jurassic and cretaceous paleomagnetic data from the southern alps italy jurassic and cretaceous paleomagnetic data from 46 sites in the venetian alps trento plateau and se lombardian basin have been compiled nine of these site mean directions have been previously published the sites can be divided into four age groups senonian hauterivian barremian kimmeridgian tithonian and callovian oxfordian for three of the age groups positive regional fold tests indicate at the 99 confidence level that the characteristic magnetization components predate the deformation structural mapping in the venetian alps allowed us to assign sites to individual thrust sheets and we observe no significant relative rotation of thrust sheets in the nappe pile indeed we observe remarkable consistency in mean direction throughout the entire sampling area for each of the four age groups the senonian and hauterivian barremian pole positions lie close to coeval poles on african apparent polar wander paths apwps this result is consistent with previous analyses of middle and late cretaceous data from the venetian alps the new jurassic poles deviate significantly from recently published african apwps reflecting either the poor definition of the african apwp in the late jurassic or about 20 anticlockwise rotation of the southern alps relative to africa during early cretaceous time the former of the two possibilities is favored by a new late jurassic early cretaceous pole from north america and by early permian paleomagnetic data from the southern alps which are consistent with coeval african data implying that the movement of the southern alps was similar to that of africa since early permian

assessing sedimentary records of paleohurricane activity using modeled hurricane climatology patterns of overwash deposition observed within back barrier sediment archives can indicate past changes in tropical cyclone activity however it is necessary to evaluate the significance of observed trends in the context of the full range of variability under modern climate conditions here we present a method for assessing the statistical significance of patterns observed within a sedimentary hurricane overwash reconstruction to alleviate restrictions associated with the limited number of historical hurricanes affecting a specific site we apply a recently published technique for generating a large number of synthetic storms using a coupled ocean atmosphere hurricane model set to simulate modern climatology thousands of overwash records are generated for a site using a random draw of these synthetic hurricanes a prescribed threshold for overwash and a specified temporal resolution based on sedimentation rates observed at a particular site as a test case we apply this monte carlo technique to a hurricane induced overwash reconstruction developed from laguna playa grande lpg a coastal lagoon located on the island of vieques puerto rico in the northeastern caribbean apparent overwash rates in the lpg overwash record are observed to be four times lower between 2500 and 1000 years b p when compared to apparent overwash rates during the last 300 years however probability distributions based on monte carlo simulations indicate that as much as 65 of this drop can be explained by a reduction in the temporal resolution for older sediments due to a decrease in sedimentation rates periods of no apparent overwash activity at lpg between 2500 and 3600 years b p and 500 1000 years b p are exceptionally long and are unlikely to occur above 99 confidence under the current climate conditions in addition breaks in activity are difficult to produce even when the hurricane model is forced to a constant el nino state results from this study continue to support the interpretation that the western north atlantic has exhibited significant changes in hurricane climatology over the last 5500 years

jurassic magnetostratigraphy 2 middle late oxfordian of aguilon iberian cordillera northern spain abstract a reproducible magnetic polarity pattern has been obtained from four overlapping stratigraphic sequences of ammonite rich gray pelagic limestones spanning part of the middle and late oxfordian g transversarium toe bimammatum ammonite zones progressive thermal demagnetization removed a present field overprint fold tests both between and within outcrops are positive the mean direction of magnetization is 322 45 95 6 which implies a paleolatitude of 26 n frequent changes of polarity were observed the magnetostratigraphic sequence contains the ammonite zones subzones and horizons of the tethyan faunal realm using the reference horizons provided by this detailed ammonite zonation the polarity zones can be readily correlated among all sections the composite polarity pattern is predominantly of reversed polarity punctuated by a number of relatively shorter duration normal polarity intervals in order to compare this sequence to that of the marine magnetic anomalies we have revised the age estimates for the pre m25 marine magnetic normaly pattern according to the most recent time scale based on those ages the sedimentary record at aguilon suggests a much greater frequency of polarity changes than does either model derived from the two sets of marine magnetic anomalies of this time this sedimentary record probably is a truer approximation of the actual geomagnetic polarity history because of the continuity of sedimentation in these sections and the inherent ambiguities involved in determining a polarity pattern from the very low amplitudes that everywhere characterize this part of the marine record

oxfordian magnetostratigraphy in the iberian range the magnetostratigraphy has been established in two sections of middle and late oxfordian age from the iberian range spain the polarity sequences correlate well with the magnetozones in sections at aguilon and tosos juarez et al 1994 a composite magnetostratigraphic sequence has been derived for all the sections in the iberian range it correlates with the handschumacher et al 1988 extension of the geomagnetic polarity time scale and ties the oceanic magnetic anomaly sequence to the oxfordian sedimentary sections

magnetostratigraphy of the jurassic cretaceous boundary in the maiolica limestone umbria italy the magnetic stratigraphy of a 110 m section of the early cretaceous maiolica pelagic limestone in the bosso valley umbria italy shows clearly defined magnetozones that are correlated with the geomagnetic polarity record derived from the m sequence marine magnetic anomalies m19 to m14 and possibly m13 using an established paleontological zonation of this section based on calpionellids the position of the jurassic cretaceous boundary is located close to the base of the negative magnetozone corresponding to anomaly m17

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

oxfordian magnetostratigraphy of britain and its correlation to tethyan regions and pacific marine magnetic anomalies a suite of 11 sections through the oxfordian upper jurassic strata in the dorset and yorkshire regions of england and the isle of skye in scotland yielded magnetic polarity patterns directly calibrated to the ammonite biostratigraphy of the boreal and the subboreal faunal provinces the sections include the leading candidate for the global stratotype gssp for the callovian oxfordian stage boundary the mean oxfordian paleomagnetic pole derived from the dorset and yorkshire sections is 71 3 n 172 6 e p 4 2 m 6 1 the integrated magneto biostratigraphic scale is consistent with results from the sub mediterranean faunal province and extends the polarity pattern to the base of the oxfordian after adjusting for the estimated durations of ammonite subzones from cycle stratigraphy the magnetostratigraphy confirms models for marine magnetic anomalies m30 through to m37 including some of the short duration features recorded by deep tow magnetic surveys in the western pacific the callovian oxfordian boundary base of quenstedtoceras mariae zone occurs in a normal polarity zone that is correlated to the youngest part of polarity chron m37n of this extension to the m sequence

a chronology of hurricane landfalls at little sippewissett marsh massachusetts usa using optical dating abstract optical dating has been applied to sediments preserved in little sippewissett marsh massachusetts usa which are associated with overwashing of the beach barrier during hurricane strikes on the coast the aims were to determine the hurricane landfall frequency and make comparisons with independent age control and the historical record written sources of hurricane activity along the american east coast are only considered reliable back to the mid 19th century but the sedimentary record is potentially much longer optical dating was applied to quartz grains extracted from thirteen samples within a sediment core from the salt marsh variability in the luminescence characteristics between aliquots was observed and 33 of the measured aliquots were discarded based upon the ratio of the fast component to the medium component the majority of the samples gave normal dose distributions implying homogeneous resetting of the luminescence signal at the time of deposition but three of the samples required application of the minimum age model mam ages ranging between 20 2 and 594 38 years were obtained and are broadly in agreement with independent chronologies thus demonstrating the potential of optical dating in this setting the hurricane record based upon optical dating extends approximately 300 years further back in time than the official national oceanic atmospheric administration noaa record the localised nature of hurricane landfalls means that it will be necessary to collect multiple cores from a number of different sites in order to build up a complete hurricane record for this part of the coast

recalibration of the geomagnetic polarity timescale the quest for improved time control to estimate rates of geologic and paleoenvironmental processes is central to the earth sciences until the middle of this century geochronology was based solely on macrofossil evolution providing the largely unmodified definition of geologic stages in the last few decades with impetus from the deep sea drilling project dsdp and the ocean drilling program odp microfossil biostratigraphy has become increasingly important although new radiometric techniques have resulted in improved absolute age precision the direct correlation of absolute ages to biozonations and hence to geologic stage boundaries remains poor this is due to the difficulty of finding materials suitable for radiometric dating which can be directly correlated to biozonations the bridge between biozonations and absolute ages and the interpolation between absolute ages are best accomplished particularly for cenozoic and late mesozoic time through the geomagnetic polarity timescale gpts the template for late jurassic to quaternary geomagnetic polarity is derived from oceanic magnetic anomalies as demonstrated by heirtzler et al 1968 the gpts can be constructed using oceanic magnetic anomaly record s assuming constant seafloor spreading rate s and interpolating between available radiometric ages in the last quadrennium there have been outstanding developments in radiometric dating and astrochronology which have greatly improved the absolute age control of the gpts

paleomagnetism and the adriatic promontory a reappraisal the geodynamic evolution of the western mediterranean area was influenced strongly by the adriatic promontory of the african plate which can be outlined at present by current seismicity and by facies and ophiolite distributions paleomagnetic results from different parts of the promontory contribute useful information about its past history the evaluation of these data is made difficult by the lack of a well defined apparent polar wander path for africa this has resulted in occasional overinterpretation of some paleomagnetic studies results from umbria and the southern alps cover a long enough period of time to define part of an apw path and support the idea that the promontory moved as an adjunct to the african plate during the late mesozoic and early cenozoic a conservative evaluation of cretaceous paleomagnetic data the most abundant for the promontory as a whole shows no strong evidence for previously proposed counterclockwise rotations of sicily or the southern alps relative to the african plate paleomagnetic data however suggest about 17 degrees counterclockwise rotation of autochthonous gargano and istria and about 25 degrees counterclockwise rotation of allochthonous umbria tectonic rotation of the middle part of the promontory appears to have occurred without significant rotation of its northern and southern extremities

pre cretaceous tectonic evolution of the pacific plate and extension of the geomagnetic polarity reversal time scale with implications for the origin of the jurassic quiet zone abstract linear magnetic anomalies resulting from seafloor spreading were mapped in the vicinity of the magnetic bight in the western pacific ocean new aeromagnetic data allowed the magnetic bight to be more accurately mapped from m21 to m28 and enabled the identification of low amplitude magnetic lineations in the jurassic quiet zone these lineations were formed by magnetic field reversals prior to m29 a revised jurassic geomagnetic polarity reversal time scale was constructed with nineteen reversals older than m29 numbered m30 m38 these reversals extend the record of geomagnetic polarity back in time by approximately 8 ma and are important constraints on the origin of the quiet zone in particular they imply that the jurassic was not a period of constant normal polarity an explanation offered by some authors further they cast doubt on a model of systematically decreasing geomagnetic field strength with increasing age during this period the early history of the northern pacific plate and pacific farallon izanagi p f i triple junction was traced by mapped magnetic isochrons the pacific plate seems to have evolved from a small plate that formed near the phoenix farallon izanagi triple junction about 180 188 m y ago at approximately 17 n 160 e in present coordinates until m21 time the evolution of the northern pacific plate was relatively simple and the p f i triple junction migrated north northwest with respect to the pacific

a 1 year mesoscale simulation of the northeast atlantic mixed layer heat and mass budgets during the pomme experiment 1 a simplified oceanic model is used to perform a realistic yearlong simulation to study fine scale mixed layer processes in an area of the northeast atlantic 21 15 w 38 45 n during the programme ocean multidisciplinaire meso echelle pomme experiment september 2000 october 2001 this simplified three dimensional oceanic model is obtained by degenerating the primitive equations system by prescribing continuously analysis derived geostrophic currents ug called guide into the momentum equation by the substitution of the horizontal pressure gradient the realism of the simulated mesoscale structures was validated by a comparison with in situ mesoscale and submesoscale data and results from the geostrophic adjustment to the guide with this adjustment being applied at all scales this model was able to simulate energetic small horizontal scales taking place around stirring eddies and frontal regions moreover filamentary mixed layer depth structures were simulated and correlated to intense vertical velocities confined in the mixed layer the circulation structure during pomme consisted of three quasi permanent mesoscale eddies and a front the mixed layer heat and mass budgets were thus strongly driven by the horizontal advection and the vertical transport associated with this mesoscale circulation although no effective detrainment or entrainment occurred at the domain scale three regions were found to be the site of intense detrainment around anticyclonic and cyclonic mesoscale eddies and along an axis of strong currents in which the lateral induction and the vertical velocity at the mixed layer base are the major components driving the detrainment respectively

lead concentrations and isotopes in corals and water near bermuda 1780 2000 abstract the history of the oceanic anthropogenic lead pb transient in the north atlantic ocean for the past 220 yr is documented here from measurements of pb concentration and isotope ratios from annually banded corals that grew in coastal seawaters near bermuda and from seawater samples collected during the last 20 yr of the 20th century anthropogenic pb emissions in this area have been dominated by the industrialization of north america beginning in the 1840s the introduction of leaded gasoline beginning in the 1920s and its phase out that began in the mid 1970s the phase out of leaded gasoline was largely completed by the late 1990s coral pb concentrations occur at a constant low level of about 5 nmol pb mol ca 15 pmol kg in seawater from the late 1700s to 1850 from 1850 to 1900 there is a small increase rising to a plateau at 25 nmol pb mol ca 80 pmol kg in seawater in the 1930s until the late 1940s at which point pb concentrations rapidly increase to 60 nmol pb mol ca 200 pmol kg in seawater in the mid 1970s pb began to decline to 25 nmol pb ca 40 pmol kg in seawater by the end of the 20th century comparable to levels occurring in the early 20th century pb isotope ratios pb i r show maximum 206pb 207pb 1 21 and 208pb 207pb 2 49 in the middle of the 19th century we conclude that this signal is a reflection of the early dominance of upper mississippi valley pb ore in the united states as previously seen in the estuarine sediments of rhode island after 1900 pb i r decrease only slightly until the 1960s when there is a significant local maximum in the 1970s to 206pb 207pb 1 19 and 208pb 207pb 2 45 as low pb i r sources were phased out in the united states then as us leaded gasoline utilization decreased more rapidly than european pb gas utilization which has lower pb i r western north atlantic pb i r decreased to 206pb 207pb 1 17 and 208pb 207pb 2 44 their lowest values in the past two centuries

magnetostratigraphy and biostratigraphy of callovian oxfordian limestones from the trento plateau monti lessini northern italy abstract callovian oxfordian ammonitico rosso limestones from the trento plateau carry a characteristic remanent magnetization indicating frequent geomagnetic polarity reversals which can be correlated to callovian oxfordian ammonite zones the characteristic magnetization component has low coercivity and blocking temperatures below 600 c suggesting that magnetite is the carrier the age of the magnetization is not constrained by field tests although sedimentological evidence for early lithification and the close stratigraphic juxtaposition of normal and reversed component directions tend to indicate that acquisition of the magnetization occurred close to the sediment water interface stratigraphic gaps and the condensed nature of the sections inhibit the correlation of polarity reversals between sections the data suggest a reversed polarity bias for the oxfordian and a normal polarity bias for the callovian

jurassic magnetic stratigraphy from umbrian italian land sections the umbrian apennines were the site of pelagic sedimentation throughout most of the jurassic magnetic stratigraphy from four sections spanning many of the jurassic stages indicates that the geomagnetic field at this time was characterized by two intervals of mixed polarity separated by an interval of predominantly normal polarity corresponding to the jurassic quiet zone in the oceanic magnetic anomaly record unfortunately ammonites are poorly preserved or absent throughout most of these sections the duration of this quiet interval cannot be well defined although it is probably restricted to the callovian and oxfordian stages

oxfordian magnetostratigraphy of the aguilon and tosos sections iberian range spain and evidence of a pre oligocene overprint abstract a composite magnetic polarity sequence has been constructed for the middle and late oxfordian late jurassic from four overlapping sections situated in both limbs of an anticline two stable magnetisation components could be isolated in every sample analyzed both components pass the fold test a low temperature secondary component with dec 340 9 and inc 44 9 95 1 7 of pre oligocene age showing always normal polarity and a high temperature primary component with dec 324 1 and inc 40 6 95 2 9 the latter shows both normal and reversed polarities and provides the geomagnetic record for the late jurassic the magnetostratigraphy of the four overlapping sections has given consistent results and indicates that a high frequency of reversals characterises the pattern of the geomagnetic field during the middle to upper oxfordian the corresponding oxfordian paleopole is p lat 251 2 p long 55 9 95 3 1

palaeogeographic evolution of the pieniny klippen basin using stratigraphic and palaeomagnetic data from the veliky kamenets section carpathians ukraine abstract a 40 m thick carbonate succession of the bajocian to berriasian age from the veliky kamenets quarry novoselica area pieniny klippen belt ukraine resembles both the czorsztyn and niedzica successions of the pieniny klippen belt traditionally considered ridge slope related deposits a total of 176 individually oriented cores collected from the bottom to the top of the sequence with sampling density dependent on inferred sedimentation rates show multicomponent remanent magnetization with magnetite as a main magnetic carrier thermal demagnetization revealed two main components of natural remanent magnetization nrm a low blocking temperature component s of normal polarity is considered of posttectonic probably thermoviscous origin due to overheating by neogene volcanics a stable high blocking temperature nrm component p shows dual polarity distribution and is considered primary it was possible to recognize 23 polarity zones that have been correlated with a biostratigraphic scale since two significant sedimentary gaps occur at 422 and 860 cm the main hiatus ms from the base the latter comprising the middle callovian early oxfordian time span 6 8 ma an obtained pattern of magnetic reversals presented in this study cannot be considered complete a palaeolatitude of 41 5 is calculated for the mid jurassic part below ms similar to that expected for the european craton at the kamenets locality the mid oxfordian limestone directly overlying the ms has palaeolatitudes around 28 6 this implies a relatively fast opening of the oceanic domain to the north from the kamenets block this conclusion combined with similarity of the kamenets sequence to ridge related sediments of the pieniny klippen belt makes it possible to speculate on the existence of the kamenets ridge a new term a structure of uncertain although possible structural links to the czorsztyn ridge palaeomagnetic declinations suggest 100 counterclockwise rotation of the whole section before the neogene

biostratigraphic correlation of mesozoic polarity chrons cm1 to cm23 at capriolo and xausa southern alps italy abstract two pelagic limestone sections in the southern alps spanning the kimmeridgian late jurassic to barremian early cretaceous interval yield magnetostratigraphies which can be correlated to oceanic magnetic anomalies m1 m3 and m8 m23 this includes the interval m11 m13 which has not previously been correlated to a sedimentary section detailed investigations of nanofossils and calpionellids in these sequences allow precise correlation of polarity chrons to biostratigraphic events and these results compare favorably to those of previous studies the close correspondence in polarity pattern between that interpreted from the m8 to m15 interval in the hawaiian lineations and that recorded at the capriolo section suggests that sedimentation rates in this sequence and spreading rates in the hawaiian lineations were rather constant during this interval in contrast the sedimentation rate at the xausa section appears to increase up section with the facies transition from the rosso ammonitico to the maiolica formation

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

magnetostratigraphy of the middle upper jurassic sedimentary sequences at yanshiping qiangtang basin china a series of important geological events occurred in the tibetan plateau area during the jurassic such as the collision of the lhasa and qiangtang terranes the closure of the meso tethyan ocean the opening of the neo tethyan ocean and the cessation of the mega monsoon the similar to 3000 m thick jurassic sedimentary sequence in the qiangtang basin on the central tibetan plateau which is called the yanshiping ysp group recorded these geological events however the chronology of the sequence is surprisingly poorly constrained here we perform a detailed palaeomagnetic analysis on the similar to 1060 m thick middle and upper portions of the ysp group the xiali and suowa formations in the ysp section of the eastern qiangtang basin three bivalve zones at stratigraphic intervals of similar to 40 140 640 800 and 940 1040 m are identified which yield a bathonian callovian age for the lower xiali fm a callovian oxfordian age for the lower suowa fm and an oxfordian kimmeridgian age for the upper suowa fm a total of 544 oriented palaeomagnetic samples were collected from the section by combining thermal and alternating field demagnetizations clear characteristic remanent magnetization chrm directions are isolated for most of the samples the robust chrm directions pass fold and reversals tests which support the primary nature of the chrms and yield a palaeopole at 76 8a degrees n 297 2a degrees e dp 2 2a degrees dm 3 7a degrees a total of 27 normal and 26 reversed polarity zones were successfully recorded in the section combined with fossil age constraints results suggest that the section is plausibly composed of a callovian early kimmeridgian age sedimentary sequence

apparent polar wander path for adria extended by new jurassic paleomagnetic results from its stable core tectonic implications abstract as a continuation of a systematic paleomagnetic research in the northern part of stable adria which provided a well defined apparent polar wander apw path for the cretaceous eocene we present new paleomagnetic results for the jurassic these new data were obtained from 15 geographically distributed localities from the trento platform eastern southern alps using standard paleomagnetic approach the lower jurassic shallow water carbonates are not considered for tectonic interpretation due to inconsistent inclinations the middle and upper jurassic rosso ammonitico provided excellent kinematic constraints with the new jurassic results an apw is now defined for adria for the 167 40 ma interval it is well constrained for timing of important changes like the speed and the sense of rotations this apw suggests that the cw rotation and southward shift changed to the opposite at 155 1 5 3 ma signifying a dramatic change in the life of the neo tethys from opening to closing the latter is manifested in fast ccw rotation and northward movement of adria up to 102 9 2 4 ma and moderate displacements in the same manner in post 103 ma times combined data sets from stable istria and the foreland of the southern alps point to an approximately 15 cw rotation with respect to africa at the end of the cretaceous and an about 25 in the ccw sense after the eocene

a high resolution study of tides in the delaware bay past conditions and future scenarios 1 tides in the delaware bay usa have been modeled from 7000 years before present 7 ka to the present day and for selected future sea level rise scenarios 100 years 300 years historic bathymetries were constructed through use of glacial isostatic adjustment models and a very high spatial resolution 100 m was used at the shoreline future bathymetries were obtained by extrapolating these glacial isostatic adjustment models and applying an additional eustatic sea level rise it was found that tides in the lower bay have remained fairly constant through time but that tides in the upper bay have increased steadily from about 4 ka to the present day a nearly 100 increase in total the future runs demonstrated spatially complex behavior with tidal range changes of up to 10

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

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

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

paleogene magnetic stratigraphy in umbrian pelagic carbonate rocks the contessa sections gubbio the umbrian sequence of pelagic carbonate rocks provides an opportunity for precise correlation between paleogene biostratigraphy and geomagnetic polarity history the red to pink paleocene to middle eocene scaglia rossa limestone the varicolored upper eocene scaglia variegata limestone and the gray green oligocene scaglia cinerea marlstone form a 250 m thick continuous exposure in the contessa valley near gubbio italy magnetostratigraphic lithostratigraphic and biostratigraphic investigations in three sections covering the entire paleogene have confirmed and dated the geomagnetic reversal sequence for most of this period the ferromagnetic mineral in the scaglia cinerea is magnetite and af demagnetization to peak fields of 20 mt is sufficient to define the characteristic remanent magnetization the scaglia variegata and pink scaglia rossa samples contain an additional hematite component which is very pronounced in dark red paleocene scaglia rossa samples changes of magnetic mineralogy take place in these limestones during heating especially above 500 c however thermal demagnetization is effective in isolating the characteristic remanence vectors which form almost antipodal clusters of directions representing normal and reversed polarities the directions are rotated counterclockwise partly due to post oligocene tectonism paleontological zonations of planktic foraminifera and calcareous nannofossils were hampered by poor preservation but the major epoch and stage 29 as in the gubbio bottaccione section paleocene eocene just above anomaly 25 eocene oligocene between anomalies 13 and 15 oligocene miocene just below anomaly 6c these correlations require slight modifications to previous conclusions on paleogene sea floor spreading rates

magnetostratigraphy of the hettangian langmoos section adnet austria evidence for time delayed phases of magnetization summary study of the magnetostratigraphy of the earliest jurassic mainly hettangian section of langmoos near adnet in austria northern calcareous alps provides a sequence of 10 magnetic polarity intervals these intervals are often evident in the natural remanent magnetization however rather than a true magnetostratigraphic sequence palaeomagnetic analyses reveal evidence for successive phases of magnetization within the section evidence includes 1 changes in lithology associated with changes in magnetic polarity 2 different combinations of components of both polarities and 3 largely non antipodal directions considering the palaeomagnetic directions we suggest that the apparent magnetostratigraphy is the result of two or three phases of magnetization which occurred at different stages of the tectonic emplacement of the northern calcareous alps

isotopic record of lead pollution in lake sediments from the northeastern united states abstract although it is common knowledge that pb concentrations have increased in lake sediments in the northeastern united states over the last 150 years the processes responsible have been the subject of debate in this study differences in lead isotopic compositions and concentrations in sediment from large lakes lake erie ontario and michigan and small ones deep lake and lake andrus are used to infer temporal changes in the source s of anthropogenic pb in the great lakes region a natural background component of pb is present in sediment deposited prior to 1860 in lake erie and the other lakes as indicated from low pb concentrations and uniform lead isotopic compositions changes in isotopic ratios of lake sediment reflect differing sources of anthropogenic pb superimposed on the natural component such as regional deforestation from 1860 1890 followed by coal combustion and ore smelting through 1930 combustion of leaded gasoline was the dominant anthropogenic pb source to the atmosphere and by inference to lake sediment from 1930 1980 temporal changes in lead isotopic compositions in lake sediment suggest that the source of the pb used in gasoline additives gradually changed from 1930 to present the best example is a distinct shift in lead isotopic ratios in lake sediment deposited after 1970 which corresponds to increased pb production from the viburnum trend deposits in missouri present in all lakes except ontario however the changes in lead isotopic compositions are much less variable than and do not parallel those calculated on the basis of annual united states mine production and imports rather anthropogenic recycling of pb as well as natural mixing processes during emission transport and deposition of pb in lake sediment control most of the variation in lead isotope ratios differences in lead isotopic ratios in lake michigan erie and deep lake sediment preserve regional differences in lead isotopic ratios from u s and canadian sources first noted in aerosols by sturges and barrie 1987 more localized sources of pb such as point discharges are needed to explain the results from lake ontario and andrus

jurassic magnetostratigraphy 1 kimmeridgian tithonian of sierra gorda and carcabuey southern spain abstract two coeval sections of red to white ammonite rich pelagic limestones spanning the complete kimmeridgian and most of the tithonian were sampled in detail all samples were treated by progressive thermal demagnetization to remove a present field overprint characteristic magnetization is carried primarily by magnetite polarity intervals are easily identified and correlate well between the two sections the tithonian polarity sequence can also be correlated to sections in northern italy the similarity between the polarity sequence and the m sequence of marine magnetic anomalies coupled with the precise biostratigraphic control allows assignment of the following ages to the m sequence the late early tithonian boundary is correlated to the end of m 20 the tithonian kimmeridgian boundary to the end of m 23 the late early kimmeridgian boundary to the latter part of m 24 and the kimmeridgian oxfordian boundary within or slightly after m 25 the mean directions of characteristic magnetization have 95 s less than 3 and demonstrate extensive differential block rotation within the subbetic province paleolatitudes during the kimmeridgian tithonian are in the range of 16 24 n

holocene sea level database for the atlantic coast of the united states we have constructed a database of holocene relative sea level rsl observations for the atlantic coast of the united states the database contains 492 index points which locate the position of rsl in time and space and 344 limiting dates which constrain the minimum or maximum limit of former sea level the majority of the index points in the database are from 6 ka bp to present with only 7 older than 6 ka bp spatially index points are distributed between maine and south carolina but there is an absence of data from georgia and the atlantic coast of florida the database is sub divided into 16 regions based on the distance from the former laurentide ice sheet and are classified depending upon their susceptibility to compaction the index points and limiting data demonstrate that rsl did not exceed present 0 m during the holocene except potentially in regions 1 and 2 eastern maine and southern maine rates of rsl change were highest during the early holocene and have decreased over time due to the diminishing response of the earth s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input along the atlantic coast of the united states the linear rate of rsl rise prior to 4 ka bp ranged from 0 5 to 4 5 mm a 1 compared to 0 6 1 8 mm a 1 from 4 ka bp to ad 1900 the database suggests minimal 0 3 mm yr changes in these rates of rsl rise during the late holocene deglaciation of the laurentide ice sheet caused the spatial variability captured by the database the maximum rate of late holocene and ongoing rsl rise occurred in mid atlantic regions new jersey and inner delaware because of collapse of the peripheral forebulge

salt marsh erosion associated with hurricane landfall in southern new england in the fifteenth and seventeenth centuries lithostratigraphic and radiocarbon data from the inland section of pattagansett river marsh connecticut show that this sheltered part of the salt marsh underwent significant erosion twice during the past 600 yr each time followed by rapid and complete infilling of the eroded space with tidal mud and low marsh and high marsh peat we argue that the erosion cannot be attributed to increases in tidal prism or to lateral migration of tidal channels the 2 age range a d 1390 1470 for the first low marsh growth in the older regressive sequence agrees well with the age range a d 1400 1440 for a hurricane deposit 60 km to the east the younger regressive sequence is dated with the greatest probability to the period a d 1640 1670 i e shortly after the hurricanes of a d 1635 and 1638 our conclusion that the most likely cause of the erosion was hurricane activity is relevant to paleostorm research and the study of marsh sensitivity to and recovery from storm erosion

jurassic early cretaceous intermediate virtual geomagnetic poles and pangaean subduction zones abstract the objective of this paper is to show that the distribution of jurassic early cretaceous intermediate virtual geomagnetic poles vgps seems to be conditioned by pangaean subducted slabs palaeomagnetic data from between 200ma and 125ma were compiled from reliable studies and their vgps repositioned in their jurassic early cretaceous geographic location considering a zero longitude motion of africa over the last 200m y and the corresponding palaeomagnetic poles from each sequence those repositioned vgps lying between latitudes of 60 were considered to be intermediate to avoid bias as a function of simple sampling numbers for those sequences with more data each vgp was weighted by love s methodology a colour scale map shadow scale map in printed issue of density of the weighted intermediate vgps was obtained and compared with the pangaean subduction zones there is a good visual correlation between the distribution of these vgps and the location of the subduction zones during the jurassic suggesting that there is a relationship between the jurassic early cretaceous geomagnetic reversals and the plate tectonic setting at that time minima of intermediate vgps correlate well with the absence of vgps predicted with a tomographic model and the intermediate vgp distribution is also well correlated with zones of faster seismic wave propagation in the lower mantle just above of the core mantle boundary which suggests that the jurassic geomagnetic polarity transitions could have been controlled by a structure of the core mantle boundary similar to that at the present time we suspect that the subducted lithospheric slabs refrigerated the deepest mantle causing more heat than average flowing out from the core and controlling the geometry of the jurassic early cretaceous polarity transitions the earth s lithospheric plate motion history could have played a controlling role in the geometry of the geomagnetic reversals

geomagnetic polarity in the early cretaceous and jurassic knowledge of the polarity history of the earth s magnetic field during the mesozoic stems primarily from oceanic m sequence magnetic anomalies certain of these anomalies have been biostratigraphically dated from sediments immediately overlying basaltic basement at deep sea drilling project d s d p sites within the m sequence the biostratigraphic control is such that these age estimates are generally imprecise and moreover the sediment ages represent only minimum ages for the basaltic basement itself magnetostratigraphy in sedimentary land sections provides improved age estimates for magnetozones which can then be correlated with m sequence anomalies magnetostratigraphy provides not only enhanced dating of the ocean floor and resolution of the behaviour of the geomagnetic field during the cretaceous and jurassic oceanic quiet zones but also a world wide correlation tool for sedimentary stratigraphy the middle cretaceous is characterized by a long period of normal polarity extending from the early aptian to the early campanian reversed magnetozones corresponding to oceanic anomalies m 0 m 1 and m 3 have been palaeontologically dated as early aptian middle barremian and early barremian respectively magnetozones corresponding to oceanic anomalies m 5 to m 15 are hauterivian to valanginian in age but have not been individually associated with stage boundaries mainly due to poor biostratigraphic control in italian pelagic limestone sections of this age however magnetozones corresponding to oceanic anomalies m 16 to m 22 have been individually correlated to lower berriasian and tithonian palaeontological zones and extrapolation of this correlation gives an age for anomaly m 25 close to the oxfordian kimmeridgian boundary the jurassic 9quiet zone in the oceans is recognized in land sections as an extended period of predominantly normal polarity and although poor biostratigraphic control in this interval limits our knowledge of its duration we consider that it extended through the oxfordian and callovian stages the bathonian and older jurassic stages are characterized by mixed polarity a precise correspondence of magnetozones to ammonite zonations and stage boundaries is only available for the aalenian to pliensbachian interval where the frequency of reversal was apparently very high