the sea level fingerprint of west antarctic collapse recent projections of sea level rise after a future collapse of thewest antarctic ice sheet for example the fourth intergovernmental panel on climate change assessment report assume that meltwater will spread uniformly that is eustatically across the oceans once marine based sectors of the west antarctic are filled a largely neglected 1977 study predicted that peak values would be 20 higher than the eustatic in the north pacific and 5 to 10 higher along the u s coastline we show with use of a state of the art theory that the sea level rise in excess of the eustatic value will be two to three times higher than previously predicted for u s coastal sites

holocene sea level record on funafuti and potential impact of global warming on central pacific atolls geomorphic features inherited from the mid holocene glacio hydro isostatic sea level highstand that affected the central pacific region influence the susceptibility of atoll islets to potentially enhanced wave erosion associated with rise in sea level from global warming shoreline morphology on multiple islets of funafuti atoll in central tuvalu reflects a relative mid holocene sea level highstand 2 2 2 4 m above modern sea level typical islets are composed of unconsolidated post mid holocene sediment resting disconformably on cemented coral rubble formed beneath now emergent mid holocene reef flats exposed remnants of the lithified islet foundations serve as resistant buttresses protecting the flanks of atoll islets from wave attack islets lacking cemented mid holocene deposits as part of their internal structure are migratory sand cays with unstable shorelines any future sea level rise 0 75 m bringing high tide above the elevation of mid holocene low tide might trigger enhanced wave erosion of stable atoll islets by overtopping the indurated mid holocene reef platforms as analogous threshold relations are inferred for other central pacific atolls the risk of future inundation of island nations cannot be evaluated solely in terms of expected sea level rise with respect to gross islet elevations

spatiotemporal variability of typhoon impacts and relaxation intervals on jaluit atoll marshall islands storms are important drivers of geomorphic change within atoll settings causing rapid island erosion while also initiating island building through the generation of vast quantities of reef derived sediment due to the combined effects of storms and sea level rise reef islands are thought to be on an erosional trajectory jaluit atoll in the marshall islands was struck by typhoon ophelia in a d 1958 causing significant geomorphic change to reef islands using aerial photographs as well as recent satellite imagery we track the impacts of the typhoon and the multidecadal recovery of islands ophelia caused a significant reduction in total land area of jaluit atoll from 9 95 km 2 to 9 45 km 2 5 1 with islands on the northeast rim collectively reducing in size from 4 72 km 2 to 4 14 km 2 12 2 between 1976 and 2006 73 of 87 islands increased in size with the total landmass exceeding the pre typhoon area 10 25 km 2 however we observe considerable spatiotemporal variability of impacts and relaxation following the typhoon results indicate that despite significant typhoon driven erosion and a relaxation period coincident with local sea level rise islands have persisted and grown

numerical modeling of low frequency wave dynamics over a fringing coral reef abstract low frequency infragravity wave dynamics on a fringing coral reef were investigated using the numerical model xbeach roelvink et al 2009 first the skill of the model was evaluated in one and two dimensions based on its predictions of short waves 0 04 0 2 hz infragravity waves 0 004 0 04 hz and water level measurements tidal and wave setup obtained during a 2009 field study at ningaloo reef in western australia the model calibration was sensitive to friction coefficients for short waves and current infragravity bed friction which were assumed independent in this model study although the one dimensional cross shore model captured the gradients in the dominant hydrodynamic processes at the site a high current ig bed friction coefficient was required this resulted in an overestimation and a phase lag between the observed and predicted wave setup signal in the two dimensional model a lower more realistic current infragravity wave friction coefficient was required to achieve optimum performance due to the presence of significant reef and lagoon mean flows in the model which led to reduced setup across the reef the infragravity waves were found to propagate from the surf zone across the reef in a dominantly cross shore direction towards the shore but with substantial frictional damping the infragravity waves were strongly modulated also over the reef by tidal depth variations primarily due to the variability in frictional dissipation rates when the total water depth over the reef varied two mean wave driven circulation cells were observed in the study area with cross shore flow becoming more alongshore dominated before exiting the system via the two channels in the reef the results reveal that short waves dominated bottom stresses on the forereef and near the reef crest however inside the lagoon infragravity waves become increasingly dominant accounting up to 50 of the combined bottom stresses

projected atoll shoreline and run up changes in response to sea level rise and varying large wave conditions at wake and midway atolls northwestern hawaiian islands abstract atoll islands are dynamic features that respond to seasonal alterations in wave conditions and sea level it is unclear how shoreline wave run up and erosion patterns along these low elevation islands will respond to projected sea level rise slr and changes in wave climate over the next century hindering communities preparation for the future to elucidate how these processes may respond to climate change extreme boreal winter and summer wave conditions under future sea level rise slr and wave climate scenarios were simulated at two atolls wake and midway using a shallow water hydrodynamic model nearshore wave conditions were used to compute the potential longshore sediment flux along island shorelines via the cerc empirical formula and wave driven erosion was calculated as the divergence of the longshore drift run up and the locations where the run up exceed the berm elevation were also determined slr is projected to predominantly drive future island morphological change and flooding seaward shorelines i e ocean fronted shorelines directly facing incident wave energy were projected to experience greater erosion and flooding with slr and in hypothetical scenarios where changes to deep water wave directions were altered as informed by previous climate change forced pacific wave modeling efforts these changes caused nearshore waves to become more shore normal increasing wave attack along previously protected shorelines with slr leeward shorelines i e an ocean facing shoreline but sheltered from incident wave energy became more accretive on windward islands and marginally more erosive along leeward islands these shorelines became more accretionary and subject to more flooding with nearshore waves becoming more shore normal lagoon shorelines demonstrated the greatest slr driven increase in erosion and run up they exhibited the greatest relative change with increasing wave heights where both erosion and run up magnitudes increased wider reef flat fronted seaward shorelines became more accretive as all oceanographic forcing parameters increased in magnitude and exhibited large run up increases following increasing wave heights island end shorelines became subject to increased flooding erosion at wake and accretion at midway with slr under future conditions windward and leeward islands are projected to become thinner as ocean facing and lagoonal shorelines erode with leeward islands becoming more elongate island shorelines will change dramatically over the next century as slr and altered wave climates drive new erosional regimes it is vital to the sustainability of island communities that the relative magnitudes of these effects are addressed when planning for projected future climates

observations of wave transformation over a fringing coral reef and the importance of low frequency waves and offshore water levels to runup overwash and coastal flooding many low lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events to quantify wave dynamics and wave driven water levels on fringing coral reefs a 5 month deployment of wave gauges and a current meter was conducted across two shore normal transects on roi namur island in the republic of the marshall islands these observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef the larger event coincided with a peak spring tide leading to energetic highly skewed infragravity 0 04 0 004 hz and very low frequency 0 004 0 001 hz waves at the shoreline which reached heights of 1 0 and 0 7 m respectively water surface elevations combined with wave runup reached 3 7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach resulting in flooding of inland areas this overwash occurred during a 3 h time window that coincided with high tide and maximum low frequency reef flat wave heights the relatively low relief characteristics of this narrow reef flat may further drive shoreline amplification of low frequency waves due to resonance modes these results 1 demonstrate how the coupling of high offshore water levels with low frequency reef flat wave energetics can lead to large impacts along fringing reef lined shorelines such as island overwash and 2 lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events negatively impacting coastal resources and infrastructure

new u pb and ar ar isotopic age constraints on the timing of eocene magmatism fort fraser and nechako river map areas central british columbia twenty three new precise eocene u pb and 40 ar 39 ar age determinations for calc alkaline volcanic rocks of the ootsa lake group and associated intrusive rocks widespread in the nechako plateau in central british columbia constrain the timing of the eocene magmatism to 53 2 47 6 ma with a local duration of as little as 2 3 million years the new dates show that magmatism in the study area is partly coeval with that responsible for the babine igneous suite newman volcanic suite 53 50 ma to the north and for the endako group 51 45 ma which overlies the ootsa lake group however locally the three magmatic suites are distinct in age and or the strata record a magmatic hiatus of as much as 7 5 million years the ages generally young from north to south 52 47 ma along the western portion of the study area the babine igneous suite newman volcanic suite represents the oldest member of this series however in the east the ootsa lake group volcanic rocks are generally older 53 51 ma the anomalously older ages may be related to the interaction of magmatism and formation of a nearby and coeval core complex which ongoing studies show was uplifted at about the same time during the eocene felsic plutonism associated with the ootsa lake group occurred between 50 5 and 47 3 ma these plutons were emplaced in an extensional setting along north northeast trending faults the new dates stratigraphic relationships and suggested correlations of eocene strata in the study area with that to the west and north require a revision of the stratigraphic nomenclature for the ootsa lake and endako groups 696

new insights into thermal history from single grain 40ar 39ar analysis of biotite single grains of biotite extracted from two hand samples of two granitoid rocks from the red lake greenstone belt of northwestern ontario were examined using a high sensitivity 40ar 39ar laser dating system for variations in age for small grains a striking correlation is seen between the ages and the grain sizes as measured by the cylindrical radii with smaller samples yielding younger ages this effect saturates at a radius of about 225 m above which the integrated age is independent of grain size by combining this grain size effect with biotite diffusion parameters taken from the literature continuous cooling curves were derived for the region these curves suggest the region cooled at a rate of about 0 3 c myr between 2635 and 2570 ma with its ability to define a grain size effect the laser probe mass spectrometer system provides new insight into thermal history

age of emplacement and basement character of the cache creek terrane as constrained by new isotopic and geochemical data new u pb and rb sr isotopic and major and trace element geochemical data are reported for late triassic to eocene granite bodies that intrude the cache creek and stikine terranes in the atlin bennett area of northwestern british columbia the u pb isotopic age data help constrain closure of the cache creek ocean and obduction of the cache creek terrane to before 172 ma middle jurassic low 87sr 86sr initial ratios 0 7037 0 7046 and lack of evidence for inheritance in zircons suggest that rocks underlying the cache creek terrane are largely primitive in nature with derivation of intrusive rocks predominantly from unevolved sources a genetic link between late triassic granitic plutons and stuhini arc volcanics of stikinia is supported by trace and rare earth element data which indicate generation of magma in a volcanic arc setting geochemical patterns for postaccretion middle jurassic and late cretaceous to early tertiary age plutons are similar to those of the late triassic indicating that middle ju

zircon upb ages of guyana greenstone gneiss terrane abstract isotopic u pb studies of zircons collected from weathered metagreywackes of the barama mazaruni supergroup of northern guyana south america demonstrate an age of origin of ca 2250 ma this is the best estimate for the age of the associated metavolcanic rocks zircons from weathered gneiss of the bartica complex adjacent to the volcanic sedimentary belts yield a similar age the contiguous greenstone gneiss terrane of eastern venezuela is also of similar age and comparable greenstone gneiss terranes of eastern suriname and french guiana are probably also of this age continental crust formation of a style closely comparable to that of the canadian archean occurred on a very widespread scale in the lower proterozoic of the guiana shield the lead losses from the weathered zircons are comparable to those from zircons from fresh rock from the adjacent terrane of venezuela and the advantages of field concentration from numerous saprolite exposures warrant use of such material in future geochronological studies of the region

imbricate architecture of the upper paleozoic to jurassic oceanic cache creek terrane central british columbia upper paleozoic to lower jurassic oceanic rocks of the cache creek terrane near fort st james in central british columbia form a stack of thrust sheets cut by steeply dipping strike slip faults paleontologically dated upper paleozoic strata include bioclastic shallow water limestone and ribbon chert isotopically dated permian rocks consist of tonalite sills and stocks and rhyolite flows intercalated with basalt flows paleontologically dated lower mesozoic rocks include greywacke sandstone siltstone argillite ribbon chert conglomerate limestone and basalt tuff trembleur ultramafite unit of the cache creek complex in places part of an ophiolite suite forms thrust sheets and klippen that overlie lower mesozoic sedimentary rocks sedimentological lithochemical paleontological petrological and textural comparisons with other areas and established models demonstrate that cache creek terrane is an accretionary complex a structurally stacked assemblage of rocks that originated in diverse and

response of reef island shorelines to seasonal climate oscillations south maalhosmadulu atoll maldives 1 the maldives experience seasonal shifts in monsoon winds from the west northwest to northeast the morphologic response of reef island beaches and shorelines to these predictable shifts in climate was examined on eight islands in south maalhosmadulu atoll based on global positioning system surveys of island shoreline planform in january and june 2002 and february 2003 surveys show that islands exhibit large gross changes 31 120 of beach area in shoreline position between seasons such changes reflect large reversals in sediment flux of 9 23 103 m3 on a biannual basis driven by seasonal reversals in wind and wave conditions annual net change is small 2 15 suggesting islands spatially exhibit a dynamic equilibrium an island oscillation index io is defined that describes the spatial extent of shoreline change around islands island shape ellipticity e is found to be positively correlated with io in the expression io 1 021e 0 275 suggesting island shape is a better indicator of the susceptibility of island shorelines to morphological change than wave energy exposure

nature and stability of atoll island shorelines gilbert island chain kiribati equatorial pacific islands rimming pacific atolls typically form narrow low lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea level rise as these low islands form the only habitable land for many island nations understanding the character of shorelines and the rates and controls that operate to bring about changes is an issue of central importance the purpose of this study is to unravel the characteristics of coastal change on atoll islands of the gilbert island chain of the equatorial pacific nation of kiribati especially as they relate to autogenic shoreline processes and el nino southern oscillation variability integration of field observations differential global positioning system data historical aerial photographs and ultra high resolution remote sensing images demonstrates the nature spatial patterns and rates of change from 17 islands on maiana and aranuka atolls the results illustrate that between 2005 and 2009 ca 50 of the shorelines on these islands displayed a discernable shift in position some shorelines were accretionary at net rates up to ca 8 m year 1 and others were erosional up to ca 18 m year 1 long term net rates of change on maiana between 1969 and 2009 were lower than short term net rates measured between 2005 and 2009 both short term and long term observations illustrate some of the greatest change occur near terminations of the largest north south oriented islands associated with longshore movement of coarse sand and gravel direct hits by tropical depressions and marked seasonality factors interpreted as being essential in island growth and shoreline dynamics elsewhere do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics similarly observations over four years suggested that shoreline variability probably is not influenced directly by marked sea level change although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long term increase in the rate of sea level rise within this framework of global change local anthropogenic effects autogenic shoreline processes and el nino southern oscillation influenced wind and wave variability control many aspects of these dynamic shorelines these results provide quantitative insights into the character and variability of rates of shoreline change information essential for evaluating and mitigating the vulnerability of island nations such as kiribati

saddle shaped 40ar39ar age spectra from young microstructurally complex potassium feldspars abstract a suite of young potassium feldspars show markedly saddle shaped 40 ar 39 ar age spectra as a result of incorporating 10 10 to 10 9 mol g of excess 40ar the minima of these age spectra record reasonable cooling ages based on the known thermal history and geology of the samples acid etching of one sample indicates that excess 40ar is concentrated near grain margins the release of a substantial portion of this excess ar at high temperatures in the laboratory requires that this component be situated in a more retentive site than radiogenic 40ar anion vacancies have been proposed to act in this role in plagioclase and we speculate that this is so in k feldspar as well such a mechanism would explain the observation that relative to radiogenic 40ar excess 40ar is incorporated at low temperatures in nature but is released at high temperatures in the laboratory oxygen diffusion provides an appropriate analogy for this phenomenon being relatively fast under natural hydrothermal conditions but extremely slow in anhydrous environments such as an ar extraction system tem observations made on two of the samples confirm that their effective grain sizes for diffusion are likely to be on the order of ten microns due to the presence of such microstructures as incoherent exsolution lamellae dislocations and stepped twins tem observations also reveal the presence in one sample of orthoclase enclaves in a microcline host

evidence for coral island formation during rising sea level in the central pacific ocean the timing and evolution of jabat island marshall islands was investigated using morphostratigraphic analysis and radiometric dating results show the first evidence of island building in the pacific during latter stages of holocene sea level rise a three phase model of development of jabat is presented initially rapid accumulation of coarse sediments on jabat occurred 4800 4000 years b p across a reef flat higher than present level as sea level continued to rise during the highstand island margins and particularly the western margin accreted vertically to 2 5 3 0 m above contemporary ridge elevations this accumulation phase was dominated by sand size sediments phase three involved deposition of gravel ridges on the northern reef as sea level fell to present position jabat has remained geomorphically stable for the past 2000 years findings suggest reef platforms may accommodate the oldest reef islands in atoll systems which may have profound implications for questions of prehistoric migration through pacific archipelagos

the heat flow from the continents the terrestrial heat flow is defined as the quantity of heat escaping per unit time from the earth s interior across each unit area of the earth s solid surface the quantity varies from place to place over the surface of the earth as well as with time throughout earth history the total heat being lost from the earth at a given time is the integral of the heat flow taken over the entire surface of earth the heat flow from the continents is therefore but a part of the larger picture of global heat loss indeed the lesser part when compared to the heat loss through the floor of the ocean basins pollack 1980 sclater et al 1980 davies 1980 this is so not only because of the lesser continental area but also because of the generally smaller heat flow found on the continents than in the ocean basins thus a full discussion of the thermal regime of the earth and the mechanisms by which it exhausts heat from the interior must center on the heat loss through the oceans a topic which lies beyond the scope of this review nonetheless because of the geological antiquity of at least some of their constituent terranes the continents provide the only direct evidence about the thermal tectonic and petrologic processes of the earth at times before the birth of any of the modem ocean basins some two hundred million years ago because inferences about earlier times are drawn wholly from materials now preserved in continents one must be cautious not to overgeneralize about global tectonothermal processes from observations confined to continents

the influence of coral reefs and climate change on wave driven flooding of tropical coastlines a numerical model xbeach calibrated and validated on field data collected at roi namur island on kwajalein atoll in the republic of marshall islands was used to examine the effects of different coral reef characteristics on potential coastal hazards caused by wave driven flooding and how these effects may be altered by projected climate change the results presented herein suggest that coasts fronted by relatively narrow reefs with steep fore reef slopes 1 10 and steeper and deeper smoother reef flats are expected to experience the highest wave runup wave runup increases for higher water levels sea level rise higher waves and lower bed roughness coral degradation which are all expected effects of climate change rising sea levels and climate change will therefore have a significant negative impact on the ability of coral reefs to mitigate the effects of coastal hazards in the future

coral mortality increases wave energy reaching shores protected by reef flats examples from the seychelles in the granitic seychelles many shores and beaches are fringed by coral reef flats which provide protection to shores from erosion by waves the surfaces of these reef flats support a complex ecology about 10 years ago their seaward zones were extensively covered by a rich coral growth which reached approximately to mean low water level but in 1998 this was largely killed by seawater warming the resulting large expanses of dead coral skeletons in these locations are now disintegrating and much of the subsequent modest recovery by new coral recruitment was set back by further mortalities a mathematical model of wave energy reaching shorelines protected by coral reef flats has been applied to 14 seychelles reefs it is derived from equations which predict 1 the raised water level or wave set up on reef flats resulting from wave breaking which depends upon offshore wave height and period depth of still water over the reef flat and the reef crest profile and 2 the decay of energy from reef edge to shoreline that is affected by width of reef flat surface roughness sea level rise and pseudo sea level rise created by increased depth resulting from disintegration of coral colonies the model treats each reef as one entity but because biota and zonation on reef flats are not homogenous all reefs are divided into four zones in each cover by both living and dead biota was estimated for calculation of parameters and then averaged to obtain input data for the model all possible biological factors were taken into account such as the ability of seagrass beds to grow upwards to match expected sea level rise reduction in height of the reef flat in relation to sea level as zones of dead corals decay and the observed rounding of reef crests as erosion removes corals from those areas estimates were also made of all these factors for a time approximately a decade ago representing a time before the mass coral mortality and for approximately a decade in the future when the observed rapid state of dead coral colony disintegration is assumed to have reached an end point results of increased energy over the past decade explain observations of erosion in some sites in the seychelles most importantly it is estimated that the rise in energy reaching shores protected by fringing reefs will now accelerate more rapidly such that the increase expected over the next decade will be approximately double than that seen over the past decade c 2005 elsevier ltd all rights reserved

two dimensional modelling of wave dynamics and wave forces on fringing coral reefs abstract two dimensional numerical modelling of swell wave dynamics on idealized fringing reefs is performed using swan covering a wide range of bathymetries climate forcing conditions and water depths over the reefs the results illustrate the impact of reef geometry and bathymetry coral species and sea level rise on key hydrodynamic parameters on the reef and on forces on corals the modelling demonstrates that one dimensional models underestimate the wave action on the reef flat wide short reefs and narrow long reefs have similar wave heights at the centre of the reef flat for a given reef length the wave height first decreases with increasing reef width then increases to a local maximum when reef width is approximately equal to the reef length and then decreases for further increases in width this pattern is a result of combined dissipation and refraction processes which combine to lead to different zones of cross reef wave transformation provided that a reef retains its hydrodynamic functions in breaking and refracting the waves sea level rise enhances the wave heights and wave orbital velocities on the reef flat if vertical coral growth does not keep pace with sea level rise loss of the hydrodynamic functions of the reef may occur on deeper reefs and result in a reduction of near bed velocities with sea level rise hydrodynamic forces on corals vary by coral species and slr changes the magnitude of the forces on different species in different ways which may lead to less favourable conditions for certain coral species for long period swell the intermediate size corals are drag dominated and behave similarly to branching corals whereas for short period swell their behavior is similar to that of the inertia dominated massive corals for intermediate corals different responses to slr may therefore be expected for different overall regional wave climates over time this process may contribute to changes in the structural complexity of reefs the influence of sea level rise on the forces on corals on the reef flat is different under swell and cyclonic wind conditions since wind influences wave period in the latter case

extrusion of high pressure cache creek rocks into the triassic stikinia quesnellia arc of the canadian cordillera implications for terrane analysis of ancient orogens and palaeogeography

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

sediment transport in the presence of large reef bottom roughness the presence of large bottom roughness such as that formed by benthic organisms on coral reef flats has important implications for the size concentration and transport of suspended sediment in coastal environments a 3 week field study was conducted in approximately 1 5 m water depth on the reef flat at ningaloo reef western australia to quantify the cross reef hydrodynamics and suspended sediment dynamics over the large bottom roughness 20 40 cm at the site a logarithmic mean current profile consistently developed above the height of the roughness however the flow was substantially reduced below the height of the roughness canopy region shear velocities inferred from the logarithmic profile and reynolds stresses measured at the top of the roughness which are traditionally used in predictive sediment transport formulations were similar but much larger than that required to suspend the relatively coarse sediment present at the bed importantly these stresses did not represent the stresses imparted on the sediment measured in suspension and are therefore not relevant to the description of suspended sediment transport in systems with large bottom roughness estimates of the bed shear stresses that accounted for the reduced near bed flow in the presence of large roughness vastly improved the relationship between the predicted and observed grain sizes that were in suspension thus the impact of roughness not only on the overlying flow but also on bed stresses must be accounted for to accurately estimate suspended sediment transport in regions with large bottom roughness a common feature of many shallow coastal ecosystems

nonhydrostatic and surfbeat model predictions of extreme wave run up in fringing reef environments abstract the accurate prediction of extreme wave run up is important for effective coastal engineering design and coastal hazard management while run up processes on open sandy coasts have been reasonably well studied very few studies have focused on understanding and predicting wave run up at coral reef fronted coastlines this paper applies the short wave resolving nonhydrostatic xb nh and short wave averaged surfbeat xb sb modes of the xbeach numerical model to validate run up using data from two 1d alongshore uniform fringing reef profiles without roughness elements with two objectives i to provide insight into the physical processes governing run up in such environments and ii to evaluate the performance of both modes in accurately predicting run up over a wide range of conditions xbeach was calibrated by optimizing the maximum wave steepness parameter maxbrsteep in xb nh and the dissipation coefficient alpha in xb sb using the first dataset and then applied to the second dataset for validation xb nh and xb sb predictions of extreme wave run up rmax and r2 and its components infragravity and sea swell band swash sig and sss and shoreline setup were compared to observations xb nh more accurately simulated wave transformation but under predicted shoreline setup due to its exclusion of parameterized wave roller dynamics xb sb under predicted sea swell band swash but overestimated shoreline setup due to an over prediction of wave heights on the reef flat run up swash spectra were dominated by infragravity motions allowing the short wave but not wave group averaged model xb sb to perform comparably well to its more complete short wave resolving xb nh counterpart despite their respective limitations both modes were able to accurately predict rmax and r2

primitive permo triassic volcanism in the canadian cordillera tectonic and metallogenic implications volcanogenic massive sulfide deposits of various ages types and geochemical affinities occur within allochthonous and para autochthonous terranes of the cordillera of western canada the terrane affiliation age and chemical association of volcanic rocks can be used as a guide in the exploration for volcanogenic massive sulfide mineralization the kutcho massive sulfide deposit occurs within volcanic rocks of the kutcho assemblage in the fault bounded king salmon allochthon in northern british columbia the kutcho creek deposit is characterized by a permo triassic age of mineralization and primitive chemical and radiogenic isotope compositions of the host rocks which are distinct from those of other volcanogenic massive sulfide deposits in the canadian cordillera the kutcho deposit is interpreted to have formed within a primitive intraoceanic are environment distinct from the setting ascribed to more typical felsic volcanic hosted kuroko massive sulfide deposits the age mineralogy and chemical and isotopic compositions of rocks from the kutcho assemblage are comparable to those of two other fault bounded silvers in the cordillera the sitlika assemblage and the venables valley red hill area these similarities suggest that rocks from the three areas may have formed within the same period and tectonic environment as such the latter two areas are prospective for volcanogenic massive sulfide exploration in the canadian cordillera

new u pb zircon ages integrated with ammonite biochronology from the jurassic of the canadian cordillera the accuracy of published jurassic time scales is compromised by a paucity of sufficiently accurate and stratigraphically well constrained isotopic dates u pb dating of volcaniclastic rocks within fossiliferous marine successions is a method suitable of providing additional useful calibration points stikinia and wrangellia two of the major accreted terranes of the canadian cordillera comprise volcanosedimentary assemblages of magmatic arc origin within them we selected sections from which we report 14 new u pb zircon ages that are integrated with ammonite biochronology at the zonal level poor zircon recovery and complex u pb systematics made it difficult to obtain precise ages for many of the samples the following ages were determined with 2 errors 194 0 9 1 1 8 ma from the plesechioceras harbledownense assemblage upper sinemurian 191 5 0 8 ma from the plesechioceras harbledownense assemblage upper sinemurian to the whiteavesi zone lower pliensbachian 185 6 6 1 0 6 ma from the frebo

40ar 39ar thermochronometry of the imataca complex venezuela the imataca complex of venezuela an archean metamorphic belt located on the northern margin of the amazonian craton underwent upper amphibolite to granulite facies metamorphism during the 2 0 ga trans amazonian orogeny 40ar 39ar plateau dates on hornblende separates from the imataca complex vary from 1972 to 1760 ma and record post trans amazonian orogeny cooling biotite and feldspar pairs which were separated from the same samples or from samples collected at the same exposure and should record identical thermal histories yield distinct results the biotite 40ar 39ar spectra are primarily plateau profiles with dates ranging from 2044 to 1254 ma whereas perthitic potassium feldspar yield stair step 40ar 39ar spectra and integrated dates ranging from 1395 to 1166 ma the internally discordant perthite spectra appear to reflect cooling at rates of 0 1 0 2 c ma 1 consistent with the cooling rates estimated from the blocking temperature and age differences between biotite feldspar pairs from the same sample two plagioclase samples yield saddle shaped 40ar 39ar spectra with 1235 and 1221 ma minimum dates these internally discordant spectra are caused by degassing of non atmospheric trapped ar from the plagioclase and of radiogenic ar sited in k rich inclusion phases the 2 0 1 7 ga biotite dates are confined to the margins of the imataca complex and record the waning stages of trans amazonian orogeny uplift and cooling the 1 4 1 2 ga biotite dates which are confined to the center of the imataca complex are correlated with their 200 350 c ar blocking temperatures as estimated from their average grain size and fe fe mg composition the 1 3 1 1 ga feldspar ages are correlated with their 200 300 c ar blocking temperatures as determined from analysis of the 40ar 39ar step heating data the extremely slow cooling rates implied by the biotite feldspar pairs suggest that between 1 7 and 1 1 ga the imataca complex cooled isobarically at intermediate crustal levels all ar mineral systems closed by 1 1 ga perhaps reflecting a renewed phase of uplift associated with the mild tectonism of the nickorie episode

identification and classification of very low frequency waves on a coral reef flat very low frequency vlf 0 001 0 005 hz waves are important drivers of flooding of low lying coral reef islands in particular vlf wave resonance is known to drive large wave runup and subsequent overwash using a five month dataset of water levels and waves collected along a cross reef transect on roi namur island in the republic of the marshall islands the observed vlf motions were categorized into four different classes 1 resonant 2 non resonant standing 3 progressive growing and 4 progressive dissipative waves each vlf class is set by the reef flat water depth and in the case of resonance the incident band offshore wave period using an improved method to identify vlf wave resonance we find that vlf wave resonance caused prolonged 0 5 6 0 hr large amplitude water surface oscillations at the inner reef flat ranging in wave height from 0 14 to 0 83 m it was induced by relatively long period grouped incident band waves and occurred under both storm and non storm conditions moreover observed resonant vlf waves had non linear bore like wave shapes which likely have a larger impact on the shoreline than regular sinusoidal waveforms as an alternative technique to the commonly used fast fourier transformation we propose the hilbert huang transformation that is more computationally expensive but can capture the wave shape more accurately this research demonstrates that understanding vlf waves on reef flats is important for evaluating coastal flooding hazards this article is protected by copyright all rights reserved

origin of the eskay creek precious metal rich volcanogenic massive sulfide deposit fluid inclusion and stable isotope evidence the eskay creek deposit is an unusual polymetallic au ag rich volcanogenic sulfide sulfosalt deposit located in the iskut river area of northwestern british columbia canada economic concentrations of precious and base metals are contained in the 21 zone which is divided into a number of subzones as of december 31 1998 total production and proven probable reserves are 1 9 million tons mt at 60 2 g t au 2 652 g t ag 3 2 percent pb 5 2 percent zn and 0 7 percent cu the 21b zone which contains the bulk of the reserves began production in 1995 the mineralization occurs mainly as well preserved stratiform clastic beds of sulfide sulfosalt debris and also as discordant footwall quartz sulfide veins the hydrothermal system that formed the eskay deposit was low temperature

strain partitioning in accretionary orogens and its effects on orogenic collapse insights from western north america changes in relative plate motions during the construction of accretionary orogens generally result in varying structural styles along the length of the orogen these disparate structural styles can be interpreted as having been formed by different tectonic regimes along the orogenic axis that formed at the same time if the orogen is considered at the large scale the differences in the way in which the crust responds during accretion can be explained by large scale strain partitioning within the same overall tectonic environment the westernmost canadian cordillera records the transition from late cretaceous dextral strike slip faulting to near orthogonal compression along the orogenic axis we postulate that the transition between strike slip dominated to compression dominated tectonics represents a late cretaceous partitioning of strain that resulted in a significant difference in crustal rheology along strike of the orogeny this had a dramatic effect on subsequent tertiary orogen scale extension we propose that plate readjustments in the tertiary led to orogen perpendicular collapse in portions of the orogen facilitated by decoupling between the middle and lower crusts along thermally weakened layers in contrast localized orogen parallel extension occurred in other portions of the orogen along kinematically linked large dextral strike slip faults where the upper crust remained coupled to the middle and lower crust new data indicate that partitioning of strain occurs across very large regions within any orogenic system and that the way in which strain is partitioned can lead to dramatic differences in future orogenic processes it becomes apparent from these data that orogens must be examined as a whole and that differing structural styles of similar ages are likely responses to the same overall tectonic regime

evolution of the hazelton arc near terrace british columbia stratigraphic geochronological and geochemical constraints on a late triassic early jurassic arc and cu au porphyry belt understanding the development of island arcs that accreted to the north american craton is critical to deciphering the complex geological history of the canadian cordillera in the case of the hazelton arc part of the stikine terrane or stikinia in northwestern british columbia understanding arc evolution also bears on the formation of spatially associated porphyry cu au epithermal and volcanogenic massive sulfide deposits the hazelton group is a regionally extensive long lived and exceptionally thick upper triassic to middle jurassic volcano sedimentary succession considered to record a successor arc that was built upon the paleozoic and triassic stikine and stuhini arcs in central stikinia near terrace british columbia the lower hazelton group telkwa formation comprises three volcanic intrusive complexes mt henderson mt o brien and kitselas that at their thickest constitute almost 16 km of volcanic stratigraphy basal telkwa formation conglomerates and volcanic rocks were deposite

geothermometry from 40ar39ar dating experiments abstract we have selected a variety of minerals from three basic intrusions within the high grade metamorphic terrane near haliburton ontario for k ar dating by application of 40 ar 39 ar incremental heating experiments we conclude that the discordant k ar mineral dates can best be explained by a slow cooling history from the stepwise heating experiments we calculated isotopic closure temperatures using dodson s theory for slow cooling and from these constructed a cooling curve this curve was then compared to independent constraints to test the overall validity of our procedures and assumptions the results are geologically reasonable insofar as 1 a the maximum calculated temperatures from hornblendes of 700 c are consistent with independent approximate metamorphic grid arguments 2 b the ar closure temperatures for biotites 350 400 c are consistent with independent evidence and 3 c minerals with older k ar dates have higher calculated closure temperatures the resultant geological cooling curve implies that a maximum temperature of 700 c was reached before 1000 ma ago and thereafter the temperature decreased via changes in uplift and cooling rates to below 200 c by 700 ma ago we have discovered that plutonic plagioclases are very sensitive indicators comparable to k felds pars of ar loss and therefore can usefully extend the range of application of the 40 ar 39 ar stepwise heating method we also describe experiments in which we have tested the effects on the ar systematics of acid leaching of plagioclases

the thermal significance of potassium feldspar k ar ages inferred from age spectrum results 40ar39ar age spectrum analyses of three microcline separates from the separation point batholith northwest nelson new zealand which cooled slowly 5 c ma 1 through the temperature zone of partial radiogenic 40ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages 80 ma corresponding to the time that the samples cooled below about 100 c the last 35 percent of 39ar released from the microclines yields plateau ages 103 99 and 93 ma which reflect the different bulk mineral ages and correspond to cooling temperatures between about 130 to 160 c theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates 5 c ma 1 diffusion parameters calculated from the 39ar release yield an activation energy e 28 8 1 9 kcal mol 1 and a frequency factor grain size parameter d0l2 5 6 3 9 14sec 1 this arrhenius relationship corresponds to a closure temperature of 132 13 c which is very similar to the independently estimated temperature from the observed diffusion compensation correlation this d0l2 implies an average diffusion half width of about 3 m similar to the half width of the perthite lamellae in the feldspars the range in microcline k ar ages from the separation point batholith is the result of relatively small temperature differences within the pluton during cooling comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous k feldspars e 40 to 52 kcal mol 1 reveals that ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state previously published u shaped age spectra are probably the result of the superimposition of excess 40ar upon diffusion profiles of the kind described here

a coral reef in the telkwa range british columbia the earliest jurassic example an end triassic mass extinction profoundly affected reef ecosystems that flourished in the late triassic tethys seaway the collapse of late triassic coral sponge reefs was followed by an early jurassic hettangian sinemurian perturbation interval with a near global absence of reefs and sharp reductions in diversity a jurassic sinemurian reef in the hazelton group of central british columbia appears to fill the gap its paleoecology and composition show it to be the first large framework example in north america and perhaps the world it demonstrates that the reef building triassic coral phacelostylophyllum survived the extinction event and was constructing reefs in early jurassic time during a global reef eclipse the reef is a 48 m thick bioherm that grew within the island arc complex of stikinia following a decrease in volcanism reef building began with bivalves growing upon water lain tuffs the reef was dominated by large dendroid phaceloid corals primarily phacelostylophyllum rugosum a spe

detection of sea level fingerprints derived from grace gravity data mass changes of ice sheets glaciers ice caps land water hydrology atmosphere and ocean cause a non uniform sea level rise due to the gravitational and self attraction and loading effects called sea level fingerprints slf slf have been previously derived from a combination of modeled and observed mass fluxes from the continents into the ocean here we derive improved slf from time series of time variable gravity data from the grace mission for april 2002 october 2014 we evaluate the grace derived slf using ocean bottom pressure obp data from stations in the tropics where obp errors are the lowest we detect the annual phase of the slf in the obp signal and separate it unambiguously from the barystatic sea level bsl at two stations at the basin scale the slf explain a larger fraction of the variance in steric corrected altimetry than the bsl which has implications for evaluating mass transport between ocean basins

sea level rise will drive divergent sediment transport patterns on fore reefs and reef flats potentially causing erosion on atoll islands these data files and matlab scripts reproduce the model data and figures as published in bramante et al in prep modeling the impacts of a changing climate on cross shore sediment transport kwajalein atoll marshall islands

geochemistry and nd isotopes of the francois lake plutonic suite endako batholith host and progenitor to the endako molybdenum camp central british columbia the endako low f granodiorite type porphyry mo deposit is hosted by the triassic to eocene endako batholith which comprises five temporally distinct plutonic suites only one of which is mineralized pre mineralization suites range in composition from diorite to granodiorite the synmineralization jurassic cretaceous francois lake suite includes two granodiorite to monzogranite bearing subsuites postmineralization phases include the eocene sam ross creek monzogranite the batholith spans a silica range of 44 80 wt and consists of metaluminous to slightly peraluminous low to high k i type granitoids the sam ross creek phase is an a type granite positive e nd t values 1 1 to 7 2 indicate derivation predominately from juvenile source materials but with variable input from an older crustal component evidence suggests generation of older plutonic suites in a juvenile arc type setting and younger k rich felsic suites via recycling of juvenile arc crust without significant mantle derived contrib

shoreline changes interpreted from multi temporal aerial photographs and high resolution satellite images wotje atoll marshall islands abstract wotje atoll is located at 9 25 n and 170 04 e within the republic of the marshall islands in the central pacific ocean as on other atolls the islands perched along the rim of wotje are low lying and considered highly vulnerable to the impacts of climate change a widely anticipated impact of continued sea level rise is the chronic erosion of island shorelines using a combination of aerial photographs and satellite imagery shoreline changes are assessed over a 67 year period characterized by rising sea level results indicate that between 1945 and 2010 shoreline accretion is more prevalent than erosion with an average net shoreline movement nsm of 1 74 m indicating accretion shorelines were accretionary along the lagoon ocean and channel facing shorelines as well as on elongate spits and small islands a high frequency assessment of shoreline change on a subset of islands in the east of wotje reveals that islands were stable with a balance between shoreline accretion and erosion shorelines interpreted from high resolution satellite imagery captured between 2004 and 2012 indicate that shorelines within this sample of islands are largely in an erosive state the post 2004 shift toward erosion may be sea level rise induced or part of an unresolved shoreline oscillation this study demonstrates the critical need for improved shoreline change monitoring within atoll settings in order to assess sea level rise impacts along island shorelines

physical modelling of reef island topographic response to rising sea levels abstract low lying coral reef islands are considered extremely vulnerable to the impacts of climate change particularly sea level rise and increasing storm magnitude inundation and erosion are expected to destabilise reef islands and render them uninhabitable within decades however such assertions are founded upon the assumption that reef islands are geomorphologically inert landforms whereas recent planform and cross sectional analysis of reef island morphodynamics demonstrates that many islands are highly dynamic landforms changing in size shape and position on the reef platform this paper describes the first physical modelling experiments to model the whole of island morphodynamic response of reef islands to changes in sea level and wave regime a wave basin is utilised to construct a 1 50 scale three dimensional model of fatato island tuvalu and document the whole of island response across a broad range of wave and water level conditions whole of island results corroborate flume studies and provide new insights into the modes and styles of island change spit rotation as well as lagoonward island recession and vertical oceanward crest accretion are identified as the core island responses to increasing water level and wave conditions however results show that the rate and magnitude of physical adjustment is strongly dependent on the rate and magnitude of sea level rise and wave conditions results challenge existing models of future island susceptibility to wave driven flooding demonstrating that washover processes can provide a mechanism to build and potentially maintain island freeboard above sea level these insights highlight an urgent need to incorporate island morphodynamics into flood risk models in order to produce accurate assessments of future wave driven flood risks and better resolve island vulnerability

geochronology of mid cretaceous to eocene magmatism babine porphyry copper district central british columbia new u pb and 40 ar 39 ar isotopic dating in the babine porphyry copper district of central british columbia documents three distinct magmatic events at 107 104 85 78 and 54 50 ma the earliest event involved emplacement of rhyolite domes into submarine volcanic rocks of the rocky ridge formation the rhyolite domes and related dacitic to basaltic volcanic rocks gave a u pb age of 107 9 0 2 ma and an 40 ar 39 ar age of 104 8 1 2 ma the rhyolites which were previously mapped as eocene are reinterpreted to be part of a previously unrecognized mid cretaceous cauldron subsidence complex the regionally extensive late cretaceous magmatic event is also recognized in the babine district and is represented by 40 ar 39 ar ages of 85 2 2 8 and 78 3 0 8 ma on two bulkley intrusions one of which has associated porphyry copper mineralization the final magmatic event is the most widespread and involved emplacement of the babine intrusions and formation of numerous porphyry copper deposits including the bell and granisle past producers twenty one new 40 ar 39 ar isotopic ages for these intrusions and coeval andesites of the newman formation have a narrow range from 53 6 0 9 to 49 9 0 6 ma whereas previous k ar isotopic dating had a possible range of 15 ma the mid cretaceous late cretaceous and eocene magmatic suites in the babine dis trict are interpreted to be part of a long lived volcano plutonic complex that was the site of periodic magmatism and porphyry copper mineralization over a 60 ma time period this complex may have evolved within a zone of extension pull apart basins situated between dextral strike slip faults that were active during periods of rapid oblique plate con vergence

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

argon retentivity of hornblendes a field experiment in a slowly cooled metamorphic terrane hornblende from samples of amphibolite and granitic gneiss collected within a single outcrop in the central adirondacks yield significantly different sup 40 ar sup 39 ark sub k dates of 948 plus minus 5 and 907 plus minus 5 ma assuming that this terrane cooled slowly following high grade metamorphism and that the samples have experienced the same thermal history the difference in dates apparently reflects a corresponding difference in blocking temperature for diffusion of radiogenic argon in these hornblende samples the fe fe mg mn of the hornblende samples are 0 8 and 0 6 the higher ratio corresponding to the younger sup 40 ar sup 39 ar sub k date transmission electron microscopy observations indicate that both hornblende samples are homogeneous and devoid of any exsolution but contain zones of fibrous phyllosilicates approximately 0 1 to 2 mu m wide parallelling 100 and 110 these alteration zones probably formed during post metamorphic cooling as a result of the migration of fluids through the hornblendes and are obvious pathways for argon escape from hornblende as these features are more abundant in the hornblende sample with the younger sup 40 ar sup 39 ar date and higher fe fe mg mn they may influence the argon blocking temperature by effectively partitioning the hornblende grains intomore diffusion domains of varying size biotite from the granitic gneiss yields an sup 40 ar sup 39 ar sub k date of 853 plus minus 2 ma with a mildly discordant step heating spectrum that in part reflects the degassing of submicroscopic inclusions precipitated during alteration of the host biotite plagioclase from the amphibolite yields a sup 40 ar sup 39 ar sub k integrated date of 734 plus minus 3 ma less

late jurassic magmatism metamorphism and deformation in the blue mountains province northeast oregon an early to mid mesozoic record of sedimentation magmatism and metamorphism is well developed in the blue mountains province of northeast oregon detailed studies both north and south of the blue mountains province e g terranes of the intermontane belt klamath mountains and western sierra nevada have documented a complex middle to late jurassic orogenic evolution however the timing of magmatic metamorphic and deformational events in the blue mountains and the significance of these events in relationship to other terranes in the western north american cordillera remain poorly understood in this study we investigate the structural magmatic and metamorphic histories of brittle to semibrittle deformation zones that indicate widespread late jurassic orogenesis in the blue mountains province folding and faulting associated with contractional deformation are primarily localized along terrane boundaries e g baker wallowa and baker izee olds ferry boundaries and within the composite baker oceanic melange terrane e g bourne greenhorn subterrane boundary these brittle to semibrittle deformation zones are broadly characterized by the development of e w oriented slaty to spaced cleavage in fine grained metasedimentary rocks of the baker terrane e g elkhorn ridge argillite approximately n s bivergent folding and n and s dipping reverse and thrust faulting on opposite flanks of the baker terrane similarly oriented contractional features are also present in late middle triassic to early late jurassic i e oxfordian stage ca 159 ma sedimentary rocks of the john day and huntington areas of northeast oregon radiometric age constraints from youngest detrital zircons in deformed sedimentary rocks and crystallization ages of postkinematic plutons which intrude the deformation zones limit deformation to between ca 159 and ca 154 ma we suggest that the widespread approximately n s directed contractional features in the blue mountains province record a short lived intense early late jurassic deformational event and preserve an example of upper crustal strain localization associated with terminal arc arc collision between the olds ferry and wallowa island arc terranes the age interval of deformation in the blue mountains province is younger than middle jurassic deformation in the canadian cordillera and klamath mountains siskiyou orogeny and predates classic nevadan orogenesis

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

mid cretaceous transtension in the canadian cordillera evidence from the rocky ridge volcanics of the skeena group the age relations geochemistry and sedimentology of the rocky ridge formation of the skeena group are used to test competing tectonic reconstructions for the mid cretaceous canadian cordillera as well as the timing and location of the accretion of the insular superterrane pollen and macrofossil assemblages indicate that these intrabasinal basalts were erupted along the southern margin of the bowser basin in the early albian to early cenomanian single crystal fusion and step heating 40ar 39ar dating of hornblendes in one basalt flow from the uppermost part of the formation yielded middle cenomanian ages of 94 3 0 4 95 6 1 6 and 95 0 1 6 ma vesicular basalt flows interbedded with crystal rich tuff breccias contain evidence for hot emplacement as pyroclastic flows individual eruptive centers are identified by their proximal facies paleoflow indicators within the lava flows paleoflow indicators within interbedded volcaniclastic fluvial deposits geochemical differences and geographic isolation of volcanic deposits major and trace element geochemistry from 20 sampled lava flows indicates an alkali basalt composition for the volcanics the basalts of the northern rocky ridge volcanic center show enrichment of light rare earth and large ion lithophile elements with strong negative nb ta anomalies whereas the basalts of the southern tahtsa lake volcanic center show depletion to slight enrichment of light rare earth elements slight enrichment of large ion lithophile elements with minimal negative nb ta anomalies the geochemistry combined with paleogeographic and regional tectonic reconstruction suggests a continental arc setting with intraarc extension the presence of deeper marine facies to the west and the lack of a western sediment source in the skeena group indicate that the technically active insular superterrane was not west of the study area during mid cretaceous time thus we reconsider the omineca belt as the main axis of a mid cretaceous continental arc placing the intermontane superterrane in the intraarc to forearc position with the rocky ridge volcanics erupted along the forearc side of the omineca arc coeval regional strike slip faulting and reconstructed oblique plate convergence suggest a transtensional setting for rocky ridge intraarc extension an electronic supplement of tables a1 a2 may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 95tc03496 mid cretaceous transtension in the canadian cordillera evidence from the rocky ridge volcanics of the skeena group kari n bassett and karen l kleinspehn diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

exploring carbonate reef flat hydrodynamics and potential formation and growth mechanisms for motu abstract atolls which develop as reef building coral platforms extend to near sea level typically consist of a shallow reef flat encircling a central lagoon often sub aerial islets known as motu or reef islands consisting of sand gravel and coral detritus can be found perched atop the reef flat here we use hydrodynamic numerical modeling xbeach to better understand the role of waves and wave driven currents on the reef flat and the processes driving motu formation and evolution by differing representative reef flat geometry e g width and water depth we investigate the effects of varying wave climate on hydrodynamics and resultant bed shear stresses across the reef flat model results suggest that as a reef flat shallows bed shear increases then after passing a critical value decreases again using these results we hypothesize that reef flats should attain a critical water depth just at the threshold for sediment mobilization resulting in a constant depth reef flat in both abrasional and depositional settings as reef flats widen prograding into the back reef lagoon shear stress decreases across the flat with a minimum in shear stress arising approximately midway on the reef flat motu formation would be expected to initiate at this mid flat nucleation site either from a storm when coarse sediment is mobilized and deposited or gradually as the reef flat widens a mid flat deposit need not be subaerial to form a motu sediment piled shallower than the critical depth would continue to accumulate once a motu is present reef flat shear stress directions reverse and the motu shoreline should prograde seawards until reaching a relatively narrow critical reef flat width 200 m together these results suggest that reef flats and motu spatially self organize through a series of morphodynamic feedbacks

a review of the geochronology of the amazonian craton tectonic implications abstract the available geochronological data for the amazonian craton permit delineation of its main age provinces and their respective tectonic development demarcation of the boundaries of each age province is primarily based on rb sr whole rock isochrons supported by k ar determinations on minerals some u pb results on zircons pb pb whole rock isochrons and sm nd model ages complement these data in key areas at the center of the amazonian craton lies the archean age central amazonian province bounded in its northern part by the maroni itacaiunas mobile belt which developed during early proterozoic times the western and southern margins of the archean core are bordered by three tectonic provinces 1 the rio negro juruena magmatic arc 2 the rondonian mobile belt and 3 the sunsas mobile belt each belt borders the western margin of the preceding belt and each records a successively younger middle proterozoic orogeny within the central amazonian province 2 7 ga age determinations have been obtained from the serra dos carajas area although the maroni itacaiunas belt includes several reworked archean nuclei rock units formed during the 2 2 1 9 ga trans amazonian orogeny predominate the isotopic evidence suggests that a mantle derived component constituted a significant portion of the crust accreted at that time the rio negro juruena province is of mid proterozoic age 1 75 1 50 ga and includes almost entirely mantle derived material juxtaposed with the pre existent continental mass along a series of successive magmatic arcs the rondonian and sunsas provinces both exhibit older sialic basements 1 5 ga the former is characterized by important tectonomagmatic events in the 1 45 1 25 ga interval whereas the latter records tectonic reworking at 1 1 0 9 ga finally the amazonian craton is bordered to the east by the late proterozoic paraguai araguaia or araguaia tocantins fold belt

infragravity waves on fringing reefs in the tropical pacific dynamic setup cross shore pressure and current observations from four fringing reefs of lengths ranging from 135 to 420 m reveal energetic low frequency 0 001 0 05 hz motions the spatial structure and temporal amplitudes of an empirical orthogonal function analysis of the pressure measurements suggest the dominant low frequency variability is modal incoming and outgoing linear flux estimates also support partially standing modes on the reef flat during energetic events a cross covariance analysis suggests that breakpoint forcing excites these partially standing modes similar to previous findings at other steep reefs the dynamics of symonds et al 1982 with damping are applied to a step reef with forcing obtained by extending a point break model of vetter et al 2010 for breaking wave setup to the low frequency band using the shoaled envelope of the incident free surface elevation a one parameter linear analytical model for the reef flat free surface elevation is presented which describes between 75 and 97 of the variance of the observed low frequency shoreline significant wave height for all reefs considered over a range of conditions the linear model contains a single dimensionless parameter that is the ratio of the inertial to dissipative time scales and the observations from this study exhibit more low frequency variability when the dissipative time scale is greater than the inertial time scale for the steep reefs considered

coupling cross shore and longshore sediment transport to model storm response along a mixed sand gravel coast under varying wave directions abstract this paper investigates the profile response of a mixed sand gravel deltaic beach playa granada southern spain forced by storm waves from varying directions beach morphology was monitored over a 36 day period with variable wave conditions and profile response was compared to model predictions using the xbeach g model and a longshore sediment transport lst formulation xbeach g was applied over 2 day periods of low energy south westerly sw storm and south easterly se storm conditions and was coupled to lst using a parametric approach which distributes the lst across the swash surf and nearshore zones a calibrated wave propagation model delft3d was used to obtain the inshore conditions required to drive the xbeach g model and the lst formulation the storm response is clearly influenced by the free board difference between the height of the berm and the total run up and is also strongly dependent on storm wave direction with the sw storm eroding the surveyed area while the se storm induced beach accretion model results indicate that xbeach g on its own is capable of adequately reproducing the response of the beach under sw storm conditions b s s 0 95 but not under se storms due to the higher lst gradients at the study location the combination of xbeach g and lst fits the measured profiles reasonably well under both sw b s s 0 96 and se b s s 0 88 storms inspiring confidence in the coupled model to predict the storm response under varying wave conditions the combined xbeach g lst model was applied to the entire 6 8 km deltaic coastline to investigate the impact of extreme sw and se storm events and the model results reiterate the importance of cross shore and longshore sediment transport in driving coastal storm response at this location the approach proposed in this work can be extended to other worldwide coasts highly influenced by both cross shore and longshore sediment transport such as beaches with different coastline orientations and or forced by varying wave directions

diachronous and independent histories of plutonism and mineralization in the cornubian batholith southwest england concordant u pb dates of magmatic monazites in the dominant coarse grained biotite muscovite granites of the late variscan cornubian batholith demonstrate that the emplacement of the six main plutons was diachronous ranging from 293 1 1 3 ma carnmenellis to 274 5 1 4 ma land9s end southern lobe 40 ar 39 ar age spectra for magmatic muscovites confirm that cooling to about 320 c at the present level of exposure was accomplished within 4 to 5 ma in each intrusion moreover age spectra for hydrothermal muscovites show that development of the major sn cu lodes of the south crofty mine commenced before 286 ma only 2 to 3 ma after cooling of the hosting cam brea granite a satellite of the carnmenellis pluton the older plutons had therefore approached ambient temperatures and had even experienced intense hydrothermal activity before emplacement of the youngest

isotope systematics in minerals biotite rejuvenation and exchange during alpine metamorphism abstract the hercynian schists and granites of the helvetic basement aar massif in the central swiss alps are overprinted by low grade alpine metamorphism and associated deformation rb sr and k ar ages of biotites are systematically reset by the later greenschist facies event this rejuvenation is apparently controlled by temperature mineral chemistry and grain size and independent of deformation and exsolution thermally activated volume diffusion best explains this behaviour with ar and sr having similar activation energies and diffusion rates for sr showing a greater dependence on biotite composition feldspars and apatite also show increasing equilibration to the alpine event and together with alpine equilibria in the micas reveal important changes in the isotopic compositions of exchanging reservoirs these spatial and temporal variations must be assessed before true mineral ages can be calculated generally the higher grade equilibria show less radiogenic exchange reflecting increased dilution by external fluids of radiogenic components released at the main front of isotopic resetting rb sr ages of alpine muscovites in the granites suggest a maximum possible age of metamorphism of 25 ma in this low grade area this implies significant diachroneity in the timing of peak metamorphism in the central alps with the relatively delayed metamorphism in this area a reflection of the later initial thickening and delayed uplift of the helvetic basement

rapid reef island formation and stability over an emerging reef flat bewick cay northern great barrier reef australia a model that resolves reef island formation in relation to both reef platform substrate development and mid holocene sea level change is presented for bewick island northern great barrier reef based on morphostratigraphic analysis and radiometrically dated island sediments and reef corals on bewick island microatolls record reef flat development at higher sea level 1 5 m by 6500 yr b p island building began on a partially emergent reef flat 5000 4000 yr b p when sea level was 0 5 m above present as sea level fell to its present level the reef platform process window closed and the island core stabilized results present the first unequivocal evidence of island building directly over a reef flat comprising microatolls and the first detailed model of island formation from the great barrier reef the model demonstrates that the interplay of sea level and reef surface elevation can vary between sites but their convergence is critical for island initiation future trajectories of island change will vary dependent on the unique relative sea level and substrate depth conditions that govern island formation

stratigraphic evolution of the paleozoic stikine assemblage in the stikine and iskut rivers area northwestern british columbia the stikine assemblage the basement of stikinia extends 500 km along the western flank of the intermontane belt east of younger coast belt plutons four different stratigraphic successions are characteristic of lower to middle devonian carboniferous and permian rocks in the stikine and iskut rivers area west of forrest kerr creek are penetratively deformed lower to middle devonian island arc volcaniclastic rocks coralline limestone and felsic tuff fringing carbonate buildups in an arc setting are best illustrated in the sequence at round lake where lower carboniferous mafic dominated bimodal submarine volcanic rocks grade upward into two distinctive coarse echinoderm limestone units and medial siliceous siltstone and limestone conglomerate conodont colour alteration indices for lower carboniferous rocks near newmont lake indicate an anomalously low temperature thermal history upper carboniferous permian polymictic volcanic conglomerate and lower permian limestone overlie these strata there t

hydraulic characteristics of bioclastic deposits new possibilities for environmental interpretation using settling velocity fractions this paper examines the hydraulic behaviour of heterogeneous bioclastic sediments using settling velocity fractions bioclastic deposits are divided into fractions by splitting hydraulically sorted samples compositional analysis of fractions shows that grains exhibit marked variation in composition shape size and density which control the hydraulic behaviour of bioclastic deposits despite the heterogeneous grain properties of fractions analogous to sieve fractions sedimentation analysis shows that they possess a narrow range of settling velocity values flume experiments also show that the settling velocity fractions possess a narrow range of threshold velocity values a threshold relationship is identified in which the velocity required to entrain mixed settling fractions increases from 20 5 to 65 0cm s 1 for settling fractions with mean settling values of 5 5 chi 2 2 cm s 1 to 1 4 chi 36 0 cm s 1 respectively heterogeneous settling fractions due to intergrain effects were found to possess larger threshold velocities than individual components showing that the composition of bioclastic deposits controls hydraulic behaviour thus caution must be exercised in using the threshold relationship for homogeneous sediments or deposits of markedly different composition as settling velocity fractions reflect narrow hydraulic settling and threshold properties of sediments the mean settling velocity of fractions is considered a good indicator with which to interpret transport and depositional processes comparison of settling and sieve size distributions shows that size distributions do not reflect the hydraulic behaviour of bioclastic deposits and should not be used to interpret environmental processes the study indicates that examination of settling velocity fractions for which hydraulic settling and threshold properties are known coupled with compositional analysis of these fractions will allow much greater environmental interpretation of deposit forming and energy processes in reef environments

fitting straight lines and planes with an application to radiometric dating conventional practice in geochronology is to fit a straight line or isochron to data consisting of two isotopic ratios by a method e g that of 1 2 or perhaps the more modern version of titterington and haliday 1979 that takes into account that fact that both ratios are measured with error in this paper we use matrix algebra to lay out a general method for fitting linear relations between any number of variables all subject to errors with known variances and covariances and the well known newton raphson method to do the optimization this leads to a good computational algorithm which may also be used e g to check whether coefficients in several linear relations are the same in many fields of science one needs to fit linear relations so our method is of wide utility its use is in no way restricted to radiometric dating

timing and tectonic setting of stikine terrane magmatism babine takla lakes area central british columbia new bedrock mapping completed as part of the nechako natmap project indicates that the area between babine and takla lakes in central british columbia is underlain by rocks of the early permian asitka late triassic takla and early to middle jurassic hazelton volcanic arc assemblages of the stikine terrane these are cut by large composite stocks of quartz diorite granodiorite and quartz monzonite previously mapped as the late triassic to early jurassic topley intrusions new u pb n 6 and laser 40ar 39ar n 10 isotopic age dates reported in this paper suggest there are two distinct ages of plutons the topley intrusive suite with isotopic ages between 218 and 193 ma and east of babine lake the new spike peak intrusive suite with isotopic ages ranging from 179 to 166 ma west of the main plutonic belt is a thick volcanic succession of subaerial porphyritic andesite flows volcanic breccias and rhyolitic ash flow tuffs that have isotopic ages between 185 and 174 ma these rocks are assigned t

bed load sediment transport on steep longitudinal slopes the results of new experiments on bed load transport on steep longitudinal slopes are presented the experiments were carried out in a large tilting duct with a fine sand median grain diameter of 208 micro m covering the range of slope angles beta of angle of repose for the sand phi sub s of 32 deg 0 56 rad measurements included bed shear stress flow discharge and the sediment pickup rate on slopes the results suggest that existing theories for bed load transport on slopes are not adequate for all bed slopes and the new data are used to formulate a semiempirical relation that satisfactorily predicts the transport rate on horizontal as well as mild and steep slopes the following are two important findings correcting the threshold term for slope in the meyer peter and muller formula adequately describes the transport rate on positive slopes elevation increasing in direction of flow and on small negative slopes while on steeper negative slopes an extra correction term is required although the value of beta phi sub s at which this term becomes necessary is a function of shear stress and the influence of slope vanishes at high shear stresses