large scale sediment transport patterns on the continental shelf and influence on shoreline response st andrew sound georgia to nassau sound florida usa abstract regional sediment transport patterns on the continental shelf seaward of cumberland island georgia and amelia island florida are documented using historical shoreline position and bathymetry data spatial variability in the net rate of shoreline change is considerable due to jetty construction at st marys entrance in the early 1900s net average shoreline progradation is documented for both islands 1 5 m yr for cumberland and 0 4 m yr for amelia however localized areas of shoreline retreat are recorded along amelia island especially for the southernmost 5 km of beach where erosion has been chronic since 1871 rapid shoreline progradation adjacent to the jetties accompanied sediment deposition by longshore sediment transport simultaneously a large quantity of sediment from the natural ebb tidal delta was reworked and transported offshore in response to jetty construction and channel dredging creating the modern ebb tidal delta patterns of sediment movement at this inlet and throughout the study area indicate a dominant direction of drift to the south southeast sediment losses and gains were quantified to evaluate long term coastal change within the framework of a sediment budget qualitative descriptions of net sediment transport were integrated with quantitative results to produce a model of large scale coastal evolution for the study area from this analysis net sediment transport in this coastal compartment is controlled by inlet and shelf hydraulics and littoral zone processes have minimal impact on net long term coastal change

clinoforms and clinoform systems review and dynamic classification scheme for shorelines subaqueous deltas shelf edges and continental margins abstract clinoforms are inclined and normally basinward dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems the study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir seal and source rocks along shoreline to basin floor profiles here we review clinoform research and propose a more systematic description and classification of clinoforms this is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions together with the genesis drivers and dynamics of their constituent sedimentary units four basic clinoform types are here distinguished in delta shorelines lacustrine and marine environments on the basis of their overall spatial and temporal scale morphology outbuilding dynamic and geodynamic and depositional setting 1 2 delta scale clinoforms which in turns are sub divided into shoreline and delta scale subaqueous clinoforms 3 shelf edge clinoforms and 4 continental margin clinoforms delta scale clinoform sets are tens of metres high and typically represent 1 103 kyr with progradation rates ranging from 1 000 100 000 m kyr for shorelines and subaerial deltas to 100 20 000 m kyr for subaqueous deltas shelf edge clinoform sets are hundreds of metres high and are nucleated and accreted in 0 1 20 myr usual progradation rates of 1 100 m kyr by successive cross shelf transits of delta scale clinoforms continental margin clinoform sets are thousands of metres high hallmark key geodynamic crustal boundaries e g continent ocean transition and slowly prograde basinwards in ca 5 100 myr with typical rates of 0 1 10 m kyr as a consequence of the very different progradation rates and of the difficulty of large scale clinothems to backstep during transgressions shorelines are the most dynamic clinoforms with regards to position continental margins the least and shelf edges are intermediate shortly after a transgression therefore the four clinoform types may prograde synchronously along shoreline to abyssal plain transects forming compound clinoform systems during the subsequent regressive cycle however due to the dissimilarity in progradation rates different clinoform types will normally merge progressively with each other giving rise to hybrid clinoforms e g shelf edge deltas and fewer depositional breaks in slope are distinguished along a single shoreline to abyssal plain transect overall all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum regulated by the cyclical backstepping of the smaller scale system within natural progradational retrogradational cycles of larger scale clinothem outbuilding all clinothem types may show either an accretionary active or draping passive style depending on the proximity to the sediment source draping clinothems are nearly always composed of condensed fine grained sediments while actively accreting clinothems can be composed of predominantly coarse grained i e reservoir forming or predominantly fine grained i e non reservoir lithotypes a novel hierarchical classification scheme for both recent and ancient clinoforms is here proposed consisting of 12 classes the four basic clinoform types delta scale shoreline delta scale subaqueous shelf edge and continental margin are sub divided into eight accretionary active and draping passive sub types 8 division each accretionary sub type is then sub divided into a sandstone prone and mudstone prone variant 12 division which can be at least tentatively predicted on the basis of the clinoform morphology even in the absence of direct stratigraphic logs

the timing of calc alkaline magmatism in parts of the alpine himalayan collision zone and its relevance to the interpretation of caledonian magmatism discussion of the timing of calc alkaline caledonian magmatism in scotland has centred on its tectonic setting the view that active subduction was responsible for the formation of 415 400 ma magmatism is in conflict with the palaeogeographical and stratigraphical evidence in order to shed light on the problem magmatism in the continent continent collision zone of modern times turkey iran and tibet is surveyed the conclusion is reached that the final stage of calc alkaline magmatism displays a time lapse and possible space shift after two continents have collided from the evidence of magmatism the timing of the major collision events in the himalayas is thought to be diachronous ranging from around or no later than 38 30 ma for the central part to later than 30 ma for the eastern part this view is supported by the available palaeogeographical and stratigraphical evidence evidence from this survey enables the scottish data to be seen in a new context by comparing modern collision zones with old ones such as those in scotland and the appalachians it is also concluded that collision related magmatism is not volumetrically trivial and is diverse in composition

getting over continent ocean boundaries the idea of a simple linear boundary between continental and oceanic crust at extended continental margins is widely recognized to be an oversimplification despite this such boundaries continue to be mapped because of their perceived utility in palinspastic and plate kinematic reconstructions to examine whether this perception is justified we review the data and models on which basis continent ocean boundaries are interpreted and map a set of such interpretations worldwide from more than 150 publications the maps show that the location of the continent ocean boundary is rarely consistently estimated within the 10 100 km observational uncertainty that might be expected of the geophysical data used for doing so that this is the case regardless of whether the transition zone behind the boundary is classified as magma rich or magma poor and that the geographical separation of estimates exceeds the width of single study continent ocean transition zones the average of global maximum separations across sets of three or more estimates is large 167 km and mostly a consequence of interpretations published over the last decade we interpret this to indicate an extra component of uncertainty that is related to authors understanding of the range of features that are interpretable at extended continental margins we go on to discuss the implications of this uncertainty for palinspastic and plate kinematic modelling using examples from the literature and from the south atlantic ocean we conclude that a precise continent ocean boundary concept with locational uncertainty defined from the ensembles is of limited value for palinspastic reconstructions because the reconstruction process tends to bunch the ensemble within a region that is i of similar width to the observational uncertainties associated with continent ocean boundary estimates ii narrower than the regions of uncertainty about rotated features implied by the propagation of uncertainties from plate rotation parameters and iii coincident within all the above uncertainties with the more easily mapped continental shelf gravity anomaly secondly we conclude that estimated continent ocean boundaries are of limited use in developing or testing plate kinematic reconstructions because i reconstructions built using them as markers do not within uncertainty limits defined from the ensembles differ greatly from those using more easily determined bathymetric or gravity anomaly contours and ii because it is impossible to segment and date them with useful precision to use as markers of the edges of rigid oceanic lithosphere outside of the constraints of a pre existing plate kinematic model

the depositional architecture and facies variability of shelf deltas in the eocene battfjellet formation nathorst land spitsbergen deltas are commonly classified according to their plan view morphology as either river dominated tide dominated or wave dominated however most deltas form under the mixed influence of these processes commonly with laterally varying process regimes it has also become clear that there is a mismatch between the plan view morphology and internal facies composition in some deltas combined outcrop and subsurface data from the eocene battfjellet formation spitsbergen provide an example of ancient shelf deltas that formed under mixed influence internally these shelf deltas are characterized by wave dominated facies that are normally associated with strike extensive nearly linear shoreline sandstones however the formation comprises partially overlapping sandstone bodies of limited lateral extent 20 km in any direction this stacking pattern is attributed to frequent autogenic lobe switching that caused localized and rapid transgressions such processes typify fluvial dominated deltas and occur less commonly in wave dominated ones thus there is an apparent mismatch between inferred plan view morphology and internal facies composition it is argued that the battfjellet deltas were flood dominated and prograded mainly during periods of high fluvial discharge however reworking of the fluvial flood facies by fair weather and storm waves as well as longshore currents resulted in a wave dominated facies character delta lobes undergoing auto retreat were particularly prone to reworking by basinal processes including tidal currents it is suggested that repeated delta progradation from inner shelf settings towards the outer shelf and shelf edge was aided by high sediment supply rather than relative falls in sea level as previously suggested this interpretation is supported by i the lack of major facies dislocations and extensive sub aerial unconformities and ii an overall relative rise in sea level as evidenced by an overall low angle 0 8 to 1 2 ascending shoreline trajectory the latter results from the combined effect of basin subsidence eustatic highstand and sediment compaction

geomorphic effectiveness sandur development and the pattern of landscape response during jokulhlaups skeiðararsandur southeastern iceland by contrast with other historical outburst floods on skeitararsandur the 1996 jokulhlaup was unprecedented in its magnitude and duration attaining a peak discharge of f53 000 m 3 s in 17 h using a combination of field sampling and remote sensing techniques landsat tm sar interferometry airphotos and laser altimetry we document the sandur wide geomorphic impacts of this event these impacts varied widely across the skeitararsandur and cannot be singularly attributed to jokulhlaup magnitude because pre jokulhlaup glacial dynamics and the extant setting largely conditioned the spatial pattern type and magnitude of these impacts topographic lowering and asymmetric retreat of the ice front during the late twentieth century has decoupled the ice sheet from the moraine sandur complex along the central and western sandur this glacial control in combination with the convex topography of the proximal sandur promoted a shift from a primarily diffuse source braided outwash system to a more point sourced channelized discharge of water and sediment deposition dominated within the proglacial depression with approximately 3 8 10 7 m 3 of sediment and along channel systems that remained connected to subglacial sediment supplies this shift to a laterally dissimilar channelized routing system creates a more varied depositional pattern that is not explicitly controlled by the concave longitudinal profile down sandur laterally contiguous units therefore may vary greatly in age and sediment character suggesting that current facies models inadequately characterize sediment transfers when the ice front is decoupled from its sandur water was routed onto the sandur in a highly organized fashion and this jokulhlaup generated major geomorphic changes including sandur incision in normally aggradational distal settings and eradication of proximal glacial landforms dating to fa d 1892 d 2002 elsevier science b v all rights reserved

rates of delta progradation during highstands consequences for timing of deposition in deep marine systems estimated times required for 24 modern river systems to form a shelf edge delta range from 8 5 ka to 116 5 ka depending on fluvial sediment supply delta width shelf volume and shelf transport rates these values indicate that transport of sand into deep marine systems is likely to be significant during third order highstands of relative sea level factors such as shelf transport dynamics may slow delta progradation while submarine canyons cutting the shelf may reduce the time before deep marine deposition occurs interpreting ancient sand rich deep marine strata as lowstand deposits without sufficient palaeogeographic information may not therefore always be appropriate

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

an occurrence of shoshonites near kilmelford in the scottish caledonides and its tectonic implications the kilmelford intrusives were emplaced in dalradian metasediments and eruptives during the late stages of the caledonian orogeny the suite of rocks includes biotite hornblende diorite and to a minor extent biotite pyroxene and biotite hornblende pyroxene diorites together with hornblende biotite quartz diorite granodiorite porphyrites of dioritic and dacitic composition and volcanic breccia the major element geochemistry shows that the kilmelford rock suite is alkali calcic having petrogenetic affinities with the igneous rocks of the new guinea 9continental arc9 the high contents of k sr ba rb zr and ce together with a high k 2 o na 2 o ratio give these rocks their shoshonitic signature which is of interest as an unusual example of the occurrence of shoshonites in the scottish caledonides the rocks have very steep ree patterns ce n yb n 10 28 and do not show a eu anomaly the shoshonitic signature of the kilmelford rocks is interpreted as due to the late orogenic nature of the magmatism which took place when subduction had abated following the collision of the two continents

piping coarse grained sediment to a deep water fan through a shelf edge delta bypass channel tank experiments 1 it is now generally accepted that deltas that prograde to the shelf edge are able to transport coarse sediment to deep water either with or without sea level changes however it is still unclear how feeder rivers behave differently in the shelf edge delta case to rivers found in a delta that progrades over the shelf a series of nine shelf edge delta experiments are presented to investigate the lateral mobility of the feeder channel at the shelf edge and the associated deep water depositional system under a range of sediment supply rates and shelf front depths in the experiments constant sediment supply from an upstream point source under static sea level led the fluviodeltaic system to prograde over the shallow shelf surface and advance beyond the shelf edge into deep water the feeder river of the fluviodeltaic system became a bypass system once the toe of the delta front reached the shelf edge after the delta front was perched at the shelf edge a submarine fan developed in deep water although remaining disconnected from the delta in this bypass stage no regional avulsion or lateral migration of the feeder river occurred and all sediment from the upstream source bypassed the river delta front and shelf front slope the duration of the bypass stage is proportional to shelf front depth and inversely proportional to sediment discharge the combined duration of the shelf transit phase of the fluviodeltaic system and the bypass phase is the characteristic time scale for the continental margin to anneal transgression inducing perturbation due to high frequency and or high amplitude relative sea level rise the sequential evolution in the experiment compares favorably to the eocene sobrarbe formation a shelf edge delta in spain although natural variations are noted this comparison justifies the application of concepts proposed herein to natural systems and provides insight into interpreting processes from ancient shelf edge delta systems

shelf sedimentation off the ganges brahmaputra river system evidence for sediment bypassing to the bengal fan the nature of shelf sedimentation seaward of the world9s largest sediment dispersal system is examined by using sedimentological and geochronological techniques on a unique suite of sediment cores and grab samples sediments from the ganges brahmaputra river system are currently accumulating on the shelf in water depths of less than about 80 m forming a clinoform like deposit similar to subaqueous deltas found off other major river systems the highest sediment accumulation rates on the shelf occur near the head of the swatch of no ground a major submarine canyon that indents the shelf west of the present river mouths this observation together with textural data suggests that river sediments are transported seaward and westward and that the swatch of no ground is currently a major conduit for the transport of sediments from the bengal shelf

shelf edge delta overreach at the shelf break can guarantee the delivery of terrestrial sediments to deep water at all sea level stands how and when sediment moves from terrestrial sources to deep water sinks is a significant area of research we have used an array of seismic borehole and gravity core data sets to explore the timing and magnitude of sediment routing to pearl river slope over the last 478 k y as predicted by existing sequence stratigraphic models most sediment dispersal to deep water is shown to have occurred during glacial sea level falls however clastic detritus was still being transported into deep water during interglacial sea level rises we suggest that sediment routing to deep water during interglacial sea level rise is caused by summer monsoon strengthening and resultant warmer and wetter climates both of which have enhanced effective precipitation and sediment supply although some models for the delivery of sediment to deep water basins stress the importance of proximity of canyon heads and coeval shorelines we observed that sediment routing to deep water could occur regardless of the distance between channel head and coeval shorelines in the present case the success of delivery is related to the combined effects of 1 the short duration and high amplitude of sea level oscillations during the past 478 k y and 2 the enhanced sediment supply caused by more humid climates and greater temperature difference between glacial and interglacial period this hypothesis is supported by 1 observations that outer pearl river deltas prograded as an apron over preexisting shelf edges for 10 15 km 6 9 mi and 2 the occurrence of slope channels extending back to prodelta reaches of pearl river shelf edge deltas

revisiting late paleocene lower wilcox deltas gulf of mexico river dominated or mixed process deltas abstract spatial and temporal changes in physical depositional processes of shallow marine deltas affect facies distributions which are critical for reconstructing paleogeography and predicting reservoir heterogeneities the updated interpretation of the classical ancient river dominated lower wilcox delta in the gulf of mexico suggests more significant process variations than previously suggested the dominance of the storm wave process is indicated by wave ripple laminae and combined flow ripple laminae in the fair weather intervals and hummocky swaley cross stratification and low angle laminae in the storm beds however the relatively simple alternation of fair weather beds and storm beds is complicated by the presence of 1 normal and inversely graded siltstone to very fine grained sandstone beds suggesting hyperpycnites generated during the river flooding season 2 mud dominated heterolithics with delicate mud rhythmites suggesting tidal modulation between the storm events the storm wave generated succession with preservation of both river flood and tidal signals during fair weather condition represents regressive shoreline to shelf outbuilding the wave dominated delta or shoreface deposits are commonly truncated by fluvial dominated tide influenced distributary channels then overlain by tidal heterolithics and gradually open shelf deposits suggesting the development of small estuaries during transgressive phases of the wilcox shoreline the interpreted mixed process delta is linked to the last growth stage of the lower wilcox group prior to inundation of the texas shelf by thick marine mudstones its depositional setting was characterized by the widest lower wilcox shelf 50 km and a weakening sediment supply resulting in a stronger wave and tide influence relative to a weak fluvial influence this work thus provides a well constrained example of the complex interplay of fluvial wave and tidal currents in a process stratigraphy where decreasing river flux and relative sea level rise allowed wave reworking to become the dominant theme even though the same system has been previously interpreted as a classic river dominated delta many existing interpretations of ancient deltas thought to have mainly been controlled by a single process may need to be revisited and revised to take into account the natural spatial and temporal variability inherent to the shallow marine realm

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

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

water level changes and their effect on deepwater sand accumulation in a lacustrine system a case study from the late miocene of western pannonian basin hungary major deepwater sand accumulations are known to be connected to sea level lowstands in marine basins due to the relative lack of accommodation space on the shelf this model was tested for the late miocene lake pannon a large endorheic lake depositing a sedimentary succession up to 3 4 km thick the progradation of the shelf between 9 7 and 6 ma was tracked along a 2d seismic network the shelf edge trajectory indicates continuous moderate lake level rise between 9 7 and 9 ma this is followed by alternating intervals of quasi steady and rapidly rising relative lake level with a period of ca 250 ky however due to the lack of significant lake level drops no third order sequence boundary was identified in the studied time span 9 7 6 ma the sand ratio of the deepwater deposits does not show strong correlation with these lake level changes moreover the units deposited under rising lake level conditions generally contain slightly larger proportion of sand these features can be explained by the climatic origin of water level rises increasing precipitation enhances not only water inflow but also sediment influx which can overwhelm the well known effect of accommodation space on the sand transport toward the deep water the results suggest that shelf margin trajectory might not be an efficient tool for predicting deepwater accumulations of sand in endorheic lacustrine basins

structural controls and origin of gold silver mineralization in the grampian terrane of scotland and ireland gold bearing mineral deposits occur over a strike distance of 300 km within the grampian terrane of scotland and ireland this terrane consists of neoproterozoic lower ordovician rocks of the dalradian supergroup that were polyphase deformed and metamorphosed during the c 470 ma grampian orogeny sulphide rich au ag deposits occur in scotland at calliachar urlar burn tombuie tyndrum and cononish and in ireland at curraghinalt omagh cavanacaw croagh patrick cregganbaun and bohaun they are hosted by 0 1 6 m thick quartz veins and have a similar overall mineralogy including native gold as cu fe pb and sn sulphides with hessite tetrahedrite and electrum present in the first six localities above the mineralized quartz veins which are characterized by open space textures crystallized at c 3 5 km depth in the crust all of the deposits were structurally controlled and apart from curraghinalt occur within second order riedel r r and t fractures resulting from a regional n s trending maximum principal stress these deposits are of upper silurian to lower devonian post scandian age and are inferred to have crystallized from hot silica rich metamorphic fluids derived from dehydration reactions at the greenschist amphibolite facies boundary curraghinalt is an older grampian thrust related deposit plutonic igneous rocks mainly granitoid contributed in part to the fluids which were channelled into major orogen parallel strike slip faults to be injected by fault valve pumping into the damage zones and fault breccias of newly formed riedel fractures any residual fluid probably percolated to the ground surface to form rhynie chert type hot springs

shelfal sediment transport by an undercurrent forces turbidity current activity during high sea level along the chile continental margin terrigenous sediment supply marine transport and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings sequence stratigraphic models predict coarse grained sediment delivery to deep marine sites mainly during sea level fall and lowstand marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves to decipher the controls on holocene highstand turbidite deposition we analyzed 12 sediment cores from spatially discrete coeval turbidite systems along the chile margin 29 40 s with changing climatic and geomorphic characteristics but uniform changes in sea level sediment cores from intraslope basins in north central chile 29 33 s offshore a narrow to absent shelf record a shut off of turbidite deposition during the holocene due to postglacial aridification in contrast core sites in south central chile 36 40 s offshore a wide shelf record frequent turbidite deposition during highstand conditions two core sites are linked to the biobio river canyon system and receive sediment directly from the river mouth however intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies high sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control holocene turbidite sedimentation and distribution shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment mass balances

evolution of the danube deep sea fan since the last glacial maximum new insights into black sea water level fluctuations abstract the danube deep sea fan nw black sea is one of the most developed deep sea sediment depositional systems in europe although the morphology and the architecture have been widely described in the past years little is known about the stratigraphy of this depositional system for the late quaternary this results from the lack of significant stratigraphic markers the scarcity of radiocarbon ages and the difficulty in constraining reservoir ages recent robust quantification of reservoir ages has allowed the construction of a new stratigraphic framework for the black sea from the end of the last glacial period to the holocene thus giving the opportunity to correlate sedimentological and geochemical features previously described on the nw black sea margin with climatic events identified in the northern hemisphere based on this approach we propose an improved chrono lithostratigraphic framework for the danube deep sea fan channel levees since the last glacial maximum we show that the danube deep sea fan was active during the last glacial maximum until the younger dryas early holocene transition ca 11 700 cal a bp when the turbidite activity abruptly terminated in the whole system throughout this period the danube river was the main source of the deep depositional system except between ca 17 200 cal a bp and 15 700 300 cal a bp at that time the deposition of red turbidites in the deep basin concomitant with the deposition of the so called red layers onto the continental shelf and the upper slope emphasises the direct impact of the increased meltwater runoff of the dnieper river as far as the danube deep sea fan some significant changes in the location of the depocentre of the danube deep sea fan occurred through time the main change in depocentre location occurred at ca 28 000 cal a bp with the northward avulsion leading to the formation of the middle channel although the middle and northern channel became the preferential turbidite depocentres after this event the deposition of turbidites has persisted in the southern channel levee until 14 700 cal a bp indicating that the southern channel was definitely not abandoned after the upstream northward avulsion unsurprisingly water level fluctuations and river sediment flux acted as the main forcings on the evolution of the danube deep sea fan based on these results and on the morphology of the danube canyon we propose that i lowstand conditions 110 m prevailed during the last glacial maximum and possibly between 15 700 300 cal a bp and 14 700 cal a bp ii water level ranged from 110 and 70 m between 14 700 and 11 700 cal a bp and iii water level ranged from 70 and 30 m from 11 700 cal a bp and until the reconnection of the black sea lake with the global ocean at ca 9000 cal a bp

the deltaic nature of amazon shelf sedimentation despite the annual discharge of more than a billion tons of sediment by the amazon river the sedimentary environment near the river mouth has little subaerial expression and thus does not meet the classic definition of a delta the river mouth however is not an estuary either these observations raise a major question as to what type of sedimentary environment the amazon river mouth represents seismic stratigraphy has been examined on the continental shelf at the mouth of the amazon river using high frequency 3 5 khz seismic records from about 6 000 km of ship track these records demonstrate three regions 1 the amazon river has built a subaqueous feature which stretches for hundreds of kilometres offshore and alongshore from its mouth the feature is prograding seaward and accreting upward and it contains fine scale stratification typical of classic deltas the feature forming at the mouth of the amazon is a subaqueous delta it differs from classic deltas primarily in its lack of subaerial expression subaqueous deltas such as the amazon represent the general case of a major river entering an energetic oceanic regime

differentiating the effect of episodic tectonism and eustatic sea level fluctuations in foreland basins filled by alluvial fans and axial deltaic systems insights from a three dimensional stratigraphic forward model many studies of foreland basins have recognized a hierarchical organization in the stacking of sequences deposited by axial deltaic and alluvial fan systems the hierarchy is often explained in terms of the competing control of eustasy and pulsed tectonic subsidence and the different frequencies at which these processes operate unravelling the relative contributions of tectonic and eustatic controls on the sequence stacking pattern is a fundamental question in foreland basin analysis yet this is difficult because of the lack of independent stratigraphic evidence in this study a three dimensional numerical model is presented which aids in the interpretation of alluvial successions in foreland basins filled by transverse and axial depositional systems under conditions of variable tectonism and eustatic sea level change the tectono sedimentary model is capable of simulating the hierarchical stratigraphic response to both eustatic and tectonic forcing and is of higher resolution than previous models of foreland basin filling numerical results indicate that the onset of tectonic activity is reflected by rapid retrogradation of both depositional systems and by widespread flooding and onlap of carbonate sediments syntectonic fluvial patterns on the axial deltaic plain are dominated by bifurcating channels swiftly relocating in response to the general rise in relative sea level induced by flexural subsidence the resulting surface morphology of the axial delta is convex upwards syntectonic eustatic sea level fluctuations result in parasequence scale packages of retrograding and prograding fan and delta sediments bounded by minor flooding surfaces and type 2 sequence boundaries incised channels are rare within the syntectonic parasequences and are formed only during phases of tectonic quiescence when eustatic falls are no longer compensated by the subsidence component in the rise in relative sea level suites of amalgamating axial channels corresponding to multiple eustatic falls delineate the resulting type 1 unconformities coarse grained incised channel fills are found in the zone between the alluvial fan fringes and the convex upward body of the axial delta as the axial streams tend to migrate towards this zone of maximum accommodation

contemporary channel levee systems in active borderland basin plains california continental borderland abstract long range large scale side scan gloria information other seismic reflection profiling studies and data from cores in the california continental borderland have defined active levee channel systems extending basinward from the lower fan of hueneme mugu submarine fan redondo submarine fan and santa cruz canyon fan in santa monica san pedro and santa cruz basins respectively the holocene distributaries have been created by a series of turbidity current events these distributaries range in length from 10 25 km and are wide 2 5 km and low relief 1 10 m in their distal parts they are also active conduits for nepheloid flows distributions of sedimentological parameters typically mimic the pattern of levee channel systems organic carbon and biogenic carbonate content roughly outline the systems channels are incised in the upper to middle fan areas and become constructional leveed channels in the lower fan and basin plain as the channel gradient adjusts to maintain a graded profile thus sediment gravity flows are generally confined to channels in the upper fan zones but deposit both channelized and over bank deposits on the lower fan and basin floor the deposits show that the canyon fan activity has continued during a rising sea level phase it is evident that canyon headward erosion rates have been equal to or greater than the transgression rate and that the canyon fan systems have remained linked with their sediment sources frequency of events was probably higher and volumes of the events were often larger during the glacially lowered sea level episodes however turbidity currents of sufficient volume to reach the basin floors continue to occur at century or multi century intervals as one progresses headward in each system the number of flows per length of core increases small flows that do not pass beyond the distributaries are much more frequent and may be decadal in frequency or even more frequent in the santa monica basin system these california borderland basins are probably typical of narrow active margins where rate of lateral sea level transgression is less than or equal to the rate of canyon headward erosion the canyons maintain connections with sediment sources during sea level rise and the systems therefore are active during the entire sea level cycle thus sediment supply is not a simple function of eustacy this contrasts with the simplified sequence model developed on passive margins where canyons turn off as sea level rises

climatic and morphologic relationships of rivers implications of sea level fluctuations on river loads the characteristics of 279 rivers that discharge into the world oceans are analyzed in terms of their basin hydrology river discharge morphometry basin slope and area river length extension of the continental shelf seaward of the river mouth and climate precipitation statistically reliable relationships are found between discharge and basin area and between sediment load and a combined function of basin area and slope these functions are used to demonstrate how river hydrologic features would be strongly influenced by sea level fluctuations particularly under the influence of continental shelf emergence a fall in sea level toward a glacioeustatic lowstand would induce the merging of rivers on the subaerial continental shelf thereby allowing giant rivers to form for example rivers of western europe would reorganize themselves into two or three very large rivers sediment concentration carried by these mega rivers would decrease and thus the number of hyperpycnal plumes generated at river

effects of intensification of the indian summer monsoon on northern andaman sea sediments during the past 700 years recent studies have revealed an intensification of the indian summer monsoon ism over the past 700 years but its influence on the sediments in the northern andaman sea is unclear to examine this influence we used radiocarbon dated sediment core stmy6 acquired 100 km offshore in the northern andaman sea from the ayeyarwady river mouth and obtained a 700 year long record of the grain size distribution and geochemistry of the sedimentary sequence the ism influences precipitation surrounding the ayeyarwady river and thus the river water and sediment discharges to the northern andaman sea near the river mouth in the ayeyarwady river and the weathering intensity in the river catchment based on the system we propose that higher sedimentation rates and larger modal grain size the most abundant size in the grain size distribution of sediments and lower carbonate concentrations after about ad 1600 can be attributed to higher ism intensity profiles of total organic carbon toc content and carbon nitrogen c n ratios however did not show any trends after about ad 1600 which suggests that the ism has had little influence on these proxies at this site

numerical modeling of falling stage topset aggradation implications for distinguishing between forced and unforced regressions in the geological record abstract distinguishing between forced and unforced regressive strata is important for identification of systems tracts prediction of sediment bypass and reconstruction of relative sea level histories conventional sequence stratigraphic models distinguish between forced and unforced regressive strata through the presence of aggradational topset no aggradation during forced regression and style of shoreline trajectory descending in forced regressive strata and flat to rising in unforced regressive strata however because present models contain implicit assumptions about sediment supply and the response of coastal plain and fluvial deposystems to falling and rising relative sea level it is probable that these two scenarios are an oversimplification of a more complex reality this work investigates how topset aggradation might develop during relative sea level fall using 1264 runs from a simple diffusional stratigraphic forward model topset aggradation is characterized for each model run by a topset foreset volume ratio t f ratio when topset strata are present the t f ratio is 0 when no topset strata are present the t f ratio is zero multiple two dimensional model runs 0 4 or 2 my duration and constant sediment supply and discharge rates representative of medium size river systems suggest that sediment transport rate may be a key control on topset aggradation modeling a range of sediment transport rates for amplitudes of relative sea level fall from 0 to 100 m shows that with relatively high rates of sediment transport multiple model runs create strata with t f ratios up to 0 08 conversely relatively low sediment transport rates lead to higher volumes of topset deposition reflected by t f ratios ranging from 0 10 to 0 37 however critically high sediment transport with no relative sea level fall leads to topset aggradation very similar to that resulting from low sediment transport and high amplitude relative sea level fall this is an example of non uniqueness showing that topset aggradation can occur during falling relative sea level as well as steady to rising relative sea level depending on rates of sediment transport this result has been tested and verified with different rates of relative sea level fall and with additional three dimensional model runs including runs in a different model the results suggest that backstripped shoreline trajectories are likely to be a more reliable method of distinguishing forced from unforced regression and that interpretation and prediction of sediment bypass history may be more complicated than current sequence stratigraphic models suggest

effects of climate sea level and tectonics unraveled for last deglaciation turbidite records of the arabian sea turbidite sedimentation in a slope basin of the active margin of southwestern pakistan makran and on the abyssal plain of the arabian sea indus fan off the passive margin of southeastern pakistan sindh was most frequent during the last sea level lowstand in both regions turbidite sedimentation rates decreased during early sea level rise it stopped on the midfan of the indus system after 11500 14c yr b p while turbidite sedimentation in the slope basin of the makran continued although at slower rates after ca 7000 14c yr b p sedimentation rates in the makran decreased further as a consequence of increasing continental aridity but turbidite sedimentation did not stop the climate signal is identified in the hemipelagic intervals by conspicuous trends in grain size and chemical composition the continued sedimentation on the makran can be attributed to the narrow shelf width which is a characteristic of active plate margins

inferring autogenically induced depositional discontinuities from observations on experimental deltaic shoreline trajectories palaeo shoreline is a commonly used proxy for palaeo sea level but only if deposition is continuous and constant will shoreline trajectory t l completely capture sea level time series e t artificial deltas were generated in the eurotank flume facility under stepwise tectonic subsidence periodic sea level fluctuation and two periodic water discharge scenarios one in phase and the other out of phase with sea level independent input variables tectonic subsidence y sea level e and water discharge q controlling sediment supply s were varied and dependent output variable shoreline trajectory twas monitored these experiments confirm that deposition is discontinuous even for continuous sediment supply and this hinders the inference of sea level curve from shoreline trajectory these results justify the here developed methodology for converting shoreline trajectory from the space domain to the time domain thereby improving the accuracy of the inferred sea level curve 2015 john wiley sons ltd

filter or conveyor establishing relationships between clinoform rollover trajectory sedimentary process regime and grain character within intrashelf clinothems offshore new jersey u s a abstract clinoform geometries and trajectories are widely used to predict the spatial and temporal evolution of sand distribution but most analytical approaches underplay the significance of topset and shelf process regime in determining how and when sediment is conveyed downdip or stored on the continental shelf we present an integrated study of clinoform rollover trajectory and detailed grain character analysis to assess the role of topset process regime in determining sand distribution and sediment character across clinothems this study targets the topset foreset and bottomset deposits of four successive miocene intrashelf clinothem sequences which represent deposition under either river dominated or wave dominated conditions seismic reflection data was combined with core analysis and grain character data derived from 664 samples collected from three cored research boreholes in river dominated clinothems the transfer of coarse grained sediment occurs under both rising and flat to falling clinoform rollover trajectories suggesting that process regime is more important in determining sediment delivery than clinoform trajectory river dominated systems are effective conveyors of sediment into deeper water wave dominated clinothems deposited exclusively under rising clinoform rollover trajectories largely retain sand within topset and foreset deposits wave dominated systems are effective sediment filters notably deposition under either river or wave dominated topset process regimes results in quantifiable differences in grain character attributes along clinoform profiles sediments in river dominated systems are coarser less well rounded and more poorly sorted and show greater intersequence and intrasequence variability than those in wave dominated systems prediction of sediment character is more challenging in river dominated systems this study highlights the need for caution when attempting to predict downdip sand distribution from clinoform trajectory alone and provides a novel perspective into downdip grain character profiles under end member topset process regime conditions the results of this study can be used to better constrain sediment grain size and grain shape distributions in process based forward models and have widespread applications in prediction of reservoir quality in both frontier and mature hydrocarbon basins

shelf edge delta regime as a predictor of deep water deposition abstract shelf edge delta depositional style and particularly the presence of river dominated shelf edge deltas is a reliable indicator of deep water sand delivery as documented by a dataset of some 29 shelf margin clinoforms shelf edge delta regime defined as the sum of the effects of fluvial tidal wave and other oceanographic currents impacting deltas as they arrive at the shelf edge is a key predictor for likelihood of sand transport off the shelf edge to deep water conventional sequence stratigraphic concepts assume that delivery of sand to the deep water occurs primarily during falling and lowstand of relative sea level and that basinward transport is associated with shelf edge incision and sediment bypass recent analysis of outcrop and subsurface datasets has shown that sediment can also be transported to the deep water during rising and highstand of sea level provided sediment flux is high in addition some examples with documented shelf edge entrenchment associated with sea level fall did not deliver significant sand volumes to the deep water in contrast to the emphasis given to sea level and supply the role of the shelf edge delta itself and especially its process regime has received relatively little attention the data suggest that the behavior and process regime of the delta at the shelf edge is critical except where shelf width is minimal

paleocene wilcox cross shelf channel belt history and shelf margin growth key to gulf of mexico sediment delivery abstract shelf margins prograde and aggrade by the incremental addition of deltaic sediments supplied from river channel belts and by stored shoreline sediment this paper documents the shelf edge trajectory and coeval channel belts for a segment of paleocene lower wilcox group in the northern gulf of mexico based on 400 wireline logs and 300 m of whole cores by quantitatively analyzing these data and comparing them with global databases we demonstrate how varying sediment supply impacted the wilcox shelf margin growth and deep water sediment dispersal under greenhouse eustatic conditions the coastal plain to marine topset and uppermost continental slope succession of the lower wilcox shelf margin sediment prism is divided into eighteen high frequency 300 ky duration stratigraphic sequences and further grouped into 5 sequence sets labeled as a e from bottom to top sequence set a is dominantly muddy slope deposits the shelf edge of sequence sets b and c prograded rapidly 10 km ma and aggraded modestly 80 m ma characterizes sequence sets d and e which is associated with smaller 9 10 m thick on average and isolated channel belts this stratigraphic trend is likely due to an upward decreasing sediment supply indicated by the shelf edge progradation rate and channel size as well as an upward increasing shelf accommodation indicated by the shelf edge aggradation rate the rapid shelf edge progradation and large rivers in sequence sets b and c confirm earlier suggestions that it was the early phase of lower wilcox dispersal that brought the largest deep water sediment volumes into the gulf of mexico key factors in this lower wilcox stratigraphic trend are likely to have been a very high initial sediment flux to the gulf because of the high initial release of sediment from laramide catchments to the north and northwest possibly aided by modest eustatic sea level fall on the texas shelf which is suggested by the early flat shelf edge trajectory high amalgamation of channel belts and the low overall aggradation rate of the sequence sets b and c

a gold and silver bearing subvolcanic centre in the scottish caledonides near lagalochan argyllshire field investigation petrographic studies and lithogeochemical sampling have defined an area of hydrothermal alteration and mineralization associated with a subvolcanic centre of late caledonian age at lagalochan near kilmelford argyllshire scotland the igneous rocks of an area of 2 5 km 2 comprise a large body of porphyrite flow banded dacitic rocks pyroclastic rocks and several bodies of hydrothermal breccia the close relationship between pyroclastic masses dacites and discordant breccia bodies within and peripheral to the porphyrite is indicative of a subvolcanic level of emplacement near a volcanic vent this subvolcanic zone evidently channelled mineralizing fluids leading to widespread alteration of the rocks and introduction of anomalously high concentrations of silver copper molybdenum zinc lead arsenic and gold

transgressive depositional systems of the mississippi delta plain a model for barrier shoreline and shelf sand development abstract depositional sequences generated in the mississippi river delta plain consist of a regressive and a transgressive component the transgressive component has been considerably less studied but accounts for the majority of the surface area on the lower mississippi river delta plain and up to 50 percent of the total sequence thickness in shallow water deltas the development and preservation of transgressive depositional systems in abandoned delta complexes follows the process of transgressive submergence in which the horizontal component of reworking occurs during shoreface retreat combined with a vertical component of submergence acting to preserve the sequence the evolution of transgressive depositional systems in each of the abandoned holocene mississippi river delta complex s can be summarized in a three stage model beginning with stage 1 an erosional headland and flanking barriers in this stage regressive sand deposits contained within abandoned deltaic headlands are reworked by the eroding shoreface and dispersed longshore into contiguous flanking barriers enclosing restricted interdistributary bays submergence of the delta plain during relative sea level rise generates an intradeltaic lagoon separating the former stage 1 sand body from the shoreline forming stage 2 a transgressive barrier island arc the landward migrating barrier island arc is unable to keep pace with relative sea level rise and the retreating mainland shoreline resulting in submergence and the formation of stage 3 an inner shelf shoal following submergence the former barrier island arc sand body continues to be reworked into a marine sand body on the inner continental shelf during stage 3 this sequence of coastal evolution provides direct evidence of barrier island formation with each stage producing a distinctive stratigraphic signature the current sea level rise models of shoreface retreat and in place drowning developed for the u s atlantic continental shelf do not adequately explain either the morphology or the stratigraphy of transgressive mississippi river delta sand bodies current models of mississippi deltaic stratigraphy emphasize the deep water artificially maintained balize delta which differs considerably from the shallow water shelf phase delta complexes that are the primary depositional constituents of he holocene mississippi river delta plain