accommodation and sediment supply controls on clastic parasequences a meta analysis this study combines data from many published case studies to undertake a quantitative characterization of clastic parasequences with the aim to determine how accommodation sediment supply and autogenic sediment storage dynamics are recorded in their sedimentary architecture and stacking patterns results of this study are used to critically evaluate the validity of paradigms and models that are routinely used to explain and predict trends in the anatomy and arrangement of parasequences data on 957 parasequences from 62 case studies of clastic shallow water successions were coded in a relational database which includes outcrop and subsurface datasets of ancient and quaternary examples these units cover the preserved records of both river dominated deltas and wave dominated coasts representing shoreline transits over a breadth of timescales likely of both local and regional extent the role of extant accommodation rates of creation of accommodation and rates of sediment supply in determining parasequence architecture is assessed through analysis of relationships between i proxies of these variables at different scales rates of aggradation and progradation facies belt shoreline trajectories systems tract type parasequence set stacking patterns parasequence progradation angle and stratigraphic rise size of feeder rivers and ii parameters that describe the geometry and stacking style of parasequences and associated shallow water sand bodies statistical analyses of database outputs indicate which proxies of accommodation sediment supply and accommodation sediment supply ratio are significant as predictors of parasequence architecture and allow for interpretations of the importance of allogenic and autogenic factors the principal results of this study reveal the following i parasequence thickness varies as a function of water depth accommodation generation and erosional truncation and these variations are also reflected across types of systems tracts and parasequence sets ii the dip length of parasequence sand bodies demonstrates scaling with measures of accommodation sediment supply ratio at multiple scales partly in relation to the possible effect of sediment supply on progradation rates iii in systems tracts stratigraphic trends in parasequence stacking due to autogenic mechanisms or to acceleration or deceleration in relative sea level fluctuations are not revealed quantitatively iv some association is seen between the abundance of deltaic or river dominated parasequences and progradational stacking v positive but modest correlation is observed between measures of river system size and the dip length of shallow marine parasequence sand bodies the resulting insights can be applied to guide sequence stratigraphic interpretations of the rock record and the characterization of sub seismic stratigraphic architectures of subsurface successions

taconic orogeny in pennsylvania a 15 20 m y apennine style ordovician event viewed from its martic hinterland abstract in pennsylvania the taconic orogeny lasted from 461 to 443 ma as cambro ordovician slope deposits were deformed into mountains edging the laurentian craton at the same time that materials from an adjacent deep water basin were being transported 50 70 km across a carbonate platform into foreland basins this paper focuses on shelf edge hinterland features mostly the martic zone as a folded stack of imbricate thrust sheets of slope materials that corresponds to vermont s taconic mountains and southern quebec s zone of taconic allochthons work of the last century is summarized corrected and combined with a new 450 ma radiometric date and fluid inclusion data from the pequea mine within the martic zone these and abundant new graptolite and conodont dates in the foreland paint a revised pennsylvania picture differing from the northern taconic areas differences are 1 transport of very large allochthonous masses of deep water material the dauphin formation far across the carbonate platform and 2 deformation migrating progressively across that platform during a 15 20 m y period incorporating it and its foreland cover into alpine scale recumbent folds and thrusts the scenario has many analogies to italy s modern apennine mountains minus the latian volcanics

orientation of in situ stresses in the oceanic crust two in situ measurements of principal stress directions have been made in dsdp holes 504b south of the costa rica rift on the nazca plate and 597c west of the east pacific rise on the pacific plate in both cases the orientations of in situ principal stresses determined from borehole breakouts are consistent with the stress directions inferred from intraplate earthquakes located near the sites

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

experimental measurement of the relative importance of controls on shoreline migration abstract shoreline position in sedimentary rocks is a sensitive recorder of the interplay of several controlling factors the most important of these are thought to be the stratigraphic trinity eustatic sea level subsidence and sediment supply in ancient rock sequences it is generally difficult to disentangle the effects of these variables here we analyze the relative influence of sea level subsidence sediment supply and other controlling variables on shoreline migration in an experimental basin equipped with a subsiding floor the experiment used a linear hinge type subsidence profile for which the rate was kept constant in time constant overall sediment supply and base level variation on two time scales that were first applied separately and then superimposed although base level was the only controlling variable that was externally varied in time the base level changes induced changes in other variables indirectly e g by changing the partitioning of sediment between the fluvial and offshore segments of the system we examine the relative importance of measured direct and indirect changes in all the governing variables through the use of a moving boundary equation for shoreline migration when measured values are used for all the variables in the equation shoreline migration rate throughout the run can be predicted with a maximum r2 of 0 92 starting with this optimal prediction of the observed shoreline behavior we successively replace variables in the equation with their run averaged values degrading the prediction the relative loss of prediction accuracy as each variable is replaced is a measure of the importance of that variable in accounting for the observed shoreline migration by this measure base level is the most important variable followed in turn by sediment supply to the foreset geometry of the foreset and the average subsidence rate over the foreset from the shoreline migration equation we also derive a quantitative version of the a s ratio often applied in sequence stratigraphy the new formulation reduces to a form comparable to the traditional descriptive a s ratio if changes in foreset slope gain or loss of sediment to the fluvial system and spatial variation in subsidence rate are all negligible

understanding fine grained river sediment dispersal on continental margins studies of fine grained sediment dispersal in the marine environment have documented diversity in the behavior of depositional systems on continental margins with different oceanographic conditions and morphologies based on the pattern and nature of sediment accumulation for twenty three case studies we propose there are five basic types of dispersal systems and these are related to river wave tide and margin characteristics data suggest that the type of dispersal system on any margin can be predicted with knowledge of sediment load mean significant wave height tidal range and continental shelf width at a river mouth and from these a hierarchical decision tree is developed analysis of the dispersal system type of more than 100 river mouths reveals that proximal accumulation dominated pad and marine dispersal dominated mdd systems are most abundant but estuarine accumulation dominated ead systems also are anticipated to be numerous globally research quantifying marine sediment dynamics in these system types is needed although less common the size and nature of subaqueous delta clinoform sdc and canyon captured cc systems also warrant future attention to their study strong correlations between physical characteristics i e significant wave height and tidal range and the depth and distance to the nearest maximum shelf depocenter provide evidence that in reality a continuum exists between the system types the process related partitioning of sediment in the five different types of marine dispersal systems has important implications for understanding the stratigraphic record and the cycling of carbon

a source to sink perspective of the waipaoa river margin abstract a fundamental goal of the earth science community is to understand how perturbations on earth s surface are preserved in the stratigraphic record recent source to sink s2s studies of the waipaoa sedimentary system wss new zealand are synthesized herein to provide a holistic perspective of the processes that generate transport and preserve sedimentary strata and organic carbon on the waipaoa margin in the late quaternary rapid uplift associated with subduction processes and weak sedimentary units have conspired to generate rapid rates of incision and erosion in the waipaoa catchment since the last glacial maximum lgm we show that although much of the sediment exported offshore during this time interval originated from valley excavation a substantial portion emanated from hillslopes mostly through deep seated landslide and earthflow processes that were vigorous during periods of rapid fluvial incision just prior to the pleistocene holocene transition lacustrine sediments deposited in naturally dammed 7 ky old lake tutira provide a record of holocene environmental controls on upper catchment sedimentation in the wss with 1400 storms identified storm frequency is modulated by the waxing and waning of atmospheric teleconnections between the tropics and antarctica furthermore clear long term changes in sediment yield are evident from the lake tutira record following human settlement as conversion to pasture is accompanied by a 3 fold increase in the long term lake sediment accumulation rate whereas there is ample evidence that waipaoa river flood deposits are routinely deposited offshore in the sheltered confines of poverty bay over the longer term waves and currents subsequently resuspend and transport these deposits both landward sandy fraction and seaward finer fraction thus the timing of sediment supply to areas of net sediment accumulation is more often driven by wave events that are not associated with river flooding therefore we conclude that asynchronicity of river sediment delivery and of wave resuspension in most instances precludes the direct preservation of flood events in the stratigraphic record of the waipaoa shelf over the longer term the sediment package preserved on the shelf and slope since the lgm can be explained in large measure by sequence stratigraphic models forced by varying sea level and ongoing tectonic deformation of the margin as sea level rose sediment supply to the slope was reduced by about a factor of 5 due to shelf trapping despite this reduction turbidites are found at similar frequency throughout the lgm present as the dominant trigger appears to be subduction earthquakes with large ones having a return interval of about 200 100 years sediment budget exercises that consider both modern river discharge versus centennial accumulation rates and post lgm terrestrial production versus offshore isopachs mass balances indicate that about half of the total sediment production from the waipaoa escapes the study area moreover a coupled sediment transport hydrodynamic model and observations of textural trends on the shelf indicate that a large fraction of the sediment is carried outside the study area along the shelf to the northeast by the river plume or by combined current wave activity therefore we conclude that the wss is an open system with sediment escape from the present day through the lgm the organic matter associated with sediment as it moves from upland source to marine sink is a product of particle history and provides a record of materials that have cycled over timescales of days to millions of years the ubiquity of fossil organic carbon oc in both the terrestrial and marine realms of the waipaoa attests both to the chronic nature of its source crumbling mudstones further destabilized by land use and its biogeochemical recalcitrance modern oc persists by virtue of its continual production along the s2s transit and is buried and preserved within the adjacent marine depocenters the waipaoa contrasts with dispersal systems on wide energetic shelves e g the amazon and fly rivers where sediment is extensively refluxed in oxygenated overlying water resulting in the biogeochemical incineration of particulate oc the waipaoa like other small mountainous rivers on active margins exhibits a high riverine oc preservation efficiency 50 in its marine depocenters because of the relatively rapid event driven accumulation of sediment

diagenesis and evolution of microporosity of middle upper devonian kee scarp reefs norman wells northwest territories canada petrographic and chemical evidence the middle upper devonian kee scarp reef complexes of norman wells northwest territories canada are oil producing stromatoporoid dominated carbonates episodic increases in the rate of sea level rise produced multiple cycles of reef growth that exhibit backstepping characteristics these carbonates composed of invariably altered limestones have original interskeletal intraskeletal and intergranular porosity mostly occluded by nonferroan dull luminescent cements secondary porosity represented by micropores of various types developed during diagenesis by aggrading neomorphism and dissolution the micropores represent the main reservoir porosity in the kee scarp limestone micropores in the kee scarp limestone can be classified into four categories based on thei shapes 1 stepwise rhombic about 1 m to 2 m in diameter developed mainly in stromatoporoids 2 intercrystalline rhombic about 1 m in diameter developed mainly in algal aggregates 3 microvugs 4 m to 10 m in diameter developed mainly in algal aggregates and 4 microchannels about 12 m in length and 0 5 m in width developed in algal aggregates and stromatoporoids the stepwise rhombic and microvugs are developed mainly at the kee scarp reef margin and constitute the best type of reservoir porosity petrographic chemical and isotopic studies of kee scarp reef components reveal a complex diagenetic history involving marine fluids modified by increasing water rock interaction and burial early diagenetic processes include marine cementation and micritization followed by neomorphic replacement of high mg calcite and aragonite reef components resulting in the creation of the first generation of microporosity via dissolution on a micron scale later diagenesis represented by microfracturing and cementation with two generations of equant calcite and stylolitization was responsible for the second generation of microporosity very minor silicification dolomitization and vertical fracturing occurred at variable depths portions of well preserved marine cements stromatoporoids an rare crinoids of postulated high mg calcite precursor mineralogy have escaped diagenetic alteration and preserve the original marine dgr18o and dgr13c signatures 4 7 0 3 pmil pdb for oxygen 1 0 0 4 pmil pdb for carbon minor and trace element data show less preservation of the postulated original marine composition neomorphic stabilization of skeletal components caused further depletion in dgr18o but very little change in dgr13c an argument for modification of the original marine fluids with increasing burial variations in magnitude of water rock interaction with depth facies changes and porosity modifications probably exerted some control on fractionation and distribution of stable isotopes and trace elements in ree components

provenance of sand on the poverty bay shelf the link between source and sink sectors of the waipaoa river sedimentary system abstract the poverty shelf north island new zealand is a segment of the waipaoa sedimentary system wss a margins source to sink focus site our petrographic analysis of sand from shelf core samples indicates that the sand fraction is mainly derived from intra and potentially extrabasinal sources but surprisingly the major fluvial system that drains into poverty bay the waipaoa river mean qfl xqyfzl is not the dominant source only one vibracore at the mouth of poverty bay contained sand qfl xqyfzl potentially derived from the waipaoa river the shelf sand mean qfl xqyfzl more strongly resembles beach sand mean qfl xqyfzl collected along the coast which is likely sourced from pervasive local cliff erosion of miocene pliocene sedimentary units that exhibit similar sandstone detrital modes mean qfl xqyfzl texturally coarser more poorly sorted and more angular sand is located along the outer shelf while finer well sorted sand characterizes the mid shelf these findings suggest a shorter transport history for the material near the outer shelf bathymetric high areas and this observation along with the composition data suggests that they were sourced by erosion of locally exposed miocene pliocene units a potential extrabasinal source of shelf sediment is indicated by anomalous prolate and equant shaped greywacke torlesse and minor red chert pebbles collected in two outer shelf box cores on the lachlan anticline these are not lithologies found within the terrestrial segment of the wss or strata comprising the outer shelf highs the clast shapes are also distinctly different from the oblate shaped pebble sized greywacke gravel clasts on beaches in hawke bay rather these sediments are more similar to torlesse stream gravel seismic and multibeam data support the possibility that during the most recent sea level lowstand the hawke bay fluvial system flowed into poverty canyon bringing these unique gravels onto what is now the poverty outer shelf the presence of the torlesse gravel is significant in that it highlights how the wss was not a closed sedimentary system in the past just as recent sedimentary research has shown in the case today

principles of regression and transgression the nature of the interplay between accommodation and sediment supply the rate of change of accommodation at the shoreline a and the rate of sediment supply s are the primary factors controlling regression and transgression in the geological record or retreat and advance of a coastal depositional system the generally accepted notion here referred to as the a s ratio concept stating that the migration of a shoreline is controlled principally by the magnitude of the ratio of a to s is insufficient and somewhat misleading partly owing to the problem of dimensional confusion the interplay of a and s inevitably results in autoretreat of the shoreline whereby the seaward advance of any shoreline is halted and is subsequently turned to landward retreat provided there is a continuous rise of relative sea level how effective the autoretreat process is depends for a given period of relative sea level rising upon the length of potential time period for the seaward advance of shoreline and is proportional to a 2 s and a super 1 5 s super 0 5 in two and three dimensional sediment dispersal modes respectively autoretreat becomes more effective as a increases and or s decreases a functions more critically to the effectiveness than s does the a s ratio concept is only approximately applicable when autoretreat is less effective i e with very low a and or very high s in this sense the autoretreat theory and the a s ratio concept are complementary to each other the autoretreat mechanism is expected to be substantially useful not only in fluvial deltas but also in many other depositional systems e g barrier islands whose evolution has been considered in terms of the a s ratio concept

stratigraphic relationships and detrital composition of the medial ordovician flysch of western new england implications for the tectonic evolution of the taconic orogeny a reply to rodgers we present new stratigraphic and petrographic data on the easterly derived medial ordovician flysch sequence of western new england and eastern new york state a conformable relationship exists between the flysch and underlying early paleozoic continental rise sediments within the western taconic allochthon farther east in the allochthon we observe a possibly disconformable relationship contrary to previous interpretations these facts suggest that at any place within this paleogeographic realm the sediments were undeformed and untransported at the initiation of flysch deposition at least three sources contributed detritus to the flysch 1 taconic sequence sediments 2 deformed and metamorphosed pelitic psammitic and volcanic lithologies and 3 igneous rocks of dominantly mafic ultramafic affinities these three sources are respectively interpretable as continental rise accretionary prism and ophiolitic volcanic arc assemblages which are recognized in the regional geology of western new eng

floodplain construction by recent rapid vertical accretion waipaoa river new zealand the rate of vertical accretion typically 14 18 mm h 1 during eight floods in the waipaoa river basin with recurrence intervals of 5 to 60 years was determined by relating the floodplain stratigraphy at mcphail s bend to the 1948 1995 flood history overbank deposits remaining after a flood that occurred in march 1996 suggest a rate of vertical accretion of 15 mm h 1 by contrast because the flow velocity across the floodplain was too high to permit deposition from suspension during the record flood of march 1988 the rate of vertical accretion was only 6 mm h 1 the sequence of deposition is highly discontinuous and the rapid vertical accretion is a response to a late 19th to early 20th century phase of deforestation in the headwaters that probably initiated a far greater change in suspended sediment yield than in discharge cross section surveys conducted since 1948 indicate that the high suspended sediment load of the waipaoa river also promoted in channel deposition which effected a progressive reduction in bankfull channel width although due to the overbank deposition channel capacity remained constant 1998 john wiley sons ltd

a unifying framework for shoreline migration 2 application to wave dominated coasts 1 the bruun rule widely used to predict transgression due to sea level rise on decade to century timescales based on a fixed nearshore profile neglects the influence of inland topography and substrate lithology leading to physically unreasonable predictions on longer timescales we use a new approach the shoreline exner equation to model shoreline transgression on wave dominated coasts over timescales of decades to millennia our results show that interactions between nearshore processes and inland topography neglected by bruun style models drive morphologic evolution which modulates shoreline retreat analytical solutions suggest that while short term shoreline retreat will sometimes follow the bruun rule long term transgression will always follow the slope of the inland topography moreover our results show that the slope of the inland landscape relative to the nearshore slope exerts a first order control on coastal morphology such that steep coasts tend to form cliff backed beaches while gentle coasts tend to form barrier island lagoon systems however compositional variations between the inland landscape and nearshore system can alter this pattern

sedimentologic and geochemical evidence for middle ordovician near trench volcanism in the central appalachian orogen the jonestown volcanic rocks are a minor but important component of the greenwich slice of the hamburg klippe of eastern pennsylvania sedimentary rocks of the greenwich slice are arranged in faultbounded coarsening upward sequences of pelagic deposits early to middle ordovician overlain by hemipelagic and turbidite deposits middle ordovician petrographic and geochemical characteristics of the sedimentary rocks indicate derivation from continental rather than volcanic sources the coarsening upward sequences of the greenwich slice are inferred to record advance of a site on oceanic lithosphere toward and ultimately into a trench by middle ordovician time rocks of the jonestown volcanic suite were extruded onto and intruded into the inferred middle ordovician near trench and trench axis mudstone and sandstone immobile element concentrations of the jonestown suite are typical of mid oceanic ridge basalts and along with the lack of associated shallow water and or volcaniclastic sedimentary rocks a

coastal progradation and sediment partitioning in the holocene waipaoa sedimentary system new zealand abstract over the late holocene highstand the shoreline at poverty bay nz migrated 12 km seaward fed by sediment from the waipaoa river paleo shorelines indicate steadily decelerating progradation possibly signaling changes in forcing on the waipaoa sedimentary system to isolate the cause of this progradation slowdown we reconstruct late holocene tectonics and stratigraphy over the waipaoa coastal plain and nearshore from 7 ka present we find that decreasing rates of sediment storage by coastal progradation were driven by increasing tectonic storage in the steadily subsiding but rapidly growing coastal plain such that net terrestrial storage remained constant at 0 8 mt yr hence changes in shoreline migration were due to autogenic increases in accommodation rather than allogenic changes in forcing furthermore while the waipaoa sediment load is primarily mud reconstructions suggest that progradation was largely controlled by the supply of coarse grained sediment our results suggest that in coastal systems such as the waipaoa where progradation is confined and wave energy is high net accumulation of muds occurs only behind the prograding sandy shoreface which shelters them from wave attack accounting for mud storage in the waipaoa coastal plain and poverty bay suggests that export of muddy sediment to the waipaoa shelf remained roughly constant at 2 0 mt yr from 7 ka until the onset of anthropogenic deforestation in the 19th century

fluvial and marine controls on combined subaerial and subaqueous delta progradation morphodynamic modeling of compound clinoform development 1 fluviodeltaic systems commonly display a compound clinoform geometry that consists of a subaerial subaqueous delta couplet the extent of subaqueous delta development varies significantly and in modern systems is a function of fluvial input and basin hydrodynamics we present a model of fluviodeltaic progradation in which the repeated occurrence of characteristic terrestrial floods and large coastal storms drives fluvial and shallow marine morphodynamics respectively we couple fluvial and shallow marine sediment dynamics via the surf zone which we collapse to a shock condition and treat as a moving boundary with steady sediment supply and sea level and simple basin geometry our model naturally develops prograding deltas with compound clinoform geometries the subaerial delta grows via fluvial aggradation and shoreface progradation whereas the subaqueous delta expands through foreset progradation with only minor topset aggradation the interplay of fluvial input with the wave current field controls the basic partitioning of sediment between subaerial and subaqueous deltas and by extension the compound clinoform geometry increasing the frequency or magnitude of coastal storms decreasing flood frequency or discharge and reducing grain size all increase the fraction of sediment delivered to the shallow marine environment and the extent of subaqueous delta progradation relative to subaerial delta development our model which emphasizes the intrinsic coupling of fluvial and shallow marine sediment dynamics and downplays the importance of allogenic fluctuations can explain many of the first order morphologic features of natural delta systems including significant lateral separation of the shoreline and clinoform rollover and differing rates of subaerial and subaqueous delta progradation

post last glacial maximum fluvial incision and sediment generation in the unglaciated waipaoa catchment north island new zealand abstract small river systems contribute a significant component of sediment delivered to oceans but the temporal evolution of fluvially eroded landscapes is needed a sequence of postglacial terraces in the unglaciated waipaoa river catchment provides the opportunity to document fluvial incision and sediment flux on an 2000 year timescale since the last glacial maximum lgm which has previously only been undertaken for the entire post lgm period this study also calculates sediment mass where previously sediment volume was calculated using a 15 m dem field mapping and surveying and tephrochronology we calculate rates of fluvial incision and sediment volumes excavated during successive age constrained postglacial incision events and correlate these with a framework of inferred climatic events established for new zealand we identify seven periods of terrace formation each succeeded by a period of fluvial incision six in total although the magnitude of the response during each incision event and thus the sediment volumes generated varied through time and across subcatchments draining two contrasting lithological terrains we conclude that incision events were essentially synchronous at least within the timeframe constrained by the ca 2000 year interval between successive eruptive airfall events slope relaxation processes were simultaneous with incision thereby indicating that both processes were likely climate driven we identify a period of accelerated fluvial incision 7 mm y 1 commencing before ca 14 0 cal ka bp during the early postglacial period and ceasing ca 7 9 cal ka bp toward the end of the early holocene warming period the magnitude of this incision response was significantly higher in subcatchments draining highly erodible lithologies in the higher uplifting parts of the catchment when river bedload was at over capacity in contrast within the remainder of subcatchments draining the more resistant lithologies and in areas of lower uplift and in parts subsiding incision and sediment generation was moderated by the presence of knickpoints overall since abandonment of the lgm to present day fluvial incision in the waipaoa and the adjacent waimata catchments generated 16 7 km3 of sediment of which 10 km3 90 of the estimated 35 mt of glacial postglacial slope and shelf sediment mass was potentially available for transport offshore of this 14 08 km3 7 4 km3 derived from upper and 6 7 km3 from remainder of subcatchments was excavated from waipaoa catchment at an average of 0 6 km3 ka 1 of which 80 was generated by ca 7 9 cal ka bp this potentially validates previous accounts of high rates of offshore sediment flux before 8000 14c ybp ca 8877 cal ybp thereafter for the period mid holocene cooling and variability mhcv ca 6 5 cal ka bp until the present day the rate of incision across all subcatchments slowed to 2 mm y 1 and generated just 20 of the total sediment volume in part this reflected a depletion of available sediment as rivers in the upper subcatchments returned to a steady state and coincidental with an increase in accommodation space in the rapidly growing coastal floodplain sediment flux to the marine depocentres was thereby limited

stress near the surface of the earth over most of the earth s surface earthquake hypocenters are concentrated in the depth range 0 15 km that is in the upper half of the crust chen molnar 1983 the exception is the subduction zones where cold litho sphere is underthrust to greater depths as a first approximation the top 10 15 km of the crust can be regarded as a region of nearly elastic response to stress with brittle fracture under sufficient stress difference this is the depth range discussed in this review the lower crust appears to be characterized by some form of ductile response to stress in large areas of the upper crust the stress field is related to large scale tectonic processes and represents the tractions acting on the plate concerned however some decoupled crustal blocks are known and are noted herein caution is necessary in generalizing the stress in a region to the plate that contains it recent reviews of crustal stress are given by ranalli chandler 1975 wyss 1977 mcgarr gay 1978 and gay 1980 in the upper crust one principal stress is generally within 20 of the vertical except beneath very rough topography and this vertical principal stress jz is usually within 10 of the lithostatic pressure j pg dz due to overlying rock mcgarr gay 1978 the horizontal principal stresses generally increase with depth and may be less or greater than the vertical pressure within a few hundred meters of the surface the rock mass is divided into blocks by numerous fractures including large and small faults on which shear displacements can be identified and joints on which no shear movement can be seen if the ambient stress is comparable to the strengths of these

autostratigraphy a framework norm for genetic stratigraphy abstract autostratigraphy is the stratigraphy generated by large scale autogenic processes and needs to be heeded because of a current overreliance on allogenic controls in sequence stratigraphy key principles of autostratigraphy emerging from the theory of autoretreat and a new understanding of alluvial grade derive from the non equilibrium stratigraphic response i e the general lack of equilibrium configuration of depositional systems the non equilibrium behavior of fluvial deltas during times t of steady dynamic forcing leads to variable stratigraphic response that is the inevitable result of length d and time scaling particular to the depositional system rather than necessarily reflecting any sudden or unsteady change in the rate of allogenic forcing some abrupt breaks in the stratigraphic record are not necessarily associated with changes in allogenic conditions but can result from purely autogenic processes of the system when t is comparable to or longer than 1 the depositional system takes the non equilibrium large scale autogenic response 2 the superposition of autogenic and allogenic components of the forcing is prominently nonlinear and thus 3 sequence stratigraphic models that have been built on the assumption of equilibrium response are incorrect autostratigraphic analysis makes it possible to detect and identify complex autogenic responses and unsteady allogenic events in the stratigraphic record by quantifying a temporal change in the magnitude of d autostratigraphy thus functions as a norm for genetic stratigraphy

is river avulsion style controlled by floodplain morphodynamics river relocation or avulsion is a fundamental process that fills alluvial basins however it is difficult to predict avulsion patterns because the landscape conditions associated with different avulsion styles are currently unknown two end member avulsion styles have been documented in modern rivers progradational avulsions during which significant floodplain deposition occurs as a new channel is built and incisional avulsions during which floodplain erosion captures flow from a parent channel here we propose that avulsion style is related to the tendency for overbank flows to erode or deposit sediment i e floodplain morphodynamics we present a scaling comparison of floodplain erosion and deposition rates test it with morphodynamic modeling and show field data from ancient deposits that are consistent with modeling results these results demonstrate that floodplain morphodynamics may determine how rivers relocate and that assessing the relative influence of floodplain erosion and deposition may be useful for predicting sedimentation patterns in avulsive systems

the influence of sea level and tectonics on late pleistocene through holocene sediment storage along the high sediment supply waipaoa continental shelf abstract we present geophysical and core evidence showing how subsidence caused by forearc shortening has accommodated late pleistocene and holocene sediments supplied to the tectonically active waipaoa shelf nz limiting off shelf export during the early sea level highstand the last glacioeustatic fall and subsequent rise exposed and then flooded a shelf segmented into subbasins separated by zones of uplift leaving key stratigraphic markers of shoreline regression and transgression that vary strongly in character across the shelf highstand sediment isopachs tied to piston cores dated using tephra correlation and a radiocarbon age model provide a sediment budget at 2000 yr intervals from the mid holocene 5500 cal yr bp to present sediment load estimates from our shelf budget are in agreement with published model estimates for suspended sediment discharge from the waipaoa river for the past 3000 yr but importantly do not show the 6 fold increase in the waipaoa s sediment output that began with human settlement 700 yr ago and accelerated with deforestation over the last century bypassing of waipaoa sediment to the slope may therefore be a recent phenomenon caused by unnaturally high sediment loads a conclusion supported by data reported elsewhere in this volume our study also reveals evidence for 1 a relatively thick mid shelf transgressive section deposited during the last eustatic rise that may correlate to estuarine sequences reported from numerous sites on the modern coastline of the north island 2 a slight decrease in total basin filling rates during the highstand and 3 variability in the partitioning of highstand sediments between individual subbasins that may reflect differing degrees of tectonic accommodation

wave induced sediment transport and sandbar migration onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood here a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach in both the observations and the model the location of the maximum acceleration induced transport moves shoreward with the sandbar resulting in feedback between waves and morphology that drives the bar shoreward until conditions change a model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45 day period

the caldwell group lavas of southern quebec morb like tholeiites associated with the opening of iapetus ocean the caldwell group belongs to the internal nappe domain of the humber zone and consists of basaltic lavas quartzo feldspathic sandstones and mudslates the lavas are clinopyroxene plagioclase olivine phyric tholeiites and are typically altered to epidote chlorite carbonate and or hematite rich secondary assemblages in most cases the high field strength elements do not appear to have been perturbed by the alteration and preserve magmatic signatures most caldwell basalts exhibit coupled major and trace element variations compatible with low to medium pressure 10 kbar where 1 kbar 100 mpa fractional crystallization paleotectonic discriminants imply an ocean floor or normal mid ocean ridge basalt n morb affinity most basalts have flat n morb normalized profiles except for the highly incompatible elements ba th nb which show slight relative enrichment melting models suggest that most of these lavas formed by about 20 melting from a mantle slightly less depleted than fertil

structures of the medial ordovician flysch of eastern new york deformation of synorogenic deposits in an overthrust environment synchronous deposition and deformation of the flysch deposits of eastern new york occurred during the westward overthrusting of the taconic allochthon in medial ordovician time an observed spatial west to east increase in the intensity of deformation is believed to represent the progressive development of structures through time folding initiated as upright kinks and buckles with fold axes north south and approximately horizontal fold axes then rotated towards an east west shear direction with fold tightness and asymmetry increasing and fold axial planes rotating to the west shear zones with a phacoidally cleaved fabric and small thrust faults strengthened the east over west structural asymmetry after attaining intermediate dips roughly 45 the fold axial planes began to rotate back toward vertical and lose asymmetry bulk flattening and shear competed in the microstructural development of the flysch with slaty cleavage and phacoidal cleavage the corresponding end products shear zones and thrust f

snake hill reconstructing eastern taconic foreland basin litho and biofacies from a giant melange block in eastern new york usa abstract exotic lithofacies and faunas have long been known from snake hill eastern new york usa the faunally diverse sandstone dominated upper ordovician succession at snake hill sharply contrasts with surrounding tectonized sparsely fossiliferous distal shale re examination of the snake hill section shows that it is a storm and wave dominated near shore facies with a benthic fauna analogous to that of the younger lorraine group ashgillian of central new york and to that of the upper martinsburg group upper caradocian of eastern pennsylvania orthograptus ruedemanni chron graptolites indicate that the snake hill succession is older than the surrounding tectonized deep water shale climacograptus spiniferous chron snake hill is best interpreted as a parautochthonous block in melange originally deposited close to the shoreline of the emergent taconic accretionary prism because the snake hill succession is sandstone dominated it is inappropriate to refer mudstone dominated facies that underlie the western margin of the taconic allochthon in the hudson river valley region to the snake hill shale as has been done in the past the thick ca 150 m lithologically distinct succession at snake hill is therefore referred to as the snake hill formation the snake hill formation is the only known example of proximal near shore facies deposited on the western side of the outer taconic arc and represents easternmost deposition in the taconic foreland basin the snake hill formation is a unique occurrence and thus is restricted to its type locality at snake hill new york

signals of watershed change preserved in organic carbon buried on the continental margin seaward of the waipaoa river new zealand abstract holocene sediments buried on the continental shelf seaward of the waipaoa river northeastern new zealand preserve a stratigraphic record of terrestrial environmental change the well characterized long term record of storms volcanism and human disturbance in this region provides an opportunity to examine how such changes are reflected in the character of organic carbon oc buried on the continental margin complimentary evidence obtained from analyses of the 14 c content and the elemental and stable carbon isotopic composition of different sedimentary fractions including charcoal wood and clay sized isolates indicates that these perturbations led to mobilization of oc components with variable storage histories in the watershed charcoal transported in the modern waipaoa river and buried in offshore depocenters includes a highly aged component that has apparently been slowly released from storage in soil or alluvial terraces the charcoal fraction ages become dramatically younger in sediments deposited after the taupo volcanic eruption 1717 cal yr bp and then polynesian settlement ca 700 cal yr bp both signaling biomass burning the mean age of woody plant fragments and clay bound oc deposited on the shelf also varies over time with older material having accumulated in the middle holocene and since human occupation deposition of older than average wood fragments and clay bound oc between about 5 and 3 6 kyr bp correlates with evidence for a period of increased storm frequency in the region and may reflect the enhanced delivery of aged soil and sedimentary rock mobilized from hill slopes via earthflows and or deep seated landslides similarly the deposition of older wood and clay bound oc commensurate with the first anthropogenic disturbance ca 700 years ago is consistent with accelerated mass wasting due to deforestation at the same time a change in the elemental and stable isotopic composition of bulk and clay bound oc buried on the shelf may reflect increased marine primary productivity and or mobilization of oc from deep levels in soil profiles deforestation of the waipaoa headwaters by european settlers beginning in the middle 19th century is evinced by a sharper rise in the age of clay associated oc buried offshore today deep gully incision into fractured sedimentary bedrock is a major source of sediment and kerogen to the river and this process has left its mark on the age of sedimentary oc delivered to the adjacent margin

dating the culmination of river aggradation at the end of the last glaciation using distal tephra compositions eastern north island new zealand an extensive terrace waipaoa 1 that can be traced for about 29 km in the waipaoa valley eastern north island new zealand is underlain by at least 10 m of coarse aggradational river gravels terrace cover beds contain tephras erupted from central north island volcanoes and these provide minimum ages for the underlying gravels tephra or tephric layers occurring in the lower cover beds were investigated at five sites using a combination of stratigraphy mineralogy and the major element composition of glass shards together with discriminant function analysis dfa the basal tephra is identified as the ca 14 700 14c years old ca 17 700 cal years b p rerewhakaaitu tephra erupted from okataina volcanic centre using the stratigraphic relationship of rerewhakaaitu tephra the end of aggradation is dated at ca 15 000 14c years ca 18 000 cal years correlation with aggradational terraces elsewhere in north island and northern south island indicates that aggradation ended at the same time over a wide area and confirms a climatic origin for the terraces subsequent downcutting was apparently rapid because rerewhakaaitu tephra also occurs at the base of cover beds on a ca 15 m lower terrace the downcutting represents a major change in river dynamics and is most likely the response to climatic change and the resultant upper catchment landscape stability

downstream fining in a rapidly aggrading gravel bed river downstream changes in particle size that occur in the waipaoa river a 104 km long gravel bed river in which rapid aggradation in the historic post 1800 period was triggered by the conversion of native forest to pasture are summarized in this paper the textural data presented are unique for a field situation not only because of the spatial resolution and extent of the sampling program but also because they provide information about the pattern of fining at different points in time they are supported by equally comprehensive topographic survey data from which local rates of aggradation can be derived despite variability induced by lateral sediment inputs there is an essentially continuous pattern of fining along the entire length of the river fining occurs in both the fine and coarse size fractions of the bed material the highest rates of fining occur in the larger percentiles of the subsurface bed material and in the surface bed material downstream fining in the waipaoa river appears to be a response to changes in flow hydraulics that are regulated by the concave configuration of the long profile the fining gradient developed rapidly in 45 years it does not appear to be influenced by the rate of aggradation nor the overall rate of sediment supply to the channel system because in the short term aggradation has a negligible impact on the inherited form of the long profile

analysis of stress induced oval fractures in a borehole at deep sea drilling project site 504 eastern equatorial pacific deep sea drilling project dsdp hole 504b is located in the eastern equatorial pacific ocean and extends to a total depth of 2111 m beneath the seafloor mbsf several acoustic televiewer logs have been obtained in this well during successive stages of drilling and the resulting digital images have revealed numerous oval shaped fractures seemingly etched into the borehole wall a theoretical examination of these stress induced features identifies a unique and ephemeral set of stress distributions and magnitudes that are necessary for their production consequently the ovals provide a basis for quantifying the magnitudes and orientations of the maximum and minimum horizontal principal stresses sh and sh at this site vertical truncated breakouts and horizontal tensile fractures define the spatial boundaries of the ovals explicit criteria for their occurrence are combined with estimates for various physical properties of the rock to yield a range of possible values for the horizontal principal stresses the conspicuous oval geometry is completed by a curved fracture that joins the vertical and horizontal components its degree of curvature is delineated by the modified griffith failure criterion and is directly related to the principal stress difference sh sh matching a series of type curves corresponding to specific values for sh sh with the actual undistorted well bore images allows the magnitude of the stress difference to be further constrained with a value for sh sh of 45 5 mpa the individual magnitudes of sh and sh are determined more precisely final estimates for the horizontal principal stresses in dsdp hole 504b at a depth of 1200 mbsf are 141 mpa sh 149 mpa and 91 mpa sh 109 mpa stress magnitudes derived from this approach rely heavily upon the values of a variety of physical properties and complementary laboratory measurements performed on relevant rock samples provide critical information uncertainties in estimating these properties translate into less precise predictions of principal stresses

from mountain source to ocean sink the passage of sediment across an active margin waipaoa sedimentary system new zealand abstract the joint us nz source to sink initiative aims to unravel the tectonic climatic and other processes that shape the landscape from the mountains to deep ocean of two focus areas chosen world wide the waipaoa sedimentary system wss of north eastern new zealand was identified as an example of a mid latitude high sediment input system it resides within the westerly wind belt and extends across the convergence zone of the australian and pacific plates accordingly the tectonic and climatic drivers are prominent and their influences on the wss are decipherable as is documented in the suite of source to sink studies presented in this special issue of marine geology the wss is forced at several temporal and spatial scales which collectively appear as short term events storms earthquakes and volcanic eruptions superimposed on long term behavioural shifts tectonic uplift and eustatic sea level change overall the wss is undergoing uplift which has been contributing to valley incision since the last glacial maximum uplift is both gradual and intermittent the latter relating to fault and subduction related earthquakes such seismic activity destabilises the landscape and together with frequent storms generates large amounts of sediment as this sediment passes through the system part is captured in traps formed by local subsidence of the coastal plain and middle continental shelf where large thicknesses of holocene and probably older sediment are sequestered e g 200 m under the coastal plain nevertheless substantial sediment still reaches the continental slope to accumulate in canyon heads and slope basins with other deposits redistributed down slope in mass flows major volcanic eruptions also affect the sediment flux via direct input from ash fall and by enhanced erosion following volcanic destruction of terrestrial vegetation frequent storms of varying intensity play a key role in the generation and transfer of sediment major events such as cyclone bola of 1988 inundated the shelf with sediment but identifiable flood deposits were preserved only locally attesting to the effectiveness of shelf physical and biological mixing regimes despite the storms earthquakes and volcanic eruptions the largest perturbation of the wss at least in the last 2400 years has been the human deforestation of the landscape the resultant influx of sediment overwhelmed the shelf s storage capacity instead of capturing 90 the fluvial input as in pre human times the modern shelf retains only 25 the remainder escaping to the slope and elsewhere

fluviodeltaic response to sea level perturbations amplitude and timing of shoreline translation and coastal onlap 1 alluvial river systems respond to changing sea level by adjusting channel length through shoreline translation and coastal onlap offlap at the alluvial basement transition the magnitude and timing of shoreline translation and coastal onlap offlap relative to the driving sea level signal depend on the dynamics of the fluvial system and have important implications for interpreting ancient fluviodeltaic deposits i obtain analytical solutions to a diffusive geometric model of fluviodeltaic response to sea level perturbations that treats the shoreline and alluvial basement transition as moving boundaries fluviodeltaic behavior is most sensitive to the ratio of the period of eustatic cycling to the fluvial response time which varies with the length and water discharge of the fluvial system the square root of this ratio provides a first order estimate of the fraction of the fluvial long profile affected by eustatic forcing the fluviodeltaic system behaves as a low pass filter with respect to eustatic cycling the amplitude of both shoreline translation and coastal onlap offlap increase with increasing cycle period within a relatively narrow bandwidth in which the fluvial response time is comparable to the cycle period only small time lags develop between shoreline response and eustatic forcing the time lag between maximum coastal onlap and maximum sea level increases without bound as the forcing period decreases relative to the fluvial response time model predictions agree with experimental data and differ considerably from the model predictions of pitman 1978 and angevine 1989 which suggest that fluviodeltaic systems are strong high pass filters to sea level cycling

reactivation of prethrusting synconvergence normal faults as ramps within the ordovician champlain taconic thrust system we present new geologic maps of the lake champlain region of west central vermont and east central new york state this region contains a shallow crustal section of an ordovician foreland basin and a far traveled thrust system that transported the upper cambrian lower ordovician platform sequence allochthonous rise facies pelites and arenites and middle ordovician basinal shales and flysch early foreland and shelf sections are cut by post depositional cross faults within the thrust system and the required stratigraphic throw across the cross faults is not matched by the amount they offset the thrust planes as thrust structures these cross faults control structural style and kinematics by laterally bounding regions that contrast sharply in amount of thrust imbrication duplexing and net transport the dominant set of normal faults in the autochthon which had time correlative slip with the thrust system cross faults is oriented parallel to the paleotrench though there is also a subordinate transverse linking set the normal faults developed in response to the migrating flexural forebulge during convergence between the laurentian margin and the accretionary prism above an outboard facing subduction zone within the thrust system any prethrust normal faults that were parallel to the paleotrench are largely masked by thrust structures however an out of sequence thrust which emplaced shelf rocks above the westernmost allochthon and surrounding parautochthonous shale may have localized on a paleotrenchparallel normal fault in the outer shelf we also identify a postthrust normal fault that significantly obscures the original thrust map pattern reactivation of synconvergence prethrust flexure induced normal faults adequately explains many otherwise puzzling stratigraphic and structural relationships in the taconic foreland

evidence for small scale mantle convection from seasat altimeter data evidence for the early development of convective instability in the thermal boundary layer associated with cooling plates has been found from gravity anomalies and residual sea surface heights derived from seasat altimeter data subtle lineated patterns trending in the direction of plate motion in the hot spot reference frame are observed over the younger portions of the fast moving pacific and indo australian plates in particular for the east central pacific ocean the seasat derived data sets reveal lineations with 1 wavelengths in the range 150 500 km perhaps increasing with plate age and 2 peak to trough amplitudes of 5 20 mgal for gravity anomalies the lineated pattern over the pacific plate which first becomes discernable over seafloor 5 to 10 m y old west of the east pacific rise is clearly oblique to the trends of the prominent pacific farallon fracture zones onset of convective instability at such early ages can be understood if young oceanic lithosphere is underlain by a layer having a viscosity of about 1018 pa s 1019 p which is about 3 orders of magnitude less than mantle viscosity inferred from postglacial rebound studies recent numerical studies of convection in fluids with a temperature and pressuredependent viscosity support an early onset time for convective instability and low viscosity zones in the upper mantle beneath young lithosphere such low viscosity zones may correspond to similarly located regions of low shear wave velocities resolved through studies of surface waves

non coaxial horizontal shortening strains preserved in twinned amygdule calcite dsdp hole 433 suiko seamount northwest pacific plate abstract core sections from the lower basaltic portions of dsdp hole 433 total depth 550 5 m in suiko seamount contain amygdule and vein fillings of calcite which contain mechanical twins analysis of the calcite twins reveals the presence of two horizontal shortening strains that are nearly orthogonal to one another the azimuthal orientation of these strains is only known with respect to stratigraphic top and bottom as the cores are not oriented in any other manner maximum shortening strain magnitudes for the best developed positive expected value pev twin lamellae set is 1 7 for the lesser developed negative expected value nev split the preserved horizontal strain magnitude is 4 3 inferred compressive paleostress magnitudes were on the order of 26 mpa horizontal differential stresses of this magnitude could be 1 associated with hotspot plumes and or 2 are transmitted to the central portions of thin oceanic plates from distant plate boundaries suiko seamount is composed of paleocene basalts overlain by lithified middle paleocene limestones and is part of the emperor seamount chain on the pacific plate the absence of secondary vein calcite in the overlying sediments suggests that the underlying amygdule calcite is paleocene in age which indicates that the twinned calcite preserves a stress field reorganization the nev split after the middle paleocene that is oriented 64 from the earlier paleocene stress field the pev split

gravity driven sediment transport on the continental shelf implications for equilibrium profiles near river mouths an analytical model is developed for equilibrium bathymetric profiles off river mouths associated with the shoreward convex upward portion of subaqueous deltas and clinoforms the model builds on recent field results demonstrating that gravity driven flux of suspended mud is important on shelves provided that wave induced suspension of sediment supports the requisite turbid hyperpycnal layer because the maximum sediment load is determined by the critical richardson number the results are independent of the properties of the suspended mud or the bed the model assumes the equilibrium state to represent a balance between the supply of sediment by a river at the coast and the downslope bypassing of sediment to deep water within wave supported turbid near bed layers progressive seaward increases in bed slope across the convex shelf profile allow the attenuation of wave agitation with depth to be compensated for by a downslope increase in the contribution of gravity the model is consistent with shelf profiles off the mouths of the eel california ganges brahmaputra bangladesh waiapu new zealand po italy and rhone france rivers the equilibrium profile is predicted to be a function of wave climate and riverine sediment supply only with deeper and broader profiles associated with decreasing sediment supply increasing wave height and or increasing wave period

oxygen and carbon isotopic composition of silurian brachiopods implications for coeval seawater and glaciations we collected 236 calcitic brachiopod shells covering the entire silurian period 30 m y at high temporal resolution from stratotype sections from anticosti island canada wales united kingdom the oslo region norway gotland sweden and podolia ukraine estonia latvia and lithuania data from petrography scanning electron microscopy cathodoluminescence isotopes and trace elements all confirmed that there was excellent preservation in most shells thus arguing for retention of primary isotope signals exceptions were samples from the oslo region the d18o and d13c values for the well preserved samples range from 2 to 6 5 and from 1 to 7 5 peedee belemnite respectively in terms of temporal trends oxygen and carbon isotopes vary in parallel with a slight decrease with declining age of 1 through silurian time with superimposed short term oscillations that are negatively correlated with sea level changes three successive positive d18o shifts in early aeronian latest aeronian and early wenlock time correlate with sea level lowstands and with glacial diamictite deposits in the amazon basin and in africa the high d18o and d13c values are attributed to cold episodes with low sea levels and low values to warm episodes with high sea levels during warm silurian episodes the d18o value of seawater is suggested to have been about 3 5 standard mean ocean water smow and the global tropical temperatures of about 20 30 c similar to the present day values in summer during glacial episodes seawater is proposed to have had a d18o value of 2 5 smow and temperature of about 14 23 c comparable to tropical temperatures proposed for the last glacial episode 14 to 28 c three positive d13c peaks in early and late wenlock and late ludlow time likely of regional to global significance appear to coincide with sea level lowstands but we are as yet unable to propose a convincing causative geologic scenario that would explain their origin

utilization of observations of well bore failure to constrain the orientation and magnitude of crustal stresses application to continental deep sea drilling project and ocean drilling program boreholes

coastal uplift mechanisms at pakarae river mouth constraints from a combined holocene fluvial and marine terrace dataset abstract one of the major environmental controls on sedimentary systems is tectonics and thus in order to make quantitative explanations and predictions of the behaviour of sedimentary systems it is important to quantify tectonic rates and mechanisms in this study we show how a combined holocene fluvial and marine terrace dataset can be used to place constraints on coastal uplift mechanisms at pakarae river mouth to the east of the waipaoa sedimentary system mapping and surveying of fluvial terraces shows that the terraces can be divided into three sets i pgt a fill terrace formed during post glacial sea level rise 10000 7000 cal yr bp ii a sequence of post 7000 cal yr bp degradation terraces and iii historical post ad 1880 flood terraces a conceptual model of terrace evolution proposes that coseismic uplift has resulted in the observed back tilting downstream divergence and successive abandonment of tectonic terraces coastal uplift mechanisms are then examined by comparing the fluvial and marine terrace uplift distribution and the uplift per event from the marine terraces with those predicted by forward elastic dislocation models the models agree with the interpretation that the terrace uplift can be explained by coseismic slip on a steeply west dipping reverse fault located close to the shore possibly in combination with rupture of the hikurangi margin subduction interface 10 24 km below this study also provides insights into the tectonic drivers and impacts on the adjacent waipaoa sedimentary system including the possible role of subduction earthquakes growth of structures on the shelf and upper slope and the role that the interplay between sea level and tectonic controls has on sediment dispersal

stress orientations from borehole wall fractures with examples from colorado east texas and northern canada azimuthally aligned breakouts in oil wells are explained as shear fractures in the zone of amplified stress difference near the borehole in a stress field having unequal horizontal principal stres

modeling suspended sediment discharge from the waipaoa river system new zealand the last 3000 years hydrotrend a hydrologic transport model is used to simulate the water and suspended sediment discharge of the waipaoa river system over the last 3 kyr a time period in which a well documented sequence of natural events and anthropogenic activities that profoundly impacted drainage basin processes occurred comparisons between observed and simulated data show that the model output replicates the frequency and distribution of flow events and the suspended sediment concentration discharge relationship and the long term trends in suspended sediment discharge are consistent with the sediment record preserved on the middle shelf water discharge tracks precipitation and average annual discharge may have been up to 20 higher and 6 lower at different times in the past suspended sediment discharge changed from 2 3 4 5 to 14 9 8 7 mt yr 1 during the anthropocene increasing by 140 after polynesian arrival by 350 after european colonization and by 660 after the catchment headwaters were deforested

hydrothermal alteration within the basement of the sedimented ridge environment of middle valley northern juan de fuca ridge the middle valley segment at the northern end of the juan de fuca ridge is a deep extensional rift blanketed with 200 500 m of pleistocene turbiditic sediment sites 857 and 858 were drilled during ocean drilling program leg 139 to determine whether these two sites were hydrologically linked end members of an active hydrothermal circulation system site 858 was placed in an area of active hydrothermal discharge with fluids up to 270 c venting through anhydrite bearing mounds on top of altered sediment the shallow basement of fine grained basalt that underlies the vents at site 858 is interpreted as a seamount that was subsequently buried by turbidites site 857 was placed 1 6 km south of the site 858 vents in a zone of high heat flow and numerous seismically imaged ridge parallel faults drilling at site 857 encountered sediments that are increasingly altered with depth and that overlie a series of mafic sills at depths of 460 940 m below sea floor sill margins and adjacent baked sediment are highly altered to magnesian chlorite and crosscut with veins filled with quartz chlorite sulfides epidote and wairakite the sill interiors vary from slightly altered with unaltered plagioclase and clinopyroxene in a mesostasis replaced by chlorite to local zones of intense alteration and brecciation in these latter zones the sill interiors are pervasively replaced by chlorite epidote quartz pyrite titanite and rare actinolite the most complete replacement is associated with brecciated horizons with low recovery and slickensides on fracture surfaces which we interpret as intersections between faults and the sills geochemically the alteration of the sill complex is reflected in significant whole rock depletions in ca sr and na with corresponding enrichments in mg al and most metals the latter results from the formation of conspicuous sulfide poikiloblasts in contrast metamorphism of the site 858 seamount includes incomplete albitization of plagioclase phenocrysts and replacement of sparse mafic phenocrysts much of the basement alteration at site 858 is confined to crosscutting veins except for a highly altered and veined horizon at the contact between basaltic basement and the overlying sediment the sill complex at site 857 is more highly depleted in 18 o 18 o 2 4 4 7 and more pervasively replaced by secondary minerals relative to the extrusives at site 858 18 o 4 5 5 5 there is no evidence of significant albitization of the plagioclase at site 857 suggesting high ca na in the pore fluids fluid inclusion data from hydrothermal minerals in altered mafic rocks and veins at sites 857 and 858 show a consistency of homogenization temperatures varying from 245 to 270 c which is within the range of temperatures observed for the fluids venting at site 858 the consistency of the fluid inclusion temperatures the lack of albitization within the site 857 sills and the apparently low water rock ratio collectively suggest that the sill complex at site 857 is in thermal equilibrium and being altered by a highly evolved ca rich fluid similar to the fluids now venting at site 858 the alteration evident in these two deep crustal drillsites is a result of the ongoing hydrothermal circulation and is consistent with downhole logging results instrumented borehole results and hydrothermal fluid chemistry the pervasive alteration of the laterally extensive sill sediment complex at site 857 determines the chemistry of the fluids that are venting at site 858 the limited alteration of the site 858 lavas suggests that this basement edifice acts as a penetrator or ventilator for the regional hydrothermal reservoir with much of the flow focussed at the highly altered and veined sediment basalt contact

holocene shoreline depositional processes at poverty bay a tectonically active area northeastern north island new zealand abstract holocene depositional processes at poverty bay have been affected by 1 tectonism 2 sea level response to climate change 3 fluvial processes responding to 1 and 2 severe storms and volcanic eruptions the height distribution of radiocarbon dated beach and estuarine shells and wood show that during the holocene relative uplift of the land has occurred at the northeastern margin of the poverty bay flats while subsidence has occurred at the southwestern margin three holocene tectonic subregions are distinguished at the poverty bay flats coast a northern gisborne wainui uplift area a central makaraka awapuni static pivotal area and a southern patutahi muriwai downdrop area periods of significant fluvial upstream degradation into gravel terrace deposits and downstream gravel aggradation are dated at ca late last glaciation 12 000 9000 and 7000 5000 bp the 12 000 9000 bp gravel deposits show tilting to the southwest major erosion and infilling events also occurred at ca 1700 and 300 bp holocene marine transgression and progradation shoreline locations are mapped and the coastal processes are reviewed in terms of the tectonic fluvial and eustatic sea level influences

channel change bankfull and effective discharges on a vertically accreting meandering gravel bed river along the lower reaches of the waipaoa river new zealand cross section survey data indicate there was a 23 per cent decrease in bankfull width and a 22 per cent reduction in channel cross section area between 1948 and 2000 as the channel responded to increased inputs of fine suspended sediment following deforestation of the headwaters in late c19 and early c20 we determined the bankfull discharge within a 39 km long reach by routing known discharges through the one dimensional mike 11 flow model the model runs suggest that the bankfull discharge varies between 800 and 2300 m3 s 1 and that the average recurrence interval is 4 2 years on the annual maximum series by contrast the effective flow 360 m3 s 1 is equaled or exceeded three times a year the variability in bankfull discharge arises because the banks tend to be lower in places where flood flows are constricted than in reaches where overbank flow is dispersed over a wide area and because scour has counteracted aggradation in some locations there is no downstream variation in shields stress or in relative shear stress within the study reach bankfull shear stress is on average five times greater than the shear stress required to initiate motion at the effective discharge it is more than twice the threshold value the effective discharge probably has more relevance than the bankfull discharge to the overall picture of sediment movement in the lower reaches of the waipaoa river but because width is constrained by the stability and resistance of the bank material to erosion during high flows that also scour the bed the overall channel geometry is likely determined by discharges at or near bankfull copyright 2006 john wiley sons ltd

in situ electrical resistivity and bulk porosity of the oceanic crust costa rica rift in situ electrical resistivity was measured in dsdp hole 504b to a depth of 1 013 m into oceanic basement apparent resistivities are about 10 m in about 600 m of pillow lavas sharply increasing to nearly 1 000 m in the underlying dykes bulk porosities calculated from resistivities show a distinct layering apparently corresponding to geophysical layers 2a 2b and 2c

hydrology of the poverty bay flats aquifers new zealand recharge mechanisms evolution of the isotopic composition of dissolved inorganic carbon and ground water ages abstract with the exception of water bearing remnants of earlier fluvial gravels overlying basement the sediments of the poverty bay flats have accumulated during the postglacial period of the past 14 000 years and have been tilted and deformed by recent tectonism a sequence of gravel aquifers separated by poorly permeable silt layers lies between surface and basement which is at depths varying between 50 and 200 m a shallow sand silt aquifer is situated near the coast this study applies evidence of chemical and isotopic properties of river and ground water to clarify the recharge mechanisms chemical evolution and age of the ground water in the aquifers particular attention is paid to the evolution of dissolved inorganic carbon content applying carbon 14 data measured by accelerator mass spectrometry most of the ground water is recharged from the waipaoa river which flows across the flats and discharges into poverty bay the two deepest aquifers matokitoki and makauri are both tritium free the deeper matokitoki gravels yield water of age about 4300 years since recharge possibly up to 1300 years greater but the makauri water is no older than 100 200 years discharging slowly through overlying aquitards near the limit of closest approach to the present coast

petrography geochemistry and origin of burial diagenetic facies siluro devonian helderberg group carbonate rocks central appalachians petrographic and geochemical studies of pore filling cements and replacement products in the helderberg group upper silurian lower devonian central appalachians document the diagenetic history of these rocks shallow ramp skeletal limestones and buildups were partially lithified by marine cements however most pore filling cement formed under shallow 300 m to deep burial 300 4 000 m conditions regional cathodoluminescent zonation patterns in early calcite cements indicate meteoric ground waters were involved in shallow burial cementation early zoned calcite cements consist of updip nonluminescent cements with thin luminescent laminae in limestone or sandstone that pass downdip into subzoned dull cements interlayered bright and dull laminae and then into nonzoned dull cement in basinward limestone the regional distribution stable isotopic compositions and timing of early zoned cements relative to other diagenetic events suggest that all of the early cements formed synchronously from meteoric ground waters that became progressively more reducing as they flowed downdip at least 150 km helderberg sandstone tongues probably were preferential conduits for meteoric gro nd waters because early calcite cements formed only on scattered skeletal grains in sandstones late void filling dull cement formed from deep burial pore fluids at burial depths of 300 to 4 000 m deep burial pore fluids were dilute to saline na ca cl brines from primary fluid inclusion data with stable isotopic compositions that probably were similar to isotopic compositions of formation waters from modern oil fields void filling dull calcite cements occluded nearly all remaining porosity before late paleozoic fracturing and deformation latest diagenetic phases include dolomite fluorite silica and fracture filling dull calcite this study shows that integrated petrographic and geochemical approaches to diagenetic studies are useful for relating various diagenetic phases and fabrics to burial history and paleoaquifer distribution

formation of taconic melanges and broken formations in the hamburg klippe central appalachian orogenic belt eastern pennsylvania abstract the hamburg klippe of the central appalachian orogenic belt exposed in eastern pennsylvania displays a complex record of poly phase melange and broken formation development in a convergent margin setting it includes an imbricate stack of tectonic slices which consist of upper cambrian to upper ordovician deep water and continental slope sedimentary rocks emplaced by gravity sliding onto the laurentian passive margin during deposition of the upper ordovician martinsburg formation based on their internal structure and stratigraphy the block matrix ratios and relations and the inferred tectonic settings of origin we have differentiated the following melanges and broken formations whose evolutionary stages coincide with specific deformational phases in a complete orogenic cycle from subduction to collision i sedimentary broken formations without exotic blocks formed by in situ and local down slope remobilization during the early stages of closure of the octoraro sea basin in the early ordovician ii two types of sedimentary melanges with exotic blocks formed at the front of the advancing accretionary wedge during the middle ordovician subduction of the laurentian continental margin beneath a microcontinent magmatic arc tectonic assembly iii layer parallel extensional broken formation and a diapiric melange formed in the outer trench and at the toe of the accretionary wedge respectively during the early late ordovician iv precursory olistostromes formed during the late ordovician collisional episodes as the hamburg klippe was emplaced in the martinsburg formation on the downgoing laurentian continental margin and v contractional deformation related broken formations formed at the base of main thrust faults overprinting the previously formed melanges and broken formations this sequential development of different melange types in the central appalachians was strongly controlled by the degree of consolidation of the layered strata and their rheological differences the structural level of melange formation within the accretionary wedge and the kinematics of deformational processes

delta allometry growth laws for river deltas 1 under projected scenarios of sea level rise subsidence and sediment starvation many deltas around the world are expected to drown delta growth dynamics which determine the ability of a delta to adapt to these changes are poorly understood due to the difficulty of measuring change in slowly evolving landscapes we use time series imagery of experimental numerical and field scale deltas to derive four laws that govern the growth of river dominated deltas land area grows at a constant rate in the absence of relative sea level change while wetted area keeps pace maintaining a constant wetted fraction over the delta surface scaling of edge lengths versus areas suggests delta shorelines are nonfractal even though the channel network is fractal consequently channel edge length which provides critical habitat grows more rapidly than delta area these laws provide a blueprint for delta growth that will aid in delta restoration and help predict how existing deltas will evolve

stress orientations from oil well fractures in alberta and texas many oil wells in alberta exhibit spalling of the walls known as breakouts which elongates the holes with the longer axis aligned northwest southeast this alignment is observed over an area in excess of 4 105 km2 in siltstones sandstones carbonate sediments and one shale formation through the stratigraphic column from devonian to cretaceous it is unrelated to dip of the beds we have elsewhere suggested that these breakouts are produced through stress concentration near the hole walls in a stress field having large unequal horizontal principal stresses and with the larger compression oriented northeast southwest it is probable that this northeast southwest principal stress is 1 this paper adds new data from oil wells in alberta and northern british columbia and shows that the breakouts and by inference the stress orientations are consistent through much of the western canadian sedimentary basin it also uses evidence from hydraulic fracturing in west central alberta and from steam injec

relations between postglacial fluvial incision rates and uplift rates in the north island new zealand 1 fluvial incision rates are increasingly being used as a proxy for rock uplift rates for inland settings we test the validity of this approach by comparing incision rates and rock uplift rates along the hikurangi margin new zealand postglacial fluvial incision rates were calculated by measuring the difference in altitude between the last glacial maximum lgm terrace tread 18 2 calendar ka and the present river bed for 10 major rivers catchment areas 1400 5900 km2 incision rates have thus been measured over a half glacial cycle they also represent average rates over the last 18 kyr during which time variations are likely due to processes such as knickpoint retreat rock uplift rates have been estimated from 1 altitude differences between the treads of pairs of fluvial fill terraces 55 and 18 calendar ka assumed to have formed at the same altitude i e rock uplift relative to the geoid 2 present day altitudes of late neogene paleoshoreline marker horizons 1 6 5 7 ma i e rock uplift relative to sea level and 3 present day altitudes of neogene mudstones for which maximum depth of burial has been calculated from porosity i e rock uplift relative to sea level these rock uplift rates overestimate tectonic uplift rates because they do not take into account isostatic compensation due to erosion mean incision rates range up to 11 7 mm yr 1 and mean rock uplift rates range up to 4 1 and 0 9 mm yr 1 for the three methods respectively we have made some qualitative and semiquantitative observations about nontectonic controls on postglacial incision rates and find that localized influence only is exerted by rainfall base level and bedrock lithology while negative or no correlations are shown with lgm fluvial fill thickness and stream power incision rates and uplift rates display a rough correlation with incision rates typically 1 5 5 times uplift rates this relation suggests that tectonic uplift is likely to exert an important control on fluvial incision in the hikurangi margin

hydrothermal alteration in oceanic ridge volcanics a detailed study at the galapagos fossil hydrothermal field abstract the galapagos fossil hydrothermal field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern galapagos rift between 85 49 w and 85 55 w the discharge zone of the hydrothermal system is revealed along scarps thus providing an opportunity to examine the uppermost mineralized and highly altered interior parts of the crust altered rocks collected in situ by the submersible alvin show complex concentric alteration zones microsamples of individual zones have been analysed for major minor trace elements and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration interlayered chlorite smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene phenocrysts and matrix grains of plagioclase are unaffected during alteration using a modification of the gresens equation we demonstrate that the trivalent rare earth elements rees are relatively immobile and calculate degrees of enrichment and depletion in other elements strontium isotopic ratios increase as sr concentrations decrease from least altered cores to most altered rims and cross cutting veins in individual samples and can be modeled by open system behaviour under low fluid rock ratio

orientation of the stress field from breakouts in a crystalline well in a seismic active area abstract the orientation of the regional stress field in the swabian jura was determined from borehole breakouts caused by stress accumulation at the borehole wall the analysis is based on caliper data recorded in the urach 3 geothermal well within an intervall of about 1450 m the azimuths of the breakouts are consistent with depth and indicate a stress direction which is in good agreement with the interpretation of fault plane solutions of nearby earthquakes

the upper hadrynian jeffers group cobequid highlands avalon zone of nova scotia a back arc volcanic complex the upper hadrynian jeffers group of the cobequid highlands avalon zone of northern nova scotia consists of volcanic rocks of the gilbert hills formation interfingering deeper water argillite of the humming brook formation and overlying turbidite lithic arkose and siltstone of the cranberry lake formation the jeffers group has a spatially inhomogeneous flat lying cleavage associated with thrust faults of late hadrynian age that were in part reactivated during carboniferous strike slip motion on the cobequid fault the basal rocks of the gilbert hills formation consist of felsic pyroclastics and minor mafic and felsic flows of the lakelands facies locally passing up into sandstone and marble overlain by the humming brook formation thrust over this sequence is the harrington river facies of the gilbert hills formation comprising flows ranging in composition from subalkalic basalt to rhyodacite and pyroclastic rocks two groups of igneous rocks are distinguished geochemically high ti basalts of the lakelands facies and associated hypabyssal intrusions have tholeiitic character enrichment in ba rb and k flat light ree spectra little or no depletion in nb and ta and high feo t and ti they are associated with voluminous felsic rocks the harrington river facies has a calc alkaline differentiation series from basalt to rhyodacite but with more enrichment in feo t p nb and zr than is found in typical calc alkaline rocks these two groups are also represented in hypabyssal rocks the jeffers group rocks are compared geochemically with other predominantly continental back arc basins in the aegean sea and bransfield strait all three basins show the presence of a rock phase derived from partial melting of mantle only slightly modified by subduction processes the lakelands facies tholeiites of the jeffers group they all also contain a more differentiated series showing more subduction related chemical characteristics the harrington river facies of the jeffers group geochemical differences between these rocks and typical calc alkali series are related to the lesser role of hydrous fluids in the back arc basins as a result titanomagnetite and amphibole are not important fractionating phases and nb and ta are not significantly depleted

mapping the miocene farallon ridge jump on the pacific plate a seismic line of weakness abstract bathymetric and magnetic data are used to obtain estimates on the pacific and nazca plates of the boundaries separating lithosphere generated at the old farallon ridge from the more recent one created at the present day east pacific rise an excellent correlation is found with the sites of known teleseismically recorded intraplate seismicity suggesting that these boundaries which are lines of age discontinuity in the plate must be zones of weakness of the lithospheric plate in particular the so called region c identified by okal et al as a major site of seismic release sits on a small piece of farallon plate in the immediate vicinity of the northern extension of the fossil roggeveen rise cut across by the east pacific rise during the ridge jump

postglacial after 18 ka deep sea sedimentation along the hikurangi subduction margin new zealand characterisation timing and origin of turbidites recent sedimentation along the hikurangi subduction margin off northeastern new zealand is investigated using a series of piston cores collected between 2003 and 2008 the active hikurangi margin lies along the pacific australia subduction plate boundary and contains a diverse range of geomorphologic settings slope basin stratigraphy is thick and complex resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the quaternary turbidites deposited since c 18 ka in the poverty ruatoria and matakaoa re entrants are central to this study in that they provide a detailed record of the past climatic conditions and tectonic activity here alternating hemipelagite turbidite debrite and tephra layers reflect distinctive depositional modes of marine sedimentation turbidity current debris flow and volcanic eruption respectively turbidites dominate the record ranging in lithofacies from muddy to sandy turbidites and include some basal reverse graded turbidites inferred to be derived from hyperpycnal flows stacked turbidites are common and indicate multiple gravity flows over short time periods the chronology of turbidites is determined by collating an extremely dense set of radiocarbon ages and dated tephra which facilitate sedimentation rate calculation and identification of the origin of turbidites sedimentation rates range from 285 cm ka during late glacial time 18 5 17 ka to 15 to 109 cm ka during postglacial time 17 0 ka turbidite deposition is controlled by 1 the emplacement of slope avalanches reorganising sediment pathways 2 the postglacial marine transgression leading to a five fold reduction in sediment supply to the slope due to disconnection of river mouths from the shelf edge and 3 the holocene pleistocene boundary climate warming resulting in a drastic decrease in the average turbidite grain size flood induced turbidites are scarce nine hyperpycnites are recognised since 18 ka and the youngest is correlated to the largest enso related storm event recorded onland lake tutira other turbidites contain a benthic foraminiferal assemblage which is strictly reworked from the upper slope and which relates to large earthquakes over the last c 7 ka they yield a shorter return time 270 430 years than the published coastal records for large earthquakes c 670 years but the offshore record is likely to be more complete the deep sea sedimentation along the new zealand active margin illustrates the complex interaction of tectonic and climate in turbidite generation climate warming and glacio eustatic fluctuations are well recorded at a millennial timescale 18 ka while tectonic deformation and earthquakes appear predominant in fostering turbidite production at a centennial timescale 270 430 years

state of lithospheric stress and borehole stability at deep sea drilling project site 504b eastern equatorial pacific hole 504b in the eastern equatorial pacific is the deepest hole to penetrate oceanic basement extending more than 1500 m beneath the seafloor two borehole televiewer bhtv logs were obtained in this hole one through the upper 1000 m of basement during deep sea drilling project leg 83 and the other extending an additional 260 m deeper into the crust during ocean drilling program leg 111 the two bhtv records have been combined and processed in terms of both acoustic amplitude and travel time in order to evaluate the extent and distribution of rock failure along the borehole wall a histogram of borehole enlargements versus azimuth depicts a dominant breakout azimuth of n122 5 e which corresponds to the direction of minimum principal stress sh and correlates well with stress orientations inferred from solutions to regional earthquake focal mechanisms furthermore the bimodality of this histogram with a secondary mode orthogonal to sh indicates that a significant number of enlargements are coalesced tensile fractures occurring along the orientation of sh the maximum principal stress the appearance of this orthogonal bimodal distribution suggests that the regional horizontal stress field is highly anisotropic a condition supported by seismic data which show all of the earthquakes in the area to be strike slip the frequency of borehole enlargements increases with increasing depth and depicts a systematic structural deterioration of the well bore the tensile fractures along the sh azimuth contribute to this degradation and appear to be induced by thermal stresses due to the injection of cold water into hot rock the frequency of these extensional features does not increase with depth rather their appearances can be directly correlated with shipboard efforts at deliberately cooling the well and or with the sudden resumption of drilling after the hole had been allowed to reequilibrate thermally for several days these latter borehole enlargements are more pronounced then those commonly associated with hydraulic fracturing the mechanisms for fracture initiation and growth based upon temperature contrasts between the well bore fluid and the adjacent rock may enhance rock failure

terrestrial palynology from marine cores as an indicator of environmental change for the waipaoa sedimentary system and north eastern new zealand diverse terrestrial palynomorph assemblages of pleistocene to recent age have been recovered from mainly marine sediment cores along the eastern new zealand margin these assemblages record a range of environmental changes including climate deforestation reforestation rates of erosion sediment provenance and age volcanic activity polynesian and european settlement strength and direction of ocean currents astronomical cyclicity and other major events many of which can be correlated with shorter onshore terrestrial sequences as such pollen yields valuable information on the dynamic new zealand landscape which is of particular relevance to a source to sink approach this paper provides an integrated summary of published and unpublished late pleistocene palynological studies off eastern north island new zealand that gives context for an analysis of cores within and marginal to the waipaoa sedimentary system pollen assemblages faithfully reflect the last glacial vegetation dominated by grass and shrub land species together with elevated tertiary pollen from enhanced erosion of the regolith the glacial termination and holocene were marked by establishment of podocarp forest a mid holocene disappearance of sediment trapping mangroves and introduction of distal pollen with establishment of coastal current systems under rising sea level these natural signals are overprinted by abrupt changes in pollen species caused by volcanic eruptions finally endemic forest and shrub pollen were markedly reduced with human colonisation associated land use changes and introduction of exotic species

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

an assessment of coastal tectonics along the sanriku coast northeast japan from a holocene sedimentary succession in the kuji plain abstract holocene sedimentary successions in tectonically active regions are key to understanding coastal tectonics because they provide information on millennial scale crustal movements recent analyses of holocene sedimentary successions along the sanriku coast near the source region of the 2011 tohoku oki earthquake have reported millennial scale subsidence in central to southern parts of the coast but only one comparable dataset is available for the northern part of the coast to obtain a comprehensive understanding of millennial scale crustal movements along the sanriku coast we obtained well dated holocene sediment cores from the kuji plain in the northern part of the coast these cores record a transgressive barrier lagoon system from ca 9500 to 8000 cal bp a regressive prodelta to delta front from ca 8000 to 6500 cal bp and a subsequent wave influenced shallow marine and fluvial environment the early to mid holocene relative sea level in the study area estimated from the sedimentary environment at that time is higher than that in the tsugaruishi plain central sanriku coast where millennial scale subsidence was previously inferred this discrepancy indicates that the kuji plain has been uplifted relative to the tsugaruishi plain on a millennial scale the contrast in the millennial scale crustal movements between relative uplift on the northern sanriku coast and recently inferred subsidence on the central to southern sanriku coast confirms that the sanriku coast contains multiple areas of crustal deformation furthermore this spatial distribution of millennial scale crustal movements is in good agreement with the recently reported mis 5 marine terrace distribution suggesting a continuous southward tilting trend along the sanriku coast since ca 100 ka

tectonic setting of outer trench slope volcanism pillow basalt and limestone in the taconian orogen of eastern new york the only pillow basalt in synorogenic sedimentary rocks at the exterior margin of the taconic orogen in eastern north america is at stark s knob in eastern new york earlier reported as extrusive into allochthonous ordovician slope and rise facies this small lens ca 125 m long 39 m thick is a fault bounded block in upper ordovician melange under the taconian frontal thrust its n morb normal mid ocean ridge basalt basalt geochemistry and spinel composition are characteristic of oceanic ridge settings at a water depth of 2 km or more abundant limestone lenses on pillows and lava shelves within pillows yielded a middle late ordovician gastropod the limestones are reconciled with this extrusion depth and with limited early paleozoic pelagic carbonate production by lime mud transport from the laurentian platform or abiotic carbonate precipitation with sea water heating during basalt extrusion a genetic relationship between the parautochthonous stark s knob basalts and the allochthonous jonestown volcanics in slope and rise facies of the hamburg klippe eastern pennsylvania is likely both are ordovician morb basalts that reflect volcanism on the subducting outer trench slope prior to the taconic arc laurentia collision taconic orogenesis may have led to basalt production on the subducting plate by 1 the setting up of orogen parallel predominantly strike slip motion on the subducting slab with morb basalt generated at offsets in a setting analogous to the gulf of california or 2 development of faults in a flexure induced extensional regime by either process mafic volcanism appears to be a rare but tectonically significant process on outer trench slopes as continental margins or oceanic plates enter subduction zones resume l unique basalte a coussinet dans les roches sedimentaires syntectoniques a la bordure exterieure de

a stress province boundary and tractions on the north american plate stress provinces characterized by nearly constant directions and relative magnitudes of horizontal principal stresses are potentially informative of the forces acting on a lithosphere plate this applies most strongly to stress provinces which occupy a large part of a plate such as the mid continent stress province of north america identified by zoback and zoback1 we have used fractures known as breakouts in oil wells which are controlled by the in situ stress to show that this stress province extends through the western canadian sedimentary basin to the arctic coast there is a strong possibility that a uniform stress orientation with greatest compression ne sw is co extensive with the north american continent east of the rocky mountains excluding the appalachian and gulf of mexico stress provinces we further report new breakout orientations in the far northwest of canada which locate the boundary between the mid continent stress province and an alaskan stress province with largest compression nnw sse probably controlled by the subduction of the pacific plate under alaska

the river it goes right on post glacial landscape evolution in the upper waipaoa river basin eastern north island new zealand abstract post glacial incision created 50 to 120 m of relief in the headwaters of the waipaoa river basin but it is not known how the signal of incision propagated along the trunk streams we addressed this issue by imposing previously determined long term rates of rock uplift that vary between 0 6 and 4 mm year 1 on the preaggradation longitudinal profile acting over the past 27 1 2 cal ka bp these rates are sufficient to passively elevate the waipaoa 1 terrace to its present level but during the last glacial maximum rates of vertical incision failed to match those of the uplifting rocks thus by the time favorable conditions for incision were reestablished after the antarctic cold new zealand late glacial reversal we estimate that the channel would have been elevated 55 m above the datum the river should otherwise have maintained the channel incised rapidly after the transition from glacial to interglacial conditions and reacquired its steady state form in the mid holocene 5 5 2 cal ka bp thereafter we suggest rates of incision matched rates of uplift no knickpoints are found on the upper waipaoa and mangatu rivers because incision commenced simultaneously along the entire length of the trunk streams and the pattern of incision is consistent with the downstream decline in the rate of rock uplift we also used hypsometric analysis to show how post glacial incision affected the surface morphology of low order 0 1 4 3 km 2 drainages in the headwaters of the waipaoa river basin values of the hypsometric integral are higher for proximal basins which the incision signal did not permeate than for low order basins bordering the upper waipaoa river and the lower reaches of tributaries that possessed enough erosive capacity to keep pace with incision along the mainstem hillslope adjustments were focused on the lower and mid sections of these basins so that the most pronounced changes to the hypsometric curve occur in the vicinity of the toe whereas the entire form of the hypsometric curve changes once mass wasting processes encroach onto hillslopes in the middle and upper sections of a basin

geological evidence for past large earthquakes and tsunamis along the hikurangi subduction margin new zealand abstract the hikurangi subduction margin new zealand has not produced large subduction earthquakes within the short written historic period 180 years and the potential of the plate interface to host large m 7 to great m 8 earthquakes and tsunamis is poorly constrained the geological record of past subduction earthquakes offers a method for assessing the location frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments we review evidence of holocene coseismic coastal deformation and tsunamis at 22 locations along the margin a consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake to identify possible subduction earthquakes we use temporal correlation of earthquakes combined with the type of earthquake evidence likely primary fault source and the earthquake certainty ranking we identify 10 past possible subduction earthquakes over the past 7000 years along the hikurangi margin the last subduction earthquake occurred at 520 470 years bp in the southern hikurangi margin and the strongest evidence for a full margin rupture is at 870 815 years bp there are no apparent persistent rupture patches suggesting segmentation of the margin is not strong in the southern margin the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved the pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes demonstrating different modes of slip behaviour occur on the central hikurangi margin evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record large uncertainties remain in regard to evidence of past subduction earthquakes on the hikurangi margin with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes however areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future

rheological evolution of the ocean crust a microstructural view rheological studies of the oceanic lithosphere have used direct observations of rocks and inferences based on thermal mechanical and experimental models modeling studies help to constrain an average crust and mantle rheology and the deep seated processes that control regional scale strength and stress field variations the smoothing of fine scale variations in such models can obscure many of the geological processes that influence strain localization and deformation partitioning in the ocean crust examination of deformation mechanisms and histories in ocean crust rocks provides a complementary approach to modeling examples of structures and deformation histories in diabases from deep sea drilling project ocean drilling program site 504b the hayes and atlantis fracture zones mid atlantic ridge and the troodos ophiolite cyprus are presented in conjunction with a synthesis of microstructural studies of the ocean crust over the last 25 years a survey of brittle quasi plastic and synmagmatic viscous deformation is used to demonstrate the influence of primary compositional and textural characteristics and variable magmatic and hydrothermal histories on deformation mechanisms and strain localization in the ocean crust geological evidence indicates that hydrothermal fluids strongly influence the nature of deformation and that effective stresses may be low due to fluid overpressures melt distribution will strongly influence strain localization at the base of the crust and synkinematic hydration during crystal plastic deformation plays a key role in the relative strengths of polyphase oceanic lithologies a schematic distribution of failure mechanisms in the ocean crust is used to discuss the controls on variations in lateral and vertical strength profiles and their possible relation to spreading rates although microstructural studies of ocean crust are still in their infancy they provide valuable constraints for rheological models and further insights to explain the distribution of seismicity at spreading centers and acoustic signatures

ultrasonic borehole televiewer investigation of oceanic crustal layer 2a costa rica rift in situ lithostratigraphy and the distribution of fracture and void zones in oceanic layer 2a were examined with an ultrasonic borehole televiewer at ipod sites 501 and 504b on the south flank of the costa rica rift these records indicate a decrease in the size of basalt pillows with depth and a corresponding increase in fracture and void density the observed increase in p wave velocity with depth in this hole as layer 2a merges into 2b is best explained by an increase in the degree to which clays and zeolites fill fractures and voids this also explains the order of magnitude drop in permeability observed in hole 504b an increase in alteration filling with age could explain the transition from convective to conductive heat flow and the correlative disappearance of layer 2a on the flanks of oceanic spreading centres

slip slidin away a post glacial environmental history of the waipaoa river basin abstract the dramatic changes that occurred to the post glacial landscape in the headwaters of the waipaoa river basin are a consequence of perturbations about the equilibrium that exists between the rate of tectonic uplift and fluvial incision at times when the amount of coarse sediment delivered to channels exceeds the capacity of streams to remove it the channel bed rises at the rate of tectonic uplift once bedload overcapacity is replaced by undercapacity and the alluvial cover is depleted streams reestablish contact with bedrock and recuperate the time lost to fluvial incision the first major perturbation occurred during the final phase of the last glaciation ca 33 17 5 cal ka when aggradation was driven by a climate forced variation in the relative supplies of sediment and water we suggest that the subsequent transformation of channels in the headwaters of the waipaoa river basin from alluvial to bedrock occurred as the atmospheric and oceanic circulation converged on their contemporary patterns ca 12 cal ka a second major perturbation that continues to the present began ca 1910 1912 ce when a massive increase in sediment load was accompanied by a modest increase in water discharge after the native vegetation cover in the headwaters was replaced by pasture the processes of terrace creation and incision are inherently unsteady and in five interim cases incision was arrested by a transient increase in the thickness of the alluvial cover that was a response to climatic forcing events that disrupted the native vegetation cover in the headwaters also modulated patterns of sediment dispersal and accumulation in other parts of the fluvial system and caused rapid storm driven infilling of the poverty bay flats tectonic subsidence dictates the course of the waipaoa river across poverty bay flats which because the modern rate of floodplain construction by vertical accretion is rapid relative to the amount of destruction by lateral channel migration has remained virtually unchanged for the past 100 years during this time the channel assumed a narrower deeper form that is in equilibrium with the contemporary supply of sediment and hydraulic regime

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

erosion thresholds and suspended sediment yields waipaoa river basin new zealand characteristics of the suspended sediment load in the waipaoa river new zealand and in two of its tributaries mangatu and te arai rivers are examined for evidence of different dominant erosion processes in the basins upstream different shapes of the suspended sediment concentration water discharge relations lead to differences in long term average yield event yield magnitude frequency relations and relative importance of large flows and rare events in the mangatu river frequent runoff events 2 1 are relatively more important to the long term yield 11 540 t km yr half of the long term average load is transported by events with return periods less than 1 year and there is little evidence of an erosion threshold limitation on sediment supply this is consistent with the predominance in the mangatu basin of hillslope erosion processes that involve scour by surface and channelized runoff particularly gully erosion this contrasts with the te arai river where sediment concentration tends to be much lower at low and moderate flows frequent runoff events transport less of the long term yield 4600 t km 2 yr than do rarer large magnitude flood events event sediment yields are an order of magnitude lower during events with subannual return periods and half of the long term average load is transported during events with a return period of 2 years some of these characteristics appear to result in part from two populations of runoff events in the te arai basin nonetheless they are consistent with field evidence that most of the sediment supplied to the te arai stream network is generated by shallow landslides which are activated once a rainfall threshold is exceeded

relative importance of fluvial input and wave energy in controlling the timescale for distributary channel avulsion 1 existing avulsion models are decoupled from nearshore processes here i explore quantitatively how the interplay of wave energy with fluvial input of sediment and water controls the aggradation rate and avulsion timescale of a single distributary channel my approach rigorously couples a diffusive moving boundary theory of fluvial morphodynamics with a diffusive treatment of shoreface morphodynamics i use this deterministic model to quantify the time required for channel belt superelevation normalized with channel depth to attain a threshold value for nodal avulsion at a specified channel location increasing the long term wave energy relative to fluvial input by an order of magnitude increases longshore sediment dispersal thereby reducing the rate of channel belt aggradation and associated seaward extension and increasing the avulsion timescale by a factor of approximately 50 far field processes eventually limit the ability of wave energy to suppress avulsion

stratigraphic solution sets for determining the roles of sediment supply subsidence and sea level on transgressions and regressions although identifying unequivocally the cause of transgressions and regressions from the rock record can be difficult we can place limits on the possible combinations of sediment supply subsidence and sea level that could generate an observed stratigraphic sequence using simple geometric models that estimate maximum rates of change in the three controlling variables and combining these with other limits derived from field observations we can plot a solution set to define the most likely range of variations in these three primary controls on shoreline migration this approach shows the amount each controlling factor must change alone or in concert to account for the stratigraphy these quantitative values can be used to decide what is geologically reasonable and what is not although a unique solution may not be available we can calculate the required parameters for the observed shoreline migrations which provide a basis for informed interpretations

a unifying framework for shoreline migration 1 multiscale shoreline evolution on sedimentary coasts 1 a unifying framework for shoreline migration is presented which synthesizes problems from coastal engineering geomorphology and stratigraphy into a common quantitative basis consideration of characteristic problems from these fields reveals that multiscale shoreline evolution problems naturally break into three classes on the basis of the morphologic unit of evolution shoreface bed versus shoreline planform versus stratigraphic shoreline trajectory shoreline evolution models correspondingly break into morphodynamic morphokinematic and hybrid approaches a generalized shoreline continuity equation is derived the shoreline exner equation which subsumes equilibrium profile models commonly used in geomorphology and engineering and provides a natural framework for interpreting shoreline trajectories preserved in the sedimentary record the shoreline exner equation provides a rigorous basis for geometric and moving boundary models which have significant untapped potential for shoreline migration problems recent advances in computational methods for evolving interface problems make hybrid models particularly attractive for problems of large scale planform shoreline dynamics such as delta evolution

event suspended sediment characteristics and the generation of hyperpycnal plumes at river mouths east coast continental margin north island new zealand abstract steepland rivers draining small coastal watersheds often have very high suspended sediment loads but the event characteristics of suspended sediment concentration and yield in this class of river is not well documented continuous monitoring at four sites in the waipaoa river basin new zealand demonstrates that during individual and composite events suspended sediment concentration versus water discharge relations typically show clockwise hysteresis and that event maximum concentration is poorly related to event peak discharge the signature of different erosion processes is also imprinted on the event yield magnitude frequency distributions gully dominated tributary basins produce relatively high yields at all frequencies reflecting greater sediment availability whereas in tributary basins where shallow landsliding is the dominant erosion process there is a steep increase in yields in relation to return period we estimate that flood discharges from the waipaoa river approach or exceed

influence of system controls on the late quaternary geomorphic evolution of a rapidly infilled incised valley system the lower manawatu valley north island new zealand abstract the manawatu incised valley estuary was rapidly infilled between 12 000 4700 cal yr bp a combination of empirical measurements of sedimentation rates a reconstruction of relative sea level rsl change and digital elevation models of key surfaces within the holocene sedimentary fill of the valley were integrated to produce a numerical model to investigate the influence of the system controls of sea level change sediment flux and accommodation space on the rapid infilling history of the palaeo estuary the numerical model indicates that sediment flux into the palaeo estuary was greatest during the holocene marine transgression between 12 000 8000 years bp the average rate of sediment deposition in the estuary during this period was 1 0 m m 3 yr 1 this rapid rate of sedimentation was controlled by the rate of accommodation space creation as regulated by the rate of sea level rise and the antecedent configuration of the valley by the time sea levels stabilised c 7500 cal yr bp the palaeo estuary had been substantively infilled limited accommodation space resulted in rapid infilling of the central basin though sediment flux into the estuary between 7100 and 4500 cal yr bp was at a lower rate of 234 000 m 3 yr 1 the limited accommodation space also influenced hydrodynamic conditions in the estuarine central basin driving export of fine grained sediment from the estuary once the accommodation space of the estuarine basin was infilled sediment bypassed the system with a consequent reduction in the sedimentation rate in the valley more accurate partitioning of the sources of sediment driving the infilling is necessary to quantify sediment bypassing post depositional lowering of rsl index points from the valley is driven by neotectonics and sediment compaction

estimation of the paleoflux of terrestrial derived solids across ancient basin margins using the stratigraphic record a simple inversion scheme for estimating sediment flux from ancient shelf margin successions is presented here by treating shelf margin clinothems as the product of deposition associated with migration of a shelf edge clinoform with constant shape at a rate equal to the shelf margin progradation rate assuming sediment conservation deposition can be broken into components of 1 response to subsidence and sea level changes and 2 basinward migration of the clinoform profile sediment flux can therefore be estimated with knowledge of progradation rate subsidence sea level change rate and clinoform dimensions an advantage of this methodology is that it requires only two dimensional data i e dip oriented cross sections rather than three dimensional volumes making it ideal for use with sparse data sets as well as with outcrops this methodology is also useful for analyzing areally limited data sets because it can predict the flux of sediment transported beyond the area of data coverage the approach is able to accurately reproduce the sediment flux estimates of previous workers from several margins the fox hills lewis zambezi new jersey and north slope margins using both volumetric and forward modeling methods not only are the predicted distributions for sediment flux across ancient shelf margins similar to distributions predicted by more data intensive theoretical models the estimated magnitudes for paleofluxes favorably compare with measured loads from modern rivers growth of continents is achieved in part by accretion of sediment on shelf margins the rates and patterns of continental expansion are therefore partially dependent on the magnitude and distribution of mass transfer from eroding hinterlands to continental margins fluxes which also play a critical role in global biogeochemical cycles flux estimates cast into a mass balance framework suggest that approximately two thirds of continental margin sediments are exported past the shelf edge into deeper water at long term geologic time scales this finding implies that two thirds of the terrestrial derived particulate organic carbon poc delivered from rivers to the ocean can be stored in deep water over geologic time scales the observations presented here indicate that repetitive delivery of sediment to margins by shelf edge deltas is fundamental to the long term process of margin accretion

port redesign and planned beach renourishment in a high wave energy sandy muddy coastal environment port gisborne new zealand redesign of port gisborne for the 21st century has encompassed a broad interdisciplinary approach this procedure has taken into account the operational requirements of the port effects of dredging and construction upon the benthic fauna and wave activity within the port confines after the proposed development added amenity value of the development to the local community is an important ancillary redesign consideration initially a major research project into the environmental impacts of the developments has been undertaken the project which commenced in 1996 and is still continuing involves an iterative approach integrating the initial design and development options with the operational feasibility construction constraints environmental constraints social acceptability and economic practicality of the port all of these require in depth assessment to obtain the necessary planning and development approvals this requires close liaison between the professional environmental research scientists port management port operation staff pilots construction engineers planners and the community interest groups numerical modelling of the hydrodynamics of poverty bay simulating waves and current effects on the various initial designs options and calibrated against data from a substantial field program has been a fundamental tool it was applied experimentally to determine the best option for the port layout as well as to assess sedimentation impacts modelling results indicated a significant increase in maintenance dredging expected as a result of deepening the navigation approach channel because this may have an impact on the nearby sandy beach by inducing erosion the best option for disposal of the sandy dredged material was determined to be disposal in the surf zone for subtidal beach profile renourishment textural analysis of the sediments trapped in the navigation channel demonstrated that they were suitable for this purpose d 2002 elsevier science b v all rights reserved

breakouts in alberta and stress in the north american plate the paper reports a detailed statistical study of breakout azimuths in 48 oil wells widely distributed in the alberta sedimentary basin bringing the number of oil wells contributing azimuths to 94 for the western canadian basin the azimuths show significant regional variation between the northern central and southern parts of the basin twenty one wells in which breakouts cover depth ranges greater than 600 m were used to investigate regression of breakout azimuths on depth ten wells give positive regression coefficients 11 are negative and no coefficient is significant at 95 confidence level if the dominant northwest southeast orientation of the long axes of breakouts gives the orientation of the lesser horizontal principal stress sh following the hypothesis of bell and gough the inferred stress orientations indicate that throughout the whole basin the direction of the maximum horizontal stress sh is northeast southwest stress measurements by strain relief techniques in a mine and from hyd

causes of concavity in longitudinal profiles of rivers a smooth concave configuration represents the most common quasi equilibrium profile of alluvial rivers in the present paper a generalized unified set of models for the longitudinal profile of rivers is presented various independent effects that drive concavity in longitudinal rivers are considered and classified the driving mechanisms considered here are 1 horizontal wavelike progradation of the river profile 2 abrasion of bed particles 3 aggradation of the river profile balancing subsidence at a constant speed and 4 the effect of tributaries adding sediment and water to the main stem of the river for simplicity it is assumed that the long term supply of water and sediment is constant hence a single discharge that is bank full discharge is used as an approximate characterization of the hydrologic regime for each point along the river sediment sorting has been studied elsewhere and is excluded from this analysis the river is assumed to have uniform bed material although the mean size may vary downstream it is concluded that the quasi equilibrium longitudinal profile created by each of the first three driving mechanisms mentioned above is concave the degree of concavity varies however depending on a set of physical conditions that can be identified by a set of dimensionless numbers a comparison of these numbers reveals the relative importance of the driving mechanisms for concavity a condition for concavity driven by the fourth mechanism that is tributary input is delineated