the shape and internal structure of the moon from the clementine mission global topographic and gravitational field models derived from data collected by the clementine spacecraft reveal a new picture of the shape and internal structure of the moon the moon exhibits a 16 kilometer range of elevation with the greatest topographic excursions occurring on the far side lunar highlands are in a state of near isostatic compensation whereas impact basins display a wide range of compensation states that do not correlate simply with basin size or age a global crustal thickness map reveals crustal thinning under all resolvable lunar basins the results indicate that the structure and thermal history of the moon are more complex than was previously believed

large scale responses of complex shaped coastlines to local shoreline stabilization and climate change 1 when modeling the large scale km evolution of coastline morphology the influence of natural forces is not the only consideration ongoing direct human manipulations can substantially drive geomorphic change in this paper we couple a human component to a numerical model of large scale coastline evolution incorporating beach nourishment periodically placing sand on the beach also called beach replenishment or beach fill beach nourishment is the most prevalent means humans employ to alter the natural shoreline system in our case study the carolina coastline beach nourishment can cause shorelines adjacent to those that are nourished to shift both seaward and landward when we further consider how changes to storm behaviors could change wave climates the magnitude of morphological change induced by beach nourishment can rival that expected from sea level rise and affect the coast as far as tens of kilometers away from the nourishment site in some instances nonlocal processes governing large scale cuspate cape coastline evolution may transmit the human morphological signal over surprisingly large hundreds of kilometer distances

venus topography a harmonic analysis a model of venusian global topography has been obtained by fitting an eighteenth degree harmonic series to pioneer venus orbiter radar altimeter data the mean radius is 6051 45 0 04 km the corresponding mean density is 5244 8 0 5 kg m 3 the center of figure is displaced from the center of mass by 0 339 0 088 km towards 6 6 10 1 n 148 8 7 7 e the figure of venus is distinctly triaxial but the orientation and magnitudes of the principal topographic axes correlate rather poorly with the gravitational principal axes however the higher degree harmonics of topography and gravity are significantly correlated the topographic variance spectrum of venus is very similar in form to those of the moon mars and especially earth we suggest that this spectral similarity simply reflects a statistical balance between constructional and degradational geomorphic processes venus and earth are particularly similar and differ from the moon and mars in that the larger bodies both exhibit a significant low degree deficit relative to the extrapolated trend of the higher harmonics

high angle wave instability and emergent shoreline shapes 2 wave climate analysis and comparisons to nature 1 recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms including capes flying spits and alongshore sand waves this instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle a maximum that occurs between 35 and 50 for several common alongshore sediment transport formulae here we introduce metrics that sum over records of wave data to quantify the long term stability of wave climates and to investigate how wave climates change along a coast for long point a flying spit on the north shore of lake erie canada wave climate metrics suggest that unstable waves have shaped the spit and furthermore that smaller scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable a shoreline aligned along the trend of the carolina capes united states would be dominated by high angle waves numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast local wave climates along these simulated capes and the carolina capes show similar trends shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability

modeling large scale shoreline change caused by complex bathymetry in low angle wave climates abstract coastlines where waves consistently approach at highly oblique angles experience anti diffusional behavior causing perturbations to grow seaward and form sand waves capes and spits coasts where waves approach at low offshore angles experience the opposite perturbations diffuse and the coastline remains or becomes smooth in this paper by coupling a 2 d large scale coastline evolution model to a spectral wave model we show that anti diffusional behavior is also possible in low angle wave climates if the nearshore wave field is altered by complex bathymetry in model simulations low angle waves refract over local shoals creating a convergence in alongshore sediment flux behind the shoals that coalesces into small minor capes depending on wave height and period shoreline features take 80 400 years to reach an equilibrium cross shore relief of 1 1 5 km over an alongshore distance of 20 km the modeled equilibrium time scale is consistent with analytically determined characteristic shoreline diffusion time scales and the modeled cross shore relief and aspect ratio are similar to observed minor capes along the u s atlantic coast where offshore bathymetric anomalies have previously been linked to shoreline change patterns better understanding of the links among nearshore bathymetry wave transformation and alongshore sediment transport is critical to understanding shoreline change patterns at the local level and how they fit into broader regional scale behavior

regional seismic stratigraphy and controls on the quaternary evolution of the cape hatteras region of the atlantic passive margin usa abstract seismic and core data combined with amino acid racemization and strontium isotope age data enable the definition of the quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of north carolina u s a seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets and enable an understanding of the evolution of this margin data reveal the progressive eastward progradation and aggradation of the quaternary shelf the early pleistocene inner shelf occurs at a depth of ca 20 40 m beneath the western part of the modern estuarine system pamlico sound a mid to outer shelf lowstand terrace also early pleistocene with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract occurs at a deeper level ca 45 70 m beneath the modern barrier island system the outer banks and northern pamlico sound seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle pleistocene shelf middle to late pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units and contain numerous filled fluvial valleys that are incised into the early and middle pleistocene deposits the stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea level fluctuations during the middle to late pleistocene expressed as falling stage lowstand transgressive and highstand systems tracts thick stratigraphic sequences occur within the middle pleistocene section suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north furthermore the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system

gravity field determination and characteristics retrospective and prospective gravimetry has had a long history using pendulums torsion balances and static spring gravimeters relative accuracy adequate for many geophysical problems was already attained by 1900 but it took another half century to build readily portable gravimeters calibration and datum definition remained problems until the 1970s when free fall absolute gravimeters were developed that now have a precision of 10 3 mgal the problems of geographic inaccessibility and field party costs notably in areas of greatest tectonic interest are now being overcome by airborne gravimetry that has already achieved accuracies of 1 3 mgal with resolutions of 10 to 20 km satellite techniques are the best way to determine the long wavelength variations of the gravity field the resolution of the models has steadily improved with the number of satellites and the precision of the observations the best current model includes tracking data from more than 30 satellites satellite altimetry and surface gravimetry and has a resolution of about 290 km harmonic degree 70 with the most recent improvements coming from doppler orbitography and radiopositioning integrated by satellite doris tracking of the spot 2 satellite and satellite laser ranging slr doris and global positioning system gps tracking of the topex poseidon satellite meanwhile radar altimetry has become the dominant technique to infer the marine geoid with a resolution of tens of kilometers or shorter similarly the gravity fields of the moon venus and mars have been determined to harmonic degrees 70 75 and 50 respectively although tracking limitations result in variations of spatial resolution modeling earth s gravity field from the abundance of precise data has become an increasingly complex task with which the development of computer capacity has kept pace contemporary solutions now entail about 10 000 parameters half of them for effects other than the fixed gravity field of earth temporal variations arising from tides have long been well modeled and nontidal changes are now being identified the improvement in gravitational models engendered corresponding advances in geophysical interpretation isostatic models were refined and expanded to account for regional thermal and tectonic histories interpretation of the long wavelength gravity field determined by satellite techniques has been mainly in terms of plate tectonics as a manifestation of mantle convection gravity has been significant in inferring that there must be a large increase in viscosity with depth most strongly from the apparent slow sinking of subducted slabs the prospects for increasing accuracy and resolution in the determination of earth s gravity field rest primarily with the development of new measurement systems airborne gravimetry is taking promising new steps using gps but significant global model improvement awaits a dedicated satellite gravimetry system and future satellite altimeter missions will do more for ocean dynamics studies than geoid improvement advances in interpretation will occur through the development of other data such as seismic tomography and larger scale computer modeling of tectonics and convection

high resolution gravity model of venus the anomalous gravity field of venus shows high correlation with surface features revealed by radar we extract gravity models from the doppler tracking data from the pioneer venus orbiter pvo by means of a two step process in the first step we solve the nonlinear spacecraft state estimation problem using a kalman filter smoother the kalman filter has been evaluated through simulations this evaluation and some unusual features of the filter are discussed in the second step we perform a geophysical inversion using a linear bayesian estimator to allow an unbiased comparison between gravity and topography we use a simulation technique to smooth and distort the radar topographic data so as to yield maps having the same characteristics as our gravity maps the maps presented cover 2 3 of the surface of venus and display the strong topography gravity correlation previously reported the topography gravity scatter plots show two distinct trends

mountain building in taiwan a thermokinematic model the taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening however a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge we propose here a new thermokinematic model of the taiwan mountain belt reconciling existing kinematic thermometric and thermochronological constraints in this model shortening across the orogen is absorbed by slip on the most frontal faults of the foothills crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge tananao complex tc where the uplift rate is estimated to 6 3 mm a 1 and beneath the westernmost internal region of the orogen hsueshan range units hr where the uplift rate is estimated to 4 2 mm a 1 our model suggests that the tc units experienced a synchronous evolution along strike despite the southward propagation of the collision it also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures exhumation of the hr units increases northward but has not yet reached an exhumational steady state presently frontal accretion accounts for less than 10 of the incoming flux of material into the orogen although there is indication that it was contributing substantially more 80 before 4 ma the incoming flux of material accreted beneath the tc significantly increased 1 5 ma ago our results also suggest that the flux of material accreted to the orogen corresponds to the top 7 km of the upper crust of the underthrust chinese margin this indicates that a significant amount 76 of the underthrust material has been subducted into the mantle probably because of the increase in density associated with metamorphism we also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field by combining available geological data on the thermal and kinematic evolution of the wedge our study sheds new light onto mountain building processes in taiwan and allows for reappraising the initial structural architecture of the passive margin

the messinian problem in the pannonian basin eastern hungary insights from stratigraphic simulations abstract earlier studies revealed a prominent unconformity in the messinian stratigraphic record of the lacustrine pannonian basin but it was unclear what factors were responsible for the formation of this unconformity and thus its origin remained controversial the problem was further complicated by the fact that stratal patterns in the messinian varied significantly along the paleo margins of the lake our study introduces quantitative stratigraphic simulations to analyze the role of subsidence sediment supply and lake level changes in the formation of the unconformity and the various architectural patterns that evolved in response to the messinian events the results suggest that a relative lake level fall occurred in the messinian accompanied and followed by tectonic inversion in several parts of the basin since the rate of tectonic subsidence and or uplift varied in space and time the size of the relative lake level fall varied significantly across the basin while various stratal architectural patterns formed in the same time interval the age of the unconformity was estimated based on seismic correlations with paleomagnetic chronozones to be between 5 6 ma which was refined by stratigraphic simulations galeacysta etrusca cysts were found in the unconformity which confirmed its late messinian age the surface is called the intra messinian unconformity imu in this paper seismic interpretations and simulations of stratal architecture led to the formulation of a basin fill model and identification of four stratigraphic architectural patterns related to messinian events including a major lake level fall and coeval and subsequent uplift events in certain parts of the basin

venus gravity a harmonic analysis an improved model of venusian global gravity has been obtained by fitting an eighteenth degree and eighteenth order spherical harmonic series to 78 orbital arcs of high altitude 950 1350 km at periapsis tracking data and 351 orbital arcs of lower altitude 150 200 km at periapsis data from the pioneer venus orbiter pvo compared to a recently published tenth degree model mottinger et al 1985 which is based on the 78 high altitude arcs only the current model provides a significant improvement in resolution and fidelity as a measure of this improvement we note that for the low altitude arcs alone the variance of the residuals for the present model is reduced to 19 of the data variance compared to 51 for the tenth degree model venus differs significantly from the earth in that it exhibits a significant correlation between long wavelength topography and gravity the gravity topography spectral admittances are inconsistent with either airy or pratt isostasy but they are consistent with dynamic support by mantle convection

inversion of the paleogene chinese continental margin and thick skinned deformation in the western foreland of taiwan abstract new structural data available seismicity data together with mechanical constraints on the eurasian continental lithosphere and reconstruction of paleostress trajectories are combined in order to re assess and discuss the dominant deformation mode thin skinned vs thick skinned in the western fold and thrust belt of the active taiwan collision zone serial balanced cross sections and computed paleostress tensors suggest that structural styles and stress trajectories at the front of the taiwan mountain belt may vary rapidly along strike depending on the presence of pre orogenic paleogene troughs in the chinese continental margin taihsi and tainan basins that are favourably oriented to be reactivated and inverted in localities of the western foreland where basin inversion and thick skinned basement involved shortening predominate the crustal seismic activity is important and characterized by strike slip faulting in these domains of the fold thrust belt the stress deviations with respect to the regional transport direction are also important by contrast in domains of significant syn orogenic subsidence a thin skinned style of deformation may be prominent due to the lack of available pre existing features the seismic activity is limited to few major faulted boundaries such as the active chelungpu sani thrust and the stress deviations are limited the timing of deformation at the belt front seems to be independent of the structural styles so that frontal folds are active since probably 0 5 ma however in inner parts of the western foothills of taiwan where superimposed thick skinned and thin skinned deformation are required out of sequence thrusting occurs to maintain the topographic profile finally we suggest that kinematics and structural styles of the western fold thrust belt are controlled by the mechanics of the eurasian continental margin in agreement with a recent study at the scale of the orogen the limited shortening amounts across the wf and in the central range as well as the absence of continental hp rocks better support a thick skinned collision model for taiwan

tectonic interpretations of holocene marine terraces east coast of coastal range taiwan abstract the east coast of the coastal range in taiwan is well known for its multiple holocene marine terraces and their very rapid uplift the study area extends from hualien to taitung over ca 150 km of coastline here we present some new data on the age and height of holocene marine terraces and we discuss their significance for holocene coastal tectonics the holocene marine terrace sequence is subdivided into a maximum of 10 steps the highest and oldest terrace mostly underlain by transgressive deposits represents the sea level position of the culmination of holocene sea level rise and reaches up to ca 80 m above sea level transgressive deposits are radiocarbon dated at several sites back to ca 13 000 yr bp the lower terraces are mostly erosional ones overlain by thin coral beds in situ less than 1 m thick and indicate successive lowering of relative sea level during the late holocene the uplift rate of the coast is very high ranging from 5 to 15 m ka three tectonic subregions a c are identified based on the pattern of marine terrace features and uplift rate the presence of many steps during holocene time implies that intermittent uplifts associated with large earthquakes at intervals of one thousand to several hundred years have repeatedly occurred in this coastal area but with different time and amount at each subregion the uplift of subregion a resulted from an onshore active fault milun fault causative faults for the uplift of the subregions b and c are not identified offshore active faults striking obliquely to the coastline appear to be causative faults

high angle wave instability and emergent shoreline shapes 1 modeling of sand waves flying spits and capes 1 contrary to traditional findings the deepwater angle of wave approach strongly affects plan view coastal evolution giving rise to an antidiffusional high wave angle instability for sufficiently oblique deepwater waves with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport 45 a one contour line numerical model shows that a predominance of high angle waves can cause a shoreline to self organize into regular quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers the numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash which is assumed to maintain a minimum barrier width systematic analysis shows that the wave climate determines the form of coastal response for nearly symmetric wave climates small net alongshore sediment transport cuspate coasts develop that exhibit increasing relative cross shore amplitude and pointier tips as the proportion of high angle waves is increased for asymmetrical wave climates shoreline features migrate in the downdrift direction either as subtle alongshore sand waves or as offshore extending flying spits depending on the proportion of high angle waves numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude a rate that is insensitive to the proportion of high angle waves the proportion of high angle waves determines the offshore versus alongshore aspect ratio of self organized shoreline undulations

venus gravity anomalies and their correlations with topography this report provides a summary of the high resolution gravity data obtained from the pioneer venus orbiter radio tracking data gravity maps covering a 70 latitude band through 360 of longitude are displayed as line of sight and vertical gravity topography converted to gravity and bouguer gravity maps are also shown in both systems topography to gravity ratios are made over several regions of the planet there are markedly different ratios for the aphrodite area as compared to the beta and atla areas

an improved gravity model for mars goddard mars model 1 doppler tracking data of three orbiting spacecraft have been reanalyzed to develop a new gravitational field model for the planet mars goddard mars model 1 gmm 1 this model employs nearly all available data consisting of approximately 1100 days of s band tracking data collected by nasa s deep space network from the mariner 9 and viking 1 and viking 2 spacecraft in seven different orbits between 1971 and 1979 gmm 1 is complete to spherical harmonic degree and order 50 which corresponds to a half wavelength spatial resolution of 200 300 km where the data permit gmm 1 represents satellite orbits with considerably better accuracy than previous mars gravity models and shows greater resolution of identifiable geological structures the notable improvement in gmm 1 over previous models is a consequence of several factors improved computational capabilities the use of optimum weighting and least squares collocation solution techniques which stabilized the behavior of the solution at high degree and order and the use of longer satellite arcs than employed in previous solutions that were made possible by improved force and measurement models the inclusion of x band tracking data from the 379 km altitude near polar orbiting mars observer spacecraft should provide a significant improvement over gmm 1 particularly at high latitudes where current data poorly resolve the gravitational signature of the planet

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

cape capture geologic data and modeling results suggest the holocene loss of a carolina cape for more than a century the origin and evolution of the set of cuspate forelands known as the carolina capes hatteras lookout fear and romain off the eastern coast of the united states have been discussed and debated the consensus conceptual model is not only that these capes existed through much or all of the holocene transgression but also that their number has not changed here we describe bathymetric lithologic seismic and chronologic data that suggest another cape may have existed between capes hatteras and lookout during the early to middle holocene this cape likely formed at the distal end of the neuse tar pamlico fluvial system during the early holocene transgression when this portion of the shelf was flooded ca 9 cal calibrated kyr b p and was probably abandoned by ca 4 cal kyr b p when the shoreline attained its present general configuration previously proposed mechanisms for cape formation suggest that the large scale rhythmic pattern of the carolina capes arose from a hydrodynamic template or the preexisting geologic framework numerical modeling however suggests that the number and spacing of capes can be dynamic and that a coast can self organize in response to a high angle wave instability in shoreline shape in shoreline evolution model simulations smaller cuspate forelands are subsumed by larger neighbors over millennial time scales through a process of cape capture the suggested former cape in raleigh bay represents the first interpreted geological evidence of dynamic abandonment suggested by the self organization hypothesis cape capture may be a widespread process in coastal environments with large scale rhythmic shoreline features its preservation in the sedimentary record will vary according to geologic setting physical processes and sea level history

venus global gravity and topography a new gravity field determination that has been produced combines both the pioneer venus orbiter pvo and the magellan doppler radio data comparisons between this estimate a spherical harmonic model of degree and order 21 and previous models show that significant improvements have been made results are displayed as gravity contours overlaying a topographic map we also calculate a new spherical harmonic model of topography based on magellan altimetry with pvo altimetry included where gaps exist in the magellan data this model is also of degree and order 21 so in conjunction with the gravity model bouguer and isostatic anomaly maps can be produced these results are very consistent with previous results but reveal more spatial resolution in the higher latitudes

long term rotation and mantle dynamics of the earth mars and venus in response to internal and surface tectonic processes the terrestrial planets have the ability to displace the axis of rotation with respect to the mantle this behavior is quantified by means of a nondimensional number defined here as the rotational number ro that allows classification of the planets into two categories the first containing mars and the earth where true polar wander is a feasible mechanism and the second to which venus belongs where rotation equilibrium is attained by means of mega wobbles driven by internal mass anomalies the number ro is related to the timescale characterizing the readjustment of the equatorial bulge during long term polar motion and to the length of the sidereal day if these two timescales are well separated the planet experiences true polar wander nonlinear liouville equations for stratified viscoelastic bodies with linear maxwell rheology are solved in order to assess the relevance of surface and mantle processes in driving long term rotation instabilities in the terrestrial planets the amount of true polar wander estimated for the earth and mars is reproduced correctly by our modeling with mantle viscosities and lithospheric thickness consistent with other studies the major difference between the earth and mars is the driving mechanism subduction for the earth and lithospheric loading for mars when mantle viscosities similar to those of the earth are considered for venus the most updated estimate for the offset of about 0 5 between the rotation axis and the axis of maximum inertia is well reproduced during the mega wobbles induced by internal mass redistribution we show that the degree 2 topography of these three planets can be affected by their rotation which is responsible for the dominance of the sectorial component on the earth and mars and for the zonal component on venus

short term changes in seafloor character due to flood derived hyperpycnal discharge typhoon mindulle taiwan july 2004 during typhoon mindulle in early july 2004 the choshui river central western taiwan discharged similar to 72 mt of sediment to the eastern taiwan strait peak concentrations were g 200 g l similar to 35 40 of which was sand box core samples and chirp compressed high intensity radar pulse sonar records taken just before and after the typhoon indicate that the hyper pycnal sediment was first deposited adjacent to the mouth of the choshui subsequently resuspended and transported northward via the taiwan warm current and redeposited as a patchy coastal band of mud dominated sediment that reached thicknesses of 1 2 m within megaripples within a month most of the mud was gone probably continuing its northward transit but more mud appeared in late august in response to typhoon aere following autumn and winter storms the entire nearshore area was again sand dominated by early spring

hardbottom morphology and relationship to the geologic framework mid atlantic continental shelf abstract high energy sediment starved continental shelves of the mid atlantic region have abundant hardbottoms that extend from the shoreface to the shelf edge because of the thin and irregularly distributed holocene sand sheet shelf morphology is determined mainly by outcropping tertiary and pleistocene stratigraphic units each unit and combination of units produces different hardbottom morphologies that depend upon the geometry and spatial relationships of the units lithology and patterns of stratification and subsequent weathering and erosion hardbottoms vary in surface relief from smooth flat surfaces to scarped surfaces with up to 10 m of relief the morphology ranges from sloping and stepped erosional ramps to vertical and undercut scarps with associated broad rubble ramps hardbottoms associated with each of the different gently dipping tertiary depositional sequences have distinctive morphologies hardbottoms developed on pleistocene units unconformably overlie the tertiary sequences as flat lying marine carbonates or cut into them as channel systems backfilled with fluvial and estuarine sediments initial dissection of hardbottoms produced highly convoluted surfaces that resulted from subaerial weathering stream erosion and karst formation during sea level lowstands during subsequent sea level highstands these rimary morphologies were greatly modified through the interaction of bioerosion and storms understanding continental shelf hardbottoms is critical for interpreting the sedimentology and stratigraphy of the atlantic coastal plain and for reconstructing paleoceanographic conditions for the following reasons 1 they are an extensive part of the stratigraphic record on shelves that are not actively subsiding and have small volumes of terrigenous input with low sediment accumulation rates 2 they are important stages in the formation of major stratigraphic unconformities condensed sections and sequence boundaries 3 they support diverse biological communities that produce primary carbonate sediments and are rapidly degraded and modified by bioerosion and physical processes supplying abundant new sediment to the continental shelf

building reliable local models of the venus gravity field from the cycles 5 and 6 of the magellan los gravity data we present a new way to build reliable local models of the venus gravity field from the cycles 5 and 6 of the magellan probe by directly considering the doppler residual profiles instead of the derived residual acceleration profiles we give an example over a test area

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

holocene depositional history of a microtidal cuspate foreland cape cape lookout north carolina abstract the holocene stratigraphy of cape lookout north carolina and the connecting barrier limb core banks displays sharply contrasting depositional histories beneath the core banks barrier chain a transgressive sequence of overwash storm deposits rests on back barrier silty sands and salt marsh peats evidence of the island s erosive landward migration however core holes drilled at cape lookout reveal a regressive vertical stacking of sediments that marks a major holocene facies change here fine grained burrowed shoreface deposits are overlain by coarse grained horizontally bedded barrier washover sands cape lookout has evolved during the late holocene as a prograding cuspate spit type of headland this accretion is a result of the combined effects of oceanic washover deposition with sand accumulated from a dominant southerly longshore transport during the past 4000 years the rate of sea level rise slowed markedly in the area resulting in a decreased rate of landward migration for core banks as the island became relatively stable with respect to sea level rise large volumes of sand were being transported along shore to cape lookout and offshore to its subaqueous shoals the slower landward retreat of the island probably allowed for a rapid southerly extension of core banks along with a buildup of the cape lookout shoals the sedimentation and growth of cape lookout over the past 4000 years probably reflects a similar history of development for other capes and shoals along the southeastern coast of the united states the large scale cuspate morphology present today may therefore be a relatively recent phenomenon

plate convergence at the westernmost philippine sea plate abstract to understand the convergent characteristics of the westernmost plate boundary between the philippine sea plate psp and eurasian plate ep we have calculated the stress states of plate motion by focal mechanisms cataloged by the harvard centroid moment tensor solutions harvard cmt and the broadband array in taiwan bats moment tensor 251 focal mechanisms are used to determine the azimuths of the principal stress axes we first used all the data to derive the mean stress tensor of the study area the inversion result shows that the stress regime has a maximum compression along the direction of azimuth n299 this result is consistent with the general direction of the rigid plate motion between the psp and ep in the study area in order to understand the spatial variation of the regional stress pattern we divided the study area into six sub areas blocks a to f based on the feature of the free air gravity anomaly we compare the compressive directions obtained from the stress inversion with the plate motions calculated by the euler pole and the global positioning system gps analysis as a result the azimuth of the maximum stress axis 1 generally agrees with the directions of the theoretical plate motion and gps velocity vectors except block c lanhsu region and block f ilan plain region the discrepancy of convergent direction near the ilan plain region is probably caused by the rifting of the okinawa trough the deviation of the 1 azimuth in the lanhsu region could be attributed to a southwestward extrusion of the luzon arc la block between 21 n and 22 n whose northern boundary may be associated with the right lateral ne sw trending fault i e huatung fault hf along the taitung canyon comparing the 1 stress patterns between block c and block d great strain energy along hf may not be completely released yet alternatively the upper crust of block c may significantly have decoupled from its lower crust or uppermost mantle

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

gravitational and topographic isotropy of the earth moon mars and venus the internal structures and surface shapes of the terrestrial planets are expected to be dominantiy isotropic we attempt to test this hypothesis by developing a criterion for recognizing statistical isotropy of spherical scalar fields and applying that test to the nonhydrostatic components of the gravitational and topographic fields of the earth moon mars and venus the criterion for topographic or geoidal surfaces is that the directional variance should be independent of azimuth that is the mean square east west slopes should be equal to the mean square north south slopes all four planets generally pass the criteria with a few minor exceptions most of the exceptions are likely to be artifacts of the current generation of planetary gravity and topography models rather than real features of the planets of the several broad band departures from isotropy which we found the only one likely to be real is the tendency for the earth s gravity and topography to have only 80 as much variance in a north south direction as in an east west direction

20th century sediment budget trends on the western gulf of lions shoreface france an application of an integrated method for the study of sediment coastal reservoirs abstract this paper presents a shoreface sediment budget established for the 20th century 1895 1984 2009 along the microtidal wave dominated coast of the western gulf of lions languedoc roussillon mediterranean sea se france the implementation of a diachronic bathymetric approach coupled with the definition of sand reservoirs upper sand unit usu by very high resolution seismic surveys and the results of lidar investigations offers a new means of defining precisely the magnitude and change trends of the sediment budget the aim of this study is to link the large scale coastal behaviour lscb of the littoral prism expressed in terms of shoreface sediment budget shoreface sediment volume and spatial distribution pattern of cells to climatic change river sediment input to the coast longshore sediment transport distribution impact of hard coastal defence structures and artificial beach nourishment the results show a significant reduction of the volume of the western gulf of lions littoral prism over 114 years 26 1 4 6 10 6 m 3 from 1895 to 1984 the overall budget is slightly positive with a volume estimated at 4 1 3 5 10 6 m 3 for 1984 2009 however the estimated sediment budgets clearly indicate that erosion is dominant over the last 25 years with a volume loss of 30 2 4 2 10 6 m 3 in relation to the long term sediment budget and longshore drift pattern the long term trend of the usu volume distribution displays strong spatio temporal contrasts linked to longshore sediment drift spatial distribution of fluvial sediment inputs and hard engineering structures locally the sedimentary reservoir is significantly eroded within a century 80 of usu since the initial amount present was low and not sustainable the emphasis is on the importance of considering the volume changes of available sediment reservoirs rather than their losses and gains erosion of the languedoc roussillon shoreface is likely to continue in the future due to the natural decrease of river sediment input and the sand removal for human purposes consequently the littoral sand prism results in sedimentary reservoirs that are gradually being used up

characterization of topographic steady state in taiwan abstract the arc continent collision in taiwan has resulted in surface uplift high relief and high rates of erosion because the collision is older in the north and has propagated southward taiwan offers the opportunity to study the evolution of topography as it evolves towards a large scale steady state in this paper we analyze a 40 m digital elevation model of taiwan to determine how topographic steady state is expressed in the landscape particular attention is paid to the eastern central range where major drainage basins are approximately aligned in the direction of the collision propagation analyses of orogen size regional topographic slope drainage basin hypsometry and local topographic slope reveal a geomorphological transition 100 125 km north of the southern tip of the island to the south of this transition topographic characteristics change with distance along the island to the north these characteristics are relatively constant which we interpret as representing large scale topographic steady state assuming that the collision has propagated southward at a rate of 55 mm yr the time to topographic steady state is 1 8 2 3 myr after emergence above sea level within the steady state region we evaluate regional variability in the topography and find that the most prominent deviations from a steady form are associated with large scale structures though our analyses of local topographic slope and river profile form suggest that spatial variations in rock strength and rock uplift rate also contribute to regional topographic variability

investigating the kinematics of mountain building in taiwan from the spatiotemporal evolution of the foreland basin and western foothills the taiwanese range has resulted from the collision between the luzon volcanic arc and the chinese continental margin which started about 6 5 myr ago in the north and has since propagated southward the building of the range has been recorded in the spatiotemporal evolution of the foreland basin we analyze this sedimentary record to place some constraints on the kinematics of crustal deformation the flexure of the foreland under the load of the growing wedge started with a 1 5 myr long phase of rapid subsidence and sedimentation which has migrated southward over the last 3 5 myr at a rate of 31 10 5 mm yr reflecting the structural evolution of the range and the growth of the topography during the oblique collision isopachs from the toukoshan 0 to 1 1 ma and cholan 1 1 to 3 3 ma formations as well as the sedimentation rates retrieved from a well on the pakuashan anticline indicate that the foreland basement has been moving toward the center of mass of the orogen by 45 50 mm yr during the development of the basin from there we estimate the long term shortening rate across the range to 39 5 44 5 mm yr by considering available data on the thrust faults of the foothills of central taiwan we show that most if not all the shortening across the range is accommodated by the most frontal structures with little if any internal shortening within the wedge the range growth appears therefore to have been essentially sustained by underplating rather than by frontal accretion in addition only the upper 7 to 9 km of the underthrusted crust participates to the growth of the orogen this requires that a significant amount of the chinese passive margin crust is subducted beneath the philippine sea plate

development of the east asian summer monsoon evidence from the sediment record in the south china sea since 8 5 ma 128 samples from ocean drilling program odp site 1143 in the southern south china sea were analyzed for grain size clay minerals biogenic opal content and quartz in order to reconstruct changes in east asian monsoon climate since 8 5 ma an abrupt change of terrigenous mass accumulation rate mar clay mineral assemblage median grain size and biogenic opal mar about 5 2 ma suggests that between 8 5 5 2 ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern vietnam a simple model of east asian summer monsoon evolution was based on the clay feldspar ratio kaolinite chlorite ratio and biogenic opal mar the summer monsoon has two periods of maximum strength at 8 5 7 6 ma and 7 1 6 2 ma subsequently there was a relatively stable period at 6 2 3 5 ma continued intensification about 3 5 2 5 ma and gradually weakening after 2 5 ma since i ma the monsoon has intensified with remarkable high frequency and amplitude variability simultaneous increase in sedimentation rates at odp sites 1143 1146 and 1148 as well as in mar of terrigenous materials quartz feldspar and clay minerals at odp site 1143 at 3 5 2 5 ma may be the erosional response to both global climatic deterioration and the strengthening of the east asian summer monsoon after about 3 4 ma c 2006 elsevier b v all rights reserved

the qs problem sediment volumetric balance of proximal foreland basin systems although the stratigraphy of sedimentary basins depends on the balance between the magnitude and grain size characteristics of the sediment supply qs and the spatial distribution of tectonic subsidence generating accommodation x qs is problematical to measure in present day sediment routing systems and formidably difficult to predict in their ancient counterparts this challenge was tackled by treating the sediment discharge from the outlet of mountain catchments as the result of incision by a drainage network with a bulk diffusivity based on the length over which the mean annual rainfall is concentrated the size relief and slope of palaeo catchments acting as feeders for sediment routing systems are used to run simulations of sediment discharge and bulk diffusivity for a range of annual precipitation values a wide range of observable geological phenomena can be used to converge on the most likely solutions for qs including depositional volumes in the basin and bedrock thermochronology and detrital cosmogenic nuclide dating to constrain catchment erosion rates modelled sediment discharges can be checked with estimates derived from global regressions the sediment efflux of mountain catchments serves as a boundary condition for down system sediment transport and deposition variations in the volumetric ratio of sediment supply to available accommodation qs x determines patterns of transverse versus longitudinal axial sediment dispersal the volumetric ratio may change as a result of variations in climatic parameters tectonic uplift rate and catchment expansion an abrupt climate change to higher precipitation values promotes higher qs x but transient landscape response causes a return to values close to the baseline generating a distinctive down system extension of a gravel spike catchment expansion has a similar but more prolonged effect on gravel progradation in contrast a change in tectonic forcing such as an increase in slip rate on a border fault causes little change in qs x because increased subsidence compensates for the increased sediment supply studies of mid eocene oligocene sediment routing systems in the south central pyrenees allow the discrimination of different types of proximal wedge top sedimentary systems on the basis of the volumetric ratio of qs to accommodation x i small steep local fan systems in tectonically ponded underfilled basins supplied by low sediment discharges ii tectonically guided long range axial systems fed by large sediment discharges from widely spaced palaeovalleys and iii large shallow sloping transverse megafans burying underlying defunct or active tectonic structures supplied by high to very high sediment discharges understanding the role of variations in qs helps to explain the syntectonic evolution of proximal foreland basin systems the oligocene miocene north alpine foreland basin switzerland is qualitatively identified as a high qs example the miocene recent northern apennines of italy as a low qs example and the eocene oligocene southern pyrenees of spain as intermediate in character

a high resolution gravity model for venus gvm 1 a spherical harmonic model of the gravitational field of venus complete to degree and order 50 has been developed using the s band doppler tracking data of the pioneer venus orbiter pvo collected between 1979 and 1982 the short wavelengths of this model could only be resolved near the pvo periapse location 14 n latitude therefore a priori constraints were applied to the model to bias poorly observed coefficients towards zero the resulting model has a half wavelength resolution of 400 km near the pvo periapse location but the resolution degrades to greater than 1000 km near the poles this gravity model correlates well with a degree 50 spherical harmonic expansion of the venus topography derived from a combination of magellan and pvo data new tracking data from magellan s gravity mission should provide some improvement to this model although a complete model of the venusian gravity field will depend on tracking of magellan after the circularization of it s orbit using aerobraking

mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations abstract theories associated with flow in the vicinity of headlands and sandbanks together with proposed mechanisms for sandbank formation and maintenance are reviewed to exemplify water and sand movement around a sandbank on a tidally dominated shelf tidal currents in the vicinity of a headland associated linear sandbank are described these data are integrated with sedimentological information on bedforms and grain size distributions the sandbank under detailed investigation the scarweather sands is located along the northern coastline of the bristol channel uk which is an area susceptible to high energy inputs the maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the atlantic ocean but the area is 460km from the shelf break detailed observations are presented from 11 long term current meter stations located within 10km of the sandbank currents are described in terms of residual water circulation shallow water harmonics and tidal ellipse characteristics bedload transport paths are inferred from the distribution of bedforms grain size and m2 m4 tidal current interactions transport vectors are predicted from near bed current meter observations combined with empirically derived formulae it is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance the results of the present study are thought to be applicable directly to headland associated sandbanks elsewhere it is shown on the basis of theoretical considerations that the pattern of residual water movement and possibly sand transport around this sandbank could be extended to continental shelves on a global basis

stratigraphic modeling of the western taiwan foreland basin sediment flux from a growing mountain range and tectonic implications abstract sediment flux signals from source to sink in foreland basins preserve a record of tectonics sea level and climate through erosion and sedimentation however longitudinal sediment transport often occurs in foreland basins thus removing part of the orogenic material flux from foreland basin records here we use mass balance calculation and stratigraphic simulations of sediment fluxes for the taiwan orogen to provide an order of magnitude estimate of how much orogenic material may bypass a foreland basin our results indicate a significant potentially more than 50 mismatch between sediment volume currently preserved in the basin and the amount of material presumably eroded from the orogen since the onset of collision in taiwan this suggests either a significant overestimation of average erosion rates over the period concerned with orogenic development of taiwan or it supports previous paleogeographic work suggesting that longitudinal sediment transport in the paleo taiwan strait served as a major bypass conduit of importance for the establishment of a steady state orogen we identify candidate submarine topography in the south china sea that may preserve taiwan s missing erosional mass

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

transition from oblique subduction to collision in the northern luzon arc taiwan region constraints from bathymetry and seismic observations we systematically study the detailed bathymetry seismicity and source parameters of large and moderate sized earthquakes that occurred in the northern luzon arc taiwan region between 1964 and 1996 the purpose is to characterize the transition from oblique subduction to regional collision in terms of the distribution of morphological features the characteristics of seismogenic structures and the corresponding state of strain to the south of 21 5 n the existence of a subduction zone is clearly shown by both bathymetry and seismicity the subducted eurasia slab reaches a maximum depth of 200 km and the depth decreases sharply as it approaches taiwan focal mechanisms indicate that the subducted slab is in downdip extension for depths 150 km but switches to downdip compression at greater depths to the north of 23 n collision is clearly the predominant process with broad deformation on both sides of the suture in between the transition is accommodated by a distributed thrust deformation zone in the frontal portion of the accretionary prism closure of the forearc basin and the right lateral ne sw striking taitung canyon fault zone tcfz these structures resolve the differential movements between the subduction and collision zones and will repeatedly change their positions as the collision propagates southwestward the present day plate boundary follows the axis of the manila trench in the south broadens significantly in the zone of transition and finally becomes a zone of several tens of kilometers in width across eastern taiwan the deformation front on the other hand is located between the western foothills and coastal plain in taiwan then connects to the manila trench to the south seismic strain tensors indicate that the region to the north of tcfz has a compression rate 15 times larger than that to the south the northern luzon arc shows characteristics of oblique subduction but the effects of collision are not as significant within the subducted eurasian lithosphere as comparing to the subducted philippine sea plate beneath the southernmost ryukyu arc

pyrrhotite as a tracer for denudation of the taiwan orogen 1 the use of pyrrhotite as an index mineral to delineate metamorphic isograds has long been proposed however details of the occurrence of pyrrhotite in different metamorphic facies and its implications have rarely been explored here by simple characterization of magnetic properties and mineral identification we demonstrate that pyrrhotite is widely distributed in low grade metamorphic terranes of taiwan s central range and in sediments derived therefrom by coupling the distribution of pyrrhotite in rocks with that in dated sediment strata we have studied the denudation history of taiwan s orogen from a source to sink perspective we suggest that pyrrhotite is a potential tracer for studying surface processes in orogens with high denudation rates similar to that in taiwan

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

venus gravity a high resolution map the doppler data from the radio tracking of the pioneer venus orbiter pv0 have been used in a two stage analysis to develop a high resolution map of the gravitational potential of venus represented by a central mass and a surface mass density the two stage procedure invokes a kalman filter smoother to determine the orbit of the spacecraft and a stabilized linear inverter to estimate the surface mass density the resultant gravity map is highly correlated with the topographic map derived from the pv0 radar altimeter data however the magnitudes of the gravity variations are smaller than would be expected if the topography were uncompensated indicating that at least partial compensation has taken place

pumice layers in marine terraces implications for tectonic uplift rates on the east and northeast coasts of taiwan over the last hundreds of years abstract two very rare pumice rich layers were recently found at two sites in taiwan more precisely in the lowermost marine terrace of the sanhsientai area on the southeast coast and in that of the yenliao area on the northeast coast the pumice rich layer in the former is about 15 cm in thickness and is composed of 60 70 gray to dark gray subangular to angular pumice fragments with barnacle shell fragments the layer in the latter on the other hand is about 10 cm in thickness and is composed of 40 50 light gray to gray subrounded to subangular pumice fragments with a few carbonized wood fragments despite their different occurrences both pumice fragments very closely resemble each other in terms of major and trace as well as isotopic compositions and therefore may be considered to have come from the same source the luzon or philippine arcs 14 c dating gives the layers an equal age ranging from around 420 to 402 cal yr bp based on the age and altitude of the marine terraces in the sanhsientai and yenliao areas however the uplift rates are 10 9 and 5 4 mm yr respectively the results strongly indicate that firstly the uplift rates may have accelerated in the last thousands of years during the holocene in the sanhsientai chengkung area and that secondly the northern coastal area of taiwan likely suffered from a spasmodic uplift in the very latest holocene

the early cambrian bradore formation of southeastern labrador and adjacent parts of quebec architecture and genesis of clastic strata on an early paleozoic wave swept shallow marine shelf abstract strata of the bradore formation have been interpreted in terms of a marine transgression developed at the onset of spreading of iapetus ocean with a basal member of fluvial origin a middle member of lagoonal origin and an upper member of tidal channel origin in labrador the formation rests directly on a low relief surface developed on metamorphic rocks of the grenville orogen with no well developed paleosoils re examination of the architecture of pebbly sandstones in the basal blanc sablon member indicate that these formed on an open storm influenced wave swept shelf as part of a low relief sand sheet with evidence of multiple accretionary events structure in sandstones in the middle crow head member is largely obscured by a high density of skolithos linearis domichnia abundance of hummocky cross stratification indicates deepening with a transition to an open storm influenced shallow shelf large scale cross stratification in the glauconite bearing upper l anse au clair member reflects shoaling with a return to deposition of medium scale marine sandwave complexes with no clear evidence of any tidal signature strata of the bradore formation were at least partly lithified prior to deposition of reefal and platformal carbonates in the overlying forteau formation paleocurrent indicators in the upper and lower members suggests that during the initial drift phase of iapetus this segment st lawrence promontory of the laurentian margin was swept by both geostrophic and storm influenced currents largely oriented parallel to the paleocoastline

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

rates of cooling and denudation of the early penglai orogeny taiwan as assessed by fission track constraints abstract as an attempt to define the timing of the peak temperature of the penglai orogeny and estimate the early cooling and denudation rates of the taiwan mountain belt fission track dating of zircon and apatite was conducted on several key metamorphic rock samples the zircon fission track ages for the metasandstone clasts collected from the central and northern parts of the coastal range were determined as 4 0 0 5 and 3 6 0 3 ma respectively both of the clasts were identified as from the ancient central range which was metamorphosed at temperatures high enough to cause a complete reset of the zircon fission track system during 1 2 ma they were exhumed and deposited in the coastal range basin due to the later penglai orogeny of taiwan obviously they have not further been annealed since their deposition in the coastal range the difference between the above fission track ages and the stratigraphical age of the host sedimentary formation represent the ancient cooling ages when they were exposed on the early central range these ancient cooling ages are comparable with the zircon fission track age of a present day outcrop of the tananao schist 1 8 0 2 ma this accordance implies that at ca 5 ma the northern and central parts of the central range achieved the peak temperature of the penglai orogeny and then they began to emerge above sea level accepting this scenario we calculate the rates of denudation and cooling of the central range to be ca 2 5 4 6 mm yr 1 and 120 c m y 1 respectively for the last 4 ma

siliciclastic sequence stratigraphic patterns in foreland ramp type basins stratal patterns within shelf depositional sequences are dependent on tectonically controlled subsidence rates and their regional patterns in active tectonic basin settings regional subsidence patterns can be very different from passive continental margin settings resulting in substantial modifications of the basic sequence stratigraphic model in ramp type foreland basins on the tectonically active side subsidence rates decrease seaward in contrast with passive continental margins where the opposite subsidence pattern exists analysis of the interplay between eustasy and subsidence suggests the existence of two tectono stratigraphic zones occurring proximally and distally with respect to the basin margin zone a is defined as the region within which the rate of subsidence always exceeds the rate of eustatic fall consequently relative sea level rises continuously during a eustatic cycle albeit at varying rates zone b is defined as the region within which the rate of eustatic fall periodically exceeds the rate of subsidence resulting in an interval of relative sea level fall during a eustatic cycle on the tectonically active sides of foreland basins zone a lies on the landward side of the basin margin proximal to the orogenic belt and zone b lies seaward off zone a away from the orogenic belt where subsidence rates are lower on passive continental margins because of the opposite subsidence patterns zone a lies seaward of zone b where subsidence rates are greater the location of the shoreline relative to these zones determines the stacking patterns and stratal discontinuities within a depositional sequence if the shoreline remains in zone a then only type 2 sequence boundaries will occur if sufficient sediment flux is available allowing the shoreline to prograde into zone b then type 1 sequence boundaries can occur in foreland basins these type 1 sequence boundaries would become type 2 sequence boundaries updip in zone a the pattern of seaward decreasing subsidence on the tectonically active sides of foreland basins results in characteristic longitudinal facies and stratal patterns when the two zones occur the updip region of the basin proximal to the orogenic belt is characterized by nearly continuous nonmarine deposition albeit at varying rates the downdip region is characterized by forced regressions and deposition primarily of lowstand and transgressive systems tracts a transitional region containing deposits of all three systems tracts commonly occurs between the updip and downdip areas

coastal lithosome preservation evidence from the shoreface and inner continental shelf off bogue banks north carolina abstract seismic and vibracore data from the continental shelf as well as borehole data from an adjacent barrier island indicate that the migrating shoreface responding to rising sea level has nearly completely removed the entire coastal sedimentary record in northern onslow bay north carolina this process was active throughout the quaternary and even the late tertiary as middle tertiary sediments and rocks directly crop out on the sea floor in vast areas of this shelf sector seaward of bogue banks a holocene barrier island located along northern onslow bay seismic sequences have been truncated by the modern shoreface which extends to about 12 m depth correlations with borehole data on the island indicate that these sequences are pleistocene and holocene in age the holocene sequences contain numerous channels which are interpreted to be relict tidal inlets however none extends vertically lower than the shoreface indicating that landward translation of the shoreface would remove most of even the deepest holocene coastal lithosomes parts of the pleistocene and even a portion of the tertiary the middle and inner portions of the continental shelf have been incised by numerous channels channel facies are an important component of shelf sedimentary and stratigraphic sequences and comprise about one third of northern onslow bay similar seismic infilling facies and vibracore data as well as the poor preservation potential of the tidal inlet throats indicate that the channels were lower coastal plain streams the infilling sediments are mostly muds with some sands and shells dates from shells via the amino acid racemization technique are pleistocene in age these channels with some having multiple infilling events assume greater importance when one recognizes that essentially they alone hold the vast majority of the quaternary record of numerous sea level fluctuations

venus topography and kilometer scale slopes during the first 8 months of the magellan mission the radar altimeter has made some three million measurements of the surface of venus covering the latitude range from 85 n to 80 s methods involving range correlation doppler filtering multi burst summation and range migration are used to focus the observations and to achieve high surface resolution results are presented as maps of the global distribution of topography meter scale roughness and power reflection coefficient the results are similar to those reported in previous experiments surface heights exhibit a unimodal distribution with more than 80 of the surface lying within 1 km of the 6051 84 km mean radius but the higher resolution of the magellan altimeter has disclosed several surprisingly steep features e g the southwest face of the maxwell montes the southern face of the danu montes and the chasmata to the east of thetis regio where average kilometer scale slopes of greater than 30 are not uncommon this conclusion is corroborated by close inspection of synthetic aperture radar imagery

mass anomaly structure of the earth gravitational interaction is the weakest among the four known forces in the universe the particular gravity equipotential field that coincides with sea level is called the geoid and satellite data have revealed anomalies in its pattern that are puzzling to explain dynamic topography solutions have offered the preferred explanation for the past 15 years but problems remain an alternative explanation presented here contends that very large mass anomalies lie deep in the earth presumably produced by topography at the coremantle boundary cmb and only much smaller mass anomalies occur at shallower depths the principal distinction is whether one is willing to accept the possibility that processes within the earth s core may generate the cmb topography an analysis of the south american regional geoid high spherical harmonic degrees 2 10 indicates that only mass anomalies shallower than 1200 km are its cause this single positive source is contrary to dynamic topography solutions that would generate negative deflections of both the surface and the cmb in response to the positive subducted mass for the earth s fourth greatest geoid high our alternate explanation is tested utilizing a set of 9274 subduction 5 cube slab bloblet center points developed from reconstructed plate history that provide estimates of the locations of material subducted into the earth s mantle two global mass solutions are offered utilizing 1 only those bloblets in the outer 800 km and 2 only those bloblets in the outer 1400 km four point masses at 3000 km depth to simulate cmb topography produced by processes within the core unrelated to mantle dynamic topography complete the two mass models both models show reasonable agreement with patterns and magnitudes of the regional geoid and its component degree parts the model cmb mass anomalies are only a factor of 3 greater than those initially estimated by gravity to geoid ratios from observed values at geoid anomaly center locations difficulties with the dynamic topography solutions matters of the density of the subducted material the proper hydrostatic flattening value to use for analyses and possible causes for the cmb topography are discussed the subduction mass models are also used to estimate the magnitude of the driving force for plate tectonics 2 78 1020 to 3 23 1021 n approximately equivalent to 7 0 1012 to 8 1 1013 n m 1 these force values are comparable to published slab force estimates based on thermal considerations

plio quaternary sedimentation processes and neotectonics of the northern continental margin of the south china sea abstract analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the south china sea permit the recognition of four quaternary high frequency type 1 sequences of the 4th order deposited during the past ca 690 kyr at the present day shelf edge only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved the prograding complexes can be considered as regressive units accumulated during relative sea level falls they exhibit internal discontinuities which might point to minor sea level fluctuations of the 5th order a preliminary regional relative sea level curve for the past 630 kyr is established using the present positions of the delta fronts mapped the neotectonics curve derived by subtracting eustatic sea level changes from the relative sea level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea level our seismo stratigraphic interpretation documents that the area off hong kong and around the dongsha islands experienced two uplift episodes during the past 5 ma namely at the miocene pliocene boundary and at the end of the lower middle pleistocene respectively these uplift events which are centred on the dongsha rise led to its subaerial exposure and to the erosion of the pliocene and most of the pleistocene strata the change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato tectonic uplift was caused by a reorientation of the tectonic regime the recent depositional environment on the northern continental margin of the south china sea is dominated by sediment accumulation within the inner shelf and the zhujiang pearl river estuary the outer shelf and upper slope especially around the dongsha islands are characterised by bypass of terrigenous material the sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits it overlies oceanic as well as transitional crust

water and sediment discharge from small mountainous rivers taiwan the roles of lithology episodic events and human activities national science council of taiwan nsc96 2628 m 001 028 u s national science foundation and naval oceanographic office

terrestrial and planetary gravity fields the determination of the gravity field together with knowledge of the surface topography provides one of the primary means of inferring the density structure and dynamics of planetary interiors phillips and lambeck 1980 hager 1985 after removing the topographic gravity signal the distribution of internal density anomalies caused by thermal or compositional differences can be studied gravity field models can also be used to study the compensation of surface topography which can provide information on the mechanical properties and state of stress of the lithosphere the determination of these models has been accomplished using a wide variety of different measurement types and solution techniques the near earth measurement types can be divided into satellite tracking measurements surface gravity measurements and satellite altimeter measurements in both near earth and interplanetary contexts tracking data are used to measure gravitational perturbations affecting satellites with the accuracy and spatial temporal distribution of the data being the most important factors in the resulting field accuracy and resolution surface gravity data provide a more direct measurement of the gravity field but acquiring data uniformly over the earth has always been difficult satellite altimetry provides precise measurements of the marine gravity field provided that satellite orbit errors and non geoidal sea surface height variations can be adequately modeled comprehensive gravity field solutions must incorporate these disparate data types in order to estimate mathematical parameters describing the gravity field such as spherical harmonic coefficients the proper combination of these data along with the desire to acquire an accurate representation of the model errors require that complex procedures be developed for computing these solutions

petrology of indus river sands a key to interpret erosion history of the western himalayan syntaxis the indus river has been progressively transformed in the last decades into a tightly regulated system of dams and channels to produce food and energy for the rapidly growing population of pakistan nevertheless indus river sands as far as the delta largely retain their distinct feldspar and amphibole rich composition which is unique with respect to all other major rivers draining the alpine himalayan belt except for the brahmaputra both the indus and brahmaputra rivers flow for half of their course along the india asia suture zone and receive major contributions from both asian active margin batholiths and upper amphibolite facies domes rapidly exhumed at the western and eastern himalayan syntaxes compositionofindussandschangesrepeatedlyandmarkedlyinladakhandbaltistan indicatingoverwhelmingsedimentflux from each successive tributary as the syntaxis is approached provenance estimates based on our integrated petrographic mineralogical data set indicate that active margin units karakorum and transhimalayan arcs provide 81 of the 250f50 10 6 t ofsedimentsreachingthetarbelareservoireachyear partitioningofsuchfluxamongtributariesandamongsourceunitsallowsus to tentatively assess sediment yields from major subcatchments extreme yields and erosion rates are calculated for both the karakorum belt up to 12 500f4700 t km 2 year and 4 5f1 7 mm year for the braldu catchment and nanga parbat massif 8100f3500t km 2 yearand3 0f1 3mm year thesevaluesapproachdenudationratescurrentlyestimatedforsouthkarakorum and nanga parbat crustal scale antiforms and highlight the major influence that rapid tectonic uplift and focused glacial and fluvial erosion of young metamorphic massifs around the western himalayan syntaxis have on sediment budgets of the indus system detailed information on bulk petrography and heavy minerals of modern indus sands not only represents an effective independent method to constrain denudation rates obtained from temperature time histories of exposed bedrock but also

a 70th degree lunar gravity model glgm 2 from clementine and other tracking data a spherical harmonic model of the lunar gravity field complete to degree and order 70 has been developed from s band doppler tracking data from the clementine mission as well as historical tracking data from lunar orbiters 1 5 and the apollo 15 and 16 subsatellites the model combines 361 000 doppler observations from clementine with 347 000 historical observations the historical data consist of mostly 60 s doppler with a noise of 0 25 to several mm s the clementine data consist of mostly 10 s doppler data with a data noise of 0 25 mm s for the observations from the deep space network and 2 5 mm s for the data from a naval tracking station at pomonkey maryland observations provided clementine provide the strongest satellite constraint on the moon s low degree field in contrast the historical data collected by spacecraft that had lower periapsis altitudes provide distributed regions of high resolution coverage within 29 of the nearside lunar equator to obtain the solution for a high degree field in the absence of a uniform distribution of observations we applied an a priori power law constraint of the form 15 10 5 l2 which had the effect of limiting the gravitational power and noise at short wavelengths coefficients through degree and order 18 are not significantly affected by the constraint and so the model permits geophysical analysis of effects of the major basins at degrees 10 12 the glgm 2 model confirms major features of the lunar gravity field shown in previous gravitational field models but also reveals significantly more detail particularly at intermediate wavelengths 103 km free air gravity anomaly maps derived from the new model show the nearside and farside highlands to be gravitationally smooth reflecting a state of isostatic compensation mascon basins including imbrium serenitatis crisium smythii and humorum are denoted by gravity highs first recognized from lunar orbiter tracking all of the major mascons are bounded by annuli of negative anomalies representing significant subsurface mass deficiencies mare orientale appears as a minor mascon surrounded by a horseshoe shaped gravity low centered on the inner and outer rook rings that is evidence of significant subsurface structural heterogeneity although direct tracking is not available over a significant part of the lunar farside glgm 2 resolves negative anomalies that correlate with many farside basins including south pole aitken hertzsprung korolev moscoviense tsiolkovsky and freundlich sharonov

the spin and inertia of venus one of the most remarkable rotational features of venus is the presence of a relatively large offset between spin and maximum inertia axis according to the most recent gravity field models this offset may amount to 0 5 considerably larger than the one which characterizes the earth s chandler wobble 0 3 at present it is not clear whether the offset of venus is the result of the limited resolution of the gravity models or alternatively it may be regarded as an evidence in support to the existence of a wobble purpose of this note is to demonstrate on quantitative grounds that an offset between spin axis and maximum inertia axis is to be expected on the time scales of mantle convection due to the peculiar rotational characteristics of venus we also show that the inertia perturbation associated to the rising of hot thermal plumes from the core mantle boundary to the surface is large enough to maintain offsets ranging between 0 1 and 1 of course this does not preclude that other processes such as venusquakes or periodic atmospheric variabilities may contribute significantly to the observed offset on shorter time scales

dynamic sedimentation and geomorphologic evolution of the laizhou shoal bohai sea northern china abstract as a headland associated sandbank off an unconsolidated coast cape in a progression process the laizhou shoal is just located at the coalescent position of the two tidal residual current circumferences its formation and maintenance dynamics sedimentation and geomorphology are different from the models proposed up till the present moment our findings indicate that 1 the tidal residual tidal current circumferences are located along the flanks of the shoal itself instead of the flanks of the headland cape and the sediments under the two circumferences are quite different from those at their coalescent position 2 the sediments made up of the shoal have an ultimate resource of river sediment instead of an erosion recession cape or seafloor nearby and are transported directly from the coastal zone through the wave resulted coastal current rather than through the tidal residual tidal eddies 3 the shoal continually migrates from southwest to northeast extending into the laizhou bay northwest the cape in the past 50 years 4 because more than 100 reservoirs have been built across the rivers in the northwestern shandong peninsula and have greatly reduced the sediments especially gravel and sand grains transported into the coastal zone some locations of the shoal have evolved from deposition to erosion and the shoal itself has become narrower but has not evolved from deposition to erosion as a whole

coldspots and hotspots global tectonics and mantle dynamics of venus magellan radar images and altimetry data and pioneer venus gravity data of major highlands and lowlands on venus are examined with the objective of relating these tectonic and volcanic landforms to convection within venus mantle two roughly circular lowlands atalanta and lavinia planitiae are bowl shaped depressions which contain compressional tectonic features and lack hotspot related features such as coronae and shield volcanoes they are identified as surface expressions of young mantle coldspots or regions of mantle downwelling highlands can be divided into two distinct groups volcanic rises and plateau shaped highlands volcanic rises are domical circular to elongate regions characterized by volcanic construction extensional tectonism large positive gravity and geoid anomalies centered on the highlands and large apparent depths of compensation volcanic rises include beta bell atla and western eistla regiones and are identified as surface expressions of large mantle hotspots or plumes plateau shaped highlands are steep sided elevated regions that range from circular alpha regio to elongate or irregular ovda regio tellus regio in shape their surfaces are dominated by complex ridged terrain rather than the shield volcanoes and flows that dominate volcanic rises most plateau shaped highlands contain compressional structures some of which commonly lie along their margins and have small gravity and geoid anomalies and small apparent depths of compensation compared to volcanic rises plateau shaped highlands which include those mentioned above and western ishtar terra thetis regio and phoebe regio are identified as surface expressions of mantle coldspots or regions of downwelling the highland coldspot features are elevated as a consequence of crustal thickening crustal thickening is absent or minor at lowland coldspots the importance of mantle downwelling in the tectonic deformation of venus suggests that its mantle like the mantle of earth is strongly heated from within the major venusian hotspots attest to the existence of large mantle plumes carrying heat upward from the planet s core

forced regressive deposits of a deglaciation sequence example from the late quaternary succession in the lake saint jean basin quebec canada differentiating between forced regressive deposits from deglacial periods in high latitude domains and forced regressive deposits from the onset of glacial periods in low latitude domains is fundamental for the accurate interpretation of glacial cycles within the geological record and then for the reconstruction of palaeogeography and palaeo climate a forced regressive deglacial sequence is documented from the lake saint jean basin quebec canada in this area the late pleistocene to holocene sediments have recorded the laurentide ice sheet retreat accompanied by the invasion of marine waters laflamme gulf from ca 129 cal kyr bp subsequently fluviodeltaic and coastal prograding wedges were deposited they followed the base level fall due to glacio isostatic rebound this succession representing a transition from glacial to post glacial periods within a previously glaciated area was investigated through recent mapping preserved landforms facies analysis and new optical stimulated luminescence and radiocarbon dates three basin scale geological sections share a common lower part made of isolated ice contact fan deposits overlying bedrock throughout the entire basin ice contact fans are capped by glacimarine muds above fluvial and coastal prograding systems were deposited and evolved through four steps i deltaic systems progressively increased in width ii coastal influence on sedimentation increased iii hydrographic drainage systems became more organised and iv deltas graded from steep gilbert delta to low angle foresets mouth bar delta deposited during the base level fall from glacioisostatic rebound the complete succession has been designated as a single falling stage system tract referred to as a deglacial falling stage system tract it is representative of a deglaciation sequence in areas previously covered by ice during glacial periods i e medium to high latitude domains diagnostic criteria are provided to identify such a deglacial falling stage system tract in the geological record which may aid identification of previously unknown glacial cycles

geology of continental shelf onslow bay north carolina as revealed by submarine outcrops lithologic and stratigraphic data from rocks dredged from the continental shelf off onslow bay north carolina provide surface control for seismic studies of the southeastern united states continental margin and help to explain the distribution of potentially economic phosphate rich sediments on this shelf outcropping miocene rocks in this area indicate that the region has long been a positive geologic feature and has received relatively little pliocene and pleistocene sedimentation leached molluscan moldic calcareous quartz sandstones of late oligocene to early miocene age belgrade formation and middle to late miocene age pungo river formation crop out in southwestern and northeastern onslow bay respectively these two areas border a band of highly phosphatic su ficial sediments probably derived from unlithified phosphatic units of the pungo river formation lower pleistocene calcarenites that correlate with the waccamaw formation crop out on the sea floor near cape fear which bounds onslow bay on the south a core on frying pan shoals off cape fear after passing through pleistocene coquina calcareous quartz sandstone and oolitic sand penetrated upper pliocene calcarenites of the bear bluff formation and middle miocene phosphatic argillaceous sandstones of the pungo river formation samples from this core hole show that phosphate increases toward the top of the unindurated pungo river formation section indicating that this formation is probably the source of the high phosphate concentrations in the surficial sediments near cape fear wher the bear bluff calcarenites also crop out upper pleistocene units include oolitic limestones adjacent to the outer shelf calcareous quartz sandstones around cape fear and molluscan coquinas near cape lookout which bounds onslow bay on the north the outer shelf is blanketed by submarine lithified algal limestones and sandstones of holocene age

sedimentary processes and depositional history of a cape associated shoal cape lookout north carolina abstract the sedimentary processes of a cape associated shoal are an integral component of the sediment budget of the surrounding cuspate foreland shoreline the manner in which sediment is delivered to a shoal and the fate of this sediment once delivered have important implications to shoreline management and yet remain largely unstudied modern sedimentary processes and the recent depositional history of cape lookout shoal a large cape associated shoal in the mixed energy environment of the north carolina continental shelf were examined in a field intensive study through high resolution seismic profiles hydraulic probes near bottom current meters sediment grab samples and detailed bathymetric surveys our findings indicate that 1 the sediment budget of the up drift littoral cell is coupled directly to cape lookout shoal 2 the sedimentary processes of the shoal remain active down its entire length but at a diminishing level with distance from the shore and 3 the shoal serves as a long term sink for littoral zone sediment and limits sediment exchange between adjacent littoral cells and shelf regions we present evidence suggesting that the position and morphology of cape lookout shoal are not controlled by underlying erosion resistant strata and that the shoal appears to have developed in the late holocene after the shelf was scoured by the transgressing shoreface