optically stimulated luminescence age controls on late pleistocene and holocene coastal lithosomes north carolina usa luminescence ages from a variety of coastal features on the north carolina coastal plain provide age control for shoreline formation and relative sea level position during the late pleistocene a series of paleoshoreline ridges dating to marine isotope stage mis 5a and mis 3 have been defined the kitty hawk beach ridges on the modern outer banks yield ages of 3 to 2 ka oxygen isotope data are used to place these deposits in the context of global climate and sea level change the occurrence of mis 5a and mis 3 shorelines suggests that glacio isostatic adjustment gia of the study area is large ca 22 to 26 m as suggested and modeled by other workers and or mis 3 sea level was briefly higher than suggested by some coral reef studies correcting the shoreline elevations for gia brings their elevation in line with other sea level indicators the age of the kitty hawk beach ridges places the holocene shoreline well west of its present location at ca 3 to 2 ka the age of shoreline progradation is consistent with the ages of other beach ridge complexes in the southeast usa suggesting some regionally contemporaneous forcing mechanism

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

radarfacies and sedimentological analysis study of sedimentary substrate from an archaeological site shell mound southern brazil integrated results of gpr ground penetrating radar and sedimentological analysis are presented for the jabuticabeira ii archaeological site shell mound santa catarina brazil by means of rada

spatial and temporal variability of coastal storms in the north atlantic basin over the past three to four decades there has been a growing awareness of the important controls exerted by large scale meteorological events on coastal systems for example definitive links are being established between short term timescales of 5 10 years beach dynamics and storm frequency this paper assesses temporal variability of coastal storms both tropical and extratropical and the wave climatology in the north atlantic basin nab including the gulf of mexico with both storm types the empirical record shows decadal scale variability but neither demonstrates highly significant trends that can be linked conclusively to natural or anthropogenic factors tropical storm frequencies have declined over the past two or three decades which is perhaps related to recent intense and prolonged el ninos some forecasts predict higher frequencies of tropical storms like that experienced from the 1920s to the 1960s to occur in coming decades results from general circulation models gcms suggest that overall frequencies of tropical storms could decrease slightly but that there is potential for the generation of more intense hurricanes these data have important implications for the short term evolution of coastal systems there is strong suggestion that extratropical systems have declined overall over the past 50 100 years but that there is an increase in frequency of very powerful storms especially at higher latitudes both enso and the north atlantic oscillation nao are shown to have associations with frequencies and tracking of these systems these empirical results are in general agreement with gcm forecasts under global warming scenarios analyses of wave climatology in the nab show that the last two to three decades have been rougher at high latitudes than several decades prior but this more recent sea state is similar to conditions from about 100 years ago the recent roughness at sea seems to be related to high nao index values which are also expected to increase with global warming thus when coupled to an anticipated continued rise in global sea level this trend will likely result in increasing loss of sediment from the beach nearshore system resulting in widespread coastal erosion

optical dating of young coastal dunes on a decadal time scale we explore the use of quartz optically stimulated luminescence osl dating for reconstructing coastal evolution on a time scale of decades to a few hundred years samples are taken from the accretionary south west coast of texel a barrier island just offshore of the northern netherlands the ages of dune ridges are known from historical sources an excellent chronology with a decadal accuracy exists for the past 260 years osl ages of less than 10 years on the youngest samples indicate that the osl signal of the quartz grains is very well zeroed prior to deposition and burial osl ages of five samples from a 250 year old dune ridge are indistinguishable and the osl ages on 17 out of 20 samples are in excellent agreement with the well known independent age controls our results highlight the potential of osl dating for high resolution reconstruction of coastal evolution over the past few centuries

luminescence dating of loess palaeosol sequences and coversands methodological aspects and palaeoclimatic implications abstract of the terrestrial archives loess palaeosol sequences provide a most complete record of climatic change this may be compared with the marine oxygen isotope stratigraphy and may help in the reconstruction of past atmospheric circulation patterns numerical chronometry of loess palaeosol sequences has generally been based on correlation of variations in climatic proxies such as magnetic susceptibility and particle sizes with marine isotopic data such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time this review presents a brief survey of the present status methodology outstanding problems and interpretational aspects of luminescence techniques and discusses the import of luminescence ages on global land sea correlations statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence recent luminescence dating studies on closely spaced samples also lead to a similar inference luminescence ages imply high variability in loess sedimentation rates this conflicts with the assumption made in some current attempts to correlate loess records with marine records of almost constant particle fluxes a review of source proximal coversand deposits of northwest europe is also presented evidence of the onset of coversand deposition at 15 ka with a peak in accretion during the younger dryas and subsequent minor reactivation episodes is discussed

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

numerical dating of a late quaternary spit shoreline complex at the northern end of silver lake playa mojave desert california a comparison of the applicability of radiocarbon luminescence terrestrial cosmogenic nuclide electron spin resonance u series and amino acid racemization methods a late quaternary spit shoreline complex on the northern shore of pleistocene lake mojave of southeastern california usa was studied with the goal of comparing accelerator mass spectrometry ams radiocarbon luminescence electron spin resonance esr terrestrial cosmogenic radionuclide tcn surface exposure amino acid racemization aar and u series dating methods the pattern of ages obtained by the different methods illustrates the complexity of processes acting in the lakeshore environment and highlights the utility of a multi method approach tcn surface exposure ages mostly 20 30 ka record the initial erosion of shoreline benches whereas radiocarbon ages on shells determined in this and previous studies within the spit supported by aar data record its construction at fluctuating lake levels from 16 to 10 ka luminescence ages on spit sediment 6 7 ka and esr ages on spit shells 4 ka are anomalously young relative to radiocarbon ages of shells within the same deposits the significance of the surprisingly young luminescence ages is not clear the younger esr ages could be a consequence of post mortem enrichment of u in the shells high concentrations of detrital thorium in tufa coating spit gravels inhibited the use of single sample u series dating detailed comparisons such as this provide one of the few means of assessing the accuracy of quaternary dating techniques more such comparisons are needed

coastal barriers fresh look at origins nomenclature and classification issues abstract based on numerous publications and field work on the northern gulf of mexico coast u s and other coastal areas the present objective is to meet the need for an improved system of the definition and classification of barriers and their components this topic includes morphological and functional interrelationships between beach ridges barriers and similar landforms the term beach ridge was applied to a plethora of sub and supratidal ridge types in contrast the presently proposed definition restricts the term to relict berm and foredune ridges composed of sand or gravel and stabilized after isolation from shore zone of active processes barriers sustain paralic hydrology sediment biotic and nutrient condition in the coastal realm in combination with adjacent lagoons and river deltas these landforms represent physical barriers that lessen marine and related influences in brackish paralic coastal environments benefiting from historic evolution of concepts and nomenclature the task also involves the correction of misattributions rooted in early publications island spit and mainland barriers thus maintain lower salinities reduce wave erosion protect nutrient rich paralic deposits and mitigate storm induced inundation fetch limited lagoonal barrier islands are considered valid barriers only in lagoons where they face inlet transmitted full marine conditions mainland barriers of several subcategories often are important sediment archives of past sea levels hydroclimate climate and tectonic isostatic changes they consist mostly of ridgeplains at the start firmly attached or later migrated and welded to the mainland shore in addition to local hydrodynamic and topographic influences formation conditions may reflect overall paleogeographic conditions including fluvial impact in progradational regressive island settings barriers consist mainly of strandplains that laterally may alternate with narrow spit like sectors they include only single marine respectively lagoon side shore ridges with secondary dune fields sandwiched between them field observations and drillcore studies of microfossil and sediment based depositional facies suggest that most barrier islands originated by the often underestimated shoal aggradation mode two additional genetic models are recognizable a fourth remains hypothetical remotely sensed images indicate that post hurricane regeneration of the largest deltaic barrier chain in the gulf of mexico stalled in recent years late pleistocene barriers significantly influenced present coastal landforms in two extensive regions dramatic changes in past decades indicate that sea level rise and stormier future hydroclimate may likely accelerate the degradation of deltaic and non deltaic barrier islands

geological characteristics and spatial distribution of paleo inlet channels beneath the outer banks barrier islands north carolina usa abstract nearly 200 km of high resolution ground penetrating radar gpr data were acquired along the outer banks barrier island system of north carolina usa gpr data combined with lithofacies and biofacies data reveal multiple depositional facies including inlet channel flood tide delta overwash peat and inner shelf previously undocumented paleo inlet channels constitute a significant portion of the shallow geologic framework between oregon inlet and cape hatteras gpr data reveal the complex stratigraphy associated with multiple sequences of cut and fill within inlet channels two types of paleochannels non migrating and migrating were classified based on geometry and fill patterns sediments and foraminifera collected from vibracores were correlated to gpr data to define the regional shallow stratigraphic framework channel fill facies are characterized by clinoform packages sometimes bounded by erosional surfaces indicating variable sediment transport directions from the ocean and sound sides channels are incised into older flood tide delta deposits corresponding to older inlet activity when barriers existed further seaward flood tide delta deposits are capped with marsh peat and overwash units migrating inlet facies occur under the widest portions of the island whereas narrow portions of the island are underlain by the non migrating inlet facies or flood tide delta overwash facies this geologic geomorphic relationship is attributed to the successional stage of island evolution during transgression and sediment transport processes associated with the different inlet types the radar facies lithofacies and biofacies provide a comprehensive dataset that will permit more precise identification of barrier island facies in the geologic record

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

barrier island response to late holocene climate events north carolina usa the outer banks barrier islands of north carolina usa contain a geologic record of inlet activity that extends from ca 2200 cal yr bp to the present and can be used as a proxy for storm activity optically stimulated luminescence osl dating 26 samples of inlet fill and flood tide delta deposits recognized in cores and geophysical data provides the basis for understanding the chronology of storm impacts and comparison to other paleoclimate proxy data osl ages of historical inlet fill compare favorably to historical documentation of inlet activity providing confidence in the technique comparison suggests that the medieval warm period mwp and little ice age lia were both characterized by elevated storm conditions as indicated by much greater inlet activity relative to today given present understanding of atmospheric circulation patterns and sea surface temperatures during the mwp and lia we suggest that increased inlet activity during the mwp responded to intensified hurricane impacts while elevated inlet activity during the lia was in response to increased nor easter activity a general decrease in storminess at mid latitudes in the north atlantic over the last 300 yr has allowed the system to evolve into a more continuous barrier with few inlets

holocene evolution of the chan may coastal embayment central vietnam changing coastal dynamics associated with decreasing rates of progradation possibly forced by mid to late holocene sea level changes abstract southeast asian coastal environments are undergoing massive transformations with unprecedented population and infrastructure development these transformations are occurring on a backdrop of intense natural and anthropogenic environmental change which are increasing the risk to the burgeoning coastal population little is known about how central vietnamese coastal environments have changed naturally since the mid holocene sea level highstand and how recent anthropogenic change and sea level variation have affected the coastal system the chan may embayment in central vietnam allows us to examine how recent changes in both anthropogenic development and sea level change have affected the coastline the embayment preserves a series of prograding beach ridges and is subject to intense human pressures with the construction of a large economic and industrial park and expansion of tourist facilities using ground penetrating radar and quartz optical dating we identify a switch from 6000 years of prograding beach ridges to transgressive dunes within the past century resulting in a decreasing rate of beach ridge progradation possibly in the last 100 years the recent modes of sediment deposition through washovers and a transgressive dune indicates that coastal progradation has slowed and might have stopped

holocene coastal response to monsoons and relative sea level changes in northeast peninsular malaysia abstract sedimentological geomorphic and ground penetrating radar gpr data are combined with optically stimulated luminescence data to define the holocene evolution of a coastal system in peninsular malaysia the setiu coastal region of northeast malaysia comprises five geological and geomorphic units representing distinct evolutionary phases of this coastline estimated marine limiting point elevations indicate deposition of an early aggradational shoreline associated with a sea level elevation of 0 1 to 1 7 m mslpmvgd datum between 6 8 ka and 5 7 ka in agreement with previous sea level studies from the malay thai peninsula a hiatus occurs in the record between 5 7 ka and 3 0 ka possibly due to a relative sea level oscillation and shoreline erosion long term relative sea level fall and possible still stands created strandplains that are interrupted by aggradational to transgressive paleo barrier and estuary formation corresponding with brief episodes of rsl rise analyses of gpr facies and osl ages suggest annual clinoform deposition with geometries dictated by variations in enso these data demonstrate the utility of high resolution studies of coastal facies as useful proxy indicators for paleoclimate studies at subdecadal to millennial time scales

timing and magnitude of recent accelerated sea level rise north carolina united states we provide records of relative sea level since a d 1500 from two salt marshes in north carolina to complement existing tide gauge records and to determine when recent rates of accelerated sea level rise commenced reconstructions were developed using foraminifera based transfer functions and composite chronologies which were validated against regional twentieth century tide gauge records the measured rate of relative sea level rise in north carolina during the twentieth century was 3 0 3 3 mm a consisting of a background rate of 1 mm a plus an abrupt increase of 2 2 mm a which began between a d 1879 and 1915 this acceleration is broadly synchronous with other studies from the atlantic coast the magnitude of the acceleration at both sites is larger than at sites farther north along the u s and canadian atlantic coast and may be indicative of a latitudinal trend

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

controls on the stratigraphic framework and paleoenvironmental change within a holocene estuarine system pamlico sound north carolina usa abstract this study examines the holocene stratigraphic record and paleoenvironmental evolution of a large estuarine system at high temporal and spatial resolution in the context of changing climate sea level and hydrodynamics new data are used to examine two time periods of increased marine influence within pamlico sound in northeastern north carolina interpreted to be the result of extensive barrier island segmentation synchronous with periods of rapid climate change during the late holocene the study reveals the controls on the stratigraphic development and the highly dynamic character of the coastal system in response to climate and sea level change as it interacts with paleotopography these findings can be used to inform projections of future environmental changes estuarine waters occupied paleovalleys in the pamlico sound region as early as ca 7500 cal bp and pleistocene interfluves separated the paleovalleys from the atlantic ocean until ca 5500 cal bp when they were flooded by rising sealevel forming the broad shallow pamlico sound initial barrier islands and shoals likely formed sometime between 5500 and 5000 cal bp providing the geomorphic setting for continued estuarine conditions behind the barriers at ca 4000 cal bp an increase in marine influence and sand content is detected in multiple cores and is correlated to seismic data within the pamlico sound basin this change is interpreted to be the result of increased segmentation of barrier islands thus a greater number of inlets or wider inlets which is consistent with a rapid transgression seen in other areas of the u s east coast the segmentation may have been partially facilitated by a rapid increase in lagoonal area and tidal prism by overtopping of interfluves greater barrier island continuity is evident from 3500 to 1200 cal bp as indicated by muddy deposits with low brackish estuarine foraminiferal assemblages at ca 1200 cal bp seismic sedimentological and micropaleontological data suggest an increase in wave and current energy and marine influence throughout southeastern pamlico sound these changes are interpreted to represent extensive segmentation of the barrier islands during the medieval climate anomaly mca since ca 500 cal bp the pamlico sound system has returned to a more restricted state as inlets have closed currently only three major inlets segment the outer banks the barrier island system fronting pamlico sound but warming climate and increasing rates of sea level rise suggest that another episode of barrier island segmentation began about a half century ago and appears that it may extend into the near future

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

caribbean sea surface temperatures two to three degrees cooler than present during the little ice age we determined the seasonal environmental conditions during the little ice age lia by interpreting isotope proxies in the coral skeleton of montastrea faveolata from the northeast caribbean the oxygen isotope composition was determined for three time intervals during the lia 1700 1705 1780 1785 1810 1815 thought to correspond to the coldest intervals the period 1984 1989 was used to represent modern calibration conditions we determined that ssts from the lia intervals are nearly 2 3 c cooler than present lia cooling in the caribbean may have resulted from regional oceanic and atmospheric circulation differences especially in winter we propose that a trough of cold air from the north atlantic may have extended farther south than present into the northern caribbean although there are indications from pacific corals that seasonality was greater during the lia this does not seem to be the case for the caribbean

millennial scale storminess variability in the northeastern united states during the holocene epoch for the purpose of detecting the effects of human activities on climate change it is important to document natural change in past climate1 in this context it has proved particularly difficult to study the variability in the occurrence of extreme climate events such as storms with exceptional rainfall1 previous investigations have established storm chronologies using sediment cores from single lakes2 3 4 5 6 7 8 but such studies can be susceptible to local environmental bias here we date terrigenous inwash layers in cores from 13 lakes which show that the frequency of storm related floods in the northeastern united states has varied in regular cycles during the past 13 000 years 13 kyr with a characteristic period of about 3 kyr our data show four peaks in storminess during the past 14 kyr approximately 2 6 5 8 9 1 and 11 9 kyr ago this pattern is consistent with long term changes in the average sign of the arctic oscillation9 suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of holocene climate variability in north america and europe

obduction why how and where clues from analog models obduction is an odd geodynamic process characterized by the emplacement of dense oceanic ophiolites atop light continental plates in convergent settings we herein present analog models specifically designed to explore the conditions i e sharp increase of plate velocities herein coined as acceleration slab interaction with the 660 km discontinuity ridge subduction under which obduction may develop as a result of subduction initiation the experimental setup comprises an upper mantle modeled as a low viscosity transparent newtonian glucose syrup filling a rigid plexiglas tank and high viscosity silicone plates convergence is simulated by pushing a piston with plate tectonics like velocities 1 10 cm yr onto a model comprising a continental margin a weakness zone with variable resistance and dip w an oceanic plate with or without a spreading ridge a preexisting subduction zone s dipping away from the piston and an upper active continental margin below which the oceanic plate is being subducted at the start of the model as for the neotethyan natural example several configurations were tested over thirty five parametric models with special emphasis on comparing different types of weakness zone and the degree of mechanical coupling across them measurements of displacements and internal deformation allow for a precise and reproducible tracking of deformation models consistently demonstrate that once conditions to initiate subduction are reached obduction may develop further depending on the effective strength of w results 1 constrainthe range of physical conditions required for obduction to develop nucleate and 2 underline the key role of such perturbations for triggering obduction particularly plate acceleration they provide an explanation to the short lived peri arabic obduction which took place along thousands of km almost synchronously within 50 10 myr from turkey to oman while the subduction zone beneath eurasia became temporarily jammed they also demonstrate that the emplacement of dense oceanic material on continental lithosphere is not a mysterious process requiring extraordinary boundary conditions but results from large scale normal oceanic then continental subduction processes

optical dating of dune sand for the study of sea level change a new widely applicable method to obtain well constrained relative sea level records presented here relies on optical dating of inorganic coastal landforms and sediments eighteen optical ages of basal dune sand from a barrier in massachusetts united states indicate that local relative sea level rose 8 m during the past 5 5 k y a sea level curve drawn from these optical ages shows good agreement with independent evidence from salt marsh peat sampled behind the barrier demonstrating the reliability of the method optical dating will be particularly useful in analyzing coastal records that contain too few organic indicators to allow high resolution 14 c based analyses

micropaleontologic record of late pliocene and quaternary paleoenvironments in the northern albemarle embayment north carolina u s a abstract micropaleontological data provide a strong actualistic basis for detailed interpretations of quaternary paleoenvironmental change the 90 m thick quaternary record of the albemarle embayment in the mid atlantic coastal plain of the usa provides an excellent opportunity to use such an approach in a region where the details of quaternary environmental change are poorly known the foraminiferal record in nine cores from the northern outer banks east of albemarle sound north carolina indicates the deposition of subhorizontal mostly open marine early to late pleistocene units unconformably upon a basement of late pliocene reduced oxygen fine grained shelf basin deposits pollen data record several warm cool fluctuations within the early to mid pleistocene deposits diatom data indicate that some fresh and brackish water units occur within the generally open marine pleistocene succession a channel cut by the paleo roanoke river during the last glacial sea level lowstand occurs in the northern part of the study area pollen indicates that the basal fluvial valley fill accumulated in cooler than modern climate conditions in the latest pleistocene overlying silts and muds accumulated under cool climatic estuarine conditions according to diatom and pollen data radiocarbon ages from the estuarine deposits indicate that the bulk of these sediments accumulated during the latest pleistocene the estuarine channel fill deposits are overlain by holocene open marine sands deposited as the rising sea transgressed into the estuary approximately 8 5 to 9 0 kyr bp within the barrier island drill cores of this study fully marine sedimentation occurred throughout the holocene however immediately west of the present barrier island mid to late holocene estuarine deposits underlie the modern albemarle sound the islands that currently form a continuous barrier across the mouth of albemarle sound have a complex history of holocene construction and destruction and large portions of them may be less than 3 kyr old the barrier island sands overlie open marine sands of colington shoal in the north and to the south overlie fluvial and marine sand filling paleo roanoke tributary valleys the pleistocene sediments underlying the northern outer banks study area are mainly of open inner to mid shelf origin if as is likely sea level continues to rise a return to such environmental conditions is likely in the near future

radiocarbon dating chronologic framework and changes in accumulation rates of holocene estuarine sediments from chesapeake bay abstract rapidly accumulating holocene sediments in estuaries commonly are difficult to sample and date in chesapeake bay we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of holocene sediment accumulation in the bay carbon in these sediments is a complex mixture of materials from a variety of sources analyses of different components of the sediments show that total organic carbon ages are largely unreliable because much of the carbon including coal has been transported to the bay from upstream sources and is older than sediments in which it was deposited mollusk shells clams oysters and foraminifera appear to give reliable results although reworking and burrowing are potential problems analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower chesapeake bay the biogenic carbonate radiocarbon ages are compatible with 210pb and 137cs data and pollen stratigraphy from the same sites post settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries including the chesapeake our data show that large variations in sediment mass accumulation rates occur among sites at shallow water sites local factors seem to control changes in accumulation rates with time our two relatively deep water sites in the axial channel of the bay have different long term average accumulation rates but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay mass accumulation rates at the two deep water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the chesapeake watershed

equivalent dose determinations for polymineralic fine grains using the sar protocol application to a holocene sequence of the chinese loess plateau abstract a single aliquot regenerative dose sar protocol involving stimulation of the same disc with an infra red laser diode followed by blue leds was applied to polymineralic fine grains infra red stimulated luminescence irsl and post ir optically stimulated luminescence osl ages are presented for a series of 19 fine grain 4 11 m samples taken from a loess section duowa in the western chinese loess plateau there are significant differences between the equivalent doses and thus the ages for the irsl and post ir osl measurements three potential explanations are investigated incomplete bleaching prior to deposition thermal transfer of charge and initial sensitivity change the question regarding which sequence of ages ir or post ir osl is correct if either is not resolved although the 19 post ir osl ages yield more consistent results it is proposed that the double sar protocol employed may not be correctly monitoring the sensitivity changes relating to either or both natural signals

the earth s palaeorotation postglacial rebound and lower mantle viscosity from analysis of ancient chinese eclipse records of the forces changing the earth s rotation tidal braking and postglacial rebound predominate at a timescale 102yr hide and dickey 1991 dickey 1992 analysis of ancient eclipse records has given values for the clock error t and the time derivative of the earth s dynamic oblateness j 2 for the past 3 300 yr since t at ut ct 2 where at is atomic cesium clock time ut is universal earth rotation time and t is the number of centuries before 1800 the oldest data have the most weight sunrise and sunset eclipses are especially valuable as they can be retrospectively timed