interdune areas of the back island dune field north padre island texas abstract the small young about 100 yrs back island dune field on north padre island south texas consists of fairly persistant oblique dunes up to 6 m high with well developed interdune areas that grade northwestward to small ephemeral transverse and barchan dunes with interconnected interdune areas thence sheet sand areas the subhumid climate is marked by rain associated with frontal systems and tropical storms winds are seasonally bimodal prevailing southeasterly are punctuated by northerly and northwesterly winds with the passage of frontal systems in winter the entire dune field and individual oblique dunes show a net migration of about 15 m yr 1 to the northwest the dunes however are on a seasonally reversing track changing their slipface direction and migration direction with frontal systems one year of monitoring shows sand transport in the dune interdune system to be complex and cyclic during the wind reversals of winter dunes are very ineffecfive sand traps owing to loss of flow separation and much sand is lost to the interdune areas interdune areas store sand during these wet winter months as a result of the wind reversals and higher moisture content during the summer the interdune areas deflate and the dunes build in size the overall dune field deposit appears to consist of three laterally contiguous zones from southeast to northwest 1 continuous climbing oblique dune and interdune deposits 2 discontinuous lenses of dune sand in overall interdune layers and 3 a chaotic mixture of dune and horizontal deposits of the sheet sand areas one year s mapping and trenching documents that interdune sedimentary structures are extremely variable laterally and vertically reflecting specific microenvironments within the interdune flat wet surface features consist of current and wave ripples channel fill miniature deltas wrinkle marks mini ripples rills algae and sand volcanoes abundant adhesion structures rain impacted ripples brecciated surfaces and microtopography reflect damp surface deposits dry surface features are predominately wind ripples others include small isolated barchan and shadow dunes organic debris lag surfaces deflation scours beetle bioturbation plant root structures associated with shadow dunes and grainfall from the adjacent dunes interdune deposits account for about 40 of the total dune field deposits which seems reasonable compared to some ancient examples by virtue of occupying a relative basin interdune deposits are selectively preserved compared to dune deposits in general interdune sedimentation is enhanced by non eolian depositional mechanisms a high water table early evaporatic cements and a variable wind regime the actual thicknesses of individual dune and interdune deposits are less on padre than ancient examples reflecting the relative scale of the bedforms in many respects sequences of sedimentary structure in padre island interdune deposits are typical of ancient coastal interdune strata but some marked departures occur adhesion structures relatively rare in some ancient examples but abundant within padre interdune deposits seem favored by the small size of dune and interdune area the climate and a variable wind regime penecontemporaneous deformation absent in padre interdune deposits but pronounced in some ancient examples probably reflects dune size and the nature of the deposits wavy laminae in ancient interdune deposits probably result from many causes but seem best represented by modern examples of evaporitic algal bacterial formed structures

deglacial sea surface temperatures of the western tropical pacific a new look at old coral 1 using secondary ion mass spectrometry sims ion microprobe techniques we generated annual sr ca cycles with subweekly resolution from chunks of porites coral retrieved from a tahiti barrier reef drill core 149 w 17 s representing the period 13 650 to 13 100 years b p the centers of pristine skeletal septa were selectively targeted with a 10 m diameter ion beam spot avoiding adjacent pore spaces occupied by secondary aragonite needles applying a sr ca sea surface temperature sst calibration equation derived from modern tahiti porites having the same low growth rate as the fossil specimens we obtained ssts 0 5 1 5 c cooler during the bolling allerod relative to the present day with no significant change in seasonality on the contrary we estimate that analysis of bulk samples would yield excessively cool sr ca based sst estimates due to the occupation by secondary aragonite crystals of up to 50 of the skeletal pore space in the ancient samples we find that growth rate effects on coral sr ca further depress the apparent mean annual derived ssts by 3 c and amplify the apparent seasonality by selectively enhancing wintertime cooling our microscale analysis of pristine skeleton and application of an appropriate growth dependent calibration yield sr ca derived ssts that are in good agreement with those derived from mg ca ratios of calcitic foraminifera which indicate a continuous postglacial warming of the western tropical pacific in phase with the warming of the tropical atlantic

crustal structure beneath the archean proterozoic terrain of north india from receiver function modeling abstract the shear velocity structure of the north indian crust comprising of the archean cratons aravalli bundelkhand and proterozoic vindhyan basin is modeled and compared with the eastern dharwar craton as well the global models for archean and proterozoic terrains the velocity structure is deduced from joint inversion of teleseismic receiver function time series and surface wave group velocity measurements the north indian archean crust is a simple two layered an average v s 3 3 0 1 km s in the upper 10 km increasing to 3 7 0 1 km s in the 26 28 km thick lower crust this upper crustal velocity is significantly less compared to those of either eastern dharwar craton 3 5 3 6 km s or the global average these results suggest presence of a highly silica rich upper crust and an intermediate composition of the lower crust the moho is modeled at a depth of 36 38 km with thin transition 2 km similar to those in eastern dharwar craton in contrast the proterozoic vindhyan basin has significantly deeper moho 44 46 km with a 4 10 km thick underplated layer v s 4 0 km s at the base of the crust the sedimentary layer thickness is 2 4 km the results support the view that proterozoic crust is thicker and underlain by a mafic layer at its base in contrast to a thin archean crust with near absence of the basal layer as observed globally

optimizing subsampling strategies for u th dating and geochemical proxies in carbonate speleothems abstract since they provide the chronological frame on which paleoclimate and paleoenvironmental reconstructions are built radiometric ages of carbonate speleothems especially u th dating are of fundamental importance to speleothem and paleoclimate sciences based on 17 aragonite calcite speleothems from the pont de ratz cave s france we propose an integrated petrographical and geochemical approach for optimizing subsampling in speleothems portable energy dispersive x ray fluorescence was used as a fast and non destructive in situ trace element screening of the speleothems these geochemical results are combined with petrographical and mineralogical information to produce distribution maps showing the growth discontinuities and the identified primary and secondary diagenetic products on the speleothem slabs because they provide a clear and precise spatial distribution of primary and secondary carbonate phases at the sample scale these maps constitute a valuable tool for selecting the position of subsamples for radiometric dating or environmental proxy analysis the efficiency and reliability of our integrative approach is convincingly demonstrated by the remarkable coherence of u th ages both within and between speleothem samples

evaluation of the effect of diagenetic cements on element ca ratios in aragonitic early miocene 16ma caribbean corals implications for deep time palaeo environmental reconstructions abstract early miocene corals siderastrea conferta and montastraea limbata from the paraguana peninsula venezuela and a modern coral s radians from bermuda were examined in order to quantitatively assess the effect of skeletal preservation on element ca proxies used for palaeo environmental reconstructions the biostratigraphic age burdigalian of the corals was confirmed via sr isotope stratigraphy to 16 5 0 4 ma light and scanning electron microscopy revealed the presence of aragonite and calcite cements in both fossil and modern corals but brucite cements were found only in the modern coral cement distribution is very heterogeneous resulting in zones of excellent preservation juxtaposed with less well preserved regions in both modern and fossil coral oil filled pore spaces were noted in the fossil specimens targeted la icpms depth profile analyses showed significant differences in sr ca mg ca b ca ba ca and u ca in aragonite and calcite cements compared to primary skeletal aragonite increased sr ca and decreased mg ca ratios were found in aragonite cements compared to skeletal aragonite whereas in calcite cements these trends were reversed b ca ratios were lower in both aragonite and calcite cements compared to primary aragonite estimates of the effect of 1 contamination by aragonite cements on coral sr ca mg ca b ca and u ca palaeo sea surface temperature reconstructions for the fossil corals produced anomalies of 1 2 c 0 2 c 0 3 c and 0 1 c respectively similar percentage calcite cement contamination produced temperature anomalies of 1 7 c 2 7 c 0 3 c and 0 1 c because of both highly elevated and depleted ba ca signatures in aragonite and calcite cements respectively care has to be exercised when reconstructing past flood or upwelling events from fossil corals when using targeted spatially resolved analysis well preserved early miocene corals may overall yield reliable deep time palaeo proxy information in much the same way as commonly utilised holo pleistocene corals

dynamic processes acting on a longitudinal seif sand dune abstract field measurements were made on a longitudinal dune in the sinai desert in order to understand its morphology and dynamics the field measurements contradicted the wind structure indicated by the helicoidal flow theory rather it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank the essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line the occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line when this angle is 40 the velocity of the deflected wind drops and deposition takes place on the lee flank the angle of incidence in each wind storm is changed intermittently between 30 and 100 along the dune because the dune meanders and because of the sinuous outline of the crest line in this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line as a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month peaks and saddles along the crest line advance at an average rate of 0 7 m per month the lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition this can explain the formation of peaks along the crest line of the dune

geochemistry based coral palaeoclimate studies and the potential of non traditional non massive porites corals recent developments and future progression understanding the natural variability of the earth s climate system and accurately identifying potential anthropogenic influences requires long term geographically distributed records of key climate indicators such as temperature and precipitation that extend prior to the last 400 years of the holocene reef corals provide an excellent source of high resolution climate records and importantly represent the tropical marine environment where palaeoclimate data are urgently required recent decades have seen significant improvement in our understanding of coral biomineralisation the associated uptake of geochemical proxies and methods of identifying and understanding the effects of both early and late post depositional diagenetic alteration these processes all have significant implications for interpreting geochemical proxies relevant to palaeoclimatic reconstructions this paper reviews the current state of the art in terms of coral based palaeoclimate reconstructions and highlights a key remaining problem the majority of coral based palaeoclimate research has been derived from massive colonies of porites however massive porites are not globally abundant and may not provide material of a particular age of interest in those regions where they are present therefore there is great potential for alternate coral genera to act as complimentary climate archives while it remains critical to consider five key factors vital effects differential growth morphologies geochemical heterogeneity in the skeletal ultrastructure transfer equation selection and diagenetic screening of skeletal material in order to allow the highest level of accuracy in coral palaeoclimate reconstructions it is also important to develop alternate taxa for palaeoclimate studies in regions where porites colonies are absent or rare currently as many as nine genera other than porites have proven at least limited utility in palaeothermometry most of which are found in the atlantic caribbean region where massive porites do not exist even branching taxa such as acropora have significant potential to preserve environmental archives increasing this capability will greatly expand the number of potential geochemical archives available for longer term temporal records of palaeoclimate

characterization of various stages of calcitization in porites sp corals from uplifted reefs case studies from new caledonia vanuatu and futuna south west pacific abstract this study focuses on the processes of calcitization under meteoric conditions based on observations and analyses of a series of subaerial fossil corals of the genus porites collected from emerged holocene and pleistocene reefs in the pacific ocean we can establish two types of low magnesian calcite lmc precipitates according to their textural characteristics after their transformation from the initial aragonitic skeleton to the calcitized corals in the first variety lmc1 the calcite contains remnants of the original exoskeleton structure in situ insoluble organic tissues pieces of aragonite needles while in the second variety lmc2 filling the primary inter skeletal macro pores such relicts are not present such textural segregation is faithfully reflected in the elemental data on some parts of calcitized corals lmc1 is characterized by mg2 sr2 and mn2 compositions inherited from the aragonite precursor indicating a formation in a semi closed intra skeleton diagenetic environment in disequilibrium with the meteoric bulk aquifer water lmc2 has a chemistry indicative of equilibrium with ambient bulk meteoric water these chemical characteristics can be likened to a two fold mechanism a fine scale process neomorphism typified by the concomitant dissolution of intra fabric aragonite and re precipitation of the lmc1 resulting from the biogenic skeleton and marine waters followed by the cementation of the inter fabric macro voids by an allochthonous subaerial and meteoric lmc2 in the other parts of calcitized corals lmc1 and lmc2 have similar trace element contents in mg2 and sr2 the chemical data are consistent with formation by partial skeletal dissolution followed eventually by cementation of primary voids lmc2 and secondary voids lmc1 by calcite in equilibrium with meteoric bulk aquifer water these two mechanisms of the calcitization of skeletal aragonite mainly differ in the space and time length scales of the intervening transport step and are commonly found juxtaposed in the same thin section taking into account such a heterogeneity is a real challenge for the development of predictive models assessing the effects of diagenetic products on paleoclimatic reconstructions

major bounding surfaces in aeolian sandstones a climatic model large areas of fixed vegetated dunes occur in the sahel and southern margin of the sahara these dunes were active during late pleistocene times and have been stabilized as a result of a change to more humid less windy conditions in the holocene the stabilized surfaces which are in part of erosional origin are of regional extent within aeolian sand sequences such surfaces form the highest order bounding surfaces since regional bounding surfaces of this type occur in all the world s major deserts it is suggested that they should also be present in some ancient aeolian sandstone sequences

diagenesis and its impact on sr ca ratio in holocene acropora corals the effect of early diagenesis on sr ca ratios encapsulated in coral skeletons was evaluated by comparing mineralogical structural and geochemical characteristics of modern and holocene branching acropora colonies the modern specimens acropora danai acropora formosa come from reunion island western indian ocean and the great barrier reef of australia respectively the sr ca ratios of modern specimens range from 9 08 to 9 37 mmol mol the fossil acroporids acropora group danai robusta were collected from a 50 m core drilled through a barrier reef in tahiti island their c 14 ages range from 3 200 to 10 200 calendar years b p fossil skeletons are 100 aragonite earlier diagenesis has occurred in the marine environment it is expressed by growth of secondary inorganic aragonite over primary skeletal aragonite needles development of syntaxial aragonite cements within intraskeletal cavities and decrease in size of original 1 1 050 m wide pores residual porosity ranges from 25 to 28 which results in a volume reduction by 34 to 49 cementation increases with increasing age of the corals later diagenesis has occurred in a mixed marine freshwater environment it includes partial dissolution of skeletal and growth of cement aragonite fibres in the form of spherolites irregular meshes of large squarely terminated laths this results in an increase in porosity from 30 to 59 by reference to modern well preserved acroporids this diagenetic alteration has led to an increase of sr ca values from 9 08 9 37 to 8 89 10 55 mmol mol this variation in sr ca ratio can be linked to the increase in the amount of sr enriched cements relative to the volume of the skeletal aragonite and to a more homogeneous distribution of these cements throughout the skeleton the uncritical use of sr ca ratios as paleothermometers from diagenetically altered skeletons may cause serious misinterpretations accordingly estimate of the degree of diagenetic alteration in skeletons is a prerequisite to any paleoclimatic reconstruction based on coral records

temporal and spatial variations in the diagenetic fabrics and stable isotopes of pleistocene corals from the ironshore formation of grand cayman british west indies abstract on grand cayman the unconformity bounded units a to f in the ironshore formation represent repeated cycles of deposition and subaerial exposure that were associated with the dramatic oscillations in sea levels that characterized the middle to late pleistocene montastrea annularis and acropora palmata the dominant corals found in units a to f in the rogers wreck point area and offshore george town area reflect these changes with their complex mosaics of marine aragonite cements bioerosion internal sediments and meteoric calcitization of coral skeleton dissolution diagenetic features the distribution of the diagenetic fabrics throughout this sequence however is not predictable the randomness in the degree of skeletal calcitization is shown by the lack of systematic variation in calcitization from units a to f and the fact that the degree of skeletal calcification in m annularis is higher than that in a palmata in the rogers wreck point area but less than in a palmata in the george town cores the stable isotope compositions 13c 18o of the corals from units a to f plot along the same trend line with their positions on that trend reflecting the amount of meteoric diagenesis they have undergone the variable styles and degrees of diagenesis evident in the corals from the ironshore formation reflect 1 the variable impact of intrinsic e g skeletal architecture porosity of coral and extrinsic e g sea level climate factors during each phase of diagenesis and 2 temporal effects associated with the diagenetic overprinting that took place during each successive phase of diagenesis this means that the diagenetic fabrics are not stratigraphically ordered and that it is impossible to correlate specific diagenetic phases with specific sea level lowstands or highstands

the middle proterozoic eastern bangemall basin western australia abstract the eastern part of the middle proterozoic bangemall basin in the gibson desert of western australia contains very extensive shallow water quartz sandstones with minor crystal tuffs siltstones stromatolitic dolomites and oolitic cherts many of the sandstones are tuffaceous in part and are characterized by an argillaceous matrix of possible volcanic origin two examples of spectacular large scale cross bedding are observed in the basin the southern undeformed margin of the basin is dominated by basal sandstones of shallow marine or coastal aeolian origin the central upper part of the basin is dominated by very large scale cross stratified sets up to 40 m thick of probable deltaic origin the sequence is correlative with and possibly transitional to the terrestrial volcanics of the middle proterozoic bentley supergroup to the east and the marine sediments of the western bangemall basin to the west the bangemall basin sediments are intruded by extensive dolerite sills dated at 1050 ma old the sequence is progressively more deformed and metamorphosed to the north where it forms part of the newly recognised late proterozoic paterson fold belt this fold belt can be traced eastward via the anketell regional gravity ridge to the western end of the musgrave block where it is represented by the petermann ranges orogen

migration modification and merging in aeolian systems and the significance of the depositional mechanisms in permian and triassic dune sands of europe and north america abstract the main depositional mechanisms acting in aeolian systems can be assessed in two different and independent ways first by the internal anatomical approach with analysis of the cross stratification fabric and second by the external morphological approach with study of shape and surface features of dunes anatomical investigations of various ancient aeolian systems in the permian and triassic of europe and north america and an extensive literature review concerning both internal anatomy and external morphology of ancient and modern dunes reveal three main depositional mechanisms operating in aeolian systems migration modification and merging migration comprises downwind movement of isolated dunes or trains of aeolian bedforms under predominantly constant wind direction the orientation of the interset surfaces partially depends on the angular relationship between the path of bedform climb and the depositional surface and also on subsidence simple systems are characterized by successive dunes of similar size whereas compound systems originate by superimposition of smaller aeolian bedforms on larger dunes or draas compound migration gives rise to the hierarchy of diastems modification comprises overprinting of existing dunes by winds coming from directions other than those that govern migration of the original aeolian bedforms the anatomical elements representing modification include both intrasets and extensive intersets depending on duration and on the scale of the changes of the winds simple modification comprises occasional origin of either only cross dipping erosional boundaries or both diastems and intraset laminae oriented in different directions a special case of modification is the creation of intrasets dipping in the same direction as the foreset inclination comprising either reactivation or relaxation surfaces depending on whether the foreset slope is steepened or lowered in angle complex modification takes place under repeatedly alternating winds of changing effectiveness small scale modification comprises minor alterations of existing dune types and medium scale modification is characterized by conversion of primary aeolian bedforms into secondary dune types small scale and medium scale modification take place during short term to smaller scale long term changes of effective wind direction large scale modification originates by large scale long term changes accompanied by a certain subsidence which result in burial of the older dunes by a younger train of aeolian bedforms within the same sand sea migrating obliquely to perpendicularly to the former wind direction very large scale modification is induced by very large scale long term changes which result int deflationary erosion of older dune fields and subsequent superimposition of a new sand sea on top of the eroded remnants of the former erg merging comprises coalescing of bedforms with only negligible erosion during burial of the first bedform by subsequent dunes merging is induced mainly when migration of dunes is stopped by a morphological barrier or ceases as a consequence of weakening winds merging further occurs during coalescence of numerous isolated barchans in rows to parallel wavy barchanoid ridges as a consequence of increasing availability of sand the main depositional mechanism in compound systems is migration of hierarchically superimposed bedforms with subordinate modification under predominantly unidirectional winds in complex systems migration modification and merging take place in different amounts under unidirectional bidirectional and multidirectional winds depending on direction and strength of both earlier and subsequent winds complex systems are either charcterized by mainly migration with subordinate modification or by considerable modification with either conversion or dissection of older dunes the effects of migration modification and merging are discussed in the light of both internal anatomy of ancient cross stratification fabrics and external morphology of recent dunes a classification of dune types based on these mechanisms divides the aeolian bedforms into primary secondary and tertiary types primary dunes originate by simple or compound migration with minor modification and comprise mainly transverse dunes secondary dunes originate by complex interaction of migration and modification or even predominantly by modification with the best examples being longitudinal dunes tertiary dunes form by merging of transverse and longitudinal elements with varying amounts of migration and modification and are mainly represented by star dunes the results of various anatomical case studies of ancient aeolianites indicate that simple migration was the dominant mechanism for construction of ergs in the northern hemisphere in permian and triassic times

sea surface temperature variability in the 16th century at bermuda inferred from coral records abstract records of skeletal 18 o in monthly and sr ca ratios in half yearly resolution were obtained from a bermuda coral diploria labyrinthiformis for the time period 1520 1603 15 yr ad within the little ice age annual and decadal averages of both sea surface temperature proxies indicate temperature variabilities of 0 5 c standard deviation and 0 3 c respectively both numbers are close to recent instrumental observations approximately 30 of the interannual time series variance of 18 o is concentrated in broad bands centered at periods of 30 16 and 7 8 yr the last two reflecting the influence of the north atlantic oscillation although this large scale climate signal is present in the record there is no correlation with other contemporaneous northern hemisphere proxy data resulting from spatial differences in climate variability

mid holocene sea level and coral reef demise u th dating of subfossil corals in moreton bay australia it is increasingly apparent that sea level data e g microfossil transfer functions dated coral microatolls and direct observations from satellite and tidal gauges vary temporally and spatially at regional to local scales thus limiting our ability to model future sea level rise for many regions understanding sealevel response at far field locations at regional scales is fundamental for formulating more relevant sea level rise susceptibility models within these regions under future global change projections fossil corals and reefs in particular are valuable tools for reconstructing past sea levels and possible environmental phase shifts beyond the temporal constraints of instrumental records this study used abundant surface geochronological data based on in situ subfossil corals and precise elevation surveys to determine previous sea level in moreton bay eastern australia a far field site a total of 64 u th dates show that relative sea level was at least 1 1 m above modern lowest astronomical tide lat from at least 6600 cal yr bp furthermore a rapid synchronous demise in coral reef growth occurred in moreton bay 5800 cal yr bp coinciding with reported reef hiatus periods in other areas around the indo pacific region evaluating past reef growth patterns and phases allows for a better interpretation of anthropogenic forcing versus natural environmental climatic cycles that effect reef formation and demise at all scales and may allow better prediction of reef response to future global change

florisphaera profunda and the origin and diagenesis of carbonate phases in eastern mediterranean sapropel units high relative concentrations of the lower photic zone nannofossil florisphaera profunda have been reported in all recent eastern mediterranean sapropels in the most recent sapropel s1 high bulk sediment sr ca ratios occur along with high f profunda contents toward the base of the unit exemplified here in four cores from 1 5 3 5 km water depth co occurring biogenic carbonates contain insufficient sr to account for these high sr concentrations and x ray diffraction and selective leaching show that the high sr ca ratios are due to aragonite the caco3 polymorph that is rarely preserved in deep marine sediments with 1 wt sr the possible sources of this aragonite include 1 precipitation with surface ocean production 2 detrital input from shallow water sediments by high continental runoff or 3 postdepositional diagenetic formation driven by increased pore water alkalinity resulting from sulphate reduction the third formation mechanism for the aragonite is favored in which case the similarity in the positions of the aragonite and f profunda abundance maxima in sapropels is probably related to corg accumulation and resulting sulphide diagenesis that produces high pore water alkalinity there is clear micropaleontological evidence that dissolution of the less soluble biogenic low mg caco3 is occurring or has occurred during early diagenesis in these sediments despite the coexistence of the more soluble high mg calcite and aragonite polymorphs similar sr ca maxima are also found associated with older sapropels always located close both to local minima in surface ocean 18o that signal maximum monsoon driven runoff and to maxima in diagenetic sediment sulphide contents high freshwater flows from monsoons are believed to drive eastern mediterranean sapropel formation through water column stabilization that favors f profunda production and later through development of deep water column dysoxia anoxia because of reduced ventilation the relative abundances of f profunda are high between 5 and 11 14c kyr b p with a maximum at 9 14c kyr b p the surface ocean production changes marked by f profunda therefore begin earlier and finish later than the formation of the s1 sapropel which only develops between 6 and 10 14c kyr b p

significance of shallow core transects for reef models and sea level curves heron reef great barrier reef a sequence of shallow reef cores from heron reef great barrier reef provides new insights into holocene reef growth models isochron analysis of a leeward core transect suggests that the north western end of heron reef reached current sea level by ca 6 5 kyr bp and then prograded leeward at a rate of ca 19 6 m kyr between 5 1 kyr and 4 1 kyr bp pre 1950 to the present reef margin a single short core on the opposing margin of the reef is consistent with greater and more recent progradation there further to the east one windward core reached modern sea level by ca 6 3 kyr bp suggesting near keep up behaviour at that location but the opposing leeward margin behind the lagoon reached sea level much more recently hence heron reef exhibited significantly different reef growth behaviour on different parts of the same margin mean reef accretion rates calculated from within 20 m of one another in the leeward core transect varied between ca 2 9 m and 4 7 m kyr depending on relative position in the prograding wedge these cores serve as a warning regarding the use of isolated cores to inform reef growth rates because apparent aggradation at any given location on a reef varies depending on its location relative to a prograding margin only transects of closely spaced cores can document reef behaviour adequately so as to inform reef growth models and sea level curves the cores also emphasize potential problems in u series dates for corals within a shallow ca 1 5 m zone beneath the reef flat apparent age inversions restricted to that active diagenetic zone may reflect remobilization and concentration of th in irregularly distributed microbialites or biofilms that were missed during sample vetting importantly the th containing contaminant causes ages to appear too old rather than too young as would be expected from younger cement

earliest steps of diagenesis in living scleractinian corals evidence from ultrastructural pattern and raman spectroscopy abstract the precise understanding of diagenetic pathways occurring during fossilization of biomineralized skeletons is of critical importance for various related fields in both paleontology and sedimentology in particular this may have fundamental implications in paleoenvironmental studies for interpreting geochemical proxies extracted from these skeletons the effects of the first diagenetic processes on both mineral and organic compounds present in skeletons of scleractinian corals were investigated in two different coral colonies lobophyllia corymbosa and leptastraea purpurea by combining mapping of skeletal ultrastructural patterns by sem and in situ analysis by raman microspectroscopy the two elementary ultrastructural features typical of scleractinian corals the centers of calcification and the sets of aragonite fibers have been characterized in the uppermost parts i e the living zone of both coral colonies diagenetic features affecting the skeleton itself and also represented by fibrous diagenetic cements have been analyzed in the oldest basal parts of each colony all raman spectra display several vibrational bands typical of aragonite but no calcite additionally several raman bands indicate the presence of organic compounds some of which likely characterize proteinous components and provide the first in situ chemical record of the skeletal organic matrices tentative assignments to ch ch2 ch3 nh2 cho cnc and so groups are proposed in the living zone some of these bands are different in the two coral species in raman spectra measured in the oldest skeletal parts of both colonies these bands decrease markedly in number and diversity or even disappear indicating that significant decay of intraskeletal organic matrices does occur in just a few years therefore early diagenesis in these skeletons results from the interaction between the degradation of organic matrices and the diagenetic processes affecting the skeletal aragonite submicron size crystals

santa ana river an example of a sandy braided floodplain system showing sediment source area imprintation and selective sediment modification abstract the santa ana river floodplain can be divided into five geomorphic environments recognized by both morphology and sedimentary characteristics braided channels bars vegetated islands sand flats and floodplain terraces braided channels which vary in width from 30 to 80 m and are bordered by sand flats flow round vegetated islands and emergent mid channel bars deep braided channels have linguoid dume bedforms which are reworked during falling flood stages if channel bars emerge in early spring vegetation is rapidly established and they may become vegetated islands bars emerging in minor channels and in areas of increased channel width may develop into extensive sand flats away from the channel margins sand flats are subject to wind erosion as the water table declines in summer and fall this sediment is deposited in sand sheets and vegetated dunes these distal sand flat environments are characterized by a well sorted medium sand sized sediment population and are separated from negatively skewed moderately sorted coarse channel sands by a mixed sediment population along channel margins the drainage basin discharge is dominated by the regional mediterranean climate the coarse channel sediment reflects the large temporal variations in drainage discharge and the resulting greater variability and competence to transport sediment major decreases in channel width during both seasonal summer drought and prolonged periodic drought exposes large areas of the floodplain to selective wind winnowing of fluvially derived sediment this process operates on a small scale today but during arid conditions in the late wisconsin interglacial interval prior to 22 000 yrs b p extensive sand flats along the santa ana river distal alluvial fans and sediment from minor tributaries were the sediment source for a major riverine dune field adjacent to the floodplain this dune field was stabilized during the late wisconsin glacial interval subsequent channel entrenchment has isolated this dune field from its source region santa ana river sediments originate from two distinct geologic provinces the san gabriel san bernardino granitic and metamorphic complex to the north and the granitic perris block to the south settling tube analysis of sediments from tributary streams draining the perris block shows a distinctive bimodal distribution characterized by minimal sediment in the very coarse sand size 1 to 0 phi size inherited from the granitic grus parent material this is imprinted onto all sediment from this source transportation results in sediment erosion sediments are better sorted and finer grained with increasing distance from their source the sediment in these intermittent tributary streams frequently represents a single sedimentary event minor flash flood and all the sediment including the fines is left behind this produces a negatively skewed sediment distribution when the fines are added to an existing deposit within the limits of a predetermined size range older alluvium is strongly negatively skewed and may indicate in situ weathering coarse channel sands from the santa ana river maintain this characteristic sediment distribution but selective deposition and winnowing by the wind on the sand flats creates a distinctive floodplain sub environment analysis of these deposits and material from tributary streams illustrates that a particle population is dependent upon grain size distribution at the initial source sediment populations are modified by subsequent erosion selective grain size transport deposition and total deposition and mixing of several source areas

early diagenesis impact on precise u series dating of deep sea corals example of a 100 200 year old lophelia pertusa sample from the northeast atlantic deep sea coral has proved useful for paleoceanographic reconstructions and for documenting 14 c ages of water masses using 230 th ages however for precise and accurate u series dating further information on coral age structure growth rate and diagenetic evolution is still needed to document such processes we used u th 226 ra systematics in a 40 cm diameter lophelia pertusa specimen collected in 1912 from the eastern atlantic sea of the hebrides external parts of the specimen are thought to have been alive when collected whereas more internal parts were likely dead the live collected and dead parts of the skeleton were sampled and analyzed for their 230 th 232 th 234 u 238 u 226 ra and ba contents by thermal ionization and multicollector inductively coupled plasma mass spectrometry 230 th 234 u ratios in the most recent parts yielded ages of 86 6 a and 92 9 a in agreement with the date of recovery the older parts yielded 230 th ages ranging from 169 15 to 211 10 a n 5 but had a 31 higher u content than more recent parts of the skeleton this raises concerns about the possibility of secondary diagenetic u uptake although an environmentally controlled u ca shift between coral growth stages cannot be ruled out 226 ra ba measurements were made and model 226 ra ba ages averaging 250 12 yr were calculated for the older part assuming a constant initial 226 ra ba ratio in bottom waters these ages are slightly older than 230 th ages suggesting either that 226 ra ba ratios of ambient seawater changed over time or that a diagenetic phenomenon have affected the u series system or both scanning electron microscope observations revealed bioerosion and secondary biomineralization in the older part of the coral skeleton supporting the hypothesis that diagenetic processes may have influenced the ages obtained by the u series toolbox modeled u series ages for such an open system are discussed however a comparison between 14 c and 230 th ages performed on both pristine and bioeroded parts of the coral gives coherent values ca 450 a for the preindustrial 14 c reservoir age of north atlantic waters it remains to be determined however whether diagenesis occurs rapidly over a short period of time or whether it continues for longer periods in the latter case diagenetic processes would hamper paleoceanographic interpretations as well as the precise calculation of 14 c ages of deep water masses based on comparative u th and 14 c chronologies copyright 2005 elsevier ltd

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

storm controlled oblique dunes of the oregon coast the large mean height 25 m spacing 300 m relatively straight crested dunes of the central oregon coast migrate an average of 3 8 m yr toward an azimuth of 26 the dunes are transverse to the strong south southwesterly winter storm winds that are responsible for their basic form orientation and migration the dry moderate north northwesterly summer winds modify the dune form but not the dune trend comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one third of the amount calculated assuming dry conditions the resultant vector mean transport rate as recalculated by comparison of the measured and initially calculated rates is 34 m 3 m yr toward an azimuth of 45 the dunes are thus oblique by our definition of an oblique dune angle between dune trend and resultant transport direction between 15 and 75 the internal structures of the dunes confirm northward migration during wet conditions evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces most summer deposits are not preserved but those on the basal apron the gentle north slope at the base of the winter slipface have a high preservation potential a depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set

effects of diagenesis on paleoclimate reconstructions from modern and young fossil corals abstract the integrity of coral based reconstructions of past climate variability depends on a comprehensive knowledge of the effects of post depositional alteration on coral skeletal geochemistry here we combine millimeter scale and micro scale coral sr ca data scanning electron microscopy sem images and x ray diffraction with previously published 18o records to investigate the effects of submarine and subaerial diagenesis on paleoclimate reconstructions in modern and young sub fossil corals from the central tropical pacific in a 40 year old modern coral we find secondary aragonite is associated with relatively high coral 18o and sr ca equivalent to sea surface temperature sst artifacts as large as 3 and 5 c respectively secondary aragonite observed in a 350 year old fossil coral is associated with relatively high 18o and sr ca resulting in apparent paleo sst offsets of up to 2 and 4 c respectively secondary ion mass spectrometry sims analyses of secondary aragonite yield sr ca ratios ranging from 10 78 to 12 39 mmol mol significantly higher compared to 9 15 0 37 mmol mol measured in more pristine sections of the same fossil coral widespread dissolution and secondary calcite observed in a 750 year old fossil coral is associated with relatively low 18o and sr ca sims sr ca measurements of the secondary calcite 1 96 9 74 mmol mol are significantly lower and more variable than sr ca values from more pristine portions of the same fossil coral 8 22 0 13 mmol mol our results indicate that while diagenesis has a much larger impact on sr ca based paleoclimate reconstructions than 18o based reconstructions at our site sims analyses of relatively pristine skeletal elements in an altered coral may provide robust estimates of sr ca which can be used to derive paleo ssts

sr ca sea surface temperature calibration in the branching caribbean coral acropora palmata 1 we measured sr ca ratios by thermal ionization mass spectrometry in radial and axial growth of modern caribbean acropora palmata corals comparison of our results with sea surface temperature sst allows radial and axial sr ca sst calibrations of sr ca mmol mol 11 30 0 07072 sst c and sr ca mmol mol 11 32 0 06281 x sst c respectively application of the calibrations to fossil acropora palmata from the last glacial maximum in barbados guilderson et al 1994 imply 7 c cooler conditions than the present much larger than the 1 1 5 cooling suggested by modern analog technique foraminifera based estimates trend staid and prell 2002 if the foraminifera based estimates are correct then the excess cooling suggested by the barbados corals could be explained by a 5 shift in the marine sr ca ratio or an addition of 20 abiotic secondary aragonite

rigorous quality control criteria for screening coral samples and radiocarbon calibration data based on 14c 230th 234u 238u and 231pa 235u dated corals a reply to the comment by yusuke yokoyama and tezer m esat on extending the radiocarbon calibration beyond 26 000 years before present using fossil corals by t c chiu r g fairbanks r a mortlock a l bloom quaternary science reviews 24 2005 1797 1808

shape effects in aeolian grain transport wind tunnel experiments are reported the results of which show that grain transport rate is responsive to characteristic grain shape it is relatively less sensitive to changes of sorting unless these involve the fraction smaller than 50 m a cubic relationship between transport rate and velocity gradient appears to be valid only for well worked natural grains having high sphericity

comparison of esr and tims u th dating of marine isotope stage mis 5e 5c and 5a coral from barbados implications for palaeo sea level changes in the caribbean abstract electron spin resonance esr dating of coral has become an efficient geochronological tool in supporting morphostratigraphic studies carried out on barbados during the last 10 years the newly developed approach for de determination de dmax plot procedure improves the precision of esr dating of pleistocene coral and therefore permits differentiation between the main marine isotope stages mis 5 7 9 and 11 and also between sub stages 5e c and a this study compares results of esr and tims uranium series dating u th of emergent last interglacial coral reef terraces from barbados and presents some implications for the timing and extent of sea level changes during marine isotope stages mis 5e c and a both dating methods indicate a distinct formation of up to three coral reef terraces during mis 5e at approximately 132 ka esr to 128 ka u th at c 128 ka esr and at c 120 ka u th to 118 ka esr it is also highly probable that three reef terraces were developed during mis 5c between c 103 ka u th and 105 ka esr the formation of two separate coral reefs during mis 5a is recognized for the first time on barbados with an age estimate for the older mis 5a 2 reef of 85 ka esr or 84 ka u th and an age estimate for the younger mis 5a 1 reef terraces of 74 ka esr or 77 ka u th assuming a constant uplift rate of 0 276 m ka at the south coast of barbados sea level reached its maximum during mis 5e 3 and mis 5e 2 between 132 and 128 ka ago after this sea level declined reaching a level of c 11 m below present sea level approx 118 120 ka ago mis 5e 1 during the substage 5c sea level was generally lower than in substage 5e it reached relative maxima at c 13 20 and 25 m during mis 5c approx 105 ka and formed three distinct coral reef terraces probably in relative short time intervals for the first time a double sea level oscillation is recognized on barbados during mis 5a an early mis 5a 2 c 85 ka with a sea level places at approx 21 m and a late mis 5a 1 sub stage c 74 or 77 ka with a sea level at approx 19 m below present sea level

coral barium calcium record of mid holocene upwelling activity in new caledonia south west pacific abstract a variety of inimical factors i e sea surface temperature nutrient input nature of substrates were invoked previously to explain the retardation in reef settlement in new caledonia during the holocene in order to clarify the respective role played by temperature and nutrient level in the growth of fringing reefs along the southwest coast of the island trace element ratios i e sr ca and ba ca were used respectively as a paleothermometer and as a tracer of nutrient load from modern and mid holocene about 6000 calendar years old massive porites coral colonies the results obtained from the modern coral record indicate that near the outer barrier reef upwelling activity is controlled by southeast winds blowing in summer by contrast along the southwest coastline the fringing reefs are subjected to barium input mainly derived from weathering of barite rich rocks cropping out in the adjacent mainland comparison between the fossil and modern coral sr ca and ba ca records shed light on three different aspects of the mid holocene climate and coral reef evolution in new caledonia 1 the variability of paleo sea surface temperature sst seems to have been similar to the modern one although the island probably experienced sst about 1 c higher than at present 2 upwelling activity appears to have been greater than at present barium being supplied from the open sea to coastal zones by strong wind generated upwelling currents in relation to cooling events 3 the onset of reef development in the southwest areas of new caledonia was delayed due to the stronger upwelling of nutrient enriched waters during the early middle holocene the flowing of upwelled waters over the southwest coastal areas began at 8200 calendar years bp and ceased at the time when the outer barrier reef crest reached present day sea level about 5500 to 5000 calendar years ago