hurricanes and climate in the caribbean during the past 3700 years bp a multiproxy analysis of lacustrine sediments cored in grand case pond at saint martin north of the lesser antilles archipelago reveals three distinct climatic periods for the last 3700 years from 3700 to 2500 yr cal bp and from 1150 yr cal bp to the present carbonate mud deposition occurred in connection with pond lowstands these periods were also punctuated by severe drought events marked by gypsum laminae and hurricane landfalls leading to marine sand inputs into the pond the intermediate time interval from 2500 to 1150 yr cal bp is typified by black organic mud deposition suggesting that hypoxic to anoxic conditions prevailed at the pond bottom these were probably linked with a perennial pond highstand and reflect more uniform and wetter climatic conditions than today the carbon isotopic composition of the ostracod perissocytheridea bisulcata shows that the lowest 13c values are recorded during the hypoxic periods as a consequence of bacterial recycling of isotopically depleted org

radiocarbon deficiencies of us gulf coast lakes compromise paleo hurricane records abstract radiocarbon assays of sediments from lake shelby us gulf coast exhibit substantial 14c deficiencies of 9 3 and 4 7 for the limnic sapropel and associated fresh water clams rangia cuneata respectively measured radiocarbon dates from the sapropel and clams require corrections of 785 80 and 365 90 14c yr 1 respectively in order to achieve consistency with the radiocarbon time scale lake sediments of the us gulf coast serve as unique repositories of pre historic hurricane strikes previously unrecognized radiocarbon deficiencies likely render compromised chronologies of the paleo hurricane records and erroneous estimates of return period and landfall probability that are derived from the storm chronologies the recalculated severe hurricane chronologies suggest that the annual landfall probabilities of the last millennium on the us gulf coast are equal to or higher than the preceding three millennia

late holocene record of lagoon evolution climate change and hurricane activity from southeastern cuba a sediment core from a lagoon in southeastern cuba was the focus of a multi proxy paleoenvironmental study to investigate lagoon response to sea level change and climate change and also to infer changes in the frequency of past hurricane strikes the proxy data examined included benthic foraminifera fossil pollen particle size analysis and macrocharcoal influx values the core was dated using 137cs and accelerator mass spectrometry ams radiocarbon methods the results show that lagoon formation began approximately 4000 years ago and that the lagoon environment evolved through four phases 1 from 4000 to 2800 cal yr bp the lagoon was a shallow polyhaline to euryhaline system with limited mangrove coverage 2 from 2800 to 2000 cal yr bp there was a decrease in salinity which facilitated the expansion of red mangrove 3 from 2000 to 1000 cal yr bp sea level rise resulted in an increase in water depth and possibly salinity and 4 from 1000 cal yr bp to the present water level continue

carbon isotope stratigraphy across the permian triassic boundary a review abstract the palaeozoic mesozoic transition is marked by distinct perturbations in the global carbon cycle resulting in a prominent negative carbon isotope excursion at the permian triassic p t boundary well known from a plethora of marine and continental sediments potential causes for this negative 13 c trend and their links to the latest permian mass extinction have been intensively debated in the literature in order to draw conclusions regarding causation a general 13 c curve was defined after consideration of all available datasets and with due reference to the biostratigraphic background the most important features of the p t carbon isotope trend are the following the 4 7 13 c decline lasting 500 000 years is gradual and began in the changhsingian at the stratigraphic level of the c bachmanni zone the decreasing trend is interrupted by a short term positive event that starts at about the latest permian low latitude marine main extinction event horizon eh indicating that the extinction itself cannot have caused the negative carbon isotope excursion after this short term positive excursion the 13 c decline continues to a first minimum at about the p t boundary a subsequent slight increase is followed by a second occasionally two peaked minimum in the lower and middle i isarcica zone the negative carbon isotope excursion was most likely a consequence of a combination of different causes that may include 1 direct and indirect effects of the siberian trap and contemporaneous volcanism and 2 anoxic deep waters occasionally reaching very shallow sea levels a sudden release of isotopically light methane from oceanic sediment piles or permafrost soils as a source for the negative carbon isotope trend is questionable at least for the time span a little below the eh and somewhat above the p t boundary

an alternative model for positive shifts in shallow marine carbonate 13c and 18o positive shifts in global seawater d 13 cdic are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in d 18 o here an alternative model is proposed for the formation of local positive isotope shifts in shallow marine settings the model involves geochemically altered platform top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition both mechanisms are active on modern sub tropical carbonate platforms and result in low carbonate d 13 ca ndd 18 o relative to typical oceanic values during high amplitude transgressive events the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced and 13 c depleted platform top water mixes with open oceanic water masses having higher isotope values both factors are recorded as a transient increase in carbonate 13 c and 18 o relative to low background values these processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas

intense southwest florida hurricane landfalls over the past 1000 years abstract recent research has proposed that human induced sea surface temperature sst warming has led to an increase in the intensity of hurricanes over the past 30 years however this notion has been challenged on the basis that the instrumental record is too short and unreliable to reveal long term trends in hurricane activity this study addresses this limitation by investigating hurricane induced overwash deposits paleotempestites behind a barrier island in naples fl usa paleotempestologic proxies including grain size percent calcium carbonate and fossil shells species were used to distinguish overwash events in two sediment cores spanning the last one thousand years two prominent paleotempestites were observed in the top 20 cm of both cores the first identified as hurricane donna in 1960 whereas an older paleotempestite 1900 1930 could represent one of three documented storms in the early 1900s an active period of hurricane overwash from 1000 to 500 yrs bp and an inactive period from 500 to 150 yrs bp correlate with reconstructed ssts from the main development region mdr of the north atlantic ocean we observe an increased number of paleotempestites when mdr ssts are warmer coinciding with the medieval warm period and very few paleotempestites when mdr ssts are cooler coinciding with the little ice age results from this initial southwest florida study indicate that mdr ssts have been a key long term climate driver of intense southwest florida hurricane strikes

reconstructing relative flooding intensities responsible for hurricane induced deposits from laguna playa grande vieques puerto rico extreme coastal flooding primarily during hurricane strikes has deposited sand rich layers in laguna playa grande a back barrier lagoon located on the island of vieques puerto rico silici clastic grain size distributions within these overwash deposits fine landward away from the barrier and toward the mainland a simple advective settling model can explain this pattern of lateral sorting and is used to constrain the relative magnitude of past flooding events a deposit associated with the a d 1928 san felipe hurricane is used as a modern analogue to test the technique which produces reasonable estimates for wave heights that exceed the barrier during the event a 5000 yr reconstruction of local flooding intensity is developed that provides a measure of the competence for each overwash event to transport coarser grained sediment a fixed distance into the lagoon this reconstruction indicates that although the laguna playa grande record exhibits large scale changes in hurricane frequency on centennial to millennial time scales the magnitude of these events has stayed relatively constant over the last 5000 yr no evidence exists for an anomalously large hurricane or tsunami event with a competence for sediment transport greater than historical hurricane events

cortlandtitic enclaves associated with calc alkaline granites from tapia asturias hercynian belt northwestern spain abstract petrographic and mineralogical characteristics of amphibole olivine and pyroxene bearing ultramafic rocks from asturias nw spain are dealt with in this paper these rocks are of cortlandtitic type and occur as small rare enclaves in basic rocks related to hercynian calc alkaline post tectonic epizonal granites in the northwest of the iberian peninsula these particular ultramafic enclaves are characterized by poikilitic cumulate microtexture olivine fo 77 81 spinel from chromite to pleonaste composition enstatite subordinated diopside and sulphides are included in large brown calcic amphibole crystals displaying an irregular zonation phlogopite and plagioclase are also found in a much lower proportion between the large amphibole crystals mineral assemblage and chemical composition of minerals indicate formation conditions of 1150 c 7 8 kbar of p total and p h 2 o p total these rocks could represent the earlier products of fractional crystallization from a hydrated high alumina basalt involved in the genesis of the calc alkaline granites this basic magma would start crystallizing at a relatively deep level carrying up the first products of its crystallization during its ascent

the cortlandt complex evidence for large scale liquid immiscibility involving granodiorite and diorite magmas abstract granodiorite and diorite plutons of the rosetown complex n y which are associated with the nearby cortlandt complex have chemical and textural characteristics indicating that large scale liquid immiscibility played a major role in their petrogenesis rare earth element zirconium niobium and phosphorus abundances are much greater in the diorite precluding the possibility that the rosetown diorite and granodiorite are related by fractional crystallization the trace element data also eliminate the possibility that the granodiorite represents 1 a partial melt of crustal rocks including basalt 2 a granitic cumulate or 3 a residue from an aqueous fluid derived either from a silicate melt or crustal rocks liquid immiscibility appears to be viable model for the origin of the rosetown granodiorite and iron rich diorite this model is supported by the following 1 the major element compositions occur in a two liquid field on a greig diagram 2 both bodies have similar sr isotope compositions 3 common phases in the two rock types have overlapping compositions 4 the major and trace element data of the diorite and granodiorite are similar to the experimentally determined partition data of immiscible liquid pairs and 5 possible ocelli of iron rich diorite are found in the granodiorite

paleotempestology database for the western north atlantic basin paleotempestology the study of past tropical cyclone activity has grown considerably over the past two decades and there is now a relatively dense network of sites across the western north atlan

hurricane records on the south carolina coast can they be detected in the sediment record abstract more than 40 short cores were collected from 10 localities in the myrtle beach to mcclellandville coastline of south carolina the localities were selected on the basis of whether or not they should have a well preserved record of recent hurricanes most notably hugo which occurred in september 1989 of the 40 cores collected results from two sites are presented here as examples price s inlet a non tidal intra beach ridge area which was directly in the path of the eyewall of hugo and sandpiper pond which is a coastal non tidal pond near murrells inlet about 50 75 km north of where the main landfall of hurricane hugo but still in the area of high storm surge these cores were analyzed for percentage organic carbon visual observations x rays and microfossils the microfossils were used to differentiate marine non marine sequences in the non tidal inlets and identify reworked sediments by means of displaced benthic foraminifera cores were dated using pb 210 techniques that provide resolution for the last 100 yr in price s inlet the hugo effect was most pronounced with an 8 cm thick sand layer containing many nearshore foraminifera showing transport from offshore in sandpiper pond we could see the trace of hugo from the offshore foraminifera contained in sediments sandwiched between the freshwater intervals both before and after hugo however there was little detectable trace in the x rays or sedimentology of this core to indicate a storm event hence we can recognize a range of responses for hurricanes in the form of different types of sediment layers and microfossil assemblages in these non tidal areas depending on where the impact point is on the coast here we are able to distinguish at least two types of signals from the same storm which has significant implications for detecting these events in the pre historic record and determining their paleo periodicity

cenozoic dolomites of carbonate islands their attributes and origin abstract dolomites found on and below carbonate islands atolls and oceanic platforms provide useful insights into the origin of dolomite insights that may not be attainable from the study of more ancient cratonic dolomites for this reason they have been the subject of study for decades a critical mass of case studies now exist and some significant conclusions can be drawn from the cumulative data in most cases the association with an island is causal and not genetic nevertheless these dolomite occurrences are referred to herein as island dolomites one type of dolomite on carbonate islands is penecontemporaneous dolomite a phase that forms while the host sediment is in its original depositional setting island examples are holocene in age occur in holocene sediments and originate as a direct precipitate from either normal or evaporated seawater these are microcrystalline poorly ordered ca rich 18o enriched and geochemically unstable phases that are susceptible to recrystallization in the setting in which they formed post depositional dolomite is the other type of dolomite associated with carbonate islands this type of dolomite replaces older precursors and forms as cement distinctive characteristics include a dominance of fabric preserving texture pore lining cement rims that may exhibit micron scale banding with low mg calcite and formation in association with precursor dissolution sr isotopic dating indicates that all examples are neogene or quaternary in age those formed during the middle miocene through pliocene are massive laterally continuous and often multigenerational in contrast younger examples tend to be localized partial replacements of a single generation sr isotope ages also suggest global synchroneity in many dolomitization events which suggests a connection between dolomitization global eustacy and or global climatic factors geochemical attributes of post depositional island dolomites are ca enrichment positive 18o and 13c low sr contents 150 300 ppm and low fe global similarity in petrography and geochemistry of replacive island dolomites argues for a similar origin inferred origins however depend primarily on how 18o and sr data are interpreted values for 18o and dsr must be assumed due to uncertainties in oxygen isotope fractionation and sr partitioning there is no consensus or uniformity in those assumptions thus interpretations can vary and be biased to a desired result covariant trends in 13c and 18o some negative 13c values and high sr all favor a mixing zone origin but examples with these attributes are few lack of covariance in the isotopes mean 18o of 2 0 to 3 5 and low sr future studies should standardize the type of data collected and the analytical techniques employed multiple geochemical attributes should be measured on microsampled components and quantitative modeling should be employed in order to constraint interpretations as much as possible also needed are a better understanding of the kinetic processes that form these dolomites more careful assessment of their recrystallization status and an improved understanding of dsr and 18o at low temperature

heterogeneous diagenetic patterns in the pleistocene ironshore formation of grand cayman british west indies abstract the ironshore formation on grand cayman consists of six unconformity bounded units a to f that developed in response to repeated transgressive regressive cycles during the middle to late pleistocene corals and matrices in limestones from the rogers wreck point rwp offshore george town gt and western onshore wo areas are characterized by complex diagenetic fabrics that reflect marine bioerosion micrite envelopes internal sediments fibrous high mg calcite acicular aragonite isopachous prismatic calcite cements freshwater phreatic circumgranular cements even random blocky calcite cements and vadose meniscus calcite cements blocky calcite cements diagenesis throughout these limestones the matrices have undergone more meteoric diagenetic alteration than the corals overall however no systematic stratigraphic patterns exist to the distribution of these diagenetic fabrics and it is generally impossible to link the different phases of diagenesis with specific unconformities that cap each unit these heterogenous patterns of diagenetic features can be attributed to many intrinsic and extrinsic factors including the original compositions of the different components in the limestones the porosity and permeability of the substrate the nature of the diagenetic fluids climate and the duration of exposure during each lowstand integration of available data however indicates that maximum diagenesis took place during the lowstands denoted by the unconformities at the top of unit c marine isotope stage 7 and unit d marine isotope stage 5e when long periods of exposure were accompanied by wet climates with high annual rainfalls

a 1500 yr record of north atlantic storm activity based on optically dated relict beach scarps understanding of long term dynamics of intense coastal storms is important for determining the frequency and impact of these events on sandy coasts we use optically stimulated luminescence osl dates on relict scarps within a prograded barrier sequence to reconstruct the chronology of large magnitude erosional events in the western gulf of maine osl dates obtained on quartz rich sediments immediately overlying relict scarps indicate severe beach erosion and retreat due to erosional events ca 1550 390 290 and 150 cal yr b p our data provide new evidence of increased storm activity most likely frequency and or intensity of extratropical storms during the past 500 yr which was preceded by a relatively calm period lasting 1000 yr the width of the coastal sequence preserved between successive paleoscarps shows strong correlation with the time interval elapsed between storms our fi ndings indicate that diagnostic geophysical and sedimentological signatures of severe erosional events offer new opportunities for assessing the impact and timing of major storms along sandy coasts

a 1900 year paleohurricane record from wassaw island georgia usa we present here the first paleotempestology record from wassaw island on the georgia bight located in the south atlantic coast of the united states in the historical period the georgia bight has experienced less frequent hits by hurricanes than other locations along the us gulf and atlantic coasts the 1900 year record inferred from the overwash sand layers from a back barrier marsh on wassaw island suggests that the island was directly struck by major storms on nine occasions during this interval the wassaw island record shows alternating regimes with periods of increased activity from 2000 a bp until 1100 a bp and 100 a bp until the present sandwiching a quiet period from 1100 to 250 a bp storm deposits from the most recent active period are perhaps amalgamated indicating that site specific conditions may result in event undercounting and suggests that the relative thickness of sand layers in the sedimentary record is not always indicative of hurricane strength copyright 2011 john wiley sons ltd

tropical cyclone wind speed constraints from resultant storm surge deposition a 2500 year reconstruction of hurricane activity from st marks fl 1 recent work suggests that the patterns of intense category 3 on the saffir simpson scale hurricane strikes over the last few millennia might differ from that of overall hurricane activity during this period prior studies typically rely on assigning a threshold storm intensity required to produce a sedimentological overwash signal at a particular coastal site based on historical analogs here we improve on this approach by presenting a new inverse model technique that constrains the most likely wind speeds required to transport the maximum grain size within resultant storm deposits as a case study the technique is applied to event layers observed in sediments collected from a coastal sinkhole in northwestern florida we find that 1 simulated wind speeds for modern deposits are consistent with the intensities for historical hurricanes affecting the site 2 all deposits throughout the 2500 year record are capable of being produced by hurricanes and 3 a period of increased intense hurricane frequency is observed between 1700 and 600 years b p and decreased intense storm frequency is observed from 2500 to 1700 and 600 years b p to the present this is consistent with prior reconstructions from nearby sites changes in the frequency of intense hurricane strikes may be related to the degree of penetration of the loop current in the gulf of mexico

passage of tropical storm allison 2001 over southeast texas recorded in δ18o values of ostracoda freshwater ostracoda collected in ephemeral pond waters derived from tropical storm allison 2001 texas recorded the unusually low oxygen isotope values of that storm therefore the potential clearly exists in locations where tropical cyclones make landfall to obtain a long term record of tropical cyclone activity from fossil ostracode calcite

evidence of similar probablility of intense hurricane strikes for the gulf of mexico over the late holocene hurricane magnitude and frequency have been linked to numerous mechanisms including the steady rise in annual sea surface temperatures el nino southern oscillation enso variations and atmospheric changes in order to better understand those factors that control hurricane magnitude and frequency a long term record spanning the entire gulf of mexico coast is needed here we present a detailed record from ca 5300 900 yr b p of past intense hurricane impacts for cores collected from laguna madre texas united states relative storm intensities were calculated for each event and the average intense storm impact probability for south texas was determined to be 0 46 annual landfall probability previous field studies in western lake florida and lake shelby alabama reveal similar probability intense hurricane strikes of 0 39 although high frequency oscillations between warm and dry and cool and wet climate conditions have occurred in texas through the late holocene there has been no notable variation in intense storm impacts across the northwestern gulf of mexico coast during this time interval implying no direct link between these changing climate conditions and annual hurricane impact probability in addition there have been no significant differences in the landfall probabilities of storms between the eastern and western gulf of mexico during the late holocene suggesting that storm steering mechanisms have not varied during this time

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

fluvial activity in major river basins of the eastern united states during the holocene in the eastern united states existing paleo reconstructions in fluvial environments consist primarily of site specific investigations of climate and human impacts on riverine processes this paper

al cr ratios of coexisting pyroxenes and spinellids in some ultramafic rocks abstract al cr atomic ratios of coexisting spinellids and ortho and clinopyroxenes show a pattern of sympathetic variation that persists through ultramafic rocks of layered mafic complexes of upper crustal type alpine complexes and the nodules found in kimberlites and alkaline basalts simple expressions are empirically derived to link al cr orthopyroxene and al cr spinel ratios in putatively equilibrated rocks equivalence of spinel compositions in shallow layered complexes and kimberlite nodules of deep seated origin negates direct crystallochemical control of al cr ratios of spinels by pressure the application of various pyroxene geothermometers evinces no correlation between al cr spinel ratios and temperature whereas high al spinels characterize simple four phase olivine orthopyroxene clinopyroxene spinel peridotites low al spinels typify peridotites with other aluminous phases garnet amphibole mica or plagioclase the role of pressure in determining spinel compositions is therefore indirect insofar as it controls the stability of other phases into which al is partitioned

the variscan calc alkalic plutonism of western corsica mineralogy and major and trace element geochemistry abstract petrographic and structural observations on the calc alkalic plutonism of western corsica revealed the existence of several successively emplaced units associated with large basic bodies the present mineralogical and geochemical study deals with the genesis evolution and relationships of these different units basic plutonism is represented by three genetically linked types of rock norites and troctolites with cumulate textures characterized by low ree contents and either no eu anomaly or a positive eu anomaly gabbros with enriched lree relatively to hree patterns probably close to an initial basaltic liquid and diorites ranging up to charnockites which represent liquids evolved to varying degrees mainly by fractional crystallization trace element data and studies on the evolution of pyroxene pairs demonstrate the consanguinity of these calc alkaline basic rocks which are derived from a high alumina basaltic melt the various granitoids granodiorites monzogranites and leucocratic monzogranites i e adamellites have distinct evolution trends as shown by the composition of their mafic minerals and by trace element distributions they cannot be considered as being derivatives of the basic suite and they cannot be related by a common fractionation sequence rather they represent distinctive batches of crustal anatexis in addition hybridization phenomena with the basic melt are noticed in granodiorites the particular problem of the low la yb eu eu and the high u th cs leucocratic monzogranites is discussed in detail in addition to more conventional trace element diagrams the simultaneous statistical treatment of all the geochemical data by correspondence factor analysis is shown to be a very use tool in distinguishing between the different units and to classify the elements according to their geochemical properties

lake sediment record of late holocene hurricane activities from coastal alabama coastal lake sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene time frederic a category 3 hurricane that struck the alabama coast on the gulf of mexico in 1979 left a distinct sand layer in the nearshore sediments of lake shelby as a result of storm tide overwash of beaches and dunes sediment cores taken from the center of lake shelby contain multiple sand layers suggesting that major hurricanes of category 4 or 5 intensity directly struck the alabama coast at ca 3 2 3 0 2 6 2 2 1 4 and 0 8 ka 14 c yr with an average recurrence interval of 600 yr the alabama coast is likely to be struck by a category 4 or 5 hurricane within the next century

origin of dolomite in the third member of feixianguan formation lower triassic in the jiannan area sichuan basin china abstract the third member of feixianguan formation jiannan area consists of marine carbonates parts of which were dolomitized to form high quality reservoirs based on petrographical features three types of dolomite phases are distinguished including very finely finely crystalline dolomite type d1 medium crystalline dolomite type d2 and coarse crystalline saddle dolomite type d3 type d1 dolomite has characteristics of micritic to fine crystals 18 o values imply partly diagenetic stabilitization during burial type d2 dolomite has characteristics of mainly medium 100 250 m subhedral crystals with zoned to uniform dull red cl the estimates from 18 o values suggest precipitation at depths of 760 1100 m values of 13 c and 87 sr 86 sr of type d2 are similar to values of host limestone suggesting that dolomitization was mediated by t 1 f 3 seawater like fluids type d3 is strictly associated with type d2 high homogenization temperatures and limited distributions indicate that type d3 formed in a deep closed environment dolostone made of type d1 dolomite is volumetrically minor and is characterized by micropores and low permeability while type d3 as a void filling cement slightly reduces the reservoir porosity high quality reservoirs are only intimately associated with dolostone made of type d2 a burial compaction model is proposed for type d2 mg 2 was derived from seawater derived compaction fluid that was expelled from the trough strata the potential high quality reservoirs are likely to occur in opposing margin shoals

evaluation of carbonate diagenesis a comparative study of minor elements trace elements and rare earth elements ree y between pleistocene corals and matrices from grand cayman british west indies abstract on grand cayman the pleistocene ironshore formation consists of six unconformity bounded units of limestones that have been partially or completely altered to calcite by post depositional meteoric diagenesis in order to examine the diagenetic history from the perspective of geochemical elements the concentrations of minor element sr na mg trace elements ba fe mn al si and rare earth elements ree and yttrium y were determined for 105 corals and 84 matrices collected from the rogers wreck point rwp western onshore area wo and offshore george town gt areas with the transformation of aragonite to calcite the sr na and ba values decreased but mg increased which are indicative of diagenetic alteration in an open water system due to intrinsic vital effects and the extrinsic diagenetic environment the variations of sr na ba and mg concentrations between acropora and montastrea from the gt area are different to those of their counterparts from rwp and wo the signatures of sr na ba and mg are in good agreement with the diagenetic history as determined from petrographic and stable isotopic criteria the ree y rey concentrations rey are higher in the matrices 0 2 6 9 ppm average 2 6 ppm than in the associated corals 0 1 5 4 ppm average 0 6 ppm shale normalized rey patterns of the pleistocene ironshore formation are similar to those of oxygenated seawater which are characterized by 1 light ree depletion relative to heavy ree average dy sn sm sn 1 7 n 35 2 positive la anomalies average pr pr 1 17 n 53 and 3 negative ce anomalies average ce ce 0 49 n 53 the preserved seawater like rey distribution pattern the lack of correlation between rey and mineralogy and the lack of correlation between rey and diagenesis sensitive stable oxygen isotope 18 o indicate that meteoric diagenesis did not have a major impact on the rey distribution patterns the matrices and corals in the gt area compared to their counterparts from rwp and wo have relatively less depleted lree and lower y in rey distribution pattern suggesting contamination by minor amounts of detrital sediments this is supported by the fact that limestones from the gt area contain abnormally high contents of detrital elements al si the variations in rey in carbonate rocks from locality to locality probably reflect variations that existed in the local depositional environments where these deposits originally formed

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

a backbarrier overwash record of intense storms from brigantine new jersey abstract analysis of aerial photographs and historic charts indicates that the barrier beach at brigantine nj has migrated landward 300 to 400 m since 1869 primarily as a result of overwash during hurricanes and winter storms a series of vibracores from the backbarrier salt marsh reveals a millennial scale stratigraphic record of overwash deposition carbon 14 c 14 and cesium 137 cs 137 radioisotopic methods were used to date overwash deposits washovers the ages of recent washovers are consistent with deposition during intense storms in 1938 1944 1950 and 1962 an additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788 two prehistoric overwash fans were likely deposited by intense storms striking the new jersey coast in the 7th to 14th centuries and 6th to 7th centuries a d the landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans the greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period the hurricane of 1821 the spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments

reconstructing 7000 years of north atlantic hurricane variability using deep sea sediment cores from the western great bahama bank q1 enso show abrupt changes around 6000 yrs b p but most coastal sedimentary records do not span this time period establishing longer records is essential for understanding mid holocene patterns of storminess and their climatic drivers which will lead to better forecasting of how climate change over the next century may affect tropical cyclone frequency and intensity storms are thought to be an important mechanism for transporting coarse sediment from shallow carbonate platforms to the deep sea and bank edge sediments may offer an unexplored archive of long term hurricane activity here we develop this new approach reconstructing more than 7000 years of north atlantic hurricane variability using coarse grained deposits in sediment cores from the leeward margin of the great bahama bank high energy event layers within the resulting archive are 1 broadly correlated throughout an offbank transect of multi cores 2 closely matched with historic hurricane events and 3 synchronous with previous intervals of heightened north atlantic hurricane activity in overwash reconstructions from puerto rico and elsewhere in the bahamas lower storm frequency prior to 4400 yrs b p in our records suggests that precession and increased nh summer insolation may have greatly limited hurricane potential intensity outweighing weakened enso and a stronger west african monsoon factors thought to be favorable for hurricane development

evaluation of olivine spinel geothermometry as an indicator of thermal history for peridotites olivine and spinel in peridotites from the miyamori ultramafic complex and the ichinogemata crater of northeast japan show a systematic variation in the mg mg fe ratio which is correlated mainly with the grain size of spinel this correlation can be explained by a diffusion model assuming a semi infinite composite sphere under cooling or heating conditions in order to obtain absolute temperatures of thermal events the olivine spinel geothermometer is applied to pairs of spinel core and olivine core average composition the calculated temperatures range over two hundred degrees and have a systematic relationship with the grain size of spinel in the miyamori complex the calculated temperatures decrease monotonically with decrease in grain size of spinel whereas in the ichinomegata lherzolite nodule those of spinel smaller than 0 2 mm increase as the grain size decreases and those of spinel larger than 0 2 mm remain constant regardless of further increase in grain size these observations in the light of the diffusion model suggest that the miyamori complex may have cooled from higher than 800 c to lower than 600 c and that the lherzolite nodule from the ichinomegata crater may have been in equilibrium at 900 c before it was heated above 1 100 c for less than a few days these two examples indicate that olivine spinel pairs of peridotites do not always indicate an appropriate equilibration temperature we cannot interpret the supposed equilibration temperatures until the existence of isothermal stages in the thermal history of peridotites is established by carefully checking the chemical heterogeneity

δ13c and δ18o values of triassic brachiopods and carbonate rocks as proxies for coeval seawater and palaeotemperature abstract a dataset of 160 isotope 13c and 18o values from anisian ladinian carnian and rhaetian articulate brachiopod shells complemented by 158 carbon and oxygen isotope values from whole rock carbonates define the first continuous stable isotope baseline trends for the triassic seawater the carbon isotope data suggest the existence of several short term high amplitude excursions in the early triassic followed by a predominance of values around 0 5 1 during the middle triassic a rise to 3 5 during the carnian plateau at this level during the late carnian to early norian and a 1 5 decline in the middle norian to values around 2 during the late norian rhaetian interval the causation scenarios for these rapid oscillations are at present equivocal but may in part reflect a biological instability of the carbon cycle following the recovery from the end permian extinction event and or an input of mantle derived co2 from enhanced volcanic activity the 18o values from well preserved brachiopods from the tethyan realm range from 3 9 to 0 6 v pdb these values require open marine triassic seawater 18o values close to 0 v smow for the calculated temperatures to be within the range of tolerance of the coexisting reef building corals a 2 18o increase within the uppermost cordevolian and early julian suggests either a distinct temperature decline in the southern alps during that time interval an increase in seawater salinity or their combination oxygen isotope values for the muschelkalk brachiopods range between 6 2 and 2 0 and likely reflect a strong influx of meteoric waters into the germanic basin that shifted the oxygen isotopes to more negative values

multiple episodes of dolomitization and dolomite recrystallization during shallow burial in upper jurassic shelf carbonates eastern swabian alb southern germany abstract the upper jurassic of the eastern swabian alb is composed of oolitic platform sands with associated microbe siliceous sponge mounds at the platform margins they are surrounded by argillaceous or calcareous mudstones and marl limestone alternations deposited in adjacent marl basins partial to complete dolomitization is predominantly confined to the mound facies six types of dolomite as well as one type of ankerite document a complex diagenetic history during shallow burial with multiple episodes of dolomite formation and recrystallization the earliest massive matrix dolomitization is ca rich has slightly depleted oxygen isotope values relative to late jurassic seawater and carbon isotopic values in equilibrium with late jurassic seawater this initial massive matrix dolomitization occurred during latest jurassic to earliest cretaceous and is related to pressure dissolution during very shallow burial at temperatures of at least 50 c hydrologic conditions and mass balance calculations indicate that burial compaction provided sufficient fluids for dolomitization mg is derived from negligibly modified seawater that was expelled from the adjacent off reef strata into the mound facies position of the mounds along the platform margins controlled the distribution of the shallow burial dolomite covariant trends between textural modification increasing stoichiometry partial changes in trace element content mn fe sr and depletion in stable isotopes as well as distinctive cl pattern illustrate two recrystallization phases of the precursor matrix dolomite during further burial at elevated temperatures strong sr enrichment of the second phase of recrystallized dolomite is ascribed to sr rich meteoric waters descending from overlying aragonite bearing reef limestones or evaporite bearing peritidal carbonates late stage coarsely crystalline dolomite cements occur as vug and fracture fillings and formed during burial ankerite associated with sulphide and sulphate minerals and saddle dolomite are assumed to have formed from hydrothermal waters that moved to higher stratigraphic levels along fracture conduit systems that developed during late cretaceous to tertiary alpine orogenesis

sedimentary evidence of hurricane strikes in western long island new york 1 evidence of historical landfalling hurricanes and prehistoric storms has been recovered from backbarrier environments in the new york city area overwash deposits correlate with landfalls of the most intense documented hurricanes in the area including the hurricanes of 1893 1821 1788 and 1693 a d there is little evidence of intense hurricane landfalls in the region for several hundred years prior to the late 17th century a d the apparent increase in intense hurricane landfalls around 300 years ago occurs during the latter half of the little ice age a time of lower tropical sea surface temperatures multiple washovers laid down between 2200 and 900 cal yr b p suggest an interval of frequent intense hurricane landfalls in the region our results provide preliminary evidence that fluctuations in intense hurricane landfall in the northeastern united states were roughly synchronous with hurricane landfall fluctuations observed for the caribbean and gulf coast suggesting north atlantic wide changes in hurricane activity

δ18o and δ13c of permian brachiopods a record of seawater evolution and continental glaciation abstract two hundred sixty four 18 o and 13 c values of permian articulate brachiopod shells were analyzed and 81 of these values were characterized as well preserved and biostratigraphically well defined these were then utilized for construction of baseline oxygen and carbon isotope curves for the permian interval in addition 21 13 c whole rock values are reported for the wordian and capitanian the early permian asselian to artinskian times are characterized by 2 5 decrease in oxygen isotope values from 0 7 to 3 3 v pdb this is attributed to a 4 7 c increase in temperature in the southern urals concomitant with the retreat of the permo carboniferous ice sheets and return of the 18 o depleted melt water into the oceans the late permian samples from iran jolfa at kuh e ali bashi and china meishan yield 18 o values and presumably temperatures similar to those that followed the termination of the large scale glaciation in the lower permian in between the upper kungurian to capitanian samples from the delaware basin guadalupe mountains are enriched in 18 o at 1 5 to 3 we have no definitive explanation for these data but tentatively suggest that the anomaly can potentially be a result of evaporative enrichment of seawater in 18 o due to intracratonic arid setting of the basin the 18 o enriched nature of the zechstein samples 1 2 to 2 5 on the other hand is in all probability a reflection of the high evaporation rates in the zechstein sea the permian interval is characterized by a relatively constant 13 c at about 4 the exceptions are again the brachiopods from the delaware basin guadalupe mountains which show 1 6 increase in the guadalupian to values of up to 5 9 in the wordian a tentative explanation as in the case of oxygen is based on the proposition that the semi enclosed delaware basin was likely stratified with sequestration of the 13 c depleted carbon to the deeper water layers and a complementary 13 c enrichment in the upper oxygenated layer the coeval open ocean water dic may have been similar to that of the remainder of the permian interval at 4 as indicated by whole rock carbonate samples from oman sicily and iran in the latest permian the trend mimics the well known 13 c drop at the permian triassic boundary

a sedimentary based history of hurricane strikes on the southern caribbean coast of nicaragua abstract multi millennial hurricane landfall records from the western north atlantic indicate that landfall frequency has varied dramatically over time punctuated by multi centennial to millennial scale periods of hyperactivity we extend the record geographically by presenting a paleostrike record inferred from a four core transect from a marsh on the caribbean coast of nicaragua fossil pollen indicates that the site was a highly organic wetland from 5400 4900 cal yr bp at which time it became a shallow marine lagoon until 2800 cal yr bp when it transitioned back into swamp marsh freshening over time with the present fresh to brackish typha marsh developing over the very recent past hurricane joan 1988 is recorded as a distinctive light colored sand silt clay layer across the top of the transect identifiable by abrupt shifts in color from the dark marsh deposits increased grain size and two upward fining sequences which are interpreted as representing the storm s traction and suspension loads the six layers identified as hurricane generated display temporal clustering featuring a marked increase in landfall frequency 800 cal yr bp this pattern is anti phase with the activity pattern previously identified from the northern caribbean and the atlantic coast of north america thereby opposing the view that hyperactivity occurs simultaneously across the entire basin

calibrating a sedimentary record of overwash from southeastern new england using modeled historic hurricane surges we present a 2000 year record of overwash deposits preserved in a backbarrier salt marsh from southeastern new england the timing of recent deposits matches well with large hurricane induced storm surge events documented by local tide gauges in 1991 1960 1954 and 1938 storm surge modeling is used to evaluate the flooding history at the site as well as to assess the pre instrumental historical record storms in 1815 1727 and 1635 likely caused significant surge that overtopped the barrier with the timing of coarse grained overwash deposition correlating well with these events we infer that twenty three prehistoric layers mapped across the site were likely also deposited by landfalling hurricanes additional records from the area will help to evaluate whether or not temporal trends at the site are a robust representation of hurricane activity for the region the frequency of overwash at mattapoisett marsh on average 1 5 events per century is significantly higher than many other overwash based reconstructions from the western north atlantic further the mattapoisett marsh record does not contain significant multi centennial gaps in overwash layers this initial comparison of the data from mattapoisett marsh with other reconstructions from the western north atlantic may point toward relatively constant tropical cyclone frequency over the last 2000 years with significant variation in the number of intense tropical cyclones

significance of enclave roundness an inherent characteristic enclaves are a ubiquitous feature of most felsic plutons and are important to understanding pluton genesis the initial shape of an enclave released in a fracture system is a function of the stress field at the crack tip and not necessarily an indication of post formation assimilation or erosion in the host magma if at the tip of a fracture the principal stresses are perpendicular to the fracture planes and there is no shearing then enclaves are angular if on the other hand shear stresses are present at the fracture tip and the shearing displacement is perpendicular to the propagating crack front then the crack will propagate in a curved fashion these enclaves when released will have a rounded or ovoid shape

testing coral based tropical cyclone reconstructions an example from puerto rico abstract complimenting modern records of tropical cyclone activity with longer historical and paleoclimatological records would increase our understanding of natural tropical cyclone variability on decadal to centennial time scales tropical cyclones produce large amounts of precipitation with significantly lower 18 o values than normal precipitation and hence may be geochemically identifiable as negative 18 o anomalies in marine carbonate 18 o records this study investigates the usefulness of coral skeletal 18 o as a means of reconstructing past tropical cyclone events isotopic modeling of rainfall mixing with seawater shows that detecting an isotopic signal from a tropical cyclone in a coral requires a salinity of 33 psu at the time of coral growth but this threshold is dependent on the isotopic composition of both fresh and saline end members a comparison between coral 18 o and historical records of tropical cyclone activity river discharge and precipitation from multiple sites in puerto rico shows that tropical cyclones are not distinguishable in the coral record from normal rainfall using this approach at these sites

the sedimentary record of the 2005 hurricane season from the mississippi and alabama coastlines abstract the instrumental record of hurricane activity is too short to fully capture the occurrence of the rare but most destructive hurricanes therefore obtaining a record of present and past landfalling hurricanes and their extent of geological and ecological impacts is one means to assess future risk reveal the spatial and temporal variability of hurricane activity and decipher its relationship with global climatic changes we rapidly dispatched survey teams to collect the readily available but perishable data of hurricanes katrina and rita storm surge from two salt marshes in mississippi and one salt marsh in alabama in mississippi we recorded hurricane katrina storm surge heights greater than 7 5 m north american vertical datum 88 navd88 with inland extents in excess of 700 m whereas in alabama the maximum recorded storm surge was 3 43 m navd88 at one salt marsh in mississippi we recorded the maximum inland extent and elevation of maximum penetration of hurricane rita as 370 m and 3 43 m navd88 respectively we observed a three dimensional distribution of hurricane induced storm surge deposits that tapered landward overlying salt marsh sediment there was a sharp or erosional boundary between the pre storm surge and storm surge sedimentary units which was accompanied by a change in color and lithology the overlying storm surge sediment unit was coarser than the pre storm surge unit with a lower organic content the thickness of the hurricanes katrina and rita storm surge sediments ranged from 9 to 13 cm and approximately 7 cm respectively foraminiferal analyses revealed a virtual absence of tests within the storm surge sediments whereas abundant agglutinated foraminifera were found in the underlying salt marsh deposits

palaeohurricane reconstructions from sedimentary archives along the gulf of mexico caribbean sea and western north atlantic ocean margins hurricanes annually threaten the atlantic ocean margins historical hurricane records are relatively short and palaeohurricane sedimentary archives provide a geological and climatic context that sheds light on future hurricane activity here we review palaeo trends in hurricane activity elucidated from sedimentary archives we discuss dating methods site selection and stat istics associated with previously published records these archives have been useful for under standing the long term evolution of coastal systems and the response of intense hurricane activity to climatic changes regional shifts in hurricane overwash on centennial to millennial timescales have been linked to various climatic modes of variability including el nino southern oscillation and the north atlantic oscillation but could also reflect regional scale controls on hurricane activity

foraminifera as an indicator of overwash deposits barrier island sediment supply and barrier island evolution folly island south carolina abstract micropaleontological analysis of four vibracores from back barrier marshes of folly island south carolina detected intervals of storm deposited sediment individual washover intervals were not detectable from lithology alone but only in conjunction with associated foraminifera washovers contained more modern offshore and oligo miocene genera and total calcareous foraminifera than background marsh samples the presence of tertiary foraminifera in the back barrier cores from folly island supports the hypothesis that much of the sediment for barrier island migration is derived from offshore foraminiferal analyses of back barrier cores were also used to calculate relative bioturbation rates by the method of officer and lynch officer c b lynch d r 1983 mixing sedimentation rates and age dating for sediment cores mar geol 46 261 278 eqs 10 14 in all cores the current depositional environment correlated well with the expected mixing parameter g the highest mixing parameter greatest signal attenuation was recorded in a core from a low marsh creek side environment whereas the lowest mixing parameter least smearing of signal was recorded in a high marsh core

600 year sedimentary archive of hurricane strikes in a prograding beach ridge plain southwestern louisiana abstract this study tests a novel approach to paleotempestology substituting the lateral time depth of a prograding beach ridge plain for the vertical time depth of an aggrading coastal lake pond lagoon swamp or marsh trenching and coring of a beach ridge plain in southwestern louisiana revealed six sand beds and one shell bed interpreted as hurricane washover deposits the sand beds are readily distinguished from enclosing marsh sediments by their higher sand content lower organic content and contrasting microfossil assemblages based on the modern analogs of hurricanes audrey 1957 rita 2005 and ike 2008 and consideration of nearby landfalling hurricanes in the historical record it was determined that the storm intensity threshold of the study site is equivalent to a category 3 hurricane there is a wide variation in hurricane strike frequency between this site and other sites bordering the gulf of mexico this variation results from differences in site sensitivity and the nature of geologic or geochemical proxies used to derive hurricane strike records the approach demonstrated by this study could have applicability at other sites around the world where beach ridge plains are subject to tropical cyclone strikes

sedimentary evidence of intense hurricane strikes from new jersey nine vibracores from the backbarrier marsh at whale beach new jersey reveal three large scale overwash deposits associated with historic and prehistoric storms the uppermost and smallest overwash fan was deposited in the ash wednesday northeaster of march 5 8 1962 a second more substantial overwash fan between 100 and 35 cm depth dates to the late eighteenth or early nineteenth century this fan was most likely deposited during the 1821 hurricane the only intense hurricane to make landfall in new jersey in the past 350 yr a third larger overwash fan between 200 and 300 cm depth was deposited between a d 1278 and 1438 and is likely the result of a prehistoric intense hurricane strike the combination of historical and stratigraphic evidence indicates that two intense hurricanes winds 50 ms 21 have likely made landfall on the southern new jersey coast in the past 700 yr resulting in an annual landfall probability of 0 3

pressure temperature dependent compositional variation of phlogopitic micas in upper mantle peridotites compositional variation of phlogopitic micas in upper mantle peridotites is reviewed phlogopitic micas in garnet peridotites are systematically lower in al or eastonite component than those in spinel peridotites the core of phlogopite megacryst and phenocryst of kimberlite is always lower in al than the rim it is apparent that al al si ratio or eastonite component in phlogopitic micas in ultramafic rocks is controlled by the equilibrium pressure and temperature in the upper mantle peridotites containing garnet or spinel the al al si ratio of phlogopitic mica decreases with increasing pressure at constant temperature phlogopitic mica is a potential thermo barometer in both garnet and spinel peridotite facies

petrography and geochemistry of the permian triassic boundary interval yangou section south china implications for early griesbachian seawater δ 13 c dic gradient with depth abstract the carbon isotopic composition 13 c carb recorded in shelf carbonates has been widely used as a proxy for the isotopic composition 13 c dic of surface ocean water to establish paleocean chemistry and circulation patterns however 13 c carb values do not necessarily preserve the 13 c dic due to post depositional diagenetic alteration in order to examine the early griesbachian surface to deep 13 c dic gradient with depth the diagenetic features of the permian triassic boundary interval beds 18 to 35 from yangou section located in the yangtze carbonate platform interior south china are delineated to compare with those of the slope gssp meishan section the petrographic and geochemical observations show that the early griesbachian carbonates in the yangou section underwent pervasive dolomitization in its early diagenetic history three types of early replacement dolomites and one type of dolomite cement are present the dolomite crystals display internal zonation with high ca calcian dolomite hcd core being encased successively by calcite and an outermost fe rich hcd cortex the initial dolomitization took place in anoxic seawater and underwent subsequent diagenetic system involved with meteoric water the two most negative 13 c values in claystones of beds 21 3 and 35 are probably related to meteoric diagenesis above and or below the meteorically influenced beds the dolomite and calcite have uniformly positive 13 c values the primary carbon isotopic compositions are probably preserved in the early griesbachian carbonate from the platform yangou section which could probably be related to the poor formation of the outermost fe rich hcd cortex compared to the slope carbonate from the meishan section the platform carbonate from the yangou section has lower primary 13 c carb values it is estimated that the 13 c dic gradient with depth between yangou and meishan is less than the previously suggested the results highlight the need for evaluation of local 13 c carb as record of 13 c dic in paleoseawater and carry important implications for understanding the permian triassic carbonate successions throughout the world

reconstruction of prehistoric landfall frequencies of catastrophic hurricanes in northwestern florida from lake sediment records abstract sediment cores from western lake provide a 7000 yr record of coastal environmental changes and catastrophic hurricane landfalls along the gulf coast of the florida panhandle using hurricane opal as a modern analog we infer that overwash sand layers occurring near the center of the lake were caused by catastrophic hurricanes of category 4 or 5 intensity few catastrophic hurricanes struck the western lake area during two quiescent periods 3400 5000 and 0 1000 14 c yr b p the landfall probabilities increased dramatically to ca 0 5 per yr during an hyperactive period from 1000 3400 14 c yr b p especially in the first millennium a d the millennial scale variability in catastrophic hurricane landfalls along the gulf coast is probably controlled by shifts in the position of the jet stream and the bermuda high

current perspectives on the capabilities of high resolution xrf core scanners abstract the introduction and application of high resolution xrf core scanners has made an enormous contribution to palaeoclimate science over the last two decades these core scanners have become essential analytical tools for the investigation of sedimentary and other natural cumulative records of environmental change their widespread adoption by the environmental and geoscience communities has had a significant impact on the ability to systematically record high resolution chemical profiles in marine and lake sediments and soils the range of applications has broadened beyond sedimentology and palaeoclimatology and now extends into scanning samples of speleothems corals mumiyo mounds rocks sedimentary nodules archaeological artefacts tree sections and melt segregations other areas exploiting the capability of xrf core scanners are mineral exploration geotechnical characterisation soil remediation studies and carbon capture and storage research as a consequence of their ability to efficiently determine detailed non destructive elemental records in sediments and soils scientific papers published since the year 2000 now number more than 1000

the origin of common dolomite fabrics clues from the pliocene abstract characteristic features common to dolomites of all ages are found in pliocene dolomites from the netherlands antilles these features include 1 pseudomorphic replacement 2 selective replacement 3 fossil moldic porosity 4 cloudy centered clear rimmed dolomite 5 sucrosic dolomite and 6 dolomite cement the development of a particular feature is controlled by 1 mineralogy of the material being replaced 2 the degree of saturation of the bulk solution with respect to the mineral being replaced and 3 the availability of dolomite nucleation sites low mg calcite lmc cement and fossils were often neither replaced by dolomite nor dissolved but aragonite and high mg calcite hmc were both replaced and dissolved the resistence of lmc to dolomitization was due to solutions saturated with respect to lmc and the lack of nucleation sites cryptocrystalline lmc was more readily replaced by dolomite because it provides more nucleation sites cloudy centered clear rimmed dolomite and sucrosic dolomite formed in sediments with abundant lmc and few nucleation sites fossil moldic porosity developed concurrent with pseudomorphic replacement suggesting that the dolomitizing solution was undersaturated with respect to the mineral being replaced dolomite cement commonly lines pores and fills intraparticle pore space dolomite cement occasionally has inclusions of a precursor lmc cement dolomite cement crystals are larger than replacement crystals because there are fewer nucleation sites for the cement crystals

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

storm erosion during the past 2000 years along the north shore of delaware bay usa abstract the recent impacts of tropical cyclones and severe storms on the u s atlantic coast brought into focus the need for extended records of storm activity from different geomorphologic settings such reconstructions are typically developed from sites that experienced repeated overwash of sand into low energy depositional environments however salt marsh sediment may also preserve a record of repeated erosion from tropical cyclones and storms we describe late holocene sediments beneath the sea breeze salt marsh delaware bay new jersey from more than 200 gouge cores positioned along seven transects the stratigraphic record documents at least seven depositional sequences consisting of salt marsh peat and mud couplets that represent dramatic changes in sedimentation regime there are a number of processes that could produce these stratigraphic sequences against a background of rising relative sea level including lateral migration of tidal creeks tidal channel network and or drainage ditch expansion changes in sediment delivery rates rapid relative sea level change tsunami and formation of salt pans the abrupt contacts between the salt marsh peat and overlying intertidal mud suggest that erosion of the peat was followed by rapid infilling of accommodation space correlation of erosional surfaces across 2 5 km suggests a common mechanism and we propose that the erosion was caused by tropical cyclones and or storms we developed a chronology of repeated salt marsh erosion and recovery using 137cs metal pollution pb concentration and stable isotopes and radiocarbon data two recent episodes of salt marsh erosion may correlate with historic tropical cyclones in ad 1903 and ad 1821 1788 that impacted the atlantic coast of new jersey but the erosive nature of the sea breeze site hinders definitive correlation prehistoric erosional sequences correlate with overwash fans preserved in the regional sedimentary record we estimated that it takes from several decades to almost 200 years for salt marshes to recover from storm erosion

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

dolomitization of the pedro castle formation pliocene cayman brac british west indies abstract the pedro castle formation pliocene on cayman brac is variably dolomitized by texture preserving but non mimetic and texture destructive replacive dolomite mimetic replacement of skeletal grains is limited to echinoderm plates and with few rare exceptions there is no mimetic replacement of red algae foraminifera green algae or any other type of skeletal grain the lack of mimetic dolomite is atypical of island dolostones found in the caribbean sea and the pacific ocean dolostones in the pedro castle formation are formed entirely of high ca calcian dolomite average of 57 4 mol caco 3 oxygen isotopes mean 1 25 pdb from the dolomite indicate that dolomitization was mediated by seawater or modified seawater carbon isotopes in the dolomite which range from 1 81 to 1 42 pdb were probably inherited from the precursor limestone the average sr content in the dolomite 360 ppm is higher than that found in most other island dolomites the sediments that now form the pedro castle formation were deposited in shallow water on an open bank during the early pliocene pre dolomitization diagenesis of those sediments included syntaxial overgrowths around echinoderm fragments dissolution of aragonitic bioclasts stabilization to low magnesium calcite and local precipitation of vadose cements thus the limestones had been extensively stabilized by the time that dolomitization took place during the late pliocene the general paucity of mimetic replacement in these dolostones can probably be attributed to the calcite stabilization that took place before dolomitization

a unique geochemical record at the permian triassic boundary a 330 metre core drilled through the marine permian triassic boundary in the carnic alps of austria allows closely correlated studies of geochemistry petrography and palaeontology across the boundary the isotope shifts and metal concentrations are extended multiple and complex and do not resemble those seen at the cretaceous tertiary boundary both the carbon isotope shifts and the chemical events including an indium anomaly may have causes related to a major regression of the sea

reconstruction of paleostorms and paleoenvironment using geochemical proxies archived in the sediments of two coastal lakes in northwest florida abstract late holocene paleoclimate records from coastal regions are important for understanding long term variability of hurricane activity here we present a nearly 4000 year record of severe storm landfalls and environmental changes based on organic geochemical proxies ogps preserved in sediment cores from two coastal lakes in northwest florida our analysis shows that there are significant variations in 13c 15n c n and c n with depth reflecting changes in lake environment which in turn affected the processes delivering water and sediment to the lake as well as biological productivity within the lake isotopic signatures of modern organic materials in the lakes and their surrounding areas show that the major sources of sedimentary organic matters in the lakes are aquatic and terrestrial c3 vegetation c4 grasses do not contribute significantly to the sedimentary organic matters in the lake although they can be found in the mostly forested watershed thus the positive c and n isotopic shifts concurrent with negative shifts in c n ratios most likely indicate shifts to a marine like environment in coastal lakes following the influx of marine water and nutrients and marine biota associated with major storm events some of these isotopic shifts observed in the sediment cores correspond to visible sand layers presumably representing overwash deposits associated with severe storm events radiocarbon dating of bulk sediment organic matters wood fragments and shells indicates that the sediment in these cores was deposited over the last 3000 4000 years based on our age model and ogp interpretation eastern lake data suggest that the recurrence interval of severe storms i e large enough to cause seawater flooding of the lakes is approximately 84 years over the last 2900 years whereas western lake data suggest an average recurrence interval of 86 years in the past 3900 years

a decadally resolved paleohurricane record archived in the late holocene sediments of a florida sinkhole article i nfo a 4500 year record of hurricane induced storm surges is developed from sediment cores collected from a coastal sinkhole near apalachee bay florida recent deposition of sand layers in the upper sediments of the pond was found to be contemporaneous with significant historic storm surges at the site modeled using slosh and the best track post 1851 a d dataset using the historic portion of the record for calibration paleohurricane deposits were identified by sand content and dated using radiocarbon based age models marine indicative foraminifera some originating at least 5 km offshore were present in several modern and ancient storm deposits the presence and long term preservation of offshore foraminifera suggest that this site and others like it may yield promising microfossil based paleohurricane reconstructions in the future due to the sub decadal 7 years resolution of the record and the site s high susceptibility to hurricane generated storm surges the average local frequency of recorded events approximately 3 9 storms per century is greater than that of previously published paleohurricane records from the region the high incidence of recorded events permitted a time series of local hurricane frequency during the last five millennia to be constructed variability in the frequency of the largest storm layers was found to be greater than what would likely occur by chance alone with intervals of both anomalously high and low storm frequency identified however the rate at which smaller layers were deposited was relatively constant over the last five millennia this may suggest that significant variability in hurricane frequency has occurred only in the highest magnitude events the frequency of high magnitude events peaked near 6 storms per century between 2800 and 2300 years ago high magnitude events were relatively rare with about 0 3 storms per century occurring between 1900 and 1600 years ago and between 400 and 150 years ago a marked decline in the number of large storm deposits which began around 600 years ago has persisted through present with below average frequency over the last 150 years when compared to the preceding five millennia

a 1 000 year annually resolved record of hurricane activity from boston massachusetts 1 the annually laminated i e varved sediment record from the lower mystic lake near boston ma contains a series of anomalous graded beds deposited by strong flooding events that have affected the basin over the last millennium from the historic portion of the record 10 out of 11 of the most prominent graded beds correspond with years in which category 2 3 hurricanes are known to have struck the boston area thus we conclude that the graded beds represent deposition related to intense hurricane precipitation combined with wind driven vegetation disturbance that exposes fresh loose sediment the hurricane signal shows strong centennial scale variations in frequency with a period of increased activity between the 12th 16th centuries and decreased activity during the 11th and 17th 19th centuries these frequency changes are consistent with other paleoclimate indicators from the tropical north atlantic in particular sea surface temperature variations citation besonen m r r s bradley m mudelsee m b abbott and p francus 2008 a 1 000 year annually resolved record of hurricane activity from boston massachusetts geophys res lett 35 l14705

700 yr sedimentary record of intense hurricane landfalls in southern new england five intense category 3 or greater hurricanes occurring in 1635 1638 1815 1869 and 1938 have made landfall on the new england coast since european settlement historical records indicate that four of these hurricanes 1635 1638 1815 and 1938 and hurricane carol a strong category 2 storm in 1954 produced significant storm surges 3 m in southern rhode island storm surges of this magnitude can overtop barrier islands removing sediments from the beach and nearshore environment and depositing overwash fans across back barrier marshes lakes and lagoons in a regime of rising sea level accumulation of marsh lake or lagoon sediments on top of overwash deposits will preserve a record of overwash deposition we examined the record of overwash deposition at succotash salt marsh in east matunuck rhode island and tested the correlation with historical records of intense storms aerial photographs taken after hurricanes in 1954 and 1938 show overwash fans deposited at the site analysis of 14 sediment cores from the back barrier marsh confirmed the presence of these fans and revealed that 4 additional large scale overwash fans were deposited within the marsh sediments the four overwash fans deposited since the early seventeenth century at succotash marsh matches the historical record of significant hurricane induced storm surge these fans were most likely deposited by hurricanes in 1954 1938 1815 and either 1638 or 1635 radiocarbon dating of two prehistoric overwash fans indicated that these were deposited between a d 1295 1407 and 1404 1446 and probably represent intense hurricane strikes in the past 700 yr at least 7 intense hurricanes struck the southern rhode island coast and produced a storm surge that overtopped the barrier at succotash marsh

a 1200 year proxy record of hurricanes and fires from the gulf of mexico coast testing the hypothesis of hurricane fire interactions abstract we present here the first high resolution pollen record of vegetation response to interactions of hurricane and fire disturbances over the past 1200 yr from a small lake in alabama on the gulf of mexico coast the paleotempestological record inferred from the overwash sand layers suggests that the alabama coast was directly struck by saffir simpson category 4 or 5 hurricanes twice during the last 1200 yr around 1170 and 860 cal yr bp suggesting an annual landfall probability of 0 17 for these intense hurricanes the charcoal data suggest that intense fires occurred after each of these hurricanes the pollen data suggest that populations of halophytic plants chenopodiaceae and heliophytic shrubs myrica expanded after the hurricane strikes probably due to saltwater intrusion into the marshes and soil salinization caused by overwash processes populations of pines pinus sp decreased significantly after each intense hurricane and the ensuing intense fire suggesting that repeated hurricane fire interactions resulted in high tree mortality and probably impeded recruitment and recovery our data support the hypothesis that the likelihood and intensity of fire increased significantly after a major hurricane producing responses by vegetation that are more complex and unpredictable than if the disturbance agents were acting singly and independently

a new high resolution δ13c record for the early triassic insights from the arabian platform a new carbon isotope record with conodont biostratigraphy is presented for the entire early triassic from the musandam peninsula united arab emirates uae this is a near continuous and exclusively shallow marine carbonate succession that allows analysis of a high resolution primary carbon cycling signature in the absence of significant depth dependent or lithologic controls the musandam carbon isotope record can be broadly correlated with global isotopic events but also resolves additional features including the presence of significant negative events during the previously identified positive excursions at both the dienerian smithian and smithian spathian boundaries a further positive event is revealed during the development of the mid spathian negative excursion a feature not previously reported in any other section these new short lived events are probably related to the occurrence of the more widely recognized early triassic excursions and may represent fluctuations in the driving mechanisms superimposed on the continued instability of the global carbon cycle in the aftermath of the end permian extinction together these features highlight additional complexities to the early triassic carbon cycle perturbations than previously documented

micro scale analysis of tree ring δ18o and δ13c on α cellulose spline reveals high resolution intra annual climate variability and tropical cyclone activity high resolution analysis of stable carbon and oxygen isotopic composition 13c and 18o of tree ring cellulose has been increasingly in demand for the study of climate seasonality droughts and tropical cyclone hurricane activity the peeling grinding method commonly used for tree ring cellulose preparation is both time consuming and labor intensive and often results in cross tracheid sampling that masks high frequency intra annual climate signals and short term climate events here we present a new method by extracting tree ring cellulose directly from wholewood spline that omits the peeling grinding step and allows for micro scale 13c and 18o analysis that facilitates high resolution seasonal climate study this ultrasound assisted non destructive extraction method has significantly increased the output of tree ring cellulose preparation while retaining the wood cell fabric wood cell wall fibers collected from the cellulose spline were directly loaded into pre weighed silver or tin capsules and packed after oven drying for stable oxygen or carbon isotope analysis a 3 045 mm annual ring subdivided over 26 sections for 13c and 18o analysis revealed remarkable intra annual isotopic variations 1 62 for 13c and 5 85 for 18o the intra annual 13c values inversely covary with the seasonal precipitation pattern suggesting moisture regulation on tree ring 13c variations the high resolution 18o analysis unravels tropical cyclone activities hurricanes frances and ivan in 2004 that are characterized by an abrupt decline in 18o values by 2 6 with a v shape pattern in tree ring latewood an algorithm is developed for establishing regional patterns of tree ring seasonal 13c and 18o for the study of the mean state of climate seasonality and its anomalies

numerical modeling and field evidence of coastal overwash in southern new england from hurricane bob and implications for paleotempestology 1 in this paper we examine the use of coastal overwash modeling in conjunction with geological proxy techniques to provide a more comprehensive tool for paleotempestology southern new england which lies in the path of north tracking hurricanes has been a prime location for paleotempestological studies hurricane bob of 1991 is the most recent landfall in this region and has the most comprehensive data for model assessment and validation using the hurricane track central pressure and radius of maximum wind as input a collection of four interoperable model components simulates the meteorological conditions astronomical tides and storm surge ocean and coastal waves and the surf zone processes and runup onto dry land the computed surface pressure winds waves and water levels give very good agreement with data from weather stations moored buoys and tide gauges near the track and in the zone of maximum wind the validated wave conditions and storm water levels define the boundary conditions for coastal overwash modeling and the results show strong correlation with aerial photographs and sedimentary records at five sites near the landfall the results provide modern analogs for the interpretation of early hurricane landfalls in southern new england that lack an instrumental record reconstruction of paleohurricanes will require geological proxy data at multiple locations for the multivariate inverse analysis with uncertain paleotopography and storm characteristics

stalagmite stable isotope record of recent tropical cyclone events we present a 23 yr stalagmite record 1977 2000 of oxygen isotope variation associated with 11 tropical cyclones tcs from actun tunichil muknal cave in central belize high resolution microsampling yielded a record of monthly to weekly temporal resolution that contains abrupt decreases negative excursions in calcite 18 o values that correspond with recent tc rain events nearby a logistic discriminant model reliably identifi ed tc proxy signals using the measurable parameters 18 o and 13 c values and single point changes in 18 o value the logistic model cor rectly identifi ed 80 of excursions as tc events and incorrectly classifi ed only 1 of nearly 1200 nonstorm sampling points in addition to enabling high resolution tc frequency reconstruction this geologic proxy also provides information about the intensity of individual tcs a multiple regression predicted tc intensity r 2 0 465 p 0 034 using sampling frequency and excursion amplitude consistent with previous low resolution studies we found that the decadal average 18 o value was lower during the 1990s when several tcs produced rainfall in the area but higher during the 1980s when only one tc struck longer accurately dated high resolution speleo them stable isotope records may be a useful new tool for paleotempestology to clarify associa tions between highly variable tc activity and the dynamic range of quaternary climate

complete biotic and sedimentary records of the permian triassic transition from meishan section south china ecologically assessing mass extinction and its aftermath abstract the meishan section south china is the global stratotype section and point gssp for the permian triassic boundary ptb and is also well known for the best record demonstrating the permian triassic mass extinction ptme all over the world this section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest phanerozoic biocrisis of life on earth many important scenarios interpreting the great dying have been proposed on the basis of data from meishan nevertheless debates on biotic extinction patterns and possible killers still continue this paper reviews all fossil and sedimentary records from the permo triassic p tr transition based on previously published data and our newly obtained data from meishan and assesses ecologically the ptme and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis eight updated conodont zones clarkina yini clarkina meishanensis hindeodus changxingensis clarkina taylorae hindeodus parvus isarcicella staeschei isarcicella isarcica and clarkina planata zones are proposed for the ptb beds at meishan major turnover in fossil fragment contents and ichnodiversity occurs across the boundary between bed 24e 5 and bed 24e 6 suggesting an extinction horizon in a thin stratigraphic interval the irregular surface in the middle of bed 27 is re interpreted as a firmground of glossifungites ichnofacies rather than the previously proposed submarine dissolution surface or hardground surface both fossil fragment contents and ichnodiversity underwent dramatic declines in beds 25 26a coinciding with metazoan mass extinction fossil fragment content ichnodiversity and all ichnofabric proxies including burrow size tiering level bioturbation level indicate that the p tr ecologic crisis comprises two discrete stages coinciding with the first and second phases of the ptme in meishan ecologic crisis lagged behind biodiversity decline during the ptme pyrite framboid size variations suggest that depositional redox condition was anoxic to euxinic in the latest changhsingian became euxinic in beds 25 26a turned dysoxic in bed 27 then varied from euxinic to anoxic through most of the griesbachian the 9 c increase in seawater surface temperature from bed 24e to bed 27 at meishan seems to result in dramatic declines in biodiversity and fossil fragment contents in beds 25 26a but had little effect on all ecologic proxies both metazoans and infauna seem not to have been affected by the pre extinction anoxic euxinic condition the anoxic event associated with the ptme may have occurred in a much shorter period than previously thought and is only recorded in beds 25 26a at meishan fossil fragment contents ichnofaunas ichnofabrics and pyrite framboid size all show that no signs of oceanic acidification and anoxia existed in bed 27 the early griesbachian anoxia may have resulted in rarity of ichnofauna and metazoans in the lower yinkeng formation in which the ichnofauna is characterized by small simple horizontal burrows of planolites and metazoan faunas are characterized by low diversity high abundance opportunist dominated communities the rapid increase of 9 c in sea surface temperature and a short anoxia or acidification coincided with the first pulse biocrisis while a prolonged and widespread anoxia probably due to a long period of high seawater temperate condition may be crucial in mortality of most organisms in the second pulse ptme marine ecosystems started to recover coupled with environmental amelioration in the late griesbachian

records of prehistoric hurricanes on the south carolina coast based on micropaleontological and sedimentological evidence with comparison to other atlantic coast records singleton swash on the south carolina coast provides an extended record of storm events for this coast we used experience gained by looking at storm traces detected as layers of offshore foraminifera intercalated with marsh sediments from a known storm in the area hugo which occurred in 1989 to detect storm horizons from the sediments that have been accumulating in singleton swash since 5700 yr b p we suggest here that the most intense storm activity occurred in the 0 1000 yr b p interval six storms only three occurred in the 1000 2000 yr b p interval and two in the 2000 3000 yr b p time interval calibrated radiocarbon years there was one giant storm in the pre 5000 yr b p interval a sea level oscillation in the 3500 5000 yr b p interval appears to have destroyed most records during that period previous work suggests that the position of the bermuda or azores high influences the direction of general storm paths for major north atlantic hurricanes a position of the bermuda high farther to the south tends to force storms into the gulf of mexico whereas a northern position allows them to track up the atlantic coast results here combined with results of other workers on the gulf coast suggest a more southern position for the bermuda high causing more storms on the gulf coast in the interval of 1000 3400 yr b p conversely a more northern position during the past 1000 yr is suggested to have contributed to higher frequencies of storms on the atlantic coast in that period to test this hypothesis modern records of the movement of the north atlantic oscillation nao which controls the position of the bermuda high have been compared with historical records of hurricane tracks over the twentieth century there does appear to be a strong correlation between the position of the nao and the track the storms have pursued in modern times

assessing the suitability of holocene environments along the central belize coast central america for the reconstruction of hurricane records since the belize coast was repeatedly affected by hurricanes and the paleohurricane record for this region is poor sediment cores from coastal lagoon environments along the central belize coast have been examined in order to identify storm deposits the paleohurricane record presented in this study spans the past 8000 years and exhibits three periods with increased evidences of hurricane strikes occurring at 6000 4900 4200 3600 and 2200 1500 cal yr bp two earlier events around 7100 and 7900 cal yr bp and more recent events around 180 cal yr bp and during modern times have been detected sand layers redeposited corals and lagoon shell concentrations have been used as proxies for storm deposition additionally hiatuses and reversed ages may indicate storm influence while sand layers and corals represent overwash deposits the lagoon shell concentrations which mainly comprise the bivalve anomalocardia cuneimeris and cerithid gastropods have been deposited due to changes in lagoon salinity during and after storm landfalls comparison with other studies reveals similarities with one record from belize but hardly any matches with other published records the potential for paleotempestology reconstructions of the barrier lagoon complexes along the central belize coast differs depending on geomorphology and deposition of washovers in the lagoon basins is limited probably due to the interplay of biological geological and geomorphological processes

variscan collisional magmatism and deformation in nw iberia constraints from u pb geochronology of granitoids u pb geochronology of variscan granitoid rocks from the west asturian leonese zone of the nw iberian belt documents the episodic nature of magmatism in this section of the western european variscides each magmatic episode is characterized by granitoids with distinct features and has a duration on the scale of several millions of years the ages of these granitoids place new constraints on the age and duration of magmatic and tectonic events that are consistent with previous structural studies and proposed models for the tectonic evolution and migration of deformation in the nw iberian variscan belt granitoid rocks in this zone belong to two main magmatic episodes syn and post tectonic relative to the variscan orogeny and are broadly representative of the granitoid types found in the nw iberian variscan belt the syntectonic association is formed by i tonalite granodiorite monzogranite intrusions emplaced synchronously with the main phase of crustal deformation d 2 at c 325 ma and ii younger leucogranite intrusions emplaced synchronously with syn convergence extensional structures at c 320 310 ma the post tectonic association is composed of i volumetrically dominant tonalite granodiorite monzogranite intrusions and associated minor mafic intermediate rocks emplaced at c 295 290 ma and ii scarce leucogranite intrusions emplaced at c 290 285 ma

2500 year paleotempestological record of intense storms for the northern gulf of mexico united states abstract the northern gulf of mexico has been devastated by recent intense storms camille 1969 and katrina 2005 are two notable hurricanes that made landfall in nearly the same location in mississippi fully understanding the risks and processes associated with hurricane impacts are impeded by a short and fragmented instrumental record however paleotempestology has the potential to employ modern analogues from intense storms in this region to extend the hurricane record beyond pre observational time existing empirically based models can back calculate surge heights over coastal systems as a function of transport distance particle settling velocity and gravitational acceleration we collected sediment cores in a pond 3 and adjacent beach 1 in hancock county mississippi grain size loss on ignition and microfossil analyses were conducted on cores in the context of a bayesian statistical age model using 137cs and 14c dating using hurricane camille to calibrate the archive similar coarse grained deposits were identified and inverse sediment transport models calculated paleosurge intensities similar in magnitude to camille over the 2500 yr record our multi millennial annual average landfall probability 0 48 closely matches previously published studies from the gulf of mexico indicating that intense hurricanes have not varied over these timescales over centennial timescales active intervals occurred between 900 to 600 and 2200 to 1900 yr bp with relative quiescence between 1900 to 900 yr bp comparisons with other published sites support the notion that southerly shifts in the loop current may be responsible for the decline in activity around 600 yr bp