normal faulting and the topographic roughness of mid ocean ridge flanks the ocean floor on the flanks of mid ocean ridges is covered by abyssal hills topographic features elongated perpendicularly to the direction of relative plate motion these topographic features are interpreted as normal fault blocks and or volcanic constructions that originated near the ridge axis and were later rafted onto the ridge flanks by seafloor spreading the purpose of this paper is to quantify the topographic roughness of a profile perpendicular to the strike of a number of normal faults given a fault population and a mechanical model for the response of the lithosphere to faulting we obtain expressions for the variation in root mean square roughness with profile length and for the power spectral density of a profile given three parameters a fault density number of faults per unit length crossed by the profile an average squared fault scarp height and a characteristic length of flexure to keep matters simple we make a number of assumptions and approximations namely that the lithosphere behaves as an elastic plate that faults have an infinite length and a vertical dip that the response of topography to a number of faults is simply the sum of the responses to each fault and that faults have random locations and scarp heights independently chosen from some statistical distribution the theory predicts that the roughness length relationship power spectral density should follow power laws for scales wavelengths less than a characteristic scale proportional to the length scale of flexure we compare the predictions of the theory with actual measurements of mid ocean ridge flank roughness and find good first order agreement in particular we use independent estimates of fault densities average squared fault scarp heights and flexural length scales to predict the topographic roughness of the east pacific rise and we find that normal faulting can explain all the observed topographic roughness nevertheless there are some differences between predictions and observations these differences are likely to be due to processes other than faulting that create topographic relief e g volcanism and to spatial correlations of fault scarp heights despite these shortcomings the approach presented here provides a first step in understanding the topographic roughness signal by quantifying the contribution of the geological processes that generate surface relief

nearcom tvd a quasi 3d nearshore circulation and sediment transport model article i nfo the newly developed nearshore circulation model shorecirc using a hybrid finite difference finite volume tvd type scheme is coupled with the wave model swan in the nearshore community model nearcom sys tem the new modeling system is named nearcom tvd and the purpose of this study is to report the capability and limitation of nearcom tvd for several coastal applications for tidal inlet applications the model is verified with the semi analytical solution of keulegan 1967 for an idealized inlet bay system to further evaluate the model performance in predicting nearshore circulation under intense wave current interaction over complex bathymetry modeled circulation patterns are validated with measured data during rcex field experiment macmahanetal 2010 forsedimenttransport applications two sedimenttransportmodelsare applied topre dict three sandbar migration events at duck nc during august to october 1994 gallagher et al 1998 the model of kobayashi et al 2008 incorporates wave induced onshore sediment transport rate as a function of the standard deviation of wave induced horizontal velocities the modeled beach profile evolution for two off shore events and one onshore event agrees well with the measured data the second model investigated here combines two published sediment transport models namely the total load model driven by currents under the effect of wave stirring soulsby 1997 and the wave driven sediment transport model due to wave asymmetry skewness van rijn et al 2011 the model study with limited field data suggests that the parame terization of wave stirring is appropriate during energetic wave conditions however during low energy wave conditions the effect of wave stirring needs to be re calibrated

the mid atlantic ridge near 13 20 n high resolution magnetic and bathymetry imaging we describe detailed magnetic and bathymetric studies around 13 n on the mid atlantic ridge a site of extensive detachment faulting inversion of closely spaced sea surface magnetic anomalies reveals a disorganized pattern of magnetization with anomalies younger than anomaly 2 being poorly delineated the brunhes anomaly width is highly variable but averages 60 of that predicted for the regional spreading rate it is often split both along and across axis by apparently reversely magnetized crust gaps in the brunhes anomaly match gaps in the neovolcanic zone inferred from acoustic backscatter a strong negative magnetization is associated with the oceanic core complex occ at 13 20 n occ1320 and is inferred to arise from exhumed old reversely magnetized lithosphere the inferred position of the magmatic axis implies 30 asymmetry of crustal accretion post anomaly 2 higher spatial resolution magnetic anomalies near the seafloor measured by autonomous underwater vehicle are qualitatively similar to earlier deep towed data but differ somewhat from the sea surface magnetics we interpret this mismatch as reflecting the differing sensitivities of the two observing geometries and the existence of a highly heterogeneous topography and magnetization this suggests that a strongly three dimensional structure exists more compatible with a geodynamic model where neighboring occs are not connected but evolve independently a modeled near seafloor profile through occ1320 shows low positive magnetization below the smooth dome a second profile running e w between two occs shows high magnetization coinciding with a large seamount reflecting recent off axis volcanism measured microbathymetry reveals extensive small volcanic cones on this seamount and confirms previous interpretations of occ morphology

hydrography and dynamics of the ria de ribadeo nw spain a wave driven estuary the ria de ribadeo a small embayment in nw spain was observed for the first time using three months of adcp acoustic doppler current profiler current meter records and three ctd conductivity temperature depth surveys a wave driven circulation pattern arises from the observations instead of the shelf wind driven circulation of other galician rias based on adcp records a unidirectional flow in the horizontal velocity field coexists with the classic two layer circulation bidirectional flow the proposed horizontal circulation pattern can then be explained as a wave driven inflow this flow enters the ria through the west side describes an anticlockwise gyre inside of it and flows out through the east side numerical simulations run with the hamsom hamburg shelf ocean model agreed with observations confirming the proposed pattern

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

crustal processes at spreading centers recent discoveries and research on mid ocean ridges mor s in the last four years have greatly increased our knowledge of this fundamental type of plate boundary the last iugg review of mor research was in 1975 aumento et al 1975 and its omission as a topic in 1978 may have reflected a feeling that spreading centers were reasonably well understood since that time however there has been a surfeit of important new observations and exciting research and there is now a turmoil of innovative ideas about the processes which create and leave their imprint on two thirds of the earth s crust new seismic measurements have been made and interpreted as evidence for the existence of shallow axial magma chambers amc beneath intermediate total opening rate 5 9 cm yr and fast 9 18 cm yr spreading centers fig 1 yet there is controversy as to whether they are steady state whether they persist beneath slow ridges as well in the steady state what the dimensions and shape of the chamber are its relation to oceanic crustal stratigraphy and its relation to observations in ophiolites black smoker hydrothermal vents have been discovered in the pacific spewing forth 350 c fluids blackened by polymetallic sulfide precipitates this discovery is embroiled in debate as to how long the vents last whether they occur at slow spreading rates as well whether the enormous heat flux of the vents freeze the magma chamber even at fast spreading rates their influence on geochemical balances in the ocean and the value of the sulfide deposits commercially it has been found that our initial view of mor s as two dimensional linear structures has served us well as an initial working model but must be significantly modified to account for variations in tectonic volcanic and hydrothermal activity along strike as well as for episodicity of these processes deep sea drilling project dsdp samples have raised fundamental questions about formation of the magnetic source layer hydrothermal circulation and fault mechanisms along the mor spreading centers which penetrate existing lithosphere along strike as propagating rifts have modified our views of how plate boundaries reorient themselves and how v shaped magnetic and topographic trends are formed we have also found that transform faults may modify spreading center processes for some distance away from their intersections with mor s and that rigid plate transform faults may fail to develop at fast spreading centers under certain conditions resulting in en echelon overlapping of spreading centers this review will focus on these developments and several others only example references to these topics will be given in the text and many important topics will not be discussed directly e g petrology and geochemistry mantle convection research on lithosphere older than 1 m y however i have tried to compile and have included an extensive bibliography for u s research on a broader range of mor topics for mid 1978 to mid 1982 which is the main purpose of this report pre 1978 references are occasionally included where appropriate abstracts are not included

comprehensive analysis of marine magnetic vector anomalies we present a comprehensive description of the analysis of marine magnetic vector anomalies the marine magnetic vector field can be measured with a shipboard three component magnetometer stcm the stcm has the advantage of measuring three components but it suffers from several types of noise sources because the principles of its measurement are more complex than that of a proton precession magnetometer we have estimated the quality of stcm data constructed an optimal filter and evaluated the reliability of the filtered data then we have organized an analytical procedure composed of four steps 1 the discrimination between two and three dimensional magnetic sources 2 the determination of magnetic boundaries 3 the calculation of the boundary strikes and 4 the estimation of the boundary magnetization contrasts we show examples of these procedures using the data near the east pacific rise 28 s 31 s collected during leg 5 of the gloria expedition all the results of the above processing are merged in order to illustrate the distinct pattern of the seafloor magnetization in the surveyed area

sedimentary facies and tectonic implications of lower mesozoic alluvial fan conglomerates of the newark basin northeastern united states abstract upper triassic to lower jurassic conglomeratic sequences of the passaic and succeeding formations along the northwest bounding fault of the newark basin in eastern pennsylvania new jersey and new york have six relatively distinct lithofacies that record continental basin filling under arid to semi arid conditions matrix supported conglomerates represent debris flows clast supported conglomerates are hyperconcentrated steamflood deposits coarse pebbly sandstones represent a braided stream channel facies and medium to fine sandstones are interpreted as a sheetflood facies deposits normally succeeded by thin mudstones of a waning flood facies associated with such mudstones at milford new jersey is a sixth pedogenic facies caliches that document pauses in deposition areal lithologic variations and analyses of vertical changes including markov analyses of facies transitions document intermittent cyclical debris flows and streamfloods on alluvial fans prograding into the basin the intermittency is best accounted for by episodic localized tectonic rejuvenation of fan provenance at the northwest bounding fault of the newark basin during the late triassic to early jurassic the final phase of basin filling penecontemporaneity of tectonism and fan deposition is corroborated by deformation of some conglomerate clasts which transmitted tectonic stresses to each other before their enclosing matrices were completely lithified some pebbles and cobbles are shattered at points of contact and clasts of relatively soft lithologies became pocked while grinding against harder fragments during post depositional tectonic episodes

concurrent correction method for modeling morphological response to dredging an offshore sandpit abstract in modeling the morphological impact of an offshore dredging pit using a process based model the hydrodynamic conditions often derived from regional scale models and sometimes incomplete measurements may not be in equilibrium with the initial bathymetry profile before dredging this lack of equilibrium causes a fast profile adjustment toward an equilibrium which may bias the model results representing the direct effect of the pit in this study a method is described which uses the parallel computing technique and evaluates only the morphological changes due to a single factor i e the dredging of a pit the hydrodynamics and morphodynamics are assumed to be in equilibrium before initial dredging of the pit the morphological evolution is computed based on the change of sediment flux due to the presence of the pit the model can avoid the computational demanding spin up period necessary to reach equilibrium conditions in particular the concurrent correction method is efficient for scenario testing with a large amount of morphological settings and hydrodynamic conditions

asymmetric generation of oceanic crust at the ultra slow spreading southwest indian ridge 64 e we describe topographic gravity magnetic and sonar data from a southwest indian ridge spreading segment near 64 e 28 s we interpret these to reveal crustal structure spreading history and volcanic and tectonic processes over the last 12 myr we confirm that the crust is some 2 km thicker north of the ridge axis though it varies along and across axis on scales of 10 km and 4 myr the plate separation rate remained approximately constant at 13 1 km myr 1 but half spreading rates were up to 40 asymmetric varying between faster to the north and faster to the south on a 4 myr timescale topography shows a dominant e w lineation normal to the n s spreading direction this is superficially similar to faulted abyssal hill terrain of the mid atlantic ridge mar but inferred fault scarps are 3 4 times more widely spaced and have greater offsets conjugate pairs of massifs on either plate are interpreted as volcanic constructions similar to the large volcano currently filling the median valley at the segment center they have temporal spacings of 4 myr and are thought to reflect episodic melt focusing along an otherwise melt poor ridge additionally there are places mainly on the southern plate where lineated topography is replaced by a much blockier topography and embryonic ocean core complexes similar to those recently reported on the mar near 13 n there is generally more extrusive volcanism on the northern plate and more tectonism on the southern one extrusive volcanism has propagated westward from the segment center since 2 ma the fuji dome core complex and adjacent seafloor to its east and west appear to be part of a single coherent block capped by extrusive rock near the segment center exposing gabbro via a detachment fault over the dome and probably exposing deeper crust or upper mantle farther west near the segment end magnetic anomalies are continuous along this block we suggest that at its eastern boundary the detachment is simply welded onto magmatically emplaced crust to the east in a similar way to young crust being welded to the old plate at ridge transform intersections

the carnian pluvial event in western europe new data from iberia and correlation with the western neotethys and eastern north america nw africa regions abstract at the beginning of the late triassic a period of increased precipitation occurred over large tracts of central pangea the carnian pluvial event it was a short lived event 1 ma coeval with a marked sea level fall and active rifting new and classical sections of carnian age in the iberian peninsula have been studied and a new correlation scheme is proposed for the iberian domain integrating field data and subsurface electric log data this is the first time that the portuguese and spanish late triassic carnian sediments are correlated the carnian pluvial event is identified in the iberian peninsula as a continental clastic wedge manuel fm and coeval sediments in between marine evaporite formations during a marked sea level drop event its age is considered to be julian early carnian by palynological and paleogeographic considerations a new correlation of the late triassic sediments of the iberian peninsula with coeval sediments of western europe nw africa and eastern north america is proposed and a new paleogeographical map of central eastern pangea for this period is presented in order to demonstrate that the geographical extent of the siliciclastic sediments related to the carnian pluvial event was much larger than accepted before

fortnightly tides and subtidal motions in a choked inlet abstract amplitudes of semi diurnal tidal fluctuations measured at an ocean inlet system decay nearly linearly by 87 between the ocean edge of the offshore ebb tidal delta and the backbay a monochromatic dynamical model for a tidally choked inlet separately reproduces the evolution of the amplitudes and phases of the semi diurnal and diurnal tidal constituents observed between the ocean and inland locations however the monochromatic model over predicts the amplitude and under predicts the lag of the lower frequency subtidal and fortnightly motions observed in the backbay a dimensional model that considers all tidal constituents simultaneously balances the along channel pressure gradient with quadratic bottom friction and that includes a time varying channel water depth is used to show that that these model data differences are associated with nonlinear interactions between the tidal constituents that are not included in non dimensional monochromatic models in particular numerical simulations suggest that the nonlinear interactions induced by quadratic bottom friction modify the amplitude and phase of the subtidal and fortnightly backbay response this nonlinear effect on the low frequency subtidal and fortnightly motions increases with increasing high frequency semi diurnal amplitude the subtidal and fortnightly motions influence water exchange processes and thus backbay temperature and salinity

implementation and modification of a three dimensional radiation stress formulation for surf zone and rip current applications regional ocean modeling system roms v 3 0 a three dimensional numerical ocean model was previously enhanced for shallow water applications by including wave induced radiation stress forcing provided through coupling to wave propagation models swan ref dif this enhancement made it suitable for surf zone applications as demonstrated using examples of obliquely incident waves on a planar beach and rip current formation in longshore bar trough morphology haas and warner 2009 in this contribution we present an update to the coupled model which implements a wave roller model and also a modified method of the radiation stress term based on mellor 2008 2011a b in press that includes a vertical distribution which better simulates non conservative i e wave breaking processes and appears to be more appropriate for sigma coordinates in very shallow waters where wave breaking conditions dominate the improvements of the modified model are shown through simulations of several cases that include a obliquely incident spectral waves on a planar beach b obliquely incident spectral waves on a natural barred beach duck 94 experiment c alongshore variable offshore wave forcing on a planar beach d alongshore varying bathymetry with constant offshore wave forcing and e nearshore barred morphology with rip channels quantitative and qualitative comparisons to previous analytical numerical laboratory studies and field measurements show that the modified model replicates surf zone recirculation patterns onshore drift at the surface and undertow at the bottom more accurately than previous formulations based on radiation stress haas and warner 2009 the results of the model and test cases are further explored for identifying the forces operating in rip current development and the potential implication for sediment transport and rip channel development also model analysis showed that rip current strength is higher when waves approach at angles of 5 to 10 in comparison to normally incident waves

tidal asymmetry and velocity skew over tidal flats and shallow channels within a macrotidal river delta 1 it is often assumed that in short shallow estuaries at leading order velocity and elevation are exactly out of phase so that duration asymmetries in the rise and fall of the tide should be manifest as skewed velocities we observed alternating ebb and flood dominant velocity skew in response to the spring neap modulation of incident asymmetry generated by the mixed mainly semidiurnal astronomical tides within the macrotidal skagit river delta in puget sound washington we describe three factors that may contribute to local asymmetries 1 ebb dominance caused by phase lags between the surface gradient and local depth 2 ebb dominance due to fluvial discharge and 3 near bed flood dominance due to baroclinicity large spring tides led to greater frictionally generated phase lags and resulted in ebb dominant velocity skew this ebb dominance caused by tidal drainage was reinforced by fluvial discharge across the tidal flat at lower low water the baroclinic component of this discharge however produced flood dominant near bed velocity skew that countered the ebb dominance of the frictional effects the balance of these processes depends strongly on the spring neap cycle magnitude of river discharge and position within the tidal flat and channel system our observations are notable in the context of previous studies describing these processes because our analyses indicate that these mechanisms are relevant over very short spatial scales of just a few kilometers and in very shallow systems

oxfordian magnetic polarity pattern reply to comment by r e sheridan and k a suydam abstract sheridan and suydam 1 raise several important points which are primarily related to the origin of reported magnetic anomalies within the jurassic magnetic quiet zone of the ocean crust and therefore are not directly relevant to our magnetostratigraphic study of oxfordian sediments 2 we will discuss only two points 1 the consistency of our oxfordian results with other evidence of mixed polarity and 2 the factors complicating the resolution of rapid magnetic reversals in the anomaly record of deep jurassic crust

tectonics of the laptev sea and moma rift systems northeastern ussr abstract examination of the topography seismicity focal mechanisms and structure of the extension of the arctic mid ocean ridge into the laptev sea suggests that the present day features of the upper crust are consistent with an asymmetric simple shear extensional system on a large scale the topographically high upper plate side alternates from severnaya zemlya and taimyr peninsula across the rift zone to the new siberian islands and then back across to the kharaulakh range and the omoloi river basin the activity of this system is indicated by moderate size normal faulting earthquakes and the extensive development of extensional structural features a weakly developed axial graben with a few teleseismic earthquakes is developed in the eastern laptev sea further south a nw striking pliocene rift system commonly known as the moma rift extends through the northern cherskii range although there is a broad zone of elevated heat flow and isolated volcanoes this system is transpressional at the present time the zone of major seismicity passes south of the rift system near the indigirka river and indicates that the rift is not acting as the plate boundary the moma rift is also asymmetric but with the lower plate southwest side being topographically higher the moma system is inactive along most of its length and only reached an early stage of development before activity ceased

continuous sea floor spreading in red sea an alternative interpretation of magnetic anomaly pattern the magnetic anomaly pattern over the red sea can be modeled as a continuous system of sea floor spreading from the early miocene to the present by using a time varying process filter the half spreading rate is approximately 1 cm yr 0 4 in yr since initial rifting the parameters that determine the process filter and development of the transition zone are the intrusion parameter a measure of the dispersion of feeder dikes or horizontal strain about the rift axis a flow parameter a measure of the average flow width and the effusion parameter a measure of the volcanic effusion and thickness of layer 2 application of a time varying process filter appears to be a powerful tool in analyzing magnetic anomalies over passive continental margins we estimate the flow parameter to be 2 7 km 1 7 mi and the intrusion parameter to be 7 5 km 4 7 mi at early rifting these values suggest that a wide distribution of axial dikes or horizontal strain is the dominant factor in forming the magnetic anomaly pattern reduction in the width of the intrusion parameter and the effusion rate as rifting proceeded resulted in focusing of the strain thinning of layer 2 and formation of the red sea deeps the interpretation of the anomaly pattern implies that basement within the main trough of the red sea is composed of a thick accumulation of volcanic sills and flows deposited during early rifting extrusion of the lavas occurred over a wide up to 60 km or 37 mi zone of strain distributed about the rift axis the development of this thickened zone of igneous crust is the second of three successive stages of extension for the red sea basin these stages are as follows 1 an initial stage of crustal stretching or listric faulting in the oligocene accompanied by probable regional uplift 2 a period of high volcanic effusion accompanied by the emplacement of stratoid basalts the stratoid volcanics form overlapping flows and sills with intercalated sediments within the main trough the spreading center narrowed from the early miocene to the present 3 steady state sea floor spreading from pliocene to present south of a transitional zone near 22 s the process filter width derived from the magnetic anomaly pattern at earliest rifting can be used to estimate the lateral variation from igneous to continental type crust in a statistical sense our data suggest that the transition from 100 continental crust to 100 igneous or stratoid type crust should occur within an interval of approximately 32 km 20 mi our modeling suggests that phase 2 or the stratoid phase began about the time of anomaly 5c or chron c5c approximately 16 ma this age is compatible with geologic estimates of the initial rifting at the late oligocene to early miocene coleman 1974 gass 1977 the opening rate for africa arabia plate motion has remained relatively constant since early rifting although the african margin appears to be accreting faster than the arabian plate

pressure gradient driven nearshore circulation on a beach influenced by a large inlet tidal shoal system 1 the nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal using a coupled wave and wave averaged nearshore circulation model it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal the model is used to predict waves and currents during field experiments conducted near the mouth of san francisco bay and nearby ocean beach the field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along ocean beach and across the ebb tidal shoal numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at ocean beach due to the resulting spatial variation in nearshore wave height wave induced setup exhibits a strong alongshore nonuniformity resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing the analysis of momentum balances inside the surf zone shows that under wave conditions with intensive wave focusing the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation inducing heterogeneous alongshore currents pressure gradient forced alongshore currents can exhibit flow reversals and flow convergence or divergence in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

structural stratigraphic and sedimentological characterisation of a wide rift system the triassic rift system of the central atlantic domain abstract the extension driven break up of the pangean supercontinent in the present day central and north atlantic domains commenced during permo triassic times permian rift processes in this region are generally attributed to crustal collapse during the latter part of the hercynian variscan orogeny but the triassic rifting style is more complex and the presence of a single over riding first order control is equivocal basement terrane structures and boundaries provide pre existing zones of weakness that had significant influences on the location timing orientation and extent of triassic rifting the 201 ma central atlantic magmatic province camp a large igneous province lip increased lithospheric heat flow at the end of rifting produced uplift and doming and also contributed to deformation and subsequent continental breakup analysis of the triassic basin structures in the central atlantic and north atlantic domains respectively georgia to nova scotia and conjugate margin and newfoundland iberia shows that four main basin types are geographically distributed 1 southern basins georgia to virginia small to medium size with limited growth structures 2 basins in the central east domain new jersey nova scotia wide basins with growth structures along long lived inherited bounding faults 3 basins in the central west domain offshore ns and morocco that comprise numerous half graben sub basins in a lower unit and an upper very wide tabular unit and 4 northern basins newfoundland portugal that are tabular and extremely wide basin architectures suggest that subsidence was regional in extent and not necessarily controlled by main faults variations in crustal characteristics are considered to have led to the development of the four main basin types stratigraphic data show that the onset of deposition in the central and southern north atlantic domain was restricted to a central segment between two main structural lineaments overall crustal rheology and inheritance exhibited first order controls on subsidence and basin development triassic basins in the central and north atlantic domain were all filled by continental deposits in various palaeo environments such as alluvial fan mega fluvial systems terminal fluvial systems fan delta fluvial systems permanent oxic and anoxic lakes playa lakes and saline lakes some of them interbedded with aeolian and volcanic deposits most basins were far from any marine domain but marine ingressions from the tethys domain are inferred from dolomite and marine fauna in portugal and from thick salt deposits in morocco and offshore canada during the late rhaetian a series of palaeogeographic maps are presented utilising plate reconstructions based on sahabi et al 2004 in order to summarize continental scale palaeo environment distribution our tectono stratigraphic model suggests that initial strain was accommodated in a central segment by inherited faults during the early and middle triassic during the carnian the rift domain was increasingly extended with the development of half graben basins in the central segment and some in the northern segment in both segments the initial strain re activated inherited faults and later the rift zones evolved towards significantly wider basins marked by the presence of a major erosional truncation surface across the basins and followed by lacustrine sedimentation that eventually overlapped paleo topographic highs subsidence of such regional extent is likely driven by thermal processes following a phase of extreme lithospheric thinning and lower crustal removal associated with mantle uplift the architecture of the triassic rifting has the characteristics of the wide rift mode very large basins with some active faults for which subsidence is driven by lower crustal flow within a high heat flow region nevertheless some faults were active during late triassic sedimentation but accounted for a relatively minor part of the overall subsidence pulses of active subsidence and topographic rejuvenation led to fluvial dominated deposition within basins non rejuvenation of hinterland led to more lacustrine dominated sedimentation and eventual connection of basins across topographic highs due to regional thermal subsidence during the latest rhaetian basins with the lowest elevations were possibly flooded by marine waters resulting in precipitation of thick salt deposits

constraints on synrift intrabasinal horst development from alluvial fan and aeolian deposits triassic fundy basin nova scotia the authors would like to acknowledge shell e and p for funding this study rob raeside at the acadia university and liz kosters for their support during the field seasons we also would like to thank brian p j williams for enthusiastic discussions in the field

some observations of wave current interaction abstract using data collected during the scawvex project the effect of depth and current changes particularly tidal on waves and the effect of waves on tidal currents were examined the possible interaction mechanisms between waves tides and surges are reviewed these include the effective surface wind stress bottom friction depth and current refraction and modulation of the absolute and relative wave period the usefulness of tidal periodicity in identifying both interactions in wave parameters and the effects of the waves on the tide is noted for correct analysis to obtain wave free tidal conditions or tidally averaged wave statistics it is particularly important to understand the interaction mechanisms for example the amplitude of the tidal current was found to be reduced in periods of high waves ideally waves and currents should always be measured simultaneously since the correct determination of either in shallow water requires knowledge of the other various remote sensing systems which can potentially do this are discussed since the algorithms are quite complex and may depend on a good first guess the future probably lies in combining remote sensing plus modelling together with ground truth in situ data

the stratigraphy and sedimentology of the fundy group triassic of the st martins area new brunswick triassic sediments exposed along the south shore of new brunswick near st martins were deposited primarily by a series of alluvial fans prograding eastward from the western margin of the fundy half graben and are interbedded with fluvial conglomerates deposited by an axially flowing river system the sediments are divisible into three formations which are described here formally for the first time these are from base to top the honeycomb point quaco and echo cove formations the basal honeycomb point formation consists of approximately 990 m of red beds exposed in several fault blocks the western outcrops consist of coarse breccias of the proximal fan the browns beach member which fines eastward into sheetflood deposits of the mid to distal fan the mccumber point member both units contain eolian sands that indicate paleowind direction from the northeast these are overlain by fluvial conglomerates of the quaco formation 190 300 m thick which were deposited by a large braided river system

an application of the response function technique to profiles of bathymetry and gravity in the gulf of aden summary the relationship between bathymetry and gravity in the eastern and the western gulf of aden is analysed by computing response functions the form of the response functions indicates that the short wavelength topography is isostatically compensated the most appropriate mechanism of compensation is one in which the topography is not locally compensated but regionally compensated by flexure of the lithosphere though the sets of profiles from the eastern and the western gulf of aden are separated by only 500 750 km the observed response functions are very different the lithosphere in the eastern gulf of aden can be modelled by an elastic plate 15 3 km thick whereas an elastic plate 3 2km thick is probably an appropriate model for the lithosphere in the western gulf of aden a different mechanism of isostasy the pratt operates in the compensation of the long wavelength topography of the mid ocean ridge in the gulf of aden a larger negative broad bouguer gravity anomaly across the western gulf of aden than across the east indicates that upper mantle temperatures increase from east to west the long wavelength shallowing of the gulf of aden and increasing elevation of the adjacent continents from east to west are therefore probably mainly the result of thermal uplift the subdued nature of the median valley and consequently other short wave length topography in the west can be explained by hot low viscosity asthenosphere and the inferred thin lithosphere in the west also suggests high temperature mantle finally a magnetic anomaly superimposed on the axial anomaly which is probably related to the depth of the curie temperature is more common in the western gulf of aden than in the east and this is also consistent with upper mantle temperatures increasing to the west there are a number of similarities between the mid ocean ridge in the western gulf of aden and the reykjanes ridge it is suggested that the western gulf of aden is anomalous because of its proximity to the afar hot spot in the same way that the reykjanes ridge is often considered to be anomalous because of its proximity to the iceland hot spot

wave current interactions in a wave dominated tidal inlet 1 wave current interactions play a major role in the dynamics of shallow tidal inlets this study investigates these interactions at a natural inlet with a strong focus on current induced changes on wave propagation the analysis of hydrodynamic data collected at the albufeira lagoon portugal revealed spatiotemporal variations of water levels and wave heights along the inlet attributed to wave current interaction processes we compared the simulations of a coupled wave circulation modeling system computed with and without waves and propagated with and without current feedback the wave induced setup inside the lagoon represented 7 15 of the offshore significant wave height the accuracy of the wave s predictions improved when current feedback was included during ebb the currents increased the wave height at the mouth of the inlet up to 20 and decreased the wave height in the inlet up to 40 due to current induced refraction steepness dissipation and partial blocking during flood the currents decreased the wave height in the inlet up to 10 and increased the wave height at the exterior parts of the ebb shoal up to 10 due to current induced refraction these effects significantly attenuate seaward sediment fluxes during ebb and contribute to the sediment accretion in the inlet

hydrodynamic and sediment transport modeling of new river inlet nc under the interaction of tides and waves the interactions between waves tidal currents and bathymetry near new river inlet nc usa are investigated to understand the effects on the resulting hydrodynamics and sediment transport a quasi 3 d nearshore community model nearcom tvd is used in this integrated observational and modeling study the model is validated with observations of waves and currents at 30 locations including in a recently dredged navigation channel and a shallower channel and on the ebb tidal delta for a range of flow and offshore wave conditions during may 2012 in the channels model skills for flow velocity and wave height are high near the ebb tidal delta the model reproduces the observed rapid onshore offshore decay of wave heights current velocities model results reveal that this sharp transition coincides with the location of the breaker zone over the ebb tidal delta which is modulated by semidiurnal tides and by wave intensity the modulation of wave heights is primarily owing to depth changes rather than direct wave current interaction the modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward directed currents near the inlet entrance numerical experiments suggest that these flow patterns are associated with the channel shoal bathymetry near the inlet similar to the generation of rip currents consistent with other inlet studies model results suggest that tidal currents drive sediment fluxes in the channels but that sediment fluxes on the ebb tidal delta are driven primarily by waves

pollen and spores date origin of rift basins from texas to nova scotia as early late triassic palynological studies of the nonmarine newark supergroup of eastern north america and of rift basins in the northern gulf of mexico facilitate correlation with well dated marine sections of europe new information emphasizes the chronological link between the newark basins and a gulf of mexico basin and their common history in the rifting of north america from pangea shales from the subsurface south georgia basin are shown to be of late karnian age early late triassic the known time of earliest sedimentation in the culpeper basin is extended from norian late late triassic to mid karnian and the date of earliest sedimentation in the richmond and deep river basins is moved to at least earliest karnian perhaps ladinian the subsurface eagle mills formation in texas and arkansas has been dated palynologically as mid to late karnian the oldest parts of the newark supergroup and the eagle mills formation mostly began deposition in precursor rift basins that formed in ladinian to early karnian time in the southern newark basins sedimentation apparently ceased in late karnian but continued in the northern basins well into the jurassic until genesis of the atlantic ended basin sedimentation

on the quality of marine magnetic anomaly sources and sea floor topography summary the quality of marine magnetic anomaly sources is described with the power density representation of a stochastic model of random temporal and spatial emplacement of the marine magnetic anomaly source in the oceanic crust typical values of sea floor spreading and emplacement parameters define a high fidelity process of recording and sea surface detection of the palaeomagnetic field reversals for spreading rates over 20mmyr an analogous stochastic model is developed for the formation of sea floor topography by normal faulting it is shown that the random process of normal faulting observed in the inner walls of the famous rift valley can account for the quality of the adjacent west rift mountains topography quality as opposed to quantity is a degree of excellence relative nature or kind or character concise oxford dictionary of clcrrent english the signal to noise ratio is a measure of quality in this paper we address the signal to noise ratio of sea floor spreading magnetic anomaly sources we use a stochastic model of discrete random temporal and spatial emplacement of magnetic source material in a spreading centre that records the ambient geomagnetic field behaviour and show that the temporal aspect i e the mean frequency of emplacement in a spreading centre is critical to the quality of sea floor spreading magnetic anomaly sources it will be shown that the sea floor topography generated by a stochastic process of extension or thinning of the brittle crust in response to discrete and random normal faulting in atspreading centre can be treated as noise the quality of sea floor topography can be estimated and expressed in terms of mean fault density and crustal thinning as a measure of the tectonic processes which formed the topography

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

a stochastic model for the creation of abyssal hill topography at a slow spreading center the present study is an attempt to model abyssal hill topography i e the randomly varying topography that is superimposed on the subsidence of the ocean floor due to thermal contraction we assume that abyssal hill topography is created by faulting and that it can be represented as the convolution of a series of stochastic fault offsets with a fault impulse response as a constraint the power spectrum of the model generated topography will have to resemble the power spectrum of a profile of abyssal hill topography across a typical slow spreading ridge such as found in the south atlantic using a series of fault offsets positively correlated in space and fault impulse responses limited to a finite width w profiles that statistically resemble abyssal hill topography have been generated if the fault offsets are constrained to be positive i e to cause uplift the synthetic profiles contain a steady state depression at the axis the fit of the synthetically derived topography to the observed topography is very sensitive to the width w of the fault impulse response our results suggest that the effects of a faulting event must be limited to distances of about 3 5 km and that tectonic activity must take place in the immediate vicinity of the inner wall of the axial valley if faulting is indeed the process that creates abyssal hill topography the best fit flexural impulse response to faulting implies a flexural rigidity of 5 1017 n m if instead constructional volcanism contributes significantly to the topography our study suggests that the emplacement of volcanic constructions must also take place within a narrow width w about the axis

tectonic control of triassic sedimentation in southern new brunswick local and regional implications both regional and local tectonics controlled the sediment distribution in the fundy half graben during the triassic locally alluvial fans built out into the basin from the western boundary fault along what is now the south shore of new brunswick the alluvial fan red beds of the honeycomb point formation are covered by fluvial conglomerates of the quaco formation which in turn are buried by a resurgence of alluvial fan deposition represented by the echo cove formation pollen recovered from the upper part of the echo cove formation indicates that regionally the system of triassic jurassic grabens along the eastern seaboard is composed of two separate graben systems one stretching from south carolina to connecticut the other from the gulf of maine to the southern grand banks initial graben formation began at the southern end of each system followed by successive grabens opening toward the north the areal distribution of both graben systems appears to have been controlled by four large transform fault systems from the middle triassic through the jurassic the age and overall distribution of sediments within the fundy basin confirm the existence of a hot spot along the kelvin seamount chain and refines determination of the position and timing of the initial rifting that led to the formation of the present atlantic ocean

three dimensional magnetic modeling of a propagating rift galapagos 95 30 w a combined deep tow and seabeam investigation at 95 30 w on the cocos nazca spreading center has revealed the crustal contact between the propagating rift and the dying rift systems the observed 27 km offset between the axes creates an ideal situation for the application of magnetic methods the normally magnetized crust of the propagating rift tip penetrates into older crust which was created when the earth s main field was reversed as the v shaped structure of the rift clearly violates the conventional two dimensional assumptions a full three dimensional analysis is required in addition the distorting influence of over 1000 m bathymetric relief must be removed from the observed field inversions have been performed on the gridded representations of the observed magnetic field and bathymetry working in the fourier domain the result is a gridded rock magnetization distribution the inversion of the surface data covers a large area 6000 km2 and demonstrates close agreement with magnetization amplitudes of rock samples at existing dredge sites in general the propagating rift process appears to be much more orderly than the dying rift process the magnetic polarity transition widths are narrower and the boundaries have fewer undulations than the dying rift which appears to be quite episodic in behavior the average propagation rate is 52 mm yr compared to the average spreading half rate of 29 mm yr the locations of the boundaries suggest that the acceleration to the normal spreading rate on the propagating rift requires about 250 000 years the inversion of the deep tow data near the seafloor provides a high resolution definition of the location of the tip of the propagating rift at 2 38 1 n 95 30 0 w

structure and development of the midocean ridge plate boundary in the gulf of aden evidence from gloria side scan sonar a gloria side scan sonar survey along the crest of the midocean ridge in the gulf of aden has provided information on the small scale morphology of its spreading centers and fracture zones spreading center offsets increase in length to the east this is thought to result from changes in the behavior of the mantle with increasing distance from the afar hot spot a 300 km long spreading center in the western gulf of aden is oriented obliquely to the spreading direction nested within the obliquely oriented median valley is an en echelon arrangement of a number of smaller elongated basins each oriented approximately normal to the spreading direction close to the axis of spreading volcanic and closely spaced tectonic structures run approximately normal to the spreading direction higher on the walls of the median valley more widely spaced normal faults have formed subparallel to the valley in the western gulf of aden there are no indications of sonar targets that might represent transform faults parallel to the nne spreading direction in the east spreading center offsets of 15 25 km are made at fracture zones which are best described as narrow zones of highly oblique spreading offsets of greater than 25 km are achieved on single transform faults and the associated tectonic fabric has a spreading direction trend the boundaries between crusts of different ages along inactive transform fault extensions lie along the bases of fracture zone scarps these scarps are situated in the older crust and face the younger this is the opposite of the situation predicted on the basis of simple plate cooling models at some places in the gulf of aden the fracture zone topography is very subdued and this is attributed to the failure of the two slabs of lithosphere at the end of the transform fault to couple completely before the younger lithosphere on the nontransform side of the spreading center completes its ascent of the median valley wall there is evidence of a change of spreading direction 3 5 m y ago from about 040 to 022 it is argued that the small scale morphology of the transform fault spreading center intersections can be understood in terms of the transfer of shear fracture on a transform fault to tensile fracture on a spreading center propagating away from the intersection it is concluded that the transform fault must be weaker than the spreading center

climatic and biotic change in the late triassic generally arid conditions that pervaded much of europe and north america during the late triassic were interrupted by a wet monsoonal climatic phase during middle and late carnian times extensive fluviatile sandstones deposited at this time throughout the region occur within a thick sequence of playa lake mudstones the sandstones occasionally contain kaolinite suggesting a humid climate an extreme 13 c depletion in a shallow marine sequence of this age in israel has been interpreted as evidence for an influx of freshwater a widespread change from carbonates to clastics in marine sequences at this time may also be climate related water course cave systems in limestone areas exposed during the late triassic indicate high levels of runoff during the middle and late carnian the marine invertebrate fauna shows a significant turnover at the end of the early carnian the terrestrial fauna and flora were relatively unaffected at this time but subsequently diversified prior to a major biotic turnover at the carnian norian boundary these periods of biotic change appear to be synchronous with the onset and cessation of a carnian humid phase the change to a monsoonal climate during this interval has been documented over more than 90 of longitude between 5 and 50 north of the triassic equator it may have been caused by rising atmospheric co 2 levels due to volcanism associated with the incipient dispersal of pangaea

the role of morphology and wave current interaction at tidal inlets an idealized modeling analysis the outflowing currents from tidal inlets are influenced both by the morphology of the ebb tide shoal and interaction with incident surface gravity waves likewise the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current the 3 d coupled ocean atmosphere wave sediment transport coawst modeling system is applied to numerically analyze the interaction between currents waves and bathymetry in idealized inlet configurations the bathymetry is found to be a dominant controlling variable in the absence of an ebb shoal and with weak wave forcing a narrow outflow jet extends seaward with little lateral spreading the presence of an ebb tide shoal produces significant pressure gradients in the region of the outflow resulting in enhanced lateral spreading of the jet incident waves cause lateral spreading and limit the seaward extent of the jet due both to conversion of wave momentum flux and enhanced bottom friction the interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume for weak outflows the outflow jet is actually enhanced by strong waves when there is a channel across the bar due to the return current effect for both strong and weak outflows waves increase the alongshore transport in both directions from the inlet due to the wave induced setup over the ebb shoal wave breaking is more influenced by the topography of the ebb shoal than by wave current interaction although strong outflows show intensified breaking at the head of the main channel