern piedmont physiographic province of pennsylvania usa long term 10 3 10 6 year watershed chemical flux losses have been determined using 10 be derived total denudation rates and zirconium normalized total chemical concentrations from bedrock and soils chemical flux losses calculated from solid phase data have three advantages they 1 permit generation of a relatively large number of equations because both major and trace analyses are included 2 eliminate the need for many years of regular e g weekly sampling and chemical analyses of stream water and atmospheric precipitation and measurement of hydrologic parameters i e precipitation stream discharge etc and 3 long term weathering rate calculations need not address biomass for brubaker run eight minerals are involved in weathering the five primary minerals are ree rich epidote ankerite almandine spessartine garnet muscovite chlorite and the three secondary products are weathered muscovite kaolinite and gibbsite the long term average weathering rates of these minerals were calculated using the six major cations and two trace elements selected from rb sr ba la pr nd sm gd and dy despite having the eight equations needed geochemically reasonable weathering rates e g positive primary mineral rates that reflect destruction could not be achieved regardless of the two trace elements used in the mass balance calculations for brubaker run this is primarily attributable to the natural heterogeneity of the trace element concentrations within the host mineral grains with trace element stoichiometries in some minerals varying by as much as an order of magnitude because the trace elements are hosted by a relatively small number of minerals the computed weathering rates of other minerals become very sensitive to small variations in trace cation stoichiometry ree rich epidote garnet and ankerite within the brubaker run watershed together host nearly all of the ca in the bedrock and completely dissolve at or near the weathering front consequently approximately all of the ca in bedrock is lost from the regolith in bedrock the mole percentages of ca hosted by ree rich epidote garnet and ankerite are 49 mol 4 mol and 43 mol respectively and are determined by the modal abundance of the mineral in the bedrock and its ca stoichiometry the weathering rates of ree rich epidote garnet and ankerite can be determined by distributing to each mineral that fraction of the total watershed ca flux loss for which it is responsible based on its mole percent ca in bedrock by using a base cation that is completely lost from the regolith and knowing the mole percentage of that element in the mineral s undergoing weathering additional equations may be added to the mass balance matrix we term this technique the flux distribution method the flux distribution method eliminates the need for additional equations established using trace elements based on the mineral weathering rates for the brubaker run watershed determined using the flux distribution method the rates at which the weathering front penetrated the bedrock the saprolitization rate are 4 5 m myr 1 and 6 5 m myr 1 for chlorite and muscovite respectively these measured long term average saprolitization rates compare very favorably with published theoretical values for the nearby northern maryland piedmont which range from 2 2 to 5 3 m myr 1

tectonic and climatic controls on rift escarpments erosion and flexural rebound of the dhofar passive margin gulf of aden oman we investigate the respective roles of climatic parameters and the flexural rigidity of the lithosphere in the erosion history and behavior of two adjacent rift escarpments along the northern coast of the gulf of aden in oman at this 25 myr old passive margin we define a type 1 scarp which is high sharp crested and has retreated 25 30 km inland from its master fault and a type 2 scarp which exhibits a more rounded profile lower relief and still coincides with its mapped normal fault trace since about 15 ma the margin has been seasonally affected by monsoon precipitation but with contrasting effects at the type 1 and type 2 escarpments depending on the position of the intertropical convergence zone in the geologic past during peak monsoon conditions both scarps experienced heavy rainfall and runoff whereas during monsoon starved conditions such as today the type 2 scarp experienced a foggy moist climate while the type 1 scarp remained much drier in order to assess the relative effects of climate and flexural parameters on the present day morphology of the dhofar margin we present onedimensional numerical models of erosion and flexure along two profiles representative of the type 1 and type 2 scarps unlike most surface process models previously published where present day topography is the only criterion by which to evaluate the quality of model outputs model behavior here is additionally constrained by independent estimates of denudation provided by geological cross sections well defined fault traces and other stratigraphic markers the best fitting models indicate that the type 1 escarpment formed under relatively arid climatic conditions and was affected by significant erosion recession and flexural uplift due to a low 7 km effective elastic thickness in contrast the morphology of the type 2 fault scarp was smoothed by a more humid climate but a high effective elastic thickness 15 km prevented it from uplifting or receding in addition we show that the sedimentary load acting at the foot of the escarpments exerts significant influence on their morphological evolution though this parameter is often neglected in other scarp evolution models

palynology of the bryn mawr formation miocene insights on the age and genesis of middle atlantic margin fluvial deposits abstract the ages of fluvial deposits at the head of chesapeake bay thought to be the updip chronostratigraphic equivalents of a well dated late oligocene to quaternary marine sequence in the salisbury embayment are poorly known we present data regarding a new occurrence of a palynoflora recovered from the bryn mawr formation in cecil county maryland the floral assemblage for the bryn mawr formation includes at least 40 taxa at the generic level where quercus cupuliferae ilex carya taxodium and pinus are important elements most of the taxa identified from the bryn mawr formation palynoflora are extant and occur within the modern middle atlantic coastal plain however several important taxa such as alangium engelhardia sciadopitys tricolporopollenites sp and cupuliferoidaepollenites sp are at present either extinct or exotic to the middle atlantic coastal plain comparison of the bryn mawr formation palynoflora to well dated marine deposits of the salisbury embayment suggests a late middle to early late miocene age late serravallian early tortonian for bryn mawr formation phase 2 deposition supporting previously proposed genetic links to the marine deposits of the choptank formation in the subsurface of the delmarva peninsula relative abundances of common extant taxa such as quercus carya pinus and nap the total non arboreal pollen vary considerably throughout late cenozoic deposits of the middle atlantic coastal plain we present data for common extant taxa in a ternary diagram to define discrete palynofacies that discriminate among middle miocene late miocene pliocene and pleistocene palynofloras these results show that relative abunances of common easily identifiable extant pollen may be as diagnostic as exotic taxa in assigning ages to middle atlantic coastal plain deposits the bryn mawr formation palynoflora like other middle to late miocene palynofloras of the middle atlantic coastal plain suggests terrestrial climatic cooling in the larger temporal scale of climate change throughout the cenozoic this change in miocene climate is one of three major events that may have had a significant impact on the rate of sediment yield from the appalachians as recorded in the volume of offshore basin sediments

glacial interglacial variation in denudation rates from interior texas usa established with cosmogenic nuclides abstract the brazos colorado and trinity rivers of texas drain a tectonically quiescent non glaciated and low relief landscape inland from the gulf of mexico where long term 10 3 10 5 a changes in denudation rates are probably driven largely by climate change here we use cosmogenic 10be to obtain spatially averaged denudation rates for these river catchments primarily from terrace deposits associated with glacial or interglacial intervals over the past half million years the denudation rates are 30 35 higher during interglacial periods than during glacial periods and correlate broadly with temperature the results are consistent with predictions from the bqart sediment flux model and support the hypothesis that increased weathering rates associated with warmer climates will accelerate landscape erosion furthermore by analyzing 26al 10be in these deposits we can estimate the bed load sourced from up catchment surfaces the stored coastal plain fraction varies from 10 to 30 and is greater during times of relatively lower sea level the results indicate that although sediment flux is moderated by coastal plain storage increased up catchment flux during warmer interglacial periods outpaces evacuation of stored sediment during glacial periods resulting in a net increase in sediment flux to the ocean during warm intervals if this temperature sediment flux relationship is valid beyond the plio pleistocene transition then global sediment flux to the ocean from passive non glaciated and low relief landscapes would have been greater during the pliocene than in the cooler quaternary

ancient channels of the susquehanna river beneath chesapeake bay and the delmarva peninsula three generations of the ancestral susquehanna river system have been mapped beneath chesapeake bay and the southern delmarva peninsula closely spaced seismic reflection profiles in the bay and boreholes in the bay and on the southern delmarva peninsula allow detailed reconstruction of each paleochannel system the channel systems were formed during glacial low sea level stands and each contains a channel fill sequence that records the subsequent transgression the trunk channels of each system are 2 to 4 km wide and are incised 30 to 50 m into underlying strata they have irregular longitudinal profiles and very low gradients within the chesapeake bay area the three main stem channels diverge from the head of the bay toward the southeast the channels are rarely coincident although they commonly intersect all three main channels pass beneath the southern delmarva peninsula forming an age progression from north oldest to south youngest beneath the peninsula and from east oldest to west youngest beneath chesapeake bay southward progradation of the tip of the delmarva peninsula during interglacial high sea level stands caused southward migration of the mouth of the bay so that the next generation of channels were incised progressively further towards the southwest the youngest paleochannel is clearly of late wisconsinan age about 18 ka and the intermediate one appears to be late illinoian in age or about 150 ka the age of the oldest paleochannel is not well constrained but it is in the range of about 200 to 400 ka the three paleochannel systems imply a dynamic coastal plain environment and at least two previous generations of the chesapeake bay both the chesapeake bay and the southern delmarva peninsula have changed considerably in the past half million years

regional analysis of bedrock stream long profiles evaluation of hack s sl form and formulation and assessment of an alternative the ds form the equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones and in continental margin and other intraplate settings as well as other base level changes such as due to sealevel fluctuations the hack sl form of the long profile which describes a straight line on a log normal plot of elevation normal versus distance logarithmic is the equilibrium long profile form that has been most widely used in such studies slope area analysis has also been used in recent years we show that the sl form is a special case of a more general form of the equilibrium long profile here called the ds form that can be derived from the power relationship between stream discharge and downstream distance and the dependence of stream incision on stream power the ds form provides a better fit than the sl form to river long profiles in an intraplate setting in southeastern australia experiencing low rates of denudation and mild surface uplift we conclude that if an a priori form of the long profile is to be used for investigations of regional landscape history the ds form is preferable in particular the ds form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance parallel shift in the ds plot to be distinguished from disequilibrium steepening due to long profile rejuvenation disordered outliers on the ds plot slope area analysis and the slope distance ds approach outlined here are complementary approaches reflecting the close relationship between downstream distance and downstream catchment area copyright 2006 john wiley sons ltd

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

a new active tectonic model for the construction of the northern apennines mountain front near bologna italy 1 we integrate existing and new geologic data retreating trench extension and accretion tectonics retreat project particularly on the origin growth and activity of the mountain front at bologna italy into a new model that explains apennine orogenesis in the context of a slab rollback upper plate retreat process the bologna mountain front is an actively growing structure driving rock uplift 1 mm year cored by a midcrustal flat ramp structure that accommodates ongoing shortening driven by adria subduction at a rate of 2 5 mm year the data we use are assembled from river terraces and associated pleistocene growth strata geodesy including releveling surveys reinterpretation of published reflection lines and a new high resolution reflection line these data constrain a simple trishear model that inverts for blind thrust ramp depth dip and slip apennine extension is recognized both in the foreland as high angle normal faults and modest stretching in the carapace of the growing mountain front and in the hinterland with larger normal faults that accomplish some crustal thinning as the upper plate retreats this coevolution of extension and shortening shares some notable characteristics with other basement involved collisional orogens including the early tertiary laramide orogeny in the american west and the oligocene to miocene evolution of the alps we propose a possible relationship between underplating and the development of the po as a sag basin as a quaternary phenomenon that may also apply to past periods of apennine deformation tortonian continued shortening on the structure beneath the bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern apennines

postrift history of the eastern central atlantic passive margin insights from the saharan region of south morocco the passive margin of south morocco is a low elevated passive margin it constitutes one of the oldest margins of the atlantic ocean with an early jurassic breakup and little geological data are available concerning its postrift reactivation so far we investigated the postrift thermal history of the onshore part of the margin with low temperature thermochronology on apatite crystals fission track and u th sm he ages we obtained are significantly younger than the breakup 190 ma fission track ages range from 107 8 to 175 16 ma with mean track lengths from 10 7 0 3 to 12 5 0 2 m u th sm he ages range from 14 1 to 185 15 ma using inverse modeling of low temperature thermochronological data we demonstrate that the south moroccan continental margin underwent a complex postrift history with at least two burial and exhumation phases the first exhumation event occurred during late jurassic early cretaceous and we attribute this to mantle dynamics rather than to intrinsic rifting related processes such as flexural rebound the second event from late cretaceous to early paleogene might record the onset of africa europe convergence we show a remarkably common behavior of the whole moroccan passive margin during its early postrift evolution the present day differences result from a segmentation of the margin domains due to the africa europe convergence finally we propose that varying retained strengths during rifting and also the specific crustal lithospheric geometry of stretching explain the difference between the topographical expressions on the continental african margin compared to its american counterpart

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

river terrace sequences templates for quaternary geochronology and marine terrestrial correlation fluvial sequences particularly terrace staircases represent archives of quaternary palaeoclimatic fluctuation and can serve as stratigraphical frameworks for geochronology and for correlation with other depositional environments in particular the global marine oxygen isotope record fluvial lithostratigraphical frameworks also provide contexts for records from fossils and artefacts of faunal evolution and human occupation conversely both records can be means of relative dating of riverine sequences three fluvial sequences are examined as case studies first is the severn avon system in the english midlands which has biostratgraphical evidence and an amino acid geochronology together with marker inputs from three different glaciations the somme sequence of northern france famous for its palaeolithic artefact assemblages again has biostratigraphy and an amino acid geochronology and has also been dated with reference to overlying loess palaeosols sequences the fluvial terraces of the river arun the final case study lack dating evidence but are interspersed within the sussex raised beach staircase although various lines of evidence suggest that the rivers discussed have formed terraces in response to climatic fluctuation an intriguing difference is that interglacial sediments occur at the bases of terrace formations in the severn avon whereas in the somme they occur at the tops of sequences beneath loessic overburden

rates and patterns of late cenozoic denudation in the northernmost atlantic coastal plain and piedmont topography of a 2800 km 2 section of the u s atlantic coastal plain and piedmont is reconstructed at five times from the late miocene to the holocene the reconstructions are based on mapping of fluvial colluvial and marginal marine deposits that are dated by radiocarbon palynostratigraphy and correlation to adjacent glacial and marine units denudation rates and patterns are calculated by subtracting successive topographies with 60 m horizontal resolution and 6 m vertical resolution the overall late miocene to holocene denudation rate of 10 m m y is similar to other estimates of long term denudation in the region the overall rate resolves spatially into a wide range of local rates varying from a minimum of 0 2 m m y on residual uplands to as high as 600 m m y in glacially rerouted stream channels the distribution of local rates shows that denudation is accomplished by stream incision in response to long term glacio eustatic decline followed by slope retreat into residual uplands from the incised channels slope retreat replaces the uplands with pediments and straths pediment landforms and sediments and observation of modern scarps and valley heads indicate that groundwater seepage from the base of residual uplands is an important mechanism of slope retreat this process is self limiting because as the volume of residual upland is reduced seepage diminishes and slope retreat slows until small residuals undergo little or no further reduction thus relict topography is preserved even as most of the landscape actively erodes

high eustatic sea level during the middle pliocene evidence from the southeastern u s atlantic coastal plain the middle pliocene approximately 3 5 2 5 ma was a period of global warmth preceding the growth of major northern hemisphere ice sheets the authors report on eustatic sea level for the middle pliocene based on microspaleontologic study of marine deposits of the duplin formation of south carolina and north carolina the duplin was deposited during a middle pliocene marine transgression that formed the orangeburg scarp a prominent wave cut geomorphic paleoshoreline of the southeastern u s atlantic coastal plain they concluded that 1 the scarp in south carolina was formed mostly during the middle pliocene 3 5 3 0 ma 2 eustatic sea level was about 35 plus minus 18 m higher than modern sea level the scarp has been uplifted about 50 65 m since the middle pliocene and 3 ocean water temperatures along eastern north america were warmer when the scarp was formed that they are at present

deep crustal configuration of the valencia trough and its iberian and balearic borders from extensive refraction and wide angle reflection seismic profiling abstract new constraints on the crustal structure of the valencia trough and its iberian and balearic borders have been obtained from a seismic experiment carried out in autumn 1989 a total of 290 sea shots were fired along three refraction wide angle reflection profiles recorded by 10 ocean bottom seismometers obss in the valencia trough and 110 land stations distributed on both flanks the huge amount of recorded data in each profile has been integrated and jointly interpreted to obtain a single 2 d velocity depth model along each line the geometry and deep crustal structure of the basin are fairly well defined in terms of laterally inhomogeneous layered media the sedimentary cover shows a layer of consolidated sediments overlain by neogene and quaternary sediments with a velocity of 5 1 km s interpreted as mesozoic carbonates at the northwestern side of the valencia trough a fairly homogeneous crystalline basement is found on all profiles at a mean depth of 4 km below sea level with a velocity of 6 0 6 1 km s the observed critical distances and arrival times of the moho reflected waves are firm evidence supporting a thinning of the crust towards the centre of the basin the moho rises up to 13 km in the axis of the trough in the nw se and e w profiles and up to 15 km in the ne sw profile moreover the analysis of the well defined pmp phase shows differences between the deep structure of the flanks and the trough respectively a sharp velocity contrast at the moho from a fairly uniform lower crust of 6 4 km s velocity is proposed in both flanks in contrast to a high velocity gradient within the lower crust interpreted near the axis of the trough an anomalous upper mantle velocity of 7 8 km s fits the data throughout the valencia trough and mallorca with slightly higher values of 7 9 km s required towards the continent these velocity values do not favour an interpretation in terms of underplating the geometry of the moho discontinuity shows a gradual deepening towards the iberian peninsula in contrast to a more abrupt slope towards mallorca depth values of 30 32 km typical of a continental crust are inferred about 40 km inland on the iberian peninsula in agreement with the crustal thicknesses already reported for the iberian range and the ebro basin the present crustal thinning resulting from rift episodes in the valencia trough and the iberian border is thus confirmed and constrained from our seismic results of the deep crust and upper mantle

reversed polarity glacial sediments and revised glacial chronology west branch susquehanna river valley central pennsylvania abstract a new exposure of glacial and glaciolacustrine sediments at antes fort allows for revision of the chronology of pre wisconsinan glaciation in central pennsylvania lacustrine sediments from a proglacial lake in the west branch susquehanna river valley have reversed remanent polarity with a site mean paleomagnetic declination of 193 8 and inclination of 13 1 the magnetization is probably a true detrital remanence from the time of deposition and is not significantly affected by postdepositional diagenesis we propose that the antes fort till was deposited during either pre illinoian glaciation f or g of g m richmond and d s fullerton 1986 quaternary science reviews vol 5 183 196 between 770 000 and 970 000 yr ago we suggest that it is equivalent to the penny hill till in the west branch susquehanna river valley and tentatively correlate it westward with the reversed polarity terrace deposits and minford silt in western pennsylvania west virginia and ohio the west lebanon till in indiana and the a4 tills or possible b tills in iowa and nebraska

paleogene stratigraphy and sea level history of the north carolina coastal plain global coastal onlap and tectonics abstract coastal onlap of paleogene depositional sequences mapped by stage and compared to curves of global coastal onlap and eustasy facilitate differentiation of the effects of local uplift and subsidence from eustasy on the onslow and albemarle blocks about the neuse hinge in north carolina differential uplift and subsidence of these blocks has controlled the stratal geometries and patterns of relative coastal onlap on each block potential mechanisms to produce the uplift and subsidence include episodic flexural deformation resulting from sediment loading in the salisbury embayment and horizontal compressional deformation resulting from plate motion danian sea level rise produced the initial paleogene siliciclastic sequences ta1 2 and ta1 3 on both blocks after deposition of the danian sequences and prior to thanetian inundation the onslow block was elevated relative to the albemarle block the ypresian ta2 5 2 9 one is generally restricted to the downdip albemarle block has a depositional updip limit and represents a major basinward shift in local coastal onlap at a time when global coastal onlap and long term eustatic curves predict a major landward shift this suggests that both blocks were uplifted during the ypresian lutetian bartonian sequences ta3 3 ta3 5 3 6 represent the most extensive landward shift in coastal onlap during the paleogene in north carolina and show erosional updip limits on both blocks differences in the degree of overstepping on the two blocks reflects post middle eocene uplift but greater relative uplift of the albemarle block the priabonian ta4 1 and either the ta4 2 or ta4 3 has erosional updip limits on both blocks and represents a significant basinward shift in local coastal onlap this shift occurs during a time when global coastal onlap and long term eustasy indicate a landward shift as great as that during the lutetian bartonian therefore both blocks were uplifted but the distribution of the priabonian on the albemarle block indicates greater relative uplift in north carolina the rupelian ta4 4 oversteps the priabonian on both blocks but not as far as predicted by global coastal onlap and eustasy based on the offlapping relationship of the erosional updip limit on both blocks both areas were uplifted prior to rupelian deposition chattian sediments tb1 1 1 4 lower part reflect a downward shift in coastal onlap which is consistent with global coastal onlap and long term eustatic fall

extricating dynamic topography from subsidence patterns examples from eastern north america s passive margin abstract global sea level eustatic histories generated by backstripping stratigraphy are predicated upon the lithosphere having a well understood tectonic history however sub plate processes play a role in governing lithospheric vertical motions with timescales and amplitudes akin to eustasy which are difficult to predict we examine how stratigraphic and geophysical observations combined with simple isostatic models can be used to disentangle histories of sub plate support and eustasy we focus on the passive margin of eastern north america where a generally accepted history of eustasy has been estimated negative long wavelength free air gravity anomalies residual ocean age depth estimates fast upper mantle shear wave velocities and geodynamic models suggest that cenozoic evolution of this passive margin has been influenced by upper mantle drawdown we build on existing analyses to backstrip sixteen wells which combined with seismic data constrain timing and extent of cenozoic subsidence results indicate up to 1000 m of water loaded subsidence between 20 0 ma centered on the baltimore canyon trough seismic data from the trough shows neogene aggrading clinoforms there is little evidence for faulting or stratigraphic growth which indicates that neogene lithospheric strain rates were low amplitude and spatial extent of neogene subsidence are difficult to explain by glacio eustasy or glacio isostatic adjustment instead sub plate support calculated from conversion of shear wave velocities to temperature and isostatic calculations indicate that upper mantle drawdown was responsible for subsidence of the margin because mantle convection is vigorous such observations are expected throughout the stratigraphic archive

quaternary soil chronosequences on terraces of the susquehanna river pennsylvania abstract susquehanna river terraces are used to establish time lines along a 150 km reach of the river from the lower piedmont to the edge of the appalachian plateau this is achieved by generating soil chronosequences at two locations marietta pa in the lower piedmont and muncy pa near the glacial border on the boundary between the valley and ridge province and the appalachian plateau these sites preserve the most complete record of fluvial incision on the susquehanna river with flights of seven quaternary terraces ranging in elevation from 3 m to 51 m above the modern river soil characteristics used to develop the soil chronosequences include complexity of horizonization thickness of b horizon clay content of b horizon soil color cbd extractable fe al and mn total extractable fe and clay mineralogy terrace age constraints are based on soil development correlation to regional glacial stratigraphy correlation to dated fluvial and glaciofluvial deposits and by paleomagnetic analysis of sediments terrace ages at the muncy site range from modern

upwelling history of the mediterranean sea revealed by stunted growth in the planktic foraminifera orbulina universa early messinian crete greece microfossil and stable isotope data 13c 18o from deep water sediments of late miocene age in the mediterranean region have revealed a stepwise restriction of the mediterranean prior to the messinian salinity crisis which was modulated by a cyclicity responding to orbital precession very little is known with regard to the effects of these changes on shallow water environments of carbonate platforms and ramps this work is based on a geological section on crete greece exposing sediments of early messinian age which documents the coeval response of pelagic and neritic systems to oceanographic changes we discuss a dataset of planktic and benthic foraminifera assemblages in conjunction with size measurements n 6 777 and isotope analyses 18o 13c of the planktic foraminifera orbulina universa with regard to reef growth patterns the planktic foraminifera fauna displays pronounced cyclical abundance changes of warm oligotrophic o universa and cold meso to eu trophic taxa globigerinids neogloboquadrinids this cyclicity corresponds to lithological changes from laminated to homogeneous marls on the precessional frequency band in beds rich in mesotrophic foraminifera o universa is rare and the test is 50 smaller than average growth and size of o universa is affected by various environmental factors including temperature trophic resources illumination and o2 content of ambient water explaining size variability by water temperature implies a change of 11 c over one precessional cycle this estimate is in disagreement with growth patterns and stable isotope data of displaced reef corals porites tarbellastraea documenting almost constant sea surface temperatures but substantial evaporation therefore moderate temperature changes in a context of intense evaporation high salinity and water column destabilization associated with upward mixing of colder water masses with higher nutrient concentrations and low o2 content better fits size variation of o universa from the presence of halimeda bioherms intercalated with the sapropel cycles we infer cyclic photic zone anoxia and at least some sections with sapropel couplets to have formed in the neritic zone we also suggest further testing of stunted growth of o universa as a proxy for enhanced nutrient availability in future palaeoceanographic studies

integrated sequence stratigraphy of neogene deposits new jersey continental shelf and slope comparison with the exxon model we have evaluated the neogene stratigraphic succession beneath the continental shelf off new jersey using high quality seismic and well data to 1 construct geologic cross sections that relate seismic geometries to lithofacies in a prograding tectonically quiescent setting 2 apply a sequence stratigraphic approach to subdivide the stratigraphic section and relate the characteristics of the deposition observed sequences to the published exxon model and 3 determine the resolution of the available biostratigraphy in the correlation of the offshore new jersey depositional sequences to the published eustatic cycle chart in the offshore new jersey area the well developed progradational geometries in the neogene section the high quality seismic data and the relatively abundant lithologic information from wells allow us to use the results of this study to predict lithofacies distribution in similar but less geologically constrained settings depositional sequences are characterized by similar overall stacking patterns within component systems tracts however the new jersey sequences are different in several ways these differences include the lack of type 2 unconformities an absence of leveed channel deposits within lowstand wedges very poorly developed transgressive systems tracts and sandstone rich high regressive highstand systems tracts these differences are explained in terms of the limited neogene accommodation on the newmore jersey shelf that resulted from slow subsidence rates and a second order miocene eustatic fall paleontologic data bracket the ages of the individual sequences but are not detailed enough at present to correlate precisely to the time scale and inferred global sea level records based on the available biostratigraphy however neogene depositional sequences from offshore new jersey have a cyclicity consistent with interpreted third order eustatic fluctuations on the global cycle chart 18 refs 6 figs 1 tab less

evidence of transient topographic disequilibrium in a landward passive margin river system knickpoints and paleo landscapes of the new river basin southern appalachians the upper new river basin of the southern appalachian mountains a major tributary of the modern ohio river represents the unglaciated headwaters of the tertiary teays river system of eastern north america dating of relict fluvial gravels have suggested that new river incision may be outpacing lowering of the surrounding uplands but physical evidence of transient topographic disequilibrium has yet to be identified we use focused topographic analysis of the upper new river basin to delineate a perched low relief paleo landscape that is experiencing transgressive dissection due to incision by the new river and its tributaries accelerated incision has decoupled hillslopes from the drainage network generating knickpoints which represent the boundary between remnants of the paleo landscape and actively adjusting topography downstream steepening of hillslopes downstream of knickpoints suggests dynamic headward migration which along with knickpoint occurrence throughout the drainage network is inconsistent with the development of fixed stream profile convexities atop strike extensive geologic contacts in the absence of tectonic forcing we favor a climatically forced drop in external base level as driver of the incision pattern we observe plio pleistocene glacial damming and diversion of the teays river to form the modern ohio river lowered regional base level for the study area potentially forcing the paleo landscape developed during the teays era to adjust to the modern drainage pattern the upper new river may therefore represent the potential for glacially driven drainage rearrangement to drive transient topographic evolution hundreds of kilometers away from the ice margin long after the disappearance of ice sheets copyright 2013 john wiley sons ltd