acoustic facies on the inner kara sea shelf implications for late weichselian to holocene sediment dynamics abstract we studied the impact of the last glacial late weichselian sea level cycle on sediment architecture in the inner kara sea using high resolution acoustic sub bottom profiling the acoustic lines were ground truthed with dated sediment cores furthermore we refined the location of the eastern lgm ice margin by new sub bottom profiles new model results of post last glacial maximum lgm isostatic rebound for this area allow a well constrained interpretation of acoustic units in terms of sequence stratigraphy the lowstand or regressive system tract sediments are absent but are represented by an unconformity atop of pleistocene sediments on the shelf and by a major incised dendritic paleo river network the subsequent transgressive and highstand system tracts are best preserved in the incised channels and the recent estuaries while only minor sediment accumulation on the adjacent shelf areas is documented the kara sea can be subdivided into three areas estuaries a the shelf b and c deeper lying areas that accumulated a total of 114 1010 t of holocene sediments

the impact of hurricane diana on the north carolina continental shelf abstract intense storms including hurricanes are believed to have an important impact upon the biota and sediment cover on the continental shelf hurricane diana crossed onslow bay north carolina during september 1984 and provided an opportunity to examine its effect on the sea floor an area in the bay transited by the hurricane had been surveyed previously by side scan sonar 3 5 khz echosounding and underwater television we re surveyed the area in november 1984 with the same techniques and collected box cores for sedimentary structure analysis the post hurricane survey yielded no unequivocal evidence of hurricane impact on the sea floor and surprisingly showed an abundance of seemingly delicate benthic organisms thriving on the impacted area sedimentary structures in the box cores included rip up clasts and cross laminations that are indicative of a dynamic sedimentary environment but they could have formed during non hurricane storm conditions the lack of a dramatic signature on the sea floor from hurricane diana is attributed to the low sediment influx and frequent occurrence of intense storms on the north carolina shelf these factors result in an armored depositional environment that shows little response to the passage of each successive storm

mega meander paleochannels of the southeastern atlantic coastal plain usa abstract paleodischarge estimates based on the slope area method and channel boundaries determined from stratigraphic cross sections indicate that large terminal pleistocene meandering paleochannels mega meanders in river valleys of the southeastern atlantic coastal plain of the united states represent bankfull flows that were at least double the magnitude of those on modern rivers correlation of radiocarbon and luminescence dated paleomeanders with previously reported pollen and eolian sedimentary records suggests that greater discharge was driven by seasonally wetter conditions resulting from dynamic changes to regional precipitation and runoff that occurred in association with global warming at the end of the pleistocene while reflecting larger channel forming flows the exceptionally large widths and radii of curvature of mega meanders were nonetheless maintained by a relatively modest discharge magnitude that was between two and four times larger than modern bankfull flow and within the size range of the present two to five year flood despite their large planform the paleochannels conveyed relatively modest bankfull discharges because a wide shallow shape limited their cross sectional area and hydraulic radius within the late quaternary evolution of fluvial systems in the region scrolled mega meanders constitute a transitional meandering planform that remained influenced by large volumes of sandy bedload following the sand bed braided channels of the late wisconsin interval circa 30 17 ka in addition to greater discharge the large planimetric dimensions of paleochannels reflect a lack of cohesive vertical accretion facies on paleomeander floodplains a sediment regime that transported large quantities of bedload sand and the influence of these factors on channel boundary composition bank stability and channel shape findings underscore the importance of reconstructing channel cross sectional dimensions and slope when estimating discharge for infilled paleomeanders this approach reduces uncertainties surrounding channel cross sectional area gradient and boundary composition inherent to studies lacking subsurface data that rely upon meander geometry to retrodict discharge

a salient region detection and pattern matching based algorithm for center detection of a partially covered tropical cyclone in a sar image spaceborne microwave synthetic aperture radar sar with its high spatial resolution large area coverage day night imaging capability and penetrating cloud capability has been used as an important tool for tropical cyclone monitoring the accuracy of locating tropical cyclone centers has a large impact on the accuracy of tropical cyclone track prediction usually the center of a tropical cyclone can be accurately located if the tropical cyclone eye is fully covered by a sar image in some cases due to the limited coverage of the sar only a part of a tropical cyclone can be imaged without the eye from a sar image processing point of view these facts make the automatic center location of tropical cyclones a challenging work this paper addresses the problem by proposing a semiautomatic center location method based on salient region detection and pattern matching a salient region detection algorithm is proposed in which the salient region map contains mainly the rain bands of a tropical cyclone in a sar image the pattern matching problem is transformed into an optimization problem solved by using the particle swarm optimization algorithm to search the best estimated center of a tropical cyclone to estimate the accuracy of the located center we compare the results with the noaa national hurricane center s best track data experiments demonstrate that the proposed method achieves good accuracy for locating the centers of tropical cyclones from sar images that do not contain a distinguishable eye signature

late neogene and quaternary evolution of the northern albemarle embayment mid atlantic continental margin usa seismic surveys in the eastern albemarle sound adjacent tributaries and the inner continental shelf define the regional geologic framework and provide insight into the sedimentary evolution of the northern north carolina coastal system lithoand chronostratigraphic data are derived from eight drill sites on the outer banks barrier islands and the mobil 1 well in eastern albemarle sound within the study area parallel bedded gently dipping miocene beds occur at 95 to n160 m below sea level m bsl and are overlain by a southward thickening pliocene unit characterized by steeply inclined southward prograding beds the lower pliocene unit consists of three seismic sequences the 55 60 m thick quaternary section unconformably overlies the pliocene unit and consists of 18 seismic sequences exhibiting numerous incised channel fill facies shallow stratigraphy b40 m bsl is dominated by complex fill patterns within the incised paleo roanoke river valley radiocarbon and amino acid racemization aar ages indicate that the valley fill is latest pleistocene to holocene in age at least six distinct valley fill units are identified in the seismic data cores in the valley fill contain a 3 6 m thick basal fluvial channel deposit that is overlain by a 15 m thick unit of interlaminated muds and sands of brackish water origin that exhibit increasing marine influence upwards organic materials within the interlaminated deposits have ages of 13 11 cal ka the interlaminated deposits within the valley are overlain by several units that comprise shallow marine sediments bay mouth and shoreface environments that consist of silty fine to medium grained sands containing open neritic foraminifera suggesting that this area lacked a fronting barrier island system and was an open embayment from 10 ka to 4 5 ka seismic data show that initial infilling of the paleo roanoke river valley occurred from the north and west during the late pleistocene and early holocene later infilling

late quaternary development of the croatan beach ridge complex bogue sound bogue banks nc usa and implications for coastal evolution abstract foraminiferal sedimentological geophysical and geochronologic data were utilized to elucidate the late quaternary geologic development of the croatan beach ridge complex cbrc bogue sound and bogue banks north carolina usa the cbrc is a relict beach ridge feature located on the mainland it is separated from the modern barrier island bogue banks by bogue sound seventeen cores along shore normal and shore parallel transects provided material for sedimentologic and foraminiferal analysis and resulted in the recognition of seven depositional facies representing a variety of coastal depositional environments chronologic and depositional facies data suggest the cbrc was initiated during mis 5a and rapid southward progradation produced a cape structure eolian reactivation of the upper sand of the cbrc occurred during the last glacial maximum 18 ka the age of flood tide delta deposits in bogue sound suggests that the holocene barrier island bogue banks had formed by 6 ka shoreface ravinement resulted in a shoreface landward of the present shoreline by 3 5 ka seaward and westward spit progradation of bogue banks began 1 7 ka and continued to 1 3 ka normal marine salinity conditions were present in bogue sound 1 1 ka suggesting removal of at least the narrowest parts of the barrier island coeval with a previously documented segmentation of the southern outer banks barrier islands previous work has linked this segmentation to climate warming and increased tropical storm activity during the medieval climate anomaly this study illustrates the complex response of this coastal system to pleistocene and holocene sea level and climate change over two major sea level cycles in particular the regional geomorphology during mis5a and the holocene sea level highstand differ significantly and this in large part was controlled by the antecedent geologic framework resulted in the contrasting more localized coastal geomorphic response

the barrier island system abstract barrier islands are part of a major coastal system composed of six interactive sedimentary environments the six environments are also elements needed to impose the designation barrier island on littoral sand bodies the elements are 1 mainland 2 backbarrier lagoon 3 inlet and inlet deltas 4 barrier island 5 barrier platform and 6 shoreface the morphodynamic and sedimentary evolution of each element affects adjacent environments as well as the entire system the interactive elements are defined and described by their morphologic sedimentologic and stratigraphic relationships to the barrier island and the barrier island system the stratigraphic relationships of the various elements of the system may be a valuable tool for paleogeographic reconstruction and sand body mapping

migration of the pee dee river system inferred from ancestral paleochannels underlying the south carolina grand strand and long bay inner shelf several generations of the ancestral pee dee river system have been mapped beneath the south carolina grand strand coastline and adjacent long bay inner shelf deep boreholes onshore and high resolution seismic reflection data offshore allow for reconstruction of these paleochannels which formed during glacial lowstands when the pee dee river system incised subaerially exposed coastal plain and continental shelf strata paleochannel groups representing different generations of the system decrease in age to the southwest where the modern pee dee river merges with several coastal plain tributaries at winyah bay the southern terminus of long bay positions of the successive generational groups record a regional southwestward migration of the river system that may have initiated during the late pliocene the migration was primarily driven by barrier island deposition resulting from the interaction of fluvial and shoreline processes during eustatic highstands structurally driven subsurface paleotopography associated with the mid carolina platform high has also indirectly assisted in forcing this migration these results provide a better understanding of the evolution of the region and help explain the lack of mobile sediment on the long bay inner shelf migration of the river system caused a profound change in sediment supply during the late pleistocene the abundant fluvial source that once fed sand rich barrier islands was cut off and replaced with a limited source supplied by erosion and reworking of former coastal deposits exposed at the shore and on the inner shelf

seismic stratigraphy and coastal drainage patterns in the quaternary section of the southern delmarva peninsula virginia usa abstract seismic stratigraphic analysis of the coastal zone and inner shelf of virginia s southern delmarva peninsula has revealed three geochronologically significant surfaces of post tertiary age that impose a relative chronostratigraphic framework on quaternary marine transgressive and regressive events characteristics of these surfaces indicate that two are sequence boundaries and one is a ravinement surface lying at depths of 18 70 m msl datum the lpb surface a late pleistocene basal unconformity represents the sequence boundary separating the tertiary chesapeake group from the overlying late pleistocene nassawadox formation high relief approximately 50 m on the lpb surface is associated with large fluvial channels higher in the stratigraphic section the lpr surface is found at depths of 6 28 m and corresponds to a late pleistocene transgressive or ravinement surface the surface dips southeastward with a regional dip of 0 04 and has local relief of less than 2 m the lpr surface may represent a ravinement which extended to the west side of the chesapeake bay prior to the development of the nassawadox barrier spit however the lpr surface may steepen between the axis of the southern delmarva peninsula and the holocene lagoon to form a shoreface attached to one of several known late pleistocene shorelines lying at depths of 0 20 m the hb surface is a basal unconformity that marks the holocene sequence boundary it deepens seaward with maximum local relief of about 15 m and has a topographic expression very similar to the present day lagoonal drainage pattern maximum thicknesses of holocene and pleistocene sediments 12 and 70 m respectively are found above channels on the hb and lpb surfaces the pleistocene channels are large and limited in number and represent high order channels of a drainage system that drained the piedmont and coastal plain the greater density of low order stream channels on the hb surface suggests a relationship to much smaller drainage basins that were confined to the seaward part of the coastal plain east of the delmarva peninsula these late wisconsinan smaller hb channels do not re occupy the former drain paths of the much larger high order lpb channels

transgressive systems tract development and incised valley fills within a quaternary estuary shelf system virginia inner shelf usa abstract high frequency quaternary glacioeustasy resulted in the incision of six moderate to high relief fluvial erosion surfaces beneath the virginia inner shelf and coastal zone along the updip edges of the atlantic continental margin fluvial valleys up to 5 km wide with up to 37 m of relief and thalweg depths of up to 72 m below modern mean sea level cut through underlying pleistocene and mio pliocene strata in response to drops in baselevel on the order of 100 m fluvially incised valleys were significantly modified during subsequent marine transgressions as fluvial drainage basins evolved into estuarine embayments ancestral generations of the chesapeake bay complex incised valley fill successions are bounded by or contain up to four stacked erosional surfaces basal fluvial erosion surface bay ravinement tidal ravinement and ebb flood channel base diastem in vertical succession these surfaces combined with the transgressive oceanic ravinement that generally caps incised valley fills control the lateral and vertical development of intervening seismic facies depositional systems transgressive stratigraphy characterizes the quaternary section beneath the virginia inner shelf where six depositional sequences sequences i vi are identified depositional sequences consist primarily of estuarine depositional systems subjacent to the transgressive oceanic ravinement and shoreface shelf depositional systems highstand systems tract coastal systems are thinly developed the quaternary section can be broadly subdivided into two parts the upper part contains sequences consisting predominantly of inner shelf facies whereas sequences in the lower part of the section consist predominantly of estuarine facies three styles of sequence preservation are identified style 1 represented by sequences vi and v is characterized by large estuarine systems ancestral generations of the chesapeake bay that are up to 40 m thick have hemicylindrical wedge geometries and occur within large coast oblique trending depressions paleo estuaries style 1 is dominated by fluvial through estuary mouth depositional systems seismic facies 1 4 style 2 sequence preservation represented by sequences iii and ii is dominantly an inner shelf and shoreface succession with a seaward thickening tabular wedge geometry that does not exceed 15 m in thickness these shoreface and inner shelf depositional systems of the upper transgressive systems tract seismic facies 9 and highstand systems tract seismic facies 7 and 11 are not associated with paleo estuaries style 3 sequence preservation is represented by sequence i the holocene sequence it consists of lower transgressive systems tract fluvial estuarine lagoonal and tidal inlet fill deposits seismic facies 1 6 and 8 overlain by upper transgressive systems tract shelf and shoreface sands seismic facies 9 style 3 has a crenulated wedge geometry and is thickest beneath and seaward of the modern chesapeake bay mouth it thins northward and landward onto late pleistocene interfluvial highs on the basinward side of the southern delmarva peninsula

late quaternary climates and river channels of the atlantic coastal plain southeastern usa abstract late quaternary river patterns and sedimentation styles reflect past climate changes in atlantic drainages of eastern georgia and the carolinas past climate episodes for the region are summarized from pollen and eolian sedimentary records that exhibit correlation to major changes in river channel patterns records of past river responses are derived from luminescence and radiocarbon dated landforms and strata slow tectonic uplift does not explain temporal changes in channel patterns drainage networks have not received meltwater from continental or mountain glaciers eustatic influence would have been most pronounced on the now submerged continental shelf prior to 6 ka and currently manifests only within 60 80 km of the present highstand shoreline human impact overshadows climatic changes during historic time but was negligible during prehistoric time the late quaternary fluvial system primarily responded to climatic fluctuations that drove changes in vegetation precipitation and runoff patterns prehistoric meandering paleochannels of the holocene stand as important references to guide natural channel rehabilitation efforts during the coldest climate phases of the late wisconsin stage ca 30 16 ka when forest vegetation was sparse and interspersed with grasses and herbs many rivers and streams were braided with eolian dunes on the floodplains the terminal wisconsin stage ca 16 11 ka exhibited rapid warming and forest expansion characterized by pronounced change from braided to meandering patterns with intermediate forms of sandy scroll bar patterns the younger dryas cold excursion is not readily apparent in the regional fluvial record unusually large meandering channels of the terminal wisconsin stage continue into the first half of the holocene and indicate significantly larger bankfull flood discharges during those times than during the last half of the holocene bankfull channels during the last half of the holocene retained meandering patterns but decreased to modern like dimensions suggesting more modern like flood regimes no clear fluvial response occurs to the presumed middle holocene climatic optimum hypsithermal the medieval warm period and little ice age or to recent instrumentally observed fluctuations in climate but little research has been done in these realms

evolution and stratigraphy of a regressive barrier backbarrier complex kiawah island south carolina analysis of 75 vibracores from the backbarrier region of kiawah island south carolina reveals a complex association of three distinct stratigraphic sequences beach ridge progradation and orientation controlled backbarrier development during the evolution of kiawah island and resulted in deposition of 1 a mud rich central backbarrier sequence consisting of low marsh overlying fine grained tidal flat lagoonal mud 2 a sandy beach ridge swale sequence consisting of high and low marsh overlying tidal creek channel and point bar sand and foreshore shoreface and 3 a regressive sequence of sandy mixed and muddy tidal flats capped by salt marsh that occurs on the updrift end of the island central backbarrier deposits formed as a result of the development of the initial beach ridge on kiawah island formation of this beach ridge created a backbarrier lagoon in which fine grained estuarine and tidal flat mud accumulated washovers oyster mounds and tidal creek deposits form isolated sand and or shell rich lenses in the lagoon spartina alterniflora low marsh prograded into the lagoon as the tidal flats aggraded barrier progradation and sediment bar bypassing at stono inlet created digitate beach ridges on the northeast end of kiawah island within the beach ridge swales tidal flats were disconformably deposited on shoreface and foreshore sand of the older beach ridges tidal creek drainage systems evolved to drain the swales these rapidly migrating creeks reworked the tidal flat foreshore and shoreface sediments while redepositing a fining upward sequence of channel lag and point bar deposits which served as a substrate for salt marsh colonization this resultant regressive sedimentary package marks the culmination of barrier island development and estuary infilling given enough time and sedimentation the backbarrier sequence will ultimately prograde over the barrier island reworking dune beach and foreshore sediments to form the upper sand rich bounding surface of the barrier lithosome preservation of the regressive sequence is dependent upon sediment supply and the relative rate of sea level rise but the reworking of barrier islands by tidal inlets and migrating tidal creeks greatly alter and complicate the stratigraphic sequence

geologic control in the nearshore shore oblique sandbars and shoreline erosional hotspots mid atlantic bight usa abstract beach and nearshore morphology defined primarily by slope and sandbar development is very dynamic and is largely controlled by waves currents and regional sediment characteristics results presented here challenge this long established concept and suggest that underlying framework geology may also exert a first order control on nearshore morphology by influencing the stability and or persistent re establishment of large scale sandbar morphology and position as well as surface sediment characteristics repeated sub bottom chirp and swath bathymetry surveys of the nearshore 2 10 m depths covering over 56 km of the north carolina outer banks and southeastern virginia indicate the following 1 development of shore oblique sandbars adjacent to large gravel outcrops that are surface exposures of the underlying geologic strata 2 identical re development or sustained maintenance of large scale sandbar morphology and position before and after very energetic conditions 3 vertical and horizontal heterogeneity of lithology and grain size and a minimum volume of sand ranging from 0 to 1 5 m thick and 4 close spatial alignment between the location of outcrops shore oblique bars and shoreline erosional hotspots a hypothesis is proposed from these findings that links framework geology to bar morphodynamics and sorted bedforms and ultimately erosional hotspots sediment transport and shoreline evolution models based solely on waves and currents and an assumption of unlimited and uniform sediment may be inadequate in similar heterogeneous sand limited regions

calculating shoreline erosion potential using nearshore stratigraphy and sediment volume outer banks north carolina 1 despite the acknowledged influence of coastal geological framework on the behavior of beaches and barrier islands and a wealth of geological and bathymetric observations from the inner shelf quantitatively connecting those observations to shoreline behavior has been difficult nearshore geologic and morphologic variability described by recent research is not well represented by conventional geologic parameters such as mean grain size and shoreface slope used in most shoreline change models we propose that total nearshore sediment volume as calculated to a continuous seismic reflection surface provides a flexible and robust metric for use in the prediction of shoreline change this method of determining the volume of sediment in the nearshore accounts for three dimensional sandbar morphologies and heterogeneous seafloor sediments the decadal scale shoreline change rate for northeastern north carolina is significantly correlated to the volume of sediment in the nearshore when a geologically defined base is used in volume determinations suggesting that the shallow stratigraphic framework of transgressive coasts is an important influence on decadal shoreline behavior nearshore sediment volume was overestimated when an arbitrary depth constant baseline was used and was not correlated to decadal shoreline change this implies that a volume metric which accounts for both framework geology and variable seafloor morphology better represents the geologic character of the shoreface and may help to improve existing models of shoreline change an empirical model of regional shoreline erosion potential demonstrates the importance of incorporating nearshore sediment volume shallow framework geology and surface morphology when predicting seasonal to decadal shoreline evolution

sand bodies and incised valleys within the late quaternary sanaga nyong delta complex on the middle continental shelf of cameroon abstract seismic data and sediment cores collected offshore from the sanaga river and nyong river mouths were used to analyse a loose mantle of yellow to reddish sandy gravel with a range of fluvial and deltaic characteristics cropping out in the middle part 25 65 m water depth of the continental shelf of cameroon contrary to most of the atlantic shelves where the lowstand systems tract was destroyed by erosion we found 80 120 ms 60 90 m of sediment mainly in the middle part of the shelf which correspond credibly to mis 2 4 fluvial paleodrainage systems are preserved beneath the shelf and individual filled channels with planar infillings were mapped that cross the shelf along two surfaces of erosion these incisions suggested westerly and northwesterly drainage shifts during presumed lowered base level the presence of closely spaced channel fills suggests repeated avulsion of a single stream during a long lasting sub aerial erosion period the seismic facies of these pleistocene deposits distinguish themselves clearly from well stratified older strata showing deformation pliocene or intense folding miocene the orientation of the paleovalleys appears strongly controlled by the n60 e trending cross faults within mesozoic cenozoic strata on the basis of approximately 80 000 years of accumulation an estimate of the yearly mass of sediment transported was calculated for the sanaga and nyong rivers and compared to the present sediment load of the two rivers it is estimated that as much as 50 of the sediment discharge must have bypassed the upper slope we show that deposition took place near the terrestrial break in slope even though the coastline had already regressed across the shelf in contrast the gradient of the lower course of the nearby niger river remains below 0 05 through several hundreds of kilometres and no lowstand deposits have been preserved we conclude that the break in slope even terrestrial is the determining factor regarding preservation of shelf deposits during relative sea level rise

influence of inherited geologic framework on barrier shoreface morphology and dynamics abstract passive margin coastlines with limited sand supplies such as much of the u s atlantic margin are significantly influenced by the geologic framework of older stratigraphic units that occur beneath and seaward of the shoreface many u s east coast barrier islands are perched barriers in which the underlying pre modern sediments determine the morphology of the shoreface and strongly influence modern beach dynamics and composition perched barriers consist of varible layers of beach sand on top of older eroding stratigraphic units with highly variable compositions and geometries along many parts of the coastal system stratigraphically controlled bathymetric features on the inner shelf modify waves and currents and thereby effect patterns of sediment erosion transport and deposition on the adjacent shoreface it is essential to understand this geologic framework before attempting to model the large scale behavior of these types of coastal systems in north carolina most shoreline features are controlled by the pre holocene stratigraphic framework of the shoreface the beaches are perched on top of pre existing pleistocene tertiary and cretaceous sediments the surficial geology of the coastal zone is subdivided into two distinct provinces resulting in different stratigraphic controls of the shoreface north of cape lookout the geological framework consists of a quaternary sequence that fills a regional depositional basin called the albemarle embayment the coastal zone south of cape lookout is dominated by tertiary and cretaceous units that crop out across the coastal plain and continental shelf with very thin quaternary units only locally preserved superimposed upon this regional stratigraphy is an ancient drainage system resulting in a series of fluvial valleys filled with younger coastal sediments separated by large interfluve areas of older stratigraphic units this results in a coastal system in which the shoreface is either nonheadland or headland dominated respectively headland dominated shorefaces are further divided into subaerial and submarine categories nonheadland dominated shorefaces are further divided into those influenced primarily by transgressive or regressive processes or channel dominated depositional processes i e inlet migration or stream valley fill examples of each of these six types of shorefaces are presented to demonstrate the control that the geologic framework exhibits on shoreface morphologies and processes

theoretical correlations and lateral discontinuities in the quaternary aminostratigraphic record of the u s atlantic coastal plain abstract aminostratigraphic correlations of emergent quaternary deposits along the u s atlantic coastal plain have employed independent radiometric data regional temperature history models and assumptions regarding the nature of the preserved late quaternary sea level record on this passive margin a substantial aminostratigraphic offset is required if regional aminozones are rigorously constrained by all available th u data new insights regarding the relation of this offset to subsurface stratigraphy in the cape fear region of southeastern north carolina can explain these conflicts as consequences of the highly incomplete post cretaceous depositional record of the region southward projection of theoretical aminostratigraphic correlation trends suggests that stage 5 correlative marine units are rarely preserved on the emergent portion of the coastal plain between cape lookout and central south carolina and that samples of this age would be most frequently found in this region only as fragmentary and or reworked deposits on the inner shelf or in the subsurface of modern barrier islands if this hypothesis is correct then the accuracy of several th u coral dates from the south carolina coastal plain must be questioned along with sea level tectonic and paleoclimatic conclusions derived from these dates

linking framework geology and nearshore morphology correlation of paleo channels with shore oblique sandbars and gravel outcrops abstract this work describes a newly discovered spatial correlation between paleo channels and nearshore morphology along the barrier islands of northeastern north carolina and southeastern virginia u s mid atlantic coast these nearshore morphological features include regions of shore oblique sandbars and coincident gravel outcrops that previously have been linked to erosional hotspots at the shoreline these new findings have direct bearing on both nearshore morphodynamics and shoreline management paleo channels were identified in the chirp seismic record and compared to shore oblique sandbar locations discerned from bathymetric data and corroborated by gravel outcrops depicted in the side scan record both graphical correlation and statistical cross correlation analyses revealed a significant spatial relationship between these features with higher statistical correlation for channels 500 m wide seismic records also indicate that the gravel outcrops seen on the updrift flanks of the shore oblique bars are surface expressions of the underlying geology we hypothesize that these outcrops are composed of relict channel fill sediments that interact with the hydrodynamic regime to produce sorted bedforms the bathymetric anomalies then serve to alter incident wave energy and affect shoreline behavior the spatial and temporal stability of these features over several years and through a variety of wave conditions suggests some degree of underlying geologic control while the mechanisms responsible for this relationship remain speculative these results may bridge the gap between studies focusing on framework geology and its influence on shoreline change and those that investigate bar morphodynamics and the initiation of sorted bedforms

controls on late quaternary incised valley dimension along passive margins evaluated using empirical data incised valleys are canyon like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium gradient profiles in response to sea level fall most of these valleys flood during sea level rise to form estuaries incised valley morphology strongly controls the rate of creation of sediment accommodation valley fill facies architecture and the preservation potential of coastal lithosomes on continental shelves and affects coastal physical processes nonetheless little is known about what dictates incised valley size and shape and whether these metrics can be used to explain principal formation processes the main control on alluvial channel morphology over human time scales is discharge this is based on numerous empirical studies and is well constrained because all variables are easily measured at this short time scale knowledge of long term river evolution over a complete glacio eustatic cycle on the contrary remains largely conceptual experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified in spite of this difficulty existing models of incised valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms highlighting sea level and shelf gradient morphology as the dominant controls on valley incision although valleys are cut by rivers whose channels are a direct reflection of discharge little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls the late quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables including sea level tectonics substrate lithology and drainage network characteristics are accurately constrained here 38 late quaternary valleys along the coast of two different passive continental margins are compared which suggests that valley shape and size are governed primarily by upstream intrinsic controls such as discharge valley width depth and cross sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea level

transition of a regressive to a transgressive barrier island due to back barrier erosion increased storminess and low sediment supply bogue banks north carolina usa abstract although back barrier erosion is a prevalent process of island narrowing it is often overlooked in conceptual models of barrier island evolution in many wave dominated barrier island settings the absence of overwash precludes landward movement of the back barrier shoreline and hence the island as a whole from sustaining its width typically regressive barriers are wide and exhibit high elevations with the most seaward dune ridge possessing the highest elevation this morphology may prevent overwash and inlets from breaching the barrier and therefore the associated sediment from reaching the back barrier shoreline for millennia back barrier shoreline erosion from sea level rise and storms can be permanent in the absence of sediment supply from rivers overwash and inlet processes with continued narrowing and lowering of the island regressive barriers may reach a critical state making overwash and inlet formation imminent and transitioning the island to a transgressive barrier the modern day morphologic variability along the 40 km long island of bogue banks north carolina includes both regressive and transgressive segments making this setting ideal for examining whether the transition between these barrier island types is gradual or threshold driven bogue banks consists of two discrete segments characterized by high elevation beach ridges large island widths and stratigraphy consistent with regressive barrier islands these regressive island segments are separated by a broad narrow section of the island devoid of any washover fans flood tide deltas or other transgressive elements analyses of seismic data from the inner continental shelf reveal paleochannels intersecting the wide sections of the island while the narrow central part of the island occupies an inter fluvial area reworking of fluvial sediment from paleochannels was an important sediment source for the barrier during regression optically stimulated luminescence osl dates from the most landward beach ridges constrained initiation of island regression at 3000 cal yr bp close to when there was a significant decrease in the rate of relative sea level rise from 5 mm yr to 0 8 mm yr transects of cores seismic data ground penetrating radar data and radiocarbon and osl dates show that prior to 1500 cal yr bp the central narrow section of the island was wide and progradational similar to adjacent areas back barrier erosion of the central part of the barrier primarily caused island narrowing as a result of increased storminess which occurred around the medieval climate anomaly 1100 cal yr bp this part of the island was more vulnerable to erosion than adjacent areas due to increased bay ravinement bogue sound is widest there and its lower elevation farther away from paleochannel sediment source relict inlet channels exist along the central portion of the island formed within the last 250 yr and likely closed shortly after formation the presence of historical inlets along the narrow central section of the island indicates bogue banks may be nearing a critical width threshold and will subsequently transition to a transgressive barrier because the change in barrier morphology associated with back barrier erosion occurred over a period of time when the rate of sea level rise was relatively low low sediment supply and increased storm frequency are shown to be the main forcing mechanisms of island narrowing these impacts in addition to a predicted increase in sea level rise rates and human modifications e g maintenance of a high elevation foredune closing of inlets prevention of island overwash and associated sediment delivery to the back barrier shoreline will likely promote rapid transition of regressive barrier islands to those dominated by transgressive processes

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

quaternary depositional patterns and sea level fluctuations northeastern north carolina abstract a detailed record of late quaternary sea level oscillations is preserved within the upper 45 m of deposits along an eight km transect across croatan sound a drowned tributary of the roanoke albemarle drainage system northeastern north carolina drill hole and seismic data reveal nine relatively complete sequences filling an antecedent valley comprised of discontinuous middle and early pleistocene deposits on interfluves lithologically similar marine deposits of different sequences occur stacked in vertical succession and separated by ravinement surfaces within the paleo drainage marine deposits are separated by fluvial and or estuarine sediments deposited during periods of lowered sea level foraminiferal and molluscan fossil assemblages indicate that marine facies were deposited in a shallow marine embayment with open connection to shelf waters each sequence modifies or truncates portions of the preceding sequence or sequences sequence boundaries are the product of a combination of fluvial estuarine and marine erosional processes stratigraphic and age analyses constrain the ages of sequences to late marine isotope stage mis 6 and younger 140 ka to present indicating multiple sea level oscillations during this interval elevations of highstand deposits associated with late mis 5 and mis 3 imply that sea level was either similar to present during those times or that the region may have been influenced by glacio isostatic uplift and subsidence

evolution of the barrier islands of southern long island new york three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the holocene transgression in southern long island new york 1 the holocene transgressive stratigraphic sequence behind the present barriers 2 the stratigraphic patterns of the inner shelf and 3 the morphology of the now buried late pleistocene coastal features the extensive preservation of backbarrier sediments radiocarbon dated between 7000 and 8000 yr bp on the inner shelf of southern long island suggests that the barriers have not retreated by continuous shoreface erosion alone but have also undergone discontinuous retreat by in place drowning of barriers and stepwise retreat of the surf zone such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked based on the presence of submerged barrier sand bodies in seismic records it is inferred that about 9000 years ago when the sea stood about 24 m below the present sea level a chain of barriers developed on the present shelf about 7 km offshore of the present barriers with continued sea level rise the 24 m barrier built upward until the sea reached about 15 m msl just prior to 7000 yr bp the barriers were then submerged by the rapidly rising sea and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline the surf zone overstepped to the landward margin of the old lagoon which had become fixed at the steep seaward face of mid wisconsinan or sangamonian coastal barriers during the past 5000 or 6000 years the shoreface has retreated continuously by about 2 km evidence from southern long island and elsewhere in regions of coastal submergence indicates that rapid sea level rise and low sand supply seem to favour the stepwise retreat of barriers whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat stationary upbuilding or seaward progradation of barriers may occur when supply of sand is great and or submergence is slowed or reversed morphologic highs on the pretransgression surface such as old barrier ridges tend to fix the migrating barrier shoreline during either continuous retreat or stepwise retreat of barriers

quaternary stratigraphy of the charlotte harbor estuarine lagoon system southwest florida implications of the carbonate siliciclastic transition abstract charlotte harbor is a complex lagoon and estuarine system in southwestern peninsular florida that is underlain by tertiary carbonates and quaternary siliciclastic sedimentary sequences high resolution seismic profiling vibracores and sediment samples from modern environments have been used to interpret the quaternary stratigraphy and evolution of this system the underlying tertiary carbonates have undergone extensive dissolution and collapse which has created isolated karst depressions and fracture controlled elongated troughs although late neogene deposition infilled most of the pre quaternary relief the quaternary drainage system was controlled by the poorly integrated vertical drainage of the karstified limestones which is unlike the well integrated paleofluvial drainage systems of the mid atlantic and northern gulf coastal plains despite these differences paleotopography and sediment availability have controlled locations and sedimentary environments as has been noted in other published studies on purely siliciclastic systems the distribution of three interpreted quaternary depositional sequences fluvial to upper estuarine point bar fining upward sequence fus transitional estuarine sequence and tidal channel delta fus and the mapped distribution of an early middle pleistocene seismic unconformity indicate that quaternary sea level fluctuations have repeatedly caused coastal systems to migrate through the area leaving records of at least two pleistocene barrier lagoon systems these systems straddled the infilled karst depressions and were apparently controlled by the availability of erodible sediment that infilled the depressions the modern barrier system is perched upon one of the pleistocene barrier platforms which has been preserved as a result of lithification of carbonate rich inlet tidal delta deposits these platforms should preserve the backbarrier deposits from future shoreface incision but localized channelization will cause extensive reworking because the paleofluvial channels do not extend offshore preservation on the inner shelf 5 7 km offshore is limited to isolated karst depressions where tertiary limestones are exposed

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

imaging the subducting slabs and mantle upwelling under the japan islands summary a high resolution p wave tomography of the crust and mantle down to 700 km depth beneath the japan islands is determined using a large number of high quality arrival time data from local earthquakes and teleseismic events simultaneously the tomography shows that the philippine sea slab is subducting aseismically down to 430 km depth under southwest japan though the seismicity within the slab ends at 180 km depth a low velocity low v zone in the mantle wedge under tohoku and kyushu is found to extend westward from the volcanic front to the backarc under the japan sea and east china sea significant low v anomalies are revealed in the deep portion of the mantle wedge 400 500 km depth above the pacific slab under southwest japan which may reflect hot mantle upwelling associated with fluids from the deep dehydration of the pacific slab low v anomalies appear at 420 700 km depths beneath the pacific slab under eastern japan which may reflect hot mantle upwelling associated with the deep subduction of the pacific slab and its collapsing down to the lower mantle

aminostratigraphic results from cape lookout n c and their relation to the preserved quaternary marine record of se north carolina abstract aminostratigraphic data were obtained for mulinia lateralis samples from closely spaced drillholes on the cape lookout north carolina barrier islands two major aminozones are recognized in the subsurface section based upon d alloisoleucine l isoleucine a i values these major aminozones can each be subdivided into two additional aminozones based upon direct comparisons with mulinia a i data from other north carolina localities correlation of the cape lookout mulinia aminostratigraphy with u series calibrated a i data in n c indicates that the sampled units represent deposition during the middle to late pleistocene the four cape lookout aminozones may be assigned to late and early stage 5 or possibly stages 5 and 7 a portion of the interval during stages 17 19 and at least one interglacial in stages 25 31 of the oxygen isotope record based on correlation to calibrated sites and kinetic model extrapolation the aminostratigraphic data obtained from the cape lookout barrier islands and nearby areas indicate that there are significant differences in the extent of preservation of the pleistocene sedimentary record to the southwest of cape lookout compared with that to the north northeast all four of the recognized cape lookout aminozones are present in the subsurface section to the north northeast of cape lookout in contrast the two late pleistocene aminozones are almost completely absent in the subsurface of the barrier islands and in onslow bay to the southwest of cape lookout these aminostratigraphic interpretations are consistent with the incomplete stratigraphic record recognized by previous investigators for the cape lookout onslow bay area the calibrated kinetic model age estimates for the cape lookout aminostratigraphic data now permit quantification of these stratigraphic gaps the detailed aminostratigraphic results from cape lookout also have significant consequences for regional aminostratigraphic correlations on the atlantic coastal plain and provide valuable information with which to test contrasting models proposed for regional correlation within the context of the preserved stratigraphic record

stratigraphic setting of transgressive barrier island reservoirs with an example from the triassic halfway formation wembley field alberta canada established models for landward barrier island migration focus primarily on the preservation pattern of transgressive facies in the shoreface which are typically thin and buried beneath finer grained marine lower shoreface to offshore sediments in contrast transgressive barrier island sandstones in the triassic halfway formation of wembley field in alberta are preserved interbedded with and overlain by backbarrier and nonmarine sediments these transgressive barrier sandstones formed from coalescing washover fans during shoreface retreat and were subsequently abandoned as the shoreline stabilized and resumed progradation the abandoned transgressive barrier sandstones were subsequently blanketed by backbarrier and nonmarine sediments as the coastline continued to p ograde abandoned transgressive barrier island sandstones in the halfway formation are 2 6 m thick up to 2 km wide and form paleocoastline parallel trends tens of kilometers in length the trends define the paleolandward limit of transgressive events the updip pinch out of these sandstones in backbarrier mudstones forms a stratigraphic trap for hydrocarbons in wembley field top seal is provided by nonmarine mudstones and evaporites which buried the abandoned transgressive barrier island the sandstone has porosities and permeabilities averaging 11 and 63 md respectively by using well logs and cores to correlate individual parasequences in the halfway formation to their updip termination it is possible to define the extent of associated marine flooding events and therefore identify exploration targets for abandoned transgressive barrier island sandstones