evaporitic and biosiliceous cyclic sedimentation in the miocene of the gulf of suez depositional and diagenetic aspects abstract the middle to late miocene evaporite bearing formations which outcrop along the gebel zeit and gems highs in the southwestern gulf of suez egypt consist of thick calcium sulphate beds rhythmically interbedded with marlstones siltstones and claystones containing various amounts of biogenic silica as well as pure diatomites the calcium sulphate beds are composed mainly of gypsum and anhydrite subaqueous crustallisation in subpermanent brine ponds of marine origin predominated during deposition of the selenite and laminated gypsum early diagenetic interstitial growth of nodular anhydrite occurred episodically when the water level dropped in response to increasing salinity associated with the precipitation of halite in the deeper troughs nevertheless most of the nodular facies resulted from the burial conversion of gypsum to anhydrite which has been sometimes rehydrated into gypsum a last phase of gypsum dehydration has occurred at the surface related to the present hot and dry climatic conditions the biosiliceous deposits contain either well preserved opal a or diagenetically altered opal ct clinoptilolite quartz and even clays diatom frustules such diagenetic changes are commonly described in the oceanic biosiliceous deposits the fossil content of these diatomitic layers implies shallow marine conditions on the shelves of highs induced by block faulting the cyclic succession of evaporited and biosiliceous deposits recorded the alternation of high sea level stands associated with high organic productivity probably enhanced by seasonal input of nutrients and low sea level stands associated with hypersaline conditions and evaporite deposition locally the sharp contact between the diatomites and gypsum argues for a rapid evolution of salinity towards high concentration up to gypsum saturation and more the formation of finely laminated diatomitic sediments is known to require either high organic productivity or anoxic conditions in bottom intermediate waters and eventually both processes in the gebel zeit and gemsa areas a local association of the biosiliceous sediments with diagenetic carbonates and native sulphur resulting from processes of bacterial sulphate reduction confirms that anoxic conditions occurred in the deep water body or in the sediments large amounts of organic compounds were involved in these diagenetic processes immature organic matter was consumed during an early diagenetic stage of transformation it is assumed that this organic matter was supplied either by the biosilica rich interbeds or the organic rich laminated carbonates the initial organic content of the biogenic deposits was impoverished as early as the first stages of sedimentation and diagenesis although a large part of the organic matter could have been destroyed by these early diagenetic processes and further oxidation in outcrops these sediments can be considered as potential source rocks in nearby less exposed sequences

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

quaternary coastal lithofacies sequence development and stratigraphy in a passive margin setting north carolina and virginia usa lithofacies analysis is fundamental to unravelling the succession of depositional environments associated with sea level fluctuations these successions and their timing are often poorly understood this report defines lithofacies encountered within the north eastern north carolina and south eastern virginia quaternary section interprets their depositional environments presents a model for coastal depositional sequence development in a passive margin setting and uses this understanding to develop the stratigraphy and quaternary evolutionary history of the region data were obtained from numerous drill cores and outcrops chronology was based on age estimates acquired using optically stimulated luminescence amino acid racemization uranium series and radiocarbon dating techniques geomorphic patterns were identified and interpreted using light detection and ranging imagery since lithofacies occurrence distribution and stratigraphic patterns are different on interfluves than in palaeo valleys this study focused on interfluves to obtain a record of highstand sea level cycles with minimal alteration by fluvial processes during subsequent lowstands nine primary lithofacies and four diagenetic facies were identified in outcrops and cores the uppermost depositional sequence on interfluves exhibits an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and is bounded below by a marine ravinement surface and above by the modern land surface older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces portions of seven depositional sequences were recognized and interpreted to represent deposition from late middle pleistocene to present erosional processes associated with each successive depositional sequence removed portions of older depositional sequences the stratigraphic record of the most recent sea level highstands marine isotope stage 5a and marine isotope stage 3 is best preserved glacio isostatic adjustment has influenced depositional patterns so that deposits associated with late quaternary sea level highstands marine isotope stages 5c 5a and 3 which did not reach as high as present sea level according to equatorial eustatic records are uplifted and emergent within the study area

numerical simulations of large scale cataclysmic floodwater a simple depth averaged model and an illustrative application a simple numerical simulation code is developed to quantitatively discuss the behaviors of past cataclysmic floods whose rigorous hydraulic descriptions would be too complex to be supported by typically available field data the code aims to keep the basic equations simple and the required computational costs low which allows greater exploration of parameter space examination of both the qualitative meaning of turbulent equations and the relative importance of terms in the shallow water equation have resulted in the adoption of the depth averaged diffusion wave approximation in two dimensions as well as manning s empirical equation for simplification on the other hand topography is included as a boundary condition since topography plays an important role in selecting flood routes the model provides important advantages over theoretical analyses or one dimensional simulations including 1 the reproduction of complicated water flow paths such as bifurcations and reconvergences 2 the reconstruction of hydrological relationships among the water paths and 3 the direct comparison among the calculated extent of the flood inundation including floodwater depths and geological and geomorphological observations preliminary reconstructions of the missoula floods demonstrate the advantages of this new approach the method of coupling field based flood information with two dimensional analysis of an entire flow path provides a basis for estimating the peak discharges and flow durations of cataclysmic megafloods on earth with direct bearing on the understanding of regional paleohydrological histories of mars

origin of glacial fluvial landforms in the azas plateau volcanic field the tuva republic russia role of ice magma interaction the basaltic azas plateau volcanic field is located in the tuva republic of the russian federation the area was glaciated multiple times and the field is characterized by the formation of subglacial volcanoes called tuyas but subaerial volcanoes and lava fields also exist a combined study of remote sensing and field observations in the vicinity of the tuyas in the southeastern azas plateau volcanic field identified landforms that are best explained by the jokulhlaup hypothesis the landforms include elongated hills paleochannels and butte and basin topography these landforms are hypothesized to have formed by both erosion and deposition caused by high energy water streams the triggering for the hypothesized jokulhlaups was either melting of ice by subglacial volcanism and or destabilization of ice dammed subglacial reservoirs the age estimation of the flood events is difficult but they probably occurred during the ice ages of the quaternary as late as in the middle late pleistocene

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

diagenesis of silica rich mound bedded chalk the coniacian arnager limestone denmark abstract the coniacian arnager limestone formation is exposed on the danish island of bornholm in the baltic sea it is composed of mound bedded siliceous chalk and x ray diffraction and scanning electron microscopy indicate a content of 30 70 insoluble minerals including authigenic opal ct quartz clinoptilolite feldspars calcite dolomite and barite opal ct and clinoptilolite are the most common and constitute 16 53 and 2 9 respectively the content of insoluble minerals varies laterally both within the mounds and in planar beds and the opal ct content varies by up to 10 vertically the mounds consist of two microfacies spiculitic wackestone and bioturbated spiculitic wackestone containing 10 22 and 7 12 moulds after spicules respectively subsequent to deposition and shallow burial dissolution of siliceous sponge spicules increased the silica activity of the pore water and initiated precipitation of opal ct the opal ct formed at temperatures around 17 c the precipitation lowered the silica activity and the si al ratio of the pore water resulting in precipitation of clinoptilolite feldspar and smectite calcite formed synchronously with the latest clinoptilolite minor amounts of quartz precipitated in pore water with low silica activity during maximum burial probably to depths of 200 250 m the dissolution of sponge spicules and decomposition of the sponge tissue also resulted in the release of ba2 sr2 mg2 ca2 and co32 facilitating precipitation of barite and dolomite precipitation of especially opal ct reduced the porosity to an average of 40 and cemented the limestone the study highlights the diagenetic pathways of bio siliceous chalk and the effects on preservation of porosity and permeability

the relation of a coastal environment to early diagenetic clinoptilolite zeolite formation new data from the late cretaceous european basin abstract clinoptilolite an authigenic mineral of the zeolite group is commonly considered as a product of rhyolitic volcanic glass transformation during diagenesis of carbonate pelagic hemipelagic sediments of cretaceous paleogene age another subordinate way of clinoptilolite formation that has been suggested in the literature is its precipitation during diagenetic transformation of carbonate sediments enriched with biogenic silica the observations concerning transformation of the latter into zeolite are scarce and mostly based on cretaceous pelagic hemipelagic and shallow marine deposits and post cretaceous sediments in which there was no volcanic material the mechanism of diagenetic clinoptilolite formation in volcanic free sediments as well as the role of the depositional setting in its precipitation is not well understood in carbonates of the nw part of the european basin west side of the ysogory dobrogea archipelago studied here the clinoptilolite is associated with opal ct from the dissolution of sponge spicules and a detrital clays are documented for the first time in a cretaceous coastal environment the carbonates were deposited in a coastal environment which was under the influence of weak currents delivering sponge spicules biogenic opal from the offshore zone and the terrestrial input was transported by rivers from a neighboring island the lush plant vegetation with numerous pteridophytes and conifers within a warm sub tropical or tropical and humid climate enhanced the terrestrial weathering of clays and feldspars this unique combination of elevated silica concentrations from sponge spicules dissolution and aluminum availability from terrestrial weathering of feldspars in a subtropical climate during the early diagenesis combined with alkalinity triggered by organic matter decomposition enhanced the clinoptilolite formation a few centimeters below the seabed the investigation demonstrates a novel route by which pore fluids enriched with silica and aluminum initiate clinoptilolite formation during the very early stage of diagenesis a few centimeters below the seafloor the clinoptilolite distribution in late cretaceous silica rich deposits with no volcanic input of the european basin is always associated with opal ct from sponge spicules and elevated terrestrial input clays taking into account the distinctive campanian maastrichtian sedimentation in the epicontinental european basin composed almost exclusively of pure pelagic carbonates the depositional settings in which the silica and aluminum were available in pore waters was restricted to the part of the basin influenced by terrestrial input this leads to the conclusion that clinoptilolite formation in volcanic free sediment is an indicator of not only enhanced sponge silica availability but also the close proximity of the source area

paleoshoreline geomorphology of boon tsagaan nuur tsagaan nuur and orog nuur the valley of lakes mongolia abstract we conducted a preliminary study of paleoshoreline features associated with boon tsagaan nuur tsagaan nuur and orog nuur lakes located in the gobi altai transition zone of the valley of lakes dolina ozor which stretches from central to western mongolia the paleoshoreline features were first identified on radarsat satellite sar imagery we investigated the features during the 1998 field season of the joint mongolian russian american archaeological expedition to the gobi altai region we identified paleoshorelines of multiple elevations in the field which are considered to be relict beach ridges and wave cut terraces other paleolake landforms include spits and gilbert type deltas these landforms are complex large and well established implying that the paleolakes were stable for extended periods the reconstructed paleolakes cover extensive areas of the valley floor implying that hydrological and climatic conditions were very different in the past paleolake expansions may have occurred under a variety of circumstances one hypothesis is that the high lake stands occurred during the wetter period corresponding to the oxygen isotope stage 3 prior to the last glacial maximum lgm during the warmest early holocene and the late holocene or during all these periods if low evaporation rates due to lower temperatures glacier meltwater and possibly increased precipitation are important factors then the expansions may have occurred during the terminal late glacial period after the last glacial maximum the greatly expanded lakes in the gobi altai could have significantly affected the quaternary human demography and migration in the region

climatic and sea level control of jurassic pliensbachian clay mineral sedimentation in the cardigan bay basin llanbedr mochras farm borehole wales

authigenic zeolites in late pleistocene sediments of the south atlantic angola basin two types of authigenic zeolites from late pleistocene hemipelagic sediments of the south atlantic were examined by xrd and sem analysis the xrd characteristics and the thermal behaviour of the zeolites suggest that type 1 is composed of clinoptilolite type 2 was identified as mordenite based on morphological features and qualitative elemental composition their authigenic nature is suggested from the shape of the crystals and their growth on and within foraminifera tests volcanic ash material acting as precursor minerals to zeolite formation could not be found nor were the zeolites directly related to siliceous remains an authigenesis from pore waters must be assumed mineral stabilities for amorphous sio2 and zeolites were calculated with the computer program solmineq88 interstitial waters proved to be oversaturated throughout the core in respect to all zeolites considered biogenic opal represents the limiting solid phase for si concentrations in pore waters therefore the dissolution of opal is regarded as the main source of si for interstitial waters below 9 m core depth where opal is only present in traces detrital feldspars and the zeolites themselves are affected by dissolution this may indicate the metastable nature of the zeolites also corroborated by the presence of two almost isochemical members of the same zeolite group

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

early diagenetic processes fluxes and reaction rates in sediments of the south atlantic abstract porewaters recovered from sediment cores gravity corers box corers and multicorers from various subrogions of the south atlantic amazon river mouth equatorial upwelling congo river mouth benguela coastal upwelling area and angola basin were investigated geochemically objectives included determination of eh ph oxygen nitrate sulfate alkalinity phosphate ammonium fluoride sulfide cal mg sr fe mn and si in order to quantify organic matter diagenesis and related mineral precipitation and dissolution processes porewater profiles from the eastern upwelling areas of the south atlantic suggest that sulfate reduction in the deeper parts of the sediment may be attributed mainly to methane oxidation whereas organic matter degradation by sulfate reduction is restricted to the near surface sediments further a prominent concentration gradient change of sulfate and related mineralization products occurred typically in the upwelling sediments at a depth of 4 to 8 m far below the zone of bioturbation or bioirrigation because other sedimentological reasons seem to fail as explanations an early diagenetic sulfide oxidation to sulfate within the anoxic environment is discussed porewater profiles from the sediments of the amazon fan area are mainly influenced by reactions with fe iii phases the remarkable linearity of the concentration gradients of sulfate supports the idea of distinct reaction layers in these sediments in contrast to the upwelling sediments the sulfate gradient develops from the sediment surface to a sulfate reduction zone at a depth of 5 3 m probably because a reoxidation of sulfide is prevented by the reaction with iron oxides and the formation of iron sulfide minerals a comparison of organic matter degradation rates from the different areas of the south atlantic show the expected relationship to primary productivity oxygen is the dominating oxidant whereas organic matter degradation by nitrate mn iv and probably also fe iii reduction is several orders of magnitude lower sulfate reduction is quantitatively of similar importance as oxygen respiration in the organic rich sediments but may also include methane oxidation reoxidation of ammonium and mn2 by oxygen or nitrate do not alter significantly the estimation of organic matter degradation in the oxic zone but may contribute to the nitrate reduction in suboxic layers

distribution of modern salt marsh foraminifera in the albemarle pamlico estuarine system of north carolina usa implications for sea level research abstract we described the distributions of foraminifera from ten physiographically distinct salt marshes in the albemarle pamlico estuarine system north carolina using 193 surface samples we defined elevation dependent ecological zones at individual sites using cluster analysis and detrended correspondence analysis additionally seven principal biozones of salt marsh foraminifera were identified that have distinctive spatial distributions reflecting a pattern of salinity regimes caused by the current configuration of barrier island inlets high salinity sites along the southern outer banks are associated with sub tidal calcareous assemblages low marshes dominated by miliammina fusca and high marsh environments defined by haplophragmoides wilberti trochammina inflata and arenoparrella mexicana in contrast lower salinity marshes have ammobaculites spp in sub tidal settings miliammina fusca dominated low marshes and high marsh settings characterized by jadammina macrescens spatial variation of foraminiferal populations and the potential for biozones to migrate in response to changing inlet configuration and salinity suggests that datasets of modern salt marsh foraminifera from multiple environments would be appropriate for reconstructing holocene relative sea level in north carolina

pollen distribution in recent marine sediments eastern canada analysis of 90 samples from coastal and continental shelf areas off eastern canada between 42 and 69 n shows that quaternary pollen and spores are present in recent marine muds throughout this region pollen and spore concentrations range from 50 000 to 100 grains per cm3 and they decrease both offshore as a function of distance from vegetation sources and northwards as a function of lower vegetation density north of the summer arctic frontal zone isopercentage contours show that maximum relative abundances of most palynomorphs occur in marine sediments adjacent to their regions of highest vegetation representation onshore however pinus and picea pollen tend to increase in percentage abundance with distance offshore presence of these tree pollen in marine sediments off baffin island implies that wind transport is an important pathway by which bisaccate pollen types enter the ocean in addition to fluvial transport q mode factor analysis shows that four major factors account for 89 of the variance amo

strong deglacial minimum in the δ13c record from planktonic foraminifera in the benguela upwelling region palaeoceanographic signal or early diagenetic imprint

hydrogeologic processes of large scale tectonomagmatic complexes in mongolia southern siberia and on mars large scale tectonomagmatic complexes are common on earth and mars many of these complexes are created or at least influenced by mantle processes including a wide array of plume types ranging from superplumes to mantle plumes among the most prominent complexes the mongolian plateau on earth and the tharsis bulge on mars share remarkable similarities in terms of large domal uplifted areas great rift canyon systems and widespread volcanism on their surfaces water has also played an important role in the development of the two complexes in general atmospheric and surface water play a bigger role in the development of the present day mongolian plateau than for the tharsis bulge as evidenced by highly developed drainages and thick accumulation of sediments in the basins of the baikal rift system on the tharsis bulge however water appears to have remained as ground ice except during periods of elevated magmatic activity glacial and periglacial processes are well documented for the mongolian plateau and are also reported for parts of the tharsis bulge ice magma interactions which are represented by the formation of subice volcanoes in parts of the mongolian plateau region have been reported for the valles marineris region of mars the complexes are also characterized by cataclysmic floods but their triggering mechanism may differ mainly ice dam failures for the mongolian plateau and outburst of groundwater for the tharsis bulge probably by magma ice interactions although ice dam failures within the valles marineris region cannot be ruled out as a possible contributor comparative studies of the mongolian plateau and tharsis bulge provide excellent opportunities for understanding surface manifestations of plume driven processes on terrestrial planets and how they interact with hydro cryospheres

diatom based tidal level transfer functions as an aid in reconstructing quaternary history of sea level movements in the uk this research analyses the diatom asssemblages recorded from six uk coastal sites and relates these diatom assemblages to tidal levels the relationship between diatom assemblages and tidal levels is examined statistically in order to develop a diatom based tidal level transfer function the results suggest that there is highly significant correlation between the diatom assemblages and water levels from mean high water of neap tides to highest astronomical tide p 0 01 99 random permutations a weighted average wa transfer function is thus established and the predictive ability of this transfer function is highly satisfactory finally this transfer function is applied successfully to estimate palaeotidal levels from fossil diatom data recorded in late holocene coastal sequences copyright 1999 john wiley sons ltd

graphic logging for interpreting process generated stratigraphic sequences and aquifer reservoir potential with analog shelf to shoreface examples from the atlantic coastal plain province u s a abstract this paper demonstrates a process based method of graphic logging and stratigraphic interpretation that is based on a new texturally based classification of clastic sediment which is independent from composition cementation and geologic environment the method integrates facies analysis with sequence stratigraphy because it requires identifying surfaces compiling vertical changes in texture and attributes between surfaces and uses these parameters to identify facies units and interpret continuously deposited intervals four clastic shelf to shoreface successions from the atlantic coastal plain province cretaceous to holocene in age with established chronostratigraphic and sequence stratigraphic frameworks provide examples of the application of this method for each graphic logs standardized for texture show the facies and bounding surfaces that define the thickness and hierarchy of event strata e g sequences beds bedsets parasequences parasequence sets these are directly compared with gamma ray log response patterns and the distribution of factors that impact potential permeability shelf to shoreface successions were chosen because these facies exhibit the greatest diversity in composition siliciclastic carbonate and glauco phosphatics but in spite of this exhibit comparable and predictable graphic and gamma ray response patterns if systematically logged using this method for the process response model examined texture i e principal grain size controls the amplitude width of the graphic log its shape is constant and independent from composition the pattern in the correlated gamma ray log parallels the log of principal grain size except that an inverse response is associated with coarser lags the amplitude of the gamma log is controlled by composition a proxy for permeability developed from standardized textural fields is applied to two of the examples to shows how aquifer or reservoir potential is systematically tied to stratigraphic and sedimentologic parameters

oxygen isotopic composition of low temperature authigenic clinoptilolite oxygen isotope ratios were obtained from authigenic clinoptilolites from barbados accretionary complex yamato basin and exmouth plateau sediments odp sites 672 797 and 762 in order to investigate the isotopic fractionation between clinoptilolite and pore water at early diagenetic stages and low temperatures dehydrated clinoptilolites display isotopic ratios for the zeolite framework 18of that extend from 18 7 to 32 8 vs smow in combination with associated pore water isotope data the oxygen isotopic fractionation between clinoptilolite and pore fluids could be assessed in the temperature range from 25 c to 40 c the resulting fractionation factors of 1 032 at 25 c and 1 027 at 40 c are in good agreement with the theoretically determined oxygen isotope fractionation between clinoptilolite and water calculations of isotopic temperatures illustrate that clinoptilolite formation occurred at relatively low temperatures of 17 c to 29 c in barbados ridge sediments and at 33 c to 62 c in the yamato basin these data support a low temperature origin of clinoptilolite and contradict the assumption that elevated temperatures are the main controlling factor for authigenic clinoptilolite formation increasing clinoptilolite 18of values with depth indicate that clinoptilolites which are now in the deeper parts of the zeolite bearing intervals had either formed at lower temperatures 17 20 c or under closed system conditions

quaternary paleolake formation and cataclysmic flooding along the upper yenisei river abstract a suite of geomorphological and sedimentological features in the catchment of the upper yenisei river in the sayan mountains of southern siberia testifies to the occurrence of cataclysmic floods that flowed down the river evidence of large scale high energy flood events includes 1 gravel dunes up to a few meters high and spaced 50 to 80 m apart in the kyzyl basin 2 landforms such as hanging valleys and paleochannels and 3 flood sediments in a tributary valley the origins of the yenisei floods were likely diverse due to complex hydrological processes operating in the sayan mountains the possibilities include failures of multiple variably impounded ice sedimentary tectonic scarp and lava flow dams paleolakes in the two large intermontane basins of darkhadyn khotgor and todza and other minor basins in the upper yenisei river catchment dating techniques applied to the paleolakes in the darkhadyn khotgor and todza basins revealed their formation during various periods in the middle late pleistocene and holocene flooding from the darkhadyn khotgor appears to explain many of the inferred flood features although contributions by flooding from other paleolake basins cannot be ruled out computer simulation of the flooding caused by a darkhadyn khotgor paleolake ice dam failure indicates a probable peak discharge of 3 5 10 6 m 3 s 1 approximately one fifth that of the floods that formed the channeled scabland in the u s a many of the outburst events probably occurred in the late quaternary but earlier floods could also have occurred

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

holocene sea level changes along the north carolina coastline and their implications for glacial isostatic adjustment models abstract we have synthesized new and existing relative sea level rsl data to produce a quality controlled spatially comprehensive database from the north carolina coastline the rsl database consists of 54 sea level index points that are quantitatively related to an appropriate tide level and assigned an error estimate and a further 33 limiting dates that confine the maximum and minimum elevations of rsl the temporal distribution of the index points is very uneven with only five index points older than 4000 cal a bp but the form of the holocene sea level trend is constrained by both terrestrial and marine limiting dates the data illustrate rsl rapidly rising during the early and mid holocene from an observed elevation of 35 7 1 1 m msl at 11062 10576 cal a bp to 4 2 m 0 4 m msl at 4240 3592 cal a bp we restricted comparisons between observations and predictions from the ice 5g vm2 with rotational feedback glacial isostatic adjustment gia model to the late holocene rsl last 4000 cal a bp because of the wealth of sea level data during this time interval the ice 5g vm2 model predicts significant spatial variations in rsl across north carolina thus we subdivided the observations into two regions the model forecasts an increase in the rate of sea level rise in region 1 albemarle currituck roanoke croatan and northern pamlico sounds compared to region 2 southern pamlico core and bogue sounds and farther south to wilmington the observations show late holocene sea level rising at 1 14 0 03 mm year 1 and 0 82 0 02 mm year 1 in regions 1 and 2 respectively the ice 5g vm2 predictions capture the general temporal trend of the observations although there is an apparent misfit for index points older than 2000 cal a bp it is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid carolina platform high or a flaw in the gia model a comparison of local tide gauge data with the late holocene rsl trends from regions 1 and 2 support the spatial variation in rsl across north carolina and imply an additional increase of mean sea level of greater than 2 mm year 1 during the latter half of the 20th century this is in general agreement with historical tide gauge and satellite altimetry data

redox sensitivity of p cycling during marine black shale formation dynamics of sulfidic and anoxic non sulfidic bottom waters abstract a high resolution geochemical record of a 120 cm black shale interval deposited during the coniacian santonian oceanic anoxic event 3 odp leg 207 site 1261 demerara rise has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo redox conditions high contents of organic matter sulfur and redox sensitive trace metals cd mo v zn as well as continuous lamination point to deposition under consistently oxygen free and largely sulfidic bottom water conditions however rapid and cyclic changes in deep ocean redox are documented by short term 15 20 ka intervals with decreased total organic carbon toc s and redox sensitive trace metal contents and in particular pronounced phosphorus peaks up to 2 5 wt p associated with elevated fe oxide contents sequential iron and phosphate extractions confirm that p is dominantly bound to iron oxides and incorporated into authigenic apatite preservation of this fe p coupling in an otherwise sulfidic depositional environment as indicated by fe speciation and high amounts of sulfurized organic matter may be unexpected and provides evidence for temporarily non sulfidic bottom waters however there is no evidence for deposition under oxic conditions instead sulfidic conditions were punctuated by periods of anoxic non sulfidic bottom waters during these periods phosphate was effectively scavenged during precipitation of iron oxyhydr oxides in the upper water column and was subsequently deposited and largely preserved at the sea floor after 15 25 ka sulfidic bottom water conditions were re established leading to the initial precipitation of cds zns and pyrite subsequently increasing concentrations of h2s in the water column led to extensive formation of sulfurized organic matter which effectively scavenged particle reactive mo complexes thiomolybdates at site 1261 sulfidic bottom waters lasted for 90 100 ka followed by another period of anoxic non sulfidic conditions lasting for 15 20 ka the observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface to mid waters from the south atlantic resulting in a lowering of the oxic anoxic chemocline in the water column alternatively sea water sulfate might have been stripped by long lasting high rates of sulfate reduction removing the ultimate source for hs production

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

geomorphology of subglacial volcanoes in the azas plateau the tuva republic russia abstract the azas plateau volcanic field is located in the tuva republic of the russian federation the compositions of the azas plateau volcanics include low viscosity trachybasalt and basanite volcanic edifices of middle late pleistocene age are widely distributed in the southeastern part of the volcanic field there are subglacial volcanoes among the volcanic edifices and their formation coincided with extensive ancient glaciations in the region the dominant subglacial volcanoes in the area are tuyas the general shapes of the tuyas flat tops with steep sides are due to eruptions into meltwater lakes and confinement of ice walls and effusive subaerial eruptions of basaltic lavas there are also non flat topped subglacial volcanoes and at least one subaerial volcanic edifice in the area degradation appears to have modified the primary shapes of the tuya edifices and such processes seem to include failures of over steepened slopes gully formation due to stream runoff and debris flows cirque valley glaciation and modification by rock glaciers the estimated thicknesses of the ice sheets covering the subglacial volcanoes during their eruptions range 300 600 m on average

authigenic zeolites and their relation to silica diagenesis in odp site 661 sediments leg 108 eastern equatorial atlantic at odp site 661 from the continental margin of northwest africa authigenic clinoptilolites were investigated in detail based on chemical data crystal size and shape and their intergrowth with associated mineral phases two types of clinoptilolite type a and b occur representing different diagenetic conditions under which the formation of zeolites took place clinoptilolite type a was found in a sediment section comprises numerous hiatuses and stratigraphically condensed sediments and could have been formed during early diagenesis in contrast clinoptilolite type b was precipitated in campanian sediments during later diagenesis after the transformation from opal a to opal ct had taken place at site 661 the silica source for the authigenesis of both clinoptilolite types is biogenic opal volcanic ash material occurs but in low amounts and thus is not a prerequisite for the formation of clinoptilolite at site 661

late holocene climate and ecosystem history from chesapeake bay sediment cores usa palaeoclimate records from late holocene sediments in chesapeake bay the largest estuary in the usa provide evidence that both decadal to centennial climate variability and european colonization

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

stetson pit dare county north carolina an integrated chronologic faunal and floral record of subsurface coastal quaternary sediments continuous split spoon samples from a drill hole penetrating 34 m of coastal plain sediments at stetson pit in dare county north carolina were taken for lithologic aminostratigraphic faunal ostracodes and floral pollen analyses three distinct aminozones are recognized in the subsurface section based upon d alloisoleucine l isoleucine a i values in each of the molluscan species mulinia lateralis and mercenaria sp ostracode zonations in the subsurface section are based on percentages of 80 thermophilic and cryophilic species those living today south and north of cape hatteras and the percentages of brackish water species five assemblage zones are delineated six pollen assemblage zones are also delineated within the subsurface section based upon study of 48 sediment samples the subsurface record at stetson pit is interpreted to represent portions of four interglacials based upon the combined faunal floral and aminostratigraphic data the two younger aminozones with amino acid age estimates of 100 000 20 000 yr 7 2 to 11 2 m msl and 300 000 500 000 yr 13 to 14 2 m msl represent portions of middle late pleistocene interglacials the lower aminozone 17 4 to 33 m msl spans an interval that probably includes at least two interglacials based upon faunal and floral records and has an age estimated to be between 800 000 and 1 300 000 yr boundaries delineated by faunal floral and amino acid methods do not always coincide due to sampling constraints and phase lags between the different records one major unconformity at 17 4 m msl in the stetson pit section is easily recognized from lithologic characteristics and may represent a hiatus of as much as 800 000 yr lithologic changes associated with all other zone boundaries are subtle and would probably not be considered significant in the absence of faunal floral or amino acid data

micropaleontologic record of quaternary paleoenvironments in the central albemarle embayment north carolina u s a abstract to understand the temporal and spatial variation of eustatic sea level fluctuations glacio hydro isostacy tectonics subsidence geologic environments and sedimentation patterns for the quaternary of a passive continental margin a nearly complete stratigraphic record that is fully integrated with a three dimensional chronostratigraphic framework and paleoenvironmental information are necessary the albemarle embayment a cenozoic regional depositional basin in eastern north carolina located on the southeast atlantic coast of the usa is an ideal setting to unravel these dynamic interrelated processes micropaleontological data coupled with sedimentologic chronostratigraphic and seismic data provide the bases for detailed interpretations of paleoenvironmental evolution and paleoclimates in the 90 m thick quaternary record of the albemarle embayment the data presented here come from a transect of cores drilled through a barrier island complex in the central albemarle embayment this area sits in a ramp like setting between late pleistocene incised valleys the data document the episodic infilling of the albemarle embayment throughout the quaternary as a series of transgressive regressive t r cycles characterized by inner shelf midshelf and shoreface assemblages that overlie remnants of fluvial to estuarine valley fill barrier island and marginal marine deposits have a low preservation potential inner to mid shelf deposits of the early pleistocene are overlain by similar middle pleistocene shelf sediments in the south of the study area but entirely by inner shelf deposits in the north late pleistocene marine sediments are of inner shelf origin and holocene deposits are marginal marine in nature pleistocene marine sediments are incised particularly in the northern half of the embayment by lowstand paleovalleys partly filled by fluvial floodplain deposits and in some cases overlain by remnants of transgressive estuarine sediments the shallowing through time of quaternary sediments reflects the eastward progradational geometry of the continental shelf the preservation potential of marginal marine deposits barrier island shoreface backbarrier deposits is not high except in topographic lows associated with late pleistocene paleovalleys and inlets because the current interglacial highstand has not yet reached its highest level given the documented increase in rate of relative sea level rise in this region shallow marine conditions are likely to return to the central albemarle embayment in the near future

standardizing texture and facies codes for a process based classification of clastic sediment and rock abstract proposed here is a universally applicable texturally based classification of clastic sediment that is independent from composition cementation and geologic environment is closely allied to process sedimentology and applies to all compartments in the source to sink system the classification is contingent on defining the term clastic so that it is independent from composition or origin and includes any particles or grains that are subject to erosion transportation and deposition modifications to folk s 1980 texturally based classification that include applying new assumptions and defining a broader array of textural fields are proposed to accommodate this the revised ternary diagrams include additional textural fields that better define poorly sorted and coarse grained deposits so that all end members gravel sand and mud size fractions are included in textural codes revised textural fields or classes are based on a strict adherence to volumetric estimates of percentages of gravel sand and mud size grain populations which by definition must sum to 100 the new classification ensures that descriptors are applied consistently to all end members in the ternary diagram gravel sand and mud according to several rules and that none of the end members are ignored these modifications provide bases for standardizing vertical displays of texture in graphic logs lithofacies codes and their derivatives hydrofacies hydrofacies codes are nondirectional permeability indicators that predict aquifer or reservoir potential folk s 1980 ternary diagram for fine grained clastic sediments sand silt and clay size fractions is also revised to preserve consistency with the revised diagram for gravel sand and mud standardizing texture ensures that the principles of process sedimentology are consistently applied to compositionally variable rock sequences such as mixed carbonate siliciclastic ramp settings and the extreme ends of depositional systems

geologic framework of the northern north carolina usa inner continental shelf and its influence on coastal evolution abstract the inner continental shelf off the northern outer banks of north carolina was mapped using sidescan sonar interferometric swath bathymetry and high resolution chirp and boomer subbottom profiling systems we use this information to describe the shallow stratigraphy reinterpret formation mechanisms of some shoal features evaluate local relative sea levels during the late pleistocene and provide new constraints via recent bedform evolution on regional sediment transport patterns the study area is approximately 290 km long by 11 km wide extending from false cape virginia to cape lookout north carolina in water depths ranging from 6 to 34 m late pleistocene sedimentary units comprise the shallow geologic framework of this region and determine both the morphology of the inner shelf and the distribution of sediment sources and sinks we identify pleistocene sedimentary units beneath diamond shoals that may have provided a geologic template for the location of modern cape hatteras and earlier paleo capes during the late pleistocene these units indicate shallow marine deposition 15 25 m below present sea level the uppermost pleistocene unit may have been deposited as recently as marine isotope stage 3 although some apparent ages for this timing may be suspect paleofluvial valleys incised during the last glacial maximum traverse the inner shelf throughout the study area and dissect the late pleistocene units sediments deposited in the valleys record the holocene transgression and provide insight into the evolutionary history of the barrier estuary system in this region the relationship between these valleys and adjacent shoal complexes suggests that the paleo roanoke river did not form the albemarle shelf valley complex as previously proposed a major fluvial system is absent and thus makes the formation of this feature enigmatic major shoal features in the study area show mobility at decadal to centennial timescales including nearly a kilometer of shoal migration over the past 134 yr sorted bedforms occupy 1000 km 2 of seafloor in raleigh bay and indicate regional sediment transport patterns between capes hatteras and lookout that help explain long term sediment accumulation and morphologic development portions of the inner continental shelf with relatively high sediment abundance are characterized by shoals and shoreface attached ridges and where sediment is less abundant the seafloor is dominated by sorted bedforms these relationships are also observed in other passive margin settings suggesting a continuum of shelf morphology that may have broad application for interpreting inner shelf sedimentation patterns

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

diagenetic clinoptilolite and opal ct from the middle eocene wittering formation isle of wight u k abstract thinly interbedded estuarine sandstones and mudstones in the middle eocene wittering formation bracklesham group isle of wight contain authigenic clinoptilolite opal ct and possibly authigenic smectite over a thickness of 8 5 m the clinoptilolite and opal ct cements have resulted in these beds being the only ones tightly cemented in the wittering formation the rest being soft sands and muds the unit contains abundant siliceous sponge spicules many of which are preserved as voids and were the likely source of the opal ct the presence of an organic rich rooted paleosol histosol immediately overlying the unit is believed to have contributed significantly to the early diagenetic history of the estuarine sediments in particular the formation of zeolite although the ph and dissolved silica of unmodified seawater are too low for zeolite formation high concentrations of dissolved silica are believed to have resulted from dissolution of siliceous sponge spicules opal a and formation of silica organic acid complexes organic acid dissolution of feldspars absent from the zeolite bearing interval is the most probable source of alumina and cations for zeolite formation ree data show that volcanic ash was never present and cannot therefore have been the source of the zeolite this investigation therefore demonstrates a novel route by which the pore fluid chemistry required for zeolite formation can be achieved

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

bulk sediment mineralogy of gas hydrate reservoir at the east nankai offshore production test site abstract bulk sediment mineralogy was measured from a gas hydrate bearing middle pleistocene deepwater turbidite interval at the offshore production test site of the eastern nankai trough area we used core samples recovered from a 60 m long section of the borehole for semi quantitative analysis of mineral and organic contents of the gas hydrate reservoir powder x ray diffraction analysis ignition loss test and field emission scanning electronic microscopy revealed the followings i ten bulk minerals vary in concentration and most of them have a good exponential correlation with median grain size ii the upper muddy section is dominated by coccolith rich hemipelagites whereas the middle and lower sections are characterized by relatively coccolith poor probably humic substance rich turbiditic sediments and iii the common occurrence of authigenic gypsum siderite and framboidal pyrite indicates early diagenesis in anoxic and relatively high salinity conditions probably associated with gas hydrate formation in some degree such mineralogical data can provide useful information on evaluation of thermal properties geomechanical characteristics effective permeability and early diagenetic mechanism of the sediments to characterize and exploit gas hydrate reservoirs