an integrated hypothesis for regional patterns of shoreline change along the northern north carolina outer banks usa combining analyses of plan view shoreline change and shoreline curvature with existing nearshore geologic and bathymetric data and the results of a recent theoretical large scale shoreline evolution model that couples geologic framework to alongshore sediment transport we propose an integrated explanation for persistent patterns of shoreline change observed on the northern outer banks of north carolina usa concentrated sources of coarse grained sediment derived from relict fluvial stratigraphy or densely grouped relict inlet channels excavated from the shoreface may both enable persistence of nearshore bathymetric anomolies and control multi km scale undulations in shoreline curvature which in turn affect gradients in wave driven alongshore sediment transport that drive long term shoreline change

the stratigraphic evolution of a large back barrier lagoon system with a non migrating barrier abstract lake st lucia the largest estuarine system in africa is enclosed by a 120 m high compound quaternary barrier dune system in northern kwazulu natal south africa it comprises several discrete sedimentary basins within a single shallow back barrier water body this paper reports the first very high resolution seismic study of the system seven seismic units a g are identified and interpreted based on their geometry acoustic properties and a sediment coring programme the units are bounded by regionally developed sequence boundaries and lower order unconformity surfaces corresponding to bay and tidal ravinement and hiatus surfaces the lowermost subaerial unconformity formed during regression related to late pliocene hinterland uplift initial infilling of this surface in the proximal areas reflects estuarine sedimentation in a mixed wave and tide dominated system during the subsequent lowstand and early transgressive systems tracts overlain by prograding highstand deltaic deposits that developed as sea levels began to stabilise distally this cycle of sedimentation is initially reflected by the infilling of a similar estuarine system that gradually transitioned to a back barrier lagoon superimposed stillstands drove imbalances in the rate of sediment supply and accommodation space and this coupled with the development of an early barrier complex caused lagoon aggradation and shallowing a second similar trend is repeated for the recent postglacial sea level cycle there appears to be no preservation of the intervening pleistocene cycles of erosion and deposition the system is capped by estuarine lacustrine deposits the onset of lower energy estuarine lake conditions began 6235 cal bp in north lake and started earlier in the proximal false bay owing to sheltering by the antecedent barrier of a rocky peninsula this study reveals a markedly different evolutionary history in adjacent basins of the same back barrier system during two full sea level cycles these are attributed to a long established non migrating barrier and to the influence of antecedent conditions on the system response to transgression unlike the us atlantic margin where migrating barriers truncate the infilling sequences the main stratigraphic unconformities within each fill sequence correspond to tidal and bay ravinement surfaces

infrared spectroscopic taxonomy for carbonaceous chondrites from speciation of hydrous components mid infrared absorption spectra for all types of carbonaceous chondrites were obtained in this study to establish a versatile method for spectroscopic classification of carbonaceous chondrites infrared spectra were measured using a conventional kbr pellet method and diamond press method spectra of hydrous carbonaceous chondrites exhibit intense o h stretching vibrations ci chondrites are identifiable by a characteristic sharp absorption band appearing at 3685 cm 1 which is mainly attributable to serpentine x ray diffraction analysis showed the presence of serpentine however yamato y 82162 c1 does not have the band at 3685 cm 1 because of its thermal metamorphism cm and cr chondrites have an intense absorption band at approximately 3600 cm 1 this absorption tends to appear in cm chondrites more strongly than cr chondrites because the intensity ratios of an oh stretching mode at 3520 cm 1 compared to 3400 cm 1 for cm chondrites are in the range of 0 95 1 04 which is systematically higher than those of cr chondrites 0 86 0 88 therefore the two types of chondrites are distinguishable by their respective infrared spectra the spectrum feature of the tagish lake meteorite is attributable to neither ci nor cm chondrites co chondrites are characterized by weak and broad absorption at 3400 cm 1 cv chondrites have weak or negligible absorption of water ck chondrites also have no water induced absorption ch and cb chondrites have a sharp absorption at 3692 cm 1 indicating the presence of chrysotile which is also supported by observations of x ray diffraction and tem the combination of spectroscopic classification and the diamond press method allows classification of carbonaceous chondrites of very valuable samples with small quantities as one example carbonaceous chondrite clasts in brecciated meteorites were classified using our technique infrared spectra for a fragment of carbonaceous clasts 1 g separated from willard b and tsukuba were measured the 3685 cm 1 band found in ci chondrites was clearly detected in the clasts indicating that they are ci like clasts

widespread oxidized and hydrated amorphous silicates in cr chondrites matrices implications for alteration conditions and h2 degassing of asteroids abstract the cr chondrites carry one of the most pristine records of the solar nebula materials that accreted to form planetesimals they have experienced very variable degrees of aqueous alteration ranging from incipient alteration in their matrices to the complete hydration of all of their components in order to constrain their chemical alteration pathways and the conditions of alteration we have investigated the mineralogy and fe oxidation state of silicates in the matrices of 8 cr chondrites from type 3 to type 1 fe l edge x ray absorption near edge structure xanes was performed on matrix fib sections using synchrotron based scanning transmission x ray microscopy stxm the fe 3 fe ratio of submicron silicate particles was obtained and coordinated with tem observations in all the least altered cr chondrites que 99177 eet 87770 eet 92042 lap 02342 gra 95229 and renazzo we find that the matrices consist of abundant submicron fe rich hydrated amorphous silicate grains mixed with nanometer sized phyllosilicates the fe 3 fe ratios of both amorphous and nanocrystalline regions are very high with values ranging from 68 to 78 in the most altered samples al rais and gro 95577 fine grained phyllosilicates also have a high fe 3 fe ratio around 70 whereas the coarse micrometer sized phyllosilicates are less oxidized down to 55 and have a lower iron content these observations suggest the following sequence submicron fe2 amorphous silicate particles were the building blocks of cr matrices after accretion they were quickly hydrated and oxidized leading to a metastable amorphous gel like phase nucleation and growth of crystalline phyllosilicates was kinetically limited in most type 3 and 2 crs but increased as alteration became more extensive in al rais and gro 95577 the decreasing fe 3 fe ratio is interpreted as a result of the transfer of fe3 from silicates to oxides during growth while aqueous alteration progressed higher temperature longer duration change of fluid composition in a fully closed system equilibrium thermodynamics suggest that the water to rock ratios typically assumed to be low fe 3 fe ratio such a high fe 3 fe value could be accounted for however if the system was partially open at least with respect to h2 and other gases as well rapid degassing of the fluid would have favored more oxidizing fluid conditions recently proposed scenarios involving some degree of water d h increase through rayleigh isotopic fractionation are supported by these results

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

non hydrostatic numerical modelling of nearshore wave transformation over shore oblique sandbars abstract observations from high resolution bathymetric surveys on the coast of north carolina indicate areas with shore parallel depth contours and other areas with shore oblique sandbars these shore oblique bars are large scale morphological features that extend up to 1000 m from shore and previous studies have shown that they are spatially correlated with higher shoreline change rates and induce erosional hotspots to investigate the influence the oblique sandbar morphology has on nearshore wave transformation and energy distribution a non hydrostatic wave model is used with the bathymetry corresponding to two areas with shore parallel depth contours and two areas with shore oblique sandbars the model is applied with a horizontal resolution of 5 m and a boundary condition representative of the directional spectrum of a typical southeast swell event an idealized approach with relatively short alongshore model domains and cyclic lateral boundary conditions is adopted due to limited availability of high resolution bathymetry however this approach elucidates the influence of shore oblique sandbars on the nearshore hydrodynamics the numerical results show that higher alongshore variability in depth due to the shore oblique bars drive large alongshore changes in cross shore wave energy flux and cause spatial variability in dissipation in the nearshore region the simulations indicate that alongshore variations in wave energy caused by the shore oblique bars results in a 50 75 reduction in wave setup and a 25 40 decrease in alongshore velocity averaged across the surf zone for the conditions investigated the results suggest that wave driven hydrodynamics can influence nearshore sediment dynamics to create erosional zones compared to areas with shore parallel bathymetric contours since the morphology of shore oblique sandbars are an important control on wave energy that impacts the beach

subtraction of powerline harmonics from geophysical records harmonic noise generated by power lines and electric railways has plagued geophysicists for decades the noise occurs as electric and magnetic fields at the fundamental frequency of power transmission typically 60 hz in north america and its harmonics it may be recorded directly during time domain measurements of electric and magnetic felds or indirectly by geophone cables during the acquisition of seismic data

chondrule fragments from comet wild2 evidence for high temperature processing in the outer solar system abstract terminal grains from c2063 1 154 1 0 track 154 and c2061 1 113 5 track 113 from the stardust collection of comet wild2 s coma have been studied by tem and nanosims terminal grain 2 of c2063 1 154 1 0 consists of an al rich diopside en 97 99 al 2 o 3 9 11 wt pigeonite en 85 wo 15 with tio 2 and al 2 o 3 contents of 0 5 and 5 2 wt and minor forsterite and enstatite the mineral assemblage and al rich ti poor composition of the grain are consistent with being a fragment of an al rich chondrule similar to those present in carbonaceous chondrites the oxygen isotopic composition of the c2063 1 154 1 0 grain was determined by nanosims analyses and found to be 17 o 10 6 5 7 18 o 7 5 2 5 and 17 o 1 4 4 3 18 o 6 5 1 6 1 errors for the two sections these figures are distinct from cais and consistent with an origin as al rich chondrule fragments terminal grain 5 of c2061 1 113 5 consists of low ca pyroxene en 86 87 fs 10 11 wo 3 4 and 2 wt al 2 o 3 and in one section 5 10 of a na rich silicate phase this assemblage may be a fragment of a low ca pyroxene bearing chondrule and mesostasis the original chondrule diameter for the c2063 1 154 1 0 and c2061 1 113 5 samples by analogy with carbonaceous chondrite chondrules might have been in the range 0 2 1 0 mm if they were of that size then the presence of large grains of high temperature material e g 1500 k for such refractory assemblages could be explained through commonly invoked models of radial drift from inner to outer solar system but only if the chondrules were first fragmented to dust within the inner solar system an alternative scenario is that some chondrule formation was associated with high temperature processing and planetesimals in the outer solar system

sedimentary heterogeneity and petrophysical characterization of barremian tsunami and barrier island inlet deposits the aliaga outcrop as a reservoir analogue galve sub basin eastern spain abstract the present study examined two sandstone deposits in the aliaga outcrop as a reservoir analogue over a distance of 200 m long and attempted to establish a correlation between sand facies and the petrophysical properties of the sandstones in order to investigate the reservoir heterogeneity the aliaga reservoir analogue represents the upper part of camarillas fm deposited during the barremian synrift phase of the galve sub basin iberian basin spain it is characterized by a transitional sedimentary interval from sandy dominant deposits to carbonate dominant deposits which were deposited under the same palaeoenvironmental conditions in relation to systems of back barrier sedimentation the description of the aliaga outcrop provided here consists of lithological descriptions of two sandstone deposits a tsunami and a barrier island inlet at both mesoscopic decimetres to tens of metres and microscopic scales millimetres to centimetres both deposits recognized at the basin scale were described in terms of sand grain size sand sorting and cementation further cores were drilled along outcrop to collect samples for porosity and permeability measurements both sandstone reservoirs are the result of different sedimentary processes that determined facies characteristics as the different petrophysical properties observed in these deposits consequently the sedimentary process controls the heterogeneity of the sandstones facies and thus the sand heterogeneity controls the distribution of the petrophysical properties the classification of sand facies in terms of sand sorting seems to be more appropriate for describing sand heterogeneity accordingly petrophysical parameters in both deposits were also influenced by sand sorting the sand facies and petrophysics heterogeneity of the described deposits can be hierarchically ordered first order heterogeneity is related to the basin scale second order heterogeneity is related to genesis and the conditions of sediment deposition and third order heterogeneity is related to synsedimentary faults and or post sedimentation events

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

mineralogical constraints on the thermal history of martian regolith breccia northwest africa 8114 abstract martian meteorite northwest africa nwa 8114 a paired stone to nwa 7034 provides an opportunity to examine the thermal history of a martian regolith and study near surface processes and ancient environmental conditions near an impact crater on mars our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains some of the pyroxene clasts show exsolution lamellae indicating a high temperature magmatic origin and slow cooling however transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re crystallised to form magnetite and a k bearing feldspathic glassy material together with relict pyroxene this breakdown event was associated with oxidation with up to 25 fe3 fe in the relict pyroxene measured using fe k xanes by comparison with previous studies this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating being held at a temperature above 700 c for at least 7 days in an oxidising regolith environment we report an approximate 40ar 39ar maximum age of 1 13 1 25 ga for an individual separated augite clast the disturbed nature of the spectra precludes precise age determination in section this clast is porous and contains iron oxide grains this shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts and has up to 25 fe3 fe we infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes after consolidation of the impact ejecta blanket high temperatures above 700 c may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut and in some cases surround the oxidised pyroxene however the veins could alternatively be the result of a hydrothermal event in the impact regolith a simple fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days low temperature hydrous alteration took place forming goethite identified via xrd xanes and ftir comparing with previous studies the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite

facies associations and controls on the evolution from a coastal bay to a lagoon system santa catarina coast brazil abstract the diverse holocene morphological features along the south coast of the state of santa catarina include lagoons and residual lakes a barrier a delta constructed by the tubarao river and pre existing incised valleys that have flooded and filled this scenario contains the sedimentary record of the transition from a bay to a lagoon system which occurred during the rise and subsequent semi stabilisation of the relative sea level during the holocene the geomorphological evolution of this area was investigated using a combination of morphology stratigraphic analysis of rotary push cores vibracores and trenches with radiocarbon dating taxonomic determination and taphonomic characterisation of holocene fossil molluscs palaeogeographic maps were constructed to illustrate how the bay evolved over the last 8000 years the relative sea level rise and local sedimentary processes were the prime forcing factors determining the depositional history and palaeogeographic changes the holocene sedimentary succession began between 8000 and 5700 cal bp with the deposits of transgressive sandsheets these deposits correspond to the initial marine flooding surface that was formed while the relative sea level rose at a higher rate than the input of sediments prior to the formation of the coastal barrier the change from a bay to a lagoon system occurred around 5700 and 2500 cal bp during the mid holocene highstand with the formation of the barrier and with the achievement of a balance between sea level rise and sedimentary supply until 2500 cal bp the presence of this barrier the following gentle decline in sea level and the initial emergence of back barrier features restricted the hydro dynamic circulation inside the bay and favoured an increase in the tubarao river delta progradation rate the final stage during the last 2500 years was marked by the increasing back barrier width with the establishment of salt marshes the arrival of the delta in the back barrier and the advance of aeolian dunes along the outer lagoon margins this study shed light on the mechanisms of coastal bay evolution in a setting existed prior to the beginning of barrier lagoon sedimentation

microstructure modifications of silicates induced by the collection in aerogel experimental approach and comparison with stardust results abstract particles from comet 81p wild 2 were captured with silica aerogel during the flyby stardust mission a significant part of the collection was damaged during the impact at hypervelocity in the aerogel in this study we conducted impact experiments into aerogel of olivine and pyroxene powder using a light gas gun in similar conditions as that of the comet wild 2 particles collection the shot samples were investigated using transmission electron microscopy to characterize their microstructure both olivine and pyroxene samples show evidence of thermal alteration due to friction with the aerogel all the grains have rounded edges after collection whereas their shape was angular in the initial shot powder set this is probably associated with mass loss of particles the rims of the grains are clearly melted and mixed with aerogel the core of olivine grains is fairly well preserved but some grains contain dislocations in glide configuration we interpret these dislocations as generated by the thermal stresses that have emerged due to the high temperature gradients between the core and the rim of the grains most of the pyroxene grains have been fully melted their high silica concentration reflects a strong impregnation with melted aerogel the preferential melting of pyroxene compared with olivine is due to a difference in melting temperatures of 300 this melting point difference probably induces a bias in the measurements of the ratio olivine pyroxene in the wild 2 comet the proportion of pyroxene was probably higher on wild 2 than expected from the samples collected into aerogel

late pleistocene barrier island development reconstructed from genetic classification and timing of erosional surfaces paleo tokyo bay japan abstract formative processes of a retrogradational barrier island system and associated transgressive erosional surfaces are reconstructed from the upper pleistocene kioroshi formation developed in paleo tokyo bay japan the kioroshi formation provides high quality sedimentary records of a preserved barrier island system three volcanic ash beds intercalated in the formation provide a high resolution chronostratigraphic framework the barrier island system of the kioroshi formation developed in a glacio eustatically forced sea level cycle during oxygen isotope stages 6 to 5e in the early stage of the transgression paleo tokyo bay was non barred and was exposed to the pacific ocean affected by open ocean wave processes shoreface erosion in such a non barred environment developed a wave ravinement surface rs1 rs1 overlies incised valley fill deposits formed in the earliest stage of the transgression and is overlain by shoreface deposits that are further overlain by embayment deposits such as lagoonal and flood tidal delta deposits formed during succeeding barrier development during the later stage of the same transgression associated with the formation and landward migration of the barrier chain tidal currents in tidal inlet and flood tidal deltas became active and a tidal ravinement surface trs was formed trs is developed on the base of tidal inlet and flood tidal delta deposits furthermore shoreface erosion on the open ocean side of the barrier chain eroded underlying embayment deposits and formed a secondary wave ravinement surface rs2 a chronostratigraphic surface in embayment deposits defined by a volcanic ash bed intersects trs and is eroded by rs2 this relationship together with associated facies architecture indicates diachroneity of the formation of these marine erosional surfaces associated with the retrogradational barrier island system

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

continuous wavelet transform theoretical aspects and application to aeromagnetic data at the huanghua depression dagang oilfield china we use the continuous wavelet transform based on complex morlet wavelets which has been developed to estimate the source distribution of potential fields for magnetic anomalies of adjacent sources they always superimpose upon each other in space and wavenumber making the identification of magnetic sources problematic therefore a scale normalization factor a n is introduced on the wavelet coefficients to improve resolution in the scalogram by theoretical modelling we set up an approximate linear relationship between the pseudo wavenumber and source depth the influences of background field random noise and magnetization inclination on the continuous wavelet transform of magnetic anomalies are also discussed and compared with the short time fourier transform results synthetic examples indicate that the regional trend has little effect on our method while the influence of random noise is mainly imposed on shallower sources with higher wavenumbers the source horizontal position will be affected by the change of magnetization direction whereas the source depth remains unchanged after discussing the performance of our method by showing the results of various synthetic tests we use this method on the aeromagnetic data of the huanghua depression in central china to define the distribution of volcanic rocks the spectrum slices in different scales are used to determine horizontal positions of volcanic rocks and their source depths are estimated from the modulus maxima of complex coefficients which is in good accordance with drilling results

an insight into subterranean flow proposition around alleppey mudbank coastal sector kerala india inferences from the subsurface profiles of ground penetrating radar the mudbank formation along south western indian coast has been a scintillating phenomenon during monsoon season and the source of mud is a debatable issue till now in the midst of many hypotheses the subterranean passage is considered a possible one but needs to have supportive scientific evidence this present study endeavours to demonstrate the potential use of the ground penetrating radar gpr in generating subsurface information to locate buried paleochannels in coastal zone which could act as the conduit for transport of mud from terrestrial sources to sea the historical maps of the late 1600 s show that the present day vembanad lake was a part of the nearshore area and the coastline was nearly 60 km inside drained by the rivers from the western ghats due to shoreline migration towards the seaside since late holocene the present day landforms came to existence while the earlier channels got buried under recent sand nearly 500 m long gpr subsurface 6 m depth penetration profile was generated and various paleochannels were traced these buried channels were categorised based on the pattern of their occurrences two erosional surfaces at around 1 and 2 m were mapped and their controls on paleochannels were derived during phase i many paleochannels were in active condition and due to heavy deposition during phase ii though these channels managed to maintain themselves but the width of their courses got narrowed and in recent times they got filled up and buried the pre monsoon and monsoon gpr profiles signify the high degree of wetness characteristics of these buried channels during monsoon season and their possibility of being passages for possible transport of water charged with fine clay materials through the unconsolidated in filled material in these buried channels this demonstrative and first hand subsurface information through gpr studies would further support to facilitate in consolidating the subsurface evidence for strengthening the subterranean passage concept in the mudbank area of the south western coast of india

mechanics and rates of tidal inlet migration modeling and application to natural examples tidal inlets on barrier coasts can migrate alongshore hundreds of meters per year often presenting great management and engineering challenges here we perform model experiments with migrating tidal inlets in delft3d swan to investigate the mechanics and rates of inlet migration model experiments with obliquely approaching waves suggest that tidal inlet migration occurs due to three mechanisms 1 littoral sediment deposition along the updrift inlet bank 2 wave driven sediment transport preferentially eroding the downdrift bank of the inlet and 3 flood tide driven flow preferentially cutting along the downdrift inlet bank because it is less obstructed by flood tidal delta deposits to quantify tidal inlet migration we propose and apply a simple mass balance framework of sediment fluxes around inlets that includes alongshore sediment bypassing and flood tidal delta deposition in model experiments both updrift littoral sediment and the eroded downdrift inlet bank are sediment sources to the growing updrift barrier and the flood tidal delta such that tidal inlets can be net sink of up to 150 of the littoral sediment flux our mass balance framework demonstrates how with flood tidal deltas acting as a littoral sediment sink migrating tidal inlets can drive erosion of the downdrift barrier beach parameterizing model experiments we propose a predictive model of tidal inlet migration rates based upon the relative momentum flux of the inlet jet and the alongshore radiation stress we then compare these predicted migration rates to 22 natural tidal inlets along the u s east coast and find good agreement

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 fall recovery orbit and composition of the tagish lake meteorite a new type of carbonaceous chondrite the preatmospheric mass of the tagish lake meteoroid was about 200 000 kilograms its calculated orbit indicates affinity to the apollo asteroids with a semimajor axis in the middle of the asteroid belt consistent with a linkage to low albedo c d and p type asteroids the mineralogy oxygen isotope and bulk chemical composition of recovered samples of the tagish lake meteorite are intermediate between cm and ci meteorites these data suggest that the tagish lake meteorite may be one of the most primitive solar system materials yet studied

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

radar enabled recovery of the sutter s mill meteorite a carbonaceous chondrite regolith breccia doppler weather radar imaging enabled the rapid recovery of the sutter s mill meteorite after a rare 4 kiloton of tnt equivalent asteroid impact over the foothills of the sierra nevada in northern california the recovered meteorites survived a record high speed entry of 28 6 kilometers per second from an orbit close to that of jupiter family comets tisserand s parameter 2 8 0 3 sutter s mill is a regolith breccia composed of cm mighei type carbonaceous chondrite and highly reduced xenolithic materials it exhibits considerable diversity of mineralogy petrography and isotope and organic chemistry resulting from a complex formation history of the parent body surface that diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to c class asteroids are interpreted

carbonate compositions in cm and ci chondrites and implications for aqueous alteration abstract carbonate minerals in fourteen cm chondrites and two ci chondrites have been analyzed by electron microprobe to provide a better understanding of the aqueous processes that affected carbonaceous chondrite parent bodies calcites in cm chondrites and dolomites and magnesites in ci chondrites display the compositions expected of stable phases formed at low temperatures dolomites in cm chondrites identified here for the first time in five members of the group have small amounts of excess ca which may reflect metastable growth the distribution of fe between dolomite and coexisting serpentine differs in the two chondrite groups if the distributions reflect an approach to chemical equilibrium then the difference implies higher alteration temperatures for the ci group than the cm group in agreement with the results of previously published oxygen isotope thermometry and mineral solubility modeling of the alteration process dolomite fe contents are relatively uniform in the two chondrite groups dolomite mn contents by contrast vary widely the variations may reflect transport controlled coprecipitation of mn resulting from a heterogeneous distribution of the element in the anhydrous precursor material if this interpretation is correct then the altering fluids were essentially immobile while hydration reactions proceeded on the meteorite parent bodies the near closed system character of the alteration process long known from bulk chemical analyses of the meteorites is a direct consequence of the limited mobility of dissolved species

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

progressive aqueous alteration of cm carbonaceous chondrites abstract cm chondrites are aqueously altered rocks that contain 9 wt h 2 o i e indigenous water bound in phyllosilicates also present are clumps of serpentine tochilinite intergrowths previously called poorly characterized phases or pcp pentlandite and ni bearing pyrrhotite we studied 11 cm chondrites that span the known range from least altered to most altered we used various petrologic properties many previously identified that provide information regarding the degree of aqueous alteration there are no known unaltered or slightly altered cm chondrites e g rocks containing numerous chondrules with primary igneous glass some cm properties result from processes associated with early and intermediate stages of the alteration sequence i e hydration of matrix alteration of chondrule glass and production of large pcp clumps other petrologic properties reflect processes active throughout the alteration sequence these include oxidation of metallic fe ni alteration of chondrule phenocrysts changes in pcp composition reflecting an increase in the phyllosilicate sulfide ratio and changes in carbonate mineralogy reflecting the development of dolomite and complex carbonates at the expense of ca carbonate on the basis of these parameters we propose a numerical alteration sequence for cm chondrites because there are no known cm samples that display only incipient alteration the least altered sample was arbitrarily assigned to subtype 2 6 the most altered cm chondrites currently classified cm1 are assigned to subtype 2 0 these highly altered rocks have essentially no mafic silicates they contain chondrule pseudomorphs composed mainly of phyllosilicate however their bulk compositions are cm like and they are closer in texture to other c2 chondrites than to ci1 chondrites which lack chondrule pseudomorphs using several diagnostic criteria we assigned petrologic subtypes 0 1 to every cm chondrite in our study que 97990 cm2 6 murchison cm2 5 kivesvaara cm2 5 murray cm2 4 2 5 y 791198 cm2 4 que 99355 cm2 3 nogoya cm2 2 cold bokkeveld cm2 2 que 93005 cm2 1 lap 02277 cm2 0 met 01070 cm2 0 the proposed cm numerical alteration sequence improves upon the existing scheme of browning et al 1996 in that it does not require a complicated algorithm applied to electron microprobe data to determine the average matrix phyllosilicate composition the new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values new neutron activation analyses of que 97990 que 93005 met 01070 murchison and crescent together with literature data confirm the compositional uniformity of the cm group different degrees of alteration among cm chondrites do not lead to resolvable bulk compositional differences this suggests that the textural differences among individual cm chondrites reflect progressive alteration of similar hypothetical cm3 0 starting materials in different regions of the same parent body with minimal aqueous transport of materials over appreciable e g meters distances

terminal particle from stardust track 130 probable al rich chondrule fragment from comet wild 2 abstract a 4 6 m terminal particle from stardust track 130 named bidi is composed of a refractory assemblage of fo 97 olivine al and ti bearing clinopyroxene and anorthite feldspar an 97 mineralogically bidi resembles a number of components found in primitive chondritic meteorites including al rich chondrules plagioclase bearing type i ferromagnesian chondrules and amoeboid olivine aggregates aoas measured widths of augite pigeonite lamellae in the clinopyroxene indicate fast cooling rates suggesting that bidi is more likely to be a chondrule fragment than an aoa bulk element concentrations including an al 2 o 3 content of 10 2 wt further suggests that bidi is more akin to al rich rather than ferromagnesian chondrules this is supported by high anorthite content of the plagioclase feldspar overall bulk composition and petrogenetic analysis using a cosmochemical al 2 o 3 ca 2 sio 4 mg 2 sio 4 phase diagram measured minor element abundances of individual minerals in bidi generally support an al rich chondrule origin but are not definitive between any of the object types oxygen isotope ratios obtained from olivine minor high ca pyroxene fall between the tf and ccam lines and overlap similar minerals from chondrules in primitive chondrites but are generally distinct from pristine aoa minerals oxygen isotope ratios are similar to some minerals from both al rich and type i ferromagnesian chondrules in unequilibrated carbonaceous enstatite and ordinary chondrites although no single piece of evidence uniquely identifies bidi as a particular object type the preponderance of data including mineral assemblage bulk composition mineral chemistry inferred cooling rates and oxygen isotope ratios suggest that bidi is more closely matched to al rich chondrules than aoas or plagioclase bearing type i ferromagnesian chondrules and likely originated in a chondrule forming region in the inner solar system

seismic stratigraphic framework of the continental shelf offshore delmarva u s a implications for mid atlantic bight evolution since the pliocene abstract understanding how past coastal systems have evolved is critical to predicting future coastal change using over 12 000 trackline kilometers of recently collected co located multi channel boomer sparker and chirp seismic reflection profile data integrated with previously collected borehole and vibracore data we define the upper

can barrier islands survive sea level rise quantifying the relative role of tidal inlets and overwash deposition barrier island response to sea level rise depends on their ability to transgress and move sediment onto and behind the barrier either through flood tidal delta deposition or via overwash our understanding of these processes over decadal or longer timescales however is limited here we use a recently developed barrier island model brie to better understand the interplay between tidal dynamics overwash fluxes and sea level rise on barrier coasts and barrier island stratigraphy model results suggest that in microtidal environments with large alongshore sediment transport fluxes tidal inlets are ephemeral and migrate rapidly these conditions lead to effective deposition of flood tidal deltas and allow inlets to constitute most of the landward sediment flux whether barrier islands can survive sea level rise depends on the combined landward sediment flux from overwash and flood tidal delta deposition likely making barrier islands with artificially stabilized inlets via jetty construction or maintenance dredging more vulnerable to sea level rise

ferric saponite and serpentine in the nakhlite martian meteorites abstract transmission electron microscopy and fe k x ray absorption spectroscopy have been used to determine structure and ferric content of the secondary phase mineral assemblages in the nakhlite martian meteorites nwa 998 lafayette nakhla gv y 000593 y 000749 mil 03346 nwa 817 and nwa 5790 the secondary phases are a rapidly cooled metastable assemblage that has preserved mg and ca fractionation related to distance from the fluid source for most of the nakhlites though one nwa 5790 appears not to have experienced a fluid pathway all nine nakhlite samples have also been analysed with scanning electron microscopy electron probe micro analysis bright field high resolution transmission electron microscopy hrtem and selected area electron diffraction by measuring the energy position of the fe k xanes 1 s 3 d pre edge transition centroid we calculate the ferric content of the minerals within the nakhlite meteorites the crystalline phyllosilicates and amorphous silicate of the hydrothermal deposits filling the olivine fractures are found to have variable fe 3 fe values ranging from 0 4 to 0 9 in lafayette the central silicate gel parts of the veins are more ferric than the phyllosilicates around it showing that the fluid became increasingly oxidised the mesostasis of lafayette and nwa 817 also have phyllosilicate which have a higher ferric content than the olivine fracture deposits with fe 3 fe values of up to 1 0 further study via tem analyses reveal the lafayette and nwa 817 olivine phyllosilicates to have 2 1 t o t lattice structure with a the d 001 spacing of 0 96 nm whereas the lafayette mesostasis phyllosilicates have 1 1 t o structure with d 001 spacings of 0 7 nm based on our analyses the phyllosilicate found within the lafayette olivine fractures is trioctahedral ferric saponite ca 0 2 k 0 1 0 3 mg 2 6 fe 2 1 3 fe 3 1 7 mn 0 1 5 7 si 6 7 al iv 0 9 fe 3 0 4 8 0 o 20 oh 4 n h 2 o and that found in the mesostasis fractures is an fe serpentine ca 0 1 mg 0 7 fe 3 1 0 al vi 0 4 2 2 si 2 o 5 oh 4 with a ferric gel of similar composition in lafayette and found as fracture fills throughout the other nakhlites

geological inheritance and its role in the geomorphological and sedimentological evolution of bedrock hosted incised valleys lake st lucia south africa abstract the morphology of lake st lucia africa s largest estuary has been strongly influenced by antecedent topography throughout its quaternary evolution the 5 20 km southern basin is bounded to landward by a 50 m high early mid pleistocene dune ridge and to seaward by a 100 m high late pleistocene holocene dune barrier nine seismic units a i are identified in the enclosed basin along with two regionally developed sequence boundaries sb1 and sb2 and two tidal ravinement surfaces trs1 and trs2 the lowermost sequence boundary sb1 is related to regional late pliocene hinterland uplift sb2 is related to the last glacial maximum lgm when sea levels fell 130 m below present lowstand fluvial sediments occupy the base of both sb1 and sb2 incisions thick central basin deposits dominate the valley fills more so in the pliocene age valleys the occurrence and thickness of which is attributed to sheltering by a seaward barrier dune system as well as to the low gradient settings prograding tidal bedforms occupy the minor incisions formed within the tidal ravinement surfaces marking the onset of lagoonal conditions in the area the system is capped by lagoonal deposits deposited above tidal flats a series of prograding spits mark the early stages of lagoonal segmentation in the holocene the preservation of only one incision and fill sequence prior to the development of an lgm aged valley succession is attributed to geological inheritance whereby older valleys were repeatedly re incised by younger valleys throughout the pleistocene causing partial preservation of pleistocene fills up to the most recent cycle the older fill remnant relates to a larger magnitude base level fall prior to the quaternary which survived erosion during subsequent sea level falls adjacent topography in the form of rocky cliffs and the seaward fronting barrier limit the accommodation space in which infilling material can be hosted outside the major valley network the competent basement rock into which these valleys have incised protected lowstand fluvial sediments from subsequent tidal ravinement

modeling hydrodynamics of large lagoons insights from the albemarle pamlico estuarine system abstract large estuaries are influenced by winds over adjacent coastal ocean and land areas causing significant spatial variations in water levels currents and surface waves in this study we apply a numerical model to simulate hydrodynamics and waves in the albemarle pamlico estuarine system a large and shallow back barrier basin in eastern north carolina over a one month study period september 2008 with observations from several storm wind events of differing time scales and directions model performance is evaluated for a spatially varying wind field from the north american regional reanalysis narr dataset in comparison to spatially uniform forcing from wind observations at offshore coastal and land based sites across the region a spatially uniform wind field from offshore winds observations results in statistically better hydrodynamic simulations of water levels r 0 88 in the estuaries than narr r 0 48 after comparison with measurements and indicates the importance of strong marine winds over most of the estuary surface area the influence of a prominent bathymetric feature on hydrodynamics in pamlico sound is also investigated by numerically removing a 30 km long and 2 3 m deep shoal from the model grid and replacing it with an idealized depth of 6 m the removal of the shoal increases water level setup by 14 at the estuarine shoreline decreases current magnitudes by up to 40 in the shoal region and increases significant wave heights locally by up to 25 in the sound indicating the importance of this relict geomorphic feature as a major control on the hydrodynamic response of the system during wind events the results suggest that increasing the water depth over the shoal can lead to higher storm surges and wave heights with the possibility of increased inundation and erosion of the back barrier and mainland coastal regions the complex bathymetry and marine wind influence are critical input conditions for modeling large and shallow lagoonal estuaries like the albemarle pamlico estuarine system

extended late holocene relative sea level histories for north carolina usa abstract we produced 3000 year long relative sea level rsl histories for two sites in north carolina usa using foraminifera preserved in new and existing cores of dated salt marsh sediment at cedar island rsl rose by 2 4 m during the past 3000 years compared to 3 3 m at roanoke island this spatial difference arises primarily from differential gia that caused late holocene rsl rise to be 0 1 0 2 mm yr faster at roanoke island than at cedar island however a non linear difference in rsl between the two study regions particularly from 0 ce to 1250 ce indicates that additional local to regional scale processes drove centennial scale rsl change in north carolina therefore the cedar island and roanoke island records should be considered as independent of one another between site differences on sub millennial timescales cannot be adequately explained by non stationary tides sediment compaction or local sediment dynamics we propose that a period of accelerating rsl rise from 600 ce to 1100 ce that is present at roanoke island and other sites north of cape hatteras at least as far as connecticut but absent at cedar island and other sites south of cape hatteras at least as far as northeastern florida is a local to regional scale effect of dynamic ocean and or atmospheric circulation

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

evidence for aqueous activity on comet 81p wild 2 from sulfide mineral assemblages in stardust samples and ci chondrites abstract the discovery of nickel copper and zinc bearing iron sulfides from comet 81p wild 2 wild 2 represents the strongest evidence in the stardust collection of grains that formed in an aqueous environment we investigated three microtomed tem sections which contain crystalline sulfide assemblages from wild 2 and twelve thin sections of the hydrothermally altered ci chondrite orgueil detailed structural and compositional characterizations of the sulfide grains from both collections reveal striking similarities the stardust samples include a cubanite cufe 2 s 3 grain a pyrrhotite fe ni 1 x s pentlandite fe ni 9 s 8 assemblage and a pyrrhotite sphalerite fe zn s assemblage similarly the ci chondrite sulfides include individual cubanite and pyrrhotite grains cubanite pyrrhotite assemblages pyrrhotite pentlandite assemblages as well as possible sphalerite inclusions within pyrrhotite grains the cubanite is the low temperature orthorhombic form which constrains temperature to a maximum of 210 c the stardust and orgueil pyrrhotites are the 4c monoclinic polytype which is not stable above 250 c the combinations of cubanite and pyrrhotite as well as pyrrhotite and pentlandite signify even lower temperatures the crystal structures compositions and petrographic relationships of these sulfides constrain formation and alteration conditions taken together these constraints attest to low temperature hydrothermal processing our analyses of these minerals provide constraints on large scale issues such as heat sources in the comet forming region aqueous activity on cometary bodies and the extent and mechanisms of radial mixing of material in the early nebula the sulfides in the wild 2 collection are most likely the products of low temperature aqueous alteration they provide evidence of radial mixing of material e g cubanite troilite from the inner solar system to the comet forming region and possible secondary aqueous processing on the cometary body

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

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2

a refractory inclusion returned by stardust from comet 81p wild 2 among the samples returned from comet 81p wild 2 by the stardust spacecraft is a suite of particles from one impact track track 25 that are ca al rich and feo free we studied three particles from this track that range in size from 5 3 x 3 2 m to 15 x 10 m scanning and transmission electron microscopy show that they consist of very fine grained typically from 0 5 to 2 m al rich ti bearing and ti free clinopyroxene mg al spinel and anorthite with trace amounts of fine perovskite feni metal and osbornite tin grains in addition to these phases the terminal particle named inti also contains melilite all of these phases with the exception of osbornite are common in refractory inclusions and are predicted to condense at high temperature from a gas of solar composition osbornite though very rare has also been found in meteoritic refractory inclusions and could have formed in a region of the nebula where carbon became enriched relative to oxygen compared to solar composition compositions of ti pyroxene in inti are similar but not identical to those of fassaite from allende inclusions electron energy loss spectroscopy shows that ti rich pyroxene in inti has ti3 ti4 within the range of typical meteoritic fassaite consistent with formation under reducing conditions comparable to those of a system of solar composition inti is 16o rich with 18o 17o 40 like unaltered phases in refractory inclusions and refractory idps with grain sizes mineralogy mineral chemistry and an oxygen isotopic composition like those of refractory inclusions we conclude that inti is a refractory inclusion that formed in the inner solar nebula identification of a particle that formed in the inner solar system among the comet samples demonstrates that there was transport of materials from the inner to the outer nebula probably either in a bipolar outflow or by turbulence

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

depositional controls on a hypertidal barrier spit system architecture and evolution pointe du banc spit north western france physical stratigraphy architecture and evolution of barrier systems in hypertidal environments tidal range above 6 m are understudied and depositional controls are poorly understood compared with wave dominated barrier systems and barrier spits in microtidal mesotidal and macrotidal settings based on vibracores ground penetrating radar radiocarbon and optically stimulated luminescence age data the formation and evolution of the hypertidal barrier system of pointe du banc north western france has been reconstructed the study shows that the barrier spit has a complex composite sedimentary architecture consisting of wave dominated and tide dominated sedimentary bodies a morpho sedimentary model is presented that demonstrates how barrier spit progradation resulting from littoral drift was the main manner of spit elongation whereas sediment convergence caused by landward migration of swash bars and seaward migration of tidal dunes caused the spit terminus to grow in height and width these results suggest that long term accretion rates varied considerably in response to changes in sediment supply variations in storminess together with the large scale topography of the coast controlled the sediment supply and thus the evolution of the barrier system during latest holocene despite architectural complexity hypertidal barrier systems preserve records of past climate changes

mineralogy and petrology of stardust particles encased in the bulb of track 80 tem investigation of the wild 2 fine grained material abstract we have characterized by transmission electron microscopy the mineralogy of samples extracted from the walls of the stardust track 80 more than 500 fragments were studied using conventional imaging electron diffraction and edx microanalysis two categories of particles are distinguishable in equal proportions wt the first one is comprised of relatively large crystalline grains 1 m on average dominated by silicates olivine and pyroxene they display a wide range of compositions and microstructures comparable to those found in terminal particles minor phases including magnetite and apatite are also present their occurrence suggests that the wild 2 material underwent aqueous alteration to some extent the second type of particle called gems like material is made of silica rich glassy clumps embedding iron sulfide beads and vesicles their microstructure is characteristic of thermally modified particles that have suffered strong interaction with the silica aerogel during the hypervelocity impact this melted material may form by shedding of melted and vaporized material but given the shape of the impact track and high diversity of surviving mineral compositions much of it originated from fine grained aggregates that disaggregated during the collection chemical mapping at the nano scale allowed the localization of individual components within the silica rich glass they are dominated by mg rich components with a size less than 300 nm the average composition of this thermally modified material is close to the solar abundance for the major elements fe mg and s the fine grained material has probably not been chemically fractionated in the protoplanetary disk before its incorporation in comet wild 2 unlike the sulfur depleted matrix of chondrites from these two categories of particles we deduce that wild 2 is likely made of an assemblage of relatively large evolved grains first category cemented by a fine grained material with primitive chemistry second category the pre impact configuration of the incident material deduced from this study seems comparable to the matrix of the most primitive chondrites 3 0 or to chondritic porous interplanetary dust particles

neoichnology of a barrier island system the mula di muggia grado lagoon italy abstract barrier islands are common landforms and biodiverse habitats yet they received scarce neoichnological attention this gap is tackled by studying the mula di muggia barrier island system grado lagoon italy focusing on morphology ecology and ethology of individual traces the following incipient ichnotaxa are identified archaeonassa arenicolites bergaueria diverging shafts helminthoidichnites lockeia macanopsis monocraterion nereites parmaichnus polykladichnus skolithos thalassinoides and squat burrows vertebrate avipeda ardeipeda like canipeda and invertebrate tracks parallel furrows are also described for each ichnotaxon tracemaker and behavior are discussed together with their position with respect to sediment barriers results suggest that sediment barriers impose a sharp contrast in terms of ichnological composition back barrier is dominated by branched burrows i e thalassinoides parmaichnus while the fore barrier presents vertical and u shaped burrows arenicolites skolithos the environmental conditions of the back barrier show that low oxygen substrates favor intense bioturbation provided that the water column is sufficiently oxygenated

wavelet spectral probe for seismic structure interpretation and fracture characterization a workflow with case studies conventional amplitude images are routinely and often exclusively used to interpret subsurface structures however the amplitude images are composite seismic response to various geologic features at different scales the interference makes it difficult to investigate structural details that are not visually discernible in the amplitude images this paper presents a new algorithmic workflow to unravel seismic structural details by differentiating waveform characteristics at varying scales using a wavelet model as a spectral probe the algorithm performs a least squares linear regression between the model and data at each sample location to calculate the absolute correlation coefficient the resulting absolute correlation coefficient attribute which is indicative of instantaneous waveform similarity relative to the wavelet spectral probe provides a superior image with enhanced precision and resolution of the structural grain two case studies in the powder river and the appalachian basins demonstrate that the new algorithm helps investigate kinematic relationships among structural elements and differentiate between structural styles in particular the algorithm helps better define the along strike structural variation and segmentation associated with cross strike lineaments in the foreland basins comparative analysis indicates that the wavelet spectral probe algorithm helps shed new light on subtle but critical structural fabrics not easily discernible from conventional amplitude images revealing such information has important implications for better defining basin structural complexities and reservoir heterogeneity detecting faults and fractures at different scales and modeling fractured reservoirs

mn cr ages of dolomites in ci chondrites and the tagish lake ungrouped carbonaceous chondrite abstract 53 mn 53 cr ages have been measured for dolomites in three ci chondrites and an ungrouped c2 chondrite tagish lake for an accurate age determination we utilized in contrast to previous works a matrix matched carbonate standard to appropriately correct the observed mn cr ratios the mn cr data of the dolomites most likely represent isochrons with chronological significances and the obtained ages are concentrated in 4563 8 4562 5 million years ago 4 4 5 7 million years after the birth of the solar system the ages of the ci and tagish lake dolomites are very similar to those of carbonates in cm chondrites although ci and cm chondrites are likely to have different alteration histories the similar carbonate ages in various carbonaceous chondrites suggest that the aqueous activities in hydrous asteroids initiated almost concurrently if this is the case the most plausible heat source for the aqueous alteration is the decay energy of short lived radionuclides especially 26 al we carried out a model calculation for the thermal history of the ci chondrite parent body assuming that 26 al is the dominant heat source by two different approaches to estimate the accretion time of the ci chondrite parent body we conclude that it accreted 3 0 3 9 million years after the birth of the solar system this is also likely to be the case for the cm chondrite and tagish lake parent bodies because the result of the calculation is not sensitive to the ice abundance therefore we stress that near the condensation front of water ice meteorite parent bodies with abundant ice accreted almost simultaneously at 3 4 million years after cai formation combining our mn cr ages of the dolomites with those of breunnerites reported previously the youngest one is 4554 6 million years ago we found that the aqueous alteration in the ci chondrite parent body lasted for at least 9 million years therefore the parent body should be large enough 50 km in radius so that the internal heat had been kept for 9 million years

review of electromagnetic induction for mapping barrier island framework geology abstract the geologic framework controls on modern barrier island transgression and the relationship of these controls to subsurface structure hydrology and island geomorphology are not well understood recent evidence suggests that alongshore variations in pre holocene geology of barrier islands modify nearshore hydrodynamic processes and sediment transport ultimately affecting how barrier islands will respond to relative sea level rise explorations of holocene barrier island geology are usually based on cores to supplement bathymetric onshore offshore seismic and or ground penetrating radar gpr surveys the advantages and limitations of these methods with respect to barrier island investigations are briefly described in this review alternative near surface geophysical methods including electromagnetic induction emi sensors are increasingly being used for coastal research because they are non invasive provide continuous subsurface information across a variety of sub environments and are capable of characterizing large areas in a short time although these emi sensors have shown promise in coastal applications a number of issues primarily related to subsurface hydrology need to be addressed to fully assess the limitations of this technique this paper reviews the theory methodology and applications of emi in support of geologic framework studies with particular reference to barrier islands resolution of these issues will allow emi sensors to complement and offer significant advantages over traditional methods in support of an improved understanding of large scale barrier island evolution

frequency estimates of seismic traces local estimates of amplitude frequency and phase have been used in the past to characterize seismic data in particular these attributes have sometimes been successfully related to well attributes at the reservoir scale net pay thickness sand fraction etc this paper introduces a method called sinfit for computing local amplitude frequency and phase estimates of seismic traces over short time windows the sinfit method uses a sine curve fitting approach the method is shown to give more accurate and robust frequency estimates than four other common methods on a set of test traces where the true frequency components are known the four methods compared with sinfit are instantaneous frequency zero crossings short time fourier analysis and a more recent time frequency method called aok in a field case with fluvial sands an average frequency over a 30 ms time window of seismic data correlates with estimated shale volume from well logs the sinfit method gives an average frequency attribute that more strongly correlates with shale volume than corresponding attributes from any of the other four methods

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

evidence for low temperature growth of fayalite and hedenbergite in macalpine hills 88107 an ungrouped carbonaceous chondrite related to the cm co clan the carbonaceous chondrite macalpine hills mac 88107 has bulk composition and mineralogy that are intermediate between those of co and cm chondrites this meteorite experienced minor alteration and a low degree of thermal metamorphism petrologic type 3 1 and escaped post accretional brecciation the alteration resulted in the formation of fayalite fa90 100 al free hedenbergite fs50wo50 phyllosilicates saponite serpentine intergrowths magnetite and ni bearing sulfides pyrrhotite and pentlandite fayalite and hedenbergite typically occur as veins which start at the opaque nodules in the chondrule peripheries crosscut fine grained rims and either terminate at the boundaries with the neighboring fine grained rims or continue as layers between these rims these observations suggest that fayalite and hedenbergite crystallized after accretion and compaction of the fine grained rims fayalite also overgrows isolated forsteritic fa1 5 and fayalitic fa20 40 olivine grains without any evidence for fe mg interdiffusion it also replaces massive magnetite sulfide grains the initial 53mn 55mn ratio of 1 58 0 26 10 6 in the mac 88107 fayalite corresponds to an age difference between the formation of fayalite and refractory inclusions in allende of either 9 or 18 ma depending upon the value of the solar system initial abundance of 53mn used in age calculations formation of secondary fayalite and hedenbergite requires mobilization and transport of ca si and fe either through a high temperature gaseous phase hua and buseck 1995 or low temperature aqueous solution krot et al 1998a b the high temperature nebular model for the origin of fayalite hua and buseck 1995 fails to explain a formation of fayalite hedenbergite assemblages after accretion of fine grained rims that lack any evidence for high temperature processing b extreme fractionation of refractory lithophile elements of similar volatility ca and al in hedenbergite and c absence of fe mg interdiffusion along fayalite forsterite boundaries we conclude that fayalite and hedenbergite in mac 88107 formed during late stage low temperature approximately 150 200 c aqueous alteration the data for mac 88107 extend the evidence for an early onset of aqueous activity on chondrite parent bodies and reinforce the conclusion that liquid water played an important role in the chemical and mineralogical evolution of the first chondritic planetesimals

origin of magnetite in oxidized cv chondrites in situ measurement of oxygen isotope compositions of allende magnetite and olivine magnetite in the oxidized cv chondrite allende mainly occurs as spherical nodules in porphyritic olivine po chondrules where it is associated with ni rich metal and or sulfides to help constrain the origin of the magnetite we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in po chondrules of allende by an in situ ion microprobe technique five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18o values from 4 8 to 7 1 and delta 17o values from 2 9 to 6 3 seven coexisting olivine grains have oxygen isotopic compositions from 0 9 to 6 3 in delta 18o and from 4 6 to 7 9 in delta 17o the delta 17o values of the magnetite and coexisting olivine do not overlap they range from 0 4 to 2 6 and from 4 0 to 5 7 respectively thus the magnetite is not in isotopic equilibrium with the olivine in po chondrules implying that it formed after the chondrule formation the delta 17o of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas we infer that the magnetite formed on the parent asteroid by oxidation of metal by h2o which had previously experienced minor o isotope exchange with fine grained silicates

cumulative versus transient shoreline change dependencies on temporal and spatial scale using shoreline change measurements of two oceanside reaches of the north carolina outer banks usa we explore an existing premise that shoreline change on a sandy coast is a self affine signal wherein patterns of change are scale invariant wavelet analysis confirms that the mean variance spectral power of shoreline change can be approximated by a power law at alongshore scales from tens of meters up to 4 8 km however the possibility of a power law relationship does not necessarily reveal a unifying scale free dominant process and deviations from power law scaling at scales of kilometers to tens of kilometers may suggest further insights into shoreline change processes specifically the maximum of the variance in shoreline change and the scale at which that maximum occurs both increase when shoreline change is measured over longer time scales this suggests a temporal control on the magnitude of change possible at a given spatial scale and by extension that aggregation of shoreline change over time is an important component of large scale shifts in shoreline position we also find a consistent difference in variance magnitude between the two survey reaches at large spatial scales which may be related to differences in oceanographic forcing conditions or may involve hydrodynamic interactions with nearshore geologic bathymetric structures overall the findings suggest that shoreline change at small spatial scales less than kilometers does not represent a peak in the shoreline change signal and that change at larger spatial scales dominates the signal emphasizing the need for studies that target long term large scale shoreline change

modal mineralogy of ci and ci like chondrites by x ray diffraction the ci chondrites are some of the most hydrated meteorites available to study making them ideal samples with which to investigate aqueous processes in the early solar system here we have used position sensitive detector x ray diffraction psd xrd to quantify the abundance of minerals in bulk samples of the ci chondrite falls alais orgueil and ivuna and the antarctic ci like chondrites y 82162 and y 980115 we find that alais orgueil and ivuna are dominated by a mixed serpentine saponite phyllosilicate 81 84 vol plus minor magnetite 6 10 sulphides 4 7 and carbonates 3 this reflects an extended period of aqueous alteration and the near complete transformation of anhydrous phases into a secondary mineral assemblage the similarity in total abundance of phyllosilicate suggests that the ci chondrites all experienced the same degree of aqueous alteration on the parent body in contrast y 82162 contains a highly disordered serpentine saponite phyllosilicate 68 vol sulphide 19 olivine 11 and magnetite 2 this mineralogy is distinct from that of the ci chondrites attesting to both a different starting mineralogy and alteration history the structure and relatively low abundance of the phyllosilicate and the high abundance of olivine are consistent with previous observations that y 82162 represents ci like material that following aqueous alteration suffered thermal metamorphism at temperatures 500 c similarly y 980115 contains disordered serpentine saponite 71 vol sulphide 19 olivine 8 and magnetite 2 confirming that it too is a thermally metamorphosed ci like chondrite we suggest that the ci like chondrites are derived from a different parent body than the ci chondrites which underwent short lived thermal metamorphism due to impacts and or solar radiation

carbonaceous xenoliths in the krymka ll3 1 chondrite mysteries and established facts abstract the results of a detailed study on mineralogy chemistry and the carbon and oxygen isotopes of two exotic krymka carbonaceous xenoliths are presented in this article the investigated xenoliths are metamorphosed and shocked and have the following characteristics which distinguish them from the krymka host 1 resemblance of their sio 2 mgo ratio to that of carbonaceous chondrites 2 higher fe content and feo feo mgo ratio 3 lower concentration of si ca al and an enrichment of s and probably of ag 4 smaller sizes and lower content 10 vol of chondrules and their clasts and correspondingly higher content of matrix 5 dominance of porphyritic chondrules and lack of nonporphyritic chondrules 6 occurrence of an amoeboid olivine grain with 16 o rich composition 7 existence of carbon in three different forms graphite carbon rich material and organic compounds the bulk chemistry of the xenoliths is similar but not identical to that of carbonaceous chondrites suggesting that they represent a chondrite parent body that has not been previously sampled among any known type of meteoritic material the mineralogy of the xenoliths corresponds only to that of other krymka graphite containing xenoliths it differs however from the latter by having a lower grade of metamorphism we infer that metamorphism of the primary carbonaceous body of the xenoliths and or shock of the krymka parent body are responsible for the major metamorphic alteration of the xenoliths including the crystallization of graphite from primary organic compounds a comparison of the features of the krymka xenoliths with the inferred characteristics of cometary meteorites attests that their genetic relationship to cometary material remains highly inconclusive

constraints on the formation age of cometary material from the nasa stardust mission we measured the 26 al 26 mg isotope systematics of a 5 m refractory particle coki returned from comet 81p wild 2 in order to relate the time scales of formation of cometary inclusions to their meteoritic counterparts the data show no evidence of radiogenic 26 mg and define an upper limit to the abundance of 26 al at the time of particle formation of 26 al 27 al 5 the absence of 26 al indicates coki formed 1 7 ma after the oldest solar system solids ca al rich inclusions cais the data presented here suggest that high temperature inner solar system material formed was subsequently transferred to the kuiper belt and incorporated into comets several million years following cai formation

mineralogy and texture of fe ni sulfides in ci1 chondrites clues to the extent of aqueous alteration on the ci1 parent body to better understand the role of aqueous alteration on the ci1 parent body we have analyzed the texture composition and mineral associations of iron nickel sulfides in four of the five known ci1 chondrites the most commonly occurring sulfide present in the ci1 chondrites is the iron deficient fe ni sulfide pyrrhotite fe ni 1 xs that has a composition close to that of stoichiometric troilite fes three of the ci1s alais ivuna and tonk also contain pentlandite fe ni 9s8 although pentlandite is a rare phase in ivuna cubanite cufe2s3 was found in both alais and ivuna in this study although it has also been reported in orgueil macdougall and kerridge 1977 the pyrrhotite grains in all four chondrites form hexagonal rectangular or irregular shapes and show no evidence of ni or co zoning the pyrrhotite grains in orgueil and ivuna are in general smaller and show more corrosions or embayments than those in alais or tonk we suggest that the precursor sulfide present in the ci1 chondrites was troilite which during brecciation and oxidation on the parent body at a temperature of 100 c or less converted the troilite to magnetite and pyrrhotite with pentlandite inclusions subsequently continued alteration on the parent body removed pentlandite partially from alais tonk and ivuna completely from orgueil leaving behind pyrrhotite with spaces corrosions where the pentlandite had been ni derived from the pentlandite was incorporated into ferrihydrite onto the surface of which the ni na sulfate ni bloedite formed based on the size and abundant corrosions within pyrrhotite grains combined with observations from other authors we conclude that orgueil and ivuna have undergone a greater degree of alteration than alais and tonk further work is needed to assess the conditions under which pentlandite would be dissolved preferentially to pyrrhotite as the study of terrestrial literature indicates that the latter mineral is preferentially removed

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

a mossbauer spectroscopy and x ray diffraction study of ordinary chondrites quantification of modal mineralogy and implications for redox conditions during metamorphism we present a method that combines mssbauer spectroscopy and x ray diffraction to quantify the modal mineralogy of unequilibrated ordinary chondrites uocs despite being a fundamental tool in the interpretation of geological systems there are no modal mineralogical data available for these meteorites this is due to their fine grained nature highly heterogeneous silicate mineralogy and the presence of poorly characterized phases consequently it has not been possible to obtain accurate modal mineralogy by conventional techniques such as point counting here we use mssbauer spectroscopy as a preliminary identification technique and x ray diffraction provides the quantification for a suite of recent uoc falls we find the most primitive uocs to contain a significant amount of phyllosilicate material that was converted during metamorphism to form ferromagnesian silicates a complete suite of antarctic samples is analyzed by each method to observe mineralogical trends and these are compared with trends shown by recent falls the fact that mineralogical relationships shown by finds and falls are in agreement allows us to be confident that we are observing the products of pre terrestrial alteration mssbauer spectroscopy reveals evidence of steadily increasing reduction with metamorphism in the uocs because this technique allows comparisons to be made between uocs and eocs our reduction sequence can be combined with other evidence showing progressive oxidation in the eocs this yields an integrated model of changing redox conditions on equilibrating ordinary chondrite parent bodies

secondary calcium iron rich minerals in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions we have characterized ca fe rich silicates salite hedenbergite pyroxenes fs10 50wo45 50 andradite ca3fe2si3o12 kirschsteinite cafesio4 and wollastonite ca3si3o9 in the type i chondrules and matrices in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions in type i chondrules in the bali like cv3 chondrites metal is oxidized to magnetite magnetite sulfide nodules are replaced by ca fe rich pyroxenes with minor andradite and pure fayalite we infer that ca fe rich pyroxenes andradite fayalite magnetite and phyllosilicates which occur in mesostases formed at relatively low temperatures 300 c in the presence of aqueous solutions thermodynamic analysis of phase relations in the si fe ca o h system and large o isotopic fractionation of the coexisting magnetite and fayalite 20 krot et al 1998 are consistent with this interpretation in type i chondrules in the allende like cv3 chondrites and dark inclusions magnetite sulfide nodules are replaced by ca fe rich pyroxenes and ferrous olivine low ca pyroxene and forsterite phenocrysts are rimmed and veined by ferrous olivine it appear that the ca fe rich pyroxenes predate formation of ferrous olivine the latter postdates formation of talc and biopyriboles brearley 1997 the allende dark inclusions are crosscut by ca fe pyroxene andradite veins and surrounded by ca rich rims that consist of ca fe rich pyroxenes andradite wollastonite and kirschsteinite calcium rich veins and rims formed after aggregation and lithification of the dark inclusions the rimmed dark inclusions show zoned depletion in ca which is due to a lower abundance of ca fe rich pyroxenes close to the rim calcium was probably leached from the inclusions and redeposited along their edges we infer that the allende like chondrites and dark inclusions experienced similar aqueous alteration to the bali like chondrites and were metamorphosed subsequently which resulted in loss of aqueous solutions and dehydration of phyllosilicates we conclude that ca fe rich silicates in the oxidized cv3 chondrites and allende dark inclusions are secondary and resulted from aqueous fluid rock interactions during progressive metamorphism of a heterogeneous mixture of hydrous ices and anhydrous materials the latter were possibly mineralogically similar to the reduced cv3 chondrites

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

modal mineralogy of carbonaceous chondrites by x ray diffraction and mossbauer spectroscopy carbonaceous chondrites are among the most analyzed geological materials on earth however despite this attention and unlike most terrestrial rocks little is known on the abundance of individual phases within them here we show how a combination of several novel x ray diffraction xrd techniques including a high brightness x ray microsource and mssbauer spectroscopy allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated fine grained chondrites for all minerals of abundance 1 wt knowledge of the modal mineralogy of a sample also allows us to calculate grain density we analyzed allende murchison tagish lake and orgueil based on our modal data the grain density estimates for allende murchison and orgueil are close to literature values in the case of tagish lake there is no published grain density although a bulk density measurement does exist taking our estimate of grain density and the measured bulk density we calculate an exceptionally high porosity of 41 for this meteorite similar to some chondritic idps and in line with a porosity calculated from an entry model for the tagish lake fireball although it is an oxidized cv magnetite is present in allende at a level of 0 5 wt or 0 3 vol a result that is substantiated by several other instrumental studies this may be an oxidized meteorite but that oxidation is not manifested in abundant magnetite in addition we note appreciable fayalitic olivine in orgueil detected by both xrd and mossbauer we employed microsource xrd to look at heterogeneity in mineral abundance in orgueil and found substantial variation with phyllosilicates varying inversely with olivine the data suggest that orgueil was initially composed primarily of anhydrous materials which have been partially but not completely altered although the data are preliminary comparison between our xrd modal assessment bulk chemistry grain density and mossbauer data suggests that our estimates of mineral abundance are robust the advent of microsource xrd allows similar modal data to be acquired from samples as small as a few hundred micrograms

three dimensional observation of carbonaceous chondrites by synchrotron radiation x ray ct quantitative analysis and developments for the future sample return missions abstract carbonaceous chondrites were observed by synchrotron radiation x ray computed tomography sr ct three dimensionally we analyzed the chemical composition of the components of the carbonaceous chondrites such as chondrules matrix and iron inclusions from the linear attenuation coefficient lac of x rays histograms of the lac were used for the analysis of chemical composition of the internal material and we could find a clear relation of the compositions between the chondrules and matrix we also analyzed the size distribution of low fe inclusions chondrules using image processing of ct images cumulative size distribution of chondrules shows power law distribution and slopes of the distribution changed for different chondrite classes results of these analyses show that the chondrule and matrix would have formed from the same precursor and were incorporated into the parent bodies without large scale mixing in the solar nebula the method will also provide important information for the analysis of future sample return missions our examinations demonstrate great potential of the quantitative determination of chondrite class nondestructively by sr ct

a life cycle model for wave dominated tidal inlets along passive margin coasts of north america abstract a regional overview of 107 wave dominated tidal inlets along the u s atlantic coast u s gulf of mexico coast and canadian gulf of st lawrence coast yielded a generalized wave dominated tidal inlet life cycle model that recognized the rotational nature of tidal inlets tidal inlets are influenced by concurrently acting processes transpiring over two timescales short term event driven processes and long term evolutionary processes wave dominated tidal inlets are classified into three rotational categories based on net longshore sediment transport direction and rotation direction along the landward back barrier portion of the inlet channel downdrift channel rotation updrift channel rotation or little to no channel rotation lateral shifting of the flood tidal delta depocenter in response to available estuarine accommodation space appears to control inlet channel rotation flood tidal delta deposits fill accommodation space locally within the estuary i e creating bathymetric highs causing the tidal inlet channel to rotate external influences such as fluvial discharge pre existing back barrier channels and impeding salt marsh will also influence inlet channel rotation storm events may rejuvenate the tidal inlet by scouring sediment within the flood tidal delta increasing local accommodation space wave dominated tidal inlets are generally unstable and tend to open concurrently migrate laterally and rotate infill and close channel rotation is a primary reason for wave dominated tidal inlet closure during rotation the inlet channel lengthens and hydraulic efficiency decreases thus causing tidal prism to decrease tidal prism estuarine accommodation space and sediment supply to the flood tidal delta are the primary variables responsible for tidal inlet rotation stability of wave dominated tidal inlets is further explained by stability s tidal prism estuarine accommodation space v volume of annual sediment supply mt rotating wave dominated tidal inlets follow a six stage evolutionary model whereas wave dominated tidal inlets that exhibit little to no rotation follow a five stage evolutionary model

storm driven erosion and inundation of barrier islands from dune to region scales abstract barrier islands are susceptible to erosion overwash and breaching during intense storms however these processes are not represented typically in large domain models for storm surge and coastal inundation in this study we explore the requirements for bridging the gap between dune scale morphodynamic and region scale flooding models a high resolution xbeach model is developed to represent the morphodynamics during hurricane isabel 2003 in the north carolina nc outer banks the model domain is extended to more than 30 km of hatteras island and is thus larger than in previous studies the predicted dune erosion is in good agreement with post storm observed topography and an excellent skill score of 0 59 is obtained on this large domain sensitivity studies show the morphodynamic model accuracy is decreased as the mesh spacing is coarsened in the cross shore direction but the results are less sensitive to the alongshore resolution a new metric to assess model skill water overpassing area w o a is introduced to account for the available flow pathway over the dune crest together these findings allow for upscaled parameterizations of erosion in larger domain models the updated topography obtained from xbeach prediction is applied in a region scale flooding model thus allowing for enhanced flooding predictions in communities along the outer banks it is found that even using a fixed topography in region scale model the flooding predictions are improved significantly when post storm topography from xbeach is implemented these findings can be generalized to similar barrier island systems which are common along the u s gulf and atlantic coasts

magnetite in comet wild 2 evidence for parent body aqueous alteration the mineralogy of comet 81p wild 2 particles collected in aerogel by the stardust mission has been determined using synchrotron fe k x ray absorption spectroscopy with in situ transmission xrd and x ray fluorescence plus complementary microraman analyses our investigation focuses on the terminal grains of eight stardust tracks c2112 4 170 0 0 c2045 2 176 0 0 c2045 3 177 0 0 c2045 4 178 0 0 c2065 4 187 0 0 c2098 4 188 0 0 c2119 4 189 0 0 and c2119 5 190 0 0 three terminal grains have been identified as near pure magnetite fe3o4 the presence of magnetite shows affinities between the wild 2 mineral assemblage and carbonaceous chondrites and probably resulted from hydrothermal alteration of the coexisting feni and ferromagnesian silicates in the cometary parent body in order to further explore this hypothesis powdered material from a cr2 meteorite nwa 10256 was shot into the aerogel at 6 1 km s 1 using a light gas gun and keystones were then prepared in the same way as the stardust keystones using similar analysis techniques to the eight stardust tracks a cr2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel

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